Method and apparatus for transitioning between control channels in a cellular system

• US 6,185,422 B1
• Filed: 06/19/1998
• Issued: 02/06/2001
• Est. Priority Date: 06/19/1998
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Mattila, Ilpo
• Primary Examiner(s): Hunter, Daniel S.
• Assistant Examiner(s): Gantt, Alan T.
• Application Number:
  US09/100,490
• Time in Patent Office: 963 Days
• Field of Search: 455/434, 455/435, 455/455, 455/552, 455/515
• US Class Current: 455/434
• CPC Class Codes: H04W 60/04 using triggered events

Abstract

A method and apparatus for transitioning between control channels in a cellular telecommunications system by using adaptive hysterisis. In an embodiment of the invention, when a mobile station attempts to transition from an analog control channel (ACCH) to a digital control channel (DCCH) and subsequently returns to the ACCH, a threshold level of DCCH received signal strength (rssi) at the mobile station that triggers a transition attempt from an ACCH to a DCCH is incrementally increased. Incrementally increasing the threshold level DCCH rssi prevents unnecessary transitions back and forth between an ACCH and a DCCH when the rssi of the DCCH is close to a minimum level that triggers a camp on the DCCH after a synchronization, or when the mobile station cannot synchronize to or camp on the DCCH successfully.

Claims

1. In a telecommunications system having at least one base station transmitting on a plurality of control channels and at least one mobile station, a method of transitioning a mobile station between control channels, said method comprising the steps of:

(a) scanning and selecting a control channel of a first type at the mobile station;

(b) receiving identifying information over said control channel of a first type, said identifying information including information identifying a control channel of a second type, wherein said control channel of a second type is preferred over said control channel of a first type for operation of the mobile station in the system;

(c) determining if a measurement parameter at the mobile station on said control channel of a second type is greater than a threshold level for triggering transition from said control channel of a first type to said control channel of a second type;

(d) performing, in response to a positive determination in said step of determining, an access attempt on said control channel of a second type; and

(e) if said access attempt is unsuccessful, incrementing said threshold level by a step increment and repeating steps (a)-(e) until said access attempt in step (d) is successful or until said mobile station otherwise is required to move off said control channel of a first type.

2. The method of claim 1, wherein, if said access attempt is successful, said method further comprises the steps of:

starting a timer;

monitoring said control channel of a second type;

falling off said control channel of a second type and stopping said timer in response to falling off;

determining whether said timer has a value less than a predetermined time duration; and

if it is determined that said timer has a value less than said predetermined time duration, incrementing said rssi threshold level by said step increment and repeating steps (a)-(e) until said access attempt of step (d) is successful or until said mobile station otherwise is required to move off said control channel of a first type;

else, if it determined that said timer does not have a value less than said predetermined time duration, moving back to step (a) without incrementing said rssi threshold level by said step increment, and repeating steps (a)-(e) until said access attempt of step (d) is successful or until said mobile station is otherwise required to move off said control channel of a first type.

3. The method of claim 2, wherein said control channel of a first type comprises an analog control channel (ACCH) and said control channel of a second type comprises a digital control channel (DCCH), and wherein said step of performing an access attempt on said control channel of a second type comprises performing a synchronization attempt on said DCCH, and further wherein said step of monitoring said control channel of said second type comprises camping on said DCCH.

4. The method of claim 1, wherein said step of scanning and selecting comprises the steps of:

(a1) determining whether said control channel of a first type was selected in a previous iteration of step (a);

(a2) and, if said control channel of a first type was not previously selected, setting a threshold level to a predetermined initial value;

(a3) else, if said control channel of a first type was previously selected, continuing to step (c) without setting said threshold to said predetermined initial value; and

wherein said step (c) comprises determining if a measurement parameter at said mobile station on said control channel of a second type is greater than said threshold level.

5. The method of claim 4, wherein said step of performing an access attempt, in response to a positive determination in said step of determining, comprises the steps of:

determining if said measurement parameters at the mobile station on said control channel of a second type and said threshold level are both less than a predetermined access threshold level;

and, if said measurement parameter at the mobile station on said control channel of a second type and said threshold level are not both less than said predetermined access threshold level, not accessing said control channel of a second type.

6. The method of claim 1, wherein said measurement parameter at said mobile station on said control channel of a second type comprises a received signal strength indication (rssi).

7. In a telecommunications system having at least one base station transmitting on a plurality of control channels, including an analog control channel (ACCH) and at least one digital control channel (DCCH), and at least one mobile station, a method of transitioning a mobile station between control channels, said method comprising the steps of:

moving into an idle state on an ACCH;

receiving identifying information over said ACCH, said identifying information including information identifying at least one DCCH, wherein said at least one DCCH is preferred over said ACCH for operation of the mobile station in the system;

determining if a measurement parameter on said at least one DCCH at said mobile station is greater than a threshold level for triggering transition from said ACCH to said at least one DCCH; and

performing, in response to a positive determination in said step of determining, successive access attempts on said at least one DCCH by repeating the steps of moving onto, receiving, determining and performing access attempts, and for each unsuccessful access attempt incrementing said threshold level by a step increment and returning to said idle state on said ACCH, said successive access attempts performed until said measurement parameter on said at least one DCCH is less than said threshold level.

8. The method of claim 7, wherein said step of performing access attempts comprises attempting to synchronize to said DCCH.

9. The method of claim 7, wherein said step of performing access attempts comprises attempting to camp on said DCCH.

10. In a telecommunications system having at least one base station transmitting on a plurality of control channels and at least one mobile station, an apparatus for transitioning a mobile station between control channels, said apparatus comprising:

(a) means for scanning and selecting a control channel of a first type at the mobile station;

(b) means for receiving identifying information over said control channel of a first type, said identifying information including information identifying a control channel of a second type, wherein said control channel of a second type is preferred over said control channel of a first type for operation of the mobile station in the system;

(c) means for determining if a measurement parameter at the mobile station on said control channel of a second type is greater than a threshold level for triggering transition from said control channel of a first type to said control channel of a second type;

(d) means for performing, in response to a positive determination in said means for determining, an access attempt on said control channel of a second type;

(e) means, if said access attempt is unsuccessful, for incrementing said threshold level by a step increment; and

(f) means for causing elements (a)-(e) to repeat the functions of scanning and selecting, receiving identifying information, performing an access attempt, and incrementing said threshold level until said access attempt performed by said means for performing an access attempt is successful or until said mobile station otherwise is required to move off said control channel of a first type.

11. The method of claim 10, wherein said means for performing an access attempt further comprises:

means for starting a timer upon acquiring said control channel of a second type;

means for monitoring said control channel of a second type;

means for stopping said timer in response to falling off said control channel of a second type;

means for determining whether said timer has a value less than a predetermined time duration, in response to stopping said timer; and

means, if it is determined that said timer has a value less than said predetermined time duration, for incrementing said rssi threshold level by said step increment; and

means for causing elements (a)-(e) to repeat the functions of scanning and selecting, receiving identifying information, performing an access attempt and incrementing said threshold level until said access attempt performed by said means for performing an access attempt is successful or until said mobile station otherwise is required to move off said control channel of a first type.

12. The method of claim 11, wherein said method further comprises:

(a1) means for determining whether said control channel of a first type has been selected by element (a) at least two consecutive times; and

(a2) means, if said control channel of a first type was not selected by element (a) at least two consecutive times, for setting a threshold level to a predetermined initial value.

13. The apparatus of claim 11, wherein said control channel of a first type comprises an analog control channel (ACCH) and said control channel of a second type comprises a digital control channel (DCCH), and wherein said means for performing an access attempt on said control channel of a second type comprises means for performing a synchronization attempt on said DCCH, and further wherein said means for monitoring said control channel of said second type comprises means for camping on said DCCH.

14. The apparatus of claim 10, wherein said measurement parameter at said mobile station on said control channel of a second type comprises a received signal strength indication (rssi).

15. In a telecommunications system having at least one base station transmitting on a plurality of control channels, including an analog control channel (ACCH) and at least one digital control channel (DCCH), and at least one mobile station, an apparatus for transitioning a mobile station between control channels, said apparatus comprising:

means for maintaining an idle state on an ACCH;

means for receiving identifying information over said ACCH, said identifying information including information identifying at least one DCCH, wherein said at least one DCCH is preferred over said ACCH for operation of the mobile station to the system;

means for determining if a measurement parameter on said at least one DCCH at said mobile station is greater than a threshold level for triggering transition from said ACCH to said at least one DCCH;

means for performing, in response to a positive determination in said means for determining, successive access attempts on said at least one DCCH according to said identifying information received by said means for receiving and according to said determination performed in said means for determining, and for each unsuccessful access attempt incrementing said threshold level by a step increment and returning to said idle state on said ACCH, said successive access attempts performed until said determination performed by said means for determining indicates said measurement parameter on said at least one DCCH is less than said threshold level.

16. The apparatus of claim 15, wherein said means for performing access attempts comprises means for attempting to synchronize to said DCCH.

17. The apparatus of claim 16, wherein said means for performing access attempts comprises means for attempting to camp on said DCCH.