Frequency domain equalization for 3.5G and 4G systems

Abstract

Nowadays, a number of important advantages have been observed in the field of joint equalization and decoding in turbo system in which the traditional equalization methods and decoding methods exchange information iteratively until convergence is achieved. The original form of the coarse channel equalizer which is used for handling the channel effects employed maximum a posteriori probability (MAP) equalization at excessively high complexity. In this project, a low-cost iterative frequency-domain-equalization (FDE) is investigated. In particular, a linear minimum-mean-square-error (LMMSE) based frequency domain turbo equalizer which is proposed to contribute further complexity reduction without noticeably degrading the performance is applied to systems that may contain the joint channel interference, such as inter-symbol interference (ISI) and cross-antenna interference (CAI). Then an SNR-variance evolution technique that is used to evaluate the performance of the proposed systems is developed. Numerical results obtained in various channel environments in single-input single-output (SISO) system as well as in multiple-input multiple-output (MIMO) system verify the well coherence between the simulated and predicted system performance. In addition, the performance is also compared with that of an alternative well-known orthogonal frequency-division multiplexing (OFDM) modulation for Doppler Effect Channel condition.