STRUCTURE, COORDINATION, SENSING AND ALLOCATION IN COGNITIVE RADIO VANETS

Abstract

With the increase in population, vehicle traffic has also increased on roads. This has caused an increase in accidents, due to which thousands of people lose their lives and millions get injured annually. Hence, a foolproof and secure Vehicular Ad-hoc Network (VANET) structure is required to reduce the number of accidents considerably. Pre-danger information must be communicated in real-time, in order to implement preventive measures to avoid accidents. VANETs are specially designed in order to communicate information about hazards. The protocol DSRC/WAVE/IEEE802.11p is proposed for VANETs, but it may not be enough to cope with increasing network traffic, especially emergency messages. Hence the use of cognitive Radio (CR) technology has been introduced. A lot of methods for coordination and channel allocation in the context of VANETs are being introduced. As such, the need of a framework to reliably compare the relative performances of different channel sensing, allocation and coordination schemes which take into account the movement of vehicles is felt. Different techniques like Independent Spectrum sensing and various forms of Cooperative techniques have been proposed in the near past. In this dissertation, a VANET structure has been proposed for highways and urban environments. In the Highway model, separate Road Side Units have been provided for the traffic on each side. In this way group formation for localized traffic will be easy on highways. Simulation results show that by using the proposed model, average throughput and end-to-end delay have improved considerably, while packet loss has also been reduced. We also propose an efficient spectrum sensing mechanism for sensing and sharing the CR spectrum by mobile vehicles, which combines best of stand-alone sensing and cooperative sensing techniques. The proposed mechanism not only improves the probability of correct detection, but also almost eliminates the probability of misdetection. Then we have introduced a framework that can be used to define and compare such schemes in a variety of scenarios. Simulation results clearly show the robustness of our technique by almost eliminating the misdetections and reducing to a great extent the false alarms. Afterwards we have proposed a sensing technique which prepares a database for small road segments, time slots for the hours of the day and different frequencies of the spectrum based on the sensing of vehicles throughout the day. Based on this database, the future utilization of the spectrum is proposed. Simulations and results clearly indicate the success and usefulness of our proposed technique. In the end we have proposed a model based on fuzzy logic for the allocation of different types of TV channels having different ON/OFF timings in different hours of the day taking time, vehicle speed, message priority and CR channel sensing results as input. The simulations performed show the utilization of every type of channel in speed versus time and message priority versus time. These results can be utilized well for the allocation patterns of CR channels.