Freq. Hoping Rules

Engineering Rules For Frequency Hopping

Reference : PE/IRC/DD/0012Version : 01.03 / ENDate : 20/07/98

Ext. ref. : ....Type : TYPProduct : PRDCat : IStatus : A

Author : S. Le Graët

Documentalist : A.M. Le Berre

Approved by : C. Moreau

Quality manager : J.C. Hamani

Abstract / Comments :

Distribution lists : ND, AE, RF Projects, RF Solution, RF Measurement, System Design,PENG, WGAl, NMO, RSV

This confidential document is the property of NORTEL MATRA CELLULAR and may not be copied or circulated without permissionCe document confidentiel est la propriété de NORTEL MATRA CELLULAR et ne peut être reproduit ou communiqué sans autorisation


Engineering Rules For Frequency Hopping Page I.2

PE/IRC/DD/0012 01.03 / EN 20/07/98

DOCUMENT AMENDMENTS

VERSION DATE COMMENTS AUTHOR

01.01/EN 25/05/98 Creation of document S. Le Graët

01.02/EN 12/06/98 Update after review S. Le Graët

01.03/EN 17/07/98 Modifications S. Le Graët

Reference : PE/IRC/DD/0012Version : 01.03 / ENDate : 20/07/98

ENGINEERING RULES FOR FREQUENCY HOPPING



Engineering Rules For Frequency Hopping Page 2/37

PE/IRC/DD/0012 01.03 / EN 20/07/98

T A B L E O F C O N T E N T S

1. INTRODUCTION................................................................................................................. 3

1.1. OBJECT................................................................................................................... 3

1.2. SCOPE .................................................................................................................... 3

2. RELATED DOCUMENTS ................................................................................................... 4

2.1. APPLICABLE DOCUMENTS................................................................................... 4

2.2. REFERENCE DOCUMENTS................................................................................... 4

3. ABBREVIATIONS & DEFINITIONS.................................................................................... 5

3.1. ABBREVIATIONS.................................................................................................... 5

3.2. DEFINITIONS .......................................................................................................... 5

4. ENGINEERING RULES FOR FREQUENCY HOPPING..................................................... 6

4.1. FREQUENCY HOPPING PRINCIPLES AND BENEFITS........................................ 6

4.1.1. FREQUENCY HOPPING PRINCIPLE ................................................................................................................64.1.2. FREQUENCY HOPPING BENEFITS..................................................................................................................84.1.3. BASEBAND FREQUENCY HOPPING .............................................................................................................114.1.4. SYNTHESISED FREQUENCY HOPPING........................................................................................................144.1.5. NORTEL CHOICE BETWEEN BASEBAND AND SYNTHESISED FREQUENCY HOPPING....................14

4.2. ENGINEERING RULES FOR SYNTHESISED FREQUENCY HOPPING ............. 18

4.2.1. SYNTHESISED FREQUENCY HOPPING PARAMETERS.............................................................................184.2.2. FRACTIONAL FREQUENCY LOAD................................................................................................................204.2.3. MAXIMUM TRX CONFIGURATION...............................................................................................................224.2.4. SFH PARAMETER SETTING FOR 1:1 PATTERN : STRATEGY 1 ...............................................................254.2.5. SFH PARAMETER SETTING FOR 1:3 PATTERN : STRATEGY 2 ...............................................................294.2.6. SUM-UP OF THE DIFFERENT STRATEGY RESULTS .................................................................................35

CONCLUSION.............................................................................................................. 36

Z END OF DOCUMENT Y................................................................................................. 37



PE/IRC/DD/0012 01.03 / EN 20/07/98

1. INTRODUCTION

1.1. OBJECTThis document aims at describing the engineering rules for frequency hopping. It hasbeen written in the context of studies lead by WGAl. The purpose of this document is todescribe and compare baseband frequency hopping and synthesised frequency hopping.It argues Nortel choice for synthesised frequency hopping. Then, according to thenetwork (frequency pattern, interference, environment,...) engineering rules forSynthesised Frequency Hopping are developed. The given engineering rules come fromfield experience and study results.

1.2. SCOPEThis document is compliant with BSS releases until V10.First this document explains frequency hopping principle and benefits. The two (2)types of frequency hopping (baseband and synthesised) are described and compared.Then, engineering rules are given for synthesised frequency hopping.



PE/IRC/DD/0012 01.03 / EN 20/07/98

2. RELATED DOCUMENTS

2.1. APPLICABLE DOCUMENTS[A1] PE/DCL/DD/0007 V10.02/EN Dictionary of parameters[A2] PE/IRC/APP/0037 V02.03/EN BSS parameters user guide

2.2. REFERENCE DOCUMENTS [R1] MOBRO-02-Q-496-98 Synthesised frequency hopping versus

Baseband frequency hopping[R2] GDC/BYT97/KH/DIV/1377Revue du cahier de test Saut de Frequence et

reponses aux questions pour l’IWG FrequencyHopping

[R3] PE/IRC/APP/00068 V10 Engineering Changes[R4] PE/BTS/DD/0421 SFS of the BTS : Measurement Processing[R5] PE/IRC/INF/0014 1/3 Reuse Pattern Engineering Information



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3. ABBREVIATIONS & DEFINITIONS

3.1. ABBREVIATIONSBER Bit Error RateBCCH Broadcast Control ChannelBCF Base Common FunctionBSC Base Station ControllerBTS Base StationDTX Discontinuous transmissionFER Frame Erasure RateFH Frequency HoppingFN Frame NumberFP Frame ProcessorHSN Hopping Sequence NumberMA Mobile AllocationMAI Mobile Allocation IndexMAIO Mobile Allocation Index OffsetMTBF Minimum Time Between FailureOMC Operation and Maintenance Centre for the radio subsystemPWC Power ControlSFH Slow Frequency HoppingTDMA Time Division Multiple AccessTEI Terminal equipment identifier (lapd protocol related)TRX Transmission/Reception subsystem of the BTSTX BTS TransmitterTS Time Slot

3.2. DEFINITIONSMTBF It is a mathematical time expectancy between two successive parts of

equipment or unit failure



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4. ENGINEERING RULES FOR FREQUENCYHOPPING

4.1. FREQUENCY HOPPING PRINCIPLES AND BENEFITS

4.1.1. FREQUENCY HOPPING PRINCIPLE

Basically, Frequency Hopping aim is to spread the spectrum of the signal to minimise the impact ofpotential interferers. Frequency Hopping consists in changing the frequency used by a channel atregular intervals.

In GSM, the transmission frequency remains the same during the transmission of a whole burst. Thus,it is possible to have different frequencies on each burst of a frame. The radio interface of GSM usesthen slow Frequency Hopping.According to the type of coupler used in the BTS, two (2) main types of Frequency Hoppingmechanism can be used :• Synthesised mode for Hybrid couplers with duplexers (hopping time slots can hop on a large

band of frequencies)• Baseband mode using Cavity couplers with duplexers (hopping time slots can hop on a set of

frequencies limited by the number of TRXs) - Only available with S4000 BTS.

Remark:It is also possible to use baseband frequency hopping for hybrid couplers with duplexers, when notusing hopping BCCH (pseudo Baseband Frequency Hopping). However the interest of havinghybrid couplers is lost (possibility to have more frequencies than TRX with hybrid couplers thoughbaseband needs exactly the same number of frequencies than TRX).

Using frequency hopping allows to adapt and maximise the frequency re-use pattern efficiency bymaximising the capacity in term of offered Erlang/Mhz/km². The pattern to use will depend on theavailable frequency band and the traffic requirement.With frequency hopping, instead of having determined frequencies for TCH, TCH TRXs can hop onseveral frequency groups.It is possible (and recommended) to mix different frequency re-use technique, as 4:12 for BCCH and1:3 or 1:1 for TCH. Indeed, a traditional 4:12 reuse pattern is appropriate to a wide spectrum allocationas for BCCH frequency (only one frequency per cell is needed). However, in order to increase thenumber of TRX per cell with a given frequency band, in keeping a low interference level, the onlysolution is to use more restricting reuse pattern, as 1:1 or 1:3.



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TCH 1x3 Re-use Pattern BasisBCCH 4*12 Re-use Pattern Basis TCH 1*1 Re-use Pattern Basis

ExampleHere below is an example of spectrum efficiency, according to the type of frequency re-use pattern.This application is supposing 30 RF carriers in a 6 MHz allocation for trisectorial cells, using a 4:12reuse pattern for BCCH.

30 Carriers - 12 for BCCH

18 for TCH

1 TRX for BCCH non hoppingup to 3 TRX hopping on 6

frequencies


frequencies

Each cell contains7 frequencies (1 + 6)

Fract . 1*3

18 /3 = 6

Each cell contains2 or 3 frequencies

1 TRX for BCCH non hopping 1 or 2 TRX on 1 frequency (no FH)

1 TRX for BCCH non hopping 1 or 2 TRX on 1 frequency (no FH)

4*12 pat tern

30 /12 = 2 or 330 Carriers

- 12 for BCCH18 for TCH


frequencies


frequencies

Each cell contains19 frequencies (1 + 18)

Fract . 1*1

It is obvious with this example that frequency hopping associated to fractional re-use patterns leads toa subsequent gain in terms of offered Erlangs per cell.



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4.1.2. FREQUENCY HOPPING BENEFITS

The two main advantages of Frequency Hopping are interferer and frequency diversity. • The first-one (interferer diversity) is minimising the standard deviation of the C/I distribution law • The second-one (frequency diversity) allows to lower the impact of Rayleigh Fading for slow

mobiles. 4.1.2.1. Benefits for RxLev The Rayleigh fading is a high attenuation of the signal at a given point, due to multiple path. Thearea with fading or fading hole has a very small size which is directly dependant on the frequency ofthe signal.Negative effects of deep Rayleigh fading holes can therefore be counter-balanced. Such a robustbehaviour is especially useful for slow-moving mobiles, which are more likely to experiment low fieldlevels due to fast fading.

When moving, the mobile is obviously less sensitive to these fading holes and looses few informationwhich does not decrease the voice quality. But when not moving or in case of slow moving (e.g.pedestrian) a mobile may stay during a long time under the same Rayleigh fading effect and loose asignificant amount of information.For two different frequencies the Rayleigh fading is not at the same place (the distance between twofading holes is λ/2). So with Frequency Hopping, during the same time the mobile can be consideredlike if it was under different fast fading effects : the frequency hopping simulates the movement for afixed mobile.

- AT HIGH S PE E D OR WIT H S PACE OR DIVE R S IT Y T E CHNIQUE S IT CAN S T AY ONL Y ONE T IME S L OT

-30

-25

-20

-15

-10

-5

0

5

10

1

-A S L OW MS CAN S T AY HE R E DUR ING S E VE R AL S PE E CH FR AME S

dB

T ime ( orF requency )

F requency 1( or T ime 1)

F requency 2( or T ime 2 )



PE/IRC/DD/0012 01.03 / EN 20/07/98

Warning : It is common to find a 6dB for the C/I gain in the GSM documents ; however a significantdeviation can be observed according to the type of mobile, type of interferers, number of frequencies inthe hopping list, physical environment,...

4.1.2.2. Benefits for RxQual

GSM Channel coding and frame interleaving allow to spread interference across the time andfrequency axes, thanks to frequency hopping activation between consecutive time slots.As shown on the next diagram, the RxQual parameter is computed as the average over all the burst ofa SACCH period (104 consecutive bursts in case of TCH channel without DTX) of the bit error rate(BER) before decoding. The frame erasure rate (FER) is evaluated once the 8 bursts which constitute afull speech frame (456 coded bits interleaved in 8 half-bursts of 57 bits each) is decoded.

c(f1) c(f2) c(f3) c(f4) c(f5) c(f6) c(f7) c(f8)

I(f1) I(f2) I(f3) I(f4) I(f5) I(f6) I(f7) I(f8)

c(fi): wanted signal, on carrier iI(fi) : jammer signal, on carrier i

RXQUAL

DecodingDe-interleaving

Speech frameerasure criterion

....

FER

In the case of networks with small spectrum allocation, high instantaneous interference levels can beexpected. However, frequency hopping allows to take advantage of jammer diversity, spreadinginterference across the network, which can therefore result in improvements of high RxQual values butalso in degradation of low RxQual values (tighter RxQual distribution).Therefore, RxQual thresholds should be increased by one (1) or two (2) units when using frequencyhopping, in order to avoid an increase of handover on quality criteria.

4.1.2.3. Benefit on FER

As frequency hopping spreads over space and time the effects of fading and interferers, FER decreaseswhen frequency hopping is enabled.



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After Forward Error Correction :

At Air Interface :

measure in BER

measure in FER

It is remained that each voice frame of 20 ms is spread over 4 frames of 5 ms each. The BER BiteError Rate) is computed on each 5 ms frame and the FER (Frame Erasure Rate) on each 20 ms frameafter the decoding/interleaving. Hence the FER is the best way to estimate the subjective voice quality.For handset mobiles, frequency hopping brings a high improvement. This gain is particularlyinteresting since four (4) frequencies are used for frequency hopping.

Furthermore, the following curve highlights that for a given frequency hopping configuration, the gainis particularly high when the speed of mobiles is low (less than 20 km/h).

FRAME ERASURE RATE versus SFH at -104 dBm

NUMBER OF FREQUENCIES FOR HOPPING

FER(

%)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

1 2 3 4 5 6 7 8

1 km/h

3 km/h

5 km/h

10 km/h

50 km/h

4.1.2.4. Sum-up of the main benefits of frequency hopping • up to 8 frequencies, the higher the number of frequencies in the hopping law, the smaller the

Fading margin taken into account in the link budget (due to Rayleigh fading). • the smaller the mobile speed and the higher the number of frequencies, the higher the benefit of the

frequency hopping. • the higher the number of frequencies in the hopping law, the narrower the Rxqual distribution.

However Rxqual mean remains the same (see figure below). Hence the Frequency Hoppingeliminates the number of bad Rxqual samples but it also reduces the number of good Rxqual ones.



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RXQUAL cdf versus SFH (1km/h, -104 dBm)cdf = cumulative distribution function

BER %

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10

NO FH4 freq8 freq16 freq

• Increase resistance to Rayleigh fading:- re-centred RxQual distribution for slow moving mobiles- better stability of the received signal level (smoothing effect )

Completion of diversity task on uplink and full benefit on downlink- high improvement for areas of weaker signal strength (inside buildings and on street level)

• Resistance to interference- spread of interference over all RF spectrum- spread of interference over time- highly loaded sites benefit from lower load on adjacent sites- more efficient error correction gain from digital processing

4.1.3. BASEBAND FREQUENCY HOPPING

4.1.3.1. Principle

Using baseband frequency hopping, each TX is dedicated to one frequency and is connected to all theFrame Processor (TDMA) via the FH bus. It is used with cavity coupling system. It uses exactly thesame number of frequencies as TRXs.

The filling is done by the FP according to the configuration of the TDMA (all the parameters for thefrequency hopping are static and not per call basis ; so even if there is no call the FP knows if it has totransmit on the BCCH frequency).



PE/IRC/DD/0012 01.03 / EN 20/07/98

Moreover the TX can have a carrier filling functionality which is not useful for the BCCH frequency(Carrier filling is already done by the FP) but which can be used in case of other frequencies carrierfilling with the use of a specific BCF load.

FP1 TX1

FP2

FP3

FP4

TX2

TX3

TX4

BCCH Freq

Filling burst when there is no informationto transmit on the BCCH frequency

For a given cell with the previous configuration (4 TRX), two Mobiles Allocations would be defined :- MA1 is used with the complete set of frequencies available to hop on (including the BCCHfrequency), then four (4) frequencies.- MA0 does not contain the BCCH to be able to hop on three (3) frequencies (MA1-BCCH frequency)with the TS in the TDMA0.

There are two possibilities for baseband frequency hopping configuration:

- hopping on TCH and BCCH

TS 0 1 2 3 4 5 6 7TDMA 0 F1 MA1 MA1 MA1 MA1 MA1 MA1 MA1 MAIO = 0TDMA 1 MA0 MA1 MA1 MA1 MA1 MA1 MA1 MA1 MAIO = 1TDMA 2 MA0 MA1 MA1 MA1 MA1 MA1 MA1 MA1 MAIO = 2TDMA 3 MA0 MA1 MA1 MA1 MA1 MA1 MA1 MA1 MAIO = 3



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- hopping on TCH, no hopping on BCCH

TS 0 1 2 3 4 5 6 7TDMA 0 F1 F1 F1 F1 F1 F1 F1 F1 MAIO = 0TDMA 1 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MAIO = 1TDMA 2 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MAIO = 2TDMA 3 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MA0 MAIO = 3

with : MA : Mobile Allocation (list of hopping frequencies for a TRX)MAIO : Mobile Allocation Index Offset between 0 and (Nb of Freq in MA - 1).F1 : BCCH frequency

Caution : it is not recommended to hop on BCCH frequency when using baseband frequency hopping,because it can lead to some troubles when downlink DTX or downlink power control are enabled.

4.1.3.2. Reconfiguration procedure

With the baseband frequency hopping mechanism, it is possible to reconfigure the frequencies incertain cases. The process is started by BSC in case of equipment failure/recovery within a TRX, for aRadio Cell which supports frequency hopping and uses the Frequency Management GSM function.This function is supported by the TRX and allows the BSC to configure or to reset a frequency on aTX which is identified by the TEI of the corresponding TRX. The loss of one TX implies the loss ofone frequency (which is not the BCCH) and of one TDMA (the one defined with the lowest priority) ifno redundant TRX.

Two symmetric mechanisms are managed by the BSC to handle the automatic frequencyreconfiguration in the case of frequency hopping cavity coupling BTS:

- loss of a frequency: the cell is stopped and restarted with new set of frequencies. This may leadto release the calls.

- recovery of all frequencies: an automatic reconfiguration is triggered by the BSC when all thefrequencies are recovered. This may lead to release the calls.

There will be a reconfiguration if the flag bscHopReconfUse = True (defined at BSC level) and if thereare more frequencies than the threshold btsThresholdHopReconf (defined at BTS level). Otherwise thecell is badly configured.When a end of fault occurs if the flag btsHopReconfRestart = True and if there are more frequenciesthan the threshold (btsThresholdHopReconf), there is a complete cell reconfiguration.



PE/IRC/DD/0012 01.03 / EN 20/07/98

4.1.4. SYNTHESISED FREQUENCY HOPPING

Using synthesised frequency hopping, each TX is associated to one FP (TDMA) and can transmit onall the frequencies. It is used with hybrid coupling systems and can use more frequencies than TRXs.The main issue is to ensure that the frequency BCCH is transmitted all the time (on all the TS of theTDMA) at a constant power even if there is no call to transmit (no voice or data burst). This is done bya specific configuration which consists in dedicating a TRX to the BCCH frequency (so the TDMAcalled BCCH does not hop)

Generally, the number of frequencies is greater than the number of TRX in order to have the smallestFading margin in the link budget.

FP1

FP2

TX1

TX2

FP3 TX3

FH bus

The TDMA configurations in case of synthesised frequency hopping are defined as follows :• F1 is the BCCH frequency.• the other two TDMA of the cell have the same MA. HSN and MAIO can be different (see

Engineering Rules in chapter 4.2).

4.1.5. NORTEL CHOICE BETWEEN BASEBAND AND SYNTHESISEDFREQUENCY HOPPING

In case of cavity (or filter) coupling system, the only way to perform frequency hopping is to usebaseband frequency hopping. The wideband coupling system (duplexer or hybrid-2ways and duplexer)allows the use of both types of frequency hopping ; however, it is more appropriated with synthesisedfrequency hopping.Here below are listed the main comparison points between baseband and synthesised frequencyhopping. It allows to decide the most appropriated frequency hopping mechanism.



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4.1.5.1. Use of downlink DTX and downlink power control

Tests have shown that if DTX downlink and Power Control downlink are activated simultaneouslywhen using baseband frequency hopping, it could lead to quality degradation and eventually to calldrops for some mobile brands.With synthesised frequency hopping, this behaviour has never been encountered whatever the mobilebrand is. So with simultaneous activation of these two features, interference are significantly reduced.Synthesized Frequency Hopping is then the only frequency hopping mechanism possible when usingdownlink DTX and downlink power control.

4.1.5.2. Parameter settings

The parameter setting for the synthesised frequency hopping with a fractional re-use pattern is easilyperformed due to the fact that the set of frequencies is the same for each cell (1*1 pattern) or a groupof cells (for example 1*3 pattern). Implementation of new sites does not imply a new frequencyplanning for the existing sites.On the contrary, two different MA per cell (one including BCCH frequency) are needed when usingbaseband frequency hopping.

4.1.5.3. Capacity and Quality impact in case of TRX loss

In case of baseband frequency hopping, the number of used frequencies is equal to the number ofTRX. As a result, in case of TRX loss, the capacity of the site will be reduced, and the number offrequencies in the hopping sequence is also reduced by one. Therefore, the overall benefit of thefrequency hopping (i.e. voice quality) is reduced.In case of synthesised frequency hopping, the capacity of the site is also reduced, but the overall loadof the fractional pattern is reduced (the number of frequency in the hopping sequence is still the same,but the number of in-service TRX is reduced by one) ; so the overall voice quality is improved.

4.1.5.4. MTBF impact of the coupling system

Cavity combiners, which are mechanical equipment, have smaller MTBF than hybrid couplercombiners which are passive equipment. Therefore, the synthesised solution with wideband couplingsystem shall be more reliable than the baseband solution with cavity coupling system.

4.1.5.5. Coupling loss impact

On one hand, cavity coupling systems have an insertion loss around 4,5 dB ; on the other hand,duplexer and hybrid 2-ways coupling systems have a respective insertion loss of 1,3 dB and 4,8 dB.Therefore, when using duplexers, a lower loss in the uplink budget allows to have a lower downlink



PE/IRC/DD/0012 01.03 / EN 20/07/98

budget (3.2 dB) to balance the path loss. Otherwise, the use of hybrid 2-ways coupling systems doesnot badly impact the link budget, in comparison with cavity coupling systems.

4.1.5.6. Frequency hopping efficiency

For limited frequency spectrum networks, the maximum configuration of BTS is limited to few TRXin case of baseband frequency hopping. This means that every timeslot is hopping on a few frequencies(often less than 4).When using synthesised frequency hopping, every timeslot (except those of the BCCH TRX) ishopping on more frequencies (not limited by the number of TRX).Now, from Nortel experience, to get the full benefit of frequency hopping, a minimum of four (4)different frequencies shall be used. This benefit is increased up to 8 frequencies available within thehopping sequence concerning fading effects. Moreover, beyond 8 frequencies, the additional interfererbenefits are still increasing.

RXLEV cdf versus SFH

FADING MARGIN (dB)

%

1

10

100

-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

NOHOP

2freq

4 freq

8 freq

Simulation for a MS with a 1 km/h speedcdf : cumulative distribution function

Then the use of Synthesised Frequency Hopping is more efficient than the use of baseband frequencyhopping.



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4.1.5.7. TRX addition in a given cell

In case of synthesised frequency hopping, it is not always mandatory to stop a sector when adding aTRX in this sector (it only requires that this additional TRX was previously declared within the OMCdatabase).On the contrary, in case of baseband frequency hopping, this is not possible due to the fact that everytime a TRX is added, the quantities of frequencies used in the cell has to be increased.Then it is more convenient to use Synthesised Frequency Hopping when adding TRX in a cell.

4.1.5.8. Conclusion

Thus, the use of synthesised frequency hopping really outperforms the use of baseband frequencyhopping.It implies less interference than the use of baseband frequency hopping and it is easier to use forparameter setting. Moreover, Synthesised Frequency Hopping is fully compliant with the use ofdownlink DTX and DTX power control.The following chapter is then describing the recommended engineering rules to follow wor synthesisedfrequency hopping.



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4.2. ENGINEERING RULES FOR SYNTHESISED FREQUENCYHOPPING

4.2.1. SYNTHESISED FREQUENCY HOPPING PARAMETERS

The parameters used to set the Frequency Hopping are the following one :HSN : Hopping Sequence Number [0, 63]MAI : Mobile Allocation IndexNf : Number of hopping frequenciesMAIO : Mobile Allocation Index Offset between 0 and Nf - 1. Each hopping TRX has a MAIOFN : Frame Number (GSM time)MA : Mobile Allocation

The hopping sequence generation algorithm uses the hopping sequence number (HSN) parameter todistinguish between the 64 possible pseudo-random sequences, and produces for each frame, a MobileAllocation Index (MAI). This parameter is therefore GSM time and HSN dependent. The number offrequencies in the Mobile Allocation is also used as an input in order to produce a MAI value withinthe range of the frequency allocation.This value (MAI) is increased by the MAIO assigned to each time slot, prior to selecting in the MobileAllocation (MA) the appropriate frequency to be used on this particular time slot.

Example:

FN HSN Nf

MAI

F3

F4

F5

F6

F7

+MAIO

Nf = 8HSN : 10MAI 1 2 7 8 2 4 5 1MAIO : 0MAI F1 F2 F7 F8 F2 F4 F5 F1MAIO : 2MAI F3 F4 F1 F2 F4 F6 F7 F3

F1

F2

F8

MA

The sequence number indicates the frequency used in a TRX with MAIO equal to 0, according to thefrequency order in the Mobile Allocation.In the upper example, the sequence number 1 corresponds to the frequency F1, because it is the firstone in the MA list. The MAIO indicates the offset of the MAI in the MA list. Thus, keeping thesequence number 1 for MAIO 0 (F1 is selected) a MAIO equal to 2 corresponds to the frequency F3

because it is the third-one in the MA list.



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MAI = 1 Î F MAIO=0 = F MAI = F1

Then: F MAIO=2 = F (MAI + MAIO) = F3

As a general rule, the frequency for a TRX using a MAIO equal to i is the following:

F MAIO=i = F (MAI + i)

HSN and 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 = 0 correspond to cyclic frequency hopping.

Thus, on a same site an identical value of HSN for each cell provides the same MAI. A differentMAIO for each TRX ensure the hopping sequence laws are orthogonal.The generation algorithm in GSM has been specified so that two sequences bearing two different HSNwill statistically collide 1/Nfth of the time, where Nf is the number of hopping frequencies.However, perfect orthogonality is ensured by assigning the same HSN but a different MAIO value totwo synchronised TDMAs. In the example above, channels 1, 2 and 3 will never collide.

HSN and MAIO rules :Two HSN and MAIO allocation strategies are possible depending on :• the implemented reuse pattern• the frequency grouping • the number of hopping TRXs per siteOn one hand, to avoid a collision between two sequences, it is better to use the same HSN anddifferent MAIO (sequences are then orthogonal). On the other hand the maximum number of MAIO ina cell is equal to the number of hopping frequencies. So this solution can not be used if the number ofhopping frequencies is too low.

Network HSN plan :Once a strategy for HSN and MAIO plans within a site has been defined, an HSN plan must beelaborated for the network. The MAIO plan will be the same for all sites. But for the HSN plan,usually a minimum distance between two (2) sites using the same HSN is defined. Furthermore, theuse of the same HSN in a cell and in its jammers is also not recommended.



PE/IRC/DD/0012 01.03 / EN 20/07/98

Example (set of frequencies is F1, F2, F3, F4, F5, F6, F7) :

HSN =1MAIO = 0

F1 F2 F6 F7 F2 F4 F5 F1

HSN = 1MAIO = 1

F2 F3 F7 F1 F3 F5 F6 F2

4.2.2. FRACTIONAL FREQUENCY LOAD

The fractional reuse pattern which can be implemented on a network depends on the fractionalfrequency load.

FrequencyLoadNbHopTRXCell

Nhfcell=

With: - NbHopTRXCell : number of hopping TRX in a cell- Nhfcell : number of hopping frequencies in a cell (= number of frequencies in the MA)

For a 1:1 pattern, as all cells within a site have the same MA list, the number of hopping frequencies ina cell is the same than the number of hopping frequencies in the corresponding site.

Nhfsite Nhfcell= in a 1:1 patternWith: - Nhfsite : number of hopping frequencies in a site

For a 1:3 pattern, as each cell within a site has a specific MA list, there are three (3) times morehopping frequencies in a site (trisectorial site) than hopping frequencies in its cells.

Nhfsite Nhfcell= 3* in a 1:3 pattern

Assuming a network with trisectorial sites with an homogeneous distribution of TRX, whatever thepattern is, there are always three (3) times more hopping TRX in a site than hopping TRX in its cells.

NbHopTRXSite NbHopTRXCell= 3*

for trisectorial sites with homogeneous distribution of TRX

With: - NbHopTRXSite : number of hopping TRX in a site

Thus, it is obvious that the defined frequency load is not comparable in a 1:1 pattern and a 1:3pattern. In order to study the capacity (number of TRX per cell) according to the type of



PE/IRC/DD/0012 01.03 / EN 20/07/98

pattern, with a given frequency band and a minimum if interference, a new function must bedefined:

FreqLoadSiteNbHopTRXCell

Nhfsite=

With: - NbHopTRXCell : number of hopping TRX in a cell- Nhfsite : number of hopping frequencies in a site

According to the previous equations for 1:1 and 1:3 patterns, the new function FreqLoadSite can berelated to the usual frequency load:

FrequencyLoad FreqLoadSite= for a 1:1 pattern

FrequencyLoad FreqLoadSite= 3* for a 1:3 pattern

The table below shows the fractional re-use pattern that can be implemented according to themaximum fractional frequency load. The results in this table come from simulations and fieldexperience. Then they have to be understood as maximum values for a good RF quality in the network.They are available only in case of using power control and DTX, both uplink and downlink.Otherwise, the maximum fractional frequency load would be smaller.

Fractional re-use pattern FrequencyLoad max FreqLoadSite max1:1 20 % 20 %1:3 50 % 16 %

The maximum frequency load is the basis of the following study for engineering rules concerning HSNand MAIO. Indeed, as the frequency load is a limitation, the aim of HSN and MAIO plans is to be asclose as possible to this limitation, and to have as less interference as possible (no adjacent frequency).

16% 20%

1/3 fractional re-use pattern

1/1 fractional re-use pattern

FreqLoadSite



PE/IRC/DD/0012 01.03 / EN 20/07/98

4.2.3. MAXIMUM TRX CONFIGURATION

With the previous results, it is possible to determine the maximum site configuration according to thenumber of frequencies and the re-use pattern (considering a 4:12 re-use pattern for the BCCH), andtaking into account the results of maximum frequency load.

Here below some examples show how to find the maximum site configuration from the number ofavailable frequencies, or the contrary, the minimum number of frequencies needed for a given siteconfiguration.

Example 1:What is the minimum number of needed frequencies for a S333 site configuration, considering one (1)no hopping TRX (BCCH) and two (2) hopping TRX (TCH) in a 1:3 pattern for TCH ?As seen before, with a 1:3 pattern: FrequencyLoad = 50 %Then: NbHopTRXCell = FrequencyLoad * Nfhcell = 4There are 3 cells, then: NbHopTRXSite = 12 TCHAs there is a 4:12 reuse pattern for BCCH, 12 frequencies are reserved for BCCH.Finally, at least 24 frequencies are needed for using Synthesised Frequency Hopping in respecting themaximal frequency load authorised.

Example 2:What is the maximum site configuration with 28 available frequencies in the site, considering atrisectorial site, a 1:1 pattern for TCH and a 4:12 pattern for BCCH ?As there is a 4:12 reuse pattern for BCCH, 12 frequencies are reserved for BCCH.Then, 14 frequencies are available for TCH: Nhfsite = 14As seen before, with a 1:1 pattern: Nhfcell = Nhfsite = 14Frequency load for a 1:1 pattern: FrequencyLoad = FreqLoadSite = 20 %Then: NbHopTRXCell � FrequencyLoad * Nfhcell = 2.8There are 3 cells, then: Nb of TRX / Cell = BCCH + NbHopTRXCell = 3Thus, the maximum configuration is: S333



PE/IRC/DD/0012 01.03 / EN 20/07/98

Example 3:What is the maximum site configuration with 28 available frequencies in the site, considering atrisectorial site, a 1:3 pattern for TCH and a 4:12 pattern for BCCH ?Frequency load for a 1:3 pattern: FrequencyLoad = 50 %As there is a 4:12 reuse pattern for BCCH, 12 frequencies are reserved for BCCH.Then, 14 frequencies are available for TCH: Nhfsite = 16As seen before, with a 1:3 pattern: Nhfcell = Nhfsite / 3 = 5.3The number of hopping frequencies in a cell is of course a whole number, and because the frequencyload is 0.5, it is better to have even numbers to optimize the number of TRX in the site.In order to have whole and even numbers: cell1: Nhfcell = 6

cell2: Nhfcell = 6cell3: Nhfcell = 4

Then: NbHopTRXCell = FrequencyLoad * NfhcellThus, for each cell: cell1 & cell2: NbHopTRXCell = 3

cell3: NbHopTRXCell = 2Then, to determine the total number of TRX: Nb of TRX / Cell = BCCH + NbHopTRXCellThus, the maximum configuration is: S443

The following tables show the maximum site configuration according to the number of frequenciesand the re-use pattern (considering a 4:12 re-use pattern for the BCCH), and taking into account theresults of maximum frequency load.

number of frequencies 96 84 72 60 54 48 471:3 fractional re-use pattern S888 S7771:1 fractional re-use pattern S8884 :12 re-use pattern S888 S777 S666 S555 S444

number of frequencies 42 37 36 32 30 27 241:3 fractional re-use pattern S666 S555 S444 S3331:1 fractional re-use pattern S777 S666 S555 S4444 :12 re-use pattern S333 S222

number of frequencies 22 18 17 121:3 fractional re-use pattern S222 S1111:1 fractional re-use pattern S333 S222 S1114 :12 re-use pattern S111



PE/IRC/DD/0012 01.03 / EN 20/07/98

Maximum TRX configuration

0

10

20

30

40

50

60

1:1 fractional re-usepattern

1:3 fractional re-usepattern

4:12 re-use pattern

re-use pattern

freq

uenc

y nu

mbe

r

S888

S777

S666

S555

S444

S333

S222

S111



PE/IRC/DD/0012 01.03 / EN 20/07/98

4.2.4. SFH PARAMETER SETTING FOR 1:1 PATTERN : STRATEGY 1

As defined in chapter 4.1.1., this strategy means the use of the same frequency group of TCH (MobileAllocation) for all cells in the network.The values of maximum frequency load in a cell (function FreqLoadSite, 20 % for 1:1, 16 % for 1:3)indicated in chapter 4.2.2. show that for a given frequency band, this strategy (1:1 pattern) leads to acapacity increase (more TRX per cell).However, this maximum frequency load must be obtained without an increase of interference. Then,the aim of the following study is to show what are the best HSN and MAIO plans to reach themaximum frequency load without increasing the interference.

HSN and MAIO general rules• In case of 1:1 fractional re-use pattern it is obviously forbidden to re-use the same value of HSN

and MAIO on two different cells of a same site. As they are synchronised, it would systematicallylead to frequency collision.

• For a 1:1 re-use pattern, it is forbidden to use different HSN in cells of a same site. It would alwayslead to frequency collision.

• Moreover, if some frequencies inside the group are adjacent (general case), the use of two adjacentMAIO in a same site is also extremely inadvisable because it would lead to interference (minimumfrequency spacing of 400 kHz).

Supposing the following abbreviations, calculations can be made to show the maximum frequencyload associated to different engineering rules, according to the MA content.

NbHopTRXSite : total number of hopping TRX (non-BCCH TRX) in the site.NbHopTRXCell : total number of hopping TRX (non-BCCH TRX) in a cell.Nhfsite : Number of Hopping Frequencies per site (MAIO step 2 leads to twice more frequencies).NbMAIO : Number of MAIO used in the site

4.2.4.1. Strategy 1A: adjacent frequencies

Frequency band for hopping TRX: F1, F1+200, F1+400, F1+600,...

Rule :The use of a unique HSN and different MAIO for each TRX within a site (with a step of 2 forthe MAIO because all frequencies inside the group are adjacent) ensure the orthogonality andthe non-adjacency of the frequencies.

Example: for a S444 with a MAIO step 2, there are 3 hopping TRX per cell, then 9 hopping TRXwithin the site.



PE/IRC/DD/0012 01.03 / EN 20/07/98

NbMAIO = 9

In this example, to avoid any frequency adjacency, the minimum number of hopping frequencies in thesite must be 18, as shown in the tables below.

With 17 frequencies, the adjacency appears when the frequency of the first TRX of the first cell is notthe first frequency of the band (F1).Cell1- TRX1MAIO = 0

F1 F5 = F1 + 800 kHz

Cell3- TRX3MAIO = 16

F17 = F1 + 3200 kHz F4 = F1 + 600 kHz

With one more frequency (18), the adjacency disappearsCell1- TRX1MAIO = 0

F1 F5 = F1 + 800 kHz


F17 = F1 + 3200 kHz F3 = F1 + 400 kHz

Then, in this example: Nb hopping frequencies in the site � 18 = 2*NbMAIO

Remark:In the above example, another solution for the MAIO rule would have been to give MAIO 0, 2, 4 toTRX in the first cell, MAIO 6, 8, 10 to TRX in the second cell and MAIO 12, 14, 16 to TRX in the thirdcell. However, the disadvantage of this solution appears when adding new TRX in a cell. For instance,a new TRX in the first cell would have MAIO 18 assigned, then the logic aspect of the MAIOassignment is lost.

For a trisectorial site with an homogeneous repartition of TRX in the cells, the frequency load due tothe previous constraints on HSN and MAIO is the following :

HSN = 1MAIO 4,10,16

HSN = 1MAIO 2,8,14

HSN = 1MAIO 0,6,12

MAIO max = 16 then Nb hopping frequencies in the site � 17



PE/IRC/DD/0012 01.03 / EN 20/07/98

- even number of frequencies in the group :As there are 3 cells per site: NbHopTRXSite NbHopTRXCell= 3*And MAIO step 2 is used, then: Nhfsite NbMAIO≥ 2 *There are as many MAIO as TRX: NbHopTRXSite NbMAIO=

Then NbHopTRXCellNhfsite

≤6

thus FreqLoadSite≤ 16%

- odd number of frequencies in the group :As there are 3 cells per site: NbHopTRXSite NbHopTRXCell= 3*And MAIO step 2 is used, then: Nhfsite NbMAIO≥ +2 1*There are as many MAIO as TRX: NbHopTRXSite NbMAIO=


≤− 1

6thus FreqLoadSite≤ 16%

4.2.4.2. Strategy 1B: no adjacent frequency

Frequency band for hopping TRX: F1, F1+400, F1+800, F1+1200,... for instance

This strategy is not representative of operator strategy, because it also means that sometimes, there willbe adjacencies between BCCH and TCH frequencies. However, it is interesting to know if the previousresult can be enhanced with this strategy.

Rule :The use of a unique HSN and different MAIO for each TRX within a site (with a step of 1 forthe MAIO because no frequency inside the group are adjacent) ensure the orthogonality and thenon-adjacency of the frequencies.


NbMAIO = 9

For a trisectorial site with an homogeneous repartition of TRX in the cells, the frequency load due tothe previous constraints on HSN and MAIO is the following :

HSN = 1MAIO 2,5,8

HSN = 1MAIO 1,4,7

HSN = 1MAIO 0,3,6

Ex : Nb hopping frequencies in the site � 9



PE/IRC/DD/0012 01.03 / EN 20/07/98

As there are 3 cells per site: NbHopTRXSite NbHopTRXCell= 3*And MAIO step 1 is used, then: Nhfsite NbMAIO≥There are as many MAIO as TRX: NbHopTRXSite NbMAIO=


≤3


As the maximum frequency load for having few interference with 1:1 pattern is 20 %, the previousresult will lead to many interference. The same HSN and MAIO plans can be kept, however thenumber of hopping frequencies per site must be higher.Thus, with this configuration (no adjacent frequency), it is possible to reach the maximumfrequency load (20 %).

Then: NbHopTRXCellNhfsite

≤5

Thus, in a 1:1 pattern, for a trisectorial site with an homogeneous repartition of TRX in thecells, the engineering rules to follow are the following :

NbHopTRXcell/Nhfsite FreqLoadSitemax

Adjacentfrequencies in MA

HSN andMAIO rule

NbHopTRXcellNhfsite

≤6

(even )16 % yes Identical HSN

MAIO step 2

NbHopTRXcellNhfsite

≤+ 1

6(odd)

16 % yes Identical HSNMAIO step 2

NbHopTRXcellNhfsite

≤5

20 % (max) no Identical HSNMAIO step 1

Caution : the only way to have a 20 % frequency load (maximum) with a 1:1 pattern is to use anunique HSN with adjacent MAIO. However, this engineering rule is only applicable if there are noadjacent frequencies in the MA (what is not generally the case). Otherwise it leads to an increase ofinterference and it is not recommended to use MAIO step 1.In the same way, the use of different HSN in each cell leads to an increase of interference whatever theHSN and MAIO rules are.



PE/IRC/DD/0012 01.03 / EN 20/07/98

4.2.5. SFH PARAMETER SETTING FOR 1:3 PATTERN : STRATEGY 2

This strategy is studied here below in the case of a trisectorial site with an homogeneous repartition ofTRX in the cells.

4.2.5.1. Strategy 2A : 3 non-continuous frequency bands

Cell1 : F1, F1+600, F1+1200,...Cell2 : F1+200, F1+800, F1+1400,...Cell3 : F1+400, F1+1000, F1+1600,...

HSN and MAIO general rules• If both HSN and MAIO are the same for each cell of a same site, there will be systematical

frequency adjacencies. Then, this configuration is not recommended.• In order to systematically ensure a non-adjacency, the only way is to use a unique HSN but different

MAIO for consecutive cells within a site.• The MAIO can be adjacent within a cell, because two (2) consecutive frequencies in a cell are not

adjacent (non-continuous frequency bands).• The use of different HSN and MAIO in each cell of a site is not recommended because it would

lead to frequency adjacencies, then to an increase of interference.


MAIO max = 8 then Nb hopping frequencies in each cell � 9

NbMAIOSite = 9

In this example, to avoid any frequency adjacency, the minimum number of hopping frequencies ineach cell must be 10, as shown in the tables below.

With 9 frequencies, the adjacency appears when the frequency of the first TRX of the first cell is notthe first frequency of the band (F1).Cell1- TRX1MAIO = 0

F11 F15 = F11 + 2400 kHz


F39 = F11 + 5200 kHz F34 = F11 + 2200 kHz

HSN = 1MAIO 6,7,8

HSN = 1MAIO 3,4,5

HSN = 1MAIO 0,1,2



PE/IRC/DD/0012 01.03 / EN 20/07/98

With one more frequency (18), the adjacency disappearsCell1- TRX1MAIO = 0

F11 F15 = F11 + 2400 kHz


F39 = F11 + 5200 kHz F33 = F11 + 1600 kHz

Then, in this example: Nb hopping frequencies in each cell � 18

Then, for a trisectorial site with an homogeneous repartition of TRX in the cells, the frequency loaddue to the previous constraints on HSN and MAIO is the following :

The reuse pattern is 1:3, then: NbMAIOSiteNhfsite

+ ≤13

As there are 3 cells per site : NbMAIOSite NbMAIOCell= 3*And MAIO step 1 is used, then: NbMAIOCell NbHopTRXCell=


≤− 1

9thus FreqLoadSite≤ 11%

Where :NbHopTRXSite : the total number of non-BCCH TRX in the site.NbHopTRXCell : the total number of non-BCCH TRX in a cell.Nhfsite : Number of Hopping Frequencies per siteNbMAIOSite : number of MAIO in the siteNbMAIOCell : number of MAIO in the Cell

The maximum value for FreqLoadSite was defined at 16 %, then this strategy is not optimised.Keeping three (3) non continuous frequency bands, a better MAIO plan can be chosen, in order toreach the maximum defined frequency load (FreqLoadSite = 16 %).An indexed frequency Fi in the MA of the first cell is not adjacent with an indexed frequency Fi in theMA of the third cell frequency (spacing of 400 kHz). However, an indexed frequency Fi in the MA ofthe first cell frequency is adjacent with an indexed frequency Fi+1 in the MA of the third cell frequency.Thus, using the same MAIO step 2 rule for both first and third cells will not lead to frequencyadjacencies between these cells.Moreover, using different MAIO with a step 2 rule for the second cell will also ensure a non frequencyadjacency with this cell.

Example: for a S444 with a MAIO step 2 in all cells, same MAIO in first and third cells, there are 3hopping TRX per cell, then 9 hopping TRX within the site.



PE/IRC/DD/0012 01.03 / EN 20/07/98

MAIO max = 5 then Nb hopping frequencies in each cell � 6

NbMAIOSite = 6

Then the following frequency groups can be defined:

Cell1 F1 F1+600 kHz F1+1200 kHz F1+1800 kHz F1+2400 kHz F1+3000 kHzCell2 F1+200 kHz F1+800 kHz F1+1400 kHz F1+2000 kHz F1+2600 kHz F1+3200 kHzCell3 F1+400 kHz F1+1000 kHz F1+1600 kHz F1+2200 kHz F1+2800 kHz F1+3400 kHz

According to the MAI, the following frequencies will be allocated to each TRX.

Then, for : MAI = 0TRX 1 TRX 2 TRX 3

Cell 1 (MAIO : 0, 2, 4) F1 F1 + 1200 kHz F1 + 2400 kHzCell 2 (MAIO : 1, 3, 5) F1 + 800 kHz F1 + 2000 kHz F1 + 3200 kHzCell 3 (MAIO : 0, 2, 4) F1 + 400 kHz F1 + 1600 kHz F1 + 2800 kHz

For MAI = 1TRX 1 TRX 2 TRX 3

Cell 1 (MAIO : 0, 2, 4) F1+ 600 kHz F1 + 1800 kHz F1 + 3000 kHzCell 2 (MAIO : 1, 3, 5) F1 + 1400 kHz F1 + 2600 kHz F1 + 200 kHzCell 3 (MAIO : 0, 2, 4) F1 + 1000 kHz F1 + 2200 kHz F1 + 3400 kHz

Whatever the MAI is, all frequencies are spaced of at least 400 kHz, then there is no frequencyadjacencies.

Then, for a trisectorial site with an homogeneous distribution of TRX in the cells, the frequency loaddue to the previous constraints on HSN and MAIO is the following :

The reuse pattern is 1:3, then: NbMAIOSiteNhfsite

≤3

As there are 3 cells but 2 with same MAIO:NbMAIOSite NbMAIOCell= 2 *And: NbMAIOCell NbHopTRXCell=


≤6


Where :NbHopTRXSite : the total number of non-BCCH TRX in the site.NbHopTRXCell : the total number of non-BCCH TRX in a cell.Nhfsite : Number of Hopping Frequencies per site

HSN = 1MAIO 0,2,4

HSN = 1MAIO 1,3,5

HSN = 1MAIO 0,2,4



PE/IRC/DD/0012 01.03 / EN 20/07/98

NbMAIOSite : number of MAIO in the siteNbMAIOCell : number of MAIO in the Cell

Thus this solution leads to a non adjacency with a 16 % frequency load. As it is the maximumfrequency load determined in the limitation, it is the right solution to choose when using noncontinuous frequency bands.

CautionAn other way to reach the maximum frequency load is to use different HSN and different MAIO foreach cell. This configuration leads to a 16 % frequency load (ideal case) but it also leads to frequencyadjacencies, then to interference increase.

4.2.5.2. Strategy 2B : 3 continuous frequency bands

Example with 4 frequencies per cell :Cell1 : F1, F1+200, F1+400, F1+600Cell2 : F1+800, F1+1000, F1+1200, F1+1400Cell3 : F1+1600, F1+1800, F1+2000, F1+2200

HSN and MAIO general rules• As in strategy 2A, if both HSN and MAIO are unique in a site, there will be systematical frequency

adjacencies. Then, this configuration is not recommended.• Moreover, as in case A, the use of different HSN and MAIO within a site also leads to adjacencies.

Then, this configuration is not recommended.• In order to ensure a systematical non-adjacency, the only way is to use a unique HSN but different

MAIO in each cell of a same site.• The MAIO can not be adjacent within a cell, because two (2) consecutive frequencies in a cell are

adjacent in this case (continuous frequency bands).

Example: for a S444 with a MAIO step 2 per cell, there are 3 hopping TRX per cell, then 9 hoppingTRX within the site.

MAIO max = 4 Nb hopping frequencies in each cell � 5

NbMAIOSite = 3

However, in this example, in order to avoid frequency adjacencies, the number of hopping frequenciesin each cell must be greater than 6.

HSN = 1MAIO 0,2,4

HSN = 1MAIO 0,2,4

HSN = 1MAIO 0,2,4



PE/IRC/DD/0012 01.03 / EN 20/07/98

With 5 frequencies per cell:Cell1- TRX1MAIO = 0

F11

Cell1- TRX3MAIO = 4

F15 = F11 + 1000 kHz

Cell2- TRX1MAIO = 0

F31 = F11 + 1200 kHz

With one more frequency (6), the adjacency disappears:Cell1- TRX1MAIO = 0

F11

Cell1- TRX3MAIO = 4

F15 = F11 + 1000 kHz

Cell3- TRX1MAIO = 0

F31 = F11 + 1400 kHz

Then, in this example: Nb hopping frequencies in each cell � 6

RemarkThe use of different MAIO in each cell would not lead to less interference, because in the proposedsolution, the non-adjacency is already ensured.

Then, for a trisectorial site with an homogeneous repartition of TRX in the cells, the frequency loaddue to the previous constraints on HSN and MAIO is the following :

MAIO step 2 is used: Nhfcell NbMAIOCell= 2 *As the same MAIO plan is used in all cells : NbMAIOSite NbMAIOCell=The reuse pattern is 1:3: Nhfsite Nhfcell= 3*

Then: NbMAIOSiteNhfsite

≤2 3*

As the same MAIO plan is used in all cells : NbMAIOSite NbMAIOCell=And: NbMAIOCell NbHopTRXCell=


≤6


Where :NbHopTRXSite : the total number of non-BCCH TRX in the site.NbHopTRXCell : the total number of non-BCCH TRX in a cell.Nhfsite : Number of Hopping Frequencies per siteNbMAIOSite : number of MAIO in the siteNbMAIOCell : number of MAIO in the Cell



PE/IRC/DD/0012 01.03 / EN 20/07/98

Thus this solution leads to a non adjacency with a 16 % frequency load. As it is the maximumfrequency load determined in the limitation, it is the right solution to choose when usingcontinuous frequency bands.It would be useless to have different HSN and MAIO, because the maximum frequency load limitationis already reached. Then it would only lead to an increase of interference without any frequency loadbenefit.

Then, in a 1:3 pattern, for a trisectorial site with an homogeneous distribution of TRX in thecells, the engineering rules to follow are the following :

TRXcell/Nfcell FreqLoadSite Adjacentfrequencies in MA

HSN and MAIO rule

NbTRXcellNhfsite

≤6

16 % (max) no(3 non continuousfrequency bands)

Identical HSNSame MAIO step 2 intwo cellsOther MAIO step 2 inthe third cell

NbTRXcellNhfsite

≤6

16 % (max) yes(3 continuous

frequency bands)

Identical HSNMAIO step 2 in a cell,same MAIO in all cells



PE/IRC/DD/0012 01.03 / EN 20/07/98

Strategy 2A (no adj freq)

4.2.6. SUM-UP OF THE DIFFERENT STRATEGY RESULTS

16% 20%

Max in 1/3 fractional re-use pattern

Max in 1/1 fractional re-use pattern

Strategy 1A (adj. freq)

FreqLoadSite

11%

Strategy 2B (adj. Freq)

Strategy 1B (no adj. freq)



PE/IRC/DD/0012 01.03 / EN 20/07/98

CONCLUSION

Synthesised frequency hopping is highly recommended by Nortel, in comparison with basebandfrequency hopping. In particular, experiments have shown that the activation of SFH lead to a decreaseof call drops and an increase of successful hand over and TCH allocation.Moreover, the maximum efficiency of Synthesised Frequency Hopping is obtained when using powercontrol and DTX, both uplink and downlink. Otherwise, the maximum fractional frequency loadwould be smaller.

Additionally, the introduction of SFH means an increase of hand over on the quality criteria, howeverthey happen instead of hand over on RxLev or power budget. This increase is particularly importantwhen frequency load is superior than the defined maximum frequency loads. Then, it is advised toadapt the quality thresholds to the fractional reuse pattern. Thus, a value of 6 in a 1:1 pattern and avalue of 5 in a 1:3 pattern is highly recommended, in order to control hand over on quality criteria.

The main benefits are found in the following areas :• Increase of both the capacity and the quality of the network• Easier frequency planning• Easier roll out (specifically in the more complex multiple vendor environment)• Easier frequency parameters settings• Increase of the flexibility for the capacity planning

The recommended strategies for 1:3 reuse pattern systematically leads to a non-adjacency offrequencies, and the maximum possible frequency load (50 %, or 16 % with the defined frequencyload in site). Furthermore, this results are obtained in using either non continuous frequency band orcontinuous frequency band (what is generally the case) in the MA.

For 1:1 pattern, the strategy to follow depends on the frequency bands constraints. In the case ofadjacent frequencies in the MA (general case), the maximum frequency load is not reached withoutinterference (16 % instead of 20 % at a maximum).However, if there is no adjacent frequency in the MA, it is possible to reach the limitation in frequencyload (20 %). But this case is rarely used by operators, because it leads to some frequency adjacenciesbetween TCH and BCCH.

Though both strategies generally lead to the same capacity (TRX number per cell) for a givenfrequency band, the 1:1 pattern is recommended because the frequency plan for TCH group iseasier to do than for the 1:3 pattern. It is particularly the case when adding cells, TRX orfrequencies in a network, because for a 1:1 pattern, the MA (TCH group) will be the same in allcells.Then, the 1:1 reuse pattern with adjacent frequency group for the Mobile Allocation is thestrategy an operator must favour. It leads to a 16 % maximum frequency load.



PE/IRC/DD/0012 01.03 / EN 20/07/98

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