Frequency Reuse

What is frequency reuse?

• Frequency reuse is the process of using the same radio frequencies on the radio transmitter within a geographic area that are separated by sufficient distance to cause minimal interference with each other.

Why do we need to re-use frequency?

• To improve coverage & capacity in cellular systems by reducing interference.

How distance between two cells are calculated?

• D=R*(3N)^1/2

D: Distance
R: Cell radius
N: Number of cell per cluster

• Reuse factor

• D/R=3N^1/2

As user increases, channel capacity decreases. Two techniques to improve channel capacity:

• Cell Splitting 
• Cell Sectoring

What is Cell Splitting?

• Process of subdividing a congested cell into smaller cell 
• Reducing the size of cell, the smaller cell cover less area so that more cells required to cover more area 
• Limitation: Handovers are frequent, channel assignments more difficult 
• Solution: Umbrella approach (making sure all area covered well)
  

What is Cell Sectoring?

• Process of replacing an omni to directional (bi-direction) antenna at the base station 
• Kinda process of implementing ICIC (Inter Cell Interference Coordination) 
• Process to change interference distribution as well as to improve the throughput on the edge of cell.  
• Reason: To overcome some limitation like co-channel interference 
• Advantages: Improve S/I ratio, reduce interference, increase capacity, enable to reduce cluster size, freedom in assigning channel. 
• Limitation: Number of antenna at base station increase, decrease in trunk efficiency, loss of traffic, no of handover also increase (since sectoring reduce the coverage area of particular group of channels. 

 
 * Frequency reuse is part of Cell Planning (Frequency Planning)


The general process of LTE Network Design.   

• Information collection 
• Network dimensioning
• Network detailed design
• Cell Planning
  

Under Cell Planning, there are:

1. Frequency Planning 
2. Cell ID Planning 
3. TA Planning 
4. PCI Planning 
5. Neighbor Cell Planning 
6. X2 Planning 
7. PRACH Planning

to be cont.


**The reason why I choose this topic is because of the interview yesterday :)