winter 08 final

# winter 08 final - EE 230B Final Examination Winter 2008...

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EE 230B Final Examination, Winter 2008 NAME:_______________________ UCLA Electrical Engineering Department Prof. G. Pottie Instructions: Attempt all five questions; they are of equal weight but not necessarily of equal difficulty. A sheet of useful formulae and other facts is attached.

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1. π /4 shifted Offset PSK Here you will compare three modulations: 4-PSK, offset-PSK, and π /4 shifted Offset PSK. The latter is like regular 4-PSK with the signal space in the odd intervals rotated 90 degrees with respect to the signal space for the even intervals. a) For a Gaussian channel, compute P(e) as a function of Eb/No for the three modulations (write down the argument behind your answers). b) Compare the modulations in terms of their power spectral density. (Note, you do not actually have to compute the psd’s to answer this). c) Compare them in terms of their resistance to phase errors d) Qualitatively compare them in terms of vulnerability to power amplifier non-linearity, when tight transmit filtering is employed e) Suggest a possible reason why π /4 shifted Offset PSK was selected in a cellular radio standard rather than offset PSK.
2. Fading Channel A radio channel experiences flat fades. The probabilities of the SNR in absolute units exceeding 16, 64, 256, and 1024 are respectively 100%, 70%, 50% and 20%. It is required that the error probability be better than 10 -6 .

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winter 08 final - EE 230B Final Examination Winter 2008...

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