US Patent 9557402 Indoor positioning system

An indoor position system, includes a plurality of anchor stations each configured to transmit a radio frequency signal and an acoustic signal. A mobile station includes a radio frequency receiver configured to receive a radio frequency signal from at least one of the plurality of anchor stations and an acoustic receiver configured to receive an acoustic signal from at least one of the plurality of anchor stations. A processing unit is configured to determine position information of the mobile unit based upon the received radio frequency signal and acoustic signal.