codes.
§9.1 Analog Modulation §9.2 Binary Digital Modulation §9.3 Error Probabilities for Binary Modulation §9.4 Effect of Rayleigh Fading on Bit Error Rats §9.5 M-ary Digital Modulation
But
Ni
2g2
fm
gn0 2
2n0 fM
S0 Si N0 n0 fM
Conclusion: The coherent SSB and DSB-SC demodulators have the same SNR performance.
Microwave and RF Design of Wireless Systems
Chapter 9
Modulation Techniques
Dr. Zhang Yonghong
Comparing with transmitting baseband signal directly, to transmit data by modulating a higher frequency
vi (t) Acos(IF m )t n(t)
n(t) x(t) cosIF t y(t) sin IF t
v1(t) vi (t) cosIFt
cos cos cos cos / 2 cos2 1 cos 2 / 2 sin 2
xt
Input narrowband noise power:
Ni
E{n2 (t)}
1 2
E{x2 (t)}
1 2
E{y2 (t)}
E{x2 (t)} E{y2 (t)}
Output noise power:
N0
E{[ 1 2
x(t)]2}
1 4
E{x2 (t)}
Ni 4
The output SNR: S0 Si N0 Ni
carrier wave has the effect on:
➢ ①controlling the radiated frequency spectrum. ➢ ②more efficient use of the allocated RF bandwidth. ➢ ③flexibility in accommodating different baseband
by the input stages of the receiver.
The demodulator LO is identical in frequency and phase with the modulator LO-synchronous or coherent demodulator.
Conclusion: SSB demodulator does not degrade the input SNR.
Ni
2 n0 2
fM
n0 fM
S0 Si N0 n0 fM
2. DSB-SC Modulation
Double-sideband suppressed carrier (DSB-SC)
vi (t)
A 2
cos(IF
m )t
A 2
cos(IF
m )t
n(t)
S0 2 Si
N0
Ni
Conclusion: the DSB-SC demodulator improves the input signal-to-noise ratio by a factor of two.
FSSB=2FDSB
§9.1 Analog Modulation
Basic analog modulation: AM (SSB, DSB), FM, PM PPM (Pulse Position Modulation) is used in UWB (ultra wideband) system.
1. Signal-Sideband Modulation 2. DSB-SC Modulation 3. DSB-LC Modulation 4. Envelope Detection of DSB-LC Modulation 5. Frequency Modulation (FM)
➢ ①more efficient use of the radio spectrum. ➢ ②usually requires less power. CDMA ➢ ③over a fading communications channel. ➢ ④more compatible with the use of error correcting
signal formats.
V (t) Acos(t )
Amplitude Frequency Phase
AM
FM
PM
➢Analog modulation (vary continuously)
➢Digital modulation (change in discrete steps)
In contrast to analog modulation, digital modulation has:
mt
A 2
cos(2IF
m )t
1 2
x(1
cos
2IF t)
1 2
y(t)
sin
2IF t
v0 (t)
A 2
cos
m
t
1 2
xt
Input signal power: Si A2 / 2
Output signal power:
S0
1 ( A)2 22
A2 8
Si 4
v0 (t)
A 2
cos
1. Signal-Sideband Modulation
m(t): bandlimited modulating waveform fM: the maximum frequency of m(t)
m(t) cos 2 fmt 0 fm fM
n0/2: two-sided power spectral density of Gaussian white noise. Contributed by the transmitter channel and noise generated