Method and apparatus for controlling co-channel interference in a wireless communication system

The present invention provides a method and an apparatus of controlling co-channel interference in a base station of a wireless communication system based on collaborative MIMO and the corresponding method and apparatus of assisting a serving base station to control co-channel interference in a mobile station of a wireless communication system based on collaborative MIMO. Since the feedback mechanism based on the codebook is employed in the collaborative MIMO system in the present invention to enable the BS to obtain the precoding information, the present invention can be used to the both TDD mode and FDD mode. Moreover, since the precoding vectors selected by the different mobile stations for a same BS are always orthogonal, multi-user co-channel interference can be reduced.

FIELD OF THE INVENTION

The present invention relates to a wireless communication system, more particularly, to a wireless communication system based on collaborative MIMO (Co-MIMO).

BACKGROUND OF THE INVENTION

The next generation wireless communication systems aim for higher targets such as higher spectrum efficiency, better coverage and higher peak data rate, etc. However, these requirements have brought a great challenge, that is, inter-cell interference (ICI), which has become a severe obstacle to the performance improvement of wireless communication systems, especially for cell-edge users. In order to overcome ICI, many technologies have been proposed, but Co-MIMO has become one of the most promising technologies due to its capability to improve the cell-edge throughput and average sector throughput at the same time.

The basic idea of Co-MIMO is to perform joint MIMO transmission among multiple base stations (BS) and multiple mobile stations (MS). Each BS performs multi-user precoding to control co-channel interference (CCI). In order to perform effective precoding, each BS needs to know the channel state information (CSI) of the MSs that it serves.

In the Time Division Duplex (TDD) mode, the channel response information of the uplink and downlink is symmetric. Therefore, each base station can obtain the uplink channel responses from the MS to each BS according to the uplink from the MS and calculate the downlink information from each BS to the MS and the corresponding respective downlink precoding matrixes according to the uplink channel responses.

However, in the Frequency Division Duplex (FDD) mode, the frequency difference of carriers between the uplink and the downlink is generally greater than the coherent bandwidth of the channel, therefore the channel fading of the uplink and downlink is not related to each other, resulting in that each BS cannot determine its downlink channel information according to the uplink channel fading. Thus, each BS cannot determine corresponding respective downlink precoding matrixes. In a single BS MIMO system, the problem is solved through the codebook feedback. That is, a preset codebook is shared between the BS and the MS. The MS estimates the downlink channel according to the reference signal such as the downlink pilot signal and etc, and then selects a suitable codeword from the codebook as the precoding matrix and feedbacks the index of the codeword to the BS. The BS performs precoding by using the feedback of the MS. Since the working flowchart and mechanism of the single BS MIMO and Co-MIMO system are very different, it is very difficult to spread the present single BS precoding technology based on the codebook feedback directly to the Co-MIMO system. Nowadays, there is no effective methods which are capable to solve this problem in the prior art.

DETAILED DESCRIPTION OF THE INVENTION

In order to solve the drawbacks described above in the prior art, the present invention provides a method and an apparatus of controlling co-channel interference in a base station of a wireless communication system based on collaborative MIMO and the corresponding method and apparatus of assisting a serving base station to control co-channel interference in a mobile station of a wireless communication system based on collaborative MIMO.

According to the first aspect of the present invention, a method of controlling co-channel interference in a base station of a wireless communication system based on collaborative MIMO is provided, wherein the method comprises the steps of: a. sending a downlink reference signal to a served mobile station and at least one coordinating mobile station; b. receiving precoding information corresponding to a downlink signal from the base station to the served mobile station from the served mobile station; c. sending the received precoding information to at least one serving base station of the at least one coordinating mobile station; d. receiving at least one precoding information corresponding to at least one downlink signal from the base station to the at least one coordinating mobile station respectively forwarded by at least one serving base station of the at least one coordinating mobile stations from the at least one coordinating mobile station; e. precoding a downlink signal from the base station to the served mobile station based on the precoding information corresponding to a downlink signal from the base station to the served mobile station, and precoding the at least one downlink signal from the base station to the at least one coordinating mobile stations respectively based on the at least one precoding information corresponding to the at least one downlink signal from the base station to the at least one coordinating mobile stations; wherein, after step b and before step e, the method comprises the steps of: m. receiving at least one precoding information corresponding to at least one precoding information of at least one downlink signal from the at least one serving base stations to the at least one coordinating mobile stations respectively forwarded by at least one serving base station of the at least one coordinating mobile station from the at least one coordinating mobile station; n. sending the received at least one precoding information to the served mobile station; o. receiving at least one precoding information corresponding to at least one downlink signal from at least one serving base station of the at least one coordinating mobile station to the served mobile station; p. sending the received at least one precoding information to at least one serving base station of the at least one coordinating mobile station respectively.

According to the second aspect of the present invention, a method of assisting a serving base station to control co-channel interference in a mobile station of a wireless communication system based on collaborative MIMO is provided, wherein the method comprises the steps of: A. receiving a downlink reference signal from a serving base station and at least one downlink reference signal from at least one coordinating base station; B. according to the received downlink reference signal from the serving base station, estimating a channel transmission matrix of a downlink channel from the serving base station to the mobile station, and according to the received at least one downlink reference signal from the at least one coordinating base stations, estimating at least one channel transmission matrix of at least one downlink channel from the at least one coordinating base stations to the mobile station respectively; C. according to the estimated channel transmission matrix of a downlink channel from the serving base station to the mobile station, selecting a precoding vector corresponding to a downlink signal from the serving base station to the mobile station from a shared codebook; D. sending precoding information corresponding to a downlink signal from the serving base station to the mobile station to the serving base station; E. receiving at least one precoding information corresponding to at least one downlink signal from the at least one coordinating base station to at least one served mobile station of the at least one coordinating base station forwarded by the at least one coordinating base station and the serving base station from the at least one served mobile station from the at least one coordinating base station; F. based on the received at least one precoding information and the estimated at least one channel transmission matrix of at least one downlink channel from the at least one coordinating base station to the mobile station, selecting at least one precoding vector corresponding to at least one downlink signal from at least one coordinating base stations to the mobile station from the shared codebook respectively; wherein the precoding vector corresponding to a downlink signal from each coordinating base station to the mobile station is orthogonal with the precoding vector corresponding to a downlink signal from the coordinating base station to the served mobile station of the coordinating base station; G. sending at least one precoding information corresponding to at least one downlink signal from the at least one coordinating base station to the mobile station to the serving base station.

According to the third aspect of the present invention, a control apparatus of controlling co-channel interference in a base station of a wireless communication system based on collaborative MIMO is provided, wherein the apparatus comprises: a first sending means, for sending a downlink reference signal to a served mobile station and at least one coordinating mobile station; a first receiving means, for receiving precoding information corresponding to a downlink signal from the base station to the served mobile station from the served mobile station; a second sending means, for sending the received precoding information to at least one serving base station of the at least one coordinating mobile station; a second receiving means, for receiving at least one precoding information corresponding to at least one downlink signal from the base station to the at least one coordinating mobile station respectively forwarded by at least one serving base station of the at least one coordinating mobile stations from the at least one coordinating mobile station; a first precoding means, for precoding a downlink signal from the base station to the served mobile station based on the precoding information corresponding to a downlink signal from the base station to the served mobile station, and precoding the at least one downlink signal from the base station to the at least one coordinating mobile stations respectively based on the at least one precoding information corresponding to the at least one downlink signal from the base station to the at least one coordinating mobile stations; wherein, the control apparatus further includes: a third receiving means, for receiving at least one precoding information corresponding to at least one precoding information of at least one downlink signal from the at least one serving base stations to the at least one coordinating mobile stations respectively forwarded by at least one serving base station of the at least one coordinating mobile station from the at least one coordinating mobile station; a third sending means, for sending the received at least one precoding information to the served mobile station; a sixth receiving means, for receiving at least one precoding information corresponding to at least one downlink signal from at least one serving base station of the at least one coordinating mobile station to the served mobile station; a seventh receiving means, for sending the received at least one precoding information to at least one serving base station of the at least one coordinating mobile station respectively.

According to the fourth aspect of the present invention, an assist control apparatus of assisting a serving base station to control co-channel interference in a mobile station of a wireless communication system based on collaborative MIMO is provided, wherein the assist control apparatus comprises: a fourth receiving means, for receiving a downlink reference signal from a serving base station and at least one downlink reference signal from at least one coordinating base station; an estimating means, for according to the received downlink reference signal from the serving base station, estimating a channel transmission matrix of a downlink channel from the serving base station to the mobile station, and according to the received at least one downlink reference signal from the at least one coordinating base stations, estimating at least one channel transmission matrix of at least one downlink channel from the at least one coordinating base stations to the mobile station respectively; a first selecting means, for according to the estimated channel transmission matrix of a downlink channel from the serving base station to the mobile station, selecting a precoding vector corresponding to a downlink signal from the serving base station to the mobile station from a shared codebook; a fourth sending means, for sending precoding information corresponding to a downlink signal from the serving base station to the mobile station to the serving base station; a fifth receiving means, for receiving at least one precoding information corresponding to at least one downlink signal from the at least one coordinating base station to at least one served mobile station of the at least one coordinating base station forwarded by the at least one coordinating base station and the serving base station from the at least one served mobile station from the at least one coordinating base station; a second selecting means, for based on the received at least one precoding information and the estimated at least one channel transmission matrix of at least one downlink channel from the at least one coordinating base station to the mobile station, selecting at least one precoding vector corresponding to at least one downlink signal from at least one coordinating base stations to the mobile station from the shared codebook respectively; wherein the precoding vector corresponding to a downlink signal from each coordinating base station to the mobile station is orthogonal with the precoding vector corresponding to a downlink signal from the coordinating base station to the served mobile station of the coordinating base station; a fifth sending means, for sending at least one precoding information corresponding to at least one downlink signal from the at least one coordinating base station to the mobile station to the serving base station.

Since the feedback mechanism based on the codebook is employed in the Co-MIMO system in the present invention to enable the BS to obtain the precoding information, the present invention can be used to both TDD mode and FDD mode. Moreover, since the precoding vectors selected by different MSs for the same BS are always orthogonal, multi-user co-channel interference can be reduced.

Wherein, through different figures above, same or similar reference numerals refer to corresponding features or functions.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to the figures, the present invention will be described in detail in the following.

FIG. 1shows a network schematic diagram of a wireless communication system based on the Co-MIMO according to a detailed embodiment of the present invention.

The wireless communication system shown inFIG. 1includes MS1a, MS1b, BS2aand BS2b. It should be noted that the technical solution of the present invention will be described later by using an example in which a wireless communication system includes 2 BSs and 2 MSs, but those skilled in the art shall be appreciated that the wireless communication system of the present invention is not limited to 2 BSs and 2 MSs.

Moreover, without loss of generality, the present invention will be described later by using an example, in which both MS1aand MS1binclude two receiving antennas, and both BS2aand BS2binclude four transmitting antennas. It should be noted that in the specific application, BS2aand BS2bmay include any number of transmitting antennas, MS1aand MS1bmay include any number of receiving antennas, which will be understood by those skilled in the art and will not be described in detail here. But it should be noted that, in order to ensure MS1aand MS1bto restore the date stream received from BS2aand BS2baccurately, the number of the receiving antennas of MS1amust be greater than or equal to the stream number of the data streams that are received from BS2aand BS2bby MS1a. Similarly, the number of the receiving antennas of MS1bmust be greater than or equal to the stream number of the data streams that are received from BS2aand BS2bby MS1b.

In the wireless communication system based on Co-MIMO shown inFIG. 1, it is assumed that, BS2asends one data stream to MS1aand MS1brespectively, and similarly, BS2balso sends one data stream to MS1aand MS1brespectively.

For BS2a, MS1ais the served MS of BS2a, and MS1bis the coordinating MS of BS2a. For BS2b, MS1bis the served MS of BS2b, and MS1ais the coordinating MS of BS2b.

For MS1a, BS2ais the serving BS of MS1a, and BS2bis the coordinating BS of MS1a. For MS1b, BS2bis the serving BS of MS1b, and BS2ais the coordinating BS of MS1b.

FIG. 2shows a flowchart of a method of controlling the co-channel interference in a wireless communication system based on the Co-MIMO according to a detailed embodiment of the present invention.

Referring toFIG. 2and in conjunction withFIG. 1, the technical solution of the present invention will be described in detail. The description forFIG. 1above will also be taken as a reference here.

Firstly, in step Si, BS2asends a downlink reference signal to MS1aand MS1b. The downlink reference signal can be a public pilot signal, or a training sequence.

Secondly, in step S2, MS1areceives the downlink reference signal from BS2a;in step S2′, MS1breceives the downlink reference signal from BS2a.

It should be noted that, there is no necessary order between step S2and S2′.

Then, in step S3, MS1aestimates channel transmission matrix Ha,aof the downlink channel from BS2ato MS1aaccording to the downlink reference signal received from BS2a;in step S3′, MS1bestimates channel transmission matrix Hb,aof the downlink channel from BS2ato MS1baccording to the downlink reference signal received from BS2a.

It should be noted that, there is no necessary order between step S3and S3′.

After MS1aestimates the channel transmission matrix Ha,aof the downlink channel from BS2ato MS1a, in step S4, according to the estimated channel transmission matrix Ha,a, MS1aselects a precoding vector va,acorresponding to the downlink signal from BS2ato MS1afrom a shared codebook.

Further, selecting a precoding vector va,afrom a shared codebook by MS1ais based on the following formula:

Wherein, C represents codebook, the above formula represents thatany column of vector c in the codebook C is traversed. The column of vector c which makes |Ha,ac|2reach the maximum value is the precoding vector va,acorresponding to the downlink signal from BS2atoMS1a.

It should be noted, that MS1aonly needs to select a column of vector which meets the above formula from the shared codebook as the precoding vector for the data stream, since in the description the technical solution is described by using an example in which BS2asends one data stream to MS1a. But those skilled in the art shall be appreciated that, if BS2asends a plurality of data streams to MS1a, MS1amust select a plurality of columns of vectors which meet the formula above from the shared codebook as the precoding vectors for the plurality of data streams.

Further, the shared codebook is shared among MS1a, MS1b, BS2aand BS2b. Still further, the codebook may be a DFT codebook, 3GPP LTE codebook, IEEE802.16e codebook, or other types of codebooks, which is intelligible for those skilled in the art and will not be described in detail here.

Typically, the codebook consists of a plurality of precoding matrixes; each matrix consists of a plurality of columns of vectors. Preferably, each column of precoding vectors in the same precoding matrix is orthogonal with each other.

Further, the number of rows of a precoding matrix is equal to the number of the BS transmitting antennas. The number of columns of a precoding matrix is equal to the maximum data stream number that can be sent by a BS. In the embodiment, since it is assumed that BS2aand BS2binclude 4 transmitting antennas respectively and the maximum data stream number that can be sent by a BS is 4, a precoding matrix in the shared codebook is a 4×4 matrix.

After MS1aselects the precoding vector va,acorresponding to the downlink signal from BS2ato MS1afrom the shared codebook, in step S5, MS1asends to BS2athe precoding information corresponding to the downlink signal from BS2ato MS1a.

It should be noted that, MS1acan send to BS2athe precoding vector va,acorresponding to the downlink signal from BS2ato MS1adirectly. Preferably, MS1acan send to BS2athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

In the following, the example, in which MS1asends to BS2athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, will be described.

Next, in step S6, BS2areceives from MS1athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a. Then, in step S7, BS2asends to BS2bthe received index of the precoding va,acorresponding to the downlink signal from BS2ato MS1a.

Above is described from the view point of BS2a, but it is intelligible to those skilled in the art, BS2balso interacts with MS1band MS1a, while BS2ainteracts with MS1aand MS1b.

More specifically, firstly, BS2bsends a downlink reference signal to MS1band MS1a. The downlink reference signal can be a public pilot signal, or a training sequence.

Secondly, MS1breceives the downlink reference signal from BS2b; in step S2′, MS1areceives the downlink reference signal from BS2b.

Similarly, there is no necessary order between the step of MS1breceiving the downlink reference signal from BS2band the step of MS1areceiving the downlink reference signal from BS2b.

Then, MS1bestimates channel transmission matrix Hb,bof the downlink channel from BS2bto MS1baccording to the downlink reference signal received from BS2b; MS1aestimates channel transmission matrix Ha,bof the downlink channel from BS2bto MS1aaccording to the downlink reference signal received from BS2b.

Next, according to the estimated channel transmission matrix Hb,b, MS1bselects a precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bfrom a shared codebook.

Further, selecting a precoding vector vb,bfrom a shared codebook by MS1bis based on the following formula:

Wherein, C represents codebook, the above formula represents that any column of vector c in the codebook C is traversed. The column of vector c which makes |Hb,bc|2reach the maximum value is the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

Then, MS1bsends to BS2bthe precoding information corresponding to the downlink signal from BS2bto MS1b.

It should be noted that, MS1bcan send to BS2bthe precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bdirectly. Preferably, MS1bcan send to BS2bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

In the following, the example, in which MS1bsends to BS2bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, will be described.

After BS2breceives from MS1bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, it sends the index of the precoding vector vb,bto BS2a.

In step S7′, BS2areceives the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bforwarded by BS2bfrom MS1b. Then, in step S8, BS2asends the received index of the precoding vector vb,bto MS1a.

It should be noted that, there is no order between step S7and step S7′ above.

Next, in step S9, MS1areceives the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bforwarded by BS2a, then, in step S10, based on the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1band the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook.

More specifically, firstly according to the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, MS1asearches the corresponding precoding vector vb,bfrom the shared codebook. Then according to the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1band the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the codebook.

Wherein, the selected precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook should be orthogonal with the selected precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

Since each column of the precoding vectors in each precoding matrix in the shared codebook is orthogonal with each other, preferably, according to the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the precoding matrix where the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bis located.

Further, selecting a precoding vector va,bfrom a shared codebook by MS1ais based on the following formula:

Wherein, C represents codebook, c′ represents the conjugate transposed matrix of c. The above formula represents that any column of precoding vector in the precoding matrix, where the precoding vector vb,bis located, in the codebook C, is traversed. The column of vector c which makes |Ha,bc|2reach the maximum value is the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1a.

After MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook, in step S11, MS1asends the index of the selected precoding vector va,bto BS2a.

Of course, MS1acan also send the precoding vector va,bto BS2adirectly.

step S12, BS2areceives from MS1athe index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1aand sends it to BS2b.

In the meantime when MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook, MS1balso selects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook.

More specifically, in step S7above, after BS2asends to BS2bthe received index of the precoding va,acorresponding to the downlink signal from BS2ato MS1a, BS2breceives the index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1aforwarded by BS2afrom MS1aand sends the index of the precoding vector va,ato MS1b.

After MS1breceives the index of the precoding vector va,a, based on the index of the precoding vector va,aand the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook.

More specifically, firstly according to the received index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, MS1bsearches the corresponding precoding vector va,afrom the shared codebook. Then according to the precoding vector va,acorresponding to the downlink signal from BS2ato MS1aand the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, MS1aselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the codebook.

Wherein, the selected precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook should be orthogonal with the selected precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

Since each column of the precoding vectors in each precoding matrix in the shared codebook is orthogonal with each other, preferably, according to the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the precoding matrix where the precoding vector va,acorresponding to the downlink signal from BS2ato MS1ais located.

Further, selecting a precoding vector vb,afrom a shared codebook by MS1bis based on the following formula:

Wherein, C represents codebook, c′ represents the conjugate transposed matrix of c. The above formula represents that any column of precoding vector in the precoding matrix, where the precoding vector va,ais located, in the codebook C, is traversed. The column of vector c which makes |Hb,ac|2reach the maximum value is the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b.

After MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook, MS1bsends the index of the selected precoding vector vb,ato BS2b.

Of course, MS1bcan also send the precoding vector vb,ato BS2bdirectly.

After BS2breceives from MS1bthe index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b, BS2bsends it to BS2a.

In step S13, BS2areceives the index of the precoding vector Vb,acorresponding to the downlink signal from BS2ato MS1bforwarded by BS2bfrom MS1b.

Next, in step S14, based on the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1band the index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, BS2aprecodes the downlink signals sent to MS1aand MS1brespectively.

More specifically, firstly, according to the received index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, BS2asearches the corresponding precoding vector va,afrom the shared codebook, and according to the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b, BS2asearches the corresponding precoding vector vb,afrom the shared codebook.

Then, according to the searched precoding vector va,a, BS2aprecodes the downlink signal which is sent by BS2ato MS1a, and according to the searched precoding vector vb,a, BS2aprecodes the downlink signal which is sent by BS2ato MS1b.

At last, BS2asends the precoded downlink signals to MS1aand MS1brespectively.

Similarly, after BS2breceives the index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1aforwarded by BS2afrom MS1a, based on the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1band the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, BS2bprecodes the downlink signals sent to MS1band MS1arespectively.

More specifically, firstly, according to the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, BS2bsearches the corresponding precoding vector vb,bfrom the shared codebook, and according to the received index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1a, BS2bsearches the corresponding precoding vector va,bfrom the shared codebook.

Then, according to the searched precoding vector vb,b, BS2bprecodes the downlink signal which is sent by BS2bto MS1b, and according to the searched precoding vector va,b, BS2bprecodes the downlink signal which is sent by BS2bto MS1a.

At last, BS2bsends the precoded downlink signals to MS1band MS1arespectively.

The technical solution of the present invention is described above from the view point of the method. In the following, the technical solution of the present invention will be described from the view point of the apparatus module.

FIG. 3shows a block diagram of a control apparatus in a BS of a wireless communication system based on the Co-MIMO for controlling the co-channel interference according to a detailed embodiment of the present invention. The control apparatus20inFIG. 3includes a first sending means201, a first receiving means202, a second sending means203, a third receiving means204, a third sending means205, a sixth receiving means206, a seventh sending means207, a second receiving means208and a first precoding means209.

FIG. 4shows a block diagram of an assist control apparatus in a MS of a wireless communication system based on the Co-MIMO for controlling the co-channel interference according to a detailed embodiment of the present invention. The assist control apparatus10inFIG. 4includes a fourth receiving means101, an estimating means102, a first selecting means103, a fourth sending means104, a fifth receiving means105, a second selecting means106and a fifth sending means107.

Hereinafter, referring toFIG. 3andFIG. 4and in conjunction withFIG. 1, the technical solution of the present invention will be described in detail. The description forFIG. 1above will also be taken as a reference here.

Firstly, the first sending means201in the control apparatus20in BS2asends a downlink reference signal to MS1aand MS1b. The downlink reference signal can be a public pilot signal, or a training sequence.

Secondly, the fourth receiving means101in the assist control apparatus10in MS1areceives the downlink reference signal from BS2a; the fourth receiving means101in the assist control apparatus10in MS1breceives the downlink reference signal from BS2a.

Then, the estimating means102in the assist control apparatus10in MS1aestimates channel transmission matrix Ha,aof the downlink channel from BS2ato MS1aaccording to the downlink reference signal received from BS2a; the estimating means102in the assist control apparatus10in MS1bestimates channel transmission matrix Hb,aof the downlink channel from BS2ato MS1baccording to the downlink reference signal received from BS2a.

After the estimating means102in the assist control apparatus10in MS1aestimates the channel transmission matrix Ha,aof the downlink channel from BS2ato MS1a, according to the estimated channel transmission matrix Ha,a, the first selecting means103in the assist control apparatus10in MS1aselects a precoding vector va,acorresponding to the downlink signal from BS2ato MS1afrom a shared codebook.

Further, selecting a precoding vector va,afrom a shared codebook by the selecting means103in the assist control apparatus10in MS1ais based on the following formula:

Wherein, C represents codebook, the above formula represents that any column of vector c in the codebook C is traversed. The column of vector c which makes |Ha,ac|2reach the maximum value is the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

It should be noted, that MS1aonly needs to select a column of vector which meets the above formula from the shared codebook as the precoding vector for the data stream, since in the description the technical solution is described by using an example in which BS2asends one data stream to MS1a. But those skilled in the art shall be appreciated that, if BS2asends a plurality of data streams to MS1a, MS1amust select a plurality of columns of vectors which meet the formula above from the shared codebook as the precoding vectors for the plurality of data streams.

Further, the shared codebook is shared among MS1a, MS1b, BS2aand BS2b. Still further, the codebook may be a DFT codebook, 3GPP LTE codebook, IEEE802.16e codebook, or other types of codebooks, which is intelligible for those skilled in the art and will not be described in detail here.

Typically, the codebook consists of a plurality of precoding matrixes; each matrix consists of a plurality of columns of vectors. Preferably, each column of precoding vectors in the same precoding matrix is orthogonal with each other.

Further, the number of rows of a precoding matrix is equal to the number of the BS transmitting antennas. The number of columns of a precoding matrix is equal to the maximum data stream number that can be sent by a BS. In the embodiment, since it is assumed that BS2aand BS2binclude 4 transmitting antennas respectively and the maximum data stream number that can be sent by a BS is 4, a precoding matrix in the shared codebook is a 4×4 matrix.

After the first selecting means103in the assist control apparatus10in MS1aselects the precoding vector va,acorresponding to the downlink signal from BS2ato MS1afrom the shared codebook, the fourth sending means104in the assist control apparatus10in MS1asends to BS2athe precoding information corresponding to the downlink signal from BS2ato MS1a.

It should be noted that, the fourth sending means104in the assist control apparatus10in MS1acan send to BS2athe precoding vector va,acorresponding to the downlink signal from BS2ato MS1adirectly. Preferably, the fourth sending means104in the assist control apparatus10in MS1acan send to BS2athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

Further, the determining means in the fourth sending means104firstly determines the index of the precoding vector va,aaccording to the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a. Then, the sixth sending means in the fourth sending means104sends to BS2athe determined index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

In the following, the example, in which the fourth sending means104in the assist control apparatus10in MS1asends to BS2athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, will be described.

Next, the first receiving means202in the control apparatus20in BS2areceives from MS1athe index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a. Then, the second sending means203in the control apparatus20in BS2asends to BS2bthe received index of the precoding va,acorresponding to the downlink signal from BS2ato MS1a.

Above is described from the view point of BS2a, but it is intelligible to those skilled in the art, BS2balso interacts with MS1band MS1a, while BS2ainteracts with MS1aand MS1b.

More specifically, firstly, the first sending means201in the control apparatus20in BS2bsends a downlink reference signal to MS1band MS1a. The downlink reference signal can be a public pilot signal, or a training sequence.

Secondly, the fourth receiving means101in the assist control apparatus10in MS1breceives the downlink reference signal from BS2b; the fourth receiving means101in the assist control apparatus10in MS1areceives the downlink reference signal from BS2b.

Then, the estimating means102in the assist control apparatus10in MS1bestimates channel transmission matrix Hb,bof the downlink channel from BS2bto MS1baccording to the downlink reference signal received from BS2b;the estimating means102in the assist control apparatus10in MS1aestimates channel transmission matrix Ha,bof the downlink channel from BS2bto MS1aaccording to the downlink reference signal received from BS2b.

Next, according to the estimated channel transmission matrix Hb,b, the first selecting means103in the assist control apparatus10in MS1bselects a precoding vector vb,bcorresponding to the downlink signal from BS2bMS1bfrom a shared codebook.

Further, selecting a precoding vector vb,bfrom a shared codebook by the first selecting means103in the assist control apparatus10in MS1bis based on the following formula:

Wherein, C represents codebook, the above formula represents that any column of vector c in the codebook C is traversed. The column of vector c which makes |Hb,bc|2reach the maximum value is the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

Then, the fourth sending means104in the assist control apparatus10in MS1bsends to BS2bthe precoding information corresponding to the downlink signal from BS2bto MS1b.

It should be noted that, the fourth sending means104in the assist control apparatus10in MS1bcan send to BS2bthe precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bdirectly. Preferably, the fourth sending means104in the assist control apparatus10in MS1bcan send to BS2bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

Further, the determining means in the fourth sending means104firstly determines the index of the precoding vector vb,baccording to the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b. Then, the sixth sending means in the fourth sending means104sends to BS2bthe determined index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

In the following, the example, in which the fourth sending means104in the assist apparatus means10in MS1bsends to BS2bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, will be described.

After the first receiving means202in the control apparatus20in BS2breceives from MS1bthe index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, the second sending means203in the control apparatus20in BS2bsends the index of the precoding vector vb,bto BS2a.

The third receiving means204in the control apparatus20in BS2areceives the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bforwarded by BS2bfrom MS1b. Then, the third sending means205in the control apparatus20in BS2asends the received index of the precoding vector vb,bto MS1a.

Next, the fifth receiving means105in the assist control apparatus10in MS1areceives the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bforwarded by BS2a, then, based on the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1band the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, the second selecting means106in the assist control apparatus10in MS la selects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook.

More specifically, firstly according to the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, the second searching means in the second selecting means106in MS1asearches the corresponding precoding vector vb,bfrom the shared codebook. Then according to the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1band the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, the third selecting means in the second selecting means106selects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the codebook.

Wherein, the selected precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook should be orthogonal with the selected precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b.

Since each column of the precoding vectors in each precoding matrix in the shared codebook is orthogonal with each other, preferably, according to the estimated channel transmission matrix Ha,bof the downlink channel from BS2bto MS1a, the second selecting means106in the assist control means10in MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the precoding matrix where the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1bis located.

Further, selecting a precoding vector va,bfrom a shared codebook by the second selecting means106in the assist control apparatus10in MS1ais based on the following formula:

Wherein, C represents codebook, c′ represents the conjugate transposed matrix of c. The above formula represents that any column of precoding vector in the precoding matrix, where the precoding vector vb,bis located, in the codebook C, is traversed. The column of vector c which makes |Ha,bc|2reach the maximum value is the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1a.

After the second selecting means106in the assist control apparatus10in MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook, the fifth sending means107in the assist control apparatus10in MS1asends the index of the selected precoding vector va,bto BS2a.

Of course, the fifth sending means107in the assist control apparatus10in MS1acan also send the precoding vector va,bto BS2adirectly.

The sixth receiving means206in the control apparatus20in BS2areceives from MS1athe index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1aand the seventh sending means207in the control apparatus20in BS2asends it to BS2b.

In the meantime when MS1aselects the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1afrom the shared codebook, MS1balso selects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook.

More specifically, after the second sending means203in the control apparatus20in BS2asends to BS2bthe received index of the precoding va,acorresponding to the downlink signal from BS2ato MS1a, the third receiving means204in the control apparatus20in BS2breceives the index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1aforwarded by BS2afrom MS1aand the third sending means205in the control apparatus20sends the index of the precoding vector va,ato MS1b.

After the fifth receiving means105in the assist control apparatus10in MS1breceives the index of the precoding vector va,a, based on the index of the precoding vector va,aand the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, the second selecting means106in the assist control apparatus10in MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook.

More specifically, firstly according to the received index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, the second searching means in the second selecting means106in MS1bsearches the corresponding precoding vector va,afrom the shared codebook. Then according to the precoding vector va,acorresponding to the downlink signal from BS2ato MS1aand the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, the third selecting means in the second selecting means106selects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the codebook.

Wherein, the selected precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook should be orthogonal with the selected precoding vector va,acorresponding to the downlink signal from BS2ato MS1a.

Since each column of the precoding vectors in each precoding matrix in the shared codebook is orthogonal with each other, preferably, according to the estimated channel transmission matrix Hb,aof the downlink channel from BS2ato MS1b, the second selecting means106in the assist control apparatus10in MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the precoding matrix where the precoding vector va,acorresponding to the downlink signal from BS2ato MS1ais located.

Further, selecting a precoding vector vb,afrom a shared codebook by the second means106in the assist control apparatus10in MS1bis based on the following formula:

Wherein, C represents codebook, c′ represents the conjugate transposed matrix of c. The above formula represents that any column of precoding vector in the precoding matrix, where the precoding vector va,ais located, in the codebook C, is traversed. The column of vector c which makes |Hb,ac|2reach the maximum value is the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b.

After the second selecting means106in the assist control apparatus10in MS1bselects the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bfrom the shared codebook, the fifth sending means107in the assist control apparatus10in MS1bsends the index of the selected precoding vector vb,ato BS2b.

Of course, the fifth sending means107in the assist control apparatus10in MS1bcan also send the precoding vector vb,ato BS2bdirectly.

After the sixth receiving means206in the control apparatus20in BS2breceives from MS1bthe index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b, the seventh sending means207in the control apparatus20in BS2bsends it to BS2a.

The second receiving means208in the control apparatus20in BS2areceives the index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1bforwarded by BS2bfrom MS1b.

Next, based on the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1band the index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, the first precoding means209in the control apparatus20in BS2aprecodes the downlink signals sent to MS1aand MS1brespectively.

More specifically, firstly, according to the received index of the precoding vector va,acorresponding to the downlink signal from BS2ato MS1a, the first searching means in the first precoding means209in BS2asearches the corresponding precoding vector va,afrom the shared codebook, and according to the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1b, BS2asearches the corresponding precoding vector vb,afrom the shared codebook.

Then, according to the searched precoding vector va,a, the second precoding means in the first precoding means209in BS2aprecodes the downlink signal which is sent by BS2ato MS1a, and according to the searched precoding vector vb,a, the second precoding means in the first precoding means209in BS2aprecodes the downlink signal which is sent by BS2ato MS1b.

At last, BS2asends the precoded downlink signals to MS1aand MS1brespectively.

Similarly, after the second receiving means208in the control apparatus20in BS2breceives the index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1aforwarded by BS2afrom MS1a, based on the received index of the precoding vector vb,acorresponding to the downlink signal from BS2ato MS1band the index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, the first precoding means209in the control apparatus20in BS2bprecodes the downlink signals sent to MS1band MS1arespectively.

More specifically, firstly, according to the received index of the precoding vector vb,bcorresponding to the downlink signal from BS2bto MS1b, the first searching means in the precoding means209in BS2bsearches the corresponding precoding vector vb,bfrom the shared codebook, and according to the received index of the precoding vector va,bcorresponding to the downlink signal from BS2bto MS1a, BS2bsearches the corresponding precoding vector va,bfrom the shared codebook.

Then, according to the searched precoding vector vb,b, the second precoding means in the first precoding means209in BS2bprecodes the downlink signal which is sent by BS2bto MS1b, and according to the searched precoding vector va,b, the second precoding means in the first precoding means209in BS2bprecodes the downlink signal which is sent by BS2bto MS1a.

At last, BS2bsends the precoded downlink signals to MS1band MS1arespectively.

The concrete embodiments of the present invention have been described above. It is understandable, that the present invention is not ted to the specific embodiments mentioned above. Those skilled in the art nay perform various variation or modification in the protection scope of the claims.