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GSM BSS Dimensioning1062A

Student GuideGuide release: 15.02

Guide status: Standard

Date: July, 2005

Part Number: 1062A

NORTEL CONFIDENTIAL FOR TRAINING PURPOSES ONLY


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Copyright 2005 Nortel Networks. All rights reserved.

NORTEL CONFIDENTIAL: The information contained in this document is the property of Nortel Networks.

Except as specifically authorized in writing by Nortel Networks, the holder of this document shall not copy or

otherwise reproduce, or modify, in whole or in part, this document or the information contained herein. The

holder of this document shall keep the information contained herein confidential and protect same from

disclosure and dissemination to third parties and use same solely for the training of authorized individuals.

THE INFORMATION PROVIDED HEREIN IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND.NORTEL NETWORKS DISCLAIMS ALL WARRANTIES, EITHER EXPRESSED OR IMPLIED, INCLUDING

THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO

EVENT SHALL NORTEL NETWORKS BE LIABLE FOR ANY DAMAGES WHATSOEVER, INCLUDING

DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL

DAMAGES, ARISING OUT OF YOUR USE OR RELIANCE ON THIS MATERIAL, EVEN IF NORTEL

NETWORKS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

Information subject to change without notice.

Nortel, Nortel Networks, the Globemark device, and the Nortel Networks logo are trademarks of Nortel

Networks.


Visit us at: nortel.com/training


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Description

This course explains the Nortel Networks method to dimension the Base Station Subsystem

(BSS) of a GSM network. This course applies to the V15.0.1 version of the BSS.

Intended audience

Anyone responsible for designing BSS networks with Nortel Networks equipment (BTS, BSC,

TCU) .

Prerequisites

Before taking this course, a general knowledge of GSM/GPRS/EDGE standards and products is

required. An excellent way to obtain it is to attend the 5 days 1061A course (GSM GPRS System

Overview - Technical), the 3 days GP1 (GPRS Technical Description), the 2 days 1597AB (GSM

GPRS System Release V15.0) and the 1 day 1599A (GSM/GPRS/EDGE System Release V15.1Delta).

Objectives

After completing this course, you will be able, from a given mobile traffic model, to dimension a

BSS and:

calculate the number of signaling and traffic radio resources per sector, the number of TRX per

sector, the number of Abis and Ater PCM links,

compute the size and configuration of the BSS equipment: BTS, BSC, TCU and PCUSN.

Course introduction

Overview



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References

The following documents provide additional information:

Document titleNTP 000-

0000-000



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Contents

1. Introduction

2. Basics on Mobile Network Dimensioning

3. BTS Dimensioning

4. BSC/TCU 12000 Dimensioning

5. BSC3000/TCU3000 Dimensioning

6. PCU Dimensioning

7. BSS Dimensioning Review

8. Exercise Solutions

9. Appendix: Erlang B Tables



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Publication History


Compliant with V15.1 BSS

Release

July

2005

15.02

Creation

Compliant with V15.0.1 BSS

Release

May

2005

15.01

CommentsDateVersion


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nortel.com/training

Section 1

Introduction


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2NORTEL CONFIDENTIAL FOR TRAINING PURPOSES ONLY

About Knowledge Services

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Training with a focus on eLearning

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certification through our industry-leading certification program


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Nortel Homepage

www.nortel.com


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Training & Certification Page

www.nortel.com

Select Training

Select the appropriate product family

Choose a product

And get the content

Select the appropriate geographic region and language - allows you to customize

your view

Point of Contacts:

CAMs (Customer Account Managers) The customer can direct

questions/issues to their internal training prime, who can be in contact with the

Nortel CAM.

CSRs (Customer Service Rep) of regional calling center number

Instructor provide business cards/email address/phone number


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Training Page

Page that appears when Training is selected

Depending on your selection, you see the training offer in your region (NA, EMEA,ASIAPAC, CALA) or the global offer.


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Curriculum Paths Page

Page that appears when Curriculum Path is selected.

You can select the appropriate training according to your job function.


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Technical Documentation

www.nortel.com

Select Support & TrainingSelect Technical Documentation


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Contents

> GSM/GPRS/UMTS Training Curriculum

> BSS Nortel Technical Publications

> Objectives

> Course Architecture


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Objectives

> Upon completion of this course, ability is acquired todetermine or compute:

Traffic radio resources number per cell

Signaling resources number per cell

TRX number per cell

BTS types and number

BSC types and number

TCU number PCU number

Number of Abis, Ater, Agprs and A interfaces PCM links

BSS size and configuration

During this course the method of dimensioning computation of BSS part of a GSM

network is explained and given.The results obtained depend mainly on Traffic Model parameter values for

transmission. Some of these values deal with field parameters as cellular planning,

subscriber activity and mobility.

Each operator must define his own traffic model.

Other assumptions are also given, relating to traffic operation. They are operator

dependent:

No Queuing (loss of excess call attempts)

Radio interface blocking rate: traffic = 2%; signaling = 0.1%

A interface blocking rate: 0.1%

Notes

This course is applicable for V15.0.1 release of Nortel Networks BSS.


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Course Architecture

> Section 1 Introduction

> Section 2 Basics on Mobile Network Dimensioning

> Section 3 BTS Dimensioning

> Section 4 BSC/TCU 12000 Dimensioning

> Section 5 BSC3000/TCU3000 Dimensioning

> Section 6 PCU Dimensioning

> Section 7 BSS Dimensioning Review> Section 8 Exercise Solutions

> Section 9 Appendix: Erlang B Tables


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Student notes


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nortel.com/training

Section 2

Basics on Mobile Network Dimensioning


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Lesson Objectives

Upon completion of this section, the student will be able to:

> Define Erlang unit

> Use Erlang Law B Tables

> Describe a Traffic Model (parameters and typical values)

> Define the Dimensioning Procedure

This is obtained through a full understanding of:> Components of the GSM System Traffic

> Definition of offered traffic, blocking rate, Erlang laws


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Contents

> Generalities about GSM/GPRS Network

> Erlang Law

> Traffic Model

> Dimensioning Procedure


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GSM/GPRS/EDGE Network

BTS

BSC

TRAU

Abis Ater

PCU

Agprs

FrameRelay

Backbone

Gb

MSC

VLR

PSTN

SGSN

GGSN

GnGn

ExternalPacket NetworksIntranet, Internet

Gi

HLR/AuC

D

C

Gr

MS

PrivateIP

Backbone

Um

A

Gb

BSS

The GSM network is the foundation of the wireless network. It provides circuit-

switched voice service from mobile users to other mobile and land line users.The General Packet Radio Service (GPRS) is a wireless packet data service that

is an extension of the GSM network. It provides an efficient method to transfer

data by optimizing the use of network resources.

New from V15.0

EDGE is an extension of the GSM/GPRS Access network. In that sense, it largely

inherits the administration, maintenance and supervision of the currently deployed

BSS.

The GPRS Coding Schemes are enhanced with 7 EDGE Modulation and CodingSchemes (MCS2, MCS3 and MCS5 to MCS9). This set of Modulation and radio

coding schemes increases the peak radio throughput of a carrier by a factor 3

compared to GPRS.

In order to benefit from those new Coding Schemes, a specific hardware is

needed on the BTS side (namely E--DRX & E--PA) and an extension of the

backhaul is requested to take benefit of the full range of MCS.

EDGE is part of the rel--99 of the 3GPP specifications, and thus, BSS complies

with that version of the specification on the radio interface. It is noted that a rel--97

SGSN also supports EDGE.


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Generalities

1 Traffic channel types: speech case

TCU BSCMSC

RadioInterfaceA Interface Ater Interface Abis Interface

NSS BSS MS

BTS

(1) depends on the AMR Full Rate mode:

4.75; 5.15; 5.9; 6.7; 7.4; 7.95; 10.2 or 12.2 kbps

(2) depends on the AMR Half Rate mode:

4.75; 5.15; 5.9; 6.7; 7.4 or 7.95 kbps

A Interface Ater Interface Abis Interface Radio Interface

Gross rate Raw rate Gross rate Raw rate

TCH/FS

TCH/EFS

TCH/AFS

TCH/HS

TCH/AHS

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

64 kbps

16 kbps

16 kbps

16 kbps

8/16 kbps

16 kbps

13 kbps

12.2 kbps

(1)

5.6 kbps

(2)

Gross rate Raw rate

16 kbps

16 kbps

16 kbps

8/16 kbps

8 kbps

13 kbps

12.2 kbps

(1)

5.6 kbps

(2)

Gross rate Raw rate

22.8 kbps

22.8 kbps

22.8 kbps

11.4 kbps

11.4 kbps

13 kbps

12.2 kbps

(1)

5.6 kbps

(2)

Speech

The raw data rate is specified by the channel type: TCH/FS: 13 kbps conveyed into a 16 kbps channel on Ater and Abis interfaces

TCH/EFS: 12.2 kbps conveyed into a 16 kbps channel on Ater and Abis

interfaces

TCH/HS: 5.6 kbps conveyed either into a 8 kbps or into a 16 kbps channel on

Ater and Abis interfaces. Not available at the present time.

TCH/AFS: there are 8 AMR Full Rate modes (4.75; 5.15; 5.90; 6.70; 7.40;

7.95; 10.20 and 12.20 kbps) conveyed into a 16 kbps channel on Ater and Abis

interfaces

TCH/AHS: there are 6 AMR Half Rate modes (4.75; 5.15; 5.90; 6.70; 7.40;

7.95) conveyed either into a 8 kbps or into a 16 kbps channel on Ater and Abis

interfaces

The speech transmission is always bi-directional.

Remarks:

On Abis and Ater interfaces, the difference between the gross rate and the raw

rate is used for signaling between TRAU and BTS. On radio interface, this

difference corresponds to the channel coding.

TCH/HS is not supported by Nortel. On Abis and Ater interfaces, from theGSM recommendation (TS 08.61) point of view, there are two possible

implementations: TRAU frame on 16 kbps or on 8 kbps channel.

For TCH/AHS, there are the same two possibilities. Nevertheless, Nortel chose

to use the 8 kbps TRAU frame but on a 16 kbps channel on Ater and on a 8

kbps channel on Abis.


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Generalities

2 Traffic channel types: data case over NSS

TCU BSCMSC

RadioInterfaceA Interface Ater Interface Abis Interface

NSS BSS MS

BTS

Ater/Abis Interface Radio Interface

TCH/F14.4

TCH/F9.6

TCH/F4.8

TCH/F2.4

TCH/H4.8

TCH/H2.4

Gross rate User Service rate

16 kbps

16 kbps16 kbps

16 kbps

8 kbps

8 kbps

14.4 kbps

9.6 kbps

4.8 kbps

2.4 kbps

4.8 kbps

2.4 kbps

Gross rate Raw rate

22.8 kbps

22.8 kbps

22.8 kbps

22.8 kbps

11.4 kbps

11.4 kbps

14.5 kbps

12 kbps

6 kbps

3.6 kbps

6 kbps

3.6 kbps

Data over NSS = Circuit Switched Data

The different bi-directional data transmission types are: TCH/F14.4, TCH/F9.6,TCH/F4.8, TCH/F2.4, TCH/H4.8 and TCH/H2.4.

Data transmission at rates of 1200 bps or less or equal than 600 bps are alsopossible. There are using either a TCH/F2.4 or a TCH/H2.4.

High Speed Circuit Switch Data (HSCSD) feature allows to one user up to 4 suchdata traffic channel type. HSCSD is really interesting with four TCH/F14.4 leadingto a raw rate of 57.6 kbps. Nevertheless, it is very resource consuming as fourradio and four terrestrial resources are allocated to the same user.

Enhanced Circuit Switch Data (ECSD) feature defines three new channel types:E-TCH/F43.2, E-TCH/F32.0 and E-TCH/F28.8 using 8PSK modulation. It allows toreach the same data rates (on radio interface) as for HSCSD but with lessterrestrial resources.


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Generalities

3 Traffic channel types: Data case over GPRS core network

MS

PCUSN BSC

RadioInterfaceAgprs Interface Abis Interface

BSS

BTSGb Interface

SGSN

GPRS Network

9.05/13.4 kbps - GMSK

15.6/21.4 kbps - GMSK

8.8/11.2 kbps - GMSK

14.8/17.6 kbps - GMSK

22.4 kbps - 8PSK

29.6 kbps - 8PSK

44.8 kbps - 8PSK

54.4/59.2 kbps - 8PSK

PDTCH/CS1-CS2

PDTCH/CS3-CS4

PDTCH/MCS1-MCS2

PDTCH/MCS3-MCS4

PDTCH/MCS5

PDTCH/MCS6

PDTCH/MCS7

PDTCH/MCS8-MCS9

Gross rate Raw rate

16 kbps

2x16 kbps

16 kbps

2x16 kbps

2x16 kbps

3x16 kbps

4x16 kbps

5x16 kbps

9.05/13.4 kbps

15.6/21.4 kbps

8.8/11.2 kbps

14.8/17.6 kbps

22.4 kbps

29.6 kbps

44.8 kbps

54.4/59.2 kbps

Gross rate Raw rate - Mod

22.8 kbps

22.8 kbps

22.8 kbps

22.8 kbps

69.6 kbps

69.6 kbps

69.6 kbps

69.6 kbps

Abis InterfaceAgprs/ Radio Interface

Data over GPRS core network = Packet Switched Data

The data transmission over the GPRS core network always uses one and only onefull rate traffic channel on the radio interface whatever the coding scheme applied

(CS1 to CS4 for GPRS or MCS1 to MCS9 for EDGE). On the other hand, for high

data rates (over 13.4 kbps for GPRS (CS2) and over 11.2 kbps for EDGE

(MCS2)), more than one terrestrial resource (16 kbps channel) is required.

For example, using MCS6, RLC user data payload is 74 bytes to be transmitted in

20 ms. For this, 26 bytes are transmitted in one "main" 16 kbps channel and 24

bytes are transmitted in each of the two "joker" channels. Therefore, the raw data

rates are not the same in each of the 16 kbps channels ("main" and "joker"). In

above table, only the global raw data rates (sum of the rate of the "main" and

"joker" channels) are indicated.Nevertheless, from the user point of view, the data transfer mode is a packet

mode. That is to say, up to 8 radio TS can be assigned to one user. And

simultaneously, one radio TS can be shared between several users. Moreover, the

number of radio TS allocated to one user in downlink can be different than the

number of radio TS allocated to the same user in uplink.

Remarks:

From Release V15.0, EDGE supports the maximum data rate of 59.2 kbps

utilizing up thru MCS8-9.


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Generalities

EDGE : Enhanced GPRS

GMSK

modulation

8PSK

modulation

59.2

8.8

22.4

17.6

MCS1

MCS2

MCS3

MCS4MCS5

MCS6

MCS7

MCS8

MCS9

EDGE

CS1

CS2

CS3

CS420.8

8.8GMSK

modulation

GPRS

GMSK

modulation

8PSK

modulation

59.2

8.8

22.4

17.6

MCS1

MCS2

MCS3

MCS4MCS5

MCS6

MCS7

MCS8

MCS9

EDGE

GMSK

modulation

8PSK

modulation

59.2

8.8

22.4

17.6

MCS1

MCS2

MCS3

MCS4MCS5

MCS6

MCS7

MCS8

MCS9

EDGE

CS1

CS2

CS3

CS420.8

8.8GMSK

modulation

GPRS

CS1

CS2

CS3

CS420.8

8.8GMSK

modulation

GPRS

EDGE offers better performances than GPRS

> Optimized throughput versus propagation channel

performance

> Enhanced Features:

Link Adaptation (GPRS/EDGE)

Measurement coding scheme adaptation Incremental Redundancy (EDGE)

dynamic redundancy added with block repetition

RLC/MAC layer improvement. No window stalling limitation

EDGE uses an additional modulation scheme (8-PSK) that enables to transmit

more information per radio symbol (3 bits, instead of 1 with GMSK). Drawback isthat it is more dependant on radio conditions.

By adapting the coding schemes to the radio channel conditions dynamically, it is

possible to optimise communication performances and throughput. This is done by

Link Adaptation: through radio measurements, the network (PCUSN) chooses the

best MCS and adapts it. Estimated best MCS is used in each position of the cell.

Moreover Incremental Redundancy provides the possibility to retransmit a data

block using a different puncturing method (additional redundancy) and to recombine

it with retransmitted packets. By this way, probability to receive a correct block is

increased.

The RLC/MAC layer has been significantly improved in EDGE development. For

handsets supporting multiple TS, performance limitations in GPRS due to the limited

size of the acknowledge window is not reproduced in EDGE, i.e. in GPRS RLC

window size is 64, i.e. the transmitter cannot transmit block N+64 if block N has not

been correctly acknowledged by the receiver. In EDGE, windows size has been

extended to 1024 blocks, avoiding loss of incorrect blocks because of too bad radio

conditions.


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Generalities

Speech on the BTS-TCU interface: Abis vs. Ater mapping

TCUBSC

BTS

Ater Interface Abis Interface

0 1 2 3 4 5 6 7TS i

TS 1/0

TS 24/31

0 1 2 3 4 5 6 7TS j

AMR HR TCH (TCH/AHS)

FR TCH (TCH/FS or TCH/EFS)

AMR FR TCH (TCH/AFS6.7, TCH/AFS5.9 or TCH/AFS4.75)

8 kbps channel carrying supplementary information in dow nlink, padding in upl ink.

0 1 2 3 4 5 6 7TS m

TS 1/0

TS 24/31

0 1 2 3 4 5 6 7TS n

TS p 0 1 2 3 4 5 6 7

8 kbps channel carrying supplementary information (in uplink and in downlink).AMR FR TCH (TCH/AFS10.2)

Reminder: The Nortel BSS does only provide Half Rate Traffic Channel with AMR

introduction:

On the Abis interface, half rate channels induce 8 kbps TS, instead of 16 kbps for

full rate channels. As the same radio TS can be used as a FR or HR channel, the

associated 16 kbps Abis TS is used as one 16 kbps TS in case of FR channel and

two 8 kbps TS in case of HR channel, using the following rules:

FR: 16 kbps

HR with T = 0: 8 kbps (the most significant bit of the 16 kbps TS)

HR with T = 1: 8 kbps (the least significant bit of the 16 kbps TS)

where T indicates the sub-channel number of the Air interface.In case of FR channel, the 16 kbps Abis TS is naturally connected to the associated16 kbps Ater TS.

In case of HR channel, the 8 kbps Abis channel is connected to the most significantbit of the 16 kbps Ater TS. The least significant bit of the 16 kbps Ater TS is notused and padded using silent pattern by the BSC, in the uplink path.

For the downlink path on the Ater interface, the TCU used always both 8 kbpswhatever the AMR channel type FR or HR. But in case of HR, the BSC ignores theleast significant bit and sends to the BTS the most significant bit.

The 8 kbps channel (on Ater) corresponding to the least significant bit, is used tomanage proprietary frame, in order to ensure a 16 kbps quality for the FR

channel for AMR FR codec modes of 6.7 kbps, 5.9 kbps and 4.75 kbps.


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Generalities

Network Engineering

System DimensioningSites layout

Capacity

Cost minimization

Required quality

Number & Type

of Equipment

and Links

Inputs

Constraints

Outputs

The result of network engineering is a definition of the equipment and links of the

networks.

These results must be optimized to minimize installation/operation/maintenance

costs while maintaining the required quality.

To reach these objectives, the available variable parameters intervene in system

dimensioning, taking into account that cellular planning is fixed. Indeed, sites/cells

layout are defined by site population (rural/urban), site topography, etc..


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Generalities

Traffic model overview

TRAFFICMODEL

Qualityof

Service

SubscribersBehavior

CellularPlanning

System Dimensioning is based on a Traffic Model. A traffic model is a set of

parameters which represent the behavior of the subscribers at the busy hour.Every operator must define his Traffic Model, which is the result of three influences:

Cellular planning: the sites/cells layout has been fixed; for instance, a higher

number of cells increases handover, then CPU capacity needs.

Quality of service: it depends on blocking rate values of traffic and signaling

channels, on network operation, on supplementary services provided, on

subscription costs.

Subscribers: higher the distribution of GSM subscribers within the population,

higher the number of communications between GSM and PSTN networks. The

rural/urban distribution of GSM subscribers, their activity rate, their mobility areother influent parameters.


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Generalities

Clutters

Radio waves behave differently depending on the environment, and the radio range

can vary from few hundred meters to several kilometers.It is then important to classify the different types of environment included in the area

to be provided with GSM service.

As an example the map presented above shows a city and its surroundings,

classified into fourteen types of environment or clutters.

A link budget is established for each clutter, defining a specific cell size.

Example of Dense Urban clutter

Areas within urban perimeter. This includes dense urban

areas with dense development where built-up featuresdo not appear distinct from each other. It also includes built-

up features of the downtown district with heights below 40

m.

Example of Mean Urban clutter

Areas with urban perimeter. The mean urban clutter

should have mean street density with no pattern, the major

streets are visible, the built-up features appear distinct fromeach other. Some small vegetation could be included.

Average height is below 40 m.


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Generalities

Theoretical cells

All areas to be provided with GSM service are characterized and classified.

For areas where traffic is the limiting factor, the site number is just resulting from thedivision of number of subscribers in the area by the maximum subscribers managed

by one site.

For each clutter where coverage is the limiting factor, one link budget is established

giving a theoretical size of the corresponding cell with which the area is paved.

This step gives a first estimation of the number and type of sites needed to reach

the marketing goals.

Before deployment, Cell Planning has to be performed carefully to determine the

exact site positions and practical coverage, taking into account the existing and

friendly sites.

This is performed with the help of a planning tool which inputs are terrain database

with clutters, sites characteristics and EIRP and signal strength coming from the link

budgets.

The final step is to deliver a list and characteristics of sites after frequency planning

is performed.

This process is iterative until theoretical site positions match to practical ones.


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Generalities

Components of the GSM/GPRS System traffic

Subscriber Activity(intentional activity)

Mobility Events(transparent for the subscriber)

Traffic Model

System

SMS(Point

toPoint)

CallAt tempts

rate

At tach/Detach

InterPLMN

Roaming

Location/Routing Area

updating

Handover

SMSCell broadcast

Periodicregistration

DataSessions

The GSM dynamic parameters which define the Traffic Model are specified:

Subscriber activity: call attempt rate is the most influent parameter.

Mobility events:

Handover: their number is linked to the cell sizes

Location updating/registration: the information concerning the location area

increases with mobility and the definition of the location area

Inter PLMN roaming: it is of negligible influence on Traffic Model

System:

Cell broadcast: this function allows the operator to send various types of

information (traffic, weather forecast, advertising for instance) on MS inidle mode

Periodic registration: this action is optional but most operators use it. It is a

periodic update supervised by the system (SDCCH)


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Erlang Law

Definition

Network dimensioning according to the busy hour traffic

Unit for occupancy averages of links = Erlang

Traffic Intensity in Erlang =Resource(s) occupancy duration

Reference period duration

The Erlang unit is not a GSM specific unit. It is used to express a traffic intensity or a traffic

activity.

In GSM, when we focus on a specific radio resource, we compute the traffic intensity of this

resource (value < 1). When we focus on the total network traffic, we compute the network

activity (value may be > 1).

Traffic in Erlangs =

1 Erlang = Total resource occupancy duration of one hour observed on the reference

busy hour.

Example 1: A traffic of 0.5 Erl may correspond to 1 resource occupied during 50% of the

busy hour or 2 resources during 25% or .

Example 2: A traffic of 3.5 Erl may correspond to 3.5 resources during 100% of the busy

hour or 14 resources during 25% or .

ERLANGS ON THE AIR INTERFACE

SDCCHTCH

TRAFFIC

(Speech, Data)

SIGNALING

(Beginning of communication)(End of communication)(Handover)

SIGNALING

(various procedures)

1

2

T

T

durationperiodreference

durationoccupancy)resource(s=


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Erlang Law

Offered and carried traffics

Equipment wi thblocking rate x%Offered Traffic Carried Traffic

Increasing b locking - Increase of subscribers number (more offered traf fic)- Decrease of grade of service, while maintaining it

sufficient

Decreasing blocking - Decrease of subscribers number (less offered traffic)

- Increase of grade of service

Assuming x = blocking rate:

Carried Traffic = (1 - x/100) * Offered Traffic

Carried Traffic < Offered Traffic (if x 0)

In this course we will use the following assumptions:

Blocking rate for traffic on Radio interface: 2%

Blocking rate for signaling on radio interface (SDCCH) = 0.1%

Blocking rate for PSTN interface = 0.5%

Blocking rate for A interface = 0.1%

Blocking rate for Abis interface = 0%

Blocking rate for Ater interface = 0.1%

Those values of blocking rate are typical values. They may change according to

the environment and the QoS we want to offer to the final subscriber.

As blocking rates are always small, we admit that:

Carried Traffic Offered Traffic


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Erlang Law

Erlang Law with losses (Erlang B)

Maximum

resource

Resources

request

Blocking factor

time1 hour

Yi = occupancy rate of resource i

Offered traffic on

each resource

A

Y1 = 0.6 EY2 = 0.75 E

Y3 = 0.45 E

Y4 = 0.35 E

Y5 = 0.4 E

Y6 = 0.5 E

A = 3.05 E

Offered traffic6

5

4

3

2

1

0

12

3

4

5

6

3 9 57

Lost calls

Carried trafficA = 2.9 E

We need 6 resources to match the requests

Average busyresource

It is assumed (teaching example):

Offered traffic needs, at some times, up to six resources. At a time, only 4 resources max. are available.

Then:

For each period equal to 3 minutes, the number of resources needed iscomputed: i.e. for first period, resources 1, 2 and 6 are requested, given 3resources.

Offered traffic on resource 1 includes 12 periods of 3 minutes, giving a trafficvalue equal to:

(12 x 3)/60 = 0.6 Erlang.

Total offered traffic is equal to 3.05 Erlangs, needing an average number of

busy resources of 3.05. Three call attempts are rejected.

Note 1

Traffic in Erlangs = Summation of events duration (for each event, on a referenceperiod):for instance, reference period = one hour.

Note 2

This teaching example only introduces the traffic notion evaluated in Erlangs.

It does not correspond to the Erlang Law which deals with:

Very high number of events

Number of events following a Poisson Law Distribution of event duration following a negative exponential law


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Erlang Law

Erlang number computation

A is the Erlang number

is the mean rate of events per unit of time

T is the average duration of an event

A = T

Example on the previous page:

T1 = duration of the observation period (usually it is the busy hour = 60)T2 = total channel occupancy duration

X = number of channel requests during T1

3.05ErlTA5.083336

183T0.6

60

36

36X'183T2'60T1

=X

T2x

T1

X

T1

T2A

hourbusytheatrequestpertimeoccupancychannelaverageX

T2T

hourbusytheduringtimeofunitperrequestschannelofnumberT1

X

======

===

==

==

==

T


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Erlang Law

Erlang B Law tables

6 1.146 1.325 1.622 1.909

n

B

0.001 0.002 0.005 0.010 0.020 0.030 0.050 0.070 0.100 0.2001

2

3

4

5

7

8

9

10

0.001

0.046

0.194

0.439

0.762

1.579

2.051

2.557

3.092

0.002

0.065

0.249

0.535

0.900

1.798

2.311

2.855

3.427

0.005

0.105

0.349

0.701

1.132

2.157

2.730

3.333

3.961

0.010

0.153

0.455

0.869

1.361

2.501

3.128

3.783

4.461

0.020

0.223

0.602

1.092

1.657

2.276

2.935

3.627

4.345

5.084

0.031

0.282

0.715

1.259

1.875

2.543

3.250

3.987

4.748

5.529

0.053

0.381

0.899

1.525

2.218

2.960

3.738

4.543

5.370

6.216

0.075

0.470

1.057

1.748

2.504

3.305

4.139

4.999

5.879

6.776

0.111

0.595

1.271

2.045

2.881

3.758

4.666

5.597

6.546

7.511

0.250

1.000

1.930

2.945

4.010

5.109

6.230

7.369

8.522

9.685

Formula for lost calls (no queuing):

N = Resources number for offered traffic

A = Erlang number

The Erlang B formula is quite complicated. A good approximate result can be

obtained by using the following formula:

Resources N = A + k (A)

with

Blocking Rate Br = 10-k

Traffic (Erlang) = A

The results of the Erlang B formula are summarized in the Erlang B tables provided

in the last section.

rateBlocking

!NA...

!1A1

!NA

]A[EN

N

N =+++

=


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Erlang Law

Erlang Law with queuing (Erlang C)

Resourcesrequest

Y1 = 0.6 Erlang

Y2 = 0.75 ErlangY3 = 0.45 Erlang

Y4 = 0.35 Erlang

Y5 = 0.4 Erlang

Y6 = 0.5 Erlang

A = 3.05 Erlang

time (minutes)

1 hourYi = occupancy rate of resource i

Offered traffic on:Resource

A

0

1

2

3

4

5

6

6

5

1

23

4

3 69 18 42 57

Time Outcalls rejected

Queued calls

Carried trafficA = 3.05

A = Offered traff ic

Offered t raffic

Maximum number ofavailable resource

Average number ofbusy resources

It is assumed (teaching example):

Offered traffic needs, at some times, up to six resources.

At a time, only 4 resources max. are available.

Then:

For each period equal to 3 minutes, the number of resources needed is

computed: i.e. for first period, resources 1, 2 and 6 are requested, given 3

resources.

Offered traffic on resource 1 concerns 12 periods of 3 minutes, giving a traffic

value equal to:

(12 x 3)/60 = 0.6 Erlang. Total offered traffic is equal to 3.05 Erlangs, needing an average number of

busy resources of 3.05.

The three call attempts which would be rejected without Queuing, are

registered and processed with some delay.

Nevertheless after a defined waiting delay, they are definitely rejected.


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21


Erlang Law

Traffic management: Queuing of TCH requests

FIFO Management on cell basis

12

Priority 0

12

64

Priority 1

12

64

Priority 7

WT1 WT7

TCH allocation request

> r01 to r00

TCH attributedTCH attributedFIFO (*)

FIFO (*) FIFO (*) TCH attributed

0 (max)

1 to 7

Available TCH in the poolTCH request priority

3

WT0

T11time out

requestrejected

Example

Emergency Call

Call Reestablishment....

PagingHandover

....

= 5= 5

64

Management performed by the BSC, only for TCH (no queuing for SDCCH).

Priority 0 to 7: In order to improve the Traffic Management, priority has been definedon call basis:

Internal priorities (0 to 7), per cell; max. priority = 0; one queue per priority

Level 0 priority can be defined for example for: emergency call, call re-establishment....

Priority threshold (allocPriorityThreshold O&M parameter; example of value: 2):

r0 resources are reserved for requests of level 0 priority in the pool of availableTCH

r0 resources must be available to allow processing of a level 1 to 7 priorityrequest

If all these r0 resources are busy, a new level 0 priority request may be queuedin level zero priority Queue.

Waiting Threshold WT0 to WT7 (allocWaitThreshold O&M parameter; example of

value: 10):

This threshold defines, for each priority level 0 to 7, in each cell, a number of

queued requests; its use is given just below.

For example:

Priority 0: WT0=5 and 3 requests are queued

Priority 1: WT1=5 and 2 requests are queued

A third request in P1 queue can not be accepted because the total number of

requests queued in the queue P0 and P1 (3+2) is equal to WT1.


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This can be explained generally with the following expression:

So, a request of priority Pi can be queued only if, at this moment, the above

condition is satisfied.

Protection Timer (T11 time out; AllocPriorityTimers O&M parameter; standard

value: 5 seconds):

TCH request still stored at end of time out is erased from the queue.Note: when the Pi Queue is full, the related level i priority request is rejected (i

range: 0 to 7).

FIFO (*): (number of Queued requests in Pj Queues) WTij

j i

=

=

0


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Erlang Law

Exercise

> How many resources are necessary for an offered traffic of 65Erl with a blocking rate value of 2%?

> What is the maximum offered traffic that 95 resources can

manage without exceeding a blocking rate value of 0.1%?

> How many resources are necessary for an offered traffic of 290

Erl with a blocking rate value of 0.1%?

> What is the maximum offered traffic that 960 resources can

manage without exceeding a blocking rate value of 10%?> What is the maximum offered traffic that 1070 resources can

manage without exceeding a blocking rate value of 2%?


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24


Traffic Model

BSS Reference call and mobili ty profi le: detailed

computations for CS voice

Mobile Originating calls

MO = 66%

Mobile Terminating callsMT = 34%

16.72 s 90.1 s

CallEstablishment

Ringing

MO and MT calls description

Successful

No response called party

Busy

MO

85%70%

Legend MT

10%

20%5%

10%

{


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Traffic ModelBSS Reference call and mobili ty profi le: detailed

computations

MO busy called-party:

- Setup

MODuration *

(s)MO callsratio 1

MO successful:

- Setup

- Ringing

- Conversation

70%

66%

120

10%

1015

25

MO callsratio 2

MO no response:

- Setup

- Ringing

10

2030

20%10

MT successful- Ringing- Conversation

85%5120 34%

MT no response- To paging- or busy- Ringing

10%

5%25

TOTAL

MTDuration

(s)MT callsratio 1

MT callsratio 2

* : This is the duration of traffic channels occupancy on the radio interface, either for traffic (ex:conversation) or for signaling (ex: setup, ringing)

46.2

6.6%

13.2%

28.9%

3.4%

1.7%

1 x 2

1 x 2

46.2%

(19.8%)

28.9%

(5.1%)

-Successful calls: 75.1%

-Unsuccessful calls: 24.9%

Successful calls(unsuccessful)

Successful calls(unsuccessful)

55.44(120 x 0.462)

11.55(25 x 0.462)

1.98(30 x 0.066)

1.32(10 x 0.132)

1.44534.66

0.425(25 x 0.017)

106.82including

conversation:90.1

TCH occupancy(s)

TCHoccupancy

(s)


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Traffic Model

Standard traffic model. Observed figures

Number of observed subscribers = 4000

Total call attempts at the busy hour = 4000

Mean TCH occupancy duration per call

attempt (traffic) = 90.1 sMean TCH occupancy duration per callattempt (signaling) = 16.72 s

Mean SDCCH occupancy duration per

call attempt = 4 sMean SDCCH occupancy duration forLoc./Rout. Area update, Attach/Detach,SMS, Supplementary Services = 4 s

Call attempts per subscriber duringthe busy hour = 1

100

20

60 100

20Average number ofrequests for SDCCH,except those for call

attempts, during the BH,for the whole subscribers= 26920

Mean TCH occupancy per call attempt (total) = 106.82 s

Exercise: ATCH ?

Exercise: ASDCCH ?

Exercise:

Find ATCH and ASDCCH for 1 subscriber at the busy hour.ATCH = TCH * TTCH

TCH ?

TTCH ?

ASDCCH = ?

What is the ratio between SDCCH and TCH traffic?

In the rest of this course we will apply this ratio. (We consider that proportionbetween signaling and traffic is constant).


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Traffic Model

High mobi lity and short call duration traffic model

0.61.6Handover per subscriber at BH

1.724.54

Loc./Rout. update, periodic

update, attach/detach, SMS, per

subscriber in BH

37 s90 sAverage cal l duration

45 s120 sAverage cal l holding time

5050Number of cells managed by the

BSC

4000040000Active subscribers in the LAC

2.251BHCA per customer

0.025 Erl0.025 ErlTraffic per customer

Short call durationHigh mobility


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Traffic Model

PS communication types

File Size

per transaction

in Kbytes

Information Service & E-commerce

UL

E-mail (without attachment)

E-mail (with attachments)

Web Access (no file downloading)

Web Access (file downloading)

0.7Simple Messaging

0.3

2.7

4

12

204612

180

8

680

10

0.3UL

UL

UL

UL

UL

DL

DL

DL

DL

DL

DL

Communication UL / DL


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Traffic Model

Subscriber Categories

Acti ve Data Terminalsin Xs network (k units) BH

Business 1038

Consumer 20132

Field Service 1028

Telemetry 323

Total221


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Traffic Model

Subscriber profile example

BusinessFile Size

pertransaction

Number oftransactions

at BH

in Kbytes

Information Services & E-commerceUL 0.300

DL 2.700

E-mail (without attachments)UL 4.000

DL 12.000

E-mail (with attachments)UL 204.000

DL 612.000

Web Access (no file downloading)UL 8.000

DL 180.000

Web Access (file downloading)UL 10.000

DL 680.000

1.95

0.98

0.24

0.19

0.05

55.485Kbytes in onehour (BH) in

UL

232.105

Kbytes in onehour (BH) inDL

GPRS and EDGE call profiles include for each type of subscriber (Business,

Consumer, Field Service and Telemetry) the types of service used and thedescription of the amount of traffic each service generates.


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Traffic Model

Busy hour throughput example

BH peak bit/s (max UL,DL) sigma

Business 10 1857 3,00

Consumer 20 986 2,00

Field Service 10 326 4,00Telemetry 3 2 20,00Network 20 503 bit/s (max UL/DL)

Subscribersrepartition

38/221

132/221

28/221

23/221

Average throughput per subscriber

according t o GPRS Busy Hours

0,0

400,0

800,0

1200,0

1600,0

2000,0

0 2 4 6 810 12 1

4 16 18 20 22

hours

Average

bit/spersubs

Total (max UL, DL)

Business

ConsumerTelemetry

Field Service

The last parameter to discuss is the subscriber Busy Hour.

If we assume that the GPRS traffic profile is gaussian like, we have a sigma and apeak time (Busy Hour) for each category. Using the number of active GPRS

subscribers per category (deduced from marketing inputs) as coefficients, it is

possible to compute an average throughput per subscriber at each time of the day

(curve Total(max UL, DL)). Its peak value is the average throughput per

subscriber at Network Busy Hour.

Thus, according to GPRS Busy Hour, the average traffic per subscriber can be very

different (almost double). If the busy hour is different for each subscriber, then the

average throughput per subscriber is reduced.

The Busy Hour is largely determined by Operator Tarifications and subscribers

behavior. It has to be considered carefully.


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Dimensioning Procedure

Network dimensioning according

to the busy hour traffic

End dimensioning

Radio Interface

Start dimensioning

Cell

BTS

Abis

BSC

Ater

TCU (TRAU)

A interface

MSC/VLR

HLR

PCU

Agprs

SGSN

GGSN

SY2

EDGE dependant

Cell organization (omni or multi-sector sites, cell dimension) depends on expected

traffic, but also on dedicated radio propagation and interference problems.These problems are in charge of radio-engineers. And cell organization is admitted

as entry data for the other part of GSM dimensioning which is described hereafter:

Radio interface: number of TCH/BCCH/SDCCH channels.

Abis/Ater/A interface: number of PCM links.

BTS: number of TRX, BTS and interface boards (possibility of drop and insert

techniques).

BSC: number of interface boards, BSC type.

TCU (TRAU): number of shelves.

Main EDGE dimensioning constraints are:

Number of PDTCH configured per cell

Number of Joker TS configured per cell

From theses assumptions are computed additional resources (number of PCMs,

HW upgrades, products adaptation) required to implement EDGE.


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nortel.com/training

Section 3

BTS Dimensioning


52/295

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Lesson Objectives

> For cell, compute:

The TCH and PDTCH numbers

The SDCCH number

The CCCH number

The TRX number

> For site, dimension:

The BTS type

The BTS configuration

Total PCM TS on Abis link, including LAPD TS and Joker DS0(EDGE)

You will also be able to quickly obtain these results using look-up tablessummarizing all above computations

Upon completion of this section, the student will be

able to

This section describes and justifies the several computation steps for BTS

dimensioning.Starting site data are:

Offered traffic

Site layout: number of sectors per site, number of TRX per cell

Blocking rate currently taken for BTS on TCH: 2%

Blocking rate currently taken for BTS on SDCCH: 0.1%


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Contents

> Overall Information

> Dimensioning Detailed Method

> Packet Logical Channels

> BTS Connections

> Terrestrial Link Optimization


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Overall Information

Cell subscriber repartit ion (Example)

100

100

100

20

60 100

100

60 60

20

20

20

20

20

20

60

40 20

20

Town

Rural

Suburb

Highway

The cellular planning determines the cell distribution per BTS; the traffic per cell is

obtained from the average number of mobile stations assumed in each cell, with afixed average value of traffic per subscriber.

For the example of the diagram:

Traffic is given per cell or per site, in Erlangs; for instance, assuming an

average traffic value of 25 mE per subscriber, 2400 subscribers correspond to

a traffic value of 60 Erlangs.

Three types of traffic area are shown:

a high traffic area with low surface cells: center of a town

two medium traffic areas: a suburban area and a straight motorway area

a low traffic area with large surface cells: countryside


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Overall Information

BTS Dimensioning methods

1. First method: detailed understanding

- TCH

- PDTCH

- SDCCH (BCCH)

- TRX

Offered traffic on si te

Site layout

TABLESAbis PCM link

PCM circuit Nbr

SDCCH/8 Nbr

BCCH Nbr

TCH Nbr

TRX Nbr

Abis Joker DS0 (EDGE)

Abis LAPD TSLAPD Nbr

2. Second method: look-up tables (for voice standard t raffic model)

CS - Voice/data traffic (Erlangs)

Signaling (Erlangs)

Blocking rate

Site layout

BTS limits

Abis PCM links

Abis LAPD TS

LAPDConcentration

(2G only)

PS - data traffic (bits/s)Abis Joker DS0 (EDGE)

First method: detailed understanding

Starting from the site data, and using the Erlang B, a didactic and detailed methodis given; it is a step by step analytic method.

This method is general, despite the choice of waiting or blocking rate values in thecomputation completed hereafter.

Second method

Computations of first method are summarized in tables.

These tables are of quick and general use for standard BTS dimensioning.

Final checks are done

On TRX number relating to radio TS number.

On BTS load constraints.


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Overall Information

> BTS Model provisioning

Radio interface dimensioning:TCH, PDTCH, SDCCH, CCCH, TRX, BTS Type

Abis interface dimensioning:

Traffic and signaling (LAPD) TS and Joker DS0 (EDGE)

BCF units dimensioning:

PCM interface boards (PCMI)

Signaling concentration boards (DSC)

CBCF units dimensioning:

PCM interface boards (CPCMI)

Radio interface dimensioning:

Three groups of channels: traffic channels TCH, PDTCH

dedicated channels SDCCH

common channels CCCH

Abis interface dimensioning:

Radio interface will be defined, as TRX number

Number of traffic TS = 2 x (TRX number)

Number of Joker DS0 depending on the expected MCS distribution within thecell (EDGE), ranging from 0 to 8

Depending on the product range BTS 18000, S12000 or S8000

( )( )integerupper

BTS18000for9or8numberTRXLAPDofNumber =


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7


Overall Information

GSM/GPRS Logical channels on radio interface TSs

FACCH

Frequency correction

Synchronization

Broadcast con trol

Access request

Subscriber paging

Answer to Access request

Broadcast inf o

Dedicated Signaling

Sys Info 5, 5bis, 5ter 6 + SMS

Traffic (speech CS data)

Associated Signal ing

BTS

0 1 2 3 4 5 6 7TS

MS

FCCH

SCH

BCCH

PCH

AGCH

CBCH

SDCCH

SACCH

TCH

FACCH

SDCCHSACCH

FCCH

SCH

BCCH

RACH

PCH

AGCH

RACH

CBCH

TCHTraffic (speech CS data)

Associated Signaling

Radio Measurement + SMS

Broadcast inf o

Dedicated Signaling

M.S. Pre-synchronization

Access request

Subscriber paging

Answer to Access request

MF51MF26

PDTCH

PACCH

Traffic (PS data)PDTCH

PACCH

Traffic (PS data)

MF52

Associated SignalingAssociated Signal ing

Three groups of logical channels:

1. Traffic channels (TCH; PDTCH), and associated channels (FACCH,SACCH; PACCH, PTCCH):

Number computed from Erlang B law, starting from offered traffic,

according to the traffic model.

2. Dedicated signaling channels (SDCCH, SACCH, CBCH):

Number computed from Erlang B law, using figures given by the traffic

model.

The CBCH is optionally used; when activated, it uses permanently one

SDCCH resource.

3. Common channels (CCCH), BCCH and synchronization channels

(FCCH, SCH)

Theoretical studies on message exchanges on radio interface have

shown that one common channel is often sufficient, for low to medium offered

traffic on CELL.

BCCH combined: common channel pattern for small capacity cells

(O1): Signaling channels SDCCH/SACCH are included in same frame as

common channels:Traffic CHannelPacket Data Traffic CHannel

TCHPDTCH

FastAssociated Control CHannelPacketAssociated Control ChannelPacket Timing advance Control

CHannel

FACCHPACCHPTCCH

Stand-alone Dedicated Control CHannelSDCCHFrequency Control CHannelFCCH

Signaling CHannelSCHCommon Control CHannelCCCH

SlowAssociated Control CHannelSACCHCommon Broadcast CHannelCBCH

RandomAccess CHannelRACHBroadcast Control CHannelBCCH

Paging CHannelPCHAccess Grant CHannelAGCH


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Overall Information

FR vs. HR TCH

BTS

Abis in terface (E1/T1)

0 1 2 3 4 5 6 7

TS n

TS 1/0

TS 24/31

16 kbps

TCH/F

2x8 kbps

TCH/H

Um interface

Capacityimprovementsthanks to AMR

introduction

0 1 2 3 4 5 6 7TSf0

TS p

4 5 70 1 2 3 6TSf1

But, there can be holes at a time being.A Full Rate call may not be establ ished.

Full Rate blocking rate increases.

AMR Half Rate allows to double the number of calls that could be carried on a Abis

PCM. Therefore, AMR HR offers the possibility to have a capacity increase in termsof Erlang with the quality of a FR speech.

Indeed, one Full Rate Traffic CHannel (TCH/F) requires one 16 kbps TS on Abis

and one complete Radio TS. Whereas, the same resources (the 16 kbps TS on Abis

and the Radio TS) can be shared by two Half Rate Traffic CHannels (TCH/H).

The Nortel BSS does only provide Half Rate Traffic Channel with AMR introduction:

Adaptative multi -rate Half rate Traffi c CHannel (TCH/AHS)

Adaptative mult i-rate Ful l rate Traf fic CHannel (TCH/AFS)


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Overall Information

BTS Product range: cell layout

8 TRXs

8 TRXs8 TRXs 8 TRXs

8 TRXs

Omni Bi sectorial Tri sectorial

8 TRXs

For BSC12000: 24 TRXs max per site

16 TRXs

16 TRXs

16 TRXs 16 TRXs

16 TRXs

Omni Bi sectorial Tri sectorial

16 TRXs

For BSC3000: 48 TRXs max per site (V15.1) with BTS18000

The Diagrams show the max. number of TRX which can be installed per cell, on one

site managed by a BTS.Note that in the case of a BSC3000, a max of 48 TRXs per site is defined only with

the introduction of the BTS 18000 and in a S161616 config.

Reminder: for high traffic densities, the solution is to create multi-sectorial sites,

instead of increasing the number of omni-sectorial sites of reduced coverage, which

would result in:

Higher installation cost

Difficulties to find sites

Currently, the most used configurations are:

Omni-sectorial layout for low traffic sites

Tri-sectorial layout for medium and high density urban sites

Bi-sectorial layout for roads


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10


Overall Information

Full Range Family

e-cell

Outdoor

Microcellular coverage

34.5 liters

S8006 Street

DeployableS8002 GSM-RS8000 Indoor S8000 Outdoor

S2000H

Integrated selfcontained cell-site

Common packageIndoor/Outdoor

No fans,natural convection

S12000 Indoor

S12000 Outdoor

Highest capacity

Lowest foot print

Up to 12 TRXs

per cabinet

S8000 Outdoor and Indoor 8 TRXs per cabinet and up to 3 (with BSC 2G) or 6 (with BSC e3) cabinets

DRX architecture: 1 (e)TRX = 1 (e)DRX + 1 ((H)e)PA Compact BCF (or CBCF)= CMCF and CPCMI boards

S8002 2 TRXs outdoor BTS (O2) designed for railway applications (R-GSM band) Environmental performances equal or better than current S8000 Re-using common S8000 equipment: CBCF, DRX, PA, RX splitter, rectifiers User compartment (6 U)

S8006 6 TRXs outdoor BTS designed for installation along streets and roads without

requirement for building permits (O6, S222, S33 and S42) Environmental performances equal or better than current S8000 Diversity radio path as standard

Re-using common S8000 equipment: CBCF, DRX, PA, RX splitter, rectifiersS2000H&L

2 TRXs outdoor/indoor BTS in 1 cabinet, expandable to 4 TRXs with an additionalcabinet

Small BCF (or SBCF) = 1 SMCF + 1 SPCMI boards Internal antenna for S2000L (optional)

e-cell 2 TRXs BTS in 1 cabinet, expandable to 4 TRXs with an additional cabinet 1 antenna (integrated or external)

S12000 Outdoor and Indoor 12 TRXs per cabinet and up to 3 (with BSC 2G) or 4 (with BSC e3) cabinets DRX architecture: 1 (e)TRX = 1 (e)DRX + 1 ((H)e)PA

CBCF with CMCF and CPCMI boards (for up to 3 cabinets) or XCBCF with CMCFPhase 3 and 4 CPCMI boards (for 4 cabinets)


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Overall Information

Full Range Family

BTS 18000 OutdoorBTS 18000 Indoor

BTS 18020 Outdoor:

Fully Integrated self contained cell-site:

18 TRXs (DRX + PA) in a single cabinet (16 TRXs limitation with BSC3000 in V15.1).

Rectifiers, battery back-up, cooling and heating and 220 Vac main (or 2 x 110 Vac live)

Optimized size versus capacity ratio : Cabinet size 150 x 135 x 70 cm

PA TX Power: 30 W (1800/1900) / 40 W (850/900) / 60 W (900 HPRM)

Extended operating temperature range: -40 C to +50 C

Max consumption : Total for cabinet : 6642 VA ( with heater on : 9442 VA and with heater on and

batteries in charge : 11234 VA )

Cabinet weight: when fully equipped = 500 kg.

BTS 18010 Indoor:

Compact packaging:

18 TRX (DRX + PA) in each cabinet. (Divided in 6 RMs)

New BCF integrated in the main cabinet and up to 3 radio cabinets.

Modular and flexible configuration: from S666, or O18 or S99 in 1 cabinet and up to S161616 in 3 cabinets

(with a BSC3000) or S888 in 2 cabinets (with a BSC 12000)

Dimensions: Height : 175 cm Width : 60 cm Depth : 60 cm

PA TX Power: 30 W 30 W (1800/1900) / 40 W (850/900) / 60 W (900 HPRM)

Max Consumption : 5123 W

Extended operating temperature range: -5 C to +45 C

Cabinet weight: when fully equipped =300 kg

Nortel Networks has also developed the BTS 18000 Combo (indoor/outdoor) which is a

UMTS/GSM BTS, and the BTS 18020 MCPA which is an outdoor 1900 GSM BTS with a MCPA

cabinet for the coupling system.


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nortel.com/training

Lesson or Module Title

Lesson or Module # or Module #

Lesson #

nortel.com/training

Dimensioning Detailed Method

This chapter gives all the computation steps needed to evaluate:

The number of traffic channels TCH in a cell. The number of signaling channels SDCCH in a cell.

The number of TRX per cell.

The total number of time slots on Abis link (including signaling and EDGE DS0

TS).

The number of boards inside the BCF.


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Traffic channels reminder

AiTi

26 frames = 120 ms

T0 A0T0 T0 T0 T0 T0 T0 T0 T0 T0 T0 T0T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 A1 time

Half Rate - Downlink & Uplink

T: TCH

(FR)A : SACCH : IDLETi : TCH (HR)

sub-channel

no. i

Ai : SACCHsub-channel

no. i

26 frames = 120 ms

Full Rate - Downlink & Uplink

timeT AT T T T T T T T T T TT T T T T T T T T T T T

Full rate speech t ransmission

When a Mobile Station is in communication mode, speech is coded every 20 ms inblocks. These blocks are coded in 8 half-bursts, whose information quantity isequivalent to 4 entire bursts. Then, one burst has to be delivered every 4.615 ms.

So, in 26 frames lasting 120 ms, 24 bursts are used for speech transmission. Oneburst is used for an SACCH. The last one in the sequence is an idle burst. Duringthis burst, the mobile is not idle, but it uses this time to monitor the neighboring cellfrequencies.

Half rate speech transmission

When the half rate speech transmission is in use, the 26 frames of a given timeslot can be separated between two users, since only 12 coded speech bursts areused per user.

So, in 26 frames lasting 120 ms, the odd burst numbers are restricted to one user,and the other numbers are for the other user. SACCH bursts are in the 13th and26th positions. In this case, the monitoring is more frequent.

4.75 kbpsAMR 4k75

5.9 kbpsAMR 5k96.7 kbpsAMR 6k7

10.2 kbpsAMR 10k2

5.6 kbpsHR

12.2 kbpsEFR

13 kbpsFR

Source coding rate


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Number of traffic channels in a cell

Erlang BLoss

Formula

Erlang BLoss

Formula/2

X

Number of

subscribers

Subscriber

activity

blocking

rate

Number of TCH/F resources

+ Number ofTCH TS

Percentage

of HR calls

Number of TCH/H

resources

XPercentage

of FR calls

X

blockingrate

.plannedcell traffic

planned

cell traffic

Subscriber activity: traffic per subscriber at busy hour = 25 mE (example).

Number of subscribers = 1700 (example). Then planned traffic in the cell includingthe 1700 subscribers = 42.5 Erlangs (example).

With only Full Rate calls:

Number of necessary resources with a blocking rate of 2%, obtained from ErlangB table: n = 53.

Conclusion: TCH channels = 53 for 42.5 Erlangs cell and blocking rate = 2%.

With 20% Half Rate calls:

Planned traffic in the cell for Full Rate calls: 0.8x42.5 = 34 Erlangs.

Number of necessary Full Rate resources with a blocking rate of 2%, obtainedfrom Erlang B table: n1 = 44.

Planned traffic in the cell for Half Rate calls: 0.2x42.5 = 8.5 Erlangs.

Number of necessary Half Rate resources with a blocking rate of 2%, obtainedfrom Erlang B table: n2 = 15.

Conclusion: TCH/F Channels = 44 + 15/2 = 52 for 42.5 Erlangs cell and blockingrate = 2%.

Another approach consists in dimensioning the number of TCH TS only consideringFull Rate TCH and then calculating the capacity increase in terms of Erlang with p%of Half Rate allocations.

53 Full Rate resources correspond to 2x53 = 106 Half Rate resources; With a

blocking rate of 2%, the Erlang B table gives a traffic of 93.8 Erlangs that is to say again of 120%.


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Number of SDCCH in a cell

planned cell

traffic (ATCH)

ASDCCH

Number

of SDCCH

resources

blocking rate

8

Number

of SDCCH

Time slots

ErlangB

Loss

Formula

X

100x

call attempts/second

location update rate

mean SDCCH occupancy time

Traffic model at X%

Since 1 SDCCH TS carries up to 8 SDCCH channels, we divide by 8 the number of

resources obtained from Erlang B table.If ATCH = 42.5 Erl, ASDCCH = 28% * 42.5 = 11.9 Erl

So the number of SDCCH resources = 24 for a blocking rate of 0.1%.

=> number of SDCCH TS = 24/8 = 3 SDCCH TS

Remark: if the number of TCH TS necessary is 7, then, the BCCH combined

configuration can be used if the number of SDCCH resources is 4.

Caution: for a given (TCH, SDCCH) configuration, an increase of the Half Rate

traffic requires a new dimensioning of the SDCCH resources.

Example:

Dimensioning for Full Rate only:

ATCH = 42.5 Erl gives NTCH = 53 for a BrTCH = 2%

Therefore, ASDCCH = 11.9 Erl requiring NSDCCH = 24 (3 SDCCH TS) for a

BrSDCCH = 0.1%

Dimensioning for full Half Rate:

NTCH = 2x53 = 106 gives ATCH = 93.8 Erl for a BrTCH = 2%

Therefore, ASDCCH = 0.28x93.8 = 26.3 Erl requiring NSDCCH = 44 (6 SDCCH

TS) for a BrSDCCH = 0.1%


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Packet Logical Channels

Multi-frame structure

0 1

Radio Blocks

Cycle of 52 TDMA frames divided in: 12 radio blocks B0-B11 (of 4 consecutive

frames)

4 idle frames (X)

Idle frames

TDMA Frame 0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142434445464748495051

Block B 0 B 1 B 2 0 B 3 B 4 B 5 1 B 6 B 7 B 8 2 B 9 B 10 B 11 3

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

GPRS Time Slot (PDCH)TDMA Frame

= 4.615 ms

The packet channels carry either RLC data blocks or RLC/MAC control blocks

(except PRACH and PTCCH UL, which use an access burst instead of normalbursts). Each of these radio blocks are mapped after channel coding and

interleaving onto 4 radio TS (called radio blocks because they carry logical radio

blocks).

The mapping in time of the packet logical channels carried by the same PDCH is

defined by a multi-frame structure. The multi-frame structure for PDCH consists in a

cycle of 52 successive TDMA frames, divided into 12 blocks (of 4 TS each) and 4

idle frames according to the above drawing.

The multiplexing of the packet channels on a PDCH is not fixed like in the GSM

system. It is managed by some parameters and the following block order: B0, B6,B3, B9, B1, B7, B4, B10, B2, B8, B5, B11. For example, if there are 4 PBCCH

blocks in the cell, those will be carried by the blocks B0, B6, B3 and B9 (on the

same TS indicated in System Information 13 on BCCH).

The idle frames are used by the MS for signal measurements and BSIC decoding

on the SCH of neighboring cells (idle 1 and 3) or for TA update (sending an access

burst on PTCCH UL in idle 0 or 2 and receiving an RLC/MAC control block on

PTCCH DL in idle 0 and 2 of 2 successive multi-frames = 4 TS in total).


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Packet Logical Channels

PDTCH Allocation

TS0 TS1 TS2 TS3 TS4 TS6TS5 TS7




TDMA2

TDMA3

TDMA4

Combined GSM/GPRS TS

Configuration TCH/PDTCH

GPRS TS (PDTCH: packet sw itched)

TDMA1

GSM TS (TCH:circuit switched)

The TS configuration is declared for each TS at the OMC-R.

Some TS are reserved for the GSM system only (circuit switched TS): TCH,some others are reserved for the GPRS only (packet switched TS: PDTCH),

some others TS can be used either as TCH or PDTCH on demand.

The possible configurations for the packet switched channels (PDTCH) are:

PDTCH

PCCCH/PDTCH

PBCCH/PCCCH

PBCCH/PCCCH/PDTCH

These configuration will result in different packet channels multiplexing on the same

PDTCH (for more details, see the multi-frame at 52 TS).


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How many TRX per cell?

Take theupperinteger

multipleof 8

Number of CCCH

Between 1 (TS 0) and 4radio time slots

(TS 0/2/4/6)

8+

Number o f SDCCH

radio time slots

Number of TCH radio

time slots

Total

radio time

slots

Number of

TRX

Number of PDTCH radio

time slots

CCCH rule

Number of CCCH radio time slots = 1 per cell.In some cases (microcell, dual band), we may need more than 1 CCCH: up to 4 in

total (TS0, 2, 4, 6) as specified in the GSM recommendations. The addition of

CCCH TS will depend on the traffic model, the LAC repartition and the environment.

2 CCCH TS may be necessary in a single layercell if, with 1 CCCH TS, the number

of TRX per cell is > 6 and the offered traffic per LAC is > 1200 Erls.

In a multi layercell, a second CCCH TS may be necessary if, with 1 CCCH TS, the

number of TRX per cell > 5.

In our example:

Number of TCH radio time slots = 53 (example: cell with 1700 subscribers).

Number of SDCCH/8 radio time slots = 3.

Total number of radio time slots: 53 + 3 + 2(CCCH) = 58.

Number of TRX (8 radio TS per TRX): 58/8 = 8 TRXs.

Exercise: In this configuration, what will be the distribution between SDCCH and

TCH for full Full Rate? For full Half Rate?

Remark: if the cell is extended, the number of TRX is obtained by dividing the total

number of radio TS by 4.


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How many traffic Abis time slots?

TRXDimensioning

/ 8*2

Total Number of

radio timeslots

number

of TRX

number of Abistraffictimeslots (64 kbps)

/ 4

2 PCM TS at 64 kbps

8 radio TS carrying 16 HR TCH

64 kbps 64 kbps

Ai r interface

8 radio TS carrying 8 FR TCH

Abis in terface

8 radio TS carrying FR & HR TCH

A PCM TS supports up to 8 half rate traffic channels with a switching matrix at 8

kbps (half rate speech). Concentration from 4 time slots on radio interface towards 1time slot on Abis interface is performed by BTS.

1 TRX handles 8 radio TS:

number of traffic time slots on Abis/Ater = (number of TRX) x 2

For the chosen example (8 TRXs):

Number of traffic TS on Abis and Ater interfaces (8 x 2) = 16 TS

Note: 16 time slots on Abis PCM link correspond to 64 Full Rate TCH traffic

channels up to 128 Half Rate TCH traffic channels on radio interface.

4 full rate traffic channels are supported by:

4 TS(on 4 radio channels)

1 TS (4x16 kbit/s)(on one PCM link)


4 TS (4x64 kbit/s)

Radio interface Abis interface Ater interface A interface

8 half rate traffic channels are supported by:

4 TS(on 4 radio channels)



8 TS (8x64 kbit/s)

Radio interface Abis interface Ater interface A interface


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LAPD Frame Reminder

FCS : Frame Check Sequence SAPI : ServiceAccess Point Identifier (0, 1, 3, 62)

F : Flag TEI : Terminal Equipment Identifier

0 to 260 octets

FCS Control AddressF

N (R) N (S) TEI SAPI

Information F

LAPD

Start o f

frameEnd of

frame

On Abis interface for each BSC and related BTS terminal port (TEI), three types of

links may be activated depending on the SAPI parameter value:The Radio Signaling Link:

Radio resource management procedures SAPI = 0

Short messages, point to point SAPI = 3

The Operation and Maintenance Link: O&M procedures SAPI = 62.

LAPD messages on Abis:

OML: software download, channel configuration, notification (event report)

RSL: paging, HO command, channel requirement

On Agprs, between BSC and PCU, same OML SAPI number = 62 is used for radio

configuration. RSL SAPI number = 0 is used for allocation of GPRS TS. An extra

link exists: GSL(GPRS Radio Signaling Link) using SAPI number = 1 for

communication between BTS and PCU for TBF (Temporary Block Flow) related

messages.


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Abis Interface Protocols

RSL = Radio Signaling

Link

OML = Operation and

Maintenance

Link

GSL = GPRS RadioSignaling Link

RSM = Radio Subsystem

Management

O&M = Operation andMaintenance

RSMO&M

RSMO&M O&M

Level 1 layer

RSL OML

TRXBCF

Level 3

layer

LAPD

Level 2

layer

BTS side BSC side

GSL

RSL OMLGSL

This interface located between BTS and BSC has these features:

Partly normalized No inter-operability (currently) proprietary

It is organized in three levels:

Level 1 PCM transmission (E1 or T1):

Speech:

Conveyed in timeslots at 4 (full rate) to 8 (half rate) x 16 kbps (remote

transcoders)

Data:

Conveyed in timeslots at 4 x 16 kbps

The initial user rate (CS), which can be 300, 1200, 1200/75, 2400, 4800

9600 or 14400 bps is adjusted to 16 kbps.

For Packet Switch data, 9.05, 13.4 kbps (GPRS CS1 and CS2), 8.8 and 11.2

kbps (EDGE MCS1 and MCS2) channels are each using a 16 kbps timeslot.

For all other PS data rates, more than one 16 kbps timeslot are used.

Level 2 LAPD protocol: Standard HDLC procedure:

RSL = Radio Signaling Link

GSL = GPRS Radio Signaling Link

OML = Operation and Maintenance Link

Level 3 application protocols:

RSM = Radio Subsystem Management

O&M = Operation and Maintenance procedure


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Concentrated LAPD with CBCF

CMCF

CPCMI

SwitchingMatrix

8 DRXs

SignalingTS

BSC

Abis

FP1 FP2 FP3 FP4 FP5 FP6 FP7 FP8

LAPDconcentrationUp to 8 DRXs(+ CBCF)

1 internal TS

(concentrated LAPD)

CMCF board

Core unit of the CBCF manages the switching matrix, the synchronization,concentration and routing tasks.

Remark: With the introduction of half rate, the number of LAPD messages per

TRX, increases. Nevertheless, considering the actual proportion of AMR mobiles

in a network, one LAPD for 8 TRX might be sufficient.

In V12.4, DRX, eDRX and DRX-ND3 are all treated and displayed as DRX. In

V14.3, eDRX becomes identifiable, while DRX and DRX-ND3 remain un-identifiable.

In V15.0, each equipment type is identified, processed and treated independently.This implementation reduces the total cost of ownership for Nortel equipment and is

then a benefit for Maintenance and Provisioning process. From V15, CMCF phase 1

and phase 2 are not fully compatible anymore from a feature point a view.

The CMCF phase 1 / phase 2 differentiation permits the operator to deploy V15

system release on BTS in the best way as some V15 features are not fully

supported by CMCF phase 1 or cannot be activated on phase 1 / phase 2 duplex

BTS.


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Abis PCM dimensioning without EDGE

LAPD

dimensioning

Engineering Rule

Total 64 kbps TS

on Abis land lines

Nbr of LAPD

from TRX

+ BCF

Nbr of ABIS

Traffic TS

Nbr of

concentrated LAPD

E1 PCM

31Number of E1

PCM = upper

integer value

T1 PCM

24

+

Number of T1

PCM = upper

integer value

Reminder: TS on Abis carry traffic time slots and signaling LAPD time slots solely.

TRX number: TRX number has been previously obtained starting from radio TS number

Example continued: 64 radio TS, then 8 TRXs

Number of Abis traffic TS = (number of TRX) x 2:

Example continued (8 x 2) = 16 TS on Abis

LAPD dimensioning (see previous page):

One concentrated LAPD on Abis processes signaling for 8 TRXs

Example continued:

8 TRXs 1 LAPD TS on Abis

Total number of Abis TS:

Example continued:

(TS for traffic = 16) + (TS for LAPD = 1) = 17 TS

E1 PCM link (32 TS. TS0 never available: used for link synchronization): 31 TS

available.

T1 PCM link: 24 TS available.

Example continued: 1 E1 PCM link necessary for 17 TS

1 T1 PCM link necessary for 17 TS


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S12000/

S8000

To be dimensioned

CBCF

PrivatePCM bus

CMCF

BSC

Switching

CMCF

DRX

CPCMI

CPCMI

CPCMIPCM

Interface

Control,Signal.Concentr.SynchronizationManagement

S8000 if the CBCF is used: CPCMI and CMCF (1+1).

S12000 with CBCF: CPCMI and CMCF (1+1).


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CBCF Units dimensioning

CBCFdimensioning rulesNumber ofAbis PCM Number ofCPCMI boards

Number of CPCMI = Upper Integer[number of Abis PCM / 2]

ExternalPCM

CPCMI

CBCF

S8000/

S12000

Internal

PCM

Available Resources:

Rules:

One CPCMI board has been designed to handle two PCM links of Abisinterface.

Example continued:

1 PCM link 1 CPCMI board

S8000 S12000

CMCF 2 2

CPCMI 3 3


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BCF Unit for BTS 18000

IFM

ICM

SPM

The BCF for the BTS 18000 is composed of the following cards:

IFM + ICM + SPM

The backplane where they are connected is called IBP.

IFM : The Interface Module provides the following access for the ICM

ICM : The Interface Control Module is designed to manage the whole BTS site in

simplex configuration. It is the equivalent of the CMCF and CPCMI modules of the

S8000 or S12000.

SPM : The Spare Module (SPM) is reserved for future use. It may be designed to

manage the whole site network packetization for example (or RLC/MAC in the

BTS).


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BCF Unit for BTS 18000

IFM board

ICM board

IFM board:

The IFM is only used in the BTS18000 base cabinet. It is not present in theextension cabinets. The IFM is composed of a single passive board with

connections on the IBP and on the front panel. The IFM provides connectivity and

secondary protection on the PCM links.

Maximum number per cabinet: 2.

Ext Abis connector: E1/T1 links to Abis interface

Shared Abis connector: E1/T1 links to ICM board

ICM board:

The ICM is only used in the BTS18000 base cabinet. It is not present in the

extension cabinets. It is designed tomanage the whole BTS18000 site in simplex or

redundant mode.

Redundancy can optionally be introduced using two ICMs in the digital rack. In such

a mode, called duplex, there is one active ICM and one passive ICM


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nortel.com/training

Lesson or Module Title

Lesson or Module # or Module #

Lesson #

nortel.com/training

EDGE Dimensioning Detailed Method

7 New Coding Schemes (MCS2, MCS3 and MCS5 to MCS9) are implemented

with EDGE. They permit to increase signif icantly the peak radio throughput (up to59.2 kbps with MCS9).

For data circuit channels using MCS3 and greater, more than one 16 kbps TS is

required. Therefore, in order to fully benefit from these new Coding Schemes, an

extension of the Abis resources is requested. Moreover, a specific hardware on

BTS side must be implemented for the BTS to be fully EDGE compatible.

To configure EDGE on a network, several steps must be followed. The purpose

of these steps are to define the number of additional TS (called DS0) that must be

configured on the Abis interface to fully benefit from the new coding schemes. Then,

Abis (and Agprs) interface dimensioning must be modified accordingly to take into

account additional DS0. Finally, BTS hardware must be checked to ensure a fullEDGE compatibility. An eye must be kept as well on the BSC3000 and PCU

dimensioning.

First step to perform is a radio interface analysis to obtain an MCS distribution at

each position of the cell. Then, using this MCS distribution, additional DS0 TS can

be computed. Radio Site Mask and Abis PCM dimensioning must be modified

accordingly to the additional DS0 number, and BTS architecture must be checked.

Lets have a look at all these steps in the follow ing sl ides.


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EDGE Dimensioning Detailed Method

Introduction: Methodology for EDGE Dimensioning

Radio interface

analysis

Throughput

Joker dimensioning

on Abis

Number of joker to

be configured

BTS hardwareprovisioning

HW Upgrades

Abis Interface

dimensioning

PCM#,Radio site Mask

Agprs Interface

dimensioning

PCM#

Upgrades

BSC/PCU

engineering

Upgrades,

Dimensioning

In section 6

In sections 5 and 6

First Step: Radio interface

Based on radio condition and network design (cell radius, C/I,) the expected radioTS throughput, the MCS distribution and the average BLER values can be

computed.

Second Step: DS0 joker on Abis

The second step consists in determining the required number of joker DS0 to be

configured on Abis to support the higher throughput per TS. This number of DS0 is

obtained from the MCS distribution provided by the radio analysis.

Third Step: Abis backhaul dimensioning

This additional number of DS0 joker must be taken into account in the radio site

mask definition and in the Abis PCM num

Documents

gsmbssdimensioning