coverage enhancement
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BSSPAR1: Chapter 8Coverage Enhancement Features
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Legal Notice
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Module Objectives
Describe Extended Cell Range for CS calls
Explain parameters controlling handovers in a Extended Cell Explain the Long Reach Timeslot for Flexi BTS
Explain the 105km Super Extended cell and related parameters
Give a brief introduction to Smart Radio Concept (SRC) feature
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Extended Cell Range
One BCCH, Two TRX solution to extend cell radius to 70km
Normal and Extended area served with different TRX
BTS Type supported
Ultra CX4.1 (with EDGE capable TRX)
Flexi EP2.0
Talk Family DF7.0
Not supported by Metrosite
Activation based on TRX licence (Flexi, Ultra) or PRFILE (Talk)
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Normal region (frequency f1)
N-TRX (Parameter eTrxInd (ETRX) = N)
Extended region (frequency f2 except timeslot 0)
E-TRX (Parameter eTrxInd (ETRX) = E)
E-TRX
(Delayed receiver)
0 1 2 3 4 5 6 7
N-TRX
0 1 2 3 4 5 6 7
f1 f1 f1 f1 f1 f1 f1 f1
BCCH/
SDCCH
Not
UsedTCH TCH TCH TCH TCH TCH
TCH TCH TCH TCH TCH TCHE-RACH SDCCH
f1 f2 f2 f2 f2 f2 f2 f2
Extended cell size
Parameter radiusExtension (EXT)
Value = 1..67km radius extension of extended cell
Value = 0 ordinary cell
Extended Cell Range (Implementation)
BB Hopping cannot be used
RF hopping cannot be used onE-TRXs
One BCCH, Two TRX solution
Receiver timing delayed onETRX
Transmitter timing same onNTRX and ETRX
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Call Setup
RACH received on N-TRX IMM ASS sent on N-TRX SDCCH on N-TRX
RACH received on E-TRX IMM ASS sent on N-TRX SDCCH on E-TRX
Overlap area: RACH is recived on N-TRX and E-TRX. BSC filters the later one out
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Cell Selection
MS can camp on BCCH (NTRX) independent of the distance to the BTSRACH from MS detected on RACH or E-RACH depending on the distance to the BTS
Failure of RACH burst Wrong cell selectedReselection on the basis of the path loss criterion C1
Handover to due Distance (Normal area Extended area)
maxMSDistanceHOThreshold (MAX) 0..63 TA => MAX; handover triggered t o extended cell
minMSDistanceHOThreshold (MIN) 0..63 TA => MIN; handover triggered to normal cell
Adjacent Cell Parameter
hoTargetArea (HOTA) indicates type of target cell (normal orextended) ;indicates type of transceiver from which the BSC tries to allocate a channel (normal orextended)
0 Normal cell1 - Allocate from N-TRX
2 Allocate from E-TRX3 Allocate from TRX of the same type as source BTS
Extended Cell(Cell Selection, Handover)
Inter-BSC HO: Only values 0, 2 are allowed for HOTA.
External HO are made only towards Extended area ifLong Reach TSL (for Flexi) is NOT in use
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The Double BCCH Allocation List (Double BA List) may be needed in the extended cell
range solution because otherwise some legacy MSs do not work properly
The intra-cell handover between an N-TRX and an E-TRX is performed by using a
HANDOVER COMMAND message.
Using the Handover Command requires that the BCCH frequency of the serving cell is
included in the BCCH allocation list.
This can be achieved by using the Double BA List.
Extended CellUse of Double BA list
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Long Reach TimeslotFlexi BTS (EP2.0)
Currently BSC allocates external handovers only towards extended area ofan extended cell higher HO failures
Used to determine if the MS is located in normal or extended area (of thetargeted cell) in case of incoming external HO
Use of LRTCH BTS measures TA by scanning both LRTCH for the handover access burst BTS sends the ACCESS DELAY information to BSC
ACCESS DELAY < maxMSDistanceHOThreshold MAX: Normal cell area ACCESS DELAY >= maxMSDistanceHOThreshold MAX : Extended cell area
Intra-cell HO from LRTCH to TCH of N-TRX or TCH of E-TRX to free up LRTCH
Transmission on first LRTCHonly Reception on both LRTCH
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Long Reach TimeslotFlexi BTS (EP2.0)
TA value sent by BTS to MS cannot be greater than 63 BTS must send anadjusted value for TA if the MS is in extended area
If TA > 1.8 * EXT
TA (adj) = TA (meas) 1.8*EXT TA (adj) = TA (meas)
UL is synchronized to E-TRX UL is synchronized to N-TRX
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105km Super Extended CellIntroduction
Radius extension upto 105km for Flexi BTS (EP2.0 CD1)
BCCH serves all three cell areas
DL of E-RACH tsl not used
E-RACH of STRX overlaps with tsl 0 and 1 of BCCH (just like E-RACH ofETRX)
SDCCH defined on S-TRX
Normal and Super Extended
areas do not overlap
TA of each area measured
separately from 063
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105km Super Extended CellHandover between areas
EXTMAX
N-area: 35 km
E-area: 35 kmS-area: 35 km
SEXT SMAX
Overlap area (N/E) Overlap area (E/S)
BTS
MINSMIN
1.
2.
3.4.
1. Mobile is moving in Normal area (away from BTS), TA MAX => handover to Extended area triggers
2. Mobile is moving in Extended area (away from BTS), TA SMAX => handover to Super extended area triggers
3. Mobile is moving in Super extended area (towards BTS), TA SMIN => handover to Extended area triggers
4. Mobile is moving in Extended area (towards BTS), TA MIN => handover to Normal area triggers
TRX Level
E-TRX Type = S
BTS LevelSuper Radius Extension (SEXT)Location of inner edge of superextended area from the BTSRange: 0, 36-70
Handover ControlMS distance HOthreshold super ext cell min (SMIN)Range: 063
MS distance HOthreshold super ext cell max (SMAX)Range: 063
External handovers
Performed thru LRTCH if it is in use If not in use, HO to super extendedarea
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SRC consists of : Downlink link enhancing feature
Intelligent Downlink Diversity (IDD) Uplink enhancing features
4-way UL Diversity (4UD) Interference Rejection Combining (IRC) High gain MHA
Up and downlink features can also be implementedseparately (except for 4UD, which is used with IDD)
BTS Support: Ultrasite CX6.0, FlexiEDGE EP2.0 TRX Support: EDGE-capable TRX and EDGE
baseband units required
SRC Concept
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Improves the mobiles receiver performance by modifying the radio
channel BTS downlink performance is boosted up to 3-5 dBAll timeslots are transmitted through 2 transceivers and 2 antennas
2nd TRX transmission is delayed and phase turnedAlso BCCH carrier is sent through 2 transmitters Phase hopping is used to change phasing between adjacent bursts (todecrease correlation between a main and auxiliary transmitter) To the BSC, the main and auxiliary TRX appear as one logical TRX Mobile receives both signals as standard multipath
IDD ConceptDelay Diversity (DD) with Phase Hopping
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EDGE
Transceiver
Combined
Uplink
signal
EDGE
Transceiver
Baseband
Units Downlink
signal
RX + TX
MHAMHA
DDU
RX div.
RX div.
RX div.+ TX aux
Masthead Amplifier compensatesfeeder loss and matches front end ofthe BTS receiver optimizing sensitivity
Very efficient Interference RejectionCombining is processed for receivedsignals giving ultimate gain for diversityreception. IRC minimizes the effect ofinterfering signals in the BTS receiver.
4-way UL Diversity
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The noise between two branches are somewhat correlated, so the
best way of combining is Interference Rejection Combining (IRC). This
takes into account the correlation between interference branches andremoves ultimately the interference from the received signal.
Uplink receiver diversity can be either 2- or 4-way diversity.
In 2-way diversity the receiver combines signals from two antennas
by using Interference Rejection Combining (IRC).
4-way diversity is based on MRC combination of two 2-way IRC
diversity branches.
The signals from four antennas are fed into two separate TRX. Two
pair-wise signals are combined by IRC in respective TRX and then the
signal from the auxiliary TRX is fed into the main TRX where signals
are combined using Maximum Ratio Combining
4-way uplink diversity using IRC
followed by MRC.
2-Way/4-Way UL Receiver Diversity(IRC/MRC)
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SRC, no MHA
SRC+MHA
combiner by-pass
SRC with Mast Head Amplifier (MHA)
SRC+MHA
SRC, no MHA
combiner by-pass, no MHA
Effective cell range:Bypass,No MHA
SRC,no MHA
SRC+ MHA
DLUL
DLUL
DL UL
combiner by-passcombiner by-pass + MHADL
UL
Bypass+MHA
Balanced link defines the cell range, not only BTS TX power
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Configuring IDD in the BSC
Main and auxiliary TRXs connected to different antenna
TRX is created/added to IDD configuration during TRX commissioning
Usage of IDD and mode of IDD TRX (main/auxiliary)
4UD is defined in the BSC with the diversityUsed (RDIV) parameter:RDIV=Y (4-way RX diversity is used).
If IDD is used only for boosting the BCCH carrier, the IDD TRX has to bedefined in the BSC as preferred BCCH TRX
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STIRC is an enhancement to Interference Rejection Combining (IRC) that is implemented inNSN Flexi EDGE, EDGE UltraSite, and EDGE MetroSite BTSs
STIRC is compatible with Smart Radio Concept for EDGE (SRC). All antenna configurationsare supported. However, 4-way uplink diversity configurations provide the best performance.
Link level simulations show interference rejection performance of GMSK channel under typicalurban (TU) conditions improving on average 4 - 10 dB gain compared to IRC (for 2-way uplinkdiversity (2UD)) - The actual gain is network and configuration dependent
STIRC can be enabled per sector (BTS object)
Space Time Interference RejectionCombining (STIRC)
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In a multiple-antenna receiver, there is a strong correlation in the interference betweendifferent branches (normal and diversity) and samples for each symbol period. Usually, the
interference correlation is different from the correlation of the desired signal.
IRC is a set of diversity combining, digital signal processing methods that removesinterference by taking these cross correlations into account.
These methods can be considered as whitening the interference (there is no correlation)between the individual branches and samples of each symbol which, if done perfectly, optimizesthe performance of the receiver, in particular the bit (0/1) detection process.
STIRC works best when there is a single dominant interferer and it is best suited for urbanareas
Whitening
Whitening
Interference RejectionCombining (IRC)
Space Time InterferenceCombining STIRC
Whitening,
jointlyestimated
STIRC & IRC
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STIRC feature control
STIRCSTIRC is
disabled
(N) (0)
Defines whether the STIRC feature is used
in the BTS.
Valid only for Nokia UltraSite, Nokia
MetroSite and Nokia Flexi EDGE Site types.
STIRC is disabled
(N) (0), STIRC is
enabled (Y) (1)
stircEnabledBTS
BSC - MML
Name
Default
value
DescriptionRange And StepAbbreviated
Name
MO
Class
Licence based feature: Capacity licence based on number ofSTIRC enabled TRXs in the BSC
STIRC activation on BTS level