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Mobile radio: the next generation

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Standards are sometimes criticised for stifling innovation, increasing costs and preventing things from happening. Get it right though, and a good standard for the right application and products can deliver enormous benefits for society and industry.

A good example is the standard that has created the mobile radio. It is now possible to land in virtually any country in the world and within a few seconds a mobile radio will allow a person to communicate with more or less anyone else in the world. This can be achieved using many different device providers, which all work more or less seamlessly together.

There have been several generations of mobile communication devices and standards and work has now commenced on the fifth generation of mobile radio networks, known as 5G. This was the subject of a recent workshop organised by the European Telecommunication Standards Institute (ETSI).

ETSI is one of the successes of the single European Community, dealing with telecommunications, broadcasting and other electronic communications networks and services. Set up in 1988 by the European Conference of Postal and Telecommunications Administrations (CEPT), there have been many landmarks over the years including standards to enable technologies that have helped to shape the modern world. ETSI was founded initially to serve European needs, but now has a global perspective and its standards are used the world over.

A new generation of mobile radio standards has appeared approximately every tenth year since 1G systems were introduced in 1981/1982. Each generation has introduced new frequency bands, higher data rates and non-backward-compatible transmission technology.

Generations of mobile phone standards

The first generation (1G) of mobile communication networks were based on analogue radio technology. Although digital data signalling was used to connect the radio base stations to the mobile radio, the voice signal itself during a call was analogue, whereas in all later generations the voice signal is coded to a digital signal. 1G systems originated in Japan and then spread to the rest of the world, but as separate standards with no interworking capability.

GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), was a second generation (2G) mobile radio standard developed by ETSI. It was first deployed in Finland in July 1991. GSM has now become the default global standard for mobile communications, with over 90% market share, operating in over 219 countries and territories with an estimated five billion users.

In 2G networks, the digitally encrypted phone conversations are significantly more efficient and have far greater mobile phone penetration levels than the analogue first generation. 2G also introduced data services, starting with SMS (Short Message System) text messages and later services such as email, picture messages and MMS (Multimedia Messaging Service). All data messages sent over 2G are digitally encrypted, allowing for the transfer of data in such a way that only the intended receiver can read the message.

2G also introduced the subscriber identification module (SIM) card, which is an integrated circuit chip to securely store the international mobile subscriber identity (IMSI) number and its related key. This is used to identify and authenticate subscribers. The original SIM cards were the size of a credit card, but with handsets getting smaller and smaller they are now micro-sized.

The Third Generation Partnership Project (3GPP) was established in 1998 to develop specifications for advanced mobile communications. It comprises of seven regional Standards Development Organisations (SDOs), including ETSI, market associations and several hundred companies, and its original scope was to produce the third generation mobile system. However today, 3GPP provides complete system specifications for a number of mobile phone network technologies including 4G and 5G.

The first 3G networks were introduced in 1998. While data transmission had been introduced with 2G it was only for up to a few kbit/s and based on circuit switched technology. This means a ‘call’ or circuit has to be established between the caller and called party, even if no data is being transmitted. 3G introduced faster and more efficient means of packet data transmission and for applications such as mobile and fixed Internet access, video calls and mobile TV, with data transfer rates of at least 200 kbit/s. Later 3G releases (sometimes denoted 3.5G and 3.75G) provided mobile broadband access of several Mbit/s to smartphones and mobile modems in laptop computers.

With the increased use of the Internet and ever faster broadband, mobiles and devices, greater mobile radio data rates were soon required in order to provide a mobile data experience as good as fixed broadband. In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) issued a set of requirements for 4G standards, setting peak speed requirements at 100Mbit/s for high mobility communication (such as from trains and cars) and 1Gbit/s for low mobility communication (such as pedestrians and stationary users).

Unlike earlier generations of GSM, 4G does not use traditional circuit-switched telephony service but introduced all Internet Protocol (IP) packet-based communications. The spread spectrum radio technology used in 3G systems was replaced by multi-carrier transmission and frequency-domain equalisation schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation (echoes). The peak bit rate was further improved by smart antenna arrays for multiple-input multiple-output (MIMO) antennas. Long Term Evolution (LTE) and LTE Advanced were formally submitted as candidate 4G systems to the ITU-T in late 2009 and standardised by 3GPP in March 2011.

4G /LTE systems are still being rolled out and in some cases fall short of the ITU-R requirements for data speeds. Nevertheless, 4G/LTE provides a significant improvement on 3G and offers a mobile data transfer experience similar, if not better, than fixed broadband.

Railway requirements

The standard for the railway version of GSM (GSM-R) is based on the GSM 2G standard. This specified the ASCI (Advanced Speech Call Items) requirements for railways such as:

VGCS (Voice Group Call Service) – allows a great number of users to participate in the same call;

VBS (Voice Broadcast Service) – compared to VGCS only the initiator of the call can speak, others who join the call can only listen;

REC (Railway Emergency Call) – a VGCS dedicated and prioritised for emergency;

SEC (Shunting Emergency Call) – a dedicated group call for shunting operations;

Multi-Level Precedence and Pre-emption Service (eMLPP) – defines a user’s priority with REC calls having the greatest priority.

Essentially GSM-R and GSM 2G are for voice communications, with limited data connectivity of only a few kbit/s, although GSM-R is being enhanced with General Packet Radio System (GPRS) to provide higher data rates and capacity for the European Train Control System (ETCS). However GSM 2G is now an old standard and system, and some commercial 2G networks have already been replaced with 4G. This means support and expertise for GSM-R based on GSM 2G will soon be difficult to obtain.

5G – The next generation.

So why the need for 5G? Well, there are a number of drivers. Mobile communications requirements and the number of devices are predicted to significantly increase by 2020. There will be new devices such as wearable computers and the Internet of Things (IoT), with mobile data requirements in all kinds of equipment both in industry and the home. Governments are looking to broadband and mobile communications to stimulate economies in order to provide greater GDP and create new jobs.

5G will have greater availability, dependability, reliability and speed, coupled with greater throughput but with less latency and cost. Backwards compatibility with earlier generations has always been a feature of GSM, but making each new generation backwards compatible constrains development. Therefore a key decision for 5G will be how many generations of GSM should it be backward compatible with? Will a new radio technology be required? These key decisions are likely to be made towards the end of 2015.

The standards for 5G will be free and open to all, in order to stimulate innovation and development. Open Source Software (OSS) is seen as one of the key initiatives within the emerging 5G standard. The next two years will be very busy for the 5G standard makers as 2020 has been chosen for the launch date – for political and marketing reasons, not technical, as it is an Olympic Games year. This means the requirements for 5G needs to be agreed by the end of 2015 with standards published by 2018.

However, there is speculation that a 5G service may be up and running for the Winter Olympics in 2018. ETSI and 3GPP are involved with the 5G standard development along with standard bodies from Japan, Korea, China, USA and, more recently, India.

Some of the areas of 4G/LTE development will form the basis of 5G. These include seamless transfer to Wi-Fi and back to licensed radio spectrum, with the objective of making better use of unlicensed spectrum to meet the growing traffic demands. Radio channel (or carrier) aggregation will be up to 32 channels as opposed to 5 with 4G/LTE. (Think of this as using lots of small pipes to carry the same amount of water (data) as one large pipe.) 5G will be a consolidation of existing and new radio technologies to provide greater coverage, speed and a more reliable ‘always-on’ experience.

Of interest to the railway community are the enhancements for mission-critical public safety services that will be included in the standard, which could be used as a basis of a successor for GSM-R. These may include Mission Critical Push to Talk (MCPTT), specific talk groups, mobile-to-mobile communications and indoor positioning for large shopping centres (and railway stations).

Currently, radio systems for mission-critical ‘blue light’ emergency services provide reliable and robust voice and narrow band data capability. An example is the TETRA standard (another ETSI success). TETRA was considered along with GSM as a solution for railway communications  with GSM-R being chosen. While some railways are now considering TETRA as a short-term replacement for GSM-R, it has similar obsolescence issues and is predominantly a voice system with limited data capability. For the emergency services, this can be very embarrassing as members of the public can transmit photos and video of incidents via 4G/LTE, but the emergency services can only talk via their radio system.

5G and the railway

Currently, the railway industry is looking to the 4G/LTE standards to form the basis of a successor to GSM-R as an ‘add-on’. However, another option is to influence the 5G standard to incorporate all the railway requirements?

Quality of service, interoperability and testing are seen as being of paramount importance, especially as there will be a step change in data rate and an order of magnitude improvement in performance and latency.

1-10Gbit/s data connections and 1 millisecond end-to-end latency are envisaged. The latency requirement will primarily be for autonomous road vehicles, but could this be a requirement for rail sometime in the future?

90% reduction in network energy usage will be a requirement with up to ten-year battery life for low power, machine-type devices. The significant savings in energy consumption over today’s networks will be required in order that the anticipated massive use of mobile connectivity is economically and ecologically viable.

It may not be possible to meet all these requirements with a single radio technology, and some, in particular the latency requirement, may not be met until well into 5G’s lifetime. Mobile edge computing will be a feature in 5G and reducing the need (and latency) to take everything back to the core of the radio network for processing.

The European Union established a 5G Public Private Partnership (5GPPP) in 2013. This programme will invest an EU budget of €700m in research, development and innovation on 5G over the next six or seven years, matching a corresponding investment by industry.

The technologies and techniques being considered include making use of new spectrum bands including low frequencies below 1GHz and millimetre wave spectrum above 6GHz, increasing use of shared spectrum, very large MIMO, non-orthogonal waveforms, moving networks, context awareness, and integrating broadcast solutions into a 5G interface. Using millimetre wave spectrum will be very challenging, in particular for the design of test equipment. The mobile radio industry will have to adopt expertise and knowledge from its military engineering colleagues who have used such frequencies for years.

With the dramatic increase in data throughput for 5G radio, additional spectrum will be required – but the problem is that radio spectrum is a finite resource with many competing uses. To date, the railway industry has been very fortunate in obtaining its own dedicated radio frequency spectrum bandwidth for GSM-R. However, it is very unlikely that the radio spectrum agencies will be able to continue to provide this luxury in the future, and railways will have to share radio spectrum with other users. This will be a challenge for the rail industry to accept, but providing rail-dedicated radio bandwidth is similar to providing each train operator with its own dedicated track. The latter is a wasteful use of limited resources and is not sustainable.

It will be interesting to watch the development of 5G over the next five years and to see if it will become a successor to 2G GSM-R.

Paul Darlington CEng FIET FIRSE
Paul Darlington CEng FIET FIRSEhttp://therailengineer.com

Signalling and telecommunications, cyber security, level crossings

Paul Darlington joined British Rail as a trainee telecoms technician in September 1975. He became an instructor in telecommunications and moved to the telecoms project office in Birmingham, where he was involved in designing customer information systems and radio schemes. By the time of privatisation, he was a project engineer with BR Telecommunications Ltd, responsible for the implementation of telecommunication schemes included Merseyrail IECC resignalling.

With the inception of Railtrack, Paul moved to Manchester as the telecoms engineer for the North West. He was, for a time, the engineering manager responsible for coordinating all the multi-functional engineering disciplines in the North West Zone.

His next role was head of telecommunications for Network Rail in London, where the foundations for Network Rail Telecoms and the IP network now known as FTNx were put in place. He then moved back to Manchester as the signalling route asset manager for LNW North and led the control period 5 signalling renewals planning. He also continued as chair of the safety review panel for the national GSM-R programme.

After a 37-year career in the rail industry, Paul retired in October 2012 and, as well as writing for Rail Engineer, is the managing editor of IRSE News.


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