FR2770671A1 - RADIOTELEMETRY SYSTEM - Google Patents

Abstract

Provided is a radio telemetry system, in which a radio telemetry system for collecting data from multiple remote units (7-12) through respective multiple radio channels, frequencies of the channels (f7 -f12) are assigned. according to the power level received in each channel so that channels having higher power are adjacent to each other in the frequency spectrum, being away from channels transmitting with lower power, so as to avoid interference between channels.Application in particular to radiotelemetry systems collecting seismic data.

Description

The present invention relates to a radio telemetry system for the

  collecting data from a network of multiple remote units, for example to collect seismic data simultaneously from seismic sensors distributed in remote locations

in the field.

  The system is a radio system which operates multiple narrowband channels which are slightly separated from each other, in the radio spectrum, for example with a center-to-center spacing of 20 kHz between the channels, in the case of a number up to 1000

data channels.

  To absorb differences in attenuation along the different transmission paths between the remote units and a common base station, the transmit power of each remote unit is variable and is adjusted so as to guarantee as much as possible a substantially optimum level receiving power in the

base station in each channel.

  However, in accordance with one aspect of the invention, variations in the received power levels of different channels due to path losses can be absorbed by assigning channel frequencies in accordance with the received power level so that channels carrying out a transmission with a higher power are adjacent to each other in the frequency spectrum, in a position distant from channels having a lower power, which makes it possible to reduce the effect

interference between channels.

  In one embodiment of the invention, in which a channel supports an uplink for the transmission of data from the remote unit to the base station, and a downlink for the transmission of data from the base station to to the remote unit, the power level received from the downlink at the remote unit being used to control its transmit power level

in the uplink.

  Preferably the power level of the channels are measured by reference to pilot signals

  individuals incorporated into each channel.

  In another aspect, the power characteristic is made as linear as possible so

  limit interference between channels.

  According to another aspect, the bandwidth of the channels is modified so as to adapt the quality of the channels with regard to the revised power level, a reduced bandwidth being used when possible with an increased rate of symbols made possible. by the superior quality of the channel so as to maintain the overall data rate required. In this way, the number of channels provided by the system in a

  given spectrum of radio frequencies can be maximized.

  According to another aspect, each channel comprises a plurality of adjacent channels situated towards the center of the total frequency band of the remote unit, the channels on each side of the central channel being available for transmitting data collected by other remote units so the remote unit can be used

  as a repeater in the radio transmission path.

  If a remote unit is used as a repeater, it is coupled via a data link to a similar remote unit, which receives data via multiple channels from said other remote units and transfers these data through the data link to the remote unit in its form as an analog baseband for further transmission. The further transmission of data in said adjacent channels is performed in a frequency band, which can be separated from the frequency of the multiple channels received in order to avoid a reduction in the sensitivity of the receiver by transmission in one of the channels. This separation of frequencies is particularly important, if we remember that the two units linked to form the repeater are preferably transceivers and

  take care of two-way communications in half

  duplex, both in the uplinks and in the downlinks. Typically, a separation of at least 2 MHz is maintained between the transmit and receive frequencies of the repeater. The downlink provides various control functions including the assignment of channel frequencies to be

  used by remote units and repeaters.

  According to another aspect of the invention, one of the channels of the telemetry system is used as

  that voice signal transmission channel.

  Preferably, the voice signal transmission channels and the data transmission channels operate simultaneously, but each use a different modulation system; for example quadrature amplitude modulation (QAM) systems for data transmission channels and a linear modulation system for data transmission channel

voice signals.

  The voice signal transmission channel can be incorporated into a downlink leading to the remote units and the channel can be used for the simultaneous transmission of control signals. Likewise an uplink can be adapted to allow the sending of voice or data signals to the base station, or for the simultaneous transmission of both

  voice and data signals in separate sub-bands.

  The base station can then be used to retransmit voice messages to other remote units in a downlink. In addition, the system can be controlled so as to achieve communication

of half-duplex voice signals.

  Other features and advantages of the

  present invention will emerge from the description given

  hereinafter taken with reference to the appended drawings, in which: - Figure 1 is a diagram of a radio telemetry system used to collect seismic data coming from a network of data collection units; FIGS. 2a to 2d show schematic representations of different transmission channels associated with a typical data collection unit, FIG. 2a representing a downlink with a control channel, FIG. 2b a downlink with a repeated control channel, FIG. 2c a data transmission uplink and FIG. 12d a repeated data transmission uplink; - Figure 3 shows a schematic representation of frequency distribution of channels in accordance with transmission losses in the channels; FIG. 4 is a schematic representation of the frequency spectrum of a data transmission channel and of the pilot tones introduced into the data transmission channel to control the loss of transmission; and FIGS. 5A to 5D show a schematic representation illustrating how the frequency spectrum of a data transmission channel can be modified to adapt to channels having different qualities. As shown in FIG. 1, this system comprises a plurality of remote units comprising a seismic network 1 to 6 connected to respective radio transmitters 7 to 12. The transmitters are arranged to transmit, during use, data towards a base station 14. Most transmitters, such as 7, 9, 11, are arranged in the line of sight of the base station 14, but in some cases an obstacle 16 prevents direct communication between the

  transmitters 8, 10, 12 and the base station 14.

  Each of the transmitters 7, 9, 11 located in the line of sight directed towards the base station 14 is assigned a single channel frequency for the transmission of data in an uplink leading to the base station. Each channel functions as a bidirectional half-duplex channel, the transmitters 7, 9, 11 being transceivers which allow the reception of control data from the base station 14 in a downlink. The control data is used to control the allocation of the channel frequencies, the power, the transmit power level of the transmitters and the switching between uplinks and

downlinks.

  The frequency spectrum of a single channel is shown in Figure 4 and has a nominal center frequency RF and two pilot signals P1 and P2 located on either side of the frequency RF in the bandwidth of the channel. These pilot signals may be pure tones, but could also be modulated tones or otherwise narrowband signals. The frequency separation between the pilot signals P1 and P2 is predetermined and is used

  in the remote unit for frequency locking.

  The remote unit searches for these two pilot signals P1 and P2 and the difference between these frequencies is measured, compared with the expected frequencies and is used to produce an error signal used to set a local clock, such as a quartz oscillator. ordered

by tension.

  The pilot signals P1 and P2 are also used to determine the transmission loss in each channel by comparing the amplitude of at least one pilot signal in the downlink, with a reference amplitude, then adjusting the transmission power of the remote transmitters 7, 9, 11 to compensate as far as possible for transmission losses, and thereby guarantee an adequate reception of power in base station 14. If the power received in base station 14 is not still not admissible due to a malfunction at the remote unit or a non-reciprocal transmission path characteristic, the base station sends a correction of

  power in the downlink.

  Simultaneously, the transmission losses in the different channels are used to adjust the allocation of power to the channels for different remote units so that to these remote units with significant different transmission losses are assigned channels at opposite ends of the spectrum. frequencies

  as shown schematically in Figure 3.

  In the drawing, it is assumed that the channels f ,, fg, fl for the transmitters 7, 9, 11 have low transmission losses and that they are grouped towards one end of the spectrum, and it is assumed that the channels fa, fo, ff2 for transmitters 8, 10, 12, served by repeaters, have high transmission losses and are

  grouped toward the opposite end of the spectrum.

  These transmitters 8, 10, 12, which are masked by an obstacle 16, communicate with the base station 14 via a repeater 18. The repeater comprises a first unit 20 in radio communication with the transmitters 8, 10 and 12, a second unit 22 in radio communication with the base station 14. In this example, the first

  and second units 20 and 22 include transmitters-

  radio receivers. The units 20 and 22 are connected to each other via a data transmission link 24. The link transmission link 24 is a transmission cable in the base band, such as for example a cable containing a plurality of electrically conductive wires although other media can be used. The units 20 and 22 are arranged so that one unit acts as a receiver while the other acts as a transmitter. Consequently, the repeater assumes two-way half-duplex communication. This ensures that hidden remote units 8, 10 and 12 can both transmit data to the base station and also receive commands from a base station command downlink channel.

through the repeater.

  Typically, the transmitter and the receiver operate at different frequencies. However, since they both operate simultaneously, there is a risk of desensitization of the receiver since the blocking performance of a receiver may be exceeded due to the proximity of a local transmitter operating at a different frequency, but possibly close. This problem can be alleviated by the use of directional antennas, but it is best solved by means of a physical separation of the first and second units (i.e. the receiver and the transmitter) by a distance sufficient to ensure that the strong off-channel signal received by the transmitter has been sufficiently attenuated so as not to impair the performance of the receiver in relation to the signals in the channel received from transmitters 8, 10 and 12. Therefore the cable link 24 serves both to allow the positioning of the units 20 and 22 in respective locations so that each of them establishes communication according to a good line of sight with the transmitters 8, 10 and 12 and the station base 14 respectively and also serves to sufficiently separate the units so that crosstalk between these units is below permissible levels. The second unit 22 can also include the installation used to receive data from a network of local seismic sensors 26 and transmit these

  data towards the base station.

  FIGS. 2a to 2d schematically represent the allocation of the frequencies in the repeater system shown in FIG. 1. The base station 14 can transmit control data towards the radio transmitters 8, 10 and 12 and also to the repeater or to each repeater 18. Consequently, the control functions can include the assignment of frequencies for transmitting or receiving repeaters, switching between the execution of uplinks and downlinks, activation or stopping of repeaters and setting transmit power levels. The downlink of the control channel has a frequency spectrum centered on the nominal center frequency fd. The second element 22 of the repeater establishes communication along the line of sight with the base station 14 and receives the data from the control channel. The frequency of this data is then reduced by conversion, and this data is transmitted at frequencies located in the baseband, via the data transmission cable 24 to the first unit 20 of the repeater. The first unit 20 uses an upward conversion of the control channel data towards a downlink of the repeated control channel having a frequency spectrum centered around a nominal frequency fd '. Additional repeaters (not shown) can receive signals from the first repeater 18 and transmit signals to this repeater and are arranged so that they can respond to the control channel at frequencies fd and fd '. Similarly, the transmitters of the seismic data network can include receiving elements also capable of responding to signals received with any frequency preassigned from the control channel or with several

  frequencies of this type including frequencies fa and fda '.

  Each of the transmitters 7 to 12 associated with a seismic network is arranged so as to transmit with a respective frequency. As shown in Figure 2c, the six transmitters shown schematically in Figure 1 (8, 10, 12, 30, 32 and 34) transmit in six narrowly spaced channels, which are adjacent to a theoretical uplink frequency fu for transmission of seismic data. The frequency of these channels is reduced by conversion by the first element 20 so that these channels can be transmitted by the data link 24. Consequently the signal transmitted by the data link comprises a plurality of weakly channels spaced. This can be considered as a frequency division multiplex data transmission. The second unit 22 receives multiplexed signals and feeds them by uplink conversion to a plurality of narrowly spaced channels centered around a frequency fa_ 'of the repeated uplink for transmitting seismic data, as shown in Figure 2d. The data received from the local seismic network 24 also undergoes a conversion in the uplink direction and in this example is retransmitted with the central frequency fa 'with additional repeated channels allocated around the central frequency. Since the transmitters 8, 10, 12, 30, 32 and 34 operate in respective channels, which are each adjacent to a central frequency, it will be noted that the frequencies of the respective incoming channels can be converted simply by mixing, with an oscillator local. This allows the frequency of independent incoming channels to be brought by conversion easily and inexpensively to another frequency for transmission in the link transmission link 24. Similarly, a mixture of frequencies can be again used to uplink incoming data for retransmission to a base station

  or their transmission to another repeater.

  The unit 22 also demodulates any signal received from the base station so as to control control signals transmitted by the base station. The repeater operates in a half-duplex mode and therefore the repeater is primarily arranged to listen to the base station so as to receive

  orders from the latter.

  When the base station is ready to receive information, it sends a command code to each of the remote units commanding them to transmit data, and also commands the repeater to change its operation so as to listen to the remote units and carry out a retransmission towards the base station until the end of a predetermined period, when it returns to listening to the station

basic.

  Therefore it is possible to provide a frequency translation radio repeater, intended to be

  used in a remote data acquisition network.

  Although the data channels are shown in Figure 4 as having a fixed bandwidth, the system can be modified to change the bandwidth of individual channels to suit the

  power level received from the channel in the base station.

  Therefore, better quality channels and lower transmission losses carry a higher number of symbol states in a quadrature amplitude modulation (QAM) system or a quadrature phase manipulation modulation system (QPSK), and therefore a narrower channel bandwidth can be used to achieve the required rate of

  data transfer for the system.

  For example, Figure 5A shows a 20 kHz channel arranged to transmit data at a rate of 60 kbits / s using a 16-symbol QAM modulation system. FIG. 5B represents a 10 kHz channel arranged so as to transmit data at the same rate of 60 kbits / s, but using a 256 QAM modulation system, which can be implemented in a quality transmission channel superior arranged to transmit data at the same rate of 60

  k.bits / s using a QPSK modulation system (4-

  QAM). Finally, Figure 5D illustrates how the adjacent channels with a bandwidth of 20 kHz each can be used in conjunction with a QPSK modulation system in each of these channels to achieve the same data rate of 60 kbits. / s in the same width

  total band of 40 kHz as in Figure 5C.

  It should be noted that a seismic telemetry system comprising up to 1000 remote units, which transmit simultaneously, requires an efficient frequency programming algorithm to allocate channels from the available bandwidth so that the performance of the system and the width yield of

  system band are optimized.

  First of all, the frequency programming algorithm must avoid the channels which are occupied by predetermined main users, i.e. users other than remote seismic units and

the base station.

  Second, the frequencies and bandwidth of the channels are affected based on loss of

  transmission in the channels, as described above.

  Thirdly, each repeater is assigned a block of adjacent channels (for example up to 7 channels) for the uplinks from the multiple hidden remote units, which are served, and a similar block of adjacent channels, the frequencies of which are converted for repeated uplinks. Similarly, the channels assigned to the remote units served by a repeater are reused in the system wherever a

  propagation conflict is not possible.

  The frequency programming algorithm is an iterative algorithm, which repeats the channel assignment process and monitors performance at the system level,

  until satisfactory performance is achieved.

Claims (12)

  1. Radio telemetry system for collecting data from multiple remote units (7-12) via multiple respective radio channels (f7-f, 2) assigned within a global radio spectrum, characterized in that frequencies of the channels are assigned in accordance with the power level received in each channel so that channels transmitting higher power are located in the vicinity of each other in the frequency spectrum, being distant from channels transmitting lower power , what   reduces the interference effect between channels.   2. System according to claim 2, characterized in   what the transmit power of each remote unit (7-   12) is variable and is adjusted so as to guarantee as much as possible a substantially optimum level of power reception at the base station (14) in each channel. 3. System according to claim 2, characterized in that a channel supports an uplink for the transmission of data from the remote unit to the base station (14), and a downlink for the transmission of data from the station base (14) to the remote unit (7-12), the power level received from the downlink at the remote unit being used to control its level   transmit power in the uplink.   4. The system as claimed in claim 2 or 3, in which the power levels of the channels are measured by reference to particular pilot signals (Pl, P2) incorporated into each channel.   5. System according to claim 4, in which the pilot signals (P1, P2) are also used for   frequency locking by remote units (7- 12).   6. Radiotelemetry system used to collect data from multiple remote units (7-12), characterized in that this data collection is carried out via multiple respective radio channels, in which the power characteristic of each channel is set to be as linear   as possible to limit interference between channels.   7. Radiotelemetry system for collecting data from multiple remote units (7-12) via respective respective radio channels (f7-f12), characterized in that the bandwidth of the channels is changed to suit the quality of the channels in terms of power level revised so that the bandwidth is reduced when an increased symbol rate is supported by higher quality channels so as to maintain an overall rate required data.   8. Radiotelemetry system for collecting data from multiple remote units (7-12) through multiple respective radio channels (f7-f, 2), characterized in that each channel is one of plurality of adjacent channels so that channels located on either side of said channel are available for transmission of data collected by others remote units.   9. Radio telemetry system for collecting data from multiple remote units via respective radio channels (f? -F12), characterized in that one of the channels of the system is used as a signal transmission channel vocal. 10. System according to claim 9, characterized in that voice and data transmission channels operate simultaneously, each of them   using a different modulation system.   11. System according to one or other of the   Claims 9 and 10, characterized in that the channel   Voice signal transmission is incorporated into a downlink leading to the remote units and this channel simultaneously carries control signals. 12. System according to any one of   Claims 9 to 11, characterized in that a connection   uplink can be adapted to allow either voice or data to be sent to the base station, or to simultaneously transmit both voice signals   and data in separate sub-bands.