Time-Domain Least Square Channel Estimation for Polarization-Division-Multiplexed CO-OFDM/OQAM Systems

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

“…Figure 10(b) shows the BER of the proposed scheme without and with updated pulse shaping filter using Eq. (10). It is confirmed that the performance is significantly degraded when the filters are not updated.…”

“…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.…”

“…They also work well when the channel delay is small with respect to the OFDM symbol period. The interference approximation method (IAM), first proposed in wireless communications, was also migrated to optical offset-QAM OFDM [8][9][10]. This method assumes prior knowledge of IMI and uses this information to design the preamble to enhance the estimation performance.…”

Volterra Expansion Based Intra Channel Nonlinear Effect Equalization Method for Optical OFDM/OQAM Systems

“…The schematic diagram of CO-OFDM/OQAM system is shown in Fig.1. For O-OFDM/OQAM, the base-band discrete-time equivalent transmitted signal can be expressed as [28] …”

“…Owing to the relaxation of the orthogonal condition from the complex field to the real field, an intrinsic imaginary interference (IMI) exists for O-OFDM/OQAM systems when faced with the influence induced by CD, and fiber nonlinear effect [26]. Numerous theoretical discussions on receiver signal processing method for suppressing IMI have been discussed recently [27][28][29]. In [30], a specially designed pilot has been proposed for O-OFDM/OQAM to improve channel estimation.…”