TRAFFIC RADAR DEVICE

The invention refers to a traffic radar device in accordance with the generic term of the requirement 1.

For the controlling of the traffic river in particular in cities traffic signaling devices are used. An efficient traffic control requires thereby the collection of the traffic volume. This traffic data acquisition necessary for it uses generally automatically working traffic sensors. Beside the well-known magnetic field sensors, like resounding sensors or loop detectors, ultrasonic sensors or radiation sensors also microwave sensors, which work generally after a radar procedure, are used for the traffic collection. A source of high frequency sends energy over an antenna on the objects, i.e. vehicles which can be seized. The reflected high frequency energy is then evaluated in the receiver. These radar detectors were used so far mainly for the collection of the speed of vehicles, in order to detect the Geschwindigkeitssünder. They were used also for the collection from vehicles to the determination of the flow of traffic for the controlling of traffic light signaling devices.

In the European disclosure writing 0,497,093 - A1 is descriptive a procedure and a mechanism for the collection of vehicles in the traffic for the controlling of traffic signaling devices, which signal generator, tax on transactions equipment and at least a radar antenna arrangement with an associated radar device as traffic sensor exhibit, whereby the signals of the vehicle detector in the controller are converted to the education by circuit criteria for the traffic signaling devices and detected by means of distance and speed selection respective vehicles. The radar device in the FM-CW-mode and/or in the angle bearing angle can be operated. For a angle bearing two azimuthal against each other transferred lobes are intended. As these formed and as the radar receive data are processed, is there not more near descriptive.

In the US-PS 4,908,615 a system and a procedure for the control of traffic light signaling devices are descriptive, which likewise uses a radar device for vehicle detection. Both approximate vehicles can detect itself and at the light signal plant stopping vehicles. With the well-known radar device it is possible to locate the vehicles. In addition with a fine, strongly the lane range which can be supervised is scanned bundled transmission jet horizontal and vertically, whereby the radar device in a very high frequency range must work. That makes a such radar device expensive, because a substantial expenditure is necessary. Besides several transmitters are necessary or the one mechanical deflector for both scanning directions in unfavorable way either, which can lead easily to disturbances. For a broad employment in the traffic collection the well-known radar device might hardly be applicable from there.

Task of the invention is it in such a manner to train a traffic radar device for the collection of vehicles and for the determination of the lane of the respective vehicle that the data won with the radar device permit a precise statement about the flow of traffic concerning lane and distance, in order to make a better controlling possible of traffic signaling devices.

This task is solved with an initially described traffic radar device with the characteristic characteristics of the requirement 1.

The radar device according to invention with mechanisms for the selection of the received echo signals after distance and radial velocity exhibits two firmly arranged radar antennas, which radiate themselves partly overlapping lobes. These two radar clubs are formed neither mechanically nor electrically by swivelling of only one transmitting beam, as this admits from the above mentioned US patent specification is. That has the advantage in relation to the well-known procedure that neither a set of mechanical parts is necessary still electrical distribution switchboards. These firmly arranged antennas produce two to each other accurately assigned and from there exactly defined Strahlungskeulen.Die from the antenna lobe range over the two radar antennas separated received echo signals in two separated channels are continued to process, whereby by correlation of the azimuth angles of respective vehicles and from this the position of the vehicles is determined is determined. In addition with an oscillator, which steered in its frequency with a relaxation oscillator, a Sendesignal is produced, which is led to the radar antennas across a divisor to in each case a waveguide. The respective received signals overlaying with the Sendesignal are digitized in each channel for itself parallelly and the frequency difference signal thus won and supplied to a distance filter bank, and this for each channel, which also in the following the case is.

At the exit orthogonale signal components, thus for respective distance sections of pairs of signals after X and Y, are applied to the distance filter bank for respective distance ranges. These are supplied to an nearly Fourier analyzer, which makes a radial velocity analysis by way of a buffer for the subsequent treatment of a double filter bank. The spectral components (spectral's pairs), resulting from it for each distance range, are supplied to a threshold value comparing unit, in which the amplitudes of all spectral components are compared with a given threshold. The spectral components lying over the threshold are processed in a signal angle processing angle of far, whereby belonging together signals, are linked so-called pairs of vectors, with one another, in order to determine a respective angle difference, with which due to the geometrical arrangement of the radar antennas the respective azimuth angle of the vehicles concerned are determined. In subordinate trace frequency discriminator mechanism from azimuth angle, which determines vehicle distance and the vehicle speed the appropriate vehicle-purely, on which the vehicle is.

Closer details and advantages of the invention result from the following description, in which on the basis the design the invention is more near described. Fig show. 1 a block diagram concerning radar device and microwave part, Fig. 2 a Zeitdiagramm with transmission and received signals, Fig. 3 a block diagram for the gating, Fig. 4 a Zeitdiagramm of the received signals over many periods and Fig. 5 a Vektordiagramm of the output signals of the doppler filter bank.

The traffic radar device shown in Fig.1 is arranged for example four meters over the road, whereby the radar antennas AA OFF illuminate and with its respective antenna lobes AKA and AKB two lanes SP1 and SP2. There are simplified shown on each trace a vehicle FZ1 and FZ2, which with different speed g1 and g2 zufahren on the radar device. The radar transmitter is formed of a Gunnoszillator GU, whose frequency over the Varaktor VR is controllable. As control signal the relaxation oscillator serves SZG. The output signal with frequency telex names the Gunnoszillators GU the divisor LT into two halves is divided and runs into one waveguide each HLA and HLB for the channels A and B, to whose end a radar antenna AA is attached and OFF in each case. The antennas AA, OFF light up themselves over two overlapping clubs AKA, AKB the road lying before the radar device. They are arranged here symmetrical and exhibit to that extent a symmetry axis, which is named SA. The two vehicles FZ1 and FZ2 reflect a part of this microwave energy. This received signal, frequency Fe, arrives over the antenna AA, OFF back into the waveguides HLA and HLB and overlays with the Sendesignal, frequency telex. In the waveguides direction diodes RDA and RDB are inserted in each case, which rectify the overlapping signal (Fs/Fe). The mixture product, characterized by the frequency difference Fb = telex, here developing - Fe, becomes filtered over the low-passes TPA and TPB and represents in the following the signals SA and self-service for the channels A and B, which can be processed, generally here with S (t) designated, as shown in Fig.2.

The temporal operational sequence from transmission and received signals is from the Fig. 2 evidently. The transmitter frequency telex starts FH from the starting frequency FST out and rises with temporally linear rise Te up to a maximum value FST +, whereby FH is the frequency departure. With the reaching of the maximum value FST + FH drops back the frequency telex with relatively steep waste the initial value FST. This procedure repeats itself now in regular time intervals Tad, the saw tooth period. The time intervall between the beginning of the saw tooth return and the renewed start is called return time Tr. The Empfangsfrequenz Fe shows in principle the same Zeitverlauf as the transmitter frequency telex with the only difference that the process of the Empfangsfrequenz Fe is temporally easily retarded in relation to the transmitter frequency telex, around the radar running time ts: ts = 2*R/c (1) R = echo distance, C = speed of light.

It is important to mark that in the context of the echo distances regarded here this running time is always small in relation to the receipt time Te. In the further the overlap range of the two saw teeth of the transmitter frequency interests telex and the Empfangsfrequenz Fe within the rising range. Because of the comparatively small amount of the running time ts this overlap range the rise range of the transmitter frequency telex can be equated.

The small Zeitverschiebung ts is in the context of the receipt total time Te negligibly, effectuation however due to the high frequency departure FH a pronounced frequency difference Fb = telex-Fe. Under the use of equation (1) the following relationship is valid: Frequency difference Fb = telex (t) - Fe (t) = H*ts/Te = 2* R * h (c*Te) (2) to assist in the understanding are indicated the used parameters as practical, concrete values: <tb><TABLE> Columns=3 <tb>FST<SEP>Startfrequenz<SEP>34,35 GHz <tb>FH<SEP>Frequenzhub<SEP>30 MHz <tb>l<SEP>Wellenlänge of the radar device (frequency FST+FH/2)<SEP>0.873 cm <tb>c<SEP>Lichtgeschwindigkeit<SEP>300000 km/s <tb>Te<SEP>Empfangszeit<SEP>25.6 mu s <tb>Tae<SEP>Entfernungs-Abtastintervall<SEP>400 mu s <tb>Tad<SEP>Sägezahnwiederholzeit<SEP>90.7 mu s <tb>R<SEP>Echoentfernung<SEP>100 m <tb>ts<SEP>Signallaufzeit<SEP>0.667 mu s <tb>Fb<SEP>Frequenzdifferenz<SEP>781 kHz. <tb></TABLE>

The wavelength l plays a crucial role with the views of speed. More generally formulated a distance-proportional receipt frequency difference Fb/m = 7,81 results kHz/m the course S for above parameters (t) of the received signals with the frequency Fb is represented in the lower line of the figure 2 as repetitive sine course.

For the gating the two received signals become S (t), i.e. SA and self-service, with an analogue-digital converter ADA and ADB (Fig.3) digitized and for a further gating analyzes and in addition a distance filter bank EFA and/or EFB supplied. That is shown and in the following is continued to describe in the block diagram in accordance with the Fig.3.

The gating contains two for the two channels A and B equal developed distance filter banks EFA, EFB with FFT analyzers downstream (double filter bank). The task of this arrangement consists of preparing the echoes of the vehicles in such a way that they are available separately in the following signal angle processing angle SWV according to vehicles.

The further description is directed toward channel A and been valid, as far as otherwise does not mention, without reservation also for channel B.

In the second line of the Fig. 2 represented received signal S (t) exhibits three characteristic characteristics: Frequency Fb characterizes amplitude = height of the sine summits phase = position of zero crossovers by the distance of zero crossovers.

The distance filter bank EFA and/or EFB consists of band-pass filters, whose center frequencies attach together and it is so dimensioned that of the interesting distance range due to the equation (2) produced frequencies to be seized. The received signal of a certain distance range El to EN appears thus at the exit of that single filter EF1, EF2,… EFm of the filter bank, which with the associated frequency Fb is co-ordinated. To each partial filter for example of the filter bank consisting of 32 single filters (m = 32) thereby a distance section El to Em (Fig.1) on the road can be assigned, whereby the absolute distance is given by the center frequency of the filter and the width of the distance section by the range of the filter.

In Fig. 1 is schematically that the respective single filters EFl to EFm of the distance filter bank EF associated distance section El to Em outlined. In the distance range Ek are to drive thereby two vehicles FZ1, FZ2 next to each other with different speed of g1, g2. These two vehicles supply output signals at the exit Ek of the distance filter EFk in the distance filter bank EF (Fig.3).

The distance filters EFl to EFm are realized appropriate way in digital technique and would drive through in each case a double computing algorithm: EMI9.1 S (tn) received signal tae action period of the signal S (t) tn scanning times of the signal S (t) k center frequency of the distance filter k n=l… Ne of scanning points (e.g. N = 64) Fig. 2 shows in the second line the individual components.

This algorithm well-known as discrete Fourieranalyse (e.g. H.Götz: Introduction to digital signal processing, B.G. Täubner, Stuttgart 1990) supplies two signal components x and y at the exit of each distance filter EF and seizes thereby the three components of the received signals: Frequency = number of the distance filter amplitude and phase represented by the orthogonalen components Exk and Eyk of the filter, co-ordinated co-ordinated with the received signal, with the received signal.

If one regards the distance filter EFk for itself, then this from Ne scanning values Exk and Eyk, whose amplitudes considerable size accepts, produce two orthogonale components only if the incoming frequency Fb of the signal S (t) in the range of the filter frequency k lies.

With the distance filter bank shown EFA and/or EFB can be selected vehicles from different distances from each other, not however the two vehicles FZ1, FZ2 within the distance range Ek. These produce a composite picture signal at the exit of the distance filter EFk. This to evaluate happens in the subordinate double filter bank FFT.

The double filter bank FFT accomplishes a radial velocity analysis of the output signals of the distance filter bank EF. To assist in the understanding for this is first the received signal S (t) to be again more near regarded, whereby the special attention of the signal phase of successive sine courses is valid.

In Fig. 2 is drawn two successive sine courses, which come from the echo of a being certain object and/or vehicle FZ. One recognizes the goal with the radial velocity zero by the fact that successive sine courses appear absolutely identical in particular always with the same phase position begin and end. In Fig.4 to it a larger number of successive sine courses of a moved object, is shown a vehicle, in contrast. The individual sine courses become in regular time intervals Tad (to saw tooth period, mu s) determined e.g. 90, see in addition also Fig. 2.

During this short time the vehicle within the millimeter range moves. This tiny change of location has negligible influence on the absolute object distance and thus on the frequency Fb, however substantial influence on the phase difference between transmission and received signal and thus on the phase of the signal S (t) resulting in the case of the overlapping procedure itself. With these phase changes the change of location of the vehicle in relation must be regarded to the radar wavelength (l=1.24 cm). With exact regarding of the Fig. 4 one recognizes the different phase position of the sine courses. In the two lower lines of the Fig. 4 is the x and/or y-components each sine course of the assigned output signal of a distance filter EF in accordance with equation (4) drawn if the signal frequency Fb lies in the pass band of the filter, i.e. produces considerable amplitudes. One recognizes, how with the phase the values of the components x and y change. The pair x, y in line suggest in each case one around 90<o> shifted sine function, whose frequency represents fd the Doplerfrequenz and thus the radial velocity of the vehicle. The doppler frequency is calculated too fd = vr/(l/2) (5) fd doppler frequency (cycles per second) vr radial velocity of the item under test in m/s l wavelength of the radar device in m equation 5 can be made understandable as follows under view of Fig.5: The reciprocal of the doppler frequency l/fd indicates the time difference, within which the sine curves of the two lower lines go through a straight full period. In this same time also the phase position of the sine courses (highest line) shifted itself 360<o>. For this phase shift an easy change of the distance between item under test and radar device is responsible. If the vehicle moved around a half wavelength, then both the way there and the way back of the microwave signal change around this amount, i.e. the entire change of way corresponds to the double amount, thus a whole wavelength. The phase relationship between transmission and Empfangsslgnal changes around an equivalent amount, thus around 360<o>. In other words thus the doppler frequency can be defined as follows: Doppler frequency fd = relative motion between traffic radar device and vehicle, measured in number of half radar wavelengths per second.

It is for the sake of completeness mentioned that naturally the frequency Fb (Fig.2) changes by the radial velocity due to the Doppler effect easily, whereby the frequency (compared to a standing vehicle) rises or falls as a function of the sign of the radial velocity. This Frequenzverschiebung is however comparatively small, so that it becomes practically not recognizable within a sine course, but affects itself only over several sine courses in the descriptive way.

With second, each distance filter EF filter bank downstream FFT this doppler frequency can be analyzed. The doppler frequency-selective filter bank is realized in the available example by an FFT analyzer (nearly Fourier analyzer). (To the detailed explanation of the FFT algorithm is referred to above the literature place already mentioned).

The used the FFT algorithm in this remark example produces out n= x (t), y (t) n= 256 spectral's pairs xd (fd) for 256 temporal pairs of scanning values, yd (fd). As temporal scanning values serve in the two lower lines of the Fig. 4 pair shown x, y. The action period interval corresponds the time to Tad (scanning interval for doppler analysis) and is equal the saw tooth period in accordance with Fig. 2.

The realization of the FFT analysis in each case 256 pair x, y (see Fig.4) become buffered in the buffer ZSP. Thus all output signals become during the period n*Tad = Td buffered. This period Td is thereby the total analysis time, which is needed for the determination by distance and speed of all interesting vehicles. The initial values of the FFT analyzers indicate the spectral components, which in by the n the pairs of scanning values x (t), y (t) given Zeitfunktionen are present. Thus Ek appear to EFk according to the distance filter two separate spectral values, to assign the speed to g1, g2 of the two vehicles FZ1 and FZ2 in accordance with Fig at the exit of the FFT analyzer for the distance range. 1. The FFT analyzer accomplishes thereby so far the not possible selection of the two vehicles.

If one regards described the evaluation the so far, then one recognizes the fact that itself the received signal S (t) branches out in matrix fashion, i.e. by the distance filter bank EF (e.g. into 32 branches) and then per distance filter EF to in each case n (for example n = 256) branches by the FFT analyzer (doppler filter bank connected at the outlet side in each case). For the reduction of the data flood accompanying with this bypass the amplitudes of all spectral components (pair) at the exits of the FFT analyzers are compared computed (AMP into Fig.3), with a threshold SW and only such signals are processed, which exceed a minimum value. In the available example by the threshold switches SWS only in each case two signal components are passed on, i.e. in the branch k by the two vehicles the FZ1, FZ2 after Fig.1 of produced echo signals.

For the determination of the lane the further views were limited to the vehicle FZ1, since for the vehicle FZ2 all remarks are valid similar. Contrary to the past now the signals of the two channels A and B are linked with one another. For this the signal angle processing mechanism serves SWV (see Fig. 3).

For simplification the signals of the vehicle FZ1 at the entrance of the signal angle processing mechanism SWV are characteristic as follows. x1A, y1A for channel A x1B, y1B for channel B.

These signals are represented in Fig.5 as vectors, whereby the angle purchases of this picture particularly interest. Regards one the vectors x1A, y1A; x1B, y1B for itself, then depends its angle direction to the x axis on a great many parameters, with which is not to be dealt further here. Interesting with it is however the angle, which these two vectors include with one another. This angle is a measure for it how far the vehicle FZ1 (Fig.1) lies on the left of or right outside of the symmetry axis SA of the two antennas AA/AB. A vehicle on the symmetry axis SA, broken line in Fig.1, exhibits same signal running time to the two antennas A and B. A vehicle above the broken line has a larger running time to the antenna B, a vehicle below the broken line has a larger running time to the antenna A.Diese of run time differences to appear than angle difference of the two vectors in accordance with Fig.5. In the first case the directions of the vectors cover themselves, in the two other cases arise in each case a angle difference with different signs. The angle difference of the vectors is thus a measure for the azimuth angle of the vehicle. According to device given run time differences in the channels A and B can be eliminated by adjusting measures.

For the computation of the angle difference WD1 one forms first a cross product and determines then its angles concerning the x axis (represented in complex way of writing, generally from mathematics admits): x+iy = (x1A*iy1A) * (x1B-iy1B) (6a) x+iy = (x1A*x1B+y1A*y1B) +i (y1A*x1B-x1A*y1B) (6b) WD1 = atn (y/x) x 0 (6c) WD1 = atn (y/x) + x 0 (6c) with the determination of the azimuth angle is now a lane regulation very simply possible. The lane FR is determined, by addressing a table at the simplest with the help of the angle value WD1 and the vehicle distance, which are given to EF by the number k of the distance filter and/or by the distance range Ek, in which the associated trace as function of distance and azimuth angle is laid down. This function accomplishes the trace frequency discriminator trace SDE. At its exit by it the vehicle FZ1, marked by its distance k, appears its speed of g1 and its lane SP1.

Concerning the lane regulation the still following is to be noticed. The descriptive determination of the azimuth angle and thus the lane is ensured only if in each case the signal echoes only one vehicle during the angle computation in equation (6) it is present i.e. an essential condition for the lane determination consists of the fact that all vehicles, which are at the same time on the road, are separately available and thus successively concerning the lane computation can be worked on. This condition is so long given, as long as the vehicles are either at different distance or drive with different speed. The procedure according to invention fails thus, if two vehicles with accurately same speed (e.g. speed difference smaller than 1 km/h) drive next to each other. In this case the FFT analyzer supplies a composite picture signal of both vehicles, whose subsequent treatment leads to incorrect trace computation. The practical experience however shows that such situations occur, are however from temporally limited duration and are recognized by plausibility checks.

With the traffic radar device according to invention it is also possible to compute from the determined radial velocity the actual speed of the individual vehicles.