lecture 6 data&signals Flashcards
data can be either
analog or digital
analog data
the information is continuous and takes continuous values
digital data
the information is discontinuous, has discrete states and takes discrete values
examples of analog data
- a clock with moving minute/hour hands
- sound of human voice
examples of digital data
- a digital clock (goes from 8:05 to 8:06)
- WhatsApp message
what is meant by discrete values
- stored on the computer in the form of 0’s and 1’s
signals can be either
analog or digital
analog signal
has an infinite number of values in a range
digital signal range and levels
- has a limited number of defined values in a range
- can have more than two levels
what is periodic analog signal
- a signal which completes a pattern within a period of time
- repeats that pattern over subsequent identical periods
non-periodic digital signal
- a signal that changes without exhibiting a pattern or repetitiveness
periodic analog signal can be classified as
- simple or composite
simple periodic analog signal consists of:
one sine wave, and it cannot be decomposed into smaller signals
composite periodic analog signal:
it is composed of various sine waves (combination)
peak value=
sqrt2 x root mean square value (rms)
period(s)=
T=1/F (inverse of frequency)
frequency(Hz)=
F=1/T (inverse of period)
peak value is called
the amplitude
frequency refers to
how many cycles (oscillations) per second
period refers to
the time taken for one cycle (oscillation)
frequency and change
- change over a short period of time = higher frequency
- change over a long period of time = lower frequency
- no change = frequency equals zero
phase shift
how much you shifted from time 0
radians=
degrees * pi/180
a cycle represents
2 pi’s and 360 degrees
frequency and wavelength
- the higher the frequency, the smaller the wavelength
2. the lower the frequency, the bigger the wavelength
frequency domain represents
a periodic sine wave using a single vertical line
why is a single frequency sine wave not
useful in data communications?
because we need to send a composite signal, which is a combination of sine waves of different frequencies, amplitudes and phases
If the composite signal is periodic, the
decomposition gives
a series of signals with discrete frequencies
if the composite signal is non-periodic,
the decomposition gives
a combination of sine waves with continuous frequencies
bandwidth(Hz)=
maximum frequency - minimum frequency
example of non-periodic composite signal
- AM and FM radio stations
number of bits per level=
Log2(level)
the more bits you can encode
the faster the data rate
a digital signal is a composite analog
signal but..
it has an infinite bandwidth
why is that what is sent, may not be what is received (what causes this effect)
- because of the bandwidth supported by the medium
baseband (unfiltered) transmission of a digital signal, that preserves its shape, is possible only if..
we have a low pass channel with an infinite or very wide bandwidth
what is a low pass channel
- a channel that allows frequencies that are near zero to be transferred
- e.g BASEBAND
bits and bandwidth in baseband transmission
- bandwidth is proportional to the bit rate
- to send bits faster, we need more bandwidth
which type of signal does baseband transmit?
DIGITAL
which type of signal does bandpass transmit?
ANALOG (CONVERT DIGITAL 2 ANALOG)
two types of channels
- baseband
- bandpass
transmission process in a bandpass channel
- input digital signal
- convert to analog
- pass through the bandpass channel
- convert to digital
- digital signal output
three causes for transmission impairment
- distortion
- attenuation
- noise
what is attenuation
amplitude has decreased
how to try to fix attenuation
by amplification
problem with amplification
will increase noise (MORE JUNK)
what is distortion
sent signal differs from received signal
what is noise
- unwanted signal(s)
what is SNR
power of signal to power of noise ratio
SNR(dB)=
power of signal/power of noise
SNR (converting to dB)
10Log10(SNR)
what device converts analog and digital signals to the other
MODEM
MODULATOR & DEMODULATOR
