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Anders J Johansson, Department of Electrical and Information [email protected]
RADIO SYSTEMS – ETIN15
Lecture no:
29 March 2017 1
4Channel models
and antennas
29 March 2017 3
Contents
• Why do we need channel models?• Narrowband models
– Review of properties– Okumura’s measurements– Okumura-Hata model– COST 231-Walfish-Ikegami model
• Wideband models– Review of properties– COST 207 model for GSM– ITU-R model for 3G
• Antennas– Efficiency and bandwidth– Mobile station antennas– Base station antennas– Dipole and parabolic antennas
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WHY DO WE NEEDCHANNEL MODELS?
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Why do we need channel models?
During system design, testing and type approval:
Simple models reflecting the important propertiesof important channels (best, average, worst case)
During network design:
More detailed models appropriate for certaingeographical areas
Models used to make sure that the system designbehaves well in typical situations.
Models used to obtain an efficient network in termsof base station locations and other parameters
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Wideband vs. narrowbandTime vs. frequency
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NARROW-BANDMODELS
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Narrowband modelsReview of properties
Narrowband models contain ”only one” attenuation, which is modeledas a propagation loss, plus large- and small-scale fading.
Large-scale fading: Log-normal distribution (normal distr. in dB scale)
Small-scale fading: Rayleig, Rice, Nakagami distributions ... (not in dB-scale)
Path loss: Often proportional to 1/dn, where n is the propagation exponent. (n may be different at different distances)
NOTE: Several of these models are found in an on-line appendix of the textbook which can be downloaded from the publisher's website (see “Literature” on course web).
Printed copies of textbook appendices areallowed during Part B of the written exam.
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Okumura’s measurementsBackground
Extensive measurement campaign in Japan in the 1960’s.
Parameters varied during measurements:
FrequencyDistanceMobile station heightBase station heightEnvironment
100 – 3000 MHz1 – 100 km1 – 10 m20 – 1000 mmedium-size city, large city, etc.
Propagation loss is given as a median value (50% of thetime and 50% of the area).
Results from these measurements are displayed in figures7.12 – 7.14.
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Okumura’s measurementsHow to calculate the prop. loss
Free spaceattenuation
1. We start by calculating the free-space attenuation2. Apply a frequency and distance dependent correction3. Apply a BS-height and distance dependent correction
4. Apply a MS-height, frequency and environment dependent correction
Fig. 7.12 Fig. 7.13 Fig. 7.14
OkuL
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Okumura’s measurementsExample
Propagation at 900 MHz in medium-size citywith 40 m base station antenna height and1.5 m mobile station antenna height.
Use Okumura’s curves to calculate thepropagation loss at a distance of 30 kmbetween base station and mobile station.
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Okumura’s measurements1. Calculate free-space loss
Attenuation between twoisotropic antennas in freespace is (free-space loss):
The obtained value does not dependon antenna heights.
900 MHz and30 km distance
=> 121 dB
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Okumura’s measurements2. Apply correction for excess loss
Exce
ss lo
ss [d
B]
Frequency [MHz]
Dis
tanc
e [k
m]
These curves are only for hb=200 m
and hm=3 m
900 MHz and30 km distance
=> 36.5 dB
FIGURE 7.12
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Okumura’s measurements3. Apply correction of BS height
BS height [m]
Dis
tanc
e [k
m]
Cor
rect
ion
fact
or [d
B]
40 m BS and30 km distance
=> -16 dB
Note: Lower base station means INCREASING
attenuation => subtract this number.
FIGURE 7.13
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Okumura’s measurements4. Apply correction of MS height
MS height [m]Fr
eque
ncy
[MH
z]
Cor
rect
ion
fact
or [d
B]
Note: Lower mobile station means
INCREASING attenuation => subtract this number.
1.5 m MS and900 MHz inmedium-size city=> -3 dB
FIGURE 7.14
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Okumura’s measurementsSummary of example
Propagation loss (between isotropic antennas) usingOkumura’s measurements:
| 121 36.5 ( 16) ( 3) 176.5 dBOku dBL
Calc. step: 1 2 3 4
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The Okumura-Hata modelBackground
In 1980 Hata published a parameterized model, based on Okumura’smeasurements.
The parameterized model has a smaller range of validity thanthe measurements by Okumura:
FrequencyDistanceMobile station heightBase station height
150 – 1500 MHz1 – 20 km1 – 10 m30 – 200 m
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The Okumura-Hata modelHow to calculate prop. loss
Small/medium-size cities
Metropolitanareas
Suburbanenvironments
Rural areas
hb and hm
in meter
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COST 231-Walfish-Ikegami modelBackground
The Okumura-Hata model is not suitable for micro cells or smallmacro cells, due to its restrictions on distance (d > 1 km).
The COST 231-Walfish-Ikegami model covers much smallerdistances and is better suited for calculations on small cells.
FrequencyDistanceMobile station heightBase station height
800 – 2000 MHz0.02 – 5 km1 – 3 m4 – 50 m
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COST 231-Walfish-Ikegami modelHow to calculate prop. loss
0 msd rtsL L L L
BS
MS
d
Freespace
Roof-topto street
Building multiscreen
Details about calculations can be found in Appendix 7.B.
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WIDEBANDMODELS
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Wideband modelsReview of properties
Let’s assume the tapped delay-line model
The power-delay profile tells us how much energy the channel hasat a certain delay τ (essentially the rms values of the αi(t)’s).
The Doppler spectrum tells us how fast the channel changes in time(essentially how fast the αi(t)’s and θi(t)’s change). There can be oneDoppler spectrum for each delay.
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Wideband modelsCOST 207 model for GSM
The COST 207 model specifies:
FOUR power-delay profiles for differentenvironments.
FOUR Doppler spectra used for differentdelays.
IT DOES NOT SPECIFY PROAGATION LOSSES FOR THEDIFFERENT ENVIRONMENTS!
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Wideband modelsCOST 207 model for GSM
[ ]s
[ ]P dB0
10
20
300 1 [ ]s
[ ]P dB0
10
20
300 1 2 3 4 5 6 7
[ ]s
[ ]P dB0
10
20
300 5 10 [ ]s
[ ]P dB0
10
20
30100 20
Four specified power-delay profiles
RURAL AREA TYPICAL URBAN
BAD URBAN HILLY TERRAIN
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Wideband modelsCOST 207 model for GSM
Four specified Doppler spectra
max max0
,s iP
max max0
max max0 max max0
CLASS GAUS1
GAUS2 RICEShortestpath in
rural areas
,s iP
,s iP ,s iP
i≤0.5 s 0.5 si≤2 s
i2 s
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GAUS2GAUS1CLASS
Wideband modelsCOST 207 model for GSM
[ ]s
[ ]P dB0
10
20
300 1 [ ]s
[ ]P dB0
10
20
300 1 2 3 4 5 6 7
[ ]s
[ ]P dB0
10
20
300 5 10 [ ]s
[ ]P dB0
10
20
30100 20
RURAL AREA TYPICAL URBAN
BAD URBAN HILLY TERRAIN
Doppler spectra:
First tapRICEhere
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Wideband modelsITU-R model for 3GThe ITU-R model specifies:
SIX different tapped delay-line channels forthree different scenarios (indoor, pedestrian, vehicular).
TWO channels per scenario (one short and onelong delay spread).
TWO different Doppler spectra (uniform & classical),depending on scenario.
THREE different models for propagation loss (onefor each scenario).
The standard deviation of the log-normal shadowfading is specified for each scenario.
The autocorrelation of the log-normal shadowfading is specified for the vehicular scenario.
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Wideband modelsITU-R model for 3G
ns
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ANTENNAS
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AntennasEfficiency
The antenna efficiency measures “how efficiently” an antennaconverts the input power into radiation. This translates directlyinto power consumption and battery life.
Antenna efficiency of mobiles has decreased mainly due tocosmetic restrictions.
What cosmetic restrictions?
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AntennasBandwidth
We can say that the bandwidth of an antenna is the width ofthe frequency range over which it fulfills some specification.
Most cellular systems have a bandwidth requirement in therange of 10% of the carrier frequency.
Example: 900 MHz GSM needs an antenna that can transmit/receive well in a total bandwidth of about 100 MHz.
What happens when we have dual- (900/1800) or triple-band(900/1800/1900) GSM phones ... or phones with 3G, 4G, andBluetooth (2.4 GHz) as well?
It is difficult to make small and efficient broadband antennas!
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AntennasMobile station antennas
Monopole Helix Patch
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AntennasMobile station antennas
The efficiency depends on many parameters, but a very importantone is its environment. Below you can see differences in antennaefficiency for 42 test persons holding the mobile.
Up to around 10 dB difference, depending
on person.
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AntennasThe dipole antenna
[Figure from Ericsson Radio School documentation]
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AntennasThe parabolic antenna
Opening area:
Effective area:
Antenna gain:
3dB beamwidth: ≈200
Ga
[degrees] 25o
[Figure from Ericsson Radio School documentation]
Aeff ≈0.55A
A= d 2
4
Ga=4
2Aeff≈0.55
2 d 2
2
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Summary
• Narrowband models: Okumura´s measurements, Okumura-Hata, COST 231-Ikegami-Walfish. Mainly models for propagation loss. Fading has to be added.
• Wideband models: COST 207 for GSM & ITU-R for 3G. Mainly specification of power-delay profile and doppler spectrum (IRT-R also gives e.g. path loss).
• Antennas: Efficiency has decreased for mobile antennas. Antenna environment changes their properties. Some specific properties for dipole and parabolic antennas.
