What is free space propagation model?
34. What is free space propagation model?
The free space propagation model, also known as the free space path loss model, is a simple and fundamental wireless communication model used to estimate the attenuation or signal loss that occurs as an electromagnetic wave propagates through free space (i.e., in the absence of obstacles or reflecting surfaces). It provides a basic understanding of how the signal strength decreases with distance in unobstructed environments and serves as a starting point for more complex channel modeling.
What is free space propagation model |
The free space propagation model is based on the inverse square law, which states that the power density of an electromagnetic wave decreases with the square of the distance from the transmitter. Mathematically, the free space path loss (FSPL) can be expressed as:
FSPL (in decibels) = 20 * log10( d / d0 )
where:
d is the distance between the transmitter and receiver in meters.
d0 is the reference distance, typically set to 1 meter.
log10 is the base-10 logarithm.
The factor of 20 is used to convert the loss to decibels.
The FSPL model assumes the following characteristics:
1. Line-of-Sight (LOS) Propagation: It assumes a direct, unobstructed line-of-sight path between the transmitter and receiver. In practical scenarios, this may not always be the case, especially in urban environments with buildings, trees, and other obstacles that cause diffraction, reflection, and scattering of the signal.
2. Isotropic Radiators: The model assumes ideal isotropic antennas at both the transmitter and receiver. Isotropic antennas radiate power uniformly in all directions, which is an idealized assumption since real-world antennas have directional patterns.
3. No Environmental Effects: The model does not consider factors such as terrain, atmospheric conditions, and interference from other sources, which can affect the actual propagation of the signal.
While the free space propagation model provides a basic estimate of signal loss, it is important to note that real-world wireless channels are much more complex and dynamic, especially in urban and indoor environments. For accurate channel characterization and performance analysis, more sophisticated channel models that consider fading, multi path, and other environmental factors are used. Nonetheless, the free space model remains useful as a reference and benchmark for understanding the basic behavior of wireless signals in open space scenarios.