1 / 12

VHT Packet Duration Signaling

VHT Packet Duration Signaling. Authors:. Date: 2010-07-12. Introduction. Bits in VHT-SIG A are very precious resource to signal important system parameters Length field in L-SIG already contains sufficient information to convey the duration of a VHT packet [1]

Download Presentation

VHT Packet Duration Signaling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. VHT Packet Duration Signaling Authors: Date: 2010-07-12 Youhan Kim, et al.

  2. Introduction • Bits in VHT-SIG A are very precious resource to signal important system parameters • Length field in L-SIG already contains sufficient information to convey the duration of a VHT packet [1] • More details are provided on how to signal the VHT packet duration using the L-SIG length field Youhan Kim, et al.

  3. 11ac Packet Length • A 4 ms long VHT packet using 80 MHz, 4 streams, 256-QAM 5/6, short GI can transport ~800 Kbytes • Requires 20 bits if length in bytes was indicated in preamble as in 11n • Number of bits required for length in bytes for VHT packets is actually higher since 11ac supports 160 MHz, max. 8 streams and 256-QAM 5/6 [2] • 22 bits required to support 4 ms packet duration • 2 symbol VHT-SIG A has 34 useful bits • 48 bits – 8 CRC bits – 6 tail bits • 22 bit length field would use 65% of the valuable VHT-SIG A resource • And this is not even considering DL MU-MIMO • Clearly, signaling the length of the packet in bytes in VHT-SIG A is not an efficient scheme Youhan Kim, et al.

  4. 11ac Packet Duration: Number of Symbols • Alternative is to signal the number of OFDM symbols of the packet • But L-SIG already has sufficient information for RX to determine the number of OFDM symbols • See following slides • Do not need to indicate VHT packet duration again in VHT-SIG A • Very efficient usage of the valuable VHT-SIG A resources Youhan Kim, et al.

  5. L-SIG Length Conveys Number of Symbols (1) • Similar to 11n, use L-SIG spoof rate of 6 Mbps for 11ac packets • 3 bytes / symbol • Long GI packet • 4 us / symbol • Legacy spoof symbols = L-SIG length / 3 bytes per symbol • VHT payload symbols = Legacy spoof symbols – VHT preamble symbols legacy spoof symbols = L-SIG length / 3 bytes per symbol 20 usec L preamble VHT preamble VHT Payload VHT payload symbols = legacy spoof symbols – VHT preamble symbols L-SIG spoof rate is fixed at 6 Mbps (3 bytes / symbol) Youhan Kim, et al.

  6. L-SIG Length Conveys Number of Symbols (2) • Short GI packet • 3.6 us / VHT symbol • End of frame may not be aligned to a 4 us boundary • Legacy devices using L-SIG may find the end of the packet to occur up to 3.6 usec after the energy on the air has disappeared • But this is existing problem in 11n Short GI symbol time= 3.6 usec 3.6 * VHT symbols L preamble VHT preamble VHT Payload Remainder <= 3.6 usec Legacy spoof time = 4 usec per symbol * legacy spoof symbols L-SIG symbol time = 4.0 usec Legacy spoof symbols = L-SIG length / 3 Youhan Kim, et al.

  7. L-SIG Length Conveys Number of Symbols (2) • Short GI packet • 3.6 us / VHT symbol • L-SIG can only indicate time in units of 4 us • End of frame may not be aligned to a 4 us boundary • Two 3.6 us short GI boundaries may map to the same4 us normal GI boundary used by L-SIG Short GI packet with N symbols 3.6 3.6 3.6 Short GI packet with N+1 symbols 3.6 3.6 3.6 3.6 L-SIG spoof with M symbols 4 4 4 Youhan Kim, et al.

  8. Short GI Packet Duration Signaling • Use two bits for short GI indication in VHT-SIG A • b00 : Long GI packet • # symbols = ceil(L-SIG length / 3) • b01 : Reserved • b10 : Short GI packet • # symbols = floor(ceil(L-SIG length / 3) * 4 / 3.6 ) • b11 : Short GI packet • # symbols = floor(ceil(L-SIG length / 3) * 4 / 3.6 ) – 1 L-SIG spoof with M symbols 4 4 4 Short GI packet with N+1 symbols Short GI: b10 3.6 3.6 3.6 3.6 Short GI packet with N symbols Short GI: b11 3.6 3.6 3.6 Youhan Kim, et al.

  9. Conclusions • Do not need to indicate VHT packet duration again in VHT-SIG A • Length field in L-SIG already has sufficient information to signal the duration of a VHT packet • Propose to use 2 bits for short GI indication in VHT-SIG A • One bit for long/short GI indication • One bit for short GI packet length ambiguity mitigation Youhan Kim, et al.

  10. Straw Poll #1 • Do you support adding the following item into the specification framework document, 11-09/0992? • R3.2.X: The number of OFDM symbols in a VHT packet shall be computed using the length field in L-SIG. Youhan Kim, et al.

  11. Straw Poll #2 • Do you support adding the following row into Table 1 in the specification framework document, 11-09/0992? Youhan Kim, et al.

  12. References [1] Kim, Y. et al., Duration in L-SIG, IEEE 802.11-10/0534r1, May 2010 [2] Stacey, R. et al., Specification Framework for TGac, IEEE 802.11-09/0992r11, May 2010 [3] Liu, Y. et al., VHT frame padding, IEEE 802.11-10/0064r5, May 2010 Youhan Kim, et al.

More Related