Method and apparatus for detecting forward and reverse link imbalance in digital cellular communication systems

• US 6,785,249 B2
• Filed: 10/05/1998
• Issued: 08/31/2004
• Est. Priority Date: 10/05/1998
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Soliman, Samir S.
• Primary Examiner(s): NGUYEN, STEVEN H D
• Application Number:
  US09/166,553
• Publication Number:
  US 20020114288A1
• Time in Patent Office: 2,157 Days
• Field of Search: 370/320, 370/330, 370/331, 370/332, 370/333, 370/335, 370/342, 375/140, 375/141, 375/227, 455/423, 455/424, 455/67.11, 455/436, 455/437, 455/438, 455/442, 455/450, 455/452
• US Class Current: 370/335
• CPC Class Codes: H04W 68/00 User notification, e.g. alerting and paging, for incoming communication, change of service or the like
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 72/542 using measured or perceived quality
• CPC Class Codes: H04W 74/00 Wireless channel access

Abstract

A method and apparatus for detecting forward and reverse link imbalances in a digital cellular communication system. The method preferably uses an indication of “maximum access probes” to determine whether a link imbalance caused a reverse link failure to occur. The maximum access probes condition indicates that a wireless unit has attempted to access a base station a pre-defined maximum number of times. The method preferable uses an indication of a lost paging channel and a traffic channel initialization (TCI) time out to determine whether a link imbalance caused a forward link failure to occur. If the wireless unit did not lose the paging channel, the method determines whether a TCI time out occurred. If the wireless unit lost the paging channel, or it did not lose the paging channel but a TCI time out occurred, the method determines the cause for the forward link failure. There are two potential causes in this scenario: (1) either the wireless unit is a significant distance from the base station; or (2) the paging channel suffers from significant interference. The method determines the cause and either instructs the wireless unit to perform an idle handoff to a neighboring base station or to exit the digital system.

Claims

1. A method of detecting link imbalances in a digital cellular communication system comprising a plurality of wireless units and a plurality of base stations, wherein transmissions from the base stations to the wireless units are made using forward radio communication links and wherein transmissions from the wireless units to the base stations are made using reverse radio communication links, and wherein each forward link includes control and forward traffic channels, and each reverse link includes control and reverse traffic channels, the method comprising the steps of:

detecting a link failure in a first radio communication link between a wireless unit and a first base station during a call initiation, the step of detecting the link failure comprising the step of determining whether the failure in the first radio communication link comprises a reverse link failure or a forward link failure;

determining whether the link failure is due to a link imbalance in the first radio communication link;

instructing the wireless unit to switch to a second radio communication link if the link imbalance exists;

determining if the reverse link failure is due to a weak reverse link, the step of determining if the reverse link failed due to a weak reverse link comprising the step of determining whether a maximum number of access probes has been transmitted by the wireless unit to the first base station, wherein a value for the maximum number of access probes is transmitted in an access parameters message which is sent by the first base station to the wireless unit over a control channel associated with a forward link of the first base station;

initiating by the wireless unit communication on a secondary communication system if the maximum number of access probes has been transmitted by the wireless unit to the first base station; and

entering by the wireless unit an idle state and then re-initiate communication with a primary digital cellular communication system if the maximum number of access probes has not been transmitted by the wireless unit to the first base station.

2. The link imbalance detection method of claim 1, further comprising the steps of:

a) determining whether the wireless unit successfully re-initiated communication with the primary digital cellular communication system and remaining on the primary digital cellular communication system if the communication was successful, else proceeding to step (b);

b) initiating by the wireless unit communication on the secondary communication system; and

c) determining whether the wireless unit successfully acquired the secondary communication system and initiating by the wireless unit communication on an analog communication system if the secondary communication system was not successfully acquired.

3. A method of detecting link imbalances in a digital cellular communication system comprising a plurality of wireless units and a plurality of base stations, wherein transmissions from the base stations to the wireless units are made using forward radio communication links and wherein transmissions from the wireless units to the base stations are made using reverse radio communication links, and wherein each forward link includes control and forward traffic channels, and each reverse link includes control and reverse traffic channels, the method comprising the steps of:

detecting a link failure in a first radio communication link between a wireless unit and a first base station during a call initiation, the step of detecting the link failure comprising the step of determining whether the failure in the first radio communication link comprises a reverse link failure or a forward link failure;

determining whether the link failure is due to a link imbalance in the first radio communication link;

instructing the wireless unit to switch to a second radio communication link if the link imbalance exists;

determining if the forward link failure is due to a weak forward link, wherein the step of determining if the forward link failed due to a weak forward link includes the steps of;

a) determining whether the control channel transmitted by the first base station was lost and proceeding to step (b) if the control channel was not lost, else proceeding to step (c);

b) determining whether the wireless unit produced a traffic channel initialization (TCI) time out and instructing the wireless unit to return to normal operation if a TCI time out was not produced, else proceeding to step (c);

c) measuring a forward channel signal strength received by the wireless unit from the first base station and proceeding to step (i) if the forward channel signal strength is sufficient, else proceeding to step (d) if the forward channel signal strength is insufficient;

d) determining whether the wireless unit received a sufficiently strong second signal from a second base station and proceeding to step (g) if a sufficiently strong second signal was received, else proceeding to step (e);

e) determining whether a received signal strength indicator received by the wireless unit is less than a predetermined threshold value;

f) entering by the wireless unit an idle operational mode if received signal strength indicator is greater than the threshold value, else initiating by the wireless unit communication on a secondary system;

g) determining whether the second base station is a neighbor base station to the wireless unit;

h) exiting by the wireless unit the digital communication system if the second base station is not a neighbor to the wireless unit; and

i) performing by the wireless unit an idle handoff and initiating communication with the second base station on a second radio communication link if the second base station is a neighbor to the wireless unit.

4. The link imbalance detection method of claim 3, wherein the pilot strength is measured by taking a ratio (in dB) of pilot energy received by a wireless unit and accumulated over one pseudo-noise (PN) chip period (E_c) to the total power spectral density in the received bandwidth (I_o).

5. The link imbalance detection method of claim 4, wherein the pilot strength is insufficient if E_c/I₀ is less than −

13 dB.

6. The link imbalance detection method of claim 4, wherein the pilot strength is sufficient if E_c/I₀ is greater than or equal to −

13 dB.

7. The link imbalance detection method of claim 3, wherein the predetermined threshold value is −

100 dBm in CDMA systems, and wherein the predetermined threshold value is −

103 dBm in PCS systems.

8. The link imbalance detection method of claim 3, wherein the predetermined threshold value is dependent upon a link budget associated with the communication link between the wireless unit and the first base station.

9. An apparatus for detecting link imbalances in a wireless communication system, comprising:

a processor; and

a storage medium coupled to the processor and containing instructions executable by said processor to;

detect a link failure in a first radio communication link between a wireless unit and a first base station during a call initiation;

determine whether the link failure is due to a link imbalance in the first radio communication link; and

initiate communication using a second radio communication link if the link imbalance exists,

wherein said processor determines whether the link failure is due to a link imbalance in the first radio communication link if a forward link failed by;

determining whether the control channel transmitted by the first base station failed; and

determining whether a traffic channel initialization time out occurred if the control channel transmitted by the first base station did not fail.

10. The apparatus as claimed in claim 9, wherein said processor initiates communication using a second radio communication link if the link imbalance exists by:

causing the wireless unit to perform an idle handoff and to initiate communication with a primary communication system on a second radio communication link if;

a pilot signal strength from a second base station of the primary communication system is sufficient; and

the second base station is a neighbor base station.

11. The apparatus as claimed in claim 10, wherein said processor causes the wireless unit to exit the communication system if the second base station is not a neighbor base station.

12. The apparatus as claimed in claim 10, wherein, said processor causes the wireless unit to initiate communication on a secondary system if:

a pilot signal strength from a second base station of the primary communication system is insufficient; and

a received signal strength indicator received by the wireless unit is less than a predetermined threshold value.

13. The apparatus as claimed in claim 12, wherein said processor further:

causes the wireless unit to initiate communication on an analog system if initiation of communication on the secondary system fails.

14. The apparatus as claimed in claim 10, wherein said processor causes the wireless unit to enter an idle state if:

the received signal strength indicator received by the wireless unit is greater than a predetermined threshold value; and

the control channel transmitted by the first base station failed.

15. The apparatus as claimed in claim 10, wherein said processor causes the wireless unit to resume normal operation if:

the received signal strength indicator received by the wireless unit is greater than a predetermined threshold value; and

the traffic channel initialization time out occurred.

16. The apparatus as claimed in claim 9, wherein said processor further causes the wireless unit to resume normal operation if:

the control channel transmitted by the first base station failed; and

the traffic channel initialization time out did not occurred.

17. The apparatus as claimed in claim 10, wherein the pilot signal strength is measured by taking a ratio (in dB) of pilot energy received by the wireless unit and accumulated over one pseudo-noise (PN) chip period (E_c) to the total power spectral density in the received bandwidth (I_o).

18. The apparatus as claimed in claim 10, wherein the pilot strength is insufficient if E_c/I_o is less than −

13 dB.

19. The apparatus as claimed in claim 10, wherein the pilot strength is sufficient if E_c/I_o is greater than or equal to −

13 dB.

20. The apparatus as claimed in claim 12, wherein the predetermined threshold value is −

100 dBm in CDMA systems, and wherein the predetermined threshold value is −

103 dBm in PCS systems.

21. The apparatus as claimed in claim 12, wherein the predetermined threshold value is dependent upon a link budget associated with the communication link between the wireless unit and the first base station.

22. A method of detecting link imbalances in a digital cellular communication system comprising a plurality of wireless units and a plurality of base stations, wherein transmissions from the base stations to the wireless units are made using forward radio communication links and wherein transmissions from the wireless units to the base stations are made using reverse radio communication links, and wherein each forward link includes control and forward traffic channels, and each reverse link includes control and reverse traffic channels, the method comprising the steps of:

detecting a link failure in a first radio communication link between a wireless unit and a first base station during a call initiation, the step of detecting the link failure comprising the step of determining whether the failure in the first radio communication link comprises a reverse link failure or a forward link failure;

determining whether the link failure is due to a link imbalance in the first radio communication link, wherein said determining whether the link failure is due to a link imbalance in the first radio communication link if a forward link failed comprises;

determining whether a control channel transmitted by the first base station failed; and

determining whether a traffic channel initialization time out occurred if the control channel transmitted by the first base station did not fail; and

instructing the wireless unit to switch to a second radio communication link if the link imbalance exists.

23. The method as claimed in claim 22, wherein initiating by the wireless unit communication using a second radio communication link if the link imbalance exists comprises:

causing the wireless unit to perform an idle handoff and to initiate communication with a primary digital cellular communication system on a second radio communication link if;

a pilot signal strength from a second base station of the primary digital cellular communication system is sufficient; and

the second base station is a neighbor base station.

24. The method as claimed in claim 23, further comprising exiting by the wireless unit the communication system if the second base station is not a neighbor base station.

25. The method as claimed in claim 23, further comprising causing the wireless unit to initiate communication on a secondary system if:

a pilot signal strength from a second base station of the primary communication system is insufficient; and

a received signal strength indicator received by the wireless unit is less than a predetermined threshold value.

26. The method as claimed in claim 25, further comprising initiating by the wireless unit communication on an analog system if initiating of communication on the secondary system fails.

27. The method as claimed in claim 23, further comprising entering by the wireless unit an idle state if:

the received signal strength indicator received by the wireless unit is greater than a predetermined threshold value; and

the control channel transmitted by the first base station failed.

28. The apparatus as claimed in claim 23, further comprising entering by the wireless unit to resume normal operation if:

the received signal strength indicator received by the wireless unit is greater than a predetermined threshold value; and

the traffic channel initialization time out occurred.

29. The apparatus as claimed in claim 22, further comprising processor further causes the wireless unit to resume normal operation if:

the control channel transmitted by the first base station failed; and

the traffic channel initialization time out did not occur.