Base Transceiver Station for W-CDMA
`System
`
`vSatoshi Maruyama vKatsuhiko Tanahashi vTakehiko Higuchi
`(Manuscript received August 8, 2002)
`
`In January 2001, Fujitsu started commercial delivery of a W-CDMA base transceiver
`station (BTS). We then dramatically increased the number of traffic channels in this
`BTS and reduced its power consumption. Then, in September 2002, we began mass
`production and delivery of the new, large-capacity BTS. This equipment conforms to
`the global standard specifications of the 3GPP (3rd Generation Partnership Project)
`and was developed using all of Fujitsu’s expertise, for example, expertise in radio
`technology, network technology, and electronic device technology.
`This paper gives an overview of this large-capacity BTS and introduces its features.
`
`1.
`
`Introduction
`Fujitsu is aggressively pursuing the develop-
`ment of a W-CDMA system that conforms to the
`third-generation mobile communications system
`(IMT-2000). While conventional mobile phone sys-
`tems center on voice services, W-CDMA systems
`will center on multimedia services. In order to pro-
`vide multimedia services, the base transceiver
`station (BTS) must realize advanced functionality
`and high-performance, including the simultaneous
`transmission of voice and a variety of high-speed
`data services as well as high-quality transmission
`on the same level as fixed telephone networks.
`Multimedia services require much more bandwidth
`than voice services, so BTSs must have greater
`capacities to keep up with the increase in demand.
`In addition, it is necessary to have flexible expand-
`ability to support different equipment environ-
`ments, reduce the installation size and power
`consumption, and provide the flexibility to adapt
`to changes in service contents.
`In 1997, Fujitsu supplied a BTS as test equip-
`ment for an NTT DoCoMo W-CDMA system,1) and
`in January 2001 we started mass production and
`
`FUJITSU Sci. Tech. J., 38,2,p.167-173(December 2002)
`
`shipment of this BTS for commercial use. Then,
`by using our proprietary, high-efficiency transmit-
`ter amplification technology and high-speed
`baseband signal processing technology, we devel-
`oped a new, high-capacity BTS. Compared to the
`equipment currently in use, our new BTS provides
`four times as much channel capacity with the
`same power consumption and size. Mass produc-
`tion and shipment of the new BTS was started in
`September 2002.
`
`2. About the W-CDMA system
`IMT-2000 is designed to support not only
`voice services, but also all manner of multimedia
`services, including fax, e-mail, high-speed data ex-
`change, high-definition image transmission,
`motion picture transmission, and Internet servic-
`es. Implementing such services requires that the
`BTSs can simultaneously transmit voice and a
`variety of high-speed data services as well as pro-
`vide high-quality transmission. Figure 1 shows
`the network configuration of W-CDMA.
`W-CDMA is a code division multiple access
`(CDMA) communication system that spreads data
`
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`

`

`CC
`
`BB (basic)
`
`Amplifier
`
`To antenna
`
`⎫⎪⎪⎬⎪⎪⎭
`
`
`
`
`
`TX-AMPTX-AMPTX-AMP
`
`
`
`
`
`SPREADSPREADSPREAD
`
`BBBB
`BB
`
`RXRXRX
`
`BB (expansion)
`
`
`Call cont.Call cont.
`Link cont.
`Link cont.
`OAM cont.
`OAM cont.
`CLK cont.,
`CLK cont.,
`etc.
`etc.
`
`
`
`
`
`SPREADSPREADSPREAD
`
`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
`
`BTSBTSBTS
`
`Um
`
`UE
`
`lub
`
`lu
`
`BTSBTSBTS
`
`RNCRNCRNC
`
`Core network
`(CN)
`
`To RNC
`
`BTSBTSBTS
`
`Figure 1
`W-CDMA network configuration.
`
`BBBB
`BB
`
`RXRXRX
`
`Figure 3
`System configuration of large-capacity BTS.
`
`Table 1
`Main specifications of large-capacity BTS.
`
`Specification
`Item
`Radio frequency band Uplink: 1940 to 1960 MHz
`Downlink: 2130 to 2150 MHz
`5 MHz
`4 carriers max.
`DS-CDMA/FDD
`6 sectors max.
`80 W/sector
`2880 voice channels or equivalent
`Voice: AMR, data: 384 kb/s max.
`6.3 Mb/s or 1.5 Mb/s
`
`Carrier separation
`Number of carriers
`Access system
`Number of sectors
`Max. RF output power
`Channel capacity
`Transmission rate
`Transmission line
`interface
`Equipment dimensions 800 × 600 × 1800 mm
`(W × D × H)
`
`Figure 2
`Large-capacity BTS.
`
`signals across a broad 5 MHz band. This system
`has various features not found in conventional
`mobile communications systems that allow it to
`provide multimedia services. These features are
`as follows:
`1)
`The bandwidth can vary from voice bandwidth
`to a maximum of 384 kb/s, and multiple mul-
`timedia services are transmitted together.
`Transmission quality is at the same level as
`in a fixed telephone network.
`3) When a mobile station moves into another
`
`2)
`
`base station zone, hitless handover is per-
`formed at zone switching without any
`interruption of communication.
`
`3. Technologies of the new BTS
`
`3.1 Main hardware
`3.1.1 Overview
`Figure 2 shows a photograph of the large-
`capacity BTS, Figure 3 shows the configuration,
`Table 1 shows the main specifications, and
`Figure 4 shows the shelf configuration.
`The large-capacity BTS consists of the fol-
`lowing parts.
`
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`

`

`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
`
`3.1.2 Features
`Our new, large-capacity BTS provides a large
`channel capacity in a compact size with less pow-
`er consumption and is designed for easy channel
`expansion and maintenance. Its main features
`are as follows:
`1) Compared to conventional models, it provides
`four times as much channel capacity with the
`same power consumption and physical size.
`Using our original high-efficiency transmit-
`ter amplifier technology and advanced
`baseband signal processing technology, we
`have achieved a capacity of 2880 voice chan-
`nels or their equivalent. Compared with
`conventional models, this is a four-fold in-
`crease in capacity, yet it has been achieved
`with no increase in power consumption or
`physical size.
` 2) The basic configuration accommodates 6 sec-
`tors, 2 carriers, and 1440 channels.
`In its basic configuration, which consists of
`the amplifier shelf and BB basic shelf, the new
`BTS can accommodate up to 6 sectors, 2 car-
`riers, and 1440 channels. More capacity can
`be added by using the BB expansion shelf.
` 3) The system can be expanded while active.
`The system can be operated without an ex-
`pansion shelf in low-traffic areas, and if traffic
`increases after system deployment, easy sys-
`tem expansion is possible by adding an
`expansion shelf while the system is running.
`
`3.2 Common control
`3.2.1 Overview
`The common control has functions for call
`processing control, radio link control, inter-sta-
`tion control, maintenance monitoring control, IP
`over ATM, remote file transfer, file memory, shared
`memory, shared bus control, transmission line
`switching, transmission line interface, reference
`clock timing generation, external interface, and
`debugging. There are also three types of trans-
`mission line interfaces that can be used according
`to the type of transmission line: 1.5 Mb/s electri-
`
`2880 ch
`
`⎫⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎬⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎭
`
`1440 ch
`
`⎫⎪⎪⎪⎪⎪⎪⎪⎪⎬⎪⎪⎪⎪⎪⎪⎪⎪⎭
`
`Expansion shelf
`
`Basic shelf
`
`Amplifier shelf
`
`Figure 4
`Shelf configuration of large-capacity BTS.
`
`1) Radio part (TX-AMP, RX)
`This part is connected to the antenna and
`features a transmission power amplifier and low-
`noise receiving amplifier for amplifying the sent/
`received RF signals. It performs D/A conversion
`of transmission signals spread on the baseband,
`thereby converting them to RF signals in quadra-
`ture modulation. It also performs quasi-coherent
`detection and A/D conversion of signals received
`from the receiving amplifier.
`2) Baseband signal processor (BB)
`This part performs error correction coding,
`framing, data modulation, and spreading modu-
`lation of transmitted data. For the received signal,
`it performs despreading, chip synchronization, er-
`ror correction decoding, data demultiplexing,
`RAKE reception, and diversity handover between
`sectors.
`3) Common Control (CC)
`This part sends and receives control signals
`to and from the base station controller and con-
`trols, sets, and releases the radio links. It also
`performs ATM processing, ATM termination, and
`clock extraction from the transmission line at the
`transmission line interface between stations.
`
`FUJITSU Sci. Tech. J., 38,2,(December 2002)
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`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
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`cal, 6.3 Mb/s electrical, or ATM Megalink optical.
`
`3.2.2 Features
`1) Mounting
`The common control is mounted on the right
`half of the MDE (Modulation and Demodulation
`Equipment) shelf.
`We integrated the common control into six
`packages by rearranging the various functional sec-
`tions that used to be individual packages (i.e., the
`shared memory, file memory, external interface,
`shared bus control, and inter-station control), there-
`by achieving a high-density mounting that occupies
`only 60% of the space of the previous model.
`2)
`Improved call processing performance
`In addition to achieving a more than four-fold
`increase in performance, we also did the following:
`(cid:129)
`Speeded up the CPU
`(cid:129)
`Speeded up the shared bus
`(cid:129)
`Added a variety of dedicated buses, and dis-
`tributed the load by optimization
`Increased the ATM-SW capacity
`
`(cid:129)
`
`3) Maintenance/operation
`The shared bus and various dedicated bus
`lines within the equipment can be monitored and
`traced by connecting a special debugging termi-
`nal. In addition, the ATM signals corresponding
`to the U-Plane and the C-Plane signals of the phys-
`ical line can be monitored by connecting
`measuring instruments to the transmission line.
`The remotely controlled file transfer function
`distributes the load of file operations during down-
`loads to decrease the load on the maintenance
`monitoring control function. In addition, hard-
`ware data can also be downloaded to allow flexible
`version upgrades.
`
`3.3 Baseband signal processor (BB)
`3.3.1 Overview
`This function generates frames and performs
`error correction coding and spreading modulation
`for transmission data. It also performs despread-
`ing, path searches, RAKE reception, error
`correction decoding, and receive data demultiplex-
`
`SPREAD card
`
`High-speed IF
`
`Ant#0
`
`[Spread processing]
`
`Ant#1
`
`Code generation
`Power control
`Phase rotation control
`Amplitude control
`
`High-speed IF
`
`Ant#0
`
`Ant#1
`
`To
`TX-AMP#0
`
`To
`TX-AMP#1
`
`BB card
`
`Channel decoding/Coding
`
`ATM-IF
`
`Payload separation
`CRC calculation
`
`UTOPIA
`
`From
`BBCOM
`
`2nd Interleaving
`Service multiplexing/
`Demultiplexing
`Rate matching
`1st Interleaving
`Channel coding
`
`Despreading/Path
`detection
`
`High-speed IF
`
`From
`RX
`
`Figure 5
`Functional block diagram of baseband signal processing section.
`
`Cell generation
`CRC calculation
`
`UTOPIA
`
`To
`BBCOM
`
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`

`

`ing of the receive signal (Figure 5).
`
`3.3.2 Features
`1) Highly flexible and highly integrated.
`To optimize the implementation of functions,
`we promote a shift to firmware so we can sup-
`port
`future enhancements
`to 3GPP
`specifications and we employ large 14 Mgate
`CE81-series ASICs in sections that perform
`large amounts of parallel processing
`(Figure 6).
`The firmware is constructed using advanced-
`function, high-performance DSPs (3600
`MIPS).
`These features enable 64 AMR (Adaptive
`Multi-Rate) channels to be processed per BB
`card.
`2) Offers improved data processing (e.g., pack-
`et transmission) performance.
`Each BB card can process 64 voice channels,
`and processing performance is further im-
`proved when voice is mixed with data (e.g.,
`packet data transmission and unrestricted
`digital data transmission).
`The new BTS can process four 384 kb/s pack-
`et DL channels and 32 AMR channels. (This
`is equivalent to processing 96 voice channels.)
`3) A dedicated spreading card (SPREAD) is used
`to optimize the functional partitioning so that
`the spreading section
`is
`independent
`(Figure 7).
`
`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
`
`4) Employs a common hardware card (BB card)
`that enables dedicated channel or common
`channel processing.
`The common CH (PRACH) card and dedicat-
`ed CH (DTCH) card can be switched by
`software. The PRACH card supports a cell
`radius of up to 50 km (Figure 8).
`
`3.4 Radio part
`3.4.1 Overview
`The radio part is composed of a modulator/
`demodulator and a transmission amplifier. It pro-
`vides up to 4 carriers per sector with a maximum
`RF output of 80 W/sector.
`
`Figure 7
`SPREAD card.
`
`Figure 6
`14 Mgate CE81 series ASIC.
`
`Figure 8
`BB card.
`
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`

`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
`
`Conventional
`method
`
`2 carriers, 6 sectors,
`720 channels
`
`4 carriers, 6 sectors,
`2880 channels
`AMP power
`consumption
`decreased by 40%
`
`High-efficiency
`AMP with digital
`predistorter
`
`AMP
`
`MDE
`
`AMP
`
`MDE
`
`System power consumption
`
`Current system
`
`New large-capacity BTS
`
`Figure 10
`Dramatic reduction in power consumption.
`
`4. Conclusion
`This paper gave an overview of our new, high-
`capacity, low power consumption W-CDMA base
`transceiver station. The system’s power consump-
`tion was reduced by using a high-efficiency
`transmitter amplifier that uses digital predistor-
`tion technology. Also, the system’s high-capacity
`was achieved by using an optimum configuration
`of DSPs and ASICs.
`Fujitsu is proceeding with the development
`of compact base stations and other equipment that
`will further accelerate high-speed data communi-
`cation services and enable fine-tuned area
`expansion.
`
`Reference
`1)
`S. Maruyama, T. Yabe, and K. Mori: Base
`Transceiver Station for W-CDMA. (in
`Japanese), FUJITSU, 51, 1, p.41-44 (2000).
`
`Figure 9
`High-efficiency TX-AMP (with digital predistorter).
`
`3.4.2 Features
`1)
`The radio part features a high-efficiency
`transmitter amplifier (TX-AMP) that per-
`forms digital predistortion (Figure 9).
`By introducing this new TX-AMP, we have
`been able to reduce the power consumption
`of the transmitting RF amplifier by as much
`as 40% compared with conventional equip-
`ment (Figure 10).
`The radio part can be flexibly configured ac-
`cording to the number of sectors.
`Each TX-AMP can be independently config-
`ured, enabling the optimum number of cards
`to be mounted for the installation environ-
`ment.
`
`2)
`
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`

`S. Maruyama et al.: Base Transceiver Station for W-CDMA System
`
`Takehiko Higuchi received the B.S.
`degree in Electronics Engineering from
`Fukuoka University, Fukuoka, Japan in
`1985. He joined Fujitsu Limited, Japan
`in 1985, where he has been engaged
`in development of radio communication
`systems.
`
`E-mail: higuchi@mhd.ts.fujitsu.co.jp
`
`Satoshi Maruyama received the B.S.
`and M.S. degrees in Electronics Engi-
`neering from Nagoya Institute of Tech-
`nology, Nagoya, Japan in 1983 and
`1985, respectively. He joined Fujitsu
`Limited, Japan in 1985, where he has
`been engaged in development of radio
`communication systems. He is a mem-
`ber of the Institute of Electronics, Infor-
`mation and Communication Engineers
`(IEICE) of Japan.
`
`E-mail: smaruyama@jp.fujitsu.com
`
`Katsuhiko Tanahashi received the B.S.
`degree in Electronics Engineering from
`Nagoya University, Nagoya, Japan in
`1982. He joined Fujitsu Limited, Japan
`in 1982, where he has been engaged
`in development of radio communication
`systems.
`
`E-mail: tanahasi@wls.ts.fujitsu.co.jp
`
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