GNURadio CFO Estimation tutorial

Description

This tutorial illustrates the use of GNURadio flowgraphs to estimate the Carrier Frequency offset between a pair of USRPs in COSMOS, ORBIT testbeds. Schmidt Cox algorithm for coarse frequency offset estimation for OFDM is used in this tutorial.

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 getting started page to get started.

Resources required

2 USRPs in COSMOS or ORBIT testbed, 2 host nodes, and 2 mmWave devices(if using mmWave) are required. This page uses the 28GHz IBM mmWave devices in ​sb1.cosmos-lab.org. As shown in the ​basic tutorial for IBM 28GHz devices, the current connections in SB1 are as shown in this ​diagram

• sdr1-in1 RF2 TX/RX — rfdev4-in1 all ICs/TX/H, sdr1-in1 RF2 RX2 — rfdev4-in1 all ICs/RX/H
• sdr1-in1 RF3 TX/RX — rfdev4-in1 all ICs/TX/V, sdr1-in1 RF3 RX2 — rfdev4-in1 all ICs/RX/V
• sdr1-in2 RF2 TX/RX — rfdev4-in2 all ICs/TX/H, sdr1-in2 RF2 RX2 — rfdev4-in2 all ICs/RX/H
• sdr1-in2 RF3 TX/RX — rfdev4-in2 all ICs/TX/V, sdr1-in2 RF2 RX2 — rfdev4-in2 all ICs/RX/V

Hence, the resources required to execute this tutorial are rfdev4-in1, rfdev4-in2 (IBM PAAMs), sdr1-in1, sdr1-in2 (USRP N310s), srv1-lg1, srv2-lg1 in sb1.cosmos-lab.org.

Tutorial Setup

Follow the steps below to gain access to the sandbox 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 SB1
3. Login into sandbox 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 sdr1-in1,sdr1-in2,rfdev4-in1,rfdev4-in2,srv1-lg1,srv2-lg1
   

5. Use the gnuradio_ofdm.ndz node image with Ubuntu 20.04, UHD 4.4, gnuradio 3.9, and a grc example used in this tutorial. Load gnuradio_ofdm.ndz on the servers.

   omf load -i gnuradio_ofdm.ndz -t srv1-lg1,srv2-lg1
   

6. Turn all the required resources on and check the status of all the resources. Use the following commands .

   omf tell -a on -t sdr1-in1,sdr1-in2,rfdev4-in1,rfdev4-in2,srv1-lg1,srv2-lg1
   

   omf stat -t all
   

7. ssh to the servers with option -Y for using GUI with gnuradio.

   ssh -Y root@srv1-lg1
   

   ssh -Y root@srv2-lg1
   

Experiment Execution

Find and prepare USRPs

• Upon logging into the servers, run eth_config_sb1.sh script on each of the servers. This sets up the 10G data interfaces DATA1, DATA2. After running the script, you should see that the data interfaces have the appropriate IP addresses assigned, as per the table for ​SB1.

  root@srv1-lg1:~# ./eth_config_sb1.sh
  root@srv1-lg1:~# ip addr
  2: DATA1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP group default qlen 1000
      link/ether 1c:34:da:42:0c:3c brd ff:ff:ff:ff:ff:ff
      inet 10.38.1.1/16 scope global DATA1
         valid_lft forever preferred_lft forever
      inet6 fe80::1e34:daff:fe42:c3c/64 scope link
         valid_lft forever preferred_lft forever
  3: DATA2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP group default qlen 1000
      link/ether 1c:34:da:42:0c:3d brd ff:ff:ff:ff:ff:ff
      inet 10.39.1.1/16 scope global DATA2
         valid_lft forever preferred_lft forever
      inet6 fe80::1e34:daff:fe42:c3d/64 scope link
         valid_lft forever preferred_lft forever
  

• Run und_find_devices to make sure that both USRP N310s can be reached from both the servers:

  root@srv1-lg1:~# uhd_find_devices
  [INFO] [UHD] linux; GNU C++ version 9.4.0; Boost_107100; UHD_4.4.0.0-0ubuntu1~focal1
  --------------------------------------------------
  -- UHD Device 0
  --------------------------------------------------
  Device Address:
      serial: 3176DEB
      addr: 10.39.6.1
      claimed: False
      fpga: XG
      mgmt_addr: 10.37.6.1
      mgmt_addr: 10.38.6.1
      mgmt_addr: 10.39.6.1
      name: ni-n3xx-3176DEB
      product: n310
      type: n3xx
  
  --------------------------------------------------
  -- UHD Device 2
  --------------------------------------------------
  Device Address:
      serial: 3176DFA
      addr: 10.39.6.2
      claimed: False
      fpga: HG
      mgmt_addr: 10.37.6.2
      mgmt_addr: 10.39.6.2
      name: ni-n3xx-3176DFA
      product: n310
      type: n3xx
  

Configure IBM 28GHz PAAM

COSMOS uses a RESTful ​service for IBM PAAM management The service can be used for

• Dynamic array management - where the user connects to the antenna using connect command, dynamically steers the antenna during the experiment using steer command, and disconnects once the experiment is done.
• Static array management - where the user can connect, steer and disconnect using a single command, configure

Details and examples for the above are provided at the ​array management page. For this experiment, we use static array management commands as shown below. First, start PAAM #1 (rfdev4-in1) in TX mode with H-polarization using 16 antenna elements on all the ICs, and configure the TX beamforming direction to be in the broadside (0,0). Check the current consumption on 2v7_0,1,2,3 to make sure all the ICs have been successfully initialized.

root@console:~# curl "http://am1.orbit-lab.org:5054/array_mgmt/configure?dev_name=rfdev4-in1.sb1.cosmos-lab.org&ics=all&num_elements=16&txrx=tx&pol=h&theta=0&phi=0"

<?xml version="1.0" encoding="UTF-8"?>
<response status="OK">
  <action service="array_mgmt" name="configure" ipaddr="10.37.7.1">
    <step name="open" duration="3.254270"/>
    <step name="initializaition" duration="0.072135"/>
    <step name="enabling" duration="0.020807"/>
    <step name="steering" duration="0.010150"/>
    <state PAAM_ID="0x24" LO_switch="PLL" if_sw1="0x0" if_sw2="0x0" if_sw3="0x0" if_sw4="0x0" txrx="tx" polarization="h" />
    <adc>
      <conv index="0" name="1v2" tADC="107" tVolt="0.261" tCurr="0.131"/>
      <conv index="1" name="1v5" tADC="345" tVolt="0.843" tCurr="1.686"/>
      <conv index="2" name="1v8" tADC="0" tVolt="0.000" tCurr="0.000"/>
      <conv index="3" name="2v7_0" tADC="262" tVolt="0.640" tCurr="1.281"/>
      <conv index="4" name="2v7_1" tADC="270" tVolt="0.660" tCurr="1.320"/>
      <conv index="5" name="2v7_2" tADC="259" tVolt="0.633" tCurr="1.266"/>
      <conv index="6" name="2v7_3" tADC="276" tVolt="0.674" tCurr="1.349"/>
      <conv index="7" name="3v3_pll" tADC="46" tVolt="0.112" tCurr="0.056"/>
      <conv index="8" name="5v_uzed" tADC="308" tVolt="0.753" tCurr="0.753"/>
      <conv index="9" name="12v" tADC="328" tVolt="0.802" tCurr="2.672"/>
      <conv index="10" name="0V" tADC="0" tVolt="0.000"/>
      <conv index="11" name="1V8" tADC="736" tVolt="1.799"/>
    </adc>
    <step name="status" duration="0.018327"/>
    <step name="close" duration="0.100188"/>
  </action>
</response>

Similarly, start PAAM #2 (rfdev4-in2) in RX mode with H-polarization using 16 antenna elements on all the ICs, and configure the RX beamforming direction to be in the broadside (0,0). Check the current consumption to make sure the ICs have been successfully initialized.

root@console:~# curl "http://am1.orbit-lab.org:5054/array_mgmt/configure?dev_name=rfdev4-in2.sb1.cosmos-lab.org&ics=all&num_elements=16&txrx=rx&pol=h&theta=0&phi=0"

<?xml version="1.0" encoding="UTF-8"?>
<response status="OK">
  <action service="array_mgmt" name="configure" ipaddr="10.37.7.2">
    <step name="open" duration="3.295830"/>
    <step name="initializaition" duration="0.071303"/>
    <step name="enabling" duration="0.019037"/>
    <step name="steering" duration="0.010038"/>
    <state PAAM_ID="0x33" LO_switch="PLL" if_sw1="0x0" if_sw2="0x0" if_sw3="0x0" if_sw4="0x0" txrx="rx" polarization="h" />
    <adc>
      <conv index="0" name="1v2" tADC="106" tVolt="0.259" tCurr="0.130"/>
      <conv index="1" name="1v5" tADC="345" tVolt="0.843" tCurr="1.686"/>
      <conv index="2" name="1v8" tADC="0" tVolt="0.000" tCurr="0.000"/>
      <conv index="3" name="2v7_0" tADC="209" tVolt="0.511" tCurr="1.022"/>
      <conv index="4" name="2v7_1" tADC="171" tVolt="0.418" tCurr="0.836"/>
      <conv index="5" name="2v7_2" tADC="219" tVolt="0.535" tCurr="1.070"/>
      <conv index="6" name="2v7_3" tADC="217" tVolt="0.530" tCurr="1.061"/>
      <conv index="7" name="3v3_pll" tADC="172" tVolt="0.420" tCurr="0.210"/>
      <conv index="8" name="5v_uzed" tADC="374" tVolt="0.914" tCurr="0.914"/>
      <conv index="9" name="12v" tADC="316" tVolt="0.772" tCurr="2.574"/>
      <conv index="10" name="0V" tADC="0" tVolt="0.000"/>
      <conv index="11" name="1V8" tADC="738" tVolt="1.804"/>
    </adc>
    <step name="status" duration="0.017713"/>
    <step name="close" duration="0.100175"/>
  </action>
</response>

Run the experiment

• Transmit an OFDM waveform from sdr1-in1+rfdev4-in1 by running the flowgraph TX_OFDM.grc on srv1-lg1. Launch gnuradio-companion on srv1-lg1

  root@srv1-lg1:~# cd GNURadioOFDMExample/
  root@srv1-lg1:~/GNURadioOFDMExample# gnuradio-companion TX_OFDM.grc 
  

• Please make sure the USRP sink (TX) in TX_OFDM.grc is configured with sdr1-in1 ("addr=10.39.6.1"). Set the carrier frequency to 3GHz (3e9) and the subdev to be "B:0" (RF3). In this flowgraph, the sampling rate is set to 62.5 MSPS and the number of OFDM subcarriers set to 64. So the maximum CFO that can be detected is 62.5/(2*64) = 0.488 MHz.

• Receive the OFDM waveform on sdr1-in2+rfdev4-in2 by running the flowgraph RX_OFDM_CFO_estimation.grc on srv2-lg1. Launch gnuradio-companion on srv1-lg1

  root@srv2-lg1:~# cd GNURadioOFDMExample/
  root@srv2-lg1:~/GNURadioOFDMExample# gnuradio-companion RX_OFDM_CFO_estimation.grc
  

• Please make sure the USRP source (RX) in RX_OFDM_CFO_estimation.grc is configured with sdr1-in2("addr=10.39.6.2"). Set the carrier frequency to 3GHz (3e9) and the subdev to be "B:0" (RF3).

• Start both the flowgraphs to see receive IQ samples and per packet estimated CFO value at the receiver.