1. PHY Mask Issues Date: 2006-11-03 Authors: November 2006 November 2006
doc.: IEEE /1646r0
November 2006
PHY Mask Issues
Date:
Authors:
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Hedberg and Petranovich, Conexant Systems, Inc.
Jim Petranovich, Conexant Systems, Inc.

2. November 2006
doc.: IEEE /1646r0
November 2006
Abstract
The presentation is to motivate discussion regarding resolution of this comments from LB84 (referenced by CID)
1564
Hedberg and Petranovich, Conexant Systems, Inc.
Jim Petranovich, Conexant Systems, Inc.

3. November 2006
CID 7164
Comment: “40 MHz Tx mask is too broad to prevent excessive interference with adjacent 40 MHz interferers; -45 dBr floor is difficult to achieve in practice when Tx power is lowered more than 10 dB from maximum allowable; at low Tx powers, -45 dBr is not necessary to avoid interference.”
Proposed Change: “Consider narrowing requirement to -28 dBr at 30 MHz offset, -38 dBr at 50 MHz offset, and -45 dBr at 60 MHz offset and above; relax floor requirement to -45 dBr or dBm/MHz, whichever is higher at given Tx power level.”
Hedberg and Petranovich, Conexant Systems, Inc.

4. Contents November 2006 Part 1
Limitation of the spectral floors at low Tx output power levels
(for both 20 MHz and 40 MHz Tx modes)
Part 2
40 MHz Tx mask revision to improve ACI discipline with lower modulation rates
Hedberg and Petranovich, Conexant Systems, Inc.

5. November 2006
Part 1
Limitation of the spectral floors at low Tx output power levels
(for both 20 MHz and 40 MHz Tx modes)
Hedberg and Petranovich, Conexant Systems, Inc.

6. Transmit Spectrum at +18 dBm
November 2006
Transmit Spectrum at +18 dBm
View of the Tx mask floor relative to other floors at higher Tx output of +18 dBm
Power density per MHz BW spectrum
FCC Part 15 limit
dBm/MHz
Radio Tx noise
floor – shown
spurious-free
Hedberg and Petranovich, Conexant Systems, Inc.

7. Transmit Spectrum at +6 dBm
November 2006
Transmit Spectrum at +6 dBm
View of the Tx mask floor relative to other floors at lower Tx output of +6 dBm
Radio Tx noise floor reduced 3 dB and well below FCC limits – but does not meet mask
FCC Part 15 limit
dBm/MHz
Radio Tx noise
floor – shown
spurious-free
Hedberg and Petranovich, Conexant Systems, Inc.

8. November 2006
Proposal
The relative floor level (-45 dBr) of the .11n draft Tx masks is not a realistic limit with reduced
Tx output powers (e.g. +6 dBm or lower)
Most external radio power amplifiers have a fixed gain and thus cannot attenuate the transceiver
output noise+spurious floor to the levels required by the mask at low Tx power levels
In addition, the mask floor levels in this scenario are well below the FCC part 15 limits for spectral
emissions in forbidden bands and don’t need to further constrain the radio Tx floor
Our proposal is to set the floor limit of Tx output power spectral density to a level corresponding
to either -45 dBr from transmitted power in dBm/MHz or dB/MHz, whichever is greater
This ensures a floor and spurious level at least 6 dB below the FCC limits for lower Tx powers
Radios are still required to meet the FCC Part 15 and other regulatory limits at all power levels
Hedberg and Petranovich, Conexant Systems, Inc.

9. Transmit Spectrum at +6 dBm
November 2006
Transmit Spectrum at +6 dBm
View of the Tx mask floor relative to other floors at lower Tx output of +6 dBm
Radio Tx noise floor is well below FCC limits – but does not meet mask
The noise floor meets the new proposed limit shown
Mask floor limit
capped above
at dBm/MHz
FCC Part 15 limit
dBm/MHz
Radio Tx noise
floor – shown
spurious-free
Hedberg and Petranovich, Conexant Systems, Inc.

10. Part 1 - Summary November 2006
Current Tx masks require a floor of -45 dBr relative to Tx power spectral density
-- which may vary over a wide range as Tx power is varied
We propose placing a minimum cap on the Tx output power spectral density
of dBm/MHz – that overrides the mask floor at lower Tx power levels
This relieves the radio design of unrealistic output noise and spurious requirements
if it transmits at lower output power levels – where the -45 dBr floor would be
unnecessarily far below the allowed FCC limit
The .11n spec should encourage practical designs that have the flexibility to
conserve power with reduced Tx output when link conditions permit
Hedberg and Petranovich, Conexant Systems, Inc.

11. November 2006
Part 2
40 MHz Tx mask revision to improve ACI discipline at lower modulation rates
Hedberg and Petranovich, Conexant Systems, Inc.

12. .11n Draft 40 MHz and 20 MHz Masks
November 2006
.11n Draft 40 MHz and 20 MHz Masks
Current draft proposal 40 MHz Tx mask allows considerably more Tx adjacent channel
power leakage than the corresponding 20 MHz Tx mask
Hedberg and Petranovich, Conexant Systems, Inc.

13. Example of Mask Limited HT-40 Spectrum
November 2006
Example of Mask Limited HT-40 Spectrum
Spectrum can approach mask limits for BPSK and QPSK transmission modes with small
PA output backoffs while meeting Tx EVM requirements
Leakage into adjacent 56-carrier signal band is 3.5 dB larger than for similar limited 20 MHz
transmissions (e.g dB relative to in-band Tx power)
56-L
56-U
Hedberg and Petranovich, Conexant Systems, Inc.

14. Mask Limited HT-20 Spectrum
November 2006
Mask Limited HT-20 Spectrum
Spectrum can approach mask limits for BPSK and QPSK transmission modes with small
PA output backoffs while meeting Tx EVM requirements
Example with same PA OBO as HT-40 but with adjacent channel leakage dB
Hedberg and Petranovich, Conexant Systems, Inc.

15. Mask Limited Legacy .11a/g Spectrum
November 2006
Mask Limited Legacy .11a/g Spectrum
Draft 20MHz HT mask is slightly more restrictive than the legacy .11a/g mask, and tends to
enforce a slight increase (e.g. 0.6 dB) in minimum PA OBO for 56-carrier HT signals
Maximum adjacent channel leakage for low rate modes is similar for 20M legacy and 20M HT
Hedberg and Petranovich, Conexant Systems, Inc.

16. November 2006
Improvement
We propose to revise the 40 MHz Tx mask slightly – to make it more consistent
with 20 MHz practice in limiting adjacent channel leakage power
Current Draft Proposed Rev
-20 dBr at 21 MHz No change at 21 MHz
-28 dBr at 40 MHz -28 dBr at 30 MHz
-38 dBr at 50 MHz (added break-point)
-45 dBr at >=60 MHz No change at >=60 MHz
The revised Tx mask does not reduce the maximum Tx power available for
high-throughput QAM transmissions – which are EVM limited
With a given PA characteristic, the maximum amount of Tx power for mask-
limited 40 MHz BPSK and QPSK modes is reduced by only a small amount
(e.g. 1.2 dB)
Hedberg and Petranovich, Conexant Systems, Inc.

17. Proposed Mask Revision
November 2006
Proposed Mask Revision
The revision tightens the limit primarily in the adjacent 20 MHz channel segment
Hedberg and Petranovich, Conexant Systems, Inc.

18. Comparison with Offset 20M-HT Mask
November 2006
Comparison with Offset 20M-HT Mask
40M and 20M masks now have similar limitations in the adjacent 20 MHz channel segment
Hedberg and Petranovich, Conexant Systems, Inc.

19. Example of Mask Limited HT-40 Spectrum
November 2006
Example of Mask Limited HT-40 Spectrum
PA output backoff increased by 1.2 dB from previous example with .11n draft mask
Leakage into (lower) adjacent channel 56-carrier upper segment reduced by 4.0 dB
Leakage into (lower) adjacent channel 56-carrier lower segment reduced by 3.6 dB
56-L
56-U
Hedberg and Petranovich, Conexant Systems, Inc.

20. Part 2 - Summary November 2006
Current 40 MHz Tx mask allows about 3 dB more adjacent channel interference
due to Tx power leakage than for the 20 MHz HT modes
We propose a revision to the 40 MHz mask break-points that puts this maximum
interference on par with that allowed in 20 MHz HT and legacy operation
With the revised 40 MHz mask, there is no impact to maximum Tx power for
16-QAM and 64-QAM 40 MHz modulations
For mask-limited BPSK and QPSK HT-40 transmission modes, the maximum
Tx power is reduced slightly by about 1.2 dB or so; but , corresponding ACI
leakage into the adjacent 20 MHz channel segments is reduced by at least
3.6 dB for these worst case interferers
The revision will enable more balanced protection as 40 MHz .11n modes
gain hold in future WLANs
Hedberg and Petranovich, Conexant Systems, Inc.

21. References 11/06-0693 PHY Comments from LB84 for TGn
November 2006
doc.: IEEE /1646r0
November 2006
References
11/ PHY Comments from LB84 for TGn
11/ PHY Mask
Hedberg and Petranovich, Conexant Systems, Inc.
Jim Petranovich, Conexant Systems, Inc.