KR100838988B1 - System and method for the detection and compensation of radio signal time of arrival errors - Google Patents

Abstract

Systems and methods are disclosed that can reduce the impact of arrival time errors. In a mobile unit, such as a CDMA device, a correlation pulse occurs when a transmitted code matches a stored reference code. In the absence of multipath effects, correlated pulses occur corresponding to multiple transmissions of the reference code from multiple transmitters. However, the multipath effect distorts the generated correlation pulses that lead to errors in the arrival time measurement. The present invention calculates the width of the correlation pulse to calculate the delay correction factor based on the pulse width. The delay correction factor is added to the measured delay time to provide a more accurate delay time, thus performing a more accurate position measurement based on the arrival time. In alternative embodiments, other signal factors may also be used to apply the delay correction factor. Actual positioning may be performed by a mobile unit or any other positioning object (PDE). The system may also apply calibration factors to the arrival time signals received from the global positioning system (GPS) satellites.

Description

System and method for detecting and compensating for arrival time error of wireless signal {SYSTEM AND METHOD FOR THE DETECTION AND COMPENSATION OF RADIO SIGNAL TIME OF ARRIVAL ERRORS}

This application is a continuation of US Patent Application 09 / 879,074, filed June 11, 2001, and US Patent 6,804,494 was issued on October 12, 2004.
FIELD OF THE INVENTION The present invention relates generally to telecommunications and, more particularly, to techniques for detecting and compensating arrival time errors in telecommunication systems.

Emergency services are often required to use a telephone number such as "911". If the caller is in a fixed location, such as a home, the computer system will use Automatic Number Identification (ANI) to track the telephone number of the incoming call to quickly determine the address from which the call originated. Thus, determining where emergency services are required is a relatively simple task.

The location of a user requesting an emergency service request via mobile communication, such as a cellular telephone, personal communication system (PCS) device, is not readily determined. Wireless triangulation techniques have long been used to position mobile units. However, such wireless triangulation techniques are known to be inherently inaccurate. Errors of thousands of meters are not uncommon. However, the error is inadequate for delivery of emergency services.

The Federal Communications Commission (FCC) has directed changes in communications technology to enable more accurate positioning. In the case of mobile communications, the FCC enacted a law that required a positioning system-based infrastructure to have 150 m accuracy (and 300 m accuracy for 95% of the time) for 67% of the time. For systems that require a modified handset, the FCC has enacted that the system must determine a location within 50 m accuracy (and 150 m accuracy for 95% of the time) for 67% of the time.

The wireless positioning system uses a time of arrival (TOA) signal input from different transmitters of known positions to triangulate and estimate the position of the mobile unit. However, arrival time signals are often distorted or error due to multiple transmission paths. 1 illustrates an example of multiple transmission paths that may be executed by a mobile telephone of a vehicle 10. In the example shown in FIG. 1, mobile unit 10 receives signals from transmitters 12 and 14 mounted on top of the tower. In the example of FIG. 1, the mobile unit 10 receives a signal directly from the transmitters 12 and 14 or also receives a signal of the transmitter 14 reflected from an adjacent building. Thus, the mobile unit 10 receives a number of signals from the transmitter 14. In the example shown in FIG. 1, the mobile unit 10 is not in the line of sight LOS of the transmitter. That is, buildings or other structures obstruct the direct line of sight between the mobile unit 10 and the transmitter 16. However, mobile unit 10 is still detecting a signal from transmitter 16 that is reflected in a building or other structure or diffracted around the edge of the building or other structure. The mobile unit 10 may also receive signals from the transmitter 16 mounted on top of the building and receive signals from the global positioning system (GPS) satellite 18 in earth orbit. As a result, mobile unit 10 receives multiple signals from transmitter 16 and does not receive direct LOS signals. Signals from GPS satellites 18 may include LOS signals and reflected signals. As a result of the multipath signal, the measurement of the arrival signal by the mobile unit is error prone. The error can be significant when a multipath signal is present, thus making it impossible or difficult to achieve what the FCC is aiming for in terms of positioning accuracy. Therefore, it can be appreciated that a system and method for improving TOA measurement for a mobile location system are highly desired. The present invention provides the above and other advantages apparent from the following detailed description and the accompanying drawings.

A system and method for correcting multipath errors in a telecommunication device location system. In one embodiment, the system includes a receiver that receives data transmitted from a remote transmitter located at an unknown distance from the receiver. The analyzer analyzes the date related to the received data and generates position data related to the position of the receiver. The analyzer also generates a calibrated position data by calculating a calibration factor based on the measured signal reference.

In one embodiment, the receiver generates a correlation pulse when the received data is correlated with the stored data. In this embodiment, the signal reference is the pulse width of the correlation pulse. The correlation pulse may be modeled as a quadratic equation with a number of coefficients determined by the amplitude value of the correlation pulse at a predetermined time. In another embodiment, a signal strength indicator is generated. In this embodiment, the signal reference is a signal strength indicator.

The system may further include a positioning object for determining the position of the receiver and the known position of the remote transmitter based on the calibrated position data. The location data may be based on the arrival time of the data received by the receiver. The arrival time of the data can be calculated as a delay time or distance and the calibration factor can be calculated as the calibration time and calibration distance.

In one embodiment, the receiver is part of a cellular telephone operating in the 800 MHz band, and the analyzer calculates position data based on the arrival time of the data transmitted from the 800 MHz band remote transmitter. Optionally, the receiver can be part of a personal communication system operating in the 1900 MHz band, and the analyzer calculates position data based on the arrival time of the data transmitted from the remote transmitter in the 1900 MHz band.

In another alternative embodiment, the remote transmitter Global Positioning System (GPS) satellite, and the receiver receives data signals from GPS satellites. In this embodiment, the analyzer calculates the position data based on the arrival time of the data transmitted from the GPS satellites.

The system also includes a data structure for storing data related to the selected signal reference in one or more calibration factors, the analyzer providing a measurement of the selected data as input to the data structure and storing stored calibration factors in connection with the measurement of the selected reference. Search for. The system optionally includes a data structure for storing a mathematical function associated with the selected signal criteria in one or more calibration factors, wherein the analyzer calculates the calibration factors using the criteria selected in the mathematical function.

1 illustrates multiple receive paths between a transmission source and a mobile unit.

2 is a functional block diagram of a system implementing the present invention.

3 is a waveform diagram illustrating a correlation signal generated by the system of FIG.

4 is a graph showing a functional relationship between a correlation peak width and a distance error.

5 is a graph showing the functional relationship between power measurements and distance error.

6 and 7 are flowcharts illustrating the operation of the present invention.

The present invention enables the measurement of the magnitude of the distance error derived as a multipath signal and provides a correction factor to be applied to the arrival time measurement to enable more accurate positioning. In an exemplary embodiment, the present invention is implemented using a portion of a conventional code division multiple access (CDMA) mobile unit. CDMA mobile units may be referred to as mobile units, cellular telephones, PCS devices, and the like. As will be described in more detail below, the present invention is not limited to any particular type of mobile communication device, nor is it limited to a particular operating frequency of the mobile device.

The invention is implemented with a system 100 shown in functional block diagram in FIG. System 100 includes a central processing unit (CPU) 102, which CPU controls the operation of the system. Those skilled in the art will appreciate that the CPU 102 is intended to include any processing device capable of operating a telecommunications system. Any such processing device includes a microprocessor, embedded controller, application specific integrated circuit (ASIC), digital signal processor (DSP), state machine, dedicated discrete hardware, and the like. The present invention is not limited to the specific hardware components selected to implement the CPU 102.

The system also includes a memory 104 that can include both read-only memory (RAM) and random access memory (RAM). The memory 104 provides instructions and data to the CPU 102. Part of the memory 104 also includes nonvolatile random access memory (NVRAM).

The system 100, typically implemented as a wireless communication device such as a cellular telephone, also includes a housing 106 that includes a transmitter 108 and a receiver 110, thereby providing a remote, such as a cell site controller (not shown). It enables the transmission and reception of data such as audio communication between the station and the system 100. The transmitter 108 and receiver 110 may be combined into a transceiver 112. The antenna 114 is attached to the housing 106 and electrically connected to the transceiver 112. The operation of transmitter 108, receiver 110, and antenna 1124 are well known in the art and need not be described herein except as specifically related to the present invention.

In an implementation for a CDMA device, the system also includes a signal detector 116 used to detect and measure the level of the signal received by the transceiver 112. Signal detector 116 detects one or more parameters, such as total energy known in the art, pilot energy per pseudo noise (PN) chip, power spectral density, and other parameters. As will be explained in more detail, the signal detector 116 performs a correlation analysis to determine the arrival time (TOA) from the same location as the transmitter 14 (see FIG. 1).

The signal detector 116 performs a correlation analysis between the reference signal and the received signal to generate a correlation output signal. Signal analyzer 120 uses the calibration data table 122 to analyze the correlation signal and generate distance calibration data. In one embodiment, calibration data table 122 includes data relating the width of the correlation pulses to the distance error. However, other criteria may be used to correct the distance error.

The system 100 includes a timer 124 to provide system timing that is used to measure the delayed time for signals from other sources (eg, transmitters 12-16) to arrive. The timer 124 may be a standalone device or part of the CPU 102.

The various components of the system 100 are connected to each other by a bus system 126, which may include a power bus, a control signal bus, and a status signal bus in addition to the data bus. However, for clarity, several buses are shown as bus system 126 in FIG. 2. Those skilled in the art will appreciate that the system 100 shown in FIG. 2 is a functional block diagram rather than a list of specific components. For example, although signal detector 116 and signal analyzer 120 are shown as two separate blocks within system 100, the blocks are actually implemented as one physical component, such as a digital signal processor (DSP). Can be. The blocks may also be present in the memory 104 as program code, which code is operated by the CPU 102. The same considerations may apply to other components, such as timer 124 listed in system 100 of FIG.

The operation of the components shown in the system 100 of FIG. 2 will be described with reference to FIGS. 3 is a series of waveform timing diagrams showing examples of correlation pulses generated by the signal detector 116. In order to assist the understanding of the present invention as appropriate, a brief description of the arrival time processing using a CDMA mobile unit will be provided as an example. A mobile unit (eg, mobile unit 10 of FIG. 1) implementing system 100 of FIG. 2 is initially assigned a pseudo noise (PN) code. The PN code may be stored in the memory 104 as a local reference. When the base station (eg, the transmitter 12) transmits data to the mobile unit 10, the base station transmits a PN code. The system 100 continues to search for correlation between local criteria (e.g., stored PN codes) and transmitted data (i.e., transmitted PN codes).

As is well known in the art, all transmitters (e.g., transmitters 12-16) transmit the same PN code, but the start of transmission of the PN code from each transmitter is delayed in time by the exactly reported offset. The time offset is measured on a number of 64 chips. The PN offset is selectively assigned to the transmitter, whereby the geographical range of offsets is enlarged as large as possible to avoid interference between transmitters. Transmitters (e.g., transmitters 12-16) may be identified by transmitted identification data, but are sometimes classified by their PN offset time. For example, transmitter 12 may itself be a PN code with an offset of PN 300. May be identified as PN 300. In this example, transmitters 14 and 16 are assigned to PN 425 and PN 610 to indicate an offset time at which each of them will transmit a PN code. Regardless of how the transmitters are classified, however, it should be appreciated that each relative offset with respect to each other can be set from the information encoded in the signal. 2 will detect a PN from each of the transmitters (eg, transmitters 12-16) in any geographic area.

If the mobile unit 10 is collocated with the transmitter 12, there will be no delay in the transmission time between the transmitter and the system 100. In such a case, the signal detector 116 (see FIG. 2) will immediately detect the correlation between the stored reference and the transmitted data. However, assuming that mobile unit 10 is at an arbitrary distance from transmitter 12, there is a delay in the detection of such correlation due to propagation delays. The signal detector 116 moves the stored reference 1/2 chip at a time until a correlation between the stored reference and the transmitted data is detected. Those skilled in the art will appreciate that a "chip" is one piece of data in a PN sequence. Since the data is transmitted at the reported rate, the chip can be used as a time measurement. Although the present description may be characterized in terms of substantial time, it is more convenient to represent time through the chip because the system 100 performs analysis and measurement through the chip.

Since the propagation speed of the wireless signal is reported, the delay measurement can also be calculated as distance. Thus, the delay time, distance and measured values on the chip may all be interchangeable.

If the propagation delay between transmitter 12 and mobile unit 10 has been reported, only two signals will be needed to determine the exact location of the mobile unit. For example, it is possible to draw a circle with a radius that corresponds to the propagation delay (meters) around the transmitter 12. The moving unit 10 should be located at any position of the circumference of this circle. The second detected PN code will be detected from the transmitter 14, which transmits the PN code in the PN slot 425. The delay time for the generation of the correlation pulse from the first transmitter (i.e., transmitter 14) allows the measurement of the second propagation delay time. A circle surrounding the transmitter 14 with a radius corresponding to the second propagation delay indicates that the mobile unit 10 should be located at any position on this circumference. With two known propagation delays, the mobile unit 10 must be located at the intersection of two circles.

However, the propagation delay between transmitter 12 and mobile unit 10 is unknown. Therefore, system 100 optionally assigns a random criterion of zero delay to the first received PN code. Thus, the first received signal is not directly included in the position measurement. Receipt of signals from two subsequent transmitters (e.g., transmitters 14 and 15) is the result of the PN offset and propagation delay, respectively, due to the distance between mobile unit 10 and transmitters 14 and 16 Has a delay for 12). The delay in generating the correlation pulse due to the PN offset at the time of transmission of the PN code is easily determined and appropriate compensation is formed at the timing. However, the time difference between the transmission of the PN code and the generation of the correlation pulse is due to the propagation delay and thus the distance between the mobile unit 10 and the individual transmitters (eg transmitters 14, 16). The position of the mobile unit 10 may be determined based on the exact TOA of the signal from the transmitters 14, 16. Thus, system 100 requires the reception of PN codes from three different transmitters. The first correlation pulse is used as the zero reference while the excess delay times associated with the other two transmitters (e.g., transmitters 14 and 16) are used to provide an appropriate delay measurement.

Waveform A of FIG. 3 shows the sample correlation output generated by signal detector 116 (see FIG. 2) when no multipath signal is present. The signal detector 116 shifts the reference data (ie, stored PN) 1/2 chip in time until it detects a correlation between the reference data and the received data. The correlation pulse generated as a result of the PN code from the transmitter 12 is not shown because it is used on an arbitrary zero basis. The delay due to the PN offset of the transmitters 14 and 16 is eliminated so that only the waveform of FIG. 3 shows the effect of the propagation delay. In the example shown in waveform A, the correlation pulse due to transmitter 14 is generated with approximately 1.5 chips from any zero reference. The 1.5 chip delay is related to the distance between the transmitter 14 and the mobile unit 10. Thus, the arrival time is determined by the delay as measured in the chip (in meters if desired).

The data transmitted from the transmitter 14 includes identification data such that the mobile unit 10 implementing the system 100 identifies the transmitter 14 as a source of correlation signal detected with 1.5 chips. In addition to the transmitter 14, the mobile unit 10 implementing the system 100 receives data from the transmitter 16. The signal detector 116 will detect a correlation between the local reference (ie, stored PN code) and the data transmitted from the transmitter 16. In the example shown in waveform A, the correlation signal due to the PN code from transmitter 16 is detected at approximately 4.5 chips from the zero reference. The 4.5 chip delay is related to the difference between the distance from the transmitter 16 to the mobile unit 10 and the distance from the transmitter 12 to the mobile unit 10. This can be seen by the following example shown in FIG. 3C. The signal generated by the transmitter 12 is delayed by 400 chips with respect to the signal generated by the transmitter 14. There is a 15 chip delay between the time that the signal transmitted from the transmitter 12 is generated and the time that the signal is received by the mobile unit 10. Similarly, a five chip delay between the time at which the signal generated by the transmitter 14 is generated and the time the signal is received by the mobile unit 10 due to the propagation delay between the transmitter 14 and the mobile unit 10. There is this. Therefore, the perceived delay in the mobile unit 10 between the reception of the signal generated at the transmitter 14 and the signal generated at the transmitter 14 will be a total of 410 chips. This 410 chip is the difference between the 415 chip delay from the time the signal is generated at the transmitter 12 and the 5 chip delay at which the signal generated at the transmitter 14 is received. As described above, the data transmitted from the transmitter 16 is indicative data such that the mobile unit 10 implementing the system 100 can identify the transmitter 12 as a source of correlation peaks detected at the 4.5 chip. It includes.

In addition, mobile unit 10 implementing system 100 detects pulses from satellites using additional base station transmitter (not shown) or satellite positioning system (GPS) signals. As is known to those skilled in the art, GPS uses the time of arrival data to determine the location of the mobile unit 10. In an exemplary embodiment, the mobile unit 10 determines the time of arrival data from three or more different transmitters. As described above, the first correlation pulse is used as a zero reference, while the relative delay time of the additional correlation pulse is used to determine the position of the mobile unit 10 based on the arrival time of the further correlation pulse. In the absence of any multipath effect, the pulses shown in waveform A are used to provide a relatively accurate measurement of the time of arrival and thus to accurately determine the position of the mobile unit 10.

Under current communication standards such as IS-801, the CDMA standard for positioning positioning, the CDMA standard can perform calculations that use the TOA to determine its location. However, the location of the mobile unit 10 is determined by part of the fixed infrastructure. In this embodiment, the mobile unit transmits indication data and delay measurement data to a remote location, such as transmitter 14. The positioning decision entity (PDE) associated with the transmitter 14 performs the calculation and determines the position of the mobile unit 10 based on the known positions of the various transmitters and the delay data measured from each transmitter. Table 1 below shows sample data transmitted from the mobile unit 10 to the PDE associated with the transmitter 14.

PN offset Delay (meters) 300 0 425 1,500 610 4,500

As is known, and as briefly mentioned above, the PN value for each transmitter (eg, transmitter 12-16) refers to the PN offset at which each transmitter starts to transmit the PN code. . In the example shown in Table 1, transient delays (ie, delays that do not contribute to the PN offset) are calculated within the chip and converted into metric delays. For waveform A of FIG. 3, two correlation pulses from the transmitter (eg, transmitters 14 and 16) result in correlation pulses at 1.5 and 4.5 chips, respectively. The data in Table 1 includes the PN offset and relative transient delay associated with each transmitter based on the time delay of the arrival pulse.

The PDE uses an identification code to determine if the transmitter is associated with each excess delay time. Since the position of the transmitter is known, it is a relatively simple calculation to determine the position of the mobile unit 10 based on the delay from each individual transmitter. The calculation process is known in the art and will not be described below.

Unfortunately, the multipath effect is present in almost all TOA measurements. Although satellite signals using GPS positioning techniques tend to have somewhat less multipath effects, these effects still exist. Multipath effects from GPS satellites (eg, GPS satellites 180) are particularly prominent in urban areas where buildings or other man-made structures interfere with the GPS signal. With transmitters 12-15 (shown in Figure 1) The same terrestrial system is also affected by the artificial structures on which the signals are reflected, so that the mobile station 10 receives multiple images of the same signal, and the system 100 can evaluate the error due to the multipath effect. The multipath signals are typically only delayed by a very small amount of time and each arrival time is very close to reach the antenna 114 of the system 100 to produce different peaks in the overall correlation function. As such, this multipath effect is referred to as a “short multipath effect.” That is, the signal arrives within such a short period of time, and the scene The output from the detector 116 is a single pulse distortion due to overlapping effects of the multiple detected signals.

In the previous example described in connection with the waveform of Figure 3, the mobile station 10 receives a single signal from the transmitters 14 and 16 without a multipath signal. The effect of the multiple signals is illustrated in the waveform of FIG. 3, where the signal detector 116 shows a correlation value with a wider pulse width due to multiple reception of the same signal within a short time period. As shown in waveform A, instead of the 1.5 narrow relatively narrow pulse, since the system is designed to detect the peak signal, the signal detector 116 generates a wide pulse that makes it difficult to accurately determine the time of arrival. Occurs. In waveform B, the signal has a peak of 1.5-2.5 chips. Similarly, the correlation value of the signal received from the transmitter 16 is also described in waveform B of FIG. Again, the multipath effect widens the pulse so that the peak is between 4.5-5.5 chips.

The effect described in waveforms A and B in FIG. 3 is merely exemplary. The multipath effect is due to the signals arriving in phase at the antenna 114 (shown in FIG. 2) such that the signal detector 116 generates a number of peaks associated with a single signal. The present invention provides at least partial compensation for errors due to multipath effects. The compensation system described below is not limited to the shape of the waveform or the excess delay described in FIG.

It has been determined that a functional relationship exists between the width W of the correlation pulse generated by the signal detector 116 and the amount of error in arrival time. That is, the width of the correlation pulse generated by signal detector 116 may be related to the amount of error in signal arrival time due to the multipath effect. The functional relationship between the pulse width W and the delay error can be characterized by the function f (W). Fig. 4 illustrates a function f (W) based on field experiments comparing the distance calculated by conventional arrival time techniques with the actual specified distance. The pulse width of the jagged curve larger than two chips is due to the relatively small sample values for two or more widths. However, the graph of Figure 4 clearly shows the relationship between pulse width and delay error.

Signal analyzer 120 (shown in FIG. 2) calculates the width W of the correlation pulse generated by signal detector 116 and applies the function f (W) to the error amount of the TOA measurement.

Although several techniques exist that can measure the width of a correlation pulse, one example is described below. System 100 models the correlation pulse in quadratic fashion and uses three measurements to determine the coefficients of the quadratic equation. The three measured values are data points selected from the correlation pulses and include one of the data points having the maximum value and one of the maximum values. This is explained by the following equation (1).

v = [y (-1), y (0), y (1)] (1)

Where v is the maximum value of the correlation function y (k) and its surroundings. The quadratic function is represented as follows.

y (x) = ax ² + bx + c (2)

The quadratic equation is a conventional quadratic equation with coefficients a, b, c, where y is the magnitude of the correlation pulse and x is time (measured chip in this embodiment).

The values of the coefficients a, b and c can be calculated by using a linear equation and substituting different values into x in equation (2), as represented in equation (3).

(3)

(3)

Here, the value of y at each data point x = -1, 0, 1 is measured and the values of the coefficients a, b, c are determined using the matrix of equation (3). The pulse width W may be determined. Corresponding to the measurement, the system 100 calculates the width of the correlation pulse at a distance D from the peak value. This is illustrated by the following equation (4).

ax2 + bx + c = max * D (4)

Where max is the maximum pulse value and D is a predetermined percentage of the maximum value. In one embodiment, the pulse width measurement is performed on a value of D = 0.01. In other words, the correlation pulse width W is determined at a point at y = 0.01 * the maximum value. At the logarithmic scale, this corresponds to the pulse width at points below 20 decibels at the peak value. The value of -20 dB is chosen to produce the corresponding result. However, those skilled in the art understand that other values can be used satisfactorily with the system 100. The invention is not limited to the particular technique in which the correlation pulse width is measured.

The correlation pulse width W can be expressed by the following equation (5).

(5)

(5)

All terms are already defined here.

The system 100 implements the function f (W) in the form of a correlation data table 122 (shown in FIG. 2). The correlation data table 122 may be part of a standalone device or memory 104. The correlation data table 122 can be easily implemented using a convenient structure of data structure. Several data structures are known in the art and can be used. The particular form of the data structure is not critical to the implementation of the correlation data table 122. In general, the pulse width W is input to the data table 122 as a data value, and the delay error occurs as an output from the correlation data table 122.

In another embodiment, the function f (W) may be implemented using a mathematical function instead of using the correlation data table 122. The equation can be easily derived and the value of the pulse width W can be inserted therein as a variable. In this embodiment, the equation is stored in a data structure such as memory 104.

Based on the field measurements described above, it can be seen that after applying the calibration factor from the calibration data table 122 the number of measurements with errors of 100 meters or less increased by 10%. Thus, the system 100 may improve the accuracy of the positioning technique when multipath signals are present.

As previously described, the current CDMA standard for positioning and positioning (IS-801) provides position measurement performed by a PDE associated with a mobile unit or infrastructure (eg transmitter 14). In the latter implementation, the current CDMA standard (IS-801) does not provide for transmitting a value having a pulse width (W), for example, to a PDE associated with the transmitter 14 (see FIG. 1). Thus, in an embodiment, the system 100 subtracts the calibration value from the calculated TOA delay distance to provide compensation in the data sent back to the PDE. Using Table 1 above, where three transmitter PN offset numbers and distance measurements are determined, signal analyzer 120 uses a calibration factor (ie delay) for each measurement based on the pulse width W associated with each transmitter. Error). For example, the first correlation pulse presented in waveform B of FIG. 3 has a width of approximately 1.3 chips. This corresponds to an error of approximately 100 meters using the function f (W) shown in FIG. The signal analyzer 120 automatically subtracts 100 meters from the calculated distance value based on the uncalibrated arrival time. For example, PN 425 with a delay of 1500 meters is calibrated to 1400 meters, since the corresponding pulse width W is 1.3 chips. The signal analyzer 120 automatically adjusts each delay using the pulse width W as described above, and sends the corrected data to the PDE associated with the transmitter 14. Thus, the PDE receives data that has already been compensated for in terms of the effects of multipath transmissions.

In another embodiment, the mobile unit can be a PDE. In this case, signal analyzer 120 determines the distance between system 100 and the various transmitters (e.g. transmitters 12-16) by adjusting the delay in the manner described above and calculating the distance using known geometric calculations. do. In this embodiment, the system 100 must be provided with identification information and information relating to the location of the various transmitters that allow the PN codes to be associated with the correct transmitter. In another embodiment, the pulse width data is transmitted directly to the PDE associated with the transmitter 14, for example, to allow the PDE to perform compensation adjustments before calculating the position of the mobile unit. Thus, the system 100 is not limited by the location of the PDE or the data type provided to the PDE. For example, the PDE associated with the transmitter 14 may be provided with pulse width data or delay data with the effect of multipath signals already compensated for.

In yet another embodiment, other measures may be used to compensate for multipath signals. For example, it can be proved that the signal strength also has a functional relationship with the delay error. In this embodiment, signal analyzer 120 receives pilot strength indicators Ec / Io from signal detector 116. This pilot strength signal indicator is the pilot energy Ec per PN chip divided by the total power spectral density Io received by the receiver 110. 5 is a diagram for excess delay versus pilot signal strength. As can be seen in the chart of FIG. 5, lower pilot strength signals often indicate excess delays (ie errors). Thus, a function can be developed for the relationship of excess delay to pilot signal strength. Such data may be stored in the form of calibration data table 122 (see FIG. 2) and used in the manner previously described. Alternatively, mathematical functions may be stored in the system 100 and processed by the signal analyzer 120. In another embodiment, a combination of selection criteria can be used to determine the excess delay. For example, a combination of pulse width W and pilot strength indicator Ec / Io can be used to determine the excess delay.

The operation of system 100 is shown in the flowcharts of FIGS. 6 and 7. At start 200, system 100 is under power and may receive data from transmitters, such as transmitters 12-16. At decision 202, system 100 determines whether a first correlation pulse has been generated by signal detector 116. As is known and described above, signal detector 116 is part of an existing CDMA mobile unit that searches for transmitted PN codes. If the PN code is detected, the signal detector 116 generates a correlation pulse. If no pulse is detected, the result of decision 202 is NO and the system returns to decision 202 to wait for correlated pulse detection. If a first PN code is detected and a first correlation pulse occurs, the decision 202 result is YES, and at step 204, the system 204 records the PN number associated with the transmitter and sets the delay time to zero. do. At decision 206, the system 100 waits for detection of PN codes from additional transmitters. If no additional correlation pulses occur, the decision 206 result is NO and the system returns to position 206 waiting for the detection of the PN code from additional transmitters. If a PN code from additional transmitters (eg transmitters 14 and 16) is detected, signal detector 116 generates a correlation pulse and the decision 206 result is YES.

Each time a correlation pulse occurs, the system 100 records the PN number and the delay time at which the correlation pulse occurs in step 210. In step 212, the system 100 subtracts the delay due to the PN time slot delay. The remaining delay is only due to the propagation delay. As previously described, system 100 must detect the PN code from at least three different transmitters. This may be a combination of terrestrial transmitters (eg transmitter 12-16), or may include one or more GPS satellites (not shown). Thus, decision 206 and steps 210 and 212 will be repeated such that system 100 has three PN numbers and an associated delay time. In step 214, as shown in FIG. 7, the system 100 calculates the pulse width W of the correlation pulses generated by the signal detector 116. In step 216 the system 100 provides f (W) to correct the delay time. As previously described, system 100 can directly apply mathematical function f (W) to calculate the delay time. Alternatively, system 100 may use calibration data table 122 to reference calibration factors for delay time based on pulse width (W). Alternatively, steps 214 and 216 may be replaced with signal strength calculations such as Ec / Io from signal detector 116 to apply the Ec / Io function to correct the delay time. Other alternatives, such as RMS signal strength, or other criteria, may be used where there is a correlation between the selected criterion and the delay error caused by the multipath effects.

Whatever calibration method is used, the function is applied to the measured delay time to generate a calibrated delay time at step 216. In step 218, the system 100 determines the location of the transmitters for which the calibrated delay time was calculated. At step 220, the PDE calculates the position of the mobile unit 10 and ends at step 222 when the mobile unit position is determined. The increased accuracy of the positioning is due to the reduction of the effects of the multipath effects.

As mentioned above, the PDE may be implemented within the mobile unit itself if the mobile unit is provided with the exact positions of the various transmitters. Under current communication standards, this information is not provided to the mobile unit but to various base stations. If the PDE is associated with a base station (eg, transmitter 12), the mobile unit transmits the detected PN numbers and delay time to the PDE associated with transmitter 12. The delay time may include the measured delay time and calibration factors or may include only the corrected delay time. In another alternative embodiment, the system 100 transmits the measured pulse widths, for example to a PDE associated with the transmitter 12, to enable calculation of calibration factors within the PDE. The present invention is not limited to the position measurement where correction factors are calculated and applied to the measured delay time, nor is it limited to the position measurement of the PDE.

Thus, the system 100 provides a technique that allows for effective multipath errors to be reduced to allow more accurate positioning of the mobile unit 10. This increased accuracy is important for the positioning of the mobile unit when emergency services are required by the user.

Although the present invention has been described through various embodiments, the present invention is not limited to these embodiments, and various modifications are possible. Accordingly, the invention is limited only by the following claims.

Claims (28)

A system for correcting multipath errors in a telecommunications device, An antenna capable of detecting telecommunication signals and as a result generating the detected electrical signals; A receiver coupled to the antenna to receive the detected electrical signals; An energy detector for analyzing the received signals and generating a correlation pulse when the received signals match a stored reference signal; A timer for determining the arrival time of the correlation pulse; And And an analyzer for calculating a pulse width of the correlation pulse and generating a calibrated arrival time by applying a calibration factor to the arrival time based on the pulse width. The multipath error correction system of claim 1, wherein the analyzer converts the arrival time into a delay time, and the correction factor is a time delay correction factor applied to the delay time. The multipath error correction system of claim 1, wherein the analyzer converts the arrival time into a distance measurement value, and the correction factor is a distance delay correction factor applied to the distance measurement value. 2. The apparatus of claim 1, further comprising a data structure for storing data relating a plurality of pulse width values to a calibration factor, the analyzer providing a measured pulse width value as input to the data structure and measuring the measured pulse width value. Multipath error correction system for retrieving stored calibration factors in relation to 2. The method of claim 1, further comprising a data structure for storing a mathematical function relating a pulse width to a calibration factor, wherein the analyzer calculates the calibration factor using the pulse width and the mathematical function. system. 2. The multipath error correction system of claim 1, further comprising a positioning entity for determining the position of the receiver based on the calibrated time of arrival and a known position of a remote transmitter. The multipath error correction system of claim 1, wherein the analyzer models the correlation pulse as a quadratic equation with a plurality of coefficients, the coefficients determined by amplitude values of the correlation pulses at predetermined times. The multipath error correction system of claim 1, wherein the analyzer calculates a maximum amplitude of the correlation pulse and measures the pulse width at a predetermined level below the maximum amplitude. 2. The multipath error correction system of claim 1, wherein the receiver generates a signal strength indicator. The multipath error correction system of claim 1, wherein the receiver is part of a cellular telephone operating in the 800 MHz band, and the analyzer calculates the position data based on the arrival time of data transmitted from the remote transmitter in the 800 MHz band. 2. The multipath error correction of claim 1, wherein the receiver is part of a personal communication system telephone operating in the 1900 MHz band, and the analyzer calculates the position data based on the arrival time of data transmitted from the remote transmitter in the 1900 MHz band. system. The system of claim 1, wherein the remote transmitter is a satellite positioning system (GPS) satellite, the receiver receives the data signal from the GPS satellites, and the analyzer is based on the arrival time of data transmitted from the GPS satellites. Multipath error correction system for calculating position data. The multipath error correction system of claim 1, wherein the receiver is part of a code division multiple access (CDMA) telephone and the analyzer calculates the position data based on the arrival time of data transmitted in the 800 MHz band from a remote transmitter. . A system for correcting multipath errors in a telecommunication location system, A receiver for receiving data transmitted from a remote transmitter, wherein the remote transmitter is located at an unknown distance from the receiver; And An analyzer for analyzing the data associated with the received data and generating position data relating to the position of the receiver, the analyzer generating a calibrated position data by calculating calibration factors based on the measured signal criteria, The receiver generates a correlation pulse when the received data is correlated with a stored data pattern, the signal reference is a pulse width of the correlation pulse, The analyzer models the correlation pulse as a quadratic equation with multiple coefficients, the coefficients determined by amplitude values of the correlation pulses at predetermined times. 15. The system of claim 14, further comprising a positioning entity for determining the position of the receiver based on the calibrated position data and a known position of the remote transmitter. 15. The system of claim 14, wherein the position data is based on a time of arrival of data received by the receiver. 17. The multipath error correction system of claim 16, wherein said arrival time is calculated as a delay time and said correction factor is a time delay correction. 15. The multipath error correction system of claim 14, wherein the analyzer calculates the maximum amplitude of the correlation pulse and measures the pulse width at a predetermined level below the maximum amplitude. 15. The system of claim 14 wherein the receiver generates a signal strength indicator and the signal reference is the signal strength indicator. 15. The multipath error correction system of claim 14, wherein the receiver is part of a cellular telephone operating in the 800 MHz band, and the analyzer calculates the position data based on the arrival time of data transmitted from the remote transmitter in the 800 MHz band. . 15. The multipath error of claim 14, wherein the receiver is part of a personal communications system telephone operating in the 1900 MHz band and the analyzer calculates the position data based on the arrival time of data transmitted from the remote transmitter in the 1900 MHz band. Calibration system. 15. The system of claim 14, wherein the remote transmitter is a satellite positioning system (GPS) satellite, the receiver receives the data signal from the GPS satellites, and the analyzer is based on the arrival time of data transmitted from the GPS satellites. And a multipath error correction system for calculating the position data. 15. The multipath error correction of claim 14, wherein the receiver is part of a code division multiple access (CDMA) telephone and the analyzer calculates the position data based on the arrival time of data transmitted in the 800 MHz band from the remote transmitter. system. 15. The apparatus of claim 14, further comprising a data structure for storing data relating a signal reference to calibration factors, wherein the analyzer provides a measurement of the signal reference as input to the data structure and of the selected reference. Multipath error correction system for retrieving stored calibration factors in relation to measured values. 15. The apparatus of claim 14, further comprising a data structure for storing a mathematical function that associates a signal reference with calibration factors, wherein the analyzer calculates the calibration factor using the signal reference and the mathematical function. Calibration system. delete delete delete

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