Abstract
In order to improve the spectral efficiency of coherent optical communication systems, it has recently been proposed to make use of the orthogonal frequency-division multiplexing offset quadrature amplitude modulation (OFDM-OQAM). Multiple optical channels spaced in the frequency domain by the symbol rate can be transmitted orthogonally, even if each channel overlaps significantly in frequency with its two adjacent channels. The solutions proposed until now in the literature unfortunately only address a single polarization communication, and therefore do not benefit from the capacity gain reached when two polarizations are used to transmit independent information signals. The aim of the present paper is to propose a receiver architecture that can decouple the two polarizations. We build an equalizer per channel at twice the symbol rate and optimize it based on the minimum mean square error (MMSE) criterion. We demonstrate the efficiency of the resulting system compared to the Nyquist wavelength-division multiplexing (N-WDM) system both in terms of performance and complexity. We also assess the system sensitivity to transmit synchronization errors and show that system can even work under significant synchronization errors.
Highlights
In wavelength-division multiplexing (WDM) optical communication systems, increasing the spectral efficiency (SE) is a key target in order to respond to higher capacity requirements
We build an equalizer per channel at twice the symbol rate and optimize it based on the minimum mean square error (MMSE) criterion
We demonstrate the efficiency of the resulting system compared to the Nyquist wavelength-division multiplexing (N-WDM) system both in terms of performance and complexity
Summary
In wavelength-division multiplexing (WDM) optical communication systems, increasing the spectral efficiency (SE) is a key target in order to respond to higher capacity requirements. The second approach, referred to as coherent orthogonal frequency-division multiplexing (CO-OFDM), results from the application of the OFDM modulation widely used for wireless communications systems to multiple optical channels. N-WDM suffers from hardware implementation limitations such as the finite length of the pulse shaping filters, the timing jitter of the data sampling and the finite resolution of the analog/digital converters These constraints translate into ISI and ICI, and affect significantly the performance. Like CO-OFDM, OFDM-OQAM requires dedicated hardware to generate a set of frequency-locked and synchronously modulated optical carriers. Both [22, 23] simulate a single-polarization OFDM-OQAM system and demonstrate that it outperforms the NWDM and CO-OFDM systems. Matrix 0M,N is the size-M × N matrix composed of zeros, matrix IN is the size-N identity matrix
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