(A) study on communication performance improvement for wireless MIMO systems

Abstract

Demands for high data rate and high quality services in wireless communications, driven by cellular mobile, wireless LANs, and multimedia services have been rapidly increased worldwide. On the other hand, the communication capacity issues cannot be resolved without a significant increase in spectral efficiency since the available radio spectrum is limited. Therefore, new inventive techniques are required to improve the spectral efficiency and transmission reliability. The utilization of multiple antennas at the receiver and/or the transmitter sides in wireless systems has been widely studied, known as multiple-input multiple-output (MIMO) communication system. The MIMO system offers a significant increase in both spectral efficiency and high-data-rate for future wireless communications. In particular, this dissertation focuses on the channel capacity for MIMO systems. The channel capacity determines the fundamental limit to the achievable transmission rates and also gives an insight into the transmission ability over the channel. The ergodic (or mean) capacity of the MIMO system in the Shannon sense is analyzed, assuming that the channel is perfectly known at the receiver but unknown at the transmitter. This analysis allows for evaluating relevant information theoretic capacity measure, which is known as the ergodic capacity. On the other hand, digital modulation is a process that impresses a digital symbol onto a signal suitable for transmission. Channel characteristic plays an important role in designing modulation schemes. Modulation schemes are chosen according to the channel characteristics in order to optimize the performance. In this dissertation, Additive White Gaussian Noise (AWGN) is considered and a new modulation scheme is proposed. The proposed modulation scheme shows better result as compared to the conventional modulations scheme in terms of bit-error rate (BER) performance.