Technical Field

Examples of the present disclosure relate to reporting or receiving a channel state information (CSI) parameter, for example from a User Equipment (UE) configured with carrier aggregation (CA) using at least one first component carrier and at least one second component carrier.

Background

To meet demand for data centric applications, the 3rd Generation Partnership Project (3GPP) is developing the 5th Generation (5G) wireless communication standard. The following are the requirements for 5G networks:

• Data rates of several tens of megabits per second should be supported for tens of thousands of users

• 1 gigabit per second to be offered simultaneously to tens of workers on the same office floor

• Several hundreds of thousands of simultaneous connections to be supported for massive sensor deployments

• Spectral efficiency should be significantly enhanced compared to 4G/LTE

• Coverage should be improved

• Signaling efficiency should be enhanced

• Latency should be reduced significantly compared to 4G/LTE

Multiple-input multiple-output (MIMO) systems can significantly increase the data carrying capacity of wireless systems. For these reasons, MIMO is an integral part of the 3rd and 4th generation wireless communication standards. 5G systems will also employ MIMO systems, also called massive MIMO systems, which may employ hundreds of antennas at the transmitter side and the receiver side. Typically, where N _t denotes the number of transmit antennas and N _r denotes the receive antennas, the peak data rate multiplies with a factor of N _t over single antenna systems in rich scattering environment.

Figure 1 shows a typical message sequence chart 100 for downlink data transfer in 5G systems. From the pilot or reference signals (cell specific I UE specific reference signals 102 from gNB 104), the UE 106 computes the channel estimates then computes the parameters needed for channel state information (CSI) reporting, shown in box 108. The CSI report consists of for example channel quality indicator (CQI), precoding matrix index (PMI), rank information (Rl) CSI-RS Resource Indicator (CRI the same as beam indicator), etc.

The CSI report is sent in step 110 to the network via a feedback channel either on request from the network aperiodically or configured to report periodically. The network scheduler uses this information in choosing the parameters for scheduling of this particular UE. For example, the gNB determines parameters for downlink (DL) transmission, such as modulation and coding scheme (MCS), power, physical resource blocks (PRBs) etc., based on the CSI, shown in box 112. The network sends the scheduling parameters to the UE in the downlink control channel 114. After that, actual data transfer takes place from network to the UE on data traffic channel 116.

Downlink reference signals are predefined signals occupying specific resource elements within the downlink time-frequency grid. There are several types of downlink reference signals that are transmitted in different ways and used for different purposes by the receiving terminal:

• CSI reference signals (CSI-RS): These reference signals are specifically intended to be used by terminals to acquire channel-state information (CSI) and beam specific information (beam RSRP). In 5G, CSI-RS is UE specific so it can have a significantly lower time/frequency density compared to 4G.

• Demodulation reference signals (DM-RS): These reference signals also sometimes referred to as UE-specific reference signals, are specifically intended to be used by terminals for channel estimation for data channel. The label “UE-specific” relates to the fact that each demodulation reference signal is intended for channel estimation by a single terminal. That specific reference signal is then only transmitted within the resource blocks assigned for data traffic channel transmission to that terminal.

Other than these reference signals, there are other reference signals, such as Phase Tracking Reference Signal (PTRS) and Tracking Reference Signals (TRS), that may be used for various other purposes.

The uplink control channel carries HARQ-ACK information corresponding to the downlink data transmission, and channel state information. The channel state information typically consists of CSI-RS resource indicator (CRI), rank indicator (Rl), channel quality indicator (CQI), precoding matrix indicator (PMI) and Layer Indicator, etc. The CSI can be divided into two categories, one for subband and the other for wideband. The configuration of subband or wideband CSI reporting is done through RRC signalling as part of CSI reporting configuration. The table below shows the contents of CSI report for PMI format indicator = Wideband, CQI format indicator = wideband and for PMI format indicator = subband, CQI format indicator = subband.

Note that for New Radio (NR), the subband is defined according to the bandwidth part of the OFDM in terms of PRBs as shown in the table below. The subband configuration is also done through RRC signalling.

The downlink control channel (PDCCH) carries information about scheduling grants. Typically, this consists of the number of MIMO layers scheduled, transport block sizes, modulation for each codeword, parameters related to HARQ, sub band locations and PM I corresponding to that sub bands. Note that downlink control information (DCI) formats may not transmit all the information as shown above, and in general the contents of PDCCH information depends on transmission mode and DCI format.

Note that with multiple antennas at the transmitter the channel characteristics such as delay spread, multipath profile etc. might vary between the antenna ports. However, some antenna ports might have the same profile. When the antenna ports have the same channel characteristic, these are called quasi collocated (QCL).

Carrier Aggregation (CA) is a technique for increasing bandwidth without any modifications to the baseband. In the case of carrier aggregation, multiple New Radio (NR) carriers can be transmitted in parallel to or from the same terminal or User Equipment (UE), thereby allowing for an overall wider bandwidth and correspondingly higher per-link data rates.

A terminal capable of carrier aggregation may receive or transmit simultaneously on multiple component carriers. It should be noted that aggregated component carriers do not need to be contiguous in the frequency domain. Rather, with respect to the frequency location of the different component carriers, three different cases can be identified

• Intra-band aggregation with frequency-contiguous component carriers

• Intra-band aggregation with non-contiguous component carriers

• Inter-band aggregation with non-contiguous component carriers.

A terminal capable of carrier aggregation has one downlink primary component carrier and an associated uplink primary component carrier. In addition, it may have one or several secondary component carriers in each direction. Different terminals may have different carriers as their primary component carrier; that is, the configuration of the primary component carrier is terminal specific.

Summary

Example embodiments of this disclosure may improve downlink throughput, while not significantly impacting uplink capacity as in conventional methods.

One aspect of the present disclosure provides a method of reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The method comprises reporting, to a first network node, for each first component carrier, an indication identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier. The method also comprises reporting, to a second network node, for each second component carrier, an indication identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

Another aspect of the present disclosure provides a method of receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The method comprises obtaining, for each first component carrier, an indication from the UE identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier. The method also comprises obtaining, for each second component carrier, an indication from the UE identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

A further aspect of the present disclosure provides apparatus for reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to report, to a first network node, for each first component carrier, an indication identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and report, to a second network node, for each second component carrier, an indication identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

A still further aspect of the present disclosure provides apparatus for receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to obtain, for each first component carrier, an indication from the UE identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and obtain, for each second component carrier, an indication from the UE identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

Another aspect of the present disclosure provides apparatus for reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus is configured to report, to a first network node, for each first component carrier, an indication identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and report, to a second network node, for each second component carrier, an indication identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

An additional aspect of the present disclosure provides apparatus for receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus is configured to obtain, for each first component carrier, an indication from the UE identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and obtain, for each second component carrier, an indication from the UE identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier.

Brief Description of the Drawings

For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:

Figure 1 shows a typical message sequence chart for downlink data transfer in 5G systems;

Figure 2 is a flow chart of an example of a method of reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier;

Figure 3 is a flow chart of an example of a method of receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier;

Figure 4 shows an example of a rank indicator (Rl) reported over time (index) for a 3.5GHz component carrier;

Figure 5 shows an example of a rank indicator (Rl) reported over time (index) for a 3.6GHz component carrier;

Figure 6 shows an example of a channel quality indicator (CQI) index reported over time (index) for a 3.5GHz component carrier;

Figure 7 shows an example of a channel quality indicator (CQI) index reported over time (index) for a 3.6GHz component carrier; Figure 8 shows an example of a cumulative distribution function plot for SNR computed during CSI generation at the UE;

Figure 9 is a schematic of an example of an apparatus 900 for reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier; and

Figure 10 is a schematic of an example of an apparatus 1000 for receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier.

Detailed Description

The following sets forth specific details, such as particular embodiments or examples for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other examples may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g. analog and/or discrete logic gates interconnected to perform a specialized function, Application Specific Integrated Circuits (ASICs), Programmable Logic Arrays (PLAs), etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, where appropriate the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g. digital or analogue) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. For NR Ml MO systems, the UE in some examples reports channel state information (CSI) either periodically or aperiodically, or by using semi persistent CSI reporting for each component carrier. For example, if the UE is configured with 4 component carriers, the UE needs to compute channel state information (CSI) parameters such as for example rank index (Rl), precoding matrix index (PMI) (X1 and X2) and channel quality indicator (CQI) for each component carrier. However, computing the CSI parameters is highly complex as the UE may for example search all the combinations of the precoding matrices to identify the best rank information, and the corresponding X1 and X2 for the PMI and the corresponding CQI for each component carrier. As an example, the table below shows the number of precoding matrices for each rank for a given number of CSI-RS ports (2 ports) with one component carrier. The table below also shows the number of bits in a CSI total payload.

That is, the size of the CSI payload depends on the reported rank. Similarly, the table below shows the number of bits needed for a CSI for each component carrier when the UE is configured with 4 CSI-RS ports.

Similarly, the table below shows the number of bits needed for a CSI for each component carrier when the UE is configured with 8 CSI-RS ports.

Similarly, the table below shows the number of bits needed for a CSI for each component carrier when the UE is configured with 16 CSI-RS ports.

Similarly, the table below shows the number of bits needed for a CSI for each component carrier when the UE is configured with 32 CSI-RS ports.

Finally, the table below shows the total number of bits for CSI payload when the UE is configured with up to 4 component carriers. It can be observed that when the number of component carriers increases, the payload size increases proportionally.

Therefore, in some examples, when the UE is configured with multiple component carriers for increasing the downlink throughput, the uplink channel capacity (either control channel or shared channel) is impacted as each carrier needs to send the channel state information for each component carrier. For example, if 4 component carriers are configured for a UE, with 32 port CSI-RS, up to 64 bits may be needed for reporting CSI compared to 16 bits for the single component carrier. Hence, an efficient solution is needed to reduce the impact on uplink capacity when multiple component carriers are configured.

Examples of this disclosure propose methods to significantly reduce the uplink channel overhead when a UE is configured with multiple component carriers (e.g. carrier aggregation, CA) without impacting or significantly impacting downlink throughput. Methods proposed herein may for example configure the UE to report one or more CSI parameters for only one or a few component carriers (including for example a reference carrier), while for the rest of the component carrier(s) only an offset or difference value from the CSI parameter(s) may be reported. Thus, for example, for each of the rest of the component carrier(s), one or more CSI parameters may be reported as an offset or difference value. In some examples the full or absolute value may be reported for other CSI parameter(s) other than those reported as an offset or difference, though in other examples all of the CSI parameters for a component carrier may be reported as offset or difference values compared to corresponding parameters reported for the reference carrier. In some examples, whether to report full or absolute values or difference/offset values for a component carrier may be based on a frequency difference between the component carrier and the reference carrier.

Figure 2 is a flow chart of an example of a method 200 of reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The method 200 comprises, in step 202, reporting, to a first network node, for each first component carrier, an indication identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier. The first CSI parameter may comprise, for example, at least one of the following parameters for the first component carrier:

• a channel state information reference signal (CSI-RS) resource indicator (CRI);

• a rank indicator (Rl);

• a layer indicator;

• a precoding matrix indicator (PMI);

• a wideband precoding matrix indicator (X1);

• a wideband channel quality indicator (CQI);

• a plurality of subband channel quality indicators (CQIs) for a plurality of subbands; or

• a subband precoding matrix indicator (X2).

In other examples, indications identifying values for multiple CSI parameters may be reported for each of the first component carrier(s), such as for example multiple ones of the CSI parameters listed above.

Step 204 of the method 200 comprises reporting, to a second network node, for each second component carrier, an indication identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier. In some examples, the offset value reported for each second component carrier may be represented by fewer bits than the “full” or absolute value that would otherwise be reported for the second component carrier, and/or the “full” or absolute value that is reported for the first component carrier(s). Thus, the CSI may be smaller in size and be represented by a smaller number of bits. In this way, for example, the CSI reported for the second component carrier(s) may have a smaller impact on uplink capacity or overhead than a “full” CSI that includes values for all of the parameters for the second component carrier(s). The indication identifying the value of the first CSI parameter for each first component carrier and/or the indication identifying the offset value for each second component carrier may in some examples be reported by the UE on a physical uplink control channel (PLICCH) or physical uplink shared channel (PLISCH).

In some examples, multiple offset values may be reported for each of the second component carrier(s), each offset value representing a difference of a value of a respective CSI parameter for the second component carrier as compared to the corresponding CSI parameter value for the one of the at least one first component carrier. In some examples, the one of the at least one first component carrier may be referred to as the reference carrier, for example as utilized above, as the reported CSI parameter value(s) may be used as reference value(s) for the offset value(s) for the second component carrier(s).

The first network node and the second network node may in some examples be the same network node, for example where the same network node provides or serves both the first and second component carriers. Alternatively, for example, particularly where the component carriers are provided or served by different network nodes, the first and second network nodes may be different network nodes. Each network node may be for example one or more base stations, base station control units (CUs), base station distributed units (Dlls) and/or core network nodes.

In some examples, reporting, to the second network node, for each of the at least one second component carrier, the indication identifying the offset value for the second component carrier, according to step 204 may be performed in response to a difference between a frequency of the one of the at least one first component carrier and a frequency of the second component carrier being below a first threshold. Therefore, for example, CSI values for second component carriers on frequencies that are further from the “reference” frequency may be reported in “full” or as absolute values, as these CSI values may be expected to differ from those of the reference frequency by a large amount. On the other hand, in some examples, CSI values for second component carriers on frequencies that are closer to the reference frequency may be reported as offset values, as these CSI parameters may be expected to be closer to those of the reference frequency due to the smaller frequency difference. Therefore, these smaller values may in some examples be represented using fewer bits than the corresponding full or absolute values.

In some examples, the method 200 may comprise receiving, from the first network node or the second network node, a configuration identifying the at least one first component carrier and/or the at least one second component carrier. This configuration may be received for example via Radio Resource Control (RRC) signalling. Additionally or alternatively, the method 200 may in some examples comprise receiving, from the first network node or the second network node, an instruction to report, to the second network node, for each of the at least one second component carrier, the indication identifying the offset value for the second component carrier. Thus for example the first or second network node, or some other network node via the first or second network node, may be able to control which component carrier(s) are treated as first component carriers or second component carriers by the UE. Additionally or alternatively, in some examples, the particular parameters that are reported for the second component carrier(s) as offset values may be specified to the UE. Additionally or alternatively, the first component carrier used as the “reference” carrier may also be specified to the UE in some examples.

In some examples, the indication identifying the value of the first CSI parameter for each first component carrier comprises an indication identifying an entry in a table of values for the first CSI parameter. The table of values may be for example pre-configured to the UE or specified in a telecommunications standard. The indication identifying the offset value for each second component carrier may comprise for example an indication identifying an offset of an entry in the table for the second component carrier from the entry in the table for the one of the at least one first component carrier. Thus, for example, if a CSI parameter for the reference carrier is entry number X in the table, and the CSI parameter for a second component carrier is entry Y, then the offset value reported may be (X-Y) or alternatively (Y- X), or more generally any value that would allow the second network node to determine the value of the CSI parameter for the second component value based on the entry in the table for the first component carrier. Therefore, for example, the difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for each second component carrier may be a difference between the entry in the table for the one of the at least one first component carrier and the entry in the table for the second component carrier.

In some examples, there may be different reference carriers at different frequencies for different second component carriers. In a particular example, the at least one first component carrier comprises a first component carrier in a first frequency band and a first component carrier in a second frequency band different to the first frequency band, and the at least one second component carrier comprises a second component carrier in the first frequency band and a second component carrier in the second frequency band. Thus, for example, the offset value for the second component carrier in the first frequency band may be based on the difference between the value of the first CSI parameter for the first component carrier in the first frequency band and the value of the first CSI parameter for the second component carrier in the first frequency band. Similarly, for example, the offset value for the second component carrier in the second frequency band may be based on the difference between the value of the first CSI parameter for the first component carrier in the second frequency band and the value of the first CSI parameter for the second component carrier in the second frequency band. Thus, in some examples, the reference carrier for a second component carrier is in the same frequency band as the second component carrier. Figure 3 is a flow chart of an example of a method 300 of receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The network node may be for example the first and/or second network node referred to above with reference to the method 200 of Figure 2. In some examples, the UE may perform the method 200 of Figure 2. The network node may comprise for example one or more base stations, base station control units, base station distributed units and/or core network nodes.

The method 300 comprises, in step 302, obtaining, for each first component carrier, an indication from the UE identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier. The first CSI parameter may comprise, for example, at least one of the following parameters for the first component carrier:

• a channel state information reference signal (CSI-RS) resource indicator (CRI);

• a rank indicator;

• a layer indicator;

• a precoding matrix indicator (PMI);

• a wideband precoding matrix indicator (X1);

• a wideband channel quality indicator (CQI);

• a plurality of subband channel quality indicators (CQIs) for a plurality of subbands; or

• a subband precoding matrix indicator (X2).

The method 300 also comprises, in step 304, obtaining, for each second component carrier, an indication from the UE identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier. Therefore, for example, the CSI reported for the second component carrier(s), as indicated above for examples of the method 200, may be smaller in size than a “full” or absolute CSI parameter value for the second component carrier and be represented by a smaller number of bits. In this way, the second CSI may have a smaller impact on uplink capacity or overhead than a “full” CSI that includes values for all of the parameters for the second component carrier (and this also applies in some examples for each second component carrier, where there are multiple second component carriers). The first component carrier may or may not be the primary component carrier in some examples. In some examples, the first subset of parameters may comprise at least one of the following parameters for the second component carrier:

• the wideband precoding matrix indicator (X1);

• the wideband channel quality indicator (CQI);

• the plurality of subband channel quality indicators (CQIs) for the plurality of subbands; and

• the subband precoding matrix indicator (X2).

As indicated above for examples of the method 200, there may also be multiple CSI parameter(s) obtained as offset values for each second component carrier, and/or there may also be full or absolute CSI parameter value(s) reported for each second component carrier, in some examples. The indication identifying the value of the first CSI parameter for each first component carrier and/or the indication identifying the offset value for each second component carrier may be obtained from the UE on a physical uplink control channel (PLICCH) or physical uplink shared channel (PLISCH) in some examples (and also via one or more other network nodes in some examples).

Step 304 of obtaining, for each second component carrier, the indication from the UE identifying the offset value for the second component carrier, may in some examples be performed in response to a difference between a frequency of the one of the at least one first component carrier and a frequency of the second component carrier being below a first threshold, similar to examples of the method 200 described above.

In some examples, the network node may send, to the UE, a configuration identifying one or more of the following: the at least one first component carrier, the at least one second component carrier; and/or an indication identifying, for each second component carrier, the one of the at least one first component carrier (which in some examples is referred to as a reference carrier). The configuration may be sent for example via Radio Resource Control (RRC) signalling. The method 300 may additionally or alternatively in some examples comprise sending, to the UE, an instruction to report, to the second network node, for each of the at least one second component carrier, the indication identifying the offset value for the second component carrier. That is, for example, the particular CSI parameter or parameters for which an offset value should be reported, instead of the full or absolute value, may be identified to the UE. The method 300 may in some examples comprise obtaining the indication identifying the value of the first CSI parameter for each first component carrier and/or the indication identifying the offset value for each second component carrier from the UE on a physical uplink control channel (PLICCH) or physical uplink shared channel (PLISCH).

Step 302 of obtaining, for each first component carrier, the indication from the UE identifying the value of the first CSI parameter for the first component carrier comprises receiving the indication from the UE or from another network node, such as another base station, core network node etc. Similarly, in some examples, obtaining, for each second component carrier, the indication from the UE identifying the offset value comprises receiving the indication from the UE or from another network node. This may be the same network node from which the indication identifying the value of the first CSI parameter for the first component carrier is received or a different network node.

As for examples of the method 200, the indication identifying the value of the first CSI parameter for each first component carrier may in some examples be an indication identifying an entry in a table of values for the first CSI parameter. The indication identifying the offset value for each second component carrier may be for example an indication identifying an offset of an entry in the table for the second component carrier from the entry in the table for the one of the at least one first component carrier. The difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for each second component carrier may be for example a difference between the entry in the table for the one of the at least one first component carrier and the entry in the table for the second component carrier.

In some examples, similar to examples of the method 200, the at least one first component carrier comprises a first component carrier in a first frequency band and a first component carrier in a second frequency band different to the first frequency band, and the at least one second component carrier comprises a second component carrier in the first frequency band and a second component carrier in the second frequency band. Thus, for example, the offset value for the second component carrier in the first frequency band is based on the difference between the value of the first CSI parameter for the first component carrier in the first frequency band and the value of the first CSI parameter for the second component carrier in the first frequency band, and the offset value for the second component carrier in the second frequency band is based on the difference between the value of the first CSI parameter for the first component carrier in the second frequency band and the value of the first CSI parameter for the second component carrier in the second frequency band. In certain example networks, such as 5G systems and future 6G systems, may use wide bandwidths, such as in the range of 50-100 MHz for example. Certain CSI parameters, such as the rank information and/or other parameter(s) may not differ significantly when two component carriers are adjacent, close in frequency or in the same band. For example, if one component carrier is at 3.5 GHz and another is at 3.6 GHz, then the rank information reported by the UE with each component carrier bandwidth of 100 MHz at these two component carriers will be similar over time. Figure 4 shows an example of a rank indicator (Rl) reported over time (index) for the 3.5GHz component carrier, and Figure 5 shows an example of a rank indicator (Rl) reported over time (index) for the 3.6GHz component carrier. It can be seen that in most cases, the rank indicator is the same, and differs only by a small amount in other cases. In the following example, the 3.5GHz carrier is referred to as a reference component carrier, and may be for example the first component carrier referred to herein, for which the “full” CSI is reported; and the 3.6 GHz carrier is referred to as the secondary component carrier, and may be for example the second component carrier referred to herein, for which the first subset of CSI parameters is reported.

If the rank is similar for these carriers, then in some examples the CQI is also similar and if the precoding index is wideband, for example, the CQI reported by the UE may be similar. Figure 6 shows an example of a CQI index reported over time (index) for the 3.5 GHz carrier, and Figure 7 shows an example of a CQI index reported over time (index) for the 3.6 GHz carrier, at 15 dB signal to noise ratio (SNR). It can be seen that the value for the CQI index is the same or differs only by a small amount for both component carriers for each time index. Thus, for example, the offset value referred to herein may be the difference between the CQI index for the 3.5 GHz carrier and the CQU index for the 3.6 GHz carrier.

For example, in most of the instances shown in Figures 6 and 7 the CQI reported for both carriers is the same or differs by either 1 or 2 CQI indices. Hence if the UE can report 4 bits of CQI information obtained for the reference component carrier (e.g. the 3.5 GHz carrier), and for the second component carrier (e.g. the 3.6 GHz carrier) it can report the difference compared to the reference component carrier, i.e. the offset value, then the overhead for reporting the CQI index of the second component carrier may be reduced compared to reporting the full or absolute index.

Another reason for the maximum CQI index difference of only 1 or 2 (in this example) is as follows. Figure 8 shows an example of a cumulative distribution function plot for SNR computed during CSI generation at the UE. The plot shows the cumulative distribution function 802 for a reference component carrier (reference CC), and the cumulative distribution function 804 for a second component carrier (secondary CC). The table below shows an example of CQI index table for reporting CQI values for a component carrier in New Radio (NR). Since the SNR between the reference component carrier 802 and the second component carrier 804 as shown in Figure 8 is around 1-2 dB, an offset value indicating that a CQI index for the second component carrier differs from the CQI index for the reference carrier by up to +1 or -1 is sufficient for reporting the second component carrier in some examples.

The table below shows an example of four quantities representing offset values (an example of an indication identifying a value of a first CSI parameter referred to herein) that could be reported for CQI for a second component carrier, and the associated offset values. In this example, only 2 bits are needed to report the quantity for the CQI for the secondary component carrier.

Where the offset value is defined as:

Offset value = CQI index for the second component carrier

- CQI index for the reference component carrier

Thus, for example, the table above could be used by the UE to determine the quantity to report based on the difference between the computed CQI index values for the reference and second component carriers. Similarly, for example, a network node such as a base station or core network node may use this table to determine the CQI index for the second component carrier from the reported quantity and the associated offset value, and from the CQI index for the reference carrier.

In some examples, the network node may inform the UE of the component carriers for which CQI should be reported with full resolution (i.e. full or absolute values), and those for which the UE should report an offset value. The network node may also inform the UE in some examples of the reference component carrier for all or each secondary component carrier.

For example, the network node may determine if the difference 8 _f between a reference component carrier frequency and another component carrier frequency for a UE is less than a pre-defined threshold or not. That is:

If the difference between the frequencies is less than a pre-defined threshold (T), that is:

8f < T then the network node may inform the UE not to transmit a full CSI parameter (e.g. CQI index value) for this other component carrier, and instead use the reference component carrier as a reference in deriving the offset value for the other component carrier, thereby reducing the uplink channel overhead for reporting the CSI parameter for the other component carrier (second component carrier) significantly.

In another example, if the CSI parameter such as a CQI index that is to be reported by the UE for one or more component carriers is below a pre-defined threshold, then the network node can inform the UE to report an offset value for the component carrier(s) and the network node may indicate the reference carrier to the UE. This is because if the parameter such as CQI is low, when reporting an offset value instead of a full or absolute value the performance impact is negligible. However, uplink overhead for reporting the parameter for the component carrier(s) can be reduced by reporting the offset value instead.

In some example deployments, the network node configures multiple component carriers that can be in different frequency bands. For example, two component carriers many be in the 2 GHz band, and three carriers may be in the 3.5 GHz band. If offset values are reported for the 3.5 GHz band carriers based on one or more of the 2GHz band carriers as reference carriers, there may be an impact on the performance as the difference in CSI parameter may be large, and by using a small number of bits (e.g. 2 bits) to report the offset values for the 3.5 GHz carriers, the CSI parameter values for the 3.5 GHz carriers may be out of range (i.e. above or below the maximum offset value from the reference carrier CSI parameter value). Therefore, in some examples, as suggested above, multiple reference carriers may be used when reporting CSI parameter values for second component carrier(s). For example, the network node may choose one component carrier in the 2GHz band to be a reference carrier for other carrier(s) in the 2GHz band, and/or one component carrier in the 3.5GHZ band for other carrier(s) in the 3GHz band.

In another example, the network node can choose the reference carrier based on a deployment scenario. For example, if there is a macro node and small cell, such as for example a Remote Radio Unit (RRU) connected to the macro cell, then a reference carrier may be chosen based on the antenna deployment. That is, for example, one component carrier can be used from the macro node as a reference carrier, and another carrier that is deployed at the small cell as another reference carrier.

In some examples, the network node can signal to the UE the number of bits that should be used when reporting an offset value for a second component carrier. For example, the network node may signal to the UE whether to report an offset value using 3 bits or 2 bits. This choice by the network node may in some examples be based on the relative frequency difference between the reference carrier and the component carriers, with a larger frequency difference (e.g. above a threshold difference) resulting in a larger number of bits being used to report the offset value.

In some examples, signaling from the network node to the UE (e.g. informing the UE of which carriers are first and second carriers, the number of bits to use when reporting an offset value, which CSI parameters for which an offset value should be reported for a second component carrier etc.) may be via higher layer signaling such as Radio Resource Control (RRC) signaling as part of CSI report setting. That is, for example, a network node such as a base station may determine which carrier(s) need to be used as reference carriers and which carrier(s) are treated as second component carriers for which offset values are to be reported. In some examples, the signaling can be part of a downlink control channel where the network node can dynamically inform the UE to perform reporting of offset values for the secondary component carriers.

The table below shows an example of the number of bits that may be used to report channel state information (CSI) for a reference carrier and one or more component carriers, including a full or absolute CQI index value, for various numbers of component carriers (e.g. where a total number of component carriers is 2 for one reference carrier and one additional component carrier), for various values of rank index (Rl). Also shown in brackets are the number of bits used to report CSI where CQI index for carrier(s) other than the reference carrier is reported as an offset value instead of a full or absolute value. It can be seen that the uplink overhead for reporting the CSI for the component carriers can be significantly reduced using methods as proposed herein. For example, in the case of four component carriers with Rl 4, using a proposed method for reporting CQI index as an offset value for the 32 ports CSI-RS case, 58 bits are used for CSI reporting compared to 64 bits using the conventional approach. Hence, in this example there is an approximately 10% reduction in uplink channel overhead. In other examples, uplink overhead can also be reduced by additionally or alternatively reporting values for one or more other CSI parameters as offset values instead of full or absolute values.

Figure 9 is a schematic of an example of an apparatus 900 for reporting a Channel State Information (CSI) parameter in a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus 900 comprises processing circuitry 902 (e.g. one or more processors) and a memory 904 in communication with the processing circuitry 902. The memory 904 contains instructions, such as computer program code 910, executable by the processing circuitry 902. The apparatus 900 also comprises an interface 906 in communication with the processing circuitry 902. Although the interface 906, processing circuitry 902 and memory 904 are shown connected in series, these may alternatively be interconnected in any other way, for example via a bus.

In one embodiment, the memory 904 contains instructions executable by the processing circuitry 902 such that the apparatus 900 is operable/configured to report, to a first network node, for each first component carrier, an indication identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and report, to a second network node, for each second component carrier, an indication identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier. In some examples, the apparatus 900 is operable/configured to carry out the method 200 described above with reference to Figure 2.

Figure 10 is a schematic of an example of an apparatus 1000 for receiving a Channel State Information (CSI) parameter in a network node from a User Equipment (UE) configured with carrier aggregation using at least one first component carrier and at least one second component carrier. The apparatus 1000 comprises processing circuitry 1002 (e.g. one or more processors) and a memory 1004 in communication with the processing circuitry 1002. The memory 1004 contains instructions, such as computer program code 1010, executable by the processing circuitry 1002. The apparatus 1000 also comprises an interface 1006 in communication with the processing circuitry 1002. Although the interface 1006, processing circuitry 1002 and memory 1004 are shown connected in series, these may alternatively be interconnected in any other way, for example via a bus.

In one embodiment, the memory 1004 contains instructions executable by the processing circuitry 1002 such that the apparatus 1000 is operable/configured to obtain, for each first component carrier, an indication from the UE identifying a value of a first CSI parameter for the first component carrier, wherein the first channel state information comprises values for a plurality of parameters for the first component carrier, and obtain, for each second component carrier, an indication from the UE identifying an offset value, wherein the offset value is based on a difference between the value of the first CSI parameter for one of the at least one first component carrier and a value of the first CSI parameter for the second component carrier. In some examples, the apparatus 1000 is operable/configured to carry out the method 300 described above with reference to Figure 3.

It should be noted that the above-mentioned examples illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative examples without departing from the scope of the appended statements. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements below. Where the terms, “first”, “second” etc. are used they are to be understood merely as labels for the convenient identification of a particular feature. In particular, they are not to be interpreted as describing the first or the second feature of a plurality of such features (i.e. , the first or second of such features to occur in time or space) unless explicitly stated otherwise. Steps in the methods disclosed herein may be carried out in any order unless expressly otherwise stated. Any reference signs in the statements shall not be construed so as to limit their scope.