1. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 1 40 / 20 MHz Interoperability for Robust, High Performance, and Compatible 802.11n Systems July 2004 Jan Boer, Agere Systems, Inc. jboer@agere.com Jeff Gilbert, Atheros Communications, Inc. gilbertj@atheros.com Eldad Perahia, Cisco Systems, Inc. eperahia@cisco.com John Sadowsky, Intel Corporation john.sadowsky@intel.com Nico van Waes, Nokia Corporation nico.vanwaes@nokia.com Wim van Houtum, Royal Philips Electronics wim.van.houtum@philips.com Takushi Kunihiro, Sony Corporation kuni@wcs.sony.co.jp Masuhiro Takagi, Toshiba Corporation masahiro3.takagi@toshiba.co.jp

2. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 2 Introduction In IEEE presentation 802.11-04/0786, we described the benefits of 40 / 20 / 10 MHz channelization for speed, robustness, and low-cost One key design issue is how to coexist and interoperate with legacy 20 MHz devices while operating in 40 / 20 MHz mode –Efficiency is critical – the legacy interop. mechanisms cannot notably degrade performance (e.g. 11g) This presentation details the 40 / 20 MHz PHY-level interoperation mechanisms

3. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 3 40 MHz PPDU Legacy short and long training and signal fields are replicated across the lower and upper 20MHz channels PLCP (signal field) indicates a packet length and rate which results in a duration long enough to cover the packet exchange Much more efficient than RTS/CTS or CTS-only protection Duplicate format legacy compatible preamble Duplicate L-STF Duplicate L-LTF HT Packet Format in 40MHz Duplicate L-SF Duplicate L-STF Duplicate L-LTF Duplicate L-SF

4. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 4 Legacy SF Coding & Modulation conv. encoder rate = 1/2 11a Interleaver BPSK map IFFT upper sub-channel 24 bit SF lower sub-channel BPSK map BPSK map BPSK map BPSK map

5. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 5 Duplicate Receiver Combining Equalizer: Simple MRC combining Note: If upper sub-channel is not present, combining weights are zero. Duplicate format supports simple receiver additional frequency diversity gain very robust legacy compatible preamble

6. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 6 20/40 MHz Interoperability 20 MHz PPDU  40 MHz receiver –Combine modulation symbols from upper & lower sub-bands –20 MHz PPDU in lower sub-channel zero combining weights in upper subchannel No loss in performance relative to a 20 MHz receiver –Use differential sub-channel energy to detect 20 v. 40 MHz signals 40 MHz PPDU  20 MHz receiver –One sub-channel is sufficient to decode the legacy SF –Detects only half of the 40 MHz signal  3 dB performance penalty for 20 MHz clients But they only have to decode the 6 Mbps legacy SF

7. doc.: IEEE 802.11-04/0772r0 Submission July 2004 J. Boer, J. Gilbert, E. Perahia, J. Sadowsky, N. Waes, W. Houtum, T. Kunihiro, M. Takagi Slide 7 Conclusions Full interoperability between 20MHz and 40MHz –Use differential sub-channel energy to detect 20MHz vs. 40MHz signal –Duplicate legacy compatible preamble in 40MHz signal 20MHz STA can decode legacy SF 40MHz STA can use simple combining scheme to decode both 20MHz and 40MHz signals