Moreover,
when comparing the differential detector to the 2NEC, the residual offsets should be less than 300 Hz.
The message we wish the reader to take away from Fig. 6.49 is that when widening the observation
window, the receiver is more susceptible to frequency offsets. This is evident by the rapid degradation
exhibited by the respective receivers.
RECEIVER DIGITAL SIGNAL PROCESSING 337
Frequency Offset Degradation Comparison
1.E??“05
1.E??“04
1.E??“03
1.E??“02
1.E??“01
0 200 400 600 800 1000 1200 1400 1600
Frequency Offset (Hz)
BER
Diff Det
1NEC
MLDD
2NEC
FIGURE 6.49 BER Performance degradation comparison for various frequency offsets.
6.7 OVERALL RECEIVER BLOCK DIAGRAM
In this section, we will build upon the above described functions and present a receiver block diagram.
The diagram will include more of the RF and baseband interface signals.
6.7.1 Direct Conversion Architecture (ZIF)
In this section the direction conversion receiver will be presented and some details highlighted. This
type of receiver architecture does not create an intermediate frequency (IF), the received carrier signal
is directly converted to baseband (see Fig. 6.50). This type of spectral down conversion is sometimes
called a Zero IF (ZIF) receiver.
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