FR2823621A1 - Multimedia wireless system outdoor unit electromagnetic signal frequency converter having local oscillator/first mixer converting second frequency and mechanism modifying local oscillator frequency within band. - Google Patents

Abstract

The frequency conversion system has a fixed frequency local oscillator (19,20) and a first mixer (17,18) receiving a first frequency input and converting to a second input frequency. There is a mechanism (23,22) modifying the local oscillator frequency within the frequency band.

Description

signals. The present invention relates to a device for converting

  frequencies of electromagnetic signals, more particularly a device of this type usable in a system for transmitting / receiving electromagnetic signals operating in frequency bands of the order of about ten GHz. At present, telecommunications of digital or analog wireless signals of interactive type are developing rapidly. The equipment for these mass market telecommunications systems must be available at a reasonable cost. This is the case, in particular for the receiver / transmitter of the user who must communicate with a base station, most often via a telecommunications satellite or within the framework of a multichannel multipoint distribution system. ("multipoint multichannel distribution system" or MMDS in English), a local multipoint distribution system ("local multipoint distribution system" or LMDS in English) or a multipoint video distribution system ("multipoint video distribution system "or MVDS in English), well known in itself. These communications are generally carried out in the microwave domain. Thus, in the context of the MMDS system, we use

  o frequency bands around 40 GHz.

  A system for receiving / transmitting basic electromagnetic signals comprises, as shown in FIG. 1, a frequency conversion device 2 generally located outside the dwelling, included in a system 1 known under the term ODU for "Out Door Unit" in English. This frequency conversion device 2 comprises a first conversion stage 3 comprising a first mixer 4, namely a harmonic mixer of order 2, on one of the channels, for example, the downlink 5 and a second conversion stage 6 comprising a second mixer 7 of the type 2 harmonic mixer, on o the other channel, namely the uplink 8, each of the mixers 4 and 7 being connected to a clean local oscillator 9, 10. The system 1 is connected on the one hand to a reception / transmission antenna 11 and, on the other hand, by connection means such as a coaxial cable 13, to a so-called indoor unit 12 or IDU for "Indoor Unit" generally located at interior of the house. This basic system has been modified in many ways, in particular to make it cheaper and easier to make. One of the main modifications made to this system was to use a single local oscillator in place of oscillators 9 and 10. An embodiment of this new system has been described in particular in French patent application No. 98 06785 in the name

from THOMSON multimedia.

  o If the system described in the French patent application mentioned above works perfectly correctly in an MVDS type system according to the MPT1560 standard, the standardization bodies have decided to extend the bandwidth allocated to MWS systems for "Multimedia Wireless System" "in English, with a value of 1 GHz, which now gives a useful frequency band between 40.5 G Hz and 43.5 G Hz. As a result, the new signal transmission / reception systems electromagnetic must be able to meet this new standard while remaining compatible with the old standard which covered the frequency band between 40.5 GHz and 42.5 GHz. In addition, these new devices must be able to support deployments, of the FDD type for "Frequence Division Duplex" in English, symmetrical or asymmetrical or deployments of the TDD type for "Time Division Duplex" in English language. All of the above elements have therefore led standardization bodies to allocate to each operator a pair of frequency bands called a block having a bandwidth B spaced from a duplex difference of fixed value, namely 1.5 GHz. in the present case, as shown in FIG. 2. Therefore, each operator OpA, OpB, OpC, OpD, OpE will be allocated a block for transmission and a block for reception of equal value B. the blocks being shifted by 1.5 GHz o but which may have different B values (OpB, OpC), as shown in FIG. 3. In fact, the systems for transmitting / receiving electromagnetic signals which have been developed for MVDS subscribers according to the MPT1560 standard currently available on the market, do not meet all the conditions imposed by the new

standard as described above.

  s Consequently, the object of the present invention is to provide a new device for converting frequencies of electromagnetic signals which meets the conditions imposed by the new

  standard while providing a low-cost, universal type subscriber terminal.

  Thus, the subject of the present invention is a device for converting frequencies of electromagnetic signals of the type comprising at least a first local oscillator of fixed frequency and a first mixer receiving on a first input the frequency to be converted and on a second input the frequency of the oscillator, characterized in that it comprises means acting on the frequency of the local oscillator to modify by step said frequency within a frequency band. According to a preferred embodiment, the means acting on the frequency of the local oscillator consist of a frequency synthesizer sweeping a given frequency band and a second mixer receiving on a first input the frequency of the local oscillator and on a second enters the frequency of the synthesizer. Preferably, the first and / or second mixers are harmonic mixers

of order 2n.

  On the other hand, the device further comprises a filtering means at the outlet of the second mixer. It also includes a coupling device for sending the frequency from the second mixer to a first channel or uplink and to a second channel or downlink, each channel comprising a first mixer, the uplink outputting the first mixer at a higher frequency. at the frequency to be converted and the downlink o giving at the output of the first mixer a frequency

  lower than the frequency to be converted.

  On the other hand, the operating frequency band is divided into two frequency sub-bands with a frequency sub-band for the uplink and a frequency sub-band for the

downward path.

  s According to another characteristic of the present invention, the device comprises a second local fixed-frequency oscillator connected

  to the second mixer via a switching means.

  Preferably, the frequencies of each local oscillator are chosen so as to be able to affect the two frequency sub-bands

  o an uplink and a downlink and vice versa.

  The present invention also relates to an electromagnetic signal transmission / reception system comprising an outdoor unit comprising a frequency conversion device as described above and an indoor unit comprising an interface capable of receiving a downlink signal and an uplink signal, each transposed into frequencies by the conversion device as well as control messages comprising control data from the frequency synthesizer. In addition, the control messages include control data from the

  switching means between the two fixed frequency oscillators.

  Other features and advantages of the present invention

  will appear on reading the description of an embodiment

  preferential, this description being made with reference to the drawings below

  annexed in which: FIG. 1, already described, represents a simplified diagram of a system for receiving / transmitting electromagnetic signals according to the

basic principle.

  Figure 2 is a diagram explaining the principle of distribution of

  frequencies according to the new MVDS standard.

  Fig ure 3 is a diagram giving an example of allocation of

  n / a pair of blocks under the new MVDS standard.

  s Figure 4 is a block diagram of a device for

  frequency conversion explaining the principle of the present invention.

  FIG. 5 represents the frequency plan in which the conversion device of FIG. 4 can operate, within the framework of an MVDS system. Figure 6 schematically represents the frequencies in

  which works the device of figure 4.

  FIG. 7 is a block diagram of a frequency conversion device according to a preferred embodiment of the

o present invention.

  Figure 8 is a block diagram of an interface used with

  the conversion device of FIG. 7.

  FIG. 9 represents the spectrum at the output of the harmonic mixer as part of the frequency conversion device of the

figure 7.

  To simplify the description, the same references are used

  in the figures to designate elements fulfilling identical functions. On the other hand, in the present application, the term "downlink o" or "downlink signal" is interpreted as a signal carried on a first channel from a receiving antenna while the term "uplink signal" or "uplink" relates to a signal carried on a second channel from an indoor unit in the home. In Figure 4, there is shown the block diagram of a device 14 for converting frequencies of electromagnetic signals according to the present invention. This device 14 is intended, as in the context of the device 1, to be connected, for example on the left side, to a transmission / reception antenna not shown and, on the right side, to a unit generally located inside of housing. As a result, the device 14 comprises a first channel 15, called the downlink, connected on the one hand to the reception antenna and, on the other hand, to the indoor unit by known means such as a diplexer. It also includes a second channel 16 known as the uplink channel which connects, via the diplexer, the indoor unit on the side

  right to the left side transmit antenna.

  As shown in the drawings, the downward path 15 essentially comprises a first mixer 17 which receives on a first input a frequency F1 and on a second input a frequency FOL coming from a circuit which will be described later. The frequency at the output of the mixer 17 is sent in a known manner to an amplifier at o intermediate frequency and then to a filtering means so as to obtain an intermediate frequency in the BIS band or Satellite Intermediate Band. The uplink 16 also includes a mixer 18. This mixer 18 receives, on an input, a baseband signal from the indoor unit, this baseband signal having passed through at least one bandpass filter in known manner centered on the frequency of the uplink baseband central signal and then an amplifier. On the other hand, on its other input, the mixer 18 receives a signal at a frequency FOL from the same circuit as for the mixer 17, which circuit will be described later. A signal is obtained at the output of the mixer 18 which is sent to a power amplifier so as to obtain at the output a transmission signal at a frequency F2 located in the band of

  operating frequencies of the transmit / receive system.

  We will now describe a schematic embodiment of the common circuit giving the frequency FOL. This circuit comprises at least one common local oscillator, the frequency of which is transposed to obtain frequency agility, namely, as shown in FIG. 6, making it possible to obtain, using the same circuit, different frequencies F1 inside d 'a sub-band referenced Zone A as well as different frequencies F2 inside a sub-band referenced Zone B. knowing that according to the new standard, F2 = F1 + F', with for F 'a constant value of , through

example, 1.5 GHz.

  As shown in FIG. 4, the circuit giving the frequency FOL sent simultaneously on the uplink and on the downlink, consists of at least one local oscillator LO1 or LO2 referenced 19 or 20. The function of the two oscillators will be explained in s detail below. One of the oscillators, namely the LO1 oscillator 19, is connected via a switching means 21 on a mixer 22. On the other input of the mixer 22 is applied a signal of determined frequency Fsynhè coming from a synthesizer 23. An FOL signal is obtained at the output, the value of which is equal, for example, to FLO1 + Fsynhé This signal of o FOL frequencies is filtered through a filter 24 so as to eliminate the undesirable lines. The thus filtered frequency signal FOL is sent via a coupling device 25 and amplifiers 27, 28

  simultaneously to the downlink 15 and to the uplink 16.

  The synthesizer 23 is constructed so as to be able to scan all of the frequencies located in one of the sub-bands, namely zone A or zone B. It can therefore scan, in the embodiment shown, a band of frequencies of 1.5 GHz, for example. The frequency output from the synthesizer depends on control information from the indoor unit, as will be explained below. Therefore, it is possible to modify the frequency of the local oscillator so as to be able to scan the allocated space with frequencies F1, F2 varying in the frequency band of zone A and zone B. knowing that according to the new MVDS standard, the difference between F1 and F2 is a constant. Thus, the allocated frequency plan in the new MVDS frequency band s varying between 40.5 GHz and 43.5 GHz with a fixed rising intermediate frequency band, for example at 300 MHz to remain compliant with the DVB-RC standard for "Digital Video Broodcast- Return Channel" in English is shown in FIG. 5. The use of the second local LO2 20 oscillator makes it possible to increase the number of

  o operators by reversing the rising and falling zones.

  Thus, the oscillator LO1 will operate in reception in zone A and in transmission in zone B while the local oscillator L02 will operate in transmission in zone A and in reception in zone B. To do this, an adequate choice of the frequency of each oscillator will be performed. The choice can be made using the following equations: In Case 1: F1 received / F2 issued

With F2 = F1 + 1.5 GHz.

IF_RX = F1 - FL01

IF_TX = F2 - FL01

  Case 2: F1 sent / F2 received o IF_RX = FL02 - F2

IF_TX = FL02-F1.

  The values of the upward and downward intermediate frequency bands F1 being determined by the standard used, in particular the DVB-RC standard, it is easy to determine for the two cases

  above the frequency of the local oscillator FL01 and associated FL02.

  With the circuit of FIG. 4, thanks to an auxiliary frequency synthesizer, it is possible to transpose in an agile manner, the sum component constitutes the frequency of one of the local oscillators with the frequency of the synthesizer and to scan all the spectral space allocated. In this case, the total excursion of the frequency synthesizer corresponds

  substantially to the allocated spectral space.

  According to another characteristic of the present invention, to facilitate the realization of the various circuits such as the synthesizer and the local oscillators, the mixers are constituted by mixers under harmonic of order 2 "which make it possible to divide by 2" the frequency of

  the local oscillator and therefore the excursion of the frequency synthesizer.

  A mode will now be described with reference to FIGS. 7 to 9.

  of preferred embodiment of the present invention.

  This embodiment relates to an MWS system (for so Multimedia Wireless System) operating in a frequency band between 40.5 GHz and 43.5 GHz according to the new standard. The particular case described relates to a symmetrical FDD (Frequency Division Duplex) type deployment system having a block width of 300 MHz. The system conventionally uses an intermediate frequency F1 which is in the frequency band BIS (Satellite Intermediate Band) of between 0.95 / 2.15 GHz in the downward direction and an intermediate frequency of between 400 and 700 MHz in ie upward direction to remain compliant with the DVB-RC standard (for Digital

Video Broadcast-Return Channel).

  As shown in FIG. 7, the external unit 20 or ODU o (for Outdoor Unit) essentially comprises a frequency conversion device 21 of the type of that described in FIG. 4 connected on its left side to a non-transmitting antenna -represented by means of a iplexcur 23 and on its right side to the internal unit, by means of the diplexer 22. The frequency conversion device comprises, like that of FIG. 4, a downlink 210 connected between diplexer 23 and diplexer 22. Downlink 210 includes a low noise amplifier 211 (a Low Noise Amplifier "or LNA) receiving as input a signal from the antenna at a frequency F1 between 40.5 and 42 GHz or between 42 and 43.5 GHz depending on the operating mode, ie depending on whether reception takes place in zone A or in zone B. The output of amplifier 211 is sent at the input of a mixer 212 which s era, according to a preferred embodiment, a 2n order harmonic mixer. The second input of the mixer 212 receives a frequency signal FLO_RX from a circuit which will be described in more detail below. The output of the mixer 212 is sent to a filter 213 and then to an intermediate frequency amplifier 214. The filter 213 allows filtering over the passband, namely the 0.95 / 2.15 GHz band, as mentioned above. The amplifier output

  intermediate frequency 214 is sent to the input of the diplexer 22.

  o On the other hand, the frequency conversion device comprises an uplink channel 215 connecting the diplexer 22 to the diplexcur 23. This uplink channel carries the emission signal or uplink signal in baseband coming from the indoor unit through the intermediate of the diplexer 22. As shown in FIG. 7, the baseband signal is amplified by an amplifier 216. The output of the amplifier 216 is connected to a first input of a mixer 217 from which the other input receives a signal from a PLL 218 operating at a high frequency of 2.6 GHz. The output of the mixer 217 sends a frequency signal varying between 3 and 3.3 GHz at the input of an amplifier 219 and a bandpass filter 220. The output of the bandpass filter is sent to the input of a mixer 221 which receives on o its other input a signal at the frequency FLO coming from a circuit which will be described in more detail below. The output of the mixer 221 is sent to a filter 222 then, in the embodiment shown, to two amplifiers 223, 224 mounted in parallel so as to obtain an output signal at the desired power, this signal having a frequency F2 lying either in the frequency band 42 to 43.5 GHz or 40.5 to 42 GHz depending on the local switched oscillator, as will be explained in more detail below. The circuit making it possible to obtain the frequency FLO of emission or reception consists, as shown in FIG. 7, of a first local oscillator 230 and of a second local oscillator 231 whose roles will be explained later. The output of each local oscillator 230 or 231 is connected to one of the two terminals of a switch 232, the third fixed terminal of which is connected to the input of a mixer 233. The switch 232 makes it possible to connect the input of the mixer 233, namely the oscillator 230, i.e. oscillator 231 as a function of the emission frequency bands and of

  selected reception, as explained with reference to Figure 4.

  In the embodiment shown, the local oscillator 230 has a fixed frequency of 10.2 GHz while the local oscillator 231 has an operating frequency of 9 GHz. These low frequencies could have been chosen because the mixers 233, 212 and 221 are mixers with harmonics of order 2, which makes it possible to divide the frequency of each local oscillator 230, 231 by 4 and facilitates the filtering of unwanted lines by

  outlet of the mixer 233, as shown in FIG. 9.

  According to the present invention, a frequency synthesizer 234 operating in a frequency band from 1.5 to 2.1 GHz, as shown in FIG. 7, is connected to the other input of the mixer 233. The output of the mixer 233 is sent through a filter 235 to a coupling device 236 making it possible to send said signal both to the uplink via an amplifier 237 and to the downlink via another amplifier 238. This circuit operates identically to what has been described with reference to FIG. 4. On the other hand, as shown in FIG. 7, to control the synthesizer 234 as well as the switch 232, the device for converting frequencies has inside the ODU 20 a first filter 239 receiving, via the diplexer 22, a signal from the internal unit as will be described below. The signal from the filter 239 is sent to a filtering circuit 240, in the embodiment shown, which makes it possible to demultiplex the three control signals which are then demodulated in a demodulator 241 so as to obtain a control signal from the switch 232 and two 234 frequency synthesizer control signals for positioning the system in the

  frequencies allocated to a specific operator.

  In the embodiment of FIG. 7, to simplify the manufacture of the circuits, the various mixers 212, 211, 233 are mixers of the sub harmonic type of order 2. This makes it possible to produce the iocal oscillators 230 and 231 at frequencies who are a quarter of the

  frequency F1 or F2 chosen, as explained above.

  An embodiment of the interface located in the indoor unit will now be described with reference to FIG. 8. This interface makes it possible to send control signals to the diplexer 22, as shown. This interface essentially comprises a microprocessor 250 responsible for simultaneously managing: the fine adjustment of the frequency of the uplink channel 215 by the blank of a PLL circuit 259 and the power level emitted from the uplink channel 215 by the blank of a digital analog converter 251. The other circuits such as controller, ASIC, modulator and amplifiers are well known to those skilled in the art and will not be described again in detail since they are not essential for understanding the invention. On the other hand, the microprocessor 250 which generates the frequency of the channels allocated to the subscriber, both in reception and in transmission, can generate

  control messages which will be sent to the filter 239 described above

  above. To generate the frequency of the channels allocated to the subscriber, three pieces of information are necessary for the ODU 20, namely, the control of the switch 232 making it possible to switch the circuit between the oscillator 230 and the oscillator 231 depending on whether the subscriber operates in transmission in zone A and in reception in zone B or in transmission in zone B and in reception in zone A, as explained above. The other two pieces of information are the control data of the frequency synthesizer, namely data and clock information. This information is low-speed information which can be transposed onto subcarriers. Thus, as shown in FIG. 8, signals from the microprocessor 250 are sent as input to a first modulator of the FSK 252 type, of a second modulator of the FSK 253 type and of a third modulator of the FSK 254 type. Each signal from the three modulators 252, 253, 254 is sent respectively to filtering means 255, 256, 257 and the outputs of the three filtering means are sent to an adder 258 then to the diplexer 22 so as to be inserted into the frequency multiplex of signals sent to the ODU. The signals from the diplexer 22 are demultiplexed and demodulated at the level

  ODU 20, as described above.

  The present invention has been described with reference to a particular embodiment for a symmetrical FDD deployment and meeting the o MVDS standards in the frequency band 40.5 GHz to 42.5 GHz and DVC.RC. It is obvious to those skilled in the art that the invention can be applied

  other types of deployments and other frequency bands.

Claims (7)

  1 - Device for converting the frequency of electromagnetic signals of the type comprising at least a first local oscillator of fixed frequency (19, 20; 230, 231) and a first mixer (17,18; 212, 221) receiving on a first input the frequency to be converted and on a second input the frequency of the local oscillator, characterized in that it comprises means (23, 234; 22, 233) acting on the frequency of the local oscillator to modify said frequency by steps inside a o frequency band.   2 - Device according to claim 1, characterized in that the means acting on the frequency of the local oscillator consist of a frequency synthesizer (23, 234) sweeping a given frequency band s and a second mixer (22, 233 ) receiving on a first input the frequency of the local oscillator (19, 20; 230, 231) and on a second   input the frequency of the synthesizer.   3 - Device according to any one of claims   o previous, characterized in that the first eVou second mixers (17, 18; 212, 224, 22, 233) are mixers in order 2 harmonics.   4 - Device according to any one of claims 1 to 3,   characterized in that it comprises a filtering means (24, 235) at the outlet of the second mixer.   - Device according to any one of claims 1 to 4,   characterized in that it comprises a coupling means (25, 236) for sending the frequency from the second mixer to a first channel or uplink "and simultaneously to a second channel or" downlink "channel, each channel having a first mixer, the "uplink" channel giving at the output of the first mixer a frequency greater than the frequency to be converted and the "descending" channel giving at the output of the first mixer a frequency less than the frequency to be converted.   6 - Device according to any one of claims 1 to 6,   characterized in that the operating frequency band is divided into two frequency sub-bands (Zone A, Zone B) with a frequency sub-band o for the "uplink" channel and a frequency sub-band for the "downward" path.   7 - Device according to any one of claims 5 and 6,   characterized in that it comprises a second local oscillator of fixed frequency connected to the second mixer via a switching means. 8 - Device according to claim 7, characterized in that the frequencies of each local oscillator are chosen so as to be able to o assign the two frequency sub-bands to a "rising" channel and to   a "downward" path and vice versa.   9 - System for transmitting / receiving electromagnetic signals, comprising an outdoor unit comprising a device for converting   frequencies according to any one of claims 1 to 8, and a unit   interior comprising an interface, capable of receiving a downlink signal and an uplink signal, each transposed in frequency by the conversion device as well as control messages, characterized in that the control messages include command data so frequency synthesizer.   - System according to claim 9, characterized in that the control messages additionally comprise commando data of the