The Effect Of Nonlinearity On A QPSK-OFDM-QAM Signal

The effect o j rionliriearity o i i a QPSKOFDM-QAM .sigiial is aiinlyzed Orie of the char-cicteristics rf ~ i r i OFDM-QAM signal is its wide rarige cf envelope fluctiiatiori: i t s crest factor, defined as the ratio of the peak iiist~iiitaneoiis power to the average (riiis) power i i i dB, is typiccilly greater thurl 10 Wheri N I I OFDM-QAM s i g ricil drives N noriliriear device, rionliriearity w i l l result i i i .sigiial conipressiori arid ir,ternioriulatit,ii among the .suh-carriers at the output An aiialyticol method is iised to predict the i i iprrt hock-off rieeded to keep the iritei-i,iodulatioii helow ciii acceptable level For siiflicieiit large riiuiiber o j sirh-ccirriers, we .show that to keep the iriterinodiilatioti power 30 dB helow the signal power. we need to bcrck-off the i i i p u t power hy 6.5 dB. HOMJever, from the BER point of view, the degradation is less thari 2 dB at BER=O 01 % eveii fiw I d B I ril,li t hack ~ f f