1.8 Analogue Modulation Techniques - Digital Data Flashcards
Describe Amplitude Shift Keying (OOK). What is the advantage and disadvantage?
(transmission of digital signal)
Transmit when 1, do not transmit when 0.
Saves power when transmitting a 0 but there is difficulty knowing if there has been loss of signal or it has transmitted a 0.
Describe Amplitude Shift Keying (Multi-Level). What is the advantage and disadvantage?
(transmission of digital signal)
Removes ambiguity by transmitting a small signal when 0.
Takes more power but there is less ambiguity when sending a 0.
How does the frequency of the ASK compare to AM?
Requires 2f_0, which is comparable to AM. WHy? Who knows.
What is ASK?
(transmission of digital signal)
Transmit a digital input using amplitude modulation. The signal switches amplitude in discrete amounts (1’s and 0’s.)
What is FSK?
(transmission of digital signal)
Frequency Shift Keying sends digital inputs through frequency modulation between discrete values.
How does FSK bandwidth compare to ASK?
Requires more bandwidth (to cover more frequencies).
What is the minimum bandwidth of FSK and why?
4f_b because two frequencies are used so it is considered as two independant signals.
Describe Continuous Phase FSK
(transmission of digital signal)
A type of FSK where the phase is constant.
Describe Phase Shit Keying
(transmission of digital signal)
The phase is changed as the digital input varies between 1 and 0.
Only a single frequency is used.
What is the bandwidth requirement of Phase Shift Keying?
Same as ASK, 2*f
Same because phase is changed at clock intervals so the frequency stays the same the whole time.
For phase modulation, it shifts continuously which would change the frequency in tandem.
Describe Quadrature Phase Shift Keying
(transmission of digital signal)
Similar to PSK except 4 values of phase are used and spaced 90 degrees apart. Each phase represents 2 bits of data.
This allows more efficient use of bandwidth.
Describe M-ary Modulation
(transmission of digital signal)
Uses symbols to represent multiplebits. This saves bandwidth and imporves bit rates.
Can use any method to modulate the signal.
What is an advantage of PSK over ASK?
Greater resistance to noise.
What is the advantage of ASK over FSK?
Smaller bandwidth, cheaper equipment.
How is data recovered in DPSK?
An XNOR gate is used to combine current bit and previous bit to recover the data.
