SCP: Verification of Simulation Software

In 1996, a Group of Experts was created with the aim of developing a Standard Computation Program (SCP) to determine whether a non-GSO Mobile Satellite Service (MSS) system would need to coordinate with existing Fixed Service (FS) systems.

The Group of Experts produced an information document for the February 96 meeting of ITU-R Working Party 8D, which was copied in a liaison statement to ITU-R WP 9D (meeting at the same time). It was clear that both groups had interests in the development of the SCP and on May 1st 1996 a Joint Rapporteurs Group (JRG 8D/9D) was set up to develop, among other things, the SCP methodology.

The need to develop an SCP was a consequence of the filings of many non-GSO MSS systems in the 1 – 3 GHz bands. Detailed coordination between each MSS systems and all potentially affect FS systems would be an enormous task, and some pre-coordination filter was needed.

In anticipation that some simulation would be needed, MSS organisations had been producing simulation software for some time.

By this time Visualyse Professional was also well enough developed to be useful for coordination and a candidate implementation of the SCP. In fact Visualyse Professional was already the industry’s leading interference analysis product, and was able to model accurately the MSS systems under consideration.

The development of Visualyse Professional and the efforts of some MSS operators in developing their own software meant there was enough experience available to allow the JRG to move ahead quickly with its work. Transfinite Systems staff had been involved in the development of methodologies for this kind of simulation since 1992 and were key members of the JRG software experts group.

Other than SCP, the JRG also addressed detailed coordination issues and in October 1997 ITU-R Recommendation M.1319 was approved. Visualyse Professional was specified in the JRG Chairman’s report as an acceptable implementation of Rec. M.1319 in the context of Resolution 716.

The task of defining the SCP methodology proved to be quite difficult. The point about the SCP is that it defines a "coordination trigger". If a non-GSO MSS system does not pass the tests set in the SCP then further detailed coordination under Rec. M.1319 is needed. The two competing parties in the JRG wanted different emphasis in the SCP, for obvious reasons, i.e. the FS operator wants to be certain that the worst case assumptions are used so that no systems which could cause interference can pass the SCP tests. On the other hand the MSS operator does not want to trigger every possible case, and thereby increase the coordination effort needed many times.

The Recommendation that captures the SCP methodology (ITU-R Rec. M.1143) was also approved in October 1997. Visualyse Professional was adapted to take account of this Recommendation and subsequently submitted to the ITU-R for accreditation, in response to an ITU circular letter (CR70), requesting software from all administrations.

The validation and verification process continued in JRG 8D/9D. Visualyse Professional was run for several test cases and the results compared to results from other programs. Results obtained were in close agreement, leading the chairman to conclude:

- Simulation results from independent SCP computer programmes [Visualyse, ICO SCP] provide very closely aligned results;

and

- the description of the methodology described in Rec. ITU-R M.1143-1 is sufficient at this stage and that no further revisions are required;

So the methodology has been defined and, Visualyse Professional has been shown to be compliant and in agreement with other simulations. Visualyse Professional is the only commercially available package that has been tested against Recs. M.1143 and M.1319 in this way.