(6.104)
6.4.5 BER Performance Degradation
In this section, we will attempt to quantify the performance degradation due to timing offsets in the
receiver signal processing. We hope the following figures would encourage system designers to fully
characterize their detectors in an effort to create a specification for timing jitter allowed for a certain
tolerable performance degradation.
Figure 6.33 clearly shows as the timing offset increases the performance degradation exponentially
increases. The curves reflect using a differential detector for /4-DQPSK modulation. The symbol
Error Signal Par(t) # c(t t ) P2
Par(t) # c(t t ) P2
RECEIVER DIGITAL SIGNAL PROCESSING 325
FIGURE 6.32 Simplified DLL timing error estimator based on noncoherent signal processing.
X
r (t)
Accum Square
+
c(t??“t ??“ ??†)
X Accum Square
c(t??“t+??†)
Error
Signal
Timing Offset Investigation
1.E??“01
1.E??“05
1.E??“04
1.E??“03
1.E??“02
2 4 6 8 10 12 14
Eb/No (dB)
BER
Pb(DQPSK)-DD
DD (1/16 Offset)
DD (2/16 Offset)
DD (3/16 Offset)
FIGURE 6.33 Differential detection performance degradation as a function of timing offset.
stream entering the differential detector is offset in time by a fixed amount as indicated above and
maintained throughput the simulation run.
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