There are three other possible network configurations of mobile broadband communication systems that seem to be better suited for the distribution of linear broadcast services:
• Standalone downlink only (“SDO”),
• Supplemental downlink (“SDL”), and
• Time division duplex (“TDD”).
The difference between SDO and SDL is that SDL is associated with uplink spectrum in another band, allowing user data to be passed back to the network (and content provider), whereas SDO operation is very similar to traditional terrestrial broadcasting.
There are relatively few bands in which SDL has been standardised to date, or in which there is the possibility of standardisation in the near future. Note that recent changes have been made to 3GPP standards that allow SDO (receive only, SIM free) use. However, at the time of writing, there are no bands standardised by 3GPP for SDO use.