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Chapter 7 Error Probabilities for Noncoherent Systems

Chapter 7 Error Probabilities for Noncoherent Systems. Noncoherent Detection of OOK Noncoherent Detection of FSK Differential Phase Shift Keying. Huseyin Bilgekul EEE 461 Communication Systems II Department of Electrical and Electronic Engineering Eastern Mediterranean University.

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Chapter 7 Error Probabilities for Noncoherent Systems

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  1. Chapter 7Error Probabilities for Noncoherent Systems • Noncoherent Detection of OOK • Noncoherent Detection of FSK • Differential Phase Shift Keying Huseyin Bilgekul EEE 461 Communication Systems II Department of Electrical and Electronic Engineering Eastern Mediterranean University

  2. Noncoherent Detection • Phase is unknown • Use filter and techniques such as envelope detection or feedback to demodulate signal Envelope Detector H(f) Threshold detector Sampler

  3. Noncoherent Detection

  4. On-off Keying

  5. On-off Keying

  6. On-off Keying

  7. On-off Keying

  8. On-off Keying Pdf if 0 is sent Rayleigh distributed noise only case • Optimum threshold value occurs where densities intersect • Threshold depends on bit SNR, problem in fading channels Pdf if 1 is sent Rician distributed Threshold

  9. On-off Keying • BER depends on the bandwidth of the bandpass filter used. • Pe becomes smaller as Bp is decreased. • Minimum bandwidth allowed with no ISI is Bp=2B=R=1/T • Noncoherent OOK is worse than coherent OOK.

  10. On-off Keying

  11. vu Env. Det Sampler H1(f) Comparator Sampler Env. Det H0(f) vL Noncoherent FSK Detector • Filters matched to RF pulses for 0 and 1 • Decide 0 if vu < vL Decide 1 if vL > vu

  12. Noncoherent FSK Detector • Noise outputs of the upper and lower receiver channels is similar. • When signal is present in the lower channel, the upper channel is only noise which is Rayleigh distributed. The lower channel is signal plus noise and it is Rician distributed.

  13. Noncoherent FSK Detector • The probability of error is thus obtained as: • OOK and FSK are equivalent on Eb/No basis. • Noncoherent FSK requires at most 1 dB more Eb/No coherent FSK. • Noncoherent FSK is much easier to build.

  14. Noncoherent FSK Detector

  15. Differential Phase Shift Keying • Phase shift keyed signals can not be detected noncoherently. • Using the delayed version of the signal as phase reference partial coherence can be obtained.

  16. Differential Phase Shift Keying • For additive white Gaussian noise the BER performance can be obtained and approximated as: • Suboptimum detection (Band pass filter) is similar to that of OOk and FSK. • Optimum demodulation of DPSK requires 1 dB more Eb/NoBPSK.

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