Cellular Network Infrastructure » Radio Access Network » OsmoBTS

How exactly quality information is passed from DSP to L1 in case of osmo-bts-sysmo? I have trouble locating that place in the code - there doesn't seem to be particular function dedicated to that.

According to void GprsMs::update_cs_ul(const pcu_l1_meas *meas) in src/gprs_ms.cpp the switch to higher/lower CS depends only on link_qual value. Not sure if some spec covers which measurement is supposed to be used for link rate adaptation. Also, it's unclear yet how to convert the values available in particular BTS to be similar to what is reported by sysmobts.

Note: the DL CS is selected separately in update_error_rate()

TS 45.008 Annex D contains an "Example Selection of Modulation and Coding Schemes" for 8PSK EGPRS (MCS5-MCS9) based on CV_BEP and MEAN_BEP. Those two values should be reported by a BTS model to the PCU.

For classic GPRS or EGPRS with GMSK, I'm still looking to find similar reference values.

Chapter 8.2 of TS 45.008 contains information on how RxQual and CV_BEP / MEAN_BEP values are computed and encoded.

Some papers:

• https://www.netlab.tkk.fi/opetus/s38310/01-02/li_280502.pdf
• http://eeweb.poly.edu/dgoodman/icc04gprs.pdf
• http://queseth.se/olav/pubs/AlgorithmsForLinkAdaptationInGPRS.pdf
• http://www.cin.ufpe.br/~nomadic/vtc2000/A18522.PDF
• http://investigacion.ac.upc.edu/conferencies/EW2004/papers/156.pdf

In genreal, it seems there are BLER and CIR (C/I) based schemes, and that C/I is generally perceived to be superior.

I think the parameters RxLev/Rssi, BER, RxQual (averaged BER) should be provided by ever PHY/L1 and thus be a good candidate for reporting measurements to the PCU for GPRS/GMSK. Plus CV_BEP and CV_MEAN for EGPRS/8PSK

Version for octphy submitted for review in gerrit # 622 - 624.

another paper: http://www.uwicore.umh.es/files/paper/2000_international/uwicore_EL00_GPRS%20Link%20Adaptation%20switching%20thresholds%20and%20intervals.pdf

Changes for l1sap and bts-pcu protocols have been merged to master. Octphy implemntation have been merged, osmo-trx is partially implemented (C/I estimation is missing, extensive testing required).

Please see https://gerrit.osmocom.org/r/Ia58043bd2381a4d34d604522e02899ae64ee0d26, which is now merged.