Emerging of inter-vehicle communication gives vehicles opportunities to exchange information within limited radio ranges and self-organize in Ad Hoc manner into Vehicular Ad Hoc Networks (VANETs). However, due to strong mobility, limited market penetration rate, and lack of roadside units, connectivity is obviously a scarce resource in VANETs. Further, only depending on direct connectivity, i.e. one-hop connected links between vehicles, is far from the continuous growing communication demands in VANETs, such as inter-vehicle amusement, cooperative collision avoidance, inter-vehicle emergency notification etc. Therefore, the indirect connectivity from multi-hop forwarding and store-carry-forward strategy is also a necessary and powerful complement especially to the case where direct connections are hardly obtained. In this article, we define a new metric named available connectivity which involves both direct and indirect connectivity. By deep analyzing the statistical properties of direct and indirect connectivity in free flow state, the proposed available connectivity is obtained and quantified to increase the information dissemination opportunities for vehicles especially in a relatively slow topology changing scenario. Numerical results show that the available connectivity could provide better references for different VANETs applications and has potential relationships with many network parameters.

In Vehicular communication networks, a robust access mechanism is essential for the successful information exchange between vehicles and roadside unit, which keeps the vehicles being aware of surroundings thus improving driving safety and reduce traffic jam. In this paper, we first analyze the drawbacks of explicit GTS (Guaranteed Time Slots) allocation suggested by IEEE 802.15.4 draft and show the importance of a wise assignment scheme and efficient scheduler especially for high dynamic vehicular environment. Then, for a given number of vehicles requesting to access the roadside unit, we propose a Time-Sensitive Weighted Round Robin scheduler (TS-WRR) considering different service delay requirements, packets arrival rates and vehicles' mobility levels. We also show the elaborate implementation procedure of TS-WRR by pseudocode. Numerical results show that our TS-WRR scheduler outperforms FCFS and WRR on the performance of transactions delay requirements guarantee and GTS utilization ratio in Vehicular Sensor Networks.