Research On Diversity Technique Of Wireless MIMO Channel

Nowadays, with the development of high data transmission service such as internet and multimedia , the demands for high speed wireless access have been rapidly increasing. However, high speed communication has two severe challenges in wireless communication environment: one is how to improve the bandwidth efficiency of limited radio spectrum; and the other is how to cope with more severe channels fading, such as frequency selective fading and time selective fading to improve the transmission quality of signals in the high speed communication ,which is also very difficult task . Because it is very difficult to solve the problem by the traditional method, a new approach should be developed to improve the performance and capacity of the wireless communication system. Recent years, a latest technique using multiple antenna elements at both transmitter and receiver,called Multiple-Input and Multiple-Output (MIMO) , has being developed .The multiple antennas in MIMO systems can be exploited in two different ways. One is the creation of a highly effective antenna diversity system; the other is the use of the multiple antennas for the transmission of several parallel data streams to increase the capacity of the system. Antenna diversity is used in wireless systems to combat the effects of fading and improve system performance. This paper is mainly on the research on diversity methods in the MIMO system, such as frequency diversity, space diversity and selection diversity of antenna and so on. The content of research is as follows:1. In this paper ,a system concatenating differential space-time block code with multiple-symbol trellis coded modulation is proposed and analyzed. We derive an analytical expression for pair-wise error probability of the proposed system when perfect inter-leavers are used . Design criteria for constructing good multiple-symbol trellis codes are then established over flat fading channels. Performance resultsshows that joint exploitation of multi-antenna diversity and multiple trellis coded modulation leads to significantly enhanced performance2. We consider the generalization of diagonal algebraic space-time (DAST) blockcodes over flat fading channels to frequency selective channels ,and propose diagonal space-frequency(DSF) block codes in frequency selective channels . At the receiver, ML decoding can be implemented by the sphere decoder at a moderate complexity .It is shown that using the codes in a multi-antenna system can achieve full diversity and almost full rate in frequency selective fading channels3. Based on MIMO-OFDM and subcarrier grouping ,we propose diagonal differential space-frequency codes in frequency selective fading channels. The code is used to exploit both space and frequency diversity . At the receiver, differential detection schemes and ML decoding is employed without requiring channel state information.4. Acquiring knowledge of the fading coefficients in a MIMO channel is already very challenging in the flat-fading case . In the frequency-selective case, estimating the MIMO channel becomes significantly more difficult due to the presence of multiple paths, which results in an increased number of channel coefficients. Based on MIMO-OFDM, the paper deal with non-coherent code design in frequency-selective fading channel and present non-coherent space-time-frequency block codes ,where neither the transmitter nor the receiver knows the channel. At the receiver, we employ maximum likelihood(ML) and generalized likelihood-ratio test(GLRT) decoding respectively and derive different design criteria. We also prove that full diversity gain can be achieved in frequency selective fading channel.6. In general, the algorithm of antenna selection requires the information of channel states information, and the antennae are chose according to channel parameters. Since estimating the channel parameters in MIMO systems greatly enlarges the system complexity, moreover, it is very difficult to estimate the channel parameters in the fast fading channels. In this paper, based on the F-2 norm of...