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Secure data communication is the need of hour today specifically when the wireless communication channel is insecure. We are proposing a protocol which can be customized in variety of situations. We want to use steganography as a complementary tool for cryptography. The protocol utilizes the nature of communication protocol and it is even useful for places where data hiding and cryptography is illegal or can’t be performed because of various reasons. We are giving a name to these kinds of networks as disturbed networks. The proposed peer to peer protocol is very useful for insecure channels and disturbed networks and we provide complete analysis to validate its utility. The method is a convenient stop and wait protocol which provides unbeatable security and suitable for mobile phones as well. At the same time, for intruder’s perspective, there is no encryption involved which is a very important aspect.

Today is the era of fast and dynamic internet and communication technologies which make communication convenient compared to the past. Communication technology, through different channels, such as mobile phones and computers, has become pervasive. In almost every means of telecommunication, retransmission protocols have played a significant role in the protocol stack layers. The primary aim of this study is to compare Automatic Repeat Request (ARQ) protocols and solve the Buffer problem. The first section compares ARQ protocols (Go-Back-N, selective repeat, stop and wait ARQ), using TCP and UDP. The study compares these protocols' efficiency and changes the behaviors of stop and wait protocols to selective repeat. The second section includes solving the buffer problems. The paper contains the theoretical part as well.

In this paper, a hybrid protocol is presented for improving the performance of Stop and Wait (S/W) ARQ with Aggressive Packet Combining (APC) schemes using Markov two states Model. APC protocols are not onlymimplemented to get a correct copy but also to reduce retransmission of duplicate copies. To reduce the retransmission of duplicate copies in conventional ARQ protocols, Packet Combining (PC) and APC have been studied. Thus, the proposed protocol is considered under two states of Markov model i.e., good and bad states channel. The simulation results have shown that in the long period of bad state that the proposed protocol still obtains better in probability of packet error, mean energy consumption, and packet throughput over PC and APC schemes but lower throughput than S/W ARQ.

System requirements are sometimes either too complex or undefined. Event-B is a formal modeling method and is being used increasingly to model various systems. Event-B models support atomicity decomposition and are quite useful for complex refinement structures. However, neither a Event-B model represents any explicit control flows among the events, nor does it support links between the new events during refinements. This work aims to model the Stop and Wait mechanism for an Automatic Repeat Request (ARQ) protocol to analyze the complexities due to communication errors during data re-transmissions. The limitation is the lack of control flows among the events during successive refinements. This has been graphically represented in this work and embedded with Event-B notations for the atomicity decomposition of the model. Finally, the successive refinements presented using an Event-B model, has been validated using the Rodin tool. This leads to a successful ARQ model.

International audience; In this paper, we present new adaptive automatic repeat request (ARQ) schemes for wireless broadcast/multicast combining erasure coding (EC) and packet retransmission. Traditional approaches rely on retransmitting the lost packets in a point-to-point or point-to-multipoint mode. The main idea behind the presented protocols is to retransmit adaptive combinations of the lost packets using EC, which can help several receivers to recover the lost information with fewer retransmission attempts.We propose two versions of EC-based ARQ protocols, and investigate theoretically the corresponding transmission bandwidths in different contexts. We show through simulation results the efficiency of the proposed protocols with respect to conventional ARQ strategies and new published ARQ works for broadcast/multicast. Finally, a new sliding window NACK feedback policy is presented for the case of a high number of receivers to avoid the feedback implosion problem.

This paper presents the performance of 8FSK base on PACTOR I data transfer protocol over AWGN channel. PACTOR I is a classic digital mode that once gain name in radio amateur community due to the reliability. The modulation type is always 2FSK and still been use in the latest advance modem of PACTOR 4 for robust mode. Using AWGN channel model, the throughput performance was studied base on 8FSK modulation to increase the performance. Simulation result was focus on PACTOR I basic data transfer with stop and wait ARQ type. Some parameters such as idle time and Huffman compression were not included in the calculation to focus more on modulation effect and throughput.

Due to its efficiency, reliability and better channel and resource utilization, cooperative transmission technologies have been attractive options in underwater as well as terrestrial sensor networks. Their performance can be further improved if merged with forward error correction (FEC) techniques. In this paper, we propose and analyze a retransmission protocol named Cooperative-Hybrid Automatic Repeat reQuest (C-HARQ) for underwater acoustic sensor networks, which exploits both the reliability of cooperative ARQ (CARQ) and the efficiency of incremental redundancy-hybrid ARQ (IR-HARQ) using rate-compatible punctured convolution (RCPC) codes. Extensive Monte Carlo simulations are performed to investigate the performance of the protocol, in terms of both throughput and energy efficiency. The results clearly reveal the enhancement in performance achieved by the C-HARQ protocol, which outperforms both CARQ and conventional stop and wait ARQ (S&amp, W ARQ). Further, using computer simulations, optimum values of various network parameters are estimated so as to extract the best performance out of the C-HARQ protocol.

Recently, relay technology has been adopted to enhance the coverage and performance of wireless networks such as Worldwide Interoperability for Microwave Access and Long-Term Evolution Advanced (LTE-A). However, using relays to forward packets may induce more packet losses than traditional single-hop wireless networks because transmissions are conducted through multiple radio links. When there are lost packets, relay stations (RSs) decide whether to retransmit these packets with automatic repeat request (ARQ) strategies. We observe that an improper ARQ strategy increases latency, blocked packets, and workloads on the multihop relay network. This paper proposes a new relay ARQ (RARQ) scheme, providing efficient acknowledgement to reduce packet latency and the number of blocked packets with small workloads. We also propose an analytic model to evaluate the performance of the proposed mechanism. Simulation results have validated the proposed model and demonstrated that our ARQ scheme outperforms conventional approaches.

Wireless broadband systems conceal the high error rates of their underlying channel from Internet protocols such as TCP using a windowed ARQ protocol. They also use a HARQ protocol at the physical layer where ACK/NACK feedback signals are sent for every packet. The higher layer “outer” ARQ protocol is needed due to the relatively high error rate of the HARQ feedback signals, especially NACK→ACK errors. The ARQ protocol feedback messages incur a relatively high protocol overhead but are sent relatively infrequently and corrects HARQ errors. Using a novel method of jointly coding successive HARQ feedback signals, this paper shows how NACK→ACK errors can be virtually eliminated and the outer ARQ protocol dispensed with. The method reduces protocol overhead and overall packet latency.

This paper implements file transfer between two computers based on the characters of ZigBee that it works at low cost, low rate and short distance. It introduces the design of each hardware node and software module, moreover, the ZigBee wireless network, related protocols (such as ARQ) and technique of package and unpack ensure correct data-transfer. Through experimental testing, the correct file transfer between two computers is possible in the case of a small amount of data.

An efficient cooperative Automatic Repeat reQuest (ARQ) protocol for distributed space-time coded cooperative networks is proposed in this paper. Conventional cooperative ARQ protocol just utilizes the relays which can decode the packet from the source in direct transmission. However, relays which can not receive the packet successfully have the ability to listen to the retransmission and decode the packet with high probability. Therefore, we consider to let these relays join in the next possible retransmission. We prove that the proposed cooperative ARQ protocol has a lower packet loss rate and average retransmission number than conventional ARQ protocol. Finally, the simulation results verify our theoretical results and show that the proposed ARQ protocol is suitable for the relay networks where the source node is close to the relay nodes.

The Primitive Bit Error Rate is much higher in severe electronic-magnetic environment, which results in much more retransmissions for an ARQ data transceiver; this means a lower efficiency of transmission. To cope with the above problem, this paper proposes a new mechanism, which is based on majority-voting. Through theoretical analysis and simulations, this novel approach shows better performance than those conventional ones.

We propose an efficient cooperative ARQ (Automatic Repeat reQuest) scheme for single-hop and multi-hop underwater acoustic communications, in which cooperative nodes are used to provide more reliable alternative paths for a specific source-to-destination connection. This alternative path has higher channel quality than that of the direct source-destination path. In addition, during a packet-relay through multiple hops, the typical acknowledgement (ACK) signal is replaced with overhearing data packet returned back from the next hop. The usage of overhearing as an ACK improves the system performance. In this paper, we evaluate the proposed scheme by comparing it with a conventional S&W ARQ in terms of throughput efficiency. Computer simulation results show that the proposed cooperative retransmission scheme can significantly improve the throughput by increasing the probability of successful retransmission.

In this paper, we propose an effective network-adaptive ARQ based error control scheme to provide video streaming services through IP networks where packet error usually occurs. If time delay and feedback channel are allowed, client can request server to retransmit lost packets through IP networks. However, if retransmission is unconditionally requested without considering network condition and number of simultaneous feedback messages, retransmitted packets may not arrive in a timely manner so that decoding may not occur. In the proposed ARQ, a client conditionally requests retransmission based on assumed network condition, and it further determines valid retransmission time so that effective ARQ can be applied. In order to verify the performance of the proposed adaptive ARQ based error control, NIST-Net is used to emulate packet-loss network environment. It is shown by simulations that the proposed scheme provides noticeable error resilience with significantly reduced traffics required for ARQ.

In the underwater communications, the acoustic channel is in poor communication conditions, such as long propagation delay, narrow bandwidth, and high bit-error rate. For these bad acoustic channels, we propose an efficient automatic repeat request (ARQ) for multi-hop underwater network by using the concepts of concurrent bi-directional transmission, multiple sub-packets, and overhearing data packet instead of the acknowledgement signal. Our results show that the proposed ARQ significantly reduces the transmission latency especially in high BER compared with the existing Stop and Wait ARQ.

This article presents a low coordination overhead cooperative Automatic Repeat reQuest (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. A comparison between cooperation with and without frame combiner is also performed. In channels with a strong Line of Sight (LOS) component and low Signal-to-Noise ratio (SNR), the efficiency of the proposed protocol is many times higher than for other ARQ schemes. For non-LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanism leads to results that can be even below the classical ARQ mechanism. In AWGN channels, the saturation throughput of the proposed scheme integrated into a IEEE 802.11 DCF based MAC is also studied. When the number of active stations is high, the cooperative ARQ without frame combiner shows to be the best option, while for light network loads, the presented scheme performs better.

Automatic Repeat reQuest (ARQ) is a very effective technique against transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose a new truncated ARQ strategy, called MAC service data unit-based ARQ (S-ARQ), where the finite number of opportunities for retransmissions are shared by multiple fragments out of an IP datagram. We describe how S-ARQ can be implemented in a practical system, and then propose another variant of S-ARQ employing a functionality called early detection of failure. Basically, we evaluate the performance of S-ARQ in two different manners. First, assuming i.i.d. error process, we analyze both the probability of the delivery failure and the average delay of IP datagram. Then, we assess the performance of S-ARQ via simulation over a 2-state Markov channel.

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.

In general, link-adaptive schemes, such as adaptive modulation and coding (AMC) and hybrid automatic repeat request (HARQ), enhance system capacity in time-varying wireless channels. For these link-adaptive schemes to be applied, resources have to be adaptively and dynamically allocated every frame. Thus, the system needs control messages to send information to users about dynamic resource allocation. Such information includes user ID, resource position, level of modulation, and coding and automatic repeat request (ARQ) information. However, the transmission of these resource-allocation messages causes control overhead. In this paper, we introduce a scheme that applies AMC to the transmission of resource-allocation messages and analyze its performance in systems that support truncated ARQ, such as link-layer ARQ and HARQ. In addition, we show that using AMC to transmit control messages is a good way to reduce control overhead; in particular, it is very effective when the number of users per frame is large, as in voice over Internet Protocol (VoIP) services.

In this paper, we consider a multichannel data communication system in which the stop-and-wait automatic-repeat-request protocol for parallel channels with an in-sequence delivery guarantee (MSW-ARQ-inS) is used for error control. We evaluate the resequencing delay and the resequencing buffer occupancy, respectively. Under the assumption that all channels have the same transmission rate but possibly different time-invariant error rates, we derive the probability generating function of the resequencing buffer occupancy and the probability mass function of the resequencing delay. Then, by assuming the Gilbert-Elliott model for each channel, we extend our analysis to time-varying channels. Through examples, we compute the probability mass functions of the resequencing buffer occupancy and the resequencing delay for time-invariant channels. From numerical and simulation results, we analyze trends in the mean resequencing buffer occupancy and the mean resequencing delay as functions of system parameters. We expect that the modeling technique and analytical approach used in this paper can be applied to the performance evaluation of other ARQ protocols (e.g., the selective-repeat ARQ) over multiple time-varying channels.

Traditional approaches to reliably transmit information over an error-prone network employ either forward error correction (FEC) or retransmission techniques. In this paper, we propose some network coding schemes to reduce the number of broadcast transmissions from one sender to multiple receivers. The main idea is to allow the sender to combine and retransmit the lost packets in a certain way so that with one transmission, multiple receivers are able to recover their own lost packets. For comparison, we derive a few theoretical results on the bandwidth efficiency of the proposed network coding and traditional automatic repeat-request (ARQ) schemes. Both simulations and theoretical analysis confirm the advantages of the proposed network coding schemes over the ARQ ones.

Hybrid FEC/ARQ, which is a mixture of forward error correction (FEC) and automatic repeat request (ARQ), is a well-known technique aiming for packet-loss recovery to guarantee quality of service (QoS) for real-time communications. In this paper, focusing on layered video transmission over wireless network environment, we propose a proactive retransmission scheme for hybrid FEC/ARQ. In the proposed scheme, a receiver host periodically sends probe packets to a sender host in order to check wireless channel state. If the sender host does not receive any probe packet during a pre-specified interval, it regards the wireless channel as being in burst loss state, and it proactively retransmits packets expected to be lost during the burst loss period. The buffer management associated with layered video coding is also taken into consideration. The performance of the proposed scheme is investigated by simulation. Numerical examples show that the proposed scheme transmits packets of the base layer more successfully than the conventional FEC/ARQ.

In this paper, we study the behavior of the transmitter buffer of a system working under a Stop-and-Wait retransmission protocol. The buffer at the transmitter side is modeled as a discrete-time infinite-capacity queue. The numbers of information packets entering the buffer during consecutive slots are assumed to be independent and identically distributed random variables. The packets are sent over an unreliable channel and transmission errors occur in a correlated manner. Specifically, the probability of an erroneous transmission is modulated by a two-state Markov chain. An expression is derived for the probability generating function of the buffer content. This expression is then used to derive several queue-length characteristics and the mean packet delay. Numerical examples illustrate the strong effect of error correlation on the system performance. The obtained analytical results are also compared with appropriate simulations.

The present paper proposes a scheme of combining soft handoff (HO) and beamforming in physical layer and automatic repeat request (ARQ) in link layer for improving the performance of data service in cellular CDMA. A stop and wait ARQ scheme has been assumed for data service. Joint effects of beamforming and soft handoff reduce delay, BER and increase throughput significantly. Impact of several parameters of soft handoff and beamforming on data performance has been evaluated. Both the cases of perfect and imperfect beamforming have been investigated. Effects of DOA (Direction of arrival) estimation error have also been indicated on data service.

In this correspondence, we present an efficient protocol for the delay-limited fading ARQ single relay half-duplex channel. The source is using an automatic retransmission request (ARQ) retransmission protocol to send data to the relay and the destination. When the relay is able to decode, both the relay and the source send the same data to the destination providing additional gains. The proposed protocol exploits two kinds of diversity: (1) space diversity available through the cooperative (relay) terminal, which retransmits the source's signals and (2) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (SNR) regime. Finally, we show the benefits of power control on the diversity by controlling the source's power level over the retransmission rounds.

Reliability-based hybrid ARQ (RB-HARQ) is a kind of incremental-redundancy ARQ recently introduced. In the RB-HARQ, the receiver returns both NAK signal and set of unreliable bit indices if the received sequence is not accepted. Since each unreliable bit index is determined by the bitwise posterior probability, better approximation of that probability becomes crucial as the number of retransmissions increases. Assuming the systematic code for the initial transmission, the proposed RB-HARQ scheme has the following two features: (a) the sender retransmits newly encoded and interleaved parity bits corresponding to the unreliable information bits; (b) the retransmitted parity bits as well as the initial received sequence are put all together to perform the message passing decoding i.e. the suboptimal MAP decoding. Finally, simulation results are shown to evaluate the above two features.

Bluetooth's default automatic repeat request (ARQ) scheme is not suited to video distribution resulting in missed display and decoded deadlines. Adaptive ARQ with active discard of expired packets from the send buffer is an alternative approach. However, even with the addition of cross-layer adaptation to picture-type packet importance, ARQ is not ideal in conditions of a deteriorating RF channel. The paper presents fuzzy logic control of ARQ, based on send buffer fullness and the head-of-line packet's deadline. The advantage of the fuzzy logic approach, which also scales its output according to picture type importance, is that the impact of delay can be directly introduced to the model, causing retransmissions to be reduced compared to all other schemes. The scheme considers both the delay constraints of the video stream and at the same time avoids send buffer overflow. Tests explore a variety of Bluetooth send buffer sizes and channel conditions. For adverse channel conditions and buffer size, the tests show an improvement of at least 4 dB in video quality compared to nonfuzzy schemes. The scheme can be applied to any codec with I-, P-, and (possibly) B-slices by inspection of packet headers without the need for encoder intervention.

In this chapter we analyze the performance of data link protocols. We consider Stop and Wait ARQ and Sliding Window protocol. In Sliding window protocol, we consider Selective Reject ARQ and Go-Back-N ARQ. There are existing results that analyze the link utilization of these protocols in the presence of error. We have experimented in a somewhat more generalized framework. We have also analyzed and experimented with the number of duplicate error-free packets that will be transmitted.

Real-time applications over wireless networks often suffers from jitter, delay and packet loss. The traditional techniques for error control are FEC (Forward Error Correction) and ARQ (Automatic Repeat Request). In this paper a hybrid FEC/ARQ mechanisms with limiting the slots number between the loss of the last retransmission of the original block n and the reception of block n + φ is analyzed in an environment of real time applications. We assume that the packet size increases when adding redundancy so that the amount of useful information contained in a packet is unchanged. We evalute analytically the performance of TFRC (TCP Friendly Rate Control) and ARC (Analytical Rate Control Protocol) as a function of the parameters of the FEC scheme, the limit number of retransmission used by ARQ scheme and the number of slots threshold Sth. We show that the combination of FEC and ARQ with limiting the Sth reduces the number of retransmissions and keeps a reasonable delay for real time traffic in wireless networks.

This paper proposes frame length optimization for wireless local area networks (WLANs) using an in-band full-duplex system that enables a WLAN access point and stations to transmit and receive frames at the same time on the same frequency channel. In in-band full-duplex WLANs, a primary sender which captures the channel transmits a frame to the intended receiver called a secondary sender and then the secondary sender transmits a frame reacting to the primary sender's transmission. The difference of time length of frames transmitted by the primary sender and the secondary sender wastes the frequency channel where more frames could be transmitted. The wasted time decreases the system throughput performance of the in-band full-duplex system. In order to solve this problem, we propose a scheme where the secondary sender adjusts the length of its frame to the length of the primary sender's frame by selecting frames used for frame aggregation properly. We evaluate the average delay, the average wasted time and the system throughput performance by computer simulations. The simulation results show that the proposed optimization reduces the delay by 49%, reduces the wasted time by 99.9% and improves the system throughput performance by 15% when the traffic is saturated.

The loss recovery techniques ARQ and error correction coding mechanisms have some drawbacks. By combining these proactive and reactive techniques, we can design a hybrid loss recovery technique which will achieve better performance. In this paper, a hybrid loss recovery technique is proposed for multipath routing. The sender initiates encoding process using partial network coding and then forwards the coded data to intermediate nodes for re-encoding. After reprocessing the encoding packets, the intermediate nodes forward those packets to the receiver for decoding operations without the need of all encoded packets. Suppose if the proactive mechanism fails to help all receivers to recover the lost packet reactive mechanism is used that consisting of Automatic Repeat Request (ARQ) protocol, which use, retransmission mechanism for those packets are lost by sending ACK from the receiver to sender. By simulation results, we show that the proposed protocol reduces the packet drop and delay with improved throughput.

This paper investigates ARQ (Automatic Repeat request) designs for PNC (Physical-layer Network Coding) systems. We have previously found that, besides TWRC (Two-Way Relay Channel) operated on the principle of PNC, there are many other PNC building blocks--building blocks are simple small network structures that can be used to construct a large network. In some of these PNC building blocks, receivers can obtain side information through overhearing. Although such overheard information is not the target information that the receivers desire, the receivers can exploit the overheard information together with a network-coded packet received to obtain a desired native packet. This leads to throughput gain. Our previous study, however, assumed what is sent always get received. In practice, that is not the case. Error control is needed to ensure reliable communication. This paper focuses on the use of ARQ to ensure reliable PNC communication. The availability of overheard Information and its potential exploitation make the ARQ design of a network-coded system different from that of a non-network-coded system. In this paper, we lay out the fundamental considerations for such ARQ design: 1) We address how to track the stored coded packets and overheard packets to increase the chance of packet extraction, and derive the throughput gain achieved by tracking 2) We investigate two variations of PNC ARQ, coupled and non-coupled ARQs, and prove that non-coupled ARQ is more efficient; 3) We show how to optimize parameters in PNC ARQ--specifically the window size and ACK frequency--to minimize the throughput degradation caused by ACK feedback overhead and wasteful retransmissions due to lost ACK., Comment: 34 pages, 6 figures, 10 Tables,Technical Report

This paper shows that the SW and GBN retransmission protocols must be generalized when used in a multichannel communications system. The generalization takes the form of packet-to-channel assignment rules. A general condition governing the packet-to-channel assignment rule is derived and important special cases are identified. Simulation results were used to demonstrate that 1) packet-to-channel assignment impacts channel utilization when the channels are different and 2) the optimal assignment rule produces a channel utilization that is better than the channel utilization that results from doing something else or nothing at all

A novel Automatic repeat ReQuest (ARQ) protocol called cooperative ARQ is presented in this letter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source terminal. The data link layer Packet Error Rate (PER) performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the source-destination channel, the new protocol outperforms the traditional one as long as the average SNR of the relay-destination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.

Indoor infrared links are anticipated to reach 100Mbit/s or even higher data rates in the future. At this high data rate, the existing Go-Back-N automatic repeat request (ARQ) scheme requires window and frame size adaptation to the corresponding optimum values for the correspondent Bit Error Rate (BER). But adaptive approaches always add a significant amount of complexity to the system. The aim of this paper is to present a new Automatic Repeat Request (ARQ) scheme, Block Window Retransmission (BWR) ARQ scheme, for achieving higher throughput efficiency over a wide range of BERs without adaptation of parameters. Simulation results show that it significantly outperforms the existing Go-Back-N ARQ scheme for next generation high speed IrDA links. We also examine the effect of window size, frame data length and minimum turn around time on the performance of the BWR ARQ scheme.

Adaptive bounded computational and memory requirements for a Viterbi decoder can be achieved using an error trapping Viterbi decoder algorithm initially develop for hybrid automatic repeat request (ARQ) implementations. Partial path metrics and a sliding window are used to eliminate unreliable paths in the decoder trellis thus reducing the computational and memory requirements. An ARQ is issued if all paths are eliminated. The algorithm is adaptive allowing the receiver to dynamically allocate memory and processing, to improve reliability or received packets, or to reject packets with lower reliability to avoid buffer overruns. The result is the ability to trade off resources versus delay and throughput.

This paper proposes a multi-stages hybrid ARQ/FEC scheme with frame skipping, reference frame selecting and intra-frame refreshing techniques for H.26L real-time video streaming over WLAN. In this paper, adaptive ARQ/FEC is adopted to save unnecessary FEC overhead; conditional frame skipping is adopted to avoid ETE delay inflation due to MAC ARQ/FEC error recovery; reference frame selecting is adopted to save bandwidth; intra-frame refreshing is adopted to prevent residual error propagation among consecutive frames. Through analysis and simulation, we show that multi-stages hybrid ARQ scheme has the following key properties: (1) high error recovery rate for real-time video frames, (2) excellent sea/ability, (3) high transmission efficiency. In case of severe unreliable channel, which causes losing a lot of IP packets, we obtain a peak signal-to-noise ratio improvement up to about 10 dB compared to the hybrid ARQ proposed in [A. Majumdar et al., June 2002].

Infrared wireless LANs may employ repetition rate (RR) coding to increase the symbol capture probability at the receiver. This paper examines the effectiveness of RR coding to utilization for infrared LANs using the physical and link layer parameter values proposed in the Advanced Infrared (AIr) protocol standard, which is developed by the Infrared Data Association (IrDA). Infrared LANs employ a Go-Back-N (GBN) automatic repeat request (ARQ) retransmission scheme at the Link Control (LC) layer to ensure reliable information transfer. To efficiently implement RR coding, the receiver may return after every DATA packet a suggestion for the suitable RR value to be used by the transmitter and implement a Stop-and-Wait (SW) ARQ scheme at the medium access control (MAC) layer. The effectiveness of employing this optional SW ARQ scheme at the MAC layer is discussed. Analytical models for the ARQ retransmission schemes are developed and employed to compare protocol utilization for different link parameter values such as window size, packet length and LC time out periods. This analysis identifies the ARQ protocol that maximizes performance for the specific link quality and the implemented link layer parameters. The effectiveness of the proposed RR coding to LAN utilization for different ARQ scheme implementation is finally explored. This analysis identifies the link quality level at which RR should be adjusted for maximum performance. It is concluded that if the packet error rate is higher than 0.1–0.4 (depending on the implemented ARQ protocol), the receiver should advise the transmitter to double the implemented RR for maximum performance. These error rate values are high and can be effectively estimated by the transmitter based on packet retransmissions. Thus, the usefulness of the receiver indicating to the transmitter to adjust RR is questionable, as the transmitter can effectively implement the suitable RR value based on packet retransmissions. Copyright © 2003 John Wiley & Sons, Ltd.

An Automatic Repeat Request (ARQ) scheme is proposed for a wireless ATM LAN based on the MEDIAN concept. Simulations have been performed to demonstrate the consequences of ARQ inclusion in terms of required buffer capacity and resulting cell end-to-end delay. In particular, the behaviour of the ARQ-enhanced system for real-time traffic under non error-free conditions has been examined. The main result of the simulations is that, due to specific properties of the MEDIAN wireless ATM LAN, the proposed ARQ scheme is suitable for real-time ATM services, while yielding virtually error-free links. Next to low cell delay, it features low overhead and low processing complexity whereas it can be readily combined with a simple and efficient MAC scheme.

The maximal number of transmission attempts in automatic repeat request (ARQ) schemes is a positive integer, thus constraining decision space in all optimization problems where it is involved. Motivated by this fact we develop a new retransmission scheme, rARQ, and introduce the expected value of maximal number of allowed transmission attempts as a decision variable, which in rARQ is a non-negative real number. Packet-loss probability and the expected number of transmission attempts are compared for an example of rARQ and traditional ARQ scheme. The analysis shows that ARQ is a subset of rARQ and that rARQ improves decision space resolution from positive integers to non-negative real numbers.

In the 4G communications standards, including Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), Automatic Repeat reQuest (ARQ) is one of the important tools to coop with error-prone transmission environments. The primary function of ARQ is to provide reliable communication between a transmitter and its receivers through the retransmission of lost ARQ blocks. The retransmission at the sender can be triggered by either of the two events. The first one is for the sender to retransmit an ARQ block whose retry timer expires. The second one is when the transmitter receives the feedback message reports, which indicate block reception situation from the receiver, the flagged lost ARQ blocks will then be sent again. There are four types of feedback messages defined in the WiMAX standard. How and when the receiver reports feedback messages will have impact on the transmission efficiency. If the receiver reports feedback messages more frequently, the lost ARQ blocks can be retransmitted more promptly at the cost of higher bandwidth consumption of the feedback channel. By contrast, if the receiver waits for a longer time before sending a feedback message, feedback messages can be formed more efficiently in terms of bandwidth usage with longer transmission time incurred. In this paper, a performance evaluation metric is defined to consider the influence of both transmission latency and the required bandwidth to transmit feedback messages. A feedback message transmission scheme is further proposed to determine the interval and the types of feedback messages dynamically, based on the condition of channel conditions. The proposed method is aimed to find a balance between the transmission delay and the bandwidth usage efficiently, and the improvement of the proposed method is confirmed by the experiment results.

In wide area Wireless Sensor Networks, end-to-end ARQ (Automatic Repeat reQuest) may incur frequent retransmissions and significant energy consumption due to packet loss in multi-hop routes. On the other hand, hop-by-hop ARQ requires each node to be equipped with sufficient buffer and energy for data caching and retransmission, which is not always practical in wide area networks. To achieve a balance between communication reliability and resource consumption, this paper proposes a novel Channel Aware Stage ARQ (CASA), which divides the multi-hop route into several ARQ segments according to the channel quality. Each ARQ segment implements packet confirmation and retransmission separately. Comparing to traditional ARQ schemes, CASA achieves required reliability with reduced network cost and energy consumption. Extensive simulation validated the performance of CASA.

In this letter, we propose an automatic repeat request (ARQ) protocol for the amplify-and-forward (AF) based two-way relay system. In the proposed ARQ scheme, the ARQ process is carried out by the relay node (RN). We assume that the RN has one buffer and it can store the signals received. With the help of the buffer, the RN can combine the signals received from different slots and choose to transmit or receive adaptively. Two combining methods, namely the maximal sum signal-to-noise ratio combining (MSC) scheme and the maximal minimum signal-to-noise ratio combining (MMC) scheme, are proposed, which are shown to improve the reliability of the relaying systems. Accepted version

In Computer and Data communication network, error Is controlled by the basic three ARQ techniques that are Stop and Wait ARQ, Go-Back-N ARQ and Selective Repeat Request ARQ. One of the important measures of peformance of the techniques Is throughput. In order to achieve higher throughput, a number of modifications of basic ARQ techniques are suggested In literature those include Sastry's modification, Morris's modification, Weidon's modification and recent Chakraborty's modification. In this paper a thorough review of the techniques have been done. Based on the critical review, we have suggested four important modifications that lead to achieve higher throughput and to tackle the dynamic channel and the error of feedback path.

This paper describes the construction and performance evaluation of a mobile video communication system composed of an H.263 video encoder, decoder, and RF transceiver equipment. It can establish a video connection using a 32 kbits/s wireless channel because it uses automatic repeat request (ARQ) as the error control scheme. Retransmission control can produce excessive transmission delay, but the improved ARQ protocol and coding-rate control scheme adopted by this system minimizes the delay. This ARQ protocol uses short ARQ frame length and an acknowledgement/negative acknowledgement (ACK/NAK) indicator. The coding-rate control scheme uses backward NAK signals to reduce the coding rate of the video encoder as necessary. We measure the transmission delay characteristics of this video system and confirm that the proposed scheme can reduce the delay over a noisy channel. Subjective assessment tests involving videophone usage are also conducted. Test results show that in a noisy channel (BER=3/spl times/10/sup -3/), this system can achieve the same mean opinion store as in a noiseless channel.

We present a throughput analysis for the memory automatic repeat request (ARQ) schemes with self-decodable frame retransmissions, taking into account frame header and frame acknowledgment failure probability. A lower bound on the throughput is obtained for a very general class of schemes which encompasses many of those proposed in the literature. Numerical results are given for several example systems, and suitable header and acknowledgment forward error correction (FEC) encodings are determined.

We propose a progressively reliable transport protocol for delivery of delay-sensitive multimedia over Internet connections with wireless access links. The protocol, termed "Leaky" ARQ, initially permits corrupt packets to be leaked to the receiving application and then uses retransmissions to progressively refine the quality of subsequent packet versions. A Web server would employ Leaky ARQ to quickly deliver a possibly corrupt first version of an image over a noisy bandlimited wireless link for immediate display by a Web browser. Later, Leaky ARQ's retransmissions would enable the browser to eventually display a cleaner image. Forwarding and displaying corrupt error-tolerant image data: (1) lowers the perceptual delay compared to fully reliable packet delivery, and (2) can be shown to produce images with lower distortion than aggressively compressed images when the delay budget only permits weak forward error correction. Leaky ARQ supports delaying of re-transmissions, so that initial packet transmissions can be expedited, and cancelling of retransmissions associated with "out-of-date" data. Leaky ARQ can be parametrized to partially retransmit audio and video. We propose to implement Leaky ARQ by modifying Type-II Hybrid/"code combining" ARQ.

For pt.I see ibid., vol.46, no.1, p.41-51, 1998. A "postponed retransmission" (PR) modification to both go-back-N (GBN) and ideal selective repeat (ISR) automatic-repeat-request (ARQ) is discussed and analyzed. A scheme for reducing the number of states involved in the calculation for multiplexed GBN ARQ is also presented. Numerical results are then shown for stop-and-wait (SW), GBN, and selective repeat (SR) ARQ (as well as the PR modified versions), under both round-robin and adaptive multiplexing.