OWA310010 WCDMA Radio Interface and Physical Layer ISSUE 1.1.pdf

8/19/2019 OWA310010 WCDMA Radio Interface and Physical Layer ISSUE 1.1.pdf

http://slidepdf.com/reader/full/owa310010-wcdma-radio-interface-and-physical-layer-issue-11pdf 1/63



WCDMA Radio Interface and Physical Layer

Confidential Information of Huawei. No Spreading Without Permission

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UTRAN: UMTS Terrestrial Radio Access Network.

The UTRAN consists of a set of Radio Network Subsystems connected to theCore Network through the Iu interface.

A RNS consists of a Radio Network Controller and one or more NodeBs. ANodeB is connected to the RNC through the Iub interface.

Inside the UTRAN, the RNCs of the RNS can be interconnected togetherthrough the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed overdirect physical connection between RNCs or virtual networks using anysuitable transport network.

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The layer 1 supports all functions required for the transmission of bit streamson the physical medium. It is also in charge of measurements functionconsisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, … It isbasically composed of a “layer 1 management” entity, a “transport channel”entity, and a “physical channel” entity.

The layer 2 protocol is responsible for providing functions such as mapping,ciphering, retransmission and segmentation. It is made of four sub-layers:MAC (Medium Access Control), RLC (Radio Link Control), PDCP (PacketData Convergence Protocol) and BMC (Broadcast/Multicast Control).

The layer 3 is split into 2 parts: the access stratum and the non accessstratum. The access stratum part is made of “RRC (Radio Resource Control)”entity and “duplication avoidance” entity. “duplication avoidance” terminates inthe CN but is part of the Access Stratum. The higher layer signalling such asMobility Management (MM) and Call Control (CC) is assumed to belong to thenon-access stratum, and therefore not in the scope of 3GPP TSG RAN. In theC-plane, the interface between 'Duplication avoidance' and higher L3 sub-layers (CC, MM) is defined by the General Control (GC), Notification (Nt) andDedicated Control (DC) SAPs.

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Not shown on the figure are connections between RRC and all the otherprotocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.

The protocol layers are located in the UE and the peer entities are in the

NodeB or the RNC.

Many functions are managed by the RRC layer . Here is the list of the mostimportant:

Establishment, re-establishment, maintenance and release of anRRC connection between the UE and UTRAN : it includes an optionalcell re-selection, an admission control, and a layer 2 signaling linkestablishment. When a RNC is in charge of a specific connectiontowards a UE, it acts as the Serving RNC.

Establishment, reconfiguration and release of Radio Bearers : anumber of Radio Bearers can be established for a UE at the same time.These bearers are configured depending on the requested QoS. TheRNC is also in charge of ensuring that the requested QoS can be met.

Assignment, reconfiguration and release of radio resources for theRRC connection : it handles the assignment of radio resources (e.g.codes, shared channels). RRC communicates with the UE to indicate

new resources allocation when handovers are managed.Paging/Notification : it broadcasts paging information from network toUEs.

Broadcasting of information provided by the non-access stratum(Core Network) or access Stratum. This corresponds to “systeminformation” regularly repeated.

UE measurement reporting and control of the reporting : RRCindicates what to measure, when and how to report.

Outer loop power control : controls setting of the target values.

Control of ciphering : provides procedures for setting of ciphering.

The RRC layer is defined in the 25.331 specification from 3GPP.

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The RLC ’s main function is the transfer of data from either the user or thecontrol plane over the Radio interface. Two different transfer modes are used:transparent and non-transparent. In non-transparent mode, 2 sub-modes areused: acknowledged or unacknowledged .

RLC provides services to upper layers:

data transfer (transparent, acknowledged and unacknowledged modes).

QoS setting : the retransmission protocol (for AM only) shall beconfigurable by layer 3 to provide different QoS.

notification of unrecoverable errors : RLC notifies the upper layers oferrors that cannot be resolved by RLC.

The RLC functions are:

mapping between higher layer PDUs and logical channels.

ciphering : prevents unauthorized acquisition of data; performed in RLClayer for non-transparent RLC mode.

segmentation/reassembly : this function performssegmentation/reassembly of variable-length higher layer PDUs into/fromsmaller RLC Payload Units. The RLC size is adjustable to the actual setof transport formats (decided when service is established).

Concatenation and padding may also be used.error correction : done by retransmission (acknowledged data transfermode only).

flow control : allows the RLC receiver to control the rate at which thepeer RLC transmitting entity may send information.

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MAC services include:

Data transfer : service providing unacknowledged transfer of MAC SDUsbetween peer MAC entities.

Reallocation of radio resources and MAC parameters :reconfiguration of MAC functions such as change of identity of UE.Requested by the RRC layer.

Reporting of measurements : local measurements such as trafficvolume and quality indication are reported to the RRC layer.

The functions accomplished by the MAC sub- layer are listed above. Here’s aquick explanation for some of them:

Priority handling between the data flows of one UE : since UMTS is

multimedia, a user may activate several services at the same time,having possibly different profiles (priority, QoS parameters...). Priorityhandling consists in setting the right transport format for a high bit rateservice and for a low bit rate service.

Priority handling between UEs : use for efficient spectrum resources utilization for bursty transfers on common and shared channels.

Ciphering: to prevent unauthorized acquisition of data. Performed inthe MAC layer for transparent RLC mode.

Access Service Class (ACS) selection for RACH transmission : theRACH resources are divided between different ACSs in order to providedifferent priorities on a random access procedure.

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PDCP

UMTS supports several network layer protocols providing protocoltransparency for the users of the service.

Using these protocols (and new ones) shall be possible without anychanges to UTRAN protocols. In order to perform this requirement, thePDCP layer has been introduced. Then, functions related to transfer ofpackets from higher layers shall be carried out in a transparent way bythe UTRAN network entities.

PDCP shall also be responsible for implementing different kinds ofoptimization methods. The currently known methods are standardizedIETF (Internet Engineering Task Force) header compression algorithms.

Algorithm types and their parameters are negotiated by RRC andindicated to PDCP.

Header compression and decompression are specific for each networklayer protocol type.

In order to know which compression method is used, an identifier (PID:Packet Identifier) is inserted. Compression algorithms exist for TCP/IP,RTP/UDP/IP, …

Another function of PDCP is to provide numbering of PDUs. This is doneif lossless SRNS relocation is required.

To accomplish this function, each PDCP-SDUs (UL and DL) is bufferedand numbered. Numbering is done after header compression. SDUs arekept until information of successful transmission of PDCP-PDU has beenreceived from RLC. PDCP sequence number ranges from 0 to 65,535.

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BMC (broadcast/multicast control protocol)

The main function of BMC protocol are:

Storage of cell broadcast message. the BMC in RNC stores the cellbroadcast message received over the CBC-RNC interface for scheduledtransmission.

Traffic volume monitoring and radio resource request for CBS. Onthe UTRAN side, the BMC calculates the required transmission rate forthe cell broadcast service based on the messages received over theCBC-RNC interface, and requests appropriate .CTCH/FACH resourcesfrom from RRC

Scheduling of BMC message. The BMC receives scheduling

information together with each cell broadcast message over the CBC-RNC interface. Based on this scheduling information, on the UTRANside the BMC generates schedule message and schedules BMCmessage sequences accordingly. On the UE side ,the BMC evaluatesthe schedule messages and indicates scheduling parameters to RRC,which are used by RRC to configure the lower layers for CBSdiscontinuous reception.

Transmission of BMC message to UE. The function transmits the

BMC messages according to the scheduleDelivery of cell broadcast messages to the upper layer. This UEfunction delivers the received non-corrupted cell broadcast messages tothe upper layer

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The layer 1 (physical layer) is used to transmit information under the form ofelectrical signals corresponding to bits, between the network and the mobileuser. This information can be voice, circuit or packet data, and networksignaling.

The UMTS layer 1 offers data transport services to higher layers. The accessto these services is through the use of transport channels via the MAC sub-layer.

These services are provided by radio links which are established by signalingprocedures. These links are managed by the layer 1 management entity .One radio link is made of one or several transport channels, and one physicalchannel.

The UMTS layer 1 is divided into two sub-layers: the transport and thephysical sub-layers. All the processing (channel coding, interleaving, etc.) isdone by the transport sub-layer in order to provide different services and theirassociated QoS. The physical sub-layer is responsible for the modulation,which corresponds to the association of bits (coming from the transport sub-layer) to electrical signals that can be carried over the air interface. Thespreading operation is also done by the physical sub-layer.

These two parts of layer 1 are controlled by the layer 1 management (L1M)entity. It is made of several units located in each equipment, which exchangeinformation through the use of control channels.

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In terms of protocol layer, the WCDMA radio interface has three types ofchannels: physical channel, transport channel and logical channel.

Logical channel: Carrying user services directly. According to the types of thecarried services, it is divided into two types: control channel and servicechannel.

Transport channel: It is the interface between radio interface layer 2 and layer1, and it is the service provided for MAC layer by the physical layer. Accordingto whether the information transported is dedicated information for a user orcommon information for all users, it is divided into dedicated channel and

common channel.Physical channel: It is the ultimate embodiment of all kinds of informationwhen they are transmitted on radio interface. Each channel which usesdedicated carrier frequency, code (spreading code and scramble) and carrierphase (I or Q) can be regarded as a physical channel.

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As in GSM, UMTS uses the concept of logical channels.

A logical channel is characterized by the type of information that istransferred.

As in GSM, logical channels can be divided into two groups: control channelsfor control plane information and traffic channel for user plane information.

The traffic channels are:

Dedicated Traffic Channel (DTCH): a point-to-point bi-directional channel, that transmits dedicated user information between a UE andthe network. That information can be speech, circuit switched data orpacket switched data. The payload bits on this channel come from ahigher layer application (the AMR codec for example). Control bits canbe added by the RLC (protocol information) in case of a non transparenttransfer. The MAC sub-layer will also add a header to the RLC PDU.

Common Traffic Channel (CTCH): a point-to-multipoint downlinkchannel for transfer of dedicated user information for all or a group ofspecified UEs. This channel is used to broadcast BMC messages.These messages can either be cell broadcast data from higher layers orschedule messages for support of Discontinuous Reception (DRX) ofcell broadcast data at the UE. Cell broadcast messages are servicesoffered by the operator, like indication of weather, traffic, location or rate

information.

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The control channels are:

Broadcast Control Channel (BCCH): a downlink channel thatbroadcasts all system information types (except type 14 that is only usedin TDD). For example, system information type 3 gives the cell identity.UEs decode system information on the BCH except when in Cell_DCHmode. In that case, they can decode system information type 10 on theFACH and other important signaling is sent on a DCCH.

Paging Control Channel (PCCH): a downlink channel that transferspaging information. It is used to reach a UE (or several UEs) in idle

mode or in connected mode (Cell_PCH or URA_PCH state). Thepaging type 1 message is sent on the PCCH. When a UE receives apage on the PCCH in connected mode, it shall enter Cell_FACH stateand make a cell update procedure.

Dedicated Control Channel (DCCH): a point-to-point bi-directional channel that transmits dedicated control information between a UE andthe network. This channel is used for dedicated signaling after a RRCconnection has been done. For example, it is used for inter-frequencyhandover procedure, for dedicated paging, for the active set updateprocedure and for the control and report of measurements.

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Common Control Channel (CCCH): a bi-directional channel fortransmitting control information between network and UEs. It is used tosend messages related to RRC connection, cell update and URA update.This channel is a bit like the DCCH, but will be used when the UE hasnot yet been identified by the network (or by the new cell). For example,it is used to send the RRC connection request message, which is thefirst message sent by the UE to get into connected mode. The networkwill respond on the same channel, and will send him its temporaryidentities (cell and UTRAN identities). After these initial messages, theDCCH will be used.

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In order to carry logical channels, several transport channels are defined.They are:

Broadcast Channel (BCH): a downlink channel used for broadcast ofsystem information into the entire cell.

Paging Channel (PCH): a downlink channel used for broadcast ofcontrol information into the entire cell, such as paging.

Random Access Channel (RACH): a contention based uplink channelused for initial access or for transmission of relatively small amounts ofdata (non real-time dedicated control or traffic data).

Forward Access Channel (FACH): a common downlink channel used

for dedicated signaling (answer to a RACH typically), or for transmissionof relatively small amounts of data.

Dedicated Channel (DCH): a channel dedicated to one UE used inuplink or downlink .

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Now we will begin to discuss the physical channel. Physical channel is themost important and complex channel, and a physical channel is defined by aspecific carrier frequency, code and relative phase. In CDMA system, thedifferent code (scrambling code or spreading code) can distinguish thechannel. Most channels consist of radio frames and time slots, and each radioframe consists of 15 time slots. There are two types of physical channel: ULand DL.

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The different physical channels are:Synchronization Channel (SCH): used for cell search procedure.There is the primary and the secondary SCHs.Common Control Physical Channel (CCPCH): used to carry commoncontrol information such as the scrambling code used in DL (there is aprimary CCPCH and additional secondary CCPCH).Common Pilot Channels (P-CPICH and S-CPICH): used for coherentdetection of common channels. They indicate the phase reference.Dedicated Physical Data Channel (DPDCH): used to carry dedicateddata coming from layer 2 and above (coming from DCH).Dedicated Physical Control Channel (DPCCH): used to carrydedicated control information generated in layer 1 (such as pilot, TPCand TFCI bits).Page Indicator Channel (PICH): carries indication to inform the UE thatpaging information is available on the S-CCPCH.Acquisition Indicator Channel (AICH): it is used to inform a UE thatthe network has received its access request.High Speed Physical Downlink Shared Channel (HS-PDSCH): it isused to carry subscribers BE service data (mapping on HSDPA) comingfrom layer 2.High Speed Shared Control Channel (HS-SCCH): it is used to carry

control message to HS-PDSCH such as modulation scheme, UE ID etc.

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The different physical channels are:

EDCH Absolute Grant Channel(E-AGCH): Carries absolute grant

determined by the scheduler

EDCH Relative Grant Channel (E-RGCH): Carries relative grant

determined by the scheduler

EDCH HARQ Indicator Channel (E-HICH): Carries HARQ ACK/NACKindicator for E-DCH

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The different physical channels are:

Dedicated Physical Data Channel (DPDCH): used to carry dedicateddata coming from layer 2 and above (coming from DCH).

Dedicated Physical Control Channel (DPCCH): used to carrydedicated control information generated in layer 1 (such as pilot, TPCand TFCI bits).

Physical Random Access Channel (PRACH): used to carry randomaccess information when a UE wants to access the network.

High Speed Dedicated Physical Control Channel (HS-DPCCH): it isused to carry feedback message to HS-PDSCH such CQI,ACK/NACK.

Enhanced Dedicated Physical Control Channel (E-DPDCH): CarriesE-DCH

Enhanced Dedicated Physical Data Channel (E-DPCCH): Carriescontrol signal for E-DPDCH

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When a UE is turned on, the first thing it does is to scan the UMTS spectrumand find a UMTS cell. After that, it has to find the primary scrambling codeused by that cell in order to be able to decode the BCCH (for systeminformation). This is done with the help of the Synchronization Channel.

Each cell of a NodeB has its own SCH timing, so that there is no overlapping.

The SCH is a pure downlink physical channel broadcasted over the entire cell.It is transmitted unscrambled during the first 256 chips of each time slot, intime multiplex with the P-CCPCH. It is the only channel that is not spreadover the entire radio frame. The SCH provides the primary scrambling codegroup (one out of 64 groups), as well as the radio frame and time slotsynchronization.

The SCH consists of two sub-channels, the primary and secondary SCH.These sub-channels are sent in parallel using code division during the first256 chips of each time slot. P-SCH always transmits primary synchronizationcode. S-SCH transmits secondary synchronization codes.

The primary synchronization code is repeated at the beginning of each timeslot. The same code is used by all the cells and enables the mobiles to detectthe existence of the UMTS cell and to synchronize itself on the time slotboundaries. This is normally done with a single matched filter or any similardevice. The slot timing of the cell is obtained by detecting peaks in thematched filter output.

This is the first step of the cell search procedure. The second step is doneusing the secondary synchronization channel.

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The S-SCH also consists of a code, the Secondary Synchronization Code(SSC) that indicates which of the 64 scrambling code groups the cell’sdownlink scrambling code belongs to. 16 different SSCs are defined. EachSSC is a 256 chip long sequence.

There is one specific SSC transmitted in each time slot, giving us a sequenceof 15 SSCs. There is a total of 64 different sequences of 15 SSCs,corresponding to the 64 primary scrambling code groups. These 64sequences are constructed so that one sequence is different from any otherone, and different from any rotated version of any sequence. The UEcorrelates the received signal with the 16 SSCs and identifies the maximumcorrelation value.

The S-SCH provides the information required to find the frame boundaries andthe downlink scrambling code group (one out of 64 groups). The scramblingcode (one out of 8) can be determined afterwards by decoding the P-CPICH.The mobile will then be able to decode the BCH.

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The Common Pilot Channel (CPICH) is a pure physical control channelbroadcasted over the entire cell. It is not linked to any transport channel. Itconsists of a sequence of known bits that are transmitted in parallel with theprimary and secondary CCPCH.

The PCPICH is used by the mobile to determine which of the 8 possibleprimary scrambling codes is used by the cell, and to provide the phasereference for common channels.

Finding the primary scrambling code is done during the cell search procedurethrough a symbol-by-symbol correlation with all the codes within the codegroup. After the primary scrambling code has been identified, the UE candecode system information on the P-CCPCH.

The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH.It is broadcasted over the entire cell. The channelization code used to spreadthe P-CPICH is always Cch,256,0 (all ones). Thus, the P-CPICH is a fixedrate channel. Also, it is always scrambled with the primary scrambling code ofthe cell.

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The Primary Common Control Physical Channel (P-CCPCH) is a fixed rate(SF=256) downlink physical channel used to carry the BCH transport channel.It is broadcasted continuously over the entire cell like the P-CPICH.

The figure above shows the frame structure of the P-CCPCH. The framestructure is special because it does not contain any layer 1 control bits. The P-CCPCH only has one fix predefined transport format combination, and theonly bits transmitted are data bits from the BCH transport channel. It isimportant to note that the P-CCPCH is not transmitted during the first 256chips of the slot. In fact, another physical channel (SCH) is transmitted duringthat period of time. Thus, the SCH and the P-CCPCH are time multiplexed onevery time slot.

Channelization code Cch,256,1 is always used to spread the P-CCPCH.

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The Page Indicator Channel (PICH) is a fixed rate (30kbps, SF=256)physical channel used by the NodeB to inform a UE (or a group of UEs) that apaging information will soon be transmitted on the PCH. Thus, the mobile onlydecodes the S-CCPCH when it is informed to do so by the PICH. This enablesto do other processing and to save the mobiles’ battery.

The PICH carries Paging Indicators (PI), which are user specific andcalculated by higher layers. It is always associated with the S-CCPCH towhich the PCH is mapped.

The frame structure of the PICH is illustrated above. It is 10 ms long, andalways contains 300 bits (SF=256). 288 of these bits are used to carry pagingindicators, while the remaining 12 are not formally part of the PICH and shallnot be transmitted. That part of the frame (last 12 bits) is reserved for possiblefuture use.

In order not to waste radio resources, several PIs are multiplexed in time onthe PICH. Depending on the configuration of the cell, 18, 36, 72 or 144paging indicators can be multiplexed on one PICH radio frame. Thus, thenumber of bits reserved for each PI depends of the number of PIs per radioframe. For example, if there is 72 PIs in one radio frame, there will be 4(288/72) consecutive bits for each PI. These bits are all identical. If the PI ina certain frame is “1”, it is an indication that the UE associated with that PIshould read the corresponding frame of the S-CCPCH.

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The Secondary Common Control Physical Channel (S-CCPCH) is used tocarry the FACH and PCH transport channels. Unlike the P-CCPCH, it is notbroadcasted continuously. It is only transmitted when there is a PCH or FACHinformation to transmit. At the mobile side, the mobile only decodes the S-CCPCH when it expects a useful message on the PCH or FACH.

A UE will expect a message on the PCH after indication from the PICH (pageindicator channel), and it will expect a message on the FACH after it hastransmitted something on the RACH.

The FACH and the PCH can be mapped on the same or on separate S-CCPCHs. If they are mapped on the same S-CCPCH, TFCI bits have to besent to support multiple transport formats

The figure above shows the frame structure of the S-CCPCH. There are 18different slot formats determining the exact number of data, pilot and TFCI bits.The data bits correspond to the PCH and/or FACH bits coming from thetransport sub-layer. Pilot bit are typically used when beamforming techniquesare used.

The SF ranges from 4 to 256. The channelization code is assigned by theRRC layer as is the scrambling code, and they are fixed during thecommunication. They are sent on the BCCH so that every UE can decode the

channel. As said before, FACH can be used to carry user data. The difference with thededicated channel is that it cannot use fast power control, nor soft handover.The advantage is that it is a fast access channel.

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The Physical Random Access Channel (PRACH) is used by the UE toaccess the network and to carry small data packets. It carries the RACHtransport channel. The PRACH is an open loop power control channel, withcontention resolution mechanisms (ALOHA approach) to enable a randomaccess from several users.

The PRACH is composed of two different parts: the preamble part and themessage part that carries the RACH message. The preamble is an identifierwhich consists of 256 repetitions of a 16 chip long signature (total of 4096chips). There are 16 possible signatures, basically, the UE randomly selectsone of the 16 possible preambles and transmits it at increasing power until itgets a response from the network (on the AICH). That preamble is scrambledbefore being sent. That is a sign that the power level is high enough and thatthe UE is authorized to transmit, which it will do after acknowledgment fromthe network. If the UE doesn’t get a response from the network, it has to selecta new signature to transmit.

The message part is 10 or 20 ms long (split into 15 or 30 time slots) and ismade of the RACH data and the layer 1 control information.

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The data and control bits of the message part are processed in parallel. TheSF of the data part can be 32, 64, 128 or 256 while the SF of the control partis always 256. The control part consists of 8 pilot bits for channel estimationand 2 TFCI bits to indicate the transport format of the RACH (transportchannel), for a total of 10 bits per slot.

The OVSF codes to use (one for RACH data and one for control) depend onthe signature that was used for the preamble (for signatures s=0 to s=15:OVSF control = C ch,256,m , where m=16s + 15; OVSF data = C ch,SF,m , wherem=SF*s/16.

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The PRACH transmission is based on the access frame structure. Theaccess frame is access of 15 access slots and lasts 20 ms (2 radio frames).

To avoid too many collisions and to limit interference, a UE must wait at least3 or 4 access slots between two consecutive preambles.

The PRACH resources (access slots and preamble signatures) can be dividedbetween different Access Service Classes (ASC) in order to provide differentpriorities of RACH usage. The ASC number ranges from 0 (highest priority) to7 (lowest priority).

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The Acquisition Indicator Channel (AICH) is a common downlink channel usedto control the uplink random accesses. It carries the Acquisition Indicators (AI),each corresponding to a signature on the PRACH (uplink). When the NodeBreceives the random access from a mobile, it sends back the signature of themobile to grant its access. If the NodeB receives multiple signatures, it cansent all these signatures back by adding the together. At reception, the UEcan apply its signature to check if the NodeB sent an acknowledgement(taking advantage of the orthogonality of the signatures).

The AICH consists of a burst of data transmitted regularly every access slotframe. One access slot frame is formed of 15 access slots, and lasts 2 radioframes (20 ms). Each access slot consists of two parts, an acquisition

indicator part of 32 real-valued symbols and a long part during which nothingis transmitted to avoid overlapping due to propagation delays.

The SF used is always 256 and the OVSF code used by the cell is indicated insystem information type 5.

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There are two kinds of uplink dedicated physical channels, the DedicatedPhysical Data Channel (DPDCH) and the Dedicated Physical ControlChannel (DPCCH). The DPDCH is used to carry the DCH transport channel.The DPCCH is used to carry the physical sub-layer control bits.

Each DPCCH time slot consists of Pilot, TFCI FBI TPC

Pilot is used to help demodulation

TFCI: transport format combination indicator

FBI:used for the FBTD. (feedback TX diversity)

TPC: used to transport power control command.

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On the figure above, we can see the DPDCH and DPCCH time slotconstitution. The parameter k determines the number of symbols per slot. Itis related to the spreading factor (SF) of the DPDCH by this simple equation:SF=256/2 k. The DPDCH SF ranges from 4 to 256. The SF for the uplinkDPCCH is always 256, which gives us 10 bits per slot. The exact number ofpilot, TFCI, TPC and FBI bits is configured by higher layers. This configurationis chosen from 12 possible slot formats. It is important to note that symbolsare transmitted during all slots for the DPDCH

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The uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlinkDPDCH and DPCCH is time multiplexed. This is main difference.

Basically, there are two types of downlink DPCH. They are distinguished bythe use or non use of the TFCI field. TFCI bits are not used for fixed rateservices or when the TFC doesn’t change.

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We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed.But the downlink DPDCH and DPCCH is time multiplexed. This is maindifference. The parameter k in the figure above determines the total number ofbits per time slot. It is related to the SF, which ranges from 4 to 512. Thechips of one slot is also 2560.

Downlink physical channels are used to carry user specific information likespeech, data or signaling, as well as layer 1 control bits. Like it wasmentioned before, the payload from the DPDCH and the control bits from theDPCCH are time multiplexed on every time slot. The figure above shows howthese two channels are multiplexed. There is only one DPCCH in downlink forone user.

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HS-SCCH uses a SF=128 and has q time structure based on a sub-frame oflength 2 ms, i.e. the same length as the HS-DSCH TTI. The timing of HS-SCCH starts two slot prior to the start of the HS-PDSCH subframe.

The following information is carried on the HS-SCCH (7 items)

Modulation scheme(1bit) QPSK or 16QAM

Channelization code set (7bits)

Transport block size ( 6bits)

HARQ process number (3bits)

Redundancy version (3bits)

New Data Indicator (1bit)

UE identity (16 bits)

In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCHcarries physical-layer signalling to a single UE. As there should be apossibility for HS-DSCH transmission to multiple users in parallel (codemultiplex), multiplex HS-SCCH may be needed in a cell. The specification

allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE mustbe able to decode four HS-SCCH.

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The uplink HS-DPCCH consists of:

Acknowledgements for HARQ

Channel Quality Indicator (CQI)

As the HS-DPCCH uses SF=256, there are a total of 30 channel bits per 2 mssub frame (3 time slot). The HS-DPCCH information is divided in such a waythat the HARQ acknowledgement is transmitted in the first slot of the subframewhile the channel quality indication is transmitted in the rest slot.

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The E-DPDCH carries data in the uplink. The spreading factor of the E-DPDCH varies from SF256 to SF2 depending on the data transmission rate. Amaximum of four E-DPDCHs can be used for parallel transmission. The SF oftwo E-DPDCHs is SF2, and the SF of the other two E-DPDCHs is SF4.

The E-DPCCH carries control information related to data transmission in theuplink. The control information consists of the E-DCH transport formatcombination indicator (E-TFCI), retransmission sequence number (RSN), andhappy bit. The SF of the E-DPCCH is fixed to 256.



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The downlink E-AGCH and E-RGCH carry the HSUPA scheduling control information.The E-AGCH is a shared channel, which carries the maximum E-DPDCH to DPCCHpower ratio, that is, absolute grants. The SF of the E-AGCH is fixed to 256.



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The E-RGCH is a dedicated channel, which is used to indicate relative grants andincrease or decrease the maximum E-DPDCH to DPCCH power ratio. The SF of theE-RGCH is fixed to 128.

To implement the HARQ function, the E-HICH is introduced in the downlink. The E-HICH carries retransmission requests from the NodeB. The SF of the E-HICH is fixedto 128.



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This page indicates how the mapping can be done between logical, transportand physical channels. Not all physical channels are represented becausenot all physical channels correspond to a transport channel.

The mapping between logical channels and transport channels is done by theMAC sub-layer.

Different connections can be made between logical and transport channels:

BCCH is connected to BCH and may also be connected to FACH;

DTCH can be connected to either RACH and FACH, to RACH andDSCH, to DCH and DSCH, to a DCH or a CPCH;

CTCH is connected to FACH;

DCCH can be connected to either RACH and FACH, to RACH andDSCH, to DCH and DSCH, to a DCH or a CPCH;

PCCH is connected to PCH;

CCCH is connected to RACH and FACH.

These connections depend on the type of information on the logical channels.

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The purpose of the Cell Search Procedure is to give the UE the possibility offinding a cell and of determining the downlink scrambling code and framesynchronization of that cell. This is typically performed in 3 steps:

PSCH (Slot synchronization): The UE uses the SCH’s primarysynchronization code to acquire slot synchronization to a cell. Theprimary synchronization code is used by the UE to detect the existenceof a cell and to synchronize the mobile on the TS boundaries. This istypically done with a single filter (or any similar device) matched to theprimary synchronization code which is common to all cells. The slottiming of the cell can be obtained by detecting peaks in the matchedfilter output.

SSCH (Frame synchronization and code-group identification): Thesecondary synchronization codes provide the information required to findthe frame boundaries and the group number. Each group numbercorresponds to a unique set of 8 primary scrambling codes. The frameboundary and the group number are provided indirectly by selecting asuite of 15 secondary codes. 16 secondary codes have been defined C 1,C2, ….C 16 . 64 possible suites have been defined, each suitecorresponds to one of the 64 groups. Each suite of secondary codes iscomposed of 15 secondary codes (chosen in the set of 16), each ofwhich will be transmitted in one time slot. When the received codesmatches one of the possible suites, the UE has both determined the

frame boundary and the group number.

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PCPICH (Scrambling-code identification): The UE determines the exactprimary scrambling code used by the found cell. The primary scramblingcode is typically identified through symbol-by-symbol correlation over thePCPICH with all the codes within the code group identified in the secondcan be read.

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Physical random access procedure

1. Derive the available uplink access slots, in the next full access slot set,for the set of available RACH sub-channels within the given ASC.Randomly select one access slot among the ones previously determined.If there is no access slot available in the selected set, randomly selectone uplink access slot corresponding to the set of available RACH sub-channels within the given ASC from the next access slot set. Therandom function shall be such that each of the allowed selections ischosen with equal probability ;

2. Randomly select a signature from the set of available signatureswithin the given ASC;

3. Set the Preamble Retransmission Counter to Preamble_ Retrans_Max ;

4. Set the parameter Commanded Preamble Power toPreamble_Initial_Power;

5. Transmit a preamble using the selected uplink access slot, signature,and preamble transmission power;

6. If no positive or negative acquisition indicator (AI +1 nor – 1)corresponding to the selected signature is detected in the downlink

access slot corresponding to the selected uplink access slot: A: Select the next available access slot in the set of availableRACH sub-channels within the given ASC;B: select a signature;C: Increase the Commanded Preamble Power;

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D: Decrease the Preamble Retransmission Counter by one. If thePreamble Retransmission Counter > 0 then repeat from step 6.Otherwise exit the physical random access procedure.

7. If a negative acquisition indicator corresponding to the selectedsignature is detected in the downlink access slot corresponding to theselected uplink access slot, exit the physical random access procedureSignature;

8. If a positive acquisition indicator corresponding to the selectedsignature is detected , Transmit the random access message three orfour uplink access slots after the uplink access slot of the last transmittedpreamble;

9. exit the physical random access procedure.

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Transmitter-antenna diversity can be used to generate multi-path diversity inplaces where it would not otherwise exist. Multi-path diversity is a usefulphenomenon, especially if it can be controlled. It can protect the UE againstfading and shadowing. TX diversity is designed for downlink usage.Transmitter diversity needs two antennas, which would be an expensivesolution for the UEs.

The UTRA specifications divide the transmitter diversity modes into twocategories: (1) open-loop mode and (2) closed-loop mode. In the open-loopmode no feedback information from the UE to the NodeB is available. Thusthe UTRAN has to determine by itself the appropriate parameters for the TXdiversity. In the closed-loop mode the UE sends feedback information up tothe NodeB in order to optimize the transmissions from the diversity antennas.

Thus it is quite natural that the open-loop mode is used for the commonchannels, as they typically do not provide an uplink return channel for thefeedback information. Even if there was a feedback channel, the NodeBcannot really optimize its common channel transmissions according tomeasurements made by one particular UE. Common channels are commonfor everyone; what is good for one UE may be bad for another. The closed-loop mode is used for dedicated physical channels, as they have an existinguplink channel for feedback information. Note that shared channels can alsoemploy closed loop power control, as they are allocated for only one user at atime, and they also have a return channel in the uplink. There are twospecified methods to achieve the transmission diversity in the open-loop modeand two methods in closed-loop mode

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The TX diversity methods in the open-loop mode are

space time-block coding-based transmit-antenna diversity (STTD)

time-switched transmit diversity (TSTD).

In STTD the data to be transmitted is divided between two transmissionantennas at the base station site and transmitted simultaneously. Thechannel-coded data is processed in blocks of four bits. The bits are timereversed and complex conjugated, as shown in above slide. The STTDmethod, in fact, provides two brands of diversity. The physical separation ofthe antennas provides the space diversity, and the time difference derived

from the bit-reversing process provides the time diversity.

These features together make the decoding process in the receiver morereliable. In addition to data signals, pilot signals are also transmitted via bothantennas. The normal pilot is sent via the first antenna and the diversity pilotvia the second antenna.

The two pilot sequences are orthogonal, which enables the receiving UE toextract the phase information for both antennas.

The STTD encoding is optional in the UTRAN, but its support is mandatory forthe UE’s receiver.

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Time-switched transmit diversity (TSTD) can be applied to the SCH. Just likeSTTD, the support of TSTD is optional in the UTRAN, but mandatory in theUE. The principle of TSTD is to transmit the synchronization channels via thetwo base station antennas in turn. In even-numbered time slots the SCHs aretransmitted via antenna 1, and in odd-numbered slots via antenna 2. This isdepicted in above Figure. Note that SCH channels only use the first 256 chipsof each time slot (i.e., one-tenth of each slot).

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The closed-loop-mode transmit diversity can only be applied to the downlinkchannel if there is an associated uplink channel. Thus this mode can only beused with dedicated channels. The chief operating principle of the closed loopmode is that the UE can control the transmit diversity in the base station bysending adjustment commands in FBI bits on the uplink DPCCH. The UE usesthe base station’s common pilot channels to estimate the channels separately.Based on this estimation, it generates the adjustment information and sends itto the UTRAN to maximize the UE’s received power.

There are actually two modes in the closed-loop method. In mode 1 only thephase can be adjusted; in mode 2 the amplitude is adjustable as well as thephase. Each uplink time slot has one FBI bit for closed-loop-diversity control.In mode 1 each bit forms a separate adjustment command, but in mode 2 fourbits are needed to compose a command.

This functions can be configured by LMT command ADD CELLSETUP.

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WCDMA Radio Interface and Physical Layer P-62

OWA310010 WCDMA Radio Interface and Physical Layer ISSUE 1.1.pdf

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