Research On Reducing PAPR Of OFDM In Underground Low Voltage Power Line Communication

China has a large number of coal mines.To meet the requirements on the underground mining,production and safety of coal mines,high demands must be set for the automatic production.Therefore,to improve the stable and reliable communication of underground coal mines and guarantee the reliability of information transmission is of practical significance.Due to the complicated underground communication environment of coal mines,harsh overall environment and limited underground space,the use of optical and fiber as the transmission media requires the re-allocation of special cables and optical cables,which may increase the complexity and cost.As for the wireless communication,due to the harsh physical environment,small channel capacity,and signal reflection caused by multiple underground paths,it also fails to meet the requirements on reliable and safe production.With the existing low voltage power line as the medium of information transmission,there is no need to pave special cable,and moreover,it not only saves the cost,but also reduces the impact of physical environment on the performance of signal transmission,becoming an important plan in the underground communication network construction.The channel of power line has such problem as the selective fading of frequency,multi-path and noise,etc.which can be overcome with OFDM technology.But OFDM suffers a high PAPR,which may lead to the high cost,great difficulty and low efficiency of system implementation.Therefore,to reduce the PAPR of OFDM system,improve the transmission performance and realize the efficient power line transmission of underground coal mines is now becoming a key research direction.Furthermore,the probability algorithm among PAPR-lowing technologies can reduce the probability of the occurrence of high PAPR signal to decrease the PAPR performance,without distortions.Due to the high computation complexity,however,the problem in which side information is also needed in the receiving terminal to recover the original data also demands for prompt solution.consequently,aiming at the excessively high PAPR in OFDM of low-voltage power line in underground coal mines,the following research is carried out:(1)Channel characteristics of underground low voltage power line are researched.Specifically,the impedance,noise and fading characteristics of the power line channel are analyzed,features and principles of the power line communication are summarized,and problems in the power line network are clarified,such as the severe selective fading of frequency,great impedance change,serious noise intervention,etc.The power line channel of underground coal mines is described with the series resonant circuit model,and OFDM technology is adopted to overcome problems in the low voltage power line channel.(2)Aiming at the excessively high PAPR in OFDM of the low voltage power line,an improved SLM algorithm is adopted.Firstly,the signal is processed by DCT to reduce PAPR.Secondly,In SLM algorithm,GCD matrix is selected as the phase sequence of SLM algorithm to reduce the PAPR of system.From simulation results,we demonstrate that the proposed algorithm achieves higher PAPR reduction compared to SLM method.(3)Aiming at the excessively high PAPR of PFDM,IDCT_PTS algorithm and clipping algorithm are combined to reduce the PAPR of system.IDCT_PTS algorithm applies IDCT as IFFT pro-coding and before PTS peak value optimization process,which greatly reduce the probability of the maximum peak.Furthermore,clipping processing also further reduces the PAPR of system.From simulation results,we demonstrate that the proposed algorithm achieves higher PAPR reduction compared to PTS method.