The log-distance path loss model is a radio propagation model that predicts the path loss a signal encounters inside a building or densely populated areas over distance.
Log-distance path loss model is formally expressed as:
P L = P T x d B m − P R x d B m = P L 0 + 10 γ log 10 d d 0 + X g , where
P L is the total path loss measured in Decibel (dB)
P T x d B m = 10 log 10 P T x 1 m W is the transmitted power in dBm, where
P T x is the transmitted power in watt.
P R x d B m = 10 log 10 P R x 1 m W is the received power in dBm, where
P R x is the received power in watt.
P L 0 is the path loss at the reference distance
d0. Unit: Decibel (dB)
d is the length of the path.
d 0 is the reference distance, usually 1 km (or 1 mile).
γ is the path loss exponent.
X g is a normal (or Gaussian) random variable with zero
mean, reflecting the attenuation (in decibel) caused by flat fading. In case of no fading, this variable is 0. In case of only shadow fading or slow fading, this random variable may have Gaussian distribution with
σ standard deviation in dB, resulting in
log-normal distribution of the received power in Watt. In case of only fast fading caused by
multipath propagation, the corresponding gain in Watts
F g = 10 − X g 10 may be modelled as a random variable with
Rayleigh distribution or Ricean distribution.
This corresponds to the following non-logarithmic gain model:
P R x P T x = c 0 F g d γ where
c 0 = d 0 γ 10 − L 0 10 is the average multiplicative gain at the reference distance d 0 from the transmitter. This gain depends on factors such as carrier frequency, antenna heights and antenna gain, for example due to directional antennas; and
F g = 10 − X g 10 is a stochastic process that reflects flat fading. In case of only slow fading (shadowing), it may have log-normal distribution with parameter σ dB. In case of only fast fading due to multipath propagation, its amplitude may have Rayleigh distribution or Ricean distribution.
Empirical measurements of coefficients γ and σ in dB have shown the following values for a number of indoor wave propagation cases.
