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PLUTO-GPS-SIM

Project closed! Development continues on multi-sdr-gps-sim.

PLUTO-GPS-SIM generates a GPS baseband signal IQ data stream, which is then transmitted by the software-defined radio (SDR) platform ADALM-Pluto.

Project based on gps-sdr-sim. Credits to Takuji Ebinuma.

Generating the GPS signal

The user is able to assign a static location directly through the command line.

The user also specifies the GPS satellite constellation through a GPS broadcast ephemeris file. The daily GPS broadcast ephemeris file (brdc) is a merge of the individual site navigation files into one.

These files are then used to generate the simulated pseudorange and Doppler for the GPS satellites in view. This simulated range data is then used to generate the digitized I/Q samples for the GPS signal which are then feed into ADALM-Pluto SDR to transmit the GPS L1 frequency.

The simulation start time can be specified if the corresponding set of ephemerides is available. Otherwise the first time of ephemeris in the RINEX navigation file is selected.

Note

The ADLAM-Pluto SDR internal oscillator is not precise enough (frequency offset) and stable (temperature drift) for GPS signal generation.

Do not run this code without Pluto oscillator modification, either by TCXO or more expensive (but highest precision) OCXO. Search for adlam pluto tcxo

Ephemeris files

NASA CDDIS anonymous ftp service has been discontinued on October 31, 2020.

The new way to get ephemeris data is as follows:

Register an account with https://urs.earthdata.nasa.gov/ (There is no way around this step).

Create a file called .netrc with the following format. machine urs.earthdata.nasa.gov login password where and are the values you set when you created your Earthdata login account. Don't forget to sudo chmod 004 .netrc so that no one can read your file and get your username and password.

You can automate with the process with following script.

#!/bin/sh
day=$(date +%j)
year=$(date +%Y)
yr=$(date +%y)

curl -c /tmp/cookie -n -L -o "brdc""$day""0.$yr""n.Z" "https://cddis.gsfc.nasa.gov/archive/gnss/data/daily/$year""/brdc/brdc""$day""0.$yr""n.Z"

uncompress "brdc""$day""0.$yr""n.Z"
echo "brdc""$day""0.$yr""n.Z"

The .netrc file along with the -n flag allows curl to automatically authenticate when attempting to retrieve the file.

Build instructions

Dependencies

Build depends on libm, libpthread and libcurl4-openssl-dev.

You will also need the latest build and install of libad9361-dev and libiio-dev. The Debian packages libad9361-dev that is available up to Debian 9 (stretch) is outdated and missing a required function. So you have to build packages from source:

The first step is to fetch the dependencies, which as of now is only libxml2. On a Debian-flavoured GNU/Linux distribution, like Ubuntu for instance:

$ sudo apt-get install libxml2 libxml2-dev bison flex libcdk5-dev cmake

Depending on the backend (how you want to attach the IIO device), you may need at least one of:

$ sudo apt-get install libaio-dev libusb-1.0-0-dev libserialport-dev libxml2-dev libavahi-client-dev doxygen graphviz

Then build in this order:

$ git clone https://github.com/analogdevicesinc/libiio.git
$ cd libiio
$ cmake ./
$ make
$ sudo make install

$ git clone https://github.com/analogdevicesinc/libad9361-iio.git
$ cd libad9361-iio
$ cmake ./
$ make
$ sudo make install

Building under Linux with GCC

$ git clone https://github.com/mictronics/pluto-gps-sim
$ cd pluto-gps-sim
$ make all

Usage

pluto-gps-sim [options]
Options:
  -e <file name>   RINEX navigation file for GPS ephemerides (required)
  -u <file name>   User motion file (dynamic mode) 10Hz, Max 3000 points
  -3               Use RINEX version 3 format
  -f               Pull actual RINEX navigation file from NASA FTP server
  -c <location>    ECEF X,Y,Z in meters (static mode) e.g. 3967283.15,1022538.18,4872414.48
  -l <location>    Lat,Lon,Hgt (static mode) e.g. 30.286502,120.032669,100
  -t <date,time>   Scenario start time YYYY/MM/DD,hh:mm:ss
  -T <date,time>   Overwrite TOC and TOE to scenario start time (use ```now``` for actual time)
  -s <frequency>   Sampling frequency [Hz] (default: 2600000)
  -i               Disable ionospheric delay for spacecraft scenario
  -v               Show details about simulated channels
  -A <attenuation> Set TX attenuation [dB] (default -20.0)
  -B <bw>          Set RF bandwidth [MHz] (default 5.0)
  -U <uri>         ADALM-Pluto URI (eg. usb:1.2.5)
  -N <network>     ADALM-Pluto network IP or hostname (default pluto.local)

Set static mode location:

> pluto-gps-sim -e brdc3540.14n -l 30.286502,120.032669,100

Set user motion mode:

> pluto-gps-sim -e brdc3540.14n -u circle.csv

Set TX attenuation:

> pluto-gps-sim -e brdc3540.14n -A -30.0

Default -20.0dB. Applicable range 0.0dB to -80.0dB in 0.25dB steps.

Set RF bandwidth:

> pluto-gps-sim -e brdc3540.14n -B 3.0

Default 3.0MHz. Applicable range 1.0MHz to 5.0MHz

Transmitting the samples

The TX port of a particular SDR platform is connected to the GPS receiver under test through a DC block and a fixed 50-60dB attenuator.

License

Copyright © 2018 Mictronics Distributed under the MIT License.