Analysis Of Shadow Fading Correlation And Its Influence On The Outage Performance Of The Downlink Distributed Antenna Systems

Radio waves suffer channel fading from absorption,occlusion,reflection,diffraction and scattering in the propagation.Wireless channel fading can be divided into large-scale and small-scale fading.Shadow fading caused by obstacles in transmission path is an important part of large-scale fading.If two geographically close links share same obstacles,the shadow fading exhibits correlation which degrades the performance evaluation of wireless communication systems.The study on the transmission characteristics of wireless fading channels and the construction of a reasonable and accurate wireless channel model can provide the guidance of performance improvement.In this thesis,we analyze shadow fading correlation in urban scenes via the combination of actual measurement and theoretical analysis.Downlink outage probability of the distributed antenna system over composited correlated shadowed fading channels is also involved.This primary works of the thesis are as follows:(1)Analyzing shadow fading correlation in urban scenes: We design the measurement scheme of shadow fading in urban scenes,including the basic principles,measurement methods,measurement equipment and areas.Large-scale fading parameters are obtained by fitting measured data.Semivariogram function is utilized to analyze the correlation of shadow fading.The influence of different measurement methods and different data processing methods on the measurement accuracy of shadow fading is also investigated.In addition,the experimental semivariogram function is fitted by several theoretical models.Analytical and measured results show obvious short-range shadow correlation in urban scenes,which provide the decision basis for the network planning and the location of the base station on wireless communication.(2)Downlink outage performance of distributed antenna systems over composite correlated shadow fading channel: The downlink probability density function(PDF)of the received signal to noise ratio(SNR)of the distributed antenna over composite fading channel is approximated by matching the first moment and the second moment.The approximation of PDF over composite correlated shadowed fading channel is also obtained by united matching.Numerical simulations evaluate the effect of the parameters of the distributed antenna system and composite fading channel on the approximation accuracy.In the end,the expression of downlink outage probability of distributed antenna systems over composite correlated shadowed fading channel is derived through the above approximations.Simulation results exhibit the effect of correlated shadowed fading on the downlink outage of distributed antenna systems.