Elements of Information Theory (2nd ed.). Thomas M. Cover and Joy A. Thomas

Mobile data traffic will continue its tremendous growth in some markets, and has already resulted in an apparent radio spectrum scarcity. There is a strong need for more efficient methods to use spectrum resources, leading to extensive research on increasing spectrum reusability on flexible radio platforms. This study solves this problem in two sub topics, millimeter wave communication on wireless backhaul for spectrum reusability, and flexible prototyping radio platform using software-defined radio (SDR).
Wireless backhaul has received significant attention as a key technology affecting the development of future wireless cellular networks because it helps to easily deploy many small size cells, an essential part of a high capacity system. Millimeter wave is considered a possible candidate for cost-effective wireless backhaul. In the outdoor deployment using a millimeter wave, beamforming methods are key techniques to establish wireless links in the 60 GHz to 80 GHz to overcome pathloss constraints (i.e., rainfall effect and oxygen absorption). The millimeter wave communication system cannot directly access the channel knowledge. To overcome this, a beamforming method based on codebook search is considered. The millimeter wave communication cannot access channel knowledge, therefore alternatively a beamforming method based on a codebook search is considered. In the first part, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. Results show significant performance improvement with reduced search time.
In the second part of this study, SDR is discussed as an approach toward flexible wireless communication systems. Most layers of SDR are implemented by software. Therefore, only a software change is needed to transform the type of radio system. The translation of the signal processing into software performed by a regular computer opens up a huge number of possibilities at a reasonable price and effort. SDR systems are widely used to build prototypes, saving time and money. In this project, a robust wireless communication system in high interference environment was developed. For the physical layer (PHY) of the system, we implemented a channel sub-bandding method that utilizes frequency division multiplexing to avoid interference. Then, to overcome a further interfered channel, Direct Spread Spectrum System (DSSS) was considered and implemented. These prototyped testbeds were evaluated for system performance in the interference environment.

Millimeter wave beamforming for wireless backhaul and access in small cell networks and practical approaches in software-defined radio

The 5th-generation mobile communication system (5G) has higher security requirements than previous systems. Accordingly, international standard organizations, operators, and equipment manufacturers are focusing extensively on 5G security technology. This paper analyzes the security requirements of 5G business applications, network architecture, the air interface, and user privacy. The development trends of 5G security architecture are summarized, with a focus on endogenous defense architecture, which represents a new trend in 5G security development. Several incremental 5G security technologies are reviewed, including physical layer security, lightweight encryption, network slice security, user privacy protection, and block chain technology applied to 5G.

Overview of 5G security technology

Millimeter-wave (mmWave) frequency bands, which offer abundant underutilized spectral resources, have been explored and exploited in the past several years to meet the requirements of emerging wireless services highlighted by high data rates, ultrareliability, and ultralow delivery latency. Yet, the unique characteristics of mmWave, e.g., continuous wide bandwidth, large path, and penetration losses, along with hardware constraints, call for innovative technologies for mmWave communication. Recently, an extensive amount of work on mmWave communication has been carried out by researchers and practitioners from both academia and industry, and various technologies have been developed for mmWave communication systems to fulfill the full potential of mmWave frequency bands. In this article, we present a comprehensive survey of the standardization of mmWave communication, the latest progress and outcomes of the research on mmWave communication technologies, and the emerging applications of mmWave communication. In particular, we provide a timely and in-depth summary of the state-of-the-art technology specifications of mmWave communication with an emphasis on the physical (PHY) layer. Then, we elaborate on a number of well-established or promising antenna architectures in mmWave communication systems and investigate the enabling PHY layer transmission technologies. Finally, we show some existing and emerging applications of mmWave communication and discuss the potential open research issues.

A Survey of Millimeter-Wave Communication: Physical-Layer Technology Specifications and Enabling Transmission Technologies

Physical layer security is a promising approach that can benefit traditional encryption methods. The idea of physical layer security is to take advantage of the propagation medium’s features and impairments to ensure secure communication in the physical layer. This work introduces a comprehensive review of the main information-theoretic metrics used to measure the secrecy performance in physical layer security. Furthermore, a theoretical framework related to the most commonly used physical layer security techniques to improve secrecy performance is provided. Finally, our work surveys physical layer security research over several enabling 5G technologies, such as massive multiple-input multiple-output, millimeter-wave communications, heterogeneous networks, non-orthogonal multiple access, and full-duplex. We also include the key concepts of each of the technologies mentioned above. Also identified are future fields of research and technical challenges of physical layer security.

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Survey on physical layer security for 5G wireless networks

Millimeter wave (mm-wave) communications, especially mm-wave relay systems, have been considered as a key technology for next-generation wireless networks due to the rich spectrum resources. However, the problem of information leakage in mm-wave relay systems has not been well investigated. In this paper, artificial noise (AN) aided two-stage secure hybrid beamforming algorithm is proposed in MIMO mm-wave relay system from the perspective of physical layer security. In each time slot of the relay communications, the RF analog beamforming matrices are designed in the first stage, and baseband digital beamforming matrices are designed in the second stage. Through the proposed algorithm, the joint optimization is avoided and the feedback is reduced, which brings low complexity. Moreover, the AN is applied to fight against the eavesdropper by deteriorating the eavesdropping channel. The simulation results show that the proposed hybrid beamforming algorithm considerably improves the performance and achieves a balance between complexity and performance.

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Artificial Noise Aided Hybrid Analog-Digital Beamforming for Secure Transmission in MIMO Millimeter Wave Relay Systems

The secret key generation rate (SKGR) of current physical layer security methods is not high enough for practical requirements. A novel SKG method based on the cross multiplication (XM) of two-way random signals is proposed for TDD-MIMO system. The principle concealed beneath the XM method is found that the XM operation not only derives the common random source for both legitimate partners, but also employs new generated cross-terms due to bilinear operation to provide more measurements of the random source and more secret keys accordingly, which is essentially superior to the existing paired multiplication (PM) method. Then, the theoretical SKGR of two-way random signals is analyzed and it is validated that SKGR is determined by the randomness of the reciprocal channel and the two-way secure transmission rates collectively. Furthermore, SKGR of XM and PM methods are derived in closed-form respectively under infinite antenna condition and the former shows a linear increase with the channel coherence interval, which are also approximately valid for finite antenna. The innovative conclusion means the slow-changing property of some channel environments can be further exploited and the proposed XM method can be applied to solve the low SKGR problem in static or quasi-static channel environment such as IoT. Finally, the simulations verify the theoretical results and show that the XM method achieves several orders of magnitude higher SKGR than the PM method.

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Secret Key Generation With Cross Multiplication of Two-Way Random Signals

When the eavesdropping channel has a certain correlation with the legitimate channel, the physical layer key is susceptible to eavesdroppers. To ensure the security of the secret key, we propose a two-layer secure (TLS) quantization algorithm in this paper. First, we model the correlation between the distance and the channel correlation and derive the joint probability density function of channel phase and the key capacity. Then, we describe the detail of the TLS algorithm and prove the validity of our algorithm. Finally, we evaluate the performances of the TLS quantization algorithm using two parameters-key rate and bit disagreement rate. The Simulation results verify the effectiveness of the algorithm.

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A Two-Layer Secure Quantization Algorithm for Secret Key Generation With Correlated Eavesdropping Channel

To solve the problem that key is susceptible to eavesdroppers in the correlated channel scenarios, in this paper, we propose a native security scheme based on physical layer chain keys, which can be used for encryption and authentication. First, the physical layer chain key is generated by performing XOR operation on the updated key and the previous chain key, where the updated key is obtained by the current channel state information. The proposed scheme uses the chain key as the authentication root, and the authentication relationship is continuously transferred as the chain grows. Then, CRC is used to realize identity authentication and message verification simultaneously. Finally, the derivation based on information theory proves the security of chain key for encryption and authentication. The simulation results show that the proposed chain key scheme can leak less information and have a lower probability of successful attack than the traditional physical layer key in the correlated channel scenarios.

Native Security Scheme Based on Physical Layer Chain Key for Encryption and Authentication

In this paper, we investigate the physical layer key generation scheme in most realistic scenarios where the correlation between the legitimate channel and the eavesdropping channel is considered. To degrade the correlation and improve the key generation capacity, a physical layer key generation scheme through scrambling the correlated eavesdropping channel is proposed. Firstly, the artificial noise is sent superimposed over pilots from the legitimate transmitter to confuse the eavesdropper. The artificial noise precoding matrix is randomly selected from decomposed unitary matrices orthogonal to the legitimate channel resulting in having no effect on legitimate channel. Then, the vector quantization algorithm and the winnow algorithm are respectively applied to quantize the channel characteristic and negotiate the generated random sequences to generate the final key. To further support the performance, we next present a power optimization scheme allocated to sending the artificial noise to maximize the generated key capacity under the total transmission power constraint. Finally, simulation results are presented to validate the effectiveness of our proposed scheme.

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Xiaoming Xu

Papers

Artificial Noise Aided Hybrid Analog-Digital Beamforming for Secure Transmission in MIMO Millimeter Wave Relay Systems

Secret Key Generation With Cross Multiplication of Two-Way Random Signals

A Two-Layer Secure Quantization Algorithm for Secret Key Generation With Correlated Eavesdropping Channel

Native Security Scheme Based on Physical Layer Chain Key for Encryption and Authentication

Physical Layer Key Generation Scheme Through Scrambling the Correlated Eavesdropping Channel