Evaluation of OFDM Channel Sounding Techniques with Three Modulation Sequences

Abstract This paper presents an evaluation of multicarrier channel sounding techniques using different random and pseudo-random sequences to modulate the OFDM sounding signal. The Random (Rand), Pseudo-Noise (PN) and Zadoff-Chu (ZC) were tested, both in laboratory simulations and in field measurements. For the laboratory simulations Matlab routines were used to generate OFDM signals modulated with each of the three sounding signals, that were then convoluted with a synthesized transfer function of a test channel with six multipath components and added Gaussian noise and Doppler fading. The resulting signals are then correlated with a copy of the original signal to provide the multipath power delay profiles. The root mean square deviation (RMSD) and the relationship between peak power and mean power (PAPR) were used as metrics for the comparison between the test transfer function and the simulation detected multipath delay profiles, showing slight advantages of the ZC sequence. The three sequences were then used in field measurements to characterize an urban channel at 700 MHz. In the field measurements, the ZC sequence showed the lowest detection threshold, allowing for the detection of a larger number of multipath components.

摘要 本研究针对采用不同随机与伪随机序列调制正交频分复用（OFDM，Orthogonal Frequency Division Multiplexing）探测信号的多载波信道探测技术展开评估。本次测试分别选取随机序列（Rand，Random）、伪噪声序列（PN，Pseudo-Noise）以及佐达夫-楚序列（ZC，Zadoff-Chu）三类序列，同步开展实验室仿真与实地测量两类实验。实验室仿真环节采用Matlab程序生成经上述三类探测信号调制的OFDM信号，随后将其与包含6条多径分量的测试信道合成传输函数进行卷积，并叠加高斯噪声与多普勒衰落效应。将生成的信号与原始信号副本进行相关运算，以得到多径功率延迟分布。研究以均方根偏差（RMSD，Root Mean Square Deviation）与峰均功率比（PAPR，Peak-to-Average Power Ratio）作为评估指标，对比测试信道传输函数与仿真检测得到的多径延迟分布，结果显示ZC序列具备小幅性能优势。随后将三类序列应用于实地测量，以表征700 MHz频段下的城市信道特性。实地测量结果表明，ZC序列具备最低的检测阈值，可实现更多多径分量的检测。