Mobile communication terminals such as smart phones are currently necessities of life, and communication traffic using these terminals has been increasing in buses, trains and air planes.
On the other hand, a leaky coaxial cable (LCX) has been used as an antenna as a measure for communication in a dead zone such as tunnels and underground malls because of its advantages in connection stability. Further, since it is possible to provide communication range along the cable, its deployment to “linear cells” is also expected.
Specifically, stable wireless network connection would be necessary at positions of arrangement over some long and narrow places referred to as the “linear cell” such as an area along a railway, tunnels, underground malls, shopping malls, planes or trains. In a linear cell environment as such, leaky coaxial cable can be used as an antenna for wireless communication because it has many potential advantages. Namely, when a leaky coaxial cable is used in a linear cell, its coverage is uniform and its installation might be simpler than other methods.
On the other hand, in order to improve frequency usage efficiency, application of MIMO (Multiple-Input Multiple-Output) technique to a system using LCX has also been studied (see Non-Patent Literature 1 listed below).
According to the method disclosed in Non-Patent Literature 1, however, a plurality of LCXs must be arranged apart from each other so as to ensure sufficiently low correlation between each other, which leads to the problem of increased cost of installation and maintenance.
As a solution to such a problem, 2×2 MIMO system using a single LCX has been proposed (see Non-Patent Literatures 2 and 3 as listed below). According to this method, it is necessary to input signals from opposite sides of LCX and, therefore, it is necessary to arrange the LCX such that its opposite ends are placed at substantially the same position, or to arrange a separate coaxial cable to the opposite end of LCX. Therefore, cost of installation increases if the LCX becomes long.
Patent Literature 1 listed below discloses a configuration of bundled leaky coaxial cables realizing MIMO communication, in which external conductors of first, second and third leaky coaxial cables respectively have slits of prescribed size formed with prescribed spacing, wherein the first to third leaky coaxial cables are bundled such that the slit angles on the outer circumference are orientated in prescribed directions different cable to cable, or such that the spacing between leaky coaxial cables is at least one half the wavelength, or such that planes of polarization are in different directions cable to cable, so as to reduce the correlation.