Low-Complexity Equalization Scheme for Multicarrier Offset-QAM Systems

Fast channel estimation and equalization scheme for offset-QAM OFDM systems

“…We also implemented three other equalization/decoding schemes for comparison: 1. multiple filter banks (MFB) scheme which employed multiple decoding blocks with each consisting of a DFT and one-tap equalizers [12]; 2. multi-tap equalizers (MTE) that used one DFT for demultiplexing and multi-tap equalizers to compensate the IMI between subcarriers [11,13]. The number of real taps was 15 to include the inter-symbol interference (ISI) from adjacent symbols and inter-carrier interference (ICI) from adjacent subcarriers; 3. subcarrierby-subcarrier equalizers (SSE) that applied a multi-tap equalizer for each subcarrier after the pulse shaping filter [13][14][15]. In MTE and SSE, least-mean-square algorithm was used to acquire the coefficients and the convergence parameter was optimized.…”

“…However, the responses of optical/electronic devices and fiber channels can break the orthogonality between IMI and the signal. In the literature, great efforts have been taken to investigate channel estimation and equalization schemes specific to offset-QAM OFDM [7][8][9][10][11][12][13][14][15][16]. In [7], four methods, including a specially designed training sequence and modified least-mean-square algorithm, were proposed to improve the system performance.…”

“…In addition, as will be shown in this paper, it cannot compensate the distortion on the pulse of each subcarrier. In [13][14][15], time-domain or frequency-domain filters were applied to equalize the channel on a subcarrier-by-subcarrier basis. However, they assume an ideally known channel response or require a long training sequence for channel estimation.…”

“…We investigate the proposed scheme in a 40-Gbit/s offset-16QAM OFDM experiment and 240-Gbit/s polarization-division-multiplexed (PDM) offset-16QAM OFDM simulations, both over 1200-km single-mode fiber (SMF). It is shown that the proposed scheme gives better performance, reduced overhead for the training sequence, and/or lower complexity than multiple filter banks [12,13], multi-tap equalization [11], and subcarrier-by-subcarrier equalization [13][14][15]. We also compare offset-QAM OFDM with the proposed scheme and conventional OFDM, and show that in addition to the elimination of cyclic prefix (CP) overhead, offset-QAM OFDM can achieve better performance and longer transmission reach for a moderate/small number of subcarriers.…”

Sparse Preamble Design for Polarization Division Multiplexed CO-OFDM/OQAM Channel Estimation

“…Multi-carrier modulations have recently attracted special attention from researchers to deal with the increasing capacity demands of optical fiber communication systems [1]- [4]. Above all, the offset-QAM for CO-OFDM modulation appears to be a promising solution to improve the spectral efficiency.…”