Global flow of information to on-board computers for calculating

Global System for Mobile Communications –Railway (GSM-R) isa wireless communications standard used globally for railway communication andapplications.

It uses a specific frequency band around 800/900 MHz (primarilybased on 2G technology). It has replaced analog systems which were widely beingused previously. It is based on European Integrated Railway Radio EnhancedNetwork (EIRENE) – Mobile Radio for Railways Networks in Europe (MORANE) specificationsGSM-R offers the highest level ofinteroperability in accordance with EIRENE. It also supports seamlessintegration of regional applications and services such as the European TrainControl System (ETCS) signalling system standard (Requiring fewer fixedinstallations, ETCS is more cost-effective than conventional trackside signalling).

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As the chosen data technology for ETCS, it is an integral component of the (EuropeanRail Traffic Management System) ERTMS. It provides substantial benefits byproviding continuous flow of information to on-board computers for calculatingspeeds and braking profiles  GSM-R enables higher train speeds (assuresperformance at speeds up to 310 mph (500 km/h) without any communication loss) andtraffic density with a high level of safety by carrying the signalling informationdirectly to the train driver. It enhances voice and data communication withtrains and allows drivers to communicate freely throughout transcontinentaljourneys (even through tunnels) enabling significant improvement of reliability,security and safety of rail services. It is also used for various other kindsof applications like cargo tracking, passenger information systems, video surveillanceetc. GSM-R statusGSM-R standard was envisioned with the goal ofachieving interoperability using a single communication platform. It is aresult of over a decade of collaboration between various European railwaycompanies.

It is a part of the European Rail Traffic ManagementSystem (ERTMS) standard. The specifications were finalised in the year 2000,basis the European Union funded MORANE (Mobile Radio for Railways Networksin Europe) projectGSM-R TechnologyThe radio sub system of the GSM-R network istypically implemented using base transceiver stations and communication towerswith antennas which are placed close to the rail track with intervals of 7-15km. The same is 3-5 km in China (with redundancy) to ensure higher availabilityand reliability.

GSM-R has to satisfy tight availability and performancerequirements of the HSR radio servicesThrough GSM-R, trains have a constant circuitswitched digital modem connection to their respective train control centre. Thetrains will automatically stop if the modem connection is lost. The enhancedMulti-Level Precedence and Pre-emption service (eMLPP) provides differentlevels of precedence for call set-up and for continuity in case of handover,thereby giving trains a greater priority compared to normal usersGSM-R Frequency SpectrumGSM-R typically uses a lower extension of the900MHz frequency: 876 MHz — 915 MHz for data transmission (uplink) and 921 MHz— 960 for data reception (downlink). However, frequencybands used differ from country to country. In Europe, the 876 MHz to 880 MHz and the 921 MHz to 925 MHz bands areused for uplink and downlink respectively.

In China, GSM-R occupies a 4 MHzwide range of the E-GSM band (900 MHz-GSM)GSM-R is a Time Division Multiple Access (TDMA) system whichmeans that the data transmissions consists of periodical frames with periods of4.615 ms for each physical channel. The modulation used is GMSK and channel spacing is 200 kHz  Limitations of GSM-RCapacity: The 4-MHz bandwidth ofGSM-R can support 19 channels of 200-KHz width. This is sufficient for voicecommunication, as voice calls are limited in time and do not occupy resourcescontinuously. In the next-generation railway system, where each train needs toestablish a continuous data connection with a radio block centre (RBC), andeach RBC connection needs to constantly occupy one time slot. Hence, for thenext-generation railway system, the current capacity turns out to be insufficient.

However, the radio capacity can be increased by using more spectrum resources.Interference: The interferencebetween GSM-R and other public networks increases because both railway andpublic operators would like to have good coverage along the rail tracks. Thisresults in an inevitable fight for coverage between them. Ideally, suchinterference can be avoided if public operators do not use frequency bandsadjacent to those of GSM-R for the areas close to rail tracks. However, this isnot well implemented in practiceCapability: As a narrow-bandsystem, GSM-R cannot provide advanced services and adapt to new requirements.The maximum transmission rate of GSM-R per connection is 9.

6 kb/s, which issufficient only for applications with low demands. Delay is in the range of 400ms, which is too high to support any real-time application and emergencycommunication 1            GSM-Rfor ETCS (applications and flexibility)ETCS is a signalling system used for railwaycontrol and GSM-R network acts as its data carrier.  It uses GSM-R radio network to send andreceive information from trainsIt has three levels of operation. GSM-R is usedonly for voice communications on the first level (ETCS-1). It is mainly used fordata transmissions on the other two levels (ETCS-2 and ETCS-3). It is veryrelevant to ETCS-2 and ETCS-3, where the train travels at a speed up to 350km/h. Hence, it is necessary to guarantee a continuous supervision of train speedand position.

The train has to automatically reduce the speed to 300 km/h(ETCS-1) or lower, when the call is lost 2            LTEand Status of LTE-R standardizationLTE offers many advantages in terms of capacityand capabilities that GSM-R doesn’t. It is better suited for datacommunications, since it is a fully packet-switched-based network. Lower packetdelay is one of the crucial requirements for providing ETCS messages. LTEoffers a more efficient network architecture and hence has a reduced packetdelayLTE consists of a number of improvements thatincrease spectral efficiency, such as advanced modulation and multiplexing.Therefore, it has a high throughput radio access.

It is also a well-establishedand off-the-shelf system and provides standardized interworking mechanisms withGSM-R. It also offers improved security protection over GSM-RFeatures ofLTE-RLTE-R inherits all the important features ofLTE. It also offers an extra radio access system to match HSR-specific needsand exchange wireless signals with On-Board Units (OBUs). However, LTE-R hasmany differences in comparison to public LTE networks such as architecture, systemparameters, network layout, services, and QoS.

Since the network must be ableto operate at 500 km/h in complex railway environments, LTE-R will beconfigured for reliability more than capacity. Hence, quadrature phase-shiftkeying (QPSK) modulation is preferredLTE-R ChallengesCurrently, there is no large scale operation of LTE-R anywhere inthe world. There are manyscientific issues which are yet to be solved at LTE-R band e.g.

propagationloss, geometry distribution of multipath components (MPCs), andtwo-dimensional/three-dimensional angular estimation in those HSR-specificenvironments. It is therefore necessary to look for extensive channelmeasurements and develop a series of channel models for the link budget and networkdesign of LTE-R