Parrot nodes consist of a microcontroller, a radio transceiver and four
pairs of ultrasonic sensors. Using ultrasound pulses to measure the
distances between each other, each node in turn sends out a radio signal
followed by an ultrasonic pulse train. Other Parrots that receive both
signals convert the time difference between receiving the radio signal
and the ultrasonic signal to a distance measurement by multiplying with
the speed of sound.
The Parrots automatically formulate an ad hoc multi-hop wireless network
to share the range information. They employ a distributed architecture
in which every Parrot will have all the distance measurements for all
the Parrots in the network, eliminating the requirement of a central
node for the coordination. Every Parrot can be both sender and receiver.
The Parrots coordinate the pining sequence such that ultrasonic pulses
from multiple Parrots do not interfere with one another
Compared with similar ultrasonic ranging nodes such as the Cricket, the
Parrot achieves a longer ranging distance of up to 15 meters with an
accuracy of 2cm. It is also more effective in detecting ultrasonic
signals by using four pairs of ultrasonic sensors, making it able to
detect ultrasonic signal from any direction and reducing the number of
nodes required by similar systems, which in turn leads to an improved
update rate of the distance measurements and make the tracking of a
moving object more efficient. Since the parrots can estimate the
direction of the signal (to approximately 90 degrees) the ambiguity
inherent to omni-directional range-only sensors is reduced, thus
improving the accuracy of standard localization and mapping algorithms
