Downlink interference analysis in DS-CDMA for unequal power requirements: The dirty user problem

Downlink interference analysis within direct-sequence code-division multiple-access (DS-CDMA) systems is considered in this paper. Although orthogonal codes are used at the base-station transmitter, multi-path and different power requirements of terminals mean that substantial multiple access interference is suffered at the terminals. With the multitude of terminals available for 2G and 3G systems, inefficient terminal design leads to the “Dirty User Problem”, that is, where a terminal requests more power from the base-station than an alternate terminal located at the same position. A “dirty user” causes higher interference on all other users in the cell and ultimately limits the capacity of the downlink link of a DS-CDMA system. This paper investigates this affect by determining the performance degradation in terms of the percentage of dirty users and their power requirement, compared to a conventional receiver.