Method and apparatus to reduce latency in a data network wireless radio receiver

• US 7,065,036 B1
• Filed: 03/11/2002
• Issued: 06/20/2006
• Est. Priority Date: 03/19/2001
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Systems Wireless Networking (Australia) Pty Limited (Cisco Systems, Inc.)
• Inventors: Ryan, Philip J.
• Primary Examiner(s): FERRIS, DERRICK W
• Application Number:
  US10/096,010
• Time in Patent Office: 1,562 Days
• Field of Search: 370/208, 370/210, 370/338, 370/474
• US Class Current: 370/208
• CPC Class Codes: H04L 1/0052 Realisations of complexity reduction techniques, e.g. pipelining or use of look-up tables
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0072 Error control for data other than payload data, e.g. control data
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A radio receiver for implementing the physical layer receiving function (PHY) of a wireless data network includes a receive processing pipeline for processing samples of a received packet of data. The samples enter the receive processing pipeline at a first sample rate. A counter generates a running count indicative of the number of samples that have entered the processing pipeline. A comparison unit coupled to the counter determines from the running count if all the samples of the received packet have entered the pipeline. An output of the comparison unit indicates whether or not all samples have entered the pipeline. A clock unit coupled to the comparison unit output provides a clock signal to the pipeline, causing the processing pipeline to process the samples entering the pipeline at a first rate compatible with the first sample rate until the comparison unit output indicates that all samples have entered the pipeline. Thereafter the clock unit causes the processing pipeline to process the samples in the pipeline at a second rate higher than the first rate until the last sample of the packet has been output by the pipeline. The processing latency for processing the complete packet is thus reduced from the case of the processing pipeline processing the samples all at the first data rate.

Claims

1. A radio receiver for implementing the physical layer receiving function (PHY) of a wireless data network, the receiver including:

a receiver front-end for receiving radio signals and including one or more analog-to-digital converters, the receiver front-end providing samples of a received packet of data;

a receive processing pipeline coupled to the receiver front-end to process the provided samples of the received packet of data, the samples entering the receive processing pipeline at a first sample rate;

a counter counting a running count indicative of the number of samples that have entered the processing pipeline;

a comparison unit coupled to the counter for determining from the running count if all the samples of the received packet have entered the pipeline, having an output indicative of whether or not all samples have entered the pipeline; and

a clock unit coupled to the comparison unit output and providing a clock signal to the pipeline, the clock unit causing the processing pipeline to process the samples entering the pipeline at a first rate compatible with the first sample rate until the comparison unit output indicates that all samples have entered the pipeline, thereafter the clock unit causing the processing pipeline to process the samples in the pipeline at a second rate higher than the first rate until the last sample of the packet has been output by the pipeline, such that the processing latency for processing the complete packet is reduced from the case of the processing pipeline processing the samples all at the first rate.

2. A radio receiver as recited in claim 1, wherein the receiver is for implementing the physical layer receiving function (PHY) of a wireless data network.

3. A receiver as recited in claim 2, wherein the wireless data network conforms to an IEEE 802.11 standard that uses COFDM.

4. A receiver as recited in claim 2, wherein the packet of data has a packet structure that includes one or more header frames containing information on the length of the packet, and

wherein the receive processing chain includes a header detector to detect when the header has been processed and to provide a packet length indication to the comparison unit.

5. A receiver as recited in claim 2, wherein the counter counts frames.

6. A radio receiver comprising:

a receive processing pipeline for processing samples of a received packet of data, the samples entering the receive processing pipeline at a first sample rate, the pipeline including;

a FIFO buffer in the pipeline to receive the samples at the first sample rate; and

a transformer in the pipeline with an input coupled to the output of the buffer for performing time-to-frequency conversion on a block of input samples to produce converted samples, the transformer including an input buffer of length at least the number of samples in the block, the transformer further producing an indication of when the transformer input buffer is full with a block of input samples for time-to-frequency conversion,

wherein the samples are read out of the FIFO at a second rate higher than the first sample rate until the indication signals that the transformer input buffer is full with a block of samples or until the FIFO is empty in the case that the FIFO is empty before the input buffer contains the block of samples.

7. A radio receiver comprising:

a receive processing pipeline for processing samples of a received packet of data, the samples entering the receive processing pipeline at a first sample rate; and

a clock generator to generate the clock signal for the receive processing pipeline to process samples at a first processing rate compatible with the first sample rate, the pipeline including;

a end of packet detector coupled to the clock generator to determine when and to output an indication of when all the samples of the packet of data have been input into the receive pipeline;

wherein the clock generator accepts the indication and in response the indication generates the clock signal for the receive processing pipeline to process samples at a second processing rate higher than the first processing rate until the last sample of the packet has been output by the pipeline.

8. A radio receiver as recited in claim 7, wherein the receiver is for implementing the physical layer receiving function (PHY) of a wireless data network.

9. A radio receiver as recited in claim 7, wherein the pipeline includes:

a FIFO buffer to receive the samples at the first sample rate; and

a transformer in the pipeline with an input coupled to the output of the buffer for performing time-to-frequency conversion on a block of input samples to produce converted samples, the transformer including an input buffer of length at least the number of samples in the block, the transformer further producing an indication of when the transformer input buffer is full with a block of input samples for time-to-frequency conversion,

wherein the samples are read out of the FIFO at a third rate higher than the first sample rate until the indication signals that the transformer input buffer is full with a block of samples or until the FIFO is empty in the case that the FIFO is empty before the input buffer contains the block of samples.

10. A radio receiver as recited in claim 8, wherein the wireless data network conforms to an IEEE 802.11 standard that uses COFDM.

11. A radio receiver as recited in claim 8, wherein the second rate is four times the first rate.

12. A radio receiver as recited in claim 8, wherein the packet of data has a packet structure that includes one or more header frames containing information on the length of the packet, and

wherein the receive processing chain includes a header detector to detect when the header has been processed and to provide a packet length indication to the end-of-packet detector.

13. A radio receiver as recited in claim 12, further comprising:

a running counter coupled to the pipeline that counts the number of frames processed by the processing pipeline and provides the count to the end-of-packet detector.

14. A radio receiver as recited in claim 13, wherein the end-of-packet detector includes a comparator that compares the running count provided by the running counter with the packet length indication to generate a signal to the clock generator to start processing at the second rate.

15. A radio receiver as recited in claim 12, further including a running counter coupled to the pipeline that counts the number of samples processed by the processing pipeline and provides the running count to the end-of-packet detector.

16. A method for processing a packet of data samples received at a radio receiver, comprising the steps of:

accepting samples from the receiver for processing;

counting an indication of the number of samples accepted;

processing the accepted samples at a first rate;

determining the indication of length of the packet;

determining when all the samples of the packet have been accepted; and

after all the samples of the packet have been accepted, processing any remaining samples at a second rate higher than the first rate.

17. A method as recited in claim 16, wherein the receiver and processing are for implementing the physical layer receiving function (PHY) of a wireless data network.

18. A method as recited in claim 17, wherein the wireless data network conforms to an IEEE 802.11 standard that uses COFDM.

19. A method as recited in claim 17, wherein the second rate is four times the first rate.

20. A method as recited in claim 17, wherein the packet of data has a packet structure that includes one or more header frames containing information on the length of the packet, and

wherein determining the packet length indication includes decoding the one or more header frames.

21. A method as recited in claim 20, wherein the counting counts the number of frames processed, and wherein determining when all the samples of the packet have been accepted includes comparing the count to the determined packet length indication.

22. A method as recited in claim 20, wherein the counting counts the number of samples processed, and wherein determining when all the samples of the packet have been accepted includes comparing the count to the determined packet length indication.

23. An apparatus for processing a packet of data samples received at a radio receiver, comprising the steps of:

means for accepting samples from the receiver for processing;

means for counting an indication of the number of samples accepted;

means for processing the accepted samples;

means for determining an indication of length of the packet;

means for determining when all the samples of the packet have been accepted; and

wherein the means for processing the accepted samples processes the accepted samples at a first rate until all the samples of the packet have been accepted, and thereafter, processing any remaining samples at a second rate higher than the first rate.

24. An apparatus as recited in claim 23, wherein the receiver and processing are for implementing the physical layer receiving function (PHY) of a wireless data network.

25. An apparatus as recited in claim 24, wherein the wireless data network conforms to an IEEE 802.11 standard that uses COFDM.

26. An apparatus as recited in claim 24, wherein the second rate is four times the first rate.

27. An apparatus as recited in claim 24, wherein the packet of data has a packet structure that includes one or more header frames containing information on the length of the packet, and

wherein determining the packet length indication includes decoding the one or more header frames.

28. An apparatus as recited in claim 27, wherein the means for counting counts the number of frames processed, and wherein the means for determining when all the samples of the packet have been accepted includes comparing the count to the determined packet length indication.

29. An apparatus as recited in claim 27, wherein the means for counting counts the number of samples processed, and wherein the means for determining when all the samples of the packet have been accepted includes comparing the count to the determined packet length indication.