Research of the Characteristics of Radio Wave Propagations around the High-Speed Railway

¦ a exp[ j (Z t Z t ) )]
i 0 d i i 1
N
(5) (6)
U0 exp[ j (Z0t Zd t ) 0 )]
This work was supported by National Natural Science Foundation of China under Grants NSFC 60332020. üüüüüüüüüüüüüüüü 1-4244-1372-9/07/$25.00 ©2007 IEEE
2 'f i S P i P i ( f i , n )
n'f i
2.1.3 Using the method of equidistance to determine the parameters of simulation
The method of equidistance refers that the distance between the adjacently discrete Doppler frequency shift is the same. The value of discrete Doppler frequency shift with the same distance calculated as below:
'x
vTc 2
v 9c 2 16S vf
9c 32S f
Ri (t ) ci , n
fi ,n
N i of
lim
¦c
n 1
Ni
i,n
cos(2S f i ,n t Ti , n ) (10)
(11) (12)
9 u 3 u 108 0.058m 5.8cm 32 u S u 460 u 106 So sampling interval is less than 'x 5.8cm , then the level of the receiving envelope changes and the decline of small-scale propagation can be reflected.
is phase change;
U0
is the
amplitude of direct wave;
) 0 is the angle of
The fading is aggravated. The rate of change
of field intensity in the scope of dozens dB can be achieved. The influence of bit error rat caused by Doppler-effect can’t be ignored. So many conclusions of land mobile communication are not applicable for railway mobile communication.
The phase shift Ti .n is the random variable of uniform distribution in > 0, 2S @ . So before the simulation, ci , n , fi , n and Ti , n must be ascertained. They are respectively known as Doppler coefficient, discrete Doppler frequency shift, Doppler phase shift.
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1. Introduction
With the development of economy, the contact of world every corner is more and more closer. And the requirement of transport is also higher. So railway as an important transport is preferred by more and more people. At the same time, the demand of the speed of railway transport is increasingly high. Then, the concept of high-speed railway is raised. To achieve the high-speed railway, the high-speed railway communication is an important problem to be solved. And the most important problem is high-speed railway mobile communication. On the condition of high-speed, there are many differences between railway mobile communication and land mobile communication. The influence of multi-path effect and shadow effect are increased.
¦ a cos(Z t ) )
i d i i 1
N
T0
9 16S f m
¦ a sin(Z t ) )
i d i i 1
N
9O 16S v
9c 16S vf
(13)
R and process.
S
are colored Gaussian random
The correspondingly spatial sampling interval is shown below:
fi ,n
'f i (2n 1) 2
fi , n f i ,n 1
n 1, 2,..., N i (14) n 2,3,..., N i (15)
'f i ,n
2.1.4 Gaussian power spectrum
Gaussian power spectrum is shown below:
2.1 The model of flat fading channel
For small-scale fading, there is a direct wave, and the rest are reflected wave and scattered wave along the railway. The carrier signal of the base station antenna is:
The conclusion should be improved and amended by experimentation and theoretical analysis so that it can be used on railway mobile communication.
2. The model of high-speed railway channel
incidence of direct wave. Formula (1) can be resolved as a random scattering component and a strong path component: S (t ) P (t ) m(t ) (4)
P (t )
m(t )
2.1.1 The theory of sine superposition
The method of Rice is one kind of the method of sine superposition. It is based on the superposition of the infinitely weighted harmonic. As show below:
Research of the Characteristics of Radio Wave Propagations around the High-Speed Railway
Lu Qu, Yinghong WenˈWeijia Song* EMC Research Section, Beijing Jiaotong University, Beijing 100044, China *Beijing Institute of Medical Device Testing, Beijing 100011, China