1.9 GHz LTE overload question

[afazel]

I don't suppose orthogonality is those "spiral waves" that made some tech headlines a couple years ago?

[Dfarley]

Trust me, you like orthogonality. Though in different ways, it is crucial to both CDMA1X and LTE.

 

AJ

I still feel stupid...but I trust you.

[shockerengr]

The statements in this thread don't feel accurate to me. Sending data over radio waves involves putting a sequence of symbols on the available channel space and transmitting them long enough for the receiver to determine what symbol is being sent. How long a single symbol needs to be sent is dependent upon the modulation frequency, as it should take time, measured in cycles, for the receiver to identify when the frequency and phase of a modulated signal has been changed to. Therefore, doubling the modulation frequency should allow you to shove twice as many symbols on the channel per second, and therefore twice the data per second. What is special about cellular telephony that this is not the case? 

 

Cellular telephony is not unique, and the reasoning is the same for any modulated signal, and that is the frequency on which the symbols are being transmitted at is not at all related to the frequency at which the symbols are being transmitted.

 

One way to think of it (and this is a gross oversimplification, but may help) if I send data at 1hz using a 1000hz radio wave, then for each symbol,  I use 1000 cycles of radiowaves.  If I increase the data rate to 10 hz, each symbol would use 100 cycles of radiowaves, or if I change the radio wave to 2000hz, then each symbol at 10 hz would use 200 cycles of radio wave.

When I went from 1hz data to 10hz data, I increased the data capacity by 10fold, but in the second case where I doubled the radio frequency, there was no change in data capacity.

 

This scales up and in general, the carrier frequency (the base radio signal) is much much higher than the data rate (essentially, the bandwidth)

 

The example you used would only really apply in cases where the bandwidth is equal to the frequency.  If I'm transmitting data at 1 hz using a 1hz radiowave, then each cycle contains one unit of data, but the only limitation there is the bandwidth can't be greater than the frequency.

 

So with band 25 and 26, the bandwidth or data rate is not changed, but the frequency is.  

 

In the real world, it's a bit more complicated, and the modulation methods, noise, coverage and everything else plays a big role in how far and fast things go, but the basics of frequency and bandwidth apply to all of them.