New OFDM SERVICE Field Format for .11e MAC FEC Month 1998 doc.: IEEE 802.11-98/xxx January 2002 New OFDM SERVICE Field Format for .11e MAC FEC Sunghyun Choi Philips Research USA Briarcliff Manor, New York sunghyun.choi@philips.com Sunghyun Choi, PHILIPS

January 2002 802.11a PPDU Format Both SERVICE and PSDU are transmitted at the rate specified by RATE field. Sunghyun Choi, PHILIPS

January 2002 The Facts 802.11a SERVICE field is modulated/encoded at the same scheme as the MPDU. A garbled SERVICE field will make the whole frame useless as it is used for the scrambler initialization. This is perfectly fine today as a single bit error in a MAC frame will result in the FCS error anyway!!! Sunghyun Choi, PHILIPS

January 2002 802.11e MAC-Level FEC An MPDU can be encode by (224,208) RS code for more reliable transmission Sunghyun Choi, PHILIPS

January 2002 Problem Statement 802.11e will have a MAC-level FEC based on RS coding (Ref. 802.11e/D2.0a) When the MPDU is encoded by the MAC-level FEC, the error performance in the SERVICE field can be the bottleneck. This was noted by Bob O’Hara, and others within TGe. The same problem will happen to 802.11g. Note: .11b does not have such a problem. Sunghyun Choi, PHILIPS

January 2002 Proposed PPDU Format The SERVICE field is transmitted at 6 Mbps by occupying a single OFDM symbol. Sunghyun Choi, PHILIPS

January 2002 New Format Usage The new format is specified via “New SERVICE” bit in the SIGNAL field; the bit is currently reserved. New SERVICE = 0: the original SERVICE format New SERVICE = 1: the proposed SERVICE format The new format can be used only for the RS-coded 802.11e QoS data frames in a selectable manner. New format will consume more bandwidth for other frames usually. Sunghyun Choi, PHILIPS

Performance Comparison (w/ 10 RS blocks for MSDU) January 2002 Performance Comparison (w/ 10 RS blocks for MSDU) 24 Mbps 12 Mbps 6 Mbps Sunghyun Choi, PHILIPS

January 2002 Comments The results shows that .11e RS coding can be useful, but can be more useful with the proposed new SERVICE field format. Don’t rely on the absolute error probability values as this is based on a simple analysis. However, the relative performance differences among different options should be valid. For 6 Mbps, the new format performance remains the same as the old one’s. Sunghyun Choi, PHILIPS