On the use of Quasi-Orthogonal Space-Time-Frequency Codes in MB-OFDM UWB

Space-time-frequency codes (STFCs), which have been proposed in the literature for multiband OFDM ultra-wideband (MB-OFDM UWB) systems to improve the system capacity, error performance and wireless communication range, are all constructed based on orthogonal structures. This paper examines the application of quasi-orthogonal STFCs (QOSTFCs) to enhance further either data rate or error performance in the proposed STFC MB-OFDM UWB systems. It was shown that QOSTFCs can provide significantly better error performance, compared to the conventional MB-OFDM UWB (without STFCs) as well as to the orthogonal STFCs (OSTFCs) of the same order, at the same data rate, without increasing the total transmission power. Equivalently, QOSTFCs can provide higher data rates with the same error performance, compared to OSTFCs.