A duplicated network structure for an LTE-Based train control communication

ng 9 - 2016 Journal of Science and Technology
 ISSN 2354-0575
Finally, we present our conclusions and future work cell. For reference, we give different cells different 
in the last section. names. It is clear that all A cells and their associated 
 network components (i.e. eNBs, EPC, etc.) 
II. LTE-R TCS with a Duplicated Network constitute a subnetwork. Similarly, all B cells and 
Structure their associated network components form another 
1. System Architecture subnetwork. At any time of operation, a train should 
 In this section, we propose two different connect to both subnetworks to ensure the highest 
duplicate network structures for an LTE-R train level of safety. Otherwise, an emergency treatment 
control system (TCS). We have prepared two will be required for the continuous operation of that 
proposals for the system. Proposal 1 is characterized train. We describe below how an on-train dual-link 
by a fully-overlapping cell arrangement as shown in model is established to facilitate the safety of train 
Fig. 1 (a). Proposal 2 is characterized by a partly- operation.
overlapping cell arrangement as shown in Fig. 1 Originally, an on-train dual-link model is 
(b). Both proposals share the same components. proposed in the literature to deal with the handover 
Notice that we do not intend to explain the whole problem. Refer to [7, 3] for examples. In essence, 
architecture of an LTE-R network. That is explained this model takes full advantage of the transmission 
in [4, 5, 6]. Instead, we highlight the radio network of distributed antennas and body length of the 
layer with the main components that can be train to eliminate transmission delay. It implies 
graphically represented as shown in the figure that performance of the LTE-R TCS will improve, 
below. with the application of the on-train dual-link model 
 and an effective handover algorithm. In addition, 
 we can again see that the distributed antenna 
 transmission will be helpful when a train connects 
 to two subnetworks simultaneously.
 (a)
 (a)
 (b)
Fig. 1. (a) Proposal 1: An LTE-R TCS with a 
fully overlapping cell arrangement, (b) Proposal 
2: An LTE-R TCS with a partly-overlapping cell 
 arrangement
 We recall that an eNodeB (eNB) is a 
network node that transmits signals to trains (or 
user equipment) and also receives signals from 
those trains. The eNBs are interconnected by means 
of the X2 interface. The eNBs are also connected 
to the Evolved Packet Core (EPC) by means of 
 (b)
an S1 interface. An Application Server (AS) will 
be used to provide the applications and services Fig. 2. An on-train dual-link model in an LTE-R 
needed for train operation. In our case, eNBs are TCS: (a) with a fully-overlapping cell arrangement, 
deployed along rail tracks. Each eNB manages one and (b) with a partly-overlapping cell arrangement
Khoa học & Công nghệ - Số 11/Tháng 9 - 2016 Journal of Science and Technology 53
ISSN 2354-0575
 Figure 2 depicts a train with an on- Recall that with the duplicated network 
train dual-link operating in the LTE-R TCS as structure, the LTE-R TCS has two logical 
described in Proposal 1 and Proposal 2. As shown subnetworks operating simultaneously. Regardless 
in the figure, with a center control station (CCS), of the types of cell arrangements, as shown in Fig. 
we can effectively control the train and ground 1, these subnetworks need to use different spectrum 
communication using two antenna sets mounted bands to avoid mutual interference. Furthermore, 
on the top of the train (at its front and its rear, at least one bandwidth greater than 1.4 MHz is 
respectively). Each individual antenna is configured required for video service, as its data rate can reach 
to only work with one dedicated subnetwork. 2.25 Mbps. Therefore, the preferred bandwidths for 
However, each set of antennas may include some the two subnetworks will be 1.4 MHz and 3 MHz. 
antennas that allow it to work with two different From now on, we will refer to these subnetworks 
subnetworks. It is obvious that communications as the 1.4 MHz subnetwork and the 3 MHz 
in an LTE-R TCS will be more reliable with the subnetwork. We assume that the frequency-division 
deployment of the on-train dual-link model. As a duplexing method is used for communications 
result, train operations are safer in that system.. in those networks. This means that we need 1.4 
 MHz of bandwidth for the uplink and another 1.4 
2. Resource Requirement and Task Division MHz of bandwidth for the downlink in the 1.4 
 At first, we estimate the traffic demand for MHz subnetwork. Similarly, two different 3 MHz 
train operations. This is important to calculate the bandwidths are required for the 3 MHz subnetwork. 
bandwidth required by the LTE-R TCS. According We can assign tasks to two subnetworks depending 
to [2], services constituting a typical train control on their own channel capacity as follows:
system are automatic train control (ATC), voice • 1.4 MHz subnetwork will support ATC 
calls, data services, and video services. The data rates and voice calls;
needed for these services are summarized in Table 1. • 3 MHz subnetwork will support data and 
 Table 1. Estimated data rates for train operation video services.
 Data rate Theoretically, as expected in LTE technology, 
 Function at 1.4 MHz and 3 MHz, the total downlink and 
 Uplink Downlink
 uplink peak rates are 11.4 Mbps (i.e. 2.1 Mbps 
 Automatic train control 530 kbps 530 kbps plus 9.3 Mbps) and 7.1 Mbps (i.e. 2.1 Mbps plus 
 Voice call 224 kbps 224 kbps 5.0 Mbps), respectively. The total traffic demands 
 defined in Table 1 will reach 4.5 Mbps downlink 
 Data service 1100 kbps
 throughput and 3.5 Mbps uplink throughput. 
 Video service 2304 kbps 2048 kbps Therefore, the LTE-R TCS can serve multiple trains 
 Total 3058 kbps 3902 kbps operating simultaneously.
 Because spectrum resources dedicated for 
railway communication are often limited, in this 3. Technical Challenges
work we assume that the allocated bandwidth is Among the technical requirements for a train 
sufficient enough for total traffic demand, which is control system, the availability and reliability of its 
defined in Table 1. In order to determine a requested communication network are the most important. 
bandwidth, we need to consider the capacity or With the duplicated network structure and on-
peak bit rate of an LTE network. Note that the train dual-link model, the reliability is obviously 
peak rate is defined as the peak data rate that user enhanced for LTE-R TCS. Since the availability 
equipment can achieve in an ideal RF condition. is typically measured as a factor of the reliability, 
Bandwidth supported by the current LTE standard as reliability increases so does availability. We 
and corresponding practical peak rates are listed in observe that throughput performance reflects 
Table 2. The mentioned peak rates are established both availability and reliability, while link quality 
in [8] for a single stream with the assumption reflects the reliability of a network. Note that in
that 64QAM and 16QAM are used for downlink LTE, the link quality is defined by the maximum 
transmission and uplink transmission, respectively. acceptable block error rate (BLER). Therefore, 
 Table 2. Practical LTE peak rates in Mbit/second in the following section, our main concern is to 
 1.4 3 5 10 15 20 identify problems that may reduce the throughput 
 MHz MHz MHz MHz MHz MHz performance and link quality of an LTE network. 
 According to [1, 3], there are two major problems 
 Downlink 2.1 9.3 17.9 35.8 53.8 73.6
 that need to be considered:
 Uplink 2.1 5.0 8.3 20.1 29.9 39.6 (1) The handover problem. This problem 
54 Khoa học & Công nghệ - Số 11/Tháng 9 - 2016 Journal of Science and Technology
 ISSN 2354-0575
is caused by train mobility. The current LTE hard there are many studies that deal with the inter-cell 
handover scheme may have a large outage probability interference problem [9-14]. They are mainly based 
and interrupt latency, which severely affects the on dynamic frequency allocation and the power 
reliability of train-to-ground communication. As control approach that often uses the fractional 
it allows the train to receive signals from only one frequency reuse technique. The dynamic frequency 
base station at a time, the on-train dual-link model allocation approach uses a technique that requires 
is not supported. two adjacent cells to allocate different physical 
 (2) The inter-cell interference problem. This resource blocks (PRBs) at a time. Clearly, these two 
problem is due to frequency reuse in adjacent cells. approaches reduce the throughput of cells, since 
Methods and algorithms to deal with inter-cell the band of each cell is narrowed. Furthermore, 
interference are not available in the current LTE methods based on these approaches require two 
standard. adjacent eNBs to cooperate to exchange channel 
 Tien et al. (2012) [3] proposed a seamless allocation information. Thus, they introduce some 
dual-link handover scheme in broadband wireless overhead that again reduces the performance of the 
communication systems for high speed rail. In our corresponding cells.
case, a seamless handover scheme of similar type We remark that existing methods and 
can be adapted to the LTE-R TCS. We deploy an on- results for the handover problem and the inter-
train dual-link model for LTE-R TCS, as shown in cell interference often relies on a single network 
Section II.1. A seamless handover scheme like the structure setup. Therefore, results obtained with 
one introduced in [3] works as follows. At the time, a duplicate network structure setup such as the 
the front antenna performs a handover to connect throughput performance and link quality may be 
to the target eNB (i.e. after handover , the eNB different and interesting.
becomes the serving eNB), while the rear antenna 
still connects with the serving eNB. When the III. Conclusion
handover procedure is done, the rear antenna should In this paper, we investigated a future 
be released, and all allocated physical resource LTE-based train control system. We proposed 
blocks and the front antenna will take the role of two different duplicate network structures for 
train and ground communication. If a handover this system, as is required for the safety of train 
fails with the front antenna, the rear antenna will operations. This implies that the availability 
continue to carry the handover and take on the role and reliability of the system can be enhanced. In 
of train and ground communication. addition, no existing methods or results concerning 
 Since the handover problem can be this issue are available. In the future, we will provide 
addressed efficiently using the on-train dual-link more results related to the reliable and continuous 
model and a seamless handover algorithm described operation of a train operation in the system. We also 
above, we will concentrate more on methods to consider the handover problem in the duplicated 
solve the inter-cell interference problem. Actually, network structure contexts created by this work.
References
 [1]. Sniady, A., Soler, J., 2013. Performance of Lte in High Speed Railway Scenarios: Impact on 
 Transfer Delay and Integrity of etcs Messages. In: et al. (Eds.), M. B. (Ed.), LNCS. Vol. 7865. 
 Springer-Verlag Berlin Heidelberg, pp. 211–222.
 [2]. Yoon, B., woo Jung, M., jin Lee, S., hong Min, K., Kim, Y.-K., 2011. Bandwidth Estimation for 
 Radio based Train Control and Communication System. In: Proc. ICWN 2011. Nevada USA, pp. 
 1–4.
 [3]. Tian, L., Li, J., Huang, Y., Shi, J., Zhou, J., 2012. Seamless Dual-link Handover Scheme in 
 Broadband Wireless Communication Systems for High Speed Rail. IEEE J. on Selected Areas in 
 Comm. 30 (4), 708–718.
 [4]. Tingting, G., Bin, S., 2010. A High-speed Railway Mobile Communication System based on Lte. 
 In: Proc. ICEIE 2010, V1(24). pp. 414–417.
 [5]. ETSI, 2013. 3GPP TS 36.331 V9.4.0: Radio Resource Control (RRC). 
 Specs/archive/36 series/36.331/.
 [6]. ETSI, 2013. 3GPP TS 36.401 V11.2.0 Release 11: E-UTRAN Architecture Description. http://
 www.etsi.org/deliver/etsi ts/136400 136499/136401/11.02.00 60/.
 [7]. Luo, W., Zhang, R., Fang, X., 2012. A Comp Soft Handover Scheme for Lte Systems in High 
Khoa học & Công nghệ - Số 11/Tháng 9 - 2016 Journal of Science and Technology 55
ISSN 2354-0575
 Speed Railway. EURASIP J. on Wireless Communications and Networking 196 (2012), 1–9.
 [8]. Dongzhe Cui, 2009. LTE Peak Rates Analysis. Wireless and Optical Communications 
 Conference, 2009.WOCC 2009, pp.1-3.
 [9]. Dai, K., Hiroyuki, S., 2012. Inter-Cell Interference Coordination (ICIC) Technology. FUJITSU 
 Sci. Tech. J., 48(1), 89-94.
 [10]. Daeinabi, et al., 2012. Survey of Intercell Interference Mitigation Techniques in LTE Downlink 
 Networks. Proc. ATNAC 2012, pp. 1-6.
 [11]. Rahman, et al., 2009. Interference Avoidance with Dynamic Inter-Cell Coordination for 
 Downlink LTE System. Proc. IEEE WCNC 2009, pp. 1-6.
 [12]. YuNan, et al., 2013. A Novel Inter-Cell Interference Coordination Scheme Based on Dynamic 
 Resource Allocation in LTE-TDD Systems. Proc. IEEE VTC 2010, pp. 1-5.
 [13]. Fraimis, et al., 2010. A Distributed Radio Resource Allocation Algorithm with IC for Multi-cell 
 OFDMA Systems. Proc. PIMRC 2010, pp. 1354-1359.
 [14]. Zhao, et al., 2010. A Modified Inter-Cell Interference Coordination Algorithm in Downlink of 
 TD-LTE. Proc. WiCOM 2010, pp. 1-4.
 KIẾN TRÚC MẠNG VÔ TUYẾN KÉP DỰA TRÊN CÔNG NGHỆ LTE CHO 
 HỆ THỐNG ĐIỀU KHIỂN TÀU CAO TỐC
 Tóm tắt:
 Hiệp hội Đường sắt Quốc tế đã quyết định sử dụng công nghệ LTE để thay thế công nghệ GSM cho 
 các hệ thống giao tiếp đường sắt. Hàn Quốc – quốc gia đi tiên phong về công nghệ LTE, sẽ áp dụng 
 công nghệ này cho hệ thống đường sắt cao tốc của họ vào năm 2016. Để đảm bảo tuyệt đối an toàn 
 chạy tàu, hệ thống thông tin điều hành tàu cao tốc phải đặc biệt tin cậy và luôn trong trạng thái sẵn 
 sàng. Yêu cầu này chỉ có thể được đáp ứng tốt nhờ hệ thống mạng vô tuyến với các tế bào chồng lấn. 
 Các giải pháp hiện nay chủ yếu dựa trên một kiến trúc mạng vô tuyến đơn lẻ. Vì vậy, mức độ tin cậy 
 của hệ thống thông tin điều hành tàu chưa đảm bảo yêu cầu. Trong bài báo này, chúng tôi thiết kế 
 một hệ thống điều hành chạy tàu với kiến trúc mạng kép. Chúng tôi đề xuất hai phương án thiết kế 
 mạng với cách sắp xếp các tế bào vô tuyến khác nhau. Trên cơ sở các đề xuất này, chúng tôi phân 
 tích, làm rõ những yêu cầu kỹ thuật, những ưu điểm và thách thức có thể gặp phải khi triển khai hệ 
 thống trong thực tiễn.
 Từ khóa: Giao tiếp đường sắt, LTE-R, tàu cao tốc, điều khiển chạy tàu, kết nối kép, đường sắt Hàn 
 Quốc
56 Khoa học & Công nghệ - Số 11/Tháng 9 - 2016 Journal of Science and Technology