If beacons – proximity radios using Bluetooth Low Energy (BLE) technology — are successful at connecting the online and offline worlds, we're about to see an explosion of them in our malls, shops and streets. There's one problem, though. According to a study done by marketing and analytics firm Aislelabs, beacons drain handset battery life. However, there are a variety of configuration settings that can ameliorate the drain.
A beacon connection (using either Apple's iBeacon standard or a similar standard like Qualcomm's Gimbal) requires two devices to send out signals: the beacon and a handset. Beacons emit a Bluetooth signal on a regular basis to try to find a phone to pair with, and phones need to do extra work to look for them, which either way requires energy. So there are several different variables that could affect the rate at which a battery drains: the frequency with which the phone looks for beacons, the frequency with which a beacon looks for a phone, and the number of beacons in the immediate area.
According to Aislelabs CTO Nilesh Bansal, as beacon prices drop, it will be quite possible to have scores of beacons in close proximity. "Increasingly, beacons could be on every product shelf," Bansal said. "A single pharmacy could have 50 active beacons." That means a lot of beacons could be asking your phone for acknowledgment.
The Aislelabs study focused on three different Android phones: the Nexus 4, the Nexus 5, and the Moto G (Android phones can receive signals from iOS devices using the iBeacon technology but they can't act as iBeacons to send out those signals). These three phones were chosen because they each have Wi-Fi/Bluetooth chips from different eras: the 2-year old Nexus 4 has a Murata SS2908001, the Nexus 5 has a Broadcom BCM4339 and the Moto G has Qualcomm's WCN3620.
All three devices had no other applications running and the device screens were off. The phones connected to three commercially available beacons, and were running a custom-written testing app.
More beacons, more battery drain
One of the primary Aislelabs findings is that newer Wi-Fi/Bluetooth chipsets require less power to make a connection, and the battery savings become more pronounced as there are more demands on that Bluetooth connection. It is also clear that both the chipset included in the handset and the number of beacons in the surrounding area determine battery drain rate.
For instance, when there are seven beacons around a Nexus 5, the battery drains at 2.23 percent per hour (assuming perfect conditions) but a Moto G only loses 1.44 percent. When you bump that number up to 10 beacons, the Nexus 5 loses a whopping 5.18 percent but the Moto G sees only a slight increase to 1.79 percent. So if you were to take a stroll through a mall packed with iBeacons, you could see your battery start dropping even if you've got a newer device.
In addition, there are still no widely adopted industry standards for how often beacons advertise their location. Apple recommends a 100ms interval, but most commercially available beacons emit their signals less often. That might be a good thing: according to the Aislelabs study, as the advertising interval decreases, battery use increases. This is tricky for businesses that use iBeacon: more frequent signal readings for the beacon can help with tracking accuracy, but risk upsetting customers.
On the device level, there are two primary variables to consider: the number of times the phone scans, and the ratio of scan time to off time. Generally, the frequency of scans matters more than the total amount of time scanning, the study found.
For instance, when a device scans every 0.2 seconds for 0.1 second, it spends half its time scanning, but Bluetooth turns on and off way more than a device that alternates five minutes on and five minutes off. The study shows that the number of intervals matters more than the total amount of time: the number of total scanning requests directly corresponds to increased battery usage, even for newer phones.
Help is on the way
Do iBeacons drain battery life? Yes, they do. Simply installing a single iBeacon in a store means that if your customers have devices that are looking to connect, their batteries will empty faster than those of other customers. However, the ultimate effect on phones in real-life conditions (unlike these tests) might not be that large, even with today's hardware. "I keep my Android Galaxy S4 on in an office full of beacons, and by the end of the day the effect on my battery is less than 2 percent," Bansal said.
In addition, BLE is a relatively new standard, and a lot of the hardware currently on the market hasn't been fully optimized for it. It's specifically built to save energy, but it can only transmit small amounts of data. As chips from companies like Texas Instruments are specifically designed to work with BLE, energy use will drop. "Chip manufacturers were not focused on BLE early on, and now hardware is optimized," Bansal said.
It's not just chips that can be improved. Scanning techniques can also be adopted to cut down on battery usage.
"In real life an app SDK can be more intelligent to reduce the battery impact," Bansal wrote in an email. "The Aislelabs SDK I use is heavily optimized — we do what we call 'adaptive' scanning. This cuts down on the number of scans in many real scenarios."
So newer devices are affected less than older devices, and it's possible to find settings that draw a solid compromise. Still there are conflicting interests involved: a beacon that pings more often is better able to accurately guess physical location, but kills phone batteries. More beacons can provide better personalized shopping experience and more useful information for retail marketers, but more beacons consume more energy on consumer devices.
Aislelabs is planning to run more studies, including one with iPhone hardware. As of now, iBeacon is opt-in: first, users have to download an iBeacon-enabled app. What's clear is iBeacons do come with battery tradeoffs for users, and it's up to businesses to make them worth it.
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