An Investigation on SYNC Detector False Alarms Month Year doc.: IEEE 802.11-yy/1634r0 An Investigation on SYNC Detector False Alarms Date: 2018-09-10 Authors: Kome Oteri(InterDigital)

SYNC templates (HDR/LDR) Introduction In [1], the responses of the HDR and LDR SYNC detectors to the HDR and LDR data fields have been studied: It was shown that, the correlation between the WUR payload and SYNC can be high, which may create a false alarm in some WURx implementations In this study, we discuss an alternative SYNC detector to lower the false alarm rate while maintaining the same miss detection Legacy SYNC Data TX: RX window SYNC detection SYNC templates (HDR/LDR) Slide e.g., WURx wakes up False alarms?

SYNC templates (HDR/LDR) SYNC Detector In [1], the SYNC detector compares the ratio of the correlation output (𝑥) and the sum samples (𝑦) with a threshold between 0 and 1 e.g., WURx wakes up RX window Legacy TX: SYNC Data Slide 𝑦 Sum of abs samples False alarms due to the high correlation? x/y≷threshold? Correlate SYNC templates (HDR/LDR) 𝑥

Threshold Selection If the threshold is set based on the statistics of the maximum of the detector output within a period for AWGN (e.g., 0.1-0.3), it has been observed that the false alarm rate is 100% for high SNR [1] A higher threshold can increase the miss detection rate. This issue can be addressed by using a different detector design 100% false alarm! Threshold

An Alternative SYNC Detector An alternative SYNC detector may estimate the noise floor (arising due to the WUR payload) by getting 𝑁 taps separated by 𝑇 𝜇𝑠 from the output of correlator (e.g., 𝑁=15, 𝑇=0.8 𝜇𝑠) and compare it with the correlator output If the SYNC is detected, LDR and HDR can be differentiated by checking the sign of correlator output e.g., WURx wakes up Legacy SYNC Signal 𝜏 𝑁 1 ×𝑇 𝜇𝑠 𝑁 2 ×𝑇 𝜇𝑠 Correlate 𝜏 SYNC template … … 𝑦 Mean( ⋅ 2 ) x/y≷th 𝑥 ⋅ 2

Simulation Results (HDR) When the alternative SYNC detector (i.e., detector 2) is employed, the false alarm rate issue is remedied significantly For HDR data, there is a trade-off between miss detection and false alarm rate as a function of the threshold 𝑁 1 = 𝑁 2 =15 and 𝑇=0.8 𝜇s

Simulation Results (LDR) Since 𝑇=0.8 𝜇𝑠 and the ON duration for LDR (i.e, 4 𝜇𝑠) is larger than ON duration for SYNC field (i.e., 2 𝜇𝑠), the detector calculates 𝑦 with the correlated samples and the false alarm rate decreases as a function of the threshold for LDR data 𝑁 1 = 𝑁 2 =15 and 𝑇=0.8 𝜇s

Conclusion In this study, we show that a SYNC detector which takes the noise floor into account can handle false alarm rate issues (i.e., detection of HDR and LDR data fields as SYNC field) without degrading the missed detection rate

References [1] S. Shellhammer and B. Tian, “Concerns about Sync Detector False Alarms” IEEE 802.11-18/1201r0, Jul. 2018