International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / IEEE 802.11e is an amendment of the medium-access control (MAC) layer of the standard for wireless local area networking IEEE 802.11. The goal of 802.11e is to provide 802.11 networks with Quality of Service (QoS). 802.11 has three physical layers (PHY) of practical importance: 802.11b, 802.11a, and 802.11g. 802.11a and 802.11g provide data rates between 6 and 54 Mbps, and 802.11b provides data rates of 5.5 Mbps and 11 Mbps. However these data rates are not the actual throughput. The actual throughput that a user will experience will be lower. The throughput depends on both the PHY and MAC layers. It is important to estimate what exactly is the throughput when the physical layer is 802.11a, 802.11b, or 802.11g, and the MAC layer is 802.11e. In other words, how does providing QoS change the throughput for each of the three physical layers? In this paper we provide answers to this problem. Analytic formulae are derived. The maximum achievable throughput and minimum delay involved in data transfers are determined. The obtained results have further significance for the design of high-throughput wireless protocols.

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This diploma thesis deals with analysis, modeling and simulation of the IEEE 802.11af wireless communication system on the physical layer. When designing the solution, it is necessary to understand in details the features and specifics of the IEEE 802.11af system. The work is primarily describes the transmitting part of the communication system with emphasis on processing IEEE 802.11af signal. Subsequently the block diagram and the basic model are created for the transmitting and receiving parts in SISO and MISO broadcast modes. The model is implemented with graphical user interface in the MATLAB programming environment. This application is used to explore the features and performance of the IEEE 802.11af based on its system parameters. System parameters are user configurable what allows to simulate different scenarios. The application also supports simulation of fading channel.

Tato diplomová práce se zabývá analýzou, návrhem a simulací modelu fyzické vrstvy bezdrátového komunikačního systému IEEE 802.11af. V práci je především popsána vysílací část komunikačního systému s důrazem na zpracování IEEE 802.11af signálu. Následně je vytvořeno blokové schéma a model pro vysílací a přijímací části ve vysílacích módech SISO a MIMO. Model je realizován s grafickým uživatelským rozhraním v programovém prostředí MATLAB. Vytvořená aplikace slouží k prozkoumání vlastností IEEE 802.11af modelu na základě jeho systémových parametrů. Systémové parametry jsou volitelné uživatelem a aplikace poskytuje možnost simulace různých přenosových scénářů.

Our world of people and objects is on the verge of transforming to a world of highly-interconnected wireless devices. Incredible advances in wireless communications, hardware design, and power storage have facilitated hasty spread of wireless technologies in human life. In this new world, individuals are often identified and reached via one or multiple wireless devices that they always carry (e.g., smartphones, smart wearable, implantable medical devices, etc.), and their biometrics identities are replaced by their digital fingerprints. In near future, vehicles will be controlled and monitored via wireless monitoring systems and various physical objects (e.g., home appliance and retail store items) will be connected to the Internet. The list of these changes goes on. Unfortunately, as different aspects of our lives are being immerged in and dependent to wireless devices and services, we will become more vulnerable to wireless service/connection interruptions due to adversarial behavior and our privacy will become more potent to be exposed to adversaries. An adversary can learn the procedures of a wireless system and analyze its stages, and accordingly, launch various attacks against the operations of the system or the privacy of the people. Existing data confidentiality and integrity services (e.g., advanced encryption algorithms) have been able to prevent the leakage of users' messages. However, in wireless networks, even when upper-layer payloads are encrypted, the users' privacy and the operation of a wireless network can be threatened by the leakage of transmission attributes at the physical (PHY) layer. Examples of these attributes are payload size, frequency offset (FO), modulation scheme, and the transmission rate. These attributes can be exploited by an adversary to launch passive or active attacks. A passive attacker may learn about the interests, sexual orientation, political views, and patentable ideas of the user through analyzing these features, whereas an active attacker exploits captured attributes to launch selective packet jamming/dropping and disrupt wireless services. These call for novel privacy preserving techniques beyond encryption. In this dissertation, we study the vulnerability of current wireless systems to the leakage of transmission attributes at the PHY layer and propose several schemes to prevent it. First, we design and experimentally demonstrate with USRPs an energy-efficient and highly disruptive jamming attack on the FO estimation of an OFDM system. OFDM is the core multiplexing scheme in many modern wireless systems (e.g., LTE/5G and 802.11a/n/ac) and is highly susceptible to FO. FO is the difference in the operating frequencies of two radio oscillators. This estimation is done by the receiver using the publicly-known frame preamble. We show that the leakage of FO value via the preamble can facilitate an optimally designed jamming signal without needing to know the channel between the transmitter and the legitimate receiver. Our results show that the jammer can guarantee a successful attack even when its power is slightly less than the transmitter's power. We then propose four mitigation approaches against the proposed FO attack. Next, we consider certain transmission attributes that are disclosed via unencrypted PHY/MAC headers. Example of these attributes are payload size, transmission rate, and MAC addresses. Beyond unencrypted headers, the adversary can estimate the frame size and transmission rate through identifying the payload's modulation scheme and measuring the transmission time. To prevent the leakage of these attributes, we propose Friendly CryptoJam scheme, which consists of three components: First, a modulation-aware encryption scheme to encrypt the headers. Second, an efficient modulation obfuscation techniques. Specifically, the proposed modulation obfuscation scheme embeds the modulation symbols of a frame's payload into the constellation of the highest-order modulation scheme supported by the system. Together with effective PHY/MAC header encryption at the modulation level, the proposed obfuscation scheme hides the transmission rate, payload size, and other attributes announced in the headers while avoiding any BER performance loss. Compared with prior art, Friendly CryptoJam enjoys less complexity and less susceptibility to FO estimation errors. The third component is a novel PHY-level identification method. To facilitate PHY/MAC header encryption when a MAC layer sender identifier cannot be used (e.g., due to MAC address encryption), we propose two preamble-based sender identification methods, one for OFDM and one for non-OFDM systems. A sender identifier is special message that can be embedded in the frame preamble. The extent of the applications of our embedding scheme goes beyond identifier embedding and include embedding part of the data frame, the sender's digital signature, or any meta-data that the sender provides. Our message embedding method can further be used to mitigate the FO estimation attack because the jammer can no longer optimize its jamming signal with respect to a fixed preamble signal. In addition, we considered friendly jamming technique in a multi-link/hop network to degrade the channels of the eavesdroppers and prevent successful decoding of the headers, while minimizing the required jamming power by optimally placing the friendly jamming devices.

Dans le contexte de l'Internet des Objets (IoT), on estime à plus de 10% la proportion de connections réalisées via les réseaux longue portée bas débit, représentant ainsi plusieurs milliards d’objet connectés. Afin de satisfaire les exigences en termes de sensibilité et de réduction du débit, deux approches sont généralement envisagées : l’approche bande étroite, et l’approche faible efficacité spectrale. En comparant les performances des systèmes existants à la limite théorique issue de la théorie de l'information et démontrée par Shannon, on constate qu’un gain en performance est atteignable, tout en travaillant toujours à de faibles niveaux de sensibilité. La théorie de l'information permet d'affirmer qu'un compromis entre l'efficacité spectrale et l'efficacité énergétique doit toujours être fait. Ainsi, une haute efficacité énergétique s'obtiendra au détriment d'une efficacité spectrale faible. A l'inverse, un système fonctionnant à une haute efficacité spectrale devra utiliser plus d'énergie pour transmettre le même nombre de bits et atteindre le même taux d'erreur.Ce travail s’intéresse à l’approche faible efficacité spectrale. En partant des modulations orthogonales, qui permettent d’atteindre la limite théorique de Shannon à des efficacités spectrales très faibles, et des processus turbo, qui atteignent d’excellentes performances à des efficacités spectrales élevées, l’utilisation conjointe d’une modulation orthogonale et d'un code correcteur associés à un récepteur itératif dans une technique dénommée Turbo-FSK est étudiée. Les différents paramètres de la technique sont optimisés en utilisant un outil classique des processus itératifs, l’Extrinsic Information Transfer (EXIT) chart. Les performances mesurées démontrent que la technique permet bien d’atteindre de très faibles niveaux de sensibilité et répond aux critères des réseaux longue portée bas débit. Cependant, la technique ne dispose de point de fonctionnement qu’à de très faibles valeurs d’efficacité spectrale : pour certaines applications ou si la portée nécessaire est réduite, il peut être bénéfique pour le système d’augmenter son efficacité spectrale. Ceci est rendu possible grâce à l’introduction d’une composante linéaire dans l’alphabet de modulation et d’un mécanisme de poinçonnage spécifique à la technique dans une version flexible appelée Coplanar Turbo-FSK. L’étude de l’influence des paramètres et des performances sur un canal à bruit blanc additif gaussien permet en effet de conclure sur la flexibilité de l’efficacité spectrale du système, tout en fonctionnant proche de la limite théorique. Finalement, l’étude jusqu’ici théorique est étendue à un contexte plus pratique, où des canaux sélectifs en fréquences sont considérés. Une encapsulation du système utilisant une architecture OFDM est considérée, et différentes mesures caractéristiques des systèmes de télécommunication sont évaluées. Les résultats sont confrontés à la solution Narrow-Band IoT proposée par l’organisme 3GPP et démontrent ici encore le potentiel de la solution Turbo-FSK pour les réseaux longue portée bas débit. / More than 10% of the Internet-of-Things (IoT) connections are expected to be realized through Low Power Wide Area (LPWA) networks, representing several billions of connected devices. Several industrial solutions have been developed and a standardization process is ongoing. The low levels of sensitivity and low data rate required for the long range communication are achieved by the means of two strategies: a narrow-band strategy and a low spectral efficiency strategy. Considering the limits of the information theory, additional gains in the communication's energy efficiency can be achieved. Nonetheless, a trade-off between spectral efficiency and energy efficiency should always be made. Reliable transmission with high energy efficiency will necessarily result in poor spectral efficiency, and in comparison, a system with a higher spectral efficiency has to consume more energy to transmit the same amount of bits with the same arbitrary level of error.This work considers the low spectral efficiency strategy. The combination of orthogonal modulations and a powerful channel code is studied. The scheme, so-called Turbo-FSK, associates the low spectral efficiency of Frequency Shift Keying (FSK) with the energy efficiency gain of a turbo receiver. Low levels of spectral efficiency can be achieved while optimizing the use of the available resource. The parameters of the scheme are optimized using a classic tool for iterative receivers, the Extrinsic Information Transfer (EXIT) chart. Performance of Turbo-FSK compared to existing LPWA solutions demonstrates the potential of the proposed solution to achieve low levels of sensitivity and to outperform existing schemes. However, the restrictions on low levels of spectral efficiency reduces the number of possible applications for the scheme. By introducing a linear component in the alphabet and a puncturing procedure, flexibility in spectral efficiency is achieved. A large range of spectral efficiencies can be obtained while maintaining performance close to the channel capacity theoretical limit. Eventually, more practical scenarios are considered for evaluating the performance of the scheme. Frequency selective channels are considered and an encapsulation in a Fast Fourier Transform (FFT) based system is implemented. Various indicators are studied and the Turbo-FSK scheme is compared to well-known technologies, such as schemes using Orthogonal Frequency Division Multiplexing (OFDM) associated with a powerful Forward Error Correction (FEC) scheme, namely Turbo Code (TC).

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