4.1.1) srsRAN Experiments

This page provides sample software code to execute AERPAW experiments that rely on srsRAN as the radio software.  The provided software is tested by the AERPAW team both in the development environment and in the AERPAW testbed. 

Additional sample experiments are expected to be added in the future. Each experiment is prefixed with SE (srsRAN Experiment) and indexed in a chronological order based on the first time they are introduced in the user manual. 

Please note that srsRAN is already installed in all Experimenter containers. Please do not install your own version (as it will likely break the development environment).

Modulation and Coding Scheme (MCS)

The srsRAN sample applications provided use the software provided by srsRAN with minimal or no modifications. As such, the MCS of the communications between nodes is both adaptive and controlled by the srsRAN software. In other words, by default (without modifications), the MCS used by the UEs and eNBs is not available as a parameter to be controlled by the AERPAW Experimenters. However, the Experimenters can monitor the current MCS during an experiment as the MCS is one of the parameters that is periodically logged by the the UE radio client (together with other radio parameters, e.g., RSRP, SNR, BLER, both for uplink and downlink etc.). Below is a sample line from the UE log that is collected by the AERPAW radio log.

Static IP assignment for UEs

The srsRAN sample applications provided use the software provided by srsRAN with minimal or no modifications. As such, the IP addresses per UE are both adaptive and controlled by the srsRAN software. In other words, by default (without modifications), the IP used by the UEs  is not available as a parameter to be controlled by the AERPAW Experimenters. However, the Experimenters can statically assign an IP address per UE by editing the following configuration file as such.

LTE Base Station (eNodeB or eNB) configuration

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/.config/srslte/user_db.csv

Default values for last line in file is shown below

COTS_UE,mil,901700000020936,4933f9c5a83e5718c52e54066dc78dcf,opc, ˓→fc632f97bd249ce0d16ba79e6505d300,9000,0000000060f8,9,dynamic

Use an editor to change "dynamic" to preferred static IP address 

example: '172.16.0.2'

COTS_UE,mil,901700000020936,4933f9c5a83e5718c52e54066dc78dcf,opc, ˓→fc632f97bd249ce0d16ba79e6505d300,9000,0000000060f8,9,172.16.0.2

Valid last digits are between .2 and .254 (.1 is reserved for the eNB). 

srsRAN Disconnect and Reconnect Behavior

The two way connection range from a single fixed node to a portable node in AERPAW's Lake Wheeler field is smaller than the length of the field. For UAVs, the portable node (usually an UE), disconnects at a distance of around 150 - 200m from the fixed node, while for the UGVs, the portable node disconnects a bit sooner.  Since our fixed nodes have a considerably higher power than our portable nodes (15W vs. 1W), the disconnection is almost always asymmetrical at lease initially (the portable node still receives transmissions from the fixed node, but not the other way around).

Once a portable node gets disconnected (usually by not hearing replies from the fixed node), it will attempt to find the eNB (on the fixed node) by performing a cell search. If it is found, it will attempt to attach itself (with a consecutive 10 random access transmission and total of 15s time out). If it fails, it will re-attempt to cell search and reattach after another 15s. Each attempt to reattach (assuming the cell search is successful) takes a bit over 30s. After five consecutive failures(ref to LTE specs) to reattach to the cell (i.e., after 2.5 minutes = 5 x 30 seconds), the UE will start a 12 minutes timer when it will not even attempt to search for the cell, and then it retries the whole procedure. If the cell search is unsuccessful, the UE will retry another cell search shortly afterwards. 

Example Publications / Reports

1. Jonathan Behnke and Bryant Delgado, "LTE Spectrum Monitoring and Analytics", NC State Course Project Report, ECE 578, Fall 2021.