ABSTRACT :
High Peak to Average Power Ratio (PAPR) is one of the major drawbacks in Orthogonal Frequency Division Multiplexing (OFDM). The High PAPR increases the complexity of Analogue to Digital (A/D) and Digital to Analogue (D/A) convertors and also reduces the efficiency of RF High Power Amplifier (HPA). In this paper we present ananalysis of Discrete Hartley Transform (DHT) pre coded OFDM system using M-QAM (where M=16, 32, 64, 256). We compare the computer simulation results of DHT pre-coded OFDM system with DFT pre coded OFDM system, Walsh Hadamard Transform (WHT) pre coded OFDM system, Selected Mapping (SLM) based OFDM system and OFDM conventional. Simulation results show that the PAPR of DHT pre-coded OFDM system is lower than WHT pre-coded OFDM system, SLM-OFDM system and OFDM conventional. We also concluded in this paper that DFT pre-coded OFDM system has zero PAPR.
Index Terms– PAPR, DFT pre-coder, DHT pre-coder, HPA
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission scheme that has become the technology of choice for next generation wireless and
Wire line digital communication systems because of its high speed data rates, high spectral efficiency, high quality service and robustness against narrow band interference and frequency selective fading. OFDM thwarts Inter Symbol Interference (ISI) by inserting a Guard Interval (GI) using a Cyclic Prefix (CP) and moderates the frequency selectivity of the Multi Path (MP) channel with a simple equalizer. This leads to cheap hardware implementation and makes simpler the design of the receiver. OFDM is widely adopted in various communication standards like Digital Audio Broad casting(DAB), Digital Video Broadcasting (DVB), Digital Subscriber Lines (x DSL), Wireless Local Area Networks(WLAN), Wireless Metropolitan Area Networks (WMAN),Wireless Personal Area Networks (WPAN) and even in the beyond 3G Wide Area Networks (WAN) etc. Additionally, OFDM is a strong candidate for Wireless Asynchronous Transfer Mode (WATM).However, among others, the Peak to Average Power Ratio (PAPR) is still one of the major drawbacks in the transmitted OFDM signal [2]. Therefore, for zero distortion of the OFDM signal, the HPA must not only operate in its linear region but also with sufficient back-off. Thus, the RF High Power Amplifier (HPA) with a large dynamic range are required for OFDM system. These amplifiers are very expensive and are major cost component of the OFDM ORTHOGONAL frequency division multiplexing (OFDM) has been attracting substantial attention due to its excellent performance under severe channel condition . The rapidly growing application of OFDM includes Wi -MAX, DVB/DAB and 4G wireless systems.