Some Thoughts on L1CAL2C Derived TEC

1
Some Thoughts on L1CA/L2C Derived TEC
Paul Kintner, Aug. 2009 Cornell University
2
Required Precision

• C/A and C code chip period 1ms
• A/D cadence is 175 ns (digitization rate)
• 1 TECU produces differential code arrival time of
  about 0.54 ns or 16 cm at L1 (10 ns 20 TECU)
• A/D samples at 175 ns so 0.5 ns is tough
• 1 TECU produce differential phase of 0.28 cycle
• Fraction of a cycle is easy to measure (IQ
  clouds)
• Examine Ithaca data from two consecutive days
  using Bradys C receiver and data from digital
  storage receiver
• Night of April 18 and 19, 2009 PRN 7
• Use L1CA and L2CL with 1 ms accumulations, DLL
  updated every 1 ms and PLL updated every 10 ms
  and PR and phase reported every 20 ms

3
Measurement Precision
0.02 cycle
TIME
PHASE
4
Effect of zero mean white noise on ranging
Early
Late
TCd
T accumulation time d fraction of chip
time C/N0 carrier-to-noise ratio TC chip time
about 1 msec
TC
TC
For C/N0 44dB, TC 1 msec, BWDLL0.3 Hz, d
1, then sDP 0.73 m or 4.5 TECU
5
Time of Arrival (TOA) TEC
6
Comparison between Day1 and Day2 TOA TEC
7
Comparison of Day1 and Day2 TOA TEC
8
Difference Day 1 with Day 2
sDTEC sqrt(2).73m9.52 TECU/m 9.8 TECU
(theoretical value from noise, neglecting
multipath)
9
Comparison of Day1 and Day2 Phase TEC
10
Some Multipath in Phase TEC
11
Difference Phase TEC Day1 with Day2Is this real?
12
Recursive Filter
Current measurement of TEC by D(dt)
Difference in consecutive measurements of TEC by
D(df)
Previous estimate of TEC
Current estimate of TEC
13
TOA TEC with Recursive Filter