4-WR 004 E1 Channel Structure-67

7/30/2019 4-WR 004 E1 Channel Structure-67

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ZTE University univ.zte.com.cnThe information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.

WR_004_E1

WCDMA Basic Theory

Channels Structure and Function

V0507

ZTE University

3G Course Team


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Course Objectives

Classification of channels

Structure and Function of channels


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Structure andFunction of channels

Agenda


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Channel Type

Physical channel

Transport channel

Logical channel

Node BRNC

Physical channel

Transport channel

Logical channel

UE


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Channel Type

Logical channels:

describe what is transported (i.e., the types of

information to be transmitted)

Transport channels:

describe how the logical channels are to be transmitted

Physical channels:

represent the transmission media providing the

platform through which the information is actually

transferred


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WCDMA Channels

Logical

Transport

Characterize how data is transmitted

Provide services to the upper layer

Mapped to physical channels

Common transport channel

Dedicated transport channels Physical

Carry one or more transport channels

Responsible for transporting data over the air

Identified by carrier frequency, orthogonal code, relative phase

One radio frame is: 10 milliseconds in duration

Divided into 15 time slots

Each slot has a duration of 0.625 milliseconds


7/67 ZTE University univ.zte.com.cnThe information contained in the file is solely property of ZTE corporation. Any kind of disclosing without permission is prohibited.

Protocol stack of the Uu interface

L3

control

control

control

control

Logical

Channels

Transport

Channels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCtGC

L2/RLC

MAC

RLCRLC

RLCRLC

RLC

RLCRLC

Duplication avoidance

UuS boundary

BMCL2/BMC

control

PDCPPDCP L2/PDCP

DCtGC

Radio

Bearers

RRC



Concept of channel

PHY layer

MAC layer

RLC layer

Transport channel

Physical channel

Logical channel

L1

L2



Logical Channels

Logical Channel lies between MAC Layer and RLC Layer.

There are the following types of logical channels according

to the content of transport information:

Control Channel (CCH) Broadcast Control Channel (BCCH)Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Traffic Channel (TCH) Dedicated Traffic Channel (DTCH)

Common Traffic Channel (CTCH)



Overview of Logical Channels (1)

Control Channels

Broadcast Control Channel (BCCH)

A downlink channel for broadcasting system control

information

Paging Control Channel (PCCH) A downlink channel that transfers paging information

Common Control Channel (CCCH)

Bi-directional channel for transmitting control information

between network and UEs

Dedicated Control Channel (DCCH)

A point-to-point bi-directional channel that transmits

dedicated control information between a UE and the

network


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Overview of Logical Channels (2)

Traffic Channels

Dedicated Traffic Channel (DTCH)

Point-to-point channel in the uplink or downlink,

dedicated to one UE, for the transfer of user

information

Common Traffic Channel (CTCH)

Point-to-multipoint unidirectional channel fortransfer of dedicated user information for all or a

group of specified UEs


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Transport Channels(1)

The transport channel:

The transport channel primarily defines how data are

transported and in what characteristic they aretransported, for example, interval of transport and the

number and size of blocks transported during each

interval.


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Transport Channel(2)

Random Access Channel (RACH)

Broadcast Channel (BCH)Paging Channel (PCH)

Forward Access Channel (FACH)Common Packet Channel (CPCH)

Common Transport Channels

Dedicated Transport ChannelsDownlink Shared Channel (DSCH)Dedicated Channel (DCH)


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There are the following types of transport channels:

Random Access Channel (RACH):

As an uplink common channel, it is used to transport packets

small in size, for example, initial access information, non-real-

time control information and user information.

Common Packet Channel (CPCH):

Also an uplink common channel, it is used to transport some

burst packets.

Forward Access Channel (FACH):

As a downlink common channel, it is used to transport some

packets small in size.


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Downlink Shared Channel (DSCH):

It is used to bear dedicated control or user information.

Broadcast Channel (BCH):

As a downlink channel, it is used to broadcast information

throughout a cell.

Paging Channel (PCH):

It is used to transport paging and notification information in the

downlink direction.

Dedicated Channel (DCH):

As a bi-directional channel, it is private for each user, and is

used to transport user data and high-layer control information.


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Transport Channels vs. Physical Channels


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Physical Channel

Dedicated Physical Channel (DPCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Uplink Physical Channels

Secondary Common Control Physical Channel (S-CCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P-CCPCH)

Synchronisation Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Downlink Physical Channels

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Dedicated Physical Channel (DPCH)


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Mapping relationship(1)


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Mapping relationship(2)

Transport ChannelsDCH

RACHCPCHBCHFACHPCH

DSCH

Physical ChannelsDedicated Physical Data Channel (DPDCH)Dedicated Physical Control Channel (DPCCH)Physical Random Access Channel (PRACH)Physical Common Packet Channel (PCPCH)Common Pilot Channel (CPICH)Primary Common Control Physical Channel (P-CCPCH)Secondary Common Control Physical Channel (S-CCPCH)

Synchronisation Channel (SCH)Physical Downlink Shared Channel (PDSCH)Acquisition Indication Channel (AICH)Page Indication Channel (PICH)


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Physical Layer (L1)

The specific functions of the physical layer are:

providing data transmission to MAC through the transmission

channel

diversity combination

transmission channel error indication

match of the transmission channel rate to the physical channel after

coding

mapping from CCTrCHs to the physical channel

spread spectrum and modulation/despread and demodulation

frequency synchronization, time synchronization

radio characteristic measurement (SIR and power interference),

closed loop power control, and RF processing


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MAC Layer (L2)

The specific functions of the MAC (Media Access Control) protocol are:

mapping between the logic and transmission channels

selection of an adequate transmission format for every transmission

channel priority processing between UE data streams

multiplex of higher-layer PDU to transmission blocks transmitted to

the physical layer through the transmission channel

multiple of transmission blocks from the physical layer to higher-

layer PDU through the transmission channel


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RLC layer (L2)

The specific functions of the RLC (Radio Link Control) protocol are:

segmentation and reassembly

padding, user data transfer

sequence-based transmission of higher-layer PDU in error

detection, copy check flow control

serial number check of the unauthenticated data transfer mode

protocol error check and recovery, ciphering

on the control plane, it provides the RRC sublayer with signaling

radio bearer services,

on the user plane, it provides service radio bearer services together

with the PDCP sublayer


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PDCP Layer (L2)

The specific functions of PDCP (Packet Data Convergence Protocol) are:

header compression and decompression of IP data streams in the

transmitting and receiving entities respectively

transmission of user data

forwarding of PDCP-SDU sent from a non-access layer to the RLC

layer

multiplex of multiple different RBs to one RLC entity.

PDCP only exists in the packet domain, which is used to adapt differenttypes of network layer protocols to the radio interface


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Broadcast /Multicast Control (BMC)

Supports broadcast/multicast transmission services (Cell

Broadcast messages) in the user plane for common data

transfer in unacknowledge mode

Storage of cell broadcast messages

Traffic volume monitoring and radio resource request

(appropriate CTCH/FACH )

Scheduling of BMC messages

Transmission of BMC messages to the UE

UE: Delivery of Cell Broadcast messages to upper layers.


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RRC (L3)

The specific functions of the RRC protocol are: setup, maintenance and release of a RRC connection between UE

and UTRAN

setup, reconfiguration and release of radio bearer

distribution, reconfiguration and release of radio resources used in

the RRC connection RRC connections mobility function management

routing for the higher-layer PDU

request for QoS control

UE measurement report and report control

outer loop power control

ciphering control, paging

initial cell selection and reselection in the idle mode


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High Layer PDU

RLC SDU

High Layer PDU

RLC

Header

RLC

Header

MAC SDU MAC SDUMAC

Header

MAC

Header

Transport Block Transport Block

CRC CRC

RLC SDU

High Layer

L2 RLC

L2 MAC

L1

segmentation

reassembly

Data Flow in Uu interface


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Function of channels

Agenda


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WCDMA frame structure


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Physical Channels(1)

Radio frame

One radio frame has a period of 10ms, and comprises 15

timeslots with the same length. Corresponding to 38400 chips, it

is a basic unit of the physical layer.

Timeslot

A timeslot is a unit composed of a bit domain, corresponding to

2560 chips. The bit number and structure of a timeslot depends

on the specific type of the physical channel.


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Physical Channels(2)

The frame structure of the physical channels is shown:


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Physical Channel


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WCDMA Downlink Physical Channels

Common Downlink Physical Channels

P-CCPCH Common Control Physical Channel (Primary)

Broadcasts cell site information

Broadcasts cell SFN; Timing reference for all DL

32kps SF 256 continues transmission

SCH Synchronization Channel

Fast Synch. P frame, S slot, time-multiplexed with P-CCPCH

S-CCPCH Common Control Physical Channel (Secondary)

Transmits idle-mode signaling and control information to UE s

Variable rate, with DTX

P-CPICH Common Pilot Channel

S-CPICH Secondary Common Pilot Channel (for sectored cells)

PDSCH Physical Downlink Shared Channel

Transmits high-speed data to multiple users

Dedicated Downlink Physical Channels

DPDCH Dedicated Downlink Physical Data Channel

DPCCH Dedicated Downlink Physical Control Channel

Transmits connection-mode signaling and control to UE s

3GPP TS 25.212


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Downlink Indicator Channels

AICH (Acquisition Indicator Channel) Acknowledges that BS has acquired a UE Random Access attempt

(Echoes the UE s Random Access signature)

PICH (Page Indicator Channel)

Informs a UE to monitor the next paging frame

AP-AICH (Access Preamble Indicator Channel) Acknowledges that BS has acquired a UE Packet Access attempt

Echoes the UE S Packet Access signature)

CD/CA-ICH

Confirms that there is no ambiguity between UE in a Packet Access

attempt

(Echoes the UE s Packet Access Collision Detection signature)

Optionally provides available Packet channel assignments

CSICH

Broadcasts status information regarding packet channel availability


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WCDMA Uplink Physical Channels

Common Uplink Physical Channels

PRACH Physical Random Access Channel

Used by UE to initiate access to BS

PCPCH Physical Common Packet Channel

Used by UE to send connectionless packet data

Dedicated Uplink Physical Channels

DPDCH Dedicated Uplink Physical Data Channel

DPCCH Dedicated Uplink Physical Control Channel

Transmits connection-mode signaling and control to BS

3GPP TS 25.212


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MODULATION

UTRA uses a base spreading rate of 3.84 Mcps in 5 MHZ

bandwidth

Variable data rates are provided

QPSK Modulation (I and Q components)

Reverse-link Mapping DPDCH -> I and DPCCH -> Q.

Forward-link: DPDCH & DPCCH are time

multiplexed into I & Q components.


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Downlink spreading and Modulation


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Uplink spreading and Modulation


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PRACH

Pilot

Npilot

bits

Data

Ndata

bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot

= 2560 chips, 10*2k

bits (k=0..3)

Message part radio frame TRACH

= 10 ms

Data

ControlTFCI

NTFCI

bits


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Synchronization Channel (1)

The Synchronization Channel (SCH) is a downlink signal used for cell

search.

The SCH consists of two sub channels, the Primary and Secondary

SCH.

The 10 ms radio frames of the Primary and Secondary SCH are divided

into 15 slots, each of length 2560 chips.

Structure of synchronization channel


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Synchronization Channel (2)

P-SCH

The Primary SCH consists of a modulated code of length 256 chips

The primary synchronization code (PSC) is transmitted once every

slot

The PSC is the same for every cell in the system.

S-SCH

The Secondary SCH consists of repeatedly transmitting a length 15

sequence of modulated codes of length 256 chips.

the Secondary Synchronization Codes (SSC), transmitted in

parallel with the Primary SCH. Each SSC is chosen from a set of 16 different codes of length 256.

This sequence on the Secondary SCH indicates which of the code

groups the cell's downlink scrambling code belongs to.


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CPICH

Unmodulated code channel with spreading factor 256 which is scrambles

with the cell-specific primary scrambling code.

Provides a known reference signal to aid channel estimation. (Amplitude

and phase information for the Rake receiver and SIR estimator)

There are two kinds of pilot signals

Primary: Cell/sector specific primary scrambling code to be used for

the whole cell/sector

Secondary: A secondary scrambling code with or without a

channelisation code of length 256 to be used in a narrow beam

(Adaptive antennas/Beam steering) e.g. hot spot areas.

Primary CPICH channel power defines the handover regions .I.e. cell

boundaries .By adjusting the CPICH channel powers of two neighbouring

base stations, the traffic load can be balanced between them.


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WCDMA Code Types

Synchronization Codes

Primary Sync. Code: Fixed 256-bit code

Unmodulated fixed for all cells

Helps UE identify the presence of a WCDMA BS

Helps UE achieve Slot Synchronization

Secondary Sync. Codes: 256-bit codes

Unmodulated different for different cells (group 64)

Pilot Codes Common (CPICH) provides coherent reference for UE

receiver

Pilot bits embedded into each time slot of the DCH


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Tasks of Uplink receiver

DPCCH is received and despreaded decoded in a slot by slot

manner while the DPDCH is first buffered and then decodedtogether with other frames that were jointly coded with it

(interleaved)

For every slot

A channel estimate (amplitude and phase) and SIR estimate

are made based on the received pilot bits.

Based on SIR determine downlink power control command

and send it

Decode the TPC bit and adjust downlink transmission power

accordingly

For every second or fourth slot

Decode FBI bits over two or four slots and adjust antenna

phase and/or amplitude accordingly depending on tranmission

diversity mode


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Tasks of Uplink receiver

For every 10 ms frame

Decode TFCI and obtain the bit rate and channel

decoding parameters for DPDCH

For Transmission Time Interval (TTI), i.e. how often datamust be delivered to higher layer protocol (10-80 ms),

decode DPDCH


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Tasks of Downlink receiver

The same as in uplink except

In downlink, the dedicated channel bit rate is constant

(except the bit rate of Downlink Shared Channel DSCH

which can vary)

FBI bits are not used

There is a Common Pilot Channel (CPICH) available which

can be used to increase the accuracy of channel and SIR

estimates

If transmission diversity option is used receiver must

estimate the channel state for the two different pilot patterns

provided by the antennas


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D li k M lti l i


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Downlink Multiplexing


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U li k M lti l i


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Uplink Multiplexing


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Acquisition

On Power-up, the mobile attempts to find a channel.

Node B send s exactly the same 256 chip code in same

slot (Primary SCH)

Mobile achieves slot level synchronization After that, Mobile looks for the 10 msec frame.

Now Secondary SCH is searched.

There are 512 possible cell specific scrambling codes

divided in to 32 groups.

Mobile tries 16 possible codes in parallel.


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Cell search procedure (1)

The cell search is typically carried out in three steps:

Step1:Slotsynchronization

During the first step of the cell search procedure the UE

uses the SCH's primary synchronization code to acquire

slot synchronization to a cell.

This is typically done with a single matched filter (or any

similar device) matched to the primary synchronization

code which is common to all cells. The slot timing of the

cell can be obtained by detecting peaks in the matched

filter output.


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Step2: Frame synchronization and code-group

identification

During the second step of the cell search procedure, the

UE uses the SCH's secondary synchronization code to

find frame synchronization and identify the code group of

the cell found in the first step.

This is done by correlating the received signal with all

possible secondary synchronization code sequences, and

identifying the maximum correlation value. Since the cyclic

shifts of the sequences are unique the code group as well

as the frame synchronization is determined.


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Step3: Scrambling-code identificationDuring the third and last step of the cell search procedure,

the UE determines the exact primary scrambling code

used by the found cell.

The primary scrambling code is typically identified through

symbol-by-symbol correlation over the CPICH with all

codes within the code group identified in the second step.

After the primary scrambling code has been identified, thePrimary CCPCH can be detected and the system- and cell

specific BCH information can be read.

Cell procedure


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Cell procedure

S f


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Summary of the process

ChannelSynchronization

acquiredNote

Primary SCH Chip, Slot, Symbol

Synchronization

Synchronization 256 chips

The same in all cells

Secondary

SCH

Frame Synchronization,

Code Group

(one of 64)

15-code sequence of secondary synchronizationcodes. There are 16 secondary synchronization

codes. There are 64 S-SCH sequences

corresponding to the 64 scrambling code groups 256

chips, different for different cells and slot intervals

Common

Pilot CH

Scrambling code (one of

8)

To find the primary scrambling code from common

pilot CH

PCCPCH Synchronization,

BCCH info

Fixed 30 kbps channel spreading factor 256

RACH d


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RACH procedure

UE decodes BCH to find out the available RACH sub-channels andtheir scrambling codes and signatures

It selects randomly one of the available sub-channels and signatures

The downlink power is measured and the initial RACH power level is

set with a proper margin due to open loop inaccuracy

UE transmits 1 ms long preamble with the selected signature

Node B replies by repeating the preamble using Acquisition Indication

Channel (AICH)

UE decodes AICH message to see whether the NodeB has detected

the preamble If AICH is not detected, the preamble is resend with 1 dB higher

transmit power

If AICH is detected, a 10 or 20 ms long message part is transmitted

with the same power as the last preamble

RACH procedure


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RACH procedure

P k t i d li k


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Packet access in downlink

Forward Access Channel Corresponds to RACH in uplink. I. e. for transmitting control

signaling and small user data packets.

Does not support fast power control, but slow power control based

on received frame quality feedback can be applied if the packet is

long. Macro diversity combining is not supported.

FACH can be decoded by all the users within the cell.

The data rate of FACH should be small to minimize interference.

FACH is usually multiplexed with the paging channel to the same

Secondary Common Physical Channel (S-CCPCH)

Paging


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Paging

Idl t C t d d


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Idle to Connected mode

Cell search procedure by scanning BCH

Camp on a cell

IDLE mode Listens to BCH (In order to communicate with UTRAN)

RRC Connection -> CONNECTED mode

Modes and States - RRC Modes


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Modes and States - RRC Modes


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4-WR 004 E1 Channel Structure-67