Once the phase offset is estimated, it is removed or compensated, so
the received signal has ideally zero phase offset. It is important to remove this phase offset since the
decision device will make decisions on the received symbol, using a fixed reference plane. Once the
symbol is detected, the symbol is then converted to a serial bit stream with the aid of the parallelto-
serial (P/S) converter.
The above procedure of estimating the received phase offset and removing it from the signal prior
to detection is called coherent detection. The classical coherent detection receiver creates a local sinusoid
at some carrier frequency which is exactly in phase and in frequency locked to the received signal.
This operation jointly, spectrally down converts the signal and phase compensates it. This
operation could also have been done separately as shown in Fig. 2.29. Here the receiver establishes a
local version of the channel phase offset to aid channel phase compensation. This procedure can be
complicated and, in some cases, may not be an option to deploy in a commercial product. An alternative
solution would be to use noncoherent detection, which has a simpler form of implementation
complexity. We must note, however, with coherent detection that the following probability of bit error
(Pb) relationship holds true:
(2.
Pages:
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136