the physical layer

RN31552EN20GLA0

The Physical layer – Rel. 99

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1 © Nokia Siemens Networks RN31552EN20GLA0

Course Content

Warming Up

The Physical Layer – Rel. 99

The Physical Layer – HSDPA, HSUPA & HSPA+

RRC Modes, System Information, Paging & Update Procedures

Cell Selection & Reselection

RRC Connection Establishment

WCDMA Measurements in the UE

Mobility Management & Connection Management

UTRAN Control Protocol Overview (without RRC)

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Module Objectives

At the end of the module you will be able to:

• Describe the WCDMA channel structure

• Explain transport channel format

• List different code types

• Name the main differences in UL and DL data transmission organisation

• Describe the UE cell synchronisation

• Outline the paging organisation and its impact on the UE

• Characterise the random access, its power control and code planning

• Describe the DPCHs, their power control, time organisation, and L1 synchronisation

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• Channel Mapping

• Transport Channel Formats

• Cell Synchronisation

• Common Control Physical Channels

• Physical Random Access

• Dedicated Physical Channel Downlink

• Dedicated Physical Channel Uplink

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In UMTS there are three different types of channels:

• Logical Channels• Logical Channels transmit specific contents. • There are e.g. logical channel to transmit the cell system information, paging information, or user data. • Logical channels are offered as data transfer service by the Medium Access Control (MAC) layer to the next

higher layer. • Consequently, logical channels are in use between the mobile phone and the RNC.

• Transport Channels (TrCH)• The MAC layer is using the transport service of the lower lower, the Physical layer. • The MAC layer is responsible to organise the logical channel data on transport channels. This process is called

mapping.• In this context, the MAC layer is also responsible to determine the used transport format. • The transport of logical channel data takes place between the UE and the RNC.

• Physical Channels (PhyCH)• The physical layer offers the transport of data to the higher layer. • The characteristics of the physical transport have to be described. • When we transmit information between the RNC and the UE, the physical medium is changing.• Between the RNC and the Node B, where we talk about the interface Iub, the transport of information is

physically organised in so-called Frames.• Between the Node B and the UE, where we find the WCDMA radio interface Uu, the physical transmission is

described by physical channels. • A physical channel is defined by the UARFCN and the a spreading code in the FDD mode.

Radio Interface Channel Organisation

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Logical Channelscontent is organised in separate channels, e.g.

System information, paging, user data, link management

Transport Channelslogical channel information is organised on transport channel

resources before being physically transmitted

Physical Channels(UARFCN, spreading code)

FramesIub interface

Radio Interface Channel Organisation

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There are two types of logical channels (FDD mode):

1) Control Channels (CCH):• Broadcast Control Channel (BCCH)

• System information is made available on this channel. • The system information informs the UE about the serving PLMN, the serving cell, neighbourhood lists, measurement parameters, etc.• This information permanently broadcasted in the DL.

• Paging Control Channel (PCCH)• Given the BCCH information the UE can determine, at what times it may be paged. • Paging is required, when the RNC has no dedicated connection to the UE. • PCCH is a DL channel.

• Common Control Channel (CCCH)• for UL & DL Control information • in use, when no RRC connection exists between the UE and the network

• Dedicated Control Channel (DCCH)• UL & DL: Layer 3 Signalling dedicated to a specific radio link.

2) Traffic Channels (TCH):• Dedicated Traffic Channel (DTCH)

• UL & DL: dedicated resources for User data transmission between the UE and the network • Common Traffic Channel (CTCH)

• DL only: User data to be transmitted point-to-multipoint to a group of UEs.

Logical Channels

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Logical Channels are mapped onto Transport Channels. There are two types of Transport Channels (FDD mode):

a) Common Transport Channels:

• Broadcast Channel (BCH)It carries the BCCH information.

• Paging Channel (PCH)It is in use to page a UE in the cell, thus it carries the PCCH information. It is also used to notify UEs about cell system information changes.

• Forward Access Channel (FACH)The FACH is a DL channel. Control information, but also small amounts of user data can be transmitted on this channel.

• Random Access Channel (RACH)This UL channel is used by the UE, when small amounts of data have to be transmitted; the UE requires no Dedicated resources. It is often used to allocated dedicated signalling resources to the UE to establish a connection or to perform higher layer signalling. It is a contention based channel, i.e. several UE may attempt to access UTRAN simultaneously.

b) Dedicated Transport Channels:

Dedicated Channel (DCH)Dedicated resources can be allocated both UL & DL to a UE. Dedicated resources are exclusively in use for the subscriber.

HS-Downlink Shared Channel (HS-DSCH) & E-DCHTransport Channels for DL HSDPA respectively UL HSUPA data transfer Note: DSCH (FDD), CPCH removed from R5 specification, 25.301 v5.6.0

Transport Channels (TrCH)

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• Physical Channels are characterised by

• UARFCN,• Scrambling Code,• Channelisation Code (optional),• start and stop time, and• relative phase (in the UL only, with relative phase being 0 or π/2)

• Transport channels can be mapped to physical channels.

• But there exist physical channels, which are generated at the Node B only, as can be seen on the next figures.

• The details of the physical channels is described in detail within this module (see following pages).

• Note: PDSCH & PCPCH have been removed from R5 specification, 25.301 v5.6.0

Physical Channels (PhyCH)

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P-CCPCHPCH

BCH

CTCH

DCCH

CCCH

PCCH

BCCH

DCH

CPICH

S-SCHP-SCH

FACH

HS-DSCH

AICH

HS-PDSCH

DPDCH

S-CCPCH

DTCH

PICH

LogicalChannels

TransportChannels

PhysicalChannels

E-AGCH

Channel Mapping DL (Network Point of View)

HS-SCCH

F-DPCH

E-RGCHE-HICH

DPCCH

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DCCH

DCH

DPDCH

DTCH

LogicalChannels

TransportChannels

PhysicalChannels

RACH

CCCH PRACH

DPCCH

Channel Mapping UL (Network Point of View)

E-DPCCH

E-DPDCHE-DCH

HS-DPCCH

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Channel configuration examples

AMR call• The data transferred during AMR call consists of

• Speech data• L3 signalling• L1 signalling

• User data is transferred on DTCH logical channel• RT connection uses always DCH transport channel• DCH transport channel is mapped on DPCH (DPDCH + DPCCH)

AMR + PS call (Multi-RAB)• Additional stream of user data

• NRT data

• Also configurations with HS-DSCH possible

NRT PS call• Different configurations utilising DCH, FACH/RACH, HS-DSCH or HS-DSCH/E-DCH

possible

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Example – Channel configuration during call

LogicalChannels

TransportChannels

PhysicalChannels

Data

DCCH0-4

DCH2-4

DPDCH

DTCH1 DPCCH

RRCsignalling

Speechdata

DCH1

AMR speech connection utilises multiple transport channelsRRC connection utilises multiple logical channelsDPCCH for L1 control data

DCH5DTCH2NRTdata

AMR speech+

NRT data

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• Part I: Channel Mapping

• Part II: Transport Channel Formats

• Part III: Cell Synchronisation

• Part IV: Common Control Physical Channels

• Part V: Physical Random Access

• Part VI: Dedicated Physical Channel Downlink

• Part VII: Dedicated Physical Channel Uplink

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Transport Channel Formats

• Transport Channels are used to exchange data between the MAC-layers in the UE and the RNC. • The data is hereby organised in Transport Blocks (TB). A Transport Block is the basic data unit. • The MAC layer entities use the services offered to them by the Physical layer to exchange Transport

Blocks. • One Transport Block can be transmitted only over one Transport Channel. Several Transport Blocks

can be simultaneously transmitted via a Transport Channel in one transport data unit to increase the transport efficiency.

• The set of all Transport Blocks, transmitted at the same time on the same transport channel (between the MAC layer and the physical layer) is referred to as Transport Format Set (TFS).

• Transport Blocks and Transport Block Sets are characterised by a set of attributes:• Transport Block Size

• The transport block size specifies the numbers of bits of one Transport Block. • If several Transport Blocks are transmitted within one TBS, then all TBs have the same size. • Please note, that the transport block size among different TBSs – which are transmitted at different times on one transport

channel - can vary.

• Transport Block Set Size• This attribute identifies the numbers of bits in one TBS. • It must be always a multiple of the transport block size, because all TBs transmitted in one TBS have the same size.

• (continued on the next text slide)

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MAC Layer MAC Layer

PHY Layer PHY LayerL1

FP/AAL2

L1

FP/AAL2

TBS

TTI radio frames in use

Transport Channel

UE RNC

TFI

TBS

The Transfer of Transport Blocks

TFI

TBS: Transport Block SetTFI: Transport Format Indicator

Node B

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Transport Blocks and Transport Block Sets are characterised by a set of attributes (continued):• Transmission Time Interval (TTI)

•The TTI specifies the transmission time distance between two subsequent TBSs, transferred between the MAC and the PHY layer. •In the PHY layer, the TTI also identifies the interleaving period. Following TTI periods are currently specified:

- 2 ms (HS-DSCH), 10 ms, 20 ms, 40 ms, and 80 ms• Error Protection Scheme

•When data is transmitted via a wireless link, it faces a lot of distortion and can thus easily corrupted. •Redundancy is added to the user data to reduce the amount of losses on air. •In UMTS, three error protection schemes are currently specified:

•convolutionary coding with two rates: 1/2 and 1/3,•turbo coding (rate 1/3), and•no channel coding (this coding type is scheduled for removal from the UMTS specifications).

• Size of CRC•CRC stands for cyclic redundancy check. Each TBS gets an CRC. •The grade of reliability depends on the CRC size, which can be 0, 8, 12, 16, and 24 bits.


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TB Transport Block TF Transport FormatTBS Transport Block Set TFS Transport Format Set

TFC Transport Format CombinationTFCS Transport Format Combination Set

DCH 2

DCH 1

TB TB TB

TB

TB

TB

TB

TB

TBS

TF

TFS

TFC

TFCS

TTI TTI

TTI

TTI

TTITTI

TB

TB

TB

Transport Formats

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• The above description refers to a situation, where the MAC-layer hands the TBS to the PHY layer. This happens in the UE. But TBSs are normally exchanged between the UE and the RNC. As a consequence, the TBS must be transmitted over an AAL2 virtual channel between the RNC and the Node B. The TBS is packet into a frame protocol defined for the traffic channel.

• Different TBSs can be transmitted in one Transport Channel.

• How do MAC and PHY layer know, what kind of TBS they exchanged?

• When a transport channel is setup – or modified – the allowed Transport Block Sets are specified.• Each allowed TBS gets a unique Transport Format Indicator (TFI).• All TFIs of a Transport Channel are summarised in the Transport Format Set (TFS).• The TF consists of two parts (FDD mode):

•Semi-static part•The attributes belonging to the semi-static part are set by the RRC-layer. •They are valid for all TBSs in the Transport Channel. •Semi-static attributes are the Transmission Time Interval (TTI), the error correction scheme, the CRC size, and the static rate matching parameter (used by the PHY layer for dynamic puncturing if the TBS is too long for the radio frame).

•Dynamic part•The dynamic part comprises attributes, which can be changed by the MAC layer dynamically. •The affected attributes are the Transport Block Size & Transport Block Set Size.


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MAC Layer

PHY Layer

RRC Layer

conf

igur

atio

n

Semi-Static Part• TTI• Channel Coding• CRC size• Rate matching

Dynamic Part• Transport Block Size• Transport Block Set Size

Transport Format

Example: semi-static partdynamic part:- TTI = 10 ms- turbo coding - transport block size: 64 64 64 128- CRC size = 0 - transport block set size: 1 2 4 2- ...

TFI1 TFI2 TFI3 TFI4

TrCHs

Transport Formats

TrCH: Transport ChannelTBS: Transport Block SetTFI: Transport Format Indicator

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• The PHY layer can multiplex several Transport Channels in one “internal“ Transport Channel, called Coded Composite Transport Channel (CCTrCH).

• This CCTrCH can be transmitted on one or several physical channels. Consequently, the TCSs of different Transport Channels can be found in one radio frame.

• The Transport Format Combination Set (TFCS) lists all allowed Transport Format Combinations (TFC).

• A Transport Format Combination Indicator (TFCI) is then used to indicate, what kind of Transport Format Combination is found on the radio frame. You can find TFCI-fields for instance in the S-CCPCH. The TFCS is set by the RRC protocol.

• The table on the following slide lists the allowed Transport Formats for the individual Transport Channels (FDD mode only).


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1...5000 bitsgranularity: 1 bit



246 bits


246 bits





20 ms

10 ms

10, 20, 40 & 80 ms

10 & 20ms

10, 20, 40 & 80 ms

BCH

FACH

RACH

PCH

DCH

convolutional 1/2

convolutional 1/2

convolutional 1/2& 1/3; turbo 1/3

convolutional 1/2

convolutional 1/2& 1/3; turbo 1/3

16

0, 8, 12, 16 & 24

0, 8, 12, 16 & 24

0, 8, 12, 16 & 24

0, 8, 12, 16 & 24

Transport Block Size

Transport Block Set Size

TTIcoding types

and ratesCRCsize

Semi-static PartDynamic Part

→ 3GPP TS 25.302 V5.9.0

Transport Format Ranges

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Example: Transport Formats in AMR call

• The AMR codec was originally developed and standardized by the European Telecommunications Standards Institute (ETSI) for GSM cellular systems. It has been chosen by the Third Generation Partnership Project (3GPP) as the mandatory codec for third generation (3G) cellular systems. It supports 8 encoding modes with bit rates between 4.75 and 12.2 kbps.

• Feature of the AMR codec is Unequal Bit-error Detection and Protection (UED, UEP).

• The UEP/UED mechanisms allow more speech over a lossy network by sorting the bits into perceptually more and less sensitive classes (A, B, C).

• A frame is only declared damaged and not delivered if there are bit errors found in the most sensitive bits (Class A).

• Acceptable speech quality results if the speech frame is delivered with bit errors in the less sensitive bits (Class B, C). Decoder uses error concealment algorithm to hide the errors.

• On the radio interface, one Transport Channel is established per class of bits i.e. DCH A for class A, DCH B for class B and DCH C for class C. Each DCH has a different transport format combination set which corresponds to the necessary protection for the corresponding class of bits as well as the size of these class of bits for the various AMR codec modes.

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Example: Transport Formats in AMR callDCH 1: AMR class A

bits

TBS size: 1TB size: 39 bits

(SID)

TBS size = 0(DTX)


TTI = 20 ms

TBS size = 0(DTX)

DCH 2: AMR class B bits

DCH 3: AMR class C bits

Convolutional coding

Coding rate: 1/3

TTI = 20 ms

Coding type: convolutional

Coding rate: 1/3

CRC size: 12 bits CRC size: 0 bits CRC size: 0 bits

TTI = 20 ms

Coding rate: 1/2

Convolutional coding

DCH 24: RRC Connection

TBS size = 0(DTX)

TBS size = 1TB size: 148 bits

TTI = 40 ms

Coding type: convolutional

Coding rate: 1/3

CRC size: 16 bits

TBS size:1TB size: 81 bits


TBS size = 0(DTX)

12.2 kbit/s3.7 kbit/s

Example

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Cell Synchronisation

• When a UE is switched on, it starts to monitor the radio interface to find a suitable cell to camp on but it has to determine, whether there is a WCDMA cell nearby.

• If a WCDMA cell is available, the UE has to be synchronised to the DL transmission of the system information – transmitted on the physical channel P-CCPCH – before it can make a decision, in how far the available cell is suitable to camp on.

• Initial cell selection is not the only reason, why a UE wants to perform cell synchronisation. This process is also required for cell re-selection and the handover procedure.

• Cell synchronisation is achieved in 3 steps*:• Step 1: Slot synchronisation

• During the first step of the cell search procedure the UE uses the SCH’s primary synchronisation code to acquire slot synchronisation to a cell. This is typically done with a single matched filter (or any similar device) matched to the primary synchronisation code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

• Step 2: Frame synchronisation and code-group identification• During the second step of the cell search procedure, the UE uses the SCH’s secondary synchronisation code to find

frame synchronisation 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 synchronisation 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 synchronisation is determined.

• Step 3: Scrambling-code identification• During 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, the Primary CCPCH can be detected. And the system- and cell specific BCH information can be read.

• If the UE has received information about which scrambling codes to search for, steps 2 and 3 above can be simplified.

* further Information about Primary- & Secondary Synchronisation Channels and Code Groups can be found on the following pages

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• Detect cells

• Acquire slot synchronisation

Phase 1 – P-SCH

Phase 2 – S-SCH

Phase 3 – P-CPICH

• Acquire frame synchronisation

• Identify the code group of the cell found in the first step

• Determine the exact primary scrambling code used by the found cell

• Measure level & quality of the found cell

PriScrCodeWCEL; 0..511; 1; no default(Range; Step; Default)

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Cell synchronisation is achieved with the Synchronisation Channel (SCH). This channel divides up into 2 sub-channels:

Primary Synchronisation Channel (P-SCH)• A time slot lasts 2560 chips.

• The P-SCH only uses the first 10% of a time slot.

• A Primary Synchronisation Code (PSC) is transmitted the first 256 chips of a time slot. This is the case in every UMTS cell.

• If the UE detects the PSC, it has performed TS and chip synchronisation.

Secondary Synchronisation Channel (S-SCH)• The S-SCH also uses only the first 10% of a timeslot

• Secondary Synchronisation Codes (SSC) are transmitted.

• There are 16 different SSCs, which are organised in a 10 ms frame (15 timeslots) in such a way, that the beginning of a 10 ms frame can be determined, and 64 different SSC combinations within a 10 ms frame are identified.

• There is a total of 512 primary scrambling codes, which are grouped in 64 scrambling code families, each family holding 8 scrambling code members.

• The 15 SSCs in one 10 ms frame identify the scrambling code family of the cell‘s DL scrambling code.


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Cp = Primary Synchronisation CodeCs = Secondary Synchronisation Code

10 ms Frame

CP CP

2560 Chips 256 Chips

Cs1 Cs2 Cs15

Slot 0 Slot 1 Slot 14

CP CP CP

Cs1

Primary Synchronisation Channel (P-SCH)

Secondary Synchronisation Channel (S-SCH)

Slot 0

Synchronisation Channel (SCH)

PtxPrimarySCH-35..15; 0.1; -3 dB(Range; Step; Default)

PtxSecSCH-35..15; 0.1; -3 dB(Range; Step; Default)

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15

15

scramblingcode group

group 00

group 01

group 02

group 03

group 05

group 04

group 62

group 63

1 1 2 8 9 10 15 8 10 16 2 7 15 7 16

1 1 5 16 7 3 14 16 3 10 5 12 14 12 10

1 2 1 15 5 5 12 16 6 11 2 16 11 12

1 2 3 1 8 6 5 2 5 8 4 4 6 3 7

1 2 16 6 6 11 5 12 1 15 12 16 11 2

1 3 4 7 4 1 5 5 3 6 2 8 7 6 8

9 11 12 15 12 9 13 13 11 14 10 16 15 14 16

9 12 10 15 13 14 9 14 15 11 11 13 12 16 10

slot number0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

11

11 11

11 11

11 11

11 11

15

15

15

15 15

15

15

15 15

15 15

5

5

SSC Allocation for S-SCH

I monitor the S-SCH

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• With the help of the SCH, the UE was capable to perform chip, TS, and frame synchronisation. •Even the cell‘s scrambling code group is known to the UE.

• But in the initial cell selection process, it does not yet know the cell‘s primary scrambling code. • There is one primary scrambling code in use over the entire cell, and in neighbouring cells, different

scrambling codes are in use. •There exists a total of 512 primary scrambling codes.

• The CPICH is used to transmit in every TS a pre-defined bit sequence with a spreading factor 256. •The CPICH divides up into a mandatory Primary Common Pilot Channel (P-CPICH) and optional Secondary CPICHs (S-CPICH).

• The P-CPICH is in use over the entire cell and it is the first physical channel, where a spreading code is in use.

•A spreading code is the product of the cell‘s scrambling code and the channelisation code.•The channelisation code is fixed: Cch,256,0. i.e., the UE knows the P-CPICH‘s channelisation code, and it uses the P-CPICH to determine the cell‘s primary scrambling code by trial and error.

• The P-CPICH is not only used to determine the primary scrambling code. It also acts as:-•phase reference for most of the physical channels,•measurement reference in the FDD mode (and partially in the TDD mode).

• There may be zero or several S-CPICHs. Either the cell‘s primary scrambling code or its secondary scrambling codes can be used. In contrast to the P-CPICH, it can be broadcasted just over a part of the cell.

Common Pilot Channel (CPICH)

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CP



P-CPICH

10 ms Frame

applied speading code =cell‘s primary scrambling code ⊗ Cch,256,0

• Phase reference• Measurement reference

P-CPICHCell scrambling

code? I get it with trial & error!

Primary Common Pilot Channel (P-CPICH)

PtxPrimaryCPICH-10..50; 0.1; 33 dBm(Range; Step; Default)

(20 W sector)

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• The UE has to perform a set of L1 measurements, some of them refer to the CPICH channel:• CPICH RSCP

• RSCP stands for Received Signal Code Power. • The UE measures the RSCP on the Primary-CPICH. • The reference point for the measurement is the antenna connector of the UE. • The CPICH RSCP is a power measurement of the CPICH. • The received code power may be high, but it does not yet indicate the quality of the received

signal, which depends on the overall noise level.• UTRA carrier RSSI.

• RSSI stands for Received Signal Strength Indicator. • The UE measures the received wide band power, which includes thermal noise and receiver

generated noise. • The reference point for the measurements is the antenna connector of the UE.

• CPICH Ec/No• The CPICH Ec/No is used to determine the “quality“ of the received signal. • It gives the received energy per received chip divided by the band‘s power density.• The “quality“ is the primary CPICH‘s signal strength in relation to the cell noise.

• (Please note, that transport channel quality is determined by BLER, BER, etc. )

• If the UE supports GSM, then it must be capable to make measurements in the GSM bands, too. The measurements are based on the GSM carrier RSSI

• The wideband measurements are conducted on GSM BCCH carriers.

CPICH as Measurement Reference

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Received Signal Code Power (in dBm)CPICH RSCP

received energy per chip divided by the power density in the band (in dB)CPICH Ec/No

received wide band power, including thermal noise and noise generated in the receiver

UTRA carrier RSSI

CPICH Ec/No = CPICH RSCPUTRA carrier RSSI

CPICH Ec/No

0: < -241: -23.52: -233: -22.5...47: -0.548: 049: >0

Ec/No values in dB

CPICH RSCP

-5: < -120-4: -119:0: -1151: -114:89: -2690: -2591: ≥ -25RSCP values in dBm

GSM carrier RSSI

0: -1101: -1092: -108:71: -3972: -3873: -37

RSSI values in dBm

P-CPICH as Measurement Reference

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• The UE knows the cell‘s primary scrambling code. • It now wants to gain the cell system information, which is transmitted on the physical channel P-

CCPCH. • The channelisation code of the P-CCPCH is also known to the UE, because it must be Cch,256,1 in

every cell for every operator. • By reading the cell system information on the P-CCPCH, the UE learns everything about the

configuration of the remaining common physical channels in the cell, such as the physical channels for paging and random access.

• As can be seen from the P-CCPCH‘s channelisation code, the data rate for cell system information is fixed.

• The SCH is transmitted on the first 256 chips of a timeslot, thus creating here a peak load. • The cell system information is transmitted in the timeslot except for the first 256 chips. By doing so, a

high interference and load at the beginning of the timeslot is avoided. • This leads to a net data rate of 27 kbps for the cell system information.• Channel estimation is done with the CPICH, so that no pilot sequence is required in the P-CCPCH.

• (The use of the pilot sequence is explained in the context of the DPDCH later on in this document.)

• There are also no power control (TPC) bits transmitted to the UE‘s.

Primary Common Control Physical Channel (P-CCPCH)

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CP



P-CCPCH

10 ms Frame

P-CCPCHFinally, I get the

cell system information

• channelisation code: Cch,256,1• no TPC, no pilot sequence• 27 kbps (due to off period)• organised in MIBs and SIBs

Primary Common Control Physical Channel (P-CCPCH)

PtxPrimaryCCPCH-35..15; 0.1; -5 dB(Range; Step; Default)

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Synchronisation Issues in UMTS. 5 different UTRAN synchronisation issues were identified:

1. Network synchronisation stands for the very accurate reference frequency, which must bedistributed to the individual UTRAN network elements.

2. Node synchronisation takes place between the Node B and the RNC. • Node Synchronisation is used to determine the run-time difference between UTRAN nodes,

which must be estimated and then compensated. • In the FDD mode, only RNC-Node B Node Synchronisation is in use.

3. While radio interface synchronisation is required between the UE and the Node B.

4. Transport channel synchronisation is a L2 synchronisation (for the MAC layer). • It is therefore done between the UE and the RNC. • Please note in this context, that a UE may be in a soft handover state, i.e. the UE may be

connected to several cells simultaneously.• Transport channel synchronisation is required to guarantee, that the transport of user data

via several channels is coordinated in such a way, that the transmitted data from several cells arrives within the UE‘s receive window.

5. Time alignment handling takes place between UTRAN and the CN for adequate timing of data transfer.

Synchronisation Issues and Node Synchronisation

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SRNC

tim

e

3112

3113

3114

3115

3116

3117

3118

RFN

tim

e

128

129

130

131

132

133

134

BFN

135

DL Node Synchronization

( T1 )

UL Node Synchronization

( T1,T2,T3 )

T1

(T4)

T2

T3

(T4 – T1) – (T3 – T2)= Round Trip Delay(RTD) determinationfor DCH services

T1, T2, T3range: 0 .. 40959.875 ms

resolution: 0.125 ms

DL offset

UL offset

user plane defined onDCH, FACH & DSCH

BFN: Node B Frame

Number counter0..4095 frames

RFN: RNC Frame

Number counter0..4095 frames

Node Synchronisation

Node B

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• A timing reference is required by the Node Synchronisation:

• Node B Frame Number (BFN)• The BFN is a counter at the Node B, based on the 10 ms framing structure of WCDMA.

• RNC Frame Number (RFN)• The RFN is a counter at the RNC, based on the 10 ms framing structure of WCDMA.

• Cell System Frame Number (SFN)• This is a counter for each cell, and is broadcasted on the P-CCPCH.

• With one Node B, several (sector) cells can be deployed. These cells overlap. • If the SCH is transmitted at the same tame in all the sector cells of the Node B, and when a UE is in

the overlapping coverage area of two of these cells, it will have difficulties to synchronise to one cell. • As a consequence, an offset can be used for neighbouring cells of one Node B: T_cell. • T_cell is a timing delay for the starting time of the physical channels SCH, CPICH, BCCH relative

to the Node B‘s timer BFN. • The timing delay is a multiple (0..9) of 256 chips due to of the length of a SCH burst. • The cell‘s timing is identified with the counter SFN = BFN + T_cell. • (Please note, that this description only applied for the FDD mode!)

Cell Synchronisation and Sectorised Cells

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Node B with threesectorised cells

cell1

cell2

cell3

1 TS

BFN

SCH

SCH

SCH

SCH

SCH

SCH

SCH

SFN = BFN + T_cell1

SFN = BFN + T_cell2

SFN = BFN + T_cell3

T_cell3

T_cell1

T_cell2

SFN: Cell System Frame Numberrange: 0..4095 frames

T_cell: n ∗ 256 chips, n = 0..9

cell3 cell2

cell1

SCH

Cell Synchronization and Sectorised Cells

TcellWCELL; 0..2304 chip;256 chip; no default

Tcell: Timing delay used for defining the start of SCH, P-CPICH, P-CCPCH in a cell relative to BFN

BFN: Node B Frame NumberRFN: RNC Frame NumberSFN: Cell Frame Number

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• The S-CCPCH can be used to transmit the transport channels• Forward Access Channel (FACH) and • Paging Channel (PCH).

• More than one S-CCPCH can be deployed.

• FACH & PCH information can multiplexed on one S-CCPCH (even on the same 10 ms frame), or they can be carried on different S-CCPCH.

• The first S-CCPCH must have a spreading factor of 256, while the SF of the remaining S-CCPCHscan range between 256 and 4.

• UTRAN determines, whether a S-CCPCH has the TFCI (Transport Format Combination Indicator) included.

• Please note, that the UE must support both S-CCPCHs with and without TFCI.

Secondary Common Control Physical Channel (S-CCPCH)

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Slot 0 Slot 1 Slot 2 Slot 14

10 ms Frame

S-CCPCH

TFCI(optional)

Data Pilot bits

• carries PCH and FACH• Multiplexing of PCH and FACH on one

S-CCPCH, even one frame possible• with and without TFCI (UTRAN set)• SF = 4..256• (18 different slot formats• no inner loop power control

Secondary Common Control Physical Channel (S-CCPCH) (1/7)

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S-CCPCH (2/7): Number of S-CCPCHs

• The S-CCPCH (Secondary Common Control Physical Channel) carries FACH & PCH transport channels

• Parameter WCEL: NbrOfSCCPCHs (Number of SCCPCHs) tells how many SCCPCHswill be configured for the cell. (1, 2 or 3)

• If only 1 SCCPCH is used in a cell, it will carry FACH-c (containing DCCH/CCCH /BCCH), FACH-u (containing DTCH) and PCH. FACH and PCH multiplexed onto the same SCCPCH.

• If 2 SCCPCHs are used in a cell, the first SCCPCH will carry FACH-u & FACH-c and the second SCCPCH will always carry PCH only.

• If 3 SCCPCHs are used in a cell, the third SCCPCH will carry FACH-s (containing CTCH) & FACH-c idle (containing CCCH & BCCH). The third SCCPCH is only needed when Service Area Broadcast (SAB) is active in a cell.

NbrOfSCCPCHsWCEL; 1..3; 1; 1

(Range; Step; Default)

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S-CCPCH (3/7): Configuration 1

• If only 1 SCCPCH is used in a cell, it will carry FACH-c (containing DCCH/CCCH /BCCH), FACH-u (containing DTCH) and PCH. FACH and PCH multiplexed onto the same SCCPCH.

• the PCH bit rate is limited to 8 kbps

• the PCH always has priority

• the SF for SCCPCH, which is carrying FACH (with or without PCH), is 64 (60ksps)

Logical channel

Transport channel

Physical channel

DTCH DCCH CCCH BCCH PCCH

FACH-u FACH-c PCH

SCCPCH 1

SF 64

PtxSCCPCH1Transmission Power of SCCPCH1

WCEL; -35..15; 0.1; 0 dB(Range; Step; Default)

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S-CCPCH (4/7): Configuration 2 a & b

• If 2 SCCPCHs are used in a cell, the first SCCPCH will carry FACH-u & FACH-c and the second SCCPCH will always carry PCH only.

• PCH bit rate limited to 8 kbps (RU10 & earlier) or can be extended

to 24 kbps (RU20 feature RAN 1202: 24 kbps Paging Channel)

• if PCH24kbps enabled, NbrOfSCCPCHs must be set to “2” or “3”

Logicalchannel

Transportchannel

Physicalchannel

DTCH DCCH CCCH BCCH PCCH

FACH-u FACH-c PCH

SCCPCH 1 SCCPCH 2

SF 64 SF 256

PCH24kbpsEnabledWCEL; 0 (Disabled), 1 (Enabled);

default: 0 (Disabled)

SF 128or

PtxSCCPCH2used for 8 kbps paging

WCEL; -35..15; 0.1; -5 dB

PtxSCCPCH2SF128used for 24 kbps paging

WCEL; -35..15; 0.1; -2 dB

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Logical channel

Transport channel

Physical channel

DTCH DCCH CCCH BCCH CTCH

FACH-u PCHFACH-s

SCCPCH connected

SCCPCH idle

PCCH

FACH-c FACH-c

SCCPCH page

For SABFor SAB

S-CCPCH (5/7): Configuration 3a & b

• if 3 SCCPCHs are used in a cell, the third SCCPCH will carry FACH-s (containing CTCH) & FACH-c idle (containing CCCH & BCCH). The third SCCPCH is only needed when Service Area Broadcast (SAB) is active in a cell.

SF 64 SF 128 SF 256

SF 128orPtxSCCPCH3

WCEL; -35..15; 0.1; -2 dB

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S-CCPCH (6/7): Summary Power Setting

• The power of SCCPCHs are set relative to CPICH transmission power, but it is based on the bitrate.

• The SF for SCCPCH, which is carrying FACH (with or without PCH), is 64 (60ksps)

• The SF for SCCPCH, which is carrying PCH only is 256 (15ksps) or 128 (30ksps)

• The SF for SCCPCH, which is carrying FACH-s/FACH-c idle for SAB, is 128 (30ksps)

• Recommended value of the SCCPCH Tx power is depended on the number of SCCPCHs:

• WCEL: PtxSCCPCH1 (SF=64) for PCH/FACH or standalone FACH

• WCEL: PtxSCCPCH2 (SF=256) for Standalone PCH (8 kbps paging)

• WCEL: PtxSCCPCH2SF128 (SF=128) for Standalone PCH (24 kbps paging)

• WCEL: PtxSCCPCH3 (SF=128) for SAB

PtxSCCPCH1WCEL; -35..15; 0.1; 0 dB


PtxSCCPCH3WCEL; -35..15; 0.1; -2 dB

SF: Spreading Factor

PtxSCCPCH2used for 8 kbps paging

WCEL; -35..15; 0.1; -5 dB

PtxSCCPCH2SF128used for 24 kbps paging

WCEL; -35..15; 0.1; -2 dB

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FACH-u FACH-c(connected)

FACH-c(idle)

TFS

TTI

Channelcoding

CRC

0: 0x360 bits(0 kbit/s)


10 ms

TC 1/3

16 bit


1: 1x168 bits(16.8 kbit/s)

2: 2x168 bits(33.6 kbit/s)

10 ms

CC 1/2

16 bit


1: 1x168 bits(16.8 kbit/s)

10 ms

CC 1/3

16 bit

FACH-s


1: 1x168 bits(16.8 kbit/s)

10 ms

CC 1/3

16 bit

PCH



2: 1x240 bits(24 kbps)

10 ms

CC 1/2

16 bit

S-CCPCH (7/7) in NSN RAN

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Paging Indicator Channel (PICH)• UMTS provides the terminals with an efficient sleep mode operation. The UEs do not have to read and

process the content, transmitted during their paging occasion on their S-CCPCH. • Each S-CCPCH, which is used for paging, has an associated Paging Indicator Channel (PICH). • A PICH is a physical channel, which carries paging indicators. • A set of (paging indicator) bits within the PICH indicate to a UE, whether there is a paging occasion for

it. Only then, the UE listens to the S-CCPCH frame, which is transmitted 7680 chips after the PICH frame in order to see, whether there is indeed a paging message for it.

• The PICH is used with spreading factor 256. • 300 bits are transmitted in a 10 ms frame, and 288 of them are used for paging indication. • The UE was informed by the BCCH, how many paging indicators exist on a 10 ms frame.

• The number of paging indicator Np can be 18, 36, 72, and 144, and is set by the operator as part of the networkplanning process.

• The higher Np, the more paging indicators exist, the more paging groups exist, among which UEs can be distributed on.

• Consequently, the lower the probability, that a UE reacts on a paging indicator, while there is no paging message in the associated S-CCPCH frame.

• But a high number of paging indicators results in a comparatively high output power for the PICH, because less bits exists within a paging indicator to indicate the paging event.

• The operator then also has to consider, if he has to increase the number of paging attempts.

• How does the UE and UTRAN determine the paging indicator (PI) and the Paging Occasion?• This is shown in one of the next slides.

The Paging Process

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PICH frame

S-CCPCH frame, associated with PICH frame

τPICH

= 7680chips

b287 b288 b299b286b0 b1

for paging indication no transmission

# of pagingindicators per frame

(Np)

18

36

72

144

τS-CCPCH

S-CCPCH & associated PICH

NpRepetition of PICH bits

18, 36, 72 144

PtxPICH-10..5; 1; -8 dB


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• The network has detected, that there is data to be transmitted to the UE. • Both in the RRC idle mode and in the RRC connected mode (e.g. in the sub-state CELL_PCH) a UE

may get paged. But how does the mobile know, when it was paged?• And in order to save battery power, we don‘t want the UE to listen permanently to paging

channel – instead, we want to have discontinuous reception (DRX) of paging messages. • But when and where does the UE listen to the paging messages?

• Cell system information is broadcasted via the P-CCPCH. • The cell system information is organised in System Information Blocks (SIB).

• SIB5 informs the mobile phones about the common channel configuration, including a list of S-CCPCH descriptions.

• The first 1 to K entries transmit the (transport channel) PCH, while the remaining S-CCPCH in the list hold no paging information.

• The UE determines the S-CCPCH, where it is paged, by its IMSI and the number of PCH/S-CCPCHscarrying S-CCPCHs K.

• When paging the UE, the RNC knows the UE‘s IMSI, too, so that it can put the paging message on the correct PCH transport channel.

• Discontinuous Reception (DRX) of paging messages is supported. • A DRX cycle length k has to be set in the network planning process for the cs domain, ps domain, and

UTRAN.• k ranges between 3 and 9. If for instance k=6, then the UE is paged every 2k = 640 ms.• If the UE is in the idle mode, it takes the smaller k-value of either the cs- or ps-domain.• If the UE is in the connected mode, it has to select the smallest k-value of UTRAN and the CN, it is not

connected to.

S-CCPCH and the Paging Process

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Node B

UTRANP-CCPCH/BCCH (SIB 5)

commonchannel

definition,including

S-CCPCH carrying 1 PCH



S-CCPCH without PCH

S-CCPCH without PCH

a lists ofUE

Index of S-CCPCHs

0

1

K-1

UE‘s paging channel:

Index = IMSI mod K

e.g. if IMSI mod K = 1

„my pagingchannel“

RNC

S-CCPCH & Paging Process

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2k framesk = 3..9

Duration:

CN domain specificDRX cycle lengths

(option)

UE

CS Domain PS Domain

Update:a) derived by NAS

negotiationb) otherwise:

system info

Update:locally with

system info

k1 k2

UTRAN

Update:a) derived by NAS

negotiationb) otherwise:

system info

k3

RRC connectedmode

stores

if RRC idle:UE DRX cycle length is

min (k1, k2)

if RRC connected:UE DRX cycle length is

min (k3, kdomain with no Iu-signalling connection)

Example withtwo CN domains

Paging & Discontinuous Reception (FDD mode)

UTRAN_DRX_length80; 160; 320; 640; 1280;

2560; 5120 ms

CNDRXLength640; 1280; 2560; 5120 ms

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UE

my pagingindicator (PI)

PI = ( IMSI div 8192) mod Np

DRX index

number of paging indicators18, 36, 72, 144

Paging Occasion = (IMSI div K) mod (DRX cycle length) + n * DRX cycle length

UE

When willI get paged? number of S-CCPCH with PCH

FDDmode

Paging Indicator & Paging Occasion (FDD mode)

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Example – Paging instant and group calculation

• UE calculates paging instant based on following information as presented before

• IMSI

• Number of S-CCPCH (K)

• DRX cycle length (k)

• Np

• User are distributed to different paging groups based on their IMSI. Paging group size can be calculated based on

• Number of S-CCPCH (K)

• DRX cycle length (k)

• Np

• Paging group size affects on how often UE has to decode paging message from S-CCPCH Power consumption

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Example – Paging instant & group calculation

K (Number of S-CCPCH with PCH) 1k (DRX length) 6DRX cycle length 64 framesIMSI 358506452377Which S-CCPCH #? 0IMSI div K 358506452377When (Paging occation, SFN)? 25 + n*DRX cycle length

Np 72 PIs/frameDRX Index 43762994My PI? 26

Number of subsc. In LA/RA 100000Number of subsc. Per S-CCPCH 100000Number of subsc. Paging occation (PICH frame) 1562.5Number of subsc. Per PI 21.7

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In the random access, initiated by the UE, two physical channels are involved:

Physical Random Access Channel (PRACH)• The physical random access is decomposed into the transmission of preambles in the UL. • Each preamble is transmitted with a higher output power as the preceding one. • After the transmission of a preamble, the UE waits for a response by the Node B. • This response is sent with the physical channel Acquisition Indication Channel (AICH), telling

the UE, that the Node B as acquired the preamble transmission of the random access.• Thereafter, the UE sends the message itself, which is the RACH/CCCH of the higher layers.• The preambles are used to allow the UE to start the access with a very low output power.

• If it had started with a too high transmission output power, it would have caused interference to the ongoing transmissions in the serving and neighbouring cells.

• Please note, that the PRACH is not only used to establish a signalling connection to UTRAN, it can be also used to transmit very small amounts of user data.

Acquisition Indication Channel (AICH)• This physical channel indicates to the UE, that it has received the PRACH preamble and is now

waiting for the PRACH message part.

Random Access

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UEPRACH (preamble)

PRACH (preamble)

PRACH (preamble)

PRACH (message part)

AICH

No responseby the

Node B

No responseby the

Node B

I just detecteda PRACH preamble

OLA!

Random Access – the Working Principle

Node B

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• The properties of the PRACH are broadcasted (SIB5, SIB6). • The candidate PRACH is randomly selected (if there are several PRACH advertised in the cell) as well

as the access slots within the PRACH. • 15 access slots are given in a PRACH, each access slot lasting two timeslots or 5120 chips.

• In other words, the access slots stretch over two 10 ms frames.• A PRACH preamble, which is transmitted in an access slot, has a length of 4096 chips. • Also the AICH is organised in (AICH) access slots, which stretch over two timeslots.

• AICH access slots are time aligned with the P-CCPCH.

• The UE sends one preamble in UL access slot n. • It expects to receive a response from the Node B in the DL (AICH) access slot n, τp-a chips later on. • If there is no response, the UE sends the next preamble τp-p chips after the first one.• The maximum numbers of preambles in one preamble access attempt can be set between 1 and 64.• The number of PRACH preamble cycles can be set between 1 and 32.• If the AICH_Transmission_Timing parameter in the SIB is set to BCCH SIB5 & SIB6 to

• 0 = then, the minimum preamble-to-preamble distance is 6 access slots, the minimum preamble-to-message distance is 6 access slots, and the preamble-to-acquisition indication is 3 timeslots.

• 1 = then, the minimum preamble-to-preamble distance is 8 access slots, the minimum preamble-to-message distance is 8 access slots, and the preamble-to-acquisition indication is 4 timeslots.

Random Access Timing

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SFN mod 2 = 0 SFN mod 2 = 0SFN mod 2 = 1

P-CCPCHAICH access

slots 0 1 1282 1175 964 13103 14 0 1 2 75 643

5120chips

Preamble

5120 chips

Preamble

AS # i

4096 chips

preamble-to-preambledistance τp-p

UE point of view

PRACHaccess slots

AICHaccess slots

Messagepart

preamble-to-messagedistance τp-m

AcquisitionIndication

preamble-to-AIdistance τp-a

AS # i

Random Access Timing

TS 25.211:Preamble-to-Preamble distance τp-p ≥ τp-p,min = 6 / 8 SlotsPreamble-to-AI distance τp-a = 3 / 4 SlotsPreamble-to-Message distance τp-m = 6 / 8 Slots

Broadcasted by P-CCPCH; NSN (WCEL):

AICHTraTime = 0, 1; 0

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RACH Sub-channels• RACH sub-channels were introduced to define a sub-set of UL access slots.• A total number of 12 RACH sub-channels exist, numbered from 0 to 11. • The PRACH access slots are numbered relative to the AICH assess slot.

• The offset is given by τp-a (see preceding slides).• The AICH is transmitted synchronised to the P-CCPCH.• An access slot of sub-channel #i is using access slot #i, when SFN mod 8 = 0 or 1. It is then using every

12th access slot following access slot #i. • You can see in the figure on the right hand side all existing sub-channels and the timeslots, they are

using.

Access Classes (AS) and Access Service Classes (ASC)• Access Service Classes were introduced to allow priority access to the PRACH resources, by

associating ASCs to specific access slot spaces (RACH sub-channels) and signatures. • 8 ASC can be specified by the operator; The UE determines the ASC and its associated resources from

SIB5 & SIB7. • The mapping of the subscribers access classes (1..15) is part of the SIB5.

RACH Access Slot Sets• Two access slot set were specified:• Access slot set 1 holds PRACH access slots 1 to 7, i.e. the PRACH access slots, whose corresponding

AICH access slots begin in a P-CCPCH with a SFN modulo 2 = 0.• Access slot set 2 holds PRACH access slots 8 to 15, i.e. the PRACH access slots, whose

corresponding AICH access slots begin in a P-CCPCH with a SFN modulo 2 = 1.

RACH Sub-channels and Access Service Classes

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SFN mod 8 of thecorresponding

P-CCPCH frame

0

1

2

3

4

5

6

7

0

12

9

6

3

1

13

10

7

4

2

14

11

8

5

3

0

12

9

6

4

1

13

10

7

5

2

14

11

8

6

3

0

12

9

7

4

1

13

10

8

5

2

14

11

9

6

3

0

12

10

7

4

1

13

Sub-channel number

1 2 3 4 5 6 7 8 9 10 11

11

8

5

2

14

0

(cited from TS 25.214 V5.11.0, chap. 6.1.1)

Node B

BCCH (SIB 5, SIB 7)

UE• ASCs & their PRACH access resources + signatures,• AC mapping into ASCs

PRACH Sub-channels and Access Service Classes (ASC)

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• In the PRACH preamble, a random preamble code is used.

• This code is composed from a• Preamble Scrambling Code and a• Preamble Signature

• There is a total of 16 preamble signatures of 16 bit length, which is repeated 256 times within one preamble.

• When monitoring the cell system information, the UE gets the information, which of the signatures are available for use in the cell. (see IE PRACH info)

• There are 8192 preamble scrambling codes, which are constructed from the long scrambling code sequences.

• The PRACH preamble scrambling codes are organised in 512 groups, with each group holding 16 members.

• There are also 512 primary scrambling codes available in UMTS, and one of them is in use in the cell.• If the primary scrambling code s is in use in the cell, then only the PRACH preamble scrambling codes

belonging to PRACH preamble scrambling code group s can be used for random access.• Consequently, 16 PRACH preamble scrambling codes are left, and the BCCH is used to inform the

UE, which PRACH preamble scrambling codes can be used. (see IE PRACH info)

PRACH Preamble

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Node B

UTRANBCCH

UE RNC

Pi Pi Pi Pi

Preamble Signature(16 different versions)

16 chip

256 repetitions

⊗PRACH Preamble Scrambling Code

• 512 groups, each with 16 preamble scrambling codes

• Cell‘s primary scrambling codes associated with preamble scrambling code group

• available signatures for random access

• available preamble scrambling codes

• available spreading factor

• available sub-channels• etc.

PRACH Preamble

AllowedPreambleSignatures

WCEL; 16-bit field;0….01111; max. 4 signatures allowed

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• The length of the PRACH message part can be 10 ms or 20 ms. • Its length is set as Transmission Time Interval (TTI) value by the higher layers. • UL, we apply code multiplexing. • L1 Control data are transmitted with SF 256, while message data can be transmitted with SF 256,

128, 64 or 32. • The message data contains the information, given by the RACH. • The control data contains 8 known pilot bits / slot. 15 different pilot bit sequences exist – they are

associated with the slot, where the transmission takes place within the 10 ms message frame. 2 bits in the control data carry TFCI bits / slot.

• Which spreading code is allocated to the message part? • The message part‘s channelisation code is determined from the signature, which was used by the UE

in the preamble. • 16 different signatures exist, and each can be correlated to a channelisation code in the

channelisation code tree with spreading factor 16. • The channelisation codes are calculated like this:

• Each signature has a number k, with 0 ≤ k ≤ 15.• For the control data, the channelisation code CCH,256,n is used, with n = 16*k + 15.• For the message data, the channelisation code CCH,SF,m is used, with m = SF*k/16.• The scrambling code is the same, which was used for the PRACH preamble.

PRACH Message Part

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10 ms Frame

RACH data

L1 control data 8 Pilot bits (sequence depends on slot number) 2 TFCI bits

data

• SF = 256• channelisation code:

CCH,256,16*k+15, withk = signature number

• SF = 256, 128, 64, or 32• channelisation code:• CCH,SF,SF*k/16, with

k = signature number

Scrambling code = PRACH preamble scrambling code

PRACH Message Part

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• When it comes to the random access, two questions have to be asked: • What kind of output power does the UE select for the first preamble? • And how does the output power change with the subsequent preambles and the message part?

Open Loop Power Control• The output power for the first PRACH preamble is based in parts on broadcasted parameters (SIB6, if

missing, from SIB5; and SIB7).• The UE acquires the Node B‘s “Primary CPICH TX Power“, a “Constant Value“, and the “UL

Interference“ level.• The UE also determines the received CPICH RSCP (variable CPICH_RSCP).• Then, it calculates the power for the first preamble:

• Preamble_Initial_Power = Primary CPICH TX power – CPICH_RSCP + UL interference + Required received C/I

• The “Required received C/I“ is an UTRAN parameter (NSN: PRACHRequiredReceivedCI; range: -35 ... -10 dB, step 1 dB default: -25dB).

• The “UL Interference“ is measured by the Node B and broadcasted via SIB 7 on P-CCPCH to the UEs.

• The power ramp steps from one preamble to the next can be set between 1 and 8 dB (step size 1dB). • The power offset between the last PRACH and the PRACH control message can be set between –5

and 10 dB (step size 1dB).• The gain factor ßc is used for the PRACH control part.

PRACH Power Setting

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Preamble_Initial_Power =

Primary CPICH TX power– CPICH_RSCP+ UL interference + Required received C/I

PRACH Power Setting

Downlink / BSDownlink / BS

Preamble 1 Message part

…. ….

Preamble n

PRACH_preamble_retrans:The maximum number of preambles allowed in 1 preamble ramping cycle

RACH_tx_Max: # of preamble power ramping cycles that can be done

before RACH transmission failure is reported,

UEtxPowerMaxPRACHWCEL: -50..33; 1; 21 dBm

PRACH_preamble_retransWCEL: 1..64; 1; 8

PowerRampStepPRACHpreamble

WCEL: 1..8; 1; 2 dB

Uplink / UEUplink / UE

PowerOffsetLastPreamble

PRACHmessageWCEL:

-5..10; 1; 2 dB

RACH_tx_MaxWCEL: 1..32; 1; 8

(Range, Steps; Default)

PRACHRequiredReceivedCIWCEL: -35..-10; 1; -25 dB

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• The AICH is used to indicate to UEs, that their PRACH preamble was received, and that the Node B is expecting to receive the PRACH message part next.

• The AICH returns an indicator of signature s, which was used in the PRACH preamble.• Spreading factor is fixed to 256 for the AICH. • The AICH is transmitted via 15 access slots, each lasting 5120 chips.

• Consequently, the AICH access slots are distributed over two consecutive 10 ms frames. • Similar to the PRACH preamble, only 4096 chips are used to transmit the Acquisition Indicator part.

• 32 real value symbols are transmitted.• Each real value is calculated by a sum of AIsbs,j. • AI is an acquisition indicator for signature s. • If signature s is positively confirmed, Ais is set to +1; a negative confirmation results in –1; if

signature s is not part of the active signature set, then Ais is set to 0. bs,j stands for signature pattern j, with j = 0..31.

• If more than one PRACH preamble signatures within one PRACH access slot is detected correctly, the Node B sends the AIs of all the detected signatures simultaneously in the 1st or 2nd

AICH access slot after the PRACH access slot.• If the number of correctly detected signatures is higher than the Node B's capability to

simultaneously decode the PRACH message parts, a negative AIs is used for generating the AIsfor those PRACH messages, which can not be decoded within the default message part transmission timing.

• A negative AI indicates to the MS that it shall exit the random access procedure.• The Node B 's capability to decode the PRACH message parts is determined in the RNC and

transmitted to the Node B.

Acquisition Indication Channel (AICH)

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Access Slot 0 Access Slot 1 Access Slot 2 Access Slot 14

20 ms Frame

a0 a1 a2 a29 a30 a31

=

=15

0js,sj bAIa

s

AICH signature pattern (fixed)

Acquisition Indicator• +1 if signature s is positively confirmed• -1 if signature s is negatively confirmed• 0 if signature s is not included in the

set of available signatures

Acquisition Indication Channel (AICH)

PtxAICH-22..5; 1; -8 dB


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Summary of RACH procedure

1- Decode from BCCH• Available RACH spreading factors• RACH scrambling code number• UE Access Service Class (ASC) info• Signatures and sub-channels for each ASC• Power step, RACH C/I requirement = “Constant”, BS interference level

2 – Calculate initial preamble power3 – Calculate available access slots in the next full access slot set and select randomly one of those4 – Select randomly one of the available signatures5 – Transmit preamble in the selected access slot with selected signature6 – Monitor AICH

• IF no AICH• Increase the preamble power• Select next available access slot & Go to 3

• IF negative AICH or max. number of preambles exceeded• Exit RACH procedure

• IF positive AICH• Transmit RACH message with same scrambling code and channelisation code related to signature

(Adopted from TS 25.214)

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• Part VI: Dedicated Physical Channel - Downlink

• Part VII: Dedicated Physical Channel - Uplink

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• The DL DPCH is used to transmit the DCH data. • Control information and user data are time multiplexed.• The control data is associated with the Dedicated Physical Control Channel (DPCCH), while the user

data is associated with the Dedicated Physical Data Channel (DPDCH). • The transmission is organised in 10 ms radio frames, which are divided into 15 timeslots.• The timeslot length is 2560 chips. Within each timeslot, following fields can be found:

• Data field 1 and data field 2, which carry DPDCH information• Transmission Power Control (TPC) bit field• Transport Format Combination Indicator (TFCI) field, which is optional• Pilot bits

• The exact length of the fields depends on the slot format, which is determined by higher layers.• The TFCI is optional, because it is not required for services with fixed data rates.• Slot format are also defined for the compressed mode; hereby different slot formats are in used, when

compression is achieved by a changed spreading factor or a changed puncturing scheme. • The pilot sequence is used for channel estimation as well as for the SIR ratio determination within the

inner loop power control.• The number of the pilot bits can be 2, 4, 8 and 16 – it is adjusted with the spreading factor.• A similar adjustment is done for the TPC value; its bit numbers range between 2, 4 and 8.

• The spreading factor for a DPCH can range between 4 and 512. The spreading factor can be changed every TTI period.

• Superframes last 720 ms and were introduced for GSM-UMTS handover support.

Downlink Dedicated Physical Channel (DPCH)

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10 ms Frame

TPCbits

Pilot bitsTFCIbits

(optional)Data 2 bitsData 1 bits

DPDCHDPDCH DPCCH DPCCH

Radio Frame0

Radio Frame1

Radio Frame2

Radio Frame71

Superframe = 720 ms

• 17 different slot formats• Compressed mode slot

format for changed SF & changed puncturing

Downlink Dedicated Physical Channel (DPCH)

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• Power offsets for the optional TFCI, TPC and pilot bits have to be specified during the radio link setup.

• This is done with the NBAP message RADIO LINK SETUP REQUEST message, where following parameters are set:

• PO1: defines the power offset for the TFCI bits; it ranges between 0 and 6 dB with a 0.25 step size.

• PO2: defines the power offset for the TPC bits; it ranges between 0 and 6 dB with a 0.25 step size.

• PO3: defines the power offset for the pilot bits; it ranges between 0 and 6 dB with a 0.25 step size.

• In the same message, the TFCS, DL DPCH slot format, multiplexing position, FDD TPC DL step size increase, etc. are defined.

• The FDD TPC DL step size is used for the DL inner loop power control.

Power Offsets for the DPCH

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Node B RNC

DCH Data Frame

Iub

UE

Uu

PO1

NBAP: RADIO LINK SETUP REQUEST

TPCbits

Pilot bitsTFCIbits

(optional) Data 2 bitsData 1 bits

PO3PO2

• Power offsets• TFCS• DL DPCH slot format• FDD DL TPC step

size• ...

P0x: 0..6 dBstep size: 0.25 dB

Power Offsets for the DPCH

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• Inner loop power control is also often called (fast) closed loop power control. • It takes place between the UE and the Node B.• We talk about UL inner loop power control, when the Node B returns immediately after the reception

of a UE‘s signal a power control command to the UE. By doing so, the UE‘s SIR ratio is kept at a certain level (the details will be discussed later on in the course).

• DL inner loop power control control is more complex. When the UE receives the transmission of the Node B, the UE returns immediately a transmission power control command to the Node B, telling the Node B either to increase or decrease its output power for the UE‘s DPCH.

• The Node B‘s transmission power can be changed by 0.5, 1, 1.5 or 2 dB. 1 dB must be supported by the equipment. If other step sizes are supported or selected, depends on manufacturer or operator.

• The transmission output power for a DPCH has to be balanced for the PICH, which adds to the power step size.

• There are 2 DL inner loop power control modes:• DPC_MODE = 0: Each timeslot, a unique TPC command is send UL.• DPC_MODE = 1: 3 consecutive timeslots, the same TPC command is transmitted.

• One reason for the UE to request higher output power is the case that the QoS target is not met. • It requests the Node B to transmit with a higher output power, hoping to increase the quality

of the connection due to an increased SIR at the UE‘s receiver.• But this also increases the interference level for other phones in the cell and neighbouring

cells.• The operator can decide, whether to set the parameter Limited Power Increase Used.

• If used, the operator can limit the output power raise within a time period.

DL Inner Loop Power Control

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DPC_MODE = 0

unique TPC commandper TS

DPC_MODE = 1

same TPC over 3 TS,then new command

two modescell

TPC

TPCest per1 TS / 3 TS

DL Inner Loop Power Control

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DL Inner Loop PC: UTRAN behaviour

UE

Measured SIR < SIR target --> TPC command is "1"

Measured SIR => SIR target --> TPC command is "0"

Compare measured SIR with SIR target

value received from DL outer loop PC

Measure received SIR on DL DPCCH

WCDMA BTS

BS sets the power on DL DPCCH andDL DPDCH following way:

TPC command = "1" --> increase power by 1 dBTPC command = "0" --> decrease power by 1 dB

DL DPCCH + DPDCHs

Send TPC command on UL DPCCH

Changed power on DL DPCCH + DPDCHs

• Receiving the TPC commands BS adjusts the DL DPCCH/DPDCH power

• UTRAN shall estimate the transmitted TPC command TPCest to be 0 or 1; it shall update the power every slot.

• After estimating the k:th TPC command, UTRAN shall adjust the current DL power P(k-1) [dB] to a new power P(k) [dB]:

P(k) = P(k - 1) + PTPC(k)

where PTPC(k) is the k:th power adjustment due to the inner loop power control

DownlinkInnerLoopPCStepSize

DownlinkInnerLoopPCStepSize

RNC: 0.5..2; 0.5; 1 dB(Range, Steps; Default)

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• The P-CCPCH is the timing reference for all physical channels.• As can be seen in the figure on the right hand side, following timing relationships exist:

• The SCH, CPICH, P-CCPCH and DSCH have an identical timing.• S-CCPCHs can be transmitted with a timing offset τS-CCPCH,n. (n stands for the nth S-

CCPCH.)• The timing offset may be different for each S-CCPCH, but it is always a multiple of 256 chips,

i.e. τS-CCPCH,n = Tn * 256 chips, with Tn ∈ {0,..,149}.• We have already seen, that some S-CCPCHs transmit paging information.• The associated PICH frame ends τPICH = 7680 chips before the associated S-CCPCH frame.

• DPCHs are also transmitted with a timing offset, which may be different for different DPCHs.• The timing offset τDPCH,k is – similar to the S-CCPCH – a multiple of 256, i.e.

τDPCH,k = Tk * 256 chips, with Tk ∈ {0,..,149}.• The timing of a DSCH, which is allociated with a DPCH, is explained later on in the course

documentation.

• AICH access slots for the RACH and CPCH also require a time organisation.• As we have seen e.g. with the RACH, an access slot combines two timeslots.• How can the timing to the P-CCPCH be identified?• The P-CCPCH transmits the cell system frame number (SFN), which increases by one with

each radio frame.• The AICH access slot number 0 starts simultaneously with the P-CCPCH frame, whose SFN

modulo 2 is zero.

Timing Relationship between Physical Channels

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SFN mod 2 = 0 SFN mod 2 = 1

P-CCPCH

AICH accessslots 0 1 1282 1175 964 13103 14 0

SCH

nth S-CCPCHτS-CCPCH,n

kth S-DPCHτDPCH,k

0..38144 (step size 256)

0..38144 (step size 256)

Timing Relationship between Physical Channels

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• A major problem arises, when the UE is connected to several cells simultaneously.• The active set cells must transmit the DL DPCH in a way that their arrival time is within a receive

window at the UE. • DLnom is the nominal receive time of a radio frame with a specific CFN at the UE. • “T0” = 4 TS later, the UE starts to transmit the a radio frame with the same CFN.• “T0” is always calculated relative to the UE transmission start point.

• Of course, due to multipath propagation and handover situations, the reception of the beginning of a DL radio frame is often not exactly at To times before the UE starts to send.

• When the UE is in a soft handover, and moving from one cell to another, the radio frames arrivingfrom one cell may arrive later and later, while the radio frames of another cell arrive earlier. I.e., the reception from the two neighbouring cells drifts apart.

• The picture on the right hand side is only valid, if the UE is in the macro-diversity state. In this case, the parameter Tm is the time difference between the nominal DL received signal DLnom and the appearance of the first P-CCPCH of the neighbouring cell.

• The serving RNC determines the required offset between P-CCPCH of the neighbouring cell and the DL DPCH.

• This information is sent as Frame Offset and Chip Offset to the target Node B.• The target Node B can change the transmission of the DL DPCH only with a step size of 256

chips, in order to be synchronised to the SCH and P-CCPCH structure.• The S-RNC informs also the UE about the Frame Offset.

Radio Interface Synchronisation

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UEcell1

UL DPCH

(e.g. CFN = 12)

T0 =1024chips

DLnom

(e.g. CFN = 12)

cell2= target

cell for HO

P-CCPCH2

(e.g. SFN2 = 2555)

earliest multipath

Tm =timing differencerange: 0..38399Res.: 1 chip

SRNC

(Frame Offset, Chip Offset)

Relative timingbetween DL DPCHand P-CCPCHrange: 0..38144res.: 256 chips

Offsetbetween DL DPCHand P-CCPCHrange: 0..38399res.: 1 chip

(Frame Offset)(TM)

Radio Interface Synchronisation

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• Part VI: Dedicated Physical Channel - Downlink

• Part VII: Dedicated Physical Channel - Uplink

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The UL dedicated physical channel transmission, we identify two types of physical channels:• Dedicated Physical Control Channel (DPCCH),

• Which is always transmitted with SF 256.• Following fields are defined on the DPCCH:

• pilot bits for channel estimation. Their number can be 3, 4, 5, 6, 7 or 8.• Transmitter Power Control (TPC), with either one or two bits• Transport Format Combination Indicator (TFCI), which is optional, and a• Feedback Indicator (FBI). Bits can be set for the closed loop mode transmit diversity

and site selection diversity transmission (SSDT)• 6 different slot formats were specified for the DPCCH. Variations exist for the compressed

mode. • Dedicated Physical Data Channel (DPDCH),

• Which is used for user data transfer.• Its SF ranges between 4 and 256.• 7 different slot formats are defined, which are set by the higher layers.

• The DPCCH and DPDCH are combined by I/Q code multiplexing with each multiframe. • Multicode usage is possible. If applied, additional DPDCH are added to the UL transmission, but no

additional DPCCHs! The maximum number of DPDCH is 6. • The transmission itself is organised in 10 ms radio frames, which are divided into 15 timeslots. The

timeslot length is 2560 chips.

Uplink Dedicated Physical Channels

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10 ms Frame

TPCbits

Pilot bits TFCI bits(optional)

Data 1 bits

Radio Frame0

Radio Frame1

Radio Frame2

Radio Frame71

Superframe = 720 ms

DPDCHSF = 256 - 4

DPCCHSF 256

FBI bits(optional)

• 7 different slot formats

• 6 different slot formats• Compressed mode slot

format for changed SF & changed puncturing

Feedback Indicator for• Closed loop mode transmit diversity, &• Site selection diversity transmission (SSDT)

Uplink Dedicated Physical Channels

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• Discontinuous transmission (DTX) is supported for the DCH both UL and DL. • If DTX is applied in the DL – as it is done with speech – then 3000 bursts are generated in one

second. (1500 times the pilot sequence, 1500 times the TPC bits)• This causes two problems:

• Inter-frequency interference, caused by the burst generation.• At the Node B, the problem can be overcome with exquisite filter equipment. This filter

equipment is expensive and heavy. Therefore it cannot be applied in the UE.• The UE‘s solution is I/Q code multiplexing, with a continuous transmission for the DPCCH.

DPDCH changes can still occur, but they are limited to the TTI period. The minimum TTI period is 10 ms. The same effects can be observed, then the DPDCH data rate and with it its output power is changing.

• 3000 bursts causes audible interference with other equipment – just see for example GSM.• By reducing the changes to the TTI period, the audible interference is reduced, too.

• Determination of the power difference between the DPCCH and DPDCH• I/Q code multiplexing is done in the UL, i.e. the DPCCH and DPDCH are transmitted with different

codes (and possible with different spreading factors). Gain factors are specified: βc is the gain factor for the DPCCH, while βd is the gain factor for the DPDCH. The gain factors may vary foreach TFC. There are two ways, how the UE may learn about the gain factors:

• The gain factors are signalled for each TFC. If so, the nominal power relation Aj between the DPDCH and DPCCH is βd/βc.

• The gain factor is calculated based on reference TFCs. (The details for gain factor calculation based on reference TFCs are not discussed in this course.)

Discontinuous Transmission and Power Offsets

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DPCCH

DPDCH

DPCCH

DPDCH

DPCCH

DPDCH

TTI TTI TTI

UL DPDCH/DPCH Power Difference:

DPCCH

DPDCH

=βd

βc

=Nominal Power Relation Aj

two methods to determine the gain factors:• signalled for each TFCs• calculation based on reference TFCs

Discontinuous Transmission and Power Offsets

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• The subscriber is mobile. The distance of the UE from a Node B is changing over time.• With growing distance and a fixed output power at the UE, the received signals at the Node B

become weaker. • UE output power adjustment is required.• But the UE‘s received signal strength can change fast – Rayleigh fading in one phenomena,

which causes this event. • As a consequence, a fast UL power control is required.

• This power control is called UL inner loop power control, though many experts also call it (fast) closed loop power control.

• At each active set cell, a target SIR (SIRtarget) is set for each UE. The active set cells estimate SIReston the UE‘s receiving UL DPCH. Each active set cell determines the TPC value. If the estimated SIR is larger than the UE‘s target SIR, then the determined TPC value is 0. Otherwise it is 1. These values are determined on timeslot basis and returned on timeslot basis.

• The UE has to determine the power control command (TPC_cmd). The higher layer control protocol RRC is used to inform the UE, which power control algorithm to apply. This informs the UE also how to generate a power control command from the incoming TPC-values. There are power control algorithm 1 (PCA1) and 2 (PCA2), which are described in the figure following the next one. Given the power control algorithm and the TPC-values, the UE determines, how to modify the transmit power for the DPCCH: ΔDPCCH = Δ TPC × TPC_cmd. Δ TPC stands for the transmission power step size.

(continued on the next text slide)

UL Inner Loop Power Control

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time

SIRest

SIRtarget

TCP = 1

TCP = 1

TCP = 0

TCP = 0 TPC TPC_cmd

in FDD mode:1500 times per second


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Power Control Algorithm 1• is applied in medium speed environments.• Here, the UE is commanded to modify its transmit power every timeslot.• If the received TPC value is 1, the UE increases the transmission output at the DPCCH by

ΔDPCCH, otherwise it decreases it by ΔDPCCH. • The ΔDPCCH is either 1 or 2 dB, as set by the higher layer protocols.• TPC values from the same radio link set represent one TLC_cmd.• TPC_cmds from different radio link sets have to be weighted, if there is no reliable

interpretation.

Power Control Algorithm 2• was specified to allow smaller step sizes in the power control in comparison to PCA1.• This is necessary in very low and high speed environments.• In these environments, PCA1 may result in oscillating around the target SIR. • PCA2 changes only with every 5th timeslot, i.e. the TPC_cmd is set to 0 the first 4 timeslots.

In timeslot 5, the TPC_cmd is –1, 0, or 1.• For each radio set, the TPC_cmd is temporarily determined. This can be seen in the next

figure.• The temporary transmission power commands (TPC_temp) are combined as can be seen in

the figure after the next one. Here you can see, how the final TPC_cmd is determined.


NSN supports only PCA 1.

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PCA2 PCA1 PCA2

algorithms for processing power control commands TPC_cmd

PCA1

TPC_cmd for each TSTPC_cmd values: +1, -1step size Δ TPC: 1dB or 2dB

PCA2

TPC_cmd for 5th TSTPC_cmd values: +1, 0, -1step size Δ TPC: 1dB

UL DPCCH power adjustment: ΔDPCCH = Δ TPC × TPC_cmd

km/h0 ≈ 3 ≈ 80Rayleigh fading can be compensated


NSN supports only

PCA 1 with step size 1 dB

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Example: reliable transmission

Cell 1Cell 2

Cell 3

TPC1 = 1 TPC3 = 0

TPC3 = 1

TPC_cmd = -1 (Down)

Power Control Algorithm 1

NSN: only PCA 1 is supported.

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TPC = 1

TPC = 1

TPC = 1

TPC = 1

TPC = 1

TPC = 1

TPC = 0

TPC = 1

TPC = 0

TPC = 1

TPC = 0

TPC = 0

TPC = 0

TPC = 0

TPC = 0

TPC_temp

0

0

0

0

1

0

0

00

0

0

0

0

0-1

• if all TPC-values = 1 TPC_temp = +1

• if all TPC-values = 0 TPC_temp = -1

• otherwise TPC_temp = 0

Power Control Algorithm 2

NSN: PCA 2 is not supported.

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• UTRAN shall start the transmission of the DL DPCCH and may start the transmission of DPDCH if any data is to be transmitted.

• The UE UL DPCCH transmission shall start• When higher layers consider the DL physical channel established, if no activation time for UL

DPCCH has been signalled to UE• If an activation time has been given, UL DPCCH transmission shall not start before the DL

physical channel has been established and the activation time has been reached.• When we look to the PRACH, we can see, that preambles were used to avoid UEs to access UTRAN

with a too high initial transmission power. • The same principle is applied for the DPCH.• The UE transmits between 0 to 7 radio frames only the DPCCH UL, before the DPDCH is code

multiplexed.• The number of radio frames is set by the higher layers (RRC resp. the operator).• Also for this period of time, only DPCCH can be found in the DL.• The UE can be also informed about a delay regarding RRC signalling – this is called SRB delay,

which can also last 0 to 7 radio frames. The SRB delay follows after the DPCCH preamble. • How to set the transmission power of the first UL DPCCH preamble?

• Its power level is• DPCCH_Initial_power = – CPICH_RSCP + DPCCH_Power_offset• The DPCCH Power Offset is retrieved from RRC messages. It’s value ranges between –164

and –6 dB (step size 2 dB). CPICH_RSCP is the received signal code power on the P-CPICH, measured by the UE.

Initial UL DCH Transmission

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receptionat UE

trans-mission

at UE

DPCCH only DPCCH & DPDCH

0 to 7 frames for power control preamble

DPCCH only DPCCH & DPDCH

DPCCH_Initial_power = – CPICH_RSCP + DPCCH_Power_offset

Initial UL DCH Transmission

DL Synch & Activation time

0 to 7 frames ofSRB delay

PCPreambleRNC: 0..7; 1; 0

SRBDelayRNC: 0..7; 1; 7

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For this course module, following 3GPP specifications were used:

• TS 25.211 V6, Physical channels & mapping of transport channels onto physical channels• TS 25.212 V6, Multiplexing and channel coding (FDD) • TS 25.213 V6, Spreading and modulation (FDD) • TS 25.214 V6, Physical layer procedures (FDD) • TS 25.215 V6, Physical layer; Measurements (FDD) • TS 25.301 V6, Radio interface protocol architecture • TS 25.302 V6, Services provided by the physical layer• TS 25.306 V5 – V8: UE Radio Access capabilities• TS 25.321 V6, Medium Access Control (MAC) protocol specification• TS 25.331 V6, Radio Resource Control (RRC) protocol specification • TS 25.402 V6, Synchronization in UTRAN Stage 2 • TS 25.433 V6, UTRAN Iub interface Node B Application Part (NBAP) signalling

NSN WCDMA Product documentation

References

the physical layer

Documents