Showing papers in "Wireless Communications and Mobile Computing in 2005"
TL;DR: An overview of UWB communications is provided, the previous research results are summarized, and further research issues that need to be tackled are identified.
Abstract: Summary Ultra-wideband (UWB) communication techniques have attracted a great interest in both academia and industry in the past few years for applications in short-range wireless mobile systems. This is due to the potential advantages of UWB transmissions such as low power, high rate, immunity to multipath propagation, less complex transceiver hardware, and low interference. However, tremendous R&D efforts are required to face various technical challenges in developing UWB wireless systems, including UWB channel characterization, transceiver design, coexistence and interworking with other narrowband wireless systems, design of the link and network layers to benefit from UWB transmission characteristics. This paper is to provide an overview of UWB communications, summarize the previous research results, and identify further research issues that need to be tackled. The emphasis is placed on the commercial wireless communications. Copyright # 2003 John Wiley & Sons, Ltd.
213 citations
TL;DR: This scheme is shown to be overall quite similar to OFDM but with some interesting additional features and improved characteristics and a detailed analysis of the system's implementation complexity as well as an evaluation of the influence of implementation-related impairments.
Abstract: As proven by the success of OFDM, multicarrier modulation has been recognized as an efficient solution for wireless communications. Waveform bases other than sine functions could similarly be used for multicarrier systems in order to provide an alternative to OFDM.
In this paper, we study the performance of wavelet packet transform modulation (WPM) for transmission over wireless channels. This scheme is shown to be overall quite similar to OFDM but with some interesting additional features and improved characteristics. A detailed analysis of the system's implementation complexity as well as an evaluation of the influence of implementation-related impairments are also reported. Copyright © 2004 John Wiley & Sons, Ltd.
184 citations
TL;DR: This paper proposes a new greedy algorithm, called S-MIS, with the help of Steiner tree that can construct a CDS within a factor of 4:8 þ ln5 from the optimal solution and introduces the distributed version of this algorithm.
Abstract: Summary Since no fixed infrastructure and no centralized management present in wireless networks, a connected dominating set (CDS) of the graph representing the network is widely used as a virtual backbone. Constructing a minimum CDS is NP-hard. In this paper, we propose a new greedy algorithm, called S-MIS, with the help of Steiner tree that can construct a CDS within a factor of 4:8 þ ln5 from the optimal solution. We also introduce the distributed version of this algorithm. We prove that the proposed algorithm is better than the current best performance ratio which is 6.8. A simulation is conducted to compare S-MIS with its variation which is rS-MIS. The simulation shows that the sizes of the CDSs generated by S-MIS and rS-MIS are almost the same. Copyright # 2005 John Wiley & Sons, Ltd.
179 citations
TL;DR: This paper investigates the saturation throughput performance achieved at the MAC layer, in both congested and error prone channels, and provides a simple and accurate analytical model to calculate the MAC throughput.
Abstract: It is well known that the medium access control (MAC) layer is the main bottleneck for the IEEE 802.11 wireless LANs. Much work has been done on performance analysis of the 802.11 MAC. However, most of them assume that the wireless channel is error-free. In this paper, we investigate the saturation throughput performance achieved at the MAC layer, in both congested and error prone channels. We provide a simple and accurate analytical model to calculate the MAC throughput. The model is validated through extensive simulation results. Our results show that channel errors have a significant impact on the system performance.
179 citations
TL;DR: It is argued that LDPC codes will be very suitable to prevent this type of jamming and an efficient anti-jamming technique for IEEE802.11b based on Reed–Solomon codes is proposed.
Abstract: In this paper, we investigate the resiliency to jamming of data protocols, such as IP, over WLAN. We show that, on existing WLAN, an adversary can successfully jam data packets at a very low energy cost. Such attacks allow a set of adversary nodes disseminated over an area to prevent communication, partition an ad hoc network or force packets to be routed over adversary chosen paths. The ratio of the jamming pulses duration to the transmission duration can be as low as 10−4. We investigate and analyze the performance of combining a cryptographic interleaver with various coding schemes to improve the robustness of wireless LANs for IP packets transmission 1. A concatenated code that is simple to decode and can maintain a low frame error rate (FER) under a jamming effort ratio of 15%. We argue that LDPC codes will be very suitable to prevent this type of jamming. We investigate the theoretical limits by analyzing the performance derived from upper bounds on binary error-control codes. We also propose an efficient anti-jamming technique for IEEE802.11b based on Reed–Solomon codes. Copyright © 2004 John Wiley & Sons, Ltd.
155 citations
TL;DR: An advanced hybrid control algorithm that uses signal-strength (SNR) information to achieve fast responses and effectively prevented many packet losses is designed and implemented, thereby achieving a much higher video quality than the statistics-based algorithm.
Abstract: Summary Streaming multimedia content in real-time over a wireless link is a challenging task because of the rapid fluctuations in link conditions that can occur due to movement, interference, and so on. The popular IEEE 802.11 standard includes low-level tuning parameters like the transmission rate. Standard device drivers for today’s wireless products are based on gathering statistics and consequently, adapt rather slowly to changes in conditions. To meet the strict latency requirements of streaming applications, we designed and implemented an advanced hybrid control algorithm that uses signal-strength (SNR) information to achieve fast responses. Since SNR readings are quite noisy, we do not use that information to directly control the rate setting, but rather as a safeguard limiting the range of feasible settings to choose from. We report on real-time experiments involving two laptops equipped with IEEE 802.11a wireless interface cards. The results show that using SNR information greatly enhances responsiveness in comparison to statistics-based rate controllers. Finally, we will present the results of an experiment with real-time video streaming to a moving laptop in an office-like environment. Our hybrid control algorithm effectively prevented many packet losses, thereby achieving a much higher video quality than the statistics-based algorithm. Copyright # 2005 John Wiley & Sons, Ltd.
80 citations
TL;DR: The design issues of an ultra wide band (UWB) receiver targeting a single-chip CMOS implementation for low data-rate applications like ad hoc wireless sensor networks are discussed and several simulation results obtained by means of a behavioral model are presented.
Abstract: Summary In this paper, we discuss the design issues of an ultra wide band (UWB) receiver targeting a single-chip CMOS implementation for low data-rate applications like ad hoc wireless sensor networks A non-coherent transmittedreference (TR) receiver is chosen because of its small complexity compared to other architectures After a brief recapitulation of the UWB fundamentals and a short discussion on the major differences between coherent and non-coherent receivers, we discuss issues, challenges and possible design solutions Several simulation results obtained by means of a behavioral model are presented, together with an analysis of the trade-off between performance and complexity in an integrated circuit implementation Copyright # 2005 John Wiley & Sons, Ltd
72 citations
TL;DR: Channel characteristics examined include the distance and frequency dependency of path loss, shadowing fading statistics, and multipath temporal-domain parameter statistics such as the mean excess delay, RMS delay spread, and the number of dominant paths.
Abstract: This paper presents a statistical characterization of an ultra wideband (UWB) indoor propagation channel based on measurements conducted in various types of high-rise apartments in several cities of Korea. Measurements were carried out in the frequency band of 3–10 GHz. Various communication links were considered including both line-of-sight (LOS) and non-LOS (NLOS) scenarios, which covered within-the-room and room-to-room propagations. The measurement procedure allows us to characterize both the large-scale and the small-scale statistics of the channel. The aim here is to study in more detail the statistical characteristics of the UWB propagation channel and to provide insight for future statistical channel modeling work. Channel characteristics examined include the distance and frequency dependency of path loss, shadowing fading statistics, and multipath temporal-domain parameter statistics such as the mean excess delay, RMS delay spread, and the number of dominant paths. Copyright © 2005 John Wiley & Sons, Ltd.
71 citations
TL;DR: This paper describes and evaluates the performance of SIGMA, a Seamless IP diversity-based Generalized Mobility Architecture, and indicates that in most cases SIGMA has a lower signaling cost than Hierarchical Mobile IPv6.
Abstract: Department of Technology Education, Korea National University of Education, San 7-1, Darakri, Chongwon-Gun, Chungbuk, 363-791, KoreaSummaryMobile IPhasbeendeveloped to handlemobility of Internet hosts at thenetworklayer.MobileIP(MIP),however,suffers from a number of drawbacks such as requirement of infrastructure change, high handover latency, highpacket loss rate, and conflict with network security solutions. In this paper, we describe and evaluate theperformance of SIGMA, a Seamless IP diversity-based Generalized Mobility Architecture. SIGMA utilizesmultihoming to achieve seamless handover of mobile hosts, and is designed to solve many of the drawbacks ofMIP, including requirement for changes in infrastructure. We first evaluate the signaling cost of SIGMA andcomparewiththatofhierarchicalMobileIPv6(anenhancementofMobileIP)byanalyticalmodeling,followedbycomparison of handover performance of SIGMA and Mobile IPv6 enhancements. Criteria for performanceevaluation include handover latency, packet loss, throughput, and network friendliness. Our results indicatethat in most cases SIGMA has a lower signaling cost than Hierarchical Mobile IPv6. Moreover, for a typicalnetwork configuration,SIGMA hasahigherhandoverperformanceoverMobileIP.Copyright#2005JohnWiley& Sons, Ltd.KEY WORDS: mobile handover; SIGMA; mobile IP; IP diversity; signaling cost1. IntroductionMobile IP (MIP) [1] has been designed to handlemobility of Internet hosts at the network layer tomanage mobile data communication. It allows aTCP connection to remain alive when a mobile host(MH) moves from one point of attachment to another.Several drawbacks exist when using MIP in a mobilecomputing environment, the most important onesidentified to date are high handover latency, highpacket loss rate [2], and requirement for change ininfrastructure. MIP is based on the concept of homeagent (HA) and foreign agent (FA) (which requiresmodificationtoexistingroutersinInternet)forroutingpackets from previous point of attachment to the newone. An MH needs to complete the following foursteps before it can receive forwarded data from theprevious point of attachment: (i) perform layer 2 (L2)handover, (ii) discover the new care of address (CoA),(iii) registering the new CoA with the HA, and (iv)
70 citations
TL;DR: An optimization algorithm for energy conscious scheduling of time slots that prevents intra-cluster collisions and eliminates packet drop due to buffer size limitations is described and an arbitration scheme is proposed that prevents collisions among the transmission of sensors in different clusters.
Abstract: Wide range of applications such as disaster management, military and security have fueled the interest in sensor networks during the past few years. Sensors are typically capable of wireless communication and are significantly constrained in the amount of available resources such as energy, storage and computation. Such constraints make the design and operation of sensor networks considerably different from contemporary wireless networks, and necessitate the development of resource conscious protocols and management techniques. In this paper, we present an energy-efficient, scalable and collision-free MAC layer protocol for sensor networks. The approach promotes time-based arbitration of medium access to limit signal interference among the transmission of sensors. Transmission and reception time slots are prescheduled to allow sensors to turn their radio circuitry off when not engaged. In addition, energy consumption due to active to sleep mode transitions is minimized through the assignment of contiguous transmission/reception slots to each sensor. Scalability of the approach is supported through grouping of sensors into clusters. We describe an optimization algorithm for energy conscious scheduling of time slots that prevents intra-cluster collisions and eliminates packet drop due to buffer size limitations. In addition, we also propose an arbitration scheme that prevents collisions among the transmission of sensors in different clusters. The impact of our approach on the network performance is qualified through simulation.. Copyright © 2004 John Wiley & Sons, Ltd.
65 citations
TL;DR: A comprehensive survey on integration of 3G and WLAN issues such as underline network architectures, integrated architectures, mobility management, and quality of service (QoS), as well as how seamless voice/multimedia/data handoff becomes possible.
Abstract: Integration of 3G and wireless LAN (WLAN) becomes a trend in current and future wireless networks, and brings many benefits to both end users and service providers. In this paper, we provide a comprehensive survey on integration of 3G and WLAN. We discuss issues such as underline network architectures, integrated architectures, mobility management, and quality of service (QoS). We particularly study handoff QoS mapping and guarantee between 3G and WLAN, as well as how seamless voice/multimedia/data handoff becomes possible. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: Simulation results show that 80% of the telecommunication cost is saved with as few as six peers, and with support from the servers in the internet, peers receive benefits of reduced telecommunication bandwidth, computation power, as well as several security features.
Abstract: Summary This paper provides a scheme to reduce the cost to distribute multimedia content to a set of nearby mobile peers, which we call chums. One peer, called the proxy, downloads multimedia content via a telecommunication link, and distributes it (which we call chumcast) to the ad hoc network formed from the set of nearby peers. Each peer in the ad hoc network takes turns serving as a proxy. Every peer is associated with a server that resides in the internet. The server for the proxy, called the active server, manages peer information, schedules the next proxy, selects a set of rebroadcasting peers, and detects partitioning of the ad hoc network. With support from the servers in the internet, peers receive benefits of reduced telecommunication bandwidth, computation power, as well as several security features. Simulation results show that 80% of the telecommunication cost is saved with as few as six peers. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: Simulations conducted in a heterogeneous system with UMTS and WLAN show that the proposed network selection technique can successfully satisfy QoS requirements for a variety of applications through a fair decision on the optimum network for mobile users at any time.
Abstract: The success of broadband service has attracted more people to surf internet with the demand of high mobility and high bandwidth. The ongoing wireless local area network (WLAN) standardization and development activities allow WLAN to provide high data rate in unlicensed spectrum. It motivates cellular network operators to adopt WLAN as a complement to cellular 3G systems in hot spot areas. Consequently, it is imperative to develop a network selection technique to assure quality-of-service (QoS) for the integrated cellular/WLAN system. In this paper, an optimization scheme for mobile users to select a network in an integrated WLAN and universal mobile telecommunication system (UMTS) system is proposed. In order to provide users a prospect of being always best connected, analytic hierarchy process (AHP) and grey relational analysis (GRA) techniques are integrated to make decision. The former defines selection criteria and the latter evaluates network alternatives. The network selection module is built at the link layer, and collects the time-varying QoS information through cross-layer message signaling. Simulations conducted in a heterogeneous system with UMTS and WLAN show that the proposed network selection technique can successfully satisfy QoS requirements for a variety of applications through a fair decision on the optimum network for mobile users at any time. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: This work presents ultra wide band MAC (U-MAC), an adaptive medium access control (MAC) protocol for UWB in which nodes periodically declare their current state so that neighbors can proactively assign power and rate values for new links locally in order to optimize global network performance.
Abstract: Ultra wide band (UWB) technology has received increasing recognition in recent years for its potential applications beyond radar technology to communication networks. UWB is a spread spectrum technology that requires careful coordination among communicating nodes to jointly control link power and transmission rates. Here, we present ultra wide band MAC (U-MAC), an adaptive medium access control (MAC) protocol for UWB in which nodes periodically declare their current state, so that neighbors can proactively assign power and rate values for new links locally in order to optimize global network performance. Simulations comparing U-MAC to the reactive approach confirm that U-MAC lowers link setup latency and control overhead, doubles the throughput and adapts better to high network loads. Simulations also reveal that the basic form of U-MAC favors nodes that are closer to the receiver. As a result, we also introduce novel mechanisms that control the radius around a receiver within which nodes can have fair access to it. We show through simulations the effect of the mechanisms on the tradeoff between network throughput and fair access.
TL;DR: Effects of various radio resource management and quality of service schemes on higher-layer protocols and real-world applications can be easily studied using NCTUns, an innovative network simulator and emulator for wireless and mobile networks.
Abstract: Summary This paper describes NCTUns, an innovative network simulator and emulator for wireless and mobile networks. Effects of various radio resource management and quality of service (QoS) schemes on higher-layer protocols and real-world applications can be easily studied using NCTUns. In this paper, we elaborate on NCTUns simulation methodology, architecture, design, functionalities, performance, and applications. NCTUns simulation for wireless ad hoc, sensor, inter-vehicle communication networks, GPRS cellular networks, and wireless mesh networks are also illustrated. More details about this tool can be found in http://NSL.csie.nctu.edu.tw/nctuns.html. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: The TCP upstream/downstream unfairness issue over WLANs with per-flow queuing employed at the access point (AP) is investigated and an efficient solution is proposed to be implemented at the AP for fairness achievement.
Abstract: Fairness is an important issue in WLANs due to their shared media nature. Essentially, IEEE 802.11 MAC protocols have been designed to provide fair access for all the competing mobile hosts. However, the fairness at MAC layer cannot be maintained at TCP layer in the presence of both mobile senders and receivers accessing to wired networks. In this paper, we investigate the TCP upstream/downstream unfairness issue over WLANs with per-flow queuing employed at the access point (AP). The interactions between the IEEE 802.11 MAC protocol and TCP are evaluated through analysis and simulation. Based on the derived analytical model, an efficient solution is proposed to be implemented at the AP for fairness achievement. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: The issues and techniques in QoS provisioning for wireless networks are overviewed, some of the recent results in this area are presented, and five sub-areas are surveyed, namely, network services models, traffic specification, packet scheduling for wireless transmission, call admission control in wireless networks, and wireless channel characterization.
Abstract: The next-generation wireless networks such as the fourth generation (4G) cellular systems are targeted at supporting various applications such as voice, data, and multimedia over packet-switched networks. Providing quality of service (QoS) guarantees for these applications is an important objective in the design of the next-generation wireless networks. In this paper, we overview the issues and techniques in QoS provisioning for wireless networks, and present some of our recent results in this area. Specifically, we survey the results in five sub-areas, namely, network services models, traffic specification, packet scheduling for wireless transmission, call admission control in wireless networks, and wireless channel characterization. For each sub-area, we address the particular issues, review major approaches and mechanisms, and discuss the trade-offs of the approaches. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: This paper presents a survey on a new analytical approach developed in the last few years to evaluate the performance of wireless cellular networks under more realistic assumptions, and applies it to the analysis of call connection performance and mobility management.
Abstract: Summary In wireless cellular networks, performance evaluation is an important part in modeling and designing effective schemes to utilize the limited resource. In the past, performance evaluation was carried out either under restricted assumption on some time variables such as exponential assumption or via simulations. In this paper, we present a survey on a new analytical approach we have developed in the last few years to evaluate the performance of wireless cellular networks under more realistic assumptions. In particular, we apply this approach to the analysis of call connection performance and mobility management under assumptions that many time variables such as call holding time, cell residence time, channel holding time, registration area (RA) residence time, and inter-service time are assumed to be generally distributed and show how we can obtain more general analytical results. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: This paper formally model BANDRA as an optimization problem and presents an integer linear programming (ILP) formulation to provide optimal solutions, and presents two routing algorithms to compute interference-optimal cost-bounded paths.
Abstract: In this paper, we study the bandwidth guaranteed routing and timeslot allocation (BANDRA) in TDMA-based multihop wireless networks with dynamic traffic. We formally model BANDRA as an optimization problem and present an integer linear programming (ILP) formulation to provide optimal solutions. This problem turns out to be a hard problem because of the impact of interference. Therefore, we propose a two-step scheme, i.e., seeking a path for routing first and then allocating bandwidth along the found path. We present two routing algorithms to compute interference-optimal cost-bounded paths. In addition, we present an optimal bandwidth allocation algorithm to allocate timeslots along the found paths for connection requests with unit bandwidth requirements. For the general case where the bandwidth requirement is larger than one, we present an effective heuristic algorithm. Our simulation results show that the average difference between solutions given by our efficient scheme and optimal ones in terms of call-blocking ratio is only 7%. Compared with the shortest path routing, our interference-aware routing algorithms combined with our bandwidth allocation algorithm always reduce call-blocking ratios. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: Three critical issues for the design of next generation systems are addressed: duplexing, scheduling and resource allocation and interference and inter-cell coordination.
Abstract: Coexistence of different access technologies, hierarchical cellular deployment, a wide variety of data services, requirements for transparent operation across different technologies, adaptivity to varying network conditions and mobility and quality of service (QoS) constraints introduce a number of challenges in the design of future generation systems and the specification of new air interfaces, such as efficiency and flexibility in the utilization of spectrum, dynamic resource allocation and exploitation of the multiuser diversity and reconfigurable interference management and inter-cell coordination. Three critical issues for the design of next generation systems are addressed: (i) duplexing, (ii) scheduling and resource allocation and (iii) interference and inter-cell coordination. A number of research directions are presented, which constitute promising potential candidates for next generation systems specification.
TL;DR: This paper validates the feasibility of automated optimization of key wideband code division multiple access (WCDMA) radio resource management parameters using control methods using a dynamic WCDMA system simulator.
Abstract: Summary This paper validates the feasibility of automated optimization of key wideband code division multiple access (WCDMA) radio resource management parameters using control methods. The parameters are regularly adjusted in order to improve performance. The parameters examined in this study include the total cell transmission power target, the received total interference target, the downlink radio link power maximums, the handover windows and the pilot channel powers. The control was based on expert-defined rules, which applied specific trade-off policies and statistics of poor quality calls, blocking, packet queuing, power and interference levels and terminal measurements to qualify the parameter values. The approach was validated using a dynamic WCDMA system simulator with a deployment of macro and micro cells on a city region. Results on automated optimization of single parameters on cell level and results on simultaneous multi-parameter optimization on cell-cluster level are presented in this paper. The use of the automated parameter optimization methods was shown to result in a significant increase of capacity in comparison to the default parameter settings. Copyright # 2004 John Wiley & Sons, Ltd.
TL;DR: Simulation results demonstrate that in general scenarios, the proposed estimator is the most efficient in computation and its statistical performance is the best among all popular ML-based DOA estimation methods.
Abstract: In this paper, we present an accurate direction-of-arrival (DOA) estimation method, which is based on the maximum likelihood (ML) principle and implemented using a modified and refined genetic algorithm (GA). With the newly introduced features—intelligent initialization and the emperor-selective (EMS) mating scheme, carefully selected crossover and mutation operators and fine-tuned parameters such as the population size, the probability of crossover and mutation etc., the GA-ML estimator achieves fast global convergence. A GA operator and parameter standard is suggested for this application, which is independent of the source and array configurations except the number of sources. Simulation results demonstrate that in general scenarios, the proposed estimator is the most efficient in computation and its statistical performance is the best among all popular ML-based DOA estimation methods.
TL;DR: An appropriate signaling protocol for the exchange of information between management modules at the network and the wireless terminal is discussed and the relevant findings are correlated with measurement results obtained from experiments over a prototype B3G network testbed.
Abstract: This work addresses aspects relevant to the optimal joint exploitation of heterogeneous wireless networks in an ‘all-IP’ integrated infrastructure, frequently called ‘Beyond 3G Systems’ (B3G) or composite radio networks. After briefly reviewing general architectural aspects pertaining to such systems, the paper focuses to the management functionality possessed by B3G systems and highlights the benefits that stem from sharing intelligence among the hybrid network (through a network management system) and the multimodal wireless terminals. In particular, the paper discusses an appropriate signaling protocol for the exchange of information between management modules at the network and the wireless terminal, investigates associated performance aspects and correlates the relevant findings with measurement results obtained from experiments over a prototype B3G network testbed. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: Results of simulations indicate that the behavior of the proposed scheme is strongly dependent upon the class of traffic in the WLAN scenario, while it is slightly affected by changes in traffic characteristics in the ad hoc case.
Abstract: Summary Modeling the resource manager of an ultra wide band (UWB) network is the main object of this paper. The model is tested in two different application scenarios: (i) a UWB WLAN access network to a backbone where the resource management module is implemented at the access points (APs); (ii) a UWB ad hoc network for either local communications or data exchange among sensors, with peer-to-peer links with distributed management. The design must include a quality of service (QoS)-aware strategy and must take into account coexistence issues raised by the use of UWB at the physical layer. Link quality is represented by the maximum end-to-end delay and minimum percentage of correct packets. From these parameters, the resource manager jointly selects the values of power and rate which must be adopted at the physical layer. In the model, radiated power by each device is supposed to be limited by an upper bound, reflecting thus the limitation imposed by regulation. QoS awareness and power constraints are satisfied, thanks to the implementation of an admission control function, which is centralized in the AP in the WLAN case and distributed in the ad hoc case. Major innovative aspects include: (i) taking into account UWB specific features; (ii) introducing QoS awareness based on network layer parameters rather than physical layer parameters; (iii) incorporating error protection functionalities for the optimization of transmission efficiency; (iv) considering both centralized and distributed resource management. Performance of the proposed resource manager module is evaluated in the presence of different classes of traffic, that is multimedia, voice, and data traffic. For each class of traffic, performance is expressed in terms of the maximum possible number of simultaneous connections for the WLAN case, and in terms of the effective achievable throughput for the ad hoc case. Results of simulations indicate that the behavior of the proposed scheme is strongly dependent upon the class of traffic in the WLAN scenario, while it is slightly affected by changes in traffic characteristics in the ad hoc case. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: This paper proposes a data rate drafting scheme and develops a variable size and variable rate (VSVR) scheme for goodput improvement, and shows that the proposed VSVR algorithm can double the channel goodput of current implementations.
Abstract: In IEEE 802.11 wireless LANs, channel quality, network load, as well as the protocol itself are time-varying, limiting the goodput performance improvement in wireless LANs. Therefore, it becomes critical to dynamically adjust parameters of MAC and PHY layers according to variations of channel quality. In this paper, we propose variable frame size and variable data rate schemes for goodput enhancement. We first propose two optimal frame size predictors: a goodput regulator to maintain the committed goodput for non-greedy applications and an optimal frame size predictor for maximizing the goodput for greedy applications. Then, we propose a data rate drafting scheme and develop a variable size and variable rate (VSVR) scheme for further goodput improvement. Our extensive simulation results show that the proposed VSVR algorithm can double the channel goodput of current implementations. Moreover, the proposed scheme can be easily integrated with the current implementations of the wireless LAN MAC protocol. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: Impact of mobility on both the radio and the core networks is addressed and potential research issues on these topics are discussed.
Abstract: Summary This paper describes the mobility management mechanisms for mobile telecommunications networks. There are two major types of mobility: radio network mobility and core network mobility. Radio network mobility supports radio link switching of a mobile user during conversation, and core network mobility provides roaming and tunnelrelated management for packet re-routing due to user movement. Impact of mobility on both the radio and the core networks is addressed in this paper. Also, potential research issues on these topics are discussed. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: This paper proposes and study proportional degradation service provisioning in wireless/mobile networks that offer multiple classes of adaptive multimedia services and proposes and studies the proportional degradation fairness model, which guarantees the proportional bandwidth degradation among different classes of services.
Abstract: Adaptive multimedia services are very attractive since resources in wireless/mobile networks are relatively scarce and widely variable, and more importantly the resource fluctuation caused by mobility and channel fading can be mitigated using adaptive services. Therefore, there are extensive research activities on Quality of Service (QoS), call admission control, as well as bandwidth degradation and adaptation for adaptive multimedia services in wireless/mobile networks in recent years. However, fairness of bandwidth degradation has largely been ignored in previous work and remains an important issue in adaptive multimedia service provisioning. In this paper, we propose and study proportional degradation service provisioning in wireless/mobile networks that offer multiple classes of adaptive multimedia services. The proposed proportional degradation fairness model guarantees the proportional bandwidth degradation among different classes of services. Two proportional degradation scenarios are studied in this paper. In the first scenario, we study the proportional degradation provisioning with two QoS parameters for adaptive multimedia: the degradation ratio (DR) and the degradation degree (DD). In the second scenario, we study the proportional degradation provisioning with a new QoS parameter for adaptive multimedia: the degradation area (DA). For each scenario, based on the QoS parameters, proportional degradation adaptation algorithms are proposed to approximate the proportional degradation model, to fairly adapt calls' degradations, to utilize the system resource efficiently, as well as to optimize QoS parameters. Performance studies show that in the first scenario, proportional DR has been achieved very well, whereas proportional DD has not been well achieved. In other words, DR outperforms DD in terms of proportional degradation. In the second scenario, proportional DA has been well achieved. Furthermore, bandwidth resources have been efficiently utilized and DA has been minimized. Copyright © 2004 John Wiley & Sons, Ltd.
TL;DR: This work introduces a new authentication architecture for fast authentication during inter-networking handoff and large-scale heterogeneous networks based on IP infrastructure and shows that the new architecture can reduce authentication latency significantly and be adaptive to user mobility and traffic.
Abstract: The successful deployment of wireless local area networks (WLAN) for high speed data transmission and cellular systems for wide coverage and global roaming has emerged to be a complementary platform for wireless data communications. In order to fully exploit potentials in 3G/WLAN integration, authentication of roaming users crossing different networks, must be coupled with mobility management, which is a challenging, yet not resolved issue. The focus of this paper is on state-of-art solutions to Wi-Fi and cellular networks based on IP infrastructure. Moreover, we introduce a new authentication architecture for fast authentication during inter-networking handoff and large-scale heterogeneous networks. We show that the new architecture can reduce authentication latency significantly and be adaptive to user mobility and traffic. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: The paper presents the statistical model for the ultra-wideband (UWB) indoor channel having a bandwidth of 2.4 GHz and a central frequency of 4.78 GHz, based on propagation experiments performed in different rooms on a floor of an office-laboratory building.
Abstract: The paper presents the statistical model for the ultra-wideband (UWB) indoor channel having a bandwidth of 2.4 GHz and a central frequency of 4.78 GHz. The model is based on propagation experiments performed in different rooms on a floor of an office-laboratory building. Within each room the receiver antenna is automatically moved over a square grid of 25 × 25 locations spaced 2 cm apart. A correlative channel sounding technique is employed; actually the carrier is modulated by a train of short duration (0.4 ns) pulses shaped by a PN-sequence. After coherently demodulating the detected signals and removing the PN-sequence modulation, we post-process the extracted channel impulse responses by best-fit procedures to set up a statistical tapped delay line model (STDL) of the UWB indoor channel. We characterize the path loss for line-of-sight (LOS) and non-line-of-sight (NLOS) conditions by distance-power laws and the shadowing by lognormal distributions. A clustered structure is observed in the average power-delay profiles; rays arrive at the receiver in groups, exponentially decaying with different decay constants. The small-scale effects are modeled by the Gamma distribution since it verifies with a 95%-confidence interval both the Chi-Square test and the Kolmogorov–Smirnov test applied to the experimental data. The shape parameters of such Gamma distributions are truncated Gaussian variables spreading in the range from 1 to 3. An implementation of the derived STDL model is finally proposed and a comparison between the simulated and the measured statistics is performed proving the validity of our approach. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: A preemptive priority handoff and adaptive resource allocation scheme that can be used in wireless part of the system along with DiffServ to give further guarantee for low delay, low jitter, and low loss services to high priority services.
Abstract: End-to-end quality of service (QoS) control for multiple traffic in wired networks is carried out through Differentiated services (DiffServ). Edge routers in DiffServ domain classify incoming flows into different per-hop behavior (PHB) groups and give a policy-based QoS guarantee to these behavior aggregates. As Internet extends into the wireless and mobile section, different traffic flows should be treated differently not only in wired core network, but also in wireless resource allocations. In this paper, we propose a preemptive priority handoff and adaptive resource allocation scheme. DiffServ PHB groups are mapped into different wireless and mobile QoS classes. Traffic flows are categorized into these classes in order to allow the system to allocate different bandwidth and make resource reservation according to their priorities. Higher priority traffic flows are permitted to preempt lower priority flows in service. Lower ones, on the contrary, can expand their bandwidth into areas reserved for higher priority traffic flows for better resource utilization. We use both analytical model and simulation to evaluate the system performance in terms of blocking probabilities, forced termination probabilities, and delay. The forced termination probability of high priority traffic flows can be decreased significantly by introducing the preemptive priority scheme. Therefore, this scheme can be used in wireless part of the system along with DiffServ to give further guarantee for low delay, low jitter, and low loss services to high priority services. Copyright © 2005 John Wiley & Sons, Ltd.