通信原理讲义-英文版
通信原理 英文
通信原理英文Communication PrinciplesCommunication principles refer to the fundamental concepts and theories that govern the process of transmitting information from one entity to another. These principles form the foundation of effective communication and play a crucial role in various communication systems, such as wireless communication, optical communication, and digital communication.One of the key communication principles is the concept of encoding and decoding. Encoding involves converting the information into a suitable form for transmission, while decoding involves the reverse process of converting the received signals back into meaningful information. This principle ensures that the information is accurately transmitted and understood by the receiving entity.Another important principle is the concept of modulation. Modulation is the process of modifying a carrier signal by varying its amplitude, frequency, or phase to carry the information. This principle is used in various communication systems to transmit information over long distances without significant loss or distortion.Furthermore, the principle of noise reduction is crucial in communication systems. Noise refers to any unwanted disturbance that affects the quality of the transmitted signal. To ensure reliable and clear communication, noise reduction techniques, such as filtering and error correction, are employed to minimize the impactof noise on the received signals.Additionally, the principle of multiplexing allows multiple signals to be transmitted over a single communication channel. This is achieved by dividing the channel bandwidth into smaller sub-channels, each carrying a different signal. Multiplexing enables efficient utilization of the available communication resources and allows for simultaneous transmission of multiple signals.Furthermore, the principle of synchronization is essential for successful communication. Synchronization ensures that the transmitting and receiving entities are operating in a coordinated manner, allowing for accurate transmission and reception of the information. Various techniques, such as clock synchronization and frame synchronization, are employed to achieve synchronization in communication systems.Lastly, the principle of error detection and correction is crucial for reliable communication. Error detection techniques, such as checksums and parity bits, are used to identify errors in the transmitted signals. Error correction techniques, such as forward error correction codes, are employed to correct the detected errors and ensure accurate transmission and reception of the information. In summary, communication principles are fundamental concepts and theories that govern the process of transmitting information. These principles, such as encoding and decoding, modulation, noise reduction, multiplexing, synchronization, and error detection and correction, ensure efficient and reliable communication in various communication systems.。
通信原理(英文版)
2.1 Classification of Signals
2.1.1 Deterministic signals and random signals
• What is deterministic signal? • What is random signal?
2.1.2 Energy signals and power signals
f (t) f (t T) t
Its frequency spectrum is
/2
C( jn0 )
1 T
/ 2 Ve j n0t dt
/ 2
1 T
V
jn 0
e
j n0 t
/ 2
V e j n0 / 2 e j n0 / 2
f (t) sin(t) Its frequency spefct(rtu)m: f (t 1)
0 t 1 t
C(
jn 0 )
1 T0
T0 / 2 s(t )e jn0t dt
T0 / 2
1 sin(t )e j 2nt dt
Solution: Let the expression of the rectangular pulse be
Then its frequency spectral density is
its
Fourier
tragns(fto)rm:
1
0
t /2 t /2
G() / 2 e jt dt 1 (e j / 2 e j / 2 ) sin( / 2)
通信原理(英文版)3精品名师资料
c(t ) A cos(0t 0 )
where, A --- amplitude
Modulating signal m(t)
Modulator
Modulated signal s(t)
0 --- angular frequency
Figure 3.1.1 Modulator
of carrier 0 --- initial phase Definition: Modulating signal m(t) －signal from the source Modulated signal s(t) － signal after being modulated Modulator － the device for modulation
2
3.2 Linear modulation
3.2.0 Basic concept Assume: the carrier is: c(t) = Acos0 t = Acos2 f0t
modulating signal is a energy signal m(t), its spectrum is M(f ) s (t ) carrier: c(t) Modulated Modulating H(f) signal signal multiplication result: s(t) s(t) m(t) Acos t filter output: s(t) “” is used to express Fourier transform: m(t ) M ( f )
Chapter 3 Analog modulation system
3.1 Introduction
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1.3.2 Advantages of Digital Communication
1.2 Message, information & signal
Message：speech, letters, figures, images…
Information：effective content of message. Different types of messages may contain the same information
Finite number of possible values of signals Correct decision may be achieved
(a) Waveforms of distored digital signal
(b) Waveforms of digital signal after shaping
Signal：the carrier of message
What transmitted in a communication system is signal.
Measurement of information：
# “quantity of message” information content
1.3 Digital Communication
1.3.1 Basic concept
Two categories of signals • Analog signal：Its voltage or current
现代通信原理课件(英文版)(ppt 35页)
from a digital source to the intended receiver(sink) 5. Analog communication system transfers
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
15
1.2 Digital and Analog source and system
2 the advantage of digital system
1）Relatively inexpensive digital circuits may be used
2） Privacy is preserved by using data encryption
8
1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
1. Selection of the information-bearing
通信原理(英文版)11[63页]
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➢Advantage of OQPSK:
Max. difference between adjacent symbols is only 90º. ➢ The anti-noise performance of the OQPSK is
a1
a3
a2
a4
a5
a7a3
a5
a7
a2
a4
a6
a8
➢ Anti-noise performance of 4 QDPSK signal is the same as that of QDPSK signal.
➢ 4 QDPSK system has already been used in the North America’s 2nd generation cellular networks (IS-136).
➢ Expression
sk
(t)
c os ( s t
ak
2T
t
k
)
(k 1)T t kT
where s 2f s ak 1
( When the input symbol is 1, ak =+1, when the input symbol is 0, ak = -1)
T － symbol duration;
k － definite initial phase of the k-th symbol.
4
sk
(t)
c os ( s t
ak
2T
t
k
)
(k 1)T t kT
➢ As can be seen from the above equation:
When ak =+1, the symbol frequency f1 = fs+1/(4T);
通信原理(英文版)3
Definition:
➢ Modulating signal m(t) －signal from the source
➢ Modulated signal s(t) － signal after being modulated
➢ Modulator － the device for modulation
Chapter 3 Analog modulation system
3.1 Introduction
Analog modulation: modulation of a carrier by a source
baseband analog signal
Carrier: a deterministic periodic waveform － cosinusoidal
ri
E
1 2
1
m'
(t
)2
A2
/ n2 (t)
∴Ratio of S/N before and after detection:
m(t)
1+m(t)
+1 = 1
0
1+m(t)
1
0
=
4
Frequency density
➢ Contain discrete carrier component ➢ When m(t) is cosinusoidal, and m＝100％,
sum of the two side band power ＝ half of carrier power
Basic principles
Let: m(t) = [1+m(t)]， |m(t)| 1， m(t)|max = m －modulation index, then we have the AM signal
通信原理(英文版)
【Example 2.4】Find the waveform and the frequency spectral density of a sample function. Solution: The definition of the sample function is
sin t Sa ( t ) t
d(t)
1
(f)
0
t
0
f
meaning of d function: It is a pulse with infinite height, infinitesimal width, and unit area. Sa(t) has the following property:
Physical
F ( ) lim
/2 / 2
cos 0 te
jt
sin[( 0 ) / 2] sin[( 0 ) / 2] dt lim 2 ( ) / 2 ( ) / 2 0 0
The frequency spectral density of d(t):
( f ) d (t )e
jt
d (t ) 0
t 0
dt 1 d (t )dt 1
7
d(t)
and its frequency spectral density:
f (t ) f (t 1) t
1
Its frequency spectrum:
1 C ( jn 0 ) T0
T0 / 2
T0 / 2
s(t )e