GE2: Channel Sounder

1) Experiment Overview

Experiment Definition: This experiment is a GNU Radio based channel sounder between two AERPAW Nodes one node acting as transmitter and one node acting as receiver. The experiment generates time-stamped relative received signal strength and signal quality. The minimal representative working environment for this experiment is with LW1 as the AFRN and any APRN. 

Experiment Goals: Pseudo-random sequence of bits are transmitted from a transmitter at a fixed node using GNURadio with a certain rate and center frequency. The transmitted signal is received and processed all in GNURadio. The processing involves correlating the IQ samples with the sequence of transmitted bits and measuring the signal strength after the correlation. The signal strength as well as a measure of the signal quality are timestamped and logged in a file. Running the receiver at a portable node following a trajectory, the channel as a function of the location of the portable node can be measured.     

Experiment Modes: Different modes offered in this experiment are TESTBED and EMULATION. The EMULATION mode is performed in the development environment by the experimenter. The experimenter can modify the code. In TESTBED mode performed by the operator the transmitter and receiver are connected to a USRP and the transmission and reception occur over the air. 

Software version

• Ubuntu version 18.04

• GNU Radio version v3.8.5

• UHD version 4.3

Configuration Parameters:

• USRP Tx/RX Gain 

• USRP Serial Number

• USRP Center Frequency

2) Performing the Experiment:

Transmitter

We assume the transmitter is a fixed node. Login to the E-VM corresponding to the fixed node. Navigate to the folder containing all the Radio scripts 

$ cd /root/Profiles/ProfileScripts/Radio 

Copy the channel sounder transmitter script as startRadio.sh

$ cp Samples/startGNURadio-ChannelSounder-TX.sh startRadio.sh 

Use an editor to uncomment the line  /Radio/startRadio.sh in /root/startexperiment.sh and run the following command:

$ /root/startexperiment.sh  

Receiver

We assume the receiver is a portable node. Login to the E-VM corresponding to the portable node. Navigate to the folder containing all the Radio scripts 

$ cd /root/Profiles/ProfileScripts/Radio 

Copy the channel sounder receiver script as startRadio.sh

$ cp Samples/startGNURadio-ChannelSounder-RX.sh startRadio.sh 

Use an editor to uncomment the line  /Radio/startRadio.sh in /root/startexperiment.sh run the following command:

$ /root/startexperiment.sh  

3) Modifying the Experiment Configuration Parameters:

Transmitter: 

The shell script /root/Profiles/ProfileScripts/Radio/Samples/startGNURadio-ChannelSounder-TX.sh calls the script /root/Profiles/ProfileScripts/Radio/Helpers/startchannelsounderTXGRC.sh which can be edited by the experimenter to modify the parameters of the transmitter

Receiver: 

The shell script /root/Profiles/ProfileScripts/Radio/Samples/startGNURadio-ChannelSounder-RX.sh calls the script /root/Profiles/ProfileScripts/Radio/Helpers/startchannelsounderRXGRC.sh which can be edited by the experimenter to modify the parameters of the receiver

4) Results:

The experiment generates timestamped measurement log of received signal strength and signal quality in EVM of the portable node (receiver) under /root/Results folder. Combining the measurement log with the GPS log generates the signal strength vs location of the vehicle. The signal quality above 70 is considered to be a reliable measurement.