Cancellation Error Statistics in a CDMA System Using Successive Interference Cancellation

Successive interference cancellation (SIC) is a promising practical scheme for increasing the capacity of CDMA systems. The interference cancellation is never perfect, and the residual cancellation errors propagate because of the successive nature of the decoding. In fact, these residual errors are the principle capacity-limiting issue in SIC systems. Until now, the statistics of these errors have been assumed to follow standard probability distributions such as lognormal and Gaussian. In this paper, the actual statistics of cancellation error are derived. A mathematical expression for the probability density function and the second order statistics is presented, and shown to depend closely on the channel statistics. These expressions were verified through simulations. A Gaussian distribution allowing accurate modelling of cancellation error is also found. The results will be useful to future research and to industry, allowing accurate modelling of cancellation error when designing CDMA systems with successive interference cancellation.