Spatial and temporal filtering for co-channel interference in CDMA

Abstract

This paper provides a review of the challenges and opportunities that arise for improving the user capacity of spread spectrum multiple access (SSMA) or code division multiple access (CDMA) based on spread spectrum techniques. Co-channel interference (CCI) in CDMA is the most dominant factor in the limitation of user capacity, while the capacities of FDMA and TDMA capacities are primarily bandwidth limited. From an information theoretical viewpoint, however, an optimum multi-user receiver for CDMA can be derived by utilizing CCI as redundant information distributed among multiple accessing users. In practical channels such as personal, indoor, mobile radio communication channels, more feasible receivers are required to combat the multipath fading that causes estimation errors of the channel characteristics due to time variance. An overview of several CCI cancellation schemes for sub-optimum but practical multi-user receivers for CDMA is provided by classifying them in the temporal domain, the spatial domain, or in both domains.