Open pespin opened 4 years ago
IgnasJarusevicius
commented
4 years ago Well as it says, channels A and B uses the same PLL clock so different frequencies can only be achieved by shifting digitally (using NCO). Digital shift is limited by RF bandwidth that is being sampled.
laf0rge
commented
4 years ago In other words, channels A and B are really only useful for MIMO and not for anything else, such as operating independend receivers/transmitters on different frequencies.
IgnasJarusevicius
commented
4 years ago Yes, channels A and B are mainly meant to be used for MIMO. The actual RF frequency will always be the same for both channels and the only possibility to transmit/receive at different frequencies is by utilizing hardware NCO and interpolation/decimation.
I'm trying to set up a 2 TRX BTS using osmo-trx and LimeSDR-USB using channels A and B. However, setting Rx frequency for channel B after having set it for channel A (different one) seems to fail:
Documentation for LMS_SetLOFrequency mentions that there's limitations when setting up frequency for both channels A and B, but it doesn't explictly state which kind of limitations:
Could you please document it in the API or at least insert some link to some place better explaining the limitations between both frequencies?
I'd like to see if some ARFCN pair can be used, or whether I must implement multi-arfcn feature from osmo-trx used in Ettus B200 for osmo-trx-lms too in order to be able to run 2 TRX with LimeSDR devices (see https://ftp.osmocom.org/docs/latest/osmotrx-usermanual.pdf section 13.2 "Multi-ARFCN mode")