HK1065210B - System for transmission of radio information between an infrastructure and mobiles - Google Patents

Description

The present invention relates to cellular systems for the radio-electric transmission of information between an infrastructure and mobile devices subject to travel along a given path.

The invention has a particularly important application in the field of local transport, and in particular in railway networks which are at least partly in tunnels, where multiple reflections are particularly dangerous.

A cellular radio-transmission system for the transmission of information is already known (EP-A-0838965 and US Patent 5 995 845) whose infrastructure has fixed transmitting-receiving stations along the path. These stations have transmitter-receivers and each cell is framed by two transmitters-receivers. The transmitters assigned to the same cell are synchronized and emit with coding to tolerate or use multiple paths.

The coding may be of the frequency-division multiplexing and orthogonal coding (OC FDM) or direct sequence spectrum-spreading coding type.

The present invention is intended in particular to increase the immunity to interference further. To this end, the invention proposes in particular a cellular system for radio-electrical transmission of information whose infrastructure consists of fixed stationary receiving stations, or radio bases, distributed along the path and assigned to successive cells, so that each cell is equipped with at least two transmitters-receivers, which frame it and whose transmitters are synchronized and allow, preferably with a coding, to tolerate or use the multiple paths; according to the invention, the transmitters-receivers of the fixed stations and at least one transmitter-receiver carried by the same transmitter-receiver are so controlled that the exchanges between the two transmitters and receivers in a mobile cell are carried out at different frequencies when the same mobile cell is assigned to the same mobile cell, when the cycles are alternated, in the same mobile cell, in the same frequency.

Such alternation reduces the disturbance caused by fixed frequency jammers, which may be external to the system or may be made up of transmitters from other cells.

Each cycle will usually consist of several exchange frames, relatively short to increase service quality. A time-multiplexing transmission mode, called TDMA or AMRT, will often be used. Frames containing critical information may be systematically broadcast on the two frequencies in succession. Some may be broadcast once and others repeated on request following a faulty transmission.

The frequency pair used in a cell will be advantageously made up of two different frequencies from those used in adjacent cells; in the open air parts of the network, where the range of transmitters may be very high, it is advantageous to make the frequency pairs from the available frequencies, so that the same frequency pair is only reused as far as possible; where a small number of frequencies are available, at least one common frequency should be used in cells likely to interfere.

A given cell may be assigned, in addition to the two transmitter-receptors that frame it, distributed intermediate transmitter-receptors.

The above and other features will be better seen when reading the following description of a particular mode of implementation, given as a non-limiting example. The description refers to the accompanying drawings, in which: Figure 1 is a very simplified diagram showing a spatial distribution of the components of fixed stations and two mobile stations placed in a cell; Figure 2 is a functional diagram showing the main components of a system; Figure 3 is a diagram intended to show how the transfer or handover from one cell to another takes place; Figure 4 shows schematically the overlap of the lob-receiver outputs belonging to two successive cells; Figure 5 is an example of a diagram showing the cross-sectional flow of the transmission between two cells; Figure 7 is an example of a diagram showing the flow of transmissions from one cell to another; Figure 6 shows a cross-sectional flow of the transmission between two cells; Figure 5 is an example of a diagram showing the flow of transmissions from one cell to another; Figure 6 shows a cross-sectional flow of the transmission between two cells; Figure 7 is an example of a diagram showing the flow of transmissions from one cell to another; Figure 6 shows a cross-sectional flow of the transmission between two cells; Figure 7 is an example of a cross-sectional flow of the transmission between two cells; Figure 7 is a diagram showing the flow of the flow of the transmission between two cells; Figure 7 and the transmission between the transmission between the transmission between the two cells.

Before describing the invention, a brief recall of the constitution of a system to which it applies is given by way of example, referring to Figure 1.

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Each base station S on one side of a cell to which it is assigned, located on one side of a cell (e.g. cell No. 1) is adjacent to another station with a transmitter-receiver E'0 or E2, assigned to cell 0 or cell 2 respectively. In the special case shown schematically in brackets for the transmitter-receiver antenna E1, each antenna has a relatively narrow front lobe, directed towards the cell, and a less intense rear lobe.

In the embodiment shown, each mobile, such as 101, 102 has a forward-facing 12V transmit-receive antenna and a backward-facing 12R transmit-receive antenna. As will be seen below, the antennas can be paired with a common transmit-receive apparatus or with separate apparatus. Each apparatus (or apparatus) is designed to add up the energies received from transmitters E1 and E'1 when the mobile is in cell #1.

A system as a whole may have the general functional constitution shown in Figure 2.

The principle architecture of the part of the system which is supported by the track (track side) can be considered as having four sub-assemblies.

A Wayside Cell Controller (WCC) is a host module for the WRF radio path function. This WCC cell control subset may include two Wayside Transmission Units (WTU) to provide redundancy. These units are located in technical and connected facilities: The network is usually operated by a network operator, which will often use an Ethernet protocol, to a zone controller, which may itself be redundant: to channel clients (transmission users), in the conventional way; by transmission lines along the channel, usually made up of EF fibre optic links, to channel radio equipment, so-called wayside radio equipment, which may have two WRU channel radio units.

In addition, an unrepresented synchronisation link is provided between the WTU line transmission units of the same cell.

All radio path units in a single cell may be connected to a single fibre optic interface electronic board in the WTU path transmission unit.

The connection between the antennas of the WRU radio path units and the antennas of the 12V, 12R mobile 10 transceivers is in hyperfrequency or microwave, usually in a band reserved for spectrum-spreading applications.

Depending on the degree of availability required for transmission, a single or two antenna receiver or two coupled transmitter-receivers attached to the same or respective antennas may be used.

The CRU equipment on board a mobile (such as a train, for example) will be more or less complex depending on the train's constitution.

If we can put antennas on the roof of the train, we'll try to use a single CRU in the middle of the train.

If, for reasons of size, it is not possible to place an antenna on the roof, then it will be necessary to place the antennas at both ends and thus to use radio equipment at each end. Two sub-assemblies, possibly on the front and tail cars, will then provide a radio distribution function on the mobile and a radio frequency selection function on the mobile respectively.

In addition to the radio part, the mobile carries an onboard control unit that performs the onboard radio functions, designated by TRF. Links to equipment and software such as communication queries, onboard clients, etc. allow the orders and information transmitted and distributed via the TRF train radio function to be transferred.

As indicated above, the exchange in a cell between the stations framing the cell and a mobile phone in the cell takes place on two different frequencies, alternating with each radio cycle. The use of more than two frequencies may be considered, but is of limited interest. The redundancy advantage of more than two frequencies for the transfer of essential information would be obtained only by transmitting this information three times.

For example, if the available frequency band is 83 MHz (which is for example the case for the ISM medical scientific instrument band 2400-2483 MHz), the band can be split into nine channels with central frequencies F1 to F9. These channels may be 6 MHz wide, leaving an interval of 8-9 MHz to reduce contribution between adjacent channels. Two of these non-adjacent channels, with frequencies Fx and Fy are associated with each cell.

The transmission will generally be in two-state or four-state phase modulation (called BPSK or QPSK), with direct sequence spectrum spread; one can advantageously use the DQPSK mode with four mutually orthogonal spread sequences.

The cell phone and cell station exchange is done in cycles with alternating between the two frequencies Fx and Fy chosen for the cell. Each cycle consists of several frames. In each frame, the rate will usually be sufficiently low to achieve high resistance to interference, fading and multiple paths. A rate of 32 or 64 Kbits per second will frequently be used although higher throughput (up to 256 kbits/s) is possible.

The following distribution in a cycle can be used, for example, data frames having a constant length of 200 bits and a cycle duration of 124 ms. The cycle is divided into slots and the rate is 64 kbps. - What?

Only the application content of the frames is encrypted.

The initialization frame shall constitute the radio database and shall be used only by the radio part of the train for configuration.

Data frames to trains have content that depends on the application and terminal customer or user on the train.

The control cell frame, used by the radio part of the train to configure itself, contains management information, such as the allocation of time slots to different trains.

The input signature frame is used by the train entering a cell to identify itself to the track radio equipment, consisting of one or two WTUs.

Finally, the data frames to the track transfer application data; these frames can be transmitted simultaneously to two radio cells when the train is in the overlap zone of two cells.

The first brief description of handover from one cell to another is given, followed by an example of transfer management from the time a train is registered as entering a cell to the time the train leaves, which is detected only by the train's failure to respond to queries.

Handshake (Figures 2 and 3)

As in the case of the previous patent, the handover is carried out in a strong field, in a zone of overlap of two radio cells, indicated by R. The two CRU AV and CRU AR train radio units of the train carry out the transfer successively.

You see that the handshake starts as soon as the train passes the last track unit of the cell it leaves.

The train signals the start of the handover by sending the signature frame. The track transmission unit then enters the train into the list of those present in the cell. It deletes the train when the train's failure to respond persists beyond a specified time (10 seconds for example) or a specified number of queries (4 for example)

Sequence of events, from entry to exit identification

A typical sequence of successive events from entering to exiting a train is given in Figure 5; the units concerned are identified by their abbreviation 1 : TRF sends the input ID frame to request the CRU search into the cell, whose frequencies Fx and Fy and the spread sequence are known, and the permission to broadcast.2, 3, 4 : CRU scans the frequencies Fx and Fy to detect the cell control frame, registers itself and broadcasts the initialization and data frames to the path.5 : TRF uses the database information contained in the initialization frame68 : CRU is synchronised to the new cell radio cycle, transmits the input ID frame until it has received a request to transmit data frames to the track.7 : WRF allocation to the train of a slot in the control cell frame, even if no track-side application requests it; assignment of this slot to a higher priority than the slots required by the track application for other trains already present in the cell.9 : The WRF track radio function, usually in a WTU unit, enters the train in the list of trains present in the cell,so that the track-side application can make requests to the new train.10, 11 : CRU issues to TRF the contents of all track data frames to the train; response to any request from the track, in the allocated tranche.12, 13, 14 : if no train responds to a request from the track, repeat and then delete the train from the list of those present in the cell.

Most cases of frames colliding which may lead to non-transmission, which may occur, for example, when two trains simultaneously occur in opposite directions at the entrance of a cell; can be solved by common measures. But processing at the intersection of several lines requires somewhat more complex measures. Figure 7 shows the case of a cross between two lines S1 and S2. In the figure, the frequencies assigned to the different cells 1 to 6 that may interfere with each other are seven in number. Possible interferences are indicated by double-dashed arrows.

We can also see that there is a cell 1 common to both lines S1 and S2.

The potential for confusion is eliminated by combining an appropriate choice of available frequencies and different spread sequences, ensuring that only one common frequency is used to reduce the likelihood of simultaneous interference on both frequencies of a cell.

It is noted that in the illustrated case the propagation sequences are different between two cells likely to interfere at a common frequency.

The protocol for allocating time slots to trains during a radio electric transmission cycle can be summarised as follows.

This is done by using control cell frames, which contain a list of trains to which a time slot or slot is allocated.

As soon as a train enters a cell, the track cell controller assigns a time slot to it, as soon as the train has identified itself as sign-in. A deterministic protocol, for example using train location using track-borne tags, can be used to resolve conflicts when multiple trains are trying to enter a cell at the same time.

The exit of a train from a cell is detected without dialogue between track and train, simply by the train not responding to requests from the track.

The track cell controller, comprising one or more track transmission units, may be provided to ask the on-board system to re-issue information not received in the cycle that has just ended, which increases the robustness of the system without increasing throughput as much as systematic repetition would. 1

Claims (7)

1. Cellular system for transmission of radio information between an infrastructure and mobiles (10, 12) constrained to move along a predetermined path, the infrastructure of which comprises fixed transceiver stations (S) distributed along the path and assigned to successive cells (cell1, cell2), and each mobile of which carries a transceiver (12R, 12V), the transceivers (E'0, E1; E'1, E2) of the fixed stations and the transceiver carried by each of the mobiles are controlled so that exchanges between the mobile and the transceivers (E1, E'1) assigned to the same cell are performed when the mobile is in the cell (cell1), alternately at two different frequencies (Fx, Fy) in two successive radio cycles.
2. System according to claim 1, wherein each cycle consists of several short exchange frames.
3. System according to claim 1 OR 2, using an AMRT time multiplex transmission mode.
4. System according to claim 1 OR 2, wherein frames containing essential information are systematically emitted on both frequencies in succession.
5. System according to one of the preceding claims, wherein the pair of frequencies used in a cell consists of two frequencies different from those used in the adjacent cells.
6. System according to one of the preceding claims, wherein the exchanges between the train and a track subsystem are performed using AMRT multiplexing and a protocol for allocating time slots to the trains with allocation of a slot to each train entering a cell from a track radio unit in response to the transmission of entry identification by the train to the track subsystem.
7. System according to claim 6, wherein the exit of the train from a cell is detected by the repeated failure of the train to respond to a request from the track radio unit assigned to the cell.