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The performance of an energy-efficient object tracking system depends on its accuracy in predicting the next destination of a mobile event. Unfortunately, a sophisticated prediction method cannot be operated in sensor nodes which have low computational power and storage. Moreover, precise prediction alone cannot be guaranteed to eliminate error in the future destination of the object in real circumstances. In this paper, we present a location error handling technique to prevent and handle this error efficiently. Real situations such as an unexpected change in the mobile event's direction, failure of event-detection and failure of transmitting an error message are considered when designing the error handling technique. This simple yet effective solution complements the weakness of the energy-efficient object tracking paradigm. From experiments on both real hardware and simulation, our method outperformed the existing work. [ABSTRACT FROM AUTHOR]

This paper proposes a new power-aware routing protocol, TDPR(Traffic load and lifetime Deviation based Power-aware Routing protocol), that does not only consider the residual battery capacity and transmission power, but also the traffic load of nodes and deviation among node lifetimes. It helps to extend the entire network's lifetime and to achieve load balancing. Simulation using ns-2 shows better the performance of the proposed routing protocol in terms of load balancing of the entire network, the consumed energy capacity of nodes, and paths reliability. TDPR has dead nodes 72% less than AODV, and 58% less than PSR. TDPR consumes residual energy capacity 29% less than AODV, 15% less than PSR. Error messages are sent maximum 38% less than PSR, and maximum 41% less than AODV. [ABSTRACT FROM AUTHOR]

Location determination of mobile users within a building has attracted much attention lately due to its many applications in mobile networking including network intrusion detection problems. However, it is challenging due to the complexities of the indoor radio propagation characteristics exacerbated by the mobility of the user. A common practice is to mechanically generate a table showing the radio signal strength at different known locations in the building. A mobile user's location at an arbitrary point in the building is determined by measuring the signal strength at the location in question and determining the location by referring to the above table using a LMSE (least mean square error) criterion. Obviously, this is a very tedious and time consuming task. This paper proposes a novel and automated location determination method called ARIADNE. Using a two dimensional construction floor plan and only a single actual signal strength measurement, ARIADNE generates an estimated signal strength map comparable to those generated manually by actual measurements. Given the signal measurements for a mobile, a proposed clustering algorithm searches that signal strength map to determine the current mobile's location. The results from ARIADNE are comparable and may even be superior to those from existing localization schemes. [ABSTRACT FROM AUTHOR]

Power saving mechanisms in wireless ad hoc network nodes mainly switch off the transmission and reception hardware for a maximal amount of time and turn it on again within a given interval. Many approaches aim to synchronize the state changes of the nodes in the network through distributed beacon generation and introduce mechanisms where nodes synchronously wake up at designated points of time to exchange announcements about pending traffic. Synchronization however is difficult to achieve, in particular in ad hoc networks. This paper describes the simulation, evaluation and refinement of a recently proposed power saving approach based on asynchronous wake-up patterns and wake-up announcements integrated with AODV. We show that significant improvements of the connectivity under low wake ratios can be achieved by carefully designed forwarding strategies of AODV route request messages. [ABSTRACT FROM AUTHOR]

In this paper we propose the use of statistical QoS guarantees for transmission over the wireless channel. Here, instead of QoS assurances we propose to guarantee the percentage of time the QoS requirements are satisfied. We present an associated scheduling algorithm for the opportunistic multiple access system. We compare the proposed scheduler with popular schedulers from the literature. We observe that the statistical QoS guarantee is an attractive alternative to the assured QoS for the wireless platform since such strict QoS assurances decrease the wireless system performance significantly. [ABSTRACT FROM AUTHOR]

We consider the state of the wireless channel in terms of the covariance stationary signal-to-noise ratio (SNR) process and parameterize it using the probability distribution function of SNR and lag-1 autocorrelation coefficient of associated autocorrelation function (ACF). In order to discriminate the state of the wireless channel we apply methods of statistical process control. Particularly, we use exponential weighted moving average (EWMA) change-point statistical test to detect shifts in the mean of the SNR process. The proposed approach is verified using SNR measurements of IEEE 802.11b wireless channel. [ABSTRACT FROM AUTHOR]

Increase of WLAN network deployments lead to the need of developing tools to predict coverage in terms of available service. In this paper we propose to establish service coverage based only on approximate floor plans by using the so-called PixelFlow algorithm. This algorithm is based on discrete version of the Huygens principle and appears to be rather robust to approximation in the floor plan. Measurements of service performances have been undertaken and used to calibrate the prediction results. Since the conventional calibration based on prediction errors is not the goal of service coverage prediction, a new metric has been developed to quantify differences between predicted and measured boundaries of the service coverage. Despite the complex impact of inaccuracies related to floor plan, wall material, radio propagation and WLAN protocols, it appears that the service coverage prediction proposed here is suitable to ease the radio network design of indoor Wi-Fi system. [ABSTRACT FROM AUTHOR]

Efficient H.264 video transmission over wireless/mobile networks, which is used as a dominant video coding standard in Digital Multimedia Broadcasting (DMB) and in other advanced video conferencing, becomes dominant. However, wireless video transmission suffers from deficient wireless channel conditions such as high bit error rate, error bursts due to channel fading and bandwidth limitations. In this paper, a novel design and analysis of unified error-control with cross-layer interaction over IEEE 802.11e Wireless LAN, in order to improve error protection performance, is proposed. This framework combines cross-layer error protection techniques, i.e., error correction code in the link/MAC layer, erasure code in the application layer and automatic retransmission across the link/MAC layer and the application layer. The performance of the proposed scheme in comparison to the generic scheme is demonstrated by simulation. [ABSTRACT FROM AUTHOR]

With the growth of broadband networks, Video-on-Demand (VoD) has become realistic. Most of the significant broadcasting schemes have been proposed to reduce the server bandwidth requirement for Constant Bit-Rate (CBR) encoded videos. The few existing proposals, which support of the bandwidth-efficient Variable Bit-Rate (VBR) encoded videos, smooth and minimize the server bandwidth requirement at the cost of data losses. The lossless and bandwidth efficient (LLBE) scheme states that minimization of the server bandwidth as a shortest path problem on a directed acyclic graph, and uses a dynamic programming method to solve the problem. However, it cannot be used for support live video broadcasting. In this paper, we propose a live harmonic broadcasting (LHB) scheme to support VBR-encoded live video broadcasting. The ideas behind the scheme are (1) support VBR-encoded videos by asynchronous downloading and playing, and hybrid division by length and size, and (2) support live videos by postponing recasting process. It is simple and effective. Using data from real videos, we conduct a simulation to evaluate our scheme. The experiment results indicate that the LHB scheme requires slightly higher server bandwidth than LLBE scheme. [ABSTRACT FROM AUTHOR]

Voice over WLAN (VoWLAN) is widely acknowledged as one of the key, emerging applications for wireless LANs. As with any multi-service network, there is the need to provision the WLANs with the QoS mechanisms capable of guaranteeing the requirements of various services. The upcoming IEEE 802.11e (EDCA) standard is on the way to define the required QoS mechanisms into the protocol architecture of IEEE 802.11 WLANs. However, recent studies have shown that EDCA performs poorly when the medium is highly loaded. This situation has led many researchers to design techniques aiming to improve the performance of EDCA. Unfortunately, the main deficiency of many of the proposed mechanisms to date comes from their inability to properly interoperate with legacy IEEE 802.11 (DCF) systems. Moreover, the implementation of many of the proposed QoS mechanisms requires important and incompatible changes to the IEEE 802.11e specifications. In this paper we introduce a novel IEEE 802.11e-based QoS protocol capable of providing QoS support to voice communications, and able to properly interoperate with legacy DCF based stations. Our design has been based on an in-depth analysis of the several operation modes of both standards. This should ensure full compatibility of operation: an important feature since the transition from the IEEE 802.11 to the IEEE 802.11e will take some time making more likely the existence of hybrid scenarios where both standards will have to coexist. Our results show that the proposed mechanism outperforms the IEEE 802.11e standard by offering better QoS guarantees to the voice service over a wider range of load conditions and traffic mix scenario. [ABSTRACT FROM AUTHOR]

We propose a novel resource allocation scheme, which can reduce MAP overhead and maximize the throughput in the MIMO-OFDM systems. Message based broadband access systems are needed to minimize the MAP overhead since the excessive MAP overhead causes degradation of system throughput. Increasing the size of resource allocation unit can reduce MAP overhead. However, multiuser diversity gain becomes smaller as the size of resource allocation unit increases. Therefore, we investigate joint optimization between multiuser diversity gain and MAP overhead size. The proposed scheme can reduce the MAP overhead size as well as achieve high throughput. [ABSTRACT FROM AUTHOR]

Orthogonal Frequency Division Multiplexing (OFDM) is used in both 802.11 and 802.16 [1] wireless network standards and is being evaluated for Fourth Generation (4G) networks. Its tolerance to frequency selective fading has made it an attractive choice for these broadband wireless networks. In both downlink and uplink directions, resources can be allocated in three dimensions, frequency, time and power. In both cases the resource allocation is performed primarily by the BS. In this paper we focus on the allocation of downlink resources when such a network is used for Quality of Service (QoS) applications. We formulate and solve the corresponding optimization problem and use the solution to design simple, practical algorithms. In doing so we take into account practical details that have not been addressed in previous work. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach for characterizing the aggregated traffic carried in the UMTS Terrestrial Radio Access Network (UTRAN). The characteristic of the incoming traffic stream of UTRAN is studied based on the measured trace traffic from the simulations. The main idea of the aggregated traffic modelling is to employ Batch Markov Arrival Process (BMAP) model as an analytically tractable model, which considers different lengths of packets and batch arrivals. In this paper, the setup and customization of the BMAP model for characterizing the aggregated traffic in UTRAN is presented. The accuracy of the BMAP model is demonstrated by comparing with simulations and Poisson traffic model. At the end the potential application of the presented approach and its advantages is briefly discussed. [ABSTRACT FROM AUTHOR]

Results for Enhanced UMTS (E-UMTS) cost/revenue optimisation are obtained, as a function of the coverage distance, R. E-UMTS traffic generation and activity models are described and characterised in an urban scenario based on population and service penetration values. By using a System Level Simulator results were obtained for blocking and handover failure probabilities. Models for the supported fraction of active users and for the supported throughput, as a function of active users, were obtained. When one amplifier is used, the maximum throughput per BS is around 600kb/s. However, it achieves values up to 2000kb/s when three amplifiers per BS are considered. Generally, the profit in percentage is a decreasing function with R. The use of three amplifiers per BS is strongly advised in order to get cheaper communications, with prices that vary from 0.016 to 0.07 /min, for R=250 and 1075m, respectively. [ABSTRACT FROM AUTHOR]

The convergence of mobile domain and data networks has been under focus in the standardization forums. However, dynamic interworking of wired infrastructure, wireless access systems and small scale Personal Area Networks has been challenging due to their heterogeneous nature. One of the most important problems to be solved is name resolution between different terminals and networks. This paper presents a new mechanism for name resolution, which relies on existing naming mechanisms. In particular the focus is on the scalability of the solution from signaling load and latency point of view. [ABSTRACT FROM AUTHOR]

The provisioning of IP services in the mobile telecommunication and the IP world differs in many aspects, especially with prepaid charging de termining an important useability distinction. Thus, the state of the art of pre paid charging systems have been analyzed in detail, elaborating on their key ca pabilities and major limitations. Additionally, economic aspects in terms of op erator's risks and major costs, addressing the technical overhead to implement prepaid charging, have been evaluated. Therefore, to enable prepaid charging for QoS-enabled and all-IP environments, key concerns for a future IP service provisioning have been determined, which remain infeasible with existing prepaid solutions, and the evaluation lead to a new scheme proposed. [ABSTRACT FROM AUTHOR]

In this paper we discuss IP layer packet filtering and an application level gateway approach used to secure handheld devices when providing and using web services. We propose a firewall management plane as a means for cross layer interaction. In our approach the application level gateway updates the IP layer firewall rules based on its knowledge about whether or not a certain source is sending malicious packets. We show that such a cross layer interaction can significantly decrease the CPU load in case of attacks, i.e., if many malicious packets arrive at the handheld device. Our measurement results show that the additional overhead for IP layer filtering is less than 10 per cent, if the number of applied rule sets is less than 200. In addition our cross layer approach can reduce the CPU load caused by the application layer gateway by about 10 up to 30 per cent. [ABSTRACT FROM AUTHOR]

The definition of the IEEE 802.1Q and IEEE 802.1p standards provided Class of Service (CoS) capabilities to Ethernet networks and, consequently, allowed new QoS services to be deployed. This is used by the Subnet Bandwidth Management (SBM) protocol, an RSVP-based protocol that provides IntServ-like services at Ethernet level. This paper proposes an alternative way to quality of service provision and resource allocation in Ethernet networks, based on the emerging IETF NSIS framework. The proposed approach was validated as a proof of concept by simulation, showing the ability of NSIS to provide QoS differentiation in Ethernet scenarios. [ABSTRACT FROM AUTHOR]

In this paper, we propose an enhanced handover mechanism with new additional primitives and parameters to the media independent handover (MIH) services as defined in IEEE 802.21. The proposed scheme can reduce handover latency for MIPv6 (mobile IPv6) by removing the router discovery time. Moreover, when the proposed mechanism is applied to a FMIPv6 (fast handovers for MIPv6), we can increase the probability that FMIPv6 can be per-formed in a predictive mode by reducing the handover initiation time. As a result, we can get the reduced handover latency in FMIPv6. In addition, with the proposed scheme, we can design the cost-effective network by reducing cover-age overlap between adjacent cells. This is due to the decreased handover initiation time in FMIPv6. From simulation results, it is proven that the proposed scheme can provide a higher goodput for UDP and TCP because it has less service disruption during handovers. [ABSTRACT FROM AUTHOR]

IP multicast is an effective technology to distribute identical data simultaneously to multiple users. However, for technical and administrative reasons, IP multicast has not been globally deployed on the Internet. Another approach to multicast is application-level multicast (ALM). In ALM, multicast related features, such as group membership management, multicast routing and packet replication, are implemented at end-hosts instead of routers. Multicast delivery tree is constructed in the application layer, so all nodes in this tree are end-hosts. Packet transmission between end-hosts uses conventional IP unicast service. Therefore, ALM is a promising alternative to IP multicast. However, application-level multicast relying on end-hosts is more fragile than IP multicast relying on routers. Especially, when a mobile host forwards packets to downstream hosts, a handover causes performance degradations on downstream hosts. In this paper, to alleviate the impact of a handover, we propose a new tree building protocol which locates mobile hosts on leaves of multicast tree. A handover of the mobile host on a leaf does not affect other end-hosts. To investigate performance of our protocol, it is compared with existing application-level multicast protocols. Our simulation results show that our protocol outperforms existing protocols from the viewpoints of loss probability, throughput and delay performance. [ABSTRACT FROM AUTHOR]

Many research work is going on in the domain of pure ad-hoc networking and even more issues are raised due to the missing central infrastructure to properly manage resources, guarantee fairness, and provide security features. On the other hand lot of research effort is spent to increase the performance of infrastructure-based access networks to cope with the steadily increasing demand for broadband data. When making a step back, the most promising evolution of heterogeneous networking is the integration of both paradigms. Taking advantage of the well controlled cellular environment and the high capacity of ad-hoc and direct node-to-node communication. The resulting hybrid networks are incorporating the best of both worlds. The concept of Cellular Assisted Heterogeneous Networking (CAHN) provides a framework to offer convenient and secure management of heterogeneous end-to-end sessions between nodes. The introduced separation of the signaling and the data plane allows to switch on power demanding broadband interfaces like GPRS, UMTS, or even WLAN only, if actually required, i.e., data has to be sent or received. The proposed out-of-band signaling enables furthermore the integration of ad-hoc links to offer best performance whenever nodes are within vicinity. Extensive simulations show that both, the integration of ad-hoc links and the selective activation of high power broadband interfaces, can significantly increase the performance of heterogeneous networks. [ABSTRACT FROM AUTHOR]

Classical micro-mobility solutions focus on accelerating local handovers and on minimizing signalling traffic. However, the micro-mobility components also slow down the service times in the user traffic domain. This is a critical drawback in terms of the hard delay requirements of future IP-based radio access networks. Network operators need algorithms to determine the optimal number and placement of anchor points within his network to balance both handover latency and user traffic delay. This paper presents a very fast and exact mathematical method for selecting the optimal number and placement of nodes supporting micro-mobility functionality for telecommunication networks. The method is in particular applicable for large networks, which is demonstrated by means of an optimization of a real wireless access network with more than 150 nodes. In order to ensure the applicability in real network scenarios we additionally provide a solution to estimate the stability of the optimal configuration. The presented method allows the autonomous and optimal configuration of the network's micro-mobility functionality as described in concepts of zero-touch networks. Due to the optimization network operators can reduce the administration cost and maximize the quality of service as well. [ABSTRACT FROM AUTHOR]

With the widespread use of wireless Internet and wireless LANs, different wireless technologies, such as 3G cellular networks and WLAN, will cooperate to support more users and applications with higher data rates over wider areas. When a mobile node moves between hybrid networks, a need arises for seamless vertical handoffs between different wireless networks in order to provide high performance data transmission. When an application with a TCP connection in a mobile node performs a vertical handoff, TCP performance is degraded due to packet loss even while the previous TCP state information is maintained during handoff, as 3G and WLAN have different available bandwidths. In this paper, a new congestion control algorithm is proposed for a vertical handoff that improves TCP performance by measuring the rough end-to-end available bandwidth and calculating the slow-start threshold. By ns-2 simulation it is shown that, compared to previous algorithms, the proposed algorithm enhances TCP performance during vertical handoffs. [ABSTRACT FROM AUTHOR]

Real-time streaming over satellite IP networks is challenging, since satellite links commonly exhibit long propagation delays and increased error rates, which impair TCP performance. In this context, we quantify the effects of satellite links on TCP efficiency and streaming video delivery. We investigate a solution-framework composed by TCP implementations which are expected to perform adequately in such environments. Furthermore, we study the supportive role of Selective Acknowledgments (SACK). Along with protocol performance, we also evaluate the impact of delayed acknowledgments. Our simulation results illustrate that most existing end-to-end solutions do not comply with the stringent QoS provisions of time-sensitive applications, resulting in inefficient bandwidth utilization and increased delays in data delivery. Finally, with the absence of a satellite-optimized TCP implementation for real-time streaming, we identify TCP Real as the most prominent solution, since it manages to alleviate most of the impairments induced by satellite links, sustaining a relatively smooth transmission rate. [ABSTRACT FROM AUTHOR]

The deployment of high performance networks and the emergence of broadband wireless access technologies challenge the performance of standard TCP. Recent years have seen a few high performance and aggressive TCP variants being proposed. These TCP variants still suffer significant performance degradation from random/transient packet losses. In this paper, we introduce and evaluate a new method to improve high performance TCP in the presence of random packet losses. It is ‘blind' in that our method does not attempt to differentiate between random and congestion-induced losses. Our method combines both TCP parallelisation and modification to the aggressiveness of studied AIMD algorithms. We show that our proposed method is no more aggressive than the studied TCP variants in the presence of congestion but more effectively utilises bandwidth in the presence of random packet losses. [ABSTRACT FROM AUTHOR]

This paper presents the Cluster-label-based mechanism for Backbones (CLaB) used in mobile ad hoc networks. The proposed mechanism provides a distributed topology control and consists of three parts: the part creating a backbone, the routing part, and the maintenance part on the backbone. The first part creates a clustered topology using a unique ID called a cluster label and establishes connections between neighboring clusters to create a backbone. The second part adapts existing routing protocols on the backbone. The third part maintains links on the backbone to minimize the influence of node movements, and needs no rerouting mechanism. The mechanism especially concentrates on maintenance by introducing constantly connected backbone elements based on cluster labels. A comparison with other backbone-based mechanisms is presented featuring different node densities and mobility levels. The results validate the effectiveness of the proposed mechanism. [ABSTRACT FROM AUTHOR]

The interaction between TCP flows and the IEEE 802.11 MAC protocol is analyzed in this paper. The goal is to provide comprehensive models capable of predicting the TCP performance (throughput) in WLAN Hot-Spot networks with persistent elastic flows. A model of the IEEE 802.11 MAC protocol is first introduced and validated through simulations. Using the MAC model as a basis, we then analyze several modeling strategies to catch the main interactions between TCP and MAC protocols. Results obtained from the models are compared among themselves and against simulations, and show the accuracy and the superior simplicity of the proposed models with respect to previously published work. [ABSTRACT FROM AUTHOR]

A novel approach to performing context discovery in ad-hoc networks based on the use of attenuated Bloom filters is proposed in this paper. In order to investigate the performance of this approach, a model has been developed. This document describes the model and its validation. The model has been implemented in Matlab, and some results are also shown in this document. Attenuated Bloom filters appear to be a very promising approach for context discovery in ad hoc networks. [ABSTRACT FROM AUTHOR]

Simulation tools are frequently used for performance evaluations of mobile ad-hoc networks. Currently the tools poorly support urban scenarios, since they do not take a spatial environment into account. In this paper, we describe a platform for the modeling of city scenarios. We extend ns-2 with corresponding mobility and wireless transmission models. By using its emulation facility, we integrate unmodified applications and real implementations of network protocols. We demonstrate the usefulness of the platform for performance evaluations by modeling a mobile application in a simulated environment of Stuttgart downtown. We show that it helps identifying application problems before deployment. [ABSTRACT FROM AUTHOR]

The needs for run-time data storage in modern wired and wireless network applications are increasing. Additionally, the nature of these applications is very dynamic, resulting in heavy reliance to dynamic memory allocation. The most significant problem in dynamic memory allocation is fragmentation, which can cause the system to run out of memory and crash, if it is left unchecked. The available dynamic memory allocation solutions are provided by the real time Operating Systems used in embedded or general-purpose systems. These state-of-the-art dynamic memory allocators are designed to satisfy the run-time memory requests of a wide range of applications. Contrary to most applications, network applications need to allocate too many different memory sizes (e.g. hundreds different sizes for packets) and have an extremely dynamic allocation and de-allocation behavior (e.g. unpredictable web-browsing activity). Therefore, the performance and the de-fragmentation efficiency of these allocators is limited. In this paper, we analyze all the important issues of fragmentation and the ways to reduce it in network applications, while keeping the performance of the dynamic memory allocator unaffected or even improving it. We propose highly customized dynamic memory allocators, which can be configured for specific network needs. We assess the effectiveness of the proposed approach in two representative real-life case studies of wired and wireless network applications. Finally, we show very significant reduction in memory fragmentation and increase in performance compared to state-of-the-art dynamic memory allocators utilized by real-time Operating Systems. [ABSTRACT FROM AUTHOR]

Cooperative relaying recently has emerged as a means of providing gains from spatial diversity to devices in a distributed manner. A cooperative relaying system deploying Alamouti's space-time coding (STC) design is investigated in this paper. According to amplify-and-forward (AF) and decode-and-forward (DF) modes, two TDMA-based cooperative transmission schemes are presented. Considering resource utilization efficiency, adaptive power allocation (PA) algorithms are proposed to adjust the power of each hop based on different channel conditions. Most importantly, the PA results also can be used to decide whether or not to relay, which recovers the loss of spectral efficiency due to the orthogonal transmission to a great extent. Numerical results indicate that the cooperative system with adaptive PA significantly outperforms the direct transmission system. Compared with the uniform power allocation (UPA), the proposed PA algorithm with power constraint of 1W can provide (52, 54)% capacity gains at most for Scheme (I, II), respectively. [ABSTRACT FROM AUTHOR]

We investigate the energy-saving potential of transport protocols. We focus on the system-related aspect of energy. Do we have to damage or enhance system fairness in order to provide energy efficiency? We depart from defining protocol potential; we compare different transmission strategies and protocol mechanisms; and we report our results on the impact of each mechanism on system energy. We highlight our conclusion that protocol fairness appears to be a key factor for system energy efficiency. [ABSTRACT FROM AUTHOR]

In this paper we propose an approach to increase TCP's fairness in multihop wireless networks, using ECN as a congestion signalling mechanism. The novel idea we introduce is that the marking probability at a wireless node is a function of the aggregate utilization in the node's neighborhood, which is determined by the sum of the receiving rates of all nodes within its collision domain. A node's received rate can be communicated to neighboring nodes by piggy-backing it on control packets, such as CTS and RTS messages, or data packets. Simulation results demonstrate that our approach can improve TCP's fairness in a multihop wireless network compared to drop tail queueing, while achieving the same aggregate throughput. Moreover, the proposed approach yields smaller average packet delay and delay jitter compared to drop tail queueing. [ABSTRACT FROM AUTHOR]

Recently, the 802.11e Working Group (WG) has proposed the Hybrid Coordination Function (HCF), which has a HCF Controlled Channel Access (HCCA) and an Enhanced Distributed Coordination Access (EDCA), in order to provide QoS in WLANs. In this paper an innovative HCCA-based algorithm, which will be referred to as Power Save Feedback Based Dynamic Scheduler (PS FBDS) providing bounded delays while ensuring energy saving, has been developed. The performance of PS FBDS has been extensively investigated using ns-2 simulations; results show that the proposed algorithm is able to provide a good trade-off between QoS and power saving at both low and high network loads. [ABSTRACT FROM AUTHOR]

A rudimentary approach to mitigate interference issues in license-exempt 802.16 systems is presented. This approach operates by permitting each Base Station (BS), and associated Subscriber Stations (SSs) to remain inactive for a specified fraction of the time. Other systems can then transmit with a reduced likelihood of interference. A simulator was developed to determine how this system performs. The results show that the throughput of the system is very sensitive to the fraction of time each BS is active; the system throughput is maximised when each BS is active less than 40% of the time for the scenarios studied. The results demonstrate a discrepancy between uplink and downlink throughput which can be attributed to the greater amount of overheads in the uplink. Finally, the results show that broadcast information being transmitted periodically at full power has a significant detrimental impact on the system. [ABSTRACT FROM AUTHOR]

Most existing WLAN access mechanisms cannot provide QoS assurances. Even those that are QoS aware can only provide relative service differentiation. Based on EY-NPMA, the HIPERLAN Medium Access Control algorithm, we propose a dynamic priority medium access scheme to provide time-bounded services. By approximating an ideal Earliest Deadline First (EDF) scheduler, the proposed scheme can offer delay and delay jitter assurances while achieving high medium utilization. Furthermore, we compare our scheme with a mechanism that enhances the IEEE 802.11 MAC protocol with QoS support. Simulation studies document and confirm the positive characteristics of the proposed mechanism. [ABSTRACT FROM AUTHOR]

In this paper, the packet error rate (PER) of IEEE 802.15.4 low rate wireless personal area network (WPAN) under the interference of IEEE 802.11b wireless local area network (WLAN) is analyzed. The PER is obtained from the bit error rate (BER) and the collision time. The BER is obtained from signal to noise and interference ratio. The power spectral density of the IEEE 802.11b is considered in order to determine in-band interference power of the IEEE 802.11b to the IEEE 802.15.4. The simulation results are shown to validate the numerical analysis. [ABSTRACT FROM AUTHOR]

In the Mobile Ad Hoc Network (MANET) paradigm, multipath routing protocols were initially proposed due to QoS needs, since they do not require initiation of the route discovery process after each link disconnection. Moreover, research on MANET routing security has shown that multipath routing provides increased resilience against security attacks of collaborating malicious nodes. Towards this direction, several secure multipath routing protocols have been recently proposed in the literature, which indeed provide such increased security protection for critical applications. However, embedding security mechanisms always imposes extra burden to the route discovery process. In this paper, we evaluate the performance of the existing secure multipath routing protocols for MANET through extensive simulations in various traffic scenarios. [ABSTRACT FROM AUTHOR]

The widespread use of Mobile Ad Hoc Networks (MANETs) in many fields of applications has led to the continuous development of routing protocols which can perform well when deployed under different scenarios, as well as offer better Quality of Service (QoS) support. In this paper, we focus on how link stability is utilized as a metric to provide accurate feedback on the network. We then introduce two mechanisms - L-REQ (Limited forwarding of Route Requests) and L-REP (Limited initiation of Route Replies by intermediate nodes) - which make use of link stability to dynamically adapt the characteristic behaviour of existing protocols to achieve better network performance. The two adaptive schemes are then applied to the Ad Hoc On Demand Distance Vector (AODV) routing protocol as proof of concept. [ABSTRACT FROM AUTHOR]

In this paper we address the problem of establishing a cost efficient multicast tree among a group of stationary nodes in a multi-hop wireless network. The flooding of broadcast discovery messages is a major limitation to the scalability of most ad hoc protocols. To avoid massive flooding, we limit the reach of broadcast discovery messages, and consider the case were joining nodes can only learn limited information about the multicast group topology from neighbors within a fixed number of hops. We propose two algorithms that satisfy this constraint. We analyze the worst case cost of the established trees and prove that the first algorithm builds a minimal cost spanning tree, while the second builds a sub-optimal tree with a worst-case approximation ratio of O(log n/loglog n). The advantage of the second algorithm is that the communication requirement for a node to join the multicast tree is smaller. We simulate and compare the proposed algorithms. Finally, we discuss the implementation issues and scenarios for using each one of them. We also describe our secure multicast application that builds on top of the proposed protocols. [ABSTRACT FROM AUTHOR]

We propose simple and computationally efficient wireless channel modeling algorithm. For this purpose we adopt the special case of the algorithm initially proposed in [1] and show that its complexity significantly decreases when the time-series is covariance stationary binary in nature. We show that for such time-series the solution of the inverse eigenvalue problem returns unique transition probability matrix of the modulating Markov chain that is capable to match statistical properties of empirical frame error processes. Our model explicitly takes into account autocorrelational and distributional properties of empirical data. We validate our model against empirical frame error traces of IEEE 802.11b wireless access technology operating in DCF mode over spread spectrum at 2Mbps and 5.5 Mbps bit rates. We also made available the C code of the model as well as pre-compiled binaries for Linux and Windows operating systems at http://www.cs.tut.fi/~moltchan. [ABSTRACT FROM AUTHOR]

In the high performance radio access networks, the number of random access channels can be used for mobile stations to transmit their bandwidth requests in contention mode via multiple random access. In this paper a collision reduced random access scheme based on m-art split algorithm in the centralized medium access control protocol is presented. In this method the splitting algorithm is used in two fold. On one hand the whole random access channels are exclusively separated into two parts; one is for initial contention where only initial access mobile stations can be served and the other is for retransmit contention where the mobile stations whose initial random access was not successful can join for their retransmission. On the other hand the m-ary split algorithm applied in the retransmit contention area to resolve the collisions. By doing so the proposed scheme achieves considerably greater performance in terms of maximum throughput, mean access delay, and delay jitter, which is one of the important criteria for real-time traffic. Through numerical examples and computer simulations the effect of the various parameters of the algorithm, initial number of random access report(s) and the split size m, on the system performance is examined. Keywords: Wireless Access Network, Random Access, m-ary split algorithm, Multimedia QoS. [ABSTRACT FROM AUTHOR]

Currently, IEEE 802.16a wireless MAN supports the contention based OFDMA-CDMA ranging subsystem for ranging operation (Initial Ranging, Periodic Ranging, Bandwidth Request)[1]. This system uses essentially the slotted ALOHA protocol. However, the number of code-slots/frame for random access transmission tends to be much greater than one and a simple Markov chain analysis may not be numerically feasible. At the same time, the frame size in number of code-slots may be dynamically adjusted based on the traffic load. In order to evaluate delay-throughput performance and stability measure of the random access protocol, we first examine the possible traffic load to be carried throughput the ranging subchannel. We the present performance analysis and numerical examples. [ABSTRACT FROM AUTHOR]

We present a framework for developing a traffic generator that produces massive, realistic network payloads. The techniques and methods in this article can be easily applied to any stress workload generator for network traffic simulation. Here, as the system to be tested, we use the UMTS/GPRS backbone including SGSN and GGSN, which utilizes GPRS Tunnelling Protocol (GTP-U) user plane messages to carry user data packets. The proposed workload generator system is characterized by high, real traffic load, economical standard hardware, scalability, and flexible extensibility. A large number of independent participants, such as mobile users and Internet servers, are modelled. The realism of traffic is achieved by using a layered modelling approach starting from the user/application level and ending at the network layer. High system throughput is obtained by exploiting preconstructed packet buffers (templates), packet filters, network interface polling, and an efficient, adjustable time resolution scheduler. [ABSTRACT FROM AUTHOR]

UMTS/WLAN integration offers considerable benefits for the users as well as for the mobile network. As soon as coverage is available, a mobile user should be able to switch seamlessly from the ubiquitous low bandwidth UMTS to a high bandwidth WLAN. This will improve his quality of service, but this also increases capacity in the cellular network. To be able to change between radio access technologies, an inter-RAT handover protocol is needed. If this handover protocol is not fast enough, the vehicular user will penetrate deep into the cell, underutilizing the available bandwidth with a lower overall performance as a result. In this paper we introduce a new vertical handover protocol which uses location information from the vehicle to predict where and when the handover should occur, thus optimizing user throughput and network performance. We consider its deployment on three UMTS/WLAN integration scenarios. [ABSTRACT FROM AUTHOR]

The last few years, research in wireless multi-hop networks is mainly driven by a search for efficient routing protocols. From an application point of view, nodes (users) will only setup connections with a specific goal, i.e. in order to use services and resources available in or reachable through the ad hoc network. Consequently, resource and service discovery (R&SD) protocols that allow nodes to learn available services in the network are indispensable. In this paper we compare the performance of two basic decentralized R&SD techniques, proactive and reactive discovery, through simulations and theoretical analysis. Our results show that the choice between them is not straightforward. It highly depends on the network and service characteristics and on the interaction with the underlying routing protocols. Therefore, our analysis provides some guidelines for developing new or extending existing R&SD protocols for operation in mobile ad hoc networks. [ABSTRACT FROM AUTHOR]

Today's public Wireless LANs are restricted to hotspots. With the current technology, providers can only target a small audience and in turn charge high prices for their service to generate revenue. Also, providers can not react appropriate to dynamic changes of the demand. With multi-hop cellular networks the coverage area can be increased and the installation costs and investment risks for the provider can be reduced. However, the individual customers play an important role in such networks and their participation must be encouraged. Therefore, we propose a cooperation and accounting scheme which introduces monetary rewards. We compare our scheme called CASHnet with the Nuglet scheme using simulations under the criteria of network liveliness as well as goodput, overhead and packet error rate. [ABSTRACT FROM AUTHOR]

For systems based on connection-oriented services, such as IEEE 802.16, call admission control (CAC) strategy is essential to provide a desired level of quality of service (QoS). Although many handoff-prioritized CAC schemes, which assume a fixed channel capacity, have been introduced, this assumption is not always valid for IEEE 802.16 that uses adaptive modulation and coding (AMC). With AMC, the modulation type of a user's connection can be changed dynamically and the ongoing connection might fail due to the change of modulation. In this paper, we approach the AMC-induced CAC problem by focusing on the guaranteed connection. Three kinds of calls, new, handoff, and modulation-changed calls, are considered. We propose a modified guard channel CAC scheme that allows the modulation-changed and handoff calls to use the guard channel. Then we analyze a Markov model for the CAC scheme with long-term AMC in mind. According to the simulation results, the proposed approach reduces the call dropping probability for modulation-changed calls, which suggests the threshold of guard channels in IEEE 802.16 can be determined based on the proposed approach. [ABSTRACT FROM AUTHOR]

In the wireless network environment, the effect of transmission errors and losses on the video quality varies depending on the intensity of the burst and which parts of the video stream are lost. Among the existing transmission error control techniques, FEC and ARQ are good solutions for combating transmission errors, but they require redundant data. Although interleaving has no error correcting capability, it can improve subjective video quality without wasting additional bandwidth, because it allows the spreading of successive errors. In this paper, we propose a content-aware packet-level interleaving method, which uses a quantitative index to indicate the degree of content-importance of the video content, so that the effect of burst packet losses is distributed intelligently. The proposed scheme improves the overall video quality in comparison with content-blind interleaving methods. Keywords: interleaving, content-aware, wireless network, video transmission. [ABSTRACT FROM AUTHOR]

Several studies in literature have investigated the performance of the proposed ieee 802.11e standard for qos differentiation in wlan, but most of them are limited both with respect to the range of the parameter settings and the considered traffic scenarios.The aim of the present study is to systematically investigate (by simulations) the impact of each of the qos differentiation parameters, under more realistic traffic conditions. In particular, we investigate flow-level performance characteristics (e.g., file transfer times) in the situation that the number of active stations varies dynamically in time. [ABSTRACT FROM AUTHOR]