Reception of radio frequency signals, for example broadcast signals received from a satellite, with an interactive return link using a spread spectrum protocol.

0001The present invention relates to an installation of transmission / reception of microwave radio signals.

0002Currently, the distribution of digital television by terrestrial (for example according to DVB-T or DVB-T2 standards) or by satellite (for example according to DVB-S, DVB-S2 or DVB-SH) is widely used worldwide. Many devices are installed in millions of users.

0003With regard to the land, the devices installed are mostly reception devices which comprise an outdoor unit including a receiving antenna (e.g., antenna "rake" receiver) which transmits microwave frequency modulated radio signals to a commonly known indoor unit digital terrestrial decoder or STB ( "Set Top Box" in English) via a coaxial cable.

0004As for the satellite channel, the installed devices are mostly receiving devices that feature an outdoor unit including a parabolic reflector which focuses the modulated microwave signals, the source called cornet, an LNB (from the English " low Noise block "which results in reception of block), the LNB transforming the microwave signals received in intermediate satellite band into electrical signals in order to transmit, via a coaxial cable to the satellite STB decoder.

0005Whether one is in transmission through terrestrial and satellite, the decoder includes a demodulation block (DVB-T, DVB-T2, DVB-S, DVB-S2 or DVB-S), which extracts a modulated signal "useful" in the modulated signal transmitted on the coaxial cable and demodulates the "useful" signal extracted. The signal "useful" demodulated can for example be used for displaying video images on a TV screen.

0006Broadcast offers digital television programs by terrestrial and satellite are now essentially purely passive, that is to say, unidirectional ( 'one-way service "in English).

0007However, it may be helpful to offer services requiring a return channel; so for example interactive services (voting, content consumption conditional access by key exchange, new services such as video on demand orders). In addition, the return path may find particularly interesting applications in the field of machine to machine communications ( "machine to machine" in English) or M2M to control some devices (alarm, heating, ...) and / or recover data measured by sensors or counters (gas, electricity ...) present in households.

0008A known solution to this problem is to use a return path using a broadband or DSL connection provided by fixed telephony operators (RTC or "Switched Telephone Network") or a type of GPRS / UMTS provided by mobile operators. This solution requires additional hardware and an additional subscription; Moreover, the telephone exchange is not particularly suitable for transmission of low-bulk messages such as voting or control messages (relatively high cost, network congestion problems ...).

0009On land, the use of a more appropriate solution, such as DVB-RCT technology (described in ETSI European Standard EN 301 958) failed for reasons of cost of the necessary infrastructure.

0010Most satellite TV offerings does not include a return path. However, one can cite an example of bidirectional broadcast system satellite television described in the patent document<patcit id="pcit0001" dnum="EP0888690A"><text>EP0888690</text></patcit> ; this system uses a forward channel wideband Ku and a narrow band return path L. This system is bulky, complex and expensive in so far as it requires the presence of two reflectors (each for Ku-band and L) or a dedicated reflector comprising a reflector capable of receiving Ku band signals and incorporating an L-band transmit antenna the system also results in the presence of two physical channel data routing, one of the Ku-band antenna to the decoder inside the house and the other from the decoder to the band antenna L. understandably, this type of installation involves a complete change of standard systems currently equipping homes and a significant additional cost.

0011Another example of bidirectional broadcast system satellite television is described in patent application <patcit id="pcit0002" dnum="WO2011076791A"><text>WO2011076791</text></patcit> filed by the applicant. This system uses a forward channel wideband Ku or Ka and a return path in close S-band or C-band signals are multiplexed on the same coaxial cable. The gain of the reflector to receive microwave signals in Ku or Ka band is used to transmit the signals back on track in the S-band or C-band amplification Despite the gains obtained by this solution, the fact remains that the loss of power of the useful signal on the return channel (including through the coaxial cable) is important and it is necessary to have sufficient amplifier in the outdoor unit level. In addition, each case used within the home should be equipped with a modulator operating according to an asynchronous protocol to multiple random access tape spread by modulation type SPREAD ALOHA, this type of modulator is relatively expensive.

0012In this context, the present invention aims to provide an installation reception of microwave radio signals also to ensure the emission reverse channel microwave radio signals efficiently in terms of performance, easily adaptable to an existing system serving one or multiple users, scalable and inexpensive.

0013To this end, the invention proposes an installation for transmission / reception of microwave radio signals comprising:<ul><li>a transmission / reception unit comprising:<ul><li>∘ means able to receive electrical signals from the processing of radio signals received terrestrially or via satellite, known path into electrical signals go; </li><li>∘ a demodulator adapted to demodulate the electric signals according to a first protocol modulation / demodulation;</li><li>∘ a modulating electrical signals according to a second protocol modulation / demodulation different from said first protocol, said second protocol being a protocol spread spectrum, said modulator modulating the signal demodulated by said demodulator;</li><li>∘ means for transforming said electrical signals modulated according to said protocol to spread spectrum signals in said electrical return path, by radio signals capable of being transmitted via satellite;</li></ul></li><li>at least one housing including a modulator capable of modulating electrical signals according to said first protocol modulation / demodulation;</li><li>a coaxial cable connecting the transmission / reception unit and the housing adapted to:<ul><li>∘ conveying said electrical signals in forward link of said transmission / reception unit to said housing;</li><li>∘ convey electrical signals from said modulator according to said first protocol of said housing to said transmission / reception unit.</li></ul></li></ul>

0014Thanks to the invention, an installation is advantageously used using two types of modulation / demodulation, for example modulation / demodulation based on a protocol suitable for wireless communication short distance (ZigBee, KNX or otherwise) to the first modulation / demodulation and modulation / a demodulation based on a spread spectrum protocol such as an asynchronous protocol to multiple random access band spread modulation type sPREAD ALOHA using interference removal techniques (note that the demodulation using this removal techniques interference is carried out at the satellite hub and will not be described in more detail in the present application). By short distance means a distance of less than 300m, and preferably less than 100m. The casing is preferably a casing located inside of a building (ie in an apartment) and the transceiver unit is advantageously located outside or close to the antenna. Thus, the unit of transmission / reception via its own demodulator will recover a digital signal (contained in the modulated signal at the housing) and modulate this digital signal via the modulator. Being back to a digital signal at the outdoor unit transmitting / receiving eliminates noise and error signal and use a low power amplifier for amplifying the modulated signal that contains very little noise.

0015The installation uses a pathway signal scattering go to users who may be terrestrial (eg, in a frequency band between 470 and 862 MHz) or satellite (eg, Ku or Ka band) and a satellite return path ( frequency band for example between 1.5 and 5 GHz, that is to say the frequency of the S-band, the use of this frequency band is not exhaustive). Note that the frequency band of the satellite return path will be chosen so that it is sufficiently far from the tape used in forward link (eg emission S-band reception and Ku-band) so we did no need to use a diplexer ( "diplexer" in English) to avoid interference from one channel to another.

0016The advantages of such an installation are multiple.

0017It uses proven technology in forward dissemination to users to transmit large signals such as television signals and a satellite return path for including the user to interact with the broadcast channel and transmit quite short messages, the modulation technique is based on a spread spectrum protocol such as an asynchronous protocol to multiple random access tape spread modulation type sPREAD ALOHA. Such a protocol is described for example in document<patcit id="pcit0003" dnum="US20100054131A"><text>US2010 / 0054131 (Rio del Herrero et al.</text></patcit>).

0018In addition, the necessary means for the modulation based on a spread spectrum protocol are only installed in the transmit / receive unit (s) unit (s) user (s) being equipped (s) of a modulator using a modulation technique preferably requiring implementation means having a cost and a lower complexity (modulation / demodulation suitable for wireless communication such as ZigBee or KNX) compared to the modulation means based on a spread protocol spectrum. The advantage of such a system is that it allows a single transmitter unit / outdoor reception and several boxes located inside (eg in different apartments), said housings having a relatively low cost of manufacture . The cost of transmitting / receiving unit can be shared between multiple users. Note that the fact of using a modulation / demodulation suitable for wireless communication such as ZigBee or KNX technology over coaxial cable allows to use this technology without loss of much greater length of cable that had the communication place in the air.

0019The system according to the invention to be easily (and without significant additional cost) suitable for existing installations insofar just come to add transmit / receive unit (preferably outside the home ) and the housing (preferably inside the housing) which are to connect to the existing coaxial cable. In addition, the transmit antenna of satellite signals is an antenna (ie means for transmitting towards a satellite microwave radio signals) very little cost omnidirectional or with a low directivity (for example, an antenna gain of less than 10 dBi), and easy to install. The signal transmitted by the antenna may be received by a satellite or a "collector" land, depending on the frequency used. It will be noted that one can dispense with the use of this antenna in the case of a forward channel using the satellite parabolic reflector for transmitting the return channel.

0020The low cost of the transmit / receive unit also is that using two different bands for transmission and reception (eg S-band transmit and receive Ku-band) it is not necessary to use a diplexer to avoid interference from one channel to another.

0021It is also noted that the system according to the invention is highly scalable. Indeed, it is quite possible to start using the system in a very large area (eg, an entire country) by issuing all return signals to a satellite, without deploying any terrestrial component; from the time the satellite capacity is no longer sufficient, or identifies the service areas where there is more messages sent. Therefore, instead of using the direct antenna connection - satellite, can provide "collectors" land, that is to say of ground receiving stations, serving as relays and to reduce the satellite's expense. The signals transmitted by the terminals, on an appropriate frequency, will then be received by the collector instead of the satellite. The capacity can thus be increased according to need, with a cost proportional to the number of terminals deployed and progressive investment.

0022The forward of terrestrial or satellite broadcast can be highly integrated to the satellite return path, since it may contain, in one of the emitted multiplex signals, useful signaling information for the proper functioning of the facility. This information may include the issuance to use (frequency, type of speed "symbol rate" spreading code) settings, system load, security keys, and other instructions for installation. The transmit / receive unit therefore contains the logic required to interpret the information present in the terrestrial or satellite broadcast channel and use it to control the transmission of signals. In addition, the transmitting / receiving unit can generate from this signal in the forward, a very stable clock signal used to transmit with very low frequency error - this allows not to use a PLL very accurate which would have a high cost.

0023The installation of the invention is particularly unusual in the case of a forward channel of terrestrial (hybrid system) for the skilled person to the extent that it was difficult to imagine a terrestrial hybrid system - satellite with a satellite return path without adding hardware therefore inducing a crippling extra cost to the user. It is precisely the use of a particular modulation for communication between the transmitting / receiving unit and the housings, a second modulation for transmission to the satellite, an inexpensive antenna, and a single cable connecting the boxes in the apartments with the transmitting / receiving unit to the outside, that can make attractive the installation of the invention.

0024The installation of transmission / reception according to the invention may also have one or more of the following characteristics, considered individually or in all technically possible combinations:<ul><li>said electrical signal modulator according to a second protocol modulation / demodulation comprises means for implementing a spread spectrum protocol operating according to an asynchronous protocol to multiple random access spread spectrum;</li><li>said first protocol modulation / demodulation is based on a protocol adapted to wireless communication of short distance such that one of the following protocols: ZigBee, KNX, WiFi, BlueTooth or WiMax;</li><li>said first protocol modulation / demodulation is based on a protocol adapted to a wired technology such as Ethernet or CPL line carrier current;</li><li>said transmission / reception unit comprises means for extracting, from the path into electrical signals go, signaling information for setting transmission parameters and / or a clock signal;</li><li>said transmission / reception unit comprises a demodulator of said electrical signals in forward such a demodulator capable of demodulating signals according to the following standards:<ul><li>∘ DVB-T;</li><li>∘ DVB-T2;</li><li>∘ DVB-S;</li><li>∘ DVB-S2;</li><li>∘ DVB-SH;</li></ul></li><li>said transmitting / receiving unit and / or said housing include wireless means such as WiFi means, WiMax, Bluetooth, ZigBee or KNX; </li><li>said electrical signals back on track are modulated in said band emission frequency band S and especially in the band [1980 MHz; 2010 MHz];</li><li>said means capable of receiving electrical signals obtained from the processing of radio signals are adapted to receive terrestrial microwave radio signals in the UHF or VHF band;</li><li>said means capable of receiving electrical signals from the processing of radio signals are able to receive satellite microwave radio signals in the Ku band or Ka-band;</li><li>said transmission / reception unit comprises means for transmitting to a satellite and / or to a ground receiving station of said radio signals capable of being transmitted via satellite;</li><li>said installation comprises a plurality of housings exchanging signals with a single transmitter / receiver unit.</li></ul>

0025The present invention also relates to a transmitting / receiving unit adapted to be integrated in an installation according to the invention, said unit comprising:<ul><li>means adapted to receive electrical signals from the processing of radio signals received terrestrially or via satellite, known path into electrical signals go;</li><li>a demodulator adapted to demodulate the electric signals according to a first protocol modulation / demodulation;</li><li>a modulating electrical signals according to a second protocol modulation / demodulation different from said first protocol, said second protocol is a spread spectrum protocol, said modulator modulating the signal demodulated by said demodulator;</li><li>means for transforming said electrical signals modulated according to said protocol to spread spectrum signals in said electrical return path, by radio signals capable of being transmitted by satellite.</li></ul>

0026Note that even if the transmitting / receiving unit is mainly described as a single device comprising all the previously described features, it can also be an arrangement of several separate devices performing these functions: one may thus envisage that the transmitting means to the satellite (ie antenna) are not directly integrated into the same device.

0027The present invention also relates to a housing suitable for integration in an installation according to the invention comprising a modulator capable of modulating electrical signals according to said first protocol of modulation / demodulation.

0028Other features and advantages of the invention will become apparent from the description which is given below, for indicative and non-restrictive, with reference to the attached figure which shows schematically a system according to one embodiment of the invention .

0029The <figref idrefs="f0001">figure 1</figref> diagrammatically shows a transmission / reception system 1 according to a first embodiment of the invention.

0030The / receiving 1 transmitting device is able to operate with a radio antenna 3 standard (eg, a "rake" antenna on the roof of a building or dwelling) for receiving UHF band signals or VHF with Digital terrestrial TV stream encoded using a protocol type DVB-T or DVB-T2.

0031The installation of transmission / reception 1 comprises:<ul><li>a transmitting / receiving unit 2 outside home;</li><li>a coaxial cable 10;</li><li>coupler / decoupler 9 microwave radio signals;</li><li>a plurality of cases (here two housings 11 and 11a are represented) to be housed inside the building (each unit is for example in an apartment).</li></ul>

0032The antenna 3 receives radio signals modulated according to the DVB-T or DVB-T2, for example in the UHF band (band 470-862 MHz).

0033The unit transmitter / receiver 2 includes: <ul><li>input means 4 suitable for receiving terrestrial electrical signals received by the antenna 3 (the antenna and the input means 4 are for example connected via a coaxial cable 20);</li><li>a coupling / decoupling 8 microwave radio signals;</li><li>modem 7 operating according to a first modulation / demodulation;</li><li>5 a modulator operating according to a second modulation / demodulation;</li><li>omnidirectional or quasi omnidirectional antenna 23 (ie an antenna with a low directivity, for example having an antenna gain less than 10 dBi) capable of converting electrical signals into S-band emission (eg in the band [1980 MHz - 2010 MHz]) in microwave radio signals and transmit these signals to a satellite 100 or 101 collector S-band;</li><li>a demodulator 6.</li></ul>

0034The modulator 5 operates for example according to an asynchronous protocol to multiple random access band spreading modulation optimized such SPREAD ALOHA for the satellite hub can use interference eliminating means (such a protocol is described for example in the document <patcit id="pcit0004" dnum="US20100054131A"><text>US2010 / 0054131 (Rio del Herrero et al.</text></patcit>));

0035The modem 7 includes a modulator 22 and a demodulator 21 and is generically a modem operating according to a protocol type FSK ( "Frequency Shift Keying" in English) or MDF modulation frequency shift or derivative of such a protocol ; the modem 7 is preferably a modem operating according to a protocol adapted for short-range wireless communications (for example less than 300m wireless operation) such as a ZigBee or KNX modem.

0036The demodulator 6 operates according to the DVB-T standard (described in ETSI EN 300 744 "Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television") or DVB-T2 (described in ETSI EN 302 755 "Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)," the extensions of the DVB-T2 standard such as DVB-T2-lite is described in the "DVB BlueBook A122").

0037The housing 11 comprises:<ul><li>coupler / decoupler 12 microwave radio signals;</li><li>a modem 14 operating according to the same protocol (first modulation / demodulation) the modem 7; the modem 14 is for example a ZigBee or KNX modem;</li><li>means 16 for wireless connection to a local network such as WiFi, WiMax, Bluetooth, ZigBee or KNX or wired LAN Ethernet or similar type; these means 16 are used to receive signals transmitted to the modem 14;</li><li>an input / output connection 15 USB-capable of exchanging signals with a digital television decoder 28 also says STB ( "Set Top Box" in English);</li><li>a coupler 31 that interconnects the modem 14 respectively with the input / output connection 15 and means of wireless connection 16.</li></ul>

0038The housing 11a is similar to housing 11.

0039The coaxial cable 10 connects the housings 11 and 11a to the unit transmit / receive 2.

0040The coaxial cable 10 is separated into two via the coupler / decoupler microwave 9 so that respectively connects the transceiver unit 2 and the housing 11 via the extension 18 of the cable 10 and the transceiver unit 2 and the housing 11a via the extension 19 of the cable 10. it will be noted that the coupler / decoupler 9 is a microwave device operating in both directions (ie it passes radio signals up and down). The same goes for other couplers / decouplers microwave installation.

0041The operation of the plant 1 will be explained with reference to exchanges between the transmitting / receiving unit 2 and the housing 11, provided that the operation is identical between the unit transmitting / receiving 2 and the housing 11a .

0042The principle of operation of the plant 1 of the invention is the use of a receiving portion (not show) wireless terrestrial antenna formed by the "rake" 3 and the input means 4 capable of receiving terrestrial electrical signals received by the antenna 3 and a transmission part in strip S.

0043The S-band transmission portion is a return path for the development of interactive services (votes, consumer conditional access content by key exchange, new services such as video commands on demand) or M2M services ( control home appliances, surveillance, monitoring a parameter measured by a sensor) with an addition of relatively small and inexpensive equipment on an existing installation. The omnidirectional antenna 23 can transmit the S-band signals directly to the satellite 100 or to terrestrial manifolds 101 in the event of an increase in capacity (in this case, the antenna 10 may be slightly directional so as to reach the collector 101).

0044The set of signals is coupled to the single coaxial cable 10.

0045Terrestrial signals received by the antenna 3 and the input means 4 are transmitted through the coupler / decoupler microwave 8 on the coaxial cable 10.

0046These signals are then recovered at the microwave coupler 12 before being transmitted to the STB 28 via a coaxial cable 17.

0047The signals to be transmitted in the S band are digital signals that are modulated by the modem modulator 14 ZigBee (ie first modulation / demodulation) of the housing 11 to an intermediate frequency (eg 868 MHz or 2.4 GHz data purely for illustrative purposes) . These return path signals are themselves derived from signals from other devices connected by wireless route (via connection 16) or wired to housing 11.

0048The modulated ZigBee signals are transmitted on the coaxial cable 18 by the coupler / decoupler 12 and the coaxial cable 10 by the coupler / coupler 9 that transmits signals to the unit transmit / receive 2.

0049The coupling / decoupling 8 of the transmission / reception unit 2 transmits the ZigBee modulated signals to the demodulator 21 of the ZigBee modem 7.

0050The demodulator 21 recovers the digital signal from the modulated signal ZigBee. It will be noted that the demodulator 21 may use error correcting means for removing the noise inherent in the analog signal transmitted on the cable.

0051Once the digital signals recovered, they are modulated by the modulator 5 operating according to the second modulation / demodulation according to an asynchronous protocol to multiple random access band spread modulation type SPREAD ALOHA on the S frequency band [1980 MHz - 2010 MHz]. Having retrieving digital information very "clean" implies that this modulated signal is little noisy and requires low amplification. Note, however, that one can consider using a low power amplifier for amplifying the modulated signals for transmission in S band to the satellite 100 or the manifold 101 via the antenna 23.

0052Note that the intermediate frequency band (868 MHz for example) chosen has the advantage of being compatible with the bandwidth of a standard coaxial cable and allows to limit losses on the coaxial cable without the need to transposition frequency at the transmission / reception unit. Furthermore, having a disjointed UHF frequency 868 MHz band avoids the interference between the transmitted signals over the same cable. Note that the use of another intermediate frequency by the ZigBee modem modulator 14, for example 430 MHz, located in the UHF band may need to perform a frequency transposition level of housing 11 so as to avoid interference on the cable 10 (for example by using a local oscillator and a frequency mixer).

0053Note also that different couplers / decouplers may be fitted filter so as to retrieve only the frequency useful part.

0054The way to go in UHF terrestrial reception also serves to retrieve useful information. This may be for example of the frequency or bandwidth to be used in return channel S-band it may be also updates related to the modulation / demodulation used by the modulator 5. d other words, the terrestrial broadcast go channel can be highly integrated to the satellite return path since the multiplex signals emitted by land may contain useful signaling information for the proper functioning of the facility. This information may include the issuance to use (frequency, type of speed "symbol rate" spreading code) settings, system load, security keys, and other instructions for installation.

0055To do so the unit transmitting / receiving 2 contains the logic required to interpret the information present in the terrestrial broadcast channel and use it to control the transmission of signals. This last point assumes that the transmit / receive unit includes a demodulator 6 operating on the DVB-T standard for extracting signaling information used to establish the way in emission parameters present in return a portion of the terrestrial electrical signals, this information is transmitted to the modulator 5. The demodulator 6 can also be sent to the modulator 5 (directly or through unrepresented signal processing means) a clock signal ( "clock") very stable (eg with a mistake frequency below 1 ppm), used to transmit the required frequency with an error in very low frequency (eg less than 2 kHz).

0056Note that the unit of transmission / reception outer 2 comprises a supply 29; this DC power supply can be directly transmitted in the uplink via the coaxial cable 10 (via extraction means unrepresented unit 2). It is also possible to recharge the power battery 29 via one or more solar panels 30.

0057The energy consumption of the transmission / reception unit 2 may be limited by feeding the modulator 5 (if necessary integrating the signal amplifier to transmit) only when a signal is issued. To do this, the unit transmit / receive 2 comprises means for supplying the modem 5 only after receiving demodulator 7 by a signal for transmission. For applications where the rate of use ( "duty cycle" in English) is reduced (eg a message every minute) such implementation allows not consume energy during periods without transmitting messages.

0058A second particularly advantageous application of the installation according to the invention relates to the field of M2M. In this case, the S-band return channel may be used for transmitting information from a device located in the home such as an alarm system; so when the alarm is triggered, a signal is transmitted from the alarm system with wireless connection means 16 (for example, means operating in ZigBee) and a message indicating the initiation of the alarm is transmitted on the return channel in S band

0059According to a variant of the invention, it is also possible to use a forward channel of satellite broadcasting as described in the patent application <patcit id="pcit0005" dnum="WO2011076791A"><text>WO2011076791</text></patcit> filed by the applicant instead of a forward channel terrestrial. In this case, the rake antenna 3 and the input means 4 suitable for receiving terrestrial electrical signals received by the antenna 3 is replaced by a parabolic reflector and a receiving block LNB ( "Low Noise Block") for the receiving signals from a satellite (eg Ku-band (10.7 GHz. - 12.75 GHz) the LNB of the transmit / receive unit converts the microwave signals received via satellite band into electrical signals to transmit, via the coaxial cable to the housing.

0060In this case, the demodulator 6 operating according to the DVB-T standard becomes a demodulator operating for example according to the DVB-S2 standard (ETSI EN 302 307 Digital Video Broadcasting (DVB); Second generation framing structure, channel coding and modulation systems for Broadcasting , Interactive Services, News Gathering and --other broadband satellite applications (DVB-S2)). According to the latter embodiment is advantageously used the gain of the reflector used to receive microwave signals in the Ku band to transmit signals back on track in the S-Band

0061According to another embodiment of the invention, rather than using modems 7 and 14 operating according to a protocol suitable for short-range wireless communications (eg ZigBee or KNX) on wireline can be used as Ethernet or current carrier online or CPL. In this case, modems 7 and 14 are replaced with PLC modems and each unit communicates with other devices within the home through the electrical grid. PLC signals received by the housing 11 are modulated by the PLC modem modulator at a frequency for example between 1 and 20 MHz and transmitted over the coaxial cable.

0062Note also that the transmitter / receiver unit can be equipped with wireless means or transmission PLC to communicate with other devices, particularly when the transmission on coaxial cable is not operational.

0063The antenna rake or the parabolic reflector is preferably an antenna or a collective reflector used on the roof of an apartment building and shared by multiple users, each equipped with a housing.

0064Of course, the invention is not limited to the embodiment which has just been described.

0065Thus, the invention has been more particularly described in the case of an S-band use but can also be used in band C.