DIGITAL MODULATION TECHNIQUES

Presented By: NIDHI BARANWAL MCA 3rd SEMESTER University of Allahabad

WHAT IS MODULATION

• Modulation = Adding information to a carrier signal• The sine wave on which the characteristics of the information signal are modulated is called a carrier signal

CONTD.

MODULATION SYSTEMS

TYPES OF MODULATION

ANALOG MODULATION: If the variation in the parameter of the carrier is continuous in accordance to the input analog signal the modulation technique is termed as analog modulation scheme

DIGITAL MODULATION: If the variation in the parameter of the carrier is discrete then it is termed as digital modulation technique

ANALOG MODULATION

DIGITAL MODULATION

• In digital modulation , an analog carrier signal is modulated by a discrete signal

• Digital modulation can be considered as digital-to-analog and the corresponding demodulation as analog-to-digital conversion

• In digital communications, the modulating wave consists of binary data and the carrier is sinusoidal wave

DIGITAL MODULATION TECHNIQUES

AMPLITUDE SHIFT KEYING In ASK, the amplitude of the signal is changed in

response to information and all else is kept fixed Bit 1 is transmitted by a signal of one particular

amplitude. To transmit 0,we change the amplitude keeping the frequency constant

FREQUENCY SHIFT KEYING

In FSK, we change the frequency in response to information

one particular frequency for a 1 and another frequency for a 0

PHASE SHIFT KEYING In PSK, we change the phase of the sinusoidal

carrier to indicate information. Phase in this context is the starting angle at which the sinusoidal starts

One phase change encodes 0 while another phase change encodes 1.To transmit 0,we shift the phase of the sinusoid by 180

M-ARY MODULATION TECHNIQUE In binary data transmission, send only one of two

possible signals during each bit interval Tb In M-ary data transmission, send one of M possible

signals during each signaling interval T In almost all applications, M = 2n and T = nTb,

where n is an integer Each of the M signals is called a symbol These signals are generated by changing the

amplitude, phase, frequency, or combined forms of a carrier.

Thus, we have: MASK MPSK MFSK MQAM

QUADRATURE PHASE SHIFT KEYING

Quadrature Phase Shift Keying can be interpreted as two independent BPSK systems , and thus the same performance but twice the bandwidth efficiency

The phase of the carrier takes on 1 of 4 equally spaced values where each value of phase corresponds to a unique pair of message bits

QUADRATURE AMPLITUDE MODULATION

If both the amplitude and the phase are varied proportional to the information signal, quadrature amplitude modulation results.

Combination of phase shifting and amplitude shifting

DIFFERENTIAL PHASE SHIFT KEYING

For the perfect detection of a phase modulated signal, the receiver needs a reference signal but if differential encoding and phase shift keying are made together at the transmitter the technique is called as Differential Phase Shift Keying

For the transmission of a symbol 1, the phase is unchanged whereas for transmission of symbol 0, the phase of the signal is changed by 180

In DPSK, the phase shift is with reference to the previous bit transmitted rather than to some constant reference signal

CONTD..

METRICS FOR DIGITAL MODULATION

POWER EFFICIENCY Power efficiency is a measure of how much signal power

should be increased to achieve a particular bit error rate (BER) for a given modulation scheme

Ability of a modulation technique to preserve the fidelity of the digital message at low power Designer can increase noise immunity by increasing signal power BANDWIDTH EFFICIENCY Ability to accomodate data within a limited bandwidth Tradeoff between data rate and pulse width Easy to implement and cost-effective to operate.

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