gprs dimensionning

Peter Stuckmann

Radio Network Dimensioning for GSM/GPRSSupporting Circuit- and Packet-Switched Services

Peter Stuckmannwww.comnets.rwth-aachen.de/~pst

Peter Stuckmann 2nd Würzburg-Workshop on IP 2

Structure

the problem

coexisting circuit-switched traffic

dimensioning rules for fixed PDCH configurations

dimensioning rules for on-demand PDCH configurations

configurations with fixed and on-demand PDCHs


Motivation

radio network dimensioning demands the relationship between

? offered traffic predicted by operator

? QoS desired by operator for his clients

? radio resources needed (number of PDCHs and TRX)

analytical complexity caused by

? radio channel attributes

? bursty traffic (no Erlang-B-formula like in CS)

system complexity – no test bench or field trials with complete protocolsoftware and hardware components available

solution: computer simulation of the system that models

? system components and their protocols

? traffic sources

? radio channel


Capacity planning and radio network dimensioning

relationship between

? offered traffic

? QoS desired

? radio resources needed

Traffic QoS

Capacity model

Simulation model Analytical model

Erlang table Erlang Formula

Radio network dimensioning


Measures and methodology

term circuit-switched packet-switchedtraffic offered traffic in Erlang offered amount of data per

time in kbit/s

QoS parameter blocking probability (GoS) throughput, delay,...

resources traffic channels packet data channels

tool simple formula or table dimensioning graphs or tables

methodology Erlang-B formula simulation results, analytical / algorithmic techniques


ProcessArrivalSession

ManagementChannel

LLC(SDL)

management)(session

SGSN

CAC

SNDCP

BSSGP

FrameRelayRelay

Frame

BSSGP

BS

LLCRelay

RLC/MAC

(SDL)

Transceiver

SNDCP

LLC(SDL)

MS

(SDL)RLC/MAC

Transceiver

Generator

SMTPHTTP WAPFTP RT Tele-matic

TCP/UDPIP

Generator

GeneratorSwitchedCircuit Internet Load Generator (SDL)

Railway

Funet

Mobitex

Packet

Channel/ErrorModel

bG U m

UplinkbG

DownlinkG b

00.20.30.4

0.60.70.80.9

1

0 10002000 5000 70008000900010000

Bloc

king

Rat

e56 RA Slots24 RA Slots88 RA Slots

0.1

0.5

4000 6000Offered Load [byte/s]30000

0.10.20.30.40.50.60.70.80.9

1

0 0.20.4 0.6 0.8 1 1.2 1.4 1.61.8 2

Railway

Funet

Mobitex

Offered Load (G)

Thro

ughp

ut (S

)

GIST Statistical EvaluationWeb Interface

Simulation Environment (E)GPRSim


Dimensioning rules for fixed-PDCH scenarios (I)

0

5

10

15

20

25

5 10 15 20 25 30

Dow

nlin

k IP

thro

ughp

ut [k

bit/s

]

Offered IP traffic [kbit/s]

downlink IP throughput over offered traffic

3 fixed PDCH4 fixed PDCH5 fixed PDCH6 fixed PDCH

0

5

10

15

20

25

0 1 2 3 4 5 6 7D

ownl

ink

IP th

roug

hput

[kbi

t/s]

Offered IP traffic / PDCH [kbit/s]

Dimensioning Graph

4 fixed PDCH5 fixed PDCH6 fixed PDCH


Dimensioning rules for fixed-PDCH scenarios (II)

define the desired QoS

estimate the number of users per cell

estimate the offered traffic per user

calculate the total offered traffic per cell

determine the acceptable traffic per PDCH with the desired QoS from the dimensioning graph

calculate the needed number of PDCHs

PDCH = estimated offered traffic / acceptable traffic per PDCH


Example

define the desired QoS

? example value: 12.5 kbit/s is desired

estimate the number of users per cell

? example value: 10 users with 540 kbyte/h per user

calculate the offered traffic per user and the offered traffic per cell

? offered traffic per user = 540 kbyte/h = 1.2 kbit/s

? total offered traffic per cell = 12 kbit/s

take the acceptable traffic per PDCH from the reference graph

? acceptable traffic per PDCH = 3.5 kbit/s/PDCH

? PDCH = 3.4

? 4 PDCHs have to be allocated for GPRS


Radio resource management

X

X X X X X X X X

X

maximum number of on-demand PDCHs

TCHs allocatedfor GPRS

TCHs allocated for CS

X X X X X

maximum number of fixed PDCHs

Transition

TCH releaseTCH shift

on-demand assignment of PDCHs for GPRS

voice connections are prioritized


Circuit switched traffic

State probability vs no. of PDCHsState probability vs no. of TCHs for 1TRX

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8

Pro

babi

lity

Number of channels

0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5 6

Pro

babi

lity

Number of channels

radio network dimensioned for voice services with blocking probability of e.g. 1 % (blocking probability = Grade of Service (GoS))

unutilized resources can be used for GPRS


GPRS performance with coexisting CS traffic (I)

downlink IP throughput per user

0

5

10

15

20

25

30

0 2 4 6 8 10 12

Dow

nlin

k IP

thro

ughp

ut [k

bit/s

]



0

0.5

1

1.5

2

0 2 4 6 8 10 12D

ownl

ink

IP d

elay

[s]


downlink IP packet delay



GPRS performance with coexisting CS traffic (II)

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12

Dow

nlin

k P

DC

Hs

assi

gned

(ave

rage

)


downlink PDCHs assigned (average)


0

20

40

60

80

100

0 2 4 6 8 10 12

Dow

nlin

k P

DC

H u

tiliz

atio

n [p

erce

nt]

Offered IP traffic offer [kbit/s]

downlink PDCH utilization



Dimensioning rules for on-demand-PDCH scenarios

simulation results show that the shared use of GSM physical channels both for CS and GPRS makes sense

dimensioning rules for on-demand-PDCH scenarios are needed

the aim is to take an existing TRX scenario as the basis and find the acceptable CS traffic so that the desired GPRS performance can be achieved

if the predicted offered traffic is exceeded a new TRX module should be added to the base station

in the following an example is given for a 3 TRX scenario


Example: 3 TRX scenario (I)

0

5

10

15

20

25

5 10 15 20 25 30

Dow

nlin

k IP

thro

ughp

ut [k

bit/s

]


downlink IP throughput per user

0.5% GoS2% GoS

10% GoS Example values

? offered CS traffic with 1.5 % GoS

? 10 GPRS users per cell

? 540 kbyte/h offered per user

? desired QoS of 12.5 kbit/s


Example: 3 TRX scenario (II)

calculate the offered traffic per cell

? total offered traffic per cell = 10 * 540 byte/h = 12 kbit/s

regard the operating point p defined by the desired user performance on the y-axis and the offered traffic per cell on the x-axis and choose the adequate GoS curve as the next that lies above the operating point

? p = (x = 12 kbit/s, y = 12.5 kbit/s)

if the offered CS traffic corresponding to the GoS is predicted to be exceeded, a new TRX should be added

? the operating point p lies just below the 2 % GoS curve

? coexisting CS traffic up to 2 % GoS is acceptable

? since 1.5 % GoS was assumed an additional TRX is not necessary in this cell


Mixed configurations

to be able to guarantee the availability of GPRS, operators might provide fixed PDCHs and the rest as on-demand PDCHs

in this case simple estimations can be done:

? scenarios with 1,2 or 3 fixed PDCHs: take pure on-demand configurations for dimensioning (probability that the first PDCHs are used by CS is low)

? scenarios with more than 3 fixed PDCHs: take a pure fixed PDCH configuration for dimensioning (probability that the on-demand PDCHs are used by CS is high)


Conclusions

fixed PDCH configurations can be dimensioned with one simple dimensioning graph

on-demand PDCH configurations are recommended, since not all physical channels are highly utilized by CS

dimensioning of on-demand PDCHs can be done by taking dimensioning graphs for the regarded TRX scenario as the basis

for mixed scenarios with both fixed and on-demand PDCHs simple estimations can be done and pure fixed or pure on-demand dimensioning rules can be applied

gprs dimensionning

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