Abstract
This paper presents the spatial domain and propagation characteristics of different wideband channels using leaky coaxial cables (LCXs) for underground environment at 1.8GHz corresponding to the Long Term Evolution for Metro (LTE-M) standards. Angular dispersion of the signal significantly affects the channel capacity, and it can be exactly predicted in both the near and far fields for underground environments by means of a multimode waveguide. A ray tracing phenomenon was exploited to visualize the wave propagation for different transmitter and receiver antenna distances by using the time domain approach for both the horizontally and vertically polarized LCXs. In order to achieve this goal, we characterized the power azimuth spectrum (PAS) and power angle profile (PAP) for different tunnel dimensions and found that the PAS can be demonstrated by a zero-mean Gaussian distribution whose angular spread (AS) is dependent on the transmitter-receiver distances and the tunnel dimensions. The results demonstrate that the horizontally polarized LCX has higher angular spread values than the vertically polarized one, and the correlation coefficient follows the decreasing function with the increment of angular spread.
Highlights
The amount of data traffic has been increased explosively during the previous few years and the number of existing licensed spectrums are inadequate; Mobile Network Operators are considering the offloading of cellular network data to Wireless Local Area Networks (WLANs) as majority of the mobile devices endorse radio access [1]
Β = k0√εr, γ = arctan ( x0 ) √z02 + h02 where (ε1 − jε1) is the complex dielectric coefficient of the tunnel walls, Γh is the reflection coefficient for horizontally polarized radiated signals, i is the number of slots, P is the period of leaky coaxial cables (LCXs) slots, x0 is the horizontal distance between left metope of space and the cable, h0 is the vertical distance between incident point and the cable, and z0 is the longitudinal distance between incident point and the cable
In order to understand the LCX based spatial channel characteristics in Nantong tunnel, we considered three properties, namely, power azimuth spectrum, power angular profile, and channel correlation coefficient
Summary
The amount of data traffic has been increased explosively during the previous few years and the number of existing licensed spectrums are inadequate; Mobile Network Operators are considering the offloading of cellular network data to Wireless Local Area Networks (WLANs) as majority of the mobile devices endorse radio access [1]. In [10, 11], the authors used the ray tracing approach to estimate the distributive coupling losses and impulse response of the leaky waveguide, and it was found that the coupling loss decreases with the increment of slots period of leaky coaxial cable, and path loss decreases exponentially with the increase of separation distance between Tx and Rx. In [12], the radio signal attenuation measurements in concrete tunnels at four different frequencies (0.455, 0.915, 2.45, and 5.8 GHz) are studied. The spatial correlation coefficients, power azimuth spectrum (PAS), power angle profile (PAP), and angular spread (AS) were explored for both the horizontally and vertically polarized LCXs in two different tunnels with different numbers of Tx and Rx antennas.
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