Nonlinear analysis of the phase noise in the OFDM communication system

Abstract

For the detailed analysis of OFDM system, we present a novel approach of the nonlinear approximation including the second order term of phase noise. Phase noise of PLL (phase locked-loop) frequency synthesizer is analyzed when the commercial components of the PLL are considered for the practical analysis. It is shown that BER results by analytical approach closely match with simulation results of the OFDM communication system using QPSK and 16QAM modulation. DF (degradation factor) that is the ratio of SNR without phase noise ((S/N)/sub without{/spl Phi/}/) to SNR with phase noise ((S/N)/sub with{/spl Phi/}/) is used for the performance measure. When the phase noise variances controlled by the PLL closed- loop bandwidth are 0.005, 0.008, and 0.012 respectively, it can be shown that there are about 0.6 dB, 1.0 dB and 1.7 dB power penalties in QPSK scheme and about 1.9 dB, 3.2 dB, and 6.7 dB in 16QAM scheme to meet BER=10/sup -4/ in AWGN channel than OFDM communication system without phase noise. Furthermore, BER performance of QPSK-OFDM communication system is considerably degraded when phase noise variance is bigger than 0.03. Difference between the results of this work and the previous work is shown more obvious if the phase noise variance exceeds 0.02.