Method and apparatus for transmitting reverse link power control signals based on the probability that the power control command is in error

• US 6,208,873 B1
• Filed: 11/23/1998
• Issued: 03/27/2001
• Est. Priority Date: 11/23/1998
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Esteves, Eduardo A. S.
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): BEAMER, TEMICA M
• Application Number:
  US09/198,320
• Time in Patent Office: 855 Days
• Field of Search: 455/67.1, 455/67.3, 455/67.6, 455/69, 455/70, 455/522, 455/574, 455/126, 455/127, 375/130, 370/342, 370/320, 370/335
• US Class Current: 455/522
• CPC Class Codes: H04W 52/18 TPC being performed according to specific parameters
• CPC Class Codes: H04W 52/56 Detection of errors of TPC bits

Abstract

A method and apparatus for controlling the transmit power of a plurality of mobile radio units transmitting to a base station in a mobile radio telephone system. For each of the mobile units in the system, a signal strength estimate is measured at the base station based on reverse link signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units. The signal strength estimate associated with each mobile unit is compared to a threshold. Next, for each mobile unit in the plurality of mobile units, if the signal strength estimate associated with the mobile unit is greater than the threshold, then a power control bit having a first value is assigned to the mobile unit; conversely, if the signal strength estimate associated with the mobile unit is less than the threshold, then a power control bit having a second value is assigned to the mobile unit. A variable gain that is a function of the difference between the signal strength estimate associated with the mobile unit and the threshold is next applied to each power control bit. The variable gain applied to each power control bit increases as the magnitude of the difference between the signal strength estimate associated with the mobile unit and the threshold increases. Each gain-adjusted power control bit is then transmitted to the mobile units.

Claims

1. A method for controlling the transmit power allocated to an information signal transmitted from a first site within a communication system, the method comprising the steps of:

(A) assessing a probability that the information signal contains erroneous information prior to transmission of the information signal from the first site;

(B) applying a variable gain to the information signal in accordance with the probability that the information signal contains erroneous information, wherein the variable gain applied to the information signal decreases as the probability that the information signal contains erroneous information increases; and

(C) after step (B), transmitting the information signal from the first site.

2. The method of claim 1, wherein step (B) further comprises selecting a value of the variable gain from a set of candidate variable gain values, the set of candidate variable gain values including at least two different non-zero candidate variable gain values.

3. The method of claim 2, wherein the set of candidate variable gain values includes a zero gain value that corresponds to an erasure of the information signal.

4. The method of claim 1, wherein the first site is a base station in a mobile radio communication system having a plurality of mobile units and the information signal is a power control bit transmitted from the base station for controlling the reverse link transmit power of a mobile unit.

5. The method of claim 4, wherein the step of assessing a probability further comprises the steps of:

(A) measuring, at the base station, at least one signal strength estimate associated with each of the mobile unit, each measurement based on reverse link signals sent from the associated mobile unit and received at the base station and comparing the signal strength estimate associated with each mobile unit to a threshold;

and wherein the step of applying the variable gain further comprises the steps of;

(B) for each mobile unit in the plurality of mobile units;

(i) assigning a power control bit having a first value to the mobile unit and applying a variable gain to the power control bit if the signal strength estimate associated with the mobile unit is greater than the threshold; and

(ii) assigning a power control bit having a second value to the mobile unit and applying a variable gain to the power control bit if the signal strength estimate associated with the mobile unit is less than the threshold;

(iii) wherein the variable gain applied in steps (i) and (ii) to each power control bit is a function of a difference between the signal strength estimate associated with the mobile unit and the threshold, and wherein the variable gain applied to the power control bit in steps (i) and (ii) increases as the difference between the signal strength estimate associated with the mobile unit and the threshold increases; and

(C) wherein the step of transmitting the information signal further comprises transmitting each power control bit to the mobile units.

6. The method of claim 5, wherein the variable gain applied in steps (i) and (ii) to each power control bit corresponds to a first gain value when a magnitude of the difference between the signal strength estimate associated with the mobile unit and the threshold is less than a first positive amount, and the variable gain applied in steps (i) and (ii) to each power control bit corresponds to a second gain value when the magnitude of the difference between the signal strength estimate associated with the mobile unit and the threshold is more than the first positive amount.

7. The method of claim 6, wherein the first gain value corresponds to an erasure and the second gain value corresponds to a positive gain.

8. The method of claim 6, wherein the variable gain applied in steps (i) and (ii) to each power control bit corresponds to a third gain value when the magnitude of the difference between the signal strength estimate associated with the mobile unit and the threshold is greater than the first positive amount and less than a second positive amount, the second positive amount being greater than the first positive amount.

9. The method of claim 5, further comprising the step of providing a plurality of power control channels for transmitting power control information from the base station to the mobile units, each of the power control channels being assigned to one of the plurality of mobile units and using one of a plurality of different orthogonal codes for transmitting the power control bits from the base station to a mobile unit in step (C).

10. The method of claim 9, wherein step (C) comprises simultaneously transmitting each power control bit to the mobile units during a time interval, wherein each power control bit is transmitted to the mobile units on a different one of the plurality of power control channels.

11. The method of claim 10, wherein transmission from said base station of said first value of said power control bit on a first power control channel represents a command to a first mobile unit to increase the transmit power of signals sent from the first mobile unit to the base station on the reverse link, and transmission from said base station of said second value of said power control bit on a second power control channel represents a command to a second mobile unit to decrease the transmit power of signals sent from the second mobile unit to the base station on the reverse link.

12. The method of claim 5, wherein steps (A)-(C) are performed repeatedly during successive time slots for each of the plurality of mobile units.

13. The method of claim 5, wherein step (A) further comprises, for each of the mobile units, measuring at the base station, a signal strength estimate based on pilot signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units.

14. The method of claim 5, further comprising the steps of:

(A) determining a received power control signal value at a mobile station by demodulating transmissions on the power control channel associated with the mobile station;

(B) comparing the received power control signal value to second and third thresholds at the mobile station;

(C) if the received power control bit value is greater than the second threshold, then increasing the transmit power of signals sent from the mobile unit to the base station on the reverse link; and

(D) if the received power control bit value is less than the third threshold, then decreasing the transmit power of signals sent from the mobile unit to the base station on the reverse link.

15. The method of claim 14, wherein the second threshold is equal to the third threshold.

16. The method of claim 14, wherein the second threshold is greater than the third threshold.

17. The method of claim 16, further comprising the step of:

(A) if the received power control signal value is less than the second threshold and greater than the third threshold, then holding constant the transmit power of signals sent from the mobile unit to the base station on the reverse link.

18. The method of claim 1, wherein the first site is a base station in a mobile radio communication system having a plurality of mobile units, the second site is one of the plurality of mobile units, and step (A) further comprises the steps of:

(A) for each of the mobile units, measuring at the base station, a signal strength estimate based on reverse link signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units, and comparing the signal strength estimate associated with each mobile unit to a high threshold and a low threshold;

step (B) further comprises the steps of;

(B) for each mobile unit in the plurality of mobile units;

(i) if the signal strength estimate associated with the mobile unit is greater than the high threshold, then assigning a power control bit having a first value to the mobile unit; and

(ii) if the signal strength estimate associated with the mobile unit is less than the low threshold, then assigning a power control bit having a second value to the mobile unit; and

(iii) if the signal strength estimate associated with the mobile unit is less than the high threshold and greater than the low threshold, then associating a power control bit erasure with the mobile unit; and

step (C) further comprises;

(C) transmitting each power control bit having the first and second value to the mobile units, wherein transmission of a power control bit is inhibited for each mobile unit having a power control bit erasure associated therewith.

19. The method of claim 18, further comprising the step of providing a plurality of power control channels for transmitting power control information from the base station to the mobile units, each of the power control channels being assigned to one of the plurality of mobile units and using one of a plurality of different orthogonal codes for transmitting power control information from the base station to a mobile unit, wherein step (B)(iii) comprises the step of:

(iii) if the signal strength estimate associated with the mobile unit is less than the high threshold and greater than the low threshold, then associating a power control bit erasure with the power control channel assigned to the mobile unit.

20. The method of claim 19, wherein step (C) further comprises simultaneously transmitting each power control bit having the first and second value to the mobile units during a time interval, wherein each power control bit having the first value or the second value is transmitted to the mobile units on a different one of the plurality of power control channels, and wherein transmission of a power control bit is inhibited during the time interval for each power control channel having a power control bit erasure associated therewith.

21. The method of claim 20, wherein transmission from said base station of said first value of said power control bit on a first power control channel represents a command to a first mobile unit to increase the transmit power of signals sent from the first mobile unit to the base station on the reverse link, and transmission from said base station of said second value of said power control bit on a second power control channel represents a command to a second mobile unit to decrease the transmit power of signals sent from the second mobile unit to the base station on the reverse link.

22. The method of claim 21, wherein steps (A)-(C) are performed repeatedly during successive time slots for each of the plurality of mobile units.

23. The method of claim 18, wherein step (A) comprises:

(A) for each of the mobile units, measuring at the base station, a signal strength estimate based on pilot signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units.

24. The method of claim 18, wherein the power control bits transmitted in step (C) are transmitted using BPSK modulation.

25. The method of claim 18, further comprising the steps of setting the high threshold above a desired signal strength value and setting the low threshold below the desired signal strength value.

26. The method of claim 25, wherein the high threshold is set k db above the desired signal strength value and the low threshold is set k db below the desired signal strength value.

27. The method of claim 20, further comprising the steps of:

(A) determining a received power control signal value at a mobile station by demodulating transmissions on the power control channel associated with the mobile station;

(B) comparing the received power control signal value to third and fourth thresholds at the mobile station;

(C) if the received power control bit value is greater than the third threshold, then increasing the transmit power of signals sent from the mobile unit to the base station on the reverse link; and

(D) if the received power control bit value is less than the fourth threshold, then decreasing the transmit power of signals sent from the mobile unit to the base station on the reverse link.

28. The method of claim 27, wherein the third threshold is equal to the fourth threshold.

29. The method of claim 27, wherein the third threshold is greater than the fourth threshold.

30. The method of claim 29, further comprising the step of:

(A) if the received power control bit value is less than the third threshold and greater than the fourth threshold, then holding constant the transmit power of signals sent from the mobile unit to the base station on the reverse link.

31. In a communication system having a first site that transmits an information signal to a second site, an apparatus for controlling the transmit power allocated to the information signal at the first site, comprising:

(A) a controller that assesses a probability that the information signal contains erroneous information prior to transmission of the information signal from the first site to the second site;

(B) an amplifier that applies a variable gain to the information signal in accordance with the probability that the information signal contains erroneous information, wherein the variable gain applied to the information signal decreases as the probability that the information signal contains erroneous information increases;

(C) a transmitter that transmits the information signal from the first site to the second site.

32. The apparatus of claim 31, wherein the controller selects a value of the variable gain from a set of candidate variable gain values, the set of candidate variable gain values including at least two different non-zero candidate variable gain values.

33. The apparatus of claim 32, wherein the set of candidate variable gain values includes a zero gain value that corresponds to an erasure of the information signal.

34. The apparatus of claim 31, wherein the first site is a base station in a mobile radio communication system having a plurality of mobile units, the second site is one of the plurality of mobile units, and the information signal is a power control bit transmitted from the base station for controlling the reverse link transmit power of a mobile unit.

35. The apparatus of claim 34, wherein the controller calculates, for each of the mobile units, a signal strength estimate based on reverse link signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units;

the controller compares the signal strength estimate associated with each mobile unit to a threshold; and

, for each mobile unit in the plurality of mobile units, the controller assigns a power control bit having a first value to the mobile unit if the signal strength estimate associated with the mobile unit is greater than the threshold, and the controller assigns a power control bit having a second value to the mobile unit if the signal strength estimate associated with the mobile unit is less than the threshold;

wherein the amplifier applies the variable gain to each power control bit, the variable gain applied by the amplifier to each power control bit being a function of a difference between the signal strength estimate associated with the mobile unit and the threshold such that the variable gain applied by the amplifier to each power control bit increases as the difference between the signal strength estimate associated with the mobile unit and the threshold increases;

and wherein the transmitter transmits each power control bit to the mobile units.

36. The apparatus of claim 35, wherein the transmitter transmits the power control bits on a plurality of power control channels, each of the power control channels being assigned to one of the plurality of mobile units and using one of a plurality of different orthogonal codes for transmitting power control information from the base station to a mobile unit.

37. The apparatus of claim 36, wherein the transmitter simultaneously transmits each power control bit to the mobile units during a time interval such that each power control bit is transmitted to the mobile units on a different one of the plurality of power control channels.

38. In a communication system having a first site that transmits an information signal to a second site, an apparatus for controlling the transmit power allocated to the information signal at the first site, comprising:

(A) means for assessing a probability that the information signal contains erroneous information prior to transmission of the information signal from the first site to the second site;

(B) means for applying a variable gain to the information signal in accordance with the probability that the information signal contains erroneous information, wherein the variable gain applied to the information signal decreases as the probability that the information signal contains erroneous information increases;

(C) means for transmitting the information signal from the first site to the second site.

39. The apparatus of claim 38, wherein the means for assessing selects a value of the variable gain from a set of candidate variable gain values, the set of candidate variable gain values including at least two different non-zero candidate variable gain values.

40. The apparatus of claim 39, wherein the set of candidate variable gain values includes a zero gain value that corresponds to an erasure of the information signal.

41. The apparatus of claim 38, wherein the first site is a base station in a mobile radio communication system having a plurality of mobile units, the second site is one of the plurality of mobile units, and the information signal is a power control bit transmitted from the base station for controlling the reverse link transmit power of a mobile unit.

42. The apparatus of claim 41, wherein the means for assessing comprises means for measuring, for each of the mobile units, a signal strength estimate based on reverse link signals sent from the mobile units and received at the base station, wherein each signal strength estimate is associated with one of the mobile units;

and means for comparing the signal strength estimate associated with each mobile unit to a threshold;

the apparatus further comprising means for assigning a power control bit having a first value to each mobile unit having an associated signal strength estimate that is greater than the threshold, and means for assigning a power control bit having a second value to each mobile unit having an associated signal strength estimate that is less than the threshold;

wherein the variable gain applied to each power control bit by the means for applying is a function of a difference between the signal strength estimate associated with the mobile unit and the threshold, and wherein the variable gain applied to each power control bit increases as the difference between the signal strength estimate associated with the mobile unit and the threshold increases; and

wherein the means for transmitting transmits each power control bit to the mobile units.

43. The apparatus of claim 42, wherein the means for transmitting transmits the power control bits on a plurality of power control channels, each of the power control channels being assigned to one of the plurality of mobile units and using one of a plurality of different orthogonal codes for transmitting power control information from the base station to a mobile unit.

44. The apparatus of claim 43, wherein the means for transmitting simultaneously transmits each power control bit to the mobile units during a time interval such that each power control bit is transmitted to the mobile units on a different one of the plurality of power control channels.