移动通信课程 Modulation Techniques for
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FM systems. AM carrier signal has time-varying envelope.
7
Amplitude Modulation
The amplitude of high-carrier signal is varied according to the instantaneous amplitude of the modulating message signal m(t).
移动通信 Mobile Communications
Chapter 3 Modulation Techniques for Mobile Communication
1
2
What is modulation
为什么需要调制？
数字基带信号具有丰
Modulation
is
the
process
of
富的低频分量
eOOK
(t
)
A 0
cos
ct 以概率P发送“1” 以概率1-P发送“0”
1 00 1 S( t )
Expression
Modulating Signal
e2ASK (t ) st cosct
Carrier Signal
Carrier Signal
2ASK
NRZ（单极性全占空）信号
s( t ) an g( t nTs ) n
More secure link
13
Digital Modulation
The modulating signal is represented as a time-sequence of symbols or pulses.
Each symbol has m finite states: That means each symbol carries n bits of information where n = log2m bits/symbol.
Demodulation is the inverse operation
extracting the baseband message from the carrier so that it may be processed at the receiver.
4
Analog/Digital Modulation
S( t )
Carrier Signal
2ASK
If the signal value is 1 then the carrier signal will be transmitted; otherwise, a signal value of 0 will be transmitted.
16
通-断键控（On Off Keying，OOK）
FM Signal
s( t ) cos2 8t 4 sin( 2 t )
Carrier Signal cos( 2 8t )
12
3.2 Digital Modulation
The input is discrete signals
Time sequence of pulses or symbols
A form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.
In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration of T seconds.
Offers many advantages
Robustness to channel impairments Easier multiplexing of various sources of
information: voice, data, video. Can accommodate digital error-control codes Enables encryption of the transferred signals
Used in current and future mobile radio systems
5
Goal of Modulation Techniques
Modulation is difficult task given the hostile mobile radio channels
Small-scale fading and multipath conditions.
The goal of a modulation scheme
Transport the message signal through the radio channel with the best quality (low BER), lowest power & least amount of frequency spectrum
All info is carried in the amplitude of the carrier There is a linear relationship between the received
signal quality and received signal power. AM systems usually occupy less bandwidth then
Analog Modulation
The input is continues signal
Used in first generation mobile radio systems
such as AMPS in USA
数字调制—用数字基带信号 控制载波，把数字基带信号
变换成数字带通信号（已调
Two classes of angle modulation techniques
Frequency Modulation
Instantaneous frequency of the carrier signal is varied linearly with message signal m(t)
8
AM Modulation/Demodulation
Source
Wireless
Sink
Channel
Modulator
Demodulator
Baseband Signal with frequency
fm (Moduwith frequency
m(t)
AM Modulator
sAM(t)
Ac cos( 2 fct )
Carrier Signal: Ac cos( 2 fct )
Modulating Message Signal: m(t)
The AM Signal: sAM ( t ) Ac [ 1 m( t )] cos( 2 fct )
Baseband signal is called modulating signal
Bandpass signal is called modulated signal
调制的实质——将调制信号的频谱搬移到所希望的频 率范围，使其转换成适合信道传输的已调信号，同时 有利于实现频分复用
3
3.1 Modulation Techniques
码元持续时间
第n个码元对应的电平值
1 以概率 p an = 0 以概率 1-p
17
Power Spectrum Density, PSD）
2ASK信号是随机的、功率型的信号
设 S( t ) 的功率谱密度为 Ps ( f ) e0 (t ) S(t )cosct e0( t ) 的功率谱密度为 PE( f )
Must make tradeoffs between these objectives
6
Amplitude Modulation (AM)
Amplitude Modulation
Changes the amplitude of the carrier signal according to the amplitude of the message signal
信号）的过程
Digital Modulation
The input is time sequence of symbols or pulses
Better performance and more cost effective than analog modulation methods (AM, FM, etc.)
10
fc 2 1.6 Hz
sAM ( t ) Ac [ 1 m( t )] cos( 2 fct )
1
f mesg 2 0.16 Hz
AM Signal: sAM ( t ) 4 [ 1 2 2 cos( t )] cos( 2 fct )
10
Angle Modulation
Angle of the carrier is varied according to the amplitude of the modulating baseband signal.
非严格推导： e02 (t) S 2 (t)cos2 ct
e02 (t ) PE ( f ) S 2 (t ) Ps ( f )
cos c t
1 2
(
f
fc ) ( f
fc )
cos2 ct
1 2
(
f
fc ) (
f
fc )
1 2
Modulation can be done by varying the
Amplitude Phase, or Frequency
of a high frequency carrier in accordance with the amplitude of the message signal.
...
0 12 3
T
One symbol (has m states – voltage levels) (represents n = log2m bits of information)
Modulator
14
Digital Modulation Method
Analog Modulation Digital keying method
Amplitude Frequency
Phase
Binary modulation
2ASK 2FSK
2PSK、2DPSK
M-ary Modulation
MASK、 QAM MFSK、MSK
QPSK
15
Binary Amplitude Shift Keying ，2ASK
Principle
1 00 1
Phase Modulation The phase q(t) of the carrier signal is varied
linearly with the message signal m(t).
11
FM Example
4
0
-
+
-
-+
-4
0.5
1
1.5
2
Message signal m( t ) 4 cos( 2 t )
encoding
information from a message source in a manner
suitable for transmission
It involves translating a baseband message signal to a bandpass signal at frequencies that are very high compared to the baseband frequency.
fc (Modulated Signal)
fc >> fm
Original Signal with frequency
fm
9
Example
20
15
1/fmesg
10
5
0
-5
-10
1/fc
-15
-20
0
2
4
6
8
10
12
14
Message signal: m( t ) 2 2 cos( t )
Carrier signal :Ac cos( 2 fct ) 4 cos( 10t )
7
Amplitude Modulation
The amplitude of high-carrier signal is varied according to the instantaneous amplitude of the modulating message signal m(t).
移动通信 Mobile Communications
Chapter 3 Modulation Techniques for Mobile Communication
1
2
What is modulation
为什么需要调制？
数字基带信号具有丰
Modulation
is
the
process
of
富的低频分量
eOOK
(t
)
A 0
cos
ct 以概率P发送“1” 以概率1-P发送“0”
1 00 1 S( t )
Expression
Modulating Signal
e2ASK (t ) st cosct
Carrier Signal
Carrier Signal
2ASK
NRZ（单极性全占空）信号
s( t ) an g( t nTs ) n
More secure link
13
Digital Modulation
The modulating signal is represented as a time-sequence of symbols or pulses.
Each symbol has m finite states: That means each symbol carries n bits of information where n = log2m bits/symbol.
Demodulation is the inverse operation
extracting the baseband message from the carrier so that it may be processed at the receiver.
4
Analog/Digital Modulation
S( t )
Carrier Signal
2ASK
If the signal value is 1 then the carrier signal will be transmitted; otherwise, a signal value of 0 will be transmitted.
16
通-断键控（On Off Keying，OOK）
FM Signal
s( t ) cos2 8t 4 sin( 2 t )
Carrier Signal cos( 2 8t )
12
3.2 Digital Modulation
The input is discrete signals
Time sequence of pulses or symbols
A form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.
In an ASK system, the binary symbol 1 is represented by transmitting a fixed-amplitude carrier wave and fixed frequency for a bit duration of T seconds.
Offers many advantages
Robustness to channel impairments Easier multiplexing of various sources of
information: voice, data, video. Can accommodate digital error-control codes Enables encryption of the transferred signals
Used in current and future mobile radio systems
5
Goal of Modulation Techniques
Modulation is difficult task given the hostile mobile radio channels
Small-scale fading and multipath conditions.
The goal of a modulation scheme
Transport the message signal through the radio channel with the best quality (low BER), lowest power & least amount of frequency spectrum
All info is carried in the amplitude of the carrier There is a linear relationship between the received
signal quality and received signal power. AM systems usually occupy less bandwidth then
Analog Modulation
The input is continues signal
Used in first generation mobile radio systems
such as AMPS in USA
数字调制—用数字基带信号 控制载波，把数字基带信号
变换成数字带通信号（已调
Two classes of angle modulation techniques
Frequency Modulation
Instantaneous frequency of the carrier signal is varied linearly with message signal m(t)
8
AM Modulation/Demodulation
Source
Wireless
Sink
Channel
Modulator
Demodulator
Baseband Signal with frequency
fm (Moduwith frequency
m(t)
AM Modulator
sAM(t)
Ac cos( 2 fct )
Carrier Signal: Ac cos( 2 fct )
Modulating Message Signal: m(t)
The AM Signal: sAM ( t ) Ac [ 1 m( t )] cos( 2 fct )
Baseband signal is called modulating signal
Bandpass signal is called modulated signal
调制的实质——将调制信号的频谱搬移到所希望的频 率范围，使其转换成适合信道传输的已调信号，同时 有利于实现频分复用
3
3.1 Modulation Techniques
码元持续时间
第n个码元对应的电平值
1 以概率 p an = 0 以概率 1-p
17
Power Spectrum Density, PSD）
2ASK信号是随机的、功率型的信号
设 S( t ) 的功率谱密度为 Ps ( f ) e0 (t ) S(t )cosct e0( t ) 的功率谱密度为 PE( f )
Must make tradeoffs between these objectives
6
Amplitude Modulation (AM)
Amplitude Modulation
Changes the amplitude of the carrier signal according to the amplitude of the message signal
信号）的过程
Digital Modulation
The input is time sequence of symbols or pulses
Better performance and more cost effective than analog modulation methods (AM, FM, etc.)
10
fc 2 1.6 Hz
sAM ( t ) Ac [ 1 m( t )] cos( 2 fct )
1
f mesg 2 0.16 Hz
AM Signal: sAM ( t ) 4 [ 1 2 2 cos( t )] cos( 2 fct )
10
Angle Modulation
Angle of the carrier is varied according to the amplitude of the modulating baseband signal.
非严格推导： e02 (t) S 2 (t)cos2 ct
e02 (t ) PE ( f ) S 2 (t ) Ps ( f )
cos c t
1 2
(
f
fc ) ( f
fc )
cos2 ct
1 2
(
f
fc ) (
f
fc )
1 2
Modulation can be done by varying the
Amplitude Phase, or Frequency
of a high frequency carrier in accordance with the amplitude of the message signal.
...
0 12 3
T
One symbol (has m states – voltage levels) (represents n = log2m bits of information)
Modulator
14
Digital Modulation Method
Analog Modulation Digital keying method
Amplitude Frequency
Phase
Binary modulation
2ASK 2FSK
2PSK、2DPSK
M-ary Modulation
MASK、 QAM MFSK、MSK
QPSK
15
Binary Amplitude Shift Keying ，2ASK
Principle
1 00 1
Phase Modulation The phase q(t) of the carrier signal is varied
linearly with the message signal m(t).
11
FM Example
4
0
-
+
-
-+
-4
0.5
1
1.5
2
Message signal m( t ) 4 cos( 2 t )
encoding
information from a message source in a manner
suitable for transmission
It involves translating a baseband message signal to a bandpass signal at frequencies that are very high compared to the baseband frequency.
fc (Modulated Signal)
fc >> fm
Original Signal with frequency
fm
9
Example
20
15
1/fmesg
10
5
0
-5
-10
1/fc
-15
-20
0
2
4
6
8
10
12
14
Message signal: m( t ) 2 2 cos( t )
Carrier signal :Ac cos( 2 fct ) 4 cos( 10t )