Forward Error Correction Codes Research Articles

Throughput-Based Design for Polar-Coded Modulation

Typically, forward error correction (FEC) codes are designed based on the minimization of the error rate for a given code rate. However, for applications that incorporate hybrid automatic repeat request (HARQ) protocol and adaptive modulation and coding, the throughput is a more important performance metric than the error rate. Polar codes, a new class of FEC codes with simple rate matching, can be optimized efficiently for maximization of the throughput. In this paper, we aim to design HARQ schemes using multilevel polar-coded modulation (MLPCM). Thus, we first develop a method to determine a set-partitioning-based bit-to-symbol mapping for high-order quadrature amplitude modulation (QAM) constellations. We simplify the log-likelihood ratio estimation of set-partitioned QAM constellations for a multistage decoder, and we introduce a set of algorithms to design throughput-maximizing MLPCM for the successive cancellation decoding (SCD). These codes are specifically useful for non-combining, chase-combining, and incremental redundancy HARQ protocols. Furthermore, since optimized codes for SCD are not optimal for SC list decoders (SCLDs), we propose a rate matching algorithm to find the best rate for SCLD while using the polar codes optimized for SCD. The resulting codes provide throughput close to the capacity with low decoding complexity when used with HARQ protocols.

Multi-Twin-SSB Modulation with Direct Detection Based on Kramers–Kronig Scheme for Long-Reach PON Downstream

As the demand for high data volumes keeps increasing in optical access networks, transmission capacities and distance are becoming bottlenecks for passive optical networks (PONs). To solve this problem, a novel scheme based on multi-twin single sideband (SSB) modulation with direct detection is proposed and investigated in this paper. At the central office, two SSB signals are generated simultaneously with the same digital-to-analog converters (DACs). The twin-SSB signal is not only robust against frequency selected power fading introduced by chromatic dispersion (CD), but also improves the spectral efficiency (SE). By combining a twin-SSB technique with multi-band carrier-less amplitude/phase modulation (multi-CAP), different optical network units (ONUs) can be supported by flexible multi-band allocation based on software-reconfigurable optical transceivers. The Kramers–Kronig (KK) scheme is adopted on the ONU side to effectively mitigate the signal–signal beat interference (SSBI) induced by the square-law detection. The proposed system is extensively studied and validated with four sub-bands using 50 Gbps 16 quadrature amplitude modulation (QAM) modulation for each sub-band using numerical simulations. Digital pre-equalization is introduced at the transmitter-side to balance the performance of different ONUs. After system optimization, a bit error rate (BER) threshold for hard decision forward error correction (HD-FEC) code with 7% redundancy ratio (BER = 3.8 × 10−3) can be reached for all ONUs over 50-km standard single-mode fiber.

IMDD Transmission at Net Data Rate of 333 Gb/s Using Over-100-GHz-Bandwidth Analog Multiplexer and Mach–Zehnder Modulator

We demonstrate intensity-modulated direct-detection optical transmission at a record-high data rate with single wavelength and single polarization. The high data rate is achieved with simple optics by using electronic and electrooptic devices with large operation bandwidths. We use a digital-preprocessed analog-multiplexed digital-to-analog converter with a >100-GHz analog multiplexer (AMUX) to drive an 80-GHz Mach–Zehnder optical modulator (MZM). The AMUX is based on 0.25-μm-emitter-width InP heterojunction bipolar transistor technology, and the MZM has InP n-i-p-n heterostructure optical waveguides with capacitance-loaded travelling-wave electrodes. We employ discrete multi-tone modulation controlled by a margin-adaptive bit-loading algorithm. In the experiment, the signal was transmitted over a 20-km dispersion-compensated single-mode fiber link and received by a single photodiode followed by a digital signal processor including a nonlinear equalizer. At a gross bit rate of 400 Gb/s, the bit error rate of the received signal was below the threshold of 20% overhead soft-decision forward error correction code. This result corresponds to a net data rate of 333 Gb/s.

Transmission of 64-Gb/s Pilot-Assisted PAM-4 Signal Over 1440-km SSMF With Phase Noise Mitigation

We propose a direct detection scheme for pulse amplitude modulation (PAM) signals over long-reach fiber transmission with phase noise mitigation. In this scheme, an optical carrier is transmitted as pilot together with the optical signal, whose frequency is located at the edge of the optical signal. The electrical field of the optical signal can be retrieved via the beating between the pilot and optical signal in one photodetector at the receiver side, which facilitates the digital compensation of chromatic dispersion effect. To enable real value signal processing, digital carrier regeneration is proposed to mitigate the phase noise fluctuation in the proposed scheme. To further improve the performance, the digital signal processing including Kramers-Kronig field reconstruction and Volterra equalizer are applied to reduce the signal-to-signal beat noise and nonlinear distortions after fiber transmission. The experimental results for both 56- and 64-Gb/s PAM-4 signal transmission cases show that the performances can be significantly improvement based on the proposed scheme and DSP methods. Both 56- and 64-Gb/s PAM-4 signal transmissions over 720- and 1440-km standard single mode fiber have been successfully achieved under 7% and 20% forward error correction codes, respectively.

Hierarchical Distribution Matching for Probabilistically Shaped Coded Modulation

The implementation difficulties of combining distribution matching (DM) and dematching (invDM) for probabilistic shaping (PS) with soft-decision forward error correction (FEC) coding can be relaxed by reverse concatenation, for which the FEC coding and decoding lies inside the shaping algorithms. PS can seemingly achieve performance close to the Shannon limit, although there are practical implementation challenges that need to be carefully addressed. We propose a hierarchical DM (HiDM) scheme, having fully parallelized input/output interfaces and a pipelined architecture that can efficiently perform the DM/invDM without the complex operations of previously proposed methods such as constant composition DM (CCDM). Furthermore, HiDM can operate at a significantly larger post-FEC bit error rate (BER) for the same post-invDM BER performance, which facilitates simulations. These benefits come at the cost of a slightly larger rate loss and required signal-to-noise ratio at a given post-FEC BER.

Channel Constrained Multiple Selective Retransmissions for OFDM System: BER and Throughput Analysis

Hybrid automatic repeat request (HARQ) retransmission is an effective method to combat time-variant channel fading. Conventional HARQ methods initiate retransmission of failed packet without exploiting channel knowledge. When a packet fails, retransmission of data corresponding to high gain sub-carriers of an orthogonal frequency division multiplexing (OFDM) modulation is not necessary and deteriorates the throughput of the communication system. In this paper, we propose accumulated channel norm constrained selective retransmission (CNSR) at physical layer (PHY) in conjunction with HARQ method, which enhances throughput of the transceiver without compromising latency. When a packet fails, medium access control (MAC) layer requests retransmission of the failed packet. The proposed CNSR method initiates retransmission of data at PHY layer transmitted over low signal-to-noise ratio sub-carriers using outdated channel information. The transceiver pair continues retransmission of the failed packet until target channel norm of the sub-carriers is achieved or maximum number of retransmissions are completed. We maximize throughput by optimizing threshold on channel norm for OFDM modulation. We also present an upper bound on bit error rate and throughput analysis of the proposed method. The proposed method achieves higher throughput as compared with the existing Chase combining with selective repeat and conventional Chase combining schemes with and without forward error correction codes.

НОВЫЙ ФОРМАТ МОДУЛЯЦИИ 2-12QAM

The 16 Quadrature Amplitude Modulation (16QAM) is the preferred modulation format for many communication and broadcasting standards. However, performance of the overall “practical” communication/ broadcasting systems employing 16QAM is far from the Shannon limit as there is a requirement for power back-up to combat non-linear distortions generated by the output of high power amplifiers. In this paper we propose moving from 16QAM to a 12QAM modulation without any change of the hardware and with only minor changes in the mapping algorithm, by eliminating the four constellation points with highest signal energy. However, to ensure that no data is lost and spectral efficiency is preserved, we propose pairing two 12QAM symbols into a 4-dimensional signal with the appropriate mapping, obtaining the desired 2-12QAM modulation. We propose the use of a rate 6/7 forward error correcting (FEC) code combined with the 2-12QAM, which maps 7 binary input digits into 2 twelve-ary symbols which select corresponding signals from the conventional 16QAM modulator. The proposed new modulation format has a spectral efficiency of 3 bits/symbol, the same spectral efficiency as the legacy 16QAM scheme when the 16QAM modulation format is coupled with a rate 3/4 FEC. The removal of the 16QAM highest energy symbols represents a peak energy gain of 2.55 dB and an average energy gain of 1,35 dB which is offset by a 0.58 dB increase in code rate, from 3/4 to 6/7. In addition, the proposed scheme has a clear advantage of employing existing 16QAM modulator/demodulator hardware and maintaining compatibility with the legacy standards, albeit with simple changes in mapping which can be achieved via a software upgrade. We show that the proposed technique allows at least 2dB power gain without sacrificing spectral efficiency or additional hardware complexity.

An Improved Blind Recognition Method of the Convolutional Interleaver Parameters in a Noisy Channel

In a digital communication system, forward error correction (FEC) codes and interleavers are implemented to code the data so as to improve the error performance, which is hindered by random and burst errors. In the context of noncooperative communication, interleaver parameter recognition, which is the prerequisite for frame synchronization, channel coding recognition subsequently, is of vital significance. Methods of blindly recognizing convolutional interleaver parameters have been proposed in published literature, but the accuracy of recognition decreases significantly when bit error rate (BER) is high. To improve the performance of the algorithm, the effect of error bits on Gauss-Jordan elimination through pivoting (GJTEP) algorithm is analyzed in this paper. The following conclusion is drawn: error bits on the principal diagonal of data storage matrix will exert a great impact on the recognition accuracy. Based on the conclusion, an improved blind recognition method with denoising, the core principle of which is reducing error bits on the principal diagonal of data storage matrix, is proposed in this paper. The simulation experiment results demonstrate that the performance on error resilience is markedly improved.

Neural network based channel identification and compensation

Under the fast fading environment, the estimated channel state information (CSI) is largely different from real channel state particularly in the last part of the packet. To mitigate this influence, an iterative channel estimation (ICE) has been proposed. This method generates the replica signals by using the demodulated signals and the channel state information can be obtained via its remodulation. Channel variation can be compensated by using the error components defined as the difference between the replica symbols and received symbols. Additionally by exploiting forward error correction code, the CSI estimation accuracy can be gradually improved as iteration. However, this method requires symbol-by-symbol operation to track the channel variation which imposes huge computation amount. To reduce the number of channel compensation process, this paper proposes a neural network based channel identification and compensation scheme for OFDM system. It can estimate the whole transition of channel states and efficiently compensate the channel variation using the generalization capability of a neural network. The computer simulation results clarifies that the proposed method can improve the BER performance even under the fast fading environment.

Low-Power SDR Design on an FPGA for Intersatellite Communications

Small satellite systems make space missions for communication, navigation, and scientific research more realizable and diversified. Small satellites flying in large cluster or constellation formation as a network can provide an economical access to accomplish more complex missions, such as distributed computation, high-resolution imaging, and spacecraft maintenance. An increasing number of satellites operating on lower earth orbit for complex missions require a wireless communication system that is both reliable and flexible. This paper presents a complete software-defined radio (SDR) model for intersatellite communications (ISCs) and its implementation on a field-programmable gate array (FPGA). The proposed SDR for transmitter and receiver only has a power consumption of 2.1 and 3.2 W, respectively, which is suitable for power-limited small satellite systems. Algorithms and parameters of each block are optimized aiming at reducing hardware resource utilization. A low-density parity-check code constructed by the Euclidean geometry method is adopted as the channel code for forward error correction. Implementations of the synchronization, demodulation, and decoding algorithms are optimized for hardware efficiency. The low-power SDR designs are implemented on an FPGA-based experimental platform and successful demonstrated by over-the-air transmissions.

SiGe-Driven Hybrid-Integrated Silicon Photonic Link Using Optical-Domain Equalization

We report 50- and 60-Gb/s hybrid-integrated optical links in the O-band with CMOS photonic components driven by silicon–germanium ICs using optical-domain feed-forward equalization. The link includes a segmented-electrode Mach–Zehnder modulator and a Ge photodetector that provide high bandwidths and the potential for tight integration with control and monitoring electronics. The combination of these features enables the demonstration of a 60-Gb/s AC-coupled link and a 50-Gb/s DC-coupled link with bit error rates below 10–12 without the use of forward-error correction codes. This result provides a promising path toward extending speeds in latency sensitive optical links.

WiFO: A hybrid communication network based on integrated free-space optical and WiFi femtocells

Developments in smart home technology and the Internet of Things have significantly increased the demand for high-speed indoor wireless links. Although the majority of the research conducted in this area is still focused on the efficient usage of radio frequency (RF) spectrum, free-space optical (FSO) networks have also been explored as an alternative due to their large bandwidth potentials and low interference. In this paper we present a hybrid FSO and WiFi system (WiFO) that seamlessly integrates optical femtocell architecture with high mobility WiFi networks. Each FSO femtocell in this indoor communication system is capable of transmitting and receiving data at a rate of 50 Mbps over a distance of up to three meters with a field-of-view of ±15°, while still achieving a low bit error rate between 10−6, and 10−4. Reed–Solomon forward error correction codes were also applied to the data stream to further reduce the bit error rate to below 10−7. Different than many other free-space optical communication network using static transceivers, mobility in our WiFO system is achieved through the integration of a WiFi channel in the network protocol. The WiFi channel provides a feedback mechanism and allows for seamless handoffs between FSO femtocells. Additionally, we have experimentally demonstrated the advantage of this WiFO architecture by comparing the throughput of our system with a standard WiFi link in a realistic scenario. Our investigation has shown that the WiFO system presented in this work offers a cost-effective and easy-to-implement approach to significantly increase the capacity of current WiFi networks.

Energy-Aware Concurrent Multipath Transfer for Real-Time Video Streaming Over Heterogeneous Wireless Networks

The advancements in networking technologies and hand-held devices enable mobile users to concurrently receive real-time multimedia streaming (e.g., high-definition video) with different radio interfaces (e.g., Wi-Fi and LTE networks). Stream control transmission protocol (SCTP) is an important transport-layer solution to implement concurrent multipath transfer (CMT) over heterogeneous wireless networks with multihomed terminals. However, it is challenging to distribute multimedia content to resource-limited mobile devices because of the contradiction between energy consumption and streaming quality. To deliver the energy-efficient and quality-aware multimedia streaming over multiple wireless networks, this paper presents an Energy and goodPut Optimized CMT (EPOC) solution. First, we develop an analytical framework to model the relationship between energy consumption and goodput performance for real-time multimedia transmission to multihomed mobile devices. Second, we propose a joint forward error correction coding and rate allocation scheme to minimize energy consumption while satisfying goodput constraint. EPOC effectively leverages the energy-goodput tradeoff and multipath diversity to optimize mobile multimedia transmission in heterogeneous networking environment. We conduct the performance evaluation through extensive semi-physical emulations in Exata involving H.264 video streaming. Compared with the reference CMT schemes using SCTP, EPOC achieves appreciable improvements in energy conservation, goodput, and video peak signal-to-noise ratio.

A High-Throughput Architecture of List Successive Cancellation Polar Codes Decoder With Large List Size

As the first kind of forward error correction (FEC) codes that achieve channel capacity, polar codes have attracted much research interest recently. Compared with other popular FEC codes, polar codes decoded by list successive cancellation decoding (LSCD) with a large list size have better error correction performance. However, due to the serial decoding nature of LSCD and the high complexity of list management (LM), the decoding latency is high, which limits the usage of polar codes in practical applications that require low latency and high throughput. In this work, we study the high-throughput implementation of LSCD with a large list size. Specifically, at the algorithmic level, to achieve a low decoding latency with moderate hardware complexity, two decoding schemes, a multi-bit double thresholding scheme and a partial G-node look-ahead scheme, are proposed. Then, a high-throughput VLSI architecture implementing the proposed algorithms is developed with optimizations on different computation modules. From the implementation results on UMC 90 nm CMOS technology, the proposed architecture achieves decoding throughputs of 1.103 Gbps, 977 Mbps and 827 Mbps when the list sizes are 8, 16 and 32, respectively.

Optimal DASH-Multicasting Over LTE

Dynamic Adaptive Streaming over HTTP (DASH) is a fast growing video streaming platform, which enables adaptive rate selection based on channel conditions. File Delivery over Unidirectional Transport (FLUTE) further enables multicasting of the DASH segments over LTE eMBMS systems. In this paper, an optimal DASH-multicasting solution is proposed to allow more DASH clients in an LTE network to receive better videos by optimizing the resource allocation, application-layer forward error correction (FEC) code rate and modulation and coding scheme (MCS) selection of each multicasting group, which corresponds to a FLUTE session. Multiple FLUTE sessions are considered to deliver multiple videos, each with different video rates, for enhancing the overall utility. We have applied the convex optimization method to find the optimal resource allocation in terms of utility for multiple FLUTE sessions. We also find the optimal FEC code rates to add redundancies to protect the video segments for each FLUTE session. Moreover, an efficient MCS selection is introduced to reduce the complexity of the algorithm. Simulation results, with realistic LTE parameters, are shown to prove the proposed scheme is optimal, with more DASH clients receiving better video representations within limited resources when compared to other existing algorithms.

Adaptive Source-FEC Coding for Energy-Efficient Surveillance Video Over Wireless Networks

Video surveillance has become an important Internet multimedia application to provide live streaming services. Energy efficiency is critical to guarantee the service time and quality of power-intensive video streaming on wireless surveillance systems. In particular, video coding and data communication constitute the majority of power dissipation in embedded multimedia devices driven by capacity-limited batteries. However, the complex power characteristics and time-varying channel status pose crucial challenges on enabling low-power high-quality video streaming. To address these critical problems, this paper presents a power-efficient and network-adaptive (PENA) framework for source- forward error correction (FEC) coding in embedded systems. First, an analytical framework is developed to characterize the rate-distortion-power tradeoff for video encoding and data transfer. Second, a joint rate control and FEC coding solution is proposed to maximize video quality under power constraint. Distinct from the existing source-FEC coding algorithms, PENA is able to effectively leverage the video rate-distortion model and system power features . We conduct the system implementation and performance evaluation with real embedded surveillance devices over wireless networks. Experimental results demonstrate PENA achieves appreciable improvements over the reference source-FEC coding schemes in terms of power conservation, perceived video quality, and end-to-end delay.

Partly systematic Luby transform codes based on improved progressive edge-growth algorithm for Mars communications

The Luby transform code is a forward error correction code and was originally designed for the erasure channel. In this paper, the Luby transform codes over the Mars communication channel are investigated. To guarantee the reliable data transmission over the Mars communication channel which are usually affected by fading and noises, the progressive edge-growth algorithm is improved and used in for encoding the Luby transform codes. And then a partly systematic Luby transform code with an improved progressive edge-growth algorithm is designed to improve the error propagation phenomenon in Mars communications. Performance evaluations of the designed partly systematic Luby transform code based on the random graph, PEG and improved progressive edge-growth algorithms, respectively, are conducted through a series of simulations. Simulation results show that the performance of the partly systematic Luby transform code based on the improved progressive edge-growth algorithm outperforms those of the partly systematic Luby transform code based on two other algorithms and has the lower bit error rate and overhead.

A Cost-Efficient Real-Time 25 Mb/s System for LED-UOWC: Design, Channel Coding, FPGA Implementation, and Characterization

In this paper, we experimentally demonstrate a cost-efficient real-time field programmable gate array (FPGA)-based system for underwater optical wireless communication (UOWC) at a data rate up to 25 Mb/s over a 10 m underwater channel. The transmitter of the system employs a commercial blue LED as a modulation light source and an FPGA unit for transmitter baseband signal processing, and an avalanche photo diode cascaded with an FPGA unit for receiver baseband signal processing at the receiver side. We also suggest a simplified system model to characterize underwater optical link. Three types of hard-decision forward error correction codes are introduced to investigate the impact on the receiver sensitivity in long distance transmission cases. By adding additional link attenuation, we experimentally measure the attenuation coefficients for different water conditions. Based on the measured results, the achievable link distance for clear ocean water is estimated up to 118 m at the transmitted electrical power of 30 dBm. The proposed UOWC system takes both implementation complexity and cost into consideration and also provides a significant guidance to the future real-time high-speed underwater optical communications.

Design of Low-Density Parity Check Codes for 5G New Radio

Turbo codes, prevalent in most modern cellular devices, are set to be replaced by LDPC codes as the code for forward error correction. This transition was ushered in mainly because of the high throughput demands for 5G New Radio (NR). The new channel coding solution also needs to support incremental-redundancy hybrid ARQ, and a wide range of blocklengths and coding rates, with stringent performance guarantees and minimal description complexity. In this article, we first briefly review the requirements of the new channel code for 5G NR. We then describe the LDPC code design philosophy and how the broad requirements of 5G NR channel coding led to the introduction of novel structural features in the code design, culminating in an LDPC code that satisfies all the demands of 5G NR.

Low Latency Parallel Turbo Decoding Implementation for Future Terrestrial Broadcasting Systems

As a class of high-performance forward error correction codes, turbo codes, which can approach the channel capacity, could become a candidate of the coding methods in future terrestrial broadcasting (TB) systems. Among all the demands of future TB system, high throughput and low latency are two basic requirements that need to be met. Parallel turbo decoding is a very effective method to reduce the latency and improve the throughput in the decoding stage. In this paper, a parallel turbo decoder is designed and implemented in field-programmable gate array (FPGA). A reverse address generator is proposed to reduce the complexity of interleaver and also the iteration time. A practical method of modulo operation is realized in FPGA which can save computing resources compared with using division operation. The latency of parallel turbo decoder after implementation can be as low as 23.2 us at a clock rate of 250 MHz and the throughput can reach up to 6.92 Gbps.