Multiuser Access Detection for CDMA Systems

We consider CDMA systems employing packet switching where multiple users can access the system simultaneously. The problem of detecting the activity of multiple new users in an efficient manner is studied. Under the optimistic assumption of a discrete delay space,, the maximum likelihood receiver that detects the presence of multiple new users, i.e the optimum multiuser access detector, has high complexity. Thus, we propose a suboptimum decorrelating receiver which has lower complexity. We then investigate how this simple detector performs under general conditions. The overall recognition of new users by the system is achieved by the decorrelating access detector followed by a bit detector that decodes users’ identification information. Performance of the overall access scheme is given and factors effecting the multiuser access capacity of the system are identified.