MIMO system has been proven to provide capacity that is linear increase with the number of antennas. But it is true only in independent channels; when the spatial fading correlation exists, the capacity may decrease. The correlation coefficient is the function of antennas spacing, angular spread (AS), power angular spectrum (PAS), and so on. In this paper, the expression for correlation coefficient and semi-correlation channel capacity is derived. The effect of PAS on the capacity is investigated. In general, capacity of Uniform PAS is higher than that of truncated Gaussian PAS, and capacity of truncated Gaussian PAS is higher than that of truncated Laplacian PAS. For multiple clusters incidence wave, the correlation coefficient and average capacity will oscillate with the increasing antenna spacing. Two typical scenarios are simulated for indoor and outdoor environments.
I. INTRODUCTIONThe future mobile communication system will be that data rate of medium access control (MAC) exceeds 10Mbps, and up to 100Mbps. One of the feasible schemes is to adopt advanced MIMO technology, which will make higher throughput and more robustness possible for future wireless communication system. This can be true only in the rich scattering environment that the capacity is linear increase with the number of the minimum transmit and receive antennas, which has been proven by [1] in flat fading and [2] in frequency selective fading channel.Nevertheless, the rich scattering environment does not always exist and channel fading correlation may exist, which means that channel capacity degrades greatly [3], [4] on the condition that transmitter is no channel state information (CSI) and receiver acquires the CSI perfectly. Correlation is denoted by correlation coefficient, which is the function of antenna spacing, angular spread (AS), mean angle of arrival (AoA), power angular spectrum (PAS), and so on. Effect of AS on the capacity was researched by [5] at different AS, which shown that the correlation is decreased with increasing the AS. Effect of antenna spacing on the capacity was studied by [5], [6] in correlation channels, which shown that the correlation is decreased with increasing antenna spacing. In this paper, we will study the effect of PAS on correlation and further investigate the joint effect of PAS, AS, and antenna spacing on the link capacity of semi-correlated MIMO channels.The rest of this paper is organized as follows. Model of semi-correlation MIMO channel of regular linear arrays is given in Section II. Spatial fading correlation between antenna signals and correlation coefficient are presented in Section III. In Section IV, MIMO capacity is discussed in semi-correlation channels and supported by simulations. Finally, Section V includes the concluding remarks and
