Self-stabilizing sliding window ARQ protocols

For mobile/personal satellite systems, an ARQ protocol with low transmitter/receiver complexity as well as high throughput performance in a long round trip delay (RTD) and even in a bad channel condition, is required. A new selective-repeat (SR) ARQ with multicopy retransmission is proposed and the performance on an AWGN channel is analyzed. The proposed scheme can viewed as a modified version for SR+Stutter (ST) Scheme 2. The basic idea of the strategy is to repeat only erroneous blocks stored in the /spl nu/N block transmitter buffer multiple times, when /spl nu/ consecutive retransmissions in SR mode is received in error, where N denotes the RTD in blocks. Numerical analysis in the case of N block transmitter/receiver buffer shows that the proposed scheme presents a better performance than the SR+ST scheme 2 of the 2N block transmitted receiver buffer, as the channel BER becomes higher.

An SR (Selective-Repeat) ARQ (Automatic Repeat reQuest) protocol is used to recover from packet errors effectively over a low-quality communication channel. This SR ARQ has a problem of large delay due to resequencing of received packets. To mitigate this problem, the PFRS (Per-Flow ReSequencing) scheme was proposed, where the resequencing is performed independently for each upper-layer flow, while detection of lost packets and associated retransmissions are performed on the basis of the whole flows multiplexed over SR ARQ. This paper models the SR ARQ protocol, where the maximum number of retransmissions is limited, by a collection of simple stop-and-wait protocols, and shows numerical calculation results for the delay distribution of retransmission and resequencing. The validity of the analysis is confirmed by comparing numerical calculations with simulation results. The results prove the effectiveness of the PFRS scheme for the case where the number of flows over SR ARQ is large.

A structural-multipath approach has been developed for constructing a spatiotemporal model of a single-mode decameter communication channel, which makes it possible to determine the two-frequency spatial correlation function of a single-mode decameter communication channel and to establish the dependences of frequency and spatial correlation intervals of fading on the operating frequency, diffuse ionosphere parameters, and radio link geometry. The method for constructing this model of a communication channel using the structural multipath approach includes four stages: 1) development of a multibeam spatiotemporal decameter model of a communication channel; 2) development of a radiophysical space-time model of radio wave propagation in a decameter radio link, taking into account the influence of inhomogeneities (diffusion) of the ionosphere based on the method of smooth perturbations; 3) identification of multipath and radiophysical models to determine the two-frequency spatial correlation function of the decameter of the communication channel; 4) determining the dependence of frequency and spatial correlation intervals of fading in a single-mode decameter communication channel on the choice of operating frequency, diffuse ionosphere parameters, and radio link geometry.

Research into a transport protocol for high-speed networks is one of the most progressive areas in the field of computer communications. In high-speed networks using optical fiber as a transmission medium that gives the bandwidth from a hundred Mbits/s to Gbits/s, the roundtrip (propagation) delay and bandwidth product becomes large. It is well known that for an increase in this product, the throughput performance of the conventional error control procedures such as the go-back-N-based-ARQ scheme does degrade significantly. Therefore, a new protocol based on a selective-repeat ARQ scheme must be developed. The authors propose the stop-and-selective repeat (SSR) ARQ protocol and analyze the throughput performance of it. The throughput formula is exactly derived in terms of the roundtrip delay, the frame error rate, and the window size of from one to two roundtrip delays. The window size needed to offer the adequate throughput greater than 95% is shown.

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

This paper studies the situation where multiple IP flows are aggregated over a single wireless channel and an error recovery by retransmissions is performed by Selective-Repeat (SR) ARQ. We propose MQ-PFRS (Multi-QoS Per-Flow Resequencing) ARQ that provides a differentiated service for an IP flow depending on its QoS class, such as real-time or non-real-time. MQ-PFRS ARQ eliminates interferences among IP flows by resequencing received packets independently for each IP flow. It also controls the maximum packet delay by limiting the persistency of retransmissions and the maximum resequencing time for each packet. This paper also presents an analysis of the probability distribution of real-time packet delays. Simulation results show that the delay variation of real-time traffic is effectively controlled by proposed MQ-PFRS ARQ and the packet delay distribution is quite consistent with the results of the analysis. This means that MQ-PFRS is effective for handling multiple QoS classes of IP flows and the quality of real-time traffic transferred by the scheme can be predicted by the analysis.

Communication in high-speed wireless local area networks such as IEEE 802.11a are known to suffer from location-dependent, time-varying, and burst errors. It is usual to implement forward error correction and automatic repeat request mechanisms in the physical and data link layer to combat this errors. In this paper we evaluate the system performance of a WLAN with the CSMA/MAC protocol with different ARQ protocols. We have implemented three different schemes: (1) selective repeat ARQ; (2) ARQ with majority voting; and (3) type II hybrid ARQ. The simulation results show that all three schemes perform well when the channel is in good condition but when the bit error rate (BER) increases the type II hybrid ARQ is superior to the other two schemes.

In this paper, we first describe a seamless switching scheme for scalable video bitstreams that fully takes advantage of both the high coding efficiency of non-scalable bitstreams and the flexibility of scalable bitstreams. Small bandwidth fluctuations are absorbed by the scalability of the bitstreams, while large bandwidth fluctuations are tolerated by switching between scalable bitstreams. Flexible and efficient switching techniques are investigated as the focus of this paper. A flexible method is proposed to switch from current scalable bitstream to one operated at lower rates at any frame without any overhead bits. Since additional bits are necessary in the proposed scheme when switching from a scalable bitstream operated at lower rates to one operated at higher rates, an efficient method is proposed to greatly reduce the amount of overhead bits. Experimental results show that the seamless switching scheme with the proposed switching techniques significantly outperforms both the approach with a single scalable bitstream and the approach of switching among multiple nonscalable bitstreams.

The integrated sensing and communication (ISAC) refers to the integration of radio sensing and wireless communications to realize the multiplexing of space, time, and frequency resources. In the sixth generation (6G) wireless networks, ISAC is considered as one of the most promising technologies. In this paper, a novel ISAC channel model combining forward and backward scattering is proposed. In addition to the non-stationarity caused by motions, the correlations between sensing and communication channels are investigated. The channel characteristics of sensing such as forward scattering and backward scattering are introduced into the communication channel model. Utilizing the correlations between sensing and communication channels, the communication channel model is divided into line-of-sight (LOS), forward scattering, and backward scattering components. These three components are summed according to probability weighting to obtain a more accurate channel model for sensing assisted communication systems. Moreover, important statistical properties of the proposed ISAC channel model are derived and simulated. The analytical and simulation results match well, demonstrating the correctness of derivations and simulations. Some derived/simulated statistical properties are verified by corresponding measurement data, which indicates the utility of the proposed ISAC channel model.

When power control is employed in a Ka-band LEO satellite system featured with a Markov channel, the long round-trip propagation delay will cause power control gaps when the channel transits from a good state to a bad state, resulting in long (large-scale) burst-errors. A novel hybrid ARQ (HARQ) scheme is proposed to combat this kind of burst error. Based on the iterative SOVA (soft-output Viterbi algorithm) decoder, the proposed scheme utilizes the side information of the turbo decoder to derive the average reliability of the desired packet. When the average reliability is below the specified threshold, a go-back-N ARQ protocol is launched. With this scheme, the large-scale burst errors are effectively detected and corrected by retransmission; the small-scale burst errors are filtered out for the interleaving and FEC coding to correct. The simulation results show that this scheme can achieve good BER performance with small cost in throughput and delay in a severe Markov satellite channel, which is especially suitable for traffic having strict delay requirement and moderate BER requirement.

Proposes a seamless switching scheme for scalable video bitstreams that fully takes advantage of both the high coding efficiency of non-scalable bitstreams and the flexibility of scalable bitstreams. Small bandwidth fluctuations are accommodated by the scalability of the bitstreams, while large bandwidth fluctuations are tolerated by switching between scalable bitstreams. The major contribution of this paper is a flexible and effective scheme for seamless switching between scalable bitstreams that significantly improves the efficiency of scalable video coding over a broad bit rate range. When the channel bandwidth drops below the effective range of a scalable bitstream operated at higher rates, the proposed scheme can switch at any frame from the current scalable bitstream to one operated at lower rates without sending any overhead bits. Additional bits are only necessary when switching from a scalable bitstream operated at lower rates to one operated at higher rates. Experimental results show that the proposed scheme significantly outperforms both the approach with a single scalable bitstream and the approach of switching among multiple non-scalable bitstreams.

The model of the communication channel with phase noises is proposed. The prototype of synchronization system, which works at the phase noises in the communication channel, is made. The research of the pseudorandom signal spectrum is carried out depending on the shift register size in the m-sequence generator. The research results of the phase noise influence on the transmitted FM signal are presented.

This paper presents an efficient technique of continuous communication channel's experimental research for identification of amplitude-frequency characteristics (AFC). The technique is based on Volterra model and founded on the application of the approximating method of identification of nonlinear dynamic system. The identification is carried out by means of compiling the linear combinations of responses from researched system to the test polyharmonic signals with different amplitudes. Designed firmware, realizing the methodology of identification, is used for construction of informational model of communication channel in the form of first and second orders AFC's on the basis of input-output experiment's data, using harmonic and biharmonic test signals.

Shared memory emulation on distributed message-passing systems can be used as a fault-tolerant and highly available distributed storage solution or as a low-level synchronization primitive. Cadambe et al. proposed the Coded Atomic Storage (CAS) algorithm, which uses erasure coding to achieve data redundancy with much lower communication cost than previous algorithmic solutions. Recently, Dolev et al. introduced a version of CAS where transient faults are included in the fault model, making it self-stabilizing. But self-stabilization comes at a cost, so in this work we examine the overhead of the algorithm by implementing a system we call CASSS (CAS Self-Stabilizing). Our system builds on the self-stabilizing version of CAS, along with several other self-stabilizing building blocks. This provides us with a powerful platform to evaluate the overhead and other aspects of the real-world applicability of the algorithm. In our case-study, we evaluated the system performance by running it on the world-wide distributed platform PlanetLab. Our study shows that CASSS scales very well in terms of the number of servers, the number of concurrent clients, as well as the size of the replicated object. More importantly, it shows (a) to have only a constant overhead compared to the traditional CAS algorithm and (b) the recovery period (after the last occurrence of a transient fault) is no more than the time it takes to perform a few client (read/write) operations. Our results suggest that the self-stabilizing variation of CAS, which is CASSS, does not significantly impact efficiency while dealing with automatic recovery from transient faults.

Разработана компьютерная модель спутникового канала связи с учетом влияния доплеровского сдвига по частоте и стороннего спутника связи. Компьютерная модель построена в графической среде имитационного моделирования Simulink, которая входит в программный пакет MATLAB. В статье рассматривается имитационная модель спутникового канала связи с использованием сигнала MSK (Minimum Shift Keying). В ходе работы изучены и применены алгоритмы цифровой обработки сигналов при разработке компьютерной модели спутникового канала связи. По заданным параметрам принимаемого сигнала определены основные параметры цифрового демодулятора сигнала MSK, такие как частота повторения бита, частота дискретизации, минимальная разрядность аналого-цифрового преобразователя (АЦП), количество уровней квантования, частота среза цифрового фильтра-дифференциатора. В результате компьютерного моделирования спутникового канала связи было исследовано влияние отстройки по частоте сигнала MSK и уровня мешающего сигнала (стороннего спутника) на помехоустойчивость модема. По результатам моделирования получены графики зависимости вероятности ошибки приема бита от уровня мешающего сигнала и вероятности ошибки от отстройки по частоте. Разработанная компьютерная модель существенно расширяет круг задач, связанных с оперативной оценкой параметров электромагнитной совместимости (ЭМС) и радиоподавления в группировках подвижных РЭС.