Physical layer security is a promising approach to enable secure communications by considering the characteristics of wireless channels. In this work, we consider a multiple antenna multiuser system with an eavesdropper which is passive and its channel state information (CSI) is not available at transmitter. We we add artificial noise (AN) in the null space of legitimate user to disturb reception of eavesdropper. For the sake of ensuring secure communication, CSI has great impact on system performance. However, in order to estimate the channel of all users at transmitter, sending pilot signals from all these users increases the system overhead. We perform a threshold based user selection at the receiver side to reduce this overhead. Also, we investigate the effects of the proposed user selection on the secrecy capacity.
Physical layer security is a promising approach to enable secure communications by considering the characteristics of wireless channels. In this work, we consider a multiple antenna multiuser system with an eavesdropper which is passive and its channel state information (CSI) is not available at transmitter. We we add artificial noise (AN) in the null space of legitimate user to disturb reception of eavesdropper. For the sake of ensuring secure communication, CSI has great impact on system performance. However, in order to estimate the channel of all users at transmitter, sending pilot signals from all these users increases the system overhead. We perform a threshold based user selection at the receiver side to reduce this overhead. Also, we investigate the effects of the proposed user selection on the secrecy capacity.
Physical layer security is a promising approach to provide secure communications by considering the characteristics of wireless channels. In this work, we propose a secure multiple input single output (MISO) multiuser system with a quantized feedback link. We assume that eavesdropper is passive and its channel state information (CSI) is not available at transmitter. In order to disrupt reception of a passive eavesdropper, we schedule more than one legitimate user. For the sake of ensuring secure communication, the CSI of legitimate users has great impact on overall performance of secrecy sum capacity. The proposed solution applies a semi-orthogonal selection with a specific codebook to reduce the quantization errors for legitimate user side while disrupting the reception of the eavesdropper. The proposed solution improved secrecy sum capacity while reducing the feedback overhead for secure MISO multiser system.
Physical layer security has recently emerged as a promising approach to provide secure wireless communications. Physical layer security technology is the key means to achieve security and communication integration. The built-in security mechanism based on the characteristics of wireless channel provides a feasible idea for the realization of “one secret at a time”. It has important application prospects in integrity protection of service data, Internet of things (IoT) lightweight encryption and blockchain wireless security technology. In this paper, we consider the scenario of a unicast multiuser multiple-input single-output (MISO) downlink system in the presence of multiple single-antenna passive eavesdroppers. Instead of assuming perfect channel state information (CSI), we investigate the artificial noise (AN)-aided robust transmit beamforming scheme with imperfect CSI on legitimate receivers and no CSI regarding eavesdroppers at the transmitter. Under the fixed total transmit power, the information symbol and the AN are transmitted concurrently. We aim to guarantee each legitimate receiver's signal-to-interference-and-noise ratio(SINR) outage probability below a preset level with minimum power. Hence, as much power as possible can be allocated to AN to confuse the eavesdroppers. In order to reduce the negative impact on the legitimate receivers, the AN is transmitted in the null space of the estimated legitimate channels. To deal with this nonconvex optimization problem, a rank relaxed formulation is obtained by employing semidefinite relaxation (SDR). Then we propose two approaches by using Bernstein-type inequality and S-procedure, respectively, to transform the probabilistic constraints into deterministic constraints. The optimization problem is reformulated as a convex semidefinite program (SDP). Simulation results show that the proposed approaches have better performances than the non-robust approach.
In this paper, we investigate a multiuser MIMO downlink with imperfect channel state information (CSI) from the physical-layer security provision. In a classical transmitter (Alice)-legitimate receiver (Bob)-eavesdropper (Eve) model using artificial noise to disturb Eve's reception, we consider a general scenario where all nodes are equipped with multiple antennas, and Bob's CSI is acquired by pilot-assisted channel estimation. For designing the secure transmit beamforming, we utilize random matrix quantization (RMQ) to quantize Bob's channel estimate, and then Bob feeds it back to Alice. Due to the effects of imperfect CSI at Alice, the secrecy performance is upper bounded in the high signal-to-noise ratio (SNR) regions. In order to avoid the interference-limited phenomenon, we present a scaled strategy for the secrecy system utilizing derived upper bound on the secrecy rate loss. Moreover, it is shown that our derived results can be easily extended to a special case where both legitimate and eavesdropping receivers equip a single antenna each, where random vector quantization (RVQ) is utilized instead. By employing our proposed feedback strategy, the secrecy rate increases with transmit power, and the certain secrecy requirement can be guaranteed.
Achieving secure transmission in wireless network is a significantly important research topic. Classic cryptography encrypts a confidential message to an unreadable cipher message. Thus only the authentic receiver with correct secrecy key is able to decrypt the message. However, with the growing computational capability of adversaries, the requirement of secrecy key generation and distribution is getting stringent. Another method to achieve wireless security, which has attracted much attention in recent years, is through physical layer processing, named physical layer security. In a typical wiretap channel model consisting of a transmitter, a legal receiver and an adversary (illegal receiver), early works have proven that it is possible to achieve positive secrecy rate using multiple antenna techniques, such as beamforming, at the transmitter. In this thesis, we focus on two types of malicious behaviors of the adversary: passive eavesdropping and active attack. For the passive eavesdropping, we first consider the multi-input-single-output (MISO) wiretap channel, in which the legitimate transmitter utilizes the artificial noise aided precoding strategy to maximize the achievable secrecy rate of the channel. Both scenarios of known and unknown channel state information (CSI) for the eavesdropper channels are considered. By deriving the closed-form expression of ergodic secrecy rate, we prove that there exists an optimal power ratio between the information signal and the artificial noise. We then extend our study to a four-node fading channel model in a wireless relay network, which includes two single-antenna users, one single-antenna eavesdropper and one relay node equipped with multiple antennas. By studying the decode-and-forward (DF) scheme, cooperative jamming (CJ) scheme and one proposed hybrid relay scheme, relay-and-jamming (RJ), we aims to find the optimal relay scheme with the condition that the transmitter and the relay node are under individual power constraints and the CSI of the illegitimate channel is only statistically known. Our analysis shows that the hybrid RJ scheme is optimal when the transmitter has a relatively small power budget and/or the transmitter is far away from the intended receiver. Besides the passive eavesdropping, the adversary could also choose the active attack. The pilot spoofing attack is one active attack conducted by the adversary during the channel estimation phase of the legitimate transmission. In practical systems, the pilot signals are usually known \textit{a priori} and repeatedly used information. In this attack, an intelligent adversary spoofs the transmitter on the estimation of CSI by sending the identical pilot signal as the legitimate receiver. By doing so, the adversary could obtain a larger channel rate in the data transmission phase, and also drastically weaken the strength of the received signal at the legitimate receiver if the adversary utilizes large enough power. Due to the serious consequences caused by such an attack, we first propose an energy ratio detector (ERD) that explores the asymmetry of received signal power levels at the transmitter and the legitimate receiver when the attack occurs. Our analysis shows that the ERD could provide very high probability of detection with certain requirement on the false alarming probability. Furthermore, we design a two-way training based scheme to provide not only attack detection but also secure transmission. The two-way training based detector (TWTD) exploits the intrusive component created by the adversary, followed by a secure beamforming-assisted data transmission. In addition to the good detection performance, our scheme could estimate both legitimate and illegitimate channels, with which the beamforming could be designed for data transmission.
We introduce an opportunistic scheduling to enhance the physical layer security with transmit antenna selection (TAS) in multiuser environment. We consider a wireless communication system composed of a single transmitter and multiple legitimate users in the presence of several eavesdroppers with each node having multiple antennas under quasi-static Rayleigh fading channel. The transmitter selects the best transmitting antenna and the best user to maximize signal-to-noise ratio (SNR) at the selected user. The user and eavesdropper can employ either selection combining (SC) or maximal ratio combining (MRC) to combine the received signals. New closed-form expressions for probability of positive secrecy and outage are derived. Moreover, asymptotic analysis reveals the outage diversity gain and array gain for the proposed scheme. The impact of number of users, eavesdroppers, and antennas on secrecy performance are clearly demonstrated with mathematical analysis and numerical results.
The problem of resource allocation for energy-efficient secure communications in multiple-input single-output (MISO) systems is investigated, wherein a malicious user tries to eavesdrop the communication between two legitimate users. The legitimate transmitter has multiple antennas, whereas the eavesdropper and the receiver have a single antenna. Unlike most papers dealing with physical layer security, in this paper the goal of the resource allocation process is not to maximize the secrecy capacity, but rather to maximize the secrecy energy efficiency (SEE), defined as the ratio between the secrecy capacity and the total consumed power. This performance metric is measured in bit/Hz/Joule, and represents the amount of information bits that can be reliably and securely transmitted per unit of bandwidth and per Joule of consumed energy. The energy-efficient resource allocation is carried out considering three different channel state information (CSI) scenarios as to the channel from the legitimate transmitter to the eavesdropper, namely perfect CSI, partial CSI, and statistical CSI.