1- planeación gsm
TRANSCRIPT
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Purpose:
Definition of technical parameters
Check for balanced up- and downlink
Fast overview of required BTS
Input for Coarse Planning with TORNADO
Method:
Max. possible pathloss calculation with input datas
Cell radius calculation using Okumura-Hata propagation model
Link Budget
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Downlink (BTS ---> MS):
Balanced Up- and Downlink
BTS
MS
TX-Power
RX-Sensitivity
Uplink (MS ---> BTS):
BTS
MS
TX-Power
RX-Sensitivity
Balance Condition: Luplink = Ldownlink
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1. Definition:
Maximum allowed attenuation between transmitter (TX) and receiver (RX) to obtainthe specified grade of quality
2. Calculation
Lmax = TX_Power - RX_SensitivityExample: Lmax = 40dBm - (-100dBm)
Lmax = 140dB
TX_Power = EiRP (effective isotropic radiated power)
2.1.Downlink
TRX
Back off
Combiner CableTX-Antenna
Example: EiRP = 46dBm - 1dB - 3dB - 3dB + 15dBi = 54dBm = 251,2W
Maximum Pathloss
EiRP= BS_Power_Output - PA_Back Off - Total_Combiner_and_Duplex_Loss - TX_Antenna_Cable_Loss + TX_Antenna_Gain
P[dBm]= 10*log(P[mW])
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RX_Sensitivity = Min_RX_Level_50%_loc._prob.
Maximum Pathloss
Min_RX_Level_50%_loc._prob. = Sensitivity_Level + RX_Antenna_Cable_Loss - Frequency_Hopping_Gain -
RX_Antenna_Gain + Interference_degradation_margin + Body_Loss
MS Cable
RX-Antenna
Interferer
Carrier
Example: Min_RX_Level_50%_loc._prob. = -102dBm + 0dB - 0dB - 0dBi + 3dB + 3dB = -96dBm
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Maximum Pathloss
2.1.Uplink
MS CableTX-Antenna
EiRP= MS_Power_Output - TX_Antenna_Cable_Loss + TX_Antenna_Gain
Min_RX_Level_50%_loc._prob. = Sensitivity_Level - Frequency_Hopping_Gain + RX_Antenna_Cable_Loss -
Tower_Mounted_Pre-Ampliufier_Gain - RX_Antenna_Gain - Antenna_Diversity_Gain +
Interference_degradation_margin + Body_Loss
BTS
Cable
RX1-Antenna
Interferer
Carrier
Cable
RX2-Antenna
TMPA
TMPA
Example: EiRP = 33dBm - 0dB + 0dBi = 33dBm = 2W
Example: Min_RX_Level_50%_loc._prob. = -107dBm - 0dB + 3dB - 0dB - 15dBi - 4dB + 3dB + 3dB = -117dBm
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Example:
Lmaxdownlink = 54dBm - 96dBm = 150dB
Lmaxuplink = 33dBm - 117dBm = 150dB
Balanced System
Untill now we always have calculated with a 50% location probability for coverage. But a
customer will not be satisfied with only 50% probability for a successfull call. Typical values for
an acceptable grade of service are location probabilities above 90%. How to calculate the
necessary receiving level for a given location probability will be shown on the next sheets. To
understand this calculation we have to look at the two main fading mechanisms.
Maximum Pathloss
Lmax = EiRP - Min_RX_Level_50%_loc._prob.
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Fading:
Long term fading due to shadowing
Short term fading (Rayleigh fading) due to reflexions
Location Probability
Receiving Level
distanceVariations dueto shadowing
Global mean
Variations due
to Rayleigh fading
Long and short term fading
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Location Probability
Rayleigh Distribution
A) Short-term fading
Receiving Level P
Pmedian
Pm in
P
Fading margin
area r
pr
ti
the probability P(P < Pmin)
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Location Probability
B) Long-term fading
ormal Distribution
area rpr
ti
the probability P(Pr < Prmin)
Re c eiv i g Le ve l r
r mi
( )r
r
Fa i g margi
r mea
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Min_Rx_Level_x%_loc._prob. = Min_Rx_Level_50%_loc._prob. + z * standard deviation
Max_Pathloss_x%_loc.prob. = Max_Pathloss_50%_loc._prob. - z * standard deviation
Location Probability
z is taken from tables for the normal distribution function
The percentage value in the normal distribution table is the probability at the cell border.
To obtain the cell coverage probability the value must be converted with the curves given by
Jakes: "Microwave Mobile Communication",1974.
75% at cell border ~ 90% cell coverage
90% at cell border ~ 98% cell coverage
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Example: Min_Rx_Level_75%_loc._prob. = -96dBm + 0,675 * 6dB = -92dBm
Max_Pathloss_75%_loc._prob. = 150dB - 0,675 * 6dB = 146dBm
Location Probability
(urban)
Dense urban : 10dB
Urban : 8dB
Suburban : 6dB
Rural / open : 5dB
Forest : 5dB
Standard deviation
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To obtain indoor coverage the Min_Rx_Level_x%_loc._prob. must be available
inside the building. For estimation of an appropriate outdoor level the average
indoor loss has to be determined. The average indoor loss depends on
morphologie of course. Typical values are:
Indoor coverage
Average Indoor Loss
Dense urban : 20dB (10-25dB)
Urban : 15dB (10-15dB)
Suburban : 10dB (5-10dB)
Rural / open : 8dB (5-10dB)
Incar : 7dB (5-8dB)
Min_Rx_Levelindoor= Min_Rx_Leveloutdoor+ Average_Indoor_Loss
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Free Space Path Loss
Propagation Prediction
L0 = 32,4 + 20 * log (f[MHz]) + 20 * log (d[km])
L0 = 91,72 + 20 * log (d[km]) fr f = 925MHz
Hata for urban area
L = 69,55 + 26,16 * log (f[MHz]) - 13,82 * log (HBS) - a(HMS) + (44,9 - 6,55 * log (HBS)) * log(d[km])
L = 147,14 -13,82 * log (HBS) - a(HMS) + (44,9 - 6,55 * log (HBS)) * log (d[km]) for f = 925MHz
a(HMS) = 0 for HMS = 1,5m
General L = A + B * log (d [km])
L: Loss in dB B: propagation index (loss per decade)
A: unit loss (at 1km) d: distance MS - BS [km]
For other morphologic classes correction factors for this formula are used.
(see the macro of the link budget calculation program)
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With L=Lmax it is possible to calculate the cell radius d
Cell Radius Calculation
d[km] = 10(Lmax - 147,14 +13,82 * log (HBS) + a(HMS) ) / (44,9 - 6,55 * log (HBS))
Example:
d[km] = 10(146dB - 147,14 +13,82 * log (30) + 0) / (44,9 - 6,55 * log (30))
d = 3,52km
The formula is valid in the following area: HBS = 30 ... 200m, HMS = 1 ... 10m, d >1km
The cell coverage area is calculated by:
Cell_Coverage = Pi * r2
for omni cell