Criteria for base station selection, including handover, in a wireless communication system

• US 6,954,643 B2
• Filed: 06/25/2003
• Issued: 10/11/2005
• Est. Priority Date: 06/25/2003
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: ArrayComm LLC (Ygomi LLC)
• Inventors: Petrus, Paul
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): DOAN, KIET M
• Application Number:
  US10/606,428
• Publication Number:
  US 20040266474A1
• Time in Patent Office: 839 Days
• Field of Search: 455/453, 455/435.2, 455/452.1, 455/450, 455/67.11, 455/67.13, 455/67.16, 455/525, 455/524, 455/150.1, 455/403, 455/502, 455/436, 370/332
• US Class Current: 455/437
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/382 for resource allocation, admission control or handover
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

The present invention provides method and apparatus for facilitating base station selection/handover by a user terminal in a distributed (e.g., cellular-type) wireless communication system. In accordance with one aspect, hysteresis is adaptively determined as a function of the variance of receive signal strength fluctuations. In turn, an adaptive hysteresis factor can be obtained and used for a subsequent handover decision, for example, based on a cost function that takes into account the hysteresis. In accordance with another aspect, base station selection depends on a number of criteria, such as received signal strength, base station load, and estimated distance between a receiving user terminal and one or more base stations.

Claims

1. A method for selecting a base station comprising:

receiving transmissions from a plurality of base stations;

deriving from the transmissions indications of received signal strength associated with each of the plurality of base stations;

ordering a set of candidate base stations in accordance with descending indications of received signal strength;

deriving from the transmissions load information associated with each of the plurality of base stations;

comparing load information between a likely selected base station and the remaining set of candidate base stations;

deriving from the transmissions distance information associated with each of the plurality of base stations;

comparing distance information between the likely selected base station and the remaining set of candidate base stations;

selecting one of the plurality of base stations as a current base station when the load of and distance to the likely selected base station does not exceed the load of and distance to each of the remaining set of candidate base stations by a first threshold; and

selecting an alternative base station when the load of and distance to the likely selected base station exceeds the load of and distance to an alternative base station of the remaining set of candidate base stations by the first threshold.

2. The method of claim 1, wherein selecting an alternative base station further comprises selecting an alternative base station when also a handover cost function (C_j) associated with the alternative base station exceeds a handover cost function (C_j) associated with the likely selected base station by a second threshold.

3. The method of claim 1, wherein deriving distance information comprises computing distance based on a reference time of transmission indicated in each of the transmissions and a received time of each of the transmissions.

4. The method of claim 1, wherein comparing load information comprises comparing load information using base station pairs in the order of descending indications of received signal strength.

5. The method of claim 1, further comprising:

eliminating a first candidate base station among a plurality of candidate base stations if the load information associated with the first candidate base station indicates the load of the first candidate base station exceeds a threshold.

6. The method of claim 1, wherein the first threshold is equal to two (2).

7. The method of claim 1, wherein the second threshold is equal to 3 dB.

8. The method of claim 1, wherein deriving received signal strength information associated with transmission from each of the plurality of base stations comprises computing a cost function based on the received signal strength of base station pairs of the plurality of base stations and a hysteresis factor.

9. The method of claim 1, wherein the hysteresis factor is adaptively determined based on standard deviation of the received strength for each base station pair.

10. A machine-readable medium having stored thereon a set of machine-executable instructions that, when executed by a data-processing system, cause the system to perform a method for selecting a base station comprising:

receiving transmissions from a plurality of base stations;

deriving from the transmissions indications of received signal strength associated with each of the plurality of base stations;

ordering a set of candidate base stations in accordance with descending indications of received signal strength;

deriving from the transmissions load information associated with each of the plurality of base stations;

comparing load information between a likely selected base station and the remaining set of candidate base stations;

deriving from the transmissions distance information associated with each of the plurality of base stations;

comparing distance information between the likely selected base station and the remaining set of candidate base stations;

selecting one of the plurality of base stations as a current base station when the load of and distance to the likely selected base station does not exceed the load of and distance to each of a the remaining set of candidate base stations by a first threshold; and

selecting an alternative base station when the load of and distance to the likely selected base station exceeds the load of and distance to an alternative base station of the remaining set of candidate base stations by the first threshold.

11. The machine-readable medium of claim 10, wherein selecting an alternative base station further comprises selecting an alternative base station when also a handover cast function (C_j) associated with the alternative base station exceeds a handover cost function (C_j) associated with the likely selected base station by a second threshold.

12. The machine-readable medium of claim 10, wherein deriving distance information comprises computing distance based on a reference time of transmission indicated in each of the transmissions and a received time of each of the transmissions.

13. The machine-readable medium of claim 10, wherein comparing load information comprises comparing load information using base station pairs in the order of descending indications of received signal strength.

14. The machine-readable medium of claim 10, wherein the method further comprises:

eliminating a first candidate base station among a plurality of candidate base stations if the load information associated with the first candidate base station indicates the load of the first candidate base station exceeds a threshold.

15. The machine-readable medium of claim 10, wherein the first threshold is equal to two (2).

16. The machine-readable medium of claim 10, wherein the second threshold is equal to 3 dB.

17. The machine-readable medium of claim 10, wherein deriving received signal strength information associated with transmission from each of the plurality of base stations comprises computing a cost function based on the received signal strength of base station pairs of the plurality of base stations and a hysteresis factor.

18. The machine-readable medium of claim 10, wherein the hysteresis factor is adaptively determined based on standard deviation of the received strength for each base station pair.

19. A user terminal comprising:

a receiver to receive transmissions from a plurality of base stations;

a receive signal strength measurement unit to derive indications of received signal strength for each of the transmissions;

a distance calculation unit to derive from the transmissions distance information associated with each of the plurality of base stations; and

a base station selection unit to;

order a set of candidate base stations in accordance with descending indications of received signal strength, to derive from the transmissions load information associated with each of the plurality of base stations;

compare load information between a likely selected base station and the remaining set of candidate base stations;

compare distance information between the likely selected base station and the remaining set of candidate base stations;

select one of the plurality of base stations as a current base station when the load of and distance to the likely selected base station does not exceed the load of and distance to each of the remaining set of candidate base stations by a first threshold; and

select an alternative base station when the load of and distance to the likely selected base station exceeds the load of and distance to an alternative base station of the remaining set of candidate base stations by the first threshold.

20. The user terminal of claim 19, wherein selecting an alternative base station further comprises selecting an alternative base station when also a handover cost function (C_j) associated with the alternative base station exceeds a handover cost function (C_j) associated with the likely selected base station by a second threshold.

21. The user terminal of claim 19, wherein the distance calculation unit derives distance information by computing distance based on a reference time of transmission indicated in each of the transmissions and a received time of each of the transmissions.

22. The user terminal of claim 19, wherein the signal strength measurement unit derives indications of received signal strength by computing a cost function based on the received signal strength of base station pairs of the plurality of base stations and a hysteresis factor.