2G vs. 3G vs. Wi-Fi battery usage on mobile phones ?

With the need to stay connected these days, battery drain becomes an important consideration for every mobile data user. Phones/tablets have a number of tweakable data connectivity settings, there are battery usage/CPU tuners/tethering/sideloading apps on the market, Android settings hint that turning off 3G may help battery usage, Wi-Fi hotspots are popping up everywhere.. yet all this seems to just add to the confusion as to what type of connectivity drains your battery faster.

Here are some generalizations that may help:

• Leaving your phone registered/idle on either 2G or 3G should produce similar battery usage. Voice-only mode without much data should produce very similar battery drain.

• If the 3G signal is poor, or coverage fluctuates, 3G will use much more power while actively transfering data.

• 2G has better, more consistent power drain when the 3G coverage is spotty or fluctuating. Use 2G-only mode if the signal is bad, and/or you do not need heavy data usage to increase battery life.

• 3G has a higher battery drain, however, it actually uses less Watts per downloaded Kilobyte compared to 2G. 3G is much better for heavy data usage, and will not use much more battery if the 3G signal is strong. If the signal is poor or fluctuating, however, it may drain your battery as much as twice as fast compared to 2G. Talk time is considerably less than 2G, however, standby drain is about the same. Overall, under typical conditions in suburban areas, you should expect about 2/3 of the 2G battery life.

• Wi-Fi is more efficient and uses less battery in modern phones than the 3G radio while associated with an access point. It will use less power than 2G if the phone is "smart enough" to power it down while idle. It will use more power while searching for a Wi-Fi signal, however. Another notable exception are some older phones that used inefficient Wi-Fi chips, they'd get warm/hot to the touch just minutes into using Wi-Fi and keep it at high power regardless of network conditions. Generally, Wi-Fi battery usage should be very similar to 2G (unless searching to associate with an AP). It may make sense to turn the Wi-Fi radio off if you only need light data usage.

All this is highly dependent on whether/which radio remains on while the phone is idle or the screen is off, whether you turn off the Wi-Fi when you're out of range (or the phone is "smart" enough to do it on its own), whether 3G gets turned off automatically when Wi-Fi is on, the strength of the 3G signal, etc.


Notes:
2G frequencies don't get along with some powered speakers (such as wired telephone headsets and PC speakers) - you may experience slower data transfers and interference.

3G requires transmit/receive of DPCCH continuously while in 2G the radio is only required to transmit/receive one timeslot out of 8 (GSM TDMA frame structure) and it can shut down its transmitter/receiver in between. Combined with the difference in modulation schemes (GMSK Vs QPSK), this leads to a more efficient power amplifier and current drain in 2G.

In voice-only mode (no data), 2G and 3G