Sharp Laboratories USA March 2001 Frame FEC Formats for 802.11e John M. Kowalski Sharp Laboratories USA Camas, Washington (360) 817-7520 kowalskj@sharplabs.com John M. Kowalski,

Outline Requirements Frame format March 2001 Outline Requirements Frame format Description of frame format & performance John M. Kowalski,

Requirements for MAC Level FEC March 2001 Requirements for MAC Level FEC Applicable to all known PHYs Provide a reduction in BER Be optional yet allow non-FEC capable stations to interpret FEC coded data. FEC enabled MACS shall not send up frames to higher layers The MAX MPDU size of 802.11-1999 is maintained. Payload delivered to higher layers (if not fragmented) is 2080 octets maximum. Delayed ACK or unacknowledged must be used to accomodate Rx/Txturnaround time for 802.11a John M. Kowalski,

Requirements for MAC Level FEC (cont.) March 2001 Requirements for MAC Level FEC (cont.) Any encryption performed is done prior to FEC encoding MAC FEC is performed on a TC. The MAC MLME, based on requests for parameterized QoS, instantiates MAC-Level FEC. ESTAs announce their FEC capability via bit 11 of the Capability Information Field . Legacy STAs cannot read the FEC fields, therefore FEC encoded MPDUs shall not be sent to them FCS is included so that legacy ESTAs can compute FCS errors in a consistent way. Another FCS (on non-parity check octets) is included to prevent errored frames from being passed to higher layers. John M. Kowalski,

Frame Format MAC Header Header FEC 32 16 Frame Body FEC FEC FEC ... 16 March 2001 Frame Format MAC Header Header FEC 32 16 Frame Body Security IV+ MSDU1 FEC FEC MSDU2 MSDUN+ICV+ FEC FCS FEC ... 16 16 208 208 up to 208 16 FCS Includes 4 octet FCS field only over uncoded octets 4 Over all octets John M. Kowalski,

Description of Fields & Performance March 2001 Description of Fields & Performance ALL coded fields use (224,208) Reed-Solomon Code. Header uses truncated code w/ header taking up the first 32 octets of an (untransmitted) 208 octet field. Assuming 10% PER, for a 1000 byte packet, uncoded, P(Header Failure) < 10-17 John M. Kowalski,

Description of Fields & Performance (Cont.) March 2001 Description of Fields & Performance (Cont.) If security field is present, it’s coded in the first block of the frame body. The FCS is done as in IEEE 802.11-1999 section 7.1.3.6 GF(256) polynomial is: f(x) = x8 + x4 + x3 + x2 + 1 f(x) = x8 + x4 + x3 + x2 + 1 (used in DVB) P(Frame body error) < 7.01X 10-11 (1000 octets) John M. Kowalski,