INTERNET OF THINGS HANDBOOK
New Bluetooth spec gives the IoT a sense of direction The recently released Bluetooth 5.1 specification builds in an efficient way of zeroing in on the location of BLE transmitters and receivers.
The newest version of the Bluetooth communication standard emerged in January. The most noteworthy feature of Bluetooth 5.1 is an efficient way of discerning the direction of Bluetooth transmitters and receivers. The spec also introduces other advances aimed at speeding communications and boosting energy efficiency. Makers of Bluetooth ICs have already released hardware that bakes in the features of the new 5.0 spec. Here’s a rundown of the changes Bluetooth 5.1 brings to the table, along with an example of how one supplier has begun applying it.
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WHERE IS IT? Bluetooth receivers have used signal strength to estimate distances to Bluetooth transmitters. The 5.1 spec provides two methods for more precise means of pinpointing locations, at the expense of using multiple transmit/receive antennae. To implement the Angle of Arrival (AoA) method, the receiver must have at least two antennae (at a minimum spacing of 6.2 cm) while the transmitter can have one. With AoA, the receiver uses its multiple received signals to deduce the angle of the source. Similarly, the Angle of Departure (AoD) method requires a transmitter with at least two antennae. The receiving device, which can have a single antenna, picks up multiple signals and from them derives the angle of the source.
Direction finding in Bluetooth 5.1 In the angle of arrival (AoA) method implemented in Bluetooth 5.1, a device such as a tag in a real-time locating system (RTLS) transmits a signal from a single antenna. The receiver contains multiple antennas arranged so the receiver sees a phase difference because of the difference in distance from each receiving antenna to the transmitting antenna. In the angle of departure (AoD) method, a device such as a Bluetooth locator beacon transmits a signal via an antenna array. The receiving device, such as a smartphone, uses a single antenna to pick up the signals that are decoded to calculate relative signal direction. This method of direction finding is intended for use in indoor positioning systems such as those for wayfinding.
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4/15/19 10:29 AM
