WRST 2/2+ IndexPlanning tasks
Module Objectives
At the end of the module you will be able to:
Understand basic radio propagation mechanisms
Understand fading phenomena
Understand basic concepts related to Node B and UE performance
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Radio network planning fundamentals
dBW = dB above Watt
dBm = dB above mWatt
dBi = dB above isotropic
dBd = dB above dipole
dBmV/m = dB above mV/m
min. UE Power: -50 dBm*
max. UE Power: 21 dBm / 24 dBm (UE Power Class 4 / 3)*
max. Node B Power/cell typically: 40 - 46 dBm
* 3GPP TS 25.101
Dispersive
In spectrum (wideband channel)
(Channelisation Codes only orthogonal
value α = [0..1]; typically:
0.4 - 0.9 (Macro Cells)
> 0.9 (Micro & Pico Cells)
Reflection
phase f - f
Diffuse reflection
phase f random phase
Scattering local to BS
No additional Doppler spread
Small delay & angle spread
Scattering
Multipath: Different radio paths have different properties
Distance Delay/Time
Direction Angle
WCDMA: RAKE Receiver to combine multipath components
Components with delay separation > 1 chip (0.26 s = 78 m) can be separated & combined
Standardized delay profiles in 3GPP specs:
TU3 typical urban at 3 km/h (pedestrians)
TU50 typical urban at 50 km/h (cars)
HT100 hilly terrain (road vehicles, 100 km/h)
RA250 rural area (highways, up to 250 km/h)
t
P
4.
3.
2.
1.
1.
2.
Multipath
propagation
1 chip 260.4 ns 78 m ( RAKE Receiver/Matched Filter)
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1 chip 260.4 ns 78 m
Environment
Angle – Angular Spread
Angular spread arises due to multipath, both from local scatterers near the mobile & near the base station and remote scatterers
Angular spread is a function of base station location, distance & environment
Angular Spread has an effect mainly on the performance of diversity reception & adaptive antennas
5 - 10 degrees in macrocellular environment
>> 10 degrees in microcellular environment
< 360 degrees in indoor environment
Angular spread:
function of BS location, distance & environment
has an effect mainly on the performance of diversity reception & adaptive antenna
typical no sectorisation in Micro- & Pico Cells
Macrocellular Environment
Frequency – Doppler Spread
Doppler Effect: with a moving transmitter or receiver, the frequency observed by the receiver will change
Rise if the distance on the radio path is decreasing
Fall if the distance in the radio path is increasing
The difference between the highest and the lowest frequency shift is called Doppler spread
v: Speed of receiver (m/s)
c: Speed of light (3*10^8 m/s)
f: Frequency (Hz)
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* or Lognormal Fading
Fading describes the variation of the total pathloss ( signal level) when receiver/transmitter moves in the cell coverage area
Fading is commonly categorised to two categories based on the phenomena causing it:
Slow fading: Caused by shadowing due to obstacles
Fast fading: Caused by multipath propagation
Time-selective fading: Short delay + Doppler
Frequency-selective fading: Long delay
Space-selective fading: Large angle
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Slow Fading – Gaussian Distribution
Measurement campaigns have shown that Slow Fading follows Gaussian distribution
Received signal strength in dB scale (e.g. dBm, dBW)
Gaussian distribution is described by mean value m, standard deviation
68% of values are within m ±
95% of values are within m ±2
Gaussian distribution used in planning margin calculations
Compensation of Slow Fading in UMTS
Rel. 99 & HSUPA: by Fast Power Control & SHO
HSDPA: by Fast Link Adaptation
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Rice Fading – the dominant (usually LOS) path exist
Rayleigh Fading – no dominant path exist
Compensation of Fast Fading in UMTS
Rel. 99 & HSUPA: by Fast Power Control
HSDPA: by Fast Link Adaptation
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Fast Fading – Rayleigh Distribution
It can be theretically shown that fast fading follows Rayleigh Distribution when there is no single dominant multipath component
Applicable to fast fading in obstructed paths
Valid for signal level in linear scale (e.g. mW, W)
+10
0
-10
-20
-30
0
1
2
3
4
Fast fading follows Rician distribution when there is a dominant multipath component, for example line-of-sight component combined with in-direct components
Sliding transition between Gaussian and Rayleigh
“Rice-factor” K = r/A: direct / indirect signal energy
K = 0 Rayleigh
K >>1 Gaussian
Propagation slope
Simplified case: isotropic antenna
Which part of total radiated power is found within surface A?
Power density S = P/A = P / 4 d2
Received power within surface A´ : P´ = P/A * A´
Received power reduces with square of distance
d
Power density at the receiving end
Effective receiver antenna area
Ps
As
Gs
Pr
Ar
Gr
d
Antenna gain is normally given by how much the given antenna is better than a dipole antenna (dBd) or an isotropic (fully omnidirectional) antenna (dBi)
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Where
3-3.4 for irregular terrain