Özge Cepheli

A High Data Rate Wireless Communication System With Improved Secrecy: Full Duplex Beamforming

We formulate a joint beamforming vector and power optimization problem for multi-antenna full duplex transmission systems and show that simultaneous transmissions of information bearing signals of legitimate nodes can be optimized to act as artificial noise against eavesdroppers. The proposed system improves the overall throughput, while maintaining secrecy and QoS levels within desired signal-to-interference-plus-noise ratio bounds, without additional power, as verified via simulations.

Hybrid Intrusion Detection System for DDoS Attacks

Distributed denial-of-service DDoS attacks are one of the major threats and possibly the hardest security problem for today’s Internet. In this paper we propose a hybrid detection system, referred to as hybrid intrusion detection system H-IDS, for detection of DDoS attacks. Our proposed detection system makes use of both anomaly-based and signature-based detection methods separately but in an integrated fashion and combines the outcomes of both detectors to enhance the overall detection accuracy. We apply two distinct datasets to our proposed system in order to test the detection performance of H-IDS and conclude that the proposed hybrid system gives better results than the systems based on nonhybrid detection.

Beamforming Aided Interference Management with Improved Secrecy for Correlated Channels

This paper targets the joint optimization of the signal-to-interference-plus-noise ratio (SINR) and secrecy in wireless networks. Although the optimization of the SINR with beamforming in wireless networks is well known, the joint optimization of the secrecy and the SINR of the users is a new problem which gets a high relevance recently. The optimization problems investigated in this paper are based on the joint optimization of the beamforming vectors and transmit powers. This paper presents closed form solutions for two optimization approaches for a simple power control scenario with a single user and a single eavesdropper. Two approaches are distinguished: beamforming without artificial interference (AI) and beamforming with AI. For both approaches, this paper investigates a max-min based beamforming problem and a minimum eavesdropper SINR problem with an SINR constraint for the legitimate receiver.

Filter Optimization Aided Interference Management with Improved Secrecy

This paper proposes a novel matched filter optimization based approach to improve secrecy in a communication among two legitimate users. The presented optimization scheme, named as QoS-based filter design, minimizes the stop-band attenuation and uses quality-of- service constraints on the legitimate receiver and an eavesdropper. The resulting problem is relaxed to a convex problem. The filter coefficients are optimal regarding the legitimate receivers matched filter auto-correlation function, however, it results in a sub-optimal filter for the eavesdropper secrecy constraints. Therefore, an additional post-processing is developed to match the secrecy constraints.

Physical layer security in cognitive radio networks: A beamforming approach

The unguided transmission nature of wireless communication channels in cognitive radio networks (CRNs) makes it easier for attackers to gather transmitted data or to avoid transmissions when compared to traditional wired systems. Furthermore, the shared spectrum concept may lead to various security threats and misusages, especially in the physical (PHY) layer with attacks such as primary user emulation and spectrum sensing data falsification. In this paper, the common PHY layer attacks are introduced from CRN perspective with the corresponding detection techniques and countermeasures. A correlation based trust factor is defined to identify attacks in CRNs, and a beamforming approach is proposed for their prevention. An optimization problem is defined to determine the beamforming coefficients that minimize the success of especially the spectrum sensing data falsification attack. The performance of the proposed method is compared with non-optimized techniques in different channel conditions and proven to be an efficient countermeasure by simulation results.

A Joint Optimization Scheme for Artificial Noise and Transmit Filter for Half and Full Duplex Wireless Cyber Physical Systems

While half and full duplex wireless enabled cyber physical systems (CPSs) are gaining more importance and research attention, maintaining the security of CPS systems remains a vital challenge. The broadcast nature of wireless channels makes it possible for unauthorized receivers, called eavesdroppers, to capture the information signal. Wireless physical layer security techniques aim to harden the secrecy characteristics of wireless systems, decreasing the signal quality of a prospective eavesdropper. This paper considers a joint optimization of artificial noise (AN) signal and transmit filter for the information signals in order to achieve a target secrecy level. As eavesdropping attacks are very critical threats in CPS networks, and the need for high secrecy techniques remains valid. The proposed framework includes a scenario with two multi-antenna legitimate parties and a multi-antenna eavesdropper node (or multiple cooperating eavesdroppers). The transmit filter and AN signal are jointly optimized by the transmitters, where receiver nodes can make use of optimal transmit filters. The problem is derived for the cases where the legitimate CPS nodes perform full duplex and half duplex transmissions. The impact of channel estimation errors and self interference are also discussed.

Filter Hopping: Physical Layer Secrecy Based on FBMC

This paper presents a novel physical layer secrecy enhancement technique for multicarrier communications based on dynamic filter hopping. Using the Filter Bank Multicarrier (FBMC) waveform, an efficient eavesdropping mitigation technique is developed using time- and frequency-varying prototype filters. Without knowledge of the filter assignment pattern, an eavesdropper will experience a high level of inter-carrier (ICI) and inter-symbol interference (ISI). With this severe receive signal-to-interference-plus-noise ratio (SINR) degradation for an illegitimate receiver, the secrecy capacity of the communication system is increased. At the same time, the interference at the legitimate receiver is designed to be negligible in comparison to the channel noise.

Adaptive Physical Layer Security Framework for Wireless Systems

Maintaining security in wireless systems has been a challenge due to the broadcast nature of wireless communication channels. Many methods have been proposed as countermeasures to eavesdropping attacks, which stand as one of the most important secrecy attack types that use the vulnerabilities of wireless channels. The majority of these methods come with the cost of additional power consumption for maintaining secrecy. In order to provide a framework that can enable a tradeoff between energy efficiency and secrecy, we provide a flexible adaptive physical layer security approach that enables tunable security levels for distinct bit streams of a single user. Our main motivation stems from the fact that not all data bits within a single bit steam require the same amount of security. The proposed adaptive power optimization framework allows the assignment of different secrecy rate constraints for distinct data streams. Via simulations, we show that the proposed approach can increase the power efficiency compared to the non-adaptive physical layer security solution, while satisfying the required secrecy constraints.

Analysis on the effects of artificial noise on physical layer security

Physical layer security has gained attention due to the increased usage of wireless communication systems. Our target is to avoid eavesdroppers to receive and decode the transmitted voice signals between the authorized transmitter and the receiver. One of the most fundamental methods of enhancing security in physical layer is artificial noise. Especially the arrival of multiantenna technologies has enabled and accelerated the studies on this field. However, artificial noise based techniques are still in theory only. As a result, practical implementation is a very crucial need for these techniques in order to deploy them in next generation wireless systems. In this study, artificial noise technique is implemented on universal software radio peripheral (USRP) kits, and performance analysis is performed under varying channel conditions and modulation levels. The measurement results are compared with the simulation results. In conclusion, it is shown that the usage of artificial noise can achieve a security level in practice, by decreasing the signal reception quality of eavesdroppers.

Implementation and performance evaluation of dynamic spectrum access using software defined radios

Along with the proliferation of wireless communication with diverse services and applications, effective spectrum usage remains a challenge. Cognitive radio networks (CRNs) stand as a solution for the increasing demand on naturally limited frequency spectrum. As opposed to broad research work on modeling and simulation of these networks, implementation studies are more confined due to the practical limitations of traditional radio devices. In this paper, the CRN test bed we implemented using software defined radio peripherals is introduced, and the performance of this testbed is evaluated with varying network parameters like primary user (PU) traffic intensity and the noise level in the environment. The real time spectrum sensing performance are given by means of miss detection, false alarm and detection rates along with system utilization. Testbed implemented provides promising results as well as being basis for our future work covering multi-hop, multi-channel CRNs.