AUSTRALIAN CAPITAL TERRITORY

Telecommunications Plan

BACKGROUND AND TECHNICAL OVERVIEW

National Capital Planning Authority

July 1995

The Web version of this document http://www.tomw.net.au/ncpatw1.html is provided as a community service by Tom Worthington, Australian Computer Society, by permission of the NCPA. See also: Draft Amendment of the National Capital Plan, Amendment No. 18 (ACT Telecommunications Plan): http://www.tomw.net.au/ncpatw2.html

Contents

1.0 BACKGROUND
11.1 Introduction
11.2 Legislative Context
Commonwealth Legislation.
National Capital Plan
Territory Plan

31.3 Planning Context
41.4 Aesthetic Context
42.0 TECHNICAL OVERVIEW
62.1 Background
62.2 Mobile Phone Technology
62.3 Technology Review
72.4 Antenna Systems
92.5 Future Trends

14 1.0 BACKGROUND

1.1 Introduction

Canberra is internationally recognised as a well planned and unique capital. It has many special qualities. In particular, it has a defined system of open spaces surrounding the city and urban areas. The open spaces serve to create a pleasant living environment and protect the natural resources. The open spaces and urban areas complement one another and combine to create this unique city form.

Modern telecommunications are essential to modern society. The emergence of new technologies creates demand for additional facilities and for the introduction of new elements into the built environment of our cities. Efficient and cost-effective communications are an important part of the functioning of Canberra and contribute to its growth and economic development.

Telecommunication facilities require a network of towers, antennas and associated structures. Frequently, hill tops are good locations because they enable signals to be picked up from and transmitted to a large area.

With the increased demand for mobile telephone services and the deregulation of the number of carriers, there has been a significant increase in the demand for such facilities.

The construction of some towers has caused community concern about the impact on the special qualities of Canberra, in particular, the visual qualities of the hilltops and ridges which give the city its particular character.

The ACT Telecommunications Plan has been prepared to provide guidance to telecommunications providers as to what is expected in designing, locating and obtaining approval for the erection of telecommunications facilities. This Telecommunications Plan is primarily concerned with antennas, microwave dishes and associated ground based installations.

1.2 Legislative Context

Commonwealth Legislation.

Under subsection 116(1) of the Telecommunications Act 1991and its Regulations, carriers are exempted from the normal planning and development controls under State or Territory Legislation.

In the Australian Capital Territory (ACT), this means that the carriers are exempt from the provisions of the Territory Plan. Carriers are not exempted from the National Capital Plan (NCP) however, as it is made pursuant to Commonwealth legislation.

Carriers remain bound by the provisions of other effective Commonwealth legislation such as the Environment Protection (Impact of Proposals) Act, the Australian Heritage Act and the Endangered Species Protection Act.

The Telecommunications National Code was created under subsection 117(1) of the Telecommunications Act 1991 and came into operation on 30 June 1994. The objects of the Code under section 2 are:

"to facilitate the provision of efficient, modern and cost effective telecommunication services to the public; and
to impose responsible and uniform national requirements on carriers that engage in prescribed activities as part of developing or providing telecommunications network infrastructure; and
to maximise competitive activity by facilitating the rapid development of efficient telecommunication network infrastructure; and
to require carriers to develop or provide that infrastructure in a manner that has full regard for the need to maximise the protection of Australia's natural environment and cultural heritage; and
to require carriers to be accountable to Government bodies and the public for their activities."

The code specifically requires each carrier to prepare a plan, called the Corporate Environmental Plan , containing a description of the manner in which the carrier proposes to engage in a prescribed activity, including the measures that it will take to ensure that:

"the aesthetic, scientific archaeological, architectural, anthropological, cultural, historical and social value of a place is preserved, as far as practicable".

Additionally, the Code requires carriers to consult with relevant State or Territory Authorities and the Australian Heritage Commission. This includes bodies responsible for planning, zoning, regulation, maintenance or management of the environment in which any proposed prescribed activity is to take place.

National Capital Plan

The object of the National Capital Plan is:

"to ensure that Canberra and the Territory are planned and developed in accordance with their national significance."

Under the National Capital Plan, a communications facility or a public utility may be permitted in the following land use policy areas: National Capital Open Space System (NCOSS) and its components of Hills, Ridges and Buffer Spaces, River Corridors, Mountains and Bushland, and Lake Burley Griffin and Foreshores; Urban Areas; Broadacre Areas and, Rural Areas.

A "communications facility" is defined in the National Capital Plan as "a facility for the purpose of transmitting air-borne signals using radio masts, towers, satellite disks and the like and includes Australia Post and Telecom communications facilities, and television/radio broadcasting facilities."

A "public utility" is defined in the National Capital Plan as "The use of land for the following utility undertakings:

(a) headwork and network undertakings for the provision of sewerage and drainage services or the reticulation of water, electricity, or gas except for gas manufacture and storage;

(b) communication facilities, including Australia Post facilities, Telecom facilities, television/radio broadcasting facilities, and air navigation communication facilities;

(c) municipal uses, including street cleaning depots, public toilets, parks and garden depots, works depots and associated uses."

Design and Siting

The Design and Siting Conditions in Appendix "H" of the National Capital Plan apply as Detailed Conditions of Planning Design and Development for Designated Areas of the National Capital Plan.

Territory Plan

The planning system in the ACT is complemented by Territory legislation, the Land (Planning and Environment) Act 1991. This Act:

combines major laws on planning, land management and environmental protection in the ACT on Territory Land
establishes the ACT Planning Authority
provides for the preparation and administration of the Territory Plan.

The object of the Territory Plan is to ensure, in a manner not inconsistent with the National Capital Plan, that the planning and development of the Territory provides the people of the Territory with an attractive, safe and efficient environment in which to live, work and have their recreation.

The Territory Plan is structured in two main parts:

general principles and policies, and
policies applying to the specific land use category in which the proposed site falls.

Support from the ACT Planning Authority for any telecommunications project would be expected to be compatible with both the general policies and principles, and with the specific land use policy controls.

Under the Territory Plan a Communications Facility may be permitted in the following land use policy areas: Commercial (Civic); Commercial (Town Centres); Commercial (Other Group Centres; Commercial (Office Sites); Industrial; Municipal Services; Broadacre; Rural; Hills, Ridges & Buffer Areas (only permissible if the facility cannot feasibly be located elsewhere); Mountains & Bushland (only permissible if the facility cannot feasibly be located elsewhere); Plantation forestry.

Communications facility is defined in the Territory Plan as "the use of land for the purpose of receiving and transmitting radiated signals using radio masts, towers and antennae systems (micro wave and satellite dishes, radars, antennae)."

Under the Land (Planning and Environment) Act 1991, a proposal for a communications facility may be subject to a Preliminary Assessment of the Environmental Impact.

1.3 Planning Context

The NCPA administers the National Capital Plan which sets out the General Policy Plan for the ACT as well as specific policies for land within Designated Areas as well as National Land outside Designated Areas.

The planning policies of the Territory Government are set down in the Territory Plan. The Territory Plan identifies land use policies for all areas in the ACT which are not Designated Areas.

If the application falls within the planning responsibility of the ACT Planning Authority, an assessment will be prepared by the ACT Planning Authority. Following assessment, the ACT Planning Authority will report to the NCPA. The NCPA will determine if the application is consistent with the National Capital Plan.

1.4 Aesthetic Context

The natural setting of Canberra complements the urban areas. The development of communication facilities should not impinge on the aesthetic qualities of the city. This means that the impact needs to be assessed in terms of the implications for both the urban and open space areas.

It is recognised that there is an acceptance by the public of the need for facilities associated with modern technology. This acceptance is however, considered to have its limitations particularly where the unique qualities of the ACT may be compromised. Accordingly, the assessment of the impact of a proposed facility needs to be carefully considered in the context of the particular area in which it will impact and the potential cumulative impact of further structures.

The specific performance requirements of a particular facility will determine the optimum siting and construction specifications. In sensitive locations the impact of a structure may be minimised by minor changes to locations and antenna design (height and head configuration). Such changes may require compromise in order to reduce visual impacts.

In other circumstances it may be appropriate to erect a larger mast or tower to either facilitate co-masting and thus prevent the proliferation of further towers, or increase the coverage and reduce the need for antennas in other locations. Conversely, it may also be appropriate in some instances to erect two small antennas which achieve the same coverage but with less impact.

2.0 TECHNICAL OVERVIEW

2.1 Background

This section considers the technical issues involved with the erection of radio towers for the provision of mobile phone and other carrier provided services. The section is intended to provide a basis for a common understanding of the current state of technology applicable in particular to mobile phone facilities. The technologies being used to provide mobile telephone services and the technical requirements for siting of antennas associated with those services are discussed.

2.2 Mobile Phone Technology

Number of Carriers

Presently there are three carriers: Telecom, Optus and Vodafone. Each carrier is in the process of installing a digital mobile telephone network using technology called Global Systems Mobiles (GSM). This technology conforms to standards agreed world-wide by the Committee Consultative Internationale Telephone et Telegraphique (CCITT).

GSM technology is used by Australia's neighbours New Zealand and Hong Kong as well as many European nations. GSM was selected by the Australian Government for use in Australia.

The main difference between the carriers is their approach to the market. The carriers' approach is dominated by market demands and their network design reflects this. Telecom has an existing network infrastructure on which to overlay its digital network, and is making best use of these sites where possible. This is a cheaper way of implementing the network but, does not focus on the customer demand for the service. This difference in approach to network development affects the way sites are selected for base stations.

Analogue System (AMPS)

The existing analogue mobile phone system uses analogue transmission techniques similar to ordinary FM radio broadcasting. The telephones and base stations transmit on one frequency and receive on a second frequency. The analogue system is quite expensive in terms of its usage of the radio frequency spectrum. To achieve adequate coverage, the system uses approximately 660 individual frequencies and many base stations.

Telecom is the only carrier which provides the infrastructure for analogue mobile phone services. Optus also provides analogue mobile phone services but leases and resells time from Telecom's network. Optus provides billing and customer services but, does not provide any hardware for the network itself.

Some of the AMPS base stations in the ACT are sited at previously existing Telecom or other Commonwealth Government sites. This has prevented good coverage in certain areas in Canberra.

The AMPS coverage of Canberra was initially provided by three sites. The predominant site was Black Mountain Tower. Black Mountain provided blanket coverage of much of the city and its environs. The power output from this station was very high at first, but as the user base increased, too many problems were caused by interference so additional base stations were installed. These new base stations used existing Telecom telephone exchange sites. The use of existing sites was cheap, but not necessarily able to provide the coverage needed. Since the installation of these additional bases, the power output from Black Mountain has been reduced significantly.

The greater number of base stations within this system causes interference between cells and telephones and increases the complexity of the network switching systems required to transfer calls between cells without losing the call as the mobile phone moves between cells. This is a common cellular network design problem.

The AMPS system relies upon use of many frequencies and many stations to achieve what is known as frequency diversity and space diversity respectively. Each base station has the capacity to transmit on a given number of frequencies depending on the density of users within that cell.

In most cases, AMPS antennas are omni-directional and the transmit and receive radiation patterns resemble a "doughnut" around the antenna tower.

Digital System

The three carriers are installing digital mobile phone networks which essentially use the same technology. Each carrier has an allocated number of channels within the band for digital mobile phones.

The design of each system is such that telephones connected to one network are not easily able to operate on the other carriers' network. Points Of Interconnection (POI) have been established between networks so that users on one network are able to call users on another network or the normal Public Switched Telephone Network (PSTN).

2.3 Technology Review

Network Planning

The part of the frequency spectrum which is available for mobile telephone use is very limited. Therefore, cellular telephone systems must use the spectrum efficiently to provide an adequate service for a large numbers of users.

Efficient use of the available frequencies is achieved by systematic re-use of channels. The diagram below shows how frequencies could be re-used over an area:

The ideal coverage area of a base station over flat terrain would be circular. The hexagonal shape is used for clarity to show how cells mesh together. In practice, the terrain causes the coverage area to be irregular. The available channels are divided into a number of sets called clusters. The number shown within each cell above represents a set of channels used within that cell. In the example given above, seven channel sets are used.

The black circles represent where base stations might be located to provide service to the surrounding cells. Each cell can handle eight simultaneous calls for each frequency set shown.

The base station sites are selected so that coverage is obtained to provide the minimum acceptable level of service to the customer. It is therefore not always based on technical radio communication paths to every part of the cell, but more towards the location of customers. Where usage is high, additional base stations may be required. When additional cells are installed frequency sets are reassigned between surrounding cells to prevent interference.

Frequency Bands

The digital telephone network uses the frequency band from 890 Megahertz (MHz) to 960 MHz. This frequency band is divided into 124 channels for use by the carriers. Each channel consists of a pair of frequencies, one for receive and one for transmit.

Each carrier has been allocated 25 channels. Telecom has been issued channels 51-75, Optus channels 76-100 and Vodafone 101-124.

Analogue v. Digital

Operational characteristics:

The digital mobile telephone system achieves a more efficient use of the frequency spectrum. This means that GSM will be able to support more mobile phone services than AMPS.

Each channel carries up to eight telephone conversations at a time by using a technique called Time Division Multiple Access (TDMA) where the usage of the channel is divided into eight time slots and each telephone which has a call in progress uses one time slot. The base station allots the time slot to each phone as a call is set up and then monitors progress of each call.

If the distance from the mobile phone to the base station is too great, the call will drop out or the base station will hand the call over to a nearer base station. This is a service limitation of GSM, limiting the distance to 35 km radius of the base station. In both systems, the more base stations within a coverage area, the higher the grade of service to the users.

With the digital system, each call is better protected from eavesdropping because the signal is digital and cannot be decoded except by another phone tuned to the same frequency and time slot. In addition, the information contained within the signal can be easily encrypted to add additional protection.

Signals:

Analogue signals appear on test instrumentation as "waves" whereas digital signals appear as bursts of energy.

The power of analogue radio transmissions is continuous during the period of transmission and is therefore at a constant level during the transmission. This is easily measurable with test instruments while the transmission is occurring.

In the case of digital transmissions the signal is transmitted in bursts occupying shorter time frames with higher instantaneous power levels. The average power transmitted over time is actually lower than most analogue transmissions.

The digital signal is usually less susceptible to interference from radio waves from such equipment as motor vehicle ignition systems, mobile radio, electric motors and welding equipment. The lower susceptibility is related to the relatively short time frame for individual bursts of energy and the error detection and correction codes incorporated in the data stream. This capability to correct errors makes the received signal more useable after detection by the radio receiver.

2.4 Antenna Systems

Types

Antennas used by the mobile telephone carriers vary from omni-directional monopole wire type devices to highly sophisticated electronically controlled directional devices. A number of techniques may be used to control the direction of radiation, the shape of the beam and the signal strength in a given direction (known as the Gain).

The towers used by the various carriers have similar design requirements, they support one or more antennas depending upon the number of cells covered by the tower's base station.

The single pole type towers generally support up to three omni-directional monopole antennas: generally one transmits and two receive.

The antennas which appear to be panels are, in fact, highly directional and are known as phased arrays. Electronic control of the phase of the signal and the antennas' proximity to each other, control the direction, shape and strength of the radiated signal in the desired direction. These radiation patterns may appear as "tear drop" shaped lobes in the three dimensional representation.

Range Vs Frequency

The energy radiated by the antenna travels in straight lines. At higher frequencies the radiated energy is absorbed or reflected by trees, buildings, vehicles and the terrain.

As frequency increases signal attenuation due to its passage through the air increases. The standard range limit for GSM is 35km. This is due to the GSM specification and does not include any additional limitations imposed by terrain or reflections. With the analogue CMTS service (AMPS), range is determined purely by field signal strength which itself is determined by attenuating factors such as terrain and objects.

In some places, a phenomenon known as fading occurs where reflected waves cancel each other out and no signal may be measured. The dead spot is usually very small at the frequencies used for mobile phones and the user may only need to move a matter of inches to regain a good signal.

Radiation Patterns

The carriers use different types of antenna as conditions dictate. For example, Optus uses 6 different types of antenna within the ACT region, and a total of 12 types nationally.

Where required, the carriers use directional antennas to cover a particular customer area. The antennas are often known as phased array devices where multiple antennas are combined into a single antenna to provide "gain", tilt and directionality to the signal. The radiation emitted by such an antenna may be uni-directional, bi-directional or any specific shape determined by the service requirement. The signal is "steered" either by the shape of the antenna, electronically or a combination of both.

Siting

In the mobile phone industry the siting of radio base stations is predominantly determined by demand. For example, if a large number of users is located within a city block, there may be more than one or even two cells required to provide an adequate service.

When planning for new sites, the carriers usually test a number of sites in a particular service area and select the best option. An important factor to be taken into account is the anticipated area which will be serviced and how this relates to a carrier's network arrangement.

Line of sight requirements

Since radio signals at high frequencies travel in straight lines, a clear path is desirable between transmitting and receiving antennas. Absorption and attenuation may be significantly reduced when antennas are placed in fairly obvious positions above buildings, near hilltops on towers or on rooftops.

Effect of height above ground

In general terms, the higher an antenna is placed above the ground, the greater the range at which the radio signal may be received. At the higher frequencies being used by cellular phones, the signal is attenuated by its passage through the air.

As it is desirable to receive the signals at ground level, in vehicles and within buildings, the signal strength must be such that it achieves a minimum specified strength within the coverage area. This requirement means that the installation engineers must site the antenna for each base station so that the minimum signal level reaches all parts of the coverage area. In some cases, this means that the top of hills, roofs of buildings or towers must be used to place the radiating elements of the antennas at the optimum height to achieve the minimum signal strength. The same signal strength could be provided by multiple base stations at lower heights.

When installing the transmit and receive antennas, the physics of radio communications requires a small distance between antennas used for transmitting and receiving.

Mast Height and Design

Mast height is determined by coverage required to meet the customers' needs. Two types of structure are in use. The most common is a concrete or steel monopole. The second is a lattice tower.

The tower serves only one function in mobile phone base station design, to support the antenna. This is unlike the towers used for commercial broadcast radio and TV where the mast itself forms the radiating element.

The carriers have almost universally selected a common mast height for the monopole tower design as would be expected since the frequency bands are similar for each carrier.

Where the terrain coupled with performance requirements has required lattice towers to be installed, these have been much higher and more noticeable on the skyline from certain angles of view.

Building and Vegetation Effects

Buildings affect the transmission of radio waves at the frequencies used by cellular phones. Mobile phone users need to be able to use their phones within buildings, and the radio waves for the phones penetrate buildings in the same manner as AM and FM radio and TV transmissions through the roof, wall and windows. Only buildings with special shielding prevent the penetration of radio, TV and phone signals.

Buildings may cause reflection of the radio waves and engineers may make use of this effect when siting antennas in heavily built up urban areas with many high-rise buildings. Building interference may also necessitate more cells than may otherwise be required.

Trees and thick scrub affect the passage of radio waves at frequencies above 30 MHz. The higher the frequency, the more the signal is affected by vegetation. Antennas need to be sited such that trees in close proximity do not interfere with the signal. This may necessitate additional mast height to minimise any effects, and allow for tree growth.

Climate and vegetation combine to affect the level of attenuation of radio signals. For example, tropical climates and rainforest type vegetation severely effect propagation at frequencies between 80 MHz and 400 MHz. In dry areas like the ACT, radio propagation is generally good at most frequencies above 400 MHz, because the level of moisture in the earth is lower.

Minimum clearance distances are maintained between antennas and buildings or trees mostly for safety reasons. Hazards include fire, storm and unauthorised access to the towers by unqualified persons who may damage the equipment or injure themselves.

The minimum distance also reduces the attenuation effect on the radiated signal strength which the buildings and trees might cause. If the signal travels in clear air for a number of multiples of the wavelength the level of attenuation caused by objects in its path is reduced. This is the main reason for siting towers and antennas so that the major signal lobes clear the nearest surrounding vegetation or buildings, even though in high-rise built up areas the buildings may provide good signal "corridors" and isolation between cells.

Transmission

Each base station site is connected to the central switching site by either cable or microwave radio relay links. These microwave links are transmitted or received through the dishes located below the mobile phone antenna systems.

In the case of Optus and Vodafone, almost all connections to the switching centre are via microwave paths. Telecom uses existing connections via fibre optic cables or microwave links on existing towers. Telecom already has connections to most of its towers because it is re-using the AMPS towers for the digital system. Telecom's towers may have more antennas installed since many services may be provided from each installation.

Co-siting and Co-masting

Co-siting of antenna towers is possible but may require coordination of frequencies in use at the site between the carriers to prevent mutual interference between bases at the site. Co-siting is avoided by carriers because of the added complexity of filtering equipment on both transmitting and receiving equipment and antenna design. The cost of co-sited base stations could be significantly increased for each carrier dependent upon the actual design of the individual base station.

In relation to co-masting the following issues of concern would be who owns the mast; who may have access to it and when may access be denied. Safety, structural strength and future expansion are also matters for consideration. As well, the tower must be correspondingly higher to accommodate the additional antennas and equipment. Not only must the tower offer physical separation between antennas but electrical separation must also be provided for the feeder routes and other control signal entry paths.

Surface Treatments

The antennas may be painted depending upon the visual impact desired or the effect on signal radiation. Parabolic dish antennas are usually painted or covered by radomes to protect them from the weather.

The Department of Defence has a number of special paints which are non-reflective to both light and electromagnetic radiation. Similar versions of these paints are available commercially, but they are quite expensive and require frequent repainting.

A surface treatment applied to the tower may be useful in reducing the visual impact particularly if the tower is illuminated by afternoon or morning sun or by lighting at night. Sites should be examined to determine if a surface treatment would make the towers and antennas blend into the environment.

Some towers need to be painted to be clearly visible for aircraft safety and the visual impact of these needs to be enhanced rather than reduced. This is particularly true where towers are under flight paths.

Emerging Antenna Technologies

The technology used by today's mobile phone system is advancing constantly. Antenna design does not advance as rapidly as other areas of electronics. The requirements to match the antenna to the atmosphere electrically do not change although shape and design of the components of antennas vary with frequency and signal type.

Antennas generally become smaller as frequency increases. Antennas are based on dimensions of one half or one quarter of a wavelength. At the microwave frequencies used for mobile phones, the wavelength is about 10 centimetres. When this wavelength is considered against the physical size of the antenna systems installed by the carriers, they seem very large. It must be recognised that the antennas on the towers are in fact systems of antennas with multiple antennas on each tower at each frequency to serve the coverage area.

2.5 Future Trends

User Connections

Each of the carriers expects to gain a significant share of the market and all confidently predict rapid growth in the market. Australians have been quick to adopt new technology generally, and the mobile phone has surpassed even the growth in the use of facsimile machines. It is expected that the digital phone market will continue to grow as the service levels improve.

Technology

Technology is constantly improving the performance of electronic devices as well as decreasing the size whilst providing additional features. The cost of catering to the ever-increasing demand for services is reflected by a larger infrastructure base.

In the case of the digital mobile telephone, the greater the number of customers the greater the number of base stations that will be required. The carriers must guarantee a minimum level of service to retain their licences. As the demand for mobile phone services grows, the need for additional sites for the construction of new facilities will increase.