Low power counting via collaborative wireless communications

Metrics that aggregate the state of neighboring nodes are frequently used in wireless sensor networks. In this paper, we present two primitives that exploit simultaneous communications in 802.15.4 radios to enable a polling node to calculate with low power the number (or set) of its neighbors where some state predicate of interest holds. In both primitives, the poller assigns transmission powers and response lengths to its respective neighbors for their simultaneous response to each of its poll requests. The two primitives adopt complementary schemes for power assignment such that the Received Signal Strength Indicator (RSSI) of the respective signal from each neighbor is significantly different from that of all others in one primitive and nearly equivalent to that of the others in the other. The first primitive, LinearPoll, suits sparse networks and consumes energy that is linear in the size of its neighborhood, whereas the second primitive, LogPoll, suits dense networks and consumes constant energy. Compared to the state-of-the-art solutions that use multiple sub-carriers, our primitives are simpler and more compute-efficient while provide estimation with comparable quality. Compared to single-carrier solutions, our primitives achieve comparable quality at less than half the energy cost or richer information at comparable energy cost. They are also compatible with other radio physical layers. Based on our implementation for CC2420 radios on the TelosB platform, we evaluate the primitives in different wireless environments and neighborhood topologies to study their performance, the tradeoff between their estimation accuracy and energy cost, and methods for tuning their critical parameters, and we compare them with baseline counting protocols.