Sunday, July 12, 2015

Why is using signal strength at a distance of 1m for estimating iBeacon’s distance not a good idea?

Apple states that:

“To provide the best user experience, it is critical to perform calibration in your deployment environment. As each beacon is installed you should perform a calibration step. Core Location uses an estimation model that requires calibration at a distance of 1 meter away from the beacon.”

This calibration has to be done ideally for every installed beacon. In this way, you will get the best distance estimate. But this is true only if you don’t change the beacon’s transmit power or you keep measuring it with the same mobile device.
Transmit power is degrading itself gradually with time.  But this is the least of your worries. The important part is measuring the beacon’s signal with the same device/antenna. As you can understand, this is applicable only to a limited number of devices. So for Apple, that’s no trouble. But when on Android, you mustn’t rely on estimating distance using this 1m away measured constant broadcasted by beacon.  The results may be misleading, since your device’s antenna may differ significantly, from the reference device’s one.
Better approach would be to build up a list of device specific calibrations and distribute it along with your app. But this is really hard to implement, even though there is at least one vendor using it. And as you can see, it only supports 2 devices so far. So there is obviously some space for improvements, right, Lime?

1 comment:

  1. The thumb rule for a online antenna is that the bigger the antenna, the better is the transmission. Even small and cheap cellular phone antennas are often capable of getting higher signal strengths compared to the more expensive internal antennas.