Turbo equalization in wireless communication

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Intersymbol interference (ISI) is a major impairment in wireless communication and hence equalization is applied to combat such interference. In addition to maximum likelihood sequence estimation equalizer and filtering equalizer, turbo equalization associates with trellis-based channel equalizer and channel decoder was proposed to overcome the ISI more efficiently. Such "turbo principle" stems from the concept of turbo coding which obtains the coding gain approaches to Shannon limit prediction. Turbo code is a refinement of the concatenated encoding structure plus an iterative and soft-input/soft output algorithm such as maximum a-posteriori (MAP) algorithm for decoding the code sequence. Similar to turbo code, turbo equalizer performs the equalization and decoding iteratively until the convergence is achieved. However, for a system with high-level modulation, the optimal MAP equalizer is prohibited due to its computational complexity. Thus, the sub-optimum equalizers such as decision feedback equalizer (DFE) have to be considered. Due to the improvement of the system performance based on the conventional DFE algorithm is limited by the error propagation, a novel low complexity DFE algorithm is proposed. The new method detects the symbols using the extra metric and the feedback symbol from previous iteration The simulation results show that the performance of the proposed DFE algorithm improves dramatically compared with the conventional DFE algorithm.