Communication solution for underground tunnels

Steve Harvey is the engineering manager of the APAC region for CommScope's Distributed Coverage and Capacity Solutions division. Harvey’s experience in the telecommunications industry spans more than 27 years. He started his career as an apprentice telecommunications tradesperson in Australia with the Overseas Telecommunications Commission (now Telstra). Harvey's personal interest in radio communications led him to the two-way radio industry as a technician working on base station and trunked radio systems for public safety and private sectors. For the last 10 years, Steve has specialised in designing and managing turnkey projects involving DAS design, construction and commissioning. Harvey will be speaking at the Comms Connect Sydney 2014 conference, being held this week from 18-19 June.

Electricity infrastructure provider Ausgrid’s CityGrid project expands the existing electricity network to support the growth of the CBD. It involves constructing up to three new zone substations, replacing and upgrading the high-voltage cables and constructing a new City East tunnel to link into the existing network of CBD cable tunnels.

Underground tunnels require sophisticated radio and phone systems to enable tunnel staff to communicate with the outside world. To provide a comprehensive communication solution, Ausgrid chose Commscope.

Commscope’s solution uses the ION‐M radio-over-fibre repeater which re-broadcasts the NSW Government P-25 radio network from two base station sites located in Ausgrid’s sub stations, said Steve Harvey, Engineering Manager, Distributed Coverage and Capacity Solutions (DCCS), Commscope.

Commenting on the communication challenges faced in underground tunnels, Harvey said, “The tunnel maintenance team is deployed at checkpoints where landline phones are available, and they use simplex radio to contact the working team further within the tunnel. The requirement of additional labour to man these checkpoints means less manpower is available to address the actual maintenance task at hand. Since the cable tunnels have expanded from the original South tunnel, the method of manning checkpoints puts additional pressure on the maintenance team.”

A radio-over-fibre repeater system enables coverage into these tunnels and provides a more efficient way for maintenance staff to communicate with the outside world using the existing GRN service. The ION-M has two basic components: a centralised master unit and multiple remote units. The master unit interfaces the RF signals from the base station, while controlling and monitoring the entire system. 

The remote units are connected via optical fibre to the master unit, which can support up to 124 remote units. The remote units in this case are single band 400 MHz, but are available in single- or multi-band configuration for a variety of frequency combinations, power classes and system designs.

The company’s RCT radiating cable, fixed to the ceiling of the tunnel, distributes the radio signals from the remote  units to the user terminals in the tunnel, providing a method of communications deep underneath Sydney’s CBD, where previously there was no way of communicating with the outside world.

“The base station/master rack has been expanded to feed the City East cable tunnel, reducing expense of building an entire new system for the new tunnel. A similar solution using a dedicated base station and ION‐M system could be used to provide GRN coverage into localised underground car parks, road and rail tunnels.”

Commscope hopes to get access to the City East tunnel towards the end of the year and complete the entire project by Q2 2015.

The logistics involved in getting access to tunnels, and planning and coordinating work with the construction schedule are the two key challenges, said Harvey. The main achievement is that Commscope’s system has been able to support the staged expansion of the tunnel systems and the migration of the Telco Authority’s GRN from an analog system to a digital system, without any upgrades.