Joint throughput and transmission range optimization for triple-hop networks with cognitive relay

The optimization of the network throughput and transmission range is one of the most important issues in cognitive relay networks （CRNs）. Existing research has focused on the dual-hop network, which cannot be extended to a triple-hop network due to its shortcomings, including the limited transmission range and one-way communication. In this paper, a novel, triple-hop relay scheme is proposed to implement time-division duplex （TDD） transmission among secondary users （SUs） in a three-phase transmission. Moreover, a superposition coding （SC） method is adopted for handling two-receiver cases in triple-hop networks with a cognitive relay. We studied a joint optimization of time and power allocation in all three phases, which is formulated as a nonlinear and concave problem. Both analytical and numerical results show that the proposed scheme is able to improve the throughput of SUs, and enlarge the transmission range of primary users （PUs） without increasing the number of hops.

认知中继网络中,传输的吞吐量和传输距离一直是衡量性能的重要指标。现有的研究多数都集中在两跳网络的优化,但其也存在着传输距离不长,只能进行单项传输等缺点。本文提出了一种新的使用认知中继的三跳网络传输方案,通过三阶段的传输过程,实现了次级用户之间的双向传输。同时,引入了叠加编码技术来处理网络中双接收节点的情况。本文将这个三阶段的联合优化问题转化为一个非线性的优化问题,并进行了求解。仿真结果表明,本文提出的优化方法可以在不增加中继跳数的情况下,延长主用户传输距离,并同时提高次级用户的传输吞吐量。