Propagation characterization is one of the main building blocks for millimetre wave(MMW) communication.The Gaussian beam has attractive features to become a prospective wave form for millimetre radio communication,especially for the utility inside tunnels.A ray tracing method embedded with spectral features of Gaussian beam is employed to analyze millimetre wave propagation in a circle tunnel in this paper.In consideration of geometrical figure of the tunnel,the superposition behaviour of direct and reflective beams is analyzed via simplified approximation of Gaussian beam spectral feature.Then the propagation models are established to derive amplitude,phase,and delay spread of received wave.A typical straight tunnel model is used to simulate the propagation behaviour,where strong multi-path effect with deeply fading of signal intensity and dramatically enhancing of delay spread emerges.For investigation of the spectral feature of the multi-path effect,a reflection loss of 14 dB is taken into consideration at a designated point.To analyze the influences of frequency and transmission distance,the propagation characteristics at three different frequencies of 45 GHz,65 GHz and 85 GHz are compared with the beam travelling down the tunnel.In addition,three different reflection losses of 14 dB,20 dB,and 26 dB at the frequency of 65 GHz are also investigated to research the influence of the reflecting coefficient.
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