EW RF Basics

8/7/2019 EW RF Basics

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1 Nortel Confidential Information

RF BasicsWireless Network Engineering


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Nortel Confidential Information

- Review of Frequency Planning constraints for GSM- C/Ic, C/Ia values for a frequency planning- Available frequencies / external constraints

- Review of standard frequency plans

- Standard reuse patterns- How to build the pattern?- Uplink/Downlink considerations- Examples of implemented reuse patterns

- Use of features to minimize the interference level- Frequency hopping- VAD/DTX- Power Control- Diversity- Comparative performance of plans using these techniques- Examples of advanced frequency plans using these techniques

- Cell Planning techniques to minimize interference problems- Antenna type, directivity and gain- Antenna Tilt (Electrical and Mechanical)- Site height

Frequency Planning Discussion

Frequency Planning Discussion Frequency Planning Discussion


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GSM recommendations for mobiles and BTS (ETSI GSM 05.08):

Co-channel interference:

C/(I+N) > 9 dB

Note: when I = N (low coverage areas), the sensitivity degradation is 3 dBNote 2: at C/(I+N) = 9 dB under fading conditions, the BER is around 7% (RxQual 6)

Adjacent Channel interference:

First adjacency (200 KHz): C/Ia1 >= - 9 dB

Second adjacency (400 KHz): C/Ia2 >= - 41 dB

Third adjacency (600 KHz): C/Ia3 >= - 49 dB

Rule: In between sites, only co-channel and adjacent channel interference arelikely to happen.1) Frequencies in neighboring cells must never be the same when transmittingcontinuously on the same frequency (see frequency hopping).2) They should as much as possible not be adjacent (200 KHz) to each other.

GSM recommendations for Interference


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Near-Far mobile effect

MS1: f1MS2: f2

Path Loss = 140 dB

Path Loss = 95 dB

MS1 received at 45 dB above MS2=> f1 and f2 need to be at least 600 KHz apart

Rule: On a same site, the frequencies should be chosen 600 KHz or more apart


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Standard Reuse Patterns

Standard reuse patterns are based on an hexagonal representation of the cells.

The frequencies are organized in groups of 3 frequencies for trisectored sites.

The reuse of the pattern is a result of the following equation:i2 + ij + j2 where i and j are integers

These patterns allow to build aplan insuring a constant reusedistance between the frequenciesand therefore allow, up to acertain extent, to minimize theneed for a propagation tool.

A

F

G

E

B

G

F

D

A

FD

G

C

AB

G

C

DE

B

B

G

C

D

E

B

A

F

G

E

E

B

F

DE

G

C

A

F

D

E

C

A

F

D

C

A

Reuse distance

REGULAR REUSE PATTERNSREGULAR REUSE PATTERNS

Dr = 21 RReuse distance Dr = 12 R

regular 4-cluster pattern (1st tier of interferers) regular 7-cluster pattern (1st tier of interferers)

A

B

D

A

B

D

B

AB

C

D

CB

A

B

CD

C

A

B

A

D

C

D

B

G

B

B

D

C

A

C

D

C

D

D

C


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12 BCCH Pattern

1*1 TCH Pattern

> The BCCH plan needs to be developedwhile prioritizing superior C/I against C/A.Maximize co-channel re-use distance asagainst adjacent channel re-use distance .

> The Propagation Models used in theFrequency Planning need to be accurate

> The TCH plan can have either staticfrequency assignment (same reuse ordifferent reuse as BCCH plan) or hoppingfrequency assignment (1x1 or 1x3).

Frequency Plan


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> 1X1 Reuse vs. 1X3 The major criteria for selecting the appropriate hopping

pattern are:

Geographical Considerations Cell Planning Grid (Antenna Azimuths) Propagation Environment (Multipath) For networks with Standard Azimuths a 1X3 hopping Pattern may

be suitable whereas for a non-standard Azimuth Network a 1X1Pattern will be suitable.

1*3 Pattern1*1 Pattern

Frequency Plan


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Use Of Features minimizing the interference level


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The frequency supporting BCCH needs to betransmitted continuously at constant powerfor radio measurement purpose:

Handover preparation Cell selection Cell re-selection

Frequency Hopping constraints


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Why using frequency hopping?

Improve network quality:

=> frequency hopping takes care of Raleigh Fading issues=> frequency hopping allows interferer diversity by spreading theinformation over several frequencies (optimal use of interleaving and errorcoding capabilities of the GSM system)

Increase the spectrum efficiency:- With frequency hopping the reuse of frequencies can be increase and

therefore the overall spectrum efficiency can be increased.


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Effect of Frequency Hopping> Resistance to interference:

spread of interference over all users spread of interference over time highly loaded sites benefit from lower load on adjacent

sites

error correction gain from digital processing

> Resistance to Rayleigh fading: re-center RxQual distribution for slow moving mobiles better stability of the received signal level high improvement for areas of weaker signal strength

inside buildings on street


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Effect of Frequency Hopping> Frequency Hopping effect on FER

FRAME ERASURE RATE ve rsus SFH at -104 dBm

0 . 0 0

2 . 0 0

4 . 0 0

6 . 0 0

8 . 0 0

10 . 0 0

12 . 0 0

14 . 0 0

1 2 3 4 5 6 7 8

NUMBER OF FREQUENCIES FOR HOPPING

F E R ( % )

1 km/ h

3 k m/ h

5 km/ h

10 km/ h

50 km/ h

FOR HANDPORTABLES, FREQUENCY HOPPING BRINGS A HIGH IMPROVEMENTFOR HANDPORTABLES, FREQUENCY HOPPING BRINGS A HIGH IMPROVEMENT


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> Adapt / maximize frequency efficiency depending on the available frequency band and the

traffic requirements

> Take full advantage of the frequency hoppingfeature benefit of / maximize the frequency hopping

improvement for slow moving mobiles benefit of / maximize interferer diversity in difficult

environments depending on the available spectrum

Why using fractional reuse?


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Frequency planning technics

> Usual frequency allocation

==> 4*12fullyacceptablefor BCCH

==> 3*9acceptable inTCH with GSMfeatures

4 sites =12groups

3 sites =9 groups

Adapted to large spectrum or low traffic


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Frequency planning techniques

Fractional reuse frequency plan Legend :BCCH1 : BCCH carrier number 1TCH1 : TCH carriers group number 1

TCH 2x6 Reuse Pattern

TCH4

TCH5TCH6

B

TCH4

TCH5TCH6

D

TCH1

TCH2TCH3

A

TCH1

TCH2TCH3

C

TCH 1x3 Reuse Pattern

TCH1

TCH2TCH3

A

TCH1

TCH2TCH3

C

TCH1

TCH2TCH3

B

TCH1

TCH2TCH3

DBCCH10

BCCH11BCCH12

BCCH2BCCH3

BCCH1

A

BCCH4

BCCH5BCCH6

C

BCCH7

BCCH8BCCH9

D

B

BCCH 4x12 Reuse Pattern TCH 1x1 Reuse Pattern

TCH1

TCH1

A

TCH1

TCH1

C

TCH1

TCH1TCH1

B

TCH1

TCH1TCH1

D

TCH1

TCH1


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Frequency efficiency

5 Mhz solution- an example

24 Carriers24 /12 = 2

Each cell contains2 frequencies

1 TRX for BCCH non hopping1 TRX on 1 frequency (no FH)

1 TRX for BCCH non hopping1 TRX on 1 frequency (no FH)

4*12 pattern

24 Carriers- 12 for BCCH

12 for TCH

1 TRX for BCCH non hopping2 TRX hopping on 4 frequencies


Each cell contains5 frequencies (1 + 4)

Fract 1*3

12 /3 = 4

24 Carriers- 12 for BCCH

12 for TCH



Each cell contains13 frequencies (1 + 12)

Fract 1*1

12 /1 = 12


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Fractional reuse principles

> Full use of advanced GSM features to decrease

the global interference level VAD / DTX Power Control Efficient diversity reception

Fractional frequency distribution of the load using synthesizedfrequency hopping and hybrid combiners

> Full benefit of the GSM digital signal processing Interleaving

Error protection> Full benefit of non uniform traffic distribution

High traffic areas benefit from adjacent lower traffic areas


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VAD / DTX feature

> No transmission on TCH during blanks

Happends usually more than 50% of the time of a normalconversation brings at least 3 dB improvement in the global interference level effect evenly distributed over all the hopping frequencies by use of

frequency hopping


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Power control

> The power Control feature allows to decrease the global interferencelevel over the network by reducing the power of mobiles and the BaseStations when full power is not necessary.

> This feature is better used together with frequency hopping in order tospread evenly the decrease in interference level among all the users.

> This feature is not active on the downlink for the TDMAs transmittedon the BCCH frequency.

> Downlink and Uplink power control on TCH channels Decreases the global interference level Effect depends on the users positioning related to the site Effect evenly distributed over all the hopping frequencies by use of

frequency hopping


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Diversity reception

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-25

-20

-15

-10

-5

0

5

10

1

dB

Time

Antenna 1

Antenna 2

Signal drops at different time on eachantennaSignal drops at different time on eachantenna

The most efficient technique is based on 2 antennas receiving

widely decorrelated signals and interferences => Improve uplink only Signal processing techniques may have different efficiency

-MRC algorithm gives a higher weight to stronger signal with better C/I-High efficiency S8000 interference cancelation algorithm


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Antenna Type, directivity and gain

-40

-30

-20

-10

00

5 10 15 20 2530

3540

4550

5560

657075

8085

9095100

105110

115120

125130

135140

145150

155160165170175180

185190195200205

210215

220225

230235

240245

250255

260265270

275280

285290295

300305

310315

320325

330335340

345 350355

65 degrees antenna90 degrees antenna

Attenuation Angle 65 degrees 90 degrees

0 0.00 dB 0.00 dB15 -0.50 dB -0.40 dB30 -2.60 dB -1.40 dB45 -5.00 dB -3.00 dB60 -8.10 dB -5.60 dB75 -11.80 dB -8.90 dB90 -15.90 dB -11.70 dB

Horizontal attenuation Pattern


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> LINK BALANCE CONCEPTS


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Rx Sensitivity

Common cable Losses

Duplexor

Combiner

Power Amplifier

DLNA

Specific Tx Cable Losses

TxPa Output Power

Combiner losses

Rx Sensitivity

Antenna Gain

Rx Diversity Gain

DLNA conf.Standard Conf.

Base Station

TxPa Output Power

Body Losses

Common cable losses

Other factors for MS

Propagation Parameters:- In car, Indoor penetration factors- Frequency 900, 1800, 1900 MHz- Antenna Height- Environment

Design Parameters:Overlapping margin

Rx Sensitivity

Antenna Gain

MS

Radio Link

RADIO BLOCK DIAGRAM RADIO BLOCK DIAGRAM RADIO BLOCK DIAGRAM


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Factors affecting RXSignal Level

BS Pwr

MS Pwr

Cable losses

Coupling losses

Antenna gain

DLNA

Diversity gain

Rx module

Tx module

Radio Link Considerations Radio Link Considerations Radio Link Considerations

Rx Sensitivity

Common cable Losses

Duplexor

Combiner

Power Amplifier

DLNA

Specific Tx Cable Losses

TxPa Output Power

Combiner losses

Rx Sensitivity

Antenna Gain

Rx Diversity Gain

DLNA conf.Standard Conf.

Base Station

TxPa OutputPower

Rx Sensitivity

Antenna Gain

MS

Radio Link

BTS Componentsaffecting Signal Level

CombinerDuplexor

Rx SplitterPower AmplifierConnectorsTX/RX modules

MS Componentsaffecting Signal Level

Tx modulerRx moduleMS antenna


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S8000 BTS Performance: Link Balanced at 55 dBm EIRP, worst case

Capacity Range from 1 to 8 TRX

S8000 BTS Performance: Link Balanced at 55 dBm EIRP, worst case

Capacity Range from 1 to 8 TRX

Antenna Gain: 18 dBiH-Plane: 60-65E-Plane: 5-6

Guaranteed Ref,Sensitivity: -110dBm

Feeder Losses:


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Frequency hopping:> No signal level gain

> FER gain after error correction

Diversity gain Diversity gain Diversity gain

RAYLEIGH FADING BEHAVIOUR ( CARRIER AND INTERFERENCE)

-30

-25

-20

-15

-10

-5

0

5

10

1

WITHOUT HOPPING A SLOW MS CAN STAY HERESEVERAL SPEECH FRAME

WITH HOPPING IT STAYS ONLY ONE TIME SLOT

Benefits of InterleavingOriginal Sequence

After Interleaving

Deep fades or burst noise destroys some contigous frames

After De-interleaving, Forward Error Correction can recover lost information

Burst Interleaving: No signal level gain FER gain after error correction

Frequency Diversity Time Diversity


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2 branch (same polarization):> 3 dB average signal level gain on the UL.

(Doubling the received power)

> 4-5 dB system level gain (UL) after MaximumRatio Combining (MRC) and Digital SignalProcessing (DSP)

> Smaller variance in link balance plots

Diversity gain Diversity gain Diversity gain

2 branch (cross polarization): Signal level gain dependent on

propagation profile. (Described later) 4-5 dB system level gain* afterMaximum Ratio Combining (MRC)and Digital Signal Processing (DSP)

Greater variance in link balance plots

Spatial Diversity Polarization Diversity


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Spatial diversity> Lack of diversity (disabled or defective

path) will result in a ~ 3 dB loss on thereported RxLev UpLink values. SinceLink Balance is typically a median valueof the set of corresponding RxLev_DL -RxLev_UL, a 3 dB positive shift wouldbe observed indicating weaker UpLink.

Effect of Diversity on Link Balance Effect of Diversity on Link Balance Effect of Diversity on Link Balance

with diversity : xwithout diversity : x + 3 dB

3 dB

RxLev (DL - UL) distribution

RxLev (DL - UL) dB


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Effect of Diversity on Link Balance Effect of Diversity on Link Balance Effect of Diversity on Link Balance

Polarization diversity Link balance plot will be spread out due to

different gains in LOS vs. non-LOS case In LOS case, different MSs antennae can be

more aligned with one of the two cross polarizedantenna elements of the site while being almostorthogonal to the other. Minimal Diversity .

In non-LOS case, due to reflections, the polaritywill be uniformly distributed. Maximum diversitywith multipath propagation.

Case 2 (Extreme)MS with antenna alignedwith the TX element andone of the two RX elements

Case1 (Extreme)MS with antenna almost

orthogonal to the TXelement but aligned withthe other RX element

Obstacle

Reflector

ReflectorCase 3 (Most common)MS with no-LOS andreflected multi-paths to theBase Station Antennae.

RxLev (DL - UL) distribution

RxLev (DL - UL) dB

Case 1:Weak DL,Strong ULz - y* dB

Case 2:Strong UL & DLNo div. gainz + 3 dB

Case 3:Normal DL &Div. gain in ULz dB

Assume z dB isthe normal link balance achievedwhen a standard2 branch spatialdiversity is used.y is the isolationfactor for thepolarization

The final distribution would look morelike the red colored curve when all thecases are statistically combined


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Feeder Losses:

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EW RF Basics