  This work presents set-membership adaptive algorithms based on time-varying
error bounds for CDMA interference suppression. We introduce a modified family
of set-membership adaptive algorithms for parameter estimation with
time-varying error bounds. The algorithms considered include modified versions
of the set-membership normalized least mean squares (SM-NLMS), the affine
projection (SM-AP) and the bounding ellipsoidal adaptive constrained (BEACON)
recursive least-squares technique. The important issue of error bound
specification is addressed in a new framework that takes into account parameter
estimation dependency, multi-access and inter-symbol interference for DS-CDMA
communications. An algorithm for tracking and estimating the interference power
is proposed and analyzed. This algorithm is then incorporated into the proposed
time-varying error bound mechanisms. Computer simulations show that the
proposed algorithms are capable of outperforming previously reported techniques
with a significantly lower number of parameter updates and a reduced risk of
overbounding or underbounding.
