Exploiting asynchrony in DS-CDMA systems through interference avoidance

User capacity in synchronous CDMA systems has been well characterized and is fixed by the processing gain and target SIR required by each user. Asynchronous systems have not been as well studied. This paper examines the user capacity of asynchronous CDMA systems. It is shown that the user capacity can be increased over synchronous systems by allowing the users to be chip asynchronous and adapting their spreading codes to decrease interference. The degree to which the system experiences a gain by asynchrony is characterized by the effective dimension of the chip waveform. Simulation results are provided to verify that the user capacity is improved by allowing asynchrony when interference avoidance algorithms are employed.