AU729292B2

AU729292B2 - A process for the configuration of cells in a cellular radio system

Info

Publication number: AU729292B2
Application number: AU58302/98A
Authority: AU
Inventors: Vinod Kumar
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel Lucent SAS
Priority date: 1997-03-13
Filing date: 1998-03-10
Publication date: 2001-02-01
Anticipated expiration: 2018-03-10
Also published as: AU5830298A; FR2760930A1; JP2000511034A; FR2760930B1; CA2230090A1; EP0865220A1; WO1998041049A1

Description

P/00/OH1 28/5/91 Regulation 3.2

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C. S S C 0O Invention Title: A PROCESS FOR THE CONFIGURATION OF CELLS IN A CELLULAR RADIO SYSTEM The following statement is a full description of this invention, including the best method of performing it known to us:- This invention relates to cellular digital radiocommunication systems with mobiles, such as those designed according to the GSM public radiotelecommunication standard.

Here GSM standard is understood to mean both the GSM 900 standard ("public Group Special Mobile systems of radiocommunication operating in the 900 MHz band) and the DCS 1800 standard (Digital Cellular System operating in the 1800 MHz band).

More precisely, the invention concerns a method for configuring a plurality of geographic cells linked to the same transmitting/receiving site covering a large area (several tens of kilometres) and having low traffic volume, in a cellular digital radiocommunication system. The invention also concerns such a transmitting/receiving site.

Generally a cellular digital radiocommunication system is used within a network of geographic cells traversed by mobile stations. One base station and only one (BTS, for Base Transceiver Station) is associated with each cell, and a mobile station communicates through the base station associated with the cell in which the mobile is located.

0O When transmitting, each base station and therefore each cell) uses a radio carrier wave, referred to as BCCH carrier, which is characteristic of the base station S@ S and which provides it in particular with a broadcast control channel (BCCH) and, with its associated reception carrier wave, bidirectional traffic channels (TCH).

Each base station usually includes a single antenna.

If the number of traffic channels TCH provided by the BCCH carrier and its associated reception carrier is sufficient for moving the anticipated traffic in the cell, 2.25 the base station antenna is connected directly to a single transceiver device (TRx) which

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:64 comprises a transmitter (Tx) using the BCCH carrier (for the downlink) and a receiver (Rx) enabling reception of the carrier associated with the BCCH carrier (for the uplink).

600 If the number of traffic channels TCH provided by the BCCH carrier and its associated reception carrier is insufficient to move the anticipated traffic in the cell., the 30 base station uses one or more other pairs of carriers which provide the base station :l with supplementary TCH traffic channels. In this case, the base station antenna is connected furthermore to a plurality of supplementary transceiver devices (TRx). Each o• connected furthermore to a plurality of supplementary transceiver devices (TRx). Each of the latter includes a transmitter (Tx) using a carrier separate from the BCCH carrier (for the downlink) and a receiver (Rx) which enables reception of the associated carrier (for the uplink). Connection of the antenna to the various transceivers namely the one using the BCCH carrier and all others using carriers distinct from this BCCH carrier, is carried out via an output combiner. The same receiver may be common to all transceivers (TRx) connected to the same antenna. According to another structure, each transceiver (TRx) has its own receiver.

In cellular digital radiocommunication systems terminology, and particularly in GSM terminology, distinction is made between the concepts of geographic cell and transmitting/receiving site.

In fact, in the simplest case, a transmitting/receiving site accommodates only one base station, and therefore corresponds to the single cell (generally omnidirectional) associated with that base station.

But sometimes a transmitting/receiving site may accommodate a plurality of base stations. In this case, the same transmitting/receiving site thus corresponds to a plurality of cells (normally divided into sectors) each associated with one of the base stations.

@6 o This invention should be seen in a particular context, namely that where a 0@66 transmitting/receiving site is situated in a large area (several tens of kilometres) which can be broken down into: an inner ring with low traffic volume (corresponding for example to the requirements of about a thousand subscribers), at the centre of which is the transmitting/receiving site, and an outer ring with very low traffic volume (corresponding for example to the requirements of several hundreds of subscribers), surrounding the inner ring.

The inner ring corresponds for example to a suburban, industrial or residential area with low traffic volume. In this case, the outer ring corresponds to the surrounding expanses (several tens of kilometres) where the traffic volume is even lower.

At present, when it is necessary to provide radio coverage of a wide area (several tens of kilometres) with low traffic volume, use is made of: either a transmitting/receiving site accommodating a single base station associated with a single omnidirectional cell, or a transmitting/receiving site accommodating a plurality of base stations associated with a plurality of cells divided into sectors.

Whatever the number of base stations accommodated by the transmitting/receiving site, the cells still have a significant area. The conventional solution thus consists in using base stations whose transmitters (Tx) include very high power amplifiers (in order to cover the entire area of each cell), and very wide dynamic range receivers (Rx) (in the same cell, a mobile station capable of being close to or a long way from the site).

Furthermore, each base station generally has to make use of several carriers in order to be able to support the traffic of every large area cell with which it is associated. In other words, each base station almost always has to include several transceivers (TRx).

One consequence of this multiplicity of carriers is that an output combiner must be used in each base station to connect the antenna to the various transceivers (TRx).

This is very inconvenient because such an output combiner introduces significant losses (from 3 to 5 dB approximately) for which it is advisable to compensate by increasing the power, already high, which the transmission-end amplifier has to produce.

0 Another result of this multiplicity of carriers is that the single receiver (Rx) (if this ooo.

o.o is the structure which is adopted), shared by all transceivers (TRx) connected to the 000 02 antenna, has to be wide-band so as to allow reception of all the carriers (BCCH and others).

svaThe above-mentioned conventional solution, especially if each base station uses several carriers, is very expensive from a material point of view. In fact, the very high power amplifiers are high cost, low reliability devices. Moreover, because the receivers have both a wide pass-band and a wide dynamic input range, they also are very expensive.

An object of the present invention is in particular to overcome these various disadvantages of the prior art.

A further object of the invention is to provide a method for configuring a 30 plurality of geographic cells linked to the same transmitting/receiving site covering a wide area which has a low traffic volume, the method allowing a reduction in the costs of the transceivers (TRx) included in the base stations.

A still further object of the invention is to provide such a method which allows the quantity and cost of material used in each base station to be optimised, by taking account of the geographic distribution of the traffic volume over the area covered by the transmitting/receiving site.

According to the invention, there is provided a method of configuring a plurality of geographic cells linked to the same transmitting/receiving site in a cellular digital radiocommunication system, the said transmitting/receiving site accommodating a plurality of base stations each associated with one of the said cells and each defined by a distinct radio carrier, referred to as BCCH carrier, providing in particular a broadcast channel, the said transmitting/receiving site being located in an area capable of being broken down into: an inner ring having a first traffic volume, and at the centre of which the said transmitting/receiving site is located, an outer ring having a second traffic volume lower than the said first traffic volume, and surrounding the said inner ring, characterised in that the traffic of the said outer ring is supported by at least two first base stations each associated with a cell divided into sectors, and in that each first base station includes a long range directional antenna which is connected directly to a single first transceiver, the said transceiver comprising a transmitter using the BCCH carrier characteristic of the said first base station.

In order to provide radio coverage of the outer ring, the general principle of the invention therefore consists in using base stations whose antenna is connected only to a single transceiver (TRx).

In this way, the use of an output combiner (which usually allows the antenna to be connected to a plurality of transceivers) can be avoided. In the transmitter (Tx) of 0 this single transceiver, the amplifier can therefore be of lower power and therefore lower cost than those usually used, since it does not have to compensate for the losses induced by the combiner.

Preferentially the traffic of the said outer ring is supported by four first base stations, each associated with one 90 0 -sector cell.

In a first preferred implementation mode of the invention, the traffic of the said inner ring is supported by a single second base station associated with an 6 omnidirectional cell, the said at least two first base stations not participating in the support of the traffic of the said inner ring.

Thus, this second omnidirectional cell straddles the sectored cells on the inner ring and completely supports the traffic on this inner ring. The second base station associated with this omnidirectional cell obviously uses a BCCH carrier which is characteristic of it.

It also will be noticed that in the transmitter of the transceiver or each transceiver (TRx), the amplifier can be of lower power and therefore lower cost than those usually used, since it aims at covering only one cell of reduced size (corresponding to the area of the inner ring).

Preferably, the said second base station associated with the said omnidirectional cell includes a short-range omnidirectional antenna which is connected: either directly to a single second transceiver which includes a transmitter using the BCCH carrier characteristic of the said second base station; or, via a combiner, to: a second transceiver which includes a transmitter using the BCCH carrier characteristic of the said second base station, and at least one third transceiver which includes a transmitter using a carrier 20 separate from the BCCH carrier characteristic of the said second base station.

The number of transceivers (TRx) included in the second base station depends on the traffic to be provided in the inner ring. It is clear that if a single transceiver is sufficient, the use of an output combiner can be avoided and the amplifier in the transmitter of this single transceiver can therefore be again of lower power and therefore again of lower cost than those generally used.

Preferably, the said at least two first base stations belong to a first set of cells, the said second base station belonging to a second set of cells separate from the said first set of cells.

It should be noted that the first and second sets of separate cells are distinct only from the radio viewpoint, but it is clear that if necessary or if it is possible, the two sets of cells can be connected to the same base station controller (BSC).

Preferentially the said first and second sets of cells each use a distinct group of frequencies. in this way, despite the omnidirectional cell and the sectored cells overlapping each other in the inner ring, any problem of interference is avoided between these two types of cell.

In a second preferred implementation mode, the said first base stations also support the traffic of the said inner ring, each first base station moreover including to that effect a supplementary short range, directional antenna which is connected to at least one second transceiver which includes a transmitter using a carrier separate from the said BCCH carrier characteristic of the said first base station.

Thus, each sectored cell comprises a first part, called the inner part, covering an area of the inner ring and a second part, called the outer part, covering the an area of the outer ring. The base station of each sectored cell provides the traffic: firstly in the outer part of the cell, by means of the antenna to which the single first transceiver is connected, and secondly in the inner part of the cell, by means of the supplementary antenna to which one or more second transceivers is connected.

It will be noted that the BCCH carrier used by the single first transceiver is unique for the whole cell and therefore covers both the outer part and the inner part of the sectored cell. In other words, in each base station the second transceiver(s), which enable the provision of traffic in the inner part of the cell, employ no BCCH

S

carrier other than that used by the single first transceiver.

.It will also be noted that in the transmitter in the second transceiver, or in each of the second transceivers, the amplifier can be of lower power and therefore of lower cost than those usually used, since it aims only to cover a reduced size cell part (corresponding to the inner part of the cell).

2.as Preferably, the said supplementary antenna is connected: either directly to a single second transceiver; or, via a combiner, to at least two second transceivers.

The number of second transceivers included in each base station depends on the traffic to be provided in the inner ring. It is clear that if a single second transceiver 30 is sufficient, the use of an output combiner can be avoided and, in the transmitter of S. this second transceiver, the amplifier can therefore be again of lower power and therefore again of lower cost than those generally used.

Preferentially the dynamic range of the signals received at the said site is divided into two dynamic subranges overlapping each other, namely: a low dynamic subrange, for receiving signals transmitted by a mobile station situated in the said outer ring, a high dynamic subrange, for receiving signals transmitted by a mobile station situated in the said inner ring, and the said first transceiver of each of the said first base stations, allowing the traffic of the said outer ring to be supported, includes a first receiver adjusted to the said low dynamic subrange.

Use of a receiver with a wide dynamic range is thus avoided. In fact, since the first receiver is designed to receive signals coming from mobile stations situated in the outer ring, the one low dynamic range can be used. This first receiver is therefore much less expensive than those generally used.

Advantageously, in the case of the first implementation mode of the invention, the said second base station, which supports the traffic of the said inner ring, includes a second receiver adjusted to the said high dynamic subrange.

Again, use of a receiver with a wide dynamic range is thus avoided. In fact, since the second receiver is designed to receive signals coming from mobile stations situated in the inner ring, the one high dynamic range can be used. This second I2 0 receiver is therefore much less expensive than those generally used.

Preferentially the said second receiver: is either included in the said single second transceiver of the said second base station; or is wideband and common to the set of the said second and third transceivers of the said second base station.

It will be noted that the second receiver is inevitably wideband if it is common to O°°c several transceivers which use different carriers.

Advantageously, in the case of the second implementation mode of the invention, each first base station also includes: in the said single first transceiver, a second receiver adjusted to the said high dynamic subrange, in the said at least one second transceiver, a third receiver adjusted to the said 9 high dynamic subrange, and each first base station also includes the means of detecting, from signals transmitted by a mobile station and received by one of the said first and second receivers, in which ring, inner or outer, the said mobile station is situated, so as to allocate to the latter: either a traffic channel supported by the first transceiver and using the said first receiver, if it is located in the said outer ring, or a traffic channel supported by the said at least one second transceiver and using the said third receiver, if it is located in the said inner ring.

There, the use of a receiver having a wide dynamic range is again avoided. In fact, since this second receiver is designed to receive signals coming from mobile stations situated in the inner ring (that is to say in the inner part of the cell), the one high dynamic range can be used. The second receiver is therefore much less expensive than those generally used.

Preferentially, the said third receiver: is either included in the said single second transceiver connected to the said :supplementary antenna; go or is wideband and common to the set of the said second transceivers o663 connected via the combiner to the said supplementary antenna.

O •20 Preferentially, the set of carriers employed at the said site is divided into two carrier subsets, namely: a first subset of carriers, including the carriers used in the said outer ring, and particularly the BCCH carriers characteristic of the said first base stations, a second subset of carriers, including the carriers used in the said inner ring, and particularly the carriers separate-from the said BCCH carriers characteristic of the said first base stations, the said first receiver of each of the said first base stations enabling reception of the carriers of the said first subset of carriers.

Thus the use of a receiver with a wide passband is avoided. In fact, the first 0 30 receiver is designed to receive only the carriers of the first subset of carriers. In this way, the first receiver is much less expensive than those generally used (if it is a matter of wideband receivers).

Advantageously, in the case of the first implementation mode of the invention, the said second receiver included in the said second base station enables reception of the carriers of the said second subset of carriers.

Again, the use of a receiver with a wide passband is avoided.

Advantageously, in the case of the second implementation mode of the invention, the said second receiver of each first base station enables reception of the carriers of the said first subset of carriers, and the said third receiver of each second base station enables reception of the carriers of the said second subset of carriers.

It will be noted that in this case, the second and third receivers both participate in the support of the traffic in the inner ring. The second receiver enables reception of the BCCH carriers characteristic of the first base stations (these BCCH carriers being used here both in the inner ring and the outer ring). The third receiver enables reception of the other carriers (the other carriers being used only in the inner ring).

According to a further aspect of the invention there is provided a transmitting/receiving site in a cellular digital radiocommunication system, the said transmitting/receiving site being of the type accommodating a plurality of base so" stations each associated with one of the said cells and each defined by a distinct radio woes carrier, referred to as BCCH carrier, providing in particular a broadcast channel, the said transmitting/receiving site being situated in an area capable of being broken down into an inner ring having a first traffic volume and at the centre of which the said transmitting/receiving site is located, and.an outer ring which has a second traffic volume lower than the said first traffic volume and surrounding the said inner ring, characterised in that it includes at least two first base stations each associated with one sectored cell, so as to support the traffic of the said outer ring, and in that each of the said first base stations includes a long range, directional antenna which is connected directly to a single first transceiver which includes a transmitter using the BCCH carrier characteristic of the said first base station.

In order that the invention may be readily carried into effect, embodiments 30 thereof will now be described in relation to figures of the accompanying drawings, in which: Figure 1 shows schematically one configuration example, in accordance 11 with a first implementation mode of the method of the invention, of 5 geographic cells linked to the same transmitting/receiving site; Figure 2 shows schematically the different base stations included in the transmitting/receiving site in Figure 1 Figure 3 shows schematically one configuration example, in accordance with a second implementation mode of the method of the invention, of 4 geographic cells linked to the same transmitting/receiving site; and Figure 4 shows schematically the various base stations included in the transmitting/receiving site in Figure 3.

The invention thus concerns a method for configuring a plurality of geographic cells linked to the same transmitting/receiving site of a cellular digital radiocommunication system.

In the remainder of the description, the cellular digital radiocommunication system is considered to be of the GSM type. It is obvious nevertheless that the invention is not limited to this particular type of system.

Conventionally, the transmitting/receiving site accommodates a plurality of base stations each associated with one cell and each defined by a distinct radio carrier, referred to as BCCH carrier.

e.GO oooo Hypothetically, the transmitting/receiving site is situated in an area capable of being broken down into: an inner ring (hatched area in Figures 1 and 2) having a first moderate value traffic volume, and at the centre of which the transmitting/receiving site is situated, an outer ring having a second traffic volume lower than the first traffic volume, and surrounding the inner ring.

According to the invention, the outer ring traffic is supported by first base o stations BTS 1 to BTS 4 each associated with one sectored cell CELL 1 to CELL 4 and 0 each including a single transceiver TRx 1 to TRx 4 connected directly to a long range, directional antenna Al to A4.

The single first transceiver TRx 1 to TRx 4 of each first base station BTS 1 to BTS 4 includes in particular: a transmitter Tx 1 to Tx 4 using a BCCH carrier fBCCH, to fBCCH,4 characteristic of this first base station, and 12 a first receiver Rx 1 to Rx 4 (Fig. Rx 18 to Rx 4 B (Fig. 4).

Thus the general principle of the invention consists in using no output combiner in the first base stations providing the traffic of the outer ring. In this way, the power required from the transmitters Tx 1 to Tx 4 is lower than that required from transmitters usually employed. Consequently, the transmitters Tx 1 to Tx 4 are less expensive than the conventional transmitters.

In the first and second implementation modes of the method of the invention, presented below, in connection with Figures 1-2 and 3-4 respectively, the traffic of the outer ring is supported by four first base stations BTS 1 to BTS 4, each associated with one 90 0 -sector cell CELL 1 to CELL 4.

However, it is obvious that the method of the invention may be applied whatever the number (greater than 2) of cells covering the outer ring, that is to say whatever the number (greater than 2) of first base stations supporting the traffic in the outer ring.

In order to further reduce the material costs, limits can be placed on the dynamic input range and/or the carriers capable of being received by the first receiver r Rx 1 to Rx 4 (Fig. Rx 1B to Rx 4 8 (Fig. 4) of the single first transceiver TRx 1 to TRx 4 of each first base station BTS 1 to BTS 4.

OOSS

In order to be able to limit the dynamic input range of the first receivers, the dynamic range of the signals received at the site 10, 30 is divided into two dynamic subranges overlapping each other, namely: S. a low dynamic subrange, for receiving signals transmitted by a mobile station located in the outer ring, a high dynamic subrange, for receiving signals transmitted by a mobile station 0 .35 located in the inner ring.

The dynamic input range of each first receiver Rx 1 to Rx 4 (Fig. Rx 1 B to Rx 00 0 4 B (Fig.4), can then be limited to the low dynamic subrange, since this first receiver is designed to receive only signals coming from mobile stations located in the outer ring.

In order to be able to limit the carriers capable of being received by the first 30 receivers, the carriers used at the site 10, 30 can be divided into two subsets of 000 carriers, namely: a first subset of carriers, including the carriers used in the outer ring, and in 13 particular the BCCH carriers fBCCH,1 to fBCCH,4 characteristic of the first base stations BTS 1 to BTS 4, a second subset of carriers, including the carriers used in the inner ring, and in particular the carriers fBCCH,5 and f 6 (Fig. 2) and f 1 to f4 (Fig. separate from the BCCH carriers characteristic of the first base stations.

The carriers capable of being received by each first receiver Rx 1 to Rx 4 (Fig.

Rx 1 B to Rx 4 B (Fig. 4) can then be limited to the first subset of carriers.

The two modes of implementation presented subsequently are differentiated in the manner of supporting the traffic of the inner ring.

In connection with Figures 1 and 2, the first implementation mode of the method of the invention is shown first of all. In this case, the traffic of the inner ring is supported by a single second base station BTS 5 associated with an omnidirectional cell CELL It will be noted that, even though the sectored cells CELL 1 to CELL 4 which are associated with them also cover the inner ring, the first base stations BTS 1 to BTS 4 do not participate in supporting the traffic of the inner ring. So as to avoid any problem due to this double radio coverage, provision can be made for: S* a relative adjustment of the transmission power levels of the transmitters Tx 1 to Tx 4 of the first base stations BTS 1 to BTS 4 on the one hand, and of the transmitters 20 Tx 51 to Tx 53 of the second base station BTS 5 on the other hand; S" the first base stations BTS 1 to BTS 4 to be part of a first set of cells, whereas the second base station BTS 5 is part of another set ce [sic]; the two sets of cells (which may be connected to the same BSC) each to use a distinct set of frequencies.

In the example given in Figure 2, the second base station BTS 5 associated with 00 the omnidirectional cell CELL 5 includes a short range, omnidirectional antenna which is connected via a combiner 50 to: a second transceiver TRx 51 which includes a transmitter Tx 51 using the BCCH carrier fBCCH,5 characteristic of the second base station BTS 5, and 30 a third and fourth transceiver TRx 52, TRx 53 which each include a transmitter Tx Tx 53 using a carrier f 6 f 7 separate from the BCCH carrier fsCCH,5 characteristic of the second base station BTS The second, third and fourth transceivers TRx 51, TRx 52 and TRx 53 each include either a receiver Rx 51, Rx 52 and Rx 53, or a common receiver Rx 5 (which is wideband in the second case).

It is clear that the number of transceivers included in the second base station BTS depends on the amount of traffic to be moved in the inner ring. Thus, if this amount of traffic is sufficiently small, the single second transceiver TRx 51 may suffice, and is then connected directly (without combiner) to the antenna In order to reduce the material costs, limits can be placed on the dynamic input range and/or the carriers capable of being received by the receiver Rx 5 common to the second, third and fourth transceivers TRx 5 1 TRx 52 and TRx 53.

In fact, the dynamic range of the common receiver Rx 5 can be limited to the above-mentioned high dynamic subrange, since it is designed to receive only signals coming from mobile stations located in the inner ring.

Likewise, this common receiver Rx 5, when receiving, can be restricted to the carriers of the above-mentioned second subset of carriers.

r In connection with Figures 3 and 4, the second implementation mode of the method of the invention is now explained. In this case, the traffic of the inner ring is also supported by the first base stations BTS 1 to BTS 4. In other words, each first base station BTS 1 to BTS 4 supports: not only the traffic in the outer part 12, 22, 32, 42 of the sectored cell CELL 1 to CELL 4 with which it is associated in Figure 3, in the non-hatched part), but also the traffic in the inner part 11, 21, 31, 41 of the sectored cell CELL 1 to CELL 4 with which it is associated in Figure 3, in the hatched part).

In order that the same BCCH carrier can be used both in the outer part and the OQ inner part of the same sectored cell, each first base station BTS 1 to BTS 4 also includes: in its single first transceiver TRx 1 to TRx 4, a second receiver Rx 1H to Rx 41 adjusted to the above-mentioned high dynamic subrange; means (not shown) which allow detection, by means of signals transmitted by a 6 30 mobile station and received by the first receiver Rx 1B to Rx 4 B or the second receiver Rx S 1H to Rx 4 H, of the ring, inner or outer, in which the mobile station is located.

00 T Thus, in each sectored cell CELL 1 to CELL 4, the first receiver Rx 1 B to Rx ~B enables reception of signals transmitted by a mobile station located in the inner part 11, 21, 31, 41 of this sectored cell, while the second receiver Rx 1H to Rx 4 H enables the reception of signals transmitted by a mobile station located in the outer part 12, 22, 32, 42 of the sectored cell. In other words, each sectored cell is entirely covered for BCCH carrier reception.

The signals transmitted by a mobile station, and which the first receivers Rx 1 to Rx 4 B and second receivers Rx 1 H to Rx 4 H can receive, are for example bursts transmitted by the mobile station in the random access channel (RACH) with the intention of gaining access to the radiocommunication channel. These "RACH bursts" are transmitted on the BCCH carrier of the uplink (which is combined with the BCCH carrier fBCCH,1 to fBCCH,4 of the downlink to form the bidirectional BCCH channel).

For each "RACH burst" received by one of its first and second receivers, each first base station BTS 1 to BTS 4 calculates the approximate distance of the mobile station in relation to the transmitting/receiving site 30, as a function of the time taken by the "RACH burst" to reach the site. Thus it can be determined in which ring, inner or outer, the mobile station is located. Such calculating means, known as TOA (Time Of Arrival) type, are standard in the GSM sphere.

S* Thus each first base station BTS 1 to BTS 4 allocates to a mobile station:

*OSS

either a traffic channel supported by the first transceiver TRx 1 to TRx 4 and using 20 the first receiver Rx 1 to Rx 4 B, if the mobile station is located in the outer part of the cell, i.e. in the outer ring, or a traffic channel supported by the second transceiver TRx 1' to TRx 4' and using a third receiver (cf below), if it is located in the inner part of the cell, i.e. in the inner ring.

So that each first base station BTS 1 to BTS 4 can also support the traffic in the inner part 11, 21, 31, 41 of its sectored cell, it further includes a supplementary short range, directional antenna Al' to A4' which is connected to one or more second transceivers TRx 1' to TRx 4'.

In the example shown in Figure 4, the supplementary antenna Al' to A4' of each first base station BTS 1 to BTS4 is connected directly to a single second transceiver TRx 1' 30 to TRx 4' which includes a transmitter Tx 1' to Tx 4' (using a carrier fl' to f 4 separate from oo. the BCCH carrier fBCCH,1 to fBCCH,4 characteristic of this first base station), and a third receiver Rx 1' to Rx 4'.

It is obvious that the number of transceivers connected to each supplementary antenna Al' to A4' depends on the amount of traffic to be moved in the inner part 11, 21, 31, 41 of each sectored cell CELL 1 to CELL 4. Thus, if the amount of traffic requires it, each supplementary antenna Al'to A4' of each first base station BTS 1 to BTS 4 may be connected, via a combiner, to several (and not a sole one as in Figure 4) transceivers.

In order to reduce the material costs, limits can be placed on the dynamic input range and/or the carriers capable of being received by the third receiver Rx 1' to Rx 4' of the single second transceiver TRx 1' to TRx 4' connected to each supplementary antenna Al'to A4'.

In fact, the dynamic range of each of these third receivers Rx 1' to Rx 4' can be limited to the above-mentioned high dynamic subrange, since it is designed to receive only signals coming from mobile stations located in the inner ring.

Similarly, each of these third receivers Rx 1' to Rx when receiving, can be restricted to the above-mentioned second subset of carriers.

It is obvious that the invention is not limited to the two particular implementation modes presented above.

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Claims

1. A method for configuring a plurality of geographic cells linked to the same transmitting/receiving site in a cellular digital radiocommunication system, the said transmitting/receiving site accommodating a plurality of base stations each associated with one of the said cells and each defined by a separate radio carrier wave, referred to as BCCH carrier, which provides in particular a broadcast channel, the said transmitting/receiving site being situated in an area capable of being broken down into: an inner ring having a first traffic volume, and at the centre of which the said transmitting/receiving site is located, an outer ring having a second traffic volume lower than the first traffic volume, and surrounding the inner ring, wherein the said outer ring is supported by at least two first base stations each associated with one sectored cell, and in that each first base station includes a long range, directional antenna which is connected directly to a single first transceiver, the said first transceiver including a transmitter using the BCCH carrier characteristic of the said first base station.

2. A method as claimed in Claim 1, wherein the traffic of the said outer ring is a. supported by four first base stations, each associated with one 90 0 -sector cell. I.

3. A method as claimed in either one of Claims 1 and 2, wherein the traffic of the 20 said inner ring is supported by a single second base station associated with an omnidirectional cell, the said at least two first base stations not participating in the support of the traffic of the said inner ring. S 4. A method as claimed in Claim 3, wherein the second base station associated with the said omnidirectional cell includes a short range, omnidirectional antenna which is 25 connected: Seither directly to a single second transceiver which includes a transmitter using the BCCH carrier characteristic of the said second base station; I.. or, via a combiner, to: a second transceiver which includes a transmitter using the BCCH carrier 30 characteristic of the said second base station, and at least one third transceiver which includes a transmitter .using a carrier separate from the BCCH carrier characteristic of the said second base using a carrier separate from the BCCH carrier characteristic of the said second base OS S 0 0 4 S. 00 9 I C

9. 01 *I I 0O I station. A method as claimed in either one of Claims 3 and 4, wherein the said at least two first base stations are part of a first set of cells, the said second base station being part of a second set of cells separate from the said first set of cells. 6. A method as claimed in Claim 5, wherein the said first and second sets of cells each use a distinct group of frequencies. 7. A method as claimed in either one of Claims 1 and 2, wherein the said first base stations also support the traffic of the said inner ring, each first base station moreover including to that effect a supplementary short range, directional antenna which is connected to at least one second transceiver which incluaes a transmitter using a carrier separate from the said BCCH carrier characteristic of the said first base station. 8. A method as claimed in Claim 7, wherein the said supplementary antenna is connected: either directly to a single second transceiver; or, via a combiner, to at least two second transceivers. 9. A method as claimed in any one of Claims 1 to 8, wherein the dynamic range of the signals received at the said site is divided into two dynamic subranges overlapping each other, namely: a low dynamic subrange, for receiving signals transmitted by a mobile station f 20 located in the said outer ring, a high dynamic subrange, for receiving signals transmitted by a mobile station located in the inner ring, and in that the said first transceiver of each of the said first base stations which enable support of the traffic of the said outer ring, includes a first receiver 25 adjusted to the said low dynamic subrange. o6•: 10. A method as claimed in Claim 9 and any one of Claims 3 to 6, the said first base 0 stations not participating in the support of the traffic of the said inner ring, wherein the 0*re Ssaid second base station, which supports the traffic of the said inner ring, includes a second receiver adjusted to the said high dynamic subrange. 30 11. A method as claimed in Claim 10 and Claim 4, wherein the said second receiver: oe either is included in the said single second transceiver of the said second base station; or is wideband and common to the set of the said second transceiver and third transceiver of the said second base station.

12. A method as claimed in Claim 9 and either one of Claims 7 and 8, the said first base stations also supporting the traffic of the said inner ring, wherein each first base station also includes: in the said single first transceiver, a second receiver adjusted to the said high dynamic subrange, in the said at least one second transceiver, a third receiver adjusted to the said high dynamic subrange, and in that each first base station also includes the means of detecting, from signals transmitted by a mobile station and received by one of the said first and second receivers, in which ring, inner or outer, the said mobile station is situated, so as to allocate to the latter: either a traffic channel supported by the first transceiver and using the said first receiver, if it is located in the said outer ring, or a traffic channel supported by the said at least one second transceiver to and using the said third receiver, if it is located in the said inner ring.

13. A method as claimed in Claim 12 and Claim 8, wherein the said third receiver: °either is included in the said single second transceiver connected to the said supplementary antenna; or is wideband and common to the set of the said second transceivers connected via the combiner to the said supplementary antenna.

14. A method as claimed in any one of Claims 9 to 13, wherein the set of carriers used at the said site is divided into two subsets of carriers, namely: a first subset of carriers, including the carriers used in the said outer ring, and in .25 particular the BCCH carriers characteristic of the said first base stations, CC a second subset of carriers, including the carriers used in the said inner ring, and in particular the carriers separate from the said BCCH carriers characteristic of the said O*a first base stations, and in that the said first receiver of each of the said first base stations is limited in reception to the first subset of carriers.

15. A method as claimed in Claim 14 and either one of Claims 10 and 11, wherein the said second receiver included in the said second base station is limited in reception to the second subset of carriers.

16. A method as claimed in Claim 14 and either one of Claims 12 and 13, wherein the said second receiver of each first base station is limited in reception to the first subset of carriers, and in that the said third receiver of each second base station is limited in reception to the second subset of carriers.

17. A transmitting/receiving site in a cellular digital radiocommunication system, the said transmitting/receiving site being of the type accommodating a plurality of base stations each associated with one of the said cells and each defined by a separate radio carrier, referred to as BCCH carrier, providing in particular a broadcast channel, the said transmitting/receiving site being situated in an area capable of being broken down into an inner ring having a first traffic volume and at the centre of which the said transmitting/receiving site is located, and an outer ring having a second traffic volume lower than the said first traffic volume and surrounding the said inner ring, wherein it includes at least two first base stations each associated with one sectored cell, so as to support the traffic of the said outer ring, and in that each of the said first base 1 5 stations includes a long range, directional antenna which is connected directly to a single first transceiver which includes a transmitter using the BCCH carrier characteristic of the said first base station. S 18. A site as claimed in Claim 17, wherein the said single first transceiver 1,a of each of the said first base stations includes a first receiver adjusted to a low dynamic subrange, so as to enable reception of signals transmitted by a mobile station located in the said outer ring. 1 9. A site as claimed in either of Claims 17 and 1 8, wherein the said first receiver of each of the said first base stations is limited in reception to one subset of carriers including the carriers used in the said outer ring, and in particular the BCCH carriers 5 characteristic of the said first base stations.

20. A process substantially as herein described with reference to Figures 1 4 of the accompanying drawings.

21. A device substantially as herein described with reference to Figures 1 4 of the accompanying drawings. 00 00 I 004 00 I 00 I 50 0 4 I 0 0 000 04 *04 00I 0004 I 0 00 0 00o o DATED THIS EIGHTH DAY OF APRIL 1998 ALCATEL ALSTHOM COMPAC NIE GNERALE d'ELECTF