Exploiting the physical layer to enhance wireless operation with cognitive radios.

摘要

Wireless communication systems have undergone considerable evolution in the past decade. This is in large part due to significant advancements made in underlying physical (PHY) layer technologies, resulting in substantial performance leaps in data rates and reliability. These strides have made wireless devices the platform of choice for communicating. Accordingly, considerable progress in the realm of Software Defined Radio (SDR) has made seamless cross-protocol communication not only plausible but a near-term certainty. This is primarily due to the openness of the physical layer to the system user and developer. Unfortunately, this same openness also provides an adversary with a powerful point of attack. It is therefore essential to consider physical layer exploits in order to enhance operation in future wireless communication networks. In this thesis, we consider using physical layer exploitation to: (1) enhance situational awareness, (2) act as an adversary, and (3) mitigate poor environments and adversarial conditions.;By enhancing its situational awareness, a device can make truly intelligent operational decisions. In order to efficiently and effectively utilize the RF spectrum a device should know what services are available and the level to which they are utilized --- perhaps even down to the identity of neighboring devices. It is also advantageous for a device to know its physical location, characteristics of its environment (e.g. indoor vs. outdoor), and of course whether or not there is an adversary in the region. In this thesis, we explore new physical layer based techniques to acquire this valuable information.;Next, we acknowledge that sometimes the best defense is a good offense as we explore attack strategies focused on the physical layer. By thinking like an adversary, one can better anticipate possible attacks and determine the appropriate remedies. Since most 3G and 4G wireless standards and protocols incorporate some form of multi-input multi-output (MIMO) technology, we pay specific attention to MIMO operation. Whereas the majority of related research has assumed the presence of an unintelligent jammer, our focus will be on truly smart attacks.;In the final part of this thesis, we consider what to do once an accurate description of the operational scenario is achieved. Accurate knowledge of the environment plays a key role in Dynamic Spectrum Access (DSA), where devices adapt modulation schemes and protocols to both optimize communications and minimize interference with existing wireless infrastructures. Additionally, accurate situational awareness provides insight into potential communication hazards --- from severe multipath conditions to adversarial attacks. In this thesis, we present unique physical layer methodologies that can be used to overcome channel degradations due to both natural phenomena and adversarial activity.;In each part of this thesis, we accompany theoretical results and findings with simulations and real-world experimentation in order to illustrate the feasibility and applicability of the proposed techniques. Real-world implementations were conducted using current SDR architectures.