Linewidth-tolerant adaptive equalization scheme for OQAM

A linewidth-tolerant adaptive equalization scheme is proposed for M-ary offset quadrature amplitude modulation (OQAM) signal at the presence of wide laser linewidth. Initially, we present a close-form mathematical expression of OQAM signal at the presence of phase noise and derive the condition to obtain the optimal tap value of adaptive equalizer. Our theoretical investigations proves that phase noise in OQAM signal may result in variation of optimal tap value of adaptive equalizer. Consequently, conventional digital signal processing (DSP) flow that separates adaptive equalization and carrier phase recovery (CPR) into two independent modules cannot apply to OQAM signal anymore. Then, we propose a linewidth-tolerant adaptive equalization scheme that incorporate both adaptive equalizer and CPR for m-ary OQAM signal. Taking the 16-OQAM into account, we comprehensively evaluate its performance to compensate residual chromatic dispersion (CD) and polarization mode dispersion (PMD) at the presence of wide laser linewidth. Simulation shows that our proposed adaptive equalization can effectively compensate residual CD that is below 400 ps/nm without performance penalty at the presence of wide laser linewidth. In particular, a tolerance of linewidth and symbol duration products of 1×10-4 is secured under conditions of CD=400 ps/nm and DGD=10 ps, given 1-dB required-OSNR penalty at BER=10-3.