Most people imagine Bluetooth beacons transmit equally in all directions. However, this isn’t usually true. The 2.4 GHz frequency that beacons use is easily blocked or affected (through electronic resonance) by items such as the casing, the battery and even the printed circuit board itself. Also, the design of the antenna, that’s usually etched onto the printed circuit board, causes the transmission to vary depending on the direction.
Printed Circuit Board (PCB) Antenna
The above 2D design leads to different radiation depending on whether you are viewing face on, sideways or end on. The following diagram from a very informative Cypress article (pdf) demonstrates how the radiation pattern can vary in the x y and z planes:
In practice, it’s best to perform tests to assess how the beacon radiation changes with beacon orientation. You can do this by measuring the change in RSSI as you orientate the beacon. You can measure the RSSI using an app such as nRF Connect.
For example, with the long 300m range iB003N-PA, we determined experimentally that the best range was when the non-battery face of the beacon was facing the observer.
iB003N-PA – Strongest signal for us was downwards in this photo
However, this was for our particular scenario. How and where the beacon is mounted can also affect transmission and hence range.
So, the next time you are testing the range or installing beacons, take some time to assess how the beacon orientation might be affecting the range.
Asset tracking systems don’t need beacons advertising of the order of hundreds of millisecs or even a second. Better better use can be made of gateways, servers and beacon battery life if the advertising period is longer. For the AKMW-iB004N PLUS (ZeroConf™) it’s set to 30 secs which gives a 10+ year battery life. The calculated life is actually much longer, of the order of 30 years. However, the shelf life of the Panasonic battery is only 10 years so other (chemical?) things might happen to the battery over this time so 10 years is a conservative estimate.
Another feature of asset tracking is that you usually have to set up lots of beacons and determine their Bluetooth MAC addresses. This can take a lot of effort and, being a tedious activity, can be prone to error. The AKMW-iB004N PLUS (ZeroConf™) comes already set up and advertising. The MAC address is on a label on the outside of the beacon.
The iB003N can transmit up to three channels: iBeacon, Custom and Accelerometer Data. If you only want to send iBeacon, the iOS and Android app ‘Config’ screen implicitly sets the state to iBeacon only transmission when you set the iBeacon parameters.
On iOS only, the Eddystone screen allows you to set the custom channel to send Eddystone that implicitly sets the state to transmit the Custom channel only.
What if you want to transmit both iBeacon and Custom channels or also send the acceleration data? What if you want to enable motion triggered broadcasting? For cases such as these, you have to set the beacon state explicitly (manually) via the Bluetooth Service Characteristic 0x2A80 as described in the iB003N user guide .