System for bidirectional data transmission between a beacon and a vehicle
First Claim
1. A land vehicle transponder unit (23) for use in a system for bidirectional transmission of electromagnetic data signals between a stationary beacon (21) and said vehicle transponder unit (23) which is located in a vehicle,wherein the stationary beacon (21) transmits, in a downlink mode, encoded data signals to the vehicle transponder unit (23), andthe vehicle transponder unit (23) transmits, in an uplink mode, encoded data signals to the stationary beacon (21) according to a semi-passive transponder principle,the vehicle transponder unit (23) comprising:
- two spatially separated antennas (1,
2) spaced apart by both of a predetermined horizontal separation in a lateral direction and a predetermined height separation in a vertical direction above a road surface on which said vehicle is situated, to assure differing reception conditions, wherein said predetermined horizontal separation and said predetermined height separation are set to minimize reflections from neighboring vehicles and reflections from the road surface, respectively; and
an evaluation circuit (25), having a respective input (3,
4) connected to each of said antennas, and including;
a single modulator/demodulator for each of said antennas, to transmit/receive respective signals with said antennas,a comparator for providing a comparison between respective signal strengths of said signals received from said antennas,means for providing a determination as to which one of said antennas provides a higher signal strength in response to said comparison, andmeans for selecting the single modulator/demodulator corresponding to said one of said antennas for use in transmitting to said beacon (21) during a following uplink mode in response to said determination.
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Abstract
A system, for bidirectional transmission of electromagnetic data signals between a stationary unit and a vehicle unit, in which at least two antennas can be used, is proposed. The antennas are aligned at a predetermined distance and at a predetermined height from one another, in such a way that reflection from the roadway and from vehicles is minimized. In the uplink mode, the antenna having the best reception properties is selected, so that reliable data transmission to the stationary unit takes place.
47 Citations
10 Claims
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1. A land vehicle transponder unit (23) for use in a system for bidirectional transmission of electromagnetic data signals between a stationary beacon (21) and said vehicle transponder unit (23) which is located in a vehicle,
wherein the stationary beacon (21) transmits, in a downlink mode, encoded data signals to the vehicle transponder unit (23), and the vehicle transponder unit (23) transmits, in an uplink mode, encoded data signals to the stationary beacon (21) according to a semi-passive transponder principle, the vehicle transponder unit (23) comprising: -
two spatially separated antennas (1,
2) spaced apart by both of a predetermined horizontal separation in a lateral direction and a predetermined height separation in a vertical direction above a road surface on which said vehicle is situated, to assure differing reception conditions, wherein said predetermined horizontal separation and said predetermined height separation are set to minimize reflections from neighboring vehicles and reflections from the road surface, respectively; andan evaluation circuit (25), having a respective input (3,
4) connected to each of said antennas, and including;a single modulator/demodulator for each of said antennas, to transmit/receive respective signals with said antennas, a comparator for providing a comparison between respective signal strengths of said signals received from said antennas, means for providing a determination as to which one of said antennas provides a higher signal strength in response to said comparison, and means for selecting the single modulator/demodulator corresponding to said one of said antennas for use in transmitting to said beacon (21) during a following uplink mode in response to said determination. - View Dependent Claims (2, 3, 4, 5, 8, 9)
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- 6. The transponder unit of claim 6, wherein the evaluation circuit (25) compares the demodulated signals using said comparator (14) to determine a maximum amplitude at an onset of the uplink mode, and then selects the antenna that had a best reception signal in order to use the selected antenna in transmitting to said beacon (21) during a following uplink mode.
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10. A method for providing a land vehicle transponder unit (23) for use in a system for bidirectional transmission of electromagnetic data signals between a stationary beacon (21) and said vehicle transponder unit (23) which is located in a vehicle, wherein the stationary beacon (21) transmits, in a downlink mode, encoded data signals to the vehicle transponder unit (23), and the vehicle transponder unit (23) transmits, in an uplink mode, encoded data signals to the stationary beacon (21) according to a semi-passive transponder principle, the steps of:
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arranging two antennas (1,
2) to be spaced apart by both of a predetermined horizontal separation in a lateral direction and a predetermined height separation in a vertical direction above a road surface on which said vehicle is situated, to assure differing reception conditions, wherein said predetermined horizontal separation and said predetermined height separation are set to minimize reflections from neighboring vehicles and reflections from the road surface, respectively;transmitting/receiving respective signals with said antennas, comparing respective signal strengths of said signals received from said antennas to provide a comparison thereof, determining which one of said antennas provides a higher signal strength in response to said comparison to provide a determination, and selecting the one of said antennas for use in transmitting to said beacon (21) during a following uplink mode in response to said determination.
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Specification