WO2025172492A1

WO2025172492A1 - Uplink wake-up signal

Info

Publication number: WO2025172492A1
Application number: PCT/EP2025/053951
Authority: WO
Inventors: Dietmar Lipka; Geordie George; Gustavo Wagner Oliveira Da Costa; Elke Roth-Mandutz; Julian Popp; Alexander GÖTZ
Original assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date: 2024-02-14
Filing date: 2025-02-13
Publication date: 2025-08-21
Anticipated expiration: 2026-08-14

Abstract

Embodiment provide a Transceiver [e.g., UE] for a [e.g., 5G/NR] wireless communication network, wherein the transceiver is configured to transmit a wake-up signal to a central transceiver that is operable in an energy saving mode [e.g., network energy saving, NES, mode] of operation [e.g., in order to switch the central transceiver from the energy saving mode into a normal/conventional operation mode; or in order to maintain the normal/conventional operation mode], wherein the transceiver is configured to determine a wake-up signal configuration for the wake-up signal and to generate the wake-up signal based on the wake- up signal configuration, wherein at least a part of the wake-up signal configuration is not explicitly signaled to the transceiver by the central transceiver and/or another central transceiver of the wireless communication network.

Description

Uplink Wake-Up Signal

Description

Embodiments of the present application relate to the field of wireless communication, and more specifically, to an uplink wake-up signal.

Fig. 1 is a schematic representation of an example of a terrestrial wireless network 100 including, as is shown in Fig. 1 (a), a core network 102 and one or more radio access networks (RANs) RANi, RAN2, ... RANN. Fig. 1(b) is a schematic representation of an example of a radio access network RANn that may include one or more base stations (BSs) gNBi to gNBs, each serving a specific area surrounding the base station schematically represented by respective cells IO61 to IO65. The base stations are provided to serve users within a cell. The term base station, BS, refers to a next generation node B (gNB) in 5G networks, an evolved node B (eNB) in UMTS/LTE/LTE-A/ LTE-A Pro, or just a BS in other mobile communication standards. A user may be a stationary device or a mobile device. The wireless communication system may also be accessed by mobile or stationary Internet of Things (loT) devices which connect to a base station or to a user. The mobile devices or the loT devices may include physical devices, ground based vehicles, such as robots or cars, aerial vehicles, such as manned or unmanned aerial vehicles (UAVs), the latter also referred to as drones, buildings and other items or devices having embedded therein electronics, software, sensors, actuators, or the like as well as network connectivity that enables these devices to collect and exchange data across an existing network infrastructure. Fig. 1 (b) shows an exemplary view of five cells, however, the RANn may include more or less such cells, and RANn may also include only one base station. Fig. 1(b) shows two users UE1 and UE₂, also referred to as user equipment, UE, that are in cell IO62 and that are served by base station gNB₂. Another user UE3 is shown in cell IO64 which is served by base station gNB4. The arrows IO81, 108₂ and IO83 schematically represent uplink/downlink connections for transmitting data from a user UE1, UE₂ and UE3 to the base stations gNB₂, gNB4 or for transmitting data from the base stations gNB₂, gNB4 to the users UE1, UE₂, UE3. Further, Fig. 1(b) shows two loT devices 110i and 110₂ in cell IO64, which may be stationary or mobile devices. The loT device 110i accesses the wireless communication system via the base station gNB4 to receive and transmit data as schematically represented by arrow 112i . The loT device 110₂ accesses the wireless communication system via the user UE3 as is schematically represented by arrow 112₂. The respective base station gNBi to gNBs may be connected to the core network 102, e.g., via the S1 interface, via respective backhaul links 114i to 114s, which are schematically represented in Fig. 1(b) by the arrows pointing to “core”. The core network 102 may be connected to one or more external networks. Further, some or all of the respective base station gNBi to gNBs may connected, e.g., via the S1 or X2 interface or the XN interface in NR, with each other via respective backhaul links 1161 to 1165, which are schematically represented in Fig. 1(b) by the arrows pointing to “gNBs”.

For data transmission a physical resource grid may be used. The physical resource grid may comprise a set of resource elements (REs) to which various physical channels and physical signals are mapped. For example, the physical channels may include the physical downlink, uplink and sidelink shared channels (PDSCH, PLISCH, PSSCH) carrying user specific data, also referred to as downlink, uplink and sidelink payload data, the physical broadcast channel (PBCH) carrying for example a master information block (MIB), the physical downlink shared channel (PDSCH) carrying for example a system information block (SIB), the physical downlink, uplink and sidelink control channels (PDCCH, PLICCH, PSSCH) carrying for example the downlink control information (DCI), the uplink control information (UCI) and the sidelink control information (SCI). For the uplink, the physical channels, or more precisely the transport channels according to 3GPP, may further include the physical random access channel (PRACH or RACH) used by UEs for accessing the network once a UE is synchronized and has obtained the MIB and SIB. The physical signals may comprise reference signals or symbols (RS), synchronization signals and the like. The resource grid may comprise a frame or radio frame having a certain duration in the time domain and having a given bandwidth in the frequency domain. The frame may have a certain number of subframes of a predefined length, e.g., 1 ms. Each subframe may include one or more slots of 12 or 14 orthogonal frequency-division multiplexing (OFDM) symbols depending on the cyclic prefix (CP) length. All OFDM symbols may be used for downlink (DL) or uplink (UL) or only a subset, e.g., when utilizing shortened transmission time intervals (sTTI) or a mini-slot/non-slot-based frame structure comprising just a few OFDM symbols.

The wireless communication system may be any single-tone or multicarrier system using frequency-division multiplexing, like the OFDM system, the orthogonal frequency-division multiple access (OFDMA) system, or any other IFFT-based signal with or without CP, e.g., DFT-s-OFDM. Other waveforms, like non-orthogonal waveforms for multiple access, e.g., filter-bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM) or universal filtered multi carrier (LIFMC), may be used. The wireless communication system may operate, e.g., in accordance with the LTE-Advanced pro standard or the NR (5G), New Radio, standard. The wireless network or communication system depicted in Fig. 1 may by a heterogeneous network having distinct overlaid networks, e.g., a network of macro cells with each macro cell including a macro base station, like base station gNB1 to gNB5, and a network of small cell base stations (not shown in Fig. 1), like femto or pico base stations.

In addition to the above described terrestrial wireless network also non-terrestrial wireless communication networks exist including spaceborne transceivers, like satellites, and/or airborne transceivers, like unmanned aircraft systems. The non-terrestrial wireless communication network or system may operate in a similar way as the terrestrial system described above with reference to Fig. 1 , for example in accordance with the LTE-Advanced Pro standard or the NR (5G), new radio, standard.

In mobile communication networks, for example in a network like that described above with reference to Fig. 1 , like an LTE or 5G/NR network, there may be UEs that communicate directly with each other over one or more sidelink (SL) channels, e.g., using the PC5 interface. UEs that communicate directly with each other over the sidelink may include vehicles communicating directly with other vehicles (V2V communication), vehicles communicating with other entities of the wireless communication network (V2X communication), for example roadside entities, like traffic lights, traffic signs, or pedestrians. Other UEs may not be vehicular related UEs and may comprise any of the above-mentioned devices. Such devices may also communicate directly with each other (D2D communication) using the SL channels.

When considering two UEs directly communicating with each other over the sidelink, both UEs may be served by the same base station so that the base station may provide sidelink resource allocation configuration or assistance for the UEs. For example, both UEs may be within the coverage area of a base station, like one of the base stations depicted in Fig. 1 . This is referred to as an “in-coverage” scenario. Another scenario is referred to as an “out-of-coverage” scenario. It is noted that “out-of-coverage” does not mean that the two UEs are not within one of the cells depicted in Fig. 1 , rather, it means that these UEs may not be connected to a base station, for example, they are not in a radio resource control (RRC) connected state, so that the UEs do not receive from the base station any sidelink resource allocation configuration or assistance, and/or may be connected to the base station, but, for one or more reasons, the base station may not provide sidelink resource allocation configuration or assistance for the UEs, and/or may be connected to the base station that may not support NR V2X services, e.g., GSM, UMTS, LTE base stations. When considering two UEs directly communicating with each other over the sidelink, e.g., using the PC5 interface, one of the UEs may also be connected with a BS, and may relay information from the BS to the other UE via the sidelink interface. The relaying may be performed in the same frequency band (in-band-relay) or another frequency band (out-of-band relay) may be used. In the first case, communication on the Uu and on the sidelink may be decoupled using different time slots as in time division duplex (TDD) systems.

Fig. 2 is a schematic representation of an in-coverage scenario in which two UEs directly communicating with each other are both connected to a base station. The base station gNB has a coverage area that is schematically represented by the circle 200 which, basically, corresponds to the cell schematically represented in Fig. 1. The UEs directly communicating with each other include a first vehicle 202 and a second vehicle 204 both in the coverage area 200 of the base station gNB. Both vehicles 202, 204 are connected to the base station gNB and, in addition, they are connected directly with each other over the PC5 interface. The scheduling and/or interference management of the V2V traffic is assisted by the gNB via control signaling over the Uu interface, which is the radio interface between the base station and the UEs. In other words, the gNB provides SL resource allocation configuration or assistance for the UEs, and the gNB assigns the resources to be used for the V2V communication over the sidelink. This configuration is also referred to as a mode 1 configuration in NR V2X or as a mode 3 configuration in LTE V2X.

Fig. 3 is a schematic representation of an out-of-coverage scenario in which the UEs directly communicating with each other are either not connected to a base station, although they may be physically within a cell of a wireless communication network, or some or all of the UEs directly communicating with each other are to a base station but the base station does not provide for the SL resource allocation configuration or assistance. Three vehicles 206, 208 and 210 are shown directly communicating with each other over a sidelink, e.g., using the PC5 interface. The scheduling and/or interference management of the V2V traffic is based on algorithms implemented between the vehicles. This configuration is also referred to as a mode 2 configuration in NR V2X or as a mode 4 configuration in LTE V2X. As mentioned above, the scenario in Fig. 3 which is the out-of-coverage scenario does not necessarily mean that the respective mode 2 UEs (in NR) or mode 4 UEs (in LTE) are outside of the coverage 200 of a base station, rather, it means that the respective mode 2 UEs (in NR) or mode 4 UEs (in LTE) are not served by a base station, are not connected to the base station of the coverage area, or are connected to the base station but receive no SL resource allocation configuration or assistance from the base station. Thus, there may be situations in which, within the coverage area 200 shown in Fig. 2, in addition to the NR mode 1 or LTE mode 3 UEs 202, 204 also NR mode 2 or LTE mode 4 UEs 206, 208, 210 are present.

Naturally, it is also possible that the first vehicle 202 is covered by the gNB, i.e. connected with Uu to the gNB, wherein the second vehicle 204 is not covered by the gNB and only connected via the PC5 interface to the first vehicle 202, or that the second vehicle is connected via the PC5 interface to the first vehicle 202 but via Uu to another gNB, as will become clear from the discussion of Figs. 4 and 5.

Fig. 4 is a schematic representation of a scenario in which two UEs directly communicating with each, wherein only one of the two UEs is connected to a base station. The base station gNB has a coverage area that is schematically represented by the circle 200 which, basically, corresponds to the cell schematically represented in Fig. 1. The UEs directly communicating with each other include a first vehicle 202 and a second vehicle 204, wherein only the first vehicle 202 is in the coverage area 200 of the base station gNB. Both vehicles 202, 204 are connected directly with each other over the PC5 interface.

Fig. 5 is a schematic representation of a scenario in which two UEs directly communicating with each, wherein the two UEs are connected to different base stations. The first base station gNB1 has a coverage area that is schematically represented by the first circle 2001 , wherein the second station gNB2 has a coverage area that is schematically represented by the second circle 2002. The UEs directly communicating with each other include a first vehicle 202 and a second vehicle 204, wherein the first vehicle 202 is in the coverage area 200i of the first base station gNBi and connected to the first base station gNB1 via the Uu interface, wherein the second vehicle 204 is in the coverage area 200₂ of the second base station gNB2 and connected to the second base station gNB2 via the Uu interface.

In a communication system as described above, procedures by which a user equipment (UE) entering the coverage region of a cellular network finds a cell and request for a connection are called the initial access procedures. The first step in initial access is a cell search procedure to find a cell and the second step is a random access procedure to request the network for establishing a connection. In the cell search, a UE first searches across predefined possible frequency positions for receiving known downlink signals, e.g., the Synchronization Signal Blocks (SSBs) in 5G-NR, that are expected to be periodically transmitted by the base stations at one of the possible frequency positions followed by associated transmission of remaining minimum system information (RMSI). Based on the synchronization and minimum system information (MSI) obtained from the cell search step, the UE can then start the random access procedures by transmitting uplink preambles, e.g., Physical Random-Access Channel (PRACH) in 5G-NR; this is followed by further exchange of random access procedure messages between the gNB and UE until a connection is established to enable DL and UL data transmission.

In the case of the 3GPP 5G-NR standard, specifically, the always-ON (i.e., periodically transmitted), DL synchronization and minimum system information (MSI) signals necessary for completing the cell search consist of the SSB and System Information Block 1 (SIB1) transmissions, as shown in Fig. 6. Specifically, Fig. 6 shows a schematic representation of regular always-ON transmission and reception of SSB/SIB1 320. As shown in Fig. 6, in this case, the gNB 300 can always transmit SSB/SIB1 320, while the UE 302 can receive the SSB/SIB1 320 from the gNB 300.

In turn, expecting active UEs sending UL signals requesting for random access, the gNB receiver also need to be kept often at high power mode (i.e., listening periodically), e.g., to receive the PRACH monitoring in 5G-NR during the PRACH monitoring occasions.

A major problem is that the network energy consumption incurred for supporting the cell search (synchronization and cell identification) procedure becomes unjustified when there is little data to transmit or during the times when there are no active user equipments (UEs) in the coverage area of a cell. Specifically, the always-ON DL signals, like the SSBs and the associated MSI, that are periodically transmitted prevent the base stations from opportunistically entering deeper sleep states to save energy during the occasions with no demand for active connections.

Conventionally, the energy consumption due to such always-ON transmission/reception of the signaling needed for the initial access procedures can be avoided by alternatively adopting an on-demand transmission of the SSBs and/or SIB1s triggered by the UL C-WUS transmissions by UEs entering the potential coverage of a cell that is in a ‘sleep mode’ or a ‘network energy saving (NES) mode’, as shown in Fig. 7. Specifically, Fig. 7 shows a schematic representation of on-demand SSB/SIB1 transmission triggered by C-WUS that may not/may depend on light version of the SSB and/or SI. As shown in Fig. 7, the gNB 300 can be in a NES mode 324 in which no or only a light version 321 of the SSB and/or SI are transmitted, wherein the gNB can be configured to switch into an on-demand SSB/SIB mode 326 in which the gNB 300 performs a regular transmission of SSB/SIB1 320 in response to a reception of a C-WUS 322 from the UE 302. Thereby, it must be ensured that the ‘sleeping cell’ or the base station in the NES mode is able to successfully receive/detect the C-WLIS and effectively get triggered for the on-demand transmission of the regular signaling needed for completing the cell search. This means that the design of such a UL C-WLIS becomes challenging depending of the assumption of the energy saving mode of the cell. For the trigger mechanism of the UL C-WUS to work, the NES mode must be a sleep mode with the potential to detect the C-WUS. In other words, the NES mode should have a cell wakeup receiver (C-WUR) activated in such a way to detect the UL C-WUS transmissions and the C-WUS transmissions has to be designed in a way to effectively reach the activated C-WUS. Such a requirement opens up several possibilities for efficient specification of the C-WUS transmission design, in order to address the trade-off between the network energy saving gains, initial access latency, UE complexity, UE power consumption, other performance metrics, specification effort etc.

The potential of having gNBs on sleep states and sending C-WUS to wake them up has been discussed on 3GPP standardization at TR 38.864 [1], While the assumption of the C-WUS based approach for on-demand SSB/SIB1 transmissions showed a lot of NES potential, there is little information on the design of C-WUS itself and practical considerations. In some of the simulations in TR 38.864 C-WUS has been combined with a simplified SSB (PSS+SSS) for synchronization prior to C-WUS or sparser (larger periodicity) SSB and SI. On the one hand, adopting a simplified version of always-ON DL common signals (e.g., SSB without SIB1 , PSS+SSS without MIB and SIB1 or PSS alone) can provide only part of the information needed for a precise UL transmission like the C-WUS (at the appropriate frequency position and with tolerable transmit power) and to correctly wake-up only the intended sleeping cell. On the other hand, having an always-ON DL signal, even if a lighter version, would greatly limit the potential of NES benefits by getting into deeper sleep modes. The design of the C-WUS and the definition of procedures to be followed have to be specified to effectively tackle these issues.

It is typically assumed that a C-WUS configuration is somehow signaled to the UE. That may be done for example as part of broadcast information on the target cell, or signaled by another cell. However, the more information that needs to be signaled to configure a C-WUS, the less energy is saved as the cell needs anyway to wake-up to perform the broadcast transmissions of this information.

Therefore, there is the need for improvements or enhancements with respect to the transmission and reception of wake-up signals when a gNB is in a network energy saving mode. It is noted that the information in the above section is only for enhancing the understanding of the background of the invention and therefore it may contain information that does not form prior art and is already known to a person of ordinary skill in the art.

Embodiments of the present invention are described herein making reference to the appended drawings.

Fig. 1 shows a schematic representation of an example of a wireless communication system;

Fig. 2 is a schematic representation of an in-coverage scenario in which UEs directly communicating with each other are connected to a base station;

Fig. 3 is a schematic representation of an out-of-coverage scenario in which UEs directly communicating with each other receive no SL resource allocation configuration or assistance from a base station;

Fig. 4 is a schematic representation of a partial out-of-coverage scenario in which some of the UEs directly communicating with each other receive no SL resource allocation configuration or assistance from a base station;

Fig. 5 is a schematic representation of an in-coverage scenario in which UEs directly communicating with each other are connected to different base stations;

Fig. 6 is a schematic representation of regular always-ON transmission and reception of SSB/SIB1 ;

Fig. 7 is a schematic representation of on-demand SSB/SIB1 transmission triggered by C-WUS that may not/may depend on light version of the SSB and/or SI;

Fig. 8 is a schematic representation of a wireless communication system comprising a transceiver, like a base station or a relay, and a plurality of communication devices, like UEs, according to an embodiment;

Fig. 9 shows a schematic representation of on-demand SSB/SIB1 transmission from a gNB, triggered by UL C-WUS repeated by a UE either blindly or based on available limited information so as to be correctly detected by the intended gNB’s C-WUR;

Fig. 10 shows a schematic representation of an example of a deployed network where physical Cell ID (PCI) is shown together with PSS and SSS (between parentheses) and a bit-string representation divided into the 4 MSBs and 6 LSBs;

Fig. 11 shows a schematic representation of on-demand SSB/SIB1 transmission from a gNB triggered by UL C-WLIS transmissions are blindly repeated from the UE, with no sync/SI information transmitted by the gNB during NES mode,

Fig. 12 shows a schematic representation of large/always-ON C-WUR occasion to detect blind UL C-WUS transmissions quickly, with no sync/SI information transmitted by the gNB during NES mode;

Fig. 13 shows in a schematic representation that gNB periodicity of gNB occasions and repetitions of C-WUS can be chosen deliberately to have different periodicities;

Fig. 14 shows in a schematic representation that the C-WUS repetitions follow a random or pseudo-random pattern until it successfully wakes-up the cell;

Fig. 15 shows a schematic representation of a wireless communication system comprising a macro Cell and C-WUR cell with optional beam, UE and network controller;

Fig. 16 shows a schematic representation of TS 23.501 Reference Point representation of nn-roaming 5g system model;

Fig. 17 shows a schematic representation of 5G/LTE NodeB connections;

Fig. 18 shows in a schematic representation of a macro base-station exchanging Xn messages with small cell base station in order to control the activation and deactivation of C-WUR and exchanging parameters which can be forwarded to the UE, Fig. 19 illustrates an example of a computer system on which units or modules as well as the steps of the methods described in accordance with the inventive approach may execute.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals.

In the following description, a plurality of details are set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

As indicated above, a major problem in existing systems is that the network energy consumption incurred for supporting the cell search (e.g., synchronization and cell identification) procedure becomes unjustified when there is little data to transmit or during the times when there are no active user equipments (UEs) in the coverage area of a cell. Specifically, the always-ON downlink (DL) signals, like the Synchronization Signal Blocks (SSBs) and the associated minimum System Information (SI) in 5G-NR, that are periodically transmitted prevent the base stations from opportunistically entering deeper sleep states to save energy during the occasions with no demand for active connections. A solution to this problem is to make the transmission of the common DL signals, needed for completing the cell search (such as the SSBs and/or the associated minimum SI in 5G-NR), on-demand rather than always-ON. This enables the cells to exploit the occasions with no such demand to opportunistically enter deeper sleep states and thereby saving energy consumption.

A mechanism to make such a ‘demand’ is to trigger the cell via an uplink (UL) wakeup signal (WUS) transmitted by a UE, namely, a cell wake-up signal (C-WLIS) transmitted in the UL, i.e. to demand the transmission of the essential common DL signals needed for completing the cell search procedure. One of the fundamental difficulties that arises in such an approach is that the UEs lacks sufficient information (e.g., that is traditionally obtained via the always-ON common signals like the SSBs and SIB1) to determine the correct resources in time, frequency and power, to do an UL transmission like the C-WUS. Specifically, the C-WUS transmitted by the UE ultimately needs to be successfully detected by the cell wake-up receiver (C-WUR) of the intended base station. For which the timing, frequency position and the tolerable received power of the C-WUR listening occasions needs to be met appropriately. Since this information, which are typically provided to the UE via the regularly transmitted SSBs and SIB1 , is lacking, alternative solutions have to be adopted.

Subsequently described embodiments allow a transmission of wake-up signal between a transceiver and a central transceiver, while the central transceiver is a network energy saving mode and there is no or no full synchronization between the transceiver and the central transceiver.

Embodiments of the present invention may be implemented in a wireless communication system or network as depicted in Figs. 1 to 5 including a transceiver, like a base station, gNB, or relay, and a plurality of communication devices, like user equipment’s, UEs. Fig. 8 is a schematic representation of a wireless communication system comprising a transceiver 400, like a base station, and a plurality of communication devices 402i to 402_n, like UEs. The UEs 402i to 402_n might communicated directly with each other via a wireless communication link or channel 403, like a radio link (e.g., using the PC5 interface (sidelink)). Further, the transceiver 400 and the UEs 402i to 402_n might communicate via a wireless communication link or channel 404, like a radio link (e.g., using the uU interface). The transceiver 400 might include one or more antennas ANT or an antenna array having a plurality of antenna elements, a signal processor 400a and a transceiver unit 400b. The UEs 402i to 402_n might include one or more antennas ANT or an antenna array having a plurality of antennas, a processor 402ai to 402a_n, and a transceiver (e.g., receiver and/or transmitter) unit 402bi to 402b_n. The base station 400 and/or the one or more UEs 402i to 402_n may operate in accordance with the inventive teachings described herein.

Embodiments provide a transceiver [e.g., UE] for a [e.g., 5G/NR] wireless communication network, wherein the transceiver is configured to transmit a wake-up signal to a central transceiver [e.g., a base station or a cell] that is operable in an energy saving mode [e.g., network energy saving, NES, mode] of operation [e.g., in order to find I detect a central transceiver being in any kind of energy saving mode, e.g., needed for (enhanced) data transmission; or in order to switch the central transceiver from the energy saving mode into a normal/conventional operation mode; or in order to maintain the normal/conventional operation mode].

In embodiments, the transceiver is configured to determine a wake-up signal configuration for the wake-up signal and to generate the wake-up signal based on the wake-up signal configuration. In embodiments, at least a part of the wake-up signal configuration is not explicitly signaled to the transceiver by the central transceiver and/or another central transceiver of the wireless communication network.

In embodiments, the transceiver is configured to transmit the wake-up signal to the central transceiver independent of a reception of a synchronization signal from the central transceiver [e.g., without a [e.g., prior] reception of a synchronization signal [e.g., PSS, SSS, SSB, SI] from the central transceiver] [e.g., to transmit the wake-up signal blindly].

In embodiments, the transceiver is configured to transmit the wake-up signal to the central transceiver using reduced synchronization information obtained by receiving a reduced synchronization signal from the central transceiver.

In embodiments, the reduced synchronization signal is a primary synchronization signal only, a primary and a secondary synchronization signal only, or a synchronization signal block [e.g., PSS+SSS+PBCH(MIB)] only.

In embodiments, in the energy saving mode of operation, the central transceiver transmits no synchronization signals, transmits only primary synchronization signals, transmits only primary and secondary synchronization signals, or transmits only synchronization signal blocks.

In embodiments, the wake-up signal configuration comprises at least one out of one or more frequencies for transmitting the wake-up signal, one or more time intervals for transmitting the wake-up signal [e.g., a time pattern] [e.g., for locating wake-up signal reception interval [e.g., occasion] of the central transceiver], an indication of a transmit power used for transmitting the wake-up signal, an indication of a waveform used for transmitting the wake-up signal.

In embodiments, the transceiver is configured to receive, in response to a transmission of the wake-up signal, a synchronization signal [e.g., SSB/SIB1] from the central transceiver [e.g., and to perform a cell search procedure based on the synchronization signal]. In embodiments, the transceiver is configured to retransmit the wake-up signal using blind repetitions.

In embodiments, the transceiver is configured to determine [e.g., obtain] an identification, ID, of the central transceiver, wherein the transceiver is configured to determine the wake-up signal configuration based on the identification, ID, of the central transceiver.

In embodiments, the transceiver is configured to determine the identification, ID, of the central transceiver based on at least one out of a reduced synchronization signal [e.g., PSS, SSS and/or SSB only] received form the central transceiver, historical information, a signaling information received from the central transceiver prior to its switching into the energy saving mode of operation, pre-configuration, a signaling information received from another central transceiver of the wireless communication network.

In embodiments, the transceiver is configured to select, based on the identification, ID, of the central transceiver, a wake-up signal configuration out of a plurality of different wake-up signal configurations.

In embodiments, the wake-up signal configuration defines at least one specific sequence or preamble associated with the identification, ID, of the central transceiver, wherein the transceiver is configured to transmit the wake-up signal comprising the at least one specific sequence or preamble.

For example, the at least one specific sequence or preamble defined by the wake-up signal configuration is different from at least one other specific sequence or preamble defined by another wake-up signal configuration, wherein the at least one other specific sequence or preamble is associated with another identification, ID, of another central transceiver.

For example, a preamble is typically a CP multiple repetitions of a sequence and then a GT. So a preamble contains sequences. For example, the wake-up signal can comprise a preamble composed of different sequences or multiple preambles concatenated. In embodiments, the at least one specific sequence or preamble is at least one physical random access channel, PRACH, sequence or preamble.

In embodiments, the wake-up signal configuration defines at least two wake-up signals and at least two specific sequences or preambles associated with the identification, ID, of the central transceiver, wherein a first wake-up signal of the at least two wake-up signals comprises a first specific sequence or preamble of the at least two specific sequences or preambles, wherein a second wake-up signal of the at least two wake-up signals comprises a second specific sequence or preamble of the at least two specific sequences or preambles, wherein the transceiver is configured to transmit the at least two wake-up signals according to the wakeup signal configuration.

In embodiments, the at least two specific sequences or preambles are associated with different portions [e.g., MSB and LSB] of the identification, ID, of the central transceiver.

In embodiments, the wake-up signal configuration defines at least one time interval for transmitting the wake-up signal, wherein the at least one time-interval is associated with the identification, ID, of the central transceiver.

For example, the at least one time interval defined by the wake-up signal configuration is different from at least one other time interval defined by another wake-up signal configuration, wherein the at least one other time interval is associated with another identification, ID, of another central transceiver.

In embodiments, the transceiver is configured to determine the at least one time interval out of a plurality of different time intervals based on the identification, ID, of the central transceiver and a time slot assigning function [e.g., hashing function, such as modulo operation].

For example, the transceiver can be configured to map the identification, ID, of the central transceiver to the at least one time interval out of a plurality of different time intervals using the time slot assigning function [e.g., hashing function, such as modulo operation].

In embodiments, the wake-up signal configuration defines at least one specific sequence or preamble, wherein the wake-up signal configuration defines at least one time interval for transmitting the wake-up signal, wherein the transceiver is configured to determine the at least one specific sequence or preamble based on a first portion of the identification, ID, of the central transceiver, and wherein the transceiver is configured to determine the at least one time interval for transmitting the wake-up signal based on a second portion of the identification, ID, of the central transceiver, different from the first portion.

In embodiments, the wake-up signal configuration defines at least one frequency for transmitting the wake-up signal.

In embodiments, the transceiver is configured to determine the at least one frequency based on at least one out of pre-configuration, a signaling information [e.g., SSB I SIB] received from the central transceiver prior to its switching into the energy saving mode of operation.

In embodiments, the at least one frequency is associated with an identification of the central transceiver.

In embodiments, the transceiver is configured to retransmit the wake-up signal, wherein the transceiver is configured to determine time instants for the initial transmission and the retransmission of the wake-up signal based on an information describing a wake-up signal reception interval of the central transceiver.

In embodiments, the information describing the wake-up signal reception interval is at least one out of a wake-up signal reception interval length, a wake-up signal reception interval periodicity, a wake-up signal reception interval duty cycle.

In embodiments, the transceiver is configured to obtain the information describing a wake-up signal reception interval of the central transceiver by at least one out of pre-configuration, a signaling information [e.g., SSB I SIB] received from the central transceiver prior to its switching into the energy saving mode of operation.

In embodiments, the transceiver is configured to retransmit the wake-up signal with a period between the initial transmission of the wake-up signals and the retransmissions of the wakeup signal that is different [e.g., smaller or larger] than a period of a wake-up signal reception interval periodicity used by the central transceiver. In embodiments, a wake-up signal transmission interval is aligned with the wake-up signal reception interval of the central transceiver.

In embodiments, the transceiver is configured to randomly distribute a time instant for the retransmissions of the wake-up signal within the wake-up signal transmission interval that is aligned with the wake-up signal reception interval.

In embodiments, the information describing the wake-up signal reception interval further describes a time offset between the reduced synchronization signal and the wake-up signal reception interval.

In embodiments, the transceiver is configured to retransmit the wake-up signal, wherein the transceiver is configured to increase the transmit power for each retransmission of the wakeup signal.

In embodiments, the transceiver is configured to increase the transmit power for each retransmission of the wake-up signal based on a power ramp-up configuration.

In embodiments, the power ramp-up configuration defines at least one out of a reference power value [e.g., which corresponds to a power value used by the central transceiver for transmitting the reduced synchronization signal], a maximum target power value, a ramp-up step, a maximum number of retransmissions.

In embodiments, at least a part of the power ramp-up configuration is pre-configured.

In embodiments, the transceiver is configured to transmit the wake-up signal in dependence on one or more of the following conditions: a location of the transceiver, an active beam of a macro cell, channel properties, channel measurements, an indication from the transceiver.

In embodiments, the transceiver is configured to receive a signaling information from another central transceiver [e.g., macro cell] of the wireless communication network, the signaling information signaling a presence of the central transceiver, wherein the transceiver is configured to transmit the wake-up signal in response to a reception of the signaling information.

In embodiments, the transceiver is configured to receive the signaling information via common signaling or direct signaling.

In embodiments, the signaling information comprises at least one out of an identification of the central transceiver, at least one parameter of the wake-up signal configuration [e.g., frequency, timing, periodicity, transmission power], a coverage area of the central transceiver, a quality of service parameter of the central transceiver, a bandwidth of the central transceiver.

Embodiments provide a central transceiver [e.g., gNB] for a [e.g., 5G/NR] wireless communication network, wherein the central transceiver is operable in an energy saving mode [e.g., network energy saving, NES, mode] of operation, wherein the central transceiver is configured to receive a wake-up signal from a transceiver [e.g., UE] of the wireless communication network, wherein the central transceiver is configured to transmit, in response to the reception of the wake-up signal, a synchronization signal [e.g., allowing for an initial cell search procedure], wherein a transmission and/or generation of the wake-up signal is based on a wake-up signal configuration, wherein at least a part of a wake-up signal configuration is not [e.g., explicitly] signaled to the transceiver by the central transceiver in the energy saving mode of operation.

In embodiments, the central transceiver is configured to not transmit any synchronization signal in the energy saving mode of operation.

In embodiments, the central transceiver is configured to only transmit a reduced synchronization signal in the energy saving mode of operation.

In embodiments, the reduced synchronization signal is a primary synchronization signal only, a primary and a secondary synchronization signal only, or a synchronization signal block [e.g., PSS+SSS+PBCH(MIB)] only. In embodiments, the central transceiver is configured to, in the energy saving mode of operation, transmit no synchronization signals, transmit only primary synchronization signals, transmit only primary and secondary synchronization signals, or transmit only synchronization signal blocks [e.g., PSS+SSS+PBCH(MIB)].

In embodiments, the central transceiver is configured to, in response to the reception of the wake-up signal, switch from the energy saving mode into a normal operation mode, or to maintain the normal operation mode.

In embodiments, the central transceiver is configured to, in the normal operation mode, to transmit regular synchronization signals [e.g., allowing for a regular initial cell search procedure].

In embodiments, the wake-up signal configuration is associated with an identification of the central transceiver.

In embodiments, the central transceiver is configured to signal its identification to the transceiver in a normal operation mode or by means of a reduced synchronization signal in the energy saving operation mode.

In embodiments, the wake-up signal configuration defines at least one specific sequence or preamble associated with the identification, ID, of the central transceiver, wherein the central transceiver is configured to [e.g., switch into the normal operation mode and] transmit the synchronization signal only in case that the wake-up signal comprises the at least one specific sequence or preamble associated with the identification, ID, of the central transceiver.

In embodiments, the at least one specific sequence or preamble is at least one physical random access channel, PRACH, sequence or preamble.

In embodiments, the wake-up signal configuration defines at least two wake-up signals and at least two specific sequences or preambles associated with the identification, ID, of the central transceiver, wherein a first wake-up signal of the at least two wake-up signals comprises a first specific sequence or preamble of the at least two specific sequences or preambles, wherein a second wake-up signal of the at least two wake-up signals comprises a second specific sequence or preamble of the at least two specific sequences or preambles, wherein the central transceiver is configured to receive the at least two wake-up signals and [e.g., switch into the normal operation mode and] transmit the synchronization signal only in case that the at least two wake-up signals comprise the at least two specific sequences or preambles associated with the identification, ID, of the central transceiver.

In embodiments, the wake-up signal configuration defines at least one time interval in which the wake-up signal is transmitted, wherein the at least one time-interval is associated with the identification, ID, of the central transceiver.

In embodiments, the wake-up signal configuration defines at least one specific sequence or preamble, wherein the wake-up signal configuration defines at least one time interval in which the wake-up signal is transmitted, wherein the at least one specific sequence or preamble is determined based on a first portion of the identification, ID, of the central transceiver, and wherein the at least one time interval for transmitting the wake-up signal is determined based on a second portion of the identification, ID, of the central transceiver, different from the first portion.

In embodiments, the wake-up signal configuration defines at least one frequency on which the wake-up signal is transmitted.

In embodiments, the central transceiver is configured to receive the wake-up signal based on a wake-up signal reception interval, wherein the transceiver is configured to determine time instants for the initial transmission and the retransmission of the wake-up signal based on an information describing a wake-up signal reception interval of the central transceiver.

In embodiments, the wake-up signal reception interval is at least one out of a wake-up signal reception interval length, a wake-up signal reception interval periodicity, a wake-up signal reception interval duty cycle. In embodiments, the energy saving mode is a first energy saving mode, wherein the central transceiver is configured to operate in a second energy saving mode in which no wake-up signals are received or in which wake-up signals are received less often than in the first energy saving mode, wherein the central transceiver is configured to receive an activation control signal [e.g., form the network] and to switch from the second sleep mode into the first energy saving mode in response to a reception of the activation control signal.

In embodiments, the central transceiver is configured to receive an activation control signal and to adjust a wake-up signal configuration in response to the reception of the activation control signal.

In embodiments, the central transceiver is configured to increase a periodicity of wake-up signal reception intervals in response to the reception of the activation control signal.

In embodiments, the central transceiver is configured to receive the activation control signal in dependence on one or more of the following condition: a location of the transceiver, an active beam of a macro cell, channel properties, channel measurements, an indication from the transceiver.

In embodiments, the central transceiver is configured to receive the activation control signal via a core network or network function.

Embodiments provide a method for operating a transceiver [e.g., UE] for a [e.g., 5G/NR] wireless communication network. The method comprises a step of determining a wake-up signal configuration for a wake-up signal. Further, the method comprises a step of generating the wake-up signal based on the wake-up signal configuration. Further, the method comprises a step of transmitting the wake-up signal to a central transceiver that is operable in an energy saving mode [e.g., network energy saving, NES, mode] of operation [e.g., in order to switch the central transceiver from the energy saving mode into a normal/conventional operation mode; or in order to maintain the normal/conventional operation mode], wherein at least a part of the wake-up signal configuration is not [e.g., explicitly] signaled to the transceiver by the central transceiver and/or another central transceiver of the wireless communication network. Embodiments provide a method for operating a central transceiver [e.g., gNB] for a [e.g., 5G/NR] wireless communication network. The method comprises a step of operating the central transceiver in an energy saving mode [e.g., network energy saving, NES, mode] of operation. Further, the method comprises a step of receiving a wake-up signal from a transceiver [e.g., UE] of the wireless communication network. Further, the method comprises a step of transmitting, in response to the reception of the wake-up signal, a synchronization signal [e.g., allowing for an initial cell search procedure], wherein a transmission and/or generation of the wake-up signal is based on a wake-up signal configuration, wherein at least a part of a wake-up signal configuration is not [e.g., explicitly] signaled to the transceiver by the central transceiver in the energy saving mode of operation.

Embodiments provide computer program for performing a method according to one of the embodiments described herein, when the computer program runs on a computer, microprocessor or software defined radio.

Embodiments provide a C-WLIS design that can reduce, minimize, or even avoid completely, the need for precise synchronization and system information obtained at the UE side through DL signaling like simplified SSB, sparse SI or discovery reference signal (DRS) from the gNB.

In embodiments, the C-WUS sequences are designed in such a way as to wake up only the intended cell with the correct cell ID, as described in section 1.

In embodiments, the gNB reduces the always-ON common DL signals as much as possible. This may include transmitting less signals and/or with a larger periodicity. In different embodiments, different levels of always-ON DL signals on a certain cell are considered, for example:

• the cell transmits no always-ON DL signals at all,

• the cell transmits only PSS,

• the cell transmits PSS + SSS, and/or

• the cell transmits the full SSB (but no SI), e.g., with very large periodicity.

Despite the severely reduced amount of DL information, in embodiments, the UE can determine a C-WUS configuration based on pre-configuration and/or this reduced set of common DL signals. In some embodiments, part of the configuration may also be explicitly signaled e.g., in another cell (for example an SCell) or by other means whether the remaining part of the C-WUS configuration is based on pre-configuration and/or reduced set of common DL signals. In embodiments, a C-WLIS configuration may include, for example, one or more out of:

• a set of frequency resources used for transmission of C-WLIS,

• a time pattern and/or time strategy to locate C-WUR listening occasions,

• constraints to the UL transmit power of C-WLIS, for example in the form of power ramp- up parameters,

• parameters of the waveforms to be used in the appropriate time/frequency resources such as a description of code or sequences to be used for transmission of C-WLIS.

Fig. 9 shows a schematic representation of on-demand SSB/SIB1 420 transmission from a gNB 400, triggered by UL C-WUS 422 repeated by a UE 402 either blindly or based on available limited information so as to be correctly detected by the intended gNB’s C-WUR. As shown in Fig. 9, the gNB 400 does not transmit sufficient synchronization or system information to the UE 402 (e.g., in a NES mode in which no SSB are transmitted or only simplified SSB 421 are transmitted) and therefore the UE 402 may repeat the UL C-WUS 422 transmissions until it reaches the gNB 400 during its C-WUR listening occasions 430 and the gNB 400 (e.g., in a normal operation mode (e.g., on-demand SSB/SIB1 mode)) starts transmitting full SSB/SIB1 420 so that the UE 402 can do the cell search procedure.

Without depending on explicit DL transmissions prior to the UL WUS, a UE can make use of predefined or pre-configured information from history regarding the C-WUR listening occasions in frequency position and in time (such as ON-duration and periodicity of the C-WUR occasions) in order to minimize latency, UE power consumption and complexity. Such variations are described in the following embodiments.

In some embodiments, an OFDM-like waveform can be specified as the UL C-WUS, which can be existing waveforms from 5G-NR or a slightly modified version thereof.

For example, the PRACH waveform can be reused or a modified version of the PRACH can be specified such that a low-power C-WUS implemented as a matched filter in time-domain can perform successful detection.

In another example, the Scheduling Request (SR) or a modified version of it can be specified such that a low-power C-WUS implemented as a matched filter in time-domain can perform successful detection. In another example, any type of PLICCH or a modified version of it can be specified. In this approach, conventional gNB receiver might have to be used as the C-WUR to receive and decode the UL C-WLIS, which also would require precise pre-synchronization and system information made available at the UE.

In some embodiments, a dedicated UL C-WUS signal can be specified which potentially supports low-power time-domain matched filter-type C-WUR implementations.

In another example, a newly specified uplink physical channel or OFDM-like signal can be specified. Again, in this approach, conventional gNB receiver might have to be used as the C- WUR to receive and decode the UL C-WUS which also would require precise presynchronization and system information made available at the UE.

Subsequently, embodiments are described in further detail.

1. Selectively waking up a cell

In this embodiment, a UE can obtain information about cell IDs, e.g., decoding PSS and/or SSS. This may be implemented, for example, if the gNB transmits only PSS, PSS+SSS or a full SSB. Also, the UE can measure the received signal strength on those reference signals in order to determine which cell has the highest received signal strength and/or if the received signal strength is above a threshold.

Other methods to obtain the cell ID of a cell to wake-up are:

• Information from history: This can be used, for example, if the UE can determine it is static and a cell with the corresponding cell ID was present there before but now it has entered an energy saving state and broadcast of signals is now missing.

• Signaling when the UE enter inactive mode.

• Pre-configuration: A UE can be configured with a cell ID to wake-up by some mean different means, such as a provisioning interface or application configuration. For example, a UE which is installed in a certain position can be configured to only wakeup cell IDs from a gNB which is covering that position.

• Signaling in other cells: In most networks some cells will be sleeping while other cells remain to provide coverage. In the coverage layer, it may be possible to the UE to obtain the cell ID of a cell to wake-up. In embodiments, based on the obtained cell ID information a UE configures a corresponding C-WLIS. Thus, in embodiments, there can be a mapping between cell IDs and C-WLIS configurations. The mapping can be, for example:

• One-to-one: Each cell ID has a corresponding C-WLIS configuration.

• Many-to-one: Multiple cell IDs correspond to a certain C-WLIS configuration.

• One-to-many: For a certain cell ID a UE can choose multiple C-WUS configurations.

• Any other correspondence between cell IDs and C-WUS configurations.

A one-to-one correspondence between cell ID and C-WUS configurations may be a preferred embodiment such that no cell is waken-up by mistake. That allows to have a precise mechanism where only and only one cell is awaken by a certain C-WUS. Many-to-one correspondences may be advantageous to reduce the signaling overhead or when there are physical limits on the available C-WUS configurations, for example, a limited number of PRACH preambles (as described on section 1.1) or timeslots (as described on section 1.2). But in this case, one C-WUS may end up waking-up some other cells as well. A correspondence of one-to-many may be desirable, for example, if requests from different UEs arrive (e.g., can come) at the same time and it would be advantageous that the C-WUR of the gNB can distinguish the requests I C-WUS. Then, a sparse mapping (e.g., more C-WUS configurations than cell IDs) may help reducing collisions.

In the following, three exemplary approaches to map a physical cell ID to a corresponding C- WUS configuration are described, namely:

• mapping physical cell IDs to PRACH sequences or preambles,

• mapping physical cell IDs to timeslots, and

• mapping physical cell IDs to a combination of timeslots and PRACH sequences or preambles.

1.1 PRACH based approach

In some embodiments, the mapping between cell ID and C-WUS configurations can be based on PRACH sequences or preambles (each of them explained in more detail below). For the sake of reusing existing receivers, it can be a preferred embodiment to use existing PRACH sequences and configurations. Since in 5G NR there are 3 PSS values and 336 SSS values corresponding to 1008 physical cell IDs, but there are only 64 possible PRACH preambles, a possible correspondence is many-to-one, with 1008 cell IDs mapped to 64 PRACH preambles. This still has the disadvantage that many cells may be inadvertently awaken when a C-WUS is sent. A preferred embodiment can be to map the cell IDs to combination of different PRACH preambles used in multiple C-WLIS transmissions. This can be implemented as follows. 1008 cell IDs may be represented with 10 bits. This 10-bit sequence may subdivided into two (or more) strings of bits, for example, 10 bits can be divided into a string of 4 bits and 6 bits or two strings of 5 bits each. As an example, a case is considered where the 10-bit sequence it is divided into 4 and 6 bits. For simplicity, the 4 bits can be the most significant 4 bits and the 6 bits can be the least significant 6 bits. Note that any other sub-selection of bits is also possible. The most significant 4 bits can be mapped to 16 out of the 64 possible preambles, whereas the 6 least significant bits can be mapped to the 64 possible preambles. After the UE obtain the cell ID, it can send a PRACH signal with the corresponding sequence which matches the 6 least significant bits. After a pre-determined time, e.g., just after or after a certain delay, the UE can send another PRACH preamble, now selected based on the 4 most significant bits.

In embodiments, a gNB receiver can re-utilize its PRACH receiver to receive such a C-WUS signal. In essence, the gNB can listen only to the PRACH sequence corresponding to its own most significant 4 bits. This can be decoded by the gNB with low complexity, as a single sequence needs to be tested, and therefore gNB implementations may be optimized to reduce the energy consumption to decode the C-WUS. If the gNB successfully receives the PRACH preamble corresponding to its 4 most significant bits, it reconfigures the receiver to decode the PRACH preamble mapped by the lowest significant bits. This reconfiguration may be applicable after the pre-determined time. If the gNB decodes successfully also this PRACH preamble it wakes up and resume normal operation, e.g., transmit the remaining common signals. Otherwise, if any it cannot decode (e.g., because the UE transmitted a different PRACH preamble) the gNB does not wake up.

Naturally, the order may also be implemented in the other way around, i.e. the UE first sends PRACH preamble corresponding to the most significant bits and then the PRACH preamble corresponding to the least significant bits.

How both these embodiments work should be clearer with a detailed concrete example. This is shown with reference to Fig. 10. Specifically, Fig. 10 shows a schematic representation of an example of a deployed network where physical Cell ID is shown together with PSS and SSS (between parentheses) and a bit-string representation divided into the 4 MSBs and 6 LSBs. Thereby, in Fig. 10, a network is shown with 4 gNBs 400i to 4004. Each gNB 400i to 4OO4 has 3 sectors, each sector being a different cell with a different physical cell ID. The physical cell IDs are indicated and are formed by NID(2) which is the number derived from the PSS sequence and NID(1) which is the number derived from SSS. For example, as indicated in Fig. 10, a first base station 400i serves the three cells with the cell IDs 531 , 532 and 533, where a second base station 400₂ serves the three cells with the cell IDs 765, 766 and 767, where a third base station 400₃ serves the three cells with the cell IDs 381 , 382 and 383, where a fourth base station 400₄ serves the three cells with the cell IDs 126, 127 and 128.

Furthermore, for each cell, 2 bit-strings are shown, together corresponding to the binary representation of the physical cell ID. The 4 most significant bits (MSBs) and the 6 least significant bits (LSBs).

As indicated in Fig. 10 by way of example, the UE 402 can be located on a position where the cell with physical cell ID 383 (e.g., formed from PSS 2 and SSS 127) has the best coverage. In that case, the UE can determine through measurements of PSS+SSS that cell ID 383 has the highest received signal strength and therefore decides to send a C-WUS with the waveform corresponding to cell ID 383. This can be formed by selecting two PRACH sequences: one corresponding to the 4 MSBs, i.e., 0101 , and another one corresponding to the 6 LSBs, i.e. 111111.

According to a first embodiment, the UE can send the PRACH sequence of 4 MSBs first (0101) and then the PRACH sequence for the 6 LSBs (111111). Assuming all cells are on the state awaiting for a wake-up signal, it can be seen from Fig. 10 that the wake-up signal reaches 3 gNBs (illustrated by C-WUS range in Fig. 10), namely gNB B 400₂, gNB C 400₃ and gNB D 400₄ and could potentially wake-up a total of 9 cells at once. The gNB A 400i is out or range of the C-WUS (but could potentially be reached later if the UE increases the C-WUS transmit power). On the C-WUR occasions, the gNB receiver for each cell attempt to decode the corresponding PRACH sequence for the 4 MSBs. As only gNB C 400₃ has the MSBs 0101 , only gNB C 400₃ moves to the next step - to try to decode a PRACH sequence corresponding to LSBs. In this second step the gNB C 400₃ will decode this value and realize the sector with physical cell ID (PCI) 383 is the one to be awaken. The sectors with PCI 381 and 382 may remain sleeping.

According to a second embodiment, the UE 402 can send the PRACH sequence of 6 LSBs (111111) first and then the PRACH sequence for the 4 MSBs later (0101). Correspondingly, the gNBs are configured to decode PRACH preambles matching the 6 LSBs of their cells. In this case all gNBs in range, i.e. gNB B 4002, gNB C 400a and gNB D 4OO4 may continue to the second phase of decoding because the cell IDs 383, 127 and 767 have the same 6 LSB bits - 111111. In the second phase of decoding, where preambles need to match the 4 MSB, gNB B 4002 will attempt to decode the preamble matched to 1011 and gNB D 4OO4 the preamble matched to 0001. However, as the UE 402 transmitted the preamble matching 0101 , only gNB C 400₃ will wake up its cell with ID 383. gNB B 400₂ and gNB D 400₄ come back to sleep mode after phase two.

The embodiment above is only exemplary and naturally this approach is applicable to any subdivision of cell IDs into two or more mappings to PRACH sequences. For example, in another embodiment the PSS value is mapped to 3 out of 64 PRACH sequences. SSS is then mapped to 2 groups of PRACH preambles. In order to wake up a cell, the UE sends a C-WUS corresponding to those 3 parts: 1 PRACH sequence mapped from PSS, another mapped from a first part of SSS and the last mapped from the remaining part of SSS.

As described above, embodiments based on PRACH may map a cell ID to multiple PRACH sequences. The exact transmission of such sequences may be accomplished in multiple ways. Existing PRACH formats (e.g., described on TS 38.211) for a PRACH preamble can be generally described as: a Cyclic Prefix (CP), followed by a number of repetitions of a Sequence (SEQ) and except for A formats they are followed by a guard time GT. So, for example, A1 is CP-SEQ-SEQ and B2 is CP-SEQ-SEQ-SEQ-SEQ-GT. In embodiments, the C-WUS can be mapped to multiple sequences, for example, SEQ1 SEQ2 and SEQ3. Some variations present in different embodiments are:

• Existing PRACH formats for PRACH preambles can be reused and in order to transmit different sequences, different preambles can be transmitted. For example, they all use the same format. For example, to transmit SEQ1 and SEQ2, the C-WUS is formed by a B1 format preamble with SEQ1 then a B1 format preamble with SEQ2. This corresponds to send CP-SEQ1-SEQ1-GT and then CP-SEQ2-SEQ2-GT.

• Existing PRACH formats for PRACH preambles can be reused and in order to transmit different sequences, different preambles can be transmitted. However, different formats can be used on each transmission. For example, to transmit SEQ1 and SEQ2, the C-WUS is formed by a A1 format preamble with SEQ1 then a B1 format preamble with SEQ2. This corresponds to send CP-SEQ1-SEQ1 and then CP-SEQ2-SEQ2-GT.

• A PRACH format for C-WUS can be defined by concatenation of CP, different sequences and optionally a GT. For example, to transmit SEQ1 and SEQ2 a C-WUS is the sequence CP-SEQ1-SEQ1-SEQ1-SEQ2-SEQ2-SEQ2-GT. In a slight variation the different sequences may be interleaved, e.g., CP-SEQ1-SEQ2-SEQ1-SEQ2- SEQ1-SEQ2-GT.

Another PRACH based approach may be based on extending the number of possible PRACH preambles, such that each cell ID is associated with one PRACH preamble. As mentioned above, there are 3 PSS values and 336 SSS values in 5G NR corresponding to 1008 physical cell IDs, but there are currently only 64 possible PRACH preambles. By extending the number of possible PRACH preambles, a one-to-one mapping may be realized. Such additional PRACH preambles may also be based on Zadoff-Chu sequences to allow for good detection properties with a low false alarm rate. Optionally, a dedicated preamble format for PRACH may be introduced which is particularly suited to be used for the C-WLIS. Such dedicated preamble format may have a pre-defined sequence length, a pre-defined number of sequence repetitions, and/or a pre-defined subcarrier spacing to be used for the C-WLIS.

1.2 Timeslot based

In some embodiments, C-WLIS targeting cells with different physical cell IDs can be mapped to different timeslots. Timeslots may be understood in a broader sense here, as a time interval. The same concept applies to timeslots, symbols, subframes, frames.

In certain embodiments, the mapping between physical cell IDs is based on hashing cell IDs to timeslots. In certain embodiments, the physical cell IDs are divided among timeslots using a modulo operation, represented hereafter with %. For example, if there are T = 20 timeslot possibilities for C-WLIS these timeslots may be numbered between 0 and T-1 (0 and 19 in the example). Then, the corresponding timeslot is selected by calculating PCI%T. If the result of this operation is 0, timeslot 0 is used. If it is 1 , timeslot 1 is used and so on. Another variation is to apply an offset before modulo calculation. Then the target timeslot may be calculated, e.g., by (PCI + offset)%T or (PCI-offset)%T.

Another variation of this embodiment is to combine this with restrictions on minimal offset as described in section 3.4. In that case, the timeslots may instead be numbered from MIN_OFF to MIN_OFF +T-1 , where N is the first timeslot which is not invalid (e.g., corresponding to 5 ms in section 3.4.) Then the timeslot for sending C-WLIS may be calculated, e.g., by (PCI%T)+ MIN_OFF.

Another timeslot based approach may be based on representing the cell-ID in binary form by transmitting or not-transmitting a signal within consecutive timeslots. Since 1008 physical cell- IDs need to be represented, a sequence of 10 bit is sufficient to represent a particular cell-ID. As an example, the cell-ID represented as 0101111111 in binary form is considered. In this example, no C-WLIS is transmitted in the 1^st time slot, a C-WLIS is transmitted in the 2^nd timeslot, no C-WLIS is transmitted in the 3^rd timeslot, and a C-WLIS is transmitted in the 4^th to 10^th timeslot. This allows for an easy representation of the cell-ID such that the corresponding cell may be woken up by the UE.

1.3 Timeslot and PRACH based

Some embodiments can implement a hybrid approach combining the PRACH approach of section 1.1. and the timeslot approach of section 1.2. For example, the cell ID may be divided into two parts, one part consisting of 6 bits of the physical cell ID and another part consisting of 4 bits of the physical cell ID. In order to send C-WLIS the UE determines one timeslot of T=16 timeslots, each corresponding to one of the 4-bit string obtained by the cell ID. The 6 bit string is then used to define which PRACH preamble/sequence should be transmitted on that timeslot to wake-up the cell.

2. Frequency Resources for C-WUS

For a UE in connected mode wanting to wake up its gNB (i.e., demanding for transmitting regular SSB/SIB1 in full), similar to the information the UE has about the frequency location of the gNB in the DL synchronization raster, the C-WUR listening frequency location of the gNB(s) also can be pre-configured in the UE’s history, such that the UE can do the C-WUS UL transmission at the correct frequency location.

For idle/inactive UEs without any information about the gNBs’ DL synchronization frequency location as depicted in Fig. 11 , the C-WUS detection latency can be reduced (or even minimized) by limiting the possible C-WUR listening frequency positions of the gNBs to predefined values. Specifically, Fig. 11 shows a schematic representation of on-demand SSB/SIB1 transmission from a gNB 400 triggered by UL C-WUS 422 transmissions that are blindly repeated from the UE 402, with no sync/SI information transmitted by the gNB 400 during NES mode. As shown in Fig. 11 , in a NES mode no sync/SI information is transmitted by the gNB 400, so that the UE 402 blindly repeats the transmissions of the C-WUS 422 until a transmission of a C-WUS 422 is located in a C-WUR occasion 430, where the gNB 400 switches from the NES mode into a normal mode (e.g., on-demand SSB/SIB1 mode) in which SSB/SIB1 420 are transmitted. For a simplest pre-configuration, C-WUR frequency location can be fixed to one particular value known to the UEs.

With predefined/preconfigured knowledge of the possible C-WUR listening frequency positions the UEs can limit the UL C-WUS repetitions to only those frequency positions until they meet the C-WUR listening occasions in time. Such receiver can be implemented with matched filterbased time-domain detectors that tolerate possible frequency offsets.

Additionally, prior to switching to inactive I sleep mode, the cell may transmit a notification including the information about frequency and optionally time (where and when) the cell would listen to the C-WUR. This notification could be broadcast by the cell using, e.g., a “regular” SSB sent including the indication about when the UEs should send a C- WUR signal to the cell, e.g., using o pdcch-ConfigSIB or any other existing or new (additional) MIB parameter providing information of the uplink frequency (optionally in addition: time) configuration I position to the UE for sending a C-WUR signal to the cell, or o pdcch-ConfigSIB of the MIB, splitting or extending the currently 8 bits including the uplink frequency (optionally in addition: time) configuration I position to the UE for sending a C-WUR signal to the cell, or any SIB (e.g., the last regular, periodically sent SIB1). Optionally, the same SIB (e.g., SIB1) may provide information of the uplink frequency (optionally in addition: time) configuration I position to the UEs for sending a C-WUR signal to the cell.

3. Time Patterns and Time Strategies for C-WUS

3.1 Suitable C-WUS ON-durations and Periodicity

In other embodiments, the blind repetition of the UL C-WUS transmissions without explicit timing synchronization with the C-WUR listening occasions can be improved via preconfigurations of the ON-durations of the C-WUR occasions and the C-WUS transmissions. Specifically, the timing of the C-WUR listening occasions in terms of the duration of each occasion and the periodicity are preconfigured and are known to the UEs such that the UE C- WUS ON-durations and periodicity, or duty cycle, can be selected to reduce (or even minimize) the latency or time taken for successful detection of the C-WUS by the C-WUR. Such preconfigurations can potentially reduce the latency incurred by increasing the probability for the C-WUS to reach the gNB during the C-WUR occasions with fewer blind repetitions. For example, the C-WUR occasions can be specified as having integer multiple of the length of the UL C-WUS ON-durations. As the C-WUR ON-duration increases, as depicted in Fig. 12, the time taken for successful detection of the UL C-WUS transmissions increases. Specifically, Fig. 12 shows a schematic representation of large/always-ON C-WUR occasion 430 to detect blind UL C-WUS 422 transmissions quickly, with no sync/SI information transmitted by the gNB 400 during NES mode. As indicated in Fig. 12, due to the large/always-ON C-WUR occasion 430, the UL C-WUS 422 transmission from the UE 402 can be detected quickly, so that the gNB can switch in response to the detection of the C-WUS 422 from the NES mode into a normal mode (e.g., on-demand SSB/SIB1 mode) in which SSB/SIB1 420 are transmitted.

A limiting case of the example in Fig. 12 then becomes an always-ON C-WUR that can detect with high probability the UL C-WUS transmitted by a UE in the correct frequency position. With the prospect of low-power consuming matched filter-based dedicated C-WUR implementation (i.e., other than the regular UL receiver at the gNB with all processing chains) doing the detection in time-domain, this approach can potentially give much better NES with low delay. In effect, such an approach does not need any time synchronization information for the C-WUS transmission.

Additionally, prior to switching to inactive I sleep mode, the cell may transmit a notification including the information about frequency and optionally time (e.g., where and when) the cell would listen to the C-WUR I C-WUS. This notification could be broadcast by the cell using, e.g., a “regular” SSB sent including the indication about when the UEs should send a C- WUR I C-WUS signal to cell, e.g., using o pdcch-ConfigSIB or any other existing or new (additional) MIB parameter providing information of the uplink frequency (optionally in addition: time) configuration I position to the UE for sending a signal to the cell, or o pdcch-ConfigSIB of the MIB, splitting or extending the currently 8 bits including the uplink frequency (optionally in addition: time) configuration I position to the UE for sending a signal to the cell, or any SIB (e.g., the last regular, periodically sent SIB1). Optionally, the same SIB (e.g., SIB1) may provide information of the uplink frequency (optionally in addition: time) configuration / position to the UEs for sending a C-WUR / C-WUS signal to the cell.

3.2 C-WUR Occasions Drifted from C-WUS Tries In some embodiments, the gNB can follow a certain periodicity of the C-WUR occasions while the UE can repeat C-WLIS with a different periodicity. For example, the gNB can attempt to receive C-WLIR for 1 ms out of every 10 ms. The UE instead can send WUS every 11 ms. Then, even if the UE starts at a time where the gNB has the receiver off, after a certain number of tries the UE C-WUS occasion will drift into the C-WUR reception occasion and the UE will wake-up the cell successfully. This causes the periods of gNB reception (C-WUR) and UE reception to drift to each other, creating some occasional matches. This can be used to create matches without any synchronization at all. This concept is illustrated in Fig. 13. In detail, Fig. 13 shows in a schematic representation that gNB periodicity of gNB occasions and repetitions of C-WUS can be chosen deliberately to have different periodicities. As shown in Fig. 13, the C-WUR occasions 430 can have a first periodicity (e.g., 10ms), where the C-WUS 422 is transmitted by the UE 402 repeatedly with a second periodicity, different from the first periodicity, e.g., 11 ms, so that one of the C-WUS 422 transmission matches a C-WUR occasion 430, so that the gNB can switch in response to the detection of the C-WUS 422 from the NES mode into a normal mode (e.g., on-demand SSB/SIB1 mode) in which SSB/SIB1 are transmitted.

This may be a preferred embodiment when there is no time reference at all, for example when there is no transmission of DL signals at all and sending of wake-up signals is relatively rare.

Note that this embodiment allows the gNB to work with a sparse duty cycle (e.g., 10%) but when a wake-up is needed the UE may need to transmit C-WUS multiple times, potentially leading to increased UE power consumption.

3.3. Matching C-WUS and C-WUR based on a pseudo random sequence

In some embodiments the periodicity of a C-WUR occasion and C-WUS repetition may be the same, but time matching can be performed by the UE transmitting in different timeslots, in the time reference of the UE itself, according to a pseudo-random sequence. This concept is illustrated in Fig. 14. Specifically, Fig. 14 shows in a schematic representation that the C-WUS repetitions follow a random or pseudo-random pattern until it successfully wakes-up the cell. As shown in Fig. 14, the C-WUR occasions 430 can have periodicity (e.g., 10ms), where the C-WUS 422 is transmitted with the same period as the C-WUR occasions 430, but each C- WUS 422 transmission in a different timeslot based on the UE time reference itself.

As a concrete example of such embodiment aiming at an assumed frame of 10 ms, the UE may divide the 10 ms into “timeslots” of 1 ms. Then, a pseudo-random sequence may generate the 10 “timeslots” in a certain sequence, e.g., 5, 8, 9, 0, 3, 2, 4, 1 , 7, 6. The UE transmit C- WUS first on timeslot 5 relative to some internal time reference (or other time reference). If not successful, it transmits on timeslot 8 after the time reference. Then timeslot 9 and so on.

In some embodiments, the periodicity of a C-WUR occasion and C-WLIS repetition may be the same, but time matching can be performed by the gNB receiving in different timeslots, in the time reference of the gNB itself, according to a pseudo-random sequence. In other words, the roles of the UE and gNB can be interchanged.

In other embodiments, the periodicity of a C-WUR occasion and C-WUS repetition may be the same, but time matching can be performed by both the UE transmitting in different timeslots and the gNB receiving in different timeslots, in the time reference of UE itself and the gNB itself, respectively, according to a respective pseudo-random sequence. The pseudo-random sequence used by the UE and the gNB may be identical or different from one another.

Using a pseudo-random sequence may particularly be advantageous if no synchronization between the UE and the gNB(s) is available. The periodicity as defined above may be preconfigured.

3.4 Offset Between Light Synchronization and C-WUR Occasions

In the absence of SIB1 (e.g., which is omitted to save energy) a UE cannot determine the point in time of the PSS+SSS or SSB compared to the gNB frame. The UE also does not know if there are other SSBs on the SSB burst. It cannot also determine what is the frame configuration and TDD pattern. This means also that the UE does not know where uplink is located in time.

In some embodiments, this difficulty can be overcome by providing a fixed time offset between light synchronization and C-WUR occasions. This fixed time can be specified for each band differently. Values between 5 ms and 15 ms may be preferred in order to avoid clashing a C- WUS occasion with any other part of a SSB burst.

Such time offset may be combined with different timeslots for C-WUS to different cell IDs (see section 1.2).

In case PSS+SSS and/or SSBs are beamformed and transmitted in a burst, multiple C-WUR occasions may exist, one corresponding to each different beam. In this case, also a fixed timing offset between PSS+SSS and C-WUR occasion can help preventing any clashing. 4. Power constraints and power control for C-WUS

In the case without any prior DL synchronization and/or system information made available at the UE before it transmits the UL C-WUS, information for doing UL power control for the C- WUS is lacking. In such case, an approach of ramping up the transmission power across the multiple repetitions of the C-WUS can be adopted. However, this is also an issue. Compared, for example, to PRACH configuration for initial access the ramping up parameters are also missing, as these parameters are normally transmitted in SIB-1 and SIB-1 is not transmitted to save energy.

A power ramp-up configuration can include, for example, one or more out of:

• a reference value which tells the UE which power the gNB used to transmit the reference signals used for UE received power measurements,

• a maximum target received power for the UL signal,

• a ramp-up step, which determines the power increase on each new try,

• a maximum number of tries.

All of that is normally transmitted in SIB-1 , for PRACH. This information is, however, missing at the point in time a UE needs to send a C-WUS.

In order to overcome this issue, in some embodiments, the UE may be pre-configured with ramp-up parameters to be used for controlling the C-WUS transmit power. These parameters may be specified separately for each band and/or GSCN range. The C-WUS transmit power parameters may include pre-defined values, such as one or more out of:

• assumed transmit power for the reference signals (e.g., PSS I SSS),

• fixed maximum target received power for C-WUS at the gNB (e.g., one value for each band),

• fixed ramp-up step, normally given in dB,

• number of repetitions of C-WUS before a power increase,

• maximum number of tries or timeout to quit sending C-WUS.

These parameters - instead of being pre-configured - can also be obtained by dedicated (implicit or explicit) configuration by a macro cell (e.g., coverage cell). A coverage cell that may be available in the area can include system information about other (neighbor) cells or small cells in the coverage area and parts of their configuration parameters. Included in these ‘foreign cell’ configuration can be the availability and state of C-WUR/WUS (active, inactive, deep sleep, etc.) and other parameters, such as one or more out of: time/frequency of WUR/WUS occasions, periodicity of C-WUR/WUS occasions, transmit power or power class of the cell, transmit power or power class of the C-WUS.

Power ramping parameters. Given at least one out of these parameters the UE can even though no SI of the C-WUR/WUS cell is available at the moment, configure the transmission of the C-WUS.

5. Conditions for C-WUS/WUR

Cells supporting C-WUR/WUS that are in deep sleep mode (instead of, e.g., ‘power off’) might listen to C-WUS very rarely or not listen to C-WUS signals at all. If the network is aware of the fact that these cells cannot receive C-WUS, the network can re-activate I re-configure listening to C-WUS of these cells if capacity or coverage or other network conditions (e.g., failover, maintenance of macro-cells, etc.) are met.

Similar to cells in a sleep mode not I no longer listening to C-WUS, cells in any type of sleep mode (rarely) listening to C-WUS may be re-configured regarding C-WUS reception, e.g., the periodicity the cell listens to C-WUS, e.g., in case of critical conditions (see e.g., conditions listed below) the periodicity may increase, and/or the cell may be able to continuously receive C-WUS, e.g., in case of critical conditions (see, e.g., conditions listed below).

In embodiments, a re-activation or re-configuration of the deep-sleep cells can be triggered also dependent on UE behavior, e.g., when a UE reaches the cell-edge of a neighbor cell or is expected to be located in an area with certain coverage conditions (high probability of RLF, handover or critical fading conditions). These conditions could for example either be measured by the current active cell (e.g., macro cell) or based on historical data.

In embodiments, the decision to re-activate a cell in deep-sleep state (i.e. enabling c-WUR, reactivate full cell operation, etc.) may therefore be based on at least one of the following conditions: location of the UE, e.g., o cell edge, o area with difficult radio conditions, o high capacity area (e.g., where the current cell already provides high capacity and there would be more capacity available), o low capacity area (e.g., where the current cell cannot provide enough capacity, but another cell could), o high user area (e.g., where a lot of users are active), o area with high chance of RLF, active beam of the macro cell, where the UE is configured, and/or o where the beam is directed in a certain area (e.g., tagged with network control properties), o where the beam is serving a high number of UEs, or o where the QoS of the beam/UE is impaired, channel properties, e.g., fading, CQI, attenuation, channel measurements of the UE, indication from the UE regarding o carrier aggregation, o handover, o QoS requirements, o link degradation, and/or o capacity needs

If the current active macro cell can estimate the position/location of the UE and if the network considers it to be suitable for the C-WUS/WUR enabled cell to leave deep-sleep state, the network can configure/inform the C-WUS/WUR cell to listen for C-WUS again. This setup is illustrated in Fig. 14. Specifically, Fig. 14 shows a schematic representation of a macro Cell 440 and C-WUR cell 400 with optional beam 444, UE 402 and network controller 442.

On the other hand, the macro cell can configure/inform the UE that a C-WUS/WUR cell is available and handover or CA to this cell can be established by sending C-WUS.

In embodiments, there are at least two possible ways to inform, e.g., ‘cell-edge’ or any further devices that could use C-WUS for a nearby cell about the availability of any type of “sleeping”, C-WUR enabled cell:

• Common signal, e.g., broadcast system information (cell-wide), e.g., from an associated macro cell or of a second carrier for cell configured with CA or any kind of associated beam the cell in (any type of) sleep mode may be associated to. Direct signaling, e.g., RRC messages, e.g., of the associated macro cell or of a second carrier for cell configured with CA or any kind of associated beam.

5.1 UE configuration and information

Given the description above where C-WLIR cells are configured to listen for C-WLIS signals sent by a UE, the UE may need to know about the presence of cells where C-WUR is configured. This is a requirement, when the C-WUR cells are not sending out periodic signals, e.g., reference signals, synchronization signals and/or SI.

In embodiments, while the UE is connected to a macro cell (or coverage cell or primary cell) and depending on conditions of the UE, the coverage cell and the C-WUR cells, the UE can be informed by system information or direct signaling (e.g., RRC, MAC CE) about the availability of one or more C-WUR cells.

In embodiments, if the C-WUR cell is already listening to C-WUS, there is not necessarily the need to do any (re-) configuration of the C-WUR cell.

In embodiments, the information sent from the macro cell to the UE can include at least one out of the following:

• cell ID of the C-WUR cell(s),

• C-WUR frequency,

• C-WUR periodicity/timing,

• transmission power of the C-WUR cell(s),

• coverage area of the C-WUR cell(s),

• QoS features of the C-WUR cell(s),

• bandwidth of the C-WUR cell(s),

• other system information.

In embodiments, there can be more than one coverage cells (e.g., in different bands, different frequencies in one band, etc). A coverage cell can have multiple beams as well, each of which can carry different information about available C-WUR cells. There can be more than one C- WUR cell available in the area of a coverage cell. There can be more than one C-WUR cell in the coverage area of a beam of the coverage cell.

In embodiments, the term coverage cell does not necessarily indicate a large coverage area.

It is more bound to the provision of “coverage” in terms of connection, while the C-WUR cell is not providing coverage by default (e.g., due to the missing ref- and sync-signals) as described above.

5.2 Scenarios

As shown in Fig. 15, one possible scenario consists of a macro cell 440 (coverage cell) and a small cell 400 that is C-WUR enabled. It is not necessary that the coverage cell 440 also supports C-WUR/WUS, but need to support configuration messages.

In embodiments, the UE 402 within reach of the small cell 402 can be configured by the macro cell 440 to store C-WUS/WUR configuration regarding the small cell. Optionally, the UE 402 can be configured to perform C-WUS procedure in order to wake-up the small cell.

Based on the above-mentioned criteria the network could configure the small cell to exit deep sleep as well (existing behaviour). The disadvantage of this procedure would be that this is independent of the actual requirement of the UE to detect the small cell and receive system information. The preemption of transmitting SI in the small cell and therefore exit a sleep state could be wrong in case the UE is not ready or willing to switch cells.

Another scenario can be to have co-located cells on different bands or with different cellconfigurations (regarding coverage). The active cell would be able to inform the UEs of a 2^nd available cell that can be used after C-WUS procedure. It would be up to the UE to enable this cell, e.g., to increase data rate or reliability via carrier aggregation or because of interference in the current band in order to detect other available cells for handover.

While the inactive (deep sleep) cell will usually not receive C-WUS, the network can switch the C-WUR on when it deems necessary, e.g., due to capacity reasons, interference, coverage.

5.3 Cell/network communication

Information about conditions can be shared via established network interfaces. Given the reference point representation in Fig. 16, the gNodeB (RAN) could make use of the N2 connection to the AMF to use load balancing functions. Specifically, Fig. 16 shows a schematic representation of TS 23.501 Reference Point representation of nn-roaming 5g system model.

The NG interface between RAN and 5GC is an open interface that can be extended (TS 38.410 Chap. 4) to fulfill new requirements. The C-WUS/WUR configuration, the message exchange between cells with and without C-WUR and overall control of these cells can be implemented using the NG interface. In this case, the base stations do not directly communicate to each other but rely on the core network or a network function to forward messages or take care of the interaction.

Fig. 17 illustrates a system overview of a combined 4G/5G network. Specifically, Fig. 17 shows a schematic representation of 5G/LTE NodeB connections. While the names of the interfaces could be different in a 5G-only network, the overall concept of connections between base stations and the core functions will be similar.

The X2-LI interface is defined for communication between RAN nodes in non-standalone mode. For a 5G-only system, the communication between two RAN nodes, e.g., gNodeBs, is defined as Xn interface.

Given that the above mentioned NG interface is point-to-point connection between the base station and the network, the Xn interface is a direct connection between two base stations.

Therefore, the interaction between two cells (e.g., coverage cell and C-WLIR cell) can be implemented via extending the Xn interface to include specific functionality to enable/disable C-WUS.

Fig. 18 shows a schematic representation of a macro base-station 440 exchanging Xn messages with small cell base station 400 in order to control the activation and de-activation of C-WLIR and exchanging parameters which can be forwarded to the UE.

5.4

Subsequently, an example procedure is provided.

1 . UE is camping on a macro cell (coverage cell).

2. Macro cell detects that UE is a. at the cell edge or b. in a high capacity area.

3. Macro cell indicates to the small cell or the network to enable C-WUR in the small cell (or a number of small cells in a logical or physical area).

4. Macro cell indicates to the UE at least on out of a. that a C-WUR cell is available, b. the cell ID of the C-WUR cell, c. basic system information of the other cell to assist in transmitting the C-WLIS.

5. UE decides upon transmitting a C-WLIS (based in pre-defined or configured parameters).

6. UE transmits C-WUS, C-WUR cell receives C-WUS.

7. C-WUR cell transmits SI.

8. UE receives SI from C-WUR cell.

9. UE can connect to C-WUR cell, trigger handover, get handover indication from network or indicate C-WUR cell properties/measurements to the network or the Macro cell.

6. Further embodiments

Embodiments described herein provide a concrete C-WUS design. In embodiments, the C- WUS design allows existing gNB receivers as a C-WUR and one which allow longer sleep periods, with minimal to no periodic DL transmissions needed for the C-WUR transmission in UL.

Embodiments described herein allow for energy saving of the cell allowed by the extended inactive I sleep mode periods: the network may save significantly energy as the cell can go to a rather deep sleep mode (significant energy saving) for extended periods as it will not need to periodically broadcast SSB I SIB messages. The cell will only be re-activated I woken up once UE(s) detect a demand for e.g., increased capacity demanding the use of the currently deactivated I sleeping cell.

Various elements and features of the present invention may be implemented in hardware using analog and/or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. For example, embodiments of the present invention may be implemented in the environment of a computer system or another processing system. Fig. 19 illustrates an example of a computer system 500. The units or modules as well as the steps of the methods performed by these units may execute on one or more computer systems 500. The computer system 500 includes one or more processors 502, like a special purpose or a general-purpose digital signal processor. The processor 502 is connected to a communication infrastructure 504, like a bus or a network. The computer system 500 includes a main memory 506, e.g., a random-access memory (RAM), and a secondary memory 508, e.g., a hard disk drive and/or a removable storage drive. The secondary memory 508 may allow computer programs or other instructions to be loaded into the computer system 500. The computer system 500 may further include a communications interface 510 to allow software and data to be transferred between computer system 500 and external devices. The communication may be in the from electronic, electromagnetic, optical, or other signals capable of being handled by a communications interface. The communication may use a wire or a cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels 512.

The terms “computer program medium” and “computer readable medium” are used to generally refer to tangible storage media such as removable storage units or a hard disk installed in a hard disk drive. These computer program products are means for providing software to the computer system 500. The computer programs, also referred to as computer control logic, are stored in main memory 506 and/or secondary memory 508. Computer programs may also be received via the communications interface 510. The computer program, when executed, enables the computer system 500 to implement the present invention. In particular, the computer program, when executed, enables processor 502 to implement the processes of the present invention, such as any of the methods described herein. Accordingly, such a computer program may represent a controller of the computer system 500. Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system 500 using a removable storage drive, an interface, like communications interface 510.

The implementation in hardware or in software may be performed using a digital storage medium, for example cloud storage, a floppy disk, a DVD, a Blue-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention may be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine-readable carrier. Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine-readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet. A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein. A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein are apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein. List of References [1] TR 38.864 v18.1.0 “Study on network energy savings for NR” , March 2023

[2] TS 23.501 v18.4.0 “System architecture for the 5G System (5GS)”, December 2023

[3] TS 38.410v 18.0.0 “NG-RAN; NG general aspects and principles” , December 2023

Abbreviations

3GPP third generation partnership project

ACK acknowledgement

ARFCN absolute radio frequency channel number

BFD beam failure detection

BFR beam failure recovery

BRP beam forming resource pool

BWP bandwidth part

BS base station

C-WLIS cell wake-up signal

CD-SSB cell-defining synchronization signal block

CDM code division multiplexing

CG configured grant

CRI CSI-RS resource indicator

CQI channel quality information

CSI channel state information

CSI-RS channel state information - reference signal

D2D device-to-device

DC dual conectivity

DCI downlink control information

DL downlink

DM-RS demodulation reference signal

DRS discovery reference signal

DRX discontinues reception

DTX discontinues transmission eNB evolved node B

FR frequency range

FR1 frequency range one

FR2 frequency range two gNB next generation node B

GSCN global synchronization channel number

HARQ hybrid automatic repeat request

IC in-coverage - within the coverage of another transceiver

ID identity IFFT inverse fast Fourier transform loT internet of things

OOC out-of-coverage - out of the coverage of another transceiver, i.e. out of the coverage area of a base station

LTE long-term evolution

MAC medium access control

MAC-CE medium access control - control element

MCC mobile country code

MCG master cell group

MIB master information block

MNC mobile network code

MSI minimum system information

NACK negative acknowledgement

NCD-SSB non cell-defining synchronization signal block

NES network energy savings

NPN non-public network

NR new radio

OFDM orthogonal frequency-division multiplexing

OFDMA orthogonal frequency-division multiple access

PBCH physical broadcast channel

PC partial-coverage - one transceiver is in-coverage, another one is out-of- coverage

PC5 interface using the sidelink channel for D2D communication

PCI Physical cell ID

PDCCH physical downlink control channel

PDSCH physical downlink shared channel

PLMN public land mobile network

PM I precoding matrix indicator

PRACH physical random access channel

PRS positioning reference signal

PSBCH physical sidelink broadcast channel

PSCCH physical sidelink control channel

PSFCH physical sidelink feedback channel

PSS primary synchronization signal

PSSCH physical sidelink shared channel

PLICCH physical uplink control channel

PLISCH physical uplink shared channel QCL quasi - colocation RACH random access channel RAN radio access networks RB resource block RE resource element RedCap reduced capability RMSI remaining minimum system information RNTI radio network temporary identifier RRC radio resource control RS reference signal RSRP reference signal received power RSRQ reference signal received quality SCI sidelink control information SCG secondary cell group SCS subcarrier spacing SI system information SIB system information block SL sidelink SPS semi persistent scheduling SR scheduling request SRS sounding reference signal SSB synchronization signal block SSS secondary synchronization signal S-SSB sidelink synchronization signal block sTTI short transmission time interval TDD time division duplex TP trigger procedure TRS tracking reference signal UAC unified access control UE user equipment, e.g., a smartphone or loT node UL uplink UMTS universal mobile telecommunication system V2X vehicle-to-everything V2V vehicle-to-vehicle WUS wake-up signal x-MSI cross-carrier minimum system information

Claims

1. T ransceiver (402) for a wireless communication network, wherein the transceiver (402) is configured to transmit a wake-up signal (422) to a central transceiver (400) that is operable in an energy saving mode of operation, wherein the transceiver (402) is configured to determine a wake-up signal configuration for the wake-up signal (422) and to generate the wake-up signal (422) based on the wake-up signal configuration, wherein at least a part of the wake-up signal configuration is not explicitly signaled to the transceiver (402) by the central transceiver (400) and/or another central transceiver of the wireless communication network.

2. Transceiver (402) according to the preceding claim, wherein the transceiver (402) is configured to transmit the wake-up signal (422) to the central transceiver (400) independent of a reception of a synchronization signal (420) from the central transceiver (400), or wherein the transceiver (402) is configured to transmit the wake-up signal (422) to the central transceiver (400) using reduced synchronization information obtained by receiving a reduced synchronization signal (421) from the central transceiver (400).

3. Transceiver (402) according to the preceding claim, wherein the reduced synchronization signal (421) is a primary synchronization signal only, a primary and a secondary synchronization signal only, or a synchronization signal block only.

4. Transceiver (402) according to one of the preceding claims, wherein in the energy saving mode of operation the central transceiver (400) transmits no synchronization signals (420), transmits only primary synchronization signals, transmits only primary and secondary synchronization signals, or transmits only synchronization signal blocks.

5. Transceiver (402) according to one of the preceding claims, wherein the wake-up signal configuration comprises at least one out of one or more frequencies for transmitting the wake-up signal (422), one or more time intervals for transmitting the wake-up signal (422), an indication of a transmit power used for transmitting the wake-up signal (422), an indication of a waveform used for transmitting the wake-up signal (422).

6. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to receive, in response to a transmission of the wake-up signal (422), a synchronization signal (420) from the central transceiver (400).

7. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to retransmit the wake-up signal (422) using blind repetitions.

8. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to determine an identification, ID, of the central transceiver (400), wherein the transceiver (402) is configured to determine the wake-up signal configuration based on the identification, ID, of the central transceiver (400).

9. Transceiver (402) according to claim 8, wherein the transceiver (402) is configured to determine the identification, ID, of the central transceiver (400) based on at least one out of a reduced synchronization signal (421) received form the central transceiver (400), historical information, a signaling information received from the central transceiver (400) prior to its switching into the energy saving mode of operation, pre-configuration, a signaling information received from another central transceiver of the wireless communication network.

10. Transceiver (402) according to one of the claims 8 to 9, wherein the transceiver (402) is configured to select, based on the identification, ID, of the central transceiver (400), a wake-up signal configuration out of a plurality of different wake-up signal configurations.

11. T ransceiver (402) according to one of the claims 8 to 10, wherein the wake-up signal configuration defines at least one specific sequence or preamble associated with the identification, ID, of the central transceiver (400), wherein the transceiver (402) is configured to transmit the wake-up signal (422) comprising the at least one specific sequence or preamble.

12. Transceiver (402) according to claim 11 , wherein the at least one specific sequence or preamble is at least one physical random access channel, PRACH, sequence or preamble.

13. Transceiver (402) according to one of the claims 11 to 12, wherein the wake-up signal configuration defines at least two wake-up signals and at least two specific sequences or preambles associated with the identification, ID, of the central transceiver (400), wherein a first wake-up signal of the at least two wake-up signals comprises a first specific sequence or preamble of the at least two specific sequences or preambles, wherein a second wake-up signal of the at least two wake-up signals comprises a second specific sequence or preamble of the at least two specific sequences or preambles, wherein the transceiver (402) is configured to transmit the at least two wake-up signals according to the wake-up signal configuration.

14. Transceiver (402) according to the preceding claim, wherein the at least two specific sequences or preambles are associated with different portions of the identification, ID, of the central transceiver (400).

15. Transceiver (402) according to one of the claims 8 to 14, wherein the wake-up signal configuration defines at least one time interval for transmitting the wake-up signal (422), wherein the at least one time-interval is associated with the identification, ID, of the central transceiver (400).

16. Transceiver (402) according to claim 15, wherein transceiver (402) is configured to determine the at least one time interval out of a plurality of different time intervals based on the identification, ID, of the central transceiver (400) and a time slot assigning function.

17. Transceiver (402) according to one of the claims 8 to 16, wherein the wake-up signal configuration defines at least one specific sequence or preamble, wherein the wake-up signal configuration defines at least one time interval for transmitting the wake-up signal (422), wherein the transceiver (402) is configured to determine the at least one specific sequence or preamble based on a first portion of the identification, ID, of the central transceiver (400), and wherein the transceiver (402) is configured to determine the at least one time interval for transmitting the wake-up signal (422) based on a second portion of the identification, ID, of the central transceiver (400), different from the first portion.

18. Transceiver (402) according to one of the preceding claims, wherein the wake-up signal configuration defines at least one frequency for transmitting the wake-up signal (422).

19. Transceiver (402) according to claim 18, wherein the transceiver (402) is configured to determine the at least one frequency based on at least one out of pre-configuration, a signaling information received from the central transceiver (400) prior to its switching into the energy saving mode of operation.

20. Transceiver (402) according to claim 18, wherein the at least one frequency is associated with an identification of the central transceiver (400).

21. T ransceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to retransmit the wake-up signal (422), wherein the transceiver (402) is configured to determine time instants for the initial transmission and the retransmission of the wake-up signal (422) based on an information describing a wake-up signal reception interval of the central transceiver (400).

22. Transceiver (402) according to claim 21 , wherein the information describing the wake-up signal reception interval is at least one out of a wake-up signal reception interval length, a wake-up signal reception interval periodicity, a wake-up signal reception interval duty cycle.

23. Transceiver (402) according to one of the claims 21 to 22, wherein the transceiver (402) is configured to obtain the information describing a wakeup signal reception interval of the central transceiver by at least one out of pre-configuration, a signaling information received from the central transceiver (400) prior to its switching into the energy saving mode of operation.

24. Transceiver (402) according to one of the claims 21 to 23, wherein the transceiver (402) is configured to retransmit the wake-up signal (422) with a period between the initial transmission of the wake-up signals and the retransmissions of the wake-up signal that is different than a period of a wake-up signal reception interval periodicity used by the central transceiver.

25. Transceiver (402) according to one of the claims 21 to 23, wherein a wake-up signal transmission interval is aligned with the wake-up signal reception interval of the central transceiver (400).

26. Transceiver (402) according to claim 25, wherein the transceiver (402) is configured to randomly distribute a time instant for the retransmissions of the wake-up signal (422) within the wake-up signal transmission interval that is aligned with the wake-up signal reception interval.

27. Transceiver (402) according to one of the claims 2 to 26, wherein the information describing the wake-up signal reception interval further describes a time offset between the reduced synchronization signal (421) and the wake-up signal reception interval.

28. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to retransmit the wake-up signal (422), wherein the transceiver (402) is configured to increase the transmit power for each retransmission of the wake-up signal (422).

29. Transceiver (402) according to claim 28, wherein the transceiver (402) is configured to increase the transmit power for each retransmission of the wake-up signal (422) based on a power ramp-up configuration.

30. Transceiver (402) according to claim 29, wherein the power ramp-up configuration defines at least one out of a reference power value, a maximum target power value, a ramp-up step, a maximum number of retransmissions.

31. T ransceiver (402) according to one of the claims 29 to 30, wherein at least a part of the power ramp-up configuration is pre-configured.

32. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to transmit the wake-up signal (422) in dependence on one or more of the following conditions: a location of the transceiver (402), an active beam of a macro cell, channel properties, channel measurements, an indication from the transceiver.

33. Transceiver (402) according to one of the preceding claims, wherein the transceiver (402) is configured to receive a signaling information from another central transceiver of the wireless communication network, the signaling information signaling a presence of the central transceiver (400), wherein the transceiver (402) is configured to transmit the wake-up signal (422) in response to a reception of the signaling information.

34. Transceiver (402) according to claim 33, wherein the transceiver (402) is configured to receive the signaling information via common signaling or direct signaling.

35. Transceiver (402) according to one of the claims 33 to 34, wherein the signaling information comprises at least one out of an identification of the central transceiver (400), at least one parameter of the wake-up signal configuration, a coverage area of the central transceiver (400), a quality of service parameter of the central transceiver (400), a bandwidth of the central transceiver (400).

36. Central transceiver (400) for a wireless communication network, wherein the central transceiver (400) is operable in an energy saving mode of operation, wherein the central transceiver (400) is configured to receive a wake-up signal (422) from a transceiver (402) of the wireless communication network, wherein the central transceiver (400) is configured to transmit, in response to the reception of the wake-up signal (422), a synchronization signal(420), wherein a transmission and/or generation of the wake-up signal (422) is based on a wake-up signal configuration, wherein at least a part of a wake-up signal configuration is not signaled to the transceiver (402) by the central transceiver (400) in the energy saving mode of operation.

37. Central transceiver (400) according to the preceding claim, wherein the central transceiver (400) is configured to not transmit any synchronization signal (420) in the energy saving mode of operation, or wherein the central transceiver (400) is configured to only transmit a reduced synchronization signal (421) in the energy saving mode of operation.

38. Central transceiver according to the preceding claim, wherein the reduced synchronization (421) signal is a primary synchronization signal only, a primary and a secondary synchronization signal only, or a synchronization signal block only.

39. Central transceiver (400) according to one of the preceding claims, wherein the central transceiver (400) is configured to, in the energy saving mode of operation, transmit no synchronization signals, transmit only primary synchronization signals, transmit only primary and secondary synchronization signals, or transmit only synchronization signal blocks.

40. Central transceiver (400) according to one of the preceding claims, wherein the central transceiver (400) is configured to, in response to the reception of the wake-up signal (422), switch from the energy saving mode into a normal operation mode, or to maintain the normal operation mode.

41. Central transceiver (400) according to the preceding claim, wherein the central transceiver (400) is configured to, in the normal operation mode, to transmit regular synchronization signals.

42. Central transceiver (400) according to one of the preceding claims, wherein the wake-up signal configuration is associated with an identification of the central transceiver (400).

43. Central transceiver (400) according to claim 42, wherein the central transceiver (400) is configured to signal its identification to the transceiver (402) in a normal operation mode or by means of a reduced synchronization signal (421) in the energy saving operation mode.

44. Central transceiver (400) according to one of the claims 42 to 43, wherein the wake-up signal configuration defines at least one specific sequence or preamble associated with the identification, ID, of the central transceiver (400), wherein the central transceiver (400) is configured to transmit the synchronization signal (420) only in case that the wake-up signal (422) comprises the at least one specific sequence or preamble associated with the identification, ID, of the central transceiver (400).

45. Central transceiver (400) according to claim 44, wherein the at least one specific sequence or preamble is at least one physical random access channel, PRACH, sequence or preamble.

46. Central transceiver (400) according to one of the claims 44 to 45, wherein the wake-up signal configuration defines at least two wake-up signals and at least two specific sequences or preambles associated with the identification, ID, of the central transceiver (400), wherein a first wake-up signal of the at least two wake-up signals comprises a first specific sequence or preamble of the at least two specific sequences or preambles, wherein a second wake-up signal of the at least two wake-up signals comprises a second specific sequence or preamble of the at least two specific sequences or preambles, wherein the central transceiver (400) is configured to receive the at least two wake-up signals and transmit the synchronization signal (420) only in case that the at least two wake-up signals comprise the at least two specific sequences or preambles associated with the identification, ID, of the central transceiver (400).

47. Central transceiver (400) according to the preceding claim, wherein the at least two specific sequences or preambles are associated with different portions of the identification, ID, of the central transceiver (400).

48. Central transceiver (400) according to one of the claims 42 to 47, wherein the wake-up signal configuration defines at least one time interval in which the wake-up signal is transmitted, wherein the at least one time-interval is associated with the identification, ID, of the central transceiver (400).

49. Central transceiver (400) according to one of the claims 42 to 48, wherein the wake-up signal configuration defines at least one specific sequence or preamble, wherein the wake-up signal configuration defines at least one time interval in which the wake-up signal is transmitted, wherein the at least one specific sequence or preamble is determined based on a first portion of the identification, ID, of the central transceiver (400), and wherein the at least one time interval for transmitting the wake-up signal is determined based on a second portion of the identification, ID, of the central transceiver (400), different from the first portion.

50. Central transceiver (400) according to one of the preceding claims, wherein the wake-up signal configuration defines at least one frequency on which the wake-up signal (422) is transmitted.

51. Central transceiver (400) according to claim 50, wherein the at least one frequency is associated with an identification of the central transceiver (400).

52. Central transceiver (400) according to one of the preceding claims, wherein the central transceiver (400) is configured to receive the wake-up signal (422) based on a wake-up signal reception interval. wherein the transceiver is configured to determine time instants for the initial transmission and the retransmission of the wake-up signal based on an information describing a wake-up signal reception interval of the central transceiver (400).

53. Central transceiver (400) according to claim 52, wherein the wake-up signal reception interval is at least one out of a wake-up signal reception interval length, a wake-up signal reception interval periodicity, a wake-up signal reception interval duty cycle.

54. Central transceiver (400) according to one of the claims 36 to 53, wherein the energy saving mode is a first energy saving mode, wherein the central transceiver (400) is configured to operate in a second energy saving mode in which no wake-up signals (422) are received or in which wake-up signals (422) are received less often than in the first energy saving mode, wherein the central transceiver (400) is configured to receive an activation control signal and to switch from the second sleep mode into the first energy saving mode in response to a reception of the activation control signal.

55. Central transceiver (400) according to one of the claims 36 to 53, wherein the central transceiver (400) is configured to receive an activation control signal and to adjust a wake-up signal configuration in response to the reception of the activation control signal.

56. Central transceiver (400) according to claim 55, wherein the central transceiver (400) is configured to increase a periodicity of wake-up signal reception intervals in response to the reception of the activation control signal

57. Central transceiver (400) according to one of the claims 55 to 56, wherein the central transceiver (400) is configured to receive the activation control signal in dependence on one or more of the following condition: a location of the transceiver (402), an active beam of a macro cell, channel properties, channel measurements, an indication from the transceiver (402).

58. Central transceiver (400) according to one of the preceding claims, wherein the central transceiver (400) is configured to receive the activation control signal via a core network or network function.

59. Method for operating a transceiver for a wireless communication network, the method comprising: determining a wake-up signal configuration for a wake-up signal, generating the wake-up signal based on the wake-up signal configuration, transmitting the wake-up signal to a central transceiver that is operable in an energy saving mode of operation, wherein at least a part of the wake-up signal configuration is not signaled to the transceiver by the central transceiver and/or another central transceiver of the wireless communication network.

60. Method for operating a central transceiver for a wireless communication network, the method comprising: operating the central transceiver in an energy saving mode of operation, receiving a wake-up signal from a transceiver of the wireless communication network, transmitting, in response to the reception of the wake-up signal, a synchronization signal, wherein a transmission and/or generation of the wake-up signal is based on a wake-up signal configuration, wherein at least a part of a wake-up signal configuration is not signaled to the transceiver by the central transceiver in the energy saving mode of operation.

61. Computer program for performing a method according to one of the claims 59 to 60, when the computer program runs on a computer, microprocessor or software defined radio.