METHODS AND SYSTEMS FOR HANDOVER USING INCREASED PROBABLITY FOR FAST RANGING SUCCESS

• US 20100103903A1
• Filed: 10/29/2008
• Published: 04/29/2010
• Est. Priority Date: 10/29/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Lee, Kuo-Chun, Lee, Chun Woo, Park, Jong Ro
• Granted Patent: US 9,026,113 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04B 17/364 Delay profiles
• CPC Class Codes: H04B 17/382 for resource allocation, admission control or handover
• CPC Class Codes: H04W 36/0033 with transfer of context information
• CPC Class Codes: H04W 36/08 Reselecting an access point
• 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 56/0065 using measurement of signal travel time

Abstract

Techniques presented herein disclose handover using increased probability of the fast ranging success. Propagation delay of the RF signal transmitted from an MS to a target BS may be estimated based on a known propagation delay to a current serving BS and a relative difference in propagation delays to the current serving BS and the target BS, for example, as indicated by different receive times of preamble sequences transmitted from the current serving BS and the target BS.

Claims

1. A method for ranging with a target base station (BS) by a mobile station (MS), comprising:

calculating a relative time difference in radio frequency (RF) signal propagation delays to a current serving BS and to the target BS;

estimating a RF signal propagation delay to the target BS based on the calculated relative time difference and a known propagation delay to the current serving BS; and

adjusting a starting time of a ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS.

2. The method of claim 1, wherein calculating a relative time difference in radio frequency (RF) signal propagation delays to the current serving BS and to the target BS comprises:

calculating a time difference between reception of preamble sequences transmitted from the target BS and the current serving BS.

3. The method of claim 2, wherein adjusting a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS, comprises:

calculating an absolute uplink starting time for the target BS based on a start time of a frame transmission from the target BS, a downlink sub-frame duration, and a downlink to uplink guard time; and

determining a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS and the calculated absolute uplink starting time.

4. The method of claim 1, further comprising obtaining the known propagation delay to the current serving BS by at least one of:

initial ranging operations with the current serving BS; and

periodic ranging operations with the current serving BS.

5. The method of claim 1, wherein the serving BS and the target BS are time-synchronized, such that each starts frame transmissions at substantially the same time as the other.

6. The method of claim 1, further comprising:

adjusting transmission power of the ranging request message (RNG-REQ) based on a received signal strength (RSS) of a transmission from the target BS, a maximum equivalent isotropic radiated power value, and a base station effective isotropic radiated power value.

7. An apparatus for ranging with a target base station (BS) by a mobile station (MS), comprising:

logic for calculating a relative time difference in radio frequency (RF) signal propagation delays to a current serving BS and to the target BS;

logic for estimating a RF signal propagation delay to the target BS based on the calculated relative time difference and a known propagation delay to the current serving BS; and

logic for adjusting a starting time of a ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS.

8. The apparatus of claim 7, wherein the logic for calculating a relative time difference in radio frequency (RF) signal propagation delays to the current serving BS and to the target BS comprises:

logic for calculating a time difference between reception of preamble sequences transmitted from the target BS and the current serving BS.

9. The apparatus of claim 8, wherein the logic for adjusting a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS, comprises:

logic for calculating an absolute uplink starting time for the target BS based on a start time of a frame transmission from the target BS, a downlink sub-frame duration, and a downlink to uplink guard time; and

logic for determining a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS and the calculated absolute uplink starting time.

10. The apparatus of claim 7, further comprising the logic for obtaining the known propagation delay to the current serving BS by at least one of:

initial ranging operations with the current serving BS; and

periodic ranging operations with the current serving BS.

11. The apparatus of claim 7, wherein the serving BS and the target BS are time-synchronized, such that each starts frame transmissions at substantially the same time as the other.

12. The apparatus of claim 7, further comprising:

logic for adjusting transmission power of the ranging request message (RNG-REQ) based on a received signal strength (RSS) of a transmission from the target BS, a maximum equivalent isotropic radiated power value, and a base station effective isotropic radiated power value.

13. An apparatus for ranging with a target base station (BS) by a mobile station (MS), comprising:

means for calculating a relative time difference in radio frequency (RF) signal propagation delays to a current serving BS and to the target BS;

means for estimating a RF signal propagation delay to the target BS based on the calculated relative time difference and a known propagation delay to the current serving BS; and

means for adjusting a starting time of a ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS.

14. The apparatus of claim 13, wherein the means for calculating a relative time difference in radio frequency (RF) signal propagation delays to the current serving BS and to the target BS comprises:

means for calculating a time difference between reception of preamble sequences transmitted from the target BS and the current serving BS.

15. The apparatus of claim 14, wherein the means for adjusting a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS, comprises:

means for calculating an absolute uplink starting time for the target BS based on a start time of a frame transmission from the target BS, a downlink sub-frame duration, and a downlink to uplink guard time; and

means for determining a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS and the calculated absolute uplink starting time.

16. The apparatus of claim 13, further comprising means for obtaining the known propagation delay to the current serving BS by at least one of:

initial ranging operations with the current serving BS; and

periodic ranging operations with the current serving BS.

17. The apparatus of claim 13, wherein the serving BS and the target BS are time-synchronized, such that each starts frame transmissions at substantially the same time as the other.

18. The apparatus of claim 13, further comprising:

means for adjusting transmission power of the ranging request message (RNG-REQ) based on a received signal strength (RSS) of a transmission from the target BS, a maximum equivalent isotropic radiated power value, and a base station effective isotropic radiated power value.

19. A computer-program product for ranging with a target base station (BS) by a mobile station (MS), comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and the instructions comprising:

instructions for calculating a relative time difference in radio frequency (RF) signal propagation delays to a current serving BS and to the target BS;

instructions for estimating a RF signal propagation delay to the target BS based on the calculated relative time difference and a known propagation delay to the current serving BS; and

instructions for adjusting a starting time of a ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS.

20. The method of claim 19, wherein the instructions for calculating a relative time difference in radio frequency (RF) signal propagation delays to the current serving BS and to the target BS comprises:

instructions for calculating a time difference between reception of preamble sequences transmitted from the target BS and the current serving BS.

21. The method of claim 20, wherein the instructions for adjusting a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS, comprises:

instructions for calculating an absolute uplink starting time for the target BS based on a start time of a frame transmission from the target BS, a downlink sub-frame duration, and a downlink to uplink guard time; and

instructions for determining a starting time of the ranging request message (RNG-REQ) transmitted to the target BS, based on the estimated RF signal propagation delay to the target BS and the calculated absolute uplink starting time.

22. The method of claim 19, wherein the instructions further comprise instructions for obtaining the known propagation delay to the current serving BS by at least one of:

initial ranging operations with the current serving BS; and

periodic ranging operations with the current serving BS.

23. The method of claim 19, wherein the serving BS and the target BS are time-synchronized, such that each starts frame transmissions at substantially the same time as the other.

24. The method of claim 19, wherein the instructions further comprise:

instructions for adjusting transmission power of the ranging request message (RNG-REQ) based on a received signal strength (RSS) of a transmission from the target BS, a maximum equivalent isotropic radiated power value, and a base station effective isotropic radiated power value.