Research On Technologies For High Spectral Efficient Transmission In Multi-antenna And Multi-Carrier Systems

Because of the scarcity of frequency spectrum resources, how to increase theinformation rate transmitted over a given authorized bandwidth has currently become animportant issue in high-speed digital communications. High spectral efficientphysical-layer enhancing techniques play an important role in enhancing the overallperformance of both wire and wireless communication systems.This thesis focuses on two kinds of promising techniques for spectral efficiencyimprovement—multi-antenna transmission and high-order modulation. Threephysical-layer enhancing techniques are discussed with respect to multi-antennatransmission, including asynchronous multi-carrier layered space-time code, distributedmulti-antenna location optimization, and multi-antenna visual cognitive radio.Meanwhile, an8.7bps/Hz4096-QAM multi-carrier transmission system is designedwith some field trials taken.Firstly, the detection performance of the asynchronous multi-carrier layeredspace-time code is analyzed over MIMO Channels with LOS component which mayseverely reduce BER performance of a traditional layered space-time code. Thetheoretical analysis and simulation results show that the asynchronous multi-carriertransmission scheme can achieve full receiving diversity with low complexity lineardetector. When jointly MMSE detector is used, the asynchronous multi-carrier layeredspace-time code outperforms its traditional counterpart with4dB BER performanceenhancement over a2×2MIMO Rician channel with K factor equals5.Secondly, the issues of finding the optimal location of distributed transmittingantennas in a multi-cell cellular system are analyzed. The effects of co-channelinterference from multiple tiers of cells on both average ergodic capacity and optimalantenna location are analyzed, and the relationship between the optimal antenna locationand the average ergodic capacity is also discussed. Numerical analysis and simulationresults show that the optimal distributed antenna location is determined by theinterference energy of the first tier of the peripheral co-channel cells. For example, in a cell with a typical radius of1000meters, the average ergodic capacity of the cellreaches the peak point while all antennas are located at about450meters away from thecenter.Thirdly, an approach for the combination of multi-antenna techniques andtraditional power control method is proposed. Traditional power control is always basedon SINR measurement to monitor the link attenuation, which makes it hard to respondto a deep shadow in the radio environments in advance. This thesis proposes a newsystem called vision assisted power control, which uses multi-antennas to obtain visualinformation for radio environments cognition. This new power control process iscompared with the traditional way, besides, numerical analysis and simulation resultsshow that visual assisted power control has lower average bit error rate than itstraditional counterpart.Finally, an8.7bps/Hz4096-QAM multi-carrier transmission system is designedwith some field trials taken. The impact of frequency synchronization errors on highorder QAM modulated OFDM signal is analyzed and an algorithm to jointly correctboth CFO and SFO is proposed. A closed-form formula for the mean square error of theestimation is given by the theoretical analysis and its reasonability is verified bysimulation results, which show that the difference between BER performance overmultipath Rician channel with and without frequency offset is less than1dB. Testresults from field trials show that the difference of BER performance between fix-pointsimulation and implementation is less than2dB.The research results above not only enrich the existing techniques for highspectrum efficiency transmission with multi-antenna and multi-carrier, but also showsome theoretical and practical values and can be applied to the next generationbroadband digital communication systems.