The Research On Iterative Equalization And Spectrum Efficient Coded Modulation Technology

Inter-symbol interference (ISI), which is traditionally eliminated by means of equalization technology, has been the focus in wireless communication. In recent years, with the rapid development of error control coding and signal processing technology, a number of new ideas have been proposed to mitigate the ISI. In 1993, C.Berrou et al. proposed Turbo codes in ICC'93. Turbo codes can effectively achieve the error control capability near the Shannon theoretic limit. Their impressive performance promoted the formation and application of "Turbo principle". One of the well-known results is Turbo equalization, which eliminates the negative effects of ISI. Recently, based on the multiplexing principle, Daoben Li proposed in 2007 a novel multiplexing technology of the overlapped multiplexing for wireless radios. It is shown that, the overlapped multiplexing technique may offer both high coding gain and spectral efficiency by intentionally imposing controlled ISI. In fact, controlled overlapping could be regarded as some kind of coding constraint, thus multiplexing is a way of exploiting the ISI mechanism rather than eliminating it in the conventional system.Firstly, the thesis discusses the basic principle and encoding/decoding structure of Turbo equalization. And then, the simulations are performed to validate the Turbo equalization. In order to reduce the equalization delay, the thesis investigates the sub-block parallel Turbo equalization implementation problem. High-speed Turbo equalization has been implemented by combining the framework of parallel equalization with Radix-4 algorithm and exchanging the sub-block boundary forward and backward itereation calculations. Both the simulation and analysis are presented to validate the applicability of the parallel Turbo equalization implementations.Secondly, the thesis introduces two overlapped multiplexing technologies, overlapped code multiplexing (OVCDM) and overlapped time multiplexing (OVTDM), which were originally proposed by Daoben Li. The basic idea of OVCDM is the overlapping between various signals to cause ISI, which could be transformed into some kind of coding constraint, thus giving rise to both coding gain and spectral efficiency improvement. As for OVCDM, the thesis compares it with the known TCM technology. Both the similarities and differences between the two technologies in terms of principle and the achieved performance are presented for comparison. Moreover, by applying the "Turbo Principle" in the OVCDM technique, the Turbo-OVCDM could be employed as well. The comparison between the Turbo-OVCDM and Turbo-TCM confirms us that, the OVCDM could be regarded as a generalized coding and modulation scheme with high spectral efficiency.Finally, both the principle and structure of the OVTDM are presented and investigated. The comparison in terms of the BER performance between the OVTDM and other modulation schemes with the same spectral efficiency shows that, due to coding constraints from the overlapping between the successive symbols, OVTDM benefits from the additional coding gain by exploiting the overlapping constraint. Moreover, it is shown that, more overlapping will give rise to higher spectral efficiency and larger coding gain in OVTDM. By employing the "Turbo Principle", Turbo-OVTDM is investigated as well. The study shows that the number of overlapping symbols will greatly affect the decoding complexity. In order to reduce the decoding delay, the segment-based parallel implementation for Turbo-OVTDM is proposed and validated through simulation.