Modify-and-Forward for Securing Cooperative Relay Communications

We proposed a new physical layer technique that can enhance the security of cooperative relay communications. The proposed approach modifies the decoded message at the relay according to the unique channel state between the relay and the destination such that the destination can utilize the modified message to its advantage while the eavesdropper cannot. We present a practical method for securely sharing the modification rule between the legitimate partners and present the secrecy outage probability in a quasi-static fading channel. It is demonstrated that the proposed scheme can provide a significant improvement over other schemes when the relay can successfully decode the source message.Comment: IEEE International Zurich Seminar on Communications, Feb. 201

협력 재밍을 이용한 중계 네트워크의 보안 통신을 위한 최적화 및 할당 기법

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2019. 2. 이재홍.Physical layer security is a promising technology in the upcoming fifth generation (5G) wireless communication because the wireless communication is vulnerable to eavesdrop and it is complex to encrypt a data signal. In physical layer security, secure transmission is satisfied by using the physical characteristics of the wireless channel. Cooperative jamming is one of the efficient techniques to enhance secrecy performance in physical layer security. In cooperative jamming, a cooperating node transmits a jamming signal to interfere the eavesdropper. However, this jamming signal effects not only the eavesdropper but also the destination, which degrades the secrecy performance and causes waste of transmit power. It means the jamming signal transmission needs to be designed properly with optimization and power allocation to enhance security. The dissertation consists of two main results. First, we investigate a two-hop relay network consists of a source, an AF relay, a destination, and an eavesdropper. In this network, cooperative jamming is utilized in which the destination and the source transmit jamming signals in phase 1 and 2, respectively. At the destination, its own jamming signal transmitted in phase 1 is perfectly cancelled, and the jamming signal from the source has negligible strength due to the weak channel condition from the source to destination. We propose an optimal source power allocation for the network to enhance the secrecy performance based on the channel knowledge available at the source. Simulation results show that the proposed source power allocation scheme achieves higher secrecy rate and lower secrecy outage probability than the fixed power allocation schemes. Second, we investigate a two-hop relay network consists of a source, multiple AF relays, a destination, and an eavesdropper. In this network, one relay is selected out of the relays to forwards the data signals. Also, cooperative jamming is utilized in which the destination and the source transmit jamming signals in phase 1 and 2, respectively. We propose power allocation and relay selection scheme to minimize secrecy outage probability with the total power constraint and the power constraints for each phases, respectively. In total power constraint case, power allocation and relay selection problem is formulated and it is divided into a master problem and a subproblem by using the primal decomposition method. Simulation results show that the proposed scheme achieves lower secrecy outage probability than the conventional jamming power allocation scheme as well as without jamming scheme.물리 계층 보안은 무선통신의 보안에 대한 취약점과 암호화의 복잡성이라는 특징으로 인하여, 5세대(5G) 이동통신을 위한 핵심 기술로 간주되고 있다. 물리 계층 보안은 무선 채널의 물리적 특성을 이용하여 보안 통신을 가능하게 한다. 협력 재밍(cooperative jamming)은 물리 계층 보안에서의 보안 성능을 향상시키는 효과적인 기술로, 협력 노드가 재밍 신호를 전송함으로써 도청자를 방해하고, 보안을 달성한다. 그러나, 이러한 재밍 신호는 도청자 뿐 아니라 수신단 역시 방해하게 되므로 과도한 재밍 신호 전송은 보안 성능 향상에 지장을 주고 전력을 낭비하게 된다. 따라서 보안 성능을 향상시키기 위해서는 재밍 신호의 전력 할당 및 최적화를 하는 것이 필수적이다. 본 논문에서의 두 가지 주요한 연구 결과는 다음과 같다. 첫째, 하나의 송신단, 증폭 후 재전송 중계기, 수신단 및 도청자가 존재하는 중계 네트워크를 분석한다. 이 때 수신단 및 송신단이 협력 재밍을 통해 각각 첫 번째 및 두 번째 페이즈에서 재밍 신호를 전송하도록 한다. 수신단이 첫 번째 페이즈에 전송한 재밍 신호는 중계기를 통해 증폭되지만 수신단이 제거할 수 있으며, 송신단의 재밍 신호는 송신단과 수신단 사이의 채널이 약하기 때문에 수신단에 미치지 못한다. 이 때 본 네트워크에서 네트워크의 보안 전송률(secrecy rate) 및 보안 불능 확률(secrecy outage probability)을 향상시키는 송신단의 각 페이즈 별 전송 전력을 송신단이 가진 채널 정보를 통해 최적화한다. 모의 실험을 통해 제안한 전력 할당 기법이 다른 고정 전력 할당 기법에 비해 높은 보안 전송률과 낮은 보안 불능 확률을 달성함을 확인한다. 둘째, 하나의 송신단, 다수의 증폭 후 재전송 중계기들, 하나의 수신단 및 도청자가 존재하는 중계 네트워크를 분석한다. 다수의 중계기 중 하나의 중계기가 선택되어 신호를 전송하게 되며, 협력 재밍을 통해 수신단 및 송신단이 재밍 신호를 전송한다. 이 때 네트워크의 보안 불능 확률을 최소화하기 위한 중계기 선택 및 전력 할당 기법을 다양한 전력 제한에 맞게 분석한다. 네트워크 전체 전력이 제한된 경우에서는 중계기 선택 및 전력 할당 문제를 풀기 위해 두 개의 부문제(subproblem) 로 분할한다. 모의 실험을 통해 제안한 기법이 기존의 기법 및 재밍 신호를 전송하지 않는 기법에 비해 낮은 보안 불능 확률을 달성함을 확인한다.Abstract i 1 Introduction 1 1.1 Background and Related Work 2 1.1.1 Physical Layer Security 2 1.1.2 Cooperative Jamming 3 1.2 Outline of Dissertation 5 1.3 Notations 6 2 Source Power Allocation for Cooperative Jamming in Amplify-and- Forward Relay Network with Eavesdropper 9 2.1 System Model 10 2.2 Source Power Allocation 16 2.2.1 Full CSI for All Links 16 2.2.2 Full CSI for Desired Links only 18 2.3 Simulation Results 23 2.3.1 Identical Channel Condition 23 2.3.2 Non-identical Channel Condition 32 2.3.3 Multiple Antenna Eavesdropper 50 2.4 Summary 50 3 Power Allocation and Relay Selection for Cooperative Jamming in AF Relay Network with Multiple Relays and an Eavesdropper 53 3.1 System Model 55 3.2 Secrecy Outage Probability Analysis 61 3.3 Power Allocation and Relay Selection 66 3.3.1 Total Power Constraint 66 3.3.2 Power Constraints for Each Phases 68 3.4 Numerical Results 70 3.4.1 Multiple Antenna Eavesdropper 86 3.5 Extension to Multiple Relay Selection 86 3.6 Summary 88 4 Conclusion 89 4.1 Summary 89 4.2 Future Works 90 A Obtainment of Optimal Values of alpha in R1 and R2 92 Bibliography 95 Korean Abstract 104Docto

Physical layer security solutions against passive and colluding eavesdroppers in large wireless networks and impulsive noise environments

Wireless networks have experienced rapid evolutions toward sustainability, scalability and interoperability. The digital economy is driven by future networked societies to a more holistic community of intelligent infrastructures and connected services for a more sustainable and smarter society. Furthermore, an enormous amount of sensitive and confidential information, e.g., medical records, electronic media, financial data, and customer files, is transmitted via wireless channels. The implementation of higher layer key distribution and management was challenged by the emergence of these new advanced systems. In order to resist various malicious abuses and security attacks, physical layer security (PLS) has become an appealing alternative. The basic concept behind PLS is to exploit the characteristics of wireless channels for the confidentiality. Its target is to blind the eavesdroppers such that they cannot extract any confidential information from the received signals. This thesis presents solutions and analyses to improve the PLS in wireless networks. In the second chapter, we investigate the secrecy capacity performance of an amplify-andforward (AF) dual-hop network for both distributed beamforming (DBF) and opportunistic relaying (OR) techniques. We derive the capacity scaling for two large sets; trustworthy relays and untrustworthy aggressive relays cooperating together with a wire-tapper aiming to intercept the message. We show that the capacity scaling in the DBF is lower bounded by a value which depends on the ratio between the number of the trustworthy and the untrustworthy aggressive relays, whereas the capacity scaling of OR is upper bounded by a value depending on the number of relays as well as the signal to noise ratio (SNR). In the third chapter, we propose a new location-based multicasting technique, for dual phase AF large networks, aiming to improve the security in the presence of non-colluding passive eavesdroppers. We analytically demonstrate that the proposed technique increases the security by decreasing the probability of re-choosing a sector that has eavesdroppers, for each transmission time. Moreover, we also show that the secrecy capacity scaling of our technique is the same as for broadcasting. Hereafter, the lower and upper bounds of the secrecy outage probability are calculated, and it is shown that the security performance is remarkably enhanced, compared to the conventional multicasting technique. In the fourth chapter, we propose a new cooperative protocol, for dual phase amplify-andforward large wireless sensor networks, aiming to improve the transmission security while taking into account the limited capabilities of the sensor nodes. In such a network, a portion of the K relays can be potential passive eavesdroppers. To reduce the impact of these untrustworthy relays on the network security, we propose a new transmission protocol, where the source agrees to share with the destination a given channel state information (CSI) of source-trusted relay-destination link to encode the message. Then, the source will use this CSI again to map the right message to a certain sector while transmitting fake messages to the other sectors. Adopting such a security protocol is promising because of the availability of a high number of cheap electronic sensors with limited computational capabilities. For the proposed scheme, we derived the secrecy outage probability (SOP) and demonstrated that the probability of receiving the right encoded information by an untrustworthy relay is inversely proportional to the number of sectors. We also show that the aggressive behavior of cooperating untrusted relays is not effective compared to the case where each untrusted relay is trying to intercept the transmitted message individually. Fifth and last, we investigate the physical layer security performance over Rayleigh fading channels in the presence of impulsive noise, as encountered, for instance, in smart grid environments. For this scheme, secrecy performance metrics were considered with and without destination assisted jamming at the eavesdropper’s side. From the obtained results, it is verified that the SOP, without destination assisted jamming, is flooring at high signal-to-noise-ratio values and that it can be significantly improved with the use of jamming

Power allocation and signal labelling on physical layer security

PhD ThesisSecure communications between legitimate users have received considerable attention recently. Transmission cryptography, which introduces secrecy on the network layer, is heavily relied on conventionally to secure communications. However, it is theoretically possible to break the encryption if unlimited computational resource is provided. As a result, physical layer security becomes a hot topic as it provides perfect secrecy from an information theory perspective. The study of physical layer security on real communication system model is challenging and important, as the previous researches are mainly focusing on the Gaussian input model which is not practically implementable. In this thesis, the physical layer security of wireless networks employing finite-alphabet input schemes are studied. In particular, firstly, the secrecy capacity of the single-input single-output (SISO) wiretap channel model with coded modulation (CM) and bit-interleaved coded modulation (BICM) is derived in closed-form, while a fast, sub-optimal power control policy (PCP) is presented to maximize the secrecy capacity performance. Since finite-alphabet input schemes achieve maximum secrecy capacity at medium SNR range, the maximum amount of energy that the destination can harvest from the transmission while satisfying the secrecy rate constraint is computed. Secondly, the effects of mapping techniques on secrecy capacity of BICM scheme are investigated, the secrecy capacity performances of various known mappings are compared on 8PSK, 16QAM and (1,5,10) constellations, showing that Gray mapping obtains lowest secrecy capacity value at high SNRs. We propose a new mapping algorithm, called maximum error event (MEE), to optimize the secrecy capacity over a wide range of SNRs. At low SNR, MEE mapping achieves a lower secrecy rate than other well-known mappings, but at medium-to-high SNRs MEE mapping achieves a significantly higher secrecy rate over a wide range of SNRs. Finally, the secrecy capacity and power allocation algorithm (PA) of finite-alphabet input wiretap channels with decode-and-forward (DF) relays are proposed, the simulation results are compared with the equal power allocation algorithm

Interference Leakage Neutralization in Two-Hop Wiretap Channels with Partial CSI

In this paper, we analyze the four-node relay wiretap channel, where the relay performs amplify-and-forward. There is no direct link between transmitter and receiver available. The transmitter has multiple antennas, which assist in securing the transmission over both phases. In case of full channel state information (CSI), the transmitter can apply information leakage neutralization in order to prevent the eavesdropper from obtaining any information about the signal sent. This gets more challenging, if the transmitter has only an outdated estimate of the channel from the relay to the eavesdropper. For this case, we optimize the worst case secrecy rate by choosing intelligently the beamforming vectors and the power allocation at the transmitter and the relay

Secure Two-Way Transmission via Wireless-Powered Untrusted Relay and External Jammer

In this paper, we propose a two-way secure communication scheme where two transceivers exchange confidential messages via a wireless powered untrusted amplify-and-forward (AF) relay in the presence of an external jammer. We take into account both friendly jamming (FJ) and Gaussian noise jamming (GNJ) scenarios. Based on the time switching (TS) architecture at the relay, the data transmission is done in three phases. In the first phase, both the energy-starved nodes, the untrustworthy relay and the jammer, are charged by non-information radio frequency (RF) signals from the sources. In the second phase, the two sources send their information signals and concurrently, the jammer transmits artificial noise to confuse the curious relay. Finally, the third phase is dedicated to forward a scaled version of the received signal from the relay to the sources. For the proposed secure transmission schemes, we derive new closed-form lower-bound expressions for the ergodic secrecy sum rate (ESSR) in the high signal-to-noise ratio (SNR) regime. We further analyze the asymptotic ESSR to determine the key parameters; the high SNR slope and the high SNR power offset of the jamming based scenarios. To highlight the performance advantage of the proposed FJ, we also examine the scenario of without jamming (WoJ). Finally, numerical examples and discussions are provided to acquire some engineering insights, and to demonstrate the impacts of different system parameters on the secrecy performance of the considered communication scenarios. The numerical results illustrate that the proposed FJ significantly outperforms the traditional one-way communication and the Constellation rotation approach, as well as our proposed benchmarks, the two-way WoJ and GNJ scenarios.Comment: 14 pages, 6 figures, Submitted to IEEE Transactions on Vehicular Technolog

Secrecy Rates and Optimal Power Allocation for Full-Duplex Decode-and-Forward Relay Wire-Tap Channels

This paper investigates the secrecy rates and optimal power allocation schemes for a decode-and-forward wiretap relay channel where the transmission from a source to a destination is aided by a relay operating in a full-duplex (FD) mode under practical residual self-interference. By first considering static channels, we address the non-convex optimal power allocation problems between the source and relay nodes under individual and joint power constraints to establish closed-form solutions. An asymptotic analysis is then given to provide important insights on the derived power allocation solutions. Specifically, by using the method of dominant balance, it is demonstrated that full power at the relay is only optimal when the power at relay is sufficiently smaller when compared with that of the source. When the power at the relay is larger than the power at the source, the power consumed at the relay saturates to a constant for an effective control of self-interference. The analysis is also helpful to demonstrate that the secrecy capacity of the FD system is twice as much as that of the half-duplex system. The extension to fast fading channels with channel state information being available at the receivers but not the transmitters is also studied. To this end, we first establish a closed-form expression of the ergodic secrecy rate using simple exponential integrals for a given power allocation scheme. The results also show that with optimal power allocation schemes, FD can significantly improve the secrecy rate in fast fading environments