Micro-Cellular Path Loss
Microcellular networks use a cell size of, say, 200 to 2,000 meters.
Propagation models for micro-cellular communication typically model the path loss law as a transition from free-space propagation to groun wave propagation if
d < d_{g}
where theoretically the turnover distance d_{g}
occurs at
d_{g} < 4h_{R} h_{T} / l, where d is the distance of the radio link under study, h_{R }
and h_{T} are the heights of the receiving and transmitting antenna respectively, and
l
is the wavelength of the transmitted wave.
Various models have been proposed, e.g. a step-wise transition from "20 log d" to "40 log d" at a certain (turnover) distance.
- Harley suggested a smooth transition, with
where r is a normalized distance, with r = d / R, with d the propagation distance in meters and R the cell size
in meters. Similarly
r_{g} = d_{g} / R
is the normalized turnover distance, and
is the local-mean power (i.e., received power averaged over a few meters to remove to effect of multipath fades). Studies indicate that actual turnover distances are
on the order of 800 meters around 2 GHz.
- Other models, such as a stepwise transition, have been proposed. Empirical values for the path loss exponents and their intervals of validity
have been reported in many papers.
A smooth transition is often considered in theoretical system studies.
Multipath in Micro-Cells
The micro-cellular propagation channel typically is Rician fading: it contains a dominant direct component, with an amplitude determined by path loss, a set of early reflected waves adding (possibly
destructively) with the dominant wave, and intersymbol interference caused by the excessively delayed waves, adding incoherently with the dominant wave.