modulation (1)

modulation (1) - Carriers and Modulation CS442 DIGITAL...

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Carriers and Modulation CS442
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DIGITAL TRANSMISSION OF DIGITAL DATA Review…
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Baseband Transmission Digital transmission is the transmission of electrical pulses. Digital information is binary in nature in that it has only two possible states 1 or 0. Sequences of bits encode data (e.g., text characters). Digital signals are commonly referred to as baseband signals . In order to successfully send and receive a message, both the sender and receiver have to agree how often the sender can transmit data (data rate ). Data rate often called bandwidth – but there is a different definition of bandwidth referring to the frequency range of a signal!
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Baseband Transmission With unipolar signaling techniques, the voltage is always positive or negative (like a dc current). In bipolar signaling, the 1’s and 0’s vary from a plus voltage to a minus voltage (like an ac current). In general, bipolar signaling experiences fewer errors than unipolar signaling because the signals are more distinct.
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Baseband Transmission
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Baseband Transmission Manchester encoding is a special type of unipolar signaling in which the signal is changed from a high to low (0) or low to high (1) in the middle of the signal. More reliable detection of transition rather than level consider perhaps some constant amount of dc noise, transitions still detectable but dc component could throw off NRZ-L scheme Transitions still detectable even if polarity reversed Manchester encoding is commonly used in local area networks (ethernet, token ring).
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Manchester Encoding
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ANALOG TRANSMISSION OF DIGITAL DATA Analog Transmission occurs when the signal sent over the transmission media continuously varies from one state to another in a wave-like pattern. e.g. telephone networks, originally built for human speech rather than data. Advantage for long distance communications: much less attenuation for analog carrier than digital
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Digital Data to Analog Transmission Before we get further into Analog to Digital, we need to understand various characteristics of analog transmission.
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Periodic Signals
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Sine Wave Peak Amplitude (A) maximum strength of signal volts Frequency (f) Rate of change of signal Hertz (Hz) or cycles per second Period = time for one repetition (T) T = 1/f Phase ( φ ) Relative position in time, from 0-2*pi General Sine wave ) 2 sin( ) ( φ π+ = ft A t s
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Varying Sine Waves
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Wavelength Distance occupied by one cycle Distance between two points of corresponding phase in two consecutive cycles 2200 λ = Wavelength Assuming signal velocity v λ = vT f = v c = 3*10 8 ms -1 (speed of light in free space)
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Frequency Domain Concepts Signal usually made up of many frequencies Components are sine (or cosine) waves Can be shown (Fourier analysis) that any continuous signal is made up of component sine waves Can plot frequency domain functions
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Frequency Components Notes: 2nd freq a multiple of 1 st 1 st called fundamental freq
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This note was uploaded on 01/20/2012 for the course EE 301 taught by Professor Ahmetçakar during the Spring '11 term at Gazi Üniversitesi.

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modulation (1) - Carriers and Modulation CS442 DIGITAL...

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