Unit 1: The wireless channel - Wireless communications...
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Transcript of Unit 1: The wireless channel - Wireless communications...
Unit 1: The wireless channelWireless communications course
Ronal D. Montoya M.http://tableroalparque.weebly.com/radiocomunicaciones.html
August 23, 2017
1/26
Outline I
1. Empirical path loss modelsOverview
2. The Okumura model
3. Hata model
4. COST 231 model
5. Standford University Interim (SUI) model
6. Indoor attenuation factors
2/26
Empirical path loss models I
◦ Mobile communication systems operate in complex propagationenvironments that cannot be accurately modeled by free-spacepath loss or ray tracing.
◦ Several path loss models have been developed over the years topredict path loss in typical wireless environments such as largeurban macrocells, urban microcells and inside buildings.
◦ These models are mainly based on empirical measurementsover a given distance in a given frequency range and aparticular geographical area or building.
1. Empirical path loss models 3/26
Empirical path loss models II
◦ Applications of these models are not always restricted toenvironments in which the empirical measurements were made(Consider an adjusted model).
◦ Many wireless systems use these models as a basis forperformance analysis.
◦ They were initially developed for urban macrocells, today areadjusted for outdoor microcells and indoor propagation.
◦ Empirical measurements of the Pr
Ptas a f (d) include the effects
of path loss, shadowing, and multipath.
1. Empirical path loss models 4/26
Empirical path loss models III
◦ In order to remove multipath effects, empirical measurementsfor path loss typically average their Pr measurements and thecorresponding path loss at a given d over several λc.
◦ This average path loss is called the local mean attenuation(LMA), and is measured in several places with similarpropagation characteristics.
1. Empirical path loss models 5/26
The Okumura model I
◦ This model is applicable over 1 ≤ d ≤ 100 Km and frequencyranges of 150 ≤ fc ≤ 1500 MHz.
◦ Okumura used extensive measurements of basestation-to-mobile signal attenuation throughout Tokyo todevelop a set of curves giving median attenuation relative tofree space of signal propagation in irregular terrain.
◦ The base station heights for these measurements were 30-100 m.
2. The Okumura model 6/26
The Okumura model IIThe path loss formula of Okumura is given by:
PL (d) [dB] = L (fc, d) + Amu (fc, d) −G (ht) −G (hr) −GAREA (1)
Where:
◦ L (fc, d) : Free space path loss at distance d and carrierfrequency fc.
◦ Amu (fc, d) : The median attenuation in addition to free spacepath loss across all environments.
◦ G (ht) : The base station antenna height gain factor.
2. The Okumura model 7/26
The Okumura model III
◦ G (hr) : The mobile antenna height gain factor.
◦ GAREA : The gain due to the type of environment.
Okumura derived empirical formulas for the base station and themobile antenna height gain factors:
G (ht) ={
20 log10 (ht/200) 30m < ht < 1000m (2)
G (hr) =
{10 log10 (hr/3) ht ≤ 3m
20 log10 (hr/3) 3m < ht < 10m(3)
2. The Okumura model 8/26
The Okumura model IV
◦ Correction factors related to terrain are also developed toimprove the model accuracy.
◦ Okumura’s model has a 10-14 dB empirical standard deviationbetween the PL predicted by the model and the measured PLused to develop the model.
2. The Okumura model 9/26
Hata model I
◦ The Hata model is an empirical formulation of the graphicalpath loss data provided by Okumura and is valid over roughlythe same range of frequencies, 150-1500 MHz.
◦ This empirical model simplifies calculation of path loss since itis a closed-form formula and is not based on empirical curvesfor the different parameters.
3. Hata model 10/26
Hata model II
The empirical path loss in urban areas under the Hata model isgiven by:
PL,urban (d) [dB] = 69, 55 + 26, 16 log10 (fc) − 13, 82 log10 (ht)
+ a (hr) + [44, 9 − 6, 55 log10 (ht)] log10 (d)(4)
3. Hata model 11/26
Hata model III
a (hr) is a correction factor for the mobile antenna height hr basedon the size of the coverage area. For small to medium sized cities,this factor is given by:
a (hr) [dB] = (1, 1 log10 (fc) − 0, 7)hr − (1, 56 log10 (fc) − 0, 8) [dB](5)
For larger cities and fc > 300 MHz:
a (hr) [dB] = 3, 2 [log10 (11, 75hr)]2 hr − 4, 97 [dB] (6)
3. Hata model 12/26
Hata model IV
Corrections to the urban model are made for suburban and ruralpropagation environments, respectively:
PL,suburban (d) [dB] = PL,urban (d) − 2
[log10
(fc28
)]2− 5, 4 [dB] (7)
PL,rural (d) [dB] = PL,urban (d) − 4, 78 [log10 (fc)]2
+ 18, 33 log10 (fc) −K [dB]
(8)
3. Hata model 13/26
Hata model VWhere K:
◦ K = 35, 94 : for the countryside.
◦ K = 40, 94 : for the desert.
Anotations:
◦ The Hata model well-approximates the Okumura model fordistances d > 1 Km.
◦ fc > 1500 MHz is not covered by this model (PCS, Wi-Fi,ZigBee, Bluetooth, WiMAX, WiBRO ?).
◦ Indoor environments are also not captured with the Hatamodel.
3. Hata model 14/26
COST 231 model I
The Hata model was extended by the European cooperative forscientific and technical research (EURO-COST) up to fc = 2 GHz,and is given by:
PL,urban (d) [dB] = 46, 3 + 33, 9 log10 (fc) − 13, 82 log10 (ht)
− a (hr) + [44, 9 − 6, 55 log10 (ht)] log10 (d) + CM
(9)
Where:
◦ a (hr) is the same as Hata model.
4. COST 231 model 15/26
COST 231 model II
◦ CM = 0 [dB] for medium sized cities.
◦ CM = 3 [dB] for metropolitan areas.
The restrictions for the COST 231 (Hata extension) model are:
◦ 500 MHz < fc < 2 GHz.
◦ 30 m < ht < 200 m.
◦ 1 m < hr < 10 m.
◦ 1 Km < d < 20 Km.
4. COST 231 model 16/26
Standford University Interim (SUI) model I
◦ It has an extension of the Hata model.
◦ 1900 MHz < fc < 3, 5 GHz.
◦ 2 m < hr < 10 m.
◦ 0, 1 Km < d < 8 Km.
◦ The SUI model describes three types of terrain Tt: terrain A, Band C.
◦ Terrain A: used to describe hilly areas with moderate or verydense vegetation, or dense populated urban area. Maximumpath loss.
5. Standford University Interim (SUI) model 17/26
Standford University Interim (SUI) model II
◦ Terrain B: used to describe the hilly terrains with rarevegetation, flat terrains with moderate or heavy tree densities,or suburban environment. Medium path loss.
◦ Terrain C: suitable for flat terrains with light vegetation orrural areas. Minimum path loss.
The basic path loss expression of The SUI model with correctionfactors is (for d > d0):
PL,Tt (d) [dB] = A (λc) + 10γ log10
(d
d0
)+X (fc) +X (hr) + S (10)
5. Standford University Interim (SUI) model 18/26
Standford University Interim (SUI) model III
Where:
◦ d0 = 100 m.
◦ A (λc) = 20 log10
(4πd0λc
).
◦ Path loss exponent γ = a− bht + cht
. Coefficients a, b, and c aregiven in the next table.
◦ γ = 2 for LOS in an urban area, 3 < γ < 5 for urban NLOSenvironment, and γ > 5 for indoor propagation.
◦ The frequency correction factor: Xf = 6 log10
(fc
2000
)5. Standford University Interim (SUI) model 19/26
Standford University Interim (SUI) model IV
◦ The receiver antenna correction factor:
X (hr) =
{−10, 8 log10
(hr2000
)Tt = A,B
−20 log10
(hr2000
)Tt = C
(11)
◦ The log normally distributed factor S, for shadow fadingbecause of trees and other clutter on a propagation paths.
◦ 8, 2 ≤ S ≤ 10, 6.
◦ fc is given in MHz and λc in m.
5. Standford University Interim (SUI) model 20/26
Standford University Interim (SUI) model V
Model parameter Tt = A Tt = B Tt = Ca 4,6 4 3,6b 0,0075 0,0065 0,005c 12,6 17,1 20
Table: SUI model parameters for different terrain types.
Homework: Read about the ECC-33 and Ericsson models.
5. Standford University Interim (SUI) model 21/26
Indoor attenuation
Figure: Indoor signal strength coverage heat plot.6. Indoor attenuation factors 22/26
Indoor attenuation factors I
◦ It’s difficult to find a generic model that can be accuratelydetermine the empirical path loss in a specific indoor setting(partition materials and dielectric properties vary widely).
◦ Indoor path loss models must accurately capture the effects ofattenuation across floors due to partitions, as well as betweenfloors.
◦ The attenuation per floor is greatest for the first floor that ispassed through and decreases with each subsequent floor.
6. Indoor attenuation factors 23/26
Indoor attenuation factors II
Partition type Partition Loss [dB]Cloth 1,4
Double plasterboard wall 3,4Foil insulation 3,9Concrete wall 13
Aluminium siding 20,4All metal 26
Table: Typical partition losses measured at 900-1300 MHz.
6. Indoor attenuation factors 24/26
Indoor attenuation factors IIIThe experimental data for floor and partition loss can be added toan analytical or empirical dB path loss model PL (d) as:
PL [dBm] = Pt [dBm] − PL (d) −Nf∑i=1
FAFi −Np∑i=1
PAFi (12)
Where:
◦ FAFi : Floor attenuation factor for the ith floor traversed bythe signal.
◦ PAFi : Partition attenuation factor for the ith floor traversedby the signal.
6. Indoor attenuation factors 25/26
Indoor attenuation factors IV
◦ Nf : Number of floors traversed by the signal.
◦ PAFi : Number of partitions traversed by the signal.
6. Indoor attenuation factors 26/26