Ranging using IEEE 802.15.4-Ultra-Wide Band

The ranging function is specified in the IEEE-802.15.4 standard and is implemented in Real Time Location Systems (RTLS) solutions offered by UWB component manufacturers like Qorvo.

UWB nodes must have 64GHz timers in order to accurately timestamp transmission and reception of frames.

Several ranging protocols can be used, such as the well-known TWR (Two-Way Ranging). TWR involves two nodes, a TWR client node and a TWR server node, exchanging 3 messages.

Testbed architecture

LocURa4IoT can be broken down into three layers: the nodes and the controllers layers, which constitute the first two hardware layers of the testbed; and data and algorithms layer, which allows the processing of data during or after the experiment.

• The nodes layer is a wireless sensor network (WSN) used for experiments. Each node is equipped with several wireless interfaces (UWB, BLE, LoRa), making it possible to address the localization problem via the most popular technologies in the IoT.
• The controllers layer includes the equipment used to configure, activate/deactivate and interact with the WSN nodes. The data collected from the nodes is presented live via an MQTT broker.
• The data and algorithms layer is dedicated to the processing and exploitation of data. This is made up of agents who, via the MQTT bus, directly exploit the data coming from the nodes and generate intermediate or final data.

A central server is responsible for running experiments on the testbed. Those experiments are described through Python scripts.

Nodes description

All nodes of the LocURa4IoT testbed are based on a Qorvo DWM1001-DEV board:

• A Nordic nRF52832 microcontroller (ARM Cortex-M4) which embeds a BLE transceiver,
• A Qorvo DW1000 transceiver (IEEE 802.15.4-compatible UWB)
• A 3-axis accelerometer (STM LIS2DH12TR),

Specific nodes have additionnal capabilities:

• A LoRa/LoRaWAN HopeRF RFM95 transceiver,
• An atmospheric pressure sensor (I2C),
• A luminosity sensor (I2C),
• A GNSS D-GPS receiver.

The node may use a variety of wireless technologies to address the problem of location determination via different physical layers and compare the performance of one technology to the other.

OS support

The firmware executed by the nodes is not constrained by a particular OS; the user can implement a basic C/C++ code in a bare-metal approach, or deploy a system or a richer protocol stack via an embedded OS like FreeRTOS or Apache MyNewt, which are the two systems that have been tested so far.