The carrier recovery algorithm will estimate this offset and adjust the locally generated carrier
in such a way as to reduce this offset, ideally this frequency/phase offset would be zero. In essence
we are derotating the baseband signal to compensate for this residual offset introduced by inaccuracies
in both the transmitter and receiver, as well as the distortion introduced by the channel. Due to
the time varying elements in the communication link, this phase offset is also time varying and should
be tracked. Figure 4.1 shows the frequency/phase offset compensation occurring in the analog
domain, we should mention that more accuracy can be obtained if this operation is performed in the
digital domain.
This can best be explained by a simple diagram shown in Fig. 4.2. Assume the received signal is
r(t) that contains not only the modulation, u(t), but also a time invariant phase offset due to the wireless
channel, f.
Here the carrier recovery (CR) algorithm estimates the received signal??™s carrier frequency, fc, and
phase offset, ?†f
. Notice any frequency offset produces a ???phase roll??? in the signal. For sake of simplicity
assume a zero frequency offset (f0) so we have the following mathematical representation
(4.
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