Space-time coded MIMO-OFDM for high capacity and high data-rate wireless communication over frequency selective fading channels

This paper presents a space-time block coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) scheme over frequency selective fading channels. The system provides spectrally efficient transmissions to increase system capacity or system throughput for individual users. The proposed technique utilizes OFDM to transform frequency selective fading channels into multiple flat fading sub channels on which space-time block coding is applied. We consider a multi-user environment with K synchronous cochannel users, each equipped with n transmit antennas. The receiver is equipped with m(/spl ges/K) receive antennas. At the receiver, signals from K users are decoded using minimum mean squared error (MMSE) interference cancellation followed by maximum likelihood (ML) decoding. It is shown that the proposed scheme, with two cochannel terminals, doubles the data rate while maintaining the frame error rate (FER) performance as a single user scheme with some additional decoding complexity.

I. Introduction

An effective approach to increase the data rate over wireless channels is to use multiple transmit and receive antennas. A MlMO system provides multiple independent transmission channels, thus, under certain conditions, leading to a channel capacity that increases linearly with the number of antenna elements [1]. Transmit diversity techniques combined with error control coding have resulted a coding technique for multiple transmit antennas called space-time coding. OFDM is an effective technique for mitigating the effects of delay spread in a frequency selective fading channel. A system that combines MIMO system, space-time coding and OFDM can provide spectrally efficient and high data rate transmission over a fading channel. Space-time codes are mainly designed for flat fading channels. The large delay spreads in frequency selective fading channels destroy the orthogonality of the received signals, which is crucial for the operation of the diversity system. It is shown in [2] that, by using OFDM modulation with a cyclic prefix, frequency selective fading channels can be transformed into multiple flat fading sub channels; thereby space-time processing techniques could be effectively applied to improve system performance, even over channels with large delay spreads.