Communication Links and Multiplexing

A source produces information and an input transducer converts a physical signal, such as sound, to an electrical one. Encoding or modulation prepares it for a transmitter and channel. A receiver detects the transmitted signal, then demodulation or decoding and an output transducer reconstruct the message.

Noise can enter the channel or electronics. Amplification boosts noise as well as signal; digital regeneration can restore bit levels when errors remain within a decision margin. A block diagram should identify what each stage does, rather than list components without their roles.

Metal wires are convenient and inexpensive over short distances but suffer resistance, interference and limited high-frequency performance. Optical fibre offers high data rates, low attenuation and immunity to electrical pickup, but needs optical conversion and precise installation. A guided fibre is harder to intercept casually than a broadcast radio signal, although it is not automatically secure.

Radio and microwaves allow wireless coverage. Long wavelengths diffract around obstacles and the Earth’s surface more effectively. Some radio bands support sky-wave paths through ionospheric refraction back towards Earth, often described as reflection. Microwaves are more directional and usually need line of sight; satellite links commonly use gigahertz frequencies, with 6 GHz uplink and 4 GHz downlink as one illustrative pairing. Separate uplink and downlink frequencies help prevent a strong transmitter de-sensitising its receiver.

Time-division multiplexing allocates recurring slots to separate data streams. A multiplexer interleaves their samples or bits into a frame and the receiver demultiplexes using matching timing. Channels retain their individual sample rates only if the combined link carries all their data fast enough.

The combined raw rate is the sum of component rates, with extra capacity for synchronisation and other overhead. A “real time” link must keep up with incoming information without an ever-growing delay. Compare available bandwidth as well as monetary cost, range and exposure to interception.

Try each problem before opening the worked solution. State the physical model, show substitutions with consistent units, and explain what your answer means.