Abstract

The “white space” model allows TV channels not being used regionally by a TV broadcaster to be re-purposed for secondary access. Unfortunately, populated areas have few unused channels. Nonetheless, Nielsen data show severe <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">under-utilization</i> with vast regions in range of TV transmitters having <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">no active TV receivers</i> even at peak TV viewing time. In this paper, we present the design, implementation, and evaluation of WiFi in active TV channels (WATCH), the first system to enable secondary WiFi transmission in the presence of kilowatt-scale TV transmitters. To protect active TV receivers, WATCH includes a smartphone-based TV remote controller or an Internet-connected TV to inform WATCH controller of TV receivers’ spatial-spectral requirements. To enable WiFi transmission in UHF bands, we design WATCH-interference cancellation and constructive addition transmission to 1) exploit the unique environment of asynchronous WiFi transmission in the presence of a strong streaming interferer, and 2) require no coordination with legacy TV transmitters. With FCC permission to test our implementation, we show that WATCH can provide at least six times the total achievable rate to 4 watt secondary devices compared to current TV white space systems, while limiting the increase in TV channel switching time to less than 5%.

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