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WO2025065234A1 - Procédé et système de synchronisation et de recherche de réseau - Google Patents

Procédé et système de synchronisation et de recherche de réseau Download PDF

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Publication number
WO2025065234A1
WO2025065234A1 PCT/CN2023/121526 CN2023121526W WO2025065234A1 WO 2025065234 A1 WO2025065234 A1 WO 2025065234A1 CN 2023121526 W CN2023121526 W CN 2023121526W WO 2025065234 A1 WO2025065234 A1 WO 2025065234A1
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WIPO (PCT)
Prior art keywords
stage
synchronization information
information
synchronization
ssb
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PCT/CN2023/121526
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English (en)
Inventor
Xing Liu
Xianghui HAN
Xingguang WEI
Jing Shi
Junfeng Zhang
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ZTE Corp
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ZTE Corp
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Priority to PCT/CN2023/121526 priority Critical patent/WO2025065234A1/fr
Publication of WO2025065234A1 publication Critical patent/WO2025065234A1/fr
Pending legal-status Critical Current
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/001—Synchronization between nodes
    • H04W56/0015—Synchronization between nodes one node acting as a reference for the others

Definitions

  • This disclosure is directed generally to wireless communications and more specifically to synchronization of mobile stations with wireless network and network search by the mobile stations.
  • Wireless communication networks based on cellular technologies are moving to more densely distributed cells in order to increase network capacity.
  • inter-cell interference increases and cell switching during mobility of wireless terminals becomes more frequent, causing hurdles for further improvement of network capacity and efficiency.
  • New technologies for wireless access are needed in order to continue increasing the system capacity without sacrificing efficiency.
  • a method for synchronization and cell/network search performed by a user equipment (UE) in a wireless network may include performing a first measurement of a set of stage-I synchronization information transmitted by a first set of wireless network nodes; selecting at least one stage-I synchronization information from the set of stage-I synchronization information according to the first measurement; determining a set of stage-II synchronization information according to the at least one stage-I synchronization information; performing a second measurement of the set of stage-II synchronization information; selecting at least one stage-II synchronization information from the set of stage-II synchronization information according to the second measurement; and performing, according to the at least one stage-II synchronization information, communication with a second set of wireless network nodes transmitting the at least one stage-II synchronization information.
  • the set of stage-I synchronization information are transmitted by the first set of wireless network nodes according to a first periodicity; and the second set of synchronization information are continuously transmitted by the second set of wireless network nodes according to a second periodicity.
  • frequency locations and time locations for the set of stage-II synchronization information are determined via a pre-configured relationship between stage-I and stage-II synchronization information or are indicated in information carried in the at least one stage-I synchronization information.
  • the frequency locations for the set of stage-II synchronization information are indicated by: frequency offsets from frequency locations of the at least one stage-I synchronization information, the frequency offsets being either predefined or indicated in the information carried in the at least one stage-I synchronization information; or frequency domain indexes in form of Absolute Ratio Frequency Channel Number (ARFCN) .
  • ARFCN Absolute Ratio Frequency Channel Number
  • a time-domain pattern of the at least one stage-II synchronization information are predefined or indicated in the information carried in the at least one Stage-I synchronization information.
  • the time-domain pattern of the at least one stage II synchronization information are indicated by a bitmap.
  • a starting time point for a first one of the at least one stage-II synchronization information relative to the at least one stage-I synchronization information within a transmission period for the at least one stage-II synchronization information is determined from the information carried in the at least one stage-I synchronization information.
  • the information carried in the at least one stage-I synchronization information indicates a time offset for the first of the at least one stage-II synchronization information relative to the at least one stage-I synchronization information.
  • each of the at least one stage-I synchronization information is mapped to a plurality of the at least one stage-II synchronization information.
  • the set of stage-I synchronization information are transmitted by the first set of wireless network nodes according to a first periodicity and the second set of synchronization information are transmitted by the second set of wireless network nodes on demand.
  • the second set of synchronization information are transmitted by the second set of wireless network nodes as triggered by a feedback to the first set of wireless network nodes from the UE in response to the first measurement of the set of stage-I synchronization information.
  • the feedback comprises at least one of: an index of the at least one stage-I synchronization information as selected from the set of stage-I synchronization information; results of the first measurement of each of the at least one stage-I synchronization information; and position information of the UE.
  • the set of stage-II synchronization information are selected by the wireless network according to the feedback from the UE.
  • the set of stage-II synchronization information are triggered for transmission according to a second periodicity within a time duration.
  • the time duration is indicated in information carried in the at least one stage-I synchronization information.
  • the time duration is specified as a multiple of the second periodicity.
  • the method further includes providing the feedback to the first set of wireless network nodes via transmitting a physical random-access channel (PRACH) .
  • PRACH physical random-access channel
  • resources for the PRACH are divided into a plurality of groups associated and the feedback to the first set of wireless network nodes is provided via an PRACH group identity of the transmitted PRACH.
  • more than one of the set of stage-I synchronization information are associated with the same PRACH for the feedback.
  • a resource for transmitting the feedback is specified in information carried in the at least one stage-I synchronization information.
  • At least one the following parameters associated with each of the set of stage-II synchronization information are configured by information carried in the at least one stage-I synchronization information: a numerology; a primary synchronization sequence length; a secondary synchronization sequence length; a transmission periodicity; a frequency location; a number of synchronization information in each transmission period; a synchronization information waveform; a physical broadcast channel (PBCH) payload size; a PBCH demodulation reference signal (DMRS) density; and a multiplexing scheme among channels/signals.
  • PBCH physical broadcast channel
  • DMRS PBCH demodulation reference signal
  • indexes for the at least one stage-II synchronization information is entirely determined from information carried in corresponding stage-I synchronization information.
  • indexes for the at least one stage-II synchronization information determined partially from information carried in corresponding stage-I synchronization information and partially from information carried in the at least one stage-II synchronization information.
  • indexes for the at least one stage-I synchronization information is determined partially from information carried in the at least one stage-I synchronization information and partially from information carried in corresponding stage-II synchronization information.
  • the first set of wireless network nodes and the second set of wireless network nodes are access points configured to provide a cell-free network.
  • the first set of wireless network nodes are cellar base stations whereas the second set of wireless network nodes are access points configured to provide a cell-free network.
  • a method for synchronization with a UE performed by a wireless network may include transmitting synchronization information in two separate stages as a set of stage-I synchronization information and a set of stage-II synchronization information for the UE to access a wireless network.
  • the set of stage-I synchronization information are transmitted with a first transmission periodicity; and the set of stage-II synchronization information are transmitted with a second transmission periodicity or triggered by a feedback from the UE in response to detecting at least one of the set of stage-I synchronization information.
  • a wireless communications apparatus may include a processor and a memory, wherein the processor is configured to read code from the memory and implement any one of the methods above.
  • a non-transitory computer readable medium may include computer instructions, when executed by a processor of a wireless communication device, may cause the wireless communication device to implement any one of the methods above.
  • FIG. 1 illustrates an example wireless cell-free access network including representative wireless access points and a representative mobile station.
  • FIG. 2 illustrates an example random access procedure
  • FIG. 3 illustrates an example wireless access network including wireless access points, cellular base stations, and a representative mobile station.
  • FIG. 4 shows an example correspondence between first-stage synchronization information and second-stage synchronization information.
  • FIG. 5 shows another example correspondence between first-stage synchronization information and second-stage synchronization information.
  • FIG. 6 illustrates an example two-stage transmission of synchronization information where the transmission of the second-stage synchronization information is triggered.
  • FIG. 7 illustrates an example scheme for synchronization information indexing in a two-stage synchronization information transmission procedure.
  • FIG. 8 illustrate an example access point or base station and a mobile station (or user equipment (UE) ) .
  • terms, such as “a” , “an” , or “the” may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context.
  • the term “based on” or “determined by” may be understood as not necessarily intended to convey an exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context.
  • Synchronization Signal/PBCH Blocks are used throughout this disclosure only as example of general synchronization information of any form for access wireless network.
  • the term can be replaced by “synchronization information” .
  • the various implementations below involving SSB applies to any type of synchronization information.
  • the various two-stage SSB transmission implementations below may be alternatively refer to two-stage synchronization information transmissions.
  • the term Stage-I (or first-stage) SSB also refers to any stage-I or first-stage synchronization information.
  • Stage-II (or second-stage) SSB also refers to any stage-II or second-stage synchronization information.
  • the synchronization information may also broadly include other system information.
  • traditional cellular networks take advantage of spatial reuse of wireless spectrum and arrange somewhat sparse base stations over an extended geographic area with each base station covering one or more cells.
  • Each cell for example, may be associated with a wireless carrier in frequency.
  • the base stations or cells may be geographically deployed with carrier frequency assignment that minimizes inter-cell interference.
  • a mobile station may gain access to and establish a communication session with one or a few cells (e.g., a single cell for single-connectivity or a master cell plus a secondary cell in dual connectivity) at a time.
  • a cell/network search and access procedure may be performed by a mobile station in order to gain time/frequency synchronization and access to a cell and the underlying base station.
  • the mobile station changes location in the cellular network during mobility, it may need to switch cells via a handover procedure.
  • the cell switch and handover procedure usually involve lengthy, resource-intensive, and overall intricate resynchronization and reconfigurations.
  • cell splitting technologies in cellular networks may be implemented and have been considered as one example approach to effectively increase capacities of wireless systems.
  • the various low-power network nodes such as micro cells, small cells, home eNodeBs, and relay nodes supporting cell splitting may be deployed as a conventional cellular network.
  • Such conventional cellular network has become heterogeneous and dense.
  • problems associated with serious inter-cell interference, frequent handovers of mobile stations or UE during mobility, and the like arise significantly and may lead to reduced system capacity and deterioration of user experience.
  • system capacity of dense conventional cellular network is interference limited as cells become smaller and the number of cells increases.
  • decrease of cell radius may encounter a turning point with respect to system capacity and performance, after which the system capacity begins to drop due to cell-interference and the network efficiency begins to deteriorate due to frequent cell switches or handovers.
  • a cell-free rather than cellular network may be deployed.
  • a plurality of access points (APs) 101 may be deployed and distributed in a large area that may otherwise be covered by a plurality of traditional cells provisioned by base stations.
  • the APs 101 may be densely deployed and may be connected and transmit data to a central processing unit (Central Processing Unit or CPU) 130 by using fronthaul links (shown as doted straight lines in FIG. 1) , and provide services to a plurality of UEs (with one example UE shown by 102) by using a same range of time-frequency resource.
  • CPU Central Processing Unit
  • the UE 102 in a connected state may be configured with a cell 120 centered on itself, and the cell 120 moves when the UE moves.
  • the UE 102 when connected to the network, is configured with a set of resources (e.g., a carrier frequency) that need not to switch as the UE moves in the large area covered by the network, whereas the particular APs involved in serving the UE and forming the UE-centric moving cell for the UE may change as coordinated by the CPU.
  • the APs that form the cell 120 for the UE 102 at the particular time in FIG. 1 are illustrated as APs 104 through 114.
  • Each UE in the cell-free network may be associated with a moving cell.
  • the cells of various UEs may overlap therebetween. In other words, a same AP may be part of multiple UE-centric cells of different UEs.
  • the cell-free network above may be alternatively referred as “de-celled” network or “de-cellular” network.
  • problems such as inter-cell interference and frequent handovers in the UE may be minimized.
  • frequency resources can still be spatially reused (e.g., UEs that are sufficiently far apart may use the same dedicated carrier or subcarriers) , they may be more efficiently managed by the CPU to reduce interference.
  • a UE may not need to switch carrier frequency unless it moves close to another UE which happens to be allocated with the same frequency, and such a need for frequency switch (or frequency handover) may be drastically reduced by intelligently and adaptively allocating carrier frequency during UE connection depending on locations of other UEs and their carrier frequencies.
  • cellular network nodes or base stations
  • cell-free APs may co-exist (as shown in FIG. 3 which is described in detail in the various embodiments below) .
  • frequency bands may be separately allocated to or shared by the cellular network portion and the cell-free network portion.
  • establishment of a network access of a UE to the cell-free portion of the network for the UE may be achieved by first establishing connection to the traditional cellular network portion of the network and then cell-switching to selected APs (as another cell or network) for cell-free access by the UE.
  • the UE may operate in the cell-free mode only after, e.g., a radio resource control (RRC) connection is first established for the UE with a particular cellular node rather than directly with multiple APs in a form of a cellular network access operation.
  • RRC radio resource control
  • the UE then performs a handover operation from the cellular system to the cell-free system.
  • the current implementation is thus mixed and still requires cellular components and operations.
  • the cellular system and cell-free system are based on two different design concepts. For example, as described above, a cell the former systems is centered on a base station, whereas a cell in the latter systems is centered on the UE.
  • the access procedure implementation above in the mixed system thus is at best a mixed approach that still rely on cellular access, and is therefore still faced with serious inter-cell interference and time delay due to cell switch/handover.
  • the further disclosure below is directed generally to wireless communications and more specifically to synchronization of mobile stations with wireless network and cell/network search by the mobile stations.
  • the various example implementations disclosed herein provide a two-stage initial access procedure for synchronization and connection by the mobile station to multiple APs in a cell-free network, so as to avoid having to access the network first in a cellular fashion followed by performing a cell switch or handover procedure in order to synchronize with and be connected to the cell-free network.
  • access of network node or nodes may be based on a random-access procedure.
  • a random-access procedure For example, in 5G cellular systems, an example scheme to support the initial access under FR1 (sub 6G Hz band) and FR2 (beyond 6G Hz band) may involve such a random-access procedure.
  • One of the key steps of such a random-access procedure is a transmission of access request in a Physical Random-Access Channel (PRACH) , which may be referred to as msg. 1 in a four-step random-access procedure or as part of msg. A in a two-step random-access procedure.
  • PRACH Physical Random-Access Channel
  • the various related components and schemes include different PRACH formats, PRACH resource configurations, relationship between the SSBs (Synchronization Signal/PBCH Blocks) and PRACH occasions, mechanism for PRACH retransmission, mechanism for PRACH power control, and the like.
  • FIG. 2 an example random-access procedure (also referred to as RACH procedure) , particularly with respect to a spatial beam management, is shown.
  • a UE may transmit a preamble in a PRACH occasion (RO) , according to a configuration of PRACH transmission and an SSB being selected.
  • RO PRACH occasion
  • Tx-Rx transmission-reception
  • Tx beam reception beam
  • Tx beam transmission beam
  • the UE may try to use/scan different Rx beams to receive SSBs from the gNB, as shown by 202, and determine the best or most suitable Rx beam (e.g., SSB receptions with a highest Reference Signal Received Power (RSRP) value or with a RSRP SSB reception value higher than a predefined threshold) . Then, according to the best or most suitable Rx beam, the corresponding Tx beam can be determined for transmitting the PRACH or random-access preamble, as shown by 204.
  • RSRP Reference Signal Received Power
  • the RO used for transmitting the PRACH may be determined according to a correspondence relationship between the SSB and RO.
  • the base station e.g., a gNB, upon receiving the PRACH channel (204) , and basing on such SSB-RO correspondence relationship and the RO on which the PRACH channel is received in 204, may be able to determine or ascertain the SSB 206 being selected by the UE.
  • the same beam corresponding to the determined SSB may then be used for transmitting subsequent DL transmissions to the UE, including, for the example of the four-step random access procedure, msg. 2 (which may be referred to as RAR, or Random-Access Response, as shown by 208) and msg.
  • RAR Random-Access Response
  • the RAR 205 may be transmitted in response to receiving the PRACH transmission 204.
  • the UE after the transmission of the msg. 1 in 204, may monitor, in 206, RAR Physical Downlink Control Channel (PDCCH) within an RAR window, which, for example, may start after the last symbol of the PRACH occasion corresponding to the PRACH transmission and at the first symbol of the earliest CORESET (COntrol REsource SET) which the UE is configured to receive PDCCH for an example Type 1-PDCCH CSS set, and extends at least a predefined number of symbols.
  • PDCCH Physical Downlink Control Channel
  • the UE may need to try different Tx beams based on the SSB reception beam for transmitting the PRACH. Then the UE may proceed to identifying a suitable Tx beam for PRACH by try-and-error, that is, by transmitting the PRACH via any beam first (or by some loose estimate) and then trying PRACH retransmission with different beams in case of failure of the previous PRACH transmission.
  • the UE sends a PRACH at 204 only for a selected SSB (beam 203) .
  • a network node that sends the SSB in 202 receives, on a specific corresponding time-frequency resource (specific RO or RO group) , the PRACH sent by the UE in 204, and then performs subsequent steps of the RACH process with the UE.
  • the UE may not support interaction with more than one network node (e.g., base station) .
  • the time domain resources for RACH transmission may be configured via RRC signaling referred to as ‘prach-ConfigurationIndex’ .
  • Each ‘prach-ConfigurationIndex’ among a set of possible indexes maps to a random-access configuration.
  • An example of such mapping is shown in Table 1 below.
  • the whole table may have a predefined number, e.g., 256, of lines, and the value of ‘prach-ConfigurationIndex’ for each line is correspondingly between 0 ⁇ 255, and each line shows a mapping of one of the ‘prach-ConfigurationIndex’ values to one of the PRACH configurations.
  • the example Table 1 below also indicates preamble format to be used corresponding to each PRACH configuration index.
  • Table 1 above represents the number of time-domain PRACH occasions within a PRACH slot, represents PRACH duration.
  • the frequency domain resource of RACH transmission may be configured via additional RRC signaling.
  • RRC signaling is given below:
  • msg1-FrequencyStart provides a frequency starting Resource Block (RB) within a current carrier
  • msg1-FDM further specifies how many PRACH transmission resource are FDMed.
  • resource for PRACH transmission i.e., RO, can be determined.
  • Embodiment 1 Periodic Two-Stage SSB
  • This embodiment describes a general scheme and method for enabling a UE to enter cell-free network mode in the initial network access phase in order to establish links with multiple service nodes that form a UE-centric cell.
  • a two-stage information transmission structure for transmitting synchronization information and/or system information may be implemented.
  • a scheme may be referred to as ‘two-stage SSB’
  • a first-stage synchronization information (generally referred to as first-stage SSB) may be transmitted by one or more first network nodes, e.g., one or more base stations or one or more APs within a first portion of the APs
  • a second-stage synchronization information (generally referred to as second-stage SSB) may be transmitted by one or more second network nodes, e.g., one or more of all APs or one or more nodes of a second portion of the APs that form a UE-centric service (or cell-free) network for the UE.
  • the first-stage SSBs may be transmitted with a first transmission periodicity.
  • the second SSB may be transmitted with a second transmission periodicity.
  • an SSB may occupy 4 symbols and 240 sub-carriers, and contains PSS (Primary Synchronization Signal) , SSS (Secondary Synchronization Signal) , PBCH (Physical Broadcast Channel) and PBCH DMRS (PBCH Demodulation Reference Signal) .
  • both of the first-stage SSB and the second-stage SSB may include SSBs of complete structure (i.e., all of PSS, SSS, PBCH and PBCH DMRS are included in a first-stage SSB and a second-stage SSB) .
  • at least one of the first-stage SSB and the second-stage SSB may include partial SSB structure (i.e., at least one of PSS, SSS, PBCH and PBCH DMRS is not included in such an SSB) .
  • PSS, SSS may be included in the first-stage SSB.
  • the second-stage SSB may include CSI-RS, PDCCH (with DMRS) and PDSCH (with DMRS) .
  • Other synchronization and/or system information may be included in the first-stage and second stage SSBs (or first-stage and second-stage synchronization information) .
  • FIG. 3 includes, as an example, two base stations, e.g., BS1 (302) and BS2 (304) , and four APs, e.g., AP1 (312) , AP2 (314) , AP3 (316) , and AP4 (318) in the network.
  • a first-stage SSB may be periodically transmitted by BS1 and BS2.
  • a UE 301 may scan and measure the first-stage SSBs and may select one or more first-stage SSBs according to the measurement result.
  • the UE 301 may further receive second-stage SSBs on specific resources for establishing access to the UE-centric (or cell-free) service network.
  • the UE-centric or cell-free service network for UE 301 may be formed by AP1, AP2, AP3 and AP4 of FIG. 3.
  • the network system of FIG. 3 may be entirely cell-free (similar to the depiction of FIG. 1) .
  • the network nodes for transmitting the first-stage SSBs in the implementations above can be one or more of the APs.
  • some of the network nodes, e.g., APs may transmit both the first-stage SSBs and the second-stage SSBs. Both the first state SSBs and the second-stage SSBs may be transmitted, for example, in a periodic manner, with a first periodicity and a second periodicity, respectively.
  • the UE 201 may not need to provide any feedback after detecting the first-stage SSBs. Instead, the cell-free network may periodically transmit second-stage SSBs, each coming from an AP or a combination of APs.
  • the time-frequency domain relationship between the first-stage SSB and the second-stage SSB may be predefined or may alternatively be indicated in information carried in the first-stage SSB.
  • the UE 201 detects and selects one or more first-stage SSBs, it can further determine resource information related to the second-stage SSBs according to the one or more first-stage SSBs it has selected and the predefined time-frequency domain relationship between the first-stage SSBs and the second-stage SSBs or by decoding the information carried in the first-stage SSBs, thereby scanning and receiving the second-stage SSBs accordingly.
  • a second frequency point or position for transmitting the second-stage SSB associated with a first-stage SSB may be determined in accordance with an indication carried in the first-stage SSB or a pre-defined rule (e.g., in a specification) .
  • a frequency domain offset between the first frequency point or position for the first-stage SSB and the second frequency point or position for the second-stage SSB may be indicated in the information carried in the first-stage SSB or may be predefined.
  • a frequency domain index e.g., Absolute Radio Frequency Channel Number, ARFCN
  • ARFCN Absolute Radio Frequency Channel Number
  • a number of the second-stage SSBs and/or a time domain pattern (e.g., time domain locations of each the SSBs within a period, e.g., half frame) of the second-stage SSBs may be predefined.
  • a bitmap may be included in the first-stage SSB which may be used for indicating actual transmitted second-stage SSBs. For example, there may be 8 candidate time-domain positions defined in total corresponding to different time locations and an 8-bit bitmap may be used for indicating which of them are actually transmitted as second-stage SSBs. For example, ‘11101100’ represents the first, the second, the third, the fifth and the sixth second-stage SSBs in the correspondingly predefined time-domain positions are actually transmitted.
  • the starting time point of the first one of the second-stage SSBs relative to one of the first-stage SSBs within a period can be determined according to the indication carried in the first-stage SSB. For example, a time domain offset between the first one or detected one of first-stage SSB and the first one of the second-stage SSBs may be indicated in the information carried in the first-stage SSBs.
  • the second-stages SSBs may be transmitted periodically.
  • the time domain location information of the first one of the second-stage SSBs may be indicated in the first-stage SSBs as generally described above.
  • the time domain location information includes at least one of, period, offset, system frame number of the starting radio frame, half frame index (i.e., first half frame or second half frame) , starting subframe index, starting slot index, starting symbol index, and the like.
  • first-stage SSBs there may be four first-stage SSBs, SSB0 (402) , SSB1 (404) , SSB2 (406) , and SSB3 (408) , located in the first frequency point.
  • Each of the first-stage SSBs may be associated with four second-stage SSBs, as indicated by the arrows of FIG. 4.
  • the first-stage SSB 0 (402) may be associated with four second-stage SSBs, i.e., SSB0 ⁇ SSB3 located in the second frequency points, as indicated by 410; the first-stage SSB 2 (406) may be associated with four second-stage SSBs, i.e., SSB4 ⁇ SSB7 located in the second frequency points, as indicated by 420; the first-stage SSB 1 (404) may be associated with four second-stage SSBs, i.e., SSB0 ⁇ SSB3 located in the third frequency point, as indicated by 430; and the first-stage SSB 3 (408) may be associated with four second-stage SSBs, i.e., SSB4 ⁇ SSB7 located in the third frequency point, as indicated by 440.
  • a combination of first-stage SSBs when selected, may be associated with a group of second-stage SSBs. Then, if a UE selects a combination of first-stage SSBs (e.g., a UE selects X first-stage SSBs with the highest RSRP measurement results, “X” being an integer 2 or larger) according to its measurement of the first-stage SSBs, the corresponding group of second-stage SSBs may be further received/detected by the UE according to the association between the combinations of first-stage SSBs and the groups of second-stage SSBs. An example is shown in FIG.
  • X can be predefined or may alternatively be indicated via the first-stage SSB, e.g., carried in the RS or indication information
  • X can be predefined or may alternatively be indicated via the first-stage SSB, e.g., carried in the RS or indication information
  • the UE selects first-stage SSB0 (402) and first-stage SSB1 (404) according to the measurement result and that the combination of SSB0 (402) and SSB1 (404) corresponds to the group of second-stage SSBs of SSB0 ⁇ SSB3 (410) located at the second frequency point or location, then, the second-stage SSB0 ⁇ SSB3 (410) as a group located at the second frequency point may be further received/detected by the UE, as indicated by arrows 502 and 504 in combination.
  • first-stage SSB0 (402) and first-stage SSB2 (406) according to the measurement result and that the combination of SSB0 (402) and SSB2 (406) corresponds to the group of second-stage SSBs of SSB0 ⁇ SSB3 (430) located at the third frequency point or location
  • the second-stage SSB0 ⁇ SSB3 (430) as a group located at the third frequency point may be further received by the UE, as indicated by arrows 506 and 508 in combination.
  • first-stage SSB1 (404) and first-stage SSB3 (408) corresponds to the group of second-stage SSBs of SSB4 ⁇ SSB7 (440) located at the third frequency point or location
  • the second-stage SSB4 ⁇ SSB7 (440) as a group located at the third frequency point may be further received by the UE, as indicated by arrows 510 and 512 in combination.
  • first-stage SSB2 (406) and first-stage SSB3 (408) corresponds to the group of second-stage SSBs of SSB4 ⁇ SSB7 (420) located at the second frequency point or location
  • the second-stage SSB4 ⁇ SSB7 (420) as a group located at the second frequency point may be further received by the UE, as indicated by arrows 514 and 516 in combination.
  • the various methods above for determining the time-frequency domain locations of the second-stage SSBs can be used here.
  • the UE may measure first-stage SSBs and determine the best one or more first-stage SSBs (e.g., with respect to received power or quality) .
  • the UE may determine the corresponding one or more second-stage SSBs and scan/detect these SSBs to determine and select the best one or more second-stage SSBs for synchronization.
  • the APs associated with the selected second-stage SSB (s) may then form the UE-centric cell in the cell-free network.
  • one or more intelligent algorithms may be executed by the network side, so as to form the predefined association between the one or more first-stage SSBs and the one or more second-stage SSBs, or for determining such association dynamically and include indication of such association in the information carried in the first-stage SSBs.
  • a method for enabling a UE to enter cell-free network mode during an initial access phase (rather than through switching or handover after cellular connection is established in an initial access stage) , that is, to establish links with multiple service nodes is provided. More specifically, a two-stage information transmission structure is defined to the initial access. A UE can determine the time-frequency domain resource of the second-stage SSBs according to the measurement of the first-stage SSB. Then, it can establish links with multiple network nodes that transmit the second-stage SSB messages during the initial access phase.
  • Embodiment 2 Two-Stage SSB with the Second-Stage SSB Being Triggered
  • the embodiment describes another general two-stage SSB scheme and method for enabling a UE to enter cell-free network mode in the initial network access phase in order to establish links with multiple service nodes that form a UE-centric cell, where constant periodic transmission of the second-stage SSBs may be avoided.
  • the first-stage SSBs described above may be transmitted with a first periodicity whereas the second-stage SSBs may be transmitted on-demand.
  • the second-stage SSBs may be transmitted according to feedback information from UE after receiving the first-stage SSBs.
  • the second-stage SSBs and the network nodes that will transmit the second-stage SSBs may be dynamically determined based on the UE’s feedback.
  • the feedback information may include at least one of, index of one or more selected first-stage SSBs, measurement result (e.g., RSRP) of each of the selected first-stage SSBs, position information of the UE, and the like.
  • Such feedback information may be used by the network to determine the second-stage SSBs to trigger for transmission.
  • the index of the selected first-stage SSBs may be implemented as a combination index of the one or more selected first-stage SSBs. Alternatively, it can be implemented as one or more separate SSB indexes, each corresponding to one of the one or more selected first-stage SSBs.
  • the second-stage SSBs may be transmitted with a second periodicity for a certain time duration.
  • the second-stage SSBs may be transmitted only once.
  • the UE selects first-stage SSB0 (602) according to its measurements.
  • the UE then sends the feedback information to the network.
  • the network may determine second-stage SSBs to trigger followed by a triggering of transmission of the determined second-stage SSBs, e.g., SSB0 ⁇ SSB3 (604) with the second periodicity and within the predefined time duration.
  • the time duration can be indicated in the first-stage SSB or predefined.
  • the time duration for example, may be 5 ms.
  • the time duration may be defined as a multiple of the second periodicity.
  • the time duration may be specified as 4, meaning that the second-stage SSBs should be transmitted for four periods.
  • at least one of the frequency domain location, time domain information, including at least one of time domain pattern, time domain period, starting point can be indicated or predefined for the second-stage SSBs as described in embodiment 1 above.
  • the feedback information above may be transmitted via a PRACH with the base stations or APs that have transmitted the first stage SSBs.
  • the PRACH resource including time-frequency domain resource (e.g., RO) and code domain resource (e.g., PRACH preamble) , may be divided into different groups, and different PRACH resource groups may correspond to different feedback information.
  • time-frequency domain resource e.g., RO
  • code domain resource e.g., PRACH preamble
  • PRACH resource groups may correspond to different feedback information.
  • the group corresponding to the selected PRACH resource would correspond to or indicate its feedback.
  • selection of an PRACH resource group may indicate to the network an RSRP measurement result by the UE.
  • an RSRP threshold may be predefined or indicated via the first-stage SSB.
  • a PRACH resource can be selected from a first PRACH resource group. Otherwise, if the measurement result is higher than or no lower than the RSRP threshold, a PRACH resource can be selected from a second PRACH resource group. Then, when the network detects a PRACH transmission on a PRACH resource belong to the first PRACH resource group, it can determine, as the feedback information, that the measurement result by the UE is lower than or no higher than the RSRP threshold, whereas when the network detects a PRACH transmission on a PRACH resource belong to the second PRACH resource group, it can determine, as the feedback information, that the measurement result by the UE is higher than or no lower than the RSRP threshold.
  • more than one first-stage SSBs may be associated with a same transmission resource of the feedback information.
  • more than one first-stage SSB may be associated with one PRACH resource, including, same group of preamble and same RO.
  • a UE may select two first-stage SSBs (e.g., two SSBs with highest RSRP) according to its measurement.
  • the UE may transmit a preamble within an RO associated with the two selected first-stage SSBs for indicating feedback associated with the two first-stage SSBs.
  • feedback information associated with multiple first-stage SSBs may be provided to the network, which may then use such feedback information to make better determination of the second-stage SSBs to trigger and the combination of APs that transmits each of the second-stage SSBs.
  • msg. A in a two-step RACH procedure (including PRACH and corresponding msg. A PUSCH) with the base stations or APs associated with the first-stage SSBs may be used to indicate the feedback information.
  • the transmission resource of feedback information may be configured via the first-stage SSB.
  • a frequency resource including, a group of consecutive resource blocks (RBs) ) within the carrier bandwidth can be configured as UL resource. Then, all of the transmission resource of the feedback information located within the frequency resource may be considered as available resource for UL transmission.
  • one or more intelligent algorithms may be executed by the network side, so as to form the predefined association between the one or more first-stage SSBs and the one or more second-stage SSBs, or for determining such association dynamically and include indication of such association in the information carried in the first-stage SSBs.
  • some intelligent algorithms e.g., pretrained machine learning, neural network, etc.
  • a method for enabling a UE to enter cell-free network mode in the initial access phase to establish links with multiple service nodes is provided. More specifically, a two-stage information transmission structure is defined. The UE can transmit feedback information to the network for helping the network to select a node combination to form a UE-centric (or cell-free) service network. Then, it can establish links with multiple network nodes that transmit the second-stage SSB messages during the initial access phase.
  • Embodiment 3 Configurable Second-Stage SSB Parameters
  • This embodiment describes another method for enabling a UE to enter cell-free network mode in the initial network access phase in order to establish links with multiple service nodes.
  • At least one of the following parameters pertaining to the second-stage SSB as shown in Table 2 below may be configured via, for example, the first-stage SSB.
  • the examples of the potential or possible values of these example configurable parameters are also provided in Table 2.
  • a method for enabling a UE to enter cell-free network mode in the initial access phase in order to establish links with multiple service nodes is provided. More specifically, the configurable parameters of a second-stage SSB are defined. Then, it can be used for establishing links with multiple network nodes that transmit second-stage SSB messages during the initial access phase.
  • Embodiment 4 cell/network search in Two-Stage SSB System
  • the example embodiment below further describes another method for enabling a UE to enter cell-free network mode in the initial access phase in order to establish links with multiple service nodes.
  • cell/network searching may be performed as a procedure by a UE to obtain time and frequency synchronization and system information of a cell in order to access the cell and the network thereof.
  • cell/network search may be performed based on information obtained from SSB.
  • Time and frequency synchronization with a UE-centric cell in the cell-free network likewise may be performed based on information in the SSBs, including e.g., either or both of the first-stage SSBs and the second-stage SSBs described above.
  • the first-stage SSB (s) and the second-stage SSB (s) may be transmitted by a same network node or a same group of network nodes (e.g., APs) .
  • the first-stage SSB may contain full information for the UE to perform cell/network searching (e.g., PCI, SFN, half frame, SSB index, sub-carrier level offset between SSB and Common Research Block (i.e., Kssb) , searchspace#0, Control Resource Set#0 (CORESET#0) , sub-carrier spacing of SIB1, Position of (first) DMRS (demodulation reference signal) for downlink and uplink, etc. ) with respect to the cell-free network, and the second-stage SSB may be used for modifying or optimizing some of the information indicated in the first-stage SSB.
  • a UE may perform cell/network search for synchronization and access the cell-free network by only detecting the first-stage SSB and the reception of the second-stage SSB may be optional or may be performed or not performed depending on UE capability.
  • the first-stage SSB may contain part of rather than full information for cell/network searching and the remaining information for cell/network searching may be provided in the second-stage SSB.
  • the UE would need to receive both of the first-stage SSB and the second-stage SSB in order to have sufficient information for performing cell/network searching and synchronization with the cell-free network.
  • the 2 LSBs (least significant bits) or 3 LSBs of such SSB index may be indicated via a sequence of PBCH DMRS for max number of SSB that is 4 or larger than 4, respectively.
  • the 3 MSBs of the SSB index may be indicated via PBCH payload for max number of SSB that is 64.
  • the SSB index may be used to identify a particular SSB within an SSB burst (e.g., in an SSB transmission period) .
  • SSB indexes in an SSB burst may be associated with a set of beams being scanned.
  • SSB index In a two-stage SSB network such as the ones described above in embodiments 1-3, at least one of the following methods can be used for indicating the SSB index:
  • the SSB index may be indicated via the first-stage SSB (i.e., PBCH DMRS or PBCH DMRS and PBCH payload, as in the SSB index indication in traditional single SSB system) .
  • the PBCH DMRS sequence may be irrelevant to the SSB index.
  • the initialization of the PBCH DMRS sequence in the second SSB may be irrelevant to the SSB index.
  • the PBCH DMRS sequence in the second-stage SSB may be the same as that of the first-stage SSB associated with this second-stage SSB.
  • the index of second-stage SSBs may be the same as that in the first-stage SSB associated with the second-stage SSBs.
  • An example is shown in FIG. 7.
  • the index of the second-stage SSBs 704 corresponding to the first-stage SSB0 (702) with SSB index 0 is also 0
  • the index of second-stage SSBs 708 corresponding to first-stage SSB1 (706) with SSB index 1 is also 1.
  • the index of second-stage SSBs 712 corresponding to first-stage SSB2 (710) with SSB index 2 is also 2
  • the index of second-stage SSBs 716 corresponding to first-stage SSB3 (714) with SSB index 3 is also 3.
  • the SSB index for the second stage SSBs may not be indicated via the first-stage SSB. Then, the initialization of the PBCH DMRS sequence in the first-stage SSB may be irrelevant to the SSB index in the second-stage SSB.
  • the SSB index of the second-stage SSB may be carried by the second-stage SSB, e.g., PBCH DMRS or PBCH DMRS and PBCH payload.
  • Part of SSB index (e.g., 3 MSBs) of the first-stage SSB may be indicated via the first-stage SSB (e.g., via PBCH DMRS or PBCH DMRS and PBCH payload) .
  • the remaining part of SSB index (e.g., 3 LSBs) of the first-stage SSB may be further indicated via the second-stage SSB (e.g., via PBCH DMRS or PBCH DMRS and PBCH payload) .
  • At least part of SSB index (e.g., 3 MSBs) of the second-stage SSB may be indicated via the first-stage SSB (e.g., via PBCH DMRS or PBCH DMRS and PBCH payload) .
  • the remaining part of SSB index (e.g., 3 LSBs) of the second-stage SSB may be indicated via the second-stage SSB (e.g., via PBCH DMRS or PBCH DMRS and PBCH payload) .
  • the physical cell ID (PCI) or UE specific service ID may be indicated via sequence of PSS and SSS of the first-stage SSB.
  • the initialization of sequence of the PSS and SSS are irrelevant to the PCI.
  • the sequence of PSS and SSS may be the same as those of the first-stage SSB, respectively.
  • part of Physical Cell ID, PCI (e.g., group ID) or UE specific service ID may be indicated via the first-stage SSB (e.g., via PSS and/or SSS) .
  • the remaining part of PCI (e.g., ID within group) or UE specific service ID may be indicated via the second-stage SSB (e.g., via PSS and/or SSS) .
  • a method for enabling a UE to enter cell-free network mode in the initial access phase in order to establish links with multiple service nodes is provided. More specifically, the function partition among the first-stage SSB and the second-stage SSB may be defined. Then, the UE can establish links with multiple network nodes that send second-stage SSB messages during the initial access phase.
  • FIG. 8 further shows an example system diagram of a wireless access network 800 described above including an access point or base station 802 serving UEs 803 and 805 via an over-the-air interface 804.
  • the wireless transmission resources for the over-the-air interface 804 include a combination of frequency, time, and/or spatial resource.
  • Each of the UEs 803 and 805 may be a mobile or fixed terminal device installed with mobile access units such as SIM/USIM modules for accessing the wireless communication network.
  • the UEs 803 and 805 may each be implemented as a terminal device including but not limited to a mobile phone, a smartphone, a tablet, a laptop computer, a vehicle on-board communication equipment, a roadside communication equipment, a sensor device, a smart appliance (such as a television, a refrigerator, and an oven) , or other devices that are capable of communicating wirelessly over a network.
  • each of the UEs such as UE 805 may include transceiver circuitry 806 coupled to one or more antennas 808 to effectuate wireless communication with the access point or base station 802.
  • the transceiver circuitry 806 may also be coupled to a processor 810, which may also be coupled to a memory 812 or other storage devices.
  • the memory 812 may be transitory or non-transitory and may store therein computer instructions or code which, when read and executed by the processor 810, cause the processor 810 to implement various ones of the methods described herein.
  • the access point or base station 802 may be capable of communicating wirelessly via the over-the-air interface 804 with one or more UEs and communicating with a CPU described above and/or a core network.
  • the access point or base station 802 may be implemented, without being limited, in the form of a 2G base station, a 3G nodeB, an LTE eNB, a 4G LTE base station, a 5G NR base station of a 5G gNB, a 5G central-unit base station, or a 5G distributed-unit base station, a cell-free access point.
  • Each type of these access points or base stations may be configured to perform a corresponding set of wireless network functions.
  • the access point or base station 802 may include transceiver circuitry 814 coupled to one or more antennas 816, which may include an antenna tower 218 in various forms, to effectuate wireless communications with the UEs 803 and 805.
  • the transceiver circuitry 814 may be coupled to one or more processors 820, which may further be coupled to a memory 822 or other storage devices.
  • the memory 822 may be transitory or non-transitory and may store therein instructions or code that, when read and executed by the one or more processors 820, cause the one or more processors 820 to implement various functions of the access point or base station 802 described herein.
  • a two-stage information transmission structure e.g., two-stage SSB
  • the UE can determine the time-frequency domain resource of the second-stage SSB according to the measurement of the first-stage SSB.
  • a UE can transmit a feedback information to the network to facilitate the network in selecting one or more network node combination to form a UE-centric service network.
  • a scheme is provided to make the parameters of the second-stage SSB configurable.

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

La présente divulgation concerne de manière générale des communications sans fil et, plus spécifiquement, la synchronisation de stations mobiles avec un réseau sans fil et une recherche de cellule/réseau par les stations mobiles. Les divers modes de réalisation donnés à titre d'exemple de la présente invention concernent une procédure d'accès initial en deux étapes pour la synchronisation et la connexion par la station mobile à de multiples points d'accès (AP) dans un réseau sans cellule, de façon à éviter d'avoir à accéder au réseau d'abord d'une manière cellulaire suivie par la mise en oeuvre d'un commutateur de cellule ou d'une procédure de transfert en vue d'une synchronisation avec le réseau sans cellule et d'une connexion au réseau sans cellule.
PCT/CN2023/121526 2023-09-26 2023-09-26 Procédé et système de synchronisation et de recherche de réseau Pending WO2025065234A1 (fr)

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US10277349B1 (en) * 2018-04-30 2019-04-30 Nxp Usa, Inc. Method and apparatus for fast and robust cell search for 5G and millimeter-wave wireless communication systems
CN110445590A (zh) * 2018-05-04 2019-11-12 华为技术有限公司 通信方法和装置
US20230300888A1 (en) * 2020-08-06 2023-09-21 Lg Electronics Inc. Method for transmitting/receiving random access channel, and device therefor

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US10277349B1 (en) * 2018-04-30 2019-04-30 Nxp Usa, Inc. Method and apparatus for fast and robust cell search for 5G and millimeter-wave wireless communication systems
CN110445590A (zh) * 2018-05-04 2019-11-12 华为技术有限公司 通信方法和装置
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