  Ranging by Time of Arrival (TOA) of Narrow-band ultrasound (NBU) has been
widely used by many locating systems for its characteristics of low cost and
high accuracy. However, because it is hard to support code division multiple
access in narrowband signal, to track multiple targets, existing NBU-based
locating systems generally need to assign exclusive time slot to each target to
avoid the signal conflicts. Because the propagation speed of ultrasound is slow
in air, dividing exclusive time slots on a single channel causes the location
updating rate for each target rather low, leading to unsatisfied tracking
performances as the number of targets increases. In this paper, we investigated
a new multiple target locating method using NBU, called UltraChorus, which is
to locate multiple targets while allowing them sending NBU signals
simultaneously, i.e., in chorus mode. It can dramatically increase the location
updating rate. In particular, we investigated by both experiments and
theoretical analysis on the necessary and sufficient conditions for resolving
the conflicts of multiple NBU signals on a single channel, which is referred as
the conditions for chorus ranging and chorus locating. To tackle the difficulty
caused by the anonymity of the measured distances, we further developed
consistent position generation algorithm and probabilistic particle filter
algorithm}to label the distances by sources, to generate reasonable location
estimations, and to disambiguate the motion trajectories of the multiple
concurrent targets based on the anonymous distance measurements. Extensive
evaluations by both simulation and testbed were carried out, which verified the
effectiveness of our proposed theories and algorithms.
