EP0917655A1 - Procede de type instant d'arrivee ameliore - Google Patents

Procede de type instant d'arrivee ameliore

Info

Publication number
EP0917655A1
EP0917655A1 EP96941929A EP96941929A EP0917655A1 EP 0917655 A1 EP0917655 A1 EP 0917655A1 EP 96941929 A EP96941929 A EP 96941929A EP 96941929 A EP96941929 A EP 96941929A EP 0917655 A1 EP0917655 A1 EP 0917655A1
Authority
EP
European Patent Office
Prior art keywords
time
leading edge
signal
reading
correlation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96941929A
Other languages
German (de)
English (en)
Other versions
EP0917655A4 (fr
Inventor
H. Britton Sanderford
John R. Souvestre
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Axonn LLC
Original Assignee
Sanconix Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sanconix Inc filed Critical Sanconix Inc
Publication of EP0917655A1 publication Critical patent/EP0917655A1/fr
Publication of EP0917655A4 publication Critical patent/EP0917655A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
    • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
    • G01S1/04—Details
    • G01S1/045—Receivers

Definitions

  • This invention relates to radio location systems and more particularly to an improved time-of- arrival method using spread-spectrum modulation.
  • the literature describes numerous radio location systems which are based on time-of-arrival information. These systems are primarily concerned with identifying a correlation peak and tracking that peak.
  • the correlation peak is time stamped to provide a radio ranging, round trip distance measurement.
  • two or more receivers can be used to calculate a hyperbolic line-of-position.
  • Additional tjme- of-arrival approaches using direct sequence spread spectrum in the prior art include a method for separating one satellite signal from other satellite signals through correlation of a locally generated precise- code sequence with encrypted precise-code signals, the use of clock recovery circuitry to cycle through M phases of a locally generated receiver clock to select the phase yielding the strongest signal, and the use of a digital correlator to determine the time of arrival of a received pseudo noise sequence.
  • Pulsed techniques capable, after compensating for pulse time detection errors, of adjusting estimated time-of- arrival as a function of the measured. Pulse slope systems are also known in the prior art. Such systems operate in the presence of background noise and multi-path reflections created by objects in the proximity of the receiver and transmitter.
  • the multi-path reflections cause errors in the time stamped reading generated by such time-of-arrival systems.
  • Existing prior art systems do not teach the determination of a correlation peak for estimating the leading edge, or the taking of additional samples at the leading edge to improve the accuracy of the time-of-arrival stamp.
  • a long time goal in the prior art has been to reduce the effects of multi-path on time-of-arrival systems.
  • a typical solution is to use a narrower chip time which, in its familiar radar equivalent, relates to wider bandwidth. The wider bandwidth yields a finer feature in the received signal in order to increase accuracy and resolution of the time-of-arrival measurement. Also, the more narrow chip time signal is less affected by later arriving multipath reflections.
  • Such front-ends are difficult and expensive to design with the desirable filter roll-off characteristics needed to defend such receivers from out-of-band interference. This can lead to intermodulation distortion and loss of desired signal.
  • the wider the front-end bandwidth becomes the easier it is to receive unintentional, fundamental or harmonic interference within the front-end pass-band. This also reduces effective signal-to-noise ratio and measurement accuracy, and leads to the loss of intended signals.
  • the radio location system In order for a radio location system to produce the most accurate time-of-arrival measurement, the radio location system identifies the repeatable feature in the received signal which is least affected by multipath. Multipath reflections travel a greater distance than a direct arriving signal.
  • leading edge radio energy should be used in order to time stamp the time-of-arrival of a received signal.
  • Prior art techniques relying on leading edge detection include the use of zero processing detection of the carrier wave for improving the accuracy of a time-of- flight stamp; pulsed, radar-type systems for measuring distance between an interrogator and a transponder based on leading edges of an interrogation pulse and a reply pulse, and for estimating a leading edge for a navigation system; and the use of leading edge as well as late arriving signal information collected from a plurality of individual detectors in a radar altimeter context.
  • leading edge detection also includes met ods for reducing multipath errors through the use of Kalman filters, and time- of-arrival trigger circuits responsive to the arrival of a direct path time-of-flight transmission.
  • These prior art references do not teach the use of direct sequence spread spectrum for finding a correlation peak, requiring only one detector, and the subsequent use of the correlation peak for estimating the leading edge of the correlation function.
  • the leading the edge of the received signal is least affected by multipath error. Unfortunately, the leading edge typically is not the highest signal-to-noise ratio portion of the signal.
  • a general object of the invention is using the least amount of bandwidth possible to yield accurate time-of-arrival readings.
  • Another object of the invention is enhanced accuracy time-of-arrival readings with minimal transmitted message dwell time to allow the greatest number of simultaneous users on a radio location system.
  • An additional object of the invention is identifying and measuring a feature in a received signal which is least affected by multipath errors.
  • a further object of the invention is obtaining accurate time-of-arrival readings with low signal-to- noise ratio, minimum detectable signals.
  • a still further object of the invention is to provide enhanced time-of-arrival readings with resolution greater than the sub-chip step size searched.
  • a receiver uses direct sequence spread- spectrum modulation to time stamp a received radio broadcast.
  • the receiver receives a spread-spectrum modulated signal from a transmitter.
  • the steps include determining, in the received spread-spectrum signal, a time position of a correlation peak and estimating, from the correlation peak, a leading edge of a correlation function.
  • the steps further include moving a receiver chip code position, corresponding to the estimated leading edge of the correlation function, backward by about one chip time, relative to the chips in the received spread-spectrum signal.
  • the receiver-chip-code position, relative to the chips in the received spread spectrum signal is then moved forward by sub-chip increments until a correlation envelope reading exceeds a preset margin.
  • the method uses the leading edge of the correlation function, as determined by the receiver-chip-code position when the correlation envelope reading exceeds the preset margin, to time stamp an arriving signal.
  • the term "receiver-chip-code position" as used herein is the position of chips in a chip sequence generated at the receiver.
  • the receiver chip sequence is used to despread the received spread-spectrum signal, as is well known in the art.
  • the method as broadly embodied herein, further includes comparing the leading edge to a level equaling a sum of an auto-correlation code noise and estimated background noise, and using the leading edge to time stamp the arriving signal only when the leading edge exceeds the sum. Signal-to-noise ratio may be enhanced by reducing the bandwidth of the receiver following estimation of the leading edge.
  • signal-to-noise ratio may be enhanced by increasing the integration time.
  • the method may also include taking a multiplicity of correlation envelope samples of the leading edge of the correlation function, each of the samples being separated by a portion of a chip time. The method then includes deriving slope information from this multiplicity of samples for enhancing the resolution of the time-of-arrival time stamp.
  • Fig. 1 illustrates delay spread effect on correlation function
  • Fig. 2 shows received signal strength output of receiver
  • Fig. 3 is a look-up table of signal increase over ambient noise vs. sub-chip position signal strength
  • Fig. 4 illustrates a receiver algorithm
  • end Fig. 5 is a receiver block diagram.
  • FIG. I when a radio wave to transmitted, regardless of modulation or bandwidth, the radio wave propagates through a multiplicity of physical paths prior to being collected at a receiving antenna.
  • the multipaths reverberate through a building or echo through a city and produce a delay spread profile.
  • Information from this delay spread profile 101 is used to time stamp a feature of the incoming signal in order to provide a time-of-arrival measurement, or relative time-off-arrival measurement.
  • the received correlation signal takes on the function as shown the dashed lines 102.
  • This function would typically provide a sharp, well-defined correlation peak 104 in the absence of multipath effects. In the presence of severe multipath, however, the well-defined correlation peak can often be lost.
  • the correlation function could indeed have two or more peaks.
  • the correlation function does not yield a well defined correlation peak but rather a rounded-off top 103 with no distinct peak to time stamp.
  • Such bandwidth compressed correlation functions previously reduced resolution in time-of-arrival readings.
  • the instant invention uses the correlation function leading edge which can still provide accurate readings.
  • the receiver first steps a chip code generator by a portion of a chip time or a whole chip time in order to search for a correlation peak.
  • the receiver uses the correlation peak information to estimate the leading edge of the correlation function.
  • the leading edge should be approximately one chip time prior to the correlation peak.
  • the receiver then either reduces bandwidth and/or increases integration time and then moves the chip code position to the corresponding estimated leading edge of the correlation function.
  • the receiver samples and stores the correlation result, moves the code position by a portion of chip time, and measures additional correlation results.
  • the correlation results can be in the form of signal strength indication, quieting detection, or lock detection from control loop means.
  • the receiver uses the sample to form a slope which more accurately predicts the leading edge of the correlation function. Alternatively, the receiver can use these samples to provide pointers to a look-up table which stores results yielding enhanced-accuracy time of arrival measurements.
  • a correlation peak can be determined in either a minimum detectable signal (MDS) or a strong signal case.
  • MDS minimum detectable signal
  • a small signal increase above the noise floor may be detected indicating the presence of a correlation peak.
  • the correlation peak can used to estimate the leading edge of the correlation function, alternatively, an intermediate step of increasing signal averaging or reducing bandwidth can enhance the correlation peak prior to making an estimation of the beginning point, or the correlation function.
  • the correlation peak can be used to estimate the leading edge of the correlation function.
  • slope information from the correlation peak can be taken from one or more readings taken a portion of a chip prior to the peak to estimate the correlation function leading edge If two correlation peaks appeared due to the results of multipath, then the leading correlation peak can be used to estimate the leading edge of the correlation function. Alternatively, an average can be calculated between the two correlation peaks in order to estimate the leading edge of the correlation function.
  • the correlation peak is first sought as an indication because it represents the highest signal-to- noise ratio (SNL) feature of the received signal.
  • SNL signal-to- noise ratio
  • the leading edge correlation slope can be used directly or entire correlation function envelope can be used to predict the leading edge of the correlation function.
  • any of the above techniques can be used to estimate the leading edge of the correlation function.
  • the more accurate this estimation the shorter the dwell time required when taking additional samples of the leading edge of the correlation function.
  • Less accurate initial measurements force a broader range of search to guarantee that the leading edge is included within the search.
  • More accurate initial measurements allow the range of the search to be reduced. Reducing the range of the search is desirable so that the on-air time of the transmitted signal can be minimized. Minimizing the on-air time of the transmitted signal results in a high volume message traffic system by reducing message collisions. In a high signal-to-noise ratio situation, the first leading edge data sample which exceeds the auto- correlation code noise plus anticipated background noise can be used as a first signal.
  • the receiver bandwidth is reduced or the baseband integration time is increased to compensate for the difference.
  • This technique has the advantage of yielding similar accuracy readings in both the strong signal and the MDS cases. Typically, MDS cases are accepted as yielding inherently poor accuracy.
  • the anticipated strength increase of the leading edge correlation function signal strength above the uncorrelated tails can be calculated as
  • This ratio is provided by an associated reduction in bandwidth and/or increase in integration time. In the instant invention, this results in an increased integration time of 17 to 1.
  • the leading edge of the correlation function can be initially estimated in a manner to purposely force an initial measurement after the leading edge of the correlation, function.
  • the receiver's chip code clock should be decremented in sub-chip steps and measurements of signal strength or quieting detector output can be made which have decreasing strength until they stabilize at the auto- correlation function's code noise level.
  • a third approach is to produce an initial estimation in between these previous two schemes. This approach makes a best estimate of the exact beginning of the leading edge of the correlation function. Then, based on that estimated beginning signal strength, the receiver's code clock can be incremented or decremented in sub-chip multiples, depending upon whether the initial reading was at the auto-correlation function's code noise level or above that level.
  • a form of a binary search based on signal strength could be used after an initial sample was taken. If two or more such samples were taken, then this information can be used to create a slope vector. If three or more samples were used, then these samples can be weighted to produce a slope vector. This weighting can take into consideration that the leading samples have lower signal-to-noise ratio but lower multipath error, and that later samples have higher signal-to-noise ratio but higher multipath error.
  • three or more samples can be stored and then used as input to a look-up table which has been pre-assigned with best estimate results based on theoretically derived or empirical data.
  • time-off-arrival resolution is limited to ⁇ V ⁇ the quantized sub-chip step size.
  • Combining signal strength and envelope information produces a vector with far greater resolution.
  • the achievable accuracy is limited by signal-to-noise ratio and multipath environment.
  • the multiplicity off envelope samples can be transferred to a central processing hub which collects time-of-arrival information from multiple receivers. This information can be combined by the hub to further reduce errors and increase accuracy.
  • This technique is equally applicable to digital parallel correlators. Bandwidth can be reduced by weighting multiple correlation results or arranging multiple correlation readings, or by other techniques as are known in the art, in order to improve signal to noise ratio.
  • FIG. 2 illustrates a graph of signal amplitude versus time of a received signal strength indicator output typical of the above techniques.
  • the initial portion of the signal 203 depicts the noise floor or the correlation function code noise being measured at a resolution bandwidth approximately equal to that of the data bandwidth.
  • the next time portion of the illustration depicts the leading edge, first arriving signal 202. This is the signal which is least affected by multipath, but is at a lower signal-to-noise ratio than the signal peak.
  • the next portion of time indicates the correlation peak 203 detected at the normal sampling bandwidth, approximately that of the data.
  • the correlation peak, or correlation envelope, or some combination thereof, is used to estimate the leading edge of the correlation function.
  • the detector bandwidth is decreased and the integration time is increased by an appropriate amount so that the leading edge of the correlation function can have a greater signal-to-noise ratio to produce an enhanced accuracy time-of-arrival reading. If the radio location system was simultaneously transmitting data during the time when synchronization was being required, then the transmitter data modulation bandwidth likewise is reduced to allow all of the received signal energy to be detected. The next portion of time, depicted first reading 204, illustrates the noise floor being reduced, in the MDS case, by increasing the integration sample time and/or reducing the bandwidth prior to detection.
  • the next period of time illustrated by first arriving signal 205, shows the expanded first arriving signal, which has been filtered and integrated over a longer time interval to increase the signal-to-noise ratio.
  • Each of these samples is taken after the receivers chip code clock has been shifted a portion of a chip time.
  • the chip code clock is shifted in 1 /8 chip steps.
  • the second reading 206 is taken once the chip code clock has been shifted a portion of a chip time.
  • the third reading 207 is taken after the second reading 206 is complete and after the chip code clock has been shifted an additional portion of a chip time. Two or more of these sample measurements are then used to predict a slope vector 208 or provide look-up table information to increase the resolution of the time-of- arrival measurement.
  • the information obtained at the leading edge of the correlation function is in two forms.
  • the first form of information is determined by finding the position of the chip code position which experiences a signal strength increase above the noise floor, or above the auto-correlation noise.
  • the other form of information is determined by noting the level of the increase in the signal strength from one sample to the next. If two samples were taken, then a simple vector can be Calculated. If three or more samples were taken, then a form of curve fitting algorithm may be used, since multi-point slope measurements are not necessarily a straight linear function.
  • a look-up table can be used as an alternative to calculating the leading edge of the correlation based on slope information.
  • Such a table can be a two-dimensional array or can be a look-up of a multiplicity of readings which will form an N-dimensional array, where N equals the number of readings taken as the chip code position is moved a portion of a chip time.
  • the table entries can be derived by numeric estimation techniques. Alternatively, empirical data can be collected from actual field experience using known position transmitters and receivers. In this way, a first reading 301 and a second reading 302, as shown in FIG. 3, can be bound to the most likely correct result. Further, the look-up table can be one of several selectable look-up tables. If the operating environment of a the transmitter were known, such as in-building, in-urban areas, in-rural area, etc.
  • FIG. 3 depicts a took-up table off signal increase over ambient noise versus sub-chip position signal strength.
  • a first reading 301 is taken in order to establish the ambient noise floor or the ambient auto-correlation noise floor. This step is not, however, essential to the invention.
  • a reading is taken representative of the noise floor, this reading is used as a base line indication of signal improvement between the noise floor and the second reading 302, third reading 303, and any additional readings.
  • a second reading 302 is used as a look-up pointer in the table.
  • a third reading 303 is used as a pointer into the table.
  • a multiplicity of pointers from readings can be used to look up a specific table entry 304 which represents data that yields the most accurate result.
  • resolutions can be achieved which are greater than the resulting fractional chip code position. This is due to the amplitude plus the fractional chip code positions resulting in vector which has a resolution of: (number of chip code fractional positions) X (resolution of the amplitude of the I sampled received signal strength indication).
  • a multiplicity of readings from the leading edge 202 may be provided to a fuzzy logic or neural network means.
  • FIG. 4 illustrates a receiver algorithm that can be applied in the present invention.
  • the receiver searches 401 for a correlation peak by slewing the chip code clock, jogging the chip code clock in fractional increments, or by any equivalent means as is known in the art.
  • the method searches 401 for a correlation peak.
  • the algorithm uses the correlation peak to estimate 402 the time position of the leading edge off the correlation function.
  • the receiver reduces 402 the bandwidth and/or increases 403 the integration time to improve the signal-to-noise ratio at the leading edge of the correlation function.
  • the receiver next moves 404 the chip code delay position to the corresponding estimation of the leading edge of the correlation function.
  • the algorithm can additionally seek two similar amplitude readings in order to verify 409 that the chip position is aligned prior to the leading edge of the correlation function. This establishes the ambient noise floor or auto-correlation noise floor.
  • the receiver samples and stores 405 the resulting correlation measurements.
  • correlation results can be stored 405 as representative improvements over ambient noise in signal strength, quieting detection output, and/or lock detection from any of the available closed loop means.
  • the - receiver moves 406 the chip code delay position by a portion of a chip time. In the instant invention, the receiver moves 406 the chip code forward by 1/8 of a chip time.
  • the next step of the algorithm repeats 407 the steps of sampling and storing 405 and moving 406 the chip code delay position for a multiplicity of samples.
  • the algorithm can suppress storage off correlation results until the improvement over ambient noise is greater than the anticipated noise spikes and/or cross-correlation of misaligned codes. This is typically 2 dB to 4dB.
  • the algorithm uses the multiplicity of samples to form 408 either a slope, which predicts the leading edge of the correlation function, or a look-up table of "best fit" results which indicate the leading edge of the correlation function. Either of these two methods can enhance the resolution of the time of arrival measurements.
  • the steps of sampling and storing 405 and moving the chip code delay position 406 can be repeated for a multiplicity off samples whereby the chip code phase time/time position is alternately both advanced and delayed by a portion of a chip time. These additional readings can be averaged to provide greater noise filtering.
  • the additional noise filtering reduces the error term generated by random noise which increases the effective signal-to-noise ratio and thereby the accuracy of the component of the signal representing time of arrival information.
  • the sub-chip position may also be used alone without amplitude information.
  • the chip code position can first be verified 409 as being aligned prior to the leading edge of the correlation function. This can be accomplished by taking one or more readings which yield similar signal strength levels regardless of adjacent sub-chip code position. If the sub-chip code position were not aligned prior to the leading edge of the correlation function, then fractional realignments off the chip code position yield readings which increase and decrease relating to the slope of the correlation function. Once the chip code position is verified 409 to be positioned prior to the leading edge of the correlation function, the chip code position is moved 410 forward in. 1/8 chip increments.
  • the chip position continues to be incremented in 1/8 chip increments until occurrence of a signal improvement is verified 411 , which is greater than, a preset margin or threshold.
  • the preset margin can be set as a calculation of anticipated auto-correlation noise predicted from fractional chip step moves.
  • anticipated random fluctuation and impulse noise, for the bandwidth and integration time searched can be added to the preset margin.
  • a signal strength improvement which is greater than the preset margin stops the further advancement of sub-chip code search. Once this advancement is stopped, the chip code position can be time stamped 412 to provide a relative time-of-arrival reading with +/- 1/16 of a chip time resolution.
  • the received signal after passing through a receiver front-end and optionally through a down conversion and appropriate filtering, as is well known in the art, is first applied to mixer 501.
  • Mixer bandwidth compresses an incoming spread spectrum signal to output a compressed non-spread spectrum signal.
  • Mixer 501 is injected on its local oscillator port either directly by chip code generator 503 or alternately by a mixer/local oscillator combination 502.
  • the mixer/local oscillator 502 provides for the optional second or third down conversion of the received signal to yield lower IF frequencies, as is well known in the art.
  • mixer 501 or mixer/local oscillator 502 can be driven by a chip code output filter 510.
  • Filter 510 can be designed to provide a sharp roll-off of the wideband spread spectrum signal so that filter 510 matches a similarly compressed transmitted signal.
  • the instant invention preferably uses a five pole elliptic filter to reduce bandwidth. Bandwidth compressed transmission has the advantage of using less spectrum and can therefore merit favorable FCC treatment.
  • a chip code generator 503 provides the spread-spectrum direct sequence modulation output.
  • Appropriate chip code generators can be fashioned from an EXCLUSIVE-OR gate tapped shift register with feedback, or a RAM/ROM look-up table wherein the appropriate chip code pattern is stored, or a serial shift register wherein the appropriate chip code pattern is stored, or any other means, as is well known in. the art.
  • the instant invention uses a sequentially addressed ROM look-up table to store and recall the chip code pattern.
  • the chip code generator 503 also has several inputs. The inputs are designed to alter the time/delay offset of the repetitive chip code output.
  • the advance input causes a time advance of the chip code position.
  • the delay input causes a time delay of the chip code position.
  • the advance and delay inputs can be in units of multiple chips, a single chip, or in units of a portion of a chip. In the instant invention, the advance and delay lines are selected in two chip, one chip, 1/4 chip, or 1/8 chip increments.
  • the chip code generator 503 is equipped with an input/output port which allows the processor 509 to read and write the chip code alignment delay.
  • the chip code delay/alignment position output port allows the processor 509 to determine the aggregate time/delay position offset which has been selected/optimized by the processor 509.
  • the processor 509 reads the chip code delay position from the chip code generator 503
  • the processor 509 is able to time stamp the delay/alignment position of an incoming received signal with a high degree of accuracy.
  • the ability to read the chip code delay position allows the processor 509 to determine relative time-of-arrival measurements and to compare the chip code delay position to either a. time reference or to another incoming received signal. The relative time-of-arrival information of the received signal can then be used to calculate a distance or a hyperbolic line of position.
  • the processor 509 can also set any chip code delay position by writing the input port of the chip code generator 503.
  • a bandpass filter 504 serves to eliminate received noise outside of the compressed output of the mixer 501 and sets the ultimate sensitivity of the receiver unless a phase-locked-loop (PLL) circuit is used in a detector 506.
  • PLL phase-locked-loop
  • a reduced bandpass filter 505 can be selected by the processor 509, to enhance the signal-to-noise ratio of the received signal.
  • the filtered signal from bandpass filter 504 or reduced bandpass filter 505 is provided to the detector 506 which makes possible a measurement of correlation.
  • the detector 506 can be fashioned from available components which either measure signal strength or quieting detection or phase lock detection.
  • the output of the detector 506 is integrated or filtered by filter 507 which is set to approximately the data bandwidth.
  • the filtering or integration can be selected by the processor 509, to reduce higher frequency noise through the use of an alternative filter 508.
  • the output of filter 507 or alternative filter 508 provides a measurement of correlation level to processor 509 so that the processor 509 can perform the enhanced time-of-arrival algorithm.
  • the detector 506 can additionally provide part, or all, of the components necessary for data demodulation.
  • the processor 509 can be a micro-computer or digital logic, or discrete components, or an ASIC, or any equivalent means which can run the enhanced time-of-arrival algorithm.
  • the instant invention uses a digital signal processor (DSP)/microprocessor with an internal analog to digital convertor to translate the correlation measurement input into a digital representation of correlation level.
  • DSP digital signal processor
  • the DSP micro-processor in the instant invention further controls the advance and delay of the chip code phase position of the chip code generator 503 and reads the phase position of a received signal for time-of-flight, or relative time-of- flight, measurements.
  • the first detection of an arriving signal may not be detection of the earliest arriving signal. Since the chip code sequence is searched one chip at a time, it is possible that the receiver may acquire a signal which is in the middle of the delay spread profile.
  • the instant invention employs one of two techniques. Technique one either enhances or delays the referenced chip code position until the signal of interest is received.
  • the direct sequence spread spectrum receiver may continually scan each of the chips which are present in the chip code pattern in use and store a historic result of chip code measurements in a table which represents at least one of every chip code position. In this manner, upon the receipt of a signal of interest, the receiver may review its table of historic delay spread information to determine the leading edge of the delay spread profile, or the first arriving signal.
  • the receiver Since the turn-on time of the transmitter is not controlled by the receiver in a one-way communications application, the receiver must scan all chip positions or scan backwards until the noise floor is detected. In a two-way communication system, it is possible to know to some degree of accuracy the initial turn-on time of the transmitter which in turn may allow a reduction in the overall code circuit positions required. In a one-way communication system, it is possible for the transmitter to turn on and within one or several chip times the receiver acquiring a signal of potential interest. In this case, however, the receiver will not have acquired sufficient historic information to determine the leading edge of the delay spread profile. The receiver must wrap around in a modulo fashion to effectively examine the chip position which could have occurred prior to the initial turn-on of the transmitter.
  • the receiver's algorithm may verify an equivalent duration quiet period, prior to a chip position yielding a correlation peak. This process serves to ensure leading edge information was found.
  • the above technique does not necessarily have to be used in conjunction with the signal-to-noise ratio enhancement techniques contained herein and may stand alone.
  • two independent co-located receivers can be used simultaneously whereby one receiver decodes data while the other provides time-of-flight/relative time-of-flight information. Once either receiver begins to detect a message, the T.O.F. receiver begins any of the enhanced T.O.A. algorithms noted herein.
  • DSP digital signal processing

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

Procédé permettant d'améliorer un système de radiodétection basé sur l'instant d'arrivée. Les systèmes de radiodétection de ce type sont limités, en ce qui concerne leur précision absolue, par le rapport signal sur bruit et par l'environnement à trajets multiples, variable en fonction du temps, dans lequel ils sont obligés de fonctionner. La présente invention concerne des techniques qui maintiennent un rapport signal sur bruit élevé, tout en identifiant une caractéristique du signal reçu moins affectée par les trajets multiples. La technique fait appel à des informations de crête/enveloppe de corrélation afin d'estimer le front avant de la fonction de corrélation (402), puis améliore les échantillons discrets au niveau du front avant de ladite fonction de façon à produire des résultats ayant un rapport signal sur bruit élevé (405-408). L'invention permet de réduire la largeur de bande d'émission nécessaire, d'accroître la résolution et la précision du système dans un rapport de 20 à 1, et de maintenir un débit élevé de trafic de messages.
EP96941929A 1996-08-10 1996-08-10 Procede de type instant d'arrivee ameliore Withdrawn EP0917655A4 (fr)

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PCT/US1996/012836 WO1998007045A1 (fr) 1996-08-10 1996-08-10 Procede de type instant d'arrivee ameliore

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EP0917655A1 true EP0917655A1 (fr) 1999-05-26
EP0917655A4 EP0917655A4 (fr) 2001-04-04

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AU1114497A (en) 1998-03-06
WO1998007045A1 (fr) 1998-02-19

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