Voice calls over 4G LTE networks are battery killers

Every mobile carrier wants to replace their old voice services with new VoIP-based systems utilizing their 4G networks, but it looks like they’ve got some big kinks to iron out in the technology first. Wireless testing and measurement vendor Spirent Communications has identified a big problem with voice over LTE (VoLTE): it consumes twice as much power as a traditional 2G call, which could have big implications for mobile phone battery life.

Metrico Wireless, a radio field testing company Spirent acquired in September, conducted voice trials on a commercial VoLTE-enabled network in two U.S. cities, comparing the power consumption of VoIP calls made over LTE against the power used by the same carrier’s CDMA systems. Spirent-Metrico didn’t name the carrier, but it’s not hard to guess.

MetroPCS(s pcs) is the only U.S. operator with a live VoLTE service and a commercially available handset. The 1540 milliamp hour (mAh)-battery on Metro’s sole VoLTE handset, the LG Connect 4G, also lines up with the battery capacity of the device Spirent tested.

The results of those tests should give carriers and consumers pause. The average power consumption for a 10-minute CDMA circuit-switched call was 680 milliwatts (mW) while the average consumption for a VoLTE call of the same duration was 1358 mW. That’s double the power drain. Spirent estimated that on a full charge, its test smartphone could support 502.6 minutes of talk time using CDMA only, but the same charge would only deliver 251.8 minutes of talk time using VoIP on the 4G network. And that’s with all other data communications turned off.

What it comes down to is that our old GSM and CDMA circuit-switched voice technologies — despite their limitations — have been optimized over the last two decadesto be energy efficient, Spirent Global Director of Insights Amit Malhotra told GigaOM in an email interview. It’s hard to replicate that kind of efficiency overnight in a generic data modem.

“The disadvantage in battery life of VoLTE compared to circuit-switched voice is driven by a few different factors,” Malhotra said. “One is the more strenuous exercise of the device, including conversion of voice to packet data, transmission and receipt over the data network, and reconversion back to voice. Another is the use of less power-efficient components such as data modems versus voice transceivers.”

If this proves to be typical for VoLTE handsets, it will be a big problem. The battery life of the first generation of LTE smartphones was atrocious, and handset vendors have tried to address the problem by slapping fat 3000+ mAh power cells onto their phones. Some carriers are already reluctant to embrace VoLTE since they can still squeeze plenty of life out of their 2G and 3G voice services. If VoLTE proves to be a battery killer, they will be even less inclined to move mobile voice into the IP age.

There is some good news in Spirent’s findings though. It found LTE performed better than CDMA when the phone is used to make simultaneous voice and data calls. When the phone was in 4G-only mode — i.e., using only the LTE network for both VoIP and data — it performed slightly more efficiently than when the 2G radio was used for voice while the 4G radio transmitted data, Spirent discovered. That makes sense since powering two radios simultaneously could take an enormous toll on battery life.

That would seem to indicate that if you tend to talk and consume data at the same time, then VoLTE is a more efficient technology. That’s true, but only to the tiniest degree. The study found that both in both scenarios the hyperactivity of the device drained tremendous amount of energy. Battery life estimates dropped below 120 minutes in both cases. No matter which radios you use, talking and surfing consumes a tremendous amount of power.

Malhotra, however, said LTE power efficiency is bound to improve as both data modem technology and network coverage gets better. Today’s LTE networks have limited footprints, forcing phones to continuously check for signals. Eventually the data modems in our handsets will be optimized for VoIP calling.

“These issues will be mitigated over time, especially as components continue to become more power efficient, and devices do not need to switch between different modes of voice call processing,” Malhotra said.