Iterative channel estimation and decoding of pilot symbol assisted turbo codes over flat-fading channels

A method for coherently detecting and decoding turbo-coded binary phase shift keying (BPSK) signals transmitted over frequency-flat fading channels is discussed. Estimates of the complex channel gain and variance of the additive noise are derived first from known pilot symbols and an estimation filter. After each iteration of turbo decoding, the channel estimates are refined using information fed back from the decoder. Both hard-decision and soft-decision feedback are considered and compared with three baseline turbo-coded systems: (1) a BPSK system that has perfect channel estimates; (2) a system that uses differential phase shift keying and hence needs no estimates; and (3) a system that performs channel estimation using pilot symbols but has no feedback path from decoder to estimator. Performance can be further improved by borrowing channel estimates from the previously decoded frame. Simulation results show the influence of pilot symbol spacing, estimation filter size and type, and fade rate. Performance within 0.49 and 1.16 dB of turbo-coded BPSK with perfect coherent detection is observed at a bit-error rate of 10/sup -4/ for normalized fade rates of f/sub d/T/sub s/=0.005 and f/sub d/T/sub s/=0.02, respectively.

[1]  Ran-Hong Yan,et al.  Iterative channel estimation using soft decision feedback , 1998, IEEE GLOBECOM 1998 (Cat. NO. 98CH36250).

[2]  Dariush Divsalar,et al.  Serial Concatenation of Interleaved Codes: Performance Analysis, Design, and Iterative Decoding , 1997, IEEE Trans. Inf. Theory.

[3]  Mathew C. Valenti.  Iterative channel estimation for turbo codes over fading channels , 2000, 2000 IEEE Wireless Communications and Networking Conference. Conference Record (Cat. No.00TH8540).

[4]  Matthew C. Valenti,et al.  Refined channel estimation for coherent detection of turbo codes over flat-fading channels , 1998 .

[5]  James K. Cavers,et al.  A comparison of pilot tone and pilot symbol techniques for digital mobile communication , 1992, [Conference Record] GLOBECOM '92 - Communications for Global Users: IEEE.

[6]  J. Cavers.  An analysis of pilot symbol assisted modulation for Rayleigh fading channels (mobile radio) , 1991 .

[7]  Matthew C. Valenti.  Iterative Detection and Decoding for Wireless Communications , 1999 .

[8]  Robert A. Nichols,et al.  The effects of channel characteristics on turbo code performance , 1996, Proceedings of MILCOM '96 IEEE Military Communications Conference.

[9]  Charles W. Therrien,et al.  Discrete Random Signals and Statistical Signal Processing , 1992 .

[10]  K. L. Li,et al.  Modified MAP algorithm incorporated with PSA technique for turbo codes in Rayleigh fading channels , 1999 .

[11]  Li-Der Jeng,et al.  Performance of turbo codes in multipath fading channels , 1998, VTC '98. 48th IEEE Vehicular Technology Conference. Pathway to Global Wireless Revolution (Cat. No.98CH36151).

[12]  Dariush Divsalar,et al.  Multiple-symbol differential detection of MPSK , 1990, IEEE Trans. Commun..

[13]  Riccardo Raheli,et al.  Per-Survivor Processing: a general approach to MLSE in uncertain environments , 1995, IEEE Trans. Commun..

[14]  Matthew C. Valenti,et al.  A bandwidth efficient pilot symbol technique for coherent detection of turbo codes over fading channels , 1999, MILCOM 1999. IEEE Military Communications. Conference Proceedings (Cat. No.99CH36341).

[15]  J. Makhoul,et al.  Linear prediction: A tutorial review , 1975, Proceedings of the IEEE.

[16]  Matthew C. Valenti,et al.  Performance of turbo codes in interleaved flat fading channels with estimated channel state information , 1998, VTC '98. 48th IEEE Vehicular Technology Conference. Pathway to Global Wireless Revolution (Cat. No.98CH36151).

[17]  Peter A. Hoeher,et al.  "Turbo DPSK": iterative differential PSK demodulation and channel decoding , 1999, IEEE Trans. Commun..

[18]  Evaggelos Geraniotis,et al.  Iterative decoding and channel estimation of DS/CDMA over slow Rayleigh fading channels , 1998, Ninth IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (Cat. No.98TH8361).

[19]  Stephen G. Wilson,et al.  Design and Analysis of Turbo Codes on Rayleigh Fading Channels , 1998, IEEE J. Sel. Areas Commun..

[20]  A. Glavieux,et al.  Near Shannon limit error-correcting coding and decoding: Turbo-codes. 1 , 1993, Proceedings of ICC '93 - IEEE International Conference on Communications.

[21]  Peter Adam Hoeher,et al.  Iterative differential PSK demodulation and channel decoding , 1998, Proceedings. 1998 IEEE International Symposium on Information Theory (Cat. No.98CH36252).

[22]  E. K. Hall.  Turbo codes for noncoherent channels , 1997 .

[23]  S. Dolinar,et al.  Weight distributions for turbo codes using random and nonrandom permutations , 1995 .

[24]  Stephen G. Wilson,et al.  SNR mismatch and online estimation in turbo decoding , 1998, IEEE Trans. Commun..

[25]  Evaggelos Geraniotis,et al.  Pilot symbol assisted QAM with iterative filtering and turbo decoding over Rayleigh flat-fading channels , 1999, MILCOM 1999. IEEE Military Communications. Conference Proceedings (Cat. No.99CH36341).

[26]  Patrick Robertson,et al.  Optimal and sub-optimal maximum a posteriori algorithms suitable for turbo decoding , 1997, Eur. Trans. Telecommun..