This section summarises:
- the technical framework underpinning spectrum licensing in the 28 GHz and 31 GHz bands;
- the operation of the s.145 Determination of unacceptable interference;
- the Advisory Guidelines that protect non-spectrum licensed devices in frequency-adjacent spectrum for the term of the spectrum licence;
- the Advisory Guidelines that protect devices operating under a spectrum licence from interference caused by frequency-adjacent non-spectrum licensed devices; and
- other important information about the technical framework.
Introduction
The technical framework for spectrum licences at 28 GHz and 31 GHz has been established by the ACMA to support the use of different types of service, including point to point and point to multipoint services.
Broadly speaking, the technical framework for spectrum licensing in the 28 GHz and 31 GHz bands is constructed from three interlocking tools.
Two of these tools are used to deal with the management of emission levels, namely the core conditions of the licences themselves, and the registration of devices under the Act. The third tool, advisory guidelines made by the ACMA under the Act, provides a framework for the co-ordination of spectrum licensed services with non-spectrum licensed services operating within the spectrum to be re-allocated, and with non-spectrum licensed services that surrounding the spectrum to be spectrum licensed.
The entire technical framework is predicated on the assumptions that:
- spectrum and non-spectrum licensees will employ good engineering practice in establishing and maintaining their services;
- receivers employed by spectrum licensees will be required to operate at a minimum level of performance based on receiver characteristics listed in Part 3 of the Radiocommunications Advisory Guidelines (Managing Interference from Non-spectrum-licensed Transmitters 28 GHz and 31 GHz Bands)1998) (see Receiver Performance below); and
- receivers employed by non-spectrum licensees will, as a minimum, meet the relevant standard made under the Radiocommunications Act 1992 or, if there is no such standard, the level of performance referred to in the advisory guideline that applies to the apparatus licensed service in question; and
- spectrum licensees will be responsible for managing interference that they, or their third party authorisees, cause to their own services through their operation of devices under any spectrum licence or any other licence.
The following general principles have also been followed in developing the technical framework:
- the ACMA has attempted to provide the maximum flexibility to spectrum licensees to establish services while minimising the level of negotiation between licensees who have adjacent spectrum licences;
- emission limits have been specified as absolute power levels rather than power levels that are relative to the transmitter power
- this allows licensees to strike a balance between the maximum radiated power of a device and its out-of-band performance; - the core conditions 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 along with frequency stability, as well as transmitter rise and fall times providing ‘internal guard bands’ as necessary.
The interference sources that the technical framework seeks to manage are those resulting from:
- unwanted in-band emissions;
- the modulation process;
- the frequency generation process;
- transient unwanted emissions such as those caused by switching a transmitter on and off; and
- intermodulation effects including ‘blooming’ and ‘spectral re-growth’.
All five of these mechanisms are dealt with by a combination of the core conditions relating to out-of-area and out-of-band emissions, and those parts of the registration process which give effect to those conditions at the point of registration of devices prior to their operation. The technical framework also provides additional controls in relation to interference, such as that caused by intermodulation effects and other co-siting interference phenomena. A licence condition imposes on spectrum licensees the responsibility to manage interference that arises from devices that are located within 200 metres of each of their transmitters.
It should be noted that in all cases, the technical framework established by the ACMA for the 28 GHz and 31 GHz bands is a basis upon which further flexibility may be achieved. The ACMA is prepared to consider alternative management arrangements for emission levels agreed between spectrum licensees and, where relevant, other licensees. Spectrum licensees should note, however, that the ACMA will not give effect to alternative arrangements unless all affected and potentially affected licensees have agreed to the arrangements and those arrangements lead to reasonable levels of spectrum productivity.
Changes to emission limits may be related to either the licence core conditions or the registration requirements (see below). In the case of changes to the core condition relating to out-of-area emission, spectrum licensees might propose alternative arrangements with the ACMA under which higher powers for smaller bandwidths inside the frequency band of the licence would be allowed. The variation to the level of power would depend on the width of the guard bands being proposed, and the notional RF selectivity expected for receivers operating in adjacent spectrum. In the case of variations to the core condition relating to out-of-band emission, all licensees operating in a particular designated spectrum licensing band would normally have to be in agreement with a specific variation before the ACMA could consider any change.
In the case of changes to the device registration requirements (device boundary criteria and deployment constraints - when applicable), licensees may agree between themselves, without direct ACA involvement, to allow emissions to spill into each other’s spectrum space. Furthermore, it should be noted that such agreements between licensees can only continue to apply while the shape of the spectrum space of the licences held by the respective licensees remain unchanged. Where trading of licences takes place and licences with new shapes are issued, these agreements will need to be renegotiated.
This re-negotiation can occur at any time, that is, before or after the trade, so that there is no loss of flexibility to licensees. When trading occurs by means of the division of a spectrum licence, a check will be required to ensure that the devices continue to comply with the conditions of the relevant licences. The ACMA intends to issue provisional licence numbers before a trade to facilitate the redistribution of devices between the licences that a licensee wishes to operate after the trade.
Core Conditions
This part of the Chapter explains what the core conditions relating to emissions are intended to achieve, and how the emissions subject to those conditions are further managed under the technical framework.
Out-of-area emissions
Emissions from a fixed transmitter operated under a spectrum licence located anywhere in the geographic area of the licence are limited by core conditions to a maximum radiated power (measured within a 1 MHz bandwidth) of:
- 79 dBm EIRP for transmitters using antennas with less than 5 degrees beamwidth; and
- 65 dBm EIRP for all other transmitters.
Radiated power is mean power measured when information is being transmitted and the radiated power must stay below the maximum limit with a 95% level of confidence. This often means that there is a practical limit of 5 dB less that the maximum limit for levels of radiated power estimated in real situations. The conditions, therefore, effectively place an overall cap on power at the boundary and also throughout the entire geographic area of a licence.
How registration requirements operate in Lower Bands, for example spectrum licences at 1.8 GHz, an additional layer of management is usually imposed at the point of registration of devices and before registering a device, an accredited person would normally calculate a device boundary of the transmitter in accordance with a determination made by the ACMA under s.145 of the Act for unacceptable levels of interference. Such a determination ensures that high levels of emission from transmitters operated under a licence are kept within the geographic area of the licence. The calculation of a device boundary for 1.8 GHz spectrum licences takes special account of the increase in emission levels caused by placing transmitters at high sites.
Calculating a device boundary involves establishing the distance, along radials from the transmitter, that is required for the emission level to drop below what the ACMA considers to be the typical level of protection required by receivers in adjacent geographic areas. The distance along each radial is based on a mathematical propagation model. The model takes account of the terrain loss of emissions by adjusting the antenna height of a device according to its height above average terrain, called its effective antenna height. Effective antenna heights are calculated every 5 minutes in distance along each radial. If the device boundary so calculated for a 1.8 GHz transmitter falls outside the geographic area of the relevant spectrum licence the ACMA will, generally speaking, refuse to register the device because the levels of emission outside the licence that it would cause will be ‘unacceptable interference’ within the meaning of s.145 of the Act. The ACMA will consider registration in these circumstances but only where all affected licensees reach alternative arrangements for the management of emission levels. The effect of these two layers of management, core condition and registration requirement, is to create ‘emission buffer zones’ along the geographic boundaries of the licences.
New concept for the 28 GHz and 31 GHz bands framework
For the management of 28 GHz and 31 GHz spectrum licences the ACMA does not intend to use device boundary criteria to create an in-band emission buffer zone along the boundaries of the geographic areas of spectrum licences (see Radiocommunications (Unacceptable Levels of Interference - 28 GHz and 31 GHz Bands) Determination of 1998). At 28 GHz and 31 GHz, the appropriate propagation model to use is free space loss and the height-gain effect of transmitters does not have to be specially managed. The use of a free space loss model helps to ensure equity in the levels of emission emanating from adjacent spectrum licences without the need for additional constraints on the basis of effective antenna height. Device boundaries are used at lower frequencies (eg 1.8 GHz) to equitably contain emissions within the spectrum space that a person is licensed to use. Instead of using device boundaries to create emission buffer zones at 28 GHz and 31 GHz the ACMA intends that licensees create these zones by the management of both the location and antenna directivity of their receivers.
Spectrum licensees must expect that certain levels of emission will legitimately cross their geographic boundaries from points within other spectrum licensed areas. Accordingly, when considering what services they might establish within their own geographic areas, spectrum licensees will have to take into account the fact that transmitters may be located at certain points within other spectrum licensed areas, and that those transmitters may radiate power into the spectrum licensee’s area at any level up to that allowed under the conditions of the licence including registration requirements. For 28 GHz and 31 GHz spectrum licences it is allowable for licences to operate at maximum power on the boundary of the geographic area. However, if the ACMA considers that transmitters are being inappropriately placed, the ACMA may impose additional further conditions on licences to manage their location.
Out-of-band emissions
Out-of-band emission limits are imposed by a core condition. To establish whether the operation of a device will cause ‘unacceptable interference’ by breaching the out-of-band emission limits, a licensee or accredited person must work out the radiated power of the device within bandwidths outside the frequency band of the licence using good engineering practice. If the power so calculated is greater than a figure specified in the relevant licence condition, two things follow:
- if the device is not yet registered - the ACMA will generally speaking refuse to register it, because the interference that it would cause will be ‘unacceptable interference’ within the meaning of s.145 of the Act, (unless, for example, all relevant licensees agree upon alternative arrangements);
- if the device is already registered - there will be a breach of the core licence condition, unless, once again, all relevant licensees have agreed upon alternative arrangements, and the ACMA varies the relevant licence or licences to reflect those varied arrangements (see s.72 of the Act).
Potential applicants should note that no allowance has been made for ‘blooming’ or ‘spectral-growth’ of transmitter signals. As a result, if an applicant wants to operate services close to the limits of the frequency band of the licence, and does not take account of ‘blooming’ or ‘spectral growth’, the amount of spectrum available for use in the frequency band will need to be reduced so as to provide appropriate guard bands as necessary.
Levels of protection not provided
How out-of-area emissions are additionally managed when licences have narrow frequency bandwidths (eg those spectrum licences involving the 500 MHz band). It should be noted that under the interference management regime established for spectrum licensing in the 500 MHz band, receivers in adjacent areas are further protected from in-band interference by ‘levels of protection’, which were enforced by means of a licence condition. This protection was afforded by requiring that the power at a receiver must not exceed a specified level measured in a certain manner. That gave protection to receivers on a sliding scale, which varied with the antenna height and distance to the boundary of the geographic area. This protection is only necessary when spectrum licences have very narrow frequency bands (eg 12.5 kHz) because a spectrum licensee has no additional frequency space in which to move in order to avoid interference.
Levels of Protection and the 28 GHz and 31 GHz bands
The method of protection described above is not necessary for the 28 GHz band and 31 GHz band, because the STU bandwidth of 50 MHz is sufficiently large for licensees to avoid interference from adjacent areas by relocating their service within their own spectrum space as necessary, including within their own frequency band.
Deployment constraints
Whilst the two core conditions aimed at emission levels provide some measure of protection from both intermodulation effects and transmitter broadband noise, the ACA does not consider it will be necessary to provide further means of protecting against this interference mechanism through the imposition of constraints on the deployment of either transmitters or receivers in both bands. The onus will lie on spectrum licensees to determine the best location for their receivers, having regard to the overall technical framework.
It is, however, important to note that (as mentioned above) the technical framework does not provide any protection from intermodulation effects or broadband noise where devices are located within 200 metres of each of their transmitters. Consequently, the ACMA proposes to impose a special condition on the spectrum licences that will have the effect of requiring spectrum licensees to come to an arrangement amongst themselves in relation to interference in such cases. Managing interference includes investigating possible causes of interference, taking steps to resolve disputes concerning interference, and taking steps to reduce the likelihood of interference occurring.
Out-of-band issues arising under the technical framework where there are no deployment constraints imposed
The elimination of deployment constraints means that, in particular, to manage out-of-band interference, spectrum licensees may have to provide themselves with additional out-of-band ‘emission buffers’ along any ‘frequency boundary’ of their licences. Accordingly, spectrum licensees who may want to operate a receiver at a high site where transmitters in adjacent bands are likely to be operating, when considering the services that they might be able to operate within this spectrum, should note that they may have to:
- provide guard bands and/or high performance filters at the edges of their spectrum; or
- negotiate with the adjacent licensee either to employ transmit filtering, or to avoid placing transmitters near the frequency boundary at that location.
In-band issues arising under the technical framework where there are no deployment constraints imposed
The removal of deployment constraints also means that spectrum licensees who want to operate a receiver at a high site will have to:
- place their receivers at a large distance from the geographic boundary; or
- negotiate with the adjacent licensees not to place their transmitters near their own geographic boundaries.
Practical examples of the operation of the technical framework and potential loss of utility of spectrum
It is likely that both point to point and point to multipoint services will be in close proximity to each other. Therefore, it is likely that a high level of negotiation could occur at prime sites. There could also be a proportionate loss of utility of that spectrum at those sites.
Potential spectrum licensees should take such expert technical and other advice as they consider necessary to inform themselves of the technical framework, and the possible effects on their proposed services of the operation of services by other spectrum and apparatus licensees under that framework. Potential spectrum licensees should similarly inform themselves of the possible losses of utility of spectrum to which the operations of other licensees might give rise.
Managing interference between non-spectrum licensed and spectrum licensed devices
The ACMA proposes that interference between devices operated under spectrum licences and devices operated under non-spectrum licences will be managed by advisory guidelines made under s.262 of the Act. The guidelines have been developed so as to, generally speaking, provide existing apparatus licensees with the level of protection from other services that they currently enjoy. The guidelines achieve this by specifying compatibility requirements between spectrum licensed services and services operated under other types of licences. The compatibility requirements are essentially a model on the basis of which spectrum and apparatus licensees are expected to develop co-ordination procedures for the management of interference to each others services, using good engineering practice. Licensees who cannot resolve interference problems between themselves may expect the ACMA to have regard to the guidelines in dealing with such disputes.
However, the guidelines are not binding either on licensees or the ACMA, and the ACA has adopted this approach in order to provide the maximum flexibility for both spectrum and apparatus licensees in how they arrange their affairs so as to avoid interference with each others services. Once again, the ACMA is prepared to consider alternative interference management arrangements agreed between spectrum licensees and, where relevant, apparatus licensees. Spectrum licensees should, however, note that the ACMA will not give effect to alternative arrangements unless all affected and potentially affected licensees have agreed to the arrangements, and are aware how subsequent trading will impact on any agreements reached.
The ACMA recommends that radiocommunications devices be registered at the system design stage to enable apparatus licensees, if they wish, to re-check the coordination and if an obvious error is detected, negotiate directly with the spectrum licensee before further costs are incurred when transmitters are not able to be operated due to interference. Licensees should be aware that it is possible for adjacent licensees to register devices purported to be at the system design stage but never intended to be operated for the purpose of inhibiting the operation of devices through the requirements of coordination. Licensees who observe this activity may wish to take the matter up with the ACCC.
The compatibility requirements that the ACMA would normally expect to be maintained in relation to apparatus licensed receivers are described in the guidelines that follow.
These guidelines apply to receivers of the following services: fixed service, fixed-satellite service, inter-satellite service, mobile service, earth exploration-satellite (passive) service, fixed-satellite and mobile-satellite services, fixed point to point service, radioastronomy, space research (deep space), earth stations and space research (passive) stations.
Incumbent receivers (a receiver that has part of the frequency band of its spectrum access, and its location, within designated spectrum space) will require protection for the re-allocation period specified in the Minister’s re-allocation declaration for the 31 GHz band. The details of these incumbent services are in the ACMA's Register and CD-ROM. In the case of receivers operating under spectrum licences, compatibility requirements are specified in the following advisory guidelines.
Broadly speaking, these guidelines specify the compatibility requirements that non-spectrum-licensed transmitters should meet in relation to receivers that have been registered for operation in the 28 GHz and 31 GHz bands under spectrum licences. (For a more detailed description of the services to which these guidelines apply, prospective spectrum licensees and non-spectrum licensees should see the guidelines themselves.). Receivers employed by spectrum licensees will be required to operate at a minimum level of performance based on characteristics listed in the guideline. The full characteristics have not been spelt out but may be in the future.
The ACMA intends to assume that all receivers operating under spectrum licences have a performance at least equal to this minimum level of performance when settling interference disputes. The ACMA intends to settle out-of-band interference occurring across a frequency boundary of a spectrum licence, by giving a first-in time registration date priority to any devices involved. Note that, excepting for spectrum licences in the 500 MHz band, levels of in-band emissions across a geographic boundary may remain at levels that are in accordance with the core conditions and registration requirements, for the full term of the spectrum licence.
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 performance. For example, a receiver with poor performance would normally deny large amounts of spectrum space for transmitters to use 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. Poor receiver performance is only a problem when a licensee uses spectrum space belonging to an adjacent licensee.
The framework provides for the operation of receivers that have an interference susceptibility equal to or better than that achieved by current technology designed according to good engineering practice and the ACMA intends for this level of performance to guide the interference settlement process. Receivers with poor interference susceptibility performance can be used, but in those cases, a licensee may have to use part of their own spectrum space as a guard band. For example, interference that results from a receiver having an IF (Intermediate Frequency) bandwidth that is larger than the frequency band of the licence, will be the licensee’s responsibility. It is the licensee’s responsibility to use receivers in a manner that is both consistent with good engineering practice and effectively copes with the levels permitted under the technical framework.
Interference that the technical framework does not prevent
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. Under the framework described in this Chapter, it is anticipated that interference will arise 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 attempt to locate the source of any interference by checking the Register of Radio-communications Licences. 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.
Registering groups of transmitters
Transmitters must be registered (unless exempted). Transmitters must always be registered either as 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 for registration purposes.
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, multi-transmitter hub stations. Mobile transmitters, customer transmitters and indoor transmitters are exempted from device registration requirements. Note that transmitters must comply with the operating details entered in the register.
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 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 must cease. Spectrum licensees must also accept interference from any overseas service operating in accordance with ITU regulations. Potential spectrum licensees should note that the ACMA will impose such additional licence conditions on spectrum licences as may be necessary to meet its international obligations.
Health and safety
Every spectrum licensee will need to take into account occupational health and safety requirements for radiofrequency devices. Occupational health and safety requirements that concern use of radiofrequency devices are currently the responsibility of the relevant State or Territory Governments. In addition, licensees will be required to comply with any health exposure standards that may be made by the ACMA for the health and safety of persons who operate, work on or use radio-communications transmitters and receivers.
Environmental and other considerations
Antenna location, height and construction may be regulated by State, Territory or local government legislation. Before planning for a device to operate in a certain location, licensees should investigate the local rules pertaining to the erection of towers and antennas.
Obtaining a permit to operate non-standard devices
A licensee who wishes to operate standard devices under a spectrum licence (that is, equipment that conforms to mandatory ACA standards) will not have to apply to the ACMA for permission to do so. However, a permit will be required to operate non-standard devices. These permits may be issued by the ACMA under s.167 of the Radiocommunications Act 1992, and will only be issued for 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 s.174 of the Act.