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

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

EEE Noncoherent Detection

EEE On-off Keying

EEE On-off Keying

EEE On-off Keying

EEE On-off Keying

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

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

EEE On-off Keying

EEE Noncoherent FSK Detector Filters matched to RF pulses for 0 and 1 Decide 0 if v u v u H1(f)H1(f) H0(f)H0(f) Env. Det Comparator Sampler vuvu vLvL

EEE Noncoherent FSK Detector 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. Noise outputs of the upper and lower receiver channels is similar.

EEE Noncoherent FSK Detector The probability of error is thus obtained as: OOK and FSK are equivalent on E b /N o basis. Noncoherent FSK requires at most 1 dB more E b /N o coherent FSK. Noncoherent FSK is much easier to build.

EEE Noncoherent FSK Detector

EEE 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.

EEE 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 E b /N o BPSK.