The Wireless Communication Channel
description
Transcript of The Wireless Communication Channel
![Page 1: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/1.jpg)
The Wireless Communication Channel
muse
![Page 2: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/2.jpg)
Objectives
• Understand fundamentals associated with free-space propagation.
• Define key sources of propagation effects both at the large- and small-scales
• Understand the key differences between a channel for a mobile communications application and one for a wireless sensor network
muse
![Page 3: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/3.jpg)
Objectives (cont.)
• Define basic diversity schemes to mitigate small-scale effects
• Synthesize these concepts to develop a link budget for a wireless sensor application which includes appropriate margins for large- and small-scale propagation effects
muse
![Page 4: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/4.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 5: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/5.jpg)
Free-space propagation
• Scenario
Free-space propagation: 1 of 4
![Page 6: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/6.jpg)
Relevant Equations
• Friis Equation
• EIRP
Free-space propagation: 2 of 4
![Page 7: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/7.jpg)
Alternative Representations
• PFD
• Friis Equation in dBm
Free-space propagation: 3 of 4
![Page 8: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/8.jpg)
Issues
• How useful is the free-space scenario for most wireless systems?
Free-space propagation: 4 of 4
![Page 9: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/9.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 10: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/10.jpg)
Large-scale effects
• Reflection
• Diffraction
• Scattering
Large-scale effects: 1 of 7
![Page 11: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/11.jpg)
Modeling Impact of Reflection
• Plane-Earth model
Large-scale effects: 2 of 7Fig. Rappaport
![Page 12: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/12.jpg)
Modeling Impact of Diffraction
• Knife-edge model
Large-scale effects: 3 of 7Fig. Rappaport
![Page 13: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/13.jpg)
Modeling Impact of Scattering
• Radar cross-section model
Large-scale effects: 4 of 7
![Page 14: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/14.jpg)
Modeling Overall Impact
• Log-normal model
• Log-normal shadowing model
Large-scale effects: 5 of 7
![Page 15: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/15.jpg)
Log-log plot
Large-scale effects: 6 of 7
![Page 16: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/16.jpg)
Issues
• How useful are large-scale models when WSN links are 10-100m at best?
Free-space propagation: 7 of 7Fig. Rappaport
![Page 17: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/17.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 18: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/18.jpg)
Small-scale effects
• Multipath
• Time and frequency response
• Models
Small-scale effects: 1 of 14
![Page 19: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/19.jpg)
Multipath
• Scenario
• Equations
Small-scale effects: 2 of 14
![Page 20: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/20.jpg)
Time and Frequency Response
• Case 1: primary and secondary paths arrive at same time (path Δ = 0)
• Multipath component: -1.7 dB down
Small-scale effects: 3 of 14
![Page 21: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/21.jpg)
Time and Frequency Response
• Case 2: primary and secondary paths arrive at same time (path Δ = 1.5m)
Small-scale effects: 4 of 14
![Page 22: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/22.jpg)
Time and Frequency Response
• Case 3: primary and secondary paths arrive at same time (path Δ = 4.0m)
Small-scale effects: 5 of 14
![Page 23: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/23.jpg)
Time and Frequency Response
• Case 4: primary and secondary paths arrive at same time (path Δ = 4.5m)
Small-scale effects: 6 of 14
![Page 24: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/24.jpg)
Real World Data
Fig. Frolik – IEEE TWC Apr. 07 Small-scale effects: 7 of 14
![Page 25: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/25.jpg)
Randomness in the Channel
• Sources
• Impact
Small-scale effects: 8 of 14
![Page 26: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/26.jpg)
Statistical Channel Models
• TWDP
Small-scale effects: 9 of 14
![Page 27: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/27.jpg)
Baseline: Rayleigh Distribution
• Scenario
• Equations
Small-scale effects: 10 of 14
![Page 28: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/28.jpg)
Cumulative Distribution Function
Small-scale effects: 11 of 14
![Page 29: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/29.jpg)
Ricean: Less Severe than Rayleigh
Small-scale effects: 12 of 14
![Page 30: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/30.jpg)
More Severe than Rayleigh?
Small-scale effects: 13 of 14
![Page 31: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/31.jpg)
Importance of Proper Model
Small-scale effects: 14 of 14
![Page 32: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/32.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 33: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/33.jpg)
Mobile vs. WSN channels
Mobile WSN
Mobile vs. WSN: 1 of 3
![Page 34: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/34.jpg)
Channel Effects
Mobile WSN
Mobile vs. WSN: 2 of 3Fig. Rappaport
![Page 35: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/35.jpg)
Real world data revisited
Fig. Frolik – IEEE TWC Apr. 07 Mobile vs. WSN: 3 of 3
![Page 36: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/36.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 37: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/37.jpg)
Diversity schemes
• Time
• Space
• Frequency
Diversity schemes: 1 of 3
![Page 38: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/38.jpg)
Approaches
• MRC
• Selection
Diversity schemes: 2 of 3
![Page 39: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/39.jpg)
Benefits
Diversity schemes: 3 of 3Fig. Bakir – IEEE TWC
![Page 40: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/40.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 41: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/41.jpg)
Link budgets
• Link parameters
Link budgets: 1 of 5
![Page 42: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/42.jpg)
Antenna Requirement?
Link budgets: 2 of 5
![Page 43: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/43.jpg)
Example Spreadsheet
Link budgets: 3 of 5
Parameter Units Value Comments
Transmitting Node
Frequency GHz 2.4 ISM band
Transmit Power dBm 0.0 1 mW - Chipcon CC2520 -20 to +5 dBm
Transmit Antenna Gain dBi 3.0 Hyperlink 'rubber-duck' antenna
Transmit EIRP dBm 3.0
Free-space loss to 1m dB -40.0 (lambda/4pi)^2
Power at 1m dBm -37.0
Losses
Path loss exponent 3.0 determined from empirical data
Range m 30.0
Median path loss dB -44.3 from log-normal model
Received Signal
Receive Antenna Gain dBi 3.0 Hyperlink 'rubber-duck' antenna
Median Received Signal Strength dBm -78.3
Receiver Sensitivity dBm -98.0 Chipcon CC2520
Fading Margin dB 19.7 Reliability?
![Page 44: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/44.jpg)
Path loss exponent
Link budgets: 4 of 5
![Page 45: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/45.jpg)
Margin Calculation
Link budgets: 5 of 5
![Page 46: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/46.jpg)
Outline
• Free-space propagation • Large-scale effects and models• Small-scale effects and models• Mobile communication channels vs. wireless
sensor network channels• Diversity schemes• Link budgets• Example Application: WSSW
![Page 47: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/47.jpg)
Example: WSSW
• Motivation
• Approach
WSSW: 1 of 2
![Page 48: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/48.jpg)
WSSW Results
WSSW: 2 of 2
![Page 49: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/49.jpg)
Conclusions - 1
• As intuitively suspected, signal strength on average decreases with T-R distance
• Large-scale effects determine the rate of signal strength degradation with distance
• Small-scale effects may severely impact signal strength in highly reflective environments
• Diversity schemes can mitigate the small-scale effects
muse
![Page 50: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/50.jpg)
Conclusions - 2
• WSN have unique constrains which may not be best modeled using mobile communication methods
• Link budgets are critical in order ascertain requisite transmit powers, expected connectivity length, etc.
• Sensor nodes themselves can be utilized to ascertain channel characteristics
muse
![Page 51: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/51.jpg)
Want to know more?
• T. Rappaport, Wireless Communications: Principles and Practice, 2nd ed., Prentice Hall.
• J. Frolik, ‘A case for considering hyper-Rayleigh fading,’ IEEE Trans. Wireless Comm., Vol. 6, No. 4, April 2007.
• L. Bakir and J. Frolik, ‘Diversity gains in two-ray fading channels,’ in review IEEE Trans. Wireless Comm.
muse
![Page 52: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/52.jpg)
Discussion of Code
Code: 1 of 5
![Page 53: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/53.jpg)
Time and Frequency Response
Code: 2 of 5
![Page 54: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/54.jpg)
Matlab Code for Channel Responsec=3e8; %speed of light
d=linspace(0, 5, 10); %relative distance in metersf=linspace(2.4e9, 2.48e9, 100); % frequency: 2.4 GHz
ISM band
for i=1:10, for k=1:100,
s1=.55; % voltage of primary path
s2=(1-s1)*exp(-j*2*pi*f(k)*d(i)/c); % voltage of multipath (1-s1) as a function of frequency and path difference
x(i,k)=20*log10(abs(s1+s2)); %received voltage (complex)
t(i)=d(i)/c; % time delay (sec)
end
%create stem plot of channel impulse response subplot(2,1,1)X=[0,t(i)];Y=[s1,abs(s2)];h=stem(X,Y);set(h(1),'MarkerFaceColor','red','Marker','square')axis([-.5e-8,2e-8, 0, 1])title('channel impulse response')xlabel('time (sec)')ylabel('volts')
%create channel frequency response plot subplot(2,1,2) plot(f,x(i,:)) axis([2.4e9, 2.48e9, -30, 5]) title('channel frequency response') xlabel('frequency (Hz)') ylabel('normalized loss (dB)')
pauseend
Code: 3 of 5
![Page 55: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/55.jpg)
CDF plots
Code: 4 of 5
![Page 56: The Wireless Communication Channel](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813a3e550346895da22820/html5/thumbnails/56.jpg)
Matlab Code for CDF• % CDF routine• Rsort=sort(Rlog); %Rlog is the data from the inband• n=max(size(Rsort));• for i=1:n,• • cdf(i)=i;• • end• cdf=cdf/max(cdf); % index equals probability• • % searching for 1/2 to make 0 dB• for i=1:n,• if cdf(i)>=0.5,• shiftzero=Rsort(i) %median value• break• end• end• Rsortzs=Rsort-shiftzero;• • semilogy(Rsortzs, cdf, 'g')• axis([-30 10 1e-3 1])• axis square• xlabel('Relative Amplitude (dB), 50% @ 0 dB')• ylabel('Cumulative Probability')
Code: 5 of 5