Research On Coded Modulation Techniques For DCT-OFDM

In recent years, with the rapid development of the mobile communication technologies, the research on the next generation system has already been widely carried out. In order to meet the greater demands for the broadband IP multimedia data services, it should achieve higher data transmission rates and system capacities. As the key technologies for the next generation system, multi-carrier technology and cognitive radio (CR) technology draw much attention, and this dissertation is focused on them. It is based on discrete cosine transform (DCT)-orthogonal frequency division multiplexing (OFDM) coded modulation technologies, and then it is extended to the CR field. And the work of this dissertation is supported by the National Natural Science Foundation of China, etc. The innovative results achieved in this dissertation can supply a good theoretical and practical reference for the research on multi-carrier technology and CR technology in the next generation system. The work in the dissertation includes the following parts.1) It is proposed and demonstrated that DCT-OFDM has an excellent frequency diversity gain over frequency-selective fading channels, and the upper bound of bit error rate (BER) performance is derived. At the same time, numerical simulations over the two different frequency selective fading channels both show the good performance of DCT-OFDM.2) A novel OFDM-NMSK/NQMSK coded modulation scheme based on DCT is proposed, which combines N minimum shift keying (NMSK) with DCT-OFDM. Compared with discrete Fourier transform (DFT)-OFDM, this new scheme has an excellent out-of-band attenuation property, and it can further resist the inter-carrier interference (ICI) caused by carrier frequency offset (CFO). At the same time, it can perform well over the wireless fading channels and mitigate the performance deterioration caused by peak to average power ratio (PAPR) hard-limiting.3) In the presence of CFO, the exact bit error probability over additive white Gaussian noise channels has been derived effectively by using the method of characteristic function and inversion theorem. In addition, the system performance has been evaluated over Rayleigh frequency-selective fading channels. And numerical simulation results have shown the excellent performance in the presence of CFO.4) A novel OFDM-NMSK(SSB) scheme applied to the CR field is proposed, which focuses on the out-of-band interference cancellation. This new scheme is based on the OFDM-NMSK/NQMSK(DCT) coded modulation scheme, and it can mitigate the out-of-band interference greatly by utilizing the fast roll-off sidelobe property of NMSK, while the system flexibility and complexity aren't affected apparently. By theoretical analysis and numerical simulations, it shows that OFDM-NMSK(SSB) has excellent out-of-band interference cancellation property, and it can perform well over wireless fading channels. Therefore, it is a good candidate for CR fields.5) The work has been summarized effectively, and the future research work to be carried out has been planned orderly. In addition, some valuable research directions in this field have been forecast.