WO2001039529A1

WO2001039529A1 - System for offering radio coverage in an environment enclosed for radio-transmission purposes

Info

Publication number: WO2001039529A1
Application number: PCT/EP2000/010307
Authority: WO
Inventors: Louis Meulstee
Original assignee: Koninklijke Kpn N.V.
Priority date: 1999-11-24
Filing date: 2000-10-19
Publication date: 2001-05-31
Also published as: NL1013659C2; AU7789200A

Abstract

System for offering radio coverage in an environment enclosed for radio-transmission purposes, for the benefit of VHF-radiotelephone traffic, comprising a number of base transceiver stations which are mounted within said enclosed environment at a number of locations, and which are capable of simultaneous transmission. All base transceiver stations are connected to one another by way of a fixed internal four-wire house-telephone line, by way of a concentrator unit, and the transmitters of the base transceiver stations retransmit the signal of an identified transmitting radiotelephone, which signal is simultaneously received on one or more receivers of the base transceiver stations, at the same frequency on all locations, by way of the concentrator unit.

Description

System for offering radio coverage in an environment enclosed for radio- transmission purposes.

The invention relates to a system for offering radio coverage m an environment enclosed for radio-transmission purposes for the benefit of VHF radiotelephone traffic [VHF = very high frequency or 30-300 MHz] , comprising several base transceiver stations, which are arranged within said enclosed environment at several locations and which are capable of transmitting simultaneously.

Such a system is disclosed m the American patent specification No. 5,432,838.

This involves the use of several base stations to achieve a more complete radio coverage in a subterranean mine or a similar environment, e.g., underwater.

In this case, simultaneous broadcasting is applied for emergency messages .

Said system, however, does not provide a solution for providing a full radio coverage in, e.g., large building complexes such as, e.g., office complexes, hospitals, prisons, tunnels and the like for the benefit of VHF radiotelepnone traffic.

There is a need, however, of a system for mobile radio communication m said complex large buildings, tunnels and the like, the users conducting direct communication with one another by way of radiotelepnones at whatever location they might be within the

Doundaπes of the system, without it being required to carry out additional actions, sucn as, e.g., the introduction of mobile or group numbers .

The invention now provides such a system, which is characterised for said purpose m that all base transceiver systems, by way of a fixed, internal four-wire house telephone, are connected to one another m a star shape, by way of a concentrator unit, and m that the transmitters of the base transceiver stations retransmit the signal received on one or more receivers of the base transceiver stations from an identified transmitting radiotelephone simultaneously at the same frequency in all locations by way of the concentrator unit .

In this manner, a relatively simple and advantageous system for mobile radio communication is provided for m complex large buildings, tunnels and the like having minimal high-frequency power, and each user having direct connection, without any additional actions, to all users and the central control within the boundaries of the service area of the system.

In particular, radio coverage may be obtained m a relatively large or specific working area without applying several channels, the government requirements relating to maximum antenna altitude and transmission capacity still being complied with.

It is noted that the application of radiotelephones as the means of communication is known per se, no time being lost due to conversation buildup, all users of the radiotelephone network being capable of listening m on a conversation and, f so required, it being possible to intervene (no congestion in the event of emergencies) .

The communication between radiotelephones, however, is limited by the maximum range thereof, and becomes worse when used m buildings.

In such cases, a choice is then sometimes made for duplex traffic, a base position in a central point receiving the signal from the transmitting radiotelephone and retransmitting it to the other radiotelephones in the network. If, however, the building in which the radiotelephones are being used is very large and, in addition, coverage is desired in cellars and/or subterranean parking places and the like, duplex traffic proves no longer to suffice.

In such case, an increase of the transmitting power of the radiotelephones might be considered, but such proves not to be the correct solution and, in addition, is not permitted due to all sorts of government regulations and rules in this area.

Below, the invention will now be explained m greater detail by reference to the drawing and the specification. By way of example, FIG. 1 schematically shows an advantageous embodiment of the invention.

FIG. 2 schematically shows the operation of the system according to FIG. 1.

By reference now to FIG. 1, a large building complex 1, 2, 3, 4, having an underground tunnel or cellar 5, is schematically shown.

E.g., sporting complexes, football stadiums, office buildings and the like might be considered.

In each building, at intentionally chosen mounting points, transceivers ZO have been placed to obtain sufficient distribution of the high-frequency field intensity. The transceivers ZO are suitable for full-duplex traffic. Moreover, measures known per se to experts have been taken to prevent possible problems caused by simultaneous transmission.

Each transceiver ZO is connected, by way of a fixed, internal four-wire house line HI, to a (usually) centrally placed Concentrator Unit 6. In this manner, a separate transmitter and receiver line is provided for.

The concentrator unit is the organ m which all four-wire line connections of the base stations enter, the connections to a fixed operating position are present, and the connection to a monitor receiver is located, which blocks the transmit command m the event of receipt from a co-user.

The concentrator unit includes the following:

DC control of both transmitter control and receipt signalling; - level compensation of receiver and transmitter audio, line monitoring of transmitting and receiving lines; phase monitoring of transmitting and receiving lines; high-frequency power monitoring of each transmitter; standard configuration having six base stations, capable of being extended to 11+17+23 etc.; emergency-current monitoring of the base stations. The length of the house- line connection between the base station and the concentrator unit advantageously amounts to under 3 km.

The transmitters operate advantageously m the 170 MHz frequency band and/or in the 80 MHz frequency band The transmitting power of the base stations is low, e.g., 500 mW ERP (Effective Radiated Power) .

To the Concentrator Unit 6 , a central control 7 is connected by way of an internal house line Hlb. The radiotelephones Pn are standard PMR and are suitable for semi-duplex traffic.

On each transceiver ZO, an antenna Cd is advantageously mounted which is suitable for said purpose, such as, e.g., a so-called Crossed Dipole antenna, which is placed within the environment enclosed for radio-transmission purposes, i.e., in the building, cellar or tunnel and the like.

Such an antenna having a specific directional pattern, and which is known to experts and therefore will not be described in further detail, has as its property that the vertically polarised field used for this application is substantially radiated out downwards and upwards. As a result, the field intensity at a distance of 800 m amounts to less than 1 dBuV, while there still is sufficient field intensity present m the building complex.

In this manner, it is possible to concentrate the high-frequency energy of the transmitters there where it is required. The operation of the system of FIG. 1 will now be explained m further detail by reference to FIG. 2.

Referring to FIG. 2, a radiotelephone Pn, which is located, e.g., in the underground tunnel 5, gives off a verbal call to two radiotelephones Pn which are located, e.g., in building 1 and building 4.

Apart from the speecn, the call also includes a lower-band tone frequency which is decoded m the respective transceivers ZO and filtered out to prevent the system coming m in response to undesirable signals. In the example of FIG. 2, tne call is received in the transceivers 2, 3 and 5 only (uninterrupted lines m bold) .

By way of the receiver lines of the four-wire house-line connection HI, the speech, combined with a "decoder ok" signal, goes to the Concentrator Unit 6. In the Concentrator Unit 6, the speech signals of the respective transceivers 2, 3 and 5 are joined to provide a constant level. One or more "decoder ok" signals m the Concentrator Unit 6 will result m a start for all transmitters ZO simultaneously.

Together with the combined speech level of the receivers, a transmitter-start signal is placed on the transmitter lines of the four-wire house-line connection HI. As a result thereof, all transmitters are switched on, and speech received on the receivers 2, 3 and 5 is retransmitted.

The radiotelephone Pn in building 1 now receives the call by way of transceivers ZO, which are placed m the buildings 1 and 2, while the radiotelephone Pn in the building 4 receives the call by way of the transceivers ZO which are placed m the buildings 2, 3 and 4 (interrupted lines in bold) .

Talking back of the, e.g., the radiotelephone Pt in building 4, takes place in an identical manner, which will not be described m further detail here.

In order to prevent possible problems with the pnase rotation of lines, as a result of which the speech becomes unintelligible, a phase-monitoring circuit may advantageously be included in the Concentrator Unit 6, as was already mentioned earlier. Such circuit is known to experts, and therefore will not be described here in further detail .

The phase control of the four-wire internal house lines HI, the "transmitter start" and the "decoder ok" signals are advantageously carried out using a DC circuit.

The system according to the invention is future-resistant, i.e., in the event of extensions or renovations of the buildings, tunnels, cellars and the like, in which the system is applied, base stations can quite simply be shifted or additionally mounted. The system according to the invention advantageously has at its disposal nine channels in the 170 MHz frequency band.

Moreover, practice shows that the system according to the invention is still able to operate at a distance of approx. 300-600 m outside the building complexes. Various modifications of the system according to the invention will be understood by experts after the above specification and drawings, and will therefore not need to oe explained m further detail .

Such modifications shall be deemed to fall within the framework and the scope of protection of the invention.

Claims

1. System for offering radio coverage in an environment enclosed, for radio-transmission purposes, for the benefit of VHF- radiotelephone traffic, comprising several base transceiver stations which are mounted within said enclosed environment at a number of locations, and which are capable of transmitting simultaneously, characterised in that all base transceiver stations, by way of fixed, internal four-wire house- elephone lines, are connected to one another, m the form of a star, by way of a concentrator unit, and m that the transmitters of the transceiver stations retransmit the signal received on one or more receivers of the base transceiver stations from an identified transmitting radiotelephone simultaneously, at the same frequency, at all locations by way of the concentrator unit.

2. System according to claim 1, characterised m that the base transceiver stations have a low transmitting power.

3. System according to claim 2, characterised m that the transmitting power amounts to approx. 500 mW ERP (Effective Radiated Power) .

4. System according to any of the claims 1-3, characterised m that the base transceiver stations are connected to antennas which are mounted within said enclosed environmen .

5. System according to claim 4 , characterised m that the antennas are "Crossed Dipole" antennas which radiate out substantially upwards and downwards .

6. System according to any of the claims 1-5, characterised m that the house-line connection between base transceiver station and concentrator unit has a length inferior to 3 km.

7. System according to any of the claims 1-6, characterised m that the transmitters operate m the 170 MHz frequency band.

8. System according to any of the claims 1-6, characterised in that the transmitters operate m the 80 MHz frequency band.

9. System according to any of the claims 1-8, characterised m that the concentrator unit is connected to a fixed control station.

10. System according to any of the claims 1-9, characterised m that the concentrator unit is connected to a monitor receiver which inhibits a transmission command m the event of receiving a coύuser.

11. System according to any of the claims 1-10, characterised in that the speech-level compensation of the receiving path is determined by the decoded receiving signal in the concentrator unit.

12. System according to any of the claims 1-11, characterised m that the phase monitoring of the four-wire internal house-telephone lines, the "transmitter start" and "decoαer ok" signals, are carried out by a DC circuit

13. System according to any of the claims 1-12, characterised m that said enclosed environment consists of a large building complex.

14. System according to any of the claims 1-13 [?] , characterised in that said enclosed environment consists of a tunnel.