Jamming Cognitive Radios

The goal of this thesis is to identify and evaluate weaknesses in the rendezvous process for Cognitive Radio Networks (CRNs) in the presence of a Cognitive Jammer (CJ). Jamming strategies are suggested and tested for effectiveness. Methods for safe- guarding the Cognitive Radios (CRs) against a CJ are also explored. A simulation is constructed to set up a scenario of two CRs interacting with a CJ. Analysis of the simulation is conducted primarily at the waveform level. A hardware setup is constructed to analyze the system in the physical layer, verify the interactions from the simulation, and test in a low signal-to-interference and noise ratio (SINR) environment. The hardware used in this thesis is the Wireless Open-Access Research Platform. Performance metrics from open literature and independent testing are compared against those captured from the jamming tests. The goal of testing is to evaluate and quantify the ability to delay the rendezvous process of a CRN. There was some success in delaying rendezvous, even in a high SINR environment. Jamming strategies include a jammer that repeats an observed channel-hopping pattern, a jammer with random inputs using the same algorithm of the CRs, a jammer that estimates channel-hopping parameters based on observations, and a random channel-hopping jammer. Results were compared against control scenarios, consisting of no jamming and a jammer that is always jamming on the same channel as one of the CRs. The repeater, random inputs to the CR algorithm, observation-based estimation jammer, and the random channel hopping jammer were mildly successful in delaying rendezvous at about 0%, 9%, 0%, and 1%, respectively. The jammer that is always on the same channel as a CR had an overall rendezvous delay about 13% of the time

ETCH: Efficient Channel Hopping for Communication Rendezvous in Dynamic Spectrum Access Networks

In a dynamic spectrum access (DSA) network, communication rendezvous is the first step for two secondary users to be able to communicate with each other. In this step, the pair of secondary users meet on the same channel, over which they negotiate on the communication parameters, to establish the communication link. This paper presents ETCH, Efficient Channel Hopping based MAC-layer protocols for communication rendezvous in DSA networks. We propose two protocols, SYNC-ETCH and ASYNC-ETCH. Both protocols achieve better time-to-rendezvous and throughput compared to previous work

DISTRIBUTED INTELLIGENT SPECTRUM MANAGEMENT IN COGNITIVE RADIO AD HOC NETWORKS

The rapid growth of the number of wireless devices has brought an exponential increase in the demand of the radio spectrum. However, according to the Federal Communications Commission (FCC), almost all the radio spectrum for wireless com- munications has already been allocated. In addition, according to FCC, up to 85% of the allocated spectrum is underutilized due to the current fixed spectrum alloca- tion policy. To alleviate the spectrum scarcity problem, FCC has suggested a new paradigm for dynamically accessing the allocated spectrum. Cognitive radio (CR) technology has emerged as a promising solution to realize dynamic spectrum access (DSA). With the capability of sensing the frequency bands in a time and location- varying spectrum environment and adjusting the operating parameters based on the sensing outcome, CR technology allows an unlicensed user to exploit the licensed channels which are not used by licensed users in an opportunistic manner. In this dissertation, distributed intelligent spectrum management in CR ad hoc networks is explored. In particular, four spectrum management issues in CR ad hoc networks are investigated: 1) distributed broadcasting in CR ad hoc networks; 2) distributed optimal HELLO message exchange in CR ad hoc networks; 3) distributed protocol to defend a particular network security attack in CR ad hoc networks; and 4) distributed spectrum handoff protocol in CR ad hoc networks. The research in this dissertation has fundamental impact on CR ad hoc network establishment, net- work functionality, network security, and network performance. In addition, many of the unique challenges of distributed intelligent spectrum management in CR ad hoc networks are addressed for the first time in this dissertation. These challenges are extremely difficult to solve due to the dynamic spectrum environment and they have significant effects on network functionality and performance. This dissertation is essential for establishing a CR ad hoc network and realizing networking protocols for seamless communications in CR ad hoc networks. Furthermore, this dissertation provides critical theoretical insights for future designs in CR ad hoc networks

Bootstrapping Cognitive Radio Networks

Cognitive radio networks promise more efficient spectrum utilization by leveraging degrees of freedom and distributing data collection. The actual realization of these promises is challenged by distributed control, and incomplete, uncertain and possibly conflicting knowledge bases. We consider two problems in bootstrapping, evolving, and managing cognitive radio networks. The first is Link Rendezvous, or how separate radio nodes initially find each other in a spectrum band with many degrees of freedom, and little shared knowledge. The second is how radio nodes can negotiate for spectrum access with incomplete information. To address the first problem, we present our Frequency Parallel Blind Link Rendezvous algorithm. This approach, designed for recent generations of digital front-ends, implicitly shares vague information about spectrum occupancy early in the process, speeding the progress towards a solution. Furthermore, it operates in the frequency domain, facilitating a parallel channel rendezvous. Finally, it operates without a control channel and can rendezvous anywhere in the operating band. We present simulations and analysis on the false alarm rate for both a feature detector and a cross-correlation detector. We compare our results to the conventional frequency hopping sequence rendezvous techniques. To address the second problem, we model the network as a multi-agent system and negotiate by exchanging proposals, augmented with arguments. These arguments include information about priority status and the existence of other nodes. We show in a variety of network topologies that this process leads to solutions not otherwise apparent to individual nodes, and achieves superior network throughput, request satisfaction, and total number of connections, compared to our baselines. The agents independently formulate proposals based upon communication desires, evaluate these proposals based upon capacity constraints, create ariii guments in response to proposal rejections, and re-evaluate proposals based upon received arguments. We present our negotiation rules, messages, and protocol and demonstrate how they interoperate in a simulation environment

Providing efficient services for smartphone applications

Mobile applications are becoming an indispensable part of people\u27s lives, as they allow access to a broad range of services when users are on the go. We present our efforts towards enabling efficient mobile applications in smartphones. Our goal is to improve efficiency of the underlying services, which provide essential functionality to smartphone applications. In particular, we are interested in three fundamental services in smartphones: wireless communication service, power management service, and location reporting service.;For the wireless communication service, we focus on improving spectrum utilization efficiency for cognitive radio communications. We propose ETCH, a set of channel hopping based MAC layer protocols for communication rendezvous in cognitive radio communications. ETCH can fully utilize spectrum diversity in communication rendezvous by allowing all the rendezvous channels to be utilized at the same time.;For the power management service, we improve its efficiency from three different angles. The first angle is to reduce energy consumption of WiFi communications. We propose HoWiES, a system-for WiFi energy saving by utilizing low-power ZigBee radio. The second angle is to reduce energy consumption of web based smartphone applications. We propose CacheKeeper, which is a system-wide web caching service to eliminate unnecessary energy consumption caused by imperfect web caching in many smartphone applications. The third angle is from the perspective of smartphone CPUs. We found that existing CPU power models are ill-suited for modern multicore smartphone CPUs. We present a new approach of CPU power modeling for smartphones. This approach takes CPU idle power states into consideration, and can significantly improve power estimation accuracy and stability for multicore smartphones.;For the location reporting service, we aim to design an efficient location proof solution for mobile location based applications. We propose VProof, a lightweight and privacy-preserving location proof scheme that allows users to construct location proofs by simply extracting unforgeable information from the received packets

ZOS: A Fast Rendezvous Algorithm Based on Set of Available Channels for Cognitive Radios

Most of existing rendezvous algorithms generate channel-hopping sequences based on the whole channel set. They are inefficient when the set of available channels is a small subset of the whole channel set. We propose a new algorithm called ZOS which uses three types of elementary sequences (namely, Zero-type, One-type, and S-type) to generate channel-hopping sequences based on the set of available channels. ZOS provides guaranteed rendezvous without any additional requirements. The maximum time-to-rendezvous of ZOS is upper-bounded by O(m1*m2*log2M) where M is the number of all channels and m1 and m2 are the numbers of available channels of two users.Comment: 10 page

Interference Mitigation in Frequency Hopping Ad Hoc Networks

Radio systems today exhibit a degree of flexibility that was unheard of only a few years ago. Software-defined radio architectures have emerged that are able to service large swathes of spectrum, covering up to several GHz in the UHF bands. This dissertation investigates interference mitigation techniques in frequency hopping ad hoc networks that are capable of exploiting the frequency agility of software-defined radio platforms