4/11/40 page 1 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Transmission Impairments

4/11/40 page 2 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Type of impairments Attenuation Delay distortion Noise

4/11/40 page 3 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Attenuation transmitter receiver P 1 watts P 2 watts Attenuation 10 log 10 (P 1 /P 2 ) dB Amplification 10 log 10 (P 2 /P 1 ) dB

4/11/40 page 4 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Delay distortion

4/11/40 page 5 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Noise Effect distorted a transmitted signal attenuated a transmitted signal signal-to-noise ratio to quantify noise S/N db = 10 log 10 S= average signal power N= noise power Type of noise crosstalk impulse noise thermal noise SNSN

4/11/40 page 6 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Crosstalk NEXT (near-enf crosstalk) interference in a wire at the transmitting end of a signal sent on a different wire FEXT (far-end crosstalk) interference in a wire at the receiving end of a signal sent on a different wire

4/11/40 page 7 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Effect of noise Signal Noise Signal+Noise Data Received Sampling times Bit error Original data

4/11/40 page 8 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Nyquist formula M Max data rate (C) bps bps bps bps M Max data rate (C) bps bps bps bps C = 2W log 2 M W = bandwidth M = number of discrete signal Theoritical capacity for Noiseless channel Channel capacity calculation for voice bandwidth (3100 Hz)

4/11/40 page 9 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Shannel-Hartley law Theoritical maximum channel capacity with noise C = W log 2 (1+ SNSN )

4/11/40 page 10 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Nyquist theorem ?In a perfectly noiseless channel, if f is the maxmimum frequency the medium can transmit, the receiver can completely reconstruct a signal by sampling it 2*f times per second Nyquist, 1920

4/11/40 page 11 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Bit rate and Baud rate Bit rate A number of bits that are tranmitted in a second Baud rate A number of line signal changed variation per second If a modem transmits 1 bit for every signal change bit rate = baud rate If a signal change represents 2 or more or n bits bit rate = baud rate *n

4/11/40 page 12 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Bandwidth efficiency Typical values range from 0.25 to 3.0 bps Hz -1 B = R/W Data rate Bandwidth of the channel

4/11/40 page 13 Department of Computer Engineering, Kasetsart University Introduction to Computer Communications and Networks CONSYL Effect of noise S*W R* N = EbEb N0N0 = S/N + 10 logW - 10 logR (dB) = E b /N 0 = signal energy to noise energy ratio S= signal power in watts R= data rate W= bandwidth N= noise power in received signal S*W N* R