VHT Packet Length Calculation March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 VHT Packet Length Calculation Date: 2010-07-12 Authors: Yuichi Morioka Sony Corporation 5-1-12 Kitashinagawa Shinagawa, Tokyo +81-3-5448-4018 Yuichi.Morioka@jp.sony.com Yuichi Morioka, Sony Corporation

Background and Motivation March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Background and Motivation 11-10-0534-01-00ac-duration-in-l-sig suggested that the Length Field in VHT SIG be eliminated in order to save precious bits in VTH SIG for other uses 11-10-0619-00-00ad-why-we-need-length-in-vht-sig identified a number of draw backs if the Length Field is not available in VHT SIG, including PPDU size limitation TxOP mechanism can not be used Receiver blind decoding Yuichi Morioka, Sony Corporation

Length in multiple of n1/n2/n3/n4 March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Our proposal Keep the Length Field in L-SIG as currently defined Include a 12-13-bit Length Field in VHT SIGA to indicate a multiple of n bytes (for e.g. n=8/16/32/64 if 2 bits are used) to be added or subtracted from the Length Field in L-SIG to form the actual length 8-bit CRC in VHT SIG-A to cover the Length Fields of L-SIG and VHT SIG Bits: 12-13 TBD 1 TBD TBD Reserved 8 6 BW STBC Group ID Nsts TBD Length CRC Tail 1 10 1-2 1 Length in multiple of n1/n2/n3/n4 bytes n1/n2 /n3/n4 +/- Slide 3 Page 3 Yuichi Morioka, Sony Corporation

VHT SIGA with this proposal Ref: 11-10-0382-02 March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 VHT SIGA with this proposal Ref: 11-10-0382-02 No of bits BW 2-3 STBC 1 GI GroupID 6 Nsts 9 Length 12-13 CRC 8 Reserved Tail Total 46-48 bits Slide 4 Page 4 Yuichi Morioka, Sony Corporation

March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Suggested VHT SIGB (user specific) with this proposal Ref: 11-10-0382-02 No of bits MCS 4 Length 8 CRC LDPC 1 Tail 6 Total 26 bits Length = 5 bits (max value = 32) size = 1-2 bits (value = 8/16/32/64 bytes) Subtract/add (from computed VHT SIG length) = 1 bit Slide 5 Page 5 Yuichi Morioka, Sony Corporation

Keeping the Length Field of L-SIG as defined March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Keeping the Length Field of L-SIG as defined Pros Maintain backward compatibility with 11a/n devices Regardless of how reliable or unreliable the auto-detection mechanism is going to be, legacy devices have the “known” Length Field to fall back on. Cons The length field is still protected by 1 parity bit – this is an inherent problem with 11a/n Slide 6 Page 6 Yuichi Morioka, Sony Corporation

Include a 12-bit Length Field in VHT SIG March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Include a 12-bit Length Field in VHT SIG Pros PPDU size is extended to 64 Kbyte (or higher if needed) to cover most applications TxOP mechanism can still be used by 11a/n devices Improve decoder’s efficiency since receiver has a knowledge of when the packet is terminated Save at least 7 precious bits in VHT SIG that may help to accommodate the full definition of Group ID, Nsts and other needed fields Cons For packet size > 2340 bytes, if the incremental count is chosen to be very high, padding may be needed. Slide 7 Page 7 Yuichi Morioka, Sony Corporation

8-bit CRC in VHT SIG to cover the Length Fields of L-SIG and VHT SIG March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 8-bit CRC in VHT SIG to cover the Length Fields of L-SIG and VHT SIG Pros Eliminate false positive problems associated with L-SIG Offer the same level of protection compared to 11n Slide 8 Page 8 Yuichi Morioka, Sony Corporation

March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Conclusions There are major drawbacks in losing the VHT-Length Field as highlighted in 11-10-0619-00-00ad-why-we-need-length-in-vht-sig PPDU Size limitation (3ms) Blind decoding without knowledge of actual end of packet TXOP Protection can not be used This proposal avoids all of the above drawbacks and offers >40% saving in the number of bits required to specify the VHT length. Slide 9 Slide 9 Page 9 Yuichi Morioka, Sony Corporation

March 2010 doc.: IEEE 802.11-10/0xxxr0 July 2010 Strawpoll Do you support keeping the length field in L-SIG and add to the specification framework the method to compute the packet length of VHT packets for SU-MIMO as shown on slide #3 in this proposal? Yes No Abstain Slide 10 Slide 10 Page 10 Yuichi Morioka, Sony Corporation

Reference July 2010 March 2010 doc.: IEEE 802.11-10/0xxxr0 Yuichi Morioka, Sony Corporation