Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
E716_lec11
Search
Ahmad El-Banna
January 06, 2015
Education
1
520
E716_lec11
7th Year, Integrated Technical Education Cluster AlAmeeria
lec#11, Mobile Communication Systems
Ahmad El-Banna
January 06, 2015
Tweet
Share
More Decks by Ahmad El-Banna
See All by Ahmad El-Banna
E716_lec12
ahmad_elbanna
0
1.4k
J601_lec12
ahmad_elbanna
1
830
E716_lec10
ahmad_elbanna
0
460
J601_lec11
ahmad_elbanna
0
860
J601_lec10
ahmad_elbanna
1
860
E716_lec09
ahmad_elbanna
0
580
J601_lec09
ahmad_elbanna
0
460
J601_lec08.pdf
ahmad_elbanna
1
940
E716_lec08
ahmad_elbanna
0
380
Other Decks in Education
See All in Education
week12@tcue2024
nonxxxizm
0
680
HCI and Interaction Design - Lecture 2 - Human-Computer Interaction (1023841ANR)
signer
PRO
0
790
Comezando coas redes
irocho
0
330
脳卒中になってしまった さあ、どうする
japanstrokeassociation
0
410
Amazon Connectを利用したCloudWatch Alarm電話通知
junghyeonjae
0
230
2409_CompanyInfo_Hanji_published.pdf
yosukemurata
0
230
Epithelium Flashcards
ndevaul
0
970
2024年度春学期 統計学 第14回 分布についての仮説を検証する ― 仮説検定(1) (2024. 7. 11)
akiraasano
PRO
0
150
Skynet to Schoolnet
draycottmc
0
160
Introduction - Lecture 1 - Web Technologies (1019888BNR)
signer
PRO
0
4.8k
Zoom-ohjeet
matleenalaakso
7
7.2k
技術を楽しもう/enjoy_engineering
studio_graph
1
400
Featured
See All Featured
XXLCSS - How to scale CSS and keep your sanity
sugarenia
246
1.3M
Measuring & Analyzing Core Web Vitals
bluesmoon
1
40
Large-scale JavaScript Application Architecture
addyosmani
510
110k
The Art of Delivering Value - GDevCon NA Keynote
reverentgeek
7
150
Building Your Own Lightsaber
phodgson
102
6k
Unsuck your backbone
ammeep
668
57k
Facilitating Awesome Meetings
lara
49
6k
JavaScript: Past, Present, and Future - NDC Porto 2020
reverentgeek
47
5k
Designing the Hi-DPI Web
ddemaree
280
34k
Navigating Team Friction
lara
183
14k
Embracing the Ebb and Flow
colly
84
4.4k
Evolution of real-time – Irina Nazarova, EuRuKo, 2024
irinanazarova
4
290
Transcript
Instructor: Dr. Ahmad El-Banna January 2015 E-716-A Mobile Communications Systems
Integrated Technical Education Cluster At AlAmeeria © Ahmad El-Banna 1 Lecture #11 Effects of Mobile Radio Propagation (p2)
Agenda Fading Doppler Shift Channel Models ISI 2 E-716-A, Lec#11
, Jan 2015 © Ahmad El-Banna
3 Fading Signal Strength (dB) Distance Path Loss Slow Fading
(Long-term fading) Fast Fading (Short-term fading) © Ahmad El-Banna • Large-scale fading (shadowing) • Long term variation in the mean signal level caused by the mobile unit moving into the shadow of surrounding objects • Small-scale fading (multipath) • Short term fluctuation in the signal amplitude caused by the local multipath E-716-A, Lec#11 , Jan 2015
Shadow Fading • Long term shadow fading due to variations
in radio signal power due to encounters with terrain obstructions such as hills or buildings. • The measured signal power differ basically at different locations even though at the same radial distance from a transmitter. • Represents the medium scale fluctuations of the radio signal strength over distances from tens to hundreds of meters. • Many empirical studies demonstrate that the received mean power fluctuates about the average power with a log-normal distribution. • Can be modeled by a Gaussian random variable with standard deviation . 4 Shadow Long term Large Scale Log-normal Slow © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
5 • Log-normal distribution: - The pdf of the received
signal level is given in decibels by where P is the true received signal level, ̅P is the area average (mean) signal level, is the standard deviation 2 2 2 2 1 P P e P p The pdf of the received signal level Shadow fading.. pdf : probability density function © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Multipath Fading • A small scale fading that describes short-term,
rapid amplitude fluctuations of the received signal during a short period of time. • The actual power received over a much smaller distance vary considerably due to the destructive/constructive interference of multiple signals that follow multiple paths to the receiver. • The direct ray is actually made up of many rays due to scattering multiple times by obstructions along its path, all travelling about the same distance. • Each of these rays appearing at the receiver will differ randomly in amplitude and phase due to the scattering. 6 Multipath Short term Small Scale Fast © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Multipath Fading.. • Small-scale fading can be further classified into
• Flat(or non-selective) Fading • Frequency Selective Fading Flat fading • Small-scale fading is defined as being flat if the received multipath components of a symbol do not extend beyond the symbol’s time duration. • If the delay of the multipath components with respect to the main component is smaller than the symbol’s duration time, a channel is said to be subject to flat fading. 7 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Flat Fading • In a flat fading channel inter-symbol interference
(ISI) is absent. • The channel has a constant gain and a linear phase response over a bandwidth that is greater than the bandwidth of the transmitted signal. • The spectral characteristics of the transmitted signal are preserved at the receiver. • The channel does not cause any non-linear distortion due to time dispersion. • However, the strength of the received signal generally changes slowly in time due to fluctuations caused by multipath. • In a flat-fading channel, the bandwidth of the transmitted signal, Bs is much less than the Coherence bandwidth, Bc of the channel. 8 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Frequency Selective Fading • Small-scale fading is defined as being
frequency selective if the received multipath components of a symbol extend beyond the symbol’s time duration • The effect of multipath fading on the reception of signals depends on the signal bandwidth. • For relatively large bandwidth, different parts of the transmitted signal spectrum are attenuated differently. • This is manifested in the inter-symbol interference (ISI) • If the delay of the multipath components with respect to the main component is larger than the symbol’s duration time, a channel is said to be subject to frequency selective fading • The received signal includes multiple versions of the same symbol, each one attenuated (faded) and delayed. • The received signal is distorted producing ISI. 9 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Frequency Selective Fading.. • The channel has a constant gain
and a linear phase response over a bandwidth that is much smaller than the bandwidth of the transmitted signal. • The spectral characteristics of the transmitted signal are not preserved at the receiver • Certain frequency components have larger gains than others. • the bandwidth of the transmitted signal, Bs is much greater than the Coherence bandwidth of the channel Bc. 10 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Multipath Fading Modeling • For flat fading, it is found
that the multipath can be modeled by using • Rayleigh statistics • Ricean statistics • With Rayleigh statistics, the pdf of the random variable (r) is given by: 11 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015 0 , 2 2 2 2 r e r r p r
Rayleigh Fading • Rayleigh fading is viewed as a reasonable
model for urban environments where there are many objects in the environment that scatter the radio signal before it arrives at the receiver • There is no dominant propagation along line of sight LOS between the transmitter and receiver. • The envelope of the channel response will therefore be Rayleigh distributed. 12 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Rician Fading • If the environment is such that, in
addition to the scattering, there is a strongly dominant signal seen at the receiver, usually caused by a LOS, then the mean of the random process will no longer be zero, varying instead around the power-level of the dominant path. • Such a situation may be better modeled as Rician fading. 13 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015 0 , 0 2 2 2 2 2 r r I e r r p r where: is the standard deviation, I0 (x) is the zero-order Bessel function of the first kind, is the amplitude of the direct signal
Doppler shift • Small-scale fading due to movements: Doppler shift
• How rapidly the channel fades will be affected by how fast the receiver and/or transmitter are moving . • Motion causes Doppler shift in the received signal components • It’s the change in frequency of a wave for a receiver moving relative to the transmitter • When they are moving toward each other, the frequency of the received signal is higher than the source. • When they are opposing each other, the frequency decreases. 14 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
15 • Thus, the frequency of the received signal is
where fC is the frequency of source carrier, fD is the Doppler frequency. • Doppler Shift in frequency: where v is the moving speed, is the wavelength of carrier. cos v f D D C R f f f MS Signal Moving speed v ϴ Doppler shift © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
16 • When a signal propagates from a transmitter to
a receiver, signal suffers one or more reflections. • This forces signal to follow different paths. • Each path has different path length, so the time of arrival for each path is different. • This effect which spreads out the signal is called “Delay Spread”. Delay Spread © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Fast and Slow Fading • Slow or fast fading depends
on the coherence time, Tc. • Coherence time is the measure of period over which the fading process is correlated. • Tc is related to the delay spread, Tc=1/ds • The fading is said to be slow if the symbol duration, Ts is smaller than Tc the coherence time (or the bandwidth of the signal is greater than the Doppler spread). 17 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015
Small-Scale Fading Summary 18 © Ahmad El-Banna E-716-A, Lec#11 ,
Jan 2015
Channel Models Summary • Gaussian (Shadow Fading) • Rician (Multipath
Flat Fading, LOS) • Rayleigh (Multipath Flat Fading, no LOS) 19 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015 AWGN : Additive White Gaussian Noise
Inter Symbol Interference (ISI) • Caused by time delayed multipath
signals. • Second multipath is delayed and is received during next symbol. • For low bit-error-rate (BER) • R (digital transmission rate) limited by delay spread td . 20 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015 d R 2 1
21 Time Time Time Transmission signal Received signal (short delay)
Received signal (long delay) 1 0 1 Propagation time Delayed signals © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015 ISI..
• For more details, refer to: • A. Goldsmith, Wireless
Communications, 2004. • T. Rappaport, Wireless Communications, principals and practice , 2002. • The lecture is available online at: • https://speakerdeck.com/ahmad_elbanna • For inquires, send to: •
[email protected]
22 © Ahmad El-Banna E-716-A, Lec#11 , Jan 2015