US007313415B2
`
`(12)
`
`United States Patent
`US 7,313,415 B2
`(10) Patent No.:
`Wake et al.
`(45) Date of Patent:
`Dec. 25, 2007
`
`
`(54) COMMUNICATIONS SYSTEM AND
`METHOD
`
`(75)
`
`Inventors: David Wake, Ipswich (GB); Keith
`Beacham, Saxmundham (GB)
`
`5,890,055 A
`6,785,558 B1*
`2001/0036843 Al*
`2004/0110469 Al*
`2005/0143091 Al*
`
`Chu et al.
`3/1999
`Stratford et al... 455/561
`8/2004
`11/2001 Thompson .....
`. 455/562
`6/2004
`Judd et al. vee 455/15
`
`Shapira et al. 0.0.00... 455/456.1
`6/2005
`
`(73)
`
`Assignee: NEXTG Networks, Inc., Milpitas, CA
`(US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 121 days.
`
`(21)
`
`Appl. No.: 10/978,501
`
`(22)
`
`Filed:
`
`Nov. 1, 2004
`
`(65)
`
`Prior Publication Data
`
`OTHER PUBLICATIONS
`
`al., “Radio Over Fibre Networks For Mobile
`Wake, David et
`Communications”, Proc. SPIE, vol. 5466, 2004.
`* cited by examiner
`
`Primary Examiner—Edward F. Urban
`Assistant Examiner—Raymond S. Dean
`(74) Attorney, Agent, or Firm—Vierra Magen Marcus &
`DeNiro LLP
`
`(57)
`
`ABSTRACT
`
`(51)
`
`US 2006/0094470 Al
`Int. Cl
`HOAB 1 38
`
`May 4, 2006
`
`A signal distribution system for distributing signals, such as
`for outdoor wireless networks, comprises a number of
`remote hubs, each of which can direct wireless signals to a
`number of antennas. The antennas are used to provide
`(2006.01)
`wireless service to the service users, such as mobile units,
`:
`within their geographic coverage area. The remote hubs are
`° bona a we . ficati a S eee h. ero ey
`connected to main hubs, which are usually located centrally.
`(58)
`Field
`of
`Classification
`Search
`.....
`;
`904-15
`lication
`fil ae 5 re. 7; ewe Each main hub can support a number of remote hubs. The
`ee application
`hile
`for complete search
`history.
`main hubs are connected to a number of base stations (again
`References Cited
`usually located centrally) in a flexible and re-configurable
`manner using a switch matrix. Some remote hubs may also
`include switched matrices for
`a further level of signal
`Touting.
`
`5
`
`(56)
`
`U.S. PATENT DOCUMENTS
`5,559,866 A *
`9/1996
`O'Neill oes 455/447
`5,623,495 A *
`4/1997
`Eng etal. we 370/397
`5,682,256 A
`10/1997
`Motley et al.
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`U.S. Patent
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`Dec. 25, 2007
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`Sheet 1 of 4
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`Page 2
`
`CommScope Ex. 1023
`
`

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`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 2 of 4
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`US 7,313,415 B2
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`Page 3
`
`CommScope Ex. 1023
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`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 3 of 4
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`US 7,313,415 B2
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`Page 4
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`CommScope Ex. 1023
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`

`

`U.S. Patent
`
`Dec. 25, 2007
`
`Sheet 4 of 4
`
`US 7,313,415 B2
`
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`Page 5
`
`CommScope Ex. 1023
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`

`

`US 7,313,415 B2
`
`2
`a
`are usually grouped together in
`The base stations
`convenient central location, sometimes known as
`a base
`station hotel. The radio signals from the centrally located
`base stations are therefore distributed to many remote anten-
`nas using an architecture containing main hubs and remote
`hubs. The switch matrix, under software control, is able to
`change the network configuration, i.e.,
`to change which
`signals from which base stations go to which antenna cluster.
`This is important in many situations, for example, to be able
`to move network capacity from under-utilized coverage
`areas to relieve congestion in over-utilized coverage areas.
`An example of this situation is the sports stadium scenario,
`where capacity requirements are very low apart from when
`an event is taking place. The switch matrix would mean that
`a dedicated base station is not necessary for the sports
`stadium, leading to a saving in capital equipment cost. There
`are many other situations where the switch matrix gives both
`capital and operational cost savings; these are described in
`Wake and Beacham cited above.
`The connections between the main hubs and remote hubs,
`and between the remote hubs and the antennas are either
`wireless links or a mixture of wireless links and cabled links.
`In most cases, the technology of choice for the cabled links
`will be optical fiber, unless the link lengths are so short that
`coaxial cable can be used. This may happen for instance if
`the main hub and one of the remote hubs are co-located. The
`technology options available for the wireless links include
`in-band radio, out-of-band radio and free-space optics. In-
`band radio means that no frequency translation is used, 1.e.,
`that the radio carrier frequency is used for transmission.
`Out-of-band radio means that the transmission frequency is
`different to that of the radio carrier and is usually at
`a much
`higher frequency (possibly millimetre-wave) to take advan-
`tage of high antenna gain and high available bandwidth.
`Free-space optics uses an optical carrier for transmission,
`and is sometimes preferred to radio because it can be used
`without an operating license and the available bandwidth is
`not subject to regulation.
`
`In most cases, the signal that is distributed over the
`transmission links is likely to be analog (either direct radio
`carriers or frequency translated radio carriers). However, the
`present invention does not preclude the transmission of
`digital signals, whether the signals are baseband or digitized
`radio (using fast analog to digital converters). Baseband
`digital signals could for example be those relating to the
`open base station initiatives (CPRI and OBSAI), where the
`base stations are split into baseband digital and radio parts
`and interconnected using digital links. A typical deployment
`scenario for the present invention may include a mixture of
`analog, digitized radio and baseband digital links.
`
`The present invention further includes a communications
`method for distributing signals employing switched wireless
`links and may further include employing distributed switch-
`ing in remote hubs.
`These and other features and advantages of embodiments
`of the present invention will be apparent to those skilled in
`the
`art from the following detailed description of the
`embodiments of the invention, when read with the drawings
`and the appended claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic representation of a signal distribu-
`tion system of the present invention.
`
`FIG. 2 illustrates a switch matrix to be used in a signal
`distribution system, such as illustrated in FIGS. 1 and 3.
`
`1
`COMMUNICATIONS SYSTEM AND
`METHOD
`
`BACKGROUND OF THE INVENTION
`
`wn
`an
`
`35
`
`45
`
`The present invention relates to a communications system
`and method and, more particularly, to a signal distribution
`system and method for switching and connecting cells in a
`communications network.
`The use of a switching matrix for wireless communica-
`tions systems based on distributed antennas is disclosed by
`Motley et al. in U.S. Pat. No. 5,682,256. Motley et al. uses
`a switching matrix to interconnect a number of base stations
`on the input ports to a number of distributed antennas on the
`output ports. The switch matrix allows any combination of
`inputs to be connected to any combination of outputs so that
`base stations can be connected to antennas in a very flexible
`manner. This allows wireless services such as cellular radio
`to be delivered to users with significant cost savings for
`network operators. The benefits of using a switched distrib-
`uted antenna system are outlined for example in a paper by
`Wake and Beacham, “Radio over fiber networks for mobile
`communications”, Proc. SPIE, vol. 5466, 2004.
`The links between the switch matrix and the distributed
`antennas are accomplished in Motley et
`al. using optical
`fiber cables using a technique known as radio over fiber.
`Radio over fiber has many advantages for this type of
`network with high quality transmission and low signal
`attenuation as a function of distance being the primary ones.
`However, there are situations where optical fiber cables are
`not available at economic cost at places where they are
`required. An example of this type of situation is a city center
`where the local telecommunications operator does not pro-
`vide ‘dark’ fiber cables, i.e., fiber cables that are not part of
`a managed service.
`Chu et al., in U.S. Pat. No. 5,890,055, discloses the use of
`wireless repeaters in a distributed antenna system (DAS)
`with a fixed configuration. This architecture avoids the
`problems of fiber availability described above. However, the
`fixed configuration described by Chu limits the operational
`benefits of a switched approach.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The present invention provides system architecture that
`gives the operational benefits of a switched-DAS, without
`the problems caused by fiber availability, by describing a
`network containing switched wireless links. Furthermore,
`the present invention describes a system architecture that
`incorporates distributed switching within remote hubs in
`order to provide fine granularity in allocating services to
`antennas.
`One embodiment of the present invention is directed to a
`transmission system for distributing signals for outdoor
`wireless networks. The transmission system comprises a
`number of remote hubs, each of which can direct wireless
`signals to a number of antennas. The antennas are used to
`provide wireless service to the service users, such as mobile
`units, within their geographic coverage area. The remote
`hubs are connected to main hubs, which are usually located
`centrally. Each main hub can support a number of remote
`hubs. The main hubs are connected to
`a number of base
`stations (again usually located centrally) in a flexible and
`re-configurable manner using a switch matrix. The base
`stations are connected to the core wireless network via
`digital transmission links.
`
`Page 6
`
`CommScope Ex. 1023
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`

`

`US 7,313,415 B2
`
`4
`This
`link.
`wireless
`the
`carrier frequency band across
`approach may have limitations concerning interference and
`antenna gain and so out-of-band radio can be used to
`minimize these problems. In these systems, the original
`radio carrier frequency band is translated to
`a different
`frequency for transmission. Normally the transmission fre-
`quency will be much higher than the original radio carrier
`frequency in order to make use of higher antenna gain and
`to ensure that adequate transmission bandwidth is available.
`An alternative approach is to use free-space optical (FSO)
`systems for the wireless links. FSO has advantages of
`license-free operation and zero interference with other radio
`systems.
`The wireless signals may be those of a cellular radio
`system such as PCS or CDMA2000, or those of other
`wireless networking systems such as public mobile radio,
`wireless LAN or broadband wireless access. Radio carrier
`frequencies range from a few hundred MHz to several GHz
`for these types of systems, but the present invention is not
`limited to this frequency range.
`FIG. 1 illustrates a nxm switch matrix 3. FIG. 2 shows an
`embodiment of such a switch matrix, with example size of
`8x4. The switch matrix comprises 8 input ports 11 and 4
`output ports 12. Each input port is connected to a 1:4 splitter
`13, and each output port is connected to an 8:1 combiner 14.
`Each output of each splitter is connected to a combiner input
`as shown in FIG. 2
`so as to ensure that any input to the
`switch matrix can be available at any output of the switch
`matrix. The connections 15 between splitters and combiners
`comprise single pole single throw switch elements 16 and
`variable attenuators 17 in series. There are therefore 32
`switch elements and 32 variable attenuators in total for this
`size of matrix even though FIG. 2 schematically illustrates
`only one switch element and attenuator. The switches can be
`set to either an “on” state or an “off’ state so that any
`combination of input signals can be routed to any combi-
`nation of output ports. The variable attenuators can be set to
`balance the path loss across all paths between input and
`output.
`FIG. 3 shows another signal distribution system of the
`present invention. FIG. 3
`illustrates many of the same
`elements of FIG. 1
`as indicated by the similar reference
`numbers. Discussion of these elements will not be repeated.
`Although FIG. 3 does not illustrate mobile units, the system
`may include mobile units as in FIG. 1.
`In the illustrated system of FIG. 3, some or all of the
`remote hubs contain switch matrices so that a further level
`of signal routing can be facilitated. These switched remote
`hubs 18 enable an architecture that provides finer granularity
`than the embodiment of FIG. 1, so that each antenna can be
`individually addressed if required. Radio channels can there-
`fore be routed at the antenna level rather than at the antenna
`cluster level, which allows greater flexibility in providing
`service. The switched remote hubs may also be intercon-
`nected and controlled by a common control system. The
`interconnecting links 19 may be either cable or wireless,
`although a cable link is shown in FIG. 3 by way of example.
`Interconnecting the switched remote hubs gives greater
`network resilience. Although FIG. 3 only illustrates one
`switched remote hub per cluster, the present invention can
`have more than one switched remote hub per cluster.
`FIG. 4 shows an embodiment of a main hub such as
`illustrated in FIGS. 1 and 3. In this example, the main hub
`connects to two remote hubs, one uses optical fiber cable and
`the other is
`a wireless link using out-of-band radio. This
`main hub is constructed as follows. The input signal from the
`switch matrix is split into forward and reverse transmission
`
`3
`a schematic representation of another signal
`is
`FIG. 3
`distribution system of the present invention.
`FIG. 4 illustrates a main hub in a
`signal distribution
`system of the present invention, such as illustrated in FIG.
`1 or 3.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`O°
`an
`
`30
`
`35
`
`40
`
`55
`
`In the following description of embodiments, reference is
`made to accompanying drawings which form a part hereof
`and in which is shown by way of illustration specific
`embodiments in which the invention may be practiced. It is
`to be understood that other embodiments may be utilized
`and structural changes may be made without departing from
`the scope of the preferred embodiments of the present
`invention.
`is a schematic representation of a signal distribu-
`FIG. 1
`tion system of the present invention. The central unit 1
`comprises a number of base stations 2 and a nxm switch
`matrix 3. The base station output ports are connected to the
`input ports of the switch matrix. The output ports of the
`switch matrix are connected to a number of main hubs 4
`using cables 5.
`In one example, the base stations could be located within
`an equipment room inside a building and the main hubs
`could be located on the top of the building. The cables would
`either be optical fiber or coaxial depending on the distance
`between the main hubs and base stations. It should be noted
`the number of cables do not have to equal the number of
`main hubs as illustrated in FIG. 1. The number of cables may
`be more or less than the number of hubs. For example,
`although a cable will typically be used to connect an output
`port of the switch matrix to a main hub, a wireless link may
`be used instead.
`The main hubs each connect to a cluster of antennas 6 via
`remote hubs 7. FIG. 1 illustrates the same number m of main
`hubs and clusters, but the present invention is not so limited.
`The number of main hubs can be greater or less than the
`number of clusters. Connections between the main hubs and
`remote hubs, between the remote hubs and antennas, and
`between remote hubs are via a mixture of cable links 8 and
`wireless links 9
`as illustrated in FIG. 1.
`In the case of
`wireless links, connection to the antennas is made using
`remote units 10. The antennas transmit and receive signals
`to and from mobile units
`or devices such as, without
`limitation, cellular telephone and PDAs. FIG. 1
`illustrates
`antenna 6 transmitting and receiving signals from a mobile
`unit or a plurality of mobile units such as mobile unit 50.
`While FIG. 1 only illustrates mobile units in contact with
`antenna 6, it is to be understood that other mobile units can
`be in contact with other antennas illustrated in FIG. 1. It is
`also to be understood that one or more mobile units may be
`in contact with more than one antenna.
`Remote units are not required for the present invention.
`The use of remote units is only necessary when the signal
`needs to be processed before being radiated by the antennas
`to mobile units. For example, in the case of wireless links,
`a remote unit 10 functions to convert the transmitted signal
`to the appropriate form (frequency, power, etc.) for radiation
`from the antenna 6 to mobile unit 50. On the other hand,
`remote hub 7a is directly connected to antenna 6a without an
`intermediary remote unit. Mobile units are thus in direct
`communication with remote hub 7a through antenna 6a.
`The wireless links may use in-band radio, out-of-band
`radio or free-space optical technology. In-band radio sys-
`tems are the simplest, in that they transmit the original radio
`
`Page 7
`
`CommScope Ex. 1023
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`

`

`US 7,313,415 B2
`
`6
`methods. While a method will be described as transmitting
`signals from the one or more base stations to one or more
`distributed antennas, it is to be understood that the method
`can be performed in reverse from one or more distributed
`antennas to one or more base stations.
`The communications method can comprise transmitting
`signals from a plurality of base stations to a switch matrix.
`As illustrated in FIG. 1, the base station 2 is connected to a
`switch matrix 3 for transmitting and receiving signals ther-
`ebetween. A plurality of base stations can thus transmit
`signals to the switch matrix.
`The method can further comprise routing the signals by
`the switch matrix as, for example, illustrated in FIG. 2. The
`method can further comprise transmitting the routed signals
`to
`a plurality of distributed antennas via communication
`links. The communication links can be wireless, cable or a
`combination of wireless and cable.
`The communications method can further comprise trans-
`mitting the routed signals to a hub, such as main hub 4 in
`FIG. 1, and then transmitting those routed signals from the
`hub to the plurality of distributed antennas. If the distributed
`antennas are in clusters, the communications method may
`comprise transmitting those routed signals from the hub to
`only one cluster. FIG. 1
`illustrates
`an example of this
`procedure. Main hub 4 only transmits the routed signals that
`it receives to cluster 1. Cluster 1
`is
`a subset of all the
`distributed antennas in the system.
`The communications method can further comprise send-
`ing routed signals from the hub to a remote hub and having
`the remote hub transmit the signals to the cluster of distrib-
`uted antennas or some smaller group of distributed antennas
`in that cluster. For example, in FIG. 1, the main hub 4
`transmits at least some of the routed signals that it receives
`to remote hub 7 which, in turns, sends the signals to certain
`distributed antennas in the cluster.
`The communications method can further comprise rout-
`ing signals by a switch matrix in the remote hub to the
`distributed antennas in the cluster or some smaller group of
`distributed antennas in the cluster. For example, FIG. 3
`shows a remote hub 18 having a switch matrix for such
`routing.
`The communications method can further comprise trans-
`mitting signals by more than one remote hub to the distrib-
`uted antennas in the cluster. As shown in FIG. 1,
`for
`example, two remote hubs send signals to different groups of
`distributed antennas in the cluster. It should be noted that a
`distributed antenna can simply be an antenna (as in 6a of
`FIG. 1) or comprise a remote unit with an antenna (as in 10
`and 6 in FIG. 1). The communications method can further
`comprise connecting the remote units
`in
`a
`cluster. For
`example, as illustrated in FIG. 1, remote units in cluster 1 are
`connected by connection 8 emanating from remote unit 7.
`The communications method is not limited to connecting
`remote units in a cluster. Remote units from different clus-
`ters can be connected as illustrated in FIG. 3.
`Although the present invention has been fully described in
`connection with the embodiments thereof and with reference
`to the accompanying drawings, it is to be noted that various
`changes and modifications will become apparent to those
`skilled in the art. Such changes and modifications are to be
`understood as being included within the scope of the present
`invention as defined by the claims.
`What is claimed is:
`1.
`Acommunications system comprising:
`a plurality of base stations transmitting signals;
`a plurality of distributed antennas in communication with
`mobile devices;
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`directions using a duplexer 20. In the forward direction, the
`signal is then split two ways using a splitter 21. One of these
`paths goes to a laser 22 via an amplifier 23. The optical
`output from the laser is transmitted to the remote hub using
`optical fiber cable 24.
`The other forward path goes to a frequency upconverter,
`which comprises an input amplifier 25, a mixer 26, a local
`oscillator 27 and an output amplifier 28.
`A further duplexer
`29 is used at the output port of the radio link in order to
`combine forward and reverse transmission directions. The
`output radio signal is radiated using an antenna 30.
`In the reverse direction, the signals enter the main hub
`either via the optical cable or the radio link. In the case of
`the optical cable, the optical signal is converted back to a
`radio signal using a photodiode 31, amplified using amplifier
`32 and combined with other reverse path signals using a
`combiner 33. In the case of the radio link, the reverse signal
`passes through the duplexer 29 and is frequency translated
`back to the original radio carrier frequency using a down-
`converter. The downconverter comprises an input amplifier
`34, a mixer 35, a local oscillator 27 and an output amplifier
`36. The remote hubs in FIGS. 1 and 3 may have a similar
`construction to the main hub illustrated in FIG. 4.
`Features of all hubs in the present invention include: one
`or more input ports, converters (if necessary) to bring a
`transmitted signal back to an in-band radio signal, a duplexer
`to separate forward and reverse transmission directions,
`splitter/combiners, an amplification of an in-band radio
`signal, converters (if necessary) to convert a signal to an
`appropriate transmission medium (e.g., out-of-band radio or
`FSO) and one or more output ports.
`The remote hubs may also be interconnected, again using
`either cable links or wireless links, to provide additional
`resilience to the system. The use of interconnecting links
`between the remote hubs, and the option of having distrib-
`uted switch matrices in the remote hubs, opens up intriguing
`possibilities for system management and control. In addition
`to greater network resilience afforded by such a meshed
`system, there are opportunities for extending the reach and
`routing around obstacles in the case of wireless links. The
`ability to route around obstacles makes the network closer to
`a line-of-sight radio system, which increases quality of
`service and reduces cost.
`The arrangement and architecture of the present invention
`described here constitutes a distributed antenna system for
`providing capacity and coverage for an outdoor wireless
`communications network. Features of the present invention
`include: the use of a switch matrix, which allows coverage
`and capacity to be allocated dynamically (thereby saving
`capital and operating costs compared to traditional DAS
`architectures); the selective use of wireless links between the
`base stations and the antennas (thereby providing a cost-
`effective transmission solution in cases where cable avail-
`ability is non-existent or impractical); an architecture that
`incorporates distributed switching within remote hubs to
`provide fine granularity in allocating services to antennas;
`and an interconnected wireless network topology that pro-
`vides resilience to failure, routing around obstacles and an
`extended reach.
`The combination of such features provides a signal dis-
`tribution system and architecture that is attractive to wireless
`network operators due to the cost savings and operational
`flexibility compared to deployments based on prior art
`systems.
`Although the present invention has been described as a
`communications system, the present invention discussed
`above can be performed as a communications method or
`
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`US 7,313,415 B2
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`7
`a switch matrix in operation with the plurality of base
`stations to route the signals to the plurality of distrib-
`uted antennas;
`a plurality of remote hubs;
`a plurality of main hubs between the switch matrix and the
`plurality of remote hubs for routing the signals to the
`plurality of remote hubs, the plurality of remote hubs,
`which are remote from the plurality of main hubs and
`between the plurality of main hubs and the plurality of
`distributed antennas, for routing the signals to
`the
`plurality of distributed antennas; and
`at least one wireless link between at least one of the main
`hubs and at least one of the remote hubs.
`2. The communications system of claim 1 further com-
`prising:
`at least one wireless link between the at least one of the
`remote hubs and at least one of the distributed antennas.
`3. The communications system of claim 1 wherein the
`plurality of distributed antennas are arranged in a plurality of
`clusters and each remote hub transmits routed signals to an
`associated cluster of distributed antennas, a different cluster
`of distributed antennas is associated with each remote hub.
`4. The communications system of claim 3, wherein at
`least one antenna in the cluster of distributed antennas
`comprises a remote unit with an antenna.
`5. The communications system of claim 3 wherein at least
`one of the remote hubs comprises a switch matrix to route
`signals from at least one of the main hubs to
`a group of
`distributed antennas in the associated cluster of distributed
`antennas.
`6. The communications system of claim 1, further com-
`prising:
`a control system, wherein each of the remote hubs com-
`prises a switch matrix controlled by the control system.
`7. The communications system of claim 1 wherein the at
`least one wireless link transmits routed signals at a radio
`carrier frequency band of at least one of the plurality of base
`stations.
`8. The communications system of claim 1 wherein the at
`least one wireless link transmits routed signals at a radio
`carrier frequency band different from a radio carrier fre-
`quency band of at least one of the plurality of base stations.
`9. The communications system of claim 1 wherein the at
`least one wireless link comprises a free space optical link
`that transmits routed signals at an optical frequency.
`10. The communications system of claim 1 further com-
`prising:
`at least one wireless link between at least one of the
`remote hubs and at least one of the distributed antennas.
`11.
`A communications method comprising:
`transmitting signals from a plurality of base stations to a
`switch matrix; and
`routing the signals by the switch matrix to a plurality of
`distributed antennas via a plurality of main hubs and a
`plurality of remote hubs, the plurality of main hubs are
`between the switch matrix and the plurality of remote
`hubs for routing the signals to the plurality of remote
`hubs, the plurality of remote hubs, which are remote
`from the plurality of main hubs and between the
`plurality of main hubs and the plurality of distributed
`antennas, for routing the signals to the plurality of
`distributed antennas, the routing uses at
`least one
`wireless link between at least one of the main hubs and
`at least one of the remote hubs.
`12. The communications method of claim 11 wherein the
`signals are routed to the plurality of main hubs, from the
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`plurality of main hubs to the plurality of remote hubs, and
`from the plurality of remote hubs to the plurality of distrib-
`uted antennas.
`13. The communications method of claim 12 wherein the
`signals are routed from each remote hub to an associated
`cluster of distributed antennas of the plurality of antennas, a
`different cluster of distributed antennas is associated with
`each remote hub.
`14. The communications method of claim 13 wherein at
`least one of the remote hubs uses a switch matrix to route
`signals to its associated cluster of distributed antennas.
`15. The communications method of claim 11, wherein:
`the signals are routed from a
`first remote hub to a second
`remote hub, and from the second remote hub to
`a
`cluster of distributed antennas of the plurality of dis-
`tributed antennas which is associated with the second
`remote hub.
`16.
`A communications system, comprising:
`a plurality of base stations;
`first, second and third distributed antennas in communi-
`cation with mobile devices;
`a first hub in communication with the first and second
`distributed antennas via respective wireless links;
`a switch matrix for routing signals from the plurality of
`base stations to the first and second distributed antennas
`via the first hub;
`a second hub in communication with the first hub via a
`respective wireless link, the second hub is between the
`first hub and the switch matrix; and
`a third hub in communication with the third distributed
`antenna via a respective wireless link, the second hub
`also in communication with the third hub via a respec-
`tive wireless link, the second hub is between the third
`hub and the switch matrix.
`17. The communications system of claim 16, wherein:
`the switch matrix routes signals from the plurality of base
`stations to the first and second distributed antennas via
`the second and first hubs, and to the third distributed
`antenna via the second and third hubs.
`18. The communications system of claim 3, wherein:
`the switch matrix is controllable to change which signals
`from which base stations go
`to which clusters of
`distributed antennas.
`19. The communications system of claim 18, further
`comprising:
`at least one wireless link between at least one of the
`remote hubs and at least one of the distributed antennas.
`20. The communications system of claim 19, wherein:
`the remote hubs perform distributed switching of the
`signals.
`21. The communications system of claim 1, wherein:
`the switch matrix has n input ports and m output p