As of March, 1997, we have had the OCAR operating for only a few weeks. However this has been enough to get a more accurate model of performance and utility. To measure an OCAR's performance, it is useful to have a figure of merit to measure it.

OCAR_range

An OCAR may be considered as distorting space so that from the consideration of propagation losses, all users are LOS. If one considers an OCAR as though it were a very large mirror, always situated in a way which allows every user to see each of the others, a single figure of merit may be used; "Distance at which operation is as though users were located at the OCAR" or "Distance at which the OCAR's gain overcomes the pathloss to it".

Without using the OCAR a user, U₁, located at the OCAR site would see:

ERPU₂-pathloss(F,OCAR_range)+RxAntU₁

from user, U₂, located at distance=OCAR_range. Through the OCAR, U₁ would see:

ERPU₂ - pathloss(F,OCAR_range) + OCAR_gain - pathloss(F,OCAR_range) + RxAntU₁

Where OCAR_Gain is the combined antenna/amplifier gain of the OCAR. Setting the two expressions equal and solving yields:

pathloss(F,OCAR_range)=OCAR_gain

and since pathloss = 37 + 20log(D) +20log(F), D in Miles and F in MHz,

OCAR_range = 10^{(OCAR_gain-37-20log(F))/20)} Miles

This distance actually is a contour with a shape which is determined by the product of the OCAR receive and transmit antenna patterns. It varies with azimuth (and/or elevation). A user located anywhere on this contour sees the same performance as he would if he were located at the OCAR location.

With this OCAR_range metric, expected performance can easily be calculated and operation verified. This is a very important to know when one is developing higher information capacity hardware and systems which need to operate properly and with small link margins.

Users not located on the contour each adjust their expectations by 20*log(D_u/OCAR_range), where D_u is the user's distance from the contour in his direction. Users closer to the OCAR will have better performance, those more distant, worse.