ARQ Error Control Research Articles

Energy Efficient Raptor Codes for Error Control in Wireless Body Area Networks

WBAN consists of several tiny sensors that are located inside and outside human body for continuous monitoring of vital parameters of patients suffering from chronic diseases. The wearable sensor unit consists of transmitter, receiver and central process unit (gateway). The gateway is used to connect wearable sensors on human body to the internet. To increase the lifetime of such networks, the energy spent by the sensors has to be minimized. In this work we analyzed the feasibility and performance of fountain code based raptor code for error correction to overcome the energy and reliability issues. Versatility of raptor code in terms of code rate and coding gain is advantageous to increase the energy efficiency of WBAN network. Simulation results considering different fading channels show that the raptor coded packet transmission is more energy efficient than that of LT code, traditional BCH code and ARQ error control technique.

Real-time Error Control Research Over Internet Communications

With the development of computer technology and Internet technology, more and more real-time error control principles are implemented. Based on research of error control technology, In this thesis, we implement data packet's cod- ing and decoding based on Reed-Solomon code through looking chart; and emulate the real-time error control systems that use error control methods of FEC and FEC/ARQ. Experiments results prove that coding and decoding based on Reed- Solomon code through looking chart can improve the efficiency of coding and decoding, and experiments results also validate the FEC and FEC/ ARQ error control methods, that are based on the Reed-Solomon code, have fine characteris- tics and fine real-time, and decrease the code error ratio by 5 % at least, at the same time, develop the data reliability and satisfy the QoS constraints.

Joint Source Coding and Network-Supported Distributed Error Control for Video Streaming in Wireless Multihop Networks

Real-time video communication over wireless multihop networks has gained significant interest in the last few years. In this paper, we focus our attentions on the problem of source coding and link adaptation for packetized video streaming in wireless multihop networks when network nodes are media-aware. We consider a system where source coding is employed at the video encoder by selecting the encoding mode of each individual macro-block, while error control is exercised through application-layer retransmissions at each media-aware network node. For this system model, the contribution of each communication link on the end-to-end video distortion is considered separately in order to achieve globally optimal source coding and ARQ error control. To reach the globally optimal solution, we formulate the problem of joint source and distributed error control (JSDEC) and devise a low-complexity solution algorithm based on dynamic programming. Extensive experiments have been carried out on the basis of H.264/AVC codec to demonstrate the effectiveness of the proposed algorithm over the existing joint source and channel coding (JSCC) algorithm in terms of PSNR perceived at the decoder under time-varying multihop wireless links.

PEEC: a channel-adaptive feedback-based error

Reliable transmission is a challenging task over wireless LANs since wireless links are known to be susceptible to errors. Although the current IEEE802.11 standard ARQ error control protocol performs relatively well over channels with very low bit error rates (BERs), this performance deteriorates rapidly as the BER increases. This paper investigates the problem of reliable transmission in a contention free wireless LAN and introduces a packet embedded error control (PEEC) protocol, which employs packet-embedded parity symbols instead of ARQ-based retransmission for error recovery. Specifically, depending on receiver feedback, PEEC adaptively estimates channel conditions and administers the transmission of (data and parity) symbols within a packet. This enables successful recovery of both new data and old unrecovered data from prior transmissions. In addition to theoretically analyzing PEEC, the performance of the proposed scheme is extensively analyzed over real channel traces collected on 802.11b WLANs. We compare PEEC performance with the performance of the IEEE802.il standard ARQ protocol as well as contemporary protocols such as enhanced ARQ and the hybrid ARQ/FEC. Our analysis and experimental simulations show that PEEC outperforms all three competing protocols over a wide range of actual 802.11b WLAN collected traces. Finally, the design and implementation of PEEC using an adaptive low-density-parity-check (A-LDPC) decoder is presented.

Adaptive source rate control for real-time wireless video transmission

Hybrid ARQ schemes can yield much better throughput and reliability than static FEC schemes for the transmission of data over time-varying wireless channels. However these schemes result in extra delay. They adapt to the varying channel conditions by retransmitting erroneous packets, this causes variable effective data rates for current PCS networks because the channel bandwidth is constant. Hybrid ARQ schemes are currently being proposed as the error control schemes for real-time video transmission. An important issue is how to ensure low delay while taking advantage of the high throughput and reliability that these schemes provide for. In this paper we propose an adaptive source rate control (ASRC) scheme which can work together with the hybrid ARQ error control schemes to achieve efficient transmission of real-time video with low delay and high reliability. The ASRC scheme adjusts the source rate based on the channel conditions, the transport buffer occupancy and the delay constraints. It achieves good video quality by dynamically changing both the number of the forced update (intracoded) macroblocks and the quantization scale used in a frame. The number of the forced update macroblocks used in a frame is first adjusted according to the allocated source rate. This reduces the fluctuation of the quantization scale with the change in the channel conditions during encoding so that the uniformity of the video quality is improved. The simulation results show that the proposed ASRC scheme performs very well for both slow fading and fast fading channels.

Performance of H.263 video transmission over wireless channels using hybrid ARQ

This paper proposes a hybrid ARQ error control scheme based on the concatenation of a Reed-Solomon (RS) code and a rate compatible punctured convolutional (RCPC) code for low-bit-rate video transmission over wireless channels. The concatenated hybrid ARQ scheme we propose combines the advantages of both type-I and type-II hybrid ARQ schemes. Certain error correction capability is provided in each (re)transmitted packet, and the information can be recovered from each transmission or retransmission alone if the errors are within the error correction capability (similar to type-I hybrid ARQ). The retransmitted packet contains redundancy bits which, when combined with the previous transmission, result in a more powerful RS/convolutional concatenated code to recover information if error correction fails for the individual transmissions (similar to type-II hybrid ARQ). Bit-error rate (BER) or signal-to-noise ratio (SNR) of a radio channel changes over time due to mobile movement and fading. The channel quality at any instant depends on the previous channel conditions. For the accurate analysis of the performance of the hybrid ARQ scheme, we use a multistate Markov chain (MSMC) to model the radio channel at the data packet level. We propose a method to partition the range of the received SNR into a set of states for constructing the model so that the difference between the error rate of the real radio channel and that of the MSMC model is minimized. Based on the model, we analyze the performance of the concatenated hybrid ARQ scheme. The results give valuable insight into the effects of the error protection capability in each packet, the mobile speed, and the number of retransmissions. Finally, the transmission of H.263 coded video over a wireless channel with error protection provided by the concatenated hybrid ARQ scheme is studied by means of simulations.

A comparison of trellis coded and Reed-Solomon coded hybrid-ARQ protocols over slowly fading Rayleigh channels

The performance of trellis coded and Reed-Solomon coded ARQ error control systems over slowly fading Rayleigh channels are compared and contrasted in this paper. First, a two-code CRC-TCM type-I hybrid-ARQ scheme based on separate error correction and error detection codes is compared to a one-code Reed-Solomon protocol in which retransmission requests are generated within the decoding process. The performance of the associated packet combining protocols is also compared. It is shown that for similar levels of complexity, a onecode Reed-Solomon approach offers both better throughput and reliability performance than the TCM schemes in almost all cases.

A sequential scheme for adaptive error control over slowly varying channels

Improved performance of error control techniques over slowly varying channels can be realized by a system which adapts itself to changes in the channel conditions. Such action requires a method for monitoring the channel state and detecting a change in it. The frequency of retransmission requests in ARQ and type-I hybrid-ARQ error control strategies provides a natural source of channel state information. The proposed scheme incorporates the retransmission requests into the scoring of a statistical sequential inspection scheme proposed by E. Page in 1954. Each transmitted packet is scored based on the outcome of the decoding process (i.e., whether it is accepted or rejected). When the cumulative score crosses a decision boundary, the coding strategy is altered and the sequential inspection scheme is restarted using the same scoring routine with different weighting and boundary constants. In this way the channel encoder/decoder is able to alter its strategy and adapt itself to changes in the channel. The analysis of this system is based on the average run length of the tests in the various channel states. These values indicate the delay the system experiences in reacting to a change in the channel and the tendency the test has to terminate prematurely. These factors are a function of the test constants which are determined algorithmatically by maximizing the system throughput using the system reliability as a constraint. Results show that the performance of this system is close to that of the ideal system with perfect channel state information. >

Throughput analysis of adaptive ARQ schemes

AbstractMany ARQ error control schemes have been proposed in data transmission, including go‐back‐N and selective‐repeat schemes. In those schemes, most of the parameters affecting performance, such as the number of continuously transmitted data blocks and the data block length, are fixed. Consequently, the performance may be greatly degraded when there is a time‐variation in the bit‐error rate or when the bit‐error rate is difficult to estimate. This paper proposes a control scheme wherein the number of continuously transmitted data blocks and the data block length are adapted dynamically to the bit‐error rate. The throughput of the proposed scheme is analyzed for go‐back‐N and selective‐repeat schemes using the half‐duplex channel. The evaluations for the go‐back‐N and the selective‐repeat schemes are obtained as special cases of the result of analysis. The effects of various parameters on performance are discussed and the performances of various schemes are compared. The results show that the proposed scheme based on the adaptive control has a performance which is very close to the scheme with a fixed number of continuously transmitted data blocks and fixed data block length, where those parameters are set optimally in a static way.

A Comparison of Block and Convolutional Codes in ARQ Error Control Schemes

ARQ methods of error control can considerably improve the reliablity of data transmission in such areas as satellite communications, computer networks, etc. A number of ARQ schemes using both block and convolutional codes have appeared in the literature. In this paper, the following problem is addressed. Given two different implementations of an ARQ scheme, one using a block code and the other using a convolutional code, such that the bit error probability of both implementations does not exceed some specific value, which implementation has the higher throughput and under what conditions will it be attained? The comparison is made for three basic retransmission schemes using both hybrid and pure ARQ: stop-and-wait, go-back- N , and selective repeat. Numerical estimates of the throughput were obtained using approximate theoretical expressions for BCH codes and simulation results for sequential decoding of rate 1/2 convolutional codes. Parameters optimizing the performance of both block and convolutional codes for different channel conditions and round trip delays were found and were used to obtain these numerical estimates. Comparison of the quantitative results indicates a trend toward preferring convolutional codes as delay and/or block length increases. A binary symmetric channel with noiseless feedback was assumed. Possible implications for the Gaussian channel are also discussed.

An Analysis of a TDMA Channel Using Stop-and-Wait, Block, and Select-and-Repeat ARQ Error Control

In this paper, the multiaccess broadcast communication channel operating under a TDMA control discipline and employing an ARQ scheme is examined. The generating function of the message delay distribution is derived. The effects of nonzero bit error rates on multipacket messages under several stop-and-wait and block ARQ systems are incorporated. Numerical results for the steady-state mean and variance of the message delay are presented for a stationary transmission error process model in which errors occur as independent events. Results for this channel under a select-and-repeat ARQ system are developed for single packet messages. Stability requirements are stated, useful bounds on the average message delay at steady state are derived, and numerical examples are presented.

The Analysis of Some Selective-Repeat ARQ Schemes with Finite Receiver Buffer

In high bit rate data transmission systems with ARQ error control, the throughput efficiency is a function of bit error rate, block or packet size, and the effect of significant round trip delays such as may be experienced in satellite communication systems. The selective-repeat ARQ scheme is capable of providing superior throughput performance independent of round trip delay, but requires excessively large receiver buffers; as a result the inferior GoBack <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> procedure is commonly adopted. This paper analyzes a class of mixed-mode ARQ protocol models which incorporate a selectiverepeat mode with finite receiver buffer. The protocol models are shown to be amenable to exact throughput analysis, but do assume that the round trip delay is constant and known, blocks are of constant length, and the ACK/NAK signals are returned error free. These assumptions might create difficulties for practical implementation. However, the analytical model results highlight those aspects of ARQ protocols which affect throughput performance as round trip delays increase. The results show that it is desirable for best throughput performance in practical systems that at least the first retransmission of a block following an error should be in the selective-repeat mode to obtain superior performance over GoBack <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> schemes. Furthermore, alternative secondary retransmission modes are considered which ensure that reliable transmission can be achieved without receiver buffer overflow, even if the selective-repeat mode retransmissions fail. It is shown that the choice of secondary mode does not have a significant effect on the throughput efficiency but has a bearing on complexity.

On Another Go-Back-N ARQ Technique for High Error Rate Conditions

A modification to the basic Go-Back- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> ARQ error control technique is described which yields improved throughput efficiency performance for all block error rates.