Method and system for subterranean wireless data transmission between at least one mobile station and a fixed network by means of a radio network

The invention relates to a method and system for underground radio data transmission between at least one mobile station and one fixed network via a radio network, preferably via WLAN in the IEEE 802.11 standard, preferably for supervising and controlling machines moving underground, wherein the fixed network has a larger number of stationary base stations, preferably arranged as access points, each base station is connected to the fixed network by at least one preferably wired transmission connection, wherein each base station and mobile station have at least one transceiver and each of the data transmission between the mobile station and the fixed network takes place in radio network wirelessly via at least one base station.

[0002] Wireless underground communication is traditionally carried out using devices operating in the VKF (UHF) band, which can be used within the range of fixed antennas. These are made as directional antennas or as a concentric radiating cable, so-called Leaky Feeder. There are also known systems that work with digital systems in the GHz range, for example based on GSM technology. All the systems mentioned so far are special solutions and are relatively expensive compared to standard methods of terrestrial communication. That is why in recent years technologies that rely on modern methods of wireless network techniques have appeared more and more often. Here, wireless local area networks are used, so-called Wireless Local Area Networks (WLANs). The standardization of these WLANs currently includes five WLAN standards, collected in the group of IEEE 802.11 standards. In addition, the so-called WiMAX standard as a new standard (IEEE 802.16) for regional radio networks. With its theoretical range of up to 50 km and very high throughput, WiMAX exceeds current WLAN technology, which in outdoor use has a range of 3 to 6 km.

[0003] Underground data transfer over a wireless local area network has several disadvantages. Thus, firstly, the network can only be used to a limited extent only for critical applications, for example for the supervision and control of machinery. Other devices occupy part of the available bandwidth, which must be shared with the critical application in the given case. With remote machine control, this can lead to uncontrolled situations. In addition, in the event of a power failure in a mine or tunnel, communication between the hardware components of the radio network is not possible, since for the operation of the fixed network at least its stationary components must be supplied with electricity. Interruption of power supply cables between components of a fixed network can lead to the fact that entire parts of the mine will be cut off from wireless network communication. In addition, in connection with machine control, it is also the case that, depending on the current situation in the tunnel or vehicle and machine settings or the like, it is not possible at all times to maintain a KF (HF) connection between a remote controlled machine and a fixed network. Also, a quick change from one access point to another access point is often not possible with devices of this prior art. Especially with mobile machines, which depend on an uninterrupted network connection, this is a disadvantage. The same is true when the network is used, for example, for telephony applications with moving people. In addition, no data can be transmitted when searching for an access point, which also leads to adverse delays.

[0004] The method according to the preamble of claim 1 is known from US Patent 5,546,397 AA. The object of the invention is to provide a method and system of the type described above, with the help of which general communication with mobile stations can be adapted to special underground requirements and simplification of monitoring of mobile stations in order to be able to quickly and reliably implement rescue steps. In addition, the task of the invention is to supervise the underground work of machines at any time and secure remote

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The control of machines via a radio network with the simultaneous high availability of the radio network also in the event of interference.

[0005] To solve the above-mentioned tasks, a method is provided with the features of claim 1. In one embodiment of the method according to the invention, the type described at the beginning is additionally provided for, that if the transmission connection between the fixed network and one base station is interrupted and / or if the radio connection between the mobile station and the base station is interrupted, the data transmission between the mobile station and the fixed network takes place via the cut off base station and at least one further base station connected to fixed network through no interruption transmission connection. This enables data transmission also in the event of the transmission link between the fixed network and the base station communicating with the mobile station being interrupted, with the data sent to the severed base station first being sent to the next base station having a working transmission connection to the fixed network. Interruption of the transmission connection between the fixed network and the base station can be, for example, a consequence of a power failure or break in the network cable. At the same time, working base stations can be connected to the fixed network both by wired and wirelessly. By switching to another base station in accordance with the invention, connected to the fixed network via an efficient transmission connection, it is also possible in the event of a power failure at one base station to transmit data between the mobile station and the fixed network via a radio network.

The mobile station can be mounted on the machine or it can be a portable element, preferably an IP telephone adapted to operate in a WLAN. Furthermore, it is possible that the method according to the invention can be used not only for underground data transmission, but in any environment in which the use of wireless local radio networks leads to similar problems, for example in buildings or industrial facilities.

[0007] In a preferred embodiment of the method according to the invention, data transmission between the severed base station and the base station connected to the fixed network takes place wirelessly via a radio network. The base station, which is preferably an access point according to the IEEE 802.11 standard, generally has at least one transceiver that is adapted for wireless data transmission. In addition, a second transceiver may be provided which is assigned to a different transmission direction or can be directed to the transceiver of one of the neighboring base stations. Both transceivers are preferably not assigned to a specific application and are always on standby. Preferably, adjacent base stations are spaced apart, which allows a radio link (radio line) to be created between the base stations. Thanks to this, if the transmission connection between the base station and the fixed network is interrupted, the necessary data can be sent to the neighboring base station, which has an efficient transmission connection to the fixed network.

[0008] These data may be, for example, data for supervising or controlling the machine at and / or on which the mobile station is located. If, in the event of a interruption of the transmission connection, the data is transferred to an adjacent base station that is already transmitting or receiving data from the mobile station, then there may be a situation that the data stream, which in the uninterrupted mode of operation would flow through the transmission connection to the fixed network, mixes with the data stream between an adjacent base station and a mobile station communicating with that base station. In this case, information may be sent to the mobile station that will inform the mobile station that normal data transmission is disturbed, e.g. indicating a malfunction. In this situation, the mobile station can automatically change the operating mode of the machine being supervised or controlled by it to be able to react appropriately to a failure. For example, in a situation with a data collision threat, the mobile station may send control information to the machine carrying the mobile station, which will reduce the machine's travel speed.

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[0009] The base station can be a central unit that can have at least one access point, one switch (so-called switch), one fiber optic media converter and power supply protected by a backup battery as required, as well as one or more antennas . The base station is arranged in such a way that the characteristics of the method according to the invention described in detail below can be realized.

[0010] Adjacent base stations in the aforementioned embodiment are placed at such a distance from each other that enables wireless data transmission by radio between neighboring base stations. In the tunnel infrastructure, directional antennas are preferably used as antennas, which allow the greatest possible range within the tunnel. If the base stations have two separate transceiver units, it is possible to adapt the base stations for use as so-called bridge or network switch. While a bridge in a computer network connects two segments together and divides the network into different collision domains, the switch allows you to connect more than two network segments in a local area network (LAN). Individual switch inputs can receive and send data independently of each other. Both the bridge and the switch allow the data received on one side from the severed base station on the other to forward. In this way, data transferred to the cut-off base station can be forwarded via a larger number of consecutive (cut-off) base stations in a hopping manner via the radio network. The step retransmission preferably takes place until the data is sent to a base station that has an efficient connection to the fixed network.

[0011] Data retransmission can take place by means of standard methods, for example in a redundant ring network by means of so-called Spanning Tree Algorithm according to the IEEE 802.1D standard, or according to the processes described below implemented in the software layer.

[0012] To reduce the time of data transmission and to choose the most effective route for transmitted data packets, it is preferably provided that one cut off base station sends a status request to at least one next, preferably to all subsequent base stations, connected wirelessly or wired to the cut off requesting base station, where the status query relates to the connection status of the next requested base stations. It requires appropriate base station software. As a result, the cut off base station preferably sends a request to all reachable neighbor base stations to obtain information on whether the neighbor base station has an efficient transmission connection to the fixed network.

[0013] After sending the status inquiry, the status inquiry may be forwarded from the query base station to the following base stations along the chain of information pattern. If the query sent from the cut-off base station is returned to that base station, this does not favorably lead to further transmission of the status request. According to the invention, however, it is envisaged that the return of a status request is understood as information that the base station returning the status request is also cut off from the fixed network.

[0014] In principle, it is also possible that after sending the status query the requested base station creates status information and sends it to the asking base station. Therefore, the answer to the status inquiry may come that the questioned base station has an interrupted or uninterrupted transmission connection to the fixed network.

[0015] The sending of the status request is preferably continued until the status request is sent to the base station which has a good connection to the fixed network. This base station reports back to the inquiring base station its contact with the network, preferably again in the manner of an information chain the status information is sent so that all base stations cut off have received information about the base station connected to the fixed network. This is done to ensure that each base station cut off from the fixed network is at least informed about the possible data transmission path to transfer data between the fixed network and the mobile station.

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EP 1 849 260 B1 [0016] In the event of irregularities or interrupted transmission connection, the first base station connected to the fixed network may send an irregularity report to the central server, the report may contain information about the base station cut off from the network. Thanks to this it is possible to find a broken transmission connection in the network quickly and easily and precise repair. It is equally possible that via a central server the availability of underground base stations or network nodes to control the ability of the entire network to function.

[0017] Based on the number of transfer steps or data jumps in the information chain, the distance between the connected base station and more base stations can be calculated to select the shortest possible connection and ensure data transmission between the fixed network and the mobile station by the shortest possible route or with the least possible data transfer times.

[0018] In an alternative preferred embodiment, it is provided that at least two, and preferably all base stations are connected to each other via a transmission network, preferably ring-shaped, preferably connected to the fixed network, and that in the event of the transmission connection being interrupted between the fixed network and any base station data transmission between the base station cut off from the fixed network and at least one further base station, connected to the fixed line network through an uninterrupted transmission connection, is carried out by wire through a transmission cable. At the heart of the invention is at this point the main idea to connect the base stations preferably in the shape of a ring or as a mesh network by means of permanently installed wires, these connections preferably still having a much greater bandwidth than the radio connection. If the connection between the base station and the fixed network is interrupted, data transmission takes place via the transmission cable to the next base station, which is connected to the fixed network via a functional transmission cable. It is possible to route the transmission cable in the form of a ring from the base station to the base station and thus create an alternative fixed network access via at least one base station. To enable ring connection of base stations, each base station has at least two network cable entries, preferably a copper or fiber optic network cable. Data transmission between two base stations connected by a network cable can preferably take place in duplex mode, with the data transmission not interfering with the functionality of the base stations.

[0019] In order to enable further operation of the base stations for a given period of time also in a situation when the power supply of the base station with electricity usually taking place via the fixed network is interrupted, in the next alternative variant of implementing the method according to the invention the type described at the beginning is provided, that in the event of a power failure to the base station in uninterrupted mode of operation via a fixed network or a separate power supply, network-independent power supply occurs. For this purpose, each base station is preferably connected to a power supply independent of the network, wherein the base station may have an electric energy storage, for example a battery. This energy store ensures that the base station continues to operate for an extended period of time, so that data transmission between the fixed network and the mobile station through the base station can still occur. In addition, it is also possible to send immediately after interruption of the base station power supply, preferably after starting the emergency power supply mode, the status status der from the previously described type to neighboring base stations in order to obtain information about the connection status of the neighboring base stations with the fixed network. In addition, in the event of a power failure, it is possible due to the emergency power supply of the base stations to find, through the transmission cable, the type described above, having the shape of a ring and directly connecting the base stations, with alternative access to the fixed network to enable data transmission between the fixed network and the mobile station.

[0020] In a further alternative embodiment of the method according to the invention, it is provided that immediately after the power supply of the base station is interrupted, identification data and / or position data of at least

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One mobile station within the radio range of the base station located before and / or after power interruption, preferably all mobile stations within the radio range are determined and sent by the base station to the fixed network, preferably to the central stationary computer . In addition to the question about the status of the previously described type and / or as an alternative to it, it may be provided according to the invention that in the event of a power failure which was caused by an accident in a mine, all base stations directly send to the fixed network the identification data of all mobile stations that at the time of the power failure were in the radio range of the affected base station and / or radio communication with the affected base stations. If the transmission of identification data and / or position data is carried out by all base stations assigned to the fixed network, a comprehensive overview of the location of all mobile stations at the time of power failure will be obtained. In the event that a power failure was caused by an accident in a mine, thanks to the invention the established position of all miners equipped with a mobile station can be and sent to the emergency service. This can immediately take a precise rescue operation, where the position of miners, depending on the situation, can be determined with an accuracy of up to several meters. The extension of this function consists in the fact that the base station supervises in a software-controlled manner certain devices or groups of devices: After a specified period of time during which the mobile device is stationary, either the alarm is raised directly in the control panel or the mobile device is alarmed first. If after this alarm a person having the given device does not press the confirmation button, then the base station raises the central alarm.

[0021] After the transmission of identification data and / or position data in a base station emergency mode, further data transmission can only be allowed to a limited extent. The base stations then again allow limited network traffic, which can for example be limited to text messaging or phone calls when needed. This ensures that there is no network congestion with negative effects on the positional data transmission.

[0022] In an emergency mode, preferably the position of all devices assigned to persons is cyclically determined and transferred to a central fixed-line network computer, preferably to a central station. In this context, it is further preferably provided that access to the identification data and / or position data can only take place in a critical situation and / or after authorization. It protects against abuse of stored data.

[0023] It is also possible for the identification data and / or the position data to be stored for a certain period of time and to be transmitted continuously or only after a power failure or in a critical situation. As a result, the emergency service can only preferably access the stored data in the event of an accident to get an overview of where people are. Further, access to data relating to a person is preferably limited in time to accommodate the request for personal data protection by miners.

[0024] The mobile station can generally also be arranged at and / or on the machine, the machine working underground, for example, moving in a tunnel. In this case, it is usually provided that the machine's mobile station forms a communication link or association with different base stations. Due to the wired transmission method in the WLAN radio network in the IEEE 802.11 standard, however, in the case of mobile machines signal blanking may occur and therefore fluctuations in the quality of communication. As a result, it is only possible to supervise and control moving machines.

[0025] Methods are known in the art in which two antennas are used to secure the most even possible quality of communication between a mobile station and a fixed network, which is referred to as "Antenna Diversity". Despite this, there are many situations in mining and tunnel construction in which communication becomes temporarily impossible. This can be caused primarily by vehicles that are

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EP 1 849 260 B1 placed between the machine and the base station or by devices which in some cases by their own size temporarily block radio contact.

[0026] In many cases, the remote-controlled machine must be stopped if it has lost the radio connection to the control unit. Restarting the machine after interrupting the radio connection is partly impossible.

[0027] In order to be able to monitor and control machines moving underground with greater safety and reliability, in an alternative embodiment of the method described at the beginning, it is provided that at least two mobile stations are placed at and / or on the machine moving underground and that, as needed, data transmission is between one mobile station and / or the other mobile station and the base station. According to the invention, the machine has two independent transceivers in this case. They can be combined in one device or mounted on and / or on the machine as two separate devices. The mobile station with the transceiver has preferably two antennas, further preferably directional antennas, wherein at least one antenna can be placed in the direction of travel of the machine and at least one further antenna in the opposite direction of travel. This facilitates the creation and maintenance of a radio connection between the mobile station at and / or on the machine and the base station assigned to the fixed network.

For linking more mobile stations or a larger number of von transceivers at and / or on the machine may be provided with a network bridge function that divides the connection into different segments and thus into collision domains. If the mobile stations are arranged in such a way that data transmission between the machine and the fixed network is possible via two independent radio connections, then it is also envisaged to use more transceivers or to use different frequency bands by a suitably integrated device.

[0028] To enable mutually independent data transmission between mobile stations located at and / or on the machine and at least one fixed base station, the mobile stations may be arranged and / or placed relative to each other so that data transmission between the machine and the network is possible. landline through at least two different channels. To specify a phase shift between two channels of a radio connection, it may be envisaged to select a certain particular antenna form or a specific type of antenna as well as to select different planes of KF signal polarization or to set portable stations at the appropriate distance.

[0029] Preferably, the data to be transmitted are substantially or, depending on the situation, temporarily redundantly transmitted by the machine's mobile stations, preferably only those data that were first sent to the base station and reached the recipient. To separate the various functions within the multifunctional wireless network, it may be provided that the radio connection between the mobile station and the base station is arranged as a virtual private network (VPN) or as so-called Virtual Lan (VLAN). A virtual private network is a computer network that uses a public network to transport private data. Virtual private network users can exchange data as in an internal LAN. Individual users do not have to be directly connected for this purpose. Through the virtual private network, mobile stations can receive access to the fixed network, namely through base stations that are assigned to the fixed network. A VLAN is a virtual local area network within a physical network that can be used to separate virtual networks from each other in terms of security, broadcast control, etc. VLANs can be connected to each other through routers. The widespread technical implementation of VLANs is partially defined in the IEEE 802.1q standard.

[0030] A further preferred embodiment of the method according to the invention provides that the quality of the data signal transmitted between the mobile station and the base station is determined, for example by measuring field strength. It is preferably provided that the quality of the data signal transmitted from is determined

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EP 1 849 260 B1 mobile station to a base station. If the machine moving underground has at least two mobile stations spaced apart, it is provided according to the invention that the signal quality for both mobile stations is determined. The predetermined signal qualities can then be sent to the data sending station, preferably by each data receiving station. As a result, the quality of the incoming data signal and the quality of the own data signal sent and received at the recipient is determined and transmitted to the sender. This allows you to decide, depending on the quality of the connection, with which base station the mobile station should establish the radio connection or with which base station the mobile station should form an association and when eventually there will be a switch to another base station, the so-called roaming.

[0031] According to the invention, the machine preferably receives continuously information about the signal quality of the data sent by the machine to each of the base stations, the signal quality being determined and transmitted continuously. In order to ensure the highest possible quality of the radio connection between the mobile station and the base station, it is preferably further provided that the signal quality of each base station or a mobile station in radio communication with the mobile station or base station. In effect, this means that for each mobile station the quality of each possible radio connection with the base station located in the radio range is determined and used as the basis for pairing the mobile station with the selected base station. When both the quality of the data signal transferred from the mobile station to the base station as well as the quality of the data signal transferred from the base station to the mobile station is determined and transferred to the machine, then the machine has information about the quality of the connection of both the data sent by the machine and received by the machine, and this for each base station with which it is associated. Depending on the quality of the radio link signal between the mobile stations located at and / or on the machine and at least one base station, it is possible to decide by which mobile station data transmission between the base station and the machine should take place.

[0032] Preferably, this decision is made by the machine control device itself, but it is generally also naturally possible that starting from a central station, which can be, for example, a dispatcher station on the surface, or from a base station for data transmission, a radio connection with the highest signal quality. Further base stations that are within the radio range of the mobile stations located at and / or on the machine can be informed about the signal quality. In this case, the mobile station sends a query to the base stations within the radio range to establish a radio connection with a specific base station after an appropriate response depending on the signal quality. In the program layer, it is therefore decided which connection can be used optimally.

[0033] Since the machine can always dispose of two independent radio connections to the base station, it is possible to take up actual data transmission substantially without delay depending on the signal quality via one radio connection and / or another radio connection. Interruption of the transmission connection, usually occurring during a physical change during an active transmission connection from one base station to another, can thus be bypassed. The best way for sending data packets from one or further mobile station of the machine to the base station is selected by a properly designed machine control unit to ensure, depending on the quality of the connection, the transmission of data packets with the least possible susceptibility to interference. In addition, it can be provided that the dispatching station connected to the fixed network is informed by the machine control module about which of the mobile stations located at and / or on the machine is intended for data exchange with the base station.

[0034] According to the invention, the base station is preferably a wireless access point, a so-called Wireless Access Point as part of the fixed network topology. An access point is an active component of the network. Unlike passive network components, such as cables, the access point is able to process network data itself. If underground data transmission is provided between the mobile station and

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According to the invention, both base stations as well as mobile stations located at and / or on the machine can be arranged as 802.11 access points in a fixed network via a WLAN network in the IEEE 802.11 standard. Thus, according to the invention, equipment compatible with access points is also used on a machine moving underground. Because it is able to maintain connections with more foreign stations, the time-consuming association of the mobile base station with certain fixed network access points can be avoided.

[0035] In this context, one or more access points on the machine can be used, so that several simultaneous connections to a fixed network can exist depending on the needs. User data can also be exchanged between the machine and the fixed network via these basic connections. This can be, for example, monitoring or / and control data. Both fixed access points of the fixed network taking part in the data transmission as well as the mobile access points provided at and / or on the machine can be adapted to independently decide, when necessary in dialogue with each other, about which connection should be the data transmission. At the same time, appropriate software may be provided, which means that data sent repeatedly cannot be repeatedly retransmitted or processed.

[0036] The susceptibility to wireless transmission interference from a mobile station to a fixed-line access point can be reduced in such a way that for underground applications underground data transmission takes place via a WLAN in the IEEE 802.11 a or g standard. This has the advantage that information can be transmitted in a multiplied manner through the subcarrier frequencies of the bandwidth used, which makes it more susceptible to interference compared to 802.11b WLANs, because for data transmission via IEEE 802.11b WLAN the entire the channel frequency band is used evenly.

[0037] To enable central control and supervision of machines moving underground, in a further alternative embodiment it is provided that the mobile station is placed at and / or on the machine moving underground, that the machine position is preferably determined continuously by the base station on the basis of data sent to the base station by the mobile station and that the base station transmits at least one position signal determining the position of the machine to at least one adjacent base station located in the direction of travel of the machine. According to the invention, it is possible to solve that the position of the machine moving underground is preferably constantly monitored by base stations arranged as access points. It is preferably provided that the position of the mobile station connected to the base station or access point via radio connection and / or position of all mobile stations within the radio range of the base station. The positioning of the machine can, for example, take place in such a way that the position data is transmitted via the mobile station to the associated base station. In principle, it is also naturally possible to create a radio link between the mobile station located at and / or on the machine and the base station as information that the machine is within the radio range of the base station and thus nearby.

[0038] According to the invention, it is therefore possible that base stations follow the path of the machine, with one of the base stations informing neighboring base stations either via a radio network or via a fixed network that a machine is approaching. In order to provide a correspondingly large radio bandwidth for data transmission from the machine to the base station depending on the situation of the communication request from the machine, it is preferably provided for, that with the creation of a radio connection or also continuously during an ongoing connection in the current machine operation between the mobile station and the base station at least one information about the request for bandwidth from the machine to the base station will be sent. Demand for bandwidth changes, for example, when one operator takes over the machine manually for remote control. Under the bandwidth request should be understood the amount of data,

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EP 1 849 260 B1 which must be sent from the mobile station to the base station and vice versa in connection with the supervision and / or control of the machine.

[0039] The bandwidth request may be sent from the base station associated with the mobile station to the neighboring base stations, which leads to the fact that the neighboring base station can automatically make a bandwidth reservation in the amount of machine bandwidth request. This can take place, for example, so that with the transmission of the bandwidth request, no further connections can be made between the neighboring base station and further mobile stations, e.g. laptops or telephones. As soon as the machine leaves the radio range of the base station, and the KF radio connection between the base station and the machine's mobile station is interrupted, the base station may return to normal operation mode. The bandwidth reservation is lifted. Depending on the situation, bandwidth reservation is particularly advantageous if the underground machine is operated manually from a stationary central station or dispatching station and at the same time, for example, is to be monitored by digital video over a WLAN.

[0040] In order to provide a sufficiently large bandwidth for the transmission connection between the mobile station located at and / or on the machine and the base station to control and monitor the machine moving underground at any time, in a further alternative embodiment of the method according to the invention described above is a system of priorities is foreseen for the quality of radio network services, wherein the data packets sent by the mobile station to the base station receive a higher priority than those data packets that are sent to the base station by mobile stations not assigned to the machine. Prioritizing data packets can be based on specific features and properties. By prioritizing data packets, the connection priority for sending data packets is set at the same time. According to the invention, it is thus provided to provide sufficient bandwidth for the transmission of control and monitoring data that data packets sent from a mobile station to a base station can be transmitted or machined first. Priority processing also naturally applies to data packets which, in connection with the search for alternative network access, are forwarded from one base station to the next. For example, if the mobile station is located at and / or on the machine, then data packets that relate to the machine bandwidth request are preferentially sent to the base station. Data packages with lower priority are not sent at all or only with a delay. It is also possible that the transmission of data packets with a lower priority will be interrupted when data packets with a higher priority will be sent.

[0041] In detail, there are many possibilities for developing the method according to the invention, on the one hand, reference is made to the dependent claims and, on the other hand, to the following detailed description of a preferred embodiment of the invention with reference to the drawing. In addition, it should be noted that the invention allows the features listed in the claims to be combined as desired, even if this is not described in detail.

[0042] The only figure in the figure shows the underground radio data transmission system 1 between more mobile stations 2 of the machine 3 moving underground and the fixed network 4 via wireless local radio network 4a. The 4a radio network in the example shown in the figure is a WLAN in the IEEE 802.11 standard. The fixed network 4 has one stationary central station 5 and a greater number of stationary base stations 6 arranged as access points according to the IEEE 802.11 standard, with each base station 6 connected to the fixed network 4 via at least one preferably wired transmission connection 7. Base stations 6 and the mobile stations 2 have at least one transceiver not shown. Data transmission between mobile stations 2 and fixed network 4 takes place in radio network 4a wirelessly for at least one base station 6.

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[0043] In the normal operating mode, data transmission is carried out between the mobile station 2, which can also be essentially an IP telephone adapted to operate in a WLAN, and a central station 5, for example an office on the surface or a central station dispatcher, via stationary base station 6 and further hardware components of fixed network 4, especially preferably network switches 8 and / or routers not detailed in detail, network bridges or the like. In order to easily adapt the infrastructure of the fixed network 4 to the topology of underground constructions, the said components are preferably integrated directly into the base stations 6. The access point can be connected to the network switch like another Ethernet port. This creates a linear structure from the switch point of view from the switch to the switch, which logically corresponds to the tree structure with the switches. If the switch in base stations 6 has more than two network connections, then it is possible to branch cables to the tunnel and, depending on the situation, create mesh networks, which due to redundancy can have great advantages. Division of various networks is then preferably carried out using the so-called VLANs as virtual Local Area Networks on the base station switch.

[0044] If a power failure occurs, all of the fixed network hardware components 4, such as base stations 6 and / or switches 8, for example, are de-energized, which leads to the interruption of the transmission connection between the fixed network and the de-energized base station 6. The same applies if the network cable breaks.

In order to nevertheless enable data transmission between the mobile station 2 and the fixed network 4 in the event of interruption of the transmission connection, according to the invention it is provided that between the base station 6 cut off from the fixed network and at least one further base station 6 connected to the network stationary 4 with uninterrupted transmission connection, provide for a direct transmission connection between neighboring base stations 6. Preferably a radio connection 9 is created. In principle, according to the invention, however, it is also possible to connect together a greater number of base stations 6 via a network cable, preferably in a ring, with the data transmission between base station 6 cut off from the fixed network 4 and at least one further base station in the event of the transmission link 7 being interrupted. 6 connected to the fixed network 4 through an uninterrupted transmission connection 7 is via a network cable.

[0046] An alternative embodiment of the invention provides that in the event of a power failure of the base station 6 provided via the fixed network 4, network-independent power supply occurs. For this purpose, according to the invention, it is provided that each base station 6 may have an electric energy storage, for example a battery.

[0047] Through the channel method of transfer from WLAN to IEEE 802.11, mobile machines 3 in ground-based application achieve signal blanking and thus change the quality of the connections. In addition, the radio connection between the machine 3 and the base station 6 is partly broken or obstructed by obstacles.

[0048] To track the movement of the machine 3 underground and to be able to supervise and control the machine 3 with high safety and reliability, it is further envisaged in accordance with the invention that the machine 3 has at least two mobile stations 2 that allow the data transmission from one mobile station 2 and / or a second mobile station 2 to base station 6. Depending on the quality of the radio connections between the mobile stations 2 and the base station 6, preferably the machine 3 can then decide through which of the two mobile stations 2 of the machine 3 data can be transmitted to the base station 6.

[0049] Alternatively, data is being transmitted from both mobile stations 2 of the machine 3 simultaneously or redundantly to different base stations 6. It may well be envisaged that from central station 5, e.g. central server or remote control module for machine 3, all data to machine 3 is transmitted via two different routes redundantly to base stations 6 with which machine 3 is just there

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EP 1 849 260 B1 connected via mobile stations 3. It can also be provided that only the data packet received first is taken into account while the next received data packet remains not taken into account. In this context, different alternative processes can be dynamically allocated and switched over depending on the operating situation of the machine and the radio network. This is done favorably in the dialogue of mobile and central programs with mobile and stationary infrastructure. The settings in this context are affected by the dynamic configuration of routers, network switches, access points and mobile clients.

[0050] In connection with the tracking of the machine 3, it may further be provided that the base station 6 automatically preferably continuously determines the position of the machine 3 on the basis of the data transmitted by the mobile station 2 to the base station 6 and generates a position signal which is transmitted or transmitted. retransmitted from one base station 6 to at least one adjacent base station 6. In this way, the adjacent base station 6 is already informed before the arrival of the machine 3 that the machine 3 is approaching the adjacent base station 6, and that the adjacent base station 6 must provide sufficient bandwidth for the data transmission of the machine 3.

[0051] The illustrated system 1 preferably has 6 access points in the 802.11 standard as base stations, preferably as combined devices in the IEEE 802.11 a / g standard. Each access point has one or two WLAN transceivers in the IEEE 802.11 standard. In addition, the access point may have at least one connection for optical or copper cable and, depending on the needs, a built-in network switch to be able to build tunnel branches, and / or a routing function for a fixed network to be able to connect the access point simultaneously with several different concentrators, e.g. switches , to fixed networks. Each transceiver unit can have at least one antenna or a pair of antennas and / or the option of connecting at least one external antenna.

[0052] Furthermore, according to the invention, it is provided that the access point is suitably adapted for use within the method according to the invention. In this context, the access point may have the function of searching for fixed network connections or available connections to the fixed network in the event of a power failure, but the search can be carried out preferably via the radio network. In addition, software functions for skipping information packets sent simultaneously to two access points are preferred. In addition, functions may be provided for storing the mobile devices associated with the access point in order to be able to transfer them continuously and / or in the event of a power failure to central systems. In addition, the access point should have the function of receiving bandwidth requests from privileged devices as well as blocking and deliberate interruption of low priority calls when a privileged bandwidth request arrives. Finally routing functions may be provided to facilitate communication with machines equipped with two portable WLAN stations.

[0053] The configuration of the access point may take place automatically from the central server or manually starting from the web search engine.

In addition, the function of storing mobile station identification data associated with a given access point for a programmable period of time may be provided in order to be able to send this identification data to the fixed network 4 or to central station 5. This ensures that the places where persons in the possession of the portable mobile station 2 are held can be read by authorized personnel only in the event that, after a hazardous event, authorized personnel request transmission. For example, tracking the path they have traveled is not available in normal mode, but only if it is useful for protecting that person's health and life.

[0054] To ensure the highest transmission security, the access point can be used with two separate frequency ranges. One frequency range, for example 2.4 GHz in the IEEE 802.11 b / g standard, can be available for general network traffic, for example the Internet, intranet, telephone connections, laptops, etc., with this standard being used by popular WLAN devices. Data exchange with machines 3 can take place preferably in the IEEE 802.11a standard in the 5 frequency range

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EP 1 849 260 B1

GHz. This frequency range is only used by special devices, so that interference from the magnifying glass overlaps with other devices that are further spread is unlikely. In addition, the access point preferably has two separate transceivers that can conduct both types of communication independently of each other. 2.4 GHz and 5 GHz WLAN transceivers can be connected to an access point switch. Thus, on the one hand, it is possible to divide data traffic on the wired network side, whereby 5 GHz WLAN data exchanged with machines are permanently connected to a specific external Ehternet port, and all 2.4 GHz WLAN data can be connected to another the external Ehternet port. As a result, one device can be used for both types of communication. These frequency bands apply to the situation in Europe. It is natural that other transmission standards may also be used and this will not go beyond the scope of the invention. The person skilled in the art understands the frequencies and standards mentioned herein as examples and may transfer the relevant radio networks into other ranges and standards.

[0055] The WLAN access point may, in addition to its described basic functions for transferring information between stationary and mobile devices, take on further functions for this by mounting additional devices to the access point. These additional devices then take over the automatic or program functions. They are built into the access point to improve e.g. power or protection against external influences. Such devices can be, for example:

• Stationary navigation and positioning aids for personnel, mobile machines or for mining surveying purposes such as position transmitters or radar reflectors.

• Stationary readers to identify materials such as scanners, active and passive RFID readers, etc.

• Computers or measuring instruments for monitoring tunnel air quality.

[0056] An access point as a basic component of an underground radio data transmission system is often already a small computer. According to the invention, the computer capacity of access points is increased, so that they can additionally take over the functions in the underground application. This is especially important because each additional device in hard underground operation is an additional source of interference and can lead to critical parts failing due to such interference. In addition, each subsequent device can only be protected with extensive operations using expensive housings, which creates additional costs.

[0057] The access point may thus also itself be built as a modular computer that takes over the tasks of the access point as one of many tasks in the underground building infrastructure. Such additional tasks can be, for example:

• • Sending support information for the accurate navigation and positioning of vehicles, machinery and personnel.

• ^ Accepting and interpreting tracking information, for example, loaded by optional connected ancillary equipment such as a laser scanner or RFID tag.

• ^ Generation and transmission of positioning information, e.g. to terrestrial servers, which are loaded either via the WLAN itself or by optional embedded or connected additional devices.

• ^ Communication with central systems according to open mining standards or any nonfree method.

• · Acceptance and computational processing of meteorological information (information, e.g. on air quality, temperature, humidity and air flows in an underground structure) for transmission to appropriate computers or to a network-based ventilation control.

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EP 1 849 260 B1 • Processing of meteorological information and a demand for fresh air supply depending on the number of people and machines (diesel if applicable) located in the access point area. This way, ventilation systems can be controlled to suit your needs: you save energy costs because only minimal ventilation is needed when there are no people in the relevant areas.

• · Receiving, supervising and forwarding information on water management.

• · Generating (depending on the needs initially anonymous) information about the movement of people and supervising the movement of people, so that in an emergency (if, for example, a person due to an accident does not move for a certain period of time), you can inform this person or the headquarters to inform your colleagues in the nearest area.

• · Generating information about people's "last known position" underground. This critical information can, for example, be used to implement accurate rescue steps. The resulting time saving can save lives.

• · Generating and processing information regarding the positioning of mobile stations by means of triangulation (measurement of different signal strengths) and / or trilateration (measurement of signal time, TOF = Time of Flieht).

[0058] This includes the implementation of the base station as a computer, comprising not only firmware set by the manufacturer of the access point, but also program control available for application programming; these memories can be in a separate device or together in one device.

[0059] This program control in connection with the base station is also meaningful because a lot of information collected on-site obtains a useful technical sense only in a substantive and functional connection possibly together with network information. The closer the processing is to the process itself, the smaller the bandwidth required, as it is also possible to completely resign from cyclic transmission and, alternatively, event-controlled, computer-induced transmission at the access point can be sent to recipients designated by the software.

[0060] Examples of the advantages of various implementations of this integration are:

• Ventilation disturbances caused, for example, by a passing machine may be recognized and eliminated from the calculation as irrelevant due to the simultaneous connection of the access point to the machine.

• Transport units recognized by the RFID reader can be assigned to a train simultaneously associated with an access point.

• Situation-dependent assessment of traffic information: If a miner carries a network device with him, changes in field strength may suggest movement. if there is no movement of the device for some time, the access point alerts the device owner (e.g. by means of a "telephone") which the owner must pick up. If this does not happen, the access point alerts the central system to be able to start a rescue operation. Since the information before this point is not transferred to the central system, the system does not provide grounds for the accusation of "controlling" personnel from the perspective of personal data protection.

• Switching on and off ventilation and / or lighting and / or other aids etc. only when the base station notices people or machines.

[0061] Particular advantages are offered by this processing for information which is to be decentralized to be collected and processed and which does not justify its own computer or data transfer.

[0062] The computer can also be used as a network bridge for further access points. The computer must preferably be equipped with two different Wireless LAN or other wireless interfaces or connector. In this way, the computer may also constitute a wireless "bridge" to further suitable devices as described above. In this way, the range of radio coverage can be increased without having to extend the accompanying infrastructure e.g. in the form of an optical or copper network cable. If

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Such devices are powered by e.g. power generators, a fuel cell or batteries, this area does not even need power.

[0063] This is particularly important as in the ever-changing infrastructure of underground structures there are always spaces in which the appropriate infrastructure does not (yet) exist or can be created temporarily only at extremely high costs.

[0064] In this case, the network bridge function can be taken over by another device (not used as a strong access point). Then, for example, telephone calls from an IP telephone can be sent through a machine (which is also a "customer" on its part) or machines as a "relay station (s)" to the next device connected to the fixed network. This method is also known as "Mesh Networks".

[0065] In a manner analogous to that of building a network bridge with an autonomously powered access point, also mobile stations can be converted into network bridges to other devices. Mobile devices also take over the tasks of a network bridge.

[0066] A machine equipped with WLAN can thus serve as a "relay station" or as a "bridge" for further devices (e.g. persons equipped with a telephone or PDA) that are further away from the fixed infrastructure.

[0067] The electronic modules described, such as a computer, for example, can be cold-started by means of the method according to the present invention. If an access point is operating underground, this modular device is a potential source of error. Sometimes, there are situations that cannot be repeated in every case. These situations can often be rectified by simply turning it off and on. Return or "Reset" is often not enough, because many registers, especially in hardware modules, are only deleted after power off. To turn the device off and on again underground, authorized people often have to travel long distances beforehand. In addition, the devices are often not equipped with on / off switches. Therefore, the electrician must first disconnect and reconnect the power supply. According to the method of the invention, a computer device with an access point can be remotely disconnected from the power supply as follows:

1. At least one or more electronic modules at the access point may be separately addressed by the network.

2. At least one of these modules receives a command from the computer on the surface to turn the device off and on again.

3. This module runs through a digital output or other relay / switch communication connector or an electronic relay in the power supply, which de-energizes the entire device.

4. Immediately after switching off or with a certain (depending on the needs adjustable) delay, the electronic relay releases the power supply and activates the individual modules of the access point either together (simultaneously) or in a set order.

[0068] Usually there is a large number of activators in the vicinity of the underground access point, such as switches and valves, activated or remotely controlled. According to the method, the extension of functionality should be seen in line with the installation of solid inputs and outputs, galvanically decoupled and - depending on the needs - according to the principles of occupational safety technology (explosion hazard). In this way, digital or analog information can be entered directly into the device or device in the vicinity of the access point can receive commands and setpoints.

[0069] Connecting transmission connections (depending on typical mining needs) is also possible. Generation of appropriate data formats compatible with the standard then takes place directly in

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EP 1 849 260 B1 access point. Examples of such connectors are serial connectors according to the German Bulletin

Mining (Bergbaubetriebsblatt) or standards based on Ethernet, e.g. based on XML.

[0070] Direct connection of sensor and activator signals can also be extended to the connection of sensors and activators. Thus, the access point is the entrance to the stationary infrastructure for wireless sensor networks, with which all kinds of information (e.g. about temperature, humidity, pressure, etc.) from underground work to manage work should be loaded. Such a set of sensors can be made in such a way that information from the sensors lying further from the access point is carried out by those lying closer, so that the entire unwired sensor network gets access to the infrastructure.

[0071] As an alternative to the described embodiments which use redundant connections, the method according to the present invention called roaming can also be used.

[0072] To further increase transmission security and availability, a further embodiment in accordance with the invention has the function of automatic retransmission or roaming. A moving mobile device is forwarded from one fixed network access point to the next next network access point. Preferably, the network is a WLAN. By this means, the connection between the mobile device and the network or its access points can be maintained with as few changes as possible.

[0073] The roaming described is achieved by the method according to the invention.

[0074] As is known, the mobile station holds the connection to the access point as long as it breaks. The mobile station then begins searching for alternative access points to create a new connection. All available channels are searched or scanned. The best connection is selected. This connection is then activated and data can be exchanged between the mobile station and the network via an access point. This method, however, requires a period of time, which is particularly long in the use of mobile machines. In addition, no data can be exchanged during the search process.

[0075] The process according to the present invention comprises the following steps:

1. Recognition step: Continuous recognition of at least one parameter for the quality of the signal received between the mobile station and the access point. Signal quality is designated as IAKTUELL. If a threshold below the user defined threshold is set, the second process step is run.

2. Search step: After dropping below the threshold, the search step for a new access point begins. The search step is carried out in parallel with the data transmission or interrupts the transmission for a short time.

3. Recognition Step: Recognizing the signal quality of the access point found, designated as INEU.

4. Comparison Step: Comparing IAKTUELL with ILMU. If the signal quality of the access point found is better than the signal quality of the current access point, i.e. IAKTUELL <INEU, step 5 is started.

5. Switching step: Switching the mobile station from the current channel, i.e. from the current access point to the new channel, and therefore to the new access point.

[0076] The IS threshold is set so that a stable connection can still be maintained when the threshold value is reached.

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[0077] Various methods can be used to determine signal quality, e.g. signal field strength, number of expected and actually received signs of life ("Heartbeat", "Beacons", etc.) from a base station in a defined period of time, etc. from the base station ("Lost Beacon Rate"), signal / noise or packet loss rate.

[0078] The search step may be included in the data transmission. In this way, the search step can be carried out more efficiently. This step may be limited in the way of configuration to those channels that are used by the network. Because few channels are usually used (e.g. three out of 13), the entire search process is accelerated.

[0079] To further accelerate the search step, especially when the search process has to interrupt transmission, it can be performed in single steps, with data transmission being able to occur again between each single step. So, for example: EXCHANGED --_> Search on channel 3 --_> EXCHANGED --_> Search on channel 3 --_> EXCHANGED.

[0080] An alternative roaming method is a location-dependent roaming method according to the invention . This method can be used especially when the machines are used in known work zones or excavations. This method does not perform search steps, i.e. you do not use search programs.

[0081] In the first step, the area of ​​operation must be measured before using the automated machine. In this case, the position and the current or prevailing position are preferably recorded. field strength of the associated channels and access points. Using this data, a field strength map of the measured area of ​​activity can be created. The measurement can be made both with a machine to be later used in this area and with another vehicle. The field strength map can, for example, be saved in the form of a table. At the same time, the table has relevant information about access points assigned to each item. For example, the position at which the channel or access point should be switched as well as the identification of the access point to which the connection should be transferred is included.

[0082] The field strength map thus contains information about the expected reception conditions for the mobile station at specific positions in the operation area. This field strength map is sent electronically to the machine control module before automatic travel.

[0083] By means of a suitable measuring device, a device for determining each position, the position of the machine is monitored on an ongoing basis. The measured position is compared in real time with the field strength map. Once the machine has reached the position at which the channel or access point should be switched, the machine control module recognizes this and switching is performed. This switching takes place quickly and therefore leads to barely noticeable roaming.

[0084] The mentioned field strength map creates one aspect of the stored table, with these places and field strengths being assigned directly (for the position of the mobile station) or indirectly (calculation of the field strength at the location of the mobile station by the position of the base station) one or several preferred base stations.

[0085] Both roaming methods described can be used both alone and together, preferably in combination with a redundant communication method.

[0086] Another alternative possibility to use underground radio installations is to use MIMO technology in the upcoming IEEE 802.11n standard. MIMO stands for the transmission system with multiple reception and multiple transmission (Multiple Input - Multiple Output). In addition, underground interference can be reduced. Interference is caused by repeated propagation of radio waves due to reflections on tunnel walls.

[0087] This alternative uses a larger number of differently positioned antennas on one transceiver module. In this way, the received signal is received repeatedly ("Multiple Input") and the transmitted signal is sent repeatedly ("Multiple Output").

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[0088] When used underground, this technology reduces the reflection that occurs permanently on the walls of the tunnels and is an important technical means to achieve good quality joints while at the same time having a large range.

[0089] The method according to the invention provides that MIMO technology can be used in an access point and / or in a mobile station. This applies especially to directional antennas that have been specially optimized for underground applications.

[0090] MIMO in underground applications can also be used simultaneously with a larger number of different transceivers in connection with transmission redundancy.

[0091] In connection with the above roaming and redundancy transmission methods, the underground use of wireless networks is thus further optimized.

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EP 1 849 260 B1