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Model of communications system - Coggle Diagram
Model of communications system
Source
Transmitter
Transmission system
Receiver
Destination
Model compounants
Source
Device that generates data
Transmitter
Transforms and encodes data
Transmission system
The physical system connecting the source and destination devices
Receiver
Preforms reverse function of Transmitter
Destination
receives the incoming data
Transmission signal
transmission signal is either some form of electrical magnetic wave(EM) or an electrical signal
. Examples of EM waves, used for data transmission include radio waves, light waves, microwaves.
Examples of electrical signals include alternating current (A/C) voltage pulses, etc. For stop.
The simplest form of signal is a sine wave.
Transmission signal
In its simplest form, a transmission system is some type of transmission medium, which may be either and guided or un-guided
guided
electrical cable, fiber optic cable
un-guided
electromagnetic waves in space.
Successful data transmission
the successful transmission of data depends on two things.
quality
characteristics
Signal characteristics
periodic repeats itself after some fixed time
Continuous
no breaks or discontinuities within signal
Eg
speech singnal
Discrete
dense a finite number of discrete values.
Eg
a computer or binary data
Aperiodic
no repetition of the signal pattern.
SineWave Characteristics
general equation
S(t) = A sin(2pie.ft+ phase)
about
Amplitude(A) is the peak value of the waveform,
frequency, (F) is the number of repetitions per second, measured in Hertz (Hz), inverse of the period,
phase (0(with a / through it)) is a measure of the relative position within a cycle of a signal, measured in degrees or radians.
All three characteristics can be varied, to give different waveforms
Fourier Analysis
about
This is of fundamental importance.
The effects of transmission media on a signal can be analyzed by examining the effects on these components sinusoidal.
any signal can be expressed as the sum of a series of sinusoidal components of different frequencies.
Singalling concepts
Spectrum.
The range of frequencies contained in a signal for the above sample signal. The spectrum ranges from f1 to 3f1
Absolute bandwidth
equals width of spectrum for the above, sample signal, the bandwidth is 2f1 ( I.e. 3f1 - f1 ),
Effective bandwidth
signals with sharp rising and falling edges in the, in the time domain, have very wide absolute bandwidth. Most energy is contained in a relatively narrow band called the effective bandwidth.
DC component
signals were component at zero frequency.
Transmission system characteristics
Transmission systems (TX systems) are limited(restricted) in the range of signal frequencies that they can carry. this restriction is known as the system bandwidth.
system bandwidth
results from
the physical properties of the components that comprise the system.
the physical properties of matter and energy.
Relationship between data rate & bandwidth
the bandwidth of a transmission system can be described as the fastest continuously oscillation signal that can be sent transmitted across the transmission system. it is represented in hertz (Hz).
The effects of system bandwidth is to limit the speed of transmission of data(data rate).
This limitation has a direct effect on the maximum data rate achievable across a transmission system, consider a transmission system that has a bandwidth of 15 megahertz(Mhz).
conclusion
In digital transmission the square wave is usually used to encode data.
from previous, previous discussions, a digital waveform has an infinite number of harmonics frequency components
All Tx Systems have a limited bandwidth.
The more limited the broadband, of the TX system, the greater the distortion, ie, not all components will get through.
In general far digital signal carrying data as a rate of WBP s very good representation can be achieved with a TX system, bandwidth of W/2 Hertz.
For example, if the data rate of a signal is fixed at 2Mbps. the TX system bandwidth required to facilitate this data rate would be approximately 1Mhz
Beware that this approximation is simply a guide, and not an absolute value.
Data and signals
data
entities that convey meaning
singal
elctromagnetic wave with encoded data
transmission system
the entity over which the signal is transmitted
each entity can be considered in terms of analogue or digital
concepts
analogue
analog data takes on continuous values on some interval, eg a voice, temperature, pressure, etc,
digital
digital data takes on discrete values, eg integers, and texts.
Signals defined
analogue signal
continuously varying electromagnetic waves(representing data) that may be propagated over a transmission medium
digital signal
sequence of discrete discontinuous voltage pulses(represent data), data may be propagated over our transmission medium.
Data transmission defined
Data transmission is the communication of data by propagation and processing of signals.
Analog data can be conveyed by an analog signal, eg ordinary telephone
Digital data can also be conveyed by an analog signal. When a modem is used.
Analog data can be conveyed by digital signal when a codec is used
Digital data may be fed by a digital signal e.g. a digital transmitter.
Analogue transmission defined
analog transmission is the propagation of analog signals, only, ie, some physical quality eg voltage that changes continuously as a function over time.
There is no regard to the content, the encoded data of the signal as a transmitted analog signal becomes attenuated with distance as an amplifier can extend the range,
Digital transmission defined
digital transmission is the propagation of
analog signals with encoded digital data or digital signals,
digital transmission systems have regard to the encoded data
As a transmitted digital signal becomes attenuated with distance, a repeater can extends the range.
A repeater receives the attenuation signal recovers the digital data and retransmits and new signal with no noise added.
Analogue vs Digital transmission
Digital is Superior
security encryption can be more easily applied to digital data
low costs of digital electronics
digital integrity signal can be maintained free of noise
capacity utilization, different digital signals can be multiplexed or de-multiplexed more easily, and thus share a single channel
integration, digital digitized analog data can be mixed with digital and shared the same facilities as other digital signals.