Performance of an asynchronous CDMA system with parallel interference cancellation

The asymptotic performance of a multistage linear partial parallel interference cancellation (PPIC) receiver for an asynchronous code division multiple access (CDMA) system over an additive white Gaussian noise (AWGN) channel using the moments of the eigenvalues of the correlation matrix is addressed. The closed-form expression for the eigenvalues of a random covariance matrix in synchronous case is known (Jonsson, D., 1982). However, for the case where the users are not synchronous, the distribution is not known. In such a case, we evaluate the behavior of the eigenvalues through numerical simulation. The figure of merit to evaluate the performance is the signal-to-interference-plus-noise ratio (SINR) that is calculated under large-system conditions where the number of active users (K) and the processing gain (N) tend to infinity, while their ratio (β=K/N) is a finite value. Simulation results show a significant degradation in performance due to asynchrony. It is also seen that, similar to the synchronous case, the SINR for the asynchronous case in a large-system scenario converges to that of the minimum mean-squared error (MMSE) receiver.