  In this paper, the bit error performance of a family of likelihood ascent
search (LAS) multiuser detectors is analyzed. An upper bound on the BER of any
LAS detector is obtained by bounding the fixed point region with the worst
initial detector. The concept of indecomposable errors developed by Verdu is
applied to tighten the upper bound. In a special instance, the upper bound is
reduced to that for all the local maximum likelihood detectors. The upper bound
is comparable with that of the optimum detector obtained by Verdu. A lower
bound on the asymptotic multiuser efficiency (AME) is then obtained. It is
shown that there are nontrivial CDMA channels such that a LAS detector can
achieve unit AME regardless of user number. The AME lower bound provides a
means for further seeking a good set of spreading sequences and power
distribution for spectral and power efficient CDMA.
