Methodology for the 700 MHz band exclusion zone informal consultation - ACMA's response to issues raised | ACMA

Methodology for the 700 MHz band exclusion zone informal consultation - ACMA's response to issues raised

On 31 August 2012, the ACMA undertook an informal consultation process on the proposed methodology for the 700 MHz exclusion zones, which closed on 28 September 2012.

In this response, the ACMA addresses technical issues raised by the respondents about the proposed methodology of generating maps under certain parts of the Radiocommunications Advisory Guidelines (Managing Interference from Transmitters - 700 MHz Band) 2012.

One stakeholder proposed that a different propagation model should be used for the calculation of the geographic separation requirement. The stakeholder proposed that the suburban Modified Hata model be used instead of Recommendation ITU-R P.1546.

Tables 1 and 2 compare separation distances calculated with the Modified Hata model (in both open areas and suburban environments) and Recommendation ITU-R P.1546. The tables validate the comment made in the 700 MHz Technical Liaison Group (TLG) Discussion Paper #2 that the Modified Hata model 'aligns well with the ITU-R JTG 5-6 model and ITU-R P.1546 under certain conditions', for a transmit antenna height of 30 m. However, for an effective antenna of 150 m, the suburban Modified Hata model predicts considerably larger separation requirements than Recommendation ITU-R P.1546.

Table 1: Back-of-antenna separation requirement

Effective antenna height (m)

Separation distance (km)

Rec. ITU-R P.1546

Modified Hata-suburban

Modified Hata-
open area

30

27

33

72

150

43

66

121

Table 2: Main-beam separation requirement

Effective antenna height (m)

Separation distance (km)

Rec. ITU-R P.1546

Modified Hata-suburban

Modified Hata-
open area

30

56

58

114

150

79

104

176

Note: These distances are based on a required path loss of 165 dB for:

  • 58 dBm EIRP base station transmission
  • maximum interference signal receive power of -98 dBm (converted from maximum interference signal field strength of 27 dBµV/m)
  • nominal DTV receive system with 14 dBi antenna gain and 5 dB feeder loss.

Applying (Daz + Dpol) factors of 3 dB (main-beam) and 16 dB (back-of-antenna) results in minimum required path losses of 162 dB and 149 dB, respectively.

Two stakeholders expressed concern over the adoption of the 150 m effective antenna height for spectrum-licensed base stations. The reasons for adopting this value have been explained in detail in the methodology paper. As one respondent claimed, 'the majority of base station antennas are located at heights between 11 m and 15 m above ground level', and a value of 30 m may be used in the work of the ITU-R JTG 4-5-6-7. The use of these heights above ground may be applicable in some cases, however the ACMA has decided to take a conservative approach to this particular case, which is likely to apply during a short transitional period.

With respect to the ACMA 700 MHz TLG, a 30 m effective antenna height for base stations was quoted in Discussion Paper #2. This paper was used in the development of the s.145 Determination for the 700 MHz band, which includes a device boundary criterion used to identify if an unacceptable level of interference from a radiocommunications device would prevent the registration of that device. The calculation of the device boundary, as defined in Schedule 2, Part 3 of the s.145 Determination, uses the effective antenna height of the transmitting station to be registered, as defined in Schedule 3 of that determination, as opposed to a generic 30 m.

One stakeholder proposed that the minimum digital TV (DTV) signal target should be set at 54 dBµV/m in rural areas, 7 dB higher in suburban areas and 14 dB higher in urban areas.

In the Australian Digital Terrestrial Television Broadcasting (DTTB) Planning Handbook, the applicable minimum median field strength for a suburban environment is 67 dBµV/m; this is 13 dB higher than for a rural environment. This has been taken into account in Table 4 of Section 6 of the methodology paper, which says:

Coverage edge at minimum median field strength (@ 10 m) equal to 54 dBµV/m-unless planning data includes an advisory note (or similar) with another value (e.g. 67 dBµV/m).

Therefore, where a DTV service has been planned to be protected to a higher median field strength (for example, repeater sites covering populated areas), this will result in the reduction of the predicted coverage area to which the 'back-of-antenna' buffer zone is added.

Another stakeholder proposed the opposite-that this limitation of the coverage area to higher field strengths should be removed. The ACMA has already adopted a conservative approach to not implementing the 'maximum server' masking to coverage areas for the development of exclusion zones. Therefore, it seems unnecessary and unreasonable to take a further step to protect weaker signal levels, which have not been planned to be protected as part of DTTB planning.

One stakeholder suggested that antenna tilt should be incorporated in metropolitan areas. 

General comment on protection level, antenna height and antenna tilt:

The ACMA understands that the deployment of base stations in metropolitan areas would typically involve lower antenna heights, use of antenna tilt and possibly even lower EIRP values than the values assumed in the ACMA's calculations. Revising the model parameters to take account of such factors could, in concept, be used towards a 'metro-area' base station model, which would result in smaller separation distances. Unfortunately, such a definition of regional and metropolitan areas is expected to require a more complex coordination process that may not be feasible for spectrum licensees or the ACMA. For example, taking the metropolitan area of Melbourne into account:

  • The Bendigo 'back-of-antenna' exclusion zone component encroaching on Melbourne could be reduced due to the use of a revised metro-area base station model. However, this reduced 'back-of-antenna' separation distance would not apply in other areas. Therefore, different buffer zone sizes would need to be applied to different parts of the Bendigo coverage area edge.
  • The exclusion zones for Melbourne area repeaters could be reduced due to the use of a revised metro-area base station model in Melbourne's suburban areas. However, such a reduction may not provide sufficient protection for DTV services from interference from high base stations, for example, on Mt Dandenong, Mt St Leonard or high-rise buildings in the CBD.

Therefore, simply defining DTV services as serving either 'metropolitan' or 'regional' areas, as suggested by one stakeholder, does not address both the concerns of spectrum licensees and the protection requirements of DTV services.

The finalised exclusion zone methodology applies a single, simple map, which is based on existing or planned DTV services. Implementing the changes proposed by industry for 'metropolitan area' base stations would require the case-by-case calculation of device boundary criteria for each base station, which would then be assessed against DTV coverage area boundaries rather than spectrum licence area boundaries. While this may provide more coordination opportunities, it would require assessment of all spectrum-licensed device registrations against DTV coverage areas, would be highly dependent on data provided by spectrum licensees, and is less transparent to all stakeholders.

Last updated: 25 July 2017