Mimo ofdm

MIMO techniques ( Multiple-Input/Multiple-Output ) for OFDM modulations
Miguel Onofre, Technical University of Lisbon, Portugal

Abstract
In the future wireless communication systems, the use of multiple antennas at the ends of a wireless connection, through the MIMO technology, will dramatically increase spectral efficiency and reliability of the connection. MIMO technology combined with technical Orthogonal Frequency Division Multiplexing (OFDM) appears to be forefront of the solution for the future mobile systems and in the next generation of fixed networks systems architecture. In this report, the fundamental concepts of MIMO OFDM V-BLAST technology will be covered.

I.

Introduction

Our present social, economic and professional life style leads to an explosion of Internet services. As a result, new applications and new multimedia communication services arise each day. However, the increase in new communication services requires higher data rates of the digital transmission systems. The request for higher rates of data translates into a requirement for greater bandwidth, but the electromagnetic spectrum and the maximum radiated power have physical limitations and regulations. Thus the only way to increase the data rate of the transmission systems with high reliability, meeting today’s demands of companies, within these limitations, is possible only through new and sophisticated techniques of digital signal processes and techniques of the encoding channel. Also high data rate wireless systems, consequently present very small periods, and in strong fading channels face Inter-Symbol Interferences (ISI) due to multipath propagation and their inherent delay spread, as a result of which the Bit-Error Rate (BER) increases. OFDM is a technique capable of mitigating the ISI and efficient in the frequency selective channel. It provides an optimal spectral efficiency due to its orthogonal carriers and their spacing. On other hand MIMO systems exploit the richly