BANDWIDTH OF TRANSMISSION SYSTEM

Bandwidth of transmission system (or channel bandwidth) is the range of frequencies a particular communication channel must be allotted in order to carry a specified piece of information -- in other words, the actual spectrum assigned for use by that system, which is not always identical to the raw bandwidth of the signal being carried. The book's own worked comparison makes the distinction concrete: an amplitude-modulation system needs a channel bandwidth of about 10 kHz to transmit a 5 kHz baseband signal, because standard AM produces sidebands on both sides of the carrier, so the required channel bandwidth ends up being twice the signal frequency being carried. A single-sideband (SSB) system carrying that same 5 kHz signal, by contrast, needs a channel bandwidth of only 5 kHz, since it transmits only one of the two symmetric sidebands and suppresses the other, halving the spectrum consumed for the identical information. Because the electromagnetic spectrum available for communication is a shared, finite resource, engineers deliberately try to reduce the channel bandwidth each individual transmission needs, since a narrower channel bandwidth per transmission lets more independent channels …