Peak-to-Average Power Ratio Reduction In OFDM Communication Systems

Communication is one of the important aspects of life. With the advancement in age and its growing demands, there has been rapid growth in the field of communications. Signals, which were initially sent in the analog domain, are being sent more and more in the digital domain these days. For better transmission, even single-carrier waves are being replaced by multicarrier. Systems like CDMA and OFDM are now a day being implemented commonly.Orthogonal Frequency Division Multiplexing (OFDM) is a communications technique that divides a communications channel into a number of equally spaced frequency bands. A subcarrier carrying a portion of the user information is transmitted in each band. Each subcarrier is orthogonal (independent of each other) with every other subcarrier. It was invented over40years ago, and has been adopted in many technologies such as Asymmetric Digital Subscriber Line (ADSL) services, IEEE802.11a/g, IEEE802.16a, Digital Video Broadcast (DVB), Digital Terrestrial Television Audio Broadcast,4G, IEEE802.1In, IEEE802.16, and IEEE802.20.OFDM is a multi-carrier modulation technique that is unlike other modulation techniques. In OFDM, the carriers have substantial overlap. For each single high frequency carrier used, OFDM transmits multiple high data rates signals concurrently using sub carriers. The sub-carriers are orthogonal with each other and hence do not interfere with each other. OFDM is currently the next choice for next generation mobile communications, primarily because it offers high bandwidth efficiency due to overlapping of spectra, its robustness to frequency selective fading channels and its efficient implementation.However, the main drawback of OFDM systems is that, it suffers from the problem of high Peak-to-Average Power Ratio (PAPR) which causes inefficient use of the High Power Amplifier and could limit transmission efficiency. OFDM consist of large number of independent subcarriers, as a result of which the amplitude of such a signal can have high peak values. In this paper, we propose an effective reduction scheme that combines DCT and SLM techniques. The scheme is composed of the DCT followed by the SLM using the Riemann matrix to obtain phase sequences for the SLM technique. The simulation results show PAPR can be greatly reduced by applying the proposed scheme. In comparison with OFDM, while OFDM had high values of PAPR-about10.4dB our proposed method achieved about4.7dB reduction of the PAPR with low complexities computation. This approach also avoids randomness in phase sequence selection, which makes it simpler to decode at the receiver. As an added benefit, the matrices can be generated at the receiver end to obtain the data signal and hence it is not required to transmit side information (SI).