MXPA00008592A - Data communication system - Google Patents

Abstract

The present invention provides a ground based video pick-up system for transmitting video signals produced on a moving object to one of a number of receivers at a fixed position and selecting the desired signal from the most appropriate one of those receivers.

Description

SYSTEM. DATA COMMUNICATION Field of the Invention This invention relates to a system for transmitting data, particularly data of audio and video signals, to and from a moving object.

Background of the Invention To provide real-time communication of the audio, video and data signals between a moving vehicle and a fixed ground station, the vehicle can be provided with an antenna to send a signal beam to a helicopter located above the car. The helicopter then transmits the signal from the car to and from a fixed ground station. This communication data system between a moving vehicle and a fixed ground station has been particularly useful in the field of automobile racing to provide video, audio and data signals from automobiles and to allow audio signals and the data is transmitted back to the car. The common onboard cameras use a Ref.122691 microwave transmitter system for communication with the helicopter. The helicopter then retransmits a signal on a second microwave frequency to the fixed location. There are a number of disadvantages associated with such a system. If a car that is providing the signal does not have a direct observation line over the helicopter, for example because of trees or large buildings on the side of the runway, then the received signal may be weakened or completely obscured. In such a situation, it is necessary that the helicopter remain almost directly above the vehicle to maintain a consistent contact with the car. This can be difficult, particularly with high-speed racing such as Formula One where the helicopter is unable to match the speed of the cars in their attempt to follow them. Alternatively, the helicopter can fly at a higher altitude to avoid objects between it and the car. However, this again may reduce the quality of the signal received by the helicopter due to the increased distance. This can also lead to problems with air traffic control. An additional problem of using a helicopter to transmit signals is its dependence on environmental conditions. If the environmental conditions become inadequate for the flight, then it is not possible to provide the function of retransmission of the signal in its entirety. An additional limitation on the use of helicopters to relay signals is the limited amount of weight that can be carried to prevent the helicopter from remaining at its station for the duration of a race. Similarly, there is a limitation on the amount of power that can be provided to operate the radiofrequency systems. Therefore according to the present invention there is provided: a communication system including: a video signal source and a transmitter provided on a mobile object for generating and transmitting said video signal on at least one first carrier frequency; at least first and second receivers for receiving the video signal transmitted on the first carrier frequency, the first and second receivers have detection areas that overlap at least partially and that are located at remote locations; a position detector for generating a position signal indicative of the position of the mobile object using the different indications of the parameters of the received video signal and the bearer; a controller that functions in response to the position signal to select one of the video signals received by the first and second receivers and output the selected signal, the controller is located at another location than the moving object. According to the present invention there is also provided a method of communicating a video signal between a mobile object and a stationary location, comprising: transmitting the video signal on a first carrier frequency from a transmitter on the mobile object.; providing at least first and second receivers at locations spaced far apart to receive the signal from the transmitter on the first carrier frequency; and determining the location of the mobile object using indications other than the parameters of the signal, the received signal or its bearer; select the signal received by one of the first and second receivers for the output at the stationary place. The present invention still further provides a method for establishing a communication system for communicating a video signal between a mobile object provided with a transmitter for transmitting the video signal on a first carrier frequency and a stationary location comprising a plurality of receivers that each have a detection area within which the receiver is able to receive the signal from the transmitter on the first carrier frequency when the transmitter is in the detection area, the method is characterized in that it comprises the steps of: placing a first receiver in a first location; calculating the distance from the first location in which reflection by a reflection surface of a signal transmitted from the mobile object will cause the power level received in the first receiver to decrease below a predetermined level to define a first detection area; determining a position for each subsequent receiver to calculate a distance at which reflection from a reflection surface will cause the received power to be reduced below the predetermined level to determine an area of the section and place the subsequent receiver at a distance from the receiver prior such that the detection area of the subsequent receiver overlaps the detection area of the previous receiver to form a continuous strip within which the signal from the transmitter can be received by at least one of the receivers; providing means whereby the signal received by at least one receiver can be provided to the stationary location; and providing means for determining the position of the mobile object using different indications of the parameters of the received signal and the bearer and to control the switching between the receivers based on the determined position. The present invention is adapted so that the switching between the receivers is carried out based on the position of the moving object. The receivers are arranged or adapted preferably so that the area in which they can receive the signal at an acceptable level overlaps with the receiver in the corresponding adjacent area. The transmitters on the mobile object can be arranged or distributed so that they are capable of transmitting on a number of different frequencies. Similarly, the receivers can also be adapted to receive a number of different frequencies. The operating frequencies of the transmitters and receivers are preferably controlled by the messages of the data sent from a central location to the moving objects and the receiving stations. Each frequency can be received by a dedicated antenna (ie, each receiver that has its own antenna) or a single antenna and an RF splitter can be used with a proportion of the RF signal that is directed to each receiver. The receiver selects the desired frequency in the RF signal. The video signal is preferably transmitted from the mobile object to the receivers using a microwave carrier. This is preferably 2.5 GHz. Other data and audio signals can be modulated on the video signal or transmitted on a separate frequency, preferably between 100 MHz and 40 GHz. The present invention requires only a single frequency to transmit a video signal because there is no retransmission of the signal as in the case of a helicopter-based system. This allows dubbing the number of signals that can be transmitted for a given number of frequencies. further, because the transmission from each transmitter is received by a receiver in a relatively narrow range, the power of the transmission can be reduced. This also allows the same frequency to be used simultaneously between another transmitter and receiver at a different site. This is not possible with helicopter-based systems in which all signals have to travel through a helicopter and thus only one transmitter could use a given frequency to avoid interference. By providing enough receivers to ensure that the transmitted signal is always received by at least one receiver, there will never be a break in the transmission. When the signal is being transmitted substantially horizontally along the ground to a track-side receiver, the trees and buildings do not present an obstruction to the signal path. The receivers are preferably provided at a receiving station on the track side. The station preferably includes an antenna and optionally additional receivers. A specific embodiment of the present invention will now be described by way of example with reference to the appended drawings, in which: Figure 1 shows an example of a distribution of the receiving stations around a section of the racing track. Figure 2 shows a representative arrangement of the related receiver stations and the respective switching positions for switching from the receiver in one station to the next; Figure 3 shows a schematic distribution of the arrangement of one of the receiving stations according to the present invention; Figure 4 shows a schematic distribution of the signal transmission system of an embodiment of the present invention; Figure 5 shows a schematic example of a node used in the signal transmission system; Figures 6A and B show an example of the range or range of detection of an antenna; and Figures 7.1 to 7.4 are diagrams to explain how the communication system according to the invention is established.

Detailed description of the invention Figure 1 shows an example of a section of the race track 1 and a suitable arrangement of the receiving stations 2 (referred to herein as stations) around such section of the track to provide continuous reception of a video signal from a camera on the edge of a racing car. The embodiment of the present invention described herein relates to a system for providing a communication of a video signal from a moving racing car to a fixed location such as an external broadcasting unit. Each station includes at least one antenna and one receiver. This is preferably a directional antenna (for example a propeller antenna) but can be an omnidirectional antenna. The dotted lines in Figure 1 provide an indication of the detection angle of the antenna on each station 2. The signal received by the antenna is fed to the receiver at the station and then fed back to a controller at a central site where the signal from one of the receivers is selected as the most appropriate. The selected signal is then used to provide the output signal from the system, for example for broadcasting. It will be evident that, by providing sufficient stations around the periphery of the track, when the car travels around the track the video signal transmitted by the car can always be received by at least one of the stations. To ensure this continuity of reception, there is some overlap in the range or range of detection of a station and its environment. This overlap (preferably at least 20 m) ensures that when the car travels from the reception area of a station to the reception area of the next station, the car passes through an area where the video signal transmitted by the car is received by the antennas of both stations. At some point in this area, the systems change or switch from the use of the signal from the first station to the use of the signal from the next station. Figure 2 shows a schematic view of a section of a track showing the antennas (A2, A3, A4, etc.) of a number of stations. When the car is introduced from the right, it goes first to the Pi position. The antenna A2 is initially receiving the signal transmitted by the car. When the car continues to the point P2, the car enters the reception range of the next A3 antenna and at that point the signal that is leaving is received by A3 as well as by A2. However, the signal that is being received by A2 is still the first one that is used to provide the output signal. When the car passes the P3 position, the system changes or switches from the use of the signal from A2 to the use of the signal from A3 although the signal from the car is still being received by A2. When the car continues through the position P4, the antenna A2 eventually becomes unable to receive the signal from the car so that only the antenna A3 is receiving the signal. This switching procedure is repeated when the car progresses around the track and moves from the reception area of one station to the next. As is clear from Figure 2 the change or commutation is carried out at a distance D2, D3 or D4 before the car reaches the antenna of the station by commonly providing the video signal which is being used. This ensures that a good quality signal is still received until the change. If the change is delayed until the car was level with the antenna, the strength of the signal received by the antenna can be considerably reduced because the car falls outside the optimum reception area of the antenna. The exact point at which switching is carried out is very important. If the switching occurs too early, for example in P2, the strength of the signal received by A3 may be weak. As described above, leaving the commutation until it is too late can lead to the signal received by A2 being too weak. If the received signal is weak then the output signal can be distorted or noisy. However, determining the appropriate switching point is not sufficient to simply measure the strength of the signal received by each receiver and then select the strongest of these. This can lead to an erroneous indication of the best signal and therefore to the wrong switching position. One of the reasons for this is the interference caused by the transmitted signal that reaches the antenna indirectly, that is to say that it has reflected some other object. This phenomenon, as multiple trajectories, leads to direct or indirect signals that have taken routes of different lengths to reach the receiver. Depending on the difference in the trajectory lengths, the two signals can constructively interfere, providing a stronger signal, or destructively interfere by reducing the strength of the signal. Also, when the car moves, this difference between the lengths of the routes or trajectories can change and thus the strength of the signal can vary between being very weak and being very strong. This variation makes it difficult to use the resistance of the signal as the only exact indicator of which receiver to use for the output signal. The system of this invention determines the appropriate time to change from one receiver to the next based on the position of the car relative to the antenna. This requires knowledge of the position of the stations and the automobile. This can be determined in several ways. On a race track, the data may be available from the care system or weather surveillance. This allows the position of the cars to be determined accurately at any time. However, there are a number of alternative ways of determining the position. Apart from well-known systems such as GPS (Global Positioning System), it might be possible to use a custom system to provide the position information, for example using the stations themselves to determine the distance from the car. Even where a highly accurate position information is not available, it is still possible to interpolate to provide an estimated position. In a car racing situation, cars follow fairly predictable speed and position routes, allowing an estimate of the car's position. On a racetrack, which may be several kilometers in length, the stations may be at a great distance from each other and from the controller at the central site. The simplest way to supply the signals received by the receivers to the central controller is by directly connecting, for example by means of a cable, each receiver to the controller. In a car race, it is desirable to have cameras on more than one car. The system can make it possible for a number of cars to provide video signals, with each car transmitting on a different frequency. Where two or more cars are in the reception area of the same station, the antenna receives both signals. This system can be further developed to allow additional cameras where the number of frequencies available for transmission is limited or if there are a large number of cars in a race. In addition, it may be desirable to have more than one signal that is produced from each automobile (for example, front and rear views or a view of the driver). Under such circumstances a large number of channels may be required. If the width of the available band is limited, it is possible to use the same frequency for the signals provided by different automobiles. This is possible since the cars that transmit on the same frequency are sufficiently far away so that the station receiving the signal from a car does not receive a significant amount of the signal from another car transmitting on the same frequency. This can be accomplished by verifying the position of the cars and where two cars using the same frequency are in danger of becoming close enough to interfere with each other, the driver will instruct the transmitter on the car to change to a different frequency which is not being used by any other automobile in close proximity or to stop transmission. The position information used to determine the switching between the stations can be used to determine the distribution of the frequencies to the transmitters. In this way, several cars in different positions around the track can use the same frequency simultaneously. This represents a considerable advantage over the helicopter-based system that only a single frequency transmitter can use. In addition to the present invention each transmitter only uses a single frequency instead of two required with the helicopter system, ie one for transmitting to the helicopter and one for transmission to the terrestrial base receiver. Having a separate connection between each receiver and the central controller leads to a large number of potentially very long cables between the receivers and the central controller. Therefore, in an alternative embodiment of the present invention a common "busbar" system to which all receivers are attached is provided. In its simplest form, this comprises two connections; one line A and one line B, each line being able to carry a video signal. These two lines are arranged or adapted to connect to the central site and each of a number of nodes. However, instead of the line going from the central site to each node, the lines are connected from the central site to the first node and then from the first node to the second node and etcetera until the last node which is connected preferably back to the central site to form a ring. Each receiver can have its own node or a node can be provided for more than one receiver. For example, for a structure comprising twenty receivers, five nodes can be provided with four receivers directly connected to each node. Figure 5 shows an example of a node to which two receivers in two stations that receive the signals provided by the antennas A2 and A3, are connected. As shown schematically in Figure 5, the signals from each receiver can be connected to either line A, line B or any line (NC). Referring to Figure 2, when the car arrives at position Pi the signal transmitted by the car is being received by an A2 which, as shown in Figure 5, is connected to line A. The received signal is then passed on. back to the line from node to node until the signal is received at the central site. When the car continues in the past P2, the signal transmitted to the car can then be received by A3 and the switch in the node connects the signal provided from the receiver for the antenna 3 to the line B. The signal received from A3 is then passed. from node to node descending on line B, again back to the central site. Accordingly, between the positions P2 and P4 the central site is provided with two video signals corresponding to the signals received on the antennas A2 and A3. As shown in Figure 4, the central site is provided with switching means. The switching means output the video signal provided on lines A or B according to the control signal provided by a controller. In this mode the control signal comprises data messages sent from the control programs that operate on a computer. The program selects which of the video signals on line A or line B is output. Therefore, initially, the program controls the switching to provide an output signal from line A, then when the car passes point P3, the program sends a message to the switch so that the output corresponds to the signal that is received on line B (that is, that received by the A3 antenna). Two synchronizers are used to ensure that the synchronization pulses of the video signals on line A and line B are coincident. When a switching command is sent, the switch waits until the next vertical blanking interval of the video signal of the current and then switches between line A and line B, or vice versa. To avoid distortion of the image, such as the ripple of the frame, when they are switched between signals that have been output by one receiver and the next, a frame memory can be used. The use of a frame memory avoids some problems due to the frames in two signals that are not synchronized. When the car continues its march, the signal from A2 will be lost. Then when the car comes within the range of A4, the node to which A2 is disconnected will disconnect A2 from line A and the node to which A4 is connected will connect the signal received by A_j to line A so that both line A as line B are transmitting the signals received from the car. Again, at the appropriate time, the program sends a message to the switch at the central site to switch from outputting the signal on line B until the signal is output on line A (which corresponds to the signal received by A4). This process is repeated when the car continues around the track with line A and line B that alternately provide the output signal. The exact timing of the disconnection of a receiver (for example A2) and the connection of the next receiver to the same line (for example A) is not essential since the signal on this line is not being used. For example, the disconnection of A2 from line A can be as soon as the signal received by A2 is too weak or it can be delayed until the time at which the signal from A4 is strong enough. Figure 5 indicates that once the RF signal has been received, it is converted back to a baseband video signal. Line A and line B are therefore independent of the received frequency and can therefore be used to provide the transmission of video signals from more than one automobile. However, the pair of A / B Lines are only capable of transmitting the two video signals required when following a single car around the track. Accordingly, to make use of the possibility of following two different automobiles around the track, a separate pair of lines for example a line C and a line D can be provided. Again, because the pair of C / D lines are independent of the frequency, they can be used in the transmission of video images from a car that transmits over any frequency within a specified reception band. The second car may be transmitting on the same frequency when the car is being followed by the pair of A / B lines. However the cars are required to be in different locations around the circuit so that the RF signals reaching the receiver from the two cars do not interfere with each other. Therefore the addition of additional line pairs allows an increase in the capacity of the system by a car. Additional pairs can also be added (E / F lines, etc.) to allow a third car and other additional cars to be tracked around the track. However, it is still possible to have several cars that transmit at the same time around the track without having a second system (C / D line). However it is only possible to delay the signal from one of these cars in a time with the signals received by the other antennas from the other cars that are not connected to the lines A or B. Alternatively, if two cars using the same frequency they get too close to each other on the track, then one of these cars could be sent a message to change their transmission frequency, thus avoiding interference.

In an alternative embodiment of the present invention, the receivers can be connected to a network (for example LAN). The network can link all the receivers or only a portion of them in conjunction with other networks. In this way, the central controller can instruct which receivers should send their received signals. The distribution of receiver stations around the track requires careful planning to provide the required coverage with the optimal number of stations. In theory it might be possible to simply place a large number of stations at regular intervals around the track to ensure that the signal transmitted by the car can be detected by at least one of them in all positions on the track. However, such a distribution introduces other problems in the system. If the stations are placed too narrow together then apart from the unnecessary additional cost of having more stations than necessary, the complexity of the switching system and the control are increased because the signal from one transmitter can be received by several antennas. Likewise having a very small number of base stations can leave areas of the track where only a poor quality or no signal can be received. Therefore, to achieve consistent coverage of the entire track, with a minimum number of receivers, the receiver's stations are distributed as follows. A typical helix antenna provides a detection area (or receiving envelope) which is a 30 ° segment of a circle with a maximum range of about 200 meters. The cutting area of the receiving envelope is from 30 to 60 meters depending on the height of the antenna above the ground (from 1.5 meters to 3 meters respectively). The 30-degree segment of a circle is described as the width of the antenna beam and is a specification supplied by the antenna manufacturer. The maximum interval is determined by the maximum distance at which the received power level is sufficiently high to produce a quality broadcasting video signal. The minimum reception power level used for broadcast quality images is -60dB. The cut area of the receiving envelope is the distance at the front of the antenna at which the video signal is broken. The break in the video image is caused by a drop in the level of the received power that results from the cancellation of the direct signal by a reflection of the same signal outside the ground or ground. The distance at which this occurs depends on the height of the transmission antenna and the height of the receiving antenna above the ground or ground. The frequency of the RF signal will also change the location of the cutoff point. The amount of the reflection and therefore its effect depends on the surface on which the wave is traveling as well as on the wavelength of the signal. The following equation of reflection can be derived: Received Power = 4P sen2 [2phrht /? D} Where P is the received power without reflection, that is to say under the conditions of free space, hr and ht are the heights of the receiver and transmitter in relation to the reflection surface and d is the distance between the receiver and the transmitter. The reflection surface can not be on the ground or earth. For example, it can be a wall or barrier. In this case the values hr and ht refer to the distance between the reflection surface and the respective antennas. The analysis of the reflection equation indicates that to maximize the reception envelope close to the antenna, it is preferable to mount the antenna below ground or ground. However, the RF signal is attenuated when the antenna becomes closer to the ground or ground, which reduces the maximum distance of the receiving envelope. The attenuation is the result of the land that is introduced to the first Fresnel zone. The Fresnel zones surround the path of direct rays between the transmitter and the receiver. The first zone of Fresnel refers to the area immediately surrounding the path of direct rays. This zone is defined in such a way that the length of the path of a ray which has been deflected between the transmitter and the receiver is within half of a wavelength of the length of the path of the direct rays. When the largest part of the signal strength passes through the first Fresnel zone, any object, including the ground or earth, that aligns with this area, will lead to the attenuation of the received signal. Therefore a compromise is established when the antennas are mounted. Usually in a Grand Prix circuit the track is surrounded by metal barriers, known as Armco, which are approximately 1 meter high or with fences which are approximately 3 meters high. The antennas are mounted half of a meter above the Armco so that the RF signal is not attenuated because it is located near the metal structure or in front of the tire wall. Therefore, because the antennas are mounted by these characteristics of the track, the most common mounting heights for the antennas are 1.5 meters and 3 meters. The assembly requirements for each site are determined by reviewing the physical distribution of the site at this point and determining the limiting factors which can prevent the optimal locations of each circuit or the conduction of one on the circuit of the site review. Having determined the height of the antenna, the height of the receiver, which lies between the outer limit of the range or range of the antennas (R4 - see Figure 6) and the inner limit (Ri, R2) determined by the point in the What happens when the signal falls, can be determined. Having determined this envelope of the receiver, it is also necessary to establish the amount of superposition with the envelope of the antenna receiver of the adjacent station to ensure a smooth transition from the use of the signal from one station to the use of the signal from the next station. Accordingly, a range or range R3 corresponding to the point at which the signal from the adjacent antenna can no longer be received is chosen by defining a region of overlap between R3 and R4. In practice, to determine the distribution of stations around a track, the position of the first station (Rxl) is selected at the end of a length, for example, of the Start / Goal network (see Figure 7.1). The operation of this site is then established, the results of which enable the previous station (Rx34) with respect to the common station (Rxl), and the subsequent station (Rx2) to be located. In Figure 7.1, Rx 1 is mounted at 3 meters high, therefore, using the reflection equipment, the abandonment point for the site will be 60 meters in front of the antenna. The operation of the system is based on an optimal superposition zone between the reception sites of 20 meters, this allowing the fluctuation in the position of the vehicle at the point at which the video is switched. If the exact position information is not available, then the overlap zone can be increased to avoid the possibility of the signal being lost by switching from one receiver to the next too soon or too late. These 20 meters are added over the abandonment point and establish the point on the track in which the subsequent station must provide clean images (points A and B). A line is projected from the point of reception or capture of the subsequent station on the inner part of the track (point A), in the direction of travel of the cars, on the perimeter fence at the maximum possible distance around the track. The projected line should provide a clear line of observation from the transmitter to the receiver and therefore should not cross any of the definition boundary lines such as perimeter fences, buildings, trees or other structures. Once complemented, the process must be repeated to the point on the outer side of the track (point B). As can be seen in Figure 7.1, the location of the resulting site may be different from that already determined. It should also be noted that if the reception station was located in position A on the perimeter fence then a clear line of the site with respect to point B of reception or collection could not be achieved because of the perimeter fence on the inside of Lap 2. The location determined through this process has to be evaluated to provide a clear observation line for the duration of the planned receiving envelope. Figure 7.1 indicates that the location C on the perimeter fence is the maximum distance around the track at which a clear observation line to point C on the track could be obtained. This implies therefore that none of the locations A or B are suitable for the receiving station. The final verification is to ensure that location C still provides a clear line of the site with respect to the point of reception or reception required. Once confirmed, then the ideal geometric location of the reception station can be set. The effect of the surrounding structures to cause the Rf signal to be reflected to the receiving station must then be determined using the reflection equation. The effect of the surrounding structures to cause destructive reflections in the receiving station RXl must be established before the location of the preceding station (RX34) can be determined. Once the maximum collection distance for the receiving station RXl has been established, then the preceding site must be located so that it has a withdrawal point of 20 meters below the distance (to ensure the correct amount of overlap). In Figure 7.2 the preceding station with respect to RXl is shown being mounted at 3 meters high and therefore must be located at an additional 60 meters below the abandonment point. Figure 7.2 also indicates the procedure for locating the subsequent site for the RX2 receiving station. Figures 7.3 and 7.4 indicate how the reflection equation is applied in a practical environment. It can be clearly seen in both figures that the height of the reception antenna (in relation to the reflection plane - in this case the fence) is a constant value. In Figure 7.3 the fence under investigation (VALLEY 1) is parallel to the direction of travel and consequently the height of the transmitter also remains at a constant distance. For Figure 7.3 the only variable becomes the distance of the transmission when the transmission vehicle moves closer to the receiving station. In Figure 7.4 it can be seen that the height of the transmission antenna will change when the distance of the transmission changes, therefore, there are two variables. The application of the reflection equation becomes more complicated when calculations are made that relate to the curved fences (as might be required for example in the establishment of the operation of the reception station RX3 in the Figures). In this case the height of the receiving antenna in relation to the fence could also change continuously when the distance of the transmission changes, and therefore the equation includes three variables. It should be noted that the abandonment distances produced by the calculations of the reflection equation can be very sensitive to small changes in the height of the antenna relative to the reflective plane. For example, if the height of the transmitter was 4 meters and the height of the receiver 5 meters, the first point of abandonment could occur at 333 meters (assuming that the frequency of the transmission was 2.5 GHz). If the height of the transmitter increases to 4.5 meters, the first point of withdrawal or abandonment could reach 373 meters. From this brief calculation it could be derived that if the vehicle follows a different route around the runway, then the way in which the reflections of the environment affect the operation of the receiving station could vary widely. This also indicates the importance of accurate location information to ensure that the planning of the theoretical system is as accurate as possible. An additional point to be considered in the application of the reflection equation is the term that is related to the wavelength of the RF signal and therefore to the frequency. If, using the first example above, the frequency was reduced to 2.4 GHz then the first abandonment point could occur at 320 meters, a difference of 13 meters. From this it can be derived that the establishment or adjustment of the system could be different depending on the frequency of the transmission.

Having determined the theoretical locations for the receiving stations, using the appropriate RF equations, then it is also possible to consider the logistical implications of the installation of the stations. The factors such as the position of the perimeter openings, the general accessibility, the distances of the cable between the receiving station and the node, the location of warning signs, the location of structures to which the antennas can be mounted, the Site location security. For example, Figure 7.2 shows that the RX34 receiving station is connected to Node 1 (NI). The run of the cable is approximately 40 meters which could be relatively quick to be removed, but there is an access point to the runway just before the site, so that a pit might need to be dug and the cable buried for the Cable protection and to keep the access road clear. The site may not be located just before the access point because the wobble in the fence could block the antenna, therefore the receiving station could be moved back to approximately the same location as Node 1 causing the cable move in a short and fast way. The net result could be to increase the overlap with the RXl station, but reduce the overlap with the RX33 station. As this example indicates, all important factors should be considered as early in the planning stage as possible, and where a possible flexibility for minor adjustments should be built into the planning of the system. The above method of observation of the receiving stations is related to the stations provided with antennas having a narrow detection range (for example 30 °). However, these principles can be applied using antennas that have a larger detection angle. Each station comprises at least one receiver. Each receiver can have its own dedicated antenna or the station can have a single antenna and a separator to separate the different received frequencies and send them to the respective receivers. The stations also include filters and demodulators 4, to extract the video signal from the received microwave transmission. The video signal can then be sent to the central controller as a baseband signal which includes the video image information and the modulated audio signals on the separated subcarriers. Alternatively, the system can send the actual signal received by the antenna stations, i.e. the microwave signal, back to the central location where the receiving units and the demodulator could be located. This type of system could require that the RF signal be modulated on the fiber optic transport system, and each site preferably have a fiber link intended, back to the central location. The antennas are preferably propeller antennas but these can be replaced by any other suitable antenna type (such as fan beam antennas, interim connection antennas or omnidirectional antennas) depending on their location and track layout. For example, an omnidirectional antenna can be used to cover an elbow or fold while a directional antenna is used for straighter sections. Directional antennas preferably have an angular range or range of between 30 ° and 120 ° depending on their location. Although this invention has been described in relation to a location of the race track, it is clearly applicable to other applications. The system is equally applicable to an unclosed track, for example a road race. In addition, the system could be used in any situation where video transmission (or other high bandwidth signals) from a moving object to a stationary object, be required. Applications could include the transmission of images from bicycles or cars (eg police cars) to road-side receivers for transmission to other police cars or to a central control room. The system could still be extended to provide a mobile video communications system. Although the modality described above refers mainly to the communication of video data, it is proposed that the system could also provide communication of audio and data signals both to and from the automobile as well as video signals back to the automobile. . Clearly, once a communications link is established, as described above, it is simply a matter of sending a signal to the car descending on the established link instead of receiving it from it.

It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (15)

1. A communication system, characterized in that it includes: a video signal source and transmitter, provided on a mobile object to generate and transmit the video signal on at least one first carrier frequency; at least first and second receivers for receiving the video signal transmitted on the first carrier frequency, the first and second receivers have detection areas that overlap at least partially and are located at far spaced locations; a position detector for generating a position signal indicative of the position of the moving object using the different indications of the parameters of the received video signal and the bearer; a controller operating in response to the position signal to select one of the video signals received by the first and second receivers and output the selected signal, the controller is located in a different place than in the mobile object.

2. A system according to claim 1, characterized in that the controller changes from receiving the signal received by the first receiver to the second receiver when the mobile object is at a predetermined distance from the first receiver.

3. A system according to claim 1 or 2, characterized in that the first and second receivers have helical antennas.

4. A system according to claim 3, characterized in that the antennas are arranged or distributed in the range from 1.5 to 3 meters in relation to the floor or ground.

5. A system according to any of claims 1 to 4, characterized in that the transmitter can be controlled to selectively transmit on a plurality of frequencies.

6. A system according to claim 5, characterized in that the transmission frequency of the transmitter is controlled by the controller.

7. A system according to any of the preceding claims, characterized in that the position detector determines the position of the moving object based on the information provided by the timing system of a racetrack.

8. A system according to any of the preceding claims, characterized in that it comprises at least one additional transmitter provided on at least one of the additional mobile objects, each transmitter that simultaneously transmits the video signals to one or more of said receivers.

9. A system according to any of the preceding claims, characterized in that the receivers and the controller are interconnected by a network.

10. A system according to claim 9, characterized in that the network comprises first and second lines of the signal; the output of each of the receivers is selectively connectable, under the control of the controller, to the first, to the second or to any of the lines of the signal in such a way that, in use, the output from one of the receivers is connected to the first line of the signal and the output of one second of the receivers is connected to the second line of the signal; and the control means outputs the signal on the line of the signal connected to the receiver that receives the desired signal.

11. A system according to claim 10, characterized in that the control means include an additional output connected to the signal line not connected to the desired receiver.

12. A method of communication of a video signal between a mobile object and a stationary location, the method is characterized in that it comprises the steps of: transmitting the video signal on a first carrier frequency from a transmitter on the mobile object; providing at least first and second receivers at locations spaced far apart to receive the signal from the transmitter on the first-carrier frequency; and determining the location of the mobile object using different indications of the parameters of the signal, of the received signal or its bearers; selecting the signal received by one of the first and second receivers for the output in the stationary location, based on the location of the moving object as determined in the determination step.

13. A method of establishing a communication system for communicating a video signal between a mobile object provided with a transmitter for transmitting the video signal on a first carrier frequency and a stationary location comprising a plurality of receivers each having an area of detection within which the receiver is able to receive the signal from the transmitter on the first carrier frequency when the transmitter is in the detection area, the method is characterized in that it comprises the steps of: placing a first receiver in a first location; calculating a distance from the first location in which the reflection by a reflection surface of a signal transmitted from the mobile object will cause the power level received in the first receiver to decrease below a predetermined level to define a first detection area; determining a position for each subsequent receiver, calculating a distance at which reflection from a reflecting surface will cause the received power to be reduced below the predetermined level to determine a detection area and place the subsequent receiver at a distance from the previous receiver. such that the detection area of the subsequent receiver overlaps the detection area of the previous receiver to form a continuous strip within which the signal from the transmitter can be received by at least one of the receivers; providing means by which the signal received by at least one receiver can be provided to the stationary location; and providing means for determining the position of the mobile object using different indications of the parameters of the received signal and the bearer and to control the switching between the receivers based on the determined position.

14. A method of establishing a communication system according to claim 13, characterized in that the reflecting surface is the floor or floor.

15. A method of establishing a communication system according to claim 13, characterized in that the position of each receiver is determined: determining a first possible position area for the receiver based on a predetermined amount of superposition of the detection areas of the receiver. current receiver and previous receiver; determining a subset of the first zone of possible locations for the receiver, to determine a second zone of practical locations for mounting the receiver; eliminating these locations in the second zone in which the area of detection of the receiver does not cover all of the required locations of the transmitter considering the topology of the floor in the detection area of the receiver and any obstructions there to define a third zone; and placing the receiver in the third zone.