UMTS Air Interface Protocols and Channel_SECTION SIX

8/6/2019 UMTS Air Interface Protocols and Channel_SECTION SIX

1/75Informa Telecoms

UMTS System Overview

UMTS Air InterfaceProtocols and Channels


2/75




UMTS Air Interface Protocols and Channels

1. PROTOCOLS THE GENERAL STRUCTURE

1.1 UMTS Planes and Strata 1

1.2 UMTS Radio Interface Protocol Structure 3

1.3 Channels 5

2. RADIO RESOURCES CONTROL (RRC)

2.1 Radio Resources Control Services 72.2 Three Logical Entities within RRC 9

2.3 RRC Service States within the User Equipment 11

2.4 RRC Functions 15

3. PACKET DATA CONVERGENCE PROTOCOL (PDCP) 19

4. BROADCAST/MULTICAST CONTROL PROTOCOL (BMC) 21

5. RADIO LINK CONTROL

5.1 Radio Link Control (RLC) Services 235.2 RLC Functions 27

6. MEDIA ACCESS CONTROL (MAC)

6.1 MAC Overview 29

6.2 Three MAC Logical Entities 31

6.3 MAC Functions 33

7. PHYSICAL LAYER

7.1 W-CDMA Physical Layer Services 35

7.2 Physical Layer Functions 377.3 Multiplexing in the Physical Layer 39

8. CHANNELS

8.1 Logical Channels 41

8.2 Transport Channels 47

8.3 The Physical Channels 57



4/75


1. PROTOCOLS THE GENERAL STRUCTURE

1.1 UMTS Planes and Strata

Information carried across the UMTS Radio Interface will include that for processes

controlled directly by the core network, such as mobility management (mm),connection management (cm) and session management (sm). Such information

passes transparently through the UTRAN without interaction, and forms the

Non Access Stratum, at the higher layers of the protocol stack.

Information which is seen by and interacts with processes within the UTRAN forms

the Access Stratum.

The protocol structure of the UMTS radio interface can be further divided into two

planes. The Control plane involves processes and protocols related to signalling and

control of the data transport, whereas the user plane is devoted to processes acting

on the actual user data, including the data transfer itself.


Informa Telecoms1


5/75

MOBILE

EQUIPMENT

UTRAN CORE

NETWORK

AccessStratum

AccessStratum

Non-Access Stratum

User Plane

Control PlaneAir Interface Iu Interface

Fig. 1 Planes & Strata

2Informa Telecoms


6/75


1.2 UMTS Radio Interface Protocol Structure

At the lowest level is the physical layer, also referred to as Layer 1 in terms of a

standard OSI protocol stack.

Above this lie the MAC (Media Access Control) layer, and then the RLC (Radio Link

Control) protocols. Both of these layers map onto Layer 2 of the OSI Model, the

Data Link layer, and as such are responsible for the reliable transmission of

information across the physical link below.

These three layers are common to both the User and Control Planes in the protocol

architecture. It is above these layers that the Control and User plane protocols differ.

In the User Plane, and still part of Layer 2, two protocols can act on data. These are

PDCP (Packet Data Convergence Protocol), which supports packet data access, andBMC (Broadcast and Multicast Control) which supports broadcast and multicast

access. A third option in the user plane is for direct communication between the

higher layers of the non-access stratum and the RLC protocols.

In the Control plane, the next layer above Radio Link Control level is Radio Resource

Control (RRC). This is equivalent to Layer 3 in the OSI model, i.e. the network layer,

responsible for setting up/releasing connections and hence providing the higher

layers (non-access stratum) with a data pipe.

The term peer entities is used to refer to the same protocol levels/logical entitieswhich are in communication, but located in different physical network entities. For

example the peer entity of RRC in the terminal could be the RRC layer located in the

Node B for one particular process, or the RRC layer in the RNC for another. In certain

situations, the MAC layer may be split between the Serving RNC and the Node B.


Informa Telecoms3


7/75

Control Plane User Plane

Physical Layer

W-CDMA Transmission

L3

L2

L1

MAC

RLC

PDCP BMC

RRC

Control

ACCES

SSTRATUM

NON-ACCESS

STRATU

M

Fig. 2 Radio Interface Protocols (Access Stratum)

4Informa Telecoms

Located in the terminal and either Node B (idle mode)

or SRNC (connected mode)


8/75


1.3 Channels

Layers in a protocol stack communicate with each other by means of Service Access

Points (SAPs). These are the input/output points of interfaces between the layers andhence define the interconnection between the different layers. In defining such

interconnection, SAPs provide a range of well defined services.

Moving from higher layers into the RLC, there will exist one connection (one SAP) per

radio bearer. At lower levels in The UMTS Radio Interface Protocol structure, SAPs

between the various layers define Channels, and it may be that channels entering a

layer may combine (or separate) onto fewer (or more) channels leaving it, through a

mapping function carried out by the protocol layer.

SAPs between the RLC and MAC layers define the Logical Channels. The set of

logical channels is defined in order to transmit each specific type of information that

may be required for communication with the higher layers. A logical channel therefore

determines the kind of information which will be used within it.

SAPs between the MAC and physical layers define the Transport Channels. In moving

down from MAC, these describe how the data is to be transmitted over the air

interface, and with what characteristics.

SAPs between the Physical layer and the actual transmission medium define the

Physical Channels. Each physical channel will have a specific transmission purpose

and characteristic, and it is these physical channels which are differentiated usingchannelisation codes in the W-CDMA spreading process.

Depending on the W-CDMA mode (FDD or TDD), and whether processes refer to

uplink or downlink connections, different numbers of each of these types of channels

may be in operation at different times. However, in every case, there will be a defined

mapping between operating higher and lower layer channels, performed by the

various layers between them.


Informa Telecoms5


9/75

Control PlaneSignalling Radio Bearers

User PlaneRadio Bearers

Physical Layer

W-CDMA Radio Transmission

PhysicalChannels

(separatedby codes)

TransportChannels

LogicalChannels

= Service Access Points

MAC

RLC

Fig. 3 Channels

6Informa Telecoms


10/75


2. RADIO RESOURCES CONTROL (RRC)

2.1 Radio Resources Control Services

Most of the control signalling between the user terminal and the UTRAN consists of

RRC messages. These messages carry all the information required to set-up, modifyand release protocol entities within the layers below. RRC signalling also controls the

mobility of the user terminal when in connected mode, through cell updates,

handovers, and the associated measurements on which these are based.

All higher layer signalling (Mobility Management, Call Management, Session

Management) is also encapsulated into RRC messages for transmission over the

radio interface.

The RRC includes various control interfaces enabling it to configure the

characteristics of the lower layer protocol entities, and thus affect the parameters for

setting up logical, transport and physical channels for example. The control interfaces

are also used to command the lower layers to make certain types of measurements,

and for the lower layers to report back these results and any error messages to the

RRC.


Informa Telecoms7


11/75

CORENETWORK

* Terminates either at Node B or Serving RNC within UTRAN

UE

*UTRAN

ACCESS

STRATUM

RRC

LAYERS 1&2*

CONTROL PLANE

NAS Signalling

Fig. 4 Radio Resources Control Services

8Informa Telecoms

Control signalling between UTRAN and user terminal

Set-up, modification and release of lower layer protocols

Control of mobility of connected terminal

Control of parameters for Channels

Measurement Commands to lower layers

Encapsulation of Non-Access Stratum Signalling


12/75


2.2 Three Logical Entities within RRC

Radio Resources Control provides a number of services to the higher layers within

the non-access stratum. These are classified into three types, handled by threedifferent entities defined within the RRC protocol:

broadcast services, targeted at multiple users and broadcasting non access stratum

information in a certain geographical area. The Broadcast Control Function Entity

(BCFE) is responsible for broadcasting system information, and one is implemented

for each cell.

paging and notification services, targeted at specific users in a certain geographical

area. The Paging & Notification control function entity (PNFE) handles this paging,

and one PNFE is allocated for each cell. Paging messages are intended for idle

mode terminals, and if a message is incoming from the higher layer, PNFE checks

whether the paged terminal already has a RRC signalling connection.

dedicated control services, support ing specific service types and their required

radio interface operation. This includes the establishment and release of a

connection, and the transfer of messages using this connection. The Dedicated

Control Function Entity (DCFE) handles all these functions and signalling, which are

specific to one UE.


Informa Telecoms9


13/75

DCFE(Dedicated)

(Per UE withRRC Connection)

PNFE(Paging &

Notification)(Per Cell)

BCFE(Broadcast)(Per Cell)

Message Routing

Fig. 5 RRC Logical Entities

10Informa Telecoms


14/75


2.3 RRC Service States within the User Equipment

The two basic operational modes of a user terminal with respect to RRC are idle

mode and connected (or dedicated) mode.

In idle mode, the peer entity of the RRC within the terminal is the RRC layer at the

Node B, whereas in connected mode the peer entity is the RRC layer at the Serving

RNC.

Idle Mode:

After turning on its power, a terminal stays in idle mode until it transmits a request

to establish a RRC connection. In this mode, the terminal can receive system

information and cell broadcast messages.

It is identified by non-access stratum identities such as the IMSI (international mobilesubscriber i.d.), or a TMSI (temporarily allocated Mobile Station I.D.) and the UTRAN

has no information about the individual idle mode terminals. Therefore it can only

address all such terminals in a cell by using a paging message.

Connected mode, following the establishment of a RRC connection, can be further

subdivided into service states, on the basis of the kind of channels the terminal is

using.

Cell_DCH:

A dedicated* physical channel is allocated to the terminal, and the terminal isknown by its serving RNC by means of a User Radio Network Temporary Identifier

(U-RNTI) and a Cell RNTI (C-RNTI).

Cell_FACH:

No dedicated physical channel is allocated to the terminal, and other common*

channels are instead used for transmitting signalling messages, plus small amounts

of user data. The terminal can also listen to the broadcast system information, for

general signalling messages.

The terminal can perform cell reselections, sending a cell update message to the

RNC and is identified by the C-RNTI on a cell level. Several terminals in a cell are

separated within the MAC layer.

Cell_PCH:

The user is only reachable via paging messages, and listens to the broadcast

channel and to cell broadcast services. In case of a cell re-selection, the terminal

will change to the Cell_FACH state in order to perform the cell change and inform

the RNC and then fall back to Cell_PCH if no other activity is triggered. Since the

paging channel includes a discontinuous reception functionality, the advantage of

Cell_PCH is that battery consumption is less than in the Cell_FACH state.


Informa Telecoms11



IDLE MODE No information within UTRAN

Cell_FACH Common channels Known by RNC C-RNTI

Cell_DCH Dedicated channel Known by RNC:

C-RNTI, U-RNTI

Cell_PCH Power save mode

URA_PCH Power save mode

CONNECTE

DMODE

RRCConnection

Release

RRCConnect

Cell

Update

Fall-

back

Fall-backURA

Update

RRCConnection

Release

RRCConnect

Fig. 6 RRC Service States


16/75


URA_PCH is a similar mode to Cell_PCH, except that the terminal does not execute a

cell update after each cell re-selection, but instead reads UTRAN Registration Area

(URA) identities from the broadcast channel. Only if this URA changes does it need to

inform the serving RNC.

A UE leaves one of these connected modes and returns to idle mode when the RRC

connection is released or at a RRC connection failure.

* A dedicated channel is one whereby the identity of the user terminal is known simply on the basis of

the channel itself (i.e. through unique allocation of the frequency, code and, if applicable, time slot).

So an essentially point-to-point link exists between UTRAN and terminal. Connections other than

Cell_DCH are based on common channels, ones intended for use by a number of users, and hence

are point to multipoint. Signals intended for specific users within a common channel must be identified

in band.


Informa Telecoms13



IDLE MODE No information within UTRAN

Cell_FACH Common channels Known by RNC C-RNTI

Cell_DCH Dedicated channel Known by RNC:

C-RNTI, U-RNTI

Cell_PCH Power save mode

URA_PCH Power save mode

CONNECTE

DMODE

RRCConnection

Release

RRCConnect

Cell

Update

Fall-

back

Fall-backURA

Update

RRCConnection

Release

RRCConnect

Fig. 6 RRC Service States


18/75


2.4 RRC Functions

In order to provide the necessary services, a number of functions are performed

within RRC. These are as follows:

Broadcasting of signalling and control information, originating from both the access

stratum (i.e. from the Node B or RNC) or the non-access stratum (the core network).

Paging & notification, for one of three purposes:

the set-up of calls or sessions originating from the core network

changing the RRC state of a terminal

indicating changes in system information

The establishment, maintenance and release of RRC connections. Only one

(or zero) connection can exist between the UTRAN and any one terminal. Where

multiple higher-layer signalling connections exist between the terminal and the core

network, these will share a single RRC connection.

The establishment, maintenance and release of radio bearers and resources,

through control of transport and physical channels. Although the channel

establishment services are actually performed in the lower layers, RRC provides

control by means of its control interfaces to these layers.

Various mobility functions, including tracking the user terminals location, performing

various handover functions, cell updates and terminal identification updates.

Initial cell selection & re-selection in Idle mode.

Downlink Outer loop power control (setting Signal to Interference Ratio targets), and

open loop power control (initial power estimates).

Arbitration of radio resources shared between multiple users on the uplink

dedicated channel.

Management of radio resources between the different cells.

Routing of higher layer packet data units, for example, messages related to mobility,

session and connection management.

Control of security functions (ciphering & deciphering) performed in the RLC

or MAC layers.

Control of congestion.


Informa Telecoms15



Fig. 7 RRC Functions

Broadcasting Control Information

Paging and Notification

Establishment, maintenance and release of RRC Connection

Control of Transport and Physical Channel resources

Mobility functions

Cell selection and re-selection in Idle Mode

Downlink Outer and Open Loop power control

Radio Resource Arbitration between users

Radio Resource Management between cells

Routing Non-Access Stratum data

Control of RLC & MAC Security functions

Congestion Control

QoS Control

Integrity Protection of signalling messages

Control of terminal measurement reporting

Timing Advance in TDD mode

Various ODMA mode functions


20/75


QoS control

Integrity protection of signalling messages, using a check-sum algorithm.

Control of terminal measurement reporting, i.e. letting it know what to report and

when, and forwarding of these reports to the RNC.

Optional timing advance in TDD mode, used to avoid interference between

consecutive timeslots in large TDD cells. Since other practical considerations mean

that TDD is likely to be used only for small cells, this is unlikely to be used in

practice.

Various additional functions, such as slow dynamic channel allocation & relay, which

are relevant to the ODMA relay mode of operation.


Informa Telecoms17



Fig. 7 RRC Functions

Broadcasting Control Information

Paging and Notification

Establishment, maintenance and release of RRC Connection

Control of Transport and Physical Channel resources

Mobility functions

Cell selection and re-selection in Idle Mode

Downlink Outer and Open Loop power control

Radio Resource Arbitration between users

Radio Resource Management between cells

Routing Non-Access Stratum data

Control of RLC & MAC Security functions

Congestion Control

QoS Control

Integrity Protection of signalling messages

Control of terminal measurement reporting

Timing Advance in TDD mode

Various ODMA mode functions


22/75


3. PACKET DATA CONVERGENCE PROTOCOL (PDCP)

The PDCP only exists for packet switched domain services, in the user plane.

Its functions are as follows:

Mapping of packet data units from a higher level network protocol onto one RLC

entity at the layer below. Currently the network protocols IPv4 and IPv6 are

supported, although the overall aim of PDCP is to make the different possible

network layer protocols transparent to the underlying transmission. Therefore in

future it is likely that updates will enable support for other or entirely new protocol

mapping within the PDCP.

Compression or decompression of any redundant control information such as

TCP/IP headers. This header compression tends to be the main function of PDCP,

and is used for increasing efficiency within the channels below.

The services offered to the higher layers by PDCP are called radio bearers.


Informa Telecoms19


23/75

To NAS Control Plane To NAS User Plane

Physical Layer

L2

L1

MAC

RLC

PDCP BMC

RRC

SignallingRadioBearers

RadioBearers

Fig. 8 Packet Data Convergence Protocol Services

20Informa Telecoms

Mapping higher layer protocols onto RLC

Compression/decompression of headers

Offers Radio Bearers to higher layers


24/75


4. BROADCAST/MULTICAST CONTROL PROTOCOL (BMC)

BMC is used to convey messages from the Cell broadcast Centre, and lies in the user

plane of the protocol architecture.

On the UTRAN side, the BMC must store Cell Broadcast Messages received over theCBC-RNC interface (IuBC), and schedule transmission on to the users.

On the terminal side, BMC delivers received messages to the upper protocol layers in

the user equipment.

In Release 99 the only service specified is the SMS Cell Broadcast service derived

from GSM. The service offered by the BMC to higher layers in the protocol stack is

called a radio bearer.


Informa Telecoms21


25/75


Physical Layer

MAC

RLC

PDCP BMC

RRC


RadioBearers

Fig. 9 Broadcast/Multicast Control Protocol Services

22Informa Telecoms

Store and forward of Cell Broadcast Messages

(SMS Cell Broadcast in Release 99)

Deliver received messages to higher layers in the terminal,

via radio bearers


26/75


5. RADIO LINK CONTROL

5.1 Radio Link Control (RLC) Services

The RLC is responsible for connection management and control of radio links,

providing segmentation & retransmission services for both user and control data.In the control plane, the services provided to higher layers are known as Signalling

Radio Bearers, used as they are by the RRC for signalling transport.

In the User plane, services provided by RLC are known simply as Radio Bearers. For

packet user data, or broadcast, the Radio Bearer would include the service-specific

protocol layers (PDCP or BMC). But for circuit switched type user data the Radio

Bearer service is provided directly by RLC for other higher-layer user plane functions,

such as speech codec.

Each RLC instance is configured by RRC to operate in one of three modes of data

transfer. These are:

Transparent

Unacknowledged

Acknowledged

Each mode provides a different set of services defining the use of that mode by the

higher layers. Transfer of user data is a service which is common to all three modes.

Transparent mode is defined for quick and dirty data transfer across the radio

interface, and is the only one of the three modes which does not involve the addition

of any header information onto the data unit. Erroneous data units are discarded or

marked as erroneous.

Transparent mode is the mode normally used by both the PNFE and BCFE entities

within RRC, for paging/notification and cell broadcast messaging.

In Unacknowledged mode, as in transparent mode, no retransmission protocol is

used, and so data delivery is not guaranteed. Received erroneous data can be either

marked or discarded, depending on configuration.

For both Transparent mode data transfer & unacknowledged mode data transfer, RLC

provides a function for the segmentation of large data units into smaller ones (and

re-assembly at the receive end). The segment lengths are defined when the channel

is established. In unacknowledged mode, segment lengths are given by a length

indicator which is within the header added to the data unit.

Unacknowledged mode additionally provides a service whereby small packet data

units can be concatenated together (again indicated within a header field), a ciphering

service, and a sequence number check which allows the receiver to check whether or

not data has been lost.


Informa Telecoms23


27/75


Physical Layer

MAC

RLC

PDCP BMC

RRC


RadiBear

Fig. 10 RLC Services

24Informa Telecoms

Transparent

Unacknowledged

Acknowledged


28/75


Acknowledged mode provides a much more reliable mechanism for transferring

data between two RLC layer entities, by including further services. These include

in-sequence delivery of data units, detection of duplicate data units, error correction

and flow control. The RLC can also set QoS levels and notify higher layers ofunrecoverable errors.

Acknowledged mode is the mode used mainly by the DCFE entity within RRC, for

dedicated control functions, although in some cases the other modes can be used,

for example unacknowledged mode for RRC release, or transparent mode for cell

update or RRC connection re-establishment requests.

For all three modes, CRC (cyclic redundancy check) error detection is performed on

the physical layer, and the result is delivered to RLC along with the actual data.

[CRC is a method for checking the accuracy of a digital transmission over a

communications link. The sending entity performs a calculation on the data and

attaches the resulting value. The receiving entity performs the same calculation and

compares its result to the original value. If they do not match, a transmission error

has occurred].


Informa Telecoms25


29/75

Transparent Unacknowledged Acknowledged

RRC USER

Fig. 11 RLC Data Transfer Modes

26Informa Telecoms

Header Retransmission

Segmentation

Concatenation

Ciphering (MAC)

Missing Data Check

CRC Check

In-sequence Delivery Duplication Detection

Error Correction

QoS Setting

User data uses AM (e.g. Packet based services), UM (e.g. VoIP), or Tr

(e.g. streaming)

Normal RLC Modes used by each RRC entity are shown

DCFE will use a number of Signalling Radio Bearers to distinguish and

prioritise different signalling types (e.g. prioritise UE-UTRAN signalling

over UE-CN)


30/75


5.2 RLC Functions

In order to provide the necessary services, a number of functions are performed

within RLC. These are as follows:

segmentation & reassembly of variable length higher layer data units into (or from)

smaller RLC units. The size of these is set according to the smallest possible bit-

rate for the service which is using the RLC entity. For variable bit-rate services, for a

time interval in which the bit-rate is higher than the smallest one, several RLC units

will be transmitted.

concatenation, in the case where higher layer data units do not fill a whole number

of RLC units. In this case the first segment of the next higher layer unit may be

added to the RLC unit containing the last segment of a previous higher layer unit.

padding, used where concatenation is not applicable (transparent mode) yet higher

layer units again dont fill the RLC units. This simply involves adding padding bits to

the remainder of the RLC data field.

transfer of user data, support ing the transparent, unacknowledged and

acknowledged modes, and controlled by a QoS setting.

error correction, relevant to acknowledged mode, where retransmission can occur.

in-sequence delivery, preserving the order of higher layer data units which are to be

transferred using acknowledged mode data transfer.

detection of duplicated received RLC data units, and making sure that only one is

delivered on to the higher layer.

flow control, which allows an RLC receiver to control the rate at which the peer RLC

entity at the transmission end can send information.

sequence number checking, in unacknowledged mode, which makes sure that

reassembled data units are not corrupted. If they are, then they will be discarded.

detection of, and recovery from, errors which occur during operation of the RLC

protocol.

ciphering is performed in the RLC for acknowledged and unacknowledged mode

data transfer. (For transparent mode transfer, ciphering is performed in the MAC.)

suspend/resume of data transfer, used during the security procedure, and

commanded by the RRC via the control interface.


Informa Telecoms27


31/75

Fig. 12 RLC Functions

28Informa Telecoms

Segmentation and re-assembly

Concatenation

Padding

Data transfer

Error correction

In-sequence delivery

Duplicate detection

Flow control

Sequence number check

Error recovery

Ciphering

Suspend/resume data transfer


32/75


6. MEDIUM ACCESS CONTROL (MAC)

6.1 MAC Overview

The MAC layer offers data transfer services to the RLC layer via Logical Channels.

These Services are characterised by the type of data that is transmitted, and aremapped onto the Transport Channels by MAC. The MAC layer is responsible for

selecting an appropriate transport format (TF) for each transport channel.

Between peer MAC entities, the transport service is unacknowledged and

un-segmented.

MAC will select an appropriate TF for each transport channel, depending on the

source rate of the logical channel to which the transport channel is to be mapped.

A TF will be applicable during a specified transmission time interval.

Single TFs may be associated with transport channels which have a very slowchanging or fixed rate, whereas fast changing transport channels will be associated

with a TF Set, which includes one TF for each rate during the transmission time

interval.

Each TF defines the format offered by the physical layer to MAC (and vice versa) for

the delivery of a set of Transport Blocks, each block typically corresponding to a RLC

data unit. This format will describe a combination of encodings, interleaving, bit rate

and mapping of the transport onto the physical channels.

MAC also performs radio resources allocation and re-allocation, under the control ofRRC. As well as actions regarding transport formats, this additionally includes

changing the identity information of the mobile equipment and any measurement

reporting and quality information provision as requested by higher layers through

control interfaces.


Informa Telecoms29


33/75

MAC

RRC

TransportChannel

TransportChannel

Fixed-rateLogicalChannel

RadioResourceAllocationFunctions

Mapping& TF

Mapping& TFCS

MultirateLogicalChannel

RLC Data Units

TF Transport Format (Describes a combination ofencodings, bit rate, interleaving and mapping)

TFCS Transport Format Combination Set

Fig. 13 MAC Overview

30Informa Telecoms


34/75


6.2 Three MAC Logical Entities

The MAC layer has three subdivisions (three logical entities), each related to particular

groups of logical channels.

MAC-b handles information mapped from the logical and transport channels

associated with broadcast. There is one MAC-b entity in each user terminal, and one

in the Node B for each cell.

MC-c/sh handles messages carried on common and shared Channels. There is one

MAC-c/sh in each terminal which is using shared channels, and one in the controlling

RNC for each cell.

MAC-d handles dedicated channels, those allocated specifically to a mobile which is

in RRC connected mode. There is one MAC-d entity in the terminal, and one for eachterminal in the Serving RNC.


Informa Telecoms31


35/75

MAC-d(SRNC)

MAC-b(Node B)

Broadcast

Information

LogicalChannels

TransportChannels

MAC-c/sh(CRNC)

Common &

Shared Channels

Dedicated Channels

(RRC Connected)

Fig. 14 MAC Logical Entities

32Informa Telecoms


36/75


6.3 MAC Functions

MAC performs the following functions:

mapping between the logical and transport channels.

selection of Transport Formats for each transport Channel.

priority handling between data flows related to one user terminal, achieved by

selecting high or low bit rate transport formats for the different data flows.

priority handling between different user terminals for common or shared downlink

transport channels. For dedicated transport channels, such priority handling has

already been performed by RRC as part of the reconfiguration function.

identification of different user terminals, on occasions when dedicated-type data

from logical channels is carried over common transport channels. To do this, the

C-RNTI or UTRAN RNTI (U-RNTI) is included in the MAC header. This process is

relevant to actions such as paging or random access attempts, for example.

Ciphering is performed within MAC if a logical channel is using the transparent RLC

mode.

multiplexing/demultiplexing of higher layer data units into/from transport blocks

delivered to/from the physical layer on common transport channels. Service

multiplexing for these common channels cannot be done in the physical layer,

hence this function falls within MAC.

multiplexing/demultiplexing of higher layer data units into/ from sets of transport

blocks delivered to/from the physical layer on dedicated transport channels.

Although the physical layer makes it possible to multiplex any type of service,

multiplexing within MAC is only possible for services with the same QoS

parameters.

Traffic volume monitoring, reporting to the RRC. Measurements reported to the RRC

may be used to trigger reconfiguration of radio bearers and transport channels if theamounts of data being transmitted are too high or too low to make most efficient

use of the assigned bearers/channels.

dynamic transport channel type switching, which involves switching between

common and dedicated transport channels, based on decisions derived from RRC.

Access service class selection, used to prioritise usage of the Random Access

channel.


Informa Telecoms33


37/75

Fig. 15 MAC Functions

34Informa Telecoms

Mapping between logical and transport Channels

Selection of Transport Formats

Priority handling (between data

flows/terminals)

Terminal identification where dedicated logical

channel data maps to common transport

channels

Ciphering (transparent RLC mode)

Multiplexing/demultiplexing of higher layer data

to/from transport blocks or sets delivered

to/from the physical layer on transport channels

Transport volume monitoring

Switching between common and dedicated

transport Channels

Access service class selection


38/75


7. PHYSICAL LAYER

7.1 W-CDMA Physical Layer Services

Physical Layer Services are offered to the MAC layer above as transport channels,

which define how and with what characteristics data are transferred over the airinterface. The physical layer maps these transport channels onto different physical

channels.

The physical layer also sets up certain physical channels which have no mapping to

the higher layers, but which are nevertheless essential to system operation and which

carry information relevant to physical layer procedures.

The physical layer must support variable bit-rate transport channels, be able to offer

bandwidth-on-demand services, and multiplex several services onto a single

connection.

Processes within the physical layer relate to achievable performance, for example

capacity and coverage issues, and have a major impact on equipment design,

complexity and cost.


Informa Telecoms35


39/75

PHYSICAL LAYER

Mapping&Multiplexing

Transport Channels

Physical Channels

Fig. 16 Physical Layer Overview

36Informa Telecoms


40/75


7.2 Physical Layer Functions

The Physical layer performs a number of functions, summarised below:

The mapping of t ransport channels onto physical channels. Each transport channel

arriving at the physical layer is accompanied by a Transport Format Indicator (TFI).

The Physical layer combines different TFIs from different transport channels into a

Transport Format Combination Indicator (TFCI). The TFCI is transmitted within a

physical control channel to inform the receiver which channels are active for a

particular frame, whilst the actual transport block is transmitted within a physical

data channel. Within the receiving physical layer, the TFCI is decoded and the

resulting TFIs are given to the higher layers for each active transport channel.

User data transmission and signalling data transmission entering in transport

channels, which are then multiplexed by the physical layer.

Multiplexing and demultiplexing of Coded Composite Transport Channels (CCTrCh).

A CCTrCh is made up of a single physical control channel, and one or more

physical data channels.

Spreading/despreading & Modulation, separating different transmissions from a

single source using channelisation codes. The application of further scrambling

codes is used to separate transmissions from different sources, although without

further spreading.

Forward error correction encoding/decoding, and error detection on transportchannels, which is indicated to higher layers through control interfaces.

Interleaving and de-interleaving of transport channels

Rate Matching, a process of matching the number of bits to be transmitted with the

number of bits available in a single frame. Processes of puncturing or repetition are

used in order to achieve this.

Fast closed loop power control, in order to overcome the uplink near-far problem,

and execute soft handover.

Open loop power control, in order to estimate power requirements when a mobilefirst sets up a connection.

Macro-diversity combining.

Power weighting & combining of physical channels.

Frequency & Time synchronisation.

Measurement and measurement reporting for higher layers (for example Signal

Interference Ratio, Interference Power, Transmit Power and so on).

RF Processing.

Various specific TDD operations, including Timing Advance and synchronisation.


Informa Telecoms37


41/75

Fig. 17 Physical Layer Functions

38Informa Telecoms

Mapping Transport Channels to Physical Channels

and combining Transport Format Indicators (TFCIs)

Data transmission

Multiplexing of Transport Channels

Spreading/despreading and Modulation

Forward Error Correction

Transport Channel error detection

Interleaving/de-interleaving of Transport Channels

Rate Matching

Fast Closed Loop power control

Open Loop power control

Macro-diversity combining

Power weighting and combining of physical channels

Frequency & Time Synchronisation

Measurement reporting

RF Processing

Specific TDD operations (Timing Advance)


42/75


7.3 Multiplexing in the Physical Layer

Services are multiplexed dynamically within the physical layer, so that the data stream

is continuous.

Considering the uplink example, the functional steps involved in multiplexing can be

summarised as follows.

The first steps are performed on each transport channel

CRC attachment, to be checked and an indication passed up to the higher layers at

the receiving side.

Concatenation or segmentation of transport blocks.

Channel coding.

Radio Frame equalisation, which ensures that data can be divided into equal-sized

blocks when transmitted over more than a single 10ms frame. This is done by

padding the necessary number of bits until the data can be divided into equal sized

blocks per frame.

Interleaving.

Radio frame segmentation.

Rate Matching.

Different transport channels are then mutliplexed on a frame-by-frame basis, with

each transport channel providing data in 10ms blocks for this operation.

There may then be segmentation into different physical channels if more than one

spreading code used, followed by 10ms frame interleaving, applied to each physical

channel.

Finally, the output from this interleaving is mapped onto the physical channels. The

number of bits at this stage for a physical channel is exactly the number that thespreading factor of that frame can transmit (or zero if the physical channel is not to

be transmitted).

The processes of downlink multiplexing are similar to the uplink, although with some

slight differences in the order of some functions, plus an indication function

associated with the support for discontinuous transmission.


Informa Telecoms39


43/75

CRC Attachment

Transport BlockConcatenation/Segmentation

Channel Coding

Radio Frame

Equalisation

Interleaving

Radio FrameSegmentation

Rate Matching

Transport ChannelMultiplexing

Physical ChannelSegmentation

Interleaving

Physical ChannelMapping

Other Transport

Channels

Fig. 18 Physical Layer Multiplexing (uplink example)

40Informa Telecoms


44/75


8. CHANNELS

8.1 Logical Channels

Moving down through the UMTS radio interface protocol stack, the first set of

channels which are defined are the Logical Channels. These are offered by the MAClayer to the RLC protocols, and a set of logical channel types is defined for the

different kinds of data transfer services.

Each logical channel type is therefore defined by the type of information transferred,

and fall into one of two basic groups. These are:

Control Channels, for control plane information

Traffic Channels, for user plane information

8.1.1 Logical Traffic Channels:

There are just two channels defined for user plane information, as follows:

CTCH Common Traffic Channel

This is a point-to-multipoint channel, and hence is relevant to communication on the

downlink only. It is used for transferring dedicated user data intended for all or a

group of specified terminals.

DTCH Dedicated Traffic Channel

The DTCH channel contrasts with CTCH in being a point-to-point channel it is

dedicated to just one mobile for the transfer of user information. This channel can

exist in both downlink and the uplink directions.


Informa Telecoms41


45/75

MAC

PHYSICAL

Fig. 19 Logical Traffic Channels

42Informa Telecoms

uplink downlink

CTCH Common Traffic Channel

DTCH

Dedicated Traffic Channel


46/75


8.1.2 Logical Control Channels:

In the Control Plane, there are five logical channels, as follows:

BCCH Broadcast Control Channel

The BCCH is used to carry control and signalling information which is to be

broadcast, and therefore is only applicable in the downlink direction.

When mapped through the lower layers, it will eventually be carried on a physical

channel which uses the same channelisation code in all cells (specifically a channel

known as the Primary Common Control Physical Channel, PCCPH). This means that

its messages can always be read by a mobile terminal, once the terminal has

detected a base stations unique scrambling code, which it does during its initial cell

search.

PCCH Paging Control Channel

This channel is used to carry paging requests. It is therefore a downlink-only channel

and is used either when the network does not know the location cell of the mobile

equipment, or when the mobile is in the RRC connected state Cell_PCH, utilising

sleep mode procedures to preserve battery power. (Also applies to URA_PCH,

which is similar to the Cell_PCH state except that location updates to the UTRAN are

performed on an UTRAN Routing Area (URA) basis, rather than a cell basis).

CCCH Common Control Channel

CCCH is a channel used for transmitting control information between the network andmobiles, and is applicable in both the uplink and downlink directions. As a common

channel, it is a resource which carries control information to and from a number of

different mobiles. It is commonly used by mobiles which currently have no RRC

connection with the network, and by those accessing a new cell after cell

re-selection.

DCCH Dedicated Control Channel

By contrast with CCCH, DCCH is a multi-purpose, point-to-point channel which is

used to carry dedicated control information, i.e. information specific to a single

mobile. It is established when a RRC connection is set-up, and is applicable in bothuplink and downlink directions.


Informa Telecoms43


47/75

MAC

PHYSICAL

Fig. 20 Logical Control Channels

44Informa Telecoms

uplink downlink content

BCCH broadcast

Broadcast Control information

PCCH paging

Paging Control requests

CCCH control

Common Control information

DCCH control info for

Dedicated Control a single mobile


48/75


8.1.3 Logical Channels for ODMA Mode

ODMA (Opportunity Driven Multiple Access) is another possible access scheme

which can be applied in UMTS, although not fully specified in R99 and unlikely to beused in the early deployments.

It is really just a relaying protocol rather than a pure access scheme, whereby a

terminal which lies outside cell coverage can use another mobile terminal as a relay

to transmit to the base station. It is only likely to prove feasible in the TDD scheme,

where reception and transmission are in the same frequency band if implemented in

FDD, it would require terminals to be able to receive in their normal transmission

band and vice versa, which is impractical to implement.

There are a number of logical channels which can be defined for future ODMA

operation.

These are a single traffic channel for user data, ODTCH (ODMA Dedicated traffic

channel), and two control channels: OCCCH (ODMA Common Control Channel) and

ODCCH (ODMA Dedicated control channel).

Both OCCCH & ODCCH are used for transmitting control information between

terminals, the difference being that OCCCH carries information common to a number

of terminals, whereas ODCCH is point-to-point, intended for a specific terminal.


Informa Telecoms45


49/75

MAC

PHYSICAL

Fig. 21 Logical Channels ODMA Mode

46Informa Telecoms

Traffic (user data) Control point-to-point

ODTCH

(ODMA Dedicated Traffic)

OCCCH

(ODMA Common Control)

ODCCH

(ODMA Dedicated Control)

Only feasible in TDD Mode.


50/75


8.2 Transport Channels

Transport Channels are the output from the MAC layer and the input to the physical

layer.

The choice of transport channel depends on the requirements of the message to be

transmitted, and so they will tend to have specific characteristics in terms of their

direction (uplink/downlink), power control requirements, data capacity and so on. The

mobile equipment is able to have one or more Transport Channels simultaneously in

the uplink and/or the downlink.

Transport Channels can be divided into Common and Dedicated types.

8.2.1 Dedicated Transport Channels

Dedicated Transport Channels describe an essentially point-to-point link between the

UTRAN and a particular mobile. Such a channel is for dedicated use, for a single user

only. The Mobile Equipment to which the transport channel belongs is identified by

virtue of the code and frequency (FDD), and the code, frequency and time slot (TDD)

for the physical channel onto which it is mapped.

For current specifications within UMTS, there is only one dedicated transport channel,

DCH, which is used in both the uplink and downlink, and in both the TDD and FDD

modes.

DCH carries all the information coming from the higher layers which is intended for

the given user. This includes user data for the actual service plus any higher layer

control information. The content carried within DCH is not visible to the physical layer,

and so both user and control data are treated the same way.

DCH is characterised by features such as fast power control, the capability for fast

data rate changes on a frame-by-frame basis, the possibility of transmission to a

certain part of the cell or sector using beam-forming, and the support of soft

handover.

For future ODMA operation within the TDD mode, an ODMA dedicated channel

(ODCH) will be available as another dedicated transport channel, applicable for both

uplink and downlink.


Informa Telecoms47


51/75

MAC

PHYSICAL

Fig. 22 Dedicated Transport Channel, DCH

48Informa Telecoms

Uplink

Downlink

TDD (ODCH for ODMA mode)

FDD

Higher layer information (user data and signalling)

Fast Power Control

Fast Data-Rate Changes

Use of beam-forming

Support for soft handover


52/75


8.2.2 Common Transport Channels 1

Common Transport Channels are intended for use by a number of users, and hence

are not to be used for a dedicated connection between the fixed network and anyspecific mobile. The link is point-to-multipoint (UTRAN to multiple mobiles), and the

resource is divided between all the users within a cell.

There are four common transport channels in particular which are required for even the

basic operation of a UMTS network, in both TDD and FDD modes. These are:

RACH Random Access Channel

The Random Access Channel is used for initial access, when a mobile requests to set

up a connection. It provides a common channel in that all mobiles sending these

initiation requests are able to make use of it.

RACH is applicable only on the uplink, and must be able to be heard over the whole

cell coverage area. To achieve this means that it is limited to low data rates. The

ability to support 16kb/s RACH is a mandatory requirement for terminals, regardless

of the types of services they provide.

As part of this initial access, RACH is also used for open loop power control.

RACH can also be used by the mobile for the transfer of small amounts of user data.

FACH Forward Access Channel

FACH is used for messages from the Node B to the mobiles known to be within one

cell, once a random access message has been received. It is used for open loop

power control, and can also be used to transfer small amounts of user data, and thus

can be regarded as the downlink companion to RACH.

There can be more than one FACH channel within a cell, although one of these must

have a low data rate to enable reception by all terminals. Additional FACH channels

can have higher data rates, and FACH channels are capable of changing data rates

on a frame-by-frame basis (i.e. every 10ms).

PCH Paging ChannelPCH is used to broadcast paging and notification messages into an entire cell

(or a group of cells). A mobile is able to remain in sleep mode, to conserve battery

power, whilst still able to receive PCH messages by monitoring only certain paging

messages which have been allocated to it, and sleeping whilst other paging

messages are being transmitted.

The paging channel is used when the network wants to initiate communication with

the terminal, for example when an incoming call or data arrives from the core

network.


Informa Telecoms49



MAC

PHYSICAL

Fig. 23 Essential Common Transport Channels

uplink downlink FDD TDD usage

RACH initial accessRandom requests

Access small user data

FACH access

Forward acknowledgement


PCH paging and

Paging notification

BCH available accessBroadcast codes and slots

OpenLoopPowerControl


54/75


BCH Broadcast Channel

BCH is used to communicate with all the mobiles within a cell, with the most typical

messages being those which inform the mobiles of the available random access

codes and access slots which exist within the cell. A terminal cannot register with thecell without decoding this channel.

The nature of this information means that BCH needs to be heard by all the mobiles

within the cell coverage area, and that even low-end terminals must be able to

decode the message. Thus the power must be relatively high and the data rate must

be kept low.


Informa Telecoms51



Fig. 23 Essential Common Transport Channels

uplink downlink FDD TDD usage

RACH initial accessRandom requests


FACH access

Forward acknowledgement


PCH paging and

Paging notification

BCH available accessBroadcast codes and slots

OpenLoopPowerControl

MAC

PHYSICAL


56/75


8.2.3 Common Transport Channels 2

As well as those transport channels which are required for basic operation of the

UMTS network, there are some further transport channels which may optionally apply.For FDD mode of access there are two further channels, which are:

DSCH Downlink Shared Channel

DSCH carries dedicated control or user traffic data, but rather than being a dedicated

channel, is a channel resource which can be shared by several users, on the

downlink. As with the unshared DCH, it supports fast power control as well as

variable bit-rate on a frame-by-frame basis, and does not need to be heard within the

whole cell area. The latter means that technologies such as beam-forming antennae

can be used.

DSCH will not exist alone, and will always be associated with an unshared (lower bit

rate) dedicated channel (DCH) which carry the physical control channel, including the

signalling for fast power control. Shared channels cannot use soft handover.

CPCH Common Packet Channel

CPCH is an extension of the RACH channel, and is intended to carry packet-based,

bursty user data, in the uplink direction. It is applicable to the FDD mode only.

Like RACH, it is shared by a number of mobiles in the cell. The main differences from

RACH are that fast closed loop power control is used in the physical layer, its data

rate can be changed on a fast basis, collision detection can be applied, and it neednot apply to the whole cell area i.e. beam-forming techniques can be applied.

CPCH transmissions may last for several frames, whereas RACH transmissions tend

to be much shorter, just one or two frames.

In TDD mode only, the Downlink Shared Channel (DSCH) has an equivalent, known as

USCH, the Uplink Shared Channel. As with DSCH, USCH is used to carry dedicated

control or traffic data, and is shared by several mobiles. As with DSCH it can utilise

beam-forming, fast power control and variable data rate.

Finally, in ODMA mode only, ORACH, the ODMA Random Access Channel can be

used as a relay link channel for random access requests.


Informa Telecoms53


57/75

Fig. 24 Optional Transport Channels

54Informa Telecoms

FDD TDD uplink downlink usage

DSCH Usually packet-

(Downlink based, burstyShared) dedicated user

data/control

data

CPCH packet-based

(Common bursty user

Packet) data

USCH

dedicated user/(Uplink control data

Shared)

ORACH random access

(ODMA request relay

Random Access) (ODMA)


58/75


8.2.4 Mapping of Logical Channels onto Transport Channels

In the downlink direction in both FDD and TDD modes, the paging and notification

logical channel PCCH maps directly onto the transport channel PCH.

Similarly, the downlink logical channel for broadcast information, BCCH maps directly

onto the transport channel BCH, in both TDD and FDD modes. However it is also

possible to map BCCH onto the transport channel FACH, for small amounts of

broadcast information.

The logical channels CTCH and CCCH, the common traffic and control channels,

both map onto the FACH transport channel in the downlink direction, for both FDD

and TDD modes. The logical channel CTCH and the transport channel FACH are not

applicable on the uplink, so in this case CCCH maps solely onto RACH, again in both

FDD and TDD modes.

The dedicated logical control and traffic channels DCCH and DTCH map onto

transport channels DCH and, optionally, DSCH and FACH in the downlink of both

FDD and TDD. In the uplink, FACH and DSCH are not applicable transport channels,

and so mapping is to DCH once again, but in this case also to RACH. In the case of

FDD, additional mapping is optional to CPCH and, in the case of TDD, to USCH.

Applicable in TDD mode only, the logical shared control channel SHCCH, is mapped

to RACH on the uplink and to FACH or DSCH on the downlink.

ODMA channel mapping follows an equivalent pattern as the TDD mode, with the

ORACH transport channel equivalent to the RACH transport channel in FDD and

TDD, and ODCCH, OCCCH and ODTCH equivalent to DCCH, CCCH and DTCH

respectively.


Informa Telecoms55


59/75

DownlinkFDD-Mode

MAC

PCCH BCCH CTCH SHCCH CCCH DCCH DTCH

PCH BCH FACH DSCH RACH CPCH DCH USCH

UplinkFDD-ModePCCH BCCH CTCH SHCCH CCCH DCCH DTCH


MAC


DownlinkTDD-ModePCCH BCCH CTCH SHCCH CCCH DCCH DTCH

MAC

UplinkTDD-ModePCCH BCCH CTCH SHCCH CCCH DCCH DTCH


MAC

LOGICAL

CHANNELS

TRANSPORT

CHANNELS

LOGICAL

CHANNELS

TRANSPORT

CHANNELS

LOGICALCHANNELS

TRANSPORT

CHANNELS

LOGICAL

CHANNELS

TRANSPORTCHANNELS

Fig. 25 Mapping of Logical Channels onto Transport Channels

56Informa Telecoms


60/75


8.3 The Physical Channels

The Physical Channels are available from the lowest layer in the protocol stack, the

physical layer, and are the channels which are directly transmitted to the receivingsystem. Each physical channel has a specific purpose and characteristic, and not all

the possible physical channels will exist in both the uplink and downlink directions,

or in both the TDD and FDD modes of transmission.

In most cases, the transport channels map directly onto a single physical channel,

although there are additional physical channels which do not map onto the higher

layers and are needed exclusively for operations across the physical radio layer.

Orthogonal Channelisation Codes are used in the physical layer to differentiate

downlink physical channels transmitted by a Node B within one cell or sector. On the

uplink, channelisation codes are used to separate the dedicated physical channels

which are being used by a mobile. A code is allocated for each data connection.

These channelisation codes provide spreading of the signal over the W-CDMA Radio

Interface.


Informa Telecoms57


61/75

Fig. 26 Physical Channel Basics

58Informa Telecoms

Directly transmitted to the receiving system

Each has specific characteristics Some physical channels do not map to

higher layers

(i.e. for use within physical layer only)

Differentiated using orthogonal

channelisation codes (OVSF)

Coding provides spreading over W-CDMA

MAC

PHYSICAL


62/75


8.3.1 Physical Channels 1

The four essential transport channels, RACH, FACH, PCH and BCH are associated

with three physical channels. These are applicable to both FDD and TDD and are:

PRACH Physical Random Access Channel

PRACH is used to transmit the random access transport channels, containing user

specific information required to contact the network for registration, location update,

cell update, and in order to initiate a call set-up. It is only applied in the Uplink.

P-CCPCH Primary Common Control Physical Channel

P-CCPCH is used in the downlink for broadcasting cell-specific information, and is

the physical channel carrying the transport channel BCH. The channel bit rate is

30kb/s, and a channelisation code with spreading factor 256 is permanently

allocated. In fact the actual bit rate is further reduced, since the P-CCPCH alternates

with another downlink physical channel, the Synchronisation Channel (SCH).

S-CCPCH Secondary Common Control Physical Channel

The S-CCPCH is used for transporting the downlink transport channels PCH (for

paging and notification messages) and FACH (for small amounts of data). These two

transport channels can either be multiplexed onto one such S-CCPCH physical

channel or can use different physical channels.

The channelisation code used for Secondary-CCPCH is carried by the Primary-

CCPCH.

Two additional essential channels are applicable to both FDD and TDD, on the

downlink only, but are unique to the physical layer, with no mapping to higher layers.

These are:

PICH Paging Indication Channel

PICH is used by the UTRAN to indicate to the mobile whether there is a paging

message. It has a fixed spreading factor of 256, and is always associated with the

Secondary CCPCH to which the PCH transport channel has been mapped. If a

paging indication has been detected, then the mobile knows to decode the pagingchannel.

SCH Synchronisation Channel

This is used for part of the initial system acquisition process by the mobile, and

consists of two sub-channels (Golay-coded). A Primary SCH carries an unmodulated

code of length 256 chips, which is transmitted once every slot. This primary

synchronisation code is the same for every base station in the system, and is used

by the mobile to obtain the timing information for the Secondary SCH.


Informa Telecoms59



Fig. 27 Physical Channels (FDD andTDD)

mapping

uplink downlink above? purposePRACH carry RACH

(Physical Random Access)

P-CCPCH broadcast:

(Primary Control) carry BCH

S-CCPCH carry PCH

(Secondary Control) & FACH

PICH Indication of a

(Paging Indication) Paging Message

SCH Acquisition &

(Synchronisation) Scrambling Codes


64/75


The secondary SCH consists of a modulated code of length 256 chips, and is

transmitted in parallel with the P-SCH, and carries information about the long

(scrambling) code group to which the long code of the base station belongs.

This enables a search of long codes by the mobile to be limited to a subset ofall the codes available.

The SCH is time multiplexed with the P-CCPCH over the air interface.


Informa Telecoms61



Fig. 27 Physical Channels (FDD andTDD)

mapping

uplink downlink above? purpose

PRACH carry RACH(Physical Random Access)

P-CCPCH broadcast:

(Primary Control) carry BCH

S-CCPCH carry PCH

(Secondary Control) & FACH

PICH Indication of a

(Paging Paging

Indication) Message

SCH Acquisition &

(Synchronisation) Scrambling

Codes


66/75


8.3.2 Physical Channels 2

There are a number of other downlink physical channels which have no mapping to

higher layers, but which are applicable only in FDD mode. These are:

AICH Acquisition Indication Channel, used by the UTRAN to indicate back to the

mobile whether a random access attempt has succeeded (requested via the uplink

RACH transport channel). In common with RACH itself, it is a mandatory requirement

for system operation.

AP-AICH Access Preamble Indication Channel, identical to AICH but used to

indicate whether the UTRAN has successfully received a request for access to the

CPCH transport channel, the extension to RACH which is used for bursty packet user

data.

Three further channels also relate to AP-AICH, being relevant specifically to access to

the CPCH transport channel:

CSICH CPCH Status Indication Channel, used to indicate the availability of each

physical channel related to CPCH transport channel access. CSICH utilises the

unused part of the AICH channel.

CD-ICH and CA-ICH Collision Detection & Channel Assignment Indication

Channels, used to indicate the success of a collision detection operation and the

status of the channel assignment respectively. These two channels are sent in parallelto the terminal.

Finally there is:

CPICH Common Pilot Channel

This is a mandatory channel, used for cell phase and time reference, and for channel

estimation for the common channels (and occasionally for the dedicated channels).

Channel estimation refers to the conditions of interference and reception quality.

In fact, there is both a Primary and a Secondary CPICH, P-CPICH and S-CPICH

respectively, which differ in their usage and the limitations on their physical features.

P-CPICH is used as the reference for the downlink channels SCH, P-CCPCH, AICH

and PICH. The same channelisation code is always used and is scrambled using the

primary scrambling code, of spreading factor 256. One P-CPICH exists in each cell,

and is broadcast over the entire cell.

The importance of P-CPICH is in measurements for handover and cell

selection/re-selection. Reducing the power applied to the channel causes some of


Informa Telecoms63



Fig. 28 FDD Only Physical Channels

physical Layer only

FDD only

downlink only

mandatory usage

AICH indicate success of

(Acquisition Indication) random access

AP-AICH indicate success of

(Access Preamble Indication) access to CPCH

CSICH indicate availability of

(CPCH Status Indication) physical channels

for CPCH

CD-ICH indicate collision

(Collision Detection Indication) detection during

CPCH access

CA-ICH indicate status of channel

(Channel Assignment Indication) assignments for CPCH

CPICH channel estimation, cell

(Common Pilot) phase & time reference

for common channels,

for handover


68/75


the terminals to hand over to other cells, while increasing it invites terminals to

handover into the cell, or to use that cell as their initial access.

S-CPICH may be used as a reference for the S-CCPCH and the Downlink DedicatedPhysical Channel, which carries the dedicated transport channel DCH. It will use an

arbitrary channelisation code of spreading factor 256, and is scrambled by either the

primary or a secondary scrambling code. It may be transmitted over only part of a

cell, and hence used for hot-spots or high density traffic areas.


Informa Telecoms65



Fig. 28 FDD Only Physical Channels

physical Layer only

FDD only

downlink only

mandatory usage

AICH indicate success of

(Acquisition Indication) random access

AP-AICH indicate success of

(Access Preamble Indication) access to CPCH

CSICH indicate availability of

(CPCH Status Indication) physical channels

for CPCH

CD-ICH indicate collision

(Collision Detection Indication) detection during

CPCH access

CA-ICH indicate status of channel

(Channel Assignment Indication) assignments for CPCH

CPICH channel estimation, cell

(Common Pilot) phase & time reference

for common channels,

for handover


70/75


71/75

Fig. 29 Dedicated and Shared Physical Channels

68Informa Telecoms

FDD TDD uplink downlink usage

DPDCH carry DCH

(Dedicated dataPhysical Data)

DPCCH carry physical

(Dedicated layer control

Physical information for

Control) DPDCH

PDSCH carry DSCH

(Physical Downlink

Shared Channel)(Always Associated (Always

with DPCH) Associated

with DCH)

PCPCH carry CPCH

(Physical Packet)

PUSCH carry USCH

(Physical Uplink Shared)

DPCH

(Dedicated Physical)


72/75


8.3.4 Mapping Transport Channels onto Physical Channels

All Transport Channels map directly onto a specific physical channel, except in the

case of the transport channels FACH (forward access channel) and PCH (PagingChannel), which are both mapped to share the single S-CCPCH (Secondary Common

Control) Physical Channel.

Applicability to uplink, downlink, FDD and TDD modes of operation therefore follow

that for the transport channels.

DPDCH and DPCCH, which carry the DCH dedicated transport channel, including the

user data, are the only channels which can apply in every combination of modes and

direction.

PRACH must exist for uplink FDD & uplink TDD, in order to carry the RACH transportchannel. PCPCH may exist in uplink FDD, and PUSCH in uplink TDD, in order to carry

the transport channels CPCH and USCH respectively.

In the downlink, SCCPCH, PCCPCH will always apply to both TDD & FDD, and carry

the paging and broadcast transport channels, PCH and BCH respectively. SCCPCH

additionally carries the FACH transport channel.

PDSCH may apply in either TDD or FDD downlink, where the DSCH transport channel

is being used.

In addition to channels mapped directly from the transport channels, the downlink of

both FDD and TDD will include the mandatory physical layer channels SCH and

PICH.

In FDD mode only, the downlink will also include the unmapped physical layer

channels AICH and CPICH, which are mandatory, plus AP-AICH, CSICH, CD-ICH and

CA-ICH, which may apply if the mobile terminal requests access to the CPCH

transport channel.


Informa Telecoms69


73/75


74/75Informa Telecoms71

TRANSPORT

PHYSICA

L

DownlinkFDD-Mode

SCCPCH+ SCH, CPICH, AICH, AP-AICH, PICH, CSICH, CD/CA-ICH (not mapped above physical layer)

PCCPCH PDSCH PRACH PCPCH DPDCH DPCCH PUSCH


CHANNELS

PHYSICAL LAYER


MAC LOGIC

AL

TRANSPORT

PHYSICA

L

UplinkFDD-Mode

SCCPCH PCCPCH PDSCH PRACH PCPCH DPDCH DPCCH PUSCH


CHANNELS

PHYSICAL LAYER


MAC LOGIC

AL



Fig. 31 Channel Mapping A Summary


75/75

TRANSPORT

PHYSICA

L

DownlinkTDD-Mode

SCCPCH+ SCH, PICH (not mapped above physical layer)

PCCPCH PDSCH PRACH PCPCH DPDCH DPCCH PUSCH


CHANNELS

PHYSICAL LAYER

PCCH BCCH CTCH CCCH DCCH DTCH

MAC LOGIC

AL

TRANSPORT

PHYSICA

L

UplinkTDD-Mode

SCCPCH PCCPCH PDSCH PRACH PCPCH DPDCH DPCCH PUSCH


CHANNELS

PHYSICAL LAYER

PCCH BCCH CTCH CCCH DCCH DTCH

MAC LOGIC

AL

Documents

UMTS Air Interface Protocols and Channel_SECTION SIX