Forward Error Correction Block Research Articles

An efficient forward error correction code for wireless sensor networks

<p>The main requirements in the design of wireless sensor network applications are to minimize energy consumption and maximize battery lifetime. Power is primarily consumed during wireless transmission and reception. Automatic repeat request (ARQ) and forward error correction (FEC) are the two basic methods to recover erroneous packets. As energy conservation is a major issue of concern in wireless sensor networks, repeat transmission because the error in the data received is not an option, and FEC would be preferred over ARQ. FEC is applied in situations where retransmissions are relatively costly or impossible. A successful data transmission means a higher energy saving and a long-life network. This paper presents a novel linear block forward error correction code for wireless sensor network applications called Low Complexity Parity Check (LCPC). The LCPC code offers lower encoding and decoding complexity than other types of codes. To validate the performance of the LCPC code, the proposed coding scheme was investigated at different values of data transmission with different types of modulations over Additive white Gaussian noise (AWGN) and Rayleigh fading channels. The simulation results show that the proposed code outperforms the renowned LDPC (8, 4), (255,175), and (576, 288) codes.</p>

Cross-Layer Resource Allocation Using Video Slice Header Information for Wireless Transmission Over LTE

In this paper, cross-layer resource allocation methods for wireless video transmission are proposed. We propose two practical metrics to measure the relative importance of each forward error correction (FEC) block to the user’s quality of experience. They can be obtained from the header information, and require no overhead bits or amendment of the header format of the existing standard video codec. We discuss adaptive modulation and coding scheme allocation, and adaptive energy allocation for the FEC blocks of a group of pictures. We also provide low-complexity resource allocation solutions. In both approaches, we consider two types of slice packetization, which affect the priority of FEC blocks. The proposed cross-layer resource allocation methods have significant performance gain over equal error protection, and similar performance to more complicated algorithms.

Throughput efficiency in body sensor networks: A clean-slate approach

In this paper, a flexible role-based architecture for Body Sensor Networks (BSNs) is introduced. The proposed non-layered context-aware architecture is application-oriented and able to incorporate future applications. Particular applications have certain requirements. Functional units (roles) instead of protocol layers are designed to perform the required tasks for applications to work properly. The role data of an application is inserted in the role headers of the container and is available for other applications with the same basic, specific or particular roles. Furthermore, the performance of Automatic Repeat Request (ARQ), Forward Error Correction (FEC) block codes and FEC convolutional codes with respect to the throughput efficiency has also been analyzed for a BSN following the proposed role-based architecture. The numerical results show that the proposed role-based architecture outperforms the traditional layered architecture with respect to the throughput efficiency for all error control schemes. FEC block codes are able to maintain a high throughput efficiency over longer distances because the hop length extension technique is applied.

Forward-Looking Forward Error Correction Mechanism for Video Streaming Over Wireless Networks

Video streaming over wireless network poses a great challenge because the high packet error rate usually decreases the quality of video streaming. Forward error correction (FEC) mechanism is generally used to protect the video quality. However, the recovery performance of the FEC mechanism decreases when burst packet loss is larger than the added FEC redundant packets. In this paper, the forward-looking forward error correction (FL-FEC) mechanism is proposed to recover lost packets for video streaming over wireless networks. The FL-FEC mechanism recovers not only the lost packet from its FEC block but also the previous FEC block from the recovered packet, repeating the recovery procedure until recovering the first FEC block. If the play-out buffer at the receiver is large, the FL-FEC mechanism can execute a chain of recovery procedures to ultimately recover all lost packets without any negative impact on application performance. The FL-FEC mechanism selects non-continuous source packets in previous FEC blocks to generate FEC redundancy with the FEC block. Hence, the FL-FEC mechanism can significantly disperse burst packet loss into different FEC blocks. The FL-FEC mechanism uses an analytical model to decide the number of FEC redundant packets in order to obtain the minimum recovery overhead. The FL-FEC mechanism is tested to show the benefits of high recovery performance and low recovery overhead in improving the peak signal-to-noise ratio and the decodable frame rate of video streaming over wireless networks.

A Clean Slate Architecture Design for VANETs

In this paper, VANET applications have been classified according to their purpose. Furthermore, a clean-slate architecture specifically designed for VANETs has been introduced. The proposed non-layered context-aware ubiquitous architecture adapts dynamically to changes, is oriented to services (VANET applications) and has a flexible structure. The vehicle and environmental context-aware information as well as the VANET communication characteristics are designed for the proper operation of the applications. In addition, the performance of Automatic Repeat Request and Forward Error Correction (FEC) block codes with respect to the throughput efficiency has also been analyzed for a VANET following the proposed clean-slate architecture. The numerical results show that the proposed clean-slate architecture outperforms the traditional layered architecture with respect to the throughput efficiency for both error control schemes. FEC block codes are able to maintain high throughput efficiency over longer distances because the hop length extension technique is applied.

Video quality protection for real time video streams over wireless networks

Received video quality is dependent on the available link rate and the packet loss ratio, which are correlated in a busy network link. Even low packet loss ratios (PLRs) can significantly reduce the video quality. In this paper, a packet level parity Forward Error Correction (FEC) is applied to the video stream in order to reduce the video PLR. A constant gross data rate is assumed, such that adding a FEC leads to a decrease in effective video data rate. The FEC block is truncated at the end of each video VOP, such that there are no inter-VOP dependencies for FEC correction. An algorithm is proposed to optimize the FEC length, based on the Quality of Experience as modelled by the ITU-T R G.1070 standard. It is shown that the optimization algorithm can significantly increase the video quality, without increasing the gross data rate. The algorithm has been evaluated both analytically and through simulations, which confirm the very significant increases in subjective video quality.

Packet Size Optimization for Improving the Energy Efficiency in Body Sensor Networks

Energy consumption is a key issue in body sensor networks (BSNs) since energy-constrained sensors monitor the vital signs of human beings in healthcare applications. In this paper, packet size optimization for BSNs has been analyzed to improve the efficiency of energy consumption. Existing studies on packet size optimization in wireless sensor networks cannot be applied to BSNs because the different operational characteristics of nodes and the channel effects of in-body and on-body propagation cannot be captured. In this paper, automatic repeat request (ARQ), forward error correction (FEC) block codes, and FEC convolutional codes have been analyzed regarding their energy efficiency. The hop-length extension technique has been applied to improve this metric with FEC block codes. The theoretical analysis and the numerical evaluations reveal that exploiting FEC schemes improves the energy efficiency, increases the optimal payload packet size, and extends the hop length for all scenarios for in-body and on-body propagation.

Dynamic FEC Algorithms for TFRC Flows

Media flows coexist with TCP-based data traffic on the Internet and are required to be TCP-friendly. The TCP protocol slowly increases its sending rate until episodes of congestion occur, and then it quickly reduces its rate to remove congestion. However, media flows can be sensitive to even brief episodes of congestion. In this paper, we are interested in protecting media flows from TCP-induced congestion while maintaining their TCP friendliness. In particular, we consider media flows carried over the TCP-Friendly Rate Control (TFRC) protocol and we design algorithms that dynamically adapt the level of forward error correction (FEC) based on the congestion state of the network. To this end, first, we investigate the loss and delay characteristics of TFRC flows in several TCP-induced congestion scenarios, and we develop novel predictors of loss events based on packet delay information. Second, we use these predictors to dynamically adapt the level of FEC protection based on the predicted level of congestion. We show that this technique can significantly improve the overhead versus reliability trade-off compared to fixed FEC. Third, we select the FEC and original media packets within each FEC block, in a rate-distortion optimized way, and we show that this technique significantly improves media quality.

An Adaptive Packet and Block Length Forward Error Correction for Video Streaming Over Wireless Networks

Video streaming over wireless networks is a challenging task due to its high error rate. Forward error correction (FEC) is a popular mechanism to recover lost packets for video streaming. Conventional FEC mechanisms use a whole redundant packet to recover the error source packet, when the packet error occurs with only a few bit errors inside. In this paper, we propose an Adaptive packet and block length FEC (APB-FEC) control mechanism. In order to overcome the high bit error rate, a small packet length reduces the packet error rate and a large FEC block length will enhance the recovery performance. Our proposed APB-FEC can obtain better recovery performance than conventional FEC mechanisms. Hence, APB-FEC can also reduce retransmission overhead. Using extensive emulations, we validate the efficiency of APB-FEC mechanism for video streaming over wireless networks.

Concurrent multipath transmission combining forward error correction and path interleaving for video streaming

Video streaming is a popular application on next generation networks (NGNs). However, video streaming over NGNs has many challenges due to the high bit error rates of these networks. Forward error correction (FEC) is often applied to improve the quality of video streaming. However, continuous lost packets decrease the recovery performance of FEC protection in NGNs. To disperse continuous lost packets to different FEC blocks, we propose a concurrent multipath transmission that combines FEC with path interleaving. Our proposed control scheme adaptively adjusts the FEC block length and concurrently sends data interleaved over multiple paths. Experimental results with our approach show improved packet loss and signal to noise ratio performance.

Estimation of packet losses due to propagation impairments: Application to TCP performance over satellite

AbstractThe transmission control protocol (TCP) is widely used to provide reliable data transmission due to its congestion and flow control mechanisms that provide reliable error recovery in higher layers. In satellite links, various atmospheric phenomena may lead to high packet loss rate (PLR) degrading the TCP throughput. Modern satellite systems operate at frequencies above 10 GHz, where rainfall is the dominant fading mechanism leading to high bit error ratio and correlated packet losses. In this paper, a mathematical analysis is presented to accurately describe the statistical properties of the packet‐error process in a dynamically varying satellite channel. The proposed method is extended to provide PLR estimations when block forward error correction (FEC) is employed. A new Markov‐based method, based on the previous analysis and adapted to the rain‐faded satellite channel, is also presented for the estimation of TCP SACK throughput and tested against simulation results. Based on the information provided by the packet‐error model, a study between the TCP performance under various FEC schemes and a proposed adaptive FEC scheme has provided indications about the superiority of the proposed model. Copyright © 2007 John Wiley & Sons, Ltd.

Performance and energy consumption analysis of 802.11 with FEC codes over wireless sensor networks

This paper expands an analytical performance model of 802.11 to accurately estimate throughput and energy demand of 802.11-based wireless sensor network (WSN) when sensor nodes employ Reed-Solomon (RS) codes, one of block forward error correction (FEC) techniques. This model evaluates these two metrics as a function of the channel bit error rate (BER) and the RS symbol size. Since the basic recovery unit of RS codes is a symbol not a bit, the symbol size affects the WSN performance even if each packet carries the same amount of FEC check bits. The larger size is more effective to recover long-lasting error bursts although it increases the computational complexity of encoding and decoding RS codes. For applying the extended model to WSNs, this paper collects traffic traces from a WSN consisting of two TIP50CM sensor nodes and measures its energy consumption for processing RS codes. Based on traces, it approximates WSN channels with Gilbert models. The computational analyses confirm that the adoption of RS codes in 802.11 significantly improves its throughput and energy efficiency of WSNs with a high BER. They also predict that the choice of an appropriate RS symbol size causes a lot of difference in throughput and power waste over short-term durations while the symbol size rarely affects the long-term average of these metrics.

무선 센서 네트워크에서 전송 효율과 에너지 소비에 대한 블록 FEC 심볼 크기 영향 분석

본 논문에서는 저속의 무선 센서 네트워크(WSN: Wireless Sensor Network)에서 블록 FEC(Forward Error Correction) 알고리즘의 심볼 크기의 변화에 따른 802.11 MAC 프로토콜의 전송 효율과 전송 에너지를 해석적으로 분석한다. 블록 FEC 알고리즘은 심볼(symbol) 단위로 오류를 복원하므로, 주어진 무선 센서 채널에서 같은 FEC 체크 비트(check bit) 량을 사용하더라도 블록 FEC 알고리즘의 오류 패킷 복원률은 블록 FEC 심볼 크기에 의존적이다. 즉, 같은 양의 FEC 체크 비트를 사용하는 경우에, 연속된 군집 오류 길이는 작으면서 군집 오류가 자주 발생하는 채널에서는 작은 FEC 심볼이, 이에 반해 군집 오류의 길이는 크고 군집 오류 개수가 작은 군집적 분포를 보이는 채널에서 큰 FEC 심볼이 효율적이다. 심볼 크기의 영향을 평가하기 위해서 본 논문에서는 센서 노드 TIP50CM을 사용하는 WSN에서 수집한 패킷 트레이스를 기반으로 WSN 채널을 Gilbert 모델로 모델링하고, 심볼 크기가 다른 RS(Reed-Solomon) 코드를 생성하고 해석하기 위한 에너지를 측정하였다. 이러한 모델링된 채널과 각 RS 코드 생성과 해석 에너지를 이용하여 FEC 심볼 크기에 따른 RS FEC 코드를 채택한 802.11 MAC 프로토콜의 전송 효율과 전송 에너지를 계산하였다. 실제 측정 데이터와 해석적으로 계산한 데이터를 결합한 계산에 의하면 비슷한 FEC 체크 비트 량을 사용하더라도 FEC 심볼 크기에 따라 전송 효율은 최대 4.2%, 그리고 소요 에너지는 최대 35%의 차이가 발생한다. This paper analytically evaluates the FEC(Forward Error Correction) symbol size's effect on the performance and energy consumption of 802.11 protocol with the block FEC algorithm over WSN(Wireless Sensor Network). Since the basic recovery unit of block FEC algorithms is symbols not bits, the FEC symbol size affects the packet correction rate even with the same amount of FEC check bits over a given WSN channel. Precisely, when the same amount of FEC check bits are allocated, the small-size symbols are effective over channels with frequent short bursts of propagation errors while the large ones are good at remedying the long rare bursts. To estimate the effect of the FEC symbol site, the paper at first models the WSN channel with Gilbert model based on real packet traces collected over TIP50CM sensor nodes and measures the energy consumed for encoding and decoding the RS (Reed-Solomon) code with various symbol sizes. Based on the WSN channel model and each RS code's energy expenditure, it analytically calculates the transmission efficiency and power consumption of 802.11 equipped with RS code. The computational analysis combined with real experimental data shows that the RS symbol size makes a difference of up to 4.2% in the transmission efficiency and 35% in energy consumption even with the same amount of FEC check bits.

Network-embedded FEC for optimum throughput of multicast packet video

Forward error correction (FEC) schemes have been proposed and used successfully for multicasting realtime video content to groups of users. Under traditional IP multicast, application-level FEC can only be implemented on an end-to-end basis between the sender and the clients. Emerging overlay and peer-to-peer (p2p) networks open the door for new paradigms of network FEC. The deployment of FEC within these emerging networks has received very little attention (if any). In this paper, we analyze and optimize the impact of network-embedded FEC (NEF) in overlay and p2p multimedia multicast networks. Under NEF, we place FEC codecs in selected intermediate nodes of a multicast tree. The NEF codecs detect and recover lost packets within FEC blocks at earlier stages before these blocks arrive at deeper intermediate nodes or at the final leaf nodes. This approach significantly reduces the probability of receiving undecodable FEC blocks. In essence, the proposed NEF codecs work as signal regenerators in a communication system and can reconstruct most of the lost data packets without requiring retransmission. We develop an optimization algorithm for the placement of NEF codecs within random multicast trees. Based on extensive H.264 video simulations, we show that this approach provides significant improvements in video quality, both visually and in terms of PSNR values.

Protocol design for scalable and reliable group rekeying

We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users.

Throughput of unslotted direct-sequence spread-spectrum multiple-access channels with block FEC coding

An analysis of unslotted random-access direct-sequence spread-spectrum multiple-access (DS/SSMA) channels with block forward error correction (FEC) coding is presented. Extending a methodology that was introduced in an earlier paper on unslotted packet code-division multiple access (CDMA) without coding, a procedure for calculating the error probability of an L-bit packet in the variable message length, FEC-coded, DS/SSMA environment is described. This procedure is then used in conjunction with appropriate flow equilibrium traffic models to compute channel throughput. Using BCH block coding as an example, the analytical model is exercised to obtain throughput versus channel traffic curves over a range of code rates, leading to an assessment of maximum achievable throughput and the associated optimum FEC code rate. The results show that the use of block FEC coding provides a significant improvement in the bandwidth-normalized channel throughput (utilization), approaching values competitive with those for comparable narrowband ALOHA channels. >