Path loss, interference, and multipath propagation all degrade a radio signal, leaving the receiver with a blurred, indistinct waveform.

* Three impairments — weaker, busier, echoey — blur the received signal. *

On a cable, data transmission is comparatively easy — the signal stays confined to the wire. Over the air, three effects work against you:

1. Path loss (Pfadverlust):

• The radio signal gets weaker the farther it travels through matter (air, walls, rain, your body)
• This is why distant phones need more transmit power and why cells have a finite radius

2. Interference (Interferenz):

• Other sources share the same frequencies — e.g., the 2.4 GHz band is used by Wi-Fi, Bluetooth, cordless phones, and even microwave ovens
• Electrical devices (motors) also emit noise that corrupts the signal

3. Multipath propagation (Mehrwegausbreitung):

• The signal reflects off buildings, the ground, and objects, so multiple copies reach the antenna at slightly different times
• These delayed copies add up constructively or destructively, smearing the symbols together (this is what causes frequency-selective fading)

The result: a blurred, indistinct signal — fuzziness at reception. Everything else in this topic (error correction, adaptive modulation, frequency hopping, power control) exists to fight one or more of these three problems.

Tip: Remember the trio as "weaker, busier, echoey" — path loss makes it weaker, interference makes the band busier, multipath adds echoes.

Go deeper:

• Multipath propagation (Wikipedia) — how reflected copies arriving at different times cause fading and smear symbols together.
• Path loss (Wikipedia) — why signal power density drops with distance and what governs the rate of decay.