Helsinki Metro's in-carriage and rooftop antennas from Orbis
HUBER+SUHNER AG is known as a European company manufacturing high quality information network components. H+S offers a broad range of modern rail traffic and automotive products that have been designed, for example for GPS-navigation, mobile phone networks, WLAN Internet connections, surveillance camera systems, passenger information and entertainment channels. Orbis is involved in Finland in various public traffic telecommunication projects as a supplier of H+S antenna and cable solutions.
At the turn of the year WLAN-network services targeted for the passengers will be launched in Helsinki metro. Helsinki City Transport's (HKL) Project Manager Harri Perkiö explains the characteristics of the network: "HKL built a wireless broadband network that will be used to implement various services in HKL's metro carriages and stations. The WLAN network targeted for the passengers is public but the rest of the network is dedicated to HKL's internal use and applications." HKL's has its own applications, for example for the VoIP calls, real time traffic information and advertising displays.
Airspan Networks Oy has been responsible for the integration of the radio systems, broadband network trackside base stations and antennas of the metro project. Orbis has been the supplier of the in-carriage and rooftop antennas for the metro trains. H+S's antennas were selected for the metro installations after demanding testing stages.
Challenges in network building for the metro
The selection of a suitable antennas for trains and metros is based on the application used (such as WLAN connection targeted for passengers, wireless data transfer from the train to the trackside network), the train type (speed, length), the track (locations of the stations) and the tunnel profiles. Because of the tunnels, a separate base station network was built along Helsinki 21 kilometres long metro rail and stations.
In addition to the tunnels, another challenging factor in the metro is the speed of movement. The quality and non-interruption of the transmission is ensured with a proven radio network protocol, while each carriage has two directional rooftop antennas. Using two antennas the radio connection is transferred alternating from one base station to another, similar to the way Tarzan used lianas in the jungle.
High quality and environmental requirements for antennas
"The rooftop antennas looking like Shark fins are H+S 2,4GHzSencity Rail® antennas. Inside the carriage on the ceiling is located H+S omnidirectional WLAN antenna for indoor coverage", says Orbis' Account Manager Matti Rautanen.
The rooftop antennas designed for rail traffic use have to withstand the harsh environmental conditions of the North such as wide ranges in moisture and temperature. The antennas are streamlined and their height has been limited for use in low tunnels. The optimised radiation beam of the antennas improves the reliability of the track side system connection and will eliminate any interference coming from the side of the track.
In railway traffic where high-voltage catenary line cables are located above the train, the antennas have to meet strict railway safety standards, for example if in the case of malfunction, a catenary line cable falls on the train roof, the antenna has to withstand a momentary 40kA short circuit current. In addition, the high voltage must be prevented from conducting along the antenna cable to the travelling compartment where it could become fatal.
Both antennas meet strict fire safety and toxicity standards. The cabling of the antennas was hidden during the installation inside the carriage roof structures.