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Clean Slate Research Projects

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5.) Clean Slate Approach to Wireless Spectrum Usage

Started: September 2006

The FCC today maintains relatively tight control of spectrum access, through a variety of regulations and licensing programs. However, this is an artifact of the past more than a harbinger of the future. We propose a "clean slate" design of wireless spectrum allocation, to deal with a future where multiple devices will share resources across broad ranges of space, time, and frequency. Our project aims for both design recommendations for wireless devices operating in a competitive environment, as well as protocol suggestions to encourage cooperation among opportunistic wireless devices. Our main methodological tools are derived from game theory, distributed control, and wireless system design. There has been tremendous growth over the last decade in devices that access the Internet via wireless technology. However, wireless spectrum regulations have not kept pace with the growth in wireless end hosts; thus it appears as though spectrum in scarce, when in reality this scarcity arises due to access restrictions imposed by the FCC. As suggested by an FCC task force in 2002, the future Internet needs to have a more flexible wireless resource allocation scheme. Our research will enable devices to find and utilize spectral holes across a wide range of space, time, and frequency; such research is ultimately vital to ensuring that spectrum availability for the future Internet is commensurate with the growth in demand for wireless services. Most work in the area of dynamic spectrum allocation is based on idealized assumptions and/or ad-hoc techniques. The proposed research aims to develop a concrete formulation of the optimization problems associated with distributed dynamic spectrum allocation and also obtained some preliminary results indicating (a) the potential spectral efficiency gains of dynamic spectrum allocation; (b) the most promising techniques to use; and (c) the most significant technical challenges involved in applying these techniques in practice (e.g. computational complexity, overhead, measuring interference, radio hardware requirements).

Status

As a first step in understanding dynamic spectrum allocation techniques, we studied competition between wireless devices with incomplete information about their opponents. Such competitive models represent situations in which several wireless devices share spectrum without any central authority or coordinated protocol. We model such interactions as Bayesian interference games. Each wireless device selects a power profile over the entire available bandwidth to maximize its data rate (measured via Shannon capacity), which requires mitigating the effect of interference caused by other devices. In contrast to games where devices have complete information about their opponents, we consider scenarios where the devices are unaware of the interference they cause to other devices. Such games, which are modeled as Bayesian games, can exhibit significantly different equilibria. We first consider a simple scenario where the devices select their power profile simultaneously. In such simultaneous move games, we show that the unique Bayes-Nash equilibrium is where both devices spread their power equally across the entire bandwidth. We then extend this model to a two-tiered spectrum sharing case where users act sequentially. Here one of the devices, called the primary user, is the owner of the spectrum and it selects its power profile first. The second device (called the secondary user) then responds by choosing a power profile to maximize its Shannon capacity. In such sequential move games, we show that there exist equilibria in which the primary user obtains a higher data rate by using only a part of the bandwidth. In a repeated Bayesian interference game, we show the existence of reputation effects: an informed primary user can ``bluff" to prevent spectrum usage by a secondary user who suffers from lack of information about the channel gains. The resulting equilibrium can be highly inefficient, suggesting that competitive spectrum sharing is highly suboptimal. This observation points to the need for some regulatory protocol to attain a more efficient spectrum sharing solution. Papers: 1. Sachin Adlakha, Ramesh Johari and Andrea Goldsmith, "Competition in Wireless Systems via Bayesian Interference Games."

Papers

Sachin Adlakha, Ramesh Johari and Andrea Goldsmith, Competition in Wireless Systems via Bayesian Interference Games


Researchers

Andrea GoldsmithAndrea Goldsmith
(Faculty) Professor of Electrical Engineering 

Ramesh JohariRamesh Johari
(Faculty) Assistant Professor, Management Science and Engineering

Ivana MaricIvana Maric
(Graduate) Postdoctoral Associate, Electrical Engineering

Sachin AdlakhaSachin Adlakha
(Student) third year Ph.D student in the Department of Electrical Engineering

Funding

This research is funded by the Clean Slate Project.

We will post papers/progress reports on this page.

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