SIGNAL CONSTELLATION DIAGRAM (SCATTER PLOT) FOR ALTERED MODULATION SYSTEM FOR THE FIXED WIMAX AND...

8/11/2019 SIGNAL CONSTELLATION DIAGRAM (SCATTER PLOT) FOR ALTERED MODULATION SYSTEM FOR THE FIXED WIMAX AN

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International Journal of Exploring Emerging Trends in Engineering (IJEETE)

Vol. 01, Issue 01, Sept, 2014 WWW.IJEETE.COM

All Rights Reserved 2014 IJEETE Page 7

SIGNAL CONSTELLATION DIAGRAM (SCATTER PLOT) FOR ALTERED

MODULATION SYSTEM FOR THE FIXED WIMAX AND MOBILE WIMAX

1Ankur Bindal,2Manish Kansal1Dept. of ECE,MMEC , Mullana ,Haryana

2

Head of Dept. ECE, Panchkula engineering College , Mouli ,Haryana

ABSTRACT

The endeavour of this paper is to analyze the

scatter plot for altered modulation system for

WiMAX physical layer with the implementation

of different modulation formats, for fixed

(IEEE802.16d) and Mobile WiMAX

(IEEE802.16e) . The Simulation also includes

the altering multipath fading (Raleigh and

Rician) channels and their parameters. Asegment of synthetic data is used for the

analysis.. In addition to this, channel assessment

is computed using a popular technique known

as interpolation. Computer simulation results

based on Scatter plot for alternation modulation

system demonstrate that the performance.

Keywords: WiMAX, IEEE802.16e,

IEEE802.16d

I INTRODUCTIONIn last decade, for high data rate applications

orthogonal frequency division multiplexing is

among the most important preference. In this

technique, instead of using single wide band

carriers a number of narrow band carriers are

used and it is also effectual to deal with

multipath fading channel. OFDM is used for

reducing the Inter symbol Interference (ISI) by

avoiding multipath in frequency selective

channels. WIMAX is short form of eWorldwide Interoperability for Microwave

Access. WiMAX is mainly used for high

bandwidth application. For the implementation

of the WiMAX model, simulation model used is

MATLAB. Based on the various modulation

techniques in this paper we are investigating the

performance of Scatter plot in altered channels.

To enhance the performance of the system here

sub allocation of carriers.

II WIMAX SIMULATION MODEL

To implement the OFDM transmission scheme,

the system is divided into three sections

Transmitter, Channel and Receiver. In the,

binary input data sequence is take place in the

transmitter. Forward Error-Correction Coding

(FEC)and interleaving is done to give frequency

diversity. The series is encoded by a

convolutional encoder. Then Interleaving isapplied to randomize the occurrence of bit

errors prior to increase performance.

After interleaving, the binary values are

converted to symbol values, on which digital

modulation scheme is applied[1]. Previously,

multi-carrier systems were implemented

through the use of separate local oscillator. This

was both inefficient and costly. With the start of

cheap powerful processors, the sub-carriers

currently be implemented by the FFT which

keep tones to orthogonal with each other the

symbol is modulated onto sub carriers by apply

the Inverse Fast Fourier Transform (IFFT).

Output is converted to serial and a cyclic

extension is added to make the system robust to

multipath propagation. [2]

In channel, additive white Gaussian noise

characteristics are taken. The receiver performs

the reverse operations of the transmitter. After

removing the cyclic extension, the signal can be

applied to a Fast Fourier transform to recoverthe modulated values of all subcarriers. The

modulated values are then demapped into

binary values, and finally deinterleaving and

Viterbi decoder decodes the information bits[4].

III SUBCARRIER ALLOCATION

WiMAX define three types of subcarriers: null

subcarriers, data and pilot. The mapped data

symbols from the very last step are arranged to

be a matrix where its rows number is equal to


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the number of data subcarriers (S). Other then

pilot, data subcarriers and NULL sub-carriers is

inserted in the input signal.

Basically one OFDM symbol consists of the

Sdata PSK or QAM symbols, Spilots and Sguardempty symbol. The total amount of sub-carriers

is calculated by the number of points required toperform IFFT. The data sub-carriers are

weighed down by the data symbols modulated.

Fig. 1Sub-carrier allocation

Pilot symbols can be used to execute frequency

offset compensation at the receiver. These pilots

are obtained by a pseudo-random binary

sequence (PRBS) generator that is based on the

polynomial x11+x9+ 1[5].

IV SYMBOL MAPPERThe interleaved bit data are then passed to the

constellation mapped, where depending upon

the data size modulation scheme is applied.

There are four different modulation schemes i.e.BPSK, QPSK, 16-QAM and 64 QAM.

Modulation is done by representing a modulated

signal by distributing the incoming bits into

groups of i bits. The number of points will be

represented on the constellation diagram, there

will be 2ipoints.

The size of I is 1, 2 ,4,and 6 for

BPSK,QPSK,16QAM,64QAM respectively.

The constellation diagram is having two

components i.e. In-phase component (I) andQuadrature component (Q). This adaptive

modulation and coding (AMC) is used

efficiently for improve the BER in the WiMAX

system.[7]

V OFDM MODUALTIONMobile radio channels introduce severe

multipath propagation due to multiple scattering

from objects in the surrounding area of the

mobile. Also the gesture of the mobile unit

introduces a Doppler shift which causes abroadening of the signal spectrum.

The multipath channel can also be frequency

selective in which case the fading envelope of

the received signal at one frequency might not

be correlated with the envelope at another

frequency. To obtain a channel which has no ISI

it is necessary that the symbol time Tsshould be

more or greater than the channel delay spreadtime and if the symbol time approaches or

falls below the channel delay spread time then

the BER becomes intolerable and the system is

unbearable.[4]

The key benefit is that the parallel transmission

enlarges the symbol time by modulating the

symbols into narrow sub-channels. This

increase in symbol time makes it more vigorous

to the channel delay spread effects.

VI CHANNEL

We use the following function for the :-

Ricianchan (Ts, fm, kFactor, tau, pdb)

Rayleighchan(Ts,Fm,tau,pdb)

To create a Rician channel and Rayleigh

channel object chan where the following

parameters are as follows:-

Input sample period is Ts,Maximum Doppler shift isfm,

A vector of Rician kfactor is kFactor,

A vector of path delays tau,

and a vector of average path power gainspdb

(in dB).

VI DOPPLER SPREAD IN CHANNELDue to the multipath propagation of radio

waves, multiple copies of the same signal are

received at the receiver end. If the user is

moving with some velocity (speed), there is ashift of frequencies in each of these received

signals [5]. This process is known as Doppler

shift.

(2)

Where, be the Doppler shift frequency, isthe velocity of moving object,

be speed of light and is an angle withrespect to reference point.


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Where,be the Doppler shift frequency,

is carrier frequency (2.500e9 Hz)

is the velocity of moving object,

be speed of light (3e8 m /s) and

is an angle with respect to reference point.

For velocity =30 Km/h, the Doppler frequency

will be:-

For velocity =60 Km/h , the Doppler frequency

will be :-

VII RECIEVER SECTION

The receiver will perform the reverse procedure

as that of the transmitter by the help of channelestimation. Firstly, down converter and filtering

and the FFT algorithm is processed. OFDM

symbol is composed by data, pilots, a zero DC

subcarrier, and some guard bands.

Thus, a process to break up all these subcarriers

is needed. Primary, the guard bands are

removed, and then, a disassembling is

performed to acquire pilots and data. The pilots

subcarriers are used in the channel estimator,

which compute the channel coefficients

VII SIMULATION RESULTSIn this simulation work, In scatter plot, the

transmitted symbol is denoted by the + and the

received signal is denoted by symbol without

equalization. The equalized signal is denoted by

the . and from these plot the effect of fading in

multipath channel on the phase and amplitude

of the symbol. The equalized signal is required

to compensate the fading effects. Fig 7.1-7.8

shows signal constellation diagram (scatter plot)

for different modulation techniques such asBPSK, QPSK, 16-QAM, 64- QAM for the fixed

WiMAX. When the arriving signal is passed

through the channel, subsequently the

performance of the system degrades due to

fading cause and Doppler spread. The channel

has three paths consisting of LOS path and two

Rayleigh components. The required signal is

corrupted by the previous multipath model.

Scatter plot comparison among the fixed

WiMAX for two different channels for the

modulation technique: - BPSK

Figure 1signal constellation diagram for BPSK in Rician

channel for fixed WiMAX

Figure 2signal constellation diagram for BPSK in

Rayleigh channel for fixed WiMAX

-2 -1 0 1 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Quadrature

In-Phase

BPSK ,Rician channel

Received signal

Equalized signal

Signal constellation

-1.5 -1 -0.5 0 0.5 1 1.5

-1.5

-1

-0.5

0

0.5

1

1.5

Quadrature

In-Phase

BPSK ,Rayleigh channel

Received signal

Equalized signal



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modulation technique: - QPSK

Figure 3signal constellation diagram for QPSK in Rician

channel for fixed WiMAX

Figure 4Signal constellation diagram for QPSK inRayleigh channel for fixed WiMAX



modulation technique: - 16-QAM

Figure 5Signal constellation diagram for 16-

QAM in Rician channel for fixed WiMAX

Figure 6Signal constellation diagram for 16-QAM inRayleigh channel for fixed WiMAX

-1 -0.5 0 0.5 1

-1

-0.5

0

0.5

1

Quadrature

In-Phase

QPSK ,Rician channel

Received s ignal

Equalized signal


-2 -1 0 1 2

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

Quad

rature

In-Phase

QPSK ,Rayleigh channel

Received signal

Equalized signal


-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

Quadrature

In-Phase

16-QAM ,Rician channel

Received signal

Equalized signal


-6 -4 -2 0 2 4 6

-6

-4

-2

0

2

4

6

Quad

rature

In-Phase

16-QAM ,Rayleigh channel

Received signal

Equalized signal



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modulation technique:- 64-QAM

Figure 7 Signal constellation diagram for BPSK in 64-

QAM channel for fixed WiMAX

Figure 8 Signal constellation diagram for 64-QAM inRayleigh channel for fixed WiMAX

Scatter plot comparison among the MobileWiMAX for Rayleigh channel having different

velocities for the modulation technique:- BPSK

Figure 9 Signal constellation diagram for BPSK in

Rayleigh channel for Mobile WiMAX(V=30km/h)

Figure 10 Signal constellation diagram for BPSK inRayleigh channel for fixed WiMAX(V= 60km/h)

-15 -10 -5 0 5 10 15

-15

-10

-5

0

5

10

15

Quadrature

In-Phase

64-QAM ,Rician channel

Received signal

Equalized signal


-15 -10 -5 0 5 10 15

-15

-10

-5

0

5

10

15

Quadrature

In-Phase

64-QAM ,Rayleigh channel

Received signal

Equalized signal


-2 -1 0 1 2-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Quadrature

In-Phase

BPSK ,Rayleigh channel , For mobile WiMAX =>>v=30km/h

Received s ignal

Equalized signal


-2 -1 0 1 2-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Quadrature

In-Phase

BPSK ,Rayleigh channel , For mobile WiMAX =>>v=60km/h

Received signal

Equalized signal



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Scatter plot comparison among the Mobile

WiMAX for Rayleigh channel having different

velocities for the modulation technique:- QPSK

Figure 11 Signal constellation diagram for QPSK in

Rayleigh channel for Mobile WiMAX(V=30km/h)

Figure 12 Signal constellation diagram for QPSK inRayleigh channel for Mobile WiMAX(V=60km/h)

CONCLUSION

In OFDM system with IEEE 802.16 standard

implementation for Fixed and mobile WiMAX,

the various modulation techniques are tested fordifferent channel conditions. The BER

performance of system through broadband

WiMAX-PHY layer based wireless

communication system adopting the RRC

Transreceiver filter and Sub allocation of

carriers along with different digital modulation

schemes is evaluated. A range of system

performance highlights the impact of digital

modulations. The most important conclusions

are given below:

From the channels, the multipath fading

effects is studied and simulated.

From the scatter plot, it is observed that

multipath fading in channel causing the

phase rotation and amplitude changes. The

desired signal is distorted by the multipath

model.

At last when the comparison of system

performance with and without equalization

is estimated. The results can be easilyanalysis by the scatter plots

From the above three main points, we can

conclude the performance factors in terms of

Scatter plot of WiMAX. Lowest multipath

fading is of the Fixed WiMAX as compared to

the Mobile WiMAX. In case of high data rate

only the higher level modulation (64- QAM)

can provide that rate. When the channel is came

into consideration Rician channel is having the

efficient utilization of the signal.

REFERENCES

[1] Vikas K. Sukhjit Singh;WiMAX Physical

Layer Simulator Using Different ModulationSchemes ;IJCER, Vol. 3 Issue. 2,Issn 2250-

3005, 2013.

[2] Hardeep Kaur, M L Singh; Bit Error Rate

Evaluation of IEEE 802.16 (WiMAX) in

OFDM System ;IJCA-09758887 , Volume40No.12 ,2013.

-3 -2 -1 0 1 2 3-3

-2

-1

0

1

2

3

Quadrature

In-Phase

QPSK ,Rayleigh channel,For mobile WiMAX =>>v=30km/h

Received signal

Equalized signal


-3 -2 -1 0 1 2 3-3

-2

-1

0

1

2

3

Quadrature

In-Phase

QPSK ,Rayleigh channel,For mobile WiMAX =>>v=60km/h

Received signal

Equalized signal



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[3] Yongxue Wang; Study of Interpolation

Algorithm for WIMAX-OFDM System ;

Journal of Information & Computational

Science9: 13 (2012) 36733681, 2012.

[4] Md Ash. Islam,Riaz Uddin, Md.Zahid;

Performance Evaluation of Wimax Physical

Layer under Adaptive ModulationTechniques and Communication Channels;

University of Rajshahi, Rajshahi,

Bangladesh;IJCSIS-vol.5,No, 2009.

[5]Theodore S. Rappaport; Wireless

Communications: Principles & Practice, 2nd

ed., Prentice Hall,2007.

[6]Israel Koffman, Vincentzio Roman;

Broadband Wireless Access Solutions Based

on OFDM Access in IEEE 802.16, IEEE

Communication Magazine,2002.

[7] J. Mountassir, M. Kovaci et.al ; A

physical layer simulator for WiMAX inRayleigh fading channel,6th IEEE

International (SACI), pp. 281-284,2011.

AUTHORS BILOGRAPHY

Ankur Bindal received his

B.Tech. degree in Electronics

and communicationEngineering from Jind Institute

of Engineering and

Technology, Jind, Haryana in

2011 and M.Tech in ECE

from Panchkula Engineering College,

Panchkula, Haryana. Presently He is working in

Department of Electronics and Communication

Engineering in M.M.E.C., M.M.U. Mullana

(Ambala).

Manish Kansal received his

B.Tech. degree in Electronics

and communication

Engineering and M.Tech in

ECE from M.M.E.C., M.M.U.

Mullana. Presently He is

working as Head of ECE department and

Assistant Professor in Department of

Electronics and Communication Engineering in

P.E.C., Mouli (Panchkula).

SIGNAL CONSTELLATION DIAGRAM (SCATTER PLOT) FOR ALTERED MODULATION SYSTEM FOR THE FIXED WIMAX AND...

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