The Analysis Of Spectral Efficiency And Pilot Contamination Problem In Massive MIMO Systems

Over the past ten years, multiple-input multiple-output (MIMO) technique which can improvethe wireless communication system performance without additional bandwidth and powerconsumption has been widely researched. With the wide popularity and application of mobile phone,high transmission data rates and communication reliability must be required. Therefore, furtherwireless communication systems must satisfy the follow requirements:(1) serving more terminalsin the same time-frequency resources;(2) higher data rate and transmission reliability;(3) lowerpower consumption. The above requirements are mutually contradictory since the more users areserved, the more interference the systems will suffer from, and the higher data rate is required, themore power is consumed.The massive MIMO technology which can effectively eliminate inter-cellular interference,proposed by Marzetta in2010, has been widely concerned. Massive MIMO systems, where severalterminals with single antenna each communicate with a base station (BS) equipped with very largeantenna arrays (roughly100or several hundreds) at the same time. Researches show that the mainbenefits of massive MIMO systems are: serving more terminals in the same time-frequencyresources simultaneously, higher data rate and lower power consumption and so on. However, theperformance of massive MIMO systems is greatly bottlenecked by pilot contamination problemwhen the aligned pilots are used in multi-cell scenario. Therefore, the spectral efficiency and pilotcontamination problem of massive MIMO systems are mainly analyzed in this paper.Chapter1mainly introduces the research background、current situation and existing problems，and then presents the structure of this paper.Chapter2mainly introduces the system model of massive MIMO time division duplexing(TDD) systems, and emphasizes analyzing the pilot contamination problem and its impact on thesystem performance. Simulation results show that the performance of massive MIMO TDD systemsis greatly limited by pilot contamination problem.Chapter3mainly researches the downlink spectral efficiency of massive MIMO systems withsimple linear precoding under ideal channel and non-ideal channel conditions; and then derives theapproximate solutions of the system rate at various precoding schemes. The accuracy of theoreticalanalysis is verified by simulation results. The approximate solutions can be used to analyze thespectral efficiency of massive MIMO systems under different conditions, so the complexcalculation process is avoided.Chapter4mainly researches the performance of massive MIMO systems under correlated channel，and then gives the simulation results which show that he performance of massive MIMOsystems becomes worse when the channel correlation coefficient increases. And when the channelcorrelation coefficient is smaller than a certain value, the performance of massive MIMO systemswill be enhanced quickly as the number of Base Station antennas increases; while the channelcorrelation coefficient is larger than the certain value, the system performance is enhanced slowly asthe number of BS antennas increases.Chapter5mainly analyzes the pilot contamination precoding method, deduces the2-cell systemspectral efficiency of the algorithm in the presence of pilot contamination and analyzes the effect oflarge scale fading estimation error on the system performance. Simulation results show that the pilotcontamination precoding can greatly eliminate the impact of pilot contamination problem on themassive MIMO system and the pilot contamination precoding method is influenced by the largescale fading estimation error which restricts the system performance improving.Chapter6summarizes the paper and gives some comments for further investigation.