Secure communication over large-scale decentralized wireless networks is an extremely challenging task due to the cost and difficulty in establishing secret keys among all the nodes in a distributed manner. For this reason, the notion of physical layer security has recently drawn significant attention, which may assist with key exchange and provide an additional layer of protection in such networks. In this paper, we investigate how the physical layer security constraints affect the network throughput. We consider a random network in which the legitimate and eavesdropper nodes are located according to independent Poisson point processes. We introduce a new metric "secrecy transmission capacity" to characterize the network throughput in terms of the area spectral efficiency of secure transmissions, subject to constraints on both the quality of service and the level of security. This capacity framework allows us to quantitatively study the throughput cost of physical layer security constraints. We observe that the throughput cost of achieving a moderate level of security is quite low, while throughput must be significantly sacrificed to realize a highly secure network.
Secure communication over large-scale decentralized wireless networks is an extremely challenging task due to the cost and difficulty in establishing secret keys among all the nodes in a distributed manner. For this reason, the notion of physical layer security has recently drawn significant attention, which may assist with key exchange and provide an additional layer of protection in such networks. In this paper, we investigate how the physical layer security constraints affect the network throughput. We consider a random network in which the legitimate and eavesdropper nodes are located according to independent Poisson point processes. We introduce a new metric "secrecy transmission capacity" to characterize the network throughput in terms of the area spectral efficiency of secure transmissions, subject to constraints on both the quality of service and the level of security. This capacity framework allows us to quantitatively study the throughput cost of physical layer security constraints. We observe that the throughput cost of achieving a moderate level of security is quite low, while throughput must be significantly sacrificed to realize a highly secure network.
In this paper, we combine sectorized transmission with artificial noise to establish secrecy in decentralized wireless networks. The locations of the legitimate nodes and the eavesdroppers are both modeled by homogeneous Poisson point processes. Using sectorized antennas, each legitimate transmitter sends an information signal in the sector which contains its intended receiver, while simultaneously emitting artificial noise in other sectors, in order to provide secrecy against the eavesdroppers. We first separately characterize the reliability performance of the legitimate link and the secrecy performance against malicious eavesdropping. Then, we derive the secrecy transmission capacity to measure the networkwide secrecy throughput. To facilitate the practical system design, we provide a sufficient condition, in terms of the system parameters and constraints, under which a positive secrecy transmission capacity is achievable. The optimal transmit power allocation between the information signal and the artificial noise for achieving the maximal secrecy transmission capacity is also investigated. Our analysis indicates that sectorized transmission provides significant secrecy enhancements in decentralized wireless networks.
Artificial noise has been considered as an effective and efficient way to improve the secrecy of wireless communications. However, most existing papers have been focused on the analysis of a single communication link between a transmitter and a legitimate receiver with some eavesdroppers. In this paper, we investigate the impact of artificial noise to the secrecy of a large scale decentralized wireless network where channels are modeled as Rayleigh fading and locations of legitimate nodes and eavesdroppers follow Poisson point processes. To study network throughput versus system parameters, we derive the secrecy transmission capacity and show how it is related to the number of transmitting antennas and the power allocation ratio between data and artificial noise. Analytical results provide insights on how system parameters can be designed to improve secrecy transmission capacity of a wireless network.
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.
This work studies the achievable secure rate per source-destination pair in wireless networks. First, a path loss model is considered, where the legitimate and eavesdropper nodes are assumed to be placed according to Poisson point processes with intensities λ and λe, respectively. It is shown that, as long as λe/λ=o((logn)−2), almost all of the nodes achieve a perfectly secure rate of Ω(n1) for the extended and dense network models. Therefore, under these assumptions, securing the network does not entail a loss in the per-node throughput. The achievability argument is based on a novel multi-hop forwarding scheme where randomization is added in every hop to ensure maximal ambiguity at the eavesdropper(s). Secondly, an ergodic fading model with n source-destination pairs and ne eavesdroppers is considered. Employing the ergodic interference alignment scheme with an appropriate secrecy pre-coding, each user is shown to achieve a constant positive secret rate for sufficiently large n. Remarkably, the scheme does not require eavesdropper CSI (only the statistical knowledge is assumed) and the secure throughput per node increases as we add more legitimate users to the network in this setting. Finally, the effect of eavesdropper collusion on the performance of the proposed schemes is characterized.
Motivated by recent developments in physical-layer security and stochastic geometry, we aim to characterize the fundamental limits of secure communication in wireless networks. Based on a general model in which legitimate nodes and potential eavesdroppers are randomly scattered in space, we define the secure communication graph (s-graph) from the point of view of information-theoretic security. For the Poisson s-graph, we provide conclusive results for: (a) the in-degree and out-degree of a node; (b) the isolation probability; and (c) the secrecy capacity between a node and each of its neighbours. Our analysis reveals the innate connections between information-theoretic security and the spatial densities of legitimate and eavesdropper nodes.
We study a random extended network, where the legitimate and eavesdropper nodes are assumed to be placed according to Poisson point processes in a square region of area n. It is shown that, when the legitimate nodes have unit intensity, ¿ = 1, and the eavesdroppers have an intensity of ¿e= O((log n)-2), almost all of the nodes achieve a perfectly secure rate of ¿ (1/¿n). The achievability argument is based on a novel multi-hop forwarding scheme where randomization is added in every hop to ensure maximal ambiguity at the eavesdropper(s). Remarkable, under these assumptions, securing the transmissions of nodes does not entail a loss in the per-node throughput in terms of scaling.