The security of traditional wireless communication relies on upper layer encryption and cannot protect the security of the physical layer. In order to overcome the shortcomings of traditional wireless communication system encryption, artificial noise generation and random precoder are used to study the secure transmission method of large-scale multiple input multiple output(MIMO) downlink system under relay cooperation. The estimated channel state information is derived and the rate expression is derived,and then the confidentiality rate on the user node is analyzed. The performance gap is analyzed and compared for the minimum mean square error precoder(MMSE) and zero forcing(ZF) precoder at the base station. Theoretical analysis and simulation results show that this method can design a secure physical layer transmission strategy for large-scale MIMO relay systems, and the MMSE precoder exhibits better security performance than the ZF precoder.
The security of traditional wireless communication relies on upper layer encryption and cannot protect the security of the physical layer. In order to overcome the shortcomings of traditional wireless communication system encryption, artificial noise generation and random precoder are used to study the secure transmission method of large-scale multiple input multiple output(MIMO) downlink system under relay cooperation. The estimated channel state information is derived and the rate expression is derived,and then the confidentiality rate on the user node is analyzed. The performance gap is analyzed and compared for the minimum mean square error precoder(MMSE) and zero forcing(ZF) precoder at the base station. Theoretical analysis and simulation results show that this method can design a secure physical layer transmission strategy for large-scale MIMO relay systems, and the MMSE precoder exhibits better security performance than the ZF precoder.
In this paper, secure transmission strategies for the relay-assisted massive multiple-input multiple-output (MIMO) downlink are investigated by using artificial noise (AN) generation and by exploiting the excess degrees-of-freedom through the random and null-space based precoders. The achievable rate expressions are derived for the estimated channel state information, and hence, the detrimental effects of channel estimation errors in designing precoders are quantified. Specifically, the achievable secrecy rate at the relayed user nodes is derived in closed-form, and thereby, the performance gap between the random and null-space based precoders is investigated. Our performance analysis reveals that the AN generation by using random precoders can be employed to design secure physical layer transmission strategies for the relay-assisted massive MIMO downlink systems. The AN generation can be useful in the finite antenna regime for guaranteeing physical layer security in the base-station-to-relay hop of the relay-assisted massive MIMO downlink. Although the AN generated at the base-station propagates to the relay-to-user hop via amplify-and-forward operation at the relay, sophisticated security provisions are needed to secure the end-to-end transmission when the relay is equipped with finitely many antennas. Consequently, the performance gap between the random and null-space based precoders gradually diminishes in the limit of infinitely many base-station antennas. Nevertheless, the achievable secrecy rate steadily vanishes with an increasing number of antennas at the passive eavesdropper.
In this paper, a secure communication system model for massive multiple-input multiple-output (MIMO) relay networks is investigated. Specifically, physical layer secure transmission is provisioned in multi-user relay networks by employing massive MIMO, linear precoder/detectors and artificial noise generation in the presence of a passive multi-antenna eavesdropper. In particular, the achievable asymptotic secrecy rate for infinitely many relay antennas is derived. The use of random artificial noise shaping matrices is advocated for massive MIMO relays for the sake of reducing the system implementation complexity. The effects of the numbers of antennas at the relay and the eavesdropper in achieving secure communication are investigated by comparing the corresponding achievable secrecy rates.
Massive Multiple-Input Multiple-Output (MIMO) has become a crucial enabling technology for 5G and beyond, providing previously unheard-of increases in energy and spectrum efficiency. It is still difficult to guarantee secure communication in these systems, particularly when it comes to passive eavesdroppers whose base station is unaware of their channel state information. By taking advantage of the inherent randomness of wireless channels, Physical Layer Security (PLS) offers a promising paradigm; however, its efficacy in massive MIMO is heavily reliant on resource allocation and transmission strategies. In this work, the performance of secure transmission schemes, such as Maximum Ratio Transmission (MRT), Zero-Forcing (ZF), and Artificial Noise (AN)-aided beamforming, is examined when passive eavesdroppers are present. This work will use extensive Monte Carlo simulations to assess important performance metrics such as energy efficiency, secrecy outage probability, and secrecy sum rate under different system parameters (e.g., number of antennas, Signal-to-Noise Ratio (SNR), power allocation). The results aim to provide comparative insight into the strengths and limitations of different PLS strategies and to highlight open research directions to design scalable, energy-efficient, and robust secure transmission techniques in future 6G networks.
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.
Physical-layer secure is an important issue for untrusted relay systems. In this paper, we investigate secure precoding design for non-regenerative multiple-input multiple-output untrusted two-way relay systems, where artificial noise (AN) is applied at the source and the relay is untrusted. We aim to maximize the secrecy sum rate by jointly designing the source's signal and AN precoders and the relay's precoder, under the sources and relay transmit power constraints. We consider two scenarios that perfect and imperfect channel state information of all the channels is available. For the former, we convert the secure precoding problem to a difference of convex programming and develop a constrained concave convex procedure based iterative algorithm which can obtain a local optimal solution. We also provide asymptotic analysis on the maximum secrecy sum rate when the relay transmit power approaches infinity, and propose alternating optimization method to compute asymptotic optimal precoders. For the latter, we model the channel uncertainties by using worst-case criterion and propose the weighted minimum mean square error based method to solve the robust secure precoding problem. Numerical simulations are presented to show the effectiveness of our proposed schemes.
In this paper, secrecy communications with cooperative jamming in a two-hop one-way untrusted relay system is studied. Assuming that all nodes are equipped with multiple antennas, new precoding designs are proposed to increase the secrecy capacity. Two situations are considered, namely only designing precoding vector for jamming signal when user signal has been determined, and designing precoding vectors for both user and jamming signals by jointly considering the source node. For each situation, two alignment algorithms are proposed, namely zero-forcing-based (ZF) alignment algorithm and minimum-mean-squared-error-based (MMSE) alignment algorithm. Both algorithms are designed to ensure that the equivalent wiretap channel matrix forms two aligned vectors. The channel vector from the destination node is designed to be aligned with that from the source node, so that the eavesdropping node cannot decode user signals. Analytical and simulation results show that all proposed scheme can achieve secure communication, and the MMSE algorithm performs better than the ZF. In addition, the destination-relay link has greater impact on the secrecy performance than the relay-destination link.