Search

We address the problem of serving plug-in hybrid electric vehicles (PHEVs) in a charging station using a local storage energy unit, with finite capacity. Our goal is to find a control policy minimizing the operational cost of the charging station. We assume that the price of the electrical power unit is determined by a Real Time Pricing scheme, in which, the price of the electrical power is continuously updated with respect to the state of the grid at each time instance. We first model the charging station as a continuous time Markov Decision Process with three control actions: the probability of blocking new arrivals, the rate of charging the battery and the proportion of cars being served by the battery. By using dynamic programming, we prove the existence of the optimal policy minimizing a discounted cost over an infinite time horizon. We also show that it is stationary and bang-bang, i.e. the admissible action set in the optimal policy assumes only the extreme values in the action set.

We consider a problem of scheduling electric power demands in a smart-grid framework. Our model consists of n energy requirements {Ai, li, ri}ni=1, needed to be scheduled in time interval [0,1]. Here Ai is the amount of energy, while li and n are respectively, the left and right constraints on the length of the time period, during which Ai has to be supplied without interruption. The triples are assumed to be i.i.d. random vectors, with A distributed according to some general distribution G, and pair (l, r) distributed uniformly in the region {0 ≤ li ≤ r ≤ 1}. Our goal is to find a scheduling policy minimizing the power peak - maximal power over [0,1] - and/or the operational convex cost of the system while satisfying all the demands. The problem becomes very complicated as the number n of demands increases. To address this issue, we consider an asymptotic approach, in which the average amount of energy in each demand is inversely proportional to n, thus keeping the total scheduled amount stable. In this paper we first introduce lower bounds for both types of costs and then introduce a scheduling algorithm, asymptotically optimal in the sense that its cost converges to a corresponding lower bound almost surely, as n increases to infinity. Moreover, the algorithm is on-line (each demand is scheduled at the time its parameters become known) and has fully linear running time.

Mobile IP is used to manage the mobility of the Internet mobile users, and to keep their connectivity while they move from place to place. The security of mobile IP considering can be divided into two aspects, first in registration process, second, when connected parties exchange data with each other. In this article, after a brief study on the existing approaches used for securing mobile IP connections and after pointing to their problems, a new method will be introduced. This method is based on using IPsec security mechanism in conjunction with MOBIKE protocol. It will be pointed out that by using this proposed approach, the security of mobile IP connections will be achieved with respect to both two mentioned aspects. And also it is shown that most of the problems of existing approaches are eliminated in this method.

IPsec security mechanism standard offers Internet key exchange protocol (IKEv2) for establishing and managing its secure sessions. In IKEv2 both two participants perform the same amount of calculations in all cases and this would cause some deficiencies, when it is used in different situations with different properties. For example in most of client-server connections it is more preferable for servers to do fewer operations in comparison with clients. In the other side in some connections, initiators are entities with less power of computing when comparing with responders. Mobile users are examples of such entities. In these connections, the initiators are the entities who need to perform fewer operations. To solve this problem, we propose two protocols with asymmetric schemes for distribution the calculations. In proposed protocols, one of the participants performs fewer computations, depending on the properties of connections. To achieve this asymmetric scheme, Schnorr signature scheme is used by the entity needs to perform fewer computations.

New version of Internet key exchange protocol (IKEv2) is introduced in this article. Despite of its several advantages, it suffers from some deficiencies when applying in client-server environments. The main problem is regarded to its inefficient method for resisting against DoS attacks. A new protocol is proposed in this article, in which besides keeping maximum fidelity to IKEv2 framework, new necessary features are added. More resistance against DoS attacks without forcing extra delays, and identity protection of initiators (clients) against active attackers are the advantage of using this protocol. Also asymmetric distribution of calculations scheme, introduced in this protocol, makes it unique, while comparing with other protocols.