22 Practical MATLAB® Applications for Engineers
Phase shift keying (PSK) is a special case of PM signals, in which the phase of the
analog high-frequency carrier is varied in accordance with the information signal
that is digital in nature. PM and FM are commonly referred to as angle modulation
(for obvious reasons).R.1.62 AM is also referred as linear modulation. It is a modulation technique that is band-
width effi cient. The bandwidth requirements vary between BW and 2 BW, where BW
refers to the bandwidth of the information signal or message m(t).* It i s i neffi cient as far
as power is concerned and its performance is poor in the presence of noise (compared
with angle modulation FM or PM). AM is widely used in commercial broadcasting
systems such as radio and TV, and in point-to-point communication systems.
R.1.63 Angle modulation (FM or PM) is commonly referred to as nonlinear modulation,
and its most important characteristics are
High BW requirements
Good performance in the presence of noise
High fi delity
Angle modulation is used in commercial broadcasting such as radio and TV with a
superior quality of the reception of the information signal m(t), compared with AM.
R.1.64 The time domain representation of the analog modulation signals is presented as
follows:
a. AM signal = A m(t) cos(wct)
b. FM signal cos w t[]cF2 k
Amkdkt
∫ ()c. PM signal = A cos[wct + 2 πkPm(t)]where wc denotes the high-frequency carrier, m(t) refers to the information or mes-
sage signal, A represents the carrier amplitude, and kP and kF are constants that
represent deviations.
R.1.65 Signals or sequences can be left- or right-sided.
a. A right-sided or causal sequence (or signal)† is defi ned by ƒ(n) = 0, for n < 0.
b. A left-sided or noncausal sequence (or signal) is defi ned by ƒ(n) = 0, for n > 0.
c. A two-sided sequence (or signal) is defi ned for all n (−∞ < n < +∞).R.1.66 A symmetric or even function (or sequence) is defi ned by
ƒ(t) = ƒ(−t) (a nalog case)
and
ƒ(n) = ƒ(−n) (discrete case)
R.1.67 An asymmetric or odd function (or sequence) is defi ned by the following relations:
ƒ(t) = −ƒ(−t) (analog case)
and
ƒ(n) = −ƒ(−n) (discrete case)
*^ For a formal defi nition of BW see Chapter 4. At this point, it is suffi cient for the reader to associate BW with
the signal quality.
† For the case of continuous signals just replace n by t.