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    psk and fsk, bandwidth

    1. Why FM is better than PM for analog communication?

    2. Why PSK is better then FSK for digital communication?

    Thanx

    •   Alt16th June 2007, 23:19

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    Why PSK is better than FSK?

    hmm, maybe:

    1. Analog: FM is easier to modulate/demodulate than PM.

    2. Digital: BFSK needs 2 times bit energy more than BPSK to get the same probability of error. (i.e points in constellation are nearer).



    •   Alt17th June 2007, 00:00

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    Re: Why PSK is better than FSK?

    Better is a matter of criteria. On circuits, like HF, where the link rapidly changes phase FSK is usually preferred. Also, low cost equipment is cheaper with FSK.



    •   Alt17th June 2007, 01:37

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    Re: Why PSK is better than FSK?

    Because for the same Eb/N0 the bit error for PSK is less than the bit error for FSK



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    Re: Why PSK is better than FSK?

    it depends mainly on channel and aval bandwidth



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    Re: Why PSK is better than FSK?

    Hi,

    Quote Originally Posted by sheraz.pervaiz
    1. Why FM is better than PM for analog communication?
    Which is better depends on the characteristics of the signal to be transmitted.
    For FM transmission of speech, it is usual to use preemphasis before FM modulation and deemphasis after FM demodulation. This is equivalent to use PM (if the cutoff frequency of the emphasis/deemphasis filters is low enough.
    This improves quality because the spectrum of voice falls at high frequencies. If the spectrum of the signal to be transmitted were flat, the use of staight FM would be better than FM with preemphasis/deemphasis (i.e. PM).

    2. Why PSK is better then FSK for digital communication?
    Binary PSK is antipodal signaling. Binary FSK (with frequency separation = a multiple of half the bit rate) is an orthogonal signaling. Thus, BPSK has an advantage of 3 dB over orthogonal BFSK. In addition, FSK is usually detected incoherently; this gives it an additional penalty.
    "Optimal" binary FSK is not orthogonal, but it is always worse than antipodal signaling.

    Regards

    Z



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    Re: Why PSK is better than FSK?


    PSK modulation techniques are in general better than FSK modulations in terms of bandwidth requirements or in other words PSK modulation schemes offer better bits/s/hz efficiency. However FSK modulation schemes are more power efficient i,e, offers better BER performance at a given S/N (signal-to-noise ratio). FSK modulation schemes also perform better in terms of adjacent channel interference in non-linear power amplifications. That is the reason why GMSK (which is a variant of FSK) has been used in GSM system.



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