Initial ranging (IR) is a process of performing power adjustment, timing offset estimation, and synchronisation between the base station (BS) and all users. It plays a vital role in mobile WiMAX standard, which establishes a communication link between BS and ranging subscriber stations (RSSs). Since RSS is located far away from the BS and uplink signal is corrupted by noise, the IR process becomes inferior. Thus, the authors propose an improved dynamic threshold-based IR method comprising three phases: (i) code detection phase, (ii) filtering phase, and (iii) parameter estimation phase. In the first two phases, the received signal is pre-processed to eliminate noise and unselected codes from the codeset by employing adaptive filter and weight-based code detection method. Then, the noise-free signal is considered for the final phase, which improves accuracy. The iterative expectation maximisation algorithm is involved in the estimation of channel coefficient and timing offset. All possible active paths are detected by setting a dynamic threshold value for each channel by the enhanced dynamic threshold method. For all active channels, round trip delay, and power level are estimated by considering particular channel coefficient and timing offset. Extensive simulation of proposed work shows considerable improvements in performance.

中文翻译：

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OFDMA系统的多阶段初始测距过程：改进的基于动态阈值的多用户检测方法

初始测距（IR）是执行功率调整，时序偏移估计以及基站（BS）与所有用户之间的同步的过程。它在移动WiMAX标准中起着至关重要的作用，该标准在BS与测距用户站（RSS）之间建立了通信链接。由于RSS的位置远离BS，并且上行链路信号被噪声破坏，因此IR处理会变差。因此，作者提出了一种改进的基于动态阈值的IR方法，该方法包括三个阶段：（i）代码检测阶段，（ii）滤波阶段和（iii）参数估计阶段。在前两个阶段，通过采用自适应滤波器和基于权重的代码检测方法对接收到的信号进行预处理，以消除代码集中的噪声和未选择的代码。然后，在最终阶段考虑无噪声信号，提高了准确性。迭代期望最大化算法涉及信道系数和时序偏移的估计。通过使用增强的动态阈值方法为每个通道设置动态阈值来检测所有可能的活动路径。对于所有活动通道，通过考虑特定的通道系数和时序偏移来估算往返延迟和功率电平。对拟议工作的广泛模拟显示出性能的显着提高。通过考虑特定的信道系数和时序偏移来估算功率和功率电平。对拟议工作的广泛模拟显示出性能的显着提高。通过考虑特定的信道系数和时序偏移来估算功率和功率电平。对拟议工作的广泛模拟显示出性能的显着提高。