Strongest-users-only detectors for randomly spread CDMA

A randomly spread direct sequence code division multiple access (DS-CDMA) system operating in flat fading is considered. Users are assumed to employ equal rates and transmit powers. The receiver ranks the users according to their received powers, and decodes only the subset that can be reliably decoded. Confining the discussion to asymptotic analysis (in terms of number of users and processing gain), we study the matched-filter detector, the linear minimum mean squared error (MMSE) detector, and the "optimum detector" under the above strongest-users decoding scheme. The total capacities under outage constraint, derived as functions of the fraction of users that cannot be reliably decoded (equivalent to the "outage probability"), are analyzed and compared.