CAPACITY PLANNING

Network Planning Objectives

Maximise Capacity– Satisfy traffic demand– Maximise service quality– Within available frequency

spectrum

Coverage-limited

Capacity-limited

carrierssite

= =⋅total no. carriers

cluster size

carriersbandwidth

bandwidth

cluster size

BaseStationdensity

Frequencyreuse

Averagechannel utilization

TDMA slotsper

carrier

Spectrumfor

operator

Channelspacing

CapacityCapacitytrafficarea

trafficchannel

channelscarrier

sitesarea

= ⋅ ⋅ ⋅carriers

site

trafficarea

trafficchannel

channelscarrier

carriersbandwidth

1cluster size

bandwidth sitesarea

= ⋅ ⋅ ⋅ ⋅ ⋅

Overview of Capacity Enhancement Methods

Channel Utilisation

Question:– For a given number of channels, how many Erlang of traffic

can be “pushed” through?

Dedicated channel:– Possible for one user to occupy one channel for one hour

can carry 1 Erlang for that hour

Channels shared between users– 100 % utilisation impossible when a certain grade of service

(blocking probability) / maximum transmit delay have to be guaranteed

Traffic Theory

Traffic– A process of events related to demands for the utilization of

resources in a telecommunication network.

Erlang – The unit of traffic– One Erlang traffic means continously holding time on a circuit for

specific time.

No.1

No. 29.00 9.30 10.00

1 hour

Call Originated Call Terminated

THTA

Traffic Theory

Call– A generic term related to the establishment, utilization

and release of a connection.

Mean time between call attempts, TA– reciprocal of mean call arrival rate λ

Mean Holding time, TH– reciprocal of mean call termination rate μ

Traffic Theory

Define λ [1/s] mean call arrival rateμ[1/s] mean call termination rate (1/μ[s] = mean call duration)

Offered traffic (traffic demand) is given byA[Erlang] = λ [1/s] / μ[1/s]

= mean call duration * no. of call attemps / time period

Channel

1

2

3

4

5

6

Record Period Record Period

Scanning IntervalScanning Interval

1 2 3

4 5

6 7

8

9 10 11

12 13 14

Traffic Measurement

-restricted by acceptable blocking rates-mainly use Erlang B to calculate -Erlang B assumptions are:*amount of subscr. (independent traffic sources) is very large which means a constant flow of required connections

*time to the next call arrival is exponential distributed*busy-time is exponential distributed

circuit switched channel

packet switched channel

-restricted by acceptable packet delay-mainly use Erlang C to calculate -Erlang C assumptions are additionally:*amount of queuing states are not limited*First-In, First-out-principle

Circuit and Packet Switched Systems

Circuit switched systems

Packet switched systems

GOS,BTraffic offered Traffic carried

Traffic lost

Traffic carried = Traffic offered - Traffic lost

Circuit Switched System

Blocking System– Probability that a call will be lost due to congestion– Erlang-B formula– Example: Speech channels on GSM

Erlang-B formula

Blocking systems– users experiencing blocked calls are not willing to wait and

give up the call attempt immediately.

– Often use lookup table

∑=

= N

i

i

N

iA

NA

B

0 !

! B: Blocking rateA: Traffic demandN: No. of circuits

Traffic Theory

Erlang-B formula– Applications:

No. of circuits N (TCH, SDCCH, TRX per cell, BTS )needed to support a traffic offered, given a maximum blocking rate B?No. of subscribers that can be supported by network with N circuits, given maximum blocking rate B?Mean blocking rate B for a given traffic load and configuration

1% 2% 3% 5%1 0.01 0.02 0.03 0.052 0.15 0.22 0.28 0.383 0.46 0.60 0.72 0.904 0.87 1.09 1.26 1.525 1.36 1.66 1.88 2.226 1.91 2.28 2.54 2.967 2.50 2.94 3.25 3.748 3.13 3.63 3.99 4.549 3.78 4.34 4.75 5.3710 4.46 5.08 5.53 6.2211 5.16 5.84 6.33 7.0812 5.88 6.61 7.14 7.9513 6.61 7.40 7.97 8.8314 7.35 8.20 8.80 9.7315 8.11 9.01 9.65 10.6316 8.88 9.83 10.51 11.5417 9.65 10.66 11.37 12.4618 10.44 11.49 12.24 13.3819 11.23 12.33 13.11 14.3120 12.03 13.18 14.00 15.25

N Blocking rateErlangs

1% 2% 3% 5%21 12.84 14.04 14.89 16.1922 13.65 14.90 15.78 17.1323 14.47 15.76 16.68 18.0824 15.30 16.63 17.58 19.0325 16.13 17.50 18.48 19.9926 16.96 18.38 19.39 20.9427 17.80 19.26 20.30 21.9028 18.64 20.15 21.22 22.8729 19.49 21.04 22.14 23.8330 20.34 21.93 23.06 24.8031 21.20 22.80 23.99 25.7732 22.10 23.70 24.91 26.7533 22.90 24.60 25.84 27.7234 23.80 25.50 26.77 28.7035 24.60 26.40 27.71 29.6836 25.50 27.30 28.64 30.6637 26.40 28.30 29.58 31.6438 27.30 29.20 30.51 32.6339 28.10 30.10 31.45 33.6140 29.00 31.00 32.39 34.60

Blocking rateErlangs

N

Erlang B Table

0

0.2

0.4

0.6

0.8

1

1.21 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97

Number of channels N

Rel

ativ

e tra

ffic

load

A/N

B = 2%B = 3%B = 5%

Erlang B - Trunking Gain

Ak x N > k x AN– omni vs. sectorised sites

Traffic Theory

Typical GSM Networks Dimensioning– Grade of Service (GOS)

Air interface (Um) 2 % blockingAsub interface 0.1 % blockingOthers 0.01 % blocking

– Erlang per SubscriberTCH 25 mErlangSDCCH 4 mErlang

Typical values for CLL– Air interface (Um):

1 % blocking75 mErl per subscriber

Sec TRX Off. Traf. Week1 Week2 Week3 Week4 Week5 Week6 Week7BTS1 1 3 14.9 10.53 9.66 10.21 9.88 10.54 9.97 10.37BTS2 2 2 8.2 7.43 7.26 7.59 6.98 7.55 8.02 8.33BTS3 3 3 14.9 11.92 11.4 12.12 11.82 11.75 12.02 12.15

Traffic Measurement

3 sector site with 3+2+3 configuration– 3 TRX ⇒ 22 TCH– 2 TRX ⇒ 14 TCH– decide acceptable GOS and apply Erlang B table ⇒

offered traffic per cell

Compare offered traffic with measurement– check for congested cells

BHCA per MS 1.10Call Characteristic

MOC 58.0%successful 65.8%

mean time for ringing (MOC) 15 sbusy 19.8%

duration of TCH occupation (busy) 3 sunanswered 14.4%

mean TCH occupation (unanswered) 30 sMTC 42.0%

successful 54.0%mean time for ringing (MTC) 5 s

unanswered 13.0%mean TCH occupation (unanswered) 30 s

no paging response 32.5%mean call duration (MOC / MTC) 115 s

Traffic Model Example

TCH channel

– mean TCH occupation per BHCA: 83 s

– traffic per subscriber: 25 m Erl

SDCCH channel

– SDCCH traffic per subscriber: 4 m Erl

Location Update (LUPD) 2.20time for a location update 5 s

time for MOC / MTC setup signaling - SDCCH 3 s

Dynamic Traffic Data

Data related to mobility– Handover rates– Location update rates– IMSI attach / detach per MS

when a mobile station is switched on / off

Directed Retry

Requests

Spectrum Resources

Requests

Resources

Handover due to Traffic Load/

Directed Retry

Redistribution oftraffic following the network structure

Redistribution of network resources following the

actual traffic distribution

Dynamic Channel Allocation/Dynamic Resources Allocation

Adaptation to load variations

Directed Retry

Handover(Out)

Handover(In)

Call Setup

Call End

Handover due toTraffic Load

AccessBarring

DirectedRetry

Handover regardingTraffic Load

ForcedRelease

Methods for Load Regulation

Packet Switched System

Queuing System– Unsuccessful call

attempts are queued and re-fed into the system as soon as channel becomes idle

– Erlang-C formula (only an approximation)

GOS,BTraffic offered Traffic carried

Queue

– Example: GPRSfor bursty traffic Erlang C is not valid

Important parameters for queueing systems

– throughput (mean, peak) – delay (mean, 95

percentile)

Channel Configurations

Number of TDMA slots per carrier

– System dependent– For GSM there are 8 TS

per carrier– Some must be allocated

to signalingExamples

– 1 TRX1 TS for signaling (incl. 4 SDCCH channels)7 TS for TCH

– 2 TRX’s: Option 1:1 TS for signaling

(incl. 4 SDCCH channels)15 TS for TCH

– 2 TRX’s: Option 2:2 TS for signaling (incl. 8 SDCCH channels)14 TS for TCH

– Option 2 is normally recommended (SDCCH congestion)

TRX 1TRX 2

TRX 1TRX 2

TS 0 - 7

TS 0 - 7TS 0 - 7Control channel

Time Organisation of TCH

Full rate channels

Half rate channels

Time Organisation of Control Channels

“Large base station”– separate 51 multiframe

structures for broadcast / common signalling channelsdedicated signalling channels

“Large Base station”Broadcast / common signalling channel structure

“Small base station”– only one 51 multiframe– all broadcast / common

signalling channels combined

Time Organisation of Control Channels

12

12

12

12

“Large Base station”Dedicated signalling channel structure

“Small Base station”Broadcast / common and dedicated signalling channels combined

Typical Configurations

Assumptions– TCH Blocking: 2% GoS (Erlang-B formula)– Traffic per subscriber: 25 mErl

– PS! Blocking on control channels should be checked

TRXs per cell Traffic channels Signaling channels Cell capacity (Erl) Subscr. supported1 7 1 2.935 1172 14 2 8.2 3283 22 2 14.896 5964 30 2 21.932 8775 37 3 28.253 1,1306 45 3 35.607 1,424

Half Rate Channels

2 TCH/H

Multiplexing of2 Traffic Channels on1 TDMA time slot

1 TCH/F

With half rate more TCH are available → more capacity

– Advantages:No additional sites / frequencies requiredMinimum investment for infrastructure upgrade

– Disadvantage:Speech quality degradation (reduction of speech bit rate from 13 kb/s to 6.5 kb/s)

- Especially mobile-to-mobile calls– Gain depends on ratio full rate users / half rate users / data

traffic

Static Split of 15 TCHs

Pool of 10 TCH/F

Pool of 10 TCH/H

Dynamic Split of TCHseach TCH slot can be used as• 1 TCH/F or• 2 TCH/H on demand.

H = 50% HR Requests H = 75% HR RequestsCapacity Gain [%] ~H/(200-H)

7 14 29 7 14 29

Gai

n [%

]

TCH Slots

35 36 36

7772 69

R

D

G

R

Dense Packing at Assignment

Regrouping

AssignmentStrategies

Random Assignment(only for comparison)

13

13

13 D G

Half Rate Channels

Channel Spacing

System dependent– for GSM channel spacing is 200 kHz– depends on modulation technique– fundamental to GSM → not affected by network planning

However,– due to adjacent channel interference adjacent channels

may not be reused within a given cell– channel spacing affects frequency reuse and hence

maximum capacity

CH1 CH2 CH3 ..... 124

200 KHz

13

42 1

342

13

42

13

42

13

42

K=4

15

43

67

2

15

43

67

2

15

43

67

2

15

43

67

2

K=7

15

43

67

28

910

1112 1

543

67

28

910

1112

15

43

67

28 9

10 1112

K=12

Frequency Reuse

Frequency re-use pattern (cluster)– determines how often frequencies can be reused– e.g. reuse pattern (cluster size) 4 means the same

frequency can be reused every 4 cells– reuse pattern depends on frequency planning (see later)– max. number of TRX’s per cell = allocated carriers / cluster

size

See frequency planning course

GSM Frequency Bands

CH1 CH2 CH3 ..... 124E-GSM

200 KHz

CH1 CH2 CH3 ..... 124E-GSM

Duplex distance 45 MHz

Uplink Downlink

GSM / E-GSM 8TDM35 MHz

• 175 carriers available (124 for Basic GSM)• typical allocation 24-60 carriers per operator

Frequency Spectrum

DCS 1800

1 2 3 ..... 374

200 KHz

1 2 3 ..... 374

Duplex distance 95 MHz

Uplink Downlink

8TDM75 MHz

• 375 carrier available ,typical allocation 50-125 carriers per operator

1710 1785 1805 1880 MHz

GSM Frequency Bands

Allocated spectrum has impact on network infrastructure for capacity limited networks

– max. number of TRX’s per cell = allocated carriers / cluster size

Example

15

43

67

28

910

1112 1

543

67

28

910

1112

15

43

67

28 9

101112

K=12Frequency reuse 122 x 10 MHz spectrum allocation⇒ 50 channels availableMax TRX’s per cell = 50 / 12 ≈

4

If this does not satisfy capacity requirement⇒ cell splitting⇒ reduce frequency reuse⇒ other capacity enhancing methods

Coverage-limited part

Capacity-limited part

Base Station Density

Theoretically capacity can be increased indefinitely by increasing the site densityLimitations

– Handover problems may occur as the cell sizes become too small

too fast handovershigh signallingload

– Interference through street canyons

8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl

8.2 Erl 2.9 Erl

2.9 Erl

2.9 Erl

2.9 Erl

2.9 Erl

2.9 Erl

2.9 Erl

2.9 Erl

Small Cell Network

Cell splitting– add sites between existing sites – reduce coverage of existing sites– result: small cell network with high capacity

Alternative: HCS

Capacity proportional to number of sites

Macro- CellMacro- CellMicroMicro

Macro- CellMacro- CellMicroMicro

HCS for Additional Capacity

Microcells for hot spots only

Microcell layer provides continuous coverage

Example: Data traffic on

lower layer

Umbrella Cell GSM900Radio Coverage Layer 4

Macro Cell GSM900Radio Coverage Layer 3

Micro Cell GSM900Radio Coverage Layer 2

Pico Cell GSM900Radio Coverage Layer 1

Hierarchical Network Structures

Why HCS?– existing network is at capacity limit– macro site locations difficult to obtain– uncovered high capacity spots in existing network

Umbrella Cell GSM900Radio Coverage Layer 5

Macro Cell GSM900Radio Coverage Layer 4

Small Cell GSM900Radio Coverage Layer 3

Micro Cell GSM900Radio Coverage Layer 2

Pico Cell GSM900Radio Coverage Layer 1

Priority Layer

5

4

3

2

1

Better Cell Handover

Forced Handover Handover due to layer

Traffic Management Example

Aim: Push traffic to lower layers– higher layers used when

no coverage on lower levelsmobile is moving fast (speed sensitive)

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

GSMBTS

DCSBTS

DCSBTS

DCSBTS

DCSBTS

GSMBSC

GSMBSCDualband

BSCDualband

BSC

MSCMSC

HO

Typically urban areas Typically rural areasHO

Multiband Operation

Network architecture (HO between GSM and DCS)

Site-to-site distance in capacity driven GSM900 networks ranging 300- 800m

contiguous GSM1800 coverage easily built-up by GSM900 site sharing

Contiguous GSM1800 coverage in congested central business areas

smooth expansion for medium and long term capacity demandsmobiles remain served by their proper layer substantially reduced signaling load compared to hot spot coveragecapacity gain

GSM900 layer

GSM1800 layer

Coverage drivenInter-band HOs

OccasionalInter-band HOs

GSM900 layer

GSM1800 hot spots

Coverage drivenInter-band HOs

Capacity drivenInter-band HOs

Hot spot coverage by GSM1800 only short term capacity relief higher signaling load due to inter-band HOs (and potential location updates) at GSM1800 cell borderscapacity loss

Issues and Options for Macro Cells

HSCSD

Higher circuit switched data rates provided over the air interface

– increased data rates over TS possible

9.6 kbit/s → 14.4 kbit/s– combine timeslots, e.g.

– up to 64 kbit/s circuit switched data possible

Reduced coding redundancy⇒ less robust against noise / interference

Timeslots belonging to the same connection

Tx

Rx

Tx / Rx from MS

Tx

Rx

Tx

Rx

Tx

Rx

Frequency hopping⇒ improved quality

HSCSD Coding Schemes

Coding schemes for different data channel types

Higher data rates– less coding redundancy– channel more vulnerable to interference / noise

TCH/F14.4 TCH/F9.6 TCH/F4.8Radio interface rate 14.5 kbit/s 12.0 kbit/s 6.0 kbit/sUser bits in data frame 290 60 60Data frame duration 20 ms 5 ms 10 msData frames in block 1 4 2Block code 4 tail bits 4 tail bits 16 tail bits per data

frameConvolutional enconding rate 1/2 1/2 1/3Puncturing 132 bits 32 bits -Interleaving 4x(114 bits over 19

bursts), diagonalas TCH/F14.4 as TCH/F9.6

“Raw bit rate over radio channel: 22.8 kbit/s

HSCSD Services

Bearer services– asynchronous– synchronous– dedicated PAD access– dedicated packed

accessTransparent / non-transparent

– transparentconstant data rate

– non-transparentlayer 2 protocol →retransmission of invalid data framesnon-constant data rate

Multislot classes recognised by HSCSDMultislotclass

Maximum number of slots

Rx Tx Sum1 1 1 22 2 1 33 2 2 34 3 1 45 2 2 46 3 2 47 3 3 48 4 1 59 3 2 510 4 2 511 4 3 512 4 4 513 3 3 NA14 4 4 NA15 5 5 NA16 6 6 NA17 7 7 NA18 8 8 NA

Condition: 1 ≤

Rx+Tx ≤

Sum

HSCSD Traffic Engineering

Circuit switching ⇒ use Erlang B formulaProblem

– how to define Erlang with various types of multi-slot connections?

Multi-slot Erlangs– specification of traffic type required when discussing

Erlangs

Voice / 1 Erlang

2 TS HSCSD / 1 Erlang

3 TS HSCSD / 1 Erlang

HSCSD Traffic Engineering

Increased blocking probability with multislotconnections

Calculating blocking rates– using lookup table impractical – tools needed for calculations

X

Occupied TS

Single TSconnection Multi-slot

connection

Blocked• Increased blocking• Increased handover failuresfor multi-slot connections

HSCSD Traffic Engineering

Examples of blocking rates– each case - same number of mean occupied TS

– with multi-slot traffic blocking increases for all traffic types

Example 1 Example 2 Example 3 Example 4Traffic 1 TS (Erl) 15 7 7 7Traffic 2 TS (Erl) - 2 2 2Traffic 4 TS (Erl) - 1 1 1Mean occupied nb. of TS 15 15 15 15Available TS 22 22 24 30Blocking for 1 TS traffic 2.11% 3.14% 1.93% 0.34%Blocking for 2 TS traffic - 6.95% 4.36% 0.81%Blocking for 4 TS traffic - 16.80% 11.01% 2.29%

HSCSD Traffic Engineering

Examples of blocking rates– effect of increasing TRX’s

– trunking effects ⇒ impact of multi-slot connections increases dramatically with less TRX’s

– preferable to keep HSCSD traffic on the macrocell layer allocate more TRX’s

7 TS 7 TS 22 TS 22 TSTraffic 1 TS (Erl) 2.93 2.34 14.9 11.92Blocking for 1 TS traffic 2.00% 2.99% 2.00 2.57%Traffic 3 TS (Erl) - 0.20 - 0.99Blocking for 3 TS traffic - 17.57% - 10.34%

GPRS

General Packet Radio Service

– packet switching in general better suited for data communications

– improve spectral efficiency - many users can share channel

As with HSCSD, higher data rates are offered by– enhanced coding schemes– time slot combining

packet switched channel

PCUPCU

GPRS Logical Architecture

CS1 (Note 1) CS2 CS3 CS4Information bits in data block 181+3 (USF) 268+3 (USF) 312+3 (USF) 428+3(USF)Data rate (kbit/s) 9.05 13.4 15.6 21.4USF precoding (Note 2) (bits) - 6 6 12Parity 40 (FIRE code) 16 16 16Tail 4 4 4 -Block coded bits 228 294 338 456Conv. encoding rate 1/2 1/2 1/2 -Puncturing (bits) - 132 220 -Interleaving, burst mapping (Note 3) as for SACCH as for SACCH as for SACCH as for SACCHNote 1 Coding for CS1 is the same as for SACCHNote 2 See belowNote 3 Interleaving and burst mapping on SACCH results in a block of 456 coded bits distributed over four

subsequent bursts

GPRS Coding Schemes

Four coding schemes defined by ETSI:

Higher data rates– less coding redundancy– channel more vulnerable to interference / noise

“Raw bit rate over radio channel: 22.8 kbit/s

9.05 kBit/s13.4 kBit/s15.6 kBit/s21.4 kBit/s

CS1 (highest reliability)

CS2CS3CS4 (no error correction)

Data transfer rates per TS: Traffic Channel-Combining:1 TS2 TS

:8 TS

Bit Rates for the MS

Depend on

Notes– all bit rates are gross bit rates – for signalling and some implementations for data transfers

CS1 is used– in general a mixture of CS types will be used

therefore the max bit rate of 171.2 kbit/s is only valid in theory

CS1 guarantees connectivity under all conditions (signalling and start of data)CS2 enhances the capacity and may be utilised during the data transfer phaseCS3/CS4 will bring the highest speed but require significant Abis interface changes

CS1 guarantees connectivity under all conditions (signalling and start of data)CS2 enhances the capacity and may be utilised during the data transfer phaseCS3/CS4 will bring the highest speed but require significant Abis interface changes

3dB7dB11dB15dB19dB23dB27dB C/I0

4

8

12

16

20CS 4

CS 3

CS 2

CS 1

used C/I depend on the operator's network

Max

imum

thro

ughp

ut p

er G

PRS

chan

nel

(net

bit

rate

, kbi

t/sec

)

Influence of Interference

4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14TU3

C/I (dB)

LLC

Dat

a R

ate

(kbp

s)

CS1, no FHCS1, ideal FHCS2, no FHCS2, ideal FH

4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14TU50

C/I (dB)

LLC

Dat

a R

ate

(kbp

s)CS1, no FHCS1, ideal FHCS2, no FHCS2, ideal FH

Influence of Interference

Frequency hopping - advantage for– slow moving mobiles– low C/I

Notes - Cell Planning

Block erasure rate (BLER) / throughput– Radio channel determines bit error pattern– C/I and bit error pattern determine BER BLER mapping– Dynamic behaviour of RLC protocol determines BLER -

Throughput mapping

Cell ranges should, under most circumstances, not bean issue for CS1/ CS2

– to be verified on case-by-case basis

As PDTCH are allocated in the BCCH band, CS2 reaches reference performance in ~ 95% of the cell, depending on actual reuse

Services offered by GPRS

Point-to-Point (PTP) – connection-oriented bearer services– connection-less bearer services

Point-to-Multipoint (PTM) bearer services– multicast– IP multicast– group call

GPRS represents a platform for IP and X.25 basedprotocols and applications:

– SMS, E-Mail, HTTP, WAP, video conferencing etc.

Capacity Design for GPRS

Quality of Service parameters def. in terms of

VIP

A PLMN may support only a subset of the possible QoSprofilesMost important parameters

– Throughput (mean, peak) – Delay (mean, 95

percentile)

maximum bit rate

mean bit rate

precedence class

delay class peak throughput class

mean throughput class

reliability class

Analogous to blocking vsoffered traffic for circuit

switching systems

Quality of Service-Parameters

Precedence classes

Precedence PrecedenceName

Interpretation

1 High priority commitments shall be maintained ahead ofprecedence classes 2 and 3.

2 Normal priority commitments shall be maintained ahead ofprecedence class 3.

3 Low priority commitments shall be maintained after precedenceclasses 1 and 2.

Delay (maximum values)SDU size: 128 octets SDU size: 1024 octets

Delay ClassMeanTransferDelay (sec)

95 percentileDelay (sec)

MeanTransferDelay (sec)

95 percentileDelay (sec)

1. (Predictive) < 0.5 < 1.5 < 2 < 72. (Predictive) < 5 < 25 < 15 < 753. (Predictive) < 50 < 250 < 75 < 3754. (Best Effort) Unspecified

Quality of Service

Delay classes

– As a minimum, the PLMN shall support the best effort delay class

the first generation of GPRS equipment will support QoS on „best effort“ basis

Quality of Service-Parameters

Reliability Classes

– Signaling and SMS shall be transferred with reliability class 3

Reliabilityclass

Lost SDUprobability

(a)

DuplicateSDU

probability

Out ofSequence

SDUprobability

CorruptSDU

probability(b)

Example of applicationcharacteristics.

1 10-9 10-9 10-9 10-9 Error sensitive, no errorcorrection capability, limitederror tolerance capability.

2 10-4 10-5 10-5 10-6 Error sensitive, limited errorcorrection capability, gooderror tolerance capability.

3 10-2 10-5 10-5 10-2 Not error sensitive, errorcorrection capability and/orvery good error tolerance

capability.

Peak Throughput Class Peak Throughput in octets per second1 Up to 1 000 (8 kbit/s).2 Up to 2 000 (16 kbit/s).3 Up to 4 000 (32 kbit/s).4 Up to 8 000 (64 kbit/s).5 Up to 16 000 (128 kbit/s).6 Up to 32 000 (256 kbit/s).7 Up to 64 000 (512 kbit/s).8 Up to 128 000 (1 024 kbit/s).9 Up to 256 000 (2 048 kbit/s).

Quality of Service

Peak throughput classes

}GPRS

Quality of Service-Parameters

Mean Throughput ClassesMean Throughput Class Mean Throughput in octets per hour

1 Best effort.2 100 (~0.22 bit/s).3 200 (~0.44 bit/s).4 500 (~1.11 bit/s).5 1 000 (~2.2 bit/s).6 2 000 (~4.4 bit/s).7 5 000 (~11.1 bit/s).8 10 000 (~22 bit/s).9 20 000 (~44 bit/s).

10 50 000 (~111 bit/s).11 100 000 (~0.22 kbit/s).12 200 000 (~0.44 kbit/s).13 500 000 (~1.11 kbit/s).14 1 000 000 (~2.2 kbit/s).15 2 000 000 (~4.4 kbit/s).16 5 000 000 (~11.1 kbit/s).17 10 000 000 (~22 kbit/s).18 20 000 000 (~44 kbit/s).19 50 000 000 (~111 kbit/s).

Erlang C Formula vs. Simulations

Using Erlang C for GPRS-TCH calculation is not always a valid approximation– key assumtions for Erlang C

infinite number of sourcesPoisson-distributed arrivals,exponentially distributed call durations

– experiencein many trials, data traffic has proven to exhibit heavy-tailed or subexponential packet length distributions

Poisson-type traffic theory is unable to describe this type of traffic appropriately ⇒ use simulations

Document size distributions on the internetThink times of human users

“Self-similar” traffic

t

A packet servicei

First packet arrivalto base station buffer

Last packeti lto base station

A packet call

The instants of packet arrivalsto base station

UMTS Packet Traffic Model

Heavy tail propertiesStructure:

– Packet sessionPacket Call

- Pac ket

Slightly adapted to GPRS

Modelling Approach: Sample Session

Bursty traffic

Dimensioning Data - An Example

t

A packet call

PACPACPAC

No PDTCH required in cell

„PacketAllocation Call“

„Packet Allocation Calls“

0

Dimensioning parameters Data volume 12Mbit/h

Bandwidth (Kbps)

Del

ay (s

.)

Mean delay 95%ile delay

0

50

Effi

cien

cy (%

)

Efficiency

0

Packet Channels unallocated Data volume 12Mbit/h

Bandwidth (Kbps)P

roba

bilit

y

Gain from Dynamic Allocation of PDTCH

– Under low and medium traffic conditions, PDTCH are not allocated for a significant percentage of time

Steps for GPRS TCH Calculation

Step 1: Calculate Erlang / subscriber

Step 2: Calculate total offered load

Step 3: Calculate mean holding time for one data packet

Erl/subsGPRS = s 3600

1*rate-data *TCH-GPRS

data

TCH-GPRS

subs .

A = Erl/subsGPRS * subsGPRS

tm = TCH-GPRS

IP

rate-data*TCH-GPRS size-packet

Assume a value for GPRS-TCHand check if it is ok in step 5

Steps for GPRS TCH Calculation

Step 4: Define acceptable delay, t, and probability that this delay is exceeded, P(>t), e.g.

Step 5: Calculate required GPRS-TCH using Erlang-C– if the result is not consistent with assumption in step 1 -

repeat process with new assumed value for GPRS-TCH until consistency is found

In case of mixed GPRS and voice traffic– check blocking probability for voice channels

t = 0.1 sP(>t) = 0.05

GSM 900Channel modelCoding Scheme

TU50/ no FH TU50/ ideal FH HT100/ no FHCS1 0 dB 0 dB 1 dBCS2 4 dB 3 dB 5 dB

GSM 1800Channel modelCoding Scheme

TU50/ no FH TU50/ ideal FH HT100/ no FHCS1 0 dB 0 dB 1 dBCS2 4 dB 4 dB 5 dB

'SC resp. SC 0dB 1dB 2dB 3dB 4dB 5dB

VoiceData RR 1.000 0.938 0.877 0.822 0.770 0.721

Range corrections:

(based on COST 231 Hata propagation model)

Sensitivity corrections:

3dB body loss??

Link Budgets

erlangs 33.2960

1.76 x 1000A ==

Capacity Requirement Analysis

Example I: – Maximum calls per hour, in one cell is 1000 and an average

calling time T is 1.76 min.The blocking probability B is 2 percent.How many radio channels are needed? The offered load A is obtain as

With the blocking probability B=2 percent, the required number of channels can be found from Erlang B formula as N=39 channels per cell.

- 5 TRX’s -> 38 channels- 6 TRX’s -> 45 channels

Erlangs 2.403600

100 x 1451A ==

channels radio 35050x7Nt ==

Capacity Requirement AnalysisExample II:

– The maximum number of calls per hour per cell is 1451. A seven- cell reuse pattern (K=7) is to be used. The required blocking probability B=2 percent and average holding time T=100 s. How many radio channels are needed for the system?

From the Erlang B formula (or table) it is found that the number of channels required is N=50 radio channels per cell.The total number of required radio channels for a K=7 reuse system is

END