LINK PLANNING AND LINK BUDGETTING

In a basic communication consisting of two radios,each with it's associated antenna and separated by a distance(x),the radio require a certain minimum signal to be collected by the antennas and passed on to their input socket.Link budget calculation refers to the determination of the feasibility of the link between two antennas.This feasibility depends on the quality of the equipment being used and on the diminishment of the signal due to distance,called path loss.
The power available for a particular wireless link can be characterised by the following factors:

• Transmit Power.It is usually expressed in dB and ranges from 30mw to 200mw or more,oftenly it is dependant on transmission rate.


• Antenna Gain. Antennas are passive devices that create the effect of amplification by virtue of their physical shape.They have the same characteristics when receiving and transmitting.Parabolic antenna have a gain of 19-24 dBi,omnidirectional antennas have 5-12dBi while sectorial antennas have roughly a 12-15 dBi gain.


• Minimum Received Signal Level.This is also referred to as the sensitivity of the received.The minimum RSL is always expressed as a negative dBm and is the lowest power of the signal the radio can distinguish. The minimum RSL is dependant on the rate , and as a general rule the lowest rate (1mbps) has the greatest sensitivity.


• Cable Losses.Some energy is inevitably lost in the cables,connectors and other devices,going from the radios to the antennas.The loss depends on the type of cable and used and on its length.

To go ahead and calculate the link budget for a particular one is required to calculate the antenna gain,Losses

Antenna gain is given by:Antenna gain of radio 1 plus Antenna gain of radio 2 if there are two radios in the system.

Losses are given by:cable losses in radio 1 plus cable losses in radio 2plus free space loss

Then finally the Link budget between radio 1 and 2 is given by:

Radio 1TX power plus Antenna gain Minus Losses.And for a feasible link this should be less than the sensitivity of radio 2 and viceversa.

WAVES AND WIRELESS COMMUNICATION

A wave is a disturbance that propagates through space or space time,often transferring energy.Every wave posses frequency,speed and wavelength.Frequency refers to the number of cycles passing througth a certain point per unit time,wavelength on the other hand refers to the distance between two corresponding points on the waves.
Waves play a very important role as far as wireless communication is concerned.For a example when one is talking to somebody a distance away using a cell phone,the sound waves with which one speaks are converted into an electrical signal within the cellphone,then the antenna of the cellphone converts the electrical signal into electromagnetic waves which are propagated in space either uni directionally or omnidirectional depending on the type of antenna in use.The antenna on the receiving end captures the electromagnetic waves and converts them into electrical waves which are further converted into audible sound waves by the earpiece of the cellphone.
During this process the signal strength or the amount of energy being transferred by the wave is very critical,hence it is the desire of every engineer,technician or whoever is establishing any form of wireless communication to minimise losses in the signal strength.There are a number of threats to signal strength ,however,as they are transmitted through through the air.Objects can cause radio waves to lose signal power by their shielding effect and absorption,usually objects containing some amount of water posses greater absorption effect than dry objects.In other words humidity is direct proportion to absorption.The other factor affecting signal power of radio waves is reflection.Radio waves reflect off the surface of metals,no wonder metals find wide application in antenna production.Interference has it's own role to play as far as enhancing signal power is concerned.Destructive interference has a negative impact on signal strength while constructive interference has positive impact towards signal strength in the sense that it boost signal power of the radio waves by increasing its amplitude.
Moreover,when it comes to frequency,the higher the frequency the higher the absorption in the same vain it's true that the lower the frequency the higher the refraction.The easier way of finding out whether an object is harmful to the radio waves is by putting it in a microwave.If it gets warm then it has an absorption effect on radio waves,hence harmful to the signal.If on the other hand it remains cool then it is safe to radio waves.