Dynamic Spectrum Access in DTV Whitespaces

This is an exciting development because DTV whites- paces are in the low frequency range (50-698 MHz) compared to typical cellular and ISM bands, thus resulting in much better propagation charac- teristics and much higher spectral efficiencies. The FCC has also mandated certain guidelines for short range unlicensed access, so as to avoid any in- terference to DTV receivers. We consider the problem of Wi-Fi like access (popularly referred to as Wi-Fi 2.0) for

enterprizes. We assume that the ac- cess points and client devices are equipped with cognitive radios, i.e., they can adaptively choose the center frequency, bandwidth and power of oper- ation. The access points can be equipped with one or more radios. In this paper, we layout the design of a complete system that (i) does not violate the FCC mandate, (ii) dynamically assigns center frequency and bandwidth to each access point based on their demands and (iii) squeezes the maximum efficiency from the available spectrum. This problem is far more general than prior work that investigated dynamic spectrum allocation in cellular and ISM bands, due to the non-homogeneous nature of the whitespaces, i.e., different whitespace widths in different parts of the spectrum and the large range of frequency bands with different propagation characteristics. This calls for a more holistic approach to system design that also accounts for frequency dependent propagation characteristics and radio frontend char- acteristics. In this paper, we first propose design rules for holistic system design. We then describe an architecture derived from our design rules. Finally we propose demand based dynamic spectrum allocation algorithms with provable worst case guarantees. We provide simulation results show- ing that (i) the performance of our algorithm is within 94% of the optimal in typical settings and (ii) and the DTV whitespaces can provide signifi- cantly higher data rates compared to the 2.4GHz ISM band. Our approach is general enough for designing any system with access to a wide range of spectrum. CategoriesandSubjectDescriptors: C.2.0 [General]: Data Com- munications; C.2.1 [Computer Communication Networks]: Net- work Architecture and Design-Wireless communication General Terms: Design, Algorithms 1. INTRODUCTION Across the world, countries are migrating from analog to digital television broadcasts. For example, in the US, this transition hap- pened on June 12, 2009; while in the UK, this transition is slated to happen in a phased manner from 2008 to 2012. In analog trans- Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. MobiCom’09, September 20–25, 2009, Beijing, China. Copyright 2009 ACM 978-1-60558-702-8/09/09 ...$10.00....

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