ijetae_0913_79

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 9, September 2013)

493

OFDM Simulator Using MATLAB Deepak Sharma

1, Praveen Srivastava

2

1Research Scholar,

2Assistant Professor, EC Department, KIT Kanpur

Abstract Orthogonal frequency division multiplexing (OFDM) is a special case of multicarrier transmission and

frequency division multiplexing, where a single data stream is

transmitted over several lower rate subcarriers, placed

orthogonal to each other. Today it is becoming the chosen

modulation technique for wireless communications. It can

provide large data rates with optimum bit error rate and

enough robustness to radio channel impairments. In this

paper, a user interface is designed using GUI tool of MATAB

which facilitates us to analyze the performance of OFDM

system in terms of SNR vs. BER variation. BPSK, QPSK and

QAM techniques are analyzed in reference to OFDM

processing. Rayleigh Fading channel and Multipath fading

channels are used as a communication channel.

Keywords AWGN, Bit Error Rate, GUI, ISI, Multi Path fading channel, OFDM, Signal to Noise ratio

I. INTRODUCTION

Wireless communications is an emerging field, which

has seen enormous growth in the last several years. The

huge uptake rate of mobile phone technology, Wireless

Local Area Networks (WLAN) and the exponential growth

of the Internet have resulted in an increased demand for

new methods of obtaining high capacity wireless networks.

Most WLAN systems currently use the IEEE802.11b

standard, which provides a maximum data rate of 11 Mbps.

Newer WLAN standards such as IEEE802.11a and

HiperLAN2, are based on OFDM technology and provide a

much higher data rate of 54 Mbps. [1]

However systems of

the near future will require WLANs with data rates of

greater than 100 Mbps, and so there is a need of technology

which supports these higher data rates and maximum

spectral efficiency. OFDM is most suitable techniques for

these high data rate applications. OFDM is presently used

in a number of wired and wireless communication systems.

It is a special case of data transmission, where a single data

stream is transmitted over a number of sub carriers (SCs) to

increase robustness against frequency-selective fading or

narrowband interference. OFDM is leading the engineers

into a new era of digital transmission and is becoming the

chosen modulation technique worldwide. This thesis

investigates the performance of various modulation

schemes by analyzing the transmitted and received OFDM

frame, frequency spectrum and their constellation diagram

for the removal of noise and inters signal interference.

II. DIGITAL MODULATION TECHNIQUES

The move to digital modulation provides more

information capacity, compatibility with digital data

services, higher data security, better quality

communications, and quicker system availability. Digital

Modulation Techniques can be classified into following

categories as [5]

Binary Amplitude Shift Keying (BASK)

Binary Frequency shift Keying (BFSK)[5]

Binary Phase Shift Keying (BPSK)

Differential Phase Shift Keying (DPSK)

Quadrature Phase Shift Keying (QPSK)

M- Array Quadrature Amplitude Modulation (QAM) (M=4, 8, 6, 64, 128, 256,etc)

This Simulator is designed only for BPSK. QPSK, 4-

QAM and 16-QAM Techniques.

III. ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS

OFDM is referred as Multi-Carrier, Multi-Tone and

Fourier Transform. The OFDM concept is based on

spreading the data to be transmitted over a large number of

carriers, each being modulated at a low rate the carriers are

made orthogonal to each other by appropriately choosing

the frequency spacing between them. A multicarrier

system, such as FDM divides the total available bandwidth

in the spectrum into sub-bands for multiple carriers to

transmit in parallel. It combines a large number of low data

rate carriers to construct a composite high data rate

communication system. [5]

Orthogonality gives the carriers a

valid reason to be closely spaced with overlapping without

ICI. Let ( ) is a function and its orthogonal function will be ( ) so the condition of Orthogonality is given by (1) and represented in Fig 1. Here different colors are for sine

and cosine component. [3]

0* dttxtx (1)

Here all the subcarriers are sine waves. The area under

one period of a sine or cosine wave, or any other sinusoidal

with some phase angle, is zero. This can be shown

diagrammatically by Fig 1.



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Figure 1 Orthogonality of two subcarriers

IV. PERFORMANCE MEASUREMENT IN O.F.D.M.

A. Bit Error Rate

Mathematically BER can be defined by (2)s.

(2)

[1]

( ) ( ) (3)

There are some more factors that affect on BER. If the

transmission speed and transmission medium are good in a

particular time but Signal-to-Noise (SNR) is high then BER

will be very low. [6]

B. Signal to Noise Ratio(SNR)

The SNR mathematically can be defined by (4)

(4)

SNR is an indicator commonly used to evaluate the

quality of a communication link. Higher value of SNR

means better quality of the communication link. [7]

V. OFDM MODELLING IN MATLAB

The basic concept behind multi-tone modulation is to

replace one wideband signal with many simultaneously

transmitted narrowband signals with the same overall

bandwidth as the original signal. [1]

To implement OFDM

in Simulink, transmitters and receivers in discrete time,

Inverse fast Fourier transform (IFFT) and Fast Fourier

transform (FFT) methods are used respectively. OFDM

transmit symbols that have a longer time duration, which is

less or equal to the maximum delay spread. To combat ISI,

guard intervals are used between OFDM symbols. Fig. 2

which is showing the basic processing involved in OFDM

system OFDM processing can be implemented through the

communication block-set of Simulink. [6]

Figure 2 OFDM System in Simulink

VI. SIMULATION RESULTS

The main objective of this paper is to implement a user

interface for the study of OFDM processing which is

shown in fig. 3. A Simulink model for BPSK technique is

shown in fig. 4. [7]

On the basis of model of BPSK

techniques, Simulink models can be designed for other

techniques also. This GUI enables us to examine the

variation of Bit error rate against the different values of

Signal to Noise ratio. Table 1 shows the simulation

parameter for proposed simulator. [8]

TABLE I

SIMULATION PARAMETER

Parameter Values

Simulation Time 0.10 ms

Cyclic Prefix Length 26

FFT Points 1024

Total Bits 7.5e+004

Doppler Spread 20 Hz

Gain -8dB

Excess delay vector: 3e-6s



495

Figure 3 GUI interface for parameter variation

Figure 4 Simulink Model of BPSK Scheme

The transmitted and received Magnitude spectrum,

OFDM frame and constellation diagram are represented

through fig 5, fig 6, Fig 8 etc under different channel

conditions. BER variation is represented by fig 9.

Figure 3 Transmitted and Received Signal Pattern for BPSK

Technique

Figure 4 Transmitted and Received Signal spectrum for QPSK

Technique



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Figure 5 Transmitted and Received Signal spectrum for 4 QAM

Technique

Figure 6 Transmitted and Received Signal spectrum for 16 QAM

Technique

Figure 7 BER vs. SNR variation

VII. CONCLUSION

Thus the purpose of this simulator has achieved. It

makes the study of OFDM processing very easy. By simply

taking the values of SNR, we can easily observe the BER

variation on a graph. If we can move in details of Simulink

models, then just by changing the values of FFT points, we

can easily observe the effect on OFDM received frame.

This simulator also enables us to monitor the change in

OFDM processing by radio button with OFDM and no OFDM. This simulator has been tested and verified for standard results as discussed in previous articles.

REFERENCES

[1] Jigisha N. Patel & Prof.(Mrs.) Upena D Dalal, A Comparative Performance Analysis of OFDM using MATLAB Simulation with M-PSK and M-QAM Mapping, International Conference on Computational Intelligence and Multimedia Applications 2007Ding,

W. and Marchionini, G. 1997 A Study on Video Browsing Strategies. Technical Report. University of Maryland at College

Park.

[2] D.K Sharma., A. Mishra & Rajiv Saxena, Analog & Digital Modulation, Techniques: An Overview, International Journal of Computing Science and Communication Technologies, Vol.3, No.1, July 2010Tavel, P. 2007 Modeling and Simulation Design. AK

Peters Ltd.

[3] An initiative Guide of OFDM, 2004.

[4] Vandana B Malode & Bhagwat P Patil, BER Performance of LBC Coded OFDM in different channels, IEEE Control and System Graduate Research Colloquium 2012.

[5] R Bhagya, Dr. A G Ananth, Performance of OFDM Multiplexing Transmission using different Digital Modulation Schemes, IJAET/Vol .II/ Issue I/January-March 2011.Brown, L. D., Hua, H.,

and Gao, C. 2003. A widget framework for augmented interaction in

SCAPE.

[6] Ashok Kamboj Geeta Kaushik, Study & Simulation of O.F.D.M System, IJMER, Vol.2, Issue.1, Jan-Feb 2012.

[7] Jun Zhang, Zhongpei Zhang, Simulation and Analysis of OFDM System based on Simulink, IEEE, 2010.

[8] Mohammed Safiqul Islam, Gouri Rani Barai , Atiq Mahmood, Performance Analysis of different modulation schemes using OFDM

Techniques in Rayleigh Fading Channel, IJFPS, Vol.1, No.1, pp. 22-27, March, 2011

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