Over-the-air BLE test systems solve wireless quality issues: Page 2 of 5

September 07, 2017 // By Allen Henley, LitePoint
Bluetooth Low Energy - BLE - performance can be difficult to verify due to packaging, but novel OTA measurement methods can overcome those problems, especially when it comes to packet error rates and receiver sensitivity.

For devices with receivers, each time they transmit an advertising packet, they listen for a brief period for a specific BLE message called a Scan_Request. This message is normally used by nearby devices that may wish to communicate with the advertiser. If the advertising device receives this Scan_Request, it will respond with a Scan_Response message. This pattern is illustrated in the power versus time plot shown in Figure 1. The advertiser sends an advertisement packet, shown in blue, which is followed by a Scan_Request message from a nearby station, (shown in orange), and the advertiser follows up with a Scan_Response message, again shown in blue.

This exchange of messages is used in normal operation of BLE devices, and the OTA test system exploits this behaviour to measure PER. During a receiver test, the DUT sends an advertisement, the test system sends a Scan_Request, and if the DUT received the packet, it acknowledges with the Scan_Response. The test system keeps track of the number of Scan_Request messages that are sent and the number of Scan_Responses received. This information is used to calculate receiver PER.

For sensitivity measurements, the test system adjusts the RF signal level to find the RF level that produces a specific PER. This RF level, known as receiver sensitivity, is a common method used to specify receiver quality. The method using the advertising packets, Scan_Request messages, and Scan_Response is implemented in the BLE OTA tester, and accurately determines receiver PER or sensitivity without any direct wired communications with the DUT.

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