CSI feedback overhead reduction for FD-MIMO

Mechanisms for reduction of channel state information (CSI) feedback overhead are disclosed for full dimensional multiple input, multiple output (FD-MIMO) systems with large dimension antenna ports. In one aspect, rank-dependent CSI antenna port measurements are used in order to limit the number of antenna ports for high rank CSI reporting. Another aspect allows a user equipment (UE) to select subband feedback for aperiodic CSI porting on an uplink shared channel when the UE is to report subband quality and precoding indicators. Another aspect provides for on-demand CSI feedback that dynamically configures CSI feedback parameters. To reduce the signaling overhead, the multiple parameter sets may be pre-configured with different values for dynamic reporting parameters.

BACKGROUND

Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to channel state information (CSI) feedback overhead reduction for full-dimensional multiple-input, multiple-output (MIMO) systems.

Background

SUMMARY

In one aspect of the disclosure, a method of wireless communication includes receiving, at a UE, an indication to report channel quality and precoding feedback for a plurality of channel state information reference signal (CSI-RS) ports in a full dimensional multiple input, multiple output (FD-MIMO) downlink transmission, transmitting, by the UE, a first channel quality and precoding feedback for each of the plurality of CSI-RS ports, wherein the first channel quality and precoding feedback includes a low rank indicator, selecting, by the UE, a second set of CSI-RS ports of the plurality of CSI-RS ports for a second channel quality and precoding feedback, wherein the selecting the second set of CSI-RS ports is based on a rank indicator associated with the second channel quality and precoding feedback, and transmitting, by the UE, a second channel quality and precoding feedback for each of a second set of CSI-RS ports of the plurality of CSI-RS ports.

In one aspect of the disclosure, a method of wireless communication includes receiving, at a UE, an indication to report the subband channel quality and precoding feedback for a plurality of subbands over a carrier bandwidth, selecting, by the UE, a subset of the plurality of subbands for reporting the subband channel quality and precoding feedback, transmitting, by the UE, the subband channel quality and precoding feedback for each of the subbands in the subset, and transmitting, by the UE, a subband selection indicator to indicate the location of the subset of the plurality of subbands.

In one aspect of the disclosure, a method of wireless communication includes receiving, at a UE, an indication to report aperiodic CSI feedback on an uplink shared channel in a FD-MIMO downlink transmission, wherein the indication includes a feedback parameter code, looking up, at the UE, a list of feedback parameters associated with the feedback parameter code, and generating, by the UE, an aperiodic CSI feedback report using each of the list of feedback parameters.

In one aspect of the disclosure, an apparatus configured for wireless communication includes means for receiving, at a UE, an indication to report channel quality and precoding feedback for a plurality of CSI-RS ports in a FD-MIMO downlink transmission, means for transmitting, by the UE, a first channel quality and precoding feedback for each of the plurality of CSI-RS ports, wherein the first channel quality and precoding feedback includes a low rank indicator, means for selecting, by the UE, a second set of CSI-RS ports of the plurality of CSI-RS ports for a second channel quality and precoding feedback, wherein the means for selecting the second set of CSI-RS ports is based on a rank indicator associated with the second channel quality and precoding feedback, and means for transmitting, by the UE, a second channel quality and precoding feedback for each of a second set of CSI-RS ports of the plurality of CSI-RS ports.

DETAILED DESCRIPTION

FIG. 1shows a wireless communication network100, which may be an LTE network. The wireless network100may include a number of eNBs110and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a Node B, an access point, or other term. Each eNB110a,110b,110cmay provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. An eNB for a femto cell may be referred to as a femto eNB or a home eNB (HeNB). In the example shown inFIG. 1, the eNBs110a,110band110cmay be macro eNBs for the macro cells102a,102band102c, respectively. The eNB110xmay be a pico eNB for a pico cell102x, serving a UE120x. The eNBs110yand110zmay be femto eNBs for the femto cells102yand102z, respectively. An eNB may support one or multiple (e.g., three) cells.

The wireless network100may also include relay stations110r. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB or a UE) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE or an eNB). A relay station may also be a UE that relays transmissions for other UEs. In the example shown inFIG. 1, a relay station110rmay communicate with the eNB110aand a UE120rin order to facilitate communication between the eNB110aand the UE120r. A relay station may also be referred to as a relay eNB, a relay, etc.

The wireless network100may be a heterogeneous network that includes eNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs, relays, etc. These different types of eNBs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network100. For example, macro eNBs may have a high transmit power level (e.g., 20 Watts) whereas pico eNBs, femto eNBs and relays may have a lower transmit power level (e.g., 1 Watt).

The wireless network100may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation.

A network controller130may couple to a set of eNBs and provide coordination and control for these eNBs. The network controller130may communicate with the eNBs110via a backhaul. The eNBs110may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.

The UEs120may be dispersed throughout the wireless network100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a smart phone, a tablet, a wireless local loop (WLL) station, or other mobile entities. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, or other network entities. InFIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 subbands for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

FIG. 2shows a down link frame structure used in LTE. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., 7 symbol periods for a normal cyclic prefix (CP), as shown inFIG. 2, or 6 symbol periods for an extended cyclic prefix. The normal CP and extended CP may be referred to herein as different CP types. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L−1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot.

In LTE, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in symbol periods 6 and 5, respectively, in each of subframes 0 and 5 of each radio frame with the normal cyclic prefix, as shown inFIG. 2. The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) in only a portion of the first symbol period of each subframe, although depicted in the entire first symbol period inFIG. 2. The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1, 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. In the example shown inFIG. 2, M=3. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe (M=3 inFIG. 2). The PHICH may carry information to support hybrid automatic retransmission (HARQ). The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. Although not shown in the first symbol period inFIG. 2, it is understood that the PDCCH and PHICH are also included in the first symbol period. Similarly, the PHICH and PDCCH are also both in the second and third symbol periods, although not shown that way inFIG. 2. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink. The various signals and channels in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available.

A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.

A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.

FIG. 3shows a block diagram of a design of a base station/eNB110and a UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. For a restricted association scenario, the base station110may be the macro eNB110cinFIG. 1, and the UE120may be the UE120y. The base station110may also be a base station of some other type. The base station110may be equipped with antennas334athrough334t, and the UE120may be equipped with antennas352athrough352r.

At the base station110, a transmit processor320may receive data from a data source312and control information from a controller/processor340. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The processor320may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor320may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor330may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)332athrough332t. Each modulator332may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator332may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators332athrough332tmay be transmitted via the antennas334athrough334t, respectively.

At the UE120, the antennas352athrough352rmay receive the downlink signals from the base station110and may provide received signals to the demodulators (DEMODs)354athrough354r, respectively. Each demodulator354may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator354may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector356may obtain received symbols from all the demodulators354athrough354r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor358may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE120to a data sink360, and provide decoded control information to a controller/processor380.

On the uplink, at the UE120, a transmit processor364may receive and process data (e.g., for the PUSCH) from a data source362and control information (e.g., for the PUCCH) from the controller/processor380. The processor364may also generate reference symbols for a reference signal. The symbols from the transmit processor364may be precoded by a TX MIMO processor366if applicable, further processed by the modulators354athrough354r(e.g., for SC-FDM, etc.), and transmitted to the base station110. At the base station110, the uplink signals from the UE120may be received by the antennas334, processed by the demodulators332, detected by a MIMO detector336if applicable, and further processed by a receive processor338to obtain decoded data and control information sent by the UE120. The processor338may provide the decoded data to a data sink339and the decoded control information to the controller/processor340.

The controllers/processors340and380may direct the operation at the base station110and the UE120, respectively. The processor340and/or other processors and modules at the base station110may perform or direct the execution of various processes for the techniques described herein. The processor380and/or other processors and modules at the UE120may also perform or direct the execution of the functional blocks illustrated inFIGS. 7, 9, and 11, and/or other processes for the techniques described herein. The memories342and382may store data and program codes for the base station110and the UE120, respectively. A scheduler344may schedule UEs for data transmission on the downlink and/or uplink.

In one configuration, the UE120for wireless communication includes means for detecting interference from an interfering base station during a connection mode of the UE, means for selecting a yielded resource of the interfering base station, means for obtaining an error rate of a physical downlink control channel on the yielded resource, and means, executable in response to the error rate exceeding a predetermined level, for declaring a radio link failure. In one aspect, the aforementioned means may be the processor(s), the controller/processor380, the memory382, the receive processor358, the MIMO detector356, the demodulators354a, and the antennas352aconfigured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means.

In order to increase system capacity, full-dimensional (FD)-MIMO technology has been considered, in which an eNB uses a two-dimensional (2D) active antenna array with a large number of antennas with antenna ports having both horizontal and vertical axes, and has a larger number of transceiver units. For conventional MIMO systems, beamforming has typically implemented using only azimuth dimension, although of a 3D multi-path propagation. However, for FD-MIMO each transceiver unit has its own independent amplitude and phase control. Such capability together with the 2D active antenna array allows the transmitted signal to be steered not only in the horizontal direction, as in conventional multi-antenna systems, but also simultaneously in both the horizontal and the vertical direction, which provides more flexibility in shaping beam directions from an eNB to a UE. Thus, FD-MIMO technologies may take advantage of both azimuth and elevation beamforming, which would greatly improve MIMO system capacity.

FIG. 4is a block diagram illustrating a typical 2D active antenna array40. Active antenna array40is a 64-transmitter, cross-polarized uniform planar antenna array comprising four columns, in which each column includes eight cross-polarized vertical antenna elements. Active antenna arrays are often described according to the number of antenna columns (N), the polarization type (P), and the number of vertical elements having the same polarization type in one column (M). Thus, active antenna array40has four columns (N=4), with eight vertical (M=8) cross-polarized antenna elements (P=2).

For a 2D array structure, in order to exploit the vertical dimension by elevation beamforming the channel state information (CSI) is needed at the base station. The CSI, in terms of precoding matrix indicator (PMI) rank indicator (RI) and channel quality indicator (CQI), can be fed back to the base station by a mobile station based on downlink channel estimation and predefined PMI codebook(s). However, different from the conventional MIMO system, the eNB capable of FD-MIMO is typically equipped with a large scale antenna system and, thus, the acquisition of full array CSI from the UE is quite challenging due to the complexity of channel estimation and both excessive downlink CSI-RS overhead and uplink CSI feedback overhead.

Solutions for FD-MIMO CSI feedback mechanisms have been proposed for FD-MIMO with a large scale two-dimensional antenna array. For example, dimensional CSI feedback provides for a UE to be configured with two CSI processes each with a 1D CSI-RS port structure either on elevation or azimuth direction.FIG. 5is a block diagram illustrating a two CSI processes configuration each with one dimensional CSI-RS ports for the dimensional CSI feedback. In dimensional CSI feedback, CSI processes will be defined for both elevation CSI-RS ports500and azimuth CSI-RS ports501. The CSI feedback for each configured CSI process will reflect only a one dimensional channel state information. For example, one CSI feedback will only reflect the CSI of elevation CSI-RS ports500. The serving eNB (not shown) may then determine a correlation between the two separate CSI processes to obtain an estimated full antenna array precoding. For example, the eNB may use the Kronecker product to combine two precoding vectors for the full antenna array precoding.

Another example CSI feedback mechanism employs a precoded CSI-RS with beam selection.FIG. 6is a block diagram illustrating a base station600configured to transmit precoded CSI-RS for CSI feedback. The UEs in UE groups #1 and #2 are positioned at various elevations in relation to base station600. In a precoded CSI-RS with beam selection, CSI-RS virtualization may be used to compress a large number of antenna ports into a fewer number of precoded CSI-RS ports. The CSI-RS ports with the same virtualization or elevation beamforming may be associated with one CSI process. For example, the CSI-RS Resource #1 may include CSI-RS ports with the same virtualization or elevation beamforming and would be associated with a first CSI process, while CSI-RS Resource #2 and #3 would also be associated with a different CSI process. A UE can be configured with one or multiple CSI processes for CSI feedback, each with different CSI-RS virtualization. In one example, UE604of UE group #1 would be configured for three CSI processes to provide measurement information on CSI-RS Resources #1, #2, and #3, respectively. The serving eNB, base station600, would determine the best serving CSI-RS beam for UE604based on reported CSI feedback.

Several problems and challenges exist with the different current solutions for FD-MIMO CSI feedback. The current solutions each only supply a subset of the CSI information of the full dimensional channel in order to reduce the processing complexity and feedback overhead for the UE. However, with only a portion of the CSI information for the full channel, the base station will not have the best data or information in order to maximize communication performance. In order to get the best data to maximize performance, full dimensional CSI feedback with 2D PMIs, where CSI is measured from 2-dimensional CSI-RS ports with joint selection of azimuth and elevation PMIs would be ideal. A full dimensional CSI-RS resource configuration would include more than 8 CSI-RS ports which are on both horizontal and vertical directions. A joint selection of azimuth and elevation PMIs would performed by a UE based on full channel measurement. In this type of full dimensional feedback, no Kronecker approximation would be needed for CSI reporting. However, such full dimensional CSI feedback uses a large amount of uplink feedback overhead in order to deal with the large number of antenna ports.

Currently, for periodic CSI on PUCCH, the maximum CSI payload size is 11 bits. For CSI on PUSCH, the payload size can be larger, but it is still limited to the assigned uplink bandwidth. The CSI payload may also be determined based on the CSI reporting mode, which is configured through RRC signaling. For example, PUSCH mode 3-2 provides for the UE to report both subband CQI and subband PMI with larger feedback overhead than other CSI modes. For FD-MIMO, the optimization on the elevation beamforming design may depend on multiple factors, such as channel condition, available uplink bandwidth, single user/multiple user operation, and the like. In an example of use with cell edge users, higher spatial resolution is used in order to maximize the signal strength for entities at the cell edge. In other words, a UE is not required to provide accurate full dimensional CSI feedback at all times. Aspects of the present disclosure may provide for both the UE and the eNB to have the flexibility to control full CSI feedback granularity and accuracy.

FIG. 7is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The blocks and features illustrated inFIG. 7will also be described with respect to the hardware and components illustrated inFIG. 8.FIG. 8is a block diagram illustrating a base station800and UE801configured to reduce CSI feedback in FD-MIMO transmissions according to aspects of the present disclosure. Base station800, which may include components similar to those detailed with regard to base station110inFIG. 3, includes a 2D-MIMO active antenna array800-AAA having four sets of elevation ports and eight sets of azimuth ports. At block700, a UE, such as UE801, receives an indication to report CQI/PMI feedback for a plurality of CSI-RS ports in a FD-MIMO downlink transmission from base station800using 2D-MIMO active antenna array800-AAA.

At block701, UE801may transmit a first COI/PMI feedback for each of the plurality of CSI-RS ports, wherein the first COI/PMI feedback includes a low rank indicator. Accordingly, UE801generates the lower-order rank CQI/PMI feedback for each select a first set of CSI-RS ports of the plurality of CSI-RS ports of 2D-MIMO active antenna array800-AAA for a first CQI/PMI feedback, wherein the first CQI/PMI feedback is associated with a low rank indicator. At block702, UE801may select a second set of CSI-RS ports of the plurality of CSI-RS ports for a second CQI/PMI feedback. Accordingly, the described aspect provides for rank-dependent CSI measurement. In example aspects, the selection of the second set of CSI-RS ports is based on a rank indicator associated with the second CQI/PMI feedback.

At block703, UE801may transmit the second CQI/PMI feedback for a second set of CSI-RS ports of 2D-MIMO active antenna array800-AAA. By considering rank-dependent limitations on the number of CSI-RS ports for CSI feedback, UE801effectively reduces the uplink overhead by selecting only a subset of the total number of CSI-RS ports of 2D-MIMO active antenna array800-AAA for high rank CSI feedback. In various examples of operation, rank 1 feedback may be based on a full set of the plurality of CSI-RS ports and rank 2 and other higher order rank feedback may be based on a part of CSI-RS ports of the plurality of CSI-RS ports. For rank 1, UE801would only report PMI for one layer. Thus, with the same feedback overhead, rank 1 could support a larger number of CSI-RS ports than rank 2 or other higher order ranks.

Secondly, rank 1 feedback is typically associated with multiuser operation. Compared with single user MIMO, the elevation beamforming design for multiuser MIMO may provide for higher spatial resolution and finer precoding granularity. Thus, the rank-dependent CSI limitation or management allows for a tradeoff between single user MIMO performance and uplink feedback overhead, which may also help to reduce UE processing complexity.

There are several options which may be utilized by UE801to determine which CSI-RS ports of 2D-MIMO active antenna array800-AAA to designate for higher order single user MIMO. In one option, CSI-RS ports for higher order rank may be considered a subset of the CSI-RS ports in 2D-MIMO active antenna array800-AAA available for rank 1. For example, the subset of higher order single user MIMO CSI-RS ports of 2D-MIMO active antenna array800-AAA may be configured via RRC signaling of a bitmap indicator from base station800.

In a second option, RRC signaling from base station800may provide fixed weights to designate virtualized CSI-RS ports. The weights received by UE801from base station800may be used to generate a virtualization matrix, T. For example, with a full channel matrix, H, and a configured CSI-RS virtualization matrix, T, generated based on the weights received from base station800, the CSI reporting for higher order ranks may be based on the transformed channel, HT, instead of simply H.

In a third option, the weights for designating the virtualized CSI-RS ports of 2D-MIMO active antenna array800-AAA may be UE-specific weights determined by UE801from rank 1 PMI feedback. For example, a rank 1 PMI may be given by, W=T1T2, where T1is a tall matrix of a UE-specific wideband precoding matrix mapping small number of antenna ports to large number of antenna elements, and T2is the subband precoding matrix for a less dimension antenna ports. In such aspects, the CSI reporting for high order rank may be based on, HT1, instead of simply H.

Currently, for aperiodic CSI reporting, PUSCH mode 3-2 provides for the UE to report both subband CQI and subband PMI. However, due to the increased feedback overhead caused by the large number of antenna ports, this mechanism is difficult to support. One solution according to additional aspects of the present disclosure is to allow UE-selected subband feedback.

FIG. 9is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The blocks and features illustrated inFIG. 9may also be described with respect to the hardware and components illustrated inFIG. 8. The blocks and features illustrated inFIG. 9may also be described with respect to the carrier1000illustrated inFIG. 10A.FIG. 10Ais a block diagram illustrating carrier1000reflecting CSI feedback operations by an UE for FD-MIMO configured according to one aspect of the present disclosure. At block900, a UE, such as UE801, receives an indication from a serving base station, such as base station800, to report subband CQI/PMI feedback for a plurality of subbands (e.g., subbands 0-MN-1) over a carrier band width, such as carrier bandwidth1001.

At block901, UE801selects a subset of the plurality of subbands for reporting subband CQI/PMI feedback. For example, assuming a bandwidth part (BP) is frequency-consecutive and consists of N consecutive subbands, for UE-selected subband feedback, a single subband out of the N consecutive subbands of a bandwidth part may be selected for CSI reporting along with an L-bit label that designates the subband location within the particular bandwidth part. There are a total of M bandwidth parts for a serving cell carrier bandwidth, such as carrier bandwidth1001.

At block902, UE801transmits the subband CQI/PMI feedback for each of the subbands in the subset. Thus, as illustrated inFIG. 8, a maximum of M subband CQI/PMIs are reported together with M subband L-bit location indicators. For example, instead of providing subband CQI/PMI feedback for each of subbands 0-MN-1, UE801selects, within bandwidth part (BP) 0, subband 0 as the best subband for BP 0, subband MN-1 as the best subband for BP M-1, and any other of the indicated best subbands for the bandwidth parts between BP 0 and BP M-1. In addition to this subband CQI/PMI feedback, UE801will transmit M L-bit location indicators that indicate the location of subband 0 within BP 0, the location of subband MN-1 within BP M-1, and the like.

It should be noted that the “best” subbands for selection by UE801may be determined “best” based on the subband within the bandwidth part that would have the most favorable conditions for downlink transmissions from base station800. In additional aspects, the determination of “best” subband may be based on additional or separate criteria as well (e.g., highest received signal strength, lowest interference, largest spectrum efficiency, and the like).

At block903, UE801transmits a wideband CQI/PMI feedback determined over the carrier bandwidth, such as carrier bandwidth1001. In order to provide a reference for the non-selected subbands, UE801may also report a wideband CQI/PMI determined across the whole cell carrier bandwidth. Base station800may then use both the individually selected subband CQI/PMI feedback and the wideband CQI/PMI feedback for the entire carrier bandwidth100as a reference for the non-selected subbands in each bandwidth part.

FIG. 10Bis a block diagram illustrating a carrier1002having subband selection by a UE configured according to one aspect of the present disclosure. As an alternative solution for the distributed UE-selected subband feedback illustrated inFIG. 10A, UE80may to select whole bandwidth parts for subband CSI reporting. For example, with regard to carrier1000, UE801may select each of the subbands, subband 0-subband N-1 for subband CSI feedback. UE801would generate the subband CQI/PMI feedback for each of subband 0-subband N-1 and report this feedback along with a label index of bandwidth part, BP0.

FIG. 11is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The blocks and features illustrated inFIG. 11may also be described with respect to UE1200illustrated inFIG. 12.FIG. 12is a block diagram illustrating a UE configured according to one aspect of the present disclosure. At block1100, a UE, such as UE1200may receive an indication to report aperiodic CSI feedback for a plurality of CSI-RS ports in a FD-MIMO downlink transmission, wherein the indication includes a feedback parameter code. For example, UE1200receives a control message from a base station (not shown) through antennas352a-rand demodulated through demodulator/modulators354a-r, which includes one or more bits of a feedback parameter code.

At block1101, UE1200looks up a list of feedback parameters associated with the feedback parameter code. In operation, UE1200, under control of controller/processor380identifies the feedback parameter code in the control signal and looks to feedback parameter table1202stored in memory382. Using the feedback parameter code, UE1200may identify the list of feedback parameters associated with the code.

At block1102, UE1200generates a CSI feedback report using each of the list of feedback parameters. Using the feedback parameters identified in feedback parameter table using the feedback parameter code, UE1200, under control of controller/processor380executes CSI processing1201using the specific feedback parameters identified by the code. UE1200may then transmit the resulting aperiodic CSI report to the requesting base station.

Thus, the additional aspects of the present disclosure described with respect toFIGS. 11 and 12provide for on-demand CSI feedback. It may also be preferable to have on-demand CSI feedback with such specific feedback parameters, such as CSI reporting mode, vertical vs. horizontal PMI, or both, and the like, as part of an aperiodic CSI triggering for more flexible aperiodic CSI reporting. In order to reduce L1 signaling for flexible CSI reporting, multiple parameter sets may be predefined, as indicated, with different values for dynamic aperiodic CSI reporting parameters. A few bits added to the DCI uplink grant for the feedback parameter code may be used to indicate which parameter set is used for flexible aperiodic CSI reporting. A UE may then use the parameter sets indicated by higher layer signalling for determining the aperiodic CSI reporting parameters. The on-demand CSI feedback via L1 signaling can provide the best tradeoff between performance and feedback overhead.

The following parameters for determining aperiodic CSI reporting and CSI measurement antenna port may be included in the parameter set:

CQI/PMI beta offset for single and multiple codewords

Bandwidth part indicator

PMI/RI reporting indicator

Vertical vs. Horizontal or both CSI indication

The configured parameter sets can apply to all the CSI processes or a particular CSI process based on higher layer configuration.

Currently, the network can trigger the aperiodic CSI-only transmission on PUSCH if there is no transport block for the UL-SCH. The following criteria are currently known for determining whether there is only aperiodic CSI feedback for the current PUSCH reporting mode. If DCI format 0 is used or, if DCI format 4 is used and only 1 transport block is enabled and, for the enabled transport block and the number of transmission layers is 1, and if the “CSI request” bit field is 1 bit and the bit is set to trigger an aperiodic report and N_PRB<=4 (e.g., for non-CA), Or the “CSI request” bit field is 2 bits and is triggering an aperiodic CSI report for more than one serving cell according to Table 7.2.1-1A and N_PRB<=20 (for CA). Now with 2D feedback for FD-MIMO operations, the above condition of N_PRB<=4 or N_PRB<=20 is modified to N_PRB<=8 or 40, respectively, due to double payload size of H- and V-PMIs.