lecture 2: wireless channel propagation & …rzheng/course/cosc6397/lecture2.pdfpl d db pl d x...
TRANSCRIPT
![Page 1: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/1.jpg)
13
Lecture 2: Wireless Channel Propagation & Modulation Techniques
![Page 2: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/2.jpg)
14
Police Radar
![Page 3: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/3.jpg)
15
Basics IRandom variable X
If a probability distribution has density f(x), then intuitively the infinitesimal interval [x, x + dx] has probability f(x) dx. Cumulative distribution function Mean:
Variance:
Ex: Gaussian distribution
( ) ( )x
F x f x dx−∞
= ∫( ) ( )E X xf x dx
∞
−∞
= ∫
2 2( ( )) ( )x E x f x dxσ∞
−∞
= −∫
2
22
1 ( )( ) exp( )2
xf x µσπσ
−= −
![Page 4: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/4.jpg)
16
Basics II
Time domain Frequency domain
Period T
1/T
-1/T
( ) ( ) exp( 2 )F s f x i xs dxπ∞
−∞
= −∫Fourier Transformation
( ) ( ) exp( 2 )f x F s i xs dsπ∞
−∞
= ∫
τ
1/τ
![Page 5: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/5.jpg)
R: reflection
D: diffraction
S: Scattering
/C fλ =Ex: 3e8/2.4e9 = 12.5cm
![Page 6: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/6.jpg)
18
Propagation Model
Large-scale propagation model: the average received signal strength at a given distance from the transmitter
Useful for estimating the radio coverage areaSmall-scale propagation model: the variability of the signal strength in close spatial proximity to a particular location or short time durations
![Page 7: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/7.jpg)
19
Free-space ModelFriis free space equation:
are the antenna gains at the transmitter and receiverλ is the wavelengthd is the distanceL is a loss factor not related to propagation
2
2 2( )(4 )
t t rr
PG GP dd Lλ
π=
,t rG G
![Page 8: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/8.jpg)
20
Free Space ModelPath loss
Only valid beyond far-field distance, D is the transmitter antenna aperture
2
2 2( ) 10 log 10log(4 )
t t r
r
P G GPL dBP d
λπ
⎡ ⎤= = − ⎢ ⎥
⎣ ⎦
22
,
f
f f
Dd
d D dλ
λ
=
200 0( ) ( )( ) ,r r f
dP d P d d d dd
= ≥ ≥
dB
dBm
dBW
![Page 9: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/9.jpg)
21
Ground Reflection (Two-Ray) Model
2 2 2 2 2" ' ( ) ( ) ,
when d is large compared to
t rt r t r
t r
h hd d h h d h h dd
h h
∆ = − = + + − − + ≈
+
2 2
4
20, for d > 3
t r t rr t t r
h h h hP PG Gd
πλ
=
![Page 10: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/10.jpg)
22
Log-normal Shadowing
00
( )[ ] ( ) ( ) 10 log( )dPL d dB PL d X PL d n Xdσ σ= + = + +
Xσ is a zero-mean Gaussian distributed random variable (in dB) with standard deviation σ (also in dB)
![Page 11: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/11.jpg)
23
Small-scale FadingFactors that contribute to small-scale fading
Multi-path propagationSpeed of the mobileSpeed of surrounding objectsThe transmission bandwidth of the signal
![Page 12: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/12.jpg)
24
Parameters of Mobile Multipath ChannelsTime Dispersion (relative to direct line-of-sight)
Mean excess delayRMS delay spreadExcess delay spread (X dB)Coherence bandwidth
Measures the range of frequencies where the channel can be considered “flat”∝ 1/RMS delay spread
Frequency dispersionTD ∝ fm
![Page 13: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/13.jpg)
25
Doppler Shift Geometry
1 cos2d
vftφ θ
π λ∆
= =∆
![Page 14: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/14.jpg)
26
Police Radar
![Page 15: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/15.jpg)
27
Two independent fading issues
![Page 16: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/16.jpg)
28
Flat-fading (non-freq. Selective)Amplitude varying channel/narrowband channels
![Page 17: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/17.jpg)
29
Rayleigh fading
2
2 2( ) exp( )2
r rp rσ σ
= −
Models a flat fading channel or an individual multipath component
![Page 18: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/18.jpg)
30
Frequency selective fadingIntroduce inter-symbol interference
![Page 19: Lecture 2: Wireless Channel Propagation & …rzheng/course/COSC6397/lecture2.pdfPL d dB PL d X PL d n X σ d σ =+= + + Xσ is a zero-mean Gaussian distributed random variable (in](https://reader035.vdocuments.us/reader035/viewer/2022081515/5ed81337cba89e334c6732d4/html5/thumbnails/19.jpg)
31
Digital Communication Systems
Modulation: to translate a base-band message signal to a bandpass signal which is suitable for transmission
AmplitudeFrequencyPhaseSpread spectrum modulation
Analog
Digital (Base band) Analog (bandpass)