Resource Allocation Strategies and Linear Precoded OFDM Optimization for Ultra-Wideband Communications

Ultra-wideband (UWB) is a fast technology that has recently attracted considerable interest in the research and standardization communities, due to its ability to provide high data rate at low cost and low power consumption. The objective of this thesis is to propose a new UWB system for high data rate wireless personal area network (WPAN) applications, based on the well-known multiband orthogonal frequency-division multiplexing (MB-OFDM) solution supported by the WiMedia Alliance. In a first step, we analytically investigate the use of a linear precoded OFDM (LP OFDM) waveform for UWB systems. The resulting scheme reduces in practice to a simple addition of a precoding matrix, or equivalently spreading sequences, to the MB OFDM transmission chain, which does not increase the system complexity significantly. The precoding function is then analytically optimized and different resource allocation strategies based on a classical target symbol-error-rate (SER) approach and on a new mean bit-error-rate (BER) approach are investigated. Efficient allocation algorithms maximizing the system range and throughput, and minimizing the system mean BER, are thus proposed for different application scenarios. The numerical results of simulations carried out on the different adaptive and non-adaptive schemes show that the LP-OFDM system outperforms the MB-OFDM system in terms of throughput and range. This is due to the spreading gain provided by the linear precoding component, and to the efficiency of the proposed algorithms. In a second step, a global UWB system approach is carried out. This system study, complementary to the analytical one, points out the advantages of appropriately adding the linear precoding to the MB-OFDM solution. Furthermore, a MIMO component is added to the LP-OFDM system in order to improve the system robustness as well as to provide a data rate of 1 Gb/s. System simulation results show that the joint use of MIMO and LP OFDM schemes in UWB leads to a significant system improvement compared to the MB-OFDM system. Thus, the proposed MIMO LP-OFDM system can be advantageously exploited for high data rate UWB applications at reasonable additional system complexity. This work was carried out at the Institute of Electronics and Telecommunications of Rennes (IETR) - National Institute of Applied Sciences (INSA). It was sponsored by Orange Labs RESA/WIN/CREM (France Telecom R&D) within an external research contract. This research was also part of the European Community ICT FP7 OMEGA project OMEGA.