Multipath propagation

Multipath propagation occurs when a transmitted signal reaches a receiver along multiple paths created by reflection, diffraction, or scattering. The paths can differ in length, delay, phase, and strength.

Multipath fading: Variation in received signal strength caused by interference among multiple propagation paths. The paths combine constructively or destructively, making the received signal fluctuate.
Orthogonal frequency-division multiplexing: A transmission method that sends data over many mutually orthogonal subcarriers. Its long symbol duration and equalization help manage frequency-selective multipath.
Reflection (physics): The return of a wave from a boundary into the medium from which it came. Reflected waves commonly create distinct routes between a transmitter and receiver.
Line-of-sight propagation: Propagation in which a direct unobstructed path connects transmitter and receiver. A dominant direct path contrasts with environments where reflected and scattered paths govern reception.
Delay spread: A measure of the range of arrival times among significant components of a received signal. Different path lengths produce arrival-time differences that can smear transmitted symbols.
Rake receiver: A receiver that combines delayed signal components arriving along distinguishable paths. It can collect energy from resolvable paths rather than treating them only as interference.
Diffraction: The spreading and bending of waves around obstacles or through openings. Diffraction can deliver signal energy beyond obstacles along additional paths.
Free-space path loss: The decrease in signal power with distance in ideal unobstructed free-space propagation. It describes distance loss without the path interactions that produce multipath fading.
Coherence bandwidth: The frequency range over which a channel's response remains strongly correlated. Delay spread determines how wide a frequency band experiences similar multipath effects.
Diversity combining: A method for combining multiple independently faded signal observations to improve reliability. Separate antennas, frequencies, or paths can reduce the risk of a deep fade.

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