A coordinate descent algorithm for multichannel multiuser detection in underwater acoustic DS-CDMA systems

Direct Sequence (DS) Code Division Multiple Access (CDMA) is considered for a network of Autonomous Underwater Vehicles (AUVs) communicating through a Base Station (BS) equipped with a receive array. A multiuser detection algorithm, based on the Cyclic Coordinate Descent (CCD) approach is proposed for this situation. The CCD technique is used to circumvent the complexity of the optimal Maximum Likelihood (ML) detector. The proposed algorithm is based on joint data detection and channel estimation using Minimum Mean Square Error (MMSE) as the overall optimization criterion. It is implemented in a multichannel configuration to exploit the array processing gain available at the BS. The complexity of the proposed CCD detector does not depend on the modulation level and is linear in the size of the receive array. The CCD detector has been tested using real data, recorded from four users transmitting asynchronously over a shallow water acoustic channel, with varying Spreading Factors. The signals were transmitted over 2 km in a 20 kHz band, demonstrating good results at the chip rate of 16 kchips/second.