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If you are tethering to the internet through your mobile and your notebook is low on power you may want that connection to use the least possible power for your notebook. A USB connection will charge your phone and drain the notebook battery. Wifi and Bluetooth also require some power.

How does energy usage for a notebook compare for the following?:

  • usb connection to a phone
  • wifi connection to a phone
  • bluetooth connection to a phone
Assume light browsing, and a low usage of bandwidth.

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up vote 3 down vote accepted

Use Bluetooth then, if your phone supports BT internet sharing.

USB is not an option, since it'll give away up to 2.5W to your phone, and SoftAP eats far more in terms of power consumption if you compare it with Bluetooth.

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Are you sure about that? Wi-Fi signals are an order of magnitude more powerful than Bluetooth (the same data rate that's transmitted at 80mW on WiFi is only transmitted at 2mW on Bluetooth). The reasons are obvious as Bluetooth is designed to be low-interference and short range. – Lèse majesté Apr 22 '12 at 4:17
@Lèsemajesté, sure about what? You probably have misread my answer, as I'm stating basically the same. In fact, SoftAP (WiFi tethering) might consume up to 3x more than in station mode. – Andrejs Cainikovs Apr 22 '12 at 13:17
I guess I did. I wrote that comment before Spiff's edit, when your answer read "SoftAP eats far less in terms of power consumption if you compare it with Bluetooth". Not sure how I glanced over your first paragraph though... – Lèse majesté Apr 22 '12 at 13:30
Ough.. I see now. Yes, this is what I actually meant :) – Andrejs Cainikovs Apr 22 '12 at 13:32

USB would be "cheapest", if WIFI and Bluetooth radios are turned off, and the phone is already charged and the display stays off.

However, plugging in an iPhone in particular causes the display to go on bright and stay on, and that creates a significant current draw. Other phones may behave differently. [NB: Actually, I discovered that this was because the phone was simply set to not turn off the display.]

Bluetooth would be the second choice, especially if you can turn on Bluetooth without WIFI (which is a bit of a trick, since they share much of the same hardware).

If you need WIFI on for other reasons then it probably doesn't matter much between WIFI and Bluetooth.

Added: As I stated above, I discovered that the iPhone display problem was simply a settings problem. Fixed that and the display turns off after the timeout. So the USB tether should always be the lowest current option, if you can turn off the radios.

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Does the display go to bright even when connected to an unpowered USB port? – Lèse majesté Apr 22 '12 at 3:57
Dunno. But it may be that the behavior I've observed is due to a setting in the phone that can be changed. – Daniel R Hicks Apr 22 '12 at 11:56
@DanH: 1. Sure, it depends on hardware, but I'm not aware of any phone that will not consume power from USB even if the battery is charged. 2. Bluetooth and WiFi often shares the same clocks, but are totally isolated on a silicon. Try to find a datasheet for one of the popular mobile combos, and you will find out that both BT and WLAN have separate reset lines, and interfaces as well - BT works via UART, while WLAN in most cases works on SDIO. So, I disagree with you. – Andrejs Cainikovs Apr 22 '12 at 13:22
@AndrejsCainikovs -- It's your right to disagree. But it's not your right to be right when you're wrong. :) – Daniel R Hicks Apr 25 '12 at 11:57
@DanH: Well, first of all, phone will always draw current from USB if connected, even if the battery is full. Secondly, here goes the proof that BT and WLAN have shared clocks but nothing else: Your iPhone has it. If you have 4S, then it's BCM4330, same idea. Sorry, but I'm too familiar with power consumption in mobile phones. I know this shit :) – Andrejs Cainikovs Apr 25 '12 at 12:44

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