The Effect of Multipath on the OFDM System

Abstract

A major problem in telecommunications is to adapt the information to be transmitted to the propagation channel. This, in order to obtain a good quality of wireless communications with high transmission rates , and the release cable users to allow them to move in large buildings. In this type of communication systems must be properly fight one effect of multipath, specifically the frequency selective fading. This led to the development and use of the technique of multiplexing by orthogonal frequency division (OFDM) appears to be a promising solution. For frequency-selective channels, a technique is the use of multi-carrier modulation in which a block of information is modulated by a Fourier transform. This known as OFDM (Orthogonal Frequency Division Multiplexing) technique has been very successful in recent years and is in the process of standardization in different standards without son (IEEE802.11a, WiMAX, LTE, and DVB). OFDM has the great merit to transform broadband multi-path channel into a set of simple to equalize sub channels single-path. Moreover, the ingenious utilization of the transmission cyclic redundancy reduces the complexity of the terminals through the use of algorithms based on FFT fast. The purpose of this chapter is to introduce the OFDM modulation. The general principles are described (transmission chain ...) and benefits (simplicity of the equalization algorithms use fast FFT) and disadvantages (lack of diversity).