1. doc.: IEEE /XXXr0
Sep 19, 2007
Jan 2013
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)‏
Submission Title: [Windowing pulse shaping for IEEE m NB-OFDM]
Date Submitted: [Jan 14, 2013]
Source: [Keiichi Mizutani, Ryuhei Funada, Hiroshi Harada]
Company [NICT]
Address [3-4, Hikarino-oka, Yokosuka, , Japan]
Voice: [ ], FAX: [ ],
Re: []
Abstract: [This document presents effectiveness of windowing for IEEE m NB-OFDM]
Purpose: [This document provides a list of the editing staff that will be working on m.]
Notice: [This document has been prepared to assist the IEEE P 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 P ]
NICT
Name - WirelessHD

2. Jan 2013
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 spectral mask.
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.
NICT

3. Jan 2013
Background
Two types of pulse shaping method by OFDM baseband signal processing
Digital pulse shaping filtering
Large number of taps required according to 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).
NICT

4. Time-domain windowing
Jan 2013
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 duration TTR, thereby decreasing effective CP.
Windowing function (Ex: Raised cosine)
Windowing pulse shaped NB-OFDM signal
NICT

5. Effectiveness of windowing(1/4) - Without Windowing-
Jan 2013
Effectiveness of windowing(1/4) - Without Windowing-
Windowing duration TTR = 0us
Additional pulse shaping required
NICT

6. Effectiveness of windowing(2/4) - Windowing duration TTR = 0.98 us-
Jan 2013
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.
NICT

7. Effectiveness of windowing(3/4) - Windowing duration TTR = 3.94 us-
Jan 2013
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 13dB margin at the channel edge.
NICT

8. Effectiveness of windowing(4/4)
Jan 2013
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.
NICT

9. Jan 2013
Conclusion
Time-domain windowing is very effective for out- of-band power suppression of the IEEE m 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.
NICT