WO2012020862A1

WO2012020862A1 - Terminal and base station, method thereof in wireless communication system

Info

Publication number: WO2012020862A1
Application number: PCT/KR2010/005315
Authority: WO
Inventors: Jianjun Li; Kyoungmin Park
Original assignee: Pantech Co Ltd
Current assignee: Pantech Co Ltd
Priority date: 2010-08-12
Filing date: 2010-08-12
Publication date: 2012-02-16
Anticipated expiration: 2013-02-12

Abstract

The present invention relates to precoding and feedback channel information in wireless communication system.

Description

TERMINAL AND BASE STATION, METHOD THEREOF IN WIRELESS COMMUNICATION SYSTEM

There are a number of multi-antenna transmission schemes or transmission such as transit diversity, closed-loop spatial multiplexing or open-loop spatial multiplexing. Closed-loop MIMO(CL-MIMO) relies on more extensive feedback from the mobile terminal.

In accordance with an aspect, there is provided a method comprising: estimating a downlink channel from a received signal transmitting a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators); and transmitting a second channel quality information reflecting the average channel quality of two or more selected subbands by a terminal.

In accordance with another aspect, there is provided a terminal comprising:an channel estimator configured to estimate a downlink channel from a received signal and transmit a first channel quality information on the estimated downlinkchannel which is an average of all subband CQIs(Channel quality indicators) and a second channel quality information reflecting the average channel quality of two or more selected subbands and a post-decoder configured to decode the received signal to recover the set of data symbols.

In accordance with another aspect, there is provided a method for the base station comprising: receiving a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators) from the terminal; and receiving a second channel quality information reflecting the average channel quality of two or more selected subbands by a terminal.

Moreover, the base station may receive the third channel quality informations which are the CQIs of the selected subbands from a terminal.

In accordance with another aspect, there is provided a base station comprising: comprising: a scheduler configured to receive a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators) from the terminal and a second channel quality information reflecting the average channel quality of two or more selected subbands and sometimes the third channel quality informations which are the CQIs of the selected subbands by the terminal and schedule at least one subband to at least one terminal based on the first and the second channel quality information; and a precoder configured to transmit data symbol via the subband to the terminal.

FIG.1 is the functional flowchartof the wireless communication system using closed-loop spatial multiplexing according to one embodiment.

FIG. 2 illustrates a diagram of a frequency-time operating resource space 200 as may be employed by an OFDMA communications system.

FIG.3 is the block diagram of the wireless communication system using closed-loop spatial multiplexing according to the other embodiment.

FIG.4 is the flowchart of a method for feedbacking the channel information for the terminal according to other embodiment.

FIG.5 is the flowchart of a method for processing the channel information for the base station according to another embodiment.

It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for purposes of promoting and improving clarity and understanding. Further, where considered appropriate, reference numerals have been repeated among the drawings to represent corresponding or analogous elements.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG.1 is the functional flowchart of the wireless communication system using closed-loop spatial multiplexing according to one embodiment.

Referring to FIG.1, the communication system 100 may be any type of wireless communication system, including but not limited to a MIMO system, SDMA system, CDMA system, OFDMA system, OFDM system, etc. In the communication system, the wireless communication system 100 using closed-loop spatial multiplexing according to one embodiment comprises a transmitter 110 and a receiver 120.

The transmitter 110 may act as a base station or an eNode(eNB), while the receiver 120 may act as a subscriber station or an user equipment(UE), which can be virtually any type of wireless one-way or two-way communication device such as a cellular telephone, wireless equipped computer system, and wireless personal digital assistant. Of course, the receiver/subscriber station 120can also transmits signals which are received by the transmitter/base station 110.

The transmitter 110 may transmit a reference singal(RS) such as a channel state information reference signal(CSI-RS) to the receiver 120 at S130. The receiver 120 estimates the downlink channel by the CSI-RS.

To assist the transmitter/base station 110 in selecting a suitable precoding matrix for transmission by thetransmitter 110, the receiver/mobile terminal 120 may report channel information such as a recommended number of layers(expressed as a Rank Indication, RI) or a recommended precoding matrix(Precoding Matrix Index, PMI) corresponding to that number of layers, depending on estimates of the downlink channel conditions at S140.

In the wireless communication system 100, the quality of the signal received by the receiver 120 depends on the channel quality from the transmitter 110, the level of interference from other cells, and the noise level. To optimize system capacity and coverage for a given transmission power, the transmitter 110 may try to match the information data rate for each user to the variations in received signal quality.

The receiver 120 may be configured to report Channel Quality Indicators(CQIs) to assist the transmitter 110 in selecting an appropriate Modulation and Coding Scheme(MCS) to use for the downlink transmission at S150. The CQI reports are derived from the reference signal.

The transmitter 110 may transmit a transmission signal to the receiver 120 at S160. The transmission signal communicated between the transmitter 110 and the receiver 120 may include voice, data, electronic mail, video, and other data, voice, and video signals.

In operation, the transmitter 110 transmits a signal data stream through one or more antennas and over a channel to the receiver 120. The receiver may combine the received signal from one or more receive antennas to reconstruct the transmitted data.

The receiver 120 recovers the original data symbols.

An operating bandwidth of the operating resource space 200 may be divided into L resource blocks(RB₁-RB_L) wherein each of the N resource blocks may be defined as a set of adjacent subcarriers. For example, a 3GPP LTE system with 5 MHz bandwidth employs 25 RBs wherein each has a 180 kHz bandwidth for a total operating bandwidth of 4.5 MHz, with the remaining 0.5 MHz providing a guard band separating transmissions on two adjacent bands on different cells.

A subband of the operating bandwidth corresponds to a collection of one or more RBs. One subband may be defined as the smallest unit for CQI reporting. The RBs may also be concatenated to form larger ones thereby fundamentally reducing the CQI reporting overhead and the control channel overhead in the downlink that signals their allocated RBs to the receivers that have been scheduled. Based on the estimated channel, interference and noise variance, the receiver 120 may compute the CQI for each subband. Some examples of CQI are SINR, recommended or supportable spectral efficiency, recommended or supportable modulation-and-coding-scheme(MCS), received signal strength and mutual information. Since the CQI is typically quantized or discrete, a set of possible CQI values is predefined along with the respective index of each.

An OFDMA system with system bandwidth divided into L resource blocks(RBs) is considered. A resource block is defined as a set of adjacent subcarriers(tones). In addition, it may be defineda subband as the smallest entity for CQI report where one subband consists of k contiguous Resource Blocks(RBs). Hence, the system bandwidth contains N subbands where Nis approximately or exactly L/k. For example, a 3GPP E-UTRA system with 10 MHz bandwidth has 50 RBs, each having 180 kHz. For k=2, there are N=25 subbands for 3GPP E-UTRA. Based on the estimated channel and interference/noise variance, the receiver 120 may compute the CQI for each of the N subbands. This is defined for each spatial stream or codeword.

In this disclosure, it is assumed that the CQI is defined in terms of a suggested or recommended data rate or spectral efficiency where the CQI may be a suggested transport block size(TBS) or modulation-and-coding scheme(MCS).

A simple method by which the receiver 120 may choose an appropriate CQI value may be based on a set of Block Error Rate(BLER) thresholds. The receiver 120 may report the CQI value corresponding to the MCS that ensures BLER ≤10^-1based on the measured received signal quality.

AMC can exploit the receiver feedback by assuming that the channel fading is sufficiently slow. This requires the channel coherence time to be at least as long as the time between the receiver's measurement of the downlink reference signals and the subframe containing the correspondingly-adapted downlink transmission on the PDSCH. This time may be typically 7-8ms(equivalent to a UE speed of -10Km/h at 1.9GHz).

The periodicity and frequency resolution to be used by the receiver/mobile terminal 120 to report the CQI are both controlled by the transmitter/base station 110. In the time domain, both periodic and aperiodic CQI reporting are supported. The PUCCH is used for periodic CQI reporting only. The PUSCH is used for aperiodic reporting of the CQI, whereby the transmitter 110 specifically instructs the receiver 120 to send an individual CQI report embedded into a resource which is scheduled for uplink data transmission.

The frequency granularity of the CQI reporting is determined by defining a number of subbands(N), each comprised of k contiguous Resource Blocks(RBs). The value of k depends on the type of CQI report considered.

The CQI reporting modes can be many kinds of CQI as explained indetail in the following. In addition, in the case of multiple transmit antennas at the transmitter 110, CQI value(s) may be reported for two or more codewords.

Referring to FIG.3, in the communication system, the wireless communication system 300 using closed-loop spatial multiplexing according to one embodiment comprises a transmitter 310 and a receiver 320.

The transmitter 310 comprises a precoder 312 and a scheduler 314.

The precoder 312 may linearly combine and map a set of N_L symbols(one symbol from each layer) to the N_A antenna port by after layer mapping by the layer mapper.

The precoder 312 may comprise two precoders to optimize the performance. In various example embodiments, the first precoder may precode a set of symbols from the layer mapper by means of a precoding matrix R of size N_{L ×} N_L. The second precoder may also precode a set of symybols from the first precoder by means of a precoding matrix W of size N_{L ×} N_A.

Then the transmitter 310 transmitsthe precoded data symbols by different antennas.

In various embodiments, separate codebooks of the transmitter 310 and the receiver 320 may be stored. In such a case, separate indices may be generated wherein each index points to a codeword in its corresponding codebook, and each of these indices may be transmitted over a feedback channel to the transmitter 310, so that the transmitter 310 may use these indices to access the corresponding codewords from the corresponding codebooks and determine a transmission profile or precoding information.

The scheduler 314 may receive the channel information such as the PMIs and the CQIs. The scheduler 314selects the receivers to be transmitted on each RB along with corresponding modulation and coding schemes. Modulation and coding is provided for the different receivers, and a resulting signal is then summed up and transmitted on a downlink channel to a plurality of the receivers, for example, the receiver 320.

The receiver 320 may comprise a channel estimator 322 and a post-decoder 324.

The channel estimator 322 of the receiver 320 estimates the downlink channel condition. The channel estimator 322 feedbacks the PMI as the channel information to the transmitter 320. The channel estimator 322 may perform many kinds of codebook based PMI feedback where the receiver/mobile terminal 320 feedbacksthe precoding matrix indicator(PMI) of the favorite matrix in the codebook to the transmitter/base station 310 to support CL-MIMO(closed MIMO) operation in wireless communication system.

Also the channel estimator 322 feedbacks the CQI as the channel information to the transmitter 310. The channel estimator 322 may perform many kinds of CQI feedback.

The channel estimator 322 may comprise a PMI calculator 322a for many kinds of codebook based PMI feedback and a CQI calculator 322b for many kinds of CQI feedback.

Based on the estimated channel, the PMI calculator 322a may selects the precoding matrix for each level from the corresponding codebooks. Once the precoding matrix for each level is decided, the PMI calculator 322a separately feedback the PMIs of multilevel, for example, both level to the transmitter 310.

After the PMIs are selected, the CQI calculator 322b may calculate many kinds of CQI such as a first channel quality information on the estimated downlink channel(the wideband CQI), second channel quality information(average M selected subband CQI) and a third channel quality information (subband CQI) for the selected PMI. The type of CQI report may be configured by the transmitter 310 by RRC signaling.

The CQI calculator 322b may report one wideband CQI value for the whole system bandwidth. In other words, wideband CQI is the average CQI of the whole band which is got by the average CQI among all the subbands. If it's assumed that there are total N subbands with CQIs as CQI_i(i=1,2,...,N), the wideband CQI, CQI_wideband, may be got by

[Equation 1]

Then the CQI calculator 322b may feedback the corresponding wideband CQI to the transmitter 310 by PUCCH, which is periodical feedback. The wideband CQI may be by fully 4bits feedback, but not limited thereto.

The type of periodic reporting is configured by the transmitter 310 by RRC signaling. For the wideband periodic CQI reporting, the period may be configured to {2, 5, 10, 16, 20, 32, 40, 64, 80, 160}ms or off.

The wideband CQI are basic feedback which have the hightest priority.

In addition, for better performance, after this, the CQI calculator 324b may check whether the M selected subband CQI needs to be fedback or not.

The CQI calculator 324b may select a set of M selected subbands of size k(where k and M are given for each system bandwidth range) within the whole system bandwidth. The CQI calculator 324b may report not only one wideband CQI value but also one CQI value reflecting the average channel quality of the M selected subbands.

The average M selected subband CQI, CQI_best-M is the average CQI of the M selected subbands or an average of the selected subband CQIs.

[Equation 2]

Where K₁=argmax({CQI₁,CQI₂,…, CQI_N})and K_j= argmax({CQI₁,CQI₂,…, CQI_N}-{CQIk₁,…, CQI_Kj-1}) j=2,3,…, M so that CQI_k1=max({CQI₁,CQI₂,…,CQI_N}) and CQI_Kj=max({CQI₁,CQI₂,…, CQI_N}-{CQIk₁,…, CQI_Kj-1}). A "argmax" stands for the argument of the maximum, that is to say, the set of points of the given argument for which the value of the given expression attains its maximum value. In other words, a argmax stands for the index of CQI which the value is maximum.

It may be that CQI_best-M ≥CQI_widebandin case the CQI is computed based on, for example, SINR.

By one example the average M selected subband CQI may be the average of the selected subband CQIs in itself.

The CQI calculator 324b may feedback the differential M selected subband CQI, CQI_diff,best-M, which is the differential value between the wideband CQI and the average M selected subband CQI.

[Equation 3]

The differential M selected subband CQI, CQI_diff,best-M, is different from the differential value, CQI_{diff, kj}, between the wideband CQI and each of the subband CQI of the M selected subbands(CQI_{diff, kj}=CQI_kj-CQI_wideband). While the latter has the M number of CQIs, the former has just only one CQI. The differential M selected subband CQI, CQI_diff,best-M, may greatly reduce the feedback overhead.

The CQI value for the average M selected subbands for each codeword is encoded differentially using 2bits relative to its respective wideband CQI by PUSCH which is aperiodical feedback as defined by "Differential M selected subband CQI=Index for average of the M selected subbands-the wideband CQI index". Possible differential CQI values may be {≤+1,+2,+3,≥+4}.

As with the periodic CQI reporting, the type of aperiodic reporting is configured by the transmitter 310 by RRC signaling. Aperiodic CQI reporting on the PUSCH is scheduled by the transmitter 310 by setting a CQI request bit in an uplink resource grant sent on the PDCCH.

The CQI calculator 324b may also report the positions of the M selected subbands using a combinationatorial index r defined, but not limited therein.

[Equation 4]

Where the set

contains the M sorted subband indices and

is the extended binomial coefficient resulting in a unique label

. N is the total number of subbands and M is the index of each of the selected subbands.

In usual case, the average M selected subband CQI is enough for CL-MIMO operation for the better performance. Once there is at least one subband which has extreme higher CQI than the M selected subband CQI, it may feedback a third channel quality information reflecting a subband CQI for each of one subband which has extreme higher CQI than the average M selected subband CQI. The third channel quality information may be reflecta subband CQI for at least one subband which has extreme lower CQI than the average M selected subband CQI. Therefore the third channel quality information may be reflect either the subband which has extreme higher CQI than the average M selected subband CQIs or the subband which has extreme lower CQI than the average M selected subband CQIs or combination thereof.

By one example, the CQI calculator 314b may feedback the differential subband CQI, CQI_diff,subband,which is the differential value between the average M selected subband CQIs and the subband CQI.

[Equation 5]

The subband CQI reports are encoded differentially with respect to the average of the M selected subbands using 2-bits defined by Subband differential CQI offset which is difference between “subband CQI index” and “Index for average of M selected subbands”. Possible differential subband CQI offsets may be {≤-1, 0, +1, ≥+2}.

Of course the subband CQI may be the subband CQI for at least one of the selected subbands in itself.

The CQI calculator 314b may also report the positions of either the subband which has extreme higher CQI than the average M selected subband CQIs or the subband which has extreme lower CQI than the average M selected subband CQIs or combination thereof using a combinationatorial index r as defined above.

The CQI calculator 314b may also feedback the subband CQI by PUSCH which is aperiodical feedback. The subband CQI is by 2-bits differential feedback.

If the transmitter 310 wishes to receive periodic reporting of the CQI, the receiver 320 may transmit the CQI reports using the PUCCH(Physical Uplink Control Channel).

In other words one of the first, the second and the third channel quality information is possible for either periodicor aperiodic CQI reporting using the PUCCH or the PUSCH.

The receiver 320 recovers the original data symbols by post-decoder 314with the previous feedback precoding matrices combination. The post-decoder 314 processes the received signal and decodes the precoded symbols.

Based on the receiver's feedback, the transmitter 310 may know the CQI of subbands in high accuracy to do the scheduling. The scheduler 314 may allocate at least one subband or RB in high accuracy to the receiver. Based on the scheduling, the transmitter 310 may transmit the data symbols to this receiver 320 with the MCS level by CQI feedback and precoded the data symbols based on the receiver's PMI feedback.

The scheduler 314 is configured to schedule at least one subband or RB to at least one terminal based on the channel information such as the PMIs and the CQIs. The precoder 312 is configured to transmit data symbol via the subband to the terminal.

FIG.4 is the flowchart of a method for feedbacking the channel informationfor the terminal according to other embodiment.

Referring to FIG.4, in the method for feedbacking the channel information for the terminal according to other embodiment 400, the terminal may estimate a downlink channel from a received signal at S410.

Then the terminal may transmit a downlink precoding matrix indicators(PMIs) of the favorite matrix in the codebook based on the estimated downlink channel as the channel information to the base station at S420. At S420 the terminal separately feedback the PMIs of multilevel, for example, both level to the base station.

Then the terminal may transmit a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators) at S425. At this time, a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.

As mentioned above the wideband CQI, CQI_wideband, may be got by the Equation 1. The type of periodic reporting is configured by the base station by RRC signaling. For the wideband periodic CQI reporting, the period may be configured to {2, 5, 10, 16, 20, 32, 40, 64, 80, 160}ms or off.

In this the multilevel differential CQI feedback scheme, the PMIs feedback and the wideband CQI are basic feedback which have the hightest priority.

After this, the terminal may check whether the M selected subband CQI needs to be fed back or not at S430.

If it is needed at S430, the terminal may transmit a second channel quality information reflecting the average channel quality of the M selected subbands by the terminal. For example, the terminal may feedback the differential M selected subband CQIbetween the wideband CQI and the average M selected subband CQI at S450. In usual case, the average M selected subband CQI is enough for CL-MIMO operation for best-M feedback.

In order to feedback the differential M selected subband CQI, the terminal may select a set of the M selected subbands of size k(where k contiguous Resource Blocks(RBs) and M are given for each system bandwidth range) within the whole system bandwidth, then calculate the average M selected subband CQI, CQI_best-M,by means of the equation 2, and then the differential M selected subband CQI, CQI_diff,best-M,by means of the equation 3.

The differential M selected subband CQI is encoded differentially using 2-bits relative to its respective wideband CQI by PUSCH(Physical Uplink Shared Channel) which is aperiodical feedback.

The terminal may also report the positions of the M selected subbands using a combinationatorial index r as defined at equation 4.

In usual case, the average M selected subband CQI is enough for CL-MIMO operation for the better performance. Once there is either the subband which has extreme higher CQI than the average M selected subband CQIs or the subband which has extreme lower CQI than the average M selected subband CQIs or combination thereof, the terminal may feedback a third channel quality information reflecting a subband CQI for either the subband which has extreme higher CQI than the average M selected subband CQI or the subband which has extreme lower CQI than the average M selected subband CQI or combination thereof.

In order to this feedback, the terminal may check whether the subband CQI needs to be fedback or not at S450.

If it is needed at S450, the terminal may transmit a third channel quality information reflecting either the subband which has extreme higher CQI than the average M selected subband CQI or the subband which has extreme lower CQI than the average M selected subband CQI or combination thereof.

For example, once there may be some subband which has extreme higher CQI than the M selected subband CQI, it's better to feedback the differential subband CQI, CQI_diff,subband, between the average M selected subband CQI and the subband CQI for better performance as defined at equation 4 at S460.

The terminal may also report the positions of either the subband which has extreme higher CQI than the average M selected subband CQI or the subband which has extreme lower CQI than the average M selected subband CQI or combination thereof using a combinationatorial index r as defined above.

The differential subband CQIis encoded differentially using 2bits relative to its respective wideband CQI by PUSCH which is aperiodical feedback.

Aperiodic CQI reporting on the PUSCH is scheduled by the transmitter 310 by setting a CQI request bit in an uplink resource grant sent on the PDCCH.

Based on the terminal's feedback, the base station may know the CQI of subbands in high accuracy to do the scheduling. The base station may allocate at least one subband in high accuracy to the terminal. Based on the scheduling, the base station may transmit the data symbols of this terminal with the MCS level by CQI feedback and precoded the data symbols based on the terminal's PMI feedback.

Referring to FIG.5, in the method for processing the channel informationthe base station according to another embodiment 500, the base station may receive a downlink precoding matrix indicators(PMIs) of the favorite matrix in the codebook based on the estimated downlink channel as the channel information to the base station at S520. At S520 the base station may separately receivethe PMIs of multilevel, for example, both level from the base station.

Then the base station may receive a first channel quality information on the estimated downlinkchannel which is an average of all subband CQIs(Channel quality indicators) at S525. Atthis time, a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.

As mentioned above the wideband CQI, CQI_wideband, may be got by the Equation 1. The type of periodic reporting is configured by the transmitter 310 by RRC signaling. For the wideband periodic CQI reporting, the period may be configured to {2, 5, 10, 16, 20, 32, 40, 64, 80, 160}ms or off, but not limited to them, may be configured to any required value.

Then the base station may receive a second channel quality information reflecting the average channel quality of the M selected subbands by the terminal. For example, the base station may receive the differential M selected subband CQI between the wideband CQI and the average M selected subband CQI at S550.

The differential M selected subband CQI is encoded differentially using 2-bits relative to its respective wideband CQI by PUSCH which is aperiodical feedback.

The base station may know the average M selected subband CQI by means of the received differential M selected subband CQI minus the received wideband CQI at S525.

The base station may also receive an information on the positions of the M selected subbands. The base station may know the positions of the M selected subbands using a combinationatorial index r as defined at equation 4.

The base station may receive a third channel quality information reflecting either the subband which has extreme higher CQI than the average M selected subband CQI or the subband which has extreme lower CQI than the average M selected subband CQI or combination thereof.

For example, The base station may receive the differential subband CQI, CQI_diff,subband, between the average M selected subband CQI and the subband CQI for better performance as defined at equation 4 at S560.

The base station may know the subband CQI by means of the differential subband CQI plus the average M selected subband CQI at S560.

The differential subband CQI may be encoded differentially using, but not limited, 2-bits relative to its respective wideband CQI by PUSCH which is aperiodical feedback. Aperiodic CQI reporting on the PUSCH is scheduled by the transmitter 310 by setting a CQI request bit in an uplink resource grant sent on the PDCCH.

The base station may also receive an information on the positions of the subband which has extreme higher or lower CQI than the average M selected subband CQI. The base station may know the positions of the subband using a combinationatorial index r as defined at equation 4.

Based on the terminal's feedback, the base station may know the CQI of subbands in high accuracy to do the scheduling. The base station may schedule at least one subband in high accuracy to the terminal. Based on the scheduling, the base station may transmit the data symbols of this terminal with the MCS level by CQI feedback and precoded the data symbols based on the terminal's PMI feedback.

The following table shows comparison of the number of indices between the multilevel differential CQI feedback and the single differential CQI feedback CQI.

Table 1

The single differential CQI is the differential value between the wideband CQI and the subband CQI for each of the M selected subbabds. In this CL-MIMO communication system, both the wideband CQI and the subband CQI are fed back from the terminal by PDCCH and PUSCH respectively. The wideband CQI is by fully 4-bits feed back while subband CQI is by 2-bits differential feedback. In this communication system, the differential value of subband CQI can be plus and minus. So 2-bits differential is too coarse for subband CQI.

The above embodiments propose the multilevel differential CQI feedback which includes the three types of CQIs such as the wideband CQI, the average M selected subband CQIand the subband CQI. The wideband CQI may be by fully 4bits feedback, while the average M selected subband CQI and the subband CQI may be by 2bits differential feedback.

The accuracy of the final subband CQI feedback is greatly improved according to the multilevel differential CQI feedback. On other words,the multilevel differential CQI feedback improves the accuracy of the final subband CQI feedback using the three types of CQIs such as the wideband CQI and the subband CQI as well as the average M selected subband CQI.

The methods and systems as shown and described herein may be implemented in software stored on a computer-readable medium and executed as a computer program on a general purpose or special purpose computer to perform certain tasks. For a hardware implementation, the elements used to perform various signal processing steps at the transmitter(e.g., coding and modulating the data, precoding the modulated signals, preconditioning the precoded signals, and so on) and/or at the receiver(e.g., recovering the transmitted signals, demodulating and decoding the recovered signals, and so on) may be implemented within one or more application specific integrated circuits(ASICs), digital signal processors(DSPs), digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays(FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. In addition or in the alternative, a software implementation may be used, whereby some or all of the signal processing steps at each of the transmitter and receiver may be implemented with modules(e.g., procedures, functions, and so on) that perform the functions described herein. It will be appreciated that the separation of functionality into modules is for illustrative purposes, and alternative embodiments may merge the functionality of multiple software modules into a single module or may impose an alternate decomposition of functionality of modules. In any software implementation, the software code may be executed by a processor or controller, with the code and any underlying or processed data being stored in any machine-readable or computer-readable storage medium, such as an on-board or external memory unit.

Although the described exemplary embodiments disclosed herein are directed to various MIMO precoding systems and methods for using same, the present invention is not necessarily limited to the example embodiments illustrate herein. For example, various embodiments of a MIMO precoding system and design methodology disclosed herein may be implemented in connection with various proprietary or wireless communication standards, such as IEEE 802.16e, 3GPP-LTE, DVB and other multi-user MIMO systems. Thus, the particular embodiments disclosed above are illustrative only and should not be taken as limitations upon the present invention, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Accordingly, the foregoing descriptionis not intended to limit the invention to the particular form set forth, but on the contrary, is intended to cover such alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims so that those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention in its broadest form.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. As used herein, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Claims

A method comprising:

estimating a downlink channel from a received signal

transmitting a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators); and

transmitting a second channel quality information reflecting the average channel quality of two or more selected subbands by a terminal.
The method in claim 1, further comprises:

transmitting a third channel quality information reflecting the channel quality of either the subband which has extreme higher CQI than the average of selected subband CQI or the subband which has extreme lower CQI than the average of selected subband CQIs or combination thereof.
The method in claim 1, further comprises: transmitting a downlink precoding matrix indicator based on the estimated downlink channel, and where a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.
The method in claim 1, further comprises:

transmitting an information on a position of the selected subbands.
The method in claim 1, where the second channel quality information is a differential value between the first channel quality information and the average of the selected subband CQIs.
The method in claim 1, where the second channel quality information is the average of the selected subband CQIs.
The method in claim 2, where the third channel quality information is a differential value between the average of the selected subband CQIs and the subband CQI for at least one of the selected subbands.
The method in claim 2, where the third channel quality information is the subband CQI for at least one of the selected subbands.
The method in claim 2, where the first second channel quality information is transmitted periodically and the second and the third channel quality information are transmitted aperiodically.
The method in claim 2, where the first channel quality information are transmitted through PUCCH(Physical Uplink Control Channel) and the second and the third channel quality information is transmitted through PUSCH(Physical Uplink Shared Channel).
A method comprising:

estimating a downlink channel from a received signal

transmitting one channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators); and

transmitting other channel quality reflecting reflecting the channel quality of either the subband which has extreme higher CQI than an average of two or more selected subband CQIs or the subband which has extreme lower CQI than an average of the selected subband CQIs or combination thereof.
The method in claim 11, further comprises: transmitting a downlink precoding matrix indicator based on the estimated downlink channel, and where a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.
The method in claim 11, where the other channel quality information is a differential value between the average of all subband CQIs(Channel quality indicators) and the subband CQI for at least one of the selected subbands.
The method in claim 11, where the one channel quality information is transmitted periodically and the ohter channel quality information is transmitted aperiodically.
The method in claim 11, where the one channel quality information is transmitted through PUCCH(Physical Uplink Control Channel) and the otherchannel quality information is transmitted through PUSCH(Physical Uplink Shared Channel).
A terminal comprising:

an channel estimator configured to estimate a downlink channel from a received signal and transmit a first channel quality information on the estimated downlink channel which is an average of all subband CQIs(Channel quality indicators) and a second channel quality information reflecting the average channel quality of two or more selected subbands and

a post-decoder configured to decode the received signal to recover the set of data symbols.
The terminal in claim 16, where the channel estimator transmitsa third channel quality information reflecting the channel quality of either the subband which has extreme higher CQI than the average of a selected subband CQI or the subband which has extreme lower CQI than the average of the selected subband CQI or combination thereof.
The terminal in claim 16, where the channel estimator transmits a downlink precoding matrix indicator based on the estimated downlink channel, and where a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.
The terminal in claim 16, where the channel estimator transmits transmitting an information on a position of the selected subbands.
The terminal in claim 16, where the second channel quality information is a differential value between the first channel quality information and the average of the selected subband CQIs.
The terminal in claim 16, where the second channel quality information is the average of the selected subband CQIs.
The terminal in claim 17, where the third channel quality information is a differential value between the average of the selected subband CQIs and the subband CQI for at least one of the selected subbands.
The terminal in claim 17, where the third channel quality information is the subband CQI for at least one of the selected subbands.
The terminal in claim 17, where the first second channel quality information is transmitted periodically and the second and the third channel quality information are transmitted aperiodically.
The terminal in claim 17, where the first channel quality information are transmitted through PUCCH(Physical Uplink Control Channel) and the second and the third channel quality information is transmitted through PUSCH(Physical Uplink Shared Channel).
A method for the base station comprising:

receiving a first channel quality information on the estimated downlinkchannel which is an average of all subband CQIs(Channel quality indicators) from the terminal; and

receiving a second channel quality information reflecting the average channel quality of two or more selected subbands by a terminal.
The method in claim 26, further comprises:

receiving a third channel quality information reflecting the channel quality of either the subband which has extreme higher CQI than the average of the selected subband CQIs or the subband which has extreme lower CQI than the average of the selected subband CQIsor combination thereof.
The method in claim 26, further comprises:

receiving a downlink precoding matrix indicator based on the estimated downlink channel, and where a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.
The method in claim 26, further comprises:

receiving a information on a position of the selected subbands.
The method in claim 26, where the second channel quality information is a differential value between the first channel quality information and the average of theselected subband CQIs.
The method in claim 27, where the third channel quality information is a differential value between the average of the selected subband CQIs and the subband CQI for at least one of the selected subbands.
The method in claim 27, where the first second channel quality information is receivedperiodically and the second and the third channel quality information are transmitted aperiodically.
The method in claim 27, where the first channel quality information are received through PUCCH(Physical Uplink Control Channel) and the second and the third channel quality information is receivedthrough PUSCH(Physical Uplink Shared Channel).
A base station comprising:

a scheduler configured to receive a first channel quality information on the estimated downlinkchannel which is an average of all subband CQIs(Channel quality indicators) from the terminal and a second channel quality information reflecting the average channel quality of two or more selected subbands by a terminal and schedule at least one subband to at least one terminal based on the first and the second channel quality information and

a precoder configured to transmit data symbol via the subband to the terminal.
The base station in claim 34, wherein the scheduler is configured to further receivea third channel quality information reflecting the channel quality of either the subband which has extreme higher CQI than the average of the selected subband CQIs or the subband which has extreme lower CQI than the average of the selected subband CQIs or combination thereof.
The base station in claim 34, wherein the scheduler is configured to further receivea downlink precoding matrix indicator based on the estimated downlink channel, and where a channel quality of the subband CQI is a channel quality when the downlink signal is precoded by the downlink precoding matrix.
The base station in claim 34, wherein the scheduler is configured to further receive an information on a position of the selected subbands.
The base station in claim 35, where the second channel quality information is a differential value between the first channel quality information and the average of the selected subband CQIs.
The base station in claim 25, where the third channel quality information is a second differential value between the average of the selected subband CQIs and the subband CQI for at least one of the selected subbands.
The base station in claim 35, where the first second channel quality information is received periodically and the second and the third channel quality information are transmitted aperiodically.
The base station in claim 35, where the first channel quality information are received through PUCCH(Physical Uplink Control Channel) and the second and the third channel quality information is received through PUSCH(Physical Uplink Shared Channel).