1. To reduce co-channel interference, co-channel cell must be separated by a minimum distance.

2. When the size of the cell is approximately the same

–  co-channel interference is independent of the transmitted power

–  co-channel interference is a function of

• R: Radius of the cell
• D: distance to the center of the nearest co-channel cell

1. Increasing the ratio Q=D/R, the interference is reduced.Where Q is called the co-channel reuse ratio

2. For a hexagonal geometry

$Q=\dfrac{D}{R}=\sqrt{3N}$

A small value of Q provides large capacity. A large value of Q improves the transmission quality - smaller level of co-channel interference

1. A tradeoff must be made between these two objectives

Table- Co-channel Reuse Ratio for Some Values of N

1. Let i0 be the number of co-channel interfering cells. The signal-to-interference ratio (SIR) for a mobile receiver can be expressed as

$\dfrac{S}{I}=\dfrac{S}{\sum^{i_o}_{i=1}}$

S: the desired signal power

Ii : interference power caused by the ith interfering co-channel cell base station

1. The average received power at a distance d from the transmitting antenna is approximated by

$P_r=P_o\left(\dfrac{d}{d_o}\right)^{-n}$

Where n is path loss exponent which range between 2 and 4.

1. When the transmission power of each base station is equal, SIR for a mobile can be approximated as

$\dfrac{S}{I}=\dfrac{R^{-n}}{\sum^{i_o}_{i=1}(D_i)^{-n}}$

Then the relationship between S/I and N will $\dfrac{S}{I}=\dfrac{\left(\dfrac{D}{R}\right)^n}{i_n}=\dfrac{(\sqrt{3N})^n}{i_n}$