Train Radio Network
(located at www.trainradio.net)
Some back ground on what a train radio is
Mobile phones are a concept we all understand and a radio is an old fashioned device used to listen to your favourite music or when you’re driving in your car. That would be most peoples idea of what a radio is. Using a radio on a train may seem a little strange until you look at legacy equipment and what it was designed to do.
A traditional radio is used to receive audio which is broadcast over the airwaves. The transmitted audio can come from a radio station that broadcasts, this would normally be a big transmitter covering a large area with high output power.
Where you have a big area to cover and you want to be able to transmit and also receive from the mobiles, then a base station is used. A large area could have 100s of fixed base stations such as the metronet train radio with about 200 bases along the rail corridor, an area that is 300Km long and 150Km wide. The mobiles need to have a base that is not so far away as the lower power output along with the smaller antenna has a limited range.
The simplest type of radio network is a 2 way radio where a number of radio are tuned to the same channel and when one person speaks, everyone can hear what is being said assuming they are in range and can pick up the signal.
Radio systems such as the WB (Wide Band radio operating on 450.0500MHz on a 12.5KHz channel) network for Sydney trains use base station repeaters to extend the range of there mobiles, especially when the radio is used in a cutting or under a platform awning at a train station. Mobiles are typically low power and can be as low as 0.5w and up to 4W, where a base station is typically 8w in the country and a little lower in the city such as the underground because the signal is dissipated via a leek feeder. This is normally a half-duplex device, that is each person takes a turn to talk.
The frequency spectrum that these devices operate on is also very important along with the type of signal used such as analogue, digital, narrow band and broadband. The AM band where many of the radio talk back shows operate on have great coverage and Sydney’s ABC operating on 702 KHz can be heard hundreds of kilometres away. This type of transmission gives good voice quality but poor music quality compared to an FM radio station. The FM stations are on a higher frequency (88MHZ to 108MHZ) with a smaller coverage area but stereo sound to give very good audio and music quality.
The train radio metronet operates in the 400MHz UHF band which some consider to be the goldilocks zone because of it range for power output and reliable performance. The narrow band analogue network uses frequency modulation (FM) with on 12.5KHz channels with a dedicated channel for TX and one for RX allowing full duplex calls to be made between the train driver and the signaller or controller. CTCSS tones improves the use of the limited spectrum allowing the same channels to be used in an area where you would normally get interference. This stops cross over from audio on the same frequency but with a different CTCSS tone.
How does a mobile phone relate to this
However a mobile phone is a 2 way radio device with full duplex allowing a conversation to be initiated or received from another mobile device. Mobile phones operate on spectrum in ranges from 700MHz to 2100MHz with some areas having access to the 2500MHz band. Depending on the type of mobile used, you may be communicating using circuit switched voice (narrow band) such as the old GSM network or a more modern IP network such as the broadband LTE network.
Mobile phones operate as a radio to bridge the air gap and like a phone to connect to individually number on the fixed network. A modern mobile phone is also a very sophisticated computer with advanced software (android OS or iphone IOS) allowing it to run specialised programs or apps to preform required tasks like maps, messages, playing music streams and even telling you where you are if you have become lost,
Mobile phone, like radio systems are used to make full duplex voice calls, however unlike radio the smart phones can do so much more. Using a modern phone for a voice call is probable the last thing a person would do if the person you wishes to contact did not respond to your text messages or email, you may even decide to have video conference call using a program like Skype, to see and hear the person called.
Why is this important for train radio
The new DTRS (Digital Train Radio System) that is currently being stalled in the Sydney metro area is an aging GSM technology that uses a circuit switched narrow band network as the core of its communication system. The 15MHz of paired spectrum in the 1800MHz is wasted on this type of technology when a more modern LTE network with high speed data could be utilised. This spectrum is often referred to as the old One Tel spectrum was used as 3G network in 2001 before the company collapsed. This spectrum was acquired by the Australian Railway Association on behalf of it members from the federal Minister for Communication Senator Stephen Conway in 2012 for $30 million, some have said this was the deal of the century. This spectrum had and still has a value of $600 million and the aim was for all the railway operators in Australia to move there train radio to GSM-R using this spectrum so we would have a uniform system across the country.
This did not happen, Melbourne moved to GSM-R in 2014 which was setup by Siemens AG and the expected commissioning of the GSM-R in Sydney in 2017-2018. Brisbane is or has looked at Tetra mobile network and Adelaide is still using an analogue system. I’m unsure what is used in Perth but do not believe it is a GSM-R system.
My proposal to resolve this
I recently completed a masters at CQU and have enrolled in the PHD program. The research I published in my master thesis showed a way forward by moving DTRS to 4MHz of paired spectrum located in the 900 MHz band. This is quite achievable in the Sydney and Melbourne metro areas only requiring the RF module in the train radio to be replaced along with some additional network configurations/additions. Freeing up the spectrum in the 1.8GHz would allow the development of a new network for all of transports along with the emergency services in the metro areas. Because it will not be used for mission critical communications, there is a lot more that can be made of this spectrum providing a more efficient use of this valuable resource than currently used at the moment.
Having high speed data communication between trains and the rail operators/signallers will allow increased safety, real time CCTV monitoring along with ecommerce applications for passengers such as on board ticketing, ordering services (accommodations, taxis, etc) and real time updates on delays or cancelled services.
About the Author
Michael Alldritt is currently enrolled in a PHD research program to look at the development of a broadband train radio that could be used in the Sydney and Melbourne Metro areas. He lives on the NSW central coast with his wife and 3 children.
You can contact him at firstname.lastname@example.org