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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) ‏

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) ‏ Submission Title: [Windowing pulse shaping for IEEE 802.15.4m NB-OFDM] Date Submitted: [Jan 15, 2013] Source: [ Keiichi Mizutani, Ryuhei Funada, Hiroshi Harada] Company [NICT]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) ‏

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  1. NICT Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)‏ Submission Title: [Windowing pulse shaping for IEEE 802.15.4m NB-OFDM] Date Submitted: [Jan 15, 2013] Source: [Keiichi Mizutani, Ryuhei Funada, Hiroshi Harada] Company [NICT] Address [3-4, Hikarino-oka, Yokosuka, 239-0847, Japan] Voice: [+81-46-847-5060], FAX: [+81-46-847-5440], E-Mail: [mizk@nict.go.jp] Re: [] Abstract: [This document presents effectiveness of windowing for IEEE 802.15.4m NB-OFDM] Purpose: [This document provides a list of the editing staff that will be working on 802.15.4m.] Notice: [This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.] Release: [The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.]

  2. NICT Summary • TVWS-NB-OFDM transmitter can use windowing process with smaller windowing duration like other OFDM systems since this processing is very effective to help to meet the FCC spectralmask. • TVWS-NB-OFDM cyclic prefix (CP) duration (31.2us) is sufficient to work in the presence of possible multipath delay and the ISI caused by windowing process. • Windowing duration and the corresponding parameters should be adjusted according to FFT size and RF circuit characteristics as well as a digital pulse shaping filter if it is employed. • This adjustment can be easily implemented owing to its simple processing.

  3. NICT Background • Two types of pulse shaping method by OFDM baseband signal processing • Digital pulse shaping filtering • Large number of taps required according to 15-12-0377 to achieve the FCC mask. • (Time-domain) Windowing • Easily implemented. • More effective with larger FFT in satisfying adjacent channel emission limits. • Adjustable for RF characteristics in operating frequency • Can be employed with a digital pulse shaping filter. • Decreases effective CP (default 31.2us in NB-OFDM).

  4. NICT Time-domain windowing • Smoothness of the transition between two consecutive OFDM symbols enables to reduce spectral leakage. • Windowing can be applied for pulse shaping with windowing function w(t), which is utilized after insertion of CP. • Windowing function and its parameter are implementation matters. Thus, implementer can use any of windowing function such as raised cosine window with any windowing duration TTR (rolloff factor). • Windowing is also used with a digital pulse shaping filter, which would require a tapped filter with moderate taps. • Windowing process induces ISI according to windowing durationTTR, thereby decreasing effective CP. Windowing function (Ex: Raised cosine) Windowing pulse shaped NB-OFDM signal

  5. NICT Effectiveness of windowing(1/4)- Without Windowing- • Windowing duration TTR = 0us Additional pulse shaping required

  6. NICT Effectiveness of windowing(2/4)- Windowing duration TTR = 0.98 us- • Windowing duration TTR = 0.98 us, i.e., less than 4% for the effective CP length, achieves suitable amount of channel power reduction.

  7. NICT Effectiveness of windowing(3/4)- Windowing duration TTR = 3.94 us- • Windowing duration TTR = 3.94 us, i.e., less than 13% for the effective CP duration, offers an additional 20dB margin at the channel edge.

  8. NICT Effectiveness of windowing(4/4) • Windowing duration 1us is sufficient to meet the FCC mask and longer windowing duration offers an additional margin. • CP length (31.2us) would be much longer than the sum of possible multipath delay and windowing duration.

  9. NICT Conclusion • Time-domain windowing is very effective for out-of-band power suppression of the IEEE802.15.4m NB-OFDM. • Windowing duration TTR = 0.98 us, i.e., less than 4% for the effective CP length, achieves suitable amount of channel power reduction. • Windowing duration TTR = 3.94 us, i.e., less than 13% for the effective CP duration, offers an additional 13dB margin at the channel edge. • CP length (31.2us) is enough to cancel the influence of the multipath delay and ISI caused by windowing.

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