Orthogonal Frequency Division Multiplexing

Abstract

Orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. The data are sent over parallel sub-channels with each sub-channel modulated by a modulation scheme such as QPSK, 16 QAM etc. The advantage of OFDM is its ability to cope with severe channel conditions compared to a single carrier modulation scheme but still maintaining the data rates of a conventional scheme with the same bandwidth. Furthermore, channel equalization is simplified because OFDM may be viewed as using many slowly modulated narrow band signals rather than one rapidly modulated wide band signal. Also, the low symbol rate naturally makes the use of guard interval between symbols reducing ISI. Orthogonal Frequency Division Multiplexing has become one of the mainstream physical layer techniques used in modern communication systems. In this paper the OFDM system for a number of subcarriers is simulated and sent over Rayleigh fading channel. The performance of OFDM along with various modulation schemes observed and presented in this paper. Orthogonal Frequency Division Multipexing

Introduction

Divides high-speed serial information signal into multiple lower-speed sub-signals:
Transmits simultaneously at different frequencies in parallel.
Modulation ( BPSK, PSK,QPSK,16QAM, …).
Pilot sub-carriers used to prevent frequency and phase shift errors.
Usage of cyclic prefix for lower multi-path distortion
Controlled overlapping of bands in one channel
Max spectral efficiency (Nyquist rate)
Easy implementation using inverse FFTs
Easy time-freq. Synchronization

Modulate by switching between time and frequency domain

Aim and Objectives

Aim :

1.To design MIMO OFDM using QAM and QPSK system

2.Estimate BER for performance analysis of MIMO OFDM system

3.Carry out efficient orthogonality of transmitter and receiver section

Objectives :

1.Verify the performance of our proposed work using Matlab r2013a

Proposed System :

Multiple input multiple output OFDM system
Simulate waveforms for orthogonality of the system
Estimate BER (Bit error rate)

Matlab

Orthogonal Frequency Division Multiplexing