WO2012108573A1

WO2012108573A1 - Terminal and base station, method thereof in wireless communication system

Info

Publication number: WO2012108573A1
Application number: PCT/KR2011/000956
Authority: WO
Inventors: Jianjun Li
Original assignee: Pantech Co.,Ltd.
Priority date: 2011-02-11
Filing date: 2011-02-11
Publication date: 2012-08-16

Abstract

The present invention relates to a wireless communication system and a method for transmitting the channel state information for Base Stations included in a Coordinated MultiPoint (COMP) set in a terminal when a wireless communication system uses a CoMP scheme.

Description

TERMINAL AND BASE STATION, METHOD THEREOF IN WIRELESS COMMUNICATION SYSTEM

The present invention relates to a wireless communication system and a method for transmitting and processing the channel state information for base Stations included in a Coordinated MultiPoint(CoMP) set when a wireless communication system uses a CoMP scheme.

The Coordinated multipoint (CoMP) transmission/reception is considered for wireless communication system as a scheme to improve the coverage of high data rates, the celledge throughput and/or to increase system throughput in both high load and low load scenarios.

In accordance with an aspect, there is provided a method for transmitting a channel state information at a terminal in a Coordinated MultiPoint(CoMP) communication system, the method comprising: receiving reference signals from a primary base station and a cooperative base station included in a CoMP set; estimating downlink channels from the received reference signals from the base stations; and transmitting one PMI(precoding Matrix Index) for the primary base station and the companion PMI for the cooperative base station regardless of the CoMP mode to the primary base station.

In accordance with other aspect, there is provided a terminal for transmitting a channel state information at a terminal in a Coordinated MultiPoint(CoMP) communication system, the system comprising: a post decoder configured to recover a signals in a same frequency band from the base stations included in a CoMP set; and a channel estimator configured to estimate downlink channels from a received signals from the base stations and feedback one PMI(precoding Matrix Index) for the primary base station and the companion PMI for the cooperative base station in the CoMP set regardless of the CoMP mode to the primary base station.

In accordance with another aspect, there is provided a method for processing a channel state information at a base station in a Coordinated MultiPoint(CoMP) communication system, the method comprising: receiving its own PMI(precoding Matrix Index) and a companion PMI for the cooperative base station in the same CoMP set regardless of the CoMP mode from a terminal; transmitting the companion PMI to the cooperative base station through an interface; and precoding the data symbols by a precoding matrix corresponding to its own PMI.

In accordance with another aspect, there is provided a base station comprising: a scheduler configured to receive its own PMI and a companion PMI(precoding Matrix Index) for the cooperative base station in the same CoMP set regardless of the CoMP mode from a terminal and transmit the companion PMI to the cooperative base station through an interface; and a precoder configured to precode the data symbols by a precoding matrix corresponding to its own PMI.

In accordance with another aspect, there is provided a method for processing a channel state information at a base station in a Coordinated MultiPoint(COMP) communication system, the method comprising: receiving a companion PMI(precoding Matrix Index) from a primary base station in the same CoMP set through an interface; and precoding the data symbols by a precoding matrix corresponding to the companion PMI in the joint processing CoMP mode and a precoding matrix which is orthogonal to the precoding matrix corresponding to the companion PMI in the coordinated scheduling/beamforming mode.

In accordance with another aspect, there is provided a base station comprising: a scheduler configured to a companion PMI(precoding Matrix Index) from a primary base station in the same CoMP set through an interface; and a precoder configured to precode the data symbols by a precoding matrix corresponding to the companion PMI in the joint processing CoMP mode and a precoding matrix which is orthogonal to the precoding matrix corresponding to the companion PMI in the coordinated scheduling/beamforming mode.

In accordance with another aspect, there is provided a CoMP set that comprise a primary base station and some cooperative station with uniform feedback for both JP and CS CoMP mode to support dynamic mode switch between them.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention.

FIG.1 conceptually illustrates a CoMP scheme applied to a wireless communication system under a multicell environment according to an exemplary embodiment.

FIG.2 conceptually illustrates the joint transmission mode according to an exemplary embodiment.

FIG.3 conceptually illustrates the coordinated scheduling/beamforming mode according to an exemplary embodiment.

FIG.4 shows the relationship between the CSI feedbacks of the terminals and the precoding matrices of the base stations according to an exemplary embodiment.

FIG.5 shows the relationship between the CSI feedbacks of the terminals and the precoding matrices of the base stations according to an exemplary embodiment.

FIG.6 is the block diagram of the wireless communication system using the MIMO CoMP operation according to an exemplary embodiment.

FIG.7 is the flowchart of a method for feedbacking the channel state information for the terminal according to an exemplary embodiment.

FIG.8 is the flowchart of a method for processing the channel state information and precoding the data symbols for the primary base station according to an exemplary embodiment.

FIG.9 is the flowchart of a method for processing the channel state information and precoding the data symbols for the cooperative base station according to an exemplary 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 conceptually illustrates a CoMP scheme applied to a wireless communication system under a multicell environment.

Referring to FIG.1, there are

base stations

110, 120 and 130 each of which may act as a base station or an enhanced base station(s) (eNB(s)) in the multicell environment according to one embodiment. The base station (eNB) may act as one or more cells.

The CoMP scheme is proposed to improve the throughput of a user at a cell edge by applying advanced Multiple Input Multiple Output (MIMO) under a multicell environment. The CoMP scheme in a wireless communication system 100 may reduce InterCell Interference(ICI) in the multicell environment. Multicell

base stations

110, 120 and 130 may provide joint data support to a terminal 140 by a CoMP operation. Also, each base station may improve system performance by simultaneously supporting one or more terminals 140. The terminal may act as a subscriber station or an user equipment (UE), which can be virtually any type of wireless oneway or twoway communication device such as a cellular telephone, wireless equipped computer system, and wireless personal digital assistant.

The wireless communication system 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 may use closedloop spatial multiplexing. For example a base station may implement Space Division Multiple Access (SDMA) based on Channel State Information (CSI) between the base station and terminals.

There are largely two CoMP operation modes or categories, joint processing (JP) mode which is cooperative MIMO based on data sharing and Coordinated Scheduling/Beamforming (CS/CB) mode.

In a closedloop wireless communication system, the CoMP feedback mechanisms may include one of an explicit channel state/statistical information feedback, an implicit channel state/statistical information feedback and feedback mechanisms that use hypotheses of different transmission and/or reception processing.

In the implicit channel state/statistical information feedback, a terminal 140 may measure the channel quality of a data transmission channel between the terminal and an base station, select a recommended precoding matrix(Precoding Matrix Index, PMI) for the base station, and transmit Channel Quality Information (CQI) representing the channel quality to assist the base station in selecting an appropriate Modulation and Coding Scheme(MCS) to use for the downlink transmission and the PMI to the base station. When the closedloop wireless communication system operates in the CoMP scheme, the terminal 140 may transmit CQIs and PMIS for base stations included in the CoMP set to a primary base station, for implementing a more efficient CoMP mode.

The CoMP set or the CoMP operating set may be a set of points directly or indirectly participating in data (PDSCH) transmission to the terminal 140.

In other words, the terminal 140 selects the precoding matrix from the codebook which has the best performance in the codebook based on the estimated channel state information (CSI).

FIG.2 conceptually illustrates the joint transmission mode.

In the joint processing(JP) mode, data to a single UE is simultaneously transmitted from multiple transmission points, e.g. to (coherently or noncoherently) improve the received signal quality and/or cancel actively interference for other terminals.

A primary or serving base station such as the base station 210 and one or more cooperative base stations such the

base stations

220 and 230 that are included in a CoMP set transmit data to the terminal 240 in the same frequency band in one of CoMP operating modes, joint processing mode, for the purpose of increasing the data rate of the terminal at a cell boundary. In the joint processing mode, data transmitted from the base stations of the CoMP set and feedback information such as CQIs and PMIs transmitted from the terminal are shared among the primary base station 110 and the cooperative or neighboring

base stations

120 and 130 included in the CoMP set via backhaul links.

So that the total transmission power and the number of Tx antennas are both increased.

FIG.3 conceptually illustrates the coordinated scheduling/beamforming mode according to another embodiment.

In the coordinated scheduling/beamforming(CS/CB) mode, data is only available at serving cell or base station (data transmission from that point) but user scheduling/beamforming decisions are made with coordination among cells or base stations corresponding to the CoMP cooperating set.

In the coordinated scheduling/beamforming(CS/CB) mode, the serving cell is the only transmission point. The other base station only need some control information via backhaul links for scheduling to reduce the interference. Interference avoidance by intersite coordinated beamforming is considered as a simple solution to avoid beam collision with limited coordination.

Beamforming can take two approaches depending on channel environment and the backhaul availability

FIG.4 shows the relationship between the CSI feedbacks of the terminals and the precoding matrices of the base stations according to an embodiment.

This shows a switching operation from the JP mode of FIG.2 to the CS/CB mode of FIG3 for the embodiment of invention.

Referring to FIGs 2 to 4, in the wireless communication system 400 the serving or primary base station 210 may broadcasts or sends a downlink reference signal(RS) such as CSIRS(Channel status IndicatorReference Signal) to the terminal 240 at S410. The cooperative base station 220 may also broadcasts or sends a downlink reference signal (RS) such as CSIRS(Channel status IndicatorReference Signal) to the terminal 240 at S420.

The terminal 240 may estimate the downlink channels from all the

base stations

210 and 220 involved in CoMP operating set based on the reference signals such as CSIRS(Channel status IndicatorReference Signal) from both the primary base station 210 and the cooperative base station 220 at S425.

Before the CSI feedback from the terminal the primary base station 210 may make a decision to one of two CoMP modes such the JP and the CS/CB modes and inform the terminal 240 of its decision at S427.

Based on the estimated channel, the terminal 240 may select a best SUMIMO PMI for the primary base station 210 and after the PMI for the primary base station is decided, the terminal 240 may select the PMI for the cooperative base station 220 which may provide the maximum enhancement to signal of the primary base station 210 at the UE side at S425.

Because the 8 transmitting antennas(8Tx) configuration codebook and the like may use two stage precoding codebook, there are two corresponding codebooks for 8Tx(8 transmitting antennas).

If the channels from the primary base station 210 and the cooperative base station 220 are H₁ and H₂ respectively, the precoding matrix W₁for the primary base station 210 may come from

where max(∥X∥) means the maximum power of matrix X and C means the codebook of the precoding matrix for the base station. The terminal 240 may select the PMI1 corresponding to the precoding matrix W₁for the primary base station 210 from the codebook(c).

If the JP mode is decided at S427, the second precoding matrix W₂ for the cooperative base station 220 may come from

. The terminal 240 may select the PMI2 corresponding to the precoding matrix W₂for the cooperative base station 220 from the codebook(c). The codebook for the cooperative base station 220 may be the same as one for the primary base station 210, but may not be limited thereto.

Then the terminal 240 may feedback the channel state information (CSI) including the two PMIs and/or the two corresponding CQIs as to the primary base station 210 at S430.

Then the primary base station may transmit or forward the PMI2 for the cooperative base station and the corresponding CQI to the cooperative base station 220 in the CoMP set through the network interface such as the X2 interface at S440.

If the JP mode is decided at S427, the primary base station 210 and the cooperative base station 220 as transmission points may simultaneously transmit the data to the terminal 240 at S450 and S460. As described above the data to the terminal is shared among the primary base station 210 and the cooperative base station 220 and is jointly processed by the primary base station 210 and the cooperative base station 220 in the CoMP cooperating set. As a result the JP mode may make both the total transmission power and the number of Tx antennas increased.

Based on the CSI feedback, the primary base station 210 may precode the data symbols by the precoding matrix W₁ corresponding to the PMI1 received from the terminal 240 at S450.

Based on the PMI2 feedback through the X2 interface, the cooperative 220 may precode the data symbols by the precoding matrix W₂ corresponding to the PMI2 at S460.

By the way if the CS/CB mode is decided at S427, The precoding matrix W₃for the base station 220 may come from

where min(∥X∥) means the minimum power of matrix X and C means the codebook of the precoding matrix for the base station.

The terminal 240 may select the PMI3 corresponding to the precoding matrix W3for the cooperative base station 220 from the codebook(c).

Then the terminal 240 may feedback the channel state information (CSI) including the two PMIs PMI1 and PMI3 and/or the two corresponding CQIs as to the primary base station 210 at S430.

If the CS/CB mode is decided at S427, the primary base station 210 as a transmission point may transmit the data to the terminal 240 at S480. As described above the data to the terminal is only available at the primary base station 210. The cooperative base station 220 may only need some control information from X2 for scheduling to reduce the interference to the terminal 240. Interference avoidance by intersite coordinated beamforming may be considered as a simple solution to avoid beam collision with limited coordination. Beamforming can take two approaches depending on channel environment and the backhaul availability.

The cooperative base station 220 may transmit the other data to the other terminal 250 within its own cell different from the terminal 240 at S480. The cooperative base station 220 may precode the data symbols by the precoding matrix W₃ corresponding to the PMI3 received from the terminal 240 at S480.

Accordingly, it may be known that the JP mode and the CS/CB mode work independently. In spite of the technical advantage of the JP mode and the CS/CB mode, there may need feedback scheme to support both operation and the dynamic switch.

Exemplary embodiments of the present invention for feedback scheme to support both operation and the dynamic switch will be provided below.

FIG.5 shows the relationship between the CSI feedbacks of the terminals and the precoding matrices of the base stations regarding to a switching operation from the joint transmission mode of FIG.2 to the coordinated scheduling/beamforming mode of FIG3 according to another embodiment.

Referring to FIGs 2 and 3, 5, in the wireless communication system 500 the serving or primary base station 210 may broadcasts or sends a downlink reference signal(RS) such as CSIRS(Channel status IndicatorReference Signal) to the terminal 240 at S510. The cooperative base station 220 may also broadcasts or sends a downlink reference signal(RS) such as CSIRS(Channel status IndicatorReference Signal) to the terminal 240 at S520.

The terminal 240 may estimate the downlink channels from all the

base stations

210 and 220 involved in CoMP operation set based on the reference signals such as CSIRS(Channel status IndicatorReference Signal) from both the primary base station 210 and the cooperative base station 220 at S525.

Before the CSI feedback from the terminal the primary base station 210 may make a decision to one of two CoMP modes such the JP and the CS/CB modes and inform the terminal 240 of its decision at S527.

Based on the estimated channel, the terminal 240 may select a best SUMIMO PMI for the primary base station 210 and after the PMI for the primary base station is decided, the terminal 240 may select the PMI for the cooperative base station 220 which may provide the maximum enhancement to signal of the primary base station 210 at the UE side at S525.

Suppose the channels from the primary base station 210 and the cooperative base station 220 in the wireless communication system 500 of FIG.5 are the same H₁ and H₂ as the channels from the primary base station 210 and the cooperative base station 220 in the wireless communication system 400 of FIG.4 respectively. Therefore, the precoding matrix W₁for the primary base station 210 may come from

.

After the PMI for the primary base station is decided, the terminal 240 may select the companion PMI for the cooperative base station 220. This companion PMI has different function for different CoMP scheme. For joint transmission CoMP, this companion PMI may be used for precoding at cooperative base station 220 which may provide the maximum enhancement to signal of the primary base station at the UE side. The optimal precoding matrix W₂ ^’ corresponding to this companion PMI, PMI2’ for this purpose may be as follows.

For CS/CB mode, the precoding matrix W₂ ^’ of the cooperative base station 220 may be the one among the codebook which has the highest interference to the terminal 240. So this PMI2’ corresponding to the precoding matrix W₂ ^’ of the cooperative base station 220 and related PMI set may not be used for precoding in the cooperative base station 220 for the other terminal such as the terminal 250.

Because two channels H₁ and H₂ are independent with each other, E

in the above final equation during the long time interval in view of the statistic. Therefore, the precoding matrix W₂ ^’ of the cooperative base station 220 may sub optimally come from

.

So the precoding matrix W₂ ^’ of the cooperative base station 220 may be selected from the above equation

for both CoMP modes.

In summary, the wireless communication system 400 of FIG.4 may select two different precoding matrices W2 from

in the JP mode and W3

in the CS/CB mode respectively. Therefore in the wireless communication system 400 of FIG.4, the terminal 240 may select and feedback one of two different PMIs, PMI2 and PMI3 which correspond to two different precoding matrices W₂ regarding to the JP mode and the CS/CB mode, respectively.

However the wireless communication system 500 of FIG.5 may have only one precoding matrix W2’ from

in both the JP mode and the CS/CB mode. Therefore in the wireless communication system 500 of FIG.5, the terminal 240 may feedback this companion PMI PMI2’ which correspond to the precoding matrix W2’ in both the JP mode and the CS/CB mode.

Then the terminal 240 may feedback the channel state information(CSI) including the general PMI1 and the companion PMI PMI2’ and/or the two corresponding CQIs as to the primary base station 210 at S530. In other words the terminal 240 may feedback the companion PMI(PMI2’) to the primary base station 210 regardless of the CoMP mode at S530.

Then the primary base station may transmit or forward the PMI2’ for the cooperative base station and the corresponding CQI to the cooperative base station 220 in the CoMP set through the network interface such as the X2 interface at S540.

If the JP mode is decided at S527, the primary base station 210 and the cooperative base station 220 as transmission points may simultaneously transmit the data to the terminal 240 at S550 and S560. As described above the data to the terminal is shared among the primary base station 210 and the cooperative base station 220 and is jointly processed by the primary base station 210 and the cooperative base station 220 in the CoMP cooperating set.

Based on the CSI feedback, the primary base station 210 may precode the data symbols by the precoding matrix W₁ corresponding to the PMI1 received from the terminal 240 at S550.

Based on the PMI2’ from the X2 interface, the cooperative 220 may precode the data symbols by the precoding matrix W₂’ corresponding to the PMI2’ feed back from the terminal 240 at S560.

By the way if the CS/CB mode is decided at S527, the primary base station 210 as transmission point may transmit the data to the terminal 240 at S570. As described above the data to the terminal is only available at the primary base station 210. The cooperative base station 220 may only need some control information for scheduling to reduce the interference to the terminal 240. Interference avoidance by intersite coordinated beamforming may be considered as a simple solution to avoid beam collision. Beamforming can take two approaches depending on channel environment and the backhaul availability.

The cooperative base station 220 may transmit the other data to the other terminal 250 within its own cell different from the terminal 240 at S580. The cooperative base station 220 may also precode the data symbols by the precoding matrix W_2┴ which may be orthogonal to the precoding matrix W₂’corresponding to the PMI2’ at S580, but is not limited therewith.

For example, the cooperative base station 220 may precode the data symbols by the precoding matrix which may have the lowest correlation with the precoding matrix W₂’corresponding to the PMI2’ received from the terminal 240 at S580. For other example, the cooperative base station 220 may also precode the data symbols by the precoding matrix which may have the longest cardinal distance with the precoding matrix W₂’corresponding to the PMI2’ at S580.

As described above, it is known that the uniform feedback may be employed for both CoMP modes regarding to another embodiment. So it’s easy to support dynamic switch between the JP and the CS/CB modes based on the feedback. In accordance with another aspect, there is provided a CoMP set that comprise a primary base station and some cooperative station with uniform feedback for both JP and CS CoMP mode to support dynamic mode switch between them.

FIG.6 is the block diagram of the wireless communication system using the MIMO CoMP operation according to further another embodiment.

Referring to FIG.6, the wireless communications system 600 may include a primary base station 610 and one or more cooperative base stations 620 in the CoMP.

The terminal 640 may comprise a postdecoder 642 and a channel estimator 644.

The terminal 640 may estimate the precoded channel by DMRS(Demodulationreference signal). Then the terminal 640 may recover the original data symbols by postdecoder 642 with precoded channel information.

The channel estimator 644 of the terminal 640 may estimate the downlink channels from all the

base stations

610 and 620 involved in the COMP operation based on the reference signals such as CSIRS(Channel status IndicatorReference Signal) from both the primary base station 610 and the cooperative base station 620. Based on the estimated channel, the channel estimator 644 may select the best SUMIMO PMI for the primary base station. For example, The PMI for the primary base station may be the PMI1 corresponding to the precoding matrix W₁which may come from

in its own codebook.

After the PMI for the primary base station 610 is decided, the channel estimator 644 may select the companion PMI for the cooperative base station 620 which can provide the maximum enhancement to signal of the primary base station at the UE side. For the JP mode, this companion PMI may be used for precoding at cooperative base station 620 which may provide the maximum enhancement to signal of the primary base station at the UE side. For CS/CB mode, this companion PMI and related PMI set may not be used for precoding in the cooperative base station 620.

For example, this companion PMI may be the PMI2’ corresponding to the optimal precoding matrix W₂ ^’ which may come from

in its own codebook. As a result the channel estimator 644 may feedback this companion PMI PMI2’ which correspond to the precoding matrix W2’ in both the JP mode and the CS/CB mode. In other words the channel estimator 644 may feedback the companion PMI(PMI2’) to the primary base station 210 regardless of the CoMP mode.

These PMIs may be codebook based PMIs. The codebook may be two stage precoding codebook as described above.

After the channel estimator 644 selects the PMI1 for the primary base station and the PMI2’ for the cooperative base station, the channel estimator 644 may calculate the post SINR as CQI for the selected PMIs when combine all the signals from all the base stations in the CoMP set. Then the channel estimator 644 may feedback the PMIs of the selected matrix and the corresponding CQIs as the channel state information to the primary base station 610.

The channel state information may be possible for either periodic or aperiodic CQI reporting using the PUCCH or the PUSCH. The PMI is reported along with one or more the CQI and the RI but not limited thereof. The PMI is reported without other.

The primary base station 610 may comprise a precoder 612 and a scheduler 614.

The scheduler 614 may make a decision to one of two CoMP modes such as the JP and the CS/CB modes. The scheduler 614 may receive the channel state information(CSI) such as the PMIs and the CQIs from the channel estimation 644 of the terminal 640. The PMIs may be the PMI1 and the companion PMI2’ regardless of the CoMP mode.

Then the scheduler 614 may transmit or forward the companion PMI2’ and the corresponding CQI to the cooperative base station 620 in the COMP set through the X2 interface.

Based on the CSI feedback, the precoder 612 may precode the data symbols by the precoding matrix W1 corresponding to the PMI1 received from the terminal 640. The precoder 612 may transmit the signal to the terminal 640 with corresponding antennas.

The cooperative base station 620 may also comprise a precoder 622 and a scheduler 624.

The scheduler 624 may receive its own companion PMI2’ and the corresponding CQI from the primary base station 610 in the CoMP set through X2 interface.

If the JP mode is decided the precoder 622 may precode the data symbols by the precoding matrix W₂’ corresponding to the companion PMI PMI2’. The precoder 622 may transmit the signal to the terminal with corresponding antennas.

If the CS/CB mode is decided the precoder 622 may precode the data symbols by the precoding matrix

which may be orthogonal to the precoding matrix W₂’corresponding to the PMI2’ received from the terminal 640, but is not limited therewith.

For example, the rank 1 codebook for 2 Tx, may be as follows:

Table 1

Codebook index	Precoding Matrix
0
1
2
3

If the channels of H1=[1,1]and H2=[1,j], the PMI for Primary base station 610 may be PMI1=1 and The companion PMI for the cooperative base station may be PMI2=3.

For the JP mode, the primary base station 610 may precode the data symbols of the terminal 640 by

and the cooperative base station 620 may precode the data symbols of the terminal 640 by

.

For the CS/CB mode, the primary base station 610 may precode the data symbols of the terminal 640 by

and the cooperative base station 620 may be precode the data symbols of the other terminal different from the terminal 640 by

which is orthogonal to

corresponding to the PMI2’ to reduce the interference.

For example, the precoder 622 may precode the data symbols by the precoding matrix which may have the lowest correlation with the precoding matrix W₂’corresponding to the PMI2’ received from the terminal 640. For other example, the precoder 622 may also precode the data symbols by the precoding matrix which may have the longest cardinal distance with the precoding matrix W₂’corresponding to the PMI2’ received from the terminal 640.

The precoder 622 may finally transmit the other data to the other terminal within its own cell different from the terminal 640.

FIG. 7 is the flowchart of a method for feedbacking the channel state information for the terminal according to another embodiment.

Referring to FIG.7, in the method for feedbacking the channel information for the terminal according to another embodiment 700, the terminal may estimate a downlink channels from all the base stations involved in CoMP operation based on the reference signals such as CSIRS(Channel status IndicatorReference Signal) from both the primary base station and the cooperative base station at S710. The terminal may be the terminal and the base stations may be the base stations as drawn in one of FIGs.2, 3, 6 and the like.

Based on the estimated channel, the terminal may select the best SUMIMO PMIs for the primary base station at S720. After the PMIs for the primary base station is decided, the terminal may select the PMI2’ as the companion PMI for the cooperative base station regardless of the CoMP mode at S730.

Before the primary and the cooperative base station may transmit the signals to the terminal, the terminal may estimate the precoded channel by DMRS. When the primary and the cooperative base station may transmit the signals to the terminal the terminal may recover the original data symbols by postdecoder with precoded channel information although not drawn in Figures.

FIG.8 is the flowchart of a method for processing the channel information and precoding the data symbols for the primary base station according to another embodiment.

Referring to FIG.8, in the method for processing the channel information and precoding the data symbols for the primary base station according to another embodiment 800, the primary base station may receive the channel state information such as the PMIs and the CQI from the terminal at S810. The PMIs may include its own PMI1 and the companion PMI2’ for the other base station in the same the CoMP set. The primary base station may be the primary base station(s) of one of FIGs.2, 3, 6 and the like. The other base station may be the cooperative base station of one of FIGs.2, 3, 6 and the like.

Then the primary base station may transmit or forward the companion PMI PMI2 and the corresponding CQI to the other base station(s) in the COMP set through any kind of interface such as X2 interface at S820.

Based on the CSI feedback, the primary base station may precode the data symbols by the precoding matrix corresponding to the PMI1 from the terminal at S830. The primary base station may transmit the signal to the terminal with corresponding antennas at S840.

FIG.9 is the flowchart of a method for processing the channel state information and precoding the data symbols for the cooperative base station according to another embodiment.

Referring to FIG.9, in the method for processing the channel information and precoding the data symbols for the primary base station according to another embodiment 900, the cooperative base station may receive its own PMI2’ as the companion PMI from the primary base station of FIG.8 in the COMP set through the X2 interface at S910.

The cooperative base station may decide one of the CoMP JP mode and the CoMP CS/CB mode at S920.

If the JP mode is decided at S930 the cooperative base station may precode the data symbols by the precoding matrix W₂’ corresponding to the companion PMI PMI2’ at S940. The cooperative base station may transmit the signal to the terminal with corresponding antennas.

If the CS/CB mode is decided at S930 the cooperative base station may precode the data symbols by the precoding matrix

at S950 which may be orthogonal to the precoding matrix W₂’corresponding to the PMI2’ received from the terminal, but is not limited therewith. The cooperative base station may finally transmit the other data to the other terminal within its own cell different from the terminal.

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, 3GPPLTE, DVB and other multiuser 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 description is 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 nonexclusive 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 for transmitting a channel state information at a terminal in a Coordinated MultiPoint(CoMP) communication system, the method comprising:

receiving reference signals from a primary base station and a cooperative base station included in a CoMP set;

estimating downlink channels from the received reference signals from the base stations; and

transmitting one PMI(precoding Matrix Index) for the primary base station and the companion PMI for the cooperative base station regardless of the CoMP mode to the primary base station.
The method in claim 1, wherein one PMI for primary basestation corresponds to the precoding matrix which comes from
where max(∥X∥) means the maximum power of matrix X and C means the codebook of the precoding matrix for the base station, H₁ is the MIMO channel form the primary base station to the terminal.
The method in claim 1, wherein the companion PMI corresponds to the precoding matrix which comes from
where max(∥X∥) means the maximum power of matrix X and C means the codebook of the precoding matrix for the base station, H₂ is the MIMO channel form the cooperative base station to the terminal.
A terminal for transmitting a channel state information at a terminal in a Coordinated MultiPoint(CoMP) communication system, the method comprising:

a post decoder configured to recover a signals in a same frequency band from the base stations included in a CoMP set; and

a channel estimator configured to estimate downlink channels from a received signals from the base stations and feedback one PMI(precoding Matrix Index) for the primary base station and the companion PMI for the cooperative base station in the CoMP set regardless of the CoMP mode to the primary base station.
The terminal in claim 4, wherein one PMI corresponds to the precoding matrix which comes from
where max(∥X∥) means the maximum power of matrix X and C means the codebook of the precoding matrix for the base station, H₁ is the MIMO channel form the primary base station to the terminal.
The terminal in claim 4, wherein the companion PMI corresponds to the precoding matrix which comes from
where max(∥X∥) means the maximum power of matrix X and C means the codebook of the precoding matrix for the base station. Moreover, H₂ is the MIMO channel form the cooperative base station to the terminal.
A method for processing a channel state information at a base station in a Coordinated MultiPoint(CoMP) communication system, the method comprising:

receiving its own PMI(precoding Matrix Index) and a companion PMI for the cooperative base station in the same CoMP set regardless of the CoMP mode from a terminal;

transmitting the companion PMI to the cooperative base station through an interface; and

precoding the data symbols by a precoding matrix corresponding to its own PMI.
A base station comprising:

a scheduler configured to receive its own PMI and a companion PMI(precoding Matrix Index) for the cooperative base station in the same CoMP set regardless of the CoMP mode from a terminal and transmit the companion PMI to the cooperative base station through an interface; and

a precoder configured to precode the data symbols by a precoding matrix corresponding to its own PMI.
A method for processing a channel state information at a base station in a Coordinated MultiPoint(COMP) communication system, the method comprising:

receiving a companion PMI(precoding Matrix Index) from a primary base station in the same CoMP set through an interface; and

precoding the data symbols by a precoding matrix corresponding to the companion PMI in the joint processing CoMP mode and a precoding matrix which is orthogonal to the precoding matrix corresponding to the companion PMI in the coordinated scheduling/beamforming mode.
A base station comprising:

a scheduler configured to a companion PMI(precoding Matrix Index) from a primary base station in the same CoMP set through an interface; and

a precoder configured to precode the data symbols by a precoding matrix corresponding to the companion PMI in the joint processing CoMP mode and a precoding matrix which is orthogonal to the precoding matrix corresponding to the companion PMI in the coordinated scheduling/beamforming mode.
A CoMP set that comprise a primary base station and some cooperative station with uniform feedback for both JP and CS CoMP mode to support dynamic mode switch between them.