Frequency Planning ConceptFrequency Planning Concept

Muhammad Muhammad EbadEbad UllahUllahRF Planning RF Planning -- Central Central

Frequency Planning

Why FP is important?

Frequency Planning

• FP is important to minimize interference b/w cells which improves quality of network

• Cellular operators have limited spectrum and it should be utilized efficiently:

Band Total Band Telenor’s Band

P-GSM 900 1 – 124 63 – 86 24ARFCNs 4.8 MHz

DCS-GSM 1800 512 – 886 586 – 629 44 ARFCNs 8.8 MHz

Basic Conceptsp•ARFCN•Telenor’s Band•Sources of interference

•External•Internal (C/I and C/A)

•Cell re-use patternF h i•Frequency hopping

ARFCN

• ARFCN (Absolute Radio Freq Channel Number) represents FDD i.e., frequency pair or ARFCN or Frequency or carrier:

ARFCN

two 0.2 MHz frequencies for UL and DL which are 45 MHz apart

• For example, ARFCN 83 in P-GSM 900 means:

•UL Freq = 890 + (0 2 x 83) = 906 6 MHz•UL Freq = 890 + (0.2 x 83) = 906.6 MHz

•DL Freq = 906.6 + 45 = 951.6 MHz

200 KHz

45 MHzFul=906.6 MHz Fdl=951.6MHz

TELENOR’s Dual BandTELENOR s Dual Band

62 63 64 65 78 79 80 81 82 85 86 87 88

B CCH = 15 ARFCNs TCH = 6 ARFCNs

900 Band

Guard Band b/w BCCH & TCH

GB – TP & Other operator

GB – TP & Other operator

585 586 587 588 627 628 629 6301800 Band

TCH = 42 ARFCNs

GB - TP & Other GB – TP & Otheroperator

GB TP & Other operator

Cell Re-use Patterns

Cell Patterns

• In theory, hexagons are used to represent cell sites • Sites can be planned using omni or sectored antennas

Cell Patterns

Cell Patterns, cluster & re-use distance

Sites can be planned using omni or sectored antennas• Cluster is a set of cells where all the available frequencies are used at least once• Frequencies can be planned according to a well defined re-use pattern like 7/21, 4/12, 3/9 etc• For example, a re-use pattern of 4/12 means that 12 frequencies are used in a cluster with 4

sites or 12 cellssites or 12 cells• Re-use distance is important, as increasing the re-use distance will decrease co-channel

interference in the network

4/12 Reuse

Cell Patterns

Cell patterns:

• In real world, cell patterns are not hexagonal

Cell Patterns

• Cells vary in size depending upon the amount of traffic they expected to carry i.e., small

cells in high traffic areas and large cells in low traffic areas

• Planning tools (Planet, Asset etc) are used which take into account irregular cell patterns

d t ffi di t ib ti t ith f land uneven traffic distribution to come up with a frequency plan

Interference

Sources of InterferenceSources of Interference

Sources of Interference

External Internal

Jammers at Banks, prisons, mosques etc.Illegal/non-licensed users

Same freq at international borders

C/ICo-channel

C/AAdjacent channel

Internal InterferenceInternal Interference

Th f i f h i i ll f h k

Internal interference

• There are two types of interference that arise internally from the network:• Co-channel interference (C/I)• Adjacent-channel interference (C/A)

Interference GSM Specification Vendor Recommendation

C/I > 9 dB > 12 dB(without freq hopping)

> 9 dB(with freq hopping)

C/A > - 9 dB > 3 dB

C/I and C/AC/I and C/A

C/I

C/AC/A

Frequency HoppingBaseband FH

Synthesizer FH

Frequency Hopping

• Call is transmitted through several frequencies in order to• Minimize the impact of Rayleigh or multipath fading (frequency diversity)

Frequency Hopping

Frequency Hopping

p y g p g ( q y y)• Average the interference (interference diversity)

• Benefits of Freq Hopping:• Tighter freq reuse & increase in capacityg q p y• More robust radio environment• Improved speech quality to subscribers

frequency diversity interference diversity

Baseband Frequency HoppingBaseband Frequency Hopping

Baseband Hopping• 1-on-1: One fixed frequency for one TRX• Number of frequencies is equal to number of TRXsq q• Bursts from TRX controller are routed to different TRXs by bus• Filter combiners can be used so 8 TRX can be connected to 1 filter combiner• Filter combiner is a narrow band combiner where freq of each TRX connected must

be tuned by adjusting a filtery j g

Synthesized Frequency Hopping (SFH)Synthesized Frequency Hopping (SFH)

Synthesizer or RF Hopping• One TRX handles all bursts that belong to a connection• Number of hopping frequencies does not depend on number of TRXspp g q p• Hybrid combiners have to be used. It is impractical to use more than 2 hybrid

combiners in cascade• Hybrid combiner is a broadband combiner that does not need tuning

SFH v/s BBH

• Quality : For low traffic cells, SFH provides higher improvements because of independency on # of TRX.p y

• Frequency Planning: SFH limits FP only to BCCH carriers while BBH requires FP for every TRX.

• BCCH Hopping: BBH allows TS1-7 of BCCH carrier to hop & hence requires two MAL and two HSN while SFH does not allow BCCH TRX to hop.p

• Flexibility: SFH provides more flexibility for capacity planning because of its non interdependence b/w all TRX in the cell.

• Capacity: SFH provides more capacity as compared to BBH for the same available spectrum.p

Frequency Planning•BCCH PlanningTCH Pl i•TCH Planning

•FLP (1x3 and 1x1)•MAIO Management & HSN planning•MRP•MRP•Free Planning

•BSIC Planning

Frequency Plan

BCCH TCH

Reuse patterns p7/21, 4/12, 3/9 etc FLP MRP

More than 7 MHzAd-Hoc or Free

PlanningMore than 6 MHz

1x1More than 3 MHz

1x3More than 5 MHz

Complex planningIRREGULAR Cell Patterns

Simple planningREGULAR Cell Patterns

BCCH Planning

• BCCH • never hops

BCCH Planning

BCCH Planning

never hops• its radio is always ON • is transmitted at higher power than TCH

• BCCH is planned according to a well defined re-use pattern like 7/21, 4/12, 3/9 etc• TELENOR is using 5/15 re-use pattern i.e, 15 BCCH frequencies are used & eachTELENOR is using 5/15 re use pattern i.e, 15 BCCH frequencies are used & each

BCCH freq will be used after 15 cells or 5 sites!!

4/12 Reuse

BCCH Planning

7/21

6/187/21 Reuse

5/15

Relax4/12

C/I

3/9

Tight

FP C/I

3/9 Reuse

Reuse PatternPattern

TCH Planning

• On TCH:

TCH Planning

TCH Planning

• Frequency hopping is used• TCH radios are not always ON (they transmit when there is traffic on that radio)• TCH radios transmit at lower power than BCCH

• Following TCH planning techniques are used:• FLP (Fractional Load Planning)• MRP (Multiple Re-use Patterns)• Ad-Hoc or Free Planning

FLP – Fractional Load Planning

FLP – Fractional Load PlanningFLP Fractional Load Planning

Fractional Loading • In Frequency hopping networks, each frequency is used for a fraction of time during a q pp g q g

call .• This fraction increases with the increase of traffic load.

1 x 3 1 x 1

FLP – Fractional Load PlanningFLP Fractional Load Planning

Fractional Load Planning• FLP offers a very simple & competitive method to achieve good quality & high p p g q g

spectrum efficiency• Effective for operators with narrow spectrum available• TRXs can be added to cells without any further FP needed• 1x3 and 1x1

593, 596, 599, 602, 605, 608. 611, 614, 617, 620, 623, 626

81 82 83 84 85 86

594, 597, 600, 603, 606, 609, 612,

81, 82,83,84,85, 86

615, 618, 621, 624, 627

595, 598, 601, 604, 607, 610, 613, 616, 619, 622, 625, 628

81, 82,83,84,85, 8681, 82,83,84,85, 86

1 x 3 1 x 1

1 x 1 FLP1 x 1 FLP

1 x 1 FLP• All hopping frequencies are used on all cells pp g q• 1 MAL for whole network• Works better if network has regular cell plan• 16% Fractional loading recommended i.e., N TRXs need 6N frequencies• All the cells of same site use same HSN if synchronized and different HSN if not

synchronized

MAL 81 82 83 84 85 86

1 x 1 FLP1 x 1 FLP

Single MAL is used all over the network

1 x 3 FLP1 x 3 FLP

1 x 3 FLP• Hopping frequencies are divided into 3 groups or MALs (Mobile Allocation Lists)pp g q g p• 3 MALs for whole network• Works well when network has a regular pattern• 50% Fractional loading recommended i.e., N TRXs need at least 2N frequencies• All the cells of same site should be frame synchronized(same BCF) & use same HSN

MAL 1 593 596 599 602 605 608 611 614 617 620 623 626

MAL 2 594 597 600 603 606 609 612 615 618 621 624 627594 597 600 603 606 609 612 615 618 621 624 627

MAL 3 595 598 601 604 607 610 613 616 619 622 625 628

1 x 3 FLP1 x 3 FLP

Same 3 MALs are repeated all over the network

SFH PARAMETERSSFH PARAMETERS

• HSN: Hopping Sequence Number (0-63)• MAI: Mobile Allocation Index• Nf: Number of Hopping Frequencies in MA List• FN: GSM Time ( TDMA Frame Number)• MA: Mobile Allocation

MAIO Management

MAIO = Mobile Allocation Index Offset

• MAIO indicates the offset of the MAI in the MA List.

MAIO Management

• Freq for TRX using MAIO =i is FMAIO=i =F(MAI+ i)

• MAIO planning in 1x1 & 1x3 FLP networks prevents

•adjacent channel interference within a cell

•co- and adjacent channel interference in co-sited cells

• Pre-requisite: cells within a site should be synchronized

MAL 81 82 83 84 85 86 MAIO 0

MAIO 2

MAIO 4

Manual MAIO PlanningManual MAIO Planning

Staggered TCH

MAL 1 593 596 599 602 605 608 611 614 617 620 623 626

MAL 2 594 597 600 603 606 609 612 615 618 621 624 627

MAIO 0 5 6 11

MAIO2 594 597 600 603 606 609 612 615 618 621 624 627

MAL 3 595 598 601 604 607 610 613 616 619 622 625 628

MAIO 1 4 7 10

MAIO 2 3 8 9

Blocked TCH

MALMAL 1 593 594 595 596 597 598 599 600 601 602 603 604

MAL 2 605 606 607 608 609 610 611 612 613 614 615 616

MAL

MAIO 0 3 6 9

MAIO 0 3 6 9MAL

3 617 618 619 620 621 622 623 624 625 626 627 628 MAIO 0 3 6 9

HSN Planning

HSN = Hopping Sequence Number

• HSN can be from 0 to 63

• HSN = 0 means CYCLIC FREQ HOPPING

•Frequencies are changed in every TDMA frame from lowest ARFCN to highest in MAL

MAL = 25, 26, 27, 28, 29, 30

. . . 29 30 25 26 27 28 29 30 25 26 . . .

HSN Planning

HSN = Hopping Sequence Number

• HSN = 1 to 63 means RANDOM FREQ HOPPING

•Frequencies are changed pseudo-randomly in every TDMA frame

•The pseudo-random sequence is stored in look-up table in MS and BTS

•The algorithm for actual frequency to be used at every instant is specified in GSM

specification 05.02

MAL = 25, 26, 27, 28, 29, 30

. . . 25 30 26 27 29 30 26 30 29 27 . . .

Random vs Cyclic Hopping Sequnces

Random vs Cyclic hopping sequences

Random vs Cyclic Hopping Sequnces

• CYCLIC: In areas where interference is not a problem (low traffic areas)

• RANDOM: In areas where interference is a problem (high traffic areas)

HSN & MAIO Properties

• Sequences bearing different HSN will statistically collide 1/Nf of time (whatever the MAIO)

• Sequences bearing the same HSN but different MAIO are orthogonal (no collision)

HSN & MAIO Properties

q g g ( )

• HSN along with MAIO ensures that 2 TRXs never use same frequency in same TDMA frame

• Neighbor sites should use different HSNs

• Since there are 63 (random) HSNs, one HSN should be repeated after every 63 sites

• Max number of MAIO in a cell is equal to the number of hopping frequencies (0,….,Nf-1)

• HSNs can be planned in Planet

• HSN planning is not important in case of free planning

1x1 FLP• To avoid freq collision, it is forbidden to reuse the same value of MAIO on two different cells

of the same site

• Also use of different HSN in the cells of same site is forbidden.

• If freq inside the Hop set are adjacent , use of two adjacent MAIO in a same cell is

extremely inadvisable because it would lead to interference.

MRP – Multiple Re-use Patterns

MRP – Multiple Reuse PatternsMRP Multiple Reuse Patterns

Multiple Reuse Patterns• Primarily used for baseband frequency hoppingq pp g• Well suited for networks with uneven traffic distribution i.e., different # of TRXs in

each cell• Good for operators with irregular cell plans and relatively large spectrum• MRP allows gradual tightening of reuse as more TRXs are installed

MRP – Multiple Reuse Patterns

Example of MRP for Baseband Freq Hopping• Let us plan a network for MRP with available band (25 – 63)• Divide the band into 4 groups:

MRP Multiple Reuse Patterns

Divide the band into 4 groups:• 1st group of 12 frequencies are re-used on BCCH TRX0• 2nd group of 12 frequencies are re-used on TCH TRX1• 3rd group of 9 frequencies are re-used on TCH TRX2• 4th group of 6 frequencies are re-used on TCH TRX34 group of 6 frequencies are re-used on TCH TRX3

• Re-use group of 2/6 on last TRX3 will be tight, since it will probably not be used on every cell

• Average reuse is (12+12+9+6)/4=9.75 for cell & (12+9+6)/3=9 for TCH frequencies

BCCH - TRX0 25 26 27 28 29 30 31 32 33 34 35 36 4/12 Reuse

TCH - TRX1 37 38 39 40 41 42 43 44 45 46 47 48 4/12 Reuse

TCH - TRX2 49 50 51 52 53 54 55 56 57 3/9 Reuse

TCH - TRX3 58 59 60 61 62 63 2/6 Reuse

Ad-Hoc or Free TCH Planning

Free TCH Planning• Suitable for operators with large spectrum available, irregular cell patterns & uneven traffic

distribution

• This non-uniform method adapts to local variations in the cell plan

• All cells in the network have different MALs

• Trade off b/w capacity and planning complexity

• More effort is required to optimize

• # of frequencies assigned to a cell depends on the amount of traffic it is carrying

• Experience shows that Free planning achieves greater capacity than FLP with irregular cell

patterns and flat terrainpatterns and flat terrain

5 Erlangs5 Erlangs25, 30, 33, 41

12 Erlangs26, 28, 31, 35, 38, 40

20 Erlangs27, 29, 32, 36, 37, 39, 40, 42

BSIC Planning

BSIC Planning

BSIC = Base Station Identity Code

• BSIC is composed of:

NCC (N k C l C d ) ll i 2 diff PLMN ( i ) i f•NCC (Network Color Code) – cells in 2 different PLMNs (or countries) using same freq

•BCC (BTS Color Code) – to identify neighbor cells or BTS

• TELENOR is using 16 BSICs (30 – 37, 40 – 47)

• Same BCCH-BSIC combination should not be used in same neighborhoodSame BCCH BSIC combination should not be used in same neighborhood

• BSICs can be planned on Planet using “Color code planning” module

FP St tFP Strategy•Formulae•BCCH/TCH Band Split

J k•Joker•Effects of:

•Load increase•Irregular Cell pattern•Irregular Cell pattern

•Optimization

FP Strategy

FP Strategy• New Frequency Plan is created

•For a new network or•For a new network or

•To improve C/I of network after expansion (Retune)

• Pre-requisites:

•there are no new sites expectedp

•All database is up to date

•Model is tuned

• Choice of Freq plan:

•Band available

•BCCH/TCH dimensioning/band split

•FLP or MRP or Free planning

•Traffic distribution: average traffic carried by each cell•Traffic distribution: average traffic carried by each cell

•TRX distribution: no of cells with 4 or 3 or 2 TRXs

•Site-to-site distance: how close the sites are to each other

•Common/Single BCCH: how many sites are dual bandg y

•Regular/irregular cell pattern

• Choice of tool: Planet or Asset

• Different BCCH/TCH split strategy for urban and remote areas

BCCH/TCH Dimensioning

BCCH/TCH Band Split• Goal is to achieve a good balance b/w speech quality on non-hopping BCCHs & speech g / p q y pp g p

quality on hopping TCHs

• Staggered BCCH/TCH

•Easier to plan BCCH

•Can manage on less BCCH carriers than blocked, may be 15 instead of 18

•More MAIOs available with maintained interference diversity as adj MAIOs can be used

•Disadv: Adjacencies b/w BCCH & TCH•Disadv: Adjacencies b/w BCCH & TCH

Staggered BCCH/TCH

BCCH 64 66 68 70 72 74 76 77 78 . . . .

TCH 65 67 69 71 73 75

BCCH/TCH Dimensioning

BCCH/TCH Band Split

• Blocked BCCH/TCHBlocked BCCH/TCH

•Higher freq utilization on TCH since there are no adjacent BCCH

•Higher gain from DL power control as DL connections will not suffer from adj BCCH &

can be down regulated much more

BCCH 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79

Blocked BCCH/TCH

BCCH 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79

TCH 81 82 83 84 85 86

JokerJoker

Role of Joker

• Sometimes 1 or 2 frequencies from available band are not assigned to BCCH & TCH bandsSometimes 1 or 2 frequencies from available band are not assigned to BCCH & TCH bands

• These unused clean frequencies are called jokers

• These joker frequencies are used later on to change particular ARFCN to improve C/I

• Joker is also used for model tuning as it requires a clean frequency

• Some operators use guard band b/w BCCH & TCH as joker frequency

BCCH/TCH Dimensioning

Effects of BCCH/TCH adjacencies

• TCH suffer from adj channel interference on DL from BCCH on the top of co-channel hits

• Max Fractional Loading in staggered BCCH/TCH is slightly lower than in blocked

• Trade off b/w performance & freq planning complexity

• Experience shows that high load can be achieved in staggered BCCH/TCH without majorExperience shows that high load can be achieved in staggered BCCH/TCH without major

impact on performance if hopping over 6 frequencies

• However the possibility to load TCH frequencies decrease with adjacencies

• Conclusion: BCCH/TCH adjacencies can be managed but not recommended

more loading

Effects of increasing load• If loading is increased to more than 16% in 1 x 1 plan, without increasing the frequencies on

a cell, adjacencies will arise b/w TCH, j

• Each frequency is only transmitted a fraction of time, so interference will be averaged out

• Conclusion: Loading can be increased beyond 16% but it is not recommended

• Sometimes fixed TCH from BCCH band is assigned

MAL 1 81 82 83 84 85 86 MAIO 0

MAL 2 81 82 83 84 85 86 MAIO 2MAL 2 81 82 83 84 85 86 MAIO 2

MAL 3 81 82 83 84 85 86 MAIO 4

6 freqs on 1 hopping TRXs = 16% FL

MAL 1 81 82 83 84 85 86 MAIO 0 1

MAL 2 81 82 83 84 85 86 MAIO 2 3

MAL 3 81 82 83 84 85 86 MAIO 4 5

6 freqs on 2 hopping TRXs = 33.33% FL

Irregular Cell PatternIrregular Cell Pattern

Effects of irregular cell pattern• With irregular cell patterns, cells with same MAL will have an overlapping area

Q li h i TCH f i i h l i ill ff d ll d• Quality on hopping TCH frequencies in the overlapping area will suffer, and calls may drop

Cells with same MAL are pointing to each other

Regular Cell Pattern Irregular Cell Pattern

Optimization

Optimization

Optimization

• Minimize overlapping between cells i.e., tilting

• Avoid overshooting i.e., redesign needed for sites with height more than 40 m

• Add micro cells, this will decrease load on macro cells, reduce number of collisions and

improve qualityimprove quality

• Keep the grid standard i.e., azimuth = 0, 120, 240 and height = 25 m

• Perform link balance

• Use features like DTX, power control, overlaid/underlaid cells etc

Thank you !