Analysis of the Throughput of Random-Access Mu CDMA Systems with Multiuser Detection *

This paper analyzes the asymptotic behavior of the throughput of random-access (RA) multichannel CDMA (MCDMA) systems with multiuser detection. It is proved that as the maximum number IS of users which the multiuser detector can handle at the same time increases, the normalized throughput function, i.e., the collision-free transmission probability for each channel, approaches a unit step function exponentially fast. This unit step function is defined as 1.0 if the average number r of simultaneous users in each channel is less than IS, as 0.50 if r = K, and as zero for r > IS. The maximum throughput of a RA/MCDMA system is found to be reached approximately at a traffic load value of fm(1i-) = K - 24T + 1 for I 9.