(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2009/0180426A1
`(43) Pub. Date:
`Jul. 16, 2009
`Sabat et al.
`
`US 20090180426A1
`
`DIGITAL DISTRIBUTED ANTENNASYSTEM
`
`Publication Classification
`
`(51) Int. Cl.
`(2009.01)
`H0474/00
`(2006.01)
`HO4B IO/OO
`(52) U.S. Cl. ......................................... 370/328:398/116
`(57)
`ABSTRACT
`A digital distributed antenna system (DDAS) that regains the
`capability to perform simulcast to multiple simulcast groups
`while using a base station's direct digital output is provided.
`The User Plane data is adapted for simulcast and also for
`eliminating time delay ambiguities across multiple simulcast
`digital radios. In addition, the Control and Management Plane
`is aggregated across multiple remote units to allow a non
`modified donor digital base station to control simulcast
`groups. The result is a low cost digital DAS that can efficiently
`distribute the capacity of a digital base station to solve cov
`erage and capacity requirements in a manner similar to that
`now accomplished using a traditional base station with RF
`in/out.
`
`
`
`04
`
`Digital
`Remote
`Rodio
`
`(54)
`
`(76)
`
`Inventors:
`
`John Sabat, Merrimack, NH (US);
`David Porte, Harvard, MA (US)
`
`Correspondence Address:
`Myers Andras Sherman LLP
`19900 MacArthur Blvd., Suite 1150
`Irvine, CA 926.12 (US)
`
`(21)
`
`Appl. No.:
`
`12/340,383
`
`(22)
`
`Filed:
`
`Dec. 19, 2008
`
`(60)
`
`Related U.S. Application Data
`Provisional application No. 61/008,763, filed on Dec.
`21, 2007.
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`502
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`
`1 to N Remotes
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`Radio
`
`Dokdo Based Remotes
`
`

`

`Patent Application Publication
`
`Jul. 16, 2009 Sheet 1 of 6
`
`US 2009/0180426A1
`
`|
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`Patent Application Publication
`
`Jul. 16,2009 Sheet 1 of 6
`
`US 2009/0180426 Al
`
`
`
`
`
`
`
`RF
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`|
`
`Page 2
`
`CommScope Ex. 1010
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`

`

`Patent Application Publication
`
`Jul. 16, 2009 Sheet 2 of 6
`
`US 2009/0180426A1
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`Patent Application Publication
`
`Jul. 16,2009 Sheet 2 of 6
`
`US 2009/0180426 Al
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`PRIOR ART
`FIG.
`2
`
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`
`Page 3
`
`CommScope Ex. 1010
`
`per Sector
`Remotes
` 1 to N
`
`
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`
`Digital
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`optical
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`|
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`|
`
`

`

`Patent Application Publication
`
`Jul. 16, 2009 Sheet 3 of 6
`
`US 2009/0180426A1
`
`
`
`
`
`
`
`
`
`Patent Application Publication
`
`Jul. 16,2009 Sheet 3 of 6
`
`US 2009/0180426 Al
`
`N Remotes
`
`per Sector
`to
`
`Dokdo Based Remotes
`
`
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`Digital
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`3
`
`FIG.
`
`Distribution
`
`Digital
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`°
`
`Digital Stream
`
`Remote
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`[>
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`
`Page 4
`
`CommScope Ex. 1010
`
`

`

`Patent Application Publication
`
`Jul. 16, 2009 Sheet 4 of 6
`
`US 2009/0180426A1
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`
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`
`019?
`
`Patent Application Publication
`
`Jul. 16,2009 Sheet 4 of 6
`
`US 2009/0180426 Al
`
`
`
`
`
`
`
`Digital Stream
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`
`Page 5
`
`CommScope Ex. 1010
`
`

`

`Patent Application Publication
`
`Jul. 16, 2009 Sheet 5 of 6
`
`US 2009/0180426A1
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`
`Patent Application Publication
`
`Jul. 16,2009 Sheet 5 of 6
`
`US 2009/0180426 Al
`
`per Sector
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`N
`
`to
`
`1
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`
`
`Page 6
`
`CommScope Ex. 1010
`
`

`

`Patent Application Publication
`
`US 2009/0180426A1
`
`þ09
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`
`Patent Application Publication
`
`Jul. 16,2009 Sheet 6 of 6
`
`US 2009/0180426 Al
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`
`
`
`Radio
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`CommScope Ex. 1010
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`

`

`US 2009/01 8042.6 A1
`
`Jul. 16, 2009
`
`DIGITAL DISTRIBUTEDANTENNASYSTEM
`
`RELATED APPLICATION INFORMATION
`0001. The present application claims the benefit under 35
`USC 119(e) of U.S. provisional patent application Ser. No.
`61/008,763 filed Dec. 21, 2007, the disclosure of which is
`incorporated herein by reference in its entirety.
`
`FIELD OF INVENTION
`0002 The present invention relates to wireless communi
`cations systems and methods. More specifically, the present
`invention relates to distributed antenna systems (DAS).
`
`BACKGROUND OF THE INVENTION
`0003 Current wireless communications systems are
`directed to providing RF coverage and/or call capacity so that
`users may connect to the wireless infrastructure. All Solutions
`rely on Some means of distributing RF energy ranging from
`high power, large coverage area towers to low power in
`building pico-cells.
`0004. There also exists a class of RF enhancement tech
`nologies known as RF repeaters. Some are bidirectional RF
`amplifiers that retransmit the signals received over the air
`from a host base station. Others are directly connected to a
`host base station and distribute the RF signals via either
`electrical, e.g., coaxial cable, or optical fiber distribution net
`works. In many cases the signals from a base station can be
`distributed to multiple antenna sites with a means called
`simulcast.
`0005 More specifically, Distributed Antenna Systems are
`used to provide wireless communications coverage where it is
`impractical to installa conventional base station. An example
`is in-building coverage where low cost radiating antennas are
`desired and base stations represent either too large or too
`expensive a solution. Distributed Antenna Systems allow a
`donor base station to be located outside the desired coverage
`area and its RF signals are distributed to multiple antennas
`using either electrical or optical means. A means to distribute
`the base station's signals to more than one antenna is termed
`simulcast. In the direction toward the wireless user, i.e.,
`downlink/forward path, the signal is replicated for each
`remote location. On the return direction, i.e., uplink/reverse
`path, the signals from multiple remote locations are Summed
`to create a single composite signal for the base station. For
`both the base station and the user's device, the multiple copies
`of the RF signal appears as multipath reflections and is com
`pensated for by the use of equalizers and rake receivers.
`0006. In FIG.1 a block schematic drawing of a Distributed
`Antenna System (DAS) having direct RF connection to the
`donor base station with analog optical distribution to the
`Remote RF Units is shown. Simulcast distribution may be
`performed either in the RF or optical domains.
`0007. In FIG. 2 a block schematic drawing of a DAS
`having direct RF connection to the donor base station with
`digital optical distribution to the Remote RFUnits is shown.
`Simulcast distribution may be performed either in the RF or
`digital electrical domains.
`0008. As shown in FIGS. 1 and 2, the current DAS solu
`tions use either analog, i.e., RF over fiber/Analog DAS,
`links or sampled digital, i.e., digital DAS, links and are
`based on an analog RF connection to the base station. The
`DAS signals are fed to one or more RF modules, through a
`technique called simulcast.
`
`0009 Simulcast is readily accomplished with a base sta
`tion providing RF inputs and outputs. These techniques are
`well known to those skilled in the art. Also, for digital distri
`bution, antenna remoting techniques are known to those
`skilled in the art.
`0010. The diagrams show a single base station sector 102,
`i.e. group of RF carriers, connected to multiple Remote RF
`Units 110. This is not just a demultiplexing operation where
`an RF carrier from the host base station is separated for
`distribution to separate Remote RF Units. All Remote RF
`Units transmit and receive the same group of RF carriers as
`the host/donor base station to which they are connected.
`0011. The Remote RFUnits are at a different geographical
`location and they provide either widely separated or partially
`overlapping coverage areas. For the latter a mobile user's
`radio may receive identical signals from multiple Remote
`Units and that composite signal will appear as multipath to
`that wireless device. As long as the time delay differentials
`from the overlapping signals are less than the multipath
`design range of the mobile device, the composite signal will
`be successfully processed.
`0012. These same multipath and time delay consider
`ations also apply in the reverse direction where a user's device
`signal is received by multiple remote units. The multiple
`received signals are Summed within the simulcast hardware
`of the DAS system to provide a single composite signal to the
`host donor base station 102. As with the user device (not
`shown), the base station 102 sets constraints on the amount of
`time delay differential that can be tolerated on the reverse
`link.
`0013 For a purely analog distribution network, illustrated
`in FIG. 1, the simulcast can be accomplished through RF
`splitters on the downlink, and RF summers on the uplink. The
`same splitting and Summing can be accomplished in the ana
`log optical domain, with the requirement that different optical
`wavelengths be used on the uplink. A digital distribution
`network, illustrated in FIG. 2, adds the extra steps of Analog
`to-Digital and Digital-to-Analog conversions at both ends of
`the DAS network. As with the analog DAS, a set of RF
`Summers and splitters can perform simulcast prior to conver
`sion to the digital domain. Simulcast can also be implemented
`in the digital domain prior to conversion to digitally modu
`lated optical signals.
`0014. There is now a new class of base stations with digital
`input and outputs that are meant to be used in conjunction
`with remote radio equipment to provide installation flexibil
`ity. Although these base stations allow the radio equipment to
`be remotely located from the base station core electronics,
`they require a one to one correspondence between each digital
`airlink stream and a remote radio unit. Detailed specifications
`of two digital base station interfaces are the Common Public
`Radio Interface (CPRI) and the Open Base Station Architec
`ture Initiative (OBSAI). With this, a wireless coverage system
`incorporating a large number of remote antennas will require
`a large number of base stations along with the attendant issues
`of frequency re-use and wireless handovers as a user's radio
`moves throughout a coverage area.
`
`SUMMARY OF THE INVENTION
`0015. In a first embodiment of the present invention, a
`digital distributed wireless communication system is pro
`vided. The wireless communication system includes a base
`station providing and receiving a digital multiplexed commu
`nication signal, a plurality of remote transceiver units, a digi
`
`

`

`US 2009/01 8042.6 A1
`
`Jul. 16, 2009
`
`tal distributed interface unit coupled to the base station and
`the plurality of remote transceiver units and providing the
`digital signal in a 1:N simulcast distribution to, and providing
`time alignment of the digital multiplexed signals from, the
`plurality of remote transceiver units.
`0016 A plurality of fiber optic digital interface links cor
`responding to each of the plurality of remote transceiver units,
`wherein the fiber optic digital interface links provide the
`digital multiplexed signal to and from the remote transceiver
`units. The digital distributed interface unit manages a remote
`digital interface delay to align a plurality of remote digital
`multiplexed signals from the plurality of remote transceiver
`units. Each of the plurality of transceiver remote units
`includes a programmable delay to equalize propagation time
`to the digital distributed interface unit.
`0017. The digital distributed wireless communication sys
`tem further includes a Control & Management (C&M) pro
`cessor for processing C&M data plane provided to the plu
`rality of remote transceiver units. The digital distributed
`interface unit provides control commands to each of the plu
`rality of remote transceiver units. The digital multiplexed
`communication signal is a Common Public Radio Interface
`(CPRI) signal. The plurality of remote digital transceiver
`units are Radio (DDR) units providing an airlink to remote
`USCS.
`0018. In another aspect of the present invention, a digital
`distribution communication network, including a host digital
`base station providing and receiving a digital multiplexed
`communication signal, a plurality of digital distributed radio
`(DDR) remotes coupled to receive the digital multiplexed
`communication signal from the base station, and a DDR Hub
`configured to provide a 1:N simulcast of the digital multi
`plexed signal, the DDR Hub coupled to the base station and to
`each of the plurality of DDR remotes.
`0019. The DDR Hub includes a multiplexercoupled to the
`host digital base station, a plurality of fiber optic digital
`interface links coupled to a plurality of multiplexers and to
`each of the corresponding plurality of DDR remotes, and a
`user plane processor for implementing Summation and split
`ting operations, and providing a programmable delay for
`providing a common delay value to the digital multiplexed
`signals to and from the plurality of DDR remotes.
`0020. The digital distribution communication further
`includes a Control and Management (C&M) processor for
`processing C&M data plane from both the host base station
`and the plurality of DDR remotes and managing the simulcast
`distribution of the data plane to the plurality of DDRs. The
`DDR hub manages a remote digital interface delay to align a
`plurality of remote digital multiplexed signals from the plu
`rality of DDR remotes.
`0021. In still another embodiment of the present invention,
`a method for providing a digital communication signal
`between a digital base station and a plurality of remote trans
`ceiver units is provided. The method includes providing and
`receiving a digital multiplexed communication signal at a
`digital base station via a digital distributed interface unit, and
`processing the digital multiplexed communication signal for
`controlled distribution of a 1:N simulcast distribution of the
`digital multiplexed communication signal to and from a plu
`rality of remote transceiver units, wherein the digital distrib
`uted interface unit manages a remote digital interface delay to
`align a plurality of remote digital multiplexed signals from
`the plurality of remote transceiver units.
`
`0022. The method further includes coupling the digital
`multiplexed signals to a plurality of fiber optic digital inter
`face links corresponding to each of the plurality of remote
`transceiver units and the digital distributed interface unit for
`providing the simulcast digital multiplexed signal to the
`remote unit. Each of the plurality of transceiver remote units
`includes a programmable delay to equalize propagation time
`to the digital distributed interface unit. The method still fur
`ther includes processing Control & Management (C&M) data
`plane from both the digital base station and the plurality of
`remote transceiver units, and managing the simulcast distri
`bution of the data plane to the plurality of remote transceiver
`units. Commanding each individual remote digital trans
`ceiver unit via a set of remote CPRI commands transmitted
`via a corresponding fiber optic digital interface link.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0023 FIG. 1 is a block schematic drawing of a Distributed
`Antenna System (DAS) having direct RF connection to the
`donor base station with analog optical distribution to the
`Remote RF Units.
`0024 FIG. 2 is a block schematic drawing of a DAS hav
`ing direct RF connection to the donor base station with digital
`optical distribution to the Remote RFUnits.
`0025 FIG. 3 is a block schematic drawing of a host digital
`base station and Digital Distributed Radio with direct digital
`connection to the donor base station with digital distribution
`to the Digital Remote Radios according to an embodiment of
`the present invention.
`0026 FIG. 4 is a block schematic drawing of a host digital
`base station and Digital Distributed Radio with a detailed
`diagram of the Digital Distributed Radio Hubs for a single
`donor base station configuration.
`0027 FIG. 5 is a block schematic drawing of a host digital
`base station and Digital Distributed Radio with Digital Dis
`tributed Hub scaled up in size to support multiple base station
`sectors according to another embodiment of the present
`invention.
`0028 FIG. 6 is a block schematic drawing of a host digital
`base station and Digital Distributed Radio with the addition of
`a digital switch to a multiple base station sector DDAS to
`provide capacity reallocation capability to the network.
`
`DETAILED DESCRIPTION OF THE INVENTION
`0029. The invention provides an improved base station
`system and method of simulcasting a digital multiplexed
`signal to and from multiple digital radio heads with the nec
`essary synchronization and control aspects to eliminate time
`delay ambiguities.
`0030 FIG. 3 is a preferred embodiment of the invention
`illustrating a simple top level diagram of a digital host base
`station 102 in conjunction with a Distributed Antenna System
`(DAS) network 300 with simulcast capability.
`0031. As shown, FIG. 3 is a block schematic drawing of a
`host digital base station and Digital Distributed Radio with
`direct digital connection to and from the donor base station
`with digital distribution to the Digital Remote Radios. This
`has a digital multiplexed communication signal with a timing
`requirement incompatible with conventional simulcast tech
`niques, as discussed above. For this and Subsequent diagrams,
`a specific digital base station interface (CPRI) will be used as
`an example for labeling and description purposes. However,
`this could be an OBSAI base station interface.
`
`

`

`US 2009/01 8042.6 A1
`
`Jul. 16, 2009
`
`0032. Accordingly, the Common Public Radio Interface
`(CPRI) detailed specification Versions 1.4, 2.4, 3.0 and 4.0,
`hereby incorporated by reference, is directed to the digital
`base station interface between radio equipment control and
`radio equipment (www.cpri.info/spec.html). Additionally,
`the Open Base Station Architecture Initiative (OBSAI) stan
`dard for base station interface is hereby incorporated by ref
`erence (www.obsai.org).
`0033. The base station 302 may be referred to as an REC
`(Radio Equipment Control). Remote transceiver units 304
`will be referred to as the Digital Distributed Radio (DDR)
`units. The simulcast portion of the network in conjunction
`with the donor base Station is referred to as the DDR Hub 310.
`Simulcast distribution is performed digitally along with delay
`management, and control aggregation in the DDR Hub.
`0034. Again referring to FIG. 3, the DDR Hub 310 takes
`Donor CPRI signals from the REC 302 and performs the
`function of 1:N simulcast on the wireless airlink signal, i.e.
`the user plane data. The DDR Hub 310 is also responsible for
`managing the CPRI delay and C&M plane aggregation. Com
`mand of each individual DDR304 is via a set of remote CPRI
`commands transmitted via a corresponding fiber optic cable
`32O.
`0035. In FIG. 4, a block schematic drawing of a host
`digital base station and DDR with a detailed diagram of the
`DDR Hub is shown for a single donor base station configu
`ration of a preferred embodiment of the present invention.
`0036 FIG. 4 provides additional detail for the DDR Hub
`310, showing the user plane and C&M plane processing rela
`tionships. The user plane is typically implemented in hard
`ware, e.g., an FPGA (field programmable gate array), as a
`simple duplication and redistribution on the forward link. On
`the reverse link, an arithmetic Summation is used to combine
`the signals from all simulcasted remote digital radios 304 to
`provide a single combined reverse-link signal to the REC 302.
`On both the donor CPRI links and remote side CPRI links
`320, the Control and Management (C&M) plane is de-multi
`plexed/multiplexed for processing in the C&M element pro
`cessor 316 via multiplexers 312 and 318. Since the host base
`station 302 and associated CPRI link have no means for
`control and maintenance for multiple remote digital radios
`304 on the control plane, information from all simulcasted
`remotes 304 is aggregated into a single entity of the entire
`simulcast group for presentation to the REC 302.
`0037. The digital interfaces, i.e., remote side CPRI links
`320, have precise accuracy requirements for the propagation
`delay to the associated remote digital radio 304. A simulcast
`group, will have different propagation delays due to the dif
`fering fiber lengths to each of the DDRs 304. To manage
`unequal fiber path delays, each DDR 304 incorporates a pro
`grammable link delay buffer 306 to equalize propagation time
`to the DDR Hub 310. Alternatively, the delay buffers 306 may
`be located within the DDR Hub 310 instead of within each
`DDR 304. These delay buffers 306 are programmed to pro
`vide an equal time delay from all remote DDRs 304 to the
`central DDR Hub 310.
`0038. The donor side digital interface, e.g., CPRI, from the
`base station cannot be simply duplicated for all simulcasted
`digital radios 304, since it's not designed for this purpose.
`Therefore, the donor side CPRI interface connection must be
`terminated at the DDR Hub 310 and multiple remote side
`digital CPRI connections 320 must be originated for commu
`nication with the DDR remote Units 304. Since the base
`station 302 uses round trip delay to the remote digital radios
`
`304 to compensate for end-to-end propagation delays, the
`donor side digital interface in the DDR Hub 310 incorporates
`a programmable delay buffer in the user plane processor 314
`to reflect the common delay value for the digital multiplexed
`signals from all of the DDR remote units 304.
`0039. Alternatively, the host base station 302 can be modi
`fied from its standard implementation to accept a time mea
`surement message through the C&M plane to reflect the DDR
`Hub 310 to the DDR remote 304 propagation delay.
`0040. For the C&M plane, the C&M element processor
`316 presents a combined view of the DDRs 304 to the REC
`302. The C&M element processor 316 must intervene since
`the C&M plane from the donor base station 302 is unable to
`individually address, nor recognize the presence of multiple
`DDRs 304 in a common simulcast. The donor base station
`302 operates in a manner consistent with communication and
`connection to a single remote radio while the C&M element
`processor 316 manages all aspects of fanning out the control
`plane to multiple DDRs 304.
`0041. Optionally, the C&M element processor 316 can
`provide a separate IP connection to a separate Network Man
`agement System, to provide individual C&M data on each
`DDR remote unit 304. This permits a connection, which is
`independent of the donor base station 302 to be provided to
`the operator of the installation.
`0042. In addition to the systems described above, more
`sophisticated embodiments based around multiple Hubs, or
`Switches, allow expansion and reconfiguration of Voice/data
`capacity, as well as, facilitate the addition of additional
`remote DDRs to the network.
`0043 FIG. 5 is a block schematic drawing illustrating a
`host digital base station and DDR with DDR Hub scaled up in
`size to support multiple base station sectors according to
`another preferred embodiment of the present invention.
`0044 As shown in FIG. 5, the DDR Hub 506 can be
`extended to multi-sector Support through a simple replication
`of the single-sector DDR Hub 310 in FIG. 4. In FIG. 5, each
`sector is treated as a separate grouping of remote units with
`their associated base station sector. In all cases, there is a 1:1
`connection from the DDR Hub 506 to the DDRS 504 over
`either separate fibers or separate wavelengths on a common
`fiber. The system may be either constructed from multiple
`copies of one sector DDR Hubs or be a single common, larger
`capacity DDR Hub. The latter may then share resources, such
`as the C&M element processor 316 for cost and space sav
`ings. In this case, all allocations of remote units 504 to base
`station sectors 502 are static.
`0045 FIG. 6 is a block schematic drawing of a host digital
`base Station 502 and remote DDR 504 with the addition of a
`switched DDR Hub 510 to a multiple base station sector
`DDAS to provide capacity reallocation capability to the net
`work, according to another embodiment of the present inven
`tion.
`0046 FIG. 6 shows an expansion of the multi-sector DDR
`Hub 510 configuration from a static arrangement to a fully
`Switch-capable arrangement. To utilize this Switch capability,
`neither the DDRs 504 northe DDR Hub 506 needs to change.
`The switch capability is an applique to the existing DDRhub
`configuration. By way of example, the Switch capability can
`take two forms. The simplest embodiment is a manual patch
`panel 508 that allows the operator to reconfigure the connec
`tion between the DDRS 504 and the base Station 502 as
`needed to fulfill capacity requirements. Any single DDR504
`can be connected to any base station sector 502 with the only
`
`

`

`US 2009/01 8042.6 A1
`
`Jul. 16, 2009
`
`constraint being the maximum simulcast per sector that is
`supported by the switched DDR Hub 510. This allows the
`operator to set up an initial capacity allocation on best a priori
`information and later still be able to redistribute capacity
`should any sector become overloaded.
`0047 Alternatively, the manual patch panel 508 can be
`replaced with a fully programmable electronic switch. The
`electronic switch embodiment eliminates the need for the
`operator to visit the DDRhub 506 to make capacity changes.
`Through IP connections, connectivity between the DDRs 504
`and multiple base stations 502 can be changed remotely. The
`remote switching capability allows the operator to redistrib
`ute capacity in the following manner:
`0048 Manually reassign as needed to deal with long
`term capacity changes.
`0049 Timed reassignments based on historical capacity
`needs on a daily or hourly basis.
`0050 Eventual automatic capacity-driven reassign
`ments to allow the DDRs to adapt to capacity loads
`dynamically.
`0051. As will be appreciated by those skilled in the art,
`from the above disclosure the invention provides a number of
`features and advantages by incorporating simulcast tech
`niques to digital distributed radio equipment. Specifically, in
`a preferred embodiment it is applied within the digital trans
`port protocol between the base station and the remote radio
`electronics while resolving any ambiguities that can be gen
`erated by having a 1:N relationship between the donor base
`station interface and that of the remote digital radios. This
`invention also discloses a method to resolve time delay and
`control/management issues arising from having multiple
`remote units connected to each digital RF carrier in the host
`base station.
`0052. The present invention is distinguished from adding a
`simulcast DAS at the user side of the remote radio which
`defeats the benefit of allowing the digital radio to be placed
`directly within the coverage area. This invention also differs
`from demultiplexing multiple airlinks from a composite digi
`tal interface and sending individual ai