In this paper, a sequential channel sensing algorithm for multichannel heterogeneous Cognitive Radio Networks (CRNs) is studied. More specifically, a new transmission algorithm is introduced and its performance is evaluated via simulations. In the proposed algorithm, referred to as “Distributed algorithm”, we assume that the secondary users select their transmission channels without coordination by a centralized entity. In evaluating the performance of the proposed algorithm, we considered the likelihood of false alarm and missed detection. Our event-driven simulations results have shown that the new transmission algorithm we have introduced improve the average secondary Mbits transmitted in each time slot, which are considerably higher than the corresponding results of (i) the “γ-persistent strategy” introduced in [7] and (ii) the p-persistent random access sequential channel sensing algorithm (PPRA) for multichannel CRNs introduced in [11].

It is our sincere pleasure to welcome you to the IEEE Workshop on Video Everywhere, which will take place on June 4 in Madrid, Spain, as part of the 14th IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM 2013). VidEv focusses on the significant challenges that must be addressed in order to enable the full potential of mobile video networking. After a very thorough and selective process, our workshop includes 6 papers which address various key issues relating to mobile video. The workshop will bring together researchers from industry and academia in order to discuss their views on the future of mobile video.

The subject of Call Admission Control (CAC) for wireless networks has been studied extensively in the literature. Another subject on which many researchers have focused their attention is that of video traffic modeling. However, user mobility, combined with the rapidly growing number of "greedy" multimedia applications, in terms of bandwidth and Quality of Service (QoS) requirements, form a challenging and yet unresolved problem for third and fourth-generation wireless networks. In recent work, we have built a Discrete Autoregressive (DAR (1)) model to capture the behavior of multiplexed H.263 videoconference movies from variable bit rate (VBR) coders. Based on this model, we propose in this work a new efficient CAC scheme for wireless cellular networks, which differs from the existing proposals in the literature in that it uses precomputed traffic scenarios combined with online simulation for its decision making. Our scheme is shown, via an extensive simulation study comparison and a conceptual comparison with well-known existing approaches, to clearly excel in terms of QoS provisioning to users receiving videoconference videoconference and Web traffic. To the best of our knowledge, this is the first work in the relevant literature where such an approach has been proposed.

User mobility, combined with the rapidly growing number of multimedia applications, form a challenging and yet unresolved problem for the development of call admission control schemes over next generation wireless cellular networks. In recent work the behavior of H.263 videoconference traces have been modeled with the use of a discrete autoregressive (DAR(Garawi et al., 2006)) model. Based on this model, a new efficient CAC scheme for videoconference traffic over cellular networks was proposed in this work, which uses precomputed traffic scenarios for its decision-making. The scheme is shown, via an extensive simulation study, to clearly excel in comparison with well-known existing approaches, in terms of quality of service (QoS) provisioning to users receiving videoconference traffic.

Powerline communications (PLC) are currently being considered as an alternative for high-speed data communications and Internet access. With multiple outlets in almost every room, power lines are already the most pervasive network in the home or small office. This work presents a new medium access control (MAC) protocol for the "last mile" access PLC networks. Via an extensive simulation study, our protocol is compared to a well-known protocol from the literature and is shown to excel both in network utilization and in the average signaling delay required for the completion of the transmission request procedure.

An efficient medium access control (MAC) protocol is critical for the performance of a wireless sensor network (WSN), especially in terms of energy consumption. In this work we discuss the efficiency of S-MAC, a well-known MAC protocol for WSNs, and propose an improvement on the protocol. Via an extensive simulation study considering the cases of both simple and complicated topologies, the enhanced protocol is shown to outperform the original version of S-MAC in energy conservation

We explore, via an extensive simulation study, the performance of call admission control (CAC) and traffic policing mechanisms proposed for transmitting multiple-layered videoconference movies over a wireless channel of high capacity, depending on the user's needs and requests. We focus both on MPEG-4 and H.263 coded movies, and, in the latter case, our scheme achieves high aggregate channel throughput, while preserving the very strict quality of service (QoS) requirements of the video traffic.

A medium access control (MAC) protocol for wireless multimedia communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice, H.263 variable bit rate (VBR) video and bursty e-mail data packet traffic over a wireless picocellular system of high capacity. Our scheme achieves high aggregate channel throughput in all examined cases of traffic loads, while satisfying the quality of service (QoS) requirements of each traffic type.

In this paper we explore, via an extensive simulation study, the performance of a new medium access control (MAC) protocol when integrating voice, video and E-mail data packet traffic over a wireless channel of high capacity, with errors. We evaluate the voice and video packet dropping probabilities and the average E-mail data message delays. Our scheme achieves high aggregate channel throughput in all cases of traffic load, despite the presence of noise in the system and the very restraining video dropping probability limit.

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice, MPEG-4 video and e-mail data packet traffic over a wireless channel of high capacity. Our scheme achieves high aggregate channel throughput in all cases of traffic load, while preserving the quality of service (QoS) requirements of each traffic type.

A new medium access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice, video and data packet traffic over a wireless channel of high capacity. Depending on the number of video users admitted into the system, our protocol varies: (a) the request bandwidth dedicated to resolving the voice users contention, and (b) the probability with which the base station grants information slots to voice users, in order to preserve full priority for video traffic. We evaluate the voice and video packet dropping probabilities for various voice and video load conditions, and the average data message delays. As proven by the comparison with a previously introduced efficient MAC scheme (DPRMA), when integrating voice and video traffic our scheme obtains higher voice capacity and aggregate channel throughput. When integrating all three traffic types, our scheme achieves high aggregate channel throughput in all cases of traffic load.

In the recent years many applications have emerged, where the demand for communicating with a very large number of small-size and low-cost nodes becomes a necessity. Such applications involve for example, radio frequency identification (RFID) and smart card networks, or even mobile computing devices, in general. A critical energy constraint is imposed on the communication (access) protocols used in these systems, so that the total time a node needs to be active for transmitting or receiving information should be minimized. Another area with great interest is that of broadcast-based information systems which, compared to traditional unicast data transfer, can be much more efficient for disseminating information to a large number of nodes in applications where there is a high degree of commonality among node interests. Unlike previous work on energy-conserving protocols with unicast data transfer, we propose and evaluate broadcast-based communication protocols with energy constraint, in which the number of time slots during which nodes need to be in the active state is minimized, while the access delays are kept low.

A new multiple access control (MAC) protocol for mobile wireless communications is presented and investigated. We explore, via an extensive simulation study, the performance of the protocol when integrating voice and data traffic over two wireless channels, one of medium capacity (referring mostly to outdoor microcellular environments) and one of high capacity (referring to an indoor microcellular environment). We evaluate the voice packet dropping probability and access delay, as well as the data packet access and data message transmission delays for various voice and data load conditions. Our protocol achieves near-optimal voice sources multiplexing results along with most satisfactory voice and data performance and quality of service (QoS) requirements servicing.

Most multimedia applications require storage and retrieval of large amounts of continuous and discrete data at very high rates. Disk drives should be servicing such mixed workloads achieving low response times for discrete requests, while guaranteeing the uninterrupted delivery of continuous data. Disk scheduling algorithms for mixed workloads, although they play a central role in this task, have been overlooked by related multimedia research efforts, which so far have mostly concentrated on the scheduling of continuous requests only. The focus of this paper is on efficient disk I/O scheduling algorithms for mixed workloads in a multimedia storage server. We propose novel algorithms, a taxonomy of relevant algorithms, and study their performance through experimentation. Our results show that our proposed algorithms offer drastic improvements in discrete request average response times, low response-time variability, while serving continuous requests without interruptions.

Sufficient conditions are derived for achieving the two most important fairness criteria in the design of access protocols for high-speed metropolitan area networks (MAN), the delay and throughput fairness criteria, a probabilistic scheduling scheme, known as the p/sub i/-persistent protocol is considered, which has been shown to be suitable for applications requiring large bandwidth over long repeater-free distances and also amenable to an approximate analytical performance evaluation. It is found that the throughput fairness criterion is easier to achieve than its delay counterpart. The delay fairness, when achieved, induces approximate throughput fairness. The current practice in the field of protocol design for unidirectional bus MANs appears to focus almost exclusively on the throughput fairness. For example, in the DQDB protocol, although a bandwidth balancing function exists, balancing delay performance has never been dealt with.>

In this paper, a noisy slotted channel is considered. It is assumed that channel feedback might be misinterpreted due to the existence of noise on the channel. Furthermore, this disturbance is dependent on the channel state (either good or bad) which varies from slot to slot according to a Markov chain. Consequently, the occurrence of the a channel feedback error is dependent on previous occurrences of errors (i.e., with error memory). Under this assumption, the throughput performance of a random multiple-access algorithm, called the Two-Cell algorithm, is analyzed and the results are compared with the throughputs of the Capetanakis (1979) tree-splitting algorithm operating over the same channels. It is shown that the Two-Cell algorithm retains positive throughputs for all possible values of channel state parameters, and for all practical purposes, it outperforms the Capetanakis algorithm in terms of insensitivity to channel feedback errors.>

The analytical evaluation of the message delay in an approximate DQDB network model is investigated. The authors extend the results obtained by C. Bisdikian (1990), which assumes that each network node can queue at most one packet, to the case of node queues each holding an entire message containing l packets, via some unobvious reselection of model definitions. Corresponding to the single-packet waiting time analysis, they obtain an expression for the number of requests queued ahead of an arriving message, from which an expression for the average message delay can be derived. One conclusion drawn from the analysis is that the average steady-state message delay is linear in sufficiently large l. Furthermore, the analytical results can provide an upper bound on the mean message delay for variable message size, and explain some observations of earlier simulation studies.>

The p/sub i/-persistent protocol, a probabilistic scheduling that is suitable for multiple-access communication applications requiring large bandwidth over very long distances, is considered. A dynamic control algorithm for the multipriority p/sub i/-persistent protocol that makes it possible to adapt to changing network conditions in a fully distributed manner is presented. Through a simulation model, the performance of the dynamic algorithm under various changing network scenarios is studied, and the ability of the protocol to provide the desired quality of service to each priority class of traffic is demonstrated.>

The effect of the Bernoulli slot occupancy approximation, which is assumed in most distributed queue dual bus (DQDB) analytical models, on the throughput-delay characteristics of DQDB networks is studied. Studies cover a variety of traffic statistics and network configurations. The results reveal that the influences of the Bernoulli slot occupancy approximation are message length, internode distance, and carried network load dependent. In general, for light to medium carried network load and relatively short message length, the analytical model tends to underestimate the mean message delay. The shorter the internode distance is, the smaller are the network load and message length values at which the analytical model starts to overestimate the mean message delay.

While a variety of medium access protocols have been proposed for metropolitan area networks (MANs), the problem of handling multipriority traffic effectively in these networks remains open. The authors present a simple and effective priority mechanism for an existing MAN protocol known as the p/sub i/-persistent protocol, a probabilistic scheduling scheme that has been shown to be suitable for applications requiring large bandwidth over long, repeater-free distances. The mechanism works by clipping the low-priority stations in a controlled manner, thereby increasing the bandwidth available to the high-priority stations. This mechanism operates entirely within the framework of the basic p/sub i/-persistent protocol and may be easily tailored to achieve specific performance goals by selection of a single operating parameter. A multipriority version of a distributed algorithm by which the stations can update their operating parameters and adapt to changing network conditions dynamically is also presented.>

A method for analyzing the delay distribution of window random-access algorithms is presented. The window size is allowed to vary during the operation of the algorithm. It is shown that the quantities of interest in the computation of the delay distribution can be related to the solution of appropriate infinite systems of linear equations. Once the constants and the coefficients of the unknowns of the system are determined, bounds on the solution can be developed by applying previously developed methodologies. The method is applied to the delay distribution analysis of the Capetanakis window random-access algorithm and the part-and-try algorithm, both under binary feedback.>

The IEEE 802-6 DQDB protocol solves the existing problems in prior round-robin high-speed MAC protocols. However, it introduces a new performance unfairness problem when the network size or channel bandwidth increases. The pi-persistent protocol, on the other hand, does not pass any control information over the channels, and was shown capable of achieving various fairness criteria, when each station knows the loads of all other stations. The authors propose a dynamic pi-persistent protocol that is capable of adjusting the network to fair operation in an environment where the station loads change over time. The protocol requires passing of some control information through the network. The information passed is not as detailed as the request information in DQDB. The authors analyze the performance of the protocol in a batch arriving model for load increase. The results show that the protocol is both fast and accurate in responding to network load changes.>

The analytical evaluation of the message delay in a distributed queue dual bus (DQDB) network is investigated. The authors extend the results obtained by C. Bisdikian et al. (1990), which assumes that each network station can queue at most one packet, to the case of station queues each holding an entire message containing l packets. An expression is obtained for the number of requests queued ahead of an arriving message. Given this expression, the average message delay can be calculated. One conclusion drawn from the analysis is that the average steady-state message delay is linear in sufficiently large l. It is also concluded that the message delay increases considerably with the network load. The analytical results predict the position-dependent characteristics of stations in a heavily loaded network and explain some observations and results of earlier simulation studies.>

Performance unfairness has been an open problem in the IEEE 802.6 (distributed queue dual bus, or DQDB) protocol. The unfairness can be amplified when erasure capability is introduced. This study is motivated by some efforts made by others in attempting to balance throughput in DQDB networks. The authors investigate two more fairness criteria-packet delay and packet blocking. The three fairness criteria are studied together with the p/sub i/-persistent protocol, assuming erasure capability in the network. For each criterion, values of various network settings which determine the achievability of the criterion are calculated analytically, and the performance characteristics of the protocol are shown. The analytical results closely match the results from simulations of the protocol. The results demonstrate that the fairness criterion on packet delay results in the best performance. However, the fair-packet delay requirement is also more difficult to maintain since it is the most sensitive to network load changes.>

A noisy slotted channel is considered. It is assumed that channel feedback might be misinterpreted due to the existence of noise on the channel. Furthermore, this disturbance is dependent on the channel state (either good or bad) which varies from slot to slot according to a Markov chain. Consequently, the occurrence of a channel feedback error is dependent on previous occurrences of errors (i.e., with error memory). Under this assumption, the throughput performance of a random multiple-access algorithm (called a two-cell algorithm) is analyzed, and the result is compared with the throughput of the J. Capetanakis (1979) tree splitting algorithm operating over the same channel. It is shown that the two-cell algorithm retains positive throughputs for all possible values of channel state parameters, and for all practical purposes, it outperforms the Capetanakis algorithm in terms of insensitivity to channel feedback errors.>

Each of the generated packets can have two different priorities (high- and low-priority packets). High-priority packets are assumed to have a more restrictive delay requirement than low priority ones. For such a system, the authors propose a class of synchronous random-access algorithms which use a small portion of the channel capacity for the announcements of the existence of high- or low-priority packets. The stability and throughput-delay performances of the algorithms are determined analytically for the cases when one or two minislots are used. Representative performance results are given and compared with a similar algorithm which does not use minislots. The algorithms give a delay advantage to the high-priority packet class without adversely affecting the delays of the low-priority packets. The algorithms use binary C-NC (collision versus noncollision) feedback, and the maximum throughput is 0.487 when two minislots are used.>

A method for delay distribution analysis of window random-access algorithms is presented. The window size is allowed to vary during the operation of the algorithm. It is shown that the quantities of interest can be obtained from the solution of appropriate infinite systems of linear equations. Once the constants and the coefficients of the unknowns of a system are determined, bounds on the solution can be developed by applying previously developed methodologies. The method is applied to the delay distribution analysis of the Capetanakis's window random-access algorithm and the part-and-try algorithm, both under binary C-NC feedback.>

The authors consider the problem of random access communication over a time-slotted channel, with binary success/failure feedback. The feedback informs the users only whether or not there was a success (single transmission) in the previous slot. They propose and analyze a limited feedback-sensing algorithm (each user is required to observe the channel feedback, from the time he generates a packet to the time that this packet is successfully transmitted). The algorithm requires central control implemented by a central receiver. The limit Poisson user model is adopted. The algorithm achieves a throughput of 0.322 and induces low delays for relatively low input rates.>

A simple full-feedback-sensing window random access algorithm is proposed and analyzed. The throughput of the algorithm is 0.429; its delay and resistance to feedback channel errors are better than those induced by J.I. Capetanakis's (ibid., vol.IT-25, p.505-15, Sept. 1979) window algorithm. In addition, the simple operations of the algorithm allow for the analytical evaluation of the output-traffic interdeparture distribution.>

A simple full-feedback-sensing window random-access algorithm is proposed and analyzed in the presence of the Poisson user model. The throughput of the algorithm is 0.43. The proposed algorithm is better than J.I. Capetanaki's dynamic algorithm (1979) with respect to its delay and resistance to channel errors. The simple operations of the algorithm, along with its regenerative properties, facilitate the computation of the output traffic interdeparture distribution. The obtained distribution is useful in the evaluation of interacting systems which adopt the algorithm for their internal transmissions.>

We examine the relation between the finite and the infinite population models for a class of random access algorithms. The algorithms in the class are a combination of random access and reservation techniques, they are synchronous, and they are studied under the condition that each of the users can monitor the channel feedback continuously (full feedback sensing). For any finite number of independent and identical users in the system, and any i.i.d. arrival process per user, the algorithms are stable, provided that the total input rate is less than one. However, as the population size increases, the stability of an algorithm in the class is determined by its throughput in the presence of the infinite population model for all practical purposes.