KR20100046345A - Apparatus and method for eliminating inter cell interference in a multiple input multiple output wireless communication system - Google Patents

Abstract

PURPOSE: A device and a method for eliminating inter cell interference in a multiple input multiple output wireless communication system are provided to control a PMI pattern of a BS according to the PMI desirability, thereby effectively performing interference elimination between BS cooperation cells. CONSTITUTION: An inter cell interference elimination device broadcast a PMI(Precoding Matrix Index) pattern of oneself and a PMI pattern least one of neighbor BS(303). The device confirms feedback information from the terminals(307). The device calculates the general favorable level of the terminals about the PMI patterns through PMI pattern favorable level of the feedback information. If the general favorable level is same or less than critical value, the device performs a PMI pattern switching process(311,313).

Description

Apparatus and method for eliminating interference between cells in a multi-input wireless communication system {APPARATUS AND METHOD FOR ELIMINATING INTER CELL INTERFERENCE IN A MULTIPLE INPUT MULTIPLE OUTPUT WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a multiple input multiple output (MIMO) wireless communication system, and more particularly, to an apparatus and method for removing inter-cell interference in a multiple input and output wireless communication system.

The 4th Generation (hereinafter referred to as '4G') communication system provides users with services of various quality of service (QoS) using a transmission rate of about 100 Mbps. There is active research going on. The representative communication system is the Institute of Electrical and Electronics Engineers (IEEE) 802.16 system. The IEEE 802.16 system orthogonal frequency division multiplexing (hereinafter referred to as 'OFDM') / Orthogonal Frequency Division Multiple Access (orthogonal frequency division multiplexing) to support a broadband transmission network on a physical channel (Physical Channel) Multiple Access, hereinafter referred to as " OFDMA "

In a broadband wireless communication system using the OFDM / OFDMA scheme such as IEEE 802.16, terminals are allocated radio resources orthogonal to each other. Therefore, the influence due to interference between terminals in one cell is not large. However, when the frequency reuse rate is 1, since the same band is used between neighboring base stations, the terminal located at the cell boundary receives interference due to the signal of the terminal using the same radio resource present in the adjacent cell. For example, as shown in FIG. 1, the terminal A 120-1 receives downlink data by decoding a signal received through a radio resource allocated from the base station A 110-1. At this time, if the radio resource allocated by the base station A 110-1 to the terminal A 120-1 and the radio resource allocated by the base station B 110-2 to the terminal B 120-2 are the same. The downlink signal to the terminal A 120-1 and the downlink signal to the terminal B 120-2 are received together with the terminal A 120-1. Accordingly, the terminal A 120-1 performs decoding on a signal in which two downlink signals are mixed, so that correct data reception is not performed. That is, the downlink signal to the terminal B (120-2) acts as a serious interference to the terminal A (120-1).

As described above, in a broadband wireless communication system using the OFDM / OFDMA scheme such as IEEE 802.16, inter-cell interference due to downlink or uplink signals transmitted in different cells through the same frequency resource and time resource (ICI: Inter Cell Interference) can cause system performance degradation. Therefore, there is a need for an alternative to efficiently remove the inter-cell interference.

Accordingly, an object of the present invention is to provide an apparatus and method for removing inter-cell interference (ICI) in a multiple input multiple output (MIMO) wireless communication system.

Another object of the present invention is to provide an apparatus and method for removing inter-cell interference through precoding of base stations in a multiple input / output wireless communication system.

Another object of the present invention is to provide an apparatus and method for determining a Precoding Matrix Index (PMI) pattern for precoding of base stations in a multiple input / output wireless communication system.

Still another object of the present invention is to provide an apparatus and method for calculating a PMI pattern likelihood from channel quality caused by PMI patterns of base stations in a multiple input / output wireless communication system.

Another object of the present invention is to provide an apparatus and method for adjusting PMI patterns of base stations using PMI pattern attractiveness in a multiple input / output wireless communication system.

According to the first aspect of the present invention for achieving the above object, the operation method of a base station in a multiple input multiple output (MIMO) wireless communication system, the terminal has its own PMI (Precoding Matrix Index) pattern (pattern) And broadcasting PMI patterns of at least one neighboring base station, checking feedback information including at least one of PMI pattern affinity, channel quality, and preferred PMI from the terminals, and using the PMI pattern affinity. The process of calculating the overall likelihood of the terminals with respect to the PMI pattern, and if the overall likelihood is less than or equal to a threshold, characterized in that to perform a PMI pattern switching procedure.

According to a second aspect of the present invention for achieving the above object, an operation method of a terminal in a multiple input / output wireless communication system includes the steps of receiving PMI pattern information of a serving base station and PMI pattern information of at least one neighboring base station; Calculating channel quality for each subband using a PMI pattern of a serving base station and a PMI pattern of the at least one neighboring base station, and calculating a PMI pattern likelihood using at least one of the PMI pattern and the channel quality And transmitting feedback information including the channel quality and the PMI pattern affinity to the serving base station.

According to a third aspect of the present invention for achieving the above object, a base station apparatus in a multiple input and output wireless communication system, a transmitter for broadcasting its own PMI pattern and PMI pattern of at least one neighboring base station, and the terminal Calculating a comprehensive likelihood of the terminals with respect to the PMI pattern using an interpreter confirming feedback information including at least one of a PMI pattern likelihood, a channel quality, and a preferred PMI, and a PMI pattern likelihood fed back from the terminals; If the overall likelihood is less than or equal to the threshold, it characterized in that it comprises a determiner for performing the PMI pattern switching procedure.

According to a first aspect of the present invention for achieving the above object, a terminal device in a multiple input and output wireless communication system, a receiver for receiving PMI pattern information of the serving base station and PMI pattern information of at least one neighboring base station, and the serving base station A channel quality calculator for calculating channel quality for each subband using the PMI pattern and the PMI pattern of the at least one neighboring base station, and a PMI pattern favorable degree using the at least one of the PMI pattern and the channel quality. And a transmitter for transmitting feedback information including the channel quality and the PMI pattern affinity to the serving base station.

Multiple Input Multiple Output (MIMO) Efficient interference cancellation between cooperative base station cells is performed by adjusting the PMI pattern of base stations according to the PMI pattern affinity calculated from the channel quality by PMI pattern in a wireless communication system. do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the specific description of the related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, the present invention describes a technique for removing inter-cell interference (ICI) in a multiple input multiple output (MIMO) wireless communication system. Hereinafter, the present invention will be described using an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) scheme as an example. The same applies to other wireless communication systems.

In the multiple input / output wireless communication system according to the present invention, a precoding matrix is used to cancel intercell interference. That is, in downlink communication, the base station multiplies the transmission signal by a precoding matrix for removing interference to an adjacent cell. The precoding matrix used for interference cancellation is one of the precoding matrices included in a pre- promised codebook, and the precoding matrices are identified using a PMI (Precoding Matrix Index). The precoding matrix may have the form of a vector according to the number of transmission streams. For convenience of description, the present invention will be described below in consideration of a precoding vector, but it is obvious that it can be extended to a precoding matrix. Also, for convenience of description, the present invention considers only four precoding vectors and five subbands below.

In the system according to the present invention, the base stations and the terminals share a codebook as shown in Equation 1 below.

는 코드북, 상기

는 k번째 프리코딩 벡터를 의미한다.In Equation 1,

Is a codebook, said

Denotes the k th precoding vector.

In this case, each base station may use one of four precoding vectors for each subband. For example, a combination of precoding vectors such as Equation 2 is possible.

는 k번째 프리코딩 벡터 조합, 상기

는 k번째 프리코딩 벡터를 의미한다.In Equation 2,

Is the k th precoding vector combination,

Denotes the k th precoding vector.

Including the examples shown in Equation 2, some of a total of 5 ⁴ precoding vector combinations may be selectively used. Hereinafter, the precoding vector combination is referred to as a 'PMI pattern', and the selected precoding vector combinations are collectively referred to as a 'PMI pattern set'.

In addition, the base stations and terminals share a PMI pattern set as shown in Equation 3 below.

는 PMI 패턴 집합, 상기

는 k번째 프리코딩 벡터 조합을 의미한다.In Equation 3,

PMI pattern set, said

Denotes a k-th precoding vector combination.

The base stations and the terminals sharing the precoding vectors and the PMI pattern set as described above eliminate the inter-cell interference as follows.

2 shows an example of distribution of terminals in two cells. As shown in FIG. 2, the terminal A1 215-1 to the terminal A5 215-5 are connected to the base station A 210, and the terminal B1 225-1 to the terminal B4 225-4. Is connected to the base station B 220.

The base station A 210 and the base station B 220 determine a PMI pattern to be used for downlink communication. The base station A 210 and the base station B 220 inform their own PMI patterns before scheduling. The communication between the base station A 210 and the base station B 220 is performed through a dedicated network for communication between the base stations or through a backbone network. In addition, the base station A 210 and the base station B 220 broadcast their PMI patterns as well as the PMI patterns of neighboring base stations to terminals in their cells.

At the same time, the terminals 215-1 to 215-5 and 225-1 to 225-4 estimate the sub-band channel matrix with the serving base station and the sub-band channel matrix with the neighboring base station. Pilot signals are used for the estimation of the channel matrix. In general, base stations adjacent to each other transmit pilot signals through resources at different locations, or multiply the pilot signals with different scrambling codes. Accordingly, the terminals 215-1 to 215-5 and 225-1 to 225-4 can distinguish pilot signals of a serving base station and pilot signals of an adjacent base station, thereby estimating a channel matrix of each base station. can do.

The terminals 215-1 to 215-5 and 225-1 to 225-4 that estimate the channel matrix with the serving base station and the channel matrix with the neighboring base station use the PMI pattern received from the serving base station. The effective channel gain for each subband is predicted. In other words, the terminals 215-1 to 215-5 and 225-1 to 225-4 multiply each of the precoding vectors of the PMI pattern with the channel matrix of the corresponding subband, and for each subband through the multiplication result. Estimate the effective channel gain. In this case, the effective channel gain for the serving base station is the reception strength of the desired signal, and the effective channel gain for the neighboring base station is the interference strength. Subsequently, the terminals 215-1 to 215-5 and 225-1 to 225-4 use SINR (Singal to Noise and Interference Ratio) and CINR (Carrier) by using the reception strength of the desired signal and the strength of the interference. to calculate channel quality for each subband, such as to Noise and Interference Ratio, and feed back channel quality information of at least one subband to the serving base station.

In addition, the terminals 215-1 to 215-5 and 225-1 to 225-4 measure how much PMI patterns of the current serving base station and the neighboring base station reduce interference to their own, and then a measurement result. Feeds back to the serving base station. Hereinafter, in the present invention, the numerical value indicating how much the PMI patterns of the serving base station and the neighboring base stations are reducing interference to itself is referred to as 'PMI pattern favorability'. For example, the PMI pattern likelihood is calculated using PMI or calculated using channel quality.

For example, in the case of using the PMI, the terminal A1 215-1 calculates a most favored PMI for minimizing interference in each subband using a channel matrix for each subband with the base station B 220. do. That is, the terminal A1 215-1 selects the best PMI by multiplying the available PMIs sequentially with the channel matrix of each subchannel and comparing the result of the multiplication, or by using the algorithm prepared in advance. Is calculated and then the best PMI that is most similar to the optimal PMI is selected. The terminal A1 215-1 calculates the PMI pattern likelihood based on a matching ratio between the best-numbered PMI for each subband and the PMI for each subband of the base station B 220. In other words, the higher the matching ratio, the higher the PMI pattern likelihood. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality.

As another example of using the PMI, the terminal A1 215-1 uses a worst-case PMI that maximizes interference in each subband using a subband-specific channel matrix with the base station B 220. Calculate That is, the terminal A1 215-1 selects the worst PMI by multiplying the available PMIs sequentially with the channel matrix of each subchannel and comparing the result of the multiplication, or using the algorithm prepared in advance. After calculating the PMI, the worst case PMI most similar to the maximum interference PMI is selected. The terminal A1 215-1 calculates the PMI pattern likelihood based on a matching ratio between the worst PMI for each subband and the PMI for each subband of the base station B 220. In other words, the higher the matching ratio, the lower the PMI pattern likelihood. In this case, the PMI pattern likelihood may be calculated for all subbands or only subbands of upper portions having poor channel quality.

For example, in the case of using the channel quality, the terminal A1 215-1 is the channel quality when the base stations 210 and 220 do not use the PMI pattern and the base stations 210 and 220 are PMI. The channel quality in the case of using a pattern is calculated. The terminal A1 215-1 calculates the difference between the channel qualities of the two cases, thereby calculating the PMI pattern favorability. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality.

The PMI pattern likelihood is calculated for each subband. However, in order to reduce the amount of feedback information, the terminals 215-1 to 215-5 and 225-1 to 225-4 may combine the PMI pattern favorability of a plurality of subbands into one value. For example, the terminals 215-1 to 215-5 and 225-1 to 225-4 add up, average, or add weights based on a specific criterion, and add the sums, or, The weights are averaged according to specific criteria. Alternatively, the terminals 215-1 to 215-5 and 225-1 to 225-4 may group a plurality of subbands into a plurality of groups, and then combine the PMI pattern similarities for each group.

The base stations 210 and 220, which have received the channel quality and the PMI pattern likelihood feedback from the terminals 215-1 to 215-5 and 225-1 to 225-4, may each subband based on the channel quality. Are allocated to the terminals 215-1 to 215-5 and 225-1 to 225-4, and downlink communication is performed according to the allocation result.

In addition, the base stations 210 and 220 calculate the overall likelihood of the UEs in the cell for the PMI pattern using the PMI pattern likelihood. For example, the base stations 210 and 220 calculate the overall likelihood by summing or averaging PMI pattern likelihoods from the terminals 215-1 to 215-5 and 225-1 to 225-4. do. If the overall likelihood is less than or equal to a threshold, the base stations 210 perform PMI pattern switching. For example, in the case of the base station A 110, the base station A 110 arbitrarily changes its PMI pattern and informs the neighbor base stations of the changed PMI pattern. Alternatively, the base station A 110 requests the PMI pattern switching to the adjacent base station which has the greatest influence on the deterioration of the overall likelihood. Accordingly, the neighboring base station, which has been requested to switch the PMI pattern, arbitrarily changes its PMI pattern and informs the neighboring base stations of the changed PMI pattern. Accordingly, in the subsequent downlink communication, the PMI pattern reflecting the PMI pattern favorability calculated according to the above-described process is used.

In the cell interference cancellation process described above, the base stations determine their own PMI pattern, and informs neighboring base stations of the PMI pattern to use. However, according to another embodiment of the present invention, the base stations determine a PMI pattern that will not be used by them, and notify neighbor base stations of the PMI pattern that will not be used. In this case, an interference cancellation process of base stations and terminals will be described with reference to FIG. 2.

Base station A 210 and base station B 220 determine a PMI pattern not to be used for downlink communication. The base station A 210 and the base station B 220 inform their own PMI patterns before scheduling. Communication between the base station A 210 and the base station B 220 is performed through a dedicated network for communication between the base stations or via a backbone network. In addition, the base station A 210 and the base station B 220 broadcast their PMI patterns as well as PMI patterns of neighboring base stations to terminals in their cells.

At the same time, the terminals 215-1 to 215-5 and 225-1 to 225-4 estimate the sub-band channel matrix with the serving base station and the sub-band channel matrix with the neighboring base station. Pilot signals are used for the estimation of the channel matrix. In general, base stations adjacent to each other transmit pilot signals through resources at different locations, or multiply the pilot signals with different scrambling codes. Accordingly, the terminals 215-1 to 215-5 and 225-1 to 225-4 can distinguish pilot signals of a serving base station and pilot signals of an adjacent base station, thereby estimating a channel matrix of each base station. can do.

The terminals 215-1 to 215-5 and 225-1 to 225-4, which estimate the channel matrix with the serving base station and the channel matrix with the neighboring base station, predict the effective channel gain for each subband. In this case, since the PMI pattern received from the serving base station is a PMI pattern that will not be used, the terminals 215-1 to 215-5 and 225-1 to 225-4 use the received PMI pattern to obtain an effective channel gain. Unpredictable Accordingly, the terminals 215-1 to 215-5 and 225-1 to 225-4 have a precoding vector maximizing an average channel quality among the remaining precoding vectors except for the precoding vector included in the received PMI pattern. Next, predict the effective channel gain when the selected precoding vector is used. In this case, the effective channel gain for the serving base station is the reception strength of the desired signal, and the effective channel gain for the neighboring base station is the interference strength. Subsequently, the terminals 215-1 to 215-5 and 225-1 to 225-4 calculate channel quality for each subband such as SINR and CINR using the reception strength of the desired signal and the strength of the interference. The PMI of the at least one subband and the PMI of the selected precoding vector, that is, the preferred PMI, are fed back to the serving base station.

In addition, the terminals 215-1 to 215-5 and 225-1 to 225-4 calculate a PMI pattern likelihood for the PMI patterns of the current serving base station and the neighboring base station. For example, the PMI pattern likelihood is calculated using PMI or calculated using channel quality.

For example, in the case of using the PMI, the terminal A1 215-1 calculates a worst PMI that maximizes interference in each subband using a channel matrix for each subband with the base station B 220. do. That is, the terminal A1 215-1 selects the worst PMI by multiplying the available PMIs sequentially with the channel matrix of each subchannel and comparing the result of the multiplication, or by using a prepared algorithm to maximize the interference. After calculating the PMI, the worst PMI most similar to the maximum interference PMI is selected. The terminal A1 215-1 calculates the PMI pattern likelihood based on a matching ratio between the worst PMI for each subband and the PMI for each subband of the base station B 220. In other words, the higher the matching ratio, the higher the PMI pattern likelihood. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality.

As another example of using the PMI, the terminal A1 215-1 uses a channel matrix for each subband with the base station B 220 to obtain a most favored PMI for minimizing interference in each subband. Calculate. That is, the terminal A1 215-1 selects the best PMI by multiplying the available PMIs sequentially with the channel matrix of each subchannel and comparing the result of the multiplication, or by using the algorithm prepared in advance. Is calculated and then the best PMI that is most similar to the optimal PMI is selected. The terminal A1 215-1 calculates the PMI pattern likelihood based on a matching ratio between the best-numbered PMI for each subband and the PMI for each subband of the base station B 220. In other words, the higher the matching ratio, the lower the PMI pattern likelihood. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality.

For example, in the case of using the channel quality, the terminal A1 215-1 is the channel quality when the base stations 210 and 220 do not use the PMI pattern and the base stations 210 and 220 are PMI. The channel quality in the case of using a pattern is calculated. The terminal A1 215-1 calculates the difference between the channel qualities of the two cases, thereby calculating the PMI pattern favorability. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality.

The PMI pattern likelihood is calculated for each subband. However, in order to reduce the amount of feedback information, the terminals 215-1 to 215-5 and 225-1 to 225-4 may combine the PMI pattern favorability of a plurality of subbands into one value. For example, the terminals 215-1 to 215-5 and 225-1 to 225-4 add up, average, or add weights based on a specific criterion, and then add up, or The weights are averaged according to specific criteria. Alternatively, the terminals 215-1 to 215-5 and 225-1 to 225-4 may group a plurality of subbands into a plurality of groups, and then combine the PMI pattern similarities for each group.

The base stations 210 and 220, which have received the channel quality and the PMI pattern likelihood feedback from the terminals 215-1 to 215-5 and 225-1 to 225-4, may select precoding vectors to be used in each subband. Decide That is, the base stations 210 and 220 allocate each subband to the terminals 215-1 to 215-5 and 225-1 to 225-4. In this case, since the terminals 215-1 to 215-5 and 225-1 to 225-4 feed back the preferred PMI for each subband, precoding vectors to be used in each subband are allocated due to the allocation of the subbands. Is determined. The base stations 210 and 220 perform downlink communication according to the allocation result of the subbands.

In addition, the base stations 210 and 220 calculate the overall likelihood of the UEs in the cell for the PMI pattern using the PMI pattern likelihood. For example, the base stations 210 and 220 calculate the overall likelihood by summing or averaging PMI pattern likelihoods from the terminals 215-1 to 215-5 and 225-1 to 225-4. do. If the overall likelihood is less than or equal to a threshold, the base stations 210 perform PMI pattern switching. For example, in the case of the base station A 110, the base station A 110 arbitrarily changes its PMI pattern and informs the neighbor base stations of the changed PMI pattern. Alternatively, the base station A 110 requests the PMI pattern switching to the adjacent base station which has the greatest influence on the deterioration of the overall likelihood. Accordingly, the neighboring base station, which has been requested to switch the PMI pattern, arbitrarily changes its PMI pattern and informs the neighboring base stations of the changed PMI pattern. Accordingly, in the subsequent downlink communication, the PMI pattern reflecting the PMI pattern favorability calculated according to the above-described process is used.

In the cell interference cancellation process according to the above-described two embodiments, the PMI pattern broadcasted by the base stations includes one PMI per subchannel. However, according to another embodiment of the present invention, the PMI pattern may include a plurality of PMIs for each subchannel.

The present invention will be described in detail with reference to the drawings the operation and configuration of the base station and the terminal for removing interference in the above-described manner.

3 is a flowchart illustrating an operation procedure of a base station in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the base station exchanges a PMI pattern with neighbor base stations in step 303. That is, the base station transmits its own PMI pattern information to neighboring base stations, and receives the PMI pattern information of the base stations. In this case, according to the first embodiment of the present invention, the PMI pattern includes sub-band PMIs used by each base station. According to the second embodiment of the present invention, the PMI pattern is not used by each base station. It consists of subband-specific PMIs. Here, the PMI pattern includes one or more PMIs per subband.

After exchanging the PMI pattern, the base station proceeds to step 303 and broadcasts its own PMI pattern and PMI patterns of neighboring base stations to terminals in the cell.

After broadcasting the PMI patterns, the base station proceeds to step 305 to transmit a pilot signal. Here, the pilot signal is transmitted together with the data signal in downlink communication or separately for channel estimation.

After transmitting the pilot signal, the base station proceeds to step 307 to determine whether the channel quality and PMI pattern likelihood information is received from the terminals. According to the second embodiment of the present invention, the channel quality and the PMI pattern likelihood information as well as the preferred PMI of the subband corresponding to the channel quality are also received. Here, the PMI pattern likelihood information may be PMI pattern likelihoods for each subband, or PMI pattern likelihoods for each subband for some subbands. In addition, the PMI pattern likelihood information may be a sum of PMI pattern likelihoods, an average of PMI pattern likelihoods, or PMI pattern likelihoods for each group.

When the channel quality and the PMI pattern likelihood information are received, the base station proceeds to step 309 to allocate downlink resources and performs downlink communication. In other words, the base station allocates each subband to the terminals based on the channel quality, and performs downlink communication according to the allocation result. In this case, according to the first embodiment of the present invention, the base station applies a precoding vector in each subband according to the PMI pattern transmitted in step 301. On the other hand, according to the second embodiment of the present invention, the base station applies the preferred PMI of the terminal allocated to each subband to each subband.

Subsequently, the base station proceeds to step 311 to calculate a comprehensive likelihood, and compares the comprehensive likelihood with a threshold. That is, the base station calculates the overall likelihood of the terminals in the cell for the PMI pattern using the PMI pattern likelihood information received from the terminals. For example, the base station calculates the overall likelihood by summing or averaging the PMI pattern likelihoods of the terminals. If the overall likelihood is greater than the threshold, the base station terminates this procedure.

On the other hand, if the combined likelihood is less than or equal to the threshold, the base station proceeds to step 313 to perform a PMI pattern switching procedure. For example, the base station changes its PMI pattern according to a preset rule or arbitrarily changes its PMI pattern. Alternatively, the base station requests PMI pattern switching to the neighboring base station that has the greatest influence on the deterioration of the overall likelihood. Alternatively, the base station requests PMI pattern switching to the neighboring base station that has the greatest influence on the deterioration of the overall favorability while changing its PMI pattern.

4 is a flowchart illustrating an operation procedure of a terminal in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the terminal determines whether PMI patterns are received from the base station in step 401. The PMI patterns include a PMI pattern of a serving base station and PMI patterns of neighboring base stations. In this case, according to the first embodiment of the present invention, the PMI pattern includes sub-band PMIs used by each base station. According to the second embodiment of the present invention, the PMI pattern is not used by each base station. It consists of subband-specific PMIs. Here, the PMI pattern includes one or more PMIs per subband.

When the PMI patterns are received, the terminal proceeds to step 403 to estimate a downlink channel matrix between the serving base station and the neighbor base stations. In other words, the terminal estimates a downlink channel per subband with the serving base station using the pilot signal from the serving base station, and subbands with the neighbor base stations using the pilot signal from the neighbor base stations. The star downlink channel matrix is estimated.

After estimating the downlink channel matrix, the terminal proceeds to step 405 to calculate channel quality for each subband. Here, the channel quality is the channel quality when the precoding vector is applied. In detail, according to the first embodiment of the present invention, the terminal uses the sub-band effective channel gains for the serving base station and the sub-band effective channel gains for each of the neighbor base stations using the PMI patterns. Predict. The terminal calculates channel quality for each subband using the effective channel gains. In contrast, according to the second embodiment of the present invention, the terminal prefers the serving base station and the neighbor base stations to maximize the average channel quality among the remaining precoding vectors except for the precoding vector included in the received PMI patterns. Select PMIs and predict the effective channel gain when the base stations use the preferred PMIs. The terminal calculates channel quality for each subband using the effective channel gains.

After calculating the channel quality, the terminal proceeds to step 407 to calculate the PMI pattern favorability. In this case, the terminal uses PMI or the channel quality to calculate the PMI pattern attractiveness. For example, when the channel quality is used, the terminal calculates the channel quality when the base stations do not use the PMI pattern and the channel quality when the base stations use the PMI pattern. By calculating the difference between the two, the PMI pattern favorability is calculated. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper part having the excellent channel quality. For example, in the case of using the PMI, the UE calculates the best PMI for minimizing interference in each subband by using a subband-specific channel matrix with neighboring base stations, and calculates the best PMI for each subband and the neighbor base stations. Based on the coincidence ratio of the PMI for each subband, the PMI pattern favorability is calculated. In this case, according to the first embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood, and according to the second embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood Lowers. Alternatively, the terminal calculates a worst case PMI for maximizing interference in each subband using a subband-specific channel matrix with neighboring base stations, and matches the worst case PMI for each subband with the subband PMI of the neighboring base stations. Based on the ratio, the PMI pattern likelihood is calculated. In this case, according to the first embodiment of the present invention, the higher the match ratio, the lower the PMI pattern likelihood, and according to the second embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood Becomes higher.

Subsequently, the terminal proceeds to step 409 and feeds back the channel quality calculated in step 405 and the PMI pattern favorable feeling calculated in step 407 to the serving base station. If, according to the second embodiment of the present invention, the terminal additionally feeds back the preferred PMI determined in step 407. Here, the PMI pattern favorability is calculated for each subband. However, in order to reduce the amount of feedback information, the terminal may combine the PMI pattern favorability of the plurality of subbands into one value. For example, the UE sums, averages, or adds weights according to a specific criterion, or adds and averages a plurality of PMI pattern favorable feelings. Alternatively, the terminal may group a plurality of subbands into a plurality of groups, and then combine PMI pattern preferences for each group.

After feeding back the channel quality and the PMI pattern likelihood information, the terminal proceeds to step 411 to perform downlink communication. That is, the terminal checks the resource allocation result performed by the base station and restores downlink data from the signal received through the allocated resource.

5 is a block diagram of a base station in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the base station includes a base station communication unit 502, a feedback information analyzer 504, a PMI determiner 506, a scheduler 508, a message generator 510, a data buffer 512, a plurality of Encoders 514-1 through 514-N, multiple symbol modulators 516-1 through 516-N, precoder 518, pilot generator 520, multiple subcarrier mappers 522-1 through 522 -N), a plurality of OFDM modulators 524-1 to 524-N, and a plurality of radio frequency (RF) transmitters 526-1 to 526-N.

The base station communicator 502 provides an interface for performing communication with adjacent base stations. That is, the base station communication unit 502 converts between bit strings and physical signals according to signal standards and protocols for communication between base stations. In particular, the base station 502 transmits the PMI pattern provided from the PMI determiner 506 to neighboring base stations, and provides the PMI patterns received from the neighbor base stations to the PMI determiner 506. In this case, according to the first embodiment of the present invention, the PMI pattern is composed of PMIs for each subband to be used, and in accordance with the second embodiment of the present invention, the PMI pattern is PMIs for each subband not to be used. It consists of. Here, the PMI pattern includes one or more PMIs per subband.

The feedback information interpreter 504 checks the information fed back from the terminal. That is, the feedback information parser 504 converts a signal representing the feedback information into an information bit string according to a predetermined feedback scheme. For example, when a codeword based feedback scheme is applied, the feedback information analyzer 504 identifies a codeword transmitted through a correlation operation between a signal received through a feedback channel and available codewords, Check the feedback information corresponding to the codeword. The feedback information parser 504 provides the confirmed feedback information to the PMI determiner 506 and the scheduler 508. Here, the feedback information includes at least one of PMI pattern likelihood information, channel quality information, and preferred PMI information of the terminal. Here, the PMI pattern likelihood information may be PMI pattern likelihoods for each subband, or PMI pattern likelihoods for each subband for some subbands. In addition, the PMI pattern likelihood information may be a sum of PMI pattern likelihoods, an average of PMI pattern likelihoods, or PMI pattern likelihoods for each group.

The PMI determiner 506 determines a PMI pattern to be used for downlink communication or a PMI pattern not to be used. That is, according to the first embodiment of the present invention, the PMI determiner 506 determines the PMI pattern to use, and according to the second embodiment of the present invention, the PMI determiner 506 will not use the PMI. Determine the pattern. In addition, the PMI determiner 506 provides a precoding vector for each subband to be used for precoding a downlink signal to the precoder 518. In this case, according to the first embodiment of the present invention, the PMI determiner 506 provides the precoding vectors constituting the PMI pattern to the precoder 518. On the other hand, according to the second embodiment of the present invention, the PMI determiner 506 includes the precoding vectors indicated by the preferred PMI of the UE allocated to each subband according to the resource allocation result of the scheduler 508. Precoder 518 is provided.

The PMI determiner 506 calculates a comprehensive likelihood using the PMI pattern likelihood information of the terminals provided from the feedback information interpreter 504, and compares the comprehensive likelihood with a threshold. For example, the PMI determiner 506 calculates the overall likelihood by summing or averaging PMI pattern likelihoods of the terminals. If the overall likelihood is greater than the threshold, the PMI determiner 506 maintains the current PMI pattern. On the other hand, if the overall likelihood is less than or equal to the threshold, the PMI determiner 506 performs a PMI pattern switching procedure. For example, the PMI determiner 506 changes the PMI pattern according to a preset rule, or optionally changes the PMI pattern. Alternatively, the PMI determiner 506 requests the PMI pattern switching to the adjacent base station which has the greatest influence on the deterioration of the overall likelihood through the base station communication unit 502. Alternatively, the PMI determiner 506 requests the PMI pattern switching to the neighboring base station which has the greatest influence on the deterioration of the overall likelihood while changing its PMI pattern. In addition, when a PMI pattern switching is requested from an adjacent base station, the PMI determiner 506 changes the PMI phantom.

The scheduler 508 allocates resources to the terminals. In other words, the scheduler 508 determines which terminal is allocated to which subband based on the channel quality of the terminals identified by the feedback information checker 504. The message generator 510 generates a control message to be transmitted to the terminal. For example, the message generator 510 generates a map message for notifying the resource allocation result of the scheduler 508. In particular, the message generator 510 generates a message for broadcasting the PMI patterns provided from the PMI determiner 506. The data buffer 512 temporarily stores data to be transmitted to the terminal, and outputs the stored data when the transmission time point arrives.

Each of the plurality of encoders 514-1 to 514 -N encodes a data bit string provided from the data buffer 512. Each of the plurality of symbol modulators 516-1 to 516-N converts the encoded bit stream into complex symbols. The precoder 518 performs precoding to remove intercell interference. That is, the precoder 518 precodes the transmission signals using the subband precoding vector provided from the PMI determiner 506. The pilot generator 520 generates pilot signals and provides the pilot signals to the plurality of subcarrier mappers 522-1 through 522-N. In this case, when pilot signals are scrambled, the pilot generator 520 multiplies a pilot signal sequence by a scrambling code, and then pilot signals multiplied by a scrambling code to the plurality of subcarrier mappers 522-1 through 522-N. to provide.

Each of the plurality of subcarrier mappers 522-1 through 522 -N configures signals in a frequency domain by mapping transmission signals and pilot signals of a transmission path corresponding to itself among the precoded transmission signals to subcarriers. . Each of the plurality of OFDM modulators 524-1 to 524 -N converts signals in a frequency domain into signals in a time domain through an inverse fast fourier transform (IFFT) operation, and then inserts a cyclic prefix (CP). Construct baseband OFDM symbols. Each of the plurality of RF transmitters 526-1 through 526 -N converts the baseband OFDM symbols into a signal of an RF band and then transmits the signals through an antenna.

6 is a block diagram of a terminal in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 6, the terminal includes a plurality of RF receivers 602-1 to 602-N, a plurality of OFDM demodulators 604-1 to 604-N, and a plurality of subcarrier dimappers ( 606-1 through 606-N), a plurality of symbol demodulators 608-1 through 608-N, a plurality of decoders 610-1 through 610-N, a data buffer 612, a message interpreter 614 , Channel estimator 616, channel quality calculator 618, affinity calculator 620, feedback information generator 622, and feedback transmitter 624.

Each of the plurality of RF receivers 602-1 through 602-N converts an RF band signal received through an antenna into a baseband signal. Each of the plurality of OFDM demodulators 604-1 through 604-N divides the baseband signal into OFDM symbol units, removes a CP, and then complex symbols mapped to a frequency domain through a fast fourier transform (FFT) operation. Restore them. Each of the plurality of symbol demodulators 608-1 through 608 -N converts the complex symbols into an encoded bit string by demodulating the complex symbols. Each of the plurality of decoders 610-1 through 610 -N decodes the encoded bit string. The data buffer 612 temporarily stores the information bit string decoded by the plurality of decoders 610-1 through 610 -N. The message interpreter 612 confirms the information included in the control message by interpreting the control message received from the base station. In particular, the message interpreter 612 identifies the PMI patterns of the serving base station and neighboring base stations via a control message.

The channel estimator 616 estimates a channel matrix with a serving base station and neighboring base stations using pilot signals provided from the plurality of subcarrier demappers 606-1 through 606-N. In other words, the channel estimator 616 estimates a downlink channel for each subband with the serving base station using the pilot signal from the serving base station, and uses the pilot signals from the neighbor base stations to determine the adjacent base stations. Estimate the downlink channel matrix for each subband of and.

The channel quality calculator 618 calculates channel quality for each subband. Here, the channel quality is the channel quality when the precoding vector is applied. In detail, according to the first embodiment of the present invention, the channel quality calculator 618 uses the PMI patterns identified by the message interpreter 614 to obtain the effective channel gain for each subband for the serving base station. And estimate effective channel gains for each subband for each of the neighbor base stations. The channel quality calculator 618 calculates channel quality for each subband using the effective channel gains. On the other hand, according to the second embodiment of the present invention, the channel quality calculator 618 is an average of the remaining precoding vectors except for the precoding vector included in the PMI patterns identified by the message interpreter 614. Select preferred PMIs for serving base station and neighbor base stations that maximize channel quality, and estimate the effective channel gain when the base stations use the preferred PMIs. The channel quality calculator 618 calculates channel quality for each subband using the effective channel gains.

The likelihood calculator 620 calculates a PMI pattern likelihood. In this case, the likelihood calculator 620 uses PMI for calculating the PMI pattern likelihood or uses channel quality. For example, in the case of using the channel quality, the favorability calculator 620 calculates the channel quality when the base stations do not use the PMI pattern and the channel quality when the base stations use the PMI pattern. By calculating the difference between the channel qualities of the PMI pattern favorability. In this case, the PMI pattern favorability may be calculated for the entire subbands or only the subbands of the upper portion having excellent channel quality. For example, in the case of using the PMI, the likelihood calculator 620 calculates the best PMI for minimizing interference in each subband using a channel matrix for each subband with neighboring base stations, and the best PMI for each subband. And the PMI pattern likelihood is calculated based on a matching ratio between PMIs of subbands of adjacent base stations. In this case, according to the first embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood, and according to the second embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood Lowers. Alternatively, the likelihood calculator 620 calculates the worst PMI for maximizing interference in each subband using subband-specific channel matrices with neighboring base stations, and calculates the worst PMI for each subband and sub-bands of the neighboring base stations. Based on the coincidence ratio of the band-specific PMIs, the PMI pattern favorability is calculated. In this case, according to the first embodiment of the present invention, the higher the match ratio, the lower the PMI pattern likelihood, and according to the second embodiment of the present invention, the higher the match ratio, the higher the PMI pattern likelihood Becomes higher.

The feedback information generator 622 generates information to be fed back to the base station. According to the first embodiment of the present invention, the feedback information generator 622 includes feedback including the channel quality provided from the channel quality calculator 618 and the PMI pattern likelihood provided from the likelihood calculator 620. Generate information. On the other hand, according to the second embodiment of the present invention, the feedback information generator 622 is the channel quality and preference PMI provided from the channel quality calculator 618 and the PMI pattern provided from the likelihood calculator 620. Generate feedback information including the likelihood. Here, the PMI pattern favorability is calculated for each subband. However, in order to reduce the amount of feedback information, the feedback information generator 622 may combine the PMI pattern likelihoods of the plurality of subbands into one value. For example, the feedback information generator 622 sums, averages, or weights a plurality of PMI pattern favours, adds them according to a specific criterion, or adds them, or weights them according to a specific criterion and averages them. Alternatively, the feedback information generator 622 may group a plurality of subbands into a plurality of groups, and then combine PMI pattern likelihoods for each group.

The feedback transmitter 624 transmits the feedback information generated by the feedback information generator 622 to the base station. That is, the feedback transmitter 624 converts the cooperative interference cancellation related information into a physical signal and transmits it through an antenna. For example, when a codeword based feedback scheme is applied, the feedback transmitter 624 identifies a codeword corresponding to the feedback information, converts the identified codeword into a physical signal, and then, through a feedback channel. Send.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

1 is a view schematically showing the generation of inter-cell interference in a wireless communication system,

2 is a diagram illustrating an example of a terminal distribution in a multiple input / output wireless communication system according to the present invention;

3 is a flowchart illustrating an operation procedure of a base station in a multiple input / output wireless communication system according to an embodiment of the present invention;

4 is a diagram illustrating an operation procedure of a terminal in a multiple input / output wireless communication system according to an embodiment of the present invention;

5 is a block diagram of a base station in a multiple input / output wireless communication system according to an embodiment of the present invention;

6 is a block diagram of a terminal in a multiple input / output wireless communication system according to an embodiment of the present invention;

Claims (4)

A method of operating a base station in a multiple input / output wireless communication system, Broadcasting a PMI pattern of the UE and a PMI pattern of at least one neighboring base station to the UEs; Confirming feedback information including at least one of a PMI pattern likelihood, channel quality, and a preferred PMI from the terminals; Calculating a comprehensive likelihood of the terminals with respect to the PMI pattern using the PMI pattern likelihood; And if the overall likelihood is less than or equal to a threshold, performing a PMI pattern switching procedure. A method of operating a terminal in a multiple input / output wireless communication system, Receiving PMI pattern information of the serving base station and PMI pattern information of at least one neighboring base station; Calculating a channel quality for each subband using a PMI pattern of the serving base station and a PMI pattern of the at least one neighboring base station; Calculating a PMI pattern likelihood using at least one of the PMI pattern and the channel quality; And transmitting feedback information including the channel quality and the PMI pattern likelihood to the serving base station. A base station apparatus in a multiple input / output wireless communication system, A transmitter for broadcasting its PMI pattern and PMI pattern of at least one neighboring base station to terminals; An interpreter for confirming feedback information including at least one of a PMI pattern favorability, a channel quality, and a preferred PMI from the terminals; Comprising a PMI pattern likelihood fed back from the terminal to calculate the overall good feeling of the terminals for the PMI pattern, and if the overall likelihood is less than or equal to a threshold, characterized in that it comprises a determiner for performing a PMI pattern switching procedure Device. A terminal device in a multiple input / output wireless communication system, A receiver for receiving PMI pattern information of a serving base station and PMI pattern information of at least one neighboring base station; A channel quality calculator for calculating channel quality for each subband using a PMI pattern of the serving base station and a PMI pattern of the at least one neighboring base station; A favorability calculator for calculating a PMI pattern likelihood using at least one of the PMI pattern and the channel quality; And a transmitter for transmitting feedback information including the channel quality and the PMI pattern likelihood to the serving base station.

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