coverage_enhancement

1 © Nokia Siemens Networks

BSSPAR1: Chapter 8 Coverage Enhancement Features


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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


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)


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

Used TCH TCH TCH TCH TCH TCH

TCH TCH TCH TCH TCH TCH E-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 on E-TRXs

• One BCCH, Two TRX solution

• Receiver timing delayed on ETRX

• Transmitter timing same on NTRX and ETRX


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


Cell Selection MS can camp on BCCH (NTRX) independent of the distance to the BTS RACH from MS detected on RACH or E-RACH depending on the distance to the BTS Failure of RACH burst Wrong cell selected Reselection 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 to extended cell minMSDistanceHOThreshold (MIN) 0..63 TA => MIN; handover triggered to normal cell Adjacent Cell Parameter hoTargetArea (HOTA) indicates type of target cell (normal or extended) ; indicates type of transceiver from which the BSC tries to allocate a channel (normal or extended) 0 – Normal cell 1 - Allocate from N-TRX 2 – Allocate from E-TRX 3 – 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 if Long Reach TSL (for Flexi) is NOT in use


• 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 Cell Use of Double BA list


Long Reach Timeslot Flexi BTS (EP2.0)

• Currently BSC allocates external handovers only towards extended area of an extended cell higher HO failures

• Used to determine if the MS is located in normal or extended area (of the targeted 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 LRTCH only • Reception on both LRTCH


Long Reach Timeslot Flexi BTS (EP2.0)

• TA value sent by BTS to MS cannot be greater than 63 BTS must send an adjusted 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


105km Super Extended Cell Introduction

• 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 of ETRX)

• SDCCH defined on S-TRX

• Normal and Super Extended

areas do not overlap

• TA of each area measured

separately from 0…63

E-TRX RX

N-TRX RX

f1 f1 f1 f1 f1 f1 f1 f1

BCCH/ Not TCH

40%

Delayed

receiver

Normal

TCH TCH TCH TCH TCH

TCH TCH TCH TCHSDCCH

i n useSDCCH

TRX

E-TRX

E-RACH TCH

S-TRX RX

80%

Delayed

receiver

TCH TCH TCH TCHSDCCH

S-TRX

E-RACH

f1 f2 f2 f2 f2 f2 f2 f2

f1 f3 f3 f3 f3 f3 f3 f3

TCH

TCH TCH

RACH/


105km Super Extended Cell Handover 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 Level Super Radius Extension (SEXT) Location of inner edge of super extended area from the BTS Range: 0, 36-70 Handover Control MS distance HO threshold super ext cell min (SMIN) Range: 0…63 MS distance HO threshold super ext cell max (SMAX) Range: 0…63

External handovers • Performed thru LRTCH if it is in use • If not in use, HO to super extended area


• 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 implemented separately (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


• Improves the mobile’s receiver performance by modifying the radio channel • BTS downlink performance is boosted up to 3-5 dB • All timeslots are transmitted through 2 transceivers and 2 antennas

• 2nd TRX transmission is delayed and phase turned • Also BCCH carrier is sent through 2 transmitters • Phase hopping is used to change phasing between adjacent bursts (to decrease 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 Concept Delay Diversity (DD) with Phase Hopping


EDGE

Transceiver

Combined

Uplink

signal

EDGE

Transceiver

Baseband

Units Downlink

signal

RX + TX

MHA MHA

DDU

RX div.

RX div.

RX div.+ TX aux

Masthead Amplifier compensates feeder loss and matches front end of the BTS receiver optimizing sensitivity

Very efficient Interference Rejection Combining is processed for received signals giving ultimate gain for diversity reception. IRC minimizes the effect of interfering signals in the BTS receiver.

4-way UL Diversity


• 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 and

removes 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)


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

DL UL

DL UL

DL UL

combiner by-pass combiner by-pass + MHA DL

UL

Bypass +MHA

Balanced link defines the cell range, not only BTS TX power


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 be defined in the BSC as preferred BCCH TRX


• STIRC is an enhancement to Interference Rejection Combining (IRC) that is implemented in NSN Flexi EDGE, EDGE UltraSite, and EDGE MetroSite BTSs

• STIRC is compatible with Smart Radio Concept for EDGE (SRC). All antenna configurations are supported. However, 4-way uplink diversity configurations provide the best performance.

• Link level simulations show interference rejection performance of GMSK channel under typical urban (TU) conditions improving on average 4 - 10 dB gain compared to IRC (for 2-way uplink diversity (2UD)) - The actual gain is network and configuration dependent

• STIRC can be enabled per sector (BTS object)

Space Time Interference Rejection Combining (STIRC)


• In a multiple-antenna receiver, there is a strong correlation in the interference between different 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 removes interference 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, optimizes the 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 urban areas

Whitening

Whitening

Interference Rejection Combining (IRC)

Space Time Interference Combining STIRC

Whitening,

jointly

estimated

STIRC & IRC


STIRC feature control

MO

Class

Abbreviated

Name

Range And Step Description Default

value

BSC - MML

Name

BTS stircEnabled STIRC is disabled

(N) (0), STIRC is

enabled (Y) (1)

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

• Licence based feature: Capacity licence based on number of STIRC enabled TRXs in the BSC

• STIRC activation on BTS level