Du Guanyao, Yu Jianjun
Computer Network Information Center, Chinese Academy of Sciences, Beijing, 100190 China.
Springerplus. 2016 May 17;5:654. doi: 10.1186/s40064-016-2203-8. eCollection 2016.
This paper investigates the system achievable rate for the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system with an energy harvesting (EH) relay. Firstly we propose two protocols, time switching-based decode-and-forward relaying (TSDFR) and a flexible power splitting-based DF relaying (PSDFR) protocol by considering two practical receiver architectures, to enable the simultaneous information processing and energy harvesting at the relay. In PSDFR protocol, we introduce a temporal parameter to describe the time division pattern between the two phases which makes the protocol more flexible and general. In order to explore the system performance limit, we discuss the system achievable rate theoretically and formulate two optimization problems for the proposed protocols to maximize the system achievable rate. Since the problems are non-convex and difficult to solve, we first analyze them theoretically and get some explicit results, then design an augmented Lagrangian penalty function (ALPF) based algorithm for them. Numerical results are provided to validate the accuracy of our analytical results and the effectiveness of the proposed ALPF algorithm. It is shown that, PSDFR outperforms TSDFR to achieve higher achievable rate in such a MIMO-OFDM relaying system. Besides, we also investigate the impacts of the relay location, the number of antennas and the number of subcarriers on the system performance. Specifically, it is shown that, the relay position greatly affects the system performance of both protocols, and relatively worse achievable rate is achieved when the relay is placed in the middle of the source and the destination. This is different from the MIMO-OFDM DF relaying system without EH. Moreover, the optimal factor which indicates the time division pattern between the two phases in the PSDFR protocol is always above 0.8, which means that, the common division of the total transmission time into two equal phases in previous work applying PS-based receiver is not optimal.
本文研究了具有能量收集（EH）中继的多输入多输出正交频分复用（MIMO - OFDM）系统的系统可达速率。首先，我们通过考虑两种实际的接收机架构，提出了两种协议，即基于时间切换的解码转发中继（TSDFR）和基于灵活功率分配的DF中继（PSDFR）协议，以实现中继处的信息处理和能量收集同时进行。在PSDFR协议中，我们引入了一个时间参数来描述两个阶段之间的时分模式，这使得该协议更加灵活和通用。为了探索系统性能极限，我们从理论上讨论了系统可达速率，并为所提出的协议制定了两个优化问题，以最大化系统可达速率。由于这些问题是非凸的且难以求解，我们首先从理论上对它们进行分析并得到一些明确的结果，然后为它们设计一种基于增广拉格朗日惩罚函数（ALPF）的算法。提供了数值结果来验证我们分析结果的准确性以及所提出的ALPF算法的有效性。结果表明，在这种MIMO - OFDM中继系统中，PSDFR在实现更高可达速率方面优于TSDFR。此外，我们还研究了中继位置、天线数量和子载波数量对系统性能的影响。具体而言，结果表明，中继位置对两种协议的系统性能都有很大影响，当中继放置在源和目的地中间时，可达速率相对较差。这与没有EH的MIMO - OFDM DF中继系统不同。此外，在PSDFR协议中表示两个阶段之间时分模式的最优因子始终大于0.8，这意味着，在先前应用基于功率分配的接收机的工作中，将总传输时间平均分为两个相等阶段的做法不是最优的。
