Transcript RNO Wind

RNO Wind
Part III
Confidential
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Part III - Content
Call Setup Time
UL Interference
PS Utilization
Cell Reselection
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Call Setup Time
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Call setup Time – Preamble PRACH
•
During drive testing can be noted that there are call setup failures where the network does not seem to respond to
RRC Connection Requests with RRC Connection Setup –message.These are problems due to the spiky UL noise
and due to that the power ramping is not aggressive enough to provide high enough Tx power for the terminal
during open loop PC
PowerOffsetLastPreamblePRACHmessage
L1ACK/AICH
PtxAICH
Downlink / BS
PowerRampStepPRACHpreamble
PRACHRequiredReceivedCI
Preamble 1
UEtxPowerMaxPRACH
….
….
Preamble n
RACH Message part
Uplink / UE
PRACH_preamble_retrans: The maximum
number of preambles allowed in one preamble
ramping cycle
RACH_tx_Max: # of preamble power ramping
cycles that can be done before RACH
transmission failure is reported,
Note: The power ramp-up process will continue until
1) A positive or negative AI is received from the network
2) RACH_tx_MAX value is reached
3) UE reaches UEtxPowerMaxPRACH value
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Call setup Time – Preamble PRACH
The parameters affecting to open loop power control are, in brackets are the recommended values:
• PRACH_preamble_retrans (7)
• RACH_tx_Max (16)
• PowerOffsetLastPreamblePRACHmessage (2 dB)
• PowerRampStepPRACHpreamble (2dB)
The PRACHRequiredReceivedCI (-20dB) allow to calculate the UEpower for the fist preambleas in the
following:
Ptx = CPICHtransmissionPower-RSCP(CPICH) +RSSI(BS) +
PRACHRequiredReceivedCI (-20dB)
Example:
CPICH = 33dBm (Parameter per Node-B)
RSCP = -80dBm (Measured by UE)
RSSI = -85 dBm
UL_Required_C/I = -25 dB (Parameter per Node-B)
UE PRACH First Preamble Power = 33 dBm – (-80 dBm) + (-85
dBm) + (-25 dB) = 8 dBm
The parameter PRACHRequiredReceivedCI can be set to -18…-20dB instead of the default -25dB (typically 20dB is enough)
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Call setup Time – Preamble PRACH
Typical improvement passing from -25dB to -20dB:
PRACH req. C/I = -20dB
PRACH req. C/I = -25dB
Clear improvement in number of needed
RRC Connection Request messages per
call. For –20dB 100% of established calls
are setup with only 1 RRC Connection
Request message
100%
88%
100%
%
80%
60%
40%
20%
0% 2%
0% 5%
2
3
0%
6%
0%
1
4
# RRC Connection Request Messages per call setup
PRACH req. C/I = -25dB
Clear improvement number of sent
preambles per RRC Connection Request
for –20dB case. For –20dB 50% of cases
the needed number of preambles is <=4
where as for –25dB it is ~6.5
PRACH req. C/I = -20dB
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
There should be significant improvement
also for call setup delay
1
2
3
4
5
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7
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Call setup Time – Preamble PRACH
The average number of acknowledged PRACH preambles during the RRI period can be calculated based on the
KPI below
M1000C176SUM_RACH_ACK_P REAMBLES
M1000C177DENOM_RACH_ACK_P REAMBLES
RACH load due to preamble can then be calculated by dividing the above further by the max number preambles
can be received during RRI
• For example if RRI period is 200ms the are 10 20ms RACH frames and in each 20ms RACH frame there are
15 RACH sub slots within each it is possible to receive and decode max 4 preambles -> therefore in 200ms it
is possible to receive 15*4*10=600 preambles
M1000C176SUM_RACH_ACK_PREAMBLES
/600*100%
M1000C177DENOM_RACH_ACK_PREAMBLES
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Call Setup Time – SRB Rate
Why 13.6kbit/s?
 Use of 13.6 kbit/s SRB also in highly loaded networks
 Decreased setup times (PDP context activation minimum 0.7s lower)
 Improved Iub efficiency
Typical improvement passing from 3.4 to 13.6
7
Nokia RAN1.5 (3.4 kbps) + M11
6
Nokia RAN04 (13.6 kbps) + M12
Nokia RAN target
Seconds
5
4
3
2
1
0
3G-3G CS call setup
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PS call setup
DCH allocation
Call setup Time – KPI
In RN2.2 the following counters are available to monitor the Call Setup Time
RRC Setup Time
M1001C221/M1001C222
RAB Setup Time
M1001C223 / M1001C224
M1001C235 / M1001C236
for CS
for DATA BACKGR
In detail we have:
M1001C221 - SUM OF RRC SETUP TIMES
Sum of RRC setup times. This counter divided by the DENOMINATOR - M1001C222 gives the average
RRC setup time. RRC setup time is defined as the time between the RRC: RRC CONNECTION REQUEST
message and the RRC: RRC CONNECTION SETUP COMPLETE message.
M1001C223/235 - SUM OF RAB SETUP TIMES FOR CS VOICE/FOR DATA BACKGR
Sum of RAB setup times. This counter divided by the DENOMINATOR - M1001C224/236 gives the average
RAB setup time. RAB setup time is defined as the time between the RANAP: RAB ASSIGNMENT
REQUEST and RANAP: RAB ASSIGNMENT RESPONSE messages during RAB establishment.
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Call setup Time – Annex1
RACH/FACH
MO-UE
Mobile-to-mobile CS call setup on common channels
Delay
RRC connection request
UE
RNC
0
RRC connection setup
RNC
UE
40
RRC connection setup completeUE
RNC
100
CM service request
UE
CS
200
Security mode command
RNC
UE
100
Security mode complete
UE
RNC
200
Setup
UE
CS
300
Call proceeding
CS
UE
100
Radio bearer setup
RNC
UE
100
Radio bearer setup complete
UE
RNC
300
Alerting
CS
UE
MT-UE
Cumulative
0
Parallel RB setup for MO40
UE and paging of MT-UE
140
(CS core feature)
340
440
640
940
1040 Paging
RNC
1140 RRC connection request
UE
1440 RRC connection setup
RNC
RRC connection setup complete
UE
Paging response
UE
Security mode command
RNC
Security mode complete
UE
Setup
CS
Call confirmed
UE
Radio bearer setup
RNC
Radio bearer setup complete UE
250 2980
CS
UE
RNC
UE
RNC
CS
UE
RNC
UE
CS
UE
RNC
UE
400
50
40
100
100
100
200
300
100
100
300
250
<3.0 s mobile-to-mobile
AMR call setup time
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1340
1390
1430
1530
1630
1730
1930
2230
2330
2430
2730
2980
RACH/FACH
Average
paging delay
of 320 ms
assumed (640
ms paging
cycle)
Typical value for CS Call Setup Time
Call setup Time – Annex2
Typical value for PS Call Setup Time
Common channels
used for setup to avoid
slow synchronized
reconfigurations later
Delay
RNC
UE
RNC
PC
UE
RNC
PC
UE
RNC
UE
0
40
100
200
100
200
250
150
300
200
Cumulative
0
40
140
340
440
640
890
1040
1340
1540
<1.6 s PS call setup
time
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RACH/FACH
RRC + PDP on common channels
RRC connection request
UE
RRC connection setup
RNC
RRC connection setup complete UE
GPRS service request
UE
Security mode command
RNC
Security mode complete
UE
PDP context activation request
UE
Radio bearer setup
RNC
Radio bearer setup complete
UE
PDP context activation accept
PC
Parallel RB setup and
RL/AAL2 setups (or prereserved Radio links)
Initial bit rate DCH allocated
directly together with SRB
UL Interference
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What’s Interference?
Overload Area
PrxTarget [dB] +
PrxOffset [dB]
Prx Target [dB]
Marginal Load Area
Feasible Load Area
LRT  UnloadedRT and
LNRT  UnloadedNRT
Unloaded Area
Own cell load factor 
Any working point turned off from the expected load curve can be considered as interference.
Interference can be internal or external.
Internal interference can be caused by not appropriate dimensioning, planning or commissioning
External is usually referred to mobile or other RF sources
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Load vs. Power
Class1_Prx/Load
45000
40000
Rel. Amplitude
35000
30000
25000
20000
15000
10000
5000
0
-5000 0
50
100
150
200
250
WBTS
ave_lrt_class_1
ave_lnrt_class_1
ave_prxtot_class_1
Typical mismatch among load and Power can be easily found in a live network.
Above is reported a qualitative behaviour in class_1 power for some Wind WBTSs that are experiencing a
1<rt_load<2 (rt_load relative value from 0 to 4) and the related nrt_load and Prx_power.
The nrt load added to rt can not give sense of the Prx spike
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NSN Load Areas & Class of Power
PrxTarget [dB] + PrxOffset [dB]
Overload Area
Class4
Marginal Load Area
Class3
Feasible Load Area_2
Class2
Prx Target [dB]
PrxTarget [dB] - PrxOffset [dB]
Feasible Load Area_1
Class1
LRT  UnloadedRT and LNRT  UnloadedNRT
Unloaded Area
Class0
Own cell load factor 
CLASS
AREA
CLASS 0
Unloaded
(Lrt=<UnloadedRT) AND (Lnrt=<UnloadedNRT)
CLASS 1
Feasible_Load_Area_1
(PrxTarget -PrxOffset >= PrxTotal ) AND ((Lrt>UnloadedRT) OR
(Lnrt>UnloadedNRT))
CLASS 2
Feasible_Load_Area_2
(PrxTarget > PrxTotal > PrxTarget -PrxOffset) AND ((Lrt>=UnloadedRT)
OR (Lnrt>= UnloadedNRT))
CLASS 3
Marginal_Load_Area
(PrxTarget + PrxOffset > PrxTotal >=PrxTarget) AND ((Lrt>UnloadedRT)
OR(Lnrt> UnloadedNRT))
CLASS 4
Overload_Area
(PrxTotal >= PrxTarget + PrxOffset) AND ((Lrt>UnloadedRT) OR
(Lnrt>UnloadedNRT))
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INCREMENTED IF
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UL Interferece Detection Method
Different approach can be applied to detect UL interference.
Mainly we have:
- Field measurement
- Counters Analysis
Using the Counters Analysis approach dedicate counters are available for UL Interfernce
detection as MAXPrxNoise and MINPrxNoise (M1000C12 and M1000C13)
The UL interference severity can be estimated by analysing: MAXPrxNoise – MINPrxNoise, but
these counters are incremented only when cell is unloaded.
Here we propose a line for a method that approximately return the WBTS interfered.
The method takes the basis from the autotuning algorithm and use the value of Prx returned to
detect the interfered cell.
The first step is the localization of reference point for each class
Then different kind of statistical model can be applied for evaluating the drawn from them
Finally a w.w.w concept is used to derive information from space and time recurrence
Some help could come from counters that trigger downgrade or release bocause of interference
(e.g. M1000C147RB_DOWNGR_DUE_PBS_INTERF
M1000C159RB_RELEASE_DUE_PBS_INTERF if PBS is enabled)
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Prx Autotuning
The auto-tuning algorithm moves the reference point of the load curve and this means
that all the areas can be shifted up and down during the day this means that a certain
value of PrxTotal (which is measured by the bts) may trigger different areas during the
day. For example the sample 4 triggers in the first case the class 2 while in the second
case the class 1, but it’s the same value of power!
Main idea is to use this gap
to detect interference
t1
t0
Prx Target_t0 [dB]
Prx Target_t1 [dB]
Overload Area
Marginal Load Area
Feasible Load Area 2
4
4
Feasible Load Area 1
Unloaded Area
Time
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Class Power Reference Point
It is not an easy task to find the expected value of Prx in each class.
Different masking effect are present either for the granularity of the measurement available that are not
appropriate for this kind of analysis or for the inherent difficulty in evaluating the real load experienced.
Here a shot for class1 considering the stay time in the class is attempted
The spike are more accentuated
for low permanence and diluited
for the high one
Permanence in Class1>45min
0.35
Prx Displacement
0.25
0.2
0.15
Permanence in Class1<15min
0.1
0.05
1.4
0
1.2
1
3
5
7
Prx Displacement
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53
WBTS
An average can be
attempted filtering off the
spike and the default value
Prx Rel. Amplitude
Prx Rel. Amplitude
0.3
1
0.8
0.6
0.4
0.2
0
1
74
147 220 293 366 439 512 585 658 731 804 877 950 1023 1096 1169 1242 1315
WBTS
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Power Class Distribution Function
Probable
Interfered
WCEL
Probable
Interfered
Prx_Dist. function
WCEL
1
Rel. Amplitude
0.8
c2
0.6
c1
c0
c3
0.4
c4
0.2
0
0
200
400
600
800
1000
1200
1400
1600
1800
WBTS
Here a Prx Distribution over the all WCELs is presented. Typical value of the reference point are
represented individuating areas where interference can be detected.
The different shape of the curve of the Feasible_Load_Area_2 and the Marginal_Load_Area_2 respect
to the Class_0, Class_1 and Class_4 seems due to the different behaviour of the algorithm.
The step visible in C2 and C3 could be due to the strict margin in term of Power Budget to react to the
load increase. The overshoot of the C0 curve over the C1 is due to to the different triggering condition
that for C0 is load based instead of Power Level driven.
Finally C1 having a greater budget maintain a smoother shape.
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F_time
W.W.W. Approach
stable interference for a
adjacent cluster of cell
+
Commissioning /
Fixed Ext. Source
Dimensioning
-
+
F_space
Adj missing
Mobile Ext. Source
periodical spot interference
-
A single interfernce event can not raise any relevant bother. A statistical analysis is needed. The
Who? When? Where? approach is used to derive information and troubleshoot the probable
interferer source. The space-time diagram has to be intended as a recurrence indicator for the
interference event. In the left side of the F_space axis are reported occurences not adjoined in
space. Same concept for F_time.
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Class 0
Class0 can act as the third dimension of the WWW Approach diagram.
Considering Class0 as the unlaoded class in the sense that the unloaded limit for RT and NRT (1% and
2% respectively) is not exceeded the interference detection in this class can have two advantages:
a)
b)
More interference sentivity because of low load
Easier discrimination between internal and external interference
The first point is assured by the triggering condition and can be strenghtened superimposing a second
condition over the load.
Imposing the LoadRT = 0 and LoadNRT = 0 we have more reliable result for interference
This condition triggered mainly during the nigh-time returns the possibility to have an easier
troubleshooting
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PS Utilization
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Traffic Mix KPI
E
The KPI provides an indication of the percentage of CS voice, CS data, PS data RAB establishment attempts
relative to the total number of RAB establishment attempts
The KPI is meaningful for cluster/cell level and on day/hour basis. Same KPI can be obtained using RAB ACC
COMP
These KPI are intended to provide a high level indication of the traffic profile loading the network:
• CS_VOICE
Traffic Mix
• CS_CONV
• CS_STREA
16%
• PS_CONV
 R• A BPS_STREA
_ ST P _ A T T _ C S_ C O N V  R A B _ ST P _ A T T _ C S_ ST R E A  R A B _ ST P _ A Voice
T T _ P S_ C O N V  R A B _ ST P _ A T T _ P S_ ST R E A  R A B _
Data Conv
51%
• PS_INTER
PS Inter
32%
PS Backg
• PS_BACKG
1%
Example for CS_VOICE:
RAB _ STP _ CS _ VOICE
RAB _ STP _ CS _ VOICE  RAB _ STP _ CS _ CONV  RAB _ STP _ CS _ STREA RAB _ STP _ PS _ INTER  RAB _ STP _ PS _ BACKG
To take into consideration that PS might
cause many attempts in each call another
option is to consider the duration counters!
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Traffic Mix KPI
For each traffic class there are counters for RAB Holding time (incremented when the RAB is released only on the
cell that was the reference when the RAB is released)
AVG _ RAB _ HLD _ TM _ PS _ INTER
/ 100( s)
DENOM _ RAB _ HLD _ TM _ PS _ INTER
For each
Traffic Class
If a distribution on cell level is required the RAB_HOLD_TIME_IN_REF_CELL can be used
For NRT traffic classes (inter and backg) there are also counters for DCH Holding time (incremented when the
RAB is released only on the cell that was the reference when the RAB is released)
AVG _ DCH _ HLD _ TM _ PS _ INTER
/ 100( s)
DENOM _ DCH _ HLD _ TM _ PS _ INTER
DCH Holding Time [s]
RAB Holding Time [s]
20
20
40
60
80
100
120
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Only for
NRT Traffic Class
40
60
80
100
120
140
160
140
180
200
More
180
160
200
More
CELL
_
DCH
UE
CELL
_
FACH
CELL_DCH
state
InactivityTimerUL(DL)DCH
CELL_FAC
H state
RLC buffer payload
(transport channel traffic volume)
From Cell_DCH to Cell_FACH
After the inactivity timer expires the RRC radio bearer reconfiguration–procedure is performed.
RRC sends an RRC: RADIO BEARER RECONFIGURATION message to the UE.
UE acknowledges by sending the RRC: RADIO BEARER RECONFIGURATION COMPLETE –
message to the
RRC signaling entity of the RNC which starts L2 reconfiguration (as well as PS is informed about the
cell state change).
Radio link and AAL2 resources are then released and UE is changed to CELL_FACH state.
In case the UE is having RT RB which has become inactive and at the same time it is having inactive
NRT RB then RADIO BEARER RELEASE procedure is used (instead of RADIO BEARER
RECONFIGURATION).
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CELL
_
FACH
UE
CELL
_
DCH
CELL_D
CH state
CELL_FA
CH state
RLC buffer payload
(transport channel traffic volume)
From Cell_FACH to Cell_DCH
TrafVolThresholdDL(UL)
High
TrafVolThresholdDL(UL)L
ow
(WCEL)
In uplink direction the need for the capacity is detected by the MAC of UE.
UE requests dedicated capacity by sending an RRC: MEASUREMENT REPORT message on RACH to the
RRC signaling entity of RNC
After the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.
In downlink direction the capacity need is detected by the UE MAC entity of RNC.
PS requests the RRC signaling entity of RNC to start transport channel reconfiguration –procedure
The RRC signaling entity sends an RRC: TRANSPORT CHANNEL RECONFIGURATION message to the
UE
on FACH, which is acknowledged with an RRC: TRANSPORT CHANNEL RECONFIGURATION
COMPLETE
After the procedure, data transmission on DCH can begin and UE is in CELL_DCH state.
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Cell-DCH/Cell-FACH KPIs
DCH Time %
10%
Percentage of time in cell dch:
20%
30%
AVG _ DCH _ HLD _ TM _ PS _ INTER
100%
AVG _ RAB _ HLD _ TM _ PS _ INTER
40%
50%
60%
70%
80%
90%
Similar KPI giving the ratio between FACH and DCH can
be constructed starting from
100%
More
M1006C90 SUM OF UE OPERATING TIME IN CELL_FACH
M1006C87 SUM OF UE OPERATING TIME IN CELL_DCH
Dividing per the number of UE is possible to have
average time for user:
CELL_FACH
CELL_DCH
CELL_FACH
M1006C90 SUM OF UE OPERATING TIME IN
CELL_FACH/M1006C92 NUM OF UE MEASURED IN
CELL_FACH
Uplink DCH
M1006C87 SUM OF UE OPERATING TIME IN
CELL_DCH / M1006C89 NUM OF UE MEASURED IN
CELL_DCH
Downlink DCH
The number of transition can be monitored as well:
M1006C45 CELL DCH STATE TO CELL FACH
NRT RB data transfer active
NRT RB inactivity timer running
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M1006C46 CELL FACH STATE TO CELL DCH
Measuring the RACH/FACH Channel
The RACH channel average throughput for both data and signaling can be measured by the following KPI
M1000C60AVE_RACH_THROUGHPUT
/1000kbps
M1000C61RACH_DENOM_3
The FACH Total throughput means all the user related data (FACH-u) and signalling (FACH-c) for a SCCPCH
including PCH can be measured by the follwing KPI
 M1000C66AVE_FACH_U_TOT_TPUT_SCCP_PCH 

 bit/s
 M1000C67FACH_USER_TOT_TPUT_DENOM_0 
Load KPI are available as well using the following counters
M1000C64 AVE SCCPCH INC PCH LOAD
M1000C65 SCCPCH LOAD DENOM 0
When the throughput approach the maximum allowed or the load the 100% for the actual configuration a
parameter tuning to avoid the starvation in CCH or an expansion of RACH and FACH channel is required. The
decision outcomes from different input:
DCH resources available
Marketing Strategy
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Cell Reselection
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Cell Reselection 2G -> 3G
Start
measurement
GSM MS starts WCDMA measurements if :
RLA_C< F(Qsearch_I) for 0<Qsearch_I<=7
or
RLA_C> F(Qsearch_I) for 7<Qsearch_I<=15
If, for suitable UMTS cell
& for a period of 5 s:
CPICH RSCP > RLA_C + FDD_Qoffset
and
CPICH Ec/No  FDD_Qmin
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WCDMA cell
reselection
2G -> 3G Measurement
Depending on operator´s 2G – 3G interworking strategy parameter Q_search_I should planned accordingly.
In the best case, 3G
cell measurements are
possible when RLA_C
level < –74 dBm
In the best case, 3G cell
measurements are
restricted to the condition:
RLA_C level > –78 dBm
GSM
GSM
3G
3G
3G
GSM
Configuration 1
RLA_C< F(Qsearch_I)
( 0<Qsearch_I<=6 )
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Configuration 2
RLA_C> F(Qsearch_I)
( 7<Qsearch_I<=15 )
Configuration 3
RLA_C<  (always).
(Qsearch_I=7)
2G -> 3G Cell Re-selection Parameters
Qsearch_I and Qsearch_P define the threshold for non-GPRS/GPRS (respectively) capable UEs to measure 3G
neighbour cells when a running average of the received downlink signal level (RLA_C) of the serving cell
below (0-7) or above (8-15) the threshold
Value
0
1
…
6
7
8
9
10
…
14
15
dBm
-98
-94
…
-74
Always
-78
-74
-70
…
-54
Never
If RLA_C > -70 UE starts 3G
measurements
UE always measures 3G
cells
If RLA_C < -94 UE starts 3G
measurements
FDD_Qoffset and FDD_GPRS_Offset the non-GPRS/GPRS (respectively) capable UEs add this offset to the
RLA_C of the GSM cells. After that the UE compares the measured RSCP values of 3G cells with signal levels
of the GSM cells
Value
0
1
2
3
…
8
…
14
15
dBm
Always
-28
-24
-20
…
0
…
24
28
Always select irrespective
of RSCP value
Reselect in case RSCP > GSM
RXLev (RLA_C) +28dB
FDD_Qmin, defines minimum Ec/No threshold that a 3G cell must exceed, in order the UE makes a cell
reselection from 2G to 3G.
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Cell Re-selection Example-Weaker WCDMA
Non GPRS case
RSCP/
RLA_C
Ec/No
Cell re-selection to WCDMA
RLA_C
Serving GSM Cell
Qsearch_I=0
(-98 dBm)
FDD_Qoffset =6 (-8 dB)
Measurements starts (serving cell)
Neighbour WCDMA Cell
FDD_Qmin=0
(-20 dB)
RSCP
Ec/N0
Minimum Quality Requirement for WCDMA
t
5 sec.
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Cell Re-selection Example-Weaker WCDMA
GPRS case
RSCP/
RLA_C
Ec/No
RLA_P
Cell re-selection to WCDMA
FDD_GPRS_Qoffset =10 (8 dB)
Serving GSM Cell (Best)
Qsearch_P=0
(-98 dBm)
RSCP
Measurements starts (serving cell)
FDD_Qmin
=-20 dB
Ec/N0
Neighbour WCDMA Cell
Minimum Quality Requirement for WCDMA
t
5 sec.
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Cell Reselection 3G -> 2G
Whilst camping in a 3G cell the UE performs intra-frequency, inter-frequency, and inter-system
measurements based on the measured CPICH EcNo.
Serving cell parameters Sintrasearch, Sintersearch and SsearchRAT are compared with Squal (CPICH
Ec/No – Qqualmin) in S-criteria for cell re-selection
1 - None
(Squal > Sintrasearch )
2 - WCDMA intra-frequency (Sintersearch < Squal  Sintrasearch)
3 - WCDMA intra- and inter- frequency, no inter-RAT cells (SsearchRAT < Squal  Sintersearch)
4 - WCDMA intra- and inter-frequency and inter-RAT cells (Squal  SsearchRAT )
Sintrasearch Sintersearch
4
3
2
1
WCDMA
CELL
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SsearchRAT
Cell Reselection 3G -> 2G
CPICH EcNo
UE starts GSM measurements if
CPICH Ec/No =< qQualMin + sSearchRAT
SintraSearch
First ranking of all the cells based on
CPICH RSCP (WCDMA) and RSSI (GSM)
SinterSearch
Rs = CPICH RSCP + Qhyst1
Rn= Rxlev(n) - Qoffset1
Serving WCDMA cell
calculation, with
hysteresis parameter
Neighbour WCDMA or GSM
cell calculation with offset
parameter
SsearchRAT
qQualMin
No
Yes
Rn (GSM) > Rs (WCDMA)
And
Rxlev (GSM) >QrxlevMin
Second ranking only for WCDMA
cells based on CPICH Ec/No
Rs = CPICH Ec/No + Qhyst2
Rn=CPICH_Ec/No(n)-Qoffset2
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Cell re-selection
to GSM
Cell re-selection to
WCDMA cell of highest
R value
Cell Reselection 3G -> 2G
UE ranks the serving cell and the measured neighboring cells to find out if reselection should be made
• All the measured suitable cells (S-criteria) are included in the ranking.
• Criteria for a suitable cell (S-criteria) is defined as
– WCDMA intra-frequency neighbour cell:
CPICH Ec/No > AdjsQqualmin and CPICH RSCP > AdjsQrexlevmin
– WCDMA inter-frequency cell:
CPICH Ec/No > AdjiQqualmin and CPICH RSCP > AdjiQrexlevmin
– GSM cell:
Rxlev > Qrxlevmin
Ranking is done using Criteria R, and the UE reselects to the cell with highest R-criteria. R-criteria is defined
as:
• For serving cell: Rs = Qmeas,s + Qhysts
• For neighboring cell Rn = Qmeas,n – Qoffsetts,n
Qmeas is CPICH Ec/No for WCDMA cell and RxLev for GSM cell
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How to avoid ping pong ?
When phone is camped on 3G, GSM measurements can start when CPICH Ec/Io of serving cell is below
Ssearch_RAT + QqualMin.
When phone is camped on GSM, cell reselection to 3G is possible if CPICH Ec/Io of the candidate is above
FDD_Qmin.
Therefore, to avoid ping pongs between 3G and GSM the following condition should be met:
FDD_Qmin >= QqualMin + Ssearch_RAT
CPICH Ec/Io
FDD_Qmin >= -12 dB
QqualMin +Ssearch_RAT
Ssearch_RAT=4 dB
QqualMin=-18 dB
Camping on 3G
Measure GSM
Camping on 3G
t
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How to avoid ping pong ?
Parameters for cell reselections
•
•
Qqualmin = -18dB Ssearch_RAT =2dB -> the 3G->2G cell reselection starts when Ec/No hits -16dB
FDDQmin(GPRSFDDQmin) = -14dB (6) and QsearchP/QsearchI = always
The cell reselection paramters 3G -> 2G and 2G -> 3G provide only 2dB hysteresis which is not enough and should be
noticed from the RNC statistics as high amount of INTR_RAT_CELL_RE_SEL_ATTS from all the RRC Connection
Setup Attempts
•
•
Recommendation is to adjust the FDDQmin from -14dB to -10dB (or even up to -8dB) to provide 6 to 8 dB hysteresis
between 3G to 2G cell reselection and 2G to 3G cell reselection
Another parameter to tune is Qrxlevmin
On top of Treselection the above parameters will slow down further the 2G to 3G and 3G to 2G cell reselections
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Treselection
How long the reselection conditions must be fulfilled before reselection is triggered?
Treselection
Impacts all cell reselections : Inter RAT, intra frequency and inter frequency
The UE reselects the new cell, if the cell reselection criteria (R-criteria, see next slide) are fulfilled during a time interval
Treselection
As this parameter impacts on all the cell reselections too long Treselection timer might cause problems in high mobility
areas but too short timer causes too fast cell reselections and eventually causes also cell reselection ping pong
Recommended value 1s should work in every conditions i.e. enough averaging to make sure that correct cell is
selected
However careful testing is needed to check the performance of different areas
• (Dense) Urban area, slow moving UEs with occasional need for fast and accurate (to correct cell) reselections e.g.
outdoor to indoor scenarios or city highways – in some cases cell by cell parameter tuning is performed to find most
optimal value between 0s and 2s but typically 1s is optimal value when workload is considered as well
• Highways, fast moving UEs must reselect correct cell – typically 1s works the best (however occasionally also 0s
might be needed in fast speed outdoor to indoor cell reselections e.g. tunnels)
• Rural areas, slow or fast moving UEs need very often reselect between different RATs and make proper cell
reselections even when the coverage is poor – typically 1s works the best
• Location Area Borders, usually the coverage is fairly poor – typically 1s works the best but sometimes to reduce
location area reselection ping pong 1s is used when going from LA1 to LA2 and 2s from LA2 to LA1
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Cell Reselection KPIs
RRC connection request amount for inter RAT cell reselection ratio to all RRC Connection request causes
• When hysteresis is increased this KPI should decrease
M1001C42INT R_RAT _C
ELL_RE_SEL_AT T S
M1001C0RRC_CONN_ST P_AT T
RRC connection request amount for registrations ratio to all RRC Connection request causes
• When hysteresis is increased this KPI should decrease
M1001C46REGISTRATI ON_ATTS
M1001C0RRC_CONN_STP_ATT
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