MIMO Channel Sounding

Description

In this tutorial, we demonstrate the TDD 2x2 MIMO channel sounding procedure using the USRP-2974s in the ​COSMOS Sandbox2 (sb2) and the ​RENEW Sounder software

• The instructions of the RENEW Platform Sounder software can be found ​here under ​RENEW license.
• The COSMOS team contributes to adding the UHD support for the Sounder software under the ​UHD license.

Author: Tingjun Chen, Duke University / Columbia University (tingjun.chen [at] duke [dot] edu)

Last updated: Sept. 21, 2020

Prerequisites

In order to access sb2, create a reservation in sb2 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 getting ​started page to get started.

Resources Required

• 2 USRP-2974 (sdr2-s1-lg1 and sdr2-md1)
• 1 Server (srv2-lg1)

Tutorial Setup

Follow the steps below to gain access to the sb2 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 sb2
3. Login into sb2 console (console.sb2.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-s1-lg1,sdr2-md1,srv2-lg1
   

5. Use the baseline-gr.ndz node image (see ​here for the list of pre-defined images) with Ubuntu 18.04, UHD 3.15, and gnuradio 3.8. Load baseline-gr.ndz on the server.

   omf load -i baseline-gr.ndz -t srv2-lg1
   

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

   omf tell -a on -t sdr2-s1-lg1,sdr2-md1,srv2-lg1
   

   omf stat -t all
   

7. Make sure that the RF switch port is set to using the USRP 2974's. If some of the RF switch ports are set to "2", set them back to "1"

   curl "am1.cosmos-lab.org:5054/rf_switch/set?name=rfsw-s1-lg1.sb2.cosmos-lab.org,rfsw-md1.sb2.cosmos-lab.org&switch=1,2,3,4&port=1"
   

8. ssh to the the same server from two terminals, use option -Y for using GUI.

   [Terminal 1] ssh -Y root@srv2-lg1,
   [Terminal 2] ssh -Y root@srv2-lg1
   

Experiment Execution

Find and prepare USRPs and the Sounder software

• The IP addresses for Ethernet Port 1(10G) on sdr2-s1-lg1 and sdr2-md1 were hard-coded to 10.118.2.2 and 10.118.3.2 respectively. To access them from srv2-lg1, configure the network interface eno2 as follows:

  root@srv2-lg1:~# ifconfig eno2 10.118.1.2 netmask 255.255.0.0 mtu 9000 up
  root@srv2-lg1:~# sudo sysctl -w net.core.wmem_max=24862979
  net.core.wmem_max = 24862979
  root@srv2-lg1:~# sudo sysctl -w net.core.rmem_max=24862979
  net.core.rmem_max = 24862979
  root@srv2-lg1:~# ifconfig 
  eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9000
          inet 10.118.1.2  netmask 255.255.0.0  broadcast 10.118.255.255
          inet6 fe80::9a03:9bff:fe61:9609  prefixlen 64  scopeid 0x20<link>
          ether 98:03:9b:61:96:09  txqueuelen 1000  (Ethernet)
          RX packets 4053772  bytes 17770502341 (17.7 GB)
          RX errors 0  dropped 0  overruns 0  frame 0
          TX packets 1727950  bytes 2972166223 (2.9 GB)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
  
  

• Run uhd_find_device to make sure that the USRP-2974s can be reached:

  root@srv2-lg1:~# uhd_find_devices --args="addr=10.118.2.2"
  [INFO] [UHD] linux; GNU C++ version 7.5.0; Boost_106501; UHD_3.15.0.HEAD-0-gaea0e2de
  --------------------------------------------------
  -- UHD Device 0
  --------------------------------------------------
  Device Address:
      serial: 318F20F
      addr: 10.118.2.2
      fpga: XG
      name: 
      product: NI-2974
      type: x300
  
  root@srv2-lg1:~# uhd_find_devices --args="addr=10.118.3.2"
  [INFO] [UHD] linux; GNU C++ version 7.5.0; Boost_106501; UHD_3.15.0.HEAD-0-gaea0e2de
  --------------------------------------------------
  -- UHD Device 0
  --------------------------------------------------
  Device Address:
      serial: 3165747
      addr: 10.118.3.2
      fpga: XG
      name: 
      product: X310
      type: x300
  

• Download and build the RENEW Sounder software on the develop branch at ​here and follow the ​instructions to build it. Note that the master branch does not have UHD support.

• Include in files/usrp-bs-serials.txt the IP address 10.118.2.2, i.e., use sdr2-s1-lg1 as the base station (BS). In files/usrp-bs-only.json, set "channel" : "AB", to enable dual-channel on sdr2-s1-lg1.

• Similarly, in files/usrp-client-only.json, set "sdr_id" : [ "10.118.3.2" ] (i.e., use sdr2-md1 as the user) and "channel" : "AB", to enable dual-channel on sdr2-md1.

Execution

Run the experiment

• In the first terminal [Terminal 1], start the client:

  root@srv2-lg1:~/git/renew-software/CC/Sounder# ./sounder files/usrp-client-only.json
  ...
  ...
  pinning client thread 0 to core 1
  scheduling TX 13 Frames (41.08 ms) in the future!
  1 uplink symbols will be sent per frame...
  Beacon detected at Time 32476200, sync_index: 13100
  Start main client txrx loop...
  

• In the second terminal [Terminal 2], start the BS:

  root@srv2-lg1:~/git/renew-software/CC/Sounder# ./sounder files/usrp-bs-only.json 
  ...
  ...
  Set HDF5 File to logs/trace-2020-9-21-18-46-29_1x2x2.hdf5 and group to /
  task thread 0 starts
  pinning thread 0 to core 1
  Recv Thread 0: waiting for release
  receiver thread 0 has 1 radios
  Sync BS host and FPGA timestamp...
  Start BS main recv loop... 
  Saving HDF5, 2000 frames saved.
  ...
  ...
  

Analyze the results

• Once the hdf5 file is recorded (in this case, logs/trace-2020-9-21-18-46-29_1x2x2.hdf5), follow the Analyze the HDF5 dataset step ​here to analyze the results. For example, we can show the pilot sequence for computing the 2x2 channel matrix H = [h00, h01; h10, h11] as follows:

  root@srv2-lg1:~/git/renew-software/PYTHON/IrisUtils# python3 plot_hdf5.py ../../CC/Sounder/logs/trace-2020-9-21-18-46-29_1x2x2.hdf5 --ref-ant 0 --ref-user 0 --ref-frame 1500
  

where --ref-ant = 0, 1 represents the BS antenna index, and --ref-user = 0, 1 represents the user index.