Back to the Modifications & News document
Implementation of Vienna Agreement 1993 method in ICS Telecom software The propagation model defined in Vienna Agreement 1993 (VA’93) is based on two different models: - Deygout geometrical model, initial version with two obstacles (1966); - the statistical model from recommendation ITU-R ITU- R P.370. P.3 70. There exists an algorithmic and software (in Fortran) implementation of Vienna Agreement called harmonized calculation method (HCM). This model was updated in Mainz February 1998 by the Technical Working Group HCM. Since we are in the transient period of Vienna Agreement, the HCM may be modified or completed again in the future. Actually, HCM offers two sub models: a statistical model derived from 370 curves adapted to prediction for mobiles and a mixed Deygout/370 model. The later actually reveals formal and intrinsic instabilities that are described in a ATDI report aimed at providing a French contribution to HCM and also a proposing a method for substitution. Here, we offer a DLL implementation for ICS Telecom, including including unstable unstable Deygout/370 component as well as the latest modifications adopted in Mainz’98. (In a first stage, we provide the propagation model only. The interference management part of the method will be implemented later). In section 1, the 4 options of available models for VA’93 are presented. In section 2, the content of these models is precised, especially its differences with respect to HCM implementation. A large proportion of VA’93 calls functions quite similar to ITU-R P.370 ICS implementation. Besides, this prop propor orti tion on has has incre increase ased d with with Mainz Mainz’9 ’98 8 modi modifi ficat catio ion, n, that that integ integrat ratee some some of the the latest latest ITU-R P.370(-7) features. Thus, for further details about the latter, the reader is invited to read the corresponding ICS Telecom manual on this implementation.
1 User level The dialog box on VA’93 offers 4 possible model selections: 1 in fast mode mode and 3 in last point mode: mode: - the fast mode: fast mode: this mode is valid only for field- strength strength computation computation on profi profiles les and covera coverages ges sinc sincee fiel field-st d-stre reng ngth th on ever every y poin pointt betw between een the the trans transmi mitte tterr and the receiver has to be computed. This mode allows to save computation time since each field-strength computation at the current point provides precomputed elements for the next point; - the last point mode: this mode is always valid. It requires no precomputed values on previous point of the profiles and, as a result, works more slowly than the fast mode. Somehow, it can be usefully selected for computations on restricted areas such as polygonal zones (e.g. (e.g. zones zones excluding the transmitter). Three models are available: - HCM: Deygout 66 –> rec re c 370 37 0 model: it is the default VA ’93 model. It is based based on Deyg Deygou outt 66 mode modell comp comput utati ation on and and switch switches es to 370 370 if the the numb number er of obstacle is above or equal to 3; - HCM: ITU-R P.370 in the fast the fast or or last point modes; modes; - Deygout 1966 (this model model is not offered by HCM in a isolated way). way).
Back to the References Manual
Back to the Modifications & News document
The right window of the dialog box, called Interference mode selection, merely forces Rx antenna height and time variability according to selected specification rules. Time value is automatically pointed out by radio buttons and the Rx antenna height is displayed (noc, no change, leaves current Rx antenna height unchanged). From now on, the statement of the parameters selected in the dialog box is saved for the next call.
2 Practice level Comments on model implementation: - Isolated Deygout 66 model is namely the model defined by Deygout (bared model), without clutter altitude correction (+10 m) required and implemented in Deygout 66 –> Rec. 370-7 for VA ’93; - models 370 fast et last point are almost the same as ICS Telecom implementation ITU-R P.370-7 (see below for differences); - Deygout 66 –> rec. 370 is directly implemented from HCM flow charts. Somehow, since it directly derives from 370-7 version (1995), it implies a few differences: 1. Existence of 5% time variability curves in addition to 1%, 10% and 50% curves in HCM; 2. The possibility to manage clutter height influence is offered in the lower field of the dialog box: either the standard (+10m) clutter height, either the height defined by the user in the ground occupancy option box of ICS Telecom, or none.
Back to the References Manual
Back to the Modifications & News document
3. Ground irregularity management: within HCM sum of k ∆h and of Rx clearance angle gain, within 370-7 ICS Telecom, choice between k ∆h or clearance angle gain. On the contrary, within HCM, implementation of rec. 370 is itself modified on a few points: 1. Effective antenna height computation on the interval [1;15] km instead of [3;15] km; 2. If h2 >10 m, the following correction is adopted. h1 is replaced by h1 ’=h1 *h2 /10, which is the correction adopted in the annex 5 of VA’93. In replacement of this correction, a more complex set of corrections was proposed by the technical working group (HCM) in Mainz (Feb. 98, Rev.3 p10) but the proposed solution enables field strength discontinuities and is thus formally rejected by ATDI (cf . the abovementioned report). If h2 =3 m (mobiles) and f > 400 MHz, an additional attenuation term is introduced: 10 dB below 50 km, 3 dB above 100 km and a linear interpolation in [50;100] km. If h2 =3 m (mobiles) and the f < 400 MHz, the attenuation term becomes: 8 dB below 50 km, 5 dB above 100 km and a linear interpolation in [50;100] km. 3. Additional loss of 2 dB for frequencies between 862 and 1700 MHz; 4. Additional loss of 9 dB for frequencies above 1700 MHz; 5. For distances below 10 km (where rec. 370 is undefined), the curve is extrapolated with the log-linear method defined in Annex 5 of VA’93. Somehow, if the option clearance angle is on, one must beware that the clearance angle correction is also integrated. The model performs first Deygout 66 model computations and then possibly switches to 370. This computation implies out to 2.5 profile complete sweeps between Tx and Rx (1 sweep to search for the primary obstacle, if this exists, 1 sweep to search for the secondary obstacle(s) and possibly, if the latter exist(s), half a sweep on average to look for a third obstacle). As a result, the method runs much more slowly than 370-7, which requires a sweep on the sole 16 km before the Rx antenna. It is also important to notice that the altitude correction (+10m), aimed at simulating an average ground occupancy, is not included on the first and the last kilometres of the profile. For short antenna heights, this may yield artificial obstacles 1 km away from the Tx and 1 km away from the Rx. Lastly, let us mention that profile computations are performed with the “natural” step of the digital elevation model included in ICS Telecom and not with the fixed (100m) step proposed in HCM.
Back to the References Manual
