This is clearly unacceptable in many applications, and demands a new, faster method. To resolve the issue, an OTA test solution must use an algorithm to rapidly determine a PER distribution curve. This method, referred to as “fast PER,” is designed to quickly determine the receiver sensitivity point that produces 50% PER.
During a fast PER test, the tester begins by sending a single packet ( Scan_Request) at an arbitrary RF level. If the packet is acknowledged, the RF level is lowered and the next packet is sent at this new lower level. If the packet wasn’t acknowledged, the RF level is increased, and the next packet will be sent at this higher level. By using an intelligent algorithm to adjust RF-level step sizes and keep record of which levels were acknowledged and those that were not, a “Packet Error distribution curve” can quickly and accurately be created with a minimal number of packets.
Figure 2 shows a traditional PER curve for a BLE device. The PER curve is most sensitive to RF-level changes at the 50% point of the curve, and for this reason the fast PER algorithm searches for this 50% point. During the RF-level changes, most of the packets are sent at an RF level near the 50% point; the RF step sizes are adjusted to smaller steps as the algorithm converges on this 50% region. This produces a very repeatable and accurate measurement of the DUT receiver sensitivity and requires fewer than 5% of the number of packets that would be necessary with a traditional brute-force PER sweep using a large number of packets at a range of different RF levels.