A next-generation base station can update an uplink-downlink (UL/DL) configuration of a cell more frequently than legacy user equipments (UEs) are configured to recognize UL/DL updates while preventing non-compliant uplink transmissions in downlink subframes. For instance, a next-generation base station can restrict updates to the uplink-downlink configuration such that uplink timeslots previously allocated for random access channel (RACH) transmission opportunities by legacy UEs remain configured for uplink transmission. Alternatively, the next-generation base station can restrict the allocation of RACH transmission opportunities of legacy UEs to timeslots that are statically configured for uplink transmission. Notably, such a restriction may be selectively applied to legacy UEs, so as to not limit the performance of next-generation UEs.