Android Power Management: Networks, Myths and Races

A simplified diagram and demonstration showing the difference in power consumption between networks.

A simplified diagram and demonstration showing the difference in power consumption between networks.

Our Android devices are only as productive add they have battery power and a lot of my recent work with clients had been to improve battery life. There are a couple of golden rules about maximizing battery life that are true to all smartphones, not just Android. The first is to reduce your use of the handset, which we’ve covered here. And the second is to optimize your use. Unfortunately, many of the power management guides contain myths without explaining how effective, or otherwise, the optimization techniques are. Today I’m going to explore the blanket statement that switching to just use 2G networks saves battery power.

As we’ll explore, in some circumstances using the older generation, slower networks can use more power.

Race to Idle

This race to idle is one of the cornerstones of energy efficiency for several industries including portable electronics. It is very relevant to Android devices because it explains why some articles are outdated or ill informed. The idea behind race to idle is that your device completes a task as quickly as possible so that it returns to an idle state. This is advantageous because modern electronics shut down when not used so that they receive no power. This can have a massive impact on power consumption.

I’m going to use the example of visiting a complicated webpage. A device needs to download and then render the page, so let me play around with some figures. Let’s suppose that the webpage will take ten seconds to download over our 3G network and a further ten seconds for the device to render the web page, which it starts as soon as it has information. We will suppose that it takes fifty seconds to scroll through the page to find the next link we are looking for.

So, looking at the page using a 3G network, it takes ten seconds to completely show the page then fifty seconds before we reach the next link. That’s ten seconds of download time, ten seconds of render time and in total a minute of on-screen time (because we download and render at the same time).

Power Used = 10 seconds 3G modem + 10 seconds render + 60 seconds screen on

If we now move to a 2G network, it will take a lot longer to download. Let’s be generous and say that it will take sixty seconds to download; now we are working our modem for sixty seconds, we are rendering the page for ten seconds and a further fifty seconds to find what we are looking for. That means we will have the screen on for one minute, fifty seconds. If we estimate that our 2G modem uses half the power of the 3G modem over the same time period, we are using three times more power just to download the page. Our screen is burning up the battery for almost twice as long: sometimes, switching to a slower network connection is precisely the wrong thing to do!

Power Used = 30 seconds equivalent 3G modem + 10 seconds render + 110 seconds screen on

Let’s model using a WiFi connection and we’ll suppose that it’s twice as quick as our 3G modern so takes five seconds to download. It still takes ten seconds to render the page, then fifty seconds to find what we’re looking for. It’s no quicker, but we are working our wireless radio for half the time. Combine that WiFi tends to use less power than a 3G modem, let’s suppose it uses eighty percent, so it’s the equivalent of four seconds of 3G modem power.

Power Used = 4 seconds equivalent 3G modem + 10 seconds render + 60 seconds screen on

Although it’s an oversimplification, it demonstrates that when being used, sometimes using a slower network is harder on the battery than using a quicker connection. It is difficult to obtain real world power consumption for the different radios in our Android devices short of experimenting with our own. We also need to consider quality of signal; one of the reasons why 3G and LTE networks use more power is that the newer generation networks have poorer coverage, so the handset boosts the radio transmitter and has to switch between 2G, 3G and LTE networks quite frequently. Locking the handset down to 2G stops it even considering using the other networks.

Where the slower networks can save battery power is during idle-but-connected time, partially because the device had fewer radios powered up and partially because it picking up notifications, emails, social network updates and similar, which are all low traffic duties. Of you are going to have your device in standby for a period of time, especially when traveling, it may be advantageous to put it into 2G only mode, just remember to use a faster network when you start using it again.

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