Transmit Diversity for Down-Link MC-CDMA Based on Energy Spreading Transform

In this paper, we investigate transmit diversity for MC-CDMA down-link mobile communications. We apply recently developed energy spreading transform (EST) in MC-CDMA systems to pick up diversity in frequency-selective wireless channels and to improve signal detection performance. It is shown by computer simulation that the required Eb/No's for a 10-2bit-error-rate (BER) are improved by about 5 dB for both an indoor channel and an urban channel compared with a MC-CDMA system without an EST. For a system with two transmit antennas and Alamouti's code, the required Eb/Nofor an EST based MC-CDMA system is improved by 2.7 dB for an indoor channel and 3.3 dB for an outdoor channel compared with a MC-CDMA system without an EST. For a system with multiple transmit antennas, symbol shuffling scheme, together with an EST, has been proposed for transmit diversity. Even though symbol shuffling scheme alone is not as good as Alamouti's code, it can be combined with Alamouti's code to reach matched filter bound (MFB) for systems with over four transmit antennas. Comparison of our transmit-diversity approach with the widely used MMSE detection for MC-CDMA systems is also provided.