A system (100), receiver (160-190) and method of operation for spread OFDM
wireless communication (single user OFDM-CDMA with cyclic-prefix) by:
equalizing the received spread OFDM signal (y) and splitting it into
first and second portions (s.sub.1, s.sub.2); making a decision on the
second portion and subtracting the second portion from the received
signal to produce a first difference signal; processing the first
difference signal to recover the first portion of the received signal in
which symbol interfering terms of the second portion are substantially
reduced; making a decision on the first portion and subtracting the first
portion from the received signal to produce a second difference signal;
and processing the second difference signal to recover the second portion
of the received signal in which symbol interfering terms of the first
portion are substantially reduced. The process may be iterated
extensively at this stage. In a second stage, the recovered received
signal is split into a greater number of portions (e.g., 4), and
processed similarly to further reduce interference. The same mechanisms
can be applied to blocks of reduced size (divided into 8, 16 etc.)
leading to a higher resolution of the decoding and a tree-like
structure.Also, minimum mean square error equalization is performed by
multiplying by a first diagonal matrix having elements dependent on
channel coefficients; and multiplying by a second matrix which is a
subset of a Walsh Hadamard matrix.This provides low arithmetical
complexity, it is possible to adjust the number of iterations to be
performed based on a performance/complexity tradeoff, it can be viewed as
a simple extension of current OFDM systems, and it yields a significant
PER performance enhancement (e.g., 3 dB).