1. Frequency and Clock Tolerance Comments
September, 2008
doc.: IEEE /1112r1
September, 2008
Frequency and Clock Tolerance Comments
Date:
Authors:
Carl Kain, Noblis
Carl Kain, Noblis

2. September, 2008
doc.: IEEE /1112r1
September, 2008
Abstract
This presentation addresses comments concerning frequency and clock tolerance, CID ; 380, , 386, 387, 388, 389, 391, 392.
Carl Kain, Noblis
Carl Kain, Noblis

3. Frequency and Clock Tolerance
September, 2008
Frequency and Clock Tolerance
Base standard specifies 10 ppm for both frequency and clock tolerance for 5 MHz channels
Base standard specifies 20 ppm for both frequency and clock tolerance for 10 MHz channels
TGp Draft 4.0 specifies 10 ppm for both frequency and clock tolerance for 10 MHz channels
Commenters who oppose tighter values want either rationale or are primarily are concerned with cost
Carl Kain, Noblis

4. Comments From Master Spreadsheet
September, 2008
Comments From Master Spreadsheet
375
Fischer, Matthew 22 41 TR
The tolerance value seems too tight. Previous specifications have always allowed +-/20ppm, which seems to be implementable.
Change the tolerance to +/- 20 ppm.
376
Hansen, Christopher
The tolerance value is too tight. This will unnecessarily increase the cost of implementations. Previous specifications have allowed +-/20ppm, which is reasonable.
377
Trachewsky, Jason
The frequency accuracy requirement is too tight.
378
Wang, Qi
"The transmitted center frequency tolerance shall be +/-10ppm maximum for 10 MHz channels used by a STA in the WAVE mode." What is the rational to have such a tight tolerance value? Previous specifications have always allowed +/-20ppm, which seems to be implementable.
Carl Kain, Noblis

5. Comments From Master Spreadsheet
September, 2008
Comments From Master Spreadsheet
380
Erceg, Vinko 22 46 TR
It is not clear to me that the transmit frequency tolerance of +/-10 PPM is required. Crystal at that tolerance level is expensive!
Change the tolerance to +/-20 ppm or show simulation results that prove that +/- 10 ppm is required.
382
Kolze, Thomas
Transmit frequency tolerance of +/-10 PPM is required but not shown to be needed.
Relax the tolerance to +/-20 ppm or present case that proves +/- 10 ppm is required.
383
Moorti, Rajendra
10ppm frequency tolerance is too restrictive and cannot be easily / cheaply implemented. moreover, there is no need for such a tight tolerance since a 20ppm error can be corrected
change to 20ppm tolerance
384
Roy, Richard
There does not appear to be any requirement for a tighter tolerance on clock frequency or transmitter center frequency than those already in the standard.. The current implementations seem to work just fine in the harshest environments, both experimentally and theoretically. Without a valid requirement to tighten these specs, they should be left alone. Note that if a manufacturer of an ITS system implementing the WAVE capability decided to require a tighter tolerance on either or both of these parameters, such a requirement could easily be imposed in the procurement procedure.
Remove this specification.
Carl Kain, Noblis

6. September, 2008
Discussion
Document ; Bob Sorrano of JHU discussed issue based on testing done on JHU campus
Conclusion was:
Results from initial testing using IEEE a devices as substitutes for p devices in a high speed environment indicated some problems could result in synching and maintaining signal lock which could be mitigated by requiring a more stringent frequency tolerance of ±10 ppm vs. the current ±20 ppm requirement that is sufficient for non-mobile and mobile platforms not required to communicate over high speeds.
Additional rationale for tighter values
Commenters are inquiring what TGp is doing differently to ensure the best possible performance for safety applications implemented in vehicles moving at high speeds
Liability is a major practical issue; standard should reflect due diligence
The technical background addressed high speed operation, which is now known not to have a significant effect on the issue of frequency or clock stability.
Carl Kain, Noblis

7. September, 2008
Recommendation
Recommend to accept comments 375,376,377,378,380,382,383,384
Instruct the editor to delete from p D4.01
Moved: Carl Kain
Second: Justin McNew
For: 10
Against:0
Abstain:3
Carl Kain, Noblis

8. September, 2008
References r0
Carl Kain, Noblis