FSK/MSK decoder

• US 9,900,796 B2
• Filed: 07/28/2016
• Issued: 02/20/2018
• Est. Priority Date: 02/25/2013
• Status: Active Grant

• Current Assignee: Itron, Inc.
• Original Assignee: Itron, Inc.
• Inventors: Seely, Danny Ray
• Primary Examiner(s): Jangbahadur, Lakeram
• Application Number:
  US15/222,519
• Publication Number:
  US 20160337891A1
• Time in Patent Office: 572 Days
• CPC Class Codes: H04W 24/04 Arrangements for maintaining operational condition
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic

Abstract

A decoder for a modulation scheme is configured to operate close to the radio noise floor. A correlation value may be constantly updated, in an effort to match to a signature to a preamble of a packet. A low clamp value may act as a floor to which a calculated correlation value is set, if it is less than the low clamp value. If a correlation threshold is exceeded, then the correlation value is examined to determine it is a peak value. If the peak is found, power of the preamble is compared to a power threshold that is relative to the radio noise floor. If the power threshold is exceeded, positive correlation is detected. A channel optimizer is used to remove the frequency misalignment. This enables the use of a filter that is approximately equal to the occupied bandwidth of the incoming signal, further rejecting noise and interference.

Claims

1. A decoder, comprising:

a correlator to;

calculate a correlation value between incoming samples and a signature of a preamble of a packet;

iteratively compare the correlation value to a correlation value threshold to find a peak correlation value, and

upon finding the peak correlation value, compare a preamble power to a power threshold to determine if a valid preamble has been detected;

a bit constructor to construct bits from a payload of the packet having the preamble; and

a channel optimizer configured to;

estimate frequency misalignment;

tune to remove the estimated frequency misalignment; and

filter at a location indicated by the tuning;

wherein;

a correlation value threshold is set to indicate correlation between the calculated correlation value of the samples and the signature of the preamble; and

the power threshold is based in part on a radio noise floor.

2. The decoder as recited in claim 1, wherein calculation by the correlator comprises:

setting a low clamp value at a level such that if a valid packet arrives, then a low value of the calculated correlation value will not prevent correlation.

3. The decoder as recited in claim 1, additionally comprising:

resetting the calculated correlation value if a preamble power value is less than a power threshold.

4. The decoder as recited in claim 1, wherein the power threshold is based in part on a radio noise floor level.

5. The decoder as recited in claim 1, additionally comprising:

tracking a noise floor to determine a level of the noise floor; and

using the noise floor to set the power threshold.

6. The decoder as recited in claim 1, wherein:

the filter is set to a width of approximately an occupied band width (OBW) of an incoming signal.

7. The decoder as recited in claim 1, wherein calculation by the correlator comprises:

using the peak correlation value to synchronize to a beginning of the payload of the packet.

8. A decoder, comprising:

a correlator to calculate a correlation value between incoming samples and a signature of a preamble of a packet, wherein the correlator comprises;

a correlation value threshold set to indicate correlation between the calculated correlation value of the samples and the signature; and

a power threshold to compare to a preamble power value, wherein;

the preamble power value is based at least in part on the incoming samples; and

the power threshold is based in part on a noise floor;

a bit constructor to construct bits from a payload of the packet having the preamble; and

a channel optimizer configured to;

estimate frequency misalignment based at least in part on measurement of rotational frequency error of incoming samples, and based at least in part on detecting a valid preamble, wherein the estimating of the frequency misalignment is performed over a full length of the preamble;

tune to remove the estimated frequency misalignment using a complex mixer; and

filter in the time domain at a location indicated by the tuning, wherein the filter is set to approximately an occupied bandwidth (OBW) of an incoming signal.

9. A decoder to decode a modulation scheme, comprising:

a correlator to calculate a correlation value between incoming samples and a signature, wherein calculating the correlation value is based at least in part on comparing power of a sample from among the incoming samples to a power threshold, and if the power threshold is exceeded, finding the correlation value to be positive, wherein the correlator comprises;

a correlation value threshold set to indicate correlation between the calculated correlation value of the samples and the signature; and

a power threshold to compare to a preamble power value, wherein;

the preamble power value is based at least in part on the incoming samples; and

the power threshold is based in part on a noise floor;

a channel optimizer configured to;

estimate frequency misalignment of the incoming samples from an intended frequency; and

tune according to the estimated frequency misalignment; and

a bit constructor to construct bits from a payload of a packet having a preamble indicated by the calculated correlation value.

10. The decoder as recited in claim 9, wherein the correlator is configured to:

restrict the calculated correlation value to a region above a low clamp value.

11. The decoder as recited in claim 9, wherein the correlator is configured to:

determine a level of a noise floor; and

use the noise floor to set a power threshold.

12. The decoder as recited in claim 9, additionally comprising:

a filter set at a width of approximately an occupied band width (OBW) of an incoming signal.

13. The decoder as recited in claim 9, wherein the channel optimizer is additionally configured to:

sum a plurality of terms; and

divide by a number of samples in the preamble of a packet;

wherein the summing of the plurality of terms ends when a correlation is found with a preamble.

14. A method of decoding a modulation scheme, comprising:

correlating incoming samples to a signature, wherein the correlating comprises;

comparing power of a preamble of a packet to a power threshold; and

if the power threshold is exceeded, finding a correlation value to be positive;

estimating frequency misalignment, between a transmitter and a receiver, based at least in part on a point of correlation to the preamble of the packet;

tuning according to the estimated frequency misalignment;

calculating a correlation value of sample bits to a signature of a preamble;

requiring the correlation value to be greater than or equal to a low clamp value; and

finding correlation when;

the correlation value exceeds a correlation value threshold; and

a correlation power value exceeds a power threshold.

15. The method as recited in claim 14, additionally comprising:

detecting a peak in the correlation value; and

using the detected peak to synchronize to a beginning of a payload of the packet.

16. The method as recited in claim 14, wherein:

estimating frequency misalignment is performed using adders and shifters;

tuning according to the estimated frequency misalignment is performed using a complex mixer; and

filtering at a location indicated by the tuning is performed by use of a filter set to approximately an occupied bandwidth of an incoming signal.