Umts Channel Ppt1

8/12/2019 Umts Channel Ppt1

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UMTS Channel


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UMTS Channel

Physical Layer

Channel Mapping

Transport Channel Format

Cell Synchronisation


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OSI Model


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OSI Model

Transmitting RAW bits over communication channel

raw transmission of the physical layer into a line that appears free from transmission errors

(Frames)

controls the operation of the subnet. The key issue here is to determine how packets are

routed from source to destination (congestion issues such as delay, transmit time and jitter)

true end-to-end layer all the way from source to destination

users on different machines to establish sessions between them

concerned with the syntax and semantics of the information

lot of protocols that are commonly needed by users (HTTP/FTP.)


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OSI Model / UMTS Protocol


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The physical layer is the radio signals, frequencies and channels.

The data link layer is divided into radio link control, RLC and medium access

control, MAC.

The network layer is the internet protocol, IP.

The transport protocol is one of the transport control protocol, TCP or the user

datagram protocol, UDP.


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The Physical Layer


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In GSM, we distinguish between logical and physical channels. In UMTS there are three

different types of channels:

1. Logical2. Transport

3. Physical

Logical Channels

Logical Channels were created to transmit a specific content.

There are for instance logical channel to transmit the cell system information, paginginformation, or user data.

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

Transport Channels (TrCH)

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.

Radio Interface Channel Organisation


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Physical Channels (PhyCH)

The physical layer offers the transport of data to the higher layer.

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.



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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



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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 downlink.

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 downlink channel.

Common Control Channel (CCCH)

Control information is transmitted on this channel.

It is in use, when no RRC connection exists between the UE and the network.

It is a bi-directional channel, i.e. it exists both uplink and downlink.

Dedicated Control Channel (DCCH)

Dedicated resources were allocated to a UE.

These resources require radio link management, and the control information is

transmitted both uplink and downlink on DCCHs.

Logical Channels


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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 onone S-CCPCH, even one frame

possible

with and without TFCI (UTRAN set)

SF = 4..256

Secondary Common Control Physical

Channel (S-CCPCH)


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The transport channel Forward Access Channel (FACH)is used, when relatively small amounts of data

have to be transmitted from the network to the UE.

The FACH is only transmitted downlink.

In-band signalling is used to indicate, which UE is the recipient of the transmitted data (see MAC PDU

with UE-ID type).

This common downlink channel is used without (fast) closed loop power control and is available all

over the cell.

FACH data is transmitted in one or several S-CCPCHs.

FACH and PCH data can be multiplexed on one S-CCPCH, but they can also be be transmitted on

different S-CCPCHs.

The FACH is organised in FACH Data Frames via the Iub-interface.

Each FACH Data Frames holds the Transmission Blocks for one TFS.

The used TFS is identified by the TFI.

A TFI is associated with one Transmission Time Interval (TTI), which can be either 10, 20, 40 or 80

ms.

The TTI identifies the interleaving time on the radio interface.

FACH Data Frame has header fields, which identify the CFN, TFI, and the Transmit Power Level.

FACH and S-CCPCH


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The Transmit Power Levelgives the preferred transmission power level for the FACH and

for the TTI time.

The values specified here range between 0 and 25.5 dB, with a step size of 0.1 dB. The value is taken as a negative offsetto the maximum power configured for the S-

CCPCHs, specified for the FACH.

The pilot bits and the TFCI-field may have a relative power offset to the power of the data

field, which may vary in time.

(The offset is determined by the network.) The power offsets are set by the NBAP message COMMON TRANSPORT CHANNEL

SETUP REQUEST, which is sent from the RNC to the Node B.

There are two power offset information included:

PO1: defines the power offset for the TFCI 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 witha 0.25 step size.

Another important parameter is the maximum allowed power on the FACH: MAX FACH

Power.

FACH and S-CCPCH


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Part V

Physical Random Access


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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 preamblesin the uplink.

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 isnow waiting for the PRACH message part.

Random Access


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Node BUE

No response

by the

Node B

No responseby the

Node B

I just detected

a PRACH preamble

OLA!

Random Accessthe Working Principle


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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.

The UE sends one preamble in uplink access slot n.

It expects to receive a response from the Node B in the downlink (AICH) access slot n, p-achips later

on.

If there is no response, the UE sends the next preamble p-pchips 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.

Random Access Timing


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RACH Sub-channels

RACH sub-channels were introduced to define a sub-set of uplink access slots. A total number of 12 RACH sub-channels exist, numbered from 0 to 11.

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 and SIB7.

The mapping of the subscribers access classes (1..15) is part of the SIB5 cell systeminformation.

RACH Sub-channels and Access Service Classes


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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 Bs 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 = UL interference

+ Primary CPICH TX powerCPICH_RSCP

+ Constant Value

The Constant Value is determined by the UTRAN side and can range between 35 and10

dB.

The UL Interference can range between 110 and -70 dBm. The UE must constantlyrecalculate this value.

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 between5 and

10 dB (step size 1dB).

PRACH Power Setting


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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

2Calculate initial preamble power

3Calculate available access slots in the next full access slot set and select randomly one ofthose

4Select randomly one of the available signatures

5Transmit preamble in the selected access slot with selected signature


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Part VI

Dedicated Physical Channel Downlink


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The downlink 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.

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 16it is adjusted with the spreading factor.

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

Downlink Dedicated Physical Channel (DPCH)


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10 ms Frame

TPC

bitsPilot bits

TFCI

bits

(optional)

Data 2 bitsData 1 bits

DPDCHDPDCH DPCCH DPCCH

Radio Frame0 Radio Frame1 Radio Frame2 Radio Frame71

Superframe = 720 ms



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Following features are supported in the downlink:

Discontinuous transmission. Rate matching is done to the maximum bit rate of the connection. Lower bit rates are

possible, including the option of discontinuous transmission.

Please note, that audible interference imposes no problem in the downlink.

Multicode usage:

Several physical channels can be allocated in the downlink to one UE. This can occur, when several DPCH are combined in one CCTrCH in the PHY layer, and

the data rate of the CCTrCH exceeds the maximum data rates allowed for the physical

channels.

Then, on all downlink DPCHs, the same spreading factor is used.

One DPCH carries DPDCH and DPCCH information, while on the remaining DPCHs, noDPCCH information is transmitted.

But also in the case, when several DPCHs with different spreading factors are in use, the

first DPCH carries the DPCCH information, while in the remaining DPCHs, this information is

omitted (discontinuous transmission).



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TS TS

maximum bit rate

TS TS TS

discontinuous transmission with lower bit rate

Multicode usage:

TS TS TS

TS TS TS

DPCH 1

DPCH 2

DPCH 3


DPCCH


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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 UEs signal a power control command to the UE. By doing so, the UEs 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 UEs DPCH.

The Node Bs transmission power can be changed by 0.5, 1, 1.5 or 2 dB. 1 dB must be supported by theequipment. 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.

One reason for the UE to request a higher output power is given, when the QoS target has not been

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 UEs 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.

Downlink Inner Loop Power Control


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Part VII

Dedicated Physical Channel Uplink


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The uplink dedicated physical channel transmission, we identify two types of physical channels:

Dedicated Physical Control Channel (DPCCH),

Which is always transmitted with spreading factor 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 compressedmode.

Dedicated Physical Data Channel (DPDCH),

Which is used for user data transfer.

Its spreading factor ranges between 4 and 256.

7 different solt 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 uplink 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

TPC

bitsPilot bits

TFCI bits(optional)

Data 1 bits

Radio Frame

0

Radio Frame

1

Radio Frame

2

Radio Frame

71

Superframe = 720 ms

DPDCH

DPCCH FBI bits

7 different

slot formats

6 different slot formats

Compressed mode slot

format for changed SF &

changed puncturingFeedback Indicator for

Closed loop mode transmit diversity, &

Site selection diversity transmission (SSDT)

Uplink Dedicated Physical Channels


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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 UEs 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 SIRest on

the UEs receiving uplink DPCH. Each active set cell determines the TPC value. If the estimated SIR is

larger than the UEs 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 howto 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:DPCCH= TPCTPC_cmd. 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

TPCTPC_cmd

UL Inner Loop Power Control

Umts Channel Ppt1

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