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    Analysis of an ASK OOK Baseband Digital Link

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    A baseband link is equipped with an equalizer such that its operating bandwidth is 1.00 MHz. Over this bandwidth the attenuation is constant at 25 dB and the phase shift is linear with frequency. The link is used for the transmission of digital signals. The transmitter and receiver have ideal RRC filters with roll off factor r = 1.0. The transmitter pulses are binary ASK using on-off keying (OOK).

    a. What is maximum pulse rate (i.e. symbol rate) for this link?

    b. What is the bit rate of the signal?

    c. If the filters in the transmitter and receiver are changed for ideal RRC filters with roll off factor r = 0.25, what is the maximum symbol rate for this link?

    d. The transmission line has an impedance of 600 ohms and is terminated in a load of 600 ohms. The transmitter delivers an average power of 0.1 W to the input of the line. What is average power at the receiving end of the line? What is the average voltage of the received pulses?

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    Solution Preview

    Operating Bandwidth B = 1 MHz

    Filter roll off factor r = 1 or (100%)

    a. Symbol Rate SR is given in terms of the Operating (or occupied) Bandwidth and the filter roll off factor by (1).

    SR = B/(1+r) (1)

    SR = 1 MHz/(1+1) = 500 KSymbols/s

    b. For an M level modulation scheme the number of bits/level or bits/symbol m is given by (2).

    m = log2{M} (2)

    As we are just considering ASK (OOK) which is an M = 2 level scheme then the number of bits/symbol is just

    m(ASK) = log2{2} = 1

    Bit rate R of the link is given as the product of the symbol rate and bits/symbol by (3) below.

    R = m*SR ...

    Solution Summary

    A baseband digital link is analysed and from known link parameters such as operating bandwidth and attenuation, rolloff factor r = 1.0 such questions as what is the maximum pulse rate (symbol rate) of the link using ASK OOK and maximum bit rate of the link are answered. If filters with rolloff of r = 0.25 are used what is the maximum symbol rate of the link? From this some transmission line parameters are defined and link derived parameters are used to determine the power delivered to the recieving end of the line and the average voltage pulse height of the recieved symbols