Why services that need to receive a signal, like Bluetooth or GPS, drain cell-phone battery?

Question

The title is self-explanative. This is an emprically contrasted fact for cell phones, although I don't know why this happens.

As far as my understanding goes the signal receiver is a passive component. Then, why does it affect battery so drastically?

Your assumption is very wrong. The receiver is an active circuit. It has an LNA, ADC and lots of DSP. — Mike, May 19 '17 at 05:17
The new "Android O" operating system helps here. Applications that are in the background asking for gps data are now handed *old* data and do not cause a re-activation of the receiver systems. The application must be moved to the foreground in order for it to cause re-activation of the hardware systems. Prior editions (and some other operating systems) activate the hardware every time the application asks for gps data. Receivers are very heavy battery users. When I was working on the Seiko message watch (years ago), it was the receiver that was the major energy hog. — jonk, May 19 '17 at 05:37
great @jonk. Given your experience, may you know some link to a quantitative analysis of the energy consumption of signal receivers for smartphones/tablets/watches, etc? — A. Fenzry, May 19 '17 at 05:41
*As far as my understanding goes the signal receiver is a passive component* Whoa, who gave you this bit of mis information ? The antenna is **passive**, maybe that is what you mean. But an antenna alone is pretty **useless** unless you feed the received signal to a receiver circuit for amplification and further processing. — Bimpelrekkie, May 19 '17 at 07:34
Exactly. I am simply ingorant on the subject and I worded it poorly, indeed I was thinking on the antenna, and I am conscious of the need of a physical process to filter and process an analog electromagnetic wave to a neat digital signal that can be handled by a cell phone. However I was not aware that this process required so much energy. Anyway, my doubt ended up being more or less solved, now I only need to look into those components to understand their physical properties. Thanks for your input — A. Fenzry, May 19 '17 at 07:47
It's not so much the recieving as the processing needed to understand GPS; the signal is extremely weak and a lot of number-crunching needs to be applied to extract it from the noise and correlate the four or more satellites involved. — pjc50, May 19 '17 at 08:28
Thanks for the input @pjc50. I am currently looking for a technical read on the subject of GPS signals, could you recommend one? — A. Fenzry, May 19 '17 at 08:31
There's an answer on here https://electronics.stackexchange.com/questions/11884/how-many-gps-channels-make-sense/ - but it really depends how much time you have and what level of background knowledge you're starting from — pjc50, May 19 '17 at 08:38
thanks again, @pjc50. In case it helps, I have a strong Applied Mathematics and Physics background (PhD level). I lack however all the engineering implementation part and also the out-of-the theory complications that may arise in practice with these devices (from multipath problems to whatever). I basically need a reference explaining the whole GPS nowadays in 2017 (further than the 4 satellites, all the other tower signals and things used) and particularly its signal processing part — A. Fenzry, May 19 '17 at 08:44
Try http://www.aholme.co.uk/GPS/Main.htm or http://lea.hamradio.si/~s53mv/navsats/theory.html ; cell towers don't have much relevance to GPS, the Google "fine location" system works by snooping nearby wifi networks (smaller cells) — pjc50, May 19 '17 at 09:05

score 5 · Accepted Answer · answered May 19 '17 at 06:03

Receivers are very much active devices that require energy to operate.

Modern Bluetooth receivers require very little energy to operate in receive mode. They should usually use a small percentage of the energy used by a cellphone in typical use.

GPS can use a significant percentage of total energy used.
Active GPS tracking is a high energy application. A GPS receiver is more complex than either broadcast, FM band or even cell-phone band equipment. Energy use does not directly scale with complexity (fortunately) but a GPS receiver needs to receive multiple satellite signals simultaneously and analyse the results to produce position, velocity time and other outputs.

A good idea of relative energy use can be obtained from your phone's records. In Samsung Android 5.x see "settings - more - battery"

Why services that need to receive a signal, like Bluetooth or GPS, drain cell-phone battery?

1 Answers1