Optimized DSP Framework for 112 Gb/s PM-QPSK Systems with Benchmarking and Complexity–Performance Trade-Off Analysis

We propose and demonstrate bi-directional (BiDi) self-homodyne coherent detection (SHCD) system experimentally, in which the multiple input multiple output free (MIMO-free) digital signal processing (DSP) is achieved with the help of BiDi-operated adaptive polarization controller (APC). Since the polarization wandering of the local oscillator (LO) is relevant to that of the counter-propagating signal within the same fiber, the APC can realize the polarization tracking and compensation for LO and the counter-propagating signal simultaneously. The power-consuming 2x2 MIMO DSP, can be eliminated in our proposed BiDi SHCD system. The frequency offset compensation (FOC), carrier phase recovery (CPR) are also omitted thanks to the SHCD. Besides, the dedicated chromatic dispersion compensation (CDC) is no longer needed due to short-reach transmission of data center interconnect (DCI). We validate in experiment the proposed system using 23GBaud DP-32QAM signal delivering 230Gb/s over 2 km of single mode fibers (SMFs) with the laser-linewidth tolerance of 1MHz. The parameters of polarization tracking algorithm are optimized to attain the polarization rotation tolerance up to 850 rad/s under the FEC threshold of 2x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> . The proposed BiDi SHCD system achieves the coherent-lite DSP without MIMO, FOC, CPR and dedicated CDC algorithm in dynamic state of polarization (SOP) rotation while maintaining the full spectral efficiency (SE) of traditional coherent system.

A novel DSP scheme for eliminating the interaction between dispersion and transient frequency offset in optical burst-mode coherent systems

The Bit-Error-Ratio (BER) floor caused by the laser phase noise in the optical fiber communication system with differential quadrature phase shift keying (DQPSK) and coherent detection followed by digital signal processing (DSP) is analytically evaluated. An in-phase and quadrature (I&Q) receiver with a carrier phase recovery using DSP is considered. The carrier phase recovery is based on a phase estimation of a finite sum (block) of the signal samples raised to the power of four and the phase unwrapping at transitions between blocks. It is demonstrated that errors generated at block transitions cause the dominating contribution to the system BER floor when the impact of the additive noise is negligibly small in comparison with the effect of the laser phase noise. Even the BER floor in the case when the phase unwrapping is omitted is analytically derived and applied to emphasize the crucial importance of this signal processing operation. The analytical results are verified by full Monte Carlo simulations. The BER for another type of DQPSK receiver operation, which is based on differential phase detection, is also obtained in the analytical form using the principle of conditional probability. The principle of conditional probability is justified in the case of differential phase detection due to statistical independency of the laser phase noise induced signal phase error and the additive noise contributions. Based on the achieved analytical results the laser linewidth tolerance is calculated for different system cases.

As a low-energy method to increase the data rate of optical links in data centers, we propose self-homodyne Nyquist optical time division multiplexing (OTDM). In Nyquist OTDM, spectrally efficient high-baud rate signals can be generated exceeding the limit of electronic signal processing. However, full integration of OTDM systems has not been reported, mainly because of the complicated signal detection scheme, which involves demultiplexing and clock recovery. In our proposal, the Nyquist pulse train is transmitted to the receiver as a local oscillator (LO) to leverage self-homodyne detection, which allows using large linewidth lasers and a simplified digital signal processing (DSP) algorithm. As the transmitted pulse train serves as an optical clock, demultiplexing and detection of the OTDM signal can be performed without using power-intensive high-bandwidth electronics and DSP. In this method, the LO pulse train needs to enter the coherent detector in exact synchronization with the OTDM signal for detecting the individual tributary correctly. For this purpose, we present a pulse delay control method suitable for photonic integration. A Nyquist pulse train with m carriers enables m-time multiplexing of optical signals. We explain and demonstrate the proposed concept in the case of m = 2, as it is the most feasible implementation. In the O-band where the chromatic dispersion (CD) is negligible, DSP-free operation can be achieved using the QPSK format. At the band edges where CD is non-negligible, it can be compensated by the DSP as in the conventional coherent detection. We verify this numerically and in an experiment involving the transmission of a 64-Gbaud QPSK signal at 1550 nm over a single-mode fiber. In terms of low energy, self-homodyne Nyquist OTDM is advantageous in wavelength division multiplexing (WDM). Taking it into consideration, we perform 4-channel WDM transmission of the 64-Gbaud QPSK signal over a 1-km dispersion shifted fiber without CD compensation. The results demonstrate a data rate of 512 Gb/s with a BER of <1 × 10-10.

The KASSPER project is a Defense Advanced Research Projects Agency (DARPA) program which has the goal of improving the performance of ground moving target indicator (GMTI) radar systems by incorporating external sources of knowledge into the signal processing chain. The KASSPER real-time signal processing architecture is a radar system scheduling and signal processing framework that is being developed at Massachusetts Institute of Technology Lincoln Laboratory (MIT LL). This paper discusses the design of the architecture, knowledge handling issues. resource scheduling issues, the current state of the prototype implementation of the framework, and the current state of the project's real-time processor testbed.

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.

Demonstration of C-band 112G PAM-4 transmission over 80-km stand-single mode fiber based on direct-detection

Polarization-multiplexing quadrature phase shift keying (PM-QPSK) has become a key ingredient in the design of 100 and 200-Gb/s dense wavelength-division multiplexed (DWDM) networks. The performance of the system using these formats varies according to the shape of the pulses employed by the optical carrier: non-return to zero (NRZ), return to zero (RZ) or carrier-suppressed return to zero (CSRZ). In this paper, we analyse the tolerance of PM-QPSK to linear and nonlinear optical impairments, including amplified spontaneous emission (ASE) noise, crosstalk, distortion by optical filtering, chromatic dispersion (CD), polarization mode dispersion (PMD) and fibre Kerr nonlinearities. The simulation results show that RZ formats with a low-duty cycle have a higher tolerance to CD, PMD and intrachannel nonlinearities due to the reduction of pulse-to-pulse interaction. Conversely, the PM–NRZ-QPSK format has a higher spectral efficiency (SE) than other options and shows better tolerance to filtering distortion and CD in filterless networks.

Cost-effective OSNR monitoring with large chromatic dispersion tolerance using random forest for intermediate nodes

The development of modern technologies has fundamentally transformed the field of radar signal and data processing. With the use of advanced algorithms and computational power, radars are now capable of extracting crucial information from received signals, facilitating improved target identification and tracking. This article presents some of the advanced technologies employed in radar signal and data processing and their impact on adaptability of radar systems. It traces the evolution of radar technology from old systems to the present, emphasizing the benefits of adaptive radar signal processing, which includes algorithms such as adaptive beamforming, Space-Time Adaptive Processing, and the integration of Machine Learning and Artificial Intelligence. In conclusion, challenges, and future prospects in the field of radar systems are discussed, with a focus on the potential integration of Artificial Intelligence methods, Cognitive radars, and Multiple Input Multiple Output technologies. Despite technical obstacles, opportunities emerge to enhance the performance of radar systems and achieve new levels of efficiency.

Nonlinear effects have been considered as the major limitations in coherent optical (CO) fiber transmission system. Digital signal processing (DSP)-based CO receiver with digital backpropagation (DBP) method has recently facilitated the compensation of fiber nonlinear impairments as well as compensating dispersion of optical fiber. In this paper, for the first time, a comprehensive design is presented for a newly introduced DSP-based CO receiver with the 8-quadrature amplitude modulation (8-QAM) circular-polarization division multiplexed (CPDM) fiber optic communication (FOC) system to investigate the impact of nonlinearities. We have examined the performance of nonlinearity compensating DSP-based CO receiver with DBP method and demonstrated that it can be effectively employed to mitigate the intrachannel nonlinearities in CPDM 8-QAM FOC system over 800-km SSMF link. Accordingly, by effectively compensating the fiber nonlinearities, we have analyzed the performance of bit error rate, optical signal-to-noise ratio (OSNR), optimum launch power, and investigate the link margin by evaluating OSNR margin for a specific launch power. Moreover, a CPDM technique helps as a very suitable means of maximizing the link capacity as well as enhancing the spectral efficiency of the FOC system.

In the recent years, there has been an unpredicted increase in data transmission. To cope with this increase, a reliable technology is required. The next-generation passive optical network 2 (NG-PON2) was used in integration with future technology that works on radio over fiber (RoF). However, the optical communication system is subject to the following nonlinear effects: Self-phased modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM), stimulated Brillouin scattering (SBS), and stimulated Raman scattering (SRS). These effects are dominant, and they risk the performance of the optical fiber system. Therefore, digital signal processing (DSP) technique is used in this study to minimize and offset the nonlinear effects. In this study, three digital filters working on (DSP) are compared for the same data transmission rate at different distances from the transmitter without using compensation techniques. The results were compared by bit error rate (BER) and the error vector magnitude (EVM). Thus, the error vector magnitude (EVM) was noticed to be ~19.58% without using DSP. Nonlinear effects were mitigated by filters of Gaussian, Bessel and DSP-64QAM raised cosine to ~9.09%, ~14.22% and ~17.54%, respectively. Hence, the bit error rate (BER) of the best technique after comparison was minimized to DSP-64QAM raised cosine. It occurred after minimizing the nonlinear effects as 1.11E−14 at a distance of 40 km and 100 km. The BER value was 3.43E−10, which is within the acceptable values of performance for the proposed optical communication system with nonlinear effects. The system was simulated using the optical simulator optisystem 15.

We investigate the computational complexity of adaptive equalization in coherent receiver digital signa l processing (DSP) for data center interconnect (DCI) systems. We propose modified DSP procedures with a first-stage static filter and a second-stage short-length adaptive equalizer. Typically, coherent DSP requires 11 and 17 adaptive equalizer taps respectively for 60 Gbaud and 80 Gbaud signals in the 100 km fiber link. The modified DSP procedures combine matched filter, chromatic dispersion compensation (CDC), and non-ideal channel effects and polarization effect s in to a static filter. Since polarization demultiplexing is partially realized by the static filter, the size of the following adaptive equalizer is substantially reduced. Results showed 35% - 87% overall complexity reduction in adaptive equalization a s compared with the reference DSP, depending on link length and symbol rate.

Today, DAW (Digital Audio Workstation) software lies at the heart of music production and has become an indispensable part of the industry. With the advancement of technology, music production is no longer confined to large studios but has also become accessible to individual users. Now, recording, mixing, and mastering processes can be carried out in a home environment using computer-based systems, without the need for expensive equipment. This fully digital workflow is referred to as "in-the-box" production. Technological developments have enabled individuals to produce music at a professional level in home studios, leading to the emergence of digital alternatives to analog devices. Digital processors have begun to replace analog equipment due to their cost-effectiveness and practicality. This study examines the differences between digital signal processors and analog devices in terms of usage, application areas, and sound processing methods. The research aims to compare digital and analog signal processors, particularly focusing on their processing methods, speed, flexibility, quality, and impact on sound. Based on the findings, it is concluded that digital signal processors, which are increasingly replacing analog processors in the music industry, do not possess the same characteristics as their analog counterparts.

We propose and experimentally demonstrate a novel sub-band multiplexed data architecture for chromatic dispersion (CD) mitigation. We have demonstrated 32 GBaud multi-sub-band (MSB) dual-polarization (DP) 16QAM transmission over 2400 km. Using this approach, the transmitted signal bandwidth is divided into multiple narrow-bandwidth sub-bands, each operating at a lower baud rate. Within each sub-band bandwidth, the CD frequency response can be approximated as a linear-phase band-pass filter, which can be considered as an analog delay that does not require compensation. Therefore, the resulting receiver digital signal processing (DSP) is simplified due to the removal of the CD compensation equalizer. In addition, this leads to efficient parallelization of DSP tasks by deploying multiple independent sub-band processors running at a lower clock rate. The proposed system reduces receiver computational complexity and offers 1 dB higher Kerr-nonlinearity tolerance and 2% extended transmission reach in comparison to the conventional single carrier systems.