The capacity of every communication channel depends on the power of the signal sent through that medium as predicted by Shannon theorem [15], and in this case the power would be limited by the intensity of light an LCD can generate. Increasing this intensity would improve signal to interference and noise ratio (SINR) in the receiver. Like RF power transmitters, LCD displays are limited in terms of the maximum power leading to the Peak to Average Power Ratio (PAPR) limitation, which is a common challenge for OFDM signals. When maximum available intensity is fixed, higher PAPR yields lower average intensity and thus lower SINR. Therefore transmission of OFDM signals over an LCD requires a trade-off between the average power transmitted and the resulting distortion due to clipping of the peaks, another issue that is addressed in this
study. Although various PAPR reduction methods are available,
they would affect QPSK-OFDM and DPSK-OFDM methods in
a same manner, and DPSK modulation would still be superior
when the same method of PAPR reduction is used. Further discussions
on clipping OFDM signals can be found in [16] and
[17].