Due to the broadcast nature of radio propagation, the wireless air interface is open and accessible to both authorized and illegitimate users. This completely differs from a wired network, where communicating devices are physically connected through cables and a node without direct association is unable to access the network for illicit activities. The open communications environment makes wireless transmissions more vulnerable than wired communications to malicious attacks, including both the passive eavesdropping for data interception and the active jamming for disrupting legitimate transmissions. Therefore, this paper is motivated to examine 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. Several physical-layer security techniques are reviewed and compared, including information-theoretic security, artificial-noise-aided security, security-oriented beamforming, diversity-assisted security, and physical-layer key generation approaches. Since a jammer emitting radio signals can readily interfere with the legitimate wireless users, we also introduce the family of various jamming attacks and their countermeasures, 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.

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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.

/pdf/a-survey-on-wireless-security-technical-challenges-recent-k705wofne7.pdf

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

We address the problem of interference aware routing in multi-radio infrastructure mesh networks wherein each mesh node is equipped with multiple radio interfaces and a subset of nodes serve as Internet gateways. We present a new interference aware routing metric - iAWARE that aids in finding paths that are better in terms of reduced interflow and intra-flow interference. We incorporate this metric and new support for multi-radio networks in the well known AODV routing protocol to design an enhanced AODV-MR routing protocol. We study the performance of our new routing metric by implementing it in our wireless testbed consisting of 12 mesh nodes. We show that iAWARE tracks changes in interfering traffic far better than existing well known link metrics such as ETT and IRU. We also demonstrate that our AODV-MR protocol delivers increased throughput in single radio and two radio mesh networks compared to similar protocol with WCETT and MIC routing metrics. We also show that in the case of two radio mesh networks, our metric achieves good intra-path channel diversity.

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Interference aware routing in multi-radio wireless mesh networks

Physical layer security (PLS) has emerged as a new concept and powerful alternative that can complement and may even replace encryption-based approaches, which entail many hurdles and practical problems for future wireless systems. The basic idea of PLS is to exploit the characteristics of the wireless channel and its impairments including noise, fading, interference, dispersion, diversity, etc. in order to ensure the ability of the intended user to successfully perform data decoding while preventing eavesdroppers from doing so. Thus, the main design goal of PLS is to increase the performance difference between the link of the legitimate receiver and that of the eavesdropper by using well-designed transmission schemes. In this survey, we propose a conceptual, generic, and expandable framework for classifying the existing PLS techniques against wireless passive eavesdropping. In this flexible framework, the security techniques that we comprehensively review in this treatise are divided into two primary approaches: signal-to-interference-plus-noise ratio-based approach and complexity-based approach. The first approach is classified into three major categories: first, secrecy channel codes-based schemes; second, security techniques based on channel adaptation; third, schemes based on injecting interfering artificial (noise/jamming) signals along with the transmitted information signals. The second approach (complexity-based), which is associated with the mechanisms of extracting secret sequences from the shared channel, is classified into two main categories based on which layer the secret sequence obtained by channel quantization is applied on. The techniques belonging to each one of these categories are divided and classified into three main signal domains: time, frequency and space. For each one of these domains, several examples are given and illustrated along with the review of the state-of-the-art security advances in each domain. Moreover, the advantages and disadvantages of each approach alongside the lessons learned from existing research works are stated and discussed. The recent applications of PLS techniques to different emerging communication systems such as visible light communication, body area network, power line communication, Internet of Things, smart grid, mm-Wave, cognitive radio, vehicular ad-hoc network, unmanned aerial vehicle, ultra-wideband, device-to-device, radio-frequency identification, index modulation, and 5G non-orthogonal multiple access based-systems, are also reviewed and discussed. The paper is concluded with recommendations and future research directions for designing robust, efficient and strong security methods for current and future wireless systems.

Classifications and Applications of Physical Layer Security Techniques for Confidentiality: A Comprehensive Survey

In this article we discuss the state of the art of (mobile) multihop ad hoc networking. This paradigm has often been identified with the solutions developed inside the IETF MANET working group, and for this reason it is called the MANET paradigm. However, they do not coincide, and in the last decade they clearly diverged. In this article, we start from the reasons why the MANET paradigm did not have a major impact on computer communications, and we discuss the evolution of the multihop ad hoc networking paradigm by building on the lessons learned from the MANET research. Specifically, we analyze four successful networking paradigms, mesh, sensor, opportunistic, and vehicular networks, that emerged from the MANET world as a more pragmatic application of the multihop ad hoc networking paradigm. We also present the new research directions in the multihop ad hoc networking field: peoplecentric networking, triggered by the increasing penetration of the smartphones in everyday life, which is generating a people-centric revolution in computing and communications.

Mobile ad hoc networking: milestones, challenges, and new research directions

Generating a secret key between two parties by extracting the shared randomness in the wireless fading channel is an emerging area of research. Previous works focus mainly on single-antenna systems. Multiple-antenna devices have the potential to provide more randomness for key generation than single-antenna ones. However, the performance of key generation using multiple-antenna devices in a real environment remains unknown. Different from the previous theoretical work on multiple-antenna key generation, we propose and implement a shared secret key generation protocol, Multiple-Antenna KEy generator (MAKE) using off-the-shelf 802.11n multiple-antenna devices. We also conduct extensive experiments and analysis in real indoor and outdoor mobile environments. Using the shared randomness extracted from measured Received Signal Strength Indicator (RSSI) to generate keys, our experimental results show that using laptops with three antennas, MAKE can increase the bit generation rate by more than four times over single-antenna systems. Our experiments validate the effectiveness of using multi-level quantization when there is enough mutual information in the channel. Our results also show the trade-off between bit generation rate and bit agreement ratio when using multi-level quantization. We further find that even if an eavesdropper has multiple antennas, she cannot gain much more information about the legitimate channel.

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Exploiting Multiple-Antenna Diversity for Shared Secret Key Generation in Wireless Networks

Measurement of available bandwidth in a network has always been a topic of great interest. This knowledge can be applied to a wide variety of applications and can be instrumental in providing Quality of Service to end users. Several probe-based tools have been proposed to measure available bandwidth in wired networks. However, the performance of these tools in the realm of wireless networks has not been evaluated extensively. In recent years, there has also been some work on estimating bandwidth in wireless networks via passively monitoring the channel and determining the 'busy' and 'idle' periods. However, such tech- niques have primarily been evaluated via simulations only. In this work, we perform an extensive experimental comparison study of both passive and active bandwidth estimation tools for 802.11-based wireless mesh networks. We investigate the impact of interference, packet loss, and 802.11 rate-adaptation, on the performance of these tools. Our results indicate that for wireless networks, a passive technique provides much greater accuracy than the probe-based tools.

Experimental Comparison of Bandwidth Estimation Tools for Wireless Mesh Networks

Wireless simulators provide full control to researchers in investigating traffic flow behavior, but do not always reflect real-world scenarios. Although previous work pointed out such shortages are due to the limitation of radio propagation models in the simulators, it is still unclear how these imperfect models affect network behavior and to what degree. In this paper, we quantify network behavioral differences between simulations and real-world testbed experiments. We compare and analyze the experimental results from indoor and outdoor experiments with the results from NS-2 and Qualnet simulations. We find that in the PHY layer, the distribution of received signal strength in experiments is usually different from simulation due to the antenna diversity. However, path loss, which is regarded as a dominating factor in simulator channel modeling, can be configured to match the real-world behavior. For the MAC layer, increasing traffic load on a flow may cause significant performance degradation in experiments, but it is not the case in simulations. Interference is inadequately captured in simulations and cannot show the flow level unfairness phenomenon. In the network layer, a few dominant routes exist in testbed experiments while routes in simulations are less stable. These findings give the wireless research community an improved overview about the differences between simulations and testbed experiments. They will help researchers to choose between simulations and experiments according to their particular research requirements.

Comparing simulation tools and experimental testbeds for wireless mesh networks

Wireless Mesh Networks are being deployed everywhere as an alternative to broadband connections. Their ease of setup and large coverage are attractive attributes. However, there are very few performance studies of mesh networks especially in the multiple channel arena. Our objective is to study the performance and characterize the 802.11b wireless mesh backbone as a linear topology with respect to multiple channel usage. We look at the relative performances of single and multiple channels, as well as the number of hops utilized. We introduce a number of communication flows into the network to study the interactions. Finally, we look at the physical placement of the antennas on an access point to determine its impact on performance. Several design decisions for the configuration of wireless mesh network deployments have been inferred from our experimental testbed.

Experimental characterization of an 802.11b wireless mesh network

Research in wireless mesh networks has been growing in recent years. Many testbeds have been created to study networking protocols in wireless mesh networks. In this work, we describe QuRiNet, an outdoor wide-area wireless mesh network deployed in a natural reserve. QuRiNet comprises of over 30 wireless nodes, spread over 2000 acres of wilderness. QuRiNet provides the backbone infrastructure for transporting ecological and environmental data from the natural reserve to the on-campus laboratories. Mesh nodes in QuRiNet are powered by solar energy, and comprise of multiple radios per node. Physical link distances in QuRiNet range from hundreds to thousands of meters. A parallel goal of deploying QuRiNet is to create a novel platform for advanced research in wireless mesh networks. In this report, we share our experiences in the deployment and maintenance of QuRiNet in its unique setting. We also describe various research efforts that have been leveraging the QuRiNet testbed. Several interesting measurement results are reported, along with the impact of various network configurations and technological variations on the functionality of the testbed. QuRiNet has been used for a variety of experimental studies including: channel assignment, network monitoring, and mobility studies. Current and future study plans include experimental evaluations of various security and reliability research.

Daniel Wu

Papers

Exploiting Multiple-Antenna Diversity for Shared Secret Key Generation in Wireless Networks

Experimental Comparison of Bandwidth Estimation Tools for Wireless Mesh Networks

Comparing simulation tools and experimental testbeds for wireless mesh networks

Experimental characterization of an 802.11b wireless mesh network

QuRiNet: A wide-area wireless mesh testbed for research and experimental evaluations