Performance Analysis Of Device-to-device Communication Assisted By Mobile Relaying

With 5G coming, the demand for higher wireless transmission rate will grow exponentially. The current 4G tends to be limited by their infrastrnctures and is lack of flexbility to shift the network capacity. Thus, it is necessary to develop the new wireless communication technologies and network infrastructures. Device-to-device (D2D) communciation underlaying cellular networks has recently attracted a significant amount of attention. By resuing the same time-frequency resources with cellular link, D2D communciation can enhance the capacity, improve the resource utilization, reduce the power consumption and obtain the high transmission rate. In cellualr network, the relay systems effectively increae the power efficiency and obtian spatial diversity gain to cope with multi-path fading. In this dissertation, the outage probability and ergodic achievable rate for the D2D communication system assisted by a relay node are investigated.Firstly, we investigate the outage probability and achievable rate for the D2D communication aided by an AF relay node (mobile or fixed user). The interference and noise at each users are considered. We derive the closed-form expressions for the outage probability and achievable rate of the D2D link. For the performance of outage probability, we discuss three special scenarios including high SNR, D2D users located far away from base station and D2D users far away from cellualr link. We also give the asymptotic expressions for each scenario. Under the condition of constant total transmit power of the D2D link, we present a power allocation strategy among D2D user and relay user to reduce the outage probability. For the achievable rate, we propose a joint-power allocation shceme to maximize the rate of both D2D and cellualr link with the constraint of per-user's maximun transmit power.Secondly, we study the outage probability of D2D communication assisted with another D2D user using two-way AF relaying protocol. We consider both interference and noisee and discuss the outage probability under strong and weak interference from cellular link and derive the exact closed-form expressions for two cases, respectively. Based on these results, tight approximations in high SNR regime under two cases are presented. Numerical results verify the correctness of the analytical results and show that the outage probability for the relay aided D2D link can be greatly enhanced without extra power.Then, the D2D communication assisted by two-way DF relay node is investigated. Based on the definition of outage probability or ergodic achievable rate, we derive the closed-form expressions for both outage probability and ergodic achievable rate in asymmetric and symmetric cases, in which two cases are determined by whether the received power at the relay node are equal or not. According to these results we give the asymptotic expressions for the high SNR scenario. Additionally, the closed-form power allocation strategies are provided in order to improve the outage performance, as well as, ergodic achievable rate, respectively.Next, we propose the strategy of transmission switching for D2D communication to maximize the achievable rate in both single-cell and multi-cell scenarios. Three transmission modes are considered: cellular communication mode, D2D communication mode and two-way DF relay assisted D2D communication mode. Our results show that when two users located nearly to each other the D2D communication mode is the best choice, while the cellular communication mode can maximize the achievable rate as the distance between two users is far enough.Finally, we investigte the ergodic achievable rate of both BF and IC strategies for a D2D communication system underlaying cellualr network with a multi-antenna BS. We derive new closed-form expressions for the ergodic achievable rate for two strategies with quantized CSI, as well as, perfect CSI. The novel lower and upper bounds are derived which are shown to be sufficiently tight. Based on thes results, we examine in detail three important special cases including high SNR, weak interference between cellular link and D2D link and BS equipped with a large number of antennas. The asymptotic expressions for each cases are presented. It is shown that an irreducible saturation value exists in high SNR and weak interference cases. Furthermore, the ergodic achievable rate under perfect CSI scales logarithmically with the number of antennas, whilst it reaches a ceiling with quantized CSI.