Providing an accurate timing source for locating the geographical position of a mobile

• US 6,493,539 B1
• Filed: 07/28/1999
• Issued: 12/10/2002
• Est. Priority Date: 07/28/1999
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Falco, Steven A., Murphy, Myles P., McKay, Bernard, Tsai, Sheng-Jen, Matusevich, Alex
• Primary Examiner(s): CRAVER, CHARLES R
• Assistant Examiner(s): Woldetatios, Yemane
• Application Number:
  US09/362,548
• Time in Patent Office: 1,231 Days
• Field of Search: 455/503, 455/436, 455/437, 455/438, 455/439, 455/440, 455/444, 455/502, 455/504, 455/422, 370/252, 370/503, 370/507, 370/508, 370/519, 370/350, 432/450, 432/457
• US Class Current: 455/67.11
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: H04B 7/2687 Inter base stations synchronisation
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The synchronization system uses a TDMA or AMPS air interface to provide timing synchronization between previously unsynchronized base stations. The synchronization of base stations is critical between when determining the geographical position of a mobile because the geographical position is determined using a time difference of arrival method. In order to synchronize a remote base station with a serving base station, the remote base station receives a signal from the serving base station and measuring the receiving time of the signal at the remote base station in relation to the clock of the remote base station. The synchronization system determines the transmission time of the signal based on the reception time of the signal and the distance between the base stations, in relation to the clock signal of the second station, and synchronizes the clock of the remote base station to the clock of the serving base station based on the offset in the clock cycles at the time the signal was transmitted.

Claims

1. A method for synchronizing a first base station and a second base station, comprising:

(a) receiving a first signal from the first base station, the first base station having a clock signal unsynchronized with a clock signal of the second base station;

(b) measuring a receiving time of the first signal in relation to the clock signal of the second base station;

(c) determining a transmission time of the first signal based on the measured receiving time of the first signal and a distance between the first base station and the second base station, in relation to the clock signal of the second base station; and

(d) synchronizing the clock signal of the second base station to the clock signal of the first base station based on a signal cycle difference between the clock signals at the transmission time.

2. The method of claim 1, further comprising:

(e) receiving a second signal;

(f) measuring a receiving time of the second signal in relation to the clock signal of the second station; and

(g) determining the difference between the transmission time of the first signal and the receiving time of the second signal.

3. The method of claim 2, wherein the second signal is received from a source other than the first station.

4. The method of claim 1, further comprising:

(e) measuring a predetermined time based on the first signal in relation to the clock signal of the second station;

(f) receiving a second signal;

(g) measuring a receiving time of the second signal in relation to the clock signal of the second station; and

(h) determining a difference between the predetermined time and the receiving time of the second signal.

5. The method of claim 4, wherein the predetermined time is indicative of a time when the first station transmits a control message.

6. The method of claim 4, wherein the second signal is received from a source other than the first station.

7. A method for synchronizing a first base station and a plurality of second base stations, comprising:

(a) transmitting a down link message to the second base stations to synchronize a symbol clock of each of the second base stations to a symbol clock of the first base station;

(b) transmitting a control message to the mobile at a predetermined time, the control message requesting a reply message from the mobile;

(c) receiving the reply message from the mobile and measuring a time that the reply message was received at the first base station as a first base station receiving time;

(d) determining a difference between the predetermined time and the first base station receiving time as a first base station time difference; and

(e) receiving messages from the second base stations representing a difference between the predetermined time and a time that the reply message was received at each second base station as a plurality of second base station time differences, so a location of the mobile can be determined.

8. The method of claim 7, prior to step (a), further comprising:

(x) transmitting a request message to a plurality of nearby stations to determine a strength of a signal originating from a mobile;

(y) receiving response messages from the nearby stations indicating the strength of the signal originating from the mobile; and

(z) determining the nearby stations having the strength greater than a predetermined amount as the second stations.

9. The method of claim 7, prior to step (a), further comprising:

(z) receiving one of a 911 call and a mobile locate call as a mobile locate request,

wherein step (a) transmits the down link message to the second stations based on the mobile locate request.

10. The method of claim 7, wherein the down link message informs the second station of the predetermined time when the control message is transmitted.

11. A synchronization system implemented on a computer, comprising:

means for receiving a first signal from the first base station, the first base station having a clock signal unsynchronized with a clock signal of the second base station;

means for measuring a receiving time of the first signal in relation to the clock signal of the second base station;

means for determining a transmission time of the first signal based on the measured receiving time of the first signal and a distance between the first base station and the second base station, in relation to the clock signal of the second base station; and

means for synchronizing the clock signal of the second base station to the clock signal of the first base station based on a signal cycle difference between the clock signals at the transmission time.

12. The synchronization system of claim 11, further comprising:

subsequent means for receiving a second signal;

subsequent means for measuring a receiving time of the second signal in relation to the clock signal of the second station; and

subsequent means for determining the difference between the transmission time of the first signal and the receiving time of the second signal.

13. The synchronization system of claim 11, wherein the second signal is received from a source other than the first station.

14. The synchronization system of claim 11, further comprising:

first subsequent means for measuring a predetermined time based on the first signal in relation to the clock signal of the second station;

subsequent means for receiving a second signal;

second subsequent means for measuring a receiving time of the second signal in relation to the clock signal of the second station; and

subsequent means for determining a difference between the predetermined time and the receiving time of the second signal.

15. The synchronization system of claim 14, wherein the predetermined time is indicative of a time when the first station transmits a control message.

16. An executable program embodied on a computer-readable medium for synchronizing a first base station and a second base station, comprising:

a receiving source code segment for receiving a first signal from the first base station, the first base station having a clock signal unsynchronized with a clock signal of the second base station;

a measuring source code segment for measuring a receiving time of the first signal in relation to the clock signal of the second base station;

a determining source code segment for determining a transmission time of the first signal based on the measured receiving time of the first signal and a distance between the first base station and the second base station, in relation to the clock signal of the second base station; and

a synchronizing source code segment for synchronizing the clock signal of the second base station to the clock signal of the first base station based on a signal cycle difference between the clock signals at the transmission time.

17. A computer data signal, comprising:

a receiving signal segment for receiving a first signal from the first base station, the first base station having a clock signal unsynchronized with a clock signal of the second base station;

a measuring signal segment for measuring a receiving time of the first signal in relation to the clock signal of the second base station;

a determining signal segment for determining a transmission time of the first signal based on the measured receiving time of the first signal and a distance between the first base station and the second base station, in relation to the clock signal of the second base station; and

a synchronizing signal segment for synchronizing the clock signal of the second base station to the clock signal of the first base station based on a signal cycle difference between the clock signals at the transmission time.