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FresnelZone
HUMACAO � CAYO SANTIAGO WIRELESS LINK Calculations Assumptions:
- Tide profile in Puerto Rico East Coast is similar to the Magueyes Island tide profile, no data where available in the NOS (National Ocean Service) site for the East Coast.
- References:
http://www.cisco.com/warp/public/cc/pd/witc/ao340ap/prodlit/airoa_ds.htm
http://www.cisco.com/warp/public/cc/pd/witc/ao340ap/prodlit/airob_ds.htm http://www.breezecom.com/HomePage.asp
PATH DESIGN
Antennas Heights:
A radio wave clear line of sight exists if a defined area around the optical line of sight (1st Fresnel Zone) is clear of obstacles.
The first Fresnel Zone radius is given by:
R = œ √ (λ x D)
λ = c / f
R: radius of the first Fresnel Zone
λ: wavelength
D: distance between sites
c : speed light constant (3*108 m/s)
f : signal frequency
For the worst case f = 2483.5 MHz?
R = œ √ ((3*108 m/s / 2483.5 MHz?) * 2 km) = 7.8 m
Taking into account the tide profile for this site, the minimum antenna height to keep the first Fresnel Zone clear of obstacles under sunny day conditions is given by:
Antenna Height = R + 0.7 = 7.8 + 0.7 = 8.5 m
To prevent signal degradation during storm conditions 0.5 + MHHW (Mean higher high water) m should be added to this height, this takes into account the 1998 George Hurricane
data .
Received power at receiving end formulas:
Pout Output power of transmitted in dBm
Ct Transmitter cable attenuation in dB
Gt Transmitting antenna gain in dBi
Gr Receiving antenna gain in dBi
Pl Path loss in dB
Cr Receiver cable attenuation is dB
Si Received power level at receiver input in dBm
Ps Receiver sensitivity is dBm
Rdl Rainy day loss.
At high rain intensity(150 mm/hr), the fading of an RF signal at 2.4 Ghz may reach a maximum of 0.02 dB/Km.
Si = EIRP - Pl + Gr � Cr - Rdl
EIRP (Effective Isotropic Radiated Power) = Pout - Ct + Gt
Pl = 32.4 + 20xLog F(MHz?) + 20xLog R(Km)
Link Parameters:
Maximum Frequency: 2483.5 MHz? (Cisco AIR-BR342 Ethernet Bridge)
Pout = 20 dBm (Cisco AIR-BR342 Ethernet Bridge transmit power 100mW)
Tx and Rx cable length (Ct and Cr) = 6.7 dBi (30 m cable type Cisco AIR-420-003346-100)
Tx and Rx antenna gain (Gt and Gr) = 21 dBi (Cisco AIR-ANT3338)
Distance between sites = 2 Km
Receiver sensitivity threshold (Ps) = +/-75dBm (Cisco AIR-BR342 Ethernet Bridge)
Link Budget Calculation
EIRP = 20 dBm - 6.7 dBi + 21 dBi = 34.3dBm
Pl = 32.4 + 20xLog 2483.5MHz + 20xLog 2.0Km = 106.3dB
Si = 34.3dB - 106.3dB + 21 dBi � 6.7 dBi - 0.04 dB = -57.74dBm
In conclusion, the received signal power is above the receiver sensitivity threshold, so the link should work.
