(cid:57)(cid:58)(cid:42)(cid:82)(cid:36)(cid:3)EX1027
`U.S. Patent No. 10,965,512
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 1 of 17
`
`5,596,329
`
`NARROW
`
`BEAM
`
`-—a
`
`o'
`
`
`WANTED
`
`MOBILE
`
`BASE STATIONee |
`
`aa
`
`oO
`v
`
`a
`
`|m
`
`rs
`
`Fig. 1(a
`
`|
`
`ri
`
`AZIMUTH
`
`BASE STATION
`
`
`Te MOBILE
`
`WANTED MOBILE
`
`
`
`ELEVATION
`
`Fig. 1(b)
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 2 of 17
`
`5,596,329
`
`Fig. 2 (a)
`
`OMNI-DIRECTIONAL CONFIGURATION
`(N = 7 RE-USE FACTOR)
`
`ist TIER
`RE-USE CELLS
`
`Fig. 2 (b)
`
`TYPICAL TRI-SECTORED CONFIGURATION
`(N = 7 RE-USE FACTOR)
`
`ist TIER
`RE-USE CELL
`NON-INTERFERING
`
`
`
`
`
`
`
`Fig. 2(c)
`
`TYPICAL HEX-SECTORED CONFIGURATION
`(N = 7 RE-USE FACTOR)
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 3 of 17
`
`5,596,329
`
`PSTN/
`ISDN
`
`
`
`Fig.3MSC OMC
`
`BSS
`
`Signalling Routes
`
`Traffic and
`
`BSS
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 4 of 17
`
`5,596,329
`
`I BASE!/N/// ANTENNA1
`potas |
`
`STATION
`
`
`
`| CELLULAR RADIO
`| NETWORK
`~~PASSIVE
`
`jL——J}, — _, ANTENNAS
`|
`
`Fig. 4 (a)
`
`CELLULAR |
`RADIO
`
`pase 1 TT
`STATION ,
`'SMARTN/7 ANTENNA1
`
`NETWORK
`
`INTERFACE
`
`ANTENNA
`|
`.
`
`ARRAY Fig.512
`
`
`
`ee, 7
`
`
`ANTENNA
`ELECTRONIC
`
`
`
`| FEEDER
`, CABLES
`
`4
`
`MICROWAVE LINK
`OR LAND LINE
`
`
`
`
`
`
`
`
`BASE
`
`BASE
`
`STATION
`
`
`
`STATION
`CONTROLLER
`
`
`46 CONTROL
`LINK
`
`17 18
`
`20
`
`

`

`USS. Patent
`
`Jan. 21, 1997
`
`Sheet 5 of 17
`
`5,596,329
`
`ONE PER
`FACET
`
`|
`
`Y yo ANTENNA ARRAY
`40
`it|| TOP OF MAST
`44
`OR BUILDING
`
`| |
`
`BEAM
`
`| |
`
`48
`
`TX/RX DIPLEXER
`
`| | | |
`
`AMPLIFIER
`
`COMBINER;| LOW NOISE
`
`
`
`
`| SINGLE CARRIER
`|, TX POWER
`/\
`| AMPLIFIERS
`CELL
`
`
`
`
`
`
`P= =
`
`62
`
`5a|
`
`54
`----
`
`ATTENUATOR
`
`AMPLIFIER
`SELECT
`SWITCH
`MATRIX
`
`|
`|
`
`|l
`
`
`
`FEEDER CABLES
`
`TO OTHER FACETS
`
`
`FROM CABIN ELECTRONICS
`TO CABIN ELECTRONICS
`
`
`
`Fig.6(a)
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 6 of 17
`
`5,596,329
`
`TO MASTHEAD ELECTRONICS
`
`66
`
` oo
`PHASE HOPPING MODULE
`
`
`FROM MASTHEAD
`ELECTRONICS
`
`
`
`TR1 TR2|TR3 TRn SWITCH
`
`
`
`
`
`84
`MATRICES
`TRANSCEIVERS
`
`ee
`ACQUISITION
`
`iteTRACKAND "es
`SWITCH MATRIX
`TRANSMIT
`
`
`
` 82
`
`86
`CABIN
`
`ELECTRONICS
`TRANSCEIVER
`
`CONTROL
`BUS
`
`88
`
`Fig. 6 (b)
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 7 of 17
`
`5,596,329
`
`bl
`b2
`bn
`BEAM INPUTS
`
`e
`e
`e
`e
`e
`
`
`
`FIG 7
`
`CONTROL
`ACQUISITION
`
`RECEIVER
`
`
`OUTPUTS
`
`

`

`U.S. Patent
`
`Sheet 8 of 17
`
`Jan. 21, 1997
`
`5,596,329
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 9 of 17
`
`5,596,329
`
` RADIATION PATTERN
`
`RADIATION PATTERN
`WITHOUT PHASE HOPPING
`
`WITH PHASE HOPPING
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 10 of 17
`
`5,596,329
`
`ARRAY OF FOUR
`ANTENNA
`
`ARRAY OF FOUR
`
`Ab =0 - 360°
`% | (A)
`
`PHASE Ap = 0 360°
`FACETS
` RELATIVE
`
`
`PHASE
`
`RELATIVE
`
`INPUT
`
`INPUT
`
`Fig. 12 (a)
`
`Fig.12 (b)
`
`Fig. 12 (c)
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 11 of 17
`
`5,596,329
`
`Fig. 13 (a
`
`
`
`
`
`
`STANDARD ORTHOGONAL
`BEAM PATTERN
`
`g”
`
`ORTHOGONAL BEAM
`PATTERN WITH
`ANGULAR DIVERSITY
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 12 of 17
`
`5,596,329
`
`Fig. 14 (a)
`
`INPHASE
`
`Fig. 14 (b)QuaDRATURE
`
`BEAM 3
`
`60
`
`61
`
`BEAM 2
`
` 59
`
` BEAM SPLITTER
`58 58
`
`BEAM SPLITTER
`
`FROM TX
`
`FROM TX
`
`Fig. 14 (ce
`
`NON- ERP LIMITED IMPROVED
`SIGNAL USING TWO INPHASE
`
`ERP LIMITED IMPROVEMENT
`USING 90° OFFSET BETWEEN
`TWO TRANSMIT BEAMS
`
`TRANSMIT BEAMS
`
`
`oo DUAL TX BEAMS
`
`
`ORIGINAL COVERAGE
`PATTERN WITHOUT
`
`

`

`5,596,329
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 14 of 17
`
`|
`
`5,596,329
`
`Fig. 15 (c)
`
`SELECTED BEAMS
`AT TIME te
`
`BASE STATION
`
`BEAM NUMBER SELECTED
`
`
`
`
`MOBILE CHANNEL ALLOCATION |
`
`
`
`
`B18
`ms1 ALLOCATED CHANNEL1
`
`
`ms2 ALLOCATED CHANNEL2
`HANDED OFF TO
`
`ADJACENT CELL
`
`
`
`B4
`ms3 ALLOCATED CHANNEL3
`
`
`ms4 ALLOCATED CHANNEL4
`B7
`
`
`
`
`TIME t1
`
`
`
`TIME t2
`
`

`

`US. Patent
`
`5,596,329
`
`Jan. 21, 1997
`
`Sheet 15 of 17
`
`YiyYgory
`
`GyKO
`
`

`

`U.S. Patent
`
`Jan. 21, 1997
`
`Sheet 16 of 17
`
`5,596,329
`
`
`CRASS.
`
`y |
`
`
`
`
`
`
`
`
`
`
`
`
`77S
`
`
`_
`
`Fig. 17 (b
`
`Fig.18
`
`FAR OUT
`INTERFERENCE
`
`-IN
`csose.n
`
`

`

`
`
`

`

`5,596,329
`
`1
`BASE STATION ANTENNA ARRANGEMENT
`
`BACKGROUND OF THE INVENTION
`
`2
`intended to convey the meaning of having radiation cover-
`age over the area corresponding to the required geographic
`area ofthe cell.
`
`This invention relates to a base station antenna arrange-
`ment, for use in a Cellular Radio communications system,
`which shall hereafter be referred to as a smart antenna.
`
`TECHNICAL FIELD
`
`Cellular radio systems are currently in widespread use
`throughout
`the world providing telecommunications to
`mobile users. In order to meet the capacity demand, within
`the available frequency band allocation, cellular radio sys-
`tems divide a geographic area to be covered into cells. At the
`centre of each cell is a base station,
`through which the
`mobile stations communicate. The available communication
`channels are divided between the cells such that the same
`group of channels are reused by certain cells. The distance
`between the reused cells is planned such that the co-channel
`interference is maintained at a tolerable level.
`
`When a new cellular radio system is initially deployed,
`operators are often interested in maximising the uplink
`(mobile station to base station) and downlink (basestation to
`mobile station) range. The ranges in many systems are
`uplink limited due to the relatively low transmitted power
`levels of hand portable mobile stations. Any increase in
`range means that less cells are required to cover a given
`geographic area, hence reducing the numberofbasestations
`and associated infrastructure costs.
`
`When a cellular radio system is mature the capacity
`demand can often increase, especially in cities, to a point
`where more, smaller size cells are needed in order to meet
`the required capacity per unit area. The process used to
`create these smailer cells is known as cell splitting. Any
`technique that can provide additional capacity without the
`need forcell-splitting will again reduce the number of base
`station sites and associated infrastructure costs. The antenna
`used at the basestation site can potentially make significant
`improvements to the range and capacity of a cellular radio
`system. The ideal base station antenna pattern is a beam of
`narrow angular width as shownin FIG. la. The narrow beam
`is directed at the wanted mobile, is narrow in both the
`azimuth and elevation planes, and tracks the mobile’s move-
`ments. When compared to an omni-directional antenna, such
`a beam will have the dual benefits of having high gain,
`leading to increased range in thermal noise limited initial
`deployments, and rejecting interference from co-channel
`reusecells allowing higher capacity without cell splitting in
`mature deployments. The narrow beam reducesinterference
`in a balanced manner on the uplink and downlink. On the
`uplink the base station receiver is protected from interfer-
`ence generated by mobile station transmitters in the co-
`channel reusecells, FIG. 1b. On the downlink the mobileis
`unlikely to be in the beamsof the base station transmitters
`in the co-channel reuse cells. The extent of the advantage of
`a narrow beam antenna over an omni-directional antenna is
`a function of the beamwidth. The narrower the beamwidth
`the greater the advantage, butthis mustbe traded off against
`the increased size and complexity of the antenna. Although
`the narrow beam is formedat radio frequencies (typically in
`the 900 or 1800 MHz bands) it can usefully be visualised as
`analogous to a laser beam that emanates from the base
`station and tracks the mobiles. When contrasted with an
`omni-directional antenna,this clearly creates a high quality
`transmission path with minimal interference. For the pur-
`poses of this document the use of the word “omni” is
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`55
`
`60
`
`65
`
`BACKGROUND ART
`
`Some of the potential benefits of narrow beam antennas,
`for cellular radio, have been recognised in the literature, see
`for example “A Spectrum Efficient Cellular Base Station
`Antenna Architecture”, S. C. Swales and M. A. Beach,
`Personal & Mobile Radio Communications Conference,
`Warwick, 1991 and “Proposed Advanced Base Station
`Antennas for Future Cellular Mobile Radio Systems”, W. S.
`Davies, R. J. Long and E. Vinnal, Australian Telecomms
`Research, Voi. 22, No. 1, pp 53-60. Within current systems
`the manner in which directive antennae are used allows
`relatively small benefits to be obtained. The use of directive
`antennas in current cellular radio systems is based on the
`principle of sectorisation as illustrated in FIG. 2. The main
`sources of interference, in a cellular system, come from the
`so called first tier reuse cells. An ommi-directional base
`station antenna will receive interference from all six first tier
`reuse cells, FIG. 2a. If an antenna with nominally 120°
`beamwidthis used, correspondingto a tri-sectored configu-
`ration, interference will be reccived from only twofirst tier
`reuse cells, FIG. 2b. If an antenna with 60° beamwidth is
`used, corresponding to a hex-sectored configuration, inter-
`ference will be received from only one of the first tier cells,
`FIG. 2c. In sectorised cells the cellular radio transceivers at
`the basestation are only connectedto onesector (or antenna)
`and cannot be used in other sectors within the samecell.
`
`The sectorised approach to the use of directive antennas
`has reachedits useful limit at 60° beamwidth and can go no
`further. There are two key disadvantages of the approach:
`a) The cellular radio transceivers are dedicated to particular
`sectors that leads to significant levels of trunking ineffi-
`ciency. In practice this means that many more transceivers
`are needed at the base station site than for an omni-
`directional cell of the same capacity.
`b) Each sector is treated by the cellular radio network (i.e.
`the base station controller and mobile switches) as a
`separate cell. This means that as the mobile moves
`between sectors, a considerable interaction is required,
`between the base station and the network, to hand off the
`call, between sectors of the same base station. This
`interaction, comprising signalling and processing at the
`base station controller and switch, represents a high
`overhead on the network and reduces capacity.
`A standard cellular radio system is comprised of several
`layers, as shown in FIG. 3. A Mobile Switching Centre
`(MSC)is the interface between the cellular system and other
`networks, e.g. PSTN, Public Switched Telephone Network
`or ISDN,Integrated Services Digital Network. Each MSC
`controls several Base Station Systems (BSS), which in some
`systems, such as GSM or PCS, are further divided into a
`Base Station Controller (BSC) which controls several Base
`Transceiver Stations (BTS). Each BSS communicates with
`several Mobile Stations (MS). At the MSC level there are
`also other facilities such as Operations and Maintenance
`(OMC) and Network Management (NMC).
`In this system the calls are allocated to transceivers at
`basebandin the cellular radio network,at either the BSC,if
`available, or at the MSC, as shown in FIG. 4a. Any change
`required in the call
`to transceiver allocation has to be
`signalled through the network, maybeas far as the MSC and
`back again. This represents a heavy loading on the signalling
`network and a time delay whilst it occurs. The basic concept
`
`

`

`5,596,329
`
`3
`of a smart antenna is disclosed in European Patent Appli-
`cation No. 92 309 520.2. A smart antenna as referred to
`hereinafter comprises a plurality of antenna arrays each
`capable of forming a multiplicity of separate overlapping
`narrow beamsin azimuth, the arrays being positioned such
`that the totality of beams formed by the arrays provides a
`substantially omni-directional coverage in azimuth, azimuth
`and elevation beamforming meansforeach array,a plurality
`of 1.f. transceivers each for transmitting and receiving rf.
`signals for one or more calls, switching matrix means for
`connecting each transceiver with one or other of the arrays
`via the beamforming means, control means for controlling
`the switch matrix means whereby a particular transcciveris
`connected to a particular array, via the beamforming means,
`to exchange rf. signals with a remote station located in the
`arca covered by one of the narrow beams.
`SUMMARYOF THE INVENTION
`
`According to the present invention there is provided a
`smart antenna comprising
`a plurality of antenna arrays each capable of forming a
`multiplicity of separate overlapping narrow beams in
`azimuth,
`the arrays being positioned such that
`the
`totality of beams formed by the arrays provides a
`substantially omni-directional coverage in azimuth;
`azimuth and elevation beamforming meansfor each array;
`a plurality of rf. transceivers each for transmitting and
`receiving rf. signals for one or morecalls;
`switching matrix means for connecting each transceiver
`with one or other of the arrays via the beamforming
`means;
`
`control means for controlling the switch matrix means
`whereby a particular transceiver is connected to a
`particular array, via the beamforming means,
`to
`exchange rf. signals with a remote station located in
`the area covered by one of the narrow overlapping
`beams;
`means for selecting for a given call more than one of the
`best received signals from the multiplicity of narrow
`overlapping beams; and
`means for combining thesignals selected bysaid selecting
`means to form a single receive signal input for the rf.
`transceiver for the given call.
`According to one aspect of the invention the smart
`antenna includes means for exchanging with a network
`within which the smart antenna arrangementis incorporated
`information relating to the position and movement of a
`remote station located within the area of coverage of the
`smart antenna arrangement.
`According to a second aspect of the invention the smart
`antenna includes means for recognising unique identifier
`signals incorporated in call signals passing through the
`antenna; and
`coherent detection means for discriminating between
`unwanted call signals and wanted call signals using
`said unique identifier signals.
`According to a third aspect of the invention the smart
`antenna includes meansforsplitting the transmission output
`of a given transceiver into two identical signals prior to
`transmission power amplification and transmitting said sig-
`nals in two adjacent narrow overlapping beams.
`According to a fourth aspect of the invention the smart
`antenna includes
`
`a plurality of receive amplifiers one for each beam of an
`antenna array,
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`59
`
`60
`
`65
`
`4
`means for combining the outputs of the plurality of
`receive amplifiers, and
`switching means for applying the combined receive sig-
`nals to the r.f. transceiver handling the given call; and
`for transmitting rf. signals for the given call there is
`provided a single powcr amplificr for applying the
`transceiver transmit signal to an individual one of the
`beams.
`According to a fifth aspect of the invention the smart
`antenna includes means for operating the antenna arrays
`whereby individual narrow overlapping beamsare utilised
`for exchangeof rf. signals with individual remotestationsin
`the areas covered by the respective narrow beams and
`simultaneously the totality of the multiplicity of narrow
`overlapping beams are utilised collectively to provide an
`omni-directional antenna radiation pattern.
`According to a sixth aspect of the invention the smart
`antenna includes means for operating two or more non-
`collocated narrow beamwidth antennaarrays to form jointly
`a broad beamwidth antenna radiation pattern wherein the
`time averaged antenna pattern is substantially null free.
`According to a seventh aspect of the invention the smart
`antenna includes communication link means for communi-
`cation with a base station network whereby, in addition to
`telecommunications message traffic passing through the
`smart antenna, control and supervisory information can be
`exchanged between the smart antenna and the basestation
`network.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`.
`
`Embodiments of the invention will now be described with
`reference to the accompanying drawings, in which:
`FIGS. la and 1b illustrate schematically the use of a
`narrow beam antenna to communicate between a base
`station and a mobile station,
`FIGS. 2a-2c illustrate schematically the principle of
`sectorisation of a base station,
`FIG. 3 is a block diagram of the main elements of a
`cellular system,
`FIGS. 4a and 46illustrate the differences in call handling
`between a conventional cellular system and one using a
`smart antenna,
`
`FIG. 5 is a block diagram of the main elements of a base
`station,
`FIGS. 6a and 6b are diagrams of the constituents of a
`multiple narrow beam basestation,
`FIG.7 illustrates the basic principle of a switching matrix,
`FIG. 8 illustrates schematically the use of an interference
`detector,
`FIG.9 illustrates schematically the use of assisted han-
`dover management,
`FIG. 10 is a block diagram of the communication link
`between the smart antenna and therest of a cellular system,
`FIG.11 illustrates pictorially the interfacet radiation pat-
`tern of a multifaceted system with and without the use of
`phase hopping,
`FIGS. 12a—12c are diagramsof different embodiments of
`phase hopping,
`FIGS. 13a and 136illustrate schematically the principles
`of angular diversity,
`FIGS. 14a—-14c are diagramsof different embodiments of
`the dual transmit beam system with an illustration of the.
`relative radiation pattern improvements to be found,
`
`

`

`5,596,329
`
`5
`FIGS. 15a-15c illustrate the operation of a multiple
`narrow beam basestation,
`FIGS. 16a and 16b illustrate schematically the reduced
`overlap at differing cell radii boundaries using cell dimen-
`sioning,
`FIGS. 17a and 17b illustrate schematically the flexibility
`in base station location by the use of cell dimensioning,
`FIG. 18 illustrates schematically the use of cell dimen-
`sioning to reduce interference problems, and
`FIG. 19 illustrates schematically the use of cell dimen-
`sioning to avoid congestion.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`The main elements of a smart antenna as shownin FIG.
`5 comprise a mast, tower or building 10 supporting the
`antenna array(s) 12 and associated antennaelectronics unit
`14, which includes beamformers, diplexers and amplifiers.
`The antenna electronics unit 14 is connected via a cabin
`electronics unit 16 to the base station 18 that is under the
`control of a base station controller 20. The smart antenna
`system replaces the conventional passive antenna normally
`attached to the base station. The use of electronics in the
`mastheadallowsthe call switching to be carried out between
`the transceivers and antennas within the smart antenna, as
`shown in FIG. 4b. The switching now occurs on the rf.
`signals and only requires local control from the attached
`base station. This requires a new interface link 17 to be
`established between the base station and the smart antenna
`system. The previous baseband information is no longer
`required, reducing the loading on the signalling through the
`cellular radio network. It is replaced by rf. assignment
`information on the new interface link between the base
`station and smart antenna. This interface is also used to
`convey control information from the MSC, OMC and NMC
`parts of the cellular system.
`For the purposesofthis description the term “base station
`network”is used to describe all parts of the cellular system
`prior to the smart antenna and its interface link, e.g. the
`radio, base station controller, mobile switching centre,
`operations and maintenance and network management.
`The detailed constituents of the smart antenna are shown
`in FIG. 6. The masthead antenna electronics is shown in
`FIG.6a and the cabin electronics in FIG. 6b. Only one of the
`antenna arrays is depicted. Each antenna array 40 comprises
`a conventional array of individual antenna elements 42
`arranged in rows and columns. Each column of elementsis
`energised via an elevation beamforming network 44. Each
`elevation beamforming network combinesthe elements of a
`column to a single feed point. The amplitude and phase
`relationships of the rf. signals coupled to the elevation
`beamformer determine the elevation beam pattern of the
`antenna for both transmit and receive. Each elevation beam-
`former is coupled to the azimuth beamformer 46. The
`azimuth beamformer has multiple ports for both transmit
`and receive, one for each elevation beamformer. The phase
`and amplitude relationship of the 1.f. signals coupled to the
`elevation beamformers contro] the azimuth beam pattern for
`both transmit and receive. As the azimuth beamformeris
`prior to the low noise amplifiers on the receive path it must
`be optimised for low loss in that path. One well-known type
`of beamformeris the Butler matrix.
`
`The transmit and receive signals for the azimuth beam-
`formerare coupled to the beamformervia individual diplex-
`ers 48. Filters that cover just the transmit or receive fre-
`
`10
`
`15
`
`25
`
`30
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`quency bands respectively can be used for this purpose. In
`the transmit path the diplexers 48 are fed via a combiner 50
`from separate single carrier power amplifiers 52. These
`amplify the rf. signals up to the power levels required for
`transmission. In the receive path the diplexers 48 feed
`separate substantially identical low noise amplifiers 62, one
`for each azimuth beam. The low noise amplifiers are
`required to amplify the weak received r.f. signals prior to any
`system losses to establish a low noise figure (high sensitiv-
`ity) in the subsequent receive path.
`In the receive path, signals are passed from the low noise
`amplifiers 62 to the receive splitter 74. On the transmit side,
`signals are passed to the single carrier transmit amplifiers
`from cell shaping attenuators 54. There is one cell shaping
`attenuator per transmit amplifier. All attenuators in any one
`beam areset to the same value to give a new beam template
`across all frequencies. This sets the maximum range in a
`particular direction, however the power required to reach a
`particular mobile in the beam can be reduced from this if
`necessary. The attenuators are controlled by the operator via
`the masthead control electronics. The cell shaping attenua-
`tors are situated prior to the amplifiers, to enable low power
`standard attenuators to be used. By placing them prior to the
`combinerthe intermodulation performance is improved, due
`to each being at a single frequency.
`Signals are passed from the transceivers 84 to the cell
`shaping attenuators, by a switching system, via an optional
`phase hopping module 66. This ensuresthat all transmittcrs
`can be connected to any beamformer input, however only
`one transmitter is connected to any one of the single carrier
`poweramplifiers, at any time. The switching system com-
`prises several levels of switchingor splitting, which ensurcs
`primarily maximum redundancy on the omni path and
`secondarily some redundancyin the traffic paths. The trans-
`ceivers 84, if required can be input to an n*n transmit switch
`matrix 78, where n is equal to the numberoftransceivers.
`The transmit switch matrix allows any one input to be
`connected to any one output, but not more than one inputto
`any one output simultaneously. This allows for redundancy
`should any cable in the mast fail, however the same function
`can be accomplished by the BTS if a suitable command
`interface exists. A combination of switches and splitters 56,
`58, 68 is used to ensure that the omni path is routed to every
`beam, whilst a single traffic channel only goes to one beam.
`This switching andsplitting function may be placedeither at
`the top or the bottom of the mast or a combination of both
`as shownin FIG.6. The preferred methadis to have the main
`facet switches 68 at the bottom of the mast and then each
`transceiver path is split to every beam, via the beam splitter
`58, where the amplifier select switch matrix 56 switches off
`the beams not required. This makes the implementation of
`the dual transmit beam concept far easier and ensures that
`the lower reliability components are in the cabin where
`access is easier.
`
`The transmit, receive and amplifier select switch matrices
`comprise an x.f. cross-bar switch that allowsany ofits inputs
`to be connected to any of it’s outputs. The switch matrix
`design is such that any numberof transmitters or receivers
`can be connected simultancously to any one beamformer
`port, thus, if necessary, all the transmitters can be connected
`to one beam port at a given time. Likewise all the receivers
`can be connected,if necessary, to the same beam port at the
`same time. In practice, should there be more transceivers
`than a single beam can handle, the numberof transmitters
`that can be connected to the beam port is limited by the
`number of Tx power amplifiers 52. The switch matrices are
`operated under the control of a control processor 80. A
`typical switch matrix structure is illustrated in FIG.7.
`
`

`

`5,596,329
`
`7
`The receive splitter 74 ensures thal all incoming signals,
`from each beam, are sent to the interference discriminator
`70; the parallel receivers 72 and both the main and diverse
`reccive switch matrices 82.
`
`The interference discriminator 70 is used to identify
`whether or not the incoming signal is from a mobilein its
`own ccll, or onc of a nearby cell or any other spurious
`source. The parallel receivers only assess signal strength,
`however, one of the strongest signals may not be from a
`mobile within the cell, as shown by the direct path signal
`from M82in FIG.8. If theseerrant signals are not identified,
`it can leadto errors in the processing within the basestation.
`All
`transmissions between a mobile and a base station
`contain a fixed pattern knownas a training sequence, every
`base station within a given area has its own unique training
`sequence, The interference discriminator selects one of the
`beams,
`in each timeslot, and searches for the training
`sequence within the received signal, usually using correla-
`tion techniques for digital signals. The beam that is selected
`is dictated by the control processor, based on information
`received from the receive switch matrices and the interfer-
`ence discriminator. It does not necessarily look at every
`beam, only those considered to be the most likely contend-
`ers. The use of an interference discriminator is one of the
`features of the smart antenna system which allows the
`frequency re-use numberto be decreased.
`A bank ofparallel receivers 72, one for each beam, allow
`every receive channel
`to be monitored on every beam
`simultaneously. For each channel the receivers measure the
`quality of the wanted mobile signal present on each beam.
`The information on which is the ‘best’ beam is passed to the
`control processor. The quality measure used by the receivers
`will vary depending on the particular cellular system con-
`cerned. In simple cases the measure will be the highest
`powerlevel in other cases carrier to interferenceratio will be
`used.
`
`10
`
`15
`
`25
`
`30
`
`35
`
`8
`thus reducing the loading on the base station
`quicker,
`controller. Having chosen the correct cell, with a conven-
`tional omni receiver there is no advantage to knowing the
`approximate azimuth position of a mobile within that cell,
`however in a multiple beam antenna each beam must be
`monitored to find the one containing the mobile. It
`is
`therefore a great advantage to know the approximate beam
`into which a mobile will appear, so that the order in which
`the beams are analysed can be weighted lo give priority to
`the knowndirection. FIG. 9 shows a mobile passing through
`cell 1 and into cell 2. The tracking algorithm of the smart
`antenna in cell 1 monitors the mobile’s progress through
`beams 12, 11, 10 and 9 and can then give a quite accurate
`prediction to cell 2 that the mobile will appear in one of
`beams 18, 19 or 20.
`The main and diverse receive switch matrices, operate
`under the control of the control proccssor, on information
`derived from the parallel receivers, and select the strongest
`and secondstrongest signals, respectively. These signals are
`then coupled by r.f. bus paths to the main and diverse ports
`of the bank of transceivers 84, one for each channel to be
`provided by the base station, where they are input to a
`maximal ratio combiner, of the type described in Mobile
`Communications Systems by J D Parsons et al, Blackie
`1989. The transceivers are operated underthe control of the
`base station controller 88, which also provides overall
`control for the switch matrix control processor 80.
`The transceiver control bus 86 provides the communica-
`tion link between the base station and the smart antenna. The
`communication link will be comprised of several buses,
`whose format will vary according to the type of base station
`to which the smart antenna is attached. Wherever possible
`the bus structure in the smart antenna will utilise the bus
`protocol of the base station. In the current implementation
`there are five bus types that carry the information outlined
`below:
`1. Operations and maintenance that carries configuration,
`supervision and alarm management information for gen-
`eral operalion purposes.
`2. Operator controlled configuration information originating
`from either the BSC or the MSC.
`3. Frequency values, timing information to identify position
`within the GSM frame structure, control
`information,
`beam power levels and mobile range. This is from the
`BTSto the smart antenna, with one bus per transceiver.
`4. Information about the mobile, e.g. signal strength, direc-
`tion, beam number. This is from the smart antenna to the
`BTS.
`
`The basic function of the control processor 80 is to control
`the transmit and receive switch matrices such that the best
`beam (normally the one pointing at the mobile stations
`geographic position) for a given channel is selected. The
`inputs to the contro] processor are the beam amplitude data
`from the parallel receivers and data from the control buses
`to the base station. The latter allow the control processor to
`monitor a given mobile station’s assignment
`to various
`control andtraffic channels in the system during the progress
`of a call. Knowledge of which channel the mobile is being
`movedto allows a prompt and non-disruptive assignment to
`the best beam. The control algorithms used will fall into two
`basic classes, one forinitial acquisition of the best beam for
`5. Signal strobes.
`50
`anew call and one for tracking of the best beam whenacall
`Theactual physical link used for communication between
`is in progress. It is anticipated that due to different multipath
`the smart antenna and the BSC and/or MSCwill preferably
`conditions the parameters within the control algorithms will
`be the existing signalling link, however a separate link as
`vary for rural and urban cells. The determination of beam
`shown in FIG. 10 mayalso be used.
`selection on the uplink is used to select the corresponding
`The key features of the invention can now be considered
`beam for the downlink. The information on a mobile’s
`in more detail and contrasted with the conventional sec-
`angular position, i.e. the present beam being used, together
`torised base station. It is not a single feature of the invention
`with real time tracking data from the tracking algorithm,
`but rather the overall architecture (the functions and their
`involving range and angular velocity, is sent back, on the
`precise disposition) which provides a practical and eco-
`transceiver control bus via the BTS, to the BSC or MSC as
`nomicrealisation of the narrow beam concept.
`required.
`the smart
`Considered from the network viewpoint,
`This information can then be directed to the next cell into
`antenna appears as an omni-directional cell site. Since any
`transceiver can be switched to any beam and hence look in
`which the mobile will pass. The choice of this next cell is
`any direction, there are no sectors. Thus, within the network
`decided based upon polling of the surroundingcells, either
`all signalling and processing associated with sector to sector
`by the mobile or by the base station controller. If it is by the
`hand-offs are eliminated. Also the fact that transceivers can
`base station controller, then the information from the smart
`be used in any direction eliminates the trunking inefficiency
`antenna can be used to prioritise the polling sequence. This
`will enable the controller to reach the correct decision
`of sectorised sites. These factors not only eliminate a sig-
`
`40
`
`45
`
`55
`
`60
`
`65
`
`

`

`5,596,329
`
`9
`nificant load from the network but allow the antenna system
`to utilise effectively narrower beamwidths than would oth-
`erwise be possible.
`An omni pattern is still necessary as a cellular radio base
`station is required to radiate the BCCh channeloverits total
`arc of coverage, at maximum power,in all time slots. It may
`also be required to radiate othercarriers at times with the full
`arc of coverage. In conventional base station configurations
`this is achieved by the use of a single omniora tri-sectored
`antenna system with all carriers having the same coverage
`pattern. For a smart antenna arrangement, however, a dif-
`ferent situation exists, in that traffic channels are radia