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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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.
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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)
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
14/43
Few Basics.
COVERAGE
14
CAPACITY QUALITY
POWER
8/11/2019 03.WCDMA RRM and Cell Procedure
15/43
Understanding Power Control
LOWER Power PerUser HIGHERNumber of Users
15
HIGHER Power PerUser LOWER
Number of Users
8/11/2019 03.WCDMA RRM and Cell Procedure
16/43
Cell Breathing
No or Improper Power Control leads to High interference that impactsCoverage, Capacity and Quality
16
Power Ctrl
ONOFF
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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.
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
20/43
Multipath Propagation
2
Multipath Propagation
20
1
3
Multiple paths possibly cause destructive interference between differentreplica of the desired signal
8/11/2019 03.WCDMA RRM and Cell Procedure
21/43
The Rake Receiver
Each multi- path 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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
25/43
PLMN Selection Automatic Mode
PLMN Priority
Home PLMN
PLMNs in USIM
Operator Controlled PLMNs
Other PLMNs according to RSCP
Cell search procedure
8/11/2019 03.WCDMA RRM and Cell 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)
8/11/2019 03.WCDMA RRM and Cell Procedure
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
Synchronisation Channel (SCH)
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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)
8/11/2019 03.WCDMA RRM and Cell Procedure
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)
8/11/2019 03.WCDMA RRM and Cell Procedure
30/43
CP
2560 Chips 256 Chips
Synchronisation Channel (SCH)
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
34/43
CP
2560 Chips 256 Chips
Synchronisation Channel (SCH)
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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)
SystemInformationBlock (SIB)
SystemInformationBlock (SIB)
...
System Information
(BCCH -> BCH -> PCCPCH)
WBTS Schedulinginformation
MasterInformationBlock (MIB)
Actual system
information
Cell selection
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
38/43
Random access procedure and open looppower control
UE
WBTS
UECN signalling
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
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)
8/11/2019 03.WCDMA RRM and Cell Procedure
41/43
Paging procedure (1/2)
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
Paging procedure (2/2)
8/11/2019 03.WCDMA RRM and Cell Procedure
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
8/11/2019 03.WCDMA RRM and Cell Procedure
43/43
Basic Mobile Originating Call Diagram