A.17.7.4 ITU-R P.1536-6

This propagation model is fully described in Recommendation ITU-R P.1546-6. Only land terrain profiles are implemented in SEAMCAT. The ranges of application are the same as for the ITU-R P.1546-4 and ITU-R P.1546-5, save for the frequency range that in this model is extended to as high as 4 GHz.
In the section about Algorithm description, only the parts of Recommendation ITU-R P.1546-6 that are different from Recommendation ITU-R P.1546-4 and ITU-R P.1546-5 are listed.

It must be emphasised that the measurements and modelling in this Recommendation intrinsically include the effect of terminal clutter, so it would be inappropriate to add a calculation of clutter separately.

Input parameters

SEAMCAT Interface to the ITU-R P.1546-6 propagation model

Table: ITU-R P.1546-6 propagation model

Algorithm

Effect of clutter shielding Transmitting/base antenna
If the transmitting/base antenna is over or adjacent to land on which there is clutter, the correction given in Annex 5, § 10 of Recommendation ITU-R P.1546-5 should be applied, irrespective of the transmitting/base antenna height above ground. This correction does not apply for an open/uncluttered transmitter. The correction should be used in all other cases, including when the antenna is above the clutter height. The correction is zero when the terminal is higher than a frequency-dependent clearance height above the clutter.
Correction =                 dB(Eq. 1a)
where is given by equation (12a) or (12b),
and:
 for R₁ >= h_a   (Eq. 1b)
  otherwise  (Eq. 1c)
h_dif1 =  m (Eq. 1d)
 degrees (Eq. 1e)
= (Eq. 1f)
f: frequency (MHz).
And R₁ is the height of clutter, m above ground level, in the vicinity of the transmitting/base terminal.

Location variability in land area-coverage prediction
Area-coverage prediction methods are intended to provide the statistics of reception conditions over a given area, rather than at any specific point. The interpretation of such statistics will depend on the size of the area considered.
When one terminal of a radio path is stationary, and the other terminal is moved, basic transmission loss will vary continuously with location, according to the totality of influences affecting it. It is convenient to classify these influences into three main categories:

• Multipath variations: Signal variations will occur over scales of the order of a wavelength due to phasor addition of multipath effects, e.g. reflections from the ground, buildings, etc. The statistics of these variations are typically found to follow the Rayleigh distribution. The impact of these effects will vary with systems, being dependent on bandwidth, modulation and coding scheme. Guidance on the modelling of these effects is given in Recommendation ITUR P.1406.
• Path variations: Signal variations will also occur due to changes in the geometry of the entire propagation path e.g. the presence of hills, etc. For all except very short paths, the scale of these variations will be significantly larger than that for local ground cover variations.
• Local ground cover variations: Signal variations will occur due to obstruction by ground cover in the local vicinity, e.g. buildings, trees, etc., over scales of the order of the sizes of such objects. The scale of these variations will normally be significantly larger than that for multipath variations.

In Recommendation ITU-R P.1546-6, and generally, location variability refers to the spatial statistics of local ground cover variations. This is a useful result over scales substantially larger than the ground cover variations, and over which path variations are insignificant. As location variability is defined to exclude multipath variations, it is not dependent on system bandwidth. This definition will be appropriate when applying Annex 5, §  3.1.1 in the implementation of this of Recommendation ITU-R P.1546-6.

A second definition relates to the variability of field strength over a small area, typically represented by a square with a side of 50 m to 1 km, this definition is appropriate when using terrain information in the calculation of h1, as described in Annex 5, § 3.1.2 of Recommendation ITU-R P.1546-6.
Extensive data analysis suggests that the distribution of local mean field strength due to ground cover variations is approximately lognormal.

Thus, for a land receiving/mobile antenna location the field strength, E, which will be exceeded for q% of locations is given by:

                   dB(uV/m) (Eq. 2)

where:
 :inverse complementary cumulative normal distribution as a function of probability
σL:standard deviation of the Gaussian distribution of the local means in the study area.

An approximation to function  is given in § 16 of Recommendation ITU-R P.1546-6.

Values of standard deviation are dependent on the prediction resolution and frequency, and empirical studies have shown a spread. In the case where terrain data is being used and the variation over a small area is required representative values of σL are given by Equation (34). The representative values relate to the 50^th percentile of the cumulative distributions of measured standard deviation of location variability.

            dB(Eq. 3)

where:
f: required frequency (MHz)
wa: prediction resolution (m).

The prediction resolution is the width of the square area over which the variability applies.

When using this Recommendation without terrain information the variation across the service area might be a more appropriate measure of σL. In this case no dependency on frequency is found however the environment type will impact the standard deviation of location variability values. Representative values of σL are 8, 10 and 12 dB for urban, suburban and open areas respectively.
Percentage location q can vary between 1 and 99. This Recommendation is not valid for percentage locations less than 1% or greater than 99%. The values given in Table 2 have been found appropriate for the planning of digital terrestrial television (DTT) services, this was found to be equivalent to the 93^rd percentile of the measurement CDF for rooftop height antenna for a 100 × 100 m area.

Table 2: Values of variability used in certain planning situations

Correction for receiving/mobile antenna height
The field-strength values given by the land curves and associated tabulations in Recommendation ITU-R P.1546-6 are for a reference receiving/mobile antenna at a height equal to the greater of the representative clutter height around receiving/mobile antenna R₂ and 10 m.
Examples of reference heights are 15 m for an urban area, 20 m for a dense urban area and 10 m for a suburban area. For sea paths, the notional value of R₂ is 10 m.