WO2005050240A2

WO2005050240A2 - Method and system for determining the range and velocity of a moving object

Info

Publication number: WO2005050240A2
Application number: PCT/IL2004/001050
Authority: WO
Inventors: Yair Shimoni
Original assignee: Elop Electro-Optics Industries Ltd.
Priority date: 2003-11-18
Filing date: 2004-11-16
Publication date: 2005-06-02
Also published as: WO2005050240A3; WO2005050240B1; IL158937A0; IL158937A

Abstract

A device for determining the range of a moving object, the device including at least one sampler, a multi-process array coupled with the sampler, and a selector coupled with the multi-process array, the sampler producing a plurality of sampled signals by sampling a received signal respective of a sequence of pulses transmitted toward the moving object, the multi-process array running a plurality of processes, each of the processes associated with one sampler, each of the processes associated with a respective time shift which is determined according to a respective radial velocity assumption of the moving object with respect to the device and with the pulse rate of the sequence of pulses, each of the processes producing a signal summation by sequentially shifting the sampled signals by the respective time shift and adding together the sampled signals, the selector determining the range according to at least one signal summation which includes a summed pulse event.

Description

METHOD AND SYSTEM FOR DETERMINING THE RANGE AND VELOCITY OF A MOVING OBJECT

FIELD OF THE DISCLOSED TECHNIQUE The disclosed technique relates to range finders in general, and to methods and systems for determining the range and velocity of a moving object, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE The range of an object can be determined by emitting a pulse, such as laser, radar, or sound, toward the object and measuring the time that elapsed until the echo from the object is detected. The range S is determined by computing,

where C is the speed of light (in case of laser pulse or radar pulse) or the speed of sound (in case of a sound pulse), and T_R is the time for the round trip of the pulse from a transmitter to a receiver. However, a shortcoming of this method is that the energy of the pulse is generally low, thereby causing difficulties in measuring the range of distant objects. This is due to the fact that the energy of the reflected pulses decreases very rapidly with increasing distance, and reliable readings can not be obtained. Methods and systems to circumvent this problem are known in the art. US Patent No. 6,100,516 issued to Nerin et al., and entitled "Velocity Measurement Device and Laser Range Finder Using a Coherent Detection", is directed to a device for amplifying the laser pulse reflected from a target, and using this amplified laser pulse to determine the range and velocity of the target. The device includes an optical means for pumping a laser amplifier material, a cavity having two quality factors Q_MAX and QM_IN, an optical separating means, an optical emission means and a detection assembly. The cavity includes the laser amplifier material, and three mirrors M M₂ and M₃. Mirror M₁ is located on one side of the laser amplifier material and mirrors M₂ and M₃ are located on the other side of the laser amplifier material. Mirror M₃ is placed in the center of the laser amplifier material and mirror M₂ is placed around mirror M₃ on the same face. The cavity is located between the optical means and the optical separating means. The optical emission means is located between the target and the optical separating means. The association of mirrors My and M₃ forms an optical resonator whose quality factor is QMAX- The association of mirrors My and M₂ forms an optical resonator whose quality factor is QMIN- A laser oscillation is maintained in the central zone of the cavity, where the quality factor is Q_MAX, a d a laser beam is emitted by mirror M₃. The laser beam is separated by the optical separating means, one part of which passes to the detection assembly as a reference beam, and another part of which is supplied to the target by the optical emission means. The laser beam is reflected or diffused by the target toward the optical emission means (which now operates as an optical reception means). The optical reception means re-reflects the laser beam to an amplifying region of the cavity constituted by the laser amplifier material and mirrors My and M₂. After amplification in this structure, the laser beam returns in the direction of the beam separating means (which now operates as a beam recombination means). The beam recombination means supplies part of the amplified signal to the detection assembly, where it interferes with the reference beam, and the detection assembly extracts the velocity information respective of the target, according to this interference. SUMMARY OF THE DISCLOSED TECHNIQUE It is an object of the disclosed technique to provide a novel method and system for determining the range and velocity of a moving object. In accordance with the disclosed technique, there is thus provided a device for determining a range of a moving object. The device includes a sampler for producing a plurality of sampled signals, a multi-process array running a plurality of processes, and a selector coupled with the multi-process array. The sampler produces the sampled signals, by sampling a received signal respective of a sequence of pulses transmitted toward the moving object. The multi-process array is coupled with the sampler, wherein each of the processes is associated with a respective sampler. Each of the processes is associated with a respective time shift which is determined according to a respective radial velocity assumption of the moving object with respect to the device. Each of the processes is further associated with the pulse rate of the sequence of pulses. Each of the processes produces a signal summation by sequentially shifting the sampled signals by the respective time shift, and adding together the sampled signals. The selector determines the range of the moving object according to at least one signal summation which includes a summed pulse event. In accordance with the another aspect of the disclosed technique, there is thus provided a method for determining a range of a moving object. The method includes the procedure of shifting a plurality of sampled signals relative to one another by a respective time shift, for each of a plurality of radial velocity assumptions for the relative radial velocity between a transceiver and the moving object. The method further includes the procedure of adding together the shifted signals for each of the radial velocity assumptions, thereby producing a signal summation for each of the radial velocity assumptions. The method further includes the procedures of detecting a summed pulse event within at least one of the signal summations, and determining the range of the moving object according to the detected summed pulse event. Each of the sampled signals represents a respective received signal detected across a period of time. Each of the received signals is received by the transceiver and associated with a respective pulse echo reflected by the moving object, wherein the respective pulse echo is assumed to be included in the received signal. Each of the respective time shifts is determined for a respective one of the radial velocity assumptions. Each of the respective time shifts represents an assumed shift in detection times of two consecutive received signals, due to the respective radial velocity assumption.

BRIEF DESCRIPTION OF THE DRAWINGS The disclosed technique will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Figure 1A is a schematic illustration of a system for determining the radial velocity of a moving object, constructed and operative in accordance with an embodiment of the disclosed technique; Figure 1B is a schematic illustration of the operation of the processors of the system of Figure 1A, together with the sampler of the system; Figure 1C is a schematic illustration of the operation of one of the processors of the system of Figure 1 A; Figure 1 D is a schematic illustration of the operation of the selector of the system of Figure 1 A; Figure 1 E is a schematic illustration of a modified sampled signal, constructed from a sampled signal of Figure 1 B, according to another embodiment of the disclosed technique; Figure 2 is a schematic illustration of a system for determining the radial velocity of a moving object, constructed and operative in accordance with a further embodiment of the disclosed technique; and Figure 3 is a schematic illustration of a method for operating the system of Figure 1A, operative in accordance with another embodiment of the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS The disclosed technique overcomes the disadvantages of the prior art by providing a system and a method which directs a sequence of pulses toward a moving object and shift-sums detected signals which are supposed to include echoes reflected from that moving object. It is noted that when the moving object is outside the range of conventional systems, the echo in a single detected signal, is of the order of the ambient noise and hence cannot be extracted there from. By shift-summing a plurality of detected signals, the method of the disclosed technique provides a summed representation of such an echo, which can be identified and detected. Thus, the disclosed technique can be used to extend the detection range of conventional pulse operated radar systems. It is noted that the disclosed technique is applicable to any pulse operated range detector known in the art, such as laser, acoustic, RF, and the like. The system samples each of the detected signals across time, and determines a number of different radial velocity assumptions for the moving object, according to different relative radial velocities between the moving object and the system. For each radial velocity assumption, the system determines a respective time shift, by which a subsequent pulse is assumed to be shifted with respect to a previous one. For each radial velocity assumption, the system shifts the sampled signals of each pulse, relative to the sampled signals of the previous echo, by the respective time shift, and produces a signal summation, by adding together the respective shifted sampled signals. When the system detects a summed pulse event within at least one of the signal summations, the system determines the radial velocity of the moving object according to radial velocity assumptions associated with those signal summations in which the summed pulse event was detected. Furthermore, the system determines the range of the moving object, according the detected summed pulse event. The term "maximal range" herein below, refers to a maximum distance between the system and the moving object, at which the system is capable to determine the radial velocity and the range of the moving object. The term "useful range" herein below, refers to a distance between the system and the moving object, at which the system is capable to determine a radial velocity substantially close to the true radial velocity of the moving object. The term "summation efficiency" herein below, refers to the ratio of the SNR of a summation of the required number of the incoming signals, to the SNR of an individual incoming signal. The term "pulse" herein below, refers to laser pulse, radar pulse, acoustic pulse (e.g., ultrasound), infrared pulse, and the like. The term "transmitter" herein below, refers to a laser source, radar transmitter, sound source, infrared source, and the like. The term "receiver" herein below, refers to a laser detector, radar receiver, sound detector, infrared detector, and the like. Reference is now made to Figures 1A, 1 B, 1C, 1 D and 1 E. Figure 1A is a schematic illustration of a system for determining the radial velocity of a moving object, generally referenced 100, constructed and operative in accordance with an embodiment of the disclosed technique. Figure 1 B is a schematic illustration of the operation of the processors of the system of Figure 1A, together with the sampler of the system. Figure 1C is a schematic illustration of the operation of one of the processors of the system of Figure 1A. Figure 1 D is a schematic illustration of the operation of the selector of the system of Figure 1A. Figure 1 E is a schematic illustration of a modified sampled signal, generally referenced 142, constructed from a sampled signal of Figure 1 B, according to another embodiment of the disclosed technique. System 100 includes a transmitter 102, a receiver 104, a sampler 106, a sampled signal memory 108 and a radial velocity determining unit 110. Radial velocity determining unit 110 includes a plurality of processors 112-), 112₂ and 112_N, and a selector 114. Receiver 104 is generally unidirectional (i.e., adapted to cover a predetermined section in space). Selector 114 includes a processor 116 and a threshold memory 118. Processors 112₁₅ 112₂ and 112_N include shift-sum memories 120^ 120₂ and 120_N. Each of processors 112^ 112₂ and 112_N is in form of an independent hardware. Alternatively, each of processors 112^ 112₂ and 112_N is a different computational process running in a single processor operating in a multitasking mode. Sampler 106 is a device (e.g., an analog to digital converter) which digitizes an analog signal. Processors 112_{1 s} 112₂ and 112_N can be integrated with processor 116. Each of sampled signal memory 108, threshold memory 118 and shift-sum memories 120-ι, 120₂ and 120N can be a magnetic memory unit (e.g., floppy diskette, hard disk, magnetic tape), optical memory unit (e.g., compact disk), volatile electronic memory unit (e.g., random access memory), non-volatile electronic memory unit (e.g., read only memory, flash memory), and the like. Each of sampled signal memory 108, threshold memory 118 and shift-sum memories 120ι, 120₂ and 120_N can be a part of sampler 106, a part of radial velocity determining unit 110, or a part of a remote memory module (not shown). A beam splitter 122 is located between transmitter 102 and an object 124. Beam splitter 122 is located in such a position relative to receiver 104, that beam splitter 122 transmits a portion of a pulse 126A from transmitter 102 toward object 124, and beam splitter 122 reflects a portion of a reflected pulse 126B reflected by object 124, toward receiver 104, as reflected pulse echoes 126C. Transmitter 102, receiver 104 and beam splitter 122 can be incorporated in a transceiver (not shown). Object 124 is a land to land missile (e.g., short range missile, intercontinental ballistic missile - ICBM), land to air missile (e.g., antiaircraft missile), air to land missile, air to air missile, aircraft, and the like. Hence, object 124 can be launched from a stationary or a moving platform located on land, from a stationary platform located on or below the surface of water (e.g., from a warship or a submarine), from an aircraft (e.g., an airplane, a rotorcraft), or from a spaceship. Sampler 106 is coupled with receiver 104 and with sampled signal memory 108. Sampled signal memory 108 is coupled with sampler 106 and with processors 112_{1 s} 112₂ and 112_N. Each of processors 112_{1 a}

112₂ and 112_N is coupled with selector 114. Processor 116 is coupled with threshold memory 118. With reference to Figure 1A, object 124 is moving toward system 100 at a radial velocity V relative to system 100. However, a system similar to system 100 can determine the radial velocity of an object which is moving away from the system. Transmitter 102 transmits a sequence of pulses 126A, toward object 124 through beam splitter 122, at a pulse rate of R_P. Thus, the interval 7 between consecutive pulses 126A is,

If the object was stationary and substantially close to the system, then the system would have been able to determine a range S thereof according to Equation 1. Furthermore, the system can determine the average radial velocity V_A of object 124 according to the information respective of two consecutive pulses, by computing,

where Sy and S₂ are determined according to Equation 1. If object 124 is moving toward system 100, then object 124 gets closer to system 100 by a differential range ΔS between the emission of two consecutive pulses 126A, such that, AS =V_A -T_P (4)

Due to this movement, echo 126C reaches receiver 104 by a period AT (i.e., shortening time) sooner than a reflected pulse (not shown) would reach the receiver, if the object was stationary, where,

In the case of the disclosed technique, the range S of object 124 from system 100 is so great that the intensity of reflected echoes 126C relative to the background noise is low (i.e., the SNR of reflected echoes 126C is substantially small). Hence, system 100 is unable to distinguish the echo from ambient noise and to determine the range S and the average radial velocity V_A of object 124 according to Equations 1 and 3, respectively. System 100 determines a plurality of different radial velocity assumptions Vy, V₂ and V_N, for object 124 and a plurality of shortening times ΔT_1t ΔT₂ and ΔT_N, respectively. Each of the shortening times ΔT-,, ΔT₂ and ΔT_N (i.e., time shifts), represents the assumed shift in detection time of a subsequent pulse relative to that of a previous one, were object 124 moving at radial velocity assumptions V V₂ and V_N, respectively, relative to system 100. System 100 stores digitized information respective of the last previous Λ/_P-1 echoes 126C in different sets Q, (i = 1 , 2, 3...N), respective of radial velocity assumptions V,-. System 100 shifts the digitized reflected pulses in each of sets C„ by an amount respective of shortening times ΔT„ and adds together the N_P -1 digitized reflected pulses, and a new digitized reflected pulse, in each of sets Q. Due to accumulation of N_P substantially weak received signals in a set, in case a target (i.e., object 124) is actually present, at least one set will indicate a peak. System 100 selects one or more sets which indicates a peak and determines the average radial velocity V_A of object 124 according to the amplitude and the relative locations of the peaks. In case the spacing between radial velocity assumptions V-i, V₂ and V_N is substantially small relative to the average radial velocity V_A of object 124, one set with a peak is adequate for system 100 to determine the average radial velocity V_A of object 124. Object 124 reflects pulses 126A as reflected pulses 126B toward beam splitter 122. Beam splitter 122 reflects reflected pulses 126B as echoes 126C toward receiver 104. It is noted that the object can reflect the pulses directly toward the receiver, in which case the system can operate without the beam splitter. In the example set forth in Figures 1 B and 1C, the predetermined number of echoes 126C N_P, is arbitrarily set to four. During the interval between detection of the first one and the last one of the four echoes 126C, processors 112_{1 ;} 112₂ and 112_N determine radial velocity assumptions V V₂ and V_N, respectively, for the average radial velocity V_A of object 124. The values of radial velocity assumptions V V₂and V_N may be distributed between a minimum radial velocity V_MIN, and a maximum radial velocity V_MAX, either uniformly or non-uniformly. Furthermore, processors 112_{1 s} 112₂ and 112_N determine rounded shifts Hy, H₂₎ H_N, respectively, respective of shortening times zl7^~y, ΔT₂ and ΔT_N, respectively. Receiver 104 detects four echoes 126C in sequence, at a rate of

R_P and sends four reflected pulse signals referenced 128 respective of the four echoes 126C, to sampler 106. Reflected pulse signal 128 is herein below referred to as "received signal". Sampler 106 samples each of the four echo signals 128 at a sampling rate of R_s and produces four sampled signals 130^ 130₂, 130₃ and 130₄. Each of sampled signals 130-ι, 130₂, 130₃ and 130₄ includes a plurality of samples N_s, where, N_S = 2R_MAXR_S/C (6) and where R_MAX is the maximal range. For example, sampled signal 13Oι includes a plurality of samples 132-), 132₂ and 132_N. In this manner, sampler 106 digitizes each of the four echo signals 128. Sampler 106 stores sampled signals 130^ 130₂, 130₃ and 130₄ in sampled signal memory 108. With reference to Figures 1 B and 10, processor 112ι computes an accurate shift H_A according to,

In most cases H_A is a real non-integer number. Since sampled signals 130^ 130₂, 130₃ and 130₄ are to be aligned relative to one another, with a resolution of an integral multiple of a sample and not a fraction of a sample, H_A has to rounded to the closest integer. This is performed by computing a rounded shift H_R according to, H_R = Round (H_A +R_e) (8) where R_e is a remainder according to, R_e = H_A -H_R (9) R_e is initially set to zero. Processor 112₁ copies sampled signal 130_! from sampled signal memory 108 to shift-sum memory 120 . Processor 112 shifts shift-sum memory 120_! by rounded shift H and adds sampled signal 130₂ to shift-sum memory 120_!. The first shifted samples are discarded, while the last shifted samples are set to zero. Processor 112_! shifts shift-sum memory 120_! by rounded shift Hi and adds sampled signal 130₃ to shift-sum memory 120_!. Processor 112 shifts shift-sum memory 120 by rounded shift Hy and adds sampled signal 130₄ to shift-sum memory 120_!. By shifting sampled signals 130 , 130 , 130₃ and 130₄ by rounded shift Hy prior to adding together sampled signals 130_!, 130₂, 130₃ and 130₄, these sampled signals are substantially aligned as in a situation which mimics a stationary object (i.e., a shortening time ΔT-_t which corresponds to the radial velocity assumption V is determined, and the rounded shift H₁ is in turn determined according to shortening time zlTy). In this manner, processor 112 produces a signal summation 134_!. In the same manner, processors 112₂ and 112_N produce signal summations 134₂ and 134_N, by incorporating rounded shifts H₂ and H_N (not shown), respectively, while adding together sampled signals 130ι, 130₂, 130₃ and 130₄. Rounded shifts H₂ and H_N correspond to shortening times ΔT₂ and ΔT_N, respectively. It is noted that processors 112_!, 112₂ and 112_N operate in parallel, thereby saving scarce computation time. Signal summation 134_! includes a plurality of summed samples 136_!, 136₂ and 136_N (Figures 1 B and 1 C). Since the echoes 126C are substantially weak and may contain a substantially large amount of noise, system 100 attempts to pinpoint the echo (not shown) which would be reflected by object 124, by examining a sum of N_P echoes 126C (i.e., artificially raising the SNR of echoes 126C). System 100 increases this SNR by a factor of approximately -JN - the example set forth in Figure

1 B the predetermined number of echoes 1260 is four and the improvement factor is 4 = 2. System 100 regards a signal summation whose relative values of summed samples, such as summed samples 136_!, 136₂ and 136_Ν are substantially the same, as a noise signal and ignores this signal summation. On the other hand, system 100 regards another signal summation which includes a summed sample with a peak value substantially above that of the other summed samples, as a signal summation which represents a summed pulse echo. System 100 determines the average radial velocity V_A of object 124 according to one of the radial velocity assumptions V V₂ and VN which corresponds to this signal summation (i.e., a signal summation which indicates a peak). Each of signal summations 134 , 134₂ and 134_N in Figures 1 B and 10 is shown in form of a sequence of summed samples, whereas each of the same signal summations in Figure 1 D is shown in form of a bar graph which indicates the relative value of each summed sample. Processors 112_!, 112 and 112_N send signal summations 134_!, 134₂ and 134_N, respectively, to selector 114. A threshold value T_SH is stored in threshold memory 118 (Figure 1 D). As illustrated in Figure 1 D, the dispersion of the values of summed samples 136_!, 136₂ and 136_N of signal summation 134_! is substantially uniform. Processor 116 compares the value of each of summed samples 136_!, 136₂ and 136_N with the threshold value T_SH and determines that the value of each of summed samples 136_!, 136₂ and 136_N is lower than the threshold value T_sw. Thus, processor 116 determines that signal summation 134_! is mostly noise, that signal summation 134ι does not correspond to radial velocity assumption V and therefore selector 114 ignores signal summation 134_!. Signal summation 134_N as illustrated in Figure 1 D, includes mostly noise and therefore selector 114 ignores signal summation 134_N in like manner. Signal summation 134₂ on the other hand, includes a summed sample 138 (Figure 1 B) whose value (i.e., summed sample value) represented by a peak 140 - Figure 1 D (i.e., a summed pulse event), is substantially greater than that of the other summed samples of signal summation 134 , and also greater than the threshold value T_SH. Processor 116 compares the value of each of the summed samples (not shown) of signal summation 134₂ with the threshold value T_SH, and determines that the value of summed sample 138 is greater than the threshold value T_SH, and that the value of all other summed samples is less than the threshold value T_SH- Therefore, selector 114 selects signal summation 134₂ as a signal which represents an echo, selector 114 associates signal summation 134₂ with radial velocity assumption V₂, and determines that the average radial velocity V_A of object 124 during the interval that the four echoes 126C were processed, is V₂. Selector 114 selects signal summation 134₂ also when the value of peak 140 is substantially equal to threshold value T_SH- When sampler 106 samples a fifth (i.e., new) reflected pulse (not shown), sampler 106 stores this new sampled signal in sampled signal memory 108. Each of processors 112_{1 ;} 112₂ and 112_N determines a new radial velocity assumption for the average radial velocity V_A of object 124. Each of processors 112_!, 112₂ and 112_N subtracts sampled signal 130_! (i.e., the least recent sampled signal) from shift-sum memories 120_!, 120₂ and 120_N) respectively, and adds the most recent sampled signal (i.e., the new or the fifth sampled signal) to shift-sum memories 120_!, 120₂ and 120_N, respectively. Processors 112 , 112₂ and 112_N shift shift-sum memories 120_!, 120₂ and 120_N, respectively, by rounded shifts Hy, H₂, H_N, respectively, before adding the new sampled signal to shift-sum memories 120_!, 120₂ and 120_N, respectively. In this manner each of processors 112_!, 112₂ and 112_N produces a new and a different signal summation (not shown), and sends this new signal summation to selector 114. Selector 114 compares the value of each of the summed samples of each of the new signal summations with the threshold value T_SH, selects the signal summation which exhibits a peak. Furthermore, selector 114 determines the average radial velocity V_A of object 124 according to the radial velocity assumption which corresponds to this selected signal summation. System 100 repeats the same cycle, when receiver 104 detects a further new reflected pulse. To keep the summation efficiency at a substantially high level, it is necessary that, H_MAX « N_S (10) where H_MAχ is the maximum accurate shift. H_MAχ after N_P echoes in units of samples is expressed by, H_MAX = 2N_PV_MAXR_S/CR_P (1 1 ) In case more than one of signal summations 134_!, 134₂ and 134N exhibits a peak, selector 114 selects all those signal summations which exhibit a peak, to determine the average radial velocity V_A of object 124. It is noted that since more peak values are available, processor 116 is able to determine the average radial velocity V_A of object 124 more accurately. Furthermore, radial velocity assumptions V V₂ and V_N are updated according to the peak of each of signal summations 134_!, 134₂ and 134_N, in order to narrow down the range of V_Mm and V_MAX, and increase the accuracy of the average radial velocity V_A which selector 114 determines. If system 100 detects that the value of one or more of the summed samples of either signal summations 134_!, 134₂ or 134_N is saturated (i.e., it has reached the maximum value or is substantially close to the maximum value), system 100 lowers the value of N_P. The sensitivity of system 100 increases as the threshold value T_SH is increased. If the threshold value T_SH is set too low, processor 116 saves the location of a summed sample of a signal summation whose value is greater than the threshold value T_SH and processor 116 saves this location in threshold memory 118. Processor 116 checks whether the next signal summation respective of the same radial velocity assumption, includes a peak at approximately the location of the summed sample of the previous signal summation. If the outcome is negative, then processor 116 ignores the signal summation. If the outcome is positive, then processor 116 detects a peak at this location and selects this signal summation for determining the average radial velocity V_A of object 124, for further determining the range of object 124. If the threshold value T_SH is set too high, then the probability of detecting signal summations with peaks, at small number of integration cycles, is lower, and thus more time is required in order to determine the average radial velocity V_A of object 124. System 100 sets the threshold value 7^~ _SH according to the expected enhanced SNR of echoes 126C (i.e., the SNR of the signal summation which is larger than the original SNR by a factor of

and according to the expected value of the enhanced signal (e.g., the value of peak 140 in Figure 1 D), in addition to other considerations which may be introduced by the designer or the operating user. System 100 is unaware of the exact time that echo 126C is supposed to reach receiver 104. Sampler 106 samples a detected signal across a period of time T T₂, which represents a range S S₂ of distances from system 100 in which object 124 is expected to be located, wherein

The resolution of system 100 is of the order of the sampling rate. Hence, it is imperative that the difference between the rounded shifts of every two consecutive processors be equal to or less than two samples. This difference is herein below referred to as "relative shift". Otherwise, system 100 would be unable to detect all echoes 126C which include information respective of the average radial velocity and the average range of object 124, and neither one of radial velocity assumptions V V₂ and V_N will be close enough to the average radial velocity V_A of object 124. The lower the number of processors 112_!, 112 and 112_N, the greater the difference between radial velocity assumptions V V₂ and V_N. Since the number of processors 112_!, 112₂ and 112_N is limited, if the difference between V_MAX and V_Mm is substantially large, the value of one or more of the relative shifts can exceed two samples. In this case, the radial velocity assumptions V V₂and V_N are off by a substantially large amount from the true average radial velocity V_A of object 124 (i.e., the respective rounded shifts are unsuitable for the true average radial velocity ^), the amplitude of the peak in the respective signal summation is substantially low (i.e., the summation efficiency is substantially low), and the signal respective of the reflected pulse is spread around the putative peak. Furthermore, the SNR of the signal summation is too low for system 100 to arrive at a radial velocity sufficiently close to the true average radial velocity V_A. In case the value of one or more of the relative shifts is equal to or greater than two samples, the system produces one or more filtered signal summations, and the selector determines the average radial velocity V_A of object 124, according to these filtered signal summations. Following is a description of a method for producing a filtered signal summation. With reference to Figures 1 B and 1 E, sampled signal 130_! includes a plurality of samples 132_!, 132_2> 132₃₎ 132₄, 132₅, 132₆, 132₇, 132₈, 132₉, 132ιo, 132n and 132₁₂. Modified sampled signal 142 includes a plurality of samples 144 , 44₂, 144₃ and 144₄. Processor 112ι produces modified sampled signal 142, by adding together N_υ (herein below referred to as "aggregation number") samples located symmetrically about every sample of sampled signal 130_!, where Nu = 3,5,7...2n+1 , where n = 1 ,2,3... In the example set forth in Figure 1 E, Nu = 3. Hence, processor 112_! produces sample 144_{1 ;} by adding sample 132 to the left of sample

132₂ and sample 132₃ to the right of sample 132₂ to sample 132₂. Processor 112_! produces sample 144₂ by adding together samples 132₂,

132₃ and 132₄. Processor 112_! produces sample 144₃ by adding together samples 132₃, 132₄ and 132₅. Processor 112_! produces sample 144₄ by adding together samples 132₄, 132₅ and 132₆. Processor 112_! determines the value of the aggregation number N_υ according to the value of rounded shift H_R, such that N_υ is preferably the smallest odd integer which is still greater than H_R. For example, if H_R = 4, then N_υ = 5. However, N_υ can be determined according to other criteria not described here. Processor 112_! shifts shift-sum memory 120_! by the value of rounded shift H_R, produces another modified sampled signal (not shown) according to sampled signal 130₂, and adds the new modified sampled signal to shift-sum memory 120_!. Processor 112_! repeats this cycle N_P times for other sampled signals, thereby adding N_P modified sampled signals (in this case four modified sampled signals), while shifting shift-sum memory 120_! by the value of rounded shift H_R, before each addition. Thereafter, processor 112ι subtracts the least recent modified sampled signal from shift-sum memory 120_!, before adding a new modified sampled signal to shift-sum memory 120_!. As long as the value of the relative shift is equal to or greater than two samples, processor 112_! repeats this cycle, thereby producing a filtered signal summation (not shown). In a like manner, processors 112₂ and 112_N produce different filtered signal summations each, and send these filtered signal summations to selector 114. Alternatively, only those processors for which the value of the relative shift is equal to or greater than two samples, produce filtered signal summations, while other processors produce signal summations. By employing filtered signal summations, the summation efficiency of system 100 increases. More particularly, the SNR of a filtered signal summation is greater than that of the respective signal summation, by a factor of /N . Alternatively, system 100 can produce a filtered signal summation (not shown) according to each of signal summations 134_{1 ;} 134₂ and 134_Ν. System 100 produces this filtered signal summation, by adding together Nu surrounding samples located symmetrically about every central summed sample of each of signal summations 134_{1 ;} 134₂ and 134_N. When the value of one of the radial velocity assumptions Vy, V₂ or V_N is off by a substantially large amount from the true average radial velocity V_A of object 124, the signals in the respective sampled pulse mix with noise and the SNR of the signal summation in fact drops. To mitigate this problem, it is necessary for system 100 to produce the filtered signal summation, by employing a relatively small value for the aggregation number N_υ. Another remedy is for selector 114 to compare the threshold value 7^~ _SH with the summed samples of both the signal summations (i.e., non-aggregated summed samples) and the summed samples of the filtered signal summations (i.e., aggregated summed samples). In case the value of one or more of the relative shifts is equal to or greater than two samples, system 100 modifies the values of radial velocity assumptions V V₂ox V_N, and hence, the values of rounded shifts Hy, H₂, H_N, respectively. This operation is possible, as long as it is performed before receiver 104 detects a new reflected pulse echo. As long as a sufficient number of incoming signals (i.e., N_P echoes 1260) are not added together, at a given radial velocity assumption which is closest to the true radial velocity of object 124, the distance between system 100 and moving object 124 does not drop to a range which is useful (i.e., the useful range). It is imperative for sampler 106 to start sampling the required number of echoes 126C (i.e., N_P echoes) at the maximal range, in order for system 100 to start operating at the useful range, earlier. The difference ΔS_P between the maximal range and the useful range is expressed in units of length, by, M_P = N_PV_MAX/R_P (12) In case a system similar to system 100 is able to estimate the radial acceleration of the object at a time in the future, each processor can shift the sampled signals by different (e.g., dynamic) rounded shifts and not for example by a constant rounded shift Hy. The samples in each of sampled signal memory 108 and shift-sum memories 120_!, 120₂ and 120_N can be addressed by pointers. The pulse rate R_P of transmitter 102 should be low enough that an echo 126C reflected from object 124 at a maximal range, is detected by receiver 104 before transmitter 102 emits a new pulse 126A. If the pulse rate R_P is substantially high, then a system similar to system 100 can include a mechanism, such as a pulse shape controller, and the like, to reduce the uncertainty in determining the average radial velocity V_A and the average range S_A of object 124. It is noted that system 100 performs the procedures necessary to determine the average radial velocity V_A of object 124, including production of the filtered signal summations, modifying the values of rounded shifts, and the like, during the interval which receiver 104 detects two consecutive echoes 126C. Object 124 can move at a radial velocity relative to system 100 which is out of the range of radial velocity assumptions V l ₂ and V_N. In this case, a shortening time ΔT is less than a sampling period T_s of sampler 106, where,

and thus, sampler 106 receives a new reflected pulse before sampler 106 has finished sampling the previous reflected pulse. Thus, it is imperative to set the sampling rate R_s according to the maximum radial velocity V_MAX (herein below referred to as "maximum detectable velocity value") of object 124 which system 100 is constructed to determine. In case object 124 is located at an average range S_A greater than the maximal range, pulses 126B do not reach object 124 and no reflected pulse reaches receiver 104. System 100 can determine the average range S_A of object 124 during the interval that the four reflected pulses are detected, according to peak 140. This can be performed by measuring a time T_R since transmitter 102 emits pulse 126A until peak 140 is detected, and by plugging in T_R in Equation 1. It is further noted that a system similar to system 100 can be employed for determining the average radial velocity of an object which is receding relative to the system. In this case, each processor similar to processor 112_! (Figure 10), shifts the sampled signals in the respective shift-sum memory, in the opposite direction. It is noted that system 100 can be a moving system and not a stationary one (e.g., coupled with a ground vehicle, marine vehicle, aircraft, rotorcraft, satellite, and the like). In this case the radial velocity assumptions V V₂ and V_N refer to a set of radial velocities of object 124 relative to the velocity of system 100. Reference is now made to Figure 2, which is a schematic illustration of a system for determining the radial velocity of a moving object, generally referenced 160, constructed and operative in accordance with a further embodiment of the disclosed technique. System 160 includes a receiver 162, a plurality of samplers 164_!, 164₂ and 164_N, a plurality of processors 166_{1 ;} 166₂ and 166_N and a selector 168. Processors 166_!, 166₂ and 166_N can be a multi-process array. Receiver 162 is coupled with samplers 164_!, 164₂ and 164_N. Samplers 164_!, 164₂ and 164_N are coupled with processors 166_!, 166₂ and 166_N, respectively. Processors 166_!, 166₂ and 166_N are coupled with selector 168. For each processor 166_!, 166₂ and 166N, the respective accurate shift is determined as an integer number of samples, of the respective sampler, associated therewith. It is noted that the sampling rates of samplers 164_!, 164₂ and 164_N may be updated dynamically, according to the radial acceleration or radial deceleration of the object. Accurate shift H_A1 in seconds is expressed by,

Likewise, accurate shifts H_A2 and H_AN can be expressed in seconds, by T_A2 and T_AN, respectively. Samplers 164_!, 164₂ and 164_N sample reflected pulses (not shown) at sampling rates of R_Sι, Rs_∑ and R_SN, respectively, and send the respective signals 17Oι, 170₂ and 170N to processors 166_!, 166₂ and 166_N, respectively. Sampling rates R_Sι, Rs₂ and R_SN correspond to sampling periods 7_Sy, T_S2 and 7_SΛ/, respectively. System 160 sets sampling rates of Rsι, Rs2 and R_SN, such that, T =τ_M (15) T =τ_A2 (16) and T T_SN ==Tτ_AN (17) Signal 170_! is associated with a sequence of sampled signals (not shown) each sampled at sampling periods of T_Sy. Therefore, it is no longer necessary for processor 166_! to shift the sequence of the sampled signals by a rounded shift, but it can directly apply the accurate shift H_A1. Similarly, processors 166₂ and 166_N apply accurate shifts H_A2 and H_AN \o the respective sequence of the sampled signals. Thus, system 160 can determine the average radial velocity V_A of a moving object (not shown), much more accurately than system 100 (Figure 1A). Reference is now made to Figure 3, which is a schematic illustration of a method for operating the system of Figure 1A, operative in accordance with another embodiment of the disclosed technique. In procedure 190, a sequence of pulses is transmitted toward a moving object. With reference to Figure 1A, transmitter 102 transmits pulses 126A toward object 124. In procedure 192, for each transmitted pulse, a received signal which is reflected by the moving object and which is supposed to include an echo of the pulse, is detected. With reference to Figure 1A, receiver 104 detects a received signal which may include echoes 126C, if echoes 126C are the reflections of pulses 126A, by object 124. In procedure 194, each of the detected signals are sampled across a period of time. With reference to Figure 1B, sampler 106 samples echo signal 128 at a sampling rate of R_s, and produces sampled signals 130ι, 130₂, 130₃ and 130₄- In procedure 196, a plurality of radial velocity assumptions is determined for the moving object, wherein each radial velocity assumption represents a different relative radial velocity between a transceiver and the moving object. With reference to Figure 1A, processors 112_{1 ;} 112₂ and 112_N determine radial velocity assumptions V \ and V_N, respectively, for object 124, relative to the velocity of the transceiver. In procedure 198, for each radial velocity assumption, a respective time shift by which a subsequent pulse is assumed to be detected with respect to a previous pulse, is determined. With reference to Figures 1A and 1 C, processor 112_! determines that were object 124 approaching detector 104 at a radial velocity l y, receiver 104 would detect two consecutive echoes 126C, at an interval shorter by ΔT (i.e., a time shift) than if the object was stationary. Processor 112_! determines according to time shift ΔT, the value of rounded shift Hy by which to shift shift-sum memory 120_! sequentially, as described herein above in connection with Equations 7, 8 and 9. In case more than one sampler, such as samplers 164_! (Figure 2), 164₂ and 164_N are employed in the system, each processor sets the sampling rate of the respective sampler according to the determined accurate shift. In the same manner, processors 112₂ and 112_N determine the values of rounded shifts H₂ and H_N, respectively. In case processor 112_! determines that the value of the relative shift (i.e., the difference between rounded shifts Hy and H₂ or between rib and H_N), is equal to or greater than two samples, processor 112_! produces modified sampled signal 142 (Figure 1 E), as described herein above. In procedure 200, for each radial velocity assumption, the sampled signals are shifted relative to each other, by the respective time shift. With reference to Figure 10, processor 112_! sequentially shifts shift-sum memory 120 by rounded shift Hy, as processor 112_! receives sampled signals 130_!, 130₂, 130₃ and 130₄ from sampler 106. In procedure 202, for each radial velocity assumption, the shifted sampled signals are added together, thereby producing a signal summation. With reference to Figures 1 B and 10, processor 112_! determines signal summation 134ι according to N_P sampled signals 130 , 130₂, 130₃ and 130₄, by sequentially shifting shift-sum memory 120_! by the value of rounded shift Hy, and adding the next one of N_P sampled signals 130_!, 130₂, 130₃ and 130₄ to shift-sum memory 120_!. Processors 112₂ and 112_N determine signal summations 134₂ and 134_N, respectively, in a similar manner. In procedure 204, a summed pulse event is detected within at least one of the signal summations. With reference to Figure 1 D, processor 116 detects peak 140 in signal summation 134₂. In case after procedure 194 processor 112_! determines a plurality of modified sampled signals similar to modified sampled signal 142 (Figure 1 E), in procedure 202 processor 112_! adds together these modified sampled signals after sequentially shifting shift-sum memory 120_!, thereby producing a filtered signal summation, and in procedure 204 processor 116 detects the peak in the filtered signal summation. Alternatively, the filtered signal summation is produced by modifying the signal summation, similar to the way each of sampled signals 130_!, 130₂, 130₃ and 130₄ is modified. In procedure 206, the radial velocity of the moving object is determined according to radial velocity assumptions associated with signal summations, in which the summed pulse event was detected. With reference to Figure 1 D, processor 116 determines that the average radial velocity of object 124 is V₂, according to signal summation 134₂ in which peak 140 was detected. In procedure 208, the range of the moving object from the transceiver is determined, according to the detected summed pulse event. With reference to Figure 1 D, processor 116 determines the range of object 124 by measuring a time T_R since transmitter 102 fires pulse 126A until peak 140 is detected, and by plugging in T_R in Equation 1. It will be appreciated by persons skilled in the art that the disclosed technique is not limited to what has been particularly shown and described hereinabove. Rather the scope of the disclosed technique is defined only by the claims, which follow.

Claims

1. Device for determining a range of a moving object, the device comprising: at least one sampler for producing a plurality of sampled signals, by sampling a received signal respective of a sequence of pulses, transmitted toward said moving object; a multi-process array running a plurality of processes, said multi-process array being coupled with said at least one sampler, wherein each of said processes is associated with one of said at least one sampler, each of said processes being associated with a respective time shift which is determined according to a respective radial velocity assumption of said moving object with respect to said device, and with the pulse rate of said sequence of pulses, each of said processes producing a signal summation by sequentially shifting said sampled signals by said respective time shift, and adding together said sampled signals; and a selector coupled with said multi-process array, said selector determining said range according to at least one signal summation which includes a summed pulse event.

2. The device according to claim 1 , further comprising a transmitter for transmitting said sequence of pulses toward said moving object.

3. The device according to claim 2, wherein said transmitter is selected from the list consisting of: laser source; radar transmitter; and acoustic source.

4. The device according to claim 1 , further comprising a receiver coupled with said at least one sampler, said receiver detecting said received signal.

5. The device according to claim 4, wherein said receiver is selected from the list consisting of: laser detector; radar receiver; sound detector; and infrared detector.

6. The device according to claim 1 , wherein said selector determines a radial velocity of said moving object according to said at least one signal summation.

7. The device according to claim 1 , wherein said sequence of pulses is selected from the list consisting of: laser; radar; and acoustic.

8. Method for determining a range of a moving object, the method comprising the procedures of: shifting a plurality of sampled signals relative to one another by a respective time shift, for each of a plurality of radial velocity assumptions for the relative radial velocity between a transceiver and said moving object, each of said sampled signals representing a respective received signal detected across a period of time, each of said received signals being received by said transceiver and associated with a respective pulse echo reflected by said moving object, said respective pulse echo assumed to be included in said received signal, each of said respective time shift being determined for a respective one of said radial velocity assumptions, each of said respective time shift representing an assumed shift in detection times of two consecutive ones of said received signals, due to said respective radial velocity assumption; adding together said shifted signals for each of said radial velocity assumptions, thereby producing a signal summation for each of said radial velocity assumptions; detecting a summed pulse event within at least one of said signal summations; and determining said range according to said detected summed pulse event.

9. The method according to claim 8, further comprising a preliminary procedure of determining each said respective time shift according to said respective radial velocity assumption and the pulse rate by which said pulses are transmitted.

10. The method according to claim 8, further comprising a preliminary procedure of determining said radial velocity assumptions.

11. The method according to claim 8, further comprising a preliminary procedure of sampling said received signals.

12. The method according to claim 8, further comprising a preliminary procedure of detecting said received signals.

13. The method according to claim 12, further comprising a preliminary procedure of transmitting said sequence of said pulses toward said moving object.

14. The method according to claim 12, further comprising preliminary procedures of: transmitting a sequence of pulses from said transceiver toward said moving object by a beam splitter; and reflecting said respective pulse echo toward said transceiver by said beam splitter.

15. The method according to claim 8, further comprising a preliminary procedure of selecting at least one sampling rate for sampling said received signals, according to a maximum detectable velocity value.

16. The method according to claim 8, further comprising a preliminary procedure of setting a sampling rate respective of each of a plurality of samplers, according to said respective determined time shift.

17. The method according to claim 8, further comprising a procedure of determining a radial velocity of said moving object according to selected ones of said radial velocity assumptions which are associated with said at least one signal summation.

18. The method according to claim 8, wherein at least one of said radial velocity assumptions are determined according to said at least one signal summation.

19. The method according to claim 8, further comprising a preliminary procedure of determining an integer value for said respective time shift.

20. The method according to claim 19, wherein said integer value is determined according to said respective time shift, and according to a difference between a previous time shift and a previous one of said integer value.

21. The method according to claim 8, wherein each of said signal summations is produced by adding together a predetermined number of said shifted signals.

22. The method according to claim 21 , further comprising a procedure of reducing said predetermined number, before performing said procedure of adding, when the value of at least one summed sample of said at least one signal summation is substantially saturated.

23. The method according to claim 8, wherein said summed pulse event is detected by comparing each of a plurality of summed samples of said at least one signal summation, with a threshold value.

24. The method according to claim 8, further comprising a procedure of subtracting a least recent one of said sampled signals from said signal summations, before performing said procedure of adding, when a new received signal is sampled.

25. The method according to claim 8, further comprising a procedure of searching for said summed pulse event in a subsequent signal summation associated with the same radial velocity assumption, when a threshold value of a plurality of summed samples of said signal summations is substantially low.

26. The method according to claim 8, further comprising a preliminary procedure of setting a threshold value for a plurality of summed samples of said signal summations, according to an expected increase in a signal to noise ratio of said summed pulse event.

27. The method according to claim 8, further comprising a preliminary procedure of setting a threshold value for a plurality of summed samples of said signal summations, according to an expected value of said summed pulse event.

28. The method according to claim 8, further comprising a procedure of producing at least one filtered signal summation by modifying said at least one signal summation, after performing said procedure of integrating, when a time shift difference respective of two consecutive radial velocity assumptions, is equal to or greater than two samples.

29. The method according to claim 28, further comprising a procedure of comparing a plurality of non-aggregated summed samples of said at least one signal summation, and a plurality of aggregated summed samples of said at least one signal summation, with a threshold value, before detecting said received signals, when a signal to noise ratio of said at least one signal summation is substantially low.

30. The method according to claim 28, wherein said modifying procedure is performed by adding together a predetermined aggregation number of adjacent samples of said at least one signal summation.

31. The method according to claim 30, further comprising a procedure of reducing said predetermined aggregation number, before performing said procedure of modifying, when a signal to noise ratio of said at least one signal summation is substantially low.

32. The method according to claim 8, further comprising a procedure of modifying said sampled signals, before performing said procedure of integrating, when a time shift difference respective of two consecutive radial velocity assumptions, is equal to or greater than two samples, thereby producing at least one filtered signal summation after performing said procedure of adding.

33. The method according to claim 8, further comprising a preliminary procedure of modifying said respective time shift, when a time shift difference respective of two consecutive radial velocity assumptions, is equal to or greater than two samples.

34. Device for determining a range of a moving object, according to any of claims 1 -7 substantially as described hereinabove.

35. Device for determining a range of a moving object, according to any of claims 1-7 substantially as illustrated in any of the drawings.

36. Method for determining a range of a moving object, according to any of claims 8-33 substantially as described hereinabove.

37. Method for determining a range of a moving object, according to any of claims 8-33 substantially as illustrated in any of the drawings.