Transcript Chapter 9. Analog Signals 第九章 類比訊號 亞洲大學 資訊工程學系碩士班

Chapter 9. Analog Signals
第九章 類比訊號
亞洲大學
資訊工程學系碩士班
呂克明教授
二○○六年十二月四日
5/25/2016
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Chapter 9. Analog Signals
(第九章 類比訊號)
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Introduction (緒言)
The Telephone Channel (電話頻道)
Single-Sideband Telephony (單旁帶話音技術)
FDM Telephony (頻分多工話音技術)
Color Television (彩色電視)
Homework Problems (習題)
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Introduction
(緒言)
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Analog signals are electrical replicas of the original signals such as
audio and video.
Base band signals are those signals which occupy the lowest, or
base, band of frequencies, in the frequency spectrum used by the
telecommunication network.
A base band (基頻) signal may consist of one or more information
signals.
Frequency-division multiplexing (頻分多工): For example, a number
of analog telephony signals may be combined into one base band
signal by the process known as frequency-division multiplexing.
Modulation (調變): In forming the multiplexed base band signals, the
information signals are modulated onto sub-carriers.
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The Telephone Channel
(電話頻道)
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Natural speech (自然的語言聲音) covers a frequency range of about
80 to 8000 Hz.
Telephone quality (話音質量): The range of 300 to 3400 Hz is
accepted internationally as the standard for telephony quality
speech, and this is termed the speech base band.
The telephone channel is often referred to as a voice frequency (VF)
channel.
In China #1 telephony signaling (中國一號訊令), a special in band
frequency of 2300 Hz is used as a control signal.
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Single-Sideband Telephony
(單旁帶話音技術)
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When the telephone signal is multiplied in the time domain with a
sinusoidal carrier of frequency Fc, a new spectrum results, in which
the original base band appears on either side of the carrier
frequency.
Double-Sideband: The band of frequency below the carrier as the
lower sideband. The band of frequency above the carrier as the
upper sideband.
To avoid distortion which would occur with sideband overlap, the
carrier frequency must be greater than the highest frequency in the
base band.
A filter may be used to select either one and reject the other. The
resulting output is termed a single-sideband (SSB) signal.
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FDM Telephony
(頻分多工話音技術)
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Frequency-division multiplexing (FDM) provides a way of keeping a
number of individual telephone signals separate while transmitting
them simultaneously over a common transmission link circuit.
Each telephone base band signal is modulated onto a separate subcarrier, and all the upper or all the lower sideband are combined to
form the frequency-multiplexed signal.
Each voice channel occupies the range 300 to 3400 Hz, and each is
modulated onto its own sub-carrier.
The sub-carrier frequency separation is 4 kHz, this allowing for the
basic voice bandwidth of 3.1 kHz plus an adequate guard band for
filtering.
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FDM Telephony
(頻分多工話音技術)(continued)
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CCITT (國際電信電話諮詢委員會, ITU-T ) modulation plan:
 Group: 12 voice-frequency channels. Overall bandwidth of a
group extends from 60 to 108 kHz.
 Super Group: 60 VF-channel super group (SG) extending from
312 to 552 kHz.
 Basic Master Group: 300 VF-channel basic master group
extending from 812 to 2044 kHz. Allowing 8-kHz guard bands
between sidebands. Basic master group consists of five (5)
super groups together: SG1 (812-1052 kHz), SG2 (1060-1300
kHz), SG3 (1308-1548 kHz), SG4 (1556-1796 kHz), and SG5
(1804-2044 kHz) supper groups. The central carrier
frequencies are 1364, 1612, 1860, 2108, and 2356 kHz,
respectively.
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FDM Telephony
(頻分多工話音技術)(continued)
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CCITT modulation plan (continued):
 Super Master Group: 900 VF-channel master super group
extends from 8516 to 12388 kHz. Super master group consists
of three (3) basic master groups (MG1, MG2, MG3). Allowing
88 kHz guard bands between sidebands. The central carrier
frequencies of three (3) MG are 10,560, 11,880, and 13,200
kHz, respectively.
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Color Television
(彩色電視)
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The base band signal for television is a composite of the visual
information signals and synchronization signals.
The visual information is transmitted as three (3) signal components,
denoted as the Y, I, and Q signals.
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The Y signal is a luminance, or intensity, component and is also the only
visual information signal required by monochrome receivers.
The I and Q signals are termed chrominance components, and together
they convey information on the hue or tint and on the amount of
saturation of the coloring which is present.
The synchronization signal consists of narrow pulses at the end of
each line scan for horizontal synchronization and a sequency (序列)
of narrow and wider pulse at the end of each field scan for vertical
synchronization.
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Homework Problems
(習題)
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9.1 State the frequency limits generally accepted for telephone
transmission of speech. What is the reason behind? Please briefly
describe.
9.10 Explain what is meant by frequency modulation.
9.26 Super Master Group: 900 VF-channel master super group
extends from 8516 to 12388 kHz. Super master group consists of
three (3) basic master groups. Allowing 88 kHz guard bands
between sidebands. The carrier frequencies of three (3) MG are
10,560, 11,880, and 13,200 kHz, respectively. Please calculate
three (3) basic sidebands.
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