TABLE OF CONTENTS The nonconstant envelope characteristic of an OFDM signal introduces another sensitivity to nonlinear devices such as A/D and D/A converters.
Assume that digital signal processors at the transmitter and receiver have the same q bit-resolution; namely, the transmitter uses a q bit-D/A converter whereas the receiver a q bit-D/A converter. Figure 4.28 shows the system model.
If we can deal with the OFDM signal as a narrowband Gaussian noise with an average of zero and power of 
, then 99.7% of amplitude values ranges in [ 3 ? s, 3 ? s] and 99.994% of amplitude values ranges in [4 ? s, 4 ? s]. Here, we call ? s "effective amplitude." At the transmitter and receiver, nonlinear distortions resulting from quantization and clipping are added to the OFDM signal.
Table 4.5 summarizes the transmission parameters for nonlinear analysis.
| Resolution of A/D and D/A converters | q = 3, 4, 5, 6, and 7 |
| Peak-to-peak quantization range | 6 ? s or 8 ? s |
| Modulation/demodulation | QDPSK or BDPSK |
| Number of subcarriers | N SC=128 |
| Guard interval length | ? G/ T S=0 |
Figures 4.29 and 4.30 show the BERs when setting the peak-to-peak quantization range to 6 ? s and 8 ? s respectively [32]. For the same...
