Reyat Yilmaz

Novel Two-Dimensional Visualization Approaches for Multivariate Centroids of Clustering Algorithms

The dimensionality reduction and visualization problems associated with multivariate centroids obtained by clustering algorithms are addressed in this paper. Two approaches are used in the literature for the solution of such problems, specifically, the self-organizing map (SOM) approach and mapping selected two features manually (MS2Fs). In addition, principle component analysis (PCA) was evaluated as a component for solving this problem on supervised datasets. Each of these traditional approaches has drawbacks: if SOM runs with a small map size, all centroids are located contiguously rather than at their original distances according to the high-dimensional structure; MS2Fs is not an efficient method because it does not take features outside of the method into account, and lastly, PCA is a supervised method and loses the most valuable feature. In this study, five novel hybrid approaches were proposed to eliminate these drawbacks by using the quantum genetic algorithm (QGA) method and four feature selection methods, Pearson’s correlation, gain ratio, information gain, and relief methods. Experimental results demonstrate that, for 14 datasets of different sizes, the prediction accuracy of the proposed weighted clustering approaches is higher than the traditional K-means++ clustering approach. Furthermore, the proposed approach combined with K-means++ and QGA shows the most efficient placements of the centroids on a two-dimensional map for all the test datasets.

A Gradual Approach for Multimodel Journey Planning: A Case Study in Izmir, Turkey

Planning a journey by integrating route and timetable information from diverse sources of transportation agencies such as bus, ferry, and train can be complicated. A user-friendly, informative journey planning system may simplify a plan by providing assistance in making better use of public transportation. In this study, we presented the service-oriented, multimodel Intelligent Journey Planning System, which we developed to assist travelers in journey planning. We selected Izmir, Turkey, as the pilot city for this system. The multicriteria problem is one of the well-known problems in transportation networks. Our study proposes a gradual path-finding algorithm to solve this problem by considering transfer count and travel time. The algorithm utilizes the techniques of efficient algorithms including round based public transit optimized router, transit node routing, and contraction hierarchies on transportation graph. We employed Dijkstra’s algorithm after the first stage of the path-finding algorithm by applying stage specific rules to reduce search space and runtime. The experimental results show that our path-finding algorithm takes 0.63 seconds of processing time on average, which is acceptable for the user experience.

Modulation diversity in two way relay channels

In this work, modulation diversity is exploited for two way relay channel through which multiple sources transmit information to each other. Under a basic framework with two sources and a single relay, a system applying modulation diversity technique together with decode-and-forward (DF) and amplify-and-forward (AF) protocols is proposed. The performance of the proposed scheme is investigated through simulation results and modulation diversity is shown to improve the performance in terms of symbol error rate for both two protocols.

Impact Of Asynchronism on Wireless Relay Channels

In this work, we investigate the effects of asynchronism arised by time delay between the source and relay transmissions over the wireless relay channel. We revise the maximum-a-posteriori (MAP) type detector designed for synchronous case and proposed a receiver for asynchronous relay channel. We also integrate source-relay cooperation with the low density parity check (LDPC) codes in decode and forward (DF) mode to enhance the system performance. The convergence threshold of the overall system is evaluated using extrinsic information transfer (EXIT) chart analysis. Also the performance of asynchronous system is comparedwith synchronous counterpart viaMonteCarlo simulations for various level of delay time. Using the convergence behaviour and simulation results, itÌs demonstrated that that the proposed receiver can cope with asynchronized transmission over the ergodic fading relay channel. Index Terms – Relay channels, fading channels, asynchronous transmission, low density parity check codes.

Multilevel Coded Cooperation for Wireless Vehicular Networks

At the physical layer of wireless vehicular networks, coded cooperation is a possible way of realizing uplink transmit diversity at the mobile vehicles equipped with single antenna. In this work, in order to increase the power and bandwidth efficiency, a multilevel coded cooperative system using orthogonal signalling is proposed. Orthogonal signalling not only enables transmission of both users data in single channel symbol but also provides independent detection at the receiver. We investigate the performance of the system by derivation of pairwise and bit error probabilities together with Monte-Carlo simulations.