GB2330985A

GB2330985A - A radio repeater comprising two transceivers connected by a data link

Info

Publication number: GB2330985A
Application number: GB9723186A
Authority: GB
Inventors: Paul George Turner; Simon James Jones; Wycliffe Timothy Budg Slingsby; Andrew Bateman; Paul Robert Clark
Original assignee: Wireless Systems International Ltd
Current assignee: Wireless Systems International Ltd
Priority date: 1997-11-03
Filing date: 1997-11-03
Publication date: 1999-05-05
Also published as: WO1999023768A1; FR2770706A1; GB9723186D0

Abstract

A first unit 20 is arranged to receive signals from remote data gathering units (eg. a seismic sensor array) 8, 10 and 12 and to send their information over a data link 24 to the second unit 22 for retransmission to the base station 14. The first unit may frequency convert each signal received to one or more other frequencies for retransmission via the data link. The incoming signals may be down converted to new frequencies. Alternatively each incoming signal may be demodulated to recover its base band signal and a plurality of base band signals may be multiplexed over the datalink. The base station can transmit control data to the radio transmitters 8, 10 and 12 and also to each repeater. The repeater units may also accept data from local sensors 26 which may be added to the data transmitted by the repeater unit. The data link may comprise electrical cables, a wave guide, a fibre optic link, a radio link or an infra red link.

Description

RADIO REPEATER The present invention relates to a radio repeater Such a repeater is suited for use in remote data acquisition systems, such as seismic data acquisition systems.

A seismic data collection system typically comprises an array of geophones. The array may be spread over a large geographical area In such an arrangement, cabled interconnection between the geophones and a recording unit becomes impractical, and consequently radio links are employed insread. A plurality of radio transmitters each associated with a respective geophone, or group of geophones, are provided to transmit data back to a base station. The radio frequencies employed are generally relatively high, for example 200MHz or more thereby restricting them to line of sight or near line of sight communication. This can present difficulties since the surface of the earth is, in general, not flat and the geophones may be located adjacent mountains or in valleys. Thus one or more of the radio transmitters may be obscured from line of sight communication with the base station. Such a transmitter is usually described as being "shadowed1,.

According to a first aspect of the present invention, there is provided a radio repeater comprising first and second units arranged to communicate with each other via a data link, wherein the first unit comprises at least a radio receiver and the second unit comprises at least radio transmitter, such that signals received by the first unit are relayed to the second unit via the data link for retransmission.

It is thus possible to provide a repeater unit which allows multiple remote radio data transmission units which are badly shadowed to operate as though they have a direct link with the base station.

As used herein, the term "data link" refers to a path or medium allowing information to be propagated in analogue or digital form.

Preferably the radio receiver in the first unit frequency converts the or each signal received from the or each remote data transmitter to one or more other frequencies for retransmission via the data link. Thus the incoming signals may be down converted to respective new frequencies. Alternatively, each incoming signal may be demodulated to recover its base band signal. The base band signal may then be processed for transmission over the data link.

This may include the multiplexing of a plurality of base band signals over the data link.

Standard multiplexing techniques, such as frequency division multiplexing or tirne division multiplexing may be used and need not be described here in detail.

Preferably the second unit converts the data received over the data link into a form suitable for the transmission to the base station. Thus the second unit may up convert each base band signal to a respective radio signal and then retransmit it. Thus the repeater is transparent to the data connection system apart from the possibility that the signals may be retransmitted on different frequencies. In general, the radio transmitter will retransmit the received radio signals at a different frequency to those received by the receiver in the first unit However the first and second units may operate on a common frequency. Mutual interference can be reduced by using directional antennas, relying on shadowing between the units, or by signal processing techniques.

Preferably the first and second units are transceivers and the data link is bi-directional. Thus the radio repeater can also relay data or commands from the base unit to the remote data collection units.

Preferably the data link comprises one or more electrical cables andior a wave guide, for example a fibre optic link, or radio or infra red links.

Preferably a second unit includes at least one data input for receiving data from one or more sensors local to the second unit. This additional data may be radio frequency modulated and transmitted to the base station in combination with the data received via the data link.

Advantageously the first unit may include at least one data input for receiving data from one or more sensors local to the first unit. This additional data may be added to the data sent over the data link.

Advantageously the second unit also comprises a data processor responsive to a receiver therein. Thus the second unit can recover control codes from signals transmitted by the base station. The control codes contain information relating to the operation of the remote units and also the radio repeater.

An embodiment of the radio repeater provides bi-directional half-duplcx communication.

Thus, the default mode of the repeater is that the second unit listens to the base station to receive a signal that instructs the remote units to send their data and also instructs the repeater to switch its operational mode so that it listens to the remote units and retransmits their signals back to the base station for a predetermined period of time before reverting to its default mode.

According to a second aspect of the present invention, there is provided a repeater unit arranged to receive data on a data link and to retransmit it, the repeater further including at least one input for receiving additional data and means for adding that data to the data transmitted by the repeater unit.

The present invention will further be described by way of example, with the reference to the accompanying drawings, which; Figure 1 is a schematic representation of a seismic data collection system, within a plurality of data collection units are shadowed from a base station; and Figure 2a to 2d schematically represent the frequency spectrums of a command channel down link, a repeated command channel down Iink, a seismic data up link, and a repeated seismic data up link, respectively.

As shown in figure 1, a plurality of seismic arrays 2, 4 and 6 are connected to respective radio transmitters 8, 10 and 12. The transmitters 8, 10 and 12 are arranged, in use, to transmit data to a base station 14. However, as shown1 an obstruction 16 prevents direct communication between the transmitters 8, 10, 12 and tbe base station 14.

In order to re-establish communication a repeater 18 is provided. Tho repeater compe * first unit 20 in radio communication with the transmitters 8,10, and 12, and second unit 22 in radio communication with the base station 14, In this example, both the first and second uruts 20 and 22 include radio transceivers. The units 20 and 22 are connected together via a data link : 24. The data link 24 is a base band relay cable, such as a cable containing a plurality of electrically conducting wires although other data transmission media may be used.

The units 20 and 22 are arranged such that one unit acts as receiver whilst the other acts as a transmitter. Thus the repeater supports half duplex bi-directional communication. This ensures that the shadowed remote units 8 to 12 can both send data to the base station and also receive commands from a command down link channel of the base station via the repeater.

The receiver and transmitter operate at different frequencies. However, since both operate concurrently, there is a danger of receiver desensitisation as the receiver's blocking performance may be exceeded by the proximity of a local transmitter operating at a different, but possibly nearby frequency. This problem is overcome by physically separating the first and second units (ie the receiver and transmitter) by a sufficient distance in order to ensure that the strong out-of-channel signal received frorn the transmitter has become sufficiently attenuated not to degrade the receiver's performance in respect of the in-channel signals received from the transmitters 8, 10 and 12. Thus the cable link 24 serves both to enable the units 22 and 20 to be positioned at respective locations such that each has good line of sight communication with the transmitters 8, 10 and 12, and the base station 14 respectively, and also serves to separate the units sufficiently such that cross talk between them is within acceptable levels. Altematively or additionally directional antennas may be used to reduce the risk of receiver desensitisation. Thus a shorter cable may be used.

The second unit 22 also may include the facility to receive data from a local seismic sensor array 26 and to transmit this data to the base station.

Figures 2a to 2d schematically illustrate the frequency allocation in the system shown in figure 1. The base station 14 can transmit command data to the radio transmitters 8, 10 and 12, and also to the or each repeater 18; Thus the control functions can include the allocation of repeater receive and transmit frequencies, switching between serving up links and down Jinks, waking up or powering down repeaters and setting transmit power levels. The command channel down link has a frequency spectrum centred around nominal centre frequency f,. The second element 22 of the repeater is in line of sight communication with the base station 14 and receives the command channel data, This data is then frequency down converted and transmitted at base band frequencies over the data cable 24 to the first unit 20 of the repeater. The first unit 20 upconverts the command channel data to a repeated command channel down link having a frequency spectrum centred around nominal frequency f'. Additional repearers (not shown) may receive signals from and transmit signals to the first repeater 18 and are arranged to be responsive to the command channel at frequencies fd and fd'. Similarly, the transmitters of the seismic data array may include receiver elements also responsive to signals received on any one or more pre-allocated command channel frequencies including the frequencies fd and f,'.

Each of the transmitters 8, it and 12 associated with a seismic array is arranged to transmit on a respective frequency. As shown in figure 2c, the six transmitters schematically illustrated in figure 1(8,10,12, 30, 32 and 34) transmit on six closely spaced channels adjacent a notional seismic data up link frequency f,. These channels are frequency down converted by the first element 20 in order that they can be transmitted along the data link 24.

Thus, the signal transmitted along the data link comprises a plurality of closely spaced channels. This can be regarded as frequency division multiplexed data transmission. The second unit 22 receives the multiplexed signals and up converts them to a plurality of closely spaced channels centred around a repeated seismic data up link frequency fu' as shown in figure 2d. The data received from the local seismic array 26 is also up converted and in this example is retransmitted at the centre frequency f, with the additional repeated channels being allocated around the centre frequency.

Given that each of the transmitters 8, 10, 12, 30, 32 and 34 operates on a respective channel, each located adjacent a centre frequency, it will be appreciated that the respective incoming channels can be frequency converted merely by mixing with a local oscillator. This allows multiple independent incoming channels to be easily and inexpensively converted to another frequency for transmission over the data link 24, and similarly, frequency mixing can again be used to up convert the incoming data for retransmission to a base station or transmission to a further repeater.

The unit 22 also demodulates any signal received from the base station in order to check for command signals sent from the base station. the repeater operates in halfduplex mode and consequently the repeater is arranged, primarily, to listen to the base station in order to receive commands therefrom.

When the base station is ready to receive information, it sends a command code to each of the remote units instructing them to transmit data, and also instructs the repeater to charge operation so that it listens to the remote units and retransmits to the base station until the end of a predetermined pcriod, when it reverts to listening to the base station.

It is thus possible to provide a frequency translating radio repeater for use in a remote data acquisition network.

Claims

CLAIMS 1. A radio repeater comprising first and second units arranged to communicate with each other via a datalink, wherein the first unit comprises at least a radio receiver and the second unit comprises at least a radio transmitter, such that signals received by the first unit are relayed to the second unit via the data link for retransmission.
2. A radio repeater as claimed in claim 1, in which the radio receiver in the first unit frequency converts the or each signal received from a or each remote data transmitter to one or more other frequencies for transmission via the data link.
3. A radio repeater as claimed in claim 1, in which the radio receiver in the first unit down converts to base band the or each signal received from a or each remote data transmitter to one or more other frequencies for transmission via the data link.
4. A radio repeater as claimed in claim 2 or 3, in which the radio receiver down converts the received signals to respective new frequencies.
5. A radio repeater as claimed in claim 1, in which the radio signals received by the first unit are frequency converted and transmitted over the data link in a multiplexed form.
6. A radio repeater as claimed in any one of the preceding claims in which the second unit converts the data received over the data link into a form suitable for transmission to a base station.
7. A radio repeater as claimed in claim 6, when dependant on claim 4 or 5, in which the second unit up converts signals received over the data link.
8. A radio repeater as claimed in any one of the preceding claims in which the second unit retransmits the received radio signals at a different frequency to those received by the first unit.
9. A radio repeater as claimed in any one of claims 1 to 7, in which the first and second units operate on a common frequency.
10. A radio repeater as claimed in any one of the preceding claims, in which mutual interference between the first and second units is reduced by using directional antennas, or by using signal processing, or by spatial separation.
11. A radio repeater as claimed in any one of the preceding claims, in which the first and second units are transceivers and the data link is bi-directional.
12. A radio repeater as claimed in any one of the preceding claims in which the data link comprises one or more of electrical cables, a wave guide, a fibre optic link, a radio link and an infra red link.
13. A radio repeater as claimed in any one of the preceding claims in which the second unit includes at least one data input for receiving additional data from one or more sensors local to the second unit.
14. A radio repeater as claimed in claim 13, in which the additional data is radio frequency modulated and transmitted to the base station in combination with the data received via the data link.
15. A radio repeater as claimed in any one of the preceding claims in which the first unit includes at least one data input for receiving additional data from one or more sensors local to the first unit.
16. A radio repeater as claimed in claim 15 in which the additional data is added to the data sent over the data link.
17. A radio repeater as claimed in any one of the preceding claims in which the second unit includes a data processor responsive to data from the receiver in the second unit for recovering and acting in response to control codes transmitted by a base station.
18. A radio repeater as claimed in claim 17, in which the radio repeater provides bi directional half duplex communication, and has a default mode in which the second unit listens to a base station to receive a signal which instructs remote units to send their data and also instructs the repeater to switch to an operational mode so that it listens to the remote units and retransmits their signals back to the base station for a predetermined period before reverting to its default mode.
19. A radio repeater as claimed in any one of the preceding claims in which the first and second units are such that each respectively is capable of receiving and transmitting signals simultaneously on a plurality of contiguous channels.
20. A radio repeater as claimed in claim 19 in which the second unit further includes at least one input separate from the data link for receiving data to be transmitted on one channel, the signals received on the data link being transmitted in channels on either side of said one channel.
21. A telemetry system comprising a base unit for receiving data, at least one remote unit for transmitting data to the base unit and at least one radio repeater as claimed in any one of the preceding claims.
22. A radio repeater unit arranged to receive data on a data link and to retransmit it, the repeater further including at least one input for receiving additional data and means for adding that data to the data transmitted by the repeater unit.