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In ETSI EN 300 328 V2.1.1 (2016-11), section 4.3.1.4.3.1 Non-adaptive frequency hopping equipment (under Requirements for Frequency Hopping equipment limitations), it is stated:

The Accumulated Transmit Time on any hopping frequency shall not be greater
than 15 ms within any observation period of 15 ms multiplied by the minimum 
number of hopping frequencies (N) that have to be used.

What is the meaning of on any hopping frequency?

  1. Accumulated over all hopping frequencies, which means that the device must not transmit at all for an accumulated period of ((15 * (N-1)) / N) within the observation period.
  2. For each hopping frequency individually, which is a lot more permissive. This one seems less likely as it seems to be covered by other FH requirements (e.g. occupancy).

Or maybe another interpretation which I didn't think of?

We use a 2.4GHz frequency range, if that's relevant.

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The standard states: "The Accumulated Transmit Time is the total of the transmitter 'on' times, during an observation period, on a particular hopping frequency." On a particular hopping frequency.

The accumulated transmit time is for each hopping frequency separately. This is backed up what is stated in 5.4.4.2.1:

  • Centre Frequency: Equal to the hopping frequency being investigated

  • Frequency Span: 0 Hz

Because the span is 0 Hz and the spectrum analyzer is equal to the channel center frequency, you are only measuring the accumulated transmit time in one channel.

The test for compliance will cover two frequencies chosen arbitraraly from the used frequencies as instructed in the standard clause 5.4.4.1. The test set described in 5.4.4.2.1 is done for a minimum of two arbitrarily chosen channels.

Basically the requirement is for ensuring that the device uses the spectrum efficiently and uses all available channels, not just hopping between a couple of them. -> if it would only use couple channels for hopping, the accumulated transmit time on a channel would be exceeded.

Also try googling "EN 300 328 test report". You'll find some test reports made by others to increase your understanding on the standard.

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  • \$\begingroup\$ Good references from the standard and good explanations. Thanks \$\endgroup\$ – Asaf Apr 15 '18 at 13:14
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If you have 100 frequencies, the observation period is 1500 ms. This affects test setup (The spectrum analyzer's Zero span time base, test length etc). The test will cover all the frequencies.

At any given channel (frequency), the maximum transmit time is 15 ms, not on all channels. Basically, your maximum TX time is 15 ms for any hop.

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