b8 rnp extension frequency hopping ed01 modified

7/29/2019 B8 RNP Extension Frequency Hopping Ed01 Modified

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Mobile Radio Network Planning 1All rights reserved 2004, Alcatel

RNP Extension: B8 Frequency Hopping

Prerequisites: Radio Network Engineering

Fundamentals


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Mobile Radio Network Planning 2

RNP Extension: Frequency Hopping

All rights reserved 2004, Alcatel

Overview

Frequency Hopping Basics

Simulation Results

Frequency Planning of Hopping Networks

Frequency Hopping Parameters


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Abbreviations BCCH Broadcast Channel

TCH Traffic Channel

FH Frequency Hopping

SFH Slow Frequency Hopping BBH Base Band Hopping

RFH Radio Frequency Hopping

MAI Mobile Allocation Index

MAIO Mobile Allocation Index Offset

HSN Hopping Sequence Number

FN Frame Number


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FFH

FH

SFH

BBH RFH

Method of FH notation FFH - Fast Frequency Hopping

SFH - Slow Frequency Hopping

BBH - Base Band Hopping

RFH - Radio Frequency Hopping (Synthesized Hopping)


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FFH Fast Frequency Hopping changes frequencies faster than the

symbol rate

GMSK modulation; payload on air interface =22 kbit/s

1 symbol is modeled with 3 bits Symbol rate on air interface around 7ksymbol/s

For FFH, > 7000 hopps per second


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SFH Slow Frequency Hopping is able to change its frequency every

timeslot

Considering one user, occupying every 8th TDMA timeslot, SFH is

leading to 216.6 hopps per second: One TDMA frame: 4.616 ms -> 1/0.004616s=216.6Hz

The frequency changes every 8 bursts but the system permits afrequency change at every burst; however there is no benefit for

the MS and for the network

Frequency Hopping used in GSM is specified in GSM 05.02 (ETSIrecommendation)


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BCCH and SFH Frequency Hopping can be applied on each traffic channel and each

signaling channel except the logical BCCH channel!

As the BCCH frequency is used for RXLEV measurements of

neighbour cells, this frequency must be on air all the time withoutpower reduction

DTX and PC are not allowed on BCCH frequency

FH is not allowed on the BCCH channel (timeslot 0 on BCCHfrequency)


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Basics of BBH


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Base Band Hopping

FFH

FH

SFH

BBH RFH


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Base Band Hopping (1) The Frame Units create the TDMA

frame structure

The Carrier Units modulate thebase band signal onto the carrierfrequency

In BBH the connections betweenFUs and CUs are changed, not

the carrier frequencies

FU 1

FU 2

FU 3

FU 4

CU 1

CU 2

CU 3

CU 4

Nhop NTRX within one cell


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TRX 1

TRX 2

TRX 3

TRX 4

BCCH

Base Band Hopping (2) As the CUs arent tuning theirtransmit frequency, RTCs (Remotetunable cavity / combiner) can beused

Less pathloss then with WBCs(Wide band combiner)

The communications (users) arehopping over the different CUs

(Carrier Units)

TS 0 of the BCCH TRX is always

transmitting on the BCCHfrequency.

Other timeslots can use otherfrequencies unless the BCCHfrequency is transmitted by anyother TRX at the same time


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Basics of RFH


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Radio Frequency Hopping

FFH

FH

SFH

BBH RFH


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FU 1

FU 2

FU 3

FU 4

CU 1

CU 2

CU 3

CU 4

Radio Frequency Hopping (1) In RFH, each Frame Unit is connected to one Carrier

Unit

Hopping is performed by changing the carrier frequencywithin the carrier unit by using a synthesizer (synthesizerhopping)

A drawback of the synthesizer hopping configuration isthat the BTS cannot be equipped with remote tunablecombiners (RTC), since the tunable filters cannotchange their frequency on a timeslot basis. Therefore awideband combiner (WBC) has to be used for theconnection between transmitter and antenna,

WBC: 5.05 dB insertion loss = 1.6 dB duplexer loss+3.45 combiner loss

RTC: 3.2 dB insertion loss (for max. 4 TRXcombination)

=> 1.85 dB increased downlink path loss for theWBC configuration


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Radio Frequency Hopping (2) As the communication

(user) is not hopping

between the CUs, but the

CU frequency itself is

hopping, there is no limit

for the number of

frequencies used for

hopping except the

software release!

TRX 1

TRX 2

TRX 3

TRX 4

BCCH

Nhop NTRX possible and mostly used

the BCCH will be on air all the time (needed for MS measurements) and

doesnt perform hopping at all


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Hopping modes (1) Cyclic hopping:

HSN = 0All BTS use a unique periodical hopping scheme

Random hopping:

HSN = 1...63

63 possible pseudo random hopping schemes to guaranteeuncorrelated hopping

HSN = Hopping Sequence Number


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Hopping modes (2)

Cyclic hopping

Random hopping

F1

F2

F3F4

F2

F3F4

F1


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Comparison between Non Hopping and Hopping

Networks


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Improved FER: 1.4% 0.6%

Reduced Call Drop Rate: 3.2%

2.4% Reduced Call Establishment Failure: 6.5%

5.5%

Increased HO rate: 10%...15%

Increased HO rate based on quality: 20%

Can be reduced by adjusting HO quality thresholds

Results from Field Trial in Jakarta

(Implementing BBH)

BUT


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Results from Field Trial in South Africa

(Implementing RFH) Improved CSSR from

Improved CDR from

Increased HO Rate due toquality from

During Optimization of HOsdue to quality, the HO rate due

to quality decrease again from

93.64% to 98.51%

1.72% to 1.32%

6% to 25%

25% to 7%

BUT

Implemented was 1x3 reuse with 37.5% RF load

Capacity increase in Bloemfontain was about 100%!!!


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21 cells, 19 with 2 TRX-es and 2 with one TRX, 18 frequencies available fortraffic carriers

Dropped call reduction

Increase of the received mean level

Possibility of using tighter schemes (like 1/3) providing higher capacity

compared with non-hopping network No degradation of audio quality

Conclusions useful for radio planning:

The number of hopping frequencies must be 4 of larger.

Hopping frequencies must be separated as much as possible.

Reuse 1*3 (4 frequencies) 1*3 (6 frequencies) 2*6 (3 frequencies) No Hopping

CDR 2.7 2 2.2 2.5

HO Rate 4000 3900 3700 3000RXQual Increased with 10 % Increased with 20 % Increased with 35 % -

Results from Telefonica Field Trial in Spain

(RFH)


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Results from Field Trial in Egypt - Ismailia (RFH)

10 sites, 21 cells with 2 TRX-es and 9 cells with 3 TRX-es

Effect of the RF Load can be noticed on the quality HO betweenReuse 3 and Reuse 1

Applying DL PC and DTX together can enhance RFH performance

Network

EvolutionNo Hopping 1*3

1*3 with Parameter

Settings

Offset_Hopping_HO

L_RXQual (PC

minimum threshold)

1*1

1*1 with

Parameters

Settings

Offset_Hop

ping_HO

L_RXQual

(PC

minimum

threshold)

1*1 with

DL PC +

DL DTX

+ EFR

DL Quality

HO15000 27000 19000 18000 13000 10000

CDR 1.3 1.2 1 0.8 0.7 0.7

QVoice

Quality

(good)

91.2 % 94 % 94 % 92.6 % 92.7 % 93.2 %


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Frequency Hopping Simulation Results


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Why Frequency Hopping? There are two advantages when using Frequency Hopping

Frequency Diversity

Cyclic and random hopping take benefit

Improves the effectiveness of the GSM error correction algorithm bytaking advantage from interleaving

improve the effect of fading

Interferer Diversity

Only random hopping takes full benefit!

Averages the interference on the hopping carriers, thus highlyinterfered cells (before hopping) gain significantly


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Fading effects


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Fading Caused by delay spread of original signal

Multi path propagation

Time-dependent variations in heterogeneity of environment

Movement of receiver

Short-term fading, fast fading This fading is characterised by phase summation and

cancellation of signal components, which travel on multiplepaths. The variation is in the order of the consideredwavelength.

Their statistical behaviour is described by the Rayleighdistribution (for non-LOS signals) and the Rice distribution (forLOS signals), respectively.

In GSM, it is already considered by the sensitivity values, whichtake the error correction capability into account.


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Fading Mid-term fading, lognormal fading

Mid-term field strength variations caused by objects in the sizeof 10...100m (cars, trees, buildings). These variations are

lognormal distributed.

Long-term fading, slow fading

Long-term variations caused by large objects like largebuildings, forests, hills, earth curvature (> 100m). Like the mid-

term field strength variations, these variations are lognormal

distributed

Fading Effect consists in quality degradation


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Frequency Diversity


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Frequency Diversity (1) Especially Slow

Moving Mobiles

suffer from fading

(fading time can

be long)

Fading means ashort breakdown

of the received

power due to

environmental

conditions-70

-60

-50

-40

-30

-20

-10

0

0.

1

2.

8

5.

4

8.

0

10.

6

13.

2

15.

9

18.

5

21.

1

23.

7

26.

3

29.

0

31.

6

34.

2

36.

8

39.

4

42.

1

44.

7

47.

3

49.

9

Distance [m]

ReceivedPower[dBm]

Lognormal fading

Raleygh fading

fading notches


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Frequency Diversity (2) Hopping over several frequencies, does not reduce the number of

frames being destroyed by fading notches, but reduces the time of

being in a fading notch!

With FH the probability to get into a fading

notch is higher, but the average duration of a

notch is shorter!

Note: The example is based on the assumption of cylic hopping

no fading notchf1

f3

f4

Hopping over

f1,f2,f3,f4 fading notch

f2


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Frequency Diversity (3) - Interleaving and itsbenefit

456 bit 456 bit

TDMA TimeSlot:

3 3 3 3 3 3

...

. . . . . .2

260 bit Data with redundancy for error correction

TIMEBurst (partly) destroyed by

fading, but only 12.5% of 456

bit affected -> high chance for

successful error correction!

Interleaving depth: 8

used frequency: f2 f3 f4 f1 f3 f4f1

Note: Only f1 suffers from

fading in this example

Creating burst structure


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Frequency Diversity (4) - Interleaving and itsbenefit GSM collects 20 ms of speech data before packing it into the 260

bits (456 bits include 260 data bits plus redundancy)

Without hopping, several consecutive bursts (456 bits) would beaffected by fading

This would affect most of the 8 sub-blocks of the 456 bit, leading tolow chance of successful error correction.

With hopping, in the regular case less consecutive blocks areaffected, leading to a good chance of error correction

As RXQUAL does not take interleaving into account, but the BER

before de-interleaving, the FH benefit is not visible in RXQUAL!RXQUAL is even worse, as the BER during good quality time ishigher.


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Interference Diversity


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Interferer Diversity (1)

Interferer Diversity means the averaging of the interferencewithin the frequency group

Each frequency within a frequency group suffers frommore or less interference

The overall interference to one communication is thereforethe average of the single frequency interferences of thefrequency group

Note: The overall interference within the network does notchange, but the standard deviation is reduced


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Interferer Diversity (2) Reducing the network wide C/I standard deviation by FH

Uncorrelated hopping is assumed in the example Random Hopping (HSN 1..63)!

C/IThr

C/IThr

C/I

C/Iwithout SFH with SFH

1 2 3 4 5 6 7

8

1 2 3 4 5 6 7

8

One MS call whichchanges the frequency

several times within the

frequency group (e.g. 8

times)


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Interferer Diversity (3)

If the average C/I in the network is below the required C/I thr, the qualitygets worse when using frequency hopping

C/IThr

C/IThr

C/I

C/Iwithout SFH with SFH

1 2 3 4 5 6 7

8

1 2 3 4 5 6 7

8

Uncorrelated hopping is assumed in the example Random Hopping (HSN 1..63)!

One MS call which

changes the frequency

several times within the

frequency group (e.g. 8

times)


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Interferer Diversity (4) If the standard deviation is quite high some mobiles suffer

from a C/I smaller then the required C/Ithr

When using FH, the C/I values are average values from the

correspondent frequency hopping group Due to this averaging, the C/I standard deviation gets smaller

Now also the bad calls have acceptable conditions


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Summary of frequency and interference

diversity

F1F2

MS1BS1

C1

I2

I1

MS2

F2

P F1

F1,F2,F3

F1

F2

MS1BS1 MS2

F2,F3,F1

P

Interference

Diversi ty

Frequency

Diversi ty

NoHopping

FrequencyHopping

I1

I2


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BBHAdvantages

The timeslots 1 to 7 of the BCCH frequency are allowed toperform frequency hopping

Combination of intelligent frequency planning with thebenefit of frequency hopping

Disadvantages

Frequency hopping performs best with at least 4 hopping

frequencies Cells must have at least 4 TRXs!


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RFHAdvantages

Hopping over more frequencies than installed TRXspossible

NHOP NTRX More benefit from Interferer Diversity

The more frequencies are used, the higher the averaging effect

Disadvantages

No hopping at all on the BCCH TRX!


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Comparison BBH vs. RFH (1) BBH is better than RFH Interference point of view

BBH intelligence integrated in the frequency plan

RFH not (so much) intelligence in the frequency plan (especially in 1*1). Thedrawback is the increased level of interference (cf. A955 simulations)

Strategy for operator for hopping mode selection: prefer BBH instead of RFH

if the available BW is sufficient migrate from BBH to RFH onlywhen the point comes to deploy a new TRX in the BBH network

without any violations


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Comparison of hopping schemes 1 x 3, 1 x 1 and BBH

(Network Design point of view)Reuse

scheme

Benefits Drawbacks

1 x 3 Allow a reuse of thehopping frequencies (for the

microcells).

Ease the transitionbetween hopping area and

non-hopping area.

From interferencereduction p.o.v. N eed a good

design of the network (same

height of the sites, regular

azimuth of the antennas, flat

area , careful tilt tuning) to be

fully efficient.Require hopping on a

number of frequencies

multiple of 3.

1 x 1 From interference

reduction p.o.v., the

requirement to have same

antenna height and a careful

tilt tuning is even higher as for

1x3, whereas there is no

requirement for same azimuth

Good cell pla nningrequired, little coverage

overlap allowed.

No re-utilization of thehopping frequencies

possible (for example for

microcells).

More difficult transitionbetween hopping area and

non-hopping area.

BBH Minimum interference +benefits of interferer and

frequency diversity

Fewer constra ints on thenetwork design: antenna

height+ azimuth, tilt tuning

are not critical factors

anymore

Higher effort for frequencyplanning


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FH field trial Field trial performed in TMN Network in Portugal 2003

The result is a comparison between RFH 1x1, BBH and RFH 1x3

TMN Network configuration

Hardware 19 BSCs with 1400 cells

dual band network

azimuths with regular patterns

Frequency policy GSM 900: 21 freq. for BCCH; 18 freq. TCH with RFH 1x1

DCS 1800: 14 freq. for BCCH; 16 freq. TCH with RFH 1x1


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FH field trial - 1x1 vs 1x3 Motivation for 1x3: network has a regular pattern

QoS Results

Drive tests results

Conclusion: reduction of Quality HO

increase of Level HO no significant modification for other QoS indicators or in QVoice

measurements

Ind ica tor 1 x1 1x3

Better cell HO 90,000

47%

90,000

47%

Quality HO 47,500

24%

44,000

23%

Level HO 5000027%

53,00028%

Bad RxQual - before Bad RxQual - after

16.7% 15.2%


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FH field trial - BBH Motivation:

TCH TRX using 1x1 have RxQual worse than BCCH more frequencies for BCCH

Using the BCCH band reduces the network RFLoad

Call Drops on the BCCH frequencies, due to interference can bereduced by hopping

BBH combines the benefits of

intelligent frequency planning

frequency hopping BBH was applied only for one BSC


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FH field trial - BBH Results QoS results

Drive testsresults

QoS indicators 1x1 Basebandhopping

Obs

SDCCH drop 1.2% 0.8% Significant improvement

RTCH assign fail 0.6% 0.4% Significant improvement,

showing clearly a reduction of

interference

Call-drop 1.1% 0.9% Significant improvement

Handover

success rate

96.2% 96.4% Improvement more visible in

some other BSCsHO causes Better-cell: 43%

Qual HO: 34%

Level HO: 19%

Better-cell: 41%

Qual HO: 32%

Level HO: 22%

Reduction of Qual HO with BBH

Interference

bands

(% in band 900)

54% 61% Improvement is visible with BBH

HO/call 0.64 0.58 Reduction with BBH even more

visible in other BSCs: shows

improvement in Voice Quality

Hopping 1x1 BasebandHopping

VQgood 88.9% 90.8%

VQsufficient 6.7% 6.8%

VQbad 4.4% 2.6%


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FH field trial - BBH Conclusion Clear reduction of network interference: real reduction of

SDDCH drop

RTCH assign fail

Call Drop Reduction of HO/call

QVoice measurements showed improvement

Due to good results, BBH was generalized for entire network (19BSCs):

SDCCH drop: 1.1% -> 0.8% RTCH assign fail: 0.5% -> 0.3%

Call-drop: 1.2% -> 1.0%

HO Success Rate 96.8% -> 97.5%

Call Success Rate: 97.2% -> 97.9%


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Hard Blocking / Soft Blocking


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Hard blocking Hard blocking is determined by the amount of available

channels

This type of blocking occurs in conventional traffic systems,

with a low interference probability The blocking is defined by the blocking probability, e.g.

Pblock=2%

With hard blocking, mobiles will not get access to the network,since all channels are in use (100% traffic load)


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The maximum capacity in a system is defined as the limit, where either the hard

blocking or the soft blocking limit is reached

Soft blocking Soft blocking occurs due to high interference or due to an

unacceptable call drop rate

This type of blocking occurs in a network design with a low reusecluster size, resulting in a high level of interference

The soft blocking limit can be defined by the traffic load, at which thequality in the network becomes unacceptable e.g. when 10% of the

mobiles will suffer from a C/I < C/IThror when the call drop rate

reaches 5%

With increasing traffic load, the capacity will be limited due to softblocking before the hard blocking limit is reached (traffic load


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DTX Discontinuous Transmission PC Power Control

Usage of Power Control and DTX DTX and PC (used only by TCH carriers) reduce interference

Capacity increase possible with remaing QoS figures

In non hopping systems, "bad" communications take much advantage from PC and DTX

"good" communications do not see any improvement

In hopping systems, due to interferer diversity, allcommunications will experience an improvement

Hopping networks with ARCS < 9 are limited by softblocking

Any interference reducing feature is more effective in such asystem

PC and DTX in UL and DL are recommended especially for hoppingnetworks!


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Simulation Results


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FH Performance Simulation - Description The next slides present the results of a hopping performance

investigation done with the Alcatel Radio Network Planning Tool

A9155

Two different approaches are used to determine the softblockinglimit:

Softblocking defined by the traffic load at which 10 % of themobiles suffer from an C/I < C/Ithr

Softblocking defined by the traffic load at which the call drop

rate reaches 5 %


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Considering softblocking based on C/I

? What is the achievable capacity when 10% of all MS sufferfrom a C/I < C/Ithr?

Parameters: BW=36, (hard)blocking=2%, 8 TCH per TRXConsidering DTX, PC, HO, GSM signal processing:

BUT: Call drop rate for the design rises up to 16%!

Configuration

Capacity (Erl/Site) 86.4 71.1 49.8Gain comp. to +74% +42% +0%

C/I Simulation (1)


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ARCS >= 12:Hard blocking

related

ARCS = 9:Hardblo

cking =

Softblocking

ARCS < 9:Soft blocking

related

C: 45Erl

D: 20Erl

A: 49.8Erl

E: 86.4Erl=+74%

16% Call dropB: 71.1Erl=+42%

0

50

100

150

200

250

3 6 9 12

ARCS

Erlangper

3sec

tors

ite

Hard Block.

Soft Block/No Hopping

Soft Block/Hopping

C/I Simulation (2)


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C/I Simulation (3) Nonhopping: The hardblocking limit would be reached at ARCS of 12

(traffic load=100%)

Hopping:

The hardblocking limit still can be reached at a ARCS of 9,meaning that the C/I or the call drop rate is still below thethreshold (traffic load=100%)

If the ARCS is 3 and the traffic load has reached 30% of thetheoretical available hardware capacity, we can see, that thesoftblocking limit with a "too" bad quality can be reached

The increased call drop rate is also based on the fact, thatthe used PC and HO algorithm were very simple

HO is based on distance only, thus with an according qualitybased emergency HO the call drop rate can further bereduced.


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C/I Simulation (4) The simulation does not take into account real

topography,morphology etc.

4*3 and 3*3: capacity can be calculated manually, soft block notreached

49.8 Erl/3 sector site = 16.63 Erl/sector *3 sectors/site

16.63 Erl : from Erl table with 24 (3*8) channels and GOS=2%

1*3 case: capacity can not be calculated manually, soft blocking isreached (hardblocking would lead to 3*84.1=252 Erl per site for 12

(TRX) *8 slots = 96 channels per sector at 2%block)

But due to the soft block (interference), the real capacity is lower

Simplification: No signalling considered


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C/I Simulation (5) Bandwidth=constant in the example

Idea of fractional loading:

Since at a ARCS of 3 the softblocking limit is reached and

only 30% of a HW will be used, it is certainly notcost effective to install all the HW if 70% of the hardware

is unused. Thus the amount of TRX is lower then the

amount of hopping frequencies

Fractional reuse (ARCS, FARCS) only possible with RFH

Summary: Optimum in terms of capacity could be achievedwith an ARCS of 1x3


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Call drop Simulation (1) Considering Softblocking based on Call Drop Rate of 5% or

hardblocking limit is reached

What is the capacity when 5% of all calls will drop?

More suitable definition of softblocking for an operatorcompared to the "C/I" criteria

Same simulation conditions as in previous example

Best results are achieved with the reuse scheme

But: no quality based handover considered in simulation Reduced call drop rate in reality can be expected


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0

10

20

30

4050

60

70

80

Configuration

Erlangp

ersite

Call drop Simulation (2) Best solution when taking

into account the call drop

rate as the softblocking limit

is achieved with ARCS of 9.

The hardblocking limit stillcould be reached: Capacity

increase here: 42%, but

when taking into account

the BCCH with an ARCS of

12, only 30% can beachieved.

Max. Capacity with softblocking based on call drop rate of 5%


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Conclusion on Simulations System simulations show:

"C/I" simulation: best result with the scheme, but withan increased amount of call drops

"Call drop" simulation: reuse scheme is the optimum

Therefore for a first introduction, NTRX=NHop should be used,aiming at an ARCS of 9 for the TCH

30% capacity increase, taking into account a BCCH withARCS of 12 in a typical scenario

Further reduction of the ARCS has to be evaluated in a secondstep with NTRX


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Frequency Planning in Hopping Networks


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Frequency Planning in Hopping Networks

Introduction


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A9155 FH planning strategy

AFP - Automatic Frequency Planning

Several frequencies can be assigned to one carrier

1*1 and 1*3 fractional reuse supported HSN and MAIO allocation done automatically

Absolute calculated interference value is taken into account duringfrequency assignment

Aim: Minimize the cost! The cost includes violation of channel

separation, interference etc.


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Required number of Frequencies

Investigations show, that most benefit is taken from FH whenhopping over at least 4 frequencies!

TU3

TU50

6

7

8

9

10

11

12

13

14

15

1 2 3 4 5 6 7 8 9 10 11 12number of frequencies in hopping sequence

required

C/I(dB)

TU3

TU50

For slow moving mobiles, the benefit of FH is much bigger!

Remark: TU3 = Typical Urban Environment with an average mobile speed of 3 km/hTU50 = Typical Urban Environment with an average mobile speed of 50 km/h


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Fractional Reuse


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Reuse Cluster Size Definition for FH

The classical definition of the Reuse Cluster Size is:

The definition of the Reuse Cluster Size for RFH conditions is:

cellperTRXofamountAverage

Bandwidth

ARCS

cellpersFrequencieofamountAverageBandwidthFARCS

FARCS = Fractional Average Reuse Cluster Size

RNP E i F H i


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Examples for ARCS

ARCS

27 frequencies for TCH TRXs

3 TCH TRXs in average per cell

93

27

/#

cellTRX

BARCS Example: Group planning with 9frequency groups, 3

frequencies each

A1

A3

A2 B1 B2

B3

A1 A2

A3

B2

B3

B1

C2

C3

C1B2B1

B3

A1 A2

A3

RNP E t i F H i


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Examples of FARCS (1)

FARCS


3 hopping groups with 9frequencies each

1 hopping group per cell

3

9

27

/#

cellf

BFARCS

REUSE 1*3

Example:3 frequency groups, 9 frequencies

each

A

C

B A B

C

A B

C

B

C

A

B

C

ABA

C

A B

C

RNP E t i F H i


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Examples of FARCS (2)

FARCS


1 hopping group with 27frequencies

same hopping group on eachcell

127

27

/#

cellf

BFARCS

REUSE 1*1

Example:1 frequency group including all

27 frequencies

A

A

A A A

A

A A

A

A

A

A

A

A

AAA

A

A A

A


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Creating Hopping Groups

RNP E t i F H i


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The GSM Hopping Sequence Generator

External Parameters which can be modified by operator

MA Mobile Allocation

MAI Mobile Allocation Index

MAIO Mobile Allocation Index Offset

FHS Frequency Hopping Sequence

HSN Hopping Sequence Number

Internal Parameters which cannot be modified

T1, T1R, T2, T3 GSM internal timers

FN Frame Number

RNP E t i F H i


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MA

MAI ARFCN

1

2

3

0

4

... ...

2

5

12

7

6

MA - Mobile Allocation

The MA is the look up table that isgiving the relation between the

different MAI numbers and the

corresponding ARFCN.

Range:The look up table has N lines.N is the number of

frequencies used in the

hopping sequence (hopping

group)

RNP E tension Freq enc Hopping


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Selection of hopping channels acc. to MA

Overall speech quality improved in relation with frequencymanagement

During the channel assignment procedure, the BSC will take intoaccount the MA of the channels before allocating the resource

The MA gives the number of frequencies over which the targetchannel hops: the bigger it is, the better the quality can be expected

Hence, the BSC will select preferably the channels with the biggestMA



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MAI - Mobile Allocation Index

The MAI is an index number, which allows to determine the correctline in the MA look up table to find the corresponding ARFCN.

Range: 0 .. N-1

Note: N is the number of frequencies used in the hopping sequence.



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MAIO - Mobile Allocation Index Offset

The MAIO is selectable for each timeslot and each TRX separately

The MAIO is constant on the TRX but it changes between the FU

Due to the fact, that normally for each timeslot within one TRX thesame FHS is used, there is no need to change the MAIO from

timeslot to timeslot. Therefore the MAIO is constant on the TRX.

It is a number that is added to the calculated MAI to avoid intra-sitecollisions due to co or adjacent channel usage.

Range: 0 .. N-1 (max. 63)



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MAIO - BBH Example (1)

TS 0 TS 1 TS 2 TS 3 TS 4 TS 4 TS 5 TS 6 TS 7

FU 1 BCCH TCH TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio freq 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0FU 2 TCH SD/8 TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio 2, 0 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1

FU 3 TCH TCH TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio 2, 1 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2


fhs_id, maio 2, 2 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3



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MA

MAI ARFCN

1

2

3

0

F2

F3

F4

F1E.g. MAI = 1 calculated

MAIO=2

F4 is used

MAIO - Example (2)

E.g. a TRX has the MAIO 2

Frequencies used on this TRX: f1, f2, f3 ,f4

The frequency hopping generator creates the MAI sequence3,0,1,2,1,1,3,0,2,

The hopping sequence will be:

f2, f3, f4,f1,f4,f4,f2,f3,f1,...



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FHS - Frequency Hopping Sequence

The FHS is the set of frequencies (max. 63) to be used in thehopping sequence (frequency hopping group). It is given by the

operator and can be different for each timeslot and each TRX of

each cell

TS 0 TS 1 TS 2 TS 3 TS 4 TS 4 TS 5 TS 6 TS 7FU 1 bc/ sd4

or

bcch

TCH TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio freq 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0

FU 2 TCH SD/ 8 TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio 2, 0 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1


fhs_id, maio 2, 1 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2


fhs_id, maio 2, 2 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3

FHS_ID = 1: all associated frequencies of the BTS are used

FHS_ID = 2: all associated frequencies of the BTS except BCCH frequency are used

(BCCH in TS 0 have to stay on its fixed frequency)


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T1, T1R, T2, T3 - GSM internal timers

Ranges of the timers:

T1: 0 .. 2047

T1R: 0 .. 63 (T1R = T1 modulo 64)

T2: 0 .. 25

T3: 0 .. 50

T2 and T3 are triggered every 8 timeslots (1 TDMA Frame). Whenboth timers switch back to 0, T1 (and T1R) is triggered (that is every

26*51= 1326 TDMA Frames).

In the GSM hopping sequence algorithm the timers T1R, T2 and T3are used. This is leading to a period of 64*26*51-1 = 84863 for the

MAI sequence (hopping sequence)



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Note: Duration of one TS 577 s

FN - Frame Number

It is incremented after every TDMA frame (8 timeslots)

At each FN increment, timers T1, T1R, T2, T3 are impacted,however only T1R, T2, T3 determine the periodicity of the MAI

sequence (hopping sequence)

FN periodicity is 26*51*2048-1 = 2 715 647 TDMA frames

Each frame has a duration of apporx. 4.62 ms

The absolute time from FN 0 to next time FN 0 is accordingly:2 715 647 * (8*577 s) = 3h 28min 53 s



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Hopping Sequence Generation - Diagram

With the before shown parameters,the used absolute frequency can

be determined

MA MAIO HSN T1 T2 T3

Algorithm specified in

GSM Rec. 05.02

ARFCN = MA(MAI)Press for

demonstration

http://c/Documents%20and%20Settings/michealwahba/Local%20Settings/Temp/Local%20Settings/Temp/MHH_Fhseqgen.xls


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The Period of the Hopping Sequence

Timer T1R is only increased, when T2 and T3 switch back to zero atthe same time (every 1326 TDMA frames)!

The total period of the 3 timers T1R, T2, T3 (=duration of FHS):

64*26*51-1 = 84863 TDMA frames 6min 32sec This means, that even if we select the same HSN on two different

(not synchronised I.e no common master clock) sites, they have a

probability of

1/84863 = 1.18*10-6

to use the same frame number.

If they have different frame numbers, the order of the used hoppingfrequencies is uncorrelated



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New understanding of reuse

A reuse ofA X B means, that A sites belong to the same reusecluster and B frequency groups are used on this site.

A

AA

A

AA

A

CB

A

CB

Re-use 1x3 Re-use 1x1



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Co-cell / co-site constraints max RF load

Co-cell constraint 2 channels spacing (ETSI recommends 3, butwith Alcatel EVOLIUM capabilities this value can be set to 2)

Co-site constraint 2 channels spacing

As on the same site the minimum distance between two frequenciesis 2, only every second frequency of a band of consecutive

frequencies can be used

This is leading to a effective usage of the spectrum resources of

maximum 50%

These 50% are the so called maximum RF load on the site



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Max RF Load

The max RF load within a cell can be calculated according thefollowing formula:

This maximum RF load is only achieved, if all TRXs within the cellare fully loaded!

If the TRXs are only fractional loaded, the effective RF load is muchlower!

CellsFrequencieCellTRXloadRF

/#/#max



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%7.16

12

2.max loadRF

%504

2.max loadRF

Max RF Load - Examples

3 sector site, 12 hopping frequencies, 2 hopping TRX per sector

1*1 reuse:

1*3 reuse:

These values (16.7% and 50%) are the theoretical maximumachivable RF loads for the two cases.This is due to the fact, that a consecutive frequency band isassumed and thus due to inter cell constraint of 2 channelsspacing only every second frequency can be used at the sametime



90/122




Real RF Load

The real RF load within a cell can be calculated according thefollowing formula:

Only active timeslots contributes to the RF Load

Average number of active timeslots are given by the traffic capacity,in Erlang

RF Load can be reduced due to the features BCCH TRX Marking(since B5.2) or TRX Prioritized Preference Quality Control (since

B6.2)

8*)/#(

/A#

CellsFrequencie

CelltimeslotsctiveloadRFreal



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3 sector site, 12 hopping frequencies, 2 hopping TRX per sector BCCH TRX Marking is used, therefore BCCH carrier is preffered to

be filled by traffic

3 TRX -> 14.896 Erlang, 2% blocking probability

14.896 timeslots active during the busy hour. The remaining 7.104timeslots guarantee a blocking probability of 2% The average timeslots active on hopping carrier is then

14.896 timeslots - 6 timeslots on first carrier = 8.896 active timeslots 1*1

reuse:

1*1 reuse:

1*3 reuse

%26.9

12*8

896.8loadRFreal

%8.274*8

896.8loadRFreal

Real RF Load - Examples



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te s o eque cy opp g


Real RF-load Proposed max. values:

Reuse

scheme

Service target Real RF load

marginal service quality (theoretical upper limit for

synchronized hopping)50 %1 x 3

service quality comparable to conventional systems30 % 35 %

marginal service quality (theoretical upper limit for

synchronized hopping)

16.6 %1 x 1

service quality comparable to conventional systems 10 %



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q y pp g


Real RF Load with Directed Retry and Fast

Traffic Handover The efficiency of TRX is increased by these features

The same number of timeslots can carry a higher amount of trafficwith the same blocking probability

The interference in the network is increased Therefore the Real RF Load has to be reduced when

these features are used

It is preferred to use these kind of features, even it lead to a reducedRF Load instead of having a high RF Load without these features



94/122


q y pp g


Inter site constraints

The maximum RF load is just a theoretical value, up to which we canavoid violating the co-cell and co-site constraints

The real RF load of a cell (e.g. the traffic in Erlang handled by thehopping carriers) is the real indicator for the interferer potential of the

cell With increasing number of used hopping TS, the probability of

having a collission with a used TS of another cell using the same

hopping frequencies is increasing



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q y pp g


Traffic / Interference relation - Examples Which scenario interferes most to your communication (yellow)?

Scenario 1 Scenario 2 Scenario 3

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

Assumptions: Cells not syncronized, cells using same hopping frequencies, BCCH not included

Interferer

Serv

er


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97/122


q y pp g


Fractional

Reuse 1*2, 1*3,

1*x



98/122


q y pp g


1*3 reuse (1) Before we create new groups, we have

to keep two things in mind:

The RF-load of 50% is not possiblewith consecutive frequencies in the

FHS

50% RF-load is only possible whenall odd or all even frequencies are

on air at the same time sameamount of odd and even

frequencies in each group

1 4 7 10

2 5 8 11

3 6 9 12

Cell A

Cell B

Cell C

Group A: 1,4,7,10

Group B: 2,5,8,11Group C: 3,6,9,12



99/122


1*3 reuse (2)

To avoid violating the GSM constarints, MAIOs have to be definedfor each TRX of the site.

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

MAI = 0

.

.

.

Frequency used by TRX 1

Frequency used by TRX 2

MAIO settings:

Group A: 0,2

Group B: 1,3

Group C: 0,2



100/122


1*3 reuse (3) In a hopping group with 4 frequencies, the MAIs 0 to 3 are possible to

be generated by the hopping sequence generator

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

MAI = 0

MAI = 3MAI = 1

MAI = 2

Assumption:

MAIOs are as defined

before

Group A: 0,2

Group B: 1,3

Group C: 0,2



101/122


1*3 reuse (4)

For each frequency group we have an own MA table

With the group allocation from before, we get:

MAI ARFCN

MA - Group B

1

2

3

2

5

8

11

0

MAI ARFCN

MA - Group A

1

2

3

1

4

7

10

0

MAI ARFCN

MA - Group C

1

2

3

3

6

9

12

0



102/122


1*2 reuse (1) On a two sector site we may have only 2 frequency groups and

therefore only an 1*2 reuse.

In a first step we allocate the frequencies according to the allocationscheme known from the 1*3 reuse

Group A

Group B

2 4 6 8 10 12

1 3 5 7 9 11

Problem: For max. possible RF load, all odd or even must be

on air at the same time. This is not possible in this case, as

all odd frequencies are in group A and all even in group B



103/122


1*2 reuse (2)

To have an equal distribution between odd and even frequencieswithin one frequency group, we change every second frequency

Group A

Group B 2 4 6 8 10 12

1 3 5 7 9 11 Group A

Group B 2 3 6 7 10 11

1 4 5 8 9 12

To be done: MAIO assignment!



104/122


1*2 reuse (3)

To assign MAIOs we assume the FN 0, and circle as manyfrequencies as TRXs are using this group. The circeled frequencies

must fulfil the GSM intra site and intra cell constraint

1 4 5 8

2 3 6 7

Cell A

Cell B

9

10 11

12MAIO TRX 1

MAIO TRX 2

MAIO TRX 3



105/122


1*4 - Exercise

The frequencies 1..24 are available (excluding BCCH freq.)

4 sectors on the site

3 TRXs are hopping in each cell

Cells are syncronized in terms of FN

Create Hopping Groups and assign MAIOs!



106/122


Fractional Reuse

1*1



107/122


Reuse 1*1 - 3 sector site

In the reuse 1 case, we use all available frequencies (1..12) on eachcell of the site

Intra site collisions are only avoided by the MAIO assignment

1 2 3 4

1 2 3 4

Cell A

Cell B

5

5 6

6 7 8 9 10 11 12

7 8 9 10 11 12

1 2 3 4Cell C 5 6 7 8 9 10 11 12

... .... ... ..........

..........................

MAIO of TRX 1

MAIO of TRX 2



108/122


Reuse 1*1 - 2 sector site

On a 2 sector site with 12 frequencies of course 3 TRXs per cell arepossible

61 2 3 4

1 2 3 4

5

5 6

7 8 9 10 11 12

7 8 9 10 11 12

Cell A

Cell B

MAIO of TRX 1

MAIO of TRX 2

MAIO of TRX 3



109/122


Reuse 1*1 - Exercise

The frequencies 1..24 are available

4 sectors on the site

4 TRXs are hopping in each cell

Cells are syncronized in terms of FN

Create Hopping Groups and assign MAIOs!



110/122


Summary: 1*2/1*3/1*4/

1

2

Cell A

Cell B

.......

.......

.......

.......

.......

3

...

Cell C

Cell ...

14

2 3

Cell A

Cell B

.......

.......

.......

.......

.......

1

2

Cell A

Cell B

3

...

Cell C

Cell ...

....... .......

.......

.......

.......

.......

MAIO TRX 1

MAIO TRX 2

MAIO TRX 3

MAIO0 2 3 4 51

Cell A

Cell B

Cell C

Cell D

.......

TRX1

TRX2

TRX3

TRX....

0

1

0

1

2

3

2

3

4

5

4

............ ..... .......

..... .......

.......

.......

.......

Only

necessary, if

the number of

frequency

groups id

evenRotate the

frequencies

through the

cells

Assign

MAIOs

according to

the standard

scheme for

Reuse 1*X



111/122


Summary: 1*1

1 2 3 4

1 2 3 4

Cell A

Cell B

5

5 6

6 7 8 9 10 11 12

7 8 9 10 11 12

1 2 3 4Cell C 5 6 7 8 9 10 11 12

... .... ... ..........

..........................

MAIO of TRX 1

MAIO of TRX 2

Cell A

Cell B

Cell C

.....

.......

TRX1

TRX2

TRX3

TRX....

0

2

4

x+2

x+4

2x+4

....

....

2x+2

.......

..... .......

..... .......

.......

.......

.......

x

....

....

Rotate the

MAIOsthrough the cells

Standard MAIO

assignment for

Reuse 1*1



112/122


FH parameter relation to Hardware - 1*3

FN

(T1R, T2, T3)

(0 84863)

HSN

(0 63)

Frequency Hopping

Sequence A

(e.g. 1,4,7,10)

Sector 1

Frequency Hopping

Sequence B

(e.g. 2,5,8,11)

Sector 2

Frequency Hopping

Sequence C

(e.g. 3,6,9,12)

Sector 3

MAIO (e.g. 2)

Hopping TRX 2

Site Cells TRXs

MAIO (e.g. 0)

Hopping TRX 1

MAIO (e.g. 1)

Hopping TRX 1

MAIO (e.g. 3)

Hopping TRX 2

MAIO (e.g. 2)

Hopping TRX 2

MAIO (e.g. 0)

Hopping TRX 1



113/122


FH parameter relation to Hardware - 1*1

FN

(T1R, T2, T3)

(0 84864)

HSN

(0 63)

Sector 1

Frequency Hopping

Sequence

(e.g. 1,2,3,4,5,

6,7,8,10,11,12)

Sector 2

Sector 3

Site Cells TRXs

MAIO (e.g. 6)

Hopping TRX 2

MAIO (e.g. 0)

Hopping TRX 1

MAIO (e.g. 2)

Hopping TRX 1

MAIO (e.g. 8)

Hopping TRX 2

MAIO (e.g. 10)

Hopping TRX 2

MAIO (e.g. 4)

Hopping TRX 1



114/122


Alcatel BTS - Hopping concepts A910 (M4M) - Evolium Micro BTS

RFH possible for each non BCCH TRX

(max. 4 TRX within one sector)

A9110-E (M5M) Micro Base Station

BBH

RFH for each non BCCH TRX

A9100 - Evolium Macro BTS

BBH

RFH for each non BCCH TRX


115/122



Frequency Hopping Parameters



116/122


BSS and CAE parameters

In the hopping case, RXQUAL does not reflect the real quality in thenetwork as explained before

To overcome this problem, Offsets are applied to RXQUAL

dedendent parameters Offset_Hopping_PC influences

L_RXQUAL_UL_P

L_RXQUAL_DL_P

Offset_Hopping_HO influences

L_RXQUAL_UL_H

L_RXQUAL_DL_H



117/122


Default Parameters for SFH

Find hereafter the parameters which are different within hopping

networks

Offset_Hopping_PC = 1.0

Offset_Hopping_HO = 1.0

HO_INTRACELL_ALLOWED = DISABLED

Note: Resolution of Offset_Hopping_XX is 0.1 since B6.2



118/122


Quality indicator for FH (1)

The RXQUAL calculation takes only the BER before de-interleaving into account

The benefit of FH is not visible in RXQUAL

The higher probability to get into a fading notch (but for ashorter time) is leading to a worse RXQUAL then without

hopping, except the non hopping frequency would be in a

fading notch at this location

FER - Frame Erasure Rate

is counted after de-interleaving takes higher error correction possibilities due to FH into

account



119/122


Quality indicator for FH (2)

Principle of quality indicator calculation within the mobile

DEMOD DECODER

ENCODER

Frame Erasure DecisionVoice

Decoder

RXQUALFrame Erasure Rate

FER

Deinterleave

Error

correct.

Inside the mobile stationAir

-



120/122


Influence of FH on RXQUAL

-110

-106

-102

RXQUAL_DL = f (RXLEV_DL)

0

1

2

3

4

5

6

7

-98

-94

-90

-86

-82

-78

-74

-70

-66

-62

-58

-54

-50

Without Hopping

With Hopping

RXQUA

L

RXLEV [dBm]

Subjective speech quality isgood with RXQUAL=5

approximately:

RXQUAL(FH)

=RXQUAL(no FH) + 1

Offset_Hopping_PC and

Offset_Hopping_HO areintroduced for correcting this

error.

Resolution : 0.1

Min value : 0; Max value : 7



121/122


FH Summary

Main benefits of frequency hopping are: frequency diversity

interference diversity

BBH is recommended since combines an intelligent frequency planand frequency hopping benefits

RFH used when the capacity increase is not possible with BBH

fractional reuse allows cluster reduction

key parameters ARE real traffic load

the level of interference

should be used in well planned and optimized networks

quality can be improved while using it with DTX and PC



122/122

What about Your network?

How to start?

Frequency Band and its subdivision

Special Cells (micro-cells, concentric cells)

Hopping useful?BBH or RFH?

Problems (RF load, interference)/Solutions

Open Discussion