Extensive research showed that the physiological response of human tissue to exposure to low-frequency electromagnetic fields is the induction of an electric current in the body segments. As a result, each segment of the human body behaves as a relay, which retransmits the radio-frequency (RF) signal. To investigate the impact of this phenomenon on the Doppler characteristics of the received RF signal, we introduce a new three-dimensional (3D) non-stationary channel model to describe the propagation phenomenon taking place in an indoor environment. Here, the indoor space is equipped with a multiple-input multiple-output (MIMO) system. A single person is moving in the indoor space and is modelled by a cluster of synchronized moving point scatterers, which behave as relays. We derive the time-variant (TV) channel transfer function (CTF) with TV path gains and TV path delays. The expression of the TV path gains is obtained from the instantaneous total received power at the receiver side. This TV total received power is expressed as the product of the TV power of the RF signal initially transmitted and received by a body segment and the TV received power of the redirected signal. These TV powers are determined according the free-space path-loss model. Also, a closed-form approximate solution to the spectrogram of the TVCTF is derived. Here, we analyse the effect of the motion of the person and the validity of the relay assumption on the spectrogram, the TV mean Doppler shift (MDS), and the TV Doppler shift (DS) of the TVCTF. Simulation results are presented to illustrate the proposed channel model.

广泛的研究表明，人体组织暴露于低频电磁场的生理反应是在人体各部分中感应出电流。结果，人体的每个部分都充当中继器，该中继器重新发送射频（RF）信号。为了研究此现象对接收到的RF信号的多普勒特性的影响，我们引入了一种新的三维（3D）非平稳信道模型来描述在室内环境中发生的传播现象。在此，室内空间配备有多输入多输出（MIMO）系统。一个人在室内空间中移动，并由一群充当中继器的同步移动点散射体建模。我们推导具有电视路径增益和电视路径延迟的时变（TV）频道传递函数（CTF）。TV路径增益的表达式是从接收器侧的瞬时总接收功率获得的。该电视总接收功率表示为主体段最初发送和接收的RF信号的电视功率与重定向信号的电视接收功率的乘积。这些电视功率是根据自由空间路径损耗模型确定的。同样，得出TVCTF频谱图的封闭形式近似解。在这里，我们分析了人的运动的影响以及中继假设对TVCTF的频谱图，TV平均多普勒频移（MDS）和TV多普勒频移（DS）的有效性。仿真结果表明了提出的信道模型。