CN102833866B

CN102833866B - Resource allocation method for cooperation relay orthogonal frequency division multiple access system

Info

Publication number: CN102833866B
Application number: CN201210316588.2A
Authority: CN
Inventors: 李有明; 赵翠茹; 汪照; 朱星; 王炯滔; 金明; 王刚
Original assignee: Ningbo University
Current assignee: Ningbo University
Priority date: 2012-08-31
Filing date: 2012-08-31
Publication date: 2015-02-04
Anticipated expiration: 2032-08-31
Also published as: CN102833866A

Abstract

The invention discloses a resource allocation method for a cooperation relay orthogonal frequency division multiple access system. The method comprises the following steps of adding constraints of different lowest velocity demands of various users when establishing an optimal resource allocation module, introducing a user velocity weighting factor in sub-carrier allocation and relay selection processes, and performing sub-carrier allocation and relay selection according to the principle that the user has the priority in sub-carrier and relay selection if the velocity weighting factor of the user is large, thus, the lowest velocity demand of various users can be ensured well. As a simple equal power allocation method is adopted in the process of simplifying the optimal resource allocation module, the calculation complexity is effectively reduced; the rest of sub-carriers are allocated to various users according to the largest transient velocity, thus, the total velocity of the system can be maximized; and the sub-carriers can be adaptively allocated to various users according to the largest user velocity weighting factor and transient velocity, thus, the change of the wireless communication environment can be adapted well.

Description

Resource allocation method of cooperative relay orthogonal frequency division multiple access system

Technical Field

The present invention relates to a resource allocation method of a wireless communication system, and more particularly, to a resource allocation method of a cooperative relay Orthogonal Frequency Division Multiple Access (OFDMA) system, which is based on Quality of Service (QoS) guarantee.

Background

The Multiple-Input Multiple-output (MIMO) technology is a major technical breakthrough in the field of wireless communication, and forms a MIMO channel structure by installing Multiple antennas at a receiving end and a transmitting end at the same time, thereby exponentially improving the capacity and reliability of a wireless communication system due to full utilization of spatial resources. However, in practical applications, due to the limitations of the size of the mobile terminal, the power supply and the complexity of the hardware system, multiple antennas of the MIMO technology are generally disposed in the base station, and it is difficult to install multiple antennas on one mobile terminal, so that the MIMO technology is difficult to be directly applied to a practical wireless communication system. However, the cooperative relay communication technology is a brand new communication mode, and completes information transmission through mutual assistance between nodes, and establishes a plurality of virtual fading links between a source node and a destination node, so that a single-antenna mobile terminal can share antennas of other terminals in a multi-user environment, thereby obtaining space diversity gain, remarkably expanding the coverage area of a network, and improving the transmission performance of a system. The cooperative relay communication technology integrates the technical advantages of a diversity scheme and relay transmission, provides a new approach for the practicability of the MIMO technology, and draws wide attention in the wireless communication field.

Orthogonal Frequency Division Multiplexing (OFDM) divides the whole Frequency band into a plurality of sub-carriers which are Orthogonal to each other and overlapped in a staggered manner, thereby avoiding the guard interval in the traditional FDM (Frequency Division Multiplexing) multi-carrier modulation system, and greatly improving the Frequency spectrum utilization rate; and it can effectively resist frequency selective fading in wireless mobile environment by converting the frequency selective fading channel into several flat fading sub-channels. Because the frequency spectrum is occupied by the overlapping of the subcarriers, the OFDM can provide higher frequency spectrum utilization rate and information transmission rate, and is very suitable for high-speed transmission under a wireless broadband channel. Orthogonal Frequency Division Multiple Access (OFDMA) provides a natural way of multiple access by allocating different subcarriers to different users. Because different users occupy different subcarriers, orthogonality of frequency resource allocation is met among users in one cell, and influence of multiple access interference among the users is almost avoided. Due to the independence of channel fading among users, the performance can be improved by utilizing multi-user diversity gain brought by joint subcarrier allocation, and the requirement of quality of service (QoS) is met. With the increasing maturity of the research of Orthogonal Frequency Division Multiple Access (OFDMA) technology, a cellular transmission system combined with cooperative relaying can obtain higher peak data rate, higher spectrum utilization rate, and better cell edge user performance, so that the development of the research of combining the OFDMA technology and the cooperative relaying technology becomes the focus of attention of researchers. The problem of resource allocation in OFDMA systems with cooperative relaying is also becoming a research focus at present.

The resource allocation problem of the OFDMA system with cooperative relaying is a joint optimization problem of subcarrier, power, bit, adaptive modulation and relay selection, which is an NP (Non-Polynomial algorithm) problem. The traditional solution is to allocate fixed sub-carriers and relays to each user, and then perform power, bit allocation and adaptive modulation according to the allocation schemes of the sub-carriers and the relays, and because the solution allocates the fixed sub-carriers and the relays, the solution cannot adapt to the change of the wireless communication environment well, such as obstacles and the ambient temperature; in addition, in a wireless communication system, the capability of guaranteeing the minimum quality of service (QoS) requirement of a user is required, and in some occasions, the wireless communication system may also put a high requirement on user fairness.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a resource allocation method of a cooperative relay orthogonal frequency division multiple access system, which has low computational complexity, can ensure the service quality requirement of a user and can well adapt to the change of a wireless communication environment.

The technical scheme adopted by the invention for solving the technical problems is as follows: a resource allocation method of a cooperative relay orthogonal frequency division multiple access system is characterized by comprising the following steps:

firstly, establishing optimized resource allocation according to minimum service quality requirements of different users in a cooperative relay OFDMA system

The satisfied constraint conditions are as follows:

A1:

model: a2:wherein max () is a maximum function, and K represents cooperative relaying

A3:a_k，j,n'∈{0,1}

A4:

A5:

<math> <mrow> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <munderover> <mi>Σ</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msup> <msub> <mi>a</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>′</mo> </msup> <msub> <mi>R</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>Q</mi> <mi>j</mi> </msub> </mrow> </math>

The relay number in the OFDMA system, K is more than or equal to 1, M represents the user number in the cooperative relay OFDMA system, and M>1, N denotes the number of subcarriers in a cooperative relay OFDMA system, N>1；a_k,j，n' denotes a pre-relaxation integer factor that characterizes whether the nth subcarrier and the kth relay are occupied by the jth user, P_TRepresenting the total power of the transmission at the base station, P_k,TRepresenting the transmit power, Q, at the kth relay_jRepresents the lowest rate value of the jth user; constraint A1 represents the total power of transmission constraint at the base station, and in constraint A1, when 1 ≦ j ≦ M, p_S,j，nRepresents the transmission power of the communication link between the base station and the jth user on the nth subcarrier, when M +1 is not less than j not more than M + K, p_S,j，nThe transmission power of the communication link of the base station and the k relay on the nth sub-carrier is represented; constraint a2 represents a transmit power constraint at each relay; constraint A3 is used to characterize whether the nth subcarrier and the kth relay are occupied by the jth user, a_k,j，n' =0 denotes that the nth subcarrier and the kth relay are not occupied by the jth user, a_k,j，n' =1 indicates that the nth subcarrier and the kth relay are occupied by the jth user; constrainingCondition a4 indicates that a subcarrier can be occupied by only one user and corresponding relay at most; constraint a5 represents the minimum quality of service requirement for different users, which is described as the minimum rate requirement for different users; r_k,j，nRepresents the instantaneous rate of the jth user on the nth subcarrier through the kth relay and

R_{k, j, n} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k, n} H_{S, M + k, n}), \log 2 (1 + p_{S, j, n} H_{S, j, n} + p_{k, j, n} H_{k, j, n})},

min () is the minimum function, p_S,M+k，nDenotes the transmission power, H, of the communication link between the base station and the k-th relay on the nth sub-carrier_S,M+k，nIndicating the channel gain, p, of the communication link between the base station and the k-th relay on the nth sub-carrier_S,j，nDenotes the transmission power, H, of the communication link between the base station and the jth subscriber on the nth subcarrier_S，j，nIndicating the channel gain, p, of the communication link between the base station and the jth user on the nth sub-carrier_k，j,nDenotes the transmission power, H, of the jth user on the nth subcarrier via the kth relay_k，j，nIndicating the channel gain of the jth user on the nth subcarrier through the kth relay;

secondly, the integer factor a before relaxation in the optimized resource allocation model is used_k，j,n' relaxation to one [0,1]The variable between, noted as a_k，j，nAnd distributing equal power to each subcarrier by using an equal power distribution method to obtain simplified optimization

The satisfied constraint conditions are as follows:

resource allocation model: b1: a_k，j，n∈[0,1]Whereinis represented by a_k,j，nFor optimizing variables

B2:

B3:

<math> <mrow> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <munderover> <mi>Σ</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mrow> <msub> <mi>a</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mi>R</mi> </mrow> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>Q</mi> <mi>j</mi> </msub> </mrow> </math>

Taking the maximum function, a_k,j，nThe method is used for representing the proportion number occupied by the jth user and the corresponding kth relay on the nth subcarrier; constraint B1 denotes a_k,j，nHas a value of [0,1]Any value within the interval; constraint B2 indicates that one subcarrier can be occupied by multiple users and corresponding relays; constraint B3 represents the minimum rate requirements of different users;

constructing a Lagrange equation related to the simplified optimization resource distribution model, and expressing the Lagrange equation as follows:

wherein, beta_nTo representThe lagrangian operator of (a) is,_k，j，ndenotes a_k，j，nLagrange operator of, mu_jTo represent

Lagrangian operator of (2);

fourthly, will

To a_k，j,nThe derivation is performed to obtain the corresponding first-order KKT requirement, which is expressed as:

here, K is more than or equal to 1 and less than or equal to K, j is more than or equal to 1 and less than or equal to M, and N is more than or equal to 1 and less than or equal to N;

fifthly, allocating an optimal subcarrier to each user and selecting a most appropriate relay according to the maximum instantaneous rate, and then allocating the rest subcarriers according to a first-order KKT necessary condition to ensure that each user can meet the requirement of the lowest rate.

In the fifth step, an optimal subcarrier is allocated to each user according to the maximum instantaneous rate, a most suitable relay is selected, and then the specific process of allocating the rest subcarriers according to the first-order KKT requirement is as follows:

fifthly, initialization: make the subcarrier set as omega_NThe user set is omega_MThe relay set is omega_K(ii) a Let total transmitted power at base station be P_TIf the equal power distribution method is adopted, the power value distributed on each subcarrier is equal toWherein N represents the number of subcarriers in the cooperative relay OFDMA system, M represents the number of users in the cooperative relay OFDMA system, and K represents the number of relays in the wireless cooperative relay OFDMA system;

-2, allocating an optimal subcarrier to each user and selecting a most suitable relay according to the instantaneous rate maximization: a1, calculating each user to obtain the subcarrier with the maximum instantaneous speed and the corresponding relay from the base station, distributing the subcarrier with the maximum instantaneous speed as the optimal subcarrier to the corresponding user, and then collecting omega from the subcarrier set_NThe best sub-carrier is deleted, and the sub-carrier with the largest instantaneous speed obtained by the jth user from the base station is assumed to be the nth^*Subcarrier, corresponding relay is kth^*One relay then has (k)^*,n^*)=arg maxR_k,j，nThen n is added^*The sub-carrier is taken as the optimal sub-carrier to be distributed to the jth user, and the corresponding kth user is distributed^*The relay is taken as the most suitable relay and thenN th^*Sub-carrier set omega_NWherein n is not less than 1^*≤N，1≤k^*K is less than or equal to K, arg () is a parameter taking function, max () is a maximum value taking function, (K)^*,n^*)=arg max R_k,j，nMeans to find out the sub-carrier with the largest instantaneous speed obtained from the base station by the jth user and the corresponding relay, which are respectively the nth^*Sub-carriers and k^*A relay, R_k,j，nRepresenting the instantaneous rate of the jth user on the nth subcarrier through the kth relay; a2, and then a method for characterizing the jth user and the corresponding kth user^*A relay is in the n^*Proportional number occupied on one subcarrierAnd updates the actual rate R of the jth user_j，Wherein,in "=" is assigned symbol, R on left_jR on the right representing the updated actual rate of the jth user_jRepresenting the actual rate, R, of the j-th user before the update_jIs set to an initial value of 0, and,indicating that the jth user passes the kth user^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j, n^{*}} H_{S, j, n^{*}} + p_{k^{*}, j, n^{*}} H_{k^{*}, j, n^{*}})},

p_{S, M + k^{*}, n^{*}}

denotes base station and kth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is, denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,indicating that the communication link between the base station and the jth user is at the nth^*The transmit power on the sub-carriers is, indicating that the communication link between the base station and the jth user is at the nth^*The channel gain on a number of sub-carriers,indicating that the jth user passes the kth user^*A relay is in the n^*Transmission power on sub-carriers of value Indicating that the jth user passes the kth user^*A relay is in the n^*Channel gain over a number of subcarriers;

fifthly, distributing the rest subcarriers: b1, obtained according to first-order KKT requirement C1_k，j，n=β_n-(1+μ_j)R_k，j，nThen according to the first-order KKT requirement C2And then according to the first-order KKT requirement C3b2 according to_k，j，n=β_n-(1+μ_j)R_k，j，nAndto obtain beta_n=(1+μ_j)R_k,j，nAnd make w_jRepresenting the rate trade-off factor, w, for the jth user_j=Q_j-R_jThen will beSimplified toWherein R is_jRepresenting the actual rate of the jth user; b3 according to beta_n=(1+μ_j)R_k，j，nAnddetermining the equivalent mu_jN-th subcarrier is allocated to j-th subcarrier when =0^*Individual user and corresponding kth^*A relay makesWhen mu is_j>When 0, the nth subcarrier is allocated to the user with the maximum instantaneous rate and the corresponding relay to maximize the total system rate, which is j^*Individual user and kth^*A plurality of relays, wherein,denotes the j (th)^*For one to useRate trade-off factor of the user, wherein j is more than or equal to 1^*Less than or equal to M; b4, finding out the user with the maximum difference between the lowest speed to be reached and the actual speed, and assuming that the found user is the j-th user^*Each user then has j^*=arg max w_jWherein j is not less than 1^*≤M，arg max w_jThe user with the maximum difference between the minimum rate to be achieved and the actual rate is found out; b5, judging the j-th found^*Per user rate tradeoff factorIf so, indicating that each user has not met the minimum rate requirement, and then continuing to step b6, otherwise, indicating that each user has met the minimum rate requirement, and then continuing to step b 7; b6 finding out satisfaction conditionAnd the corresponding relay, assuming that the found subcarrier is the nth subcarrier^*Sub-carriers and the corresponding relay is the kth^*For each relay, the nth relay^*Sub-carriers allocated to the jth^*The number of users, among others,represents finding the jth^*The sub-carrier with the maximum instantaneous speed and the corresponding relay are obtained from the base station by each user, and the number is n^*Sub-carriers and k^*The number of the relays is one,denotes the j (th)^*Instantaneous rate of each user on the nth subcarrier through the kth relay; then the n-th^*Sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*A relay is in the n^*Of a proportional number occupied on a single subcarrierAnd update the jth^*Of individual usersActual rate Wherein,in "=" is assigned symbol, leftRepresents updated jth^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j^{*}, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j^{*}, n^{*}} H_{S, j^{*}, n^{*}} + p_{k^{*}, j^{*}, n^{*}} H_{k^{*}, j^{*}, n^{*}})},

denotes base station and kth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is, denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,denotes the base station and j^*The communication link of the subscriber is at the nth^*The transmit power on the sub-carriers is, denotes the base station and j^*The communication link of the subscriber is at the nth^*The channel gain on a number of sub-carriers,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The transmit power on the sub-carriers is, denotes the j (th)^*The user passes the k-th^*A relay is in the n^*Channel gain over a number of subcarriers; continuing to execute the step b 8; b7, finding out the user with the maximum instantaneous speed and the corresponding relay for the rest sub-carriers, assuming the nth sub-carrier as the rest sub-carrier, and assuming the user with the maximum instantaneous speed found for the nth sub-carrier as the jth sub-carrier^*Each user and the corresponding relay is the kth^*One relay then has (k)^*,j^*)=arg maxR_k,j，n′Wherein (k)^*,j^*)=arg maxR_k，j，n′It is expressed that the user with the maximum instantaneous speed and the corresponding relay are found out for the nth subcarrier, which is respectively the jth subcarrier^*Individual user and kth^*A relay; then the nth sub-carrier is selected from the sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*Of a proportional number of relays occupying on the nth sub-carrierAnd update the jth^*Actual rate of individual user Wherein,in "=" is assigned symbol, leftRepresents updated jth^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*The instantaneous rate of the number of relays on the nth subcarrier,

R_{k^{*}, j^{*}, n} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n} H_{S, M + k^{*}, n}), \log 2 (1 + p_{S, j^{*}, n} H_{S, j^{*}, n} + p_{k^{*}, j^{*}, n} H_{k^{*}, j^{*}, n})},

p_{S, M + k^{*}, n}

denotes base station and kth^*This relays the transmit power of this communication link on the nth sub-carrier, denotes base station and kth^*This relays the channel gain of this communication link on the nth sub-carrier,denotes the base station and j^*The transmit power of this communication link for this user on the nth sub-carrier, denotes the base station and j^*The channel gain of the communication link of the user on the nth sub-carrier,denotes the j (th)^*The user passes the k-th^*The transmit power of the relay on the nth subcarrier, denotes the j (th)^*The user passes the k-th^*Channel gains of the relays on the nth subcarrier; continuing to execute the step b 8; b8, judging a subcarrier set omega_NAnd if the number is the empty set, indicating that the subcarrier allocation and the relay selection are finished, otherwise, returning to the step b4 to continue the execution.

In the step (r), the value of K is 3, 4 or 5, the value of M is 6, 8, 10 or 12, and the value of N is 128, 256, 512 or 1024.

Compared with the prior art, the invention has the advantages that:

1) according to the method, the constraint conditions of different minimum rate requirements of each user are added when an optimized resource allocation model is established, then the user rate balance factor is introduced in the subcarrier allocation and relay selection process, and the subcarrier allocation and relay selection are carried out according to the criterion that the larger the rate balance factor is, the higher the priority of selecting subcarriers and relays is, so that the minimum rate requirements of each user can be well guaranteed, namely the service quality requirements of each user are guaranteed.

2) The method adopts a simple equal power distribution method in the process of simplifying and optimizing the resource distribution model, and effectively reduces the calculation complexity.

3) The method of the invention maximally allocates the rest sub-carriers to each user according to the instantaneous rate, thereby maximizing the total rate of the system.

4) The method of the invention allocates the sub-carrier to each user in a maximum self-adaptive way according to the user rate balance factor and the instantaneous rate, and is a dynamic resource allocation method, thereby being capable of adapting to the change of the wireless communication environment well.

Drawings

Fig. 1 is a multi-cooperative relay single-cell downlink communication system model;

FIG. 2 is a comparison of the user acquisition rate and the minimum rate requirement under different resource allocation methods;

fig. 3 shows the total system rate at different snr for different resource allocation methods.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

The resource allocation method of the cooperative relay orthogonal frequency division multiple access system provided by the invention is applied to a multi-cooperative relay single-cellular downlink communication system model as shown in figure 1. In order to ensure that each user in a multi-cooperation relay single-cell downlink communication system can receive signals sent by a base station, a half-duplex cooperation transmission mode is selected, and in a first time slot, the base station sends information to a relay and the user; in the second time slot, the relay decodes and forwards the received information to the user, and supposing that a multi-cooperative relay single-cell downlink communication system comprises a base station BS located at the center, K relay stations RS and M users, the total available bandwidth of the system is B, the whole frequency band is divided into N orthogonal subcarriers, and the total transmitting power at the base station is P_TSimultaneously order N₀Representing gaussian white noise single-sided power spectral density.

The resource allocation method of the present invention specifically includes the steps of:

The satisfied constraint conditions are as follows:

A1:

A3:a_k,j，n'∈{0,1}

A4:

A5:

The relay number in the OFDMA system, K is more than or equal to 1, M represents the user number in the cooperative relay OFDMA system, and M>1, N denotes the number of subcarriers in a cooperative relay OFDMA system, N>1, in the actual simulation process, the value of K can be 3, 4, 5, the value of M can be 6, 8, 10, 12, the value of N can be 128, 256, 512, 1024, which are common values; a is_k,j，n' denotes a pre-relaxation integer factor that characterizes whether the nth subcarrier and the kth relay are occupied by the jth user, P_TRepresenting the total power of the transmission at the base station, P_k,TDenotes the kthTransmission power, Q, at each relay_jRepresents the lowest rate value of the jth user; constraint A1 represents the total power of transmission constraint at the base station, and in constraint A1, when 1 ≦ j ≦ M, p_S,j，nRepresents the transmission power of the communication link between the base station and the jth user on the nth subcarrier, when M +1 is not less than j not more than M + K, p_S,j，nThe transmission power of the communication link of the base station and the k relay on the nth sub-carrier is represented; constraint a2 represents a transmit power constraint at each relay; constraint A3 is used to characterize whether the nth subcarrier and the kth relay are occupied by the jth user, a_k,j，n' =0 denotes that the nth subcarrier and the kth relay are not occupied by the jth user, a_k,j，n' =1 indicates that the nth subcarrier and the kth relay are occupied by the jth user; constraint a4 indicates that a subcarrier can be occupied by only one user and corresponding relay at most; constraint a5 represents the minimum quality of service requirement for different users, which is described as the minimum rate requirement for different users; r_k,j，nRepresents the instantaneous rate of the jth user on the nth subcarrier through the kth relay and

R_{k, j, n} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k, n} H_{S, M + k, n}), \log 2 (1 + p_{S, j, n} H_{S, j, n} + p_{k, j, n} H_{k, j, n})},

min () is the minimum function, p_S,M+k，nDenotes the transmission power, H, of the communication link between the base station and the k-th relay on the nth sub-carrier_S,M+k，nIndicating the channel gain, p, of the communication link between the base station and the k-th relay on the nth sub-carrier_S，j，nDenotes the transmission power, H, of the communication link between the base station and the jth subscriber on the nth subcarrier_S，j，nIndicating the channel gain, p, of the communication link between the base station and the jth user on the nth sub-carrier_k，j，nDenotes the transmission power, H, of the jth user on the nth subcarrier via the kth relay_k，j，nIndicating the channel gain of the jth user on the nth subcarrier through the kth relay.

The satisfied constraint conditions are as follows:

resource allocation model: b1: a_k,jn∈[0,1]Whereinis represented by a_k,j，nFor optimizing variables

B2:

B3:

Taking the maximum function, a_k,j，nThe method is used for representing the proportion number occupied by the jth user and the corresponding kth relay on the nth subcarrier; constraint B1 denotes a_k,j，nHas a value of [0,1]Any value within the interval; constraint B2 indicates that one subcarrier can be occupied by multiple users and corresponding relays; constraint B3 represents the minimum rate requirements of different users.

Lagrange operator of (2).

Fourthly, will

here, K is 1. ltoreq. K, j is 1. ltoreq. M, and N is 1. ltoreq. N.

In this embodiment, the specific process of assigning an optimal subcarrier and selecting an optimal relay to each user according to the instantaneous rate maximization in step (c), and then assigning the remaining subcarriers according to the first-order KKT requirement is as follows:

fifthly, initialization: make the subcarrier set as omega_NThe user set is omega_MThe relay set is omega_K(ii) a Let total transmitted power at base station be P_TIf the equal power distribution method is adopted, the power value distributed on each subcarrier is equal toWherein N represents the number of subcarriers in the cooperative relay OFDMA system, M represents the number of users in the cooperative relay OFDMA system, and K represents the number of relays in the wireless cooperative relay OFDMA system.

-2, allocating an optimal subcarrier to each user and selecting a most suitable relay according to the instantaneous rate maximization: a1, calculating each user to obtain the subcarrier with the maximum instantaneous speed and the corresponding relay from the base station, distributing the subcarrier with the maximum instantaneous speed as the optimal subcarrier to the corresponding user, and then collecting omega from the subcarrier set_NThe best sub-carrier is deleted, and the sub-carrier with the largest instantaneous speed obtained by the jth user from the base station is assumed to be the nth^*Subcarrier, corresponding relay is kth^*One relay then has (k)^*,n^*)=arg maxR_k,j，nThen n is added^*The sub-carrier is taken as the optimal sub-carrier to be distributed to the jth user, and the corresponding kth user is distributed^*The relay is used as the most suitable relay, and the nth relay is used^*Sub-carrier set omega_NWherein n is not less than 1^*≤N，1≤k^*K is less than or equal to K, arg () is a parameter taking function, max () is a maximum value taking function, (K)^*,n^*)=argmaxR_k，j,nMeans to find out the sub-carrier with the largest instantaneous speed obtained from the base station by the jth user and the corresponding relay, which are respectively the nth^*Sub-carriers and k^*A relay, R_k，j，nIndicating the instantaneous speed of the jth user on the nth subcarrier through the kth relay; a2, and then a method for characterizing the jth user and the corresponding kth user^*A relay is in the n^*Proportional number occupied on one subcarrierAnd updates the actual rate R of the jth user_j，Wherein,in "=" is assigned symbol, R on left_jR on the right representing the updated actual rate of the jth user_jRepresenting the actual rate, R, of the j-th user before the update_jIs set to an initial value of 0, and,indicating that the jth user passes the kth user^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j, n^{*}} H_{S, j, n^{*}} + p_{k^{*}, j, n^{*}} H_{k^{*}, j, n^{*}})},

p_{S, M + k^{*}, n^{*}}

denotes base station and kth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is, denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,indicating that the communication link between the base station and the jth user is at the nth^*The transmit power on the sub-carriers is, denotes the base station and the jthThe communication link of the user is at the n-th^*The channel gain on a number of sub-carriers,indicating that the jth user passes the kth user^*A relay is in the n^*Transmission power on sub-carriers of value Indicating that the jth user passes the kth user^*A relay is in the n^*Channel gain on a number of subcarriers.

Fifthly, distributing the rest subcarriers: b1, obtained according to first-order KKT requirement C1_k，j，n=β_n-(1+μ_j)R_k，j，nThen according to the first-order KKT requirement C2And then according to the first-order KKT requirement C3b2 according to_k，j，n=β_n-(1+μ_j)R_k，j，nAndto obtain beta_n=(1+μ_j)R_k，j，nAnd make w_jRepresenting the rate trade-off factor, w, for the jth user_j=Q_j-R_jThen will beSimplified toWherein R is_jRepresenting the actual rate of the jth user; b3 according to beta_n=(1+μ_j)R_k，j，nAnddetermining the equivalent mu_jN-th subcarrier is allocated to j-th subcarrier when =0^*Individual user and corresponding kth^*A relay makesWhen mu is_j>When 0, the nth subcarrier is allocated to the user with the maximum instantaneous rate and the corresponding relay to maximize the total system rate, which is j^*Individual user and kth^*A plurality of relays, wherein,denotes the j (th)^*Rate tradeoff factor for individual user, where 1 ≦ j^*Less than or equal to M; b4, finding out the user with the maximum difference between the lowest speed to be reached and the actual speed, and assuming that the found user is the j-th user^*Each user then has j^*=arg max w_jWherein j is not less than 1^*≤M，argmax w_jThe user with the maximum difference between the minimum rate to be achieved and the actual rate is found out; b5, judging the j-th found^*Per user rate tradeoff factorIf so, indicating that each user has not met the minimum rate requirement, and then continuing to step b6, otherwise, indicating that each user has met the minimum rate requirement, and then continuing to step b 7; b6 finding out satisfaction conditionAnd the corresponding relay, assuming that the found subcarrier is the nth subcarrier^*Sub-carriers and the corresponding relay is the kth^*For each relay, the nth relay^*Sub-carriers allocated to the jth^*The number of users, among others,represents finding the jth^*For one to useThe user obtains the subcarrier with the maximum instantaneous speed and the corresponding relay from the base station, which are respectively the nth^*Sub-carriers and k^*The number of the relays is one,denotes the j (th)^*Instantaneous rate of each user on the nth subcarrier through the kth relay; then the n-th^*Sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*A relay is in the n^*Of a proportional number occupied on a single subcarrierAnd update the jth^*Actual rate of individual user Wherein,in "=" is assigned symbol, leftRepresents updated jth^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j^{*}, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j^{*}, n^{*}} H_{S, j^{*}, n^{*}} + p_{k^{*}, j^{*}, n^{*}} H_{k^{*}, j^{*}, n^{*}})},

denotes base station and kth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is, denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,denotes the base station and j^*The communication link of the subscriber is at the nth^*The transmit power on the sub-carriers is, denotes the base station and j^*The communication link of the subscriber is at the nth^*The channel gain on a number of sub-carriers,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The transmit power on the sub-carriers is, denotes the j (th)^*The user passes the k-th^*A relay is in the n^*Channel gain over a number of subcarriers; continuing to execute the step b 8; b7, finding out the user with the maximum instantaneous speed and the corresponding relay for the rest sub-carriers, assuming the nth sub-carrier as the rest sub-carrier, and assuming the user with the maximum instantaneous speed found for the nth sub-carrier as the jth sub-carrier^*Each user and the corresponding relay is the kth^*One relay then has (k)^*,j^*)=argmaxR_k，j,nWherein (k)^*,j^*)=arg maxR_k，j，nIt is expressed that the user with the maximum instantaneous speed and the corresponding relay are found out for the nth subcarrier, which is respectively the jth subcarrier^*Individual user and kth^*A relay; then the nth sub-carrier is selected from the sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*Of a proportional number of relays occupying on the nth sub-carrierAnd update the jth^*Actual rate of individual user Wherein,in "=" is assigned symbol, leftRepresentation updateJ (last)^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*The instantaneous rate of the number of relays on the nth subcarrier,

R_{k^{*}, j^{*}, n} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n} H_{S, M + k^{*}, n}), \log 2 (1 + p_{S, j^{*}, n} H_{S, j^{*}, n} + p_{k^{*}, j^{*}, n} H_{k^{*}, j^{*}, n})},

p_{S, M + k^{*}, n}

The following is a simulation experiment performed on the method of the present invention to illustrate the effectiveness and feasibility of the method of the present invention.

By adopting a 6-path fading channel, the maximum Doppler frequency shift is 30Hz, the time delay is expanded to 5 mus, the available bandwidth B =1MHz of the multi-cooperative relay single-cell downlink communication system, and the bit error rate BER =10^-3White gaussian noise single-sided power spectral density N₀=10^-8The number of relays is 3 (K = 3), and the number of users is 6 (M = 6).

Fig. 2 depicts the results of comparing the user rate and the minimum rate requirement obtained by the method of the present invention, the resource allocation algorithm for guaranteeing fairness and QoS, and the static resource allocation method obtained by 100 times of repeated experiments, and the number of subcarriers available to the system is 256 (N = 256). It can be seen from fig. 2 that the user rate obtained by the method of the present invention can reach the minimum user rate requirement, whereas the conventional static resource allocation method can only enable individual users to reach the required rate. The simulation experiment result shows that the method is an effective self-adaptive method capable of meeting the speed requirements of different users.

Fig. 3 shows a comparison of the total system rates of the method, the algorithm in [9] and the static resource allocation method of the present invention at different snr when the number of available subcarriers of the system is 256, and it can be seen from fig. 3 that the method of the present invention obtains a higher system rate than the conventional static resource allocation method and the algorithm in [9 ]. The simulation experiment result shows that the method is an effective resource allocation method capable of improving the total rate of the system.

The simulation result shows that the resource allocation method of the invention can obtain high system capacity under the condition of meeting the service quality requirement of each user.

The Algorithm in [9] in fig. 2 and fig. 3 refers to "An effective resource allocation Algorithm for OFDMA Cooperative Relay Networks with resources and QoS" published by Asem a.salah et al at page 188-.

Claims

1. A resource allocation method of a cooperative relay orthogonal frequency division multiple access system is characterized by comprising the following steps:

establishing an optimized resource allocation model according to the minimum service quality requirements of different users in a cooperative relay OFDMA system:the optimized resource allocation model satisfies the following constraint conditions:

A3:a_k,j,n'∈{0,1}；

wherein max () is a function of taking the maximum value, K represents the relay number in the cooperative relay OFDMA system, K is more than or equal to 1, M represents the user number in the cooperative relay OFDMA system, and M represents the user number in the cooperative relay OFDMA system>1, N denotes the number of subcarriers in a cooperative relay OFDMA system, N>1；a_k,j,n' denotes a pre-relaxation integer factor that characterizes whether the nth subcarrier and the kth relay are occupied by the jth user, P_TRepresenting the total power of the transmission at the base station, P_k,TRepresenting the transmit power, Q, at the kth relay_jRepresents the lowest rate value of the jth user; constraint A1 represents the total power of transmission constraint at the base station, and in constraint A1, when 1 ≦ j ≦ M, p_S,j,nRepresents the transmission power of the communication link between the base station and the jth user on the nth subcarrier, when M +1 is not less than j not more than M + K, p_S,j,nThe transmission power of the communication link of the base station and the k relay on the nth sub-carrier is represented; constraint a2 represents a transmit power constraint at each relay; constraint A3 is used to characterize whether the nth subcarrier and the kth relay are occupied by the jth user, a_k,j,n' 0 means that the nth subcarrier and the kth relay are not occupied by the jth user, a_k,j,n' 1 denotes that the nth subcarrier and the kth relay are occupied by the jth user; constraint a4 indicates that a subcarrier can be occupied by only one user and corresponding relay at most; constraint a5 represents the minimum quality of service requirement for different users, which is described as the minimum rate requirement for different users; r_k,j,nRepresents the instantaneous rate of the jth user on the nth subcarrier through the kth relay andlog2(1+p_S,j,nH_S,j,n+p_k,j,nH_k,j,n) Min () is the minimum function, p_S,M+k,nDenotes the transmission power, H, of the communication link between the base station and the k-th relay on the nth sub-carrier_S,M+k,nTo representChannel gain, p, of the communication link between the base station and the kth relay on the nth subcarrier_S,j,nDenotes the transmission power, H, of the communication link between the base station and the jth subscriber on the nth subcarrier_S,j,nIndicating the channel gain, p, of the communication link between the base station and the jth user on the nth sub-carrier_k,j,nDenotes the transmission power, H, of the jth user on the nth subcarrier via the kth relay_k,j,nIndicating the channel gain of the jth user on the nth subcarrier through the kth relay;

secondly, the integer factor a before relaxation in the optimized resource allocation model is used_k,j,n' relaxation to one [0,1]The variable between, noted as a_k,j,nAnd an equal power distribution method is adopted to distribute equal power for each subcarrier, so as to obtain a simplified optimized resource distribution model:the simplified optimized resource allocation model satisfies the constraint conditions: b1: a_k,j,n∈[0,1]；

<math> <mrow> <mi>B</mi> <mn>2</mn> <mo>:</mo> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <munderover> <mi>Σ</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <msub> <mi>a</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>≤</mo> <mn>1</mn> <mo>;</mo> <mtext>B3:</mtext> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>K</mi> </munderover> <munderover> <mi>Σ</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>a</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <msub> <mi>R</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>j</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>Q</mi> <mi>j</mi> </msub> <mo>;</mo> </mrow> </math>

Wherein,is represented by a_k,j,nTo optimize the maximum function of the variables, a_k,j,nThe method is used for representing the proportion number occupied by the jth user and the corresponding kth relay on the nth subcarrier; constraint B1 denotes a_k,j,nHas a value of [0,1]Any value within the interval; constraint B2 indicates that one subcarrier can be occupied by multiple users and corresponding relays; constraint B3 represents the minimum rate requirements of different users;

wherein, β_nTo representThe lagrangian operator of (a) is,_k,j,ndenotes a_k,j,nLagrange operator of, mu_jTo representLagrangian operator of (2);

fourthly, will

To a_k,j,nThe derivation is performed to obtain the corresponding first-order KKT requirement, which is expressed as:

C1:R_k,j,n-β_n+_k,j,n+μ_jR_k,j,n＝0

C2:_k,j,na_k,j,nwhere K is 1. ltoreq. K, j is 1. ltoreq. M, N is 1. ltoreq. N;

2. The resource allocation method of a cooperative relay ofdma system according to claim 1, wherein the step (c) allocates an optimal subcarrier and selects a most suitable relay to each user according to the instantaneous rate maximization, and then allocates the remaining subcarriers according to the first-order KKT requirement is as follows:

-2, allocating an optimal subcarrier to each user and selecting a most suitable relay according to the instantaneous rate maximization: a1, calculating each user to obtain the subcarrier with the maximum instantaneous speed and the corresponding relay from the base station, distributing the subcarrier with the maximum instantaneous speed as the optimal subcarrier to the corresponding user, and then collecting omega from the subcarrier set_NThe best sub-carrier is deleted, and the sub-carrier with the largest instantaneous speed obtained by the jth user from the base station is assumed to be the nth^*Subcarrier, corresponding relay is kth^*One relay then has (k)^*,n^*)＝argmaxR_k，j,nThen n is added^*The sub-carrier is taken as the optimal sub-carrier to be distributed to the jth user, and the corresponding kth user is distributed^*The relay is used as the most suitable relay, and the nth relay is used^*Sub-carrier set omega_NWherein n is not less than 1^*≤N，1≤k^*K is less than or equal to K, arg () is a parameter taking function, max () is a maximum value taking function, (K)^*,n^*)＝argmaxR_k,j,nMeans to find out the sub-carrier with the largest instantaneous speed obtained from the base station by the jth user and the corresponding relay, which are respectively the nth^*Sub-carriers and k^*A relay, R_k,j,nRepresenting the instantaneous rate of the jth user on the nth subcarrier through the kth relay; a2, and then a method for characterizing the jth user and the corresponding kth user^*A relay is in the n^*Proportional number occupied on one subcarrierAnd updates the actual rate R of the jth user_j，Wherein,wherein ═ is an assigned symbol, R on the left_jR on the right representing the updated actual rate of the jth user_jRepresenting the actual rate, R, of the j-th user before the update_jIs set to an initial value of 0, and,indicating that the jth user passes the kth user^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j, n^{*}} H_{S, j, n^{*}} + p_{k^{*}, j, n^{*}} H_{k^{*}, j, n^{*}})}, p_{S, M + k^{*}, n^{*}}

denotes base station and kth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is, denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,indicating that the communication link between the base station and the jth user is at the nth^*The transmit power on the sub-carriers is,indicating that the communication link between the base station and the jth user is at the nth^*The channel gain on a number of sub-carriers,indicating that the jth user passes the kth user^*A relay is in the n^*Transmission power on sub-carriers of valueIndicating that the jth user passes the kth user^*A relay is in the n^*Channel gain over a number of subcarriers;

fifthly, distributing the rest subcarriers: b1, obtained according to first-order KKT requirement C1_k,j,n＝β_n-(1+μ_j)R_k,j,nThen according to the first-order KKT requirement C2And then according to the first-order KKT requirement C3b2 according to_k,j,n＝β_n-(1+μ_j)R_k,j,nAndto obtain beta_n＝(1+μ_j)R_k,j,nAnd make w_jRepresenting the rate trade-off factor, w, for the jth user_j＝Q_j-R_jThen will beSimplified toWherein R is_jRepresenting the actual rate of the jth user; b3 according to beta_n＝(1+μ_j)R_k,j,nAnddetermining the equivalent mu_jWhen the number is 0, the nth sub-carrier is allocated to the jth sub-carrier^*Individual user and corresponding kth^*A relay makesWhen mu is_j>When 0, the nth subcarrier is allocated to the user with the maximum instantaneous rate and the corresponding relay to maximize the total system rate, which is j^*Individual user and kth^*A plurality of relays, wherein,denotes the j (th)^*Rate tradeoff factor for individual user, where 1 ≦ j^*Less than or equal to M; b4, finding out the user with the maximum difference between the lowest speed to be reached and the actual speed, and assuming that the found user is the j-th user^*Each user then has j^*＝argmaxw_jWherein j is not less than 1^*≤M，argmaxw_jThe user with the maximum difference between the minimum rate to be achieved and the actual rate is found out; b5, judging the j-th found^*Per user rate tradeoff factorIf so, indicating that each user has not met the minimum rate requirement, and then continuing to step b6, otherwise, indicating that each user has met the minimum rate requirement, and then continuing to step b 7; b6 finding out satisfaction conditionAnd the corresponding relay, assuming that the found subcarrier is the nth subcarrier^*Sub-carriers and the corresponding relay is the kth^*For each relay, the nth relay^*Sub-carriers allocated to the jth^*The number of users, among others,represents finding the jth^*The sub-carrier with the maximum instantaneous speed and the corresponding relay are obtained from the base station by each user, and the number is n^*Sub-carriers and k^*The number of the relays is one,denotes the j (th)^*Instantaneous rate of each user on the nth subcarrier through the kth relay; then the n-th^*Sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*A relay is in the n^*Of a proportional number occupied on a single subcarrierAnd update the jth^*Actual rate of individual userWherein,wherein ═ is an assigned symbol, leftRepresents updated jth^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The instantaneous rate on the sub-carrier(s),

R_{k^{*}, j^{*}, n^{*}} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n^{*}} H_{S, M + k^{*}, n^{*}}), \log 2 (1 + p_{S, j^{*}, n^{*}} H_{S, j^{*}, n^{*}} + p_{k^{*}, j^{*}, n^{*}} H_{k^{*}, j^{*}, n^{*}})},

representing a base station andkth^*The communication link is relayed at the n-th^*The transmit power on the sub-carriers is,denotes base station and kth^*The communication link is relayed at the n-th^*The channel gain on a number of sub-carriers,denotes the base station and j^*The communication link of the subscriber is at the nth^*The transmit power on the sub-carriers is,denotes the base station and j^*The communication link of the subscriber is at the nth^*The channel gain on a number of sub-carriers,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*The transmit power on the sub-carriers is,denotes the j (th)^*The user passes the k-th^*A relay is in the n^*Channel gain over a number of subcarriers; continuing to execute the step b 8; b7, finding out the user with the maximum instantaneous speed and the corresponding relay for the rest sub-carriers, assuming the nth sub-carrier as the rest sub-carrier, and assuming the user with the maximum instantaneous speed found for the nth sub-carrier as the jth sub-carrier^*Each user and the corresponding relay is the kth^*One relay then has (k)^*,j^*)＝argmaxR_k,j,n', wherein (k)^*,j^*)＝argmaxR_k,j,n'It is expressed that the user with the maximum instantaneous speed and the corresponding relay are found out for the nth subcarrier, which is respectively the jth subcarrier^*Individual user and kth^*A relay; then the nth sub-carrier is selected from the sub-carrier set omega_NDeleting; then order is used to characterize the j^*Individual users and corresponding kth^*Of a proportional number of relays occupying on the nth sub-carrierAnd update the jth^*Actual rate of individual userWherein,wherein ═ is an assigned symbol, leftRepresents updated jth^*Actual rate of individual user, rightRepresents j (th) before update^*The actual rate of the individual users is,is set to an initial value of 0, and,denotes the j (th)^*The user passes the k-th^*The instantaneous rate of the number of relays on the nth subcarrier,

R_{k^{*}, j^{*}, n} = \frac{1}{2} \min {\log 2 (1 + p_{S, M + k^{*}, n} H_{S, M + k^{*}, n}), \log 2 (1 + p_{S, j^{*}, n} H_{S, j^{*}, n} + p_{k^{*}, j^{*}, n} H_{k^{*}, j^{*}, n})}, p_{S, M + k^{*}, n}

denotes base station and kth^*This relays the transmit power of this communication link on the nth sub-carrier, denotes base station and kth^*This relays the channel gain of this communication link on the nth sub-carrier,denotes the base station and j^*The transmit power of this communication link for this user on the nth sub-carrier,denotes the base station and j^*The channel gain of the communication link of the user on the nth sub-carrier,denotes the j (th)^*The user passes the k-th^*The transmit power of the relay on the nth subcarrier,denotes the j (th)^*The user passes the k-th^*Channel gains of the relays on the nth subcarrier; continuing to execute the step b 8; b8, judging a subcarrier set omega_NAnd if the number is the empty set, indicating that the subcarrier allocation and the relay selection are finished, otherwise, returning to the step b4 to continue the execution.

3. The method as claimed in claim 1 or 2, wherein in step (r), K has a value of 3, 4 or 5, M has a value of 6, 8, 10 or 12, and N has a value of 128, 256, 512 or 1024.