1. Green Field Compromise
October 2006
doc.: IEEE /1560r1
December 2006
Green Field Compromise
Date:
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Eldad Perahia (Intel)
Matthew Fischer (Broadcom)

2. October 2006
doc.: IEEE /1560r1
December 2006
Introduction
There are 32 CIDs with Proposed Change of “make GF mandatory”
Straw Poll Held on July 18, 2006 (06/968)– Shall the ability to process GF preambles be mandatory; Yes = 48, No = 78, Abstain = 9
There does not appear to be 75% support for making GF mandatory
However, there does not appear to be 75% support for rejecting these comments
We need a compromise
Eldad Perahia (Intel)
Matthew Fischer (Broadcom)

3. Currently Accepted Modifications to D1.0
October 2006
doc.: IEEE /1560r1
December 2006
Currently Accepted Modifications to D1.0
In D1.0: Green Field – … An HT device which does not support the reception of a GF packet shall be able to detect that GF transmissions are HT transmissions (as opposed to non-HT transmissions) and treat them as HT packets with a failing HT-SIG cyclic redundancy check (CRC).
In D1.05: Green Field – … An HT STA that does not support the reception of a Greenfield packet shall be able to detect that Greenfield transmissions are HT transmissions (as opposed to non-HT transmissions). In this case the receiver shall decode the HT-SIG and determine if the HT-SIG cyclic redundancy check (CRC) passes.(Ed: CID 130, 7379)
Eldad Perahia (Intel)
Matthew Fischer (Broadcom)

4. Accepted Compromise in 06/1571r7
October 2006
doc.: IEEE /1560r1
December 2006
Accepted Compromise in 06/1571r7
Given that a non-GF HT device must check the validity of the GF HT-SIG CRC, it enables two options for the non-GF HT device
Evaluate the contents of the HT-SIG and defer based on TXTIME
Keep CCA busy until the received level drops below the CCA sensitivity level as adopted in r7 (minimum modulation and coding rate sensitivity + 10 dB)
Compromise:
CRC check can be performed without evaluating the contents of the HT-SIG, so non-GF HT devices are not required to evaluate the contents of the GF HT-SIG
GF packets will be robustly protected from non-GF devices based on the CCA procedure adopted in r7
Given that the receive procedure in r7 enhances the CCA threshold post a valid 8-bit CRC, the non-GF HT device is very well protected against false alarms
Eldad Perahia (Intel)
Matthew Fischer (Broadcom)

5. October 2006
doc.: IEEE /1560r1
December 2006
Proposed Resolution
Counter all the “GF Mandatory” comments based on 06/1571r7
CIDs: 3150, 1665, 10377, 7474, 8283, 1731, 7171, 105, 289, 1494, 3617, 4185, 4572, 7011, 1502, 1513, 1612, 7183, 4679, 109, 134, 1725, 135, 10376, 136, 3430, 6766, 2131, 8171, 11242, 811, 7425
Eldad Perahia (Intel)
Matthew Fischer (Broadcom)