The co-channel interference modeling is vital for evaluating the secrecy performance in random wireless networks, where the legitimate nodes and eavesdroppers are randomly distributed. In this paper, a new interference model is proposed from the user-dominant perspective. The model can provide a better analytical assessment of secrecy performance with interference coordination for the presence of eavesdroppers. The typical legitimate is assumed to be located at the origin, and chooses the closest base station (BS) as its serving BS. The field of interferers is obtained by excluding the desired BSs (including the serving BS and its cooperative BS(s)). In contract with the exiting interference model, it is assumed that desired BSs and interferers belong to the same Poisson Point Process (PPP), and eavesdroppers are distributed according to another independent PPP. Based on this model, the average secrecy transmission capacity is derived in simply analytical forms with interference coordination. Analysis and simulation results show that the secrecy performance can be significantly enhanced by exploiting interference coordination. Furthermore, the average secrecy transmission capacity increases with increasing number of cooperative BSs.
The co-channel interference modeling is vital for evaluating the secrecy performance in random wireless networks, where the legitimate nodes and eavesdroppers are randomly distributed. In this paper, a new interference model is proposed from the user-dominant perspective. The model can provide a better analytical assessment of secrecy performance with interference coordination for the presence of eavesdroppers. The typical legitimate is assumed to be located at the origin, and chooses the closest base station (BS) as its serving BS. The field of interferers is obtained by excluding the desired BSs (including the serving BS and its cooperative BS(s)). In contract with the exiting interference model, it is assumed that desired BSs and interferers belong to the same Poisson Point Process (PPP), and eavesdroppers are distributed according to another independent PPP. Based on this model, the average secrecy transmission capacity is derived in simply analytical forms with interference coordination. Analysis and simulation results show that the secrecy performance can be significantly enhanced by exploiting interference coordination. Furthermore, the average secrecy transmission capacity increases with increasing number of cooperative BSs.
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.
Motivated by recent developments in wireless communication, this thesis aims to characterize the secrecy performance in several types of typical wireless networks. Advanced techniques are designed and evaluated to enhance physical layer security in these networks with realistic assumptions, such as signal propagation loss, random node distribution and non-instantaneous channel state information (CSI). The first part of the thesis investigates secret communication through relay-assisted cognitive interference channel. The primary and secondary base stations (PBS and SBS) communicate with the primary and secondary receivers (PR and SR) respectively in the presence of multiple eavesdroppers. The SBS is allowed to transmit simultaneously with the PBS over the same spectrum instead of waiting for an idle channel. To improve security, cognitive relays transmit cooperative jamming (CJ) signals to create additional interferences in the direction of the eavesdroppers. Two CJ schemes are proposed to improve the secrecy rate of cognitive interference channels depending on the structure of cooperative relays. In the scheme where the multiple-antenna relay transmits weighted jamming signals, the combined approach of CJ and beamforming is investigated. In the scheme with multiple relays transmitting weighted jamming signals, the combined approach of CJ and relay selection is analyzed. Numerical results show that both these two schemes are effective in improving physical layer security of cognitive interference channel. In the second part, the focus is shifted to physical layer security in a random wireless network where both legitimate and eavesdropping nodes are randomly distributed. Three scenarios are analyzed to investigate the impact of various factors on security. In scenario one, the basic scheme is studied without a protected zone and interference. The probability distribution function (PDF) of channel gain with both fading and path loss has been derived and further applied to derive secrecy connectivity and ergodic secrecy capacity. In the second scenario, we studied using a protected zone surrounding the source node to enhance security where interference is absent. Both the cases that eavesdroppers are aware and unaware of the protected zone boundary are investigated. Based on the above scenarios, further deployment of the protected zones at legitimate receivers is designed to convert detrimental interference into a beneficial factor. Numerical results are investigated to check the reliability of the PDF for reciprocal of channel gain and to analyze the impact of protected zones on secrecy performance. In the third part, physical layer security in the downlink transmission of cellular network is studied. To model the repulsive property of the cellular network planning, we assume that the base stations (BSs) follow the Mat´ern hard-core point process (HCPP), while the eavesdroppers are deployed as an independent Poisson point process (PPP). The distribution function of the distances from a typical point to the nodes of the HCPP is derived. The noise-limited and interference-limited cellular networks are investigated by applying the fractional frequency reuse (FFR) in the system. For the noise-limited network, we derive the secrecy outage probability with two different strategies, i.e. the best BS serve and the nearest BS serve, by analyzing the statistics of channel gains. For the interference-limited network with the nearest BS serve, two transmission schemes are analyzed, i.e., transmission with and without the FFR. Numerical results reveal that both the schemes of transmitting with the best BS and the application of the FFR are beneficial for physical layer security in the downlink cellular networks, while the improvement due
In this paper, for the conventional MISO wiretap channel, we take into account the locations' random nature regarding those eavesdroppers and the ambient interferers in the wireless networks. For the convenience of mathematical analysis, these location distributions are modeled as Poisson point processes (PPPs). We assume that the transmitter Alice has no channel state information (CSI) about the other nodes except that it knows the statistical CSI of links about the legitimate user Bob and those eavesdroppers. In order to improve the security of Bob, we further set up a protected zone (PZ) to prevent excessive eavesdroppers from overhearing confidential signals. We investigate the probabilities of connection outage and secrecy outage to derive the closed form expression of secrecy transmission rate. Afterwards, we formulate an secrecy rate maximization problem and solve it to determine the optimized beamforming vector. The numerical results reveal the superiority of the proposed beamforming optimization over the relevant eigen beamforming design in [1].
Due to the nature of a wireless medium, a wireless channel is susceptible to malicious nodes, which encourages the consideration of secrecy in many applications such as satellite networks, social networking services, etc. Motivated by the social characteristic that makes nodes more likely to communicate with nearby neighbors, we study the secrecy capacity of large-scale wireless networks with social relationships. We consider two distributions of legitimate nodes: They are homogeneously placed based on a Poisson point process (PPP), or they are inhomogeneously distributed as multiclustering topology. In particular, we consider two scenarios: 1) the noncolluding case, where each eavesdropper decodes its receiving message independently; and 2) the colluding case, where eavesdroppers can cooperate to decode the message. We adopt a rank-based model to describe the social characteristic and investigate its impact on the secrecy capacity using the technique of self-interference cancelation. We employ a passive attack model, where eavesdroppers can only listen to transmissions among legitimate nodes. Our important findings include the following: 1) In the noncolluding case, secrecy capacity is not influenced by eavesdroppers in order sense, but it varies with the density of eavesdroppers and social impacts in the colluding case. 2) The proposed scheme can achieve optimal secrecy throughput neglecting polylogarithmic factor in homogeneous wireless networks.
In a conventional cellular wireless networks, single cell processing (SCP) is usually considered where inter-cell interference is treated as noise. As we know, interference can cause severe information leakage for secret communication, the paper studies the secrecy performance with coordination beamforming (CBf) scheme in the downlink of a two-cell multi-user MIMO (MU-MIMO) cellular network. For CBf, the BSs can jointly design their respective beamformers to control inter-cell interference. Based on regularized channel inversion (RCI) precoding, we derive the concise formulas for the signal-to interference plus noise (SINR) at a legitimate user and the colluding malicious users, and the achievable secrecy sum-rate for the CBf scheme. Furthermore, we obtain their corresponding approximation in large-system regime, in which the number of users per cell K and the number of antenna at BS N tend to infinity, while with their ratio β = K/N being held constant. The analytical results are validated with finite-size system by simulation. Compared with SCP without BS cooperation, simulation results show that the secrecy performance can be significantly enhanced by exploiting CBf scheme.
We investigate the secrecy performance of a multiuser diversity scheme for an interference-limited wireless network with a base station (BS), N legitimate users, and an eavesdropper in the presence of a single dominant interferer. Assuming interference dominates noise power at the eavesdropper and at each legitimate user's receiver, the BS transmits information to the legitimate user with the kth best (highest) signal-tointerference ratio. We derive a closed-form expression for the secrecy outage probability for an arbitrary N and an asymptotic expression for a fixed k and large N. Furthermore, we derive a closed form asymptotic expression for the ergodic secrecy capacity of the kth best user and shows that it scales like O (log(N)) for a fixed k and large N.