WO2017025114A1

WO2017025114A1 - Adaptive channel state information reporting for lte licensed-assisted access

Info

Publication number: WO2017025114A1
Application number: PCT/EP2015/068246
Authority: WO
Inventors: Timo Erkki Lunttila; Esa Tapani Tiirola; Klaus Hugl; Michal Cierny; Cassio Barboza Ribeiro
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2015-08-07
Filing date: 2015-08-07
Publication date: 2017-02-16
Anticipated expiration: 2018-02-07

Abstract

There is provided a method comprising receiving a trigger to determine and provide channel state information for at least one first carrier, determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point and providing information to the access point, said information comprising an indication of the determination.

Description

Title

ADAPTIVE CHANNEL STATE INFORMATION REPORTING FOR LTE LICENSED- ASSISTED ACCESS

Field

The present application relates to a method, apparatus and system and in particular but not exclusively, to channel state information feedback for cellular network operation on unlicensed spectrum, aka licensed-assisted access (LAA).

Background

A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communications may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non- limiting examples of services provided include two-way or multi-way calls, data

communication or multimedia services and access to a data network system, such as the Internet.

In a wireless communication system at least a part of communications between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). The wireless systems can typically be divided into cells, and are therefore often referred to as cellular systems.

A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and/or receive communications on the carrier.

The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. An example of attempts to solve the problems associated with the increased demands for capacity is an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is being standardized by the 3^rd Generation Partnership Project (3GPP). The various development stages of the 3GPP LTE specifications are referred to as releases.

Summary of the Invention

In a first aspect there is provided a method comprising receiving a trigger to determine and provide channel state information for at least one first carrier, determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point and providing information to the access point, said information comprising an indication of the determination.

The method may comprise determining whether the reference signal for the at least one carrier is being transmitted by the access point in dependence on an indication of channel occupancy received from the access point.

Determining whether the reference signal for the at least one carrier has been transmitted by the access point may comprise detecting the presence of the reference signal.

The indication of the determination may comprise a bit or a codepoint. The method may comprise providing the indication of the determination using the same encoding and resource mapping as a rank indicator field.

The method may comprise providing the indication of the determination using the same encoding and resource mapping as a HARQ-ACK signalling field. The method may comprise providing the indication of the determination using the codepoint used to indicate full rank.

If, according to the determination, said reference signal for the at least one carrier is being transmitted by the access point, the method may comprise determining channel state information and providing said channel state information to the access point.

If, according to the determination, said reference signal for the at least one carrier is not being transmitted by the access point, the method may comprise causing uplink data to be transmitted to the access point using resources allocated for providing channel state information. When the indication of the determination is sent using the same encoding and resource mapping as a rank indicator field, said resources may comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre- coding matrix indicator.

When the indication of the determination is sent using the same encoding and resource mapping as a HARQ-ACK signalling field, said resources may comprise at least one of resources allocated for providing rank indicator, resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator

The carrier may be a licensed assisted access carrier.

In a second aspect there is provided a method comprising causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment and receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point. The method may comprise providing an indication of channel occupancy to the at least one user equipment.

Whether the reference signal for the at least one carrier is being transmitted by the access point may be determined by the user equipment detecting the presence of the reference signal. The indication of the determination may comprise a bit or a codepoint. The method may comprise receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a rank indicator field. The method may comprise receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a HARQ-ACK signalling field.

The method may comprise receiving the indication of the determination using the codepoint used to indicate full rank. If, according to the indication of the determination, said reference signal for the at least one carrier is being transmitted by the access point, the method may comprise receiving determined channel state information for the at least one carrier from the at least one user equipment.

If, according to the indication of the determination said reference signal for the at least one carrier is not being transmitted by the access point, the method may comprise receiving uplink data on resources allocated for providing channel state information for the at least one carrier from the at least one user equipment.

When the indication of the determination is received using the same decoding and resource mapping as a rank indicator field, said resources may comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

When the indication of the determination is received using the same decoding and resource mapping as a HARQ-ACK signalling field, said resources may comprise at least one of resources allocated for providing rank indicator, resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

The carrier may be a licensed assisted access carrier.

In a third aspect there is provided an apparatus, said apparatus comprising means for receiving a trigger to determine and provide channel state information for at least one first carrier, means for determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point and means for providing information to the access point, said information comprising an indication of the determination.

The apparatus may comprise means for determining whether the reference signal for the at least one carrier is being transmitted by the access point in dependence on an indication of channel occupancy received from the access point.

Means for determining whether the reference signal for the at least one carrier has been transmitted by the access point may comprise means for detecting the presence of the reference signal.

The indication of the determination may comprise a bit or a codepoint. The apparatus may comprise means for providing the indication of the determination using the same encoding and resource mapping as a rank indicator field.

The apparatus may comprise means for providing the indication of the determination using the same encoding and resource mapping as a HARQ-ACK signalling field.

The apparatus may comprise means for providing the indication of the determination using the codepoint used to indicate full rank.

The apparatus may comprise means for determining channel state information and providing said channel state information to the access point, if according to the

determination, said reference signal for the at least one carrier is being transmitted by the access point. The apparatus may comprise means for causing uplink data to be transmitted to the access point using resources allocated for providing channel state information, if, according to the determination, said reference signal for the at least one carrier is not being transmitted by the access point.

When the indication of the determination is sent using the same encoding and resource mapping as a rank indicator field, said resources may comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre- coding matrix indicator.

The carrier may be a licensed assisted access carrier.

In a fourth aspect, there is provided an apparatus, said apparatus comprising means for causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment and means for receiving information from the at least one user equipment, said information comprising an indication of a

determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point. The apparatus may comprise means for providing an indication of channel occupancy to the at least one user equipment.

Whether the reference signal for the at least one carrier is being transmitted by the access point may be determined by the user equipment detecting the presence of the reference signal. The indication of the determination may comprise a bit or a codepoint.

The apparatus may comprise means for receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a rank indicator field.

The apparatus may comprise means for receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a HARQ-ACK signalling field.

The apparatus may comprise means for receiving the indication of the determination using the codepoint used to indicate full rank.

The apparatus may comprise means for receiving determined channel state information for the at least one carrier from the at least one user equipment if, according to the indication of the determination, said reference signal for the at least one carrier is being transmitted by the access point.

The apparatus may comprise means for receiving uplink data on resources allocated for providing channel state information for the at least one carrier from the at least one user equipment if, according to the indication of the determination, said reference signal for the at least one carrier is not being transmitted by the access point.

The carrier may be a licensed assisted access carrier.

In a fifth aspect, there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to receive a trigger to determine and provide channel state information for at least one first carrier, determine whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point and provide information to the access point, said information comprising an indication of the determination. The apparatus may be configured to determine whether the reference signal for the at least one carrier is being transmitted by the access point in dependence on an indication of channel occupancy received from the access point.

The apparatus may be configured to detect the presence of the reference signal.

The indication of the determination may comprise a bit or a codepoint. The apparatus may be configured to provide the indication of the determination using the same encoding and resource mapping as a rank indicator field.

The apparatus may be configured to provide the indication of the determination using the same encoding and resource mapping as a HARQ-ACK signalling field. The apparatus may be configured to provide the indication of the determination using the codepoint used to indicate full rank.

The apparatus may be configured to determine channel state information and provide said channel state information to the access point, if, according to the determination, said reference signal for the at least one carrier is being transmitted by the access point,

The apparatus may be configured to cause uplink data to be transmitted to the access point using resources allocated for providing channel state information if, according to the determination, said reference signal for the at least one carrier is not being transmitted by the access point. When the indication of the determination is sent using the same encoding and resource mapping as a rank indicator field, said resources may comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre- coding matrix indicator.

The carrier may be a licensed assisted access carrier.

In a sixth aspect there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to cause a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment and receive information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.

The apparatus may be configured to provide an indication of channel occupancy to the at least one user equipment.

The apparatus may be configured to receive the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a rank indicator field.

The apparatus may be configured to receive the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a HARQ- ACK signalling field.

The apparatus may be configured to receive the indication of the determination using the codepoint used to indicate full rank.

The apparatus may be configured to receive determined channel state information for the at least one carrier from the at least one user equipment if, according to the indication of the determination, said reference signal for the at least one carrier is being transmitted by the access point. The apparatus may be configured to receive uplink data on resources allocated for providing channel state information for the at least one carrier from the at least one user equipment if, according to the indication of the determination, said reference signal for the at least one carrier is not being transmitted by the access point.

The carrier may be a licensed assisted access carrier.

In a seventh aspect there is provided a computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising receiving a trigger to determine and provide channel state information for at least one first carrier, determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point and providing information to the access point, said information comprising an indication of the determination. The process may comprise determining whether the reference signal for the at least one carrier is being transmitted by the access point in dependence on an indication of channel occupancy received from the access point.

Determining whether the reference signal for the at least one carrier has been transmitted by the access point may comprise detecting the presence of the reference signal. The indication of the determination may comprise a bit or a codepoint.

The process may comprise providing the indication of the determination using the same encoding and resource mapping as a rank indicator field.

The process may comprise providing the indication of the determination using the same encoding and resource mapping as a HARQ-ACK signalling field. The process may comprise providing the indication of the determination using the codepoint used to indicate full rank.

If, according to the determination, said reference signal for the at least one carrier is being transmitted by the access point, the process may comprise determining channel state information and providing said channel state information to the access point. If, according to the determination, said reference signal for the at least one carrier is not being transmitted by the access point, the process may comprise causing uplink data to be transmitted to the access point using resources allocated for providing channel state information.

The carrier may be a licensed assisted access carrier.

In an eighth aspect there is provided a computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment and receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.

The process may comprise providing an indication of channel occupancy to the at least one user equipment.

Whether the reference signal for the at least one carrier is being transmitted by the access point may be determined by the user equipment detecting the presence of the reference signal.

The indication of the determination may comprise a bit or a codepoint.

The process may comprise receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a rank indicator field.

The process may comprise receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a HARQ-ACK signalling field.

The process may comprise receiving the indication of the determination using the codepoint used to indicate full rank.

If, according to the indication of the determination, said reference signal for the at least one carrier is being transmitted by the access point, the process may comprise receiving determined channel state information for the at least one carrier from the at least one user equipment. If, according to the indication of the determination said reference signal for the at least one carrier is not being transmitted by the access point, the process may comprise receiving uplink data on resources allocated for providing channel state information for the at least one carrier from the at least one user equipment. When the indication of the determination is received using the same decoding and resource mapping as a rank indicator field, said resources may comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

The carrier may be a licensed assisted access carrier.

In a ninth aspect there is provided a computer program product for a computer, comprising software code portions for performing the steps of the method of the first and/or second aspects when said product is run on the computer.

In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above. Description of Figures

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices; Figure 2 shows a schematic diagram, of an example mobile communication device;

Figure 3 shows a flowchart of an example method for feedback in an LAA communication system; Figure 4 shows a flowchart of an example method for feedback in an LAA communication system;

Figure 5 shows resource element mapping for different UL control information fields in LTE; Figure 6 shows a schematic diagram of an example control apparatus;

Detailed description

Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 2 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in figure 1 , mobile communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatus. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller. The control apparatus may provide an apparatus such as that discussed in relation to figure 6.

LTE systems may however be considered to have a so-called "flat" architecture, without the provision of RNCs; rather the (e)NB is in communication with a system architecture evolution gateway (SAE-GW) and a mobility management entity (MME), which entities may also be pooled meaning that a plurality of these nodes may serve a plurality (set) of (e)NBs. Each UE is served by only one MME and/or S-GW at a time and the (e)NB keeps track of current association. SAE-GW is a "high-level" user plane core network element in LTE, which may consist of the S-GW and the P-GW (serving gateway and packet data network gateway, respectively). The functionalities of the S-GW and P-GW are separated and they are not required to be co-located.

In Figure 1 base stations 106 and 107 are shown as connected to a wider

communications network 1 13 via gateway 1 12. A further gateway function may be provided to connect to another network.

The smaller base stations 1 16, 1 18 and 120 may also be connected to the network 1 13, for example by a separate gateway function and/or via the controllers of the macro level stations. The base stations 1 16, 1 18 and 120 may be pico or femto level base stations or the like. In the example, stations 1 16 and 1 18 are connected via a gateway 1 1 1 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided. A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) or mobile device such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile

communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

The communication devices 102, 104, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long term evolution (LTE) of the Universal Mobile Telecommunications

System (UMTS) radio-access technology. The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Radio Link Control/Medium Access Control/Physical layer protocol (RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system include those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). A base station can provide coverage for an entire cell or similar radio service area.

Wireless communication systems may be licensed to operate in particular spectrum bands. A technology, for example LTE, may operate, in addition to a licensed band, in an unlicensed band. Operating in an unlicensed band may be referred to as Licensed- Assisted Access (LAA). LTE-LAA may imply that a connection to a licensed band is maintained while using the unlicensed band. Moreover, the licensed and unlicensed bands may be operated together using, e.g., carrier aggregation or dual connectivity. For example, carrier aggregation between primary cell (PCell) on a licensed band and one or more secondary cells (SCells) on unlicensed band may be applied. In LTE LAA, standalone operation using unlicensed carrier only may be precluded.

The following is described with reference to an LTE-A communication system and, in particular, Listen-Before-Talk related arrangements for LTE operation on unlicensed spectrum LAA, considering especially Channel State Information (CSI) feedback for LAA Downlink (DL). CSI may comprise one or more of Rank Indicator (Rl), Channel Quality Indicator (CQI), and Precoding Matrix Indicator (PMI), as well as any other suitable channel state information metric.

Licensed-Assisted Access using LTE is being considered for 3GPP Release 13. One objective of LAA discussions is to enhance LTE to enable licensed-assisted access to unlicensed spectrum while coexisting with other technologies and fulfilling regulatory requirements. In some jurisdictions, unlicensed technologies may need to abide by certain regulations, e.g. Listen-Before-Talk (LBT), in order to provide fair coexistence between LTE and other technologies such as Wi-Fi as well as between LTE operators. In LTE-LAA, before being permitted to transmit, a user or an access point (such as eNodeB) may, depending on regulatory requirements, need to monitor a given radio frequency, i.e. carrier, for a short period of time to ensure the spectrum is not already occupied by some other transmission. This requirement is referred to as Listen-before-talk (LBT). The requirements for LBT vary depending on the geographic region: e.g. in the US such requirements do not exist, whereas in e.g. Europe and Japan the network elements operating on unlicensed bands need to comply with LBT requirements. Moreover, LBT may be needed in order to guarantee co-existence with other unlicensed band usage in order to enable e.g. fair co-existence with Wi-Fi also operating on the same spectrum and/or carriers. Unnecessary transmissions on unlicensed carriers, or channels, should be kept at a minimum level to avoid interfering other devices or access points operating on the same carrier frequency or preventing such devices from accessing the channel due to LBT requirements/operation. LBT requirements may mean that access points and UEs operating on an unlicensed carrier may need to stop transmission from time to time in order to give other nodes the chance to start their transmission as well (i.e. in order to provide fair co-existence) and in order to monitor whether the channel is still available. If a channel is still sensed as free according to LBT rules, the eNodeB or UE may resume transmission. If the channel is sensed as occupied (i.e. another node is transmitting on that channel), the eNodeB or UE will need to continue to suspend transmission until the channel is sensed as unoccupied according to LBT rules.

Listen-before-talk requirement may have an impact on the Channel State Information (CSI) measurements and reporting performed by a UE. During LAA, upon negative LBT (i.e. channel has been sensed as occupied) at an eNodeB, the reference signals, such as cell-specific reference signals (CRS) or channel state information reference signals (CSI- RS), necessary for CSI measurement as well as other signals used for reference including e.g. Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) will not be transmitted by the eNB. Therefore, the reference signals (RS) will not be available to the UE at the time of CSI measurement. Hence, a meaningful CSI measurement cannot be provided by the UE. Moreover, depending on the LAA control signalling and frame structure the UE may (or may not) know when the eNB sends the RS necessary for CSI measurement.

For example, in Aperiodic CSI (A-CSI) reporting, CSI reports for multiple carriers are triggered via a single UL grant on one carrier. Due to the extremely tight measurement and processing timeline (an LBT slot may have a duration in the order of 10

microseconds), it may be that the eNodeB does not know the LBT state of all the carriers at the time of the A-CSI triggering, and hence may ask a UE to determine and deliver CSI reports for carriers where no transmission (including reference signals used for CSI determination) takes place. As a consequence, the UE may determine, and thus report, an incorrect and meaningless CSI report consisting of Rank Indicator (Rl) + multiple Channel Quality Indicators (CQI) as well as Precoding Matrix Indicators (PMI) even though no related reference signals for CSI determination have been transmitted. Transmission of such a CSI report is unnecessary, given that it cannot be relied on to contain useful information. The sizes of aperiodic CSI reports may depend on the Aperiodic CSI reporting mode, eNodeB antenna configuration as well as supported DL PDSCH transmission rank, and may be large as can be seen in Table 1 below.

2^*2 antenna configuration

Mode 3-1 (closed loop wideband PMI)

2^*2 antenna configuration

4^*4 antenna confi uration

Mode 3-2 (closed loop frequency selective PMI)

2^*2 antenna confi

4^*4 antenna confi

Table 1

Table 1 shows the size of Aperiodic CSI reports per carrier for different A-CSI reporting modes, antenna configurations, and ranks for a 20MHz LTE DL carrier configuration. Rank Indicator and Cyclic Redundancy Check (CRC) bits are not included into the calculation.

As Table 1 shows, the payload of Aperiodic CSI reports may be up to 1 12 bits per carrier, excluding CRC and Rl bits. Since the payload of the CSI reports depends on the Rank Indicator, Rl is encoded separately from the rest of the CSI (namely CQI, PMI).

After requesting for one or more Aperiodic CSI reports, each corresponding to a component carrier, the eNodeB expects to receive all reports - otherwise the reception of the reports as well as any simultaneous PUSCH data would be erroneous. Following the existing CSI reporting definition, for a carrier with no reference signals (CRS or CSI-RS) present, the UE would most probably report Rank =1 , one or multiple "Out-of-Range" CQIs, and undefined PMIs, i.e. up to 82 completely redundant bits (assuming A-CSI reporting mode 3-2). This may cause a significant, unnecessary UL overhead. As discussed above, the UE behaviour in light of the current 3GPP specification would be to report a full Aperiodic CSI when it is requested to do so, leading to a significant signalling overhead.

Therefore, the Aperiodic CSI reporting design for LAA should aim to minimize CSI reporting of carriers having no reference signals for CSI determination transmitted at the time of CSI determination.

In principle, a UE may know when an eNodeB is occupying the channel (i.e. whether LBT has been successful at the eNodeB) and whether the CSI measurements can take place in a given subframe or not. This may be implied by the following agreement from 3GPP RAN1 LTE LAA AdHoc meeting (Paris, March 2015), wherein interference measurement for CSI is not allowed outside of the serving cell transmission periods. Hence, in order to be able to perform interference measurements in line with this agreement, the UE will need to know its serving cell's transmission periods.

One option may be to simply omit the reporting of an A-CSI for a carrier where the UE assumes that CSI measurements should not be conducted due to LBT. This option may be problematic for the LTE system, since potential DL signalling errors (where the presence of reference signals is indicated/signalled to the UE by the eNB) or a wrong RS presence detection by the UE (where the UE is autonomously required to detect the RS presence) may lead into a situation where the eNodeB expects a report from the UE, but the U E has dropped the CSI report instead, or vice versa. Where A-CSI was requested for

M carriers, even if the probability of error on a single carrier (p_e) is low, probability of error on at least 1 in M carriers is larger than M*p_e. An error on a single carrier may lead to resource element mapping mismatch and consequent loss of CSI as well as UL data transmissions on PUSCH.

Figure 3 shows a flowchart of an example method of channel state information feedback for LAA which aims to address the problem described above, while still being able to minimize the A-CSI overhead.

In step 320, the method comprises receiving a trigger to determine and provide channel state information for at least one first carrier. In step 340, the method comprises determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point.

In step 360 the method comprises providing information to the access point, said information comprising an indication of the determination of step 340.

The method of Figure 3 may be carried out at a UE.

Figure 4 shows a flowchart of an example method for channels ate information feedback.

In step 420, the method comprises causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment. In step 440, the method comprises receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.

The method of Figure 4 may be performed at an access point, e.g. an eNB. Methods such as those of Figures 3 and 4 may provide a signalling arrangement, where a UE indicates to an eNodeB whether a full Aperiodic CSI report is provided for a given carrier, or if the UE assumes that no RS necessary for CSI measurement for a given carrier were present and at least some of the Aperiodic CSI information or the full A-CSI report of such a carrier is therefore not provided. The eNB may know by the time of the indication of the determination by a UE, or the A-CSI report, if it has transmitted RS at a point of time between the triggering and reception of the indication and/or report. The indication allows the eNB to operate under the same assumption as the UE.

The at least one carrier may be a licensed assisted access carrier.

The indication of the determination may comprise an indication that CSI measurements could not be performed for the at least one carrier. In an embodiment, if a UE is aware that a given carrier was not transmitting anything when CSI was supposed to be measured ( i.e. determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by the access point), the UE reports an indication that CSI measurements could not be performed for the given carrier and, hence, that not all the Aperiodic CSI information of such a carrier is transmitted by the UE. The UE may transmit PUSCH data on the CSI resources (e.g. RI/CQI/PMI resources) that become vacant as a result of not transmitting CSI, which may lead to reduced control signalling overhead. The method may comprise determining whether the reference signal for the at least one carrier is being transmitted in dependence on an indication of channel occupancy received from the access point. The indication of channel occupancy may comprise DL signalling indicating an eNB's channel occupancy (i.e. transmission). The indication of channel occupancy may be transmitted on each unlicensed carrier that performs LBT to avoid issues with extremely fast inter-carrier communication.

Alternatively, or in addition, determining whether the reference signal for the at least one carrier is being transmitted may comprise detecting the presence of the reference signal at the UE, e.g. based on blind detection by the UE.

The indication of the determination may comprise a bit, or codepoint, of a channel state information report. The bit may be referred to as an A-CSI validity bit. The indication of the determination may be transmitted together with Rl bits and/or with HARQ-ACK bits. The A-CSI validity bit or a codepoint may be jointly encoded with the Rl or HARQ-ACK bits, i.e. may be provided using the same encoding and resources as Rl field or HARQ-ACK signalling field respectively. When the A-CSI validity bit is encoded with the Rl field, for each carrier for which the corresponding A-CSI validity bit/codepoint is toggled, no CQI/PMI(s) are reported in that subframe. When the A-CSI validity bit is encoded with HARQ-ACK, for each carrier for which the corresponding bit is toggled, no RI/CQI/PMI(s) (i.e. the full CSI) are reported in that subframe. If, according to the determination, said reference signal for the at least one carrier is being transmitted by the access point, the method may comprise determining channel state information and providing said channel state information, e.g. Rl, CQI and/or PMI, to the access point.

If, according to the determination, said reference signal for the at least one carrier is not being transmitted, uplink data may be caused to be transmitted using resources allocated for providing CSI. When the indication of the determination is sent using the same encoding and resource mapping as a Rl field, said resources may comprise resources allocated for providing CQI and/or resources allocated for providing PMI. When the indication of the determination is sent using the same encoding and resource mapping as a HARQ-ACK signalling field, said resources may comprise resources allocated for providing Rl, resources allocated for providing CQI and/or resources allocated for providing PMI. The data may be PUSCH data. In an embodiment, the Rank Indicator field itself (or an extension of it) may be utilized for providing the indication of the determination of whether or not CSI could be measured for that carrier and that therefore the e.g., CQI /PMI information for such carrier is not reported. This is possible because Rl (requiring a small number of bits, i.e. 1 -3 bits) and CQI/PMI (constituting most of the CSI reporting overhead, potentially more than 100 bits) are separately encoded. This may reduce the overhead compared to a reference case such as those of Table 1 (e.g., a reduction of more than 100 bits for CQI/PMI per carrier may be possible). If the A-CSI validity bit is toggled for a carrier, the corresponding CQI(s) and PMI(s) are not reported. Instead, PUSCH data may be transmitted on those resources. The possible error cases that may occur if a UE, e.g., omits reporting CSI when it assumes there are no RS to measure, when in fact there are, may be avoided.

In an embodiment, for each carrier configured to be measured, the size of the Rank Indicator field may be increased by one bit, the said bit indicating whether the CSI measurement could be performed successfully, or not.

Alternatively, or in addition, the indication of the may be provided using the codepoint used to indicate full rank. In an embodiment, a one-bit signalling field, dedicated to indicate whether the UE was able to measure CSI or not, may be introduced. This signalling field bit may be jointly encoded with the Rl bit(s).

It may be possible to reserve just one signalling state out of the Rl, e.g., the signalling state indicating full rank (instead of an additional Rl bit). However full rank may not then be available.

The "full rank" and "indicator state" may share the same signalling state and the interpretation depends on what an eNodeB transmitted. If an eNB did not transmit related RS, the eNB may interpret full rank as report without CQI/PMI. However, if eNB transmitted related RS, then it will interpret full rank as "true full rank".

One approach may be to encode the Rl (including the dedicated one-bit signalling field) jointly for all carriers. For example, if an Rl has 2 bits (4 states), adding a "no CSI" state would lead to 5 possible states per carrier. For 5 carriers this would mean 5⁵=31 25 states, which can be encoded by 1 2 bits, compared to 5*3=1 5 bits needed if the 5 states are encoded for each carrier separately.

Alternatively or in addition, the indication of the determination may be sent in a HARQ- ACK signalling field. In an embodiment, a HARQ-ACK signalling field may be utilized for indicating that CSI, including Rl, PMI and CQI, could or could not be measured for that carrier and is therefore not reported. In this case, whether A-CSI of that carrier is reported may be indicated based on an indicator jointly encoded with the HARQ-ACK signalling. As a result, there would be no need to reserve any Rl bits for carrier that could not be measured and in this case, the full A-CSI report (including Rl, CQI and PMI) can be dropped from the UL transmission. If the A-CSI validity bit is toggled for a carrier, the corresponding Rl, CQI(s) and PMI(s) are not reported. Instead, PUSCH data may be transmitted on those resources.

For each carrier configured to be measured, the size of the HARQ-ACK field may be increased by one bit, the said bit indicating whether the CSI measurement could be performed successfully, or not. In the case when the UE has no HARQ-ACKs to report, the said indicator may still be reported using HARQ-ACK resources and related channel coding procedures. If the A-CSI validity bit is jointly transmitted with Ack/Nack, the Rl information is separately coded for that carrier. If no HARQ-ACK bits are to be transmitted, the A-CSI validity bit may be sent alone, using channel coding and multiplexing

mechanisms defined for HARQ-ACK.

The Rl, CQI/PMI, and HARQ-ACK resource mapping in LTE uplink are depicted in Figure 5. The resources not occupied by Rl, CQI/PMI or HARQ-ACK, when it is determined that a reference signal for allowing channel state information measurement for at least one first carrier, may be used for PUSCH data.

An embodiment may be as follows. If a RS for a carrier has been determined to be present, i.e. it is determined that a reference signal for allowing channel state information measurement for the given carrier is being transmitted by an access point, the UE determines the CSI (such as rank indicator, CQI and PM I). The UE sets the bit (or codepoint) of a valid A-CSI report for that carrier to 1 (or 0). The indication of the determination, e.g. the A-CSI validity bit or codepoint, may be provided together with the Rl field or the HARQ-ACK signalling field as described above, however what is included in the A-CSI report is not affected. The UE then causes the reporting of A-CSI for that carrier (Rl, CQI and potentially PMI) to the eNodeB according to the configured A-CSI reporting mode in the same sub frame as the UE transmits the A-CSI validity bit.

If RS on a carrier and the corresponding A-CSI was indicated by the UE to be valid (i.e. according to the determination by the UE, the reference signal is being transmitted by the access point), the eNB assumes the A-CSI report to be fully present for that carrier (including the presence of CQI/PMI/RI). The eNodeB may then take this information into account in its PUSCH data decoding (i.e. determination of PUSCH resource element mapping). The eNodeB may utilize the available CSI from that UE for that specific carrier.

If a RS for a carrier is determined not to be present (i.e. according to the determination by the UE, the reference signal is not being transmitted by the access point), the UE sets the bit of a valid A-CSI report (or A-CSI validity bit) to 0 (or 1 ). In a first option, the Rl bits may be transmitted together with the bit(s) indicating the A-CSI to be not valid and the UE refrains from transmitting CQI and PMI for such a carrier.

In a second option, the UE may transmit the A-CSI validity bit jointly coded with HARQ- ACK and indicate the A-CSI to be not valid and therefore the UE is not transmitting the A- CSI report for that carrier (i.e. the UE refrains from transmitting RI/CQI/PMI). If no HARQ- ACK bits are to be transmitted, the A-CSI validity bit(s) may be sent alone, using the channel coding and multiplexing mechanisms defined for HARQ ACK.

In an embodiment, if RS on a carrier and the corresponding A-CSI was indicated to be not valid (and measurements could not be performed), the eNB may assume the full A-CSI report for that carrier to not be present. The eNodeB will not take into account the A-CSI report (the CQI/PMI report in case of Option 1 described above, and the full A-CSI report including RI/CQI/PMI bits in case of Option 2 described above) in determination of PUSCH resource element mapping (i.e. the UE may assume that PUSCH data has been mapped to these resources instead). Since the UE has not transmitted a valid CSI information in that time instance, the available CSI of that UE for that specific carrier may not need to be changed.

Methods such as those described above may be applicable to the case of periodic CSI reporting as well as Aperiodic CSI reporting. In Periodic CSI reporting, Rl (and potentially also the precoder type indicator, PTI) is reported in different subframes than CQI/PMI. In such case, the report containing RI/PTI can be extended to include one further bit, accommodating the indication that the given carrier could not be measured. If RS on a carrier and the corresponding periodic CSI was indicated to be not valid, the U E shall not transmit subsequent periodic CSI reports containing CQI and/or PMI. The amount of unnecessary CSI feedback may be reduced and the released resources may be used for UL payload data. Error cases due to the UE and the eNodeB having a different understanding on whether the LBT was successful at the eNodeB (i.e. whether there were RS available for CSI measurement and whether the CSI is transmitted, or not) may be prevented. It should be understood that each block of the flowchart of Figure 3 or 4 and any combination thereof may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry.

Embodiments described above by means of figures 1 to 5 may be implemented on a control apparatus as shown in figure 6 or on a mobile device such as that of figure 2. Figure 6 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a base station or (e) node B, or a server or host. In some embodiments, base stations comprise a separate apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example the control apparatus 300 can be configured to execute an appropriate software code to provide the control functions. Control functions may include causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment and receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point. It should be understood that the apparatuses may include or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities. It is noted that whilst embodiments have been described in relation to LTE, similar principles can be applied to any other communication system or radio access technology, such as 5G. In addition, although embodiments have been described from an LAA viewpoint, this disclosure may be equally valid for other co-existence scenarios. For example, Licensed Shared Access (LSA) is an example of a co-existence scenario. LSA is a spectrum sharing concept enabling access to spectrum that is identified for IMT but not cleared for IMT deployment. LSA may be focused on bands subject to harmonization and standardized by 3GPP (2.3 GHz in EU & China, 1 .7 GHz and 3550-3650 MHz in US). Co- primary sharing is another example of a co-existence scenario. Co-primary sharing refers to spectrum sharing where several primary users (operators) share the spectrum dynamically or semi-statically. Co-primary sharing may be suitable e.g. for small cells at 3.5 GHz. Spectrum sharing between operators may happen if regulators require it and/or operators need it. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. Embodiments as described above by means of figures 1 to 5 may be implemented by computer software executable by a data processor, at least one data processing unit or process of a device, such as a base station, e.g. eNB, or a UE, in, e.g., the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium or distribution medium and they include program instructions to perform particular tasks. An apparatus- readable data storage medium or distribution medium may be a non-transitory medium. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it. Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non- transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi-core processor architecture, as non-limiting examples.

Embodiments described above in relation to figures 1 to 5 may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1 . A method comprising receiving a trigger to determine and provide channel state information for at least one first carrier; determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point; and providing information to the access point, said information comprising an indication of the determination.

2. A method according to claim 1 , comprising determining whether the reference signal for the at least one carrier is being transmitted by the access point in dependence on an indication of channel occupancy received from the access point.

3. A method according to claim 1 , wherein determining whether the reference signal for the at least one carrier has been transmitted by the access point comprises detecting the presence of the reference signal.

4. A method according to any preceding claim, wherein the indication of the determination comprises a bit or a codepoint.

5. A method according to claim 4, comprising providing the indication of the determination using the same encoding and resource mapping as a rank indicator field.

6. A method according to claim 4, comprising providing the indication of the determination using the same encoding and resource mapping as a HARQ-ACK signalling field.

7. A method according to claim 4, comprising providing the indication of the determination using the codepoint used to indicate full rank.

8. A method according to any preceding claim, comprising: if, according to the determination, said reference signal for the at least one carrier is being transmitted by the access point, determining channel state information and providing said channel state information to the access point.

9. A method according to any one of claims 1 to 7, comprising: if, according to the determination, said reference signal for the at least one carrier is not being transmitted by the access point, causing uplink data to be transmitted to the access point using resources allocated for providing channel state information.

10. A method according to claim 9, wherein when the indication of the determination is sent using the same encoding and resource mapping as a rank indicator field, said resources comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

1 1 . A method according to claim 9, wherein when the indication of the determination is sent using the same encoding and resource mapping as a HARQ-ACK signalling field, said resources comprise at least one of resources allocated for providing rank indicator, resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator

12. A method according to any preceding claim, wherein the carrier is a licensed assisted access carrier.

13. A method comprising: causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment; and receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.

14. A method according to claim 13 comprising: providing an indication of channel occupancy to the at least one user equipment.

15. A method according to any one of claims 13 and 14, wherein the indication of the determination comprises a bit or a codepoint.

16. A method according to claim 15, comprising receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a rank indicator field.

17. A method according to claim 15, comprising receiving the indication of the determination from the at least one user equipment using the same decoding and resource mapping as a HARQ-ACK signalling field.

18. A method according to claim 15, comprising receiving the indication of the determination using the codepoint used to indicate full rank.

19. A method according to any one of clams 1 3 to 1 8, comprising: if, according to the indication of the determination, said reference signal for the at least one carrier is being transmitted by the access point, receiving determined channel state information for the at least one carrier from the at least one user equipment.

20. A method according to any one of claims 13 to 18, comprising: if, according to the indication of the determination said reference signal for the at least one carrier is not being transmitted by the access point, receiving uplink data on resources allocated for providing channel state information for the at least one carrier from the at least one user equipment.

21 . A method according to claim 20, wherein when the indication of the determination is received using the same decoding and resource mapping as a rank indicator field, said resources comprise at least one of resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

22. A method according to claim 20, wherein when the indication of the determination is received using the same decoding and resource mapping as a HARQ-ACK signalling field, said resources comprise at least one of resources allocated for providing rank indicator, resources allocated for providing channel quality indicator and resources allocated for providing pre-coding matrix indicator.

23. A method according to claims 13 to 22, wherein the carrier is a licensed assisted access carrier.

24. An apparatus comprising means for performing a method according to any one of claims 1 to 23.

25. A computer program product for a computer, comprising software code portions for performing the steps of any of claims 1 to 23 when said product is run on the computer.

26. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: receive a trigger to determine and provide channel state information for at least one first carrier; determine whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point; and provide information to the access point, said information comprising an indication of the determination.

27. An apparatus comprising: at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: cause a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment; and receive information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.

28. A computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising: receiving a trigger to determine and provide channel state information for at least one first carrier; determining whether a reference signal for allowing channel state information measurement for the at least one first carrier is being transmitted by an access point; and providing information to the access point, said information comprising an indication of the determination.

29. A computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising: causing a trigger to determine and provide channel state information for at least one carrier to be sent to at least one user equipment; and receiving information from the at least one user equipment, said information comprising an indication of a determination by the at least one user equipment whether a reference signal for the at least one carrier is being transmitted by an access point.