I'd like to find out the power consumption of a mobile phone in watts.
It is a certainty that the cell phone industry uses every trick in the
book to maximize the battery life of portable cell phones. The
various air-interface standards (Analog, GSM, GPRS, Edge, CDMA,
etc...) all go to great lengths to minimize current consumption by
incorporating various power-saving features into the cell phones and
into the air interface signalling being used.
For example, when "ringing" a cell phone, the base station will use a
specific timing sequence which will allow the cell phone receiver to
go to sleep for the majority of the time it is not actively engaged in
communication. (In analog, this was the Overhead Message Paging
Channel, or something to that effect.) BTW - This is also related to
how the cell site "knows" which particular cell site to use to contact
the subscriber, and relates to cell site capacity issues.
Essentially, the base station will send out a synchronization preamble
(or its equivalent), and the phones will "wake-up" periodically, sync
and listen for their ID. If no match, then back to sleep.
Note: This is a gross over-simplification of a very complex signalling
scheme.
Now, for transmit:
In all air-interface standards I'm aware of (for PCS and Cellular
anyway), the base station controls the RF Output power of the cell
phone. If the cell site is having trouble "hearing" the phone (i.e.,
low received signal at the cell site), it will instruct the cell phone
to increase its RF output within certain limitations. If this doesn't
solve the problem, the cell site will terminate the call. Similary,
if the cell site has too much signal from the mobile phone, it will
instruct it to turn down its transmitter power (to save battery life
AND more importantly, to avoid overloading the cell site's RF receiver
distribution amplifier systems - which are shared by all users using a
particular cell site.)
There are many reasons signal can change at either end during a call,
which I won't get into now.
The point is: the phone's RF Output power may change many times a
second during a typical call.
Note: Again, this is an over-simplification of a very complex
signalling scheme.
To make matters more interesting, the cell site's output power may
also change.
This can be caused by active (non-linear) cell site transmitter
combining where the more channels (or carriers) are connected
(dynamically) to antennas, the fewer watts are available for
individual channels or carriers on the air.
Another factor is dynamic frequency re-allocation of the cell
provider, which may cause the cell site frequencies and coverage(s) to
change dynamically with use. In other words, overloaded Cell Site
-"A" might "borrow" some idle bandwidth from an adjacent (available)
Cell Site "B". Because of RF intermodulation and co-channel or
adjacent channel interference issues, this can also affect RSSI and
cell site performance -- It's a non-optimal solution to congestion,
but it's better than dropping the call.(?) I don't know how wide
spread the practice of dynamic allocation is, but you can reasonably
expect it in conjested areas, or in areas that have infrequent,
periodic usage demands - such as sports staduims, etc...
And note: This is all transparent to the average user.
Except perhaps the "4-bars" or "5-bars" discussions people sometimes
have.
This is usually an indication of the strength of the signalling
channels, NOT the voice channels.
So if the Cell Provider amps up their messaging channel transmitters,
this can give a false sense of performance. (I have seen this only
one time, and I won't name names.) But this can be one explanation
why you sometimes can't make a call even though you have 4-bars of
signal. (And more likely, the reason is one of several dozen other
things that can go wrong, which is too much to get into here.)
If you want to do some more research on battery-saver features of air
interface signalling schemes, I would suggest starting with a much
simpler one. Do a google search on "POCSAG", or "GOLAY", which were
two widely used signalling schemes used with Pagers (beepers).
These will be "simpler" because those devices operated in a
predominately one-way fashion.
Do you see now why you can't go by the battery nameplate?
-mpm