A Novel Multiple Access System Based on TDS-OFDM Linglong Dai (Ph.D candidate), Jian Song (Professor) Tsinghua University, Beijing, China

Contents 1 2 3 TDS-OFDMA System Simulation Results Conclusion

Time domain synchronous-OFDM (TDS-OFDM) Frame Structure in TDS-OFDM System Key technology of the Chinese digital television terrestrial broadcasting (DTTB) standard GI: PN sequence instead of cyclic prefix (CP) [Song07] Higher spectrum efficiency (10%) Faster synchronization (5%) TDS-OFDMA

Major Problem of TDS-OFDMA: Mixed Interferences CP-OFDMA cyclic prefix (CP) cyclicity property linear convolution circular convolution Simple CE and equalization TDS-OFDMA PN sequence Cyclicity destoryed Mixed interferences Iterative interference cancellation (IC) CE and IC are mutually conditional Impossible for multiple users cyclicity TDS-OFDMA

Channel estimation (CE) and interference cancellation (IC) CP-OFDMA: two-dimensional pilots [802.16e06] [Hoeher97] [Li00][Morelli01] two-dimensional interpolation MIMO-OFDM: Orthogonal pilots [Jeon00] [Siew02] [Suh03] WiMAX, LTE, B3G TDS-OFDMA

Channel estimation (CE) and interference cancellation (IC) Single-user TDS-OFDM system: iterative interference subtraction [Wang05] Long spread of multi-path High complexity, mutual precondition of CE and IC Partial-decision aided CE [Tang08] Partly destroy the mutual precondition of CE and IC Still High complexity Based on “virtual frame” [Tang07] Decrease the complexity Only suitable for fixed PN PN reconstruction [Yang08] Still based on iteration Problems: CE and IC are mutually conditional High complexity of iterative IC (30% chip area) Decreased performance in mobile environment TDS-OFDMA

Overview of the TDS-OFDMA System Key ideas Separate CE and IC Joint cyclicity reconstruction Joint CE TDS-OFDMA System Diagram TDS-OFDMA

“time-space two-dimensional frame structure” TDS-OFDMA

Joint cyclictiy reconstruction TDS-OFDMA

Joint channel estimation TDS-OFDMA

Complexity comparison J: iteration number Computation [Wang05] [Tang07] [Yang08] Proposed IFFT/FFT 256 3 IFFT/FFT 2048 4(J+1) 2(J+1) 3(J+1) IFFT/FFT 3780 2 1 IFFT/FFT 4200 5(J+1) IFFT/FFT 8192 J=1, the complexity of [Tang07] is 68% of [Wang05] J=1, the complexity of [Yang08] is 24% of [Wang05] Proposed: no iteration, J=0, the complexity is 6% of [Wang05] TDS-OFDMA

TDS-OFDMA System Introduction Contents 1 TDS-OFDMA System Introduction 2 Simulation Results 3 Conclusion TDS-OFDMA

Simulation Results (1) M=2 7.56 MSPS interleaved Np=255 Ls=76 Lt=153 Static Multi-path User number M=2 Modulaton QPSK Symbol rate 7.56 MSPS Carrier assignment interleaved Length Np=255 Ls=76 Lt=153 Channels Brazil A/D TDS-OFDMA

Simulation Results (2) Brazil A/D 30Hz Rayleigh Channel Modulaton QPSK Rayleigh channel Brazil A/D Max. Doppler spread 30Hz TDS-OFDMA

TDS-OFDMA System Introduction Contents 1 TDS-OFDMA System Introduction 2 Simulation Results 3 Conclusion TDS-OFDMA

Brief Conclusions A novel TDS-OFDMA scheme The new "time-space two-dimensional frame structure " Joint cyclicity reconstruction Joint channel estimation Extend TDS-OFDM from broadcasting to other senarios TDS-OFDMA

References [Song07] J. Song, Z. Yang, L. Yang, et al., “Technique review on Chinese digital terrestrial television broadcasting standard and measurements on some working modes, ” IEEE Trans. Broadcast., vol.53, no.1, pp.1-7, Mar. 2007. [802.16e 06] IEEE Standard for Local and Metropolitan Area Networks part 16:Air Interface for Fixed and Mobile Broadband Wireless Access Systems,Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1,IEEE Std.802.16e,2006. [Hoeher97] P.Hoeher,S.Kaiser, “Pilot-aided Channel Estimation in Time and Frequency,” In Proc.IEEE GLOBECOM’97, Phoenix, USA,1997, 1190-1196. [Li00] Ye Li, “Pilot-symbol-aided channel estimation for OFDM in wireless systems”. IEEE Transactions on Vehicular Technology，2000，49(4)，P:1207-1215. [Morelli01] Morelli M.and Mengali U.,“A comparison of pilot-aided channel estimation methods for OFDM systems”, IEEE Trans on processing Signal vol.49, pp. 3065-3073, Dec 2001. [Jeon00] W. G. Jeon，K. H. Paik，and Y. S. Cho, “An Efficient Channel Estimation Technique for OFDM Systems with Transmitter Diversity,” Proc. IEEE International Symposium on Personal，Indoor and Mobile Radio Commun.，vol.2，London，UK，Sept. 2000，P:1246-1250. [Siew02] J.Siew et al. , “A Channel Estimation Method for MIMO-OFDM Systems,” Proc. London Commun. Symp.，London，England，Sept.2002，P:1-4 [Suh03] C.Suh，C.-S. Hwang，and H. Choi, “Comarative study of time-domain and Frequency-domain channel estimation in MIMO-OFDM systems,” in Proc. IEEE PIMRC’03，vol.2，pp.1095-1099，7-10 Sept. 2003. [Yang02] Z. Yang, J. Wang, C. Pan, L. Yang, and Z. Han, “Channel estimation of DMB-T,” in 2002 IEEE Int. Conf. Communications, Circuits and Systems and West Sino Expositions , vol. 2, pp. 1069-1072, 2002. [Wang05] J. Wang, Z. Yang, C. Pan, J. Song, and L. Yang, “Iterative padding subtraction of the PN sequence for the TDS-OFDM over broadcasting channels,” IEEE Trans. Consumer Electron., vol. 51, no. 4, pp. 1148–1152, Nov. 2005. [Tang07] S. Tang, F. Yang, K. Peng, C. Pan, and Z. Yang, “Iterative channel estimation for block transmission with know symbol padding - a new look at TDS-OFDM,” in Proc. IEEE 2007 Global Telecommunications Conf. (GLOBECOM’07), Washington, DC, Nov. 2007, pp. 4269–4273. [Tang08] Shigang Tang, Kewu Peng, Ke Gong, et al., “Novel Decision-Aided Channel Estimation for TDS-OFDM Systems,” in Proc. IEEE International Conference on Communications (ICC '08), May. 2008, pp. 946-950. [Yang08] Fang Yang, Jintao Wang, Jun Wang, et al., “Channel Estimation for the Chinese DTTB System Based on a Novel Iterative PN Sequence Reconstruction," in Proc. IEEE International Conference on Communications (ICC '08), May. 2008, pp. 285-289. [Sarwate79] D.S.Sarwate, “Bounds on crosscorrelation and autocorrelation of sequences,” IEEE Trans. Inf. Theory, vol.25, no6, pp.720-724, Nov.1979. TDS-OFDMA

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