KR20060092400A - System and method for allocation resource based on channel state information feedback in a mimo-ofdma communication system - Google Patents

Abstract

 The present invention relates to an orthogonal frequency division multiplexing communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmitting antennas and a plurality of receiving antennas. And dividing the entire frequency band into a plurality of sub-channels, wherein the plurality of sub-channels are preset such that a plurality of logical groups consisting of a preset number of sub-channels are assembled. And feeding back channel information to be used by the unit to the base station.

 Multiple inputs Multiple outputs, feedback, channel status information, subchannels

Description

 Channel status information feedback and resource allocation system and method using the same in MIMO-OPEMMA communication system {SYSTEM AND METHOD FOR ALLOCATION RESOURCE BASED ON CHANNEL STATE INFORMATION FEEDBACK IN A MIMO-OFDMA COMMUNICATION SYSTEM}

 1A and 1B schematically illustrate a structure of a transmitter / receiver in a general MIMO-OFDM communication system.

2 is a view schematically showing a receiving end structure according to a first embodiment of the present invention;

3 is a diagram illustrating grouping and average SNR calculation of an SBA-GS scheme according to a first embodiment of the present invention.

4 is a diagram illustrating performing bit allocation on a grouped sub-channel basis according to the first embodiment of the present invention.

5 is a flowchart illustrating an operation of a receiving end using the SBA-GS scheme according to the first embodiment of the present invention.

6 is a flowchart illustrating an operation of a transmitting end using the SBA-GS scheme according to the first embodiment of the present invention.

7A and 7B are graphs showing bit error rate performance using the SBA-GS scheme according to the first embodiment of the present invention.

8A to 8B schematically illustrate a structure of a transmitting and receiving end using an SRA scheme according to a second embodiment of the present invention.

9A and 9B are diagrams illustrating a process of performing resource allocation by applying an SRA scheme according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a result of resource allocation completed by a transmitter according to a second embodiment of the present invention. FIG.

11 is a diagram illustrating an error propagation phenomenon when the SRA technique according to the second embodiment of the present invention is applied.

12 is a flowchart illustrating an operation performed by a transmitter using an SRA scheme according to a second embodiment of the present invention.

FIG. 13 is a diagram schematically illustrating a structure of a transmitting and receiving end using a modified SRA scheme according to a third embodiment of the present invention.

14A to 14D are diagrams illustrating a resource allocation procedure using a modified SRA scheme according to a third embodiment of the present invention.

15 is a flowchart illustrating an operation performed by a transmitting end using a modified SRA scheme according to a third embodiment of the present invention.

16A and 16B are graphs comparing the system performance efficiency between the modified SRA technique and the SRA technique.

 The present invention relates to a communication system using a multiple input multiple output (Orthogonal Frequency Division Multiplexing) method (hereinafter referred to as 'MIMO-OFDM communication system'), in particular The present invention relates to a system and a method for performing resource allocation using channel state information fed back at a receiving end.

Current wireless mobile communication systems are actively being implemented or researched for the purpose of multimedia services of high quality, high speed, and large data transmission. Unlike the wired channel environment, the wireless channel environment exists in such a wireless mobile communication system due to various factors such as multipath interference, shadowing, propagation attenuation, time-varying noise and interference. A signal distorted in the transmission signal is received. Here, the fading due to the multipath interference is closely related to the mobility of the reflector or the user, that is, the user terminal, and is received in a form in which the actual transmission signal and the interference signal are mixed.

Thus, the received signal becomes a form that is severely distorted in the actual transmission signal to act as a factor that degrades the performance of the entire mobile communication system. As a result, the fading phenomenon may distort the amplitude and phase of the received signal, which is a major cause of disturbing high-speed data communication in a wireless channel environment, and many studies have been conducted to solve the fading phenomenon. It is becoming. As a result, in order to transmit data at a high speed in a mobile communication system, loss due to characteristics of a mobile communication channel such as fading and user-specific interference should be minimized. One of the techniques proposed to solve this problem is a multiple input multiple output (hereinafter referred to as 'MIMO') technique.

The MIMO technology is classified into an open loop method and a closed loop method according to whether channel state information (hereinafter, referred to as “CSI”) feedback.

First, there is a singular value decomposition (SVD: SVD) method as a closed loop method. The SVD scheme can theoretically achieve optimal performance, but the receiver has to feed back all channel values to the transmitter.

Next, in the open loop scheme, a space time block code (STBC) technique according to a data transmission scheme, and a blast (BLAST: Bell Labs Layered Space-Time (BLAST) technique) are used. And the layered STBC (Layered STBC) technique.

Here, the BLAST scheme has a high data transmission efficiency but no diversity gain, resulting in performance degradation, and there is a constraint that the number of receiving antennas must be greater than or equal to the number of transmitting antennas. In order to make up for the shortcomings of the BLAST technique, there is a V-BLAST (Vertical-BLAST) technique developed by Bell Laboratories of Lucent Technologies.

The V-BLAST technique is a method of greatly improving the data transmission speed by transmitting different signals for each Tx antenna without requiring complicated encoding at the transmitting end. More specifically, in the V-BLAST scheme, data streams are independently encoded and transmitted through different transmit antennas. The receiver performs ordered successive interference cancellation (OSIC) to remove interference between signals received through the different antennas.

The MIMO communication system using the V-BLAST scheme is called Orthogonal Frequency Division Multiplexing (OFDM) using multiple subcarriers to increase frequency efficiency and efficiently cope with a multipath fading channel. Or in combination with an OFDMA scheme, a MIMO-OFDM or MIMO-OFDMA communication system.

1A and 1B schematically illustrate a structure of a transmitting / receiving end of a general MIMO-OFDM communication system.

Referring to FIGS. 1A and 1B, first, a transmitter in FIG. 1A is a channel encoder 102, a modulator 104, a serial to parallel converter (hereinafter referred to as 'S / P'). 106), Inverse Fast Fourier Transform (hereinafter referred to as IFFT) 108, 110, Parallel to Serial Converter (P / S) 112, 114, and guard interval inserters 116, 118.

In FIG. 1B, the receiving end of the guard interval removers 168 and 170, the S / Ps 168 and 170, the Fast Fourier Transform (hereinafter referred to as 'FFT') (160 and 162), V A BLAST detector 158, a P / S 156, a demodulator 154, and a channel decoder 152.

Next, a process of transmitting a signal from a transmitter to a receiver will be described.

First, when user data bits and control data bits to be transmitted are generated, the user data bits and the control data bits are input to the channel encoder 102. Here, the user data bits and the control data bits will be referred to as 'information data bits'. The channel encoder 102 inputs the information data bits, codes them according to a preset coding scheme, and outputs them to the modulator 104.

The modulator 104 modulates the coded bits output from the channel encoder 102 by a predetermined set modulation scheme and outputs them to the S / P 106. The modulation scheme may be a quadrature phase shift keying (QPSK) scheme or a quadrature amplitude modulation (16QAM) scheme. The S / P 106 inputs and converts the modulation symbols in parallel and outputs them to the IFFT units 108 and 110.

The IFFT groups (108, 110) is N _c a signal output from the S / P (106) - to the output point (N _c -point) after performing the IFFT of said P / S (112, 114) do. The P / Ss 112 and 114 input and output the signals output from the IFFT devices 108 and 110 and output them to the guard period inserters 116 and 118. The guard interval inserters 116 and 118 insert a guard interval into a signal output from the P / S 112 and 114 and then M transmit antennas (Ant # 1 to Ant #M). Transmit over a wireless channel via.

The guard interval removers 168 and 170 of the receiver, which have received a signal through the wireless channel from the transmitter, remove the inserted guard interval and output the removed guard interval to the S / Ps 164 and 166. The S / Ps 164 and 166 input a signal in which the guard interval is removed, convert the signals in parallel, and output them to the FFT units 160 and 162. The FF T groups 160 and 162 input the parallel-converted signal to perform an FFT and output to the V-BLAST detector 158. The V-BLAST detector 158 performs V-BLAST detection on each subcarrier and outputs it to the P / S 156. The P / S 156 serially converts the V-BLAST detection signal and outputs the demodulated signal to the demodulator 154. The demodulator 154 demodulates the signal in a demodulation scheme corresponding to the modulation scheme performed by the modulator 104 of the transmitting end and outputs the signal to the channel decoder 152. The channel decoder 152 decodes the signal by a decoding method corresponding to the coding method performed by the channel encoder 102 and outputs information data bits.

Meanwhile, as described above, the V-BLAST scheme, which is one of the BLAST schemes, has an open loop shape that does not require CSI feedback from the receiver to the transmitter. However, several methods have been proposed to feed back CSI from the receiver to the transmitter to improve system performance. One of the proposed methods is an adaptive bit and power allocation (hereinafter referred to as 'ABPA') method.

비트가 필요하고, 전력 할당 피드백 정보는

비트가 추가로 필요하다.The ABPA method is a method in which a receiver of a MIMO-OFDMA communication system determines various modulation schemes (ie, number of allocated bits) and power for each subchannel according to a channel state and feeds back to a transmitter. The ABPA method shows almost optimal performance in terms of bit error rate performance, but has a disadvantage in that a large amount of information is fed back from a receiving end to a transmitting end, and an amount of computation for bit and power allocation is excessive. Therefore, it is impossible to apply to the actual channel environment considering the feedback delay. In the ABPA method, when the number of modulation schemes applicable to each subchannel is S, the power allocation quantization level is Q, the number of subcarriers is N _{c '} , and the number of transmitting antennas is M, the bit allocation feedback information is

Bits are required, and power allocation feedback information

An additional bit is needed.

비트의 정보를 송신단으로 피드백한다. 예컨대, 상기 수신단은 사용하고자 하는 서브 채널의 경우 '1'로, 사용하지 않으려는 서브 채널의 경우 '0'으로 명시하여 송신단으로 피드백한다.Accordingly, what is proposed to compensate for the shortcomings of the ABPA method is the Simplified Bit Allocation (SBA) method. The SBA method allocates the same number of bits to only some channels having excellent channel characteristics, thereby reducing the amount of feedback information from the receiving end to the transmitting end and the amount of computation for bit allocation. For a more detailed description, consider a general MIMO-OFDM communication system using N _c subcarriers and M transmit antennas. The SBA method does not transmit data through poor subchannels. Therefore, the receiving end determines whether or not to use a subchannel for data transmission, and 1 bit for each subchannel, that is, the total

Feedback the bit information to the transmitter. For example, the receiving end feeds back to the transmitting end by specifying '1' for the subchannel to be used and '0' for the subchannel not to be used.

Therefore, to increase the modulation order of the system (the number of bits to be allocated that is, each sub-channel) to decrease the available sub-channels can compensate in order to transmit one and the same R _b bits and typical MIMO-OFDM communication system for the OFDM symbol time do. Assuming that the increased number of additional bits is ΔK, B ≡ K + ΔK bits should be allocated to each subchannel. Therefore, the number D _SBA of subchannels to which bits are allocated is determined by Equation 1 below.

비트만큼 수신단에서 송신단으로 피드백한다.That is, as shown in Equation 1, the SBA is

It feeds back a bit from the receiving end to the transmitting end.

Meanwhile, the SBA method is a resource allocation algorithm for a single user. Therefore, it is impossible to apply to a MIMO-OFDMA communication system in which a plurality of user equipments exist. In addition, the SBA method is more efficient in the amount of information and calculation amount fed back than the conventional ABPA method in the MIMO-OFDM system for a single user, but the SBA method is applied to the MIMO-OFDMA communication system in which a plurality of user terminals exist. In this case, collisions between subchannels that each user terminal intends to use may occur. Accordingly, there is a great need for a resource allocation algorithm for efficiently applying the SBA scheme to an environment in which a plurality of user terminals exist.

 The present invention provides a system and method for reducing the amount of channel state information for bit allocation and resource allocation in MIMO-OFDM and MIMO-OFDMA communication systems.

The present invention provides a system and method for efficient resource allocation in a MIMO-OFDM communication system in which only a single user exists and a MIMO-OFDMA communication system in which a plurality of user terminals exist.

The first method of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, a method for feeding back channel state information to a base station by a user terminal includes: The plurality of subchannels are divided into a plurality of subchannels, and the plurality of subchannels are preset so that a plurality of logical groups including a preset number of subchannels are collected and configured, and the user terminal is used by the logical group unit. And feeding back channel information to the base station.

The second method of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme in which a signal is transmitted and received using a plurality of transmitting antennas and a plurality of receiving antennas, a method for performing bit allocation by a user terminal includes: Dividing into sub-channels, and the plurality of sub-channels are pre-configured to form a plurality of logical groups composed of a preset number of sub-channels, and initializing the number of allocated bits of the sub-channels to 0; The method may further include measuring channel states of each of the logical groups and sequentially performing bit allocation from subchannels of logical groups having a good channel state according to the channel state measurement result.

The third method of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system in which multiple user input and output signals are transmitted and received using a plurality of transmit antennas and a plurality of receive antennas, a base station performs resource allocation to transmit a signal. A method comprising: receiving sub-channel state information from each of the user terminals, repeating resource allocation to each of the user terminals in a round robin manner from a sub-channel having a good channel state, and all the sub-allocated sub-channels. And transmitting a signal by applying the same modulation scheme to the channels.

A fourth method of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system in which multiple user input and output signals are transmitted and received using a plurality of transmit antennas and a plurality of receive antennas, a base station performs resource allocation to transmit a signal. In the method, receiving feedback from the plurality of user terminals with candidate subchannel information that the plurality of user terminals want to use, and the user terminals among the candidate subchannels do not collide with each other with reference to the received information. A first process of detecting candidate subchannels not allocated and assigning them to respective user terminals, a second process of detecting candidate subchannels colliding between user terminals among the candidate subchannels, and predetermined collision candidate subchannels; Conflicts between user terminals based on Not assigned claim characterized in that it comprises a fourth step of assigning additional bits for the third process, a user terminal is allocated resources do not meet the data rate to.

The first system of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, a system for transmitting and receiving channel state information, the entire frequency band of a plurality of subchannels The plurality of subchannels are preconfigured so that a plurality of logical groups consisting of a preset number of subchannels are collected and fed back to the base station for channel information to be used by the logical group. And a base station for allocating resources in consideration of channel state information received in units of logical groups from the user terminal.

A second system of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme that transmits and receives a signal using a plurality of transmit antennas and a plurality of receive antennas, a system for performing bit allocation in a plurality of subchannels The plurality of subchannels are preset to be configured by a plurality of logical groups consisting of a preset number of subchannels, and initialize the number of allocated bits of the subchannels to 0, and the logical groups And measuring a channel state and performing bit allocation sequentially from subchannels of logical groups having a good channel state according to the channel state measurement result.

The third system of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using multiple input multiple output schemes for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, and in a system for performing resource allocation to transmit and receive signals In the present invention, a base station exists, calculating a 2-norm value of a weight vector for all subchannels, feeding back a signal to a base station, receiving a signal from the base station, and detecting an original signal using a V-BLAST scheme. In this case, the user terminal is assigned to another user terminal and performs nulling only on a subchannel causing interference with the arbitrary user terminal, and receives subchannel state information from each of the user terminals. Each channel in round robin fashion Repeating the resources allocated to the user terminal, it characterized in that it comprises a base station for transmitting a signal to apply the same modulation scheme in all the sub-channels of the resource allocation.

A fourth system of the present invention for achieving the above objects; In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, and in a resource allocation and signal transmission / reception system, a base station includes Each user terminal detects candidate user sub-channels that exist and do not collide with each other among user terminals among the candidate sub-channels with reference to the feedback information. Assigning to the terminals, detecting candidate subchannels colliding with the user terminals among the candidate subchannels, assigning the collision candidate subchannels so as not to collide with the respective user terminals by a predetermined criterion, and assigning a data rate Allocating Unsatisfactory Resources And a base station for allocating additional bits for the received user terminal.

 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation of the present invention will be described, and other background art will be omitted so as not to distract from the gist of the present invention.

In the present invention, multiple input multiple output-orthogonal frequency division multiplexing (hereinafter referred to as 'MIMO-OFDM') or multiple input multiple output-orthogonal frequency division multiplexing (Multiple Input Multiple Output) In a communication system using an Orthogonal Frequency Division Multiple Access (hereinafter referred to as "MIMO-OFDMA"), the amount of channel state information (hereinafter referred to as "CSI") fed back from a receiver to a transmitter. We propose a way to reduce the In addition, in a multiple input multiple output-orthogonal frequency division multiple access (hereinafter referred to as 'MIMO-OFDMA') communication system in which a plurality of user equipments exist. A new resource allocation algorithm is proposed.

To this end, in the first embodiment of the present invention, a 'simple bit allocation-grouping sub-channel' based on a sub-channel grouped to reduce the amount of CSI and bit allocation calculation amount fed back to the transmitting end by a single user terminal, that is, a receiving terminal (Simplified) Bit Allocation based on Grouped Sub-channels, hereinafter referred to as 'SBA-GS'). In the second embodiment, resource allocation of the multi-user terminals is performed in a MIMO-OFDMA communication system in which multi-user terminals exist. For this purpose, a Simplified Resource Allocation (SRA) scheme is proposed, and in the third embodiment, a modified SRA (modified SRA) scheme is provided. Suggest a solution.

<First Embodiment (SBA-GS)>

Next, the first embodiment SBA-GS will be described with reference to FIG. 2.

2 is a diagram schematically illustrating a receiving end structure according to a first embodiment of the present invention.

Referring to FIG. 2, the receiving end is similar to the receiving end structure shown in FIG. 1B, and has a CSI measuring instrument 222 and a buffer 224. Therefore, the detailed description thereof will be omitted with reference to the description of FIG. 1B, and only the parts related to the present invention will be described in detail. On the other hand, the transmitter structure corresponding to the receiver has the same structure as that of FIG. 1A. That is, the transmitting end plays a role of allocating data symbols to a subchannel to be used by using the CSI fed back by the receiving end according to the first embodiment of the present invention.

Before describing the operation of the receiver of FIG. 2, the SBA-GS scheme according to the first embodiment of the present invention performs grouping of all available subchannels by a predetermined number in advance. The average signal-to-noise ratio (hereinafter referred to as 'SNR') of each subchannel is measured as an average of 2-norm values of weight vectors. In this regard, it will be described using Equation 16 and will be omitted here.

비트인 반면에, 본 발명의 SBA-GS 기법은 (

)/G 비트만큼의 CSI를 피드백하게 되어 피드백하는 CSI의 양이 적어지게 된다. 여기서, 상기 G는 하나의 그룹당 서브 채널 개수를 의미하며, 주어진 채널 환경에 의해 결정되는 코히어런스 주파수 대역폭(Coherence Bandwidth)을 초과하지 않는 범위 내에서 전체 서브 채널 개수 N_c의 약수로 설정됨이 바람직하다. 또한, 상기 M은 송신 안테나 개수를 의미한다.Therefore, the amount of CSI fed back from the receiver to the transmitter by the conventional SBA

Bit, while the SBA-GS scheme of the present invention

The CSI is fed back as much as) / G bits, thereby reducing the amount of CSI fed back. Here, G means the number of subchannels per group, and is set to a divisor of the total number of subchannels N _c within a range not exceeding the coherence frequency bandwidth determined by a given channel environment. desirable. In addition, M means the number of transmit antennas.

Next, the operation of the receiving end will be described.

A vertical-bell labs layered space-time (V-BLAST) detector 208 of the receiving end calculates a 2-norm value of the weight vector of each subchannel and outputs it to the CSI measuring instrument 222. The CSI measurer 222 measures SNR values for subchannels grouped by a preset number for each subchannel, selects groups having relatively good quality subchannels, and selects a bit in each selected group. Allocate At the same time, the receiving end feeds back the CSI indicating usage information of each group to the transmitting end, and stores it in the buffer 224. Thereafter, the V-BLAST detector 208 performs a V-BLAST detection by distinguishing between subchannels to which data symbols are assigned and subchannels to which data symbols are assigned, for a signal received in a next downlink frame reception interval. Can be reduced.

Hereinafter, a method of detecting a signal at a receiving end using a general V-BLAST scheme will be described in detail with reference to the following equations.

은 c번째

서브 캐리어에 대한 k번째

송신 안테나에서

번째

수신 안테나로의 복소 페이딩 채널 계수이며, 그 값이 한 OFDMA 심 벌 간격 동안 변화하지 않는다고 가정할 때 c번째 부반송파에 대한 크기

인 순시 채널 행렬

를 하기 수학식 2와 같이 표현할 수 있다. First, the V-BLAST detector 158 performs V-BLAST detection on each of the subcarriers output from the FFT units 160 and 162 of FIG. 1B. here

Is c

Kth for subcarrier

On the transmit antenna

th

Complex fading channel coefficient to the receiving antenna, the magnitude of which is for the c-th subcarrier, assuming that its value does not change during one OFDMA symbol interval

Instantaneous channel matrix

Can be expressed as in Equation 2 below.

크기의 신호 벡터

를 하기 수학식 3과 같이 정의한다.C subcarriers transmitted through M transmit antennas

Magnitude signal vector

Is defined as in Equation 3 below.

크기의 벡터로 표현할 수 있다. Here, the superscript ^T means Transpose operation. When the transmission signal of Equation 2 passes through the channel represented by Equation 1, the received signal y _c is expressed as Equation 4 below.

It can be expressed as a vector of magnitudes.

는 각 성분이 평균 0, 분산

인 가우시 안 잡음 벡터를 의미한다.In Equation 4 above

Where each component has an average of 0,

Means Gaussian noise vector.

로부터 전송 신호

를 결정하기 위한 ZF (Zero Forcing) 형태의 V-BLAST 검출 방식의 상세 과정은 하기 수학식 5 내지 14와 같다. 먼저 채널 행렬

의 의사역행렬 (Pseudo Inverse Matrix)을 하기 수학식 6과 같이 정의한다.Received signal of Equation 4

Transmission signal from

Detailed process of the V-BLAST detection method of the ZF (Zero Forcing) type to determine the Equation 5 to 14. First channel matrix

The pseudo inverse matrix of is defined as in Equation 6 below.

i = 1

는 무어-펜로즈 일반화 의사 역행렬(Moore-Penrose Generalized Pseudo Inverse Matrix)을 나타낸다. 이와 같이 구해진 c번째 서브 캐리어에 대한 초기 역행렬

로부터 하기 수학식 7을 수행한다. Where superscript

Denotes the Moore-Penrose Generalized Pseudo Inverse Matrix. Initial inverse of the c-th subcarrier thus obtained

The following equation (7) is performed.

는 행렬

의

크기의 j번째 행벡터를 의미한다. In Equation 7,

Is a matrix

of

The j-th row vector of size.

In the V-BLAST detection process, Equations 5 to 7 are processes for setting an initial value for detecting a receiver signal, and then repeats the operations of Equations 8 to 14.

는 수신단에서 전송 심벌

를 검출하기 위해 전송된 신호 성분을 제거하는 순서를 의미한다. 또한, 상기 수학식 8에서 행렬

의 k_i번째 행벡터를 널링 벡터 (Nulling Vector)

로 정의하여, 이를 수신 신호 벡터

에 곱해 수학식 9의

를 구하고, 수학식 10을 이용해 전송 신호 벡터

의 k_i번째 신호 성분에 대한 추정치

를 얻을 수 있다. 여기서

는 이진 결정 함수이다. 한편,

의 k_i번째 신호 성분이 완벽히 추정되었다고 가정한 후 (즉,

), 하기 수학식 11에서와 같이 i번째 단계에서의 수신 신호 벡터

에서 k_i번째 검출된 간 섭 신호 성분을 제거하고 (i+1)번째 단계에서의 연산을 위한 수신 신호 벡터를 결정한다.In Equation 8, i denotes an iteration of the i th operation,

Symbol at the receiving end

It means the order of removing the transmitted signal component in order to detect. Further, the matrix in Equation 8

Nulling the _i-th row vector of the k vector (Nulling Vector)

By defining it as a received signal vector

Multiply by

And transmit signal vector using Equation (10).

Estimate for the k _i th signal component of

Can be obtained. here

Is a binary decision function. Meanwhile,

After assuming that the k _i th signal component of

), The received signal vector at step i as shown in Equation 11 below.

Removes the k _i -th detected interference signal component and determines a received signal vector for operation in the (i + 1) th step.

는 채널 행렬

의 N

1 크기의 k_i번째 열벡터를 의미하고, 상기 수학식 12에서,

은 수학식 11의 연산을 통해 이미 검출된 신호 성분을 제거함으로써

의 k_i번째 열벡터 성분을 모두 0으로 널링한 행렬을 의미한다. 이를 이용하여 나머지 간섭 신호 성분 검출을 위해 상기 수학식 12와 같이 새로운 역행렬을 구성한다. In Equation 11,

Is the channel matrix

N

A k _i th column vector having a size of 1, and in Equation 12,

By removing the signal components already detected through the operation of Equation 11

It means the matrix nulling all k _i th column vector components of. Using this, a new inverse matrix is constructed as shown in Equation 12 to detect the remaining interference signal components.

i = i + 1

In Equation 13, the optimal detection order for the next step is determined using the new inverse matrix obtained using Equation 12 in the same manner as in Equation 7. This process is applied to all subcarriers used to detect the original data from the received signal.

에 대한 검출 후 SNR

는 하기 수학식 15를 이용해 구할 수 있다.Estimated through this V-BLAST detection process

SNR after detection for

Can be obtained using Equation 15 below.

은 기대값 연산을 의미한다. 상기 수학식 15로부터

는

에, 즉 2-norm 값에 비례함을 알 수 있다. 따라서, 수신단은 상기

를 각 서브 채널에 대한 채널 이득(channel gain)으로 간주하여 각 서브 채널들에 대한 가중치 벡터

의 2-norm 값을 통해 채널 특성을 고려한 비트 할당 알고리즘을 수행할 수 있다.In Equation 15,

Means the expected value operation. From Equation 15

Is

In other words, it is proportional to the 2-norm value. Thus, the receiving end

Is a channel gain for each subchannel, so that the weight vector for each subchannel

Through 2-norm of, the bit allocation algorithm considering channel characteristics can be performed.

Meanwhile, the receiver using the SBA-GS scheme according to the first embodiment of the present invention obtains an average SNR as an average of 2-norm values of weight vectors of predetermined groups (that is, groups having a predetermined number of subchannels). Calculate This will be described in detail with reference to FIG. 3 and the following equations.

3 is a diagram illustrating grouping and average SNR calculation of the SBA-GS scheme according to the first embodiment of the present invention.

Referring to FIG. 3, first, the number of subchannels constituting each group and the subchannel grouping accordingly are predetermined in system design. In the case of FIG. 3, three subchannels constitute one group. In general, a subchannel may be referred to as a set of one or more subcarriers. The subchannel of the present invention to be described below is configured with one subcarrier for convenience of description. For each of these groups, the receiver measures the SNR as the average of the 2-norm values of the weight vectors.

That is, the receiver measures the average SNR per group and sequentially allocates the same number of bits from the subchannels of the groups having the larger average SNR value. To this end, a description will be given of the process performed by the receiving end.

를 획득한다. 상기 i=1, m=1로 초기화한다. 여기서, m은 N_c/G로 전체 그룹수를 의미한다. 이후, 하기 수학식 16을 이용해 각 그룹별 평균 SNR을 계산한다.First, the receiver sets the number of bits to be allocated to each subchannel to '0', and then determines the V-BLAST detection order for each subcarrier. Weight vector of all subchannels according to the determined V-BLAST detection order

Acquire. I = 1 and m = 1 are initialized. Here, m is N _c / G, which means the total number of groups. Then, the average SNR for each group is calculated using Equation 16 below.

Here, Equation 16 is repeatedly performed for all groups of all transmission antennas by increasing m by 1 and i by 1. Thereafter, the receiving end performs bit allocation to satisfy the data rate in consideration of the average SNR for each group calculated using Equation (16).

4 is a diagram illustrating performing bit allocation on a grouped sub-channel basis according to the first embodiment of the present invention.

Referring to FIG. 4, the receiver distinguishes between a group determined to be used and a subchannel not to be used, and initializes the number of bits to be allocated to each subchannel to '0'. In FIG. 4, three subchannels constitute one group.

가 된다. 여기서, 상기 B는 각 서브 채널들에 할당되는 비트수로서 전체 비트 할당 과정동안 고정된 정수값을 가진다. 또한, 상기 G는 한 그룹당 서브 채널 개수를 의미한다. 비트가 할당된 서브 채널 그룹은 다음 비트 할당 과정에서 제외되고, 이러한 과정은 할당할 수 있는 전체 R_b 비트가 모두 할당될 때까지 반복 수행된다. Next, the receiver allocates bits by finding a group having the largest average SNR value. 4 illustrates allocation of B bits for each group. That is, the number of bits allocated to one group

Becomes Here, B is the number of bits allocated to each subchannel and has a fixed integer value during the entire bit allocation process. In addition, the G means the number of sub-channels per group. The subchannel group to which bits are allocated is excluded in the next bit allocation process, and this process is repeated until all of the allocated R _b bits are allocated.

집합이 얻어진다. 따라서, 상기 수신단은 V-BLAST 검출 과정에서 선택되지 않은 서브 채널들을 배제하고 V-BLAST 검출을 수행하게 된다.New weight vector for V-BLAST detection except subchannels not selected by this bit-assigned result

A set is obtained. Therefore, the receiver excludes subchannels not selected in the V-BLAST detection process and performs V-BLAST detection.

Then, the bit allocation process will be described using the following equations.

First, the initialization process uses the following equations 17 to 19.

The repeating process after the initialization process uses the following Equations 20 to 23 repeatedly.

Equation 20 means finding a group having a large average SNR value.

Equation 21 means that a bit is assigned to a group found using Equation 20.

Equation 22 means to accumulate the allocated number of bits.

Equation 23 means that a bit-allocated group is excluded.

의 집합을 이용해 V-BLAST 검출을 수행한다.That is, the receiving end is performed repeatedly until the mathematical expression 20 to 23 R _'b = R _b. When bit allocation is completed, a new weight vector for the transmit antenna used for each subcarrier as described above.

V-BLAST detection is performed using a set of.

5 is a flowchart illustrating an operation of a receiving end using the SBA-GS scheme according to the first embodiment of the present invention.

의 집합을 이용해 V-BLAST 검출을 수행한다.Referring to FIG. 5, in step 502, the receiving end initializes the number of bits to be allocated to each subchannel to '0' and proceeds to step 504. In step 504, the receiving end calculates an average SNR for each group consisting of a predetermined number of subchannels, and proceeds to step 506. In step 506, the receiving end sequentially allocates bits in order of the group having a larger average SNR value. In step 508, when the bit allocation is completed, the receiving end receives a new weight vector for the transmit antenna used for each subcarrier.

V-BLAST detection is performed using a set of.

6 is a flowchart illustrating an operation of a transmitter using the SBA-GS scheme according to the first embodiment of the present invention.

Referring to FIG. 6, first, in step 602, the transmitter receives CSI fed back by the receiver and proceeds to step 604. In step 604, the transmitting end can recognize the sub-channels to be used by the receiving end according to the CSI reception, and performs resource allocation to the sub-channel determined by the receiving end, i.e., the sub-channels to which bits are allocated. Proceed. The transmitting end transmits resource allocation information to the receiving end.

)/G 비트가 된다. 이는 종래의 SBA 기법을 이용하는 수신단이 송신단으로 피드백하는 정보량 N_cㅧ M 비트에 비해 크게 감소된 정보량임을 알 수 있다. 또한, 상기 SBA-GS 기법 역시 SBA 기법과 동일하게 전력 할당 정보 송신이 필요하지 않다.In conclusion, in the SBA-GS scheme according to the first embodiment of the present invention, the amount of information fed back from the receiver to the transmitter is (

) / G bit. This can be seen that the receiving end using the conventional SBA technique is a significantly reduced amount of information compared to the amount of information N _c ㅧ M bits fed back to the transmitting end. In addition, the SBA-GS scheme does not need to transmit power allocation information in the same manner as the SBA scheme.

Next, a simulation result performed to evaluate the performance of the SBA-GS technique will be described.

First, the simulation environment considers a frequency-selective Rayleigh fading channel consisting of 18 paths each with root-mean-square delay spread (RMS) of 81ns, 436ns, and 1490ns. Table 1 below shows the delay and average gain for each path for the three types of channel models.

The Doppler frequencies of the channel models according to Table 1 are considered 300 Hz, and it is assumed that channel estimation and system synchronization have been performed completely. In addition, it is assumed that the bandwidth for MIMO-OFDM is 100 MHz and the number of subcarriers is 2048, and the OFDMA symbol period is set to 20.48 ms. A convolutional code using a hard decision Viterbi algorithm was used as the channel code, and a system having two transmit and receive antennas (ie, M = N = 2) was considered. (16 QAM, code rate r = 1/2) and (QPSK, code rate r = 2/3) were used as the modulation method and channel code rate combination.In all systems, the bit rate is the same at 200 Mbps with R _b = 4096. Assume the situation.

7A and 7B are graphs illustrating bit error rate performance using the SBA-GS scheme according to the first embodiment of the present invention.

First, FIGS. 7A and 7B show BER performance in a channel environment with a delay spread of 81 ns. FIG. 7A shows a performance graph using QPSK, r = 2/3, and FIG. 7B uses 16 QAM and r = 1/2. to be. 7A and 7B illustrate performance comparisons of the conventional SBA scheme and the SBA-GS scheme of the present invention (when the number of subchannels G in a group is set to two or four). If the delay spread is 81ns, it can be seen that the SBA and SBA-GS techniques exhibit almost the same BER performance. Therefore, compared to the same BER performance, the SBA-GS scheme having 2 subchannels in a group needs only 2048 bits, and the SBA-GS scheme having 4 needs only 1024 bits to be fed back to the transmitter.

Second Embodiment (SRA)

The SRA scheme according to the second embodiment of the present invention is a resource allocation scheme for a MIMO-OFDMA communication system in which a plurality of user terminals exist. Each user terminal calculates a CSI (2-norm value) for each subchannel and feeds it back to a transmitting end, that is, a base station, and the transmitting end allocates resources to each user terminal using the received CSI. Here, the transmitting end transmits resource allocation information about which user terminal each subchannel is allocated to the user terminals according to the resource allocation result.

Next, a transmission / reception structure using the SRA scheme according to the second embodiment of the present invention will be described with reference to FIGS. 8A to 8B.

8A to 8B schematically illustrate a structure of a transmitting and receiving end using an SRA scheme according to a second embodiment of the present invention.

First, referring to FIG. 8A, first, the transmitting end 800 receives feedback of the receiving end 850, that is, the CSI of each of the user terminals. The feedback information is input to the SRA performer 802 of the transmitting end 800, the SRA performer 802 allocates resources to the respective user terminals through a predetermined procedure, and allocates the allocated resource information to the respective user terminals. Send to Here, the predetermined procedure is a general adaptive resource allocation scheme different from each subchannel modulation scheme, whereas the SRA scheme uses the same modulation scheme for each subchannel, and the resource in a greedy method Means the procedure of assigning. In this case, the SRA scheme can greatly reduce the overhead information for informing the user terminals of the resource allocation result compared to the general adaptive resource allocation scheme. More detailed description thereof will be described later.

Referring to FIG. 8B, the receiving end 850 receives resource allocation information from the transmitting end 800 and deteriorates system performance due to error propagation due to interference cancellation using a V-BLAST detector that performs nulling only. System performance can be improved.

On the other hand, assuming that the number of bits to be allocated to the k-th user terminal is R _k , the transmitting end may use a round robin method to equally allocate resources having good channel characteristics to each user terminal. That is, the transmitter sequentially allocates resources to each user terminal using Equations 27 to 30 below. The resources allocated up to the previous allocation step and the user terminal where the resource allocation is completed are excluded from the next resource allocation process. When the number of bits allocated to each resource, that is, each subchannel is the same as the B bits, the entire resource allocation process may be represented by Equations 24 to 30, and among the equations 24 to 26, an initialization process for resource allocation is performed. Using the equations (27) to (30), a repeating process is performed until all user terminals are allocated all the resources needed.

Equation 24 means that the bit value to be allocated to the k-th user terminal to use the c-th subchannel in the i-th transmit antenna is initialized to '0'.

Equation 27 means finding a subchannel having a large average SNR value.

Equation 28 means that as much as B bits are allocated to the subchannel found using Equation 27.

Equation 29 means to accumulate the allocated number of bits.

Equation (30) means that all subchannels required by all user terminals are allocated while excluding a bit-allocated subchannel.

9A and 9B are diagrams illustrating a process of performing resource allocation by applying the SRA scheme according to the second embodiment of the present invention.

9A and 9B, the transmitting end performs resource allocation using CSI fed back from each user terminal. Here, resource allocation is sequentially performed to each user terminal using a round robin method. For example, if there are four user terminals, the user terminal 1 is allocated a resource having the best SNR of the channel state among all the resources, the user terminal 2 is allocated a resource having the next good state, and the user allocates the resource allocation. Performing up to terminal 4 sequentially is a round robin method.

The user terminal to which all necessary resources for data transmission are allocated is excluded in the next resource allocation process, and the resource allocation process is repeated until all the user terminals are allocated all necessary resources.

10 is a diagram illustrating a result of completing a resource allocation by a transmitter according to a second embodiment of the present invention.

Referring to FIG. 10, the transmitting end allocates resources such that there is no subchannel colliding from user terminal # 1 to user terminal #K using the round robin scheme. The transmitting end performing resource allocation transmits the resource allocation information to each user terminal.

11 is a diagram illustrating an error propagation phenomenon when the SRA technique according to the second embodiment of the present invention is applied.

Referring to FIG. 11, first, the transmitting end completes resource allocation for all user terminals. However, in a MIMO-OFDMA communication system, one subchannel has different channel characteristics for each user terminal. Therefore, in a MIMO-OFDMA communication system using a V-BLAST detector that performs interference cancellation, system performance is greatly degraded due to error propagation, and thus, diversity gain for multi-user terminals cannot be obtained. In other words, a subchannel having a good channel state assigned to a specific user terminal may cause serious error propagation in a signal detection process due to the subchannel. That is, the first user terminal suffers an error propagation due to the subchannel allocated to the K-th user terminal in FIG. 10. Accordingly, the receiver according to the second embodiment of the present invention prevents system performance deterioration due to error propagation due to interference cancellation and improves system performance, compared to conventional ordered successive interference cancellation (OSIC). In order to accomplish this, it is preferable to use a V-BLAST detector which performs only nulling by calculating an inverse of the channel matrix and multiplying the received symbol vector without performing interference cancellation.

As a result, the SRA scheme can significantly reduce the amount of computation compared to the conventional adaptive resource allocation scheme that applies the modulation scheme of each subchannel differently using a lagrange multiplier solution. This means that the SRA scheme uses the same modulation scheme for all subchannels, in which case This is because resources are allocated using a greedy method that is sequentially assigned to sub-channels having a large channel SNR until the data rate is satisfied. That is, the Lagrange multiplier requires a very complex calculation for each resource allocation, but the SRA scheme is the largest channel for each user among the remaining subchannels except subchannels already allocated in the previous allocation process. Since it is necessary to find a subchannel having an SNR, the amount of computation is greatly reduced, and only the information on which user each subchannel is assigned to is informed to each user, thereby greatly reducing the amount of information transmitted from the transmitter to each terminal. In addition, the amount of information transmitted by the transmitting end to each user terminal can be reduced. Equation 31 shows an overhead transmitted to each user terminal from a transmitter according to a general adaptive resource allocation scheme, and equation 32 represents an overhead transmitted to each user terminal to a transmitter according to the SRA scheme.

In Equations 31 and 32, D denotes the number of available modulation schemes for each subchannel, K denotes the number of user terminals, M denotes the number of transmit antennas, and N _c denotes the number of subcarriers.

12 is a flowchart illustrating an operation performed by a transmitter using an SRA scheme according to a second embodiment of the present invention.

Referring to FIG. 12, first, in step 1202, the transmitting end receives CSI for each subchannel from each of a plurality of user terminals and proceeds to step 1204. In step 1204, the transmitter uses the round robin and greedy schemes to allocate resources evenly in the order of subchannels having good channel states.

비트(bits)가 된다. 여기서, 상기

는 각 송신 안테나별 서브 채널에 할당되는 정보 비트량을 의미한다. 따라서, 후술할 본 발명의 제3 실시예에서는 상기 SRA 기법을 개선하여 각 사용자 단말기들이 피드백하는 정보량을 감소시킨 modified SRA 기법에 대해 설명하기로 한다.However, although the SRA scheme reduces downlink overhead compared to the conventional adaptive resource allocation scheme, there remains a problem that the amount of channel state information fed back to the transmitter by each user terminal is still excessive. This is because each user terminal feeds back a 2-norm value of the weight vector for the entire subchannel to the transmitter. That is, the amount of channel state information that each user terminal feeds back to the transmitting end is

Bits. Where

Denotes the amount of information bits allocated to each subchannel of each transmitting antenna. Therefore, in the third embodiment of the present invention to be described later, a modified SRA technique in which the amount of information fed back by each user terminal is reduced by improving the SRA technique will be described.

<Modified SRA>

이 된다.The modified SRA technique is a technique for reducing the amount of channel state information fed back from each user terminal to the transmitter. That is, each of the user terminals determines a subchannel to be used and a subchannel not to be used similarly to those described in the first embodiment, and feeds back the determined information to the transmitter. Accordingly, the amount of information fed back to the transmitter by each of the plurality of user terminals is

Becomes

First, each user terminal selects candidate subchannels to use using an SBA algorithm. If a bit to be allocated by the k-th user terminal is R _k , the k-th user terminal measures a channel state using the following equations and feeds back to the transmitter.

R ' _k = 0

S = {(i, c): i = 1, ..., M; c = 1, ..., N _c }

Here, each of the user terminals measures the channel state independently of each other. In this case, collisions between candidate subchannels intended to be used by the respective user terminals may occur. Therefore, the transmitting end must perform a resource allocation algorithm to prevent collision between sub-channels to be allocated between respective user terminals. The procedure regarding this resource allocation algorithm is the main point of the modified SRA scheme according to the third embodiment of the present invention. That is, the modified SRA scheme includes an initial resource allocation process for assigning candidate subchannels without collision to each user terminal first, an intermediate resource allocation process for properly assigning collision occurrence candidate subchannels to each user terminal; In addition, an additional bit allocation process for allocating additional bits for user terminals that do not allocate the necessary amount of resources allocates resources to a plurality of user terminals.

FIG. 13 is a diagram schematically illustrating a structure of a transmitter / receiver using a modified SRA scheme according to a third embodiment of the present invention.

으로, 상기 수신단(850)이 송신단(800)으로 피드백하는 채널 상태 정보량

에 비해 현저하게 감소된다. 결론적으로, 상기 도 13에 송신단 및 수신단의 상세한 내부 장치 구조는 도시하지는 않았지만, 상기 도 13에 따른 modified SRA 장치 구조는 도 8의 SRA 장치 구조와 동일하며, 수행되는 자원 할당 알고리즘만이 상이할 뿐이다. Referring to FIG. 13, first, the transmitting end 1302 has the same structure as the transmitting end 800 of FIG. 8. However, the SRA performer 802 of the transmitter 800 of FIG. 8 is replaced with the modified SRA performer according to the third embodiment of the present invention, and the modified SRA performer (not shown) performs the modified SRA resource allocation algorithm. Keep in mind. In addition, the structure of the receiving end, that is, each of the plurality of user terminals 1352 and 1354 is also the same as that of the receiving end 850 of FIG. 8. However, the amount of channel state information fed back to the transmitting end by each user terminal constituting the receiving end according to the third embodiment of the present invention.

Thus, the amount of channel state information fed back to the transmitter 800 by the receiver 850.

Significantly reduced compared to In conclusion, although the detailed internal device structures of the transmitter and the receiver are not shown in FIG. 13, the modified SRA device structure according to FIG. 13 is the same as the SRA device structure of FIG. 8, and only the resource allocation algorithm that is performed is different. .

Next, a resource allocation process using the modified SRA scheme will be described with reference to FIGS. 14A to 14D.

14A to 14D are diagrams illustrating a resource allocation procedure using a modified SRA scheme according to a third embodiment of the present invention.

FIG. 14A illustrates an initial resource allocation process for allocating candidate subchannels with no collision to each user terminal, and FIG. 14B illustrates an intermediate resource allocation process for appropriately assigning conflicting candidate subchannels to respective user terminals. FIG. 14C illustrates a process of randomly selecting sub-channels pre-allocated to user terminals that have not been allocated resources corresponding to a desired data rate, and FIG. 14D illustrates additional bits in randomly selected sub-channels. Is a diagram illustrating a process of assigning a.

First, an initial resource allocation process of the modified SRA scheme will be described with reference to FIG. 14A.

In the initial resource allocation process, the transmitting end receives feedback information about candidate subchannels to be used by each of the user terminals from the user terminals. The transmitting end may recognize subchannels that do not collide with each user terminal according to the feedback information. Accordingly, the transmitter performs a resource allocation process corresponding to the following equations for allocating non-colliding subchannels.

로, i번째 안테나에 c번째 서브 채널 서브 채널의 비트 할당 정보를

라 정의하고, 하기 수학식 40과 같이 상기

및

를 초기화 한다.First, user allocation information of the c-th subchannel subchannel is input to the i-th antenna.

Bit allocation information of the c-th subchannel subchannel to the i th antenna

It is defined as, and as shown in Equation 40 below

And

Initialize

In addition, the S _k for the k-th number of stacked sub-channel assigned to the user terminal, R 'be defined as a _k number of accumulated bits assigned to the k th user terminal, and performs initialization, such as Equation 41.

를 계산하여, 다른 사용자 단말기들의 후보 서브 채널들과 충돌이 발생하지 않는

=1인 서브 채널들을 검출한다. 여기서,

는 k번째 사용자 단말기로부터 피드백 받은 i번째 송신 안테나에 c번째 서브 채널의 상태 정보를 의미한다.The transmitter performing the parameter initialization according to Equations 40 and 41 for all subchannels

By calculating a, collision with candidate subchannels of other user terminals does not occur

Detect subchannels that are = 1. here,

Denotes state information of the c-th subchannel in the i-th transmit antenna fed back from the k-th user terminal.

=1이 i번째 송신 안테나의 c 번째 서브 채널에서는

인 사용자 단말기가 하나만 존재하며 다른 사용자 단말기의 경우

이므로 하기 수학식 42를 통하여 어떤 사용자가 i번째 송신 안테나의 c번째 서브 채널을 후보 서브채널로 선정하였는지를 판단할 수 있다.The sub-channels thus detected are allocated to the k-th user terminal using Equations 42 to 44 below.

= 1 in the c subchannel of the i th transmit antenna

Only one user terminal exists and for other user terminals

Therefore, through Equation 42, it is possible to determine which user selects the c-th subchannel of the i-th transmit antenna as a candidate subchannel.

는 i번째 송신 안테나의 c번째 서브 채널에 할당된 사용자가

임을 의미하며, 이 때 할당된 비트 수가 B 비트임을 의미한다.In Equation 43,

Is a user assigned to the c subchannel of the i th transmit antenna

In this case, the allocated number of bits is B bits.

Equation 44 is When subchannels are allocated to the user terminal by Equations 42 and 43, this means that the number of allocated subchannels is increased by one.

As described above, the transmitting end performs an initial resource allocation process for the non-conflicting sub-channels for each user terminal, and then excludes all the user terminals assigned the sub-channels satisfying the data rate, and collides with the candidate sub-channels. You will then perform an intermediate resource allocation process.

An intermediate resource allocation process of the modified SRA scheme will be described with reference to FIG. 14B.

In the intermediate resource allocation process, first, the transmitting end initializes i and c, which mean indexes of the transmitting antenna and the subchannel, to 1, respectively.

(즉, 충돌이 발생하는 후보 서브 채널들)인 서브 채널들을 검출하고, 상기 검출된 서브 채널들 각각에 대해 하기 수학식 45 내지 49들을 적용하여 상기 충돌이 발생하는 후보 서브 채널들을 각 사용자 단말기에 충돌이 발생하지 않도록 할당한다. 초기 자원할당 과정에서 각 사용자들이 할당받은 서브채널들에 할당된 비트 수는 B 비트로 모두 동일하다. 따라서, 하기 수학식 45를 통하여 어떤 사용자가 할당해야 할 여분의 비트 수가 가장 많이 남아있는지를 알 수 있으며 가장 많은 여분의 비트가 남아있는 사용자에게 해당 서브 채널을 할당한다.Thereafter, the transmitting end is configured for all subchannels, that is, from the first transmit antenna to the i th transmit antenna, from the first subchannel to the N _c th subchannel, in order to detect candidate subchannels in which a collision occurs between user terminals. Increasing the values of i and c sequentially

(Ie, candidate subchannels in which collision occurs) and detect subchannels, and apply candidate subchannels in which collision occurs to each user terminal by applying Equations 45 to 49 to each of the detected subchannels. Allocate it so that no conflict occurs. In the initial resource allocation process, the number of bits allocated to subchannels allocated by each user is the same as B bits. Accordingly, it is possible to know which user has the most number of extra bits to allocate through Equation 45, and allocates the corresponding sub-channel to the user with the most spare bits remaining.

에 해당하는 서브 채널들, 즉 사용자 단말기간 충돌이 발생하지 않는 후보 서브 채널들에 대해서는 상기 수학식 45 내지 49에 상응하는 과정을 수행하지 않음은 물론이다.On the other hand, the transmitting end is

The sub-channels corresponding to the corresponding sub-channels, that is, the candidate sub-channels where the collision between the user terminals does not occur, are not performed.

에 해당하는 모든 서브 채널들에 대해 각 사용자 단말기별로 할당을 수행하며, 모든 i에 대해 할당을 수행하게 된다.The transmitter, which has finished allocating to the user terminal for the c-th subchannel of the i-th transmit antenna, increases c by 1 from 1 to N _c for each i as shown in Equations 50 and 51.

All sub-channels corresponding to the sub-channels are allocated to each user terminal and all i are allocated.

Through the above processes, the transmitting end completes a procedure of allocating sub-channels having different characteristics to respective user terminals. However, even after the process is completed, the transmitting end should perform an additional bit allocation process for the user terminal that is allocated resources that do not reach the set data transmission rate. The additional bit allocation process will be described with reference to FIGS. 14C and 14D.

As an example, it is assumed that user terminal # 1 and user terminal # 2 have been allocated subchannels that do not satisfy the set data rate.

를 하기 수학식 52를 이용하여 결정한다.Accordingly, the transmitting end has a number of subchannels to which an ΔB bit should be additionally allocated for the user terminals # 1 and # 2.

Is determined using Equation 52 below.

를 인지하게 된다. 이에 따라, 상기 송신단은 상기 사용자 단말기 #1 및 #2 각각에 기할당되어 있던 서브 채널들 중 상기

에 해당하 는 수의 서브 채널들을 랜덤하게 선택한다. 상기 선택된 서브 채널들에 상기 송신단은 △B 비트만큼씩 추가로 비트를 할당한다. 이러한 추가 비트 할당 과정을 하기 수학식 53 내지 57들을 이용하여 설명하기로 한다.According to Equation 52, the transmitting end number of subchannels to be additionally allocated to user terminals # 1 and # 2.

Will be recognized. Accordingly, the transmitting end of the sub-channels previously assigned to each of the user terminal # 1 and # 2

Randomly select the subchannels corresponding to the number. The transmitter further allocates bits by ΔB bits to the selected subchannels. This additional bit allocation process will be described using Equations 53 to 57.

는 상기 결정된

를 카운트하기 위해 1로 초기화된 카운트 변수이다.In Equation 53,

Determined above

This is a count variable initialized to 1 to count.

이다.Equation 54 means that a subchannel is randomly selected from among subchannels previously allocated to a k-th user terminal for additional bit allocation. Herein, the number of randomly selected subchannels is

to be.

Equation 55 means that an additional bit of ΔB is additionally allocated to each of the selected subchannels.

Equation 56 means that the accumulated bit value allocated to user terminal k is further accumulated by the additionally allocated ΔB bits.

값을 1씩 증가시킴을 의미한다.Equation 57 is a case where a bit is additionally allocated to a randomly selected subchannel.

It means to increase the value by 1.

가 될 때까지 반복 수행된다. 결과적으로, 도 14d에 나타낸 바와 같이, 상기 송신단은 상기 사용자 단말기 #1에 대해 기 할당되어 있던 서브 채널들 중 세 개의 서브 채널을 랜덤하게 선택하여 추가적으로 △B 비트를 할당하였으며, 상기 사용자 단말기 #2에 대해 기 할당되어 있던 서브 채널들 중 두 개의 서브 채널을 랜덤하게 선택하여 추가적으로 △B 비트를 할당하였다.Equations 53 to 57 are

It is repeated until As a result, as shown in FIG. 14D, the transmitting end randomly selects three subchannels among the pre-allocated subchannels for the user terminal # 1 and additionally allocates ΔB bits. Two subchannels among the pre-allocated subchannels are randomly selected to further allocate ΔB bits.

Table 2 below shows the amount of uplink information fed back from the receiving end to the transmitting end and the resources transmitted from the transmitting end to the receiving end when the SRA scheme according to the second embodiment and the modified SRA scheme according to the third embodiment are used. This table compares the amount of allocation information. In Table 2, K is the number of user terminals, Q is the quantization level for the 2-norm value of the weight vector, N _c is the number of subchannels, D is the number of modulation schemes used, and M is the transmit antenna. It means number, and the unit of information amount is Bits.

배만큼 감소함을 알 수 있다. 그러나, 송신단, 즉 기지국은 수신단, 즉 사용자 단말기에 비해 감당할 수 있는 로드량이 현저히 크므로 상기

만큼의 부가 로드는 치명적인 로드로 작용하지 않는다.As shown in Table 2, the modified SRA scheme has a larger amount of resource allocation information transmitted in downlink than the SRA scheme, while the amount of information fed back uplink

It can be seen that the decrease by a factor. However, since the transmitting end, i.e., the base station has a significantly larger load load than the receiving end, i.e., the user terminal,

As many additional loads do not act as fatal loads.

15 is a flowchart illustrating an operation performed by a transmitter using a modified SRA scheme according to a third embodiment of the present invention.

Referring to FIG. 15, first, in step 1502, the transmitting end receives subchannel state information determined to be used from each of a plurality of user terminals and proceeds to step 1504. In step 1504, the transmitting end allocates subchannels to each user terminal that each user terminal wants to use but does not occur with each other through the initial resource allocation process as described above, and proceeds to step 1506. After completing the initial resource allocation process in step 1506, the transmitter detects sub-channels colliding with user terminals in an intermediate resource allocation process and proceeds to step 1508. In step 1508, the transmitter performs resource allocation so that the subchannels to be allocated to each user terminal do not collide using Equations 45 to 51 and proceeds to step 1610. In step 1610, the transmitting end satisfies the set data transmission rate by performing an additional resource allocation process for the user terminal that has not been allocated the necessary amount of resources. The additional resource allocation process is performed using Equations 52 to 57.

16A and 16B are graphs comparing system performance efficiency between the modified SRA technique and the SRA technique.

In the channel environment in which the simulations of FIGS. 16A and 16B are performed, two transmit / receive antennas are used, 16 QAM is used as a basic modulation method, and a delay spread is 1490 ns. In addition, the graphs of FIGS. 16A and 16B refer to a bit error rate performance in a system to which the SRA and modified SRA schemes are applied, according to a carrier to interference ratio (SIR) according to the number of user terminals. It is a comparative figure.

As shown in the graphs above, the SRA resource allocation scheme according to the second embodiment of the present invention shows an average performance gain of about 3 dB compared to the modified SRA resource allocation scheme according to the third embodiment of the present invention. It can be seen. On the other hand, as shown in Table 2, the system overhead due to information transmission in the uplink is significantly lower than the SRA scheme, but the system performance deterioration is minimal. Therefore, when the performance gain is important in system design, the SRA scheme may be selected as the system resource allocation algorithm, and when the system load is considered, the modified SRA scheme may be selected as the system resource allocation algorithm.

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 defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

 As described above, according to the present invention, in a MIMO-OFDM communication system in which a single user terminal exists, the receiving end significantly reduces the amount of feedback information compared to the conventional method by feeding back only state information of channels that are pre-grouped into a predetermined number of subchannels. There is an advantage to this. In addition, the resource allocation algorithm according to the present invention can be efficiently performed in the MIMO-OFDMA communication system in which the multi-user terminal exists. In addition, there is an advantage that can reduce the amount of information fed back to the transmitting end to prevent system performance degradation while minimizing system overhead.

Claims (38)

 In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, a method for feeding back channel state information to a base station by a user terminal, The entire frequency band is divided into a plurality of subchannels, and the plurality of subchannels are preset to form a plurality of logical groups consisting of a predetermined number of subchannels. And the user terminal feeds back channel information intended to be used by the logical group to the base station.  The method of claim 1, Wherein each of the plurality of subchannels is a subchannel in which modulation is performed in a same modulation scheme at a transmitting end.  In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, The entire frequency band is divided into a plurality of sub-channels, and the plurality of sub-channels are preset so that a plurality of logical groups composed of a preset number of sub-channels are assembled. Initializing the number of allocated bits of the subchannels to 0; Measuring a channel state of each of the logical groups; And sequentially performing bit allocation from subchannels of logical groups having a good channel state according to the channel state measurement result.  The method of claim 3, And performing the bit allocation repeatedly until all the predetermined number of bits are allocated.  The method of claim 3, The channel state measurement may be performed by measuring an average signal to noise ratio of subchannels constituting the logical group.  The method of claim 5, The average SNR may be determined as an average of 2-norm values of weight vectors for a set number of subchannels constituting a logical group of signals received from a transmitter, as shown in Equation 58 below.

Here, i denotes a transmission antenna I, m denotes the total number of logical groups, and G denotes the number of subchannels constituting the logical group.  The method of claim 6, The number of groups (G) of subchannels constituting the logical group is determined as a divisor of the total number of subchannels within a range not exceeding a coherence frequency bandwidth determined by a given channel environment. The method.  The method of claim 3, The transmission power of the sub-channels that are not allocated the bit is 0.  The method of claim 3, Storing, by the user terminal, the sub-channel information determined to be used by allocating the bits while feeding back to the base station in logical group units; And detecting the signal received from the base station by using a vertical-bell labs layered space-time (V-BLAST) method.  The method of claim 9, The V-BLAST detection is performed by using the pre-stored feedback information to distinguish between subchannels to which data is allocated and subchannels to which data is not allocated.  In an orthogonal frequency division multiple communication system in which multiple user input and output signals are transmitted and received using a plurality of transmit antennas and a plurality of receive antennas, a base station performs resource allocation to transmit a signal. In the method, Receiving sub-channel state information from each of the user terminals; Repeating resource allocation to each user terminal in a round robin manner from a sub-channel having a good channel state; And transmitting the signal by applying the same modulation scheme to all the resource allocated subchannels.  The method of claim 11, The base station further comprises the step of transmitting the entire resource information allocated to all the user terminals to the user terminals.  The method of claim 11, The base station sequentially allocates each user terminal from a subchannel having a good channel state until the data rate is satisfied, and the allocated subchannels are excluded at the next resource allocation.  In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving a signal using a plurality of transmit antennas and a plurality of receive antennas, the channel state information feedback of the plurality of user terminals And in the signal receiving method, Any one of the plurality of user terminals calculates a 2-norm value of a weight vector of all sub-channels and feeds it back to the base station; Subsequently, when receiving a signal from the base station and detecting the original signal using the V-BLAST scheme, only nulling is performed on a subchannel allocated to another user terminal and causing interference to any user terminal. And detecting the original signal.  In an orthogonal frequency division multiple communication system in which multiple user input and output signals are transmitted and received using a plurality of transmit antennas and a plurality of receive antennas, a base station performs resource allocation to transmit a signal. In the method, Receiving feedback of candidate subchannel information desired by the plurality of user terminals from the plurality of user terminals; A first process of detecting candidate subchannels which do not collide with each other among user terminals among the candidate subchannels with reference to the feedback information, and assigning the candidate subchannels to respective user terminals; Detecting candidate subchannels colliding between user terminals among the candidate subchannels; A third process of allocating the collision candidate subchannels so as not to collide with the respective user terminals based on a predetermined criterion; And a fourth process of allocating an additional bit to a user terminal allocated to a resource that does not satisfy a data rate.  The method of claim 15, The first process of detecting candidate subchannels that do not collide with each other among the user terminals and assigning the candidate subchannels to each user terminal is detecting a subchannel having a state value of 1 of all subchannels among all subchannels. Characterized in that the method.  The method of claim 15, The second process of detecting candidate subchannels colliding with the user terminals is to detect a subchannel having a value of at least one state information of each subchannel among all subchannels.  The method of claim 15, The method as claimed in claim 3, wherein the collision candidate subchannel is allocated to the corresponding user terminal using Equation 59 below.

Where here

Denotes a user assigned to the c-th subchannel of the i-th transmit antenna, B denotes the number of allocated bits, S _k to the cumulative sub-channel number assigned to the k-th user terminal, and R _k to the k-th user terminal. It means one cumulative number of bits.  The method of claim 15, The method as claimed in claim 1 or 3, wherein all subchannels allocated to each user terminal are allocated with the same number of bits.  The method of claim 15, The fourth process of allocating the additional bit may include; Determining the number of subchannels that should be additionally allocated to the user terminal; Randomly selecting subchannels previously allocated to the user terminal to correspond to the determined number of subchannels by the determined number of subchannels; Allocating additional bits to the selected subchannels.  In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, in a system for transmitting and receiving channel state information, The entire frequency band is divided into a plurality of sub-channels, and the plurality of sub-channels are preset so that a plurality of logical groups consisting of a predetermined number of sub-channels are collected and configured to be used by the logical group. A user terminal for feeding back channel information to the base station; And a base station for allocating resources in consideration of channel state information received in units of logical groups from the user terminal.  In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, a system for performing bit allocation The entire frequency band is divided into a plurality of subchannels, and the plurality of subchannels are preset so that a plurality of logical groups consisting of a preset number of subchannels are collected and configured. It initializes to 0, and measures the channel state of each of the logical groups, and according to the channel state measurement result comprises a user terminal for sequentially performing bit allocation from the sub-channels of the logical groups having a good channel state Said system.  The method of claim 22, And the user terminal repeats bit allocation until all the predetermined number of bits is allocated.  The method of claim 22, The user terminal measures the channel state by the average signal to noise ratio of the sub-channels constituting the logical group.  The method of claim 24, The user terminal determines the average SNR as the average of the 2-norm value of the weight vector for the set number of sub-channels constituting a logical group of the signal received from the transmitter.  The method of claim 25, The number of groups (G) of subchannels constituting the logical group is determined as a divisor of the total number of subchannels within a range not exceeding a coherence frequency bandwidth determined by a given channel environment. The system.  The method of claim 25, The system characterized in that the transmission power of the sub-channels not assigned the bit is 0.  The method of claim 25, The user terminal stores the sub-channel information determined to be used by allocating the bits while feeding back to the base station in logical group units, and V-BLAST (V-BLAST) method for the signal received from the base station. The system, characterized in that for detecting the original signal using.  The method of claim 28, The user terminal performs the V-BLAST detection by distinguishing the sub-channel to which data is allocated from the sub-channel to which data is allocated using the pre-stored feedback information.  In an orthogonal frequency division multiple communication system using multiple input multiple output schemes for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, and in a system for performing resource allocation to transmit and receive signals In If there is a base station, and calculates the 2-norm value of the weight vector for all the sub-channels and feeds back to the base station, and then receives a signal from the base station, and detects the original signal using the V-BLAST method A user terminal which is assigned to a user terminal and detects an original signal by performing nulling only on a subchannel causing interference with the arbitrary user terminal; Receives subchannel state information from each of the user terminals, repeats resource allocation to each user terminal in a round robin manner from a subchannel having a good channel state, and applies the same modulation scheme to all the subchannels allocated to the resource. System comprising a base station for transmitting a signal.  The method of claim 30, The base station transmits the entire resource information allocated to all user terminals to the user terminals.  The method of claim 30, The base station sequentially allocates each user terminal from a subchannel having a good channel state until the data rate is satisfied, and the allocated subchannels are excluded at the next resource allocation.  In an orthogonal frequency division multiple communication system using a multiple input multiple output scheme for transmitting and receiving signals using a plurality of transmit antennas and a plurality of receive antennas, and in a resource allocation and signal transmission / reception system, A user terminal which has a base station and feeds back candidate subchannel information desired to be used to the base station; The candidate subchannels which do not collide with each other among the user terminals among the candidate subchannels are detected by referring to the feedback information, and the candidate subchannels which are collided between the user terminals among the candidate subchannels are detected. And a base station for detecting channels, allocating the collision candidate subchannels so as not to collide with respective user terminals based on a predetermined criterion, and allocating additional bits to a user terminal assigned a resource that does not satisfy a data rate. The system, characterized in that.  The method of claim 33, wherein The base station is characterized in that for detecting the sub-channel having a value of the state information of each sub-channel of the total sub-channels as candidate sub-channels that do not collide with each other between the user terminals.  The method of claim 33, wherein The base station is characterized in that for detecting the sub-channel having a value of the state information of each sub-channel among all the sub-channels as candidate sub-channels between the user terminals.  The method of claim 33, wherein The base station assigns a collision candidate subchannel to a corresponding user terminal using Equation 60 below.

here,

Denotes a user assigned to the c-th subchannel of the i-th transmit antenna, B denotes the number of allocated bits, S _k to the cumulative sub-channel number assigned to the k-th user terminal, and R _k to the k-th user terminal. It means one cumulative number of bits.  The method of claim 33, wherein The base station allocates the same number of bits to all subchannels allocated to each user terminal.  The method of claim 3, The base station determines the number of subchannels that should be additionally allocated to the user terminal allocated resources that do not satisfy the data rate, and assigns the subchannels previously allocated to the user terminal to correspond to the determined number of subchannels. And randomly selecting the determined number of subchannels and allocating additional bits to the selected subchannels.

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