Acquisition-based capacity estimates for CDMA with imperfect power control

Abstract

One of the major advantages of a code division multiple access (CDMA) system is the flexibility in frequency assignment, which allows all the users to share the same frequency band and, possibly, to partially overlay the spectrum allocation of different services. However, before synchronism to the desired sequence is achieved, the presence of multiple access interference (MAI) is a major impairment which determines the performance of the code acquisition sub-system. It has been argued that the acquisition performance in the presence of MAI may pose limits to the capacity of a CDMA system which are more stringent than those coming from bit error probability specifications. We introduce a general definition for acquisition-based capacity of a CDMA system. This quantity is evaluated for an acquisition sub-system with non-coherent correlator/detector and straight serial search in the time uncertainty region. The effect of imperfect power control is also analysed, showing that the capacity may be substantially decreased when the residual standard deviation of the received power level is above 1 dB.<>