Probabilistic Shaping and Forward Error Correction for Fiber-Optic Communication Systems

The transmission of video traffic over the Internet is a fundamental issue of network design. Video applications require quality of service guarantees from the network in terms of limited packet loss, end-to-end delay, and delay variation. The question of today’s research and development is how to provide these guarantees considering the architecture of the present Internet. In the last years a variety of admission control schemes based on per-hop or end-to-end measurements has been suggested to control delay and loss sensitive streams with very little or no support at the routers. Most of these solutions, however, have to apply the same acceptance threshold for all streams, a significant limitation considering the diverse quality requirements of the applications. In this work we investigate how source shaping and forward error correction (FEC) can be used together to achieve application specific quality differentiation in terms of end-to-end delay and packet loss probability. While source shaping and FEC have been proposed independently to decrease the probability of packet loss due to buffer overflow, their joint use has not been studied before.As the two control functions use the same scarce resource, end-node delay, and their efficiency to decrease loss probability is proportional to the introduced delay but with a decreasing marginal gain, combining the two a better performance can be achieved than by using only one of them.The performance evaluation focuses on the optimal delay allocation for shaping and FEC, such that the loss probability is minimized. We investigate how shaping can be used to substitute FEC redundancy and the sensitivity of the quality differentiation to the background traffic characteristics.KeywordsQuality of Servicesource shapingFEC

Probabilistic amplitude shaping (PAS) combines an outer shaping layer with an inner, systematic forward error correction (FEC) layer to close the shaping gap. Proposed for PAS, constant composition distribution matching (CCDM) produces amplitude sequences with a fixed empirical distribution. We show that CCDM suffers from high rate losses for small block lengths, and we propose to use Enumerative Sphere Shaping (ESS) instead. ESS minimizes the rate loss at any block length. Furthermore, we discuss the computational complexity of ESS and demonstrate that it is significantly smaller than shell mapping (SM), which is another method to perform sphere shaping. We then study the choice of design parameters for PAS. Following Wachsmann et al., we show that for a given constellation and target rate, there is an optimum balance between the FEC code rate and the entropy of the Maxwell-Boltzmann distribution that minimizes the gap-to-capacity. Moreover, we demonstrate how to utilize the non-systematic convolutional code from IEEE 802.11 in PAS. Simulations over the additive white Gaussian noise (AWGN) and frequency-selective channels exhibit that ESS is up to 1.6 and 0.7 dB more energy-efficient than uniform signaling at block lengths as small as 96 symbols, respectively, with convolutional and low-density parity-check (LDPC) codes.

We report the implementation experience and experimental evaluation of a staggered adaptive forward error correction (FEC) system for video multicast over wireless LANs. In the system, the parity packets generated by a cross-packet FEC code are transmitted at a time delay from the original video packets, i.e. staggercasting video stream and FEC stream in different multicast groups. The delay provides temporal diversity to improve the robustness of video multicast, especially to enable the clients to correct burst packet loss using FEC and to achieve seamless handoff. A wireless client dynamically joins the FEC multicast groups based upon its channel conditions and handoff events. We have implemented the system including the streaming server and client proxy. A novel software architecture is designed to integrate the FEC functionality in the clients without requirement for changing the existing video player software. We conduct extensive experiments to investigate the impact of FEC overhead and the delay between the video stream and FEC stream to the video quality under different interference levels and mobile handoff durations. The efficacy of staggered adaptive FEC system on improving video multicast quality is demonstrated in real system implementation.

Information rates of probabilistically shaped coded modulation for a multi-span fiber-optic communication system with 64QAM

In this paper, a rate adaptive geometric constellaion shaping (GCS) scheme which is fully backward-compatible with existing state of the art bit-interleaved coded modulation (BICM) systems is proposed and experimentally demonstrated. The system relies on optimization of the positions of the quadrature amplitude modulation (QAM) points on the I/Q plane for maximized achievable information rate, while maintaining quantization and fiber nonlinear noise robustness. Furthermore, ‘dummy’ bits are multiplexed with coded bits before mapping to symbols. Rate adaptivity is achieved by tuning the ratio of coded and ‘dummy’ bits, while maintaining a fixed forward error-correction block and a fixed modulation format size. The points' positions and their labeling are optimized using automatic differentiation in a many-to-one fashion such that the performance of the ‘dummy’ bits is sacrificed in favor of the performance of the data bits. The proposed GCS scheme is compared to a time-sharing hybrid (TH) QAM modulation and the now mainstream probabilistic amplitude shaping (PAS) scheme employing a Maxwell-Boltzmann probability mass function. The TH without shaping is outperformed for all studied data rates in a simulated linear channel by up to 0.7 dB. In a linear channel, PAS is shown to outperform the proposed GCS scheme, while similar performances are reported for PAS and the proposed GCS in a simulated nonlinear fiber channel. The GCS scheme is experimentally demonstrated in a multi-span recirculating loop coherent optical fiber transmission system with a total distance of up to 3000 km. Near-continuous zero-error flexible throughput is reported as a function of the transmission distance. Up to 1-2 spans of increased reach gains are achieved at the same net data rate w.r.t. conventional QAM. At a given distance, up to 0.79 bits/2D symbol of gain w.r.t. conventional QAM is achieved. In the experiment, similar performance to PAS is demonstrated.

With the volumes of transmitted information growth, the task of increasing the noise immunity and reliability of data transmission networks arises. The presence of interference such as nonlinear loss, chromatic dispersion, polarization mode dispersion, and inter-channel interference decreases the performance of fiber optical communication systems. Forward Error Correction (FEC) codes are vital in optical communication systems to achieve highly efficient and highly reliable communication. The paper presents research on a simulation model where FEC channel-coding schemes based on the Bose-Chaudhuri-Hocquenghem (BCH) cycling block code are integrated with non-return-to-zero on-off-keying (NRZ-OOK) modulated wavelength division multiplexed (WDM) fiber optical communication systems. The results highlight the selection of coding parameters in the adopted FEC approach. In our paper, the BCH (255, 231), BCH (255, 223), and BCH (255,191) FEC channel-coding schemes are chosen for integration in the NRZ-OOK modulated WDM optical transmission system. The paper shows the main advantages and drawbacks of the selected FEC coding scheme and provides a comparison of the proposed schemes based on their main features, such as bit error ratio (BER), which were obtained through the simulations of 25 Gbit/s NRZ-OOK WDM fiber optical system. The dynamics of changes in BER was investigated using the Monte Carlo (MC) method for precise results. The paper shows that integration of FEC channel-coding schemes based on the BCH codes improves the noise immunity and reliability of the WDM Fiber Optical Communication Systems.

We generalize probabilistic amplitude shaping (PAS) with binary codes [1] to the case of non-binary codes defined over prime finite fields. Firstly, we introduce probabilistic shaping via time sharing where shaping applies to information symbols only. Then, we design circular quadrature amplitude modulations (CQAM) that allow to directly generalize PAS to prime finite fields with full shaping.

Ultra-wideband (UWB) technology enables high-speed and low-power consumption transmission for communication systems by utilizing an extremely wide bandwidth. However, its large frequency bandwidth poses significant challenges for integration with conventional wavelength-division multiplexing (WDM) techniques, thereby limiting further enhancement of communication capacity density. Although orbital angular momentum (OAM) multiplexing, operating independently of the wavelength dimension, offers a promising avenue to increase the capacity density of UWB communication systems, mode coupling in few-mode fibers (FMF) leads to severe inter-mode crosstalk, resulting in signal distortion and a substantial degradation in communication performance. To address this issue, we propose incorporating probabilistic amplitude shaping (PAS) into an OAM-multiplexed UWB system. This scheme combines a constant composition distribution matcher (CCDM) with a low-density parity-check (LDPC) coding module to achieve joint shaping and error correction. Concurrently, discrete Fourier transform (DFT) precoding is introduced to equalize the signal-to-noise ratio (SNR) across subcarriers and suppress high peak-to-average power ratio (PAPR). Experimental results demonstrate the successful transmission of a 4-channel OAM-multiplexed UWB signal at 1.89 × 4 Gbit/s over 5 km FMF. Compared to the original 64-QAM signal, the unshaped (uniformly distributed) 64-QAM signal achieved improvements in optical receiver sensitivity of 7.5 dB, 6.5 dB, and 6.0 dB at symbol rates of 3.0, 3.6, and 4.0 bits/QAM symbol, respectively. The application of probabilistic shaping, which reduces the occurrence probability of high-amplitude symbols, yielded an additional sensitivity gain of 0.5 dB. These results validate the effectiveness of the proposed scheme and its significant potential for enhancing the performance of multiplexed transmission systems.

Parallel, additive white Gaussian noise (AWGN) channels with an average sum power constraint are considered. It is shown how the waterfilling Shannon capacity can be approached by higher order modulation and probabilistic amplitude shaping (PAS). This is achieved by a new distribution matching approach called product distribution matching (PDM). The asymptotic performance of PDM is analyzed by achievable rates. A heuristic for optimizing the input distribution is proposed, which enables signaling at a target spectral efficiency with a fixed-rate forward error correction (FEC) code, while the optimal power allocation is ensured by mercury-waterfilling and a simple bit-loading strategy. Finite blocklength simulation results with 5G low-density parity-check codes show power savings of around 1 dB compared to a conventional scheme with uniform input distributions.

Wireless Billboard Channels (WBCs) are a proposal for novel broadcast advertisement channel which will be integral to realising the Consumer-centric Business Model (CBM) within the new emerging Ubiquitous Consumer Wireless World (UCWW), their primary goal of facilitating the service of Advertisement, Discovery and Association (ADA) of wireless access networks and teleservices in the UCWW. In the principal research presented in this thesis the author has investigated the conceptualisation, design, implementation and testing of a WBC established over a Digital Video Broadcasting – Handheld (DVB-H) platform. The thesis addresses how realising this goal the following objectives were successfully achieved in the research work and are described in the thesis:  The creation of a foundational WBC infrastructure.  The elaboration of a WBC framework, interface and protocol architecture.  The development of a fully operational WBC system prototype.  The investigation and implementation of suitable WBC carrier technologies. The WBC system proposed and designed has been developed along three architectural layers – physical, link and service layers. In designing the service layer, to achieve an extensible, flexible, configurable and maintainable system, the WBC Service Provider (WBC-SP) and Mobile User (MU)’s software architecture has been proposed. A number of intelligent algorithms have been developed for advertisement’s collecting, clustering, scheduling, indexing, discovery and association in Multi-Agents System (MAS) environment. A new WBC Advertisements Delivery Protocol (ADP) has been designed and developed for delivering advertisement over unidirectional WBCs to MU simultaneously. In the link layer, and specifically dictated by DVB-H link layer conditions, a novel cross-layer Multi-Protocol Encapsulation - Forward Error Correction (MPE-FEC) coding and decoding schemes were proposed for improving reliability. Realising the DVB-H physical layer was achieved through a specially constructed laboratory testbed infrastructure, using a DVB-H physical layer simulator. Besides the design and implementation of this layered, distributed, intelligent, and heterogeneous WBCs system, the research work included the proofing and refining of aspects of the designs. Also carried out was the operational testing, performance evaluation and scalability evaluation of the core WBCs elements. WBC carrier technologies other than DVB-H were also explored, e.g. Terrestrial- Digital Multimedia Broadcasting (T-DMB). The work has yielded over 20 internationally published research papers to date, including one in the IEEE Transactions on Consumer Electronics and two in EURASIP Journal on Wireless Communications and Networking.

We proposed two kinds of visible light communication(VLC) systems which respectively based on 64QAM/square geometrical shaping(SGS) 128QAM time domain hybrid modulation scheme (SGSHY) and 64QAM/128QAM time domain hybrid modulation scheme (REGHY). These two systems can operate around specific forward error correction (FEC) threshold and maximize the achievable information rate (AIR) of the system. The principles of SGSHY and REGHY are proposed in detail, which has very low computation complexity compared with probabilistic shaping. The SGSHY outperforms REGHY at high peak to peak voltage (Vpp). Experimental results show that at high Vpp like 1.4 V, which means the system is suffering from high nonlinear distortion, the AIR of SGSHY outperforms that of REGHY by 0.12Gb/s at the 2×10–2 FEC threshold. The AIR of the REGHY is at most 0.36Gb/s higher than that of 64QAM at 0.8V Vpp and 7% FEC threshold, while the (achievable information rate) AIR of SGSHY is at most 0.40Gb/s higher than that of 64QAM at 1.4 V Vpp and 20% FEC threshold.

In this paper, an orthogonal circulant matrix transform (OCT) precoding technique is proposed to combine with the entropy loading in the multiple-input multiple-output and orthogonal frequency division multiplexing (MIMO-OFDM) visible light communication (VLC) system where the space-time coding (STBC) is chosen for its robustness to the channel correlation. Benefitting from the OCT precoding technique, the uniform signal-to-noise ratio (SNR) among all the subchannels can be achieved. As a result, only one SNR value is required to be fed back, and the same distribution matcher is employed during probabilistic shaping (PS), which means much lower feedback overhead and system complexity than the conventional entropy loading scheme. Experimental results show that the OCT precoding does not cause the system performance loss where the achievable information rate (AIR) of the proposed system is comparable with the conventional system without precoding. With an available bandwidth of ∼25 MHz, the proposed scheme can realize the AIR of 50.75 Mb/s at the expense of 0.45% average forward error correction (FEC) overhead (OH).

Polar codes with dynamically frozen bits are combined with probabilistic amplitude shaping (PAS). At the transmitter, constant composition distribution matching (CCDM) is used to match uniformly distributed input bits to symbols having a desired amplitude distribution. At the receiver, a type check exploits the constant composition properties of CCDM in successive cancellation list (SCL) decoding. For 64 amplitude shift keying (ASK) symbols and a spectral efficiency of 1.5 bits per ASK symbol, polar coded PAS with outer cyclic redundancy check (CRC) codes and SCL decoding with type check outperforms PAS with state-of-the-art LDPC codes by 2dB and performs within 0.8dB of Shannon's sphere packing bound (SPB).

Optical fiber transport is the key technology to enable the delivery of fast and affordable bandwidth for all services, such as 5G/mobile, business and residential broadband, cloud computing, and video transport. Coherent optics, a game-changer optical fiber transport technology, has completely transformed optical transmission systems and enabled a widespread upgrade and new deployment of DWDM networks to speeds of 100 Gb/s, 200 Gb/s, and 400 Gb/s per wavelength. Over the past decade, coherent optics has moved beyond its long-haul application origins and is now firmly entrenched in metro networks. 2020 marked the 10th anniversary of digital coherent optical technology being officially deployed in service providers' networks. Further development in CMOS processing, design simplification, and cost reduction of opto-electronic components, and the need for more efficient optical transport technologies have been factors driving coherent solutions into new market applications, specifically short-haul applications in edge and access networks. This migration model has been demonstrated in the optical industry before: the DWDM system technology started in long haul and subsequently migrating to metro and edge access; forward error correction encoding and decoding followed the same pattern. Benefiting from initial long-haul technology development, coherent optics for access networks is poised to follow the same natural progression.

This paper describes the effort within the Project54 program at the University of New Hampshire to develop a software based implementation of an APCO Project 25 (P25) compliant packet data base station, utilizing a standard PC interfaced to a commercial analog VHF FM transceiver. The goal is to develop an affordable system (under $10,000) to provide P25 compliant packet data for smaller public safety agencies requiring only a single data capable channel. The base station system is comprised of a standard PC interfaced to a commercial VHF FM transceiver. Software running on the PC implements the standard IP network interface, the P25 Common Air Interface packet assembly, forward error correction encoding, and finally the packet baseband modulation. The resulting analog baseband modulated signal is then input to the commercial VHF FM transceiver which performs the RF modulation. The process is reversed for data packet reception. This paper will focus on the overall design of the software based P25 packet data transmitter, the testing of the various stages for P25 compliance, and the testing of the final result for interoperability with commercial P25 compliant mobile radios.