Project: Updating NZ rail

In a move to improve system reliability and flexibility, while providing a platform for mobile data capability, KiwiRail, the organisation responsible for managing New Zealand’s rail network, has begun a major upgrade to the nationwide radio system used to help the safe movement of trains and track workers around the country.

The upgrade is to use radio over IP (RoIP) equipment supplied by Xworks to perform analog to digital conversion and audio compression at up to 150 hilltop and tunnel VHF repeater sites.

At the same time, aging radio equipment will be replaced and the series-connected narrowband UHF networks linking the sites to the National Train Control Centre (NTCC) in Wellington will be successively phased out.

As an initial step in the wider radio system upgrade and forming an integral component of the Project Dart improvements to rail infrastructure in the Auckland metropolitan area, KiwiRail has implemented a system incorporating ORC400 RoIP gateways and XWIRE RoIP server software to provide:

• Centralised, software-based voting between multiple audio streams received from repeaters in the region;
• Retransmission of selected audio streams to groups of repeaters, depending on the original source of the stream;
• Selcall decode of repeater IDs in audio streams received from the NTCC, and subsequent selection of destination repeater(s) for the traffic;
• Selcall encode of trailing repeater IDs in audio streams sent to the NTCC, based on the source repeater receiving the traffic.

RoIP gateways have been installed at five sites around the region, providing coverage of the rail corridor through seven repeaters.

These are connected to the centrally located RoIP server at 512 Kbps using broadband wireless access through Kordia’s integrated services network (ISN).

The equipment replaces a number of system components that are now difficult to obtain and support, including Tait Sinad voters and custom Selcall encode/decode boards fitted to the original Tait T300 and T800 radios.

A dedicated RoIP gateway has also been installed in Auckland to interface with the legacy analog dispatch system currently in use at the NTCC. This provides two independent audio interfaces, which appear as standard analog lines to the dispatch system in Wellington.

Audio signals are transported across the gap using existing frame relay equipment. The gateway also performs all Selcall encode/decode functions necessary for interoperability with the NTCC selective calling system.

During the installation and commissioning process, XWIRE RoIP client was useful for testing the operation of the new repeaters before they were fully integrated with the legacy dispatch system.

By running a client remotely across the WAN, an engineer in Wellington was able to connect to the server in Auckland and communicate with a technician via portable radio, thus exercising the system end to end.

The completed RoIP system supports simple migration from first-in, first-served race voting to a technique based on received signal strength if required.

It also provides many additional benefits, especially to maintenance and technical staff who can now remotely diagnose faults and perform configuration changes from the comfort of their office.

This feature will, no doubt, become all the more important as further sites are upgraded in isolated and outlying locations.

KiwiRail’s willingness to adopt current technology trends and make the shift from traditional analog linking and voting to a system based on the widely accepted standards used for voice over IP telephony has resulted in a flexible and cost-effective solution that will easily expand to accommodate future growth.

The end result is a system that integrates new technology with old, allowing the railway organisation to future-proof its network, while remaining compatible with existing back-end systems.

Xworks NZ Limited
www.xworks.co.nz