diff options
| author | Vadim Yanitskiy <vyanitskiy@sysmocom.de> | 2021-01-26 23:55:22 +0100 |
|---|---|---|
| committer | Vadim Yanitskiy <vyanitskiy@sysmocom.de> | 2021-01-27 01:01:50 +0100 |
| commit | 2a637a5c9c1b6e77c00701004ba504ba9d020b28 (patch) | |
| tree | 54d5ed98c0303e384d81fe52ffc9d1bcb0de3bce /Transceiver52M/Transceiver.cpp | |
| parent | 819cad1776e09782fffdf433a2e843fe5720d6c8 (diff) | |
Transceiver: use proper factor for amplitude scaling
In Transceiver::addRadioVector() we scale the I/Q samples by scaling
the output voltage of the DAC. A relative factor/divisor/ration in
the voltage domain cannot be used 1:1 in the power domain.
There exist two similar formulas:
a) X_dB = 10 * log10(X_lin / X_ref)
b) Y_db = 20 * log10(Y_lin / Y_ref)
both of them are correct, and according to [1]:
a) If you convert a quantity X that relates to power or energy,
=> the factor is 10.
b) If you convert a quantity Y that relates to amplitude,
=> the factor is 20.
Therefore we should be using 20 instead of 10. This change makes
osmo-trx apply per-lchan attenuation values correctly. Otherwise
it would double the values indicated in TRXD messages.
[1] https://dspillustrations.com/pages/posts/misc/decibel-conversion-factor-10-or-factor-20.html
Change-Id: I98bc00bd25df4913d45e55eb008d715aca76fc7c
Related: SYS#4918
Diffstat (limited to 'Transceiver52M/Transceiver.cpp')
| -rw-r--r-- | Transceiver52M/Transceiver.cpp | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp index 3188c70..6de266c 100644 --- a/Transceiver52M/Transceiver.cpp +++ b/Transceiver52M/Transceiver.cpp @@ -396,7 +396,7 @@ void Transceiver::addRadioVector(size_t chan, BitVector &bits, else burst = modulateBurst(bits, 8 + (wTime.TN() % 4 == 0), cfg->tx_sps); - scaleVector(*burst, txFullScale * pow(10, (double) -RSSI / 10)); + scaleVector(*burst, txFullScale * pow(10, (double) -RSSI / 20)); radio_burst = new radioVector(wTime, burst); |