Vehicular communications promise to bring us safer driving and better traffic control. Dedicated Short Range Communications (DSRC) and IEEE 802.11p are now well established standards for the inter-vehicle and vehicle-to-road side unit (RSU) communication. These channels, however, are of limited capacity and are not sufficient to support the broad range of services envisioned in VANETs. Thus, vehicles will utilize WiFi (802.11 a/b/g) and unlicensed ISM band to acquire more capacity. Unfortunately, the WiFi channels in urban area are already heavily subscribed by residential customers. In this paper, we propose CoVanet, a cognitive vehicular ad hoc network architecture that allows vehicles opportunistic access to WiFi channels. CoVanet is the first approach to use cognitive radios in a VANET. It differs from conventional cognitive radio strategies in that it uses unlicensed band and operates in an ad hoc, multihop mode. In CoVanet, network topology and channel environment change frequently due to high node mobility. The main contribution of this work is a Cognitive Ad hoc Vehicular Routing Protocol (CoRoute) that utilizes geographical location and sensed channel information. Simulation results demonstrate CoRoute efficiency and robustness to mobility and external interference.

Cognitive radio network research has mostly focused on licensed spectrum sensing and empty spectrum use while protecting licensed band primary users. However, the wide deployment of WiFi access points in unlicensed bands in urban areas brings difficult challenges regarding co-existence of ad hoc mobile users with residential access points. In this paper, we propose a new mobile user protocol for dynamic channel selection via channel workload estimation. The mobile node senses channel usage in unlicensed ISM band and selects the maximum residual capacity channel for own packet transmission. The new protocol is implemented on Microsoft's SORA software defined radio system that enables fast prototyping. We have evaluated the performance using a Campus deployed SORA testbed. Experimental results show the efficiency of our approach in avoiding external interference.

Abstract An inelastic flow is a flow with an inelastic rate, i.e., the rate is fixed, and it cannot be dynamically adjusted to traffic and load condition as in elastic flows like TCP. Real time, interactive sessions, and video/audio streaming are typical examples of inelastic flows. Reliable support of inelastic flows in wirelessad hocnetworks is extremely challenging because flows and routes dynamically change and flows compete for the shared wireless channel. Bandwidth must be reserved for inelastic flows at session set up time. To avoid repeated attempts to set up reservations in a ‘volatile’ network and prevent serious network capacity degradation due to call set up overhead, a Call Admission Control strategy robust to mobility must be developed. In this paper we propose ProbeCast, a probe based call admission control scheme with QoS guarantees for inelastic flows. ProbCast was designed for multicast streams but can also work, by default, for unicast. In ProbeCast, a path (or a tree) is probed for capacity availability. If an intermediate link along the probed path fails to meet the QoS requirement, the flow is ‘pushed back’ via backpressure upstream to an intermediate branch or possibly to the source. The backpressure principle is simple; however, its implementation requires some care to avoid unfairness and eventual capture by one of the flows sharing a congested bottleneck. We show that proportional fairness among inelastic contenders will prevent capture. To achieve this, we have developed the Neighborhood Proportional Drop (N‐PROD) scheme. N‐PROD guarantees fair rejection of unfeasible flows and maintains the same proportional drop rate among surviving flows in the same contention domain. We demonstrate the efficacy and robustness of ProbeCast for unicast as well as multicast scenarios using the Qualnet simulation platform. Copyright © 2010 John Wiley & Sons, Ltd.

ABSTRACT Vehicular communications promise to bring us safer driving and better traffic control. Dedicated short range communications and IEEE 802.11p are now well established standards for vehicular communications. Channels for those systems, however, are of limited capacity and are dedicated to safety applications. Thus, they are not sufficient to support the broad range of services envisioned in VANETs. It is anticipated that vehicles will utilize Wi‐Fi (802.11 a/b/g) to acquire more capacity. Unfortunately, the Wi‐Fi channels in urban areas are already quite heavily subscribed by residential customers. To evade the residential load, in this paper, we propose CoVanet, a cognitive vehicular ad hoc network architecture that allows vehicle radios to access the Wi‐Fi channels ‘opportunistically’, finding least loaded channels. In CoVanet, network topology and channel environment change frequently because of high node mobility. The main contribution of this work is a cognitive ad hoc vehicular routing protocol (CoRoute). CoRoute is a hybrid that utilizes both geographical location and sensed channel information to establish stable, minimum delay routes to the destination. Simulation results show that CoRoute is robust to mobility and to external interference and improves packet delivery ratio on average by 70% with respect to routing without cognitive radios. Copyright © 2011 John Wiley & Sons, Ltd.

Providing vehicles' position is essential in VANETs. Currently, GPS positioning is widely used, but the accuracy is not adequate for emerging safety applications. In order to provide accurate positioning, this paper proposes RF-GPS, a RFID-assisted localization system that reliably supports lane-level position accuracy. It improves accuracy of the GPS system by employing a DGPS-like concept. It also allows vehicles without GPS to compute their position by contacting GPS equipped neighbors. We evaluate the performance of the proposed localization system via simulation.

Mobile wireless networks with intermittent connectivity, often called Delay/Disruption Tolerant Networks (DTNs), have recently received a lot of attention because of their applicability in various applications, including multicasting. To overcome intermittent connectivity, DTN routing protocols utilize mobility-assist routing by letting the nodes carry and forward the data. In this paper, we study the scalability of DTN multicast routing. As Gupta and Kumar showed that unicast routing is not scalable, recent reports on multicast routing also showed that the use of a multicast tree results in a poor scaling behavior. However, Grossglauser and Tse showed that in delay tolerant applications, the unicast routing overhead can be relaxed using the two-hop relay routing where a source forwards packets to relay nodes and the relay nodes in turn deliver packets to the destination via “mobility,” thus achieving a perfect scaling behavior of Θ(1). Inspired by this result, we seek to improve the throughput bound of wireless multicast in a delay tolerant setting using mobility-assist routing. To this end, we propose RelayCast, a routing scheme that extends the two-hop relay algorithm in the multicast scenario. Given that there are nssources each of which is associated with ndrandom destinations, our results show that RelayCast can achieve the throughput upper bound of Θ(min(1, n/nsnd)). We also analyze the impact of various network parameters and routing strategies (such as buffer size, multi-user diversity among multicast receivers, and delay constraints) on the throughput and delay scaling properties of RelayCast. Finally, we validate our analytical results with a simulation study.