This section provides a general guide to the interference management rules for spectrum licensing in the 500 MHz bands, and must be read in conjunction with the legal instruments listed at the foot of the page which are the definitive authority for interpretation of the interference management rules.
Introduction
As a general principle, spectrum licensees are required to manage interference caused by devices operated under their licences. Managing interference includes taking steps to reduce the likelihood of interference occurring, investigating possible causes of interference and taking remedial action should interference occur.
While the ACMA’s objective is to provide for technology neutrality in spectrum licensing, it also recognises that the most likely uses of the 500 MHz band are mobile or point to multipoint services with a radius of up to 40 km in urban areas. Although the interference management rules are designed to facilitate this expected use of the spectrum, it also aims to be compatible with a range of alternative possible services.
With this in mind, the interference management framework is based on the following principles:
- That high power transmitters may only transmit at high sites in the lower band or at low sites in the upper band. Conversely, receivers are entitled to relatively high levels of protection at high sites in the upper band and low sites in the lower band.
- Spectrum licensees have the responsibility to manage interference that arises within 200 metres of devices registered under their licences.
- Emission limits are specified as absolute power levels (in EIRP) rather than power levels that are relative to the transmitter power. This will allow licensees to strike a balance between the maximum radiated power of a device and its out-of-band performance.
- The core conditions, in conjunction with the Radiocommunications (Unacceptable levels of Interference) Determination No. 1 of 1996 indirectly specify frequency stability by requiring the emission limits outside the band to be maintained under all conditions. This allows a licensee to balance emission bandwidths and frequency of operation along with frequency stability.
- Receivers will meet certain performance standards and that licensees must accept interference to receivers that do not meet the performance standard or where the level of interference is below the protection level set out in the Radiocommunications (Unacceptable levels of Interference) Determination No. 1 of 1996.
Core conditions
The core conditions of a spectrum licence specify the spectrum space in which the licensee is authorised to operate. This is defined in terms of the maximum permitted emission levels at the geographic and frequency boundaries of each licence.
Maximum permitted out-of-area emission levels
Emissions from a device operated under a spectrum licence located anywhere in the geographic area of the licence must not exceed a horizontally radiated power (measured within a 12.5 kHz bandwidth) of 49.2 dBm EIRP.
Maximum permitted out-of-band emission levels
The out of band emission levels specified in a licence are intended to manage unwanted emissions caused by the modulation process, the frequency generation process (including broadband noise), and any frequency combining processes. It is also intended to manage transient unwanted emissions, such as those caused by a carrier being switched on or off.
A spurious emission limit for receivers has also been imposed. A stricter limit has been imposed for receivers because, generally speaking, receivers are operated continually. The details are contained in the Radiocommunications Spectrum Marketing Plan (500 MHz Band) 1996.
In the ACMA’s view, compliance with the maximum out-of-band emission levels can be achieved by using equipment with appropriate characteristics or by using suitable guard bands. For example, guard bands must be provided when a licensee wants to operate transmitters with very short rise times (about 200 kHz needed for rise times around 1 micro sec). Licensees should seek such advice as they consider necessary on managing out of band emissions.
Device registration
All high power transmitters must be registered before they can be operated under a spectrum licence. The public registration process is intended to facilitate coordination of devices by licensees with minimum ACMA involvement.
Transmitters must always be registered as either an individual transmitter or as part of a group of transmitters. If two or more transmitters are operated for the purpose of communicating with the same receiver or same group of receivers and they have identical emission characteristics, then those transmitters may be treated as a group in order to simplify the registration process. A transmitter may belong to more than one group. Groups are defined to help minimise the work associated with the registration process of similar transmitters, for example, subscriber transmitters and multiple transmitters at a hub. Subscriber transmitters may be registered as a group (or one logical device), and in some cases one logical device may operate in a number of locations called effective mobile locations. Lists of effective mobile locations are available from the ACMA. An effective mobile location has an associated effective radius which is used to further expand the device boundary to take account of the distribution of subscriber transmitters. Mobile and indoor transmitters are exempted from device registration requirements. Licensees may decide whether to register receivers based on a risk assessment of the benefits achieved through coordination to manage out-of-band interference (see below).
The ACMA will, generally speaking, refuse to register a device whenever it would give rise to levels of emission outside the licence that would be ‘unacceptable interference’ within the meaning of section 145 of the Act. Consequently, accredited persons are required to issue an Interference Impact Certificate (IIC) before a device will be registered.
The Radiocommunications (section 145(3) Certificates) Determination 2000 specifies three options for the issue of IICs in a spectrum licence. The general method for certification is through adherence to the requirements detailed in the relevant s.145 Determination for a band – see Radiocommunications (Unacceptable levels of Interference) Determination No.1 of 1996).
The ACMA has also provided two alternative methods to issue an IIC, these are:
- where it is shown that there is sufficient internal guard space to manage potential interference within the spectrum space of the licensee; or
- where there is a written agreement in place with all affected licensees to accept higher levels of interference.
Guidance on the registrations of radiocommunications devices via guard space and agreements is provided in the information paper Registration of radiocommunications devices under spectrum licences. Additional guidance is also provided in Radiocommunications Advisory Guidelines (Coordinating the operation of transmitters in the 500 MHz Bands).
Calculating a device boundary for a transmitter
The device boundary calculation for a transmitter establishes in effect an emission ‘buffer zone’ along the area boundaries of the licence.
The calculation of a device boundary involves establishing the distance that is required, along 36 radials from the transmitter, for the emission level to drop below what the ACMA considers to be the usual sensitivity achieved by receivers in adjacent geographic areas. The distance along each radial is based on a mathematical propagation model (as opposed to measured field strengths that may be taken into account for settling interference disputes). Terrain loss is accounted for by calculating the antenna height of a device according to its height above average terrain, called its effective antenna height.
Calculating a device boundary for a receiver
Registration of receivers is not compulsory, hence the calculation of a device boundary for a receiver may best be regarded as a guide to whether the receiver is prone to interference. If the registration of a receiver is necessary for it to be taken into account in some future coordination procedure, licensees must follow the specified procedures when calculating a device boundary.
Under the technical framework, receivers operated under a spectrum licence are required to accept higher levels of interference the closer they are to the boundary of the spectrum licence. In addition, receivers are required to accept still higher levels of interference as their effective antenna height increases. Also, relatively high levels of protection are only given to receivers at low sites in the lower band and at high sites in the upper band. This is described as the level of protection (LOP). A device boundary may only be calculated for certain values of LOP and effective antenna height. These are specified in the Marketing Plan.
A receiver may be operated without regard to its LOP because actual levels of interference depend upon the existence of any nearby interfering transmitters. Licensees are allowed to manage their own spectrum by weighing up the likelihood of interference. For example, in remote areas where the likelihood of interference is low, a receiver with a poor LOP under the framework may operate quite successfully.
As in the case of apparatus licensing, the time at which competing services commence may be a major factor for consideration in interference settlement procedures, and that the time of registration might assist in resolution of disputes.
Receiver performance
As mentioned above, licensees will need to take account of the emission limits permitted under the technical framework when deciding the level of performance they require for their receivers. Receivers will cope with emission levels with differing degrees of success depending on their interference susceptibility. For example, a receiver with poor performance would normally deny large amounts of spectrum space for transmitters in order to protect it from interference. The ACMA does not intend to enforce receiver standards. It is for each licensee to balance the cost of receiver performance against the cost of spectrum space denied to their transmitters.
Interference probability
No matter how rigorous the engineering analysis of a device, there is always a possibility of actual interference when devices are deployed in the field. This is because the technical framework is designed according to certain levels of acceptable interference probability.
Under the framework described in this chapter, it is anticipated that interference between spectrum licensed devices will occur at about the same rate as between apparatus licensed devices, that is, in less than one percent of cases. Such interference may be caused by emissions at frequencies either inside or outside licensees’ spectrum space.
Licensees are strongly advised before making an interference complaint to try and locate the source of any interference by checking the Register of Radiocommunications Licences available on CD or on the ACMA website.
This investigation may reveal the cause of the interference and it may be possible to settle the problem without the ACMA’s intervention. If the ACMA becomes involved, licensees may be charged for any work undertaken.
International co-ordination
The ITU Radio Regulations have international treaty status and are binding on Australia. Transmitters operated under a spectrum licence, other than in accordance with ITU Radio Regulations, must not cause interference to any services of any other country (for example, Papua New Guinea or Indonesia) which are operating in accordance with ITU Radio Regulations. If operation of a transmitter does cause harmful interference to overseas services operating in accordance with ITU Radio Regulations, the transmission will be required to cease. Spectrum licensees must also accept interference from any overseas services operating in accordance with ITU regulations. Spectrum licensees should note that the ACMA may impose such additional licence conditions on spectrum licences as may be necessary from time to time to meet its international obligations.
Health and safety
Operators of radiocommunications devices need to take into account the occupational health and safety requirements for radiofrequency devices of the relevant State or Territory Governments. Licensees will also be required to comply with any health exposure standards that may be made by the ACMA from time to time for the health and safety of persons who operate, work on, use or are exposed to emissions from radiocommunications transmitters and receivers.
Environmental and other considerations
A spectrum licence does not confer any rights to erect infrastructure. Antenna siting, height and construction may be regulated by State, Territory or local government legislation and licensees should investigate the local rules pertaining to the erection of towers and antennas before deployment. The holders of carrier licences under the Telecommunications Act 1997 may, in some circumstances, obtain limited immunity from such legislation for the erection of certain infrastructure. The ACMA recommends that applicants seek legal and other specialist advice on this issue.
Obtaining a permit to operate or supply non-standard devices
No further approval from the ACMA is required if a licensee wishes to operate standard devices under a spectrum licence (that is, equipment that conforms to mandatory the ACMA standards). However, a permit is required to operate any non-standard devices. These permits may be issued by the ACMA under section 167 of the Radiocommunications Act 1992, and will only be issued during the term of the licence. Permits to supply non-standard devices for operation under a spectrum licence may also be issued by the ACMA under section 174 of the Act.
The legal instruments that define the technical framework for the 500 MHz band are listed below:
- Radiocommunications Spectrum Marketing Plan (500 MHz Band) 1996
- Radiocommunications Spectrum Conversion Plan (500 MHz Band)1996
- Radiocommunications (Spectrum Licence Allocation - 500 MHz Band) Determination 1996
- Radiocommunications (Unacceptable levels of Interference) Determination No. 1 of 1996
- Radiocommunications Advisory Guidelines (Coordinating the operation of transmitters in the 500 MHz Bands)
In addition, the Radiocommunications Spectrum Marketing Plan (500 MHz Band) 1996 Variation (No. 1) 2007 was made in 2007 to exclude 500 MHz spectrum licences due to expire 31 May 2007, so they could be re-allocated under the Radiocommunications Spectrum Marketing Plan (500 MHz Band) 2003 which was also varied.