ITU-R REPORT BS.945-2 PDF

Introduction

The usable field strength, E_u, is defined in Recommendation 638 and maybe used as a criterion for the interference situation in a given channel and in a given area. It takes account, in principle, of natural and man·made noise as well as of the combined effect of the entirety of interfering transmitters. If the usable field strength is large, the influence of the interfering transmitters is also large, whereas this influence is small if the usable field strength is small.

The usable field strength is independent of the characteristics of the wanted transmitter and does not normally exhibit large variations with location. It can be determined for any location of interest. For international planning purposes, it may be convenient to calculate the usable field strength at the site of the wanted transmitter. As a first approximation, this value may be considered to be representative of the situation in the whole coverage area.

For the calculation of these interferences basically two categories of methods are in use:

— statistical methods;

— non-statistical methods.

Normally use is made either of the 'simplified multiplication method' as an example of a statistical method or of the non-statistical 'power-sum method'. Experience has also been gained in the successful use of the statistical 'log-normal method' [Kubrakov et al., 1985].

These three methods are described and indications are given for their efficient use.

The simplified multiplication method and the log-normal method incorporate the effects of location variability on the assumption that they follow a Gaussian law and are intended for use at VHF and higher frequencies. The power-sum method applies for point-to-point reception and must be applied successively with different receiver locations in coverage studies.

Details for the use of the simplified multiplication method and its physical bases are to be found in Annex I and in [O'Leary and Rutkowski, 1982), while similar information on the log-normal method is contained in Annex II and in [Bobkova and Pavliouk, 1987].