Then continue
with a presentation of space-time equalization where joint equalization and antenna combining
is performed for the purposes of improved performance. Due to an increased interest in the wireless
community of operating in the frequency domain, we present an overview of frequency domain equalization
(FDE). We then move on to symbol timing recovery (STR), channel quality estimation (CQE),
and automatic frequency control (AFC). We conclude the chapter with an overall receiver block diagram
to put the above mentioned signal processing algorithms into perspective.
6.1 TEMPORAL EQUALIZATION (EQ)
In channels with memory, such as multipath frequency selective fading channels, the received signal
is composed of multiple-delayed versions (or echoes) of the transmitted signal. These delayed versions
sum and subtract to result in Inter-Symbol Interference (ISI). This ISI cannot be eliminated by
increasing the transmitter power or reducing the receiver noise figure. A method used to remove the
ISI is through equalization. Equalizers make use of the ???time diversity??? of the received signal (as with
RAKE receivers in CDMA systems) to extract the multiple-delayed echoes and form a combined
symbol. Some commonly used methods are as follows:
Linear equalization
Decision feedback equalization
Maximum likelihood sequential estimation
These methods are shown in Fig.
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