Frequency-Domain Channel Estimation for Polarization-Division-Multiplexed CO-OFDM/OQAM Systems

Abstract

Intrinsic imaginary interference (IMI) induced by multiple-path fading channel is an important impairment for orthogonal frequency division multiplexing offset-quadrature amplitude modulation (OFDM/OQAM) systems. Therefore the accurate channel estimation is highly desired for such system. Recently both the simulation studies and the experimental demonstrations for coherent optical OFDM/OQAM (CO-OFDM/OQAM) have been reported. However, there are no theoretical discussions on the IMI effect and the channel estimation method for polarization-division-multiplexed (PDM) CO-OFDM/OQAM systems so far. In this paper, we systematically analyze the frequency-domain optical fiber channel transmission model for PDM CO-OFDM/OQAM systems with the IMI effect induced by chromatic dispersion (CD) and polarization mode dispersion (PMD). The full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods are discussed to mitigate the IMI effect. The computational complexities and robustness against CD and PMD are also compared for both of the FL and the HL methods. The theoretical analysis is validated by numerical Monte Carlo simulations of PDM CO-OFDM/OQAM systems. IndexTerms-Optical communication, coherent communication, orthogonal frequency division multiplexing offset-quadrature amplitude modulation (OFDM/OQAM), channel estimation. I.The authors are with the State

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

“…Among those, the E-IAM-C gives a greater |t m | than the others. However, only IAM-R was exploited in [14] for coherent optical communications. Therefore as an additional contribution of this paper, we show that the E-IAM-C could also be considered for coherent optical communications.…”

“…Note that changing signs of all pilots in (18) results in the same |t 0 |. Hence, on y polarization, we propose to apply (18) on S 1 and the reverse signs of (18) on S , in order to satisfy the condition in (14). An intuitive illustration of the proposed pattern is shown in Fig.…”

“…Indeed, IAM is a well-known channel estimation method for OFDM/OQAM, which was originally proposed for radio communications in [12], [13]. This method was introduced for PDM CO-OFDM/OQAM in [14]- [16]. In fact, the shifted versions of the CO-OFDM/OQAM prototype filter in frequency and time domains can be viewed as a grid of filters for different frequency-time (FT) positions.…”

“…There are several variances of IAM with different preamble patterns. Unfortunately, only the IAM pattern with real pilots (IAM-R) was considered in [14]- [16]. In this paper, we show that another IAM pattern, namely the enhanced IAM with complex pilots (E-IAM-C), can also be applied for PDM CO-OFDM/OQAM systems with remarkable BER performance improvement.…”

“…The proposed solution achieves a gain in BER with a lower PAPR compared to the E-IAM-C method. In comparison with the IAM-R method in [14], the proposed SP design attains a significant gain in BER with an equivalent PAPR.…”