协同无线通信系统中的分布式自适应功率分配

在系统总功率一定的情况下,通过在协同节点间进行优化的功率分配以改善系统的接收性能.针对单中继协同传输,推导了节点间最优功率分配因子的闭式表达式,给出了中继节点的激活条件,仅当信道的衰落特性满足该条件时,中继节点才发送信号到目的节点,否则进入空闲状态.多节点协同传输场景下,直接根据系统的输出信噪比难以得到节点间最优功率分配因子的闭式表达式.因此,推导了系统输出信噪比的上界,在此基础上,提出了一种新的功率分配方法.将整个功率分配过程分成两步,采用迭代的方法实现节点间的最优功率分配.仿真结果表明,对于单中继节点的情况,所提出的功率分配方案能够获得约1~2 dB的性能增益,随着参与协同传输的节点数的增大,迭代的功率分配可使系统获得显著的性能提升.

Distributed adaptive power allocation in cooperative wireless communication systems

The performance of the cooperative transmission system can be improved significantly by allocating powers optimally among cooperative nodes when the system has a total power constraint.For a two-hop cooperative transmission system with only one relay node,the closed-form expression of the optimal power allocation factor was derived and a relay activation condition was acquired.If and only if the fading characteristics of the channels satisfy this condition,the relay transmits signals to the destination;otherwise,it will stay in the idle state.For a system with more than one relay node,the closed-form power allocation factors are difficult to derive directly based on the output signal-to-noise ratio(SNR) of the system.So,an SNR upper bound was derived and a novel power allocation scheme was proposed.The whole power allocation was divided into two stages and the optimal power allocation was implemented by using an iterative algorithm.Simulation results show that for a system with only one relay node,the proposed power allocation scheme can yield about 1~2 dB performance gains compared to the equal power allocation,as the number of relays increase,the performance of the system improved greatly when using the iterative power allocation method.