Method and apparatus for detecting zero rate frames in a communications system

• US 6,208,699 B1
• Filed: 09/01/1999
• Issued: 03/27/2001
• Est. Priority Date: 09/01/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Chen, Tao, Patel, Shimman
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/388,029
• Time in Patent Office: 573 Days
• Field of Search: 375/140, 375/147, 375/224, 375/225, 375/262, 375/265, 375/316, 375/324, 375/340, 375/341, 375/349, 704/236, 704/242, 704/243, 704/244, 714/704, 714/708, 714/758-760, 714/794-796
• US Class Current: 375/340
• CPC Class Codes: H03M 13/3738 with judging correct decoding
• CPC Class Codes: H04B 2201/70705 Rate detection
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 1/208 involving signal re-encoding
• CPC Class Codes: H04W 52/26 using transmission rate or quality of service QoS [Quality of Service]

Abstract

Techniques for detecting zero rate frames in a received data transmission. A modulated signal is received and demodulated in accordance with a particular demodulation format to generate demodulated symbols. The demodulated symbols are partitioned into a number of received frames. For each received frame, a quality metric is computed and compared against a threshold value. The threshold value is selected based, in part, on the quality metrics of received frames. Based on the comparison result, the received frame is indicated as being either transmitted and received in error (i.e., erased or bad) or not transmitted at all (i.e., zero rate or empty). The quality metric can relate to an energy of a received frame, a distance between a received frame and a codeword corresponding to the received frame, or other metrics. The threshold value can be selected based on the quality metrics computed for decoded frames or received frames identified as good, and can be dynamically adjusted based on current information available at the receiver. The method is advantageously used in a CDMA communications system.

Claims

1. A method for identifying zero rate frames in a received data transmission, the method comprising:

receiving a modulated signal;

demodulating the modulated signal in accordance with a particular demodulation format to generate demodulated symbols;

partitioning the demodulated symbols into a plurality of received frames;

computing a quality metric for each of the plurality of received frames;

comparing the quality metric for a particular received frame against a threshold value, wherein the threshold value is selected based, in part, on the quality metrics of received frames; and

identifying the particular received frame as being a zero rate frame or not a zero rate frame based on the comparing.

2. The method of claim 1, wherein the quality metric relates to an energy of a received frame.

3. The method of claim 2, wherein the quality metric for each received frame is computed as a sum of squared symbols for the received frame.

4. The method of claim 1, wherein the quality metric relates to a distance between a received frame and a codeword corresponding to the received frame.

5. The method of claim 4, further comprising:

decoding each received frame into a decoded frame; and

re-encoding the decoded frame in accordance with an encoding format to generate the codeword for the decoded frame.

6. The method of claim 4, further comprising:

decoding each received frame into a decoded frame, and

wherein the codeword comprises the decoded frame.

7. The method of claim 1, further comprising:

decoding each received frame in accordance with a particular decoding hypothesis to generate a decoded frame.

8. The method of claim 7, wherein the particular decoding hypothesis includes a particular frame format and a particular rate selected from among a set of possible frame formats and rates.

9. The method of claim 8, wherein the set of possible frame formats includes 5 msec and 20·

L msec frames, where L is an integer one or greater.

10. The method of claim 8, wherein the set of possible rates includes full, half, quarter, and eight rates.

11. The method of claim 7, wherein the threshold value is selected based, in part, on the quality metrics of decoded frames identified as good frames.

12. The method of claim 11, further comprising:

checking CRC bits associated with a decoded frame to identify whether the decoded frame is a good frame.

13. The method of claim 7, wherein the particular received frame is decoded and identified as not being a good frame.

14. The method of claim 1, wherein the threshold value is selected based, in part, on statistics of the quality metrics of received frames.

15. The method of claim 14, wherein the quality metrics of received frames are weighted equally to generate the statistics.

16. The method of claim 14, wherein the quality metrics of received frames are weighted unequally to generate the statistics.

17. The method of claim 1, wherein the threshold value is dynamically adjustable.

18. The method of claim 1, further comprising:

denormalizing the demodulated symbols with an energy of a pilot signal transmitted with the data transmission.

19. The method of claim 1, wherein the demodulation format is specified by IS-2000 or IS-95-A standard.

20. A receiver subsystem in a communications system comprising:

a demodulator configured to receive and demodulate a modulated signal in accordance with a particular demodulation format to generate demodulated symbols; and

a data processor operatively coupled to the demodulator, the data processor configured to

partition the demodulated symbols into a plurality of received frames,

compute a quality metric for each of the plurality of received frames,

compare the quality metric for a particular received frame against a threshold value, wherein the threshold value is selected based, in part, on the quality metrics of received frames, and

identify the particular received frame as being a zero rate frame or not a zero rate frame based on the comparison.

21. The receiver subsystem of claim 20, wherein the data processor includes:

a symbol accumulation circuit configured to receive and accumulate the demodulated symbols.

22. The receiver subsystem of claim 20, wherein the data processor includes:

a decoder configured to receive and decode the plurality of received frames to generate a plurality of decoded frames.

23. The receiver subsystem of claim 22, wherein the data processor further includes:

a CRC circuit coupled to the decoder, the CRC circuit configured to receive and check the plurality of decoded frames to identify good frames among the decoded frames.

24. The receiver subsystem of claim 22, wherein the data processor further includes:

an encoder coupled to the decoder, the encoder configured to receive and re-encode the decoded frames.

25. The receiver subsystem of claim 20, wherein the quality metric relates to an energy for a received frame.

26. The receiver subsystem of claim 25, wherein the quality metric for a received frame is computed as a sum of squared symbols for the received frame.

27. The receiver subsystem of claim 20, wherein the quality metric relates to a distance between the received frame and a codeword corresponding to the received frame.

28. In a CDMA communications system, a receiver subsystem operable to identify zero rate frames in a received data transmission, the receiver subsystem comprising:

a demodulator configured to receive and demodulate a modulated signal in accordance with a particular demodulation format to generate demodulated symbols;

a decoder operatively coupled to the demodulator, the decoder configured to receive the demodulated symbols as a plurality of received frames, and to decode the plurality of received frames into a plurality of decoded frames;

a CRC circuit coupled to the decoder, the CRC circuit configured to receive and check the plurality of decoded frames to identify good frames among the decoded frames; and

a metric calculation unit operatively coupled to the demodulator or the decoder, the metric calculation unit configured to

compute a quality metric for each of the plurality of received frames,

compare the quality metric for a particular received frame against a threshold value, wherein the threshold value is selected based, in part, on the quality metrics of received frames, and

identify the particular received frame as being a zero rate frame or not a zero rate frame based on the comparison.