Power control method for bidirectional AF relay-assisted D2D communication

Abstract

The invention discloses a power control method for bidirectional AF relay-assisted D2D communication, which relates to the technical field of wireless communication, and comprises the following steps: acquiring signals received by a first time slot RU and a downlink CU, then acquiring amplified and forwarded signals received by a second time slot DU1 and DU2 and received signals of an uplink BS, and combining a self-interference elimination technology so as to realize the power control of the bidirectional AF relay-assisted D2D communication. Obtaining a signal to interference plus noise ratio SINR1 and a signal to interference plus noise ratio SINR2 at the DU1 and the DU2 after the self-interference is eliminated; a cellular network adopts a time division duplex mode, a cellular link and a D2D link share the same spectrum resource, two possible transmission schemes are provided according to the relationship between the uplink and downlink stages of cellular communication and the two stages of bidirectional D2D communication, and when a base station has perfect instantaneous channel state information, the transmission efficiency of the base station is improved. According to the power control scheme, the performance of the D2D link is optimized by using the two performance indexes of the D2D link while the QoS requirement of the cellular link is met, so that the spectrum utilization rate can be improved, and the power loss is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communications, and in particular to a power control method for bidirectional AF relay-assisted D2D communication. Background Art

[0002] The fifth generation (5G) mobile communication system is expected to achieve a data rate 1000 times higher than the current 4G system, and has attracted worldwide research interest in recent years. Today, 5G has begun to be deployed around the world and will greatly change people's lives and society. Device-to-device (D2D) communication has been widely studied as one of the important technologies of 5G mobile communication systems. Unlike traditional cellular communications where all communication signals must pass through the base station (BS), D2D communication can reduce the traffic of cellular networks by enabling nearby mobile devices to communicate directly with each other. Therefore, D2D communication has the advantages of improving cellular coverage and reducing transmission delay. Underlay D2D communication can improve spectrum efficiency by reusing spectrum resources, but it will cause interference between D2D and cellular users. This interference can be mitigated by power control and resource allocation.

[0003] So far, most of the research on D2D communication has considered the scenario where D2D users can establish direct links. However, in practical applications, the advantages of D2D communication may be limited when D2D users are far away from each other or the channel conditions between D2D users are poor. In order to significantly extend the range of D2D communication, a promising approach is to use relay-assisted D2D communication. In order to compensate for the spectrum efficiency loss of a unidirectional relay system, the present invention proposes a power control method for bidirectional AF relay-assisted D2D communication to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a power control method for bidirectional AF relay assisted D2D communication to solve the problems existing in the prior art mentioned in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A power control method for bidirectional AF relay assisted D2D communication, comprising the following steps:

[0007] S1: Get the signal received by the first time slot RU and the downlink CU, then get the amplified and forwarded signal received by the second time slot DU1 and DU2 and the received signal of the uplink BS, and combine the self-interference cancellation technology to get the signal-to-interference-to-noise ratios SINR1 and SINR2 at DU1 and DU2 after self-interference cancellation;

[0008] S2: Use the QoS required by cellular communication to obtain the base station transmission power P b , Cellular user transmission power P c , and further obtain the relay user transmission power P r The optimal value of , thereby converting SINR1 and SINR2 obtained in S1 into a formula for the transmission power P1 of D2D user 1 and the transmission power P2 of D2D user 2;

[0009] S3: The power control problem is expressed as an optimization problem of D2D link performance. The performance index of the D2D link is combined with SINR1 and SINR2 obtained in S2 to maximize the smallest one of SINR1 and SINR2.

[0010] S4: Calculate the solutions under the three boundary conditions in S3, compare these possible optimal solutions, and the solution that maximizes the objective function is the optimal solution;

[0011] S5: Use another performance indicator of the D2D link combined with SINR1 and SINR2 obtained in S2 to maximize the sum rate of DU1 and DU2;

[0012] S6: The non-convex optimization problem in S5 is approximated as a convex function difference optimization problem, and an iterative algorithm is used to solve the power optimization value.

[0013] Preferably, in the cellular network, the full-duplex bidirectional relay-assisted D2D link reuses the frequency band of the cellular link for communication, and in S1, SINR1 and SINR2 are expressed as:

[0014]

[0015] Where β is the scaling factor, h0 is the required channel between BS and CU, h1 and h2 represent the required channels between DU1, DU2 and RU; f0 represents the interference channel between BS and RU, f1 and f2 represent the interference channels between DU1, DU2 and CU respectively, and N0 is the variance of composite additive white Gaussian noise.

[0016] Preferably, in S2, the QoS required for cellular communication is:

[0017]

[0018] where τ u and τ d They represent the signal-to-interference-and-noise ratio requirements for the uplink and downlink of the cellular link respectively.

[0019] Preferably, in S3, the optimization problem is established as:

[0020]

[0021] st,0<P1|f1| 2 +P2|f2| 2 ≤η,

[0022] 0<P1,

[0023] in are the maximum transmit powers of RU, DU1 and DU2, and the maximum transmit powers of BS are

[0024] Preferably, the optimization problem in S5 is established as:

[0025]

[0026] Preferably, in S6, the non-convex optimization problem is well approximated to the convex optimization problem, and an iterative algorithm is used to solve the power optimization value. The solution improved by the iterative algorithm always converges, so that the iterative process stops after a finite number of iterations.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the present invention, the cellular network adopts the time division duplex mode, and the cellular link and the D2D link share the same spectrum resources. According to the relationship between the uplink and downlink stages of the cellular communication and the two stages of the two-way D2D communication, two possible transmission schemes are proposed. In each scheme, when the base station (BS) has perfect instantaneous channel state information (CSI), the power control scheme optimizes the performance of the D2D link by utilizing the two performance indicators of the D2D link while meeting the QoS (quality-of-service) requirements of the cellular link, thereby improving the spectrum utilization, reducing the power loss, and greatly optimizing the communication performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is an operation flow chart of the power control method of the present invention.

[0030] Figure 2 This is a cell model in which a bidirectional AF relay-assisted D2D link and a cellular link coexist in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0032] A single cellular scenario includes two types of communications: traditional cellular communication and D2D communication with the aid of a two-way AF relay; in this system, the cellular link consists of a cellular user (CU) and a BS, while the D2D link consists of a pair of D2D users (DU1 and DU2) and an auxiliary relay user (RU), and the cellular link and the D2D link share the same spectrum resources; DU1 and DU2 communicate through the RU, and the RU adopts a two-way AF relay protocol. According to the relationship between the uplink and downlink phases of cellular communication and the two phases of two-way D2D communication, there are two possible transmission schemes. In transmission scheme I, the first phase of two-way D2D communication shares the downlink resources of cellular communication, while the second phase of two-way D2D communication shares the uplink resources of cellular communication. In transmission scheme II, the first phase of two-way D2D communication shares the uplink resources of cellular communication, while the second phase of two-way D2D communication shares the downlink resources of cellular communication. For the two transmission schemes, the power control algorithm is similar, and the present invention is mainly aimed at the first one.

[0033] See also Figure 1-2 , the present invention provides the following technical solutions:

[0034] A power control method for bidirectional AF relay assisted D2D communication, comprising the following steps:

[0035] S1: Get the signal received by the first time slot RU and the downlink CU, then get the amplified and forwarded signal received by the second time slot DU1 and DU2 and the received signal of the uplink BS, and combine the self-interference cancellation technology to get the signal-to-interference-to-noise ratios SINR1 and SINR2 at DU1 and DU2 after self-interference cancellation;

[0036] Get the signal received by the first time slot RU and the downlink CU:

[0037]

[0038] Where h0 is the desired channel between BS and CU, h1 and h2 represent the desired channels between DU1, DU2 and RU; f0 represents the interference channel between BS and RU, f1 and f2 represent the interference channels between DU1, DU2 and CU respectively; the composite additive white Gaussian noise (AWGN) at BS, CU, RU, DU1 and DU2 is represented by n b 、n c 、n r , n1 and n2 represent that its mean is 0 and its variance is N0.

[0039] Then obtain the amplified and forwarded signals received by the second time slot DU1 and DU2 and the received signal of the uplink BS:

[0040]

[0041]

[0042] Among them, the proportional factor β is:

[0043]

[0044] In the cellular network, the full-duplex bidirectional relay-assisted D2D link reuses the frequency band of the cellular link for communication, and SINR1 and SINR2 are expressed as:

[0045]

[0046] Substituting β into SINR1 and SINR2 yields:

[0047]

[0048] S2: Use the QoS required by cellular communication to obtain the base station transmission power P b , Cellular user transmission power P c , and further obtain the relay user transmission power P r The optimal value of , thereby converting SINR1 and SINR2 obtained in S1 into a formula for the transmission power P1 of D2D user 1 and the transmission power P2 of D2D user 2;

[0049]

[0050] where τ u and τ d They represent the signal-to-interference-and-noise ratio requirements for the uplink and downlink of the cellular link respectively.

[0051] Considering the constraints P r Relay user transmission power P r The optimized value of is:

[0052]

[0053] in is the maximum transmit power of CU, is the maximum transmit power of RU, DU1 and DU2, and the maximum transmit power of BS is expressed as

[0054] Then, SINR1 and SINR2 are converted into the formulas about the transmit power P1 of D2D user 1 and the transmit power P2 of D2D user 2:

[0055]

[0056] in:

[0057]

[0058] The QoS required for cellular communication is as follows:

[0059]

[0060] S3: Represent the power control problem as an optimization problem for D2D link performance. By using the performance metrics of the D2D link and combining the SINR1 and SINR2 obtained in S2, maximize the smaller one of SINR1 and SINR2. The optimization problem is established as follows:

[0061]

[0062] s.t., 0 < P1|f1| 2 +P2|f2| 2 ≤ η,

[0063] 0 < P1,

[0064] where are the maximum transmit powers of RU, DU1, and DU2, and the maximum transmit power of BS is

[0065] S4: Calculate the solutions in the three boundary cases in S3, compare these possible optimal solutions, and the solution that maximizes the objective function is the optimal solution;

[0066] To solve the optimization problem in S3, it should be noted that the following two theorems are used: (1) SINR1 = SINR2. Proof: SINR1 is a monotonically increasing function of P1 and a monotonically increasing function of P2, and SINR2 is a monotonically increasing function of P1 and a monotonically decreasing function of P2. Assume that at the optimal solution where SINR1 > SINR2, we can decrease the value of P2, decrease SINR1, increase SINR2 until SINR1 = SINR2, and at the same time increase the smaller SINR. Assume that at the optimal solution where SINR1 < SINR2, we can increase SINR1 and decrease SINR2 by decreasing the value of P1 until SINR1 = SINR2, and at the same time increase the smaller SINR. Therefore, we can conclude that SINR1 = SINR2 at the optimal solution. (2) The optimal solution must be on the boundary of the feasible region. Prove by contradiction: Assume that the optimal solution is inside the feasible region, then there exists a constant λ:

[0067]

[0068] such that On the boundary of the feasible region, we can get:

[0069]

[0070] Since both SINRs are improved, the smaller SINR is improved. This is consistent with the assumption It is a contradiction that the optimal solution is a contradiction. Therefore, we can conclude that the optimal solution must be on the boundary of the feasible domain. The boundary of the feasible domain can be divided into three cases. The present invention further studies each case.

[0071] (1)

[0072] (2)

[0073] (3)P1|f1| 2 +P2|f2| 2 =η

[0074] Quadratic equations can be obtained in all three cases, and the corresponding solutions can be solved. Finally, the possible optimal solutions of the three boundary conditions are compared, and the solution that maximizes the objective function is the optimal solution.

[0075] S5: Use another performance indicator of the D2D link combined with SINR1 and SINR2 obtained in S2 to maximize the sum rate of DU1 and DU2;

[0076] The optimization problem is formulated as:

[0077]

[0078] S6: The non-convex optimization problem in S5 is approximated as a convex function difference optimization problem, and an iterative algorithm is used to solve the power optimization value. The solution improved by the iterative algorithm always converges, so that the iterative process stops after a finite number of iterations.

[0079] It means P = [P1, P2] T , the objective function can be expressed as:

[0080] log2(1+SINR1)+log2(1+SINR2)=f1(P)-f2(P)

[0081] in:

[0082]

[0083] f2(P)=log2(A1P1+A2P2+A3)+log2(B1P1+B2P2+B3)

[0084] The term f2(P) can be found at point P (k) The first-order Taylor expansion approximation is Then, we can choose a feasible initial value P by solving the following optimal solution to the convex optimization problem: (0) , and get P at the kth iteration (k+1) :

[0085]

[0086] st,0<P1|f1| 2 +P2|f2| 2 ≤η,

[0087] 0<P1,

[0088] This optimization problem can be solved using standard convex optimization techniques, such as Figure 1 As shown, the power control method of the present invention can well implement power control.

[0089] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A power control method for bidirectional AF relay-assisted D2D communication, characterized in that: The following steps are involved: S1: Get the signal received by the first time slot RU and the downlink CU, then get the amplified and forwarded signal received by the second time slot DU1 and DU2 and the received signal of the uplink BS, and combine the self-interference cancellation technology to get the signal-to-interference-to-noise ratios SINR1 and SINR2 at DU1 and DU2 after self-interference cancellation; S2: Use the QoS required by cellular communication to obtain the base station transmission power P b , Cellular user transmission power P c , and further obtain the relay user transmission power P r The optimal value of , thereby converting SINR1 and SINR2 obtained in S1 into a formula for the transmission power P1 of D2D user 1 and the transmission power P2 of D2D user 2; S3: The power control problem is expressed as an optimization problem of D2D link performance. The performance index of the D2D link is combined with SINR1 and SINR2 obtained in S2 to maximize the smallest one of SINR1 and SINR2. S4: Calculate the solutions under the three boundary conditions in S3, compare these possible optimal solutions, and the solution that maximizes the objective function is the optimal solution; S5: Use another performance indicator of the D2D link combined with SINR1 and SINR2 obtained in S2 to maximize the sum rate of DU1 and DU2; S6: The non-convex optimization problem in S5 is approximated as a convex function difference optimization problem, and an iterative algorithm is used to solve the power optimization value.

2. The power control method for bidirectional AF relay assisted D2D communication according to claim 1, characterized in that: In a cellular network, a full-duplex bidirectional relay-assisted D2D link reuses the frequency band of a cellular link for communication. In S1, SINR1 and SINR2 are expressed as: Where β is the scaling factor, h0 is the required channel between BS and CU, h1 and h2 represent the required channels between DU1, DU2 and RU; f0 represents the interference channel between BS and RU, f1 and f2 represent the interference channels between DU1, DU2 and CU respectively, and N0 is the variance of composite additive white Gaussian noise.

3. The power control method for bidirectional AF relay assisted D2D communication according to claim 2, characterized in that: In S2, the QoS required for cellular communication is: where τ u and τ d They represent the signal-to-interference-and-noise ratio requirements for the uplink and downlink of the cellular link respectively.

4. The power control method for bidirectional AF relay assisted D2D communication according to claim 2, characterized in that: In S3, the optimization problem is established as: s.t.,0<P1|f1| 2 +P2|f2| 2 ≤η, in are the maximum transmit powers of RU, DU1 and DU2, and the maximum transmit powers of BS are 5. The power control method for bidirectional AF relay assisted D2D communication according to claim 2, characterized in that: The optimization problem in S5 is established as:

6. The power control method for bidirectional AF relay assisted D2D communication according to claim 1, characterized in that: In S6, the non-convex optimization problem is well approximated to the convex optimization problem, and an iterative algorithm is used to solve the power optimization value. The solution improved by the iterative algorithm always converges, so that the iterative process stops after a limited number of iterations.

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