Avoidance of service interruptions in visited public land mobile network (VPLMNs)

• US 7,773,990 B2
• Filed: 02/09/2006
• Issued: 08/10/2010
• Est. Priority Date: 05/23/2005
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Karlsson, Magnus, Wichert, Jan, Hokfelt, Johan, Ekstedt, Tomas
• Primary Examiner(s): Patel; Ajit
• Assistant Examiner(s): NGUYEN, KHAI MINH
• Application Number:
  US11/351,222
• Publication Number:
  US 20060264215A1
• Time in Patent Office: 1,643 Days
• Field of Search: 455/435.3, 455/435.1, 455/434, 455/432, 455/450, 455/432.1
• US Class Current: 455/435.3
• CPC Class Codes: H04W 48/18 Selecting a network or a communication service
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

By evaluating a cell selection criterion S during scans for available public land mobile networks (PLMNs), a user equipment (UE) can avoid network service interruptions by not selecting PLMNs for which there exist no suitable cells. The cell selection criterion can be evaluated based on cell parameters either read during the PLMN selection procedure or locally stored before the PLMN selection procedure. It is possible to reduce the time required for PLMN scans and UE power consumption.

Claims

1. A method in a user equipment of selecting among available public land mobile networks (PLMNs), each PLMN including at least one cell, comprising the steps of:

scanning for available PLMNs when the user equipment is connected to a visited public land mobile network (VPLMN);

picking an available PLMN for evaluation;

reading system information of at least one cell in the picked available PLMN, wherein the system information includes a minimum required quality level in the cell, a minimum required receive level in the cell, and a maximum transmit power level to access the cell on a random access channel;

evaluating a cell selection criterion based on the read system information;

repeating the picking, reading, and evaluating steps for remaining available PLMNs; and

selecting an available PLMN having a highest priority and having a cell fulfilling the cell selection criterion;

wherein the scanning step includes a step of determining a list of available PLMNs, and the evaluating step includes a step of removing a picked available PLMN from the list if the cell selection criterion is not fulfilled by the at least one cell in the picked available PLMN.

2. The method of claim 1, further comprising the step of, after selecting the available PLMN having the highest priority, searching for a cell in the selected PLMN.

3. The method of claim 1, wherein the reading step includes reading the system information from a memory, the system information having been stored in the memory before performing the scanning step.

4. The method of claim 3, wherein the system information is stored in the memory according to respective PLMN and at least one of absolute radio frequency channel number and primary scrambling code.

5. The method of claim 3, wherein the system information stored in the memory is either deleted after lapse of a period of time or stored according to first-in, first-out.

6. An apparatus in user equipment for selecting among available public land mobile networks (PLMNs), each PLMN including at least one cell, comprising:

a processor configured to scan for available PLMNs when the user equipment is connected to a visited public land mobile network (VPLMN);

to pick an available PLMN for evaluation;

to read system information of at least one cell in the picked available PLMN, wherein the system information includes a minimum required quality level in the cell, a minimum required receive level in the cell, and a maximum transmit power level to access the cell on a random access channel;

to evaluate a cell selection criterion based on the read system information;

to repeat the picking, reading, and evaluating for remaining available PLMNs; and

to select an available PLMN having a highest priority and having a cell fulfilling the cell selection criterion; and

wherein the processor is configured, in scanning for available PLMNs, to determine a list of available PLMNs; and

in evaluating the cell selection criterion, to remove a picked available PLMN from the list if the cell selection criterion is not fulfilled by the at least one cell in the picked available PLMN.

7. The apparatus of claim 6, wherein the processor is further configured to search, after selecting the available PLMN having the highest priority, for a cell in the selected PLMN.

8. The apparatus of claim 6, wherein the processor is configured, in reading system information, to read the system information from a memory, the system information having been stored in the memory before scanning for available PLMNs.

9. The apparatus of claim 8, wherein the processor is configured to store system information in the memory according to respective PLMN and at least one of absolute radio frequency channel number and primary scrambling code.

10. The apparatus of claim 8, wherein the processor is configured either to delete system information stored in the memory after lapse of a period of time or to store system information in the memory according to first-in, first-out.

11. Non-transitory computer-readable medium containing a computer program for causing a receiver to select among available public land mobile networks (PLMNs), each PLMN including at least one cell, the computer program implementing the steps of:

scanning for available PLMNs when the user equipment is connected to a visited public land mobile network (VPLMN);

picking an available PLMN for evaluation;

reading system information of at least one cell in the picked available PLMN, wherein the system information includes a minimum required quality level in the cell, a minimum required receive level in the cell, and a maximum transmit power level to access the cell on a random access channel;

evaluating a cell selection criterion based on the read system information;

repeating the picking, reading, and evaluating steps for remaining available PLMNs; and

selecting an available PLMN having a highest priority and having a cell fulfilling the cell selection criterion; and

wherein the scanning step includes a step of determining a list of available PLMNs, and the evaluating step includes a step of removing a picked available PLMN from the list if the cell selection criterion is not fulfilled by the at least one cell in the picked available PLMN.

12. Non-transitory computer-readable medium of claim 11, wherein the computer program further implements the step of, after selecting the available PLMN having the highest priority, searching for a cell in the selected PLMN.

13. Non-transitory computer-readable medium of claim 11, wherein the reading step includes reading the system information from a memory, the system information having been stored in the memory before performing the scanning step.

14. Non-transitory computer-readable medium of claim 13, wherein the system information is stored in the memory according to respective PLMN and at least one of absolute radio frequency channel number and primary scrambling code.

15. Non-transitory computer-readable medium of claim 13, wherein the system information stored in the memory is either deleted after lapse of a period of time or stored according to first-in, first-out.