Path-time coding for downlink multi-user CDMA over multipath channels

Abstract

A new BLAST MIMO transceiver is proposed for the downlink of high data rate CDMA systems over frequency-selective multipath channels. We consider the scenario in which multiple antennas are used at both the base station (BS) and each mobile station (MS). The high data-rate stream is first demultiplexed into multiple substreams, which are then encoded across different paths and time delays by a set of "path-time" encoders for achieving path diversity, and spread by a set of precoders designed to suppress the multiple access interference (MAI) and equalize the multipath channels without the use of channel information. These coded substreams are transmitted simultaneously by multiple antennas for an increased spectral efficiency. At each MS, the received data is passed through a simple matched filter (MF) with a modified code sequence to blindly suppress the residual ISI. A multi-user detection scheme is then employed to separate the mutually interfering signals from the multiple transmit antennas and restore the diversity gain due to path-time coding (PTC). The proposed scheme can effectively provide spatial multiplexing and diversity gain at the same time. Moreover, significant enhancement in performance can be achieved at the receiver by incorporating suitable iterative interference cancellation strategies.