AU669394B2

AU669394B2 - Mobile radio system

Info

Publication number: AU669394B2
Application number: AU50229/93A
Authority: AU
Inventors: Manfred Dr. Bohm
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1992-11-13
Filing date: 1993-10-25
Publication date: 1996-06-06
Anticipated expiration: 2013-10-25
Also published as: DE4238295A1; AU5022993A

Description

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Patents Act 1990

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Invention Title: "MOBILE RADIO SYSTEM" The following statement is a full dlescription of this invention, including the best method of performing it known to uIS:- Co0 6 2 4 to 5 0 C1 93 I_ I This invention relates to a mobile-radio network for serving an area divided into radio cells and a correspondingly designed base station.

Such mobile-radio networks are known as cellular networks and work via analog or digital radio-transmission processes.

A mobile-radio network for an area divided into radio cells is known in which each radio cell within the mobile-radio network has a base station which is connected to a mobile switching centre.

Such cellular networks require a dynamically and technically complex control of the transmission level of the base station for various reasons. The 10 intention here is to supply, amongst other things, mobile stations within a radio cell with a reception level as constant as possible, so that simple receivers with low dynamics can be used within the mohil stations, For example, mobile-radio networks specified according to GSM-recommendations contain base stations with the transmission level dynamically controlled between approx. 10 mW and 35 W.

It is an object of the present invention to provide a cellular network with base stations of simple design.

According to the invention, there is provided a mobile-radio network for S serving an area divided into radio cells wherein at least one of the radio cells is 20 subdivided into N subcells which are supplied with constant transmitting/receiving parameters from a base station by means of transceivers individuF. to each subcell.

The invention instructs about the division of a radio cell into several subcells and the supply of the subcells by means of individual transceivers and where the transmitting/receiving parameters are constant and individual to each subcell. The result is a cellular network with simple base stations whose transmitting and receivi'ng characteristics do not require dynamic modification, such as for example control of transmission signal level.

Preferably, a radio cell is subdivided into N subcells in a ring formation, so that the base station supplies a mainly concentrically subdivided radio cell.

This structure permits, particularly in level radio areas, a good rnatching to the radio coverage conditions within the radio cell. Each subcell will therefore always cover a large area with homogeneous radio-traffic, which means that a ~a II I--ar -e small number of transceivers serve the total radio cell.

Preferably, the subcells are designed so that they each cover ares with largely homogeneous radio-traffic intensities. The subdivision of the radio cells is therefore matched to the structure of the radio traffic, whereby typical traffic areas such as, e.g, inner city districts, ring streets, city outskirts, can each be covered by one subceil. The supply within these subcelis can be matched advantageously to the corresponding radio traffic, by e.g. supplying a basic-load supply for the individual traffic section and a peak-load supply corresponding with the changing traffic volume within the subcells. Supply and distribution 10 can be directed e.g. by means of allocating radio channels to subcells by the mobile switching centre with economic use of frequencies.

Preferably, one mobile switching centre integrated in the mobile-radio network is equipped for central signal processing, so that the base stations can be designed as channel translators in compact design. The mobile-radio network 15 enables a simple set-up and expansion as only the mobile switching centre represents a larger and more complex technical installation. By moving the mobile switching centre away from ,reas with dense infrastructure (urban centres or similar) into areas with a lower infrastructure the costs for setting-up and maintaining a mobile switching centre can be reduced.

20 Preferably, the radio channels required to supply the radio cells are connected to and from the base station via a transmission path. The transceivers translate the radio channels into communication channels, which are then transmitted together over the broad-band transmission path (fibre-optic cable or similar), for example in a frequency multiple. The base stations are therefore of a simple and compact technical design due to N channel translators.

In order that the invention may be readily carried into effect, an embodiment thereof will now be described in relation to the accompan,.ing drawings, in which: Figure 1 shows a mobile-radio network in accordance with the invention with subdivided radio cells in a ring shaped formation Figure 2a shows a radio channel allocation with the corresponding transmission levels for a subdivided radio cell Figure 2b shows the corresponding propagation of the reception level within this radio cell Figure 3 shows two neighbouring radio cells and the radio channel allocation, which is directed centrally by means of broad-band transmission paths.

The mobile-radio network according to Figure 1 comprises four radio cells C1 C4, which are each supplied by a base station BTS1 BTS4. The radio cells overlap for complete coverage of a radio area. Each radio cell is subdivided into three subcells SC13, SC23 SC32, SC33, which overlap in a ring formation.

10 The subcells have radio channels A E available to supply the radio cells.

Each radio channel is to be equipped for a full duplex-radio connection in the practical example. Here, each radio channel has a RF-carrier for an outgoing connection (downlink) and a RF-carrier for an incoming connection (uplink) connected which lie in the frequency range of 935 960 MHz, resp. 890 915 15 MHz. and which maintain a duplex range of 45 MHz to each other. The radio connections are made by the TDMA-method (Time Division Multiple Access), so that several, e.g. eight, mobile radio subscribers can access one radio channel.

To avoid common channel interference, directly neighbouring or partially overlapping subcells do not use the same radio channel, i.e. in this example not 20 the same RF-carrier pair. As shcwn in Figure 1, the outer subcell SC13 of the first radio cell C1 has radio channels C and E. The partially overlapping outer subcell SC23 of second radio cell C2 has channel A allocated, which avoids common channel interference in the overlapping portion of both subcells and enables a unique allocation of a mobile station to one of the subcells by means of channel allocation. Radio channels C, E and A can be reused in those subcells that are at a suitable distance from said subcells, according to the "frequency reuse" principle, With a minimum number of radio channels, which is equal to the number of subcells per radio cell, i.e. in the practical example with three radio channels, the total mobile-radio network could cover the area to be serviced with economic use of frequencies and in a continuous manner.

Each base station supplies its three subcells by means of individual transceivers. The subcells stretch across areas with nearly constant radio link attenuation. The transmission levels of the transceivers are set to the corresponding radio attenuation, which will be explained in the following in more detail with the aid of Figs. 2a and 2b. Furthermore, the receiving sensitivity of the transceivers is limited to the maximum propagation of the corresponding subcell. The transceivers supplying an inner subcell work with a lower sensitivity than transceivers supplying an external subcell. This avoids that e.g.

a mobile station, which transmits on channel A within the external subcell SC23 in the second radio cell C2, is erroneously received by the transceiver supplying the inner subcell SC11 of the first radio cell C1 and that the mobile station is allocated to this subcell SC11.

e 10 As is shown in Figure 2a in diagrammatic form, the inner, first subcell S SC11 oI radio cell C1 is supplied by the first transceiver TRC11 with a constant transmitting power of e.g. P 300 mW and with the not-directly neighbouring radio channels A, D, Furthermore, the middle, second subcell SC12 is supplied by the second transceiver TRC12 with a constant transmitting power of P 3 15 W and with radio channel B. The external subcell SC13 of radio cell C1 is supplied by the third transceiver TRC13 with a transmitting power of P 30 W and with radio channels C, E.

The transmitting power is set to a radio link attenuation characteristic for the individual subcell, such as e.g. the maximum radio attenuation at the 20 external subcell edge. As is shown in a further diagram in Figure 2b, a lowoscillating, distance-dependent receiving level E is achieved in each subcell without having to equip the base station with a device for dynamic control of transmission power. The diagram in Figure 2b shows a receiving level E, which drops by an amount AE of approx. 10 dB within each individual subcell SC11 SC13 when proceeding from the maximum receiving level and with increasing distance s to the base station, A mobile station which is operated within the mobile-radio network according to the invention, must generally be able to compensate such changes to its receiving level AE.

The maximum receiving level within a subcell is determined by setting the transmission power. The expansion of the subcells always determines the value AE, by which the receiving level drops within a subcell, As shown in Figs. 2a and 2b, the transmission power and expansion of the subcells in this practical example are matched so that the receiving level within the subcells maintains a I fixed, and for the mobile station optimum range of change AE, which is regulated within the mobile station on a narrow band.

When transmitting from the mobile station to the base station, the distance-dependent variations of receiving level in the base station are compensated by means of a narrow band control of the mobile station's transmission level. Tne transceivers in the base stations are the broad-band variety so that they transmit ;nd receive on several radio channels, i.e. RF carriers, simultaneously. A broad-band control of e.g. transmission level and receiving sensitivity within the base station is not necessary. By using the 0 shown subcell structure and the fixed setting of the transmitting/receiving parameters in the base stations, the small, remaining level variations within the .connection can easily be compensated by means of narrow-band controllers in the corresponding mobile station.

Figure 3 shows two neighbouring radio cells C1, C2 of the said described 15 mobile-radio network and the corresponding base stations BTS1, BTS2, each of which is connected by its individual transmission path TRANS, such as e.g. a fibre-optic cable, to a mobile switching centre MSC, As shown in Figure 3, the base station BTS1, as an example for all base stations in the mobile-radio network, comprises three transceivers TRC11..TRC13, each with an optical S 20 signal connector OG and an electrical RF signal connector EG. By means of the optical signal connectors, modulated optical carrier signals such as, e.g.

modulated laser beams, and by means of electrical RF signal connectors modulated RF carriers are exchanged as radio signals between one of the transceivers and the peripherals described in the following. Therefore the optical signal connectors OG and the electrical signal connectors EG are used to couple the transceivers to optically conducted communication channels a, e resp. to radio channels A, E. One communication channel and one radio channel are always dedicated uniquely by having their optical, resp, electrical modulations correspond. The necessary channel translation is carried out within the corresponding transceivers by means of mixer levels and opto/electronic transducers. In this practical example described in accordance with Figure 3, two communication channels a,b are translated into the two corresponding radio channels A,D within the transceiver TRC1 1.

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The transceivers are connected to the following peripherals by means of their signa, connectors: the electrical RF signal connectors EG are coupled to a common transmitting and receiving antenna by means of a full-duplex directional coupler ECP. This results in the supply of the subcells with one or more radio channels A, each, which are supplied by transceivers TRC11..TRC13. The transceivers are furthermore coupled to an optical fibre-optic cable TRANS by means of their optical signal connector OG and an optical coupler OCP, TRANS itself being connected to the mobile switching centre MSC.

Signal processing of the signals carried in the channels, i.e. in particular 10 coding and decoding as well as modulation and demodulation, is advantageously conducted in the mobile switching centre MSC, so that the individual transceivers TRC11 TRC13 need only be equipped for the said channel translation.

The mobile switching centre MSC cpntrally manages the radio channels 15 A..E available in the mobile-radio network by allocating, dependent on the radio traffic intensity in the subcells, communication channels to the corresponding transceivers, said channels being uniquely allocated to a determined radio channel The traffic-adaptive channel allocation is carried out, e.g. by exchanging signalling records between mobile station MS and the 20 mobile switching centre MSC via organisation channels, which are established in the radio transmission paths and the optical transmission paths. This however requires processor controlled levels within the base stations.

A particularly simple adaptation of the capacity to the current radio traffic intensity is implemented as follows in the shown practical example: within the optical coupler OCP optical filters are employed in such a manner that each communication channel is only allocated to one particular transceiver.

Furthermore, using electrical filters within the directional coupler ECP, the radio channels are selected correspondingly, This achieves a simple, even though not optional, channel allocation, In this practical example therefore, the base stations BTS1, BTS2 are of very simple and compact design by means of channel translators TRC11 TRC13 (transceivers) which work with constant set amplifying leve's, By using the central signal processing and central channel allocation, the here displayed mobile-radio network requires only one complex technical device, which is the mobile switching centre. The broad-band coupling of the base stations to the mobile switching centre enables a simple connection of additional channel translators to expand the radio channel capacity within the mobile-radio network.

Apart from signal processing and channel allocation, the mobile switching centre MSC also controls the allocation of a mobile station MS to a certain subcell. This allocation can be made, for example, by an evaluation of the current radio signal transit time. Consequently, the radial distance of the mobile 10 station MS to its base station determines the subcell allocation of this mobile station while establishing a radio connection, with subcell change or during radio cell change (handover).

The following advantageous variation of the mobile-radio network according to the invention is furthermore possible: in densely populated centres with heavy radio traffic the installation of technical devices is generally more costly than in lesser populated, rural areas. The broad-band coupling of the base station in compact design and acting as channel translator, enables a costeffective installation of the mobile-radio network, by having its large and elli extensive equipment, such as the mobile switching centres MSC, relocated to 20 rural areas (as for instance, the city outskirts). The signal processing of the city's radio traffic could be done effectively within those mobile switching centres that have already been installed in the outskirts and have redundant capacity.

The described mobile-radio network and the base stations designed for it only give an example design of the invention. The subdivision of the radio cells can be quite individually specific, particularly dependent on the given topography so that, e,g, individual subcells can cover patch-like radio areas by means of heavily directed antenna characteristics.

Setting the transmitting/receiving parameters to a constant, and for the corresponding subcell optimumn value, can also be done by setting the antenna gain, such as e.g. the setting of the antenna height above ground. This means that the transceiver, in particular the power amplifiers of the transmitters, can be designed uniformly.

The individual base stations can also be coupled to the mobile switching centres by directional radio links. This is an advantage particularly when wired networking, as for example with far distant base stations, is simply too cost intensive.

The expansion of individual radio cells is limited mainly by the maximum transmission power of the mobile stations operated within the mobile network.

Macro-cells with a diameter of, e.g. 30 km and more can be divided appropriately into subcells with many transceivers. The mobile-radio network according to the invention can have variously sized and variously subdivided 10 radio cells, each appropriately configured to the area to be supplied, 0 *ooo• o •go o *om

Claims

4. A base station for serving a radio cell wherein said the base station comprises N transceivers each of which supplies a portion of the radio cell with constant transmitting/receiving parameters, so that the radio cell is subdivided into N subcells, said subcells each forming a ring around the location of the base station. A base station as claimed in claim 4, wherein each of the transceivers supplies its subcell with at least one radio channel, said base station being connected to a transmission path over which the radio channels, after being translated in the transceivers, are transmitted together as communication channels.
6. A mobile radio network substantially as herein described with reference to Figures 1-3 of the accompanying drawings, DATED THIS THIRTEENTH DAY OF MARCH 1996 ALCATEL N.V p: ABSTRACT Mobile-radio networks for areas divided into radio cells are known as cellular networks. In common cellular networks each radio cell is supplied by a base station whose transmission level is dynamically controlled. The present invention provides a cellular network with simply designed base stations. The mobile-radio network according to the invention comprises radio cells (C1, C4), which are each divided into N subcells (SC11, SC13; SC21, SC23; SC31, SC33) and for each radio cell it comprises a base station (BTS 1, BTS4), each of which supplies one of the subcells by means of N transceivers with constant set transmitting/receiving parameters. The base stations in particular do not require a complex technical, dynamic control of the transmission level, as the reception level within any one subcell only drops insignificantly, e.g. by 10 dB. (Figure 1) oo