FR2715522A1 - Unidirectional expander device of mobile radio cell, and corresponding network. - Google Patents

Abstract

A one-way mobile telephone network cell expander device, and the related network, are disclosed. Each expander device includes a two-channel retransmitter circuit (0) for a mobile station/base station channel in a first frequency band and a base station/mobile station channel in a second frequency band. A first directional transceiver antenna (1) is linked to the retransmitter circuit (0) to provide reception in the first frequency band and transmission in the second frequency band for the mobile station/base station channel, and a second directional transceiver antenna (2) is linked to the retransmitter circuit (0) to provide reception in the second frequency band and transmission in the first frequency band for the base station/mobile station channel. The antennas (1 and 2) are electromagnetically separate, and the axis of the radiation pattern of the first and second antennas lies in two substantially parallel vertical planes. Said device is useful for providing GSM-type mobile telephone networks.

Description

UNIDIRECTIONAL EXTENSION DEVICE OF CELL
MOBILE RADIOTELEPHONY. AND CORRESPONDING NETWORK
The invention relates to a mobile radio cell unidirectional expander device, and the network thus obtained through the implementation of several of these extender devices.

 In order to enable mobile radiotelephone communication in a given coverage area, current mobile radio systems provide for the installation of base stations, which provide coverage of an area by subdivision into elementary cells to which are allocated. a group of frequencies in a transmit band and in a receive band. In order to avoid the phenomena of interference from one elementary cell to a neighboring adjacent cell, it is imperative to organize frequency distribution planes, in order to generate a maximum distance between two cells provided with the same frequency bands.

 For such cellular mobile radio systems, the surface coverage of the zones imposes a very high frequency space consumption. For these systems, a large majority of telecommunications traffic is actually in urban areas and on the roads connecting them. In rural areas with low population density, such a surface coverage is no longer essential, and it therefore seems advantageous to provide, in such areas, a coverage that is no longer surface but substantially linear with respect to the road axes, which are the seat. of the majority of the traffic.

 However, the radiofrequency coverage of a mobile radio cell, such as the GSM radiotelephone network, is very limited. On the one hand, the standardization criteria of the GSM radio network currently set a limit beyond which the signal transmitted by a mobile is no longer received by its base station at a distance of 35 km. On the other hand, the usual mobiles have a limited power of emission for reasons of power supply while the relief of the ground, even the vegetation, impose important attenuation of propagation.

Thus, in the best case, one can not hope to cover a distance greater than 25 km from a single base station, in the presence of a favorable environment free of any masking and any unevenness. In the most unfavorable cases, the radiofrequency coverage distance of an elementary cell can then be reduced to a few kilometers in rough terrain.

 In order to ensure the radiofrequency coverage of a road, it is therefore necessary to implement a very large number of successive base stations, which, in addition to the very high cost of implementation for the network operator, poses a very delicate problem of planning the allocation of frequencies as mentioned above, with the aim of reducing or eliminating the phenomena of interference.

 The object of the present invention is to extend the radiofrequency coverage of a GSM mobile telephone cell up to the limit value authorized by the corresponding normative provisions, by the use of a single base station and a base station. one and the same group of frequencies.

 Another object of the present invention is the implementation of a unidirectional mobile radio cell expander device allowing a large economy of infrastructures while ensuring a substantially linear radio frequency coverage along roads, highways or axes. rail.

 Another object of the present invention is also the implementation of a unidirectional mobile radio cell expander device making it possible to provide radio frequency coverage along long-distance roads, highways or railroads. , without, however, abusing the authorized frequency spectrum for portable radiotelephony.

 The unidirectional mobile radio cell expander device, a cell comprising a base station provided with a transceiver in a first and a second transmission or reception frequency band, object of the present invention, is remarkable in that it comprises a dual-channel mobile / base station transponder circuit in a first frequency band, base / mobile station in the second frequency band. A first directionally transmitting transmission antenna interconnected by means of the transponder makes it possible to ensure reception in the first frequency band and transmission in the second frequency band, for the respectively mobile base station / mobile station / base station channel. A second directional transmit-receive antenna interconnected to the re-transmitter circuit ensures the reception in the second frequency band and the transmission in the first frequency band, for the respectively mobile base station / mobile station / base station channel. The first and second antennas are electromagnetically decoupled, the axis of the radiation pattern of the first and second antennas being contained in two substantially parallel vertical planes.

 The unidirectional mobile radio cell expander device, object of the present invention, finds application to the mobile radio network equipment of road axes, highway or rail including.

It will be better understood from reading the description and from the following drawings in which: FIG. 1 represents a functional diagram of the device
unidirectional expander of radiotelephone cell
object of the present invention, FIG. 2 represents radiation diagrams
specific antennas used for the implementation
of an expander device as shown in FIG. 1; FIG. 3 represents a preferred arrangement of
different components of the expander device
mobile radio cell object of this
FIG. 4 represents an illustrative diagram of a re-transmission
dual-channel transmitter used for the implementation of a
unidirectional cell expander device
mobile radiotelephone according to FIG. 1; FIG. 5a represents an implantation diagram, from
of a base station of a radiotelephone cell
mobile, of a plurality of expander devices unidirec
to form a radioactive network
mobile telephony implanted along a road axis,
motorway or rail, - Figure 5b shows the structure of the signal frames
issued by a base station and a mobile with a
portable radiotelephone equipment; FIG. 5c represents an explanatory theoretical diagram of the
interference phenomenon between two extensor devices
successive or between a base station and a device
extender object of the present invention.

 A more detailed description of a mobile radio cell unidirectional expander device according to the subject of the present invention will now be given in connection with FIG. 1 and the following figures.

 In general, it is recalled that a mobile radio cell comprises a base station, the base station being denoted SB, this base station being provided with a transceiver means in a first and a second band of transmission or reception frequencies. The first and the second frequency band are denoted Afl respectively bof2. Typically, it is recalled that the transmission path in the SB / mobile base station direction is designated downstream and the mobile transmission path / base station SB is designated uplink. In a conventional manner, the downstream channel makes it possible to transmit the signals from the base station SB to the mobile in the second frequency band Af2 while the upstream channel makes it possible to transmit the signals from the mobile to the base station SB in the first band. of frequencies Af 1.

 According to a first advantageous characteristic of the mobile radio cell unidirectional expander device object of the present invention, it comprises a dual-channel repeater circuit, noted 0 in Figure 1, this retransmitter circuit 0 for mobile communication / base station SB in the first frequency band Afl respectively the base / mobile station communication in the second frequency band Af2.

 A first directional antenna, denoted 1, transceiver is interconnected to the transceiver circuit 0 to ensure reception in the first frequency band and the transmission in the second frequency band mentioned above for the mobile uplink / base station SB respectively the base station / mobile downlink.

 A second receive transmit directional antenna, denoted 2, is interconnected to the retransmitter circuit 0 to provide reception in the second frequency band Af2 and transmission in the first frequency band Afl for the downstream channel base station / mobile channel respectively. mobile riser / SB base station.

 According to a particular characteristic of the unidirectional expander device of mobile radio cell object of the present invention, the first and second antenna are electromagnetically decoupled, the electromagnetic decoupling being represented by a dotted line, referenced E, in Figure 1.

 In addition, it is indicated that the axis of the radiation pattern of the first respectively of the second antenna is contained in two substantially parallel vertical planes, as will be described later in the description.

 In general, it is indicated that the first and second antennas used are antennas of very high gain, the most directional possible and whose radiation pattern has side lobes, denoted LS, very weakened so as to limit the risk of coupling by air between the first and second antennas mentioned above.

 Figures 2a, 2b and 2c show typical radiation patterns of the first and / or second antenna, the main lobe being noted LP, and the secondary lobes LS.

 As shown in FIG. 2a in particular, the first 1 and the second antenna 2 have, in the vertical plane, a radiation pattern having an opening angle of less than or equal to 10 ".

 In addition, as shown in FIG. 2b, the first antenna 1 has, in a horizontal plane, orthogonal to the vertical plane and containing the axis of the radiation pattern of this antenna, an opening angle of between 45.degree. and 70, as shown in the above figure.

 Regarding the second antenna 2, as shown in Figure 2c, it has in a horizontal plane an aperture angle radiation pattern of less than 10.

 In general, it is indicated that relative to the first and second antennas, each of these antennas has a front-rear decoupling greater than or equal to 30 dB.

 By way of non-limiting example, it is pointed out that the first antenna, the function of which is to allow radiation towards or from the mobiles, may be constituted by a Kathrein antenna, bearing the reference K 73 226, this antenna having a radiation opening angle in the horizontal plane of the order of 60 and an opening angle of the radiation pattern in the vertical plane of the order of 8 ".

 Regarding the second antenna 2, it is indicated that it may be constituted by a parabolic antenna Andrew KP 10 820 A type or KP 13 820 B. It is indicated that with regard to this type of antenna , the gain thereof is between 25 and 28 dB.

 As furthermore shown in FIG. 3, it is indicated that the first and the second antenna 1, 2 can be mounted on a metal support, denoted SM, forming a pylon, each antenna being connected to the double-channel repeater circuit. 0 by coaxial cable connections for example.

 In order to ensure the electromagnetic decoupling between the first and the second antenna 1, 2, these are mounted on the pylon or metal support Sm so that the origin of the transmitting-receiving point is distant in a substantially parallel direction vertically a distance, denoted d0, greater than or equal to 10.X, where k denotes the maximum wavelength of the transmission signal of the first and the second frequency band Afl, Af2.

 Finally, it is stated that the aforementioned antennas may comprise a radiating element constituted by a dipole demionde for example, the parabolic structure of the antenna being however reserved for the second antenna.

 A more detailed description of the dual-channel repeater circuit O will now be given in connection with FIG.

 As will be observed in the above figure, the retransmitter circuit 0 advantageously comprises a first channel, denoted I, comprising in cascade a bandpass filter 11 for transmitting the first frequency band Afl and an amplifier HF, noted 12. It is indicated that the HF amplifier 12 is a very linear adjustable gain amplifier, class A for example.

 The dual-channel repeater circuit 0 also comprises a second channel, denoted II, comprising in cascade a band-pass filter 21 enabling the transmission of the second frequency band Af2 and an HF amplifier, denoted 22, analogous to the HF amplifier 12. .

 The first and second channels 1, 2 are interconnected in parallel by means of a first and a second duplexer 10, 20. The first duplexer 10 receives and transmits a signal in the first frequency band Afl for the mobile uplink / base station, this signal being successively filtered by the band filter 11 and then amplified by the HF amplifier 12 and delivered to the second duplexer 20. The second duplexer 20 receives and transmits a signal in the second frequency band Af2 for the channel downstream base / mobile station, this signal being delivered to the band filter 21 and then to the RF amplifier 22 and finally to the first duplexer 10. The first duplexer 10 thus provides respectively the reception of a signal transmitted by the mobile to the base station in the first frequency band Afl and the transmission to the same mobile of a signal from the base station in the second frequency band bof2. The second duplexer 20 receives a signal on the mobile base station downlink in the second frequency band Af2 and the transmission on the mobile uplink / base station in the first frequency band Afl.

 Preferably, it is indicated that the aforementioned frequency bands bfl and hf2 may have values equal to 25 MHz, the first frequency band Af 1 may be between 890 and 915 MHz and the second frequency band Af2 may be between 935 and 935 MHz. and 960 MHz.

 Of course, it will be understood that the transmission of the downlink signals between base station SB and mobile respectively on the uplink between mobile and base station can be carried out via one or more unidirectional mobile radiotelephone object of the present invention, each mobile radio cell, through the implementation of the aforementioned extender devices, then being configured in a real network as will be described hereinafter in the description in connection with the figures Sa , 5b, 5c.

FIG. 5a shows a base station, denoted SB, in a succession of mobile radio cell unidirectional expander devices, denoted
El to En, these devices being installed on metal supports as previously described in the description.

 In general, it is indicated that the first expander device E1 is remote from the base station SB by a distance d1, the successive extender devices E2 to En-1 being separated by a distance d2 to dn-1 so as to cover a total distance of coverage, denoted Dn, according to the direction of a road in one direction, to another successive base station SB + 1.

 The mobile radiotelephone communication network thus constituted comprises, for a base station SB and between two successive base stations forming a mesh, a plurality of substantially identical adjacent unidirectional extender devices as previously described in the description.

 In general, it is indicated that a base station SB and a unidirectional expander device adjacent to this base station SB as well as two adjacent unidirectional expandable devices, such as the extender devices E1, E2 to En-2, En-1, form two successive transmit-receive stations vis-à-vis a mobile with a mobile radio device.

 According to a first particularly advantageous aspect of the mobile radiotelephone telecommunications network object of the present invention, it is indicated that for two successive unidirectional expanders devices, the uplink / downlink link gains, these gains being adjustable in particular at the level of the double repeater circuit 0 previously described, are taken as close as possible to the propagation attenuation between two successive unidirectional successive aforementioned extender devices.

In addition, according to a particularly advantageous characteristic of the network thus constituted, it is indicated that the configuration and the arrangement of the antennas on the metal supports SM is such that the hypothesis of the propagation in free space between two successive unidirectional extender devices respectively between station SB base and adjacent expander device is checked. For this purpose, it is indicated that the equivalent antenna heights satisfy the simplified Fresnel criterion according to the relation

A particular configuration of a network obtained in the context of the implementation of the unidirectional expander device of a type of mobile radio telephone
GSM along a motorway axis will now be given in the description with the usual assumption that the transmission power of the base station SB is 20 watts and the mobile power is 8 watts, such an assumption corresponding to most likely case in open country.

 As regards the choice of antennas, these can be constituted as previously mentioned in the description, antennas very high gain the most directional possible side lobes very weakened, so as to limit the risk of coupling by the airway can generally be used. It is also indicated that it is possible to couple two elementary antennas to form a single antenna, the first and / or the second antenna, to improve the gain and directivity of the entire system.

 In general, and taking into account the hypotheses formulated above, the sensitivity of the receivers and the transmission power of the mobiles limit the coverage of a GSM mobile radio cell at a maximum distance Dm of less than 25.6 km. .

 For an 8 watt transmitter, the coverage is limited to 25.6 km and it is therefore practically necessary to install a base station every 51 km along a road to obtain full coverage.

 In view of the above assumptions, the insertion of a first extension device at a distance of about 25.6 km does not pose any particular problem insofar as, by setting at its maximum value the gain of double-channel repeater, we obtain a higher power in the direction of the downlink for any distance less than the aforementioned limit value 25.6 km separating this first expander device from the base station.

 However, the balance of the downlink requires that the distance between the above-mentioned expander and any mobile is less than a specific value of 14.2 km.

 In the case where a second expander device is now cascaded with the first, a particularly advantageous measurement, as mentioned previously in the description, consists, in terms of coverage, of imposing that the gains of the uplink and the downlink are at least equal to the propagation attenuation between two repeaters.

 In order that the distance separating two successive extender devices be as great as possible, the active and passive gains, antennas gains, must be as high as possible. Given the antennas used, the maximum distance d2 to dn-l separating two aforementioned extender devices can not be greater than dn-1 = 8.9 km.

 Under these conditions, according to a particularly advantageous aspect of the network of extender devices, object of the present invention, a chain of a determined number N of expander device between two base stations SB can be used, which makes it possible to increase the cover initially limited to 25.6 km.

 In view of the foregoing, it is indicated that the separation of two successive extender devices by approximately dn-1 = 9 km does not increase the propagation losses.

Taking into account the hypothesis of free space propagation between two extender devices, the equivalent antenna heights satisfy the previously mentioned criterion, which implies - for dn-1 = 8.9 km the equivalent height of the antenna is
h = 30 m, - for dn-1 = 25.6 km, the antenna equivalent height is
h = 50 m.

 Given the specifications of the GSM mobile radiotelephone protocol limiting the radiofrequency coverage to about 35 km, notably because of the synchronization time of the mobiles on the base station and the guard time of each burst allowing the transmission of the radiotelephone calls, these parameters limiting the access time between a given mobile and the base station at the beginning of communication, the interest of the extender circuits is then limited to the maximum coverage by implanting a single expander circuit according to the subject of the present invention.

 In fact, if we take into consideration the delay due to the propagation delay in the expander circuit of all the signals transmitted on the uplink and the downstream channel, this delay is at most 3 ps, this corresponding to a distance of 900 meters for a wave propagating at the speed of light. The maximum coverage is reduced to 34.1 km.

 However, according to a particularly advantageous aspect of the mobile radio network object of the present invention, it is possible to increase the radiofrequency coverage distance up to substantially 120 km by allocating for each mobile, as shown in Figure 5b, two intervals of time on the eight time slots of the TDMA frame instead of one. This distance corresponds to the initial 35 km plus the distance corresponding to half a time interval of the frame, ie 577 ps, as represented in the lower part of FIG. 5b.

 In the upper part of FIG. 5b, there is the classical case in which the delay between the base station SB and the mobile MS is limited to a value t0. The duration of tO being encoded on 64 bits and for a bit rate of 271 kb / s, tO is limited to 118 us, which corresponds to about 35 km.

 In the opposite case, according to the representation in the lower part of FIG. 5b, the association of two time slots on the same mobile MS makes it possible to obtain a maximum delay of T / 2 + t0, which corresponds to a distance from 121.9 km.

 In such a case, by allocating to each mobile MS two time slots, it is therefore possible to associate up to nine extender devices according to the subject of the present invention, each separated by a distance of 8.9 km. . The whole of a base station and the aforementioned devices is therefore likely to constitute the mesh of a general network to provide coverage of a road, highway or rail.

 In general, it is indicated that a base station and a unidirectional expander device adjacent to this base station as well as two adjacent unidirectional extender devices form two successive transmission receiving stations vis-à-vis a mobile MS considered .

 According to a particularly advantageous aspect of the network which is the subject of the present invention, each unidirectional expander device is remote from a base station or from a unidirectional extender device adjacent a distance, denoted by dl respectively dn-1 in FIG. greater than or equal to a critical distance for suppressing the co-channel interference of two successive transmitting-receiving stations with respect to the mobile.

 Indeed, as shown in FIG. 5c, there are zones of the road or motorway route provided with a network according to the subject of the present invention, where a mobile traveling on this road or motorway axis receives signals to the same frequency on the part of two transmitting-receiving stations successive base stations respectively extender device as previously mentioned.

 In the case 1 of Figure 5c wherein the mobile vis-à-vis the downstream channel is downstream of two successive extender circuits, Enkl and Enk or SB + 1, this mobile receives signals at the same frequency of the from the two expander devices or from the base station and the first expander device.

The respective travel times are written for the signals received by the mobile
Relationship (1)
tl = dn-k + d
c

<tb> Relationship <SEP> (2)
<tb><SEP> t2 <SEP> = <SEP> dn-k <SEP> + <SEP> t <SEP> + <SEP> d2 + h2 <SEP> - <SEP> dn-k <SEP> + <SEP> d <SEP> + <SEP> t
<tb><SEP> c <SEP> c <SEP> c
<tb> from where
Relationship (3)
t2 - tl = t
with t <3 ps, transmission delay of each repeater
double track.

In the case where, on the contrary, the mobile MS is in the downstream path upstream of an extension device, the mobile MS being interposed between the two extender devices Enk1, Enk for example, the previous relations s' write
Relationship (4)
tl = d
c

<tb> Relationship <SEP> (5)
<tb><SEP> t2 <SEP> = <SEP> dn-k <SEP> + <SEP> t <SEP> + <SEP> Y <SEP> (dn-kd) 2 + h2 <SEP> h2 <SEP > dn-k <SEP> + <SEP> t <SEP> + <SEP> dn-kd
<tb><SEP> c <SEP> c <SEP> c <SEP> c
<tb> from where
Relationship (6)
t2 - tl = 2 (Dd) + x.

c
The condition t2-tl <16 ps implies
Relationship (7)
d> dnk - 1.95 km.

 However, the normalization provisions of the GSM system require the receiver to equalize delays up to 16 pus, any successive signals whose delays do not exceed 16, us being thus considered as one and the same signal.

 Given this condition, the risk of interference appears for a distance d on both sides of the downstream expander device in the downward direction d> dnk - 1.95 km.

 In the context of two co-channel signals, the GSM standard according to recommendation 0505 ETSI requires a separation of the co-channel signals greater than or equal to 9 dB.

 This value leads to two values d 'and d "of the distance d between which the aforementioned separation ratio imposed by the GSM standard is not respected.

 However, it can be ensured that the system operates if, in the interval defined by the values of and d ", the delays are less than 16 ps.

 Theoretical studies have shown that for a minimum value h according to the previously mentioned Fresnel criterion corresponding to the distance dnk, we find that for dnk <10.2 km, the condition is realized.

 However, between the base station and the first expander device, there is an interference zone for which the delays are greater than 16 ps.

 Theoretical calculations show that, under the conditions previously indicated, the length of this zone is given by A = about 1 km.

 For a distance dl = 25.6 km previously indicated, there is therefore an interference zone of 1 km long between 22.6 km and 23.6 km from the base station and in which the ratio of the signal to the cocanal interference can go down to values of 2dB.

 Consequently, the distance dl = 25.6 km mentioned above is too important and it is advantageous to reduce this distance dl to 10.2 km to overcome the problems due to interference, which allows the implementation of the implementation of several successive expanders to reach maximum coverage.

 It is then indicated that the successive distances d2, dn-1 to dn separating two successive extender devices can then be chosen equal to 8.9 km as already mentioned in the description.

 In conclusion, it is indicated that the successive association of nine repeaters or extender devices according to the subject of the present invention mounted on 30-meter pylons and for which the separation distance between the base station and the first expander device is 10.2 km, each successive expander device being separated by 8.9 km, covers about 100 km, Dn = 91.6 km of a road with a single base station. In addition, the above concept can easily be extended in view of the fact that a base station can transmit and receive in both directions a road or rail route with an appropriate overhead system, thereby obtaining a radiofrequency coverage from a single base station covering approximately 200 km.

 Considering studies carried out concerning the study of the case where a mobile near a expander device saturates the amplifier and the intermodulation following the cascading of repeaters, it is indicated that it may be appropriate. to implement the control of the transmission power of the mobiles at the base station. This control is a parameter available to the network operator.

 Finally, it is indicated that the use of two time slots of the TDMA frame per mobile makes it possible to obtain a greater coverage, as described above, although the number of possible simultaneous communications is, however, halved.

 Finally, it is pointed out that the network as described previously in the description can be completed by means of radiating cables for the passage of road, motorway or railway tunnels, for example, and that, under these conditions, the portable radio network subject of the The present invention has a very great flexibility of implantation and use.

Claims (8)

 1. A mobile radio cell unidirectional expander device, a cell comprising a base station provided with a transceiver means in a first and a second transmission or reception frequency band, characterized in that said expander device comprises  - a double mobile channel / base station re-transmitter means in the first frequency band, a base / mobile station in the second frequency band  a first transmitting-receiving directional antenna interconnected with said retransmitter means for receiving in the first frequency band and transmitting in the second frequency band, for the mobile channel / base station respectively base station / mobile station;  a second transceiver directional antenna interconnected with said retransmitter means for receiving in the second frequency band and transmitting in the first frequency band, for the mobile channel / base station respectively base / mobile station, said first and second antennas being electromagnetically decoupled, the axis of the radiation pattern of the first and second antennas being contained in two substantially parallel vertical planes.  2. Device according to claim 1, characterized in that the first and the second antenna have in the vertical plane a radiation pattern having an opening angle less than or equal to 10.  3. Device according to claim 2, characterized in that said first antenna has in a horizontal plane orthogonal to the vertical plane and containing the axis of the radiation pattern of this antenna an opening angle between 45 "and 70" and in said second antenna has in a horizontal plane an aperture angle radiation pattern of less than 10 ".  4. Device according to one of the preceding claims, characterized in that to ensure the electromagnetic decoupling between the first and the second antenna, the axis of the radiation pattern of said antennas at the origin of the transmitting-receiving point is remote in a direction substantially parallel to said vertical plane, a distance d 2 10. where X denotes the maximum wavelength of the transmission signal of the first and the second frequency band.  5. Device according to one of claims 1 to 4, characterized in that said dual channel transmitter means comprises  a first channel comprising in cascade a band pass filter enabling transmission of the first frequency band, an HF amplifier,  a second channel comprising in cascade a band pass filter enabling the transmission of the second frequency band, an HF amplifier,  a first and a second duplexer, the first and second channels being interconnected in parallel via the first and second duplexers, said first and second duplexers respectively receiving a signal in the first frequency band for the mobile channel; base station, respectively transmitting and receiving a signal in the second frequency band for the base / mobile station channel on an input-output port.  A mobile radiotelephone telecommunications network, comprising a plurality of base stations each provided with a transceiver means in a first and a second transmission-reception frequency band, characterized in that said network comprises between two stations successive base layers, a plurality of substantially identical adjacent unidirectional extender devices according to one of claims 1 to 4, a base station and a unidirectional expander device adjacent to said base station respectively two adjacent unidirectional extender devices forming two successive transmitting-receiving stations with respect to a mobile unit, each unidirectional expander device being remote from a base station or from an adjacent unidirectional extender device of a distance greater than or equal to a critical distance allowing to remove cocanal interference from two radio stations successive transmission-reception vis-à-vis the mobile.  7. The network of claim 6, characterized in that each mesh of the network allows an intercommunication between mobile and transmitting station on a single pair of first respectively second frequency band.  8. Use of a network according to one of claims 6 or 7 along a taxiway.