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Modulator output power level

Started by nbtech 3 years ago8 replieslatest reply 3 years ago96 views

Hello all,

For a given frequency band e.g. L-band, how is the modulator output power level selected? What decides that the output power level shall be e.g. -40dBm to 0dBm or -35dBm to +5dBm.

Any reference documents will be helpful.

Thank you

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Reply by OZ1DUGDecember 4, 2018
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Reply by shafie7December 4, 2018

Even for Radio or TV broadcasting stations where the transmitter output a fixed RF power, there is a need for dynamic range to account for part to part and temperature variations.

Your mobile phone, UE, moves and depending on its location, it transmit different power level to connect the link.  It is supposed to transmit just enough power to connect to the base station, anything more than that will pollute radio waves as well as short battery life time.

This is also true for SATCOM UT, user terminal, different satellite are at different location and the baseband and radio front end require to have dynamic range to account for part to part, temperature, frequency (i.e. at air interface), geography, and installation variations.

Dynamic range is one of the key metrics for both transmitter and receiver chains.

Shahram Shafie

https://ortenga.com/

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Reply by nishit10December 4, 2018

There might be many parameters that will effect the output power value. Below are some parameters (on a high level) which are within my knowledge.

1. The Link Budget Analysis will guide through this: Mainly your channel symbol rate and Modulation and Coding with TX-RX's cable and connector loss and Path Loss will govern this value.

2. Once you have such a 'dBm' number then it is checked across your limitations - like any regulatory limitations, if you have a Power Amplifier connected then the P1 dB margin will govern the max output power for this MODEM.

3. Then based on the power control mechanism (open-loop or closed-loop) you will derive/get power corrections based on the channel conditions.


Nishit Shetty

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Reply by nbtechDecember 4, 2018

Thank you Nishit for the excellent response. I was looking for this analysis.


Could you please refer any documentation that would help understand item 1 and 2 in your reply?

Thank you


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Reply by shafie7December 4, 2018

Here is the list of constraints that you need to find out, in order to design and budget analog vs. digital dynamic range.

  • Maximum RF output power, FCC for North America, ETSI for Europe and other geography
  • Minimum RF output power, the minimum distance will drive that
  • Inband Spurious level of radio front end
  • Out of band emission, FCC for North America, ETSI for Europe and other geography
  • Linearity of radio front end
  • Required BER/EVM or C/N for given modulation schemes (MODCOD or MCS for SATCOM or 3GPP waveforms, respectively)
  • Transducer power gain of radio front end
  • Quantization noise level of DAC
  • Phase noise level of LO
  • Etc.
  • Some of the above constraints are dependent on geography
  • Many of the above constraints are dependent on the radio front end

This is part of link budget analysis, i.e. bits to bits from modulator to demodulator analysis of the complete transmitter and receiver chain plus MODEM SoC.


Shahram Shafie

https://ortenga.com/

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Reply by nbtechDecember 5, 2018

Thank you Shahram

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Reply by shafie7December 5, 2018

You are welcome.

Please let me know if your company would like ORTENGA to do the link analysis and budget for you.

Best regards,

Shahram Shafie (info@ortenga.com)

https://ortenga.com/

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Reply by nishit10December 7, 2018

All mentioned above are from work experiences :/ Hence I don't have any consolidated document detailing the same. 

Sorry for stating the obvious - If in your work you stumble upon some questions then you can paste it here and we can try answering them.