002 wcdma radio interface physical layer

8/9/2019 002 WCDMA Radio Interface Physical Layer

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WCDMA Radio Interface Physical Layer

Huawei Technologies Co., Ltd.All rights reserved


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WCDMA Radio Interface Physical Layer Confidentiality level: Customer

Mexico Training Center Confidential information of Huawei. Page 2/60

Revision Record

Date Version Change descriptionAuthor

28-02-2007 1A Victor Toledo


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Table of Contents

1 Physical layer Overview..........................................................................................................9 Protocol structure for radio interface...............................................................................10

Spreading technology......................................................................................................14Channelization Codes .....................................................................................................15Scrambling codes............................................................................................................16

2 Physical layer key technology .............................................................................................19 Logical channels..............................................................................................................19Transport channels ..........................................................................................................21Physical channel ..............................................................................................................22Cell broadcast channels...................................................................................................25Paging channels...............................................................................................................29Random access channels................................................................................................32Dedicated channels..........................................................................................................35High speed downlink shared channels ............................................................................37Channel mapping .............................................................................................................40

3 Physical layer processing procedure..................................................................................41 Coding and multiplexing technology ...............................................................................41Spreading technology......................................................................................................47Modulation technology .....................................................................................................50

4 Physical layer procedures....................................................................................................51 Cell search procedure .....................................................................................................51Channel timing relationship.............................................................................................52Random access procedure .............................................................................................53Transmit Diversity Mode...................................................................................................55 Transmit Diversity-STDD .................................................................................................56 Transmit Diversity TSTD ..................................................................................................57 Closed Loop Mode ...........................................................................................................58


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Foreword

The physical layer offers data transport services to higher layers.

The access to these services is through the use of transport channels via the MACsub-layer.

The physical layer is expected to perform the following functions in order to providethe data transport service, for example Modulation and spreading/demodulation anddespreading, Inner - loop power control etc.


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Objectives

Upon completion of this course, you will be able to:

• Understand radio interface protocol Architecture.

• Understand key technology of UMTS physical layer.

• Understand UMTS physical layer procedures.


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References

TS 25.104 UTRA (BS) FDD Radio Transmission and Reception

TS 25.201 Physical layer-general description

TS 25.211 Physical channels and mapping of transport channels onto physical

channels (FDD)

TS 25.212 Multiplexing and channel coding (FDD)

TS 25.213 Spreading and modulation (FDD)

TS 25.214 Physical layer procedures (FDD)

TS 25.308 UTRA High Speed Downlink Packet Access (HSDPA); Overall

description; Stage 2

TR 25.877 High Speed Downlink Packet Acces (HSDPA) - Iub/Iur Protocol

Aspects

TR 25.858 Physical layer aspects of UTRA High Speed Downlink Packet Access


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Physical Layer Overview

Figure 1.- UTRAN Protocol structure.

UTRAN:UMTS Terrestrial Radio Access Network.

The UTRAN consists of a set of Radio Network Subsystems connected to the Core Networkthrough the Iu.

A RNS consists of a Radio Network Controller and one or more Node Bs. A Node B isconnected to the RNC through the Iub interface.

Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnectedtogether through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over directphysical connection between RNCs or virtual networks using any suitable transport network.

Iur

Node B

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B

Iu Iu

Iub Iub Iub Iub


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Protocol Structure for radio interface

Figure 2.- Radio Interface Protocol structure.

The radio interface (Uu) is layered into three protocol layers:

the physical layer (L1) the data link layer (L2) the network layer (L3).

The layer 1 supports all functions required for the transmission of bit streams on the physicalmedium. It is also in charge of measurements function consisting in indicating to higher layers,for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power,transmit power. It is basically 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 sublayers: MAC (Medium Access Control),RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC(Broadcast/Multicast Control).

The layer 3 is split into 2 parts: the access stratum and the non access stratum. The accessstratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance” entity.The non access stratum part is made of CC, MM parts.


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Not shown on the figure are connections between RRC and all the other protocol 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 node B or the RNC.

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

Establishment, re-establishment, maintenance and release of an RRCconnection between the UE and UTRAN: it includes an optional cell re-selection, anadmission control, and a layer 2 signaling link establishment. When a RNC is in charge of aspecific connection towards a UE, it acts as the Serving RNC.

Establishment, reconfiguration and release of Radio Bearers: a number ofRadio Bearers can be established for a UE at the same time. These bearers are configureddepending on the requested QoS. The RNC is also in charge of ensuring that therequested QoS can be met.

Assignment, reconfiguration and release of radio resources for the RRCconnection: 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 to UEs. Broadcasting of information provided by the non-access stratum (Core

Network) or access Stratum. This corresponds to “system information” regularly repeated. UE measurement reporting and control of the reporting: RRC indicates 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.

The RLC’s main function is the transfer of data from either the user or the control plane overthe Radio interface. Two different transfer modes are used: transparent and non-transparent. Innon-transparent mode, 2 sub-modes are used: 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 be configurable by

layer 3 to provide different QoS. Notification of unrecoverable errors: RLC notifies the upper layers of errors

that cannot be resolved by RLC.


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The RLC functions are:

mapping between higher layer PDUs and logical channels, ciphering: prevents unauthorized acquisition of data; performed in RLC layer for

non-transparent RLC mode, segmentation/reassembly: this function performs segmentation/reassembly of

variable-length higher layer PDUs into/from smaller RLC Payload Units. The RLC size is

adjustable to the actual set of transport formats (decided when service is established).Concatenation and padding may also be used,

error correction: done by retransmission (acknowledged data transfer modeonly),

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

MAC services include:

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

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

Reporting of measurements: local measurements such as traffic volume andquality indication are reported to the RRC layer.

The functions accomplished by the MAC sublayer are listed above. Here’s a quickexplanation for some of them:

Priority handling between the data flows of one UE: since UMTS ismultimedia, a user may activate several services at the same time, having possibly differentprofiles (priority, QoS parameters...). Priority handling consists in setting the right transportformat for a high bit rate service 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 in the MAC

layer for transparent RLC mode. Access Service Class (ACS) selection for RACH transmission: the RACH

resources are divided between different ACSs in order to provide different priorities on arandom access procedure.

PDCP

UMTS supports several network layer protocols providing protocol transparency for theusers of the service.

Using these protocols (and new ones) shall be possible without any changes to UTRANprotocols. In order to perform this requirement, the PDCP layer has been introduced. Then,functions related to transfer of packets from higher layers shall be carried out in a transparentway by the UTRAN network entities.

PDCP shall also be responsible for implementing different kinds of optimization methods.The currently known methods are standardized IETF (Internet Engineering Task Force) headercompression algorithms.


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

Header compression and decompression are specific for each network layer protocol type.

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

Another function of PDCP is to provide numbering of PDUs. This is done if lossless SRNSrelocation is required.

To accomplish this function, each PDCP-SDUs (UL and DL) is buffered and numbered.Numbering is done after header compression. SDUs are kept until information of successfultransmission of PDCP-PDU has been received from RLC. PDCP sequence number ranges from0 to 65,535.

BMC (broadcast/multicast control protocol)

The main functions of BMC protocol are:

Storage of cell broadcast message. the BMC in RNC stores the cell broadcast messagereceived over the CBC-RNC interface for scheduled transmission.

Traffic volume monitoring and radio resource request for CBS. On the UTRAN side, theBMC calculates the required transmission rate for the cell broadcast service based on themessages received over the CBC-RNC interface, and requests appropriate .CTCH/FACHresources from 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 UTRAN side the BMC generates schedule message and schedules BMC messagesequences accordingly. On the UE side, the BMC evaluates the schedule messages andindicates scheduling parameters to RRC, which are used by RRC to configure the lower layersfor CBS discontinuous reception.

Transmission of BMC message to UE. The function transmits the BMC messagesaccording to the schedule

Delivery of cell broadcast messages to the upper layer. This UE function delivers thereceived non-corrupted cell broadcast messages to the upper layer

The layer 1 (physical layer) is used to transmit information under the form of electrical

signals corresponding to bits, between the network and the mobile user. This information can bevoice, circuit or packet data, and network signaling.

The UMTS layer 1 offers data transport services to higher layers. The access to theseservices is through the use of transport channels via the MAC sublayer.

These services are provided by radio links which are established by signaling procedures.These links are managed by the layer 1 management entity. One radio link is made of one orseveral transport channels, and one physical channel.


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The UMTS layer 1 is divided into two sublayers: the transport and the physical sublayers.All the processing (channel coding, interleaving, etc.) is done by the transport sublayer in orderto provide different services and their associated QoS. The physical sublayer is responsible forthe modulation, which corresponds to the association of bits (coming from the transport sublayer)to electrical signals that can be carried over the air interface. The spreading operation is also

done by the physical sublayer. These sublayers are well described in chapters 6 and 7.

These two parts of layer 1 are controlled by the layer 1 management (L1M) entity. It ismade of several units located in every equipment, which exchange information through the useof control channels.

Spreading Technology

Spreading consists of 2 steps：

Channelization operation ， which transforms data symbols into chips. Thus

increasing the bandwidth of the signal, The number of chips per data symbol is called the

Spreading Factor （ SF） .The operation is done by multiplying with OVSF code.

Scrambling operation is applied to the spreading signal .

Figure 3.- Spreading and scrambling

Spreading is applied to the physical channels. It consists of two operations. The first is thechannelization operation, which transforms every data symbol into a number of chips, thusincreasing the bandwidth of the signal. The number of chips per data symbol is called theSpreading Factor (SF). The second operation is the scrambling operation, where a scramblingcode is applied to the spread signal.


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Channelization codes

OVSF code is used as channelization code

The channelization codes are uniquely described as Cch,SF,k, where SF is the

spreading factor of the code and k is the code number, 0 ≤ k ≤ SF-1.

Figure 4.- Walsh codes.

The channelization codes are Orthogonal Variable Spreading Factor (OVSF) codes.

They are used to preserve orthogonality between different physical channels. They alsoincrease the clock rate to 3.84 Mcps. The OVSF codes are defined using a code tree.

In the code tree, the channelization codes are individually described by Cch,SF,k, where SF

is the Spreading Factor of the code and k the code number, 0 ≤ k ≤ SF-1.

A channelization sequence modulates one user’s bit. Because the chip rate is constant, thedifferent lengths of codes enable to have different user data rates. Low SFs are reserved forhigh rate services while high SFs are for low rate services.

The length of an OVSF code is an even number of chips and the number of codes (for oneSF) is equal to the number of chips and to the SF value.

The generated codes within the same layer constitute a set of orthogonal codes.

Furthermore, any two codes of different layers are orthogonal except when one of the two codesis a mother code of the other. For example C4,3 is not orthogonal with C1,0 and C2,1, but isorthogonal with C2,0.

Each Sector of each Base Station transmits W-CDMA Downlink Traffic Channels with up to512 code channels.


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Code tree repacking may be used to optimize the number of available codes in downlink.Exercise: Find code Cch,8,3 and code Cch,16,15.

OVSF shortage Scrambling enables neighboring cells to use the same channelization codes. This allows the

system to use a maximum of 512 OVSF codes in each cell. Notice that the use of an OVSF code

forbids the use of the other codes in its branch. This reduces considerably the number ofavailable codes especially for high rate services. This may lead to an OVSF shortage. In such acase, secondary scrambling codes may be allocated to the cells and enable the reuse of thesame OVSF in the same cell.

Scrambling Codes

Scrambling code ： GOLD sequence.

Scrambling code period : 10ms ,or 38400 chips.

The code used for scrambling of the uplink DPCCH/DPDCH may be of eitherlong or short type, There are 224 long and 224 short uplink scrambling codes. Uplink

scrambling codes are assigned by higher layers.

For downlink physical channels, a total of 218-1 = 262,143 scrambling codes can

be generated. scrambling codes k = 0, 1, …, 8191 are used.

Uplink scrambling code

All the physical channels in the uplink are scrambled. In uplink, the scrambling code can bedescribed as either long or short, depending on the way it was constructed. The scrambling code

is always applied to one 10 ms frame. Different scrambling codes will be allocated to differentmobiles.

In UMTS, Gold codes were chosen for their very low peak cross-correlation.


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Primary Scrambling Codes

Figure 5.- Primary Scrambling Codes.

Downlink link scrambling code

The scrambling codes used in downlink are constructed very much like the long uplinkscrambling codes. They are created with two 18-cell shift registers.

218-1 = 262,143 different scrambling codes can be formed using this method. However, notall of them are used. The downlink scrambling codes are divided into 512 sets, of one primaryscrambling code and 15 secondary scrambling codes each.

The primary scrambling codes are scrambling codes n=16*i where i=0…511. The 15secondary scrambling codes associated to one primary scrambling code are n=16*i + k, wherek=1…15. For now 8192 scrambling codes have been defined.


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Primary Scrambling code group

Figure 6.- Primary Scrambling code groups.

There is a total of 512 primary codes. They are further divided into 64 primary scramblingcode groups of 8 primary scrambling codes each. Each cell is allocated one and only oneprimary scrambling code. The group of the primary scrambling code is found by the mobiles ofthe cell using the SCH, while the specific primary scrambling code used is given by the CPICH.The primary CCPCH and the primary CPICH channels are always scrambled with the primaryscrambling code of the cell, while other channels can be scrambled by either the primary or thesecondary scrambling code.


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Physical layer key technology

Physical Channel Structure and Functions

In terms of protocol layer, the WCDMA radio interface has three channels: Physicalchannel, transport channel and logical channel.

Logical channel: Carrying user services directly. According to the types of the carriedservices, it is divided into two types: Control channel and service channel. Each logical channeltype is defined by is transferred.

Transport channel: It is the interface of radio interface layer 2 and physical layer, and isthe service provided for MAC layer by the physical layer. According to whether the informationtransported is dedicated information for a user or common information for all users, it is dividedinto dedicated channel and common channel. Each transport channel is described by and with data is transmitted over the radio interface.

Physical channel: It is the ultimate embodiment of all kinds of information when they are

transmitted on radio interfaces. Each kind of channel which uses dedicated carrier frequency,code (spreading code and scramble) and carrier phase (I or Q) can be regarded as a dedicatedchannel. A physical channel provide the real transmission resource, being in charge of theassociation between bits and physical symbols (electrical signals). It corresponds, in UMTS, to afrequency, a specific set of codes and phase.

As a conclusion:

Physical Channel = information container

Transport Channel = characteristics of transmission

Logical Channel = specification of the information global content

Logical Channel

Figure 7.- Logical 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 is transferred.For example, some channels are used to transfer dedicated information, some for transfer of

general control information, etc..

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

The traffic channels are:

Dedicated Traffic CHannel (DTCH): a point-to-point bi-directional channel, thattransmits dedicated user information between a UE and the network. That information can bespeech, circuit switched data or packet switched data. The payload bits on this channel comefrom a higher layer application (the AMR codec for example). Control bits can be added by theRLC (protocol information) in case of a non transparent transfer. The MAC sublayer will also adda header to the RLC PDU.

Common Traffic CHannel (CTCH): a point-to-multipoint downlink channel for transfer

of dedicated user information for all or a group of specified UEs. This channel is used tobroadcast BMC messages. These messages can either be cell broadcast data from higherlayers or schedule messages for support of Discontinuous Reception (DRX) of cell broadcastdata at the UE. Cell broadcast messages are services offered by the operator, like indication ofweather, traffic, location or rate information.

The control channels are:

Broadcast Control CHannel (BCCH): a downlink channel that broadcasts all systeminformation types (except type 14 that is only used in TDD). For example, system informationtype 3 gives the cell identity.UEs decode system information on the BCH except when incell_DCH mode. In that case, they can decode system information type 10 on the FACH andother important signaling is sent on a DCCH.

Paging Control CHannel (PCCH): a downlink channel that transfers paging information.It is used to reach a UE (or several UEs) in idle mode or in connected mode (cell_PCH orURA_PCH state). The paging type 1 message is sent on the PCCH. When a UE receives apage on the PCCH in connected mode, it shall enter cell_FACH state and make a cell updateprocedure.

Dedicated Control CHannel (DCCH): a point-to-point bi-directional channel thattransmits dedicated control information between a UE and the network. This channel is used fordedicated signaling after a RRC connection has been done. For example, it is used for inter-frequency handover procedure, for dedicated paging, for the active set update procedure and forthe control and report of measurements.

Common Control CHannel (CCCH): a bi-directional channel for transmitting controlinformation between network and UEs. It is used to send messages related to RRC connection,cell update and URA update. This channel is a bit like the DCCH, but will be used when the UEhas not yet been identified by the network (or by the new cell). For example, it is used to sendthe RRC connection request message, which is the first message sent by the UE to get intoconnected mode. The network will respond on the same channel, and will send him itstemporary identities (cell and UTRAN identities). After these initial messages, the DCCH will beused.


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Transport Channel

Figure 8.- Transport Channel.

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

Broadcast CHannel (BCH): a downlink channel used for broadcast of systeminformation into the entire cell.

Paging CHannel (PCH): a downlink channel used for broadcast of control informationinto the entire cell, such as paging.

Random Access CHannel (RACH): a contention based uplink channel used for initialaccess or for transmission of relatively small amounts of data (non real-time dedicated controlor traffic data).

Forward Access CHannel (FACH): a common downlink channel used for dedicatedsignaling (answer to a RACH typically), or for transmission of relatively small amounts of data.

Dedicated CHannel (DCH): a channel dedicated to one UE used in uplink or downlink.


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Physical Channel

A physical channel is defined by a specific carrier frequency, code (scrambling code,spreading code) and relative phase.

In UMTS system, the different code (scrambling code or spreading code) can distinguishthe channels.

Most channels consist of radio frames and time slots, and each radio frame consists of 15time slots.

Two types of physical channel:UL and DL

Figure 9.- Physical Channel

Now we will begin to discuss the physical channel.

Physical channel is the most important and complex channel. A physical channel is definedby a specific carrier frequency, code and relative phase. In CDMA system, the different code

(scrambling code or spreading code) can distinguish the channel. Most channels consist of radioframes and time slots, and each radio frame consists of 15 time slots. There are two types ofphysical channel: UL and DL. Let’s look at the uplink physical channel first.


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Downlink Physical Channel

Figure 10.- Downlink Physical Channels.

The different physical channels are:

Synchronization CHannel (SCH): used for cell search procedure. There is theprimary and the secondary SCHs. Downlink.

Common Control Physical CHannel (CCPCH): used to carry common controlinformation such as the scrambling code used in DL (there is a primary CCPCH and additionalsecondary CCPCH). Downlink.

Common Pilot CHannels (P-CPICH and S-CPICH): used for coherent detection

of common channels. They indicate the phase reference. Downlink.

Dedicated Physical Data CHannel (DPDCH): used to carry dedicated datacoming from layer 2 and above (coming from DCH). Uplink and Downlink.

Dedicated Physical Control CHannel (DPCCH): used to carry dedicated controlinformation generated in layer 1 (such as pilot, TPC and TFCI bits). Uplink and Downlink.

Page Indicator CHannel (PICH): carries indication to inform the UE that paginginformation is available on the S-CCPCH. Downlink.

Acquisition Indicator CHannel (AICH): it is used to inform a UE that the networkhas received its access request. Downlink.

High Speed Packet Downlink Shared CHannel (HS-PDSCH) : it is used to carrysubscribers BE service data (mapping on HSDPA) coming from layer 2.Downlink

High Speed Shared Control Channel (HS-SCCH): it is used to carry controlmessage to HS-PDSCH such as modulation scheme, UE ID etc. Downlink.


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Uplink Physical Channel

Figure 11.- Uplink Physical Channels.

The different physical channels are:

Dedicated Physical Data Channel (DPDCH): used to carry dedicated data comingfrom layer 2 and above (coming from DCH). Uplink and Downlink.

Dedicated Physical Control Channel (DPCCH): used to carry dedicated controlinformation generated in layer 1 (such as pilot, TPC and TFCI bits). Uplink and Downlink.

Physical Random Access Channel (PRACH): used to carry random accessinformation when a UE wants to access the network. Uplink.

High Speed Dedicated Physical Control Channel (HS-DPCCH): it is used to carryfeedback message to HS-PDSCH such CQI, ACK/NACK. Uplink.

Uplink PhysicalChannel

• Uplink Dedicated Physical Channel

– Uplink Dedicated Physical Data Channel(Uplink DPDCH) – Uplink Dedicated Physical Control

Channel (Uplink DPCCH)

– High-Speed Dedicated Physical Channel(HS-DPCCH)

Uplink Common Physical Channel

Physical Random Access Channel(PRACH)


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Figure 12.- Functions of physical channels.

Cell Broadcast Channels

Common Pilot Channel (CPICH)

The Common Pilot Channel (CPICH) is a pure physical control channel broadcasted overthe entire cell. It is not linked to any transport channel. It consists of a sequence of known bitsthat are transmitted in parallel with the primary and secondary CCPCH.

The CPICH is used by the mobile to determine which of the 8 possible primary scramblingcodes is used by the cell, and to provide the phase reference for common channels.

Finding the primary scrambling code is done during the cell search procedure through asymbol-by-symbol correlation with all the codes within the code group. After the primaryscrambling code has been identified, the UE can decode system information on the P-CCPCH.

There are two types of common pilot channels, the primary and secondary CPICH. The useof the S-CPICH is optional.

l Primary Common Pilot Channel (P-CPICH)

The Primary Common Pilot Channel (P-CPICH) has the following characteristics:- The same channelization code always used.- Primary scrambles used.- Only one CPICH in each cell.- Broadcasting in the whole cell.


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The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH. It isbroadcasted over the entire cell. The channelization code used to spread the P-CPICH isalways Cch,256,0 (all ones). Thus, the P-CPICH is a fixed rate channel. Also, it is alwaysscrambled with the primary scrambling code of the cell. Figure 13 shows the structure of theCPICH.

Figure 13.- Primary Common Control Physical Channel structure.

If it is used, the S-CPICH provides the phase reference for the secondary CCPCH and the

downlink DPCH. It is transmitted over the entire cell or only over a part of the cell. It is spreadby an arbitrary channelization code of SF=256, and scrambled with the primary or with asecondary scrambling code.

Il Secondary Common Pilot Channel (S-CPICH)The Secondary Common Pilot Channel (S-CPICH) has the following characteristics:

- Any channelization code with SF = 256 can be used- Primary or auxiliary scrambles may be used- Zero, one or more secondary CPICHs may exist in every cell- Transmission allowed in the whole or part of the cell- The secondary CPICH may be the reference for the secondary CCPCH and downlink

DPCH. In this case, the high-layer signaling will notify the UE.

Common Pilot Channel (CPICH) Carries pre-defined sequence. Fixed rate 30Kbps ， SF=256 Primary CPICH:

Uses the fixed channel code--Cch, 256,0Scrambled by the primary scrambling codeOnly one CPICH per cellBroadcast over the entire cellThe P-CPICH is a phase reference for SCH, Primary CCPCH, AICH,

PICH. By default, it is also a phase reference for downlink DPCH.

Pre-defined symbol sequence

Tslot = 2560 chi s , 20

1 radio frame: Tr = 10 ms


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Primary Common Control Physical Channel (P-CCPCH)

The Primary Common Control Physical Channel (P-CCPCH) is a fixed rate (30 kbps,SF=256) downlink physical channel used to carry the BCH transport channel. It is broadcastedcontinuously over the entire cell like the P-CPICH.

Figure 14.- Primary Common Control Physical Channel.

The figure 14 shows the frame structure of the P-CCPCH. The frame structure is specialbecause it does not contain any layer 1 control bits. The only bits transmitted during a P-CCPCHslot are data bits from the BCH transport channel. It is important to note that the P-CCPCH isnot transmitted during the first 256 chips of the slot. In fact, another physical channel (SCH) istransmitted during that 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. Also, it isalways scrambled by the primary scrambling code of the cell.

The P-CCPCH only has one fix predefined transport format combination.

Fixed rate , fixed OVSF code（ 30kbps ， Cch,256,1） Carry BCH transport channel The PCCPCH is not transmitted during the first 256 chips of each time slot. Only data part STTD transmit diversity may be used


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Synchronization Channel (SCH)

When a UE is turned on, the first thing it does is to scan the UMTS spectrum to find a UMTScell. After that, it has to find the primary scrambling code used by that cell in order to be able todecode the BCCH (for system information). This is done with the help of the SynchronizationChannel.

The SCH is a pure downlink physical channel broadcasted over the entire cell. It istransmitted unscrambled during the first 256 chips of each time slot, in time multiplex with the P-CCPCH. It is the only channel that is not spread over the entire radio frame. The SCH providesthe primary scrambling code group (one out of 64 groups), as well as the radio frame and timeslot synchronization.

The SCH consists of two sub-channels, the primary and secondary SCH. These sub-channels are sent in parallel using code division during the first 256 chips of each time slot.

Primary Synchronization Channel

The P-SCH is repeated at the beginning of each time slot. The same code is used by all thecells and enables the mobiles to detect the existence of the UMTS cell and to synchronize itselfon the time slot boundaries. This is normally done with a single matched filter or any similardevice. The slot timing of the cell is obtained by detecting peaks in the matched filter output.Figure 15 shows the structure of the PSCH.

Figure 15.- Primary Synchronization Channel.

This is the first step of the cell search procedure. The second step is done using thesecondary synchronization channel.

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


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Secondary Synchronization Channel

The S-SCH also consists of a code: the Secondary Synchronization Code (SSC) thatindicates which of the 64 scrambling code groups the cell’s downlink scrambling code belongs to.16 different SSCs are defined. Each SSC is a 256 chip long sequence.

Figure 16.- Secondary Common Control Physical Channel.

There is one specific SSC transmitted in each time slot, giving us a sequence of 15 SSCs.There are a total of 64 different sequences of 15 SSCs, corresponding to the 64 primary

scrambling code groups. These 64 sequences are constructed so that one sequence is differentfrom any other one, and different from any rotated version of any sequence. The UE correlatesthe received signal with the 16 SSCs and identifies the maximum correlation value.

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


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Paging Channels

Secondary Common Control Physical Channel

Figure 17. - Structure of the Secondary Common Control Physical Channel.

The Secondary Common Control Physical Channel (S-CCPCH) is used to carry the FACHand PCH transport channels. Unlike the P-CCPCH, it is not broadcasted continuously. It is onlytransmitted when there is a PCH or FACH information to transmit. At the mobile side, the mobileonly 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 (page indicatorchannel), and it will expect a message on the FACH after it has transmitted something on theRACH.

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

The figure above shows the frame structure of the S-CCPCH. There are 18 different slotformats determining the exact number of data, pilot and TFCI bits. The data bits correspond tothe PCH and/or FACH bits coming from the transport sublayer. Pilot bit are typically used whenbeamforming techniques are used.

The SF ranges from 4 to 256. The channelization code is assigned by the RRC layer as isthe scrambling code, and they are fixed during the communication. They are sent on the BCCHso that every UE can decode the channel.

As said before, FACH can be used to carry user data. The difference with the dedicatedchannel is that it cannot use fast power control, nor softhandover. The advantage is that it is afast access channel.

Carry FACH and PCH.

Two kinds of SCCPCH: with or without

TFCI. UTRAN decides if a TFCI should

be transmitted, UE must support TFCI.

Possible rates are the same as that of

downlink DPCH

SF =256 - 4.

FACH and PCH can be mapped to thesame or separate SCCPCHs. Ifmapped to the same S-CCPCH, theycan be mapped to the same fame.


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Paging Indicator Channel

Figure 17.- Paging Indicator Channel structure.

The Page Indicator Channel (PICH) is a fixed rate (SF=256) physical channel used by thenode B to inform a UE (or a group of UEs) that a paging information will soon be transmitted onthe PCH. Thus, the mobile only decodes the S-CCPCH when it is informed to do so by the PICH.This enables to do other processing and to save the mobile’s battery.

The PICH carries Paging Indicators (PI), which are user specific and calculated by higherlayers. It is always associated with the S-CCPCH to which the PCH is mapped.

The frame structure of the PICH is illustrated above in figure 17. It is 10 ms long, and alwayscontains 300 bits (SF=256). 288 of these bits are used to carry paging indicators, while theremaining 12 are not formally part of the PICH and shall not be transmitted. That part of theframe (last 12 bits) is reserved for possible future use.

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

PICH is a fixed-rate(SF=256) physical channel used to carry the Paging Indicators (PI). PICH is always associated with an S-CCPCH to which a PCH transport channel is

mapped.

Frame structure of PICH ： one frame of length 10ms consists of 300 bits of which 288bits are used to carry paging indicators and the remaining 12 bits are not defined.

N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72, or 144. If a paging indicator in a certain frame is set to 1, it indicates that UEs associated with

this paging indicator should read the corresponding frame of the associated S-CCPCH.


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Random Access Channels

Physical Random Access Channel

The Physical Random Access Channel (PRACH) is used by the UE to access the network

and to carry small data packets. It carries the RACH transport channel. The PRACH is an openloop power control channel, with contention resolution mechanisms (ALOHA approach) to enablea random access from several users.

The PRACH is composed of two different parts: the preamble part and the message partthat carries the RACH message. The preamble is an identifier which consists of 256 repetitionsof a 16 chip long signature (total of 4096 chips). There are 16 possible signatures whichcorrespond to the 16 OVSF codes of SF=16. Basically, the UE randomly selects one of the 16possible preambles and transmits it at increasing power until it gets a response from the network(on the AICH). That preamble is scrambled before being sent. That is a sign that the power levelis high enough and that the UE is authorized to transmit, which it will do after acknowledgmentfrom the network. If the UE doesn’t get a response from the network, it has to select a newsignature to transmit. The message part is 10 or 20 ms long (split into 15 or 30 time slots) and is

made of the RACH data and the layer 1 control information.

Figure 18.- The PRACH transmission structure.

The PRACH transmission is based on the access frame structure. The access frame isaccess 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 least 3 or 4 accessslots between two consecutive preambles.

The random-access transmission data consists of two parts: One or several preambles ： each preamble is of length 4096chips and

consists of 256 repetitions of a signature whose length is 16 chips， 16

available signatures totally

10 or 20ms message part. Which signature is available and the length of message part are determined

by higher layer.


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The PRACH resources (access slots and preamble signatures) can be divided betweendifferent Access Service Classes (ASC) in order to provide different priorities of RACH usage.The ASC number ranges from 0 (highest priority) to 7 (lowest priority).

Figure 19.- PRACH Access timeslot structure.

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

The OVSF codes to use (one for RACH data and one for control) depend on thesignature that was used fo the preamble (for signatures s=0 to s=15: OVSFcontrol=Cch,256,m, where m=16s + 15; OVSFdata= Cch,SF,m, where m=SF*s/16.

Figure 20.- PRACH message structure.


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Acquisition Indicator Channel (AICH)

Figure 21.- Acquisition Indicator Channel structure.

The Acquisition Indicator Channel (AICH) is a common downlink channel used to control theuplink random accesses. It carries the Acquisition Indicators (AI), each corresponding to asignature on the PRACH (uplink). When the node B receives the random access from a mobile,it sends back the signature of the mobile to grant its access. If the node B receives multiplesignatures, it can sent all these signatures back by adding the together. At reception, the UE canapply its signature to check if the node B sent an acknowledgement (taking advantage of the

orthogonality of the signatures).

The AICH consists of a burst of data transmitted regularly every access slot frame. Oneaccess slot frame is formed of 15 access slots, and lasts 2 radio frames (20 ms). Each accessslot consists of two parts, an acquisition indicator part of 32 real-valued symbols and a long partduring which nothing is transmitted to avoid overlapping due to propagation delays.

s (with values 0, +1 and -1, corresponding to the answer from the network to a specific user)and the 32 chip long sequence is given by a predefined table. There are 16 sequences, each corresponding to one PRACH signatures. A maximum of 16 AIs can be sent ineach access slot. The user can multiply the received multi-level signal by the signature it used toknow if its access was granted.

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

Frame structure of AICH： two frames, 20 ms ， consists of a repeated sequence of 15consecutive AS, each of length 20 symbols(5120 chips). Each time slot consists of two

parts， an Acquisition-Indicator(AI) and a part of duration 1024chips with no transmission. Acquisition-Indicator AI have 16 kinds of Signature. CPICH is the phase reference of AICH.


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Dedicated Channels

Uplink Dedicated Physical Channels (DPDCH & DPCCH)

Now look at the feature of uplink dedicated physical channel.

Pilot is used to help demodulate.TFCI: transport format combination indicator.FBI: Used for the FBTD. (Feedback TX diversity).TPC: used to transport power control command.

Dedicated channels are established between one UE and the network to carry userdedicated data and control.

There are two kinds of uplink dedicated physical channels, the Dedicated Physical DataChannel (DPDCH) and the Dedicated Physical Control Channel (DPCCH). The DPDCH isused to carry the DCH transport channel. The DPCCH is used to carry the physical sublayercontrol bits.

There can be up to 6 uplink DPDCHs, but only one DPCCH is associated to these DPDCHs

on each radio link. More than one DPDCH is used for data rates above 960 ksps (maximumcapacity of one DPDCH). Thus, the maximum channel bit rate for one UE is 960 * 6 = 5.76 Mspsin uplink, which can correspond to a user bit rate of 2.048 Mbps.

Figure 22.- Frame structure of uplink DPDCH/DPCCH.

DPDCH and DPCCH are I/Q code multiplexed within each radio frame. DPDCH carries data generated at Layer 2 and higher layer. DPCCH carries control information generated at Layer 1. Each frame is 10ms and consists of 15 time slots, each time slot consists of 2560 chips. The spreading factor of DPDCH is from 4 to 256. The spreading factor of DPDCH and DPCCH can be different in the same Layer 1

connection.

Each DPCCH time slot consists of Pilot, TFCI ， FBI， TPC.


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Downlink Dedicated Physical Channels (DPDCH & DPCCH)

Downlink physical channels are used to carry user specific information like speech, data orsignaling, as well as layer 1 control bits. Like it was mentioned before, the payload from theDPDCH and the control bits from the DPCCH are time multiplexed on every time slot. The figureabove shows how these two channels are multiplexed. There is only one DPCCH in downlink.

Figure 23.- Frame structure of downlink DPCH.

We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed. But thedownlink DPDCH and DPCCH is time multiplexed. This is main difference. The chips of one slotare also 2560. Because the SF of downlink DPCH can be 512, so the k can be 7.

Downlink physical channels are used to carry user specific information like speech, data orsignaling, as well as layer 1 control bits. Like it was mentioned before, the payload from theDPDCH and the control bits from the DPCCH are time multiplexed on every time slot. The figureabove shows how these two channels are multiplexed. There is only one DPCCH in downlink.

Basically, there are two types of downlink DPCH. They are distinguished by the use or nonuse of the TFCI field. TFCI bits are not used for fixed rate services or when the TFC doesn’t

change.

The parameter k in the figure above determines the total number of bits per time slot. It isrelated to the SF, which ranges from 4 to 512.

DCH consists of dedicated data and control information. Control information includes ： Pilot、 TPC、 TFCI(optional). The spreading factor of DCH can be from 512 to 4,and can be changed during

connection. DPDCH and DPCCH is time multiplexed.


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High Speed Downlink Shared Channels

High Speed Physical Downlink Shared Channel

Figure 24.- Structure of High-Speed Physical Downlink Shared Channel (HS-PDSCH).

HS-PDSCH is a downlink physical channel that carries user data and layer2 overhead bitsmapped from the transport channel: HS-DSCH.

The user data and layer2 overhead bits from HS-DSCH is mapped onto one or several HS-PDSCH and transferred in 2 ms subframe using one or several channelization code with fixedSF=16.

Bear service data and layer2 overhead bits mapped from the transport channel. SF=16, can be configured several channels to increase data service.


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High Speed Shared Control Channel HS-SCCH

Figure 25.- High-Speed Shared Control Channel (HS-SCCH).

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

The following information is carried on the HS-SCCH (7 items)1. Modulation scheme (1bit) QPSK or 16QAM2. Channelization Code Set (7bits)3. Transport Size ( 6bits)4. HARQ process number (3bits)

5. Redundancy version (3bits)6. New Data Indicator (1bit)7. UE identity (16 bits)

In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCH carries physical-layer signalling to a single UE. As there should be a possibility for HS-DSCH transmission tomultiple users in parallel (code multiplex), multiplex HS-SCCH may be needed in a cell. Thespecification allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE must beable to decode four HS-SCCH.

Carries physical layer signalling to a single UE ,such as modulation scheme (1bit) ,channelization code set (7 bit), transport Block size (6bit),HARQ process number(3bit), redundancy version (3bit), new data indicator (1bit), Ue identity (16bit).

HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channel used to carrydownlink signalling related to HS-DSCH transmission.


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High-Speed Dedicated Physical Control Channel (HS DPCCH)

Figure 26.- High-Speed Dedicated Physical Control Channel (HS-DPCCH).

The uplink HS-DSCH related physical layer signaling consists of:

1. Acknowledgements for HARQ.2. Channel Quality Indicator (CQI).

As the HS-SCCH uses SF=256, there are a total of 30 channel bits per 2 ms sub frame (3time slot). The HS-DPCCH information is divided in such a way that the HARQ

acknowledgement is transmitted in the first slot of the subframe while the channel qualityindication is transmitted in the rest slot.

HS-DPCCH carries information to acknowledge downlink transport blocks and feedbackinformation to the system for scheduling and link adaptation of transport block.

CQI and ACK/NACK Physical Channel ,Uplink, SF=256,power control.


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Channel Mapping

Mapping between Channels

Figure 27.- Mapping of the logical, transport and Physical channels.

This page indicates how the mapping can be done between logical, transport and physicalchannels. Not all physical channels are represented because not all physical channelscorrespond to a transport channel.

The mapping between logical channels and transport channels is done by the MAC sublayer.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 and DSCH, toDCH and DSCH, to a DCH or a CPCH; CTCH is connected to FACH; DCCH can be connected to either RACH and FACH, to RACH and DSCH, toDCH 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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Physical layer processing procedure

Coding and multiplexing technology

Error detection is provided on transport blocks through a Cyclic Redundancy Check (CRC).The size of the CRC is 24, 16, 12, 8 or 0 bits and it is signalled from higher layers what CRC sizethat should be used for each TrCH.

TB Concatenation and Code Block Segmentation

All transport blocks in a TTI are serially concatenated.

The maximum size of the code blocks depends on whether convolutional coding or turbocoding is used for the TrCH.

Convolutional code: if TBS SIZE>504, segmented to multiple code block of thesame size. Turbo code: if TBS SIZE>5114, segmented to multiple code block of the samesize. No coding: no segmentation. If codes cannot be segmented evenly, fill in “0” bits at the beginning of the firstcode block. If the code block length of Turbo code


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Channel Coding

The following channel coding schemes can be applied to TrCHs:

Convolutional coding, coding rates 1/3 and 1/2 are defined. Turbo coding, The coding rate of Turbo coder is 1/3. No coding.

Usage of coding

BCH、 PCH and RACH——1/2 Convolutional coding.

DCH and FACH——1/2or1/3 Convolutional coding ,1/3Turbo coding, nocoding.

The following channel coding schemes can be applied to TrCHs:

- Convolutional coding;- Turbo coding.

Usage of coding scheme and coding rate for the different types of TrCH is shown in aboveslide.

Multiplexing of TrCH

Every 10 ms, one radio frame from each TrCH is delivered to the TrCHmultiplexing. These radio frames are serially multiplexed into a coded composite

transport channel (CCTrCH).

The format of CCTrCH is indicated by TFCI.

TrCH can have different TTI before multiplexing.

2 types of CCTrCH: Common and dedicated.

Common CCTrCH should be multiplexed by common TrCH; Dedicated CCTrCH should be multiplexed by dedicated TrCH.

There is only one CCTrCH in uplink and one or several CCTrCH in downlink forone user.


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Figure 28.- Example of coding and multiplexing.

Figure 29. - Example of coding and multiplexing.

TrCh#1Transport block

CRC attachment

CRC

Tail bit attachment

Convolutionalcoding R=1/3, 1/2

Rate matching

81

81

303

Tail

893

303+NRM1 1st interleaving

12

Radio framesegmentation

#1a

To TrCh Multiplexing

303 +NRM1

NRF1 = (303 +NRM1)/2

NRF2 = (333+ NRM2)/2

NRF3 = (136+ NRM3)/2

#1b

TrCh#2

103

103

333

Tail

8103

333 +NRM2

#2a

TrCh#3

60

60

136

Tail

860

136 +NRM3

#3a

136 +NRM3

#3b

333 +NRM2

#2b

NRF1 NRF1 NRF2 NRF2 NRF3 NRF3


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Figure 30. - Example of coding and multiplexing (3.4 Kbps).

Figure 31. - Example of coding and multiplexing

Transport block

CRC attachment

CRC

Convolutionalcoding R=1/3

Rate matching

148

148

516*B

Tail

8*B

(516+NRM)*B

1st interleaving

16 bits

Radio framesegmentation

#1

[ (129+NRM)*B+NDI]/

4

To TrCh Multiplexing

(516+NRM)*B+NDI

#2 #4

Tail bit attachment

164*B

#3

TrBk concatination B TrB s (B =0,1)

164*B

(516+NRM)*B+NDI

Insertion of DTXindication*

[ (129+NRM)*B+NDI]/

4

[ (129+NRM)*B+NDI]/

4

[ (129+NRM)*B+NDI]/

4

* Insertion of DTX indication is used only if the position of the TrCHs in the radio frame is fixed.

12.2 kbps data 3.4 kbps data

TrCH

multiplexing

30 ksps DPCH

2nd interleaving

Physical channel

mapping

#1#1a #1c

1 2 15

CFN=4Nslot

Pilot symbol TPC

1 2 15

CFN=4N+1slot

1 2 15

CFN=4N+2slot

1 2 15

CFN=4N+3slot

#1b #2#2a #2c#2b #3#1a #1c#1b #4#2a #2c#2b

#1a #2a #1b #2b #1c #2c #1a #2a #1b #2b #1c #2c #1 #2 #3 #4

510 510 510 510

12.2 kbps data


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Rate Matching

Rate matching means that bits on a transport channel are repeated or punctured.

The number of bits on a transport channel can vary between different transmission timeintervals (TTI). In the downlink the transmission is interrupted if the number of bits is lower than

maximum. When the number of bits between different transmission time intervals in uplink ischanged, bits are repeated or punctured to ensure that the total bit rate after TrCH multiplexing isidentical to the total channel bit rate of the allocated dedicated physical channels.

Rate matching means that bits on a transport channel are repeated or punctured. Theobjective of rate matching is to Balance the multiplexing of Eb/I0 of each TrcH mapped to thesame CCTrCH, to Match channel(uplink) and to Avoid multi-code transmission. Rate matchinghas two types: dynamic matching and static matching.

Interleaving

Function： reduce the influence of fast fading.

Two kinds of interleaving： 1st interleaving and 2nd interleaving.

The length of 1st interleaving is TTI of TrCH, 1st interleaving is a inter-frameinterleaving. The length of 2nd interleaving is a physical frame , 2nd interleaving is a intra-frame

interleaving.

Radio Frame Segmentation

When the transmission time interval (TTI) is longer than 10 ms, the input bitsequence is segmented and mapped onto consecutive Fi radio frames.

Following radio frame size equalisation in the UL the input bit sequence length isguaranteed to be an integer multiple of Fi.

Following rate matching in the DL the input bit sequence length is guaranteed tobe an integer multiple of Fi.

Fi: Number of radio frames in the transmission time interval of TrCH i .

Insertion of discontinuous transmission (DTX) indication bits

In the downlink, DTX is used to fill up the radio frame with bits.

DTX indication bits only indicate when the transmission should be turned off, theyare not transmitted.

1st insertion of DTX indication bits This step of inserting DTX indication bits is used only if the positions of

the TrCHs in the radio frame are fixed.

2nd insertion of DTX indication bits The DTX indication bits inserted in this step shall be placed at the end of

the radio frame.


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Physical Channel Segmentation and Mapping

When multiple physical channels are used, one CCTrCH radio frame can bedivided into multiple physical frames –multicode transmission.

Each physical channel of multicode transmission must have the same SF.

DPCCH and DPDCH of uplink physical channel is code multiplexed.

DPCCH and DPDCH of downlink physical channel is time multiplexed.

Uplink physical channel must be fully filled except when cpmpressed mode isused.

In downlink, the PhCHs do not need to be completely filled with bits that aretransmitted over the air. Values correspond to DTX indicators, which are mapped to theDPCCH/DPDCH fields but are not transmitted over the air.

Figure 32.- Transport channel multiplexing structure for downlink.


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Spreading Technology

Uplink DPCCH/DPDCH Spreading

The DPCCH is always spread by code cc = Cch, 256,0. When only 1 DPDCH exists,(Cd,1 = Cch,SF,k ) k=SF/4.

The code used for scrambling of the uplink DPCCH/DPDCH may be of eitherlong or short type.

Figure 33.- Uplink DPCCH/DPDCH Spreading.

The figure above illustrates the principle of the uplink spreading of DPDCH and DPCCH.First each channel is spread by an OVSF code. As it was mentioned before, channelizationcodes are only used to spread the information in uplink.

The channelization code used for DPCCH is always Cch,256,0 (all ones). If only oneDPDCH is used, it is spread by code Cch,SF,k , where k is linked to SF by k=SF/4. When morethan one DPDCH is used, they will all have a SF equal to 4. DPDCHn is spread by code cd,n =

Cch,4,k , where k=1 for n ∈ {1,2} , k=3 for n ∈ {3,4} , and k=2 for n ∈ {5,6}. Thus, the samechannelization code can be used by two different DPDCHs in uplink. After channelization, thechip rate is equal to 3.84 Mcps.

After channelization, the spread signals are weighted by a gain factor (βc for DPCCH and βdfor all DPDCHs). These gain factors are quantized into 4 bits, giving values between 0 and 1.

There is at least one of the values βc and βd that is equal to 1. These gain factors may vary foreach TFC, and are either signaled or computed.

Then, the streams of chips are summed up giving a multilevel signal. After this addition, thereal-valued chips on the I and Q branches are summed up and treated like a complex-valuedstream of chips. This stream is scrambled by a complex-valued scrambling code. For DPDCHand DPCCH, a unique scrambling code of 38,400 chips (corresponding to one radio frame) is

used. That code can be either of long or short type.

Finally, the complex chips are I and Q multiplexed and sent over the air interface. The resultof all this is a BPSK modulation, which gives us 1 bit per symbol. We will study that part in thenext section.


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There can be up to 6 uplink DPDCHs, but only one DPCCH is associated to these DPDCHson each radio link. More than one DPDCH is used for data rates above 960 ksps (maximumcapacity of one DPDCH). Thus, the maximum channel bit rate for one UE is 960 * 6 = 5.76 Mbpsin uplink, which can correspond to a user bit rate of 2.048 Mbps.

Uplink PRACH Spreading

Message part is shown in the following figure， the value of gain factors is the

same with DPDCH/DPCCH.

Figure 34.- Uplink PRACH Spreading.

This is the PRACH spreading figure. The value of gain factors is the same withDPDCH/DPCCH

The preamble signature s , 0 ≤ s ≤ 15, points to one of the 16 nodes in the code-tree thatcorresponds to channelization codes of length 16. The sub-tree below the specified node is used

for spreading of the message part. The control part is spread with the channelization code cc ofspreading factor 256 in the lowest branch of the sub-tree, i.e. cc = Cch,256,m where m = 16 s +

15. The data part uses any of the channelization codes from spreading factor 32 to 256 in theupper-most branch of the sub-tree. To be exact, the data part is spread by channelization codecd = Cch,SF,m and SF is the spreading factor used for the data part and m = SF s/16.

The scrambling code used for the PRACH message part is 10 ms long, and there are 8192different PRACH scrambling codes defined.

jβccc

cd βd

Sr-msg,n

I+jQ

PRACH message

control part

PRACH message

data partI


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Downlink Spreading

Downlink physical channel except SCH is first serial-to-parallel converted , spread by thespreading code, and then scrambled by a complex-valued scrambling code.

The beginning chip of the scrambling code is aligned with the frame boundary of P-CCPCH.

Each channel have different gain factor.

Figure 35.- Downlink Spreading.

Each pair of two consecutive real-valued symbols is first serial-to-parallel converted andmapped to an I and Q branch. The mapping is such that even and odd numbered symbols aremapped to the I and Q branch respectively.

The I and Q branches are then both spread to the chip rate by the same real-valuedchannelization code Cch,SF,m. The channelization code sequence shall be aligned in time withthe symbol boundary. The sequences of real-valued chips on the I and Q branch are then treatedas a single complex-valued sequence of chips.

Figure 36.- Downlink Spreading.

Each complex-valued spread channel, corresponding to point S in the Figure, is separatelyweighted by a weight factor Gi. The complex-valued P-SCH and S-SCH, are separately weightedby weight factors Gp and Gs. All downlink physical channels are then combined using complexaddition.

I

Data of

physical

channel

except

SCH

S

→→→→P

Cch,SF,m

j

Sdl,n

Q

I+jQ S

Different physical

hannel come from point S

ΣΣΣΣ

G1

G2

GP

GS

S-SCH

P-SCH ΣΣΣΣ


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Modulation Technology

Uplink Modulation

The chip rate is 3.84Mbps. In the uplink, the complex-valued chip sequence generated by the spreading

process is QPSK modulated.

Figure 36. - Uplink modulator.

The complex-valued sequence S after spreading is split into real part and imaginary part.Then the real part is multiplied by cos(wt) after pulse shaping. The imaginary part is multiplied by –sin (wt) after shaping.

Downlink Modulation

The chip rate is 3.84Mbps. In the downlink, the complex-valued chip sequence generated by the spreading

process is QPSK modulated.

Figure 37.- Downlink modulation.

The complex-valued sequence S after spreading is split into real part and imaginary part.Then the real part is multiplied by cos(wt) after pulse shaping. The imaginary part is multiplied by –sin(wt) after shaping.

S

Im{S}

Re{S}

cos(ωt)

Complex-valuedsequenceafterspreading

-sin(ωt)

Splitreal &imagparts

Pulseshaping

Pulseshaping

S

Im{S}

Re{S}

cos(ωt)

Complex-valuedsequenceafterspreading

-sin(ωt)

Splitreal &imagparts

Pulseshaping

Pulseshaping


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Physical Layer Procedures

Synchronization Procedure—Cell Search

Figure 38.- Cell search procedure.

The purpose of the Cell Search Procedure is to give the UE the possibility of finding a celland of determining the downlink scrambling code and frame synchronization of that cell. This istypically performed in 3 steps:

PSCH (Slot synchronization): The UE uses the SCH’s primary synchronization code toacquire slot synchronization to a cell. The primary synchronization code is used by the UE to

detect the existence of a cell and to synchronize the mobile on the TS boundaries. This istypically done with a single filter (or any similar device) matched to the primary synchronizationcode which is common to all cells. The slot timing of the cell can be obtained by detectingpeaks in the matched filter output.

SSCH (Frame synchronization and code-group identification): The secondarysynchronization codes provide the information required to find the frame boundaries and thegroup number. Each group number corresponds to a unique set of 8 primary scrambling codes.The frame boundary and the group number are provided indirectly by selecting a suite of 15secondary codes. 16 secondary codes have been defined C1, C2, ….C16. 64 possible suiteshave been defined, each suite corresponds to one of the 64 groups. Each suite of secondarycodes is composed of 15 secondary codes (chosen in the set of 16), each of which will betransmitted in one time slot. When the received codes matches one of the possible suites, the

UE has both determined the frame boundary and the group number.

CPICH (Scrambling-code identification): The UE determines the exact primaryscrambling code used by the found cell. The primary scrambling code is typically identifiedthrough symbol-by-symbol correlation over the CPICH with all the codes within the code groupidentified in the second step. After the primary scrambling code has been identified, the PrimaryCCPCH can be detected and the system- and cell specific BCH information can be read.


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Synchronization Procedure— Channel Timing Relationship

Figure 39.- Channel timing relationship.

This page shows the transmission timing of the various downlink channels. The 256 chipsgap in the beginning of each of the PCCPCH slots is to accommodate the transmission of theSCH. The SCH is always transmitted from the base station and is transmitted at the same timingreference as the CPICH. The SCCPCH is only transmitted when there is data available.Therefore ,it has its own transmission timing. The timing offset is a multiple of 256 chips. ThePICH has a fixed time offset time offset with respect to the SCCPCH to be able to tell UE thatthere is paging coming on the PCH mapped onto the SCCPCH.


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Random Access Procedure

Figure 40.- The random access procedure.

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 theones previously determined. If there is no access slot available in the selected set, randomlyselect one uplink access slot corresponding to the set of available RACH sub-channels within thegiven ASC from the next access slot set. The random function shall be such that each of theallowed selections is chosen with equal probability.

2. Randomly select a signature from the set of available signatures within the given ASC.

3. Set the Preamble Retransmission Counter to Preamble_ Retrans_ Max.

4. Set the parameter Commanded Preamble Power to Preamble_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 theselected signature is detected in the downlink access slot corresponding to the selected uplinkaccess slot:

A: Select the next available access slot in the set of available RACH sub-channelswithin the given ASC;

B: select a signature;


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C: Increase the Commanded Preamble Power;

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

7. If a negative acquisition indicator corresponding to the selected signature is detected

in the downlink access slot corresponding to the selected uplink access slot, exit the physicalrandom access procedure Signature.

8. If a positive acquisition indicator corresponding to the selected signature is detected,Transmit the random access message three or four uplink access slots after the uplink accessslot of the last transmitted preamble.

9. Exit the physical random access procedure.


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Transmit diversity Mode

Application of Tx diversity modes on downlink physical channel

Figure 41. - Transmit diversity modes.

Transmitter-antenna diversity can be used to generate multipath diversity in places where itwould not otherwise exist. Multipath diversity is a useful phenomenon, especially if it can becontrolled. It can protect the UE against fading and shadowing. TX diversity is designed fordownlink usage.Transmitter diversity needs two antennas, which would be an expensive solutionfor the UEs.

The UTRA specifications divide the transmitter diversity modes into two categories: (1)open-loop mode and (2) closed-loop mode. In the open-loop mode no feedback information fromthe UE to the Node B is available. Thus the UTRAN has to determine by itself the appropriateparameters for the TX diversity. In the closed-loop mode the UE sends feedback information upto the Node B in order to optimize the transmissions from the diversity antennas.

Thus it is quite natural that the open-loop mode is used for the common channels, as theytypically do not provide an uplink return channel for the feedback information. Even if there was afeedback channel, the Node B cannot really optimize its common channel transmissionsaccording to measurements made by one particular UE. Common channels are common foreveryone; what is good for one UE may be bad for another. The closed-loop mode is used fordedicated physical channels, as they have an existing uplink channel for feedback information.Note that shared channels can also employ closed loop power control, as they are allocated foronly one user at a time, and they also have a return channel in the uplink.There are two specifiedmethods to achieve the transmission diversity in the open-loop mode and two methods in closed-loop mode.


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Transmit Diversity-STTD

Space time block coding based transmit antenna diversity(STTD）

4 consecutive bits b0, b1, b2, b3 using STTD coding.

Figure 42.- Transmit Diversity STDD.

The TX diversity methods in the open-loop mode are:

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

(2) time-switched transmit diversity (TSTD).

In STTD the data to be transmitted is divided between two transmission antennas at thebase station site and transmitted simultaneously. The channel-coded data is processed in blocksof four bits. The bits are time reversed and complex conjugated, as shown in figure 42. TheSTTD method, in fact, provides two brands of diversity. The physical separation of the antennasprovides the space diversity, and the time difference derived from the bit-reversing processprovides the time diversity.

These features together make the decoding process in the receiver more reliable. In additionto data signals, pilot signals are also transmitted via both antennas. The normal pilot is sent viathe first antenna and the diversity pilot via the second antenna. The symbol sequence for thesecond pilot is given in the two pilot sequences are orthogonal, which enables the receiving UEto extract the phase information for both antennas.

The STTD encoding is optional in the UTRAN, but its support is mandatory for the UE’sreceiver.


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Transmit Diversity-TSTD

Time switching transmit diversity (TSTD) is used only on SCH channel.

Figure 43.- Transmit Diversity TSTD.

Time-switched transmit diversity (TSTD) can be applied to the SCH. Just as with STTD, thesupport of TSTD is optional in the UTRAN, but mandatory in the UE. The principle of TSTD is totransmit the synchronization channels via the two base station antennas in turn. In even-numbered time slots the SCHs are transmitted via antenna 1, and in odd-numbered slots viaantenna 2. This is depicted 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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WCDMA Radio Interface Physical Layer Confidentiality l

002 wcdma radio interface physical layer

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