Base Station Antenna Arrangement
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Europaisches Patentamt European Patent Office © Publication number: 0 593 822 A1 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 92309520.2 int. CIA H01Q 25/00, H01Q 3/24 @ Date of filing: 19.10.92 @ Date of publication of application: © Applicant: NORTHERN TELECOM LIMITED 27.04.94 Bulletin 94/17 World Trade Center of Montreal, 380 St. Antoine Street West, 8th Floor © Designated Contracting States: Montreal, Quebec H2Y 3Y4(CA) AT BE CH DE DK ES FR GB GR IE IT LI LU MC NL PT SE @ Inventor: Searle, Jeffrey Graham 5 Langdon Lane, Galmpton Brixham, Devon TQ5 OPQ(GB) Inventor: Dean, Stuart James 20 Southfield Road Paignton, Devon TQ3 2SU(GB) Inventor: Broome, Keith Roy 8 Seaton Close, Babbacombe Torquay, Devon TQ1 3UH(GB) Inventor: Chrystie, Peter John 32 Stoke Gabriel Road Galmpton, Brixham TQ5 ONQ(GB) Inventor: Cox, Christopher Richard "Channel View", Rickham, East Portlemouth Salcombe, Devon TQ8 PJ(GB) © Representative: Ryan, John Peter William et al Northern Telecom Europe Limited Patents and Licensing West Road Harlow, Essex CM20 2SH (GB) © Base station antenna arrangement. CM CM © A base station antenna arrangement comprising control means for controlling the switching matrix 00 a plurality of antenna arrays each capable of forming means whereby a particular transceiver is connected 00 a multiplicity of separate overlapping narrow beams to a particular array via the beamforming means to Oi in azimuth, the arrays being positioned such that the exchange r.f. signals with a remote station located in m totality of beams formed by the arrays provides a the area covered by one of the narrow beams. substantially omni-directional coverage in azimuth, azimuth and elevation beamforming means for each array, a plurality of r.f. transceivers, switching matrix means for connecting each transceiver with one or other of the arrays via the beamforming means, Rank Xerox (UK) Business Services (3. 10/3.09/3.3.4) EP 0 593 822 A1 Fig. 4. ELEVATION BEAMFORMERs|--''>'> TOP OF MAST OR BUILDING LINEAR L LOW POWER T NOISE ANTENNA- —■ amplifiers! AMPLIFIERS ELECTRONICS UNIT TRANSMIT I RECEIVE AZIMUTH 1 AZIMUTH BEAMFORMERl BEAM FORMER I RF FEEDER CABLES- Fig.4. (cont.) PORTS TO OTHER ANTENNA PORTS FROM OTHER ANTENNA ELECTRONICS UNITS 1 ELECTRONICS UNITS v-frf—- ~ | PARALLEL 62^ RECEIVERS n BEAMS I I n BEAMS «*= PER PORT 3E PER PORT ACQUISITIONr (ACQUISITION TRANSMIT SWITCH CONTROL RECEIVE SWITCH MATRIX PROCESSOR MATRIX 58 TRACK 60 CABIN • ±L ELECTRONICS TRANSCEIVERS - -TRTR TR TRANSCEIVER UNIT ... CONTROL 6U- -TR1 TR2 TRn BUS BASE STATION CABIN IT KEY BASE 66 1 t STATION NETWORK CONTOLLER RF CONTROL PATHS PATHS 2 1 EP 0 593 822 A1 2 This invention relates to a base station antenna cells. The extent of the advantage of a narrow arrangement for use in a Cellular Radio commu- beam antenna over an omni-directional antenna is nication system. a function of the beamwidth. The narrower the Cellular radio systems are currently in wide- beamwidth the greater the advantage, but this must spread use throughout the world providing tele- 5 be traded off against the increased size and com- communications to mobile users. In order to meet plexity of the antenna. the capacity demand, within the available frequen- Although the narrow beam is formed at radio cy band allocation, cellular radio systems divide a frequencies (typically in the 900 or 1800 MHz geographic area to be covered into cells. At the bands) it can usefully be visualised as analogous to centre of each cell is a base station, through which io a laser beam which emanates from the base station the mobile stations communicate. The available and tracks the mobiles. When contrasted with an communication channels are divided between the omni-directional antenna this clearly creates a high cells such that the same group of channels are quality transmission path with minimal interference. reused by certain cells. The distance between the Some of the potential benefits of narrow beam reused cells is planned such that co-channel inter- 75 antennas for cellular radio have been recognised in ference is maintained at a tolerable level. the literature, see for example "A Spectrum Effi- When a new cellular radio system is initially cient Cellular Base Station Antenna Architecture", deployed, operators are often interested in max- S.C. Swales and M.A. Beach, Personal & Mobile imising the uplink (mobile station to base station) Radio Communications Conference, Warwick, 1991 and downlink (base station to mobile station) range. 20 and "Proposed Advanced Base Station Antennas The ranges in many systems are uplink limited due for Future Cellular Mobile Radio Systems", W.S. to the relatively low transmitted power levels of Davies, R.J. Long and E. Vinnal, Australian hand portable mobile stations. Any increase in Telecomms Research, Vol 22, No. 1, pp 53-60. range means that less cells are required to cover a Within current systems the manner in which direc- given geographic area, hence reducing the number 25 tive antennas are used allows relatively small bene- of base stations and associated infrastructure fits to be obtained. The use of directive antennas in costs. current cellular radio systems is based on the When a cellular radio system is mature the principle of sectorisation as illustrated in Fig. 2. capacity demand can often increase, especially in The main sources of interference in a cellular sys- cities, to a point where more smaller size cells are 30 tern come from the so called first tier reuse cells. needed in order to meet the required capacity per An omni-directional base station antenna will re- unit area. The process used to create these smaller ceive interference from all six first tier reuse cells cells is known as cell splitting. Any technique (Fig. 2a). If an antenna with nominally 120° beam- which can provide additional capacity without the width is used, corresponding to a tri-sectored con- need for cell-splitting will again reduce the number 35 figuration, interference will be received from only of base station sites and associated infrastructure two first tier reuse cells (Fig. 2b). If an antenna with costs. 60° beamwidth is used, corresponding to a hex- The antenna used at the base station site can sectored configuration, interference will be received potentially make significant improvements to the from only one of the first tier cells (Fig. 2c). In range and capacity of a cellular radio system. The 40 sectorised cells the cellular radio transceivers at ideal base station antenna pattern is a beam of the base station are only connected to one sector narrow angular width as shown in Fig. 1a. The (or antenna) and cannot be used in other sectors narrow beam is directed at the wanted mobile, is within the same cell. narrow in both the azimuth and elevation planes, The sectorised approach to the use of directive and tracks the mobiles movements. When com- 45 antennas has reached its useful limit at 60° beam- pared to an omni-directional antenna, such a beam width and can go no further. There are two key will have the dual benefits of having high gain, disadvantages of the approach: leading to increased range in thermal noise limited a) The cellular radio transceivers are dedicated initial deployments, and rejecting interference from to particular sectors which leads to significant co-channel reuse cells allowing higher capacity 50 levels of trunking inefficiency. In practice this without cell splitting in mature deployments. The means that many more transceivers are needed narrow beam reduces interference in a balanced at the base station site than for an omni-direc- manner on the uplink and downlink. On the uplink tional cell of the same capacity. the base station receiver is protected from interfer- b) Each sector is treated by the cellular radio ence generated by mobile station transmitters in 55 network (i.e. the base station controller and mo- the co-channel reuse cells, Fig. 1b. On the down- bile switches) as a separate cell This means that link the mobile is unlikely to be in the beams of the as the mobile moves between sectors, a consid- base station transmitters in the co-channel reuse erable interaction is required between the base 3 3 EP 0 593 822 A1 4 station and the network to hand off the call tion beamforming network combines the elements between sectors of the same base station. This of a column to a single feed point. The amplitude interaction, comprising signalling and processing and phase relationships of the r.f. signals coupled at the base station controller and switch, repre- to the elevation beamformer determine the eleva- sents a high overhead on the network and re- 5 tion beam pattern of the antenna for both transmit duces capacity. and receive. The transmit and receive signals for According to the present invention there is each elevation beamformer are coupled to the provided a base station antenna arrangement com- beamformer via individual diplexers 46. Filters prising a plurality of antenna arrays each capable which cover just the transmit or receive frequency of forming a multiplicity of separate overlapping io bands respectively can be used for this purpose. In narrow beams in azimuth, the arrays being posi- the transmit path the diplexers 46 are fed from tioned such that the totality of beams formed by separate linear power amplifiers 48, one for each the arrays provides a substantially omni-directional elevation beamformer. These amplify the r.f. sig- coverage in azimuth, azimuth and elevation beam- nals up to the power levels required for transmis- forming means for each array, a plurality of r.f. 15 sion. The power amplifiers need to have high lin- transceivers each for transmitting and receiving r.f.