Showing papers in "Telecommunication Systems in 2009"
TL;DR: An adaptive cross-layer mapping algorithm that dynamically maps MPEG-4 video packets to appropriate access categories according to both the significance of the video data and the network traffic load is proposed.
Abstract: This paper proposes an adaptive cross-layer mapping algorithm to improve the transmission quality of MPEG-4 video stream over an IEEE 802.11e wireless network. Instead of classifying video data to a specific access category in an 802.11e network, we propose an algorithm that dynamically maps MPEG-4 video packets to appropriate access categories according to both the significance of the video data and the network traffic load. Our proposed cross-layer architecture passes information about the significance of video packets from the application layer to the media access control layer. The queue length of a specific access category is used to deduce the network traffic load. We conducted a performance evaluation of our proposed cross-layer approach under both light and heavily loaded network conditions. Our simulation results demonstrate: (a) superior performance of our proposed approach (under both light and heavy loads) over 802.11e (Enhanced Distributed Channel Access (EDCA) and static mapping schemes, (b) not only guarantees prioritized transmission of essential video data but also provides efficient queue length utilization.
80 citations
TL;DR: This paper takes the position that evolving the naming in the Internet by splitting the address into separate Identifier and Locator names can provide an elegant integrated solution to the key issues listed above, without changing the core routing architecture, while offering incremental deployability through backwards compatibility with IPv6.
Abstract: Internet users seek solutions for mobility, multi-homing, support for localised address management (i.e. via NATs), and end-to-end security. Existing mobility approaches are not well integrated into the rest of the Internet architecture, instead primarily being separate extensions that at present are not widely deployed. Because the current approaches to these issues were developed separately, such approaches often are not harmonious when used together. Meanwhile, the Internet has a number of namespaces, for example the IP address or the Domain Name. In recent years, some have postulated that the Internet's namespaces are not sufficiently rich and that the current concept of an address is too limiting. One proposal, the concept of separating an address into an Identifier and a separate Locator, has been controversial in the Internet community for years. It has been considered within the IETF and IRTF several times, but always was rejected as unworkable. This paper takes the position that evolving the naming in the Internet by splitting the address into separate Identifier and Locator names can provide an elegant integrated solution to the key issues listed above, without changing the core routing architecture, while offering incremental deployability through backwards compatibility with IPv6.
80 citations
TL;DR: The proposed Fuzzy Attributed Relational Graph (FARG) is a new approach for graph matching that resemble the human thinking process and is found to match users’ satisfaction to a high degree.
Abstract: Finding an image from a large set of images is an extremely difficult problem. One solution is to label images manually, but this is very expensive, time consuming and infeasible for many applications. Furthermore, the labeling process depends on the semantic accuracy in describing the image. Therefore many Content based Image Retrieval (CBIR) systems are developed to extract low-level features for describing the image content. However, this approach decreases the human interaction with the system due to the semantic gap between low-level features and high-level concepts. In this study we make use of fuzzy logic to improve CBIR by allowing users to express their requirements in words, the natural way of human communication. In our system the image is represented by a Fuzzy Attributed Relational Graph (FARG) that describes each object in the image, its attributes and spatial relation. The texture and color attributes are computed in a way that model the Human Vision System (HSV). We proposed a new approach for graph matching that resemble the human thinking process. The proposed system is evaluated by different users with different perspectives and is found to match users' satisfaction to a high degree.
59 citations
TL;DR: Experimental results show that fuzzy c-means performs significantly better than other, purpose built colour quantisation algorithms, and also confirm that the fast fuzzy clustering algorithms provide similar quantisation results to the full conventional fuzzy c -means approach.
Abstract: The aim of colour quantisation is to reduce the number of distinct colour in images while preserving a high colour fidelity as compared to the original images. The choice of a good colour palette is crucial as it directly determines the quality of the resulting image. Colour quantisation can also be seen as a clustering problem where the task is to identify those clusters that best represent the colours in an image. In this paper we investigate the performance of various fuzzy c-means clustering algorithms for colour quantisation of images. In particular, we use conventional fuzzy c-means as well as some more efficient variants thereof, namely fast fuzzy c-means with random sampling, fast generalised fuzzy c-means, and a recently introduced anisotropic mean shift based fuzzy c-means algorithm. Experimental results show that fuzzy c-means performs significantly better than other, purpose built colour quantisation algorithms, and also confirm that the fast fuzzy clustering algorithms provide similar quantisation results to the full conventional fuzzy c-means approach.
58 citations
TL;DR: A cost based evaluation model is developed that evaluates the location update cost, the packet delivery cost, and the wireless power consumption cost based on the protocol operations used and demonstrates that Proxy Mobile IPv6 always outperforms Hierarchical Mobile IPv 6.
Abstract: This paper presents comparative results on Hierarchical Mobile IPv6 and Proxy Mobile IPv6. The two mobility support protocols have similar hierarchical mobility management architectures but there are, however, clearly different perceptions: Hierarchical Mobile IPv6 has specific properties of a host-based mobility support protocol, whereas Proxy Mobile IPv6 is based on a network-based mobility support protocol. Thus, it is important to reveal their mobility characteristics and performance impact factors. In this paper, a cost based evaluation model is developed that evaluates the location update cost, the packet delivery cost, and the wireless power consumption cost based on the protocol operations used. Then, the numerical results are presented in where impacts of the various system parameters are evaluated. The results demonstrate that Proxy Mobile IPv6 always outperforms Hierarchical Mobile IPv6 due to its ability to avoid the mobility signaling sent by the mobile host, and its reduced tunneling overhead during communications with other nodes.
58 citations
TL;DR: This paper uses a cluster based virtual MIMO cognitive model with the aim of changing operational parameters (constellation size) to provide energy efficient communication and determines the routing path based on the virtual M IMO communication cost to delay the first node death.
Abstract: Virtual multiple input multiple output (MIMO) techniques are used for energy efficient communication in wireless sensor networks. In this paper, we propose energy efficient routing based on virtual MIMO. We investigate virtual MIMO for both fixed and variable rates. We use a cluster based virtual MIMO cognitive model with the aim of changing operational parameters (constellation size) to provide energy efficient communication. We determine the routing path based on the virtual MIMO communication cost to delay the first node death. For larger distances, the simulation results show that virtual MIMO (2×2) based routing is more energy efficient than SISO (single input single output) and other MIMO variations.
49 citations
TL;DR: This work presents the first localized protocol for constructing a fault-tolerant bi-connected robotic network topology from a connected network, in such a way that the total movement of robots is minimized.
Abstract: Teams of multiple mobile robots may communicate with each-other using a wireless ad-hoc network. Fault-tolerance in communication can be achieved by making the communication network bi-connected. We present the first localized protocol for constructing a fault-tolerant bi-connected robotic network topology from a connected network, in such a way that the total movement of robots is minimized. The proposed distributed algorithm uses p-hop neighbor information to identify critical head robots that can direct two neighbors to move toward each other and bi-connect their neighborhood. Simulation results show that the total distance of movement of robots decreases significantly (e.g. about 2.5 times for networks with density 10) with our localized algorithm when compared to the existing globalized one. Proposed localized algorithm does not guarantee bi-connectivity, may partition the network, and may even stop at connected but not bi-connected stage. However, our algorithm achieved 100% success on all networks with average degrees ?10, and over 70% success on sparse networks with average degrees ?5.
38 citations
TL;DR: The present work investigates the impact of variety of parameters on RSS by experimenting with Tmote Sky nodes in real-field outdoor environments and finds that besides the operating frequency, the transmitter–receiver distance, the variation of transceivers, the antenna orientation, and the environment specifics were found as important factors for creating accurate models.
Abstract: The use of Received Signal Strength Indicator (RSSI), obtained automatically with the received messages in most sensor radios, is a popular way for estimating the location of a mobile wireless object. The great variation of Received Signal Strength (RSS), which may result in inaccurate estimations, is compensated by the fact that RSS does not require any additional hardware, and may reduce the sensor node power consumption, size and cost. The present work investigates the impact of variety of parameters on RSS by experimenting with Tmote Sky nodes in real-field outdoor environments. Besides the operating frequency, the transmitter---receiver distance, the variation of transceivers, the antenna orientation, and the environment specifics were found as important factors for creating accurate models, which would serve in tracking and localization applications.
38 citations
TL;DR: The proposed method merges Reference Frame Selection, Intra Redundancy Slice and Adaptive Intra Refreshment techniques in order to prevent temporal error propagation in error-phone wireless video streaming and can be used and integrated into H264/AVC without violating the standard.
Abstract: The H.264/AVC standard introduces enhanced error robustness capabilities enabling resilient and reliable transmission of compressed video signals over wireless lossy packet networks. Those robustness capabilities are achieved by integrating some new error resilience tools that are essential for a proper delivery of real-time video services. Those tools include the Intra Refreshing (IR), Arbitrary Slice Ordering (ASO), Sequence Picture Parameter Sets (PPS), Redundant Slices (RS) tools and Flexible Macroblock Ordering (FMO). This paper presents an error resilient algorithm in wireless H.264/AVC streaming. The proposed method merges Reference Frame Selection (RFS), Intra Redundancy Slice and Adaptive Intra Refreshment techniques in order to prevent temporal error propagation in error-phone wireless video streaming. The coding standards only specify the decoding process and the bitstream syntax to allow considerable flexibility for the designers to optimize the encoder for coding performance improvement and complexity reduction. Performance evaluations demonstrate that the proposed encoding algorithm outperforms the conventional H.264/AVC standard. Both subjective and objective visual quality comparative study has been also carried out in order to validate the proposed approach. The proposed method can be used and integrated into H264/AVC without violating the standard.
31 citations
TL;DR: Three complementary protocols, TinySec, LEAP and TinyPK, are modelled using the high-level formal language HLPSL, and verified using the model checking tool AVISPA, where two main security properties are checked: authenticity and confidentiality of messages.
Abstract: In this paper, a formal analysis of security protocols in the field of wireless sensor networks is presented. Three complementary protocols, TinySec, LEAP and TinyPK, are modelled using the high-level formal language HLPSL, and verified using the model checking tool AVISPA, where two main security properties are checked: authenticity and confidentiality of messages. As a result of this analysis, two attacks have been found: a man-in-the-middle-attack and a type flaw attack. In both cases confidentiality is compromised and an intruder may obtain confidential data from a node in the network. Two solutions to these attacks are proposed in the paper.
29 citations
TL;DR: The key contribution of the HVE-mobicast routing protocol is that it is more power efficient than existing mobicast routing protocols, especially by considering different moving speeds and directions.
Abstract: In this paper, we propose a new mobicast routing protocol, called the HVE-mobicast (hierarchical-variant-egg-based mobicast) routing protocol, in wireless sensor networks (WSNs). Existing protocols for a spatiotemporal variant of the multicast protocol called a "mobicast" were designed to support a forwarding zone that moves at a constant velocity, $\stackrel{\rightarrow}{v}$ , through sensornets. The spatiotemporal characteristic of a mobicast is to forward a mobicast message to all sensor nodes that are present at time t in some geographic zone (called the forwarding zone) Z, where both the location and shape of the forwarding zone are a function of time over some interval (t start ,t end ). Mobicast routing protocol aims to provide reliable and just-in-time message delivery for a mobile sink node. To consider the mobile entity with the different moving speed, a new mobicast routing protocol is investigated in this work by utilizing the cluster-based approach. The message delivery of nodes in the forwarding zone of the HVE-mobicast routing protocol is transmitted by two phases; cluster-to-cluster and cluster-to-node phases. In the cluster-to-cluster phase, the cluster-head and relay nodes are distributively notified to wake them up. In the cluster-to-node phase, all member nodes are then notified to wake up by cluster-head nodes according to the estimated arrival time of the delivery zone. The key contribution of the HVE-mobicast routing protocol is that it is more power efficient than existing mobicast routing protocols, especially by considering different moving speeds and directions. Finally, simulation results illustrate performance enhancements in message overhead, power consumption, needlessly woken-up nodes, and successful woken-up ratio, compared to existing mobicast routing protocols.
TL;DR: A cross-layer mobility management scheme based on SIP and the Host Identity Protocol (HIP) which is a new protocol designed to provide secure and continuous communications between two nodes by separating the identifier and the locator roles of the traditional IP address is proposed.
Abstract: In the all-IP wireless networks, mobility management is a crucial issue, and it can be operated at different layers in the traditional Transmission Control Protocol/Internet Protocol (TCP/IP) stack. Session Initiation Protocol (SIP) is an application layer protocol used for the signaling and the mobility management without any modifications of the lower layer protocols, especially in the voice over IP environment. However, since it always gets the lowest priority in the networking model, it will produce the large handoff latency, the packet loss, and the handoff blocking probability. To provide an efficient mobility management, SIP can be combined with other protocols. In this paper, we propose a cross-layer mobility management scheme based on SIP and the Host Identity Protocol (HIP) which is a new protocol designed to provide secure and continuous communications between two nodes by separating the identifier and the locator roles of the traditional IP address. In the proposed scheme, the mobile node and the correspondent node use their host identity tags to establish the session connections, and the mobile nodes uses the HIP location update scheme instead of the SIP location update scheme to update its IP address when it moves to a new subnet. We discuss the proposed scheme's architecture and the major mobility procedures, including the session setup, the handoff and the location update in this paper. We also develop an analytical model to study the handoff performance of the proposed scheme, the typical SIP, and the hybrid SIP/Mobile IP, respectively. The analytical results demonstrate that the proposed scheme outperforms the typical SIP and the hybrid SIP/Mobile IP in terms of the handoff latency, the packet loss, and the handoff blocking probability.
TL;DR: Simulation results show that the proposed cross-layer resource allocation algorithm can provide substantial transmit power reductions compared to existing PHY layer and MAC layer solutions designed for multiuser OFDM systems.
Abstract: The resource allocation problem on the downlink of a multiuser OFDM-based cognitive radio (CR) system is formulated using a cross-layer (MAC and PHY layers) approach with the aim of satisfying quality of service (QoS) requirements in real-time applications. The number of subchannels available to the CR system is time-varying as a result of the stochastic nature of the activities of the primary users (PUs). The MAC layer QoS requirements are dynamically converted to PHY layer rate requirements; the conversion depends on the delivery status of queued packets as well as the number of available subchannels. Simulation results show that the proposed cross-layer resource allocation algorithm can provide substantial transmit power reductions compared to existing PHY layer and MAC layer solutions designed for multiuser OFDM systems.
TL;DR: Experimental results have been carried out to verify the ability of modified PNN in achieving good classification rate over traditional PNN, BPNN and KNN.
Abstract: Probabilistic neural network (PNN) is a kind of supervised neural network, proposed by Specht as an alternative to back-propagation neural network. The key advantages of PNN are that, training requires only a single pass, and decision surfaces are guaranteed to approach the Bayes-optimal decision boundaries, as the number of training samples grows. Furthermore, shape of the decision surface can be made as complex as necessary, or as simple as desired, by choosing an appropriate value of the smoothing parameter; erroneous samples can be tolerated, and sparse samples are adequate for network performance. This paper reviews the PNN, modified PNN, various learning approaches employed to train the PNN and some comparisons of various types of PNN. Experimental results have been carried out to verify the ability of modified PNN in achieving good classification rate over traditional PNN, BPNN and KNN.
TL;DR: An energy-efficient interface selection scheme for MMTs in the integrated WLAN and cellular networks is proposed that takes advantage of existing out-of-band paging channel of cellular networks, so that the WLAN interface can be completely turned off during the idle state leading to reduction in energy consumption.
Abstract: With the advent of a number of wireless network technologies such as WCDMA and WLAN, current mobiles are equipped with multiple network interfaces, so called Multi-Mode Terminal (MMT). MMTs are capable to access different kinds of networks by performing a vertical handover between heterogeneous wireless networks, where during the idle state, the MMTs consume a lot of energy since their WLAN interface must wake up for listening to periodical beacons. However, previous studies on the vertical handover did not address how to select the optimal interface taking into account the characteristics of MMTs, especially energy consumption. Therefore, in this paper, we propose an energy-efficient interface selection scheme for MMTs in the integrated WLAN and cellular networks. The proposed interface selection scheme takes advantage of existing out-of-band paging channel of cellular networks, so that the WLAN interface can be completely turned off during the idle state leading to reduction in energy consumption. Simulation results show that the proposed scheme outperforms conventional approaches in terms of energy consumption with reduced signaling overhead and handover delay.
TL;DR: This paper focuses on the subcarrier and power allocation problem in the downlink of an OFDM system under the cognitive radio environment, and formulate the optimization problem subject to a total transmit power constraint and interference constraints, from which a power limited multilevel water-filling algorithm is derived.
Abstract: In this paper, we focus on the subcarrier and power allocation problem in the downlink of an OFDM system under the cognitive radio environment. We aim to maximize the weighted sum rate of secondary users, without causing adverse interferences to primary users. We formulate the optimization problem subject to a total transmit power constraint and interference constraints, and give the optimality conditions, from which we derive a power limited multilevel water-filling algorithm. Simulation results show that our proposed algorithm yields significant improvement in terms of weighted sum rate, and provides good convergence with low computational burden.
TL;DR: By applying the cognitive behaviour of the real ant colonies, P2PSI owns the capability of adaptive learning of routing path and is able to cope with mobility problem without flooding and also adopts cross-layer design to reduce the redundant message overhead and query latency.
Abstract: Peer-to-peer file sharing over mobile ad hoc networks (MANET) has become a popular application due to the rapid growing number of mobile devices. However, the fact that mobile nodes in a MANET dynamically alter their locations and join/leave the P2P system has posted many challenges in designing a robust and scalable P2P system. Although, in the literature, flooding-based P2P approach has been shown to be robust in a highly dynamic network, it leads to poor efficiency in terms of bandwidth usage and scalability. A new design is required in which cross-layer designs and cognitive approaches could be applied such that it could interact with the requests of users and respond to dynamic change of network topology. In this paper, we propose an efficient and scalable P2P file sharing system over MANET based on Swarm Intelligence, referred to as P2PSI. By applying the cognitive behaviour of the real ant colonies, P2PSI owns the capability of adaptive learning of routing path and is able to cope with mobility problem without flooding. Moreover, P2PSI also adopts cross-layer design to reduce the redundant message overhead and query latency. Performance of P2PSI is evaluated and compared to two existing cross-layer design service discovery protocols through simulations. Our simulation results show that P2PSI achieves better performance in terms of control overhead and request success ratio.
TL;DR: This paper aims to cover some of the most interesting business alternatives in providing the new 3G and beyond services including cases where the operator already has an existing second-generation cellular network and perhaps even a license for the 3G UMTS network, and casesWhere the operator does not have any existing network.
Abstract: The importance of analyzing different business models and technologies in the mobile industry has become more crucial for the investment policy of the telecom operators. This paper aims to cover some of the most interesting business alternatives in providing the new 3G and beyond services including cases where the operator already has an existing second-generation cellular network and perhaps even a license for the 3G UMTS network, and cases where the operator does not have any existing network. Three cases for incumbents and new entrants are foreseen, leaving alternatives for new competing 3G technology deployment or acting as a mobile virtual network operator (MVNO) without owning any radio infrastructure. A techno-economic approach has been used to identify business opportunities and quantify the potential profitability of different kind of business players. The scenarios have been analyzed in the Western European context by different country groups that are not exactly representative of any defined country, but rather share typical demographic characteristics.
TL;DR: An intelligent video authentication algorithm which integrates learning based Support Vector Machine classification with Singular Value Decomposition watermarking is presented which outperforms existing video authentication algorithms.
Abstract: In law enforcement applications such as surveillance and forensics, video is often presented as evidence. It is therefore of paramount importance to establish the authenticity and reliability of the video data. This paper presents an intelligent video authentication algorithm which integrates learning based Support Vector Machine classification with Singular Value Decomposition watermarking. During video capture and storage, intrinsic local correlation information is extracted from the frames and embedded in the frames at local levels. Tamper detection and classification is performed using the inherent video information and embedded correlation information. The proposed algorithm is independent of the choice of watermark and does not require any key to store. Further, it is robust to global tampering such as frame addition and removal, local attacks such as object alteration and can differentiate between acceptable operations and malicious tampering. Experiments are performed on an extensive database which contains non-tampered videos and videos with several types of tampering. The results show that the proposed algorithm outperforms existing video authentication algorithms.
TL;DR: A cross layer approach based on queuing and adaptive modulation for MIMO systems has been presented and the obtained results present the advantages of using the proposed cross layer architecture.
Abstract: A cross layer approach based on queuing and adaptive modulation for MIMO systems has been presented. To realize the system, an adaptive modulation scheme using MIMO systems combined with finite-length queuing at the data link layer has been designed. A finite state Markov chain for MIMO channels has been constructed to persue the queuing analysis. The packet loss rate, the average throughput, and the average spectral efficiency have been computed. Furthermore, the packet error rate for adaptive modulation to minimize the packet loss rate and maximize the average throughput is extracted. The obtained results present the advantages of using the proposed cross layer architecture.
TL;DR: An analytical model is proposed that allows a general behavior for the packet size distribution while the inter-arrival times are assumed to be of Phase-Type and can easily be relaxed to be generally distributed if needed.
Abstract: This paper presents an approach to evaluate the performance of an optical switch equipped with both limited-range wavelength conversion and Fiber Delay Lines to resolve contention. We propose an analytical model that allows a general behavior for the packet size distribution while the inter-arrival times are assumed to be of Phase-Type and can easily be relaxed to be generally distributed if needed. As the set of reachable wavelengths is a major issue in limited-range wavelength conversion, we first focus on a simple wavelength set configuration that allows the comparison of different policies and their effect on the loss rate of the system. In addition, a linear association between the loss rate of the simple and a more complex set configuration is identified. Using this association and the results from the analytical model, we derive an approximation for the more complex case, where the interactions among adjacent wavelengths play an important role. The approximation works well for different parameter instances and is particularly useful for the mid load case, when simulations become computationally prohibitive.
TL;DR: A novel and pragmatic cross-layer approach with joint congestion and contention window control scheme to improve the performance of TCP in IEEE 802.11 wireless environments and enables TCP to distinguish between congestion loses and transmission errors, thus to take proper remedial actions.
Abstract: Neither the current TCP protocol nor the standard backoff algorithm of IEEE 802.11 protocol is able to distinguish corruption loss from congestion or collision loss. Hence, high transmission errors and a varying latency inherent in wireless channel would have a seriously adverse effect on the performance of TCP. In this paper, we propose a novel and pragmatic cross-layer approach with joint congestion and contention window control scheme to improve the performance of TCP in IEEE 802.11 wireless environments. In addition to theoretical analysis, simulations are conducted to evaluate the proposed scheme. As it turns out, our design indeed provides a more efficient solution for frequent transmission loss and enables TCP to distinguish between congestion loses and transmission errors, thus to take proper remedial actions.
TL;DR: A stochastic approach is proposed, which can generate multiple Pareto solutions in a single run and is illustrated by considering several network design problems using a single weighted average of objectives and a direct multiobjective optimization approach using the Pare to dominance concept.
Abstract: The paper deals with the design of resilient networks that are fault tolerant against link failures. Usually, fault tolerance is achieved by providing backup paths, which are used in case of an edge failure on a primary path. We consider this task as a multiobjective optimization problem: to provide resilience in networks while minimizing the cost subject to capacity constraint. We propose a stochastic approach, which can generate multiple Pareto solutions in a single run. The feasibility of the proposed method is illustrated by considering several network design problems using a single weighted average of objectives and a direct multiobjective optimization approach using the Pareto dominance concept.
TL;DR: This paper presents static and dynamic intelligent mobility models that are based on the inherent clusters’ information of a sparsely connected network and provides insights into the applicability of these mobility models in different application scenarios.
Abstract: In wireless sensor and actor network research, the commonly used mobility models for a mobile actor are random walk model, random waypoint mobility model, or variants thereof. For a fully connected network, the choice of mobility model for the actor is not critical because, there is at least one assured path from the sensor nodes to the actor node. But, for a sparsely connected network where information cannot propagate beyond a cluster, random movement of the actor may not be the best choice to maximize event detection and subsequent action. This paper presents static and dynamic intelligent mobility models that are based on the inherent clusters' information of a sparsely connected network. Simulation results validate the idea behind the intelligent mobility models and provide insights into the applicability of these mobility models in different application scenarios.
TL;DR: A multilevel power adjustment (MLPA) mechanism for WSNs to prolong the individual node lifetime and the overall network lifetime by reducing the average transmission power is proposed and two approximated power configuration methods are proposed.
Abstract: Restricted to the limited battery power of nodes, energy conservation becomes a critical design issue in wireless sensor networks (WSNs). Transmission with excess power not only reduces the lifetime of sensor nodes, but also introduces immoderate interference in the shared radio channel. It is ideal to transmit packets with just enough power. In this paper, we propose a multilevel power adjustment (MLPA) mechanism for WSNs to prolong the individual node lifetime and the overall network lifetime. The energy conservation is achieved by reducing the average transmission power. The analytical model is built for the MLPA mechanism enabled with k distinct power levels (k-LPA). Under a free space loss (path loss exponent ?=2) model, the closed-form expression of optimal power setting is derived and the average transmission power can be minimized as (k+1)/2k of original fixed power. For wireless environment other than the free space loss model (??2), a recursive formula expression set is established to acquire the optimal power configuration and the minimum average transmission power, which is 2P/(?+2) as k approaches infinity. Furthermore, to reduce the computing complexity and the effort of measuring path loss exponent, two approximated power configuration methods are proposed. The analytical results show that both the proposed approximate methods are near-optimal solutions for most of the wireless communication environments. It can be shown that lim? k?? P avg ~I (k,?)=lim? k?? P avg ~II (k,?)=lim? k?? P avg min? (k,?)=2P/(?+2).
TL;DR: A cross-layer approach is followed by defining a synchronous engine built across the radio and MAC and network layers, based on the results of previous research efforts dealing with various experimental platforms and experimental trials.
Abstract: The development and deployment of robust and highly populated Wireless Sensor Networks require addressing a wide variety of challenges. Among them, the synchronization and energy management of the nodes composing the network have been identified as two of the main challenges to be addressed. In this paper, we follow a cross-layer approach by defining a synchronous engine built across the radio and MAC and network layers. The design of our proposal has been based on the results of our previous research efforts dealing with various experimental platforms and experimental trials.
TL;DR: This paper develops the hysteresis mechanism provided by OLSR, based on hello packets, to include signal strength measurements and proposes to use signal strength to determine if the link-quality is improving or deteriorating.
Abstract: Mobility causes frequent link failures in ad-hoc networks. This results in a severe degradation of performance specially in case of high mobility of nodes. This is because the routing protocols for ad-hoc networks are not equipped to handle high mobility. In this paper, we have presented a new link management algorithm to locally manage links. This new mechanism is based on signal strength measurements. Researchers over the years have presented approaches which use signal strength measurements but their focus has been on re-active protocols while our algorithm is aimed at pro-active protocols. Pro-active protocols are used since they provide greater flexibility to take advantage of the mesh configuration. We develop the hysteresis mechanism provided by OLSR, based on hello packets, to include signal strength measurements. The mechanism in OLSR uses Hello packets received/lost to decide to establish link or not. The problem with this approach arises when there is high mobility in which case the time to break the link and use a new path becomes significant. To overcome this, we propose to use signal strength to determine if the link-quality is improving or deteriorating. This combination of the two mechanisms, makes the link management more robust and also helps in anticipating link breakages thereby greatly improving performance.
TL;DR: This paper addresses a cross-layer issue of long-term average utility maximization in energy-efficient cognitive radio networks supporting packetized data traffic under the constraint of collision rate with licensed users.
Abstract: In this paper, we address a cross-layer issue of long-term average utility maximization in energy-efficient cognitive radio networks supporting packetized data traffic under the constraint of collision rate with licensed users. Utility is determined by the number of packets transmitted successfully per consumed power and buffer occupancy. We formulate the problem by dynamic programming method namely constrained Markov decision process (CMDP). Reinforcement learning (RL) approach is employed to finding a near-optimal policy under undiscovered environment. The policy learned by RL can guide transmitter to access available channels and select proper transmission rate at the beginning of each frame for its long-term optimal goals. Some implement problems of the RL approach are discussed. Firstly, state space compaction is utilized to cope with so-called curse of dimensionality due to large state space of formulated CMDP. Secondly, action set reduction is presented to reduce the number of actions for some system states. Finally, the CMDP is converted to a corresponding unconstrained Markov decision process (UMDP) by Lagrangian multiplier approach and a golden section search method is proposed to find the proper multiplier. In order to evaluate the performance of the policy learned by RL, we present two naive policies and compare them by simulations.
TL;DR: A comprehensive discrete-event simulator for a G/M/1 queueing system is developed in order to understand and evaluate the QoS behaviour of self-similar traffic and performance evaluations of multiple classes of input traffic in terms of expected queue length, packet delay and packet loss rate are carried out.
Abstract: Traffic patterns generated by multimedia services are different from traditional Poisson traffic. It has been shown in numerous studies that multimedia network traffic exhibits self-similarity and burstiness over a large range of time-scales. The area of wireless IP traffic modeling for the purpose of providing assured QoS to the end-user is still immature and the majority of existing work is based on characterization of wireless IP traffic without any coupling of the behaviour of queueing systems under such traffic conditions. Work in this area has either been limited to simplified models of FIFO queueing systems which do not accurately reflect likely queueing system implementations or the results have been limited to simplified numerical analysis studies. In this paper, we advance the knowledge of queueing systems by example of traffic engineering of different UMTS service classes. Specifically, we examine QoS mapping using three common queueing disciplines; Priority Queuing (PQ), Low Latency Queuing (LLQ) and Custom Queueing (CQ), which are likely to be used in future all-IP based packet transport networks. The present study is based on a long-range dependent traffic model, which is second order self-similar. We consider three different classes of self-similar traffic fed into a G/M/1 queueing system and construct analytical models on the basis of non-preemptive priority, low-latency queueing and custom queueing respectively. In each case, expressions are derived for the expected waiting times and packet loss rates of different traffic classes. We have developed a comprehensive discrete-event simulator for a G/M/1 queueing system in order to understand and evaluate the QoS behaviour of self-similar traffic and carried out performance evaluations of multiple classes of input traffic in terms of expected queue length, packet delay and packet loss rate. Furthermore, we have developed a traffic generator based on the self-similar traffic model and fed the generated traffic through a CISCO router-based test bed. The results obtained from the three different queueing schemes (PQ, CQ and LLQ) are then compared with the simulation results in order to validate our analytical models.
TL;DR: New insights into the performance analysis of queuing systems with correlated arrivals and service interruption are presented and closed-form expressions for various performance measures, such as mean and variance of system contents and customer delay can be derived.
Abstract: In this paper, we consider a practical queuing system with a finite number of input links and whose arrival process is correlated and consists of a train of a fixed number of fixed-length packets and a single server which is subjected to random interruptions. We model the server interruptions by a correlated Markovian on/off process with geometrically distributed on and off periods. We first derive an expression for the functional equation describing the transient evolution of this queuing system. This functional equation is then manipulated and transformed into a mathematical tractable form. This allows us to derive the probability generating function (pgf) of the system occupancy. From this pgf, closed-form expressions for various performance measures, such as mean and variance of system contents and customer delay can be derived. Finally, we illustrate our solution technique with some numerical examples, whereby we demonstrate the negative effect of correlation in the interruption process on the performance of the system. The paper presents new insights into the performance analysis of queuing systems with correlated arrivals and service interruption and it also covers some previously published results as a special case.