An asymptotic lower bound on the capacity of M-ary CDMA transmission with non-Gaussian multi-user interference

Using an appropriate multi-access channel model, we consider CDMA network transmission with single-user demodulation and decoding at the receiver. We derive the asymptotic distribution of the multi-user interference in case of high-rate transmission that can exceed the conjectured CDMA capacity with Gaussian multi-user interference. We show that the considered multi-user interference is non-Gaussian distributed, having a compound Poisson distribution in the asymptotic case of many active CDMA users. Consequently, we derive and prove a lower bound on the sum capacity of CDMA transmission with single-user demodulation and decoding. The derived capacity lower bound C≥2×e^-1Σ_j=2^∞log₂(j)/(j-)!≈1.6544 bits per CDMA chip exceeds significantly the previously conjectured CDMA capacity limit of 0.72 bits per CDMA chip in case of multi-user interference with Gaussian distribution. Finally, we also present numerical results illustrating accuracy of the derived lower bound.