References:
- “The wireless channel.” Available: https://web.stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter2.pdf
- D. Tse and P. Viswanath, Fundamentals of Wireless Communication, 1st ed. Cambridge University Press, 2005. doi: 10.1017/CBO9780511807213.
- A. Goldsmith, “Wireless Communications.” Chapters 1-9, Feb. 18, 2020. [Online]. Available: https://web.stanford.edu/class/ee359/doc/WirelessComm_Chp1-9_Feb182020.pdf
- Youtube.com, 2026. https://www.youtube.com/watch?v=6LmSnL3mJ8M (accessed Jan. 30, 2026).
- T. S. Rappaport, Wireless communications: principles and practice, 2. ed., 18. printing. in Prentice Hall communications engineering and emerging technologies series. Upper Saddle River, NJ: Prentice Hall, 2009.
What is wireless channel?
In wireless communication, a wireless channel refers to the physical medium, the air or space, through which electromagnetic signals travel from a transmitter to a receiver.
Unlike a wired connection (like fiber optics or Ethernet cables) where the signal is contained within a physical “pipe,” a wireless channel is open and unpredictable. The signal interacts with the environment, leading to various distortions that engineers must account for.
Key Characteristics of a Wireless Channel
To understand how a wireless channel behaves, it helps to look at the primary phenomena that affect the signal:
1. Path Loss
As a signal travels away from the transmitter, its power decreases. This is similar to how a voice sounds quieter the further away you stand. In a vacuum, this follows the Inverse Square Law, but in the real world, it’s affected by terrain and atmosphere.
2. Shadowing
This occurs when a large obstruction (like a building or a hill) stands between the transmitter and receiver. It creates a “shadow” zone where the signal strength significantly drops.
3. Multipath Fading
This is perhaps the most complex aspect of a wireless channel. A signal doesn’t just travel in a straight line; it reflects off buildings, refracts through glass, and scatters off small objects.
- Constructive Interference: When reflected signals arrive in phase and strengthen the original signal.
- Destructive Interference: When signals arrive out of phase and cancel each other out, leading to “dead zones.”
4. Interference and Noise
- Interference: Signals from other devices using the same frequency (e.g., your microwave interfering with your Wi-Fi).
- Thermal Noise: Background “hiss” generated by the electronics in the receiver itself.
Mathematical Representation
In digital communications, the relationship between the transmitted signal x and the received signal y is often modeled by the following linear equation:
$y=hx+n$
Where:
- $y$: Received signal.
- $h$: Channel Coefficient (representing the fading and phase shift).
- $x$: Transmitted signal.
- $n$: Additive White Gaussian Noise (AWGN).