SYSTEM AND METHOD FOR DEMODULATING AN INCOMING SIGNAL

• US 20140254636A1
• Filed: 06/12/2013
• Published: 09/11/2014
• Est. Priority Date: 03/11/2013
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Stephens, James A., Delbecq, Dominique, Perrine, Daniel M.
• Granted Patent: US 9,143,190 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: H04B 1/709 Correlator structure

Abstract

Methods and receiver circuits are provided for correlating an incoming signal with PN codes. An embodiment of the method includes receiving I/Q baseband samples in the I/Q domain; converting the I/Q baseband samples to phase baseband samples; generating a pseudonoise (PN) code; converting the PN code to PN phase data; performing a correlation on the phase baseband samples using the PN phase data to generate correlated I/Q values; performing an adding operation on the correlated I/Q values to generate demodulated I/Q values; converting the demodulated I/Q values into demodulated phase values; performing a frequency correction operation on the demodulated phase values to generate frequency correction data; converting the demodulated I/Q values into demodulated magnitude values; and performing signal decoding and synchronization on the magnitude values to generate output data. The operation of performing correlation on the phase baseband samples using the PN phase data is accomplished using scalar subtraction.

Claims

1. A method for correlating an incoming signal with PN codes, comprising:

receiving I/Q baseband samples in the I/Q domain;

converting the I/Q baseband samples to phase baseband samples;

generating a pseudonoise (PN) code;

converting the PN code to PN phase data;

performing a correlation on the phase baseband samples using the PN phase data to generate correlated I/Q values;

performing an adding operation on the correlated I/Q values to generate demodulated I/Q values;

converting the demodulated I/Q values into demodulated phase values;

performing a frequency correction operation on the demodulated phase values to generate frequency correction data;

converting the demodulated I/Q values into demodulated magnitude values; and

performing signal decoding and synchronization on the magnitude values to generate output data,

wherein the operation of performing correlation on the phase baseband samples using the PN phase data is accomplished using scalar subtraction.

2. The method of claim 1, wherein the correlation further comprises:

subtracting the PN phase data from the phase baseband samples to generate a current residual signal;

subtracting a correction value from the current residual signal to generate correlated phase values; and

converting the correlated phase values to the correlated I/Q values,

wherein the correction value is one of;

a current frequency offset, an immediately previous residual signal, or an older residual signal generated prior to the immediately previous residual signal.

3. The method of claim 2, wherein when the correction value is the older residual signal, the correlated phase values represent the current frequency offset.

4. The method of claim 3, wherein

the operations of receiving I/Q baseband samples, converting the I/Q baseband samples, generating a pseudonoise (PN) code, converting the PN code, and performing a correlation, are performed multiple times to generate a plurality of sets of correlated I/Q values,

the operations of performing an adding operation on the correlated I/Q values to generate demodulated I/Q values, converting the demodulated I/Q values into demodulated phase values, and performing a frequency correction operation are performed multiple times to convert the plurality of sets of correlated I/Q values to a plurality of sets of frequency correction data, and

a final set of frequency correction data is selected to be a set of frequency correction data associated with a set of correlated I/Q values having a largest correlation magnitude.

5. The method of claim 2, wherein when the correction value is the frequency offset, the correlated phase values represent correlated phase data.

6. The method of claim 2, wherein when the correction value is the immediately previous residual signal, the correlated phase values represent an estimated frequency offset.

7. The method of claim 6, wherein during a preamble,

the correlation operation requires two clock cycles, and

the estimated frequency offset is used as the current frequency offset.

8. A receiver circuit, comprising:

a first conversion circuit configured to convert received I/Q baseband samples in the I/Q domain to phase baseband samples in the phase domain;

a symbol buffer configured to store one symbol length of phase baseband samples;

a pseudonoise (PN) code generator configured to generate a PN code;

a correlator circuit configured to correlate one symbol length of the phase baseband samples with the PN code in the phase domain to generate correlated I/Q data using frequency correction data;

an I/Q adder tree configured to perform an adding operation on the correlated I/Q data to generate demodulated I/Q data;

a third conversion circuit configured to convert the demodulated I/Q data to demodulated magnitude data and demodulated phase data;

a frequency correction circuit configured to generate the frequency correction data based on the demodulated phase data; and

a symbol decode and synchronization circuit configured to generate decoded output data based on the demodulated magnitude data,

wherein the correlator circuit is configured to correlate the phase baseband samples with the PN code using scalar subtraction.

9. The receiver circuit of claim 8, wherein the correlator further comprises N correlator sub-blocks connected in series with each other, an i^th correlator sub-block including:

an i^th PN conversion circuit configured to convert the PN code to i^th PN phase data;

an i^th PN subtractor configured to subtract the i^th PN phase data from an i^th portion of the phase baseband samples to generate an i^th residual signal;

an i^th correction subtractor configured to subtract an i^th correction value from the i^th residual signal to generate an i^th correlated phase value; and

a phase conversion circuit configured to convert the i^th correlated phase value to an i^th correlated I/Q value,

wherein the i^th correction value is one of;

an i^th frequency offset, an (i−

1)^th residual signal, or an (i-x)^th residual signal,

where i is an integer that varies from 1 to N, and

where x is an integer greater than 1.

10. The receiver circuit of claim 9, wherein when the i^th correction value is the (i-x)^th residual signal, and the i^th correlated phase values represent the current frequency offset.

11. The receiver circuit of claim 9, wherein

the correlator circuit is further configured to correlate a plurality of symbol lengths of the phase baseband samples with the PN code in the phase domain to generate a plurality of sets of correlated I/Q data using the (i-x)^th residual signal in each of the correlator sub-blocks,

the frequency correction circuit is further configured to generate the frequency correction data based on a plurality of sets of demodulated phase data, and

a final set of frequency correction data is selected to be a set of frequency correction data associated with a set of correlated I/Q data having a largest correlation magnitude.

12. The receiver circuit of claim 9, wherein when the correction value is the i^th frequency offset, the i^th correlated phase values represent correlated phase data.

13. The receiver circuit of claim 9, wherein when the correction value is the (i−

1)^th residual signal, the i^th correlated phase values represent an estimated frequency offset.

14. A receiver circuit, comprising:

means for receiving I/Q baseband samples in the I/Q domain;

means for converting the I/Q baseband samples to phase baseband samples;

means for generating a pseudonoise (PN) code;

means for converting the PN code to PN phase data;

means for performing a correlation on the phase baseband samples using the PN phase data to generate correlated I/Q values;

means for performing an adding operation on the correlated I/Q values to generate demodulated I/Q values;

means for converting the demodulated I/Q values into demodulated phase values;

means for performing a frequency correction operation on the demodulated phase values to generate frequency correction data;

means for converting the demodulated I/Q values into demodulated magnitude values; and

means for performing signal decoding and synchronization on the magnitude values to generate output data,

wherein the means for performing correlation on the phase baseband samples using the PN phase data is configured to perform the correlation using scalar subtraction.

15. The receiver circuit of claim 14, wherein the means for performing a correlation further comprises:

means for subtracting the PN phase data from the phase baseband samples to generate a current residual signal;

means for subtracting a correction value from the current residual signal to generate correlated phase values; and

means for converting the correlated phase values to the correlated I/Q values,

wherein the correction value is one of;

a current frequency offset, an immediately previous residual signal, or an older residual signal generated prior to the immediately previous residual signal.

16. The receiver circuit of claim 15, wherein when the correction value is the older residual signal, the correlated phase values represent the current frequency offset.

17. The receiver circuit of claim 14, wherein

the means for performing a correlation is further configured to generate a plurality of sets of correlated I/Q values,

the means for performing a frequency correction operation is further configured to convert the plurality of sets of correlated I/Q values to a plurality of sets of frequency correction data, and

a final set of frequency correction data is selected to be a set of frequency correction data associated with a set of correlated I/Q values having a largest correlation magnitude.

18. The receiver circuit of claim 15, wherein when the correction value is the frequency offset, the correlated phase values represent correlated phase data.

19. The receiver circuit of claim 15, wherein when the correction value is the immediately previous residual signal, the correlated phase values represent an estimated frequency offset.

20. The receiver circuit of claim 19, wherein during a preamble,

the correlation operation requires two clock cycles, and

the estimated frequency offset is used as the current frequency offset.