Historical Spectrum Sensing Data Mining for Cognitive Radio Enabled Vehicular Ad-hoc Networks

In vehicular ad-hoc network (VANET), the reliability of communication is associated with driving safety. However, research shows that the safety-message transmission in VANET may be congested under some urgent communication cases. More spectrum resource is an effective way to solve transmission congestion. Hence, we introduce cognitive radio enabled VANET (CR-VANET), where CR device can detect possible idle spectrum for VANET communications and assist to timely broadcast safety-message. Given high-speed mobility of vehicles and dynamically-changing availability of channels, a novel prediction algorithm is proposed to pick out the channel with the greatest probability of availability, which can meet the quality of service (QoS) requirement of urgent communications and effectively avoid conflict with licensed users.

Specifically, the spatiotemporal correlations among historical spectrum sensing data are exploited to form prior knowledge of channel availability probability, and Bayesian inference is used to derive posterior probability of channel availability. Comparing with other spectrum detection methods, the proposed algorithm has more than 8% detection performance improvement at false alarm probability 0.2, and thus can avoid access conflict with licensed users dramatically. Furthermore, the proposed algorithm always has larger packet reception probability (PRP) and lower transmission delay compared with conventional VANET broadcasting. Hence, the proposed algorithm can improve reliability of safety-message transmission and enhance driving safety significantly.

Securing vehicular ad-hoc networks connectivity with roadside units support

This paper evaluates three inter-vehicle spacing models based on exponential, Generalized Extreme Value, and Exponential with robustness factor statistical distributions [1], [2], [3]. Vehicles adjust transmission range as a function of its spatial density on a road segment to increase its network connectivity with other vehicles.

This connectivity can be secured by deploying this scheme [4] which secures communications among vehicles through trusted road-side units that distribute secret keys to vehicles under their coverage.

Message Authentication Using Proxy Vehicles in Vehicular Ad Hoc Networks

Normally, authentication in vehicular ad hoc networks (VANETs) uses public key infrastructure to verify the integrity of messages and the identity of message senders. The issues considered in the authentication schemes include the level of security and computational efficiency in the verification processes. Most existing schemes mainly focus on assuring the security and privacy of VANET information. However, these schemes may not work well in VANET scenarios. For instance, it is difficult for a roadside unit (RSU) to verify each vehicle’s signature sequentially when a large number of vehicles emerge in the coverage areas of an RSU. To reduce the computational overhead of RSUs, we propose a proxy-based authentication scheme (PBAS) using distributed computing.

In the PBAS, proxy vehicles are used to authenticate multiple messages with a verification function at the same time. In addition, the RSU is able to independently verify the outputs from the verification function of the proxy vehicles. We also design an expedite key negotiation scheme for transmitting sensitive messages. It is shown from the analysis and simulations that an RSU can verify 26 500 signatures per second simultaneously with the help of the proxy vehicles. The time needed to verify 3000 signatures in the PBAS can be reduced by 88% compared with existing batch-based authentication schemes.

Decentralized RSU-based real-time path planning for vehicular ad hoc networks

As the number of vehicles increases significantly, traffic congestion has become a major social problem in recent years. Such a situation can be alleviated effectively with the emerging of vehicular ad hocnetwork (VANET)-based real-time path planning systems. However, existing systems face the challenges of poor anti-congestion capability and high complexity. To address the related issues, an road side unit (RSU)-based architecture is proposed in this paper, in which a city is divided into different areas, each with an RSU.

Based on the architecture, a decentralized and hierarchical real-time path planning algorithm is proposed. The path planning problem is formulated from two layers, i.e., area path selection in upper layer and intra-area routing in bottom layer, both of which target to minimize the average travel time. Numerical results show that, our proposed algorithm inherits the anti-congestion capability and owns the advantage of low complexity, as compared with the shortest path algorithm and centralized algorithm.

Channel-aware spectrum sensing and access for mobile cognitive radio ad hoc networks

In hardware-constrained cognitive radio (CR) ad hoc networks, secondary users (SUs) with limited sensing capabilities strive to discover and share available spectrum resources without impairing primary user (PU) transmission. Sensing strategy design objectives include high CR network throughput, resolved SU competition, distributed implementation, and reliable performance under node mobility. However, these objectives have not been realized by previously investigated sensing strategies. A novel sensing strategy is analyzed where the reward is adapted to the SU link channel state information (CSI) prior to sensing, thus randomizing sensing decisions and boosting the network throughput.

Moreover, CSI-aided sensing is combined with a novel first-come-first-served (FCFS) medium access control (MAC) scheme that resolves SU competition prior to sensing. Finally, a pilot-based CSI prediction method is developed to enable the proposed CSI-aided sensing strategies for mobile scenarios. Analytical and numerical results demonstrate that the proposed sensing and access methods significantly outperform non adaptive sensing strategies for practical mobile CR scenarios with CSI mismatch and pilot overhead.

Performance Evaluation of ETSI GeoNetworking for Vehicular Ad Hoc Networks

The Geo Networking protocol provides single-hop and multi-hop communication in vehicular ad hocnetworks based on IEEE 802.11p/ITS-G5. It has been standardized by the ETSI Technical Committee ITS as part of its Release 1 set of specifications and is expected to be deployed in the next years. This paper presents a performance evaluation of the Geo Networking protocol in its recently published version. Our study assesses the performance of the broadcast forwarding algorithms for multi-hop packet transport that are used to disseminate information in geographical areas for road safety and traffic efficiency applications.

From the algorithms specification in the standard, we derive six variants with different combinations of protocol mechanisms with increasing complexity and assess their performance in terms of reliability, latency, and overhead. The algorithms are evaluated in a reference freeway scenario with bidirectional road traffic and a realistic trace-based mobility model with varying vehicle density. The obtained results indicate that the combination of contention-based and greedy forwarding shows the best overall performance; further functional improvements have a limited performance gain in the studied scenario.

A traffic flow theory based density adopted emergency message dissemination scheme for vehicular ad hoc networks

In traffic safety applications for vehicular ad hoc networks (VANETs), emergency messages have to be disseminated quickly and extensively in order to inform as many vehicles as possible in a short period of time. Hence, the broadcast storm problem is prone to occur. In the past, several approaches have been proposed to solve the problem. Among them, we find counter-, distance-, location-, cluster-, and probabilistic-based schemes. In this paper, we analyze existing protocols and present a novel scheme that is designed to mitigate the broadcast storm problem, reduce the end-to-end latency in real urban scenarios, and deal with the faults that occur during transmission.

The proposed routing protocol assigns a density adopted dynamic back-off time based on traffic flow theory to vehicle. It ensures the dissemination of the emergency message onto every part of the road, and when there is no relay vehicle, the emergency message will be re-transmitted. We use the Groove Net simulator to demonstrate that the proposed scheme has a low collision probability, low overhead and a short end-to-end latency.

Sensing capacity of Cognitive Radio Mobile Ad Hoc Networks

This paper addresses a Cognitive Radio Mobile Ad Hoc Network (CRMAHN) where the licensed users (Primary users – PUs) are mobile nodes. In this scenario, the non-licensed users (Secondary Users – SUs) may opportunistically use the PUs’ band when it is available. Because the availability of the band is determined by the spectrum sensing adopted by each SU, this work characterizes the transmission capability of the SUs (Sensing Capacity) through the characterization of the cases when the SUs sense the spectrum as being vacant. Admitting that PUs are mobile, the SUs must declare the band as being used when the PUs within their sensing region use the band.

Contrarily to other works, our main contribution is the assumption that PUs may also be detected active when they are located outside the SUs’ sensing region, which may frequently occur in CRMAHNs. This effect, known as Spatial False Alarm (SFA), is taken into account through the probability of detection of the PUs located outside the SU’s sensing region, which is derived in this work. Finally, it is shown that SFA degrades the sensing capacity of CRMAHNs, when the number of mobile PUs increases and/or the level of activity of the PUs also increases.

A Street-centric Routing Protocol Based on Micro Topology in Vehicular Ad hoc Networks

In a vehicular ad hoc network (VANET), high mobility and uneven distribution of vehicles are important factors affecting the performance of routing protocols. The high mobility may cause frequent changes of network topology, while the uneven distribution of vehicles may lead to routing failures due to network partition, and even high density of vehicles may cause severe wireless channel contentions in an urban environment. In this paper, we propose a novel concept called the micro topology (MT), which consists of vehicles and wireless links among vehicles along a street as a basic component of routing paths and even the entire network topology.

We abstract the MT model reflecting the dynamic routing-related characteristics in practical urban scenarios along streets, including the effect of mobility of vehicles, signal fading, wireless channel contention and existing data traffic. We first analyze the end side-to-end side routing performance in an MT as a basis of routing decision. Then we propose a novel Street-centric Routing Protocol based on Micro Topology (SRPMT) along the streets for VANETs. Simulation results show that our proposed SRPMT protocol achieves higher data delivery rate and shorter average end-to-end delay compared with the performance of the GPSR and GyTAR.

MAC-CPI-A protocol that prevents collisions at MAC layer in Ad Hoc networks

Collisions due to interference at MAC layer limit the throughput of Ad Hoc networks using IEEE 802.11 protocol at medium and high load conditions. The proposed MAC layer MAC-CPI-A (Collision Prevention due to Interference) protocol prevents collisions due to interference completely. In the proposed protocol every node refrains from beginning its transmission if any node within its `maximum interference range’ is currently engaged in a data transfer.

The `maximum interference range’ for all nodes is pre-computed as a function of average distance between a transmitter and its receiver, the minimum acceptable Signal to Interference and Noise Ratio (SINR), path loss exponent, the carrier sensing range of a receiver and the maximum noise around a receiver. If the sudden change in signal received by a node is more than a `significant’ value defined by the `maximum interference range’, then the node infers that another node within its `maximum interference range’ has begun its transmission. A scheme for generation of a new signal indicating a sudden increase or decrease in received signal of greater than `significant’ value has been detailed.