Abstract: Orthogonal frequency division multiplexing (OFDM) is a form of digital modulation used in a wide array of communications systems. This paper will explain what OFDM is, why itís important, where itís used, and what test instrumentation is required to maintain it. Perhaps we should first explain what is so special about OFDM. Three things stand out. OFDM is spectrally efficient, carrying more data per unit of bandwidth than such services as GSM and W-CDMA. Figure 1 shows a comparison of the spectral efficiency of the leading cellular technologies and how they compare to WLAN and WiMAX. Fourth Generation technology, often referred to as the Long Term Evolution of wireless (LTE) and Ultra Mobile Broadband (UMB) for cellular devices, plans to use OFDM or OFDMA. Orthogonal frequency division multiplexing (OFDM) has become one of the most important modulation methods in many fields, such as high-speed communication systems. It is proposed that OFDM technique can offer variable bandwidth, improved protection to shadow and multipath fading and enhanced robustness thanks to the insertion of the guard interval. In this paper, we introduced the principles of OFDM at first, then analyses the Advantage and disadvantages of OFDM system, and finally discussed its application in contemporary high-speed communication systems, especially in wireless mobile networks.

Keywords: OFDM; ISI; GI; IDFT; DFT