| Summary: | 碩士 === 元智大學 === 通訊工程學系 === 103 === The object of this thesis is to sound the wireless channel in Intra-Moving-Vehicle (IMV) environment with a self-developed compact and low-cost channel sounder and investigate the small-scale fading (SSF) characteristics such as probability density function (PDF) and Doppler spectrum. Through the results of real-world experiments and analysis, the wireless channel model of IMV channel can be verified.
First, we survey some literature about the characteristics of wireless channel in Intra-Stationary-Vehicle (ISV) and IMV. In literature, researchers viewed the ISV environment as a metallic cavity, and modeled it as a time-Invariant Two-Wave with Diffuse power (TI-TWDP) channel model. Because the channel model will result in more severe fading characteristics than Rayleigh channel, it can be regarded as so-called Hyper-Rayleigh fading channel.
Therefore, we assume that the stationary TWDP channel for the ISV environment can be extended to a time-varying TWDP (TV-TWDP) channel model. The channel model consists of two line-of-sight (LOS) signals with different Doppler frequency. The first is the LOS with low Doppler frequency in vehicle and the other is the LOS with high Doppler frequency which is reflected by scatters outside and re-enters through the window called re-entering wave. The re-entering wave will have destructive interference effect on the LOS signal in vehicle and decrease the performance of signal transmission. Through the simulation and analysis of the channel model we also find that, the time-varying fading PDF of TWDP channel model may exhibit two-peak feature rather than single peak Rayleigh or Ricean. From the cumulative distribution function (CDF) we can also know that the statistics characteristics of TWDP channel model is worse than traditional Rayleigh channel.
In order to measure and model the IMV wireless channel, we develop a low-cost and high performance channel sounder as well as its transmit and receive algorithms. We use the narrowband sounding signal to sound the TV-TWDP channel simulated by C2 channel emulator and the real-world wireless channel in IMV circumstance and analyze the statistical characteristics. We also conduct a compact channel sounding platform based on USRP which can sound the wireless channel in IMV environment using wideband CAZAC sounding signal and resolve the multipath fading process to analyze the time-varying feature of different specular waves.
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