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Comparative Evaluation of the Different Radiating Cables and Systems Technologies

Objective

The objective of this project is to determine the suitability of different cable systems for communications in difficult environments particularly in urban areas.
The objective of the project was to determine the suitability of leaky feeders systems for road to vehicles communications in difficult environments particularly in urban areas.
A survey of the state of the art including a review of existing systems and research and development regarding the application of leaky feeders to road traffic systems and in other environments with similar characteristics for example mines and underground railways has been performed.
A requirement analysis presents the main functional specifications of leaky feeders for road vehicles communications focusing on other applications than tunnel communications and including economical data.
The systems and interfaces work studies the electronic environment of the leaky feeders including number of channels, repeaters, coverage, etc. Economical data are also provided. This extensive analysis covers European, Japanese and American leaky feeders systems.
As current radiating systems use carriers ranging from a few kHz to 1.7 GHz and slotted waveguide systems are working at much higher frequencies, it is necessary to consider European standards for bandwidth, modulation technique, harmonic suppression and radiated power.
Leaky feeders systems are very long antennas and are good interference collectors when laid close to power lines, overhead lines, etc. Cars and onboard computers are also good perturbations generators but are vulnerable to electromagnetic perturbations. So the electromagnetic compatibility (EMC) is considered to be important into a road transport informatics (RTI) environment. European standards dealing with EMC and cars are studied. Then theoretical and experimental studies are presented to develop a performance prediction method. This activity has developed theoretical tools to characterise leaky feeders in terms of electromagnetic performances. The basic mechanism of the various types of leaky feeders are thoroughly theoretically studied. Using examples, some experimental res ults emphasising the main features of a radiating cable are compared to the results already outlined in the theoretical part. An important work is devoted to a comparison between measured values of coupling losses and the ones predicted by the theoretical model. As a conclusion, some comments are presented on the help that such a modelisation can bring to the conception of planned infrastructures using a leaky cable system.

Radio data systems (RDS) on frequency modulation (FM) channels for road transport informatics (RTI) purposes will be widely used in the next few years. As these data transmissions are at a relatively low rate, good quality transmission must be achieved. Starting from this condition and from the fact that RDS tunnel communications have to be maintained, we have studied the performance of RDS transmissions using leaky feeders.

We have made error rate measurements of RDS FM radio retransmissions using leaky feeders. As the radiation modes in tunnels are quite different from open areas and are also dependent on the tunnel shape and on the leaky feeder used, these performances have been measured on several test sites in France and in Belgium.

The results show that good retransmission of signals is possible in shadow areas. Some difficulties occur at both ends of the link where there are beating phenomena between the conventional radio signal and the leaky cable one. A comparison of microwave (10 GHz) and leaky cable (100 MHz) signals was also made. Although these 2 technologies are difficult to compare, the results show that much lower masking effects are noticed using leaky cables than microwave beacons. This could be important for specific applications such as automatic tolling. A new application of leaky cables is described. This is the RDS beacon which makes it possible to transmit locally a specific RDS TMC traffic management control message without new equipment in the car. This system uses the same frequency as a conventional broadcast to transmit information into a small cell specific RDS or RDS TMC using a short length of leaky feeder laid along the road.

In considering electromagnetic compatibility (EMC) problems we found that the disturbance voltage at the leaky cable terminals induced by ignition systems or the local oscillator was negligible although the disturbance voltage at the car receiver input induced by the ignition system was not negligible. Additionally, we found that the local oscillator perturbation at the car receiver was not negligible but could be avoided by correct frequency allocation.

Leaky cables provide an effective solution to the problem of radiopropagation where receivers are momentarily in a radiomagnetic shadow area (eg, in tunnels, in urban environments or in hilly countries). This research investigated the properties of some specific system architectures which can solve most of the problems encountered. These analyses are based on experimental findings in a number of European countries.

Technically, our studies have shown that suitable telecommunication systems can be divided into 2 groups. One using direct amplification of the signals and the other using a carrier frequency to transmit the audio signals between various transceivers. Direct amplification should be used when the leaky cable area is not isolated enough from that of other transmitters using the same frequency. A carrier system, thanks to the low attenuation of the carrier frequency is highly flexible, as different parts of the system (transmitters, receivers, control circuits, antennae etc) can be isolated.

In general, a radiating cable ensures the continuity of radio links in areas where radio signals do not freely propagate produces a spatially limited axial radiation which avoids interference in other areas. We have also shown that with an adequate system architecture, communication can be maintained even when there is a cable break. The theoretical models developed help in the choice of cable type and in evaluating the architecture of the system. The models proposed, when applied to radiated mode and coupled mode cables, lead to coupling loss values in agreement with those measured on site.
This project is divided into eight workpackages:
1. A survey of the a state of the art, including a review of all existing systems and R&D regarding the application of cables to road traffic systems and in other environments with similar characteristics for example mines and underground railways. As a result of this workpackage the rest of the project will focus on the 2 or 3 most important systems.
2. A requirements analysis with the objective of defining the main functional specifications of cable systems (such as the type of messages to be carried, interfaces to other systems etc.)
3. This workpackage `Systems and Interfaces' will study the electronic environment of the cables including number of channels, repeaters, coverage and transitions between radio systems and cable systems.
4. Studies frequency allocation. As current radiating systems use carriers ranging from a few kHz to 2.5 GHz it is necessary to agree European standards for bandwidth, modulation technique, harmonic suppression and radiated power.
5. Concerns electromagnetic compatibility.
6. Comprises theoretical and experimental work to develop a methodology permitting the prediction of radiating cable performance on site on the basis of their commercial specifications.
7. Measures and compares the results obtained from test sites chosen to be representative of different cable technologies.
8. Synthesizes the results of the above workpackages.
Main Deliverables:
Report describing the role of the cable systems in RTI applications including a comparison with alternative technologies.
A method for predicting what the performance of radiating cables will be in any given site.

Coordinator

Institut National de Recherche sur les Transports et leur Sécurité (INRETS)

Participants (5)

ENI
Belgium
INIEX
Belgium
POLITECNICO DI TORINO
Italy
Address
Corso Duca Degli Abruzzi 24
Régie Autonome des Transports Parisiens
France
Address
53 Ter Quai Des Grands Augustins
75006 Paris
UNIVERSITE DES SCIENCES ET TECHNIQUES DE LILLE
France
Address

Lille