AU1662199A

AU1662199A - Dedicated short range communication process (DSRC) and transponder for implementing the same

Info

Publication number: AU1662199A
Application number: AU16621/99A
Authority: AU
Inventors: Wolfgang Detlefsen; Wilhelm Grabow; Thomas Wixforth
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-11-12
Filing date: 1998-10-30
Publication date: 1999-05-31
Anticipated expiration: 2018-10-30
Also published as: AU738566B2; DE19750047A1; KR20010031948A; BR9814163A; WO1999025087A1; EP1040613B1; ES2378297T3; EP1040613A1

Description

WO 99/25087 PCT/DE98/03176 Dedicated short range communication process (DSRC) and transponder for implementing the same The invention relates to a dedicated short range communication process (DSRC) and a transponder for the same with the further characteristics of the preamble of the Claims 1 and 5. Various dedicated short range communication processes are known for a range of applications. Belonging to these applications is an electronic access control for vehicles or persons, for example for the automated debiting of toll fees for the use of autobahns or tunnels or the transmitting of vehicle information to travelling vehicles. These short range communication processes are generally given the abbreviation DSRC for the English "Dedicated Short Range Communication". Common to all these processes is that fixed beacons can transmit information via radio waves to an on board unit designed as a transponder (downlink). For the transmitting of information of the respective vehicle etc. to the beacon, arranged, for example, above a toll booth etc., the beacon transmits an unmodulated carrier which is received by the transponder and returned, modulated by a message signal. For motor vehicle applications, for example for the automated debiting of autobahn tolls etc., systems in particular with wavelengths in the ISM band are used. In particular the lower band of 5.795 to 5.805 GHz with two 5 MHz broad channels and a carrier wave of 5.8 GHz is planned for traffic telematics applications. For a mass-application, in particular in motor vehicles, it is necessary that the on board units are constructed simply, lightly and economically so that the purchase and operating costs for such a device are low. The necessary infrastructure should be concentrated on the beacons. In very simple on board units in the form of transponders, the power of the sideband signals of the wave sent back from the transponder is naturally dependent on the WO 99/25087 PCT/DE98/03176 2 power density which the carrier wave coming from the beacon at the place of the transponder possesses. Figures 1 and 2 show in schematic representation a vehicle 12 approaching a radio beacon 10. In this example an on board unit, ie. a transponder 14, is arranged in the vicinity of the rear view mirror. In the socalled "downlink", ie. the transmitting of information from the radio beacon 10 to the vehicle 12 or the transponder 14, a modulated carrier wave 16, for example of the frequency 5.8 GHz, is used. Figure 2 shows schematically the so-called: "uplink", ie. the transmitting of information from the vehicle 12 to the radio beacon 10. The unmodulated 5.8 GHz carrier transmitted from the radio beacon is modulated by a message signal in the transponder 14, so that the reflected or returned, modulated carrier wave 18 transmits the necessary information, for example for the vehicle identification etc. to the beacon 10. In certain exceptional circumstances the distance between the transponder 14 and the beacon 10 can be so small that too high, disturbing power levels of the uplink signals based on too a high power density of the unmodulated carrier at the place of the transponder result. The can be the case, for example, when a transponder is located in an unfavourable position on a higher vehicle, for example a truck. Solutions from prior art are known, as for example, the so-called automatic gain control, known by the acronym 'AGC'. The disadvantage of a circuit of this kind for the even distribution of the strength of a received signal, as is used for example in high value radio receivers, can be seen in that the involved construction and the associated manufacturing costs are too high. An AGC circuit, therefore, runs counter to the goal of having available as simple and economical device as possible, usable in a wide variety of applications as a transponder.

WO 99/25087 PCT/DE98/03176 3 Furthermore, from prior art the so-called limiter diodes are known in which disadvantageous upper waves are formed. The task of the invention, then, is to improve a process of this type in such a way that even in unfavourable spatial constellations of beacon and transponder, too high uplink levels can be avoided and the transponders to be used for the process stand out due to a simple construction and correspondingly low production costs. The solution of the task with a process of this type is characterised in that, in one step, the power level of the received, modulated signal is measured and, dependent on falling below or exceeding a threshold value, the returning carrier wave is modulated with a modulation depth which can be selected in steps, determined dependent on the measured power level. In a transponder of this type, the solution is characterised according to the invention by means of the stepwise regulation of the degree of modulation. It is preferably planned that the reception unit feature a threshold value indicator (3) which, when a threshold value for the received, if applicable modulated carrier wave, generates a control signal for the regulation of the degree of modulation. In order to make possible an inexpensive and simple construction which is adequate, for example, for applications in motor vehicles for automated toll debiting, it is especially preferred, according to the invention, that the modulator features two differing preregulated degrees of modulation. The invention will be described in greater detail in the following on the basis of a depicted embodiment. Shown in the drawing is: Figure 1 a schematic representation of a vehicle equipped with an OBU and approaching a beacon during the downlink phase, Figure 2 the motor vehicle of Figure 1 during the uplink phase, WO 99/25087 PCT/DE98/03176 4 Figure 3 a schematic representation of a transponder in accordance with the invention and Figure 4 a schematic representation of various degrees of modulation. Figures 1 and 2 have already been described in the introduction. Figure 3 shows a transponder 1 according to the invention with means for the power limitation of the side band signals on the transmission output A5. The transponder 1 features a receiving piece 2 with a threshold value indicator 3, and a modulator 4 and, in accordance with the invention, a control unit 5. The receiver 2 possesses an input El for a modulated signal SI (reference number 16 in Figure 1) and an output A2 for a corresponding demodulated signal S2. The information contained in the signal S2, for example the identification code of a beacon etc. can be further processed in a microprocessor not depicted. Further, the receiver 2 possesses one or more outputs A3j (i = 1 ... to I). These outputs serve to transmit control signals S 3 ; of the integrated threshold value indicator 3, which signify whether the signal SI exceeds or falls below certain power levels. In this way the threshold value indicator 3 can be designed as a simple Schmitt trigger, ie. only the exceeding of a threshold value is recorded, synonymous with too slight a gap (cf. Figure 2) of the OBU 14 and the transponder 1 of the beacon / transmitter 10. The modulator 4 possesses an input E4 for an unmodulated carrier signal S4 (5.8 GHz carrier in Figure 2) and an output A5 for a modulated signal S5, with the help of which, during the uplink phase, information is transmitted from the vehicle 12 to the beacon 10 (Figure 2). $V ) 44 -- (AJ~ WO 99/25087 PCT/DE98/03176 5 If necessary, both signals S4 and S5 can apply to one gate. Further, the modulator possesses an input E6 for a modulator signal S6 which, for example, can be generated by a microprocessor not depicted and, for example, the identification code of the vehicle 12 can signalise or represent the credit in a clearing unit etc. The modulator can be regulated in various levels on a different degree of modulation respectively. Either one or several inputs E 7 (j = 1 ... J) are planned for the regulation. The power of the modulated output signal S5 is (in specified limits) proportional to the power of the carrier signal S4. A modulation of the carrier S4 only takes place when the modulation signal S6 is present. The controlling section 5 processes the signals S3j and S 7 j. It is planned, in accordance with the invention, that the difference of the power level (in dBm) of the signals SI (modulated carrier wave received by the receiving piece) and S4 (unmodulated carrier wave received by the modulator 4) will be held within certain tolerances. As, at the time of the decision on the degree of modulation to be selected when the control registers a threshold value above or below, based on the moving vehicle, the exact power level of the signal S4 is not known exactly, the procedure of the invention assumes strictly, for the power limiting of the side band signals in the modulated signal S5 that the difference of the power level of the signal SI at the time (a) "Control registered threshold value fallen below / exceeded" and, of the signal S4 in the time interval (b) "Carrier signal S4 is modulated with modulation signal S6" lies in a certain known tolerance area or in all probability will. If the received signal SI determines, by the threshold value indicator 3, a certain threshold value, then a degree of modulation of the modulator 4 will be selected via the control 5 by means of a control signal S7j in such a way that the power in the side bands of the modulated signal S5 does not exceed a given limiting value, and in spite of the vehicle further approaching the beacon and therefore the possible increase of the power level of the signal S4, will in all probability not exceed it.

WO 99/25087 PCT/DE98/03176 6 Figure 4 illustrates the possible reduction of the side band power by the choice of various degrees of modulation m. The limiting in levels, in the simplest case two different modulation depths as opposed to a continuous regulation, is very much more simple and economical to realise and is suited in particular to inexpensive mass products such as transponders for the vehicle applications referred to. 5

RA,

Claims

1. Transponder (1), in particular for the exchange of data in the vicinity using carrier waves in the medium microwave range (DSRC), in particular for use in vehicles as on board units (OBUs) with a reception unit (2) and a modulator (4) for the modulation of a received carrier wave (S4) with a modulation signal (S6) and a modulator (4) for the modulation of a received carrier wave (S4) with a modulation signal (S6), characterised by means for the stepwise regulation of the degree of modulation.

2. Transponder as in Claim 1, characterised in that the receiver unit (2) features a threshold value indicator (3) which, when a threshold value for the received, if applicable modulated carrier wave (16), generates a control signal for the regulation of the degree of modulation .

3. Transponder as in one of the preceding claims, characterised in that the modulator (4) features exactly two different, previously regulated degrees of modulation.

4. Transponder as in one of the previous claims, characterised by a timing element, while that of the modulator (4) is switched into another modulation level.

5. Dedicated short range communication process (DSRC), in which signals are transmitted to a mobile unit (OBU) (14) from a stationary beacon (10) using a modulated carrier wave (16), preferably in the GHz range, and signals from the transponder (14;1) to the beacon (10) are returned, an unmodulated carrier (17) transmitted by a beacon being received, modulated and returned, characterised in that UT/DE98/03176 8 * in a first step the power level of the received, modulated signal (16) is measured and, dependent on the exceeding or falling short of a threshold value in a next step, the wave (17) to be returned is modulated (18) with a certain modulation depth dependent on the measured power level which can be selected in steps.

6. Dedicated short range communication process (DSRC) in which signals are transmitted to a mobile unit (OBU) (14) in the form of a transponder (1) using a modulated carrier wave (16), preferably in the GHz range, and signals are returned from the transponder (14; 1) to the beacon (10), an unmodulated carrier (17) transmitted from the beacon being received, modulated and returned by the beacon, characterised in that in a first step, the control (5) registers and stores an exceeding or falling below the threshold (dependent on the received modulated signal [16; 51 ]) in order s in a next step to regulate the degree of modulation of the modulator (4) via appropriate means, eg. control signals (S7) dependent on the information registered / stored in the first step.