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An improved road impedance function in conformity with Chinese city road traffic is designed for calculating the actual transportation time based on real-time traffic information and the complex road environment in the city. The objective function minimizes the total distribution cost, including fixed cost, transportation cost, damage cost, energy cost, penalty cost, and carbon emission cost. A mathematical model is constructed for cold-chain logistics distribution path optimization considering the influence of road impedance. The model is solved using three particle swarm optimization algorithms with improved weights. The experimental results show that the self-adaptive weighted particle swarm optimization algorithm is more efficient in solving this model. Experimental results obtained from the cold-chain logistics path optimization model considering road impedance compared to those of the model without road impedance indicate that the former are closer to the actual situation. Based on the changes in carbon emission and total cost under different carbon taxes, we analyze the critical carbon tax value and the optimal carbon tax value range to improve the economic and environmental benefits in the distribution process. This study should prove to be of great practical significance and application value for logistics enterprises to conduct rational planning of path problems.

Content prefetching at road side units (RSUs) in vehicular networks can improve users’ experience by reducing the average data access latency. Prefetching algorithms proposed in the literature usually rely on a fixed modulation scheme, that corresponds to the lowest possible data rate for RSU-to-vehicles transmission. As a consequence, the network bandwidth is often inefficiently used. In this article, we propose to study the problem of efficient content broadcasting in vehicular networks and express it as a joint data-prefetching and broadcast transmission scheduling optimization problem, subject to cache size constraints and transmission rate adaptation constraints. In our study we consider a highway scenario covered by several RSUs, and take into account the deadline requirement of interactive applications. We express the problem as an integer linear programming problem, and solve it using a heuristic algorithm that determines: the content prefetching schedule, the broadcast transmission schedule and the rate adaptation schedule sequentially. Simulation results show that, i) it is beneficial to use adaptive rates to broadcast data instead of relying on single-rate with unicast transmissions; ii) using vehicular trajectories and content popularity in conjunction yields better results than simply relying on content popularity for content prefetching and caching; and iii) this holds even with inaccurately predicted vehicle locations and with delay-sensitive contents. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of scheduling real-time traffic in wireless networks under a conflict-graph interference model and single-hop traffic. The objective is to guarantee that at least a certain fraction of packets of each link are delivered within their deadlines, which is referred to as delivery ratio. This problem has been studied before under restrictive frame-based traffic models, or greedy maximal scheduling schemes like LDF (Largest-Deficit First) that can lead to poor delivery ratio for general traffic patterns. In this paper, we pursue a different approach through randomization over the choice of maximal links that can transmit at each time. We design randomized policies in collocated networks, multi-partite networks, and general networks, that can achieve delivery ratios much higher than what is achievable by LDF. Further, our results apply to any traffic (arrival and deadline) process that evolves as an unknown positive recurrent Markov chain. Hence, this work is an improvement with respect to both efficiency and traffic assumptions compared to the past work. We further present extensive simulation results over various traffic patterns and interference graphs to illustrate the gains of our randomized policies over LDF variants. [ABSTRACT FROM AUTHOR]

In recent years, noticeable progress has been made in the development of quantum equipment, reflected through the number of successful demonstrations of Quantum Key Distribution (QKD) technology. Although they showcase the great achievements of QKD, many practical difficulties still need to be resolved. Inspired by the significant similarity between mobile ad-hoc networks and QKD technology, we propose a novel quality of service (QoS) model including new metrics for determining the states of public and quantum channels as well as a comprehensive metric of the QKD link. We also propose a novel routing protocol to achieve high-level scalability and minimize consumption of cryptographic keys. Given the limited mobility of nodes in QKD networks, our routing protocol uses the geographical distance and calculated link states to determine the optimal route. It also benefits from a caching mechanism and detection of returning loops to provide effective forwarding while minimizing key consumption and achieving the desired utilization of network links. Simulation results are presented to demonstrate the validity and accuracy of the proposed solutions. [ABSTRACT FROM AUTHOR]

Wireless sensor networks (WSNs) have gained much attention in today's research domain for supporting a wide variety of applications including the multimedia applications. Multimedia applications that are regarded as the quality-of-service (QoS)-aware, delay sensitive, and bandwidth hungry applications require enough energy and communication resources. WSNs being the energy-scarce network have now been designed in such a way that they can support these delay-sensitive and time-critical applications. In this paper, we propose an energy-efficient routing protocol for heterogeneous WSNs to support the delay sensitive, bandwidth hungry, time-critical, and QoS-aware applications. The proposed QoS-aware and heterogeneously clustered routing (QHCR) protocol not only conserves the energy in the network, but also provides the dedicated paths for the real-time and delay sensitive applications. The inclusion of different energy-levels for the heterogeneous WSNs also provides the stability in the networks while minimizing the delay for the delay-sensitive applications. Extensive simulations have been performed to validate the effectiveness of our proposed scheme. Our proposed routing scheme outperforms other state-of-the-art schemes in terms of the delay performances.

The past decade witnessed the dramatic evolution from Quality of Service (QoS) to Quality of Experience (QoE) in the design of wireless networks, especially on the aspect of link scheduling. In many applications, end users are concerned more about transmission quality of an individual task rather than the quality of a link, where a task may refer to a piece of music, video, etc. and may include many packets. This paper proposes a new network model aiming at improving user experience by pushing the scheduling problem to the task layer. A novel QoE requirement is designed to generalize the QoS requirements of a task, which is the ratio requirement. Following this design, a corresponding scheduling policy is proposed to capture it for each task and then reach an application-aware transmission allocation. We theoretically analyze the performance of the scheduling policy, and discuss the design of an optimal solution and the impact of the QoE requirements. Finally, the simulation results indicate that our scheduling policy can significantly improve QoE. [ABSTRACT FROM AUTHOR]

In transportation-based cyberphysical systems (TCPS), also known as intelligent transportation systems (ITS), to increase traffic efficiency, a number of dynamic route guidance schemes have been designed to assist drivers in determining optimal routes for their travels. To determine optimal routes, it is critical to effectively predict the traffic condition of roads along the guided routes based on real-time traffic information collected by vehicular networks to mitigate traffic congestion and improve traffic efficiency. In this paper, we propose a Dynamic En-route Decision real-time Route guidance (DEDR) scheme to effectively mitigate road congestion caused by the sudden increase of vehicles and to reduce travel time and fuel consumption. DEDR considers real-time traffic information generation and transmission by vehicular networks. Based on the shared traffic information, DEDR introduces the trust probability to predict traffic conditions and to dynamically, en route, determine alternative optimal routes. DEDR also considers multiple metrics to comprehensively assess traffic conditions so that drivers can determine the optimal route with a preference to these metrics during travel. DEDR considers effects of external factors (bad weather, incidents, etc.) on traffic conditions as well. Through a combination of extensive theoretical analysis and simulation experiments, our data show that DEDR can greatly increase traffic efficiency in terms of time efficiency, balancing efficiency, and fuel efficiency, in comparison with existing schemes. [ABSTRACT FROM PUBLISHER]

The emerging vehicular ad hoc network (VANET) enables vehicles to access the Internet through roadside access points (APs). An important issue in system deployment is determining how many roadside APs shall be installed on a road. However, the existing works fail to provide rigorous and accurate analysis for VANETs. In this paper, we propose a general structure for Internet access in VANETs. It allows both real-time traffic and delay-tolerant traffic to be delivered to users in the most efficient ways. An analytical model is also proposed to analyze the system performance with random arrival of the vehicles. We finally develop an AP placement algorithm based on theoretical results derived from the model to deploy the minimal number of roadside APs with quality-of-service (QoS) guarantees. The simulation results have demonstrated the accuracy of the proposed analytical model and the efficiency of the proposed algorithm. [ABSTRACT FROM PUBLISHER]

Motivated by the regular service requirements of video applications for improving quality of experience (QoE) of users, we consider the design of scheduling strategies in multihop wireless networks that not only maximize system throughput but also provide regular interservice times for all links. Since the service regularity of links is related to the higher-order statistics of the arrival process and the policy operation, it is challenging to characterize and analyze directly. We overcome this obstacle by introducing a new quantity, namely the time-since-last-service (TSLS), which tracks the time since the last service. By combining it with the queue length in the weight, we propose a novel maximum-weight-type scheduling policy, called Regular Service Guarantee (RSG) Algorithm. The unique evolution of the TSLS counter poses significant challenges for the analysis of the RSG Algorithm. To tackle these challenges, we first propose a novel Lyapunov function to show the throughput optimality of the RSG Algorithm. Then, we prove that the RSG Algorithm can provide service regularity guarantees by using the Lyapunov-drift-based analysis of the steady-state behavior of the stochastic processes. In particular, our algorithm can achieve a degree of service regularity within a factor of a fundamental lower bound we derive. This factor is a function of the system statistics and design parameters and can be as low as two in some special networks. Our results, both analytical and numerical, exhibit significant service regularity improvements over the traditional throughput-optimal policies, which reveals the importance of incorporating the metric of time-since-last-service into the scheduling policy for providing regulated service. [ABSTRACT FROM AUTHOR]

In this paper the problem of Quality of Service (QoS) provisioning for the Real-Time secondary traffic in Cognitive Radio Networks (CRNs) is investigated. Supporting the Real-Time (RT) traffic in CRNs is a complicated task which requires elaborate consideration in different aspects of the network. Here we consider a practical model for the network. Furthermore, a novel packet scheduling scheme is proposed which can efficiently provide the QoS requirements of the RT Secondary Users (SUs). The variations of the SNR of wireless frequency channels which result in variable transmission rates on the channels are also taken into account in the proposed scheme. The resulting QoS parameters of the RT SUs are calculated analytically. The obtained results are also verified by simulations. The results provide helpful insight for the support of RT traffic in CRNs. [ABSTRACT FROM PUBLISHER]

In IEEE 802.16 specifications, a CRC field can be attached in the rear of a WiMAX MPDU. Thus, each intermediate node (relay node or base station) in an 802.16-based multihop network can perform error detection on a received WiMAX MPDU. On the sender, the ARQ mechanism will be enabled to retransmit the MPDU if a transmission error occurs and an ACK message cannot be received. However, the ARQ mechanism is unsuitable for real-time traffic due to the delay consideration and the CRC field becomes an option to reduce the overhead of a WiMAX MPDU. Once the CRC field is removed from a WiMAX MPDU, the error occurrence cannot be detected by the intermediate nodes in time, and the erroneous data is still forwarded in the network but discarded by the destination. The resources of nodes in a network are wasted. Hence, the error detection mechanism should be retained for real-time traffic, but the overhead of CRC should be reduced. In this paper, we study an efficient discrete-error-checking scheme (DECS) to reduce the CRC overhead for real-time traffic. The DECS only needs several CRC checking bits, which are attached behind some WiMAX MPDUs. The DECS can efficiently provide the error detection for the intermediate nodes to discard these erroneous and useless data early. Thus, the utilization of node resources and wireless bandwidth can be improved significantly. [ABSTRACT FROM AUTHOR]

The proliferation of different wireless access technologies, together with the growing number of multi-radio wireless devices suggest that the opportunistic utilization of multiple connections at the users can be an effective solution to the phenomenal growth of traffic demand in wireless networks. In this paper, we consider the downlink of a wireless network with N access points (\ssr APs) and M clients, where each client is connected to several out-of-band \ssr APs, and requests delay-sensitive traffic (e.g., real-time video). We adopt the framework of Hou and study the maximum total timely throughput of the network, denoted by C{\ssr T^{3}}, which is the maximum average number of packets delivered successfully before their deadline. Solving this problem is challenging since even the number of different ways of assigning packets to the \ssr APs is N^M. We overcome the challenge by proposing a deterministic relaxation of the problem, which converts the problem to a network with deterministic delays in each link. We show that the additive gap between the capacity of the relaxed problem, denoted by Cdet and C{\ssr T^{3}} is bounded by 2\sqrtN(Cdet+N\over4), which is asymptotically negligible compared to Cdet, when the network is operating at high-throughput regime. In addition, our numerical results show that the actual gap between C{\ssr T^{3}} and Cdet is in most cases much less than the worst-case gap proven analytically. Moreover, using LP rounding methods we prove that the relaxed problem can be approximated within additive gap of N. We extend the analytical results to the case of time-varying channel states, real-time traffic, prioritized traffic, and optimal online policies. Finally, we generalize the model for deterministic relaxation to consider fading, rate adaptation, and multiple simultaneous transmissions. [ABSTRACT FROM PUBLISHER]

This paper studies the problem of congestion control and scheduling in ad hoc wireless networks that have to support a mixture of best-effort and real-time traffic. Optimization and stochastic network theory have been successful in designing architectures for fair resource allocation to meet long-term throughput demands. However, to the best of our knowledge, strict packet delay deadlines were not considered in this framework previously. In this paper, we propose a model for incorporating the quality-of-service (QoS) requirements of packets with deadlines in the optimization framework. The solution to the problem results in a joint congestion control and scheduling algorithm that fairly allocates resources to meet the fairness objectives of both elastic and inelastic flows and per-packet delay requirements of inelastic flows. [ABSTRACT FROM PUBLISHER]

In this paper, our recent work interval-based orderly scheduling strategy (IOSS) is extended by adding quality-of-service (QoS) provisioning. A revised medium access control (MAC) protocol is introduced, which supports priority-based QoS in wavelength division multiplexing (WDM) networks with star topology. The proposed interval-based prioritized orderly scheduling strategy (IPOSS) operates in a distributed manner, and has the capability of handling channel collision and destinations conflicts in order to provide a collision-free scheduling scheme. Each node in the network is equipped with a tunable transmitter and a fixed receiver, assuring that the scheme is scalable with respect to the number of nodes and channels. Also, each node may accept high- and low-priority packet arrivals. IPOSS favors high-priority packets, without regarding packets' length or packets' destination. Moreover, the proposed scheme differentiates the packet's schedule order by prioritizing the long-length over the short-length packets. It is found that the adopted access control scheme achieves a critically high throughput-delay performance for real-time traffic. Furthermore, IPOSS presents a little bit improved throughput performance than IOSS scheme, since it handles in a different way the case in which two or more requests demand the same amount of transmission time. The traffic involved in the simulation results follows Bernoulli and Poisson distribution, regarding the arrival of the requests. [ABSTRACT FROM PUBLISHER]

Currently, there is a trend towards the implementation of industrial communication systems using wireless networks. However, keeping up with the timing constraints of real-time traffic in wireless environments is a hard task. The main reason is that real-time devices must share the same communication medium with timing unconstrained devices. The VTP-CSMA architecture has been proposed to deal with this problem. It considers an unified wireless system in one frequency band, where the communication bandwidth is shared by real-time and non-real-time communicating devices. The proposed architecture is based on a virtual token passing (VTP) procedure that circulates a virtual token among real-time devices. This virtual token is complemented by an underlying traffic separation mechanism that prioritizes the real-time traffic over the non-real-time traffic. This is one of the most innovative aspects of the proposed architecture, as most part of real-time communication approaches are not able to handle timing unconstrained traffic sharing the same communication medium. A ring management procedure for the VTP-CSMA architecture is also proposed, allowing real-time stations to adequately join/leave the virtual ring. [ABSTRACT FROM PUBLISHER]

Based on the requirements of beyond 3G mobile communication systems, the access network architecture and media access control technique for B3G systems are studied. The proposed novel access network architecture, which can reduce network complexity and improve system performance, is introduced. Centralized mini-slot packet reservation multiple access (CMPRMA), based on OFDMA, is proposed, which not only can inherit the advantages of MPRMA and support real-time traffic well, but can also supply the resource reservation scheme for data traffic and support transmission for data traffic efficiently [ABSTRACT FROM PUBLISHER]

As the wireless environment becomes ever more populated and complex, individual networks offering single or restricted services will become ever more uncompetitive. Common radio resource management algorithms and strategies are used in heterogeneous or converged wireless networks to integrate multiple physical radio interfaces to support different levels of data rates, mobility, and traffic. Admission control in a common RRM environment is used to select the most appropriate wireless access based on service type, user preference, and network load. This is used to provide a balance between real-time and non-real-time traffic across the available access technologies. The development of common radio resource management strategies requires a suitable platform of coupled access networks and is the motivation behind the development of a converged wireless test platform. The tightly coupled platform supports voice and data call setup and delivery over UMTS and WLAN [ABSTRACT FROM PUBLISHER]

Recent advances in signal processing techniques have enabled wireless networks to have multi-packet reception (MPR) capability at the physical layer, where it is possible to receive more than one packets when concurrent transmissions occur. In this paper, we propose a novel multi-reservation multiple access (MRMA) scheme for future wireless multimedia networks based on such an MPR channel model. MRMA can fully exploit the channel's MPR capacity while fulfilling the quality of service requirements of different multimedia traffic. Similar to many existing reservation protocols, MRMA guarantees (i) bounded access delay for real-time traffic by dropping packets not transmitted within the required delay bound, and (ii) satisfaction of the required packet loss ratio when applied in conjunction with a connection admission control method to limit the number of admitted traffic streams. MRMA further incorporates a priority control mechanism to differentiate guaranteed and best-effort services for real-time voice/video and connectionless data, respectively. Analytical and simulation results are presented to illustrate the effectiveness of MRMA in service differentiation and increasing the number of admitted traffic streams [ABSTRACT FROM PUBLISHER]

The IEEE 802.16 standard defines three types of scheduling services for supporting real-time traffic, unsolicited grant service (UGS), real-time polling service (rtPS), and extended real-time polling service (ertPS). In the UGS service, the base station (BS) offers a fixed amount of bandwidth to a subscriber station (SS) periodically, and the SS does not have to make any explicit bandwidth requests. The bandwidth allocation in the rtPS service is updated periodically in the way that the BS periodically polls the SS, which makes a bandwidth request at the specified uplink time slots and receives a bandwidth grant in the following downlink subframe. In the ertPS service, the BS keeps offering the same amount of bandwidth to the SS unless explicitly requested by the SS. The SS makes a bandwidth request only if its required transmission rate changes. In this article we study the performance of voice packet transmissions and BS resource utilization using the three types of scheduling services in IEEE 802.16-based backhaul networks, where each SS forwards packets for a number of voice connections. Our results demonstrate that while the UGS service achieves the best latency performance, the rtPS service can more efficiently utilize the BS resource and flexibly trade-off between packet transmission performance and BS resource allocation efficiency; and appropriately choosing the MAC frame size is important in both the rtPS and ertPS services to reduce packet transmission delay and loss rate [ABSTRACT FROM PUBLISHER]

In the emerging IEEE 802.11e MAC protocol, the enhanced distributed channel access (EDCA) is proposed to support prioritized QoS; however, it cannot guarantee strict QoS required by real-time services such as voice and video without proper network control mechanisms. To overcome this deficiency, we first build an analytical model to derive an average delay estimate for the traffic of different priorities in the unsaturated 802.11e WLAN, showing that the QoS requirements of the real-time traffic can be satisfied if the input traffic is properly regulated. Then, we propose two effective call admission control schemes and a rate control scheme that relies on the average delay estimates and the channel busyness ratio, an index that can accurately represent the network status. The key idea is, when accepting a new real-time flow, the admission control algorithm considers its effect on the channel utilization and the delay experienced by existing real-time flows, ensuring that the channel is not overloaded and the delay requirements are not violated. At the same time, the rate control algorithm allows the best effort traffic to fully use the residual bandwidth left by the real-time traffic, thereby achieving high channel utilization [ABSTRACT FROM PUBLISHER]

Recently, polling has been included as a resource sharing mechanism in the medium access control (MAC) protocol of several communication systems, such as the IEEE 802.11 wireless local area network, primarily to support real-time traffic. Furthermore, to allow these communication systems to support multimedia traffic, the polling scheme often coexists with other MAC schemes such as random access. Motivated by these systems, we develop a model for a polling system with vacations, where the vacations represent the time periods in which the resource sharing mechanism used is a non-polling mode. The real-time traffic served by the polling mode in our study is telephony. We use an on-off Markov modulated fluid (MMF) model to characterize telephony sources. Our analytical study and a counterpart validating simulation study show the following. Since voice codec rates are much smaller than link transmission rates, the queueing delay that arises from waiting for a poll dominates the total delay experienced by a voice packet. To keep delays low, the number of telephone calls that can be admitted must be chosen carefully according to delay tolerance, loss tolerance, codec rates, protocol overheads and the amount of bandwidth allocated to the polling mode. The effect of statistical multiplexing gain obtained by exploiting the on-off characteristics of telephony traffic is more noticeable when the impact of polling overhead is small [ABSTRACT FROM PUBLISHER]

AM and FM radio has long been the primary source of mobile entertainment and information. Radio's conversion to digital broadcasting through deployment of the FCC approved HD radio technology with drive new and innovative telematics services. In the digital world, the radio will be transformed to a centralized source of expanded entertainment and information services along with enhanced in-vehicle systems. At a fraction of the cost of other wireless services, HD radio technology will provide platform-specific customer retention information, real-time traffic for navigation system overlay, PVR-like functionality, on-demand audio, mobile commerce and much more, dramatically upgrading automobile manufacturers' ability to reach and profit from radio's 200 million listeners per day [ABSTRACT FROM PUBLISHER]

In multi-service wireless networks, asymmetric bandwidth allocation has been proposed to satisfy the requirements of asymmetric traffic load introduced by some data applications. However, it is difficult to promptly adjust bandwidth allocation on uplink and downlink according to the dynamics of traffic load. Inappropriate call admission control (CAC) policies in this environment may admit superfluous real-time (RT) calls or non real-time (NRT) calls and thus lead to low bandwidth utilization. In this paper, we propose and evaluate two new CAC schemes to address the problems caused by the mismatch of bandwidth allocation and traffic changing in multi-service wireless networks with bandwidth asymmetry between uplink and downlink. By determining the admissible regions for the RT calls and the NRT calls, the proposed schemes prevent the calls of a specific class from overusing the bandwidth resources. Mathematical analysis and simulation experiments are employed to study and compare the performance of the proposed schemes and the existing schemes. The numerical results show that the proposed schemes can achieve better performances in terms of call blocking probability and bandwidth utilization compared to some existing schemes, even those performing well in bandwidth asymmetry wireless networks. [ABSTRACT FROM AUTHOR]

While backbone networks have experienced substantial changes in the last decade, access networks have not changed much. Recently, passive optical networks (PONs) seem to be ready for commercial deployment as access networks, due to the maturity of a number of enabling technologies. Among the PON technologies, Ethernet PON (EPON) standardized by the IEEE 802.3ah Ethernet in the First Mile (EFM) Task Force is the most attractive one because of its high speed, low cost, familiarity, interoperability, and low overhead. In this paper, we consider the issue of upstream channel sharing in the EPONs. We propose a novel multiple-access control scheme to provide bandwidth-guaranteed service for high-demand customers, while providing best effort service to low-demand customers according to the service level agreement (SLA). The analytical and simulation results prove that the proposed scheme performs best in what it is designed to do compared to another well-known scheme that has not considered providing differentiated services. With business customers preferring premium services with guaranteed bandwidth and residential users preferring low-cost best effort services, our scheme could benefit both groups of subscribers, as well as the operators. [ABSTRACT FROM PUBLISHER]

One of the major challenges in the design of future-generation high-speed networks is the provision of quality-of-service (QoS) to real-time traffic. In this paper, we propose a novel scheduling scheme, namely differentiated dropping scheduling (DDS), which is designed to handle real-time traffic in passive star-coupled wavelength division multiplexing (WDM) optical networks. By taking channel and destination availability into account, DDS can dramatically improve network performance in terms of message loss rate. Moreover, this scheme has the capacity of preventing channel collision and destination conflict. In order to evaluate the proposed DDS algorithm, extensive discrete-event simulations and mathematical performance comparison are conducted by comparing its performance with Moore and Hodgson's algorithm and the earliest-due-date (EDD) algorithm. The results show that DDS can achieve the best performance among the three algorithms. [ABSTRACT FROM PUBLISHER]

MobiWeb is a proxy-based network architecture designed to enhance the performance of adaptive real-time streams over 3G wireless links. MobiWeb includes a priority scheme that preserves media smoothness despite short-term fluctuations of the link, as well as an adaptation mechanism applied to streams responding to long-term link changes and handoffs. A set of timers permits the rapid exploration of the link, increasing the utilization of resources when they are abundant, while forcing enhanced streams to back off to more moderate resource usage when resources are scarce. MobiWeb uses admission control for real-time traffic in order to provide a base level of quality, while remaining transparent to unaware best-effort traffic. This article validates the enhanced performance of adaptive real-time streams when MobiWeb is used through the evaluation of several scenarios simulated on NS-the Network Simulator tool [ABSTRACT FROM PUBLISHER]

A new ATM AAL2 to support low-bit-rate and delay-sensitive applications in an ATM environment has been approved by the ITU-T and ATM Forum. AAL2 allows multiplexing of voice/data packets (minicells) from different users in a single ATM connection, thus improving the utilization of the network resources. This article identifies issues related to AAL2 such as the application environment, the gain obtained by multiplexing voice packets from different users on a single ATM connection, buffer requirements, and cell assembly delay. To analyze these issues, we modeled and simulated ATM trunking between a base transceiver station and the mobile switching center. The performance simulations show that the multiplexing gain obtained by AAL2 is significant, and the output buffer requirement at the ATM node is small. In addition, the results show that a timeout mechanism is needed to limit the ATM cell assembly delay in order to meet the delay requirements of real-time traffic such as voice [ABSTRACT FROM PUBLISHER]

This paper studies the problem of scheduling in single-hop wireless networks with real-time traffic, where every packet arrival has an associated deadline and a minimum fraction of packets must be transmitted before the end of the deadline. Using optimization and stochastic network theory we study the problem of scheduling to meet quality of service (QoS) requirements under heterogeneous delay constraints and time-varying channel conditions. Our analysis results in an optimal scheduling algorithm which fairly allocates data rates to all flows while meeting long-term delay demands. We also prove that under a simplified scenario our solution translates into a greedy strategy that makes optimal decisions with low complexity. [ABSTRACT FROM PUBLISHER]

Traditional wireless sensor networks (WSNs) working in the license-free spectrum suffer from uncontrolled interference as the license-free spectrum becomes increasingly crowded. Designing a WSN based on cognitive radio can be promising in the near future in order to provide data transmissions with quality of service requirements. In this paper we introduce a cognitive radio sensor network (CRSN) and analyze its performance for supporting real-time traffic. The network opportunistically accesses vacant channels in the licensed spectrum. When the current channel becomes unavailable, the devices can switch to another available channel. Two types of channel switchings are considered, in periodic switching (PS) the devices can switch to a new channel only at the beginning of each channel switching (CS) interval, while in triggered switching (TS) the devices can switch to a new channel as soon as the current channel is lost. We consider two types of real-time traffic, i) a burst of packets are generated periodically and the number of packets in each burst is random, and ii) packet arrivals follow a Poisson process. We derive the average packet transmission delay for each type of the traffic and channel switching mechanisms. Our results indicate that real-time traffic can be effectively supported in the CRSN with small average packet transmission delay. For the network using PS, packets with the Poisson arrivals experience longer average delay than the bursty arrivals; while for the network using TS, packets with the bursty arrivals experience longer average delay. [ABSTRACT FROM PUBLISHER]