unit 1: the wireless channel - wireless communications...

Unit 1: The wireless channelWireless communications course

Ronal D. Montoya M.http://tableroalparque.weebly.com/radiocomunicaciones.html

ronalmontoya5310@correo.itm.edu.co

August 23, 2017

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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

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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