Channel state information overhead reduction for multiplexed data transmission in massive MIMO systems with hybrid beamforming

Abstract

A network node sends a plurality of CSI-RS resource sets to multiple terminals and transmits CSI reference signals via the CSI-RS resource sets using a hybrid beamforming antenna system comprising a baseband precoder and time domain beam forming module. The network node receives CSI reports comprising CSI-RS Resource Indicators (CRIs) corresponding to reference signals received over the CSI resource sets with the corresponding CSI. The CSI for less preferred CRIs includes differential values relative the CSI corresponding to the most preferred CRI. The network node evaluates the CSI reports received from the multiple terminals and selects a time domain beamforming matrix for transmitting multiplexed data for multiple terminals.

Description

CHANNEL STATE INFORMATION OVERHEAD REDUCTION FOR MULTIPLEXED DATA TRANSMISSION IN MASSIVE MIMO SYSTEMS WITH HYBRID BEAMFORMINGField

[0001] This invention generally relates to wireless communications and more particularly to channel state information (CSI) multiplexed data transmission in massive MIMO systems with hybrid beamforming.Background

[0002] Many conventional wireless communication systems employ network nodes such as, base stations or gNBs, to transmit and receive wireless signal to and from terminals, such as user equipment (UE) devices. A network node may include an antenna array with multiple antenna elements. The antenna array is often part of an antenna system having a plurality of logical antenna ports that are mapped to the multiple antenna elements of the antenna array. Communication through the antenna array is often managed by precoding signals and adjusting parameters to manipulate the antenna pattern of the antenna array. In order to select the appropriate precoder and antenna parameters to maximize efficient communication with a terminal, a terminal measures reference signals transmitted by a network node and transmits a report to the network node. A technique employed in conventional systems includes sending Channel State Information Reference Signals (CSI-RSs) that are received and measured by the terminal where the network node sends a CSI-RS configuration message to the terminal. The precoding parameters are determined by the reported CSI and applied to the antenna system by the network node.Summary

[0003] A network node sends a plurality of CSI-RS resource sets to multiple terminals and transmits CSI reference signals via the CSI-RS resource sets using a hybrid beamforming antenna system comprising a baseband precoder and time domain beam forming module. Each terminal receives and measures the CSI refence signals transmitted over the identified CSI-RS resource sets and identifies a preferred CSI-RS Resource Indicator (CRI) corresponding to the received reference signals exhibiting the most optimal characteristics. The terminals report the CSI to the network node for at least some of the measured reference signals over the CSI resources where the preferred resource set is indicated with the CRI in a CSI report. Other less preferred CRIs corresponding to other CSI-RS resource sets are also reported along with the corresponding CSI where the CSI for the less preferred CRIs include differential values relative the CSI corresponding to the most preferred CRI. The network node evaluates the CSI reports received from the multiple terminals and selects a time domain beamforming matrix for transmitting multiplexed data for multiple terminals. In some situations, the terminal provides absolute CSI information for the less preferred CRIs which may be in response to channel conditions, instructions from the network, or other circumstances.

[0004] FIG. 1A is a block diagram of an example of a system where a networknode receives Channel State Information (CSI)from multiple terminals for multiple CSI reference signal (CSI-RS) sets transmitted using hybrid beamforming andwhere each terminal provides CSI with CSI-RS Resource Indicator (CRI) prioritization that at least indicates a mostpreferred CRI.FIG. 1B is a block diagram of the system for an example where the network node multiplexes data for multiple terminals in a multiplexed transmission with hybrid beamforming where the time domain beamforming configuration of the hybrid beamforming is at least partially based on CSI reports received from the terminals.FIG. 2 is a block diagram of an example of CSI report with full CSI for a most preferred CRI and differential CSI for one or more less preferred CRIs that are less preferred than the most preferred CRI.FIG. 3 is a block diagram of an example of a base station suitable for use as a network node.FIG. 4 is a block diagram of an example of a UE device suitable for use as the terminal devices.FIG. 5 is a block diagram of an example of hybrid beamforming antenna system suitable for use as the antenna system connected to other transmitter components.FIG. 6 is a flow chart of an example of a method of managing multiplexed hybrid beamforming transmission.FIG. 7 is a flow chart of an example of reporting CSI and receiving multiplexed data at a terminal.

[0005] Multiple-input multiple-output (MIMO) systems can significantly increase the throughput of wireless systems. As a result, MIMO is an integral part of 4th and 5th generation (4G and 5G) wireless systems. Some 5G systems employ MIMO systems with a large number of antennas which are often referred to as massive MIMO systems. Typically, a massive MIMO system is set up with Nt transmit and Nr receive antennas, also called Nt Transmit and Nr Receive (TR) antennas. A conventional 32 TR system consists of 32 baseband ports and 32 radio branches. In some situations, the number, Nt, of Transmit antennas may be different from the number, Nr, of receive antennas.

[0006] Some conventional massive MIMO systems, referred to as active antenna systems (AAS), can support 192 antenna elements (AE) deployed in a frequency range of 3-4 GHz, regardless of the number of TRs. An antenna panel with 192 antenna elements, for example, may include 8 columns and 2 rows with cross-polarization (i.e. (8x2x2x6=192 AE). Often, a 32 TR massive MIMO system includes a radio branch connected to 6 elements, referred to as subarrays. Beamforming may be performed at both the baseband and the antenna panel.

[0007] Massive MIMO systems are likely to be deployed at higher frequencies where a larger number of smaller antenna elements in an array may be deployed due to the shorter wavelength of the signals. Frequencies in the range of 7-20 GHz are being considered for allocation to terrestrial communication systems, for example.

[0008] In order to support the larger antenna arrays of extremely massive MIMO systems, the subarray size may be increased while maintaining the conventional number of radio branches to 32. For example, the subarray may be increased to 12 or 24 such that a 32 TR system could use a 1X12 subarray to support a 384 AE antenna array or use a 1X24 subarray to support a 768 AE antenna array. With an increased subarray size, however, antenna beams are narrow and produce many sidelobes that can cause interference to other terminals.

[0009] Another potential option for supporting a larger antenna array includes increasing the baseband / radio ports to a higher value while maintaining a reasonably sized subarray. For example, a 1x6 subarray could be used in a 64 TR system to support a 384 AE antenna array or a 1x3 subarray could be used in a 128 TR system to support a 384 AE antenna array. Similarly, a 1x6 subarray could be used in a 128 TR system to support a 768 AE antenna array.

[0010] Hybrid beamforming systems can be used to expand the baseband ports in the time domain while keeping the subarrays size the same as that of the baseline. The time domain beamforming matrix can be implemented either in the digital domain or analog domain. As a result, a hybrid beamforming system may employ phase shifters or a delayed version of the baseband signal. As an example, in a hybrid beamforming antenna system with 384 antenna elements, each baseband port can be configured to drive two power amplifiers where each power amplifier drives a 1X6 subarray. In a conventional system for 32 TR, a single power amplifier drives the 1X6 subarray configuration for 32 TR. Therefore, subarray sizes in the hybrid beamforming system are the same as those in the conventional system.

[0011] Although significant increases in performance can be achieved with hybrid beamforming, conventional hybrid beamforming techniques are limited in efficiency in situation where terminal devices are receiving relatively low amounts of data (i.e., small file transfers). In such situations, conventional hybrid beamforming systems falter due to an inherent design constraint resulting in the inability to multiplex users with distinct time domain digital beamforming matrices. This limitation arises from the prerequisite that multiplexed users must share the same time domain digital beam. The design constraint results in a significant bottleneck in the efficiency of hybrid beamforming systems. Where terminals are receiving smaller amounts of data, a considerable number of resource elements within an Orthogonal Frequency-Division Multiplexing (OFDM) symbol remain unused. This inefficiency manifests as empty, unused, spaces within the OFDM symbol, leading to a wastage of valuable spectral resources.

[0012] For the examples herein, however, the efficiency of communication using massive MIMO systems, such as those with more than 32 TRs, is significantly increased by multiplexing users on a transmission with a time domain digital beamforming matrix suitable for each terminal. The network node configures each terminal, of a plurality of terminals, to measure multiple sets of CSI-RS resources. The reference signals are transmitted using different time domain digital beamforming matrices over the different sets of CSI-RS resources. Each terminal measures the reference signals received over the identified CSI-RS resources and identifies, to the network node, a preferred set of CSI-RS resources as well as channel information for less preferred CSI-RS resources. Such a scheme results in a significant increase in overhead for communicating the CSI information in conventional systems. For some examples herein, however, the terminals report a plurality of CRIs with associated CSI where the CSI information includes absolute information for a preferred CRI and includes differential CSI for other, less preferred CRIs. As discussed herein, absolute information means the full information that convey the value of every parameter in the CSI without a reference. Differential CSI information for a CRI includes at least some CSI parameters that are relative to a reference which, for the examples herein, is the value of the parameter in the absolute CSI information for the preferred CRI. The network node manages transmissions by multiplexing data for multiple terminals based on the reported CRIs and CSI. Where multiple terminals report the same preferred CRI, the network node may multiplex the data for the two terminals over a transmission using the time domain beamforming matrix identified by the reported preferred CRI. The network node may also multiplex data for terminals on a transmission using a time domain beamforming matrix associated with a CRI common in the CSI reports from the terminals although one or more of the terminals does not identify the common CRI as the preferred CRI.

[0013] In some situations, the CSI report from each terminal may have one of at least two formats where one format includes absolute CSI information for the preferred CRI and for at least some of the less preferred CRIs and another format includes absolute CSI information for the preferred CRI and differential CSI for at least some of the less preferred CRIs. The selection of the CSI report format may be based on instructions from the network node and / or channel conditions where the channel conditions may be determined by the terminal generating the CSI report or information received from the network node. Such a technique may be useful to dynamically adjust the resolution of the information in the CSI reports based on conditions. For example, a differential CSI parameter value may be limited to a maximum number of bits to reduce overhead such that reporting the differential value provides less information than reporting the absolute CSI value. When channel conditions are poor, it may be advantageous to transmit absolute CSI at the cost of increased overhead.

[0014] In some examples, the terminals may only provide CSI reports in the format that includes absolute CSI information for the preferred CRI and differential CSI for at least some of the less preferred CRIs. In some situations, the network node only supports CSI report format that includes absolute CSI information for the preferred CRI and differential CSI for at least some of the less preferred CRIs.

[0015] A network node is any apparatus, equipment, device, or combination of devices, on the network side of the communication system that is connected to the communication network or is part of communication network. Some examples of a network node include a base station, a node B, an E-UTRA Node B, Evolved Node B, eNodeB, eNB, a New Generation eNB (ng-eNB), a gNodeB (also known as a gNB) in new radio (NR) technology, a macro station, pico station, and a femto station. The network node may form, or be a part of, the radio access network (RAN) that provides a connection between the core network and terminal communication devices. A RAN may be organized into three functional blocks including a Radio Unit (RU), a Distributed Unit (DU) and a Centralized Unit (CU). The RU transmits, receives, amplifies, and digitizes radio frequency signals and typically located near, or integrated into, the antenna. The DU and CU perform computations and / or processing to send and receive digitalized radio signals to and from the core network. The DU is typically located at or near the RU and the CU may be closer to the core network. The infrastructure or connection between the RU and the DU is often referred to as fronthaul and the infrastructure or connection between the DU and the CU is often referred to as a midhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0016] A terminal communication device (terminal), such as a remote terminal and a relay terminal, is a communication device on the terminal side of the communication system and is sometimes referred to as user equipment (UE), a UE device, a terminal device, wireless mobile device, wireless communication device and other terms. Some examples of a terminal communication device include a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, and laptop computer. In some situations, the terminal communication device is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. In addition, the terminal communication device may be, or may be a part of, a wearable device or a vehicle where the vehicle may be terrestrial vehicle, watercraft, or aircraft (including unmanned aerial vehicles). The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0017] FIG. 1A is a block diagram of an example of a system 100 where a network node 102 receives Channel State Information (CSI) 104, 106 from multiple terminals 108, 110 for multiple CSI reference signal (CSI-RS) sets 124, 125 transmitted using hybrid beamforming and where each terminal 108, 110 provides CSI 104, 106 with CSI-RS Resource Indicator (CRI) prioritization that at least indicates a most preferred CRI. The network node 102 transmits and receives signals through a hybrid beamforming antenna system 114 that includes at least a multi-element antenna array 116, a time domain beam forming module 118, and baseband precoder 120.

[0018] The network node 102 configures each terminal 108, 110 to receive and measure CSI reference signals 124, 125 transmitted over multiple CSI-RS resource sets 122, 123 and to report the results of the measurements including a prioritization of the preference of the CSI-RS resource sets where the prioritization at least identifies the most preferred CRI associated with the CSI-RS resource set identified as the most optimal for communication with the terminal 108, 110. For the example, the network node transmits one or more CSI-RS configuration messages 128 to the first terminal 108 where the CSI-RS configuration messages 128 identify a number (N) of CSI-RS resources sets 122. The network node 102 transmits N CSI-RSs 124 where each CSI-RS is associated with a CSI-RS resource set of the N CSI-RS resource sets 122. In FIG. 1A, the CSI-RS resource sets 122, 123 are represented by blocks having different shading or cross-hatching within a resource block of subcarriers and OFBM symbols. In some situations, multiple CSI-RSs are transmitted within the same resource block. In other situations, at least some of the CSI-RSs are transmitted in different resource blocks.

[0019] The first terminal 108 receives and measures the CSI-RSs 124. In accordance with the information provided in the CSI configuration message(s), the first terminal 108 receives the reference signals transmitted over the CSI-RS resource sets and measures parameters of the received signals. Based on the measurements, the first terminal 108 generates a CSI report 104 that at least indicates a most preferred CRI identifying the optimal beam for communication with the network node 102. For at least some of the examples herein, the CSI report provides information regarding the relative quality of the beams associated with the CSI-RSs transmitted over the CSI-RS resource sets. Accordingly, the terminal 108 may indicate to the network node, a priority of the beams for communication. The terminal may also only indicate the most preferred CRI and provide CSI for the less preferred CRIs without providing a priority of the less preferred CRIs.

[0020] Continuing with the example, the network node 102 also transmits reference signals (CSI-RSs) 125 over the N CSI-RS resource sets 123 to the second terminal 110. Typically, the reference signals 125 and N CSI-RS resource sets 123 to the second terminal 110 are different from the reference signals 124 and N CSI-RS resource sets 122 to the first terminal 108. In some situations, the reference signals (CSI-RSs) 124, 125 may be the same to both terminals.

[0021] The second terminal 110 receives and measures the CSI-RSs 125. In accordance with the information provided in the CSI configuration message(s), the second terminal 110 receives the reference signals transmitted over the CSI-RS resource sets and measures parameters of the received signals. Based on the measurements, the second terminal 110 generates a CSI report 106 that at least indicates a preferred CRI identifying the optimal beam for communication with the network node 102. For at least some of the examples herein, the CSI report 106 provides information regarding the relative quality of the beams associated with the CSI-RSs transmitted over the CSI-RS resource sets. As discussed above, the terminal 110 may indicate, to the network node, a priority of the beams for communication or only identify the most preferred CRI without prioritizing the less preferred CRIs.

[0022] As discussed below in further detail, the CSI reports 104, 106 include CSI for the reported CRIs. Therefore, each terminal 108, 110 reports the most preferred (most optimal) CRI with CSI and other acceptable, less preferred, CRIs with CSI without prioritizing the other CRIs or may report a prioritization of the CRIs with the associated CSI for each. For the examples herein, the CSI for the preferred CRI is absolute CSI and the CSI for the less preferred CRIs is differential CSI. The differential CSI includes differential values for all of the CSI parameters. In some situations, however, one or more of the CSI parameters in differential CSI may include absolute values.

[0023] In some examples, the format of the CSI report may be dynamically adjusted based on conditions or other factors. In one example, the format is selected from at least two formats where one format includes absolute CSI information for the preferred CRI and for at least some of the less preferred CRIs and another format includes absolute CSI information for the preferred CRI and differential CSI for at least some of the less preferred CRIs. The selection of the CSI report format may be based on instructions from the network node and / or channel conditions where the channel conditions may be determined by the terminal generating the CSI report or information received from the network node. For the example of FIG. 1A, therefore, additional messages may be transmitted from the network node to the terminals either providing channel conditions, format selection criteria, or explicit instructions regarding selection of the CSI report format.

[0024] FIG. 1B is a block diagram of the system 100 for an example where the network node 102 multiplexes data for multiple terminals 108, 110 in a multiplexed transmission with hybrid beamforming 140 where the time domain beamforming configuration of the hybrid beamforming is at least partially based on CSI reports 142, 144 received from the terminals 108, 110. The example of FIG. 1B is a continuation of the example of FIG. 1A where the CSI reports 128, 130 are CSI reports 142, 144 with a prioritization of multiple CRIs with CSI. Accordingly, the CSI report 142 is an example of the CSI report 128 that includes a plurality of CRI indicators 146 indicating CRIs 147-150, an indicator 152 of the CRI preference for each CRI 147-150, and Channel State Information (CSI) 154 associated with each CRI 147-150. For the example, the CSI 154 includes parameters for CQI 156, PMI 158 and RI 160. Similarly, the CSI report 144 is an example of the CSI report 130 that includes a plurality of CRI indicators 162 indicating CRIs 163-166, an indicator 168 of the CRI preference for each CRI 163-166, and CSI 170 associated with each CRI 163-166. For the example, the CSI 170 includes parameters for CQI 172, PMI 174 and RI 176.

[0025] The CRI preference indicator 152, 168 may include values that indicate a ranking of the CRIs in terms of preference for the terminal. In other situations, the CRI preference indicator 152, 168 only identifies the most preferred CRI and no values or indicators are provided for the less preferred CRIs. The CRI preference indicator 152, 168, may be a value where a lower value indicates a higher preference or vice versa. In other situations, the order of the CRIs in a list within the CSI report may provide the preference ranking and may provide the CRI preference indicator 152, 168. In some examples, the inclusion of a CRI in a CRI report indicates that the CRI is a preferred CRI acceptable for communication. In other situations, CSI for CRIs that are not acceptable may also be included in the CSI report.

[0026] After receiving the CSI reports 142, 144, in one example, the network node 102 evaluates the CRI preference of each terminal to identify a CRI that is suitable for communication with both terminals. Where both terminals indicate the same CRI as the optimal and preferred CRI, the network node chooses the preferred CRI as the selected CRI. For the example of FIG. 1B, the preferred CRI for the first terminal is CRI_B and the preferred CRI for the second terminal is CRI-C and the next preferred CRI is CRI_B. An example of a suitable technique for selecting the selected CRI when the two terminals do not identify the same CRI as the most preferred CRI includes selecting a preferred CRI of one terminal and a prioritized CRI of the other terminal. For the example of FIG. 1B, therefore, such a technique may include selecting CRI_B since CRI_B is the preferred CRI 148 for the first terminal and is prioritized by the second terminal as the second most preferred CRI 164. In another example of the technique for FIG. 1B, the network node chooses the CRI_C as the selected CRI since CRI_C is the preferred CRI 165 for terminal 2 and is prioritized by the first terminal as the second most preferred CRI 149.

[0027] In other examples, the network node 102 chooses the selected CRI based on the most preferred CRI of one terminal and any terminal including the selected CRI in the CSI report. The network node also evaluates the CSI information 154, 170 in each report when choosing the selected CRI. The network node may apply other factors in choosing the selected CRI, such as the QoS of the data to each terminal and other scheduler priorities.

[0028] For the example of FIG. 1B, the network node 102 has first data 178 to transmit the first terminal 108 and second data 180 to transmit to the second terminal 110. With conventional techniques, the first data 178 is transmitted in a different hybrid beamformed transmission than the hybrid beamformed transmission used for transmitting the second data 180. In some situations, there is not a significant amount of data to transmit to at least one of the terminals and, as a result, at least one the transmissions may include unused portions of OFDM symbols. For the examples herein, however, the network node transmits both sets of data 178, 180 over the same hybrid beamforming transmission 140. The network node 102 multiplexes the data 178, 180 for the two terminals and applies the parameters to the time domain beamforming module 118 corresponding to the selected CRI. The network node applies the appropriate baseband precoding matrix to each set of data 178, 180 before the resource element mapping the data 178, 180 to resources 182, 184 in a resource block. The resulting signal is then further processed before the time domain beamforming module applies the beamforming matrix corresponding to the selected CRI before the resulting signal is converted to an analog signal that is mixed, amplified and transmitted through the antenna array 116. Each terminal 108, 110 receives the multiplexed transmission with hybrid beamformed signal 140 and retrieves the data 178, 180 from the resources 182, 184.

[0029] FIG. 2 is a block diagram of an example of CSI report 200 with full CSI 202 for a most preferred CRI 204 and differential CSI 206 for one or more less preferred CRIs 207-209 that are less preferred than the most preferred CRI 204. The CSI report 200 identifies the most preferred CSI 204 and at least one other less preferred CSI 207-209 and provides CSI for all the CRIs where at least some of the CSI is differential CSI 210 for at least some of the less preferred CRIs 207-209. For the example of FIG. 2, CRI_A 204 is the most preferred CRI 204 and CRI_B 207, CRI_C 208, and CRI_D 209 are less preferred CRI. The CSI parameters for CQI 212, PMI 213, and RI 214. Different CSI parameters may include such that some parameters may be omitted, and additional CSI parameters may be included. Differential CSI is provided for all CSI parameters corresponding to the less preferred CRIs 207-209. For the example, therefore, CSI for CRI_B 207 includes parameters indicating differential values for CSI including CQI_DIFF_B 216, PMI_DIFF_B 217, and RI_DIFF_B 218. CSI for CRI_C 208 includes parameters indicating differential values for CSI including CQI_DIFF_C 220, PMI_DIFF_C 221, and RI_DIFF_C 222. CSI for CRI_D 209 includes parameters indicating differential values for CSI including CQI_DIFF_D 224, PMI_DIFF_D 225, and RI_DIFF_C 226. In some situations, however, full CSI may be provided for one or more of the parameters for CQI 212, PMI 213, and RI 214 for the less preferred CRIs 207-209. Differential CSI parameters indicate a difference in value of a particular CSI parameter relative to the CSI parameter for the most preferred CRI 204. For example, if the CSI parameter of L1-RSRP (signal strength) for the preferred CRI is -90 dBm and the L1-RSRP for another CRI is -98 dBm, the CSI parameter for the preferred CRI is reported as an absolute value of “-98” and the CSI parameter for the other CRI is reported as a differential value of “-8”.

[0030] For the example of FIG. 2, the CSI report includes a CRI preference indicator 228 that indicates the relative preference of each CRI 204, 207-209. In some situations, however, only an indicator that identifies the most preferred CRI is included and the relative preference of the less preferred CRIs 207-209 is not provided. Therefore, the CSI report 200 includes a plurality of CRI identifiers 230 that identify the CSI resource sets measured by the terminal where at least a preferred CRI is indicated and CSI information for other, less preferred, CRIs is provided. For the examples herein, the CSI includes the at least the CSI parameters of CRI, CQI, PMI, and RI. In some situations, the CSI parameters may include one or more other CSI parameters such as SSBRI, LI, and L1-RSRP.

[0031] FIG. 3 is a block diagram of an example of a base station 300 suitable for use as a network node 102. The base station 300 includes electronics 304, a transmitter 306, a receiver 308, and the antenna system 114, as well as other electronics, hardware, and code. The base station 300 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the base station 300 and network node 102 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The base station 300 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. Although the base station may be referred to by different terms, the base station is typically referred to as a gNodeB or gNB when operating in accordance with one or more revisions of the 3GPP communication specification. In some situations, the base station 300 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station 300 may be a portable device that is not fixed to any particular location.

[0032] The electronics 304 include any combination of hardware, software, and / or firmware for communicating with and controlling other base station components to execute the functions described herein as well as facilitating the overall functionality of the base station 300. The electronics 304, therefore, cooperatively operate with other base station 300 components to initiate tasks and perform the operations and functions of the base station 300. An example of suitable electronics 304 includes code running on a microprocessor or processor arrangement connected to memory 314. The transmitter 306 includes electronics configured to transmit wireless signals. In some situations, the transmitter 306 may include multiple transmitters. The receiver 308 includes electronics configured to receive wireless signals. In some situations, the receiver 308 may include multiple receivers. The receiver 308 may receive signals through multiple antennas or through a selected antenna of the antenna system 114. The antenna system 114 may include separate transmit and receive antennas in some situations. The antenna system 114 is discussed in further detail with reference to FIG. 5 below.

[0033] The transmitter 306 and receiver 308 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 308, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 306 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions. The required components may depend on the particular functionality required by the base station 300.

[0034] The transmitter 306 includes a modulator (not shown), and the receiver 308 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at the base station 300 in accordance with one of a plurality of modulation orders. The electronics 304 in conjunction with the transmitter 306 apply a precoder matrix and a time domain beamforming matrix to signals transmitted through the multiple antennas 310.

[0035] The base station 300 includes a communication interface 312 for communicating with other base stations and other network components, and other entities, such as servers and databases. The communication interface 312 may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface 312, therefore, may include wireless communication functionality and may utilize some of the components of the transmitter 306 and / or receiver 308.

[0036] The electronics 304, in conjunction with the receiver 308, measure and evaluate signals transmitted by UE devices. The electronics 304 and the receiver 306, therefore, can receive, measure, and evaluate uplink signals including reference signals transmitted by UE devices. Signal measurements and evaluations can be stored in a memory 314 and are used to determine the location of UE devices in some circumstances.

[0037] The electronics 304, in conjunction with the transmitter 306 and antenna system 114, process outgoing signals to precode signals transmitted to terminals (UE devices). Accordingly, the electronics 304, components of the antenna system 114, and transmitter 306 apply the appropriate precoder and beamforming to signals transmitted to specific UE devices. As discussed herein, the base station 300 may transmit reference signals and receive feedback from the terminals in order to determine the appropriate precoders, antenna system settings, and other transmission parameters.

[0038] FIG. 4 is a block diagram of an example of a UE device 400 suitable for use as the terminal devices 108, 110. In some examples, the UE device 400 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 400 is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 400, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 400 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0039] The UE device 400 includes at least electronics 402, a transmitter 404 and a receiver 406. The electronics 402 include any combination of hardware, software, and / or firmware for communicating with and controlling other UE device components to execute the functions described herein as well as facilitating the overall functionality of a communication device. The electronics 402, therefore, cooperatively operate with other UE device components to initiate tasks and perform the operations and functions of the UE device 400. An example of suitable electronics 402 includes code running on a microprocessor or processor arrangement connected to memory 410. The transmitter 404 includes electronics configured to transmit wireless signals. In some situations, the transmitter 404 may include multiple transmitters. The receiver 406 includes electronics configured to receive wireless signals. In some situations, the receiver 406 may include multiple receivers. The receiver 406 and transmitter 404 receive and transmit signals, respectively, through antenna 408. The antenna 408 may include separate transmit and receive antennas. In some circumstances, the antenna 408 may include multiple transmit and receive antennas.

[0040] The transmitter 404 and receiver 406 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 406, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 404 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.

[0041] The transmitter 404 includes a modulator (not shown), and the receiver 406 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders.

[0042] The UE device 400 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with base stations. The electronics 402, in conjunction with the receiver 406, measure an evaluate signals transmitted by other devices, such as base stations and UE devices. The electronics 402 and the receiver 406, therefore, can receive, measure, and evaluate downlink reference signals transmitted by a base station. Signal measurements and evaluations can be stored in the memory 410.

[0043] FIG. 5 is a block diagram of an example of hybrid beamforming antenna system 500 suitable for use as the antenna system 114 connected to other transmitter components 501. The various functions and operations of the blocks described with reference to antenna system 500 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. In the interest of brevity and clarity, multiple signals are represented with a single arrow and functions including multiple inputs and outputs are represented with a single block. For example, certain functions represented with a single block may be applied to each baseband logical port such that the functional block represents multiple functional blocks to process multiple logical ports.

[0044] The input bits of the data 178, 180 to be transmitted to the terminals 108, 110 are passed through the forward error correction code and rate matching (FEC / rate matching) module 502 where additional parity bits are added for error protection. The resultant bits 503 are passed through the scrambling module 504 which adds cell-specific scrambling operation for interference avoidance from other neighboring cells. The resultant bits 505 are passed through the modulator 506 which converts the bitstream to complex symbols 507. The resultant symbols 507 are passed through the layer mapping module 508 which maps the resultant modulated symbols to different layers. The resultant symbols per layer 509 are processed by the baseband precoder 120 where a precoder matrix is applied and are then mapped to resource elements assigned to the terminal by the resource element (RE) mapping module 510. Within a radio portion, the resultant streams 511 are processed by an inverse fast Fourier transform (IFFT) module 512 to convert the streams from the frequency domain to the time domain. Although not explicitly illustrated in FIG. 5, the IFFT module 512 processes each baseband port. Therefore, if the system 100 is utilizing 64 logical ports, the IFFT module includes 64 IFFT blocks. The resultant time-domain signals per branch 513 are processed by the time domain beam forming (TDBF) module 118 before being converted to analog signals by a Digital to Analog converter (DAC) 514. The resultant analog signals 515 are mixed with a local oscillator (LO) signal in the LO mixer 516 before amplification by power amplifiers 518. The amplified signals 519 are transmitted through the subarrays of the antenna array 116.

[0045] FIG. 6 is a flow chart of an example of a method of managing multiplexed hybrid beamforming transmission. The method may be performed in a system such as the system 100 discussed herein. For the example, the method is performed by a network node, such as the network node 102. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the network node may facilitate the generation, formatting, reception, and transmission of signals and messages as well as facilitating measurements, evaluations and determinations. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 6. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 6.

[0046] At step 602, CSI configuration messages are transmitted to multiple terminals where each CSI configuration message identifies, to the receiving terminal, multiple CSI resource sets. For the example, the network node 102 determines the resources that will be used to transmit CSI reference signals to the terminals and generates a CSI configuration message identifying the multiple sets. In some situations, RRC messaging other than a CSI configuration message can be used.

[0047] At step 604, CSI-RSs are transmitted to the multiple terminals over the CSI resource sets identified to the terminals. In some situations, the network node simultaneously transmits at least some of the CSI reference signals to the terminals. In other situations, the CSI-RSs are transmitted at different times within a relatively short time period.

[0048] At step 606, CSI reports from the multiple terminals are received. Each CSI report includes CSI for the reference signals transmitted over each of the CSI resource sets. For the example, the CSI report indicates a preferred CRI that is most preferred by the terminal. The CSI report also includes other (less preferred) CRI. Each CRI is associated with reference signals transmitted over a CSI-RS resource set and includes CSI measured by the terminal. For the example, the preferred CRI includes absolute CSI information and the other CRIs include differential CSI where the information included in the CSI report are relative values to the CSI of the most preferred CSI. As discussed above, the format of the CSI report may be selected in some situations where one format includes providing absolute CSI information for the less preferred CRIs.

[0049] At step 608, a time domain beamforming matrix is selected for hybrid beamformed transmissions to the terminals. Based at least partially on the CSI reports, the network node selects a time domain beamforming matrix that can be used for transmitting a multiplexed transmission to two or more terminals. The network node evaluates the CSI of the most preferred CRI and other less preferred CRIs of each terminal reported in the CSI report and determines the weighting of the time domain beamforming matrix that can be used of transmission. In some situations, the network node considers the relative preference of the CRIs that may be provided by the terminal while, in other situations, the network node considers only the reported CSI to make the selection. The network node determines the weighting and other parameters of the time domain beamforming matrix at least partially based on the CSI reports.

[0050] At step 610, a hybrid beamformed multiplexed transmission is transmitted to at least two terminals where the transmission includes at least first data for a terminal and second data for second terminal. The hybrid beamformed multiplexed transmission is transmitted using the selected time domain beamforming matrix and comprises data for multiple terminals.

[0051] Therefore, the network node transmits a plurality of Channel State Information (CSI) resource sets to a plurality of terminals and transmits CSI reference signals (CSI-RSs) to the terminals in each CSI resource set. The network node then receives, from each of the plurality of terminals, a CSI report comprising CSI for at least some of the plurality of the CSI resource sets. Each CSI report identifies a most preferred CSI-RS Resource Indicator (CRI) identified by the terminal transmitting the CSI report and comprises absolute CSI for the most preferred CRI and differential CSI for at least one other CRI. The differential CSI comprises a differential value for at least one CSI parameter relative to an absolute value of the CSI parameter for the most preferred CRI. The network node selects a time domain beamforming matrix based at least partially on at least two CSI reports and transmits a hybrid beamformed multiplexed transmission with hybrid beamforming using the time domain beamforming matrix where the transmission comprises first data for a first terminal and second data for a second terminal.

[0052] As discussed above, the CSI report from each terminal may have one of at least two formats where one format includes absolute CSI information for the preferred CRI and for at least some of the less preferred CRIs and another format includes absolute CSI information for the preferred CRI and differential CSI for at least some of the less preferred CRIs. The selection of the CSI report format may be based on instructions from the network node and / or channel conditions where the channel conditions may be determined by the terminal generating the CSI report or information received from the network node. Such a technique may be useful to dynamically adjust the resolution of the information in the CSI reports based on conditions. Accordingly, the network node may perform additional steps to the example of FIG. 6 in managing CSI reporting where the additional steps may include transmitting instructions to the terminals on which format to use for the CSI reports. Other steps may include providing criteria for the terminals to evaluate to determine which format to apply. The network node may transmit information to the terminals to assist in selection of the CSI report format where such information may include channel conditions and / or network capacity.

[0053] FIG. 7 is a flow chart of an example of reporting CSI and receiving multiplexed data at a terminal. The method may be performed in a system such the system 100 discussed herein. For the example, the method is performed by a terminal, such as the first terminal 108 and second terminal 110. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the network node may facilitate the generation, formatting, reception, and transmission of signals and messages as well as facilitating measurements, evaluations and determinations. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 7. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 7.

[0054] At step 702, a CSI configuration message is received from the network node 102. The CSI configuration message identifies multiple CSI resource sets. In some situations, RRC messaging other than a CSI configuration message can be used to receive the CSI configuration.

[0055] At step 704, the multiple CSI-RSs are received over the CSI resource sets identified by the CSI configuration message. CSI parameters of the CSI-RSs are measured in accordance with CSI configuration message.

[0056] At step 706, the terminal determines whether an absolute CSI report format or a differential CSI report format should be used for CSI reports. The selection may be based on various criteria, instructions, and / or measurements. In one example, an explicit instruction received from the network node indicates which format should be used. In another example, the network node provides criteria to be evaluated by the terminal to determine the appropriate format. The criteria may include values of specific parameters that have been measured by the terminal which may include measurements of the CSI-RSs or other refence signals. In some situations, the format selection criteria are preconfigured. The format selection criteria may be based on combinations of criteria and may be dynamically adjusted. In one situation, for example, preconfigured format selection criteria may be overridden by an instruction received from the network node. If the differential format is selected, the method continues at step 708. Otherwise, the method proceeds to step 710.

[0057] At step 708, a CSI report is generated and transmitted to the network node 102. The CSI report includes CSI for the reference signals transmitted over each of the CSI resource sets. For the example, the CSI report indicates a preferred CRI that is most preferred by the terminal. The CSI report also includes other (less preferred) CRI. The preferred CRI includes absolute CSI information and the other CRIs include differential CSI where the information included in the CSI report are relative values to the CSI of the most preferred CSI. For the example, the criteria for selecting the preferred CRI are provided by the network node 102 via RRC signaling. In some situations, the preferred CRI selection criteria may be preconfigured. The terminal evaluates the appropriate measured parameters of the received CSI-RSs and determines the most preferred CRI.

[0058] At step 710, a CSI report is generated and transmitted to the network node 102 in the absolute format. The CSI report includes CSI for the reference signals transmitted over each of the CSI resource sets where the CSI report indicates a preferred CRI that is most preferred by the terminal. The CSI report also includes other (less preferred) CRI where the most preferred CRI and three less preferred CRIs include absolute CSI information.

[0059] At step 712, a hybrid beamformed multiplexed transmission is received from the network node 102 that includes data for the terminal and at least one other terminal. The hybrid beamformed multiplexed transmission is transmitted by the network node using a selected time domain beamforming matrix and comprises data for multiple terminals.

[0060] In some situations, steps 706 and 710 are omitted and the terminal only reports the CSI with differential CSI information for the less preferred CRIs. Therefore, the terminal receives, from the network node, a plurality Channel State Information (CSI) resource sets and CSI reference signals (CSI-RSs) in the CSI resource sets. The terminal measured CSI parameters of the CSI-RSs and identifies the most preferred CSI-RS Resource Indicator (CRI) based on the CSI parameters. The terminal then generates a CSI report comprising CSI for at least some of the plurality of the CSI resource sets where the CSI report identifies the most preferred CRI and comprises absolute CSI for the most preferred CRI. The CSI report also comprises differential CSI for at least one other CRI where the differential CSI comprises a differential value for at least one CSI parameter relative to an absolute value of the CSI parameter for the most preferred CRI. The terminal receives a hybrid beamformed multiplexed transmission transmitted with hybrid beamforming using a time domain beamforming matrix where the transmission comprises first data for a first terminal and second data for a second terminal.

[0061] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and / or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof. (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and / or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0062] When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer-readable medium. Computer readable media includes both computer storage media and communication media including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0063] Therefore, the methods and apparatus of this invention may take the form, at least partially, of program logic or program code (i.e., instructions) embodied in tangible media, such as a machine-readable storage medium. When the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code that is transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via any other form of transmission. When the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0064] Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present disclosure. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Therefore, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0065] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

[0066] The present application claims priority to Provisional Application No. 63 / 625,715, entitled “A Method to Reduce CSI Overhead in Massive MIMO Systems”, docket number KWIC 00003 PRO, filed January 26, 2024, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.

Claims

1. A method comprising: transmitting a plurality of Channel State Information (CSI) resource sets to a plurality of terminals; transmitting CSI reference signals (CSI-RSs) to the terminals in each CSI resource set; receiving, from each of the plurality of terminals, a CSI report comprising CSI for at least some of the plurality of the CSI resource sets, each CSI report having a format comprising a first format identifying a most preferred CSI-RS Resource Indicator (CRI) identified by a terminal transmitting the CSI report and comprising absolute CSI for the most preferred CRI and differential CSI for at least one other CRI, the differential CSI comprising a differential value for at least one CSI parameter relative to an absolute value of the CSI parameter for the most preferred CRI; selecting a time domain beamforming matrix based at least partially on at least two CSI reports; and transmitting a hybrid beamformed multiplexed transmission with hybrid beamforming using the time domain beamforming matrix and comprising first data for a first terminal and second data for a second terminal.

2. The method of claim 1, wherein CSI parameters of the absolute CSI include at least one of a Reporting Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), and a Rank Indicator (RI) and wherein CSI parameters of the differential CSI include at least one of CQI, PMI, and RI.

3. The method of claim 2, wherein the selecting the time domain beamforming matrix comprises evaluating the CSI parameters of the CSI reports to identify optimal CSI-RS resources for transmission of the hybrid beamformed multiplexed transmission.

4. The method of claim 1, wherein the selecting the time domain beamforming matrix comprises selecting the time domain beamforming matrix based on the most preferred CRI identified in one of the received CSI reports.

5. The method of claim 1, wherein the selecting the time domain beamforming matrix comprises selecting the time domain beamforming matrix based on highest priority common CRI identified in the CSI reports received from the plurality of terminals.

6. The method of claim 1, further comprising transmitting a Radio Resource Control (RRC) signal to each terminal, the RRC signal comprising criteria for selecting the most preferred CRI.

7. The method of claim 1, wherein the format of each CSI report is one of at least two formats comprising: the first format; and a second format identifying the most preferred CSI-RS Resource Indicator (CRI) identified by the terminal transmitting the CSI report and comprising absolute CSI for the most preferred CRI and absolute CSI for at least one other CRI.

8. The method of claim 7, wherein the format of each CSI report is based on one of channel conditions determined by the terminal transmitting the CSI report or channel conditions reported by the network node to the terminal transmitting the CSI report.

9. The method of claim 7, wherein the format of each CSI report is based on instructions provided by the network node to the terminal transmitting the CSI report.

10. A method comprising: receiving, from a network node, a plurality Channel State Information (CSI) resource sets; receiving, from the network node, CSI reference signals (CSI-RSs) in the CSI resource sets; measuring CSI parameters of the CSI-RSs; identifying a most preferred CSI-RS Resource Indicator (CRI) based on the CSI parameters; generating a CSI report comprising CSI for at least some of the plurality of the CSI resource sets, the CSI report having a format comprising: a first format identifying the most preferred CRI and comprising absolute CSI for the most preferred CRI and differential CSI for at least one other CRI, the differential CSI comprising a differential value for at least one CSI parameter relative to an absolute value of the CSI parameter for the most preferred CRI; and receiving a hybrid beamformed multiplexed transmission transmitted with hybrid beamforming using a time domain beamforming matrix and comprising first data for a first terminal and second data for a second terminal.

11. The method of claim 10, wherein CSI parameters of the absolute CSI include at least one of a Reporting Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), and a Rank Indicator (RI) and wherein CSI parameters of the differential CSI include at least one of CQI, PMI, and RI.

12. The method of claim 10, wherein the format of the CSI report is one of at least two formats comprising: the first format; and a second format identifying the most preferred CRI and comprising absolute CSI for the most preferred CRI and absolute CSI for at least one other CRI.

13. The method of claim 12, further comprising: selecting the format of the CSI report based on channel conditions.

14. The method of claim 12, further comprising: receiving format instructions from the network node; and selecting the format of the CSI report based on the instructions.

15. The method of claim 10, further comprising receiving a Radio Resource Control (RRC) signal from the network node, the RRC signal comprising criteria for selecting the most preferred CRI.

16. A terminal comprising: a receiver configured to receive, from a network node, a plurality Channel State Information (CSI) resource sets and CSI reference signals (CSI-RSs) in the CSI resource sets; a controller configured to measure CSI parameters of the CSI-RSs and identify a most preferred CSI-RS Resource Indicator (CRI) based on the CSI parameters, the controller configured to generate a CSI report comprising CSI for at least some of the plurality of the CSI resource sets, the CSI report having format comprising: a first format identifying the most preferred CRI and comprising absolute CSI for the most preferred CRI and differential CSI for at least one other CRI, the differential CSI comprising a differential value for at least one CSI parameter relative to an absolute value of the CSI parameter for the most preferred CRI; and the receiver configured to receive a hybrid beamformed multiplexed transmission transmitted with hybrid beamforming using a time domain beamforming matrix and comprising first data for a first terminal and second data for a second terminal.

17. The terminal of claim 16, wherein CSI parameters of the absolute CSI include at least one of a Reporting Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), and a Rank Indicator (RI) and wherein CSI parameters of the differential CSI include at least one of CQI, PMI, and RI.

18. The terminal of claim 16, wherein the format of the CSI report is one of at least two formats comprising: the first format; and a second format identifying the most preferred CRI and comprising absolute CSI for the most preferred CRI and absolute CSI for at least one other CRI.

19. The terminal of claim 18, wherein the controller is configured to determine channel conditions and to select the format of the CSI report based on the channel conditions.

20. The terminal of claim 18, wherein: the receiver is configured to receive channel conditions from the network node, and the controller is configured to select the format of the CSI report based on the channel conditions.

21. The terminal of claim 18, wherein: the receiver is configured to receive format instructions from the network node, and the controller is configured to select the format of the CSI report based on the instructions.

22. The terminal of claim 16, wherein the receiver is configured to receive a Radio Resource Control (RRC) signal from the network node, the RRC signal comprising criteria for selecting the most preferred CRI.

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