(f) Given the sampling period & give an example of two different angular frequencies ₁,2 that will produce exactly the same samples at the sample times t=0,6,26,... (the two frequencies and w are called aliases of each other). (g) Building on the previous exercise, give necessary and sufficient conditions on the angular frequencies wy, such that the signals ac and art are equal at the sample times 0,6,26,.... (h) Given that is the sampling period and given an angular frequency w such that w<0, Give a formula for the smallest possible positive angular frequency w, that will give the same samples as w

Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
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Please do Exercise 3 part E-H and please show step by step and explain

In problems 3f,g,h, the series of samples for w1 and w2 should be equal TO EACH OTHER, but this doesn't mean that both series of samples have to be constant series. One example would be the case where the series of samples for w1 is 1,i,-1,-i,1,i,-1,-i, ... , and the series of samples for w2 is exactly the same.

Digital signals
Most modern communications systems are digital. "Digital" means that in some sense the signal is associ
ated with a discrete set of discrete values rather than a continuous range of values. So when the signal is
received it's not measured continuously, but rather it is sampled by taking signal values at fixed regular in-
tervals. The fixed interval between samples is called the sampling period, which we will denote by 8 (Greek
letter 'delta'). As specific example, the complex signal ael (here a is a complex number) sampled with
sampling period & beginning att - 0 gives the sequence of values: a, a, a,... In theory this is an
infinite sequence, but it can repeat so that it only assumes a finite number of different values.
Exercise 3.
(a) Give an example of a complex signal of the form act which, when sampled with sampling period
6 = 1, gives the values: 1, i, -1, -i,1, i, —1, -i... (the sequence repeats).
(b) Notice that in (a), the four values assumed by the signal are the four 4th roots of unity. Given that the
signal frequency is w, give a formula for a sample period & such that the sampled signal 1, 2,..
takes values equal to the 4th roots of unity.
(c) Now generalize your answer to (b) for the case of arbitrary nth roots of unity. Given that the signal
frequency is w, give a formula for & such that the sampled signal takes values equal to the nth roots of
unity (your formula will be in terms of " and w).
(d) Give the smallest possible sampling period & such that the complex wave exift/N sampled with period
& gives the N'th roots of unity. (Your formula for & will be in terms of f.)
(e) Given that the sampling period is equal to & and given that the sample when t=0 has value 1, find all
possible values for the angular frequency w such that the N+1th sample (when t = Nó) is also equal
to 1 (in other words, the signal repeats itself after N sample intervals).
(f) Given the sampling period & give an example of two different angular frequencies ₁,2 that will
produce exactly the same samples at the sample times t=0,8,25,... (the two frequencies w and w
are called aliases of each other).
(g) Building on the previous exercise, give necessary and sufficient conditions on the angular frequencies
wy, w such that the signals ae and aes are equal at the sample times 0,5, 25,....
(h) Given that is the sampling period and given an angular frequency w such that w<0, Give a formula
for the smallest possible positive angular frequency w, that will give the same samples as w.
0
The above exercise establishes the following facts:
• For certain combinations of sample period and angular frequency, the signal repeats;
• Given any integer N and sampling period 6, there are certain regularly-spaced angular frequencies
ww2....such that signals with these angular frequencies will repeat every N samples;
• Signals with different angular frequencies can result in the same samples. However, in such cases
there is always a smallest positive angular frequency that produces the given samples.
Transcribed Image Text:Digital signals Most modern communications systems are digital. "Digital" means that in some sense the signal is associ ated with a discrete set of discrete values rather than a continuous range of values. So when the signal is received it's not measured continuously, but rather it is sampled by taking signal values at fixed regular in- tervals. The fixed interval between samples is called the sampling period, which we will denote by 8 (Greek letter 'delta'). As specific example, the complex signal ael (here a is a complex number) sampled with sampling period & beginning att - 0 gives the sequence of values: a, a, a,... In theory this is an infinite sequence, but it can repeat so that it only assumes a finite number of different values. Exercise 3. (a) Give an example of a complex signal of the form act which, when sampled with sampling period 6 = 1, gives the values: 1, i, -1, -i,1, i, —1, -i... (the sequence repeats). (b) Notice that in (a), the four values assumed by the signal are the four 4th roots of unity. Given that the signal frequency is w, give a formula for a sample period & such that the sampled signal 1, 2,.. takes values equal to the 4th roots of unity. (c) Now generalize your answer to (b) for the case of arbitrary nth roots of unity. Given that the signal frequency is w, give a formula for & such that the sampled signal takes values equal to the nth roots of unity (your formula will be in terms of " and w). (d) Give the smallest possible sampling period & such that the complex wave exift/N sampled with period & gives the N'th roots of unity. (Your formula for & will be in terms of f.) (e) Given that the sampling period is equal to & and given that the sample when t=0 has value 1, find all possible values for the angular frequency w such that the N+1th sample (when t = Nó) is also equal to 1 (in other words, the signal repeats itself after N sample intervals). (f) Given the sampling period & give an example of two different angular frequencies ₁,2 that will produce exactly the same samples at the sample times t=0,8,25,... (the two frequencies w and w are called aliases of each other). (g) Building on the previous exercise, give necessary and sufficient conditions on the angular frequencies wy, w such that the signals ae and aes are equal at the sample times 0,5, 25,.... (h) Given that is the sampling period and given an angular frequency w such that w<0, Give a formula for the smallest possible positive angular frequency w, that will give the same samples as w. 0 The above exercise establishes the following facts: • For certain combinations of sample period and angular frequency, the signal repeats; • Given any integer N and sampling period 6, there are certain regularly-spaced angular frequencies ww2....such that signals with these angular frequencies will repeat every N samples; • Signals with different angular frequencies can result in the same samples. However, in such cases there is always a smallest positive angular frequency that produces the given samples.
O
Exercise 3
Xeiwt
Give an example of a complex signal of the form
which, when sampled with sampling period
8=1 gives the values: 1, 1,-1,-1,₁ 1,₁ 1,-1,-1.00 (repeat)
-As the complex signal xe , & € C sampled with sampling
int
2
period & beginning at t=0 gives the sequence of values
aixe ins
3iw
xe
• for 6=1; the sequence of valves is x, xe'w xe 2iw
0
2iwo
O
, xe
M
and it is equal to 1, 1,-1, -i , 1,... On comparing each term
we have α = 1 ⇒ x = 1
xeiwi eiw = 1 ⇒ cosw+isinw=1=w = 17/1/₂
Xe2iw=-1
= eiπ = -1
Biwi
x = 1₁
xe
and so on all the values holds
✓ W = 17/1/₂
w=
complex signal form is e
21(1/2)
31(π/2)
also e
and e
xetin
3iw
i(7/2₂) t
086
(b) Notice that in (a), the four values assumed by the signal
are the four roots of unity. Given that the signal frequency
is w, give a formula for a sample period & such that the sampled
Signal 1, eiws, e2/w8
4... takes values equal to the 4th roots
of unity
2iKT
(b) fourth root of unity is given by e ²14T where K=0₁1₁2₁3
for k=0 e º = 1
2ir/4 in/₂2
for k=1 e
Fe
4/4 im
for k=2, e
=
+
3ir/2
for k= 3, e
•• Comparing these values with the sequence in (a), we can
Say that the sampled signal, 1, eiws Liws
values equal to the 4th root of unity
O
=
cos (1/2) +isin (7/₂) = i
= COS (1T) + isin(TT) = -1
Cos (3/2) +isin (3/2) = - i
(C)
Now generalize your answer to b for the case of arbitrary
Inth roots of unity, Given that the signal frequency is w,
give
a formula for 8 such that the sampled signal takes
values equal to the nth roots of unity (your formula will
be in terms of n and up)
2TT
ws
⇒1/8 = 2πt w
12
1411/06/1
As we have seen that the sequence 1, eiws, eziws
land 1, e
eiblin
and they repeat are equal
On comparing 2nd term we get that w8 = 2π/²
"PT
2πi (n-1)
000, e
te
27/0
(d) Give the smallest possible sampling period of such that
sampled with period & gives the
the wave e
N
th roots of unity. (Your formula for & will be
in terms of f)
1
By part C, smallest possible period & is 8 = 1/ /f
(*.*
QHIPS 2ni
2kmi
N
N Nth root of unity e ² + ² ⇒ f S = 1 ⇒ 8 = 1/f)
Transcribed Image Text:O Exercise 3 Xeiwt Give an example of a complex signal of the form which, when sampled with sampling period 8=1 gives the values: 1, 1,-1,-1,₁ 1,₁ 1,-1,-1.00 (repeat) -As the complex signal xe , & € C sampled with sampling int 2 period & beginning at t=0 gives the sequence of values aixe ins 3iw xe • for 6=1; the sequence of valves is x, xe'w xe 2iw 0 2iwo O , xe M and it is equal to 1, 1,-1, -i , 1,... On comparing each term we have α = 1 ⇒ x = 1 xeiwi eiw = 1 ⇒ cosw+isinw=1=w = 17/1/₂ Xe2iw=-1 = eiπ = -1 Biwi x = 1₁ xe and so on all the values holds ✓ W = 17/1/₂ w= complex signal form is e 21(1/2) 31(π/2) also e and e xetin 3iw i(7/2₂) t 086 (b) Notice that in (a), the four values assumed by the signal are the four roots of unity. Given that the signal frequency is w, give a formula for a sample period & such that the sampled Signal 1, eiws, e2/w8 4... takes values equal to the 4th roots of unity 2iKT (b) fourth root of unity is given by e ²14T where K=0₁1₁2₁3 for k=0 e º = 1 2ir/4 in/₂2 for k=1 e Fe 4/4 im for k=2, e = + 3ir/2 for k= 3, e •• Comparing these values with the sequence in (a), we can Say that the sampled signal, 1, eiws Liws values equal to the 4th root of unity O = cos (1/2) +isin (7/₂) = i = COS (1T) + isin(TT) = -1 Cos (3/2) +isin (3/2) = - i (C) Now generalize your answer to b for the case of arbitrary Inth roots of unity, Given that the signal frequency is w, give a formula for 8 such that the sampled signal takes values equal to the nth roots of unity (your formula will be in terms of n and up) 2TT ws ⇒1/8 = 2πt w 12 1411/06/1 As we have seen that the sequence 1, eiws, eziws land 1, e eiblin and they repeat are equal On comparing 2nd term we get that w8 = 2π/² "PT 2πi (n-1) 000, e te 27/0 (d) Give the smallest possible sampling period of such that sampled with period & gives the the wave e N th roots of unity. (Your formula for & will be in terms of f) 1 By part C, smallest possible period & is 8 = 1/ /f (*.* QHIPS 2ni 2kmi N N Nth root of unity e ² + ² ⇒ f S = 1 ⇒ 8 = 1/f)
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