Patent AU-2020203288-A1 (AU)
Title: Methods and devices for Global Navigation Satellite System (GNSS) signal acquisition
Inventor: YU WEI
IPC: G01S19/24
Filed: 2020-05-20
Abstract: A method is provided for acquiring a signal from a satellite in a global navigation satellite 
system. The signal includes a pseudorandom code. The method includes, for each time period 
of a plurality of time periods: generating samples of the signal, segments of the samples of 
the signal are correlated with a local copy of the pseudorandom code, thereby producing 
correlation values for the time period. A discrete Fourier transform is performed using, as 
inputs, the correlation values for the respective time period, thereby producing a frequency 
representation of the correlation values for the time period. The frequency representations of 
the correlation values for the plurality of time periods are combined according to a data 
hypothesis. When a magnitude of the combined frequency representations meets predefined 
criteria, a frequency corresponding to the magnitude is selected as a tracking frequency for 
the satellite.  
- 47-
10/16 
1000 
For each respective time period of a plurality of time periods: /1002 
Generate a plurality of samples of a signal from a satellite in a 
global navigation satellite system (GNSS). The signal includes a -1004 
pseudorandom code for the satellite.  
r ------------------------1 
Generating the plurality of samples of the signal includes: 
initially sampling the signal at an initial multiple of a frequency f N1006 
hypothesis; and 
decimating the initially sampled signal to produce the plurality 
of samples of the signal.  
Correlate a plurality of segments of the plurality of samples of the 
signal with a local copy of the pseudorandom code for the satellite, -1008 
thereby producing a plurality of correlation values for the respective 
time period.  
ICorrelating the plurality of segments of the plurality of samples I 
Iof the signal with the local copy of the pseudorandom code for I 
I the satellite for each respective time period of the plurality of I1010 
Time periods includes correlating n segments of the plurality of 
Samples of the signal with the local copy of the pseudorandom I 
code, wherein n is an integer. I 
A 
Figure 10OA
11/16 
A 
For each respective time period of a plurality of time periods: /1002 
Perform a discrete Fourier transform (DFT) using, as inputs, the 
plurality of correlation values for the respective time period, thereby 1012 
producing a frequency representation of the correlation values for 
the respective time period.  
--------------------------- 1 Performing the DFT for a respective time period of the plurality 
of time periods includes: using, as inputs, the n correlation 
values for the respective time period. The n correlation values 
are shifted by n inputs of the DFT compared with the n 
correlation values for a previous and adjacent time period of 
the plurality of time periods.  
The DFT is an m-point DFT, wherein m is an integer greater 1016 
than n.  
I Performing the DFT includes using, as inputs, m - n zero I 
1 values in addition to the n correlation values for the respective 1018 
time period. 
I Each correlated segmentof the plurality of samples ofthe 
I signal corresponds to a length of time. The plurality of | 
|samples of the signal are generated using a coarse frequency L /'-1020 
Hypothesis. The generating, correlating, performing the DFT, | 
|and combining operations are repeated with adjacent coarse| 
| frequency hypotheses that are separated by an amount less | 
than or equal to an inverse of the length of time. | 
Combine the frequency representations of the correlation values for the -1022 
plurality of time periods according to a data hypothesis.  
In accordance with a determination that a magnitude of the combined 
frequency representations of the correlation values for the plurality of -1024 
time periods meets predefined criteria, select a frequency corresponding 
to the magnitude as a tracking frequency for the satellite.  
Figure 1OB
12/16 
1100 
Sample a signal at a respective frequency. The signal is from a satellite 
in a global navigation satellite system (GNSS). The signal includes a -1102 
pseudorandom code for the satellite having a predefined chip length for a 
complete instance of the pseudorandom code.  
r -- ------------------------------ 1 The respective frequency is an integer multiple of a frequency 1104 
hypothesis.  
Store a first portion of the sampled signal in a buffer, the buffer having a 
size that is less than the predefined chip length sampled at the respective -1106 
frequency.  
For each respective code shift hypothesis of a plurality of code shift 
hypotheses: /1108 
Correlate the first portion of the sampled signal with a local copy of 
a portion of the pseudorandom code. 1110 
Correlating the first portion of the sampled signal with the local 
copy of the portion of the pseudorandom code for each 1112 
respective code shift hypothesis of the plurality of code shift 
hypotheses comprises a first iteration of a plurality of buffer 
shift iterations.  
Prior to correlating the first portion of the sampled signal with the 
local copy of a portion of the pseudorandom code, buffer the local 9 1114 
copy of the portion of the pseudorandom code.  
In accordance with a determination that the correlation of the first portion 
of the sampled signal with the local copy of the portion of the 
pseudorandom code for the respective code shift hypothesis meets -1116 
matching criteria, select the code shift hypothesis for tracking the 
satellite.  
A 
Figure 1 1A
13/16 
A 
I Determine that none of the correlations from the plurality of code shift I 
hypotheses meets the matching criteria. k--1118 
r --------------------------
Store a second portion of the sampled signal in the buffer. The second 
portion of the sampled signal is distinct from the first portion of the 1120 
sampled signal.  
For each respective code shift hypothesis of the plurality of code shift 1122 
hypotheses, correlate the second portion of the sampled signal with the 
local copy of the portion of the pseudorandom code.  
Correlating the second portion of the sampled signal with the local 
copy of the portion of the pseudorandom code for each respective 1124 
code shift hypothesis of the plurality of code shift hypotheses 
comprises a second iteration of the plurality of buffer shift iterations.  
Correlating the second portion of the sampled signal with the local 
copy of the portion of the pseudorandom code is performed without 1126 
re-buffering the local copy of the portion of the pseudorandom 
code.  
I accordance with a determination that the correlation of the second 
portion of the sampled signal with the local copy of the portion of the 
pseudorandom code for the respective code shift hypothesis meets /1128 
matching criteria, select the code shift hypothesis for tracking the I 
satellite.  
B 
Figure 11 B
14/16 
B 
I Determine whether exhaustion criteria, with respect to the sampling of 1130 
I the signal using the respective frequency, have been satisfied.  
I F--------------------------1 I The exhaustion criteria include a criterion that is met when a 
maximum number of buffer shift iterations has been exhausted 1,-1134 
without selecting a code shift hypothesis for the satellite.  
IIn accordance with a determination that exhaustion criteria, with respect L-1136 
Ito the sampling of the signal using the respective frequency, have been I 
Satisfied: 
re-sample the signal at a second frequency different from I 
Ithe respective frequency; 
store a third portion of signal sampled at the second 
Frequency in the buffer; 
for each respective code shift hypothesis of the plurality of I 
Icode-shift hypotheses: 
correlate the third portion of the signal sampled at I 
Ithe second frequency with the local copy of the portion of the 
Ipseudorandom code; 
in accordance with a determination that the correlation of I 
Ithe third portion of signal sampled at the second frequency with the local I 
Copy of the portion of the pseudorandom code for the respective code I 
Shift hypothesis meets matching criteria, select the code shift hypothesis I 
Ifor tracking the satellite.  
IAdd an offset to the code shift hypothesis for tracking the satellite basedI 
Iat least in part on an offset between the first portion of the sampled signal I1138 
and the second portion of the sampled signal.  
L _ _ _ _ _ _ _ __------------- _
Determine a position of the GNSS receiver using the acquired signal at 
least in part by tracking the signal from the satellite using the selected -1140 
code shift hypothesis.  
C 
Figure 11C
15/16 
C 
-- - - - --I- - - ---i 
Acquire a signal from a second satellite in a second global navigation 
satellite system (GNSS) distinct from the global navigation satellite L-1142 
system. The second signal includes a second pseudorandom code for 
the second satellite having a second predefined chip length. The buffer 
has a size that is greater than the second predefined chip length sampled 
at the respective frequency.  
--------------------------- I 
For each respective code shift hypothesis of the plurality of code | | 
shift hypotheses: | | 
1144 
correlate the first portion of the sampled signal with a local | | 
copy of a portion of the second pseudorandom code; and | | 
| | 
in accordance with a determination that the correlation of the | 
First portion of the sampled signal with the local copy of the portion | | 
|of the second pseudorandom code for the respective code shift | | 
|hypothesis meets the matching criteria, select the code shift | | 
|hypothesis for tracking the second satellite. | | 
Figure 11D