Every problem is an opportunity
Pure RF is problematic
- Too imprecise (large granularity)
- In-building propagation is hard to model
Solution: use RF + ultrasound (US)
- Speed of light >> speed of sound! (c = 1 foot/ns vs v = 1 foot/ns)
- When first RF bit arrives, note time
- When US pulse detected, check time difference (dt)
- Distance estimate = v * dt