Search

Numerous approaches have been proposed to solve shortest path query problems (SPQPs) in either static or time-dependent spatial networks; however, these approaches are neither appropriately nor efficiently used to find the nearest shelter with fastest paths in disaster evacuations. In disasters, segments of a path computed and saved as the fastest might become impassable. The nearest shelter differs for people depending on their locations and can also change on the basis of an unpredictable and highly dynamic edge cost (e.g., maximum passable vehicle speed), which is influenced by disaster events. To solve this problem, this paper proposes a dynamic network model, which is called an event-dependent network, to represent a spatial network in a disaster. Effective approaches using multiple algorithms are proposed for on-the-fly computation of the nearest shelter and fastest paths in a disaster. A distributed system consisting of a server and multiple mobile clients using our approaches is presented for navigating the fastest paths for people to evacuate a disaster area. Real-world maps, such as a map of California, were used in our experiments. The results revealed that our approaches require less than 2 ms to find a new nearest shelter and its fastest paths, which is faster than other approaches for solving the fastest-path problem. [ABSTRACT FROM AUTHOR]

An important concept in the fifth generation of mobile networks is multitenancy, which allows diverse operators sharing the same wireless infrastructure. To support this feature in conjunction with the challenging performance requirements of future networks, more automated and faster planning of the required radio capacity is needed. Likewise, installing small cells is an effective resource to provide greater performance and capacity to both indoor and outdoor places. This paper proposes a new framework for automated cell planning in multitenant small cell networks. In particular, taking advantage of the available network data, a set of detailed planning specifications over time and space domains are generated in order to meet the contracted capacity by each tenant. Then, the network infrastructure and configuration are updated according to an algorithm that considers different actions such as adding/removing channels and adding or relocating small cells. The simulation results show the effectiveness of various methods to derive the planning specifications depending on the correlation between the tenant's and network's traffic demands. [ABSTRACT FROM PUBLISHER]

This paper considers the performance of time-domain power-allocation schemes with average and peak power constraints and proposes a constant-power allocation (CPA) scheme. In a Nakagami-m fading environment, an exact closed-form expression for the ergodic capacity of the proposed CPA scheme is derived, and the effect of the fading parameter m on the performance degradation due to a peak power constraint is investigated. The proposed scheme shows a near-optimum performance within 5% of the optimal capacity and provides a noticeable performance improvement as it reduces the peak-to-average power ratio (PAPR) with a signal-to-noise ratio (SNR) gain of approximately 8.5 dB while also mitigating the intercell interference in the uplink. [ABSTRACT FROM AUTHOR]

The IEEE 802.11 standard has enabled low-cost and effective wireless local area network (WLAN) services. It is widely believed that WLANs will become a major portion of the fourth-generation cellular system. The seamless handoff problem in WLANs is a very important design issue to support the new astounding and amazing applications in WLANs, particularly for a user in a mobile vehicle. The entire delay time of a handoff is divided into probe, authentication, and reassociation delay times. Because the probe delay occupies most of the handoff delay time, efforts have mainly focused on reducing the probe delay to develop faster handoff schemes. This paper presents a new fast handoff scheme (i.e., the DeuceScan scheme) to further reduce the probe delay for IEEE-802.11-based WLANs. The proposed scheme can be useful to improve wireless communication qualities on vehicles. A spatiotemporal approach is developed in this paper to utilize a spatiotemporal graph to provide spatiotemporal information for making accurate handoff decisions by correctly searching for the next access point. The DeuceScan scheme is a prescan approach that efficiently reduces the Iayer-2 handoff latency. Two factors of stable signal strength and variable signal strength are used in our developed DeuceScan scheme. Finally, simulation results illustrate the performance achievements of the DeuceScan scheme in reducing handoff delay time and packet loss rate and improving link quality. [ABSTRACT FROM AUTHOR]

This paper presents the design and analysis of general packet radio service (GPRS)-wireless local area network (WLAN) mobility gateway (GWMG) for the integration of GPRS and WLANs. The interworking between GPRS and WLANs is achieved by the GWMG that resides on the border of GPRS and WLAN systems. The design goal is to minimize the modifications in GPRS and WLANs as both systems are already widely available. By deploying the GWMG, users can seamlessly roam among the two systems. Unlike other related work, the proposed GWMG could be used when either the GPRS or WLAN is a user's home network. Both mathematical analysis and simulation are developed to analyze the performance. The proposed GWMG has also been implemented in a testbed comprising a commercial GPRS system. The results show that the GWMG could achieve a design goal that will effectively integrate GPRS and WLANs. [ABSTRACT FROM AUTHOR]

Universal mobile-telecommunication system supports IP multimedia services through the IP multimedia core-network subsystem (IMS). This paper proposes a prepaid application server (PAS) to handle both the prepaid calls and messaging services in the IMS. When both voice and messaging are simultaneously offered, a potential problem is that the delivery of a message during a call may result in force-termination of that call due to credit depletion. To address this issue, we describe a strategy to determine if a prepaid message can be sent out during a call session. We propose an analytic model to investigate the performance of this strategy. This paper provides guidelines to select appropriate input parameters for the PAS. [ABSTRACT FROM AUTHOR]

The support of voice over Internet Protocol (VoIP) services in next-generation wireless systems requires the coupling of mobility with quality of service. The mobile node can experience disruptions or even intermittent disconnections of an ongoing real-time session due to handovers. The duration of such interruptions is called disruption time or handover delay and can heavily affect user satisfaction. Therefore, this delay needs to be minimized to provide good-quality VoIP services. In this paper, the focus is on the network layer mobility, specifically on mobile Internet Protocols (MIPs), since they are natural candidates for providing mobility at layer 3. Using analytical models, the authors evaluate MIPv4, MIPv6, fast MIPv6 (FMIPv6), and hierarchical MIPv6 (HMIPv6) and compare their performances in terms of handover delay for VoIP services. To optimize the handover delay, the authors propose to use the adaptive retransmission timer described in this paper. The results obtained using the adaptive timer technique show that for a 3% frame error rate and a 128-kb/s channel, the handoff delay is about 0.075 s (predictive) and 0.051 s (reactive) for FMIPv6. It is around 0.047 s [intra-mobile anchor point (MAP)] and 1.47 s (inter-MAP) for HMIPv6, around 1 s for MIPv6, and 0.26 s for MIPv4. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) have recently received significant attention in improving traffic safety and efficiency. However, communication trust and user privacy still present practical concerns to the deployment of VANETs, as many existing authentication protocols for VANETs either suffer from the heavy workload of downloading the latest revocation list from a remote authority or cannot allow drivers on the road to decide the trustworthiness of a message when the authentication on messages is anonymous. In this paper, to cope with these challenging concerns, we propose a new authentication protocol for VANETs in a decentralized group model by using a new group signature scheme. With the assistance of the new group signature scheme, the proposed authentication protocol is featured with threshold authentication, efficient revocation, unforgeability, anonymity, and traceability. In addition, the assisting group signature scheme may also be of independent interest, as it is characterized by efficient traceability and message linkability at the same time. Extensive analyses indicate that our proposed threshold anonymous authentication protocol is secure, and the verification of messages among vehicles can be accelerated by using batch message processing techniques. [ABSTRACT FROM AUTHOR]

Vehicular networks allow vehicles to exchange information that can be used to improve traffic efficiency and drivers' safety. In addition to these new applications, Internet connectivity is also expected to be available in the cars of the near future, speeding up the global adoption of vehicular communication systems. One of the requirements for connecting vehicles to the Internet is their ability to autoconfigure Internet Protocol (IP) addresses. In this paper, we propose an optimization to Geographically Scoped stateless Address Configuration (GeoSAC), which is an IP address autoconfiguration mechanism for geographically aware location vehicles. The benefits of this optimization are twofold: 1) It can reduce the IP address configuration time, and 2) it can be used to reduce the signaling overhead of GeoSAC. The optimization requires no changes to the GeoSAC operation, being fully compatible with the original solution. We derive an analytical model for the probability of our optimization being effective in realistic scenarios and for the IP address configuration time. We also provide a thorough evaluation of the performance improvements of the optimization, including simulations with a realistic model for wireless technology, real vehicular traces, and experiments with a real prototype, which provide strong support for our analytical model. [ABSTRACT FROM PUBLISHER]

Broadcast is a fundamental operation of wireless ad hoc networks (WANETs) and has widely been studied over the past few decades. However, most existing broadcasting strategies assume nonsleeping wireless nodes and thus are not suitable for uncoordinated duty-cycled WANETs, in which each node periodically switches on and off to save energy. In this paper, we study the minimum-transmission broadcast problem in uncoordinated duty-cycled WANETs (MTB-UD problem) and prove its NP-hardness. We show that modifications of existing broadcast approaches can only provide a linear approximation ratio of O(n) (where n is the number of nodes in the network). We propose a novel set-cover-based approximation (SCA) scheme with both centralized and distributed approximation algorithms. The centralized SCA (CSCA) algorithm has a logarithmic approximation ratio of 3(ln Δ + 1) and time complexity of O(n3) (Δ is the maximum degree of the network). The distributed SCA (DSCA) algorithm has a constant approximation ratio of at most 20 while keeping both linear time and message complexities. We have conducted both theoretical analysis and simulations to evaluate the performance of the proposed algorithms. Results show that both the CSCA and DSCA algorithms outperform the modified versions of existing broadcast approaches by at least 50%. [ABSTRACT FROM AUTHOR]

Internet protocol (IP) autoconfiguration in mobile ad hoc networks (MANETs) has attracted much attention. Efficient duplicate address detection (DAD) schemes should be devised to provide each node with its unique address in the network. Generally, DAD schemes can be categorized into two classes: 1) active DAD and 2) passive DAD (PDAD). In this paper; we focus on PDAD schemes over on-demand ad hoc routing protocols. Specifically, we have three goals: 1) improving the accuracy of detecting address conflicts; 2) improving the successful detection success ratio; and 3) reducing the time taken to detect these conflicts. Unlike current approaches, we propose several schemes that exploit additional information, such as sequence number, location, and neighbor knowledge. Simulation results show that our approaches achieve better accuracy and shorter time to detect conflict addresses when compared with existing schemes. [ABSTRACT FROM AUTHOR]

In this paper, we study the asymptotic performance of absolute-threshold-and normalized-threshold-based generalized selection combining (AT-GSC and NT-GSC) schemes over generalized fading channels for high average signal-to-noise ratios (ASNRs). By evaluating the asymptotic moment-generating function of the threshold-based GSC output SNRs, we derive the diversity and combining gains for AT- and NT-GSCs with a large class of modulation formats and versatile fading conditions, including different types of fading channels and nonidentical SNR statistics across diversity branches. Our analytical results reveal that the diversity gains of AT- and NT-GSC are equivalent to that of maximal-ratio combining, and the differences in the combining gains for different threshold values and modulation and diversity formats are derived by using the concept of modulation factors. [ABSTRACT FROM AUTHOR]

The integration of different wireless networks to provide seamless and continuous network access services is a major issue in beyond-third-generation (B3G) networks. To avoid modifying the existing protocols in the network nodes, the application-level approach is proposed for heterogeneous network integration. In the application-level integration, a mobility gateway (MG) is introduced to serve as an agent through which users can use different kinds of mobile devices through different kinds of networks to access Internet applications. There are two major tasks in an MG, including content format translation and data tunneling for handoff users. When the service area of an MG is larger, the MG must handle the content format translation for more users, and the computation overhead of an MG increases significantly. On the other hand, when the service area of an MG shrinks, a served user more likely hands off between different MGs, and more network resources are consumed to tunnel the data for handoff users. In this paper, an analytical model is proposed, and simulation experiments are conducted to study how to properly plan the service area of an MG so that better system performance can be achieved. [ABSTRACT FROM AUTHOR]

Vehicular networks are experiencing rapid growth and evolution under the increasing demand of vehicular traffic management and ubiquitous network connectivity. In particular, the amount of information to be downloaded from the roadside-deployed gateways is dramatically increasing. Infected by high mobility, intermittent connectivity, and unreliability of the wireless channel, it is challenging to satisfy the need for massive data transmission in vehicular networks. In this paper, we propose a novel protocol called vehicular cooperative media access control (VC-MAC), which utilizes the concept of cooperative communication tailored for vehicular networks, particularly for gateway-downloading scenarios. VC-MAC leverages the broadcast nature of the wireless medium to maximize the system throughput. Spatial diversity and user diversity are exploited by concurrent cooperative relaying to overcome the unreliability of the wireless channel in vehicular networks. We theoretically analyze the selection of an optimal relay set using a weighted independent set (WIS) model and then design a backoff mechanism to select the optimal relays in a distributed manner. We have carried out extensive simulations to demonstrate that VC-MAC effectively enhances cooperative information downloading and significantly increases the system throughput compared with existing strategies. [ABSTRACT FROM AUTHOR]

Interference is a serious problem in wireless communications. In a wireless network, the signal sent by a terminal will be received by all its neighboring nodes. If a neighbor (except the destinations) is receiving data from some other terminals at the same time, the signals will collide, and the useful signal will be destroyed, which may result in transmission failure. Previous solutions to this problem focused on the avoidance of signal collisions through careful medium access control (MAC) and/or scheduling. However, this needs some sophisticated protocols and may waste system resources such as bandwidth. In this paper, we shall put forward some practical schemes to recover the useful signal from the collided signals for different types of wireless channels; thus, the throughput and network efficiency can greatly be increased. The proposed schemes are based on the network coding technique and performed on the physical layer. One feature of our schemes is that neither strict synchronization nor power control is needed among the different terminals; thus, it is very fit for distributed networks. Simulation results will show that the bit error rate (BER) of the recovered signal by our developed schemes is almost the same as that of the signal with no collision, which proves their efficiency in eliminating the interference. [ABSTRACT FROM AUTHOR]

A heterogeneous wireless network consists of various wireless networks [e.g., Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Fidelity (WiFi)] and cellular communications [e.g., beyond the third generation (B3G) and the fourth generation (4G)]. Vertical handoff is an important mechanism for achieving continuous seamless transmissions in these networks. In contrast to horizontal handoff, vertical handoff considers not only the received signal strength (RSS) but also the service-class mapping between handoff-in and handoff-out networks. Most previous works have adopted the RSS-based mechanism to determine handoff thresholds, which causes a serious ping-pong effect that increases unnecessary handoff. Although integrating the RSS-based mechanism with a hysteresis method reduces the unnecessary handoff, it suffers from high dropping [i.e., high Sum of Weighted Grade of Service (SWGoS)] and low utilization. Therefore, this paper proposes a cross-layer-based adaptive vertical handoff algorithm with predictive RSS to reduce the unnecessary handoff while significantly increasing utilization and decreasing connection dropping. The proposed approach determines the optimal target network in two phases, i.e., polynomial regression RSS prediction and Markov decision process analysis. Furthermore, fast changes in bandwidth caused by vertical handoff result in inaccurate Transmission Control Protocol (TCP) congestion control and, thus, redue the TCP goodput. The cross-layer scheme provides a TCP receiver to reply to the TCP sender with the wireless network's protocol type. By using the cross-layer information, the TCP sender can accurately predict the available bandwidth and increase the network goodput. Numerical results indicate that the proposed cross-layer-based approach out-performs the other approaches in the number of vertical handoffs and SWGoS while yielding competitive utilization. In addition, the cross-layer scheme cooperates with existing TCP algorithms to increase goodput by up to 18%. [ABSTRACT FROM AUTHOR]

This paper considers the optimal distributed assignment of rates to elastic users in a broadband multicell code-division multiple-access (CDMA) network with variable rate assignments, which is connected to a traditional wired Internet Protocol (IP) network. We show that by using an optimization framework, it is possible to construct a distributed rate assignment algorithm similar to current congestion control protocols that addresses both media access control and transport layer issues (i.e., addresses both interference and congestion control). Practical implementation of this algorithm, as well as its impact on convergence and performance, is also addressed. [ABSTRACT FROM AUTHOR]

Voice over Internet protocol (VoIP) is one of the most important applications for IEEE 802.11 wireless local area networks (WLANs). For network planners who deploy VoIP over WLANs, one of the important issues is the VoIP capacity. Directly implementing VoIP over infrastructure WLANs will create the bottleneck problem at the access point (AP). In this paper, we propose the use of the service differentiation provided by the new IEEE 802.11e standard to solve the bottleneck problem and improve voice capacity. In particular, we propose the allocation of a higher priority access category (AC) to the AP while allocating lower priority AC to mobile stations. We develop a simple Markov chain model, which considers the important enhanced distributed channel access (EDCA) parameters and the channel errors under saturation and nonsaturation conditions. Based on the developed analytical model, we analyze the performance of VoIP over EDCA. By appropriately selecting the EDCA parameters, we are able to differentiate the services for the downlink and uplink. The experimental results are very promising. With the adjustment of only one EDCA parameter, we improve the VoIP capacity by 20%-30%. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel probabilistic method for evaluating concurrent search in all-Internet protocol (IP) networks. It is expected that the next-generation Internet will consist of a variety of wireless-access networks. To be independent of wireless-access technology and to reduce the cost of mobility management in a heterogeneous environment, we propose integrating IP Paging with concurrent search, which was originally proposed for homogeneous cellular networks. We focus on the case in which the call-arrival process is general and has stationary independent increments. Since a number of calls could arrive simultaneously, the blocking probability is not equal to the probability with the system that is full. Therefore, we resort to renewal theory to accurately derive the blocking probability. Furthermore, we obtain the throughput, the average system size, and the average system delay. Our analytical results are consistent with simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we study the effect of channel estimation error at the receiver on the mutual information of a multiple-input-multiple-output (MIMO) channel obeying correlated Rayleigh fading. We assume that perfect knowledge of the channel correlation is available at the receiver and find upper and lower bounds on the mutual information for Gaussian input signals. We prove that for a generic input covariance matrix, the gap between these two bounds at high transmit powers does not exceed a certain value, which depends on the number of nonzero eigenvalues of the receive correlation matrix. We also show that in a system with uncorrelated transmit antennas and correlated receive antennas and with uniform power distribution over the transmit antennas, these bounds are asymptotically tight for a large number of transmit antennas. We show that when the correlation information is available at the transmitter, the transmitting strategy that maximizes the mutual information lower bound is to transmit toward the directions of the eigenvectors of the transmit correlation matrix. We further derive upper and lower bounds on the mutual information of a MIMO multiple-access channel with imperfect channel estimation at the receiver. We also prove that when the input power at each user is uniformly distributed over its transmit antennas, the bounds on the mutual information are asymptotically tight for Gaussian input signals, and this tightness increases when the number of users increases. Numerical simulations are conducted to corroborate theoretical results. [ABSTRACT FROM AUTHOR]

Trellis-coded modulation (TCM) has been shown as an attractive coding scheme for broadband wireless networks due to its band-width efficiency. Various hybrid automatic repeat request (ARQ) schemes using TCM as underlying forward error control have been proposed in the literature. In this paper, we study the performance of the hybrid ARQ with concatenated two-state TCM (CT-TCM) over Rayleigh fading channels. The throughput of the CT-TCM hybrid ARQ (CT-TCM-HARQ) scheme over a quasi-static Rayleigh fading channel is evaluated by both analysis and simulation. Besides, the performance of the CT-TCM-HARQ over fully interleaved Rayleigh fading channels is evaluated by simulation and compared with other existing TCM-based hybrid ARQ schemes. The numerical results demonstrate that the CT-TCM-HARQ achieves improved coding gain and throughput. [ABSTRACT FROM AUTHOR]

This paper presents a generalized channel preemption model (GCPM) for multiclass traffic in mobile wireless networks. In the proposed model, a mobile call is identified by four parameters—call type, traffic class, channel requirement, and preemption ratio—in which different classes of traffic can have different priority levels. To effectively reduce dropping probability, high-priority handoff calls are allowed to fully or partially preempt low-priority ongoing calls when the mobile network becomes congested. A fully preempted call can be completely disconnected, whereas a partially preempted call can still communicate with certain degree of quality-of-service degradation. We introduce an analytical model with multidimensional Markov chains. In the model, a cost function, which is expressed as a weighted sum of the ongoing calls to be preempted and the bandwidth reduction rate in the preempted calls, is defined to select candidate calls from a certain traffic class. The statistical result from the model allows us to tune the parameters of the GCPM to support high-priority handoff calls and therefore offers new insights in understanding the tradeoffs in supporting multiclass traffic. [ABSTRACT FROM AUTHOR]

Many applications in wireless sensor networks re- quire sensor nodes to obtain their absolute or relative geographical positions. Although various localization algorithms have been recently proposed, most of them require nodes to be equipped with range-determining hardware to obtain distance information. In this paper, we propose a concentric anchor beacon (CAB) localization algorithm for wireless sensor networks. CAB is a range-free approach and uses a small number of anchor nodes. Each anchor emits beacons at different power levels. From the information received by each beacon heard, nodes can determine in which annular ring they are located within each anchor. Each node uses the approximated center of intersection of the rings as its position estimate. We also propose two heuristics, namely CAB with Equal Area and CAB with Equal Width, to determine the transmitting power levels of the beacons. Simulation results show that the estimation error is reduced by half when anchors transmit beacons at two different power levels instead of at a single power level. CAB also gives a lower estimation error than some other range-free localization schemes (e.g., Centroid and Approximated Point-In-Triangulation) when the anchor-to-node range ratio is less than 4. [ABSTRACT FROM AUTHOR]

In multiaccess wireless networks, dynamic allocation of resource such as link qualities and transmitted powers is an important means to combat time-varying fading environments and cochannel interferences (CCIs). In most prior work, every link's quality is maintained by having a fixed signal-to-interference-noise-ratio (SINR) requirement. We discover that such a constraint is too strong and can degrade the performance of entire wireless networks; because a user with a bad channel response requires too much transmitted power and, therefore, causes unnecessary CCI to other users. In this paper, we alleviate this constraint and explore the time and multiuser diversity. For each user, the lime-average link quality is maintained as a constant to ensure fairness. For the whole system, we want to minimize the overall transmitted power. In order to solve this problem, each user provides the system with a SINR range that is acceptable, according to the channel conditions and transmission history. Then, the system allocates the resources according to these ranges, channel conditions, and other practical constraints. Each time, some users may sacrifice their performances to reduce the overall network transmitted power. These users' temporary sacrifices will improve the system performance and will be paid back in the long term. This scheme can be conceived of as "water filling" the wireless network resources to different users at different times. In addition, by combining the proposed scheme with beamforming, we can have one more degree of freedom to combat CCIs in different directions of arrivals and different channel conditions over time. [ABSTRACT FROM AUTHOR]

In this paper, we perform a comparative study of both the achievable performance and the associated computational complexity of two major time-domain prediction strategies proposed for employment in wireless mobile communication systems. Specifically, we investigate the intrinsic design tradeoffs of the so-called stationary robust predictor and the adaptive Recursive-Least-Squares (RLS) predictor. We demonstrate that the RLS predictor outperforms its robust counterpart at a cost of slightly higher computational complexity, and hence, the RLS predictor constitutes a better alternative for employment in wireless transceivers. [ABSTRACT FROM AUTHOR]

In mobile ad hoc networks (MANETs), hierarchical architecture and distributed approaches are more practical than flat architecture and centralized approaches. In this paper, we propose a suite of protocols that achieve a distributed planning and routing scheme for MANETs. The proposed suite, which is composed of three protocols, offers scalability and extends network lifetime. The first protocol, i.e., the fast distributed connected dominating set (FDDS), constructs the virtual backbone by designing a fast distributed hierarchical algorithm that finds a connected dominating set (CDS) in the network graph. The constructed virtual backbone takes into account the node's limited energy, mobility, and traffic pattern. The second protocol, i.e., FDDS-M, proposes a distributed maintenance protocol that preserves the integrity of the hierarchical structure constructed by FDDS. The third protocol, i.e., FDDS-R, uses an intelligent path-selection fuzzy logic controller that can easily be incorporated in any existing link state routing protocol to select energy-efficient routes. We conducted extensive simulations that compare the operational properties (energy efficiency and network lifetime) of our schemes with others. The results show that our proposed schemes can achieve scalability and energy efficiency and outperform some of well-known approaches in the literature. [ABSTRACT FROM AUTHOR]

In wireless sensor networks (WSNs), the field information (e.g., temperature, humidity, airflow) is acquired via several battery-equipped wireless sensors and is relayed toward a sink node. As the size of the WSNs increases, it becomes inefficient (in terms of power consumption) when gathering all information in a. single sink. To tackle this problem, one can increase the number of sinks. The set of sensor nodes that are sending data to sink k is called commodity k. In this paper, we formulate the lexicographically optimal commodity lifetime (LOCL) routing problem. A stepwise centralized algorithm called the LOCL algorithm is proposed, which can obtain the optimal routing solution and lead to lexicographical fairness among commodity lifetimes. We then show that, under certain assumptions, the lexicographical optimality among commodity lifetimes can be achieved by providing lexicographical optimality among node lifetimes. This motivates us to propose our second algorithm, which is called the lexicographically optimal node lifetime (LONL) algorithm, which is suitable for practical implementation. Simulation results show that our proposed LOCL and LONL algorithms increase the normalized commodity and node lifetimes compared with the maximum lifetime with multiple sinks (MLMS) and lexicographical max-min fair (LMM) routing algorithms. [ABSTRACT FROM AUTHOR]

Location privacy of mobile users (MUs) in wireless communication networks is very important. Ensuring location privacy for an MU is an effort to prevent any other party from learning the MU's current and past locations. In this paper, we propose a novel anonymous mutual authentication protocol with provable link-layer location privacy preservation. We first formulate the security model on the link-layer, forward-secure location privacy, which is characterized by the fact that even when an attacker corrupts an MU's current location privacy, the attacker should be kept from knowing how long the MU has stayed at the current location. Then, based on the newly devised keys with location and time awareness, a novel anonymous mutual authentication protocol between the MUs and the access point (AP) is proposed. To the best of our knowledge, this is the first developed anonymous mutual authentication scheme that can achieve provable link-layer, forward-secure location privacy. To improve efficiency, a Preset in Idle technique is exercised in the proposed scheme, which is further compared with a number of previously reported counterparts through extensive performance analysis. [ABSTRACT FROM AUTHOR]

Location management of mobile users is of primary importance in personal communication networks (PCNs), and it is mainly aimed to facilitate the delivery of incoming calls to destination users and to make a more efficient use of network resources. In practical PCNs, the location management algorithms need to keep track of mobile users in a dynamic manner, and it is a design concern to minimize the generated signaling traffic. In this paper, we present the cost analysis for the dynamic movement-based location update scheme. Our model is based on renewal theory arguments, and it is general enough to include a variety of probability distributions for modeling cell residence times (CRTs) in hyperexponentially distributed location area residence times and exponentially distributed intercall times. We compare the location update cost for the dynamic and static schemes. We present numerical results regarding the exponential and circular CRT distributions and discuss the optimal threshold distance for location update that minimizes the cost of the dynamic movement-based scheme. [ABSTRACT FROM AUTHOR]

This paper deals with the application of Hybrid-Automatic-Repeat-reQuest (H-ARQ) techniques to reliable end-to-end data communications in satellite networks, whose applications have to cope with accurate Quality-of-Service (QoS) requirements. Particularly, we face this problem by introducing a modified H-ARQ scheme based on the use of the turbo codes' error-correction capabilities. According to our scheme, each packet is turbo coded, and packet retransmissions are lowered by keeping track of previous erroneous packet-decoding results. Moreover, two kinds of these techniques are proposed and applied, respectively, to consecutive received packet replicas or to decoding algorithm outputs. The benefits achieved through this approach have a positive effect both on the error-recovery strategies and, above all, on the congestion-control protocols, since they rely on a retransmission scheme. By means of analytical derivations carried out under the assumption of a wideband-code-division multiple-access communications, it has been possible to highlight noticeable performance improvements in terms of bit- and frame-error rates and link throughput. Computer simulations performed focusing on a typical satellite-universal-mobile-telecommunication-system environment validate analytical predictions and point out a remarkable gain without requiring a significant hardware-complexity increase. As a result, it has been possible to allow active users a better QoS, in terms of error rate, throughput, and delivery delay, or to increase access-network capacity, besides avoiding transmitted-power wasting. [ABSTRACT FROM AUTHOR]

In the future, secondary radio (SR) may exploit the use of spectrum holes (SHs) that are available over a given spectrum band for transmission, provided that the performance of the primary radio (PR) using the same spectrum band is not significantly degraded. However, random or quasi-random PR activities result in SHs that will sporadically be available. Hence, to study their impact on SR transmission, it is first required to statistically characterize the duration of SHs. We define the duration in which an SH is first available to the instance when it just becomes unavailable as the opportunity time (OT) for SR transmission. Our model partitions the spectrum band under consideration into N frequency bins (FBs). Between any two FBs, the PR activities are assumed to be independent, and the PR activities in each FB follow an exponential on/off process. We derive the theoretical probability density function (pdf) of the OT using a lumped Markov chain model. Our analysis shows that the pdf follows a hyperexponential distribution, and when the PR activity factors are pair-wise distinct for all the N FBs, the pdf is given by the weighted sum of (2N - 1) exponential terms. In particular, if the N FBs have identical PR activity factors, the pdf will only consist of N exponential terms. The statistics of the OT could provide insightful information for the secondary usage of the spectrum. [ABSTRACT FROM AUTHOR]

We study the problem of accurate localization of static or mobile nodes in a wireless ad hoc network using the distance estimates of a group of untrusted anchors within the communication range of the nodes. Some of the anchors may be malicious and may independently lie about the distance estimate. The malicious anchors may also collude to lie about the distance estimates. In both cases, accurate node localization may be seriously undermined. We propose a scheme that performs accurate localization of the nodes in the network despite the presence of such malicious anchors. We also show how to identify most of these malicious anchors. In the case where measurements are error free, we derive a critical threshold B for the number of malicious anchors that can be tolerated in the localization process without undermining accuracy. We also show how to correctly localize a node and identify all the malicious anchors in this setting. In the presence of measurement errors, we propose a convex optimization-based localization scheme that can accurately localize a node, as long as the number of malicious anchors in its communication range is no more than B. Simulation results show that our schemes are very effective. When the measurements are error prone and the number of malicious anchors is no more than B, our scheme localizes a node with an error less than 8% and is also able to identify a significant number of malicious anchors. Our schemes guarantee that a true anchor is not identified as malicious. [ABSTRACT FROM AUTHOR]

Wireless communications and IP networks will evolve into a new converged vision, which is called "beyond the third generation," where charging and billing will be essential tools for customer care to fight competition and to assure operator's revenue. This contribution proposes a business model for video-call billing founded on Bayes' decision testing. It is based on the end-to-end Quality of Service (QoS) estimated by exploiting the tracing watermarking procedure, which has recently been introduced into the literature. In particular, we employ the watermark embedded in each transmitted video sequence to monitor the QoS of the communication link and adequately charge the calling user, depending on the received video quality. Adopting such a Bayesian business model, we translate the network operator's paradigm of "pay as you talk (and watch)" to "pay how you talk (arid watch)," maximizing the operator's profit under a constrained video quality for end users. Wide simulation trials are conducted to characterize the effectiveness of the proposed method, using different business scenarios, confirming the validity of such an approach. [ABSTRACT FROM AUTHOR]

In vehicular networks, mobile users in vehicles can access the Internet and enjoy various kinds of services such as Voice over IP (VoIP) and online streaming video. To provide satisfactory quality of service (QoS), we need to appropriately place gateways to link mobile nodes to the Internet or any other information networks. In this paper, we address the problem of optimally placing gateways in vehicular networks to minimize the average number of hops from access points (APs) to gateways, so that the communication delay can be minimized. Moreover, we also investigate how to minimize the total power consumption, and we show that, when the average number of hops is minimized, the average capacity of each AP can be maximized. [ABSTRACT FROM AUTHOR]

Future intelligent transportation systems (ITS) will necessitate wireless vehicle-to-infrastructure (V2I) cominunications. This wireless link can be implemented by several technologies, such as digital broadcasting, cellular communication, or dedicated short-range communication (DSRC) systems. Analyses of the coverage and capacity requirements are presented when each of the three systems is used to implement the V2I link. We show that digital broadcasting systems are inherently capacity limited and do not appropriately scale. Furthennore, we show that the Universal Mobile Telecommunications System (UMTS) can implement the V2I link using either a dedicated channel (DCH) or a multimedia broadcastlmulticast service (MBMS), as well as a hybrid approach. In every case, such V2I systems scale well and are capacity limited. We also show that wireless access in vehicular environment (WAVE) systems scale well, provide ample capacity, and are coverage limited. Finally, a direct quantitative comparison of the presented systems is given to show their scaling behavior with the number of users and the geographical coverage. [ABSTRACT FROM AUTHOR]

Different emerging IEEE 802.15.4 wireless personal area networks (WPANs) are one solution for wireless sensor networks (WSNs), where applications are restricted by low data rate, short transmission distance, and low power consumption. The frame transmission mechanism of the IEEE 802.15.4 standard, which adopts the blind random backoff mechanism, was designed to minimize power consumption. However, it cannot provide satisfactory performance in a realistic hidden-node environment, because it may incur a hidden-node collision chain situation and unexpectedly limit the overall network capacity. For each successful data transmission, any inefficient transmission mechanism will incur prolonged access delay and will consume too much power. Moreover, the current design becomes inefficient as the number of devices significantly increases. As a solution, we propose a new multiple access protocol with improved efficiency at the sublayer between the media access control layer and the physical layer, i.e., a carrier sense multiple access with collision freeze (CSMA/CF) protocol, which comprises a collision resolving scheme and a P-frozen contention strategy. The CSMA/CF protocol can quickly alleviate aggravated collision situations in a hidden-node environment. Such a particular collision phenomenon is denoted as a collision chain problem (CCP). The impact from CCP is thoroughly discussed and analyzed. As confirmed by the results of analysis and performance evaluations, the proposed CSMA/CF protocol can achieve significant performance improvement in energy conservation, access delay reduction, and transmission reliability enhancement. [ABSTRACT FROM AUTHOR]

We analyze the problem of tracking a single target, from which measurements are taken using noisy sensors. Each measurement is associated with the measurement error, usage cost, and physical and computational constraints. As it is acceptable for many real applications that target dynamics are modeled as a linear system that is impaired by white Gaussian noise. Moreover, it is assumed that sensor measurements are linearly distributed with white Gaussian noise. Optimal sensor scheduling is achieved by finding the sensor sequence that minimizes the total cost, which consists of the measurement error and sensor usage cost for the entire time horizon subject to specific system constraints. To handle this discrete optimization problem, we propose well-performing suboptimal methods for different energy constraints in sensor nodes. First, we propose a suboptimal method called the best step look-ahead technique, which performs very well when the energy constraints can safely be removed due to their negligible influence on the overall system. We also show that, under certain assumptions, the Viterbi algorithm can be applied as a suboptimal method to obtain attractive results. Second, the energy constraints are relaxed using Lagrangian multipliers to formulate the problem as a Min-Max optimization problem. We use particle swarm optimization to tune the Lagrangian multipliers and Viterbi algorithm to find the optimal sensor sequence. To illustrate the effectiveness of our algorithms in realistic settings, we study a numerical problem of single target tracking with several noisy sensors and convincingly show that the proposed methods perform better than existing methods. [ABSTRACT FROM AUTHOR]

Most existing routing protocols for mobile ad hoc networks (MANETs) use a single routing strategy for different types of networks. Routing protocols suitable for small networks may not scale well in large networks. Routing protocols that perform well in sparse networks may not be suitable for dense networks. To achieve good performance, different routing strategies should be used for different types of networks. This philosophy motivates our design of a new routing protocol called the adaptive cell relay (ACR) routing protocol. Our ACR protocol can adapt the routing strategy for networks with different node density so high efficiency, low delay, and scalability can be achieved. Extensive simulation results demonstrate that the ACR has much better performance and scalability than a popular routing protocol—location-aid routing (LAR). In addition, both the analysis and the simulations show that the ACR routing protocol incurs only about 25% of the routing overhead of the LAR routing protocol. [ABSTRACT FROM AUTHOR]

We analyze the performance of different handoff algorithms on the forward link or downlink of a code-division multiple-access (CDMA) cellular system. Unlike the reverse link, soft handoff on the forward link requires additional resources such as CDMA codes and transmit power and also causes additional interference. If handoff requests can be processed and completed instantaneously, transmission from the base station with the best link to the user would achieve a significant fraction of the macro- diversity gain without utilizing additional resources. However, in practical systems, there is a nonzero handoff completion delay and soft handoff provides the required robustness to delays, although it comes at the expense of additional network resources. Thus, there is a tradeoff between the extent of soft handoff required and the handoff execution delay. We compare the performance of hard and soft handoff schemes and study their sensitivity to the delay in the execution of the handoff. Outage probability and the total average power required are used as performance metrics. We present an analytical framework to study this tradeoff and also discuss simulation results with field data. The results provide insights on the conditions under which soft handoff can be eliminated and on the effect of relevant handoff thresholds on the performance. [ABSTRACT FROM AUTHOR]