Search

Wireless local area networks (WLAN) has been in the spotlight as a potential solution to solve the exponentially growing demand of wireless services due to its wide availability and there have been a plenty of research works on WLAN including mathematical modeling and analysis. However, the spatial modeling and analysis of WLAN have received little attention due to the complexity in the dynamics of WLAN. In this paper, we provide spatial modeling and analysis based on stochastic geometry theory to investigate the impact of the spatial distribution on the performance of WLAN. Specifically, this paper is concerned with the correlation between consecutive packet transmissions. Throughout our analysis and simulation study we provide the conditions where the independence assumption on individual transmission results holds, which is widely assumed in most of the previous works on WLAN. [ABSTRACT FROM AUTHOR]

In this paper, we propose a probabilistic preemption scheme in cognitive radio networks that will simultaneously ensure the primary user (PU) packets' Quality of Service (QoS) and the secondary user (SU) packets' transmission continuity. This scheme differs from a complete preemption scheme or a complete non-preemption scheme in conventional cognitive radio networks in that a PU packet can interrupt an SU packet's transmission and preempt the channel with a certain probability that is termed the preemptive probability. In order to decrease the possible negative influence of SU packets on PU packets' QoS, we introduce an access threshold, i.e. a limit on the size of the SU packet buffer, which controls the access of the SU packets. As part of the mathematical analysis of the probabilistic preemption scheme, we establish a discrete-time priority queueing model and then characterize it by a two-dimensional Markov chain. Based on the steady-state solution of the system we give formulas for several performance measures of the network users. We also provide numerical results to highlight the influence of the preemptive probability and the access threshold on the system performance. Moreover, we also compare the system performance of the proposed probabilistic preemption scheme with the preemptive and non-preemptive schemes by using numerical results. Finally, we build an optimization framework by the help of properly chosen net benefit function to optimize the preemptive probability and the access threshold jointly. [ABSTRACT FROM AUTHOR]

This paper studies the impact of service outsourcing under three supply chain power structures: manufacturer-Stackelberg, vertical-Nash and retailer-Stackelberg supply chains. We first investigate price and service decisions by comparing the integrated channel and the decentralized channel with service outsourcing. It is found that a lower retail price or a higher service level could occur in the decentralized channel with service outsourcing compared to those in the integrated channel, but they never occur simultaneously. Next, we examine the manufacturer's channel strategies, and demonstrate that service outsourcing can always help the manufacturer earn more profit from the decentralized channel than from the integrated channel in the manufacturer-Stackelberg and retailer-Stackelberg markets, as long as the retailer's service investment is sufficiently efficient. However, in the vertical-Nash supply chain, this occurs only when the manufacturer is inefficient and the retailer is efficient enough in service provision. Finally, comparisons of channel efficiency and numerical analysis are provided. [ABSTRACT FROM AUTHOR]

Circular economy is a theoretical concept that is widely discussed in recent literature as a way to achieve increased sustainability. However, published literature focuses on how to increase circularity without analysing the status quo of circularity, which necessitates answering the question of how to measure the effectiveness of any actions implemented to advance Circular economy. Currently, there is no agreed methodology in literature on measuring the existing circularity. Therefore, this article proposes an analytical way to measure and map a regional waste economy's circularity. The framework can be applied at a granularity of an individual materials level as well as overall at a regional level, and can quantify with a potential to improve towards a more circular economy in value as well as in volume. Data mining, conditioning, and, mathematical analysis was conducted across a number of public and private databases such as ORBIS and The Environment Agency. The proposed framework was tested taking a case of a region in the North East of England with 35,116 active companies. The methodology was validated on a different data set from another region. The results show that the methodology is able to measure a regional circularity overall as well as at an individual material level. The outcome of this research would be useful for policy makers as well as manufacturing organisations, and waste management companies as benchmarking allows a comparison between effectiveness of regional environmental regulations with their influence on driving sustainability and circular economy. [ABSTRACT FROM AUTHOR]

Consider a system which is subject to occasional failures over its lifetime. Under general stochastic assumptions concerning the occurrence of these failures, the duration of the repair times, and the length of the system's lifetime, the distribution of the total uptime the system accumulates over its lifetime may be determined. While the distribution is unfortunately complicated except in certain circumstances, it is possible to derive useful bounds based on the aging characteristics of the distributions of interfailure times, repair times, and system life. Bounds are developed for the cases where the system lifetime follows (1) a degenerate distribution (or constant mission duration), (2) an exponential distribution, and (3) a general distribution. These bounds may be interpreted as extensions of well-known bounds based on aging notions from renewal theory. Conditions are identified for when the bounds are sharp, and examples are used to show the computational tractability and usefulness of the results. [ABSTRACT FROM AUTHOR]