s a second multiplexing scheme called TDM (Time Division Multiplexing). The introduction of TDM leads two reference architectures termed SH-A and SH-B: SH-A uses OFDM both on the satellite and the terrestrial link. SH-B uses TDM on the satellite link and OFDM for the terrestrial link. The system relies on a hybrid satellite/terrestrial infrastructure where the signals are broadcast to mobile terminals on two paths [23]: A direct path from a broadcast station to the terminals via the satellite. An indirect path from a broadcast station to terminals via terrestrial repeaters as shown in Figure 9.14. The higher frequency S-band is recommended for DVB-SH since UHF is preoccupied in many countries. S-band operates between 2-4 GHz whereas UHF is mainly operated between 400 or 700 MHz (in particular for mobile TV). Thus, DVB-SH will require better signal coverage which will require a dense repeater network. Additional repeaters will increase the cost of the network as compared to DVB- H networks. An advanced forward error correction called Turbo codes is used to enhance the signal robustness. DVB-SH uses a highly flexible channel interleaver that offers time diversity from about one hundred milliseconds to several seconds depending on the targeted service level and corresponding capabilities (essentially memory size) of terminal class. It requires stringent procedures to minimize time Direct-to-mobile DVB-SH satelite DVB-SH signal Content Distribution signal Service & DVB-SH Network broadcast Head-end head-end TDM/OFDM TR(b) personal gap fillers TR(c) transmitters TR(a) transmitters Broadcast Distribution Network Reception cell Figure 9.14 DVB-SH network architecture. Reproduced with permission from C 2009 DVB [22] Next Generation Mobile Communications Ecosystem delay SO the users' perception is maintained like a regular terrestrial network (particularly in the case of channel switching). Like DVB-H, DVB-SH doesn't define transport protocols, electronic service guide, higher layer functions, and SO on. It also relies on