1. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 1 INDUSTRY GROUP UIC ERTMS Conference Budapest April 2006 Capacity Enhancement For GSM-R Networks Valerio Di Claudio

2. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 2 INDUSTRY GROUP Headline  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  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 data for ETCS means that a dedicated connection per train must be maintained  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

3. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 3 INDUSTRY GROUP Conventional Approach With Circuit- Switched Voice/Data  CSD is a switching technique that establishes a dedicated and uninterrupted connection between the sender and the receiver  This implies: Constant bandwidth occupation irregardless of the actual amount of transmitted data, for the whole duration of the call Guaranteed quality of service Non-optimal bandwidth utilization  Circuit-switching systems are ideal for communications that require data to be transmitted in real-time, as voice or video

4. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 4 INDUSTRY GROUP Methods Of Optimizations In CS Domain  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)  In GSM-R it could be possible, the extension of HR channels in group calls, but this is not supported  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  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

5. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 5 INDUSTRY GROUP CSD Optimization Benefits  In CSD, the maximum gain factor in capacity using HR channels is “2”  This benefits can be considered for Point to Point voice calls only  The extension to data and group calls isn’t an easy task, also for the future

6. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 6 INDUSTRY GROUP Principles Of GPRS  GPRS uses packet switched mode to send and receive data  Flexible channel allocation: One to Eight TS Shared resources among active users Independent up-link and down-link channel allocation Four different coding schemes (9.05, 13.4, 15.6, 21.4 Kb/s)  SMS transport optimization  Always on connection  Inter-working with IP data networks  Packet-switching systems are ideal for communications where some amount of delay is acceptable

7. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 7 INDUSTRY GROUP The Packet Multiplexing Concept CH1 CH2 CH3 CH4 MUX Bandwidth Delay

8. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 8 INDUSTRY GROUP The Advantages Of GPRS  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: intermittent, non-periodic (bursty) data transmissions, where the time between successive transmissions greatly exceeds the average transfer delay 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 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

9. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 9 INDUSTRY GROUP Efficient Applications Of GPRS In GSM-R  Mapping the previous scheme in the railway sphere, applications taking benefit by using GPRS bearers are: 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 ERTMS/ETCS Frequent transmission of small value of data without using a dedicated 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. WEB Browsing, file download, database access, onboard e- ticketing... Typically short transactions with larger volumes of data with asymmetrical characteristic, that fit at the best the typical behaviour of standard GPRS terminals (1 x TS uplink, 4 x TS downlink)

10. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 10 INDUSTRY GROUP Availability Of Products For GPRS  GSM-R networks are already ready to support GPRS, depending on customer needs  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 clarified  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  In this perspective, GSM-R GPRS mobiles terminals, covering different categories, are already available from industry

11. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 11 INDUSTRY GROUP Some Examples Of GPRS Terminals KAPSCH GSM-R MT2 SELEX ESVM101 SAGEM TiGR 150R HANDHELD 2W MODEM 8W MODEM

12. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 12 INDUSTRY GROUP Consideration Of IP Routing And Addressing  Addressing in CSD is based on E.164 numbering  In GPRS (PS domain) the addressing scheme is based on IP (Internet Protocol), which is the world wide standard for data communications. This ensures: A future proof solution A complete suite of upper layer protocols (TCP/IP, UDP/IP…) A wide range of commercially available products A “native” integration with other data networks, both wired and wireless  GPRS allows static and dynamic addressing, where the first one is best suited for terminals to be reached from the centre (SCADA applications, PIS), while dynamic addressing is better for roaming, database access, web browsing

13. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 13 INDUSTRY GROUP ERTMS Status  CSD as bearer for ETCS L2 is available, tested, approved and already in commercial operation  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  To be ready, now it is the right time to start evaluation of GPRS for ETCS in order to define specifications, interoperability, approval, etc.

14. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 14 INDUSTRY GROUP ERTMS Over GPRS  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: GPRS allows to multiplex up to 7 user over a single TS, with a nearly 4 times increment of users compared to HR data  Main still open issues are: the EURORADIO protocol stack shall be replaced by an equivalent one, based on IP E.164 to IP addressing migration CSD to PSD coexistence and inter-working Cell reselection time in GPRS GPRS QoS aspect for ERTMS

15. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 15 INDUSTRY GROUP Other Ideas For The Future  Migration of data services to GPRS allows an optimal utilization of radio resources, thus providing four level of QoS to different users  The IP based architecture allows applications, using standard devices  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  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 with slow moving trains, leaving the global architecture unchanged  EGPRS could be considered an evolution of GPRS, but its adaptive coding seems not to provide true benefits for moving trains

16. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 16 INDUSTRY GROUP On-Board IP Scenario

17. ALSTOM FREQUENTIS HFWK KAPSCH SELEX NORTEL SAGEM SIEMENS WENZEL 17 INDUSTRY GROUP Conclusions  Radio Resources reserved for GSM-R are limited and an optimized use of them will be mandatory in dense areas  The path to capacity enhancement is the same followed in public GSM networks, tailored to railway needs Advanced cell/frequency planning Use of AMR for voice calls Migration of ETCS to IP Extensive use of GPRS for data application, as it provides the best efficiency when combined with an optimal QoS management