The Internet of Things, and the billions or trillions of devices that will be communicating in coming years, is driving the need to make LTE more power-efficient. With that in mind, researchers at Ericsson (NASDAQ:ERIC) are proposing a number of ways to make LTE more suitable for IoT applications.
"In IoT the ability of many low-cost devices to stay operational for long periods of time may make or break the future visions," said Tuomas Tirronen of Ericsson Research in a blog post.
One target area for slashing power consumption is LTE's discontinuous reception (DRX) mode. This is used to save power in end-user devices by having them switch off at least part of their circuitry during the DRX period to save power. "The current specifications for LTE limits the longest possible DRX cycle to 2.56 seconds," said Tirronen.
Such a short cycle is far too energy-sapping for many IoT applications. So, one solution would be to enable much longer DRX cycles to drastically lower power consumption, Tirronen wrote. Optimization of timers in the DRX mechanism that dictate how long a device needs to listen under certain parameters would also help save power, he added.
"Calculations of using very long DRX cycles and optimized LTE procedures show that it could be possible to reach lifetimes of even over 10 years using off-the-shelf and relatively cheap batteries," Tirronen wrote.
3GPP is expected to freeze Release 12 specifications in the second half of this year, and those include a new power saving mode (PSM) that is conceptually close to allowing longer DRX cycles.
According to Tirronen: "In the PSM mechanism the devices periodically contact the network to check if there is downlink data for them, and these periods can be in the order of tens of minutes compared to DRX cycles where the UE can sleep only few seconds at most with the current specifications."
However, he cited a drawback to PSM, which is the possible signaling load. Tirronen said this could be quite high if there are numerous devices in the same cell or area. "In such cases an extended DRX solution might provide a more efficient alternative," he wrote.
Tirronen also noted that any solution relying upon extended sleep time for devices has a disadvantage in that the network cannot reach those devices when they are sleeping. "On the other hand, the devices can initiate uplink transmissions when they want to using the normal procedures," he said.
3GPP working groups have also addressed ways to enable user equipment to go to sleep faster, Tirronen noted.
In addition, 3GPP is examining methods for lowering the cost of LTE modems by doing things such as reducing the number of receiver chains from two to one and slashing the peak data rate and the used bandwidth. Release 12 specs will include a new LTE UE category that includes lower complexity requirements, Tirronen said.
- see this Ericsson Labs blog post
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