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Recent years have witnessed a growing interest in Internet access from space assisted by low earth orbit (LEO) satellite networks. In the domain of the last-mile access for the Internet of Vehicles (IoV), hybrid free-space optical (FSO)/radio-frequency (RF) communication has recently attracted worldwide research efforts. While the transmission control protocol (TCP) is the most widely deployed transport protocol on the Internet, its performance in the error-prone environment of LEO satellite-assisted hybrid FSO/RF vehicular networks is not well understood. This paper develops a comprehensive analytical model based on the cross-layer approach for TCP performance, considering the FSO and RF satellite fading channels, modeled by the Gamma-Gamma and Nakagami- $m$ distributions, respectively. The error-control solutions, including the Reed-Solomon (RS) code and Selective repeat automatic repeat request (SR-ARQ), are also employed. Numerical results quantitatively demonstrate the impact of transmission errors at last-mile links and different parameters/settings of error-control solutions on the TCP performance. The paper also supports the selection of proper TCP variants for the considered networks.

The 5th generation mobile networks (5G) and mobile edge computing (MEC) hold great promises of enabling new capabilities in the industrial Internet of Things. However, the system designs enabled by the 5G ultra-reliable low-latency communication (URLLC) and MEC paradigms come with challenges. In this paper, the system characteristics of the generic industrial fault diagnostics and detection (FDD) applications are first discussed. Then, the proposed system model and a new measure for the FDD task execution efficiency in the communication-edge-computing (CEC) loop are presented. Based on the proposed measure, a new reliable uplink scheme “ReFlexUp” is proposed for achieving an optimal FDD task execution efficiency. Based on the numerical results, the proposed scheme outperforms the typical schemes such as Selective Repeat ARQ, Hybrid ARQ, and Occupy CoW in terms of latency, reliability, and efficiency., 2020 IEEE International Systems Conference (SysCon), August 24 - September 20, 2020, Montreal, QC, Canada

The fifth-generation (5G) wireless network technologies and mobile-edge computing (MEC) provide great promises of enabling new capabilities for the industrial Internet of Things (IoT). However, the solutions enabled by the 5G ultrareliable low-latency communication (URLLC) paradigm come with challenges, where URLLC alone does not necessarily guarantee the efficient execution of time-critical fault detection and diagnostics (FDD) applications. Based on the Tennessee Eastman (TE) process model, we propose the concept of the communication-edge-computing (CEC) loop and a system model for evaluating the efficiency of FDD applications. We then formulate an optimization problem for achieving the defined CEC efficiency and discuss some typical solutions to the generic CEC-based FDD services (FDDS) and propose a new uplink (UL)-based communication protocol called “ReFlexUp.” From the performance analysis and numerical results, the proposed ReFlexUp protocol shows its effectiveness compared to the typical protocols, such as Selective Repeat automatic repeat request (ARQ), hybrid ARQ (HARQ), and “Occupy CoW” in terms of the key metrics, such as latency, reliability, and efficiency. These results are further convinced from the mmWave-based simulations in a typical 5G MEC-based implementation.

Modern mobile networks in the era of 5G have ambitious performance goals. One envisioned goal is to have communication that is ultra-reliable and ultra-low latency (uRLLC). To ensure reliability, Automatic Repeat Request (ARQ) processes are usually deployed, sometimes combined with forward error correction. As an evolution of the Long Term Evolution (LTE) system, 5G may be foreseen to use similar methods, and so we assume LTE’s Hybrid ARQ on the Medium Access Control (MAC) layer, and a Selective Repeat ARQ on the Radio Link Control (RLC) layer. Simulation of LTE systems is a time-consuming endeavor due to its complexity, and when latency and reliability are the key performance indicators, it may be preferable to isolate the ARQ processes. In this manner, this paper presents a mathematical model of the two stacked ARQ processes that are used in today’s LTE system. It is based on the method of Signal Flow Graphs (SFGs) and allows the analysis of either ARQ process in isolation, and of both stacked on top of each other. Analytic results are shown for a realistic set of parameters, and in the spirit of Open Science, the MATLAB implementation files are made available in the conclusion to interested researchers, so that verification and an adaption to similar ARQ processes is easily made.

Nowadays, Machine-to-Machine and Internet of Things traffic sources puts the terrestrial networks under great pressure. While 5G is still on its way, satellites are used to deliver a fraction of such an enormous traffic rate. In this work, we investigate the use of the Constrained Application Protocol (CoAP) to reliably deliver Machine-to-Machine and Internet of Things traffic in a push fashion, which also implements a Selective Repeat Automatic Repeat reQuest and a sender-based variant of the TCP Friendly Rate Control protocol. We aim at providing an analytical model to evaluate the working point of the system in non-saturated conditions as a function of the MAC parameters in use, when such a closed-loop congestion control mechanism is in use over a random access satellite channel. The proposed analytical model is then validated against simulation results, showing a good precision.

In this paper, two novel automatic-repeat-request (ARQ) based protocols are proposed, which exploit coopera- tion opportunity inherent in secondary retransmission to cre- ate access opportunities. If the signal was not decoded cor- rectly by destination, another user can be acted as a relay to reduce retransmission rounds by relaying the signal. For comparison, we also propose a Direct ARQ Protocol. Specif- ically, we derive the exact closed-form outage probability of three protocols, which provides an effective means to evalu- ate the effects of several parameters. Moreover, we propose a new metric to evaluate the performance improvement for cognitive networks. Finally, Monte Carlo simulations were presented to validate the theory analysis, and a comparison is made among the three protocols.

We consider the well-known Sliding Window Protocol which provides reliable and efficient transmission of data over unreliable channels. A formal proof of correctness for this protocol faces substantial difficulties caused by a high degree of parallelism which creates a significant potential for errors. Here we consider a version of the protocol that is based on selective repeat of frames. The specification of the protocol by a state machine and its safety property are represented in the language of the verification system PVS. Using the PVS system, we give an interactive proof of this property of the Sliding Window Protocol.

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.

An efficient combination of repetitive coded L-PPM with an ARQ protocol is presented which can estimate the channel state and adjust the link transmission rate. The protocol operation is modelled as a Markov chain and analysis results indicate the enhanced performance of the proposed scheme under adverse channel conditions.

Fifth generation (5G) wireless systems will provide connectivity for a wide range of new applications with diverse requirements. In part, the network needs to support ultra-reliable communications with low-latency (URLLC) for mission-critical applications. For these applications, the generated data should be delivered with a limited number of transmission attempts with high success probability. This paper considers the optimal transmission and resource allocations for URLLC in cellular systems. The resource allocations are derived for the fixed and adaptive transmission attempt assignments. The analysis results reveal that both fixed and adaptive transmission assignments, applicable to automatic repeat request (ARQ) and hybrid ARQ (HARQ) schemes, can reduce the required resources compared to the equal transmission assignment.

This paper proposes a new retransmission scheme for achieving high-speed transmission by reducing the retransmission delay time caused by packet loss. High-speed data packet transmission can be realized by sending user datagram protocol (UDP) packets continuously over long-distance wireless systems. The UDP characterizes connectionless communication, requiring the use of a retransmission scheme for reliable quality. However, the transmission speed will reduce with repeated retransmissions over time. The key advantage of the proposed scheme is that the retransmission waiting time can be dramatically reduced by transmitting data packets in descending order from the last data packet. It is verified via a computer simulation that the average peer-to-peer network configuration receiving time can be approximately halved and a 20% improvement in throughput with a packet error rate of 0.1 can be achieved by the proposed scheme.

The adoption of satellite systems in providing broadband transmissions to mobile users such as trains, buses and vans is expected to be an interesting solution. The scenariowe considered refers to a hybrid network architecture, where a geostationary satellite forward link and a terrestrial 3G return link are used in order to exploit both the high bandwidth of a satellite channel and the lower propagation delay of a terrestrial path. The resulting round-trip delay is much shorter than that one experienced by using both the forward and return link via satellite. This is particularly appealing for overcoming the TCP efficiency degradation in high delay-bandwidth product and error prone channels. In this hybrid scenario, we used simulation results to compare the goodput of four of the most popular TCP variants, in the presence of a GOOD-BAD satellite channel, as the one experienced by mobile users. We applied an AdaptiveCoding and Modulation (ACM) technique as well, and studied its impact on TCP efficiency, when used both alone and in cooperation with an Automatic Repeat reQuest (ARQ) scheme of the Selective Repeat (SR) type with low persistency. Results obtained indicate that this hybrid architecture is advantageous for TCP transmissions in terms of average goodput, and that ACM is effective only if it is jointly used with ARQ schemes.

Various Automatic Repeat Request (ARQ) schemes have been used to combat errors that befall information transmitted in digital communication systems. Such schemes include simple ARQ, mixed mode ARQ and Hybrid ARQ (HARQ). In this study we introduce extended ARQ schemes and derive expressions for their throughput performance. We then compare their performance with mixed mode ARQ schemes where it is shown that extended ARQ schemes outperform the mixed mode ARQ schemes. We also show how the parameters for the schemes can be chosen to maximize performance. Keywords : ARQ, extended ARQ, HARQ, mixed mode ARQ, throughput

In wireless sensor networks, cooperative communication can combat the effects of channel fading by exploiting diversity gain achieved via cooperation communication among the relay nodes. A cooperative automatic retransmission request (ARQ) protocol based on two-relay node selection was proposed in this paper. A novel discrete time Markov chain model in order to analyze the throughput and energy efficiency was built, and system throughput and energy efficiency performance of proposed protocol and traditional ARQ protocol were studied based on such model. The numerical results reveal that the throughput and energy efficiency of the proposed protocol could perform better when compared with the traditional ARQ protocol.

International audience; A new coding mechanism is provided to automatically detect and recover lost packets in wireless lossy networks. Contrary to the majority of automatic repeat request (ARQ) algorithms relying on acknowledgment, our mechanism extracts feedback on packet delivery by analyzing received network coded messages and automatically reacts when packet loss is sensed. Compared to traditional end-to-end ARQ, our proposed mechanism shows significant reduction in the number of transmissions required to exchange the same amount of data.

Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission technique for high-data-rate wireless broadband systems, capable of coping with highly dispersive channels at the uplink. Packet combining (PC) ARQ with an iterative block decision feedback equalization (IB-DFE) technique can be used to cope with errors. However, extracting the IB-DFE's packet error rate (PER) for MAC-layer simulations can be time consuming. Most works that model the DS-CDMA behavior with PC ARQ use simplified asymptotic PER models in the study of the system performance, which are not precise for low signal-to-noise ratios and for a low number of mobile terminals (MTs). In this paper, the MAC performance is modeled using a discrete-time Markov chain that relies on a PER model. As an example, this paper describes a PER analytical model for an uncoded prefix-assisted DS-CDMA system with PC ARQ that considers the following inputs: the number of MTs accessing the channel, the MTs' number of transmissions, and the channel realizations for a given bit energy over noise ratio. The results show that the model portrays with better accuracy the simulations' results, compared with an alternative asymptotic model.

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.

International audience; In this paper, we propose a cross-layer analytical model for the study of Network Coding (NC)- based Automatic Repeat reQuest (ARQ) Medium Access Control (MAC) protocols in correlated slow faded (shadowed) environments, where two end nodes are assisted by a cluster of relays to exchange data packets. The goal of our work is threefold: i) to provide general Physical (PHY) layer theoretical expressions for estimating crucial network parameters (i.e., network outage probability and expected size of the active relay set), applicable in two-way communications, ii) to demonstrate how these expressions are incorporated in theoretical models of the upper layers (i.e., MAC), and iii) to study the performance of a recently proposed NC-aided Cooperative ARQ (NCCARQ) MAC protocol under correlated shadowing conditions. Extensive Monte Carlo experiments have been carried out to validate the efficiency of the developed analytical model and to investigate the realistic performance of NCCARQ. Our results indicate that the number of active relays is independent of the shadowing correlation in the wireless links and reveal intriguing trade-offs between throughput and energy efficiency, highlighting the importance of cross-layer approaches for the assessment of cooperative MAC protocols.

Conference of 2014 IEEE International Conference on Communications Workshops, ICC 2014 ; Conference Date: 10 June 2014 Through 14 June 2014; Conference Code:107217; International audience; Small cell overlay combined with unitary frequency reuse is one of the most promising deployment options to satisfy the ever increasing rate demand in beyond 4G cellular networks. It has been shown that cooperation between small base stations and macro base stations has a great potential in these hierarchical deployments. However, a significant number of cooperation strategies require that small base stations be reached through low latency and high speed backhaul links. The latency of this backhaul is often an obstacle to efficient cooperation between macro cell and small cell layers. To answer this problem we provide a protocol based on hybrid ARQ procedure combined with a parsimonious use of over-the-air communications between small base stations and macro base stations. The proposed protocol is compatible with latency figures that are observed on affordable digital subscriber links. The performance of this protocol are assessed and compared to conventional LTE hybrid ARQ strategy using theoretical derivations and numerical experiments. Significant gains are observed on the reverse links in 3GPP LTE context.

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

This paper studies the effect of optimal power allocation on the performance of communication systems utilizing automatic repeat request (ARQ). Considering Type-I ARQ, the problem is cast as the minimization of the outage probability subject to an average power constraint. The analysis is based on some recent results on the achievable rates of finite-length codes and we investigate the effect of codewords length on the performance of ARQ-based systems. We show that the performance of ARQ protocols is (almost) insensitive to the length of the codewords, for codewords of length $\ge 50$ channel uses. Also, optimal power allocation improves the power efficiency of the ARQ-based systems substantially. For instance, consider a Rayleigh fading channel, codewords of rate 1 nats-per-channel-use and outage probability $10^{-3}.$ Then, with a maximum of 2 and 3 transmissions, the implementation of power-adaptive ARQ reduces the average power, compared to the open-loop communication setup, by 17 and 23 dB, respectively, a result which is (almost) independent of the codewords length. Also, optimal power allocation increases the diversity gain of the ARQ protocols considerably., Accepted for publication in GLOBECOM 2014

This paper introduces a novel technique for access by a cognitive Secondary User (SU) to a spectrum with an incumbent Primary User (PU), which uses Type-I Hybrid ARQ. The technique allows the SU to perform selective retransmissions of previously corrupted SU data packets. The temporal redundancy introduced by the primary ARQ protocol and by the selective SU retransmission process can be exploited by the SU receiver to perform Interference Cancellation (IC) over the entire interference pattern, thus creating a "clean" channel for the decoding of the concurrent message. The chain decoding technique, initiated by a successful decoding operation of a SU or PU message, consists in the iterative application of IC, as previously corrupted messages become decodable. Based on this scheme, we design an optimal policy that maximizes the SU throughput under a constraint on the average long-term PU throughput degradation. We show that the optimal policy can be found by first optimizing the SU access policy using a Markov Decision Process formulation, and then applying a chain decoding protocol defined by five basic rules. Such an approach enables a compact state representation of the protocol, and its efficient numerical optimization. Finally, we show by numerical results the throughput benefit of the proposed technique.

Many papers analyze selective repeat automatic repeat request schemes by means of a Markov chain representation for the channel and, by extension, the whole transmission system. This Markov approach precisely characterizes the queueing behavior and the statistics of several delay terms. In the vast majority of the investigations, the round-trip time of the channel, which determines the instant of reception of the feedback from the receiver, is taken as a fixed value. This letter explores the relaxation of this assumption, still framing the system within a Markov chain. The main conclusion is that the impact of a variable round trip time on the delay statistics is rather limited. The used approach can be promptly applied to any similar analysis of retransmission-based error control systems.

In this paper we derive performance metrics closed-form expressions of retransmission schemes such as Automatic Repeat reQuest (ARQ) and Hybrid ARQ (HARQ) in the case of memoryless block fading channels. As performance metrics, we consider the Packet Error Rate (PER), the efficiency, and the packet delay. The novelty of the paper is twofold: i) the metrics are considered at the Network level; ii) we introduce a new general framework which enables us to derive analytically the considered performance metrics for most retransmission schemes, including recent cross-layer strategies with the Network layer. The metrics at the Medium Access Control (MAC) level are obtained as a byproduct. Among the considered retransmission schemes, we especially consider the Incremental Redundancy HARQ scheme with different lengths redundancy packets.

The reliability of bidirectional communication link can be guaranteed with Automatic Repeat Request Procedures (ARQ). The standard STANAG 5066 describes the ARQ procedure for HF communications that can either be applied to existing HF physical layers modems or adapted to future physical layer designs. In this contribution the physical layer parameters of an HF modem (HFDVL), developed by the authors over the last decade, are chosen to optimize the performance of the ARQ procedure described in STANAG 5066. Besides the interleaving length, constellation size and coding type, the OFDM-based HFDVL modem permits the selection of the number of receiver antennas. It will be shown that this parameter gives additional degrees of freedom and permits reliable communication over low SNR HF communication links.

International audience; In today's wireless communication systems, automatic repeat request (ARQ) is implemented at the MAC layer in order to retransmit packets that have been erroneously transmitted at the physical (PHY) layer. Following a joint PHY-MAC design, information provided by the ARQ scheme can be exploited at the PHY layer in order to improve the system's performance. This paper extends the work presented in [1] in the context of SISO channels to the context of MIMO block-fading channels. Based on statistical channel knowledge at the transmitter, it provides an analysis of the natural tradeoff that exists between the PHY layer transmission rate and the number of ARQ retransmissions. We derive a very accurate analytical formulation of the optimum transmission rate (and, equivalently, the optimum PHY packet error-rate) that maximizes the goodput, as a function of the system parameters, namely the SNR, the number of antennas and the diversity order of the channel. Interestingly, we find that the PHY layer has to be made more reliable for MIMO channels than for SISO channels, and also that the MIMO ARQ system is less sensitive to a wrong choice of the rate of transmission than the SISO ARQ system.

This paper studies the effect of ARQ retransmissions on packet error rate, delay, and jitter at the application layer for a real-time video transmission at 1.03 Mbps over a mobile broadband network. The effect of time-correlated channel errors for various Mobile Station (MS) velocities is evaluated. In the context of mobile WiMAX, the role of the ARQ Retry Timeout parameter and the maximum number of ARQ retransmissions is taken into account. ARQ-aware and channel-aware scheduling is assumed in order to allocate adequate resources according to the level of packet error rate and the number of ARQ retransmissions required. A novel metric, namely,goodput per frame, is proposed as a measure of transmission efficiency. Results show that to attain quasi error free transmission and low jitter (for real-time video QoS), only QPSK 1/2 can be used at mean channel SNR values between 12 dB and 16 dB, while 16QAM 1/2 can be used below 20 dB at walking speeds. However, these modes are shown to result in low transmission efficiency, attaining, for example, a total goodput of 3 Mbps at an SNR of 14 dB, for a block lifetime of 90 ms. It is shown that ARQ retransmissions are more effective at higher MS speeds.

Two-way relay (TWR) communication, a new cooperation paradigm that allows two terminals to share one relay node to communicate with each other in two phases, has played an increasingly valuable role in wireless networks to meet the stringent throughput requirement. In this paper, we focus on the designing of automatic repeat-request (ARQ) protocols for the two-way wireless relay systems. According to different feedback schedules, we propose three basic ARQ protocols to improve the throughput of two-way relay systems, namely, relay-only ARQ (Ro-ARQ), terminal only ARQ (To-ARQ) and relay-terminal ARQ (RT-ARQ). Through analyzing the outage throughput of these three ARQ protocols, it is verified that all three protocols can improve the system performance. In addition, simulation results reveal that the RT-ARQ protocol has the closest performance to the theoretical throughput upperbound among all given methods without severe deterioration on system complexity.

The notion of joint network-coded ARQ for multiple unicast flows and superposition coding (multilayering) is introduced. We consider a single sender and multiple receiving users with feedback channels. Much like in a cellular system downlink, each user expects to receive different information. Superposition coding transforms each fading channel into several (or infinite number of) layers of packet erasure channels, and network-coded ARQ is utilized on groups of layers over the users. The expected sum-rate is considered, and optimized. Numerically optimized results indicate roughly additive gains due to layering and network coding. Some analytical results on special cases regarding number of users and layers, are given. For instance, for NC unicast ARQ, one layer and arbitrary number of users, we derive the optimal expected sum-rate in a novel parameterized closed form. Refereed/Peer-reviewed

Copyright 2011 IEEE; International audience; Hybrid ARQ (HARQ) schemes operate at the PHY and Medium Access (MAC) layers and their performance have been naturally studied at the MAC level. However, all the modern systems are going to be running under the IP protocol. Therefore, in order to get realistic performance of the whole system considering the multiple layer stacks, performance analysis at the IP layer is crucial. Very little work has been done so far in this direction, except in \cite{rossi2003analysis} which studies the delay statistics of IP packets with Selective-Repeat ARQ, and \cite{choi_etal_05} which proposes a cross-layer optimization strategy between MAC and IP layers for ARQ, and in \cite{spawc2009,vtc2009} which consider the HARQ case. In this paper, we study the effect of erroneous feedbacks at the MAC layer on the performance at the IP layer considering both conventional HARQ schemes as well as the cross-layer strategy mentioned above. We derive in closed-form expressions the performance in terms of packet error rate (PER), efficiency, and delay with respect to the error probability of the feedback channel.

Copyright 2011 IEEE; International audience; We aim to study a specific cross-layer optimized Hybrid Automatic Retransmission reQuest (HARQ) recently introduced and called early-drop HARQ. We remind, for that allocation strategy, that instead of giving a transmission credit per MAC packet (as usually done) it is proposed to share the transmission credit among all the MAC packets belonging to the same IP packet. The early-drop version stops the retransmission as soon as the number of remaining MAC packets is higher than the number of possible transmission attempts. As the early-drop has never been analyzed neither through simulations or analytical derivations, the purpose of this paper is to fill this gap. As the packet error rate and the delay are not modified, we only focus on the efficiency which is expressed in closed-form.

This paper proposes an algorithm to be used in IEEE 802.16e networks for adapting MAC PDU size to wireless channel behavior when ARQ is adopted at MAC layer. The algorithm is based on an analytical approach for dynamically evaluating the optimal packet size. The latter is derived from an expression of the ARQ protocol efficiency, obtained by exploiting a finite-state Markov error model which also takes into account Adaptive Modulation/Coding. The effectiveness of the designed algorithm in improving TCP performance has been evaluated.

In this paper, we introduce a mechanism to improve the performance of ARQ over underwater links. Our scheme aims at reproducing a Selective Repeat ARQ strategy: to do this, it sets up a form of time-division duplex link between the transmitter and its receiver, by leveraging on the propagation delay incurred by underwater sound. In fact, such delay typically allows to interlace the transmission of data and ACK packets in such a way that the two operations do not interfere or cause nodes to be deaf to the transmissions of each other. We consider two different versions of our protocol (in terms of channel access persistence) and compare them against ALOHA and CSMA with and without ARQ, in both static and mobile scenarios. We conclude that in multiuser networks our form of Selective Repeat ARQ outperforms other ACK-based protocols at low and intermediate traffic.

The maximum achievable throughput and the steady-state throughput of the Butterfly networks are investigated and compared in the context of three types of automatic repeat request (ARQ) schemes of, namely, the stop-and-wait ARQ (SW-ARQ), go-back-$N$ ARQ (GBN-ARQ) and the selective-repeat ARQ (SR-ARQ). Our studies show that, at a given packet error rate (PER), the SW-ARQ scheme yields the lowest throughput while the SR-ARQ scheme can attain the highest throughput, among the three ARQ schemes considered. At a very low PER, the GBN-ARQ may achieve a similar throughput as the SR-ARQ. However, as the PER increases, the throughput achieved by the GBN-ARQ converges to that of the SW-ARQ.

The average burst delay and the standard deviation (SD) of burst delay in the context of the Butterfly networks are investigated and compared, when three types of automatic repeat request (ARQ) schemes, namely, the stop-and-wait ARQ (SW-ARQ), go-back-$N$ ARQ (GBN-ARQ) and the selective-repeat ARQ (SR-ARQ), are considered. We assume that packets in a burst arrive at a constant rate and that the packet error rate (PER) is the same for all the links. Our studies show that, among the three ARQ schemes, the SW-ARQ scheme yields the highest average burst delay and also the highest SD of burst delay, while the SR-ARQ scheme is capable of attaining the lowest delay and also the lowest SD of burst delay. At very low PER, the GBN-ARQ may achieve a similar delay performance as the SR-ARQ. However, as the PER increases, the delay performance of the GBN-ARQ converges to that of the SW-ARQ.

International audience; This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.

This paper investigates throughput-efficient relay ARQ protocols for single carrier MIMO systems with amplify-and-forward relaying. We focus on reducing the multiplexing loss due to the half-duplex operation at the relay. We introduce two new relaying protocols where both ARQ and relaying are jointly targeted. Compared to the conventional relaying techniques, the proposed mechanisms require only one time slot duration for transmitting the entire data packet at each ARQ round. We also focus on performance evaluation, and show that the new techniques provide significant improvement in average throughput while maintaining good outage probability performance.

We address the issue of efficient iterative (turbo) packet combining for broadband space-time coded transmission with hybrid-automatic repeat request (ARQ) over co-channel interference (CCI)-limited multiple-input-multiple-output (MIMO) channel. We introduce a new frequency domain turbo combining scheme where multiple transmissions are combined at the signal level using soft minimum mean square error (MMSE) processing. The proposed technique allows to recursively combine received signal packets in the frequency domain, and does not require to explicitly store signals and channel frequency responses (CFR)s corresponding to multiple ARQ rounds. We analyze both the computational complexity and memory requirements of the proposed scheme and show that are quite insensitive to the ARQ delay, i.e., the maximum number of ARQ rounds. Block error rate (BLER) performance is investigated to examine the gains offered by the new technique.

A multiple antenna multihop relay network consisting of a source, a relay, and a destination node, is considered. The diversity-multiplexing-delay tradeoffs (DMDT) for various multihop ARQ protocols are obtained. It is shown that the tradeoff region is limited by the performance of the weakest link, and hence the optimal ARQ protocol should balance the link performances by allocating the ARQ rounds among all links. Based on this argument, a Variable Block-Length (VBL) ARQ protocol is proposed and its DMDT-optimality is shown.

We analytically investigate the packet delay statistics of the selective repeat ARQ scheme with non-instantaneous feedback, with correlation both in the channel errors and the packet arrival process. We highlight interesting trends of the delay terms, which can be extremely useful for multimedia real time services over wireless.

Under limited channel state information at the transmitter the communication suffers from the outage events produced by a data rate selection not supported by the current channel realization. Automatic repeat request (ARQ) protocols are a useful tool to deal with those outage events in delay-tolerant services. This work looks into how Automatic Repeat Request (ARQ) protocols are applied to the half-duplex relay-assisted transmission with a decode-and-forward (DF) relay. The exploitation of ACK feedback channels from destination and relay leads to two possible implementations: 1) only-source manages the retransmission procedure or 2) both source and relay control the retransmissions. We analyze both options under a chase-combining ARQ protocol with limited number of transmission rounds, providing integral expressions for the throughput. This study allows the optimization transmission rate and the amount of resources allocated for the relay transmission. Keywords-Hybrid ARQ, relay-based systems

We present in this paper the analysis of an IEEE 802.11 network in the presence of hidden and exposed terminals when a Cooperative ARQ (C-ARQ) scheme is executed at the MAC layer. When spontaneous helpers transmit to assist in a failed transmission, the area exposed to the original transmission increases in comparison to non-cooperative ARQ schemes. In this paper we quantify this effect and we evaluate the relevance of designing efficient protocols to combat the exposed terminal problem.

Video content can be provided to an end user by transmitting video data as a sequence of internet protocol (IP) packets over the network. When the network contains a wireless link, packet erasures occur because of occasional deep fades. In order to maintain a sufficient video quality at the end user, video packets must be protected against erasures by means of a suitable form of error control. In this contribution, we investigate two types of error control: (1) forward error correction (FEC), which involves the transmission of parity packets that enables recovery of a limited number of erased video packets, and (2) the use of an automatic repeat request (ARQ) protocol, where the receiver requests the retransmission of video packets that have been erased. We point out that FEC and ARQ considerably reduce the probability of unrecoverable packet loss, because both error control techniques provide a diversity gain, as compared to the case where no protection against erasures is applied. We derive a simple analytical expression for the diversity gain resulting from FEC or ARQ, in terms of the channel coherence time, the allowable latency, and (for FEC) the allowable overhead or (for ARQ) the time interval between (re) transmissions of copies of a same packet. In the case of HDTV transmission over a 60 GHz indoor wireless link, ARQ happens to outperform FEC. Copyright (C) 2008 Julie Neckebroek et al.

In conventional (noncooperative) automatic repeat request (ARQ) protocols for radio networks, the corrupted data frames that cannot be correctly decoded at the destination are retransmitted by the source. In cooperative ARQ protocols, data frame retransmissions may be performed by a neighboring node (the relay) that has successfully overheard the source's frame transmission. One advantage of the latter group of ARQ protocols is the spatial diversity provided by the relay. The first delay model for cooperative ARQ protocols is derived in this paper. The model is analytically derived for a simple set of retransmission rules that make use of both uncoded and coded cooperative communications in slotted radio networks. The model estimates the delay experienced by Poisson arriving frames, whose retransmissions (when required) are performed also by a single relay. Saturation throughput, data frame latency, and buffer occupancy at both the source and relay are quantified and compared against two noncooperative ARQ protocols.

These research tasks present a measurement platform of Bluetooth asynchronous links in order to get the intrinsic time constraints of this network and communications protocols. These time measurements are necessary for the application we wish to implement for mobile robot control through Bluetooth link communication. We present the platform as well as the measurement protocol which we have carried out from real-time communicating operating systems. We have developed an application of radio and time data processing allowing a real-time evaluation of the global behavior of the communicating system.

In this paper, a packet size control algorithm, fully compliant with the IEEE 802.16e standard, has been proposed. This algorithm aims to optimize the performance of a data link ARQ protocol, trying to evaluate dynamically the packet size that maximizes the mean advancement of the sender window. It offers the possibility to maximize system throughput in every mobile scenario, even in presence of wireless time-variant channels. The effectiveness of the defined algorithm has been evaluated, through computer simulation, in terms of normalized TCP goodput. Simulation results have shown that the dynamic choice of the packet size plays an important role in maximizing TCP performance.