lecture-7-cho_pte587_sensornet1-feb-24-2011

Offsets from ref usc 51 pte587 frequency compensaon

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Sink 3/2/11 USC  ­ PTE587 44 Time Synchroniza;on 14.85 13.86 12.87 11.88 10.89 9.90 8.91 7.92 6.93 5.94 4.95 3.96 2.97 1.98 0.99 0 •  •  •  •  9.9 9.9 11 14 9.9:11:14 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 14.975 T2 = T1 + Propaga;on Delay + Timer Offset1 T4 = T3 + Propaga;on Delay – Timer Offset2 Propaga;on Delay ≈ ( ( 12  ­ 9.9 ) + ( 14.85  ­ 14 ) ) / 2 = 0.975 T1 T1 T4 T3 T1 T1 T4 14 Timer Offset ≈ ( ( 12  ­ 9.9 )  ­ ( 14.85  ­ T3 ) ) / 2 = 0.125 0.125 3/2/11 USC  ­ PTE587 45 Example: Ranging 15.475 14.85 15 15 15.5 0.125 14.975 • T2 = T1 + P = (Time Arrived – T Offset1 •   Distance ropaga;on Delay + Timer ime Sent) x Speed of the Signal •  T4 = T3 + Propaga;on Delay – Timer Offset2 •   If Acous;c, Distance 1 (15.475 (–1 4.85  ­x 14 ) ) / 2 m 0.975 = T 15) 340.29 = eters/sec ≈ • Propaga;on Delay ≈ ( ( 12  ­ 9.9 ) + T4 T3 T 1 162 Offset ≈ (+ E11  ­ f9rom T ime S ync ) ) / 2 = 0.125 meters ( T T.9 )  ­ ( 1 4.85  ­ T 4 rror T4 13 •  Timer 2 1 3/2/11 USC  ­ PTE587 46 Sources of Errors •  Local Clock –  Environmental –  Oscillator behavior •  Pla{orm configura;on Blink { } implementa;on { components Main, BlinkM, SingleTimer, LedsC; Main.StdControl  ­> BlinkM.StdControl; Main.StdControl  ­> SingleTimer.StdControl; BlinkM.Timer  ­> SingleTimer.Timer; BlinkM.Leds  ­> LedsC; } –  Hardware latencies –  Sooware processing •  Propaga;on –  Environmental –  Distance 3/2/11 USC  ­ PTE587 47 Oscillators and Frequency Stability   Temp vs. Freq drio curves •  Frequency Tolerance •  Frequency Stability F +25C 3/2/11 USC  ­ 48 PTE587 Exploi;ng the Differences •  Two Inexpensive Crystals –  –  –  –  Exploit differences in the stability Differen;al Frequency Error (DFE) Variety of inexpensive b...
View Full Document

This note was uploaded on 05/31/2012 for the course PTE 587 taught by Professor Alejandrobugacov during the Fall '11 term at USC.

Ask a homework question - tutors are online