On 12/7/07, Philip Levis <[EMAIL PROTECTED]> wrote: > > On Dec 6, 2007, at 4:39 PM, Timothy J. Salo wrote: > > > > > > Do any of the 802.15.4 chips support a "wake on receive" > > capability? Does this capability (assuming it exists) > > require that the radio be powered on continuously? That is, > > does this capability power-down _only_ the processor, but > > not the radio? Does this capability really save enough > > power to meet the needs of many battery-powered, hopefully > > long-lived wireless sensor networks? > > > > This doesn't work like you think it does. To hear a signal, your > radio has to be on. The energy cost of demodulation is not the > principal issue. > > Phil
Yes, to hear a signal the radio needs to be on. So "wake on receive" is hard unless you consider dual radios. The concept of "dual radios" has existed in theory. A second, always-on, radio can wake up the "main" radio to give you wake on receive functionality. However, the power consumption of the always-on second radio will cost you a lot more (in terms of energy) compared to duty-cycling the "main" radio. Thats why dual radios with wake-on-receive have largely remained a theoretical concept. See this work http://www.st.ewi.tudelft.nl/~koen/papers/wakeup-radio.pdf for a working prototype of a dual radio (EUR 5 per radio) that has acceptable energy costs in always-on mode. The current problem, however, is that the range of the wake-up radio is fairly small. Second problem is that to keep the energy costs low, you will end up with a "bare-bones" radio that is not even sophisticated enough to do addressing. You end up waking up a lot of neighbors if you don't know how to address a particular one (don't know if they have already solved this). Increasing the range while keeping energy costs acceptable is an on-going work at the startup from where one of the authors is from. _______________________________________________ > 6lowpan mailing list > [email protected] > https://www1.ietf.org/mailman/listinfo/6lowpan > -- Cheers, Muneeb Ali | http://muneeb.org
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