Straight path is clear of obstacles between the receiver and sender called line-of-sight. For high frequencies require line-of-sight more better than low frequency.
There are two terms
● Optical Line-of-sight, the two stations can optically see each other
● Radio line-of-sight, no reflection or
line-of-sight Calculation is necessary when you build wireless network outside the building (outdoor). You can find how to calculate Link budget for outdoor Propagation in this blog. we can used excell to provide a calculator to help you calculate radio links outdoor.
There are 4 parameters that are used to calculate the W-LAN systems outdoor work well:
● System Operating Margin (SOM), associated with strength sender, the type of antenna, coaxial cable length and distance.
As an illustration of calculation, on the 802.11b specification, the recipient (Receiver) has a sensitivity of -80 to -85 dBm. On the client side, normally we use a directional antenna, such as antenna parabola with the addition of 19-24 dBm. Loss of signal for coaxial cable between 2-3 dB. To cover the operating margin (SOM) 10-15 dB is highly dependent on type of antenna used on the Access Point. If using an antenna (Discussed next) omnidirectional with the addition of 10-12 dB, we get a coverage area of 4-5 km. If using a sectoral antenna (Directional).with the addition of 12-14 dB, we can cover 6-8 Km.
Free Space Loss (FSL): lost power after a distributed radio at a certain distance.
Example:
FSL for a distance of 5 km at a frequency of 2.4 GHz is 114 dB. Normally (by Onno W. Purbo) per distance of 1 km at 2.4 GHz will have the FSL in the range of 100dB.
Fresnel Zone Clearance (FZC), to see the need for high antenna to go through obstacle.
Fresnel Zone is an area not there are barriers between the two terminal. Usually for the 1st 80% Fresnel Zone. formula:
R = 43.3 sqrt (d / 4f)
Where:
R : Radius Freznel Zone
d : Path length 2 node
f : frequency
Here is a table FZC to 1-7 km distance to the terminal Wi-Fi operates at 2.4 GHz
Antenna bearing, tilt down the antenna and the coverage radius antennas need to know to cover an area.
Where Hb is the height of the BTS antenna and receiver antenna height Hr is and A is the angle in radians.
For example: for a BTS with a height of 30 m to cover distance of 3 km, take the angle of degrees to achieve 0:35 receiving antenna height of 10 m. In some cases we need the approximate area of coverage can be calculated by the formula:
Where H is the height of the BTS, A is the antenna tilt angle, BW is the width of coverage (beam).
For example:
to an access point with antenna height 30 m, and beam width 10 degrees with 0.2 degree angle, we will achieve the inner 150 m radius and outer radius of 8.7 km.
Antenna
The antenna is needed if we install a wireless network infrastructure for outdoor. The antenna will change from electric signals into electromagnetic signals. The amount of energy that can be amplified by the antenna on the side recipient or the sender is called the antenna gain.
Directional Antenna
antenna which amplifies the signal from the sender to dirambatkan on one or two directions. There are two categories: parabolic and phased arrays. Parabolic used for medium or long distances and can provide gain
between 18-28 dBi. Example:
Yagi Phased Array
This antenna is suitable for short distances with a gain of 7-15 dBi
● Sectoral Antenna
is a phased array type that divides the coverage area of a circle into several sectors to help the channel allocation and use of repeated. A sectoral antenna has a beam of approximately 120 degrees that divides one area of the circle into 3 areas.
By used sectoral antenna would be more efficient rather than the use of omnidirectional installation.
No comments:
Post a Comment