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 2 3 TDS-OFDMA System Simulation Results 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%)
TDS-OFDMA

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
TDS-OFDMA

5. 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

6. 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

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

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

9. Joint cyclictiy reconstruction
TDS-OFDMA

10. Joint channel estimation
TDS-OFDMA

11. 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

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

13. 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

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

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

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
TDS-OFDMA

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
[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 e,2006.
[Hoeher97] P.Hoeher,S.Kaiser, “Pilot-aided Channel Estimation in Time and Frequency,” In Proc.IEEE GLOBECOM’97, Phoenix, USA,1997,
[Li00] Ye Li, “Pilot-symbol-aided channel estimation for OFDM in wireless systems”. IEEE Transactions on Vehicular Technology，2000，49(4)，P:
[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 , 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:
[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 ，7-10 Sept
[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 , 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
[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
[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
[Sarwate79] D.S.Sarwate, “Bounds on crosscorrelation and autocorrelation of sequences,” IEEE Trans. Inf. Theory, vol.25, no6, pp , Nov.1979.
TDS-OFDMA

18. Thank you for your suggestions !