| Equipment | Signal | Time latency (ms) | Accuracy |
---|---|---|---|---|
Swadloon [27] | Anchor speakers; smartphones with one microphone and inertial sensors | Continuous wave around 20 kHz | 250 | The mean error of direction finding is around 2.1\(^{\circ }\) when the range is 32 m, 90-percentile errors are under 0.92Â m |
FingerIO [46] | Smart devices with one speaker and two microphones | OFDM in the range of 18–20 kHz, the bandwidth of each subcarrier is 375 Hz | 5.92 | The average accuracy of 2D tracking for smartphones is 8 mm, for smart watches is 1.2 cm |
LLAP [34] | Smart devices with one speaker and two microphones | Multiple continuous waves(cosine waves) with frequencies in the range of 17–23 kHz | 15 | The tracking accuracy for 1D is 3.5 mm, for 2D is 4.6 mm |
Strata [77] | Smart devices with one speaker and two microphones | Single-carrier modulated signal with the frequency in the range of 18–22 kHz, 26-bit GSM training sequence | 12.5 | The distance tracking error is 0.3 cm, the 2D tracking error is 1 cm, the drawing error in 2D is 0.6 |
Vernier [81] | Two anchor speakers (e.g., speakers on the TVs); smart device with a microphone | Continuous wave (sine wave with the frequency at 20 kHz or 17.5 kHz for 2D) | 10 | The median error is under 2 mm for 1D when the distance between the speaker and the receiver is 7 m, the median error for 2D is under 4 mm |