Wideband Channel Sounding with USRP 2974s

Description

Channel sounding is the process of evaluating the characteristics of a radio environment. Evaluating the power delay profile (PDP) of a radio channel helps in developing statistical models for channel simulation.

This tutorial demonstrates how to use the RFNoC channel sounder design for obtaining the PDP of channels up to 100MHz wide. An FPGA correlator module computes real time correlation power, and an averaging module, averages contiguous sets of PDP over time, and sends the result to host CPU. This design is compatible with 3rd generation Ettus USRP devices. This tutorial uses USRP 2974s on COSMOS SandBox1.

Prerequisites

In order to access the test bed, create a reservation and have it approved by the reservation service. Access to the resources is granted after the reservation is confirmed. Please follow the process shown on the COSMOS work flow page to get started.

Resources required

2 rooftop USRP 2974s (sdr2-md1, sdr2-s1-lg1) are required for this experiment.

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 sandbox 1
3. Login into sandbox 1 console (console.sb1.cosmos-lab.org) with two SSH sessions.
4. Make sure all the nodes and devices used in the experiment are turned off:

   omf tell -a offh -t sdr2-md1,sdr2-s1-lg1  
   

5. The image channel-sounder.ndz has UHD, Gnu Radio installed, with RFNoC enabled. Custom RFNoC modules required for channel sounding are also installed. Load channel-sounder.ndz on sdr2-md1,sdr2-s1-lg1.

   omf load -i channel-sounder.ndz -t sdr2-md1,sdr2-s1-lg1
   

6. Turn all the required resources on and check the status

   omf tell -a on -t sdr2-md1,sdr2-s1-lg1
   

   omf stat -t system:topo:allres
   

7. ssh to the nodes, use option -Y for using GUI.

Prepare the USRPs

• Check if USRPs have the modules required for the experiment by running uhd_usrp_probe on each on of them.

  root@sdr2-md1:~# uhd_usrp_probe --args="type=x300"
   
  |   |     _____________________________________________________
  |   |    /
  |   |   |       RFNoC blocks on this device:
  |   |   |
  |   |   |   * DmaFIFO_0
  |   |   |   * Radio_0
  |   |   |   * Radio_1
  |   |   |   * DDC_0
  |   |   |   * DUC_0
  |   |   |   * Corrmag63avg8k_0
  |   |   |   * Spreader_0
  |   |   |   * SpecSense2k_0
  |   |   |   * FIFO_0
  |   |   |   * FIFO_1
  

  If you see the above at the end of uhd_usrp_probe output, the USRPs are ready. Spreader_0 is used to spread the transmit signal, and Corrmag63avg8k_0 is the correlator on the receive side.

Set up web based streaming

• Set up a web proxy for the receive node Use run-websock command to set up the proxy (this is required for remote web based streaming)

  prasanthi@console.grid:~$ run-websock 5100 10.10.20.1:5100 --daemon
  WARNING: no 'numpy' module, HyBi protocol will be slower
  WebSocket server settings:
    - Listen on :5100
    - Flash security policy server
    - No SSL/TLS support (no cert file)
    - Backgrounding (daemon)
  

Run the experiment

• Start transmit application on the TX node. If you were assigned a group, the command below will start the application on the assigned TX USRP, with a bandwidth of 100MHz.

  root@node19-1:~# /root/uhd/host/build/examples/rfnoc_tx_mobicom --group red
  

  The same application can be run by passing different command line parameters as shown below

  root@node19-1:~# /root/uhd/host/build/examples/rfnoc_tx_mobicom --args"addr=10.10.23.16,type=x300,skip_ddc,skip_duc" --freq 3e9 --gain 20 --duc-args="input_rate=50000000.0,output_rate=200000000.0"
  

• Start receive application on the RX node. If you were assigned a group, the command below will start the application on the assigned RX USRP

  root@node20-1:~# ./uhd/host/build/examples/rfnoc_rx_mobicom --group red
  

  or the following could be used, when not using a topology

  root@node20-1:~# ./uhd/host/build/examples/rfnoc_rx_mobicom --args"addr=10.10.24.16,type=x300,skip_ddc,skip_duc" --freq 3e9 --gain 10 --ddc-args="output_rate=50000000.0,input_rate=200000000.0"
  

• Download channel_sounding_display.html attached to this tutorial and open it in your browser. Once you click the start button, you should see PDP of the channel.