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As more options become available for where and how patients receive medical care and treatment, it's never been more important to have clear communication between primary and specialty care providers. [...]

Problem statement: A MANET is an autonomous collection of mobile users that communicate over relatively bandwidth constrained wireless links. Since the nodes are mobile, the network topology may change rapidly and unpredictably over time. Approach: A Stable Weight-based On demand Routing Protocol (SWORP) that uses the weight-based route strategy to select a stable route was created by Wang. But SWORP only evaluated in a limited setting of simulation, more simulation parameter have to test with SWORP to evaluate how far this protocol can go on. In this project, SWORP was implemented in simulation environment with two other routing protocols, AODV and DSR. Results: These three protocols were implemented in Network Simulator 2 (NS2) and the performance was compare with performance metrics, end-to-end delay, number of packet drop and packet delivery ratio. Conclusion: As expected, SWORP had outperformed AODV and DSR in the overall routing performance. Key words: Mobile ad hoc network, on-demand routing protocol, on-demand routing, weight-based routing, stable route, INTRODUCTION A wireless ad hoc network is a dynamic network consisted of a group of mobile device in which communicate with each other by wireless media. Communication can be done [...]

In the reported metrics of the existing literature, the realistic wireless channel situation is generally ignored in selecting the appropriate next-hop relay node during packet forwarding in wireless sensor networks (WSNs). In this paper, we propose a new energy-efficient local metric, which is called the efficient advancement metric (EAM), for sensor networks. EAM considers both the maximum forwarding distance and the packet's successful transmission probability by taking into account the wireless channel condition. This will enable the forwarding node to choose the most energy-efficient relay node in the geographic-informed routing protocol. Theoretically, we show the existence of the unique optimal relay node to maximize EAM over a typical Nakagami-m channel of a code-division multiple-access (CDMA)-based WSN. Furthermore, based on the proposed metric EAM, we present a cross-layer packet-forwarding protocol channel-aware geographic-informed forwarding (CAGIF) by optimally selecting the relay nodes. CAGIF only requires that nodes have the knowledge of their own location information and the location information of the source and destination nodes. Numerical examples are presented to show the characteristics of EAM and the optimal distance. Compared with the previous geographic packet-forwarding schemes in WSNs, CAGIF consumes much lower energy and generates a significantly decreased signal overhead. Index Terms--Energy efficiency, Nakagami-m-fading wireless channel model, packet forwarding, wireless sensor networks (WSNs).

Routing in multihop wireless networks is challenging, mainly due to unreliable wireless links/channels. Geographic opportunistic routing (GOR) was proposed to cope with the unreliable transmissions by exploiting the broadcast nature of the wireless medium and the spatial diversity of the network topology. Previous studies on GOR have focused on networks with a single channel rate. The capability of supporting multiple channel rates, which is common in current wireless systems, has not carefully been studied for GOR. In this paper, we carry out a study on the impacts of multiple rates, as well as candidate selection, prioritization, and coordination, on the performance of GOR. We propose a new local metric, i.e., the opportunistic effective one-hop throughput (OEOT), to characterize the tradeoff between one-hop packet advancement and packet forwarding time. We further propose a local rate adaptation and candidate-selection algorithm to approach the optimum of this metric. The simulation results show that the multirate GOR (MGOR) incorporating the rate adaptation and candidate-selection algorithm achieves higher throughput and lower delay than the corresponding single-rate and multirate traditional geographic routing and single-rate opportunistic routing protocols. Index Terms--Geographic routing (GR), multihop wireless networks, multirate, opportunistic routing, throughput.

To achieve fully mobile communications, considering different environments and modern service requirements, a multiple-segment architecture is the most suitable to guarantee service continuity with acceptable performance. Handover (HO) procedures can be invoked either out of necessity (if the current network connection is going off) or to improve performance (if different bandwidth or quality of service is required). In this scenario, to provide uninterrupted communication services, efficient intersegment HO capability must be implemented. The architecture considered includes a satellite segment and a number of Wi-Fi hot spots. A mobile node (MN) can switch from a segment to other exploiting services of mobile Internet protocol (MIP). This architecture introduces great flexibility and ensures capillary coverage; it also strongly affects Transmission Control Protocol (TCP)-based application performance. To efficiently face HO consequences, particularly when the TCP runs as a transport protocol, an innovative protocol architecture based on cross-layer (CL) exchange of information is proposed. Analyses of TCP dynamics during HOs and the performance improvement introduced with the proposed CL architecture, evaluated through the network simulator Ns-2, are presented. Index Terms--Cross layer (CL), handover (HO), multisegment networks, Transmission Control Protocol (TCP).

Power scheduling and localization play important roles in network topology management. Distributed power scheduling is an efficient way to construct a reliable and energy-efficient network topology. Localization provides geographical information for topology management. However, during the course of transmission power control, localization based on the received signal strength (RSS) is a challenging problem because of the inconsistent RSS indication (RSSI) measurements in wireless sensor networks. This paper presents an algorithm that takes advantage of the information from the ongoing wireless communication links to calculate the estimated position of sensor nodes. Considering the existing transmit-power-aware medium access control (MAC) protocols, we propose a localization algorithm based on particle filtering for sensor networks assisted by multiple transmit-power information. Therefore, the primary contribution of this paper is the elegant strategy on how to incorporate the practical multiple transmit-power information into the process of particle filtering. Furthermore, a general message-passing framework of the transmit-power-aware MAC is seamlessly integrated with the tracking service. The proposed particle-filtering-based localization algorithm uses the RSS information from the beacons or the neighboring nodes to infer the position of the concerned node without the requirement of any additional hardware instruments. Theoretical analysis and simulation results are presented to demonstrate the performance of the proposed localization method. The simulation results show that the proposed algorithm outperforms the existing algorithms that do not utilize multiple power information. Index Terms--Medical information systems, networks, wireless LAN.

Traditional routing protocols designed for multihop wireless networks, e.g., the mobile ad hoc network (MANET), select a route with the smallest hop count. The end-to-end through-put in the route may not be the maximum when the network has multiple link data rates, as a small hop number implies a large geographic distance (link distance) for each hop. Due to the radio signal attenuation, this results in a low SNR at the receiving node and, consequently, a low available link data rate. Reducing the link distance by using routes with more hop counts can increase the link data rate. However, this may not necessarily improve the end-to-end throughput because more nodes have to be included in the routes. In this paper, we first investigate and analyze the impact of link distance on end-to-end throughput in multirate multihop wireless networks. Analysis and simulation results show that changing the link distance affects the network throughput. To achieve a high network throughput, a proper link distance requirement has to be set for each hop, depending on different parameters such as load density. Based on this finding, we then propose a crossing-layer adaptive searching range (ASR) routing algorithm. ASR can be integrated into existing routing protocols. According to the local network load density, ASR can help improve the network performance by adjusting the link distance in the routes. Index Terms--Crossing-layer protocol, data rate control, link adaptation, multihop wireless networks, network capacity.

We characterize the capacity region of a mobile ad hoc network (in which nodes employ the store--carry-forward communication scheme) and move according to an arbitrary ergodic mobility process. We identify the class of scheduling policies achieving maximum throughput and introduce a joint scheduling and routing formulation that maps the problem into a multicommodity flow over an associated contact graph. Previous capacity results have been derived under the strong assumption that nodes are identical and uniformly visit the entire network area, resulting in a fully connected homogeneous contact graph in which a simple two-hop routing scheme is optimal. Our approach allows extending the analysis to heterogeneous nodes with anisotropic mobility patterns, as typically encountered in realistic mobility traces. In particular, we apply our framework to an experimental network based on vehicular mobility and show that, in scenarios with inhomogeneous contact times, the two-hop routing strategy can significantly be inefficient in terms of throughput and delay. Index Terms--Delay-tolerant networking (DTN), network capacity, routing.

Cross-layer optimization solutions have been proposed in recent years to improve the performance of wireless users that operate in a time-varying, error-prone network environment. However, these solutions often rely on centralized cross-layer optimization solutions that violate the layered network architecture of the protocol stack by requiring layers to provide access to their internal protocol parameters to other layers. This paper presents a new systematic framework for cross-layer optimization, which allows each layer to make autonomous decisions to maximize the wireless user's utility by optimally determining what information should be exchanged among layers. Hence, this cross-layer framework preserves the current layered network architecture. Since the user interacts with the wireless environment at various layers of the protocol stack, the cross-layer optimization problem is solved in a layered fashion such that each layer adapts its own protocol parameters and exchanges information (messages) with other layers that cooperatively maximize the performance of the wireless user. Based on the proposed layered framework, we also design a message-exchange mechanism that determines the optimal cross-layer transmission strategies, given the user's experienced environment dynamics. Index Terms--Autonomous decision making, cross-layer optimization, environmental dynamics, information exchange, layered dynamic programming (DP) operator.

Vehicular ad hoc networks (VANETs) allow vehicle-to-vehicle communication and, in particular, vehicle-generated announcements. Provided that the trustworthiness of such announcements can be guaranteed, they can greatly increase the safety of driving. A new system for vehicle-generated announcements is presented that is secure against external and internal attackers attempting to send fake messages. Internal attacks are thwarted by using an endorsement mechanism based on threshold signatures. Our system outperforms previous proposals in message length and computational cost. Three different privacy-preserving variants of the system are also described to ensure that vehicles volunteering to generate and/or endorse trustworthy announcements do not have to sacrifice their privacy. Index Terms--Privacy, protocol design, secret sharing, security, threshold signatures, vehicular communications.

Cooperative communications significantly improve the performance of wireless networks with the help of relay nodes, whereas multiuser diversity (MUD) is a kind of diversity inherent in multiuser systems. In this paper, we present a framework to analyze the performance of MUD in the multiuser two-hop cooperative relay networks (TCRNs). Based on this framework, we derive tight closed-form expressions of outage probability and symbol error probability (SEP) for the amplify-and-forward (AF), fixed decode-and-forward (DF), and selective DF protocols with MUD. Both the theoretical analysis and simulations show that in multiuser TCRNs, MUD orders of 2K, K, and 2K can be achieved for AF, fixed DF, and selective DF, respectively (where K is the number of users). Index Terms--Amplify-and-forward (AF), cooperative communications, decode-and-forward (DF), multiuser diversity (MUD), outage probability, relay systems, symbol error probability (SEP).

We present a new method for data gathering that maximizes lifetime for wireless sensor networks. It involves three parts. First, nodes organize themselves into several static clusters by the Hausdorff clustering algorithm based on node locations, communication efficiency, and network connectivity. Second, clusters are formed only once, and the role of the cluster head is optimally scheduled among the cluster members. We formulate the maximum lifetime cluster-head scheduling as an integer-programming problem and propose a greedy algorithm for its solution. Third, after cluster heads are selected, they form a backbone network to periodically collect, aggregate, and forward data to the base station using minimum energy (cost) routing. This method can significantly lengthen the network lifetime when compared with other known methods. Index Terms--Communication protocol, energy efficiency, Hausdorff clustering, sensor networks.

One major concern for mobile networks consists of finding efficient ways of handling user mobility so that the handover process has minimum effect on users' ongoing sessions. Given the dominance of Internet-based applications in next-generation mobile networks, Mobile IP (MIP) has become an important protocol for accommodating the IP mobility. To overcome the excessive delay and signaling involved in the first version of MIP, the Hierarchical Mobile IPv6 (HMIPv6) protocol has been introduced. The key concept behind HMIPv6 is to locally handle handovers by the usage of an entity called mobility anchor point (MAP). Although the new protocol provides a more efficient way for mobility management in IP networks, it does not control traffic among multiple MAPs in the network. Thus, in many cases, the selected MAP is overloaded, and extensive delays are experienced during the routing process. To tackle this problem, this paper proposes a new technique, i.e., dynamic efficient MAP selection (DEMAPS). The proposed scheme works similar to HMIPv6 when the network is not overloaded. When the network gets heavy loads, the selection of MAPs is based on an estimation of MAP load transition using the exponential moving average method. Simulation results demonstrate that DEMAPS can efficiently balance the signaling traffic load among MAPs and provides a superior network performance compared with traditional HMIP schemes. Index Terms--Exponential moving average (EMA), Hierarchical Mobile IPv6 (HMIPv6), Mobile Internet Protocol (MIP), Mobile IPv6 (MIPv6), mobility anchor point (MAP), mobility management.

In this paper, we propose an analytical model for the distributed reservation protocol (DRP), which is defined in the WiMedia specification for ultra-wideband (UWB)-based wireless personal area networks (WPANs). We model the tagged user as a discrete-time queue with vacations, which captures the joint behavior of a queue length variation and a time-varying UWB channel due to shadowing under a given reservation pattern. Furthermore, we consider two reservation methods: hard reservation and soft reservation. With the hard reservation, a time slot is exclusively used by the owner, whereas the unused time slots can be accessed by other users using the soft reservation. Closed-form expressions of important performance metrics such as the mean service time, the waiting time, and the throughput are derived. Through numerical results, we validate the accuracy of the proposed analytical model and investigate the interaction between the DRP and various system parameters. This paper should provide insights into the performance of the DRP and useful guidelines to further improve the protocol to support isochronous applications with a tight delay requirement in UWB-based WPANs. Index Terms--Channel model, distributed reservation protocol (DRP), matrix-geometric approach, shadowing, ultra-wideband (UWB), vacation queue, wireless personal area network (WPAN).

For purposes of simulating contemporary communication systems, it is, in many cases, useful to apply error models for specific levels of abstraction. Such models should approximate the packet error behavior of a given system at a specific protocol layer, thus incorporating the possible detrimental effects of lower protocol layers. Packet error models can efficiently be realized using finite-state models; for example, there exists a wide range of studies on using Markov models to simulate communication channels. In this paper, we consider aggregated Markov processes, which are a subclass of hidden Markov models (HMMs). Artificial limitations are set on the state transition probabilities of the models to find efficient methods of parameter estimation. We apply these models to the simulation of the performance of Digital Video Broadcasting-Handheld (DVB-H). The parameters of the packet error models are approximated as functions of the time-variant received signal strength and speed of a mobile vehicular DVB-H receiver, and it is shown that useful results may be achieved with the described packet error models, particularly when simulating mobile reception in field conditions. Index Terms--Broadcasting, communication channels, Markov processes, mobile communication, simulation.

Wireless Medium Access Control (MAC) protocols such as IEEE 802.11 use distributed contention resolution mechanisms for sharing the wireless channel. In this environment, selfish hosts that fail to adhere to the MAC protocol may obtain an unfair throughput share. For example, IEEE 802.11 requires hosts competing for access to the channel to wait for a 'back-off- interval, randomly selected from a specified range, before initiating a transmission. Selfish hosts may wait for smaller back-off intervals than well-behaved hosts; thereby obtaining an unfair advantage. We show in this thesis that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. This study is a complementary of DOMINO System model to enhance the detection system in the MAC layer of IEEE 802.11; our enhanced system is a piece of software to be installed in or near the Access Point. The system can detect and identify greedy stations without requiring any modification of the standard protocol. We illustrate these concepts by simulation results. Key words: MAC, IEEE 802, 11, misbehavior, wireless LAN, hotspot, INTRODUCTION IEEE 802.11 (1) wireless LANs were originally meant to be deployed in (relatively) protected locations such as corporate offices; as a result, security, billing, and guarantee of fair access [...]

Urban target recognition at intersections using multimodality wireless sensor networks is a very promising system for the reduction of accidents by detecting unusual events in real time. To provide an alarm signal about an incoming car to a pedestrian using sound or to notify a driver about a pedestrian using infrastructure-to-vehicle communication, the deployed sensor system collects the sensed data from multimodality sensor nodes, performs data fusion, and conducts reactions to avoid the imminent accident. To facilitate the application, we design and implement an application-aware event-oriented MAC protocol (App-MAC) to support prioritized event delivery, provide inter-event fairness, improve the performance of channel utilization, and reduce energy consumption. App-MAC leverages the advantages of contention-and reservation-based medium access control (MAC) protocols to coordinate channel access and propose channel contention and reservation algorithms to adaptively allocate the time slots according to application requirements and current events status. To evaluate App-MAC, we have conducted simulations through the TOSSIM simulator and empirical studies using Berkeley TelosB motes with synthesized target recognition events and compared App-MAC with three state-of-the-art MAC protocols, i.e., sensor MAC (S-MAC), time-division multiple access (TDMA), and traffic-adaptive medium access (TRAMA), in terms of the proposed performance metrics, namely, average event delivery latency, event fairness index, channel utilization efficiency, and energy consumption efficiency. We found that App-MAC tremendously outperforms the other protocols in this application scenario. Index Terms--Application aware, energy efficient, event oriented, medium access control (MAC), multimodality, wireless sensor network (WSN).

We address the problem of self-configuration of user stations in a wireless environment with overlapping coverages. We propose and investigate a solution operating on top of the transport layer [called Autonomic Interface SeLEction (AISLE)] that exploits nodes featuring multihoming capabilities, i.e., with more than one network interface. Our solution is independent of the technology used at the physical and medium access control (MAC) layers. To evaluate the performance of AISLE, we first analytically derive the optimal way in which mobile stations should partition across multiple overlapping wireless networks, and we then verify through simulation the AISLE ability to achieve the optimal station partitioning. Different scenarios are considered, which include the case of heterogeneous networks, such as 802.11 wireless local area networks (WLANs) and third-generation (3G) cellular networks, with stations moving across an area with different degrees of overlapping coverages, as well as the case of heterogeneous stations, in which only some stations adopt AISLE. Index Terms--Multi-homing, transport layer protocols, wireless network access.

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, reduce 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 outperforms 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%. Index Terms--Adaptive prediction, cross layer, heterogeneous wireless networks, received signal strength (RSS), vertical handoff.

In this paper, we propose a group-based location service protocol named GrLS for Mobile Ad hoc NETworks (MANETs). The novelty of GrLS is in its exploitation of group mobility to improve the efficiency of the location service. GrLS uses different location management strategies for single nodes and for groups of nodes. A single node is responsible for recruiting its own location servers and performing location update. On the other hand, in a group of nodes, only the group leader recruits the location servers and updates its location to a specific home region called group home region. Since the location update cost normally dominates the location service cost for all practical purposes, the overhead of the location service protocol is significantly reduced. Furthermore, when the nodes join or leave groups, GrLS can provide seamless location service handoff. To the best of our knowledge, GrLS is the first location service protocol in MANETs that has explored group mobility and developed group location management for mobile nodes. Both theoretical analysis and simulation results show that GrLS can achieve a higher success ratio of location query and better load balance with much lower overhead than the existing protocols without considering group mobility. Index Terms--Group location management, group mobility, location service, Mobile Ad hoc NETworks (MANETs).

Because of the proliferation of indoor wireless local area network (WLAN) communication systems, portable radio measurement devices are becoming quite advantageous. This paper reports on the development of an advanced portable and compact broadband WLAN IEEE 802.11b channel sounder, which directly exploits the physical layer characteristics of the WLAN system. The measurement system and experimental procedures have been presented with the measurement results. The channel sounder provides very good results compared to a vector network analyzer (VNA). Moreover, the measured and reconstructed cross-correlation functions from the estimated power taps are in excellent agreement with a root mean square error (RMSE) of 3%. Hence, this system has been developed to be used in conjunction with a WLAN modeling system to calibrate indoor empirical and deterministic models. Index Terms--Channel impulse response (CIR), channel sounder, cross correlation, high resolution, physical layer convergence protocol (PLCP), times of arrival (ToA), wireless local area network (WLAN).

A queuing subsystem is proposed to the round robin receiver/transmitter ([R.sup.3]T) optical code-division multiple-access (OCDMA) protocol. The corresponding state diagram and its mathematical model are outlined. We prove that significant improvement in terms of system throughput and blocking probability can be achieved by only adding a single buffer at each user node. Furthermore, the modified [R.sup.3]T protocol can support higher traffic loads with acceptable delay and good efficiency. Index Terms--Chip-level receivers, OCDMA networks, OCDMA protocols, on-off keying, queuing.

Ongoing next-generation networks are expected to be deployed over current existing networks in the form of overlayed heterogeneous networks, particularly in hot-spot areas. Therefore, it will be necessary to develop an interworking technique, such as load balancing, to achieve increased overall resource utilization in the various heterogeneous networks. In this paper, we present a new load-balancing mechanism termed 'soft' load balancing, where the Internet Protocol (IP) traffic of a user is divided into subflows, each of which flows into a different access network. The terminology of soft load balancing involves the use of both load-sharing and handover techniques. Through a numerical analysis, we obtain an optimal load-balancing ratio (LBR) to determine the volume of traffic delivered to each network over an overlayed multicell environment. Using the optimal LBR, a more reliable channel transmission can be achieved by efficiently reducing the outage probability for given user traffic. Index Terms--Load-balancing ratio (LBR), loading factor, load sharing, outage probability, quality of service (QoS), soft load balancing.

The IEEE 802.15.3 medium access control (MAC) protocol is designed to support high-data-rate wireless personal area networks (WPANs). This protocol operates on a time-division multiple-access (TDMA) basis within a piconet, which guarantees interference-free connections. However, it is found that the protocol is not efficient for simultaneously operating piconets (SOPs). In the current protocol, SOPs can be linked by a parent/child (P/C) or parent/neighbor (P/N) configuration for interference mitigation. However, the throughput is limited because the same superframe is shared by the P/C and P/N piconets. In this paper, an adaptive channel time allocation (CTA) is proposed, including public and normal CTAs, to adaptively manage the interpiconet interference in SOPs. In a mobile environment, the public and normal CTAs can also be adaptively allocated based on the link status in the SOPs, thereby reducing interference and improving the efficiency of channel time usage. The proposed scheme is able to achieve a greater throughput than the P/C and P/N configurations. In addition, the link success probability can also be kept at a high value. Based on the SOPs of the direct-sequence ultrawideband (DS-UWB) system, the simulation results demonstrate that the proposed scheme effectively supports the coexistence of SOPs. Furthermore, it not only significantly improves the throughput of the SOPs but also maintains a high link success probability. Index Terms--Adaptive channel time allocation (CTA), direct-sequence ultrawideband (DS-UWB), IEEE 802.15.3 medium access control (MAC), simultaneously operating piconets (SOPs), superframe coordination.

Geographical routing is powerful for its ability to discover a path to the destination without the help of global states. However, stateless geographical routing usually involves a large number of hops when detouring around voids of the network. In this paper, we propose an efficient path pruning (PP) strategy to reduce the excessive number of hops caused by the detouring mode of geographical routing protocols. The PP algorithm finds routing shortcuts by exploiting the channel listening capability of wireless nodes and is able to reduce a large number of hops with the help of a little state information passively maintained by a subset of nodes on the route. We also discuss algorithm properties and implementation considerations and provide simulation results demonstrating the effectiveness of the proposed algorithm in shortening the routing path and improving delivery rate when it is applied to existing geographical routing protocols. Index Terms--Face routing, geographical routing, location-based routing, path shortening, wireless ad hoc networks.

Future-generation wireless networks will consist of heterogeneous radio access technologies (RATs) with Internet Protocol-based infrastructure and support multiple bearer services having different quality-of-service (QoS) requirements. However, a major issue is how to jointly utilize the resources in the different RATs in an efficient manner while simuitaneously achieving the desired QoS and minimizing the service cost from both the user and service provider perspectives. To resolve this issue, this paper proposes an adaptive common radio resource management (CRRM) scheme in the context of CDMA2000 and IEEE 802.11 wireless technologies, which are examples of today's wireless wide-area network (WWAN) and wireless local area network (WLAN) RATs, respectively. The key parameters of the scheme, i.e., service type, user mobility and location information, and service cost, are described. The effectiveness of the proposed CRRM scheme is analytically assessed using the theory of Markov chains. Numerical results show that the proposed CRRM scheme minimizes the rate of unnecessary vertical handoffs, thereby providing stable communication without degrading call-blocking probabilities in all mobility and loading scenarios considered. The proposed CRRM scheme also minimizes service cost, which makes it attractive for implementation in heterogeneous wireless networks. Index Terms--Common radio resource management (CRRM), heterogeneous wireless networks (HWNs), network selection, vertical handoff (VHO).

Most network operators have considered reducing Label Switched Routers (LSR) label spaces (i.e. the number of labels that can be used) as a means of simplifying management of underlaying Virtual Private Networks (VPNs) and, hence, reducing operational expenditure (OPEX). This letter discusses the problem of reducing the label spaces in MultiProtocol Label Switched (MPLS) networks using label merging--better known as MultiPoint-to-Point (MP2P) connections. Because of its origins in IP, MP2P connections have been considered to have tree-shapes with Label Switched Paths (LSP) as branches. Due to this fact, previous works by many authors affirm that the problem of minimizing the label space using MP2P in MPLS--the MERGING PROBLEM--cannot be solved optimally with a polynomial algorithm (NP-complete), since it involves a hard-decision problem. However, in this letter, the MERGING PROBLEM is analyzed, from the perspective of MPLS, and it is deduced that tree-shapes in MP2P connections are irrelevant. By overriding this tree-shape consideration, it is possible to perform label merging in polynomial time. Based on how MPLS signaling works, this letter proposes an algorithm to compute the minimum number of labels using label merging: the Full Label Merging algorithm. As conclusion, we reclassify the MERGING PROBLEM as Polynomial-solvable, instead of NP-complete. In addition, simulation experiments confirm that without the tree-branch selection problem, more labels can be reduced. Index Terms--Label space reduction, MP2P, label merging, NHLFE, MPLS, RSVP-TE.

This paper introduces a new definition of stochastic protocols for networked control systems (NCS) and the stochastic analog of the notion of uniform persistency of excitation of protocols first presented in the Proceedings of the 44th IEEE Conference on Decision and Control. Our framework applies directly to common wireless and wireline NCS, including those built on carrier-sense multiple access (CSMA) style protocols, with Ethernet and 802.11a/b/g as prime examples of this class. We present conditions for a general class of nonlinear NCS with exogenous disturbances using stochastic protocols in the presence of packet dropouts, random packet transmission times and collisions that are sufficient for [L.sub.p] stability from exogenous disturbance to NCS state with a linear finite expected gain. Within the same framework, we extend the results of Nesic and Teel (see IEEE Trans. Autom. Control, vol. 49, no. 10, pp. 1650-1667, Oct. 2004) to provide an analysis of deterministic protocols, including try-once-discard (TOD), in the Presence of random packet dropouts and intertransmission times and provide a stochastic analog of the Lyapunov-theoretic stability properties for network protocols introduced therein. Index Terms--Networked control systems (NCS), protocols, stochastic systems.

Next-generation mobile networks (NGMNs) are envisaged to offer interconnectivity among existing and emerging wireless technologies through a common Internet Protocol (IP)-based packet network. Interconnectivity through a common framework will enable individual networks to independently evolve (adoption/modification of a new/current system), allow new technologies to seamlessly integrate with the existing framework, and facilitate ubiquitous roaming for the mobile users. Dimensioning provides a theoretical bound for provisioning the required NGMN capacity to meet the projected traffic demand that arises from the participating networks. Although conventional network dimensioning (e.g., second generation, third generation, etc.) encompasses radio and core networks, the independence of networks within the NGMN framework confines its dimensioning process to the core network. Based on cell loading bounds (the number of users that are simultaneously supported in a cell), future traffic projection, and data rate variability, this paper proposes a dimensioning algorithm that derives an approximate estimate bound of core network dements [the number of base stations/access points (BSs/APs) per access router (AR), the number of ARs per mobility anchor point (MAP), and the number of MAPs per gateway (GW)]. The estimate bound is governed by the appropriate selection of the wired link capacities. A macrocell-based approach is considered within the proposed hierarchical NGMN architecture to address stationary, pedestrian, and vehicular users. Index Terms--Core network dimensioning, multiclass traffic, next-generation mobile network (NGMN).

In this paper, we present two physical layer cooperative protocols for heterogeneous sensor networks. There is one cooperator near the transmitter and a second cooperator (as a relay) near the receiver. Although the focus is on heterogeneous sensor networks, the methods can be applied to homogeneous sensor networks as well. Analytical and simulation results show that, under an additive white Gaussian noise channel assumption for the links between the transmitter and its partner and between the receiver and its partner, the proposed protocols achieve a diversity order of three or four by using the amplify-and-forward cooperation strategy and maximal ratio combining in the receiver. In addition, the proposed methods outperform the noncooperative single-hop transmission in the clustered heterogeneous sensor network and save a considerable amount of energy relative to the noncooperative transmission. Index Terms--Amplify-and-forward (AF) cooperation, cooperative diversity, heterogeneous sensor networks, maximal ratio combining.

The use of the controller area network communication protocol for H-bridge multilevel (HBML) inverters, and localized pulsewidth modulation generation and automated voltage regulation is proposed in this paper. It is shown that the performance and reliability of conventional distributed controllers for HBML inverters can be improved with less communication hardware requirements, when using the proposed method. It is also shown that the expansion and modularization capability of the HBML inverter is improved since individual inverter modules operate more independently. The proposed hardware is described in detail and the validity of the proposed system is verified experimentally on a 6600-V 1400-kW induction motor drive. Index Terms--Controller area network (CAN), H-bridge multilevel (HBML) inverter, pulsewidth modulation (PWM) phase-shift, PWM synchronization, serial communication.

Allow Improved Access in the Network via Cooperation and Energy Savings (ALLIANCES) is a recently proposed cooperative random access protocol for wireless networks that capitalizes on the broadcast nature of the wireless channel. When a collision occurs, a set of nodes forms an alliance and retransmits the collision signal that they heard. The initial collision and retransmissions provide the diversity that is exploited to resolve collisions and, thus, attain high throughput. In this paper, we modify the original model to include node location information. We derive pair-wise error probability (PEP) under a Rayleigh flat-fading channel and a power-law attenuation environment. Based on the PEP analysis, we propose a location relay selection scheme that achieves significant bit-error-rate gains as compared to the random relay selection scheme in the original ALLIANCES. Index Terms--Collision resolution, cooperation, cooperative protocols for wireless networks, cross-layer approach for wireless networks, diversity, multiple-input-multiple-output (MIMO), relay selection.

In this paper, we develop medium access control (MAC) schemes for both contention and contention-free accesses over wireless local area networks and give performance analysis of these MAC protocols. User detection and multirate adaptation (MRA) modules are proposed in the physical layer (PHY) to assist link differentiation. With these two modules, for contention accesses, a new distributed queuing MAC protocol (PALD-DQMP) is proposed. Based on different users' channel states, PALD-DQMP makes use of a distributed queuing system to schedule transmissions. To support multimedia transmissions, an enhanced PALD-DQMP (E-PALD-DQMP) is designed by providing two-level optimized transmission scheduling for four access categories, thus eliminating both external and internal collisions among mobile stations. For contention-free accesses, based on the same PHY-assisted link differentiation provided by the two modules, a new multipolling MAC protocol (PALD-MPMP) is proposed, which not only reduces the polling overhead but also prioritizes transmissions according to their delay requirements. Performance analysis and simulation results show that our proposed protocols outperform the standard MAC protocols for both delay-sensitive and best-effort traffics. All these improvements are mainly attributed to the awareness of cross-layer channel state information and the consequent MRA scheme. Index Terms--Cross-layer design, medium access control (MAC), physical-layer-assisted link differentation (PALD), user detetion, 802.11 wireless local area network (WLAN).

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 layer-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. Index Terms--Fast handoff, fourth generation (4G), IEEE 802.11, spatiotemporal, wireless local area networks (WLANs).

The conventional layered-protocol architecture does not provide optimal performance for wireless mesh networks (WMNs). The method of optimization decomposition of the protocol stack can achieve optimal network performance. This method usually results in a clean-slate protocol architecture that is different from the protocol architecture of WMNs. Such a difference actually demonstrates the need for a cross-layer design. Specific features pertaining to WMNs also show the need for cross-layer optimization across different protocol layers. In this paper, motivations for cross-layer design in WMNs are stated first. Moreover, cross-layer optimization schemes and algorithms between different protocol layers are investigated with an objective of shedding light on open research problems and new approaches. Guidelines for carrying out cross-layer design in WMNs are also provided in this paper. Index Terms--Control, cross-layer design, medium access, optimization decomposition, routing, wireless mesh networks.

Channel conditions in wireless local area networks (WLANs) are variable due to mobility and interference. Autorate algorithms are commonly used in WLANs to maximize the data rate over the variable physical channel. However, the widely used automatic rate fallback (ARF) algorithm does not work properly in the presence of multiaccess collisions due to its inability to differentiate frame losses caused by link errors from those caused by collisions. This paper proposes an improved ARF algorithm that is capable of differentiating between these two types of losses with minimal modifications to the existing medium access control protocol. The performance evaluations show substantial throughput improvements over ARF and other existing algorithms. Index Terms--Autorate, distributed coordination function (DCF), loss differentiation (LD), protocol design, wireless local area networks (WLANs).

In recent years, many location-aware routing protocols have been proposed for mobile ad hoc networks. The efficiency of the routing protocols can be improved by considering the location information of the mobile nodes (MNs). However, the mobility characteristics of the MNs have not been taken into account in most of the related work. In this paper, the proposed velocity-aided routing (VAR) algorithm determines its packetforwarding scheme based on the relative velocity between the intended forwarding node and the destination node. The routing performance can further be improved by the proposed predictive mobility and location-aware routing (PMLAR) algorithm, which incorporates the predictive moving behaviors of MNs in protocol design. The region for packet forwarding is determined by predicting the future trajectory of the destination node. The routing performance can be effectively enhanced by adopting both the proactive maintenance and the VAR mechanisms within the proposed PMLAR scheme. Simulation results show that the PMLAR protocol associated with its derivative schemes outperforms other routing protocols under different network topologies. Index Terms--Location-based ad hoc routing protocol, Mobile Ad hoc NETwork (MANET), mobility model, prediction mechanism.

The Internet has been studied as a typical example of real-world complex networks. In this brief, we study the traffic performance of the Internet when it encounters a random or intentional attack. Different from previous approaches, the congestion control protocols are considered so that the bandwidth can be real-located among flows. In this way, cascading breakdown is less likely to happen. The flow rates are adjusted when a node is attacked and out of function. Consequently, the traffic utility and the utilization ratio of bandwidth are affected. We compare the real Internet data with the classic random graph and scale-free network models. The simulated results also show that the 'robust yet fragile' property previously observed in the study of cascading failures in the scale-free networks is still valid in this scenario. Index Terms--Bandwidth allocation, complex networks, Internet, vulnerability.

Due to the recent popularization of mobile multimedia broadcasting, broadcasting continuous media data such as audio and video has attracted great deal of attention. In general continuous media data broadcasting, since clients have to wait to receive data before playing it, various schemes to reduce waiting time have been studied. Some reduce the waiting time by dividing the data into several segments and broadcasting preceding segments frequently with a single channel. However, by dividing the data into numerous segments and producing an effective broadcast schedule, the waiting time can be further reduced. In this paper, we propose a scheduling protocol to reduce waiting time with large-scale data segmentation. Index Terms--Broadband communication, broadcasting, interactive TV, protocols, satellite broadcasting.

In this paper, we present the characteristics of a vehicular ad hoc network (VANET), which is the Shanghai urban vehicular network (SUVnet). We construct a mobility model using the GPS data collected from more than 4000 taxis in Shanghai. The model is both realistic and large scale. Based on this model, network topology and connectivity of SUVnet are studied. Because of the sparse distribution and dynamic topology of SUVnet, simply utilizing the conventional mobile ad hoc network routing protocols in SUVnet may not achieve a satisfactory performance. Therefore, we apply the delay-tolerant network model to SUVnet and evaluate the epidemic routing protocols. We propose a new protocol, which is the distance aware epidemic routing (DAER), to improve the bundle delivery ratio. Results show that DAER performs well for a VANET. This paper provides a basis in studying a realistic urban VANET. Index Terms--Delay-tolerant network (DTN), epidemic routing, mobility model, performance, vehicular ad hoc network (VANET).

Reliable preparation of entanglement between distant systems is an outstanding problem in quantum information science and quantum communication. In practice, this has to be accomplished by noisy channels (such as optical fibers) that generally result in exponential attenuation of quantum signals at large distances. A special class of quantum error correction protocols, quantum repeater protocols, can be used to overcome such losses. In this work, we introduce a method for systematically optimizing existing protocols and developing more efficient protocols. Our approach makes use of a dynamic programming-based searching algorithm, the complexity of which scales only polynomially with the communication distance, letting us efficiently determine near-optimal solutions. We find significant improvements in both the speed and the final-state fidelity for preparing long-distance entangled states. entanglement | optimal control | quantum information | quantum repeater

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios. Index Terms--Fairness, relay channel, time division multiaccess, user cooperation, wireless networks.

Due to low cost, ease of deployment, increased coverage, and enhanced capacity, multiradio mesh networks that utilize inexpensive and readily available Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless interfaces are touted as the new frontier of wireless networking. In a multihop mesh system, the close interaction between topology control and routing selection affects the system throughput of a wireless network. This paper proposes a novel joint topology control and routing (JTCR) protocol for a multiradio multichannel wireless mesh network to exploit both channel diversity and spatial reusability. It resides between medium access control and the network layer and aims to improve the network throughput by coordinating transmission power, channel assignment, and route selection among multiple nodes in a distributed way. JTCR jointly coordinates the transmission power at each node, the channel selection on each wireless interface, and the route selection among interfaces based on the traffic information that is measured and exchanged among two-hop neighbor nodes. An equivalent channel air time metric (ECATM) is presented to quantify the difference of various adjustment candidates. This protocol achieves the efficient utilization of available channels by selecting a feasible adjustment candidate with the smallest ECATM value and coordinating affected nodes to realize the adjustment. Our NS-2-based simulation results show that the network throughput can be significantly improved by using our proposed solution. Index Terms--Distributed algorithm, IEEE 802.11, routing, topology control, wireless mesh.

Contention-based Geographic Forwarding (CGF) is a state-free forwarding technique. In this paper, we develop a general analytical framework to evaluate the performance of CGF with different forwarding areas in wireless multi-hop networks. In particular, we compare the performance of CGF for three typical forwarding areas, analytically and by extensive simulations. We further investigate the impact of several important assumptions on our analytical results. Our study provides guidelines regarding the selection of a specific forwarding area during the design phase of a CGF protocol. It also serves as a general performance evaluation framework for CGF protocols as well as traditional geographic forwarding protocols. Index Terms--Ad hoc and sensor networks, geographic forwarding, performance evaluation, void handling, wireless networks.

Due to the recent proliferation of digital broadcasting systems, various schemes for broadcasting continuous media data such as music or movies have been studied. In general broadcasting systems, since clients have to wait until their desired data are broadcast, these schemes reduce the waiting time by dividing the data into several segments of equal size. However, continuous media data often have units for playing portions of the data. For example, data encoded by MPEG2 can be played every GOP (Group of Pictures). In this paper, we propose a scheme to reduce the waiting time considering the units. Our proposed scheme divides a continuous media data at every unit. By scheduling divided data so that clients finish receiving a unit before starting to play the unit, waiting time is effectively reduced. Index Terms--Broadband communication, broadcasting, interactive TV, protocols, satellite broadcasting.

This paper provides a general framework for analyzing the stability of general nonlinear networked control systems (NCS) with disturbances in the setting of [L.sub.p] stability. Our presentation provides sharper results for both [L.sub.p] gain and maximum allowable transfer interval (MATI) than previously obtainable and details the property of uniformly persistently exciting scheduling protocols. This class of protocols was shown to lead to [L.sub.p] stability for high enough transmission rates and were a natural property to demand, especially in the design of wireless scheduling protocols. The property is used directly in a novel proof technique based on the notions of vector comparison and (quasi)-monotone systems. We explore these results through analytical comparisons to those in the literature, as well as through simulations and numerical comparisons that verify that the uniform persistence of excitation property of protocols is, in some sense, the "finest" property that can be extracted from wireless scheduling protocols. Index Terms--Networked control, scheduling, stabilization, wireless networks.