Interference alignment by motion

Recent years have witnessed increasing interest in interference alignment which has been demonstrated to deliver gains for wireless networks both analytically and empirically. Typically, interference alignment is achieved by having a MIMO sender precode its transmission to align it at the receiver. In this paper, we show, for the first time, that interference alignment can be achieved via motion, and works even for single-antenna transmitters. Specifically, this alignment can be achieved purely by sliding the receiver's antenna. Interestingly, the amount of antenna displacement is of the order of one inch which makes it practical to incorporate into recent sliding antennas available on the market. We implemented our design on USRPs and demonstrated that it can deliver 1.98× throughput gains over 802.11n in networks with both single-antenna and multi- antenna nodes.National Science Foundation (U.S.

Design of Wireless Automatic Microwave Antenna Alignment System

Microwave link aligning is an important operation in communication systems. Misalignment in line of sight link due to rain, wind etc considered the basic problem that faced the microwave system. This problem caused a direct terminating of the microwave link. Automatic antenna alignment will guarantee best communication at the link’s ends without any risks of human interface. This paper presented a low cost design of an automatic antenna alignment system based on arduino and using Xbee wireless technology. The design in the paper is automatically adjusting the horizontal and vertical angles in the transmitter and receiver sides of the microwave link. The controller compared the measured values of these two angles with a reference values. The correction of the error in the angles is done by moving the antenna towards the correct position. The design was tested in different angles positions and the results were reported in the paper. The simulation results ensure that the system works successfully

Guaranteeing Spoof-Resilient Multi-Robot Networks

Multi-robot networks use wireless communication to provide wide-ranging services such as aerial surveillance and unmanned delivery. However, effective coordination between multiple robots requires trust, making them particularly vulnerable to cyber-attacks. Specifically, such networks can be gravely disrupted by the Sybil attack, where even a single malicious robot can spoof a large number of fake clients. This paper proposes a new solution to defend against the Sybil attack, without requiring expensive cryptographic key-distribution. Our core contribution is a novel algorithm implemented on commercial Wi-Fi radios that can "sense" spoofers using the physics of wireless signals. We derive theoretical guarantees on how this algorithm bounds the impact of the Sybil Attack on a broad class of robotic coverage problems. We experimentally validate our claims using a team of AscTec quadrotor servers and iRobot Create ground clients, and demonstrate spoofer detection rates over 96%

IoT Networking: Path to Ubiquitous Connectivity

University of Minnesota Ph.D. dissertation. August 2019. Major: Computer Science. Advisor: Tian He. 1 computer file (PDF); xii, 105 pages.Internet of Things (IoT) is upon us with the number of IoT connected devices reach- ing 17.68 billion in the year 2016 and keeps an increasing rate of 17%. The popularity of IoT brings the prosperity and diversity of wireless technologies as one of its founda- tions. Existing wireless technologies, such as WiFi, Bluetooth, and LTE, are evolving and new technologies, such as SigFox and LoRa, are proposed to satisfy various needs under emerging application scenarios. For example, WiFi is evolving to provide higher throughput with the novel 802.11ac technology and the Bluetooth SIG has proposed the Bluetooth Low Energy (BLE) technology to support low-power applications. However, wireless technologies are victims of their own success. The vastly increasing wireless devices compete for the limited wireless spectrum and result in the performance degradation of each device. What makes it worse is that diverse wireless devices are using heterogeneous PHY and MAC layers designs which are not compliant with each other. As a result, sophisticated wireless coordination methods working well for each homogeneous technology are not applicable in the heterogeneous wireless scenario for the failure to communicate among heterogeneous devices. This dissertation aims at fundamentally solving the burden of communication in today’s heterogeneous wireless environment. Specifically, we try to build direct communication among heterogeneous wireless technologies, referred to as the cross-technology communication (CTC). It is counter-intuition and long believed impossible, but we find two opportunities in both the packet level and physical (PHY) layer to make the challenging mission possible. First, wireless devices are commonly able to do energy-sensing of wireless packets in the air. Energy sensing is capable to figure out packet-level information, such as the packet duration and timing. Based on the energy-sensing capability, we design DCTC, a CTC technology that piggybacks cross-technology messages within the timing of transmitted wireless packets. Specifically, we slightly perturb the timing of packets emitted from a wireless device to form detectable energy patterns to establish CTC. Testbed evaluation has shown that we can successfully transmit information at 760bps while keeping the delay of each packet no longer than 0.5ms under any traffic pattern. Second, in the PHY layer, high-end wireless technologies are flexible, i.e., a larger symbol set, in the modulation and demodulation. With careful choices of symbols, those wireless technologies are able to emulate and decode the PHY layer signal of a low-end one. We propose two systems BlueBee and XBee which aim at building direct com- munication between two heterogeneous IoT technologies, Bluetooth and ZigBee, with the idea of signal emulation and cross-decoding respectively. The former achieves signal emulation by carefully choosing the Bluetooth payload bits so that the output signal emulates a legitimate ZigBee packet which can be successfully demodulated by a com- modity ZigBee devices without any changes. The latter proposes a general method to support the bidirectional communication in the PHY-layer CTC by moving the complex- ity to the high-end receiver for the demodulation of signal from a low-end transmitter. Our testbed evaluation has shown that our technologies successfully boost the data rate of the state of the arts by over 10,000x times, which is approaching the ZigBee standard. This result makes CTC possible to play more roles in real-time applications, such as network coordination. In summary, this dissertation provides a new communication paradigm in a heteroge- neous wireless environment, which is to provide direct communication for heterogeneous wireless devices. Such communication is built upon two opportunities: (i) wireless de- vices are capable to sense energy in the air so that specifically designed energy patterns can transmit cross-technology information; (ii) a high-end wireless technology is more flexible and possible to emulate and demodulate the signal from a low-end technology for communication. The technologies developed in the dissertation will be the build- ing blocks for the future designs of efficient channel coordination and ubiquitous data exchange among heterogeneous wireless devices

Research on efficiency and privacy issues in wireless communication

Wireless spectrum is a limited resource that must be used efficiently. It is also a broadcast medium, hence, additional procedures are required to maintain communication over the wireless spectrum private. In this thesis, we investigate three key issues related to efficient use and privacy of wireless spectrum use. First, we propose GAVEL, a truthful short-term auction mechanism that enables efficient use of the wireless spectrum through the licensed shared access model. Second, we propose CPRecycle, an improved Orthogonal Frequency Division Multiplexing (OFDM) receiver that retrieves useful information from the cyclic prefix for interference mitigation thus improving spectral efficiency. Third and finally, we propose WiFi Glass, an attack vector on home WiFi networks to infer private information about home occupants. First we consider, spectrum auctions. Existing short-term spectrum auctions do not satisfy all the features required for a heterogeneous spectrum market. We discover that this is due to the underlying auction format, the sealed bid auction. We propose GAVEL, a truthful auction mechanism, that is based on the ascending bid auction format, that avoids the pitfalls of existing auction mechanisms that are based on the sealed bid auction format. Using extensive simulations we observe that GAVEL can achieve better performance than existing mechanisms. Second, we study the use of cyclic prefix in Orthogonal Frequency Division Multiplexing. The cyclic prefix does contain useful information in the presence of interference. We discover that while the signal of interest is redundant in the cyclic prefix, the interference component varies significantly. We use this insight to design CPRecycle, an improved OFDM receiver that is capable of using the information in the cyclic prefix to mitigate various types of interference. It improves spectral efficiency by decoding packets in the presence of interference. CPRecycle require changes to the OFDM receiver and can be deployed in most networks today. Finally, home WiFi networks are considered private when encryption is enabled using WPA2. However, experiments conducted in real homes, show that the wireless activity on the home network can be used to infer occupancy and activity states such as sleeping and watching television. With this insight, we propose WiFi Glass, an attack vector that can be used to infer occupancy and activity states (limited to three activity classes), using only the passively sniffed WiFi signal from the home environment. Evaluation with real data shows that in most of the cases, only about 15 minutes of sniffed WiFi signal is required to infer private information, highlighting the need for countermeasures

Practical interference mitigation for Wi-Fi systems

Wi-Fi's popularity is also its Achilles' heel since in the dense deployments of multiple Wi-Fi networks typical in urban environments, concurrent transmissions interfere. The advent of networked devices with multiple antennas allows new ways to improve Wi-Fi's performance: a host can align the phases of the signals either received at or transmitted from its antennas so as to either maximize the power of the signal of interest through beamforming or minimize the power of interference through nulling. Theory predicts that these techniques should enable concurrent transmissions by proximal sender-receiver pairs, thus improving capacity. Yet practical challenges remain. Hardware platform limitations can prevent precise measurement of the wireless channel, or limit the accuracy of beamforming and nulling. The interaction between nulling and Wi-Fi's OFDM modulation, which transmits tranches of a packet's bits on distinct subcarriers, is subtle and can sacrifice the capacity gain expected from nulling. And in deployments where Wi-Fi networks are independently administered, APs must efficiently share channel measurements and coordinate their transmissions to null effectively. In this thesis, I design and experimentally evaluate beamforming and nulling techniques for use in Wi-Fi networks that address the aforementioned practical challenges. My contributions include: - Cone of Silence (CoS): a system that allows a Wi-Fi AP equipped with a phased-array antenna but only a single 802.11g radio to mitigate interference from senders other than its intended one, thus boosting throughput; - Cooperative Power Allocation (COPA): a system that efficiently shares channel measurements and coordinates transmissions between independent APs, and cooperatively allocates power so as to render received power across OFDM subcarriers flat at each AP's receiver, thus boosting throughput; - Power Allocation for Distributed MIMO (PADM): a system that leverages intelligent power allocation to mitigate inter-stream interference in distributed MIMO wireless networks, thus boosting throughput