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GSM Planning & Engineering.

GSM Reference Model

A

MSMS BTS BSC

Um Abis

MSC HLR

EIR

VLR

AuC

VLROMC

MSC PSTN ISDN

E

FC

B D

G

General Planning ProcessMobility and traffic models

for the considered areaEquipment quantity

(BTS, BSC, MSC, links, ...)

Sites positioning

(radio planning)BTS layout andcharacteristics

Frequency plan

Frequency

allocation

Dimensioning

(Erlang, QoS)

BSS design(site positions and

interconnection network)

NSS, IN, WAP design (equipment positions and interconnection network)

Global network design

interconnection

BSCs and MSCsBTSs and BSCs

interconnection

Interconnection with

other networks

Planning Process• Business Plan• No. of Subscribers• Traffic per subscribers• Subs distribution• GOS• Spectrum availability• Frequency Reuse• Types of coverage• RF parameters• Field strength studies• Available sites• Site survey

• Business Plan• No. of Subscribers• Traffic per subscribers• Subs distribution• GOS• Spectrum availability• Frequency Reuse• Types of coverage• RF parameters• Field strength studies• Available sites• Site survey

CapacityStudies

CapacityStudies

Coverage &C/I study;Search Areas

Coverage &C/I study;Search Areas

• Plan Verification• Quality Check• Update documentation

• Plan Verification• Quality Check• Update documentation

Initial DesignPlan

ImplementationPlan

ImplementationMonitorNetworkMonitorNetwork

Network OptimisationNetwork

Optimisation

• Capacity Studies• Coverage Plan and Coverage Studies• Frequency plans and Interference Studies• Antenna Systems& Orientation Studies• BSS parameter planning• Database and documentation of approved sites• Expansion plans

• Capacity Studies• Coverage Plan and Coverage Studies• Frequency plans and Interference Studies• Antenna Systems& Orientation Studies• BSS parameter planning• Database and documentation of approved sites• Expansion plans

****

****

Acquisition of Sites

Acquisition of Sites

and re-design

GSM PLANNING: THE BASIC PROCESS

1. CAPACITY PLANNING

2. COVERAGE PLANNING

4. EQUIPMENT PLANNING

3. PARAMETER PLANNING

5. OPTIMIZATION.

CELLULAR MOBILE RADIO SYSTEM DESIGN

• Concept of frequency reuse channels• Co-channel interference reduction factor• Desired carrier to interference ratio• Hand off mechanism• Cell splittingNote:Limitation in the system is the frequency

resource

CELLULAR MOBILE RADIO SYSTEM DESIGN

Challenge is to serve the greatest number of customers

1.How many customers can we serve in a busy hour ?

2.How many customers can we take into our system?

3.How many frequency channels do we need?

GSM NETWORK PLANNING PROCESS - I

• Service Area• Estimation of traffic demand• Available frequency resources.• Evolving an optimum coverage scheme

of placing the cells over the entire service area so as to provide complete mobility to the subscribers.

GSM NETWORK PLANNING PROCESS- II

• Traffic demand estimation-Population distribution-Car usage distribution-Income level distribution-Land usage distribution-Telephone usage distribution.

GSM NETWORK PLANNING PROCESS-III

• Estimation of Cell Radius– Service Area

• Terrain conditions• Density of foilage • Man made structures

– Signal level at an unit distance from base station

– Signal strength decay per decade of distance.

GSM NETWORK PLANNING PROCESS-IV

• MOBILE RADIO NETWORK PLANNING SOFTWARE TOOLS– Propagation Predictions based upon various

propagation models e.g OKUMARA- HATA, WALFISCH-IKEGAMI or special external models written by the users

– Interference analysis – Automatic frequency planning – Coverage analysis by contour plots– Comparison with actual radio field measurements– Efficient tool to load,analyze and display system

performance evaluation

Traffic ModelCall Mix for other services• FAX/DATA subscribers - 5% in 40mE cities

and 2% in other cities.• IN subscribers - 70% of total subs

– Prepaid subscribers - 80% of IN subs– Freephone (FPH) - 5% – MVPN - 5%– Premium Rate (PRM) - 5%– Universal Access No. - 5%

Traffic Model

• Voice Mail - 100% of subscribers.• SMSC should be dimensioned for 50% of the

total subscribers with:– 2 messages per subscriber per day– Max. length of SMS message 160 chars.

• WAP subscribers - 10% for high traffic cities and 5% for others with:– 50% on Circuit Switched Data (CSD)– 50% on SMS

Design Parameters

• Grade of Service– MSC-MSC/PSTN - 1%– MSC-BSS - 0.5%– Um interface - 2%– BSC-BTS - 0%

• Handover– Total HO - 50%– Inter MSC - 5%– Inter BSC - 10%– Intra BSC - 85%

Design Parameters

• Location Update– Normal

• Intra MSC (New LAI) - 0.3 nr/sub• Intra MSC (new registration) - 0.18 nr/sub

– Periodic - 0.5 nr/sub– Attach

• Subscribers registered earlier - 0.25 nr/sub• New registration - 0.1 nr/sub

– Detach

GSM Cell Planning Requirement

• Provision of required Capacity

• Optimum use of the available frequency spectrum

• Minimum number of cell sites

• Provision of easy and smooth expansion of the network in future

• Provision of adequate Coverage of the given area, for a minimum specified level of interference

Example : Basic Planning (1/3)• Say the service provider wants to launch his network

with 20 sites or for 10,000 subscribers in a city• The following assumptions are made in the planning process :• 25 mE average traffic per subscriber• Grade of Service 2%

• Mobile to Mobile traffic 10%

• Mobile to PSTN traffic 70%

• Land to Mobile traffic 20%

• Average call duration 90 seconds

Contd..

Example : Basic Planning (1/3) contd….

Traffic capacity of 1 carrier with 7 TCHs = 2.94E(approximately 120 subscribers ); a 1/1/1 site will have capacity of approximately 350 subscribers.

Traffic capacity of 2 carrier with 15 TCHs = 8.2E (approximetly 330 subscribers). A 2/2/2 site will have a capacity of about 990 subscribers.

Example - Basic Planning (2/3)Case 1: For specified number of sites (20)

• 1/1/1 sites (350 subs per site) … 7000 subscribers.

• 2/2/2 sites (990 subs per site) … 19800 subscribers.

Case 2: For specified capacity requirement (10000)

• 1/1/1 sites….10000/350 …. 30 sites.

• 2/2/2 sites….10000/990 …. 11sites.

For 10000 capacity, at 25mE traffic, the total traffic is 250E. We assume a hypothetical distribution of traffic as shown below:

• We may choose 2/2/2 sites for first 3area types and 1/1/1 sites for the rest.

• This makes a total of 18 sites. After customer’s approval,site selection is done.

Example - Basic Planning (3/3)

Area Type % tfc tfc 1/1/1 2/2/2Urban high density 20 50E 6 2

Urban 30 75E 10 3

Industrial 15 37.5E 5 2

Suburban 25 62.5E 7 3

Highways 5 12.5E 2 1Quasi open 5 12.5E 2 1Total 100 250E 32 12

Cell Planning (1/2)• What is the area to be covered ?• How many sites are required for this area ?

(cell radius of 1km means an approximate coverage area of 3 Sq.kms).

• Do we need so many sites? Can some sites be bigger?

• Decide number of sites based on capacity and coverage requirements.

• Divide city into clutter types such as: > Urban> Suburban> Quasi Open> Water.

• Identify “search areas” covering all clutter types.• Customer selects a few sample sites.

Cell Planning (2/2)• Survey sites with reference to

> Clutter heights> Vegetation levels> Obstructions> Sector orientation> Building strength and other Civil requirements

• Prepare Power budgets• Conduct Propagation tests• Calculate coverage probabilities• Verify against predictions and modify planning tool

parameters

• Prepare final coverage map

Cell Planning and C/I issuesAssume all cell are of the same sizeAll cells transmit the same power.

The path loss is not free space and is governed by the attenuation constant .

The reuse distance D and cell radius R are related to the C/I as given below:

(D/R) = 6 (C/I)

The C/I is in absolute value.

SELECTING A PROPER CELLSITE

When a cell site is selected• Determine whether an UHF TV station is

nearby and whether any new ongoing construction would affect the coverage

• Check the local noise level and no spurious signals fall in the freq.band

• Existing multi-antenna tower can be used with proper earthing and shielding

RF LINK DESIGN

Radio link design is one of the most important problem for design engineers

Fundamental parameters:1.Transmitted power2.Co-channel reuse design

In order to provide quality transmission ie.a specified bit error rate (BER) and allowable outage is decided.(outage is defined as the fraction of the service area over which the required transmission quality cannot be maintained within the service area)

CELLULAR CONCEPTS-ESSENTIAL FEATURES

• Frequency reuse-refers to the use of radio channels on the same carrier frequency to cover different areas,which are physically separated from each other sufficiently to ensure that co-channel interference is not objectionable.

• Cell splitting-when the demand for service exceeds the number of channels allocated to a particular cell, cell splitting is used to handle the additional growth in traffic in within the particularcell.Cell splitting involves a revision of cell boundaries, so that the local area formerly regarded as a single cell can now contain a number of smaller cells.These cells are called micro cells.The transmitted power and antenna height of these base stations are correspondingly reduced and the same set of frequencies are reused.

Freq Reuse & C/I Requirement

N D/R= 3N C/I= 10log(1/6(D/R)3.5

3 3.00 8.917 dB

4 3.46 13.29 dB

7 4.58 21.80 dB

9 5.19 25.62 dB

12 6.00 29.99 dB9

CO-CHL INTERFERENCE

DR

A Multi Cell Environment

Frequency Planning AspectsA1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3

1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 2425 26 27 28 29 30 31 32 33 34 35 36

A1A2

A3 B1B2

B3

D1D2

D3 C1C2

C3

Traffic Capacity of Cells

Control CCHNo. of TRX No. of TCH

11 7

22 14

23 22

25mE SUBS SUPPORTED

TFC CAP IN ERLANG*

40mE SUBS SUPPORTED

1182.94 74

3288.20 205

59614.9 373

34 29

35 37

36 45

84021 525

113228.3 708

142435.6 890

* GOS AT 2%

Traffic Capacity of BTS

* GOS AT 2%

No. of TRXBTS CONFGN

No. of CELLS

31-1-1 3

41-1-2 3

51-2-2 3

25mE SUBS SUPPORTED

No. of A-bisTS reqd.

40mE SUBS SUPPORTED

3549 221

56411 353

77413 484

62-2-2 3

72-2-3 3

82-3-3 3

98415 615

125217 783

152019 950

93-3-3 3

103-3-4 3

178821 1118

203223 1270

Traffic Capacity of BTS ..contd..

* GOS AT 2%

No. of TRXBTS CONFGN

No. of CELLS

113-4-4 3

124-4-4 3

134-4-5 3

25mE SUBS SUPPORTED

No. of A-bisTS reqd.

40mE SUBS SUPPORTED

227625 1423

252027 1575

281230 1758

144-5-5 3

155-5-5 3

165-5-6 3

310433 1940

339636 2123

368838 2305

175-6-6 3

186-6-6 3

398040 2488

427242 2670

Traffic Capacity of BTS ..contd..

* GOS AT 2%

No. of TRXBTS CONFGN

No. of CELLS

1Omni 1 1

2Omni 2 1

3Omni 3 1

25mE SUBS SUPPORTED

No. of A-bisTS reqd.

40mE SUBS SUPPORTED

1183 74

3285 205

5967 373

4Omni 4 1

5Omni 5 1

6Omni 6 1

8409 525

113211 708

142413 890

22000/2C 1

2HW 1-1 2

3285 205

2356 147

A-bis Connectivity Types

Multi-drop configurationBSCMSC

Star configuration

BSCMSC

BSC

MSC

Ring configuration

BSC

MSCUrban star configuration

Basic Planning• For 30000 lines @40mE traffic, the total traffic would be 1200E.

Assuming the IMPCS specification for traffic distribution:

TYPE OF AREA % OF TFC

URBAN INDOOR 40%

URBAN INCAR 40%

URBAN OUTDOOR 20%

1/1/1TFC IN ERLANG* 2/2/2

54480 E 20

54480 E 20

27240 E 10

TOTAL 100% 1271200 E 50

6/6/65/5/5

57

57

33

1317

• Decision on choice of BTS type and TRX configuration is very crucial to provide the specified capacity and coverage

Coverage Model

• Indoor Coverage: – Commercial areas, airports, etc

• In-car coverage– Residential areas, industrial areas, roads, all

national/state highways, by-passes and important rail routes, etc.

• Outdoor coverage– Remaining areas of the coverage area.

Coverage Model

HIGH TRAFFIC CITIESCOVERAGE OTHER CITIES

40%INDOOR 25%

40%INCAR 40%

20%OUTDOOR 35%

TRAFFIC DENSITY

SIGNAL LEVEL MEASURED AT STREETCOVERAGE

SHOULD BE BETTER THAN -75 dBmINDOOR

SHOULD BE BETTER THAN -85 dBmINCAR

SHOULD BE BETTER THAN -95 dBm IN 90% OF TOTAL COVERAGE AREAOUTDOOR

SIGNAL LEVEL FOR 95% OF THE TIME FOR THE COVERAGE

Coverage Planning

• Involves designing two aspects of Radio:– Link Budget– Power Balance

• LINK BUDGET brings out whether the uplink or the downlink is the limiting factor for coverage.

• POWER BALANCE ensures that the coverage of DL is equal to that of UL

RADIO LINK ANALYSIS

• ‘Link budget’ or ‘link power budget’ is the totalling of all the gains and losses incurred in operating a communication link.It provides a detailed accounting of three broadly defined items:

1.Apportionment of the resources available to the transmitter and the receiver

2.Sources responsible for the loss of signal power3.Sources of noise

RF LINK BUDGET UL DLTRANSMITTING END MS BTS

Tx RF Output 33 dBm 43 dBmBody Loss -2.0dB 0dBCombiner Loss 0dB 0dBFeeder Loss (@2dB/100m) 0dB 1.5dBConnector Losses 0dB 2dBTx Antenna Gain 0dB 17.5dBEIRP 31dBm (A) 57dBm ( C)

RECEIVING END BTS MS

Rx sensitivity -107 dBm -102 dBm

Rx. Antenna gain 17.5dB 0dBDiversity Gain 3dB 0dBConnector Loss 2dB 0dBFeeder Loss 1.5dB 0dBInterference Degradation Margin 3dB 3dBBody Loss 0dB 3dBDuplexer Loss 0dB 0dBRx Power -121dBm -96dBmFade Margin 4dB 4dBRequired Isotropic Rx .Power -117dBm (B) -92dBm ( D)

Maximum Permissible Path 148dB 149dB

RF LINK BUDGET

Propagation Loss• LFS = 10 log ( 4 d / )2

• LFS = 32.44 +20 log (f )+ 20 log (d)Where f = frequency in MHz

d = distance in Kms

• LFS = Lo + 10 log ( d)

Where is the SLOPE of the attenuation characteristic

BTS

Multipath Environment

Classical Propagation Models

• Basically curve fitting exercises• Okumara• Basically curve fitting exercisesCosat 231 - Hata

(similar to Hata:for 1500-2000Mhz)• Walfisch - Ikegami Cost 231• Walfisch - Xia JTC• XLOS

Okumara ModelThe Okumara tests are valid for :• 150-2000 Mhz• 1-100 Kms• BTS heights of 30 -100 meters• MS antenna height , typically 1.5 m (1-10m)• The results of Okumara tests were graphically represented

PROPAGATION MODELS

• Hata Model • The basic equation for the 150-1000 MHz band is given by• Lp=69.55+ 26.16 log(f) -13.82 log (hbts)-a (hm)

+ {44.9- 6.55log(hbts)} log(d)

Where f=frequency in MHzHbts =BTS antenna height in meters (30-100m)d=distance in Kms (1 to 20 Kms)hm=mobile antenna height in meters (1-10m)a(hm)=correction for mobile height if hm is >1.5 meters

=3.2 [log(11.75hm)-4.97 for Dense urban and ={1.1 log(f)-0.7} hm-{1.56 log (f)-0.8} for Urban areas

Okumara-Hata ModelThe path loss equation can be rewritten as :

•Lp=Lo + {44.9-6.55 log (hbts)} log(d)

• Where Lo=[69.55+26.16 log(f)-13.82 log (hbts)-a(hm)].OR more conveniently

•Lp=Lo +10 log (d) is the SLOPE and is ={44.9-6.55log (hbts)} /10

typically varies from 3.5 to 4 for urban environments.

Calculate the path loss in a BTS site in an Urban environment, given the following parameters

• Frequency : 900 MHz

• Cell radius : 5Kms

• BTS antenna height 30 m• Mobile antenna height 3m.

• Also calculate the Attenuation slope for this site. • Lp =[69.55+26.16 log(f)- 13.82 log (hBTS) -a (hm)]+ [44.9 -6.55 log (hBTS)] log(d).• a(hm) = { 1.1 log (f) -0.7 } hm -{1.56 log (f) -0.8}

26.16 log (f) = 77.28 dB13.82 log (hBTS) = 20.41dB

[44.9-6.55log (hBTS)]log (d) = 24.62 dBa(hm) = 3.81 dB

Path Loss Lp =69.55+77.28 -20.41 +24.62 -3.81 = 147.23dB.Attenuation Slope = [44.9-6.55 log (hBTS )]/10 =35.225/10 =3.5225.

Propagation…Okumara-Hata ModelThe receive signal strength RSS is given by :

RSS = ERP- {Lo +10 log(d)}.

The distance d can be calculated from :

d= 10 [ERP -Lo-RSS]/10

Or, from the equation for RSS,

Log (d) =[ERP-RSS-Lo]/10

ie.., d=antilog [ERP-RSS-Lo)/10 ]

Lo=69.55+26.16 log (f)-13.82 log(hbts)-a(hm).

Example- To Calculate cell radius (d)Calculate the cell radius for a site that has:Frequency : 900 MHz BTS height: 30meters

Mobile height: 3 meters BTS ERP: 55dBm

Expected RSS at the cell boundary (d=R) = -75dBm.

Lo= 122.61 dB; = 3.5 (calculated in the previous example).

122.61 -75+35 log (d) =55 dBm.

log (d) = 7.39/35 =0.2111

Therefore d= antilog (0.2111) =1.62 Kms.

Calculating the Signal Strength• After the terrain has been acquired in the database for the entire

site signal strength calculations can be made on the individual stations

• The propagation model calculates the path loss using the following components.

– Basic Path Loss - Okumura’s Model– Diffraction Effects - Picquenard’s Multiple Knife Edge Diffraction

model – Water Enhancement– Antenna Patterns, Tilt amount, Tilt type– Curvature of the Earth– Morphology

Morphological CategoriesWaterBushesWet Farm landDense Residential AreaHeavy Urban TreesDry Farm LandLight Residential AreaLight UrbanHeavy Urban

Location Area PlanningHLR

MSC/VLR

MSC/VLR

1 location area = several cells

Drive Test Analysis

• Drive test gathers accurate propagation data for candidate site for evaluation and approval.– Uses both Omni-directional and sector antenna.– Radiation center and ERP modeling.– Measurement integration performed to improve modeling

efficiency.

• Based on drive data and prediction, the optimum antenna radiation center, ERP and sector orientation determined.

BSS Parameters setting

• GSM base station parameters setting achieves the following functions

• MS measurement of serving and neighbouring stations• Call set up - Call Processing, Paging, System Access, & Short Message

Service.• Radio functions: DTX, DRX, Frequency Hopping• BTS Radio Resource Management• Mobiles’ uplink Power Control• Timing Advance• Handover - Based on PWRBGT (Power budget), RXLEV, RXQUAL,

distance and intra-cell

Signal Variations

Fast Fading

Slow Fades

Long term average

Distance

RSS

Standard Deviation

Example

The RSS values obtained from a drive test in a BTS area in a city

- 80 dBm , - 79 dBm , - 77 dBm , -82.5 dBm , - 84.35 dB - 78.65 dBm

• Mean RSS “M” = -79.97 dBm

• Standard deviation = 6.068

Confidence Interval

M- 3 M- 2 M- M M+ M+2 M+3

99.72 %

95.44 %

68 %

Probability

• Probability (P) that a random sample of RSS will have a value of - 92dBm or better (ASSUME M=-79 & = 8)

• Compute z =( x-M)/ = -92 -( - 79 )/8 = - 1.625• Refer the standard table for normal distribution curve

we get P=94.74%

• Probability that RSS value would be better than -92 dBm isP (RSS -92 dBm ) = 94.74%

Typical values for building penetration loss

• If the minimum RF signal strength for 90 % coverage on the street is ,say - 92 dBm , then for 75 % in building coverage in a central business area ,we should have a signal level of - 72 dBm on the road;

This shall provide - 92 dBm inside the building.

Area 75% Coverage

50 % Coverage

Central Business area 20 dB 15 dBResidential area 15 dB 12 dBIndustrial area 12 dB 10 dBIn Car 6 to 8 dB