Call Drops & Spectrum - The Real Linkage

Everyone knows that spectrum is directly linked to capacity, and hence one would like to have more of it. But, capacity can also be created by reusing the same the block of spectrum by packing more number of sites to able to serve more customers. Then why do we need additional spectrum? Why can't the operators add additional sites and be done with it? Though it might require additional investments (in Capex & Opex), but will surely save them from the painful process of auctions and ever increasing spectrum price!! 

The answer lies in the physics of wireless communication. The strength of the radio waves decreases with distance from the source. In free space, the rate of attenuation of radio waves is much lower than in the presence of clutter, where the rate of decrease in strength is directly proportional to the inverse of the square of the distance traversed. But, in the presence of clutter other factors including frequency at which radio wave is transmitting plays a dominating role and attenuates the radio signals at a much faster rate than in free space. So when the towers are tightly packed together with an objective of increasing capacity, the opportunity for the ground clutter to attenuate the RF waves reduces. This increases the opportunity of the radio signals of adjacent towers to collide with each other and thereby decreasing the overall capacity.However, one might be wondering how networks operating in unlicensed bands with access points closely packed deal with this problem? They do so by using frequency hopping techniques and use a disproportionate amount of spectrum (10 to 20 times more) compared to those using licensed spectrum band (see my earlier note on spectrum management for dummies). Through frequency hopping, access points and user terminals dynamically choose different spectrum blocks which have lesser interference from adjacent users and access points, quite unlike those operating in licensed bands which use the full block of spectrum all the time (see figure under).

Hence, even if there is an opportunity to add additional sites the operators cannot go beyond a limit with an objective of increasing capacity to decongest their networks. 

(Views expressed are of my own and does not reflect that of my employer)