.
.
As discussed above this is a form of interference that is created by the system designer. Frequency
bands can be placed closer together to increase the overall system capacity; however, greater in-band
distortion and performance degradation can occur if spectral regrowth is not properly addressed or
managed. Recall our earlier attention that spectral regrowth occurs when the transmitting signal
encounters a nonlinear, transmit power amplifier.
3.6 PROPAGATION PATH LOSS
In this section a comparison of methods used for predicting path loss is given. Here path loss is
defined as the difference between the received power and the transmitted power. The methods presented
herein are based on both empirical data and mathematical formulation [94, 95].
3.6.1 Free Space Path Loss
When the medium/environment between the transmitter and receiver has no obstructions, but simply
a direct line of sight, then the free space propagation model can be used to predict the received
signal power. Typically path loss models predict the received power decreases as the difference
between the transmit and receive distance is raised to a power. The free space path loss model is
defined as
(3.56)
where PRx predicted receive power, PTx transmit power, GTx gain of transmitting antenna,
GRx gain of receiving antenna,
carrier wavelength, d distance separation between the transmitter
and receiver.
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