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Advances in Communications-Based Train Control Systems by F. Richard Yu

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177
Chapter 9
Networked Control
fora Group of Trainsin
Communications-Based
Train Control Systems
with Random
Packet Drops
Bing Bu, F. Richard Yu, and Tao Tang
Contents
9.1 Introduction ............................................................................................. 178
9.2 Related Work ...........................................................................................179
9.3 Trains’ Control in CBTC Systems ............................................................180
9.3.1 Communication Procedures with Packet Drops ...........................180
9.3.2 Trains’ Control System and Equivalent NCS ................................181
9.3.2.1 Trains’ Control System in CBTC ...................................181
9.3.2.2 Equivalent NCS ..............................................................183
9.3.3 Analytical Formulation of CBTC .................................................184
9.4 Packet Drops in Train–Ground Communications ...................................186
9.4.1 Packet Drops due to Random Transmission Errors ....................... 186
9.4.2 Packet Drops due to Handover .....................................................187
9.4.2.1 Handover Time ..............................................................187
178 Advances in Communications-Based Train Control Systems
9.1 Introduction
Rail-guided transport systems have attracted more and more attention, because
they can provide greater transport capacity, superior energy eciency, lower car-
bon emission, and outstanding features of punctuality and safety compared with
other mass transit methods. e traditional rail system is a track-based train control
system, which uses track circuit to coarsely determine the location of a train to
transmit unidirectional ground–train control information. e coarse train posi-
tioning and low unidirectional communication throughput lead to low line capac-
ity in TBTC rail systems. e typical minimum headway which is the time interval
between two neighboring trains of TBTC is several minutes [1].
As a modern successor to TBTC, CBTC systems use continuous, high- capacity,
bidirectional train–ground communication to transmit status and control com-
mands of trains to realize automatic train control functions. e line capacity can
be increased. e typical minimum headway of CBTC is 90s or even less [1,2].
For urban transit systems, WLANs are commonly used due to the open stan-
dards and the available commercial o-the-shelf equipment [3]. Numerous WLAN-
based CBTC systems have been deployed around the world, such as Beijing Metro
Line 10 from Siemens [4] and Las Vegas Monorail from Alcatel [5]. However,
WLANs are not originally designed for high-speed scenario; random transmission
delays and packet drops are inevitable in train–ground communication.
Although the two key technologies of CBTC systems, trains’ control and train
ground communication, are closely related, by now they are designed independently.
9.4.2.2 AP’s Coverage Area .........................................................188
9.4.2.3 Overlapping Coverage Area ............................................ 191
9.4.2.4 Rate of Packet Drops Introduced by Handovers .............191
9.5 Trains’ Control in CBTC with Packet Drops ...........................................193
9.5.1 Currently Used Control Scheme in CBTC Systems ...................... 193
9.5.2 States Estimation under Packet Drops ..........................................194
9.5.3 Eects of Packet Drops on the Stability of the Trains’
ControlSystem .............................................................................197
9.5.4 Eects of Packet Drops on the Performances of the Trains’
Control System .............................................................................198
9.5.5 Two Proposed Novel Control Schemes .........................................199
9.6 Field Test and Simulation Results ............................................................201
9.6.1 Field Test Results on the Packet Drop Rate ..................................201
9.6.2 Design of the Closed-Loop Control Systems .................................202
9.6.3 Simulation Results of Trains’ Control System Impacted by
Packet Drops.................................................................................203
9.7 Conclusion .............................................................................................. 208
References .........................................................................................................210

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