Abstract:
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n this paper, the application of three blind (or selfreference)
spatial diversity signal processing methods to Spread
Spectrum (SS) communications is described. These methods do
not require any kind of side information beyond knowledge of
the signal structure, in contraposition to methods that depend
on training sequences.
Each self-reference method is specifically designed for a particular
SS transmission scheme and uses a particular signal’s
structural information. All three methods, however, are derived
under the common goal of finding the optimum beamformer, in
the sense of maximum signal to interference-plus-noise ratio, in
a blind manner.
The Code Reference Beamformer for Frequency Hopping systems
is an approach based on the knowledge of the hopping
sequence or code structure of the signal. This method is the
best alternative for array signal processing on this particular
SS scheme. Two recently proposed beamforming methods,
which are based on the knowledge of the redundancy structure
of the desired signal, are described under the common
framework of efficiently using the inherent diversity – either
in frequency or time – of two signalling formats, namely, Frequency
Diversity (FD) SS and DS-CDMA. The former uses
frequency diversity, while the latter uses time diversity. The
diversity approach presented for FDSS seems to be the best
choice at the moment. Regarding DS-CDMA, for which many
beamforming algorithms have been developed in the literature,
the self-reference beamforming is simply an alternative blind
method that shows very good performance. These diversity approaches
were compared via simulations to the standard Time
Reference Beamformer (TRB) and showed a performance similar
to it (with 10% of the bits as a training sequence) even
without the need of any side information whatsoever. |