Ahmet Akbulut

Conjunction of heuristic algorithms with multidimensional scaling for localization at wireless ad-hoc networks

In wireless networks, the nodes are generally distributed in a field randomly. The topological information about the nodes is only supported from the distances between each node. This distance information may not be available due to the imperfect conditions among nodes. The positions of the distributed nodes on the field by using available distance data is called node localization problem. One of the methods which can be solved this problem is classical multidimensional algorithm (cMDS). In this study, cMDS is improved with the aid of heuristic algorithms. Three heuristic algorithms (simulated annealing, particle swarm optimization and genetic algorithm) are applied and results are compared with each other.

Node Localization with MDS-Based Hybrid Algorithms at Mobile Ad-Hoc Networks

—In wireless ad-hoc networks, the nodes are randomly distributed in a field; and in most cases, only the distances in between the nodes are available practically. The main goal in such a problem is to obtain the coordinates from the data regarding the distance pairs. One of the tools for solving this problem is the Multidimensional Scaling Method (MDS). Additionally, due to the imperfect conditions in the field, the measurement data contains noise and uncertainties. In this study, a sequentially-executed method is proposed with the aid of the combination of Scaling by Majorizing a Complicated Function (SMACOF) method and the Particle Swarm Optimization (PSO). The results show that the proposed framework reduces the error under different environmental conditions.

Solving the frequency assignment problem by using meta-heuristic methods

Frequency assignment, as a subclass of general assignment problem, is a non-deterministic polynomial-time hard (NP-hard) optimization problem. Main difficulty in these types of problems is the time required to find an optimum solution, since the solution time increases exponentially as the size of the problem grows. To solve the problem in a limited computation time, meta-heuristic methods are adopted. In this study, a frequency assignment problem with conflicting objectives is described. This multi-objective optimization problem is reduced to a single objective one using a scalarization approach. Genetic Algorithm and Particle Swarm Optimization are used to find a solution to the problem. Comparisons of the performances of alternative methods are carried out for the identified problem. Results show that the proposed methods can get a solution which is quite acceptable in terms of interference levels.

A Comparative Study of Tuning of a PID Controller Using Simulated Annealing for a Pitch Attitude Control System

This paper presents an approach based on simulated annealing in order to tune a proportional-integral- derivative (PID) controller for an attitude pitch control system. The PID controllers, thanks to their simplicity and efficiency, are widely used in industrial applications. Studies on designing these controllers have focused on new approaches such as simulated annealing in order to satisfy requirements for diversifying applications. The main objective is to minimize defined performance metrics for tuning the PID parameters. Simulations are done using MATLAB and Simulink. The obtained results are compared with the conventional tuning methods (Ziegler-Nichols, Chien-Hrones-Reswick, Approximate MIGO step response and Skogestad IMC). The results demonstrate that simulated annealing provides less overshoot than other methods and reduces the performance metrics.

Modeling and Simulation of a Small Unmanned Aerial Vehicle

This paper aims to demonstrate a design of low-cost, and Inertial Measurement Unit (IMU) based autopilot that is ArduPilot, and its applications. ArduPilot’s control algorithm possesses two control loops, which are used to control the navigation and the control surfaces such as actuators. Due to using PID control and being able to tune and update the PID parameters (Kp, Ki, Kd) even during the flight, ArduPilot becomes very efficient autopilot also. It’s also possible to export and analyze the data such as airspeed, air pressure, latitude-longitude-altitude, roll-pitch-yaw angles, accelerometer-gyro information, servo outputs, and moreover on Matlab®, after or during the flight. In order to go one step further, a model aircraft, which has nearly the same physical parameters as the one used for the real tests, designed on Plane Maker®, and simulated on Xplane® simulator. Using the simulator made this study easy to tune and test the whole flight parameters before real flight. This paper will lead the students who are interested in automatic control applications especially Unmanned Aerial Vehicles (UAV).

Variable bit rate video transmission through RF/FSO link

This paper presents a channel-adaptive video streaming scheme which adjusts video bit rate according to channel conditions and transmits video through an hybrid RF/free space optical (FSO) laser communication system. The design criteria of the FSO link for video transmission to 2.9 km distance have been given and adaptive bit rate video streaming according to the varying channel state over this link has been studied. It has been shown that the proposed structure is suitable for uninterrupted transmission of videos over the RF/FSO network with reduced packet delays and losses even when the received power is decreased due to weather conditions.

Painting with words: one step beyond 'Paint by numbers'

In this study, we propose a procedure in order to compose a painting complying with some basic artistic and aesthetic rules by means of introducing the main theme to the computer with words. An implementation of the approach on a case study is presented. The proposed approach implemented in the current study might be considered to be lacking of spirit due to very restricted rules. In order to overcome this barrier and add a humanistic essence to the output, incorporation of fuzzification and defuzzification procedures at necessary steps are recommended.