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A Novel Multiple Access System B ased on TDS-OFDM

This paper introduces a novel Time Domain Synchronous OFDM (TDS-OFDM) system for multiple access communication. The system utilizes key technologies of the Chinese digital television terrestrial broadcasting standard and offers higher spectrum efficiency and faster synchronization compared to conventional methods. The paper also discusses the major problem of mixed interferences in TDS-OFDMA and proposes a solution through joint cyclicity reconstruction and channel estimation. Simulation results demonstrate the effectiveness of the proposed system.

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A Novel Multiple Access System B ased on TDS-OFDM

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

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

  3. 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%)

  4. 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

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

  6. Channel estimation (CE) andinterferencecancellation (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] • Decrease the complexity • Still based on iteration Problems: • CE and IC are mutually conditional • High complexity of iterative IC (30% chip area) • Decreased performance in mobile environment

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

  8. “time-space two-dimensional frame structure”

  9. Joint cyclictiy reconstruction

  10. Joint channel estimation

  11. Complexity comparison J: iteration number J=1, the complexity of[Tang07]is68%of[Wang05] J=1, the complexity of[Yang08]is24%of [Wang05] Proposed: no iteration, J=0, the complexity is6%of[Wang05]

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

  13. Simulation Results (1) 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

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

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

  16. 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

  17. 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.

  18. Thank you for your suggestions !

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