LTE-Based Mobile Train Radio Communication

Introduction to LTE-Based Mobile Train Radio Communication

• This chapter provides technical details on Long Term Evolution (LTE), Evolved Packet Core (EPC), and LTE-based Mobile Train Radio Communication Systems
• The content aligns with LTE and FRMCS specifications from 3GPP and UIC
• Future Railway Mobile Communications System (FRMCS) project has been set by the UIC to prepare for the introduction of a GSM-R successor

LTE vs GSM-R

• GSM-R was created by adding extra functionality to GSM standards
• The UIC aims to incorporate railway-specific functions directly into the LTE standard
• LTE may offer more functionality for the railway industry compared to GSM
• Mobile Train Radio Communication Systems using LTE are under development
• GSM-R is becoming obsolete and is predicted to be so by 2030

Limitations of GSM-R

• Increasing communication demands necessitate strong data communication support
• GSM-R lacks packet-switched transmission, relying on Circuit-Switched Data (CSD)
• CSD cannot efficiently allocate network resources based on real-time demand
• GSM-R transmits data over virtual circuits, similar to voice frames
• Bursty data transmissions are inefficient over GSM-R's fixed circuits, leading to underutilization and wasted resources

LTE Overview

• Long Term Evolution (LTE) represents the latest in 4G mobile communication standards, developed by 3GPP
• LTE prioritizes high spectral efficiency, peak data rates, low round trip times, and flexible bandwidth

Key LTE Network Components

• Key components of the LTE network subsystem include:
• E-UTRAN eNodeB
• Serving Gateway (S-GW)
• Packet Data Network Gateway (PDN-GW)
• Mobility Management Entity (MME)
• Home Subscriber Server (HSS)
• Policy and Charging Rules Function (PCRF)
• Policy and Charging Enforcement Function (PCEF)
• IP Multimedia Core Network Subsystem (IMS)

E-UTRAN eNodeB

• Base station for LTE radio, equivalent of BSS in GSM-R
• Responsible for radio transmission and reception to/from User Equipment (UEs)
• Connects to EPC nodes via the S1 interface
• Connects to neighboring eNodeBs via the X2 interface

Serving Gateway

• It handles user plane functions, transporting IP data traffic between User Equipment (UE) and external networks
• The point of interconnect between the radio side and the EPC
• Routes incoming and outgoing IP packets, serving as the UE's gateway
• Anchor point for intra-LTE mobility and handovers between eNodeBs and other 3GPP accesses
• Logically connected to the PDN GW.

Packet Data Network Gateway (PDN-GW)

• Point of interconnect between the EPC and external IP networks
• Routes packets to and from the PDNs
• Performs functions like IP address/prefix allocation, policy control, and charging
• Though 3GPP specifies gateways separately, vendors may combine them

Mobility Management Entity (MME)

• Deals with the control plane, handling signaling for mobility and security for E-UTRAN access
• Responsible for tracking and paging UEs in idle-mode
• Termination point for the Non-Access Stratum (NAS)

Home Subscriber Server (HSS)

• Database containing user and subscriber information
• Supports mobility management, call and session setup, user authentication, and access authorization

Policy and Charging Rules Function (PCRF)

• Combination of Charging Rules Function (CRF) and Policy Decision Function (PDF)
• Ensures service policy and sends Quality of Service (QoS) information for sessions
• Also shares accounting rule information, enforced in the eNodeB.

Policy and Charging Enforcement Function (PCEF)

• Enforces policies and detects service data flow, enabling data to flow through the P-GW
• Responsible for QoS on IP packets in the P-GW
• Enforces rules for data packets to pass through the gateway

IP Multimedia Core Network Subsystem (IMS)

• All-IP system designed to help mobile operators deliver advanced services by using an architecture with Internet flexibility
• Supports voice, pictures, text, video, and combinations
• Functions as a core component within 3G, cable TV, and next-gen telecoms networks for delivering multimedia

LTE Key Features

• Fully packet-switched IP-based mobile communication standard from 3GPP
• Real-time and data communication services run via IP protocol
• LTE networks allocate resources based on user and application needs
• It contains a simplified core network, EPC with fewer elements
• Based on OFDMA for downlink, SC-FDMA for uplink,
• OFDMA (Orthogonal Frequency Division Multiple Access) is used for the downlink
• SC-FDMA (Single Carrier Frequency Division Multiple Access), also known as DFT (Discrete Fourier Transform) spread OFDMA is used for the uplink
• OFDMA is combined with higher order modulation (up to 64QAM), large bandwidths (up to 20 MHz) and spatial multiplexing creating high data rates
• Radio interface offers spectral efficiency by dynamically adjusting modulation and coding
• Link adaptation allows balancing throughput and reliability

LTE Frequency and Spectral Flexibility

• Developed for various frequency bands, E-UTRA operating bands ranging from 450 MHz to 5.925 GHz
• Supports Time Division Duplex (TDD) and Frequency Division Duplex (FDD) technologies
• E-UTRA operates in spectrum allocations of 1.4, 3, 5, 10, 15 and 20 MHz as per 3GPP/ETSI in paired and unpaired spectra
• Able to delivers content over aggregated radio band resources in varied band configurations

Data Rate and Transmission Latency

• LTE enables downlink peak data rate of 100 Mb/s within a 20 MHz spectrum (5 bps/Hz)
• LTE enables uplink peak data rate of 50 Mb/s within a 20 MHz spectrum (2.5 bps/Hz)
• Highest theoretical peak data rate on the transport channel is 75 Mbps uplink and 300 Mbps downlink with spatial multiplexing
• LTE (4G) features low transmission latency, both in User and Control Planes
• Data travel time between UEs and eNodeB is less than 5 ms (User Plane)
• UE switching time from standby to active is less than 100 ms (Control Plane)
• User Plane and Control Plane transmission latency are further improved in the 5G system

Network Capacity, Mobility, and Coverage

• Supports at least 200 active users per cell for spectrum allocations up to 5 MHz
• E-UTRAN optimized for low mobile speed from 0 to 15 km/h
• Supports higher mobile speed between 15 and 120 km/h and maintains mobility across cellular networks at speeds from 120 to 350 km/h
• Coverage (cell range) depends on cell edge throughput, spectrum availability, and efficiency

Enhanced Multimedia Broadcast Multicast Service (MBMS)

• Reduces terminal complexity with unified modulation, coding, and multiple access approaches
• Provides simultaneous dedicated voice and MBMS services
• Available for paired and unpaired spectrum configurations

Interoperability and Architecture

• Supports co-existence with GERAN/UTRAN on adjacent channels
• E-UTRAN terminals also supporting UTRAN and/or GERAN, should measure and handover to/from 3GPP UTRAN and GERAN
• Real-time service handover interruption between E-UTRAN and UTRAN (or GERAN) should be less than 300 msec
• Supports packet-based architecture, systems supporting real-time and conversational traffic
• Minimizes single point of failure in E-UTRAN architecture

Architecture and Management

• E-UTRAN architecture supports end-to-end QoS
• Backhaul communication protocols are optimized
• Radio Resource Management includes enhanced QoS support, efficient higher-layer transmission, and load/policy management across radio access
• Complexity of options are minimized, eliminating mandatory features

Mobile Train Radio Communication System (LTE)

• Railway LTE is comprised of user equipment, Evolved Universal Terrestrial Radio Access Network, Evolved Packet Core, IP Multimedia Subsystem (IMS)/ Session Initiation Protocol (SIP) Core
• It is also comprised of applications/solutions severs on LTE
• It is compatible with train automation systems like European Train Control and interoperable with legacy systems such as GSM and UMTS

Users in FRMCS

• Driver(s)
• Controller(s)
• Train staff: Train conductor(s), Catering staff, and Security staff
• Trackside staff: Trackside maintenance personnel and shunting team member(s)
• Railway staff: Engine and Catering scheduler(s), RU and IM operator(s), and engineering personnel
• Station managers: station and depot personnel
• Members of the public: passengers and other persons on platforms or at level crossings
• Systems: ATC, ATO, On-board, Ground, Trackside and Trackside warning systems, Sensors along trackside, and Trackside elements controlling entities
• Network and Public emergency operators

Communication Requirements are divided between the following categories.

• Critical: Train movements, safety, or legal obligations, such as emergency communications, shunting, presence, trackside maintenance, and ATC
• Performance: Improve railway operation, such as train departure and telemetry
• Business: Support general railway business operation, such as wireless internet

Critical Communication Applications Include:

• On-train outgoing and incoming voice communication between the driver and controllers
• The driver can initiate voice communication to any controller responsible for the train's movement
• An authorized controller can set up voice communication with a driver
• Multi-train voice communication with ground users
• Drivers can set up voice communications with entitled ground users and other drivers
• Ground users can initiate voice communications with drivers and other entitled ground users, based on train location and functional identity
• Voice communication can be bidirectional or unidirectional
• Banking voice communication
• Drivers of different locomotives within the same train can set up voice communication
• Entitled controllers can join ongoing voice communications without driver action and can be invited by the driver Note: Locomotives may or may not be coupled mechanically and/or electrically
• Trackside maintenance and shunting voice communication
• Trackside workers or controllers can set up voice communications with authorized users
• Communication can be bidirectional or unidirectional
• Shunting voice communication and Train integrity monitoring data communication
  • A shunting user can set up uninterrupted voice communication with other shunting users and/or entitled controllers
  • Voice communication can be user-to-user or multi-user, with the system automatically addressing entitled controllers and other shunting users
• Public emergency call
• Ground to ground voice communication
• Automatic train control and operation communication
• Provision of a reliable communication bearer supports radio-based ATC systems
• ATC systems have a reliable communication bearer for efficient data transfer between on-board and ground systems
• Data communication for possession management
• Supports processes for taking possession of railway infrastructure for engineering purposes
• Trackside maintenance warning communication
• The trackside maintenance warning system can initiate data communication to trackside maintenance workers
• Remote control of engines communication
• Monitoring and control of critical infrastructure
• Data communication is possible between infrastructure systems and ground/train-based systems for monitoring critical infrastructure
• Railway staff and public train emergency communication
• Authorized users can set up railway emergency communication to other users in an automatically configured area
• On-train safety device to ground communication
• Voice/data communication is automatically set up towards a ground user when triggered by a Driver Safety Device (DSD)
• Working alone monitoring
• Voice and Data recording and access
• Shunting data communication
• Train integrity monitoring data communication
• Public emergency warning
• On-train outgoing/incoming voice communication from/to train staff
• Railway staff emergency communication
• Critical Real time video
• Critical Advisory Messaging services
• Virtual and On-train wireless backbone coupling data communication
• Train parking protection

Performance Communication Applications Include:

• Multi-train voice communication for drivers excluding ground users communications
• Lineside Telephony.
• Station public address communications
• On-train telephony and telemetry
• Non-critical real-time video
• Wireless on-train data communication for train staff on platforms and on the train
• On-train remote equipment control
• Train Driver advisory
• Train departure data
• Messaging
• Transfer of data
• Record and broadcast of information
• Real time video and augmented reality data communication These communications include on-train voice, infrastructure telemetry, monitoring and control of non-critical systems.

Business Communication Applications

• Information and Emergency help point for public.
• Wireless internet on train and on platforms.

Critical Support Applications

• Assured Voice and Data Communication

Traffic Control Applications

• Multi user, Traffic Control
• Role management.
• Location services
• Authorization of communication and applications
• QoS Class Negotiation.
• Key management communications
• Inviting user messaging
• Arbitration.

Applications in Indian Railways

• Emergency Communications (train to control, train-train, etc.)
• Automated Signalling Systems (ETCS Level 2/TCAS)
• Live surveillance camera feeds and their prevention of security breaches

Future Applications

• Indian Railway Automatic Train Protection System (IRATP) through Train Collision Avoidance System
• Mission Critical Push to Talk (MC PTT) Application
• Video Surveillance System in locomotives
• Onboard Passenger Information System
• Internet of Things (IoT) based Asset reliability monitoring
• Onboard Video Surveillance System (VSS) for Passenger Security
• Broadband Internet on Running Train (Onboard Wi-Fi facility through LTE)

Frequency Allocations

• TRAI has allocated 5 MHz (paired) Spectrum in the 700 MHz band (703-748 MHz Uplink & 758-803 MHz Downlink, also specified as Band 28 in 3GPP/ETSI standards) to Indian Railways

Miscellaneous Facts relating to Indian Railways

• All mobile users in the LTE network have to be assigned certain addresses or identities in order to identify, authenticate and localize them
• Uniform Numbering Scheme for Mobile Communication Network
• It is proposed that the future projects of Railway Automation System and Broadband Services may be designed with LTE
• It is also required that LTE system proposed for Indian Railways should be fit for bearer network for TCAS/ETCS Level 2/3 for desired speed.

The various identifiers include

• International Mobile Subscriber Identity The IMSI is a string of decimal digits, up to a maximum length of 15 digits, which identifies a unique subscription
• The MSIN is the third field of the IMSI, can be up to 10 digits in length, and is administered by the relevant MNC assignee to identify individual subscriptions
• Country and Network code

LTE FDD System Throughput

• 1.4 MHz -4.4 Mbps
• 3 MHz - 11.1 Mbps
• 5 MHz - 18.3 Mbps
• 10 MHz - 36.7 Mbps
• 15 MHz - 55.1 Mbps
• 20 MHz - 75 Mbps

Uniform Numbering Scheme Specifics

• Mobile Country Code (MCC): The first field of the IMSI, three digits long, identifies the country
• Mobile Network Code (MNC): The second field of the IMSI, two or three digits long, administered by the national numbering plan administrator
• Mobile Subscription Identification Number (MSIN): The third field of the IMSI, up to 10 digits long, administered by the MNC assignee for individual subscriptions
• MS ISDN: Mobile Subscriber International Subscriber Directory Number
• Country Code (CC): Up to three digits
• National Destination Code (NDC): Typically two or three digits
• Subscriber Number (SN): A maximum of 10 digits