Transcript Power spectral density (PSD)… of ASK,PSK and FSK

Power spectral density (PSD)…
of ASK,PSK and FSK
• Note that the bandwidth of FSK is higher
than
ASK or PSK.
• Conclusion is that ;polar signaling is the
most efficient scheme from the point of
view of the noise immunity.
 The PSK, being polar, requires 3dB less
power than ASK or FSK for the same noise
immunity i.e. for the same error probability.
M-ary orthogonal pulses
 Fig.3.33 shows just one possible M-ary scheme
(multi-amplitude signaling).
 There are other possible ways to structure M
waveforms. For example we may use M
orthogonal pulses φ1(t), φ2(t), …, φM(t), with
the following property:-
  (t ) (t )dt  
T0
i
0
j
C i j
0 i j
M-ary orthogonal pulses
Fig.3.34 shows one possible set of M orthogonal
signals
M-ary orthogonal pulses…
• Cross correlation between any two rows
is zero for e.g.. Hadamard matrix 4x4:•
1 1 1 1
•
1 -1 1 -1
•
1 1 -1 -1
•
1 -1 -1 1
More on quantization
• Block diagram of formatting and transmission
of baseband signals Fig.2.2.
More on quantization…
More on quantization…
• The ordinate in fig.2.16 is labeled with
quantization levels and their code numbers.
• Each sample of the analog signal is assigned to
the quantization level closest to the value of
sample.
• Beneath the analog waveform x(t) are seen
four representations of x(t) as follows:• The natural sample values, quantized sample
values, the code numbers and the PCM
sequence.
More on quantization…
More on quantization…
• Suppose that analog signal is a musical, which
is sample at a Nyquist rate (fs ≥ 2fm).
• Also suppose that when we listen to the music
in digital form, it’s quality is not good.
• What could we do to improve the fidelity?
• We know that process of quantization
replaces the true signal with an approximation
(i.e., adds quantization noise). Thus increasing
the number of levels will reduce the
quantization noise.
More on quantization…
• Now, each sample will be represented by 4bits, consequently we would have high data
rates, improved signal quality or fidelity.
• In real time communication message must not
be delayed, and bits must move faster.
• This is how one can generally obtain better
fidelity at the cost of more transmission
bandwidth
• Next Fig.2.18 compares the quantization of a
strong versus a weak signal for uniform and
More on quantization…