Bluetooth 5.1 allows producers to create location applications based on the Angle of Departure (AoD) and the Angle of Arrival (AoA). Accordingly, it is conceivable to design proper Indoor Positioning Systems (IPS), for instance, for the traceability of resources, assets, and people.
The specification introduced in 
highlights that Bluetooth 5.1 requires modifications to the radio frequency “stack”, i.e., the software protocol. Moreover, also hardware enhancements are expected depending on the chip manufacturer. It is beneficial to heed that, as the main feature, the updated protocol attaches a CTE to every Bluetooth data employed for radiogoniometry. Otherwise, packets remain unchanged to be practiced for conventional BLE transmission 
. The analysis of 
denotes that CTE is not modulated and transmitted at 250 kHz or, seldom, more than 500 kHz when employing the more effective throughput method of Bluetooth. Its continuance is between 16 and 160 μs. More in detail, as introduced in 
, CTE is composed of an “unwhitened” series of “1” communicated large adequate to permit the receiver to obtain the IQ information without modulation’s influences. As the CTE is transferred at the end, the Cyclic Redundancy Check (CRC) of the packet is not influenced.
Another notable enhancement to the spec 
greatly simplifies protocol configuration for IQ sampling. This arrangement comprises arranging both the antenna switched and the sample timing, i.e., two fundamental values for the position estimation accuracy. Ordinarily, although several IQ sampling timing arrangements can be practiced, an IQ representation is registered every 1 or 2 μs inside the associate time per antenna. Moreover, the outcomes are reported in the Random Access Memory (RAM) of the BLE SoC. Figure 1 shows how the received signal phase varies as different array antennas sample it.
A single transmitter signal shows a different phase when it reaches the antennas at different distances from the source.