Certain aspects of the disclosure relate to combining uplink and downlink location technologies into a single location-service system, to obtain the benefits offered by both of technologies while eliminating many of their individual shortcomings. Mobile devices that support downlink can then be located...http://www.google.com/patents/US7110774?utm_source=gb-gplus-sharePatent US7110774 - Dual mode uplink/downlink location measurement and multi-protocol location measurement
