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1.  Digital modulation signal of data using

a)  ASK modulation

Enter the frequency of carrier=30

Enter the frequency of pulse=5

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 b)  BPSK modulation

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c)  QPSK modulation

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Compare and discuss the result

For ASK modulation, amplitude level of the carrier signal is switched according to the

binary information, keeping the phase and frequency fixed. We also can see that when the

bit “0”, the ASK signal is none but when bit “1”, the signal will produced . 

For BPSK modulation, that has a possible result two exit phases for the carrier with a

single frequency. An exit phase represents a logical 1 and the other one a logical 0. As the

input digital signal changes the state, the phase of the exit carries moves between two

angles that lie 180 degree outside of phase.

A QPSK modulated carrier four distinct changes in phase that are represented as symbolsand can take on the values of π/4, 3π/4, 5π/4, and 7π/4. Each symbol represents two binary

bits of data.

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2. Analyze the system in figure below;

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From the observation discuss your findings.

Based on the results, it shows that there is signal at eye diagram scope for in-phase amplitude.

However, for signal trajectory scope, there is no signal or output at quadrature amplitude. For 

scatter plot scope, there is two points which is at -1(bit 0) and 1(bit 1). It uses two opposite signal

 phases (0 and 180 degrees). 

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3. Investigate the input and output of the system.

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Analyze the results and give your comments

The result shows that the output at the eye diagram scope, discrete time signal trajectory scope

and discrete time scatter plot scope is not too smooth because there is noise. The value of SNR 

that put in the parameter is 10. Theoretically, the SNR needs to be as high as possible. The

higher the value of SNR, the better will be the signal strength.

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4. Analyze the digital communication system

Table below is the results after run the simulation with different SNR value.

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SNR (db) BER 

0 0.3227

1 0.2747

10 0.002997

11 0

100 0

1000 0

-1 0.3736

-10 0.6414

-100 0.7742

-1000 0.7742

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From the analysis discuss your results.

Based on the table, the results for bit error rate versus SNR shows that when the value of SNR is

higher, their bit error rate value is become smaller. The value of bit error rate is 0 is when the

value of SNR is above then 10. The bit error rate is increasing when the value of SNR is below

then 10. We can see that when the SNR value is 1000db, their bit error rate value is 0. However,

when the value of SNR is -1000db, their bit error rate is 0.7742. So, the more the value of SNR is

 better because the error that produce is 0.

ANALYSIS

In amplitude Shift keying (ASK), logic levels are represented by different amplitudes of 

signals. Usually, one amplitude is zero for logic digital logic zero while is logic 1 represented by

the actual amplitudes of some sine wave signal. Result shows the waveforms in ASK. The ASK 

signal’s envelopes are the same shape as the data stream (although the lower envelope is

inverted). Recovery of the original data at the receiving end can be implemented using a simple

envelope detector and filter.

Recall that ASK uses the digital data’s 1s and 0s to switch a carrier between two

amplitudes. FSK uses the 1s and 0s to switch a carrier between two frequencies. An alternative

to these two methods is to use the data stream’s 1s and 0s to switch the carrier between two

 phases. This is called Binary Phase Shift Keying (BPSK). For Binary PSK (BPSK) the state of 

θ1 -θ0 = 180 °simplifies the modulator design. Moreover, π radian between phases of PSK 

signals will be most appropriate from error- performance point of view. For example, (θ0 ,

θ1 ) phase values can be chosen as (0, π) or (π/2, 3π/2). 

QPSK sends two bits of data at a time, it is tempting to think that QPSK is twice as fast

as BPSK but is not so. Converting the digital data from series of individual bits to a series of bit-

 pairs necessarily halves the data’s bit-rate. This cancels the speed advantages of sending two bits

a time

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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 unitless performance measure,

often expressed as a percentage. 

.

DISCUSSION

Amplitude-shift keying (ASK) is a form of amplitude modulation that

represents digital data as variations in the amplitude of a carrier wave.  ASK uses a finite

number of amplitudes, each assigned a unique pattern of binary digits. Usually, each amplitude

encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the

 particular amplitude. The demodulator, which is designed specifically for the symbol-set used by

the modulator, determines the amplitude of the received signal and maps it back to the symbol it

represents, thus recovering the original data.

BPSK (also sometimes called PRK, phase reversal keying, or 2PSK) is the simplest form

of phase shift keying (PSK). It uses two phases which are separated by 180° and so can also be

termed 2-PSK. It does not particularly matter exactly where the constellation points are

 positioned, and in this result they are shown on the real axis, at 0° and 180°. This modulation isthe most robust of all the PSKs since it takes the highest level of noise or distortion to make

the demodulator reach an incorrect decision. It is, however, only able to modulate at 1 bit/symbol

(as seen in the figure) and so is unsuitable for high data-rate applications.

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In QPSK, the data bits to be modulated are grouped into symbols, each containing two

 bits, and each symbol can take on one of four possible values: 00, 01, 10, or 11. During each

symbol interval, the modulator shifts the carrier to one of four possible phases corresponding to

the four possible values of the input symbol. In the ideal case, the phases are each 90 degrees

apart, and these phases are usually selected such that the signal constellation matches the

configuration. 

Additive white Gaussian noise (AWGN) is a channel model in which the only

impairment to communication is a linear addition of wideband or white noise with a

constantspectral density (expressed as watts per hertz of bandwidth) and a Gaussian

distribution of amplitude. The model does not

accountfor fading, frequency selectivity, interference, nonlinearity or dispersion. However, it

 produces simple and tractable mathematical models which are useful for gaining insight into the

underlying behavior of a system before these other phenomena are considered.