az United States Patent
`(10) Patent No.:
`US 6,801,767 B1
`Schwartz et al.
`(45) Date of Patent:
`Oct. 5, 2004
`
`
`US006801767B1
`
`(54) METHOD AND SYSTEM FOR
`DISTRIBUTING MULTIBAND WIRELESS
`COMMUNICATIONS SIGNALS
`
`(75)
`
`.
`Inventors: (US) David Hart Suanyeale, CA.
`
`5,519,691 A
`5,694,232 A
`5,809,395 A
`5,832,368 A
`5,880,863 A
`5,969,837 A
`
`Darcie et al. oe 370/331
`5/1996
`*
`* 12/1997 Parsay et al. oe 398/42
`*
`9/1998 Hamilton-Piercy et al.
`. 725/106
`* 11/1998 Nakano et al... 455/63.1
`*
`3/1999
`Rideout et al.
`we 398/59
`10/1999
`Farber et al.
`veesessessssen 359/132
`
`(US); John Eisenberg, Los Altos, CA
`(US); Peter Forth, San Jose, CA (US)
`
`* cited by examiner
`
`.
`Primary Examiner—Charles Appiah
`Assignee: LGC Wireless, Inc., San Jose, CA(US) — Assistant Examiner—Naghmeh Mehrpour
`(74) Attorney,
`Agent,
`or
`Firm—Lumen
`Property Services, Inc.
`ABSTRACT
`67)
`This invention provides a method and system for distribut-
`ing multiband wireless communications signals. Downlink
`RF signals in a plurality of downlink frequency bands are
`received and then combined into a combined downlink RF
`signal at the main unit. The combined downlink RF signal is
`Subsequently split into multiple downlink RF-parts, which
`are converted to multiple downlink optical signals and
`optically transmitted to the remote units. At each remote
`unit, a delivered downlink optical signal is first converted
`back to a downlink RF-part which is subsequently separated
`into a plurality of downlink RF-groups by frequency band.
`Each downlink RF-group is individually conditioned (e.g.,
`filtered and amplified). The individual-conditioned down-
`link RF-groups are then combined and transmitted to
`a
`dedicated downlink antenna.
`
`Intellectual
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 555 days.
`
`Appl. No.: 09/771,320
`4.
`Jan. 26, 2001
`Filed:
`Tint, C1? coceccccccccsssseecsssssseecsssseeeessseeeee H04Q 7/20
`US. Ch.
`eeceecccecrtssseee 455/426.2; 398/115; 455/131
`Field of Search ......cccccssssssssseseseeee 455/131,
`132
`455/133,
`150.1,
`151.2,
`151.4,
`154.1
`190 L
`192. 1
`73 22 87, 550.1. 553.1. 552.1.
`554.2. 353 355 107. 4 168.1 i 3. 46.2.
`,
`,
`,
`,
`507: 308 AS
`,
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,295,153 A
`5,424,864 A
`
`*
`
`370/335
`3/1994 Gudmundson
`6/1995 Emura ....ccceccecseeseceees 359/173
`
`56 Claims, 12 Drawing Sheets
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`
`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 1 of 12
`
`US 6,801,767 B1
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`Page 2
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`CommScope Ex. 1021
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`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 2 of 12
`
`US 6,801,767 B1
`
`Downlink Operation at Main Unit:
`
`
`
`a
`
`
`
`Receiving downlink RF-sets
`| ~ 20!
`from wireless networks
`
`
`
` Performing first global-
`- — — pe
`frequency-translation
`
`
` L
`
`919
`=
`
`
`
`al-—~___- 999
`Combining the downlink RF-sets into
`combined downlink RF signal
`
`
`
`
`
`
`
`Injecting a calibration tone
`
`
`
` =“
`Y
`~
`~ me ~ ~n
`Splitting the combined RF signal (or
`the calibration tone) into multiple (~~ 298
`
`
`downlink RF-parts
`
`213
`‘a
`
`
`
`
`
`- — —
`
`Injecting a gain-control-signal
`to each downlink RF-part
`
`
`Y
`Converting downlink RF-parts
`to downlink optical signals {~~~ 294
`
`
`
`
`
`
`
`Y
`Optically transmitting
`downlink optical signals
`]
`|
`
`9
`[ ~~ 05
`
`1
`
`
`( Expansion unit)
`
`
`( Remote unit X )
`
`
`
`|
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`
`Y
`
`More remote
`units )
`
`
`
`
`
`(
`
`Cascade remote units
`
`)
`
`
`
`Fig. 2A
`
`Page 3
`
`CommScope Ex. 1021
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`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 3 of 12
`
`US 6,801,767 B1
`
`Downlink Operation at Remote Unit X:
`
`
`
`234
`
`
`
`Converting a delivered downlink optical
`signal to
`a downlink RF-part
`
`
`
`221 035
`
`
`
`Extracting a gain-control- |
`signal and adjusting gain
`
`
`
`
`
` Diverting a fraction of the
`downlink RF-part to other
`
`
`remote units
`
`232
`
`r~222
`RF-part into downlink RF-
`
`groups by frequency band
`
` Separating the downlink
`
`
`
`Performing first local-
`frequency-translation
`
`
`
`Y
`
`233
`A
`
`Performing Individual
`downlink-signal-conditioning
`
`on each downlink RF-group
`
`
`
`223
`
`231
`
`
`
`
`
`Performing second
`local-frequency- —} ----------- P hate anne nn nn ned
`‘jlobaltre. rene i
`
`
`translation
`
`
`9
`translation
`y
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`v
`Recombining and
`Transmitting downlink
`_ M224
`
`RF-groups
`
`995
`
`
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`Actuating an RF-switch
`
`
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`y
`
`(—
`
`TDD antenna
`
`Y
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`
`
`Ne
`
`
`
`/
`
`
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`_
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`__!DD
`signals
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`FDD signals
`
`Fig. 2B
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`
`
`
`
`Y
`.
`[
`Dedicated downlink )
`
`Page 4
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`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 4 of 12
`
`US 6,801,767 B1
`
`Uplink Operation at Remote Unit X:
`
`
`
`
`
`Transmitting the uplink optical signal AZ
`
`
`
`a
`
`
`
`
`Converting the combined uplink RF
`signals to an uplink optical signal
`
`| 299 pe,
`O
`
`
`
`q
`
`_Injectinga
`= Le -
`gain-control-signal
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`t-
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`=
`
`
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`Delivering additional
`uplink RF signals from
`other remote units
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`
`p 254
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`~~ 253
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`Combining uplink RF-
`groups into an uplink
`RF-part
`:
`T
`Performing second
`uplink local-frequency- }---------- >
`
`translation
`Performing Individual
`uplink-signal-conditioning’
`on each uplink RF-group
` Performing first uplink
`local-frequency-
`
`translation
`Separating uplink RF_
`| —~___.959
`C
`signals into uplink RF-
`groups by frequency band
`y
`
`
`
`
`261
`
`
`
`Receiving uplink RF
`signals
`,
`
`L—_954
`
`257
`TOD signals]
`—
`
`signais
`Actuating an RF-switch
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`TDD antenna
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`y
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`(
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`
`[
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`Fig. 2C
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`
`
`
`Dedicated uplink
`antenna
`
`)
`
`
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`
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`Page 5
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`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 5 of 12
`
`US 6,801,767 B1
`
`Uplink Operation at Main Unit :
`
`
`
`Transmitting the combined uplink
`{ “273
`RE signal to wireless networks
`
`
`
`A
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`281
`
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`Combining uplink RF-parts into
`al._,
`combined uplink RF signal
`
`
`272
`
`:
`°
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`Extracting a gain-
`control-signaland
`adjusting gain
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`Page 6
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`A
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`(7 \—~ 271
`Converting uplink optical
`signals to uplink RF-parts
` A
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`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 6 of 12
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`US 6,801,767 B1
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`U.S. Patent
`
`Oct. 5, 2004
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`Sheet 7 of 12
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`US 6,801,767 B1
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`384
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`Page 8
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`U.S. Patent
`
`Oct. 5, 2004
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`Sheet 8 of 12
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`US 6,801,767 B1
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`370
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`U.S. Patent
`
`Oct. 5, 2004
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`Sheet 9 of 12
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`US 6,801,767 B1
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`Page 10
`
`CommScope Ex. 1021
`
`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 10 of 12
`
`US 6,801,767 B1
`
`Fig. 4B
`
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`Page 11
`
`CommScope Ex. 1021
`
`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 10 of 12
`
`US 6,801,767 B1
`
`Fig. 4B
`
`378
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`Page 11
`
`CommScope Ex. 1021
`
`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 11 of 12
`
`US 6,801,767 B1
`
`
`
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`
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`
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`
`Page 12
`
`CommScope Ex. 1021
`
`

`

`U.S. Patent
`
`Oct. 5, 2004
`
`Sheet 12 of 12
`
`US 6,801,767 B1
`
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`Page 13
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`CommScope Ex. 1021
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`

`

`US 6,801,767 B1
`
`1
`METHOD AND SYSTEM FOR
`DISTRIBUTING MULTIBAND WIRELESS
`COMMUNICATIONS SIGNALS
`
`FIELD OF THE INVENTION
`
`This invention relates generally to wireless communica-
`tions systems. More particularly, it relates to a novel method
`and system for distributing multiband wireless communica-
`tion signals.
`
`BACKGROUND ART
`
`in
`As wireless communications become a way of life
`society, a challenge to wireless communications network
`operators is to transport and distribute multiband wireless
`communications signals in an efficient, flexible, and eco-
`nomical manner. And the challenge is particularly acute in
`areas that are not traditionally covered by macro-networks.
`Such areas reside mostly in indoor environments, including
`airports, malls, office buildings, tunnels, hotels, convention
`centers, and sports arenas.
`Distributed radio systems are conventionally used in the
`art to provide the radio coverage to the indoor environments,
`employing an architecture of one distributed antenna system
`supporting one wireless radio frequency (RF) band. Such an
`architecture entails that in order to support multiple RF
`bands, separate distributed antenna systems must be
`installed in parallel, each accommodating a specific RF
`band. This is a rather inefficient, and at times, cumbersome
`undertaking.
`
`The past few years have seen a few other approaches in
`the art, attempting to distribute multiband wireless commu-
`nication signals in a more efficient manner. For example,
`US. Pat. No. 5,969,837 by Farber et
`al. describes a com-
`munications system in which multiple RF signals from
`multiple wireless communications networks are first com-
`bined at a base unit. The combined RF signal is then split
`into multiple outputs, which are subsequently converted to
`optical signals and transmitted to remote units by optical
`fibers. At each remote unit, the received optical signal is
`converted back to an RF signal. The RF signal is then split
`and routed to separate antennas, wherein each antenna is
`designated to a specific frequency band (e.g., PCS, GSM, or
`paging).
`A notable disadvantage of the above prior art system is
`that each frequency band requires a dedicated antenna,
`which handles both downlink and uplink RF signals by way
`of a duplexer. (And it should be noted that the duplexer (84)
`as disclosed by Farber et al. cannot feasibly separate more
`than one frequency band, particularly intertwined bands
`such as cellular and iDEN bands.) Such a configuration can
`become considerably bulky and inefficient, especially when
`dealing with multiple (e.g., more than two) frequency bands.
`There are additional shortcomings common to the above and
`other prior art multiband distributed systems, summarized as
`follows:
`
`star
`art systems typically employ a
`1. The prior
`architecture, in which each remote unit is connected to
`a main (or base) unit by a dedicated fiber-optic cable.
`Such an architecture is inflexible and inefficient for
`many applications.
`
`2. Strong downlink RF signals transmitted by the main
`unit tend to interfere with the reception of weak uplink
`RF signals in a remote unit by saturating the front-end
`radio receivers.
`
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`2
`3. Intermodulation products produced by the nonlineari-
`ties in the downlink amplifiers tend to
`fall into the
`uplink frequency bands, thereby desensitizing the
`uplink receivers.
`4. Intermodulation products produced in one downlink
`frequency band often fall into other downlink fre-
`quency bands, thereby causing regulatory violations.
`5. Adjacent and/or intertwined frequency bands (e.g.,
`iDEN and cellular bands) cannot be feasibly separated
`and therefore effectively filtered and amplified.
`6. The prior art systems cannot support Time Division
`Duplex (TDD) protocols, in which the downlink and
`uplink RF signals share the same frequency band but
`are interleaved in time.
`7. The prior art systems are devoid of carrying out an
`end-to-end gain calibration, such that a prescribed gain
`for each of the frequency bands is established in each
`of the remote units.
`a need in the art for a
`In view of the forgoing, there is
`multiband distributed wireless communications system that
`overcomes the prior art problems.
`
`SUMMARY
`
`The aforementioned need in the art is provided by a novel
`method and system for distributing multiband wireless com-
`munication signals according to the present invention. In a
`multiband distributed wireless communications system of
`the present invention, a main unit is linked to multiple
`remote units by optical fibers in
`a hybrid star/cascaded
`architecture. As a way of example, the main unit can be
`directly connected to individual remote units, and/or con-
`nected to one or more cascaded chains of remote units. The
`main unit can also be linked to some of the remote units via
`one or more expansion units in an hierarchical (or tree-like)
`structure. Such a hybrid star/cascaded architecture of the
`present invention provides a modular and flexible way of
`distributing multiband wireless communications signals,
`particularly in an indoor environment.
`In the present invention, multiband wireless communica-
`tions signals are transported and distributed as follows. On
`the downlink, a plurality of downlink RF-sets in a plurality
`of downlink frequency bands transmitted from a plurality of
`wireless communication networks are received at the main
`unit. The downlink RF-sets each contain downlink RF
`signals in one of the downlink frequency bands. Some of
`these downlink RF signals are frequency-division-duplexed
`(FDD), such that downlink and uplink RF signals are
`separate in frequency; while others are time-division-
`duplexed (TDD), such that downlink and uplink signals
`share the same frequency band but are separated in time.
`The received downlink RF-sets are then combined into a
`combined downlink RF signal, which is subsequently split
`into multiple downlink RF-parts. Each downlink RF-part is
`essentially a “copy” of the combined downlink RF signal in
`that it contains the downlink RF signals from all of the
`downlink RF-sets. The downlink RF-parts are then con-
`verted to downlink optical signals in
`a one-to-one
`correspondence, which are subsequently transmitted to the
`remote units by way of optical fibers.
`At each of the remote units, a delivered downlink optical
`signal is converted to
`a delivered downlink RF-part. The
`delivered downlink RF-part is then separated into a plurality
`of downlink RF-groups by frequency band. Individual
`downlink-signal-conditioning is subsequently performed on
`each of the downlink RF-groups, wherein the downlink-
`signal-conditioning includes one
`or more steps of
`
`Page 14
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`CommScope Ex. 1021
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`

`

`US 6,801,767 B1
`
`3
`RF-amplifying, gain-adjusting, and RF-filtering. By per-
`forming amplification on
`the downlink RF-groups
`separately, nonlinear intermodulation products amongst the
`downlink RF-groups can be effectively avoided. The
`individual-conditioned downlink RF-groups are then com-
`bined and transmitted to a downlink antenna. Note that in the
`present invention, each remote unit is in RF-communication
`with at least one downlink antenna dedicated to handle the
`downlink RF signals transmitted from the remote unit.
`in
`Likewise, each of
`the remote units
`is
`also
`RF-communication with at least one uplink antenna dedi-
`cated to handle the uplink RF signals to be received by the
`remote unit. Having separate uplink and downlink antennae
`enables the reception of uplink RF signals and the transmis-
`sion of downlink RF signals to occur with spatial separation
`in the present invention. Such spatial separation creates
`propagation loss between the transmit (uplink) and receive
`(downlink) antennae, which helps protect the sensitive
`uplink receiver from being desensitized by strong downlink
`RF signals and/or by downlink intermodulation products
`that fall into one or more uplink frequency bands.
`On the uplink, multiple uplink RF signals in a plurality of
`uplink frequency bands are
`first received by the uplink
`antenna connected to the remote unit. The received uplink
`RF signals are then separated into a plurality of uplink
`RF-groups by frequency band. Individual uplink-signal-
`conditioning is subsequently performed on each of the
`uplink RF-groups, which includes one or more steps of
`RF-amplifying, gain-adjusting, and RF-filtering. The
`individual-conditioned uplink RF-groups are then combined
`into an uplink RF-part, which is further converted to an
`uplink optical signal. As such, multiple uplink optical sig-
`nals corresponding to multiple uplink RF-parts are optically
`transmitted from the remote units to the main unit.
`At the main unit, the received uplink optical signals are
`first converted back to
`the uplink RF-parts. The uplink
`RF-parts are then combined into a combined uplink RF
`signal, which is subsequently transmitted to the wireless
`communications networks.
`The present invention advantageously utilizes various
`frequency translations to allow for separation of downlink
`RF signals into downlink RF-groups by frequency band
`using feasible means (such as RF-filtering), whereby these
`downlink RF-groups can be individually conditioned (e.g.,
`filtered and amplified) at a remote unit before being trans-
`mitted to
`a downlink antenna. The frequency translations
`can also be effectively used to prevent the interference
`effects and intermodulation products amongst different
`(downlink and uplink) frequency bands. For instance, a first
`frequency-translation may be performed on one or more
`downlink RF-sets, so as to place the downlink RF-sets in
`disjoint frequency bands that are sufficiently far apart to
`allow for economical separation of downlink RF signals in
`different frequency bands by RF-filtering. Such a task would
`otherwise be very difficult—if not entirely impossible—to
`accomplish, particularly when dealing with adjacent (and/or
`intertwined) frequency bands. At each of the remote units, a
`second frequency-translation may be subsequently per-
`formed on one or more downlink RF-groups, which sub-
`stantially undoes the effect of the first frequency translation
`and thereby places the downlink RF signals back to their
`original downlink frequency bands respectively. There can
`also be first and second frequency-translations performed on
`one or more downlink RF-groups at a remote unit, whereby
`the downlink-signal-conditioning (e.g., RF-filtering,
`and
`RF-amplifying) on these downlink RF-groups can be per-
`formed more effectively in one or more intermediate fre-
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`first and second
`quency bands. Similarly, there can be
`frequency-translations performed on one or more uplink
`RF-groups at
`a remote unit, so as to perform the uplink-
`signal-conditioning on these uplink RF-groups more effec-
`tively in one or more intermediate frequency bands. As such,
`these frequency translations effectively facilitate the trans-
`portation and distribution of multiband RF signals, and are
`particularly desirable when dealing with RF signals in,
`adjacent (and/or intertwined) frequency bands.
`The present invention further entails carrying out an
`end-to-end gain calibration, thereby setting a prescribed gain
`for each of the downlink RF-groups. To maintain the pre-
`scribed gain over temperature changes and other effects, a
`downlink-gain-control signal (e.g., a pilot or an Frequency-
`Shift-Key signal) that is set to a frequency outside of any of
`the frequency bands used by the wireless communications
`networks (and frequency-translated bands) can be injected to
`and transmitted along with each of the downlink RF-parts to
`the remote units. At each of the remote units, the downlink-
`gain-control signal is detected and thereby used to maintain
`the gain for each of the downlink RF-groups at the pre-
`scribed level.
`In the present invention, the downlink and uplink optical
`signals between the main unit and remote units can be
`further transmitted via one or more expansion units. For
`example, a downlink optical signal can be first transmitted
`from the main unit to an expansion unit, where it is amplified
`and further split into multiple secondary-optical-signals. The
`secondary-optical-signals are then transmitted to additional
`remote units (and/or one or more lower-level expansion
`units). On the uplink, a plurality of uplink optical signals
`from a number of the remote units can be first transmitted to
`an expansion unit, where they are amplified and further
`combined to
`a combined optical signal. The combined
`optical signal is then transmitted to the main unit (or to a
`higher-level expansion unit). The deployment of the expan-
`sion units enhances the flexibility and efficiency of the
`present invention in transporting and distributing multiband
`wireless communication signals.
`In an exemplary embodiment of a multiband distributed
`wireless communications system according to the present
`invention, the main unit comprises an RF-downlink-
`interface for receiving a plurality of downlink RF-sets in a
`plurality of downlink frequency bands from a plurality of
`wireless communications networks; a downlink
`RF-combining means for combining the downlink RF-sets
`into
`a combined downlink RF signal;
`a downlink
`RF-splitting means for splitting the combined downlink RF
`signal into multiple downlink RF-parts; and multiple RF-to-
`optical converters for converting the downlink RF-parts to
`downlink optical signals. The main unit further comprises
`multiple optical-to-RF converters for converting the
`received uplink optical signals to uplink RF-parts; an uplink
`RF-combining means for combining the uplink RF-parts
`into
`a combined uplink RF signal;
`and an RF-uplink-
`interface for transmitting the combined uplink RF signal to
`the wireless communications networks.
`Each of the remote units comprises a downlink optical-
`to-RF converter for converting a delivered downlink optical
`signal to a delivered downlink RF-part; a downlink splitting-
`filtering means for separating the downlink RF-part into a
`plurality of downlink RF-groups by frequency band; a
`plurality of downlink-signal-conditioning assemblies for
`performing individual downlink-signal-conditioning on
`each of the downlink RF-groups, and a downlink filtering-
`combining means for combining the individual-conditioned
`downlink RF-groups into a downlink RF-transmit signal,
`
`Page 15
`
`CommScope Ex. 1021
`
`

`

`US 6,801,767 B1
`
`5
`which is to be transmitted to a dedicated downlink antenna.
`The downlink splitting-filtering means can be provided by a
`series of RF-filters configured in parallel, each characterized
`by a distinct frequency passband. Each of the downlink-
`signal-conditioning assemblies can be in the form of one or
`more RF-amplifiers, gain-adjusting elements, and RF-filters.
`Note that in the present invention, each of the remote units
`is in RF-communication with at least one downlink antenna,
`dedicated to handle downlink RF signals in a plurality of
`frequency bands.
`in
`is
`the remote units
`of
`Moreover, each
`least one dedicated uplink
`RF-communication with at
`antenna, from which multiple uplink RF signals in a plural-
`ity of uplink frequency bands are received by the remote
`unit. Each of the remote units further comprises an uplink
`splitting-filtering means for separating the received uplink
`RF signals into a plurality of uplink RF-groups by frequency
`band; a plurality of uplink-signal-conditioning assemblies
`for performing individual uplink-signal-conditioning on
`each of the uplink RF-groups; an uplink filtering-combining
`means for combining the individual-conditioned uplink
`RF-groups into an uplink RF-part; and an uplink RF-to-
`optical converter for converting the uplink RF-part to an
`uplink optical signal. Each of the remote units may be
`further coupled to an auxiliary antenna by an RF-switching
`means, whereby downlink RF signals in
`a TDD frequency
`band from the remote unit are transmitted to, and uplink RF
`signals in the TDD frequency band are received at the
`remote unit from this TDD antenna by actuating the
`RF-switching means. The RF-switching means can be pro-
`vided by an RF-(Transmit/Receive)switch coupled to
`a
`downlink power-detect means, whereby it
`is actuated
`according to the power level of the downlink RF signals in
`the TDD frequency band as determined by the downlink
`power-detect means. Alternatively, a downlink RF-switch
`and an uplink RF-switch can be separately implemented
`along a downlink TDD RF-path and an uplink TDD
`RF-path, and further coupled to
`a downlink power-detect
`means in a remote unit. By detecting the power level on the
`downlink TDD RF-path, the downlink power-detect means
`enables the downlink TDD signals to be transmitted, along
`with the downlink (FDD) RF signals in other downlink
`frequency bands, to the downlink antenna; while permitting
`the uplink TDD signals to be received, along with the uplink
`(FDD) RF signals in other uplink frequency bands, from the
`uplink antenna when there is no downlink transmission.
`The multiband distributed wireless communications sys-
`tem of
`the present invention may further comprise a
`frequency-translation means for performing various
`frequency-translations on downlink and uplink RF signals,
`to allow for feasible separation of downlink RF signals into
`downlink RF-groups by frequency band and to prevent the
`interference effects and intermodulation products amongst
`different (downlink and uplink) frequency bands. By way of
`example, the frequency-translation means may comprise a
`global-tone mixer (coupled to
`a global-tone generator) in
`RF-communication with the downlink RF-combining means
`at
`the main unit,
`so
`as
`to perform one or more first
`frequency-translations on one or more downlink RF-sets and
`thereby place the downlink RF-sets in disjoint frequency
`bands that are sufficiently far apart to allow for economical
`separation of downlink RF signals in different bands by way
`of RF-filtering. The frequency-translation means may fur-
`ther comprise multiple remote global-tone mixers coupled to
`the remote units, such that there are one or more remote
`global-tone mixers in each of the remote units, for perform-
`ing one or more second frequency-translations and thereby
`
`10
`
`30
`
`55
`
`6
`placing the downlink RF-groups back into their original
`frequency bands respectively. (The remote global-tone mix-
`ers may be coupled to a remote global-tone generator, which
`is substantially the same as the one used in the main unit, or
`receive a global-tone signal from the main unit.) The
`frequency-translation means may also be in the form of one
`or more downlink-local-tone mixers (coupled to a downlink-
`local-tone generator), in RF-communication with at least
`one of the downlink-signal-conditioning assemblies in
`a
`remote unit. The downlink-local-tone mixers serve to place
`one or more downlink RF-groups in one or more interme-
`diate frequency bands where the downlink-signal-
`conditioning on these downlink RF-groups can be more
`effectively performed, and subsequently place these down-
`link RF-groups back into their respective original frequency
`bands. The frequency-translation means may further be in
`the form of one or more uplink-local-tone mixers (coupled
`to
`an uplink-local-tone generator), in RF-communication
`with one or more uplink-signal-conditioning assemblies in a
`remote unit. The uplink-local-tone mixers likewise serve to
`place one or more uplink RF-groups in one or more inter-
`mediate frequency bands, such that
`the uplink-signal-
`conditioning on these uplink RF-groups can be performed
`more effectively. Moreover, the frequency-translation means
`can be in the form of a combination of global-tone and
`local-tone mixers (and other frequency-translation means
`known in the art) implemented in the main unit and the
`remote units, for performing various frequency-translations
`on downlink and uplink RF signals, so as to best facilitate
`the distribution of multiband RF signals.
`The multiband distributed wireless communications sys-
`tem of the present invention may further comprise a gain-
`calibration means for carrying out an end-to-end gain cali-
`bration (initially
`or when there
`is
`no transmission of
`downlink RF signals), thereby setting a prescribed gain for
`each of the downlink RF-groups. As a way of example, the
`gain-calibration means may be provided by a calibration-
`tone generator in RF-communication with the downlink
`RF-combining means in the main unit that injects a calibra-
`tion tone. The frequency of the calibration tone is set to lie
`within the frequency band of each downlink RF-group to be
`calibrated. To maintain the prescribed gain against tempera-
`ture changes and other effects, one or more gain-control-
`signal combiners can be implemented in the main unit, for
`injecting a gain-control-signal (e.g., a pilot or FSK signal) to
`each of the downlink RF-parts to be transmitted to
`the
`remote units. The gain-control-sig