ISSN (Online) : 2278-1021 ISSN (Print) : 2319-5940 International Journal of Advanced Research in Computer and Communication Engineering Vol. 4, Issue 1, January 2015 Copyright to IJARCCE DOI 10.17148/IJARCCE.2015.4152 237 Behavior and Techniques for Improving Performance of OFDM Systems for Wireless communications Alcardo Alex Barakabitze 1 , Md. Abbas Ali 2 School of Communication Engineering, Chongqing University, China 1,2 Abstract: Orthogonal frequency division multiplexing (OFDM) is a special case of multicarrier transmission which transmits a stream of data over a number of lower data rate subcarriers. OFDM splits the total transmission bandwidth into a number of orthogonal and non-overlapping subcarriers and transmit the collection of bits called symbols in parallel using these subcarriers. This paper gives a total insight of various Peak -to Average Power Reduction (PAPR) techniques and principles of OFDM systems used in wireless communications. The research paper places a focus also on OFDM behaviors and techniques like Carrier Frequency Offset (CFO) estimation that improves performance of OFDM for wireless communications. Finally, the paper provides a number of wireless communication standards and many of the applications where OFDM systems are used. Keywords: OFDM, Peak-to-Average Power Reduction (PAPR), Inter-Carrier Interference (ICI), Channel estimation, Cyclic Prefix, Bit Error Ratio (BER). I. INTRODUCTION The recent years has witnessed the demand for higher data rate services such as voice, data and multimedia over both wired and wireless communication links [1]. This demand has increased due to the rapid growth of digital communication systems [2]. The wired and wireless communication environments has been requiring new technologies with new applications like the mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing,3D television and cloud computing[109]. The mobile communication systems like 4G and 5G are expected to provide substantially high data rate transmissions in order to meet the requirements of future high performance services such as multimedia, voice, and data applications. For example, in March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) set requirements specification of 4G standards called the International Mobile Telecommunications Advanced (IMT-Advanced) specification [9].The ITU-R set a maximum speed for 4G service at 100Mbps for high mobility communication (i.e. from trains and cars) and 1Gbps for low mobility communication such as pedestrians and stationary users[9]. However, the current 4G communication system suffers from some common problems such as attenuation, multipath fading, delay spread, self-jamming.etc[11]. New techniques and solutions are required to be embedded in 4G and 5G communication systems in order to eliminate and solve the problems which can hinder the performance of communications. OFDM is a promising candidate technology and a modulation technique which is used to provide such a high data rate in the emerging mobile communication systems like 4G and 5G.OFDM in the 4G and 5G community, provide high data rate transmissions with high spectral efficiency, multipath delay speed tolerance, immunity to frequency selective fading channels and power efficiency[3]. OFDM is a special form of Multi-Carrier Modulation (MCM) technique that was developed in early 1960s [13]. MCM involves splitting the input signal to a number of different signals over one frequency range. Each of these signals are then transmitted, modulated and demodulated over the channel. Several high-frequency military systems such as KINEPLEX [15], ANDEFT [16], and KATHRYN [17] started to use the OFDM technique in 1960s where by the variable-rate data modem was built for the high-frequency band (i.e., in KATHRYN) which used up to 34 parallel low-rate phase-modulated channels with a sub-carrier spacing of 82 Hz. Since its development in early 1960s, OFDM was then proposed tobe used in wireless applications in 1980s [14]. Due to its reasonable prices of hardware implementations which rely on a very high speed digital signal processing, OFDM has been recognized as an outstanding technique for high-speed data communication systems (e.g. 4G, 5G, LTE- Advanced).In order to maintain a high data rate transmission, OFDM takes and divides the total available bandwidth into a number of sub-carriers which are then transmitted in parallel from the transmitter to the receiver through a channel. Every sub-carrier is then modulated by a low rate data stream. On reaching to the receiver, these sub-carriers are combined together so as to form a composite high-data rate communication system. The sub- carriers in OFDM systems are orthogonal to each other and this orthogonality condition enables the sub-carriers to be closely spaced and overlap without Inter-Carrier- Interference (ICI). Although FDMA,TDMA, CDMA are the well-known multiplexing techniques used in wireless communication systems over a number of years, the overall problems encountered in these techniques includes Inter-Symbol Interference (ISI) resulted from time dispersion, multipath