Fortunately for me, the slow cell was in the B8 (900MHz) band so I successfully worked it around by disabling that band supplying a modified band mask to the AT!BAND command. All other cells in the same eNB are in the B1 band. Now I have a 3x faster HSDPA download at 25 Mbit/s and a full-speed upload at 5 Mbit/s again. I’ll probably make a shell script that can quickly re-enable B8 when I leave the coverage of the slow cell.
For others, encountering a similar issue
To change bands, first you need to authenticate with AT!ENTERCND command to enable password-protected commands.
The following command creates a custom band with index 10 and a band mask excluding B8.
AT!BAND=10,"Europe 3G w/o B8",0000000000400000,0000000000000000
More information about band mask calculation can be found here.
Don’t forget to activate the band.
AT!BAND=10
No modem reset required, the modem will move to another cell seamlessly.
Users of MC8805 should note that they may not be able to add custom bands above band index 08, at least with firmware version SWI9X15C_01.08.16.02. I ran into random issues with that, however after a few tries I could manage to add my custom band with index 10 as described above. In case you can’t, you’ll need to overwrite one of the factory bands using the same name. Be careful with that and always save the original list, available via the AT!BAND=? command, to some good place.
Thanks @mlw, for your clarifications & ideas.