采用分布式Alamouti编码的虚拟全双工中继通信方案

A Virtual Full-Duplex Relay Communication Scheme Based on Distributed Alamouti Protocol

针对单输入单输出系统无法获得发射分集的缺陷以及全双工中继(FDR)通信中存在自干扰(SI)降低系统性能的问题,提出了一种采用分布式Alamouti编码的虚拟全双工(VFD)中继传输方案(DA-VFD)。该方案先将3个时隙划分为一组并在第1、2个时隙内传输发送符号以及发送符号的复共轭至中继节点和目的节点,再在第3个时隙将前两个时隙的接收符号联合解调,由于联合解调时的公式具有Alamouti的形式,因此目的节点可以获得二阶发射分集,抵抗信道衰落对系统误码性能造成的不利影响;同时,由于2个半双工节点在地理位置上隔离,其中一个节点发送的信号不会被另一个节点接收到,避免了全双工通信中SI带来的系统性能下降以及对SI消除带来的硬件需求;最后通过2个半双工中继之间的相互配合,达到近似于全双工(FD)通信的频谱效率。仿真结果表明:DA-VFD方案的误码性能不受残余自干扰(RSI)的影响,并比Alamouti FD方案具有更好的误码性能;在消除质量参数为0.5的情况下,频谱效率为1.33 b/(s·Hz)时,可以获得约2 dB的性能增益;频谱效率为2.67 b/(s·Hz)时,可以获得约6 dB的性能增益。

A distributed Alamouti-based protocol for virtual full-duplex(VFD)relaying networks(DA-VFD)is proposed to solve the problem that single-input single-output(SISO)system cannot achieve the transmit diversity,and self-interference(SI)in full-duplex(FD)system degrades the system performance.In order to obtain the second-order transmit diversity against the channel fading,which leads to drawbacks of the BER performance,DA-VFD combines three time slots as a group for transmission:The source transmit symbols and the complex conjugate of the symbols are transmitted to the relay node and the destination node within the first and the second time slots,and the receiving symbols from the first two slots are demodulated together in the third time slot.Since the formula used for joint demodulation has the form Alamouti,the destination can obtain the second-order transmission diversity,which can resist the adverse effect of channel fading on system error performance.At the same time,because the two half duplex nodes are isolated geographically,the signals sent by one node will not be received by the other node,which avoids the system performance degradation brought by SI in full-duplex communication and the hardware requirements by SI elimination.Finally,the spectral efficiency of full duplex communication is achieved through the coordination between two half duplex relays.Simulation results show that the BER performance of DA-VFD is not affected by RSI and outperforms the existing Alamouti FD.When the spectral efficiency is 1.33 b/(s·Hz)and the quality of SI cancellation is 0.5,DA-VFD obtains about 2 dB more BER gains than Alamouti FD;when the spectral efficiency is 2.67 b/(s·Hz)and the quality of SI cancellation is 0.5,DA-VFD obtains about 6 dB more BER gains than Alamouti FD.