Asymptotically-Optimal Incentive-Based En-Route Caching Scheme

Content caching at intermediate nodes is a very effective way to optimize the operations of Computer networks, so that future requests can be served without going back to the origin of the content. Several caching techniques have been proposed since the emergence of the concept, including techniques that require major changes to the Internet architecture such as Content Centric Networking. Few of these techniques consider providing caching incentives for the nodes or quality of service guarantees for content owners. In this work, we present a low complexity, distributed, and online algorithm for making caching decisions based on content popularity, while taking into account the aforementioned issues. Our algorithm performs en-route caching. Therefore, it can be integrated with the current TCP/IP model. In order to measure the performance of any online caching algorithm, we define the competitive ratio as the ratio of the performance of the online algorithm in terms of traffic savings to the performance of the optimal offline algorithm that has a complete knowledge of the future. We show that under our settings, no online algorithm can achieve a better competitive ratio than $\Omega(\log n)$, where $n$ is the number of nodes in the network. Furthermore, we show that under realistic scenarios, our algorithm has an asymptotically optimal competitive ratio in terms of the number of nodes in the network. We also study an extension to the basic algorithm and show its effectiveness through extensive simulations

On The Continuous Coverage Problem for a Swarm of UAVs

Unmanned aerial vehicles (UAVs) can be used to provide wireless network and remote surveillance coverage for disaster-affected areas. During such a situation, the UAVs need to return periodically to a charging station for recharging, due to their limited battery capacity. We study the problem of minimizing the number of UAVs required for a continuous coverage of a given area, given the recharging requirement. We prove that this problem is NP-complete. Due to its intractability, we study partitioning the coverage graph into cycles that start at the charging station. We first characterize the minimum number of UAVs to cover such a cycle based on the charging time, the traveling time, and the number of subareas to be covered by the cycle. Based on this analysis, we then develop an efficient algorithm, the cycles with limited energy algorithm. The straightforward method to continuously cover a given area is to split it into N subareas and cover it by N cycles using N additional UAVs. Our simulation results examine the importance of critical system parameters: the energy capacity of the UAVs, the number of subareas in the covered area, and the UAV charging and traveling times.We demonstrate that the cycles with limited energy algorithm requires 69%-94% fewer additional UAVs relative to the straightforward method, as the energy capacity of the UAVs is increased, and 67%-71% fewer additional UAVs, as the number of subareas is increased.Comment: 6 pages, 6 figure

Efficient 3D Placement of a UAV Using Particle Swarm Optimization

Unmanned aerial vehicles (UAVs) can be used as aerial wireless base stations when cellular networks go down. Prior studies on UAV-based wireless coverage typically consider an Air-to-Ground path loss model, which assumes that the users are outdoor and they are located on a 2D plane. In this paper, we propose using a single UAV to provide wireless coverage for indoor users inside a high-rise building under disaster situations (such as earthquakes or floods), when cellular networks are down. We assume that the locations of indoor users are uniformly distributed in each floor and we propose a particle swarm optimization algorithm to find an efficient 3D placement of a UAV that minimizes the total transmit power required to cover the indoor users.Comment: 6 pages, 7 figure

Performance measurement systems : an examination of the influence of the contextual factors and their impact on performance with a specific emphasis on the balanced scorecard approach

In an attempt to understand the performance measurement systems, this study utilises the contingency theory theoretical framework to examine the contingent relationships between several contextual factors and the usage of financial and non-financial performance measures for performance measurements and evaluation purposes. The contextual factors consist of business strategy, organisational structure, perceived environmental uncertainty, intensity of competition, organisation size, total quality management and just in time manufacturing approaches. This study also investigates the implications of fit (internal consistency) between the above contextual factors and the extent of performance measurement diversity usage on organisational effectiveness (i.e. organisational performance and level of satisfaction). Nine performance measurement categories are investigated including: financial, customer, operational, innovation, employee, supplier, environment, quality and community categories. During the 1990s and until recently, considerable publicity and interest has been given to the balanced scorecard approach (BSC). This study also gathers empirical data to investigate various issues relating to BSC approach. The major aims of the study are to examine how the manufacturing companies are dealing with this approach and to determine the extent to which the above contextual factors influence the extent of balanced scorecard usage. The findings are based on a questionnaire mailed to a target sample of 900 UK manufacturing companies with an annual sales turnover in excess of £50 million. A total of 163 usable responses were received representing a response rate of 19.7%. For the purpose of data analysis, the study utilises descriptive statistics and multivariate statistics (i.e. structural equation modelling using EQS 5.7 and multiple regression). The results of the descriptive analysis show that financial, customer, operational and quality performance categories are extensively used for performance measurements and evaluation purposes. Other non-financial performance categories (i.e. innovation, supplier, employee, and environment) are also used but to a lesser extent. Despite the popularity of the balanced scorecard (BSC) approach, only a minority of companies (30%) reported using it in their performance measurement systems. The findings also emphasise the inconsistency between companies following the BSC approach, particularly the number and types of perspectives used. The results of structural equation modelling suggest a strong support for the cost strategy, formalisation, regulatory aspects of perceived environmental uncertainty, size, aspects relating to the intensity of competition and the extent of the use of both total quality management and just in time manufacturing approaches have a significant influence on the extent of performance measurement diversity usage (i.e. financial and non-financial performance measures). The results also indicate that the different approaches to fit utilised in this study (i.e. bivariate and systems approaches), based on structural equation modelling, result in insightful findings relating to the contingent relationships between the anticipated contextual factors, the extent of performance measurement diversity usage and organisational effectiveness. The results using multiple regression indicate that formalisation, raw material aspects of perceived environmental uncertainty, size and the extent of the use of total quality management significantly influence the extent of balanced scorecard usage. A distinguishing feature of this study is that it extends previous BSC studies in determining the extent of balanced scorecard usage. The results suggest that using financial and non-financial performance measures does not necessarily imply that the companies are really balanced scorecard users. This finding therefore raises implications for future balanced scorecard researchers, and by drawing off contingency theory literature, it overcomes some of the deficiencies of previous research relating to balanced scorecard approach. Finally, this study contributes to the literature by utilising the structural equation modelling method, which has several advantages over other multivariate data analysis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo