Question

What is interference? Explain co-channel and adjacent channel interference and how do you combat them.

Calculate the frequency re-use distance and the co-channel re-use ratio if the cell radius 2, i=3 and j=2.

Answer 1

Co-channel interference occurs when 2 or more AP's are using the same channel. It causes unnecessary contention as all AP's and clients will be forced to defer transmissions until the medium is clear. 802.11 is designed to cope with this situation but it can cause a loss of throughput.

Adjacent channel interference is more serious and occurs when 2 or more AP's are on overlapping channels, for example channel 1 + 4 on the 2.4Ghz band. ACI creates overlap in the frequency space causing corrupted data and layer 2 re-transmissions.

N is the number of cells which collectively use the complete set of available frequencies is called a Cluster. The value of N is calculated by the following formula:

N = I2 + I*J + J2

^{N= 9+6+4}

^N=19

The distance between any two Co-Channels can be calculated by the following formula:

 D = R * (3 * N)1/2

Where,
R = Radius of a cell
N = Number of cells in a given cluster

Then

D=2√57

Frequency reuse distance d=√3R

d=2√3 answer