Channel utilization efficiency and throughput of random-access multichannel CDMA systems with multiuser detection

All multiuser detection (MD) algorithms proposed so far are constrained by either complexity or implementation costs. This fact makes it impossible to apply these algorithms directly in a traditional single channel CDMA system to support a large number of simultaneous users. Multichannel CDMA (MCDMA) communication systems are considered to support a much larger population of simultaneous users than can be achieved by applying an MD algorithm directly to a traditional single channel CDMA system. Our system design makes it possible to apply the Verdu (1986) optimum MD algorithm or the suboptimal MD algorithms independently in each channel to improve system performance. The probability distribution function of the number of empty channels is found for a random-access (RA) MCDMA system using MD with finite channels and finite simultaneous users. It is shown that with a probability close to 1.0 that there is no empty channel in a RA/MCDMA system with MD. The throughput of RA/MCDMA systems with MD is studied. It is shown that when the average number τ of simultaneous users in each channel is in the region of half or less than the maximum number K of users which the multiuser receiver can handle at the same time, perfect throughput can be achieved. When τ>K, the throughput drops gradually to zero. The maximum throughput and the throughput in the range of τ near it is severely constrained by K