FUTURE INSTITUTE OF ENGINEERING AND MANAGEMENTKOLKATA

FINAL YEAR PROJECT PRESENTATION ON

A COMPARATIVE STUDY OF OFDM USING QPSK & QAM AS MODULATION

TECHNIQUES IN NOISY ENVIRONMENT

SUBMITTED BY 4th YEAR B.TECH ECE STUDENTS:-

SHEIKH ASIF ISMAIL(roll-071480103039) DEBARKA CHAKRABORTY(roll-071480103044) ATANU DAS(roll-071480103043) SWARNAVA BERA(roll-071480103055) KALYAN DEY(roll-071480103058) ARNAB PODDER(roll-071480103078)

Project GuideDEBASHIS CHAKRABORTY

ASST. PROF., ECE DEPT

CONTENTS

•Introduction•History of OFDM•Why OFDM•Theory•OFDM Transceiver Block diagram•Serial to Parallel Conversion•Role of IFFT in OFDM•MATLAB Coding•MATLAB Simulation Results•The Comparative Analysis-QAM vs QPSK•Advantages & Disadvantages•Applications•Conclusion•Future Scope

The orthogonal frequency division multiplexing (OFDM) is a wide band wireless digital communication technique i.e. based on block modulation. With the wireless multimedia applications becoming more & more popular, the required bit rates are achieved due to OFDM multi carrier transmissions.The OFDM digital modulation technique can support high speed video communication along with audio with elimination of ISI & ICI. At the same time it supports multi user technique where it can accommodate more number of users showing spectral efficiency. It is a multiplexing access scheme that has many favourable features required for 4th generation wireless communication system.

INTRODUCTION

HISTORY OF OFDM Orthogonal Frequency Division Multiplexing(OFDM),a special form of

Multi-Carrier Modulation(MCM),with densely spaced subcarriers and overlapping spectra was patented in the US in 1966 by Chang,Bell Labs.

1971 Weinstein and Ebert proposed the use of Fast Fourier Transform(FFT) and guard interval.

1985 OFDM was described for mobile communication

1987 Alar and Lasalle suggested the use of OFDM for digital broadcasting

1997 Digital Video Broadcast was created

The principle of OFDM was already around in the 50’s & 60’s but system implementation was delayed due to some technological difficulties like digital implementations of FFT & IFFT which was not possible to solve then.

.

WHY OFDM

One of the main reasons to use OFDM is to increase robustness against frequency selective fading or narrowband interference.

In a single-carrier system, a single fade or interferer can cause the entire link to fail, but in a multicarrier system, only a small percentage of the subcarriers will be affected.

Error-correction coding can then be used to correct for the few erroneous subcarriers.• Multipath ImmunityAchieved using cyclic-prefix > channel delay-spread

Saving of Bandwidth

Upto 50% Bandwidth Saving

Bandwidth (Spectral) Efficiency Achieved using subcarrier orthogonality

Conventional multicarrier techniques

Orthogonal multicarrier techniques

Frequency

Frequency

THEORY

MULTI-CARRIER MODULATION • orthogonality property

DIGITAL MODULATIONQPSKQAM

CYCLIC PREFIXING

∫ cos(nωt).cos(mωt)dt=0,m≠nT

OFDM TRANSCEIVER BLOCK DIAGRAM

DATA

Serial to parallel

converter

QAM/QPSK mod

IFFTD/A

Conver-ter

Parallel to serial conver-

ter

LPFA/D

Conver-ter

Serial Parallel conver-

ter

FFT

QAM/ QPSK

demod parallel to serial

converter

DATA

QAM/QPSK mod

QAM/ QPSK

demod

………………………………

……

……………………………………………

……

S6 S5 S4 S3 S2 S1

OFDM Frame (T)

S3 S2 S1

S6 S5 S4

S9 S8 S7

S12 S11 S10

OFDM Symbol (T)

SERIAL TO PARALLEL CONVERSION

OFDM block assigned to a

carrier

If size of OFDM Frame is DAfter conversion an (m×n) matrix is obtained, where (m×n)=D

ROLE OF IFFT IN OFDM

IFFT block operates on each column of the complex (m×n) matrix at a time which is obtained at the output of the QPSK/QAM modulator.

The source symbols obtained from the modulators are assumed to be in frequency domain and hence IFFT is performed to bring them into time-domain.

The basis functions of an N point IFFT are N orthogonal subcarriers. These subcarriers have different frequency. Each input symbol acts like a complex weight for the corresponding sinusoidal basis function.

Thus, the IFFT block provides a simple way to modulate data onto N orthogonal subcarriers.

MATLAB CODING

OFDM TRANSMISSION USING M-ary QAM MODULATION

with M=8 and M=16.

OFDM TRANSMISSION USING M-ary QPSK MODULATION with M=8 and M=16.

MATLAB SIMULATION RESULTS

16-QAM Before HPA & after HPA

Peak –to-average-Power Ratio improves significantly on using a High Power Amplifier

MATLAB SIMULATION RESULTS (contd…)

For the same value of M, the BIT ERROR RATE(BER) of M-QPSK is higher than M-QAM for the same SNR.

MATLAB SIMULATION RESULTS (contd…)

For both M-QPSK and M-QAM,increase in M increases the BIT ERROR RATE(BER).

THE COMPARATIVE ANALYSIS-QAM vs QPSK

QPSK QAM

M=8 M=16 M=8 M=1649 1100 41 8047 1004 21 7452 1101 30 6951 1102 24 8450 1140 23 53

Observation of Bit Error

QPSK QAM

M=8 M=16 M=8 M=16

0.0016 0.0367 0.0014 0.0027

0.0016 0.0335 7.0000e-004 0.0025

0.0017 0.0367 1.0000e-003 0.0023

0.0017 0.0367 8.0000e-004 0.0028

0.0018 0.0380 7.6667e-004 0.0018

Observation of Bit Error Rate

ADVANTAGES & DISADVANTAGES

ADVANTAGESEfficient spectrum usage by allowing overlapEffect of ISI and ICI can be completely removed by OFDM through the use of cyclic prefixBy dividing the channel into narrowband flat fading sub channels, OFDM is more resistive to frequency selective fading than single carrier systems areUsing adequate channel coding and interleaving one can recover symbols lost due to the frequency selectivity of the channel

DISADVANTAGES

OFDM is more sensitive to frequency offset and phase noiseOFDM has a relatively large peak to average power ratio(PAPR),which tends to reduce the power efficiency of the RF amplifier Co-channel interference in cellular systems

APPLICATIONS

1. (DAB) Digital Audio Broadcasting: Its principal advantage is that it is able to establish single frequency network, this means that transmitters which are separated at a distance, can send the same signal simultaneously.

2. (DVB) Digital Video Broadcasting: It is used for broadcasting of digital television signals using MPEG-2 source compression, that reduces a standard television channel to 3M bps, also reduces the HDTV Channel to 20Mbps.

3.(WLAN)Wireless Local Area Network: A wireless local area network (WLAN) links two or more devices using some wireless distribution method (typically spread-spectrum or OFDM radio), and usually providing a connection through an access point to the wider internet.

CONCLUSION

1. Spectral width of 16-QAM is narrower than that of 16-QPSK for same information rate.

2. BER performance of 8-QPSK is better than 16-QAM at the expense of spectral width.

3. 16-QAM can carry more traffic comparable to 8-QPSK, at the expense of BER which is obvious in context of digital modulation technique.

4. PAPR solely depends on coding technique not on modulation technique also verified from the simulation.

Hence, analysis of the paper yields logical results in context of OFDM.

FUTURE SCOPE Optical OFDM is a digital modulation scheme that has the potential

to replace traditional expensive laser modulation equipment

OFDM can be used for wireless ATM in rural communication

OFDM provides raw data rates up to 54 Mbits/s in a 20-MHz channel. In addition to supporting high data capacity and resisting degradation from various types of radio effects

OFDM transmitter can be implemented in FPGA by using VHDL & Spartan-3 and used in developing SDR(Software Defined Radio) and prove as a harbinger of 4G.