Skip to content

Latest commit

 

History

History
115 lines (59 loc) · 4.95 KB

README.md

File metadata and controls

115 lines (59 loc) · 4.95 KB
Raw

GNSS-GPS-SDR

See detailed introduction on my tech blog: Some efforts on GPS signal replay (GPS重放)

-------------*NEWS:----------------------------------------------------

ADS-B out is verified by HACKRF --> air --> rtl-sdr dongle. blog

See adsb directory and video:

http://youtu.be/xpLDqBkUiKc (out of China)

http://v.youku.com/v_show/id_XNzE4NzIzNDIw.html (in China)

---------------*Purpose:----------------------------------------------

Some efforts were put on replaying GPS signal, but it is only partially successful, not fully successful. Some tools/scripts, as side products, are useful. Learn many things from here: http://www.aholme.co.uk/GPS/Main.htm

WARNING：DO NOT SEND ANY REAL GPS SIGNAL. USE CHAMBER AND CLOSE-LOOP CABLE! MAKE SURE ALL YOUR OPERATIONS ARE LEGAL!

Get codes, program and sample GPS signals here: https://github.com/JiaoXianjun/GNSS-GPS-SDR

To build the C program "gps_test" in "c" directory (front part of software GPS receiver) after you get the whole repo:

cd c
make

To let this make smooth, make sure you have fftw library installed correctly (sudo apt-get install ...). There should be /usr/lib/libfftw.a.

1. offline GPS simulation method

1.1 use C program "gps_test" to receive GPS signal generated by Matlab script gps_sig_gen.m

a. generate GPS signal file by running gps_sig_gen.m in Matlab

    gps_sig_gen.m

to get file gps_sig_tmp.bin

b. use "gps_test" program to do some initial demodulation and check C/A codes:

    gps_test gps_sig_tmp.bin 2.046e6 8.184e6 5000

Above program gps_test performs initial GPS signal capture by multi-bins correlation in frequency domain.

gps_sig_tmp.bin: input GPS signal generated by gps_sig_gen.m (MATLAB).

2.046e6: carrier frequency

8.184e6: sampling rate

5000: maximum frequency offset for frequency searching

You will find that C/A codes results are aligned with GPS signal we generate by Matlab script.

1.2 use C program "gps_test" to receive GPS signal captured by others instead of my our Matlab script gps_sig_gen.m

    gps_test gps.samples.1bit.I.fs5456.if4092.bin 4.092e6 5.456e6 5000

gps.samples.1bit.I.fs5456.if4092.bin: captured by others and can be downloaded here: http://www.jks.com/gps/gps.html

You will find C/A codes results are equal to those shown here: http://www.jks.com/gps/gps.html

2. over the air GPS test method

2.1 playback gps.samples.1bit.I.fs5456.if4092.bin( http://www.jks.com/gps/gps.html )

a. run gps_bin1bit_log2bin.m in Matlab to generate playback file for HACKRF (they capture GPS signal with 1bit quantization. we convert it to 8bit format which is needed by HACKRF): gps.samples.8bit.IQ.fs5456.baseband.bin

b. run gps_Nottingham.grc to playback gps.samples.8bit.IQ.fs5456.baseband.bin over the air. And meanwhile/immediately,

c. use rtl-sdr to capture signal:

    rtl_sdr -g 60 -f 1575.42e6 -s 2.8e6 -n 19.2e6 rtl_2.8Msps_1575.42MHz.bin

d. run proc_rtl_bin_for_gps('rtl_2.8Msps_1575.42MHz.bin') in Matlab to convert 8bit file to 1bit file which is needed by gps_test program：rtl_2.8Msps_1575.42MHz_1bit.bin

e. see C/A codes initial capture result by running gps_test program:

    gps_test rtl_2.8Msps_1575.42MHz_1bit.bin 0.62e6 2.8e6 100000

You will find C/A codes results are equal to those shown here: http://www.jks.com/gps/gps.html

2.2 playback gps_sig_tmp_for_hackrf_tx.bin (generated by gps_sig_gen.m) to air by gps.grc.

a. run gps.grc to playback gps_sig_tmp_for_hackrf_tx.bin over the air. And meanwhile/immediately,

b. capture air GPS signal by:

    rtl_sdr -g 60 -f 1574.8e6 -s 2.8e6 -n 19.2e6 rtl_2.8Msps_1574.8MHz.bin

c. convert captured 8bit file to 1bit bin file which is needed by gps_test: rtl_2.8Msps_1574.8MHz_1bit.bin

    proc_rtl_bin_for_gps('rtl_2.8Msps_1574.8MHz.bin'); (MATLAB)

d. RUN:

    gps_test rtl_2.8Msps_1574.8MHz_1bit.bin 0.62e6 2.8e6 100000

to see GPS signal capture result: C/A codes are supposed to align with our expectation (Matlab script).

e. you can also capture air GPS signal with different intermediate frequency by:

    rtl_sdr -g 60 -f 1575.42e6 -s 2.8e6 -n 19.2e6 rtl_2.8Msps_1575.42MHz.bin

f. convert captured 8bit file to 1bit bin file which is needed by gps_test: rtl_2.8Msps_1575.42MHz_1bit.bin

    proc_rtl_bin_for_gps('rtl_2.8Msps_1575.42MHz.bin'); (MATLAB)

g. RUN:

    gps_test rtl_2.8Msps_1575.42MHz_1bit.bin 0.62e6 2.8e6 100000

to see GPS signal capture result: C/A codes are supposed to align with our expectation (Matlab script).