There are currently two main technology choices used for railway radio communications, mobile telephone (GSM/LTE) or Wi-Fi. GSM-R private networks are used predominately for main line track-to-train voice and ETCS (European Train Control System) data applications, with LTE/5G likely to be the choice for the future.
Public LTE networks are used for general maintenance and operational communications, and for providing customer data communications to trains. Public LTE also provides connections for some non-safety-critical operational data requirements and may supplement dedicated private networks.
Wi-Fi networks include systems for general business communications in offices and stations, passenger data communications on trains and at stations, together with customer information systems at stations. Wi-Fi is used by some train operators to supplement the public GSM/LTE internet connections to trains and some Communication-Based Train Control (CBTC) systems for metros also use Wi-Fi for train control purposes.
The future for Wi-Fi technology will be IEEE 802.11ax, also known as Wi-Fi 6. Both 5G and Wi-Fi 6 will offer Gbit of data transmission, so will the future for data wireless communications be 5G or Wi-Fi6?
Mobile telephone standards across the years
Early mobile radio telephone systems, available as a commercial service and with their own telephone numbers, were mainly mounted in vehicles, although there were some suitcase ‘transportable’ models. Motorola launched its Mobile Telephone Service in the USA in 1946, while the first service in the UK covered the Manchester area in 1951, although with restricted coverage and requiring all calls to be connected by an operator.
The first generation (1G – although this term only came into use once 2G was developed) of mobile communication networks to use wireless cellular technology was launched in 1979 in Japan and then in the 1980s elsewhere. It was a hybrid of digital signalling, that connected the radio towers to the rest of the network, and analogue radio technology for the voice call itself, although this was modulated to a higher frequency.
The second generation (2G) mobile radio standard was truly digital. A GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile) service was launched in Finland in 1991. GSM-R (R for Railway), the specification for which was finalised in 2000, is based on 2G GSM.
The Third Generation Partnership Project (3GPP) was established in 1998 to develop specifications for advanced mobile communications. The original scope of 3GPP was to produce the third-generation GSM mobile system, with increased data capability. However today 3GPP provides the complete system specifications for 4G and 5G.
In March 2008, a new set of requirements for 4G were issued. Long Term Evolution (LTE) technology was submitted as a candidate 4G system in late 2009. LTE systems, in some cases, fall short of the 4G requirements for data speeds but are nevertheless known as 4G LTE.
5G is the next generation of radio offering even greater speed, lower latency and larger scale of deployment.
There are other radio technologies used in society and industry, such as Bluetooth, for short range communications, but they are not the subject of this article.
The standardisation body for wireless phone communications is 3GPP (3rd Generation Partnership Project), which developed from the telephony industry and various governmental bodies. Originally, the technology was for voice only, with data a later addition that only really started to be prominent from the 3rd generation mobile radio systems (3G) onwards.
3GPP mobile phone-based technology developed using licensed spectrum, which is obtained for a period of time by the mobile network operators from governments. Mobile ‘cellular’ radio evolved with ever-improving standards migrating from 2G GSM/GPRS to 3G, Edge, 4G, LTE and now 5G. Confusingly, the standards body is still called 3GPP and not 5GPP.
2G GSM formed the basis of the GSM-R main line railway track-to-train radio system, which provides the radio link within the European Railway Traffic Management System (ERTMS). This will be replaced by Future Railway Mobile Communication System (FRMCS) which is likely to use LTE/5G from the mid-2020s.
Wi-Fi originated for wireless computer data communications, and this year celebrates its 20th birthday. The standards were derived from IEEE 802.11, which originated in the computer industry. The IEEE has a large engineering membership, many of which are sponsored by their employer companies, and this has influenced its development. Wi-Fi is now one of the world’s most valued and widely used technologies.
The Wi-Fi Alliance IEEE 802.11 standards group developed Wi-Fi standards in the unlicensed frequency bands. These have been allocated on license-free arrangements based on a set of rules, such as limited power so that interference range is limited. The bands are called ISM (industrial, scientific and medical) and now exist in the 2, 5 and 60 GHz bands of spectrum. The Wi-Fi Alliance is a worldwide network of companies from multiple industries who collaborate to promote the interoperability, adoption, quality, performance, security, and capability standards for Wi-Fi.
It has been a huge success and there are now more Wi-Fi devices in use than there are people on Earth, and more than half the internet’s traffic traverses Wi-Fi networks.
This was not always the case. When Wi-Fi was being developed in the late 1990s, the standardisation of 3G was progressing well and promising high data rates. 3G modems connected-to or integrated-in devices were envisioned to provide ubiquitous connectivity. The general view was that the unlicensed Wi-Fi technology would soon disappear and that mobile data using the licensed spectrum would dominate.
However, Wi-Fi developed to operate in the unlicensed ISM bands and satisfy the needs for wireless connectivity indoors, in-home or in-building, areas where 3G was not able to penetrate adequately. Wi-Fi also rapidly increased its data rate and expanded its capabilities by moving from the 2.4GHz band into the 5GHz band, and it is expected to further increase data rates by going to 60GHz.
Wi-Fi’s capability has also been supplemented with the introduction of range extender technologies and, more recently, distributed Wi-Fi (Wi-Fi Mesh) technology.
Opex or Capex?
Mobile radio using 3G/LTE requires a paid subscription to telephone operators and, possibly, roaming charges. By comparison, Wi-Fi was, and is, almost free, as the incremental cost for Wi-Fi via a fixed telephone, ISDN and, later, broadband ADSL, was limited. Many companies and government bodies are structured to spend capital to reduce operating costs, which also helped the development of Wi-Fi.
In some parts of the world, some wired operators compete directly with the wireless operators. Ironically, some wireless operators initially discouraged the use of 3G for data, due to concern for the voice service collapsing if 3G was ‘overused’, an action that supported the use of Wi-Fi for data.
This is why most computers and tablets have only two radios: Wi-Fi and Bluetooth (for short ranges). 3G-licensed radios and their successors were rarely integrated in computers or tablets because Wi-Fi offered a cost-effective and versatile internet connection. An integrated 3G radio, plus SIM card subscription, was just too expensive by comparison. When a mobile solution was required, a device such as a 3G dongle or, more recently, using an LTE mobile phone as a hotspot, provided a solution.
One might assume that the demarcations between the two technologies would be clear: Wi-Fi for private areas such as home and office and GSM/LTE for everywhere else, but this is not the case.
The telephone operators in 3GPP were naturally quite suspicious about the development of so-called ‘data hotspots,’ public places where people could get access to high speed internet without needing a subscription. Fortunately for the telephone operators, it turned out that running a large number of hotspots was not trivial, particularly for large retail and hotel chains, cities and trains. Public hotspot companies have been slowly absorbed by the telephone operators in some countries. The situation has also been influenced by the introduction of ‘Wi-Fi calling’ which provides a voice service capability over the Wi-Fi data-only IP connection.
Consumers and companies found that running Wi-Fi networks was becoming more complex, and some telephone and cable operators used private Wi-Fi as business opportunities – helping organisations and smaller companies to run their Wi-Fi networks.
The next change was the rapid growth of data traffic, for example via video applications such as YouTube, which required operators to increase capacity. However, obtaining more frequency bands was not easy or cheap. A faster way of increasing this capacity, next to leveraging Wi-Fi, was that the successor of 3G, 4G or LTE technology can also run in the ISM band. This resulted in the concept of LTE with licensed assisted access (LAA). The 3GPP specifications now provide for both Wi-Fi and LTE-LAA to be used in the same 5GHz spectrum.
Spectrum is a finite limited resource and, at the 2019 World Radio Conference, it is hoped that significant new allocations for both Wi-Fi and 5G to support the increasing demands for wireless data communications will be made.
The IEEE 802.11 is introducing higher speed versions, 11n and 11ac, and is in the process of completing 11ax – also known as Wi-Fi 6. 3GPP is investing heavily in 5G and both 5G or IEEE Wi-Fi 6 will be able to deliver high data rates (Gbps). 5G is claiming that it will have “way better indoor penetration”, but that is questionable with the higher frequency spectrum that may be used in some 5G networks.
The standards body for Wi-Fi 6 is using the slogan “5G has arrived and it is called Wi-Fi 6.” Wi-Fi 6 is an evolution of Wi-Fi 5, but it offers new, additional capabilities that greatly improve its capacity and ability to share spectrum efficiently in high density, high load situations. So, will 5G or Wi-Fi 6 be the winner?
Wi-Fi 6 is designed to host existing and emerging uses, from streaming ultra-high-definition movies to mission-critical business applications requiring high bandwidth and low latency, and to staying connected and productive while traversing large, congested networks in airports and railway stations. It is understood that Wi-Fi 6 will offer speeds that are roughly 30 per cent faster than Wi-Fi 5, with theoretical maximum transfer speeds of around 10Gbps.
The reach will be reduced, although this will be mitigated with a distributed Wi-Fi (Wi-Fi Mesh) architecture and the use of multiple channels to connect multiple access points in different locations to the main router. The focus of IEEE 802.11ax is to provide full indoor coverage into every space within a home or office building covered with the same high data rate. This will not be easily achieved with 5G.
5G’s higher data rates also create a penalty on its range. It is anticipated that range will probably decrease to less than half, forcing the number of base stations to more than quadruple, due to the square nature of coverage. In dense urban areas, where finding sites to place base stations is difficult, rolling out 5G infrastructure will be expensive.
Both 5G and Wi-Fi 6 will use orthogonal frequency division multiple access (OFDMA) to increase efficiency and to lower latency for high demand applications, multi-user multiple input multiple output (MU-MIMO) allowing more data to be transferred at one time, and beamforming to enable higher data rates at a given range to increase network capacity.
5G “New Radio” (NR) promises improvements in efficiency over LTE, with more use of MIMO, and new millimetre-wave – very high frequency – spectrum. These improvements are also shared with Wi-Fi 6, which will deliver comparable performance.
It is argued by some that Wi-Fi 6 will have more proven methods for sharing spectrum in overlapping networks, along with simpler network and device management. Wi-Fi 6 is also likely to reach the market in advance of any wide-scale deployment of 5G NR. 5G is likely to go live in 2020, although only in some cities in the world, and its use in railways is likely to be some years away (2025) with 4G LTE able to do all that railways really require for some time.
Wi-Fi 6 routers from Cisco, Netgear, Asus and TP-Link are already rolling out, including mesh options for the Netgear Orbi and TP-Link Deco, with release dates set for the second half of the year. The Samsung Galaxy S10 is reported as being the first phone to support Wi-Fi 6, and other devices will quickly follow, such as the iPhone and the next generation of laptops and Wi-Fi smart building devices.
Wi-Fi has been used successfully for a number of metro railway CBTC systems. Although a few CBTC systems have been deployed using alternative radio bearers – such as waveguides or induction loops – the majority of the CBTC implementations since 2013 have used Wi-Fi-based radio systems to bridge the train-to-lineside gap, but this is changing.
The limitations that Wi-Fi presents to CBTC systems – on range, quality of service, mobility and (especially) interference – have made some rail operators and suppliers look for alternatives. A series of incidents in CBTC systems in China instigated the China Association of Metros to stipulate in 2014 that all future CBTC deployments in China would use LTE as their radio bearer and 2018 saw the first wave of CBTC over LTE projects entering service, almost all of them in China.
The deployment in Hong Kong, however, continues to use Wi-Fi as the primary radio bearer, with a mobile network operator (HKT) providing an LTE radio backup. Future CBTC over LTE projects currently in development include Shanghai Metro Lines 15 (2019) and 14 (2020), as well as the ATC project in Perth, Australia, currently scheduled for 2024.
Wi-Fi was developed to provide connections to static locations, where as GSM/LTE/5G has always been designed for efficient handover from node to node, such that a moving transmitter/receiver always has a reliable connection. Handover to a moving object is possible with Wi-Fi, but its not what it was designed for and the solutions are a compromise.
So, to answer the question, is the future 5G or Wi-Fi 6?
Both 5G and Wi-Fi 6 will have very particular characteristics that will be beneficial for connecting devices to the internet. Therefore, what is likely to happen is that operators and system engineers will exploit both technologies to their advantage and implement a strategy that leverages both technologies for the customer, allowing seamless migrations between the two standards when necessary.
So, the ultimate winner may not be 5G or Wi-Fi, but could well be the system user.