Presentation

Doc. 22-14-0012-00-000bNovember 2013

Dominique Noguet, CEA-LETISlide 1

FBMC for TVWSDate: 2014-01-22

Name Affiliations Address Phone email Dominique Noguet CEA-LETI France dominique.noguet[at]cea.fr

Authors:

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributingindividual(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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modificationsthereof, in the creation of an IEEE Standards publication; to copyrightin the IEEE’s name any IEEE Standards publication even though it may includeportions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standardspublication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22.Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedureshttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), includingpatent applications, provided the IEEE receives assurance from thepatent holder or applicant with respect to patents essential for compliance with bothmandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard isessential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved forpublication. Please notify the ChairApurva Mody <apurva.mody@ieee.org> as early as possible, in written or electronic form, if patentedtechnology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 WorkingGroup.If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org.

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Summary / motivation

• Regulators demand very low adjacent channel leakage for secondary TVWS usage

• FBMC is a multi-carrier PHY, which allows mitigating ACL though maintaining good spectrum efficiency

• CEA-LETI has worked on how to apply this PHY to the TVWS context

• This was presented at the White Space Summit in Paris in Dec. 2013.

• The 802.22 chair invited CEA-LETI to present this work in order for the WG to appreciate the potential interest of this technology for its work.

• This presentation stresses why we think FBMC is very suitable to White Space communication

Slide 2 Dominique Noguet, CEA-LETI

January 2014

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Need a flexible radio

Need to control interference

Cognitive Radio for White Spaces

ANALYSE

ACT

DECIDESENSE

Incumbent protection

Dynamic Spectrum Usage

ACT

Slide 3

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Key parameters from regulationFCC has approved communication parameters in the TVWS in 2009 [1]

[1] FCC final rule, “Unlicensed Operation in the TV Broadcast Bands”, US Federal Register Vol. 74, No.30, pp 7314-7332, Feb. 17 2009

Parameter FCC [1] NotePower for FD in adjacent band Not allowedPower for FD in non-adjacent band with geo-location capability

30dBm (1W) FCC: 36dBm EIRP with a gain antenna

Power for PPD in adjacent band 16dBm (40mW)

Gain antenna not allowed

Power for PPD in non-adjacent band with geo-location capability

20dBm (100mW)

Gain antenna not allowed

Power for PPD in non-adjacent band withoutgeo-location capability

17dBm (50mW)

Out-of-band performance <55dB Relative to in-band power

FD: Fixed DevicePPD: Personal Portable Device

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What kind of radio?

Broadband scenarios ���� Few Mpbs to 10s Mbps

Regulators require high rejection for adjacent incumbent protection in TVWS - e.g., 55dB requires by the FCC����Low adjacent channel leakage (= high ACLR)

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Is it enough?� UHF band is already fragmented� Dynamic Spectrum Access may

increase fragmentation

Source: Nekovee, M., “A Survey of Cognitive Radio Access to TVWhite Spaces”, International Journal of Digital Multimedia Broadcasting, Volume 2010, Hindawi

� Example Central London� 96 MHz of spectrum available, 16

MHz of contiguous spectrum maximum

• Maximizing spectrum usage implies the use of non contiguous spectrum

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GuidelinesBroadband scenarios

���� Few Mpbs to 10s Mbps

Regulators require high rejection for adjacent incumbent protection, eg 55dB required by the FCC����Low adjacent channel leakage (high ACLR)

Adapt spectrum allocation to occupancy changes���� Flexibility

Exploit potentialy fragmented spectrum (spectrum asset may not be contiguous)���� Spectrum pooling

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What can we do?

Flexible PHY which can adapt its spectrum profile to allowed and / or available spectral resource

Multi-Carrier approaches have such a flexibility, thanks to the possibility to adjust each subcarrier transmit power in order to shape the overall spectrum profile

OFDM is the initial choice for CR PHY for the following reasons:• OFDM is deployed in broadcast applications, as well as WLAN and in

mobile wireless communication

• Simple equalization over frequency selective channels leads to simple receiver implementation

• High spectrum efficiency

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Is OFDM fulfilling our expectations?

In the frequency domain, the sum of sinc functions result in adjacent leakage power

∑−

=

∆=

1

0

.2],[

1],[

N

k

TfN

kij s

eknsN

indπ

fTs

∆=1

� Typically, first side-lobe of an OFDM spectrum is at -13dB compared to the main lobe

� Classical turnarounds are:� to add filtering

� to decrease signal bandwidth

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Change prototype filter

What can be done?

CP-OFDM FBMC-OQAM

Balian-Low theorem states that we cannot have simultaneously:

• A prototype filter well localized in time and frequency• A maximal spectrum efficiency• Complex orthogonality

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Filter Bank Multi Carrier (FBMC)

� Keep the flexibility of Multi-Carrier modulation� Control frequency response of each carrier by introducing a

filter bank centered on every active carrier and based on the same prototype response

� This prototype filter can be selected to minimize (null) adjacent channel interference

� The filtering is embedded in the digital modulation scheme

� No additional filter is required

� More flexibility

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FBMC architecture

h0[n]

h1[n] ++

iFF

T

hN-1[n]

ChannelChannel

Synthesis filter bank

z-(N-1)

↑N/2

↑N/2

↑N/2

z-1

OQ

AM

pre

-pro

cess

ing

x0[k]

x1[k]

xN-1[k] ↓N/2

z-1

z-(N-1)

↓N/2

↓N/2 h’0[n]

h’N-2[n]

h’N-1[n]

FF

T

OQ

AM

pos

t-pr

oces

sing

y0[k]

y1[k]

yN-1[k]

Analysis filter bank

Can be implemented through usual iFFT / FFT for time/frequency domain conversion

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FBMC in the TVWS contextACLR and spectrum efficiency comparison: OFDM vs FBMC

Standard

Spectral Efficiency Gain relative to filtered OFDM

Frequency Domain

Time DomainTotal Gain

DVB-T 10 % 3 % 13 %

802.11a/g 3.8 % 15.8 % 19.6 %

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FBMC modulation complexity

( )( )( )( )( )( )( ) TxFilterOFDMCP

FBMC

NNNNC

KNNNNC

..243log2

243log24

2

2

++−⋅=⋅++−+⋅⋅=

−

N is the number of FFT carriers The FBMC prototype filter spans over K OFDM symbols

Filtered OFDM vs FBMC

FFT and IFFT filter

0,0E+00

5,0E+04

1,0E+05

1,5E+05

2,0E+05

2,5E+05

3,0E+05

3,5E+05

4,0E+05

4,5E+05

5,0E+05

40% 60% 80% 100%

Filtered OFDM

FBMC

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Doc. 22-14-0012-00-000bSpectrum pooling

• Concept of spectrum pooling where sub carriers are switched ‘on’ or ‘off’ according to available spectrum resource

• This shapes the spectrum to fill the available gaps, while avoiding interference in the band used by other systems (e.g. primary systems)

Source: T. A. Weiss, F. K. Jondral, "Spectrum pooling: an innovative strategy for the enhancement of spectrum efficiency", IEEE Communications Magazine, vol. 42, no. 3, pp.S8-S14, March 2004.

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Spectrum pooling with FBMC

Since OFDM does not meet ACLR performance, only filtered OFDM is considered for comparison

In the example hereunder, 15kHz subcarrier spacing is considered in both cases

� The benefit of filtering on top of OFDM mitigates interference on both sides of the overall band

� It does not reject the signal inside the notch channels

� With FBMC, ACLR requirement is met both on adjacents and in the notch

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Conclusion

• TVWS is a context where spectrum efficiency, incumbent protection and flexibility are required

• CEA-LETI has investigated options to tackle these issues

• Multi-Carrier approaches were favored due to good spectrum efficiency and easy equalization at the RX (not presented herein)

• FBMC was considered as a serious contender to OFDM

• High ACLR and flexible access to fragmented spectrum are possible with FBMC, which outperforms OFDM in this regard

• Feedback from the group is very welcome

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Acknowledgement

This presentation is supported by theEuropean Community’s SeventhFramework Programme (FP7) under GrantAgreement number 318563 (CRS-i)

Slide 18