Aalto University School of Electrical Engineering ELEC ...

Aalto UniversitySchool of ElectricalEngineering

ELEC-E4750Radiowave Propagation and ScatteringSession 6: Terrestrial and Satellite Links

ELEC-E475014.10.2020

1



Schedule

2

Wk Date Location Lectures, exercises and deadlines

42Mon. 12 Oct. Online Exercise return session 5Wed. 14 Oct. Lecture 6: terrestrial and satellite links

43Mon. 19 Oct. Exercise return session 6Wed. 21 Oct. Lecture 7: cellular links

44Mon. 26 Oct. Exercise return session 7Wed. 28 Nov. Lecture 8: radio channel characterization

45Mon. 02 Nov. Exercise return session 8Wed. 04 Nov. ELE lab Lecture 9: measurements and analysis

46Mon. 09 Nov. Online Exercise return session 9Wed. 11 Nov. Lecture 10: fading and radio link

performance


Books, Topics and Exercises Books

Main books S. Saunders, Antennas and Propagation for Wireless Communication Systems, Chapters 3, 5,

6-8, 10, 12 15, Wiley. H. L. Bertoni, Radio propagation for modern wireless systems, Chapters 2-6, Prentice Hall. A. F. Molisch, Wireless Communications, Chapters 1, 5 and 8, Wiley. R. Vaughan and J. B. Andersen, Channels, propagation and antennas for mobile

communications, Chapter 3.2.1, IEE Press. Supplemental book

D. M. Pozar, Microwave Engineering, Chapters 1 and 14, Wiley.

Topic 6: Terrestrial and satellite links (Ch. 5 and 7, Ch. 4) Exercise 1: Two-ray multipath model Exercise 2: Rain attenuation

Topic 7: Cellular links (Ch. 12, Ch. 2) Exercise 1: Physical propagation modeling in microcells Exercise 2: Pathloss and small-scale fading

3



Cellular Scenarios

4

Satellite links(Mega cells)Macrocells

Microcells

Pico cells



Two-Ray Model of Radio Propagation

5



Two-Ray Model of Radio Propagation

6

For 𝑑𝑑 ≫ ℎb• Wave propagation distances of

line-of-sight and ground reflection becomes almost the same.

• Ground reflection becomes almost glazing incidence

• Reflection coeff. approaches +1 for “┴” pol and -1 for “||” pol.

𝜃𝜃

𝜃𝜃


Q1: for a two-ray radio propagation, thereceived power behaves like the figure. Which explanation is incorrect?

A. Constructive and destructive addition of the two rays leads to the fluctuation.

B. A spatial standing wave is seen.C. The variation happens because radio waves are coherent.D. The variation looks exactly the same for horizontal and

vertical polarizations of the transmitted waves.

Figure: normalized received power with respect to the line-of-sight power E0


Q2: for horizontal polarization where the reflection coefficient of the grazing incidence to the ground is -1, the received field at the RX isstronger than the line-of-sight field when

A. r1 + r2 - r0 = λ/2.B. r1 + r2 - r0 = λ.C. r1 + r2 - r0 = 2λ.D. r1 + r2 - r0 = 300λ.

λ: wavelength



Cellular Scenarios

9

Satellite links(Mega cells)Macrocells

Microcells

Pico cells



Atmosphere Around Earth’s Surface

10



Excess Losses in Satellite Linksin reference to free-space loss

11

Effects of non-ionized atmosphere• Absorption in gases• Absorption, scattering and

depolarization by hydrometeors • Antenna beam-divergence due to

refraction• Scintillation due to time-varying

reflective index• Attenuation due to objects around

earth station, e.g., buildings and trees

• Critical for > 1 GHz RF and low elevation angles

• ITU-R P.618

Effects of ionized atmosphere• Critical frequency due to

change of refractive index• Change of polarization states

due to Faraday rotation• Group delay dispersion• Scintillation due to time-

varying reflective index• Critical for < 1 GHz radio

frequency (RF)• ITU-R P.531



Ionosphere

12

… is a region of ionized plasma; ions are trapped in the Earth’s magnetic field.

Electromagnetic radiation of the sun makes the ionization.



Ionosphere Effects on Radio Propagation

13

• Key parameter: electron concentration per cubic meter N

• The electron concentration influences the refractive index:

(Critical frequency)


A. At the critical frequency,the refractive index is almost 0.

B. Refractive index is smaller at night than in a day inionosphere.

C. Radio waves from the ground do not penetrate the ionosphere below the critical frequency.

D. The densest ionization leads to higher critical frequency.

Q3: Which statement is wrong?



Tropospheric Refraction

15


Gaseous Absorption

Oxygen atom

Hydrogen atom

Watervapor

Oxygen molecules have quantized rotational energy state (resonances). They have energy corresponding to energy quantum with wavelength of approximately 5 mm.

Oxygen molecule



Rain Attenuation• Which level of rain attenuation is most problematic for

satellite links?

17Khan et al., TAP 2003.


Q4: When discussing the rain attenuation,we usually care a rainfall rate of

A. The smallest 1 % value of a year.B. A mean value of a year.C. A median value of a year.D. The largest 1% value of a year.



Outage Probability due to Rain Attenuation

19

• Heavy rain fall rate produces the most severe attenuation.

Khan et al., TAP 2003.

Correction factor

1 % most severe rainattenuation



Rain Attenuation and Path Length

20

… is proportional to total rainy slant path length rR.

The effective rain height hR varies

for latitude.

The length rRdepends on local cloud distribution.



Depolarization due to Hydrometeor

21

Attenuation depends on the polarization direction with respect to orientation of the hydrometeor.

XPD proportional to rain attenuation loss,(Reasonably accurate above 10GHz)


Q5: which statement is wrong?A. Rain attenuation depends on the radio frequency.B. Low elevation satellite path is influenced by more

rain attenuation than high elevation satellite path.C. Rain attenuation is polarization-selective.D. Greater link margin is required in the mild climate

areas than in tropical areas.



Improving the Outage - Diversity

23

Rain cell sizeRain cell size

ff f


Q6: which one is right as to the diversity in satellite links?

A. Use of multiple radio frequencies in a single ground station is as effective as having multiple ground stations to attain link diversity.

B. A second ground station placed just next to the first ground station leads to low correlation of rain attenuation between the two links.

C. If correlation of rain attenuation between two links is low, there is no improvement of outage.

D. Two ground stations must be separated much greater than the average rain cell size of the site to leverage diversity efficiently.



Forthcoming Contact Sessions• Learning outcomes of the exercise problems for topic 7 are to

– Get familiarized with physical propagation modeling in an urban street canyon (problem 1)

– Understand characteristics of pathloss and small-scale fading (problem 2)• During the contact sessions, you

– solve the exercise problems by referring to relevant parts of the course books.• a limited number of course books are available in the room.

– are encouraged to discuss with other students and teachers.– should contact teachers once your solutions are ready.

• if you prepare exercise solutions in an electronic format (recommended), upload the solution to MyCourses first and then contact teachers.

– will propose points for your ready solutions to the teachers.– will not get exercise points without discussing with teachers!

• The discussions MUST happen in the contact sessions.– Are reminded that six exercise problems must be completed in total before the

end of the next Monday session on 19th October.

Aalto University School of Electrical Engineering ELEC ...

Documents

Transcript of Aalto University School of Electrical Engineering ELEC ...