Research of Methods of Decrease in the Peak-Factor of Signals With Orthogonal Frequency Multiplexing
The article considers the theoretical part of systems with orthogonal frequency multiplexing (an OFDM system). The systems with the use of the signals with orthogonal frequency multiplexing are enumerated. Also the advantages and disadvantages of the system are given. The main advantage of an OFDM system is resistance to the intersymbol interference and frequency selective fadings. The main drawback of OFDM systems has been revealed which is a big peak-factor PAR. A peak-factor is the correlation between the maximum signal amplitude and its root mean square value. The task to reduce peak-factors in OFDM systems has been set. Peak-factor origins have been found. Three widespread methods of decrease in the peak-factor of signals with orthogonal frequency multiplexing have been considered: block coding, amplitude limiting (clipping) and probabilistic method. The first method of decrease in the peak-factor (block coding) is based on coding. The purpose of this method is selecting a key word which minimizes or reduces the peak-factor of the transmitted signal, but the data transmission rate will decrease in this case. Block coding is applicable for very small number of subcarriers and its practical usefulness is very limited. The second method (amplitude limiting) is based on signals cut-off. This method is the simplest one, its purpose is to limit peak value of the input signal, by means of amplitude break. The third of the said methods (probabilistic) is based on noise suppression, having reduced the probability of clipping emergence. The advantages and disadvantages of each of the enumerated methods of decrease in the peak-factor have been considered. Separate probabilistic methods were connected with the general formula. Research has been conducted and a conclusion has been drawn that a probabilistic method is the most perspective one for the solution of the problem with the peak-factor in OFDM systems.