Application Of Multiuser Detection Technology In Distributed Wireless Communication System

With the development of mobile communications technology, we are experienced inFDMA and TDMA as the key technology of the two previous generations of communicationsystems, due to its design of standards and quality of service of the system are lower than theactual demand, especially in the system capacity, and the next generation of cellular systemsdiffers greatly, so that the third generation mobile communication system came into beingwith the key CDMA technology. Cellular system, to some extent, alleviated the problem ofinsufficient capacity, the performance is also greatly improved, however, still manydrawbacks of the structure, based on this, we proposed distributed wireless communicationsystem (DWCS). However, CDMA system is a self-interference system, especially with a lotof users, multiple access interference and the distance effect are very serious, the performancedecreased significantly. And MUD technique can overcome multiple access/multi-pathinterference practically, and improve the system capacity greatly,so it has been widely used.First, the introduction of the traditional cellular mobile communication system, leads to adistributed antenna system, and established the DWCS system further and gain acomprehensive overview of the basic principles, detailing several new concepts of the DWCSsystem, including distributed processing centers, virtual cell and virtual base station, and abrief description of the main features of DWCS system.Secondly, the paper focuses on multiuser detection technology of CDMA. Although theDWCS system has many advantages, but it still belongs to the CDMA system, there areinterference between users, limits the capacity of the system severely. We were on theresearch of the model of CDMA system in additive white Gaussian noise (AWGN) channeland multipath fading channel to explore the various multi-user detection techniques further,experiments show that multi-user detection techniques can inhibit all kinds of interferencebetween users excellently, and improve the communication quality well.Then analyzed the application of decorrelating detection technology based on space-timediversity coding with Rayleigh fading channel, proved that the performance of thedecorrelating MUD in SISO systems is lower than that in MIMO systems significantly withAWGN channel; the performance of MUD in Rayleigh fading channels smoothly is muchlower than that in AWGN channel. Decorrelating MUD achieves a compromise betweenperformance and complexity.Finally, the paper analyzed the Spatial-Frequency-Time-domain MMSE multiuserdetection technology mostly, combining distributed antenna array of DWCS system withMUD, MUD can suppress interference from the time-domain, and distributed antenna arraycan suppress interference from both spatial and frequency-domain, with these advantages, simulation results show that the capacity and performance of the system has been greatlyimproved.At the end, the paper analyzes some problem to be solved in the future.