**Branch :**Computer Science and Engineering

**Subject :**Wireless Communication

## Capacity of Cellular Systems

**Introduction: **

Channel capacity for a radio system can be defined as the maximum number of channels or users that can be provided in a fixed frequency band.Radio capacity is a parameter which measures spectrum efficiency of a wireless system.This parameter is determined by the required carrier-to-interference ratio (C/I) and the channel bandwidth B_{c}

**Reverse channel ****interference:**

- In a cellular system the interference at a base station receiver will come from the subscriber units in the surrounding cells.This is called reverse channel interference

**Forward channel interference:**

- For a particular subscriber unit, the desired base station will provide the desired forward channel while the surrounding co-channel base stationswill provide the forward channel interference
- Considering the forward channel interference problem
- Let D be the distance between two co-channel cells and R be the cell radius.Then the minimum ratio of D/R that is required to provide a tolerable level of co-channel interference is called the co-channel reuse ratio and is given by

â€•(1)

- The radio propagation characteristics determine the carrier-to-interference ratio (C /I) at a given location
- As shown in Figure7.14, the M closest co-channel cells may be considered as first order interference in which case C/I is given by

Figure 7.14 |

â€•(2)

where

n_{0} is the path loss exponent in the desired cell,

D_{0} is the distance from the desired base station to the mobile,

D_{k} is the distance of the k th cell from the mobile

n_{k} is the path loss exponent to the k th interfering base station

- If only the six closest interfering cells are considered, and all are approximately at the same distance D and have similar path loss exponents equal to that in the desired cell, then C/I is given by

â€• (3)