GB2242338A - Leaky feeder communication system - Google Patents

Abstract

The system has a plurality of transmitting and receiving stations S1, S2, S3 which communicate with a leaky feeder cable 4. Transmitted signals from the stations are picked up by the leaky feeder cable and conducted to a routing controller which retransmits the signals at a different frequency to route the information to the receiving station tuned to that frequency. The transmitting and retransmitting frequencies may have fixed associations, or the retransmit frequency may be dependent on information content of a transmitted signal. The stations S1, S2, S3 may provide on functional devices (6), (Fig 1), such as mobile platforms, manipulators, vision systems, instrumentation and other process machinery in a hazardous nuclear or chemical environment, the routing controller being in a safe area. <IMAGE>

Description

LEAKY FEEDER DATABUS SYSTEM This invention relates to the use of wide-band leaky feeder communication systems in association with distribtited fixed, mobile and semi-mobile stations, to permit the srultaneous and relatively independent duplex transmission of command signals and data between them.

The use of leaky feeder systems to replace or supplement conventional radio transmission systems in tunnels, or in tunnel-like situations such as mines, is well known and widely described in the literature. Their use for extending radio-telephone and similar signals of relatively low intelligence bandwidths into mine tunnels is especially well known, and is often characterised by the use of carrier frequency conversions, booster stages and special-to-purpose cable layout and interconnection geometries. This is to achieve the best compromises between signal coverage and system installation costs. This is especially true of systems installed in mines, where there is often a need for spurs and loops, and where the intelligence being transmitted is essentially voice and equipment status data.

In some leaky feeder systems it is usual for a transmitter or receiver to operate at a given frequency, all receivers and transmitters having the same frequency being in comunication. Such an arrangement can be inflexible. An alternative is to have tuneable receivers and transmitters, but this leads to increased complexity.

The present invention is directed towards providing a system that enables flexible consundcation on a leaky feeder system without additional complexity for mobile or semi-mobile receivers and transmitters.

According to the invention there is provided a leaky feeder communication system comprising a leaky feeder cable, transmitting and receiving stations and a routing controller in which signals transmitted on a first frequency from a transmitting station are conducted via the leaky feeder cable to the routing controller and retransmitted on the leaky feeder on a different frequency.

It will be appreciated that the leaky feeder cable may behave as a high speed databus, and the various transmitting and receiving stations which are connected may each interact in a flexible manner with the rest of the system, as a given application may require from time to time.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 schematically illustrates a leaky feeder installation within an enclosure, and Figure 2 is a schematic diagram of the communication process of the invention.

The drawings illustrate a leaky feeder system where the stations communicating via the leaky feeder are in an enclosed area. Such a requirement may be necessary for hazardous environments, for example materials handling in a nuclear environment. However, use of the invention is not restricted to such enclosures and general use in leaky feeder systems is also envisaged. The enclosed environment is used to illustrate the invention because the requirments are more stringent in that access for servicing is limited and therefore simplicity of component; within the enclosure is particularly desirable.

Referring specifically to Figure 1, an enclosure 1 accommodates a plurality of functional devices 6, which may perform a variety of different operations. The enclosure is sounded by a wall or partition 2 that also separates the enclosure from a control area 3. A leaky feeder cable 4 extends across the enclosure and passes out through the wall 2 to the control area. A seal 5 around the leaky feeder prevents egress of the environment within the enclosure. The seals may also be configured to facilitate replacement of the leaky feeder cable.

The devices 6 may each be mobile, semi-mobile or stationary, or a combination, and they may perform a range of functions such as material movement or manipulation, or provide information such as via video cameras, for which co-operative movement of the devices may be required. The control signals for the movearaent are passed by way of the leaky feeder from the control area 3.

In the control area a system management computer 11 receives information from the devices transnitted via the leaky feeder and reroutes that information to stations tuned to different frequencies by retransmitting. The retransmiSsion may be automatic on a frequency basis, for example all incoming data on frequency F1, always being retransmitted on F2 and F3, F2 being and data on frequency retransmitted for example on F1 and F3. Alternatively the incoming information may be selectively rerouted depending on its content, for example a mobile unit may transmit information relating to its location which then determines which of other stations it communicates with to perform a subsequent co-operative function.This selection procedure may be triggered on automatic controls, such as location signals or be programmed by an operator. The system may also compare location or availability data from other stations before determining the rerouting of the signal. Additional control information may also be added to the retransmitted signal.

Referring now to Figure 2, a schematic block diagram of an embodiment of the invention is shown in more detail. The leaky feeder 4 picks up a signal emanating from a station S1 on carrier frequency fll. Station S1 is tuned (or set) to receive on frequency f21.

The signal is an encoded modulation of the carrier frequency, and on transmission from the station S1 part of the radiated energy is picked up by the leaky feeder. Of the radiated energy that is picked up, part is transmitted towards a terminating impedance RT where it is absorbed and the other part passes along the feeder cable and via a directional coupler 12 to a bank of receivers R1, R2, R3, R4 One of the receivers is tuned to receive frequency f11 and the signal passes through that receiver to a corresponding decoder element D1 where the signal is decoded and routed to the system management computer.

In the system management computer the decoded signal is processed and/or retransmitted depending upon the system design and/or the information carried. In the enbodiment shown in Figure 2 the decoded signal is routed to encoder E2 and then transmitter T1 where it is retransmitted on carrier frequency f22 and launched back into the feeder by way of the directional coupler. Energy radiating from the feeder on frequency f22 is picked up by the receiver operating at that frequency on station S2.

It will be realised that the signal originating on frequency f11 could have been similarly rerouted by the system to more than one station either by virtue of retransmission on more than one frequency and/or by different stations being set to receive the same frequency. Some incoming information on the leaky feeder may not need to pass through the system computer, either because of fixed routing or because of use at the control area, e.g. display of a video picture.

This process of transmitting, routing and re-directing signals may be configured up to limits imposed by the bandwidth of the feeder cables and the bandwidth requirements of the signals. However, multiple cables may be employed, either to increase the total system bandwidth further, or to provide a means of redundancy, or to isolate major system-critical functions.

In such a system as has been described, the carrier frequencies applied to the feeder cable may be typically in the range 30 NHz to 1 GHz, individual signal bandhddthss are typically 10 NHz and a single cable system may accommodate the control, typically of up to 25 independently operating devices such as mobile platforms, manipulators, vision systems, instrumentation and other process machinery.

The feeder goemetry may be of a simple linear form as indicated in Figure 1, or may be readily adapted to suit the area to be controlled. It may therefore operate in tunnels, or at varying levels in -a building structure, or along paths, roads, railway tracks or any approximate combination of these. It may be broken into discrete sections and controlled as individual sections of a larger system.

Similarly, signals may be received or injected at any termination or junction of the cable(s), provided the appropriate matching conditions are satisfied to minimise distortion.

The invention enables a plurality of relatively simple sub-systems to ' communicate interactively with and be controlled by one or more computer sub-systems or human operators, singly or in combination, but located remotely from the sub-system and communicating via the leaky feeder cable.

Detailed geometry of an installation can readily be altered to suit a purpose in hand without the need for major changes in interconnection facilities.

A particular advantage of the invention is that it enables component sub-systems to be located in for example a hazardous or inaccessible location and computing devices and human operators to be located- in a benign or convenient situation elsewhere. In the instance of, for example, a nuclear or chemical environment the task of decontamination is minimised by the minimising of interconnecting cables, and the use of simple fixed frequency components requires less maintenance and is more reliable in adverse environment.

Any practicable combination of carrier frequencies and device, or target, addressing schemes may be employed, but the use of a wide range of individual carrier frequencies allows simplification of addressing. Use of simple transmitters and receivers, with automatic frequency control receivers where necessary, minfmise cost of the vulnerable hardware.

Claims (10)

1. A leaky feeder communication system comprising a leaky feeder cable, transmitting and receiving stations and a routing controller in which signals transmitted on a first frequency from a transmitting station are conducted via the leaky feeder cable to the routing controller and retransmitted on the leaky feeder on. a different frequency.

2. A leaky feeder communication system according to claim 1 in which the routing controller retransmits at least some specific frequency incoming signals on at least one predetermined different frequency.

3. A leaky feeder communication system according to claim 1 in which the routing controller retransmits at least some of the incoming signals on a frequency determined by information carried by the signals.

4. A leaky feeder communication system according to claim 1 in which the retransmission frequency is selected in response to external input to the routing controller.

5. A leaky feeder communication system according to any proceding claim in which the leaky feeder cable serves at least two substantially independent groups of transmitting and receiving stations.

6. A leaky feeder communication system according to any preceding claim in which transmitting and-receiving stations are associated with functional devices.

7. A leaky feeder communication system according to claim 5 in which the functional devices receive and/or transit on respective fixed frequencies.

8. A leaky feeder comnication system according to claim 6 in which all the fixed frequencies for transmission differ from all the fixed frequencies for reception.

9. A leaky feeder communication system according to claim 6 in which at least one fixed frequency for transmission is the same as one fixed frequency for reception, thereby enabling communication via the leaky feeder without passing to the routing controller.

10. A leaky feeder communication system according to any proceding claim in which a plurality of leaky feeder cables are utilised.