A Performance Evaluation Framework for Direction Finding Using BLE AoA/AoD Receivers

Bluetooth low energy (BLE) has been significantly contributed to the Internet of Things applications due to its advantages, such as low power consumption and scalability. To further expand its applications, BLE has adopted the Angle of Arrival (AoA) and the angle of departure (AoD) to improve the accuracy in direction finding (DF). The AoA/AoD is calculated using the phase difference (PD) between slots in the received BLE data. The PD performance of BLE receiver (RX) in all directions should be evaluated in detail because it directly determines the accuracy of AoA/AoD. In the traditional test method, the reference PD is converted by an antenna array with switches, which is inaccurate due to the conversion errors and path mismatches. Moreover, because of the mechanical rotation of the turntable, the test processing is very time consuming. This article proposes a BLE test waveform generation method that directly includes the reference PD. A commonly used vector signal generator (VSG) is the only required instrument in the evaluation. The compact test setup not only eliminates the requirement of antenna array, switch, turntable, and anechoic chamber but also eliminates the measurement errors caused by these devices. After creating and downloading all BLE test waveforms with reference PD in the range of -180 degrees to 180 degrees by user-defined steps, the PD performance of BLE RX can be quickly evaluated by switching the test waveforms using commands or running them in the sequence mode. Furthermore, three enhanced test cases with automatic test procedures are proposed to evaluate the detailed PD accuracy of BLE RX under the low signal-to-noise ratio (SNR), carrier frequency offset, and modulation frequency deviation environments. Experimental results show that the PD error of the proposed method is 0.19 degrees, and it needs 360 ms to evaluate the PD accuracy of CC2640R2F in all directions in 1 degrees steps.