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在单光源室内可见光通信(VLC)系统中,为了准确评价多径效应对系统性能的影响,提出一种室内VLC多径信道建模方法。用迭代法计算视线传输(LOS)和反射传输冲激响应,分析接收端抽样周期和发光二极管(LED)调制带宽之间的关系,并定义码间干扰(ISI)。以LOS信道时延作为建模起点,将接收端相邻抽样间隔之间的所有冲激响应之和作为多径信道路径增益。正交频分复用(OFDM)技术能有效抵抗ISI,在室内多径信道下,考虑非线性限幅噪声影响时,推导了直流偏置光OFDM(DCO-OFDM)和非对称限幅光OFDM(ACO-OFDM)的理论误码率(BER),并建立了蒙特卡罗仿真模型。研究光电检测器(PD)位置、LED的半功率角、PD视场角(FOV)和直流偏置参数对系统BER性能的影响。仿真结果表明,当PD在房间中心时,受多径干扰影响最小,BER性能最好;PD移到墙壁位置时,受多径干扰影响大,BER性能差;随着FOV和LED半功率角的增大,PD接收到的反射光功率增加,多径干扰增大,BER性能变差;直流偏置越大,DCO-OFDM系统BER性能越差。
In a single-source indoor VLC system, in order to accurately evaluate the effect of multipath effect on the system performance, an indoor VLC multipath channel modeling method is proposed. The iterative method is used to calculate the line-of-sight (LOS) and reflected transmission impulse responses. The relationship between the sampling period at the receiving end and the modulation bandwidth of the light emitting diode (LED) is analyzed and the intersymbol interference (ISI) is defined. Taking the LOS channel delay as a starting point for modeling, the sum of all impulse responses between adjacent sampling intervals on the receiving end is taken as the multipath channel path gain. Orthogonal frequency division multiplexing (OFDM) technology can effectively resist ISI. In the indoor multipath channel, considering the influence of nonlinear clipping noise, DC offset optical OFDM (DCO-OFDM) and asymmetric limiting optical OFDM (ACO-OFDM) theoretical bit error rate (BER), and established a Monte Carlo simulation model. The influence of PD position, LED half power angle, PD field of view (FOV) and DC bias parameters on BER performance of the system was investigated. Simulation results show that when PD is in the center of the room, it is least affected by multipath interference and BER performance is the best. When PD is moved to the wall position, it is greatly affected by multipath interference and has poor BER performance. With the FOV and LED half-power angle The power of the reflected light received by the PD increases, multipath interference increases, and the BER performance becomes worse. The greater the DC offset is, the worse the BER performance of the DCO-OFDM system is.