EXPLAIN M07 - 1 Capacity Planning

1 NOKIA 6-90204/ CAPACITY PLANNING/ v 1.0

CapacityCapacityPlanningPlanning


Objectives

9 DESCRIBE TRAFFIC THEORY PRINCIPLES

9 CALCULATE CAPACITY OF DIFFERENT CONFIGURATIONS

9 DESCRIBE SIGNALLING CHANNELS AND CALCULATE SIGNALLING CAPACITY

9 DESCRIBE MAIN FEATURES OF CAPACITY ENHANCEMENT

At the end of this module you will be able to


Content of Capacity Planning

9 TRAFFIC

9 SIGNALLING

9 CAPACITY ENHANCEMENTS


Capacity Planning

9 TRAFFIC9 SIGNALLING9 CAPACITY ENHANCEMENTS


TrafficTraffic Estimations

Estimate number of subscribers over time Long-term predictions Numbers available from marketing people?

Expected traffic load per subscriber Different subscriber segments? Expected behaviour of user segments

Particular phone habits of subscribers e.g. mainly heavy indoor usage Phoning while in traffic jams?

Busy hour conditions Time of day Traffic patterns


TrafficTraffic Patterns

Traffic is not evenly spread across the day (or week)

Dimensioning must be able to cope with peak loads busy hour is typically twice the average hour load

0102030405060708090

100

0 2 4 6 8 10 12 14 16 18 20 22 24 hr

%peak timeoff-peak


Cell loaddt

12 12.2 12.4 12.6 12.8 130

2

4

6

8The cell load

Time / hours

N

u

m

b

e

r

o

f

r

e

s

e

r

v

e

d

t

i

m

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s

l

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.


M potential customers

m available resourcesM >> m

Problem: many customers, limited number of resources

How many resources do we need to satisfy the demand?

Trunking Basics


Trunking Trunking Effect

Trunking increases effective usage of limited resources When we increase the traffic, we may not need that many new lines

Main parameter: accepted blocking probability

Blocking depends on Number of available resources Traffic statistical distribution


time

CH 1CH 2CH 3CH 4

CH ...CH 5

CH n-2CH n-1CH n

Offered newtraffic

Trunking Trunking Effect


ErlangDefinition

Erlang is the unit of traffic Definition

2 formulas Erlang B: for systems that support no queuing Erlang C: for systems that support queuing

Seconds 3600)()( Erlangs timeonconversatiaveragehourpercallsx =

Agner Krarup Erlang (1878-1929)


Erlang Erlang Formulas

Erlang B No queuing: blocked calls are dropped Depends on call lengths & statistical distribution of calls Applicable in mobile systems (e.g. air interface)

Erlang C Queuing Applicable in trunking systems

=

=

M

i

i

k

k

i

kp

0!/

!/

=

+=> 1

0 !1!

)0(Pr C

k

kC

C

kA

CACA

Adelayob


Blocking Probability Blocking ProbabilityChannels 1% 2% 3% 5% Channels 1% 2% 3% 5%

1 0,01 0,02 0,03 0,05 21 12,80 14,00 14,90 16,202 0,15 0,22 0,28 0,38 22 13,70 14,90 15,80 17,103 0,46 0,60 0,72 0,90 23 14,50 15,80 16,70 18,104 0,87 1,09 1,26 1,52 24 15,30 16,60 17,60 19,005 1,36 1,66 1,88 2,22 25 16,10 17,50 18,50 20,006 1,91 2,28 2,54 2,96 26 17,00 18,40 19,40 20,907 2,50 2,95 3,25 3,75 27 17,80 19,30 20,30 21,908 3,13 3,63 3,99 4,54 28 18,60 20,20 21,20 22,909 3,78 4,34 4,75 5,37 29 19,50 21,00 22,10 23,80

10 4,46 5,08 5,53 6,22 30 20,30 21,90 23,10 24,8011 5,16 5,84 6,33 7,08 31 21,20 22,80 24,00 25,8012 5,88 6,61 7,14 7,95 32 22,00 23,70 24,90 26,7013 6,61 7,40 7,97 8,83 33 22,90 24,60 25,80 27,7014 7,35 8,20 8,80 9,73 34 23,80 25,50 26,80 28,7015 8,11 9,01 9,65 10,60 35 24,60 26,40 27,70 29,7016 8,88 9,83 10,50 11,50 36 25,50 27,30 28,60 30,7017 9,65 10,70 11,40 12,50 37 26,40 28,30 29,60 31,6018 10,40 11,50 12,20 13,40 38 27,30 29,20 30,50 32,6019 11,20 12,30 13,10 14,30 39 28,10 30,10 31,50 33,6020 12,00 13,20 14,00 15,20 40 29,00 31,00 32,40 34,60

Erlang Erlang B Table


Cell CapacityTraffic

Traffic capacity of a cell is determined by the number of available traffic timeslots

Trunking effect gives significant gains

TCH

SDCCH

BCCH/CCCH

TRX 1 1 2 3 4 5 6 7BCCH + CCCH 0,5 0,5 0,5 0,5 0,5 0,5 1 1SDCCH 1,5 0,5 1,5 1,5 2,5 2,5 3 3TCH 6 7 14 22 29 37 44 52Erl (2% blocking) 2,27 2,93 8,20 14,89 21,04 28,25 34,68 42,12


Capacity Planning



Logical ChannelsDefinitions

TDMA Frame = 8 Time Slots (0.577 ms each)

Physical Channel = 1 TS of the TDMA Frame on 1 specific carrier

Logical Channel = the "purpose" a physical channel is used for

0 0

TDMA frame 4.615 msBURST PERIOD

0 7 0


0 7

TDMA frame 4.615 ms

26 Multiframe = 120 ms 51 Multiframe 235 msTCH SIGN.0 1 2 24 25 0 1 2 49 50

Hyperframe = 2048 Superframes 3.5 h

Superframe = 26x51 or 51x26 Multiframes= 6.120 sec

Logical ChannelsStructure


Same in GSM900 and GSM1800

FCH

Traffic Channels(TCH)

TCH/9.6FTCH/ 4.8F, HTCH/ 2.4F, H

Dedicated Channels(DCH)

Broadcast Channel(BCH)

Control ChannelsCommon ControlChannel (CCCH)

SCH BCCH(Sys Info)

TCH/FAGCH RACH SDCCH FACCH/ Bm

FACCH/ Lm

TCH/HPCH

Common Channels(CCH)

Logical Channels

SACCH

Logical ChannelsOverview of Logical Channels


Logical ChannelsBroadcast Channels (BCH)

Frequency Correction Channel (FCCH) Unmodulated carrier: like a flag for the MS which enables it to find the frequency

among several TRXs

Synchronisation Channel (SCH) Contains the Base Station Identity Code (BSIC) and a reduced TDMA frame

number

Broadcast Control Channel (BCCH) Contains detailed network and cell specific information as: Frequencies,

Frequency hopping sequence, Channel combination, Paging groups, Information on neighbour cells

Careful frequency plan needed BCCH is not allowed to involve in FH, PC


Logical ChannelsCommon Control Channels (CCCH)

Paging Channel (PCH) It is broadcast by all the BTSs of a Location Area in the case of a mobile

terminated call

Random Access Channel (RACH) It is used by the mobile station in order to initiate a transaction, or as a response

to a PCH

Access Grant Channel (AGCH) Answer to the RACH. Used to assign a mobile a SDCCH


Logical ChannelsDedicated Channels (DCH)

Stand Alone Dedicated Control Channel (SDCCH) System signalling: call set-up, authentication, location update, assignment of

traffic channels and transmission of SMS

Slow Associated Control Channel (SACCH) Transmits measurement reports (UL) Power control, time alignment, short messages (DL)

Fast Associated Control Channel (FACCH) Mainly used for handover signalling It is mapped onto a TCH and replaces 20 ms of speech

Traffic Channels (TCH) Transfer user speech or data, which can be either in the form of Half rate traffic

(6.5 kbit/s) or Full rate traffic (13 kbit/s).


FCCHSCH

SDCCH

PCH

AGCH

BCCH

CCCH

Common Channels

Dedicated Channels

Logical ChannelsDownlink

SACCHFACCH

SDCCH

TCH/F

TCH/H

DCCH

TCH


RACH CCCHCommon Channels

SDCCHSACCH

FACCH

TCH/F

TCH/H

DCCH

TCH

Dedicated Channels

Logical ChannelsUplink


Search for frequency correction burst FCCHSearch for synchronisation sequence SCHRead system informations BCCH

Listen for paging PCHSend access burst RACHWait for signalling channel allocation AGCHCall setup SDCCH

FACCHTraffic channel is assigned TCHConversation TCHCall release FACCH

idle mode

'off' state

dedicatedmode

idle mode

Logical ChannelsUse


Beware of "home-made" bottlenecks

Logical ChannelsMapping - 1 Example

Example of mapping: combined CCCH/SDCCH/4 configuration

Downlink 51 TDMA frames = 235 ms

1. 2. 3. 4.

f s bb b b c fc fc s c c c c cc c c fc fs t t t t tt t t f ft t t t tt t t fs fs s s s ss s ss i

t t tt r r s fs ss s s s r r rr r r rs fr r r r r rr r r r fr r r r tr t t tr ft t t r tr t tt t

Uplink 51 TDMA frames = 235 ms


Mainly realised by Stand-alone Dedicated Control CHannel (SDCCH)

SDCCH is mainly used in 5 cases: Call set-up SMS Location updates Emergency call Call re-establishment

SDCCH channel is key in achieving successful & efficient call set-up

Cell CapacitySignalling


Cell CapacitySDCCH Configurations

TS0 of BCCH TRX always for BCCH + CCCH

TS0 may be configured to carry DCCH

SDCCH channels may be configured in any other TS. Convention (but not law!) is to put it on TS1

2 basic configurations Combined Non-combined

Combined configuration

0 7

ts0=bcch/sdcch/4/pch/agch

Non-combined configuration

0 7

ts0=bcch/pch/agchts1=sdcch/8


Cell CapacitySDCCH Dimensioning

Efficient network design is required to achieve 2 goals An appropriate signalling dimensioning strategy, on a cell per cell basis An appropriate upgrade philosophy

SDDCH channels may be dimensioned in 3 ways On a cell per cell basis On a generic macro layer (not linked to macro/ micro cell layer definitions) On both of the above


1 TRX and 7 Traffic channels means that There can be 7 simultaneous GSM data or speech calls

The total traffic over a hour period (=busy hour) is 2.5 Erl and 1% of call attempts is blocked

Extra capacity of 64% (= (7-2.5)/7) is needed to guarantee 1% blocking

(compare to the situation of 2 TRX => trunking effect!!)

1 TRX and 1 signalling channel means that All signalling channels (BCCH, PCH, AGCH, SDCCH) are sent on the 1st time slot

PCH and SDCCH capacities are the possible bottlenecks!

Capacity Planning Conclusion: Traffic and Signalling Channels


Traffic channel capacity need is calculated / estimated

1. Based on the average traffic per subscriber (= 25 mErl = 90 s) and number of subscribers (250 Subs) and the total traffic need = 250 Subs x 25 mErl/Subs = 6.25Erl

2. Next the required number of traffic channels will be found from the Erlang-B table based on the quality criteria that is usually 1% blocking in GSM.

3. Erlang-B shows that 13 channels give 6.61 Erl @ 1% blocking which exceeds the capacity demand 6.25 Erl.

4. Next it can be noted that 2 TRX equals 14 TCHs and 2 SCHs (= 7.35 Erl = 6.25 + 1.1 extra capacity for the future).

5. 2 TRX will be implemented to the cell!

Capacity Planning Example: to estimate the Service for Subscribers


Capacity Planning



COVERAGE BUILDING

CAPACITY

TIME

ADDING TRX, CELL SPLITTING

NOKIA INTELLIGENT CAPACITY

DUAL BAND

INDOOR

MICROCELLULAR

NOKIA SOFT CAPACITY,

FREQUENCY HOPPING

SUBS

CRIB

ER

GROW

TH

IntroductionCapacity Evolution Scenarios


Measure for network spectral efficiency: Erl/ (MHz * sq.km)

A function of Bandwidth Frequency efficiency of technology Frequency re-use Cell sizes Trunking gains

Frq. hoppingFrq. hopping

DTXDTX

DirectedRetry

DirectedRetry

PowerControl

PowerControl

IUOIUO

Half-rateHalf-rate

Use all available BSS featuresbefore going into microcells

Loaddistribution

Loaddistribution

Trafficreason HO

Trafficreason HO

multiple cellcoverage

multiple cellcoverage

IntroductionNetwork Capacity


Large Cells2 .. 30 km

Small Cells1.. 5 km

Microcells100m.. 1 km

Indoor cells10m .. 100 m

Layered networkMacro cells

IntroductionCell Size Evolution


Macro cell

Micro cell

Micro cellIndoor cell

IntroductionLayered Network


Ways to increase capacity Increase spectrum More bandwidth: up to the authorities, not in operators control Decrease cell Area Microcellular solution: larger number of sites; very expensive Reduce reuse factor Intelligent Underlay Overlay, Frequency Hopping (software capacity): investments in new sites can be delayed

Network Capacity SpectrumChannel Bandwidth Cell Size useFactor C I

Re ( / )

IntroductionFactors


EXPLAIN Software Capacity

IUO FH IFH


IUOBasics

Intelligent Underlay-Overlay implements a 2-layer network by using different RuFs

Conventional RuF is applied to regular layer (coverage) Aggressive RuF is used in super layer (capacity)

IUO is a Nokia feature but works with any mobile

Can be combined with other concepts, e.g. microcells


Super layer (RuF = e.g. 7)

Regular layer (reuse = 12)

Super layer (RuF = e.g. 7)

Regular layer (reuse = 12)Regular layer (RuF = e.g. 12) Regular layer (RuF = e.g. 12)

Service region of super layer is controlled by interference

Calls are handed over from super layer to regular layer when interference becomes excessive

The super reuse frequencies are intended to serve MS close to the BTS

Regular frequency is used when the MS is further away from the BTS

IUOFeature Description


IUOThe Functionality

Call set-up and inter-cell HO always to regular TRX

C/I is constantly calculated while call continues according to IUO algorithm

If C/I is better than good_C/I_threshold, the call is handed over to super layer If C/I decreases below bad_C/I_threshold, the call is handed back to regular layer

The intelligence of IUO is in the dynamic measurement of interference of every MS

Call is always kept under affordable conditions


IUOExample

Measured server, C0 = -75 dBmMeasured interferer, I0 = -90 dBm

Ratio between server and interferer = (C0/I0)linear = (C0I0)dB = 15 dB

Defined conditions for handover:good_C/I_threshold = 14 dB bad_C/I_threshold = 11 dB

the call is handed over to super layer!


IUOResults

Normal network Reuse 12

3 TRXs/cell

Capacity: 14,9 Erl/cell

IUO network Reuse 12 in regular layer

Reuse 6 in super layer

2 regular + 2 super TRXs/cell

Capacity: 19,7 Erl/cell

Available bandwidth 7,2 MHz (=36 channels)

Capacity gain of more than 30 %


IUOIn Practice

Use a separate band for super layer Easier to maintain an overview Manual allocation also possible

Do not use adjacent channel in the same cell If adjacent channel has to be used on the same site

Interference free area reduced Quality not affected (C/I control)

Finding a frequency on super layer is easier than on regular layer Generate interferer lists for co-channel and adjacent channel

Manually time consuming


What is Frequency Hopping?

Changing the carrier frequency in the radio link between mobile station and base station during the connection.


FHBasics

Frequency Hopping is a sequential change of carrier frequency on the radio link between BS and MS

It averages the interference (interference diversity) and Minimizes the impact of fading (frequency diversity)

This quality improvement allows a tighter RuF And a bigger RuF means an enhanced capacity

It is a standardised feature it is supported by all mobilesFrequency

Time

F1

F2

F3


BRTSL 0 1 2 3 4 5 6 7

TRX-1

TRX-2

TRX-3

TRX-4

f1 B = BCCH timeslot. It does not hop.

f2

f3

f4

Time slot 0 of TRX-2,-3,-4 hop over f2,f3,f4.

Time slots 1...7 of all TRXshop over (f1,f2,f3,f4).

The TRXs operate at fixed frequencies: consecutive bursts in each time slot are switched through different TRXs

The 1st time slot of the BCCH TRX is not allowed to hop

The number of frequencies to hop over is determined by the number ofTRXs (biggest limitation!)

FHBase-Band Frequency Hopping


BTRX-1

Non-BCCH TRXs are hopping overthe MA-list (f1,f2,f3,...,fn) attached to the cell.

TRX-2

B = BCCH timeslot. TRX does not hop.

f1,f2,f3,fn

f1,f2,f3,fn

. . . .

All the TRXs except the BCCH TRX change their frequency for every TDMA frame

Thus the BCCH TRX doesnt hop at all

The number of frequencies to hop over is limited to 63, which is the maximum length of the Mobile Allocation (MA) list

FHSynthesised Frequency Hopping

BB-FH is feasible with large configurationsRF-FH is viable with smaller configurations


Issues in Frequency Hopping

Frequency and interference diversity gains? Gain vs. reuse BB or RF FH? Cyclic or random sequence? Channel separation? Frequency allocation strategy? Minimum Effective Reuses? The Best Frequency Allocation reuse Maximum frequency load? PC / HO gain with FH? PC / HO parameters? Support of planning and optimisation tools? KPIs vs. subjective speech quality


FH ImplementationFH Implementation

MSC

PSTN

BB-FH F1(+ BCCH)

F2F3

Dig. RF

TRX-3

TRX-1

RF-FH

F1, F2, F3

Dig. RF

TRX-1

TRX-2

BSCTCSM

BCCH

Frequency

Time

F1F2F3

MS does not seeany difference

BB-FH is feasible with large configurations RF-FH is viable with all configurations


Average TRXs/cell : 3.3

Site Ce ll TRX countA 1 2

2 3B 1 4C 1 4

2 43 3

D 1 32 43 2

E 1 32 4

F 1 42 33 4

G 1 42 3

HoppingTRXs

1233322312332332

Average frequency load 7.4 % (max. 9.9 %) OK

Average frequency load 7.4 % (max. 9.9 %) OK

21 frequencies reserved for non-BCCH TRXs

21 frequencies reserved for non-BCCH TRXs

Effective reuse = 21 frequencies / 2.4 hopping TRXs per cell = 8.8 OKEffective reuse = 21 frequencies / 2.4 hopping TRXs per cell = 8.8 OK

Network layout:Network layout:

Average hopping TRXs/cell : 2.4

A B

C

DE

F G

1

2 11

1 1

1

1

2

2

2

2

2

3

3

3

Average frequency load: 7.4%

Single MA List Planning Case(1/1 Frequency allocation reuse)


Site C

The sectors share the same HSN

The sectors share the same HSN

MAIO Offset determines the MAIO of the first hopping TRX in each sector

MAIO Offset determines the MAIO of the first hopping TRX in each sector

MAIOs for the rest of the hopping TRXs are determined by adding MAIO Step to the MAIO of the previous hopping TRX

MAIOs for the rest of the hopping TRXs are determined by adding MAIO Step to the MAIO of the previous hopping TRX

MAI value for each TDMA frame is calculated by BTS and MS by using HSN and TDMA frame number

MAI value for each TDMA frame is calculated by BTS and MS by using HSN and TDMA frame number

No co- or adjacent channel interference between sectors

No co- or adjacent channel interference between sectors

Transmitted frequencies for each TRX during each TDMA frame

Transmitted frequencies for each TRX during each TDMA frame

Single MA List Planning Case (1/1 Frequency allocation reuse) MAIO Example


Combined FH + IUO High capacity gain

Average 70% increase compared to a conventional network

FH allows to use lower C/I threshold for IUO Same IUO RuF better traffic absorption Smaller IUO RuF more TRX/cell

BSS 7 offers FH on both layers at the same time; separate FH parameters for regular and super layers

RF FH is more flexible Can be used with smaller configurations More frequencies larger hopping gain

Evolution from FH or from IUO networks

IFHIntelligent Frequency Hopping


EXPLAINMicrocell Planning


More capacity required

Increase reuse

Make smaller cells

Microcells

Depends on: spectrum, environment, antenna location, reducing interference.

Make cells smaller, increase TRX => need better isolation between cells (reduce interference).

Increasing Capacity


Microcells make sense just in urban areas

Use urban building structures to separate microcells

Keep microcell antennas well below the rooftop level

f 1

f 2 f 2

Microcell PlanningSite Location


Hot Spots

Maximum capacity relief Targeted capacity First phase of capacity increment Frequency division does not affect

Continuous Layer

MetroSite BTSs are optimal for continuous layer within cluster area Additional capacity with:

cell splitting add TRXs

Capacity increment depends on frequency division

Microcell PlanningDifferent Approaches


Paper map Bus stations, railway stations, hotels, shopping malls, etc

NMS performance data from an existing network Traffic, blocking, timing advance, average field strength

level Visualise by plotting the traffic data to a geographical

information system

Test transmitter Placed where hot spot is expected to be NetHawk measuring the abis of the serving cell

Microcell PlanningHot Spot Analysis


27 ch Macro

9 ch Micro

Bulk Frequency Division

27 ch Macro

9 ch Micro

Interleaved Frequency Division

21 ch Macro

Multi Layer Super Reuse6 Sup

6 Sup

9 ch Micro

Microcell PlanningFrequency Division Strategy


Bad quality samples on also high field strength levels Level distribution concentrated around -80 dBm

Network QualityMacrocells

-

100

300

500

700

900

1100

1300

1500

112 -109 -106 -103 -100 -97 -94 -91 -88 -85 -82 -79 -76 -73 -70 -67 -64 -61 -58 -55

LEVEL dBm

Bad QualityGood Quality

No Of Samples


100

300

500

700

900

1100

1300

1500

-108 -105 -102-99 -96 -93 -90 -87 -84 -81 -78 -75 -72 -69 -66 -63 -60 -57

Level dBm

No Of Samples

Bad QualityGood Quality

Less bad quality samples with high field strength levels Number of high field strength samples increased

Network QualityMicrocells

-110-112


CoverageBefore Microcells


CoverageAfter Microcells


CoverageStreet Channel Effect


CoverageOvershooting Microcells


Important Parameters for Microcells

BTS TX power

Antenna type Horizontal/Vertical beamwidth

Diversity configuration Space/Polarisation diversity

Frequency hopping Achievable gain

=> TARGET to BALANCE POWER BUDGET!


Microcell Antennas


Diversity in Microcellular Environment

Both space and polarisation diversity give good gain in microcellularenvironment

Large angular spread Random polarisation in NLOS

Diversity gain from frequency hopping small due to large coherence bandwidth

Interference averaging from frequency hopping


Planning Tools for Microcells

Propagation prediction in microcell environment difficult Ray-tracing

Accurate information about surrounding environment needed Computationally very demanding

Measurements Use of test transmitters for site selection

Experience

Maps with high resolution


Antenna Installation and Site Selection

Nominal site locations: According to area survey results Possible sites Propagation environment

BTS site configuration: BTS type TX power Sectorised sites TRX/cell

Antenna planning: Height Controlled coverage area

city structures antenna positioning

Low antennas instead of downtilting Antenna hiding Directional on walls Short cabling


Antenna Installation Restrictions

Antenna height >10m Interference with other operators minimised BTS at low antenna heights might block receiving end of mobile at other

operators band (if difference above 40 dB ) If height lower, low transmission powers needed

Minimum distances due to EMR and EMC requirements Fresnels first zone should be free from obstacles


EMC Safety Distance

Field strength versus distance

02468

1012141618

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

distance [m]

field strength[V/m]

0 dBi5 dBi7 dBi

Antenna gain [dBi]

Power: 1 W

Equipment Class: Immunity requirement:[V/m] RMS

Industrial 10Medical 3Medical in X-rayshielded environment

1


EXPLAIN Dual Band


Dual Band means combining both GSM 900 and GSM 1800 (previously DCS) in the same network

GSM 900 and GSM 1800 are twins from the technical point of view

BSCGSM900/1800

GSM1800

GSM900/1800

GSM900

Dual Band NetworkBasics


Capacity with GSM900 is limited: Subscriber growth Increased usage

Quality and capacity required: New services

WLL Wireless Office Data Services

Roaming: High revenue from roaming traffic

Dual Band NetworkBasics


Traffic management First priority is to camp on GSM 1800 cells Transferring the Dual Band mobiles from GSM 900 cells to GSM 1800 cells is the

key process Setting special BSS parameters.

Planners should pay more attention to: Careful set of HO parameters Dualband network configuration LAC planning

Dual Band NetworkEffect on RNP


Idle Mode Parameters

MS will calculate the C1 and C2 for the serving cell, every 5 s

MS will calculate the C1 and C2 for the six best neighbor cells,

every 5 s

Cell re-selection is needed if

Path Loss criterion C1 < 0 for cell camped on, for more than 5 seconds.

Any of the neighbors have a higher C1 after 5 seconds.

There is DL signaling failure.

The cell camped on has become barred.

There is a better cell in terms of C2 criterion

A random access attempt is still unsuccessful after "maxNumberRetransmission"

repetitions.


C1 Algorithm

Radio Criteria

C1 = (A - Max(B,0))

A = Received Level Average - p1 B = p2 - Maximum RF Output Power of the Mobile Station p1 = rxLevelAccessMin Min. received level at the MS required for access to the system p2 = msTxPowerMaxCCH Max. Tx power level an MS may use when


C2 Algorithm

Three different equation depending on penalty time value. If penalty time = 640 s, eq. 3 is in use, otherwise eq. 1 and 2.

1) C2 = C1 + cellReselectOffset temporaryOffset T penaltyTime

OR3) C2 = C1 cellReselectOffset, when penaltyTime = 11111(640s)


C1/C2 Parameter Example Microcells

High RxLevAccessMin, -85/-90 dBm High CellReselectOffset, +20 dB Temporary offset 0 dB Penalty time NOT 640!! When cell above RxLevAccessMin, high (permanent) positive offset

Macrocells

RxLevAccessMin -105 dBm Penalty time = 640 CellReselectOffset 10 dB Decreases individual macrocell range by CellReselectOffset (if needed) Affects on GPRS cell selection!!!!!


LAC/BSC Borders Typically BSC and LAC areas are compact and bounded to

geographical location Microcells connected to same BSC with surrounding macrocells Compact BSC areas enable the effect use of Nokia features e.g.

AMH and traffic reason HO Intra BSC HO success rate better than Inter BSC HO success

rate Better candidate evaluation in Intra BSC HO

Optimised LAC borders decrease signalling load User mobility Highways and railroads Geographical areas


Dual Band Network Same LAC and BSC

MSC

BSCa BSCb

GSM900

GSM1800

GSM900

GSM1800

GSM900

GSM1800

GSM900

GSM1800

LACa LACb


Exercises / Questions

9 If you need to provide capacity for 20 Erlangs, 2 % blocking, how many TRXs do you need?

9 How many TRXs do you need to provide capacity for 10 Erlangs, 1 % blocking?9 How many subscribers can you serve with 2 TRX/cell, 1% blocking, with average

usage 20 mErl?

9 How many cells would you therefore need to give capacity for Helsinki area (49.2 % penetration, population 1 million)?

9 In China the average usage is 30 mErl. How many subscribers can you serve with 2 TRX/cell (1% blocking)?

9 In a small town A, with 1000 residents, the collected statistic data shows that the average air-time in busy hour is 90 seconds. If we want to cover this town by onecell, how many TRXs do we need to achieve the blocking probability of 1%?


References

1. W.C.Y. Lee, Mobile Communications Design Fundamentals, John Wiley & Sons, 1993.

2. J. Lempiinen, M. Manninen, Radio Interface System Planningfor GSM/GPRS/UMTS, Kluwer Academic Publishers 2001.

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EXPLAIN M07 - 1 Capacity Planning

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