Controlled Pilot Transmitter for Location Based Services in cdma2000 1x Cellular Systems

Controlled pilot transmitter (CPT) is proposed to improve location based services (LBS) in cdma2000 1x cellular systems for the areas where gpsOne is not satisfactory such as in-buildings and subway stations. CPT transmits two paths components pilot channel containing its identification (ID) information. Mobile station (MS) detects the path components of CPT during normal cell search operation, especially MS operates in traffic state, and reports the searching result to the positioning server where CPT ID is computed. And then, the positioning server estimates MS location from the known CPT location. There is no need to change the software of MS so existing gpsOne subscribers are also served. The lowest possible CPT level is investigated by evaluating the partial correlation property of cdma2000 1x system PN sequence. The capacity reduction of cdma2000 1x system due to CPT is given. Both laboratory and field test results are given. It is shown that CPT reduces the system capacity negligibly and improves the position accuracy remarkably so it makes LBS possible at in-buildings and subway stations