认知无线电中基于MIMO波束成形的协同频谱接入设计

协同认知无线电技术由于其高效的频谱利用效率已经吸引越来越多的关注.在协同认知网络中,当第一用户(Primary User,PU)之间的信道状况恶劣时,特定的第二用户(Secondary User,SU)被选为中继协同PU完成 信息传递,作为回报,PU分配一定的信道资源给SU,使其用于传输自己的信息.当SU系统中一个节点拥有多天线时,假设其可以很好的获悉其与PU之间的信道状态信息,通过波束成形设计可以使其在中继PU信息的同时完成自身信息的发送,而且使两者之间的信号互不干扰.这种频谱共享式的接入方式可以节约信道资源,提高频谱利用率.本文对采用放大转发(Amplify and Forward,AF)中继协议的SU发射端分别采用最小化加权均方误差和准则( Minimizing Sum of Weighted Mean Square Errors,MSWMSE)和迫零准则(Zero Forcing,ZF)对波束成形参数进行设计.仿真结果表明,两种设计方式都可以满足消除用户间干扰的要求；另外,由于基于MSWMSE准则的波束成形参数能够更好的平衡噪声和用户间干扰项对信号的损耗,因而获得更优的性能表现,而且通过调整加权系数可以满足PU用户不同的性能要求.

Cooperative Spectrum Access Based on MIMO Beamforming in Cognitive Radios

Cooperative cognitive radio networks(CCRNs) are attracting more and more attentions for its high spectrum efficiency.When the channel state between the primary users(PUs) is worse in the CCRNs,PUs can give out a dedicated portion of channel resource to some secondary users(SUs) in exchange for the SUs’ helping them to complete their communications.Suppose the SUs can perfectly know the channel state information(CSI) between them and the PUs,and the SU source node is equipped with multiple antennas,beamforming technologies can be employed to provide SU the capability of accomplishing its own signal transmission and the assisting the PUs to transmit their messages at the same time without interfering with each other.By this way,the spectrum utilization efficiency is greatly improved.In this work,we design the beamforming parameters based on zero-forcing(ZF) and minimizing sum of weighted mean square errors(MSWMSE) at the source SU node,respectively.Simulation results show that both criteria can provide the co-channel interference(CCI) cancellation,and the MSWMSE has a much better performance in the average sum of mean square errors(ASMSE) of the PUs and SUs because it can optimally balance CCI and noise at the destinations.Moreover,different performance of the PUs link can be achieved by adjusting the weight factor.