Uplink power control algorithm

• US 6,952,591 B2
• Filed: 11/20/2001
• Issued: 10/04/2005
• Est. Priority Date: 11/20/2001
• Status: Active Grant

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Das, Arnab, Budka, Kenneth C., Murti, Kamala, Zhang, Yinglu
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US09/989,335
• Publication Number:
  US 20030109274A1
• Time in Patent Office: 1,414 Days
• Field of Search: 455/522, 455/68, 455/69, 455/88, 455/561, 455/517, 455/67.11, 375/146, 375/135, 375/295, 375/297, 375/358, 370/310, 370/346, 370/328
• US Class Current: 455/517
• CPC Class Codes: H04W 52/24 using SIR [Signal to Interference Ratio] or other wireless path parameters
• CPC Class Codes: H04W 52/265 taking into account the quality of service QoS
• CPC Class Codes: H04W 52/36 with a discrete range or set of values, e.g. step size, ramping or offsets

Abstract

In a system having a base station transmitter for transmitting data blocks to one or more mobile stations over a radio link, there is a method for determining an uplink transmit power level at which to transmit a current data block over a radio link from the mobile to the base transmitter station. The method evaluates airlink quality measurements in the radio link over a measurement interval, wherein each time a message is sent to the mobile station, it is evaluated whether a specified number of uplink blocks have transmitted by the mobile station since the start of the measurement interval. Based on the evaluated airlink quality measurement, the method determines the uplink transmit power level that the mobile should be using for the current block, and adjusts the transmit power level, if necessary, for the current block.

Claims

1. A method for determining an uplink transmit power level at which a mobile station transmits a current data block over a radio link to a base transceiver station, comprising:

obtaining link quality measurements over a given measurement interval; and

applying the link quality measurements to bit error rate (BER)-based and block error rate (BLER)-based power step calculation techniques to determine how much to adjust the mobile station'"'"'s transmit power for transmitting the current block.

2. The method of claim 1, wherein the base transceiver station and mobile station are part of a general packet radio service (GPRS) system.

3. The method of claim 1, further comprising transmitting the current block at the adjusted transmit power level.

4. The method of claim 1, wherein the method employs no timers, but is driven or initiated by at least one external event selected from the group comprising temporary block flows (TBF), receipt of an uplink block of data, transmission of a packet uplink acknowledgement/negative acknowledgement message, transmission of a TBF reassignment message, and termination of a TBF.

5. The method of claim 1, wherein applying further includes implementing an expediting procedure to more quickly determine the initial uplink transmit power of the mobile station by monitoring the quality of the first several uplink blocks sent on a temporary block flow (TBF), in order to determine if the initial uplink transmit power commanded by the base transceiver station at the start of the TBF is too low.

6. The method of claim 5, wherein the expediting procedure is controlled by a single flag indicating whether the expediting procedure is enabled or not.

7. The method of claim 1, wherein each time a message is sent to the mobile station, it is evaluated whether a specified number of uplink blocks have been transmitted by the mobile station since the start of the measurement interval.

8. The method of claim 1, wherein the BER-based power step, Δ

_BER(s), which represents the excess power being used by the mobile station, is determined for each mobile station uplink temporary block flow (TBF) on a time slot s.

9. The method of claim 1, wherein Δ

_BER(s) is determined from the following equation;

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>s=\frac{1}{\mathrm{\mu <br><br>}}<br><br>\log <br><br>\left(\frac{n_1<br><br>\left(s\right)<br><br>b_1+n_2<br><br>\left(s\right)<br><br>b_2+n_3<br><br>\left(s\right)<br><br>b_3+n_4<br><br>\left(s\right)<br><br>b_4}{\hat{b}<br><br>\left(s\right)}\right),$

where μ

represents a slope of a log(BER) versus C/I (dB) plot at time slot s, {circumflex over (b)}(s) represents the expected number of bit errors in a given measurement interval at time slot s, n_j(s) represents the number of RLC blocks received from the mobile station on time slot s that which were not in error, and b_j(s) is the target number of bit errors per RLC block for the mobile station at time slot s.

10. The method of claim 1, wherein the BLER-based power step ,Δ

_BLER(s), which represents the excess power being used by the mobile station, is determined for each mobile station uplink TBF on a time slot s.

11. The method of claim 10, wherein Δ

_BLER(s) is determined from the following equation;

$\mathrm{\Delta <br><br>}<br><br>\left(s\right)=\frac{-k_{\mathrm{sum}}<br><br>\left(s\right)+\left(N_1<br><br>\left(s\right)<br><br>B_1+N_2<br><br>\left(s\right)<br><br>B_2+N_3<br><br>\left(s\right)<br><br>B_3+N_4<br><br>\left(s\right)<br><br>B_4\right)}{N_1<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_1+N_2<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_2+N_3<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_3+N_4<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_4},$

where k_sum(s) is the total number of RLC blocks received from the mobile station on time slot s which were in error, N_j(s) represents the number of RLC blocks received from the mobile station on time slot s during the measurement interval, B_j(s) is the target block error rate for the mobile station at time slot s, and β

_j represents the slope of a BLER versus C/I (dB) plot at time slot s.

12. The method of claim 1,

wherein if a calculated power step results in an increase in mobile transmit power, the mobile is commanded to increase its transmit power by the total power step, and

wherein if the calculated power step results in a decrease in mobile transmit power, the mobile is commended to reduce its power by a fraction of the calculated power step.

13. The method of claim 12, wherein reducing the transmit power by only a fraction of the calculated step provides a method that is robust to estimation errors and to short term fluctuations in channel quality of the mobile station.

14. The method of claim 1, wherein obtaining further includes

assessing the quality of individual RLC blocks received from the mobile station in the base transceiver station, and if the quality is substantially poor within a first polling interval, sending a message commanding a higher mobile transmit power from the mobile station.

15. The method of claim 14, wherein assessing further includes determining whether to send a message or not by determining whether the total number of block errors in the RLC blocks is greater than or equal to a given parameter, and if so, sending a message commanding higher mobile transmit power from the mobile station.

16. A base transceiver station (BTS) in a general packet radio system (GPRS), comprising:

a transceiver for transmitting and receiving data packets to and from a plurality of mobile stations; and

a processor which determines the uplink transmit power to be used by at least one mobile station before transmitting its uplink block to the transceiver of the BTS, the processor including a power control application which obtains link quality measurements from a radio link established between a mobile station and the BTS over a given measurement interval, and which applies the link quality measurements to bit error rate (BER)-based and block error rate (BLER)-based powet step calculation techniques to dtermine how much to adjust the mobile station'"'"'s transmit power.

17. The method of claim 16, wherein each time a message is sent to the mobile station, it is evaluated whether a specified number of uplink blocks have been transmitted by the mobile station since the start of the measurement interval.

18. The base transceiver station of claim 16,

wherein if a calculated power step results in an increase in mobile transmit power, the processor sends a command to the mobile station to increase its transmit power by the total power step, and

wherein if the calculated power step results in a decrease in mobile transmit power, the processor sends a command to the mobile station to reduce its power by a fraction of the calculated power step.

19. The base transceiver station of claim 16, wherein said power control application assesses the received quality of individual RLC blocks received from the mobile stations and if the quality is substantially poor within a first polling interval, the processor sends a message commanding a higher mobile transmit power from the mobile station.

20. The base transceiver station of claim 16, wherein the power control application employs no timers, but is driven or initiated by at least one external event selected from the group comprising temporary block flows (TBF), receipt of an uplink block of data, transmission of a packet uplink acknowledgement/negative acknowledgement message, transmission of a TBF reassignment message, and termination of a TBF.

21. The base transceiver station of claim 16, wherein the BER-based power control step Δ

_BER(s), which represents the excess power being used by the mobile station, is determined for each mobile station uplink TBF on a time slot s.

22. The base transceiver station of claim 21, wherein Δ

_BER(s) is determined from the following equation;

$\mathrm{\Delta <br><br>}<br><br>\left(s\right)=\frac{1}{\mathrm{\mu <br><br>}}<br><br>\log <br><br>\left(\frac{n_1<br><br>\left(s\right)<br><br>b_1+n_2<br><br>\left(s\right)<br><br>b_2+n_3<br><br>\left(s\right)<br><br>b_3+n_4<br><br>\left(s\right)<br><br>b_4}{\hat{b}<br><br>\left(s\right)}\right),$

where μ

represents a slope of a log(BER) versus C/I (dB) plot at time slot s, {circumflex over (b)}(s) represents the expected number of bit errors in a given measurement interval at time slot s, n_j(s) represents the number of RLC blocks received from the mobile station on time slot s that which were not in error, and b_j(s) is the target number of bit errors per RLC block for the mobile station at time slot s.

23. The base transceiver station of claim 16, wherein the BLER-based power control step Δ

_BLER(s), which represents the excess power being used by the mobile station, is determined for each mobile station uplink TBF on a time slot s.

24. The base transceiver station of claim 23, wherein Δ

_BLER(s) is determined from the following equation;

$\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(s\right)=\frac{-k_{\mathrm{sum}}<br><br>\left(s\right)+\left(N_1<br><br>\left(s\right)<br><br>B_1+N_2<br><br>\left(s\right)<br><br>B_2+N_3<br><br>\left(s\right)<br><br>B_3+N_4<br><br>\left(s\right)<br><br>B_4\right)}{N_1<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_1+N_2<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_2+N_3<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_3+N_4<br><br>\left(s\right)<br><br>{\mathrm{\beta <br><br>}}_4},$

where k_sum(s) is the total number of RLC blocks received from the mobile station on time slot s which were in error, N_j(s) represents the number of RLC blocks received from the mobile station on time slot s during the measurement interval, B_j(s) is the target block error rate for the mobile station at time slot s, and β

_j represents the slope of a BLER versus C/I (dB) plot on time slot s.

25. The base transceiver station of claim 16, wherein the power control application includes an expediting procedure to more quickly determine the initial uplink transmit power of the mobile station by monitoring the quality of the first several uplink blocks sent on a temporary block flow (TBF) in order to determine if the initial uplink transmit power commanded by the base transmitter station at the start of the TBF is too low.

26. The base transceiver station of claim 25, wherein the power control application controls the expediting procedure based on a single flag indicating whether the expediting procedure is to be enabled or not.

27. In a general packet radio system (GPRS), a closed-loop power control method requiring interaction between a first algorithm and a second algorithm,

wherein the first algorithm informs the second algorithm about a weakest coding scheme that is to be used over an airlink, in a next measurement interval, between at least one target mobile station and a base station of the system, and

wherein the second algorithm selects target mobile bit error rate (BER) or target mobile carrier-to-interference level (C/I) based on the information from the first algorithm, and sets a flag for when attenuation to be used in said next measurement interval exceeds a preset threshold.

28. The closed-loop power control method of claim 27, wherein the method maintains uplink channel BER of the mobile within a desired range by commanding the target mobile to decrease its transmit power where target BER is below the desired range, and by commanding the target mobile to increase its transmit power where target BER is above the desired range.

29. The closed-loop power control method of claim 27, wherein said coding schemes used by the first algorithm are selected from one of CS-1, CS-2, CS-3 and CS-4 GPRS coding schemes.

30. The closed-loop power control method of claim 29, wherein a set flag indicates that target mobile transmit power is low, so that the first algorithm uses high throughput coding schemes CS-3 and CS-4.

31. The closed-loop power control method of claim 29, wherein an unset flag indicates that target mobile transmit power is high, so that the first algorithm is limited to low throughput coding schemes CS-1 and CS-2.