B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

References 729
Figure 1 2.28
Average SER of
the OFDM
subcarriers
before and after
disabling five
worst channels.
10-1
10-3
Ideal channel
--8-- Using all subcarriers
--B- Disabling 5 poor subcarriers
10 -4 ---------------------------'
10 15 20 25 30
SNR, dB
across all 32 subchannels, the larger SERs tend to dominate and make the overall SER of the OFDM
system much higher.
To make the OFDM system more reliable, one possible approach is to apply bit loading. In fact, one
extreme case of bit loading is to disable all the poor subchannels (i.e., to send nothing on the subchannels
with very low gains). We can see from the SER comparison of Fig. 12.28 that by disabling 5 of the worst
channels among the 32 subcarriers, the overall SER is significantly reduced (improved).
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