Vehicular Ad-hoc networks（VANETs） are kinds of mobile Ad-hoc networks（MANETs）, which consist of mobile vehicles with on-board units（OBUs） and roadside units（RSUs）. With the rapid development of computation and communication technologies, peripheral or incremental changes in VANETs evolve into a revolution in process. Cloud computing as a solution has been deployed to satisfy vehicles in VANETs which are expected to require resources（such as computing, storage and networking）. Recently, with special requirements of mobility, location awareness, and low latency, there has been growing interest in research into the role of fog computing in VANETs. The merging of fog computing with VANETs opens an area of possibilities for applications and services on the edge of the cloud computing. Fog computing deploys highly virtualized computing and communication facilities at the proximity of mobile vehicles in VANET. Mobile vehicles in VANET can also demand services of low-latency and short-distance local connections via fog computing. This paper presents the current state of the research and future perspectives of fog computing in VANETs. Moreover, we discuss the characteristics of fog computing and services based on fog computing platform provided for VANETs. In this paper, some opportunities for challenges and issues are mentioned, related techniques that need to be considered have been discussed in the context of fog computing in VANETs. Finally, we discuss about research directions of potential future work for fog computing in VANETs. Within this article, readers can have a more thorough understanding of fog computing for VANETs and the trends in this domain.
This paper proposes a relay selection scheme based on geometric optimum principle to maximize the cognitive link＇ s connectivity with limited interference to primary user in cooperative cognitive systems. A dual-hop cognitive relay system is considered, in which the channel impulse response follows independent non-identical distribution （i. n. d. ） each hop, such as Rician, Rayleigh and Nakagami-m distribution. Then, closed-form expressions in terms of outage probability and average bit error rate （ABER） are obtained using amplify-and-forward （AF） relaying protocol over such mixed fading channels. Furthermore, the best range of the relay is derived. Extensive simulation re- suits are conducted to verify the theoretical analysis, which is useful to the network optimal design.
As for safety applications of vehicular Ad-hoc network （VANET）, many valuable broadcast protocols have been proposed nowadays, most of which are based on either senders or receivers. In fact, sender-based protocols would fall into invalidation due to high mobility of network, while receiver-based ones would generate extra delay. Combining both the advantages of the two schemes, this paper proposes an efficient and reliable broadcast protocol based on quality of forwarding （ERBPQF） of candidate nodes. In ERBPQF, a double-phase relay scheme is presented to reach fast message dissemination in the first phase and to ensure high packet delivery ratio （PDR） in the second phase. Then, considering signal fading, channel contention, queuing delay, broadcast interference and high mobility of vehicles, a new metric called quality of forwarding （QoF） for relay selection is further proposed. The simulation results show that the delay and dissemination efficiency （DE） of ERBPQF outperforms slotted-1 protocol, accompanying with the achievement of more than 95% PDR.
