9/21/2015© 2009 Raymond P. Jefferis III Lect Geographic Information Processing Radio Wave Propagation Line-of-Sight Propagation in cross-section and relief - Hupfer et al.

9/21/2015© 2009 Raymond P. Jefferis III Lect Radio Wave Transmission Electromagnetic energy in orthogonal fields –Electric field energy –Magnetic field energy Radiate from source antenna –Power spread over spherical wavefront –Power/Area decreases with distance as area of sphere increases and as losses dissipate energy –Energy can be focused in desired direction

9/21/2015© 2009 Raymond P. Jefferis III Lect Radio Wave Reception Receiver responds to vector sum of arriving waves (out-of-phase waves interfere) Subject to receiver sensitivity limits Antennas with directional gain can focus energy from particular direction(s)

9/21/2015© 2009 Raymond P. Jefferis III Lect Engineering Problem Specify transmitter power and antenna gain in direction of receiver Specify receiver sensitivity and the operable corresponding antenna gain Determine path loss over topography Compare received power with sensitivity limit and modify conditions as necessary

9/21/2015© 2009 Raymond P. Jefferis III Lect Path Criterion A radio wave takes the path of minimum time. In free space (no diffraction or reflection) this will be a straight line.

9/21/2015© 2009 Raymond P. Jefferis III Lect Reduction in Output/Input ratio of amplitude of radio wave Usually measured in decibels (dB) –Power Attenuation: –Voltage Attenuation: Attenuation

9/21/2015© 2009 Raymond P. Jefferis III Lect Energy in Electric Field Where: –w = Energy Density [Joules/m 2 ] –E = electric field intensity [V/m] –  = dielectric permittivity of free space

9/21/2015© 2009 Raymond P. Jefferis III Lect Energy in Electric Field Where: –p = Average Power Density [Watts/m 2 ] –E = Electric field intensity [V/m] –R o = Impedance of free space [~377 Ohms]

9/21/2015© 2009 Raymond P. Jefferis III Lect Radio Wave Attenuation Factors Distance Diffraction from objects in propagation path Reflection from objects near path Conduction/reflection/refraction by various atmospheric effects Scattering by objects and atmospheric components

9/21/2015© 2009 Raymond P. Jefferis III Lect Transmission Losses Transmitted electromagnetic energy is lost on its way to a receiving station due to a number of factors, including: – Antenna efficiency– Path loss – Antenna aperture gain– Atmospheric loss – Path loss– Diffraction loss

9/21/2015© 2009 Raymond P. Jefferis III Lect Issues with Reflection Out-of-Phase waves cancel primary wave –Various reflecting surfaces => different arrivals –Random arrival phasea produce noise floor Digital symbols –Inter-symbol interference –Data rate must be limited to allow each symbol to extinguish itself before next

9/21/2015© 2009 Raymond P. Jefferis III Lect Transmitter Power P t = 10 Log 10 P mW [dBm] Example: 5 Watts = 5000 mW P t [dBm] = 10 Log = 37 dBm Example: 40 Watts = mW P t = 10 Log = 46 dBm For propagation loss calculations, dBm units are more convenient than power.

9/21/2015© 2009 Raymond P. Jefferis III Lect Antenna Gain A e = effective antenna aperture G = 4  A e /  2 (Antenna Gain) d = antenna diameter λ = wavelength  = aperture efficiency

9/21/2015© 2009 Raymond P. Jefferis III Lect Path Losses Effective Aperture (transmit or receive): A e =  A Effective Radiated Power: EIRP = P t G t = P t  ta A t where, G t = 4  A et /  2 G r = 4  A er /  2 Path Loss (for path length R): L p = (4  R/  2 Received Power: P r = EIRP*G r /L p

9/21/2015© 2009 Raymond P. Jefferis III Lect Receiver Sensitivity Usually specified in microvolts on 50-Ohm input connector Can be converted to power by: For typical sensitivity of 0.18 microVolts: [Watts]

9/21/2015© 2009 Raymond P. Jefferis III Lect Receiver Sensitivity [dBm] dBm => dB milliWatts P r [dBm] = 20 log 10 [P r /10 -3 ] where P r is given in Watts Converting the receiver sensitivity to dBm, For proper reception, the transmitted signal must not fall below this level. [dBm]

9/21/2015© 2009 Raymond P. Jefferis III Lect Received Power - dB Model (Pratt & Bostian, Eq. 4.11) P r = EIRP +G r - L p - L a - L t - L r [dBW] –EIRP => Effective radiated power –G r => Receiving antenna gain –L p => Path loss –L a => Atmospheric attenuation loss –L t => Transmitting antenna losses –L r => Receiving antenna losses

9/21/2015© 2009 Raymond P. Jefferis III Lect Path Models Free-Space Partially Obstructed Largely Obstructed Totally Obstructed

9/21/2015© 2009 Raymond P. Jefferis III Lect Free-Space Model No obstructions in or “near” path Note: Path is elliptical (Fresnel) volume surrounding line-of-sight ray path. Obstructions must be outside first “Fresnel Zone” - See next slide

9/21/2015© 2009 Raymond P. Jefferis III Lect Fresnel Zones Elliptical zones of radiated energy between transmitted and receiver Wikipedia -

9/21/2015© 2009 Raymond P. Jefferis III Lect Partially Obstructed Path Model Obstructions in, but not occluding, path Note: Path is elliptical (Fresnel) volume surrounding line-of-sight ray path. Obstructions inside first “Fresnel Zone” but not by more than 40%

9/21/2015© 2009 Raymond P. Jefferis III Lect Highly Obstructed Path Model Obstructions in, but not occluding, path Note: Path is elliptical (Fresnel) volume surrounding line-of-sight ray path. Obstructions inside first “Fresnel Zone” and occlude it by more than 40% but not completely

9/21/2015© 2009 Raymond P. Jefferis III Lect Fully Obstructed Path Model Obstructions occluding, path Note: Path is elliptical (Fresnel) volume surrounding line-of-sight ray path. Obstructions inside first “Fresnel Zone” occlude it completely. Energy confined to higher-order Fresnel zones.

9/21/2015© 2009 Raymond P. Jefferis III Lect Free-Space Path Loss Model Free space loss [Watts]: Free space loss [dB]: Log f [MHz] + 20 Log d [Km] –f is the radio frequency [MHz] –d is the distance [km] between the transmitting and receiving antennas

9/21/2015© 2009 Raymond P. Jefferis III Lect Loss Calculation #1 Let f = 146 MHz, d = 10 km Loss dB = log 10 (146) + 20log 10 (10) Loss dB = = 95.7 dB The receiver signal strength for 40-Watts is: P r [dBm] = = dB Conclusion: 10 km free-space signal path is okay at this frequency.

9/21/2015© 2009 Raymond P. Jefferis III Lect Loss Calculation #2 Let f = 146 MHz, d = 100 km Loss dB = log 10 (146) + 20log 10 (100) Loss dB = = dB The receiver signal strength for 40-Watts is: P r [dBm] = = dB Conclusion: 100 km free-space signal path is too long for reliable reception at this frequency.

9/21/2015© 2009 Raymond P. Jefferis III Lect MHz Digital Data Sensitivity

9/21/2015© 2009 Raymond P. Jefferis III Lect Loss Calculation #3 Let f = 1300 MHz, d = 20 km Loss dB = log 10 (1300) + 20log 10 (20) Loss dB = = dB The receiver signal strength for 10-Watts is: P r [dBm] = = dB Conclusion: 20 km free-space signal path is too long at this frequency.

9/21/2015© 2009 Raymond P. Jefferis III Lect Antenna Gain Antenna radiation patterns direct energy, resulting in gain in certain directions. Antenna gain [dB] adds to the reference propagation gain (subtracts from propagation loss) in certain directions.

9/21/2015© 2009 Raymond P. Jefferis III Lect Ex. #3 with 16 dB Antenna Gain Let f = 146 MHz, d = 100 km Loss dB = log 10 (146) + 20log 10 (100) Loss dB = = dB The receiver signal strength for 40-Watts is: P r [dBm] = = dB Conclusion: 100 km free-space signal path is okay for reliable reception at this frequency, if trans- mitter and receiver each have 8 dB antenna gain.

9/21/2015© 2009 Raymond P. Jefferis III Lect Diffraction Model

9/21/2015© 2009 Raymond P. Jefferis III Lect Obstruction Loss Model Horizontal axis is

Obstruction of Fresnel Zone 9/21/2015© 2009 Raymond P. Jefferis III Lect Building roof at edge of 1st Fresnel zone

Conclusions A building reaching to edge of the 1st Fresnel zone produces 6 dB loss (loss of ¾ of radiated power) Obstruction of entire 1st Fresnel zone would be a significant loss to a communication system 9/21/2015© 2009 Raymond P. Jefferis III Lect

9/21/2015© 2009 Raymond P. Jefferis III Lect Obstruction Loss Calculations Use value of , enter previous graph, and read loss in dB, or calculate knife-edge loss J(  )as:

9/21/2015© 2009 Raymond P. Jefferis III Lect Obstructed Fresnel Zones in Path From Lewis Girod, Graph attributed to Rappaport, Wireless Communications: Principles and Practice, Prentice Hall, 1996, p 97

9/21/2015© 2009 Raymond P. Jefferis III Lect More Exact Fresnel Loss Fresnel loss, where C = Fresnel cosine integral S = Fresnel sine integral

9/21/2015© 2009 Raymond P. Jefferis III Lect Fresnel Loss Magnitude Square root of F(  ) * F * (  )

9/21/2015© 2009 Raymond P. Jefferis III Lect Logarithmic Fresnel Loss This loss should be added to the free-space propagation loss in dB.

9/21/2015© 2009 Raymond P. Jefferis III Lect Practical Problem Calculate the path loss between two points on a topographic map having a free-space path between them with no obstructions near the first Fresnel zone.

Fresnel Radius(f) For d 1 = d 2 = d the Fresnel radius at the midpoint becomes: 9/21/2015© 2009 Raymond P. Jefferis III Lect

9/21/2015© 2009 Raymond P. Jefferis III Lect LOS Distance Attenuation

9/21/2015© 2009 Raymond P. Jefferis III Lect Path Shaded by LOS Attenuation 1300 GHz radio path over rough terrain, showing First Fresnel zone. Terrain is tinted according to the Line-of-Sight propagation losses. (Blue is max. loss)

Line-of-Sight Path Get starting point and its antenna height Get destination point with antenna height Draw air path between these points Calculate and plot terrain below air path Calculate radiation-terrain clearance on path Identify interfering terrain Add transmission loss from terrain 9/21/2015© 2009 Raymond P. Jefferis III Lect

Example Point A Antenna antlat = N antlon = W anthgt = 40.0 [meters] Point B Fire truck trklat = N trklon = W trkhgt = 2.5 [meters] 9/21/2015© 2009 Raymond P. Jefferis III Lect

Radiation Path Black line on terrain at lower right is path 9/21/2015© 2009 Raymond P. Jefferis III Lect

Close-up of Radiation Path Point A (Left) is on a hilltop Point B (Right) is in a developed area 9/21/2015© 2009 Raymond P. Jefferis III Lect

Path and Cross-Section 9/21/2015© 2009 Raymond P. Jefferis III Lect

Discussion of Programming Discussion in class... 9/21/2015© 2009 Raymond P. Jefferis III Lect