30-11-2012, 05:22 PM
Telecommunication Systems 1
[attachment=41950]
Signal and System
Signals are variables that carry information
System is an assemblage of entities/objects, real or abstract, comprising a whole with each every component/element interacting or related to another one.
Systems process input signals to produce output signals
Examples
Motion, sound, picture, video, traffic light…
Natural system (ecosystem), human-made system (machines, computer storage system), abstract system (traffic, computer programs), descriptive system (plans)
Definitions
Voltage – the force which moves an electrical current against resistance
Waveform – the shape of the signal (previous slide is a sine wave) derived from its amplitude and frequency over a fixed time (other waveform is the square wave)
Amplitude – the maximum value of a signal, measured from its average state
Frequency (pitch) – the number of cycles produced in a second – Hertz (Hz). Relate this to the speed of a processor eg 1.4GigaHertz or 1.4 billion cycles per second
Signal Basics
Continuous time (CT) and discrete time (DT) signals
CT signals take on real or complex values as a function of an independent variable that ranges over the real numbers and are denoted as x(t).DT signals take on real or complex values as a function of an independent variable that ranges over the integers and are denoted as x[n]. Note the subtle use of parentheses and square brackets to distinguish between CT and DT signals.
Analog or Digital
Analog Message: continuous in amplitude and over time
AM, FM for voice sound
Traditional TV for analog video
First generation cellular phone (analog mode)
Record player
Digital message: 0 or 1, or discrete value
VCD, DVD
2G/3G cellular phone
Data on your disk
Your grade
Digital age: why digital communication will prevail
A/D and D/A
Analog to Digital conversion; Digital to Analog conversion
Gateway from the communication device to the channel
Nyquist Sampling theorem
From time domain: If the highest frequency in the signal is B Hz, the signal can be reconstructed from its samples, taken at a rate not less than 2B samples per second
Wireless (2)
Radio transmits at 10KHz to 1KHz
Microwaves transmit at 1GHz to 500GHz
Infrared transmits at 500GHz to 1THz
Radio transmission may include:
Narrow band
High-powered
Frequency hopping spread spectrum (the hop is controlled by accurate timing)
Direct-sequence-modulation spread spectrum (uses multiple frequencies at the same time, transmitting data in ‘chips’ at high speed)
[attachment=41950]
Signal and System
Signals are variables that carry information
System is an assemblage of entities/objects, real or abstract, comprising a whole with each every component/element interacting or related to another one.
Systems process input signals to produce output signals
Examples
Motion, sound, picture, video, traffic light…
Natural system (ecosystem), human-made system (machines, computer storage system), abstract system (traffic, computer programs), descriptive system (plans)
Definitions
Voltage – the force which moves an electrical current against resistance
Waveform – the shape of the signal (previous slide is a sine wave) derived from its amplitude and frequency over a fixed time (other waveform is the square wave)
Amplitude – the maximum value of a signal, measured from its average state
Frequency (pitch) – the number of cycles produced in a second – Hertz (Hz). Relate this to the speed of a processor eg 1.4GigaHertz or 1.4 billion cycles per second
Signal Basics
Continuous time (CT) and discrete time (DT) signals
CT signals take on real or complex values as a function of an independent variable that ranges over the real numbers and are denoted as x(t).DT signals take on real or complex values as a function of an independent variable that ranges over the integers and are denoted as x[n]. Note the subtle use of parentheses and square brackets to distinguish between CT and DT signals.
Analog or Digital
Analog Message: continuous in amplitude and over time
AM, FM for voice sound
Traditional TV for analog video
First generation cellular phone (analog mode)
Record player
Digital message: 0 or 1, or discrete value
VCD, DVD
2G/3G cellular phone
Data on your disk
Your grade
Digital age: why digital communication will prevail
A/D and D/A
Analog to Digital conversion; Digital to Analog conversion
Gateway from the communication device to the channel
Nyquist Sampling theorem
From time domain: If the highest frequency in the signal is B Hz, the signal can be reconstructed from its samples, taken at a rate not less than 2B samples per second
Wireless (2)
Radio transmits at 10KHz to 1KHz
Microwaves transmit at 1GHz to 500GHz
Infrared transmits at 500GHz to 1THz
Radio transmission may include:
Narrow band
High-powered
Frequency hopping spread spectrum (the hop is controlled by accurate timing)
Direct-sequence-modulation spread spectrum (uses multiple frequencies at the same time, transmitting data in ‘chips’ at high speed)