Rohan Murty

White space networking with wi-fi like connectivity

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 Net7, the first Wi-Fi like system constructed on top of UHF white spaces. Net7 incorporates a new adaptive spectrum assignment algorithm to handle spectrum variation and fragmentation, and proposes a low overhead protocol to handle temporal variation. 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 evaluation of the system in terms of a prototype implementation and detailed experimental and simulation results.

SenseLess: A database-driven white spaces network

The most recent FCC ruling proposes relying on a database of incumbents as the primary means of determining white space availability at any white spaces device (WSD). While the ruling provides broad guidelines for the database, the specifics of its design, features, implementation, and use are yet to be determined. Furthermore, architecting a network where all WSDs rely on the database raises several systems and networking challenges that have remained unexplored. Also, the ruling treats the database only as a storehouse for incumbents. We believe that the mandated use of the database has an additional opportunity: a means to dynamically manage the RF spectrum. Motivated by this opportunity, in this paper we present SenseLess, a database driven white spaces network. As suggested by its very name, in SenseLess, WSDs obviate the need to sense the spectrum by relying entirely on a database service to determine white spaces availability. The service, using a combination of an up-to-date database of incumbents, sophisticated signal propagation modeling, and an efficient content dissemination mechanism ensures efficient, scalable, and safe white space network operation. We build, deploy, and evaluate SenseLess and compare our results to ground truth spectrum measurements. We present the unique system design considerations that arise due to operating over the white spaces. We also evaluate its efficiency and scalability. To the best of our knowledge, this is the first paper that identifies and examines the systems and networking challenges that arise from operating a white space network, which is solely dependent on a channel occupancy database.

CitySense: An Urban-Scale Wireless Sensor Network and Testbed

In this paper, we present the vision for an open, urban-scale wireless networking testbed, called CitySense, with the goal of supporting the development and evaluation of novel wireless systems that span an entire city. CitySense is currently under development and will consist of about 100 Linux-based embedded PCs outfitted with dual 802.11a/b/g radios and various sensors, mounted on buildings and streetlights across the city of Cambridge. CitySense takes its cue from citywide urban mesh networking projects, but will differ substantially in that nodes will be directly programmable by end users. The goal of CitySense is explicitly not to provide public Internet access, but rather to serve as a new kind of experimental apparatus for urban-scale distributed systems and networking research efforts. In this paper we motivate the need for CitySense and its potential to support a host of new research and application developments. We also outline the various engineering challenges of deploying such a testbed as well as the research challenges that we face when building and supporting such a system.

Measurement of Orbital Decay in the Double Neutron Star Binary PSR B2127+11C

We report the direct measurement of orbital period decay in the double neutron star pulsar system PSR B2127+11C in the globular cluster M15 at the rate of (-3.95 ± 0.13) × 10-12, consistent with the prediction of general relativity at the ~3% level. We find the pulsar mass to be mp = 1.358 ± 0.010 M☉ and the companion mass mc = 1.354 ± 0.010 M☉. We also report long-term pulse timing results for the pulsars PSR B2127+11A and PSR B2127+11B, including confirmation of the cluster proper motion.

A campus-wide testbed over the TV white spaces

We have deployed a wireless network that operates in the white spaces of the TV band spectrum and covers most of Microsoft campus in Redmond, WA. Since the campus is large (approximately 1 mile x 1 mile), there are several shuttles that move employees from one building to another. We have used the white spaces network to enable a key productivity scenario on campus - Internet connectivity in campus shuttles. We have modified one such shuttle to operate over the TV band white spaces. A white space radio in this shuttle communicates with two base stations deployed on buildings on campus. Inside the shuttle, we bridge the white space connection to Wi-Fi, so that an employees laptop that does not have an integrated white space radio can nevertheless connect to the Internet, using Wi-Fi within the shuttle, and white spaces between the shuttle and the base stations. To the best of our knowledge, this is the first network deployed over the TV white spaces.

Scalable, Self-Organizing Technology for Sensor Networks

Sensor networks will often need to organize themselves automatically and adapt to changing environmental conditions, failures, intermittent connectivity, and in response to power considerations. We review a series of technologies that we find interesting both because they solve fundamental problems seen in these settings, and also because they appear to be instances of a broader class of solutions responsive to these objectives.

JULIET: a distributed fault tolerant load balancer for .NET Web services

The execution time of computationally-intensive applications such as protein folding and fractal generation can be reduced by implementing these applications as Web services that run in parallel. Additionally, some of these Web services may save state periodically to resume execution later on. However, currently, there is no solution to load balance this class of Web services, and to replicate the saved state for the purposes of resumption. This paper describes the architecture of JULIET, a system that load balances .NET Web services across a Windows cluster in a distributed fashion. The system is also fault tolerant since it supports failovers and replication of data generated by the Web services at the application level. The system is designed to be minimally-visible to the Web service and the client that consumes it.