Wavelength is a characteristic of signals that depends on both the signal's frequency and the transmission medium. Wavelength is the distance a signal can travel in one period. It is normally measured in micrometers. There are two main approaches to transmitting digital signals: baseband transmission, which sends the digital signal directly over the channel without changing it to analog, and broadband transmission, which uses modulation. Baseband transmission requires a dedicated channel with bandwidth starting from zero Hertz. The bandwidth needed is proportional to the bit rate - higher bit rates require more bandwidth.

1. 3.1
Lecture 3_Part 2
Data and Signal Transmission
Computer Networks I and Data Transmission
Assist. Prof. Dr. Salah Abdulghani
Computer Engineering Department
University of Mosul

2. Computer Networks I and Data Transmission
‫ﺍﻟﺒﻴﺎﻧﺎﺕ‬ ‫ﻭﻧﻘﻞ‬ 1 ‫ﺍﻟﻜﻤﺒﻴﻮﺗﺮ‬ ‫ﺷﺒﻜﺎﺕ‬
Lecture 3_Part 2
2 ‫ﺍﻟﺠﺰﺀ‬ _3 ‫ﺍﻟﻤﺤﺎﺿﺮﺓ‬
Data and Signal Transmission
‫ﻭﺍﻹﺷﺎﺭﺍﺕ‬ ‫ﺍﻟﺒﻴﺎﻧﺎﺕ‬ ‫ﻧﻘﻞ‬
Assist. Prof. Dr. Salah Abdulghani
‫ﺍﻟﻐﻨﻲ‬ ‫ﻋﺒﺪ‬ ‫ﺧﺎﻃﺊ‬ .‫ﺩﻛﺘﻮﺭ‬ .‫ﺃ‬ .‫ﻳﺴﺎﻋﺪ‬
Computer Engineering Department
‫ﺍﻟﺤﺎﺳﺒﺎﺕ‬ ‫ﻫﻨﺪﺳﺔ‬ ‫ﻗﺴﻢ‬
University of Mosul
‫ﺍﻟﻤﻮﺻﻞ‬ ‫ﺟﺎﻣﻌﺔ‬
3.1
١.‫ﻉ‬

3. Wavelength
Wavelength is another characteristic of a signal traveling through a transmission
medium. Wavelength binds the period or the frequency of a simple sine wave to
the propagation speed of the medium

4. Wavelength
‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬
Wavelength is another characteristic of a signal traveling through a transmission
‫ﺍﻹﺭﺳﺎﻝ‬ ‫ﻋﺒﺮ‬ ‫ﺗﻨﺘﻘﻞ‬ ‫ﺍﻟﺘﻲ‬ ‫ﻟﻺﺷﺎﺭﺓ‬ ‫ﺃﺧﺮﻯ‬ ‫ﺧﺎﺻﻴﺔ‬ ‫ﻫﻮ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬
medium. Wavelength binds the period or the frequency of a simple sine wave to
‫ﺑﺴﻴﻄﺔ‬ ‫ﺟﻴﺒﻴﺔ‬ ‫ﻟﻤﻮﺟﺔ‬ ‫ﺍﻟﺘﺮﺩﺩ‬ ‫ﺃﻭ‬ ‫ﺍﻟﻔﺘﺮﺓ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ ‫ﻳﺮﺑﻂ‬ .‫ﻣﺘﻮﺳﻂ‬
the propagation speed of the medium
‫ﺍﻟﻮﺳﻂ‬ ‫ﺍﻧﺘﺸﺎﺭ‬ ‫ﺳﺮﻋﺔ‬

5. While the frequency of a signal is independent of the medium, the
wavelength depends on both the frequency and the medium.
Wavelength is a property of any type of signal. In data
communications, we often use wavelength to describe the
transmission of light in an optical fiber. The wavelength is the
distance a simple signal can travel in one period.
The wavelength is normally measured in micrometers (microns)
instead of meters. For example, the wavelength of red light
(frequency = 4 × 1014) in air is

6. While the frequency of a signal is independent of the medium, the
‫ﻓﺈﻥ‬ ، ‫ﺍﻟﻮﺳﻴﻂ‬ ‫ﻋﻦ‬ ‫ﻣﺴﺘﻘﻼ‬ ‫ﺍﻹﺷﺎﺭﺓ‬ ‫ﺗﺮﺩﺩ‬ ‫ﻳﻜﻮﻥ‬ ‫ﺑﻴﻨﻤﺎ‬
wavelength depends on both the frequency and the medium.
.‫ﻭﺍﻟﻮﺳﻴﻂ‬ ‫ﺍﻟﺘﺮﺩﺩ‬ ‫ﻣﻦ‬ ‫ﻛﻞ‬ ‫ﻋﻠﻰ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ ‫ﻳﻌﺘﻤﺪ‬
Wavelength is a property of any type of signal. In data
‫ﺍﻟﺒﻴﺎﻧﺎﺕ‬ ‫ﻓﻲ‬ .‫ﺍﻹﺷﺎﺭﺍﺕ‬ ‫ﻣﻦ‬ ‫ﻧﻮﻉ‬ ‫ﻷﻱ‬ ‫ﺧﺎﺻﻴﺔ‬ ‫ﻫﻮ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬
communications, we often use wavelength to describe the
‫ﻟﻮﺻﻒ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ ‫ﻧﺴﺘﺨﺪﻡ‬ ‫ﻣﺎ‬ ‫ﻏﺎﻟﺒﺎ‬ ، ‫ﺍﻻﺗﺼﺎﻻﺕ‬
transmission of light in an optical fiber. The wavelength is the
‫ﻫﻮ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ .‫ﺍﻟﻀﻮﺋﻴﺔ‬ ‫ﺍﻷﻟﻴﺎﻑ‬ ‫ﻓﻲ‬ ‫ﺍﻟﻀﻮﺀ‬ ‫ﺍﻧﺘﻘﺎﻝ‬
distance a simple signal can travel in one period.
.‫ﻭﺍﺣﺪﺓ‬ ‫ﻓﺘﺮﺓ‬ ‫ﻓﻲ‬ ‫ﺑﺴﻴﻄﺔ‬ ‫ﺇﺷﺎﺭﺓ‬ ‫ﺗﻘﻄﻌﻬﺎ‬ ‫ﺃﻥ‬ ‫ﻳﻤﻜﻦ‬ ‫ﺍﻟﺘﻲ‬ ‫ﺍﻟﻤﺴﺎﻓﺔ‬
The wavelength is normally measured in micrometers (microns)
(‫)ﻣﻴﻜﺮﻭﻥ‬ ‫ﺑﺎﻟﻤﻴﻜﺮﻭﻣﺘﺮ‬ ‫ﻋﺎﺩﺓ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ ‫ﻳﻘﺎﺱ‬
instead of meters. For example, the wavelength of red light
‫ﺍﻷﺣﻤﺮ‬ ‫ﻟﻠﻀﻮﺀ‬ ‫ﺍﻟﻤﻮﺟﻲ‬ ‫ﺍﻟﻄﻮﻝ‬ ، ‫ﺍﻟﻤﺜﺎﻝ‬ ‫ﺳﺒﻴﻞ‬ ‫ﻋﻠﻰ‬ .‫ﺍﻷﻣﺘﺎﺭ‬ ‫ﻣﻦ‬ ‫ﺑﺪﻻ‬
(frequency = 4 × 1014) in air is
‫ﻫﻮ‬ ‫ﺍﻟﻬﻮﺍﺀ‬ ‫ﻓﻲ‬ (1014 × 4 = ‫)ﺍﻟﺘﺮﺩﺩ‬

11. Transmission of Digital Signals
The fundamental question is, How can we send a digital
signal from point A to point B? We can transmit a digital
signal by using one of two different approaches:
baseband transmission or broadband transmission (using
modulation).
Baseband Transmission means sending a digital signal over
a channel without changing the digital signal to an analog
signal.

12. Transmission of Digital Signals
‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺍﺕ‬ ‫ﻧﻘﻞ‬
The fundamental question is, How can we send a digital
‫ﺭﻗﻤﻲ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻳﻤﻜﻨﻨﺎ‬ ‫ﻛﻴﻒ‬ ، ‫ﻫﻮ‬ ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﺴﺆﺍﻝ‬
signal from point A to point B? We can transmit a digital
‫ﺭﻗﻤﻲ‬ ‫ﻧﻘﻞ‬ ‫ﻳﻤﻜﻨﻨﺎ‬ ‫ﺏ؟‬ ‫ﺍﻟﻨﻘﻄﺔ‬ ‫ﺇﻟﻰ‬ ‫ﺃ‬ ‫ﺍﻟﻨﻘﻄﺔ‬ ‫ﻣﻦ‬ ‫ﺇﺷﺎﺭﺓ‬
signal by using one of two different approaches:
:‫ﻣﺨﺘﻠﻔﺘﻴﻦ‬ ‫ﻃﺮﻳﻘﺘﻴﻦ‬ ‫ﺃﺣﺪ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻹﺷﺎﺭﺓ‬
baseband transmission or broadband transmission (using
‫)ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻭﺍﺳﻊ‬ ‫ﺍﻹﺭﺳﺎﻝ‬ ‫ﺃﻭ‬ ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺇﺭﺳﺎﻝ‬
modulation).
.(‫ﺗﻌﺪﻳﻞ‬
Baseband Transmission means sending a digital signal over
‫ﻋﺒﺮ‬ ‫ﺭﻗﻤﻴﺔ‬ ‫ﺇﺷﺎﺭﺓ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻧﻘﻞ‬ ‫ﻳﻌﻨﻲ‬
a channel without changing the digital signal to an analog
‫ﺍﻟﺘﻨﺎﻇﺮﻳﺔ‬ ‫ﺇﻟﻰ‬ ‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬ ‫ﺗﻐﻴﻴﺮ‬ ‫ﺩﻭﻥ‬ ‫ﻗﻨﺎﺓ‬
signal.
.‫ﺍﻹﺷﺎﺭﺓ‬

13. Baseband transmission requires that we have a low-pass
channel, a channel with a bandwidth that starts from zero.
This is the case if we have a dedicated medium with a
bandwidth constituting only one channel. For example, the
entire bandwidth of a cable connecting two computers is
one single channel.
In baseband transmission, the required bandwidth is
proportional to the bit rate; if we need to send bits
faster, we need more bandwidth.

14. Baseband transmission requires that we have a low-pass
‫ﻣﻨﺨﻔﺾ‬ ‫ﺗﻤﺮﻳﺮ‬ ‫ﻟﺪﻳﻨﺎ‬ ‫ﻳﻜﻮﻥ‬ ‫ﺃﻥ‬ ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺍﻧﺘﻘﺎﻝ‬ ‫ﻳﺘﻄﻠﺐ‬
channel, a channel with a bandwidth that starts from zero.
.‫ﺍﻟﺼﻔﺮ‬ ‫ﻣﻦ‬ ‫ﻳﺒﺪﺃ‬ ‫ﻧﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﺫﺍﺕ‬ ‫ﻗﻨﺎﺓ‬ ، ‫ﻗﻨﺎﺓ‬
This is the case if we have a dedicated medium with a
‫ﺑﺎﻣﺘﺪﺍﺩ‬ ‫ﻣﺨﺼﺺ‬ ‫ﻭﺳﻴﻂ‬ ‫ﻟﺪﻳﻨﺎ‬ ‫ﻛﺎﻥ‬ ‫ﺇﺫﺍ‬ ‫ﺍﻟﺤﺎﻝ‬ ‫ﻫﻮ‬ ‫ﻫﺬﺍ‬
bandwidth constituting only one channel. For example, the
‫ﻣﻠﻒ‬ ، ‫ﺍﻟﻤﺜﺎﻝ‬ ‫ﺳﺒﻴﻞ‬ ‫ﻋﻠﻰ‬ .‫ﻓﻘﻂ‬ ‫ﻭﺍﺣﺪﺓ‬ ‫ﻗﻨﺎﺓ‬ ‫ﻳﺸﻜﻞ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬
entire bandwidth of a cable connecting two computers is
‫ﻫﻮ‬ ‫ﻛﻤﺒﻴﻮﺗﺮ‬ ‫ﺟﻬﺎﺯﻱ‬ ‫ﺑﻴﻦ‬ ‫ﻳﺮﺑﻂ‬ ‫ﺍﻟﺬﻱ‬ ‫ﻟﻠﻜﺎﺑﻞ‬ ‫ﺍﻟﻜﺎﻣﻞ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬
one single channel.
.‫ﻭﺍﺣﺪﺓ‬ ‫ﻗﻨﺎﺓ‬
In baseband transmission, the required bandwidth is
‫ﺍﻟﻤﻄﻠﻮﺏ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﻳﻜﻮﻥ‬ ، ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻓﻲ‬
proportional to the bit rate; if we need to send bits
‫ﺑﺖ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﺇﻟﻰ‬ ‫ﺑﺤﺎﺟﺔ‬ ‫ﻛﻨﺎ‬ ‫ﺇﺫﺍ‬ ‫؛‬ ‫ﺍﻟﺒﺘﺎﺕ‬ ‫ﻣﻌﺪﻝ‬ ‫ﻣﻊ‬ ‫ﻳﺘﻨﺎﺳﺐ‬
faster, we need more bandwidth.
.‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﻦ‬ ‫ﻣﺰﻳﺪ‬ ‫ﺇﻟﻰ‬ ‫ﻧﺤﺘﺎﺝ‬ ، ‫ﺃﺳﺮﻉ‬ ‫ﺑﺸﻜﻞ‬

15. Solution
The answer depends on the accuracy desired.
a. The minimum bandwidth, a rough approximation, is
B = bit rate /2, or 500 kHz. We need a low-pass channel with
frequencies between 0 and 500 kHz.
b. A better result can be achieved by using the first and the third
harmonics with the required bandwidth B = 3 × 500 kHz = 1.5 MHz.
c. A still better result can be achieved by using the first, third, and
fifth harmonics with B = 5 × 500 kHz = 2.5 MHz.
Example 3.22
What is the required bandwidth of a low-pass channel if
we need to send 1 Mbps by using baseband transmission?

16. Example 3.22
3.22 ‫ﺍﻟﻤﺜﺎﻝ‬
What is the required bandwidth of a low-pass channel if
‫ﺇﺫﺍ‬ ‫ﻣﻨﺨﻔﺾ‬ ‫ﺗﻤﺮﻳﺮ‬ ‫ﻟﻘﻨﺎﺓ‬ ‫ﺍﻟﻤﻄﻠﻮﺏ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﻫﻮ‬ ‫ﻣﺎ‬
we need to send 1 Mbps by using baseband transmission?
‫ﺍﻷﺳﺎﺳﻲ؟‬ ‫ﺍﻹﺭﺳﺎﻝ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻟﺜﺎﻧﻴﺔ‬ ‫ﻓﻲ‬ ‫ﻣﻴﺠﺎﺑﺖ‬ 1 ‫ﺇﺭﺳﺎﻝ‬ ‫ﺇﻟﻰ‬ ‫ﻧﺤﺘﺎﺝ‬
Solution
‫ﺍﻟﻤﺤﻠﻮﻝ‬
The answer depends on the accuracy desired.
.‫ﺍﻟﻤﻄﻠﻮﺑﺔ‬ ‫ﺍﻟﺪﻗﺔ‬ ‫ﻋﻠﻰ‬ ‫ﻳﻌﺘﻤﺪ‬ ‫ﺍﻟﺠﻮﺍﺏ‬
a.
.‫ﺃ‬
The minimum bandwidth, a rough approximation, is
‫ﺗﻘﺮﻳﺒﻲ‬ ‫ﺗﻘﺮﻳﺐ‬ ‫ﻭﻫﻮ‬ ، ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻟﻌﺮﺽ‬ ‫ﺍﻷﺩﻧﻰ‬ ‫ﺍﻟﺤﺪ‬
B = bit rate /2, or 500 kHz. We need a low-pass channel with
B = ‫ﻣﻊ‬ ‫ﻣﻨﺨﻔﻀﺔ‬ ‫ﺗﻤﺮﻳﺮ‬ ‫ﻗﻨﺎﺓ‬ ‫ﺇﻟﻰ‬ ‫ﺑﺤﺎﺟﺔ‬ ‫ﻧﺤﻦ‬ .‫ﻫﺮﺗﺰ‬ ‫ﻛﻴﻠﻮ‬ 500 ‫ﺃﻭ‬ ، 2 / ‫ﺍﻟﺒﺖ‬ ‫ﻣﻌﺪﻝ‬
frequencies between 0 and 500 kHz.
.‫ﻫﺮﺗﺰ‬ ‫ﻛﻴﻠﻮ‬ 500 ‫ﻭ‬ 0 ‫ﺑﻴﻦ‬ ‫ﺗﺮﺩﺩﺍﺕ‬
b.
.‫ﺏ‬
A better result can be achieved by using the first and the third
‫ﻭﺍﻟﺜﺎﻟﺚ‬ ‫ﺍﻷﻭﻝ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺃﻓﻀﻞ‬ ‫ﻧﺘﻴﺠﺔ‬ ‫ﺗﺤﻘﻴﻖ‬ ‫ﻳﻤﻜﻦ‬
harmonics with the required bandwidth B = 3 × 500 kHz = 1.5 MHz.
.‫ﻫﺮﺗﺰ‬ ‫ﻣﻴﺠﺎ‬ 1.5 = ‫ﻫﺮﺗﺰ‬ ‫ﻛﻴﻠﻮ‬ B = 3 × 500 ‫ﺍﻟﻤﻄﻠﻮﺏ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﻣﻊ‬ ‫ﺍﻟﺘﻮﺍﻓﻘﻴﺎﺕ‬
c.
.‫ﺝ‬
A still better result can be achieved by using the first, third, and
‫ﻭ‬ ‫ﻭﺍﻟﺜﺎﻟﺚ‬ ‫ﺍﻷﻭﻝ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺃﻓﻀﻞ‬ ‫ﻧﺘﻴﺠﺔ‬ ‫ﺗﺤﻘﻴﻖ‬ ‫ﻳﻤﻜﻦ‬
fifth harmonics with B = 5 × 500 kHz = 2.5 MHz.
.‫ﻫﺮﺗﺰ‬ ‫ﻣﻴﺠﺎ‬ 2.5 = ‫ﻫﺮﺗﺰ‬ ‫ﻛﻴﻠﻮ‬ B = 5 × 500 ‫ﻣﻊ‬ ‫ﺍﻟﺨﺎﻣﺴﺔ‬ ‫ﺍﻟﺘﻮﺍﻓﻘﻴﺎﺕ‬

17. 3.9
Figure 3.19 Bandwidths of two low-pass channels

18. Figure 3.19
3.19 ‫ﺍﻟﺸﻜﻞ‬
Bandwidths of two low-pass channels
‫ﺍﻟﺘﻤﺮﻳﺮ‬ ‫ﻣﻨﺨﻔﻀﺘﻲ‬ ‫ﻟﻘﻨﺎﺗﻴﻦ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬
3.9
‫ﺹ‬.‫ﻉ‬

19. 3.10
Figure 3.20 Baseband transmission using a dedicated medium
if we have a medium, such as a coaxial or fiber optic cable,
with a very wide bandwidth, two stations can communicate by
using digital signals with very good accuracy, as shown in
Figure 3.21. Note that f1 is close to zero, and f2 is very high.

20. Figure 3.20
3.20 ‫ﺍﻟﺸﻜﻞ‬
Baseband transmission using a dedicated medium
‫ﻣﺨﺼﺺ‬ ‫ﻭﺳﻴﻂ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻧﻘﻞ‬
if we have a medium, such as a coaxial or fiber optic cable,
، ‫ﺑﺼﺮﻳﺔ‬ ‫ﺃﻟﻴﺎﻑ‬ ‫ﻛﺎﺑﻞ‬ ‫ﺃﻭ‬ ‫ﺍﻟﻤﺤﻮﺭ‬ ‫ﻣﺘﺤﺪ‬ ‫ﻛﺒﻞ‬ ‫ﻣﺜﻞ‬ ، ‫ﻭﺳﻴﻂ‬ ‫ﻟﺪﻳﻨﺎ‬ ‫ﻛﺎﻥ‬ ‫ﺇﺫﺍ‬
with a very wide bandwidth, two stations can communicate by
‫ﻃﺮﻳﻖ‬ ‫ﻋﻦ‬ ‫ﺍﻟﺘﻮﺍﺻﻞ‬ ‫ﻟﻤﺤﻄﺘﻴﻦ‬ ‫ﻳﻤﻜﻦ‬ ، ‫ﻟﻠﻐﺎﻳﺔ‬ ‫ﻋﺮﻳﺾ‬ ‫ﺗﺮﺩﺩﻱ‬ ‫ﻧﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﻣﻊ‬
using digital signals with very good accuracy, as shown in
‫ﻓﻲ‬ ‫ﻣﻮﺿﺢ‬ ‫ﻫﻮ‬ ‫ﻛﻤﺎ‬ ‫ﺟﺪﺍ‬ ‫ﺟﻴﺪﺓ‬ ‫ﺑﺪﻗﺔ‬ ‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺍﺕ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬
Figure 3.21. Note that f1 is close to zero, and f2 is very high.
.‫ﺟﺪﺍ‬ ‫ﻣﺮﺗﻔﻊ‬ f2 ‫ﻭ‬ ، ‫ﺍﻟﺼﻔﺮ‬ ‫ﻣﻦ‬ ‫ﻗﺮﻳﺐ‬ f1 ‫ﺃﻥ‬ ‫ﻻﺣﻆ‬ .3.21 ‫ﺍﻟﺸﻜﻞ‬
3.10
١٠.‫ﻉ‬

21. 3.11
In baseband transmission, the required bandwidth is
proportional to the bit rate; if we need to send bits faster,
we need more bandwidth.
Table 3.2 shows how much bandwidth we need to send data
at different rates.
Table 3.2 Bandwidth requirements

22. In baseband transmission, the required bandwidth is
‫ﺍﻟﻤﻄﻠﻮﺏ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﻳﻜﻮﻥ‬ ، ‫ﺍﻷﺳﺎﺳﻲ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻓﻲ‬
proportional to the bit rate; if we need to send bits faster,
، ‫ﺃﺳﺮﻉ‬ ‫ﺑﺸﻜﻞ‬ ‫ﺍﻟﺒﺖ‬ ‫ﻭﺣﺪﺍﺕ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﺇﻟﻰ‬ ‫ﺍﺣﺘﺠﻨﺎ‬ ‫ﺇﺫﺍ‬ ‫؛‬ ‫ﺍﻟﺒﺘﺎﺕ‬ ‫ﻣﻌﺪﻝ‬ ‫ﻣﻊ‬ ‫ﻳﺘﻨﺎﺳﺐ‬
we need more bandwidth.
.‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﻦ‬ ‫ﻣﺰﻳﺪ‬ ‫ﺇﻟﻰ‬ ‫ﺑﺤﺎﺟﺔ‬ ‫ﻧﺤﻦ‬
Table 3.2 shows how much bandwidth we need to send data
‫ﺍﻟﺒﻴﺎﻧﺎﺕ‬ ‫ﻹﺭﺳﺎﻝ‬ ‫ﻧﺤﺘﺎﺟﻪ‬ ‫ﺍﻟﺬﻱ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﻘﺪﺍﺭ‬ 3.2 ‫ﺍﻟﺠﺪﻭﻝ‬ ‫ﻳﻮﺿﺢ‬
at different rates.
.‫ﻣﺨﺘﻠﻔﺔ‬ ‫ﺑﻤﻌﺪﻻﺕ‬
Table 3.2
3.2 ‫ﺍﻟﺠﺪﻭﻝ‬
Bandwidth requirements
‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﺘﻄﻠﺒﺎﺕ‬
3.11
١١.‫ﻉ‬

23. 3.12
We have a low-pass channel with bandwidth 100 kHz.
What is the maximum bit rate of this
channel?
Solution
The maximum bit rate can be achieved if we use the first
harmonic. The bit rate is 2 times the available bandwidth,
or 200 kbps.
Example 3.22

24. Example 3.22
3.22 ‫ﺍﻟﻤﺜﺎﻝ‬
We have a low-pass channel with bandwidth 100 kHz.
.‫ﻫﺮﺗﺰ‬ ‫ﻛﻴﻠﻮ‬ 100 ‫ﺗﺮﺩﺩﻱ‬ ‫ﻧﻄﺎﻕ‬ ‫ﺑﻌﺮﺽ‬ ‫ﻣﻨﺨﻔﻀﺔ‬ ‫ﺗﻤﺮﻳﺮﺓ‬ ‫ﻗﻨﺎﺓ‬ ‫ﻟﺪﻳﻨﺎ‬
What is the maximum bit rate of this
‫ﻟﻬﺬﺍ‬ ‫ﺑﺖ‬ ‫ﻣﻌﺪﻝ‬ ‫ﺃﻗﺼﻰ‬ ‫ﻫﻮ‬ ‫ﻣﺎ‬
channel?
‫ﻗﻨﺎﺓ؟‬
Solution
‫ﺍﻟﻤﺤﻠﻮﻝ‬
The maximum bit rate can be achieved if we use the first
‫ﺍﻷﻭﻝ‬ ‫ﺍﺳﺘﺨﺪﻣﻨﺎ‬ ‫ﺇﺫﺍ‬ ‫ﺑﺖ‬ ‫ﻣﻌﺪﻝ‬ ‫ﺃﻗﺼﻰ‬ ‫ﺗﺤﻘﻴﻖ‬ ‫ﻳﻤﻜﻦ‬
harmonic. The bit rate is 2 times the available bandwidth,
، ‫ﺍﻟﻤﺘﺎﺡ‬ ‫ﺍﻟﺘﺮﺩﺩﻱ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻋﺮﺽ‬ ‫ﺿﻌﻒ‬ ‫ﻫﻮ‬ ‫ﺍﻟﺒﺖ‬ ‫ﻣﻌﺪﻝ‬ .‫ﻣﺘﻨﺎﺳﻖ‬
or 200 kbps.
.‫ﺍﻟﺜﺎﻧﻴﺔ‬ ‫ﻓﻲ‬ ‫ﻛﻴﻠﻮﺑﺖ‬ 200 ‫ﺃﻭ‬
3.12
١٢.‫ﻉ‬

25. Broadband Transmission (Using Modulation)
Broadband transmission or modulation means changing
the digital signal to an analog signal for transmission.
Modulation allows us to use a bandpass channel—a
channel with a bandwidth that does not start from zero.
This type of channel is more available than a low-pass
channel
Note that a low-pass channel can be considered a bandpass channel
with the lower frequency starting at zero.

26. Broadband Transmission (Using Modulation)
(‫ﺍﻟﺘﻌﺪﻳﻞ‬ ‫)ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻟﻌﺮﻳﺾ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺇﺭﺳﺎﻝ‬
Broadband transmission or modulation means changing
‫ﺍﻟﺘﻐﻴﻴﺮ‬ ‫ﻳﻌﻨﻲ‬ ‫ﺍﻟﻌﺮﻳﺾ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺗﻌﺪﻳﻞ‬ ‫ﺃﻭ‬ ‫ﻧﻘﻞ‬
the digital signal to an analog signal for transmission.
.‫ﻟﻺﺭﺳﺎﻝ‬ ‫ﺗﻨﺎﻇﺮﻳﺔ‬ ‫ﺇﺷﺎﺭﺓ‬ ‫ﺇﻟﻰ‬ ‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬
Modulation allows us to use a bandpass channel—a
‫ﺃ‬ — ‫ﻧﻄﺎﻕ‬ ‫ﻣﻤﺮ‬ ‫ﻗﻨﺎﺓ‬ ‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻟﺘﻌﺪﻳﻞ‬ ‫ﻟﻨﺎ‬ ‫ﻳﺴﻤﺢ‬
channel with a bandwidth that does not start from zero.
.‫ﺍﻟﺼﻔﺮ‬ ‫ﻣﻦ‬ ‫ﻳﺒﺪﺃ‬ ‫ﻻ‬ ‫ﻧﻄﺎﻕ‬ ‫ﺑﻌﺮﺽ‬ ‫ﻗﻨﺎﺓ‬
This type of channel is more available than a low-pass
‫ﺍﻟﻤﻨﺨﻔﻀﺔ‬ ‫ﺍﻟﻘﻨﻮﺍﺕ‬ ‫ﻣﻦ‬ ‫ﺃﻛﺜﺮ‬ ‫ﻣﺘﺎﺡ‬ ‫ﺍﻟﻘﻨﻮﺍﺕ‬ ‫ﻣﻦ‬ ‫ﺍﻟﻨﻮﻉ‬ ‫ﻫﺬﺍ‬
channel
‫ﻗﻨﺎﺓ‬
Note that a low-pass channel can be considered a bandpass channel
‫ﻧﻄﺎﻕ‬ ‫ﻣﻤﺮ‬ ‫ﻗﻨﺎﺓ‬ ‫ﺍﻟﻤﻨﺨﻔﺾ‬ ‫ﺍﻟﺘﻤﺮﻳﺮ‬ ‫ﻗﻨﺎﺓ‬ ‫ﺍﻋﺘﺒﺎﺭ‬ ‫ﻳﻤﻜﻦ‬ ‫ﺃﻧﻪ‬ ‫ﻻﺣﻆ‬
with the lower frequency starting at zero.
.‫ﺍﻟﺼﻔﺮ‬ ‫ﻣﻦ‬ ‫ﻳﺒﺪﺃ‬ ‫ﺃﻗﻞ‬ ‫ﺑﺘﺮﺩﺩ‬

27. 3.14
Figure 3.24 Modulation of a digital signal for transmission on a bandpass
channel

28. Figure 3.24
3.24 ‫ﺍﻟﺸﻜﻞ‬
Modulation of a digital signal for transmission on a bandpass
‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﻤﺮ‬ ‫ﻋﻠﻰ‬ ‫ﻟﻺﺭﺳﺎﻝ‬ ‫ﺭﻗﻤﻴﺔ‬ ‫ﺇﺷﺎﺭﺓ‬ ‫ﺗﻌﺪﻳﻞ‬
channel
‫ﻗﻨﺎﺓ‬
3.14
١٤.‫ﻉ‬

29. 3.15
If the available channel is a bandpass
channel, we cannot send the digital signal
directly to the channel;
we need to convert the digital signal to an
analog signal before transmission.
Note

30. Note
‫ﻣﻠﺤﻮﻇﺔ‬
If the available channel is a bandpass
‫ﻧﻄﺎﻕ‬ ‫ﻣﻤﺮ‬ ‫ﻋﻦ‬ ‫ﻋﺒﺎﺭﺓ‬ ‫ﺍﻟﻤﺘﺎﺣﺔ‬ ‫ﺍﻟﻘﻨﺎﺓ‬ ‫ﻛﺎﻧﺖ‬ ‫ﺇﺫﺍ‬
channel, we cannot send the digital signal
‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻳﻤﻜﻨﻨﺎ‬ ‫ﻻ‬ ، ‫ﻗﻨﺎﺓ‬
directly to the channel;
‫؛‬ ‫ﺍﻟﻘﻨﺎﺓ‬ ‫ﺇﻟﻰ‬ ‫ﻣﺒﺎﺷﺮﺓ‬
we need to convert the digital signal to an
‫ﻣﻠﻒ‬ ‫ﺇﻟﻰ‬ ‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬ ‫ﺗﺤﻮﻳﻞ‬ ‫ﺇﻟﻰ‬ ‫ﻧﺤﺘﺎﺝ‬
analog signal before transmission.
.‫ﺍﻹﺭﺳﺎﻝ‬ ‫ﻗﺒﻞ‬ ‫ﺗﻨﺎﻇﺮﻳﺔ‬ ‫ﺇﺷﺎﺭﺓ‬
3.15
١٥.‫ﻉ‬

31. 3.16
An example of broadband transmission using
modulation is the sending of computer data through a
telephone subscriber line, the line connecting a resident
to the central telephone office. These lines are designed
to carry voice with a limited bandwidth. The channel is
considered a bandpass channel. We convert the digital
signal from the computer to an analog signal, and send
the analog signal. We can install two converters to
change the digital signal to analog and vice versa at the
receiving end. The converter, in this case, is called a
modem which we discuss in detail in Chapter 5.
Example 3.24

32. Example 3.24
3.24 ‫ﺍﻟﻤﺜﺎﻝ‬
An example of broadband transmission using
‫ﺑﺎﺳﺘﺨﺪﺍﻡ‬ ‫ﺍﻟﻌﺮﻳﺾ‬ ‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻋﻠﻰ‬ ‫ﻣﺜﺎﻝ‬
modulation is the sending of computer data through a
‫ﺃ‬ ‫ﺧﻼﻝ‬ ‫ﻣﻦ‬ ‫ﺍﻟﻜﻤﺒﻴﻮﺗﺮ‬ ‫ﺑﻴﺎﻧﺎﺕ‬ ‫ﺇﺭﺳﺎﻝ‬ ‫ﻫﻮ‬ ‫ﺍﻟﺘﻌﺪﻳﻞ‬
telephone subscriber line, the line connecting a resident
‫ﺍﻟﻤﻘﻴﻢ‬ ‫ﺑﻴﻦ‬ ‫ﻳﺮﺑﻂ‬ ‫ﺍﻟﺬﻱ‬ ‫ﺍﻟﺨﻂ‬ ، ‫ﺍﻟﻬﺎﺗﻒ‬ ‫ﻣﺸﺘﺮﻙ‬ ‫ﺧﻂ‬
to the central telephone office. These lines are designed
‫ﺍﻟﺨﻄﻮﻁ‬ ‫ﻫﺬﻩ‬ ‫ﺗﺼﻤﻴﻢ‬ ‫ﺗﻢ‬ .‫ﺍﻟﻤﺮﻛﺰﻱ‬ ‫ﺍﻟﻬﺎﺗﻒ‬ ‫ﻣﻜﺘﺐ‬ ‫ﺇﻟﻰ‬
to carry voice with a limited bandwidth. The channel is
‫ﺍﻟﻘﻨﺎﺓ‬ .‫ﻣﺤﺪﻭﺩ‬ ‫ﺗﺮﺩﺩﻱ‬ ‫ﺑﻨﻄﺎﻕ‬ ‫ﺍﻟﺼﻮﺕ‬ ‫ﻟﻨﻘﻞ‬
considered a bandpass channel. We convert the digital
‫ﺍﻟﺮﻗﻤﻲ‬ ‫ﺑﺘﺤﻮﻳﻞ‬ ‫ﻧﻘﻮﻡ‬ .‫ﺍﻟﻨﻄﺎﻕ‬ ‫ﻣﻤﺮ‬ ‫ﻗﻨﺎﺓ‬ ‫ﺗﻌﺘﺒﺮ‬
signal from the computer to an analog signal, and send
‫ﻭﺇﺭﺳﺎﻟﻬﺎ‬ ، ‫ﺗﻨﺎﻇﺮﻳﺔ‬ ‫ﺇﺷﺎﺭﺓ‬ ‫ﺇﻟﻰ‬ ‫ﺍﻟﻜﻤﺒﻴﻮﺗﺮ‬ ‫ﻣﻦ‬ ‫ﺇﺷﺎﺭﺓ‬
the analog signal. We can install two converters to
‫ﺇﻟﻰ‬ ‫ﻣﺤﻮﻟﻴﻦ‬ ‫ﺗﺜﺒﻴﺖ‬ ‫ﻳﻤﻜﻨﻨﺎ‬ .‫ﺍﻟﺘﻨﺎﻇﺮﻳﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬
change the digital signal to analog and vice versa at the
‫ﻓﻲ‬ ‫ﺑﺎﻟﻌﻜﺲ‬ ‫ﻭﺍﻟﻌﻜﺲ‬ ‫ﺍﻟﺘﻨﺎﻇﺮﻳﺔ‬ ‫ﺇﻟﻰ‬ ‫ﺍﻟﺮﻗﻤﻴﺔ‬ ‫ﺍﻹﺷﺎﺭﺓ‬ ‫ﺑﺘﻐﻴﻴﺮ‬ ‫ﻗﻢ‬
receiving end. The converter, in this case, is called a
‫ﻳﺴﻤﻰ‬ ، ‫ﺍﻟﺤﺎﻟﺔ‬ ‫ﻫﺬﻩ‬ ‫ﻓﻲ‬ ، ‫ﺍﻟﻤﺤﻮﻝ‬ .‫ﺍﻟﻨﻬﺎﻳﺔ‬ ‫ﺗﻠﻘﻲ‬
modem which we discuss in detail in Chapter 5.
.5 ‫ﺍﻟﻔﺼﻞ‬ ‫ﻓﻲ‬ ‫ﺑﺎﻟﺘﻔﺼﻴﻞ‬ ‫ﻧﻨﺎﻗﺸﻪ‬ ‫ﺍﻟﺬﻱ‬ ‫ﺍﻟﻤﻮﺩﻡ‬
3.16
١٦.‫ﻉ‬