Shared autonomous vehicles (SAV) have the potential to have a transformative impact on future urban transportation. In this study, we analyze the qualitative and quantitative effects of the introduction of SAV to commuters traveling in a central Tokyo district with a well-developed rail network using the large-scale agent-based transport simulator MATSim. First, we conducted a scenario in which no SAV were introduced and reproduced the modal split error for Tokyo within 1.2%. We then conducted multiple scenarios, varying the number of SAV and fare of SAV, to examine the impact on the mode share for number of vehicles introduced and fare of SAV. The results demonstrated that approximately 14%–32% of the population would shift to SAV, and those who traveled 2.0–8.0 kilometers by rail or bicycle were likely to shift to SAV and fare of SAV do not affect mode share of SAV. The results also confirmed that if the total number of SAV is increased too much, it is possible that people who used to walk or bicycle, that is, those using modes of transportation that have a smaller environmental effect and improve health, will shift to SAV. This suggests that it is important to limit the total number of SAV to an appropriate amount from the perspectives of environmental impact and health impact.

In this paper, we investigate influences of the network delay on haptic cooperative work in a networked virtual environment by experiment. In the work, two users carry an object cooperatively in a networked maze system by manipulating haptic interface devices. We handle two carrying methods in our experiment. In one method, the two users hold the object. In the other method, one user holds the object and the other user pushes it. We measure the operation time and reaction force, and we compare them between the two methods. Experimental results demonstrate that the former method has smaller average operation time than the latter method, but the average reaction force is larger in the former.

In this paper, we propose an end-to-end dynamic bandwidth allocation scheme based on QoS demand in Software Defined Networking (SDN). The proposed scheme aims to provide high performance of different network traffic and efficient use of network resources by providing network resources to network traffic according to their QoS demands and the current network status. We demonstrate the effectiveness of the proposed scheme on our emulated SDN network by experiment. The proposed scheme is compared with the traditional single path and flow-based multipath routing schemes. Experimental results demonstrate that the proposed scheme provides higher performance in terms of packet loss rate and average network delay for high priority flows than the other two schemes.

In this paper, we propose a QoS-aware traffic engineering method in software-defined networks. Traditional shortest path based routing cannot guarantee future traffic demands because the routing only uses the minimum hop counts. The QoS-aware routing is more efficient than the traditional shortest path based routing; however, QoS parameters like link utilization and link delay are needed to perform such kinds of routing. The estimation of the link utilization and link delay may increase the controller computational time and load. To reduce the controller's computational time and improve the network resource utilization, the proposed QoS-aware routing method combines mainly two parts: the initial path calculation phase and link utilization aware path calculation phase. When the network is initialized, the first phase collects all possible paths for each pair of source and destination together with the link capacities and link delays. When the network topology changes occur or the collected paths do not satisfy traffic demands, the second phase re-calculates paths based on the link utilization and reroutes the traffic through the optimal path. Experimental results of throughput and packet loss rate show that our proposed method outperforms the other two methods.

In this paper, we deal with four types of stabilization control for a remote robot system in which a user remotely operates an industrial robot arm with a force sensor by using a haptic interface device while watching video. The four types of control include the stabilization control with filters, the stabilization control by viscosity, the reaction force control upon hitting, and the switching control. To make a comparison of them quantitatively, we carry out the quality of experience (QoE) assessment in which we treat work of pushing four balls with different softness by a metal rod attached to the tip of the industrial robot arm.

The last few years, significant advances provide better solutions for interconnectivity and security in Intelligent Buildings (IBs). An overview of these advances is presented in this paper. Also, in this paper, we presented a patient monitoring system for hospital buildings and a Building Management System (BMS) layered design. Then, we made a comparative analysis of our system over other similar systems and presented the benefits that our approach has. Moreover, we proposed some security solutions that came out from the design and from further research. Also, a comparative analysis of our system over other similar systems is shown in this paper. Then, the benefits of our design are listed and explained. Finally, we have studied and used the Contiki OS and the Cooja emulator, and we have created simulations, which helped us have a more detailed and realistic image of our system. The results from the transmission of the packets of data are significant, since the protocol we use (CoAP), has a very low percentage, if not zero, of the packets, lost. Using the Cooja emulator we track the trafficc in and out of the network in real time. So, it seems to be a very useful tool which offers, except the traffic, diagrams and other metrics which describe our system. As future work, we are going to emulate our entire system with such tools like the Cooja emulator. Then, if the results are the expected, we will move on with the implementation of such a system. This paper will be a start point for better future decisions in designing intelligent building systems.

The last few years, significant advances which improve healthcare have been done in Internet of Things, in cloud computing, in video coding, and in mobile devices. This paper provides an overview of these advances. Also, we propose an IoT-based surveillance system for ubiquitous healthcare monitoring. The system consists of sensors, actuators, and cameras. Mesh topology was decided to be used as it provides important advantages. Moreover, the Constrained Application Protocol (CoAP) is used for the data compression and transferring, and the Scalable High-Efficiency Video Coding (SHVC) is used for the video compression and transferring. The SHVC can deliver the same video quality in half of the bit rate than the High-Efficiency Video Coding (HEVC). Furthermore, cloud services are provided, such as storage and real-time monitoring. Finally, we made a comparative analysis between our proposed system architecture and two other approaches. From this analysis, we can say that our system architecture has some benefits instead of other similar architectures. Also, we made an analysis of the bandwidth and the network throughput. The results are significant since the bandwidth required for the transmission of data and video is reduced.

In this paper, we carry out QoE (Quality of Experience) assessment of operability of haptic interface device for each player and fairness between players for soft objects in a networked real-time game. We handle a balloon bursting game in which two players burst balloons (i.e., soft objects) in a 3D virtual space by using haptic interface devices. Assessment results show that the operability depends on the network delay, and the fairness is mainly dependent on the difference in network delay between the players' terminals.

In this paper, we propose an accurate approximation framework for separable edge-preserving filtering. Naïve implementation of edge-preserving filtering, such as bilateral filtering and non-local means filtering, consumes enormous computational costs. Separable implementation of such filters is an efficient approximation method for real-time filtering. The accuracy of the conventional separable representation, however, is inadequate when the kernel size is immense. To improve the accuracy, we prepare dual kernels that have different kernel weights for horizontal and vertical filtering of separable filtering. In the experiment, we validate the proposed implementation by using three kinds of filters; bilateral filtering, dual bilateral filtering, and non-local means filtering. Experimental results show that the proposed implementation has higher accuracy while the computational time is almost the same. Moreover, the proposed implementation is practical for denoising and disparity map refinement applications.

We propose a fast post filter set for removing coding distortions of depth maps. Lossy coding generates various distortions, such as mosquito and block noises, edge blurs, and over quantization. These distortions seriously deteriorate image quality of synthesized views in free viewpoint image rendering. Thus, we propose the post filter set which includes median filter, Gaussian filter, min-max blur remove filer, and binary weighted range filter to remove these noises. In experiments, we use various codecs, which are JPEG, JPEG-LS, JPEG2000, and H.264/AVC, for depth map coding, and synthesize views with the coded depth maps. Experimental results show that our post filter set can improves every codecs performance. Improvement of PSNR is larger than the conventional post filter, and especially JPEG is large. The computational time of the filter set, which is implemented by C++ with SIMD optimization, is within 5.2 ms at high bit rate cases, and within 15.3 ms at low bit rate cases.

In this paper, we propose a free viewpoint image rendering method combined with filter based alpha matting for improving the image quality of image boundaries. When we synthesize a free viewpoint image, blur around object boundaries in an input image spills foreground/background color in the synthesized image. To generate smooth boundaries, alpha matting is a solution. In our method based on filtering, we make a boundary map from input images and depth maps, and then feather the map by using guided filter. In addition, we extend view synthesis method to deal the alpha channel. Experiment results show that the proposed method synthesizes 0.4 dB higher quality images than the conventional method without the matting. Also the proposed method synthesizes 0.2 dB higher quality images than the conventional method of robust matting. In addition, the computational cost of the proposed method is 100x faster than the conventional matting.

In this paper, we propose dynamic control of output timing of fragrance in a networked virtual environment to improve Quality of Experience (QoE). The control changes the output timing of fragrance dynamically according to the movement speed and direction of an object which is a fragrance source. We implement the control in a remote ikebana system using olfactory and haptic media and investigate the effect of the control by QoE assessment. As a result, we demonstrate that Mean Opinion Score (MOS) in the case where the control is used is high and does not largely depend on the average movement speed and movement direction of a flower, which is a fragrance source.

In this paper, we handle an air hockey game which two users play with haptic interface devices as an example of networked real-time games. In order to improve the interactivity of the air hockey game, we propose the adaptive Δ (delta)-causality control scheme with prediction, which keeps the consistency and causality high and predicts positional information after a constant time. In QoE (Quality of Experience) assessment, we assess the output quality and interactivity of local mallet, output quality of opponent's mallet, output quality and interactivity of puck, and comprehensive quality. As a result, we illustrate that the proposed scheme is effective and there exists the optimal value of the prediction time.

Free viewpoint video attracts many researchers. With the video, users can change viewpoint of the video freely at the user side. Transmitting such media over IP network, the network delay deteriorates qualities of the media. In this paper, we investigate the influence of network delay in free-viewpoint video transmission by QoE (Quality of Experience) assessment. We address two transmission methods for free-viewpoint normal and stereoscopic videos. One is the synthesized image transmission method, and the other is the depth and image transmission method. Depth and image are data for synthesizing an image. We assess the image quality, the interactivity of viewpoint change, and the comprehensive quality. Assessment results demonstrate that the image quality of the synthesized image transmission method is higher than that of the depth and image transmission method, which is advantageous in terms of interactivity. The results also illustrate that the free-viewpoint stereoscopic video has higher image quality than the normal one.

In this paper, we investigate the influence of network delay on the quality of experience (QoE) for a tele-operation system with 3D (i.e., stereoscopic) video and haptic media. We assess the video output quality, operability of the haptic interface device, inter-stream synchronization quality (or inter activity), and comprehensive quality as QoE. We also evaluate the application-level quality of service (QoS). By multiple regression analysis, we demonstrate that it is possible to estimate QoE parameters from QoS parameters with a high degree of accuracy.

In this paper, we carry out a transparency (i.e., haptic realism) analysis and propose a haptic synchronization scheme for a force-reflecting teleoperation over time-varying network delay. Although previous researches proposed several haptic synchronization schemes to efficiently compensate for delay jitter, defining a proper synchronization delay for transparency improvement remains a challenge. Therefore, the transparency analysis quantifies the force feedback distortion caused by network delay and packet loss, and predicts the maximally allowable delay and loss for predefined transparency requirements. In order to minimize the force feedback distortion, the proposed haptic synchronization scheme controls the playout times of the delayed transmitted haptic events based on the transparency analysis. According to simulation and experimental results, the transparency analysis provides an acceptable quantification method about haptic interaction quality with respect to network delays and packet losses. It is also verified that the proposed scheme guarantees more transparent haptic interaction than existing synchronization schemes tailored for networked haptics.

In this paper, we propose a method of free viewpoint image generation with super resolution. In the conventional approaches, such as nearest neighbor and linear interpolation, the synthetic image on zoomed virtual view tends to have low resolution, because the reference images do not have enough textures. To overcome this problem, we reconstruct the image with super resolution. Super resolution can generate higher image resolution than the input image one, and then we combine super resolution with free viewpoint image generation. In the experiment, we use a camera array which contains 11 × 11 aligned cameras and use 4 × 4 cameras subset per pixel to reconstruct image by means of super resolution. The experimental results show that synthesized image in the effective range has about 4.5 dB higher PSNR than ones created by the nearest neighbor and 2.5 dB higher than ones created by the linear interpolation.

This paper analyzes the influences of frame delay and packet loss on stereoscopic vision when stereoscopic video is transferred over a IP network. We employ live action videos which are transferred to a head-mount-display (HMD) and do the assessment on stereoscopic perception. As a result, we found that speed and movement direction of the attention object play a great role on the deterioration when frame delay and packet loss exist.

In this paper, we deal with a remote haptic instruction system in which a teacher teaches a student how to write characters by using haptic interface devices. We have two cases in the system. In one case, a pen is attached to only the student terminal, and video is transmitted from the student terminal to the teacher terminal. In the other case, a pen is attached to each of the two terminals, and video is transmitted bi-directionally between the terminals. In both cases, we make a comparison between two-way transmission and one-way transmission of the sense of force by subjective assessment.

By subjective assessment, this paper investigates the effects of group (or inter-destination) synchronization control in networked virtual environments where users have a conversation with each other by using avatars constructed by computer graphics (CG) and live voices. Assessment results show that the fairness among the users can be maintained high under the group synchronization control in networked competitive work. We also demonstrate that the synchronization quality of networked collaborative work can be improved under the group synchronization control. In addition, we make an experiment in which we use videos instead of avatars, and we examine the difference between results of the avatar case and those of the video case.

In this paper, we deal with a remote haptic calligraphy system in which a teacher instructs multiple students at remote location show to write characters while conveying the sense of force by multicast communications. We also propose an error control scheme which transmits important media units (MUs) multiple times which include the positional information in the case where the speed of the teacher's brush stroke is faster than a threshold value by adding the MUs to the succeeding MUs as well as transmitting them independently. By experiment, we demonstrate that the proposed scheme can keep the media output quality high at the expense of slight increase of the traffic amount.

In this paper, we enhance group (or inter-destination) synchronization control, which adjusts the output timing among multiple destinations, for a remote drawing system using haptic media. Under the control, an instructor and a learner can draw figures while watching the identical virtual space. By subjective assessment, we demonstrate that Mean Opinion Score (MOS) of the instructor can be improved greatly at the expense of slight deterioration in MOS of the learner. Also, we show that MOS of the learner can be improved by reducing the spring constant used in calculating the reaction force.

In this paper, we propose a remote control system which controls a haptic interface device with another remote haptic interface device. Haptic feeling can be transmitted by the system. Applications of the system are a remote calligraphy system, a remote drawing instruction system, a remote medical operation system, and so on. The paper deals with the remote drawing instruction system by which an instructor trains a learner how to draw pictures or figures while conveying the sense of force through the Internet. In order to clarify what kinds of control are needed in the system, we examine the influences of network delay, delay jitter and packet loss on the output quality of haptic media by subjective assessment of drawing figures

This paper proposes an adaptive scheme in which causality and prediction control is exerted to preserve the consistency among players. The proposed scheme carries out the adaptive \Delta-causality control with prediction when the network load is light. When the network load is heavy, the dead-reckoning is used instead of the prediction in the scheme. By experiment, we make a performance comparison among six schemes including the proposed scheme. As a result, we illustrate that the proposed scheme is superior to the other schemes in terms of the consistency among players and the interactivity. %

This paper deals with collaborative work in which two users lift and move an object cooperatively by using haptic interface devices while one of the two is instructing the direction of the object’s movement by voice. By experiment, we investigate the influences of the network latency of voice and haptic media on the efficiency of the work. We also clarify the effect of voice by making a comparison of the

By experiment, this paper examines the influence of network latency on the fairness among players in a networked real-time game where we use haptic interface devices. In the experiment, we subjectively and objectively clarify the influence by changing the difference in network latency between two players. Experimental results show that the difference which leads to unfairness depends on the network latency. We also demonstrate that the differences larger than 30 ms or 40 ms lead to unfairness in the experimental system. Furthermore, we hardly perceive unfairness when the network latency of the two players is less than around 30 ms in the experiment.

This paper addresses an inter-stream synchronization issue between haptic media and voice in networked virtual environments. The paper proposes a media synchronization algorithm for the two types of media stream by enhancing the virtual-time rendering (VTR) algorithm, which the authors previously proposed. The new algorithm employs two types of error range in order to keep high quality of intra-stream synchronization at the expense of slight deterioration in the inter-stream synchronization quality. One is the imperceptible range of inter-stream synchronization error, and the other is the allowable range of the error. If the error is beyond the allowable range, the algorithm tries to reduce the error gradually until the error becomes within the imperceptible range. Otherwise, it accepts the error. By carrying out an experiment in which two users do collaborative work with haptic media and voice in a virtual space, we demonstrate the effectiveness of the algorithm quantitatively.

This paper proposes two group synchronization schemes, which adjust the output timing among destinations, in networked virtual environments where voice and video streams are output in a 3-D virtual space. We introduce the concept of the global importance of each media object, which includes a voice stream and a video one. The global importance is determined by the positional relations among media objects, and it represents how strongly each object attracts observer's attention in the virtual space. We enhance a centralized group synchronization control scheme called the synchronization maestro scheme and a distributed control scheme, which were previously proposed by the authors, in order to adjust the output timing of media streams among destinations according to the global importance. In addition, we illustrate the effectiveness of the proposed schemes by experiment.

This paper presents experimental results of inter-destination synchronization control in an integrated wired and wireless network. The experimental system consists of interconnected wired and wireless networks; the former is a router-based IP network, and the latter is a wireless LAN with two base stations. A server in the wired network multicasts a pair of audio and video streams to a terminal in the same wired network and a wireless terminal, which performs handover from one base station to the other. We exert inter-destination synchronization control between the two terminals using the synchronization maestro scheme, which the authors previously proposed. In the experiment, we measured the synchronization quality of inter-destination as well as intra-stream and inter-stream when handover occurred, and we confirmed the effectiveness of the control.

This paper studies user-level (or perceptual) QoS for multimedia applications over the Internet and demonstrates that media can compensate for each other from a perceptual point of view. For this study, we formulate the problem of the mutually compensatory property in terms of QoS mapping relation between application-level and user-level; we then conduct a simple experiment on lip synchronization to investigate the property. As a result, we observe the existence of the mutually compensatory property between voice and video. It is also shown that the property exists within a limited range of combinations of application-level QoS parameters. Furthermore, we point out the advantage of QoS control utilizing the property.

This paper proposes a distributed control scheme for causality and media synchronization in networked games where plural media streams such as computer data, voice, and video are dealt with together. According to the network load, the scheme adaptively preserves the temporal and causal relationships which exist among the media streams. It also performs group (or inter-destination) synchronization control, which adjusts the output timing among terminals for keeping the fairness among them. Furthermore, it exerts error control over computer data and video traffic control. We demonstrate the effectiveness of the scheme by carrying out an experiment of a networked shooting game.

This paper proposes a media synchronization scheme with adaptive /spl Delta/-causality control for networked multimedia applications in which the temporal and causal relationships exist among media streams such as computer data, voice, and video. In the scheme, the adaptive /spl Delta/-causality control, which varies the value of /spl Delta/ of the /spl Delta/-causality control according to the network load, is performed for causality, and the virtual-time rendering (VTR) algorithm, which the authors previously proposed, is used for media synchronization. The scheme also performs group (or inter-destination) synchronization control, which adjusts the output timing among terminals for preservation of the fairness among them, as well as error control and traffic control. We demonstrate the effectiveness of the scheme by carrying out an experiment of a networked shooting game.

This paper studies effect of packet scheduling algorithms at routers on media synchronization quality in live audio and video transmission by experiment. In the experiment, we deal with four packet scheduling algorithms: first-in first-out, priority queueing, class-based queueing and weighted fair queueing. We assess the synchronization quality of both intra-stream and inter-stream with and without media synchronization control. The paper clarifies the features of each algorithm from a media synchronization point of view. A comparison of the experimental results shows that weighted fair queueing is the most efficient packet scheduling algorithm for continuous media among the four.

This paper assesses the quality of media synchronization of recovery control schemes from asynchrony, which are referred to as reactive control schemes here, in terms of objective and subjective measures. We deal with four reactive control techniques: skipping, discarding, shortening and extension of output duration, and virtual time-contraction and time-expansion. We have carried out subjective and objective assessment of the media synchronization quality of nine schemes, which consist of combinations of the four techniques. The paper makes a comparison of media synchronization quality among the schemes. It also clarifies the relations between the two kinds of quality measures.

By experiment, this paper studies the responsiveness of layered multicast and feedback control for video traffic in reacting to network congestion over the Internet. We examine the influence of the responsiveness on the performance in our lip synchronization experimental system, where video and voice streams are multicast under controllable traffic and delay conditions. The paper also demonstrates the possibility of performance improvement by using the two techniques together. This scheme tries to solve the problem of large leave latency in layered multicast by taking advantage of the quickness in feedback control.

This paper proposes a transport-layer error recovery scheme using retransmission for live audio-video streams transferred over QoS non-guaranteed networks. The scheme employs an enhanced version of the virtual-time rendering (VTR) media synchronization algorithm, which adjusts media rendering-time according to the network condition and is referred to as RVTR (retransmission with VTR). By an experiment, we assess the synchronization quality of both intra-stream and inter-stream in RVTR and four other schemes for audio-video transmission. A comparison of the experimental results indicates that joint application of retransmission control and the VTR synchronization control as in RVTR is effective in the improvement of media synchronization quality and that either control alone does not produce much improvement.

This paper considers a networked multimedia application like distance learning in which a tutor distributes a stored video stream to students, and he/she sometimes explains the contents of the stored video with live voice and video streams. We propose a joint synchronization mechanism among the media streams. The mechanism takes advantage of the difference in the features of live and stored media. It makes the buffering time of the stored video stream at the destination longer than that of the live media streams. We also demonstrate the effectiveness of the mechanism by experiment. Furthermore, we examine the influence of the buffering time of the stored video stream on performance.

This paper presents results of an experiment in which plural video and voice streams transmitted over a network are output synchronously in networked virtual environments. We propose an adaptive QoS (quality of service) control scheme for video and voice traffic. According to the importance of each media object, CPU load and network load, the scheme adjusts the rendition rate of a 3D virtual space and the video resolution as well as the accuracy of media synchronization; also it can display a CG object instead of a less-important video object. In addition, the paper quantitatively examines the effect of the adaptive QoS control on the performance.

This paper makes a survey of algorithms proposed for continuous media synchronization in network environments. We classify media synchronization control techniques used in the algorithms into four categories: basic control, preventive control, reactive control and common control. We also pick four representatives from among the media synchronization algorithms and give outlines of them in order to explain how the techniques are employed in each algorithm. Furthermore, we make a comparison among 38 algorithms in terms of factors such as clocks, advance information on network delay bounds and synchronization control techniques, which determine the design of each algorithm.

For networked multimedia applications like distance learning in which a tutor explains the contents of a stored video stream to students with live voice and video streams, this paper proposes a joint synchronization mechanism between live and stored media. The mechanism makes the buffering time of stored media at each destination longer than that of live media. It also carries out retransmission control over stored media and group synchronization control, which adjusts the output timing among destinations in a multicast group. By experiment, we demonstrate the effectiveness of the mechanism.

This paper proposes a media synchronization scheme with causality control for distributed multimedia applications in which the temporal and causal relationships exist among media streams such as computer data, voice and video. In the scheme, the /spl Delta/-causality control is performed for causality, and the virtual-time rendering (VTR) algorithm, which the authors previously proposed, is used for media synchronization. The paper deals with a networked shooting game as an example of such applications and demonstrates the effectiveness of the scheme by experiment.

This paper presents a performance comparison between the single-stream and the multi-stream approaches for lip synchronization of live media (voice and video). The former transmits a single transport stream of interleaved voice and video, while the latter treats the two media as separate transport streams. Each approach has an option not to exert the synchronization control at the destination, which leads to four basic schemes. On an interconnected ATM-wireless LAN, we implemented the four basic schemes with RTP/RTCP on top of UDP and two variants which exercise dynamic resolution control of JPEG video. By the performance measurement of the six schemes, we compare them to identify and evaluate the advantages and disadvantages of each approach.

This paper makes an experimental comparison of performance among six media synchronization schemes in collaborative systems, where drawing on a shared window, voice and video streams need to be synchronized with each other. Five of the six schemes are based on the virtual-time rendering (VTR) algorithm proposed by the authors, and they differ from each other in the relation between master and slave streams. The remaining one employs another algorithm. In our experimental system using an interconnected ATM-wireless LAN, live drawing voice and video input at a source workstation are transferred separately and then they are synchronized and output at a destination workstation. This paper also presents the system performance such as mean square error of inter-stream synchronization and average delay time. In addition, we examine the effect of intrastream and inter-stream synchronisation control on the performance.

This paper proposes a group synchronization mechanism, which synchronizes slave destinations with the master destination, for stored media in multicast communications. At the master and slave destinations, intra-stream and inter-stream synchronization mechanisms which were proposed by the authors are employed to output the master media stream and slave media streams synchronously. We achieve group synchronization by adjusting the output timing of the master media stream at each slave destination to that at the master destination. We also deal with traffic control by media scaling and control of joining an in-progress multicast group. Furthermore, the paper presents experimental results using an ATM network. It shows the validity of the mechanism and illustrates the influence of parameters on the system performance.

An adaptive control procedure is proposed for the go-back-N and selective-repeat automatic repeat-request (ARQ) schemes. The procedure is to dynamically vary the number and length of continuously transmitted data blocks according to the bit error rate. The throughput of the adaptive ARQ schemes for a half-duplex transmission line is compared with the throughput of corresponding conventional schemes. Numerical results indicate that adaptive ARQ schemes are superior to conventional ARQ schemes when the bit error rate is not known or varies with time.>

The dynamic behavior of a reservation system with a slotted ALOHA reservation channel is analyzed in this paper. It is assumed that each user handles one message at a time and that each message consists of a group of packets with a general probability distribution for group size. An approximate Markovian model of the system is developed on the assumption that the state transition can occur only at the beginning of each frame. The model is analyzed by an approximate analytical technique called equilibrium point analysis. The throughput and average message delay characteristics are obtained, and the system stability behavior is demonstrated. A procedure is also given to get the optimum set of system parameters under constraint that the system is stable.