claro network dimension ing ppt
TRANSCRIPT
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(E)GPRS NetworkDimensioning
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CONTENTS
Introduction
Inputs & Outputs Procedure
Summary
Example
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INTRODUCTION
Current GSM networks were design only for speech services:
Simple design (utilizing the ErlangB formula) Do not include dimensioning for PS services
The procedure here presented allows to dimension an (E)GPRS network:
With few and simple input parameters For an average PS load (kbps/cell) Optionally, with guaranteed capacity and/or quality
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INPUTS & OUTPUTS
(E)GPRS NETWORKDIMENSIONING
Without guarantees
With guarantees(optional)
CS load (Erlangs CS)CS blocking allowedPS load (kbps/cell)
Active features (DTX, PC, ...)TSL capability
Average user throughputMinimum user throughputMinimum PS load supported
Number of TRXs
Number of TRXsNumber of dedicated timeslots
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PROCEDURE
Using ErlangB formula
Calculate Erlangs PS and Timeslot capacity in an iterative way. Obtain the minimum number of TRXs needed to support this load.
Calculate the reduction factor (how resources are shared). Evaluate quality indicators (maximum, average andminimum PS load supported, average user throughput, etc).
Guarantee an average and a minimum user throughputs increase the number of TRXs if not achieved. Guarantee a minimum PS load in the cell depends on the number of channels dedicated for PS.
1. CSdimensioning
2. PSdimensioning
3. Calculateperformance
4. Guaranteeingperformance
OPTIONAL(only if operator wants
to guarantee somecapacity or quality)
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SUMMARY
DIMENSIONING CS dimensioninng (Erlang B formula) Calculate PS load (Erlang PS) Timeslot capacity [kbps] Calculate number of TRXs for those loads
PERFORMANCE Calculate Reduction Factor (how PS resources are shared) Evaluate performance:
E.g. Average user throughput = Average timeslot capability x RF x Timeslot capacity
GUARANTEING PERFORMANCE Incrementing the number of TRXs (more traffic can be supported or
the same with better quality) Dedicating timeslots for PS (a minimum capacity is guaranteed)
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EXAMPLE OF DIMENSIONING (1/10)
First phase: without guaranteeing capacity nor quality
EGPRS deployed on hopping layer (number of frequencies 12) CS traffic in busy hour is 5 Erlangs/cell PS traffic in busy hour is 200 kbps/cell CS blocking allowed is 2% Average MS timeslot capability is 3 timeslots DTX and PC for CS features are active
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Timeslot capacity
0
10
20
30
40
50
60
0 2 4 6 8 10 12 14
EFL [%]
TimeslotC
apacity[kbit/s]
Reuse 1/1 (9; 3) Reuse 1/1 (18; 3)
EXAMPLE OF DIMENSIONING (2/10)
First phase: without guaranteeing capacity nor quality
Step 2: Calculate Erlangs PS (1st iteration)
Initial TSL capacity = 40 kbps (EGPRS, BCCH)
Timeslot capacity = 37 kbps
Step 1: CS traffic dimensioning
ErlangB (5 Erlangs, T timeslots) < 2% T= 10 timeslots
==kbps
kbps
40
200Erlangs PS 5
Step 3: Calculate the timeslot capacity
Error 8.1 % Another iteration would be provide more accurate values=
= 10037
3740
Step 4: Compute accurate values
Backoff gain = 0.2 (assumed that transmission uses always 8-PSK)Equivalent Erlangs PS 7.2 EFL = = 7.5%=
+=
2
)2.05()2.05(
CSErlangsPSErlangs
)(12)(8
2.7
freqTSL
Timeslot capacity
= 37 kbps
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EXAMPLE OF DIMENSIONING (4/10)
First phase: without guaranteeing capacity nor quality
Step 5: Timeslots needed to support average PS load
Ns= int 5.4 = 6 timeslots
Step 6: Minimum number of TRXs for the average CS and PS loads
Assuming 2 or 3 TRXs, dedicated timeslots = 2 and guard timeslots = 2:
Total no. TSL = Max {10, (int 5 +2) + (int 5.4 - 2) }+ 2 = 13 timeslots
The number of TRXs is the minimum that fulfills: 12 timeslots < timeslots available for traffic
Number of TRXs Number of timeslots
1 7
2 14
3 22
4 30
5 37
Table 1. Timeslots available for traffic
2 TRXs are needed to support the average CS and PS loads
Shared timeslots = 10 Dedicated timeslots = 2 Guard timeslots = 2
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EXAMPLE OF DIMENSIONING (5/10)
First phase: without guaranteeing capacity nor quality
Step 7: Calculate the reduction factor
Using the RF table for EGPRS and 2 TRXs, and the interpolation procedure:
PS usage (%)
Erlangs PSP1
P0
P2
P3
P
( )%1.77
0185.0152212
4.5100(%) =
+=usagePS
RF = 0.175
Repeating this procedure withthe 10th percentiles,10th percentile of RF = 0.02126
where:P (5 ErlangsCS, 59.2% PS usage, RF)P0 (4, 70%, 0.208)P1 (4, 80%, 0.333)P2 (5.333, 80%, 0.198)P3 (5.333, 70%, 0.121)
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EXAMPLE OF DIMENSIONING (6/10)
First phase: without guaranteeing capacity nor quality
Step 8: Evaluate the performance of the EGPRS network
Maximum possible PS load = 12 timeslots available for PS traffic x 37 kbps/TSL = 444 kbps/cell
Average PS load supported = [12 TSL available for PS 5 ErlangsCS ] x 37 kbps/TSL = 259 kbps/cell
Minimum PS load supported = 2 dedicated TSLs x 37 kbps = 74 kbps
Average user throughput = 3 (timeslot capability) x 0.175 (RF) x 37 kbps/TSL = 19.4 kbpsMinimum user throughput = 3 (timeslot capability) x 0.02126 (10th perc. RF) x 25 kbps (TSL capacity at
the border of the cell for EGPRS) = 1.6 kbps
It should be noticed that the supported load (259 kbps/cell) is greater than the requirement (200 kbps/cell), so thedesign is correct.
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EXAMPLE OF DIMENSIONING (7/10)
Second phase: guaranteeing capacity and quality(optional, only if operator wants to guarantee
some capacity and/or quality) Average throughput per MS is 64 kbps Minimum throughput (90% of the time at the cell
border) per MS is 32 kbps Minimum PS traffic supported is 100 kbps/cell
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EXAMPLE OF DIMENSIONING (8/10)
Second phase: guaranteeing capacity and quality
Step 9: Guarantee a certain capacity and quality
a) Guarantee an average user throughputAverage user throughput = 3 (TSL capability) x 0.175 (RF) x 37 (TSL capacity)
= 19.4 kbps < 64 kbps another TRX is needed repeat from step 7
Step 7: Calculate the reduction factor: 3 TRXs RF = 0.986, 10th
percentile of RF = 0.980Step 9a) Guarantee an average user throughput
Av. user throughput = 3 x 0.986 x 37 = 109.4 kbps > 64 kbps 3 TRXs are enough
b) Guarantee a minimum user throughput (90% of connection time in bad radio link conditions)Minimum user throughput = 3 (TSL capability) x 0.980 (10th perc. RF) x 25 (min TSL capacity) =
= 73.5 kbps > 32 kbps 3 TRXs are enough
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EXAMPLE OF DIMENSIONING (9/10)
Second phase: guaranteeing capacity and quality
Step 9: Guarantee a certain capacity and quality
c) Guarantee a minimum PS loadminimum load [Erlangs PS] = 100 (kbps/cell) / 37 (kbps) = 2.7 Erlangs PS
dedicated TSLs = 2.7 = 3
The following condition should be fulfilled:10 TSLs (CS) + 3 TSLs (dedicated) = 13 < 22 TSLs available for traffic OK
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EXAMPLE OF DIMENSIONING (10/10)
Second phase: guaranteeing capacity and quality
Step (810): Evaluate the performance of the EGPRS network
Maximum possible PS load = 20 timeslots available for PS traffic x 37 kbps/TSL = 740 kbps/cell
Average PS load supported = [20 TSL available for PS 5 ErlangsCS ] x 37 kbps/TSL = 555 kbps/cell
Minimum PS load supported = 3 dedicated TSLs x 37 kbps = 111 kbps
Average user throughput = 3 (timeslot capability) x 0.986 (RF) x 37 kbps/TSL = 109.4 kbpsMinimum user throughput = 3 (timeslot capability) x 0.980 (10th perc. RF) x 25 kbps (TSL capacity at
the border of the cell for EGPRS) = 73.5 kbps
With 3 TRXs all the requirements are fulfilled.