Xworks Selects QNX for Mission-Critical Railway Communications System

Radio over IP system helps New Zealand Railways perform major upgrade of nationwide radio network.

by Robert Cameron, Symmetry Innovations Pty Ltd

ONTRACK, the government organization responsible for New Zealand’s rail network, operates a nationwide radio system to facilitate the safe movement of trains and track workers. The system, which comprises 148 hilltop and tunnel VHF repeaters, interlinked by a narrowband UHF network to a central control center, has had no major upgrades since it was installed in the early 1980s.

In a bold move to improve the system’s reliability, flexibility, and support for mobile data, ONTRACK has embarked upon a major upgrade, replacing the UHF-linking infrastructure with an Internet Protocol (IP) network. This project requires installation of radio over IP (RoIP) conversion equipment at each repeater site. VHF analogue radio will continue to provide voice and data communication from the hilltop to the train due to its excellent coverage properties.

ONTRACK considered several RoIP solutions before commissioning Xworks to develop a custom system based on the QNX Neutrino RTOS. The system, a four-channel RoIP device called the ORC, serves as a bridge between conventional VHF/UHF radio networks and an IP network. The ORC performs many functions, including:

• bandwidth-efficient G.729A audio compression
• integrated Selcall and CTCSS (CCIR) encode/decode
• serial control and diagnostics of Spectra Engineering MX800 base station radios
• integrated gigabit Ethernet switch
• extensive front-panel diagnostic capabilities
• remote management via SNMP and web browser
• local I/O for site monitoring and control
• support for data-only radios

The result is a fully integrated, low-bandwidth, vendor-neutral RoIP solution that operators can manage and control remotely from New Zealand’s National Train Control Centre.

Figure 1 - A single ORC RoIP unit can access up to four remote radio networks via local or wide area networks, including the Internet.

24/7 reliability

The ORC has to operate flawlessly 24/7, for two key reasons:

• It forms an integral component of the hilltop repeaters, which transmit all voice communications between rail vehicles and the train control center.
• It must decode any CCIR tone sequences, including emergency calls, that a train may transmit if a derailment or other critical event occurs.

To achieve the required level of high availability, Xworks selected the QNX Neutrino RTOS because of its inherent fault tolerance and dynamic upgradeability.

Vehicle visibility on the nationwide rail corridor is paramount. Thus, the system uses special extended Selcall packets in areas of poor GPRS coverage to guarantee 100% visibility. The ORC intercepts these position reports, decodes and verifies them, then sends them back to the Train Control Centre over the IP network.

Because many repeater sites are located in remote areas with helicopter access only, the ORC includes several remote control and diagnostic facilities; it can even be cold-started remotely. The network connectivity features offered by the QNX TCP/IP stack enable operators to perform diagnostic functions remotely via Telnet or the integrated QNX Web server. Field upgrades can be performed via FTP, and extensive non-volatile logs are kept in battery-backed static RAM. The ORC also supports DHCP, which was a key requirement, and an industry-compliant MIB, which allows access to almost all ORC functions.

Time constraints

The Xworks team had to complete this complex project within 18 months. To deliver on time, the team leveraged its previous experience with the QNX Neutrino RTOS and the QNX Momentics Tool Suite.

To complete the project, the team used many QNX software components, including the high availability manager, TCP/IP stack, DHCP client, Telnet server, FTP server, Web server (Slinger), data server, flash memory driver, RAM memory driver, 16550 serial driver (13 serial ports), and AC97 audio driver.

Code reuse was a key consideration. Thanks to the message passing architecture and resource manager framework of the QNX Neutrino RTOS, the development team was able to reuse many proven device drivers previously developed for processor-specific hardware and peripherals. No code modifications to the drivers were required.

To further reduce development time, Xworks licensed signal-processing algorithms, such as the G.729 audio codec, from Vocal Technologies of Buffalo NY, USA.

Figure 2 — To help ensure high uptimes and fault tolerance, the Xworks ORC uses the QNX high availability manager.

Nationwide deployment

Xworks has supplied 100 ORC units to ONTRACK for deployment throughout New Zealand. After rigorous on-site testing, ONTRACK’s chief radio engineer Trevor Pollock is delighted with the outcome and says “The ORC is loaded with every conceivable feature for operating a mobile radio system over an IP network. The voice quality is amazing and it’s a real miser on IP bandwidth.”

Future directions

The ORC can work in any industry that uses conventional (analog) mobile radio equipment. Potential applications include:

• Internet access to conventional voice radio networks
• Bridging of disparate radio networks (police, fire, etc.)
• Leased line and UHF link replacement
• Control and monitoring of repeater sites
• Interoperability between radio and telephone networks

Xworks also uses the QNX Neutrino RTOS in many other products, including the KMC mobile communications controller and GPS tracking device. This device is deployed in commuter trains and maintenance vehicles operating on the New Zealand rail network.

The Xworks team that developed the ORC hardware and software consisted of Aaron Croad, Kevin Buckle, and Kelvin McVinnie.

Visit Xworks at http://www.xworks.co.nz/index.shtml.