SRD/MG
Doc. FM(15)094 Annex 41
Date issued: 23 January 2015
Source: Chairman
Subject: SRD/MG Analysis on Urban Rail Systems
This analysis has been developed by SRD/MG for consideration at WGFM#82 (9-13 February 2015).
Contents
Executive Summary for WGFM#82 ................................................................................................................... 2
Excerpt WGFM#81 Minutes .............................................................................................................................. 4
Discussions at SRD/MG#63 (10-12 December 2014) ........................................................................................ 5
SRDoc proposals ................................................................................................................................................ 8
Range of frequencies required ........................................................................................................................ 10
Urban Rail CBTC ............................................................................................................................................... 11
ITS documentation: ......................................................................................................................................... 13
ITS communications architecture .................................................................................................................... 16
Radio - principle features ................................................................................................................................ 16
Two ‘uncoordinated’ standardization mandates ............................................................................................ 16
Existing ITS regulations .................................................................................................................................... 17
Can ITS be applied for Urban Rail Systems? .................................................................................................... 17
Frequency options ........................................................................................................................................... 19
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Executive Summary for WGFM#82
1. Concerning 5855-5875 MHz (spectrum covered by ECC/REC/(08)01)
This existing regulation is recommended to be used by Urban Rail systems for non-safety related
applications.
2. Concerning 5875-5905 MHz (spectrum covered by ECC/DEC/(08)01)
This existing regulation (also covered by an EC Decision) is recommended to be used by Urban Rail systems.
It should be further investigated how the ITS regulation together with the ETSI available ITS related
standards and specifications which were developed under standardisation mandate M/453 can be used
also for urban rail CBTC applications. SRD/MG noted that current ITS applications in the ITS BSA (Basic Set
of Applications) do not contain urban rail CBTC similar applications but only so-called cooperative
awareness applications.
3. Concerning 5905-5925 MHz (future ITS applications)
This spectrum is currently also under investigation under the 5 GHz mandate for WAS/RLAN applications. It
is expected that WAS/RLAN applications are considered as applications in the mobile service and under
general authorisations. This is most likely not a tolerable situation for urban rail CBTC applications (to be
co-frequent with licence-exempt applications) without any further mitigation / spectrum management
solution. Future ITS applications are also under considerations for more autonomous driving (similarity to
driverless metros). A broader investigation, together with ETSI (TC ITS and Urban Rail, i.e. TC RT) may be
better suited to accommodate future applications in the transportation field (noting that this frequency
range is identified for future ITS applications in ECC/DEC/(08)01).
Unconfirmed but also considered as a possibility in SRD/MG: 5915-5925 MHz may be an option as long as
no ‘clash’ with unlicensed WAS/RLAN applications may occur (pending study results in SE24 under the 5GHz
mandate).
Spectrum in the range 5905-5925 MHz should not be considered for Urban Rail systems alone but only
together with future ITS applications. In this context, one may also consider the spectrum opportunity cost
and impact with regard to the competing request for WAS/RLAN applications. Therefore, a technical
solution in 5875-5905 MHz may be seen as a preferred solution, although currently not encouraged by
urban rail stakeholders.
4. SRD/MG agreed that frequencies around 5.9 GHz are considered better suited to urban rail
applications than lower frequency or higher frequency ranges. This is discussed in this analysis
more in detail in the analysis.
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5. Urban Rail Systems to use ITS standards and specifications
SRD/MG recommends looking first into the frequency options option 1 (and 2) in 5875-5925 MHz before
other frequency options are considered:


Shared Use the current ITS spectrum also for Urban Rail CBTC in 5875-5905 MHz;
CBTC shared use with future ITS applications in 5905-5925 MHz
SRD/MG proposes to WGFM#82 to liaise with ETSI (ERM, ITS, RT) with this analysis paper as an
attachment.
Urban rail systems can potentially use ITS standards and specifications, possibly with some extensions. EN
302 571 seems acceptable for CBTC communication systems. Channels and selectivity are compatible with
the need for communication of CBTC. A CBTC system is designed with 2 channels per line used for
permanent redundancy and frequency diversity. It would be possible to design a CBTC communication
system based on 802.11p which would work today (note that 802.11p is integrated in the base 802.11
specifications). In order to share common frequencies/channels, a Detect-And-Avoid functionality should
be applied to all users of these frequencies. It is the role of the standardisation to consider common
technical solutions. ETSI should investigate the use of ITS for Urban Rail Systems in the frequency ranges
5875-5905 MHz (for CBTC) but also in the context with future ITS applications in the frequency range 59055925 MHz. The decentralised common congestion control, maximum channel loading specifications and
prioritisation of certain applications in ITS may need to be specified (if not done yet to the extent
necessary) to ultimately avoid spectrum congestion situations. Urban Rail applications such as CBTC should
be included in the ITS basic set of applications, if necessary, as a new class of applications.
4 channels are needed for Urban rail CBTC. Therefore, the considerations may need to encompass the full
frequency range 5875-5925 MHz, depending on the channel bandwidth and spectrum access
considerations (5MHz channels requested for CBTC).
CEPT Reports 14 and 44 recommend that, whenever possible foster the equal access to spectrum, avoid
fragmentation of the spectrum use, bundle applications within the transportation sector and having
similar requirements. Only in case of valid reasons consider a dedicated spectrum solution. A technical
solution with ITS needs therefore to be studied as an alternative to the provision of dedicated spectrum
and may be a more spectrum efficient solution than a dedicated solution for urban rail systems.
6. Guidance and information to national administrations on how to deal with Urban Rail systems in
general may be provided in an ECC Report.
7. SRD/MG does not propose to request WGSE to conduct compatibility studies for Urban Rail
systems in addition to on-going studies under the 5 GHz mandate
8. Two existing standardisation mandates
M/453 for ITS and M/486 for programming and standardisation addressed to the European Standardisation
Bodies in the field of Urban Rail. M/486 has not taken into account Urban Rail CBTC at the time it was
3/20
written. A better co-ordination inside ETSI is recommended. The existence of these standardisation
mandates can also provide access to funding to facilitate standardisation activities to bring together urban
rail and the ITS standardisation. This will on the other side lead to more efficient spectrum use which can
be considered as a public interest/concern.
Excerpt WGFM#81 Minutes
6.2 Spectrum requirements for Urban Rail Systems
(1)
The ETSI Liaison Officer introduced Document(14)159r1 containing a liaison statement with
an attached System Reference Document TR 103 111 on spectrum requirements for urban
rail systems in the 5.9 GHz range in order to support (a) primarily trackside/infrastructureto-train communications, and (b) optionally train-to-train communications.
(2)
The intended applications include (a) fundamental time-critical CBTC (CommunicationBased Train Control) and safety relevant applications with very low latency, and (b) nonsafety relevant applications including railway traffic management tasks and other
applications.
(3)
The SRdoc proposes to designate 20 MHz for CBTC and safety relevant critical
applications, preferably within the frequency range 5.905 GHz to 5.925 GHz. It is also
proposed to designate 20 MHz, i.e. 5.855 GHz to 5.875 GHz, for non-safety related urban
rail applications. In addition, it also requested to consider in a future review of the proposed
ECC Decision the designation of 5.925 GHz to 5.945 GHz for future urban rail applications.
(4)
Mr Thomas Weber (ECO) informed WG FM about the considerations on the SRdoc that
took place at the recent SRD/MG meeting since the overlap with ITS was obvious.
(5)
WG FM considered that the principle of equal access to shared spectrum is important in
this context for applications in the traffic and transport telematics sector and tasked the
SRD/MG to analyse the ETSI SRdoc on urban rail applications first, before any new studies
for urban rail applications will be requested from WG SE.
(6)
This principle could potentially facilitate the opportunity to deploy ITS and urban rail
cooperative traffic safety and traffic flow-regulating services in the future and helps
frequency management to avoid fragmentation of the spectrum use but may also raise
coexistence issues.
(7)
WG FM recognises that many (but not all) physical layer and spectrum access parameters
are identical for cooperative ITS and urban rail applications as set out in ETSI TR 103 111.
(8)
WG FM agreed to send a liaison statement to WG SE and SE24 to take into account urban
rail systems set out in ETSI SRdoc TR 103 111 in the ongoing studies regarding
compatibility between WAS/RLANs and public transport automation systems in the 5.915-
4/20
5.935 GHz band and compatibility between WAS/RLANs and ITS in the bands 5855-5875
MHz (non-safety ITS), 5875-5905 MHz (safety-related ITS) and 5905-5925 MHz (ITS
extension band), as appropriate.
(9)
In this regard, WG FM observed that the proposals contained for urban rail systems cover
slightly different frequency ranges (see chapter 8.1 figure 5 of the SRdoc): 5905-5925 MHz
for urban rail safety applications as well as future ITS applications and 5925-5945 MHz for
urban rail applications.
Discussions at SRD/MG#63 (10-12 December 2014)
It has been confirmed that the ETSI SRDoc TR 103 111 has been published in 10/2014 (the SRDoc has been
created in ETSI TC RT).
http://www.etsi.org/deliver/etsi_tr/103100_103199/103111/01.01.01_60/tr_103111v010101p.pdf
SRD/MG discussed in December several input documents on Urban Rail systems:
1. SRDMG(14)083 – the published ETSI SRDoc for Urban Rail Systems in the 5.9 GHz range
2. SRDMG(14)098 – a discussion Paper intended to support SRD/MG deliberations on Urban Rail
systems
3. SRDMG(14)101 – a presentation from the UITP Spectrum User Group (SUG)
4. SRDMG(14)110 – background information from the UITP SUG concerning the spectrum need for
Urban Rail systems
The following was noted from the presentation of the ETSI SRDoc and the UITP presentation:
-
-
-
5/20
The UITP SUG has been created in 2011 (www.uitp.org). The group represents 26 operators and 5
manufacturers;
Dedicated bandwidth of 20 MHz for real-time urban rail related safety applications is requested;
This consists of 4 channels of 5 MHz including 2 channels per line for permanent redundancy and a
scenario of 2 lines in the same place (crossing or parallel). A CBTC radio communications system
requires always two channels for its transmissions;
Frequencies around 5.9 GHz are requested and considered better suited by the urban rail
proponents than lower frequencies below 1 GHz or even around 2 GHz due to the propagation
conditions at the given dimensions of urban rail tunnels/tubes. Consideration of frequencies above
6 GHz has also been conducted in SRD/MG but found also less suitable for a number of reasons
(see considerations in the chapter on the range of frequencies. Higher frequencies may be
discussed in the future if the preferred frequency range turns out to be impracticable;
Interference to the urban rail radio system leads to stopping of the urban rail trains (stopping done
by means of the emergency brake which can lead to train passenger safety risk);
The intended applications include (a) fundamental time-critical CBTC (Communication-Based Train
Control) and safety relevant applications with very low latency (around 100 ms), and (b) – in a
-
-
-
-
-
-
-
6/20
lower band (5855-5875 MHz)- non-safety relevant applications including railway traffic
management tasks and other applications;
The spectrum request for CBTC is for dedicated spectrum under individual authorisation and hence
for coordinated use of spectrum;
The request for European harmonisation of the spectrum use is firstly motivated by economy-ofscale considerations on the market (not too many frequency options amongst the urban rail radio
system implementations, i.e. ‘technical harmonisation’) and also by some (limited) cross-border
operations of urban rail systems;
In Europe, there are about 45 cities with metro operations. Current implementations of urban rail
radio systems in the 5.9 GHz range under individual authorisations are already existing in Denmark
and Finland (5925-5975 MHz), France, Spain and Sweden (5915-5935 MHz) with some more ongoing implementation projects in Europe and also outside of Europe, e.g. in China, (precise
spectrum usage varies from implementation-to-implementation and an individual implementation
may not cover 20 MHz of bandwidth). There are also implementations in other frequency bands.
The market for unattended urban rail operations as of 2013 was 32 cities, 674 km track length, 48
lines and with 700 stations and is expected to grow to nearly 2000 km of track lines in 2025
(estimated 37% of the growth in Europe);
Current urban rail system implementations operate in the bands in 5.915 MHz-5.925 MHz and
above 5925 MHz. The band 5.905-5.925 MHz is designated in ECC/DEC/(08)01 for future ITS
applications (G5D) . Urban rail systems operate above 5925 MHz under individual authorisations
and are coordinated with FS use on a national basis (so far FS exists in the respective country);
The use of the frequencies occurs in tunnels as well as in the open air;
The required power level (EIRP) range is from 3 dBm to 33 dBm to achieve communication
distances of up to 1 000 m. The related maximum power spectral density (EIRP) is 23 dBm/MHz.
Trackside-to-train applications will require a much shorter communications distance than 1 000 m,
and therefore lower power levels than 33 dBm are involved on average. If it is considered an
average range of 700 m in rural areas, one needs an EIRP not exceeding 20 dBm. This emission
levels are very similar to ITS emission levels. Both ITS and Urban Rail Systems use Transmit Power
Control (TPC). The occupied bandwidth (99 % of the total mean power) is less than 3 MHz. Typical
channel bandwidths considered are 5 MHz (for CBTC) to 10 MHz wide channels;
Only one urban rail system transmitting device in a defined geographic area uses a frequency
channel at the same time and uses listen-before-talk (or TDMA), duty cycle restriction and
transmitter power reduction in congestion situations. This is very similar to ITS communications
where only one ITS transmitting device uses an ITS frequency channel at the same time using listen
before talk, transmitter power reduction and duty cycle restriction;
The receiver sensitivity of an urban rail system is -95 dBm in a 3 MHz channel, receiver selectivity is
50 dBc for a 5 MHz channel, and the blocking capability is for a relatively strong -10 dBm incoming
signal;
Link Data rates in the urban rail system are modest and in the range of 10 kbit/s to 64 kBit/s, except
for video transmissions (train video) which may need up to 2 Mbit/s per link (latter one described
as not relevant for urban rail safety in the ETSI SRDoc, but for security). Some extra coding is
needed for reliability for urban rail safety applications. In addition, there are several links per line
which are used for several trains. The duty cycle per channel can increase in certain situations such
-
-
-
-
-
-
7/20
as a lot of train traffic at one station (first estimate, it could be around 50%). At this moment, there
is not a single way on how exactly the channels are in use by different urban rail system
implementations. The capacity requested may be increased by the fact that a single trackside radio
may have multiple trains to communicate with, such as multiple-platform stations and train
yards/depots. Chapter 8.2 of the SRDoc provides a consideration on the bandwidth requested,
though during the discussions in SRD/MG, some assumptions have been questioned such as the
number of trains at a location and with regard to individual CBTC link data rates.
The ITS communications architecture standard, ETSI EN 302 665 and the EN 302 663 for highreliability safety related ITS services is only noted in the SRDoc for urban rail systems;
Its proponents re-iterated in SRD/MG that the proposed spectrum partly overlaps (5 915 MHz to 5
925 MHz) with spectrum currently designated to ITS-G5 (see ECC DEC(08)01) for future ITS
applications. Like for CBTC, there are also considerations in the ITS community for more
autonomous ITS applications (in the direction of autonomous driving, e.g. track platooning) and
beyond the scope of those already existing and known ITS applications under ‘cooperative
awareness’ ITS applications which provide alert messages. Any usage by Urban Rails would require
conformance to the ITS specifications for usage in this band. Such conformance would also provide
the opportunity to deploy ITS and Urban Rail cooperative traffic safety and traffic flow-regulating
services;
France, the United Kingdom and Netherlands indicated in SRD/MG that administrations should
apply the principles set out in CEPT Reports 14 and 44, i.e. whenever possible foster the equal
access to spectrum, avoid fragmentation of the spectrum use, bundle applications within the
transportation sector and having similar requirements. Only in case of valid reasons consider a
dedicated spectrum solution. A technical solution with ITS needs therefore to be studied as an
alternative to the provision of dedicated spectrum and may be a more spectrum efficient solution
than a dedicated solution for urban rail systems. These views were also supported by other
administrations in SRD/MG;
The Netherlands and the UK expressed that other spectrum options may also be considered, at
higher frequencies, such as 63-64 GHz, which may not be used heavily by ITS nowadays. Even
when sharing this spectrum with applications under general authorisation, the total spectrum of 1
GHz may provide sufficient mitigation to have reliable urban rail communications. This option
should be considered if the preferred solution at 5875-5925 MHz turns out to be impracticable;
The United Kingdom reported to have received the information that a similar urban rail
implementation in the UK is proposed to use 2.4 GHz ISM-band frequencies. This was later on
clarified in the SRD/MG discussions that also the London Urban Rail implementation is looking to
overcome challenges by using frequencies in the 5.9 GHz range. The UK clarified the position set
out by UITP in the document SRDMG(14)101, that London Underground support the general
concept of 5.9 GHz bandwidth for metro CBTC systems rather than the 5905-5925 MHz frequency
range itself, per se.
Even a dedicated spectrum solution for urban rail systems may not mean that spectrum is blocked
for other applications since the number of urban rail systems is limited in Europe and they occur
only in metropolitan areas;
Urban rail CBTC safety applications are not seeking the same status of safety service as defined in
of the radio regulations (RR 1.59);
-
-
The urban rail systems’ proponents made clear in the discussions that they do not support a mixing
of urban rail CBTC applications with applications under general authorisations. The meeting noted
however, that this are the auspices for the ‘ITS spectrum’ under ECC/DEC/(08)01 and also spectrum
in 5905-5925 MHz that is under investigation for WAS/RLAN usage following the 5 GHz mandate.
In this regard, the United Kingdom remarked that a dedicated urban rail spectrum solution in 59055925 MHz under individual authorisation and with coordination needs would have an impact which
could be regarded as a spectrum opportunity cost not to be neglected. This view was shared also by
other administrations in the SRD/MG and therefore, a technical solution with ITS would need to be
studied first.
In this context, it was noted that the draft amended ECC/DEC/(08)01 and ECC/REC/(08)01 were
changed to be open to all traffic modes for traffic safety applications / traffic applications
respectively.
SRDoc proposals
5850
ITS non-safety
applications
(ITS-G5B) and
Urban Rail
non-safety
applications
ITS road safety (ITSG5A)
Urban Rail
safety
applications +
Future ITS
applications
(ITS-G5D)
5860
5880
5910
5870
5890
5900
5920
Future
frequency
band for
Urban Rail
applications
5930
5940
5950
Frequency (MHz)
Urban Rail spectrum proposal including current and possible future ITS designations
1. Concerning 5855-5875 MHz (spectrum covered by ECC/REC/(08)01)
This existing regulation is recommended to be used by Urban Rail systems for non-safety related
applications.
2. Concerning 5875-5905 MHz (spectrum covered by ECC/DEC/(08)01)
8/20
This existing regulation (also covered by an EC Decision) is recommended to be used by Urban Rail systems.
It should be further investigated how the regulation together with the ETSI available ITS related standards
and specifications which were developed under standardisation mandate M/453 can be used also for urban
rail CBTC applications. SRD/MG noted that current ITS applications in the ITS BSA (Basic Set of Applications)
do not contain urban rail CBTC similar applications but only so-called cooperative awareness applications.
3. Concerning 5905-5925 MHz
This spectrum is currently under investigation under the 5 GHz mandate for WAS/RLAN applications. It is
expected that WAS/RLAN applications are considered as applications in the mobile service and under
general authorisations. This is most likely not a tolerable situation for urban rail CBTC applications (to be
co-frequent with licence-exempt applications) without any further mitigation / spectrum management
solution. Future ITS applications are also under considerations for more autonomous driving (similarity to
driverless metros). A broader investigation, together with ETSI (TC ITS and Urban Rail, i.e. TC RT) may be
better suited to accommodate future applications in the transportation field (noting that this frequency
range is identified future ITS applications in ECC/DEC/(08)01). This should be included in a response to ETSI.
Note: ITS (when not considering any mitigations) had originally to fulfil -65 dBm/MHz above 5925 MHz for
the protection of FS. WAS/RLAN: There is a placeholder in the PT SE24 Report for these studies but nothing
has been done so far. WAS/RLAN using BW of 20 MHz, 40 MHz, 80 MHz -< it could prove difficult to use
spectrum up to the edge of the band. A new generation of Wi-Fi (known as IEEE 802.11ac) will be able to
achieve throughput rates sufficient enough to extend existing high-speed fixed broadband infrastructures
wirelessly (providing data rates of 30 or 100 Mbps or more when using 80 MHz and/or 160 MHz channels).
Unconfirmed but also considered as a possibility in SRD/MG: 5915-5925 MHz may be an option as long as
no ‘clash’ with unlicensed WAS/RLAN applications may occur (pending study results in SE24 under the 5GHz
mandate).
Spectrum in the range 5905-5925 MHz should not be considered for Urban Rail systems alone but only
together with future ITS applications. In this context, one may also consider the spectrum opportunity cost
and impact with regard to the competing request for WAS/RLAN applications. Therefore, a technical
solution in 5875-5905 MHz may be seen as a preferred solution, although currently not encouraged by
urban rail stakeholders.
4. Concerning spectrum above 5925 MHz
Spectrum above 5925 MHz may become the lowest frequency band for the FS in the foreseeable future.
Urban rail systems may use frequencies in this range on a national basis, e.g. in tunnels/subways, or there is
no FS in parts of the band or coordinated on national basis with other use such as FS. SRD/MG does not see
the need for compatibility studies in WGSE for this purpose and notes that there are already a number of
current implementations in several countries. National coordination would occur between fixed
stations/tracks of urban rail systems and other fixed stations/services. ECC Report 173 includes the
following overview:
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CEPT channel plan
Frequency band
5925-6425 MHz
REC Number
Typical
capacity
High
ERC/REC 14-01
CEPT
Implementation
(Number of
administrations)
28
Typical trends
Slow growth
Tracks above ground may often be used also for other trains and hence use other systems such as ETCS (in
GSM-R).
Guidance and information to national administrations on how to deal with Urban Rail systems in general
and including this as well as other frequency ranges may be provided in an ECC Report.
Range of frequencies required
1. In tunnel
The narrower the tunnel, the more important is greater the attenuation of low frequency bands.
Typically, frequencies below 2 GHz are better transmitted via radiating cables than in the free air. That is
why when radio FM VHF/UHF voice radio is required for security e.g. in long tunnels (Mont Blanc, etc.) they
are equipped with leaky feeder cables throughout.
It is costly to install, but also costly to maintain, as the environment in tunnels is not clean, but humid and
with an atmosphere that can contains metallic dust, which leads to blocking the slots which enable the
leaky feeder to receive the signals transmitted by the trains or to transmit signals generated by the wayside equipment.
Inversely, higher than 2GHz, transmission though the air is more efficient than transmission through cable,
all the more so through leaky cables
Moreover, tunnels can be nearly completely "blocked" by a train, preventing the train behind to reach a
wayside antenna installed ahead. Here also the important parameter is the relationship between the wave
length and the space left free around the train. In that perspective, frequencies above 5 GHz are much
better that 2 GHz.
2. Outside of tunnels
The free air propagation equation below enables evaluation of the level of signal received:
Prx= Ptx +Grx+Gtx – 33 – 20 log FMHz – 20 log dkm
With Prx the power at the input of the receiver,
Ptx the active transmit power,
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Grx the gain of the antenna of the receiver and Gtx the gain of the antenna at transmitter
level,
FMHz the frequency in MHz,
And dkm the distance between transmitter and receiver in km.
The 20 log FMHz term does not favor higher frequencies, but it is generally compensated for by antennas
with higher gain for the same size of antenna (which is an important criterion to enable them to be
installed on trains and in tunnels); on each side, the gain is higher when the frequency is higher (can follow
a square law of the frequency , i.e. +20 log FMHz).
It has to be noted that:
•
6 GHz is a current limitation of WLAN chip sets (if specific chips had to be designed for
railways it would be at a very high cost, due to the small size of the market);
•
there is a technological gap somewhere between 6 GHz and 10 GHz for the radio device
technologies;
•
an operation at a frequency much beyond 6 GHz is not appropriate for outside propagation.
The attenuation induced by rain, snow and moisture becomes significant with frequencies
over 8 GHz, and requires additional margins, therefore more RF power. In addition, there are
losses in connecting, cabling and passive devices for both on-board and at trackside
installations.
Therefore both tunnel conditions of propagation and outside conditions of propagation lead to choosing a
frequency range between 5GHz and 6 GHz.
Urban Rail CBTC
CBTC systems allow running trains only 90 seconds apart with total safety for the passengers and the staff
(or even less, the headway depending upon time spent by the train at every station for passengers to leave
and board trains; upon distance between stations and profile of the line; and upon acceleration, maximum
speed and deceleration possible for the train).
CBTC has been standardised by the IEEE in IEEE 1474 (1999), which gives the following definition:
A CBTC system is a continuous, automatic train control system utilizing
•
high-resolution train location determination, independent of track circuits;
•
continuous, high-capacity, bidirectional train-to-wayside data communications;
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•
and trainborne and wayside processors capable of implementing automatic train protection
(ATP) functions, as well as optional automatic train operation (ATO) and automatic train
supervision (ATS) functions.
CBTC is defined in almost identical terms by the IEC standard 62290
SRDoc chapter 9.2.1:
The spectrum for CBTC services should be individually licensed.
Description in the SRDoc:
CBTC means: fundamental time-critical CBTC and safety relevant applications with very low latency
CBTC (Communication-Based Train Controls) is providing automatic train control with or without driver. To
drive automatically a train, a Data Communication System is needed. When trains are moving the wireless
system allows communication with a central system. The wireless system is used to transmit traction order
or breaking order in a safe mode. If trains can’t transmit messages, they won’t be authorised to move.
Each train sends its location 5 times a second and the central system sends an authorization to move for
each train in the line. All the messages use the wireless DCS. This system allows reducing time between
trains in automatic mode (85 s instead of 105 s with human drivers)
Concerning the spectrum demand for CBTC, section 8.2 of the SRDoc includes the following description:
If a 200 Bytes - 1 000 Bytes CBTC packet content is assumed for each train (100 Bytes - 500 Bytes each
direction) per second, then the next step is to assume the quantity of trains that need to be controlled. The
worst case scenario is usually not along the main line, but in a train yard/depot. In this scenario, dozens of
trains and maintenance vehicles can be stationary, yet still in full CBTC communication with the wayside
controller. In the same position, basic data should be downloaded and uploaded, e.g. with 500 Byte packets.
An assumption of 50 communicating mobile units that communicate each second leads to:
500 Bytes/packet × 2 directions/radio link × 8 bits/Byte × 50 packets/second = 400 kbps.
The supported protocol - not specified in the SRDoc - is expected to provide efficiency under 20 %, including
duty cycle, gaps, and access mechanism. This means a need for a rough rate of 2 000 kbps at least.
It is reasonable to assume that a phase-modulated radio will be used, and that some protection will be
expected from the coding and modulation process. A minimum of 6 Db looks reasonable. Assuming a
modulation with the minimal spectral efficiency of QPSK leads to an RF Baud rate of 4 Mbaud (2 bits per
symbol from 4 × 2 Mbps). So the nominal bandwidth, with a QPSK signal changing at 4 Mbaud, is about 4
MHz. Allowing a guard band between channels, 5 MHz is the minimum channel spacing.
Trains report around 5 times per second their position to the trackside train control infrastructure,
and regularly receive an authorisation to run until a certain position (MAL -Movement Authority Limit)
also 5 times per second. The MAL is calculated by the trackside, based on the position received from all
trains in the area, and is valid for a certain time.
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In case a train has not received any MAL message for more than a freshness time which is typically
between one and five seconds, it will stop immediately.
In case the trackside has not received any position report from a train for more than a certain time, it
will stop the trains in the complete area.
Safe train protection involves a number of operational functions; noticeably the emergency braking that
must be anticipated to guarantee the safety of standing passengers: indeed emergency braking from 80
km/h to a full stop will occur if latency time is greater than 1 second. Emergency braking causes huge
discomfort and may even lead to injury to metro passengers. For this reason, the CBTC's radio must
provide a low latency or delay, even under a significant load of the radio.
It is of course very important for the train to be sure that the MAL message received is valid, that is to
say up to date.
ITS documentation:
http://www.etsi.org/technologies-clusters/technologies/intelligent-transport
EN 302
637-2
Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of
Applications; Part 2: Specification of Cooperative Awareness Basic Service
EN 302
637-3
Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of
Applications; Part 3: Specifications of Decentralized Environmental
Notification Basic Service
TS 101
556-3
Intelligent Transport Systems (ITS); Infrastructure to Vehicle Communications; Part
3: Communications system for the planning and reservation of EV energy supply
using wireless networks
EN 302
895
Intelligent Transport Systems (ITS); Vehicular Communications; Basic Set of
Applications; Local Dynamic Map (LDM)
TR 101
612
Intelligent Transport Systems (ITS); Cross Layer DCC Management Entity for
operation in the ITS G5A and ITS G5B medium; Report on Cross layer DCC
algorithms and performance evaluation
TS 102
894-2
Intelligent Transport Systems (ITS); Users and applications requirements; Part 2:
Applications and facilities layer common data dictionary
EN 302
636-5-1
Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking;
Part 5: Transport Protocols; Sub-part 1: Basic Transport Protocol
EN 302
636-4-1
Intelligent Transport Systems (ITS); Vehicular Communications; GeoNetworking;
Part 4: Geographical addressing and forwarding for point-to-point and point-tomultipoint communications; Sub-part 1: Media-Independent Functionality
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TS 102
687,
Intelligent Transport Systems (ITS); Decentralized Congestion Control Mechanisms
for Intelligent Transport Systems operating in the 5 GHz range;
Access layer part
TS 103
175
Intelligent Transport Systems (ITS); ETSI TS 103 175; Intelligent Transport
Systems (ITS); Cross layer DCC management entity for operation in the ITS G5A
and ITS G5B medium
Note: there may be several options (CAM, DEMN, or others) which can enable the exchange of information
between fixed and vehicular users providing each other’s position, dynamics and attributes. An extension
of the appropriate standard and specifications (or new standardisation deliverable) may be considered for
Urban Rail.
The BSA – Basis Set of Applications exists in ITS in EN 302 637-3:
trafficCondition(1)
accident(2)
roadworks(3)
adverseWeatherCondition-Adhesion(6)
hazardousLocation-SurfaceCondition(9)
hazardousLocation-ObstacleOnTheRoad(10)
hazardousLocation-AnimalOnTheRoad(11)
humanPresenceOnTheRoad(12)
wrongWayDriving(14)
rescueAndRecoveryWorkInProgress(15)
adverseWeatherCondition-ExtremeWeatherCondition(17)
adverseWeatherCondition-Visibility(18)
adverseWeatherCondition-Precipitation(19)
slowVehicle(26)
dangerousEndOfQueue(27)
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vehicleBreakdown(91)
postCrash(92)
humanProblem(93)
stationaryVehicle(94)
emergencyVehicleApproaching(95)
hazardousLocation-DangerousCurve(96)
collisionRisk(97)
signalViolation(98)
dangerousSituation(99)
Conclusions:
1. These incidents basically give a driver an alert/warning about a possible situation ahead. On the
other side, it has nothing to do with autonomous driving / driverless controls;
2. As one can see there is a major difference between road-safety related alerting and e.g. automatic
train control without a driver. Such a class of application as needed for CBTC does not exist so far
in ITS;
3. Future ITS may develop similar applications like Urban Rail Systems CBTC (in the direction of
autonomous driving/ driverless driving);
4. If CBTC implemented in ITS, then it would need a new class of applications inside of the ITS Basic
set of applications (BSA) for this purpose.
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ITS communications architecture
There is a possibility to ‘interface with ITS, see the ITS communications Architecture, e.g. to communicate
priorities.
en_302665v010101p
.pdf
Interfaces can enable to use different technologies for urban rail and ITS and at the same time foster coexistence including the resolution of priorities as needed for CBTC of urban rail systems. Need to
understand each other by using an interface.
Radio - principle features
ITS radio communications support in principles all features needed for CBTC:
1. Bandwidth 10 MHz for ITS while 5 MHz requested for CBTC
2. Power levels 33 dBm (23 dBm/1MHz) are the same
3. ITS: Detect and Avoid Mechanism under priorities, Decentralised congestion Control , ATPC and
duty cycle restrictions; to be investigated for Urban Rail CBTC with priorities as needed for CBTC
4. If necessary, limited channel loading (in support of low latency and high reliability), see ETSI TS 102
687, TS 103 175.
5. Possibility to prioritise certain messages at the application level (if defined in ITS BSA and if an
interface exists); to be investigated for Urban Rail CBTC
Two ‘uncoordinated’ standardization mandates
Two standardisation mandates exist: M/453 for ITS and M/486 for programming and standardisation
addressed to the European Standardisation Bodies in the field of Urban Rail. M/486 has not taken into
account Urban Rail CBTC at the time it was written. A better co-ordination inside ETSI could be requested
by CEPT administrations. The existence of these standardisation mandates can also provide access to
funding to facilitate standardisation activities to bring together urban rail and ITS standardisation. This will
on the other side lead to more efficient spectrum use which is a public concern.
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Existing ITS regulations
Frequency range
5 905 MHz to 5 925 MHz
5 875 MHz to 5 905 MHz
5 855 MHz to 5 875 MHz
Usage
Future ITS applications
ITS safety
(not limited to road safety!)
ITS non-safety applications
Channel name
G5-SCH4
G5-SCH3
G5-SCH1
G5-SCH2
G5-CCH
G5-SCH5
G5-SCH6
Carrier centre frequency fc
(MHz)
5 860
5 870
5 880
5 890
5 900
5 910
5 920
Regulation
ECC Decision (08)01]
ECC Decision (08)01
Commission Decision
ECC Recommendation(08)01
Maximum channel bandwidth
(MHz)
10
10
10
10
10
10
10
The CCH channel may be used by first ITS implementations on the market
Can ITS be applied for Urban Rail Systems?
This question was discussed with the UITP during the discussions in SRD/MG. EN 302 571 seems acceptable
for CBTC communication systems. Channels and selectivity are compatible with the need for
communication of CBTC. As described before, a CBTC system of communication is designed with 2 channels
per line used for permanent redundancy and frequency diversity.
It would be possible to design a CBTC communication system based on 802.11p which would work today
(note that 802.11p is integrated in the base 802.11 specifications).
In order to share common frequencies/channels, a Detect-And-Avoid functionality should be applied to all
users of these frequencies, setting the highest priority to the most critical services at low level.
Using the ITS G5/802.11p MAC protocol should be able to give the needed priority to CBTC (from a
statistical point of view), there is a concern that the achievable priority level may not be sufficient.
The main parameters of such a spectrum access mechanism are:
•
a Channel Availability Check time. This is the time during which a system shall monitor a
channel used by a high priority traffic before initiating a transmission in that channel. It
should be at least 10ms to be sure that the channel is not yet over-crowed;
•
a Channel Move Time. This is the time - less than a second, to avoid stopping the trains - for
the low priority system to clear the channel.
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It was noted in SRD/MG that the current ITS planned implementations are using in principle these spectrum
access features.
The system architecture for CBTC communications systems requires a high level of redundancy which
should not be constrained by ITS specifications. Moreover, the communications system contributes to the
overall safety of the CBTC system, as described in the standard EN 50159 "Railways applications –
Communication, signaling and processing systems – safety-related communication in transmission
systems". The transmitted messages are safety messages, answering to the requirements of the EN 50159,
and the communications system must ensure the authentication of all devices participating in the
communication and the encryption of all the safety messages. .
It is the role of the standardisation to consider common technical solutions. ETSI should investigate the use
of ITS for Urban Rail Systems in the frequency ranges 5875-5905 MHz (for CBTC) but also in the context
with future ITS applications in the frequency range 5905-5925 MHz. The decentralised common congestion
control, maximum channel loading specifications and prioritisation of certain applications in ITS may need
to be specified (if not done yet to the extent necessary) to ultimately avoid spectrum congestion
situations. Urban Rail applications such as CBTC should be included in the ITS basic set of applications, if
necessary, as a new class of applications.
4 channels are needed for Urban rail CBTC. Therefore, the considerations may need to encompass the full
frequency range 5875-5925 MHz, depending on the channel bandwidth and spectrum access
considerations (5MHz channels requested for CBTC).
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Frequency options
Option 1: Shared Use the current ITS spectrum also for Urban Rail CBTC in 5875-5905 MHz
Pro: no new spectrum necessary and perhaps more spectrum efficient
solution, can even be facilitated under general authorisation
Cons: requires considerable standardisation efforts. All applications using this
spectrum need to apply common spectrum access rules as part of a
decentralised congestion control). Not fully clear yet whether all possible
congestion situations can be handled.
In relation to other proposed applications in the 5 GHz frequency bands; in its
Mandate to CEPT (RSCOM13-32rev3), to study and identify harmonised
compatibility and sharing conditions for Wireless Access Systems including
Radio Local Area Networks in the bands 5350-5470 MHz and 5725-5925 MHz,
the commission required that the operational sharing conditions for
WAS/RLANs should in particular ensure that protection is guaranteed for
priority systems supporting EU policies, such as Intelligent Transport Systems
(in 5875-5905 MHz). If spectrum outside the current ITS allocation in 58755905 MHz is designated for Urban Rail, the protection guaranteed to existing
ITS allocations by this mandate, will not apply.
Option 2: consider CBTC shared use with future ITS applications in 5905-5925 MHz
Pro: less likely to be used by general authorised applications including
WAS/RLAN (taking also into account FS protection needs)
Con: Potential mix with WAS/RLAN under general authorisation. Not fully
clear yet whether all possible congestion situations can be handled between
urban rail and WAS/RLAN.
For both options 1 and 2, the issue is to avoid congestion situations between
ITS and Urban Rail CBTC applications, as well as to allow a defined
prioritisation of CBTC within the ITS specifications.
Option 3: look for a different frequency range for CBTC
Pro: wider bandwidth may be available at higher frequencies, e.g. 63-64 GHz,
see ECC Reports 113 and 114
Con: option totally outside of the SRDoc request
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General authorisation regulations worldwide with considerably high
emission limits
May also need a new standardization efforts
This option may be interesting to look into if options 1 and 2 turn out to be impracticable.
SRD/MG proposes to WGFM#82 at the moment to investigate options 1 and 2 and liaise with ETSI (ERM,
ITS, RT).
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