why is moving towards higher frequencies so important in frequency spectrum?

Question

As we know, as frequencies becomes higher, bandwidth becomes higher.And, according to channel capacity theorem, channel capacity increases with higher bandwidth.

Also, energy is directly proportional to frequency(E=hf). So, if frequency increases, signals possesses higher energy and can travel far.

Which one of them would be more relevant to prove our need of higher frequency? Why not the other one?

Answer 1

So, if frequency increases, signals possesses higher energy and can travel far.

Not really, it's more the other way round:

When transmitting signals with radiowaves in free-space, most telecommunications engineers use the Friis equation which gives the amount of received power $(P_r)$ according to emitted power $(P_t)$, distance between emitter and receiver ($R$) and wavelength ($\lambda$) : $$ \frac{P_r}{P_t} = G_tG_r\left(\frac{\lambda}{4\pi R}\right)^2 $$ $G_t$ and $G_r$ being the transmitter and receiver's antenna gain. We see with this equation that $\frac{P_r}{P_t}$ is proportionnal to $\frac{1}{f^2}$ (because $\lambda = \frac{c}{f}$) which means that the higher the frequency, the higher the loss (and ^2 higher !). The equation $E = h\nu$ is more related to quantum physics and has no practical use in telecommunications. Maybe it means that higher frequency signals are "more energetic" that low frequency ones, I don't really know honestly, maybe someone else* can answer better.

So the need to increase frequencies is mostly due to :

1. Saturation of the currently used spectrum : if you read international and national regulations and standards, you'll see that being able to emit on the RF spectrum is very expensive, because it's actually saturated, every frequency is reserved for a certain application (e.g. GSM signals is my country are transmitted in 200 KHz wide canals around 900 Mhz-ish frequencies). Still in my country, a new mobile phone operator had to pay billions of € to the governement to access some mobile comm. bands. Increasing the frequencies will give everyone more "room" to transmit radiowaves.
2. Increasing data rates, because having a higher carrier frequency also allows to widen the communication channel
3. Miniaturization (higher frequencies = lower wavelengths = smaller antennas and systems)

*edit :

your claim on signal energy and frequency relation, which is based on photo-electricity (E=hv) effect is improper. First of all, the physical nature of waves has nothing to do in developing the mathematical notion of waves and their spectral representation by periodic signals. And even though it's true that the magnitude-squarred |x(t)|2 signal power relation is basicly adopted from power calculations in physics, that power (and energy) is implied to be the energy carried out by the waveform of a classical physics kind.

from Fat32's comment above

Answer 2

I'd like to make a comment about the relevance of this question in relation to 5G standards, where the lack of available spectrum is making researchers consider more and more to use of millimetre waves. This is a simple article about it: http://www.radio-electronics.com/info/cellulartelecomms/5g-mobile-cellular/millimetre-wave-links.php and this one is a bit more complete: http://spectrum.ieee.org/telecom/wireless/millimeter-waves-may-be-the-future-of-5g-phones note that this is from 2013. At the moment there are lots of publications talking about this topic and it is creating even a bit of controversy :D