Papr Reduction Using VLM Precoding With Companding Techniques For Ofdm Systems

OFDM is a multicarrier modulation technique, where a high speed data stream is further splited into number of parallel streams of low data rate and these low rates data streams are transmitted simultaneously over a number of orthogonal subcarriers. It provides the high data rate and high frequency spectral efficiency and low implementation complexity [2]. Because of these advantages, OFDM is used in systems such as wireless local area networks, LTE and WiMAX, digital audio broadcasting (DAB) and digital video broadcasting (DVB) [3],[4]. One of the major drawbacks of OFDM is the high Peak to Average Power Ratio (PAPR) value of the transmitted signals [5],[ 7]. This problem came into existence from modulation itself, it comes on adding multiple sub carriers while formulating the transmitting signal. On the other hand, when the numbers of subcarriers are increased with the same phases, then the OFDM signals will have a large envelope fluctuation which leads to high PAPR values. Due to this high PAPR, system requires large back-off; which creates a side effect of reducing efficiency of HPA. There are many PAPR reduction techniques, including SLM (selected mapping) [6], [8], PTS (partial transmit sequences) [9], [13], interleaving [10], TR (tone reservation), and TI (tone injection) [11]. However, these techniques provide different sets of tradeoffs that may include data rate, and BER (bit error rate) performance and computational complexity.