Basic transmission loss, or path loss (PL), is the signal attenuation between transmit (TX) and receive (RX) antennas due to the TX to RX separation and multipath (scattering). Basic transmission lossdetermines the range of a wireless link. Basic transmission loss is given by

where P_t is the transmitted power, P_r is the received power, G_t is the transmit antenna gain, and G_r is the receive antenna gain. An ideal free space (FS) path (no ground reflection, no multipath) has a path loss which is proportional to the square (n = 2) of the separation d

where l is the wavelength. This typically represents the minimum path loss and serves as a lower limit. Values of n on the order of 4 are more representative of realistic, cluttered environments. The figure below shows an example of measured path loss measured in a suburban environment (near to the ITS Boulder Labs location). The free space is shown for reference. Also shown is a least squares fit which yields an attenuation exponent of 4.9.

Measured path loss in a suburban environment.

(CLICK image to enlarge.)