Multipath Propagation
Multipath propagation is when the same signal reaches the receiver not only over the direct path but also reflected off the ground, walls, roof and metal surfaces, arriving with different delays. It is unavoidable in metal-heavy industrial environments. Depending on their phase, the arriving components can either reinforce or cancel each other; the result is an irregular signal map that varies with position.
Because the reflected component travels a longer path than the direct component, it arrives late and phase-shifted. If the phase difference is close to zero the total signal increases, if it is close to 180 degrees the two components cancel each other.
- Position sensitivity: moving by something of the order of half a wavelength can reverse the situation. At 433 MHz that means about 35 cm, at 2.45 GHz about 6 cm.
- Metal environments are the hardest: container yards, steel-structure workshops and ship decks are strong reflectors.
- Delay spread causes symbol interference at high data rates; since data rates in remote controls are low, the real problem is fading.
In practice this means that trying a single spot is not enough when positioning the receiver antenna. Shifting it 20–30 cm on the same enclosure can noticeably change the signal level; several positions should be tried during installation and the most stable one chosen.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety