November 2013 FBMC for TVWS Date: 2014-01-22 Doc. 22-14-0012-00-000b Authors: Name Affiliations Address Phone email Dominique Noguet CEA-LETI France dominique.noguet[at]cea.fr 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 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. 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 Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Apurva Mody <apurva.mody@ieee.org> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org. Slide 1 Dominique Noguet, CEA-LETI
January 2014 Summary / motivation Doc. 22-14-0012-00-000b 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
Doc. 22-14-0012-00-000b Cognitive Radio for White Spaces Incumbent protection Need to control interference ANALYSE SENSE DECIDE ACT Dynamic Spectrum Usage Need a flexible radio Slide 3
Doc. 22-14-0012-00-000b Key parameters from regulation FCC has approved communication parameters in the TVWS in 2009 [1] Parameter FCC [1] Note Power for FD in adjacent band Not allowed Power for FD in non-adjacent band with geolocation capability 30dBm (1W) FCC: 36dBm EIRP with a gain antenna Power for PPD in adjacent band 16dBm Gain antenna not allowed (40mW) Power for PPD in non-adjacent band with geolocation 20dBm Gain antenna not allowed capability (100mW) Power for PPD in non-adjacent band without geo-location capability 17dBm (50mW) Out-of-band performance <55dB Relative to in-band power FD: Fixed Device PPD: Personal Portable Device [1] FCC final rule, Unlicensed Operation in the TV Broadcast Bands, US Federal Register Vol. 74, No.30, pp 7314-7332, Feb. 17 2009 Slide 4
What kind of radio? Doc. 22-14-0012-00-000b 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) Slide 5
Doc. 22-14-0012-00-000b UHF band is already fragmented Dynamic Spectrum Access may increase fragmentation Is it enough? Example Central London 96 MHz of spectrum available, 16 MHz of contiguous spectrum maximum Maximizing spectrum usage implies the use of non contiguous spectrum Source: Nekovee, M., A Survey of Cognitive Radio Access to TVWhite Spaces, International Journal of Digital Multimedia Broadcasting, Volume 2010, Hindawi Slide 6
Broadband scenarios Few Mpbs to 10s Mbps Guidelines Doc. 22-14-0012-00-000b 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 Slide 7
What can we do? Doc. 22-14-0012-00-000b 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 Slide 8
Doc. 22-14-0012-00-000b Is OFDM fulfilling our expectations? In the frequency domain, the sum of sinc functions result in adjacent leakage power d[ n, i] = 1 N N 1 k = 0 s[ n, k] e k j 2πi f. T N s 1 = f T s 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 Slide 9
What can be done? Doc. 22-14-0012-00-000b Balian-Low theorem states that we cannot have simultaneously: A prototype filter well localized in time and frequency A maximal spectrum efficiency Complex orthogonality Change prototype filter CP-OFDM FBMC-OQAM Slide 10
Doc. 22-14-0012-00-000b 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 Slide 11
FBMC architecture Can be implemented through usual ifft / FFT for time/frequency domain conversion Doc. 22-14-0012-00-000b x 0 [k] x 1 [k] x N-1 [k] O Q A M p r e - p ro c e s s in g if F T Synthesis filter bank h 0 [n] N/2 h 1 [n] N/2 z -1 + h N-1 [n] N/2 z -(N-1) Channel Analysis filter bank z -(N-1) z -1 N/2 h 0 [n] N/2 h N-2 [n] N/2 h N-1 [n] F F T O Q A M p o s t-p ro c e s s in g y 0 [k] y 1 [k] y N-1 [k] Slide 12
Doc. 22-14-0012-00-000b FBMC in the TVWS context ACLR and spectrum efficiency comparison: OFDM vs FBMC Standard Spectral Efficiency Gain relative to filtered OFDM Frequency Total Time Domain Domain Gain DVB-T 10 % 3 % 13 % 802.11a/g 3.8 % 15.8 % 19.6 % Slide 13
Doc. 22-14-0012-00-000b FBMC modulation complexity C C FBMC CP OFDM Filtered OFDM vs FBMC 4 ( N 2 + ( N( log2( N ) 3) + 4) + KN 2) 2 ( N( log ( N ) 3) + 4) + 2. N. NTxFilter = = 2 FFT and IFFT filter 5,0E+05 4,5E+05 4,0E+05 3,5E+05 3,0E+05 2,5E+05 2,0E+05 1,5E+05 1,0E+05 5,0E+04 0,0E+00 40% 60% 80% 100% N is the number of FFT carriers The FBMC prototype filter spans over K OFDM symbols Filtered OFDM FBMC Slide 14
Spectrum pooling Doc. 22-14-0012-00-000b 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. Slide 15
Doc. 22-14-0012-00-000b 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 Slide 16
Conclusion Doc. 22-14-0012-00-000b 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 Slide 17
Doc. 22-14-0012-00-000b Acknowledgement This presentation is supported by the European Community s Seventh Framework Programme (FP7) under Grant Agreement number 318563 (CRS-i) Slide 18