1-2 umts radio channel&key technologies

UMTS Radio Channel & Key Technologies

ZTE University

Content

Classification of channels Physical layer procedure RAKE Receiver Handover Control Admission Control Load Control

RNS RNS

CN

RNCRNC

Iu Iu

Iur

Iub IubIub Iub

Architecture of UMTS

UE

NodeBNodeBNodeBNodeB

Concept of channel

PHY layer

MAC layer

RLC layer

Transport channel

Physical channel

Logical channel

L1

L2

Channel Type

Logical channels: Describe what is transported (i.e., the information to be

transmitted)

Transport channels: Describe how the logical channels are to be transmitted.

Physical channels: Represent the “transmission media” providing the

platform through which the information is actually transferred.

Logical Channels

Control Channel (CCH) Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Traffic Channel

(TCH)

Dedicated Traffic Channel (DTCH)

Common Traffic Channel (CTCH)

Transport Channel

Random Access Channel (RACH)

Broadcast Channel (BCH)

Paging Channel (PCH)

Forward Access Channel (FACH)

Common Packet Channel (CPCH)

Common Transport Channels

Dedicated Transport Channels

Downlink Shared Channel (DSCH)

Dedicated Channel (DCH)

Physical Channel

Dedicated Physical Channel (DPCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Uplink Physical Channels

Secondary Common Control Physical Channel (S-CCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P-CCPCH)

Synchronization Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Downlink Physical Channels

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Dedicated Physical Channel (DPCH)

Logic Channel

TransportChannel

CCCHDCCHDTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCHDCCHDTCH

CCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship

TransportChannel

CCCHDCCHDTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCHDCCHDTCH

CCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship

Transport Channels

DCH

RACH

CPCH

BCH

FACH

PCH

DSCH

Physical Channels

Dedicated Physical Data Channel (DPDCH)

Dedicated Physical Control Channel (DPCCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P-CCPCH)

Secondary Common Control Physical Channel (S-CCPCH)

Synchronization Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Frame structure

The frame structure of the physical channels is shown:

Tslot #1Tslot #2 Tslot #I Tslot #15

Ttimeslot= 2560 chip

Frame #0Frame #1 Frame #I Frame #71

Tframe=10 ms

Tsuperframe=720 ms

Content


Cell Search

UE has to get the system information before it registers with the network and access to services.

The system information is beared in the BCH channel, and its data is mapped into the Primary CCPCH.

So the cell search procedure is mainly to decode the data of P-CCPCH.

Cell search procedure (1)

The cell search is typically carried out in three steps:

Step1: Slot synchronization During the first step of the cell search procedure the UE

uses the SCH channel's primary synchronization code to acquire slot synchronization to a cell.

This is typically done with a single matched filter (or any similar device) matched to the primary synchronization code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

Sketch of Slot Synchronization


Step2: Frame synchronization and code-group identification During the second step of the cell search procedure, the

UE uses the SCH channel's secondary synchronization code to find frame synchronization and identify the code group of the cell found in the first step.

This is done by correlating the received signal with all possible secondary synchronization code sequences, and identifying the maximum correlation value. Since the cyclic shifts of the sequences are unique the code group as well as the frame synchronization is determined.

…

Downlink Scrambling Code Grouping

No. 511 Scrambling Code Group

8176

8177

8191

8176 ： PSC

8177 ： SSC

…

8191 ： SSC


8160

8161

8175

8160 ：主扰码8161 ：辅扰码…

8175 ：辅扰码


8064

8065

8079

8064 ：主扰码8065 ：辅扰码…

8079 ：辅扰码

…


112

113

127

8176 ： PSC

8177 ：辅扰码…

8191 ：辅扰码


16

17

31

16 ： PSC

17 ： SSC

…

31 ： SSC


0

1

15

0 ： PSC

1 ： SSC

…

15 ： SSC

No.63 Primary Scrambling Code Group

… …

No.0 Primary Scrambling Code Group

Mapping of the Secondary Synchronization Code


Step3: 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 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 so that the cell specific BCH information can be read.

Summary of the process

ChannelSynchronization

acquiredNote

Primary SCH

Chip, Slot, SymbolSynchronization

Synchronization 256 chips

The same in all cells

Secondary SCH

Frame Synchronization,Code Group

(one of 64)

15-code sequence of secondary synchronization codes. There are 16 secondary synchronization codes. There are 64 S-SCH sequences corresponding to the 64 scrambling code groups 256 chips, different for different cells and slot intervals

Common Pilot CH

Scrambling code (one of 8)

To find the primary scrambling code from common pilot CH

PCCPCH Synchronization,BCCH info

Fixed 30 kbps channel spreading factor 256

Content


Multi-path characteristics of radio channel

Electromagnetic propagation: direct radiation 、 reflection 、 diffraction and scattering

Signal attenuation: Path loss ： Loss of electromagnetic waves in large scope of the spread

reflects the trend of the received signal in the spreading 。 Slow fading ： Loss because of being blocked by the building and hill in

the propagation path Fast fading ： Electromagnetic signals rapidly decline in a few dozens

wavelength ranges

= +

+

Pathloss

Slow fading

Fast fading

distance

Signal Rx Level

Multi-Path Effects

receiving signalreceiving signal

timetime

strengthstrength

00

sending signalsending signal

RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path

interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.

RAKE Receiver can effectively overcome the multi-path RAKE Receiver can effectively overcome the multi-path

interference, consequently improve the receiving performance.interference, consequently improve the receiving performance.

RAKE Receiver

The multi-path signals contain some useful energy , therefore the UMTS receiver can combine these energy of multi-path signals to improve the received signal to noise ratio.

RAKE receiver adopts several correlation detectors to receive the multi-path signals, and then combines the received signal energy.

RAKE Receiving

d1 d2

t t t

d3

transmitti

ng

Receivin

gRake

combinationnoise

RAKE Receiving

receiverreceiver

Single receiving

Single receiving

Single receiving

searcher calculatecalculate

combining

tt

s(t) s(t)

signal

RAKE Receiving overcomes multi-finger interference, improves receiving performance

Content


What’s ？

When UE is moving from the coverage area of one site to another, or the quality of service is declined by external interference during a service, the service must be handed over to an idle channel for sustaining the service.

Handover is used to guarantee the continuity of service.

Handover is a key technology for mobile networking.

Category of Handover

Intra-RNC, inter-Node B Inter-RNC

Soft handover (SHO)

Same Node B, Inter-sector

Softer handover

Intra-frequency Inter-frequency Inter-system (UMTS&GSM) Inter-mode (FDD&TDD)

Hard handover (HHO)

UMTS system support

multiple handover technology

Handover Demonstration

Hard

Handover

Soft

Handover

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

A

B

C

Soft Handover/Softer Handover

Soft Handover

Soft-Softer Handover

Softer Handover

Hard Handover

During the hard handover procedure, all the old radio links with the UE are abandoned before new ones are established, so there must be service interruption during the HHO.

Hard handover may occur in the following main cases

When the UE is handed over to another UTRAN carrier, or another technology mode.

When soft handover is not permitted (if O&M constraint)

Hard Handover

Node B

SRNCRNC or BSC

CN

Node B or BTS

Soft/Softer Handover

The soft/softer handover allows to migrate from one cell to another without service interruption or without deleting all old radio links.

UE can connect to more than one cell simultaneously and take benefit from the macro-diversity.

Soft Handover Softer Handover

CN CN

Iur

The two Node Bs may belong to the

same RNC

The two Node Bs may belong to the Same RNC


SRNC DRNC

CN

Node B

SRNC

CN


Node B

CN

UMTS General Handover Trilogy

Measurement Control UTRAN demands the UE to start measurement through

issuing a measurement control message.

Handover decision UTRAN makes the decision based on the measurement

reports from UE. The implementation of handover decision is various for different vendors. It impacts on the system performance critically.

Handover execution UTRAN and UE execute different handover procedure

according to the handover command.

(A) RNC sends measurement control message to UE (Measurement Control)

(B) UE starts measurement task with the parameters included in the message, and reports measurement results （ Measurement Report）

(C) RNC stores the measurement results according to frequencies and cells

(D) RNC Estimates the quality of each carrier (including intra-frequency and inter-frequency)

(E) Quality

Decision

(G) Allocate resource in target cell, prepare to execute handover

(F) maintain the active set and monitored set

(H) Allocate resource in target cell, prepare to execute handover

Current carrier has good quality

Other system has good quality

Other carrier has good quality

（ I ） If handover is required, RNC sends handover command with target cell to UE

Handover Flows

Concepts Related to Handover

Active Set: A set of cells that have established radio links with a

certain mobile station. User information is sent from all these cells.

Monitored Set: A set of cells that are not in the active set but are

monitored according to the list of adjacent cells assigned by the UTRAN.

Detected Set: A set of cells that are neither in the active set nor in the

monitor set.

Soft handover event

Event Description

1AQuality of target cell improves, entering a report range of relatively activating set quality

1BQuality of target cell decreases, depart from a report range of relatively activating set quality

1CThe quality of a non-activated set cell is better than that of a certain activated set cell

1D Best cell generates change

1EQuality of target cell improves, better than an absolute threshold

1FQuality of target cell decreases, worse than an absolute threshold

An Example of SHO Procedure

Pilot Ec/Io of cell 1

time

PilotEc/Io

Connect to cell1 Event 1A Event 1C Event 1B （ add cell2 ）（ replace cell1 with cell 3 ）（ remove cell3 ）



⊿ t ⊿ t ⊿ t

Content


Admission Control

The admission control is employed to admit the access of incoming call. Its general principal is based on the availability and utilization of the system resources.

If the system has enough resources such as load margin, code, and channel element etc. the admission control will accept the call and allocate resources to it.

Purpose of Admission Control

When user initiates a call , the admission control should implement admission or rejection for this service according to the resource situation.

The admission control will sustain the system stability firstly and try the best to satisfy the new calling service’s QoS request, such as service rate, quality (SIR or BER), and delay etc. basing on the radio measurement.

Admission control is the only access entry for the incoming services, its strategy will directly effect the cell capacity and stability, e.g. call loss rate, call drop rate.

Admission Control in Uplink

Itotal_old+ΔI >Ithreshold

The current RTWP (Received Total Wide Power) value of cell, which is reported by Node B

AccessThreshold

Interference capacityService priorityReserved capacity for handover

Iown-cell

0~N

Iother-cell

The forecasted interference including the delta interference brought by the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment

Admission Control in Downlink

Ptotal_old+△P>=Pthreshold Access Threshold

The forecasted TCP value including delta power required for the incoming service is calculated by the admission algorithm, and its result depends on the QoS and transmission propagation environment.

The current TCP value of cell, which is reported by Node B（ Transmitted Carrier Power*Pmax ）

Max TCP of cellService priorityReserved capacity for handover

Content


Load control

The purpose of load control is to keep the

system load under a pre-planned threshold

through several means of decreasing it, so as to

improve the system stability.

The speed and position

changing of UE may

worsen the wireless

environment.

Increased transmitted

power will increase the

system load.

Purpose of Load Control

Load Control Flows

Start

DecisionLight loaded Over loaded

Normal loaded

1.Handover in andaccess are forbidden2. TCP increase isforbidden3. RAB service ratedegrade4. Handover out5. Release call (call drop)

1. Handover in and access are allowed2. Transmitted code power (TCP) increase is allowed3. RAB service rate upgrade is allowed

1. Handover in and access are allowed2. TCP increase is allowed

Load Control in Uplink

Triggers RTWP (Received Total Wide-band Power) value from

measurement report exceeds the uplink overload threshold; Admission control is triggered when rejecting the access of

services with lower priority due to insufficient load capacity in uplink.

Methods for decreasing load Decrease the target Eb/No of service in uplink; Decrease the rate of none real time data service; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.

Methods for increasing load Increase the service rate.

Load Control in Downlink

Triggers TCP (Transmitted Carrier Power) value from measurement report

exceeds the downlink overload threshold; Admission control is triggered when rejecting the access of

services with lower priority due to insufficient load capacity in downlink.

Methods for decreasing load Decrease the downlink target Eb/No of service in downlink; Decrease the rate of none real time data service; Handover to coverage-shared light loaded carrier; Handover to GSM system; Decrease the rate of real time service, e.g. voice call; Release calls.

Methods for increasing load Increase the service rate.

Cell breathing is one of the means for load control

The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-

spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to

improve the utilization of system capacity.improve the utilization of system capacity.

The purpose of cell breathing is to share the load of hot-The purpose of cell breathing is to share the load of hot-

spot cell with the light loaded neighbor cells, therefore to spot cell with the light loaded neighbor cells, therefore to

improve the utilization of system capacity.improve the utilization of system capacity.

Cell Breathing Effect

Example for load control

Cell Breathing EffectCell Breathing Effect With the increase of activated

terminals and the increase of high

speed services, interference will

increase. The cell coverage area will shrink. Coverage blind spot occurs Drop of call will happen at the edge

of cell

Coverage and

capacity are

interrelated

DL/UL: Add carrier six sectors

DL/UL: Add carrier six sectors

UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR

UL Tower Mounted Amplifier (TMA) 4 Rx Div OTSR

DL transmission diversity (Tx Div) high power amplifier

DL transmission diversity (Tx Div) high power amplifier

Add basestation

“last choice”

Add basestation

“last choice”

Optimization methods

To overcome Cell Breathing Effect caused by increased traffic and meet different requirements for capacity and coverage in different environment, following solutions can be applied:

Factors Impact on UMTS capacity

RAKE Receiver

The advanced receiving and baseband processing technology is introduced to overcome the fast fading

Power Control Reducing interference, saving power and Increasing capacity

Handover Control

Impacting the capacity through applying different proportion and algorithm of soft handover

Admission Control

Admitting a connection base on the load and the admission threshold of planned capacity

Load Control Monitoring system load and adjusting the ongoing services to avoid overload

OVSF Code The Allocation of codes impacts the maximum number of simultaneous connections.

Wireless Environment

Wireless environment such as interferences, UE position and mobility etc. can influent the cell capacity

Factors affects UMTS Capacity

1-2 umts radio channel&key technologies

Documents

bch channel

frame synchronization

primary scrambling code

transmittedtransport

primary ccpch

system information

data of p

slot synchronizationduring