RaptorQ Codes Research Articles

RaptorQ codes aided secure data delivery strategy for vehicular networks

Abstract This paper deals with security issues in the presence of an eavesdropper for a vehicular scenario. The proposed secure data delivery scheme implements Fountain Codes, namely RaptorQ (RQ) codes, at the application layer (AL) to increase communication security against eavesdroppers’ attacks. For RQ coded transmission scheme, the receiver has to collect a sufficient number of coded packets to reconstruct the original source data. Secure delivery can be achieved if the legitimate user obtains enough RQ coded packets before the eavesdropper does. To satisfy this condition, it is proposed to use a road side unit (RSU) cooperation method when the eavesdropper has better channel conditions than the legitimate user to scatter the coded packets from multiple RSUs. The aim is to reduce the probability that the eavesdropper receives the sufficient number of coded packets and recover the source data before the legitimate user. An optimisation framework which jointly selects the RQ code rate at the AL and Modulation and Coding Scheme (MCS) at the physical (PHY) layer to ensure the secure data transmission by allowing the user to decode the file with a certain probability of decoding success while minimising the intercept probability at the eavesdropper is presented. To evaluate the proposed system, a realistic end-to-end system level simulator is developed. Simulation results show that the proposed scheme can provide secure and efficient data transmission over vehicular networks by significantly reducing the intercept probability at the eavesdropper.

SCDP: Systematic Rateless Coding for Efficient Data Transport in Data Centers

In this paper we propose SCDP, a general-purpose data transport protocol for data centres that, in contrast to all other protocols proposed to date, supports efficient one-to-many and many-to-one communication, which is extremely common in modern data centres. SCDP does so without compromising on efficiency for short and long unicast flows. SCDP achieves this by integrating RaptorQ codes with receiver-driven data transport, packet trimming and Multi-Level Feedback Queuing (MLFQ); (1) RaptorQ codes enable efficient one-to-many and many-to-one data transport; (2) on top of RaptorQ codes, receiver-driven flow control, in combination with in-network packet trimming, enable efficient usage of network resources as well as multi-path transport and packet spraying for all transport modes. Incast and Outcast are eliminated; (3) the systematic nature of RaptorQ codes, in combination with MLFQ, enable fast, decoding-free completion of short flows. We extensively evaluate SCDP in a wide range of simulated scenarios with realistic data centre workloads. For one-to-many and many-to-one transport sessions, SCDP performs significantly better compared to NDP and PIAS. For short and long unicast flows, SCDP performs equally well or better compared to NDP and PIAS.

Satellite forward VDES channel modeling and impact on higher‐layer performance

SummaryVHF data exchange system (VDES) is an emerging maritime communications standard that is meant to provide ship‐to‐shore, shore‐to‐ship, and ship‐to‐ship information services. VDES also includes a satellite component to extend the service coverage also to the high sea. Ships can receive important information via VDES and access this service via satellite when they are far from the shore. This paper uses data taken during a measurement campaign to develop an ON‐OFF model for the VDE‐SAT downlink channel taking the multipath effects caused by sea reflections into account. This model has been used to evaluate the impact of packet‐level forward error correction (FEC) schemes (i.e., ideal codes, RaptorQ codes, and 2‐Dimension Reed‐Solomon codes) to further protect transmissions from deep fading events and to evaluate the impact at the transport level considering the possibility to adopt the transmission control protocol (TCP) for a file map delivery service.

Bounds on the Error Probability of Raptor Codes Under Maximum Likelihood Decoding

In this paper upper and lower bounds on the probability of decoding failure under maximum likelihood decoding are derived for different (nonbinary) Raptor code constructions. In particular four different constructions are considered; (i) the standard Raptor code construction, (ii) a multi-edge type construction, (iii) a construction where the Raptor code is nonbinary but the generator matrix of the LT code has only binary entries, (iv) a combination of (ii) and (iii). The latter construction resembles the one employed by RaptorQ codes, which at the time of writing this article represents the state of the art in fountain codes. The bounds are shown to be tight, and provide an important aid for the design of Raptor codes.

Experimental Analysis and Evaluation of RaptorQ Codes for Video Multicasting Over Wi-Fi

This paper presents a reliable and efficient high quality video streaming solution for use in challenging outdoor environments over Wi-Fi. An application layer forward error correction based on RaptorQ codes was implemented in a practical Wi-Fi based server and client system to enhance reliability. Thus, this paper presents the first detailed analysis on the implementation of RaptorQ codes for streaming high definition video over Wi-Fi. The measurements were performed in central Bristol with parameters such as RaptorQ symbol size, code rate, buffering time and modulation and coding scheme, and user quality of experience based on these parameters was evaluated. For multicast live video streaming it is demonstrated that system performance is mostly dominated by hardware and software limitations on constrained host platforms where the incoming packet rate exceeds the device`s ability to consume the traffic, i.e., Wi-Fi clients are a major source of packet loss, even in ideal channel conditions. Client limitations were found to be a function of modulation and coding schemes and RaptorQ coding parameters. Therefore, the optimum system design parameters such as RaptorQ symbol size, code rate and buffering time with respect to modulation and coding schemes were suggested considering practical limitations from real-world measurements.

Dynamic Code Selection Method for Content Transfer in Deep-Space Network

To maximize file transfer from deep-space vehicles, a space-to-earth content-transfer protocol that combines turbo codes, RaptorQ codes, real-time channel prediction, and dynamic code-rate selection is proposed. The protocol features a signal-to-noise ratio prediction model that facilitates the periodic adjustment of turbo encoder to achieve adaptive-rate transmission, and fountain codes to eliminate retransmission of specific packets. Simulation results indicate that an increase of about 132% in file transfer rate is achievable compared to fixed-rate transmission scheme.

Reduction of end-to-end delay using threaded RaptorQ codes in VANETs

Multimedia data transmission, a prevalent and significant requirement in Vehicular Adhoc Networks (VANETs) demands less end-to-end delay. The transmission of data in VANET scenarios is challenging as the vehicles are mostly on move resulting in dynamic topology. RaptorQ (RQ) codes help in error correction, where the redundant symbols sent along with the actual symbols help in correcting the errors encountered in the receiver(s), eliminating the requirement of retransmission. In this work, the reduction of end-to-end delay of the video data transmitted in VANETs is achieved with the usage of RaptorQ codes, while encoding in the transmitter and decoding in the receiver. Multithreading is introduced in both the ends to further reduce the delay incurred. The various scenarios exhibiting all possible combinations of single or multiple hops, single transmission or multiple transmission are observed and the results showing the influence of RQ encoder and decoder in reducing the end-to-end delay are presented.

Online AL-FEC policy problem on mobile unicast services

Forward error correction (FEC) is a method for error control of data transmission adopted in several mobile multicast standards. FEC is a feedback free error recovery method where the sender introduces redundant data in advance with the source data enabling the recipient to recover from different arbitrary packet losses. Recently, the adoption of FEC error control method has been boosted by the introduction of powerful Application Layer FEC (AL-FEC) codes, e.g. RaptorQ codes. Furthermore, several works have emerged aiming to address the shortcomings of AL-FEC protection application utilizing deterministic or randomized online algorithms to enhance the efficiency of AL-FEC error control method. In this work, since the investigation of AL-FEC application as primary or auxiliary error protection method over mobile multicast environments is a well investigated field but the opportunity of utilizing the AL-FEC over mobile unicast services as the only method for error control replacing common feedback based methods that are now considered to be obsolete, we provide an analysis on the feasibility of AL-FEC protection over unicast delivery utilizing online algorithms in conjunction with AL-FEC codes with exceptional recovery performance.

Bounds on the Reliability of RaptorQ Codes in the Finite-Length Regime

In this paper we analyze the bounds on the reliability of RaptorQ codes under maximum likelihood decoding, especially in the finite-length regime. RaptorQ code ensembles by a high-order low density generator-matrix (LDGM) code as pre-code and an inner Luby transform (LT) code. By investigating the rank of the product of two random coefficient matrices of the high-order LDGM code and the inner LT code, we derive the expressions for the upper and lower bounds of decoding failure probability (DFP) on the RaptorQ code. Then, the accuracy of our derived theoretical bounds are verified through the Monte Carlo simulations with different degree distributions and short packets. The high accuracy bounds are then exploited to design near-optimum finite-length RaptorQ codes, enabling a tight control on the tradeoff between decoding complexity and DFP.

Mobile 4K / 2K / HD video streaming supported by real-time FEC raptorQ codes

With the growth of packet-switch networks in the mobile consumer electronics market, fountain codes are coming to play an increasingly important role as they allow high packet loss rates while still supporting high QoS. This is particularly critical for video streaming in multimedia delivery on moving handheld mobile consumer devices. A powerful forward error-correction mechanism is the fountain coding scheme implemented by RaptorQ codes, defined over GF(256), whose decoding algorithms are very complex from a computational perspective, but highly suitable for parallelization. With multimedia delivery for handheld consumer electronics in mind, this paper proposes several decoding schemes for embedded mobile SoCs, exploiting both the parallel potential of the GPU and CPU, sharing a common memory space. The OpenCL and OpenMP frameworks are used to exploit both accelerators for the roles of matrix multiplication and inversion that comprise the bulk of computation in RaptorQ decoding. Reported results indicate low-power requirements within the range of typical handheld consumer devices (1.5~2.4W) for data processing rates of dozens of Mbit/s that are fully within the real-time requirements of HD, 2K and 4K coded video streaming resolutions and beyond.

Merge‐and‐forward: a cooperative multimedia transmissions protocol using RaptorQ codes

Recently, nodes cooperation has emerged as a popular means for improving the quality of multimedia delivery over fifth-generation cellular networks. However, in the conventional relaying scheme such as amplify-and-forward (AaF), there is a higher probability of duplicate packets at the receiver node which affect the decoding probability and consequently deteriorate the quality of multimedia transmission. In this study, the authors propose a cooperative multimedia transmission protocol based on a novel merge-and-forward relaying and the best relay selection (RS) schemes. Their best RS scheme is based on two important parameters: (i) two-hop link distances and (ii) minimum block error rate value. Moreover, to combat the packet loss for enhanced and reliable video delivery, they adopt application layer forward error correction scheme which is based on the most improved and advanced version of fountain codes (i.e. RaptorQ codes). They evaluate the performance of the proposed scheme under different time-sharing scenarios between the direct and best indirect transmission links in terms of decoding failure probability, decoding overhead, peak signal-to-noise ratio, and mean opinion score. Simulation results show that the proposed scheme outperforms the conventional AaF relaying scheme.

GLDPC-Staircase AL-FEC codes: a fundamental study and new results

This paper provides fundamentals in the design and analysis of Generalized Low-Density Parity Check (GLDPC)-Staircase codes over the erasure channel. These codes are constructed by extending an LDPC-Staircase code (base code) using Reed-Solomon (RS) codes (outer codes) in order to benefit from more powerful decoders. The GLDPC-Staircase coding scheme adds, in addition to the LDPC-Staircase repair symbols, extra-repair symbols that can be produced on demand and in large quantities, which provides small rate capabilities. Therefore, these codes are extremely flexible as they can be tuned to behave either like predefined rate LDPC-Staircase codes at one extreme, or like a single RS code at another extreme, or like small rate codes. Concerning the code design, we show that RS codes with “quasi” Hankel matrix-based construction fulfill the desired structure properties, and that a hybrid (IT/RS/ML) decoding is feasible that achieves maximum likelihood (ML) correction capabilities at a lower complexity. Concerning performance analysis, we detail an asymptotic analysis method based on density evolution (DE), extrinsic information transfer (EXIT), and the area theorem. Based on several asymptotic and finite length results, after selecting the optimal internal parameters, we demonstrate that GLDPC-Staircase codes feature excellent erasure recovery capabilities, close to that of ideal codes, both with large and very small objects. From this point of view, they outperform LDPC-Staircase and Raptor codes and achieve correction capabilities close to those of RaptorQ codes. Therefore, all these results make GLDPC-Staircase codes a universal Application-Layer FEC (AL-FEC) solution for many situations that require erasure protection such as media streaming or file multicast transmission.

Reducing the decoding complexity of RaptorQ codes for delay sensitive applications using a simplified and scaled-down matrix

RaptorQ codes, a class of fountain codes, are widely used as a way to achieve forward error correction at the application layer. Whereas RaptorQ codes perform impressively in terms of symbol recovery, its high computational complexity limits its applicability in demanding real-time scenarios. As a way to resolve this inefficiency, we propose using a novel matrix structure designed to reduce the decoding complexity of RaptorQ codes. Specifically, we replace Luby Transform codes and Low-density Parity Check (LDPC) codes in RaptorQ code operations using a novel binary matrix based on Kolchin’s Theorem. Our proposed improvements remove the need for LDPC codes to decrease the dimension of the matrix, and it reduces the latency resulting from matrix inversions. Given that the resulting latency from this process dominates the entire RaptorQ code decoding process, our changes offer the potential for reducing the latency dramatically. Based on an extensive set of simulations using our proposed matrix structure under various configurations, we show that the proposed decoding latency is faster than that of RaptorQ codes, while maintaining an at-par decoding-failure probability.

Fast decoding for RaptorQ codes using matrix dimensionality reduction

A very fast decoding algorithm using matrix dimensionality reduction for RaptorQ codes is proposed. The algorithm exploits a pre-calculated inverse matrix to achieve dimensionality reduction for the received code constraint matrix. As a result, the decoding complexity is decreased significantly, whereas the failure-overhead curve is still identical to that of conventional approaches. Simulations show that the decoding speed of the proposed algorithm can be as fast as 17.5 times the state-of-the-art algorithm when the erasure probability is relatively low.

Low-Complexity Decoding for RaptorQ Codes Using a Recursive Matrix Inversion Formula

In this letter, we propose a low-complexity recursive decoding algorithm for rateless RaptorQ codes, the next generation error correction codes adopted by several standards such as DVB-H. Conventionally, the decoding of RaptorQ codes requires inverting a huge receive code generator matrix (RCGM). Instead of such costly matrix inversion, we propose to calculate the inverse of the transmit code generator matrix (TCGM) beforehand. Then, based on this pre-calculated inverse, the Sherman-Morrison formula is applied to recursively compute the inverse of the RCGM at run time. Most computations are thus shifted offline. Moreover, this recursive decoding distributes the computations among different time slots, thereby significantly shortening the decoding latency and improving the hardware utilization. Numerical simulations demonstrate that the computational complexity of the proposed recursive decoding is as low as 6.5% of that required by the conventional method using direct matrix inversion.

Protection of HEVC video delivery in vehicular networks with RaptorQ codes.

With future vehicles equipped with processing capability, storage, and communications, vehicular networks will become a reality. A vast number of applications will arise that will make use of this connectivity. Some of them will be based on video streaming. In this paper we focus on HEVC video coding standard streaming in vehicular networks and how it deals with packet losses with the aid of RaptorQ, a Forward Error Correction scheme. As vehicular networks are packet loss prone networks, protection mechanisms are necessary if we want to guarantee a minimum level of quality of experience to the final user. We have run simulations to evaluate which configurations fit better in this type of scenarios.

Recovery Capabilities of Rateless Codes on Simulated Turbulent Terrestrial Free Space Optics Channel Model

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially in high data rate links. Innovative solutions require an improvement of FSO link performances, together with testing models and appropriate channel codes. In this paper, we describe a high-resolution time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical turbulence. Concerning the same channel, we also report simulation results on the error mitigation performance of Luby Transform, Raptor, and RaptorQ codes.