Mobile satellite communication

Mobile satellite communication

1. Mobile Satellite Communication Tanjarul Islam Mishu [@tanjarul26] Dept. of CSE Jatiya Kabi Kazi Nazrul Islam University

2. Outlines 1. Satellite 2. Mobile Satellite Communication 3. Classification Of Mobile Satellite Communication 4.Propagation Channel Impairment. 5.Impairments. 6. Fading. 7. Mobile Satellite Propagation Environment 8. Probability Distribution Functions(PDF ) 9. Major Channel Models 10. Comparison of Models

3. Satellite The word "satellite" refers to a machine that is launched into space and moves around Earth or another body in space. The moon is the of natural satellites of earth. Thousands of artificial, or man-made, satellites orbit Earth.

4. Mobile Satellite Communication A Satellite communication is a technology that is used to transfer the signals from the transmitter to a receiver with the help of satellites. Satellite services include fixed satellite service, broadcasting satellite service and mobile satellite service. Mobile satellite service (MSS) is the term used to describe telecommunication services delivered to or from the mobile users by using the satellites. Mobile Satellite Communication is the communication system of Mobile satellite service (MSS ).

5. Mobile Satellite Communication

6. Classification Of Mobile Satellite Communication Geostationary Earth Orbit (GEO ) Medium Earth Orbit (MEO) Low Earth Orbit (LEO) Highly Elliptical Orbit (HEO )

7. Classification Of Mobile Satellite Communication A highly elliptical orbit (HEO) is an elliptic orbit with a low-altitude (often under 1,000 kilometres and a high-altitude (often over 35,786 kilometres .

8. Geo-Stationary Earth Orbit Advantages 1.    It is possible to cover almost all parts of the earth with just 3 geo satellites . 2.    Antennas need not be adjusted every now and then but can be fixed permanently . 3.    The life-time of a GEO satellite is quite high usually around 15 years. Disadvantages 1.    Larger antennas are required for northern/southern regions of the earth . 2.    High buildings in a city limit the transmission quality . 3.    High transmission power is required . 4.    These satellites cannot be used for small mobile phones . 5.    Fixing a satellite at Geo stationary orbit is very expensive

9. Medium Earth Orbit  Advantages of Medium Earth Orbit 1.    Compared to LEO system, MEO requires only a dozen satellites . 2.    Simple in design . 3.    Requires very few handovers . Disadvantages of Medium Earth Orbit 1.    Satellites require higher transmission power . 2.    Special antennas are required.

10. Low Earth Orbit Advantages of Low Earth Orbit 1.    The antennas can have low transmission power of about 1 watt . 2.    The delay of packets is relatively low . 3.    Useful for smaller foot prints . Disadvantages of Low Earth Orbit 1.    If global coverage is required, it requires at least 50-200 satellites in this orbit . 2.    Special handover mechanisms are required . 3.    These satellites involve complex design . 4.    Very short life: Time of 5-8 years. Assuming 48 satellites with a life-time of 8 years each, a new satellite is needed every 2 months . 5.    Data packets should be routed from satellite to satellite.

11. Mobile satellite service (MSS ) The basic MSS has several services : Maritime mobile satellite service (MMSS ) Land Mobile Satellite Service (LMSS ) Aeronautical Mobile Satellite Service(AMSS ) Personal Mobile Satellite Service (PMSS ) Broadcast Mobile Satellite Service (BMSS)

12. Maritime mobile satellite service (MMSS) This service consists of different types of earth stations such as mobile earth station (MES); ship earth station (SES); and communication earth station (CES ). This service is mainly used in shipyards and military ships

13. Land Mobile Satellite Service (LMSS ) The Land mobile satellite service has a mobile earth station located on different types of trains and other transportation systems. This service consists of a personal location terminal that acts as an earth station. This service can be used in different applications such as military applications remote and rural environments.

14. Aeronautical Mobile Satellite Service(AMSS ) A mobile satellite service in which earth stations are located onboard aircraft, survival aircraft, airplanes and helicopters is known as aeronautical mobile satellite service (AES ).

15. Personal Mobile Satellite Service (PMSS) This is a communication service provided by the satellite for supporting mobile, fixed and broadband communication systems.

16. Broadcast Mobile Satellite Service (BMSS ) A broadcast satellite system service is a one-way radio communication solution that transmits signals by earth stations, and retransmits the signals by space stations . Audio broadcasting Video broadcasting Data broadcasting

17. Aeronautical Mobile Satellite Service(AMSS ) A mobile satellite service in which earth stations are located onboard aircraft, survival aircraft, airplanes and helicopters is known as aeronautical mobile satellite service (AES ).

18. Propagation Channel Impairments The path of transmission from the transmitter to that of the receiver can vary for obstacle such as building, mountain etc is know as propagation channel impairment.

19. Basic Propagation Mechanisms Reflection Diffractin Scattering

20. IMPAIRMENT one unwanted effect of multipath propagation is that multiple copies of a signal may arrive at different phases. If these phases add destructively, as shown in figure 2.2 and 2.3, the signal level declines relative to noise this makes signal detection difficult at the receiver.

21. Refraction Refraction occurs because the velocity of an electromagnetic wave is a function of the density of the medium through which it travels. It is only in vacuum that electromagnetic wave such as light or radio wave travels at approximately 3x108 m/s. In other medium like air, water, glass and other transparent or partially transparent media, electromagnetic waves travel at lesser speed than 3x108 m/s. In a situation where an electromagnetic wave moves from a medium of one density to a medium of another density then its speed changes. The effect is to cause a one-time bending of the direction of the wave at the boundary between the two media. Waves that travel into a denser medium are bent towards the medium. This is why LOS radio waves are being bent towards the earth: the density of the atmosphere is higher closer to the ground. Figure 2.5(b) below shows refraction, the shaded portion is the denser region.

22. Shadowing Figure 2.5(a) above describes the blocking or shadowing which is an extreme form of attenuation of radio signals due to large obstacles. The higher the frequency of a signal, the more it behaves like light. Even small obstacles like wall, a truck on the street or trees in an alley may block the signal.

23. Attenuation and attenuation distortion Attenuation is a more complex function of distance and the makeup of the atmosphere for an unguided medium. Attenuation introduces three factors for the transmission engineering A received signal must have enough strength so that the electronic circuitry in the receiver can detect and interpret the signal. To avoid error at the receiver the signal must maintain a level sufficiently higher than the noise. At higher frequencies attenuation is greater and it causes distortion. In other to handle the first two factors amplifier and repeaters are used to maintain good signal strength. The third factor which is attenuation distortion, the received signal is distorted because the attenuation varies as a function of frequency reducing intelligibility. To overcome this problem, techniques are available for equalizing attenuation across a band of frequencies. One approach is to use amplifier that amplifies high frequencies more than lower frequencies.

24. Free Space Loss In free space radio signals propagate as light does, they follow a straight path from transmitter to the sender (LOS). The signal still experiences free space loss even if there is vacuum. For any type of wireless communication the signal disperses with distance. Forsatellite communication this is the primary mode of signal loss. Even if no other sources ofattenuation or impairment are assumed, a transmitted signal attenuates over distance becausethe signal is being spread over a larger area. Free space loss is expressed in terms of the ratio of the radiated power Pt to the power Pr received by the antenna or in decibels, by taking 10times the logarithm of that ratio. For ideal isotropic antenna, the free space loss is

25. Noise Any unwanted signal that are inserted somewhere between the transmission and the reception is referred to as noise. Noise is the major limiting factor in communications system performance. There are four categories of noise namely Thermal noise, Intermodulation noise, Crosstalk and Impulse noise . Thermal noise is due to thermal agitation of electrons. It is present in all electronic devices and transmission media and is a function of temperature. It is uniformly distributed across the frequency spectrum hence is often referred to as white noise. This type of noise cannot be eliminated therefore it places an upper bound on communications system performance. It is particularly significant for satellite communication. The amount of thermal noise to be found in a bandwidth of 1Hz in any device is N0 = kT (W/Hz ) where, N0 = noise power density in watts per 1Hz of bandwidth k = Boltzmann’s constact = 1.3803x10-23 J/K T = temperature, in kelvins (absolute temperatur e)

26. Intermodulation noise is as a result of signals at different frequencies share the same transmission medium. This type of noise produces signal at a frequency that is the sum or difference of the two original frequencies or multiples of those frequencies. Crosstalk is an unwanted coupling between signal paths. It can occur when unwanted signals are picked up by microwave antennas. Typically, crosstalk is of the same order of magnitude as or less than thermal noise. Impulse noise is noncontinuous, consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude. It is from a variety of causes including external electromagnetic disturbances, such as lightning, faults and flaws in the communications system.

27. Atmospheric Absorption Atmospheric absorption is another loss that can be experience between the transmittingantenna and the receiving antennas. Water vapour and oxygen contribute most to this type ofloss by attenuating the signal strength. The Speed of Mobile The relative motion between the transmitting antenna and the mobile unit results in random frequency modulation due to different Doppler shifts on each of the multipath components. Doppler shift will be positive or negative depending on whether the mobile receiver is moving toward or away from the transmitter.

28. What is Fading?? In wireless communication, fading is variation of the attenuation of a signal with various variables. These variables include time, geographical position, and radio frequency. Fading is often modeled as a random process.

29. Types of Fading The term fading refers to the time variation of a received signal power caused by changes in the transmission medium or paths. In a fixed setup, fading is affected by changes in atmospheric conditions such as rainfall. Fading can be classified based on i) Multipath time delay spread ii) Doppler spread

30. Large Scale Fading Large Scale Fading Large-scale fading is the result of signal attenuation due to signal propagation over large distances and diffraction around large objects in the propagation path. Relative Path Loss (loss due to distance) In free-space, the attenuation of a signal due to distance follows the 1/d 2 law, where d is the distance between the transmitter and the receiver. This is the case for line-of-sight (LOS) signals (path B). In the case of non-line-of-sight (NLOS) signals (path A), the attenuation is more likely to be anywhere from 1/d 3 to 1/d 6 . This additional loss of power in propagation channels occurs when part of the reflected signal is lost. Shadowing Log normal shadowing is the result of the signal being blocked by large objects in the propagation path (path D). These are typically distant objects in the environment such as mountains, hills, or large buildings. The length of time it takes for a moving receiver to pass through the "shadow" of these obstacles brings about the term "slow fading". The statistical model used to describe shadowing is the log-normal distribution of the mean signal power .

31. Multipath fading Flat fading: This form of multipath fading affects all the frequencies across a given channel either equally or almost equally. When flat multipath fading is experienced, the signal will just change in amplitude, rising and falling over a period of time, or with movement from one position to another. Selective fading: Selective fading occurs when the multipath fading affects different frequencies across the channel to different degrees. It will mean that the phases and amplitudes of the signal will vary across the channel. Sometimes relatively deep nulls may be experienced, and this can give rise to some reception problems. Simply maintaining the overall amplitude of the received signal will not overcome the effects of selective fading, and some form of equalization may be needed.

32. Fading Based on Doppler Spread Fast Fading This is a type of fading occurring with small movements of a mobile or obstacle. Higher Doppler spread Coherence time less than symbol period Channel variations faster than baseband signal variation. Slow Fading This kind of fading is caused by larger movements of a mobile or obstructions within the propagation environment. Low Doppler spread Coherence time is greater than symbol period Channel variations slower than baseband signal variations.

33. Mobile Satellite Propagation Environment

34. Probability Distribution Functions(PDF) Difference between major mobile satellite models is the variation in the method of mixing 3 basic distribution functions: Rayleigh Distribution- for urban environment Rician Distribution- describes unshadowed component Log-normal Distribution- describes shadowed propagation

35. Major Channel Models Loo’s Model Corazza’s Model Lutz’s Model Nakagami’s Model Norton’s Model

36. Loo’s Model Presents signal with amplitude that has a Rician distribution and a random LOS described by lognormal distribution PDF Merits Suitable for open areas where environment is uniform Demerits Not suitable for dense urban area where random numerous multipaths exist

37. Corazza’s Model Dependence on R(Rice) and S(lognormal) component gives below PDF of Corazza’s model with amplitude r Merits Includes the effect of slow fading(shadowing) Demerits Shadowing affects both the LOS and multipath components. may not be a proper model to describe a dense urban setting

38. Lutz’s Model Incorporates Suzuki model with the Rice distribution function, a total shadowing model. Describes good(Rician distribution) and bad(Suzuki model) channel PDF of Suzuki and Lutz model Merits Suitable to describe all mobile environments Demerits Has a lot of parameters

39. Nakagami’s Model General formula for fading, known as m-distribution Describes good(Rician distribution) and bad(Suzuki model) channel PDF Merits Reduces to Rayleigh for m = 1 and to one-sided Gaussian distribution for m = ½ Approximates Rician distribution and lognormal distributions Demerits Needs variations in environment

40. Norton’s Model Combines both Nakagami and Rice distributions PDF Merits Used for point to point microwave link Demerits Principally designed for point to point link

41. Comparison of Models Model Open Area Shadowed Area Semi-Open Semi-Shadowed Overall Performance Relative MSE Norton 0.8737 1.3680 1.4593 1.2340 1.8 Loo 0.8107 1.2554 1.4365 1.1680 1.7 Corazza 0.8177 0.9373 0.9316 0.8960 1.3 Nakagami 0.5310 1.0890 0.8622 0.8270 1.2 Lutz 0.4545 0.7823 0.8290 0.6890 1.0

42. References [1] W. Stallings. Wireless Communications and Networks, third Indian Reprint . Pearson Education Ltd., India, 2003. ISBN 81-7808-560-7. [2] Theodore S. Rappaport. Wireless Communications, principles and practice, second edition . Pearson Education, Inc., India, 2005. ISBN 81-203-2381-5. [3] Jochen schiller. Mobile Communications, second edition . Pearson Education Ltd., India, 2006. ISBN 81-7758-263-1. [4] J. D Parsons. The Mobile Radio Propagation Channel, second edition . John Wiley and Sons Ltd., . 2000. Online ISBN 0-470-84152-4. [5] Ray E. Sherriff and Y. Fun Hu. Mobile Satellite Communication Networks. John Wiley and Sons Ltd., . 2000. Online ISBN 0-470-84555-2. [6] A. Mehrnia and H. Hashemi. Mobile Satellite Propagation Channel, Part I – A comparative evaluation of current models . Proceedings of VTC’1999-Fall Conference, Amsterdam, September 19-22, 1999 .

43. Continue [7] E. Lutz. Land Mobile Satellite Channel – recording and modeling . Proceedings of the 4th International Conference on Satellite Systems for Mobile Communications and Navigation, London, October 1988, pp. 15 – 19. [8] C. Loo. A statistical model for land mobile satellite link . IEEE Transactions on Vehicular Technology, vol. 34. no. 3, pp. 122-127, August 1985. [9] H. Suzuki. A Statistical Model for Urban Radio Propagation . IEEE Transactions on Vehicular Technology, Vol. Com-25. No. 7, pp. 673-680, July 1977. [10] E. Lutz, D. Cygan, M. Dippold, F. Dolainsky and W. Papke. The Land Mobile Satellite Communication Channel – Recording, Statistics and Channel Model. IEEE Transactions on Vehicular Technology, vol. 40. no. 2, pp. 375-386, May 1991. [11] Seong-Youp Suh and Warren L. Stutzman. A land mobile satellite communications propagation simulator.

44. Thanks!