OFDM Transmission Over FR3

This experiment transmits an analog OFDM signal over the FR3 bands. The OFDM signal is generated at 1.5 GHz by the USRP-2974 (Krypton), up-converted by a Pi-Radio FR3 front-end and transmitted,in this example, at 10 GHz). A second ​Pi-Radio front-end down-converts this signal back to 1.5 GHz for a USRP-2974 receiver, that converts it back into analog baseband. The actual modulation and demodulations is done with a GNURadio running on 2974s. Pi-Radio web UI is used to configure the FR3 conversion.

Prerequisites

• COSMOS account and active reservation in Sandbox 1.
• Familiarity with USRP-2974 (embedded X310, 10 MHz–6 GHz, 160 MHz BW).
• FR3 hardware access (2×​Pi-Radio FR3 front-ends) and the fr3-tutorials.ndz disk image for the USRPs.
• ​GNURadio familiarity

Resources required

• Nodes: sdr1-piradio, sdr2-piradio, rfdev-sdr1-piradio, rfdev-sdr2-piradio.
• Antennas: 2× Vivaldi (Tx/Rx) connected to the Pi-Radio front-ends. (See FR3 hardware pages for antenna layout.)
• Browser access to Pi-Radio web UI on the rfdev-* nodes (port 5006).

Tutorial Setup ===

Follow the steps below to gain access to the sandbox 1 console and set up nodes with appropriate images.

1. If you don't have one already, sign up for a ​COSMOS account
2. Create a resource reservation on COSMOS sandbox 1
3. Login into sandbox 1 console (console.sb1.cosmos-lab.org) with an SSH sessions.
4. Make sure all the resources in the domain are turned off:

   omf tell -a offh -t system:topo:allres  
   

5. Load fr3-tutorials.ndz on sdr1-piradio and sdr2-piradio nodes.

   omf load -i fr3-tutorials.ndz -t sdr1-piradio,sdr2-piradio
   

6. Turn all the required resources (2 USRPs and 2 Pi-Radio SDRs) on:

   omf tell -a on -t sdr1-piradio,sdr2-piradio,rfdev-sdr1-piradio,rfdev-sdr2-piradio
   

7. Check the node status to confirm that the nodes are up.

   omf stat -t sdr1-piradio,sdr2-piradio,rfdev-sdr1-piradio,rfdev-sdr2-piradio
   

8. After a minute (giving internal PCs enough time to boot), ssh to the USRP 2974s nodes and start the chrome remote desktop session (follow the instructions for setting remote access).
9. Open a Chrome browser sessions in each of the two CDRs and access the Pi-Radio configuration pages

    https://sdr1-piradio.sb1.cosmos-lab.org:5006
    https://sdr2-piradio.sb2.cosmos-lab.org:5006
   

Experiment Execution

Use the Pi-Radio web UI Frequency panel on both rfdev pages (Tx and Rx) and set:

• Low LO Frequency (GHz): 1.500000
• High LO Frequency (GHz): 10.000000

This example pairs a 1.5 GHz IF with a 10 GHz high-side LO (and a 1.5 GHz low-side LO) to place the RF tone at ~10 GHz, and back to 1.5 GHz on the receive path. (Exact placement depends on mixer sign/paths; the screenshot below shows the working settings used in this demo.) Leave Filters, Gain (except where noted), and LO Suppression at defaults for the first run.

GNURadio OFDM transmitter

Open a new terminal on sdr1-piradio and execute

sudo -s
cd /root/OFDM-Tutorial/
gnuradio-companion tx_ofdm.grc

That will bring up the GNURadio companion with OFDM transmitter block diagram. Make sure to configure it to use the internal X310 (RIO device).

Run the transmitter:

GNURadio OFDM receiver

Open a new terminal on sdr2-piradio and execute

sudo -s
cd /root/OFDM-Tutorial/
gnuradio-companion rx_ofdm.grc

That will bring up the GNURadio companion with OFDM receiver block diagram. Make sure to configure it to use the internal X310 (RIO device).

Run the receiver: