Forward Error Correction Codes Research Articles

Efficient Channel Coding for Dimmable Visible Light Communications System

Visible light communication (VLC) offers wireless communication within short-range based on wavelength converters and light-emitting diode (LED). In the VLC system, conventional forward error correction (FEC) codes are not guaranteed to provide flicker mitigation and dimming support. Consequently, modified coding schemes are introduced for reliable VLC. These methods require complicated coding structures, use of lookup tables, and the addition of large redundancy, resulting to increased computational complexity and low transmission efficiency. In this article, we propose a coding scheme that is flicker-free and enhances the transmission efficiency for VLC systems. The proposed scheme is based on polar codes (PC) and Knuth balancing code with enhanced prefix coding technique. The results show that the proposed algorithm exhibits improved transmission efficiency compared to the PC without and with run-length limited code, for dimming values 75% (or 25%) and 87.5% (or 12.5%). Also, the proposed scheme presents a significant bit error rate (BER) performance gain compared to the schemes in literature. The proposed scheme is flicker-free, provides a simple encoding structure, does not utilize lookup tables, generates minimal number of redundancies for energy efficiency. Thus, the approach is flexible, and it is more suitable for real-time VLC systems.

Performance Enhancement of Fiber Optic and Optical Wireless Communication Channels by Using Forward Error Correction Codes

Abstract The study has outlined the different correction codes based optical wireless communication channel and security management in free space optics communication systems. The used codes that are namely forward error correction (FEC) code, Reed Solomon (RS) code, and Redundancy check (RC) code. The output power, maximum Q-parameter coefficient and minimum data error rates are estimated with these codes with variations of input signal power and propagation distances. The performance of optical wireless channel is enhanced with FEC code in compared to other proposed codes under the same operating conditions.

Physical deployment of enhanced visible light communication system using forward error correction codes

SummaryWith the development of new generation lighting sources, visible light communication (VLC) system has become a complementary solution to traditional radio frequency wireless system. However, the error performance of VLC system is degraded because of multipath effects and interference from other lighting sources that, in turn, reduce the communication range. This work targets the issue of performance degradation of VLC systems in terms of communication range and demonstrates a VLC system design that utilizes forward error correction (FEC) codes as the main tool to fix this issue. Furthermore, the work also covers practical implementation of the proposed VLC system using UART modules programmed in MATLAB. The hardware results demonstrate that the communication range of the proposed VLC system is enhanced up to 0.5 m. Over and above, it is also shown through simulations that the coding gain of the proposed design is more when compared with existing VLC system(s).

Modeling and Analysis of Chaos-based Spread Spectrum Scheme using Irregular LDPC Code and Non-Coherent 16-DCSK under Fading and Jamming

In chaos-based spread spectrum systems, the use of spreading code and chaotic binary sequence expands the bandwidth of the information-bearing signal but this expansion results in SNR degradation under the constraint of constant channel capacity according to Hartley-Shannon law. To compensate for this drawback, our proposed model employs an irregular low-density parity-check (LDPC) code with its iterative decoding algorithm. Coupled with this forward error correction (FEC) coding, we used non-coherent (NC) 16-ary differential chaos shift keying (16-DCSK) that additionally provides the ability of data encryption due to its use of chaotic signals compared with the conventional modulation schemes. Analytical expressions of bit error probability (BEP) are derived under the assumption of the three-ray model along with partial band noise jamming (PBNJ) over a Rayleigh fading channel. Simulation results assert that the proposed system can mitigate the effect of PBNJ via lowering BEP by coding gain and processing gain under identical transmission power. It is also confirmed that a higher level of security can be provided by the use of proposed two iteration functions of Duffing Map-based chaotic binary sequence than the security level of one iteration function of Logistic Map, based on the balance and autocorrelation analysis.

Shaped On–Off Keying Using Polar Codes

The probabilistic shaping scheme by Honda and Yamamoto (2013) for polar codes is used to enable power-efficient signaling for on–off keying (OOK). As OOK has a non-symmetric optimal input distribution, shaping approaches that are based on the concatenation of a distribution matcher followed by systematic encoding do not result in optimal signaling. Instead, these approaches represent a time-sharing scheme, where only a fraction of the codeword symbols is shaped. The proposed scheme uses a polar code for joint distribution matching and forward error correction which enables asymptotically optimal signaling. Numerical simulations show a gain of 1.8 dB compared to uniform transmission at a spectral efficiency of 0.25 bits/channel use for a blocklength of 65 536 bits.

Near-Capacity Detection and Decoding: Code Design for Dynamic User Loads in Gaussian Multiple Access Channels

This paper considers the forward error correction (FEC) code design for approaching the capacity of a dynamic multiple access channel (MAC) where both the number of users and their respective signal powers keep constantly changing, resembling the scenario of an actual wireless cellular system. To obtain a low-complexity non-orthogonal multiple access (NOMA) scheme, we propose a serial concatenation of a low-density parity-check (LDPC) code and a repetition code (REP), this way achieving near Gaussian MAC (GMAC) capacity performance while coping with the dynamics of the MAC system. The joint optimization of the LDPC and REP codes is addressed by matching the analytical extrinsic information transfer (EXIT) functions of the sub-optimal multi-user detector (MUD) and the channel code for a specific and static MAC system, achieving near-GMAC capacity. We show that the near-capacity performance can be flexibly maintained with the same LDPC code regardless of the variations in the number of users and power levels. This flexibility (or elasticity) is provided by the REP code, acting as “user-load and power equalizer”, dramatically simplifying the practical implementation of NOMA schemes, as only a single LDPC code is needed to cope with the dynamics of the MAC system.

High-Speed Railway Communication System Using Linear-Cell-Based Radio-Over-Fiber Network and Its Field Trial in 90-GHz Bands

A linear-cell-based radio-over-fiber (LC-RoF) system is proposed and demonstrated for efficient mobile communication in high-speed trains without hard handover processes. The configuration of the LC-RoF network and possible router architectures are discussed for the field trial test of the proposed system and for advanced systems in the future. Via the LC-RoF network, 90-GHz, millimeter-wave radio access between the ground and a train car is operated in a centralized manner. The resulting throughput of 1.5 Gbit/s is achieved in the field trial test, which is comprised of 250-Mbaud four-subcarrier differential quadrature phase-shift keying with a forward-error correction code implemented in field-programmable gate arrays to the Shinkansen train traveling at 240 km/h without any interruptions in the connections at the change of radio access units.

Adaptive Uniform Entropy Loading for SSB-DMT Systems

In this paper, we proposed a simple uniform entropy loading (UEL) algorithm to adaptively load the same entropy for all the subcarriers according to the channel state information. Thanks to the signal-to-noise ratio (SNR) equalization effect of precoding, only one distribution matcher is used for UEL, maximally reducing the complexity of entropy loading. The proposed algorithm is based on the relationship between the optimal information bits per symbol (IBPS) and SNR for probabilistically shaped quadrature amplitude modulation (PS QAM) under the constraint of normalized generalized mutual information (NGMI) considering the implementation of constant composition distribution matching (CCDM) and off-the-shelf forward error correction (FEC) code. Different from generalized mutual information (GMI), IBPS intuitively represents practical performance. Besides, the relationship between IBPS and SNR for conventional QAM and time domain hybrid QAM (TDHQ) are also calculated to perform the well-known bit power loading (BPL) algorithm, Levin-Campello (LC) algorithm, and TDHQ assisted adaptive loading (AL) algorithm, respectively. Based on theoretical analysis, to our best knowledge, we first found that precoding procedure adopted by TDHQ assisted AL and UEL scheme degrades Shannon capacity compared to water-filling algorithm, the upper limit of BPL algorithms. However, benefiting from shaping gain of PS QAM, the proposed UEL algorithm achieves higher net data rate (NDR) and lower peak-to-average power ratio (PAPR) than the LC algorithm, which is demonstrated by the simulations and experiments in single sideband discrete multi-tone (SSB-DMT) systems. According to the experimental results, up to 3.2% NDR improvement and 0.82 dB PAPR reduction are realized by the UEL algorithm compared to the LC algorithm. The UEL algorithm also outperforms TDHQ assisted AL algorithm by the average NDR gain of up to 8.0%. The simple and effective advantages make the proposed UEL scheme suitable for the short-to-medium reach optical fiber communication systems.

Enhanced Receiver Based on FEC Code Constraints for Uplink NOMA With Imperfect CSI

Non-orthogonal multiple access (NOMA) has been envisioned as a useful component of fifth generation (5G) mobile networks. As imperfect channel state information (CSI) due to channel estimation errors poses problems for most wireless receivers, it presents even greater challenges in successive interference cancellation (SIC) reception of NOMA signals. We present a novel approach to the multi-user detection problem by exploiting the important constraints of forward error correction (FEC) code word. We devise our new receiver based on the minimum output energy (MOE) criterion while preserving a distortionless response to the user equipment (UE) of interest. In particular, we efficiently adopt the UE signatures presented by the FEC channel codes under distinct permutations to separate desired signals of interest from interfering UEs. We formulate our receiver optimization into a quadratic-programming problem anchored with a set of code constraints. Our simulations demonstrate that the proposed code-anchored quadratic programming (CQP) receiver can accurately improve SIC performance and provide robustness to CSI errors better than other legacy schemes.

Coded Modulation for 100G Coherent EPON

Geometrically shaped (GS) 8-, 16, and 32- ary modulation formats are investigated for use in coherent passive optical networks. The modulation formats are designed to improve receiver sensitivity when paired with a binary, soft-decision forward error correction code (SD-FEC), such as a low density parity check (LDPC). Herein we consider the LDPC code specified in the draft 50G EPON standard, and show how this type of code can be particularly advantageous in a coherent transmission system. A receiver sensitivity of $-$ 26.7 dBm is achieved at a post-FEC bit error rate below 3.8 $\times 10^{-6}$ for a polarization-scrambled 32- ary GS modulation format at 25 GBd, received using a single-polarization, phase-diverse coherent receiver. This yielded a bit rate of 100 Gbit/s, net of coding and pilot overhead. This modulation format was shown to perform equally well in transmission, with no observed dispersion penalty after 80 km standard single mode fiber. Finally, this modulation format was received, at a reduced data rate of 50 Gbit/s, using a heterodyne coherent receiver based on a single balanced photodiode. The receiver sensitivity for this simplified receiver configuration was $-$ 28.5 dBm, yielding a power budget of 34.2 dB.

The RBCMLSA problem on space division multiplexing elastic optical networks

Abstract The introduction of space division multiplexing (SDM) is a promising solution to cope with ever-increasing Internet traffic. Multi-core fibers (MCFs) are a potential solution for the capacity crunch problem. In this article, the Routing, Baud rate, forward error correction (FEC) Coding, Modulation Level, and Spectrum Assignment (RBCMLSA) problem in elastic optical networks (EONs) employing MCFs and SDM is studied. An Integer Linear Program (ILP) model is used to define the studied problem and find the optimum solution in static traffic. Since the RBCMLSA problem is an NP-hard problem, for the dynamic traffic, the crosstalk-aware path routing algorithm (CAPRA) is proposed to solve this problem. Three core-selecting schemes, named Minimum Load (ML), Minimum Conflict (MC), and Minimum Weight (MW) are proposed. Simulation results show that the proposed algorithm can get lower blocking probability when compared to the algorithm for the existing simpler Routing, FEC Coding, Modulation Level, and Spectrum Assignment (RCMLSA) and Routing, Modulation Level, and Spectrum Assignment (RMLSA) problems.

Multiple TAS-OSTBC in MIMO with Outer BCH Concatenation under Nakagami-m Fading

Transmit Antenna Selection (TAS) technique with Orthogonal Space Time Block Code (OSTBC) addresses the problem of hardware complexity in multiple antenna systems and improves Bit Error Rate (BER) significantly by using various antenna selection algorithms. TAS technique is not able to provide the coding gain. To achieve the coding gain benefits with improvement in BER, it is necessary to concatenate TAS system with an outer code. In literature, it is observed that the concatenation of Forward Error Correction (FEC) codes and Space Time Block Code (STBC) for MIMO systems provides the high coding gain with improved BER. In this paper, a multiple TAS-OSTBC system is proposed with concatenation of channel coding techniques such as BCH and TURBO. The proposed system is concatenated with BCH as outer code in series with TURBO as inner code. This combination provides the capacity benefits of TAS-OSTBC system with improved coding gain. The channel is assumed to be faded by Nakagami- m fading. It is observed that for multiple TAS-OSTBC system this new concatenation of BCH-TURBO code gives improvement of 5 dB at 10-6 as compared to concatenation of TURBO code at m =0.5 for Nakagami- m fading parameter.

Blind parameter estimation of turbo convolutional codes: Noisy and non-synchronized scenario

Blind estimation of forward error correction code parameters at the receiver plays a significant role in non-cooperative communication, adaptive modulation and coding systems, and reconfigurable receiver systems. Turbo convolutional codes, a parallel concatenation of multiple convolutional codes, are used in digital communication and storage systems to achieve low bit error rate. The present paper proposes innovative algorithms for the blind estimation of code parameters and reconstruction of turbo convolutional encoder over noisy scenario. The turbo convolutional code is designed using two component codes along with an interleaver. Recursive systematic convolutional codes are used as component codes. Any imperfection in synchronization of received data for the proposed code parameter estimation algorithm is compensated through a bit position adjustment parameter. The performance of the proposed algorithms in terms of parameter estimation accuracy is investigated for different modulation order, code rate, and constraint length values. It is observed that the performance improves with decrease in modulation order and constraint length values.

Performance Enhancement of Bit Error Rate with Increased Capacity using Modified SIC-MUD for Polar Code based OFDM-IDMA System for 5G

In the era of mobile data revolution there is a mass-market of smart phones culminating into an extensive growth in mobile services and applications. However, bandwidth is limited and valuable resource available. In this paper hybrid combination of OFDM-IDMA system is proposed using polar code as forward error correction code and Gold code based interleaver. It presents a method to improvebit error rate with 10 users and normalizedcarrier frequency offsets of 0.1 to 0.5.The simulation is done in the presence of Rayleigh and AWGN channel with 64 QAM modulation technique. A modified successive interference cancellation multi-user detection algorithm is proposed to cater multiple access interference.It is observed that proposed system withnormalized CFO of 0.1 for10 users at required SNR of 15 dB enhances the bit error rate to 1.021*10-4over available existing systems. Hence the capacity of the system and data rate increases by three times to support multimedia application within available bandwidth.

Net-400-Gbps PS-PAM transmission using integrated AMUX-MZM.

Simple high-speed optical transmission technologies are desired for use in intra-and inter-datacenter networks. In this study, we demonstrate simple single-carrier intensity-modulated direct-detection (IMDD) transmissions at a net data rate of 400 Gbps (516.7 Gbps gross) over 20 km with a compact transmitter subassembly. The subassembly consists of a 2:1 analog multiplexer (AMUX) and an InP Mach-Zehnder modulator (MZM) placed close to each other and connected via wires. We employed 162-Gbaud single-carrier probabilistically shaped pulsed amplitude modulation (PS-PAM). The baseband signals with a bandwidth of around 81 GHz to drive the MZM were generated by a super-digital-to-analog converter (super-DAC) consisting of two sub-DACs and the AMUX. Digital nonlinear pre-distortion enabled us to transmit the signals with normalized generalized mutual information (NGMI) larger than the threshold of a soft-decision forward error correction (SD-FEC) code of 0.857. Truncation of the PS-PAM symbol distribution further enhanced performance. To the best of our knowledge, this is the first net-400-Gbps single-carrier IMDD transmission using a compact transmitter subassembly.

Optimizing Forward Error Correction Codes for COFDM With Reduced PAPR

Coded orthogonal frequency-division multiplexing (COFDM) is a popular modulation technique for wireless communication that guarantees reliable transmission of data over noisy wireless channels. However, a major disadvantage in implementing it is its resulting high peak to average power ratio (PAPR). Including forward error correction (FEC) in the orthogonal frequency division multiplexing (OFDM) system enables the avoidance of transmission errors. Nevertheless, the selected code may impact the value of PAPR. The objective of this paper is to analyze the impact of FEC on the PAPR for the COFDM system based on the autocorrelation of the signal, before the inverse fast Fourier transform (IFFT) block in the COFDM system, the evaluation of the complementary cumulative distribution function (CCDF) of PAPR, and the bit error rate (BER). The autocorrelation of the COFDM system is calculated based on a Markov chain model. From the results, we can reach a conclusion on the characteristics we need to consider in order to choose the codes relating to the PAPR performance in the COFDM system.

The RBCMLSA problem on EONs with flexible transceivers

Next generation optical networks will require high levels of flexibility, being able to fit rate, bandwidth, modulation level, forward error correction (FEC) coding and optical reach requirements of different connections. For serving transmission on an elastic optical network, the flexible lightpath routing and the spectrum allocation algorithm for the connection request should be developed. In this paper, the routing, baud rate, FEC Coding, modulation level and spectrum allocation problem are defined and studied. An integer linear programming model is proposed to define the studied problem. Moreover, three heuristic algorithms, which integrate the single-path and multiple-path routing schemes, are also proposed to solve it. The proposed algorithms are examined through simulations, and the results show that the proposed algorithms can achieve good results.

An Experimental Demonstration of Rate-Adaptation Using Shaped Polar Codes for Flexible Optical Networks

In this paper, we propose a polar-coded transmission system with adjustable data rate for coherent optical transmission employing quadrature amplitude modulation (QAM). The proposed system is based on a many-to-one constellation shaping method for achieving a range of data rates with arbitrarily small rate steps. An implicitly punctured polar-coded modulation system is then designed by combining polar coded bit-interleaved coded modulation system with many-to-one labelings. The scheme is experimentally evaluated in a wavelength division multiplexed (WDM) system with five carriers modulated at 16 GBaud with polarization multiplexed (PM) 256QAM. Data rates ranging from 121 to 182 Gb/s per carrier are experimentally demonstrated and the system can be directly extended to achieve higher data rates. Synchronization and equalization of PM-256QAM received symbols are performed with a pilot rate of 5%. The experimental results show 1.2 dB of shaping gain over the conventionally punctured polar codes in the optical back-to-back scenario. The maximum transmission system reach is increased by 200 to 400 km w.r.t the conventionally punctured polar codes. It is shown that the rate adaptation does not require a change of modulation format and/or underlying forward error-correction code. Finally, the performance of all five WDM channels is validated for the optimal input power.

Blind Identification of Block Interleaved Convolution Code Parameters

Most of the digital communication system uses forward error correction (FEC) in addition with interleaver to achieve reliable communication over a noisy channel. To get useful information from intercepted data, in non-cooperative context, it is necessary to have algoritihms for blind identification of FEC code and interleaver parameters. In this paper, a matrix rank-based algebraic algorithm for the joint and blind identification of block interleaved convolution code parameters for cases, where interleaving length is not necessarily an integer multiple of codeword length is presented. From simulations, it is observed that the code rate and block interleaver length are identified correctly with probability of detection equal to 1 for bit error rate values of less than or equal to 10-4.

Enumerative Sphere Shaping for Wireless Communications With Short Packets

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.