Since I started working on wireless sensor networks in the late 90s, we’ve dropped the power consumption by four or five orders of magnitude. In the DARPA-sponsored Smart Dust program, we built little boards with cordless phone radios and 8-bit microprocessors on them. We showed that you could do multi-hop routing between nodes, or “motes” as we called them, in honor of our dusty roots. The motes were always listening to see if their neighbors had something to say, they burned about 100mW, and our AA battery-powered nodes lasted about two weeks.

During the middle of the last decade, as a community we found many ways of letting our routing nodes turn their radios off most of the time, and still be able to wake up and exchange packets with their neighbors, trading off power consumption and latency. The best of these protocols are now standardized in several places, most importantly the new IEEE 802.15.4E standard for reliable, low power medium access. These protocols allow routing nodes to leave their radios off an amazing 99.99% of the time, and still forward packets with only a few seconds of latency.

“Sleepy” routers account for most of the power savings in the last decade, but there have been tremendous improvements in radio power consumption as well. Since the early days of Smart Dust, the standard radio bit rate has increased by a factor of 25, to 250kbps, but the power consumption has dropped by more than a factor of 10, to under 10mW.

Between the savings in the hardware, and the improvements in the algorithms, we can now run an IPv6 router on a few tens of microwatts. That gives you more than 10 years of lifetime on a single AA lithium battery, or indefinite lifetime with a postage-stamp sized solar cell or other energy scavenger.

Kris Pister
Dust Networks CTO
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