Distance Between multiple arduinos

hi

i'm beginning project involves calculation of distance between 2 or more arduinos.
i need time difference of arrival (tdoa) method, sending rf signal synchronize arduinos , manage calculate distance difference between time of arrival of rf signal , time of ultrasound arrival.
the link below have image illustrating method:



so, project have rf zigbee module synchronization , ultrasonic module each arduinos .
i need decent coverage angle ultrasonic modules found ping))) parallax (http://www.parallax.com/product/28015).
my idea put 4 ping))) in each arduino, each facing different directions decent coverage.

so, wonder if ping))) ultrasonic modules work in type of project (one transmitting , 1 receiving).  
and if works, putting 4 ping))) arduino a transmitting simultaneously , 4 ping))) arduino b receiving simultaneously possible?

thanks!

quote

so, wonder if ping))) ultrasonic modules work in type of project (one transmitting , 1 receiving).

it idea read documentation various bits of hardware use, before designing system. question answered both on ping))) product page, , in documentation: http://www.parallax.com/downloads/detecting-distance-ping-ultrasonic-sensor

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