DOI: 10.25349/d9ks3w
title: Aerial Measurements from Outdoor 2.4GHz 802.15.4 Network

description: Unmanned Aircraft Systems (UAS), i.e. drones, have been commercially
 successful in both the consumer and industrial sectors in part due to the
 wide variety of applications they benefit. In environmental monitoring and
 precision agriculture, UASs can be utilized for data collection from rural
 IoT sensor networks. These networks frequently operate over some variant
 of the IEEE 802.15.4 standard, taking advantage of the standard's low
 power usage. Consumer 802.15.4 radios are widely available in compact form
 factors, making them ideal for application in environmental and
 agricultural sensor networks. Unlike other wireless standards, 802.15.4 is
 well studied on the ground but has not received rigorous evaluation in
 three dimensional aerial communication, which introduces new challenges,
 such as antenna radiation patterns and extreme ranges. This data provides
 an initial look at the performance of 2.4GHz 802.15.4 for data collection
 from a UAS. We provide experimental performance measurements using an
 outdoor aerial testbed, examining how factors, such as antenna
 orientation, altitude, antenna placement, and obstruction affect signal
 strength and reception rate of packets.
description: In March 2019, we performed experimental measurements in an
 outdoor aerial testbed near our university. In our experiments, IoT nodes
 running the 802.15.4 protocol were placed on the ground, broadcasting
 messages at 500ms intervals. The UAS was flown over the network to collect
 data. We conducted nine total experimental runs divided evenly across
 three locations. Each run comprised thirteen altitudes, spanning roughly
 one hour of flight time, for a total of nine hours of flights.
 We used six Digi WRL-15126 XBee3 RF 2.4GHz transceivers utilizing
 802.15.4. The advertised outdoor range for each node is 1200m at a power
 of 8dBm and a receiver sensitivity of -103dBm. We selected the XBee3
 2.4GHz (as opposed to 900MHz or 868MHz) radio. Four
 XBee radios served as IoT transmitters, mounted on a SparkFun XBee
 Explorer with a USB-to-Serial converter, and controlled by a SparkFun
 Teensy LC. An external battery supplied power to the Teensy LCs through
 its own USB-to-Serial converter and forwarded power to the XBee. The nodes
 were configured to broadcast packets, 23 bytes each, every 500ms. The
 packet contained unique device and sequence identifiers and a randomly
 generated floating point number to simulate sensor data.
 For each trial, transmitters were placed in a line approximately
 11m apart with no obstruction within the 15cm vicinity. XBee placement was
 randomized for each trial, and GPS coordinates were recorded manually from
 repeated readings using a smartphone GPS. The UAS was a
 DJI Matrice 100, which communicates with a remote control at 5.725 - 5.825
 GHz (outside our monitoring frequency of 2.4GHz). We equipped the UAS with
 two XBees set to receive only. They were mounted to the bottom of the UAS
 with the \textit{horizontal receiver} parallel to the ground and the
 \textit{vertical receiver} perpendicular to the ground. Packets and their
 associated received signal strength indicator (RSSI) reported by the XBee
 radios were stored via a USB-attached on-board Raspberry Pi2 Model B. The
 location of the UAS for the duration of each trial was recorded from the
 Matrice 100 GPS connected via UART to the Pi, sampling at a rate of 50Hz.
 The UAS was flown in a straight line approximately over the transmitters
 at an average speed of about 2.2m/s (5mph). The flight path of each trial
 and altitude varied, as the flights were manually executed under varying
 wind conditions. Each flight reached a total horizontal distance of
 250-300m in both directions from the nearest transmitter (depending on
 local topography). For each trial, we flew at 13 altitudes (in relation to
 the lowest transmitter): 30ft, 40ft, 50ft, 60ft, 70ft, 80ft, 90ft, 100ft,
 150ft, 200ft, 250ft, 300ft, and 400ft