so why are 3G phones poor on battery and why are 4G phones even worse !

Posted on January 10, 2013


It’s a question I get asked from time to time,  why are 3G phones,  smartphones,  so rubbish with their battery life ? and now a days I also get asked if 4G will make it any better ?

To understand this we need to think a little about how phones use their radio,  because simply put the radio consumes about 1/3rd of the batter, the CPU/RAM also a third,and the screen the rest,  which funnily enough is a third too,  did you see that coming ?

So what about the radio then:

Now, the older 2G system had a time share system.  the phone is given a frequency to transmit on,  and one of seven time slots.  that slot is yours,  the frequency is yours.  Because you get one of 7 time slots your radio is only transmitting 1/7th of the time,  the rest of the time it is off air,  allowing the other phones to use their time slots.
Now you might be thinking, hang on a minute, if the phone only gets one slot,  how come the call is not also fragmented. Well the phone will compress the audio and as long as the compression is better than 7 times,  then it can squeeze all the audio into the available slot.
That’s OK for voice,  and for data the same time slots are used,  and to gain higher throughput a device cold ask for more slots across various frequencies.

So what’s different with 3G:
well one of the problems with 3G is that it cannot provide enough time slots to support all the phones in the market.  the density of connections is too low.  In part 3G was invented to solve this density problem.  How to get more users connected with the same amount of radio resource (frequency range).
The way it does this is very clever,  and involves some clever maths, but in plain language it makes use of the whole spectrum.  The 2G system had defined frequencies with spaces between to prevent cross talk.  With 3G all devices use all the frequencies,  and all the time.  So that all the phones are transmitting all the time, across the range of frequencies.  where the clever maths comes in, is that each phone is given a code,  and this is then used by the base station (the computer listening to the radio) to separate out each phone’s signal.  Much like the way your ears can follow a conversation in a noisy pub,  your brain learns the timbre and cadence of the other persons voice and is able to filter it out.

The upshot of this is two fold:
more devices can connect using the same amount of frequency, and
The phone is transmitting all the time,  meaning that it uses up to 7 times more radio energy.

And that is the snag.  Because the radio is always on, it is always drawing energy.  Simples.

and 4G:

I’ll not go into great detail suffice to say that 4G also has a continuous radio usage so will also require more power,  and,  and if you want those super fast speeds then 4G uses MIMO which stands for multiple In Multiple Out,  which simple put means that the phone will have several different connections to the tower, means yet more radio power being required.

So in the short term 4G is not going to help with battery life,  quite the opposite.

However with software improvements, better radio aerial designs (fractal ?), and the intriguing possibility of all digital radios, then this will improve the efficiency,  and so we will hopefully get back to phones that run and run, without you chasing a power source.




Posted in: mobile