Physical Layer Securities in Wireless Communication Systems

Due to the tremendous advancement in the semiconductor and microelectronics technologies, wireless technologies have blossomed in the recent decades. The large scale deployment of wireless networks have revolutionized the way people live. They bring a great deal of convenience and enjoyment to us. Undoubtedly, we have become more and more dependent on these wireless technologies. These include cellular and radio frequency identification (RFID) technologies. However, with great technologies also come great risks and threats. Unlike wired transmissions, the nature of wireless transmissions result in the transmitted signals over the channel can be easily intercepted and eavesdropped by malicious adversaries. Therefore, security and privacy of the employed wireless communication system are easily compromised compared to the wired communication system. Consequently, securing wireless network has attracted a lot of attention in the recent years and it has huge practical implications. Securing wireless networks can be and indeed are performed at all layers of a network protocol stack. These include application, network, data link and physical (PHY) layers. The primary focus of our research is on the PHY layer approaches for securing and attacking wireless networks. In this thesis, we identify three research topics and present our results. They are: 1) PHY layer phase encryption (P-Enc) vs XOR encryption (XOR-Enc); 2) PHY layer signaling scheme to ensure the confidentiality of the transmitted messages from the tag to the reader in RFID systems. 3) Active eavesdropping attack framework under frequency hopping spread spectrum (FHSS) RFID systems. In the first work, we introduce a new OFDM encryption scheme which we call OFDM-Enc, different from convectional XOR-Enc, OFDM-Enc encrypts data by multiplying each of in-phase and quadrature component of the time domain OFDM symbol by a keystream bit. We then perform an initial investigation on the security of OFDM-Enc. We show it is secure against all attacks that are considered in this work. Moreover, depending on the modulation type, OFDM would potentially reduce the keystream size required for encryption, while still achieving the required security level. We also conduct simulations to compare OFDM-Enc with conventional XOR-Enc. We show indeed OFDM-Enc is viable and can achieve good performances. Then we extend OFDM-Enc to general communication systems. Since the encryption is essentially done by changing the phase of the data constellations, we just adopt the term P-Enc. In addition, we form mathematical formulations in order to compare between P-Enc and XOR-Enc in terms of efficiency, security and hardware complexity. Furthermore, we show P-Enc at the PHY layer can prevent traffic analysis attack, which cannot be prevented with the upper layer encryptions. Finally, simulations are conducted again to compare the performance of P-Enc and XOR-Enc. In the second work, we are interested in protecting tag's data from leaking or being compromised to malicious adversaries. As discussed earlier, due to the nature of wireless channels, communications between the tag and the reader is susceptible to eavesdropping. The conventional method uses encryption for confidentiality protection of transmitted messages. However, this requires to pre-share keys between the reader and the tag. As a result, a key management and distribution system needs to be put in place. This introduces heavy system overhead. In this work, we first propose a new PHY layer RFID privacy protection method which requires no pre-shared keys and would achieve the same goal. We also perform theoretical analysis to first validate of our proposed scheme. Finally, we conduct experiments to further verify the feasibility our proposed scheme under the passive eavesdropping attack model. In the third work, we present a new attack on the FHSS RFID system called active eavesdropping attack. In most semi-passive and passive RFID systems, tag to reader communications are accomplished via backscattering modulation. This implies the tag is not required to identify the frequency of the legitimate reader's transmitted signal, it simply responds to a reader's query by setting its impedance in the circuitry to low and high to represent bit 1 and 0. The attacker exploits this design weakness of the tag and broadcasts his own continuous wave (CW) at a different frequency. Consequently, the eavesdropper receives two copies of responses: one from his own broadcasted CW and one from reader's CW. We perform theoretical analysis to show the optimal strategy for the attacker in terms of the decoding error probability. Finally, we conduct simulations and experiments to verify with our theoretical results

Space-time coding with imperfect channel estimates.

This thesis proposes a new decision rule for the space-time block (STB) coded wireless communication system in Rayleigh faded channel with partial knowledge of the channel state information (CSI). Also proposed is the frame-based iterative channel estimation algorithm for the same system with no knowledge of CSI. This thesis proposes a simpler modified decision rule which performs better in terms of bit error rate than the existing state-of-the-art technique using gray coded 16-QAM scheme with 2 transmitter antennas and 1 receiver antenna. The thesis also proposes the frame-based iterative channel estimator when no knowledge of CSI is available at the receiver. The algorithm exploits the inherent orthogonal property of the STB code. The BER performance reaches within 1 dB of the perfect knowledge of CSI for the simplest case with BPSK (Binary Phase Shift Keying) modulation having 2 transmitter antennas and 1 receiver antenna. The proposed algorithm outperforms the state-of-the-art iterative decision-directed channel tracking algorithm at the expense of increased receiver complexity. (Abstract shortened by UMI.)Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .M67. Source: Masters Abstracts International, Volume: 43-03, page: 0940. Adviser: Behnam Shahrrava. Thesis (M.A.Sc.)--University of Windsor (Canada), 2004

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

Satellite Communications

This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking

Spectrally and Energy Efficient Wireless Communications: Signal and System Design, Mathematical Modelling and Optimisation

This thesis explores engineering studies and designs aiming to meeting the requirements of enhancing capacity and energy efficiency for next generation communication networks. Challenges of spectrum scarcity and energy constraints are addressed and new technologies are proposed, analytically investigated and examined. The thesis commences by reviewing studies on spectrally and energy-efficient techniques, with a special focus on non-orthogonal multicarrier modulation, particularly spectrally efficient frequency division multiplexing (SEFDM). Rigorous theoretical and mathematical modelling studies of SEFDM are presented. Moreover, to address the potential application of SEFDM under the 5th generation new radio (5G NR) heterogeneous numerologies, simulation-based studies of SEFDM coexisting with orthogonal frequency division multiplexing (OFDM) are conducted. New signal formats and corresponding transceiver structure are designed, using a Hilbert transform filter pair for shaping pulses. Detailed modelling and numerical investigations show that the proposed signal doubles spectral efficiency without performance degradation, with studies of two signal formats; uncoded narrow-band internet of things (NB-IoT) signals and unframed turbo coded multi-carrier signals. The thesis also considers using constellation shaping techniques and SEFDM for capacity enhancement in 5G system. Probabilistic shaping for SEFDM is proposed and modelled to show both transmission energy reduction and bandwidth saving with advantageous flexibility for data rate adaptation. Expanding on constellation shaping to improve performance further, a comparative study of multidimensional modulation techniques is carried out. A four-dimensional signal, with better noise immunity is investigated, for which metaheuristic optimisation algorithms are studied, developed, and conducted to optimise bit-to-symbol mapping. Finally, a specially designed machine learning technique for signal and system design in physical layer communications is proposed, utilising the application of autoencoder-based end-to-end learning. Multidimensional signal modulation with multidimensional constellation shaping is proposed and optimised by using machine learning techniques, demonstrating significant improvement in spectral and energy efficiencies

Algorithms for 5G physical layer

There is a great activity in the research community towards the investigations of the various aspects of 5G at different protocol layers and parts of the network. Among all, physical layer design plays a very important role to satisfy high demands in terms of data rates, latency, reliability and number of connected devices for 5G deployment. This thesis addresses he latest developments in the physical layer algorithms regarding the channel coding, signal detection, frame synchronization and multiple access technique in the light of 5G use cases. These developments are governed by the requirements of the different use case scenarios that are envisioned to be the driving force in 5G. All chapters from chapter 2 to 5 are developed around the need of physical layer algorithms dedicated to 5G use cases. In brief, this thesis focuses on design, analysis, simulation and he advancement of physical layer aspects such as 1. Reliability based decoding of short length Linear Block Codes (LBCs) with very good properties in terms of minimum hamming istance for very small latency requiring applications. In this context, we enlarge the grid of possible candidates by considering, in particular, short length LBCs (especially extended CH codes) with soft-decision decoding; 2. Efficient synchronization of preamble/postamble in a short bursty frame using modified Massey correlator; 3. Detection of Primary User activity using semiblind spectrum sensing algorithms and analysis of such algorithms under practical imperfections; 4. Design of optimal spreading matrix for a Low Density Spreading (LDS) technique in the context of non-orthogonal multiple access. In such spreading matrix, small number of elements in a spreading sequences are non zero allowing each user to spread its data over small number of chips (tones), thus simplifying the decoding procedure using Message Passing Algorithm (MPA)

Journal of Telecommunications and Information Technology, 2001, nr 3

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