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CC1310: Help with clarifying FCC and wake-on-radio

Jan Elfstrom29
Intellectual 280 points
Part Number: CC1310

Hi,

I have trouble getting a product through certification. It is based on the CC1310 and wake-on-radio. The interval is 500ms to balance energy and response time.

Nemko that is the agency we use claim that the duty cycle is measured during 100ms. As the preamble is 500ms we will not pass. I have however found a paper from you:

http://www.ti.com/lit/an/swra048/swra048.pdf

p12

“For both Table 9 and Table 10, the duty cycle is defined as the maximum total transmitter on time as a

fraction, expressed as a percentage, of the total time in a *one hour* period. Additionally, the duration of

one individual transmission and the minimum off time between two consecutive transmissions are limited,

as detailed in Table 11.”

I know that for 2.4GHz the duty cycle is measured during 100ms. Can you comment on the above please? I also read something about the duty cycle being unimportant if transmission power was under a certain level.

Thanks,

Jan

  • 0
    TI__Mastermind 39860 points
    The tables you refer to are applicable for operation under EN 300 220 in Europe. They are not applicable for FCC certification.

    In US there are two relevant standards for operation in the 915 MHz band; 15.247 and 15.249

    15.249: Maximum output power is approx -1.2 dBm. Continuous transmission is allowed

    15.247: Using frequency hopping spread spectrum. Maximum +30 dBm output power (+6 dBi antenna gain). Maximum dwell time is 400 ms (i.e. time spent on one channel)

    15.247: Using wide band digital modulation. 6 dB BW > 500 kHz. Maximum +30 dBm output power (+6 dBi antenna gain). Maximum power spectral density is +8 dB/3 kHz, and this will in many cases limit the output power to less than +30 dBm. Continuous transmission is allowed

    The 100 ms duty cycle you refer to is used to calculate a duty cycle correction factor for spurious emission above 1 GHz. The general limits for the emission of intentional or unintentional radiators are given in section 15.209. Above 960 MHz the limit is -41.2 dBm (500 uV/m at 3 m distance).
    - When operating under section 15.249 the general limits apply.
    - When operating under section 15.247 the spurious emission must only be 20 dB below the carrier UNLESS it falls within one of the restricted bands defined in section 15.205. When operatingin the 902-928 MHz frequency range the 3rd, 4th and 5th harmonic falls within restricted bands. In the restricted bands the general limits of -41.2 dBm apply. However, pulsed transmissions allow higher peak harmonic and spurious emissions above 1 GHz because an averaging detector is called for in the measurements (15.35). If the duty cycle factor of the periodic signal is known, measuring the peak value and adding a duty cycle relaxation factor can determine the average value. The relaxation factor is 20 log (TX on-time/100 ms) [dB]. The average limit must be below -41.2 dBm.
  • 0 in reply to Sverre
    Intellectual 280 points

    Hi,

    Thank you for the answer.

    As I understand it the 100ms apply for 15.247 to calculate a duty cycle relaxation factor as well (20 log (TX on-time/100 ms) [dB]).

    Do you have an advice how to use the wake-on-radio mode for sub-GHz in both Europe and the US? Frequency used must of course be adjusted to local regulations.

    Is the only possible way forward to use e.g. a 10ms pre-amble? If that is the case it will ruin the battery life.

    I have seen elsewhere that the TI 15.4 stack supports frequency hopping, could that be a way forward and based on the use case I initially described? Battery life is important.

    Thanks,

    Jan

  • 0 in reply to Jan Elfstrom29
    TI__Mastermind 39860 points
    Correct: 100 ms is the period over which the duty cycle relaxation period is calculated and is used under 15.247 above 1 GHz.

    Wake-on-radio (WoR) with a 500 ms preamble will not work in the US with FHSS as the maximum dwell time is 400 ms. If you go for a FHSS system you need to use a lower preamble length and preamble + payload needs to be less than 400 ms. I assume the challenge will be to synchronize the network since the TX unit might not be on for each "hop". I am no expert on this so I suggest you start a new thread where you ask how FHSS can support a transmitter that is on at random times. Sorry I could not be of more help on this.

    Operation under 15.249 allows wake-on-radio with 500 ms preamble, but in this case the output power is limited to -1.2 dBm. The range will thus be degraded compared to 15.247 which allows higher output power.

    Wideband digital modulation is an option for WoR, but in this case you need 6 dB above 500 kHz so the data rate needs to be high. This will again degrade the sensitivity and hence the range.