井下低压电力线OFDM系统中PAPR抑制的研究

发布时间：2018-04-10 20:05

本文选题：低压电力线 + OFDM　；参考：《太原科技大学》2017年硕士论文

【摘要】：我国有大量的煤矿,为了保证煤矿井下开采、生产、安全的要求,就必须对煤矿的自动化生产有很高的要求。因此提高煤矿井下稳定又可靠的通信,保证信息传输的可靠性具有现实的意义。煤矿井下通信环境比较复杂,整体环境比较恶劣,井下空间有限,采用光纤和电缆作为传输介质的方案,需要重新配置专用电缆和光缆设备,增大复杂度与成本;无线通信方案下,面临物理环境相对恶劣的问题,无线通信信道容量小,并且井下巷道路径多,容易发生反射,存在无线通信障碍,也难以满足井下可靠、安全生产的需求。利用井下现有的低压电力线作为传输信息的介质,不需要专门敷设电缆,节约了成本,降低了物理环境对信号传输性能的影响,正在成为井下通信网络构建的重要方案。电力线信道中存在的频率选择性衰落、多径和噪声等问题,可以通过采用正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术来克服以上所提到的问题。但是OFDM技术最大的缺点是峰均比(Peak to Average Power Ratio,PAPR)过高,使得系统实现时的成本高、难度大、工作效率低。因此降低电力线OFDM系统中的峰均比,提高传输性能,从而实现高效的井下电力线通信,正在成为研究的关键方向。而在降低PAPR的技术中概率类算法能够有效地降低峰值高的信号出现的概率来达到降低PAPR性能,不会产生失真,但是其计算复杂度相对较高,在接收端还需要边带信息才能恢复出原始数据的问题也同样亟待解决。因此,本文针对煤矿井下低压电力线中OFDM中峰均比过高的问题,主要进行了以下内容的研究:(1)对煤矿井下低压电力线的信道特性进行研究,主要对电力线信道的阻抗特性、噪声特性、衰减特性进行了分析,总结了电力线通信的特点及原理,明确电力线网络存在的频率选择性衰落严重、阻抗变化大、多径效应明显、噪声干扰严重等问题。利用串联谐振电路模型来描述电力线信道,并采用OFDM技术来克服低压电力线信道存在的问题。(2)针对煤矿井下低压电力线OFDM中PAPR过高的问题,采用了一种改进的SLM(Selective Mapping,SLM)算法。首先对信号作DCT变换预处理,其次在SLM算法中选用GCD(Greatest Common Divisor,GCD)矩阵作为相位序列来降低系统的PAPR。实验结果表明,本算法相比传统的SLM算法降低PAPR性能更好,且减少了计算的复杂度。(3)针对井下低压电力线OFDM峰均比过高的问题,采用一种IDCT_PTS算法与限幅算法的联合算法。在传统的PTS算法基础上加入IDCT变换,使得高峰值信号出现的概率明显降低,以此降低系统的PAPR。并通过限幅处理进一步有效的降低系统的PAPR。实验结果表明,本算法相比传统的PTS算法降低PAPR性能更好。
[Abstract]:There are a large number of coal mines in our country. In order to ensure the requirements of mining, production and safety in underground coal mines, we must have very high requirements for the automatic production of coal mines.Therefore, it is of practical significance to improve the stable and reliable communication in coal mine and to ensure the reliability of information transmission.The underground communication environment of coal mine is more complex, the whole environment is worse, and the underground space is limited. The scheme of using optical fiber and cable as transmission medium needs to reconfigure the special cable and optical cable equipment to increase the complexity and cost.Under the wireless communication scheme, facing the problem of relatively bad physical environment, the wireless communication channel capacity is small, and the underground roadway path is many, easy to produce reflection, the existence wireless communication barrier, also is difficult to satisfy the underground reliable, the safety production demand.Using downhole low voltage power line as the medium for transmitting information, it is not necessary to lay cable specially, which saves cost and reduces the influence of physical environment on signal transmission performance. It is becoming an important scheme of underground communication network construction.The problems of frequency selective fading, multipath and noise in power line channel can be overcome by using orthogonal Frequency Division Multiplexing OFDM (OFDM) technique.However, the biggest drawback of OFDM technology is that the peak to Average Power ratio (PAPR) is too high, which makes the cost, difficulty and work efficiency of the system high.Therefore, it is becoming a key research direction to reduce the peak-to-average ratio in power line OFDM system, improve the transmission performance and realize the efficient underground power line communication.In the technique of reducing PAPR, the probabilistic algorithm can effectively reduce the probability of the signal with high peak value to reduce the performance of PAPR without distortion, but its computational complexity is relatively high.The problem that sideband information is needed to recover the original data at the receiver also needs to be solved.Therefore, aiming at the problem of high peak-to-peak ratio of OFDM in underground low voltage power line, this paper mainly studies the channel characteristics of low voltage power line in coal mine, mainly the impedance characteristic of power line channel.The characteristics of noise and attenuation are analyzed, and the characteristics and principles of power line communication are summarized. It is clear that the power line network has serious frequency selective fading, large impedance variation, obvious multipath effect and serious noise interference.The series resonant circuit model is used to describe the power line channel, and OFDM technology is adopted to overcome the problem of low voltage power line channel. Aiming at the problem of too high PAPR in the low voltage power line OFDM in coal mine, an improved SLM(Selective mapping algorithm is adopted.Firstly, the signal is preprocessed by DCT transform, and then the GCD(Greatest Common Divisor GCD) matrix is chosen as the phase sequence in the SLM algorithm to reduce the PAPRs of the system.The experimental results show that the proposed algorithm reduces the PAPR performance better than the traditional SLM algorithm and reduces the computational complexity. Aiming at the problem of too high PAPR in downhole low-voltage power line, a joint algorithm of IDCT_PTS algorithm and amplitude limiting algorithm is adopted.Based on the traditional PTS algorithm, IDCT transform is added to reduce the probability of the high peak signal, so as to reduce the PAPR of the system.Furthermore, the PAPRs of the system are further reduced by limiting processing.The experimental results show that the proposed algorithm can reduce the PAPR performance better than the traditional PTS algorithm.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TD655;TN913.6

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