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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.

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

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.

User scheduling and multiuser multi-antenna (MU-MIMO) transmission are at the core of high rate data-oriented downlink schemes of the next-generation of cellular systems (e.g., LTE-Advanced). Scheduling selects groups of users according to their channels vector directions and SINR levels. However, when scheduling is applied independently in each cell, the inter-cell interference (ICI) power at each user receiver is not known in advance since it changes at each new scheduling slot depending on the scheduling decisions of all interfering base stations. In order to cope with this uncertainty, we consider the joint operation of scheduling, MU-MIMO beamforming and Automatic Repeat reQuest (ARQ). We develop a game-theoretic framework for this problem and build on stochastic optimization techniques in order to find optimal scheduling and ARQ schemes. Particularizing our framework to the case of "outage service rates", we obtain a scheme based on adaptive variable-rate coding at the physical layer, combined with ARQ at the Logical Link Control (ARQ-LLC). Then, we present a novel scheme based on incremental redundancy Hybrid ARQ (HARQ) that is able to achieve a throughput performance arbitrarily close to the "genie-aided service rates", with no need for a genie that provides non-causally the ICI power levels. The novel HARQ scheme is both easier to implement and superior in performance with respect to the conventional combination of adaptive variable-rate coding and ARQ-LLC., Submitted to IEEE Transactions on Communications, v2: small corrections

This paper presents an analytical model for the study of hybrid ARQ techniques on discrete time Markov channels by means of an appropriate Markov chain, which tracks the transmission outcome and can be used to evaluate several performance metrics, including throughput, loss probability, number of retransmissions, and delay. The analysis is carried out with the assumptions that the information frame is encoded by the source with a linear block code and hard decoding is used at the receiver side. We finally present numerical evaluations for the performance of a truncated type II hybrid ARQ technique based on Reed Solomon erasure codes.

We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols. We further maximize the throughput by optimizing the packet length and modulation level and will show that substantial gains can be achieved by this joint optimization. Since both the packet length and modulation level are usually discrete in practice, a computationally efficient algorithm is further proposed to obtain the discrete optimal packet length and modulation level.

In this paper, we present a new method to analyze the throughput and delay of the selective-repeat (SR) automatic repeat-request (ARQ) protocol. Previous work on SR ARQ has concentrated on reliable feedback or two-state Markovian feedback errors. We solve a wider class of problems by characterizing both the forward and reverse channels by general hidden Markov models (HMMs). The moment-generating function (MGF) technique is used to find throughput and delay. To calculate the MGF, we construct matrix signal-flow graphs for the hidden Markov process. This procedure can be useful for a variety of other HMM problems, and is of interest by itself. Practical issues such as erasure errors and timeouts are included in our analyses, which are verified by extensive simulations

In this letter, a new hybrid automatic repeat request (ARQ) approach is presented to enhance receiver performance for communication systems employing forward error-correction codes in frequency-selective fading environments. This new approach involves a simple modification to the traditional turbo equalizer by combining multiple ARQ transmissions via integrated channel equalization. This modification leads to better computational efficiency, better exploitation of channel diversity, better channel-estimation ability, and improved performance (frame-error rates) when concatenated with an outer code. These improvements are verified through evaluations of extrinsic information transfer charts and ARQ simulations when compared with iterative combining of multiple transmissions.

Adaptive automatic repeat request (ARQ) schemes are quite effective for throughput enhancement in time-varying mobile channel environments. In this paper, both throughput and packet error rate are analyzed for a selective-repeat ARQ scheme based on a constant-power variable-rate adaptive M-QAM system combined with selection transmit diversity over multiple-input multiple-output Markovian-Nakagami channels. In this analysis, the impact of using outdated and/or imperfect channel state information on the performance of the system is considered.

We analyze an automatic repeat-request (ARQ) scheme of the Consultative Committee for Space Data Systems file-delivery protocol for the single-hop file-transfer operation. With regard to performance measures, this paper is mainly concerned with the time taken to transfer a file (file-delivery time) and throughput efficiency. We discuss the ARQ timer-setting rule that minimizes the expected file-delivery time under the constraint that the throughput efficiency is maximized. Then, for that timer-setting rule, we derive the expected file-delivery time.

A type II hybrid automatic repeat request scheme is considered as a retransmission strategy in a direct-sequence code-division multiple-access packet mobile radio network. An analysis based on equilibrium point analysis is presented to model the behavior of the system in a message-based traffic generation model. A simulation approach is introduced to validate the proposed analytical model, obtaining results that closely match those derived theoretically.

The performances of the go-back-N ARQ scheme with selective repeat in intra-block (GBN-SR) and revised GBN-SR (Rev-GBN-SR) schemes are analyzed. Using the derived generating function of the service time of a packet, the throughputs of the proposed schemes are compared with that of Benelli's (1986) scheme. It is shown that the proposed Rev-GBN-SR scheme shows good performance in a wider range from low to high packet error rate regions.

Turbo-codes are decoded using iterative decoding algorithms with somewhat elusive convergence properties. In this paper, the modes of convergence observed in an extensive series of turbo-code simulations are categorized by examining the bit convergence behavior for each frame. Based on these results, a new method for decoder termination based on average log-likelihood ratios is presented and compared with other methods. As an application, a selective repeat automatic repeat request (ARQ) system is considered.

Based on an assumption that a steady state exists in the full-memory multidestination automatic repeat request (ARQ) scheme, we propose a novel analytical method called steady-state function method (SSFM), to evaluate the performance of the scheme with any size of receiver buffer. For a wide range of system parameters, SSFM has higher accuracy on throughput estimation as compared to the conventional analytical methods.

This paper considers truncated type-II hybrid automatic repeat-request (ARQ) schemes with noisy feedback over block fading channels. With these ARQ techniques, the number of retransmissions is limited, and, similar to forward error correction (FEC), error-free delivery of data packets cannot be guaranteed. Bounds on the average number of transmissions, the average coding rate as well as the reliability of the schemes are derived using random coding techniques, and the performance is compared with FEC. The random coding bounds reveal the achievable performance with block codes and maximum-likelihood soft-decision decoding. Union upper bounds and simulation results show that over block fading channels, these bounds can be closely approached with simple terminated convolutional codes and soft-decision Viterbi decoding. Truncated type-II hybrid ARQ and the corresponding FEC schemes have the same probability of packet erasure; however, the truncated ARQ schemes offer a trade-off between the average coding rate and the probability of undetected error. Truncated ARQ schemes have significantly higher average coding rates than FEC at high and medium signal-to-noise ratio even with noisy feedback. Truncated ARQ can be viewed as adaptive FEC that adapts to the instantaneous channel conditions.

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.

This paper outlines an efficient method to concurrently optimize a multiplicity of design variables for continuous selective-repeat (SR) and go-back-N (GBN) automatic repeat request (ARQ) strategies, both in noiseless and noisy feedback channels. For these ARQ protocols, we adapt either the number of identical message blocks sent in each transmission (in the case of GBN scheme) or the number of copies of a block retransmitted to handle a NACKed codeword (for the SR protocol) dynamically to the estimated channel condition. The channel state information is obtained by counting the contiguous acknowledgment (ACK or NACK) messages. Exploiting the asymptotic properties of the steady state probability expressions, we show analytically that the optimum solution indeed lies in the infinite space. Subsequently, a simple expression to estimate the suboptimal design parameters is suggested. Our approach of minimizing the mean-square error function yields to a quantitative study of the appropriateness of the selected parameters. Exact analytical expressions that allows us to compute the throughput crossover probability between any two arbitrary multicopy transmission modes are derived. The results provide fundamental insights into how these key parameters interact and determine the system performance.

In this paper, a model is developed for a slotted time-division multiplexing system used for assigning transmissions over a set of time-varying channels. Two schemes, a "round-robin" and an adaptive multiplexing scheme, are studied for use with three standard automatic-repeat-request (ARQ) protocols, namely, stop-and-wait (SW), go-back-N (GBN), and ideal selective repeat (ISR). In round-robin multiplexing, transmission slots are assigned periodically to each channel, With the adaptive scheme, the multiplexer selects at each time slot the channel whose state is estimated to have the lowest retransmission probability. The throughputs of these ARQ protocols under either multiplexing scheme are analyzed and compared. The present paper contains a description of the system model and an analysis of the ARQ protocols under both multiplexing schemes. In Part II, a modification to GBN and selective repeat ARQ for reducing the detrimental effects of feedback errors is discussed and analyzed, followed by a throughput performance comparison of all ARQ and multiplexing schemes.

This letter presents a simple method to simultaneously optimize a multiplicity of design parameters for the adaptive automatic repeat request strategy previously reported, and subsequently provides a quantitative measurement that reflects the appropriateness of the selected parameters. An exact analytical expression that allows us to compute the throughput crossover probability between the two different protocols is derived. The results provide fundamental insights into how these key parameters interact and determine the system performance.

Automatic-repeat-request (ARQ) protocols have been analyzed for quite some time, but the issue of errors in the feedback channel has not received much attention. In some applications, such as digital mobile communications, this issue can be important. Accordingly, this paper examines the effect of feedback errors on the throughputs of the stop-and-wait (SW), go-back-N (GBN), and selective repeat (SR) ARQ protocols for the ease of a point-to-point channel under some feedback information assumptions. It is shown that the deleterious effects of feedback errors on the throughputs of continuous (e.g., GBN and SR) ARQ protocols can be greatly reduced by a simple modification in the retransmission operation, provided that the "complete state" of the receiver is sent back with each acknowledgment.

This article presents a new generalized selective repeat automatic repeat request (ARQ) scheme for error control in broadcast and point-to-point satellite communication systems. In the proposed scheme, each bit in a packet is repeated m times consecutively to increase the transmission reliability. Finite capacity buffers have been assumed at the earth stations. The throughput, theoretically derived for the proposed scheme, is optimized with respect to the number of copies transmitted per bit. A suitable algorithm to adaptively choose this number in relation to the transmission channel propagation conditions can also be used. In comparison with classical and modified versions of the selective repeat ARQ scheme as described in the literature, the proposed scheme provides enhanced throughput, especially with poor channel conditions and a high number of receiving earth stations.

An automatic-repeat-request (ARQ) Go-Back-N (GBN) protocol with unreliable feedback and time-out mechanism is studied, using renewal theory. Transmissions on both the forward and the reverse channels are assumed to experience Markovian errors. The exact throughput of the protocol is evaluated, and simulation results, that confirm the analysis, are presented. A detailed comparison of the proposed method and the commonly used transfer function method reveals that the proposed approach is simple and potentially more powerful.

We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented. >

Type I hybrid ARQ systems use an error-control code of fixed rate for error-correction in each transmitted packet. In such systems, the code rate must be carefully chosen to match the channel bit error rate (BER) in order to maximize system throughput. Whenever there is a mismatch between code rate and channel BER, the throughput suffers. In this paper, we proposed a type I hybrid ARQ system which automatically adjusts its code rates to match channel BERs. The proposed system is very simple to implement and yet performs significantly better than type I hybrid ARQ systems of fixed code rate. >

An efficient multicast hybrid ARQ scheme is proposed by incorporating the generalized minimum distance (GRID) decoding of maximum distance separable (MDS) codes with Metzner's (1984) scheme. Erroneous frames are stored in the receiver buffer and recovered after receiving one or more redundant frames. The throughput and the average transmission delay of the proposed scheme are analyzed on memoryless symmetric channels. The proposed scheme can circumvent the degradation of the throughput due to an increase of the number of receivers, which is the most serious defect in the conventional multicast ARQ schemes, at the expense of the transmission delay.

In this paper, efficient stop-and-wait, go-back-N and selective-repeat hybrid ARQ protocols with adaptive forward error correction (AFEC) using convolutional coding are proposed and analyzed. The basic idea is to vary the coding rate for error correction according to system parameters, such as the signal-to-noise ratio, the round trip delay and the buffer size at the receiver, so as to maximize the throughput efficiency. The performances of the proposed ARQ protocols are evaluated for two channel models: a non-fading and an ideally-interleaved Rayleigh-fading additive white Gaussian noise channel. In all cases it is found that the hybrid ARQ protocols with AFEC yield a comparatively high throughput under all channel conditions. >

The paper provides a performance analysis of automatic-repeat-request (ARQ) protocols in connection-oriented transmission. Each message arriving at a transmitter is divided into several packets, which are continuously transmitted to a receiver according to go-back-N ARQ or selective-repeat ARQ protocols. Because of connection-oriented transmission, messages are served on a first come first served basis, i.e., transmission of a message is commenced after all packets in the previous message are successfully transmitted. For the two ARQ protocols, the authors derive the probability generating functions of message waiting time and queue length at an arbitrary instant, from which the average performance measures are explicitly obtained. >

Hybrid automatic-repeat-request (ARQ) error control schemes make use of both error detection and error correction in order to achieve high throughput and low undetected error probabilities on two way channels. Two hybrid ARQ schemes, termed hybrid go-back-N (HGB-N) and hybrid selective-repeat (HSR), are proposed for point-to-multipoint communications over broadcast channels. Both schemes incorporate a concatenated code for error correction and error detection. The performance study of the hybrid schemes is based on a two-state Markov model of a burst noise channel. An analytic solution is derived for the throughput efficiency of the HSR scheme, while approximations and computer simulation are used to evaluate the throughput efficiency of the HGB-N scheme. It is shown that the schemes perform considerably better than the corresponding pure ARQ schemes in which a block code is used for error detection only, especially in environments with a large number of receivers and large channel roundtrip delays, such as satellite broadcast links. >

A communications system in which multiple parallel channels are available to carry traffic from a transmitter to a receiver is considered, and an extension of the selective-repeat automatic repeat request (SR-ARQ) protocol that dynamically assigns packets to channels for each (re)transmission is presented. Because of selective retransmission, packets arrive at the receiver out of order and must be stored in a resequencing buffer. A queuing model for the resequencing buffer is constructed. The generating function of the buffer occupancy and the packet-delay distribution are derived, and procedures for simplifying the computation are presented. The dynamic assignment scheme is compared with, and shown to have performance superior to, a static assignment scheme. >

Several modifications of an efficient automatic repeat request (ARQ) scheme proposed by Weldon (see IEEE Trans. Commun., vol.COM-30, p.480, 1982) are studied. Unlike Weldon's scheme, in which all erroneous data packets are discarded, the present schemes make use of copies of the data packet which may contain errors. A number of channel models are considered, namely, a binary symmetric channel, a nonfading, and a Rayleigh fading channel with additive white Gaussian noise. In most cases, it is found that the throughput can be substantially increased. Under poor channel conditions, the use of forward error correction can lead to further improvement. A type-II ARQ scheme which does not suffer the throughput degradation under good channel conditions due to overhead parity bits associated with conventional forward error correction is also analyzed. >

The authors propose retransmission error control schemes for broadcast channels. In their selective-repeat-ARQ (automatic repeat request) method, they incorporate some aspects of implementation that they believe were ignored by all the previous work. Based on this protocol, they also propose a type-2 hybrid ARQ scheme that uses parity retransmission. They apply the dynamic programming optimization technique of Wang and Silvester (1987), with some modification, to their schemes. Analysis shows that their schemes outperform all the existing schemes. As special cases of their proposed schemes, the authors can obtain point-to-point ARQ schemes which also outperform all the existing point-to-point schemes. Thus, their schemes extend the useful range of retransmission error control schemes for these channels. >

The authors introduce a form of automatic repeat request (ARQ), referred to as variable-rate type-I hybrid ARQ, in which the code rate varies in response to the fluctuations in the power received from a meteor trail. For one implementation, the source or the destination periodically obtains estimates of the signal power at the destination, and the source uses these estimates to select the rate of the code. For an alternative approach, the code rate is determined completely by the decoding successes and failures during previous transmissions. The performance measure is the throughput per trail, which is defined as the expected number of information bits received correctly for a given meteor trail. Numerical results for Reed-Solomon codes are included to illustrate the relative performance of the various schemes. It is shown that the throughput is larger for both implementations of variable-rate type-I hybrid ARQ than for fixed-rate type-I hybrid ARQ and ARQ without forward error correction. >

The authors investigate throughput efficiencies for two basic automatic-repeat-request (ARQ) strategies, go-back-N and selective repeat disciplines, assuming that forward and backward channels have Markov error characteristics and they are mutually independent. For the two ARQ schemes, simple analytical formulas for the throughput efficiency are obtained. Particularly, in the case of the go-back-N scheme the authors show that the result of throughput analysis can be extended to a general form that includes results presented by C.H.C. Leung et al. (1988). >

A generalized type II automatic-repeat-request (ARQ) scheme using punctured convolutional coding on a two-state Markov model of a nonstationary channel is analyzed. A simple ARQ scheme with memory is also analyzed. It is shown that the simple memory ARQ scheme offers a substantial throughput improvement over a conventional ARQ scheme at severe channel conditions. Furthermore, the generalized type II ARQ scheme yields a better performance than the conventional type II ARQ scheme under all channel conditions, thus making it attractive for use over time-varying channels. >

A simple and efficient system utilizing the class of Hamming codes in a cascaded manner is proposed to provide high throughput over a wide range of channel bit error probability. Comparisons with other adaptive schemes indicate that the proposed system is superior from the point of view of throughput, while still providing the same order of reliability as an ARQ (automatic repeat request) system. The main feature of this system is that the receiver uses the same decoder for decoding the received information after each transmission while the error-correcting capability of the code increases. As a result, the system is kept to the minimum complexity and the system performance is improved. >

The authors consider an SR ARQ (selective-repeat automatic-repeat-request) protocol with the one source and multiple receivers, where each receiver acknowledges all packets and handles its resequencing buffer based only on the packets that it receives error-free. An analysis of the resequencing delay and buffer occupancy at a receiver is presented. They construct a model that allows them to derive steady-state results and that makes into consideration system parameters such as number of receivers, propagation delay, and error probabilities of packets and acknowledgements. The main results of the analysis are the distribution of the resequencing delay and the distribution of the number of packets occupying the receiver's buffer. They also derive simple expressions for the mean buffer occupancy at the limit as the packet error probability tends to one. Numerical results are provided to illustrate the effects of system parameters on the behavior of the expected resequencing delay and the expected buffer occupancy. >

The performance of type-II hybrid automatic repeat request (ARQ) is compared to that of fixed-rate type-I hybrid ARQ for meteor-burst communications. Maximum throughput is obtained for meteor-burst communications by using a transmission scheme for which the information rate of the code, varies in response to the fluctuations in the power received from a meteor trail. For type-II hybrid ARQ, a variation in the code rate is inherent in the coding scheme. On the first transmission that is made for a data block, a code of relatively high rate is used, but if an additional transmission is required, only redundant symbols are sent, and this reduces the overall rate of the code. The performance measure is the throughput per trail, which is defined as the expected number of successfully received information bits for a given meteor trail. The authors also develop an approximation for the average value of the throughput, averaged over the parameters of the meteor trail. Numerical results for Reed-Solomon codes are included to illustrate the relative performance of the various schemes. It is shown that the throughput is larger for type-II hybrid ARQ than for either fixed-rate type-I hybrid ARQ or ARQ without forward-error-correction. >

The authors analyze an ARQ (automatic repeat request) scheme using parity retransmissions. By dividing each transmission block into subblocks, the combination of a transmission block and its retransmission block has the structure of a concatenated code. They derive formulae for calculating an upper bound on the probability of undetected errors and a lower bound on the throughput for such an ARQ scheme. Numerical results show that even with extremely simple code design, such an ARQ scheme has satisfactory performance. >

The authors present and analyze an efficient partial retransmission automatic repeat request (ARQ) strategy using convolutional coding and sequential decoding in conjunction with code combining. In the proposed ARQ scheme, whenever a packet of data needs to be retransmitted that packet is not repeated entirely as in the case of conventional full retransmission ARQ strategies. Instead, symbols of that packet are repeated a few at a time, sequentially, as needed, hence making a more effective use of the channel. It is shown that partial repetitions and code combining still yields an increase of the apparent Pareto exponent of sequential decoding, as in the case of full repetition-code combining. A throughput analysis shows that the partial retransmission ARQ strategy yields a substantial throughput improvement over the full retransmission-code combining ARQ strategies. >

The design, analysis, and implementation of an end-to-end transport protocol that is capable of high throughput consistent with the evolving high-speed physical networks based on fiber-optic transmission lines and high-capacity switches are presented. Unlike current transport protocols in which changes in control/state information are exchanged between the two communicating entities only when some significant event occurs, this protocol exchanges relevant and full state information periodically and frequently. It is shown that this reduces the complexity of protocol processing by removing many of the procedures required to recover from network inadequacies such as bit errors, packet loss, and out-of-sequence packets and makes it more amenable to parallel processing. Also, to increase channel utilization in the presence of high-speed, long-latency networks and to support diagrams, and efficient implementation of the selective repeat method of error control is incorporated in the protocol. An implementation using a Motorola 68030-based multiprocessor as a front-end processor is described. The current implementation can comfortably handle 10-15 kpackets/s. >

A selective-repeat automatic-repeat request (SR ARQ) system model in which packets arrive at the transmitter according to a general renewal process is analyzed. The overall delay of a packet in a system that operates under the SR ARQ protocol consists of the queuing delay at the transmitter and the resequencing delay at the receiver. The joint distribution of the buffer occupancies at the transmitter and at the receiver is derived, and the tow types of delay are compared using numerical examples. >

An analysis is presented of the selective-repeat type II hybrid ARQ (automatic-repeat-request) scheme, using convolutional coding and exploiting code combining. With code combining, at successive decoding attempts for a data packet, the decoder for error correction operates on a combination of all received sequences for that packet rather than only on the two most recent received ones as in the conventional type II hybrid ARQ scheme. It is shown by means of analysis and computer simulations that with code combining, a significant throughput is achievable, even at very high channel error rates. >

This paper analyzes the end-to-end delay of a selective-repeat ARQ protocol which tries to adaptively use the channel idle time. The end-to-end delay consists of three parts: queueing delay at the transmitter, transmission delay over the channel, and resequencing delay at the receiver. Although this paper succeeds only in obtaining approximate end-to-end delay, the agreement with simulation is generally good. >

A hybrid automatic-repeat-request system combined with adaptive forward error correction (ARQ/AFEC) which adaptively alters the error-correcting capability according to channel state using a nonsystematic Reed-Solomon code is presented. lt is shown that the system can alter the error-correcting capability by varying the number of information symbols fed to the decoder only, and not change the hardware of the encoder. Performance evaluations indicate that the ARQ/AFEC system has much higher frame efficiency than ARQ without AFEC for low-bit error rate and has high frame efficiency in a wide range of bit error rates. >

The throughput of conventional automatic-repeat-request (ARQ) protocols, such as the stop-and-wait, go-back-N, and selective repeat, can be improved by dynamically adapting the protocol block length so that it approaches the optimum value for varying channel bit error rates. A very simple algorithm to implement such an adaptive scheme is presented. The algorithm assumes a known block error rate, estimates the bit error rate, and determines the best block length. Results of a simulation study show that in spite of its simplicity, the algorithm performs well. >

In this paper the behavior of the Stop and Wait and Go Back- N error detection and retransmission (ARQ) protocols in an environment characterized by nonrandom errors are studied. Analytic models are developed for the case that the error process is modeled as a Markovian process. These models may be used to predict performance measures such as expected queue length and expected delay for the case of the Stop and Wait protocol and the Go Back- N protocol when N is very large. The models can also be used to determine maximum throughputs for both protocols. The results of these models are compared with simulation results for the Selective Repeat ARQ protocol.

The conventional go-back- N ARQ is modified so as to be applicable to point-to-multipoint communication by using a control block that indicates the occurrence of retransmission to all the receivers. This paper also presents a "tandem error control scheme," in which the up-link and the down-links use separate go-back- N ARQ's. The throughput efficiency of the tandem go-back- N ARQ is analyzed. Specifically, the mathematical formula for the throughput efficiency is obtained for cases in which there is a single receiver. The throughput efficiencies of these schemes are also evaluated by simulation.

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

In this paper we consider the problem of designing a good ARQ protocol for a message transmission environment characterized by high error rates and/or long propagation delays. We derive the average queue length for an idealized ARQ protocol for such an environment. We also describe a modification that can be made to existing ARQ protocols which can significantly decrease queue lengths in such an environment. We show that for the case of low message traffic rates, the modified Go Back- N protocol approaches the idealized scheme in performance.

A hybrid automatic repeat request (ARQ) system (HARQ-II) with parity retransmission for error correction, which combines ARQ and forward error correction is discussed, and the successful application of these codes to HARG-II is illustrated. A method of constructing the codes whereby conventional BCH codes can be changed into separable codes is proposed. A scheme is presented that has the advantages that, the code lengths are always made equal and that even in parity retransmission new information symbols can be sent along with the necessary parity-check symbols. The performance of the proposed schemes on the binary symmetric channel is discussed. The numerical results show that they outperform conventional schemes. >