Mobile station assisted timing synchronization in a CDMA communication system
In the present invention, the slave base station attains synchronization with the reference base station through messages transmitted from and received by a mobile station either in the soft handoff region between the reference base station and the slave base station or within a range which allows the mobile station to communicate with the slave base station. When the mobile station is not in communication with both the reference base station and the slave base station, then the round trip delay between the mobile station and the reference base station is measured by the reference base station. The reference base station communicates the PN code used by the mobile station over the reverse link to the slave base station. The slave base station acquires the signal from the mobile station and determines when the signal from the mobile station arrives. The slave base station then makes and estimate as to the length of the delay between transmission of a signal from the mobile station to the slave base station. Based upon these measurements and estimates, the slave base station determines the error which is present in the slave base station system time.
1. A system for time synchronizing a second base station with a first base station comprising:
a first base station configured to:
measure a round trip delay interval of transmissions from said first base station to a mobile station in communication with said first base station and back from the mobile station to said first base station; and
a second base station configured to:
receive communications transmitted by the mobile station and note the time of reception;
determine an estimate of a delay which occurs between transmission by the mobile station and reception by said second base station; and
compute a timing correction value based upon the estimate of the delay, the time of reception, and the measured round trip delay interval.
2. The system of claim 1 wherein said second base station is further configured to receive a message indicative of the identity of the mobile station to assist said second base station to receive communications from the mobile station.
3. The system of claim 2 wherein said first base station is further configured to send the message indicative of the identity of the mobile station to said second base station.
4. The system of claim 3 wherein said first base station is further configured to send the message to said second base station via a base station controller in communication with said first base station and said second base station.
5. The system of claim 3 wherein said first base station is further configured to:
receive communications from a plurality of mobile stations; and
select a mobile station most likely to be able to communicate with said second base station.
6. The system of claim 5 wherein said first base station is configured to select the mobile station most likely to be able to communicate with said second base station as a mobile station furthest from said first base station.
7. The system of claim 5 wherein said first base station is configured to select the mobile station most likely to be able to communicate with said second base station in accordance with the state of a PN spreader in the mobile station.
8. The system of claim 5 wherein said first base station is configured to select the mobile station most likely to be able to communicate with said second base station in accordance with the sector of said first base station being used for communication with the mobile station.
9. The system of claim 5 wherein said first base station is configured to select the mobile station most likely to be able to communicate with said second base station in accordance with said measured round trip delay interval.