Telecommunications – Transmitter and receiver at separate stations – Frequency or phase modulation
Patent
1996-09-25
1998-03-31
Vo, Nguyen
Telecommunications
Transmitter and receiver at separate stations
Frequency or phase modulation
455517, 342 51, H04B 726
Patent
active
057349657
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND INFORMATION
The invention relates to an on-board unit having at least one receiving and transmitting antenna for the bidirectional transmission of data in accordance with a predetermined transponder method. German Patent Application No. 42 13 881 discloses an on-board unit, which works in accordance with a transponder method in the microwave range, and this on-board unit is used in traffic control systems to exchange data with a fixed beacon. This German Patent Application also describes a downlink transmission of data from the beacon to the on-board unit by means of an amplitude modulation. In accordance with this transponder method described by the German Patent Application, an unmodulated carrier signal is transmitted in an uplink transmission from the beacon, modulated by the on-board unit, and retransmitted to the beacon. When signals are transmitted between the beacon and the vehicle, the waves propagate to their destination not only over a direct path, but also by way of reflections, e.g., on the road surface, on the hood, or on other vehicles driving past. This multipath propagation gives rise to interference of the individual waves at the receiving location, so that depending on the phase relation of the individual waves, the result is either an increase or decrease in the total field strength. This effect, known as interference fading, can have a disruptive effect on the reliability of a transmission. This is especially true of an uplink operation, because the transmission distance has to be run through twice. Current systems solve this problem for example, by means of space diversity or antenna diversity, where at least two antenna elements are used on the on-board unit, in that the antenna element which receives the largest signal level is selected for the modulation in the uplink operation. However, this method is not reliable enough for all operating states, so that interference can nevertheless occur in the transmission.
SUMMARY OF THE INVENTION
In contrast, the advantage of the on-board unit according to the present invention is that the receiving signal that is influenced by interference fading or fading is initially amplified by a high-frequency amplifier before it is demodulated. Therefore, one is able to compensate for heavy fluctuations in the level of the receiving signal, making the data transmission more reliable. Another advantage is that amplifying the receiving signal increases the transmission range of the transmission distance, so that even at high vehicle speeds, there is still ample time to transmit all the data.
Furthermore, it is especially advantageous that the amplifier for the uplink signal is also adjustable in downlink operation in accordance with a predetermined algorithm, which is adaptable to the path of the signals. In accordance with the present invention, the high frequency amplification is performed in accordance with a squaring formula Vul=Vdl.times.Vdl, wherein Vul is an uplink amplification factor and Vdl is a downlink amplification factor.
The amplified high-frequency signal is supplied to a downstream demodulator/modulator circuit, which demodulates the received downlink signal in a downlink operation and modulates the received carrier signal in an uplink operation.
It is advantageous in this case that, in part, the same components are used both in a downlink operation for the demodulation, as well as in an uplink operation for the modulation.
When an amplifier is used, one single antenna element is sufficient to receive the downlink signal or the unmodulated carrier signal in an uplink operation, so that this also renders possible a simply designed on-board unit. The simplified design favors a small type of construction, so that the on-board unit can be mounted, e.g., in the area of the windshield or rear window of the vehicle. The on-board unit of the present invention can be used in the range of reception of a beacon to transmit traffic control data, vehicle guidance data, or for toll collection.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
REFERENCES:
patent: 5537672 (1996-07-01), Grabow et al.
Detlefsen Wolfgang
Grabow Wilhelm
Kersken Ulrich
Robert & Bosch GmbH
Vo Nguyen
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