03.WCDMA RRM and Cell Procedure

8/11/2019 03.WCDMA RRM and Cell Procedure

1/43

Radio Resource Management

RRM is responsible for optimal utilisation of the radio resources: Transmission power and interference Logical codes

The trade-off between capacity, coverage and quality is done all thetime

Minimum required quality for each user (nothing less andnothing more)

Maximum number of users The radio resources are continuously monitored and optimised by

several RRM functionalities

1

servicequality

cell coverage cell capacity

Optimizationand Tailoring


2/43

RRM Functionalities

LC Load Control

AC Admission Control

PS Packet Scheduler

RM Resource Manager

PC Power Control

HC HO Control

2

PC

HC For each connection/user

LC

AC For each cell

PS

RM


3/43

Radio Resources Management

3

Network Based Functions Admission Control (AC)

Handles all new incoming traffic. Check whether new connection canbe admitted to the system and generates parameters for it.

Load Control (LC)Manages situation when system load exceeds the threshold and somecounter measures have to be taken to get system back to a feasibleload.

Packet Scheduler (PS)Handles all non real time traffic, (packet data users). It decides when apacket transmission is initiated and the bit rate to be used.

Connection Based Functions Handover Control (HC)

Handles and makes the handover decisions.Controls the active set of NodeB of UE.

Power Control (PC)Maintains radio link quality.Minimize and control the power used in radio interface, thusmaximizing the call capacity.


4/43

Admission Control Principle

If the air interface loading is allowed to increase excessively, the coverage areaof the cell is reduced below the planned values, and the quality of service of theexisting connections cannot be guaranteed. Before admitting a new UE,admission control needs to check that the admittance will not sacrifice theplanned coverage area or the quality of the existing connections.

Admission control accepts or rejects a request to establish a radio access bearerin the radio access network. The admission control algorithm is executed when abearer is set up or modified. The admission control functionality is located inRNC where the load information from several cells can be obtained.

4


5/43

Load Control (Congestion Control)

One important task of the RRM functionality is to ensure that the system is not overloadedand remains stable. If overload is encountered, however, the load control functionalityreturns the system quickly and controllably back to the targeted load, which is defined bythe radio network planning.

The possible load control actions in order to reduce load are listed below:

Downlink fast load control: Deny downlink power-up commands received from the UE. Uplink fast load control: Reduce the uplink Eb=No target used by the uplink fast powercontrol.

Reduce the throughput of packet data traffic.

Handover to another WCDMA carrier. Handover to GSM. Decrease bit rates of real time UEs, e.g. AMR speech codec. Drop low priority calls in a controlled fashion.

5


6/43

Load Control (LC)

LC performs the function of load control in association with AC & PS

LC updates load status using measurements & estimations provided by AC andPS

Continuously feeds cell load information to PS and AC;

Interference levels (UL)

BTS power level (DL)

LC

AC

PSNRTload

Load changeinfo

Loadstatus


7/43

Load thresholds set by radio network planningparameters

Overloadthreshold x

Load Targetthreshold y

P o w e r

Time

Load Margin

Overload

Normal load

Measured loadFree capacity

Load Control (LC)-Load Status


8/43

Packet Scheduler

The WCDMA packet scheduler is located in RNC. The base station providesthe air interface load measurements and the mobile provides uplink trafficvolume measurements for the packet scheduler.

The user-specific part controls the utilization of Radio resource control(RRC) states, transport channels and their bit rates according to the trafficvolume. The cell-specific part controls the sharing of the radio resourcesbetween the simultaneous users.

WCDMA supports three types of transport channel that can be used to

transmit packet data: common, dedicated and shared transport channels.

8


9/43

Resource Manager (RM)

Responsible for managing the logical

radio resources of the RNC in co-operation with AC and PS

CODE ALLOCATION

On request for resources, from either AC(RT) or PS(NRT), RM allocates:

DL Spreading Code (ChannelisationCodes)

UL Scrambling Code

Code Type Uplink Downlink

Scrambling

CodeUser Separation Cell Separation

ChannelisationCode

User Data & L1Control Data from

same UE

UEs within thesame cell

Code Tree Management: Code selection

Code Tree re-arrangement


10/43

Handover Control (HC)

HC is responsible for: Managing the mobility aspects of an RRC connection as UE

moves around the network coverage area Maintaining high capacity by ensuring UE is always served by

strongest cell

Soft handover

MS handover between different base stations Softer handover

MS handover within one base station but between differentsectors

Hard handover

MS handover between different frequencies or between WCDMAand GSM

10


11/43

Handover Control

11

Softer Handover A MS is in the overlapping coverage of2 sectors of a NodeB.Concurrent communication via 2 airinterface channels2 channels are maximally combinedwith rake receiver

Soft Handover A MS is in the overlapping coverage of2 different NodeB.Concurrent communication via 2 airinterface channelsDownlink: Maximal combining withrake receiverUplink: Routed to RNC for selectioncombining, according to a framereliability indicator by the NodeB.

A Kind of Macro diversity


12/43

Hard Handover

Hard handovers are typically performed between WCDMA frequencies andbetween WCDMA and GSM cells

12

GSM/GPRSGSM/GPRS

f 1

f 2

f 1

f 2f 2f 2

Inter-System Handovers (ISHO)

Inter-Frequency Handovers (IFHO)


13/43

Power Control

TX Power is adjusted regularly so that each connection is received withthe required Eb/No of its service Uplink: Avoid Near -Far- Problem Downlink: Power share allocation

Policy: No one gets a higher Eb/No quality than he needs. Everyonegets exactly the required quality or is not served at all no unnecessary increase of interference for other mobiles no waste of common power resource in the downlink

13

PC Gain:Lower Eb/No


14/43

Few Basics.

COVERAGE

14

CAPACITY QUALITY

POWER


15/43

Understanding Power Control

LOWER Power PerUser HIGHERNumber of Users

15

HIGHER Power PerUser LOWER

Number of Users


16/43

Cell Breathing

No or Improper Power Control leads to High interference that impactsCoverage, Capacity and Quality

16

Power Ctrl

ONOFF


17/43

Power control

RNC

Open Loop Power Control UL

Fast Closed Loop PowerControl (1500 Hz)

Outer Loop Power Control DL

UE

Open Loop Power Control DL

Outer Loop Power Control UL (1-100 Hz)

C o n

t i n u o u s

p r o c e s s

N o n - r e p e a

t a b l e

p r o c e s s

WBTS


18/43

Closed and outer loop power control

UL SIR target

WBTS SRNCUE

DL SIR target BLER targetvs

UL SIRvs

DL SIRvs

UL QE

TX powerestimatedby theOpen LoopPC.


19/43

UL/DL Capacity Limitation

Scenario 1: Capacity limitation due to UL interference The cell cant serve UE1 because the increase in UL interference by adding

the new user would be too high, resulting in a high risk of drops

Scenario 2: Capacity limitation due to DL power The cell cant serve UE2 because its using all its available power to maintain

the connections to the other UEs

19

UE 1

UE 2

Scenario 1 Scenario 2


20/43

Multipath Propagation

2

Multipath Propagation

20

1

3

Multiple paths possibly cause destructive interference between differentreplica of the desired signal


21/43

The Rake Receiver

Each multipath component is called a finger

Estimation of radio channel properties for each finger: delay amplitude and Phase

The Rake receiver combines multi-path components by coherent combiningof multi-path components belonging to the respective user.

21

b


22/43

Maximum ratio combining RAKE

22

Each finger tracks a different multipath component and other cellsduring Soft Handover A maximum ratio combining produces the outputSearch Finger is used to determine when to perform handovers

C

O

M

B

I

N

E

R

Power measurements ofneighbouring NodeBs

Sum of individualmultipath components

Finger #1

Finger #2

Finger #3

Finger #N

Buffer/delay

CorrelatorsChannel

Searcher Finger

C ll d


23/43

Cell procedures

PowerOFF

PLMNselection

IDLE mode

CONNECTE D mode

Cell search

Cellselection

System information(BCH)

Power ON

Locationregistration

Cellreselection

RACHprocedure

RACHprocedure

RRCConnection

Paging

PLMN l i d


24/43

PLMN selection procedure

The first procedure executed in the UE after the power is switched ON.

The UE starts PLMN search if the previously used PLMN is not available.

Also, the UE periodically searches for the home PLMN if it is roamed in other PLMN inthe same country.

Two modes of the PLMN selection (depending on the UE settings):

Automatic mode

UE performs selection with a given priority order:

1) Home PLMN.

2) User controlled PLMN list (SIM).

3) Operator controlled PLMN list (SIM).

4) Randomly one of the detected PLMNs with CPICH received at least at the level of -95 dBm (RSCP).

5) The other detected PLMN with the highest RSCP.

Manual mode

The UE searches through all frequencies and provides user with a list of detected

PLMNs with RSCP above -95 dBm.

PLMN Selection Automatic Mode


25/43

PLMN Selection Automatic Mode

PLMN Priority

Home PLMN

PLMNs in USIM

Operator Controlled PLMNs

Other PLMNs according to RSCP

Cell search procedure


26/43

Cell search procedure

(P-SCH)PrimarySCH(S-SCH)Secondar y SCH

CPICH

P-CCPCH P-CCPCH

Slotsynchronisation to

a cell

10 ms

The Primary CCPCH isdetected using the identifiedprimary scrambling code

After the cell search, systemand cell specific BCHinformation can be read.

Frame synchronisation andidentification of the cell code

group

Determination of the exact

primary scrambling codeused by the found cell

Phase 1

Phase 2

Phase 3

Synchronisation Channel (SCH)


27/43

Cp = Primary Synchronisation CodeC

s = Secondary Synchronisation Code

10 ms Frame

CP CP

2560 Chips 256 Chips

C s1 C s2 C s15

Slot 0 Slot 1 Slot 14

C P CP CP

C s1

Primary Synchronisation Channel (P-SCH)

Secondary Synchronisation Channel (S-SCH)

Slot 0


PtxPr imarySC H

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

PtxSecSCH -35..15; 0.1; -3 dB

(Range; Step; Default)

SSC Allocation for S SCH


28/43

15

15

scrambling

code groupgroup 00group 01

group 02group 03

group 05group 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 monitorthe S-SCH

Common Pilot Channel (CPICH)


29/43

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

But in the initial cell selection process, it does not yet know the cells 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 factor256. The CPICH divides up into a mandatory Primary Common Pilot Channel (P-CPICH) andoptional Secondary CPICHs (S-CPICH).

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

A spreading code is the product of the cells scrambling code and the channelisation code. The channelisation code is fixed: C ch,256,0 . i.e., the UE knows the P- CPICHs channelisationcode, and it uses the P- CPICH to determine the cells primary scrambling code by trial anderror.

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).

Common Pilot Channel (CPICH)

Primary Common Pilot Channel (P CPICH)


30/43

CP



P-CPICH

10 ms Frame

applied speading code =cells primary scrambling code C ch,256,0

Phase reference Measurement reference

P-CPICH Cell scrambling

code? I get it

with trial & error!

Primary Common Pilot Channel (P-CPICH)

PtxPr imaryCPI CH

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

(20 W sector)

CPICH as Measurement Reference


31/43

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 bands power density. The quality is the primary CPICHs 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

P CPICH as Measurement Reference


32/43

Received Signal Code Power (in dBm)CPICH RSCP received energy per chip divided by the power density in theband (in dB)CPICH Ec/No

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

UTRA carrierRSSI

CPICH Ec/No = CPICH RSCP

UTRA carrier RSSI

CPICH Ec/No

0: < -241: -23.52: -23

3: -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: -109

2: -108:71: -3972: -3873: -37

RSSI values in dBm

P-CPICH as Measurement Reference

Primary Common Control Physical Channel


33/43

The UE knows the cells 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 mustbe C ch,256,1 in every cell for every operator.

By reading the cell system information on the P-CCPCH, the UE learns everythingabout 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- CCPCHs channelisation code, the data rate for cellsystem 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. There are also no power control (TPC) bits transmitted to the UEs.

Primary Common Control Physical Channel(P-CCPCH)

Primary Common Control Physical Channel


34/43

CP



P-CCPCH

10 ms Frame

P-CCPCH Finally, I get the

cell system

information

channelisation code: C ch,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)

PtxPr imaryCCPC H

-35..15; 0.1; -5 dB

(Range; Step; Default)

Broadcast of system information


35/43

Broadcast of system information

SIB 1 PLMN info, timers, and counters.

SIB 2 Cell URA identify.

SIB 3 Parameters for cell (re)selection.

SIB 4 Parameters for cell (re)selection in connectedmode(optional).

SIB 5 Configuration of common physical channels(parameters for RACH, CPCH, and pagingprocedure).

SIB5bis Band indicators to allow new frequency bandIV&IX, HSPA cell indicator and MBMS S-CCPCH system info

SIB 6 Configuration of common physical channels inthe cell used in Connected mode.

SIB 7 Uplink interference level (Open Loop PowerControl).

SIB 11 Measurement Control information to be usedin the cell (neighbour list).

SIB11bis Extension segments for SIB11

SIB 12 Measurement Control information to be usedin Connected mode (parameters for SHO,neighbour list).

SystemInformationBlock (SIB)



...

System Information

(BCCH -> BCH -> PCCPCH)

WBTS Schedulinginformation

MasterInformationBlock (MIB)

Actual system

information

Cell selection


36/43

Cell selection

Cell selection the aim is to find a suitable cell to camp on. A cell that provides normal service to a user. Belongs to the selected PLMN (RAT). Is not barred. Fulfils the selection criteria (S-criteria) at the UE location.

Information regarding status of the cell (barred/reserved) is provided in theappropriate SIB.

The selection criteria are based on a minimum quality and signal level thresholdsfor the CPICH transmitted by a detected cell.

Values of these thresholds are provided to the UE in SIB 3. If cell selection procedure fails, the UE goes back to PLMN search.

Cell Selection


37/43

Cell Selection

UE attempts a cell selection (S-criteria) when- UE is switched on

- After several failed RRC connection request UE returns toIdle mode from Connected state

- UE returns to Idle mode from Emergency call on any PLMN

Random access procedure and open loop


38/43

Random access procedure and open looppower control

UE

WBTS

UECN signalling


39/43

UE CN signalling

Location Update Authentication Security Mode Setup Paging Call Setup

RNC MGW

MSC /VLR

WBTS

UE

Ciphering and Integrity Protection

Location registration


40/43

Location registration

With registration the UE reports registration area information to core network(CN).

The procedure is triggered after: The UE performs successful initial cell selection. The UE detects (SIB 1) after cell reselection that the current serving cell

belongs to new registration area. The timer expired for periodic location area updating (routing area updating).

When UE is registered it can be reached by paging from CN (CS and PS domains). In case that the UE enters new location area (routing area), adequate CN signalling

is performed between the current VLR (Visitor Location Register) and the old VLR.

Relevant entry in the HLR (Home Location Register) is also updated.

Paging procedure (1/2)


41/43


The UE is paged in order to enable connection between the UE and the network.

The UE is paged in the IDLE mode over the whole location area (CS paging) or routingarea (PS paging).

PICH and S-CCPCH that carries PCH are involved in the paging procedure. There are two phases of the paging procedure:

1) The UE detects indication in PICH;2) The UE decodes the paging message from S-CCPCH and checks whether it is forthis particular UE.

Radio frame n Radio frame n+1 Radio frame n-1PICH

S-CCPCH Radio frame n Radio frame Radio frame n-1

10 ms

3 slots



42/43

ag g p ocedu e ( / )

A cell can have configured more than one S-CCPCH + PICH for paging. The configurationtype is specified in SIB 1 and SIB 5.

UE reads System info (SIB5)

UE evaluateswhich S-CCPCH

UE evaluates how oftento check PI from PICH

UE evaluates whento check PI from

PICH UE evaluates which PI

to check

Pagingprocedure

MOC Call Setup


43/43

Basic Mobile Originating Call Diagram

03.WCDMA RRM and Cell Procedure

Documents

Transcript of 03.WCDMA RRM and Cell Procedure