Novel OFDM-CPM signals for wireless communications: Properties, receivers and performance

A new class of multicarrier signals called OFDM-CPM that uses correlated phase states using a well defined mapping process is introduced to enhance error rate performance. The subclasses of signals introduced include OFDM CPFSK, OFDM-multi-h CPFSK, OFDM-multi-h CPFSK with asymmetric parameters and OFDM-multiamplitude CPM. These signals are described and their inherent PAPR properties are examined. Firstly, we present a combined coding and weighting technique to control PAPR of OFDM-CPM signals. Secondly, an adaptive algorithm for reduction of PAPR is proposed. It is shown that PAPR of a 128-carrier OFDM-CPFSK system can be reduced by more than 4 dB.; A novel multi-symbol receiver for optimum detection of OFDM-CPM signals has been derived and examined for BER over a multipath fading channel. This receiver observes n blocks of received signal to produce an estimate of data transmitted in one of the blocks. Error rate bounds that are tight at high SNR are derived and using these it is shown that OFDM-CPM out performs conventional OFDM-PSK by nearly 3.5 dB. While the optimum receiver provides the inherent ability of OFDM-CPM signals to perform over the multipath fading channels, its complexity grows exponentially as a function of observation length and the number of subcarriers in the system. Low complexity suboptimum receivers are derived and investigated for error performance. The suboptimum receivers are obtained using high- and low-SNR approximations in the likelihood functions of the optimum receiver. A class of post-FFT receivers are derived and examined for error rate performance. These are: (i) Minimum BER receiver; (ii) Sequence Averaged Receiver; (iii) Decision-Directed Receiver, and (iv) Viterbi Receiver. While in the first three receivers symbol decisions are arrived at after observing the received samples over n blocks, the Viterbi Receiver produces maximum likelihood estimate of the sequence transmitted. A comparison of the complexity of these receivers is also presented.; The proposed signals and various receivers are finally examined over realworld mobile radio channels using an industry-standard SIRCIM channel simulator. The error rate analysis are presented for open plan, hard partitioned and soft partitioned buildings. It is shown that OFDM-CPM offers superior performance over conventional OFDM.