Update README.md

README.md

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 - [`hardware`](https://github.com/greatscottgadgets/hackrf) **HackRF** - A low cost, open source Software Defined Radio platform.
 - [`hardware`](https://github.com/RfidResearchGroup/proxmark3) **proxmark3** - Swiss-army tool of RFID, allowing for interactions with the vast majority of RFID tags on a global scale.
 - [`software`](https://www.gnuradio.org) **GNU Radio** - Free software development toolkit that provides signal processing blocks to implement software-defined radios and signal processing systems.
-- [`software`](https://gage.upc.edu/en/learning-materials/software-tools/glab-tool-suite) - **gLAB** - Developed under an European Space Agency (ESA) Contract by the research group of Astronomy and Geomatics (gAGE) from the Universitat Politecnica de Catalunya (UPC), is an interactive educational multipurpose package to process and analyse GNSS data.
-- [`software`](https://www.rtklib.com/) - **RTKLIB** - Another An Open Source Program Package for GNSS Positioning.
 - [`reading`](https://www.ieee.li/pdf/essay/quadrature_signals.pdf) **Book Quadrature Signals: Complex, But Not Complicated.**
 - [`reading`](https://www.researchgate.net/publication/3321471_How_I_learned_to_love_the_trellis) **How I learned to love the trellis.**
 - [`reading`](http://whiteboard.ping.se/SDR/IQ) **I/Q Data for Dummies.**
-- [`reading`](https://content.u-blox.com/sites/default/files/products/documents/GLONASS-HW-Design_AppNote_%28GPS.G6-CS-10005%29.pdf) **GLONASS & GPS HW design.**
 - [`reading`](https://s3.amazonaws.com/embeddedrelated/user/6420/lets_assume_system_synchronized_2_94379.pdf) **Let's Assume the System is Synchronized** - By Fred Harris.
 - [`code`](https://people.scs.carleton.ca/~barbeau/SDRCRBook/index.shtml) **Software Radio for Experimenters with GNU Radio** - Implemented in Octave and Python by Michel Barbeau.
 
+### GNSS
+- [`software`](https://gage.upc.edu/en/learning-materials/software-tools/glab-tool-suite) - **gLAB** - Developed under an European Space Agency (ESA) Contract by the research group of Astronomy and Geomatics (gAGE) from the Universitat Politecnica de Catalunya (UPC), is an interactive educational multipurpose package to process and analyse GNSS data.
+- [`software`](https://www.rtklib.com/) - **RTKLIB** - Another An Open Source Program Package for GNSS Positioning.
+- [`reading`](https://content.u-blox.com/sites/default/files/products/documents/GLONASS-HW-Design_AppNote_%28GPS.G6-CS-10005%29.pdf) **GLONASS & GPS HW design.**
+- [`code`](https://geodesy.noaa.gov/gps-toolbox/) **GPS Toolbox** - GPS Toolbox topical collection of the journal GPS Solutions. It provides a means for distributing the source code and algorithms discussed in the GPS Toolbox topical collection.
+
 ## Optimization Theory
 
 - [`course`](https://see.stanford.edu/Course/EE364A) [`reading`](https://web.stanford.edu/class/ee364a/) [`reading`](https://github.com/cvxgrp/cvxbook_additional_exercises) **EE364A, Convex Optimization I** - Stanford Engineering Everywhere - Stephen Boyd.