Bipin Sankar Gopalakrishna Pillai

End-to-End Energy Modeling and Analysis of Long-Haul Coherent Transmission Systems

In this paper, we model and analyze the end-to-end energy consumption of 100-Gbps coherent long-haul transmission systems. In particular, we investigate the impact of forward error correction (FEC) on the end-to-end energy consumption. We compare the energy efficiency of commonly used modulation formats in 100-Gbps transmission, namely dual polarization-quadrature phase-shift-keying (DP-QPSK) and dual polarization-16-quadrature amplitude modulation (DP-16-QAM), for different transmission distance and input bit error rate. Our energy model includes consumption of transmitter, booster, link amplifier as well as receiver. Compared with previous digital signal processing models, we provide a very detailed model that not only includes all the significant functional blocks (such as timing and carrier recovery, chromatic and polarization mode dispersion compensation, and FEC), but also takes into account impact of the number of samples processed every clock cycle and of operations other than multiplications. We have found that receiver energy consumption dominates in transmission systems that use electronic dispersion compensation over long transmission distances. Our results show that for short transmission distances where hard-decision decoding is adequate for both modulation formats, DP-16-QAM is more energy efficient than DP-QPSK. However, as the transmission distance increases, the energy saving due to the low symbol rate of DP-16-QAM is offset by the energy consumption of soft-decision decoding. In this case, the two modulation formats have approximately similar energy consumption.

Flexible Optical Networks: An Energy Efficiency Perspective

High energy efficiency is expected to become a mandatory design criterion in optical networks of the future. This paper investigates schemes for enhancing the energy efficiency of core optical networks based on multicarrier transmission. Such networks of the future will incorporate flexible techniques, namely: 1) adaptive modulation and coding, 2) flexible spectrum allocation, 3) wavelength conversion, and 4) traffic grooming. We investigate the problem of energy efficient routing and spectrum allocation in core optical networks incorporating these flexible techniques. We propose a heuristic solution that provides an energy minimized design of long-haul optical networks by avoiding under-utilization of network resources such as optical fibers, transponders, and amplifiers. A fixed architecture that does not employ the aforementioned flexible techniques is used as a benchmark for comparison. The numerical results in the west European (24-node US) core optical network show that the energy efficiency of the flexible architecture can outperform the fixed architecture by a factor of 4.2 (6.4) for low and 1.8 (1.9) for high traffic demands, respectively.

Analytical Characterization of Optical Pulse Propagation in Polarization-Sensitive Semiconductor Optical Amplifiers

In this paper, we perform analytical characterization of optical pulses propagating through a polarization-sensitive semiconductor optical amplifier (SOA). We derive analytical expressions for the carrier density, gain and phase evolution along the SOA and show how these expressions prove useful in optical signal processing applications. The propagation of counter-propagating pulses as well as pulse streams across SOAs have been analysed and expressions for energy gain have been derived in all these cases. We also show that our analytical results reduce to corresponding results of polarization insensitive SOAs already published. The analytical results are in excellent agreement with detailed numerical simulations done in MATLAB using the NIMROD portal. The analytical calculations lead to significant savings with regard to simulation time and processing capacity requirements. We further prove that the energy gain difference for counter-propagating pulse streams is directly proportional to the difference delay between in them and hence can be used as a measure of the delay difference. This theoretical result agrees well with experimental results

Chromatic dispersion compensation — An energy consumption perspective

We estimate the energy consumption of digital-signal-processing-based chromatic dispersion (CD) compensation in wavelength-division-multiplexed (WDM) systems and show that energy efficiency of digital electronic compensation is comparable to that of optical fibre-based compensation.

Quality of service provisioning and energy minimized scheduling in software defined flexible optical networks

The over-provisioning of capacities in optical networks is not a sustainable approach in the long run. In this paper, we propose a software defined networking scheme for quality of service provisioning through energy efficient assignment of optical transponders, employing bandwidth variable distance adaptive modulation and coding. Our scheme enables avoiding over-provisioning of transponder capacity as well as short-term major changes in equipment allocation for networks with dynamic traffic. We make use of the seasonal auto-regressive integrated moving average model to forecast the statistics of network traffic for an arbitrary time span based on the requirements and the constraints of the service provider. The quality of service measure is defined as the probability of congestion at the core router ports. A stochastic linear programming approach is used to provide a solution for energy efficient assignment of optical transponders and electronic switching capacity while ensuring a certain level of quality of service to core routers. The scheduling of optical lightpath capacities is performed for the entire duration of time under consideration, whereas the scheduling of electronic switching capacities is performed based on the short-term dynamics of the traffic. Numerical results show up to 48% improvement in the energy efficiency of optical networks and 45% reduction in the number of optical lightpaths through the implementation of the proposed technique, compared to a design based on employing conventional fixed optical transponders and no traffic rerouting, where both schemes satisfy the congestion probability requirements.

The impact of error control on energy-efficient reliable data transfers over optical networks

In this paper, we study the efficacy of error control schemes for energy-efficient reliable delivery of large files (hundreds of GBs) over core optical networks. Specifically, we examine two schemes: automatic repeat request (ARQ), and hybrid ARQ (i.e. ARQ combined with forward error correction (FEC) capability). We focus on Reed-Solomon (RS) FEC codes (in hybrid ARQ) and propose a new model, incorporating different block sizes as well as code error-correction capability, to estimate the energy consumption for performing encoding and decoding operations in optical networks. The model considers the impact of varying pre-FEC bit-error rates (BER) of the optical channel, and the signal processing blocks used to implement RS codes. Our results show that when the pre-FEC channel BER is in excess of 10-5, hybrid ARQ offers better performance than ARQ in terms of energy efficiency. However, both hybrid ARQ and ARQ have similar performance under lower BER.

Power-efficiency considerations for adaptive long-haul optical transceivers

Adaptive optical transceivers are considered among the candidates for future optical communications, especially in long-haul and metro applications. In this paper, the hardware requirements of the adaptive digital coherent transceivers are studied. Challenges and solutions for power-efficient implementation of the electro-optical front-end and digital signal processor are investigated. Different power-saving modes are also presented.

Multi-user encoding for forward error correction in passive optical networks

We propose a method and hardware architecture for error-correction encoding of downstream traffic in a passive optical network. The encoder can handle multiple users using multiple error-correction codes. Our solution further allows transmission of a codeword across multiple timeslots allotted to a user. his ability to spread out the user payload allows decimation of the data processing rate at the user end, leading to lower energy consumption. Hardware emulation based on the developed design shows that our multi-user encoder consumes significantly less power than a system using conventional encoders in parallel.

On EDFA and Raman Fiber Amplifier Energy Efficiency

We compare the energy efficiency of Distributed Raman Amplifiers (DRFA) and Erbium-Doped Fiber Amplifiers(EDFA) used in long-haul transmission systems. This comparison accounts for the interaction between optical link power, signal quality (as measured by the Bit Error Rate (BER)), and the use of Forward Error Correction (FEC). We show that deploying DRFAs in some scenarios may be more energy efficient than EDFAs, despite their intrinsic requirement for higher pump powers, depending upon the link parameters.

Clustering approaches for cost-effective deployment of Australia's National Broadband Network

We propose a new clustering approach that identifies the area within an exchange service area where broadband could be delivered economically using passive optical networks. Our analysis uses GIS data and takes into account road layout between the houses.