Full-Duplex Wireless using USRP N210

Description

In this tutorial, we'll use node11-10 in the main grid (equipped with a USRP N210) to transmit and receive a single frequency over the air to demonstrate full-duplex wireless capability using the Columbia ​FlexICoN's Gen-1 Frequency-Flat Amplitude- and Phase-based RF Canceller. Pictures of the FlexICoN RF canceller and node11-10 in the main grid equipped with full-duplex capability are below:

Figure 1: The ORBIT-FlexICoN Full-Duplex Node
(a) The FlexICoN RF Canceller	(b) Full-Duplex SDR at node11-10 in the ORBIT grid

For more information, please read:

T. Chen, J. Zhou, N. Grimwood, R. Fogel, J. Marasevic, H. Krishnaswamy, and G. Zussman, “Demo: Full-duplex Wireless based on a Small-Form-Factor Analog Self-Interference Canceller,” in Proc. ACM MobiHoc'16, 2016. ​(PDF) ​(DOI)

Please email Tingjun Chen (tingjun [at] ee.columbia.edu) if you are using (or plan to use) the full-duplex node, or if you have any questions. We also thank Mahmood Baraani Dasterjerdi and Steven Alfano for their great contributions.

Hardware / Software Resources Utilized

1. The Columbia FlexICoN Gen-1 RF Canceller, which is a frequency-flat amplitude- and phase-based RF canceller implemented using discrete components on a PCB. The Gen-1 RF canceller is optimized to have a center operating frequency at 900MHz.
2. USRP N210 with node11-10 in the ORBIT main grid.
3. ​SUB-20 is a multi-interface USB adapter for providing popular interfaces between PC (USB host) and different hardware devices. Specifically, we use the SUB-20 SPI module to control and configure the Gen-1 RF canceller (see Fig. 1(a)). The user manual can be found ​here.
4. ​UHD is already installed with the imaged SDR node.
5. The Eigen C++ Library is used for basic algebra used in channel estimation and digital self-interference cancellation. The Eigen releases can be found on the ​this website. We used the latest stable release Eigen 3.3.4 through our testings and experiments.

All the source code is also publicly available at ​here.

Set Up

Before you can access the testbed, you need to ​make a reservation and get it approved by the reservation service. After receiving the reservation's confirmation (approval) email:

• Login into reserved domain: ssh username@conslole.grid.orbit-lab.org
• Make sure that the full-duplex node is powered down for loading the desired image: omf tell -a offh -t node11-10
• Load an image on the node (this process can take about a few minutes so please be patient): omf load -i orbit-flexicon.ndz -t node11-10
• Turn on the node: omf tell -a on -t node11-10
• Login into the node: ssh root@node11-10 After login into the node, a flexicon_orbit folder should exist under the home directory of node11-10:~/ which contains the source code of this example. You can always retrieve the most recently updated code from ​here.

Run the Experiments

You will need to login into the full-duplex node (by ssh root@node11-10) in two separate terminal windows lo for running the experiment: one for the main full-duplex transceiver UHD program and one for controlling the RF canceller

In Terminal 1 (UHD)

• Build the example:

  cd ~/flexicon_orbit/fd_transceiver_simple/uhd/
  mkdir build
  cd build
  cmake ../
  make
  

• Check the conection and serial number of the USRP N210 using command uhd_find_devices. The serial number should be F331D4.
• Run the example with IQ rate rate, carrier frequency freq, TX gain tx-gain, and RX gain rx-gain:

  ./fd_transceiver_simple --tx-args="serial=F331D4" --rx-args="serial=F331D4" --rate 1e6 --freq 900e6 --tx-gain 10 --rx-gain 10
  

  The default sine wave has an amplitude ampl=0.3 and wave frequency of 100kHz wave-freq=100e3. This terminal window will show the power level at RX baseband, after RF cancellation (before digital) and after digital cancellation, respetively.

In Terminal 2 (SUB-20)

• Build the RF canceller configuration code:

  cd ~/flexicon_orbit/fd_transceiver_simple/sub20/
  make
  

• Check the connection to the SUB-20 device using command lbusb. You should see a XDIMAX devices connected to the USB hub.
• Program and configure the RF canceller with the desired values:

  ./rf_canc_config ATT-CODE PS-CODE C1-CODE C2-CODE C3-CODE
  

  In particular, the ATT-CODE=0,1,2,...,127 and PS-CODE=0,1,2,...,255 codes are for configuring the 7-bit attenuator and 8-bit phase shifter of the Gen-1 RF canceller. It is recommended to use C1-CODE=16, C2-CODE=3, C3-CODE=9. You can play with the values of ATT and PS until you see good cancellation profile (e.g., low residual self-interference power level) in Terminal 1.

A Secondary Transmitter Using Node13-8

Once the full-duplex node11-10 is up and running, you can turn on another SDR to transmit to the full-duplex node. Below, we use node13-8 as an example in the 3rd terminal window (Terminal 3).

• Load image, power on, and login into node13-8:

  omf tell -a offh -t node13-8
  omf load -i baseline-sdr.ndz -t node13-8
  omf tell -a on -t node13-8
  ssh root@node13-8
  

• Configure the USRP Ethernet interface: ifconfig eth2 192.168.10.1 netmask 255.255.255.0 up
• Set up a secondary transmitter sending a sine wave at a different frequency (e.g., 200 kHz) than that of the full-duplex node:

  ./tx_waveforms --args="serial=F331D4" --rate 1e6 --freq 900e6 gain 10 --wave-type SINE --wave-freq 200e3
  

  Now by analyzing the RX baseband data at node11-10, you will observe the received tone at 200kHz while the self-interence tone at 100kHz is cancelled to the USRP noise floor, which is around -90dBm.