Disadvantages Of Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM)

Leow Min Huay Amy

Nanyang Technological University

School of Electrical and Electronic Engineering

Information Engineering and Media (IEM) [e-mail] U1422183H Abstract — This EE4152/IM4152 research report gives an overview of the concepts on Orthogonal Frequency Division Multiplexing (OFDM). It provides a summary of the advantages and disadvantages of OFDM.

Keywords --- frequency division multiplexing, intersymbol interference, modulation, orthogonal

I. INTRODUCTION

Orthogonal Frequency Division Multiplexing also known as OFDM in short, is one of the signal modulation formats that breaks a long stream of high data rate modulating stream into multiple slow modulated narrowband

Since the main issue with Code Division Multiple Access (CDMA) systems is complexity of channel equalization that is used across the entire channel. An OFDM uses many sub-channels, making it easy to apply channel equalization.

B. Disadvantages of OFDM

As far as we may know about the advantages of OFDM, there are also several disadvantages regarding the use of OFDM. Although OFDM is widely used, the disadvantages should also be taken into consideration. The disadvantages are OFDM has a high peak to average power ratio and it is sensitive to the carrier offset and drift.

i. High peak to average power ratio

There are noise such as amplitude variation in the OFDM signal with a high peak to average power ratio. It causes the efficiency of radio frequency amplifier to suffer because it will require the amplifiers to be linear in order to suit the different variations of the amplitudes. Hence, the amplifier is not able to operate in such high efficiency level.

ii. Sensitive to carrier offset and drift

Single carrier systems are not as sensitive to the carrier offset and drift as compared to OFDM.

V. PARAMETERS OF OFDM

A. Data

Flash OFDM is created by Flarion. Flash OFDM is a quick hopped type of OFDM. Flash OFDM applies to many tones and quick hopping to distribute signals through a spectrum band.

• OFDMA, A stands for Access. OFDMA is yet another variant of OFDM. It is a scheme used to deliver a multiple access capability for applications.

• Vector OFDM is commonly known as VOFDM. This type of OFDM applies the fundamental idea of MIMO (Multiple Input Multiple output technology). MIMO is created by CISCO Systems. MIMO applies to many antennas to transmitter’s and receiver’s signals. Therefore, multi-path effects improve reception of the signal and speed of transmission.

• WOFDM stands for Wideband OFDM. WOFDM uses the concept of OFDM by applying some gap between the channels. It is important to have a gap that is big enough to take in any frequency errors between transmitter and receiver so that it will not make any changes to performance of the system. WOFDM is used in Wi-Fi systems.

All types of OFDM use the same fundamental concept. They use orthogonal carriers which are close-spaced to one another. Those carriers carry low data rate signals. Hence, when it is in its demodulation phase, data will be added together to produce the whole complete