2G, 3G, 4G and Your Battery

Back in March 2013, I penned an article discussing why sometimes switching to a slower network isn’t good for your Android device battery. The article illustrates that modern connected devices are designed to complete a task as quickly as possible so that they may return to lower power states.

4gmastSince March 2013, the UK cell operators have finally started rolling out their LTE networks and I’ve had the opportunity to both experience 4G LTE (long term evolution) for myself and talk to network engineers. And it turns out that the marketing spiel that 4G LTE is all about speed isn’t the whole story.

LTE is the first mobile data service designed around data. GPRS, EDGE, UMTS and HSPA technologies are all derived from circuit-switched networks, that is, designed to co-operate with voice connections. LTE dispenses with the need for voice (although voice over LTE is being re-engineered back into the service) and instead is focussed entirely on mobile data.

There are many advantages to having a network designed without a concession to voice and it’s true, most are based around speed. But it’s important to point out that the focus here is not just on data transfer speeds but also on the response of the network. LTE offers significantly reduced latency, that being, how quickly the network responds to your request.

My friendly network engineer told me that a HSPA 3G modem takes “a moment” to transition from being connected-but-idle to being connected in high speed (and high power) mode. For my devices on the networks I’ve used, this is usually somewhere from one to two seconds. A LTE modem takes a screen refresh to transition from connected-but-idle mode to full speed mode.

Because it takes a couple of seconds to switch up to the high speed, high power mode, this isn’t a great user experience. To help improve matters, the modem stays in the higher power mode for thirty seconds after network activity. This means that the modem is using more battery than it needs to for thirty seconds, but does mean if the user is browsing a website and follows a link inside this time, the device is much quicker to respond.

One of LTE’s major differences is that it’s significantly faster when switching modes. Because of this, as soon as network activity is complete the modem drops down to the idle state. This can save a significant amount of power. Essentially, the LTE modem wins the race to idle compared with HSPA on two accounts: one, it should perform the network activity quicker and two, it’s faster to drop to idle once activity is finished.

LTE isn’t, however, perfect. I’ve written above that voice calls are not carried over the 4G radio, which means the smartphone will drop to either a 2G or 3G radio in order to deal with a call. This can mean it takes a little longer to connect calls and can cause delays when switching up to LTE after finished a call. The technologies used by carriers to manage the handover vary from network to network, with some implementing much faster handovers compared with other carriers.
If you’ve been sitting on the fence wondering if you should switch to a device with LTE or not, in my experience there’s very little difference in battery life. If anything, I’ve noticed a small improvement but difficult to quantify. What I have noticed, however, is how quickly one gets used to significantly quicker networking. It makes dropping to a 3G connection, even a fast one, difficult.

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