# Some efforts and tools on GPS simulation and RF signal replay **URL:** \ **Category:** GNU Radio\ **Created:** [November 2, 2014, 1:04pm UTC](https://www.ruby-forum.com/t/some-efforts-and-tools-on-gps-simulation-and-rf-signal-replay/232883 "2014-11-02T13:04:39Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [November 2, 2014, 1:04pm UTC](https://www.ruby-forum.com/t/some-efforts-and-tools-on-gps-simulation-and-rf-signal-replay/232883/1 "2014-11-02T13:04:39Z")
Some efforts were put on replaying GPS signal [http://sdr-x.github.io/Some%20efforts%20and%20tools%20on%20GPS%20signal%20replay%20(GPS重放模拟)/](http://sdr-x.github.io/Some%20efforts%20and%20tools%20on%20GPS%20signal%20replay%20%28GPS%E9%87%8D%E6%94%BE%E6%A8%A1%E6%8B%9F%29/), 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](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: > **[GitHub - JiaoXianjun/GNSS-GPS-SDR: Some efferts on GPS replay, receive and test.](https://github.com/JiaoXianjun/GNSS-GPS-SDR)** > > Some efferts on GPS replay, receive and test. Contribute to JiaoXianjun/GNSS-GPS-SDR development by creating an account on GitHub. 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: [Raw GPS signal samples data set for testing GPS receivers](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](http://www.jks.com/gps/gps.html) 2. over the air GPS test method 2.1 playback gps.samples.1bit.I.fs5456.if4092.bin( [Raw GPS signal samples data set for testing GPS receivers](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](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).