IMST Develops Radiation Performance Tests for LoRa Certification

About one year ago, IMST was selected as an accredited LoRa Alliance certification test house for LoRaWAN™ certification. The Certification testing against LoRaWAN V1.0.1 has lead to a large number of certified end devices. However the possibility of connecting an end-device to an operator’s network successfully also depends on the quality of the radio implementation of the end-device.

To ensure consistent services to all end-users, operators should impose a minimum end-device radio performance criteria. They can do this by adding radiation performance measurements to the product test cycle. Over the last year, IMST has worked closely with Keysight Technologies to create a test set up to evaluate radiation performance.

From a regulatory point of view the main requirement for 868 MHz ISM devices is that their ERP (effective radiated power) should not be more than +14 dBm (or 25 mW) for any orientation. This sets the upper bound on the end-device radiated power and also includes the duty cycle restrictions. In general, with the measured effective TRP (Total Radiated Power) the first quality characteristic of an end device can be derived.

The operator needs to ensure that the end device actually radiates as much power as possible to maximize the robustness and usable data rate of the uplink. In addition to this a measurement of the device’s receiver performance is also required. This is derived from the fact that LoRaWAN networks are symmetrical, bi-directional networks implying that the receiver performance of the end-device is also important.

To analyze receiver performance the TIS (Total Isotropic Sensitivity) is measured, allowing for bi-directional performance characterisation of the end device.

Both measurements are performed in the accredited radio metrology laboratory at IMST. The software required on the end-devices is already installed on the end device if it has already passed the LoRaWAN Certification, which can also be performed in their laboratories.

The report that IMST provides as the output from LoRaWAN Radiation Performance measurement gives antenna diagrams showing the minimum and maximum values for the TRP and TIS. Based on these figures, a network operator can grade devices to ensure good/smooth network availability and performance while manufacturers can improve their designs.