wcdma lec 2_27nov2013

8/11/2019 Wcdma Lec 2_27nov2013

1/27

WCDMA/UMTS Network

Advanced Mobile Communication

Lec-2

Physical Layer

8/11/2019 Wcdma Lec 2_27nov2013

2/27

UMTS Terrestrial Radio Access (UTRA) Protocol

Architecture

WCDMA/UMTS Networks 2

Layered Architecture of the UTRA protocol

architecture also known as Access Stratum.

Layer 3

RRC: Controls all the layers of Access

Stratum. Performs variety of functions such

as connection setup and management in

UTRAN, paging, measurement control and

reporting etc.

Layer 2

RLC: Major functions include segmentation

reassembly, retransmission etc of

user/signaling data.

MAC: Mapping of logical to transport

channels, identification of UE on common

channels etc.

Layer 1

Physical Layer: Performs wide variety of

functions including all in the WCDMA Tx/Rx,

closed loop power control, soft handover,

measurements etc

8/11/2019 Wcdma Lec 2_27nov2013

3/27

Each layer communicates with the peer entity on the Tx/Rx side and utilizes the services

offered by the layer below.

The concept of Radio Bearers (RBs), logical channels, transport channels and

physical channels


UTRA Protocol Architecture

8/11/2019 Wcdma Lec 2_27nov2013

4/27


Channels in UTRA

The logical, transport and physical channels have different purpose:

Logical channels carry information about different tasks the network and the MS should perform

in different moments in time. Logical channels are grouped by information contentwhat type of information

is transfered:

User data.

Layer 3 control and signallingrefered to as mobility management

(e.g. measurement reports, handover commands).

. Transport channels are used by RNC to carry different information flow over the Uuinterface and

the physical elements. Transfer channels are grouped by method of transferhow data is transfered,

e.g. different coding can be applied.

Physical channels provide physical connectivity Uuinterface. Physical channels perform the actual

transmission of data bits. They are distinguished by:

RF frequency.

Channelization code.

Spreading code.

Modulation phase (uplink).

8/11/2019 Wcdma Lec 2_27nov2013

5/27

Logical channels are used to provide data transfer services of the Medium Access Control (MAC) layer. They are

generally classified into two groups:

Control Channels, used to transfer control information.

Broadcast Control Channel (BCCH). It is used for broadcasting system information in downlink direction.

Paging Control Channel (PCCH). It is a downlink channel used to transfer paging information.

Dedicated Control Channel (DCCH). It is a point-to-point bi-directional channel used to transmit dedicated control

information between a UE and the RNC.

Common Control Channel (CCCH). It is a bi-directional channel used to transmit control information between the

network and UEs.

Traffic Channels, used to transfer user information.

Dedicated Traffic Channel (DTCH). It is a point-to-point bi-directional channel, dedicated only to one UE for user

information transfer.

Common Traffic Channel (CTCH). It is a point-to-point channel transmitted in downlink direction only, used to transfer

a dedicated user information for all or a group of specified UEs.


Logical Channels

8/11/2019 Wcdma Lec 2_27nov2013

6/27

The purpose of Transport channels is to provide varying bitrate services and multiplexing of several servicesover the air interface.

Common Transport Channels: Shared by all the users/group of users in a cell. Used mainly for signaling,

can be used for data as well.

Broadcast Channel (BCH): Downlink Only. Transmission of system level information

Forward Access Channel (FACH): Downlink Only. Transmission of common control information. Also can carry smallamount of data.

Paging Channel (PCH):Downlink Only. Used to carry paging messages.

Random Access Channel (RACH): Uplink Only. Used to carry control information like connection setup. Can also be

used to carry small amount of data.

Dedicated Transport Channels: Only one such channel.

Dedicated Channel (DCH): Downlink and/or Uplink. The channel carries all information intended for a given user

coming from layers above the physical layer, including data for the actual service as well as higher layer control

information. The DCH carries both the service data, such as speech frames, and higher layer control information, such

as handover commands or measurement reports from the terminal.


Transport Channels

8/11/2019 Wcdma Lec 2_27nov2013

7/27


Channels: Transport Channel Content

8/11/2019 Wcdma Lec 2_27nov2013

8/27

Physical channels carry higher layer data over the air interface. . The physical layer supports transport channelsof variable bit rate in order to offer bandwidth on demand services, and to be able to multiplex several servicesto one connection.

Common Physical Channels.

Primary Common Control Physical Channel (PCCPCH). Downlink Only

Secondary Common Control Physical Channel (SCCPCH). Downlink Only

Random Access Channel (PRACH). Uplink Only

Dedicated Physical Channels

Dedicated Physical Data Channel (DPDCH). Downlink/Uplink

Dedicated Physical Control Channel (DPCCH). Downlink/Uplink

Other Physical Channels. Not visible to higher layers. Only for Layer 1 functions. Downlink only

Synchronisation Channel (SCH).

Common Pilot Channel (CPICH).

Paging Indication Channel (PICH)

Acquisition Indication Channel (AICH)


Physical Channels

8/11/2019 Wcdma Lec 2_27nov2013

9/27


Physical Channels: Carriers of Transport Channels

8/11/2019 Wcdma Lec 2_27nov2013

10/27


Channel Mapping

Uplink Downlink

8/11/2019 Wcdma Lec 2_27nov2013

11/27


Downlink Spreading Factors

Channel Bit Rate [kbps] Symbol Rate [ksps] Spreading Factor

15 7.5 512

30 15 256

60 30 128

120 60 64

240 120 32

480 240 16

960 480 8

1920 960 4

8/11/2019 Wcdma Lec 2_27nov2013

12/27

Basic Frame is of 10 msec duration with 15 slots. Each slot has 2560 chips => Total number of chips in the

frame = 38400.

Each basic frame is identified by a System Frame Number (SFN) ranges from 0 to 4096.

SFN is transmitted in system information carried by BCH over PCCPCH.


Basic Physical Frame Structure

8/11/2019 Wcdma Lec 2_27nov2013

13/27

Operates at a data rate of 30 kbps => SF=256

Predefined bit sequence equal to all 1s transmitted continuously

Channelization Code Cch,256,0

Primary Scrambling Code of the cell is used for scrambling.

The channel serves as reference for serving as well as neighboring cell physical layer measurements to be

done by the UE.

The channel also serves as reference for coherent detection of other physical layer channels such as PICH,

AICH and PCCPCH as these do not carry pilot bits.


Common Pilot Channel (CPICH)

Data Bit Code Chip XOR Operation

0 0 0

0 1 1

1 0 1

1 1 0

8/11/2019 Wcdma Lec 2_27nov2013

14/27


DL Slot and Frame Structure for Dedicated PDCHs

Dedicated Physical Data and Control Channels

are time multiplexed onto the same physical

slot.

17 different DL timeslot formats with varying

count of data and control bits.

TPC: Power Control bits. Either all 0s or all 1s,

indicating to decrease or increase power.

TFCI: Transport Format Combination

Indication. Gives information regarding the

Transport formats being used.

Pilot bits: Used for coherent detection.

Note that all the control bits in DPCCH are

related to Layer 1 only and are transmitted at

higher power than the user data in DPDCH.

8/11/2019 Wcdma Lec 2_27nov2013

15/27


DL Slot and Frame Structure for P-CCPCH

Operates at a data rate of 30 kbps => SF=256

Channelization Code Cch,256,1

Primary Scrambling Code of the cell is used for

scrambling.

The first 10% of the slot i.e. 256 chips is not

occupied by PCCPCH.

Transmitted continuously over the entire cell and

carries the broadcast control channel (BCH) data.

PCCPCH will be transmitted in every slot,although there will generally be different BCH

data in each slot.

8/11/2019 Wcdma Lec 2_27nov2013

16/27


DL Slot and Frame Structure for S-CCPCH

Data rates on this channel range from 30kbps to

1920 kbps corresponding to spreading factors of

256 to 4.

The data can be varied as required using the TFCI.

Primary Scrambling Code of the cell is used forscrambling.

Transmitted only when there is information to be

sent.

This is the physical channel that carry the paging

messages that are sent through PCH and small

amount of data in the form of FACH.

8/11/2019 Wcdma Lec 2_27nov2013

17/27


Synchronization Channel (SCH) slot and Frame structure

In UTRA the synchronization channel is used

by UEs in the initial cell search process.

Time multiplexed with P-SCCPCH such that

first 10% of the timeslot is used by SCH.

Consists of two sub-channels that are

transmitted simultaneously;

Primary SCH: Same 256 word length

chip sequence in every timeslot and

every Node B.

Secondary SCH: 15 different 256 chip

length are transmitted in each of the 15

timeslots of a 10msec frame. In other

words the SSC changes from slot to slot

such that the sequence of 15 SSCs are

used to determine the Primary

Scrambling Code used in the cell.

8/11/2019 Wcdma Lec 2_27nov2013

18/27


DL Slot and Frame Structure for PICH and AICH

To be discussed with Paging and Access Procedures.

8/11/2019 Wcdma Lec 2_27nov2013

19/27


WCDMA Downlink Transmitter

8/11/2019 Wcdma Lec 2_27nov2013

20/27


WCDMA Downlink Transmitter

8/11/2019 Wcdma Lec 2_27nov2013

21/27


Downlink data path through Physical layer

Tx

Rx

8/11/2019 Wcdma Lec 2_27nov2013

22/27

Example: DL Speech RAB Mapping


8/11/2019 Wcdma Lec 2_27nov2013

23/27

Uplink Spreading Factors


Channel Bit Rate [kbps] Symbol Rate [ksps] Ndata SF

15 15 10 256

30 30 20 128

60 60 40 64

120 120 80 32

240 240 160 16

480 480 320 8

960 960 640 4

8/11/2019 Wcdma Lec 2_27nov2013

24/27


UL Slot and Frame Structure for Dedicated PDCHs

In the Uplink, DPDCH and DPCCH are not timemultiplexed but rather are transmitted

simultaneously. Carried by I and Q branches.

OVSF code tree is used to spread the channels.

DPCCH is always spread by channelization code

Cch,256,0. DPDCH is spread using channelization

code Cch,SF,SF/4.

If the data requirement from higher layer is such

that more DPDCH are required, then SF=4 is

used.

One of the 224possible uplink scrambling codes is

assigned to UE at the time of connection setup.

This is used to scramble DPDCH and DPCCH

channels in the uplink.

8/11/2019 Wcdma Lec 2_27nov2013

25/27


UL Slot and Frame Structure for PRACH

To be discussed with Access Procedure

8/11/2019 Wcdma Lec 2_27nov2013

26/27


WCDMA Uplink Transmitter and Uplink data path

through Physical layer

8/11/2019 Wcdma Lec 2_27nov2013

27/27


WCDMA Uplink Transmitter

wcdma lec 2_27nov2013

Documents