Satellite Coordination Calculation & Software (http://www.satcom.co.uk/article.asp?article=19)

Introduction
The pages which follow are the slides of a lecture presented by Mark C J Posen of RPC Telecommunications Ltd.

The slides were created using Microsoft PowerPoint and converted to HTML. During conversion the slides were combined into 7 sections.

You can navigate between these sections at will from the left hand side. However, bear in mind that for the slides to make the most sense, it is suggested that you read through them in order.

Please note that this presentation contains the lecturers notes, and so in some places are not complete. If you have any questions regarding these lectures please contact the author here.

Coordination Tasks
What do we need to be able to do for successful coordination?

Link and interference analysis:

  • Link budget / C/N analysis
  • Interference analysis
  • Margin analysis
  • Proposing technical solutions

Data gathering and processing:

  • Collecting information about other networks
  • Understanding regulatory issues
  • Analysing transmission parameters to support technical analysis
Software Tools
Software tools can assist with all these tasks:
  • Data searching, manipulation and analysis
  • Pre-calculation dataset preparation
  • Calculation and technical analysis

Software is available from a number of sources, but the main "software" needed to do successful coordination is in your own brain! 

So we will look at some manual analysis before we review software tools.
Link & Interference Analysis
Link budget refresher:
  • Received Carrier Power:
    Pr = Pt + Gt – Lp + Gr (dBW)
  • Received Noise Power:
    Pn = 10 log (k T B) (dBW)
  • Carrier to Noise Ratio:
    C/N = Pt – Pn
    = Pt + Gt – Lp + Gr – 10 log (T) - 10 log (B) – 10 log (k) (dB)

Carrier to Interference refresher:

  • Received Wanted Carrier Power:
    Pw = Pt + Gt (θ) – Lp + Gr (φ) (dBW)
  • Received Interfering Carrier Power
    Pi = P’t + G’t(θ’) – L’p + Gr(φ’) (dBW)
  • So carrier to interference ratio:
    C/I = Pw – Pi
    = [Pt + Gt (θ) – Lp + Gr (φ)] – [P’t + G’t(θ’) – L’p + Gr(φ’)]

Normally simplify by assuming that Lp = L’p.
Note that the Gr terms both refer to the same antenna (the receiving system gain).

Define receive antenna discrimination, Dr = Gr (φ) - Gr (φ’), typically –3 or –4 dB for a satellite receive antenna, generally much higher, say +20 to +40 dB for an earth station receive antenna.

So simplify terms:
C/I = Pt + Gt (θ) + Dr – P’t – G’t(θ’) (dB)

This is a very simple equation; satellite to satellite coordination is not technically difficult to analyse!

Some additional complications to bear in mind:

  • Pt and P’t can be power spectral densities (dBW/Hz) or powers (dBW).
  • If Pt and P’t are densities then strictly you have calculated Co/Io not C/I (Co/Io ~ C/I for digital carriers).
  • If Pt and P’t are powers then they may have different bandwidths - normalise C/I inside the bandwidth of the wanted carrier.
Protection Ratio Analysis
Protection ratio is the minimum acceptable single entry C/I for a wanted carrier. 

This is defined by ITU-R Recommendations. Recommendation ITU-R S.741 summarises the protection ratios for different wanted carrier types. Protection ratios are generally defined in terms of an "allowable" interference level as a proportion of the thermal noise in a link.

Examples for different wanted carrier types:

Digital carrier

  • 6% of thermal noise
  • PR = C/N + 12.2 dB

FM/TV carrier

  • 4% of thermal noise
  • PR = C/N + 14 dB

FDM/FM (multiplexed telephony) carrier

  • 800 pW0p in 7500 pW0p noise budget, i.e. 10.67% of thermal noise
  • PR = C/N + 9.7 dB
Databases, Data Gathering & Processing
Coordination analysis needs information on "wanted" and "interfering" satellite networks.

Some regulatory information:

  • ITU status of network
  • ITU "findings" for specific assignments
  • ITU "priority" (date of protection) for assignments

Detailed technical information:

  • Satellite beam parameters (gain, footprint, service area, noise temperature)
  • Earth station parameters (gain, sidelobe, noise temperature)
  • Transmission parameters (carrier type, modulation, max and min power and power density)

The ITU maintains a comprehensive database of all networks (satellite and terrestrial) undergoing coordination and those that have completed coordination and are recorded as in use (Master International Frequency Register - MIFR). 

This database should be the source of all regulatory and technical data used for coordination. Most software tools use this database.
ITU Software Tools
The ITU is responsible for the publication and registration of satellite networks filed by administrations. 

To support this work the ITU produces a number of software tools available for download and/or purchase via the ITU’s web site (see here). 

Some of these are available to public users, others need ITU "TIES" password (limited).
ITU Space Radiocommunications Stations Database (SRS)
This database is a subset of the MIFR dealing with all space networks.

It is available online via the SNS online system, updated daily. It is also available on CD-ROM - SRS CD-ROM, published every six months. Also a weekly CD-ROM of new networks added to the database, called the International Frequency Information Circular (IFIC) is available.
ITU SNS Online
Access to the online data can be found here.

It gives access to:

  • Published networks (i.e. those with regulatory "status")
  • Pre-publication networks (i.e. those as yet without regulatory "status", for information)
  • Regulatory information - "Priority" date, regulatory findings, coordination requirements
  • Technical information -Network technical parameters for use in analyses
ITU SpaceQuery
SpaceQuery software offers similar functionality to the SNS Online system. It is a CD-ROM based database tool. It allows a user to query and extract information from the SRS database.
ITU GIMS
GIMS - "Graphical Information Management System".

This software allows access to and viewing of (as well as creation of new) satellite beam footprint diagrams. It can be used linked with SpaceQuery or in a stand-alone mode.

The API is published so can be integrated with your own software.
Other ITU Tools
ITU has a number of other tools:

Data management tools:

  • SpaceCap – Creates new network databases
  • SpacePub – Prints network databases in publication format

Data analysis tools:

  • APP29 – Article S8 analysis
  • MSPACE – Interference analysis (mainly for plans)
Proprietary Software Tools
A number of commercially available software tools are available to undertake various tasks:
RPC Software Tools
C/I Analysis Tool
  • Excel-based set of spreadsheets to calculate the carrier-to-interference ratio between the emissions of a pair of networks.
  • Is used for undertaking carrier-to-interference calculations as part of the preparatory work for and participation in coordination meetings.

Priority Analysis

  • Investigates the relative “priority” of the bands and beams in a set of ITU filings.

MSMI Analysis

  • Automatically prepares “Most Sensitive Most Interfering” carrier datasets for use in C/I analyses.

CSum Analysis

  • Provides a summary of a filing.

Transponder Analysis

  • Graphically displays frequency overlap between networks (transponder plans).

 

Conclusions
Calculating C/N and C/I quickly and accurately is a key requirement of successful coordination. 

There are several software tools exist to assist in this but the ability to make quick manual calculations is a useful skill. 

Also accurate data gathering and processing, using ITU software and other tools can ensure a successful coordination result.

Copyright 2002 Satcom Online (http://www.satcom.co.uk)
09/02/2010  00:28:00