May 1999 doc IEEE 802 11 99115 Proposal

May 1999 doc. : IEEE 802. 11 -99/115 Proposal for an improved long training symbol phase Masahiro Morikura and Masato Mizoguchi NTT morikura@ansl. ntt. co. jp Phone: +81 -468 -59 -3132 fax: +81 -468 -55 -1172 Submission 1 Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 A comment on the long training symbol phase Clause number; 17. 3. 3 PLCP preamble (SYNC) Comment; The phase relation between short preamble (t 1 -t 10) and long preamble (T 1, T 2) in draft 5. 0 causes degradation in timing detection accuracy. This is because the matched filter output for detecting the short preamble pattern has large side-lobe in boundary region between t 10 and T 1 when the phase relation in D 5. 0 is used. This large side-lobe badly affects the timing decision value when multi-path delayed signals are superimposed. Submission 2 Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 A symbol timing detection scheme Received training signal t 8 t 9 t 10 Matched filter T 1 Detecting disappearance of correlation peak signal Matched filter output Received signals GI 2 Digital filter Symbol timing decision Detected symbol timing Remove cyclic extension Submission 3 Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 An effect of the long training symbol phase Short sequence Long sequence Q ch I ch Relative phase I ch Draft 3. 0 t 1 t 2 Received signals t 3 t 4 t 5 t 6 t 7 t 8 t 9 t 10 I ch Draft 5. 0 T 1 Matched filter The Matched filter output of this region depends on relative phase between short and long preamble symbol Submission Q ch 4 A computer search is carried out to find the phase relation that generates low correlation sidelobe Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 Searched results of Matched filter output Draft 5. 0 Draft 3. 0 3 /4 radian rotation Proposal Time Submission I ch Draft 5. 0 Proposal t 9 Q ch t 10 T 1 5 Q ch I ch The low sidelobe is obtained by the proposed long preamble phase Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 Influence of the high correlation side-lobe on timing detection accuracy Matched filter output for direct path signal Disappearance of correlation peak signal Matched filter output for delayed signal t 9 Submission Large correlation side-lobe degrades symbol timing detection accuracy t 10 T 1 6 Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 PER performance in multipath propagation with AWGN Packet length = 64 byte Linear channel Draft 5. 0 Packet error rate 24 Mbit/s (16 QAM, R=1/2) Draft 5. 0 Proposed Eb/N 0 [d. B] (b) Delay spread = 150 ns (a) Delay spread = 100 ns Packet error rate versus Eb/N 0 Submission 7 Masahiro Morikura, NTT

May 1999 doc. : IEEE 802. 11 -99/115 Conclusions • A search was carried out to find the long preamble phase that gives low correlation side-lobe. • Recommendation : Change Eq. (8) so as to rotate the all signal phase +(3/4) L-26, 26={-1+j, +1 -j, -1+j, … , . . . , -1+j}/sqrt (2. 0) • By only changing the preamble phase, the irreducible packet error is improved to less than 1/3 that of Draft 5. 0 Submission 8 Masahiro Morikura, NTT