Abstract – With the advent of new FCC policies on spectrum allocation for next generation wireless devices, we have a rare opportunity to redesign spectrum access protocols to support demanding, latency-sensitive applications such as high-def media streaming in home networks. Given their low tolerance for traffic delays and disruptions, these applications are ill-suited for traditional, contention-based CSMA protocols. In this paper, we explore an alternative approach to spectrum access that relies on frequency-agile radios to perform interference-free transmission across orthogonal frequencies. We describe Jello, a MAC overlay where devices sense and occupy unused spectrum without central coordination or dedicated radio for control. We show that over time, spectrum fragmentation can significantly reduce usable spectrum in the system. Jello addresses this using two complementary techniques: online spectrum defragmentation, where active devices periodically migrate spectrum usage, and non-contiguous access, which allows a single flow to utilize multiple spectrum fragments. Our prototype on an 8-node GNU radio testbed shows that Jello significantly reduces spectrum fragmentation and provides high utilization while adapting to client flows ’ changing traffic demands. 1

Guardbands are designed to insulate transmissions on adjacent frequencies from mutual interference. As more devices in a given area are packed into orthogonal wireless channels, choosing the right guardband size to minimize cross-channel interference becomes critical to network performance. Using both WiFi and GNU radio experiments, we show that the traditional “one-size-fits-all” approach to guardband assignment is ineffective, and can produce throughput degradation up to 80%. We find that ideal guardband values vary across different network configurations, and across different links in the same network. We argue that guardband values should be set based on network conditions and adapt to changes over time. We propose Ganache, an intelligent guardband configuration system that dynamically sets and adapts guardbands based on local topology and propagation conditions. Ganache includes three key mechanisms: an empirical model of guardband sizes based on power heterogeneity of adjacent links, network-wide frequency and guardband assignment, and local guardband adaptation triggered by realtime detection of cross-band interference. We deploy a Ganache prototype on a local 8-node GNU radio testbed. Detailed experiments on different topologies show that to minimize interference, traditional fixed-size configurations allocate more than 40 % of available spectrum to guardbands, while Ganache does the same using only 10 % of the spectrum, leading to a 150 % gain in throughput.

Proliferation and innovation of wireless technologies require significant amounts of radio spectrum. Recent policy reforms by the FCC are paving the way by freeing up spectrum for a new generation of frequency-agile wireless devices based on software defined radios (SDRs). But despite recent advances in SDR hardware, research on SDR MAC protocols or applications requires an experimental platform for managing physical access. We introduce Papyrus, a software platform for wireless researchers to develop and experiment dynamic spectrum systems using currently available SDR hardware. Papyrus provides two fundamental building blocks at the physical layer: flexible non-contiguous frequency access and simple and robust frequency detection. Papyrus allows researchers to deploy and experiment new MAC protocols and applications on USRP GNU Radio, and can also be ported to other SDR platforms. We demonstrate the use of Papyrus using Jello, a distributed MAC overlay for high-bandwidth media streaming applications and Ganache, a SDR layer for adaptable guardband configuration. Full implementations of Papyrus and Jello are publicly available.

Abstract—FPGAs are known to be very effective at accelerating certain classes of algorithms. A variety of FPGA platforms are available today, but because of the absence of a standardized platform architecture, each platform comes in the form of a board with a diverse set of devices and communication endpoints. Therefore, FPGA programmers typically have to spend significant effort in building interfaces to devices and adapting their applications to work with the semantics of these devices. Further, an FPGA board by itself is in many cases incapable running full real-world applications – software support is required. Working out communication protocols between the FPGA and software is another unnecessary time sink for programmers who would rather focus on the high-level functionalities of their applications. Finally, there is little support for building and allocating flexible memory hierarchies on FPGA platforms. All of these problems are further exacerbated by the fact that switching FPGA platforms usually requires the programmer to re-do a significant portion of this work. These are all non-issues for software programmers who live in a world of block and character devices, hardware-managed memory hierarchies with rich memory management libraries, and a plethora of portable communication protocols. We attempt to bridge this gap between platform support for software and FPGA application development by proposing LEAP Virtual Platforms. LEAP (Logic-based Environment for Application Programming) provides an FPGA application with a consistent set of useful services and device abstractions, a memory hierarchy and a flexible communication protocol across a range of FPGA physical platforms. Tying these functionalities together is a modular development and build infrastructure. In this paper we describe the services provided by LEAP and explain how they are implemented using a multi-layered stack of abstractions. I.

Dynamic spectrum access is a maturing technology that allows next generation wireless devices to make highly efficient use of wireless spectrum. Spectrum can be allocated on an on-demand basis for a given geographic location, time duration and frequency range. However, a major obstacle to adoption remains. There are no effective solutions to protect licensed users from spectrum misuse, where users transmit without properly licensing spectrum, and in doing so, interfere and disrupt legitimate flows to whom the spectrum is assigned. Given the flexibility of today’s cognitive radios, an application can easily transmit on frequencies outside of its allocated range, either accidentally due to misconfiguration, or intentionally to avoid spectrum licensing costs. In this paper, we propose a system to secure dynamic spectrum transmissions, where authorized users embed secure spectrum permits into data transmissions, thus enabling patrolling trusted devices to detect devices transmitting without authorization. We focus our attention on the development of spectrum permits, and describe Gelato, a spectrum misuse detection system that minimizes both hardware costs and performance overhead on legitimate data transmissions.