Ericsson Baseband Pooling

Advanced baseband technology in third-generation radio base stations Zhongping Zhang, Franz Heiser, Jürgen Lerzer and Helmut Leuschner

WCDMA, one of the technologies selected for the air interface of the 3GPP standard, is widely used in emerging third-generation mobile communication systems. This interface supports data rates of up to 2 Mbit/s on a common 5 MHz frequency carrier. Moreover, with the introduction of HSDPA, the peak service rate for packet access in the downlink can be increased to more than 10 Mbit/s. Ericsson’s radio base station has been designed to comply with the 3GPP standard. The kernel part of WCDMA technology has been implemented in the baseband of the radio base station. Compared to previous generations, the baseband signals in WCDMA are spread with a high chip-rate code at 3.84 megachips per second on a 5 MHz frequency band. This is much wider than the frequency band used in GSM, cdmaOne and CDMA2000, or PDC. Therefore, to process the signals, more advanced technology is deployed in WCDMA baseband. Ericsson’s baseband technology uses the very latest ASIC, DSP, and FPGA technologies. Numerous requirements are being channeled toward the baseband platform, both to support a technical implementation of WCDMA and to satisfy operator and radio network management points of view. Being the kernel in WCDMA, the baseband platform must be able to efficiently handle the entire life cycle of an RBS, from initial deployment, with a lowcost, low-content focus, to subsequent scaling for newly developed services and traffic growth. Moreover, it must do so while networks are evolving and expanding with more users and new mixes of end-user services. New radio network functions and features will also be added through base station hardware and software to perfect the WCDMA system. The authors describe the implementation of Ericsson’s WCDMA baseband. They also show how it has been prepared to grow with and meet the needs of future developments by facilitating small, incremental upgrades and thanks to a flexible architecture that supports the expansion of the uplink and downlink together with critical functionality that resides in loadable hardware.

Figure 1 Indoor RBS and baseband subrack.

Architecture of the radio base station The functionality of a radio base station (RBS) is divided into two main parts: userplane functions and control-plane functions. The user-plane functions are associated with transport, baseband, radio and the antenna. The control-plane functions pertain to the transmission of user data and operation and maintenance (O&M) data. Ericsson’s RBS is based on the connectivity packet platform (CPP, formerly called Cello packet platform)—that is, the RBS employs the infrastructure of hardware and software modules provided in CPP.1 Figure 1 shows a typical indoor RBS with power subrack, baseband subrack, radio frequency subrack and power amplifier subrack.2 User-plane signals from the radio network controller (RNC) via the Iub interface are input directly via CPP boards to the baseband parts, whereas control-plane signals are input to the baseband parts via the traffic and O&M control parts of the main processor. Figure 2 shows the architecture of the Ericsson RBS3000.3 Please note that for simplicity’s sake the CPP parts and main processor are not shown. The architecture can be broken down into a cell-specific part and a non-cell-specific part. The cell-specific part contains transceiver (TRX) boards, multicarrier power amplifier (MCPA) boards and antenna interface unit (AIU) boards, whereas the common part contains boards for baseband processing. In Figure 2, the baseband processing has been split between the transmitter (TX) and random access and receiver (RAX) boards. The TX board handles downlink processing and enables coding, spreading and modulation. The RAX board handles uplink processing and enables demodulation, de-spreading and decoding.

Baseband functions The physical layer functions on the baseband boards have been implemented to include • the mapping and de-mapping of physical channels and transport channels; • multiplexing and demultiplexing; • channel coding and decoding; • spreading and de-spreading; • modulation and demodulation; • physical layer procedures; and • physical layer measurements. In addition, the baseband boards in a radio base station perform the following functions: 32

Ericsson Review No. 1, 2003

• • • •

radio base station configuration; cell control; the distribution of system information; radio link configuration for dedicated and common channels; • Iub data-stream handling; and • node synchronization and distribution. The baseband functions in the radio base station thus provide a platform for radio network functions, configuration functions, and O&M functions. Accordingly, the baseband constitutes a platform of resources for handling common and dedicated channels for higher layers. Figure 3 gives an overview of standard channel mapping between logical channels, transport channels and physical channels.4,5 The upper part pertains to the downlink channels and the lower part (shown in dark blue) pertains to the uplink channels. The Third-generation Partnership Project6 (3GPP) has defined the • synchronization procedures for cells, common channels and dedicated channels; • random-access procedures; and • inner- and outer-loop power control procedures. To improve the performance of the radio link connection, the 3GPP has recommended possible enhancements, such as open-loop and closed-loop transmit diversity. After the baseband boards have been configured properly with respect to the interfaces to other subsystems, they can be put into traffic operation. If the traffic load on the baseband is light, all or part of the board can be put into power save mode to reduce power consumption. By contrast, supervision and protection mechanisms reduce the risk of dropped calls when the traffic load on the baseband boards is too heavy.

Transciever board

Interface between downlink and uplink baseband processing

Multicarrier power amplifier and antenna interface unit board

TX board Cell Baseband From RNC (user plane)

MCPA and AIUB

TRXB

TXB

Cell

To RNC (user plane)

MCPA and AIUB

TRXB RAXB Cell

TRXB Random access and RX board

MCPA and AIUB

Baseband bus

Data and/or “fast” control

Figure 2 Baseband in RBS and interfaces.

Figure 3 Channel-mapping model. Area marked in red is for HSDPA. RNC

RBS

RNC control

RBS/RNC control link

Logical channel

RBS control BCCH

Transport channel

Physical channel SCH

BCH

P-CCPCH CPICH

Baseband design aspects Ericsson’s baseband has been designed to comply with 3GPP standards for WCDMA. In addition, the baseband architecture has been designed to meet requirements for operating radio base stations. These include configuration flexibility, effective use of resources, easy roll-out, compatibility and future-proof hardware. By introducing the very latest in digital signal processor (DSP), field-programmable gate array (FPGA) and application-specific integrated circuit (ASIC) technologies, Ericsson has significantly increased the capacity for traffic and control signaling, measured in terms of channel elements for the dedicated physical Ericsson Review No. 1, 2003

Logical channel

PICH

lub data stream

PCH

S-CCPCH

DCCH CCCH DTCH

FACH

S-CCPCH

DTCH DCCH

DCH

DPDCH DPCCH

PCCH

AICH MAC-hs

DCCH CCCH DTCH DTCH DCCH

Downlink channels

HS-SCCH HS-DSCH

HS-PDSCH

RACH

HS-PDCCH PRACH

DCH

DPDCH/ DPCCH

Uplink channels

33

channels. A channel element is defined as the equivalent baseband resource (hardware and software) needed to transmit a voice channel at 30 kbit/s. Configuration flexibility and efficient use of resources

Operators want a radio base station that can be adapted to handle different site and radio configurations. Ericsson’s baseband implementation gives operators this flexibility, allowing them to change radio configurations without having to physically visit the site. Flexible interfaces have been provided between the subsystems of the radio base station, and the baseband parts have been designed in a modular fashion. Each baseband unit provides a certain amount of traffic capacity for dedicated and common transport channels. This modular design enables op-

erators to configure the radio base station for various traffic scenarios and load. Baseband board types—TX board and RAX board

Obviously, the use of separate baseband downlink and uplink modules makes it easier to upgrade the system and to better adapt it to the asymmetric traffic associated with third-generation services. Ericsson’s RBS3000 has two baseband board types: the TX board handles downlink traffic, and the RAX board handles uplink traffic. Traffic over the air interface is expected to be asymmetrical—that is, there will be more traffic in the downlink than in the uplink. By adding separate TX and RAX boards, operators can increase capacity in small or large increments either symmetrically or asymmetrically.

BOX A, TERMS AND ABBREVIATIONS

3GPP

Third-generation Partnership Project AICH Acquisition indication channel AIU Antenna interface unit ASIC Application-specific integrated circuit BCCH Broadcast control channel BCH Broadcast channel BP Board processor CCCH Common control channel CCH Common channel CCTrCH Coded composite transport channel CDMA Code-division multiple access CPICH Common pilot channel CPP Connectivity packet platform CRC Cyclic redundancy check DCCH Dedicated control channel DCH Dedicated channel DL-TPC Downlink TPC DP Data processing DPCCH Dedicated physical control channel DPCH Dedicated physical channel DPDCH Dedicated physical data channel DSCH Downlink shared channel DSP Digital signal processor DTCH Dedicated traffic channel DTX Discontinuous transmission FACH Forward access channel FP Frame protocol FPGA Field-programmable gate array GPRS General packet radio service GSM Global system for mobile communication HS-DPCCH High-speed dedicated physical control channel

34

HS-PDSCH High-speed physical downlink shared channel HSDPA High-speed downlink packetdata access HS-SCCH High-speed shared control channel MCPA Multicarrier power amplifier MUX Multiplexing unit O&M Operation and maintenance PCCH Paging control channel P-CCPCH Primary common control physical channel PCH Paging channel P-CPICH Primary CPICH PDC Personal digital cellular PICH Paging indicator channel PRACH Physical random access channel RACH Random access channel RAKE Name of WCDMA receiver RAX Random access and receiver RBS Radio base station RF Radio frequency RNC Radio network controller S-CCPCH Secondary common control physical channel SCH Synchronization channel SIR Signal-to-interference ratio TFCI Transport format combination indicator TPC Transmission power control TrCH Transport channel TRX Transceiver TX Transmitter UE User equipment UL-TPC Uplink TPC WCDMA Wideband CDMA

Ericsson Review No. 1, 2003

Modularity of the baseband

Traffic load and distribution vary over time in different sectors and frequencies. The Ericsson baseband architecture employs pooling to optimize the use of available resources. This approach also guarantees that configurations can be flexible. Figure 4 shows the advantages of modularity and pooled resources in two different radio configurations. Some operators require redundancy in the radio base station. The modular baseband design easily restricts the loss of traffic due to, say, a faulty component or unit in baseband processing.

Baseband resources

Baseband resources

Frequency 1

Frequency 1

Change in traffic

Easy roll-out of third-generation infrastructure

Established GSM and GSM/GPRS operators can more easily roll out third-generation infrastructure by reusing site locations and infrastructure. Most operators starting out in the third-generation business want lowcost, low-capacity RBSs. Later, when the number of subscribers has increased and more advanced services are to be introduced, they will need RBSs that can handle greater traffic capacity in individual cells. The baseband boards have been designed with scalability in mind—greater capacity can be had by adding hardware units (TX boards and RAX boards). Another way of increasing traffic capacity is to deliver and install prepared hardware on site. As operator needs grow, more capacity can be activated successively by means of software functions. This approach advocates the use of simple, standard hardware configurations. A further advantage of baseband scalability is that the RBS can be equipped with as many baseband units as needed to satisfy traffic, site conditions, and air-interface capacity for a given frequency band. This helps operators to avoid wasting unnecessary resources. Future-proof and compatible

As mentioned above, most operators just starting out in the third-generation business want low-cost, low-content RBSs. Later, however, apart from increasing capacity in the RBS, they will also need more functionality and more advanced features. In designing the baseband, Ericsson has carefully considered various evolution scenarios, making allowances for customer-specific requirements for functions, services, capacity, redundancy, and site conditions. Ericsson Review No. 1, 2003

Frequency 2

Frequency 2

Number of users in a cell

Figure 4 Baseband modularity and pooled resources.

In general, the functions in the physical layer have been implemented in hardware (ASIC) or close to hardware (DSP); the control functions have been implemented in software on DSPs and board processors. To avoid the logistical problems and costs associated with frequent on-site updates or upgrades, Ericsson has prepared the hardware for future functions—these can become available via remote software and firmware updates. Ericsson calls this feature forward hardware compatibility. On the other hand, new baseband boards must work in environments that use old baseband boards. This is called backward hardware compatibility. Ericsson’s baseband hardware and software are forward hardware and backward hardware compatible. Future-proofness—in terms of additional radio configurations, services, functions, and greater capacity—is an importance aspect of Ericsson’s baseband design. Figure 5 illustrates the forward hardware compatibility concept. Function Z has been provided in hardware. A remote software upgrade can thus activate the entire func-

Figure 5 Forward hardware compatibility.

Function A Function B Function C Function D Function Z (fo rward hardware Software Hardware

prep.)

Remote software upgrade

Function A Function B Function C Function D Function Z (forward ha rdware prep .)

35

Software Hardware

BB unit A

Hardware addition

BB unit B

BB unit A

BB unit B

BB unit C (new)

Figure 6 Backward hardware compatibility.

tion. Figure 6 shows the backward hardware compatibility concept. The baseband unit, C, is added to the existing RBS to improve functionality and capacity.

Downlink processing board—TX board Downlink processing functions

Figure 7 shows the main function blocks for processing the downlink. Each of these blocks also contains other baseband functions (not pictured). The first process is frame protocol (FP) handling (pictured left). After confirming when the data frames on the common channels (paging channel, PCH, and forward access channel, FACH) and the dedicated channels (DCH) arrived from the Iub interface, the frame protocol handler aligns the frames and extracts the payload part of the data frame. The payload part contains the data of the uncoded transport channels. For the dedicated channels, the encoding function block • generates the cyclic redundancy check (CRC); • concatenates the transport blocks; • segments the coding blocks; • performs convolutional coding or turbo coding; 36

• inserts the first discontinuous transmission (DTX); • matches rates; and • performs the first interleaving. To fit the 10 ms radio frame, the transport blocks from different transport channels are multiplexed in the multiplexing unit (MUX) function block. This activity is followed by insertion of the second DTX, the second interleaving, and multicode splitting. Data and control information are then sent to the cell-split function block. The control information contains transport format combination indicator (TFCI) bits and corresponding transmission power control (TPC) commands which have been mapped with pilot bits onto the dedicated physical control channel (DPCCH). After the frame protocols have been handled, the broadcast channel (BCH, which is mapped to the primary common control physical channel, P-CCPCH, and to PCH and FACH) and PCH and FACH (which are mapped to the secondary common control physical dedicated channel, S-CCPCH) are processed in a manner similar to that described for the dedicated channels. The cellsplit function identifies the common and dedicated physical channels that belong to one cell carrier. These processes are followed by modulation, spreading and weighting, Ericsson Review No. 1, 2003

lub l/f

l/f to TRX BCH encoding

PCH FP

PCH encoding

FACH FP

FACH encoding

DCH FP

DCH encoding

Modulation spreading

MUX

Cell split

Figure 7 Downlink processing function blocks.

DL/UL l/f

with power information for the downlink power control, and scrambling. TX board implementation

Figure 8 shows the downlink processing board (TX board), which is divided into two main parts: the board processor and boardspecific hardware. The board processor controls the board and parts of the traffic. The board-specific hardware, which processes user data sent to the air interface, contains the Iub user-plane interface handler, symbol-rate processor, chip-rate processor, and the physical layer processing controller. The Iub user-plane interface handler handles the Iub interface user-plane protocol for the DCH and CCH data streams to the radio network controller. The symbol-rate processor handles the transport channel (TrCH), the coded composite transport channel (CCTrCH), the physical channel for the primary and secondary common control physical channels, the paging indicator channel (PICH), and the dedicated physical channel (DPCH). The chip-rate processor handles the distribution of physical channels, generates the synchronization channel (SCH), the primary common pilot channel (P-CPICH) and acquisition indicator channel (AICH), and transmits the distributed output sequences Ericsson Review No. 1, 2003

to the TRX. It also measures the transmitted code power and handles all cell-carrier processing-related functionality. The physical layer processing controller handles the configuration of the symbol-

Figure 8 TX board implementation.

37

Figure 9 TX board of the RBS3000 series.

and chip-rate processing parts with respect to the control of measurements, set-up, release, and reconfiguration of cell-carriers and channels. The functionality of the Iub user-plane interface handler and the physical layer processing controller is implemented in DSPs to give flexible implementation of • the controller functions; • external interfaces to the RNC for the user data interface; and • interfaces to the board processor for the control interface. The symbol-rate processing functionality is implemented in FPGAs due to processing delay and varying requirements put on the throughput of user data. Some flexibility is also provided in view of changing requirements for the implemented functionality. The chip-rate processing functionality is implemented in ASICs. This approach employs parallel processing to meet the demand for limited processing delay. It also allows synchronous transmission of the distributed output sequence to the TRX. Figure 9 shows a TX board used in an RBS3000. The board can handle multiple cell-carriers with more than one antenna branch. Interface between the TX and RAX boards

The interface between the TX and RAX boards supports fast signaling for controlling 38

call set-up and power. When the user equipment (UE) sets up a call to the RBS, the corresponding RAX board in the RBS reserves sufficient resources. The RAX board then sends a layer-1 acknowledgement signal via the TX board to the UE, indicating that the UE may send the RACH message part. To control power in the downlink, the RAX board detects the TPC commands and sends them to the TX board, which adjusts downlink transmission power. To control power in the uplink, the RAX board compares the signal-to-interference ratio (SIR) target with the SIR of the received signals and generates the TPC commands, which it sends to the UE in the downlink DPCCH.

Uplink processing board—RAX board Uplink processing functions

In the uplink, the signals received from the air interface are input to the baseband in a digital signal format from the TRX radio part of the RBS (Figure 10). For the dedicated physical channel (DPCH), the incoming signals from the TRX are processed in the demodulator function block, which contains a searcher and RAKE receiver. The demodulator • performs de-spreading; Ericsson Review No. 1, 2003

DL/UL l/f lub l/f

l/f to TRX

RACH FP

DCH FP

RACH demodulator

RACH decoder

DCH decoder

RAKE

DMUX

Preamble detection

Searcher

Cell combiner

DCH demodulator RAKE

Searcher

Figure 10 Uplink processing function blocks.

• recovers the uplink control channel data and DPDCH data; • generates uplink TPC (UL-TPC) commands; • detects downlink TPC (DL-TPC) commands; and • decodes and de-maps the TFCI. Searcher

In multipath propagation environments, the RAKE receiver must know when the multipath rays arrive—that is, it must determine the position of the multipath rays along the delay axis, so that it can allocate the RAKE fingers to positions where the multipath components hit with signal power. The task of the searcher in the baseband is to synchronize the RAKE fingers. To speed up the searching process, a narrow searcher window is placed where the multipath rays are expected. However, in some cases, such as soft-handover set-up, the propagation delay is unknown; therefore, a wide searcher window is needed that corresponds to the entire cell range. The searcher also estimates the profiles of radio channel delay and sends them to the RAKE receiver. RAKE receiver

The RAKE receiver separates the multipath components and combines them coherently into a large signal vector that provides good demodulation conditions. This increases the Ericsson Review No. 1, 2003

probability of making correct decisions and improves receiver performance. Given the proper spreading code, the RAKE receiver can de-spread all detected multipath rays. Using the pilot bits to estimate channel amplitude, phase, frequency offset and Doppler spread, the RAKE receiver processes the multipath rays with the corresponding weighting, and combines the rays. Before combining the rays, however, each ray is processed by one RAKE finger. To make efficient use of the hardware resources, the RAKE fingers can be treated as a pool of hardware resources. They can also be flexibly allocated between users on the same RAX. This allocation is made according to the position information delivered by the searcher. Fewer RAKE fingers are needed in rural settings with a line-of-sight connection between UEs and the radio base station than in urban settings with multipath fading. During softer handover, which is the handover between cells in the same RBS and on the same carrier, the detected signals are combined. The DPCH signals are demultiplexed and de-mapped to the DCH of the transport channel for the next step of processing in the decoder. The decoder input signal consists of interleaved soft bits from the demodulator. The following tasks are performed in the decoder block: 39

BP

CCH symbol-rate processing ASIC

DSP/FPGA

DCH symbol-rate processing ASIC

DSP/FPGA

L1 acknowledge to TXB

CCH chip-rate processing ASIC

DCH chip-rate processing ASIC

Iub control frames from TXB

Iub user plane to RNC

DSP/FPGA

DSP/FPGA

Synchronization, power control and feedback information to TXB

UU L1 data from TRX

Figure 11 RAX board implementation.

• the second de-interleaving; • desegmentation of the physical channel; • service demultiplexing; • rate matching; • radio frame de-segmentation; • the first de-interleaving; • convolutional and turbo decoding; and • error detection by the CRC. When the UE tries to contact a radio base station, the random-access receiver detects the preamble that contains the signature used for the RACH message part. When it has detected the preamble, it determines which signature the RACH message part is using, and whether sufficient baseband resources are available. If so, it sends a layer-1 Ack or Nack message to the UE via downlink processing and begins processing the RACH message part in a similar manner as described for the DCH. The frame protocol function for the DCH and RACH assembles frame protocol data, which consists of a header part and a payload part (user data). Frame protocol data frames are sent to the RNC via the Iub user plane. The RAX board recovers and restores the information originally transmitted from the incoming radio signal for random access and dedicated channels. The 3GPP has defined the requirements put on uplink reception 40

Reception sensitivity, performance.7 signal-to-interference performance, and the capacity of the physical channels determine the characteristics of the receiver. RAX board implementation

The uplink processing board (RAX board) is divided into two main parts: the board processor (BP), and board-specific userdata-processing (DP) hardware. The board processor controls the board and parts of the traffic. The DP hardware processes user data received from the air interface to the Iub interface. Figure 11 shows the blocks on a RAX board in the RBS3000. The DP part contains blocks for processing the CCH chip rate, DCH chip rate, CCH symbol rate, and DCH symbol rate. The CCH chip-rate processing block detects the preamble, generates the acquisition indicator, and detects and extracts the messages (DPDCH/DPCCH) for the physical random access channel (PRACH) from the data received on the air interface. The DCH chip-rate processing block detects and extracts the DPCH (DPDCH/DPCCH) from the data available on the air interface, including power control support. The CCH symbol-rate processing block processes the CCTrCH provided by the CCH chip-rate processing block into decoded TrCH, which is sent via the Iub frame protocol to the radio network controller. The DCH symbol-rate processing block processes the CCTrCH provided by the DCH chip-rate processing blocks into decoded TrCH, which is sent via the Iub frame protocol to the radio network controller. Algorithms and functionality for processing stable user data have been implemented in fixed hardware (ASIC) to yield high capacity. By contrast, algorithms for processing variable user data, such as channel estimation, are allocated in loadable hardware (DSP or FPGA). New functionality, due to enhancements to 3GPP standards, is also implemented in loadable hardware (DSP and FPGA). The block structure (Figure 11) and the mix of fixed and loadable hardware results in a future-proof architecture: • Reception sensitivity can be improved by upgrading the algorithms in loadable hardware and software. • The hardware has been prepared to support future 3GPP functions (future releases). This means that basic functionalEricsson Review No. 1, 2003

ity and extensions of the 3GPP physical layer can be upgraded. • The scalable nature of the DCH and CCH ensures that the capacity of each block can be increased using new ASIC, FPGA, and DSP technologies. • The block structure supports integration within as well as between processing blocks. This also leads to greater capacity. Ericsson’s use of modular building blocks enables operators to vary the implementation as needed. For example, a low-capacity DCH/CCH solution would make use of separate low-capacity DCH/CCH chiprate processing and combined symbol-rate processing, whereas a high-capacity DCH/CCH solution would make use of separate, scalable, high-capacity DCH chip- and symbol-rate processing and combined CCH chip- and symbol-rate processing. Figure 12 shows a RAX board used in the RBS3000. The board supports two-way diversity and can handle multiples of 16channel elements serving up to six cell carriers.

Future baseband enhancements High-speed downlink packet-data access

High-speed downlink packet-data access (HSDPA) can be introduced in the downlink for best-effort services. This enhancement can increase the bit rate to more than 10 Mbit/s in the existing frequency band.3 HSDPA can be implemented in the TX board for the downlink by exploiting more advanced baseband technology. Interference cancellation

Interference cancellation can be introduced in the uplink DCH receiver to improve coverage or to increase capacity. The main effect of interference cancellation is reduced interference received from users in the same cell as the target user. This technique can either increase the amount of uplink traffic or reduce the interference margin in the dimensioning, thus increasing coverage. The configuration can be serial or parallel. Serial configurations yield the greatest improvement in performance and require less processing power, but result in greater delay. Parallel configurations, which offer a reasonable improvement in performance, reEricsson Review No. 1, 2003

Figure 12 RAX board of RBS3000 product series.

quire greater processing power, but result in shorter delay. Parallel configurations are thus preferred for voice service.

Conclusion The baseband part of Ericsson’s RBS3000 provides a hardware platform for thirdgeneration radio network functions and complies in full with the 3GPP WCDMA standard. All physical layer functions and frame protocol processing are implemented on the baseband boards. The baseband design supports free allocation of baseband resources to frequency and sectors, thereby supporting operator needs for flexibility in configuring the radio network for different sites. The architecture scales easily to meet operator demands for capacity. The baseband software and hardware support forward hardware preparation—for future functional enhancements. The baseband architecture is also backward compatible—that is, operators will be able to insert future-generation hardware into an existing platform running the RBS infrastructure. Planned enhancements to the baseband include HSDPA, to increase the bit rate for best-effort service in the downlink, and interference cancellation, to improve coverage or capacity in the uplink.

REFERENCES 1 Kling, L., Lindholm, Å., Marklund L. and Nilsson G: CPP—Cello packet platform, Ericsson Review Vol. 79(2002):2, pp. 6875 2 Zune, P.: Family of RBS 3000 products for WCDMA systems, Ericsson Review Vol. 77(2000):3, pp. 170-177 3 Hedberg, T. and Parkvall, S.: Evolving WCDMA, Ericsson Review Vol. 77(2000):2, pp. 124-131 4 3GPP WCDMA Technical Specification 25.211 5 3GPP WCDMA Technical Specification 25.301 6 3GPP WCDMA Technical Specification 25.214 7 3GPP WCDMA Technical Specification 25.104

41