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Antenna Switching for LE Direction Finding Packets

NI Bluetooth Generation Toolkit 19.1 Help

Edition Date: October 2019

Part Number: 373432K-01

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The Bluetooth Generation Toolkit enables the phase and amplitude modulation on per transmit slot basis in the constant tone extension (CTE) field of LE packet resulting in the emulation of different paths taken by the CTE portion through the RF Switch and different antennas in the DUT.

Figure 1 - Transmission of CTE field through elements of antenna array

The IQ Samples Dynamic Range, AoD Receiver Test requires that a variable attenuation be applied on the line while sending a packet with a CTE field, such that the input power level to the receiver is set to the values for each antenna. The toolkit allows you to specify the phase value per slot in addition to the amplitude values.

Refer to LabVIEW»Examples»RF Toolkit»BT»Generation»niBT Generate LE-TP Packet Example or Documents»National Instruments»Bluetooth Toolkit»Examples»C»Generation»Generate LE-TP Packet which shows the antenna switching capabilities in the Bluetooth Toolkit.

Configuring the Direction Finding attributes for Antenna Switching Emulation:

Antenna Switching emulation is applicable when the Direction Finding Mode property is set to either Angle of Arrival or Angle of Departure. To enable the antenna switching emulation, set the Antenna Switching Enabled property to True.

Valid Antenna Switching Patterns:

  1. For example if the Number of Antennas is set to 4, there are two supported antenna switching pattern formats:
    1. A0A1A0A0A0A2A0A0A0A3A0A0
    2. A0-A1-A2-A3

    Some examples of invalid patterns for the above configurations include: A0-A1A2A3, A-A1-A2-A3, A-0-A1-A2-A3.

  2. The only valid characters in the pattern are “A”, 0 to 255 and “-“.
  3. The pattern must include all the valid Antenna Indices. For Number of Antennas set to 4, the antenna pattern must include all the antenna indices from 0 to 3.

If the antenna switching pattern is exhausted before the end of the CTE field, it shall be repeated from the beginning. If the pattern has not been completely used by the end of the Constant Tone Extension, any remaining terms shall be ignored. This is according to the definition present in the Section 5.1, Vol 6, Part A of the Bluetooth Core Specification Version 5.1.

Configuring Relative Amplitude and Relative Phase Values

The phase and amplitude values of the non-reference antenna are specified with respect to the reference antenna A0. The number of elements in these array properties must be at least Number of Antennas - 1. The first element of the Relative Phase (deg) array property corresponds to the phase of antenna A1, the second element of the array corresponds to phase of antenna A2, and so on. Similarly, the first element of the Relative Amplitude (dBm) array property corresponds to the amplitude of antenna A1, the second element of the array corresponds to amplitude of antenna A2, and so on.

Average power of the reference antenna A0 is equal to the average power of the portion of the LE packet before the Constant Tone Extension field. This power level is configured through the niRFSG Power Level property or the NIRFSG_ATTR_POWER_LEVEL attribute.

The Guard period and switching slots in the CTE field are utilized to make transitions from one phase value to another and from one amplitude level to another for the duration reported by the Antenna Switching Duration Used (s) property. The Antenna Switching Duration Used (s) property is derived using the Oversampling Factor and Antenna Switching Duration (s) properties.

For an antenna switching pattern of A0-A1-A0-A0-A0-A2-A0-A0-A0-A3 and CTE slot duration of 1us, an example of a plot of amplitude transitions is as shown in the following image.

Figure 2 - Amplitude response in the CTE field when Antenna Switching emulation is enabled

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