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TRANSMISI DATA Sujoko
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TRANSMISI DATASujoko

Objektif Konsep dan Terminologi Transmisi data analog dan digital Gangguan transmisi (Impairment) Analisis Fourier Kuat sinyal (Signal Strength) dan Decibels

Sources of signal impairmentSignal carried on transmission medium affected by:

- Attenuation - Limited Bandwidth - Delay Distortion - Noise

Sources of signal impairment

AttenuationSignal Attenuation: Decrease in signal amplitude as it propagates along transmission medium- Consequence: Limit length of cable to be used - Solution : Amplifiers (Repeaters) used to restore signal to original level. - Property : Signal attenuation increases as a function of frequency.

Possible remedies : - Non Linear amplifiers or Equalizers

Attenuation (lanjutan)Signal Amplification ( Gain ): Increase in signal amplitude

Contoh (Attenuation)

Contoh (Lanjutan)

Signaling Rate vs. Data Bit Rate

Limited Bandwidth Bandwidth of a communication / transmission medium: band of sinusoidal frequency components (f1to f2) that will be transmitted by the channel unattenuated

Question: What is the effect of channel bandwidth on transmitted signal ?

Fourier analysis A periodic signal is made of an infinite series of sinusoidal frequency components - Fundamental frequency component : same frequency as initial periodic signal, cycles per sec (Hz) - Harmonics : other frequency components, multiples of fundamental frequency.

Fourier analysisg g

v(t ) ! a an cos n([ 0)t bn sin n([ 0)tn !1 n !1

V(t) = tegangan sinyal (periodis) sebagai fungsi waktu W0 = komponen frekuensi fondamental (rad/sec) T= 2 /W0 atau W0 = 2 f0

Aplikasi analisis Fourier(Untuk transmisi data)Possible binary sequences (periodic) : (1) 1 0 1 0 1 0 period = 2 bit cell intervals (2) 1 1 0 1 1 0 .. period = 3 bit cell intervals (3) 1 1 1 0 1 1 1 0 . period = 4 bit cell intervals Note: (1) has shortest period, highest fundamental frequency component: worst-case sequence

Aplikasi analisis Fourier(Untuk transmisi data) Basic Binary Signal Types: Unipolar Signal (Return to zero, RZ) Amplitudes : +V, 0; Mean Signal Level = V /2 Bipolar Signal (Non ReturnToZero , NRZ) Amplitudes : +V, -V; Mean Signal Level = 0

Aplikasi analisis Fourier(Untuk transmisi data)

Aplikasi analisis Fourier(Untuk transmisi data)

Aplikasi analisis Fourier(Untuk transmisi data) General Observations: A periodic binary sequence is made of an infinite series of sinusoidal signals made of-A fundamental frequency component, f0 -A third harmonic component , 3f0 -A fifth harmonic component , 5f0

Note: Odd harmonics only

Aplikasi analisis Fourier(Untuk transmisi data)/Lanjutan The amplitude of the harmonics diminishes with increasing frequency T (Signal Period) = 2*Tb (Bit Period)Tb = T/2; 1/ Tb = 2/T = 2 * 1/T R (bit rate) = 2 * f0 (fundamental frequency)

When binary data signal transmitted on a channel, only those frequency components that are within channel bandwidth will be received A channel with a bandwidth :From 0 to fundamental frequency (half the bit rate) can often give satisfactory performance

Aplikasi analisis Fourier (Untuk transmisi data)Analysis Effect of Limited Bandwidth:

Aplikasi analisis Fourier(Untuk transmisi data)Effect of Limited Bandwidth

Aplikasi analisis Fourier(Untuk transmisi data)Effect of Limited Bandwidth:

Contoh : A binary signal of R (bit rate) = 500 bps is transmitted on a communication channel What is the minimum bandwidth required, assuming(a) Fundamental frequency only (b) Fundamental and third harmonic (c) Fundamental,third and fifth harmonics

Solution :For R = 500bps, f0 = R/2 = 250 Hz (a) 0 250 Hz (b) 0 750 Hz (c ) 0 1250 Hz

Laju transfer informasi maksimumUntuk kanal transmisi (noiseless) (the Nyquist Formula) C = 2W log2M where W : bandwidth of the channel (Hz) M: number of levels per signaling element log2M : number of bits/signaling element

Laju transfer informasi maksimum (Contoh)Data is sent over a PSTN with : M = 8 levels /signaling element W = 3,000 Hz Q: What is the Nyquist maximum data transfer rate ? A:C = 2W log2M = 2*3000*log28 = 2*3000*3 = 18,000 bps

Bandwidth Efficiency of a Transmission ChannelB = R/W = 1/(W* Tb) bps Hz-1Observations: The higher the bit rate relative to the available bandwidth, the higher the bandwidth efficiency Typical values for B: 0.25 - 3.0bps Hz-1, (B=3.0 requires a high signal rate) Another expression for bandwidth efficiency:R = RS. m = RS log2 M B = R/W = (R S log2 M) /W

WhereM is number of levels per signaling element log2 M is number of bits per signaling element

Delay Distortion Rate of propagation of a signal over a channel is function of frequency of signal Consequence: Delay Distortion different frequency components arrive with different delays Delay distortion increases with bit rate Inter symbol interference : frequency components of a bit start to interfere with a later bit Use of an eye diagram : oscilloscope displays all possible signals superimposed

Delay Distortion (Lanjutan)

Noise Line Noise level : Random perturbations on the line, even when no signal present. Consequence: Interference between (attenuated) transmitted signal and line (background) noise Signal-to noise ratio: (SNR) SNR = 10log10(S/N) dBS : average power in received signal (watts) N : noise power (watts)

Noise (Lanjutan)Theoretical data rate of a transmission channel (Shannon Hartley law)

C = W log2(1 + S/N) bpsWhere W = Bandwidth (Hz). S = Average signal power (watts) N = Random noise power (watts)

Noise (Lanjutan)Theoretical data rate of a transmission channel (Shannon Hartley law)Given a PSTN with: W = 3000 Hz, and SNR = 20 dB determine maximum theoretical data rate A: SNR = 10log10(S/N) 20 = 10log10 (S/N) , untuk S/N = 102 = 100. C = W log2(1 + S/N) = 3000 log2(1+100) = 19,963 bps.

Noise (Lanjutan) Cross Talk: Noise caused by unwanted electrical coupling between adjacent lines Near End Cross Talk (NEXT) or Self Cross Talk: Strong signal output from transmitter circuit interferes with weak signal at receiver circuit Solution: Adaptive NEXT cancellers Impulse Noise: Caused by external electrical activity impulses (lightning, impulses from old switching systems) Observation : Both cross talk and impulse noise are caused by electrical activity external to transmission line

Noise(Lanjutan)