1. Real-Time Signal-To-Noise Ratio Estimation Techniques for Use in Turbo Decoding Javier Schlömann and Dr. Noneaker

2. Motivation For Research Turbo codes: high-performance error- correcting codes that achieve nearly-optimal performance over Gaussian noise channels Signal-to-Noise Ratio (SNR): measure of received signal energy to noise power density For optimum performance, turbo decoders need accurate knowledge of the SNR

3. Purpose of Research Analyze existing SNR estimation techniques Devise, analyze, and compare other SNR estimation techniques that can be implemented into turbo decoders

4. The Communications System s(t) – transmitted binary antipodal modulated signal n(t) – additive white Gaussian noise process v(t) – filter with impulse response matched to the transmitted signal Z i = matched filter output sampled at time (i+1)T v(t) Matched Filter t = (i+1)T n(t) s(t) r(t) Z i Data Modulator (b 0, b 1, …)

5. General Transmission Formats Our focus (two special cases):  SNR estimation using data-modulated signal Bit polarities, b i, are unknown a priori at receiver  SNR estimation using training sequence Bit polarities, b i, are known a priori at receiver Training Seq. Data Data…

6. Estimation Using Data Signal Relationship between statistics and SNR Estimate SNR using empirical approximation to ratio

7. Estimator Performance

8. Two Alternative Estimators Minimizes sensitivity to z offset Easy to implement  No table look- up required

9. Approximation 2 Performance

10. Training Sequence Estimation

11. Hybrid Technique Uses minimum of data-signal and training sequence SNR estimations Results for 13-bit training sequence:

12. Conclusions Without Training Sequence  Use Approximation 2 With Training Sequence  Use Max SNR Limiting Estimator  Hybrid Estimator Best overall performance

13. Future Work SNR estimation for channel with a time-varying SNR Estimating SNR in multi-path channels  SNR estimate is useful in some equalization techniques

14. Any Questions?

15. Estimation Limiting Max SNR

16. Real-Time Signal-To-Noise Ratio Estimation Techniques for Use in Turbo Decoding Javier Schlömann and Dr. Noneaker