Eli5: Why are fiber optic cables still used if we can use satellites for communication?

Question

Pardon my lack of knowledge about this.

In: 11

Answer 1

Some elaboration on why fiber has more bandwidth than satellite, and why it’s easier to increase bandwidth with fiber than copper.

Transfer of any data over a channel is bandwidth limited. For a satellite channel (or a broadcast tv or radio channel, or an analog telephone modem) the limit is based on the frequency of the carrier wave. For a simplified example, clap your hands about 1x/second. Consider that as sending a series of “1s” at the rate of 1Hz (one/second). Now skip a clap every once in a while – you’ve now demonstrated the ability to send 0s (no clap) and 1s. Increasing the frequency at which you do this increases the bandwidth. There’s a physical limit to every transmission mechanism for the maximum amount of data that can be encoded in a carrier wave.

For satellite communications the major limitation is that there are a limited number of Ku-band frequencies that are available for use by all commercial satellites – your data has to share bandwidth with everyone else in your region (where the satellite transmitter/receiver is pointing). No matter how fast it is there’s only so much data that can flow through the pipe.

Copper wires are point-to-point, so are less convenient than satellites in some ways, but copper wires are very fast – electrons move at decent fraction of the speed and with shielding to insulate wires from one another they can be bundled together. However shielding is expensive and as bandwidth needs have increased copper became less practical.

Fiber optic cables are also point-to-point. Unintuitively, light transmission through fiber optic cables is actually slower than electricity through copper, the bandwidth on any given strand of fiber is less than that of a copper wire. However because of how light reflects down a relatively straight strand of fiber the light in that strand stays within the strand, so there is zero interference between strands in a fiber optic cable bundle. That means you can get an incredible amount of bandwidth out of the many strands of fiber that make up a cable.

So when you hear people say that fiber has more bandwidth what they’re really saying is that a fiber cable, made up of many data transmission channels (1/strand) has more bandwidth than a less easily multiplexed copper or satellite transmission channel.