Results of Ballot on Draft Standard D3.0
Forgotten Comments on clauses 12 and 16

	15.2.3.5
15.2.6

	WD	T	Y	The intention of the Signal field in the PLCP header, which is currently specified in multiples of 100 Kbps is to make the standard compatible with future developments. This would allow future PHYs, which may utilize different speed and modulation techniques beyond the PLCP header to be coexistant with the current specified PHY, so that such a PHY could operate in the same band.

The function of the length field in the PLCP Header is actually two fold. It does at one hand specify the duration of the “Medium Busy” condition, while on the other hand it does specify the octet boundary of the end of the frame, such that the MAC can locate the CRC. In a situation where the receiving station can not decode the data modulation, it is desirable that such a station can still perform the “Medium Busy” function, to allow coexistence between the stations.
The current Rx State Machine as defined in figure 84, makes it impossible to design an 802.11 modem for future to be defined rates, and still provide the coexistence function, by defering for such a station for the duration as defined in the correctly received PLCP header. According to the current description the PHY does reset the Rx State Machine when an other then the currently defined 1 and 2 Mbps rates are specified in the PLCP header, although the text does not say so.
This makes the Signal field specification as it is now useless for migration purposes.

The suggested change is to modify the PLCP length field definition such that the current specified modems can easily perform the “Medium Busy” function, to allow the coexistence.
This is achieved by specifying the length field to be in units of the 1 usec symbol rate, rather then in Octets. This allows a station to assert the “Medium Busy” for the duration as indicated by the length field, independent of the rate specified in the Signal field. The modems that do understand the new rate, can still derive an octet boundary of the bitstream being decoded so that the proper end of the frame is indicated to the MAC.
This change is completely independent of the MAC, sinse the Octet to time conversion is done in the PHY.	Change the definition of the Length field in section 15.2.3.5:

- The PLCP LENGTH field shall be an unsigned 16 bit integer which indicates the number of symbols in units of 1 usec (8 symbols per Byte for 1 Mbps and 4 symbols per Byte for 2 Mbps)

Add the following at the end of section 15.2.7:

-If the PLCP is received succefully (as indicated by the CRC), then the DSSS PHY  shall assure that the CCA indicates a busy medium for the intended duration of the received frame, as indicated by the PLCP LENGTH field in usec.

Update figure 84 accordingly, by deleting the Validate PLCP state, and change the “SETUP MPDU RX” state.

Seq. #	Section number	your initials	Cmnt type
E, e, T, t	Part of NO vote	Comment/Rationale	Corrected Text	Disposition/Rebuttal