Ali Boyaci

Towards green and secure vehicle-to-vehicle communications: A protocol for establishing the network

In this study, initial part of establishing a Green and Secure Vehicle-to-Vehicle Communications Network (GSV2VCN) is proposed. Different from IEEE 1609.3, the protocol proposed focuses solely on a universal control channel (CC) to agree on a master of the group of close-by nodes within the same physical region. Also, unlike IEEE 1609.3, the proposed protocol does not take advantage of multi-channel transceiver mode. Instead, once the master is agreed on, the slave nodes switch to a specific service channel (SC) decided by the master. An object-oriented simulation framework is designed and run to obtain statistics for the proposed protocol. Results are provided along with the relevant discussions. Future work towards GSV2VCN is given as well.

Dynamic Feature Selection for Spam Detection in Twitter

Social Networks continue to increase their popularity day by day. With the widespread availability of Internet access, interest of people in social networks has also increased significantly. The fact that, popularity of social media makes it tempting to use social media platforms for bad purposes. Malicious people are attempting to gain unfair profits by using fake accounts and various techniques. Among these initiatives, SPAM is one of the most frequently used methods. Today, SPAM attacks on social networks are increasing and many social network users are exposed to this and similar attacks. To identify SPAM users among billions of social network users, the examination of massive amounts of data requires a challenging large-scale data analysis. In this study, we group similar Twitter users and introduce a dynamic feature selection technique that use different features for each user groups instead of use static feature set and apply machine learning algorithms to classify spam users on Twitter.

An IEEE 802.11x Implementation for V2X Communications Towards IoT and Big Data

Green transportation is an integral part of green environment concept. Next generation transportation systems are desired to achieve high performances with reduced fuel consumption and carbon emission. In this regard, vehicle maintenance status along with some other critical diagnostic data should steadily be checked and tracked. It is known that vehicles that are poorly maintained or not maintained in a timely manner lead to both emissions exceeding the standards and low performance. Vehicle telematics along with some other conveniences such as infotainment systems, location–based services and applications are expected to improve safety, availability, and reliability of next generation transportation systems. From this perspective, intelligent transport systems (ITS) seems to be a promising solution candidate which encompasses all of the aforementioned topics as well as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-cloud (V2C) opportunities. Therefore, in this study, a conceptual model that links vehicle telematics to the cloud along with V2V communications facility is proposed and a prototype based on IEEE 802.11x protocol suite is implemented. Mobile data collection and measurements are obtained. Results are presented along with relevant discussions as well as the end point storage and usage of the data are introduced. In the proposed model, the mobile data are transferred to cloud computing platform to create the big data for further research opportunities for car manufacturers, policy makers, and researchers with the concern of ethics and security issues.

Monitoring, Surveillance, and Management of the Electromagnetic Spectrum: Current Issues in Electromagnetic Spectrum Monitoring

This paper discusses the current aspects of the surveillance and management of the electromagnetic spectrum under various topics that are vital to wireless communications. On the basis of the recent technological advancements in conjunction with the discussions on the global approaches toward electromagnetic spectrum monitoring, the paper addresses short-, medium-, and long-term strategies in wireless communications for monitoring, governing, and managing the electromagnetic spectrum of leading countries and multinational organizations. Furthermore, it proposes a novel spectrum monitoring strategy for next-generation wireless systems and outlines the implications of the proposed strategy.

Statistical modeling of propagation channels for Terahertz band

Digital revolution and recent advances in telecommunications technology enable to design communication systems which operate within the regions close to the theoretical capacity limits. Ever-increasing demand for wireless communications and emerging numerous high-capacity services and applications mandate providers to employ more bandwidth-oriented solutions to meet the requirements. Trend and predictions point out that marketplace targets data rates around 10Gbps or even more within the upcoming decade. It is clear that such rates could only be achieved by employing more bandwidth with the state-of-the-art technology. Considering the fact that bands in the range of 275GHz-3000GHz, which are known as Terahertz (THz) bands, are not allocated yet for specific active services around the globe, there is an enormous potential to achieve the desired data rates. Although THz bands look promising to achieve data rates on the order of several tens of Gbps, realization of fully operational THz communications systems obliges to carry out a multidisciplinary effort including statistical propagation and channel characterizations, adaptive transceiver designs, reconfigurable platforms, advanced signal processing algorithms and techniques along with upper layer protocols equipped with various security and privacy levels. Therefore, in this study, several important statistical parameters for line-of-sight (LOS) channels are measured. High resolution frequency domain measurements are carried out at single-sweep within a span of 60GHz. Impact of antenna misalignment under LOS conditions is also investigated. By validating exponential decay of the received power in both time and frequency domain, path loss exponent is examined for different frequencies along with the frequency-dependent path loss phenomenon. Furthermore, impact of humidity is also tested under LOS scenario. Measurement results are presented along with relevant discussions and future directions are provided as well.

Fractional-rate radiometer for spectrum sensing based on I/Q branch separation

Radiometer has a peculiar place among spectrum sensing techniques available in the literature, because it has a simplistic design and is known to be the optimal detector in the absence of a priori knowledge about the signal to be detected. In this study, it is shown that simplicity in the traditional radiometer design could further be improved while its performance is maintained. The proposed method exploits the inherent orthogonality between the I/Q branches and reduces the total number of addition and multiplication operations at baseband. Results are validated by the experimental data collected under different digital modulation scenarios. Relevant discussions and future directions are outlined as well.

High-resolution multi-band spectrum occupancy measurements and evaluations at 900MHz downlink band for Istanbul metropolitan

Radio frequency spectrum is one of the most important resources for both contemporary and next generation wireless communications (NGWC) systems. Therefore, utilization of the radio frequency spectrum is a critical task. Reliable occupancy statistics are key to such utilization. Considering the fact that Turkey will migrate to digital terrestrial TV broadcast in the near future, a specific portion of the radio frequency spectrum will be available. Hence, occupancy statistics and relevant analyses are mandatory for both contemporary and NGWC systems. Results of high-resolution multi-band spectrum occupancy measurements at 900MHz downlink band for Istanbul metropolitan are presented. Two of the prominent evaluation methods and corresponding occupancy statistics are given in a comparative manner. It is observed that parameters of the evaluation methods affect the occupancy statistics drastically.

A symmetric U-slot microstrip patch antenna design

In this paper a U-shaped slotted microstrip patch antenna that aims to work in 8.86-8.98GHz frequencies was designed and simulated. First antenna design was in shape of U- slot, then it was changed into [] shaped slot. Sonnet Suites version 13.56 was used as simulation program [1]. Air thickness is 20mm and the distance between ground ant the patch is 5mm. S11 is nearly -11.20dB. Antenna has 7.55dB gain at resonance frequency.

On error variance for autoregressive process-based spectrum occupancy prediction with energy detector for cognitive networks

Spectrum sensing is considered to be the most important task for both cognitive radio (CR) networks and next generation wireless networks (NGWNs). Spectrum sensing operation allows wireless nodes to identify vacant bands so that radio frequency (RF) spectrum could be used more efficiently. It is clear that a powerful spectrum sensing method equipped with an effective prediction strategy will carry utilization of the RF spectrum to the utmost level. Analysis of the performances of prediction strategies plays a critical role in quantifying the efficiency of the overall spectrum sensing operation. Therefore, in this study, autoregressive process-based prediction strategy for energy detection is investigated. It is shown that prediction error variance relies heavily on both the intercept of the autoregressive model and the threshold value selected. Theoretical findings are validated and verified by measurement data which are obtained by capturing the complete Global System for Mobile (GSM) downlink band at Nyquist rate of in-phase/quadrature (I/Q) level. Results and relevant discussions are provided along with future research directions as well.

Identification of shadowed fast fading interference in celullar mobile radio systems

In this study, a method that identifies shadowed fast fading interference is proposed on downlink transmission for frequency division duplexing (FDD)-based cellular mobile radio communications systems. The method proposed exploits the independence of shadowing and fast-fading processes along with the difference between their occurrence scales in spatial dimension and provides an analytical approach to identify the interference with the aid of a metric defined.