Commonwealth of Australia

Radiocommunications Act 1992

Radiocommunications Advisory Guidelines

(Protection of Molonglo Observatory Synthesis Telescope) 1998

THE AUSTRALIAN COMMUNICATIONS AUTHORITY makes the following guidelines under subsection 262 of the Radiocommunications Act 1992

Dated 4 February 1998.

A J Shaw                                                                                                                        Chairman

        R Horton                                                                                                                    Deputy Chairman

Australian Communications Authority

PART 1GENERAL INFORMATION

Title

 1.1 These guidelines are called the Radiocommunications Advisory Guidelines (Protection of Molonglo Observatory Synthesis Telescope) 1998.

Commencement

 1.2 These guidelines commence on 4 February 1998.

Interpretation

 1.3 In these guidelines:

  “compatibility requirement” means the requirement set out in Part 2;

  “coordination threshold distance” means the maximum distance from the MOST receiver within which a transmitter operated under spectrum licence needs to be coordinated;

  “EIRP” means equivalent isotropically radiated power;
  “the MOST” means the radio telescope operated by the University of Sydney located about 30 km east of Canberra, ACT at latitude 35° 22’ 30” S, longitude 149° 25’ 35” E.  The telescope has a receive frequency of 843 MHz with a 3 dB bandwidth of +/- 1.5 MHz.
[Note: Australian Map Grid coordinates - Zone: 55, Easting: 720420, Northing: 6082653.].

 Purpose of these guidelines

 1.4 The purpose of these advisory guidelines is to set out the compatibility requirement and provide a basis upon which spectrum licensees in the 825-845 MHz band may coordinate the operation of their transmitters so as to prevent interference being caused to the MOST.  If such interference is caused to the MOST the ACA will have regard to whether or not the spectrum licensee has coordinated the transmitters in a manner that meets the compatibility requirement set out in these guidelines, during interference settlement.

 1.5 The compatibility requirement is intended to reflect the ACA’s policy of providing adequate interference protection to the MOST.  This does not alter the fact that the ACA will deal with each interference scenario on a case by case basis according to its own circumstances.

 1.6 The compatibility requirement set out in these guidelines is based on the results of tests[1] conducted to determine the interference susceptibility of the MOST.  These tests were undertaken jointly by the Spectrum Management Agency, the Department of Communications and the Arts and the University of Sydney.  The compatibility requirement and the methodology presented in these guidelines have been developed in consultation with industry.  Spectrum licensees should take all reasonable steps to ensure that, whatever coordination methods are used, the compatibility requirement set out in these guidelines is met in respect of any transmitters to be operated under a spectrum licence.

 1.7 The compatibility requirements for the MOST are set out in Part 2.

                         PART 2compatibility requirement

 2.1 The compatibility requirement for spectrum licensees to protect the MOST is as follows:

 Ptx - L = Prx

 Prx = Prx0 - G() - G(f)

where:
Ptx is the EIRP of the proposed transmitter in the direction of the MOST (dBm);
L is the transmission loss (dB) (definition ref: ITU-R Rec. P.341-4 );
G() is the relative gain of the MOST as a function of the bearing to the
         transmitter (dB) found from Table 2;
G(f) is the relative gain of the MOST as a function of frequency (dB) found from
         Table 3;
Prx is the received power at the MOST; and
Prx0 (the worst-case protection level) = -174 dBm.

 2.2 The average power received by the MOST within its 3 dB bandwidth (3 MHz) should not exceed the compatibility requirement for more than 10 % of the time as a result of variations in propagation conditions (ref:  ITU-R Rec. RA.1031-1).

 2.3 The coordination methodology set out in Parts 3 to 6 inclusive may be used to determine whether a transmitter proposed for operation under a spectrum licence (‘the proposed transmitter’) will meet the compatibility requirement.

 PART 3FINDING OUT if detailed COORDINATION is necessary

Distance to the MOST

 3.1 Calculate the distance between the proposed transmitter and the MOST.

 3.2 If the proposed transmitter is within 10 km of the MOST and is intended to operate within the frequency range 825-845 MHz the spectrum licensee should not operate the transmitter unless steps are taken as set out in Part 6.

 3.3 If the proposed transmitter is more than 10 km from the MOST and is intended to operate in the frequency range 825-845 MHz, the procedure described in clauses 3.4 to 3.11 inclusive may be used to determine if the compatibility requirement can be met.  For mobile transmitters intended to operate in the frequency range 825-840 MHz, and exempt from device registration as provided for in the spectrum licence, the compatibility requirement does not apply.

Coordination threshold distance

 3.4 Table 1[2] may be used to evaluate whether a detailed coordination assessment  is necessary by determining the ‘coordination threshold distance’ for a proposed transmitter.

 3.5 Before using Table 1, spectrum licensees should take note of the underlying principles used in developing the table as set out in clauses 4.1 to 4.2 and make a judgement as to whether these assumptions are appropriate for their proposed transmitter(s).  If the assumptions are not appropriate, or the range of values of effective antenna height or EIRP is not sufficient, then Table 1 should not be used and a detailed coordination assessment will be necessary as described in Part 5.

 3.6 The methodology for using Table 1 to find the coordination threshold distance is set out in Part 4.  Determining the coordination threshold distance from Table 1 is a two stage process.  The first stage determines an initial distance and the second stage refines the required protection level, thereby allowing a reduced distance to be determined from the table in many cases.  The second stage is unnecessary if the distance between the proposed transmitter and the MOST is greater than the initial distance determined from the table.

 3.7 The initial coordination threshold distance should be found from Table 1 as described in clause 4.3.

 3.8 If the proposed transmitter is outside this coordination threshold distance then no coordination with the MOST is required and the transmitter may be operated (providing other relevant conditions of the spectrum licence are met).

 3.9 If the proposed transmitter is closer to the MOST than the initial coordination threshold distance then the coordination threshold distance should be refined, if possible, as described in clauses 4.4 to 4.6.

 3.10 If the proposed transmitter is closer to the MOST than the revised coordination threshold distance then the spectrum licensee should conduct a detailed coordination assessment as set out in Part 5.

 3.11 If the proposed transmitter is outside the revised coordination threshold distance then no coordination with the MOST is required and the transmitter may be operated (providing other relevant conditions of the spectrum licence are met).

 PART 4Using the coordination threshold distance table (Table 1)

Validity of Table 1 for the path between the proposed transmitter and the MOST

 4.1 Table 1 was produced using the spherical Earth propagation model to calculate the coordination threshold distances listed in the table.  Parameters used in the calculations included an effective Earth radius (k) of 5.5 and a receiver (the MOST) antenna height of 10 m.  The transmitter antenna height used in each calculation was the effective antenna height listed in the same row of the table as the calculated distance.

 4.2 Generally, the spherical Earth propagation model used in calculating the coordination threshold table will give less loss than the actual propagation path.  However, care should be taken if the path is either unobstructed or obstructed by a single knife edge, as these propagation paths can result in less loss than the spherical Earth propagation model.  In such cases the coordination threshold distance table should not be used.

Initial coordination threshold distance

 4.3 Looking first at the upper part of Table 1 (upwards from and including the row titled “EIRP”):  For a given EIRP and effective antenna height[3], a distance can be read from the table.  This distance is the initial coordination threshold distance.

Refining the coordination threshold distance

 4.4 For a proposed transmitter closer to the MOST than the initial distance determined by using the upper part of Table 1, a further stage can be undertaken to determine whether the compatibility requirement can be reduced.  By considering the directionality and frequency response of the MOST the compatibility requirement can be reduced thereby reducing the coordination threshold distance.

 4.5 The total reduction in the compatibility requirement can be determined as follows:

 (a) determine the bearing of the proposed transmitter from the MOST.  Then look up the relative gain figure corresponding to this bearing in Table 2;

 (b) using Table 3 find the frequency range relevant to the proposed transmitter’s frequency bandwidth and then look up the corresponding frequency response figure;

 (c) the total reduction in the compatibility requirement is the sum[4] of the two figures determined in sub clauses (a) and (b).

 4.6 The left hand column in the lower part of Table 1 lists the amount by which the compatibility requirement has been reduced.  Find the appropriate figure in the left hand column corresponding to the reduction in the compatibility requirement calculated in clause 4.5.  If the appropriate figure is not listed, the next lowest figure should be used.  (eg if the compatibility requirement is reduced by 29 dB, find 27 dB in the left column).  The lowest value of EIRP that is equal to or greater than that of the proposed transmitter should then be located in the row corresponding to this reduction in the compatibility requirement.  Once the appropriate EIRP is found in a particular column, this column can then be used in the upper part of the table to find the new coordination threshold distance for the appropriate effective antenna height.

 PART 5 Detailed COORDINATION ASSESSMENT

Detailed coordination

 5.1 For a proposed transmitter to be sited closer to the MOST than the distance determined from the coordination threshold distance table, detailed coordination studies will be needed to determine if the transmitter can operate without interference to the MOST.

 5.2 The methodology to be applied in conducting the detailed coordination has not been specified due to the range of possible system applications and potential interference scenarios.  It is the responsibility of spectrum licensees to ensure that the studies are conducted with due care using supportable and valid methodologies such as those presented in ITU-R recommendations, ACA guidelines, or ACA radiocommunications assignment and licensing instructions (RALIs).

 5.3 The objective in undertaking a detailed coordination study is to determine whether the signal level at the MOST from the proposed transmitter is below the level specified by the compatibility requirement.  This level will range from -174 dBm to ‑104 dBm depending upon the proposed frequency and the bearing on which the signal

arrives at the MOST.  The appropriate compatibility requirement can be calculated by adding the reduction in the compatibility requirement determined in clause 4.4 to -174 dBm.  The signal levels from proposed transmitters should not exceed this compatibility requirement for more than 10% of the time as a result of variations in propagation conditions.  (ref: ITU-R Rec. RA.1031-1).

 5.4 Detailed coordination studies can take into account the actual terrain between the MOST and the proposed transmitter(s).  Knowing the nature of the terrain may allow a different propagation model to be used in calculating the propagation loss between the proposed transmitter and the MOST.  If greater propagation loss results from using a different propagation model the coordination distances will be reduced.  However, as noted in clause 4.2 some propagation paths may result in less loss than the spherical Earth propagation model that was used in calculating the coordination threshold distance table.

 PART 6Coordination of transmitters close to the MOST

 6.1 Transmitters operating in the band 825-845 MHz and within 10 km of the MOST could cause interference by overloading the low noise amplifiers resulting in a blocking effect.  The susceptibility of the MOST to this type of interference has not been characterised. 

 6.2 Spectrum licensees proposing to operate transmitters within this range should approach the Sydney University’s Department of Astrophysics with a view to undertaking test transmissions to determine if such operation is feasible.

Notes: 1. Calculated distances are based on the spherical Earth diffraction loss model (loss not exceeded for 10 % of the time).

 2. Protected receive level Prx=-174 dBm.

 3. If a value of EIRP, effective antenna height or protection reduction is not listed then the next highest value should be used.  Alternatively, the results obtained from using both the higher               and lower values could be interpolated

Notes: 1. Calculated distances are based on the spherical Earth diffraction loss model (loss not exceeded for 10 % of the time).

 2. Protected receive level Prx=-174 dBm.

 3. If a value of EIRP, effective antenna height or protection reduction is not listed then the next highest value should be used.  Alternatively, the results obtained from using both the higher               and lower values could be interpolated

Note:  Round all bearings to a whole number before using table.

[1] Reference: Spectrum Planning Report SPP 5/96, “Interference Susceptibility of the Molonglo Observatory Synthesis Telescope.

[2] Note that due to the range of EIRP values shown in the table, the table spans two pages.  These two pages can be joined horizontally to form one complete table.

[3] The effective antenna height of the transmitting antenna may be determined with any valid methodology.  The ITU-R defines the effective antenna height as the height of the transmitting antenna over the average level of
the ground between distances of 3 and 15 km from the transmitter in the direction of the receiver (ref: ITU-R Rec. P.370-7).  An alternative methodology developed by the ACA could also be used.  This alternative method is used in spectrum licensing for evaluating the geographic device boundary for spectrum licensed transmitters.

[4] The absolute value of the sum should be used in Table 1.