Background of communication
systems
For ICS&N experiments
DE-1. Analogue and Digital
Signals
DE-1. Analogue and Digital Signals
Analogue signals
Analogue signals can vary in frequency, amplitude, or both.
Digital signals
Digital signals are a series of pulses consisting of just two
states: ON (1) or OFF (0). There are no values in
between.
Signals in the Time and Frequency Domain
Time domain : how the signals change over time
Frequency domain : how much signals lie in the frequency range
Effect of Filtering on Waveshape and Spectrum
Noise Signals in the Time and
Frequency Domain
NRZ and RZ with Bipolar and Unipolar Forms
DE-2. Sampling and Time
Division Multiplex
Sampling Analogue Signals
8 bits: 2^8 = 256 steps
Nyquist Theorem
Suppose the highest frequency component,
in hertz, for a given analogue signal is fmax.
According to the Nyquist Theorem, the
sampling rate must be at least 2fmax, or twice
the highest analogue frequency component.
DE-3. Amplitude Modulation
and ASK
Double Sideband Amplitude
Modulation with Full Carrier
Modulation index m
Amplitude Shift Keying
DE-4. Calculate Bit Error Rate
using BERTool
Bit Error Rate and SNR
The bit error rate (BER) is the number of bit
errors per unit time. Lower the better.
Signal-to-noise ratio (abbreviated SNR or
S/N) is the ratio of signal power to the noise
power, often expressed in decibels. Higher the
better quality of the channel.
BER and SNR
DE-6. Fourier Synthesizer
Fourier Synthesis
Waveform
Harmonics
1*
Square
2
3
4
5
6
7
8
100 0
33
0
20 0
14
0
(0°)
(180°)
(0°)
(180°)
Triangular 100 0
11
0
4
0
2
0
(0°)
(0°)
(0°)
(0°)
Sawtooth 100 50
33
25
20 17
14
12.5
(see note (90°) (270°)(90°) (270°)(90°) (270°)(90°) (270
below)
°)
Rectified 100 20
8.3 4.8 3.3 2.1 13
12
cosine
(0°) (180°)(0°) (180°)(0°) (180°)(0°) (180
°)
Parabola 100 25
11
6.7 4
3
2
1.5
(0°) (0°) (0°) (0°) (0°) , (0°). (0°) (0°)
9
11
(0°)
1.2
(0°)
11
(90°)
0.9
(0°)
1.2
(0°)