This paper focuses on the problem of secure transmission in wireless communication, especially in the physical layer. In Cyber-Physical systems, interconnected devices under wireless environments facilitate information exchange but challenge network security. In order to proliferate secrecy, with the assumption of channel reciprocity, the legitimate users share the same channel which is independent of the channels between the legitimate users and the eavesdropper. It is because of the broadcast nature of the wireless medium makes it vulnerable to two types of major attacks denial of service, and information leakage. Here the security may decrease due to the correlation between the generated secret bits. To address these challenges, this framework includes two multi-antenna legitimate parties and a multi-antenna eavesdropper node. In order to maximize the secrecy rate, interleaver along with jointly optimized transmit filter and multi secrecy techniques are used at transmitting section. Optimum receive filter and Equalization technique are used at the receiver section. At last, this paper provides channel estimation errors and self-interference implemented for both duplex systems. So combining with them is a kind of key technology in future physical layer wireless communication.
This paper focuses on the problem of secure transmission in wireless communication, especially in the physical layer. In Cyber-Physical systems, interconnected devices under wireless environments facilitate information exchange but challenge network security. In order to proliferate secrecy, with the assumption of channel reciprocity, the legitimate users share the same channel which is independent of the channels between the legitimate users and the eavesdropper. It is because of the broadcast nature of the wireless medium makes it vulnerable to two types of major attacks denial of service, and information leakage. Here the security may decrease due to the correlation between the generated secret bits. To address these challenges, this framework includes two multi-antenna legitimate parties and a multi-antenna eavesdropper node. In order to maximize the secrecy rate, interleaver along with jointly optimized transmit filter and multi secrecy techniques are used at transmitting section. Optimum receive filter and Equalization technique are used at the receiver section. At last, this paper provides channel estimation errors and self-interference implemented for both duplex systems. So combining with them is a kind of key technology in future physical layer wireless communication.
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.
In this paper, the physical-layer security of a cooperative wireless system with multi-antenna full-duplex (FD) destination is examined. More specifically, we consider a cooperative transmission scenario in which a source communicates with a destination through a relay in the presence of an eavesdropper. In order to degrade the wiretap channel, the FD destination simultaneously transmits an interference signal towards the eavesdropper, while receiving information from the relay. A joint transmit and receive beamformer design is proposed to maximize the signal-to-interference-plus-noise ratio (SINR) at the destination, while guaranteeing that the SINR at the eavesdropper is below a certain threshold. We reformulate the optimization problem as a semidefinite relaxation problem in terms of a transmit beamforming matrix. To balance the performance and system complexity, we investigate suboptimum beamforming designs based on zero-forcing criterion. We derive exact closed-form expressions for the average secrecy rates of the proposed suboptimum designs. Our results reveal that optimum and suboptimum beamforming schemes along with friendly jamming significantly improve the secrecy performance. Moreover, simulation results demonstrate that the optimum scheme outperforms suboptimum schemes, especially in high transmit power regimes.
Traditional approaches for providing confidentiality of wirelessly transmitted signals are often based on cryptographic techniques. While these techniques ensure that messages are encrypted and secured against eavesdropping, they are not sufficient to protect important transmission attributes at the physical (PHY) layer. Specifically, several elds in the headers of PHY and medium access control (MAC) frames are typically sent unencrypted to maintain proper protocol functionality (e.g., sender/receiver identification). As a result, they leak side-channel information (SCI), including payload size, frequency and phase oset, modulation and coding scheme, identities of communication nodes, frame type, transmission rate, etc. These SCI can be exploited by an adversary to launch various passive (eavesdropping) and active (jamming) attacks. To complement cryptographic techniques used at upper layers and prevent the leakage of SCI at the PHY/MAC layers, PHY-layer security techniques have been introduced. These techniques exploit the characteristics of the wireless channel along with multiple-input multiple-output (MIMO) technologies, in which multiple transmitting and receiving antennas are utilized to prevent information leakage to eavesdroppers and/or avoid jamming attacks. In particular, if the signal-to-interference-plus-noise ratio (SINR) at an adversary is lower than the one at a legitimate receiver, secure communication can be achieved through the so-called wiretap coding. MIMO systems enable the transmitter and/or the receiver to generate artificial noise, called friendly jamming (FJ), so as to reduce the SINR at the adversary without impacting the SINR at the legitimate receiver. In this dissertation, we focus on exploring the security threats to next-generation wireless systems. We develop MIMO-based PHY-layer security methods to achieve reliable and secret communications in these systems. First, we consider a broadcast channel, in which a multi-antenna transmitter (Alice) sends K confidential information signals to K legitimate receivers (Bobs) in the presence of L eavesdropping devices (Eves). Alice uses MIMO precoding to generate the information signals along with her own Tx-based friendly jamming (TxFJ). Interference at each Bob is removed via a technique called MIMO zero-forcing. This TxFJ, however, leaves an eavesdropping \vulnerability region" in the proximity of each Bob, which can be exploited by a nearby Eve. Specically, because of the high correlation in the channel state information (CSI) at a Bob and nearby Eves, the TxFJ becomes less effective in preventing eavesdropping at these Eves. We address this problem by augmenting TxFJ with receiver-based friendly jamming (RxFJ), generated by each Bob. Specifically, we allow each Bob to use self-interference suppression (SIS) techniques to transmit a friendly jamming signal while simultaneously receiving an information signal over the same channel. These SIS techniques exploit circulators to attenuate the self-interference power of RxFJ at Bobs and utilize analog/digital cancellation methods to clean out any remaining residual self-interference. Considering the resulting broadcast channel, we rst study a two-user scenario and develop a secrecy encoding scheme for constructing the signals intended to two Bobs. We characterize the corresponding achievable secrecy sum-rate and formulate an optimization problem to maximize this metric. We then extend our approach to K-user scenarios and study a power minimization problem. Particularly, in our analysis we minimize the powers allocated to information and friendly jamming signals (both TxFJ and RxFJ) while guaranteeing individual secrecy rates for various Bobs. The problem is solved for the cases when the eavesdropper's CSI (ECSI) is known or unknown (but with a known distribution). Simulations show the effectiveness of the proposed solutions. Furthermore, we discuss how to schedule transmissions when the rate requirements need to be satised on average rather than instantaneously. In low and high power regime, a scheduling algorithm that serves only the strongest receivers is shown to outperform the one that schedules all receivers. Next, we consider a single-cell massive MIMO system in which a base station (BS) with a large number of antennas transmits simultaneously to several single antenna users. The BS acquires the CSI for various receivers using uplink pilot transmissions. We demonstrate the vulnerability of the CSI estimation process to a pilot-contamination (PC) attack that aims at minimizing the sum-rate of downlink transmissions by contaminating uplink pilots. We rst study PC attacks for two downlink power allocation strategies under the assumption that the attacker knows the locations of the BS and its users. Later on, we relax this assumption and consider the case when such knowledge is probabilistic. The formulated problems are solved using stochastic optimization, Lagrangian minimization, and game-theoretic methods. A closed-form solution for a special case of the problem is obtained. Furthermore, we analyze the \achievable individual secrecy rates" under PC attacks, and provide an upper-bound on these rates. We also study this scenario without a priori knowledge of user locations at the attacker by introducing chance constraints. Another attack model is considered, where the attacker generates jamming signals in both the CSI estimation and data transmission phases by exploiting inband full-duplex techniques. Our results indicate that such attacks can degrade the throughput of a massive MIMO system by more than 50%, and reduce fairness among users significantly.
Physical layer security (PLS) is an approach that provides secrecy based on information-theoretic model which does not account for any computation capability assumption or pre-installed standardized secret key generation algorithm and it is a good additional protection on the top of the existing security scheme. This work includes four different topics which are about improving PLS with full-duplex radio. In the first topic, we develop a fast algorithms for computing power allocations in subcarriers, subject to power and rate constraints, to maximize the secrecy capacity of a three-node network consisting of a source, a full-duplex capable destination and an eavesdropper. The optimal power allocation at the destination is found to be significant especially when its power budget is high. The second topic is about the analysis of a two-phase scheme for secret information transmission with the technique of anti-eavesdropping channel estimation (ANECE), which requires full duplex transceiver and it can better handle Eve with any number of antennas. The analysis is based on the assumption that everyone has a prior statistical knowledge of the channel state information (CSI) anywhere and it yields lower and upper bounds on secure degrees of freedom as functions of the number of antennas on Eve and the size of information packet. For the third topic, we present optimal designs of the pilots for ANECE based on two criteria. The first is to optimize the minimum mean squared error (MMSE) channel estimation for the users, and the second is to maximize the mutual information between the pilot-driven signals observed by the users. Closed-form optimal pilots are shown under both criteria but subject to a symmetric and isotropic condition. Algorithms for computing the optimal pilots are shown for general cases. In the fourth topic, we analyze the secure degree of freedom and the asymptotic expression of the achievable secret key rate from a two-phase key generation scheme which consists of channel training phase and secure information transmission phase. Based on the asymptotic form, we develop an effective algorithm for coherence time allocation between the two phases to maximize the achievable secret key rate.
Wireless communications offer data transmission services anywhere and anytime, but with the inevitable cost of introducing major security vulnerabilities. Indeed, an eavesdropper can overhear a message conveyed over the open insecure wireless media putting at risk the confidentiality of the wireless users. Currently, the way to partially prevent eavesdropping attacks is by ciphering the information between the authorised parties through complex cryptographic algorithms. Cryptography operates in the upper layers of the communication model, bit it does not address the security problem where the attack is suffered: at the transmission level. In this context, physical layer security has emerged as a promising framework to prevent eavesdropping attacks at the transmission level. Physical layer security is based on information-theoretic concepts and exploits the randomness and the uniqueness of the wireless channel. In this context, this thesis presents signal processing techniques to secure wireless networks at the physical layer by optimising the use of multiple-antennas. A masked transmission strategy is used to steer the confidential information towards the intended receiver, and, at the same time, broadcast an interfering signal to confuse unknown eavesdroppers. This thesis considers practical issues in multiple-antenna networks such as limited transmission resources and the lack of accurate information between the authorised transmission parties. The worst-case for the security, that occurs when a powerful eavesdropper takes advantage of any opportunity to put at risk the transmission confidentiality, is addressed. The techniques introduced improve the security by offering efficient and innovative transmission solutions to lock the communication at the physical layer. Notably, these transmission mechanisms strike a balance between confidentiality and quality to satisfy the practical requirements of modern wireless networks.
The issues of the physical layer security are studied, where one transmitter (Alice), one full‐duplex (FD) legitimate receiver (Bob) and one multi‐antenna jammer (Charlie) are considered to defend against multiple passive and non‐colluding eavesdroppers (Eves), for multiple‐input multiple‐output wiretap channels. With the assumption that the complete channel state information (CSI) for main channels and the statistical CSI for Eves' channels are available, an improved secrecy transmission design is proposed to minimise the secrecy outage probability (SOP), under the minimum secrecy rate requirement. In addition to integrating artificial noise aided transmit beamforming and multi‐antenna cooperative jammer to impair Eves' channels, which is widely used in many existing works, a FD legitimate receiver is applied together to further enhance physical layer security. Based on the basic probability theory and convex optimisation, the accurate closed‐form expression of the SOP is derived, and the impacts on secrecy performance are described, including the qualities of main channels, the Alice's transmit power and the number of Eves. Numerical results show that the proposed scheme using the FD Bob can significantly enhance the system security, as compared with that employing the half‐duplex Bob.