Research On Key Technologies Of Optimum Distributed Signal

Distributed transmit antenna is promised as a key technology in future wirelesscommunication systems due to its unique merits such as large system capacity,lowtransmit power,uniform and enhanced coverage and low radiation on the human body.Distributed transmit antenna is drawing intensive attention both from academic andindustry.In distributed transmit antenna systems,there exist the following problems:(1) How to place transmit antennas so as to obtain the minimum bit errorprobability.(2) The transmit antennas are not co-located,but distributed in different locations,making the distance from different transmit antennas to the mobile stationdifferent.Hence,the transmit signals from different transmit antennasexperience different channel propagation delays to arrive in the mobile station.Because of the asynchronous arrival of transmit signals in distributed transmitantenna systems,the signal design methods in traditional MIMO systems canno longer be applied in distributed transmit antenna systems.Novel transmitsignal design method is needed to solve this problem.This thesis presents some research work in these problem mentioned above:For distributed transmit antenna systems with orthogonal frequency divisionmultiplexing,a cyclic prefix criterion is proposed.On the basis of the criterion,themobile station cannot suffer from inter-symbol interference caused by asynchronousdelay.Symbol error ratio is derived to demonstrate this result.Some simulation resultsare presented to confirm the theoretical analysis.For single frequency networks(SFNs),employing multiple distributed transmitantennas,this thesis focuses on how designing transmit signals so as to improve thesystem performance.Considering the effect of multipath fading,pairwise errorprobability conditioned on shadowing is analyzed and signal design criterion is derived.Our analysis show that the achievable diversity order of SFNs increases as the numberof resolvable channel taps between transmit and receive antennas increases.Onetransmit signal is proposed to obtain the achievable diversity order,and two full-ratefull-diversity transmit signals are proposed.Moreover,based on interleaved-partitionsubcarrier grouping,the signals with low computation complexity are proposed.By thecomputer simulation,it is observed that the SFN using the proposed transmit signaloutperforms the SFN without the proposed transmit signal about 8 dB.Further,based on interleaved-partition subcarrier grouping for single frequencynetworks,we show that different interleaving methods result in different performancedue to asynchronous delays caused by unequal distances between distributed transmitantennas and mobile receivers.To optimize the proposed transmit signal,one interleaving scheme,establishing a tradeoff between mobile receivers' location andperformance,is introduced in terms of the asynchronous delays.Simulation results arepresented in a representative scenario to demonstrate the performance gains about5～9dB offered by the proposed optimum transmit signal.The proposed scheme does notintroduce any changes at the mobile receivers.Based on the standard of DVB-T ETSIEN300 747,simulation results show that the proposed optimum transmit signal offeredperformance gains about 1.9～2.5dB.For a linear cell downlink distributed antenna system with space-time block codedorthogonal frequency division multiplexing,this thesis focuses on where to placetransmit antennas so as to obtain the best performance.Aiming to solve this problem,the AABEP is derived,considering the effects of path loss,correlated shadowing,multipath fading,background noise and mobile station location.Our analysis shows thatthe antennas should be located symmetrically about the cell center in order to achievethe minimum AABEP.Based on the result,optimal transmit antenna location is derived.By the computer simulation,it is observed that the simulation results agree with thetheoretical analysis.Furthermore,simulation results show that the gap between thesimulation results and the theoretical results decreases as SNR increases.The research results of distributed transmit antenna systems in this paper can beapplied in the signal processing techniques of the next generation distributed antennasystems based distributed cellular mobile communication networks,distributed wirelesslocal area networks,distributed digital TV/Radio wireless communication networks,which are of great theoretical importance and economic value.