Set Top Boxes, Cable TV, Frequency Spectrum & 4G Services

I've been looking for the technical reasons why Indian Government is making Set Top Boxes compulsory and I found out that real reason behind the move is to free up the air off the frequencies required by cable TVs so that room for 4G services can be made. I'd however love to have further details on this. The questions I've in my mind -

1. What's the frequency of the signal required by cable TV antennas?
2. What is the corresponding frequency required by dish TVs? I've heard it's significantly lower.
3. How'd this freeing up of bandwidth help penetration and nation-wide roll out of 4G services?