Abstract:Physical-layer security has become a critical technique in current wireless networks.The existing conventional physical layer security techniques,e.g. artificial-noise-aided transmit beamforming,do not apply well to multicast transmission from large multicast user and eavesdropper user numbers.To address this problem,an enhanced secure multicast algorithm based on user clustering scheme was proposed.Firstly,the multicast users with close channel vectors were divided into a cluster and different clusters were served on different channels.Secondly,a heuristic joint power allocation and beamforming design algorithm based on this user clustering scheme were proposed to maximize the globally achievable secure multicast rate.Finally,to reduce the overall computation complexity,the new searching method was put forward to solve power allocation and beamforming design jointly.Simulation results showed that the enhanced secure multicast algorithm can support a much higher secure transmission rate than conventional secure multicast (CSM) schemes,and the proposed joint power allocation and beamforming design algorithm outperform existing CSM schemes with the ergodic searching method greatly in terms of computation complexity.
Abstract:Physical-layer security has become a critical technique in current wireless networks.The existing conventional physical layer security techniques,e.g. artificial-noise-aided transmit beamforming,do not apply well to multicast transmission from large multicast user and eavesdropper user numbers.To address this problem,an enhanced secure multicast algorithm based on user clustering scheme was proposed.Firstly,the multicast users with close channel vectors were divided into a cluster and different clusters were served on different channels.Secondly,a heuristic joint power allocation and beamforming design algorithm based on this user clustering scheme were proposed to maximize the globally achievable secure multicast rate.Finally,to reduce the overall computation complexity,the new searching method was put forward to solve power allocation and beamforming design jointly.Simulation results showed that the enhanced secure multicast algorithm can support a much higher secure transmission rate than conventional secure multicast (CSM) schemes,and the proposed joint power allocation and beamforming design algorithm outperform existing CSM schemes with the ergodic searching method greatly in terms of computation complexity.
Recently, physical layer security has been recognized as a new design paradigm to provide security in wireless networks. In contrast to the existing conventional cryptographic methods, physical layer security exploits the dynamics of fading channels to enhance security of wireless communications. This paper studies optimization frameworks for a multicasting network in which a transmitter broadcasts the same information to a group of legitimate users in the presence of multiple eavesdroppers. In particular, power minimization and secrecy rate maximization problems are investigated for a multicasting secrecy network. First, the power minimization problem is solved for different numbers of legitimate users and eavesdroppers. Next, the secrecy rate maximization problem is investigated with the help of private jammers to improve the achievable secrecy rates through a game theoretic approach. These jammers charge the transmitter for their jamming services based on the amount of interference caused to the eavesdroppers. For a fixed interference price scenario, a closed-form solution for the optimal interference requirement to maximize the revenue of the transmitter is derived. This rate maximization problem for a nonfixed interference price scenario is formulated as a Stackelberg game in which the jammers and transmitter are the leaders and follower, respectively. For the proposed game, a Stackelberg equilibrium is derived to maximize the revenues of both the transmitter and the private jammers. To support the derived theoretical results, simulation results are provided with different numbers of legitimate users and eavesdroppers. In addition, these results show that physical layer security based jamming schemes could be incorporated in emerging and future wireless networks to enhance the quality of secure communications.
In this thesis, we study the physical layer security in downlink multi-user wireless networks. Traditionally, security has been addressed by cryptography at the higher layers of the communication stack. Security at the physical layer has been a major research topic in recent years. We study two different precoder designs alongside artificial noise (AN) to mitigate multi-user interference and deteriorate reception at the eavesdropper (Eve). We study the large scale analysis to calculate the secrecy sum-rate for these two cases and analyze the effect of AN on the system. First, we consider the worst case scenario, when eavesdropper's (Eve's) rate is not deteriorated by the interference caused by the legitimate users. Later, we investigate how interference from legitimate users would affect the large scale security sum rate. At the end, we assume more practical situation where the channel state information at the transmitter is not perfect due to feedback limitation and estimation error. We first study block diagonalization (BD) precoding. We derive the asymptotic secrecy sum-rate of BD for physical layer security in downlink multi-user wireless networks using artificial noise (AN). We first derive the secrecy sum-rate assuming that the channel of the eavesdropper is not known at the transmitter and derive the asymptotic secrecy sum-rate. Then we derive the optimum power allocation for asymptotic secrecy sum-rate. We design the system based on large scale analysis for different special cases. Simulation results show that the proposed precoders outperform channel inversion (CI) and regularized channel inversion (RCI) schemes at all SNRs. We also show that as the number of receive antennas of each user increases, the sum-rate gap between the proposed scheme and existing methods increases. We, then, study two methods of regularized block diagonalization (RBD) precoding using artificial noise (AN) for physical layer security in downlink multi-user MIMO wireless networks. We compare the complexity analysis of these two methods in terms of floating point operations per second (FLOPS). We derive the secrecy and asymptotic secrecy sum-rates for these schemes. We also derive closed form expressions for the asymptotic optimal power allocation to the AN signal and legitimate users. Simulations show RBD precoding outperform regularized channel inversion (RCI) in terms of secrecy sum-rate with a margin of 0.5 bits/s/Hz. Also, simulation results show our closed-form asymptotic secrecy sum-rates matches closely with the simulations for perfect and imperfect CSIT. We also study the effect of interference on BD precoding scheme. In the first two studies the worst case scenarios was considered and the effect of interference was not considered at the eavesdropper. We first derive the closed-form secrecy and asymptotic secrecy sum-rates for this scheme. Then, we derive the optimum power allocation. Using the derived optimum power allocation, we determine the conditions under which adding AN helps. We also investigate the optimum number of users, number of antennas at the eavesdropper, and the number of transmit antennas to fully study the conditions where using AN improves performance. We show that as the number of users increases or the number of receive antennas at the eavesdropper decreases, improved performance is achieved by allocating a smaller fraction of the total power to transmit the AN. The closed form expressions for the secrecy sum rate (SSR) and optimum power allocation closely match our simulation results. In Chapter 5, we study the effect of imperfect channel state information at the transmitter (CSIT) for each case studied in earlier chapters. We first study the effect of imperfect CSIT for BD precoding in both scenarios when interference does and does not exist at eavesdropper. We show that the imperfect CSI play the same role as interference for the desired users. Then, we study the effect of imperfect CSIT for RBD precoding when interference does not exist at eavesdropper. We show as channel estimation error increases, the secrecy sum-rate decreases. This is due to the fact that channel estimation error just affects the desired users' rate and has no effect on eavesdropper's performance. Finally, in the last chapter, we conclude our thesis and provide some road map for future--Author's abstract
We investigate the physical layer security for multiple-input single-output (MISO) multigroup multicast system in the presence of multiple eavesdroppers (Eves). To elaborate, we aim to tackle the secrecy rate maximization (SRM) problem of the multicast system by proposing an algorithm for secure beam-forming. Here, we adopt the concept of artificial noise (AN) which is used for disturbing Eves by sending noise deliberately. Thus, we simultaneously design beamforming vectors and AN vector to maximize the secrecy rate of the system. We formulate the SRM problem in the form of non-convex max-min fair problem which is hard to solve due to its non-convexity. Therefore, in order to tackle this problem, we first reformulate this SRM problem to epigraph form, and we utilize the minorization maximization (MM) algorithm and rank-1 reduction technique. Simulation results show that our proposed algorithm improves the secrecy rate of given system model and outperforms the conventional algorithm for secure beamforming.
In this paper, we investigate physical layer security of a multicast network consisting of multiple legitimate users in the presence of an eavesdropper. Besides information receivers, the legitimate users are assumed to be able to act as jammers for interfering with the eavesdropper to improve secrecy. The joint user selection and power control problem for maximizing the average sum secrecy rate of the multicast network under the transmit power constraints is investigated with perfect channel state information (CSI) or with unknown CSI related to the eavesdropper, and heuristic algorithms are proposed correspondingly. Simulation results are presented to verify the proposed algorithms. It is shown that the proposed algorithms significantly outperform the reference algorithms in terms of average sum secrecy rate.
Security has become an increasingly significant and urgent issue in wireless networks. The growing computational capability of the eavesdropper (Eve) and more and more complicated secure key management in large scale and heterogeneous networks, pose more and more stringent requirement to the cryptographic protocols. As a new design paradigm, physical layer security has been recognised as a promising solution to enhance the security of wireless links relying on the channel properties and advanced signal processing, and can act as either an alternative or a complementary solution to the conventional cryptographic methods. Without complicated secure key generation and management, physical layer security is quite suitable for the large scale distributed networks. In this thesis, we aim to improve the secrecy performance in emerging wireless communication systems relying on different physical layer security techniques. Firstly, the security of an amplify-and-forward successive relaying network with multiple untrusted relay nodes is investigated, where the conventional detrimental inter-relay interference is exploited to jam the untrusted nodes without assistance of external helpers. Considering different complexity requirements, several relay selection schemes are proposed, and the closed-form expressions of the lower bound of the secrecy outage probability and the maximum secrecy diversity order are derived accordingly. It is shown that the maximum secrecy diversity order of N-1 can be achieved for an N relay nodes network. Secondly, the artificial noise (AN) aided secure transmission strategy for a multiple-input single-output multiple-Eve (MISOME) system with a secure user (Bob) and a normal user (NU) is investigated. The power allocations among Bob, NU and AN, as well as the wiretap code rates, are jointly optimized to maximize the effective secrecy throughput (EST), under the average throughput constraint of NU. An alternative optimization algorithm with guaranteed convergence is proposed to obtain the optimal parameters. It is shown that the EST increases with the transmitting power and the number of transmit antennas, and decreases with the throughput constraint of NU, and the EST can be improved through injecting AN and concurrent transmission of Bob and NU. Thirdly, physical layer security in a multi-antenna small-cell network is investigated, where the multi-antenna base stations (BSs), cellular users, and Eves are all randomly distributed according to independent Poisson point processes. Stochastic geometry is applied to analyze the connection and secrecy outage probabilities and the average achievable secrecy rate. The impact of different parameters, including power allocation, BS and Eve density, and the adaptive eavesdropping or jamming on the secrecy performance is analyzed. It is shown that the average secrecy rate is a quasi-concave function of the power allocation factor and monotonically decreases with the ratio of the Eve-BS density. Finally, we study the physical layer security in a large-scale heterogeneous network consisting of both sub-6 GHz massive multi-input multi-output (MIMO) macro cells and millimeter wave (mmWave) small cells. By considering pilot spoofing attacks from the Eves, the coverage and secrecy probabilities are derived using stochastic geometry and the conditions under which the millimeter wave tier outperforms the sub-6 GHz counterpart are discussed in terms of both coverage and secrecy.It is shown that the mmWave small cell can provide better coverage performance in the high transmission code-rate region, and the secrecy performance of the mmWave system outperforms the sub-6 GHz counterpart in the low redundant rate region, which reveals the advantage of using mmWave for secure communication.
We investigate physical layer security in massive multiple-input multiple-output multicast transmission where the base station only knows the statistical channel state information of the legitimate user terminals and the eavesdropper. We first introduce a tight lower bound of the achievable secrecy multicast rate as the design objective. Then, we find the closed-form transmit directions, i.e., the eigenvectors of the optimal multicast transmit covariance matrix, which simplifies the matrix-valued multicast transmit strategy design into a beam domain power allocation problem. We further propose an efficient iterative power allocation algorithm with guaranteed convergence to a local optimal solution by invoking the concave-convex procedure. We also derive the deterministic equivalent of the optimization objective to reduce the computation complexity. Numerical results demonstrate the performance gains of the proposed approach over the conventional approach.