US006785558B1
`
`US 6,785,558 Bl
`(10) Patent No.:
`az United States Patent
`Stratford et al.
`(45) Date of Patent:
`Aug. 31, 2004
`
`
`(54) SYSTEM AND METHOD FOR
`DISTRIBUTING WIRELESS
`COMMUNICATION SIGNALS OVER
`
`vee TELECOMMUNICATION
`
`(75)
`
`Inventors:
`
`Scott B. Stratford, Santa Clara, CA
`(US); Simon P. S. Yeung, Cupertino,
`CA (US); Lance K. Uyehara, San Jose,
`CA (US); Robin Y. K. Young, San
`Jose,
`CA (US)
`
`(73)
`
`Assignee: LGC Wireless, Inc., San Jose,
`
`CA (US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`US.C. 154(b) by 5 days.
`
`(21)
`}
`(22)
`(51)
`(52)
`
`(58)
`
`(56)
`
`Appl. No.: 10/313,900
`.
`Dec. 6, 2002
`Filed:
`nt C17 accccccsscccssssseessesssseenssseeeenseseee H04Q 7/20
`US. CMe cecceseccsssceeee 455/561; 455/562.1; 455/560;
`455/522: 455/69
`
`.
`Field of seat SL S60. 399 aoe, on oN
`“”
`awe
`?
`;
`
`.
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,627,879 A
`5,852,651 A
`6,023,625 A
`6,112,086 A
`
`Russell et al.
`5/1997
`........ceee 379/59
`Fischer et al.
`12/1998
`379/56.2
`Myers, Jr.
`....
`2/2000
`. 455/503
`
`8/2000 Wala ......eceecceeseeeseeeees 455/434
`
`Slabinski ................. 455/562.1
`4/2002
`6,374,124 B1 *
`Siuvetal. ...
`... 370/338
`2/2003
`6,522,641 Bl *
`1/2004 Koonen .....
`... 398/70
`6,674,966 B1 *
`5/2002 Arnon et al.
`2002/0055371 Al *
`wa 455/562
`2002/0187809 Al * 12/2002 Mani et al.
`w 455/561
`2003/0040337 Al *
`2/2003
`Yilitalo
`......
`... 455/562
`2003/0114103 Al *
`6/2003
`Dinkel et al.
`eevee 455/17
`2003/0162539 Al *
`8/2003
`Fiut et al.
`...ccesseeesseeee 455/424
`
`
`
`* cited by examiner
`
`Primary Examiner—Edward F. Urban
`Assistant Examiner—Huy Phan
`(74) Attorney,
`Agent,
`or
`Firm—Lumen _ Intellectual
`Property Services, Inc
`(57)
`
`ABSTRACT
`
`A method for transporting wireless communication signals
`between a base station hotel and remote cell sites with
`separately digitized RF carrier signals is provided. Sepa-
`rately digitized carriers are transmitted over a digital net-
`work between the hotel and the remote sites, remaining in
`digital format until reaching terminal antenna units. At the
`antenna units, downlink digital signals are converted to
`analog RF signals and transmitted, while uplink analog
`signals are received and converted to digital signals. A
`corresponding system comprising a base station hotel, at
`least one remote site, and a digital data network connecting
`the hotel to the remote site is provided. The hotel includes
`a plurality of base stations and a digital hub for interfacing
`the hotel to the network. The remote site includes a set of
`antenna units connected via a local data link to a network
`access node for interfacing to the network.
`
`19 Claims, 11 Drawing Sheets
`
`Network
`ry
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`povoveeseneee sooesearooecornnrr TT -
`:
`Antenna
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`14
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`
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`
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`
`|
`
`Page 1
`
`CommScope Ex. 1022
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`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 1 of 11
`
`US 6,785,558 B1
`
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`Page 2
`
`CommScope Ex. 1022
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 2 of 11
`
`US 6,785,558 B1
`
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`Page 3
`
`CommScope Ex. 1022
`
`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 3 of 11
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`US 6,785,558 Bl
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 4 of 11
`
`US 6,785,558 B1
`
`
`
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`
`Page 5
`
`CommScope Ex. 1022
`
`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 5 of 11
`
`US 6,785,558 B1
`
`600
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`Page 6
`
`CommScope Ex. 1022
`
`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 6 of 11
`
`US 6,785,558 B1
`
`
`Remote Site
`810
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`
`FIG. 9
`
`Page 7
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 7 of 11
`
`US 6,785,558 B1
`
`16 bits 8 bits
`
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`Page 8
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 8 of 11
`
`US 6,785,558 B1
`
`
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`a
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`Page 9
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 9 of 11
`
`US 6,785,558 B1
`
`
`
`1410+
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`
`Page 10
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`

`

`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 10 of 11
`
`US 6,785,558 B1
`
`pie ee nn en nn en ne nn te nn nn nnn ne nnn rn tenses nsscesy
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`Page 11
`
`CommScope Ex. 1022
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`

`

`_| RF/Digital TRX _
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`U.S. Patent
`
`Aug. 31, 2004
`
`Sheet 11 of 11
`
`US 6,785,558 B1
`
`
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`Page 12
`
`CommScope Ex. 1022
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`

`

`US 6,785,558 B1
`
`1
`SYSTEM AND METHOD FOR
`DISTRIBUTING WIRELESS
`COMMUNICATION SIGNALS OVER
`METROPOLITAN TELECOMMUNICATION
`NETWORKS
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to wireless com-
`munication systems. More specifically, it relates to tech-
`niques for transporting signals from a base station hotel to
`remote transmitters using optical fibers.
`
`BACKGROUND OF THE INVENTION
`
`Wireless communication systems, and cellular system in
`particular, are evolving to better suit the needs of increased
`capacity and performance demands. Currently cellular infra-
`structures around the world are upgrading their infrastruc-
`ture to support the third generation (3G) wireless frequency
`spectrum. Unfortunately, the tremendous capital resources
`required to upgrade the entire cellular system infrastructure
`inhibits the deployment of these 3G systems. It is estimated
`that up to 3 million 3G cell sites will be needed around the
`world by 2010.
`Traditionally, a cellular communications system includes
`multiple remote sites, each providing wireless service to a
`geographic service area, or cell. As shown in FIG. 1,
`a
`cellular base station (BTS) is normally located in each
`remote site 100, together with an antenna tower, antennas, an
`equipment room, and a number of other relevant compo-
`nents. This traditional approach of deploying all the cell site
`equipment locally at each remote site has several drawbacks
`that contribute to the expense of the infrastructure, and
`upgrades to the infrastructure. At each remote site, a BTS
`room or cabinet to host the large base station equipment is
`required, as well as additional electric power supplies for the
`base station. This increases both the costs of the equipment
`at each site, as well as the costs of acquiring and renting the
`physical location for the equipment. The remote cell site
`equipment must be designed for future coverage and capac-
`ity growth, and upgrades to the equipment require physical
`access to the remote site.
`
`To mitigate these problems, some cellular systems have
`been designed with a different architecture, as shown in FIG.
`2. The base stations 240 for multiple remote sites 200 are
`centralized in a base station hotel 210, while the antenna
`towers and antennas remain located at various remote sites
`at a distance from the base station hotel. Separating the base
`stations 240 from the antennas, however, makes it necessary
`to transport RF signals between the base station hotel and the
`various cell sites that it serves, typically using signal con-
`verters 250, network interface equipment 260, and a broad-
`band communication network 220. When broadband fiber
`optic cables are used, RF signals from the base stations are
`converted to optical format and communicated over the fiber
`optic cable and then converted back to analog RF signals at
`the remote sites. After the optical/RF conversion, the signal
`is sent to one of several sector transmitters 230 and radiated
`over the air via the antenna to provide cellular coverage. The
`BTS hotel concept is especially valuable in metropolitan
`areas where fiber is abundant but equipment space comes at
`a premium. In these types of areas it is getting increasingly
`more difficult to deploy new cell sites due to a variety of
`factors including regulatory and space constraint issues.
`
`Unfortunately, a significant portion of the metropolitan
`fiber networks already are configured to carry particular
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`types of traffic such as telephony and data. While there is
`capacity available for additional traffic it must be transmitted
`in
`a format that
`is compatible with the existing traffic.
`Simply applying the RF signals to the fiber in an analog
`fashion would require the use of expensive optical compo-
`nents to optically multiplex the analog signals on to the fiber
`using some type of wavelength division multiplexing. This
`assumes that the existing network even supports wavelength
`division multiplexing which is
`not always the case. In
`addition, non-standard access equipment would be required
`to combine the optical signal carrying the RF signals with
`the optical signals containing the existing digital traffic.
`
`Several techniques have been proposed for the digital
`transport of cellular signals over existing switched data
`networks. The typical approach, such as that disclosed in
`US. Pat. No. 5,627,879 to Russell et
`al.,
`is to digitize a
`broadband RF signal comprising several dozen RF carriers
`using a single A/D converter. The digitized broadband signal
`is then transmitted to the remote sites where a D/A converter
`is used to recover the broadband analog signal containing
`the multiple RF carriers. It should be emphasized that the
`A/D and D/A converters at each end of the communication
`link convert an
`entire broadband RF signal containing
`multiple RF carriers. U.S. Pat. No. 5,852,651 to Fischer et
`al. describes a similar technique. Broadband RF signals from
`different sectors may be combined with each other or may
`remain separated, but in either case A/D and D/A conversion
`is performed on the entire broadband signal associated with
`each antenna. It should also be emphasized that the conver-
`sion at the remote site always takes place at the remote site’s
`centrally located interface to the switched network, so that
`the broadband signal is communicated in analog RF form
`between the central network interface and the various sector
`antenna transmitters and their associated antennas.
`
`SUMMARY OF THE INVENTION
`
`The present invention introduces an improved technique
`for transporting wireless communication signals between a
`set of base stations in
`a base station hotel and a
`set of
`remotely located cell sites. In contrast with prior techniques
`that digitize the entire broadband RF signal associated with
`each antenna, the present invention proposes a technique
`that separately digitizes each RF carrier signal within the
`broadband RF signal. Separately digitizing each RF carrier
`has significant advantages, such as easing the dynamic range
`requirements on both the receiver and A/D converter. The
`separately digitized carriers are transmitted over a digital
`network between the base station hotel and the remote sites.
`In contrast with prior techniques, however, the present
`invention provides a technique wherein the digitized carrier
`signals are not converted to analog format when they first
`arrive at the remote site, but remain in digital format as they
`are distributed within the remote site to the various antenna
`units of the remote site. In other words, the remote site A/D
`and D/A converters are terminally located at the antenna
`units rather than positioned at an intermediate point in the
`signal transport path, such as the remote site’s interface with
`the digital network.
`Because signals are transported in a purely digital form
`until the very end of the digital transport (i.e., all the way up
`to the antenna units), the method of the invention enjoys
`some key benefits over prior systems that use analog trans-
`port at the remote site to distribute the RF signals to separate
`antenna units. Optical effects that limit analog systems such
`as attenuation, dispersion and reflection do not directly affect
`the cellular signal when digital transport is used. As a result,
`the system can send signals over much longer distances
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`US 6,785,558 B1
`
`3
`without degradation. Also, dynamic range is unaffected by
`distance since the digital samples suffer no degradation due
`to the transport process as long as reliable communications
`exist. Signal reconstruction techniques can also be used with
`digital
`data to ensure data integrity through the
`entire
`transport process. For example, error-coding algorithms can
`be used to detect and correct bit errors. These benefits apply
`to both downlink and uplink directions.
`In one aspect of the invention, a method of downlink
`wireless communication is implemented by a system com-
`prising a base station hotel, at least one remote site, and a
`digital data network (e.g., a fiber optic network) connecting
`the hotel to the remote site. The base station hotel houses a
`plurality of base stations and a digital hub which connects
`the base stations to the digital network. The remote site has
`a set of antenna units, where transmitters and antennas are
`located, and a network access node connecting the remote
`site to the digital network. A local data link (e.g., dedicated
`fiber optics, or conventional LAN) within the remote site
`connects the antenna units to the network access node.
`In
`an aspect of the invention providing transport of
`downlink signals, each of the base stations generates a set of
`carrier signals, where each carrier signal comprises multiple
`information channels (e.g., multiple user signals code-
`modulated onto a carrier frequency of the carrier signal). In
`some systems, a base station will generate several carrier
`signals at various distinct carrier frequencies. In addition, a
`base station may also generate several carrier signals
`intended for transmission to distinct sectors of a remote site.
`Each carrier signal is then individually digitized by the
`digital hub to produce a digitized carrier signal. The digi-
`tized carrier signals are then formatted appropriately and
`communicated via a digital data network to various remote
`sites. Typically, there
`is
`a one-to-one correspondence
`between base stations and remote sites,
`so
`that a given
`carrier signal will be sent to a single corresponding remote
`site. In some cases, however, a base station can multicast to
`multiple remote sites, or various base stations can provide
`carrier signals to the same remote site. Once received at the
`appropriate remote site, the digital carrier signal is sent via
`a local digital link to an antenna unit where it is converted
`to an analog carrier signal. The analog carrier signal is then
`frequency up-converted, amplified, and transmitted from an
`antenna to subscribers assigned to the various information
`channels of
`the
`carrier
`signal.
`In systems that use
`sectorization, the set of carrier signals comprises carrier
`signals for each of the various sectors at a cell site.
`In another aspect of the invention, an analogous method
`of uplink communication is provided in the same system.
`According to this method, analog carrier signals are received
`at antenna units and separately digitized there prior to being
`transported over a local digital link to a network access node
`at the remote site. The digital carrier signal is then sent over
`the digital data network to the base station hotel. Other
`carrier signals from the same antenna unit, from other
`antenna units at the same remote site, or from other remote
`sites are similarly sent to the base station hotel in digital
`format. The separate digital carrier signals are then con-
`verted to analog carrier signals and received by the appro-
`priate base station in the hotel.
`In a preferred embodiment of the invention, the cellular
`communication system is
`a 3rd generation cellular system
`where each of the multiple carriers within the broadband RF
`signal uses CDMA (code division multiple access) to mul-
`tiplex several information channels onto the same RF car-
`rier. In such systems, it is important to accurately maintain
`proper signal power levels. Accordingly, in order to com-
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`4
`pensate for any signal power level distortions introduced
`during conversion and processing, the preferred embodi-
`ment uses a power control channel to transport power
`measurement signals between the base station hotel and the
`remote sites. After the RF carrier signals have been digitally
`transported, the power measurement signals are then used to
`appropriately scale the signal power level of each RF carrier
`to compensate for any distortions.
`In systems that employ CDMA (code-division multiple
`access), a time-diversity technique of the present invention
`may be used as well. In the downlink, after a carrier signal
`is transported to an antenna unit, both the original signal and
`a time-delayed copy of the signal are transmitted via sepa-
`rate antennas. This technique provides an additional diver-
`sity signal to the subscribers without requiring any addi-
`tional bandwidth between the base station hotel and the
`antenna units. In the uplink, primary and diversity signals
`received at the remote site can be superimposed with a
`relative time delay and then transported as one digital signal.
`At the base station, the two superimposed signals are auto-
`matically separated by the base station’s RAKE receiver.
`In another aspect of the invention, the method is imple-
`mented in a cellular system using a digital hub at the base
`station hotel for performing the required A/D and D/A
`conversions, signal processing, and interfacing with the
`switched data network. A similar network access node is
`used at each remote site. In the downlink direction (from the
`base station to mobile user) the digital hub digitizes the RF
`signals emanating from the base station and formats the
`digitized samples into a standard telecommunication proto-
`col such as OC-X (OC-3, OC-12, OC-48, OC-192, etc.),
`STM-n (STM-1, STM-4, STM-16, etc.) or Gigabit Ethernet.
`The appropriate format is determined by the specific type of
`transport network deployed. Using this standard data format,
`the digital hub uses network access equipment such as an
`add/drop multiplexer to interface to the digital network. The
`digital network is then used to transport the digitized RF
`signals to the remote cell site. At the remote cell site
`a
`remote version of the digital hub, the network access node
`(NAN), is then used to recover the digital RF carrier signals
`from the network. After being distributed to the appropriate
`antenna radio units, the digital signals are converted to
`analog RF signals and broadcast over the air to the mobile
`users using an amplifier and suitable antennas.
`In the uplink direction, similar reciprocal functions exist.
`At the remote site
`the antenna units receive analog RF
`signals over the air through a receiving system that typically
`consist of an antenna, amplifiers and filters. The received
`analog signal is then down-converted, digitized and sent
`over a local data link to the remote site’s NAN where the
`digital carrier signal is formatted into a standard telecom-
`munication protocol, multiplexed onto the digital network,
`and sent over the digital network to the base station hotel. At
`the base station hotel, the digital hub is used to extract the
`data from the telecom network, and convert the digitized RF
`carrier signals from the network data format back into their
`native analog RF format. Finally, the RF analog signals are
`provided to the appropriate base stations for processing. In
`most instances, the same telecommunication protocol will
`be used in both the downlink and uplink directions. There
`may be situations, however, (especially with asymmetric
`services and applications) where different protocols can be
`used in each direction.
`The techniques of the invention are independent of the
`specific wireless protocol (W-CDMA, CDMA-2000, GSM,
`TEEE802.11x, Bluetooth, etc.) and the protocol used over the
`telecommunications network. Preferably, the technique also
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`US 6,785,558 B1
`
`5
`provides signaling between the digital hub and the NAN
`such that control, operational, administrative and mainte-
`nance information may be exchanged between the base
`station hotel and the remote site. This signaling can also be
`used to transport other services such as data for the support
`and application of location-based services.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`is a block diagram illustrating a first communica-
`FIG. 1
`tion system network architecture according to the prior art.
`FIG. 2 is
`a block diagram illustrating a second commu-
`nication system network architecture according to the prior
`art.
`a block diagram illustrating a communication
`is
`FIG. 3
`system network architecture according to
`a preferred
`embodiment of the present invention.
`FIG. 4 is a diagram illustrating the technique of wideband
`digitizing according to the prior art.
`FIG. 5 is a diagram illustrating the technique of narrow-
`band digitizing according to a preferred embodiment of the
`present invention.
`a point-to-
`FIG.
`6
`is
`a block diagram illustrating
`multipoint network architecture for a communication system
`according to a preferred embodiment of the invention.
`FIG. 7
`is
`a block diagram illustrating a ring network
`architecture for a communication system according to
`a
`preferred embodiment of the invention.
`FIG. 8
`is
`a block diagram illustrating a daisy chain
`architecture for a communication system according to
`a
`preferred embodiment of the invention.
`FIG. 9
`is
`a diagram illustrating a digital data frame
`structure used in
`a preferred embodiment of the present
`invention.
`a diagram illustrating a digital data header
`FIG. 10 is
`structure used in
`a preferred embodiment of the present
`invention.
`a diagram illustrating a data interleaving
`is
`FIG. 11
`technique used in a preferred embodiment of the present
`invention.
`
`FIG. 12 is a functional block diagram illustrating the main
`components of
`a digital hub according to
`a preferred
`embodiment of the present invention.
`
`FIG. 13 is a functional block diagram illustrating the main
`components of an RF/digital transceiver according to
`a
`preferred embodiment of the present invention.
`FIG. 14 is a functional block diagram illustrating the main
`components of
`a
`digital hub according to
`an alternate
`embodiment of the present invention.
`FIG. 15 is a functional block diagram illustrating the main
`components of a remote site network interface unit accord-
`ing to a preferred embodiment of the present invention.
`FIG. 16 is a functional block diagram illustrating the main
`components of a remote site antenna/radio unit according to
`a preferred embodiment of the present invention.
`FIG. 17 is a functional block diagram illustrating the main
`components of
`a remote site antenna/radio unit having
`downlink diversity according to an preferred embodiment of
`the present invention.
`
`35
`
`50
`
`FIG. 18 is a functional block diagram illustrating the main
`components of
`a remote site antenna/radio unit having
`uplink diversity according to a preferred embodiment of the
`present invention.
`
`65
`
`FIG. 19 is a functional block diagram illustrating the main
`components of a remote site antenna/radio unit having both
`
`6
`uplink and downlink diversity according to
`embodiment of the present invention.
`
`a preferred
`
`DETAILED DESCRIPTION
`
`Preferred embodiments of the invention will now be
`described in detail with reference to the drawing figures.
`Those skilled in the art will appreciate that the following
`description of the preferred embodiments contains many
`specifics for the purpose of illustration only, and that the
`principles of the invention are not necessarily limited by
`these details.
`In the present description, the term “carrier signal” is used
`to mean a spectrum bandwidth that is modulated by some
`standard modulation technique to carry an information sig-
`nal. For example, one type of carrier signal is a narrow band
`frequency carrier containing one AMPS subscriber channel
`or afew TDMA subscriber channels. Another type of carrier
`signal is
`a wideband CDMA signal containing many code-
`modulated subscriber channels. The term “channel” is used
`in the broad sense as including not only frequency channels
`as
`in FDMA, but also code channels such as
`a CDMA
`channel, time/frequency channels such as in TDMA, and
`generally any type of information channel derived by divid-
`ing the wireless spectrum using a multiplexing technique
`involving frequency, time, code, space, etc. In this general
`use of the term, each channel typically corresponds one-to-
`one with a subscriber information signal that is allocated to
`the channel.
`A block diagram of a wireless communication system
`implementing the techniques of a preferred embodiment of
`the present invention is shown in FIG. 3. A series of base
`stations (BTS) reside in a BTS hotel 300. The base stations
`are connected to
`a digital hub 310 that also resides in the
`BTS hotel. The digital hub 310 is connected via a digital
`network 320 to one or more remote sites 330. Each remote
`site has a network access node (NAN) 340 and several
`remote antenna units 350 connected to the NAN 340 by
`digital communication links 360. Downlink cellular signals
`from a base station are digitized at the digital hub 310 and
`sent as standard formatted data over the digital network 320
`to the NANs 340. The NANs remove the network formatting
`and send the digital signals to the antenna units 350 where
`they are converted back to RF analog signals which are then
`transmitted to wireless subscribers. In the uplink direction,
`the antenna units 350 receive RF transmissions from the
`subscribers. These analog RF signals get digitized then sent
`to the NAN 340 where they are formatted and sent over the
`optical fiber to the digital hub 310. The digital hub converts
`the uplink data back to analog RF signals which then get
`passed on to the appropriate base stations (BTS).
`RF/Digital Conversion
`The technique of
`the invention employs narrowband
`digitizing rather than wideband digitizing when digitizing
`cellular RF signals. In other words, each cellular carrier
`signal is separately converted from analog to digital format
`(and vice versa). Wideband digitizing and narrowband digi-
`tizing are illustrated in FIGS. 4 and 5, respectively. As
`illustrated in these figures, an RF wideband signal 400 may
`contain several distinct narrowband carriers 410 (e.g.,
`CDMA carriers, each having multiple code-multiplexed
`channels). FIG. 4 illustrates the method employed by the
`prior art, where a w