In this in-class hands-on activity, you will run a digital QPSK receiver in a python notebook (on google colab).

The input to the activity is from Shout. You or your instructor used Shout to transmit and receive a narrowband wireless signal that is QPSK modulated.

Background and protocol

The packet included the following structure:

Preamble (64 bits)

Sync Word (16 bits)

Data (434 bits, or 62 characters each 7 bits)

For QPSK, two bits are converted to one symbol, ie, one complex number, as specified in the constellation diagram. The constellation diagram is specified as part of the wireless digital communication protocol. For us it is

QPSK constellation diagram, showing four symbols, each with two bits. The 00 symbol is at (3,3), the 01 symbol is at (-3,3), the 11 symbol is at (-3,-3), and the 10 symbol is at (3,-3).

Figure: QPSK constellation diagram, showing four symbols, each with two bits. The 00 symbol is at (3,3), the 01 symbol is at (-3,3), the 11 symbol is at (-3,-3), and the 10 symbol is at (3,-3).

The transmitted signal uses the square-root raised cosine pulse shape with parameter alpha=0.5. The pulse vector is 12 symbol periods long, six periods on each side of time=0 (at which the pulse is maximum).

For more information, you can read and run the code we used to create the QPSK signal at:

https://colab.research.google.com/drive/1P6s73nT77oUhYIoGA1PBQ15cNx5dNjbz?usp=sharing

We then use Shout to repeatedly transmit and receive the packet, from a specified transmitter and receiver, at approximately the same time. I use my instructions at my github tx_rx_processing repo. Shout creates several files, including a file with the IQ data received (measurements.hdf5), and a copy of the json file that Shout used. We use a zip of these files in our receiver.

Instructions

My (mostly filled in) receiver is here:

https://colab.research.google.com/drive/11iUQHVfmwBqeZB1wPD6y0s1ymcbIYOyC?usp=sharing

You will need to download (and upload to Colab) the following receiver file: Shout_meas_01-19-2025_QPSK.zip

Go to this colab python notebook and demodulate the message. Your instructions are in the text blocks of the colab. Please make a copy (the linked notebook is read only) and read through. Complete the code as instructed. All sections that NEED your completion and attention are marked with a :raised-hand: emoji like this ✋. Run all code through the end of the notebook. At the end, you'll get a string message that will verify (by being readable English words) that you coded the receiver correctly.