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ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAG EM SIEMENS WENZEL 1

INDUSTRY GROUP

UIC ERTMS ConferenceBudapest April 2006

Capacity Enhancement For GSM-R Networks

Valerio Di Claudio


INDUSTRY GROUP

Headline

Ø The frequency spectrum allocated for GSM-R is limited to 4 MHz, which means 19 frequency channels in most countries, thus providing a limited numbers of circuit switched channels

Ø This numbers seems to be a critical point in dense areas (large train stations for example), especially when ETCS level 2/3 will be extensively deployed, as the current use of circuit switched dat a for ETCS means that a dedicated connection per train must be maintained

Ø In order to prevent this limitation, the guideline could be an advanced use of cell/frequency planning of the radio coverage, use of AMR in Circuit Switched Mode, migration to GPRS for services where it provides the best efficiency


INDUSTRY GROUP

Conventional Approach With Circuit-Switched Voice/Data

Ø CSD is a switching technique that establishes a dedicated and uninterrupted connection between the sender and the receiver

Ø This implies:

ü Constant bandwidth occupation irregardless of the actual amount of transmitted data, for the whole duration of the call

ü Guaranteed quality of serviceü Non-optimal bandwidth utilization

Ø Circuit-switching systems are ideal for communications that require data to be transmitted in real-time, as voice or video


INDUSTRY GROUP

Methods Of Optimizations In CS Domain

Ø In the circuit switched approach the strategy for capacity enhancement relies on network optimization (see smaller cells) and bandwidth reduction for calls (ex. AMR for voice and HR data)

Ø In GSM-R it could be possible, the extension of HR channels in group calls, but this is not supported

Ø The drawback is that vocoder shall be the same on a cell basis, requiring the availability of this feature by all mobiles in the cell

Ø Half Rate data is not specified in ETSI/3GPP and there is no interest to standardize it at the moment, because everybody is asking for MORE bandwidth today. To standardize it, the support of network and mobile suppliers would be necessary, not only from the ones engaged in GSM-R. The complexity of this task is considered to be very high


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CSD Optimization Benefits

Ø In CSD, the maximum gain factor in capacity using HR channels is “2”

Ø This benefits can be considered for Point to Point voice calls only

Ø The extension to data and group calls isn’t an easy task, also for the future


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Principles Of GPRS

Ø GPRS uses packet switched mode to send and receive data

Ø Flexible channel allocation:ü One to Eight TSü Shared resources among active usersü Independent up-link and down-link channel allocationü Four different coding schemes (9.05, 13.4, 15.6, 21.4 Kb/s)

Ø SMS transport optimization

Ø Always on connection

Ø Inter-working with IP data networks

Ø Packet-switching systems are ideal for communications where some amount of delay is acceptable


INDUSTRY GROUP

The Packet Multiplexing Concept

CH1

CH2

CH3

CH4

MUX

Bandwidth

Delay


INDUSTRY GROUP

The Advantages Of GPRS

Ø GPRS allows an efficient use of network resources for packet mode data applications like those exhibiting one of more of the following characteristics, as stated in ETSI:ü intermittent, non-periodic (bursty) data transmissions, where

the time between successive transmissions greatly exceeds the average transfer delay

ü frequent transmissions of small volumes of data, for example transactions consisting of less than 500 octets of data occurring at a rate of up to several transactions per minute

ü infrequent transmission of larger volumes of data, for example transactions consisting of several kilobytes of data occurring at a rate of up to several transactions per hour


INDUSTRY GROUP

Efficient Applications Of GPRS In GSM-R

Ø Mapping the previous scheme in the railway sphere, applications taking benefit by using GPRS bearers are:ü Supervisory Control and Data Applications (SCADA),

passenger information ...Large amount of devices with permanent logical connections, but with bursty transmission of few data during the whole day

ü ERTMS/ETCS Frequent transmission of small value of data without using a ded icated connection per train, like in circuit switched mode: GPRS uses radio resources only when data is actually sent, with a significantly better usage of the available bandwidth, thus allowing a larger number of trains in dense areas.

ü WEB Browsing, file download, database access, onboard e -ticketing ...Typically short transactions with larger volumes of data with as ymmetrical characteristic, that fit at the best the typical behaviour of standard GPRS terminals (1 x TS uplink, 4 x TS downlink)


INDUSTRY GROUP

Availability Of Products For GPRS

Ø GSM-R networks are already ready to support GPRS, depending on customer needs

Ø The inter-working of eMLPP with GPRS resource allocations in GSM-R is not specified. It is not clear whether eMLPP calls are able to pre-empt GPRS resources. If so this behaviour is not desired if GPRS is used for ETCS: the issue needs to be clarifie d

Ø But this issue seems not to be a blocking one, as the use of dedicated or switch-able ASCI/GPRS mobiles could address most railway applications by now

Ø In this perspective, GSM-R GPRS mobiles terminals, covering different categories, are already available from industry


INDUSTRY GROUP

Some Examples Of GPRS Terminals

KAPSCH GSM-R MT2

SELEX ESVM101

SAGEM TiGR 150R

HANDHELD

2W MODEM

8W MODEM


INDUSTRY GROUP

Consideration Of IP Routing And Addressing

Ø Addressing in CSD is based on E.164 numberingØ In GPRS (PS domain) the addressing scheme is based on IP

(Internet Protocol), which is the world wide standard for data communications. This ensures:ü A future proof solutionü A complete suite of upper layer protocols (TCP/IP, UDP/IP…)ü A wide range of commercially available productsü A “native” integration with other data networks, both wired and

wirelessØ GPRS allows static and dynamic addressing, where the first one i s

best suited for terminals to be reached from the centre (SCADA applications, PIS), while dynamic addressing is better for roami ng, database access, web browsing


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ERTMS Status

Ø CSD as bearer for ETCS L2 is available, tested, approved and already in commercial operation

Ø GPRS as bearer for L2 is a future solution in order to solve capacity issues when L2, L3 and ETCS regional will be implemented on a lot of tracks

Ø To be ready, now it is the right time to start evaluation of GPRS for ETCS in order to define specifications, interoperability, approval, etc.


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ERTMS Over GPRS

Ø Migration of ERTMS to GPRS allows to solve capacity problem in dense areas as GPRS radio resources are shared among all trains in the area, ensuring permanent connections to all: ü GPRS allows to multiplex up to 7 user over a single TS, with a

nearly 4 times increment of users compared to HR data Ø Main still open issues are:ü the EURORADIO protocol stack shall be replaced by an

equivalent one, based on IPü E.164 to IP addressing migrationü CSD to PSD coexistence and inter-workingü Cell reselection time in GPRSü GPRS QoS aspect for ERTMS


INDUSTRY GROUP

Other Ideas For The Future

Ø Migration of data services to GPRS allows an optimal utilizationof radio resources, thus providing four level of QoS to differen t users

Ø The IP based architecture allows applications, using standard devices

Ø Advanced routing capability provided by available IP equipments allows sharing of a single GSM-R GPRS radio access between multiple devices for both on -train and fixed installations

Ø In an evolutionary scenario, where still more bandwidth will be required, GPRS could be easily integrated with alternative broadband radio access solutions, especially in dense areas withslow moving trains, leaving the global architecture unchanged

Ø EGPRS could be considered an evolution of GPRS, but its adaptive coding seems not to provide true benefits for moving trains


INDUSTRY GROUP

On-Board IP Scenario


INDUSTRY GROUP

Conclusions

Ø Radio Resources reserved for GSM-R are limited and an optimized use of them will be mandatory in dense areas

Ø The path to capacity enhancement is the same followed in public GSM networks, tailored to railway needsü Advanced cell/frequency planningü Use of AMR for voice callsü Migration of ETCS to IPü Extensive use of GPRS for data application, as it provides the

best efficiency when combined with an optimal QoS management

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