Research On Par Of OFDM System

OFDM system is a very promising technology since it has many advantages, such as its high-efficient spectrum and ICI interference avoidance. It can also easily connect with MIMO and access technologies like FDMA, TDMA, and CDMA. Because different subcarriers can adopt different coding and modulation methods, the capacity of the channel is able to reach the optimum value. The principal difficulty with OFDM is that when the sinusoidal signals of the n carriers add mostly constructively the peak envelop power is as much as n times the mean envelop power. Thus OFDM has the high PAPR(peak-to-average ratio) which is its inherent disadvantage. These large peaks cause saturation in high-powered amplifier, leading to the intermodulation noise among the subcarrieies disturbing out-of-band power, and increasing the complexity of A/D and D/A convertor. Therefore it is highly desirable to reduce PAPR of the OFDM transmitted signals. This paper has Particularly researched on methods of PAPR reduction for OFDM .First of all, this paper introduces the basic theory of OFDM briefly and analyzes the reason and probability characteristic of PAPR of OFDM system. After this, this paper introduces several methods which reduce the PAPR, including signal distortion techniques, coding and signal scrambling techniques. This paper has concentrated on two ways in signal scrambling which are SLM(selective mapping) and PTS(Partial transmit sequence). I set up an OFDM system using simulation tools, Matlab 7.0, apply these two algorithms in the OFDM system. Finally, The two schemes are compared by simulation results with respect to the capability of PAPR reduction, the required system complexity and transmit signal redundancy. An improved method has been proposed, and analyze data gained from the simulation to get the advantages, shortcomings and the degree of the improvement of this algorithm to testify the correctness of these algorithm and the advantages over the traditional algorithms.