Cross-correlation index and multiple-access performance of spreading codes for a wireless system

Cross-correlation index is a measure of multi-user interference combating a spread-spectrum signal. Its magnitude (relative to auto-correlation index of a reference user) is a critical parameter affecting the system performance. In this work, a mathematical model is presented for cross-correlation index of spreading codes, and thereafter the system loading capacity and bit-error-rate performance. The model was tested for different sets of Gold codes. Results show that 63-chip Gold codes have the capacity to support a maximum of about four users, above which bit-error-rate increases rapidly, ultimately resulting in emergence of error floor. The point at which the cross-correlation index equals to auto-correlation index marks the turning point around which the system performance revolves. The outcome was found to be in close agreement with results of simulations obtained for the system performance.