15.9 LOOKING AHEAD

The chapters leading up to this point have examined communication systems operating over a wide variety of transmission media, together with the networking and internetworking technologies that allow information to be exchanged between computers around the world. Throughout these discussions, however, the communication infrastructure has generally been assumed to be fixed.

Modern communication increasingly depends upon mobility. Smartphones, tablets, connected vehicles, wearable devices, and billions of IoT sensors communicate while moving between locations or operating without fixed physical connections.

Supporting mobile users introduces new challenges. Radio links replace fixed wired connections, signal strength varies with distance and the surrounding environment, and users move continuously between areas served by different base stations. Communication systems must therefore maintain reliable connections while making efficient use of the limited radio spectrum.