Description:
Despite recent interests in developing vertical handoff decision algorithms, an essential component of the architecture of the next generation heterogeneous wireless networks, very few studies have so far reported any meaningful comparative performance analysis. This paper attempts to fill this gap in the literature by presenting a comprehensive study on the performance of three vertical handoff decision algorithms, namely, SAW (Simple Additive Weighting), TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), and MDP (Markov Decision Process). We have used both analytical and simulation tools (ns-2.29) to evaluate and compare expected total QoS offerings in the mean duration of a service under different state transition probability distributions, user perception models on the importance of QoS parameters, and network switching costs. To our surprise, we have observed TOPSIS achieving the best performance despite MDP's using the optimal policy. We suspect that the user satisfiability model used in MDP to estimate link rewards might have contradicted the underlying user perception model used to estimate normalised weight of each QoS parameter, which will be investigated in future.
Description:
In this paper, we propose a method for indexing and retrieval of images based on shapes of objects. The concept of connectivity is introduced. 3D models are used to represent 2D images. 2D images are decomposed a priori using connectivity which is followed by 3D model construction. 3D model descriptors are obtained for 3D models and used to represent the underlying 2D shapes. We have used spherical harmonics descriptors as the 3D model descriptors. Difference between two images is computed as the Euclidean distance between their descriptors. Experiments are performed to test the effectiveness of spherical harmonics for retrieval of 2D images. The proposed method is compared with methods based on principal components analysis (PCA) and generic Fourier descriptors (GFD). It is found that the proposed method is effective. Item S8 within the MPEG-7 still images content set is used for performing experiments.
Description:
In this paper, we discuss the problems associated with the present contention resolution mechanism of IEEE 802.11 DCF and present a new, dynamic and robust approach to improve it. Our new MAC, using OFDMA in the physical layer, can incorporate multiple concurrent transmissions or receptions in a dynamic manner and can adjust the collision probability based on the traffic load when nodes are endowed with a single half-duplex radio only. Simulation results show that our system improves throughput by up to 40 percent, reduces collision in control messages by up to 80 percent and reduces the average delay for data transmission by up to 20 percent.
Description:
Decentralized content sharing (DCS) is emerging as a suitable platform for smart mobile device users to generate and share contents seamlessly without the requirement of a centralized server. This feature is particularly important for places that lack Internet coverage such as tourist attractions where users can form an ad-hoc network and communicate opportunistically to share contents. Existing DCS approaches when applied for such type of places suffer from low delivery success rate and high latency. Although a handful of recent approaches have specifically targeted improvement of content delivery service in tourist spot like scenario, these and other DCS approaches do not focus on contents’ demand and supply which vary considerably due to visitor in-and-out flow and occurrence of influencing events. This is further compounded by the lack of any content distribution (replication) scheme. The content delivery service will be improved if contents can be proactively distributed in strategic positions based on dynamic demand and supply and medium access contention. In this paper, we propose a dynamic content distribution scheme (DCDS) considering these practical issues for sharing contents in tourist attractions. Simulation results show that the proposed approach significantly improves (7
Description:
Decentralized content sharing (DCS) is emerging as a suitable platform for smart mobile device users to generate and share contents seamlessly without the requirement of a centralized server. This feature is particularly important for places that lack Internet coverage such as tourist attractions where users can form an ad-hoc network and communicate opportunistically to share contents. Existing DCS approaches when applied for such type of places suffer from low delivery success rate and high latency. Although a handful of recent approaches have specifically targeted improvement of content delivery service in tourist spot like scenario, these and other DCS approaches do not focus on contents’ demand and supply which vary considerably due to visitor in-and-out flow and occurrence of influencing events. This is further compounded by the lack of any content distribution (replication) scheme. The content delivery service will be improved if contents can be proactively distributed in strategic positions based on dynamic demand and supply and medium access contention. In this paper, we propose a dynamic content distribution scheme (DCDS) considering these practical issues for sharing contents in tourist attractions. Simulation results show that the proposed approach significantly improves (7
Description:
Trade-off between energy-efficiency and reliability in wireless sensor networks is application dependent. Without the reliability, the extended lifetime of a network is of limited use. Due to the inherent correlation between reliability and congestion, it is necessary to reduce congestion to improve reliability. Existing congestion control algorithms in wireless sensor networks are reactive. They attempt to reduce the congestion only after its detection. In this paper, we present Location Aided Congestion Aware Routing (LACAR) protocol that proactively avoids congestion formation and improves data delivery success rate in data gathering wireless sensor networks. Location, energy and congestion information of neighbours together with the location information of the base station determine appropriate routes. Simulation results show that LACAR achieves high packet success rate in an energy-efficient way.
Description:
Obstacles present in the line of sight transmission path of a wireless signal severely attenuates the received signal power. Extreme fluctuations of the received signal power caused by shadowing can create "blind spots". Blind spots are areas within the cellular coverage area from where no communication is possible to the base station (BS). For single path packet based services link failures results in total loss of communication. The problem of link failure and blind spots can almost be eliminated in the recently proposed multipath cellular architecture (MCA) which provisions up to three different communication links from the mobile node (MN) to three adjacent BSs through overlapped coverage. Voice and/or multimedia packet delivery can thus benefit by establishing communication from the best interface in terms of received signal power. In this paper, we evaluate the performance of the multi-path MCA model in reducing link failure and blind spot communication problems in presence of multiple obstacles and shadow fading. Obstacle mobility model is utilized as the preferred user mobility model. Video transmission performance improves significantly in terms of reduced packet loss and improved reproduced signal quality at the receiver for the multipath MCA model compared to the existing single path cellular network architecture
Description:
Spectrum allocation scheme in cognitive radio networks (CRNs) becomes complex when multiple CR users concomitantly need to be allocated new and suitable bands once the primary user returns. Most existing schemes focus on the gain of individual users, ignoring the effect of an allocation on other users and rely on the 'periodic sensing and transmission' cycle which reduces spectrum utilization. This paper introduces a scheme that exploits collaboration among users to detect PU's return which relieves active CR users from the sensing task, and thereby improves spectrum utilization. It defines a Capacity of Service (CoS) metric based on the optimal sensing parameters which measures the suitability of a band for each contending user and takes into consideration the impact of allocating a particular band on other band seeking users. The proposed scheme significantly improves capacity of service, reduces interference loss and collision, and hence, enhances dynamic spectrum access capabilities. (C) 2015 Elsevier Ltd. All rights reserved.
Description:
In recent years, the drive for the Healthcare Monitoring Application (HMA) aims to provide continuous remote monitoring of a patient's health. For this to happen, the sensors in the monitoring component of the Body Area Wireless Sensor Networks (BAWSN) need to continuously send data to a Healthcare Application. We show that to provide continuous health data, the BAWSN depends on the collective data delivered by all the sensor nodes and not on a single sensor because medical diagnosis is rarely performed from a single data point. In addition, the arrival time of data should occur within the expected time to be indicative of the actual health of the patient. In this paper, we characterize the HMA as a time-critical application because the BAWSN has stringent timing requirements concerning the arrival of data from the sensor nodes within the defined critical time. Thereby, we formulate the critical time parameters to evaluate the BAWSN operations.
Description:
With the increasing popularity of digital products, there is a strong desire to protect the rights of owners against illegal redistribution. Traditional encryption schemes alone do not provide a comprehensive solution to digital rights management, since they do not prevent users who are authorized to use a digital product for their own use from transferring the cleartext content to unauthorized users. However, traceability schemes can be used to trace the illegitimate redistributors effectively. Two types of traceability schemes have been proposed in the literature - traceability codes (TA codes), and codes with the identifiable parent properties (IPP codes). TA codes are special IPP codes, and many TA codes implement an efficient identification algorithm which can determine at least one redistributor. However, many IPP codes are not TA codes, in which case, no efficient identification algorithms are available. In this paper, we generalize the definition of TA codes to derive a new family of traceability codes that is much larger than the family of traditional TA codes. By using existing decoding algorithms with respect to the Lee distance, an efficient identification algorithm is proposed for generalized TA codes. Furthermore, we show that the identification algorithm of generalized TA codes can find more redistributors than those of traditional TA codes.
Description:
With the increasing popularity of digital products, there is a strong desire to protect the rights of owners against illegal redistribution. Traditional encryption schemes alone do not provide a comprehensive solution to digital rights management, since they do not prevent users who are authorized to use a digital product for their own use from transferring the cleartext content to unauthorized users. However, traceability schemes can be used to trace the illegitimate redistributors effectively. Two types of traceability schemes have been proposed in the literature - traceability codes (TA codes), and codes with the identifiable parent properties (IPP codes). TA codes are special IPP codes, and many TA codes implement an efficient identification algorithm which can determine at least one redistributor. However, many IPP codes are not TA codes, in which case, no efficient identification algorithms are available. In this paper, we generalize the definition of TA codes to derive a new family of traceability codes that is much larger than the family of traditional TA codes. By using existing decoding algorithms with respect to the Lee distance, an efficient identification algorithm is proposed for generalized TA codes. Furthermore, we show that the identification algorithm of generalized TA codes can find more redistributors than those of traditional TA codes.
Description:
Mining interesting knowledge from the huge amount of data gathered from WSNs is a challenge. Works reported in literature use support metric-based sensor association rules which employ the occurrence frequency of patterns as criteria. However, consideration of the binary frequency of a pattern is not a sufficient indicator for finding meaningful patterns because it only reflects the number of epochs which contain that pattern in the dataset. The share measure of sensorsets could discover useful knowledge about trigger values associated with a sensor. Here, we propose a new type of behavioral pattern called share-frequent sensor patterns (SFSPs) by considering the non-binary frequency values of sensors in epochs. SFSPs can find a correlation among a set of sensors and hence can improve the performance of WSNs in a resource management process. In this paper, a share-frequent sensor pattern tree (ShrFSP-Tree) has been proposed to facilitate a pattern growth mining technique to discover SFSPs from WSN data. We also present a parallel and distributed method where the ShrFSP-Tree is enhanced into PShrFSP-Tree and its performance is investigated for both homogeneous and heterogeneous systems. Results show that our method is time and memory efficient in finding SFSPs than the existing most efficient algorithms.
Description:
Fixed spectrum licensing policies are unsuitable to meet RF spectrum demand by emerging technologies. Spectrum scarcity is hindering the enhancement of current services or deployment of new services operating in RF spectrum. On the contrary, many portions of the licensed spectrum remain unused or underused for significant period of time creating possibility of opportunistic spectrum access without license. Spectrum sensing is practiced in most of the existing opportunistic spectrum access methods. However, these methods consider identical fading or shadowing channels and ignore spatial variation of unlicensed users, hence fail to capture realistic scenario. We introduce an improved cooperative spectrum sensing technique which incorporates non-identical fading and shadowing, and weighs each non-licensee user's contribution appropriately considering the received power and positional displacements of the users. The proposed method demonstrates better detection accuracy and higher spectrum utilization with fewer cooperating users than other existing methods.