In the present generation digital modulation technique is most friendly and popular which is frequently used in the cellular communication systems. As the difference of the analog and digital is that the digital techniques conducts will more cost impact while compare to the analog modulation techniques. By considering this types of uses in the digital modulation which can be countable and taking this is an advantage which can be useful for the development of the Very Large Scale Integration (VLSI) and also in Digitla System Processing (DSP). As compare to the analog modulation techniques the digital modulation has more and most popular advantages. It also consists of the ability techniques such as correction of error, higher spectral efficiency, and good solitude, good protection and so on. MQAM is also more effectiveness for the use of the digital modulation techniques.
It gives the rejection for the noisy signals and offers determination of the multiplexing for the different types of data information, and it decreases the arrogance to the channel. This type of techniques enables most protection for the efficiency. Providing the data information to the appropriate transition of wired and wireless medium is the general procedure of the digital modulation. By accepting the digital bit of cascade, ditial modulation can be done by modulation analog singles. By this the digital modulation transfers many process for the development. Such as: affinity of the digital services, improving the quality, data information protection, fastness of the system (Andrea |Goldsmith, 2005).
Digital modulation is generally used for the transferring the data to the short range to the long range. Coming to the short range transmission is relay up on the base band modulation which is very useful for referring the line coding. As for the long range transmission is relay up on the "carrier Modulation". The influenced different elements of the digital modulation can be explained in the below information. Those elements such as: phase, amplitude and Frequency. By accepting these elements can be converted into 3 modulated techniques. They are:
Phase Shift Keying (PSK)
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
This modulation can also be innovated by the two advanced schemes. They are:
Quadrature Amplitude Modulation (QAM)
Quadrature Phase Shift Keying (QPSK).
1.2 QPSK:
This QPSK is the modulated phase algorithm. The frequency modulation is adapted from the phase modulation, by changing each phase shift the digital information will be encoded the bits from the phase of carrier waves. The ''PSK'' is the frame of the phase angle modulation, which can be able to perform the number discrete states. Instead of the analogue modulation channel, the digital modulation can easily transmit the data pulses or the information with the consistent amplitude. The binary input of the signal of the QPSK can be considered as into 2 variations. This is named as the bits. Each bit can provides into four different possible outputs. Each bit has its own waveform to transmit the carrier signals while completion of the modulation.
In QPSK very frequently and friendly used modulated technique in the wireless and the mobile communications systems. Because, by increasing the bandwidth efficiency it doesn't gives the trouble from the abjection of the BER. In this technique, it reduces the bandwidth requirement; this can be the advantage of the QPSK. By transmitting the two bits of the signal modulated symbols, QPSK has double the bandwidth efficiency as compared to the BPSK. This carrier signals will occupies in to the equally spaced distance such as: 0, π/2, π, and 3π/2. The QPSK can be defined as
So/p M(t) = sqrt(2E/T)*cos[2πfct+(i-1)*π/2]0≤t≤T,i=1,2,3,4 .............................. [1]
Where 'T' referred as the duration of the symbol and also it is two times the bit period. By taking the trigonometric functions the above equation can be written in the intervals 0<=t<=T, as follows
So/p M (t) = sqrt(2E/T)*cos(2Ï€fct)*cos[(i-1)*Ï€/2]- sqrt(2E/T)*sin(2Ï€fct)*sin[(i-1)*Ï€/2]............[2]
Assume that
C1(t)=sqrt(2/T)*Cos(2Ï€fct)..................................................[3]
C2(t)=sqrt(2/T)*Cos(2Ï€fct)...................................................[4]
By substituting above equations 3&4 in the 2nd equations we get the result for the four intervals
So/p M(t)=sqrt(E)*C1(t)*Cos{(i-1)* π/2}-sqrt(E)*C2(t)Sin{(i-1)* π/2}i = 1,2,3,4........................[5]
Fig 1.1: QPSK modulation signal, inphase signal and the Quadrature signal.
Fig 1.2: QPSK diagram with the carrier phases with 90°,180°,270°,360°
Fig 1.3:QPSK diagram with carrier phases of 45°,135°,225°,315°
1.3 QPSK Modulator:
This modulator mainly contains on the shift registers for converting the serial to parallel. This conversions is normally uses to gives information input bit stream to dual bit stream like 'Quadrature bit' (Q) and 'Phase bit'(I). Each bit of I and Q is provides to the unipolar(return zero) converter to the bipolar(non-return zero) converter. The signals like the bipolar and the carrier waves will accomplish by the oscillator and is provided to the analogue multiplier. The two signals of the multiplier provides the two stages and in the each stage of the resulted multiplier is added to the summing amplifier that signals are passed from the band pass filter to get the output of the QPSK signals. This can be done from the analogue multiplier. This can be shown in the below fig 1.4 block diagram. The output of the QPSK signals is transfer to the QPSK demodulator which will considered as the input and which takes the signals from the receiver.
Fig 1.4: Block diagram of the QPSK Modulator.
1.4 QPSK demodulator:
This is the shift key changes the phase by the quaternary signals. The input is taken as an icon from the modulation signal which can be represents as a baseband. As a provided from the model of the coherent carrier signal waves, the circuit is much critical to the demodulation section. The decomposed signals from the modulation which is taken as an input by considering the two consistent frequencies are the outputs of 90°, also produces two times the values of an oscillator. The PCM signals are referred from the conversion of the parallel to serial which can also translates the dibits to bits, along with the utilization of the two low pass filters. The resulted of the two bits of each part from the low-pass filter is provided to the multiplexer to represent the input information.
1.5 Advantages and disadvantages of QPSK:
The Quadrature phase shift keying has its own advantages and disadvantages, some of them provided in the below discussion.
1.5.1: Advantages:
As increasing the bandwidth efficiency QPSK doesn't gives any trouble from the abjection of the BER.
Since the QPSK has two bit which transmits and also connected to the dibits, this QPSK need 50% of the bandwidth which can be uses in the BPSK modulators. As providing the 50% of the bandwidth, QPSK will increases by the rate of transmission. (J.S. CHITODE, 2008).
1.5.2: Disadvantages:
The information is looses at a particular highest level.
This gives the phase shift of the maximum 180°, and will be in middle of even and odd bits. (J.S. CHITODE, 2010).
At transmitter end as operating the low efficiency of the power amplifier the side lobes of the shape will be lost.
1.6 Operational Amplifiers:
1.6.1 OPAMP Introduction:
An operational amplifiers is favourably distinguishes by Op-Amp. Op amp consists of different inputs and with the single output. Generally op-amp is a DC coupled with the high gain voltage of an electronic amplifier. Apart from this we can also say that, the op-amp brings out the voltage of an output with maximum thousands times higher than the input voltage terminals.
Fig 1.5: OP-AMP
The provided fig 1.5 gives the information of the basic format of an operational amplifier. The above op-amp has provided with the two inputs and single output. By explaining the two terms of inputs named as inverting input and the non inverting input. Basically one term inverting input is signifies with the negative (-ve) symbol and the other non inverting terminal is signified by the positive (+ve) symbol. The remaining terminal output which measures the coming values and notice the signals.
The main basically components of an Op-amp take the help of the 2 power supplies. In this two power supplies one is connected to the positive side of the power supply and the other is connected to the negative side pf the power supply. Usually the second one of the negative power supply is treated as a ground for every signal.
Commonly, at the output term an Op-amp will assumes the high gain. The differential between of the two input terms as inverting and the non-inverting o an Op-amp is can be calculates from the output. By this can say that, if the inverting terminal is higher the value then the output can be seen in the negative range while the other non-inverting is in the higher the value then the output can be in the positive range. Maximum of the circuits are used from the AC coupling circuits, because, AC circuits has the capacity to control the gain.
Op-amp can also use the feedback paths as +ve and -ve. Negative path means in the middle of output and inverting terminal of input a resister is attached, because at the inverting terminal a minute threshold voltage can be found. For that we need to use the resister. As in the same way in the middle of the output and the non inverting terminals a capacitor or the resistive characterise component should be attached.
1.6.2: Pin configuration:
Fig 1.6: pin configuration of an op=amp ic 741
The above fig 1.6 gives sketch of pin configuration of an op-amp. This 741IC consists of the eight (8) pin with the dual line configuration packages of an op-amp. Each pin has its own name and has its own character. 1st pin is an operation for the Offset null, which is no connection for the practical usage. 2nd and 3rd pins are the operations for providing the inputs named as inverting and non inverting terminals. 4th pin is an operation for the negative power supply which is also providing as the ground. 5th and 8th pins are used to balance the signals. 6th pin is an output. And the 7th pin is connected to the positive power supply and naming itself positive power supply.
1.6.3 Ideal Operational amplifier:
Generally in the practical period the ideal Op-amp is very rare to use. Generally this can be defined in two separate paths named as +ve feedback path and -ve feedback path . Op-amp can also use the feedback paths as +ve and -ve. Negative path means in the middle of output and inverting terminal of input a resister is attached, because at the inverting terminal a minute threshold voltage can be found. For that we need to use the resister. As in the same way in the middle of the output and the non inverting terminals a capacitor or the resistive characterise component should be attached.
1.6.4 Characteristics of ideal Op-amp:
Input impedance will be high which is nearly close to infinite.
Open loop gain is in high position which cannot be the infinite.
It produces the low amount of current at the input terms.
The rejection ratio will be in the common mode.
1.6.5 Implementations:
Subtractor
Differential amplifiers
Integrator
It can also achieve as a buffering voltage.
It can implement differentiator.
It also achieves the conversion of voltage to current.
CHAPTER 2
In this present globalization each and every person is racing behind the technologies. Mainly, internet technologies are moving very fast. If a person wants to communicate the information to other, information can receive in a fraction of seconds. Means the communications gap is decreasing in these days. This type of technologies can be observed in the wireless technologies. From this technology, mobile technologies are moving very expose to human life. Now a day we can say that, wireless technology is a part of the human life. Because of the higher usage of human power and advanced technology equipment, wireless technology has got fame. Apart from this, it is most reliable, high density; it takes less power with the less noise.
Any how this digital world as faced many problems, which is invented because of higher the number of sources with higher the number of wireless users in the limited bandwidth region. For sending the digital data information to recover at the destination part, we use in 3 different types of digital modulation technologies. By associating these 3 technologies we get another modulation, named as quadrature modulation. While in the modulation process, it provides the high bandwidth. This is the major disadvantage.
As in this portion we provided the Quadrature Phase Shift Keying modulation and de-modulation to decrease the higher bandwidth in Quadrature Amplitude Modulation (QAM). In one modulation symbol it can transmit 2 bits of digital data information, which can be very useful to produce good amount of BER in the QPSK. The carrier phase will be equally space in 4 values of degrees. They are: 0, π/2, π, 3π/2 and each has its own massage bits.
Offset QPSK:
Commonly, in the modulation and the demodulation the QPSK of the amplitude of the signal waves are consistent entire the process. OPSK is the variation from the PSK which is used by the differential values. These four differential values are transmits from the phase. This OPSK is also named by Staggered Quadrature Phase Shift Keying (SQPSK). These are in the pulse shaped waveforms, with this pulse waveforms the constant information may lose. Signal cannot intersect the values zero, because, it can allow only 1 bit to change the symbol in a particular time. To construct the QPSK symbol, it allows only 2bits of ther phase signals to move as easily as into 180 degrees in a perticulat time span.
If the signal is in low pass filter, there is a fluctuation in the signals by providing huge amplitude in phase shift output and also the gaining quality of the communication will be unacceptable. Even by keeping the offset time in the odd or even bits, the phase and the quadrature character doesn't change at common time. By this can say that the phase shift cannot cross at a time the 90 degrees. This produces the low amplitude of fluctuations as compare to the non-OPSK. The difference between QPSK and OPSK is, in the QPSK the signal can change 180degrees in one time, whereas the OPSK signal doesn't change more than 90degrees.
Chapter 3
3.1 Methodology:
To designing the QPSK modulator and demodulator which is done on the bread board. Bread board acts as short time of a circuit. This is mainly used for the testing the circuit or to get an idea of the design or the section. This bread board mainly comes without soldering. If without soldering, it is very comfortable to adjust the equipments or the connection of the circuit. With this, there is no damage of the components and also can be reuse. This is the main advantage of the bread board. In modern days this is coming by the name is solder less breadboard. This is also called as Plug Board.
Bread board is of two types. One is soldering and the solderless brad boards. Commonly, soldering bread board is used at the high frequencies, but solderless bread board is doesn't act and cannot give an accurate information.
3.1.1 Requirements of the Bread board:
As in the coming bread boards includes with the nickel spring clips. This is done under the breach.
As the bread board gap between every hole is 0.1 mm.
These holes can be used for the connection of the equipments. Such as : resistors, capacitors, inductors, IC's and etc.,
3.1.2 Restraints of Bread board:
As the presence of using the stray capacitance and large inductance in the middle of connections the bread board can damage. Because of these types of bread boards are mainly used for the low frequencies, i.e., 10MHz.
As using the large resistance power is also can be a bad situation (problematic) for the DC and low frequencies.
For these types of bread boards the voltage and current is also a restraint.
For designing the complicated circuits it is difficult to handle, because of huge amount of connections are used for the solder less bread boards.
3.2 Implementation of OPSK modulator:
3.2.1 QPSK Modulator:
This modulator mainly contains on the shift registers for converting the serial to parallel. This conversions is normally uses to gives information input bit stream to dual bit stream like 'Quadrature bit' (Q) and 'Phase bit'(I). Each bit of I and Q is provides to the unipolar(return zero) converter to the bipolar(non-return zero) converter. The signals like the bipolar and the carrier waves will accomplish by the oscillator and is provided to the analogue multiplier. The two signals of the multiplier provides the two stages and in the each stage of the resulted multiplier is added to the summing amplifier that signals are passed from the band pass filter to get the output of the QPSK signals. This can be done from the analogue multiplier. This can be shown in the below fig 1.4 block diagram. The output of the QPSK signals is transfer to the QPSK demodulator which will considered as the input and which takes the signals from the receiver.
Fig 1.4: Block diagram of the QPSK Modulator.
As mention in the above block diagram, these blocks can be briefly explained. The blocks involves such as:
Serial to parallel shift register
Unipolar to bipolar converter
Multiplier
Summing amplifier
90° phase shifter
Band pass filter
3.2.2 Shift register:
Shift registers are one of type of sequential logic circuits, which can be very supported to digital counters. These registers are highly used for the storing the digital data information. These registers are the groups named as a flip flops. These flip flops are arranged in the link order, with this link order the output of the flip flop is converts into the input of the coming flip flop. Each flip flop contains the storage of 1 bit.
3.2.2.1 Basic shift register:
As mentioned in the above, the shift registers are arranged in the link format with the group of the flip flops. These flip flops are used for the developing an applications to store the data information and to transfer the data. Generally shift registers are used to store the data or to transfer the data from the output source to the internal source. The data will be in the form of 1's and 0's. The general block diagram can be seen in the below figure.
Fig 3.2 flip flop data storage
In generally registers will perform in two different actions, i.e., to store the data and data movement. From the above fig says that, when 1 is on to the D flip flop the clk will sents into the higher level and it comes as an output 1. As in the same other, when 0 is on to the D flip flop the clk will sets into the lower level and gives an output as 0.
3.2.2.2 Serial to parallel shift Register
Fig serial to parallel shift register
The provided fig is the two bit serial to parallel shift register. By the mane itself can be say that the data input is provided in serially to the shift register. As provided input to the shift register the output will achieve to the parallel. Due to the information data is stored at every stage of an output, so the output bits are obtained in the form of simultaneously.
The i/p administers the next data admittance, because of the coming data information is less. Not only administrating the data admittance but also it can accommodate the 1st flip flop at the newest pulse. If the CLK i/p is higher or lower, then the serial i/p may be changed. The shift register illustrates that in the acknowledgement transition of the CLK in the form of low to high (Anil Kumar Maini, 2007).
As for the practical implementation, instated of the shift register we use the 2bit of SN7474DR. This will be in the two way of triggered D filp flop. This is an IC. This is the 14 pin configuration, which will be in the dual line assortment. The pins are follows like: clear, preset, clk, i/p data, o/p data, gnd, supply. This 14 pin configuration can be seen in the below fig.
Fig : D type flip flop
From the provided fig we can say that, the i/p (digital data) can be gives to the 2nd pin will applies to the 3rd pin CLK. The CLK is same for both the pins as 3rd and 11th. The o/p can be seen from the pin like 5th and 9th. For the 14th pin the power supply is given.
3.2.3 Unipolar to Bipolar Converter:
This converter holds as the i/p as square pulse waveforms and the noise pulses. For every pulse of the width the time duration is will be increments. This converter assistance when the series of an action is achieved to the result of the components of 0 to 5 volts. It alos provides the good result when the process is going with the -5v to +5v for the design of the circuit. This is happen when the every period of the shift registers and analogue multiplier is in the middle of the unipolar to bipolar converter. This can be seen in the below fig .
Fig : Unipolar to bipolar converter
The transfer behaviour of the unipolar to bipolar is derived as
Vout = V2*[Re/(R2+Re)]*[1+(Rf/R1)]-V1(Rf/R10 ………………………….. Eq [1]
3.2.3.1Derivation:
This can be derived by taking the help of superposition theorem. This theorem gives the information of the effect of the complete current in linear circuit is absolutely same for every algebraic sum of the provided current which is individually separated. By taking the experiments on the below figures as that V2 is under the GND and calculate the Vo2.as in the same of the other V1 is under GND and calculate Vo1. Add these two results.
As in the above sentences, firstly connect the resister (R2) to GND instead of V2 supply. As connecting in this form we can find that circuit is an inverter. So the inverter is achieved as a non inverted i/p which is attached to the GND. Hence, the below fig appears.
Fig : Inverter
Vo1 = -V1*[Rf/R1] ……………………………………………………………Eq[2]
Let's go to remove the V1 and instead of V1 attach the ground to the resistor (R1). By connecting R1 to GND id becomes as non inverting amplifier.
Vo2 = V*{1+[Rf/R1]}…………………………………………………………..Eq [3]
As R1 and Rf are attenuator to the V1, so V comes as
V = V2 * {Re/[R2+Re]}…………………………………………………………..Eq [4]
The below circuit is non inverting amplifier.
Fig : non inverting amplifier
By adding the above three equations Vo is same of Eq 1
Fig: square waveforms of unipolar and bipolar.
3.2.4 90° phase shift circuit:
Op-amp has certain number of phase shift circuits. All frequencies of an operational amplifier of interior loop ckts will have the path in the way of a unity gain. The signal frequencies will be adjusted due to the i/p phase signal changes. The below fig is about the 90° phase shift ckt. For this the i/p will be in the sine wave carrier signal. By adjusting the resistance value of the circuit, we can observe 90° phase shift. It comes closer to the non inverting terminal which is attached to the variable resistance. Hence the, in this case the accurate phase shifts at 0° to 180° . The 90° phase shift circuit can be observed in the below figure.
Fig : 90° Phase shift circuit.
By choosing the capacitance and the variable resistance values, we can find the phase difference of the provided circuit. This can be given in the form of
(Phase difference) degree = tan {[(2*W/R*C)/((W^2)-(1/R*C)^2))]}^-1........................Eq [5]
Assumptions:
In this case phase difference will in the form of 90° and W = 2*Ï€*frequency
As in the practical section the frequency can be selected at 10 KHz.
By substituting this in the provided above equation we get
Fc = 2*Ï€*RC..........................................................................................................Eq [6]
Where C is the capacitance which is 10nF and R is the 5 KΩ..
Hence the carrier sinusoidal and the phse shift waveforms can be shown in the below figure.
Fig : 90° phase shift carrier signal
3.2.5 Analog Multiplier:
Normally in the electronic section is, by holding the two i/p analog signals gives the result as their product. Commonly analog multiplier is helps to multiply i/p analog or digitls and in the case of the continuous signals or discontinuous signals. In this circuit it contains 2 i/p ports and a single o/p port. If and only 2 i/p signals multiply then the resultant o/p will be formed. The below figure gives the basic information on the multiplier.
Fig: Basic multiplier circuit
Fig : The above figures are the i/p and o/p wave forms.
As for the practical usage of the QPSK modulator need to take with the help of an IC. That IC named as AD633JN. The pin configuration can explained in the below fig.
Fig pin configuration
Frm the figure we can observe that, 1st and 3rd pins are used as i/p for the analo multiplier, 7th pin is used as a output. As in the same way the 2nd and 4th pins are using as ground (GND). Finally 5th pin is used for the negative (-ve )power supply and the 8th pin us used for the positive (+ve) power supply. This positive power supply can be connected from 8v to 18 v ( Analog Devices, 2010).
3.2.5.1 Highlights of AD633JN:
Ic AD633JN has 4 quadrant multiplier. It connects with the 8 dip with lead packages.
This is cheaper in the price to supply.
To operate this IC AD633JN there is no need of any out source of equipments or no need of using with the hi-fi calibrations.
Due to the manufacture of the monolithic and the laser calibrations, the IC AD633L will be more constant and also be adjustable.
Because of the high i/p resistance the source of the signal is negligible. The resistance value comes as (10 MΩ).
3.2.5.2 Applications of AD633JN:
This IC AD633JN can be used in many portions. From that few portions can be provided few applications such as :
In can be a major part of the modulation and the demodulations.
It is much utilizable for controlling the automatic gain systems.
Voltage controlled amplifiers
Frequency doublers
Power measurements
3.2.6 Summing Amplifier:
As provided below circuit is shown as the summing amplifier. This is an adjustable circuit part of the QPSK modulator. It is operated by taking with the help of the inverting amplifier. This amplifier is much establishes as in the form of the inverting OP-Amp. Here we can observe that, both the i/p resistance of the inverted amplifier and the inverting Op-Amp is attached. By connecting both the amplifiers will get another resistor which can be corresponded to the i/p resistance attached by the R end with the other Op-Amp. This process is comes as summing amplifier. This total process can be seen in the below circuit diagram. Summing amplifier is also named as summing inverter or voltage adder.
Fig Summing amplifier
The proportional of the two separated i/p's is the resulted output (Vout).
Vout = -[Rf/R]*[V1+V2] ...............................................................................................Eq (7)
Where R = R1 = R2 because of the two separated i/p resistance values are equal (James William Nilsson and Susan A. Reidel 2008).
3.2.7 BandPass Filter:
Generally, filter has its own place and utilization in the digital world. Band pass filter can be explained as, it provides the frequencies to allow under the cut off frequencies and also it adjustable to provide the frequencies higher the cut off frequency.
In the QPSK modulator operation, this filter will decrease the noise signal. Apart from decreasing the noise it also assists to transmit the information which across the channel. Band pass filter which admits within the specified range of frequencies and also it can controls the higher and lower frequency ranges (ECELab, 2006). The band ass filter circuit diagram can be seen in the below figure.
Fig Band pass filter
From the above circuit diagram we can observe that the output of the summing amplifier is i/p for the band pass filter (ECELab, 2006). By using the variable resistance the signal can be tenable to the required signal.
