The OFDM based terrestrial digital video broadcasting system (DVB-T) can be utilized for asymmetric Internet access with a downlink peak bit rate of 10-20Mbps. A narrow-band cellular communications system can be used as uplink. This paper is a comparison of centralized dynamic radio resource management schemes for this downlink packet radio system. Spectrum efficiency in bit/s/Hz/transmitter, and fairly shared spectrum efficiency in bit/s/Hz/transmitter, are evaluated for a best-effort traffic snapshot model. The Dynamic Packet Assignment (DPA) algorithm performs combined packet scheduling and rapid Dynamic Channel Allocation. Even better performance is achieved by the Dynamic Single Frequency Networks (DSFN) scheme. It exploits the macro-diversity capability of OFDM modulation. The base station transmitters are dynamically divided into groups that send the same information at the same channel frequency simultaneously.