DSSS preamble detection for smart utility networks
AssigneeTexas Instruments Incorporated
InventorTimothy Mark Schmidl
Life of this patent
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Abstract
Embodiments of the invention provide a method to detect DSSS preambles in smart utility networks. A DSSS signal is received by a receiver and a digital sequence of samples is formed. A difference value is calculated between pairs of samples in the digital sequence of samples to form a sequence of differential values. A known preamble differential value sequence is correlated with the sequence of differential values to form a sequence of correlation values. A location of the preamble is located in the digital sequence of samples corresponding to a peak in the sequence of correlation values that exceeds a threshold value.
Claims14
A method for detecting a preamble in a direct sequence spread spectrum (DSSS) signal by a receiver, the method comprising:
- receiving the DSSS signal by the receiver,
- four times oversampling the received DSSS signal;
- O-QPSK (offset-quadrature phase shift keying) demodulating the oversampled received DSSS signal;
- forming a sign bit of a digital sequence of samples representative of the demodulated DSSS signal;
- calculating a difference value between pairs of samples in the digital sequence of samples to accumulate an extended sequence of differential values;
- correlating a known preamble differential value sequence with the accumulated extended sequence of differential values to form a sequence of correlation values;
- and
- identifying a location of the preamble in the digital sequence of samples corresponding to a peak in the sequence of correlation values that exceeds a threshold value and that identifies the preamble.
A process of detecting a direct sequence spread spectrum (DSSS) preamble comprising:
- O-QPSK (offset-quadrature phase shift keying) demodulating a four times oversampled received wireless DSSS packet signal that includes a preamble:
- performing a differential chip detection in each of four timing phases at 1 Mchip/s for each phase;
- taking a sign bit of each of the differential chip estimates so all values will be +/−1;
- accumulating the differential chip estimates over 40 preamble words in groups of eight words;
- cyclically correlating the differential chip estimates with a 64 chip length of a differential preamble word in a frequency domain;
- comparing the correlations to a threshold;
- and
- finding the DSSS preamble when the value of any of the 64 correlations is above the threshold.
A smart utility meter comprising:
- metrology to measure consumption of the utility and having a metrology output;
- a radio frequency front end having an antenna, an input, and an output;
- a communications unit coupled to the metrology output and the radio frequency front end input and output, the communications unit including a sampler, a processor unit, and memory, the communications unit detecting a direct sequence spread spectrum (DSSS) preamble by:
- receiving wireless DSSS packet signals that includes a preamble;
- four times oversampling the received wireless signal;
- O-QPSK demodulating the oversampled received wireless;
- performing a differential chip detection in each of four timing phases at 1 Mchip/s for each phase;
- taking a sign bit of each of the differential chip estimates so all values will be +/−1;
- accumulating the differential chip estimates over 40 preamble words in groups of eight words;
- cyclically correlating the differential chip estimates with a 64 chip length of a differential preamble word in a frequency domain;
- comparing the correlations to a threshold;
- and
- finding the DSSS preamble is when the value of any of the 64 correlations is above the threshold.
Dependencies are inferred from the claim text.