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

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115
Chapter 7
Novel
Communications-Based
Train Control System
with Coordinated
Multipoint Transmission
and Reception
Li Zhu, F. Richard Yu, and Tao Tang
Contents
7.1 Introduction .............................................................................................116
7.2 CBTC Systems .........................................................................................119
7.2.1 Impacts of Communication Latency on CBTC Systems ............... 119
7.2.2 Proposed CBTC System with CoMP ............................................121
7.3 System Models .........................................................................................122
7.3.1 Train Control Model ....................................................................123
7.3.2 Communication Channel Model .................................................. 125
7.4 Communication LatencyinCBTCSystems with CoMP .........................126
7.4.1 Coordinated Multipoint Transmission and Reception ..................126
7.4.2 Data Transmission Rate and BER .................................................126
7.4.3 Communication Latency ..............................................................128
116 Advances in Communications-Based Train Control Systems
7.1 Introduction
In existing train–ground communication systems, the mobile terminal (MT) on a train
communicates with an independent wayside base station to realize train–ground com-
munications. Trains travel fast on the railways, and the received signal-to-noise ratio
(SNR) changes rapidly. e communication latency will be a serious problem when
the MT on a train is in deep fading. More importantly, when a train moves away from
the coverage of a base station and enters the coverage of another base station along the
railway, a hando procedure occurs. In the current communications-based train control
(CBTC) systems, only the traditional hard hando scheme is supported, where a train
can only communicate with a single base station at any given time. It may result in com-
munication interruption and long latency due to the weak wireless signals in the hando
zone and high moving speed of trains. Both of these two challenges can severely aect
train control performance, train operation eciency, and the utilization of railway.
Recently, some research has been done on the train–ground communication
issues in the railway environment. In [1], a fast handover algorithm suitable for
dedicated passenger line is proposed by setting a new neighboring list. A novel
handover scheme based on on-vehicle antennas is introduced in [2]. A cross-layer
hando design is studied in [3] for multiple-input and multiple-output (MIMO)-
enabled wireless local area networks (WLANs).
Although these above works consider the impacts of railway environment on
the communication performance, the hando schemes in most current research
7.5 Control Performance OptimizationinCBTC Systems with CoMP ......... 129
7.5.1 SMDP-Based CoMP Cluster Selection and Hando
DecisionModel ............................................................................129
7.5.1.1 Decision Epochs .............................................................130
7.5.1.2 Actions ...........................................................................130
7.5.1.3 States ..............................................................................131
7.5.1.4 Reward Function ............................................................131
7.5.1.5 State Transition Probability ............................................132
7.5.1.6 Constraints .....................................................................134
7.5.2 Solutions to SMDP-Based CoMP Cluster Selection and
Hando Decision Scheme ............................................................134
7.5.2.1 Reduced-State Bellman Equation ...................................135
7.5.2.2 Online Value Iteration AlgorithmviaStochastic
Approximation................................................................135
7.5.3 Optimal Guidance Trajectory Calculation ...................................137
7.6 Simulation Results and Discussions .........................................................139
7.6.1 Train Control Performance Improvement ..................................... 140
7.6.2 Hando Performance Improvement .............................................143
7.7 Conclusion ............................................................................................... 145
References .........................................................................................................146

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