There are key differences from ETSI EN 300 328 v1.7.1 and its successor, v1.8.1. The new version includes a total of 12 technical requirements; however they do not all necessarily apply to the Equipment Under Test (EUT). Certain requirements apply to all equipment, while others apply to specific modulation types or equipment characteristics, such as frequency-hoppers and non-frequency-hoppers. It’s complex – but crucial to know, so that your products remain compliant.
Changes In Requirements And Test Methods
RF Output Power
Radio Frequency (RF) Output Power applies to both frequency-hopping and non-frequency-hopping equipment. Although the limit remains the same, this is a much more complex test procedure when compared to v1.7.1. It is no longer just a simple Power Meter (PM) measurement.
The test method requires a power meter with a sampling speed of at least 1MS/s, and requires significant data processing for the final result. It’s the raw data from each sample that needs to be stored and mathematically processed to determine the RF Output Power. For devices with multiple antenna chains, measurements must be synchronized so that the power sensors are triggered to start sampling at the same time. For example, for a MIMO device with four antenna chains, this involves collecting and sampling 4 million samples per second.
Duty Cycle, Tx-sequence, Tx-gap
There are new requirements designed to help ensure efficient spectrum use:
- Duty Cycle: This is an entirely new requirement in v1.8.1. Duty Cycle refers to measuring the ratio of the total transmitter on time over a specified period.
- Tx-sequence and Tx-gap: These requirements provide a closer look at digital transmission bursts. If the two transmission bursts are separated by less than the manufacturer’s declared Tx-gap value, then the duration of those two bursts is considered Tx-sequence. V1.8.1 provides a limit on the duration of the maximum Tx-sequence and the minimum Tx-gap, and it’s different for frequency-hopping and non-frequency-hopping equipment. These requirements do not apply to equipment with e.i.r.p < 10mW, or to equipment that operates in a non-adaptive mode.
These tests also require data processing for the final result. The test lab uses the sample values from the RF Output Power test to construct individual transmissions so that the Duty Cycle, Tx-sequences, and Tx-gaps can be measured.
Power Spectral Density
Power Spectral Density is an existing requirement from v1.7.1, but the test method has changed and is more complex. It is no longer just a simple Spectrum Analyzer (SA) measurement where the spectral plot is used to show compliance. As with v1.7.1, it only applies to non-frequency-hopping (non-FHSS) equipment and the limit is still 10mW/MHz e.i.r.p.
As with the RF Output Power test, Power Density also requires some data processing. Spectrum analyzer trace data is stored and the individual bins are normalized and then summed over 1MHz segments from the final result.
As previously mentioned, the test methods to evaluate frequency-hopping characteristics are new; v1.8.1 better defines the limits. No longer can a manufacturer simply declare compliance as one did with v1.7.1; there are now prescribed test methods for everyone to follow.
Specific technical requirements include Dwell Time, Minimum Frequency Occupation, Hopping Sequence, and Hopping Frequency Separation. Again, the test lab uses the analyzer trace data, but only for the Dwell Time and Minimum Frequency Occupation tests. The Hopping Sequence and Hopping Frequency Separation are determined directly from a spectral plot.
Medium Utilization (MU) Factor
The Medium Utilization (MU) Factor requirement is a measurement to quantify the amount of resources (Power and Time) used by non-adaptive equipment. The goal here is to ensure equal access to the spectrum, and although the methods weren’t previously defined in v1.7.1, this test procedure was developed to show compliance to the Medium Access Protocol requirements from v1.7.1.
This is not applicable to equipment with e.i.r.p less than 10mW. It includes the Duty Cycle measurement in combination with the RF Output Power measurement to determine compliance. The MU Factor is calculated as the ratio of Measured Power, to the Power Limit of 100mW, multiplied by the Duty Cycle.
The limit for both hopping and non-frequency-hopping equipment is 10%, (i.e. if the device is operating at the maximum 100mW output power, the Duty Cycle has to be limited to 10% for compliance.)
Adaptivity is a mechanism where equipment can adapt to its environment by identifying other transmissions present in the band. Once again, the goal of this test is to help ensure spectrum sharing, and it was also developed to show compliance to the Medium Access Protocol requirements of v1.7.1.
Adaptivity only applies to equipment with e.i.r.p ≥ 10 mW, and covers frequency-hopping and non-frequency-hopping equipment using both Listen Before Talk (LBT) and non-LBT-based technologies.
The test procedure differentiates between adaptive frequency-hopping equipment using Detect and Avoid Mechanisms (DAA) and adaptive equipment using modulations other than Frequency-Hopping Spread Spectrum (FHSS). The test includes injecting a band-limited noise interference signal as well as a CW-blocking signal into the Equipment Under Test (EUT). The carrier reaction determines compliance. It covers both the Adaptivity and receiver-blocking technical requirements of v1.8.1.
Occupied Channel Bandwidth / Transmitter Unwanted Emissions in the Out-of-Band Domain
Two new requirements replaced the Frequency Range requirement of v1.7.1. Likewise, there is also a revised, more complex test procedure. It is no longer just a simple spectral plot, but rather two distinct measurement methods. The Occupied Channel Bandwidth requirement includes a 99% occupied bandwidth measurement; the results determine if the emission is contained in the 2.4GHz band. The requirement for Transmitter Unwanted Emissions in the out-of-band domain uses an emission mask as the limit.
The method for the emissions in the out-of-band domain uses the Occupied Channel Bandwidth results for determining compliance with the mask.
Transmitter Unwanted Emissions in the Spurious Domain / Receiver Spurious Emissions
V1.7.1 included both Transmitter Unwanted Emissions in the spurious domain and the Receiver Spurious Emission requirements, but both the test procedures and the limits have changed. The test procedures are now aligned with other harmonized standards, and include changes to the measurement setting like Resolution Bandwidth (RBW), Video Bandwidth (VBW) and the Detector Type.
Furthermore v1.8.1 does not distinguish the limits and methods between narrowband and wideband emissions, as v1.7.1 did. This means that the additional test and limits for wideband emissions no longer apply.
The limit for transmitter spurious emissions is also new, and now includes several bands below 1GHz, with more stringent requirements.
Use of Test Modes: We Can No Longer Rely On Traditional Test Modes
There are other changes not related to the test procedures or limits, but the use of test modes is probably the one that is getting the most attention.
ETSI EN 300 328 v1.8.1 does not allow for the use of traditional test modes that were once so commonly relied upon.
Some of us may be familiar with the test modes that force a continuous transmitted signal at 100% Duty Cycle. To show compliance with most radio standards, this is typically how most devices are configured. Well, that’s no longer allowed: v1.8.1 states that measurements must be performed in a realistic mode of operation, specifically with the equipment operating under a worst-case modulation scheme.
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Test requirements like Duty Cycle and RF Output Power require the use of these realistic modes to show a true picture of how the device works under normal conditions. This is something that traditional modes typically do not offer, and in fact there can be instances where test modes behave differently from when a device is configured for normal operation. This is yet another reason for the “no test mode” requirement.
However, it may be more difficult than anticipated to achieve a worst-case normal mode. The test lab may still need some special firmware to force specific characteristics, such as bandwidth, data rate, or packet types.
An additional bonus of the switch to using normal modes is that the market surveillance authorities test the products without contacting the manufacturer to ask for special tools or software.
The differences between v1.7.1 and v1.8.1 are significant; many of the new technical requirements insist on far more complicated testing, and new inclusions and exclusions of certain equipment. ETSI may be a Europe-based organization, but their standards are respected across the globe; to comply with v1.8.1, partner with a credible, experienced test lab with the knowledge to ensure your products remain compliant.