Research On Deversity-Multiplexing Tradeoff In Corrlated Channels

With the coming of Informative Society, the new generation mobile communication systems have set requirements for higher data rate and better service quality. By fully exploring space resources without additional transmission power and frequency band expenditure, Multiple-Input Multiple-output (MIMO) systems can increase channel capacity as well as spectrum efficiency. Research shows that MIMO systems can provide diversity gain and multiplexing gain at the same time, which would guarantee the reliability of communication and increase data rate of the systems. Given a MIMO channel, both gains can be obtained simultaneously, but there is a tradeoff on how much of each type of gain any coding scheme can extract. The optimal diversity-multiplexing tradeoff is a fundamental performance limit of a MIMO channel.Through the analysis of fading channel models and capacity of independent and identical distributed (i.i.d) MIMO systems, the advantages of MIMO systems are fully exhibited in this paper. Then, some discussions are made concerning the diversity-multiplexing tradeoff in i.i.d MIMO systems. I.i.d fading models are ideal and have many important characteristics, which are widely used for theoretical research. In a real world scenario, however, the channel fadings usually have certain correlation, such as spatial fading correlation caused by small antenna separation and the non-ideal distribution of scatters. These realistic characteristics would have significant effects on MIMO systems. For this reason, the spatial correlated coefficients are deduced in this paper, combining the effects of antenna separation, angular spread, average Direction of Arrival (DOA) and the spectrum of DOA. Furthermore, the models and capacity of spatial correlated channels are given. The effects of spatial correlation on MIMO systems are evaluated both by theoretical derivation and analysis.Based on the correlated channel models, the diversity-multiplexing tradeoff are studied in this paper, by researching the distrubution of eigenvalues of correlated channel matrices. Results show that the tradeoff curves of correlated channels are lower than those of i.i.d channels, especially when the correlated matrices are rank-deficient. The tradeoff characteristic shows the performance of correlation MIMO channel in the aspects of diversity and multiplexing, which provides a guideline to design and evaluate systems.