Subscriber unit and method of cell selection for a cellular communication system

• US 6,584,325 B1
• Filed: 11/15/1999
• Issued: 06/24/2003
• Est. Priority Date: 03/17/1999
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Shakhgildian, Vagan
• Primary Examiner(s): Bost, Dwanye
• Assistant Examiner(s): RAMOS FELICIANO, ELISEO
• Application Number:
  US09/439,452
• Time in Patent Office: 1,317 Days
• Field of Search: 455/525, 455/524, 455/436, 455/437, 455/438, 455/439, 455/515-517, 455/67.1, 455/67.3, 455/226--22, 455/561, 455/423, 455/62, 455/63, 455/466, 455/522, 455/69, 370/331-335
• US Class Current: 455/525
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

The current invention relates to a cellular communication system. Known communication systems performs cell selection based on measurements of downlink pilot signal levels. However, this is inefficient as uplink conditions can have significant impact on the performance. In the current invention a subscriber unit (300) comprises receiving means (305) for receiving uplink characteristics information transmitted from a target set of base stations (201,203). The subscriber unit (300) further comprises base station selection means (309) for determining at least one serving base station in response to said uplink characteristics information, and transmitting means (311) for accessing the cellular communication system through said at least one serving base station. Preferably, the subscriber unit (300) comprises means for calculating an access message transmit power level and the base station having the lowest calculated access message transmit power level is selected. The invention is particularly applicable to 3^rd generation cellular communication systems such as UMTS.

Claims

1. A subscriber unit for use in a cellular communication system having a plurality of base stations supporting at least said subscriber unit and transmitting a pilot signal and uplink characteristics information, the subscriber unit comprising:

receiving means for receiving the uplink characteristics information from a target set of base stations selected from said plurality of base stations;

means for calculating, when in idle mode, a random access message transmit power level of a random access message in response to said uplink characteristics information;

base station selection means for determining, when in idle mode, at least one serving base station in response to said calculated random access message transmit power level; and

transmitting means for exiting idle mode by accessing the cellular communication system through said at least one serving base station by transmitting the random access message at the calculated random access message transmit power level.

2. A subscriber unit as claimed in claim 1 further comprising means for determining a received pilot signal quality indicator in the subscriber unit and wherein the determination of the at least one serving base station is in response to both the uplink characteristics information and the pilot signal quality indicator.

3. A subscriber unit as claimed in claim 1 wherein said uplink characteristics information is an uplink interference level.

4. A subscriber unit as claimed in claim 1 wherein said uplink characteristics information is an uplink congestion indicator.

5. A subscriber unit as claimed in claim 1 wherein the target set of base stations are determined in response to a received pilot signal power level.

6. A subscriber unit as claimed in claim 1 wherein the at least one serving base station is selected in response to only the uplink characteristics information for a short data message and in response to both the uplink characteristics information and the received pilot signal quality indicator for a call setup.

7. A subscriber unit as claimed in claim 1 further comprising means for instigating selection of the at least one serving base station in connection with transmitting an access message.

8. A cellular communication system comprising at least one subscriber unit as claimed in claim 1.

9. A method of cell access in a cellular communication system having a plurality of base stations supporting at least said subscriber unit and transmitting a pilot signal and uplink characteristics information, the method comprising the steps of:

receiving the uplink characteristics information from a target set of base stations selected from said plurality of base stations in the subscriber unit;

calculating, when in idle mode, a random access message transmit power level of a random access message in response to said uplink characteristics information;

determining, when in idle mode, at least one serving base station in response to said calculated random access message transmit power level; and

the subscriber unit exiting idle mode by accessing the cellular communication system through said at least one serving base station by transmitting the random access message at the calculated random access message transmit power level.

10. A method as claimed in claim 9 further comprising the step of determining a received pilot signal quality indicator in the subscriber unit and wherein the determination of the at least one serving base station is in response to both the uplink characteristics information and the pilot signal quality indicator.

11. A method as claimed in claim 9 wherein the step of determining the at least one serving base station comprises the steps of determining an uplink performance indicator in response to the uplink characteristics information, a downlink performance indicator in response to the pilot signal quality indicator, and a combined performance indicator in response to both the uplink characteristics information and the pilot signal quality indicator, and

if a base station has both a better uplink performance indicator and a better downlink performance indicator selecting that base station as the at least one serving base station; and

otherwise selecting the base station having the best combined performance indicator as the at least one serving base station.

12. A method as claimed in claim 9 wherein the step of determining the at least one serving base station comprises the steps of determining an uplink performance indicator in response to the uplink characteristics information, a downlink performance indicator in response to the pilot signal quality indicator, and a combined performance indicator in response to both the uplink characteristics information and the pilot signal quality indicator, and

if a base station has both a better uplink performance indicator and a better downlink performance indicator selecting that base station as the at least one serving base station;

and

if no base station has both a better uplink performance indicator and a better downlink performance indicator then selecting the base station having the best uplink performance indicator as the at least one serving base station for a short data message; and

otherwise selecting the base station having the best combined performance indicator as the at least one serving base station.