Purpose: TIS/TRP testing is an optional test for 802.15.4 Zigbee compliance, but is a mandatory test for some ecosystems. This KBA introduces how to test and estimate TIS/TRP.
1. TIS/TRP overview
Total Isotropic Sensitivity (TIS)
A measure of the average sensitivity of a receiver-antenna system, when averaged over the entire 3-dimensional sphere. The result will be strongly related to the antenna's radiation pattern. The TIS would be equal with the conducted sensitivity value if an ideal isotropic antenna was utilized, but when using a real antenna the TIS is weaker than the conducted sensitivity and depending on the antenna efficiency.
Total Radiated Power (TRP)
A measure of how much power is radiated by an antenna when the antenna is connected to an actual radio transmitter. TRP is an active measurement, in that a powered transmitter is used to transmit through the antenna. The total received power is calculated over the entire 3-dimensional sphere, and the result is the Total Radiated Power. The result will be strongly related to the antenna's radiation pattern. The TRP would be equal with the conducted power (antenna input power) if an ideal isotropic antenna was utilized, but when using a real antenna the TRP is weaker than the conducted power and depending on the antenna efficiency.
2. Test Environment
The test environment involves three main components as follows:
RF test equipment and Test PC with software: The test software is running on a Test PC controlling the test measuring instruments, e.g. Signal generator and Spectrum analyzer, and the command module.
Command module: This module receives the test commands from the Test PC and forwards these commands in a consumable format to the DUT. It reports ACK results received from the DUT to the Test PC.
DUT: The device under test placed within an anechoic RF chamber.
3. Test channels
The minimum channels for TIS and TRP testing are shown in the Table below and only test device supported frequency bands (868MHz, 915MHz and/or 2.4GHz range) should be tested.
4. Test method and procedure
The TIS and TRP tests should follow the guidelines outlined in CTIA documents listed below. These tests are usually done and reported by a professional, certified test laboratory.
CTIA: “Test Plan for Wireless Device Over-the-Air Performance"
CTIA: "Test Plan for Mobile Station Over the Air Performance”
4.1 TIS Test method and procedure
The DUT is placed in a free-space holder on a rotation table within the anechoic RF chamber and the communication between the DUT and the command module is established via over-the-air inside the chamber. The command module converts the commands of Test PC to control the DUT to the required test channel. To determine the TIS the reference antenna in the RF chamber transmits at the DUT, and the TX power is lowered until the radiated sensitivity BER or PER limit reaches a given threshold. The DUT then rotates in increments of 30 degrees along the vertical axis. At each vertical position, the horizontal axis steps in increments of 30 degrees. The horizontal and vertical polarization are measured at each position. After all measurements are completed, the sensitivity is calculated at each measurement point and the TIS is automatically calculated. Repeat this procedure on all test channels.
The test procedure as follows:
4.2 TRP Test method and procedure
The DUT is placed in a free-space holder on a rotation table within the anechoic RF chamber and the communication between the DUT and the command module is established via over-the-air inside the chamber. The command module converts the commands of Test PC to control the DUT to the required test channel and output power level. To determine the TRP the reference antenna in the anechoic RF chamber receives signal from the DUT, and the incoming signal strength is measured by a Spectrum Analyzer via the reference antenna. The DUT is then rotated along the vertical axis in 15° increments. At each vertical position, the horizontal axis is stepped also in 15° increments. Measurements are taken for both horizontal and vertical polarization at each position. After all the measurements have been taken, the power is calculated at each measurement point and the TRP is automatically calculated. Repeat this procedure on all test channels.
The test procedure as follows：
5. A simple method to estimate TRP/TIS
DUT's TX/RX conducted performance should be measured and antenna efficiency is used to estimate the TRP/TIS. This method can only be used for estimation, since there might be errors between the calculated result and the actual radiated TIS/TRP, and the reasons can be the followings.
Firstly, the antenna is picking up noise from all the electronic equipment that make up the system under test. That means, the antenna picks up added noise which can deteriorate the radiated sensitivity (which may have not been observed during conducted receiver tests). Also, the antenna efficiency is always less than 0 dB (100%) due to the lossy material of the antenna (and possible non-perfect antenna match), so the TIS will always be worse (higher) then the receiver’s conducted sensitivity.
Secondly, TRP/TIS measures the radiated performance in an actual live system. As a result, it is a function of not just the radio/transmitter, but also the antenna, and the connection between these. Even though both the radio/transmitter/receiver impedance and antenna impedance are designed to be 50 Ω, in reality they can slightly deviate from 50 Ω thus a small part of the RF power is likely reflected at the connection (i.e. mismatch loss).
5.1 TIS estimation
The procedure as follows:
5.2 TRP estimation
The procedure as follows:
6. Additional Details
Additional background and details can be found in the reference Zigbee Alliance specification document of "docs-19-01701-00-Zigbee RF Performance (TRP/TIS) Specification & Test Plan".
For the test code/FW description for TRP/TIS measurements please refer to the following KBA: How to build and use the StandardizedRfTesting sample in EmberZnet SDK?