Robust precoded MIMO-OFDM for mobile frequency-selective wireless channels

We present a new multiple input multiple output (MIMO) technique, based on Walsh Hadamard Transform (WHT) precoding, to improve the robustness of space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems. The WHT is applied to the data symbols prior the Alamouti encoder at the transmitter and to the output of the Alamouti decoder at the receiver. The computational complexity of the proposed system is evaluated in terms of complex additions and multiplications where the numerical results show that the proposed system has a lower complexity as compared to other precoded OFDM systems. Moreover, the proposed system is highly robust to the channel time and frequency selectivity as compared to conventional SFBC, space time block coded (STBC) and other precoded OFDM systems.

I. Introduction

Orthogonal frequency division multiplexing (OFDM) has attracted significant attention in wireless communications because of its ability to convert severe frequency-selective fading channels into flat sub-channels. Furthermore, OFDM simplifies the receiver complexity because channel equalization can be performed using single-tap equalizers. Despite the fact that OFDM has some limitations such as high peak to average power ratio (PAPR) [1], owing to its remarkable advantages, OFDM has been adopted for several wireless communication standards such as LTE and LTE-A [2], and it is considered as a strong candidate for the fifth generation (5G) standard.