ASIC Design Exploration of Phase Recovery Algorithms for M-QAM Fiber-Optic Systems

We develop circuit implementations and explore design optimizations for one blind and one pilot-based carrier phase-recovery algorithm, where the former algorithm is shown to dissipate 1.8-4.5 pJ/bit and the latter 0.5-0.3 pJ/bit, using 16 to 256QAM

Towards FPGA Emulation of Fiber-Optic Channels for Deep-BER Evaluation of DSP Implementations

We introduce an FPGA-based fiber-optic channel emulator, including both AWGN and carrier phase noise, which can be used to perform deep-BER simulations of DSP implementations and accurately evaluate DSP implementation penalties

Cycle-Slip Rate Analysis of Blind Phase Search DSP Circuit Implementations

Using FPGA-accelerated simulations, we study the cycle-slip rate of 16QAM blind phase search implementations. While block averaging suffers from degraded BER when compared to sliding-window averaging, it results in lower cycle-slip rates and power dissipation

ASIC Design Exploration for DSP and FEC of 400-Gbit/s Coherent Data-Center Interconnect Receivers

We perform exploratory ASIC design of key DSP and FEC units for 400-Gbit/s coherent data-center interconnect receivers. In 22-nm CMOS, the considered units together dissipate 5W, suggesting implementation feasibility in power-constrained form factors

Implementation of Carrier Phase Recovery Circuits for Optical Communication

Fiber-optic links form a vital part of our increasingly connected world, and as the number of Internet users and the network traffic increases, reducing the power dissipation of these links becomes more important. A considerable part of the total link power is dissipated in the digital signal processing (DSP) subsystems, which show a growing complexity as more advanced modulation formats are introduced. Since DSP designers can no longer take reduced power dissipation with each new CMOS process node for granted, the design of more efficient DSPalgorithms in conjunction with circuit implementation strategies focused on power efficiency is required.One part of the DSP for a coherent fiber-optic link is the carrier phase recovery (CPR) unit, which can account for a significant portion of the DSP power dissipation, especially for shorter links. A wide range of CPR algorithms is available, but reliable estimates of their power efficiency is missing, making accurate comparisons impossible. Furthermore, much of the current literature does not account for the limited precision arithmetic of the DSP.In this thesis, we develop circuit implementations based on a range of suggested CPR algorithms, focusing on power efficiency. These circuits allow us to contrast different CPR solutions based not only on power dissipation, but also on the quality of the phase estimation, including fixed-point arithmetic aspects. We also show how different parameter settings affect the power efficiency and the implementation penalty. Additionally, the thesis includes a description of our field-programmable gate-array fiber-emulation environment, which can be used to study rare phenomena in DSP implementations, or to reach very low bit-error rates. We use this environment to evaluate the cycle-slip probability of a CPR implementation

Overhead-optimization of pilot-based digital signal processing for flexible high spectral efficiency transmission

We present a low-complexity fully pilot-based digital signal processing (DSP) chain designed for high spectral efficiency optical transmission systems. We study the performance of the individual pilot algorithms in simulations before demonstrating transmission of a 51 724 Gbaud PM-64QAM superchannel over distances reaching 1000 km. We present an overhead optimization technique using the system achievable information rate to find the optimal balance between increased performance and throughput reduction from adding additional DSP pilots. Using the optimal overhead of 2.4%, we report 9.3 (8.3) bits/s/Hz spectral efficiency, or equivalently 11.9 (10.6) Tb/s superchannel throughput, after 480 (960) km of transmission over 80 km spans with EDFA-only amplification. Moreover, we show that the optimum overhead depends only weakly on transmission distance, concluding that back-to-back optimization is sufficient for all studied distances. Our results show that pilot-based DSP combined with overhead optimization can increase the robustness and performance of systems using advanced modulation formats while still maintaining state-of-the-art spectral efficiency and multi-Tb/s throughput

Energy-Efficient Digital Signal Processing for Fiber-Optic Communication Systems

Modern fiber-optic communication systems rely on complex digital signal processing (DSP) and forward error correction (FEC), which contribute to a significant amount of the over-all link power dissipation. Bandwidth demands are evergrowing and circuit technology scaling will due to fundamental reasons come to an end; energy-efficient design of DSP is thus necessary both from a sustainability perspective and a technical perspective. This thesis explores energy-efficient design of the sub-systems that are estimated to contribute to the majority of the receiver application-specific integrated-circuit power dissipation: chromatic-dispersion compensation, dynamic equalization, nonlinearity mitigation, and forward error correction. With a focus on real-time-processing circuit implementation of the considered algorithms, aspects such as finite-precision effects, pipelining, and parallel processing are explored, the impact on compensation and correction performance is investigated, and energy-efficient circuit implementations are developed. The sub-systems are investigated both individually, and in a system context. DSP designs showing significant energy-efficiency improvements are presented, as well as very high-throughput, energy-efficient, FEC designs. The subsystems are also considered in the context of datacenter interconnect links, and it is shown that DSP-based coherent systems are feasible even in power constrained settings

Power Consumption and Joint Signal Processing in Fiber-Optical Communication

The power consumption of coherent fiber-optical communication systems is becoming increasingly important, for both environmental and economic reasons. The data traffic on the Internet is increasing at a faster pace than that at which optical network equipment is becoming more energy efficient, which means that the overall power consumption of the Internet is increasing. In addition, wasted energy leads to higher costs for network operators, through increased electricity expenses but also because the heat generated in the equipment limits how closely it can be packed.This thesis includes both power consumption modelling and trade-off studies, as well as investigations of novel schemes for joint signal processing that may lead to an improved energy efficiency and increased performance in future systems. The power consumption modelling part includes a model of optical amplifier power consumption, which is connected to a performance model based on the Gaussian-noise model. Using these models, the trade-offs between amplifier power consumption and the choice of modulation format and forward-error-correction (FEC) scheme can be analyzed. Furthermore, the power consumption for a coherent link with minimal digital signal processing (DSP) is studied as well.In the second part we investigate joint signal processing for phase-coherent superchannel systems based on optical frequency combs or multicore fiber. We find that the phase-coherence of optical frequency comb lines enables joint carrier recovery, which can increase performance and reduce the power consumption of the digital signal processing. The possible power consumption savings are quantified for a blind phase search method for phase tracking. Finally, we quantify the performance of joint carrier recovery for wavelength division multiplexed multicore fiber transmission in presence of nonlinear interference and inter-core skew

Next-generation High-Capacity Communications with High Flexibility, Efficiency, and Reliability

The objective of this dissertation is to address the flexibility, efficiency and reliability in high-capacity heterogeneous communication systems. We will experimentally investigate the shaping techniques, and further extend them to more diverse and complicated scenarios, which result in more flexible systems. The scenarios include 1) entropy allocation scheme under uneven frequency response for multi-carrier system, 2) fiber-free space optics link using unipolar pairwise distribution, and 3) flexible rate passive optical network with a wide range of received optical powers. Next, we perform efficiency analysis in inter-data center and long-haul communications. We will characterize the impact of the laser linewidth, jitter tones, and the flicker noise on coherent systems with different baud rates and fiber lengths through theoretical analysis, simulation, and experimental validation. The trade-off analysis indicates the importance of setting up frequency noise power spectral density masks to qualify the transceiver laser design. Besides efficiency analysis, we will also work on efficient system architecture and algorithm design. We investigate the combined impact of various hardware impairments using proposed simplified DSP schemes in beyond 800G self-homodyne coherent system. The proposed scheme is very promising for next-generation intra-data center applications. On the other hand, to improve the data efficiency of the nonlinearity correction algorithm in broadband communication systems, we leverage the semi-supervised method and Lasso. Experimental results validate that Lasso can reduce the required pilot symbol number by exploiting the sparsity of the tap coefficients. Semi-supervised method can further enhance the system performance without introducing additional overhead. Last but not least, regarding reliability, we propose and experimentally demonstrate an ultra-reliable integrated millimeter wave and free space optics analog radio over fiber system with algorithm design. The multiple-spectra operation shows superior performance in reliability and sensitivity compared to the conventional systems, even in extreme weather conditions and strong burst interference.Ph.D