go np11 e1 1 gsm capacity planning-39(old)

7/28/2019 GO NP11 E1 1 GSM Capacity Planning-39(Old)

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Capacity Planning

ZTE university



Contents

Capacity Planning Overview

Capacity and Traffic Distribution Prediction

Capacity Planning

Channel Configuration Location Area Planning

Capacity Increase Methods



Capacity Planning verview

Capacity Planning Overview Before planning the capacity of a cell

network, you should first decided thecapacity requirements, namely, howmany subscribers will the system provideservices to, and how much traffic will begenerated. This is the basis for the

engineering design of the entire cellnetwork.

The purpose of system capacity analysisis to obtain data of the actual networkrequirements and future capacity needs,so as to estimate the amount of channels

needed in the system. Network planning is implemented based

on the early-stage and later call trafficdistribution of the system, calculatedaccording to statistical data.




BTS Capacity Refers to the number of channels

configured for a BTS of a cell, includingradio voice channels and control channels;

Network Capacity Refers to the sum of capacities of all BTSs;

Capacity Planning Refers to the process to plan BTS locations

and configurations based on the current

subscriber amount and development trends;




Erlang-B Table The Erlang-B modeling formula describes the relationships

between the amount of TCHs, Grade of Service(GoS), and thetotal amount of traffic. According to the Erlang formula, we cancalculate the traffic under different call loss ratios and indifferent channels, which can be summarized into the Erlang-B

Table. Traffic per user on busy hour

is the traffic of a subscriber on the busy hour.

is the number of calls made of a subscriber in a day is

the call timeis the busy hour concentration coefficient(ration betweenbusy hour traffic and traffic of the day)

In a common pre-planned project, the traffic per user onbusy hour is usually 0.025～0.03Erl/user

36001

0

0



Contents

Capacity Planning Overview Capacity and Traffic Distribution Prediction

Capacity Planning





Growth Trend

Prediction

Growth curve

CapacityPrediction

Population

Prevalance

Rate

Secondary

curve


Capacity Prediction Methods




Example: secondary curve To predict mobile subscribers, we can create an empirical formular

based on the subscriber development data of the previous years,according to which formular we can predict the future subscriber growth.

x represents the year, and y represents the number of subscribersin the mobile communications network.

Input the number of subscribers in the previous years, and chooseconstants a, b, and c with the least square method.

cbxax y 2




Unevenness of Traffic Distribution The call traffic is mainly distributed in middle and

large cities, forming a dense traffic area in thecity center, in which traffic hot spots with higher traffic exist. The traffic is low in suburban areasand counties.

Necessity for Traffic Distribution Prediction If sites are evenly located during networkconstruction, then areas with a heavy call trafficmay have insufficient capacity, while areas with alow call traffic may have redundant resources.This affects investment result and network QoS.To solve this problem, we must predict andinvestigate traffice density and distribution. Theprediction result shall be used as the basis toplan BTS location and frequency multiplexingmethods.



Traffic Distribution Prediction Methods

In the early phase, we can predict thegeographical distribution of traffic needsaccording to statistical data such aspopulation distribution, income level, vehicleusage in different locations, and call terminalusage in different places;

Refer to data of an existig network in thesame region;

After the network is constructed, we canobtain a comprehensive report on the trafficdistribution of the network from the OMC,which can be referred to during network

optimization and capacity expansion.

Traffic density prediction methods

Percentage allocation

Linear prediction

Linear prediction plus manual adjustment





Example: Percentage allocation

Divide the service area into the high density areas, medium density areasand low density areas (such as city center, common urban areas andsuburban areas).

Determine the percentage of subscribers in each area against the totalpredicted subscribers.

Calculate the number of subscribers in an area based on the percentage

allocated to the area and the total predicted subscribers. Calculate subscriber density according to the size of this area.

DU

MU

SU

RU

Road



Contents


Capacity Planning





Capacity Prediction

1Traffic distribution

analysis

2Determine Site Type

and Configuration

3 4Determine Site

Quantity

5Determine Site

Locations

Capacity Planning-Basic Policies

Basis for Capacity Planning Correct prediction of subscriber capacity and distribution in the

planned area

Traffic model for voice and data services

Available frequency band resources, and selection of the adequate

frequency multiplexing method Ability to configure wireless system products

Wireless environment and subscriber distribution features in theplanned area; site configuration for different areas

Capacity Planning-Basic Policies



System Capacity How much Erlang, or how many subscribers?

The number of subscribers in each phase, or percentage of subscribers?

The system should have 10-20% redundant capacity.

Capacity assignment of each city Given by the operator

Check the population of each city, distributedaccording to percentage+weight. Reference

site:www.world-gazetteer.com Refer to subscriber distribution of an existing network

Capacity Planning-Capacity Needs Analysis

http://www.world-gazetteer.com/






Capacity Planning-Traffic Model Analysis

Voice Service Traffic Model Traffic per user on busy hour;

GOS；

HR/FR；

Data service trafic model User penetration rate of data services;

Concurrent user activation rate of data service;

Data service rate per user on busy hour (bps) or data throughput per user on busy hour (KB)



Frequency Resource Total Frequency Bands and

Frequency Points

Frequency Multiplexing 4*3 and aboveBCCH and the

minimum multiplexing coefficient tobe satisfied

3*3

1*3

1*1 Use of DFCA/GPS

synchronization technologies Needs system simulation support

Calculate:

What is the largest BTS supported by 8 MHz?

How about SDR devices (6M+2M)?

Capacity planning—Frequency resource andcalculation of the largest BTS



Estimate the BTS type and capacity according to frequeency resources and frequency multiplexing methods; the

number of BTSs needed can be calculated by the total traffic divided by the maximum capacity of the BTS Give the amount of BTSs in different areas for different phases of the network

Give the number of channels configured in a cell/BTS (service channels and control channels), and the traffic

and number of subscribers they provide

Give the total capacity provided by all BTSs, namely, total capacity of the network.

Start

Frequency Resources

Capacity of a Single Cell

Single BTS CapacityBTS Type and Quantity

FrequencyMultiplexing Method

Largest BTS Type

ChannelPlanning/Data

Services

Erlang-B Table

Traffic Model

BTS Type Configuration

Total Traffic andDistribution Percentage

Network Scale Coverage Planning

Capacity planning—Calculation of BTSquantity



Coverage

Planning

Capacity

PlanningNetwork

Scale

Capacity Planning

Capacity planning is the

preliminary planning.After wireless coverage planning and

analysis, the number of BTSs

may be added or subtracted,

and BTS type configuration may

also need to change.

Network planning is a process

that needs repeated rectification

and improvement. The number

of BTSs and BTS type in thenetwork should be determined

according to coverage effects

and network capacity.



Calculation Methods for Capacity Planning - Capacity Restricted Area

Based on frequency resources and frequency multiplexing mode,

estimate the largest BTS type for different areas;

Based on the traffic model and the Erlang B table, obtain thecapacity of each BTS

Divide the total traffic by the BTS capacity to obtain the number of BTSs needed

Calculation Methods for Capacity Planning - Coverage Restricted Area

For areas of different types, divide the area size by the BTS coveredarea (estimated value) to obtain the number of BTSs needed tocover the specific area.

Multiply the area covered by the cell (estimated value) by thecorresponding traffic density to obtain the target traffic of the cell

Check the Erlang-B table to estimate the number of voice channels

and control channels needed

Add the number of voice channels and control channels together, anddivide the result by 8 to obtain the number of carriers needed by theBTS cell.

Capacity Planning



Contents


Capacity Planning





CCCH, BCCH Each cell is assigned one BCCH

Dual frequency network Co-BCCH

SDCCH

SDCCH Structure

SDCCH Traffic Model

TCH

HR/FR PDCH

Channel Configuration



CCCH Structure

The CCCH contains the AGCH, PCH and RACH; The uplink channel sends channel request messages,

and the downlink channel sends access grant andpaging messages;

CCCH Configuration Type

CCCH ConfigurationNumber of CCCH message

chunks in a BCCH multi-frame

One basic physical channel used by CCCH in combination with

SDCCH3

One basic physical channel used by CCCH, not in combination

with SDCCH9

Two basic physical channels used by CCCH, not in combination

with SDCCH18




SDCCH Structure

Combined Channel

BCCH＋CCCH＋SDCCH/4（TS0）

Non-combined (Independent) Channel:

BCCH+CCCH (TS0)+ X*SDCCH/8

(Timeslots 1-7 for BCCH carrier, or any timeslot for other carriers)

Grade of Service of SDCCH

The GoS of SDCCH/8 is one quarter of the GoS of TCH

The GoS of SDCCH/4 is half of the GoS of TCH




Major Bearer Services of SDCCH

Location update, periodical location update

IMSI attach/detatch

Call establishment

SMS Facsimile and supplementary services




Recommended CCCH and SDCCH Configurations

Number of

Carrier s

Channel

quantity

CCCH Number of

SDCCHs

Number of

TCHs

Capacity(Erlang)

Channel Structure GoS=2%

1 8 (1BCCH+9CCCH)+SDCCH/8 1 6 2.28

2 16 (1BCCH+9CCCH)+SDCCH/8 1 14 8.2

3 24 (1BCCH+9CCCH)+2*SDCCH/8 2 21 14.9

4 32 (1BCCH+9CCCH)+2*SDCCH/8 2 29 22

5 40 (1BCCH+9CCCH)+2*SDCCH/8 2 37 28

6 48 (1BCCH+9CCCH)+2*SDCCH/8 2 45 35.5

7 56 (1BCCH+9CCCH)+3*SDCCH/8 3 52 42.12

8 64 (1BCCH+9CCCH)+3*SDCCH/8 3 60 49.64





TCH Half Rate Channel Open Percentage

HR channel open percentage=number of FR channels that areconverted to HR channels/total FR channels before HR channels areopen

HR channel open percentage=total open HR channels /total channels(HR+FR) after HR channels are open

After opening certain percentage of HR channels (such as 60%),signaling load on the system may increase. To solve this problem, youmay need to increase the number of SDCCHs.

Number of TCHs for voice services Number of TCHs=Number of TRX carriers ×8-BCCH quantity-SDCCH

quantity

Number of TCHs after opening data services Number of TCHs=Number of TRX carriers ×8-BCCH quantity-SDCCH

quantity-static DPCH quantity



PDCH

Assign dynamic PDCHs and static PDCHs

Parameter Option Unit

Number of voice subscribers in a cell A

User penetration rate of dataservices

B

Concurrent user activation rate of data services

C

Number of data subscribers per cellon busy hour

D=A*B*C

Average data service rate per user on busy hour

E bps

Average data service rate per cell onbusy hour

F=D*E/1000 kbps

iEffective rate of the IP layer for thewireless coding interface

G kbps

iCode percentage H

Average bearer rate per IP layer channel for each PDCH层 I=SUMi(G*H) i=CS1～CS4,MCS1～MCS9 kbps

Total PDCHs needed per cellPDCH J=F/I

$




Contents


Capacity Planning





Location Area Overview

The entire GSM network is divided intodifferent service areas according to differentlocation area codes.

One location area may include one or moreBSCs, but it belongs to only one MSC; One

BSC or MSC may include multiple locationareas.

The location area is the basic unit in thepaging range of the GSM system. The pagingmessages of a mobile subscriber are sent in

all the cells of a location area The general principle of location area

planning is to reduce the location updatetimes to the minimum while ensuring a lowpaging load.

Location Area Planning



For an existing

network, calculate

according to the

background statistical

data! LAC Capacity Calculation Example:For a new network, based on the following assumptions of the traffic model:

1. Average call last time: 60 seconds, namely 1/60Erl

2. 【Times of MS being called successfully (resulting in paging and generating TCHtraffic)+ paging times generated by short messages】/【total paging times+short

message paging times】*100%: 30%. 3. Suppose 75% of the MSs respond during the first paging, and 25% of the MSs

respond during the second paging. Then an MS can be successfully called after itis paged 1.25 times.

4. Suppose the paging channel is congested after the paging traffic is 50% more thanthe maximum allowed traffic, i.e., if no paging message will be lost before the

paging traffic reaches 150% of the maximum allowed traffic. Please calculate: What is the theoretically allowed traffic of a location areawhen the IMSI paging mechanism is used, AGB=2, and the non-combinedBCCH is used? What would be the result if the IMSI paging mechanism isused, AGB=1, and the combined BCCH is used? What would be the resultif the TMSI paging mechanism is used?





Tips: 1 frame=4.615 ms, 1 multi-frame=51 frames=0.2354 s. Suppose thenumber of allowed reserved chunks for access grant is AGB, then thenumber of paged chunks per second can be calculated using thefollowing formula:

For non-combined BCCH: number of paged chunks per second =(9-AGB)/0.2354 (paged chunks/second)

For combined BCCH: number of paged chunks per second = (3- AGB)/0.2354 (paged chunks/second)

Maximum times of sending chunks per second (P) can be calculatedusing the following formula:

For non-combined BCCH: P = (9-AGB)/0.2354 (pagedchunks/second)× X (paging times/paged chunks)

For combined BCCH: P = (3-AGB)/0.2354 (pagedchunks/second)× X (paging times/paged chunks)



Contents


Capacity Planning






Necessity of Capacity Planning Adjustment Change of subscriber behavior

Non-linear affects of channel configuration

The traffic model for different phases of network constructionshould be analyzed and predicted periodically

In case of traffic congestion, the traffic model should be modified,taking into the consideration the traffic to be added in order to solvethe congestion.



Capacity Increase Methods Cell splitting

Use denser frequency multiplexing

Add micro-cellular devices

Expand the frequency band Use half-rate channels

900M

900M Lower-level subcell

Upper-level subcell

IntraCell Handover




Review questions

Question 1:

The geographical area of a city is 1436.4 Km^2, and thearea to be covered occupies 5% of the geographical area,which all belongs to the MU. The population of the city isabout 59,000, with a user penetration rate of 60%(MU).The operator can use 6 MHz radio frequencies. Please listthe network scale estimation process. The parametersmay be reasonably assumed according to common ZTEequipments.

Question 2:Please give several capacity increase methods, and listpossible difficulties that may be encountered in thecapacity increase process.

go np11 e1 1 gsm capacity planning-39(old)

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