ETSI EN 300 328 has requirements for frequency hopping systems (section 4.3.1) and wide band modulation systems (section 4.3.2). Because ZigBee systems do not frequency hop, then ZigBee is a wide band modulator covered by section 4.3.2. Note that section 4.3.2 states the normal operating frequency of these wide band systems can be changed when interference is detected, but this is different than having a frequency hopping system. This is what ZigBee does with its frequency agility. Section 188.8.131.52.2 specifies for adaptive or non-adaptive equipment using wide band modulation the maximum output power shall be +20dBm. However, this is misleading since section 184.108.40.206 on Power Spectral Density limits the maximum PSD to +10dBm per MHz. This is the test that limits output power to +12dBm in Europe on DSSS radios. Section 220.127.116.11.2.2.2 specifically notes using CCA energy detect as per 802.11 or 802.15.4 is okay with some specific notes and requirements. So, our interpretation is that EN 300 228 is not particularly well worded in that it would appear to allow going to +20dBm, but the reality is the PSD limits the output power to +12dBm. More to the main point, it allows 15.4 CCA checking as suitable for use without further listen before talk (LBT) or adaptive controls.
Several customers have tested against EN 300 328 standard version 1.8.1 or later which brings in the requirement to test the adaptivity or medium sharing of a radio transmitter. To our knowledge and that of our customers, the EN 300 328 standard doesn’t explicitly reference to the 802.15.4 specification, but what some customers have done is to simply prove that the listen before talk mechanism is functional within the requirements of the standard. Another option is to limit the duty cycle, but most customers want to avoid this. As of EmberZNet 5.7.3, the nodetest application includes the command "setcheckcca" which enables or disables CCA checking (disabled by default, enabled with "setcheckcca 1", disabled with "setcheckcca 0"). Manufacturing library supports a similar feature with mfgLibSetOptions(). In this test setup, an interferer is then brought in and turned up to the point where the transmitter will stop transmitting in order to prove the effectiveness of the LBT (or CCA mechanism). In order to prove adaptivity compliance, test houses need to see the transmitter stop transmitting when an in-band interferer is added and its power level increased above a certain threshold.
Alternatively, customers can write a simple application (to be installed on hardware tested for compliance) where the node under test sends a lot of unicasts to a supporting equipment (coordinator). Use about 30 maximum length messages per second plus MAC and APS acknowledgements to cause lots of traffic. Also the coordinator needs to be able to change the network’s channel, because this test needs to be run on at least the top and bottom channels (and depending on the test house perhaps also the middle channel). When the interferer is brought in (or its signal level increased), the device under test stops transmitting, which should satisfy the requirements of passing this test.
We recommend customers consult with the test house prior to testing to determine if they have experience with 802.15.4 compliance testing. The compliance test requirements should be fully understood by both the customer and the test house before testing begins.