Neighbour coverage: a dynamic probabilistic route discovery for mobile ad hoc networks

Blind flooding is extensively use in ad hoc routing protocols for on-demand route discovery, where a mobile node blindly rebroadcasts received route request (RREQ) packets until a route to a particular destination is established. This can potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. Such a phenomenon induces what is known as broadcast storm problem, which has been shown to greatly increase the network communication overhead and end-to-end delay. In this paper, we show that the deleterious impact of such a problem can be reduced if measures are taken during the dissemination of RREQ packets. We propose a generic probabilistic method for route discovery, that is simple to implement and can significantly reduce the overhead associated with the dissemination of RREQs. Our analysis reveals that equipping AODV with probabilistic route discovery can result in significant reduction of routing control overhead while achieving good throughput

Performance evaluation of an efficient counter-based scheme for mobile ad hoc networks based on realistic mobility model

Flooding is the simplest and commonly used mechanism for broadcasting in mobile ad hoc networks (MANETs). Despite its simplicity, it can result in high redundant retransmission, contention and collision in the network, a phenomenon referred to as broadcast storm problem. Several probabilistic broadcast schemes have been proposed to mitigate this problem inherent with flooding. Recently, we have proposed a hybrid-based scheme as one of the probabilistic scheme, which combines the advantages of pure probabilistic and counter-based schemes to yield a significant performance improvement. Despite these considerable numbers of proposed broadcast schemes, majority of these schemes’ performance evaluation was based on random waypoint model. In this paper, we evaluate the performance of our broadcast scheme using a community based mobility model which is based on social network theory and compare it against widely used random waypoint mobility model. Simulation results have shown that using unrealistic movement pattern does not truly reflect on the actual performance of the scheme in terms of saved-rebroadcast, reachability and end to end delay

Cybercrime and Risks for Cyber Physical Systems

Cyber Physical Systems (CPS) is the integration of computation and physical systems that make a complete system such as the network, software, embedded systems, and physical components. Major industries such as industrial plants, transport, national grid, and communication systems depend heavily on CPS for financial and economic growth. However, these components may have inherent threats and vulnerabilities on them that may run the risk of being attacked, manipulated or exploited by cyber attackers and commit cybercrimes. Cybercriminals in their quest to bring down these systems may cause disruption of services either for fame, data theft, revenge, political motive, economic war, cyber terrorism, and cyberwar. Therefore, identifying the risks has become imperative in mitigating the cybercrimes. This paper seeks to identify cybercrimes and risks that are associated with a smart grid business application system to determine the motives and intents of the cybercriminal. The paper identified four goals to mitigate the risks: as business value, organizational requirements, threat agent and impact vectors. We used the Analytical Hierarchy Process (AHP) to determine the importance of the goals that contribute to identifying cybercrime and risks in CPS. For the results, a case study is used to identify the threat and vulnerable spots and the prioritized goals are then used to assess the risks using a semi-quantitative approach to determine the net threat level. The results indicate that using the AHP approach to identify cybercrime and risk on CPS provides specific risk mitigation goals

Measuring the economic benefits and costs of Bluetongue virus outbreak and control strategies in Scotland

This paper provides an ex-ante economic analysis, comparing six alternative control strategies for the eradication of Bluetongue virus 8 against five incursion scenarios in cattle and sheep populations. The economic analysis assumes a common baseline unavoidable cost of public and private measures that together contribute to prevention of incursion of BTV8 into Scotland. These costs continue over the five year horizon of this analysis regardless of whether a BTV8 epidemic ensues in Scotland and their total present value was found to be approximately £141m over the 5year period. The benefit of this investment is the costs of a BTV8 outbreak avoided; which depends on the time, location and nature of the incursion, on the control strategies adopted to counter each incursion, on the persistence of the incursion and on the opportunities to mitigate the damage. Specific variations in all these aspects were explored. The benefit-cost ratios were ranked within each incursion scenario to evaluate the efficiency of control outlays. Although the economic model found that benefit-cost ratios were greater than 1 for all interventions strategies examined, the control strategy option with 100% vaccination and protection zone set at Scottish Borders were economically preferable. This implies that if avoided this control option would deliver the greatest benefit from investment in baseline prevention costs. However, in terms of outbreak losses, this vaccination strategy was always most costly. On the other hand, the control strategy with 50% vaccination and all Scotland as a protection zone often provides the lowest benefits in all control options examinedbluetongue virus, epidemiology, direct and indirect costs, benefit analysis, Risk and Uncertainty,

Social networks, rice value chain participation and market performance of smallholder farmers in Ghana

This paper examines the impact of rice value chain participation and social networks on smallholder farmers' market performance outcomes (paddy price, quantity of paddy traded, and net returns), using data from a recent survey of 458 smallholder rice farmers in northern Ghana. We employed a treatment effects model to account for potential selection bias associated with observable and unobservable factors. The empirical results reveal that smallholder farmers' participation in a rice value chain is associated with increased paddy price, quantity traded, and net returns. We also find that value chain participation decisions and market performance are positively and significantly influenced by social networks. The empirical results also suggest that sex, farm size, mobile phone ownership, and access to credit significantly increase paddy prices, quantity traded, and net returns of smallholder rice farmers in the value chain

Onfarm evaluation of maize varieties in the transitional and savannah zones of Ghana: determinants of farmer preferences

Maize is one of the most important food crops in Ghana even though its production has not reached self sufficiency levels. Drought and striga infestation are among the most important production constraints of maize in Ghana. Promising high yielding, drought and striga tolerant maize varieties are being evaluated by CSIR and IITA in participatory on-farm trials and demonstrations. These varieties however need to meet farmers’ varietal preferences in order for them to adopt. This study therefore sought to assess farmers’ preference for the different drought tolerant maize varieties, and determine factors that influence their choices. Kendall’s coefficient of concordance was used to test the level of agreement between farmers on their preferences. The ordered logistic regression was used to estimate the determinants of farmer’s preference using cross-sectional observations from 120 maize farmers in the Transitional and Savannah zones of Ghana. Results indicate that maize varieties that are early maturing (2.38) and drought tolerant (2.45) were most preferred by farmers. Area under maize cultivation, fertilizer usage and family size are the factors that were found to influence farmers’ preference for improved maize varieties. These factors should therefore be considered in varietal promotion

Diversification and agrarian change under environmental constraints in rural China: Evidence from a poor township of Beijing municipality

Working paper du GATE 2007-11This article illustrates the impact of changes related to market reforms and environmental policies on the economic structure in rural China by providing a comparative analysis of several villages in a poor township in Beijing municipality. Two main concomitant phenomena are affecting agricultural and non-agricultural choices in the studied area. First, the introduction of market mechanisms is encouraging local population to engage in new activities that are closer to local comparative advantages. Second, rural households are facing new constraints in the form of environmental protection measures, which have weakened traditional insurance channels provided by forest resources and cattle stock. Drawing on household-level survey data and interviews with village heads conducted in ten villages of Labagoumen township in December 2003, this article analyzes households decisions in response to market reforms and environmental constraints. We find large disparities both between villages and households in the diversification process and discuss the reasons of observed inertia in the region, most households still heavily relying on corn production