Please use this identifier to cite or link to this item: http://hdl.handle.net/10266/6111
Title: Performance Analysis of Optical Nyquist WDM Superchannel systems using Hybrid Modulation Techniques
Authors: Goyal, Shivani
Supervisor: Kaler, R. S.
Singh, Hardeep
Keywords: Nyquist Superchannel;Hybrid Modulation;TA-MCF;MC-MMF;PON
Issue Date: 15-Jun-2021
Abstract: In modern times, internet traffic is increasing by leaps and bounds to fulfil the demand of different services such as multimedia, over the top platforms, cloud services, online gaming etc. This all has resulted in network congestion and to cope up with these demands, high capacity optical transmission systems with efficient use of channel spacing are required. There are a lot of challenges in both short-reach and long-haul optical access networks when the system capacities are upgraded. The earlier capacity growth has been achieved by improving the intensity modulation rate and using the DWDM techniques. However, due to electronics devices limitations and their failure to compensate channel impairments, it has been very tough to increase the data rate beyond 100 Gb/s for each channel. With the development of DWDM in association with digital coherent techniques, the capacity of the system has been increased up to 100 Gb/s for each channel. But Coherent techniques require a hybrid receiver structure to retrieve the phase of the electrical signal. With the help of phase information, distortions like polarization mode dispersion (PMD) and chromatic dispersion (CD) can be compensated. Therefore, more advanced modulation formats and polarization division multiplexing become feasible, enabling a channel speed to 100Gb/s and beyond. Going beyond and to the 100Gb/s per WDM channel requires the use of multiple carriers to make up a single WDM interface. The resulting multiplex, called a super-channel (or superchannel), and creates a multi-wavelength signal in which each wavelength will operate at the maximum data rate. In this, multiple carriers are transmitted over a signal channel. To utilize the channel spacing between these subcarriers, the Nyquist WDM superchannel technique is used which can provide terabit signal transmission for each channel. Nyquist WDM superchannels with different algorithms have been developed as they provide terabit transmission, higher spectral efficiency and have less bandwidth requirement as compared to CO-OFDM. Further, the Nyquist WDM superchannel with different combinations of modulation techniques (Nyquist DP-16QAM, DPSK, and POLSK) has come into the picture to increase the data rate beyond 100 Gb/s for each channel and for simultaneous transmission of unicast and multicast data. For data transmission through fiber, Nyquist WDM superchannels technique is an adequate and efficient way of communication but its development poses several challenges like ISI, ICI, high OSNR and high power etc. This thesis deals with the performance analysis of Nyquist superchannel systems and in association with hybrid modulation techniques for high capacity long haul and short reach transmission by efficiently utilizing the channel bandwidth. Nyquist superchannel with hybrid modulation technique is the most promising technique to improve the channel capacity with more tolerance to distortions. Further, the need of 1Watt power to each channel has forced to move towards the transmission of Nyquist superchannels through multi core or multi-mode fibers instead of standard single mode fiber. MC-MM utilizes the space division multiplexing for the transmission of signals and increases the fiber capacity by multiple numbers of cores or modes. Transmission through multi core or multi-mode fiber also protects the system from fiber non-linearities and fiber fuses. Next, the aim has been to access the networks in the field of passive optical network (PON) that are very cost-effective. Long-range and large splitting ratios are the key requirements for low cost PON. But splitters in the modern day networks cause unavoidable upstream losses, which have to be eliminated to improve the power budget and to increase the long reach. Therefore, MC-MMF with a mode combiner is proposed to reduce the upstream losses by removing the requirement of multiple feeder fibers in the field of a passive optical network. Now in the thesis, the main objectives are to examine the optimum channel spacing for the optical WDM Nyquist Superchannel system and reducing both inter-channel interference (ICI) and inter-symbol interference (ISI) effects. Nevertheless, ICI and ISI effects are unavoidable due to tight channel spacing and they can also cause substantial performance degradations. Hence, the key research goal is to combat the ISI and ICI via a novel techniques named as driver signal adjust control algorithm that consists of band pre-distortion algorithm and root raised cosine (RRC) filtering. Here, a driver signal adjust algorithm is proposed that enables the transmitter in Nyquist superchannel system to remove the predistortions. Besides the driver signal adjust algorithm, the RRC filtering is also used to further reduce the channel spacing and that channel spacing is utilized to transmit more number of subcarriers in one Nyquist superchannel. Then the proposed system evaluates the scaling coefficient according to the raised cosine filtering by using m-quadrature amplitude modulation (m-QAM) mapping and finally, it compensates the delay by using convolution with the inverse fast fourier transform (IFFT) and FFT. Due to this, the channel spacing between subcarriers has been reduced from 32.5 GHz to 26.5 GHz and this can be further utilized to improve spectral efficiency significantly. This proposed system has achieved a speed of 21 Tb/s with spectral efficiency × distance product of 18500 b/s/Hz.km using driver signal adjust algorithm and RRC filtering. Further in the next objective, the Nyquist superchannel system with a hybrid modulations technique is proposed to support both unicast and multicast transmission simultaneously as compared to the conventional Nyquist superchannel system. At the same time, the channel spacing is reduced from 27 GHz to 15 GHz and has more tolerance to distortions. The performance of the Nyquist superchannel system using a multicast overlay system along with a hybrid modulation technique is analysed. The Hybrid modulation technique consists of Nyquist dual polarization quadrature amplitude modulation (DP-16QAM), polarization shift keying (POLSK) modulation, and differential phase shift keying (DPSK) modulation to transmit unicast and multicast data. The multicast overlay system transmits a total of 5.1 Tb/s data rate using 8×640 GB/s unicast signal and 40 Gb/s multicast signals. But in this system, 1Watt power is required to each channel which causes high OSNR, fiber non-linearities, and fiber fuses. Thus, a novel trench assisted multicore fiber (TA-MCF) with SDM is proposed that can be easily interfaced with wavelength division multiplexing (WDM) in standard single mode fiber (SSMF). The parameters of TA-MCF are optimized to cover the long distance for Terabit transmission of Nyquist superchannels at multiple spans. However in multiple spans, the performance of the system varies as signal travel through multiple cores of MCF. So to avoid these variations, core to core rotation (CCR) scheme has also been proposed to transmit different Nyquist superchannels through TA-MCF. Using TA-MCF, five Nyquist superchannels are transmitted (each at 4.224 Tb/s data rate), which covers the 2688km distance at different loops by utilizing the 7.5 GHz channel spacing between Nyquist superchannels without any distortions. In one Nyquist superchannel 15 subcarriers are transmitted each at 35.2 Gbaud rate using proposed Hybrid modulation technique with acceptable inter-core crosstalk over seven trench assisted cores. Further, the last objective is to investigate high speed optical Nyquist signals for passive optical network. To achieve this, an optimized multicore multimode fiber (MC-MMF) is proposed to enhance the capacity of the network and spatial efficiency. In passive optical networks (PON), the MC-MMF is preferred as compared to TA-MCF. However, TA-MCF covers large distance as compared to MC-MMF but it has large inter-core crosstalk and large upstream losses which are not tolerable in the PON system. MC-MMF with SDM comprises of MM fiber (that transmits information independently via individual mode) and MCF (with core multiplexing in which a single fiber is constructed with a high indexed core to transmit the information independently) to reduce the cost per subscriber. A single MC-MMF also transmits the signals for upstream/downstream data transmission without multiple feeder fibers and accepts the multiple signals from multiple ONU’s in PON with a lesser number of splitters/combiners. The simulation results reported that with the proposed MC-MMF system, the total link losses are reduced to -10 dB with average acceptable crosstalk of -42 dB in the PONs network and achieved BER is <10-9 for all the modes for 50 Km transmission distance. The Nyquist superchannels system inscribed in MC-MMF can be used for accessing low cost passive optical networks. This system has great scope in submarine, terrestrial, and access networks areas and where high power delivery to fiber and upstream losses are major issues.
URI: http://hdl.handle.net/10266/6111
Appears in Collections:Doctoral Theses@ECED

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