Combined transmit antenna diversity and chip equalization for the downlink of SS/TDM systems

Most of the traffic carried by future wireless systems will be data-oriented. The majority of data applications have bursty and asymmetric traffic. Hybrid spread spectrum/time division multiplexing (SS/TDM) is a promising scheme for the air interface of future high bitrate wireless data networks, especially for the downlink. In SS/TDM systems, while spread spectrum transmission provides implicit path diversity, the diversity gain reduces considerably if the delay spread of the channel is less than one chip or if the arriving paths are highly correlated. This may result in unsatisfactory bit error rates. In this paper, we combine transmit antenna diversity with chip equalization to achieve both robustness against fading and interference suppression in the downlink of SS/TDM systems. We show through chip-level simulations that the combined scheme performs better than simple chip equalization. The improvement is significant at high SNR (signal to noise ratio) levels.