EP3831690A1

EP3831690A1 - Telecommunications system and method for a railway infrastructure

Info

Publication number: EP3831690A1
Application number: EP20210885.8A
Authority: EP
Inventors: Pasquale Donadio
Original assignee: Comesvil SpA
Current assignee: Comesvil SpA
Priority date: 2019-12-02
Filing date: 2020-12-01
Publication date: 2021-06-09
Also published as: IT201900022629A1

Abstract

It is disclosed a telecommunication system for a railway infrastructure. The system comprises a mobile apparatus suitable for being installed on board a train of the railway infrastructure and a plurality of fixed apparatuses suitable for being installed along a railway line along which the train moves. The mobile apparatus comprises a radio transceiver module and an optical receiver module. Each fixed apparatus comprises a radio transceiver module and an optical transmitter module. The radio transceiver module of the mobile apparatus and the radio transceiver module of the fixed apparatus are configured to set up a radio link between them, and the optical transmitter module of the fixed apparatus is configured to transmit data to the optical receiver module of the mobile apparatus on a light link.

Description

TECHNICAL FIELD

The present invention relates in general to the telecommunications field. More particularly, the present invention relates to a telecommunication system for a railway infrastructure.

BACKGROUND ART

It is known that the Compound Annual Growth Rate (CAGR) of wireless traffic has been 60% over the last 10 years (see e.g., P. J. Winzer, D. T. Neilson, "From scaling disparities to integrated parallelism: a decathlon for a decade", Journal of Lightwave Technology, vol. 35, no. 5, March 1, 2017). If this data is confirmed for the next 20 years, which is expected to be reasonable given the rapid spread of Internet-of-Things (loT) technologies and of the so-called machine type communications (MTC), it will be expected that the bandwidth demand for wireless communications will be unmanageable, since the request can probably reach some THz. However, the entire spectrum of radio frequencies is "only" 0.3 THz wide.
For this reason, alternative technologies for wireless communications have been introduced in recent years, based on the use of light. In particular, the Light-Fidelity (Li-Fi) technology is based on the use of light for data transmission. The use of light for transmitting data allows to exploit a wider bandwidth, it is enough to think that the width of the spectrum of light and infrared radiation is about 2600 times the width of the spectrum of radio frequencies. The use of light also allows to overcome some further limitations of radio frequency based communication apparatuses. In fact, Li-Fi communications enable higher throughputs to be achieved and can be used even in environments unsuitable for the use of radio communications for electromagnetic interference problems (e.g. aircraft cabins, military areas, hospitals, nuclear power stations), or in protected environments where the use of radio communication devices is often prohibited (e.g. oil platforms).
As known, a railway infrastructure is generally provided with a wireless communication system based on radio apparatuses. Generally, the system comprises a radio apparatus located on board a railway train (or train) and a set of radio apparatuses distributed along the railway line. The on-board radio apparatus communicates with the radio apparatuses distributed along the line to transmit and receive:

(i) vital data, i.e. signaling messages for management, control and protection of railway traffic, such as for example signaling messages of the CBTC (Communication-Based Train Control) system; and
(ii) non-vital data, for example video data provided by possible closed-loop cameras (CCTV) present on the trains, or service information for travellers, etc.

In general, the vital data stream has a relatively low throughput, typically less than 1 Mb/s. The flow of non-vital data, on the other hand, typically has a higher throughput, generally between 10 Mb/s and 100 Mb/s. On the other hand, while the transmission of non-vital data does not require any protection or redundancy mechanisms, the transmission of vital data requires instead this type of mechanism, because the continuity of the transmission of vital data is essential for the safety of the railway train and passengers.
For example, EP 3199421 A1 , in the name of the Applicant, describes an apparatus and a radio system for a railway infrastructure. The apparatus comprising two separate radio units operating in nonoverlapping frequency ranges (for example, 2.4-5 GHz and 868-900 MHz). The system comprises a mobile radio apparatus on board the railway train and several fixed radio apparatuses distributed along the railway line, each having two separate radio units. In the mobile radio apparatus, the radio unit operating at the highest frequency transmits and/or receives data using a radio link established with a single fixed radio apparatus at a time. Substantially at the same time, the radio unit operating at the lower frequency transmits and/or receives the same data using radio links established with several fixed radio apparatuses. The apparatus and the radio system therefore have a redundant structure, which allows to implement mechanisms for protection of the transmission of data between the fixed side and the mobile side (in particular of the data that are vital for the safety of the railway infrastructure).

SUMMARY OF THE INVENTION

The Applicant has noted that, as far as railway infrastructures are concerned, the insufficient availability of radio resources inevitably leads to a degradation of the performance of the communication systems, due to the need to reuse the radio frequencies and to the consequent occurrence of electromagnetic interferences. In addition, the new high-speed rail transport systems, up to futuristic technologies such as Hyperloop, provide that the trains move at very high speeds (even above 100 km/h), which makes it impossible to have reliable radio connections at a low cost.
The Applicant has therefore pursued the object of providing a telecommunication system for a railway infrastructure which allows to overcome the limitations indicated above. In particular, the Applicant has pursued the object of providing a telecommunication system for a railway infrastructure which is robust to electromagnetic interference and which can be implemented in high-speed rail transport systems in an economically efficient manner.
The above mentioned object, in addition to others, is achieved by a telecommunication system comprising a network of communication devices, called "microcells", in turn comprising radio modules, in particular, for example, multi-frequency radio modules, and optical modules, in particular, for example, optical transceiver modules based on the Li-Fi technology.
According to a first aspect, the present invention provides a telecommunication system for a railway infrastructure. comprising a mobile apparatus suitable for being installed on board a train of the railway infrastructure and a plurality of fixed apparatuses suitable for being installed along a railway line along which the train travels, wherein:

the mobile apparatus comprises a radio transceiver module and an optical receiver module;
each fixed apparatus comprises a radio transceiver module and an optical transmitter module,

Preferably, the system further comprises a management apparatus configured to be connected to the plurality of fixed apparatuses.
Preferably, both the radio transceiver module of the mobile apparatus and the radio transceiver module of the fixed apparatus is a multi-frequency radio transceiver module configured to operate in at least two different frequency ranges.
In particular, preferably, both the radio transceiver module of the mobile apparatus and the radio transceiver module of the fixed apparatus comprise at least two radio units, each being configured to receive and transmit data using a radio communication technology operating in range of frequencies comprised between 70 MHz and 6 GHz.
According to one embodiment, both the radio transceiver module of the mobile apparatus and the radio transceiver module of the fixed apparatus comprise a first radio unit configured to receive and transmit data using a Wi-Fi technology and a second radio unit configured to receive and transmit data using a long-range (LoRa) radio-frequency wireless technology.
Preferably, the optical transmitter module of the fixed apparatus is configured to transmit data to the optical receiver module of the mobile apparatus by establishing a light link according to a light-fidelity (Li-Fi) communication technology.
Preferably, the optical receiver module of the mobile apparatus is configured to transmit data to the optical transmitter module of the stationary apparatus using an infrared communication technology.
Preferably, the optical transmitter module of the fixed apparatus comprises a light source and an optical gateway module. Preferably, the optical gateway module is connected to the management apparatus of the telecommunication system via the radio transceiver module and is configured to receive data from the management apparatus and to drive the light source so as to transmit the data received from the management apparatus to the optical receiver module of the mobile apparatus.
Preferably, the light source comprises a LED lamp.
Preferably, the optical receiver module of the mobile apparatus comprises a light sensor configured to receive optical signals diffused by the light source of the optical transmitter module.
Preferably, the data received from the management apparatus comprises a routing table comprising one or more signaling commands for controlling the train which are to be transferred to the train at one or more predetermined locations along the railway line, and geo-localization data of the places where commands are to be applied.
Preferably, each fixed apparatus is configured to determine an aggregate routing table comprising data derived from the routing table and further data, the further data comprising data indicative of the quality of the radio link and/or light link between the fixed apparatus and the mobile apparatus, and a next hop indicator which identifies, when the mobile apparatus is connected to a given fixed apparatus, the next fixed apparatus to which the mobile apparatus can connect.
Preferably, the data indicative of the quality of the radio link and/or the light link between the fixed apparatus and the mobile apparatus comprise a received signal strength indicator for the radio link and/or a modulation index for the light link and/or a throughput for the light link.
Preferably, the mobile apparatus comprises a buffer memory configured to store the aggregate routing table.
According to a second aspect, the present invention provides a method for transmitting and receiving data in a railway infrastructure comprising a train and a railway line along which the train travels, the method comprising:

transmitting and receiving said data using a radio link established between a radio transceiver module of a mobile apparatus installed on board the train and a radio transceiver module of a fixed apparatus of a plurality of fixed apparatuses installed along the railway line; and
alternatively, transmitting and receiving said data using a light connection established between an optical transmitter module of the fixed apparatus and an optical receiver module of the mobile apparatus.

Preferably, the method comprises, in case a light connection is used to transmit and receive said data, which is established between the optical transmitter module of the fixed apparatus installed along the railway line and the optical receiver module of the mobile apparatus installed on board the train, substantially at the same time, establishing a radio link between a radio transceiver module of the mobile apparatus and a radio transceiver module of a further fixed apparatus of the plurality of fixed apparatuses installed along the railway line.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will become clearer from the following detailed description, given purely by way of non-limiting example, to be read with reference to the attached Figures, in which:

Figure 1 schematically illustrates a telecommunication system for a railway infrastructure according to embodiments of the present invention;
Figures 2a and 2b are block schemes of a mobile microcell and a fixed microcell, respectively, according to embodiments of the present invention;
Figures 3a and 3b are block schemes of the components of a radio transceiver module according to embodiments of the present invention,
Figures 4a and 4b are block schemes of an optical transmitter module and an optical receiver module, respectively, according to embodiments of the present invention;
Figure 5 schematically illustrates a non-combined handover procedure according to embodiments of the present invention;
Figure 6 schematically illustrates a geometric model for determining the size of a buffer memory for a mobile microcell according to embodiments of the present invention; and
Figure 7 schematically illustrates a combined handover procedure according to embodiments of the present invention.

DETAILED DESCRIPTION

Figure 1 schematically shows a telecommunication system 1 for a terrestrial transport infrastructure on rail or other means, according to embodiments of the present invention. In the following description, reference will be made, for the sake of simplicity, to an infrastructure for railway transportation. However, the system according to the present invention can also be applied to other types of transport infrastructures, for example transport infrastructures using buses or trams.
The transport infrastructure considered in the present description and schematically shown in Figure 1, by way of non-limiting example, is a railway infrastructure 2 comprising a railway train (or train) 20 and a line along which the train 20 travels. The railway infrastructure 2 may be, for example, an underground railway infrastructure, in which the railway line has underground sections and/or sections in tunnels and/or open sections, or a high-speed railway infrastructure. The infrastructure considered can also be the infrastructure of the Hyperloop technology.
The telecommunication system 1 comprises a set of apparatuses interconnected by means of a communication network. The set of apparatuses of the telecommunication system 1 comprises at least two types of apparatus, which will be hereinafter also referred to as "microcells":

one or more mobile apparatuses (or mobile microcells) MM which are configured to be associated with the railway train 20 (for example to be positioned on board the railway train 20). In the following description, for the sake of simplicity, reference will be made to a single mobile microcell MM; and
a number n of fixed apparatuses (or fixed microcells) FM1, FM2, ..., FMn which are configured to be installed in fixed positions distributed along the railway line along which the railway train 20 travels. In the following description, the generic fixed microcell will be indicated by the notation FMk, in which k=1,2, ..., n is preferably an integer number greater than 1. The fixed apparatuses FM1, FM2, ..., FMn are preferably distributed along the railway line 2 at a mutual distance D from each other. The fixed apparatuses FM1, FM2, ..., FMn can for example be positioned at the stations along the railway line. In particular, as will be better described below, according to advantageous embodiments of the system according to the present invention, the fixed apparatuses FM1, FM2, ..., FMn, which comprise a light source, are positioned in correspondence with lighting stations of the railway line.

Preferably, the telecommunication system 1 also comprises a management apparatus MA. The management apparatus MA is preferably located at a control center CC of the railway infrastructure 2. Preferably, the management apparatus MA is connected to the fixed apparatuses FM1, FM2, ..., FMn through a fixed communication network (or backbone network), for example an optical fiber communication network, and through respective connection interfaces, for example Gigabit Ethernet interfaces.
The telecommunication system 1 according to the present invention provides that the fixed microcells FM1, FM2,..., FMn and the mobile microcell MM implement a mobile network of bi-directional wireless links which allow the mobile microcell MM to exchange data flows (for example, a flow of vital data and a flow of non-vital data) with the fixed microcells FM1, FM2,..., FMn while the mobile microcell MM (which is installed on the train 20) is moving in the direction indicated by the arrow F in Figure 1. According to the present invention, the wireless links that each fixed microcell FMk and the mobile microcell MM can establish with each other are radio wave links (for simplicity, radio links) and links using electromagnetic waves in a different frequency band with respect to the radio wave frequency band, in particular, links using visible light (which will be referred to, for simplicity, as "light links" or "light connections") and/or links using infrared radiation.
In general, a bidirectional communication is established between the railway train 20 and the control center CC, in particular the management apparatus MA. The control center CC sends data packets to the railway train 20, for example control data packets containing instructions for the correct movement of the train itself, as it will be described in more detail below. The source of the data is the control center CC and the destination is the mobile microcell MM present in the railway train 20. This communication uses the fixed microcells FM1, FM2, ..., FMn as intermediate nodes. A communication is also established from the mobile microcell MM present in the railway train 20 toward the control center CC. Also in this case, the fixed microcells FM1, FM2,..., FMn act as intermediate nodes. In this case, the data source is the mobile microcell MM in the railway train 20, which sends data packets to the control center CC. Such data packets may comprise vital data connected, for example, to the verification of the closure of a door, which is indispensable for starting the running of the railway train 20, and/or non-vital data, such as the images of its interior acquired by the on-board closed-loop cameras and sent from the train 20 to the control center CC.
Figures 2a and 2b show a block scheme of a mobile microcell MM and a fixed microcell FMKk, respectively. Each microcell comprises a module configured to implement a radio communication technology (in particular, preferably, a multi-frequency radio technology) and a module configured to implement an optical communication technology based on the use of visible light (in particular, preferably, the Li-Fi technology). For this purpose, the mobile microcell MM preferably comprises a radio transceiver module RTM and an optical receiver module ORM. The fixed microcell FMk preferably comprises a radio transceiver module RTM' and an optical transmitter module OTM.
The radio transceiver module RTM, RTM' is preferably a multi-frequency radio transceiver module. In particular, the radio transceiver module RTM present in a mobile microcell MM is similar to the mobile radio apparatus described in EP 3199421 A1 , and the radio transceiver module RTM' present in a fixed microcell FM is similar to the fixed radio apparatus also described in EP 3199421 A1 .
In the following description, only some aspects of the structure and operation of the radio transceiver modules RTM, RTM' will be described, i.e. the structural and functional aspects relating to the present invention.
According to particularly advantageous embodiments of the present invention, the radio transceiver module RTM, RTM' present both in each fixed microcell FMk and in each mobile microcell MM has a modular hardware structure. In particular, each of these modules RTM, RTM' preferably comprises a base board, which includes a set of housings, connectors and links. An exemplary base board is schematically shown in Figure 3a. In particular, the base board BB schematically shown in Figure 3a comprises an electrical connector EC adapted to connect the board BB to an electrical power source. Each radio transceiver module RTM, RTM' further comprises units and/or components, which are housed in the slots of the base board BB. The units or components present in the radio transceiver module RTM, RTM', in particular housed in the board BB, comprise:

at least one radio unit RU1, RU2 configurable to receive and transmit data using any radio communication technology or standard operating in a frequency range from 70 MHz to 6 GHz (e.g. Wi-Fi a/b/g/n/ac, LTE, GSM, GSM-R, TETRA, LoRa, etc.). Preferably, each radio RU1, RU2 comprises a modem which is software configurable according to a Software Defined Radio (SDR) technology. More in particular, as shown in Figure 3b, each radio unit RU1, RU2 comprises at least one network processor NP, at least one Field Programmable Array Gateway (FPGA) component, one or more Graphic Processing Units (GPUs), a digital/analog converter D/A, a radio frequency transceiver TX/RX and at least one antenna AN. The transceiver TX/RX and the antenna AN are preferably adapted to operate in the entire frequency range 70 MHz-6 GHz. The FPGA component is preferably programmable so as to control the other components of each radio unit RU1, RU2 to implement any radio communication technology or standard in the frequency range 70 MHz-6 GHz supported by the transceiver TX/RX and the antenna AN, for example Wi-Fi. Therefore, if it is desired to modify the radio communication technology or standard implemented by the radio unit RU1, RU2 (for example it is desired to switch from Wi-Fi to LTE), it is sufficient to reconfigure the radio unit RU1, RU2 by means of software, by reprogramming the FPGA component in a suitable manner, without the need of any modification to the other hardware components of the radio unit;
a programmable converter AC/DC PAD configured to allow selection of the input and output voltage via software;
a network switch NS configured to implement the interconnection of the other modules of the apparatus to the backbone network;
a GPS (Global Positioning System) unit GM configured to detect the geographical coordinates of the microcell;
a test board (or "dummy board") DB adapted to implement diagnostic tests or to test the implementation of a new radio communication technology or standard on the fixed or mobile apparatus;
a format converter MC, configured to convert the data exchanged by the fixed microcell with the backbone network between the format of the board (Ethernet, for example) and the optical format of the backbone network (for example, format for single fiber or format for multimode fiber). The format converter MC may optionally be connected to an optical connector.

In particular, the radio transceiver module RTM implemented in a mobile microcell MM according to preferred embodiments of the present invention preferably comprises a first radio unit RU1, a second radio unit RU2, a network switch NS and a programmable converter AC/DC PAD housed on the base board BB. Optionally, the radio transceiver module RTM also comprises a test board DB, also housed on the base board BB. In addition, the radio module RM preferably comprises a GPS module GM, also housed on the base board BB.
The network switch NS is connected to the radio units RU1, RU2, to the GPS module GM and also to the test board DB (if present), preferably through respective Ethernet connections.
The radio transceiver module RTM further preferably comprises, for each radio unit RU1, RU2, at least one radio antenna connector. According to an advantageous variant, the radio transceiver module RTM preferably comprises six radio antenna connectors RAC (i.e. three for each radio unit RU1, RU2), which allow each radio unit to implement a 3x3 Multiple Input Multiple Output (MIMO) connection.
As already mentioned above, the radio transceiver module RTM' implemented in each fixed microcell FMk preferably has a hardware structure similar to that of the radio transceiver module RTM implemented in a mobile microcell MM, with the only difference that, instead of the GPS module GM, a format converter MC is preferably present connected to an optical connector adapted to connect the radio transceiver module RTM' to the optical fiber of the backbone network.
The first radio units RU1 present in the radio transceiver modules RTM of the mobile microcell MM and in the radio transceiver modules RTM' of the fixed microcells FM are configured to implement a first radio communication technology or standard operating in a first frequency range. The first technology may be, for example, the Wi-Fi technology in the 2.4 - 5.9 GHz frequency range. Further, preferably, the second radio units RU2 are configured to implement a second radio communication technology or standard in a second range of frequencies that are lower than the frequencies of the first range. The second technology may be for example the Long-Range (LoRa) wireless radio frequency technology operating at frequencies of about 433 MHz or about 868 MHz.
The management apparatus MA preferably has a hardware structure similar to that of the radio transceiver module RTM' of the fixed microcell FMk, with the only difference that it does not have the radio antenna connectors RAC and that instead of the radio units RU1, RU2 it comprises a first radio network controller and a second radio network controller. The management apparatus MA according to the present invention preferably comprises the hardware components of the management apparatus described in EP 3199421 A1 . In the following description, only some aspects of the structure and operation of the management apparatus MA will be described, i.e. the structural and functional aspects relating to the present invention.
Returning to Figures 2a and 2b, each fixed microcell FMk also comprises an optical transmitter module OTM, while each mobile microcell MM also comprises an optical receiver module ORM. According to the present invention, the optical transmitter module OTM and the optical receiver module ORM are configured to implement an optical communication technology based on the use of visible light, preferably the Li-Fi technology, and to establish a light link for transmitting data, in particular data at high transmission rate, from the fixed microcell FMk to the mobile microcell MM. For example, the implementation of the Li-Fi technology currently allows data transfer with rates of between 40 Mb/s and 120 Mb/s from the fixed microcell FMk to the mobile microcell MM. Such data are carried on a light signal (i.e., an optical signal with carrier in the visible spectrum) emitted by a suitable light source at the fixed microcell FM. At the mobile microcell MM, the data is captured by a light sensor.
The optical receiver module ORM is in turn configured to transmit data to the optical transmitter module OTM, in particular data at low transmission rate. This communication channel is preferably used to transmit control data packets. The link between the optical receiver module ORM and the optical transmitter module OTM is preferably implemented by means of a different optical communication technology, in particular a technology operating in a different portion of the electromagnetic spectrum with respect to that of visible light. For example, this channel can be implemented through an infrared communication technology in the wavelength band of between 100 µm and 1 mm. This advantageously allows interference to be avoided.
The optical transmitter module OTM is schematized by way of example in Figure 4a. It preferably comprises a light source LSo and an optical gateway module OG. The light source LSo is preferably configured to diffuse light signals. The light source LSo preferably comprises one or more LED lamps. As already mentioned above, the light source LSo may comprise one or more LED lamps also used for lighting the railway line. Advantageously, a LED light source typically diffuses the light in a directional manner. Thus, the light diffused by the LED light source is confined within a limited region.
The optical gateway module OG preferably comprises an optical transmission port OTP through which it is connected to the light source LSo. The optical transmission port OTP is preferably configured to drive the light source LSo.
Preferably, the optical gateway module OG further comprises an optical modulation port LMP through which it can be connected to a corresponding optical gateway module OG of an optical receiver module ORM present in a mobile microcell MM, as it will be described in greater detail below. In particular, the optical modulation port LMP is preferably configured to receive data from said optical receiver module ORM. For example, the optical modulation port LMP may comprise an infrared receiver. For the sake of simplicity, the input signals to the optical gateway module OG through the optical modulation port LMP are schematically indicated in Figure 4a with the reference symbol "IR".
Moreover, preferably, the optical gateway module OG comprises a data connection port DCP, through which the optical gateway module OG is connected to the radio transceiver module RTM' and to the backbone network. The optical gateway module OG is in fact preferably configured to convert data packets (in particular, Ethernet data packets) coming from the backbone network through the data connection port DCP into optical signals, and vice versa. For simplicity, the input/output data packets from the optical gateway module OG through the data connection port are schematically indicated in Figure 4a with the reference symbol "ETH".
Finally, preferably, the optical gateway module OG comprises one or more electrical supply ports for the optical transmitter module OTM. In particular, with reference to the exemplary structure of Figure 4a, the one or more electrical supply ports comprise a first electrical supply port P1 and a second electrical supply port P2. The first electrical supply port P1 is for example a Power over Ethernet (PoE) supply port, while the second electrical supply port P2 is for example a direct current (DC) supply port operating in the range 12 - 24 V. For simplicity, the input signals to the optical gateway module OG through the first and second electrical supply ports P1, P2 are schematically indicated in Figure 4a with the reference symbols "ETH-POE" and "DC" respectively.
Returning to Figure 2a, each mobile microcell MM also comprises an optical receiver module ORM. The optical receiver module ORM is schematized by way of example in Figure 4b. It preferably comprises a light sensor or photosensor LSe and an optical gateway module OG'. The optical gateway module OG' is structurally similar to the optical gateway module OG present in an optical transmitter module OTM, with some differences which will be highlighted in the following. The analogous components in the two optical gateway modules OG, OG' will be indicated with the same names and with identical reference symbols.
The light sensor LSe is preferably configured to receive light signals diffused by the light source LSo present in an optical transmitter module OTM.
The optical gateway module OG' preferably comprises an optical reception port ORP through which it is connected to the light sensor LSe. The optical reception port ORP is preferably configured to receive a light signal from the light sensor LSe.
Preferably, the optical gateway module OG' further comprises an optical modulation port LMP' through which it can be connected to a corresponding optical gateway module OG of an optical transmitter module OTM present in a fixed microcell FM, as it will be described in greater detail herein below. In particular, the optical modulation port LMP' is preferably configured to transmit data to said optical transmitter module OTM. For example, the optical modulation port LMP' may comprise an infrared transmitter. For the sake of simplicity, the output signals from the optical gateway module OG' through the optical modulation port LMP' are schematically indicated in Figure 4b with the reference symbol "IR".
Moreover, preferably, the optical gateway module OG' comprises a data connection port DCP, through which the optical gateway module OG' is connected to the radio transceiver module RTM and to the mobile network on board the railway train 20. The data connection port DCP may be, for example, an Ethernet port, or, more in particular, a Gigabit Ethernet port. The optical gateway module OG' is in fact preferably configured to convert data packets (in particular, Ethernet data packets), for example, control data packets, coming from the mobile network through the data connection port DCP into optical signals (which will then be transmitted to the optical transmitter module OTM via the optical modulation port LMP'), and vice versa to convert the optical signals coming from the optical transmitter module OTM into data packets. For simplicity, the input/output data packets from the optical gateway module OG through the data connection port DCP are schematically indicated in Figure 4b with the reference symbol "ETH".
Finally, preferably, the optical gateway module OG' comprises one or more electrical supply ports for the optical receiver module ORM. In particular, with reference to the exemplary structure of Figure 4b, the one or more electrical supply ports comprise a first electrical supply port P1 and a second electrical supply port P2. The first electrical supply port P1 is for example a Power over Ethernet (PoE) supply port, while the second electrical supply port P2 is for example a direct current (DC) supply port operating in the range 12 - 24 V. For simplicity, the input signals to the optical gateway module OG' through the first and second electrical supply ports P1, P2 are schematically indicated in Figure 4b with the reference symbols "ETH-POE" and "DC" respectively.
Finally, each mobile microcell MM preferably also comprises a variable size buffer memory (not shown in the drawings) for storing data coming from the management apparatus MA and the fixed microcells FM1, FM2,..., FMn, as it will be described herein below.
Each fixed microcell FMk as well as the mobile microcell MM further comprises hardware/software modules configured to perform a programmed logic comprising a set of operations aimed at processing the data exchanged between the control center and the fixed microcells and between the fixed microcells and the mobile microcell, and at managing the handover procedures, as it will be described in more detail below.
With reference to Figures 5, 6 and 7, the operation of the telecommunication system 1 according to some embodiments of the present invention will now be described. In particular, as already mentioned above, wireless links (light links and/or radio links) are established in the telecommunication system 1 which allow the mobile microcell MM to exchange data streams (for example, a vital data stream and a non-vital data stream) with the fixed microcells FM1, FN2,..., FMn while the mobile microcell MM (which is installed on the train 20) is moving in the direction indicated by the arrow F of Figure 1.
In order to maintain a stable communication between the mobile microcell MM, which moves together with the railway train 20 (in the direction of the arrow F shown in Figure 1), and the fixed microcells FM1, FM2, ..., FMn which follow each other along the railway line 2, some so-called handover procedures must be established, which allow the connection of a mobile microcell MM to be transferred from a fixed microcell FM1 along the line to the next one FM2.
In particular, the telecommunication system according to the present invention provides that, depending on the scenario, a first type of so-handover procedures called "non-combined handover" and/or a second type of handover procedures so-called "combined handover" can be applied. In this way, as it will become clear from the following description, according to the present invention it is possible to maintain the continuity and stability of the communication between the fixed and the mobile apparatuses by using both the procedures described for switching from the radio communication technology to the optical communication technology and vice versa according to the situations of radio-light coverage which occur along the line.
The non-combined handover is applied when the mobile microcell MM moves together with the railway train 20 on which it is installed, and the continuity of the link with the fixed microcells FM1, FM2, ..., FMn is maintained using only the radio communication technology or only the optical communication technology. For example, such non-combined handover procedures are advantageously usable in the following situations:

when a radio link is established between the mobile microcell MM and a first fixed microcell FM1 and the link between the mobile microcell MM and a subsequent second fixed microcell FM2 can still be established by means of the radio communication technology; or
when a light link is established between the mobile microcell MM and a first fixed microcell FM1 and the link between the mobile microcell MM and a subsequent second fixed microcell FM2 can still be established by means of the optical communication technology.

The combined handover is instead applied when the mobile microcell MM moves and the continuity of the connection with the fixed microcells FM1, FM2, FMn is maintained using in combination the radio communication technology and the optical communication technology. In particular, these procedures provide that, when a mobile microcell establishes a certain link with a fixed microcell, it can disconnect from this fixed microcell only after having established a new link with the next fixed microcell. In this case, as it will become clearer from the following description, the mobile microcell simultaneously uses both the radio communication technology and the optical communication technology.
For example, such combined handover procedures can be advantageously used in the following situations:

when a light link is established between a mobile microcell MM and a first fixed microcell FM1, and there is no possibility of activating another light link between the mobile microcell MM and the subsequent fixed microcell FM2, while it is possible to activate a radio link (for example, when there is no Li-Fi coverage in the proximity of the next fixed microcell FM2 because it is outside the railway tunnel where the LED lamps used to implement the optical communication technology are and/or due to interfering light emissions); and/or
when a radio link is established between a mobile microcell MM and a first fixed microcell FM1 and there is no possibility of activating another radio link between the mobile microcell MM1 and the next fixed microcell FM2, while it is possible to activate a light link (for example, when there is no radio coverage or the radio coverage is limited in the proximity of the second fixed microcell FM2 due to interferences).

According to advantageous embodiments of the present invention, the management apparatus MA preferably generates a routing table DRT containing a first set of navigation information for the fixed microcells FM1, FM2, ..., FMn and for the mobile microcell MM present on the railway train. The navigation information present in the routing table DRT is information available at the management apparatus MA and which must be provided to the fixed microcells FM1, FM2, ..., FMn and to the mobile microcell MM for the railway traffic management, control and protection functions that are to be implemented on board the railway train. In particular, the navigation information is part of the so-called vital data already defined above and includes information typically contained in the signaling messages for the management, control and protection of railway traffic, such as for example the signaling messages of the CBTC system containing the CBTC commands.
In particular, according to exemplary embodiments of the present invention, the navigation information contained in the routing table DRT comprises so-called "static" data available a priori at the control center CC of the railway infrastructure. The static data entered in the routing table DRT preferably comprises:

one or more signaling commands (for example CBTC commands) to be transferred to the railway train, for example commands for adjusting the train ride (for example, setting the train speed or operating the brakes) at certain predetermined positions or locations along the railway line, in which there are, for example, curves, stations, tunnels, bridges, exchanges, etc.;
geo-localization data of the positions or locations in question (e.g. latitude and longitude) at which the commands are to be applied.

Table 1 below illustrates, by way of example, the static data contained in a routing table DRT generated by the management apparatus MA.

Table 1

Latitude	Longitude	Location	Command
40.842224	14.218988	Straightaway	Speed 80
40.843285	14.221135	Bridge	Speed 70
40.842256	14.206738	Tunnel	Speed 50
40.839215	14.204523	Curve	Speed 30
40.881368	14.133109	Sharp curve	Speed 20
40.829292	14.190802	Station	Speed 10

40.825859	14.1894993	Rail crossing	Stop 30 sec

Each row in Table 1 contains a set of four data associated with a command to be transmitted to the railway train. The first two columns of the table contain the coordinates (latitude and longitude) for the geo-localization of the command's location of application. The third column contains information indicative of the location itself, which specifies for example what type of location it is. In the example of Table 1 this information is self-explanatory. The fourth column, on the other hand, comprises information indicative of the command to be applied. The syntax used in Table 1 is merely illustrative and does not correspond to the syntax of the CBTC commands. In Table 1, in fact, the commands are reported in terms of actions imparted by the control center on the railway train. For example, the first line contains the expression "Speed_80", which indicates a command which provides that, each time the railway train is in correspondence with the straightaway located at the indicated coordinates, a command is transferred to the railway train itself which allows the speed of the railway train to be set at 80 km/h. The last line contains the expression "Stop_30_sec", which indicates a command which provides that, whenever the railway train is in correspondence with the rail crossing located at the indicated coordinates, a command is transferred to the railway train which allows to stop the train for 30 seconds.
Preferably, the routing table DRT generated by the management apparatus MA is periodically sent to the fixed microcells FM1, FM2, ..., FMn according to a known "flooding" mechanism. The transmission of the routing table DRT from the management apparatus MA to the fixed microcells FM1, FM2, ..., FMn is preferably periodic, for example with a period equal to 100 ms This period is added to the typical latency of the fiber network (greater than or equal to about 50 ms) and takes into account the time necessary to control the railway train between one command and the next one. Alternatively or in addition to the periodic transmission described above, the routing table DRT generated by the management apparatus MA can be sent to the fixed microcells FM1, FM2, ..., FMn whenever the management apparatus MA inserts a new datum within the table or modifies a datum already present therein.
Once the routing table DRT has been received, each fixed microcell FMk preferably filters the data of the routing table DRT received from the management apparatus MA based on its position. In particular, preferably, each fixed microcell FMk filters the data of the routing table DRT by eliminating the data relating to the locations which are at a distance from the fixed microcell FMk greater than a predefined distance, to the right and to the left of the fixed microcell FMk, for example, at a distance greater than 100 m to the right and 100 m to the left of the fixed microcell FMk. In this way, each fixed microcell selects a subset of the data contained in the routing table DRT received from the management apparatus MA, such subset comprising only the data relating to the commands to be applied at the locations included in a certain area around the fixed microcell FMk.
It is to be noticed that the coverage area of the fixed microcell FMk is preferably a dynamic coverage area, and has an average diameter of about 2 km, being extended for about 1 km to the right of the fixed microcell FMk and for 1 km to the left of the fixed microcell FMk.
Moreover, preferably, each fixed microcell FMk determines an aggregate routing table DRT' comprising the data obtained from the routing table DRT and some further navigation information necessary for the mobile microcell MM to carry out the handover procedures. In particular, each fixed microcell FMk compiles the aggregate routing table DRT' by adding to the data obtained from the routing table DRT further data necessary for the mobile microcell MM to carry out the selection of the fixed microcell FMk to connect to during the movement of the train along the railway line. More in particular, each fixed microcell FM preferably compiles the aggregate routing table DRT' by aggregating some "dynamic" data to the static data contained in the routing table DRT.
In the following description, the set of static data and dynamic data will be referred to as "aggregate data".
The dynamic data preferably comprises data indicative of the quality of the radio link and/or of the optical link between the fixed microcells FM1, FM2, ..., FMn and the mobile microcell MM. Such data are preferably measured at each fixed microcell FMk once the mobile microcell MM is in the proximity of the considered fixed microcell FMk. Such data may comprise the values of some parameters relating to the radio signal and/or the light signal received by the fixed microcell FMk. In particular, such parameters may comprise the received signal strength indicator (RSSI) for the radio signal and the modulation index m and/or the throughput THR for the light signal. Other parameters that can be used with respect to the light signal are: the wave width, the frequency, the power, the light intensity, the illumination intensity. The RSSI is an indicator of the received radio signal strength. Within the scope of the present invention, the RSSI is an estimated measure of the power of the radio signal between the fixed microcell FMk and the mobile microcell MM. The RSSI measurement allows to determine whether a signal is sufficient to establish a radio connection or whether it is necessary to use an alternative transmission technology (for example, to activate the part implementing the optical communication technology of the microcell). As the distance between the fixed microcell FMk and the mobile microcell MM increases, the power of the radio signal decreases and the bandwidth of the data connection decreases.
The light modulation index m is a parameter indicating how much the light is modulated. Usually, the modulation index is indicated in percent. The value of such index can typically vary between 0 (0%) and 1 (100%); when the index assumes a value greater than 100%, a distortion effect usually occurs, producing a disturbance called overmodulation.
The dynamic data preferably further comprises a parameter which identifies, for the mobile microcell MM connected to the considered fixed microcell FMk, the next fixed microcell to which the mobile microcell MM can connect according to a handover procedure. This parameter can be, for example, the IP address of the next fixed microcell. In the following description, this parameter will also be referred to as the "next hop identifier".
This part of the table is populated by the fixed microcells FM1, FM2, ..., FMn preferably on the basis of the experience recorded at the passage of the railway train near the microcells themselves. In particular, according to the present invention, a self-learning technique allows to store, at the first passage of the train in the proximity of a fixed microcell FM1, a certain value of a parameter indicative of the quality of the radio and/or light link, for example the RSSI. On the basis of this parameter, the fixed microcell FM1 can identify the next fixed microcell to which the mobile microcell MM can connect, such as the adjacent fixed microcell FM2. The next hop identifier, in this case, can then be the IP address of the adjacent fixed microcell FM2. At the second passage of the train in the proximity of the fixed microcell FM1, the fixed microcell FM1 again measures the parameter indicating the quality of the link and, for example, determines an average between the value measured at this second passage and the value measured at the first passage. In this way, on the basis of this average value, the fixed microcell FM1 can determine a new next fixed microcell, which can still be the adjacent fixed microcell FM2 or a subsequent fixed microcell. If the quality of the link allows, the method can in fact also provide for "jumping" the adjacent fixed microcell FM2 and determining that the next fixed microcell is the one that is at a double distance from the fixed microcell FM1, or even at a greater distance. Thanks to the mechanism described above, each fixed microcell FMk thus determines successive instances of the aggregated routing table DRT' which are periodically sent to the mobile microcell MM.
Advantageously, the presence, among the dynamic data, of the next hop identifier allows the mobile microcell to know in advance what is the next fixed microcell to which to connect during a non-combined handover procedure and possibly to skip it. The length of the hop, i.e. the number of fixed microcells that can be skipped, depends on the data present in the aggregate routing table provided to the mobile microcell, i.e. on the autonomy that the aggregate routing table provides to the mobile microcell in the implementation of the commands that it finds along the railway line. If the routing table contains, for example, CBTC commands that can be implemented even without a connection with the fixed microcell, then, as the train moves along the railway line, the mobile microcell can skip all the fixed microcells along the railway line until the last CBTC command is implemented. The mobile microcell will begin to search for a new connection to a fixed microcell only when the commands contained in the routing table run out.
In the following lines, an exemplary algorithm will be described which illustrates the operations performed by the fixed microcell FMk upon receipt of a routing table DRT from the management apparatus MA.
According to this exemplary algorithm:

1. the fixed microcell FMk (FixedNode#k) preferably calculates its position Localization, for example by means of the GPS module GM integrated in the radio transceiver module RTM', and implements two functions getLatitude and getLongitude to determine respectively its latitude and longitude:
```
      Localization = {FixedNode#k.getLatitude,
      FixedNode#k.getLongitude}
```
2. The fixed microcell FMk preferably performs in a cyclic manner (the Loop command indicates an infinite cycle which corresponds to the syntax while<condition>do) the following operations: It reads the last instance of the routing table DRT sent by the management apparatus MA by means of a Read_DRT function, which receives in input the position of the fixed microcell FMk and outputs a reduced routing table (basicDRT) obtained on the basis of the position of the fixed microcell FMk, as described above:
```
      Loop:
      basicDRT = Read_DRT(Localization);
      completeDRT = null;
```
3. The fixed microcell FMk preferably checks whether it is possible to establish a radio connection or a light connection with the mobile microcell MM; in case it is impossible to establish a radio connection or a light connection, the reduced routing table basicDRT is discarded and the fixed microcell FMk reads again the last instance of the routing table DRT sent by the management apparatus MA (see step 2 above, Loop command):
```
      if
      (RadioConnectionCheck()&&LightConnectionCheck()
      )==false) {
      discard(basicDRT)
      exit()
      }
```
If instead the fixed microcell FMk verifies that it is possible to establish a radio connection or a light connection, the fixed microcell FMk preferably completes the table with the dynamic data, stores the aggregate routing table (compleDRT), and sends the aggregate routing table (compleDRT) to the mobile microcell MM. The functions for storing the aggregate routing table at the fixed microcell FMk and sending the aggregate routing table to the mobile microcell MM are indicated as StoreDataLocally and SendDataToMobileNode, respectively:
```
      else {
      StoreDataLocally (completeDRT)
      SendDataToMobileNode (completeDRT)
      }
```
4. At this point, the fixed microcell FMk waits for a certain time interval, equal for example to 10 ms, and then repeats the operations indicated above in steps 2 and 3. As a result, the fixed microcell FMk, in the presence of a connection with the mobile microcell, periodically sends to it, with a period of 10 ms, the data of the aggregate routing table completeDRT
delay (10 ms) ;

Herein below the functions that can be used to verify the connectivity between the fixed microcell FMk and the mobile microcell MM, RadioConnectionCheckand and LightConnectionCheck will be described by way of example. The RadioConnectionCheck function reads the value of the power of the radio signal (RSSI) exchanged between the radio transceiver module RTM' of the fixed microcell FMk and the radio transceiver module RTM of the mobile microcell MM via the getRSSI function. In case the RSSI parameter is lower than value - 50, the fixed microcell FMk preferably determines that there is no radio connection between the two transceiver modules, while if the RSSI is between the values -50 and -20 it determines that the connection exists and then updates the reduced routing table basicDRT with the dynamic data, to obtain the aggregate routing table DRT' (compleDRT) which also includes the RSSI parameter and the next hop identifier, identified by the function getNextFixedModule().

 boolean RadioConnectionCheck(){
 RSSI={FixedNode#k.etRSI}
 if (RSSK-50){
 return false
 } else {
 if (RSSI>-50)&&(RSSIC-20)
 completeDRT = (basicDRT; Localization; RSSI;
 getNextFixedModule())
 }
 return true
 }

The function LightConnectionCheck reads the value of the luminous flux (lumen), of the modulation index and of the throughput in transmission between the optical transmitter module OTM of the fixed microcell FMk and the optical receiver module ORM of the mobile microcell MM, by using the functions getLumen, getMDepth% and getThroughput, respectively. In case the throughput is equal to 0, the fixed microcell FMk preferably determines that it is not possible to establish a light connection between the modules OTM and ORM, while if the throughput is different from 0 it determines that the connection is possible and then updates the reduced routing table basicDRT with the dynamic data, to obtain the aggregate routing table DRT' (completeDRT) which comprises also the dynamic data like the throughput THR and the next hop identifier, which is identified by means of the getNextFixedModule function:

 boolean LightConnectionCheck() {
 LightFlow = {FixedNode#k.getLumen}
 ModulationDepth = {FixedNode#k.getMDepth%}
 TxThroughput = {FixedNode#k.getThroughput}
 if (TxThroughput=0) {
 return false
 } else {
 completeDRT=(basicDRT;Localization;TxThroughput;
 getNextFixedModule())
 }
 }

The getNextFixedModule function returns the IP address (IPAddress) of the next physically available fixed microcell, to which the mobile microcell MM can connect:

 IPAddress getNextFixedModule () {
 IPAddress = {FixedNode#k.getNextIPAddress}
 return IPAddress
 }

Table 2 below illustrates, by way of example, the information that is added to the routing table DRT (in particular, to the reduced routing table as results from the data filtering operation described above) at the fixed microcells FM1, FM2, ..., FMk. In practice, considering, in an exemplary manner, the whole table 1 illustrated above, two columns are added. For each row, therefore, the aggregate routing table DRT' comprises:

in the first two columns, the geo-localization data (e.g. latitude and longitude) of the location where the command given in the fourth column is to be applied;
in the third column, information indicative of the locfation itself;
in the fourth column, an information indicative of the command to be applied;
in the fifth column, the RSSI value, for example, relating to the quality of the radio link between the fixed microcell FMk closest to the geographical position of the location in question and the mobile microcell MM;
in the sixth column the value of the throughput THR indicative of the quality of the light link;
in the seventh column, the next hop identifier indicating the next fixed microcell to which the mobile microcell MM can connect according to a handover procedure starting from the fixed microcell FMk which is closest to the geographical position of the location in question.

Table 2

RSSI	THR	Next fixed microcell
-20	0	192.168.100.1
-30	0	192.168.100.2
-32	10	192.168.100.3
-40	5	192.168.100.4
-50	8	192.168.100.5
-60	3	192.168.100.6

-30	0	192.168.100.10

As already mentioned above, the data of the aggregate routing table DRT' are periodically forwarded by the fixed microcell FMk to the mobile microcell MM according to a known "flooding" mechanism. This technique provides for the periodic sending of the aggregate routing table DRT' from the fixed microcell FMk to the mobile microcell MM on the railway train. The period for sending the aggregate routing table DRT' from the fixed microcell FM to the mobile microcell MM is for example equal to 10 ms The aggregate data, once received at the mobile microcell MM, is preferably stored in the buffer memory of the mobile microcell MM.

Once the aggregate routing table DRT' has been received, the mobile microcell MM periodically has the navigation information of the railway train.

Advantageously, once the mobile microcell MM has stored the aggregate data received from the fixed microcells FM1, FM2, ..., FMn, it is able to recover the information necessary for the control of the railway train and to carry out handover procedures. In particular, in view of what has been described above, the mobile microcell MM has the information relating to the commands to be transferred to the railway train at the relevant locations along the railway line (the static data of the routing table). Moreover, the mobile microcell MM has the information necessary to be able to carry out handover procedures from one fixed microcell to the other (the dynamic data of the routing table). The object of the above description is particularly advantageous if, for a short period of time, the connection between the mobile microcell MM and the fixed microcells FM1, FM2, ..., FMn is lost. This occurs, for example, in the situation in which a mobile microcell MM, which is connected to a fixed microcell by means of a light link due to the unavailability of a radio link, when moving with the railway train exits from the visibility cone of the fixed microcell, and it is not yet in visibility of the subsequent fixed microcell. According to the present invention, since the aggregate data is already stored in the mobile microcell MM, it can autonomously implement the train control commands contained in the aggregate routing table DRT' without the need to establish a link with the fixed microcells FM1, FM2, ..., FMn.

In the following description, the operation of the system according to the present invention will be described in greater detail, in particular with regard to handover procedures.

As already described above, operatively, the control center CC, in particular the management apparatus MA, periodically sends, for example every 100 ms, a new instance of the routing table DRT to all the fixed microcells FM1, FM2, ..., FMn which are located along the railway line, by the above-mentioned flooding mechanism. Each fixed microcell FMk, based on its own position, filters the data contained in the routing table DRT by eliminating the data relating to the locations that are at a certain distance from the fixed microcell FMk itself. Moreover, the fixed microcell FMk aggregates the static data resulting from the filtering operation of the routing table DRT to the dynamic data. When the fixed microcell FMk communicates with a mobile microcell MM, the fixed microcell FMk periodically sends to the mobile microcell MM successive instances of the aggregate routing table DRT', which represents a radio-light coverage profile for the connection between the fixed microcell FMk and the mobile microcell MM in the area around the fixed microcell FMk. In fact, as the number of passages of the railway trains in the proximity of the fixed microcell FM increases, the self-learning mechanism allows to refine the radio-light coverage profile relative to the fixed microcell FMk, updating the data contained in the aggregate routing table DRT' which is stored in the fixed microcell FMk and sent to the mobile microcell MM. The communication of the aggregate data between fixed microcells FM1, FM2, ..., FMn and mobile microcell MM takes place through the radio link or the light link, as it will be described in more detail below.

With reference to the scheme of Figure 5, the operation of the system according to the present invention for the implementation of a non-combined handover procedure will be described in greater detail hereinafter.

As shown schematically in Figure 5, it is assumed that the mobile microcell MM, in the proximity of a first fixed microcell FM1, establishes with it a link based on the considered radio communication technology (the link is represented by a continuous line in Figure 5). In this case, the radio transceiver module RTM' of the fixed microcell FM1 is connected to the radio transceiver module RTM of the mobile microcell MM. Under these conditions, the mobile microcell MM receives the aggregate routing table DRT' from the first fixed microcell FM through the radio link.

At this point, the mobile microcell MM reads the aggregate routing table DRT', implements the related command and decides which next fixed microcell to connect to. If for the implementation of the next command contained in the aggregate routing table DRT' a connection to a fixed microcell is not necessary, the mobile microcell MM avoids the connection to the next fixed microcell indicated in the aggregate routing table DRT' and eventually hops to the even subsequent fixed microcell. Otherwise, the mobile microcell MM connects to the next fixed microcell, for example the second fixed microcell FM2 of Figure 5.

In this case, therefore, while the train 20 moves in the direction of the arrow F, the mobile microcell MM processes the data of the aggregate routing table DRT' and performs a handover which allows to move the link between the radio transceiver module RTM of the mobile microcell MM and the radio transceiver module RTM' of the fixed microcell from the first fixed microcell FM1 to the second fixed microcell FM2 which is subsequent along the direction of the arrow F. Figure 5 shows the handover from the first fixed microcell FM1 to the next second fixed microcell FM2, schematically indicated by the arrow FH1.

Similarly, a non-combined handover procedure occurs when the mobile microcell MM, in the proximity of the first fixed microcell FM1, establishes a light link therewith. As already mentioned above, this technology can be advantageously used in the case where there is no radio coverage. or in the case where the radio links cannot be established or are not very reliable due to interference problems or jamming or due to the high speed of the railway train 20.

As shown schematically in Figure 5, it is assumed that the mobile microcell MM, in the proximity of a first fixed microcell FM1, establishes with it a light link (the link is represented by a continuous line in Figure 5). For example, such a link can be advantageously implemented in a scenario in which the railway train 20 is in a tunnel illuminated by LED lamps which also operate as light sources LSo for the optical transmission modules OTM of three fixed microcells FM1, FM2. FM3 present in the tunnel.

In this case, the optical transmitter module OTM of the first fixed microcell FM1 is connected to the optical receiver module ORM of the mobile microcell MM. Under these conditions, the mobile microcell MM receives the aggregate routing table DRT' from the first fixed microcell FM1 through the light link.

As the train 20 moves in the direction of the arrow F, to maintain the continuity of the link between the mobile microcell MM and the fixed microcells FM1, FM2, FM3, the mobile microcell MM autonomously processes the data of the aggregate routing table DRT' and autonomously performs a handover which allows to move the link between the optical receiver module ORM of the mobile microcell and the optical transmitter module OTM of the fixed microcell from the first fixed microcell FM1 to the next second fixed microcell FM2 along the direction of arrow F (the new link is represented by a dashed line in FIG. 5). Figure 5 shows the handover from the first fixed microcell FM1 to the next second fixed microcell FM2, schematically indicated by the arrow FH2.

The possibility for the mobile microcell to have available the commands for the control of the railway train and to determine autonomously the next fixed microcell to be connected to according to the handover procedure described above even in the absence of a radio or light link with the fixed microcells, depends on the availability of the buffer memory. The size of such buffer memory therefore depends on the duration of the time interval during which the mobile microcell may not have any connection with a fixed microcell. In other words, the size of the buffer memory depends on two factors: the speed of the mobile microcell, i.e. the speed at which the railway train moves, and a distance of no connection, i.e. a distance at which the mobile microcell has no connection with the fixed microcells.

Figure 6 shows a geometric model which schematizes the relative position of a mobile microcell MM and of two successive fixed microcells, FM1, FM2. This model will be used in the following description to describe an exemplary procedure for sizing the buffer memory. In Figure 6, D is the distance between the two fixed microcells FM1, FM2 (in particular the distance between the two light sources LSo present in the two fixed microcells FM1, FM2), H is the height of the light sources LSo with respect to the railway line, A is the angle of diffusion of the light diffused by the light source LSo, and L is the distance of no connection. The diffusion angle A may be in the range from about 10° to 80°.

Under these conditions, the distance of no connection L can be defined by the following formula:

L = D - 2 * \tan (A) * H .

Assuming that V is the speed of the railway train 20, the duration of the time interval of nof connection T can be defined by the following formula:

T = L / V .

Assuming that TR is the average data transfer rate, the size of the buffer memory must satisfy the following condition:

buffer_dim > TR * T

that is, the size of the buffer memory must exceed the estimated amount of data that can be transferred therein during the time interval of no connection T.

With reference to the scheme of Figure 7, the operation of the system according to the present invention for implementing a combined handover procedure will be described in the following lines. As anticipated, the combined handover procedure applies in a scenario in which the telecommunication system according to the present invention implements in parallel the considered radio communication technology and optical communication technology. In this case, the radio links can be used to transfer high throughput data (e.g., Internet, CCTV over LTE/Wi-Fi, etc.), while light links can be used to transfer medium throughput data (e.g., CBTC messages).

As schematically shown in Figure 7, it is assumed that the mobile microcell MM, in the proximity of a first fixed microcell FM1, establishes with it a light link. In this case, the optical transmitter module OTM of the first fixed microcell FM1 is connected to the optical receiver module ORM of the mobile microcell MM (this link is represented by a continuous line in Figure 7). As already described above, the mobile microcell MM receives the aggregate routing table DRT' from the first fixed microcell FM through the light link. At this point, the mobile microcell MM preferably processes the data contained in the aggregate routing table DRT', in particular the data relating to the next fixed microcell with which to establish a connection, so that the radio transceiver module RTM of the mobile microcell MM can establish a link with the radio transceiver module RTM of the next fixed microcell along the direction indicated by the arrow F. Then, the mobile microcell MM establishes a radio link with the second fixed microcell FM2 in parallel with respect to the light link established with the first fixed microcell FM1. Figure 7 shows the mobile microcell MM simultaneously connected both to the first fixed microcell FM1, with a light link, and to the second fixed microcell FM2, with a radio link (also this link is represented by a continuous line in Figure 7). Advantageously, the radio link constitutes a backup link in case the light link is interrupted. As the train moves in the direction of the arrow F, when the mobile microcell MM reaches the proximity of the second fixed microcell FM2, the mobile microcell MM can therefore carry out a handover which allows to move the link between the optical receiver module ORM of the mobile microcell and the optical transmitter module OTM of the fixed microcell from the first fixed microcell FM1 to the second fixed microcell FM2 (this new link is represented by a dashed line in Figure 7.) Figure 7 shows the handover from the first fixed microcell FM1 to the next second fixed microcell FM2, schematically indicated by the arrow FH3.

If a combined handover procedure such as that described above is established, then the connection between the microcell and the fixed microcells is made using the two radio and optical communication technologies in parallel. This ensures continuity of the link between the fixed microcells and the mobile microcell even when, for example, the mobile microcell exits from the visibility cone of the fixed microcell to which it is connected. Therefore, advantageously, the aggregate routing table DRT' can be periodically continuously transmitted from the fixed microcells to the mobile microcell, without the need to store the aggregate data in the buffer memory.

In the light of the above description, in an application scenario of the present invention in which the fixed microcells and the mobile microcells determine a complete radio-light coverage along the railway line, the described telecommunication system may advantageously implement in parallel the considered radio communication technology and optical communication technology and apply the combined handover procedures described above. The non-combined handover procedures can advantageously be implemented in the presence of holes in the radio-light cover. In fact, if the radio link is no longer available/reliable, the telecommunication system can advantageously maintain a communication continuity through the light link by applying the non-combined handover procedures described above. Similarly, in the case where the light link is no longer available/reliable, the telecommunication system can advantageously maintain a communication continuity through the radio link applying again the non-combined handover procedures described above. At this point, if also the last established link becomes unreliable or is no longer available, the mobile microcell can retrieve the data of the aggregate routing table from the buffer memory so as to always have available the navigation information for the railway train and autonomously apply the handover procedures.

In the following description, three different examples of application scenarios for the system of the present invention will be illustrated.

Hvperloop

As known, Hyperloop is a transport system currently under development by three consortia of companies: Hyperloop One, Hyperloop Transportation Technologies (HTT) and TRanspod.

This system provides for the high-speed transport of goods and passengers to take place inside low-pressure tubes or capsules which are pushed by linear induction motors and air compressors. The infrastructure linked to the Hyperloop system should consist of a double overhead tube in which the transport capsules can slide. The capsules move on an air cushion generated through multiple openings in the base, so as to further reduce friction.

The inventor has noted that in the Hyperloop system it is not possible to use the multi-frequency radio communication technology operating in the frequency range from 70 MHz to 6 GHz due to the interference that would be generated and the high speed. By applying the system of the present invention it would instead be possible to use the optical communication technology to connect a set of fixed microcells along the Hyperloop infrastructure and mobile microcells installed on board the capsules. The handover could be carried out using the non-combined handover procedure described above. In this situation, it is possible to provide a sizing of the system of the present invention (in particular of the buffer memory provided in the mobile microcells) using the following parameters:

D=350 m (worst case) or 10 m;
V=1200 KM/h;
H=3 m;
TR=10 Mb/s; and
A=80°.

By applying the above formulae [1]-[3] and the indicated parameters, the inventor has determined a possible sizing of the buffer memory. In the worst case where it is assumed that the distance D between the light sources is 350 m, the buffer memory must have a size greater than about 9.479 Mb. In the case where the light sources are spaced by 10 m, the size of the buffer memory is smaller since the lower limit is equal to about 0.196 Mb.

High speed

The so-called "high speed" (HV/HC) refers to a railway transport system consisting of a set of infrastructures, trains, signaling systems and telecommunication systems, standards and technical regulations which is implemented to make trains travel at a speed higher than the traditional one (about 300 km/h).

In this context it is possible to apply the system of the present invention and the combined and non-combined handover procedures.

In this context, the sizing of the system of the present invention (in particular of the buffer memory provided in the mobile microcells) can be carried out using the following parameters:

D=350 m (worst case) or 10 m;
V=300 KM/h;
H=3 m;
TR=10 Mb/s; and
A=80°.

By applying the above formulae [1]-[3] and the indicated parameters, the inventor has determined a possible sizing of the buffer memory. In the worst case where it is assumed that the distance D between the light sources is 350 m, the buffer memory must have a size greater than about 37.917 Mb. In the case where the light sources are spaced by 10 m, the size of the buffer memory is smaller because the lower limit is about 0.784 Mb.

Subway

The underground (or partially underground) metropolitan transport systems include the fast-transit electrified train systems currently present all over the world (Metro in Italy, U-Bahn in Germany, Tube or Underground in Great Britain, etc.).

In this scenario, according to the present invention, it is possible to use the optical communication technology (for example, Li-Fi) and non-combined handover procedures in tunnels, directly connecting the LED light sources provided for the fixed microcells to the lamps of the tunnels themselves. Outside the tunnels, the multi-frequency radio communication technology and combined handover procedures can be used.

D=350 m (worst case) or 10 m;
V=80 KM/h;
H=3 m;
TR=10 Mb/s; and
A=80°.

By applying the above formulae [1]-[3] and the indicated parameters, the inventor has determined a possible sizing of the buffer memory. In the worst case where it is assumed that the distance D between the light sources is 350 m, the buffer memory must have a size greater than about 142.187 Mb. In the case where the light sources are spaced by 10 m, the size of the buffer memory is smaller because the lower limit is equal to about 2,941 Mb.

In view of the above, the size of the buffer memory in the described scenarios can therefore vary in a range of from about 0.7 Mb to about 3 Mb. These are, advantageously, values which are fully compatible with those of commercially available low-cost memories.

Advantageously, the system according to the present invention combines a radio communication technology and an optical communication technology for connecting fixed and mobile telecommunication apparatuses in a railway infrastructure. This entails some advantages already discussed above, such as for example the possibility of carrying out safe handover procedures which guarantee the continuity of the links between the fixed and mobile apparatuses. As shown above, the described system can advantageously be used in high and very high speed transport systems (e.g. Hyperloop, high speed trains, aircrafts), where radio communication technology is often not sufficient to implement a robust system due to the speeds involved (as is known, in fact, speeds above 100 km/h can put a Wi-Fi system in crisis). This system can also be used in environments where radio communication technology is prohibited due to the risks associated with it, such as for example in petrochemical plants and on oil platforms.

Finally, advantageously, the system of the present invention can be easily integrated within traditional infrastructures. For example, the light sources already used by the infrastructure can be easily integrated into the described fixed apparatuses (by connecting thereto the optical gateway module described above).

Claims

A telecommunication system (1) for a railway infrastructure (2), comprising a mobile apparatus (MM) suitable for being installed on board a train (20) of said railway infrastructure (2) and a plurality of fixed apparatuses (FM1, FM2, ..., FMn) suitable for being installed along a railway line of said railway infrastructure (2) along which said train (20) moves, wherein:
- said mobile apparatus (MM) comprises a radio transceiver module (RTM) and an optical receiver module (ORM);

- each fixed apparatus (FMk) comprises a radio transceiver module (RTM') and an optical transmitter module (OTM),
and wherein said radio transceiver module (RTM) of said mobile apparatus (MM) and said radio transceiver module (RTM') of said fixed apparatus (FM) are configured to set up a radio link between them, and said optical transmitter module (OTM) of said fixed apparatus (FMk) is configured to transmit data to said optical receiver module (ORM) of said mobile apparatus (MM) on a light link.
The telecommunication system (1) according to claim 1, further comprising a management apparatus (MA) configured to be connected to the plurality of fixed apparatuses (FM1, FM2, ..., FMn).
The telecommunication system (1) according to claim 1 or 2, wherein each one of said radio transceiver module (RTM) of said mobile apparatus (MM) and said transceiver module (RTM') of said fixed apparatus (FMk) is a multi-frequency radio transceiver module configured to operate in at least two different frequency ranges.
The telecommunication system (1) according to claim 3, wherein each of said radio transceiver module (RTM) of said mobile apparatus (MM) and said radio transceiver module (RTM') of said fixed apparatus (FM) comprises at least two radio units, each radio unit being configured to receive and transmit data by using a radio communication technology operating in a range of frequencies comprised between 70 MHz and 6 GHz.
The telecommunication system (1) according to claim 3 o 4, wherein each of said radio transceiver module (RTM) of said mobile apparatus (MM) and said radio transceiver module (RTM') of said fixed apparatus (FM) comprises a first radio unit (RU1) configured to receive and transmit data by using a Wi-Fi technology and a second radio unit (RU2) configured to receive and transmit data by using a Long-Range radiofrequency wireless technology.
The telecommunication system (1) according to any of the preceding claims, wherein said optical transmitter module (OTM) of said fixed apparatus (FMk) is configured to transmit data to said optical receiver module (ORM) of said mobile apparatus (MM) by setting up a light link according to a Light-Fidelity communication technology.
The telecommunication system (1) according to any of the preceding claims, wherein said optical receiver module (ORM) of said mobile apparatus (MM) is configured to transmit data to said optical transmitter module (OTM) of said fixed apparatus (FMk) by using an infrared communication technology.
The telecommunication system (1) according to any of claims 2 to 7, wherein said optical transmitter module (OTM) of said fixed apparatus (FMk) comprises a light source (LSo) and an optical gateway module (OG), wherein said optical gateway module (OG) is connected to said management apparatus (MA) of said telecommunication system (1) through said radio transceiver module (RTM') and is configured to:
- receive data from said management apparatus (MA); and

- operate said light source (LSo) to transmit said data received from said management apparatus (MA) to said optical receiver module (ORM) of said mobile apparatus (MM).
The telecommunication system (1) according to claim 8, wherein the light source (LSo) comprises a LED lamp.
The telecommunication system (1) according to claim 8 or 9, wherein said optical receiver module (ORM) of said mobile apparatus (MM) comprises a light sensor (LSe) configured to receive optical signals diffused by said light source (LSo) of said optical transmitter module (OTM).
The telecommunication system (1) according to any of claims 8 to 10, wherein said data received from said management apparatus (MA) comprises a routing table comprising one or more signalling commands for controlling the train (20), which has to be transferred to the train (20) at one or more predetermined locations along said railway line, and geo-localization data of said locations.
The telecommunication system (1) according to claim 11, wherein each fixed apparatus (FMk, FM1) is configured to determine an aggregate routing table comprising data obtained from said routing table and further data, said further data comprising data indicative of the quality of the radio and/or light link between said fixed apparatus (FMk, FM1) and said mobile apparatus (MM), and a next hop indicator that identifies, when said mobile apparatus (MM) is connected to said fixed apparatus (FM1), the next fixed apparatus (FM2) to which the mobile apparatus (MM) may connect.
The telecommunication system (1) according to claim 12, wherein the data indicative of the quality of the radio and/or light link between said fixed apparatus (FMk, FM1) and said mobile apparatus (MM) comprise a received signal strength indicator for the radio link and/or a modulation index for the light link and/or a throughput for the light link.
The telecommunication system (1) according to claim 12 or 13, wherein said mobile apparatus (MM) comprises a buffer memory configured to store said aggregate routing table.
Method for transmitting and receiving data in a railway infrastructure (2) comprising a train (20) and a railway line along which said train (20) moves, said method comprising:
- transmitting and receiving data on a radio link set up between a radio transceiver module (RTM) of a mobile apparatus (MM) installed on board said train (20) and a radio transceiver module (RTM') of a fixed apparatus (FMk) of a plurality of fixed apparatuses (FM1, FM2, ...FMn) installed along said railway line; and

- in alternative, transmitting and receiving said data on a light link set up between an optical transmitter module (OTM) of said fixed apparatus (FMk) and an optical receiver module (ORM) of said mobile apparatus (MM).