Fast orthogonal frequency division multiplexing (Fast-OFDM) for wireless communications

This thesis presents research that has addressed various design issues related to an adapted orthogonal frequency division multiplexing scheme, namely Fast-OFDM. A comparative study of the system with conventional OFDM in various signal mapping conditions has been investigated. The thesis reports on performance assessment in terms of bit-error-rate (BER), spectral efficiency, peak-to-average-power ratio (PAPR), nonlinear effects and adjacent channel interference (AG) analysis. The results show that the performance of Fast-OFDM is comparable to OFDM for single dimensional modulation scheme, whereas for complex modulation schemes, the performance of Fast-OFDM degrades severely due to the loss of orthogonality between subcarriers. Two multi-carrier CDMA schemes, multi-carrier direct sequence CDMA (MC-DS-CDMA) and multi-tone CDMA (MT-CDMA), have been studied in different modulation scenarios. The performance of the overlapping multi-carrier CDMA schemes compared to OFDM and Fast-OFDM has been evaluated in terms of BER, spectral efficiency, PAPR and ACI analysis. The results reveal that the overlapping multi-carrier CDMA systems are comparable to the Fast-OFDM system under single user condition. It is thus feasible to apply multi-carrier CDMA detection techniques in Fast-OFDM systems. Therefore, two different types of linear detectors, zero-forcing (ZF) and minimum mean square error (MMSE) have been employed in complex modulated Fast-OFDM, leading to improvement of system performance. Overall, the theoretical design and performance assessment issues addressed in this thesis provide an insight into the performance of Fast-OFDM in the presence of additive white Gaussian noise (AWGN). The results obtained can be used by receiver designers for improving signal recovery of complex modulated Fast-OFDM in future wireless communication systems.