Multiuser MIMO-OFDM for Next-Generation Wireless Systems

This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems

A Survey of Positioning Systems Using Visible LED Lights

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe

Wireless Device Authentication Techniques Using Physical-Layer Device Fingerprint

Due to the open nature of the radio signal propagation medium, wireless communication is inherently more vulnerable to various attacks than wired communication. Consequently, communication security is always one of the critical concerns in wireless networks. Given that the sophisticated adversaries may cover up their malicious behaviors through impersonation of legitimate devices, reliable wireless authentication is becoming indispensable to prevent such impersonation-based attacks through verification of the claimed identities of wireless devices. Conventional wireless authentication is achieved above the physical layer using upper-layer identities and key-based cryptography. As a result, user authenticity can even be validated for the malicious attackers using compromised security key. Recently, many studies have proven that wireless devices can be authenticated by exploiting unique physical-layer characteristics. Compared to the key-based approach, the possession of such physical-layer characteristics is directly associated with the transceiver\u27s unique radio-frequency hardware and corresponding communication environment, which are extremely difficult to forge in practice. However, the reliability of physical-layer authentication is not always high enough. Due to the popularity of cooperative communications, effective implementation of physical-layer authentication in wireless relay systems is urgently needed. On the other hand, the integration with existing upper-layer authentication protocols still has many challenges, e.g., end-to-end authentication. This dissertation is motivated to develop novel physical-layer authentication techniques in addressing the aforementioned challenges. In achieving enhanced wireless authentication, we first specifically identify the technique challenges in authenticating cooperative amplify-and-forward (AF) relay. Since AF relay only works at the physical layer, all of the existing upper-layer authentication protocols are ineffective in identifying AF relay nodes. To solve this problem, a novel device fingerprint of AF relay consisting of wireless channel gains and in-phase and quadrature imbalances (IQI) is proposed. Using this device fingerprint, satisfactory authentication accuracy is achieved when the signal-to-noise ratio is high enough. Besides, the optimal AF relay identification system is studied to maximize the performance of identifying multiple AF relays in the low signal-to-noise regime and small IQI. The optimal signals for quadrature amplitude modulation and phase shift keying modulations are derived to defend against the repeated access attempts made by some attackers with specific IQIs. Exploring effective authentication enhancement technique is another key objective of this dissertation. Due to the fast variation of channel-based fingerprints as well as the limited range of device-specific fingerprints, the performance of physical-layer authentication is not always reliable. In light of this, the physical-layer authentication is enhanced in two aspects. On the one hand, the device fingerprinting can be strengthened by considering multiple characteristics. The proper characteristics selection strategy, measurement method and optimal weighted combination of the selected characteristics are investigated. On the other hand, the accuracy of fingerprint estimation and differentiation can be improved by exploiting diversity techniques. To be specific, cooperative diversity in the form of involving multiple collaborative receivers is used in differentiating both frequency-dependent and frequency-independent device fingerprints. As a typical combining method of the space diversity techniques, the maximal-ratio combining is also applied in the receiver side to combat the channel degeneration effect and increase the fingerprint-to-noise ratio. Given the inherent weaknesses of the widely utilized upper-layer authentication protocols, it is straightforward to consider physical-layer authentication as an effective complement to reinforce existing authentication schemes. To this end, a cross-layer authentication is designed to seamlessly integrate the physical-layer authentication with existing infrastructures and protocols. The specific problems such as physical-layer key generation as well as the end-to-end authentication in networks are investigated. In addition, the authentication complexity reduction is also studied. Through prediction, pre-sharing and reusing the physical-layer information, the authentication processing time can be significantly shortened

A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends

This paper examines the security vulnerabilities and threats imposed by the inherent open nature of wireless communications and to devise efficient defense mechanisms for improving the wireless network security. We first summarize the security requirements of wireless networks, including their authenticity, confidentiality, integrity and availability issues. Next, a comprehensive overview of security attacks encountered in wireless networks is presented in view of the network protocol architecture, where the potential security threats are discussed at each protocol layer. We also provide a survey of the existing security protocols and algorithms that are adopted in the existing wireless network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term evolution (LTE) systems. Then, we discuss the state-of-the-art in physical-layer security, which is an emerging technique of securing the open communications environment against eavesdropping attacks at the physical layer. We also introduce the family of various jamming attacks and their counter-measures, including the constant jammer, intermittent jammer, reactive jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the integration of physical-layer security into existing authentication and cryptography mechanisms for further securing wireless networks. Finally, some technical challenges which remain unresolved at the time of writing are summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201