Robust erasure detection and erasure-rate-based closed loop power control

• US 8,516,314 B2
• Filed: 08/09/2011
• Issued: 08/20/2013
• Est. Priority Date: 06/18/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sutivong, Arak, Agrawal, Avneesh, Julian, David Jonathan
• Primary Examiner(s): CHAUDRY, MUJTABA M
• Application Number:
  US13/206,206
• Publication Number:
  US 20110296279A1
• Time in Patent Office: 742 Days
• Field of Search: 714/774, 714/704
• US Class Current: 714/704
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04W 52/125 cascaded outer loop power control
• CPC Class Codes: H04W 52/20 using error rate

Abstract

Techniques for performing erasure detection and power control for a transmission without error detection coding are described. For erasure detection, a transmitter transmits codewords via a wireless channel. A receiver computes a metric for each received codeword, compares the computed metric against an erasure threshold, and declares the received codeword to be “erased” or “non-erased”. The receiver dynamically adjusts the erasure threshold based on received known codewords to achieve a target level of performance. For power control, an inner loop adjusts the transmit power to maintain a received signal quality (SNR) at a target SNR. An outer loop adjusts the target SNR based on the status of received codewords (erased or non-erased) to achieve a target erasure rate. A third loop adjusts the erasure threshold based on the status of received known codewords (“good”, “bad”, or erased) to achieve a target conditional error rate.

Claims

1. An apparatus which controls a transmit power for a physical channel in a wireless communications system, comprising:

a first sub-system utilizing an inner loop operable to adjust the transmit power for the physical channel to maintain a received Signal-to-Noise Ratio (SNR) substantially at a target SNR value;

a second sub-system utilizing an outer loop operable to adjust the target SNR value which achieves a target erasure rate; and

a third sub-system utilizing a third loop is operable to adjust an erasure threshold to achieve a target conditional error rate.

2. The apparatus of claim 1, wherein the first sub-system further comprises:

an SNR estimator operable to determine an of estimate the received SNR at a base station; and

a transmit power control (TPC) generator, functionally coupled to the SNR estimator, operable to determine a comparison between the estimate of the received SNR with the target SNR value, and generate TPC commands based the comparison.

3. The apparatus of claim 2, wherein the TPC generator receives the target SNR associated with a control channel from the second sub-system, and provides TPC commands over a forward link to a mobile terminal.

4. The apparatus of claim 3, wherein the TPC commands include at least one of an UP command to direct an increase in transmit power for the control channel or a DOWN command to direct a decrease in channel power.

5. The apparatus of claim 1, wherein the second sub-system further comprises:

a metric computation unit operative to determine a metric for received codewords obtained from a control channel;

an erasure detector, functionally coupled to the metric computation unit, operable to perform erasure detection for the received codewords based on the determined metric for the received codeword and the erasure threshold; and

a target SNR adjustment unit, functionally coupled to the erasure detector, operable to obtain the status of the received codewords and adjust the target SNR for the control channel.

6. The apparatus of claim 5, wherein the erasure detector is further operable to provide a status of the received codewords are defined as being one of erased or non-erased.

7. The apparatus of claim 5, wherein the target SNR adjustment unit is further operable to provide the target SNR to the first sub-system.

8. The apparatus of claim 1, wherein the third sub-system further comprises:

a decoder operable to decode received known codewords and determine whether the codewords are correct, and generate a codeword status based upon the determination; and

an erasure threshold adjustment unit, functionally coupled to the decoder, operable to determine the erasure threshold based upon the generated codeword status, and provide the erasure threshold to the second sub-system.

9. The apparatus of claim 8, wherein the codeword status is defined as one of good, bad or erased.

10. The apparatus of claim 1, wherein the inner loop, the outer loop, and the third loop are updated at different rates.

11. The apparatus of claim 10, wherein inner loop is the fastest loop, the outer loop is the next fastest loop, and the third loop is the slowest loop.

13. The method of claim 1, further comprising:

determining an of estimate the received SNR at a base station; and

determining a comparison the estimate of the received SNR with the target SNR value; and

generating transmit power control (TPC) commands based the comparison.

14. The method of claim 13, further comprising:

receiving the target SNR for a control channel from the second sub-system; and

providing the TPC commands over a forward link to a mobile terminal.

15. The method of claim 14, wherein the TPC commands include at least one of an UP command to direct an increase in transmit power for the control channel or a DOWN command to direct a decrease in channel power.

12. A method for controlling a transmit power for a physical channel in a wireless communications system, comprising:

adjusting the transmit power for the physical channel within a first loop to maintain a received Signal-to-Noise Ratio (SNR) substantially at a target SNR value;

adjusting the target SNR value within a second loop which achieves a target erasure rate;

adjusting an erasure threshold within a third loop to achieve a target conditional error rate.

16. The method of claim 12, further comprising:

determining a metric for received codewords obtained from a control channel;

performing erasure detection for the received codewords based on the determined metric for the received codeword and the erasure threshold;

obtaining the status of the received codewords; and

adjusting the target SNR for the control channel.

17. The method of claim 16, further comprising providing a status of the received codewords which are defined as being one of erased or non-erased.

18. The method of claim 16, further comprising providing the target SNR to the first loop.

19. The method of claim 12, further comprising:

decoding received known codewords and determining whether the codewords are correct, and generating a codeword status based upon the determination; and

determining the erasure threshold based upon the generated codeword status, and providing the erasure threshold to the second sub-system.

20. The method of claim 19, wherein the codeword status is defined as one of good, bad or erased.

21. The method of claim 12, further comprising updating the inner loop, the outer loop, and the third loop at different rates.