Capacity Planing

7/27/2019 Capacity Planing

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Huawei ConfidentialHuawei Technologies Co., Ltd.

GSM Radio

Network

Capacity Planning

India NTS Technical Support


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Page 2Huawei Technologies Co., Ltd.

Basic Knowledge

Capacity Planing Strategy

BTS Configuration

Channel Configuration

Capacity Solution

Contents


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Basic Knowledge

Traffic Load

BHCA: Busy Hour Call Attempt

GoS

Grade of Service

It is the probability of a call in a circuit group being blocked or delayed for

more than a specified interval.

For a Lost Call system, the GoS can be measured using such equation:

)(3600

TimeHoldingCallAvg.BHCABH@LoadTrafficAvg. Erlang

callsofferedofNumber

callslostofNumberServiceofGrade


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Basic Knowledge

Erlang-B Table

Assumption: All traffic through the network is pure-chance traffic

i .e. al l call arr ivals and termin ations are independent random

events

There is statistical equilibrium

i .e., the average number of cal ls does not ch ange

Full availability of the network

i .e., every outlet from a switch is access ible from every inlet

Any call that encounters congestion is immediately lost.

Erlang-B equation of GoS

A = Expected traffic intensity in Erlangs; N = Number of circuits in group.

N

K

K

N

KA

NAerviceGrade of S

0

!

!


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Basic Knowledge

Capacity Planning Strategy

BTS Configuration


Capacity Solution

Contents


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Key point of RNP

Its always changing along with the network developing

Initial phase

Mainly pay attention to coverage, capacity is not the problem

Capacity planning is very easy:

Coverage

Dimension

Coverage

area per Site

Traffic model

Subscribers

Distribution

Traffic Load

pre Site

TRX/Channel/

.

Configuration


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Developing phase

Pay attention to both coverage and capacity:

Coverage

Dimension

Coverage

area per Site

Traffic model

Subscribers

Distribution

Traffic Load

pre Site

TRX/Channel/

Configuration

LimitationJudgment

Figure out the

max. configuration

Frequency

Planning

Channel

Configuratio

n

END

Traffic Load

per Site

Coverage

area per Site

Coverage

limitation

BTS Quantity

Capacity

limitation


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Mature phase

Pay more attention to capacity while coverage is good enough

Solve the congestion by

Cell sp l i t

Micro c el ls

Special In-Bu i ldin g Coverage system

Dual-band network

Capaci ty enhancement technolog y


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Capacity Estimation

Capacity requirement contains

No. of subscribers

Population, distribution and increasing rate

Mobile penetration & market share

Roaming factor, active factor, events (festival),

Traffic model

Which relate to the actual situation such as society, economy, user habit

and so on.

Capacity estimation

Method

Short-term, Long-term; Analogy, Modeling,

Reference

Population, existing radio networks, PLMN, GDP,


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Basic Knowledge


BTS Configuration


Capacity Solution

Contents


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Basic Knowledge of Frequency Planning

GSM frequency resource

GSM900

fUL(n) = 890 + n * 0.2 MHz

fDL(n) = fUL(n) + 45 MHz

DCS1800

fUL(n) = 1710 + (n 511) * 0.2 MHz

fDL(n) = fUL(n) + 95 MHz

C/I & CA

C/I request in GSM: 9dB (extra 3dB margin in the project)

Carrier/Interference, interference from the signal with same frequency

CA request in GSM: -9dB (extra 3dB margin in the project)

Interference from the signal with adjacent frequency, in GSM is 200KHz

890MHz 915MHz 935MHz 960MHz

1710MHz 1785MHz 1805MHz 1880MHz


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loose

Frequency Reuse

Frequency reuse

{f1, fj, fk}

{f1, fj, fk} {f1, fj, fk}

Reuse Reuse

More and more mobile subscribersfnfn

fn

RD

fn

fn

fnfn

Frequency reuse factor

i .e. number of cel ls in a frequency reuse clusterTRX

ARFCN

reuse

N

Nf

0 12 20t igh t

High efficiency

Serious interference

Good quality, easy to plan

Low efficiency


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Frequency Reuse

Frequency reuse pattern

Common frequency reuse pattern

4*3 (or 3/12)

A clu ster has 4 si tes

3 cel ls per site

General ly for BCCH frequency planning

Tight frequency reuse

MRP (Multiple frequency Reuse Pattern)

Grouping frequency

Use dif ferent reus e pattern for d if ferent TRX layer

Frequency Hopping (1*3, 1*1)

No. of ARFCNs in MA shou ld be at least 2 times more than no. of

TRXs

Usual ly BCCH layer doesnt adopt hopping for good q uali ty

IUO

Use tight reuse pattern for o verlay-cel ls

B3

A1

C1

B1

D1A2

A3B2

B3

C2

C3D2

D3

B1B2

B3

D3A1

C1

B1

D1A2

A3

B2

B3

C2

C3D2

D3

A1

C1

A2

A3


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BTS Configuration

Frequency resource, Capacity and Quality

Max. BTS Configuration China Unicom has 6MHz GSM900 frequency (29 ARFCNs)

max. BTS configuration while 4*3 reuse?

max. BTS configuration while 1*3 hopping?

Capacity

Quality

Balance

AvailableFrequency

Frequency

Reuse Pattern

Interference

RxQual BER Range

MOS

Non-

Hop

Hop

0 12.8% E E


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Basic Knowledge


BTS Configuration


Capacity Solution

Contents


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Basic Knowledge of GSM Channels

Logical channel

Traffic CHannel and Control CHannel

4 kinds of CCH according to the function

BCH: Broadcast Channel

CCCH: Common Control Channel

DCCH: Dedicated Control Channel

CBCH: Cell Broadcast Channel

Channel combination types (GSM Phase 2)

TCH/F + FACCH/F + SACCH/TF

FCCH + SCH + BCCH + CCCH FCCH + SCH + BCCH + CCCH + SDCCH/4(0..3) + SACCH/C4(0..3)

SDCCH/8(0..7) + SACCH/C8(0..7)

CCH

BCH

CCCH

DCCH

CBCH

FCCH

SCH

BCCH

PCH

AGCH

RACH

SDCCH

SACCH

FACCH


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Basic Knowledge of GSM Channels

BCCH

It carries very important information such as

list of frequencies used in cell, cell ID, location area ID, list of neighbor cells,

access control and DTX information, etc.

It transmit at a constant power all the time from the BTS.

Usually the BCCH TRX doesnt hopping, 4*3 reuse

SDCCH

SDCCH bears such traffic as following:

Mobility management such as location update;

Radio resource management such as call setup;

Point to point SMS, etc.

SDCCH/8 & SDCCH/4


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BCCH Configuration

Only 1 BCCH per cell; TS0 of TRX0 Combined BCCH (considering SDCCH traffic)

TCH Configuration

8 channels (i.e. time slots) per TRX

n = No. of TRX

Consult Erlang-B table

Exercises

No.SDCCH-No.BCCH8TCHofNo. n

TRX No. TCH No. GoS Traffic (Erl)

2 ? 2% ?

? ? 2% 15

? ? 5% 15


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SDCCH Configuration

SDCCH capacity requirement

Which relate to

Traffic model, user habit, network structure, etc.

Default value:

~5mErl/user @ BH

20%~25% of voice traffic load

Event Normal

Cell

Inner Cell Edge Cell Notes

Location update 0.4 0 1.2 1, Unit:

mErl/user

2, TCH traffic

load

assumption:

25mErl/user

Periodic location update 1.8 1.8 1.8

IMSI attach/detach 0.8 0.8 0.8

Call setup 0.9 0.9 0.9

Point to point SMS 1.0 1.0 1.0

Other applications 0.2 0.2 0.2

SUM 5.1 4.7 5.9


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SDCCH Configuration (cont.)

GoS of SDCCH

SDCCH/8, of TCHs GoS

SDCCH/4, of TCHs GoS

For instance, TCH GoS = 2%, and then

GoS of SDCCH/8 = 0.5%

GoS of SDCCH/4 = 1%

SDCCH type

SDCCH/4, combine with BCCH (TS0); 4 sub-channels

SDCCH/4 + CBCH, 3 sub-channels

SDCCH/8, on any time slot except for BCCH time slot, 8 sub-

channels

SDCCH/8 + CBCH, 7 sub-channels


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SDCCH Configuration (cont.)

SDCCH configuration suggestion

TRX

No.

Without CBCH With CBCH

Normal cell Inner cell Edge cell Normal cell Inner cell Edge cell

1 SDCCH/4 SDCCH/8

2 SDCCH/8 SD/8 + SD/4

3 SDCCH/8 + SDCCH/4

4 2*SDCCH/8 SD/8 + SD/4 2*SDCCH/8

5 2*SDCCH/82*SDCCH/8

+ SDCCH/4

62*SDCCH/8

+ SDCCH/42*SDCCH/8 2*SDCCH/8 + SDCCH/4

7 2*SDCCH/8 + SDCCH/4 3*SDCCH/82*SDCCH/8

+ SDCCH/43*SDCCH/8

8 3*SDCCH/83*SDCCH/8

+ SDCCH/4

Simply calculating: 1 SDCCH/8 per 2 TRXs


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Basic Knowledge


BTS Configuration


Capacity Solution

Contents


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Half Rate Solution

Half Rate theory

Half Rate is a speech encoding system for GSM

Since the codec, operating at 5.6 kbit/s, requires half the

bandwidth of the Full Rate codec, network capacity for voice

traffic is doubled

HR Channel Allocation Principle

Be used in area with little interference

HR dynamic allocation

When network busy: HR > FR, for more capacity

When network idle: FR > HR, for better quality

Others

Priority ofSingle > Couple

Allocate channels on the TRX which cannot adjust rate firstly


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Half Rate Solution

Capacity enhancement by HR

A S6 cell, 42 traffic time slots; GoS = 2%

Half rate ratio

By TRX: = HR_TRX_No. / Total_TRX_No.

By time slot: = HR_TS_No. / Total_TS_No.

By channel: = 2*HR_TS_No. / (2*HR_TS_No. + FR_TS_No.)

Ratio of Full

Rate Call

Required

TCHF No.

Capacity

(Erl)

Capacity of

all FR (Erl)

Capacity

Enhancemen

t

20% 14 59.1332.84

80%30% 20 53.43 62.7%

40% 24 49.64 51.2%


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Capacity Planing