dualband radio architecture

hi, I have a simple question about the architecture of dualband radio front-end (for example: GSM900 and GSM1800).

Supposed the antenna is dual-band, does the conventional radio front-end operates at two frequency band simultaneously? If yes, so the radio frontend should have two sets of local oscillators, bandbass filter and LNA for each band, right?

Or does the radio front-end has just one set of components but the LO can be tuned to two different frequencies?

Furthermore, how about the RF frontend architecture for tri-band (including UMTS) or quad-band systems (GSM, UMTS, GPS, WLAN....)?

Any good books and articles related to this topics will be appreciated
Thanks.

Only one band works at one time.