Enhanced power control algorithms for fixed wireless access systems

• US 6,587,442 B1
• Filed: 10/28/1999
• Issued: 07/01/2003
• Est. Priority Date: 10/28/1999
• Status: Expired due to Fees

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Tripathi, Nishith D.
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): TORRES, MARCOS L
• Application Number:
  US09/429,856
• Time in Patent Office: 1,342 Days
• Field of Search: 455/522, 455/69, 455/3.05, 455/504, 455/505, 455/506, 370/318, 370/320, 370/311
• US Class Current: 370/311
• CPC Class Codes: H04W 52/20 using error rate
• CPC Class Codes: H04W 52/221 using past power control commands
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets

Abstract

A method for efficient power control in a (CDMA based) fixed wireless system. The method comprises the steps of (1) monitoring a transmission link of the fixed wireless system for an occurrence of a fade, (2) recording a number of power increases to the transmission link due to said fade, and (3) reducing the power to an appropriate level when said fade is over. The adjusting step includes the steps of determining an appropriate power-down step size, which results in saving power, wherein the step size is influenced by a frame error rate (FER) and selected to maintain a desired FER, and dynamically decreasing the power by the appropriate power-down step size, thereby conserving power and increasing system capacity.

Claims

1. A method for efficient power control in a wireless communications system, said method comprising the steps of:

monitoring a transmission link of said wireless communications system for an occurrence of a fade, indicated by a received message;

opening an observation window on receipt of said message, wherein said observation window is a period beginning when a fade is first indicated by receipt of said message and ending when the fade is no longer present as indicated by a receipt of consecutive good frames;

recording time instances and a number of power increases to said transmission link due to said fade;

closing said observation window when consecutive good frames are received;

calculating an initial step down size Lo reduce the power level by an amount substantially equal to a combined amount of power increases during said fade utilizing the number of power increases following a recorded time instant within said observation period, wherein said combined amount of power increases is determined based on receipt of a first good frame of said consecutive good frames within a set number of frames following a time instance of a gain increase after the beginning of said fade; and

reducing power to said transmission link by said calculated initial step down size when said fade ends.

2. The method of claim 1, wherein said reducing step comprises:

determining a number of unnecessary power increases due to said fade; and

decreasing said power by said number of unnecessary power increases.

3. The method of claim 2, wherein:

said determining step further comprises the step of analyzing which one of a sequence of gain increases is sufficient to overcome said fade; and

said decreasing step comprises the step of reducing said power by all gain increases subsequent to said sufficient gain increase.

4. The method of claim 1, further comprising adjusting a basic power control loop of said transmission link to include (1) a first power down on said transmission link substantially equal to a combined sum of all unnecessary power increases during said fade and (2) a second power down initiated as a sequence of small steps that become smaller as the loop approaches a completion phase.

5. The method of claim 4, wherein said adjusting step includes the steps of:

selecting a predetermined power-down step size, which results in conserving power, wherein said step size is influenced by a frame error rate (FER) and selected to maintain a desired FER; and

dynamically decreasing said power by said predetermined power down step size, thereby conserving power and increasing system capacity.

6. The method of claim 1, further comprising:

delineating a power-down time period of said power control loop into at least a first time period and a second time period corresponding respectively to an earlier time period and a later time period; and

effecting a larger gain decrease during said power-down in said earlier time period and a smaller gain decrease in said later time period.

7. The method of claim 5 wherein:

said selecting step further includes the steps of monitoring said FER; and

said dynamically decreasing step further includes the step of adjusting said power based on said FER, wherein said gain is increased when said FER is too high and decreased when said FER is too low, to substantially improve system capacity.

8. The method of claim 1, further comprising:

receiving, at a base station, a power measurement report message (PMRM) from a mobile station to report frame errors, wherein, when said PMRM is a first PMRM received after a sequence of good frames are received;

said PAM operating as the message that triggers the opening of the observation window; and

increasing a digital gain upon receipt of said PMRM.

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

selecting a reference variable, T, corresponding to a number of frames received;

determining if a first good frame of said consecutive good frames occurred within T frames of a gain increase; and

reducing said digital gain by an amount equal to all subsequent gain increases after said gain increase, when said first good frame occurred within T frames of said gain increase, thus implementing a fast power-down operation.

10. A method for increasing capacity of a wireless communications system, said method comprising:

monitoring a transmission link of said wireless communications system for a measurable condition that indicates an occurrence of a fade, said measurable condition from among (1) increase in a frame error rate (FER) and (2) receipt of a power measurement report message

initiating a measurement period when an initial one of said measurable condition is detected following receipt of a sequence of good frames;

terminating said measurement period when a first sequence of good frames is received following the initiating step;

recording a number of power increases to said transmission link during said measurement period;

determining which ones of said number of power increases were not required to maintain a FER of said transmission link before said fade;

calculating an initial step down size to reduce the power level by an amount substantially equal to a combined amount of the number of power increases during said fade wherein said combined amount of power increases is determined based on receipt of a first good frame of said sequence of good frames within a set number of frames following a time instance of a gain increase after the beginning of said fade; and

reducing said power to a level required to maintain said pre-fade FER by implementing an immediate power down step substantially equal to the initial step down size and then subsequently reducing said power by a step size that is a fractional part of one of said power increases during said fade, wherein said reducing of said power by said immediate power down step effectuates an increase in capacity of said fixed wireless system.

11. A system for implementing a feedback based power control algorithm in a wireless communications system, said system comprising:

means for monitoring a transmission link of said wireless communications system for an occurrence of a fade, indicated by a received message;

means for opening an observation window on receipt of said message, wherein said observation window is a period beginning when a fade is first indicated by receipt of said message and ending when the fade is no longer present as indicated by a receipt of consecutive good frames;

means for recording time instances and a number of power increases to said transmission link due to said fade;

means for closing said observation window when consecutive good frames are received;

means for calculating an initial step down size to reduce the power level by an amount substantially equal to a combined amount of power increases during said fade utilizing the number of power increases following a recorded time instant within said observation period, wherein said combined amount of power increases is determined based on receipt of a fist good frame of said consecutive good frames within a set number of frames following a time instance of a gain increase after the beginning of said fade; and

means for reducing power to said transmission link by said calculated initial step down size when said fade ends.

12. The system of claim 11, wherein said reducing means further comprises:

means for determining a number of unnecessary power increases due to said fade; and

means for decreasing said power by said number of unnecessary power increases.

13. The system of claim 12 wherein:

said determining means further comprises means for analyzing which one of a sequence of gain increases is sufficient to overcome said fade; and

said decreasing step comprises means for reducing said power increase by all gain increases subsequent to said sufficient gain increase.

14. The system of claim 11, further comprising means for adjusting a basic power control loop of said transmission link to include (1) a first power down on said transmission link substantially equal to a combined sum of all unnecessary power increases during said fade and (2) a second power down initiated as a sequence of small steps that become smaller as the loop it approaches a completion phase.

15. The system of claim 14, wherein said adjusting means includes:

means for selecting a pre-determined power-down step size, which results in conserving power, wherein said step size is influenced by a frame error rate (FER) and selected to maintain a desired FER; and

means for dynamically decreasing said power by said predetermined power down step size, thereby conserving power and increasing system capacity.

16. The system of claim 11, further comprising:

means for delineating a power-down time period of said power control loop into at least a first time period and a second time period corresponding respectively to an earlier time period and a later time period; and

means for effecting a larger gain decrease during said power-down in said earlier time period and a smaller gain decrease in said later time period.

17. The system of claim 15, wherein:

said selecting means further includes means for monitoring said FER; and

said dynamically decreasing means further includes means for adjusting said power based on said FER, wherein said gain is increased when said FER is too high and decreased when said FER is too low, to substantially improve system capacity.

18. The system of claim 11, further comprising:

means for receiving, at a base station, a power measurement report message (PMRM) from a mobile station to report frame errors, wherein, when said PMRM is a first PMRM received after a sequence of good frames are received, said PMRM operating as the message that triggers the opening of the observation window; and

means for increasing a digital gain upon receipt of said PMRM.

19. The system of claim 11, further comprising:

means for selecting a reference variable, T, corresponding to a number of frames received;

means for determining if a first good frame of said consecutive good frames occurred within T frames of a gain increase; and

means for reducing said digital gain by an amount equal to all subsequent gain increases after said gain increase, when said first good frame occurred within T frames of said gain increase, thus implementing a fast power-down operation.