Research On Performance Of Virtual MIMO Based Device-to-Device Communication

Device-to-Device (D2D) communication is a new technology introduced in LTE-Advancedsystem recently. D2D communication can improve the efficiency of frequency usage while facing aproblem of lacking application due to short distance constraint. Virtual MIMO based D2Dcommunication is researched in this thesis to expand application for D2D.Firstly, D2D communication with assistance of multiple relays where the source node ismiddle-distanced apart from destination node is researched. According to different moments whenrelays forward information, two methods of multiple relays communication is presented. Andperformance is compared between these two methods. As branch of the virtual MIMO technology,multiple relays assisted communication provides multiple paths for signal transmission. Simulationresults shows that, with the help of multiple relays, the proposed methods can reduce the transmitpower of relays and obtain the diversity gain.Secondly, the optimization of multiple relays assisted D2D communication is studied. In thescenario of dense communications, there exists many D2D pairs require for the same free relays.Considering efficiency of frequency as well as practical quality of service, an algorithm forassignment of multiple relays to D2D pairs is proposed. The algorithm increases the total rates ofD2D group while maintaining equality. Another aspect of optimization is power distribution ofrelays whose sum power is constrained. The expression of optimal power assignments of relays isdeduced. And the simulation verifies the benefit form optimization.For large-distanced D2D communication, a novel communication method is researched bywhich D2D pairs use surrounding free devices to construct virtual antenna arrays and obtain MIMOcapacity gains. According to the situation whether cooperation node can decode signal, twostrategies of D2D link based virtual MIMO communication is studied. The cooperation clusters cantransmit and receive signals adaptively, which is more reliable than direct link. Finally, theprocedure for virtual MIMO communication is presented.