OFDM for 4G

摘要

Multicarrier modulation techniques like OFDM are rapidly moving from the textbook to the real world of modern communication systems. OFDM stands for 'Orthogonal Frequencies Division Multiplexing'. Instead of modulating a single carrier as is the case with FM or AM, the idea to utilize a number of carriers, spread regularly over a frequency band, in such a way that each of them is modulated with just a small portion of the available energy. Recently, a worldwide convergence has occurred for the use of Orthogonal Frequency Division Multiplexing (OFDM) as an emerging technology for high data rates. In particular, many wireless standards (Wi-Max, IEEE802.11a, LTE, Digital Video Broadcasting) have adopted the OFDM technology as a mean to increase dramatically future wireless communications. OFDM is a particular form of Multi-carrier transmission and is suited for frequency selective channels and high data rates. The principles of orthogonal frequency division multiplexing (OFDM) modulation have been in existence for several decades. However, in recent years these techniques have quickly moved out of textbooks and research laboratories and into practice in modern communications systems. The techniques are employed in data delivery systems over the phone line, digital radio and television, and wireless networking systems. What is OFDM? And why has it recently become so popular? This article will review the fundamentals behind OFDM techniques, and also discuss common impairments and how, in some cases, OFDM mitigates their effect. A brief overview of use of OFDM in LTE, 4G cellular technologies will conclude the article.