White Spaces Research

Rohan Narayana Murty


My dissertation research focuses on architectures for opportunistic wireless networking, also known as Dynamic Spectrum Access (DSA). In particular, I study white spaces networking, which is an instance of opportunistic wireless networking. Over the past two years I have built, measured, and evaluated various white spaces networking solutions. Here is a comprehensive list of white spaces related projects I have worked on, have published, or are under submission.

WhiteFI: White Space Networking with Wi-Fi like Connectivity

WhiteFI is the first published attempt at building a white spaces network spanning multiple nodes and links by opportunistically. In this work, we first understand why and how are the white spaces different from the ISM bands. We then show the implications these differences in spectra have on the networking stack and the resulting challenges. We then propose solutions to each one of these challenges. Via implementations on hardware and in a simulator, we demonstrate the feasibility of our solutions.

Abstract: Networking over UHF white spaces is fundamentally different from conventional Wi-Fi along three axes: spatial variation, temporal variation, and fragmentation of the UHF spectrum. Each of these differences gives rise to new challenges for implementing a wireless network in this band. We present the design and implementation of WhiteFi, the first Wi-Fi like system constructed on top of UHF white spaces. WhiteFi incorporates a new adaptive spectrum assignment algorithm to handle spectrum variation and fragmentation, and proposes a low overhead protocol to handle temporal variation. WhiteFi builds on a simple technique, called SIFT, that reduces the time to detect transmissions in variable channel width systems by analyzing raw signals in the time domain. We provide an extensive system evaluation in terms of a prototype implementation and detailed experimental and simulation results.

White Space Networking with Wi-Fi like Connectivity, Paramvir Bahl, Ranveer Chandra, Thomas Moscibroda, Rohan Murty, and Matt Welsh, SIGCOMM 2009 (Best Paper Award)

Click here for my WhiteFi talk from SIGCOMM

SenseLess: A Database-Driven White Spaces Network

The FCC’s initial ruling on white spaces proposes cataloging the list of incumbents and using this information to aid the operation of a white spaces network. This is in part due to the complexity imposed by requiring sensing at low thresholds. Hence, sensing is the key bottleneck that must be tackled. In this work, we investigate whether it is indeed feasible to eliminate such requirements across most white spaces devices while still ensuring the safety of incumbents by driving the entire white spaces network with a database of incumbents. We build SenseLess, a white spaces network that does not require sensing at client devices. Instead, it relies on a database of incumbents to predict the availability of white spaces. We compare the performance of such a system with the ground truth measurements gathered across a 1500+ mile drive in the state of WA during the summer of 2009.

Abstract: The recent FCC ruling has opened up the possibility of wireless network deployments over white spaces, i.e., vacant UHF TV channels. A key requirement for any white space device is that it must ensure that none of of its trans- missions interfere with incumbents, namely TV transmitters and wireless microphones. For this purpose, there has been a lot of effort on spectrum sensing techniques that allow white space devices to decide which parts of the spectrum is currently occupied by primary users. While potentially feasible, spectrum sensing at the low thresholds required to protect incumbents is technically challenging. In this paper, we propose and design an alternative approach to opportunistic wireless networking in white spaces that does not require any sensing. Governed by unique system design constraints characteristic to white space wireless networks, we design and implement SenseLess a system that combines sophisticated signal propagation modeling with an efficient content dissemination mechanism to ensure efficient, scalable, and safe white space network operation. We compare our results to ground truth spectrum measurements and present detailed evaluation of our infrastructure and service.

SenseLess: A Database Driven White Spaces Network, Rohan Murty, Ranveer Chandra, Thomas Moscibroda, and Paramvir Bahl, In Proceedings of IEEE DySpan, May, 2011

SenseLess: A Database Driven White Spaces Network, Rohan Murty, Ranveer Chandra, Thomas Moscibroda, and Paramvir Bahl, MSR Technical Report MSR-TR-2010-127, Filed September 20th, 2010

(NEW) Click here to see my on-going work on the design and implementation of a database based service to predict the availability of white spaces. The service uses TV signal propagation modeling and analysis to predict white spaces at any specified location in the continental United States.

The service also exports API that can be embedded into your own applications or research projects.

SATYA: Enabling Spectrum Sharing in Secondary Market Auctions

Abstract: Wireless spectrum is a scare resource, but in practice much of it is under-used by current owners. To enable better use of this spectrum, we propose an auction approach to dynamically allocate the spectrum in a secondary mar- ket. Unlike previous auction approaches, we seek to take advantage of the ability to share spectrum among some bidders while respecting the needs of others for exclusive use. Thus, unlike unlicensed spectrum (e.g. Wi-Fi), which can be shared by any device, and exclusive-use licensed spectrum, where sharing is precluded, we enable efficient allocation by supporting sharing alongside quality-of-service protections. We present SATYA (Sanskrit for “truth”), a strategyproof and scalable spectrum auction algorithm whose primary contribution is in the allocation of a right to contend for spectrum to both sharers and exclusive-use bidders. We demonstrate SATYA’s ability to handle heterogeneous agent types involving different transmit powers and spectrum needs through extensive simulations.

This paper is currently under submission. Click on the link below to access the tech report.

Enabling Spectrum Sharing in Secondary Market Auctions, Ian Kash, Rohan Murty, and David Parkes