Low symbol rate rapid carrier acquisition with extremely large frequency offset for digital communication receiver
View Patent ↗A method of rapid non-data aided carrier signal acquisition for a low symbol rate carrier signal, comprising receiving and converting an analog intermediate frequency carrier to a digital carrier signal, down-converting the signal to substantially baseband, reducing a sampling rate of the digital carrier signal using a decimation filter, determining a highest Fast Fourier Transform (FFT) based on a result of one or more FFT's generated by an FFT module using a peak finder, selecting an input source for the FFT module using a multiplexer, generating a frequency estimate of the digital carrier signal using a walking coarse detector, tuning a carrier recovery loop (CRL) based on the frequency estimate generated by the walking coarse detector, determining a final carrier frequency offset estimate using a result of the FFT module, modulation removal, and the peak finder, and programming an oscillator within the CRL to the final carrier frequency offset estimate.
1. A method of rapid non-data aided carrier signal acquisition for a low symbol rate carrier signal, the method comprising:
receiving, by a receiver, an analog intermediate frequency carrier signal;
converting the analog intermediate frequency carrier signal to a digital carrier signal using an analog-to-digital converter;
down-converting the digital carrier signal to a frequency substantially at baseband using a digital quadrature tuner;
reducing a sampling rate of the digital carrier signal using a decimation filter;
determining a highest Fast Fourier Transform (FFT) based on a result of one or more FFT's generated by an FFT module using a peak finder;
selecting an input source for the FFT module using a multiplexer;
generating a frequency estimate of the digital carrier signal using a walking coarse detector (WCD);
tuning a carrier recovery loop (CRL) based on the frequency estimate generated by the walking coarse detector;
determining a final carrier frequency offset estimate using a result of the FFT module, a modulation removal, and the peak finder;
programming an oscillator within the CRL to the final carrier frequency offset estimate using a processor such that carrier signal lock is achieved;
correlating a received modulated carrier signal with a delayed version of the received modulated carrier signal using the walking coarse detector (WCD); and
calculating a first frequency estimate of the digital carrier signal by the walking coarse detector (WCD) using an arctangent function and a multiplier of 4Rs/(2π) where Rs equals a symbol rate of the digital carrier signal.
2. The method of claim 1 , wherein the oscillator within the CRL is programmed to have a sampling rate equal to four times a symbol rate of the carrier signal.
3. The method of claim 1 , wherein a first discrete complex matched filtered output signal of the walking coarse detector (WCD) is defined as I[n]+jQ[n].
4. The method of claim 3 , further comprising inputting the first discrete complex matched filtered output signal of the walking coarse detector (WCD) back into the walking coarse detector (WCD).
5. The method of claim 4 , wherein a subsequent discrete complex matched filtered output signal of the walking coarse detector (WCD) equals X+jY where X and Y are determined by the walking coarse detector (WCD) as:
X
=
1
N
∑
n
=
1
N
(
I
[
n
]
I
[
n
-
1
]
+
Q
[
n
]
Q
[
n
-
1
)
Y
=
1
N
∑
n
=
1
N
(
I
[
n
-
1
]
Q
[
n
]
-
I
[
n
]
Q
[
n
-
1
]
)
.
6. The method of claim 5 , further comprising calculating an incremental frequency estimate of the digital carrier signal by the walking coarse detector (WCD) as:
f
W
=
fs
W
C
D
2
π
·
Tan
-
1
(
Y
X
)
where:
f w =frequency estimate per walk of WCD; and
fs WCD =walking coarse detector (WCD) sampling rate which is equal to 4 times a symbol rate (Rs) of the digital carrier signal.
7. The method of claim 6 , further comprising storing, by the walking coarse detector (WCD), a polarity or sign of the first frequency estimate of the digital carrier signal for comparison with a polarity or sign of a subsequent frequency estimate of the digital carrier signal.
8. The method of claim 7 , further comprising adding subsequent frequency estimates to the first frequency estimate when the sign or polarity of the subsequent frequency estimate is the same as the sign or polarity of the first frequency estimate until a subsequent frequency estimate has a sign or polarity that differs from that of the first frequency estimate.
9. A system for rapid non-data aided carrier signal acquisition for a low symbol rate carrier signal, the system comprising:
a receiver configured to receive an analog intermediate frequency carrier signal;
an analog-to-digital converter configured to convert the analog intermediate frequency carrier signal received by the receiver to a digital carrier signal;
a digital quadrature tuner configured to down-convert the digital carrier signal to a frequency substantially at baseband;
a decimation filter configured to reduce a sampling rate of the digital carrier signal substantially at baseband using a decimation filter;
an FFT module configured to generate a result of one or more FFT's and determine a highest Fast Fourier Transform (FFT) based on the result using a peak finder;
a multiplexer configured to select an input source for the FFT module;
a walking coarse detector (WCD) configured to generate a frequency estimate of the digital carrier signal; and
a carrier recovery loop (CRL) configured to be tuned based on the frequency estimate generated by the walking coarse detector (WCD), the CRL further comprising an oscillator configured to achieve carrier signal lock by being programmed to a final carrier frequency offset estimate that is determined by a processor using a result of the FFT module, a modulation removal, and the peak finder; and
wherein the walking coarse detector (WCD) is further configured to correlate a received modulated carrier signal with a delayed version of the received modulated carrier signal and calculate a first frequency estimate of the digital carrier signal using an arctangent function and a multiplier of 4Rs/(2π) where Rs equals a symbol rate of the digital carrier signal.
10. The system of claim 9 , wherein the oscillator within the CRL is programmed to have a sampling rate equal to four times a symbol rate of the carrier signal.
11. The system of claim 9 , wherein a first discrete complex matched filtered output signal of the walking coarse detector (WCD) is defined as I[n]+jQ[n].
12. The system of claim 11 , wherein the walking coarse detector (WCD) is further configured to receive as an input the first discrete complex matched filtered output signal that was previously output by the walking coarse detector (WCD).
13. The system of claim 12 , wherein a subsequent discrete complex matched filtered output signal of the walking coarse detector (WCD) equals X +jY where X and Y are determined by the walking coarse detector as:
X
=
1
N
∑
n
=
1
N
(
I
[
n
]
I
[
n
-
1
]
+
Q
[
n
]
Q
[
n
-
1
)
Y
=
1
N
∑
n
=
1
N
(
I
[
n
-
1
]
Q
[
n
]
-
i
[
n
]
Q
[
n
-
1
]
)
.
14. The system of claim 13 , wherein the walking coarse detector (WCD) is further configured to calculate an incremental frequency estimate of the digital carrier signal by the walking coarse detector (WCD) as:
f
W
=
fs
W
C
D
2
π
·
Tan
-
1
(
Y
X
)
where:
f w =frequency estimate per walk of WCD; and
fs WCD =walking coarse detector (WCD) sampling rate which is equal to 4 times a symbol rate (Rs) of the digital carrier signal.
15. The system of claim 14 , wherein the walking coarse detector (WCD) is further configured to store a polarity or sign of the first frequency estimate of the digital carrier signal for comparison with a polarity or sign of a subsequent frequency estimate of the digital carrier signal.
16. The system of claim 15 , wherein the walking coarse detector (WCD) is further configured to add subsequent frequency estimates to the first frequency estimate when the sign or polarity of the subsequent frequency estimate is the same as the sign or polarity of the first frequency estimate until a subsequent frequency estimate has a sign or polarity that differs from that of the first frequency estimate.