Abstract: Lithium ion batteries are currently used for many applications including satellites, electric vehicles and mobile electronics. Their ability to store relatively large amount of energy in a limited space make them most appropriate for critical applications. Evaluation of the life of these batteries and their reliability becomes crucial to the systems they support. Reliability of Li-Ion batteries has been mainly considered based on its lifetime. However, another important factor that can be considered critical in many applications such as in electric vehicles is the cycle duration. The present work presents the results of an experimental investigation on the degradation behavior of a Laptop Li-ion battery (type TKV2V) and the effect of applied load on the battery cycle time. The reliability was evaluated using an accelerated life test. Least squares linear regression with median rank estimation was used to estimate the Weibull distribution parameters needed for the reliability functions estimation. The probability density function, failure rate and reliability function under each of the applied loads were evaluated and compared. An inverse power model is introduced that can predict cycle time at any stress level given.
Abstract: Vehicular Ad-hoc Network (VANET) is an emerging and very promising technology that has great demand on the access capability of the existing wireless technology. VANETs help improve traffic safety and efficiency. Each vehicle can exchange their information to inform the other vehicles about the current status of the traffic flow or a dangerous situation such as an accident. To achieve these, a reliable and efficient Medium Access Control (MAC) protocol with minimal transmission collisions is required. High speed nodes, absence of infrastructure, variations in topology and their QoS requirements makes it difficult for designing a MAC protocol in vehicular networks. There are several MAC protocols proposed for VANETs to ensure that all the vehicles could send safety messages without collisions by reducing the end-to-end delay and packet loss ratio. This paper gives an overview of the several proposed MAC protocols for VANETs along with their benefits and limitations and presents an overall classification based on their characteristics.
Abstract: Connected vehicles are equipped with wireless sensors
that aid in Vehicle to Vehicle (V2V) and Vehicle to Infrastructure
(V2I) communication. These vehicles will in the near future
provide road safety, improve transport efficiency, and reduce traffic
congestion. One of the challenges for connected vehicles is how
to ensure that information sent across the network is secure. If
security of the network is not guaranteed, several attacks can occur,
thereby compromising the robustness, reliability, and efficiency of
the network. This paper discusses existing security mechanisms and
unique properties of connected vehicles. The methodology employed
in this work is exploratory. The paper reviews existing security
solutions for connected vehicles. More concretely, it discusses
various cryptographic mechanisms available, and suggests areas
of improvement. The study proposes a combination of symmetric
key encryption and public key cryptography to improve security.
The study further proposes message aggregation as a technique to
overcome message redundancy. This paper offers a comprehensive
overview of connected vehicles technology, its applications, its
security mechanisms, open challenges, and potential areas of future
research.
Abstract: In this communication, a low-cost circularly
polarized wire antenna exhibiting improved gain performance for
Dedicated Short Range Communications (DSRC), vehicle-to-vehicle
(V2V) and vehicle-to-infrastructure (V2I) communications is
presented. The proposed antenna comprises a Y-shaped quarterwavelength
monopole antenna surrounded by two iterations of eight
conductive arched walls acting as parasitic elements to enhance the
overall antenna gain and to shape the radiation pattern in the H-plane.
A hemispherical radome shell is added to protect the antenna
structure and its effect on the antenna performance is discussed. The
designed antenna demonstrates antenna gain of 8.2 dB with
omnidirectional far-field radiation pattern in the H-plane. The gain of
the proposed antenna is also compared with the characteristic of the
stand-alone Y-shaped monopole to highlight the advantages of the
proposed approach.
Abstract: A perfect secret-sharing scheme is a method to distribute a secret among a set of participants in such a way that only qualified subsets of participants can recover the secret and the joint share of participants in any unqualified subset is statistically independent of the secret. The collection of all qualified subsets is called the access structure of the perfect secret-sharing scheme. In a graph-based access structure, each vertex of a graph G represents a participant and each edge of G represents a minimal qualified subset. The average information ratio of a perfect secret-sharing scheme realizing the access structure based on G is defined as AR = (Pv2V (G) H(v))/(|V (G)|H(s)), where s is the secret and v is the share of v, both are random variables from and H is the Shannon entropy. The infimum of the average information ratio of all possible perfect secret-sharing schemes realizing a given access structure is called the optimal average information ratio of that access structure. Most known results about the optimal average information ratio give upper bounds or lower bounds on it. In this present structures based on bipartite graphs and determine the exact values of the optimal average information ratio of some infinite classes of them.