Coded noncoherent OFDM in frequency hopping multiple access networks

Recently, orthogonal frequency division multiplexing (OFDM) has received increasing attention in wireless systems. However, all the work was concentrated on coherent modulation schemes like phase shift keying (PSK). In some cases, it is very difficult to maintain phase coherence, like frequency hopping (FH) multiple access (MA) systems. Hence, a new modulation scheme is proposed in this work, it is a combination of the well known OFDM and noncoherent amplitude shift keying (NCASK). This system is proposed as an alternative to the conventional modulation scheme used in these cases, i.e. noncoherent frequency shift keying (NCFSK). In addition, it can be considered as a reduced complexity alternative for coherent systems.; The system performance was investigated in several channel conditions, AWGN channels, FH MA channels and Rayleigh fading channels. The results obtained have shown that the proposed system will significantly improve the system performance compared to NCFSK. In this work, binary and M-ary signals were considered.; It is known that MA channels have high bit error rates (BERs), even for very high signal to noise ratios (SNRs). A common solution is to use forward error control coding. In this work, the effect of using convolutional codes was investigated, hard and soft decision Viterbi decoding were considered.; One of the major disadvantages of coherent OFDM systems is their high sensitivity to imperfect synchronization conditions like carrier frequency offsets and symbol timing offsets. The performance of the proposed system was investigated under the two conditions. The proposed system has shown very high robustness against frequency offsets and timing offsets.; Doppler shifts usually introduce carrier frequency offsets in single carrier (SC) system. In OFDM systems, Doppler shifts can destroy the orthogonality between the subcarriers. However, it was found in this work that this effect is negligible for speeds in the range of practical interest.; The peak to average power (PAP) problem was considered in this work. Despite the fact that the phase has no importance in SC NC systems, it was shown that it is priceless in NC OFDM systems. Using the freedom in selecting the subcarriers phase has enabled more than 12 dB reduction in the peak power for an OFDM system with 32 subcarriers.