PDF of this tutorialAt the hub site, which typically serves up to 20,000 homes, broadcast video signals are received over 1550-nm transmission, converted to RF, and then released at 1310 nm. The 1310 transmitters contain two RF inputs, a common, or broadcast port, and a unique or narrowcast port. In this manner, local video, advertising, and any interactive services, such as data and voice, can be inserted.
Power ranges such as 1012 dBm, as shown on the left in Figure 8, target about 2,000 homes, assuming 500 home nodes. On the right, lower-power 4-dBm or 6-dBm transmitters take the narrowcasting down to 500 homes, with a 20-percent to 30-percent cost premium on the transmitters. Each transmitter carries both broadcast and narrowcast or interactive information.
Figure 8. Power Ranges
High-power 1550 technology is used to carry only the broadcast information. As indicated in Figure 9, a 22-dBm ytterbium erbium-doped fiber amplifier (YEDFA) can hit 64 nodes or 32,000 subscribers, yielding a significantly lower broadcast cost. For the narrowcast information, a low-cost 1310 transmitter, optimized for carrying only QAM channels, is used. The two wavelengths are then optically combined for delivery to the node.
Figure 9. YEDFA Technology
Aside from lowering the cost of deployment, this architecture logically separates the two types of information, allowing each to evolve independently. The narrowcast path now also becomes optional, only being deployed when and if required. This architecture, although just beginning to be deployed by the major multiple service operators (MSOs), is almost universally used by new network operators in the United States, as well as new builds in countries such as Spain, Italy, and China. This combination of low broadcast cost and zero narrowcast cost is what drives the feasibility of the integrated FITL network shown earlier.
