  In this work we examine blind adaptive and iterative decision feedback (DF)
receivers for direct sequence code division multiple access (DS-CDMA) systems
in frequency selective channels. Code-constrained minimum variance (CMV) and
constant modulus (CCM) design criteria for DF receivers based on constrained
optimization techniques are investigated for scenarios subject to multipath.
Computationally efficient blind adaptive stochastic gradient (SG) and recursive
least squares (RLS) algorithms are developed for estimating the parameters of
DF detectors along with successive, parallel and iterative DF structures. A
novel successive parallel arbitrated DF scheme is presented and combined with
iterative techniques for use with cascaded DF stages in order to mitigate the
deleterious effects of error propagation. Simulation results for an uplink
scenario assess the algorithms, the blind adaptive DF detectors against linear
receivers and evaluate the effects of error propagation of the new
cancellations techniques against previously reported approaches.
