Cognitive radio (CR) has emerged as a promising technology to solve problems related to spectrum scarcity and provides a ubiquitous wireless access environment. CR-enabled secondary users (SUs) exploit spectrum white spaces opportunistically and immediately vacate the acquired licensed channels as primary users (PUs) arrive. Accessing the licensed channels without the prior knowledge of PU traffic patterns causes severe throughput degradation due to excessive channel switching and PU-to-SU collisions. Therefore, it is significantly important to design a PU activity-aware medium access control (MAC) protocol for cognitive radio networks (CRNs). In this paper, we first propose a licensed channel usage pattern identification scheme, based on a two-state Markov model, and then estimate the future idle slots using previous observations of the channels. Furthermore, based on these past observations, we compute the rank of each available licensed channel that gives SU transmission success assessment during the estimated idle slot. Secondly, we propose a PU activity-aware distributed MAC (PAD-MAC) protocol for heterogeneous multi-channel CRNs that selects the best channel for each SU to enhance its throughput. PAD-MAC controls SU activities by allowing them to exploit the licensed channels only for the duration of estimated idle slots and enables predictive and fast channel switching. To evaluate the performance of the proposed PAD-MAC, we compare it with the distributed QoS-aware MAC (QC-MAC) and listen-before-talk MAC schemes. Extensive numerical results show the significant improvements of the PAD-MAC in terms of the SU throughput, SU channel switching rate and PU-to-SU collision rate.
The rapid increase of vehicular traffic and congestion on the highways began hampering the safe and efficient movement of traffic. Consequently, year by year, we see the ascending rate of car accidents and casualties in most of the countries. Therefore, exploiting the new technologies, e.g. wireless sensor networks, is required as a solution of reduction of these saddening and reprehensible statistics. This has motivated us to propose a novel and comprehensive system to utilize Wireless Sensor Networks for vehicular networks. We coin the vehicular network employing wireless Sensor networks as Vehicular Ad Hoc and Sensor Network, or VASNET in short. The proposed VASNET is particularly for highway traffic .VASNET is a self-organizing Ad Hoc and sensor network comprised of a large number of sensor nodes. In VASNET there are two kinds of sensor nodes, some are embedded on the vehicles-vehicular nodes-and others are deployed in predetermined distances besides the highway road, known as Road Side Sensor nodes (RSS). The vehicular nodes are used to sense the velocity of the vehicle for instance. We can have some Base Stations (BS) such as Police Traffic Station, Firefighting Group and Rescue Team. The base stations may be stationary or mobile. VASNET provides capability of wireless communication between vehicular nodes and stationary nodes, to increase safety and comfort for vehicles on the highway roads. In this paper we explain main fundamentals and challenges of VASNET.
Recent advances in wireless communications are diffusing into many new applications. The tiny sensor node, which consists of sensing, data processing and communicating components, led to the idea of sensor networks. A sensor network composed of a large number of sensor nodes that are densely deployed either inside the phenomenon or very close to it. The applications envisioned for sensor networks vary from monitoring inhospitable habitats and disaster areas to operating indoors for intrusion detection and equipment monitoring. In most cases the network designer would have little control over the exact deployment of the network. Nowadays Vehicular Networks are drawing lots of attention due to the wide variety of applications that they can provide. These applications include traffic monitoring, positioning, security etc. A lot of research work is being conducted to define the standard for vehicular communication. These include frequency allocation, standards for physical and link layers, routing algorithms, security issues and new applications. In this paper we discuss the disadvantages of the traffic monitoring by traditional methods and by using GPS equipped sensors. Then we propose a new routing protocol for a fixed topology containing both stationary and mobile nodes. We also try to optimize the energy of the sensor nodes. We simulate our routing algorithm in MATLAB and evaluate it for different possible cases
Many routing protocols have been proposed for AdHoc and sensor networks. Finding the best routing protocol without performance evaluation is not possible. Accurate performance evaluation and comparison of routing protocols needs a high quality simulator, precise configuration and high accuracy analysis method to interpret simulation results properly. Although there are a lot of advancements to design simulators, there is no salient study in the field of simulation results evaluation. To the best of our knowledge, there is not a method to evaluate routing protocols during the simulation and also compound results of some evaluation measurements together to get a unique result. In this paper we introduce an intelligence environment, named SELECTOR; for optimizing evaluation of routing protocols. SELECTOR simulates and also evaluates routing protocols during simulation procedure based on evaluation measurements by learning automata and finally based on the measurements and obtained results, it introduces the most optimum protocol.
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