Overhead is kept small by a scalable control channel design suitable for OFDMA-based systems with many resource elements and many active users. For instance, optimization of control information in a wideband OFDMA-based radio system with up to 200 resource elements and multiple spatial layers and up to 1000 active users is possible. In contrast to existing approaches in LTE and WINNER, optimized flexible-length downlink control information is shown, which reduces overhead by a combination of slow and fast control signalling, of broadcast and multicast signalling, as well as of individual and table-based allocation information.