While the battery-draining potential of 4G LTE networks is still a big concern in the wireless ecosystem, voice-over-LTE (VoLTE) can no longer be singled out as the biggest culprit.

Test and measurement vendor Spirent Communications plc has been tracking VoLTE's effect on battery life since MetroPCS Inc. launched its first VoLTE-capable handset last year. In December, it found that VoLTE drained the battery twice as fast on the LG Connect 4G than calls made on the 3G network. Revisiting the test in March on the LG Spirit 4G with a second-generation chipset showed a 35 percent improvement in VoLTE drain. Combined with advances to the phone's battery, as well as improvements in the network, it brought about a 122 percent overall improvement. (See 4G Voice Services Drain Battery Life.)

The improvements came about in such a short timeframe that Rich McNally, director of service experience for Spirent, is confident that by the time VoLTE handsets are mainstream -- whether they're sporting second-generation or third-generation chips -- the battery life should be comparable to 3G. (See Verizon Preps Network, Waits on Marketing Nod for VoLTE and AT&T Amplifies its 4G Voice.)

"There is always a bit of a ramp when any new service comes out where device and optimization have not been made yet," McNally says. "There is a point where it crosses the threshold and becomes usable. VoLTE is already past that point."

The 4G battery trade-off
Battery life is more than just a chipset issue, however. VoLTE brings with it new radio protocol enhancements to reduce its spectrum usage and battery power, but the problem is that these protocols -- semi-persistent scheduling (SPS), TTI bundling and discontinuous reception (DRX) -- aren't activated in many networks today, even if the chips are up to speed.

Mike Barrick, global account manager at fellow testing vendor Anritsu Corp., says that if a network does not have SPS, TTI Bundling, and DRX enabled and configured correctly, battery life of a VoLTE phone will not be optimal and could be less than a traditional 3G phone. Anritsu showed off its new wireless network simulator that tests against a simulated network with all three protocols last month at CTIA.

In reality, VoLTE is just another data stream, and battery life on the faster network is something all device makers and operators will grapple with for a while. LTE generally runs the handset at a higher average transmitter power level than 3G or 2G, according to Mobile Experts analyst Joe Madden, meaning 4G phones won't outlast 3G phones anytime soon.

"This is not the kind of issue that is fixed with a software patch, because it is related to the way that the network commands the handset to boost its power for the best high-speed data service," Madden writes in an email to Light Reading.

For their part, handset makers are also looking to alleviate the issue with envelope tracking technology, which constantly adjusts the power amplifier to make it run as efficiently as possible in any given scenario. It's a step, but Madden doesn't think it'll be enough to make LTE comparable to GSM in power performance -- at least not for a while.

"It's hard to improve on the GSM signal for carrying a long distance with continuous voice coverage in all conditions," he says.

— Sarah Reedy, Senior Editor, Light Reading