Linear and DF joint detectors for DS-CDMA communications using periodic long codes

Detection structures for a direct sequence (DS) code division multiple access (CDMA) multiuser uplink using codes with a period of several symbols, called long codes, are investigated. In a first part, we propose a multirate description of the uplink. Based on this formalism, we revisit the linear and decision feedback minimum mean square error (MMSE) detectors. In order to identify the best attainable performance, we focus on the infinite size versions. In a second part, reduced complexity solutions are put forward and discussed. Finally, the performance of the proposed detectors is investigated and compared with that of the classical rake receiver and the single-bit horizon detectors. The relevance of the different solutions is discussed in the light of the channel length.