Academic literature on the topic 'Forward Error Correction'

<p>The main goal in this thesis is to select and test Forward Error Correction (FEC) schemes suitable for network video transmission over RTP/UDP. There is a general concern in communication networks which is to achieve a tradeoff between reliable transmission and the delay that it takes. Our purpose is to look for techniques that improve the reliability while the realtime delay constraints are fulfilled. In order to achieve it, the FEC techniques focus on recovering the packet losses that come up along any transmission. The FEC schemes that we have selected are Parity Check algorithm, ReedSolomon (RS) codes and a Convolutional code. Simulations are performed to test the different schemes.</p><p>The results obtained show that the RS codes are the more powerful schemes in terms of recovery capabilities. However they can not be deployed for every configuration since they go beyond the delay threshold. On the other hand, despite of the Parity Check codes being the less efficient in terms of error recovery, they show a reasonable low delay. Therefore, depending on the packet loss probability that we are working with, we may chose one or other of the different schemes. To summarize, this thesis includes a theoretical background, a thorough analysis of the FEC schemes chosen, simulation results, conclusions and proposed future work.</p>

The unprecedented growth in demand for digital media has led to an all-time high in society’s demand for information. This demand will in all likelihood continue to grow as technology such as 3D television service, on-demand video and peer-to-peer networking continue to become more common place. The large amount of information required is currently transmitted optically using a wavelength division multiplexing (WDM) network structure. The need to increase the capacity of the existing WDM network infrastructure efficiently is essential to continue to provide new high bandwidth services to end-users, while at the same time minimizing network providers’ costs. In WDM systems the key to reducing the cost per transported information bit is to effectively share all optical components. These components must operate within the same wavelength limited window; therefore it is necessary to place the WDM channels as close together as possible. At the same time, the correct modulation format must be selected in order to create flexible, cost-effective, high-capacity optical networks. This thesis presents a detailed comparison of Differential Quadrature Phase Shift Keying (DQPSK) to other modulation formats. This comparison is implemented through a series of simulations in which the bit error rate of various modulation formats are compared both with and without the presence of forward error correction techniques. Based off of these simulation results, the top performing modulation formats are placed into a multiplexed simulation to assess their overall robustness in the face of multiple filtering impairments.

A deep learning algorithm for improving the performance of the Sum-ProductAlgorithm (SPA) based decoders is investigated. The proposed Neural NetworkDecoders (NND) [22] generalizes the SPA by assigning weights to the edges ofthe Tanner graph. We elucidate the peculiar design, training, and working of theNND. We analyze the edge weight’s distribution of the trained NND and providea deeper insight into its working. The training process of NND learns the edgeweights in such a way that the effects of artifacts in the Tanner graph (such ascycles or trapping sets) are mitigated, leading to a significant improvement inperformance over the SPA.We conduct an extensive analysis of the training hyper-parameters affectingthe performance of the NND, and present hypotheses for determining theirappropriate choices for different families and sizes of codes. Experimental resultsare used to verify the hypotheses and rationale presented. Furthermore,we propose a new loss-function that improves performance over the standardcross-entropy loss. We also investigate the limitations of the NND in termsof complexity and performance. Although the SPA based design of the NNDenables faster training and reduced complexity, the design constraints restrictthe neural network to reach its maximum potential. Our experiments show thatthe NND is unable to reach Maximum Likelihood (ML) performance thresholdfor any plausible set of hyper-parameters. However for short length (n 128)High Density Parity Check (HDPC) codes such as Polar or BCH codes, theperformance improvement over the SPA is significant.<br>En djup inlärningsalgoritm för att förbättra prestanda hos SPA-baserade (Sum-Product Algorithm) avkodare undersöks. Den föreslagna neuronnätsavkodaren(Neural Network Decoder, NND) [22] generaliserar SPA genom att tilldela viktertill bågarna i Tannergrafen. Vi undersöker neuronnätsavkodarens utformning,träning och funktion. Vi analyserar fördelningen av båg vikter hos en tränadneuronnätsavkodare och förmedlar en djupare insikt i dess funktion. Träningenav neuronnätsavkodaren är sådan att den lär sig bågvikter så att effekternaav artefakter hos Tannergrafen (såsom cykler och fångstmängder‡) minimeras,vilket leder till betydande prestandaförbättringar jämfört med SPA.Vi genomför en omfattande analys av de tränings-hyper-parametrar sompåverkar prestanda hos neuronnätsavkodaren och presenterar hypoteser för lämpligaval av tränings-hyper-parametrar för olika familjer och storlekar av koder. Experimentellaresultat används för att verifiera dessa hypoteser och förklaringarpresenteras. Dessutom föreslår vi ett nytt felmått som förbättrar prestanda jämförtmed det vanliga korsentropimåttet§. Vi undersöker också begränsningar hosneuronnätsavkodaren med avseende på komplexitet och prestanda. Neuronnätsavkodarenär baserad på SPA vilket möjliggör snabbare träning och minskadkomplexitet, till priset av begränsningar hos neuronnätsavkodaren som gör attden inte kan nå ML-prestanda för någon rimlig uppsättning tränings-hyperparametrar.För korta (n &lt;= 128) högdensitetsparitetskoder (High-DensityParity Check, HDPC), exempelvis Polarkoder eller BCH-koder, är prestandaförbättringarnajämfört med SPA dock betydande.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2007.<br>Thesis Advisor(s): Clark Robertson. "March 2007." Includes bibliographical references (p.47-48). Also available in print.

Most of the real-time applications use user data protocol (UDP) as their transport protocol. The reason is that UDP does not provide flow control or error recovery and does not require connection management. Consequently it is a fast protocol suitable for applications that only need to transmit little data or for delay sensitive applications. Nevertheless, UDP has a major drawback, if some packets are dropped then there is no way to recover them. Some applications as video or audio could accept lower quality and most of the times the lost of some packets is less critic than the delay introduced by error recovery methods. Since more applications with real-time constraints such as video image and audio are introduced both over the wired Internet and over wireless some improvements should be made in order to obtain better performance. The main contribution of this thesis is to study an intermediate solution providing more reliability to the communication between applications running on top of UDP and at the same time support its fast connection quality using already existing protocols. In order to obtain it, real-time transport protocol (RTP) has been chosen as upper level protocol (to provide ”flowcontrol”) and an adaptive forward error correction (AFEC) technique has been studied (to provide error management). The idea of AFEC is to inject an adaptive amount of redundancy packets in every sent block (or datagram) in order to achieve a desired recovery rate at the receiver without using any retransmission mechanism. The sender dynamically uses feedback information from the receiver to decide the optimal amount of redundancy to introduce in every sent block. This decision task is managed by a control system at the sender side. Using the network simulator, ns-2, the performance of three different controllers using AFEC is evaluated. The results show in various scenarios that the amount of discarded blocks due to the corruption of some of its packets (block loss probability after decoding) decrease considerably when the AFEC mechanism is introduced.

The Internet is rapidly becoming the dominant platform for video contribution and distribution, but today’s Internet provides a best-effort service without any guarantee of quality. Internet video streaming has to cope with this lack of guarantees. Due to congestion and the heterogeneous infrastructure of the Internet a video transmission will be plagued by packet loss, variability in throughput, and latency. To mitigate some of these these problems f.o.r.w.a.r.d e.r.r.o.r c.o.r.r.e.c.t.i.o.n (F.E.C) can be employed. The aim of this thesis is to present a theoretical introduction to error correcting codes, implement and integrate f.o.r.w.a.r.d e.r.r.o.r c.o.r.r.e.c.t.i.o.n into an existing video streaming application, and test the implementation in both simulated and real-world conditions. Parameters of the F.E.C algorithm will be tweaked and guidelines for parameter selection will be developed

This research discusses how the design of a tornado forward error correcting channel code (FEC) sends digital data stream profiles to the receiver. The complete design was based on the Tornado channel code, binary phase shift keying (BPSK) modulation on a Gaussian channel (AWGN). The communication link was simulated by using Matlab, which shows the theoretical systems efficiency. Then the data stream was input as data to be simulated communication systems using Matlab. The purpose of this paper is to introduce the audience to a simulation technique that has been successfully used to determine how well a FEC expected to work when transferring digital data streams. The goal is to use this data to show how FEC optimizes a digital data stream to gain a better digital communications systems. The results conclude by making comparisons of different possible styles for the Tornado FEC code.

Wireless Sensor Networks (WSN) are used in many applications, for example industrial applications, automatic control applications, monitoring applications, to name but a few. Although WSN can employ different standards in order to achieve short range wireless communication, the mainstream of the market is toadopt the low-power, low-rate IEEE 802.15.4 standard. However, this standard does not specify any block codes on the Physical layer (PHY) and the MAC sublayer. Reliability and energy efficiency are two important metrics used to evaluate the WSN performance. In order to enhance the reliability of the WSN performance, schemes such as Forward Error Correction (FEC) and HybridAutomatic Repeat-reQuest (HARQ) can be introduced on the PHY and MACsublayer when transmitting signals. However, this will reduce the energy efficiency of the WSN. In order to investigate what does affect the reliability and energy efficiency, this thesis has been conducted with the assistance of Matlab simulations, which simulate different transmission schemes proposed by the authors. Based on the simulations, both the reliability and energy efficiency can be evaluated and the results are illustrated for both metrics. The objective of this thesis is to determine a scheme that is able to meet these metric requirements.