1. Introduction

The purpose of this paper identify options for the introduction of access to the 70 90 GHz band for short haul point to point linking in New Zealand.¹

There is growing demand for high-capacity digital connectivity to facilitate applications such as broadband and streaming video. The growth of broadband services is recognized as a national priority.² Connectivity is the keystone of New Zealand Digital Strategy. This is giving rise to exploration of new and better ways of providing transmission paths in both the private and public sectors, in conjunction with major developments in optical fibre.

One of the problems facing all countries is the need to provide optical fibre to the many points that need high speed connectivity. A number of radio solutions have been identified to provide timely high speed connection but all have limitations.³

A recent development that may be worthy of consideration in the New Zealand context is the use of the so-called ‘millimeter wave’ bands. Europe, North America and Australia have already put arrangements in place for access to the 71-76 and 81 86 GHz bands for short haul high capacity point-to-point linking.

There are a number of manufacturers now producing equipment in these bands that will support up to 10 Gbps full duplex services over line-of-sight paths up to about 8 km in length.⁴

At these frequency ranges very small antennas of 30 cm or less can give high antenna gains and produce very narrow beams. Because of the very narrow beams and the requirement for strict line-of-sight paths, careful path planning and the use of local shielding for strategic antenna placement can lead to even higher frequency re-use. Dozens of such links could traverse a city providing short range point to point links to compliment the deployment of optical fibre networks.

Because of the possibilities for significant geographic re-use of these frequencies, very little inter-system coordination is required. Most countries that have opened these bands for use have done so by the adoption of ‘minimal’ licensing regimes where the licensee is responsible for overcoming any inter-system interference. In the UK and Australia this has been termed ‘self coordination’.

Unlike with most other technologies there are very few detailed specifications for fixed-links operating in these bands. Most administrations have adopted requirements that are limited to specifying maximum transmitter and radiated powers, minimum antenna gain and the frequency band to be used. Other technological choices (e.g. the mode of modulation) are left to the developers and the end users to determine.

Use of technology in the 70-90 GHz band range is desirable because of lower atmospheric absorption. Within the 60 GHz ⁵ band the oxygen in the air is highly absorptive. With atmospheric absorption peaking at some 10dB per km at 60 GHz only very short range communication (typically less than 2km) is possible. In the 70-90 GHz bands the atmospheric absorption is less than 1 dB per km, hence the communications range is increased making it a more cost effective approach for longer paths.

Typical applications identified by the Australian Communications Media Authority (ACMA)⁶ are:

• Fibre (Backbone) POP access
• redundant access – network diversity
• enterprise campus connectivity
• local area network extension
• local loop
• metropolitan area network
• wide area network access
• central office bypass
• storage access
• wireless backhaul
• high definition video

A search of the New Zealand Register of Radio Frequencies⁷ indicates that there is currently a licensed trial of 70-90 GHz technology underway in New Zealand.

The Auckland University of Technology, Centre for Radiophysics and Space Research confirm that they are not carrying out any radio astronomy observations in these bands.

Footnotes

¹For an overview of radio spectrum policies in New Zealand see Review of Radio Spectrum Policy in New Zealand

²See the Digital Strategy website http://www.digitalstrategy.govt.nz

³For a discussion of the US situation see Cisco 02-146 ExParte FCC WTB of May 18 2003

⁴See www.e-line.com/technolgy.cfm

⁵See www.gigabeam.com/technology.cfm

⁶See ACMA paper “Planning of the 71-76 GHz and 81-86 GHz Bands for Millimetre Wave High Capacity Fixed Link Technology” December 2006 at http://www.acma.gov.au/WEB/STANDARD/pc=PC_310066

⁷SMART data base on www.rsm.med.govt.nz/pls/web/dbssiten.main