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WL1837MOD: “PerSubBandRxTraceLoss” parameters in .ini file (swru422a)

Kaisa_K
Prodigy 100 points
Part Number: WL1837MOD
Other Parts Discussed in Thread: , WL1835MOD

What is the purpose of “PerSubBandRxTraceLoss” parameters in .ini file (swru422a):

  1. “for the correct RSSI reading on the solution boundary” -> what is the benefit in practice compared to plain RSSI seen by the SoC?
  2. There are module specific (e.g. WL1837MOD) .ini files available with different PerSubBandRxTraceLoss configuration -> does it mean that each particular configuration normalizes the RSSI per sub band to the antenna port of the module (=solution boundary), instead of the SoC?
  3. If PerSubBandRxTraceLoss is set to zero, is plain RSSI seen by the SoC reported?

  • 0
    TI__Mastermind 35795 points

    Hi , 

    PerSubBandRxTraceLoss is used for Ant-point RSSI. We calculate RSSI at ANT. 

    Thanks

    Saurabh

  • 0 in reply to S
    Prodigy 100 points

    Hi,

    I assume you are referring to ANT pin of the WL1837MOD?

    Could you please explain the benefits of using ANT-point RSSI. We are considering to set this RX trace loss to zero in order to have the real RSSI for any RSSI-based decision making. Do you see any drawbacks by setting the RX trace loss to zero?

    Best regards,

    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi Kaisa,

    If you set the PerSubBandRxTraceLoss to 0, you will get 1dB lower output power (assuming this parameter is set to 1dB trace loss). What happens is that the trace loss is an estimate of the loss to the antenna. Thus when you add 1dB here, you tell the Module to deliver 1dB more power so that you get the equivalent power at the antenna port.

    If you have this set to 0, you will see a lower power as you are not accounting for the trace loss to the antenna. Its best to leave this as is.

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Hi Riz,

    how is PerSubBandRxTraceLoss related to TX power? In .ini file there is also a separate PerSubBandTxTraceLoss, isn't this the one that affects to TX power? We also have quite long antenna traces in our own design, so default trace loss values are anyway not correct for us if the idea is to indicate the loss all the way to the antenna.

    Best regards,

    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi,

    My apologies, I thought you were referring to TX trace loss! As Saurabh stated, the RX trace loss is adjusted such that it is the RSSI back to the output pin of the module. Thus is providing the value that the module sees and not what is seen at the antenna. If you lave this at zero, you will be off on your value by the 1dB since you did not compensate for it in the RSSI calculation.

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Hi Riz,

    I'm still a little bit confused as it is not clear for me which antenna are you referring to? Are the default trace loss values adjusted for some TI reference design or evaluation board?

    Thanks,

    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi Kaisa,

    This is referring to the primary antenna (ANT1)  and is based on our WL1837MOD reference design ()

    Thanks,

    Riz 

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Hi again,

    one more round to make sure that we are on the same page.

    Let's take for example 2.4GHz and ANT1, for which we have 3 levels / reference points:
    1) BG2 inside of the WL1837MOD
    2) RF_ANT1 which is the module pin of the WL1837MOD
    3) ANT1 which is an actual antenna on the WL1837MODCOM8I reference design

    Between which 2 reference points (list above) are PerSubBandRxTraceLoss and PerSubBandTxTraceLoss calculated in the official WL1837MOD_INI_FCC_CE.ini file (1dB)? Based on comments in the actual .ini file and example in the WL18xx.INI File document (swru422a, page 12) I understood that answer would be points 1 and 2.

    Thanks & best regards,
    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi Kaisa,

    You are almost correct! When we refer to the antenna port this is actually item 3 as you have listed above. So in the official .INI file the trace loss includes the loss outside of the module to the input port of the antenna.

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Hi Riz,

    So the default TraceLosses for WL1837MOD are defined between reference points 1 and 3? Then how am I able to determine correct trace losses for my own design, if default values include losses both inside and outside of the WL1837MOD?

    It also doesn't seem to make sense that there are separate TraceLoss values for ANT1 and ANT2 on 2.4GHz but only one value for 5GHz sub-bands. Why is that and how should I determine trace losses for my own design on 5GHz, when I’m using both antennas and trace losses for these are not the same?

    Br,

    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi Kaisa,

    For the wL1837MOD the trace loss on the PCB we consider is to the U.FL connector, which is very close to the output of the WL1835MOD port. Thus this is minimal. Yes, there is larger trace going to the antenna when you do radiated measurements, but for purposes of certification here, we consider this to be part of the antenna.

    So in your calculation, you can assume for the WL1837MOD that the loss in the .INI file is from the SoC to the Module boundary. So you can add your PCB trace loss to this.

    IF you look at the radio internal, we have to BG band radios and 1 5GHz radio, thus the path loss from the SoC to the module boundary needs to be defined for these 3. Thus you have 2 path losses for 2.4GHz. For 5GHz, we consider transmission only on the primary antenna, thus one path loss. The RSSI that is used in the FW for 5GHz is based on the primary path, thus the one loss.

    I hope this closes out your understanding here. I would suggest that you take our EVM board and start to play with the traces loss parameters to see what happens to output power. This would be the best way to really get an understanding of what this is going on. Note that there is a limit to what you can adjust the trace parameters too. You don't want to include too much trace loss or you will start to fail other parameters such as spectral mask or error vector magnitude as this is making our PA work harder to account for the additional trace loss.

    If you are re-using our certification you also want to keep these parameters alone as we are certified with this .INI file.

    Thanks

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Rizwan Murji said:
    For 5GHz, we consider transmission only on the primary antenna, thus one path loss. The RSSI that is used in the FW for 5GHz is based on the primary path, thus the one loss.

    According to http://www.ti.com/lit/an/swaa161/swaa161.pdf, 5GHz switched diversity measures RSSI in both primary and secondary antennas, so dedicated RX loss values for both antenna paths would make sense. Switched diversity should also be enabled for transmission, so also dedicated TX loss values for both antenna paths would make sense. Or are the primary and secondary paths assumed to be fully identical on 5GHz?

    Thanks

    Kaisa

  • 0 in reply to Kaisa_K
    TI__Genius 12260 points

    Hi,

    On the 5GHz path the primary and secondary paths are the same. You can see this in the product datasheet foe wl1837MOD.

    Thanks,

    Riz

  • 0 in reply to Rizwan Murji
    Prodigy 100 points

    Hi,

    ok this further confirmes that PerSubBandTxTraceLoss and PerSubBandRxTraceLoss are only related to module internal losses. It could be a good idea to clarify this in the documentation (SWRU422A) as it makes no sense for end-user to change these values.

    Thanks & best regards,
    Kaisa