Method and apparatus for dynamically determining a mobile station's active set during a connection rescue procedure

• US 20020111158A1
• Filed: 12/04/2001
• Published: 08/15/2002
• Est. Priority Date: 12/04/2000
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Tee, Lai King
• Granted Patent: US 7,006,821 B2
• Time in Patent Office: Days
• US Class Current: 455/421
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

A method for allowing a mobile station (MS) to dynamically adjust its T_ADD_R and T_DROP_R pilot signal strength thresholds (established by pilot E_c/I_o values) used to add or drop pilots from the MS'"'"'s active set during rescue. Dynamic adjustment of T_ADD_R and T_DROP_R allows the MS to select and add BSs (sectors) with sufficient forward link quality into their active sets and drop BSs (sectors) with poorer forward link quality during a call recovery procedure to recover an active connection before it is dropped. In addition, the effectiveness of recovering an active connection is improved through corresponding actions at the BS. The BS may use the signal strength measurements, active set information, and other pilot information to update its own active set for use in generating a forward rescue channel.

Claims

1. In a system comprising a network and at least one mobile station (MS) for enabling communications with the at least one MS, the system capable of performing a rescue procedure for rescuing a MS having a connection with the network that has become a potentially failing connection, a method for adjusting pilot signal strength add and drop thresholds T_ADD_R and T_DROP_R used by the MS having the potentially failing connection in determining an updated active set of pilots for use by the MS in the rescue procedure, the method comprising:

incrementally lowering T_ADD_R and T_DROP_R by an amount STEP_dec_thres at one or more specific time instants t_N, N=1, 2, . . . M during the rescue procedure, each time instant separated by a time Td.

2. The method as recited in claim 1, further including lowering T_ADD_R and T_DROP_R in accordance with pilot signal strengths (Ec/Io values) measured at the MS.

3. The method as recited in claim 1, further including lowering T_ADD_R and T_DROP_R by not more than a total amount MAX_dec_thres during the rescue procedure.

4. The method as recited in claim 1, further including incrementally adjusting Td between time instants T_N.

5. The method as recited in claim 2, further including increasing Td between one or more time instants T_N if a combined pilot Ec/Io for the updated active set of the MS is higher than a predetermined desired combined pilot Ec/Io.

6. The method as recited in claim 2, further including:

increasing Td between one or more time instants T_N if a difference between a combined pilot Ec/Io for the updated active set of the MS and the combined pilot Ec/Io for a previous updated active set of the MS is larger than a predetermined threshold; and

decreasing Td between one or more time instants T_N if the difference between the E for the updated active set of the MS and the E for a previous updated active set of the MS is smaller than the predetermined threshold.

7. The method as recited in claim 1, further including incrementally adjusting STEP_dec_thres at one or more time instants T_N.

8. The method as recited in claim 7, further including adjusting STEP_dec_thres at each time instant T_N, the step of adjusting STEP_dec_thres at each time instant T_N comprising:

determining a number of complete rescue cycles K that could be completed before a rescue procedure timer reaches its terminal count; and

computing (T_ADD_H-MAX_dec_thres)/(K−

1) as a value for STEP_dec_thres at each time instant T_N, wherein T_ADD_H is an initial value for T_ADD_R at the start of the rescue procedure.

9. The method as recited in claim 7, further including increasing STEP_dec_thres at each time instant T_N, the step of increasing STEP_dec_thres at each time instant T_N comprising:

determining a number of complete rescue cycles K that could be completed before a rescue procedure timer reaches its terminal count;

determining δ

=2*(MAX_dec_thres)/(K−

1)K, where δ

is an initial value for STEP_dec_thres at the start of the rescue procedure; and

computing δ

*N as a value for STEP_dec_thres at each time instant T_N, wherein N=1, 2, . . . (K−

1).

10. The method as recited in claim 7, further including:

decreasing STEP_dec_thres at one or more time instants T_N, N=1, 2, . . . M, if a difference between a combined pilot Ec/Io for the updated active set of the MS at a particular time instant T_N and the combined pilot Ec/Io for a previous updated active set of the MS at an immediately previous time instant T<sub>N−

1</sub> is larger than a predetermined threshold; and

increasing STEP_dec_thres at one or more time instants T_N, N=1, 2, . . . M, if the difference between the combined pilot Ec/Io for the updated active set of the MS at the particular time instant T_N and the combined pilot Ec/Io for the previous updated active set of the MS at the immediately previous time instant T<sub>N−

1</sub> is smaller than or equal to a predetermined threshold.

11. The method as recited in claim 2, further including determining MAX_dec_thres, the determination of MAX_dec_thres comprising:

selecting a desired combined pilot Ec/Io that gives a high probability of producing a good link as (Ec/Io)_desired;

measuring or estimating an Ec/Io value from a strongest pilot in the updated active set as (Ec/Io)_max; and

solving (Ec/Io)_max+(N−

1) (Ec/Io)_min≧

(Ec/Io)_desired for (Ec/Io)_min, where N is a maximum allowed active set size; and

computing MAX_dec_thres as T_ADD_R-(Ec/Io)_min.

12. The method as recited in claim 2, further including:

measuring Ec/Io for all pilots detectable by the MS having the potentially failing connection;

placing the measured pilots in a list in order of decreasing Ec/Io; and

starting with the pilot in the list having the highest Ec/Io and going through the list in order of decreasing Ec/Io,

measuring the combined Ec/Io for all pilots in the updated active set,

for a current pilot from the list, determining the combined Ec/Io for all pilots in the updated active set plus the current pilot, and

adding the current pilot to the updated active set if the current pilot increased the combined Ec/Io measurement by a predetermined percentage.

13. The method as recited in claim 1, the method for additionally determining an updated active set of pilots for use by the network in the rescue procedure, the method further comprising:

transmitting a uniform energy signal from the MS having the potentially failing connection; and

for each of one or more BSs in a neighborhood of the MS having the potentially failing connection, measuring a strength of the uniform energy signal, and adding the BS to the updated active set used by the network if the strength of the uniform energy signal for that BS is above a predetermined threshold.

14. The method as recited in claim 13, wherein the uniform energy signal is a reverse link pilot signal.

15. The method as recited in claim 13, wherein the uniform energy signal is a data signal at a predetermined data rate with predetermined data.

16. The method as recited in claim 1, the method for additionally determining an updated active set of pilots for use by the network in the rescue procedure, the method further comprising:

for each of one or more BSs in a neighborhood of the MS having the potentially failing connection, adding the BS to the updated active set used by the network in accordance with a location of the MS and network planning information.

17. The method as recited in claim 1, the MS having the potentially failing connection capable of transmitting a uniform energy signal, the method for additionally determining an updated active set of pilots for use by the network in the rescue procedure, the method further comprising:

for each of one or more BSs in a neighborhood of the MS having the potentially failing connection, measuring a strength of the uniform energy signal, and adding the BS to the updated active set used by the network if the strength of the uniform energy signal for that BS is above a predetermined threshold.

18. The method as recited in claim 17, wherein the uniform energy signal is a reverse link pilot signal.

19. The method as recited in claim 17, wherein the uniform energy signal is a data signal at a predetermined data rate with predetermined data.

20. A mobile station (MS) for communicating with a network and for assisting in performing a rescue procedure when the MS has a connection with the network that has become a potentially failing connection, the MS comprising:

a processor programmed for incrementally lowering pilot signal strength add and drop thresholds T_ADD_R and T_DROP_R by an amount STEP_dec_thres at one or more specific time instants t_N, N=1, 2, . . . M during the rescue procedure, each time instant separated by a time Td;

wherein T_ADD_R and T_DROP_R are used by the MS for determining an updated active set of pilots for use in the rescue procedure.

21. The MS as recited in claim 20, the processor further programmed for lowering T_ADD_R and T_DROP_R in accordance with pilot signal strengths (Ec/Io values) measured at the MS.

22. The MS as recited in claim 20, the processor further programmed for lowering T_ADD_R and T_DROP_R by not more than an total amount MAX_dec_thres during the rescue procedure.

23. The MS as recited in claim 20, the processor further programmed for incrementally adjusting Td between time instants T_N.

24. The MS as recited in claim 21, the processor further programmed for increasing Td between one or more time instants T_N if a combined pilot Ec/Io for the updated active set of the MS is higher than a predetermined desired combined pilot Ec/Io.

25. The MS as recited in claim 21, the processor further programmed for:

increasing Td between one or more time instants T_N if a difference between a combined pilot Ec/Io for the updated active set of the MS and the combined pilot Ec/Io for a previous updated active set of the MS is larger than a predetermined threshold; and

decreasing Td between one or more time instants T_N if the difference between the E for the updated active set of the MS and the E for a previous updated active set of the MS is smaller than the predetermined threshold.

26. The MS as recited in claim 20, the processor further programmed for incrementally adjusting STEP_dec_thres at one or more time instants T_N.

27. The MS as recited in claim 26, the processor further programmed for adjusting STEP_dec_thres at each time instant T_N by:

determining a number of complete rescue cycles K that could be completed before a rescue procedure timer reaches its terminal count; and

computing (T_ADD_H-MAX_dec_thres)/(K−

1) as a value for STEP_dec_thres at each time instant TN, wherein T_ADD_H is an initial value for T_ADD_R at the start of the rescue procedure.

28. The MS as recited in claim 26, the processor further programmed for increasing STEP_dec_thres at each time instant T_N by:

determining a number of complete rescue cycles K that could be completed before a rescue procedure timer reaches its terminal count;

determining δ

=2*(MAX_dec_thres)/(K−

1)K, where δ

is an initial value for STEP_dec_thres at the start of the rescue procedure; and

computing δ

*N as a value for STEP_dec_thres at each time instant T_N, wherein N=1, 2, . . . (K−

1).

29. The MS as recited in claim 26, the processor further programmed for:

decreasing STEP_dec_thres at one or more time instants T_N, N=1, 2, . . . M, if a difference between a combined pilot Ec/Io for the updated active set of the MS at a particular time instant T_N and the combined pilot Ec/Io for a previous updated active set of the MS at an immediately previous time instant T<sub>N−

1</sub> is larger than a predetermined threshold; and

increasing STEP_dec_thres at one or more time instants T_N, N=1, 2, . . . M, if the difference between the combined pilot Ec/Io for the updated active set of the MS at the particular time instant T_N and the combined pilot Ec/Io for the previous updated active set of the MS at the immediately previous time instant T<sub>N−

1</sub> is smaller than or equal to a predetermined threshold.

30. The MS as recited in claim 21, the processor further programmed for determining MAX_dec_thres by:

selecting a desired combined pilot Ec/Io that gives a high probability of producing a good link as (Ec/Io)_desired;

measuring or estimating an Ec/Io value from a strongest pilot in the updated active set as (Ec/Io)_max; and

solving (Ec/Io)_max+(N−

1) (Ec/Io)_min≧

(Ec/Io)_desired for (Ec/Io)_min, where N is a maximum allowed active set size; and

computing MAX_dec_thres as T_ADD_R —

(Ec/Io)_min.

31. The MS as recited in claim 21, the processor further programmed for:

measuring Ec/Io for all pilots detectable by the MS having the potentially failing connection;

placing the measured pilots in a list in order of decreasing Ec/Io; and

starting with the pilot in the list having the highest Ec/Io and going through the list in order of decreasing Ec/Io,

measuring the combined Ec/Io for all pilots in the updated active set,

for a current pilot from the list, determining the combined Ec/Io for all pilots in the updated active set plus the current pilot, and

adding the current pilot to the updated active set if the current pilot increased the combined Ec/Io measurement by a predetermined percentage.

32. A communications system for determining an updated active set of pilots used in a rescue procedure for rescuing a mobile station (MS) having a connection with a network that has become a potentially failing connection, the system comprising:

a MS, the MS comprising a processor programmed for

incrementally lowering pilot signal strength add and drop thresholds T_ADD_R and T_DROP_R by an amount STEP_dec_thres at one or more specific time instants t_N, N=1, 2, . . . M during the rescue procedure, each time instant separated by a time Td, wherein T_ADD_R and T_DROP_R are used by the MS for determining the updated active set of MS pilots for use in the rescue procedure, and

transmitting a uniform energy signal during a time when the MS is having the potentially failing connection; and

a network communicatively coupled to the MS, the network including one or more pilots in a neighborhood of the MS for communicating with the MS, each pilot including a processor programmed for receiving and measuring a strength of the uniform energy signal and adding the pilot to the updated active set used by the network in performing the rescue procedure if the strength of the uniform energy signal is above a predetermined threshold.

33. The system as recited in claim 32, wherein the uniform energy signal transmitted by the MS is a reverse link pilot signal.

34. The system as recited in claim 32, wherein the uniform energy signal transmitted by the MS is a data signal at a predetermined data rate with predetermined data.

35. The system as recited in claim 32, the method for additionally determining the updated active set of pilots for use by the network in the rescue procedure, the method further comprising:

for each of one or more BSs in the neighborhood of the MS having the potentially failing connection, adding the BS to the updated active set used by the network in accordance with a location of the MS and network planning information.

37. The network as recited in claim 36, wherein the uniform energy signal is a reverse link pilot signal.

38. The network as recited in claim 36, wherein the uniform energy signal is a data signal at a predetermined data rate with predetermined data.

36. A network for communicating with a mobile station (MS) and for assisting in performing a rescue procedure when the MS has a connection with the network that has become a potentially failing connection, the MS having the potentially failing connection capable of transmitting a uniform energy signal, the network comprising:

one or more BS sectors in a neighborhood of the MS for communicating with the MS, each BS sector including a processor programmed for receiving and measuring a strength of the uniform energy signal and adding the BS sector to an updated active set used by the network in performing the rescue procedure if the strength of the uniform energy signal is above a predetermined threshold.

39. In a system comprising a network and at least one mobile station (MS) for enabling communications with the at least one MS, the system capable of performing a rescue procedure for rescuing a MS having a connection with the network that has become a potentially failing connection, a method for adjusting pilot signal strength add and drop thresholds T_ADD_R and T_DROP_R used by the MS having the potentially failing connection in determining an updated active set of pilots for use by the MS in the rescue procedure, the method comprising:

at one or more specific time instants t_N, N=1, 2, . . . M during the rescue procedure, each time instant separated by a time Td,

computing temporary rescue add and drop threshold values by lowering present values for T_ADD_R and T_DROP_R by an amount STEP_dec_thres; and

computing add and drop threshold algorithms specified in Sections 2.6.6.2.5.2 and 2.6.6.2.3 of the IS-2000-5 Standard, respectively, after replacing static add and drop threshold values in those algorithms with the temporary rescue add and drop threshold values, to generate new values for T_ADD_R and T_DROP_R, respectively.