System and method for using a handoff threshold associated with a slot cycle index to determine whether to perform an access terminal handoff

• US 8,848,688 B1
• Filed: 10/03/2008
• Issued: 09/30/2014
• Est. Priority Date: 10/03/2008
• Status: Expired due to Fees

• Current Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Original Assignee: Sprint Spectrum LP (Deutsche Telekom AG)
• Inventors: Wurtenberger, Andrew M., Narendran, Rajveen, Marupaduga, Sreekar
• Primary Examiner(s): Renner, Brandon
• Assistant Examiner(s): Choudhury, Faisal
• Application Number:
  US12/245,168
• Time in Patent Office: 2,188 Days
• Field of Search: 370/331, 455/436
• US Class Current: 370/351
• CPC Class Codes: H04W 36/00835 Determination of neighbour cell lists
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/008375 based on historical data

Abstract

A method and system for using a handoff threshold associated with a slot cycle index to determine whether to perform access terminal handoff from a current pilot signal to a target pilot signal. The determination may be conditioned on whether the current pilot signal and target pilot signal are transmitted from base stations within a common subnet. If the base stations are within a common subnet, handoff of the access terminal is based on a default handoff threshold. On the other hand, if the base stations are not within a common subnet, then the determination of whether to perform access terminal handoff from a current pilot signal to a target pilot signal may be made based on the handoff threshold associated with the slot cycle index. As a result, ping-ponging of the access terminal from one subnet to another may be reduced or prevented.

Claims

1. A method comprising:

storing, within a data storage device, correlation data that comprises (i) a plurality of slot cycle indices including at least a first slot cycle index and a second slot cycle index that differs from the first slot cycle index, and (ii) a plurality of handoff thresholds including at least a first handoff threshold and a second handoff threshold that differs from the first handoff threshold, wherein the correlation data associates each slot cycle index of the plurality of slot cycle indices with a handoff threshold of the plurality of handoff thresholds, and wherein the first slot cycle index is associated with the first handoff threshold that differs from the second handoff threshold and the second slot cycle index is associated with the second handoff threshold that differs from the first handoff threshold;

an access terminal operating at a particular slot cycle index of the plurality of slot cycle indices, wherein the access terminal uses the particular slot cycle index to determine how often to monitor overhead messages from a base station serving the access terminal;

querying the correlation data to determine, from among the plurality of handoff thresholds, a handoff threshold associated with the particular slot cycle index;

the access terminal making a first determination of whether a signal strength of a target pilot signal received at the access terminal exceeds a signal strength of a current pilot signal received at the access terminal by the determined handoff threshold associated with the particular slot cycle index the access terminal uses to determine how often to monitor overhead messages from the base station serving the access terminal;

if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the determined handoff threshold, the access terminal thereafter handing off to the target pilot signal, and

if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the determined handoff threshold, then the access terminal thereafter idling on the current pilot signal.

2. The method of claim 1,

wherein the current pilot signal is received from a given base station within a first subnet, and

wherein the access terminal making the first determination is conditioned on whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet,

the method further comprising:

the access terminal maintaining a default handoff threshold;

the access terminal making a second determination of whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet;

if the access terminal determines that target pilot signal is received from a base station within the first subnet, the access terminal thereafter making a third determination of whether the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold,

if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold, the access terminal thereafter handing off to the target pilot signal,

if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the default handoff threshold, then the access terminal thereafter idling on the current pilot signal, and

if the access terminal determines that target pilot signal is received from a base station that is not within the first subnet, the access terminal thereafter making the first determination.

3. The method of claim 2, further comprising:

the access terminal receiving a neighbor list from the given base station,

wherein the current pilot signal is transmitted from a given sector of the given base station,

wherein the neighbor list contains (i) a list of PN codes, each of the listed PN codes being associated with a respective sector neighboring the given sector, and (ii) for each of the listed PN codes, a parameter that indicates whether the neighboring sector associated with that PN code is a sector that transmits a target pilot signal from a base station within the first subnet or from a base station that is not within the first subnet,

wherein the received target pilot signal is transmitted from a neighboring sector associated with a listed PN code and contains one of the listed PN codes, and

wherein making the second determination includes the access terminal querying the received neighbor list so as to determine the parameter associated with the PN code contained in the received target pilot signal.

4. The method of claim 2,

wherein the first subnet comprises a first logical set of base stations, the first logical set of base stations including the given base station,

wherein the base station that is not within the first subnet is a base station within a second subnet, and

wherein the second subnet comprises a second logical set of base stations.

5. The method of claim 1, wherein storing the correlation data and querying the correlation data are performed by the access terminal.

6. The method of claim 1,

wherein the correlation data is stored by an access network that serves the access terminal,

the method further comprising:

the access network determining that the access terminal is operating at the particular slot cycle index, wherein querying the correlation data to determine the handoff threshold associated with the particular slot cycle index is carried out by the access network after determining that the access terminal is operating at the particular slot cycle index; and

thereafter, the access network providing the access terminal with data that indicates the determined handoff threshold.

7. The method of claim 1,

wherein the current pilot signal contains a first PN code,

wherein the target pilot signal contains a second PN code,

wherein idling on the current pilot signal includes the access terminal monitoring overhead messages containing the first PN code, and

wherein, after handing off to the target pilot signal, the access terminal monitors overhead messages containing the second PN code.

8. The method of claim 1,

wherein the signal strength of the target pilot signal is represented as a ratio of received energy of the target pilot signal and a total received energy, and

wherein the signal strength of the current pilot signal is represented as a ratio of received energy of the current pilot signal and the total received energy.

9. The method of claim 1, the method further comprising:

after the access terminal hands off to the target pilot signal, the access terminal idling on the target pilot signal.

21. The method of claim 1, wherein the particular slot cycle index is one of the first slot cycle index and the second slot cycle index.

22. The method of claim 21, wherein the particular slot cycle index is a user-selected slot cycle index.

10. An access terminal comprising:

a processor;

a receiver to receive a current pilot signal and a target pilot signal; and

a data storage device storing computer-readable program instructions that are executable by the processor and correlation data that comprises (i) a plurality of slot cycle indices including at least a first slot cycle index and a second slot cycle index that differs from the first slot cycle index, and (ii) a plurality of handoff thresholds including at least a first handoff threshold and a second handoff threshold that differs from the first handoff threshold, wherein the correlation data associates each slot cycle index of the plurality of slot cycle indices with a handoff threshold of the plurality of handoff thresholds, and wherein the first slot cycle index is associated with the first handoff threshold that differs from the second handoff threshold and the second slot cycle index is associated with the second handoff threshold that differs from the first handoff threshold;

wherein the computer-readable program instructions include instructions that (i) cause the access terminal to operate at a particular slot cycle index of the plurality of slot cycle indices, wherein the access terminal uses the particular slot cycle index to determine how often to monitor overhead messages from a base station serving the access terminal, (ii) cause the access terminal to query the correlation data to determine, from among the plurality of handoff thresholds, a handoff threshold associated with the particular slot cycle index, and (iii) cause the access terminal to make a first determination of whether a signal strength of the target pilot signal exceeds a signal strength of the current pilot signal by the determined handoff threshold associated with the particular slot cycle index the access terminal uses to determine how often to monitor overhead messages from the base station serving the access terminal,

wherein if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the determined handoff threshold, the access terminal thereafter hands off to the target pilot signal, and

wherein if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the determined handoff threshold, the access terminal thereafter idles on the current pilot signal.

11. The access terminal of claim 10,

wherein the current pilot signal is received from a given base station within a first subnet,

wherein the data storage device further stores (i) a default handoff threshold, (ii) program instructions that cause the access terminal to make a second determination of whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet, and (iii) program instructions that cause the access terminal to make a third determination of whether the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold,

wherein execution of the program instructions that cause the access terminal to make the first determination is conditioned on whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet,

wherein if the access terminal determines that the target pilot signal is received from a base station that is within the first subnet, the processor responsively executes the program instructions that cause the access terminal to make the third determination,

wherein if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold, the access terminal thereafter hands off to the target pilot signal,

wherein if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the default handoff threshold, then the access terminal thereafter idles on the current pilot signal, and

wherein if the access terminal determines that the target pilot signal is received from a base station that is not within the first subnet, the processor responsively executes the program instructions that cause the access terminal to make the first determination.

12. The access terminal of claim 11,

wherein the receiver receives a neighbor list from the given base station,

wherein the data storage device thereafter stores the received neighbor list,

wherein the current pilot signal is received from a given sector of the given base station,

wherein the neighbor list contains (i) a list of PN codes, each of the listed PN codes being associated with a respective sector neighboring the given sector, and (ii) for each of the listed PN codes, a parameter that indicates whether the neighboring sector associated with that PN code is a sector that transmits a target pilot signal from a base station within the first subnet or from a base station that is not within the first subnet,

wherein the received target pilot signal is transmitted from a neighboring sector associated with a listed PN code and contains one of the listed PN codes, and

wherein the program instructions that cause the processor to make the second determination include instructions that cause the access terminal to query the neighbor list maintained in the data storage device so as to determine the parameter associated with the PN code contained in the received target pilot signal.

13. The access terminal of claim 11,

wherein the first subnet comprises a first logical set of base stations, the first logical set of base stations including the given base station,

wherein the base station that is not within the first subnet is a base station within a second subnet, and

wherein the second subnet comprises a second logical set of base stations.

14. The access terminal of claim 10,

wherein the current pilot signal contains a first PN code,

wherein the target pilot signal contains a second PN code,

wherein, while the access terminal idles on the current pilot signal, the access terminal monitors overhead messages containing the first PN code, and

wherein, after the access terminal hands off to the target pilot signal, the access terminal monitors overhead messages containing the second PN code.

15. The access terminal of claim 10,

wherein the signal strength of the target pilot signal is represented as a ratio of received energy of the target pilot signal and a total received energy, and

wherein the signal strength of the current pilot signal is represented as a ratio of received energy of the current pilot signal and the total received energy.

16. A method comprising:

storing, within a data storage device of an access terminal, correlation data that comprises (i) a plurality of slot cycle indices including at least a first slot cycle index and a second slot cycle index that differs from the first slot cycle index, and (ii) a plurality of handoff thresholds including at least a first handoff threshold and a second handoff threshold that differs from the first handoff threshold, wherein the correlation data associates each slot cycle index of the plurality of slot cycle indices with a handoff threshold of the plurality of handoff thresholds, and wherein the first slot cycle index is associated with the first handoff threshold that differs from the second handoff threshold and the second slot cycle index is associated with the second handoff threshold that differs from the first handoff threshold;

the access terminal operating at a particular slot cycle index of the plurality of slot cycle indices, wherein the access terminal uses the particular slot cycle index to determine how often to monitor overhead messages from a base station serving the access terminal;

the access terminal querying the correlation data to determine, from among the plurality of handoff thresholds, a handoff threshold associated with the particular slot cycle index;

the access terminal making a first determination of whether a signal strength of a target pilot signal received at the access terminal exceeds a signal strength of a current pilot signal received at the access terminal by the determined handoff threshold associated with the particular slot cycle index the access terminal uses to determine how often to monitor overhead messages from the base station serving the access terminal;

if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the determined handoff threshold, the access terminal thereafter handing off to the target pilot signal, and

if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the determined handoff threshold, then the access terminal thereafter idling on the current pilot signal.

17. The method of claim 16,

wherein the current pilot signal is received from a given base station within a first subnet, and

wherein the access terminal making the first determination is conditioned on whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet,

the method further comprising:

the access terminal maintaining a default handoff threshold;

the access terminal making a second determination of whether the target pilot signal is received from a base station within the first subnet or from a base station that is not within the first subnet;

if the access terminal determines that target pilot signal is received from a base station within the first subnet, the access terminal thereafter making a third determination of whether the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold,

if the access terminal determines that the signal strength of the target pilot signal exceeds the signal strength of the current pilot signal by the default handoff threshold, the access terminal thereafter handing off to the target pilot signal,

if the access terminal determines that the signal strength of the target pilot signal does not exceed the signal strength of the current pilot signal by the default handoff threshold, then the access terminal thereafter idling on the current pilot signal, and

if the access terminal determines that target pilot signal is received from a base station that is not within the first subnet, the access terminal thereafter making the first determination.

18. The method of claim 17,

wherein the first subnet comprises a single radio network controller and a logical set of base stations, the logical set of base stations including the given base station, and

wherein each base station of the logical set of base stations is controlled by the radio network controller.

19. The method of claim 17,

wherein the first subnet comprises multiple radio network controllers and a logical set of base stations, the logical set of base stations including the given base station, and

wherein each of the radio network controllers controls at least one base station of the logical set of base stations.

20. The method of claim 16, further comprising:

prior to storing the correlation data within the data storage device, receiving the correlation data at the access terminal from a wireless access network.