  A novel linear blind adaptive receiver based on joint iterative optimization
(JIO) and the constrained constant modulus (CCM) design criterion is proposed
for interference suppression in direct-sequence ultra-wideband (DS-UWB)
systems. The proposed blind receiver consists of two parts, a transformation
matrix that performs dimensionality reduction and a reduced-rank filter that
produces the output. In the proposed receiver, the transformation matrix and
the reduced-rank filter are updated jointly and iteratively to minimize the
constant modulus (CM) cost function subject to a constraint. Adaptive
implementations for the JIO receiver are developed by using the normalized
stochastic gradient (NSG) and recursive least-squares (RLS) algorithms. In
order to obtain a low-complexity scheme, the columns of the transformation
matrix with the RLS algorithm are updated individually. Blind channel
estimation algorithms for both versions (NSG and RLS) are implemented. Assuming
the perfect timing, the JIO receiver only requires the spreading code of the
desired user and the received data. Simulation results show that both versions
of the proposed JIO receivers have excellent performance in suppressing the
inter-symbol interference (ISI) and multiple access interference (MAI) with a
low complexity.
