Using statistically ascertained position for starting synchronization searcher during diversity handover

• US 6,980,803 B2
• Filed: 12/03/2001
• Issued: 12/27/2005
• Est. Priority Date: 12/04/2000
• Status: Expired due to Fees

• Current Assignee: Optis Cellular Technology LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Johansson, Steffan
• Primary Examiner(s): D AGOSTA, STEPHEN M
• Application Number:
  US09/998,921
• Publication Number:
  US 20020068567A1
• Time in Patent Office: 1,485 Days
• Field of Search: 455436-444, 455450-4522, 4554561-4566, 455/516, 455/517, 455/552.1, 370331-334
• US Class Current: 455/438
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 36/322 by location data
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 92/20 between access points

Abstract

A code division multiple access communication system comprises a source base station (BS_S), a destination base station (BS_D)having a synchronization searcher (S), and a time position estimator (100) which establishes a start position of a synchronization search window for the synchronization searcher of the destination station. In accordance with an aspect of the present system, the time position estimator establishes the start position (SP) of the synchronization search window based on a statistical estimate of the time position at which other mobile stations previously initiated handover from the source base station to the destination base station. In a non-limiting example embodiment, the time position estimator uses an average time position (T_new) at which other mobile stations previously initiated handover from the source base station to the destination base station as the statistical estimate. In an example illustrated embodiment, the time position estimator is situated at a radio network control node (26) of the code division multiple access communication system, but can be located at other nodes.

Claims

1. A method of operating a code division multiple access communication system having a source base station and a destination base station where a specified mobile station establishes a connection with the source base station, the method comprising:

initiating a handover of the connection involving the specified mobile station to the destination base station;

establishing a start position of a synchronization search window for the specified mobile station at a statistically-ascertained search window time position based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station, the statistically-ascertained search window start time position for the specified mobile station being an average search window start time position for other mobile stations which previously initiated handover from the source base station to the destination base station;

maintaining a filter which calculates a filter output value of the average search window start time position for the specified mobile station, wherein maintaining the filter comprises;

using a search window start time position found for a last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

using an output value of the filter prior to the filter being updated with the search window start time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station.

2. The method of claim 1, wherein the statistically-ascertained search window start time position is calculated using the expression

T_new=a*T_old+(1−

a)*T_last

where;

T_new is the filter output value of the average time position for the specified mobile;

T_last is the search window start time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station;

T_old is the output value of the filter prior to the filter being updated with the search window start time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

a is a weighting factor.

3. The method of claim 1, further comprising maintaining the filter at a radio network control node of the code division multiple access communication system.

4. The method of claim 1, further comprising:

determining the statistically-ascertained search window start time position at a radio network controller node; and

communicating the statistically-ascertained search window start time position from the radio network controller node to the destination base station.

5. The method of claim 4, further comprising maintaining at the radio network control node a table which, for each of plural scenarios of source base stations and destination base stations, stores a corresponding scenario-specific statistically-ascertained search window start time position.

6. The method of claim 1, wherein if the specified mobile station is not found at the search window start time position, the method further comprises attempting to find a transmission of the specified mobile station by looking at a search window position which neighbors the search window start time position.

10. The method of claim 1, further comprising synchronizing the destination base station with a transmission from the specified mobile station using the search window to detect a transmission of the specified mobile station received at the destination base station.

7. A method of operating a code division multiple access communication system having a source base station and a destination base station where a specified mobile station establishes a connection with the source base station, the method comprising:

initiating a handover of the connection involving the specified mobile station to the destination base station;

establishing a start position of a synchronization search window for the specified mobile station at a statistically-ascertained search window time position based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

if the specified mobile station is not found at the search window start time position, attempting to find a transmission of the specified mobile station by looking at a search window position which neighbors the search window start time position; and

with a failure to find the transmission of the specified mobile station, looking at progressively remote neighboring search window positions relative to the search window start time position.

8. A method of operating a code division multiple access communication system having a source base station and a destination base station where a specified mobile station establishes a connection with the source base station, the method comprising:

initiating a handover of the connection involving the specified mobile station to the destination base station;

establishing a start position of a synchronization search window for the specified mobile station at a statistically-ascertained search window time position based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

if the specified mobile station is not found at the search window start time position, attempting to find a transmission of the specified mobile station by looking at a search window position which neighbors the search window start time position; and

if the specified mobile station is not found at the search window start time position, attempting to find the transmission of the specified mobile station by;

looking a first neighboring search window position on a first side of the search window start time position; and

then, if necessary,

looking at a second neighboring search window position on a second side of the search window start time position.

9. The method of claim 8, wherein the first neighboring search window position on the first side of the search window start time position and the second neighboring search window position on the second side of the search window start time position comprise a set of most neighboring search window positions, and wherein, upon failure to find the transmission of the specified mobile station at either of the most neighboring search window positions, looking at progressively remote sets of neighboring search window positions.

11. A code division multiple access communication system comprising:

a source base station;

a destination base station having a synchronization searcher;

a time position estimator which establishes a start position of a synchronization search window for the synchronization searcher of the destination base station, the synchronization search window being used to detect a transmission of a specified mobile station received at the destination base station during a handover of a connection involving the specified mobile station from a source base station to the destination base station, the time position estimator establishing the start position of the synchronization search window as a statistically-ascertained search window time position based on time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

wherein the statistically-ascertained time position for the specified mobile station is an average search window start time position for other mobile stations which previously initiated handover from the source base station to the destination base station, wherein the time position estimator maintains a filter which calculates a filter output value of the average time position for the specified mobile station;

wherein the filter uses a search window start time position found for a last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

wherein the filter uses an output value of the filter prior to the filter being updated with the time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station.

12. The apparatus of claim 11, wherein the statistically-ascertained time position is calculated using the expression

T_new=a*T_old+(1−

a)*T_last

where;

T_new is the filter output value of the average time position for the specified mobile;

T_last is the search window start time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station;

T_old is the output value of the filter prior to the filter being updated with the time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

a is a weighting factor.

13. The apparatus of claim 11, wherein the time position estimator resides at a radio network control node of the code division multiple access communication system.

14. The apparatus of claim 13, wherein the radio network controller node communicates the search window start time position to the destination base station.

15. The apparatus of claim 11, wherein the time position estimator maintains a table which, for each of plural scenarios of source base stations and destination base stations, stores a corresponding scenario-specific search window start time position.

16. The apparatus of claim 11, wherein if the specified mobile station is not found at the search window start time position, the destination base station attempts to find a transmission of the specified mobile station by looking at a search window position which neighbors the start time position.

20. The apparatus of claim 11, wherein the destination base station starts synchronization of a mobile-to-source leg when the searcher sees a predetermined transmission from the specified mobile station.

17. A code division multiple access communication system comprising:

a source base station;

a destination base station having a synchronization searcher;

a time position estimator which establishes a start position of a synchronization search window for the synchronization searcher of the destination base station, the synchronization search window being used to detect a transmission of a specified mobile station received at the destination base station during a handover of a connection involving the specified mobile station from a source base station to the destination base station, the time position estimator establishing the start position of the synchronization search window as a statistically-ascertained search window time position based on time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

wherein if the specified mobile station is not found at the search window start time position, the destination base station attempts to find a transmission of the specified mobile station by looking at a search window position which neighbors the start time position; and

wherein, with a failure to find the transmission of the specified mobile station, the destination base station looks at progressively remote neighboring search window positions relative to the start time position.

18. A code division multiple access communication system comprising:

a source base station;

a destination base station having a synchronization searcher;

a time position estimator which establishes a start position of a synchronization search window for the synchronization searcher of the destination base station, the synchronization search window being used to detect a transmission of a specified mobile station received at the destination base station during a handover of a connection involving the specified mobile station from a source base station to the destination base station, the time position estimator establishing the start position of the synchronization search window as a statistically-ascertained search window time position based on time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

wherein if the specified mobile station is not found at the search window start time position, the destination base station attempts to find a transmission of the specified mobile station by looking at a search window position which neighbors the start time position; and

wherein if the specified mobile station is not found at the start time position, the destination base station attempts to find the transmission of the specified mobile station by looking at a first neighboring search window position on a first side of the search window start time position, and then, if necessary, looking at a second neighboring search window position on a second side of the search window start time position.

19. The apparatus of claim 18, wherein the first neighboring search window position on the first side of the search window start time position and the second neighboring search window position on the second side of the search window start time position comprise a set of most neighboring search window positions, and wherein, upon failure to find the transmission of the specified mobile station at either of the most neighboring search window positions, the destination base station looks at progressively remote sets of neighboring search window positions.

21. A time position estimator situated at a node of code division multiple access communication system comprising, the time position estimator serving to establish a start position of a synchronization search window for a synchronization searcher of a destination base station, the synchronization search window being used to detect a transmission of a specified mobile station received at the destination base station during a handover of a connection involving the specified mobile station from a source base station to the destination base station, the time position estimator establishing the start position of the synchronization search window as a statistically-ascertained search window start time position based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station;

wherein the statistically-ascertained time position for the specified mobile station is an average search window start time position at which other mobile stations previously initiated handover from the source base station to the destination base station, wherein the time position estimator maintains a filter which calculates a filter output value of the average search window start time position for the specified mobile station;

wherein the filter uses a search window start time position found for a last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

wherein the filter uses an output value of the filter prior to the filter being updated with the time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station.

22. The apparatus of claim 21, wherein the statistically-ascertained time position is calculated using the expression

T_new=a*T_old+(1−

a)*T_last

where;

T_new is the filter output value of the average time position for the specified mobile;

T_last is the search window start time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station;

T_old is the output value of the filter prior to the filter being updated with the time position found for the last mobile station which initiated handover from the source base station to the destination base station prior to the specified mobile station; and

a is a weighting factor.

23. The apparatus of claim 21, wherein the time position estimator resides at a radio network control node of the code division multiple access communication system.

24. The apparatus of claim 23, wherein the radio network controller node communicates the search window start time position to the destination base station.

25. The apparatus of claim 21, wherein the time position estimator maintains a table which, for each of plural scenarios of source base stations and destination base stations, stores a corresponding scenario-specific search window start time position.

26. A synchronization searcher for a destination base station of a code division multiple access communication system, the synchronization searcher using a synchronization search window to detect a transmission of a mobile station during a handover of a connection involving the mobile station to the destination base station, there being a start position of the synchronization search window, the start position of the synchronisation search window being based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station, wherein if the specified mobile station is not found at the search window start time position, the synchronization searcher attempts to find the transmission of the mobile station by looking at a search window position which neighbors the search window start time position;

wherein, with a failure to find the transmission of the specified mobile station, the synchronization searcher looks at progressively remote neighboring search window positions relative to the search window start time position.

27. The apparatus of claim 26, wherein the synchronization searcher starts synchronization of a mobile-to-source leg upon seeing a predetermined transmission from the mobile station.

28. A synchronization searcher for a destination base station of a code division multiple access communication system, the synchronization searcher using a synchronization search window to detect a transmission of a mobile station during a handover of a connection involving the mobile station to the destination base station, there being a start position of the synchronization search window, the start position of the synchronization search window being based on search window start time positions for other mobile stations which previously initiated handover from the source base station to the destination base station, wherein if the specified mobile station is not found at the search window start time position, the synchronization searcher attempts to find the transmission of the mobile station by looking at a search window position which neighbors the search window start time position;

wherein if the specified mobile station is not found at the search window start time position, the synchronization searcher attempts to find the transmission of the mobile station by looking at a first neighboring search window position on a first side of the search window start time position, and then, if necessary, looking at a second neighboring search window position on a second side of the search window start time position.

29. The apparatus of claim 28, wherein the first neighboring search window position on the first side of the search window start time position and the second neighboring search window position on the second side of the search window start time position comprise a set of most neighboring search window positions, and wherein, upon failure to find the transmission of the specified mobile station at either of the most neighboring search window positions, the synchronization searcher looks at progressively remote sets of neighboring search window positions.