CN1529948A - Systems and methods for detecting and compensating for radio signal time-of-arrival errors - Google Patents

Abstract

A system and method are disclosed by which the effects of time of arrival errors may be reduced. In a mobile unit, such as a CDMA device, a correlation pulse is generated when a transmitted code matches a stored reference code. In the absence of multipath effects, correlation pulses are generated in response to the detection of multiple transmissions of the reference code from multiple transmitters. However, multipath effects distort the generated correlation pulses leading to errors in the time of arrival measurements. The present invention calculates the width of the correlation pulses and determines a 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 permitting more accurate location measurements based on time of arrival. In alternative embodiments, other signal factors may also be used to apply delay correction factors. The actual location determination may be performed by the mobile unit, or any other positioning determining entity (PDE). The system is also capable of applying correction factors to time of arrival signals received from global positioning system (GPS) satellites.

Description

Systems and methods for detecting and compensating for radio signal time-of-arrival errors

Field of Invention

This invention relates generally to telecommunications, and more particularly to techniques for detecting and compensating for time-of-arrival errors in telecommunications systems.

Background of the Invention

Emergency services are usually requested with a phone number like "911". If the caller is in a fixed location, such as a residence, the computer system can use Automatic Number Identification (ANI) to track the telephone number of the incoming telephone call and quickly determine the address from which the call originated. As such, determining where to call for emergency services is a relatively simple task.

However, the location of a user who is requesting emergency services via mobile communications, such as cellular telephones, personal communication system (PCS) devices, etc., cannot be readily determined. Radio triangulation techniques have long been used to determine the location of mobile units. However, this radio triangulation technique is known to be inherently inaccurate. Usually the error is on the order of several kilometers. However, such inaccuracies are unacceptable for emergency service delivery.

The US Federal Communications Commission (FCC) has specified changes in communication technology that would allow greater accuracy in location determination. In the case of mobile communications, the FCC has produced a rule requiring infrastructure-based location systems to have an accuracy of 150 meters 67% of the time (and 300 meters 95% of the time). For systems requiring modified handsets, the FCC has specified that such systems must determine location within 50 meters 67% of the time (and within 150 meters 95% of the time).

Radio location systems use time-of-arrival (TOA) signals from various transmitters with known locations to triangulate and estimate the location of a mobile unit. However, due to multiple transmission paths, the time-of-arrival signal is usually distorted or erroneous. FIG. 1 illustrates an example of multiple transmission paths that a mobile phone within a vehicle 10 may experience. In the example depicted in FIG. 1, mobile unit 10 is receiving signals from transmitters 12 and 14 mounted on tower tops. In the example of FIG. 1, mobile unit 10 receives signals directly from transmitters 12 and 14, but also receives signals from transmitter 14 reflected from nearby buildings. Thus, mobile unit 10 receives many signals from transmitter 14 . In the example depicted in FIG. 1 , mobile unit 10 is not within line of sight (LOS) of transmitter 16 . That is, a building or other structure blocks the direct line of sight between the mobile unit 10 and the transmitter 16 . However, the mobile unit 10 still detects signals from the transmitter 16 that reflect off the building or other structure or diffract along the edges of the building or other structure. In addition, the mobile unit 10 receives signals from a transmitter 16 mounted on top of a building and possibly from a Global Positioning System (GPS) satellite in orbit around the earth. Thus, mobile unit 10 receives multiple signals from transmitter 16, none of which are direct LOS signals. Signals from GPS satellites 18 may also include LOS signals and transmit signals. As a result of such multipath signals, time-of-arrival measurements made by mobile units suffer from errors. In the presence of multipath signals, this error can be significant, making it difficult or impossible to achieve an FCC indication of position accuracy. Accordingly, it can be appreciated that a system and method to improve TOA measurements for mobile location systems is highly desirable. The present invention provides this and other advantages, which will become more apparent from the following detailed description and accompanying drawings.

Summary of Invention

The present invention is embodied in a system and method for correcting multipath errors in a telecommunications 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 data related to the received data and generates position data related to the position of the receiver. The analyzer also calculates correction factors based on the measured signal standards to produce corrected position data.

In one embodiment, the receiver generates a correlation pulse when correlating received data with stored data. In this embodiment, the signal criterion is the pulse width of the relevant pulse. The correlation pulses can be modeled as a quadratic equation, the coefficients of which are determined by the magnitude values of the correlation pulses at predetermined times. In another embodiment, the receiver generates a signal strength indicator. In this embodiment, the signal criterion is a signal strength indicator.

The system may also include a location determination entity that determines the location of the receiver based on the corrected location data and the known location of the remote transmitter. The location data may be based on the time of arrival of the data received by the receiver. Arrival time data may be calculated as delay time or distance, and correlation factors may be calculated as corrected time or corrected 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 time of arrival of data sent from a remote transmitter in the 800 MHz band. Alternatively, the receiver may be part of a personal communication system operating in the 1900 MHz band, and the analyzer calculates position data based on the time of arrival of data sent from a remote transmitter within the 1900 MHz band.

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

The system may also include a data structure to store data for associating selected signal standards with one or more correction factors, wherein the analyzer provides measurements on the selected data as input to the data structure, and retrieves The correction factor stored in association with the measurement for the selected standard. The system may alternatively include a data structure to store a mathematical function that relates the selected signal standard to one or more correction factors, wherein the analyzer uses the selected standard in the mathematical function to calculate the correction factor.

Brief description of attached drawings

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

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

FIG. 3 is a waveform diagram illustrating a correction signal generated by the system of FIG. 2 .

Figure 4 is a graph illustrating the correlation peak width as a function of distance error.

Figure 5 is a graph illustrating the functional relationship between power measurements and range error.

Figures 5 and 7 together form a flowchart illustrating the operation of the present invention.

Detailed description of the preferred embodiment

The present invention allows for a quantitative measurement of range error introduced by multipath signals and provides correction factors to apply to time-of-arrival measurements, allowing more accurate position determination. In the exemplary embodiment, the present invention is implemented using portions of a conventional Code Division Multiple Access (CDMA) mobile unit. A CDMA mobile unit may be referred to as a mobile unit, cellular telephone, PCS device, or the like. As will be discussed in more detail below, the present invention is not limited to a particular form of mobile communication device, nor to a particular frequency of operation of the mobile device.

The present invention is embodied in system 100 depicted in the functional block diagram of FIG. 2 . System 100 includes a central processing unit (CPU) 102, which controls the operation of the system. Those skilled in the art will understand that CPU 102 is intended to encompass any processing device capable of operating a telecommunications system. This includes microprocessors, embedded controllers, application-specific integrated circuits (ASICs), digital signal processors (DSPs), state machines, application-specific discrete hardware, and more. The invention is not limited to the particular hardware components chosen to implement CPU 102.

The system also preferably includes memory 104, which may include both read only memory (ROM) and random access memory (RAM). Memory 104 provides instructions and data to CPU 102. A portion of memory 104 may also include non-volatile random access memory (NVRAM).

System 100 is typically contained within a wireless communication device such as a cellular telephone. System 100 also includes housing 106 that contains transmitter 108 and receiver 106 to allow transmission and reception of data between system 100 and a remote location, such as Cellular location controller (not shown), data such as audio communication. Transmitter 108 and receiver 110 may be combined into transceiver 112 . Antenna 114 is attached to housing 106 and is electrically coupled to transceiver 112 . The operation of transmitter 108, receiver 110 and antenna 114 is known in the art and need not be described here unless it is specifically related to the present invention.

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

The signal detector 116 performs correlation analysis between the reference signal and the received signal, and generates a correlation output signal. Signal analyzer 120 analyzes the correlation signal and uses correction data table 122 to generate distance correction data. In one embodiment, the correction datagram 122 includes data relating the relative pulse width to the range error. However, other criteria may also be used to correct for distance errors.

System 100 includes timer 124 to provide system timing used to measure delay times within the arrival of signals from various sources (eg, transmitters 12-16). Timer 124 may be a separate device or part of CPU 102 .

Various components of the system 100 are coupled together through a bus system 126, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. However, for simplicity, the individual buses are illustrated in FIG. 2 as bus system 126 . Those skilled in the art will appreciate that the system 100 depicted 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 illustrated as two separate blocks within system 100, they may actually be contained within one physical component, such as a digital signal processor (DSP). They may also reside in memory 104 as program code, such as the code executed by CPU 102. The same considerations apply to other components listed in system 100 of FIG. 2 , such as timer 124 .

The operation of the components shown within the system 100 of FIG. 2 will now be described with reference to FIGS. 3-7. FIG. 3 is a series of waveform timing diagrams illustrating examples of associated pulses generated by signal detector 116 . In order to assist in a proper understanding of the present invention, a brief description of time-of-arrival processing using a CDMA mobile unit will now be given by way of example. A mobile unit implementing system 100 of FIG. 2 (eg, mobile unit 10 in FIG. 1) is initially assigned a pseudonoise (PN) code. The PN code may be stored in memory 104 as a local reference. When a base station (eg, transmitter 12) transmits data to mobile unit 10, the base station transmits the PN code. System 100 continuously searches for correlations between local references (ie, stored PN codes) and transmitted data (ie, transmitted PN codes).

As is 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 an accurately known offset. displacement. Time offsets are measured in multiples of 64 chips. The PN offsets are selectively assigned to transmitters such that the offsets are as spread as possible within a geographic area to avoid inter-transmitter interference. Transmitters (eg, transmitters 12-16) may be identified by transmitted identification data, but are sometimes tagged with their PN offset times. For example, transmitter 12 may be identified as PN 300 to indicate that it transmits a PN code at an offset of 300. In this example, transmitters 14 and 16 may be identified as PN 425 and PN 610, respectively, to indicate the offset times at which the respective PN codes are transmitted. It should be understood, however, that regardless of how the transmitters are marked, the relative bias of each transmitter relative to the other transmitters can be established from information encoded within the signal. Receiver 110 (see FIG. 2) within mobile unit 10 detects the PN from each transmitter (eg, transmitters 12-16) within the geographic area.

If the mobile unit 10 is co-located with the transmitter 12, there should be no delay in the transmission time between the transmitter and the system 100. In this way, the signal detector 116 (see FIG. 2) will immediately detect the correlation between the stored reference and the transmitted data. However, assuming the mobile unit 10 is some distance away from the transmitter 12, there will be a delay in detecting this correlation due to propagation delays. Signal detector 116 shifts the stored reference by half a chip at a time until whenever a correlation is detected between the stored reference and the transmitted data. As understood by those skilled in the art, a "chip" is a single piece of data within a PN sequence. Since data is sent at a known rate, chips can be used as a measure of time. Although this description may be characterized in terms of actual units of time, it is more convenient to refer to chip times because system 100 performs its analysis and measurements in chip times.

Since the propagation speed of radio signals is known, delay measurements can also be calculated as distances. In this way, the measurements of delay time, distance and chips are all interchangeable.

If the propagation delay between transmitter 12 and mobile unit 10 is known, only two signals are required to determine the exact location of the mobile unit. For example, it is possible to draw a circle whose radius corresponds to the propagation delay (in meters) around the transmitter 12 . The mobile unit 10 must be located somewhere on the circumference of this circle. The second detected PN code will be detected from the transmitter 14 which transmits the PN code at PN slot 425 . The delay time to the generation of the correlated pulse from the second transmitter (ie, transmitter 14) would allow the second propagation delay time to be measured. The radius of the circumference around the transmitter 14 corresponds to the second propagation delay, which indicates that the mobile unit 10 must be located somewhere on the circumference. Based on two known propagation delays, the mobile unit 10 must be located at the junction of the two circles.

However, the propagation delay between transmitter 12 and mobile unit 10 is unknown. Thus, system 100 arbitrarily assigns an arbitrary reference of zero delay to the first received PN code. In this way, the first received signal is not directly included in the position measurement. The reception of signals from two subsequent transmitters (e.g., transmitters 14 and 16) are delayed relative to transmitter 12, which is the result of PN offset and propagation due to the distance between mobile unit 10 and transmitters 14 and 16, respectively. Delayed results. Delays in correlation pulse generation due to PN offsets in PN code transmission can be easily determined and appropriately compensated for in timing. However, the time-of-arrival difference between PN code transmission and associated pulse generation is due to propagation delays, and thus due to the distance between mobile unit 10 and corresponding transmitters (eg, transmitters 14 and 16). The location of mobile unit 10 can be determined from the accurate TOA of the signals from transmitters 14 and 16 . Thus, system 100 requires receiving PN codes from three different transmitters. The first correlation pulse is used as a zero reference, while the excess delay times associated with the remaining two transmitters (eg, transmitters 14 and 16) are used to provide an appropriate delay measurement.

Waveform (A) of FIG. 3 shows the sampled correlation output generated by signal detector 116 (see FIG. 2 ) in the absence of any multipath signal. The signal detector 116 shifts the reference data (ie, the stored PN) half a chip at a time until a correlation between the reference data and the received data is detected. The correlation pulse due to the PN code from transmitter 12 is not shown because it is used as an arbitrary zero reference. Delays introduced by the PN biasing of transmitters 14 and 16 are also eliminated so that the waveforms of FIG. 3 show only the effects of propagation delays. In the example depicted by waveform (A), the correlation pulse due to transmitter 14 occurs 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 . In this way, the time of arrival can be determined from the delay measured in chips (or meters if desired).

The data sent from transmitter 14 also includes identification data so that mobile unit 10 implementing system 100 can identify transmitter 14 as the source of the signal of interest detected at 1.5 chips. Mobile unit 10 implementing system 100 receives data from transmitter 16 in addition to transmitter 14 . The signal detector 116 detects the correlation between the local reference (ie, the stored PN code) and the transmitted data from the transmitter 16 . In the example depicted by waveform (A), the correlated signal due to the PN code from transmitter 16 is detected approximately 4.5 chips away from the null reference. The 4.5 chip delay is related to the difference between the distance from transmitter 16 to mobile unit 10 and the distance from transmitter 12 to mobile unit 10 . This can be understood by the example described below in Figure 3c. The signal generated by transmitter 12 is delayed by 400 chips relative to the signal generated by transmitter 14 . From the time the signal transmitted by the transmitter 12 is generated to the time the signal is received by the mobile unit 10, there is a delay of 15 chips. Likewise, there is a delay of 5 chips from the time transmitter 14 generates a signal to the time the signal is received by mobile unit 10 due to the propagation delay between transmitter 14 and mobile unit 10 . Thus, between the reception of the signal generated at transmitter 12 and the reception of the signal generated at transmitter 14, the delay observed at mobile unit 10 would be a total of 410 chips. The 410 chips is the difference between the 415 chip delay from the moment the signal was generated at transmitter 12 and the 5 chip delay of receipt of the signal generated at transmitter 14 . As noted above, the data sent from transmitter 16 also includes identification data so that mobile unit 10 implementing system 100 can identify transmitter 12 as the source of the correlation peak detected at 4.5 chips.

Additionally, mobile unit 10 implementing system 100 may detect pulses from additional base station transmitters (not shown), or from satellites using Global Positioning System (GPS) signals. To determine the location of the mobile unit 10, GPS also uses time-of-arrival data, as is known in the art. In an exemplary embodiment, mobile unit 10 determines time-of-arrival data from three or more different transmitters. As mentioned above, the first correlation pulse is used as a zero reference, and the relative delay times of the other correlation pulses are used to determine the position of the mobile unit 10 based on the arrival times of the other correlation pulses. In the absence of any multipath effects, the pulses depicted in waveform (A) provide relatively accurate time-of-arrival measurements and can therefore be used to accurately determine the location of mobile unit 10 .

Under current telecommunications standards, such as IS-801, which is a CDMA standard for position location, mobile unit 10 may be able to perform calculations using the TOA data to determine its location. However, the location of the mobile unit 10 may also be determined using part of the fixed infrastructure. In this embodiment, the mobile unit sends the identification data and delay measurement data to a remote location, such as transmitter 14 . A Position Decision Entity (PDE) associated with the transmitters 14 performs calculations and calculates the position of the mobile unit 10 from the known positions of the various transmitters and the delay data measured from each transmitter. Table 1 below illustrates the sampled data sent from the mobile unit 10 to the PDE associated with the transmitter 14: PN bias Latency (in meters) 300 0 425 1500 610 450

Table 1

As is known in the art, and discussed briefly above, the PN value for each transmitter (eg, transmitters 12-16) refers to the PN offset at which each transmitter begins transmitting the PN code. In the example described in Table 1, the excess delay (ie, the delay not attributable to PN bias) is calculated in units of chips and converted to a delay in meters. For waveform (A) of FIG. 3, two correlation pulses from transmitters (eg, transmitters 14 and 16) generate correlation pulses at 1.5 and 4.5 chips, respectively. The data in Table 1 includes the PN offset associated with each transmitter and the relative excess delay time based on the delay of the pulse arrival time.

The PDE uses the identification codes to determine which transmitters are associated with each excess delay time. Since the locations of the transmitters are all known, determining the location of the mobile unit 10 from the delays from each respective transmitter is a relatively simple calculation. This calculation process is known in the art and need not be described here.

Unfortunately, multipath effects exist in almost all TOA measurements. Although satellite signals using GPS location technology tend to have fewer multipath effects, these effects still exist. Multipath effects from GPS satellites (eg, GPS satellite 18) are particularly prevalent in urban areas where buildings and other man-made structures interfere with GPS signals. Terrestrial systems, such as transmitters 12-16 (see FIG. 1), are also affected by man-made structures, causing signals to be refracted and/or reflected. Thus, mobile unit 10 receives multiple images of the same signal. System 100 is capable of estimating errors resulting from multipath effects. These multipath effects may be referred to as "short multipath effects" because multiple signals are typically only delayed by a small amount of time and can arrive at the antenna 114 (see FIG. 2 ) of the system 100 such that the corresponding arrival times are so close that produce distinct peaks in the overall correlation function. That is, the signal arrives within such a short period of time that the output of signal detector 116 is a single distorted pulse arising from the overlapping effects of multiple detected signals.

In the example previously discussed with respect to waveform (A) of FIG. 3, mobile unit 10 received a single signal from transmitter 14 and transmitter 16, without multipath signals. The effect of multiple signals is illustrated in waveform (B) of FIG. 3, where signal detector 116 shows a correlation value with a much wider pulse width as a result of multiple receptions of the same signal within a short period of time. As shown in waveform (A), the signal detector 116 produces a wide pulse rather than a relatively narrow pulse at 1.5 chips, making it difficult to accurately determine the time of arrival because the system is designed to detect peak signals. In waveform (B), the signal peaks between 1.5-2.5 chips. Similarly, the correlation values generated from the signal received from transmitter 16 are also illustrated in waveform (B) of FIG. 3 . Also, multipath effects cause the pulse to broaden such that the peak is between 4.5-5.5 chips.

It should be noted that the effects described in waveforms (A) and (B) of FIG. 3 are illustrative only. Multipath effects may cause signals to arrive out of phase at antenna 114 (see FIG. 2 ), causing signal detector 116 to produce multiple peaks associated with a single signal. The present invention provides at least partial compensation for errors resulting from multipath effects. The compensation system described herein is not limited to the waveform shape or excess delay time described in FIG. 3 .

It has been determined that there is a functional relationship between the width (W) of the associated pulse produced by the signal detector 116 and the amount of error in the time-of-arrival measurement. That is, the width of the correlation pulse produced by the signal detector 116 may be a function of the amount of error in the time-of-arrival signal due to multipath effects. The functional relationship between the pulse width W and the delay error can be characterized by the function f(W). Figure 4 illustrates the function f(W) based on field experiments in which the actual measured distances are compared with those calculated by conventional time-of-arrival techniques. It should be noted that the aliasing of the curves for pulse widths greater than 2 chips may be the result of relatively few samples of width greater than 2. However, the graph of Figure 4 clearly shows the relationship between pulse width and delay error.

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

Although there are many different techniques for measuring the width of the pulse of interest, an example is described here. System 100 models the correlated pulse as a quadratic equation and uses the three measurements to determine the coefficients of the quadratic equation. These three measurements are data points selected from the relevant pulses and include the data point with the maximum value as well as data points either side of the maximum value. This is illustrated in equation (1) below:

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

where v is the maximum value of the correlation function (y(k)) and its two neighbors. The quadratic equation is given as follows:

y(x)=ax ² +bx+c (2)

It is a regular quadratic equation with coefficients a, b, and c, y is the amplitude of the associated pulse, and x is the time (measured in chips in this case).

The values of systems a, b and c can be calculated using linear equations and substituting different values of x into equation (2), as shown in equation (3) below:

${<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \&rsqb;</span>}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\left[\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 1</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; V</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

where the value of y is measured at each of the data points x=-1, 0, 1, and the matrix of equation (3) is used to determine the values of the coefficients a, b and c. The pulse width W can now be determined. For measurement consistency, the system 100 calculates the width of the correlated pulse at a distance D from the peak. This is expressed in equation (4) below:

ax ² +bx+c=max*D (4)

where max is the maximum value of the pulse and D is a predetermined percentage of the maximum value. In one embodiment, the pulse width measurement is performed for a value of D = 0.01. That is, the relevant pulse width W is determined at the point where y=0.01 times the maximum value. On a logarithmic scale, this corresponds to the pulse width at a point 20 decibels (dB) below the peak (ie, -20dB). Choose a value of -20dB to produce consistent results. However, those skilled in the art will recognize that other values may be satisfactorily used for system 200 . The present invention is not limited by the particular technique with which the relevant pulse width can be measured.

The relevant pulse width W can be expressed by the following equation (5):

$\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; =</span>\frac{\sqrt{{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; D.</span>}<span\; class="notranslate">\; )</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

where all items are defined previously.

The system 100 implements the function f(W) in the form of a calibration data table 122 (see FIG. 2). Correction data table 122 may be a separate device or part of memory 104 . The correction data table 122 can be implemented in any convenient form of data structure. Many data structures are known in the art and can be used satisfactorily. The particular form of the data structure is not critical to the satisfactory implementation of correction data table 122 . In general, the pulse width W is input into the correction data table 122 as a data value, and the delay error is generated as an output from the correction data table 122 .

In other implementations, the function f(W) may be implemented as a mathematical function instead of the correction data table 122 . A mathematical equation can be easily derived and the value W of the pulse width inserted there as a variable. In this embodiment, the mathematical equations are stored in a data structure, such as memory 104 .

From the field measurements discussed above, it has been found that after applying the correction factor from the correction data table 122, the number of measurements with an error below 100 meters increases by 10%. Thus, the system 100 does improve the accuracy of positioning techniques in the presence of multipath signals.

As mentioned above, the current CDMA standard for position location, IS-801, provides position measurements, either performed by the mobile unit, or by a PDE associated with the infrastructure (eg, transmitter 14). In the latter implementation, current CDMA standards (ie, IS-801) include no provision for the value W of the pulse width to be provided to the PDE associated with the transmitter 14 (see FIG. 1). Thus, in an exemplary embodiment, the system 100 subtracts the correlation value from the calculated TOA delay distance to provide compensation in the data sent back to the PDE. Using the example of Table 1 above, where 3 transmitter PN offset numbers and distance measurements were determined, signal analyzer 120 calculates a correlation factor for each measurement (i.e., delay error ). For example, the width of the first correlation pulse shown in waveform (B) of FIG. 3 is about 1.5 chips. By using the function f(W) described in FIG. 4, this can correspond to an error of about 100 meters. The signal analyzer 120 automatically subtracts 100 meters from the distance value calculated from the uncorrected time of arrival. For example, a PN 425 with a delay of 1500 meters would be corrected to 1400 meters due to the corresponding pulse width W of 1.3 chips. As described above, the signal analyzer 120 automatically adjusts each delay with the pulse width W and sends the corrected data to the PDE associated with the transmitter 14 . In this way, the PDE receives data that has been compensated to compensate for the effects of multipath transmission.

In another embodiment, the mobile unit itself may be a PDE. In this event, signal analyzer 120 automatically adjusts the delays in the manner described above, and calculates these distances using known geometric calculations to determine the distances between system 100 and the various transmitters (eg, transmitters 12-16). In this embodiment, the system 100 must be provided with information regarding the location of the previous transmitter, as well as identification data, to allow the PN code to be associated with the correct transmitter. In yet another embodiment, the pulse width data may be sent directly to, for example, a PDE associated with transmitter 14, thereby allowing the PDE to perform compensation adjustments prior to calculating the position of the mobile unit. Thus, system 100 is not limited by the location of the PDE or the type of data provided to the PDE. For example, the PDE associated with transmitter 14 may be provided with pulse width data, or with delay data that has been compensated for the effects of multipath signals.

In yet alternative embodiments, other measurements may be used to compensate for multipath effects. For example, it can be shown that signal strength is also a function of delay error. In this embodiment, signal analyzer 120 receives a pilot strength indicator (E _c /I _o ) from signal detector 116 . The pilot strength signal indicator is a measure of the pilot energy per PN chip (E _c ) divided by the total power spectral density (I _o ) received by the receiver 110 . Figure 5 is a graph of excess delay versus pilot signal strength. It can be noted from the flowchart of FIG. 5 that lower pilot strength signals sometimes indicate excessive delay (ie, error). Thus, a function can be formed relating the excess delay to the pilot signal strength. This data may be stored in the form of correction data table 122 (see FIG. 2) and used in the manner described above. Alternatively, the mathematical functions may be stored within the system 100 and processed by the signal analyzer 120 . In yet another embodiment, a combination of selection criteria may be used to determine excess delay. For example, a combination of pulse width W and pilot strength (E _c /I _o ) can be used to determine excess delay.

The operation of system 100 is illustrated in the flowcharts of FIGS. 6 and 7 . Beginning 200, the system 100 is operational and capable of receiving data from a transmitter (eg, transmitters 12-16). In decision 202 , system 100 determines whether the first correlation pulse was generated by signal detector 116 . As is known in the art, and briefly described above, the signal detector 116 is part of a conventional CDMA mobile unit and searches the transmitted PN code. When a PN code is detected, signal detector 116 generates an associated pulse. If a pulse is not detected, the result of decision 202 is "No" and the system returns to decision 202 to wait for the relevant pulse to be detected. When the first PN code is detected and the first correlation pulse is generated, the result of decision 202 is "Yes", and in step 204 the system records the PN number associated with the transmitter and sets the delay time to zero. In decision 206, system 100 waits to detect PN codes from other transmitters. If no other correlation pulses are generated, the result of decision 206 is "No" and the system returns to position 206 waiting to detect PN codes from other transmitters. When PN codes from other transmitters (eg, transmitters 14 and 16) are detected, signal detector 116 generates a correlation pulse, and the result of decision 206 is "Yes".

Each time a correlation pulse is generated, the system 100 records the PN number and the delay time for generating the correlation pulse in step 210 . In step 212, the system 100 subtracts the delay due to the PN slot delay. The remaining delay is attributable only to propagation delay. As previously stated, system 100 must detect PN codes from at least three different transmitters. This may be a combination of terrestrial transmitters (eg, transmitters 12-16) or may include one or more GPS satellites (not shown). Therefore, decision 206 and steps 210 and 212 will be repeated so that system 100 has three PN numbers and associated delay times. As shown in FIG. 7 , in step 214 the system 100 calculates the pulse width W of the associated pulse generated by the signal detector 116 . In step 216, the system 100 applies f(W) to correct the delay time. As previously mentioned, the system 100 may directly apply a mathematical f(W) to calculate the delay time. Alternatively, the system 100 may use the correction data table 122 to look up a correction factor for the delay time based on the pulse width W. Alternatively, steps 214 and 216 can be replaced with a calculation of signal strength, such as ( _Ec / _Io ) from the signal detector 116, and a function f of ( _Ec / _Io ) applied to correct the delay time. Other metrics, such as RMS signal strength, or other criteria may also be used if the chosen criterion correlates with delay time errors caused by multipath effects.

Regardless of which correction method is chosen, in step 216 a function is applied to the measured delay times to produce corrected delay times. In step 218, the system 100 determines the location of the transmitter for which the corrected delay time has been calculated. In step 220, the PDE calculates the location of the mobile unit 10 and ends the process at 222, where the location of the mobile unit has been determined. The increased accuracy of location decisions is due to the reduction of the negative effects of multipath effects.

As previously mentioned, PDE can be implemented within the mobile unit itself, given the exact location of the individual transmitters of the mobile unit. Under current telecommunication standards, this information is not provided to mobile units, but to individual base stations. The mobile unit sends the detected PN number and delay time to the PDE associated with the transmitter 12 if the PDE is associated with the base station (eg, transmitter 12). The delay time may include the measured delay time and a correction factor, or may include only the corrected delay time. In yet another embodiment, system 100 may send the measured pulse width to a PDE associated with, for example, transmitter 12 to allow calculation of correction factors within the PDE. The present invention is not limited by where the correction factor is calculated and applied to the measured delay times, nor by the location of the PDE.

Thus, system 100 provides a technique by which effective multipath errors can be eliminated, thereby enabling a more accurate determination of the location of mobile unit 10 . This increased accuracy can be critical in locating the mobile unit should the user call for emergency services.

It should be understood that, even though various embodiments and advantages of the invention have been presented in the above description, that the above disclosure is illustrative only and that changes may be made in detail which are within the broad principles of the invention. Accordingly, the invention is limited only by the appended claims.

Claims (28)

1. system that is used for proofreading and correct multipath error at telecommunication apparatus, described system comprises:

Antenna can detect telecommunication signal and produce the signal of telecommunication that is detected as its result;

Receiver with the antenna coupling is used to receive the signal of telecommunication that is detected;

Energy detector is used to analyze the signal that receives and produces a coherent pulse when the signal that receives mates with the reference signal of being stored;

Timer is used for determining time of advent of coherent pulse;

Analyzer, be used to calculate the pulse duration of coherent pulse and according to pulse duration to using a correction factor time of advent, to produce the calibrated time of advent.

2. the system as claimed in claim 1 is characterized in that, described analyzer is converting time of delay the time of advent to, and correction factor is the time delay correction factor that is applied to time of delay.

3. the system as claimed in claim 1 is characterized in that, described analyzer is converting range measurement the time of advent to, and correction factor is the range delay correction factor that is applied to range measurement.

4. the system as claimed in claim 1, it is characterized in that also comprising a data structure, be used to store the data that a plurality of pulse width values are associated with correction factor, wherein analyzer provides a pulse width values that records, as to the input of data structure, and search the correction factor of the storage relevant with the pulse width values that records.

5. the system as claimed in claim 1 is characterized in that also comprising a data structure, is used to store the mathematical function that the pulse width is associated with correction factor, and wherein analyzer uses pulse duration and mathematical function to come the calculation correction factor.

6. system that is used for proofreading and correct multipath error in the telecommunication apparatus navigation system, described system comprises:

Receiver is used to receive from being positioned at the data that the distance transmitter that leaves the receiver unknown distance sends; And

Analyzer is used to analyze the data relevant with receiving data, and is used to produce the position data relevant with receiver location, and described analyzer also comes the calculation correction factor according to the signal standards that records, to produce calibrated position data.

7. system as claimed in claim 6 is characterized in that also comprising a location judgement entity, and it is used for determining according to the known location of calibrated position data and distance transmitter the position of receiver.

8. system as claimed in claim 6 is characterized in that described position data is based on the time of advent of the received data of receiver.

9. system as claimed in claim 8 is characterized in that be calculated as time of delay the described time of advent, and correction factor is that time delay is proofreaied and correct.

10. system as claimed in claim 6 is characterized in that, when the data that receive were relevant with the data pattern of being stored, described receiver produced a coherent pulse, and described signal standards is the pulse duration of coherent pulse.

11. system as claimed in claim 10 is characterized in that, described signal analyzer is modeled as the quadratic equation with a plurality of coefficients to coherent pulse, and described coefficient is determined by the range value of the coherent pulse of locating at the fixed time.

12. system as claimed in claim 10 is characterized in that, described signal analyzer calculates the amplitude peak of coherent pulse, and measures pulse duration being lower than under the predetermined level of amplitude peak.

13. system as claimed in claim 6 is characterized in that, described receiver produces a signal strength indicator, and described signal standards is a signal strength indicator.

14. system as claimed in claim 6 is characterized in that, described receiver is a cellular part that is operated in the 800MHz frequency band, and described analyzer is according to the calculating location data time of advent of the data of the transmission of the distance transmitter in the 800MHz frequency band.

15. system as claimed in claim 6, it is characterized in that, described receiver is a part that is operated in the PCS Personal Communications System phone of 1900MHz frequency band, and described analyzer is according to the calculating location data time of advent of the data of the transmission of the distance transmitter in the 1900MHz frequency band.

16. system as claimed in claim 6, it is characterized in that, described distance transmitter is global positioning system (GPS) satellite, and described receiver receives data-signal from gps satellite, and described analyzer is according to the calculating location data time of advent of the data that send from gps satellite.

17. system as claimed in claim 6 is characterized in that, described receiver is the part of code division multiple access (CDMA) phone, and described analyzer is according to the calculating location data time of advent of the data of the transmission of the distance transmitter in the 800MHz frequency band.

18. system as claimed in claim 6, it is characterized in that also comprising a data structure, be used to store the data that signal standards is associated with correction factor, wherein analyzer provides the measurement of selected standard, as the input of data structure, and search the correction factor stored relevant with the measurement of selected standard.

19. system as claimed in claim 6 is characterized in that also comprising a data structure, is used to store the mathematical function that signal standards is associated with correction factor, wherein analyzer comes the calculation correction factor with selected standard and mathematical function.

20. a method that is used for proofreading and correct in the telecommunication apparatus navigation system multipath error, described method comprises:

Use receiver, be used to receive from being positioned at the data that the distance transmitter that leaves the receiver unknown distance sends;

Analyze the data relevant with the data that receive, and the generation position data relevant with the position of receiver; And

Come the calculation correction factor to produce calibrated position data according to the signal standards that records.

21. method as claimed in claim 20 is characterized in that also comprising: the position of calculating receiver according to the known location of calibrated position data and distance transmitter.

22. method as claimed in claim 20 is characterized in that, described position data is based on the time of advent of the data that receive.

23. method as claimed in claim 20 is characterized in that also comprising: when the data that receive are relevant with the data pattern of being stored, produce a coherent pulse, described signal standards is the pulse duration of coherent pulse.

24. method as claimed in claim 20 is characterized in that also comprising: calculate the maximum of coherent pulse, and measure pulse duration with the predetermined level that is lower than amplitude peak.

25. method as claimed in claim 20 is characterized in that also comprising: produce a signal strength indicator, described signal standards is a signal strength indicator.

26. method as claimed in claim 20, it is characterized in that, described distance transmitter is a global positioning system (GPS) satellite, and described receiver receives data-signal from gps satellite, and the calculating of described position data is based on the time of advent of the data of sending from gps satellite.

27. method as claimed in claim 20 is characterized in that also comprising: storage in advance is associated signal standards with correction factor data, wherein the calculation correction factor comprises: search the correction factor stored relevant with selected standard.

28. method as claimed in claim 20 is characterized in that also comprising: storage is associated signal standards with correction factor mathematical function, wherein selected standard and mathematical function have been used in the calculating of correction factor.

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