How to limit the advertising range of a beacon?

Question

Is it possible to limit the ranging of the beacon, so that only devices within a certain close range(or proximity) can identify and connect to the beacon? Lets say for example the devices outside 0.5 meter zone shouldn't be able to see or connect to the beacon. I am using a iOS device as a beacon. In the Apple's CoreLocation API, there is a method called peripheralDataWithMeasuredPower in the CLBeaconRegion class which says:

peripheralDataWithMeasuredPower: Retrieves data that can be used to advertise the current device as a beacon.

(NSMutableDictionary *)peripheralDataWithMeasuredPower:(NSNumber *)measuredPower

Parameters:

measuredPower: The received signal strength indicator (RSSI) value (measured in decibels) for the device. This value represents the measured strength of the beacon from one meter away and is used during ranging. Specify nil to use the default value for the device.

Can this be used to limit the range of beacon? If yes, I am unable to understand how to decide the value to set for measurePower parameter? What are they trying to say by ...value represents the measured strength of the beacon from one meter away..?

Please forgive if this is a very basic question. I've recently started iOS development and will appreciate your help. Thanks.

Answer 1

Unfortunately, there is no easy way to adjust the range of an iBeacon without special hardware.

1. The power field that you mention is simply a calibration value transmitted by an iBeacon. It doesn't affect the actual physical radio range of the iBeacon. If the transmitter can be seen by an iPhone 50 meters away, altering the power field value will not change this at all. The only thing it does is change is the calibration constant which is an input to the distance estimation algorithm (used for the accuracy and proximity fields) inside the iOS software. Altering the power field will affect the estimated distance returned by the API, but it won't change the actual distance at which the iBeacon is first detected.

2. Altering the transmit power of a standard bluetooth iBeacon is practically impossible. In theory you can use metal shielding to construct a "faraday cage" around the transmitter to mute its power, but my experience is that it isn't very effective and it is highly susceptible to tiny imperfections in the shielding. If you want to change the transmit power you have to have somebody build you custom hardware.

The software alternative is to use the ranging API to track an iBeacon while it is visible, and only perform an action when the estimated distance is close enough, say 0.5 meters as you suggest. This works great -- only in the foreground.

If you require actually waking up your app in the background at a close range, this won't work. The best you can do is have the monitoring API wake up your app when the iBeacon is first detected, and then send a notification to the user and start ranging. If the user elects to bring the app to the foreground (at 50 meters) you can keep monitoring and then perform your desired action at 0.5 meters. If the user does not elect to bring the app to the foreground, iOS will only give you about 5 seconds of time to continue ranging before it suspends your app. It is very unlikely that the distance will change from 50 meters to 0.5 meters in this time.