1. 10/19/20051 Turbo-NFSK: Iterative Estimation, Noncoherent Demodulation, and Decoding for Fast Fading Channels Shi Cheng and Matthew C. Valenti West Virginia University Don Torrieri U.S. Army Research Laboratory This work sponsored by the Xenotran Corporation, Glen Burnie, MD

2. 10/19/20052 Outline Iterative M-ary NFSK demodulation and decoding ML estimator using EM algorithm Performance of iterative estimation, NFSK demodulation and decoding Methods to reduce the complexity of the estimator Conclusions

3. BICM-ID: Bit Interleaved Coded Modulation with Iterative Decoding Binary Encoder Bitwise Interleaver Binary to M-ary mapping M-ary- modulator Soft-In Binary Decoder Bitwise Deinterleaver LLR Bit Metric Calculation Receiver front end AWGN Complex flat-fading Bitwise Interleaver Soft-Output Estimates of Coded Bits

4. 10/19/20054 Noncoherent M-FSK Using A Priori Probabilities Bit LLRs are calculated based on the channel observation and the extrinsic information feedback from the decoder Where

5. BICM ID and CM Capacity Minimum Eb/No (in dB) BICM ID Performance using CDMA2000 length 6138 codeword 20 iterations, BER = 10 -4 Reference: M.C.Valenti and S. Cheng, “Iterative demodulation and decoding of turbo coded M-ary noncoherent orthogonal modulation” IEEE Journal on Selected Areas in Communications, Sept. 2005. Code Rate R

6. 10/19/20056 Block Fading Channel Fading coefficient is fixed within one block. Independent fading from block to block 07674 1 2192 N=4 N=8 0767 8 8 3 2 1 96... CDMA 2000 turbo codeword rate ½ length 1530 with 16-NFSK

7. 10/19/20057 Estimation of One Block Channel state information is needed to calculate bit LLRs Perform estimation of A and B independently block by block, where Soft-In Binary Decoder Bitwise Deinterleaver LLR Bit Metric Calculation Channel Estimator Bitwise Interleaver

8. 10/19/20058 Channel Estimator with Known Transmitted Sequence Form the log-likelihood function based on the known sequence d =[d 0,d 1,…,d N-1 ] of Solving A and B to maximize L Where

9. 10/19/20059 ML Estimator with A Priori Information of the Sequence The sequence d is never known. Form log-likelihood function based on the a priori information of d Too complex to find the solution to maximize this function. We resort to EM algorithm.

10. 10/19/200510 ML Estimator using EM Algorithm 0. Select 1. 2. 3. Normalization factor Inner Iteration Outer Iteration

11. 55.566.577.588.599.510 -4 10 -3 10 -2 10 10 0 N=32 N=16 N=8 N=4 N=1 BER of 16-ary NFSK in Rayleigh Fading Channel with Different Block Size Eb/No (dB) BER CDMA2000 Turbo Code, Rate ½, Length 1530 Independent Block Fading Iteration #20 Estimator Perfect CSI

12. 456789101112 10 -4 10 -3 10 -2 10 10 0 M=2 M=4 M=16 M=64 BER of NFSK in Rayleigh Fading Channel with Different Alphabet Size Eb/No (dB) BER CDMA2000 Turbo Code, Rate ½, Length 1530 Data Rate = 24bits/ block Estimator Perfect CSI Iteration #20

13. BER of 16-ary NFSK in Rician Fading Channel (K=10dB) Eb/No (dB) BER CDMA2000 Turbo Code, Rate ½, Length 1530 Independent Block Fading Estimator Perfect CSI Iteration #20

14. 10/19/200514 Methods to Reduce the Complexity of the Estimator 0. Select 1. 2. 3. Normalization factor Inner Iteration Outer Iteration Linear approximation of F Making hard decision

15. 10/19/200515 Methods to Reduce the Complexity of the Estimator 0. Select 1. 2. 3. Outer Iteration Linear approximation of F Making hard decision

16. Linear Approximation of F 012345678910 0 0.5 1 1.5 x F ( x ) Linear Approximation

17. Complexity of Different Estimators 5.65.866.26.46.66.87 0 0.5 1 1.5 2 2.5 3 x 10 7 Decoder Demodulator EM estimator Linear EM Hard Linear EM CPU Cycles/BICMID iteration Eb/No (dB) 16-ary NFSK, CDMA2000 turbo codeword with rate ½ and length 1530. N=4 symbols per block independent Rayleigh fading

18. BER Performance of Low Complexity Estimators Eb/No (dB) BER 16-ary NFSK, CDMA2000 turbo codeword with rate ½ and length 1530. N=4 symbols per block, independent Rayleigh fading, iteration #20

19. 10/19/200519 Conclusions Robust noncoherent channel estimator, dealing with severe channel conditions. The estimator works without needing to know the fading statistics model. The only requirement is the coherence time of the fading amplitude is larger than 4 symbols. Although the estimator using the exact EM algorithm is complex, linear approximation of F(x) = I 1 (x)/I 0 (x) and hard decision of can be used to reduce the comlexity. For 16-NFSK, when fading block size is larger than 4 symbols per block, the system has acceptable BER performance. When there are 4 symbols per block, the BER of the iterative estimation, demodulation and decoding is about 0.6~0.8dB away from the one with perfect CSI.