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原文传递 Operational Communications for Tunnels TWO-WAY FM RADIO SYSTEMS COMBINED COST SAVINGS AND PERFORMANCE IMPROVEMENT RECOMMENDATIONS

题名：	Operational Communications for Tunnels TWO-WAY FM RADIO SYSTEMS COMBINED COST SAVINGS AND PERFORMANCE IMPROVEMENT RECOMMENDATIONS
作者：	Charles W. Isherwood, P.E.
关键词：	Tunnels; Communications; TWO-WAY FM RADIO SYSTEMS; COST SAVINGS; PERFORMANCE IMPROVEMENT; RECOMMENDATIONS
摘要：	2 Parsons Transportation Group has a long history of designing Intelligent Transportation Systems for use in the transportation industry. Our work with Highway Departments and Transportation Authorities has included a great deal of work below ground in highway and train tunnels. One of the greatest technical challenges has been providing the means to bring operational radio communications below ground and into these tunnels. The traditional approach has nearly always included the use of underground repeaters and leaky coaxial cable to provide this contact with the $outside# world. This system works well for short tunnels where the length of the antenna runs and therefore, the number of repeater sites can be kept to a minimum. Conventional systems normally required only one or two transceivers at each repeater site, making this design economically feasible. Modern trunked systems may require twenty or more transceivers at each site. These additional transceivers add the cost and complexity of the system. This means that the signals must be combined onto one or two the antennas, creating a significant amount of loss to the overall system. Trunked radio provides a much easier and more efficient way of communicating than the conventional, dedicated radio channels of the older systems. This has made it a very appealing system but, the trunked radio system is also expensive due to the amount of rather sophisticated equipment required to execute the trunking operation and the number of base stations employed at each site. A system of combiners and multicouplers are necessary to combine all of these frequencies onto a leaky coax antenna. Leaky coax is often chosen even though it presents high signal loss because it is the only type of antenna that can handle a wide range of frequencies and provide a signal over a large area. The leaky coax is also very expensive which has often contributed to high overall system cost. For the sake of completeness, we are presenting three possible alternatives to radio system design for use in tunnels. The three alternatives are considered in the interest of performing a thorough and impartial evaluation. They are not intended to be all inclusive but rather, a sample of some of the available alternatives. The solution chosen should be suited to the tunnel and the frequencies available for use in that tunnel.. The first option calls for the use of the traditional repeater/leaky coax approach. This approach requires the use of repeaters in various locations throughout a tunnel complex. Large numbers of combiners, base stations, filters, and lengthy runs of leaky coax would have to be employed to provide the required coverage. The second option calls for the use of directional antennas. These antennas would be driven by repeaters located through out the tunnel complex. From the performance perspective, these antennas offer an advantage in that they offer signal gain instead of the pure loss associated with leaky coax. This gain also allows the use of fewer and less powerful repeaters since the gain of the antenna can compensate for the decreased power output. The third option offers a dramatic increase in efficiency that makes it ideally suited to longer tunnels and subway systems. Regardless of whether the choice is leaky coax or directional antennas, the coaxial cable that connects the antenna to the transceiver presents one of the greatest losses to the system. This is especially true where the antennas are located some distance from the repeater. Substituting fiber optic cable for coaxial cable allows us to reduce the losses to nearly zero on runs from the transceiver to the antenna.
总页数：	ITS America. Meeting (10th : 2000 : Washington, D.C..). revolutionary thinking, real results : ITS 2000 : conference proceedings. 2000. pp16
报告类型：	科技报告