PAPR Reduction Technologies Based On Companding Transforms In OTFS Systems

In high mobility scenarios,communication channels encounter significant Doppler frequency shifts and multipath effects,which cause severe subcarrier interference and affect the performance of orthogonal frequency division multiplexing(OFDM)systems.To solve these problems,orthogonal time frequency space(OTFS)modulation technology has emerged.The OTFS signal is multiplexed in the delay-Doppler domain,thereby converting the time-varying channel experienced by conventional multicarrier communication into a time-invariant channel and achieving better performance in high-speed mobile communication systems compared to traditional modulation schemes.The OTFS system,which also is a multicarrier modulation system,encounters the problem of high PAPR.From the perspective of compression transformation technology,the focus is on addressing the problem of high PAPR in OTFS.Firstly,the traditional framework of OTFS system is analyzed,the OTFS system model is described,the PAPR definition of OTFS system and its performance are analyzed,the PAPR upper bound of OTFS system is determined,and the common PAPR companding algorithms are compared and analyzed.The companding transform algorithm process for the OTFS system was subsequently proposed to address the issue where the compressed and expanded signal cannot be normally recovered by the receiver when applying the companding process of the OFDM system to the OTFS system.Secondly,a three-segment linear companding algorithm is proposed to solve the problem that the traditional segmented linear companding algorithm without considering the signal amplitude distribution and simply divides the signal into two parts according to the amplitude,which leads to the poor BER performance of the signal after the companding process.In the algorithm,the signal is divided into three parts according to the distribution of amplitude.The area with a relatively concentrated signal distribution and the highest probability of occurrence is designated as the medium amplitude area,where the signal’s amplitude change is not processed and directly outputted as the companding signal.Additionally,the large amplitude signals are compressed to reduce signal amplitude and suppress signal PAPR,while the small amplitude signals are expanded to increase the amplitude,compensating for the average power decrease caused by compressing large signals.The results show that the algorithm achieves better BER performance than the conventional segmented linear companding algorithm with good PAPR suppression performance and lower algorithmic complexity in signal processing.Finally,an average power-conserving law companding algorithm is proposed to address the problem of increasing the average power of OTFS signals when the conventional mu-law companding algorithm(MC-OFDM)is used to companding the amplitude of OTFS signals in OFDM systems.An exponential-based amplitude improvement factor is added to the original MC algorithm,and the relationship between this improvement factor and the companding parameters is obtained by qualifying the companding function with the average power conservation.The results show that the algorithm has the same PAPR suppression performance,the same algorithm complexity and similar BER performance as the original MC algorithm while maintaining the average power conservation.