New developments in indoor positioning technology

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There has been a long-standing interest in accurate indoor positioning technology, with a wide range of interesting use cases involving the tracking of either people or objects.
To improve accuracy, the Bluetooth Special Interest Group (SIG), has introduced new capabilities with Bluetooth 5.1 including the detection of the angle of arrival of a Bluetooth packet.
This works by having a multiple antenna array in the Anchor and measuring the phase difference of the same signal received at the different antennas, typically separated by a half wavelength i.e. c.
• The accuracy with which the phase of the received signal can be measured for each antenna
The accuracy with which the phase can be measured depends on the precision of the IQ sampling carried out by the BLE device, which is affected by the internal precision of the IQ demodulator and the short term frequency drift of the crystal oscillators used in both the tag and the anchor.
Similar calculations show that for a 4 antenna array the accuracy of the angle estimation is improved respectively to +/-1° close to the axis and +/-1.5° at 45°.
Above: A signal arrives at an angle to the antenna array The other main method of indoor positioning is Ultra-Wide Band (UWB).
Since pulse width is directly related to the inverse of bandwidth and UWB systems typically use a 500MHz bandwidth, this technique could achieve an accuracy of the order of 0.5/500MHz =1ns or 30cm.
However, UWB systems use very high frequency sampling of the incoming pulse train and correlation to a known reference train to improve accuracy.
Assuming the high frequency sampling captures the phase of the pulse to within +/-45°, the accuracy would be related to ¼ of the carrier frequency period.
In the case of 6.5 GHz UWB this implies an accuracy of 0.25/6.5 GHz or 38ps, equivalent to 1cm positioning precision

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