INTERVIEW 3G Atunu Gorai
WCDMA Frequency and Spectrum • Uplink=1920MHz -1980 MHz • Downlink= 2110MHz -2170MHz • Bandwidth=60 MHz Actual B.W assign to operator is 5MHz And out of that 3.84 MHZ is utilize. In WCDMA frequency reuse factor =1 because time and frequency remains constant.
=
• Eb /NO
Bit energy/Noise energy • Ec/No = Chip Energy /Noise Energy.
• Ec/No= Eb/No - process gain • As per Eb/No is fixed for each service for Ex: voice =2 and video=4 • Ec/N0= 2- 10= -8 for voice(for voice -8 is good limit) • Ec/N0= 4-18= -14 for video(for video -14 is good limit)
• Process gain(voice) = chip rate/bit rate= 10dB • Process gain (video) = chip rate /bit rate= 18dB • Chip rate = 3.84Mchips in WCDMA. •
T h e e rro r-p ro te cte d sig n a l is th e n m u ltip lie d b y a p a rticu la r ch a n n e liza tio n co d e to p ro vid e th e n e ce ssa ry ch a n n e lse p a ra tio n . T h is is n e ce ssa ry sin ce a ll th e ch a n n e ls w ill b e a d d e d to g e th e r, w h ich w ill p ro d u ce a co m p o site d a ta stre a m . C yclic R e d u n d a n cy C h e ck ( C R C ) is u se d to d e te ct if th e re a re a n y u n co rre cte d e rro rs le ft a fte r e rro r co rre ctio n T h e n ext p a rt in th e tra n sm itte r is Fo rw a rd E rro r C o rre ctio n ( FE C ). T h e fu n ctio n o f th is b lo ck is to h e lp th e re ce ive r co rre ct b it e rro rs ca u se d b y th e a ir in te rfa ce .
Channelization codes In th e d o w n lin k , th e ch a n n e liza tio n co d e s a re u se d to se p a ra te th e d iffe re n t d a ta ch a n n e ls co m in g fro m e a ch ce ll. Fo r th e d e d ica te d ch a n n e ls, th is re p re se n ts th e d iffe re n t u se rs sin ce o n ly o n e scra m b lin g co d e is u se d fo r a ll d o w n lin k tra n sm issio n fro m th e ce ll. In th e u p lin k , th e ch a n n e liza tio n co d e s a re u se d to se p a ra te th e d iffe re n t d a ta ch a n n e ls se n t fro m th e U E to th e e a ch ce ll. T h e se p a ra tio n o f th e d iffe re n t U E s w ill h e re b e d o n e w ith d iffe re n t scra m b lin g co d e s. T h e n u m b e r o f co d e s u se d in th e d o w n lin k is re stricte d to 8 1 9 2 in to ta l. T h is is d o n e to sp e e d u p th e p ro ce ss fo r th e U E to fin d th e co rre ct scra m b lin g co d e . 5 1 2 o f th e se a re p rim a ry co d e s ( th e re st a re se co n d a ry co d e s, 1 5 co d e s p e r p rim a ry ) d ivid e d in to 6 4 co d e g ro u p s e a ch g ro u p co n ta in in g 8 d iffe re n t co d e s. T h e U E ca n d e te rm in e w h ich scra m b lin g co d e g ro u p a ce ll is u sin g b y th e syn ch ro n iza tio n p ro ce d u re ( se e ch a p te r 5 ). N o te th a t th e re a re n o re strictio n s fo r th e n u m b e r o f co d e s g e n e ra te d b y th e 2 4 b its sta rt ke y in th e u p lin k ca se
Data Drive • There is 3 modulation technique QPSK,16QAM,64QAM. • For high through put 16QAM and 64QAM should have high Utilization • So, if There is less Utilization of QPSK in downlink than data throughput is also high • CQI is like SQI in speech which ensure good channel quality for data transfer. • Retransmission of HS- DSCH( High-Speed Downlink Shared Channel) packet is high than also throughput is decreases. • In case of stationary Data Test- 2Mbits speed can be achieved • In case of moving Vehicle – 800kbits to 1.2 Kbits speed can be achieved. • Application throughput is always 85% of physical layer data rate throughput because at application level IP inclusion and overhead information will be there. • Latency time is round trip time from server and for 3G it
• The modulation scheme and coding is changed on a per-user basis depending on signal quality and cell usage. The initial scheme is Quadrature phase-shift keying (QPSK), but in good radio conditions 16QAM and 64QAM can significantly increase data throughput rates. With 5 Code allocation, QPSK typically offers up to 1.8 Mbit/s peak data rates, while 16QAM offers up to 3.6 Mbit/s. Additional codes (e.g. 10, 15) can also be used to improve these data rates or extend the network capacity throughput significantly. • Data Throughput will be also depend on MS class which support 5,10 and 15 codes resp. • CQI- Channel quality indication may include carrier level received signal strength indication (RSSI) and bit error rate (BER). I • Channel quality indicators are messages that are sent on a communication system (such as a mobile communication system) that provide the remote
N o te s o n q u a n titie s d e n o tin g sig n a l p o w e r
KEY PERFORMANCE INDICATORS
Accessability (Call set-up success rate)
Retainability (Dropped calls)
Mobility (Handover success rate)
Integrity (BLER and throughput)
Integrity- quality
Integrity-throughput
W h a t is th e m a jo r d iffe re n ce in lin k b u d g e ts b e tw e e n U M T S a n d G S M /T D M A ? In U M T S yo u g e n e ra lly h a ve a lin k b u d g e t fo r e a ch se rvice ( vo ice , d a ta , vid e o e tc ), in G S M yo u u su a lly o n ly u se 1 fo r vo ice . E a ch se rvice h a s a d iffe re n t E b / N o ta rg e t. In U M T S yo u h a ve to co n sid e r th e ta rg e t tra ffic lo a d yo u w ill h a ve a n d a d d a n o ise -rise m a rg in , in G S M yo u m a y h a ve a slig h t in te rfe re n ce m a rg in b u t n o t n o rm a lly re la te d to tra ffic . In U M T S so m e se rvice s ( like vo ice ) w illsh o w u p a s u p lin k lim ite d b u t o th e r se rvice s ( like H S D PA , 3 8 4 kb p s se rvice ) w ill sh o w a s d o w n lin k lim ite d . In U M T S yo u u su a lly h a ve to co n sid e r th a t a ll u se rs u se th e sa m e p o w e r fro m th e B T S th e re fo re th e m o re n u m b e r o f u se rs th e lo w e r th e
K PI ca lcu la tio n KPI
Requirements
Formula
CPICH RSCP
≥-95dBm
N/A
CPICH Ec/Io
≥-12dB
N/A
Voice call setup success rate Voice call setup time (Mobile to 1764440)
Min %
≥98%
≤10s
≥99%
≤9s
≥95%
Voice call drop rate
Max %
≤2%
PDP activation successful rate PDP activation delay
Min %
≥99%
≤2s
≥99%
PS 384k FTP DL
Avg Throughput
280kbps
PS 384k FTP UL
Avg Throughput
280kbps
HSDPA FTP
Avg Throughput
4.5Mbps
HSUPA FTP
Avg Throughput
1.1Mbps
(nbr_of_samples_RSCP>=-95dBm)/ (tot_nbr_of_samples_RSCP) (nbr_of_samples_EcIo>=-12dB)/ (tot_nbr_of_samples_EcIo) (nbr_of_successful_voice_call_setup)/ (nbr_of_voice_call_attemp) (nbr_of_voice_call_setup_time≤10s)/ (nbr_of_successful_voice_call_setup) voice_call_setup_time =[T(CC_alerting) - T(first_RRC_connection_request)] (nbr_of_voice_call_setup_time≤9s)/ (nbr_of_successful_voice_call_setup) voice_call_setup_time =[T(CC_alerting) - T(first_RRC_connection_request)] (nbr_of_voice_call_drop)/ [(call_duration_time)/90sec] (nbr_of_PDP_context_activation_accept)/ (nbr_of_PDP_context_activation_request) (nbr_of_PDP_activation_delay≤2s)/ (nbr_of_PDP_context_activation_accept) (downloaded_data_kbit)/ PDP_activation_delay= [T(PDP_context_activation_accept)(data_session_duration) T(PDP_context_activation_request)] (uploaded_data_kbit)/ (data_session_duration) (downloaded_data_kbit)/ (data_session_duration) (uploaded_data_kbit)/ (data_session_duration)
Case 1: Drop due to missing neighbor
Problem: Detected Nighbor (DN) UE sends a Measurement Report that contains an event1a means adding a new RL (cell) to Active Set If the reported cell is not in the current neighbor cell list and the reported Ec/No is better than the best serving cell Ec/No in AS by some dBs (set by a RNC parameter) If for any reason the new cell can not be added to AS, call will be released
2. If th e U E re co n n e cts to th e n e tw o rk im m e d ia te ly a fte r ca ll d ro p a n d th e scra m b le o f th e ce ll th a t U E ca m p s o n is d iffe re n t fro m th a t u p o n ca ll d ro p , m issin g n e ig h b o r ce ll is p ro b a b le . C o n firm it b y m e a su re m e n t co n tro l ( se a rch th e m e ssa g e s b a ck fro m ca ll d ro p fo r th e la te st in tra -fre q u e n cy m e a su re m e n t co n tro l m e ssa g e . C h e ck th e n e ig h b o r ce ll list o f th is m e a su re m e n t co n tro l m e ssa g e )
3. U E s m ig h t re p o rt d e te cte d se t in fo rm a tio n . If co rre sp o n d in g scra m b llin g co d e in fo rm a tio n is in th e m o n ito r se t b e fo re ca ll d ro p , th e ca u se m u st b e m issin g n e ig h b o r ce ll.
W e a k C o v e ra g e
Weak coverage usually refers to weak RSCP Uplink or downlink DCH power helps to confirm the weak coverage is in uplink or downlink by the following methods.
If the uplink transmission power reaches the maximum before call drop, the uplink BLER is weak ,the call drop is probably due to weak uplink coverage.
Out of Uplink coverage may be caused by not only by low CPICH_RSCP But also by high UL_RSSI
If the downlink transmission power reaches the maximum before call drop and the downlink BLER is weak, the call drop is probably due to weak downlink coverage
High downlink RSSI received by UE is an indication of weak coverage during that time UE tries to increase its target SIR to listen to the network. Multipath propagation yields signal paths of different lengths with different times of arrival at the receiver. Typical values of time delays (μs) are 0.2 in Open environment, 0.5 Suburban and 3 in Urban. When coded data rates of services are incompatible, “Rate Matching” is used to equalize the data rates. – Rate Matching may be performed by: � Padding with extra bits � Puncturing of bits using a pseudo-random algorithm
Case 2: Drop due to Poor Coverage (low RSCP)
Problem: Poor DL coverage
When UE gets to an area with low RSCP ( < -105 dBm)
regardless Ec/No values there is high risk for drop.
UE will likely ramp up the transmitted power and reach its
max power. The UL BLER will probably increase and SIR
target cannot maintain anymore, finally the call drops. E xp la in th e co n ce p t o f C e ll B re a th in g . H o w is th e a cco u n te d fo r in th e lin kB u d g e t? A n s: Io o r N o ( th e in te rfe re n ce p a rt o f E c / Io a n d E b / N o ) in cre a se a s th e tra ffic o n th e n e tw o rk in cre a se s sin ce e ve ryo n e is u sin g th e sa m e fre q u e n cy. T h e re fo re a s Io o r N o in cre a se s th e U E o r B T S n e e d s to u se m o re p o w e r to m a in ta in th e sa m e E b / N o o r E c / Io . W h e n th e p o w e r re q u ire d is m o re th a n th e m a xim u m p o w e r a llo w e d , th e co n n e ctio n ca n n o t b e m a d e . U se rs a t th e ce lle d g e a re u su a lly th e first to lo se se rvice , h e n ce th e se rvice a re a o f a ce ll sh rin ks. A s tra ffic d e cre a se s th e re ve rse h a p p e n s a n d th e se rvice a re a in cre a se s. T h e y sh o u ld sa y th a t it is a cco u n te d fo r in th e N o ise R ise M a rg in fo u n d in th e Lin k B u d g e t.
In te rfe re n ce Ø In d o w n lin k , w h e n th e a ctive se t C P IC H R S C P is g re a te r th a n –8 5 d B m a n d th e a ctive se t E c / Io is > = –1 2 d B , th e ca ll d ro p is p ro b a b ly d u e to d o w n lin k in te rfe re n ce D o w n lin k in te rfe re n ce u su a lly re fe rs to p ilo t p o llu tio n Ø In te rfe re n ce in U p lin k is d e te cte d w h e n th e U p lin k R T W P exce e d s a ce rta in co n fig u ra b le T h re sh o ld . In g e n e ra l E xp e cte d le ve l o f R T W P is fo rm e d b y su m o f th e th e fo llo w in g co m p o n e n ts.
e q u ip m e n t)
1 . T h e rm a l n o ise flo o r ( KT B =-1 0 8 . 1 3 2 d B m ) 2 . N o d e B n o ise fig u re ( Typ ica lly 1 . 8 d B fo r o u r
3 . N o ise ra ise d u e to lo a d ( 5 0 % lo a d in U p lin k co rre sp o n d s to 3 d b ) 4 . C o m p e n sa tio n fo r in a ccu ra cie s in R a d io N / W a lg o rith s ( 2dB ) W H A T IS T H E P ILO T P O LLU T IO N ? A re a w h e re th e S IR ( S ig n a l in te rfe re n ce ra tio ) is to o lo w a n d b e lo w th e exp e cte d va lu e ( E c / Io > = -1 2 d B ), th e re is to o m u ch in te rfe re n ce => th e m o b ile ca n n o t u n d e rsta n d th e p ilo t ch a n n e l
Pilot Pollution Excessive strong pilots exist at a point, but no one is strong enough to be primary pilot. 1. Definition of strong pilot
(CPICH_RSCP > ThRSCP )
2. Definition of Excessive
CPICH_Number > ThN
3. Definition of "no best server strong enough” CPICH_RSCP1st -CPICH_RSCP (ThN1 + )th
< ThRSCP_Relative
Following is the case from cluster Mongkok West Probable Solution : adjust engineering parameters of an antenna so that a best server forms around the antenna. For handover problems caused by pilot pollution, adjust engineering parameters of other antennas so that signals from other antennas becomes weaker and the number of pilots drops For this case reduce antenna height of site SGI. Many definitions: A cell that has a high signal strength at a location but is not part of the active set. A cell that meets thecriteria for addition into the Active Set but can not enter because the active set is full.
1 . UE fails to receive active set update command Handover )
( Delayed
After UE reports measurement message, the Ec/Io of original cell signals decreases sharply. When the RNC sends active set update message, the UE powers off the transmitter due to asynchronization. The UE cannot receive active set update message. This may be due to, Ec/Io of original cell decreases sharply and that of the target cell increases greatly (Turnings) 2. The best server changes frequently. Two or more cells alternate to be the best server. The RSCP of the best server is strong. The period for each cell to be the best server is short. Probable solution : Lower the triggering time for event 1a adjust antennas to expand the handover area adjust the antenna to form a best server reduce Ping-pong handover by setting the handover parameter of 1B event
Radio Interface Protocol Architecture P acket Data Convergence Protocol:
U-plane information
C-plane signalling
Is only for PS domain services.
GC
Nt
DC
Duplication avoidance GC
Nt
DC UuS boundary
L3 control RRC PDCP
L2/PDCP
control control
control
PDCP control
Radio Interface Protocol Architecture
RLC
RLC
RLC RLC
RLC
RLC
RLC
BMC
L2/BMC
RLC
L2/RLC
Logical Channels
Logical Channel
MAC
Transport Channels
Transport Channel (SAP) Physical Channels
L2/MAC
PHY
L1 17
UTRA Protocol Architecture C-plane signalling GC
Nt
U-plane information
DC RRC
L3
RLC
RLC
GC NT DC RRC RLC MAC
RLC RLC
General Control Notification Dedicated Control Radio Resource Control Radio Link Control Medium Access Control
L2/RLC Logical Channels
L2/MAC
MAC Transport Channels PHY
L1
Radio Interface protocol architecture 18
Logical Channel Structure Control Channel (CCH)
Synchronisation Control Channel (SCCH) (TDD) Broadcast Control Channel (BCCH) Paging Control Channel (PCCH) Dedicated Control Channel (DCCH) Dedicated Control Channel (DCCH) Common Control Channel (CCCH) Shared Channel Control Channel (SHCCH)(TDD) ODMA Dedicated Control Channel (ODCCH) ODMA Common Control Channel (OCCCH) (ODMA)
Traffic Channel (TCH)
Dedicated Traffic Channel (DTCH) ODMA Dedicated Traffic Channel (ODTCH)(ODMA) Common Traffic Channel (CTCH) 19
Channels Tra n sp o rt C h a n n e ls : D e d ica te d Tra n sp o rt C h a n n e l ( D C H ) , U L / D L , mapped to DCCH and D TC H B ro a d ca st C h a n n e l ( B C H ) , D L , mapped to BCCH F o rw a rd A cce ss C h a n n e l ( FA C H ) , D L , mapped to BCCH , CCCH , C TC H , D C C H and D TC H P a g in g C h a n n e l ( P C H ) , D L , mapped to PCCH R a n d o m A cce ss C h a n n e l ( R A C H ) , U L , mapped to CCCH , DCCH and D TC H U p lin k C o m m o n P a ck e t C h a n n e l ( C P C H ) , U L , mapped to DCCH and D TC H D o w n lin k S h a re d C h a n n e l ( D S C H ) , D L , mapped to DCCH and D TCH T h e sp e e ch se rvice in U M T S w ill e m p lo y th e A d a p tive M u lti - ra te te ch n iq u e . � T h is is a sin g le in te g ra te d co d e c w ith e ig h t so u rce ra te s: 1 2 . 2 , 1 0 . 2 , 7 . 9 5 , 7 . 4 0 , 6 . 7 0 , 5 . 9 0 , 5 . 1 5 a n d 4 . 7 5 kb p s. To fa cilita te in te ro p e ra b ility w ith existin g ce llu la r n e tw o rks so m e o f th e m o d e s a re th e sa m e a s in existin g n e tw o rks.
20
Channels P h y sica l C h a n n e ls : P rim a ry C o m m o n C o n tro l P h y sica l C h a n n e l ( P C C P C H ) , m a p p e d to BCH S e co n d a ry C o m m o n C o n tro l P h y sica l C h a n n e l ( S C C P C H ) , m a p p e d to FA C H , P C H P h y sica l R a n d o m A cce ss C h a n n e l ( P R A C H ) , m a p p e d to R A C H D e d ica te d P h y sica l D a ta C h a n n e l ( D P D C H ) , m a p p e d to D C H D e d ica te d P h y sica l C o n tro l C h a n n e l ( D P C C H ) , m a p p e d to D C H P h y sica l D o w n lin k S h a re d C h a n n e l ( P D S C H ) , m a p p e d to D S C H P h y sica l C o m m o n P a ck e t C h a n n e l ( P C P C H ) , m a p p e d to C P C H S y n ch ro n isa tio n C h a n n e l ( S C H ) C o m m o n P ilo t C h a n n e l ( C P IC H ) A cq u isitio n In d ica to r C h a n n e l ( A IC H ) P a g in g In d ica tio n C h a n n e l ( P IC H ) C P C H S ta tu s In d ica tio n C h a n n e l ( C S IC H ) C o llisio n D e te ctio n / C h a n n e l A ssig n m e n t In d ica tio n C h a n n e l ( C D / C A IC H ) 21
AMR T h e b it ra te o f th e A M R sp e e ch co n n e ctio n is co n tro lle d b y th e ra d io a cce ss n e tw o rk d e p e n d in g o n th e a ir in te rfa ce lo a d in g a n d th e q u a lity o f th e sp e e ch co n n e ctio n s. D u rin g h ig h lo a d in g , su ch a s d u rin g b u sy h o u rs it is p o ssib le to u se lo w e r A M R b it ra te s to o ffe r h ig h e r ca p a city w h ile p ro vid in g slig h tly lo w e r sp e e ch q u a lity. A lso if th e m o b ile is ru n n in g o u t o f th e ce ll co ve ra g e a re a a n d u sin g its m a xim u m tra n sm issio n p o w e r a lo w e r A M R b it ra te ca n b e u se d to exte n d th e ce ll co ve ra g e a re a . A d a p tive m u lti-ra te a lso co n ta in s e rro r co n ce a lm e n t. T h e p u rp o se o f fra m e su b stitu tio n is to co n ce a l th e e ffe ct o f lo st sp e e ch fra m e s. If se ve ra l fra m e s a re lo st m u tin g is u se d to p re ve n t p o ssib ly a n n o yin g so u n d s a s a re su lt o f th e fra m e su b stitu tio n . In P5 , w ith A M R N B it is p o ssib le to u se lo w e r sp e e ch co d e c ra te s th a n 1 2 . 2 kb p s. T h e ra d io n e tw o rk a lso su p p o rts 7 . 9 5 kb p s, 5 . 9 kb p s a n d 4 . 7 5 kb p s A M R co d e cs. T h e re is n o a d a p ta tio n in th e se n se th a t A M R co d e cs a re ch a n g e d d u rin g a n o n g o in g sp e e ch co n n e ctio n ; ra th e r th e re is a p o ssib ility to a d a p t th e ra te a t in itia l se le ctio n .
Link Budget •C e ll ra n g e & ce ll ca p a city a re lim ite d b y th e sa m e p a ra m e te rs : ✓In te rfe re n ce in u p lin k ✓Po w e r in d o w n lin k
•C e ll b re a th in g p h e n o m e n o n
23
“Power” Link Budget Tx power + All Gains – Path Loss – Other losses = Rx power
Path loss = Tx Signal + All Gains – Rx power
Max Path loss = Tx Signal + All Gains – sensitivity
Other losses –
Other losses –
Rx
Initial Cell Search nitial Cell Search is carried out in three steps : Step 1: Slot synchronisation - using the primary synchronisation channel.
tep 2:
Frame synchronisation and code-group identificationusing the secondary synchronisation channel.
p 3:
Scrambling-code identification-identified through symbo by-symbol correlation over the primary CCPCH with the scrambling codes within the code group.
25
P-SCH1
P-SCH2
Slot Synchronization P-SCH3
1 Slot = 667µ s P - SCH1 S - SCH1
P - CCPCH
P - SCH2 S - SCH2 P - SCH3 S - SCH3
P - CCPCH
P - CCPCH P - CCPCH
P - CCPCH
P - CCPCH P - CCPCH
UE synchronizes on the strongest correlation peak 26
P-SCH
Frame Synchronization S - SCH
512 Primary Scrambling Codes divided into 64 groups Scrambling Code Group
#0
#1
#2
#3
#4
#5
slot number #6 #7 #8
#9
#10
#11
#12
#13
#14
Group 0 Group 1 Group 2 Group 3 Group 4 … Group 61 Group 62 Group 63
1 1 1 1 1
1 1 2 2 2
2 5 1 3 16
8 16 15 1 6
9 7 5 8 6
10 3 5 6 11
15 14 12 5 15
8 16 16 2 5
10 3 6 5 12
16 10 11 8 1
2 5 2 4 15
7 12 16 4 12
15 14 11 6 16
7 12 15 3 11
16 10 12 7 2
9 9 9
10 11 12
13 12 10
10 15 15
11 12 13
15 9 14
15 13 9
9 13 14
16 11 15
12 14 11
14 10 11
13 16 13
16 15 12
14 14 16
11 16 10
Slot # ?
Slot # ?
Slot # ?
P - SCH
acp
acp
acp
S - SCH
16
11
2
256 chips
……..
Group 4 Slot 12,13,14
2560 chips 27
P-SCH1
P-SCH2
Slot Synchronization P-SCH3
1 Slot = 667µ s P - SCH1 S - SCH1
P - CCPCH
P - SCH2 S - SCH2 P - SCH3 S - SCH3
P - CCPCH
P - CCPCH P - CCPCH
P - CCPCH
P - CCPCH P - CCPCH
UE synchronizes on the strongest correlation peak 28
Cell Information P-SCH: Coverage indication, Slot Synchronization S-SCH: Frame Synchronization, Group identification P-CPICH: Scrambling Code Identification P-CCPCH: System Information Broadcast
Logical Channel
Transport Channel
Physical Channel
BCCH
BCH
P-CCPCH
Bit Rate: 12.3 kbps
RLC Mode: transparent Mac-B: transparent
OVSF Cch,256,1 Primary Scrambling Code Transmitted during 9/10th slot
29
Quality
Intra-Frequency Cell Reselection sample Treselections
Serving Cell
Serving Cell
Qmean,s + Qhyst2s
Qqualmin + SIntraSearch
Qmean, n - Qoffset2s,n
Qqualmin Neighboring Cell Neighboring cell criterion S is fulfilled and is ranked UE perform intra-frequency measurements
Neighboring cell UE perform cell better ranking reselection than Serving cell
Neighboring Cell Time
30
Cell selection and reselection ： Cell Selection criteria The cell selection criterion S is fulfilled when:
for FDD cells:
Srxlev > 0 AND Squal > 0
for TDD cells:
Srxlev > 0
for GSM cells:
Srxlev > 0
w h e re
Squal = Qqualmeas – Qqualmin Srxlev = Qrxlevmeas - Qrxlevmin - Pcompensation Pcompensation ＝ max(UE_ TXPWR_MAX_R ACH – P_MAX, 0)
31
Cell Selection Parameters
Parameter
Object
Range
Default Value
Recommended Value
Class
qQualMin
CellSelectionInfo
Int [-24..0] (dB)
-10
-16
C2
qRxLevMin
CellSelectionInfo
Int [-115..-25] Step = 2 (dBm)
-45
-115
C2
maxAllowedUlTxPower
UlUsPowerConf
Int [-50..33] (dBm)
33
33
C3
P_Max = maximum UE output power (dBm) according to its class Power Class
Maximum Output Power (dBm)
1
33
2
27
3
24
4
21
32
Cell Reselection Procedure Squal
Threseholds given as example
SintraSearch
If
SinterSearch Measurement on same frequency
Squal
SinterRAT Measurement on other frequencies
Measurement on other RAT
= CPICH_Ec/No – qQualMin < Threshold
Associated measurements are performed
Thresholds are broadcasted in SIB 11 In UMTS02, 2 types of measurements are done: Intra frequency and inter RAT
33
Cell Reselection Parameters Parameter
Object
Range
Default Value
Recommended Value
Class
qHyst1
CellSelectionInfo
Int [0..40] (dBm) Step = 2
10
4
C2
qHyst2
CellSelectionInfo
Int [0..40] (dB) Step = 2
4
6
C2
qOffset1sn
GSMCell
Int [-50..50] (dB)
0
TBD
C0
qOffset2sn
UMTSFDDNeighbouring
Int [-50..50] (dB)
0
TBD
C0
CPICH_EcNo or CPICH_RSCP
CPICH_EcNo
N.A.
Static
Int [0..31] (s)
31
6
C2
qualMeas tReselection
CellSelectionInfo
34
Measurements
The different types of air interface measurements are:
• • Intra-frequency measurements: measurements on downlink physical channels at the same frequency as the active set. A measurement object corresponds to one cell.
• • Inter-frequency measurements: measurements on downlink physical channels at frequencies that differ from the frequency of the active set. A measurement object corresponds to one cell.
• •
Inter-RAT measurements: measurements on downlink physical channels belonging to another35
Handover (Handoff)
• There are following categories of handover (also referred to as handoff):
• •
• •
means that all the old radio links in the UE are removed before the new radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is not perceptible to the user. In practice a handover that requires a change of the carrier frequency (inter-frequency handover) is always performed as hard handover.
Hard handover
means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN. Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time.
Soft handover
• •
36
Softer handover
is a special case of soft handover where the radio
Handover (Handoff) •
The most obvious cause for performing a handover is that due to its movement a user can be served in another cell more efficiently (like less power emission, less interference). It may however also be performed for other reasons such as system load control.
• •
• •
is defined as the set of Node-Bs the UE is simultaneously connected to (i.e., the UTRA cells currently assigning a downlink DPCH to the UE constitute the active set). The maximum active set size at the RNC is determined by the parameter MaxAciveSetSize 3 to 4 cells, the larger the active set size the more likely it is that Iub link efficiency is reduced (more than one resource for a single connection due to SHO) Active Set
• •
Cells, which are not included in the active set, but are included in the CELL_INFO_LIST belong to the Monitored Set.
• •
Cells detected by the UE, which are neither in the CELL_INFO_LIST nor in the active set belong to the Detected Set. Reporting of measurements of the detected set is only applicable to intra-
37
PRIMARY CELL ELECTION ALGORITHM (MONITORED SET UPDATE) •
• •
• •
The primary cell election algorithm applies to soft HO. It is used for monitored set determination and a pointer to mobility parameter. The Monitored Set should be updated each time the primary cell of active set changes. A measurement control message is sent (with measurement commend set to modify) is sent to the UE in order to update the monitored set. The message contains the cell to add/remove from the monitored and should follow the ACIVE SET UPDATE message.
Measurement control used for monitored set update
The primary cell algorithm is called from SHO algorithm; therefore it is performed each time a MEASUREMENT REPORT is received by the SRNC. 38
Compressed mode •
Compressed mode is when the mobile goes into a slotted transmit mode whereby it opens up an idle period (transmission gap) where it can monitor another carrier or technology (GSM). The impact is that to maintain the same bit rate, it halves the SF, and therefore increases power level causing higher interference to the network. If the SF cannot be halved then the bit rate of the bearer decreases. If they seem knowledgably, ask them if they know what messages and events trigger and configure compressed mode on/off. 2D event for on, 2F for off. Messages would for configuration would be RADIO BEARER RECONFIGURATION, TRANSPORT CHANNEL RECONFIGFURATION or PHYSICAL CHANNEL RECONFIGURATION.
Compressed Mode •
During inter-frequency handover the UE’s must be given time to make the necessary measurements on the different WCDMA carrier frequency. 1 to 7 slots per frame can be allocated for the UE to perform this intra frequency (hard handover).
•
Why is
compressed
–
•
mode needed?
In UTRAN FDD, transmission/reception by the mobile is continuous : no idle periods are available for monitoring other frequencies if the UE has only a single receiver
How is it done? – –
Transmission gaps are created in the radio frame in DL and/or UL to allow the UE to switch to another frequency, perform measurements on another carrier (FDD, TDD or GSM) and switch back Transmission gaps are positioned in one radio frame or at the boundary of 2 radio frames in regular intervals referred to as a transmission gap pattern sequence •
•
How is it done? –
Two approaches can be taken in creating the transmission gaps of the transmission gap pattern sequence • •
– •
no more than 7 slots are used in any one radio frame to create the transmission gap.
Modifiy the physical layer parameters (by puncturing or spreading factor reduction) to allow all information bits to be transmitted. Restrict the bit rate (by higher layer scheduling) to match the fewer available transmission slots in a compressed radio frame.
In both approaches, the goal is to not loose transmission frames
Who controls it? – –
Compressed mode is under the control of the UTRAN Compressed mode is configured by the RNC per UE in the form of transmission gap pattern sequences • • •
given to the UE via RRC signalling given to the node B via NBAP signalling a transmission gap pattern sequence is associated with a specific measurement purpose: – – –
–
FDD measurements, TDD measurements, GSM initial BSIC identification, GSM BSIC reconfirmation, GSM RSSI measurement
40
Physical layer Aspects Compressed Mode Methods
• Three methods are available to create transmission gaps – Puncturing: Puncturing additional puncturing/fewer repetitions are performed compared to normal mode • • •
to be used only in DL to be used only in the case of mapping to fixed positions scrambling and channelisation code remain unchanged
– Spreading Factor Reduction: Reduction SF is divided by 2 • • • • •
can be used in UL and DL can be used with mapping to flexible positions to be used only when SF>4 only 2nd DTX insertion and physical channel mapping is modified may lead to channelisation code shortage and the need to use a secondary scrambling code
41
Cell Shakedown • Purpose – – – – – – –
To test Call Setup (Voice and FTP) in each cell To test Handoffs (Soft and Softer) between Cells Verify antenna orientation Primary Pilot Ec/Io Scrambling Code for each cell UE transmit power Path Balance
• Method – By driving clockwise and anticlockwise within a designated route around the the base station (about 30% of the site coverage area).
– 42
Difference between Scanner data & UE Data Collection An overview of cluster performance based on scanner Best Serving CPICH RSCP and Ec/Io measured data.
•Difference in data collection ✓Antenna ✓Cable ✓Sampling
•Solution : Perform a calibration drive . •
Scanner
•
Primary Common Pilot Channel (PCPICH) scrambling code measurements Continuous Wave (CW) measurements Spectrum analysis Synchronization Channel (SCH) code word measurements
• • • • •
•
UE
• • •
Data/Voice/Video Calls Layer 3 messages logging Layer 2 messages logging (Transport channel) RRC State logging UE Transmit Power SIR Serving Cell / Active Set / Monitored Set Events GSM neighbor measurements
• • • • • •
•
• • •
43
Inner loop & Scanner E xp la in In n e r a n d O u te r lo o p p o w e r co n tro la n d w h o co n tro ls th e m . If th e y sta rt ta lkin g a b o u t O p e n a n d C lo se d Lo o p P C , te ll th e m yo u w a n t In n e r/ O u te r C lo se d Lo o p P C . In n e r lo o p p o w e r co n tro l is p e rfo rm e d b y th e N o d e B to se t th e tra n sm itp o w e r o f th e U E a n d B T S to co m p e n sa te fo r sig n a l va ria tio n s d u e to fa d in g o r p a th lo ss to m a in ta in th e se t S IR ( o ccu rs u p to 1 5 0 0 tim e s p e r se c ). O u te r lo o p p o w e r co n tro l is p e rfo rm e d b y th e R N C to se t th e ta rg e t S IR b a se d o n th e re q u ire d B E R / B LE R fo r th e re q u e ste d se rvice s ( occurs up to 100 times per sec ).
•
•
In pre-launch optimization, how are missing neighbors usually detected? Usually you use a scanner and compare the best pilots in Ec/Io from the scanner against that of the active set and monitored set from an active UE. If there is a stronger pilot from a nearby cell that appears on the scanner but not on the UE, there is a possible missing neighbor. One would thenverify that the neighbor appears in defined neighbor list
Drop after active set update Symptom:
•
•
Normally, the observed sequent messages in the UE side are: –
UTRAN -> UE: Active set update (to request the UE to remove a cell, e.g. SC281)
–
UE -> UTRAN: Active set update complete
–
UTRAN -> UE: Measurement Control (update neighbour list)
–
UE -> UTRAN: Measurement report (to propose to add7)
–
UTRAN -> UE: Active set update (to request the UE to add SC 137)
–
DROP.......(since no Active set update completion was sen after 12 secs )
The radio performances no matter DL and UL are very good.
Possible solution: No solution, check this problem with UE vendor.
• • • • • •
In Soft Handover the UE is connected to more than one Radio Base Station (RBS) simultaneously. At least one radio link is always active and there is no interruption in the dataflow during the actual handover. The signals are received in the UE and combined in the RAKE receiver to give protection against fading.
45
Soft/Softer Handover Radio Link Addition and Radio Link Removal.
R e fe re n ce : U se r D e scrip tio n a n d E n g in e e rin g G u id e lin e s 7 5 / 1 5 5 1 -H S D 1 0 1 0 2 / 1 U e n B 2 © Ericsson AB 2003 - All Rights Reserved
46
Drop after active set update, Cont.
BLER is getting worse
RF condition is o.k. 47
Drop after active set update, Cont.
No Active Set Completion was sent after Active Set Update.
48
FINAL WORDS
•
For network tuning, we need to relay on field measurements which require extensive drive tests
•
Finding the best possible configuration for antenna heights, tilts, azimuths and parameter setting for all the present cells/sectors in the network and also for any new sites that might be needed to improve coverage
•
Power adjustment can also be used for network tuning but can become complicated and result in poor network performance
•
Use of Remote Electrical Tilt (RET) Antenna is preferred over mechanical tilt antenna
•
Neighbour definition is of prime importance in UMTS network (Soft handover gain and interference reduction). Keep neighbour list upto 20.
•
Automated tools are needed that could suggest the best possible neighbour relations, antenna heights and tilts by using both the field measurements and the propagation models & simulations
•
Skilled people, right methods and advanced tools are needed to perform 3G tuning and optimisation
Name the 4 RRC Connected Modes (states) and describe the characteristics of each. Cell-DCH: UE has been allocated a dedicated physical channel in uplink and downlink. Cell-FACH: UE listens to RACH channel (DL) and is allocated a FACH channel (UL). Small amounts of UL/DL data can be transfers in this state. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. Cell-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. No data can be transferred in the UL in this state. URA-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the URA level.
If a UE is on a data call (CELL-DCH state) and there is in no activity for awhile what would you expect to see occur? UE should go from CELL-DCH to CELL-FACH then if still no activity to either CELL-PCH or URA-PCH (via CELL-FACH). If they talk about inactivity timers and mention that the state goes from CELLDCH straight to CELL-PCH or URA-PCH, that is also possible. Bonus they say they would see RADIO BEARER RECONFIGURATION messages when the states are changing.
Power control In the uplink the base station measures the received Signal-toInterference Ratio (SIR) and compares this to a target SIR. If the measured SIR is below the target then the base station requests the mobile to increase its power (and vice versa). This type of power control is known as the Inner-loop power control and is capable of adjusting the transmit power in steps of, for example 1 dB at a rate of 1500 times per second. Inner-loop power control is only applicable for connections on dedicated channels
