radio network dimensioning for gsm/gprs supporting circuit ... · radio network dimensioned for...
TRANSCRIPT
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 3
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 4
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 5
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 6
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 7
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 8
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 9
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 10
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 11
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 12
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
]
Offered IP traffic [kbit/s]
0 fixed PDCH1 fixed PDCH2 fixed PDCH
0
0.5
1
1.5
2
0 2 4 6 8 10 12D
ownl
ink
IP d
elay
[s]
Offered IP traffic [kbit/s]
downlink IP packet delay
0 fixed PDCH1 fixed PDCH2 fixed PDCH
Peter Stuckmann 2nd Würzburg-Workshop on IP 13
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
)
Offered IP traffic [kbit/s]
downlink PDCHs assigned (average)
0 fixed PDCH1 fixed PDCH2 fixed PDCH
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
0 fixed PDCH1 fixed PDCH2 fixed PDCH
Peter Stuckmann 2nd Würzburg-Workshop on IP 14
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 15
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
]
Offered IP traffic [kbit/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
Peter Stuckmann 2nd Würzburg-Workshop on IP 16
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
Peter Stuckmann 2nd Würzburg-Workshop on IP 17
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)
Peter Stuckmann 2nd Würzburg-Workshop on IP 18
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