阅读说明：本技术 一种环境反向散射阵列通信系统中的协作传输优化方法 (Cooperative transmission optimization method in environment backscatter array communication system ) 是由 许威 周少卿 于 2019-08-23 设计创作，主要内容包括：本发明公开了一种环境反向散射阵列通信系统中的协作传输优化方法,所述方法包括：接收机使用非相干检测方法接收信号,根据接收信号中的主链路信号分量,构建主链路的平均传输速率上界计算模型；根据连续干扰消除检测方法和最大比合并方法,构建次链路的传输速率计算模型；最大化这两个速率的问题是一个二元非凸非线性的多目标向量优化问题,为得到该优化问题的帕累托最优解,使用交替优化方法并辅助以一维搜索来解决,得到最优的射频源发送波束成形向量和协作接收机接收合并向量,并获得两条链路的可达传输速率。本发明应用于实际的协作环境反向散射阵列通信系统,兼顾主次链路速率,具有收敛速度快、计算复杂度较低等优点。(the invention discloses a cooperative transmission optimization method in an environment backscatter array communication system, which comprises the following steps: the receiver receives signals by using a non-coherent detection method, and an upper bound calculation model of the average transmission rate of a main link is constructed according to main link signal components in the received signals; constructing a transmission rate calculation model of a secondary link according to a continuous interference elimination detection method and a maximum ratio combination method; the problem of maximizing the two rates is a binary non-convex non-linear multi-target vector optimization problem, in order to obtain the pareto optimal solution of the optimization problem, an alternative optimization method is used and one-dimensional search is used for assisting to solve the problem, the optimal radio frequency source sending beam forming vector and the cooperative receiver receiving combining vector are obtained, and the reachable transmission rates of the two links are obtained. The invention is applied to the actual cooperative environment backscatter array communication system, gives consideration to the primary and secondary link rates, and has the advantages of high convergence rate, low calculation complexity and the like.)

1. a method for cooperative transmission optimization in an environmental backscatter array communication system, the method comprising:

step 1, setting the communication system, including 1 radio frequency source, 1 environment backscattering transmitter and 1 cooperative receiver, wherein, the radio frequency source and the cooperative receiver are respectively equipped with M and N antennas, and the environment backscattering transmitter is equipped with 1 antenna, M, N are positive integers, the radio frequency source carries out transmitting beam forming, which is represented by w, w is an M multiplied by 1 dimensional vector; an environment backscatter transmitter drives an internal circuit by using energy collected from a radio frequency signal waveform, a signal to be transmitted is modulated on a radio frequency signal and is backscattered to a cooperative receiver, the transmission symbol period of the environment backscatter transmitter is K times of the transmission symbol period of a radio frequency source, K is greater than 1 and is an integer, the cooperative receiver receives and combines the received signal, the receiving and combining vector is represented by v, and v is an Nx 1-dimensional vector;

step 2, a transmission link from the radio frequency source to the cooperative receiver is called a main link, a transmission link from the radio frequency source to the cooperative receiver via the environment backscatter transmitter is called a secondary link, H1 represents a channel from the radio frequency source to the cooperative receiver, represents a channel from the radio frequency source to the environment backscatter transmitter, and hBC represents a channel from the environment backscatter transmitter to the cooperative receiver, wherein H1 is an N × M dimensional matrix and is a 1 × M dimensional vector, hBC is an N × 1 dimensional vector, and superscript H represents a conjugate transpose of the matrix;

step 3, adopting a non-coherent detection method when the cooperative receiver receives signals to construct an upper bound calculation model of the average transmission rate of the main link;

step 4, constructing a transmission rate calculation model of the secondary link according to a continuous interference elimination detection method and a maximum ratio combination method;

Step 5, establishing a cooperative transmission rate optimization problem model by using the rate calculation model;

and 6, solving the cooperative transmission rate optimization problem model by using a one-dimensional search-assisted alternative optimization method to obtain an optimal radio frequency source transmitting beam forming vector and a cooperative receiver receiving combined vector, and calculating the reachable transmission rates of the two links.

2. The method of claim 1, wherein the method comprises: in step 3, the cooperative receiver receives signals from the primary link and the secondary link, and after receiving and combining, the signals may be represented as:

wherein s (k) represents a transmission signal of a radio frequency source in a kth symbol period, namely a transmission signal of a main link, k represents a sequence number of the symbol period, c represents a backscatter signal, namely a transmission signal of a secondary link, α ∈ (0, 1) represents a reflection coefficient of an environmental backscatter transmitter, n (k) represents a zero-mean additive gaussian noise vector, and by using a non-coherent detection method, an upper bound calculation formula of an average transmission rate of the main link is as follows:

Where P denotes the transmission power of the radio frequency source, and σ 2 denotes the variance of the noise vector n (k).

3. the method as claimed in claim 1 or 2, wherein in step 4, according to the successive interference cancellation detection method and the maximum ratio combining method, the transmission rate of the secondary link is calculated as follows:

4. The method of claim 1, wherein in step 5, a cooperative transmission rate optimization problem model is established by using the rate calculation model, and is represented as follows:

subject to‖w‖＝‖v‖＝1

Wherein maxize ([ ■ ] denotes the maximum value of a vector [ ■ ] containing several objective functions, i.e. maximizing all elements in the vector at the same time, ([ denotes the variable to be optimized, ], "-") denotes the constraint, "· denotes the modulo-2 norm of the vector within the symbol;

the pareto optimal solution is that no other variable value taking mode exists, so that one or more objective functions are increased and all the remaining objective functions are not decreased, and according to the definition of the pareto optimal solution, the cooperative transmission rate optimization problem is further simplified as follows:

subject to‖w‖＝‖v‖＝1。

5. The method of claim 4, wherein in step 6, the vector optimization problem is scaled and transformed into a single-objective optimization problem by using a one-dimensional search method and selecting a weighted sum function, which is expressed as follows:

subject to‖w‖＝‖v‖＝1

wherein z represents an objective function, λ ∈ [0, 1] represents a weight coefficient of the objective function, and the weight coefficient of the objective function is represented by 1- λ;

And then, using an alternative optimization method to solve the single-target optimization problem, initializing variables w and v to be optimized, and then updating w and v in sequence until the target function z converges, wherein the specific method comprises the following steps:

the specific way of updating the variables w, v to be optimized in turn is as follows: according to the initialized v, calculating a square matrix update w as mu max, wherein the mu max represents a feature vector corresponding to the maximum feature value of the square matrix A; calculating the matrix update v ═ η max according to the updated w, wherein η max represents the feature vector corresponding to the maximum feature value of the matrix B; according to the updated v, calculating the square matrix A again and updating w; repeating continuously until the target function z converges;

And w and v obtained when the target function z converges are pareto optimal solutions of the original problems, namely an optimal radio frequency source sending beam forming vector and a cooperative receiver receiving combined vector are respectively substituted into the average transmission rate upper bound calculation formula of the main link in the step 3 and the secondary link transmission rate calculation formula in the step 4 to obtain the reachable transmission rate of the corresponding link.

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a cooperative transmission optimization method in an environment backscatter array communication system.

Background

The environmental backscattering technology is a wireless communication technology with good development prospect in recent years, is expected to realize low-cost communication free of battery constraint, is convenient and energy-saving, and has wide attention in Radio Frequency Identification (RFID) systems and Internet of things (IoT) applications. In the environment backscatter communication, an environment backscatter transmitter acquires energy from an ambient radio frequency signal in an energy acquisition mode to drive an internal circuit to work. At the same time, it modulates the received radio frequency signal to implement the function of transmitting information to the adjacent receiver at a low rate. The source of the ambient radio frequency signal may be a base station in a cellular network, commonly referred to as a radio frequency source. The receiver of the cellular communication and the receiver of the backscatter communication may be the same device, and are referred to as cooperative receivers.

the environmental backscattering technology is different from the traditional amplifying and forwarding relay technology, because the power is limited, the environmental backscattering technology can only carry out communication in a signal reflection mode and does not have the capacity of generating a new signal, so most of the existing theoretical results can not be directly applied to the environmental backscattering technology, and related communication theories are still to be perfected, for example, the influence of the environmental backscattering on the performance of a communication system is introduced in the current cellular communication, the optimal design of a signal processing scheme at a transmitting and receiving end in array communication and the like. Aiming at a cellular array communication system introducing an environment backscattering technology, the invention respectively constructs an upper bound calculation model of the average transmission rate of a cellular communication link and a transmission rate calculation model of the environment backscattering communication link based on a concept of spectrum sharing, and further establishes a cooperative transmission rate optimization problem. For the binary non-convex non-linear optimization problem, an alternating optimization method is used and one-dimensional search is assisted to obtain the optimal radio frequency source transmitting beam forming vector and the optimal cooperative receiver receiving combination vector. The method can obtain the signal processing scheme of the transmitting and receiving end through a small amount of simple iterative calculation, and can give consideration to the rate performance of a cellular communication link and an environment backscattering communication link.

Disclosure of Invention

The purpose of the invention is as follows: the invention provides a method for forming a low-complexity radio source transmitting beam and receiving and combining a cooperative receiver, which aims to solve the technical problem of signal processing at a transmitting and receiving end in a cellular array communication system with an environment backscattering function, effectively allocates resources and overall stages of rate performances of two links of cellular communication and environment backscattering communication.

The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a cooperative transmission optimization method in an environment backscatter array communication system specifically comprises the following steps:

step 1, setting the communication system to include 1 radio frequency source, 1 environment backscatter transmitter and 1 cooperative receiver, wherein the radio frequency source and the cooperative receiver are respectively equipped with M and N antennas, and the environment backscatter transmitter is equipped with 1 antenna, and M, N are positive integers. The radio frequency source performs transmit beamforming, denoted by w, which is an M x 1 dimensional vector. The environmental backscatter transmitter drives internal circuitry with energy collected from the radio frequency signal waveform, modulates the signal to be transmitted onto the radio frequency signal, and backscatter to the cooperating receiver. The transmission symbol period of the ambient backscatter transmitter is K times the transmission symbol period of the radio frequency source, K >1 and K is an integer. The cooperative receiver performs reception combining processing on the received signals, where a reception combining vector is denoted by v, and v is an N × 1-dimensional vector.

and step 2, a transmission link from the radio frequency source to the cooperative receiver is called a main link, and a transmission link from the radio frequency source to the cooperative receiver through the environment backscatter transmitter is called a secondary link. H1 denotes the channel from the radio source to the cooperative receiver, denotes the channel from the radio source to the ambient backscatter transmitter, and hBC denotes the channel from the ambient backscatter transmitter to the cooperative receiver, where H1 is an N × M dimensional matrix that is a 1 × M dimensional vector, hBC is an N × 1 dimensional vector, and superscript H denotes the conjugate transpose of the matrix.

And 3, constructing an upper bound calculation model of the average transmission rate of the main link by adopting a non-coherent detection method when the cooperative receiver receives signals.

and 4, constructing a transmission rate calculation model of the secondary link according to the continuous interference elimination detection method and the maximum ratio combination method.

and 5, establishing a cooperative transmission rate optimization problem which is a two-variable two-target non-convex non-linear optimization problem by using the rate calculation model.

And 6, solving the cooperative transmission rate optimization problem by using a one-dimensional search-assisted alternative optimization method, obtaining an optimal radio frequency source transmitting beam forming vector and a cooperative receiver receiving combined vector, and obtaining the reachable transmission rates of the two links.

In a further preferred scheme, in step 3, the cooperative receiver receives signals from the primary link and the secondary link, and after receiving and combining, may be represented as:

Wherein, s (k) represents the transmission signal of the radio frequency source in the kth symbol period, i.e. the transmission signal of the main link, k represents the serial number of the symbol period, c represents the backscatter signal, i.e. the transmission signal of the secondary link, α ∈ (0, 1) represents the reflection coefficient of the environmental backscatter transmitter, and n (k) represents a zero-mean additive gaussian noise vector, and by using a noncoherent detection method, the upper bound calculation formula of the average transmission rate of the main link is as follows:

Where P denotes the transmission power of the radio frequency source, and σ 2 denotes the variance of the noise vector m (k).

Further preferably, in step 4, according to the successive interference cancellation detection method and the maximum ratio combining method, the transmission rate calculation formula of the secondary link is as follows:

In step 5, according to the upper bound of the average transmission rate of the primary link obtained in step 3 and the transmission rate of the secondary link obtained in step 4, a further preferred scheme is to establish a cooperative transmission rate optimization problem, which is expressed as follows:

subject to‖w‖＝‖v‖＝1

Where maxize ([ ■ ] denotes the maximum value of the vector [ ■ ] containing several objective functions, i.e. all elements in the vector are maximized simultaneously, () denotes the variable to be optimized, subject to denotes the constraint, "· |" denotes the modulo 2 norm of the vector within the symbol.

the pareto optimal solution is such that there are no other variable-valued ways, such that one or more objective functions are increased and all remaining objective functions are not decreased. According to the definition of the pareto optimal solution, the cooperative transmission rate optimization problem is further simplified into that:

subject to‖w‖＝‖v‖＝1

In step 6, a one-dimensional search method is used to select a weighted sum function, and the vector optimization problem is scaled and quantized to be converted into a single-target optimization problem, which is expressed as follows:

subject to‖w‖＝‖v‖＝1

Where z represents the objective function and λ ∈ [0, 1] represents the weight coefficient of the objective function, and accordingly, the weight coefficient of the objective function is represented by 1- λ.

and then, using an alternative optimization method to solve the single-target optimization problem, initializing variables w and v to be optimized, and then updating w and v in sequence until the target function z converges.

The specific way of updating the variables w, v to be optimized in turn is as follows: according to the initialized v, calculating a square matrix update w as mu max, wherein the mu max represents a feature vector corresponding to the maximum feature value of the square matrix A; calculating the matrix update v ═ η max according to the updated w, wherein η max represents the feature vector corresponding to the maximum feature value of the matrix B; according to the updated v, calculating the square matrix A again and updating w; and repeating until the objective function z converges.

and w and v obtained when the target function z converges are pareto optimal solutions of the original problems, namely an optimal radio frequency source sending beam forming vector and a cooperative receiver receiving combined vector are respectively substituted into the average transmission rate upper bound calculation formula of the main link in the step 3 and the secondary link transmission rate calculation formula in the step 4 to obtain the reachable transmission rate of the corresponding link.

Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:

1. The method of the invention simultaneously considers the cellular communication transmission rate and the environmental backscattering communication transmission rate to carry out resource allocation, and the optimal resource allocation mode which is obtained meets the following conditions: other better resource allocation modes do not exist, so that the rate performance of another link is not lost when the rate performance of a certain link is improved;

2. The method has the advantages of high convergence speed and low calculation complexity.

drawings

Fig. 1 is a flowchart of a cooperative transmission optimization method in an ambient backscatter array communication system according to the present invention;

Fig. 2 is a system block diagram of a cooperative transmission optimization method in an ambient backscatter array communication system according to the present invention;

Fig. 3 is a graph of the transmission rate of the primary and secondary links when the optimal signal processing scheme is used at the transceiver end of the communication system under different reflection coefficients of the environmental backscatter transmitter.

Detailed Description

The invention will be further described with reference to the accompanying drawings and specific examples:

as shown in fig. 2, the ambient backscatter array communication system comprises 1 rf source, 1 ambient backscatter transmitter, and 1 cooperative receiver, wherein the rf source and the cooperative receiver are respectively equipped with M and N antennas, and the ambient backscatter transmitter is equipped with 1 antenna, and M, N is a positive integer. The radio frequency source performs transmit beamforming, denoted by w, which is an M x 1 dimensional vector. The environmental backscatter transmitter drives internal circuitry with energy collected from the radio frequency signal waveform, modulates the signal to be transmitted onto the radio frequency signal, and backscatter to the cooperating receiver. The transmission symbol period of the ambient backscatter transmitter is K times the transmission symbol period of the radio frequency source, K >1 and K is an integer. The cooperative receiver performs reception combining processing on the received signals, where a reception combining vector is denoted by v, and v is an N × 1-dimensional vector.

(1) the transmission link from the radio frequency source to the cooperating receiver is called the primary link and the transmission link from the radio frequency source to the cooperating receiver via the ambient backscatter transmitter is called the secondary link. H1 denotes the channel from the radio source to the cooperative receiver, denotes the channel from the radio source to the ambient backscatter transmitter, and hBC denotes the channel from the ambient backscatter transmitter to the cooperative receiver, where H1 is an N × M dimensional matrix that is a 1 × M dimensional vector, hBC is an N × 1 dimensional vector, and superscript H denotes the conjugate transpose of the matrix.

(2) the cooperative receiver receives signals from the primary link and the secondary link, and after receiving and combining, the signals can be expressed as:

Wherein, s (k) represents the transmission signal of the radio frequency source in the kth symbol period (i.e. the transmission signal of the main link), k represents the sequence number of the symbol period, c represents the backscatter signal (i.e. the transmission signal of the secondary link), α ∈ (0, 1) represents the reflection coefficient of the environmental backscatter transmitter, and n (k) represents a zero-mean additive gaussian noise vector, and the upper bound calculation formula of the average transmission rate of the main link is as follows by using the incoherent detection method:

Where P denotes the transmission power of the radio frequency source, and σ 2 denotes the variance of the noise vector n (k).

(3) according to the successive interference cancellation detection method and the maximum ratio combining method, the transmission rate calculation formula of the secondary link is as follows:

(4) Establishing a cooperative transmission rate optimization problem according to the upper bound of the average transmission rate of the main link obtained in the step 3 and the transmission rate of the secondary link obtained in the step 4, which is expressed as follows:

subject to‖w‖＝‖v‖＝1

where maxize ([ ■ ] denotes the maximum value of the vector [ ■ ] containing several objective functions, i.e. all elements in the vector are maximized simultaneously, () denotes the variable to be optimized, subject to denotes the constraint, "· |" denotes the modulo 2 norm of the vector within the symbol.

The pareto optimal solution is such that there are no other variable-valued ways, such that one or more objective functions are increased and all remaining objective functions are not decreased. According to the definition of the pareto optimal solution, the cooperative transmission rate optimization problem is further simplified into that:

subject to‖w‖＝‖v‖＝1.

(5) firstly, a one-dimensional search method is used, a weighting sum function is selected, the vector optimization problem is quantized and converted into a single-target optimization problem, and the method is represented as follows:

subject to‖w‖＝‖v‖＝1.

where z represents the objective function and λ ∈ [0, 1] represents the weight coefficient of the objective function, and accordingly, the weight coefficient of the objective function is represented by 1- λ.

and then, using an alternative optimization method to solve the single-target optimization problem, initializing variables w and v to be optimized, and then updating w and v in sequence until the target function z converges.

The specific way of updating the variables w, v to be optimized in turn is as follows: according to the initialized v, calculating a square matrix update w as mu max, wherein the mu max represents a feature vector corresponding to the maximum feature value of the square matrix A; calculating the matrix update v ═ η max according to the updated w, wherein η max represents the feature vector corresponding to the maximum feature value of the matrix B; according to the updated v, calculating the square matrix A again and updating w; and repeating until the objective function z converges.

and w and v obtained when the target function z converges are pareto optimal solutions of the original problems, namely an optimal radio frequency source sending beam forming vector and a cooperative receiver receiving combined vector are respectively substituted into the average transmission rate upper bound calculation formula of the main link in the step 3 and the secondary link transmission rate calculation formula in the step 4 to obtain the reachable transmission rate of the corresponding link.

fig. 3 is a graph of the change in transmission rate of primary and secondary links when both the rf source and cooperating receiver in the communication system employ the optimal signal processing scheme. The different line types represent the change in the reflection coefficient of the ambient backscatter transmitter. It can be seen from the figure that the cooperative transmission optimization method in the environmental backscatter array communication system provided by the invention can intuitively and effectively balance the cellular communication transmission rate and the backscatter communication transmission rate, thereby realizing optimal resource allocation.

the above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention. All the components not specified in the present embodiment can be realized by the prior art.