Abstract
We experimentally demonstrate a novel digital signal processing (DSP) structure for reduced guard-interval (RGI) OFDM coherent optical systems. The proposed concept is based on digitally slicing optical channel bandwidth into multiple spectrally disjoint sub-bands which are then processed in parallel. Each low bandwidth sub-band has a smaller delay-spread compared to a full-band signal. This enables compensation of both chromatic dispersion (CD) and polarization mode dispersion using a simple timing and one-tap-per-symbol frequency domain equalizer with a small cyclic prefix overhead. In terms of the DSP architecture, this allows for a highly efficient parallelization of DSP tasks performed over the received signal samples by deploying multiple processors running at a lower clock rate. It should be noted that this parallelization is performed in the frequency domain and it allows for flexible optical transceiver schemes. In addition, the resulting optical receiver is simplified due to the removal of the CD compensation equalizer compared to conventional RGI-OFDM systems. In this paper we experimentally demonstrate digital sub-banding of optical bandwidth. We test the system performance for different modulation formats (QPSK, 16QAM and 32QAM) over various transmission distances and optical launch powers using a 1.5% CP overhead in all scenarios. We also compare the proposed RGI-OFDM architecture performance against common single carrier modulation formats. At the same total data rate and signal bandwidth both systems have similar performance and transmission reach whereas the proposed method allows for a significant reduction of computational complexity due to removal of CD pre/post compensation equalizer.
Highlights
Digital signal processing (DSP) has played an important role in supporting the recent capacity expansion of optical networks
In recent publications [4,6,7,8,10,11,12] we proposed a new way to structure the digital signal processing for OFDM receivers that allows for a reduction of the required cyclic prefix (CP)
The CP length used for all the experiments was 16 samples per 1024 samples of the OFDM frame, which was interpreted as 1 symbol overhead per sub-band and a CP overhead of 1.5%
Summary
Digital signal processing (DSP) has played an important role in supporting the recent capacity expansion of optical networks. In order to reduce DSP resource allocated to CD compensation equalizer, filter bank (FB) based digital sub-banding has been proposed [4] Using this approach, the transmitted signal bandwidth is divided into multiple sub-bands operating at lower baud rates. The transmitted signal bandwidth is divided into multiple sub-bands operating at lower baud rates This bandwidth partitioning allows for compensation of CD on a per sub-band basis using elementary timing and equalization techniques, achieving higher DSP efficiency as well as a simplified parallelization scheme. Since all sub-bands share the same optical transmission path, some of the channel properties are common for all sub-bands This fact allows for the utilization of more accurate and simplified impairment compensation techniques by jointly processing multiple sub-bands simultaneously and taking advantage of information from other sub-bands. The FB signal processing approach is applicable in both long-haul and metro optical communication systems and may provide significant energy efficiency savings of 30%-50% in both the power consumption and the area of DSP ASICs [7]
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