Next we plot the performance degradation for the various noncoherent detectors presented earlier:
differential detection, 1NEC, 2NEC, and MLDD. Generally speaking, increasing the time offset
degrades performance. Moreover, the performance of the detectors with the larger observation window
is still better than that of the conventional differential detector for small timing errors. These
curves were plotted assuming an Eb/No equal to 8 dB (see Fig. 6.34).
326 CHAPTER SIX
Timing Offset Degradation Comparison
1.E??“01
1.E??“03
1.E??“02
0 2 5
Timing Offset (x???s Ts/16)
BER
Diff Detect
1NEC
2NEC
MLDD
1 3 4 6
FIGURE 6.34 Timing offset degradation comparison for various detection techniques.
The detection techniques with the larger observation window degrade at a faster rate than those
with a smaller observation window.
6.5 CHANNEL QUALITY ESTIMATION (CQE)
In this section, we will provide an overview of some techniques used to estimate the quality of the
communication link, they will be called CQE. The many actual uses of the CQE will not be discussed,
but suffice it to say that generally speaking they can be used for performance improvement, power
reduction, receiver mode selection, and so on. We leave this up to the system designer to be creative.
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