A mobile device positioning system determines ranges between a plurality of communication devices, including at least one mobile communication device. A method includes receiving receive messages transmitted from a plurality of other communication devices. Each receive message includes a transmit count stamp corresponding to a remote counter value. A first communication device generates a receive count stamp for each receive message. The method includes dynamically associating and disassociating the mobile communication device with a plurality of sub-groups of the plurality of other communication devices. The associating and disassociating are based at least in part on receiving receive messages from a predetermined number of other communication devices for each sub-group. For each sub-group currently associated with the mobile communication device, the method includes generating range estimates between the mobile communication device and the other communication devices in the particular sub-group. The range estimates are based on a combination of the transmit count stamps and the receive count stamps.