In this work, we provide a qualitative comparison between existing geocast protocols and then we present an efficient geocast routing protocol for VANET. This protocol is a semantic and self-decision geocast routing protocol for disseminating safety and non-safety information over VANET (SAS-GP). SAS-PG initially executes an algorithm to locally determine the semantic geocast area. Then, the protocol disseminates the information in three phases: Spread, Preserve, and Assurance, which utilize the traffic information system and the digital map. SAS-GP principally employs timer-based techniques in order to avoid overhead and broadcast storm problems; nonetheless, novel factors are enhanced to calculate the timer’s values in each phase. Simulation results demonstrate effective and reliable dissemination in terms of delivery ratio and number of false warnings compared to existing protocols when evaluated in high scale and realistic scenarios. Also, SAS-GP performs faster in notifying vehicles resulting in a higher geocast distance before approaching the location of the event.

The performance of many protocols and applications of Vehicular Ad hoc Networks (VANETs), depends on vehicles obtaining enough fresh information on the status of their neighbouring vehicles. This should be fulfilled by exchanging Basic Safety Messages (BSMs) also called beacons using a shared channel. In dense vehicular conditions, many of the beacons are lost due to channel congestion. Therefore, in such conditions, it is necessary to control channel load at a level that maximizes BSM dissemination. To address the problem, in this thesis algorithms for adaptation of beaconing to control channel load are proposed. First, a position-based routing protocol for VANETs is proposed and the requirement of adaptive beaconing to increase the performance of the protocol is indicated. The routing protocol is traffic-aware and suitable for city environments and obtains real-time traffic information in a completely ad hoc manner without any central or dedicated control, such as traffic sensors, roadside units, or information obtained from outside the network. The protocol uses an ant-based algorithm to find a route that has optimum network connectivity. Using information included in small control packets called ants, vehicles calculate a weight for every street segment that is proportional to the network connectivity of that segment. Ant packets are launched by vehicles in junction areas. To find the optimal route between a source and destination, a source vehicle determines the path on a street map with the minimum total weight for the complete route. The correct functionality of the protocol design has been verified and its performance has been evaluated in a simulation environment. Moreover, the performance of the protocol in different vehicular densities has been studied and indicated that in dense vehicular conditions the performance of the protocol degrades due to channel load created by uncontrolled periodic beaconing. Then, the problem of beaconing congestion control has been formulated as non-cooperative games, and algorithms for finding the equilibrium point of the games have been presented. Vehicles as players of the games adjust their beacon rate or power or both, based on the proposed algorithms so that channel load is controlled at a desired level. The algorithms are overhead free and fairness in rate or power or both rate and power allocation are achieved without exchanging excess information in beacons. Every vehicle just needs local information on channel load while good fairness is achieved globally. In addition, the protocols have per-vehicle parameters, which makes them capable of meeting application requirements. Every vehicle can control its share of bandwidth individually based on its dynamics or requirements, while the whole usage of the bandwidth is controlled at an acceptable level. The algorithms are stable, computationally inexpensive and converge in a short time, which makes them suitable for the dynamic environment of VANETs. The correct functionality of the algorithms has been validated in several high density scenarios using simulations.

There are still many challenges in the field of VANETs that encouraged researchers to conduct further investigation in this field to meet these challenges. The issue pertaining to routing protocols such as delivering the warning messages to the vehicles facing Non-Line of Sight (NLOS) situations without causing the storm problem and channel contention, is regarded as a serious dilemma which is required to be tackled in VANET, especially in congested environments. This requires the designing of an efficient mechanism of routing protocol that can broadcast the warning messages from the emergency vehicles to the vehicles under NLOS, reducing the overhead and increasing the packet delivery ratio with a reduced time delay and channel utilisation. The main aim of this work is to develop the novel routing protocol for a high-density environment in VANET through utilisation of its high mobility features, aid of the sensors such as Global Positioning System (GPS) and Navigation System (NS). In this work, the cooperative approach has been used to develop the routing protocol called the Co-operative Volunteer Protocol (CVP), which uses volunteer vehicles to disseminate the warning message from the source to the target vehicle under NLOS issue; this also increases the packet delivery ratio, detection of NLOS and resolution of NLOS by delivering the warning message successfully to the vehicle under NLOS, thereby causing a direct impact on the reduction of collisions between vehicles in normal mode and emergency mode on the road near intersections or on highways. The cooperative approach adopted for warning message dissemination reduced the rebroadcast rate of messages, thereby decreasing significantly the storm issue and the channel contention. A novel architecture has been developed by utilising the concept of a Context-Aware System (CAS), which clarifies the OBU components and their interaction with each other in order to collect data and take the decisions based on the sensed circumstances. The proposed architecture has been divided into three main phases: sensing, processing and acting. The results obtained from the validation of the proposed CVP protocol using the simulator EstiNet under specific conditions and parameters showed that performance of the proposed protocol is better than that of the GRANT protocol with regard to several metrics such as packet delivery ratio, neighbourhood awareness, channel utilisation, overhead and latency. It is also successfully shown that the proposed CVP could detect the NLOS situation and solves it effectively and efficiently for both the intersection scenario in urban areas and the highway scenario.

Diploma work includes summary of aeroplanes accidents, incurred by human factor malfunction in general aviation and in ultralight aeroplanes category on Czech Republic territory since year 2000. It analyses accidents enclosures with a view to discover similarities near particular accidents. From ascertained lockworks ared proposal created for possibly steps, how prevent rise of these accidents. Part of this work are also attachments (formularies, etc.).