Technical Annex

APPLICATION OF APPENDIX 8 AND COORDINATION ARCS

The following excerpt is taken from a paper presented at the BR Seminar in Mexico 2001. It provides details of how the approaches to coordination triggering are (or should be) applied by Administrations.

For any new or modified GSO network the need for coordination exists with other 'existing' GSO networks which have already initiated the coordination process. For collecting information about the existing GSO networks and their technical parameters required, Administrations may check the CD-ROM on SRS (Space Radiocommunication Stations) for:

• all 'existing' GSOs under status $\mathbf{C}$ (Coordination) or $\mathbf{N}$ (Notification) having overlap with the frequency bands for the incoming satellite network.
• details of orbital position; service area; earth station geo-coordinates; space station, earth station transmitting and receiving antenna gain characteristics; transmission gains; Noise temperatures ${\mathbf{T}}_{\mathrm{E}}$, and ${\mathbf{T}}_{\mathbf{S}}$ Precise frequency overlaps are established in either uplinks or downlinks.

Whether the process of coordination between the new and the "existing" GSO networks is necessary or not, may be determined by the following approach:

$\Delta \mathrm{T}/\mathrm{T}$ shall be calculated by treating the uplinks and downlinks of the wanted (or affected) satellite network, separately in accordance with the procedures mention in paragraphs 2.2.1.2 & 3.2 of Appendix 8.

The results can be categorised as follows:

• If the Value of $\Delta T_E/T_E$ or $\Delta T_S/T_S$ is greater than $6\%$ and the existing GSO network lies within the coordination arc, coordination with the incoming network is necessary.
• If the Value of $\Delta T_E/T_E$ or $\Delta T_S/T_S$ is greater than $6\%$ and the existing GSO network lies outside the coordination arc, the responsible administration for the existing network may request the BR for inclusion in the process of coordination with the incoming network.

The above approach works in those bands that have coordination arcs defined. For other bands, it is still, in theory, necessary to consider the frequency strapping information i.e. the way uplinks and downlinks are connected - and to look at the overall link performance. However, this is not considered necessary, and a separate comparison of the uplink and downlink DT/T to the 6% criterion is applied (see Section 2.2.1.2 for a discussion).

BASIC CALCULATIONS

This section describes the fundamental calculations that Visualyse GSO V3 performs when assessing whether coordination is needed between two networks.

The calculations are based on information taken from BR-IFIC and SRS databases, which is the method used to publish data submitted under Appendix 4 of the Radio Regulations.

$\Delta \mathrm{T}/\mathrm{T}$ Method

The basis of the $\Delta T/T$ method is that every radiocommunications link has inherent noise on it which can be expressed as a temperature value $(T)$. Think of the noise as caused by electrons moving around and as the temperature rises the electrons become increasingly energized. Therefore a higher noise temperature means more noise on the link.

In $\Delta T/T$ analysis, the interference is characterised by calculating the rise in the noise temperature of the link that the interfering signal causes $(\Delta T)$ and comparing this with the noise temperature of the link without interference. The method is equivalent to looking the ratio of $\mathrm{I}/\mathrm{N}$

The calculated value of $\Delta T/T$ is compared to a threshold criterion of $6\%$. Values above $6\%$ act as a trigger for detailed analysis.

The basic calculation method, taken from Appendix 8 of the Radio Regulations, is given below.

Let $A$ be a satellite link of network $R$ associated with satellite $S$ and $A^{\prime }$ be a satellite link of network $R^{\prime }$ associated with satellite $S^{\prime }$. The symbols relating to satellite link $A^{\prime }$ bear primes, those relating to satellite link $A$ do not bear primes.

The parameters are defined as follows:

$T_S$ the receiving system noise temperature of the space station, referred to the output of the receiving antenna of the satellite $(\mathrm{K})$

$T_E$ the receiving system noise temperature of the earth station, referred to the output of the receiving antenna of the Earth station (K)

$\Delta T_S$ apparent increase in the receiving system noise temperature of the satellite $S$, caused by an interfering emission, referred to the output of the receiving antenna of this satellite (K)

$\Delta T_E$ apparent increase in the receiving system noise temperature of the earth station $e_R$, caused by an interfering emission, referred to the output of the receiving antenna of this Earth station (K)

maximum power density per $\mathrm{Hz}$ delivered to the antenna of satellite $\mathrm{S}$ (averaged over the worst $4\mathrm{kHz}$ band for a carrier frequency below $15\mathrm{GHz}$ or over the worst $1\mathrm{MHz}$ band above $15\mathrm{GHz})(\mathrm{W}/\mathrm{Hz})$

$g_3(\eta )$ transmitting antenna gain of satellite $S$ in the direction $\eta$ (numerical power ratio)

nA angle, from satellite $S$, of the receiving earth station $e^{\prime }{}_R$ of satellite link $A$

$\eta e^{\prime }$ angle, from satellite $S$, of the receiving earth station $e^{\prime }{}_R$ of satellite link $A^{\prime }$

${\mathrm{P}}_{\mathrm{e}}$ maximum power density per $\mathrm{Hz}$ delivered to the antenna of the transmitting earth station ${\mathrm{e}}_{\mathrm{T}}$ (averaged over the worst $4\mathrm{kHz}$ band for a carrier frequency below $15\mathrm{GHz}$ or over the worst $1\mathrm{MHz}$ band above $15\mathrm{GHz}$ (W/Hz) ${\partial }_A$ angle, from satellite $S$, of the transmitting earth station $e_T$ of satellite link $A$

${\partial }_{e^{\prime }}$ angle, from satellite $S$, of the transmitting earth station $e^{\prime }{}_T$ of satellite link $A^{\prime }$

${\theta }_{\mathrm{t}}$ topocentric angular separation in degrees between the two satellites

${\theta }_g$ geocentric angular separation in degrees between the two satellites, taking the longitudinal station-keeping tolerances into account

$g_1\left({\theta }_t\right)$ transmitting antenna gain of the earth station $e_T$ in the direction of satellite $S^{\prime }$ (numerical power ratio)

$g_4\left({\theta }_t\right)$ receiving antenna gain of the earth station $e_R$ in the direction of satellite $S^{\prime }$ (numerical power ratio)

k Boltzmann's constant $\left(1.38\times 10^{-23}\mathrm{J}/\mathrm{K}\right)$

$I_d$ free-space transmission loss on the downlink (numerical power ratio), evaluated from satellite $S$ to the receiving earth station $e_R$ for satellite link $A$

Iu free-space transmission loss on the uplink (numerical power ratio), evaluated from the earth station ${\mathrm{e}}_{\mathrm{T}}$, to satellite $S$ for satellite link $A$

Based on the above parameters the uplink and downlink $\Delta T$ are given by:

$$\Delta T_S=\frac{p^{\prime }{}_e{g}^{\prime }{}_1\left({\theta }_t\right)g_2\left({\partial }_{e^{\prime }}\right)}{k{l}_u}\Delta T_e=\frac{p^{\prime }{}_s{g}^{\prime }{}_3\left({\eta }_e\right)g_4\left({\theta }_t\right)}{k{l}_d}$$

WORST CASE CALCULATION

When assessing a $\Delta T/T$ value for a specific overlap, it is important that we are sure to be looking at the worst case that can occur for that overlap.

The worst case can be influenced by geometric and RF factors.

For each frequency assignment within a network filing there are often associated multiple carrier parameters and power levels. In other places, you may see reference to Most Sensitive Most Interfering (MSMI) analysis. The idea is that you find the wanted assignment with the lowest value of $T$, and the interfering carrier with the highest EIRP density. This pair is then assumed to produce the largest $\Delta T/T$ value.

In Visualyse GSO V3, for each overlap all possible values of $\Delta T/T$ are calculated for all possible pairs and the highest value is displayed. This eliminates the need for MSMI analysis.

In combination with assumptions about worst case geometry', this produces a better estimate of the highest $\Delta T/T$ that might be found.

SEPARATE UPLINK AND DOWNLINK CALCULATIONS

The methods of Appendix 8 and Recommendation ITU-R S. 738 are based on the premise that uplinks and downlinks are combined and that DT/T calculations for the overall link take this into account.

This requirement has lead to a proliferation of data required for the analysis - the so-called strapping tables.

Each strapping i.e. each possible pair of uplinks and downlinks has an associated parameter called the processing gain, and noise on the uplink is propagated through to the downlink.

1 Visualyse GSO V3 assumes that the topocentric angle $=1.1$ times geocentric angle as per Recommendation ITU-R S. 728

The requirement to link the uplink and downlink for "simple frequency-changing transponders" results in a large number of permutations in the filing and in a large amount of review work for the BR.

Many proposals have been made to eliminate the need for this strapping information and to treat uplinks and downlinks separately in all cases.

This is what is implemented in Visualyse GSO V3. It can be shown that this separate treatment of uplinks and downlinks has little impact on the effectiveness of the coordination process, whilst greatly simplifying the filing and the data analysis.

In particular, it can be shown that separately comparing uplink and downlink $\Delta T/T$ values against the $6\%$ criterion will identify all the necessary cases for coordination just as thoroughly as comparisons done with the $△T/T$ for each uplink and downlink combination.

In some cases, calculations using only separate uplink and downlink parameters may cause networks to be brought into the coordination process that would not be included on the basis of the combined link calculations. However, the extra analysis is not too much of burden when compared to the simplification it brings.

A study by the BR has indicated that:

"Treatment of uplinks & downlinks separately for calculating increases by about 5-6%, the number of administrations involved in coordination and by about $10\%$ the number of networks involved in coordination. Number of networks omitted, when compared to the overall $\Delta T/T$ approach, is marginal."

Coordination Arcs

Coordination Arcs are an attempt to simplify the coordination triggering process. The idea is that spatial separation of the satellites can provide sufficient advantage to ensure that no interference will be seen. Therefore coordination is triggered if two systems operate via satellites that are within a predefined orbital separation.

WRC-2000 implemented a coordination-arc approach to replace the Appendix 8 (∆T/T) coordination threshold, in certain frequency bands. The coordination-arc approach affects the 6/4, 14/11, and 30/20 GHz “commercial” satellite bands.

The coordination arcs are shown in the table

It remains possible to call for coordination with systems outside these arcs, provided you can demonstrate by calculation that the DT/T values due to a new network exceeds the 6% trigger.

A co-frequency GSO FSS satellite network within the coordination arc may also be excluded from the coordination when the increase in system noise to the network is less than 6%.

Visualyse GSO V3 can be used to check which systems are within the coordination arc relevant to the frequency band in question.