Interleaved frequency Division Multiple Access with Multiple Antennas and Block spreading for Mobile Broadband Communications

Abstract

In this thesis, we study and propose enhancements to improve the performance of interleaved frequency division multiple access (IFDMA) in the uplink transmission of mobile broadband system. Our theoretical performance analysis of coded IFDMA system shows that receivers using maximum likelihood sequence estimation (MLSE) can maximize the available channel diversity if the required system design criteria are met. We formulate a generalized signal model for coded IFDMA system with different numerical configurations of transmit and receive antennas and proposed an iterative soft QRD-M algorithm for joint detection and decoding scheme of coded IFDMA systems based on the model. The proposed algorithm achieves similar diversity order as MLSE at a much lower complexity cost and its performance approaches the theoretical ideal lower bound within a few iterations. We also introduce a novel transmit diversity for IFDMA system. This antenna spreading diversity (ASD) can be used with a single receive antenna and be easily scaled up to work in systems with different number of numbers of transmit antennas. Moreover, we use block spreading (BS) with IFDMA to suppress inter-cell interference (ICI) while maintaining intra-cell orthogonality for low mobility users. The use of block spreading also allows more sub-carriers to be assigned to each user, thereby increasing the available frequency diversity for each user. To counter the loss of code orthogonality due to the presence of high mobility user in the system, we propose a novel scheme where the allocation of the users? operating sub-carriers and spreading codes is dependent on their mobility and a mobility-based multiple access interference (MAI) cancellation scheme is used at the receiver to maintain system performance.