Wireless Communication And Frequency Shift Keying Computer Science Essay

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Wireless communication is broad field that has tremendous excitement and advancement in science and technology over the few past decades. Several digital modulation techniques are currently recommended for wireless communication. This report introduces Frequency shift keying (FSK) modulation that is known to be very less susceptible to interfering signals. Frequency shift keying (FSK) modulation is basis for Orthogonal Frequency Division Multiplexing (FDMA), Frequency Division Multiple Access (OFDM) and advance technique in wireless communication. However, FSK is not always used for high-speed data communications, since it is far less efficient in both power and bandwidth than most other modulation techniques. FSK is demonstrated through the simulation of BPSK technique using Matlab. The simulation results show that how the digital data can is transmitted using FSK.

Modulation is a process to aid transfer of message signal from one source to destination through some medium. Sound transmission in the air has limited range of amount power required for the lungs can be generated. In order to extend the range your voice can be reached therefore we need other medium than Air, such as the phone line or radio. The process in which the data can send from one pace to the other is called modulation.

All of these techniques depend upon variation of parameter of sinusoid to represent the information we want to send. In a sinusoid three parameters can be changed. These parameters are phase, amplitude and frequency. Modulation is the process that takes input signal and convert it with respect to sine wave and then transmit the sine wave, leaving the actual signal input. On the other side the sine wave remapped to get the original signal. The medium is the thing through which the sine wave travel so that the air, water etc. the sine wave is a carrier. the signal through which the information can be sent is called message signal and once the sine wave is mapped with the message signal then it is no longer the sine wave and we usually called it the Signal.

Frequency Shift Keying (FSK)

Modulation in wireless communications involves modifying the phase or amplitude, or both, of a sinusoidal carrier. One of the simplest, and widest used system, is frequency modulation. This exists in a great variety of forms In FSK, the frequency of the carrier is changed as a function of the modulating signal (data) is being transmitted. Amplitude remains unchanged.

Figure 2. FSK modulation.[2]

FSK (Frequency Shift Keying) is used in many applications including cordless and paging systems. Some of the cordless systems include DECT (Digital Enhanced Cordless Telephone) and CT2 (Cordless Telephone 2). Frequency-shift keying is used in all single-channel, radiotelegraph systems that use automatic printing systems. 

ADVANTAGES OF FSK :

The advantage of FSK over on-off keyed cw is that it rejects unwanted signals (noise) that are weaker than the desired signal. This is true of all fm systems. Also, since a signal is always present in the FSK receiver, automatic volume control methods maybe used to minimize the effects of signal fading caused by ionospheric variations. The amount of inherent signal-to-noise ratio improvement of FSK over AM is approximately 3 to 4 dB. This improvement is because the signal energy of FSK is always present while signal energy is present for only one-half the time in AM systems. Noise is continuously present in both FSK and AM, but is eliminated in FSK reception. Under the rapid fading and high-noise conditions that commonly exist in the high frequency (hf) region; FSK shows a marked advantage over AM. Overall improvement is sometimes expressed as the RATIO OFTRANSMITTED POWERS required giving equivalent transmission results over the two systems. Such a ratio varies widely, depending on the prevailing conditions. With little fading, the ratio may be entirely the result of the improvement in signal-to-noise ratio and may be under 5 dB. However, under severe fading conditions, large amounts of power often fail to give good results for AM transmission. At the same time, FSK may be satisfactory at nominal power. The power ratio (FSK versus AM) would become infinite in such a case. FSK has the advantage of being very simple to generate, simple to demodulate and due to the constant amplitude can utilize a non-linear PA. Significant disadvantages, however, are the poor spectral efficiency and BER performance. This precludes its use in this basic form from cellular and even cordless systems. [3]

binray Frequency Shift Keying (BFSK):

Binary Frequency Shift Keying is a modulation scheme in which the digital information to be send is encoded in the frequency. The simplest way to carry this kind of encoding into practice is to switch the frequency of the continuous carrier in digital binary manner for the data. In binary FSK (BFSK or 2FSK), a "1" is represented by one frequency and a "0" is represented by another frequency.

Block Diagram:

Frequency Modulator

Kf = 5*Ï€

Carries Generator

c = Cos (2* π*4*t)

c = Cos (2* π*2*t)

FM signal (Ç¿fm)

a(t)

Procedure:

The block diagram in fig.1 is of a Frequency modulator system.

The inputs to phase modulator block are:

A triangular wave message signal "a(t)".

A carrier signal generated through an oscillator.

The o/p of phase modulator block is given by:

 (1)

Where kf is phase modulated variation factor. and

 (2)

Simulation results:

Carrier signal with fc = 4 HZ

C(t) = cos(2* π* fc*t )

NOTE: In general carrier frequency is very higher than message signal.But here, in order to visualize the effect of frequency variation in the modulated signal we take small frequency.

kf = 5*Ï€.

For periodic triangular wave form as "a(t)" and

Conclusion:

It is clear from the above simulation results and eq. (1) that with the change of message signal slope/amplitude, the frequency of modulated signal varies. This technique is less immune to noise and using FSK the inter symbol interference (ISI) can be avoided up to much extent. This modulation technique helps us to understand Advance techniques in Wireless Communication like OFDM (Orthogonal Frequency Division Multiplexing) and FDMA (Frequency Division Multiple Access).

Code:

t=0:0.001:6.002;

% Triangular wave form generation.

t1=0:0.001:0.5;

x1=2.*t1;

t2=(0.5+0.001):0.001:1.5;

x2=-2.*t2+2;

t3=(1.5+0.001):0.001:2;

x3=2.*t3-4;

a=[x1 x2 x3 x1 x2 x3 x1 x2 x3];

plot(t,a);grid;

title('Periodic triangular wave form of "a(t)"');

xlabel('------ t ------->');ylabel('------ amplitude ------->');

c=cos(2*pi*4*t);

figure, plot(t,c);grid; title('carrier signal "c(t)"');

xlabel('------ t ------->');ylabel('------ amplitude ------->');

kf=5*pi;

FM=cos(2*pi*4*t+(kf*a));

figure,

plot(t,FM);grid;title('Frequency modulated signal of "a(t)"');

xlabel('------ t ------->');ylabel('------ amplitude ------->');

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