Radio wakeup using Rf-Id: New MAC for opportunistic communication

The wireless chipsets in the market today have a mindset to conserve power by switching OFF most circuits during sleep (or idle) mode, and they just keep the radio amplifier and some minimal DSP active to recognize the presense of a signal, and then wake up the rest of the radio. However, if you look at the Rf-Id design, they power up using the energy in the wireless medium itself, and the passive Rf-Id chips do not need any external power source at all. Broadly, the idea is to use this kind of a Rf-Id circuit to wake up the entire radio whenever there is some energy in the medium. This idea of hierarchical radios is not entirely new. Have a look at the following papers:

Reconsidering wireless systems with multiple radios. P Bahl, A Adya, J Padhye, A Wolman.
Turducken: Hierarchical power management for mobile devices. J Sorber, N Banerjee, M Corner, S Rollins

However, what is interesting is that such a model completely changes the MAC design as well. For example, now you don't have to do Inquiry/Paging in Bluetooth, and you don't need careful time synchronization for Zigbee, and no backoff timers for WiFi.

A number of further optimizations are possible. This is paper from Mobicom 2005.

Challenges: Communication through silence in wireless sensor networks. Y Zhu, R Sivakumar

Their basic idea is to go back to morse code telegrahy from 150 years ago by transmitting information in pulses to save on power. We can use it for communicating low bandwidth control information. For example, a node can send its identity in pulses and only the correct receiver needs to wake up then. Scheduling information can also be sent out similarly. We will need to take care of contention in the control channel though - maybe have a FDD scheme for it. The electronic design should not be complicated at all - just a timing circuit and a bunch of shift registers strung togteher - and it should be possible to achieve zero-power scheduled and intelligent wakeup this way.

We should find out what is the bandwidth in which a Rf-Id tag can differentiate between frequencies. And what is the relation between the transmit power needed to wake up a Rf-Id tag, and the distance to that tag. This will tell us more about the sanity of the idea.