1. New OFDM SERVICE Field Format for .11e MAC FEC
Month 1998
doc.: IEEE /xxx
January 2002
New OFDM SERVICE Field Format for .11e MAC FEC
Sunghyun Choi
Philips Research USA
Briarcliff Manor, New York
Sunghyun Choi, PHILIPS

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

3. 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

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

5. January 2002
Problem Statement
802.11e will have a MAC-level FEC based on RS coding (Ref e/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 g.
Note: .11b does not have such a problem.
Sunghyun Choi, PHILIPS

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

7. 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 e QoS data frames in a selectable manner.
New format will consume more bandwidth for other frames usually.
Sunghyun Choi, PHILIPS

8. 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

9. 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