Mumbai University > Electronics and Telecommunication > Sem 7 > Mobile Communication

Marks: 10 M

Year: Dec 2012, May 2013, May 2015

1. Signal to noise ratio depends upon radius (R) of a cell and interference due to co-channel cells. Signal to noise ratio is given by

   $\frac{s}{i} = \frac{s}{\sum_{i = 1}^{io}I_i}$

   Where, io = total number of co-channels

   Ii = interference due to $t^{th} co - channel cell$

   s = desired signal power from base station

2. We know that as the distance between transmitter and receiver increases, average received signal strength deceases. The average received power Pr at distanced from transmitting antenna is given by,

   $Pr = Po(\frac{d}{do})^{-n}$

   Where,

   Po = power received at reference point at distance do

   d= distance between transmitting antenna and desired point

   do= distance between transmitting antenna and reference point

   n= path loss exponent

3. Signal strength S inversely depends on radius of a cell S ∝$R^{-n}$ and interference I is inversely proportional to minimum safe distance D, $I ∝D^{-n}$

   $\frac{s}{I} = \frac{R^{-n}}{\sum_{i = 1}^{io}D^{-n}}$

4. Every cell has co-channel at same distance hence total distance will be D,

   $\frac{s}{I} = \frac{R^{-n}}{io D}$ $\frac{s}{I} = \frac{(\frac{D}{R})^n}{io}$ $\frac{s}{I} = \frac{\sqrt{3N}^n}{io} ..... (\frac{D}{R} = \sqrt{3N})$

Above equation gives us the relation between signal to noise ratio (S/I) and cluster size (N).

According to FCC S/I should be greater than 18 db.