What consumes less battery on a smartphone - WiFi or 3G? Why?

Wifi antenna in your phone has a typical range of few meters. It finds a wifi router withing that range. So the power of the signal should be enough that it should be able to survive for few meter. On the other hand, for 3G data transfer, you need to send the signals to the receiving antenna which could be a upto a few kilometers from where you are. So the signal should be strong enough to survive few kilometers. To give an idea: lets assume your wifi router is at a distance of: 5 meters and the 3G receiver antenna of service provider is at a distance of: 2 kms or 2000 meters we know that the signal strength is inversely proportional to the square of distance. So, in order that we have the same signal strength at the receivers antenna of wifi and 3G; the transmitted signal should be of ratio: (2000/5)^2 = 160000 So the 3G signal should be 160000 times stronger than wifi signal. Hence 3G data transfer consumes more power. P.S. we have not considered packet loss when sending data over longer distances, which altough less significant cpntributes in more power requirement of 3G transmission

Signal Strength plays a key role in determining the battery usage. If a connection is being tried to be established on either WiFi or 3G and if the signal strength is low, the transmitter in the smartphone will have to amplify the signal to high levels which increases battery usage. Similarly if the signal keeps dropping and the smartphone will have to scan regularly for either of the signals, the battery power would be used up significantly. In addition to searching for a signal and transmitting, a smartphone will also have to page the base station or cell tower frequently updating that it is alive and transmit other information all of which may contribute to the battery draining quickly.

There is no simple answer. If you are sitting nearby an antenna, forgetting the technology, the energy needed is much lower. So if we'd pick distance, GSM is much more efficient. Try to measure the consumption at 10m, 100m, 1km or 10km of an gsm or an wifi antenna. Oh wait, forget the wifi won't work at those distances. Forgetting distances, the GSM protocols are much more optimised and efficient than WiFi. Try to measure the energy consumption on a crowded place - a stadium with gsm, some big Starbucks with wifi. Basically if the signal is poor, your battery will die.

In both cases, it would depend on the appropriate quality/strength of your forward link, link from the 3G tower or WiFi transmitter to your phone. The weaker this is, the higher your phone will increase its transmitter power to keep up with the said end. Kind of like the farther away someone is from you the louder you'll talk to reach him. And that's power consuming. That's the concept. You can use some battery monitor app to figure out actual consumption.

Thanks for A2A 3G eats much more battery than WiFi. Even with Mobile Data switched off. Infact 3G eats the most battery, more than 2G, more than 4G too. Battery use is like 3G > 4G > WiFi + 2G > 2G > WiFi only Same occurence on any phone, OS doesnt matter. Unfortunately, I dont know the technical reason behind it.

This depends on several factors.If you're at home and WiFi is accessible, using the WiFi radio will yield better battery results overall.  A 3G radio in your phone or tablet needs to bounce data off of a cell tower and the signal may fluctuate during that process.If you're not at home or at the office, turning off WiFi is a good idea.  The reasoning for this is due to the WiFi radio query networks it discovers and trying to connect.  This is fine if you visit a hot spot like maybe Starbucks or the like, but in this case both the 3G and WiFi radios will be running and the drain will be that more noticeable.If you want the best battery life while traveling, put your phone in Airplane Mode until needed.  Keep in mind that you won't receive calls during this time, but if having more battery for later when you reach your destination is your goal, this will help.

Do refer this the same question asked before

When you are in good reliable WiFi coverage, WiFi will definitely consumer less power than 3G. WiFi uses something called Power Save Mode to conserve power and to wake up only to maintain the connection. The only problem is if your desk happens to be located somewhere in the middle of two access points where your phone keeps switching (hand off) from one AP to another. In this situation you are out of luck and this can cause considerable battery drain. One thing to note - even if you decide to use WiFi, you may still have to keep your 3G connection on. The reverse may not be true if you decide to use 3G only. Edit: Actually with the iPhone I believe when your device sleeps (screen off and idle) WiFI is actually shut down. When you turn your phone ON (by pressing the power button) the connection us quickly re-established so you may not actually face the roaming issue.

WiFi employs a short range transmitter of about 100mW. This is why the range is limited to a house. Cellular transmitters may transmit up to 10 miles. It depends upon how close you are to a base station. So the transmitter for a cellular link may burn as much as 0.5 to 2 watts (this depends upon which of four different classes and which of six different frequency bands one is located in). The cellular link may burn as much as 20x the power the WiFi link burns.