Information Theoretic Analysis Of MIMO Wireless Communication Systems And Space Time Coding

The increasing requirements on data rate and quality of service for wireless communications systems call for new techniques to increase spectrum efficiency and to improve link reliability. Multiple input multiple output (MIMO) systems using multiple transmit and receive antennas are widely recognized as the vital breakthrough that will allow future wireless systems to achieve higher data rates with limited bandwidth and power resources. However, the capacity benefits of MIMO systems depend strongly on how well the channel can be tracked at the transmitter and the receiver; whether the fades associated with different transmit and receive antennas are correlated. An effective approach to exploit the enormous capacity gains predicted by information theory is to employ the space-time coding techniques appropriate to multiple transmit antennas. Many new kinds of space-time codes were presented to address the issue of decoding complexity. However, the capacity of these codes cannot achieve rate one in some circumstances. This thesis presents the progress we have made towards determining the capacity benefits of multiple antennas under different assumptions about the underlying channel and the capacity of different ST codes under different antenna configurations. Following issues were discussed:The optimal transmission strategy of a single user MIMO wireless communication system is studied for the case in which the transmitter has only imperfect feedback of channel state information (CSI). When this CSI is in terms of channel covariance feedback, the transmit directions for achieving ergodic capacity correspond with the eigenvectors of the channel covariance matrix, while the optimal power distribution can not be solved in closed form. We analyze the ergodic capacity function by exploiting its property of schur-concavity, and develop a necessary condition for eigenvalues of the optimal input covariance matrix to characterize the properties of the transmit power distribution for achieving capacity. Theoretical results is illustrated by numerical simulation.In previous work, necessary conditions for the optimal transmission power allocation to achieving maximum capacity were derived. We then further the research and determine a necessary and sufficient condition for the optimum power allocation at the transmitter to maximize the average mutual information. Furthermore, we apply this result to extend the discussion on optimality of beamforming to general cases of transmitting in m directions for achieving capacity.