This section summarises:
- the technical framework underpinning spectrum licensing in the 3.4 GHz bands;
- the operation of the s.145 Determination of unacceptable interference;
- the two Advisory Guidelines that manage in-band and out-of-band interference; and
- other important information about the technical framework.
Introduction
The technical framework for 3.4 GHz has been established by the ACMA to support the use of both point-to-point and point-to-multipoint services in an unbiased manner. It has evolved from the frameworks of previous spectrum licence allocations and there are several new ways in which flexibility has been increased for 3.4 GHz.
The 3.4 GHz framework maximizes flexibility and certainty for access to the spectrum space of the licence and is based on the circumstances existing at the date of issue of the Marketing Plan. The framework seeks to minimise negotiation between adjacent licensees for the management of both in-band and out-of-band interference. These three main design objectives create a benchmark spectrum utility that is independent of any ability or cost to negotiate with adjacent licensees about management of interference. Based on this benchmark utility and in relation to specific equipment, it is possible to establish the value of the spectrum for a business plan, given that the cost of spectrum is an important aspect of network viability.
While the benchmark spectrum utility is always available, the framework also provides for both the sharing of spectrum and varied compatibility requirements through agreements with adjacent licensees. This facility provides licensees with the choice of either managing their spectrum in accordance with the benchmark utility or, where adjacent licensees are satisfied with alternative levels of flexibility and certainty achieved through negotiation, designing other, possibly simplified, methods of spectrum management. Although existing equipment standards are taken into account to create harmonised generic emission limits for out-of-band and out-of-area emissions, the spectrum lots offered and subsequent issue of spectrum licences, may or may not align with the channel plans or out-of- band emission limits of a particular standard.
The inherent flexibility of a spectrum licence acquired in this allocation is left for the licensee to extract. However, this needs to be based on a careful technical and commercial assessment before the auction taking into account the harmonised generic emission limits and amount of spectrum available and purchased in relation to the performance of the equipment the bidder desires to operate.
The spectrum lots and subsequently issued licences are not pre-designed to accommodate any particular standard. However, they may accommodate the operation of a particular standard (or even non-standard equipment) at a particular location and frequency,depending on the size and shape of the licence that a bidder has acquired.
The technical framework is constructed from three interlocking tools. Two of these tools are used to keep significant levels of emission within the space of the licence, 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 specific devices as required, normally spectrum licensed and apparatus licensed services operating within the re-allocated and surrounding spectrum.
The entire technical framework is predicated on the assumptions that:
- spectrum and apparatus licensees will employ good engineering practice in establishing and maintaining their services; and
- receivers employed by spectrum licensees will, as a minimum, meet the minimum receiver performance levels set out in Schedule 1 of the Radiocommunications Advisory Guidelines (Managing Out-of-band Interference in Receivers Operating in Spectrum Licensed Space - 3.4 GHz Band) 2000 (see Receiver Performance below); and
- receivers employed by apparatus licensees will, as a minimum, meet the relevant standard made under the Radiocommunications Act 1992 or, if there is no such standard, any 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 apparatus 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;
- absolute power levels have been specified as emission limits rather than power levels relative to the transmitter power allowing 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 allowing 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 mechanisms that the technical framework seeks to manage are those caused by:
- unwanted in-band emissions;
- emissions falling outside the frequency band of the licence;
- transient unwanted emissions such as those caused by switching a transmitter; and
- intermodulation effects.
All four 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 out-of-band interference, such as that caused by intermodulation effects. Firstly, when no guard band is provided, constraints are imposed on the deployment of transmitters by means of the registration process. Secondly, a licence condition imposes on spectrum licensees the responsibility to manage out-of-band interference that arises from devices being located within 200 metres of each other.
As described above, the technical framework is a benchmark upon which further flexibility may be negotiated between licensees. Spectrum licensees may negotiate among themselves and, where relevant, apparatus licensees, for alternative management arrangements about emission levels. Spectrum licensees should, however, note that alternative arrangements are not possible unless all affected and potentially affected licensees have agreed to the arrangements. In this allocation, the ACMA has amended a number of parts of the technical framework for the bands to provide explicitly for agreements between spectrum licensees apparatus licensees. Included in these procedures is a prescribed Form of Agreement (included in the Radiocommunications Spectrum Marketing Plan (3.4 GHz Bands) 2000. The form of agreement provides a template for any agreements that relate to licensees agreeing to accept emissions that would, in the absence of those agreement, exceed the core conditions of the licence. For example, spectrum licensees might agree alternative arrangements with other licensees for higher levels of emission outside the frequency band of the spectrum licence or for higher levels of radiated power closer to a geographic area boundary than would have otherwise been allowed. The new arrangements introduced in the 3.4 GHz bands explicitly provide core conditions on the licence to give effect to the agreement between licensees.
Applicants are advised to review carefully the arrangements set out for agreements between spectrum licensees and between spectrum licensees and apparatus licensees contained in the Radiocommunications Spectrum Marketing Plan (3.4 GHz Bands) 2000.
It should also be noted that agreements between licensees can only continue to apply while the size and the shape of the spectrum space owned by the licensees remains the same. Where trading of licences takes place and new boundaries are formed, these agreements will need to be re-negotiated. 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 spectrum space, and agreements are not in place, a check will be required to ensure that the ‘device boundaries’ of devices that are to continue operating remain within the geographic area of the relevant licence.
Core conditions
This part of the Section 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 horizontally radiated power (measured within a 30 kHz bandwidth) of 52 dBm eirp. The conditions, therefore, effectively place an overall cap on power at the boundary and also throughout the entire geographic area of a licence. This condition allows a constant power spectral density throughout the space of a licence and although it may not be immediately obvious, aids the management of intermodulation interference by placing an upper limit on the level of mixing signal components. In addition, except where the occupied bandwidth of a transmitter is less than 30 kHz, the core condition does not place a limit on the total radiated power of a transmitter. However, in practice the total radiated power is limited indirectly by the cost of high power amplifiers, the general requirement to use low powers in cellular systems, and the emission limits outside the band becoming increasingly difficult to satisfy as total transmitter power increases.
If over the 15 year licence term, mobile transmitters become available, emissions from a mobile transmitter are limited to a horizontally radiated power (measured within a 30 kHz bandwidth) of 25 dBm. The framework does not provide for a transmitter located on an airship or on a balloon. However, when the size of the space of a licence allows, special arrangements may be negotiated with the ACMA for the operation of a transmitter at these types of locations.
An additional layer of management is imposed at the point of registration of devices. Before registering a device a licensee or accredited person must, in addition to checking that the core conditions are maintained, calculate the device boundary of the transmitter in accordance with the relevant determination made by the ACMA under s.145 of the Act – see the Radiocommunications (Unacceptable Levels of Interference – 3.4 GHz Band) Determination 2000. This 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 sensitivity that will be achieved 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. The ACMA publishes software tools for calculating tables of effective antenna heights for any location in Australia.
The device boundary is an important element of the framework because it specifies an exact and direct procedure to determine the maximum radiated power of a transmitter (based on the effective antenna height and distance from the boundary) that cannot be challenged by an adjacent licensee. The direct nature of the limit means that licensees can work closer to the geographic boundary of the licence than otherwise because no reliability margins are required to ensure a specified field strength occurs at a boundary. In addition, licensees can accurately plan for transmitters operated by adjacent spectrum licensees across the area boundary at any time in the future. Also, the device boundary may or may not be based on actual propagation models depending on the outcome required. And, it provides a simple
facility for establishing agreements between licensees for sharing spectrum space across area boundaries by employing a single parameter which may be varied to expand or contract the device boundary to provide more or less in-band protection respectively.
If the device boundary 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. An exception to this general rule can be made where there is an agreement in the form prescribed in the Radiocommunications Spectrum Marketing Plan (3.4 GHz Bands) 2000. In these circumstances, the agreement provides that a device boundary may exceed the licence boundary of a licensee because the adjacent licensee has specifically agreed to that and accepts any interference caused to its use of the spectrum.
The effect of the device boundary procedure is to create ‘emission buffer zones’ along the geographic boundaries of the licences. However, it is possible to register a device in these circumstances where all affected licensees reach alternative arrangements for the management of emission levels, thereby, either reducing or increasing the extent of the emission buffer zone as required. In particular, because the city lot areas for 3.4 GHz were selected before the development of the technical framework, the device oundary may not lie within the city lot area when the horizontally radiated power is very high, for example, when using narrow band emissions, and some utilisation of the regional area may be required. Potential spectrum licensees should take such expert technical and other advice as they consider necessary to inform themselves of this aspect of the technical framework.
The corollary of this aspect of interference management is that 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 relevant s.145 determination of unacceptable interference or levels otherwise negotiated with the relevant spectrum licensees.
Out-of-band emissions
Emission limits outside the band are imposed by a core condition. However, varied levels may be negotiated with affected adjacent licensees. The form of agreement described above also applies to these agreements with spectrally adjacent licensees. 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 to establish whether the operation of a device will cause ‘unacceptable interference’ by breaching these emission limits. 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 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 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 to the alternative arrangements.
Levels of protection not provided
It should be noted that under the prototype interference management regime, established for spectrum licensing in the 500 MHz band, receivers in adjacent areas were 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. Such a mechanism is not necessary for the 3.4 GHz band, because the STU bandwidth, made up of a minimum aggregation of 10 contiguous 250 kHz segments (2.5 MHz), is sufficiently large for licensees to avoid interference from adjacent areas. Interference would be avoided 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 intermodulation effects, the ACMA considers it will be necessary to provide further means of protection against this interference mechanism. To this end, when a licensee does not provide certain guardspace, the ACMA proposes to impose constraints on the deployment of transmitters. The ACMA does not intend to impose deployment constraints on receivers, and the onus will lie on spectrum licensees to determine the best siting for their receivers, having regard to the overall technical framework.
It is, however, important to note that the technical framework does not provide any protection from intermodulation effects where transmitters are sited within 200 metres of each other. Consequently, the ACMA proposes to impose a special condition on the spectrum licences that will have the effect of requiring spec rum licensees to come to an arrangement with neighbours in relation to interference in such cases.
The deployment constraints vary from band to band. The constraints are expressed in terms of effective antenna height, which is calculated using the average ground height within approximately 10 kilometres of each device. For a more detailed explanation of effective antenna height, please see the relevant s.145 determination. Note that there is an allowance of 48 metres for rolling terrain when calculating effective antenna height in the Lower Band.
3.4 GHz Lower Band, 3425 MHz – 3475 MHz
The ACMA anticipates that receivers in this band will normally be located at high sites and the deployment constraint, which only applies to transmitters using antennas with a beamwidth greater than 5 degrees, effectively provides protection from both in-band and out-of-band interference to high sited receivers operating in the space of adjacent licences (across either the frequency or area boundaries).
While there is no deployment constraint for transmitters using antennas with a beamwidth equal to or less than 5 degrees, there is a limitation that no more than three transmitters operating on the same frequency are allowed at any one site.
For licensees to operate transmitters using antennas with a beamwidth greater than 5 degrees they must either deploy those transmitters at an effective antenna height of no more than 10 metres or provide guard space in accordance with the information paper Registration of radiocommunications devices under spectrum licences.
This constraint manages out-of-band interference and provides for the deployment of both point-to-multipoint and point-to-point services in essentially an unbiased manner. Potential licensees should have regard to this when considering potential sites and the utility of the spectrum.
A number of problems need to be considered by licensees when the deployment constraint is avoided through the use of guard space. To manage out-of-band interference, spectrum licensees may have to utilise the guard band provided by the adjacent licensee to install filters at the edges of their spectrum and/or negotiate with the adjacent licensee either to employ transmit filtering, or to avoid placing transmitters near the frequency boundary at certain locations. In addition, to manage in-band interference from transmitters that do not comply with the deployment constraint, the guard area provided by an adjacent licensee should provide levels of isolation for receivers to the same extent as provided by the s.145 Determination.
These issues may be important when considering the operation of time domain duplex (TDD) based equipment in the lower band. These examples of how the interference management regime might affect proposed services and spectrum utility are not intended to be exhaustive. 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.
3.4 GHz Upper Band A, 3475 MHz – 3492.5 MHz and Upper Band B, 3542.5 MHz – 3575 MHz
In the 3.4 GHz upper bands, transmitters may be deployed at any effective antenna height.If spectrum licensees follow this anticipated siting of transmitters, interference from intermodulation effects will normally be a co-siting issue (again, except where TDD equipment is to be used and where guard bands may need to be provided by a licensee), and require resolution between spectrum licensees and others under the special condition requiring negotiation where transmitters are sited within 200 metres of each other. 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.
Managing interference between apparatus and spectrum licensed devices
Interference between devices operated under spectrum licences and devices operated under apparatus licences is managed by advisory guidelines made under s.262 of the Act. The guidelines have been developed, generally speaking, to provide apparatus licensees existing before the issue date of the Marketing Plan, with continuing levels of protection that they currently enjoy under the apparatus licensing system. The guidelines achieve this by specifying compatibility requirements between spectrum licensed services and apparatus licensed services. 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 other’s 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.
Apparatus licences issued after the date of the Marketing Plan, undergo an in-band coordination process with the space of spectrum licences that provides a spectrum licensee with the same level of protection from apparatus licensed transmitters as if the device boundary criterion is applied to the apparatus licensed transmitter. The co-ordination process also ensures that the necessary compatibility requirement is provided to the apparatus licensed receiver in a manner that does not reduce the utility of the spectrum licence as long as transmitters are operated in accordance with the spectrum licence conditions. In the case of out-of-band interference, a compatibility requirement is applied on the basis of first-in-time device registration.
The guidelines are not binding either on licensees or the ACMA, and the ACMA 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 other’s 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 that subsequent trading of spectrum will impact on any agreements reached. The ACMA also recommends that radio-communications devices be registered at the system design stage. This will 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 cannot be operated due to interference. However, the registration of devices that are never intended to be operated or have entrepreneurial objectives as their primary purpose should not occur because they have the potential to inhibit the operation of devices by adjacent licensees through the coordination requirements.
The compatibility requirements that the ACMA would normally expect to be maintained in relation to apparatus licensed receivers licensed before the issue of the Marketing Plan (including incumbent services during the time of the re-allocation period), are described in the guidelines as follows.
These guidelines apply to receivers operating on the basis of ACA RALI FX14. For the 3.4 GHz bands, the details of these receivers and related transmitters are to be found in the ACMA’s Register of Radiocommunication Licences CD-ROM. An overview of propagation models is given in the guidelines to assist licensees in the development of suitable coordination procedures.
Incumbent receivers (a receiver that has part of the frequency band of its spectrum access, and its location, within re-allocated spectrum space or a receiver which communicates with an incumbent transmitter), will require protection for the re-allocation period. Receivers for which apparatus licences were issued before the date of issue of the Marketing Plan, and which are:
- outside the bands to be spectrum licensed; and/or
- outside the areas to be spectrum licensed
may require continuing co-channel and adjacent channel protection for the full term of the spectrum licences. The ACMA will rely on these s.262 advisory guidelines to establish a benchmark against which complaints of intereference will be investigated and resolved.
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 apparatus licensed transmitters, issued after the date of the Marketing Plan, should meet in relation to receivers registered as operating within the space of a spectrum licence. The guidelines may also be used to settle interference between two spectrum licensees, for example, across the frequency boundary between the lower and upper bands at 3475 MHz. The compatibility requirement for a fixed receiver operated in the space of a spectrum licence is based on a minimum receiver performance level and applied only if the receiver is registered before any of the transmitters causing the interference (first-in-time registration). The receiver also needs to be operated or authorised to operate by the licensee and have a certain manner of deployment, having regard to the band in which it is operated, the effective antenna height and the beamwidth of the antenna.
A minimum receiver performance level is specified to enable licensees to develop appropriate co-ordination procedures. Although a licensee may operate a receiver of any performance level, the ACMA intends to assume that all receivers operating under spectrum licences have a performance at least equal to the minimum performance when settling interference disputes. For a more detailed description of the services to which these guidelines apply, prospective spectrum licensees and apparatus licensees should see the guidelines themselves.
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.
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 commensurate with that achieved by current technology and 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 guard space. For example, interference that results from a receiver having an RF or IF 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. This is because the technical framework is designed according to certain levels of acceptable interference probability. Under the framework described in this Section, it is anticipated that interference between spectrum licensed devices will occur at about the same rate as between apparatus licensed devices, that is, 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 Radiocommunications 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
Unless exempted, 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 that 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.
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 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 siting, 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 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 s.174 of the Act.