Blind despreading of short-code DS-CDMA signals in asynchronous multi-user systems

The problem of blind synchronization and despreading of multiple asynchronous short-code direct-sequence code division multiple access signals is addressed in this paper. A novel algorithm applicable in asynchronous multi-user systems is proposed in which no prior knowledge of the used spreading codes is needed. The algorithm exploits the structure of the signal correlation matrix and estimates the timing offsets and spreading codes in an iterative manner, thereby improving existing methods so that also sources with nearly equal timing offsets can be estimated. Simulation examples demonstrate that nearly ideal processing gain is obtained already at a very low signal-to-noise ratio (SNR) in an AWGN channel. The algorithm can be used in interference cancellation as well as in non-cooperative applications such as spectrum monitoring, emitter localization and electronic intelligence. As an example, high-resolution DOA estimation of spread spectrum signals at low SNR is demonstrated.