Lecture 3 Data Encoding and Signal Modulation. Introduction Data Encoding and Signal Modulation Advantages of Signal Modulation Amplitude Modulation Amplitude Modulation of Digital Signals Reducing Power and Bandwidth of AM Signals Frequency Modulation
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A network and transport layers basic services comprise the end-to-end transport of the bit streams over a set of routers (switches). They are produced using six basic mechanisms:
c. Error control
d. flow control
e. congestion control
f. and resource allocation.
Combines data streams of many such users into one large bandwidth stream for long duration. Users can share communication medium.
a. Switch b. Multiplexer/Demultiplexer
a. Fully connected networkb. network with shared links.
Signal Modulation is
s > 2B
Sc( t ) = A · cos ( 2 f t+ )
A. Amplitude Modulation (AM), or Amplitude Shift Keying (ASK): The amplitude A of the carrier signal changes in direct proportion to the baseband signal.
B. Phase Modulation (PM), or Phase Shift Keying (PSK): The phase of the carrier signal changes in direct proportion to the baseband signal.
C. Frequency Modulation (FM), or Frequency Shift Keying (FSK): The frequency f of the carrier changes in direct proportion to the baseband signal.
Are the processes of transmitting several signals over the same medium by using many carrier waves, each with a different frequency
To receive an electromagnetic signal using an antenna, the dimensions of the antenna must be of the same order of magnitude as the wavelength of the signal being transmitted.
Transmitting a 1 kHz sinusoidal waveform with radio waves would require an antenna on the order of one signal wavelength, or 300,000 meters.
Sc ( t ) = A · cos ( 2 fc )
range (fc + f) and (fc - f) .
fc =10 MHz
Sm ( t )
Sm ( t ) = Ac + Am · cos ( 2 fm t)
Sm ( t ) = Ac · cos ( 2 fm t)
Baseband Signal with DC shift
Since the phase of the transmitted signal can take one of two values (phase jumping), this type of modulation is called binary phase-shift keying (BPSK). It is a constant-amplitude method of modulation.
If we add together two BPSK signals that are offset by a 90 degree phase shift, there are four possible phase jumping during every sampling period. Instead of one possible shift of 180º, there are three possible transitions: +90º, 180º, and ‑90º (+270º). The signal can be represented by the following formula:
Time domain representation of QPSK signal, created by combining BPSK signals S1 and S2.
In all forms of amplitude modulation, the two sidebands contain identical information.
Selecting the type of transmission can depend on the following factors:
• Bandwidth limitations
• Simplicity of Demodulation Equipment
Pt : Total transmitted power, Ac :Carrier Signal Amplitude
k : Constructional coefficient of the modulator
Sm ( t ) = Am · sin (2 fm )
In this equation B is effective bandwidth of baseband signal,
but BT is absolute bandwidth of FM signal
s > 2B
“1” is converted to signal voltage high, and
“0” is converted to signal voltage low.
This is called Non-Return to Zero-Level (NRZ-L) encoding.
Bit rate is twice the frequency
0: Signal low (first half) / Signal high (second half)
1: Signal high (first half) / Signal low (second half)
Bit rate = signal frequency