In today's world, public transportation, whether high-speed trains, subways or other commuting options, no longer simply face just the task of transporting passengers from point A to point B. Further considerations beyond vehicle operations apply, including public safety as well as passenger's experience. In the US, 81% of commuters spend an average of at least one hour a day commuting to and from work.
In Europe, the average stands at 45 minutes and in Asia, the average is even longer. With time being a valuable resource, a commuter's time on mass transportation is a valuable commodity. In today's fast paced world, most passengers cannot afford to tune out for such a long periods of time. Passengers utilize this time to unwind, catch up on work or news, listen to music and more, creating a greater demand for wireless solution in mass transportation.
Different Technologies Offer a Variety of Solutions
There are a number of technologies that provide multiple solutions for public transportation broadband wireless. Each technology has its value and limitations. Wireless broadband solutions have multiple functions on trains: the basic, critical function of command, control and operation of the train; public safety via in-cart video that transmits all onboard activity back to HQ, as well as info regarding driver and passenger experience. We must also keep in mind that the greater the distance and speed covered by the train, the greater the challenge of providing a reliable broadband wireless solution.
Train-to-ground communication is mostly conducted by radio, which is mostly voice and analog. To overcome this gap between analog radio communications and the current demand for wireless broadband, operators usually deploy several radios, each with a different purpose. These include: TETRA/ 3RP, P25, IEEE 802.11a/n WiFi and GSM-R.
Fast handoff requirement for transmitting onboard information back to HQ poses another great challenge for train broadband wireless communications. Average handoff time takes a few seconds, however, a high-speed train has less than a second for handoff.
Train-to-ground communications in urban and N-LOS areas poses yet another challenge. In most cases, Professional Mobile Radio (PMR or Private Mobile Radio) combined with TETRA or P25 is used. This mostly delivers the demand for voice communications, command and control, but offers very limited bandwidth and a UHF spectrum that is often congested by other users.
Another option would be WiFi & CBTC DCS technologies. These do provide large bandwidth capacity, low packet loss rate and can overcome N-LOS barriers. However there is a need for a WiFi infrastructure to be placed alongside the train's rails and routes. This becomes more challenging in long distance routes such as the Shanghai- Lassa train in China, spanning over 2,000Km. There is also a range limitation – radio coverage between 200m to 500m due to Dynamic Frequency Selection (DFS).
The GSM-R (GSM- 2G+) technology is a more advanced option that carries both signaling information and voice. The GSM-R is part of the new European Rail Traffic Management System (ERTMS) standard. This technology offers low bandwidth, fast handover and the ability to transmit speech communications in multiple modes: broadcast mode, group call and emergency calls. However, very few communications manufacturers offer this technology.
The Next Generation of Wireless Broadband Solutions for Trains
To overcome the above challenges, more and more train operators seek LTE based broadband wireless solutions. LTE is basically the global 4G wireless standardization. It provides high performance, fast handoff, high bandwidth, greater coverage, flexibility and easy deployment, and is also embraced by most communications solution providers. Collaborating 4G technology with MESH topology takes this even further to deliver a best-of-breed solution. This collaboration enables a greater frequency range that allows for the division of multiple broadband wireless functions on trains based on frequency range. High frequency range for shorter distances (greater coverage), low frequencies for higher speed and greater distances. Price wise, MESH topologies usually require less HW and no infrastructure, making the overall maintenance and operation cost-effective and simple. This is the estimated path for a train and public transportation broadband wireless future.
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