MRC DIVERSITY RECEPTION OF PI/4 QDPSK IN FREQUENCY SELECTIVE RICIAN FADING

Abstract

Mobile radio communication is a fast-changing field and has undergone drastic changes over the last decade. Two major problems facing mobile radio communications are the limitation of the available frequency spectrum and the need of high capacity data transmission. Due to the large and rapid growth of subscribers, high capacity communication systems which need minimal bandwidth are required.

The major restriction to high speed data transmission is the spread in delay times seen at the receiver, i.e., the frequency-selectivity of a propagation channel. These delays introduce intersymbol interference which brings severe distortions to the transmitted signal and in turn create an irreducible error floor.

In this dissertation, bit error rate (BER) performance of ?/4 quaternary differential phase shift keying (?/4 QDPSK) on frequency selective, Rician fading channel with diversity reception in the presence of multiple independent co channel interferers, random FM noise, additive white Gaussian noise (A WGN) and intersymbol interference (ISI) induced by multipath propagation delay spread is theoretically analyzed for three different shapes of delay profile: Gaussian, one-side exponential and double spike profiles. The use of L-branch post detection maximal ratio combining (MRC) is considered to improve the system performance. The influences of various system and channel parameters such as delay spread, Rician factor, fading bandwidth, and diversity order are also examined in detail.

Further, an analytical model has been used to evaluate the performance of a realistic microcellular mobile radio system with a dual path loss law. The numerical results show that the reuse distance, cluster size, traffic intensity (i.e., the blocking probability), turning point, and cell size all play a major role in the design of an efficient microcellular system. A proper compromise has to be achieved between bit error rate and spectrum efficiency. This study would be useful for the designers in developing any type of microcellular systems. Since Rician fading are present m picocells, the analytical model can also be used in indoor communications.