ME1100 DIGITAL RF COMMUNICATIONSME1100 DIGITAL RF COMMUNICATIONS
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Definition:
Literally
A process by which information is exchanged between individuals through a common system of symbols, signs, or behavior (source: www.merriam-webster.com ).
Technically
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1876
1904
1936
1972
appliances; digital TV, digital pagers, digital cellular phones
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Communication Systems
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Terminology
Signal
An impulse or fluctuating electric quantity, such as voltage, current, or electric field strength, whose variations could represent information.
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t
intensity
System
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Source
Analog source: produces analog messages, e.g., microphone (where its output voltage describes the information in the sound).
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DATA PROCESSOR
DATA PROCESSOR
TRANSMISSION CHANNEL
Transmitter
Processes the input signal to produce a transmitted signal that suits the characteristic of the transmission channel.
E.g., modulation, coding, amplification, filtering
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Classified into two categories: wired and wireless
Wired channel:
fiber optic cables, waveguide
Elements of Communication Systems (cont’d)
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Receiver
To extract the desired signal from the output channel and to convert it to a form suitable for the output transducer.
E.g., amplification, filtering, demodulation
Sink
The received signal will be converted back (by the respective output transducer) to the form desired by the systems.
E.g., speaker, monitor
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signal
optic cables
original signal
computer)
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Information-bearing waveform selection
Effect of the system noise on the received signal
Cost of the system
Analog Communication System
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Demodulates the analog bandpass signal into the analog baseband signal
Analog
Demodulator
Modulates the analog baseband signal into the analog bandpass signal
Analog
Modulator
ExamplesOutput
Function
Subsystem
Digital Communication System
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ASK, FSK, and PSK
Digital Modulator
Digital codeword
reduce bit errors caused by channel noise (error control coding)
Channel Encoder
Digital data
Converts the analog signal into the digital signal for digital processing (Pulse Code
Modulation)
Analog-digital
Converter
Output
Function
Subsystem
D I G I T A L
A N A L O G
Advantages: Inexpensive Privacy preserved (data encryption) Can merge different data Error correction can be implemented
Disadvantages: Expensive No privacy preserved Cannot merge different data No error correction capability
Disadvantages: Larger bandwidth required Synchronization problem is relatively difficult
Advantages: Smaller bandwidth Synchronization problem is relatively easier
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The total span of frequencies and corresponding wavelengths used in Communication Systems is called the EM/frequency spectrum.
The overall useful EM spectrum ranges from 50 Hz to several billion hertz!
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Spectrum
Radio
Microwave
Infrared
Visible
signal
Signal to be
transmission, e.g., wires, air, and fib er
optic cables
original signal
desired by the systems