Blind Demodulation of Direct-Sequence CDMA Signals Using an Antenna Array

Recent work on Direct-Sequence (DS) Code Division Multiple Access (CDMA) has shown that blind adaptive interference suppression techniques can be used for reliable demodulation, provided that the timing of the desired signal is known. The blind demodulator has since been used as a building block for a scheme for joint timing acquisition and demodulation. In this paper, we consider a blind adaptive demodulator that uses spatial diversity in the form of an antenna array in addition to the inherent time diversity of the DS signals exploited in previous work. Our results show that, as expected, the use of an antenna array leads to a substantial increase in system capacity, but that the convergence of an adaptive implementation using a stochastic gradient algorithm may be too slow for many applications. On the other hand, the large number of taps in the space-time lter imply that a faster least squares implementation is quite complex. Our results therefore point out the need for devising faster adaptive algorithms with reasonable complexity. It is shown that, while the blind demodulator requires knowledge of the DoA of the desired signal, a \sectorization" scheme can be used to get around this requirement.