PRESENTATION ON

Comparison Of Digital Modulation Techniques

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ASK FSK:8FSK,16FSK PSK:BPSK,QPSK,8PSK,16PSK,DPSK QAM:GENERAL QAM, RECTANGULAR QAM

DIFFERENT TYPES OF DIGITAL MODULATORS:

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK)

Here modulation order is 8 i.e. M=8.

8FSK(FREQUENCY SHIFT KEYING):

MATLAB\8fsk11.fig

BER VS Eb/No plot

Phase shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal(carrier wave).

 In this system, the demodulator determines the changes in the phase of the received signal rather than the phase (relative to a reference wave) itself.

DBPSK(Differential binary phase shift keying modulation):

Since this scheme depends on the difference between successive phases, it is termed differential phase-shift keying (DPSK).

DPSK can be significantly simpler to implement than ordinary PSK since there is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the received signal.

BER VS Eb/No plot

MATLAB\dbpsk1.fig

Quadrature amplitude modulation (QAM) conveys two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using amplitude-shift keying (ASK) digital modulation scheme.

The two carrier waves, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components-hence the name of the scheme.

The modulated waves are summed, and the resulting waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK).

General QAM (Quadrature amplitude modulation):

BER VS Eb/No plot:

MATLAB\16QAMgeneral1.fig

Rectangular QAM constellations are, in general, sub-optimal in the sense that they do not maximally space the constellation points for a given energy.

However, they have the considerable advantage that they may be easily transmitted as two pulse amplitude modulation (PAM) signals on quadrature carriers, and can be easily demodulated.

Rectangular QAM (Quadrature amplitude modulation):

The non-square constellations, dealt with below, achieve marginally better bit-error rate (BER) but are harder to modulate and demodulate.

Constellation diagram

BER VS Eb/No plot

MATLAB\rec16qam.fig

This is known as differential quaternary PSK. With four phases, QPSK can encode two bits per

symbol by modulating phase of carrier. The mathematical analysis shows that QPSK can be

used either to double the data rate compared with a BPSK system while maintaining the same bandwidth of the signal.

DQPSK(Diffential quadrature phase shift keying modulation):

To maintain the data-rate of BPSK but halving the bandwidth needed.

The advantage of QPSK over BPSK becomes evident: QPSK transmits twice the data rate in a given bandwidth compared to BPSK - at the same BER

BER VS Eb/No plot

MATLAB\dqpsk1.fig

Eb/N0 (the energy per bit to noise power spectral density ratio) is an important parameter in digital communication or data transmission.

It is a normalized signal-to-noise ratio (SNR) measure, also known as the "SNR per bit".

It is especially useful when comparing the bit error rate (BER) performance of different digital modulation schemes without taking bandwidth into account.

Comparison b/w different modulation techniques using BER tool

BER=The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unit less performance measure, often expressed as a percentage.

In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.

BER:

BER VS Eb/No plot:

Link to comparison between various digital modulation techniques.

MATLAB\dbsk22197.fig

The rest of this section studies both the bit and symbol error rates using BER Tool.

Theoretical output is somewhat similar to practical one.

We find that BER Output was best in following order:

Fsk<Dbpsk<General QAM<Rectangular QAM<Dqpsk

Increase in the value of Eb/No lowers the number of errors produced, the length of each simulation must be increased to ensure that the statistics of the errors remain stable.

CONCLUSION:

As we decrease the value of M,BER OUTPUT becomes better and more accurate.

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