Mobile station assisted timing synchronization in a CDMA communication system

• US 6,151,311 A
• Filed: 01/27/1999
• Issued: 11/21/2000
• Est. Priority Date: 09/19/1997
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tiedemann, Edward G. Jr., Wheatley, Charles E. III
• Primary Examiner(s): Nguyen, Chau
• Assistant Examiner(s): Vanderpag, Ken
• Application Number:
  US09/238,125
• Time in Patent Office: 664 Days
• Field of Search: 370/335, 370/350, 370/328, 370/342, 370/441, 370/503, 370/507, 370/508, 370/509, 370/516, 370/519, 370/470, 375/356, 375/252, 455/676, 455/442, 455/502
• US Class Current: 370/335
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 92/20 between access points

Abstract

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 in the soft handoff region between the reference base station and the slave base station. First, the round trip delay between the mobile station and the reference base station is measured by the reference base station. Once the mobile station acquires the signal from the slave base station, it measures and reports the difference between the amount of time it takes a signal to travel from the reference base station to it and the amount of time it takes a signal to travel from the slave base station to it. The last measurement necessary is a measurement by the slave base station of the time difference between the time it received the reverse link signal from the mobile and station the time it transmitted a signal to the mobile station. A series of computations described in detail herein are performed upon the measured time values to determine the time difference between the slave base station and an adjustment of the slave base station timing is performed in accordance therewith.

Claims

1. A method for time synchronizing a slave base station with a reference base station, comprising the steps of:

measuring a round trip delay for at least one signal transmitted from said reference base station to a mobile station and back from said mobile station to said reference base station;

measuring a first time difference between the time of receipt at said mobile station of a signal transmitted from said slave base station and the time of receipt at said mobile station of a related signal transmitted from said reference base station;

measuring a second time difference between the receipt at said slave base station of a signal transmitted from said mobile station and the time of transmission of a related signal from said slave base station; and

computing a timing correction value in accordance with said measured round trip delay, said first time difference, and said second time difference.

2. The method in accordance with claim 1, further comprising the step of handing off transmissions between said reference base station and said mobile station to said slave base station and said mobile station.

7. The method in accordance with claim 1, further comprising the step of adjusting said slave base station timing to coincide with the timing of said reference base station if said time correction value exceeds a predetermined value.

8. The method in accordance with claim 7, further comprising the step of making said measurements repeatedly and disregarding aberrant measurements prior to making a timing adjustment computation.

9. The method in accordance with claim 8, further comprising the step of using an average of said repeated measurements to make a timing adjustment computation.

10. The method in accordance with claim 1, wherein said round trip delay for at least one signal transmitted from said reference base station to a mobile station is measured at said reference base station.

17. The method in accordance with claim 1, wherein said timing correction value is in accordance with a timing error between said slave base station and said reference base station and said timing error equals (RTD₁ +→

T-RTD₂)/2;

wherein RTD₁ is a round trip delay for at least one transmission from said reference base station to a mobile station and a transmission from said mobile station to said reference base station;

wherein →

T is a time difference between the time a transmission from said slave base station is received at said mobile station and the time a transmission from said reference base station is received at said mobile station; and

wherein RTD₂ is a round trip delay for at least one transmission between said slave base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said slave base station from said mobile station and the time a related transmission is transmitted from said slave base station to said mobile station.

3. An article of manufacture comprising a digital signal storage medium embodying machine readable instructions executable by a digital signal processing apparatus, wherein said machine readable instructions are capable of governing a function of a hardware device, and wherein said machine readable instructions comprise the steps of:

measuring a round trip delay interval of transmissions from said reference base station to a mobile station in communication with said reference base station and back from said mobile station to said reference base station;

measuring at said mobile station a first time difference between the time of receipt of a forward link signal from said slave base station and the time of receipt of a forward link signal from said reference base station;

measuring at said slave base station a second time differences between the receipt of a reverse link signal from said mobile station and the time of transmission of a forward link signal from said slave base station; and

computing a timing correction value in accordance with said measured round trip delay interval, said first time difference and said second time difference.

4. The article of manufacture in accordance with claim 3, wherein the machine readable instructions further comprise adjusting said slave base station timing to coincide with the timing of said reference station if said time correction value exceeds a predetermined value.

5. The article of manufacture in accordance with claim 4, wherein the machine readable instructions further comprise handing off transmissions between said reference base station and said mobile station to said slave base station and said mobile station after said slave station timing, if necessary, is adjusted.

18. The article of manufacture in accordance with claim 3, wherein said timing correction value is in accordance with a timing error between said slave base station and said reference base station and said timing error equals (RTD₁ +→

T-RTD₂)/2;

wherein RTD₁ is a round trip delay for at least one transmission from said reference base station to a mobile station and a transmission from said mobile station to said reference base station;

wherein →

T is a time difference between the time a transmission from said slave base station is received at said mobile station and the time a transmission from said reference base station is received at said mobile station; and

wherein RTD₂ is a round trip delay for at least one transmission between said slave base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said slave base station from said mobile station and the time a related transmission is transmitted from said slave base station to said mobile station.

6. A signal processing machine used to synchronize base stations in a communications system, comprising:

a first base station that is in signal synchronization with said communication system;

a mobile station that is in signal synchronization with said communication system; and

a second base station that is not in signal synchronization with said communication system;

a digital processing means capable of processing digital instructions for;

measuring a round trip delay interval for transmissions from said first base station to said mobile station;

measuring a first time difference between the time said mobile station receives a forward link signal from said second base station and the time said mobile station receives a forward link signal from said first base station;

measuring a second time difference between the time said second base station receives a reverse link signal from said mobile station and the time of transmission of a forward link signal from said second base station; and

computing a timing correction value in accordance with said measured round trip delay interval, said first time difference, and said second time difference.

16. The signal processing machine in accordance with claim 6, further comprising a means for adjusting said second base station'"'"'s synchronization to harmonize with the synchronization of said communication system if said time correction value exceeds a predetermined value.

19. The signal processing machine in accordance with claim 6, wherein said timing correction value is in accordance with a timing error between said second base station and said first base station and said timing error equals (RTD₁ +→

T-RTD₂)/2;

wherein RTD₁ is a round trip delay for at least one transmission from said first base station to a mobile station and a transmission from said mobile station to said first base station;

wherein →

T is a time difference between the time a transmission from said second base station is received at said mobile station and the time a transmission from said first base station is received at said mobile station; and

wherein RTD₂ is a round trip delay for at least one transmission between said second base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said second base station from said mobile station and the time a related transmission is transmitted from said second base station to said mobile station.

11. A method for time synchronizing a slave base station with a reference base station, comprising the steps of:

measuring at said reference base station a round trip delay for at least one transmission from said reference base station to a mobile station and a transmission from said mobile station to said reference base station;

acquiring at said slave station a transmission from said mobile station;

adjusting said slave base station time reference, if necessary, to allow said mobile station to receive a transmission from said slave base station;

acquiring at said mobile station a transmission from said slave station;

measuring at said mobile station a first time difference between the time of receipt at said mobile station of a transmission from said slave base station and the time of receipt at said mobile station of a transmission from said reference base station;

communicating said first time difference to said reference base station and said slave base station;

measuring at said slave base station a round trip delay for at least one transmission between said slave base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said slave base station from said mobile station and the time a related transmission is transmitted from said slave base station to said mobile station; and

computing at a base station controller a timing correction value for said slave station in accordance with said measurements.

12. The method in accordance with claim 11, further comprising the step of adjusting said slave base station timing in harmony with the timing of said reference station if said time correction value exceeds a predetermined value.

20. The method in accordance with claim 11, wherein said timing correction value is in accordance with a timing error between said slave base station and said reference base station and said timing error equals (RTD₁ +→

T-RTD₂)/2;

wherein RTD₁ is a round trip delay for at least one transmission from said reference base station to a mobile station and a transmission from said mobile station to said reference base station;

wherein →

T is a time difference between the time a transmission from said slave base station is received at said mobile station and the time a transmission from said reference base station is received at said mobile station; and

wherein RTD₂ is a round trip delay for at least one transmission between said slave base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said slave base station from said mobile station and the time a related transmission is transmitted from said slave base station to said mobile station.

13. An article of manufacture comprising a digital signal storage medium embodying machine readable instructions executable by a digital signal processing apparatus, wherein said machine readable instructions are capable of governing a function of a hardware device, and wherein said machine readable instructions comprise the steps of:

measuring at said reference base station a round trip delay for at least one transmission from said reference base station to a mobile station and a transmission from said mobile station to said reference base station;

acquiring at said slave station a transmission from said mobile station;

adjusting said slave base station time reference, if necessary, to allow said mobile station to receive a transmission from said slave base station;

acquiring at said mobile station a transmission from said slave station;

measuring at said mobile station a first time difference between the time of receipt at said mobile station of a transmission from said slave base station and the time of receipt at said mobile station of a transmission from said reference base station;

communicating said first time difference to said reference base station and said slave base station;

measuring at said slave base station a round trip delay for at least one transmission between said slave base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said slave base station from said mobile station and the time a related transmission is transmitted from said slave base station to said mobile station; and

computing at a base station controller a timing correction value for said slave station in accordance with said measurements.

14. The article in accordance with claim 13, wherein said machine readable instructions further comprise the step of adjusting said slave base station timing in harmony with the timing of said reference station if said time correction value exceeds a predetermined value.

15. An apparatus used to synchronize base stations in a communications system, comprising:

at least one mobile station communicatively coupled to said communications system and in signal synchronization with said communication system;

a first base station communicatively coupled to said communications system and in signal synchronization with said communications system, said first base station including a first means for measuring a round trip delay for at least one transmission from said first base station to a mobile station and a transmission from said mobile station to said first base station;

a second base station communicatively coupled with said mobile station but not in signal synchronization with said communications system, said second base station including a second means for measuring a round trip delay for at least one transmission between said second base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said second base station from said mobile station and the time a related transmission is transmitted from said second base station to said mobile station;

wherein said mobile station includes a third means for measuring the time difference between the time a transmission from said second base station is received at said mobile station and the time a transmission from said first base station is received at said mobile station;

a means for computing a second base station synchronization adjustment timing correction value using said measurements; and

a means for adjusting said second base station'"'"'s synchronization to harmonize with the synchronization of said first base station if said time correction value exceeds a predetermined value.

21. The apparatus in accordance with claim 15, wherein said timing correction value is in accordance with a timing error between said second base station and said first base station and said timing error equals (RTD₁ +→

T-RTD₂)/2; and

wherein RTD₁ is a round trip delay for at least one transmission from said first base station to a mobile station and a transmission from said mobile station to said first base station;

wherein →

T is a time difference between the time a transmission from said second base station is received at said mobile station and the time a transmission from said first base station is received at said mobile station; and

wherein RTD₂ is a round trip delay for at least one transmission between said second base station and said mobile station, said round trip delay corresponding to the time a transmission is received at said second base station from said mobile station and the time a related transmission is transmitted from said second base station to said mobile station.