Method for determining handover margins in a cellular communication system

• US 6,044,249 A
• Filed: 11/12/1996
• Issued: 03/28/2000
• Est. Priority Date: 11/12/1996
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Chandra, Claudia, Jeanes, Timothy M., Leung, Wu-Hon Francis
• Primary Examiner(s): CUMMING, WILLIAM D
• Application Number:
  US08/745,523
• Time in Patent Office: 1,232 Days
• Field of Search: 455/456, 455/513, 455/430, 455/442, 455/437, 455/62, 455/444, 455/439, 375/200, 370/335, 370/331, 370/347
• US Class Current: 455/62
• CPC Class Codes: H04W 36/20 for optimising the interference level
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

Optimal handover margins in a cellular communication system (100) are determined by computing a power budget (701) for each base station/neighbor combination in the communication system (100) and determining a probability distribution function (703) for each base station/neighbor combination in the communication system (100). Once the probability distribution function for each base station/neighbor combination is known, optimal handover margins are determined by maximizing communication system traffic over all base stations while at the same time holding call quality to acceptable levels.

Claims

1. A method for determining a handover margin (H) in a communication system, the method comprising the steps of:

measuring a signal quality of a serving base station and a neighbor base station to produce a comparison in signal quality between the serving and the neighbor base station;

determining a percentage of traffic absorbed by the neighbor base station for a given handover margin based on the comparison in signal quality between the serving and the neighbor base station; and

adjusting the handover margin between the serving base station and the neighbor base station based on the step of determining, wherein a handoff occurs from the serving base station to the neighbor base station when PL(c)-PL(n)≧

H, where PL(n) is a pathloss from a remote unit to the neighbor base station and PL(c) is a pathloss from the remote unit to the serving base station.

2. The method of claim 1 wherein the step of measuring the signal quality of the serving base station comprises the steps of:

measuring by a remote unit, a downlink power level of the serving base station;

measuring by the remote unit a downlink power level of the neighbor base station; and

reporting the measurements to the serving base station.

3. The method of claim 1 wherein the step of determining the percentage of traffic absorbed by the neighbor base station for the given handover margin comprises the step of determining a distribution function (F) of a power budget measurement, wherein a percentage of remote units that will be absorbed from the serving base station to the neighbor base station is 1-F(H).

4. The method of claim 1 wherein the step of adjusting the handover margin between the serving base station and the neighbor base station comprises the step of operating the communication system at a predetermined capacity while maintaining a predetermined call quality.

5. The method of claim 4 wherein maintaining the predetermined call quality comprises the steps of:

determining if the neighbor base station can adequately serve a remote unit; and

ensuring that the remote unit is handed over to base stations that are close to a location of the remote unit.

6. A method for determining a handover margin (H) in a cellular communication system, the method comprising the steps of:

measuring by a remote unit, a downlink power level of a serving base station;

measuring by the remote unit a downlink power level of a neighbor base station;

determining a percentage of traffic absorbed by the neighbor base station for a given handover margin based on the downlink power measurements; and

adjusting the handover margin between the serving base station and the neighbor base station to maximize a communication system capacity, based on the step of determining, wherein a handoff occurs from the serving base station to the neighbor base station when PL(c)-PL(n)≧

H, where PL(n) is a pathloss from the remote unit to the neighbor base station and PL(c) is a pathloss from the remote unit to the serving base station.

7. The method of claim 6 wherein the step of determining the percentage of traffic absorbed by the neighbor base station for the given handover margin comprises the step of determining a distribution function (F) of a power budget measurement, wherein a percentage of remote units that will be absorbed from the serving base station to the neighbor base station is 1-F(H).

8. The method of claim 6 wherein the step of adjusting the handover margin between the serving base station and the neighbor base station comprises the step of operating the communication system at a predetermined capacity while maintaining a predetermined call quality.

9. The method of claim 8 wherein maintaining the predetermined call quality comprises the steps of:

determining if the neighbor base station can adequately serve the remote unit; and

ensuring that the remote unit is handed over to base stations that are close to a location of the remote unit.

10. A method for adjusting a handover margin (H(c,n)) between a serving base station (c) and a neighbor base station (n), the method comprising the steps of:

determining a power budget (PBGT(c,n)) of the serving base station where PBGT(c,n)≅

PL(c)-PL(n), PL(n) is a pathloss from a remote unit to the neighbor base station (n), and PL(c) is the pathloss from the remote unit to the serving base station (c);

determining a distribution function (F) of PBGT(c,n), wherein a percentage of remote units that will be absorbed from the serving base station to the neighbor base station is 1-F(H(c,n));

determining, based on the distribution function, if the remote unit will handover to the neighbor base station when the handover margin is set to a certain value, wherein the remote unit will handover to the neighbor base station when PBGT(c,n) is approximately equal to H(c,n); and

adjusting H(c,n) based on the handover determination.

11. The method of claim 10 wherein the step of adjusting H(c,n) comprises the step of maximizing capacity of a communication system while maintaining a predetermined call quality.

12. The method of claim 11 wherein maintaining the predetermined call quality comprises the steps of:

determining if the neighbor base station can adequately serve the remote unit; and

ensuring that the remote unit is handed over to base stations that are close to a location of the remote unit.

13. The method of claim 10 wherein the step of adjusting H(c,n) comprises the steps of:

##EQU8## S(c) is a percentage of traffic that will be retained by base station c with the optimized settings of H(c,n), G(c,n) is a percentage of traffic that base station c gives up to the neighbor base station n when the handover margin is set to H(c,n), and H(c,n) is the handover margin setting from base station c to neighbor base station n.

14. A method comprising the steps of:

measuring downlink power levels of a serving base station and a neighbor base station to produce a power budget measurement; and

determining a percentage of traffic absorbed by the neighbor base station for a given handover margin based on the power budget measurement, wherein a handoff occurs from the serving base station to the neighbor base station when the power budget measurement is greater than the given handover margin, and the power budget is equal to PL(c)-PL(n) where PL(n) is a pathloss from a remote unit to the neighbor base station and PL(c) is a pathloss from the remote unit to the serving base station.

15. The method of claim 14 further comprising the step of adjusting the handover margin between the serving base station and the neighbor base station based on the step of determining.

16. The method of claim 14 wherein the step of measuring downlink power levels of a serving base station comprises the steps of:

measuring by a remote unit, the downlink power level of the serving base station;

measuring by the remote unit the downlink power level of the neighbor base station; and

reporting the measurements to the serving base station.

17. An apparatus for adjusting a handover margin in a cellular communication system, the apparatus comprising:

means for determining a power budget (PBGT(c,n)) of the serving base station where PBGT(cn)≅

PL(c)-PL(n), PL(n) is a pathloss from a remote unit to the neighbor base station (n) and PL(c) is the pathloss from the remote unit to the serving base station (c);

means for determining a distribution function (F) of PBGT(c,n), wherein a percentage of remote units that will be absorbed from the serving base station to the neighbor base station is 1-F(H(c,n));

means for determining, based on the distribution function, if the remote unit will handover to the neighbor base station when the handover margin is set to a certain value, wherein the remote unit will handover to the neighbor base station when PBGT(c,n) is approximately equal to H(c,n); and

means for adjusting H(c,n) based on the handover determination.