1. Response to Comments on Optional Enhanced ACR and AACR Values
IEEE p
September 2008
September 2008
Response to Comments on Optional Enhanced ACR and AACR Values
Date:
Authors:
Carl Kain, Noblis (USDOT)
Carl Kain, Noblis (USDOT)

2. IEEE p
September 2008
September 2008
Abstract
Responses to Comments Concerning Clause 17 Optional Enhanced ACR and AACR Values, including suggested modifications to the p Draft.
Carl Kain, Noblis (USDOT)
Carl Kain, Noblis (USDOT)

3. Response to Comments Concerning Clause 17 Enhanced ACR and AACR Values
September 2008
Response to Comments Concerning Clause 17 Enhanced ACR and AACR Values
CIDs 395, 398, 399, 400, 401, 404, 403, 404
Carl Kain, Noblis (USDOT)

4. Comment Summary September 2008 Carl Kain, Noblis (USDOT) 395
Audeh, Malik 23 2 T
This section provides improved (more stringent) adjacent and non-adjacent channel rejection numbers. Yet they are written as optional/recommended. With the numbers in the base standard, anyone for any implementation can make improved rejection numbers. I do not understand why these specific values are here compared to any others. Enchanced performance as described might be advantageous for any number of applications, not just WAVE. It is not clear to me this enchanced specification is necessary.
Remove this section and Or explain why this application needs such improved numbers.
398
Erceg, Vinko 10 TR
Did anyone confirm that adjacent channel rejection of 37 dB for BPSK R=1/2 is possible? I really don't think so. Even 25 dB rejection seems excessive.
Lower adjacent channel rejection by 10 dB for all modulation/coding levels or show proof that the adjacent channel rejection defined in the table is possible.
399
Fischer, Matthew
Adjacent channel rejection requirement seems too stringent.
Reduce ACR requirement by about 10dB.
Carl Kain, Noblis (USDOT)

5. Comment Summary September 2008 Carl Kain, Noblis (USDOT) 400
Kolze, Thomas 23 10 TR
Adjacent channel rejection of 37 dB for BPSK R=1/2 is unnecessarily difficult --- not supported with justification.
Relax adjacent channel rejection by 10 dB for all modulation/coding levels or present case that the adjacent channel rejection requirements are feasible, reasonable, and necessary.
401
Moorti, Rajendra
Adjacent and Nonadjacent channel rejection requirements are too tight for practical implementation
revert to 11a adjacent and non-adjacent rejection requirements
402
Trachewsky, Jason
Adjacent channel rejection requirement will be too costly too meet.
Reduce adjacent channel rejection requirement by 10dB.
403
Wang, Qi
Without apparent rational, adjacent channel rejection requirements specified here seem too stringent.
Reduce ACR requirement by about 10dB.
404
Bavafa, Moussa
Adjacent channel rejection requirements (as stated on table 17-13a) seem to be really high.
Relax Adjacent Channel Requirement figures to more practical values.
Carl Kain, Noblis (USDOT)

6. September 2008
Comment Summary
Most commenters want optional enhanced ACR and AACR reduced by 10 dB
Some Commenters want justification for tighter values
There is a more significant issue related to the transmission mask of the interfering signal used in the test described in the base document.
This issue defines what enhanced values should be reasonable, and should address the concerns of the commenters
Carl Kain, Noblis (USDOT)

7. Test defined in Current Base Standard (Clause 17)
September 2008
Test defined in Current Base Standard (Clause 17)
The nonadjacent channel rejection shall be measured by setting the desired signal’s strength 3 dB above the rate-dependent sensitivity specified in Table 17-13, and raising the power of the interfering signal until a 10% PER occurs for a PSDU length of 1000 octets.
Example in this document for illustrative purposes will be BPSK R=1/2; AACR for 10 MHz Channel
Receiver Sensitivity is -85 dB
Desired Signal = -85 dBm + 3dB = -82 dBm
The power difference between the interfering and the desired channel is the corresponding nonadjacent channel rejection.
AACR from Table for this example is 32 dB
The interfering signal in the nonadjacent channel shall be a conformant OFDM signal, unsynchronized with the signal in the channel under test. For a conformed OFDM PHY, the corresponding rejection shall be no less than specified in Table
Carl Kain, Noblis (USDOT)

8. Test in Current Base Standard
September 2008
Test in Current Base Standard
AACR=32
Carl Kain, Noblis (USDOT)

9. Some Additional Information
September 2008
Some Additional Information
The base standard specifies a 5 dB implementation margin
If the adjacent (or alternate adjacent) interferer has a transmission mask that allows in-channel interference higher than the desired signal, the error rate will be irreducible.
The desired situation is to have the interfering signal be below the noise floor in the middle of the desired channel (where you cannot filter it out), and build filters in the receiver to handle the adjacent and alternate adjacent channel interference.
In the example on the previous slide, that is exactly the case in the base standard.
802.11p needs an enhanced ACR and AACR because there are possible geometries and situations where adjacent and alternate adjacent channels may be in use in close proximity (same as for any ); however, the potential interference in the base standard is not acceptable for vehicle safety applications.
Carl Kain, Noblis (USDOT)

10. Some Additional Background
September 2008
Some Additional Background
The current base standard assumes the transmission mask, A, so if you set the ACR and AACR for the least stringent mask (Mask A), any other mask will make standards compliance easier.
The real problem is not that the values are too stringent, it is that to be consistent with the base standard, and provide improved performance for ITS applications, the transmitters operating at the medium and higher power levels (in the US) need to use the Mask C, which is identical to the Mask M that is already in the base standard (Annex I, Figure I.2-Transmit spectrum masks for the U.S. 4.9 GHz public safety band)
Next slide (Courtesy of Jerry Landt, Transcore) illustrates the current problem
Carl Kain, Noblis (USDOT)

11. Optional AACR Example with Alternate Adjacent Interferer using Mask A
September 2008
Optional AACR Example with Alternate Adjacent Interferer using Mask A
AACR=47
15 dB above noise floor
Carl Kain, Noblis (USDOT)

12. Proposed Solution September 2008
Make the enhanced ACR and AACR values testing with conformant signals that use the transmit Mask C (same as Mask M in base standard)
Mask C out of band values are set to 8 dB below the test signal (5dB for implementation loss + 3 dB above receiver sensitivity level as specified in base standard)
Reduction in current (802.11p D4.0) enhanced values would be between 2-6 dB, but by specifying the transmit mask of the interferer, the filter design constraints are significantly relaxed– a good compromise that is in agreement with the concerns of the commenters.
Implementers desiring better performance for safety applications will use the optional enhanced ACR/AACR values AND the transmit Mask C.
Carl Kain, Noblis (USDOT)

13. Changes required in 802.11p September 2008
Replace the existing optional enhanced performance ACR and AACR values in table 17-13a with the following reduced values:
mod coding ACR AACR
BPSK 1/
BPSK 3/
QPSK 1/
QPSK 3/
16-QAM 1/
16-QAM 3/
64-QAM 1/
64-QAM 3/
Insert the following into and
An optional enhanced performance specification is provided for systems requiring low bit error rate (BER). If dot11ACRType = 2, the optional enhanced receiver performance specifications given in Table 17-13a shall apply. The interfering signal in the adjacent channel shall be a conformant OFDM signal, using transmit mask M (See Figure I.2), unsynchronized with the signal in the channel under test. For a conformant PHY meeting the optional enhanced receiver performance specifications, the corresponding rejection shall be no less than specified in Table 17-13a. The corresponding minimum receiver sensitivities for each modulation and coding rate are the same as in Table
Carl Kain, Noblis (USDOT)

14. Resolution and Motion September 2008
We agree with the commenters that the enhanced receiver ACR and AACR were too stringent
We recognize that the enhanced values should only apply to conformant signals using transmitter Mask M, and relaxed the values accordingly
The interfering signal under test (using Mask M) will inject less out of band interference, thus simplifying receiver filter design
The official resolution to the comments is “counter”; referring to this document
Move to accept the proposed changes in p as proposed in this document
Special thanks to Jerry Landt for providing the analysis of the linkage between the ACR/AACR values and the transmit mask of the interfering signal under test.
Moved:
Second:
For
Against
Abstain
Carl Kain, Noblis (USDOT)