Measurement Based Statistical Channel Characterization of Air-to-Ground Path Loss Model at 446 MHz for Narrow-Band Signals in Low Altitude UAVs

Powered by the advances in microelectronics technologies, unmanned aerial vehicles (UAVs) provide a vast variety of services ranging from surveillance to delivery in both military and civilian domains. It is clear that a successful operation in those services relies heavily on wireless communication technologies. Even though wireless communication techniques could be considered to reach a certain level of maturity, wireless communication links including UAVs should be regarded in a different way due to the peculiar characteristics of UAVs such as agility in 3D spatial domain and versatility in modes of operation. Such mobility characteristics in a vast variety of environmental diversity render links including UAVs different from those in traditional, terrestrial mobility scenarios. Furthermore, UAVs are critical instruments for network operators in order to provide basic voice and short messaging services for narrow band communication in and around disaster areas. It is obvious that such widespread use of UAVs under different scenarios and environments requires a better understanding the behavior of the communication links that include UAVs. Therefore, in this study, details of a measurement campaign designed to collect data for large-scale propagation characterization of air-to-ground links operated by UAVs at 446MHz under narrowband assumption are given. Data collection, post-processing, and measurement results are provided.Comment: This work is accepted to 2020 IEEE 91st Vehicular Technology Conference: VTC2020-Spring on January 11, 202

Location aware vertical handover in a VLC/WLAN hybrid network

Visible light communication (VLC) has emerged as a promising technology for wireless communication as it offers higher data rates and secure data transmission along with providing indoor illumination. However, VLC is restricted by the line of sight (LoS) nature of the optical channel that consequently results in light path blockages. Therefore, an effective solution would be to combine VLC with a radio frequency (RF) system to form a hybrid VLC/RF network that would take into account the preferences of an end-user with the practicality of implementation. In such networks, an efficient vertical handover (VHO) technique is the most critical element as it ensures a seamless transition between the two networks. In this work, we propose a vertical handover technique that utilizes the user's location information to make a handover decision. We found that the frequency of light path blockages increases with the increasing number of users in a confined space, resulting in significant performance deterioration. This additional information is then utilized so that the VHO algorithm effectively selects the most feasible network. The proposed algorithm has been tested against the immediate vertical handover algorithm (I-VHO) and the dwell vertical handover algorithm (D-VHO) with two different dwell times. The average number of handovers, quality of experience (QoE), and packet loss have been set as performance metrics. We show from several simulation scenarios that the proposed method results in a fewer number of handovers while maintaining higher QoE and lower packet loss.Türkiye Bilimsel ve Teknolojik Araştırma Kurumu (TÜBİTAK

A novel one-base station hybrid positioning method

In wireless networks, the need for accurate and low complexity localization methods are growing. Although many positioning methods based on signals' time difference of arrival (TDOA) and angle of arrival (AOA) have been proposed, these methods require multiple base stations (BS) and calculations with high complexity. Furthermore, the distance between a target and the BSs are usually larger than the distance between different BSs, which causes geometric dilution of precision (GDP) problem. To circumvent these issues, we propose a novel and linear method for positioning by only one BS. Our method uses both AOA and TDOA of incoming signals and called 'positioning using one BS (PuOB)'. In this method, we take measurements from one BS at different time instances instead of taking measurements from multiple BSs simultaneously. The ability to estimate the mobile transmitter position accurately by using one BS is the highlighted advantage of the PuOB over the conventional methods. The positioning accuracy of PuOB for different BS numbers are presented. According to simulation results, PuOB outperforms TDOA and AOA methods using three and two BSs, respectively

Busy tone implementation for coexistence of IEEE 802.22 and 802.11af systems

Bu bildiride, IEEE 802.22 ve IEEE 802.lIaf sistemlerinin TV beyaz boşlugunda birlikte varolabilmeleri için meşgul ton tabanlı yeni bir algoritma önerilmiştir. Önceki meşgul ton tabanlı çalışmalardan farklı olarak 802.11af erişim noktasmm meşgul tonu dinlemesinin yanı Sıra, erişim noktasınan bağlı kullanıcılar da meşgul ton sinyali dinlemekte ve bu sinyali duyduklarmda erişim noktasına iletmektedirler. Böylelikle 802.22 sistemlerine yapılan girişim azaltılmaktadır. Bu çalışmada standartlara uygun iletişim parametreleri ve kanal modelleri dikkate almaları ve önerilen sistemin iyileştirme performansı girişim yapan paket oranı cinsinden değişik duyma bölgeleri için elde edilmiştir.In this paper, a new algorithm based on busy tone approach has been proposed for the coexistence of IEEE 802.22 and IEEE 802.11af systems in TV white space. Different from the earlier study, in addition to 802.11af access points listening to the busy tone signal, their clients also listen to the busy tone and let the access points know once they hear it. Accordingly, interference caused to 802.22 systems has been reduced. This study quantifies the improved system performance in terms of interfering packet rate for different hearing regions considering the communication parameters and channel models adapted for the standards. © 2015 IEEE

A practical physical-layer security method for precoded OSTBC-based systems

In this work, we investigate the security performance obtained by employing a practical precoded orthogonal space time block coding method (POSTBC) in MISO wireless networks. In particular, space time codewords are precoded with an optimum matrix that minimizes the error rate at only the legitimate user (Bob). The acquired results depict that there exists a security gap region in the resulting BER performance as a consequence of using POSTBC. Moreover, we enhance the performance more by developing a new hybrid and green security method called precoding along with partial pre-equalizing (PCPPE). In this method, the transmitted symbols are precoded by a new precoder composed of both the original precoder and a new designed unitary matrix that maps Bob's channel amplitudes or phases estimated over the transmitting antennas into 2D orthonormal matrix. Additionally, three issues associated with the proposed security method have been tackled. Including: The slight increase in the transmit power, the appropriate selection process of the optimal precoding matrix, and the effect of imperfect channel estimation and reciprocity. The comparative simulation results prove that PCPPE method provides a secure link among the legitimate parties without sacrificing Bob's reliability although an eavesdropper is assumed to be fully aware of the used method and the original selected precoding matrix indicator (PMI)

Achieving secure communication through pilot manipulation

Raising concerns about the security of wireless communication led researchers develop new concepts to keep information secret from eavesdroppers. Among them, physical layer security relies on the features of the wireless channels. Most of the work in physical layer security does focus on data transmission. On the other hand the focus of this work is to use manipulation of pilot tones to enhance communication security and to reduce eavesdroppers' ability to estimate the wireless channel. Particularly, we are introducing two novel algorithms, which manipulate pilot tones according to legitimate channels' phase and amplitude characteristics. Both algorithms decrease the channel estimation quality of the eavesdropper considerably, while the amplitude based algorithm provides high quality reception at the legitimate receiver. We provide resulting pilot error rates due to proposed algorithms. In addition, we show the effect of threshold selection to channel estimation quality both at the legitimate receiver and eavesdropper

Busy tone based coexistence algorithm for WRAN and WLAN systems in TV white space

WOS: 000441140700015TV White Space (TVWS) refers to frequency band reserved only for licensed terrestrial TV broadcasting and is opened to unlicensed use under regulatory conditions. While regulations protect licensed systems from interference, interference among unlicensed systems is left mainly to manufacturers. Consequently, there is a need to develop new coexistence approaches between TVWS networks. Busy tone broadcasting is a coexistence method, which can be used by TVWS networks to announce the selected frequency band is occupied. In this paper, a busy tone based coexistence algorithm is proposed for IEEE 802.11af and IEEE 802.22 networks and analyzed by considering different client distributions experiencing log-normal shadowing, where the exact interfering packet rate and successful packet transmission rate expressions are obtained and validated by simulations for different scenarios. The results show that with the proposed coexistence approach, a WLAN can reliably detect the busy tone signal to change its frequency band and can reduce interference to WRAN. Even if there is no available frequency band for the WLAN, the WRAN still maintains its enhanced successful packet transmission performance. The deployment of the proposed algorithm is important for successful coexistence between cognitive wireless networks, where interference is not regulated, such as in TVWS bands.Turk Telekom; Argela under the TT Collaborative Research Awards programme; TUBITAK programme [2232]This research was supported by Turk Telekom and Argela under the TT Collaborative Research Awards programme. The work of Tuncer Baykas is supported by TUBITAK 2232 programme

Analysis of extended busy tone performance for coexistence between WRAN and WLAN TVWS networks

TV White Spaces indicate spectrum bands, which were reserved for licensed terrestrial TV broadcasting and opened to unlicensed use under regulatory conditions. One important regulation which is common in all regulatory domains is no harmful interference is created to licensed devices. On the other hand, interference between unlicensed devices is not regulated. As a result system designers developed new methods to improve coexistence between TVWS networks. Extended busy tone, one of such methods, is designed for coexistence between wireless regional area and wireless local area networks based on IEEE 802.22 and 802.11af standards, respectively. In this paper we analyse the performance of extended busy tone at different range conditions and verify via simulations under realistic conditions. Our results indicate that the method can reduce interference considerably at intermediate distances and enable networks to operate without a significant reduction in throughput. © 2015 IEEE

A novel indoor channel model for tvws communications based on measurements

In this paper, we present an indoor measurement campaign for TV white space bands inside a university building. The measurement results are compared with different indoor propagation models in the literature. We observed large estimation errors for the total path loss value from all existing models. Consequently, we are proposing a new indoor propagation model for TVWS frequencies, which concatenates the effects of frequency dependent path loss with penetration losses due to walls and windows. Performance comparison with existing models show that the proposed model achieves superior performance compared to existing models in terms of Root-Mean-Squared Error (RMSE)

A new approach for coexistence of IEEE 802.11af and IEEE 802.22 systems

Bu bildiride, birden fazla teknik kullanılarak IEEE 802.11af ve IEEE 802.22 kablosuz sistemlerinin TV beyaz bo¸slugunda birlikte varolabilmeleri için algoritmalar geli¸stirilmi¸stir. ˘Me¸sgul tonu, güç kontrolü ve çok sekmeli haberle¸sme teknikleri kullanılarak daha önce yapılan çalı¸smalar temelinde iyile¸stirmeler yapılmı¸stır. IEEE 802.22 sistemlerinin korunumu birinci planda yer alırken, aynı zamanda IEEE 802.11af sistemlerininde haberle¸smeye devam etmesi saglanmı¸stır. Standartlara uygun ˘haberle¸sme parametreleri ve kanal modelleri kullanılan bu çalı¸smada, her iki sistemin de paket giri¸sim oranları ve ba¸sarılı paket oranları farklı senaryolar için incelenmi¸s ve iyile¸stirilmi¸s sonuçlar ortaya konulmu¸stur.In this paper, various algorithms are proposed to help IEEE 802.11af and IEEE 802.22 wireless systems to coexist in TV white space by considering multiple techniques. By using busy tone, power control and multihop communication techniques, improvements have been made compared to prior approaches. With this approach, while IEEE 802.22 systems are protected from intra-network interference, IEEE 802.11af systems are still able to continue transmitting packets. Considering the communication parameters and channel models compliant for the standards, IEEE 802.11af and IEEE 802.22 system performances are investigated in terms of interfering packet rate and successful packet transmission rate for different scenarios and the improved results are presented.IEEEHuaweiAselsanNETA