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An adaptive three-mode system based on mbox{Go-Back-N} (GBN) protocol is analyzed within this paper. An ideal mode selection procedure based on a-priori known packet error probability is defined. When packet error probability is unknown the system state transition is controlled by several system parameters. A procedure for optimal parameters selection is proposed and tested on a simulated system. The procedure is based on minimization of mean square deviation of the system throughput from the ideal one.

To mitigate spectrum scarcity, the cognitive radio (CR) paradigm has been invoked for improving the overall exploitation of the licensed spectrum by identifying and filling the free spectrum holes without degrading the transmission of primary users (PUs). Hence, we conceive a CR communication scheme, which enables a cognitive user (CU) to sense the activity of the PUs over a primary radio (PR) channel, which is exploited to transmit data using the modified Go-Back-N hybrid automatic repeat request (GBN-HARQ) protocol, when PR channel is free from the PUs. This arrangement is termed as the cognitive GBN-HARQ (CGBN-HARQ), whereby the activity of the PUs on the PR channel is modeled as a two-state Markov chain having “ ON” and “ OFF” states. However, the CU may wrongly detect the “ ON”/“ OFF” activity of the PUs in the channel, hence resulting in false-alarm or misdetection. Therefore, the two-state Markov chain is extended to four states by explicitly considering all the wrong sensing decisions. In this paper, we analytically modeled the CGBN-HARQ scheme with the aid of a discrete time markov chain (DTMC). Explicitly, an algorithm is developed for deriving all the legitimate states and for eliminating the illegitimate states, which assists us in reducing both the dimensionality of the state transition matrix and the associated computational complexity. Furthermore, based on DTMC modeling, we derive closed-form expressions for evaluating the throughput, the average packet delay, and the end-to-end packet delay of CGBN-HARQ in realistic imperfect sensing environment. The results are also validated by our simulations. Our performance results demonstrate that both the achievable throughput and the delay are significantly affected by the activity of the PUs as well as by the reliability of the PR channel and by the number of packets transmitted per time-slot (TS). To attain the maximum throughput and/or the minimum transmission delay, the number of packets transmitted within the TS should be carefully adapted based on the activity level of the PUs and on the quality of the PR channel.

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.

We propose a fountain coding aided CCSDS file-delivery protocol (FCFDP) and analyze its deferred negative acknowledgment (NAK) automatic repeat-request (ARQ) scheme. For ideal fountain codes, an expression for the expected number of retransmission spurts in the FCFDP is derived. The analytical and simulation results show that the expected number of retransmission spurts decreases with the increase of redundant packets. If there are sufficient redundant packets, the expected number of retransmission spurts is close to zero. Therefore, the delays introduced by propagation in deep space communications are dramatically reduced.

The performance of symbol-level combining (SLC) and bit-level combining (BLC) in multiple-input multiple-output (MIMO) multiple automatic repeat request (ARQ) systems is investigated. Considering the zero-forcing (ZF) detection under the assumption of perfect packet elimination for SLC, the two performance characteristics of Chase combining (CC) with SLC and BLC in MIMO multiple ARQ (MMARQ) systems are analyzed. First, the performance of a packet with the highest hybrid ARQ (HARQ) round in CC-SLC-ZF is not affected by the HARQ rounds of the other packets simultaneously sent. Second, the performance gain of CC-SLC-ZF over CC-BLC-ZF for a packet can be improved when the packets with higher HARQ rounds are simultaneously sent. The latter indicates that CC-SLC can provide an improved error performance for the packets transmitted only once when there is at least one retransmitted packet simultaneously sent. Therefore, even though incremental redundancy (IR) provides a significantly larger coding gain than CC, CC-SLC can provide a better throughput than IR-BLC as the average block error rate of a retransmitted packet approaches zero. Simulation results verify that the analyses remain valid regardless of the detection scheme and the throughput of CC-SLC at the high SNR region can be better than IR-BLC in MMARQ systems.

To improve the amount of data transmission of mars missions, a new protocol, Proximity-1 Space Link Protocol, is developed by Consultative Committee for Space Data Systems (CCSDS) in order to provide short-range communications among landers, probes and orbiting relays. The implementation and testing of the Data Link Layer (DLL) of the Proximity-1 are mainly discussed in this paper. The implementation, which consists of two Proximity-1 protocol units and one On-Board Computer (OBC), is able to start up a communication session with a remote entity, handle data exchange, and reconfigure the transceivers parameters if needed. A complete procedure of full-duplex mode is developed in this paper. And importantly, how to determine the transmission window size is focused on in order to improve the efficiency of the link and hence increase the effective data throughput. At last, a prototype of Proximity-1 is developed and verified on a FPGA platform.

Cognitive radio (CR) techniques have been proposed for improving the spectral efficiency by exploiting the temporarily unoccupied segments of the licensed spectrum, provided that the transmission of primary users (PUs) is not hampered. In this paper, we propose a cognitive Go-Back-N Hybrid Automatic Repeat reQuest (CGBN-HARQ) scheme that enables the cognitive user (CU) to opportunistically transmit data over a primary radio (PR) channel. Based on the sensing decisions by the CU, it decides about the availability of the PU's channel for its own transmission using the proposed CGBN-HARQ scheme. In addition, it enables the CR transmitter to receive feedback concerning the success/failure of its prior transmissions during the sensing and transmission phases of the time-slot (TS). A discrete time Markov chain model is invoked for the theoretical analysis of the proposed system, where we conceive an algorithm to generate all possible states of the CR transmitter. Both the throughput and delay of the CGBN-HARQ scheme is analyzed by deriving a range of closed-form formulas, which are validated by simulation results. The occupation of the channel by the PU and the reliability of the CU's channel significantly affect both the achievable throughput and the delay of the CGBN-HARQ scheme. Finally, our studies show that the number of packets transmitted within a TS should be adapted according to the communication channel for attaining the maximum throughput and the lowest average transmission delay.

We consider the problem of cross-layer resource allocation with information-theoretic secrecy for uplink transmissions in time-varying cellular wireless networks. Particularly, each node in an uplink cellular network injects two types of traffic, confidential and open at rates chosen in order to maximize a global utility function while keeping the data queues stable and meeting a constraint on the secrecy outage probability. The transmitting node only knows the distribution of channel gains. Our scheme is based on Hybrid Automatic Repeat Request (HARQ) transmission with incremental redundancy. We prove that our scheme achieves a utility, arbitrarily close to the maximum achievable. Numerical experiments are performed to verify the analytical results and to show the efficacy of the dynamic control algorithm.

In order to support reliable medium access control (MAC) layer multicast services in Broadband Wireless Access (BWA) networks, we here propose spreading codes (Cumulative ACK (CA) code and ARQ Feedback Request (AFR) code) based reliable multicast feedback scheme. The status indications based on the automatic repeat request (ARQ) mechanism are needed in some multicast services. In accordance with various wireless channel environments, we demonstrate the performance excellency of our proposed scheme with respect to required uplink resources compared with the original feedback scheme based on unicast ARQ feedback messages. In addition, we analyze packet error rate (PER) against the various wireless channel environments.

This paper addresses some specific problems of the retransmission protocols, collectively known as automatic repeat request (ARQ), which enhance the link quality overlaid on noisy channels. Because the foundation for almost all the efficient versions of ARQ such as hybrid-ARQ is the selective-repeat ARQ, this paper revisits this protocol and identifies a few key issues which affect the practical implementation. It reiterates some of the procedures described in the previous literature but suggests fine adjustments required.

Reliable data transfer speeds using underwater acoustic communication systems are limited by long propagation delays, small link data rates, and high bit error rates. We consider the practical problem of transferring a data file or data stream reliably from one half-duplex underwater node to another. In a typical automatic repeat request (ARQ) approach, a node transmits one or more packets and waits for the corresponding acknowledgments (ACKs). With long propagation delay, the long waiting time for ACKs results in low average throughput. The long propagation delay, however, presents an opportunity for two nodes to simultaneously transmit data and ACKs toward each other in a juggling-like approach, potentially reducing the average waiting time for ACKs. The approach needs to satisfy certain timing constraints, and its performance is largely dependent on the network settings and chosen parameters. Through analytical and numerical studies, we provide key insights into appropriate choice of ARQ strategies and protocol parameters under different internodal propagation delays. We show that the juggling-like ARQ (J–ARQ) provides good data streaming throughput but performs poorly for small file transfers. We propose a novel rate-less code-based J–ARQ protocol that overcomes this limitation and offers high data transfer speeds for small files in long propagation delay environments.

Network-coded (NCed) automatic repeat request (ARQ) techniques have been shown to provide significant throughput improvements over basic ARQ systems in two-way wireless systems. Most results derived so far, however, used the assumption of no extra overhead. In practical systems, NCed-ARQ requires more information exchange between base-station and end-nodes, and therefore it is crucial to study the impact of the extra-overhead on such systems. In this paper, we analyze the performance of a practical NCed-ARQ system. We assume M end-users wish to exchange information with a base-station. We derive first the average number of extra acknowledgments required to facilitate NCed-ARQ scheme. Then, we derive both downlink and uplink throughput expressions and study the tradeoff between feedback and re-transmission. Finally, we numerically optimize the throughput with respect to the number of end-users.

Wireless sensor network (WSN) is a typical kind of low-power and lossy network, in where ARQ (Automatic Repeat reQuest) schemes are often used to improve packets reliability. However, the ARQ related packets may incur significant load and consume more energy. This paper proposes a novel energy efficient ARQ protocol called ARQ+, which uses the nearest-first scheme and NAK aggregation scheme to reduce the amount and transmission hops of the ARQ related packets. Consequently, the energy consumption is significantly decreased. Theoretical analyses of ARQ+ on energy consumption, packet arrive ratio and latency are provided. Performance improvement of ARQ+ is validated by extensive simulations. They both show that ARQ+ has satisfactory energy efficiency, good packets arriving ratio and reasonable average packet delay comparing to traditional ARQ schemes.

Relay-assisted network-coding (RANC) automatic repeat request (ARQ) protocols are ARQ protocols that lever- age both opportunistic retransmission and network coding. This paper proposes an RANC ARQ protocol, called the decode-and- cooperate (DC) protocol, which can readily integrate space-time cooperation. The closed-form formulas for saturation through- put, segment delay, and buffer occupancy are derived for DC in slotted wireless relay networks. Extensive analysis and simulation results, which validate each other, confirm that compared to a stop-and-wait cooperative ARQ protocol, DC achieves significant performance gains in terms of throughput and delay.

This paper examines throughput performance, and its optimization, for lossless and truncated automatic repeat request (ARQ) schemes in Gaussian block fading channels. Specifically, ARQ, repetition redundancy, and in part also incremental redundancy-hybrid ARQ, are considered with various diversity schemes. We propose a parameterization-based method that allows (semi-)closed-form expressions, linking optimized throughput, optimal rate, and mean SNR, to be derived for any ARQ and repetition redundancy-HARQ method even when a non-parameterized closed-form does not exist. We derive numerous throughput and optimal throughput expressions for various ARQ schemes and diversity scenarios, potentially useful for benchmarking purposes or as design guidelines Refereed/Peer-reviewed

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.

The relay-assisted, network-coding (RANC) automatic repeat request (ARQ) protocols are ARQ protocols that leverage both opportunistic retransmission and network coding for wireless relay networks. This paper proposes two single-relay RANC ARQ protocols, the listen-and-supersede (LS) protocol and the hold-and-proceed (HP) protocol. LS offers a fundamental limit to any single-relay RANC ARQ protocol. HP is a simple yet efficient RANC ARQ protocol with near-zero overhead. Moreover, we analyze saturation throughput and segment delay for both LS and HP. Their performances are compared with a representative cooperative ARQ protocol, the opportunistically forwarding (OF) protocol. Through extensive analysis and simulation results, we show that HP has a performance close to LS and outperforms OF significantly.

Just about all communication systems attempt to ensure that the data gets to the other end of the link without errors. Since it is impossible to build an error-free physical layer (although some short links can get very close to error-free operation) this means there is a requirement for any packets that do arrive with errors in them to be re-transmitted. What the receiver and transmitter then do about it is the subject of this one. Protocols that guarantee to get data to the destination correctly (or inform the layer above them that the attempt has failed) are known as reliable protocols. All reliable protocols need a bi-directional communication link, as the receiver has to be able to transmit short packets (called acknowledgements) back to the transmitter, informing the transmitter whether the information has arrived correctly, or not. Since these acknowledgements (or ACKs) can be efficiently combined with those required for flow control, this function is often done at the same layers: usually the transport layer and/or the data link layer. If a packet fails to arrive, or arrives in error, the receiver can send back a negative acknowledgement (or NAK), which asks the transmitter to resend the information. This process is known as ARQ (Automatic Repeat request).

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.

In this paper, we propose a cooperative automatic repeat request (ARQ) scheme for cognitive radio networks with full duplex (FD) capability. Cognitive system takes advantage of opportunities arising during primary's ARQ retransmission rounds for transmission of data whilst cooperating with primary network at the same time. This requires self-interference cancellation as well as known interference cancellation capabilities of destination nodes in the secondary network which are achievable with recent advances in FD technology. It is shown that the proposed protocol will achieve non-trivial throughput gain for the secondary network during primary's ARQ rounds without any degradation of the primary's performance. The validity of this method has been investigated in terms of data link layer Packet Error Rate (PER) as an important and practical figure of merit. Performance of the proposed protocol is analyzed mathematically and its effectiveness is verified via simulations.

Network Coding (NC) constitutes a promising technique of improving the throughput of relay-aided networks. In this context, we propose a cross-layer design for both amplifyand- forward (AF-) and decode-and-forward two-way relaying (DF-TWR) based on the NC technique invoked for improving the achievable throughput under specific Quality of Service (QoS) requirements, such as the maximum affordable delay and error rate.We intrinsically amalgamate adaptive Analog Network Coding (ANC) and Network Coded Modulation (NCM) with truncated Automatic Repeat reQuest (ARQ) operating at the different OSI layers. At the data-link layer, we design a pair of improved NC-based ARQ strategies based on the Stop-andwait and the Selective-repeat ARQ protocols. At the physical layer, adaptive ANC/NCM are invoked based on our approximate packet error ratio (PER). We demonstrate that the adaptive ANC design can be readily amalgamated with the proposed protocols. However, adaptive NC-QAM suffers from an SNR-loss, when the transmit rates of the pair of downlink (DL) channels spanning from the relay to the pair of destinations are different. Therefore we develop a novel transmission strategy for jointly selecting the optimal constellation sizes for both of the relay-to-destination links that have to be adapted to both pair of channel conditions. Finally, we analyze the attainable throughput, demonstrating that our truncated ARQ-aided adaptive ANC/NCM schemes attain considerable throughput gains over the schemes dispensing with ARQ, whilst our proposed scheme is capable of supporting bidirectional NC scenarios.

In this paper, we consider a multiple-access broadcast channel (MABC) with ARQ feedback, in which M endusers wish to exchange messages with a central node or basestation. In this scenario, an end-user may overhear other endusers' messages prior to the re-transmission phase. We propose a new network coded (NCed)-ARQ scheme with reverse-link-assistance (RLA) that exploits this overheard information in uplink transmission to increase the downlink throughput. We derive throughput expressions for the new NCed-ARQ scheme in wireless additive white Gaussian noise with Rayleigh fading channel, which we numerically evaluate. For low/moderate SNRs, NCed-ARQ with RLA greatly improves the performance of downlink throughput.

In this paper, we are interested in the optimal redistribution of the available budget in average transmit power per packet among potential packet transmission attempts for improved Automatic Repeat reQuest (ARQ) protocol. A conventional ARQ protocol was combined in [5], with both Adaptive Modulation and Coding (AMC) and Power Control (PC) to improve spectral efficiency, while satisfying an average transmit power constraint. The optimal power level as well as the most adequate modulation and coding scheme (MCS) are jointly selected, as a function of the channel state. However, the selected power level remains the same for all retransmission attempts of the same packet. We propose in this paper to wisely distribute this optimally selected power budget among potential retransmissions of a given packet, such that throughput is further maximized, while keeping a fixed average power spent by packet. To do this, a heuristic algorithm based on a dichotomic search approach is performed. The enhancement in performance brought by the improved version of the ARQ protocol to the joint AMC-PC-ARQ scheme is then assessed.

In this paper, we propose a cognitive Go-Back-N Hybrid Automatic Repeat reQuest (CGBN-HARQ) scheme for a cognitive radio (CR) system to opportunistically transmit data over a primary radio (PR) channel. We model the activity of PR users (PRUs) occupying the PR channel as a Markov chain with two states: `ON' and `OFF'. In order to use the PR channel, the CR system first senses the availability/unavailability of the PR channel. Once it finds that the PR channel is free, the CR system transmits data packets over the PR channel's spectrum, whilst relying on the principles of GBN-HARQ. In this paper, we investigate both the throughput and delay of CGBN-HARQ, with a special emphasis on the impact of various system parameters involved in the scenarios of both perfect and imperfect spectrum sensing. Our studies demonstrate that the activity of PRUs, the transmission reliability of the CR system as well as the number of packets transmitted per time-slot may have a substantial impact on both the throughput and the delay of the CR system.

In this paper, a cooperative spectrum sharing protocol is proposed for cognitive radio networks (CRNs) which operates in underlay mode with an automatic repeat-request (ARQ)- based primary user (PU) including primary transmitter (PT) and primary receiver (PR) nodes and a bidirectionally communicating secondary user (SU) which consists of the nodes S1 and S2. In ARQ-based PU, ACKnowledgement/Negative-ACKnowledgement (ACK/NACK) messages are send from PR to PT and listened by S1 and S2 to control the PU's package achievement. PU transmits its package by accessing the spectrum alone or by cooperating with SU or under interference caused by SU. It is shown by analytical and simulation results for the throughputs of PU and SU that the proposed protocol significantly improves the PU's throughput compared to conventional non-CR model while stabilizing the secondary user throughput.

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.

Automatic repeat request (ARQ) protocols are normally studied under slow-fading or quasi-static channel assumption where the fading coefficients are assumed to remain fixed during the transmission of a codeword or for the duration of all ARQ retransmission rounds, respectively. This letter investigates the performance of basic ARQ and incremental redundancy hybrid ARQ protocols in fast-fading channels where a number of channel realizations are experienced in each retransmission round. Long-term throughput, delay-limited throughput and outage probability of the ARQ schemes are obtained. Compared to slow-fading and quasi-static channels, a fast-fading channel results in a higher performance for both basic and incremental redundancy ARQ. The fast-fading channel, however, can be mapped to an equivalent slow-fading model at low signal-to-noise ratios. Finally, we show that the efficiency of ARQ protocols is overestimated if the fast-fading variations during a codeword transmission are approximated by their average value.

This contribution analyzes the steady-state throughput of network coding nodes, when data is transmitted based on the stop-and-wait automatic repeat request (SW-ARQ) scheme. The state transition of network coding nodes employing SW-ARQ is analyzed, which shows that the operations of network coding nodes can be modeled by a finite state machine. Therefore, the throughput expressions of network coding nodes can be derived based on the properties of finite state machines. Furthermore, the throughput performance of network coding nodes is investigated either by simulations or by evaluation of the expressions obtained. It can be shown that the simulation results converge closely to the numerical results and justify the effectiveness of our analytical expressions obtained.

This work investigates the progressive linear precoder design for packet retransmissions in multi-input multi-output (MIMO) systems with multiple codewords and automatic repeat request (ARQ) bundling feedback. Assuming perfect channel state information, a novel progressive linear ARQ precoder is proposed in the perspective of minimizing the packet error rate. We devise the ARQ precoder by combining power loading and subchannel pairing between current retransmission and previous transmissions. Furthermore, we extend the design to the case that the channel estimation error exists. Numerical results show that the proposed scheme can improve the performance of MIMO ARQ systems significantly regardless of the channel estimation error.

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.

Although the wireless communication systems offer limitless possibilities of service utilization, these systems are not error free. Variable error rate of these systems is the main reason of being concerned with error control techniques. Selection of suitable error control techniques is very important and depends on performance. We can choose from three basic techniques Send-and-wait, Go-back-N and Selective repeat. Nowadays, Hybrid Automatic repeat request techniques have the best aptitude for solving the problem with error detection. The thesis deals with division and functioning of Automatic repeat request schemes. In particular, we focus on the efficiency criterions of Automatic repeat request schemes--throughput and computational complexity. These criterions are presented based on simulations for Go-back-N scheme.

In this paper, we introduce a new hybrid ARQ technique for broadcasting or multicasting in erasure channel. The system is tested according to the objective criteria--quantity of information sent by the source, loses, and number of negative acknowledgments (NACKs) sent by the receiver nodes (end nodes). We compare our proposed method with automatic repeat request (ARQ), hybrid ARQ II (HARQ II), and also with a forward error correction (FEC) transmission technique based on Reed Solomon code (RS). The main focus of the presented HARQ is to reduce the quantity of redundant information sent by the source as well as the number of NACKs sent by the receivers, maintaining the condition that all the information is being recovered successfully by the receivers.

Wireless multicasting (also called common information broadcasting) is a technique where a common information message is transmitted to multiple users. This is typically accomplished by having the basestation broadcast out a signal representing this message. In this paper, we consider a multicasting scheme where the basestation transmits the multicasting signal without any a-priori knowledge of the users' channel state information. In this set-up, a hybrid automatic repeat request (ARQ) control is employed to improve the reliability of multicasting communication. In most hybrid ARQ set-ups, each user is usually allocated a dedicated feedback channel to tell the basestation if the previously transmitted signal was correctly decoded. However, dedicated feedback channels waste significant uplink resources, especially when the number of users is large. To mitigate this problem, we consider a negative acknowledgement (NACK) based hybrid ARQ control where the failed users are allowed to transmit the NACK signal (which is assumed to be the same for all users) through a common channel while the other users remain silent. We consider the effect of feedback error and multicasting signal decoding error on our hybrid ARQ system performance as the number of users grows large. Specifically, it is shown that the throughput performance of the proposed hybrid ARQ scheme using repetition retransmission is not severely degraded relative to the throughput performance of the noiseless feedback case. In addition, we show that the performance improvement obtained by replacing repetition encoding with incremental redundancy becomes insignificant for the large number of users asymptote. On the other hand, it is shown that the improvement provided by incremental redundancy is significant when some of the users are allowed to fail to decode the message.

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.

This paper proposes a new cooperative GBN-ARQ（Go-Back-N Cooperative Automatic Repeat Request: GBN-CARQ）algorithm which is suitable for the single source and single relay wireless communication system based on TDMA, establishing the queuing model of single source and single relay wireless communication system based on TDMA and providing the expressions of its throughput and delay performance. By comparing with GBN-ARQ algorithm and normal cooperative ARQ（Cooperative ARQ：CARQ）algorithm, it is shown that GBN-CARQ algorithm has better average throughput performance.

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.

In this paper, we propose an adaptive Go-Back-N (GBN) ARQ protocol over two parallel channels with slow state transition. This proposed protocol sophisticatedly determines the order of priority of the channel usage for sending packets, by using the channel-state feedback information. We exactly analyze the throughput efficiency of the protocol and obtain its closed-form expression under the assumption that the time-varying channel is modeled by a two-state Markov chain, which is characterized by packet error rate and the decay factor. The analytical results and numerical examples show that, for a given round-trip time, the throughput efficiency depends on both the average packet-error rate and the decay factor. Furthermore, it is shown that the throughput efficiency of the proposed protocol is superior to that of the non-adaptive Go-Back-N protocol using the two channels in a fixed order in the case of slow state transition (i.e. the decay factor is positively large).

We introduce a novel packet retransmission technique which improves the efficiency of automatic retransmission query (ARQ) protocols in the context of satellite broadcast/multicast systems. The proposed coded ARQ technique, similarly to fountain coding, performs transmission of redundant packets, which are made by linear combinations of the packets composing the source block. Differently from fountain codes, the packets for the linear combinations are selected on the basis of the retransmission requests coming from the user terminals. The selection is performed in a way that, at the terminals, the source packets can be recovered iteratively by means of simple back-substitutions. This work aims at providing a simple and efficient alternative to reliable multicast protocols based on erasure correction coding techniques.