RU2357267C2 - Method of positioning remote device - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: invention relates to a method of positioning a remote device using the global satellite system for positioning - GPS. In the method the mobile device receives Doppler information from the satellite, situated in its the field of vision. Information is received from the base station of the cellular communication system.

EFFECT: positional information is computed in the mobile device using Doppler information.

30 cl, 11 dwg

Description

FIELD OF THE INVENTION

The present invention relates to receivers that provide satellite positioning information, and more particularly to receivers that find application in the global satellite positioning system (GPS), and also to methods for determining the location of a remote device.

State of the art

GPS receivers allow you to accurately determine your location by calculating the relative arrival times of signals transmitted simultaneously from multiple satellites of the GPS system (or NAVSTAR). These satellites transmit satellite position data as part of their message, as well as clock data of the so-called “ephemeris” data. The process of finding and detecting GPS signals, reading ephemeris data for multiple satellites and calculating the location of the receiver from these data takes up to several minutes. In most cases, this rather large processing time is unacceptable, and, in addition, a significant drawback when using microminiature portable devices is the limited battery life.

Another disadvantage of modern GPS signal receivers is that their operation is limited by situations in which multiple satellites are located directly in the field of view, that is, in the absence of obstacles, and when a good-quality antenna is properly oriented to receive such signals. As such, they are usually not used in portable, handheld versions, in places where there are obstacles in the form of foliage or buildings, and when used inside buildings.

There are two main functions of GPS signal receiving systems: (1) calculating pseudoranges to various GPS satellites and (2) calculating the location of the carrier of the receiving system using these pseudoranges, synchronization data for satellites, and ephemeris data. Pseudoranges are measured time delays between a received signal from each satellite and a local clock signal. Satellite ephemeris and synchronization data are obtained from a GPS signal that is detected and tracked. As stated above, obtaining this information usually takes a relatively long period of time (from 30 s to several minutes) and should be carried out at a sufficient level of the received signal to achieve low values of the error repetition rate.

In fact, all known GPS receivers use correlation methods for determining pseudorange. These correlation methods are implemented in real time, often using hardware correlators. GPS signals include high repetition signals, called pseudo-random (PS) sequences. The codes used for civilian use are called C / A codes and have a frequency of binary phase values or a frequency of repetition of code elements of 1.023 MHz and a repetition period of 1023 code elements for a period of 1 ms. Code sequences are part of the family of "golden codes". Each GPS satellite broadcasts a signal with a unique gold code.

The received signal from the GPS satellite is downconverted to the main frequency band, after which the correlation receiver multiplies the received signal by a saved copy of the corresponding code that is contained in its local memory, and then integrates the product (or performs low-pass filtering) to indicate the presence of the signal . This processing procedure is defined as correlation processing. By subsequently adjusting the relative synchronization of this stored copy with respect to the received signal and analyzing the result of the correlation processing, the receiver can determine the time delay between the received signal and the local clock signal. The initial determination of the presence of such an output signal is called "detection". Immediately after detection, the process goes into the “tracking” phase, in which the synchronization of the local reference signal is adjusted in small increments to maintain the output signal with a high degree of correlation. The correlation output signal at the tracking stage can be considered as a GPS system signal from which the pseudo-random code is removed, or, according to generally accepted terminology, as a "compressed" signal. This signal has a narrow frequency band, comparable with the data signal with binary phase shift keying at a speed of 50 bit / s, which is superimposed on the GPS system signal.

The procedure for determining correlation requires a considerable time, especially if the received signal is weak. To reduce the detection time in most GPS signal receivers, many correlators are used (usually up to 12), which allow a parallel search for correlation maxima.

Some well-known GPS receivers use the Fast Fourier Transform (FFT) method to determine the Doppler frequency of the received GPS signal. These receivers use well-known correlation processing operations to compress the GPS signal and produce a narrowband signal with a bandwidth in the range from 10 kHz to 30 kHz. The resulting narrowband signal is then subjected to Fourier analysis using FFT algorithms to determine the carrier frequency. The determination of such a carrier frequency simultaneously provides an indication that the local MS reference signal is tuned to the correct phase value of the received signal and provides an accurate measurement of the carrier frequency. This frequency can then be used in receivers in tracking mode.

US Pat. No. 5,420,592 describes the use of FFT algorithms for calculating pseudorange at a central processing point, rather than a mobile device. According to this method, instant data sampling is performed by a GPS signal receiver and then transmitted via a data channel to a remote receiver, in which FFT processing is performed. However, this known method calculates only one direct and inverse fast Fourier transform (corresponding to four periods of the PS sequence) to perform many correlation determination operations.

As will be clear from the description of the present invention, higher sensitivity and higher processing speed can be achieved by performing a large number of FFT operations together with special operations of preliminary (pre-processor) and subsequent (post-processor) processing.

In the present description, the terms “correlation”, “convolution” and “matched filtering” are used. The term "correlation", used for two sequences of numbers, means the term-by-time multiplication of the corresponding elements of two sequences with the subsequent summation of the sequences. Such a procedure is sometimes called "sequential correlation" and results in an output signal that is a single number. In some cases, a series of correlation operations are performed on consecutive data groups.

The term “convolution”, which is used for two sequences of numbers, means a processing method widely used in the art that is equivalent to filtering a second sequence of length m using a filter that corresponds to the first sequence having an impulse response of length n. The result is a third sequence of length m + n-1. The term “matched filtering” refers to convolution or filtering, the aforementioned filter having an impulse response corresponding to the complex conjugate of the time-reversed first sequence. The term "fast convolution" is used to indicate a sequence of algorithms for calculating the convolution operation in an efficient way.

Sometimes the terms “correlation” and “convolution” are used interchangeably. For clarity, however, in the present description, the term “correlation” always refers to the sequential correlation operation, which is described above.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a method for determining the location of a remote device, the method comprising receiving Doppler information of a satellite in view of a remote device in a remote device from a cellular transmission cell in a cellular communication system, and calculating location information for a satellite in a remote device using Doppler information, without receiving and without using satellite ephemeris information. In addition, other features of the method are described.

Another embodiment of the present invention provides a mobile device that uses data representing GPS signals to provide a location for a mobile device, comprising a receiver configured to communicate via a cellular communication channel in a transmission cell to receive Doppler information of a satellite in view a mobile device, a processing device associated with the receiver for receiving Doppler information and calculating location information zhenii for said satellite by using the Doppler information without receiving and without using satellite ephemeris information. In addition, various aspects of the implementation of a mobile device are described.

Another embodiment of the present invention provides a method of using a base station to provide a communication channel with a GPS mobile device, comprising determining Doppler information of a satellite in the field of view of a GPS mobile device, wherein Doppler information is used in the GPS mobile device to determine location information for said satellite, transmit Doppler information of said satellite in view from a transmission cell in tem in the cellular mobile GPS unit wherein the mobile GPS unit determines the location information without receiving and without using satellite ephemeris information. In addition, other features of the method are described.

Another embodiment of the present invention provides a base station for providing a cellular communication channel to a GPS mobile device, comprising a Doppler information source for a satellite in the field of view of a GPS mobile device, a transmitter associated with a Doppler information source, the transmitter being adapted to transmit Doppler information via a channel cellular communication in a cellular cell transmitting to a mobile GPS device, wherein the mobile GPS device determines location information without receiving and without using satellite ephemeris information. In addition, various aspects of the implementation of the base station are described.

Another embodiment of the present invention provides a method for determining the location of a remote device, which comprises transmitting satellite information, including Doppler information, to a remote device from a base station via a cellular data channel via a cell in a GPS cellular communication system, and receiving it at a remote device satellite information and GPS signals from satellites in view are calculated in a remote pseudorange device to satellites in For example, when calculating pseudo-ranges, Doppler information is used, while pseudo-ranges are determined in the remote device without receiving and without using satellite ephemeris information, pseudo-ranges are transmitted to the base station from the remote device via the cellular data channel, and the location of the remote device is calculated in the base station, using pseudorange. In addition, other features of the method are described.

Brief Description of the Drawings

The invention is illustrated by example with reference to the drawings, which represent the following:

figa is a structural diagram of the main components of a remote or mobile GPS receiving system using the methods according to the present invention; shows the data channels that may exist between the base station and the remote device;

1B is a block diagram of an alternative GPS mobile device;

figs is a structural diagram of another alternative mobile GPS device;

2A and 2B are structural diagrams of two alternatives for the RF and IF parts of a receiver made in accordance with the present invention;

FIG. 3 is a flowchart (for example, performed by software) of a programmable digital signal processor according to methods of the present invention; FIG.

figure 4 - waveforms at various stages of processing in accordance with the methods according to the invention;

5A is a base station system according to an embodiment of the invention;

5B is a base station system in accordance with another embodiment of the invention;

6 is a mobile GPS device containing means for correcting or calibrating the local oscillator in accordance with one aspect of the invention;

7 is a flowchart of a power control procedure for a mobile device in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to devices and methods for calculating the location of a mobile or remote object to enable the remote device hardware to have low power dissipation losses and operate at very low levels of the received signal. This means that power consumption is reduced and receiver sensitivity is increased. This is ensured by the implementation of the reception functions of the remote device, as shown in FIG. 1A, as well as the transmission of Doppler information from a separately located base station 10 to a remote or mobile GPS device 20.

It should be noted that to calculate the location of the remote device, you can use pseudorange in accordance with various methods, examples of which are given below:

1. Method 1. By relaying satellite information messages to the remote device 20 from the base station 10, the remote device 20 can combine this information with pseudorange measurements to calculate its location (see, for example, US Pat. No. 5,365,450). Typically, the location of the remote device 20 is calculated in that device 20 itself.

2. Method 2. The remote device 20 can receive satellite ephemeris data by receiving GPS signals in a conventional manner, which is widely used in the art. This data, usually valid for one to two hours, can be combined with pseudorange measurements until the location calculation in the remote device is complete.

3. Method 3. The remote device 20 may transmit pseudo-range communication channel 16 to the base station 10, which can combine this information with satellite data ephemeris to calculate the location (see, for example, US patent No. 5225842).

In the above methods 1 and 3, it is assumed that the base station 10 and the remote device 20 have a common field of view of all satellites of interest and are located close enough to each other to resolve time ambiguity, which is associated with the repetition rate of pseudorandom codes of the GPS system. This is satisfied for the distance between the base station 10 and the remote device 20 equal to half the product of the speed of light by the repetition period of the pseudorandom sequence (1 ms) or about 150 km.

To explain the present invention, it is assumed that method 3 is used to complete the calculation of location coordinates. However, it is apparent from this description that various aspects and embodiments of the present invention can be implemented using any of the above or other methods. For example, in modifications of method 1, satellite data information, for example satellite ephemeris data, can be transmitted using a base station to a remote device, and this satellite data information can be combined with pseudo-ranges, which are calculated according to the present invention, using buffered GPS signals to obtain latitude and longitudes (and sometimes elevations) for the remote device. It should be borne in mind that the location information that comes from the remote device can be limited by latitude and longitude and can be more complete information, which includes the latitude, longitude, altitude, speed and azimuth of the remote device. In addition, local oscillator correction and / or power control aspects, respectively, of the present invention can be used in these modifications of method 1. Moreover, Doppler information can be transmitted to the remote device 20 and used in the remote device 20, in accordance with aspects of the present invention.

In method 3, it is understood that the base station 10 instructs the remote device 20 to perform a measurement by means of a message transmitted over communication channel 16 for transmitting data (FIG. 1A). The base station 10 also sends in this message Doppler information for satellites in view, which is a form of satellite data information. This Doppler information typically has a frequency information format, and the message will also determine the identification parameters of specific satellites in view or other initialization data. This message is received using a separate modem 22, which is part of the remote device 20 and stored in memory 30, which is connected to a low-power microprocessor 26. The microprocessor 26 processes the data information transmitted between the processing elements 32-48 of the remote device and the modem 22, and controls the functions power control in the remote device 20, as will be described below. In normal mode, the microprocessor 26 sets most or all of the hardware of the remote device 20 to a state of low power or a complete power outage, except for a state in which pseudorange calculations and / or other calculations using GPS signals are performed, or an alternative power source can be used. However, the receiving part of the modem is turned on at least periodically (at full power) in order to determine whether the base station 10 has transmitted a location command to the remote device.

This aforementioned Doppler information is very short in duration since the required accuracy of such Doppler information is not high. For example, if accuracy of 10 Hz is required and the maximum Doppler frequency is approximately ± 7 kHz, then an 11-bit word will be sufficient for each satellite in view. If there are 8 satellites in view, then 88 bits will be required to determine all such Doppler frequencies. The use of this information eliminates the need to search for Doppler frequency for the remote device 20, thereby reducing the processing time by more than 10 times. The use of Doppler frequency information also allows the GPS mobile remote device 20 to more quickly process a sample of GPS signals, which reduces the time that the processor 32 needs to receive full power to calculate location information. This reduces the power consumed by the remote device 20, and increases the sensitivity of the receiver. Additional information may also be sent to the remote device 20, including periods (superframes) of data in the GPS message.

A received data channel signal may use a precision carrier frequency. The remote device 20 (FIG. 6), which is described below, can use an automatic frequency control (AFC) loop to synchronize with this carrier and thus further calibrate its own reference oscillator. A message transmission time of 10 ms, with a signal-to-noise ratio for the received signal of 20 dB, will provide a frequency measurement using AFC with an accuracy of 10 Hz or better. This is sufficient to satisfy the requirements of the present invention. This feature will also improve the accuracy of location calculations that are performed by conventional methods or using the fast convolution methods of the present invention.

In one embodiment of the invention, the communication channel 16 forms a commercially available narrow-band radio frequency communication medium, for example, a two-way paging system. This system can be used in embodiments in which the amount of data transmitted between the remote device 20 and the base station 10 is relatively small. The amount of data that is required to transmit the Doppler frequency and other data (e.g., initialization data, such as satellite identification data that are in view) is relatively small, and similarly, the amount of data required for location information (e.g., pseudorange), also relatively small. Therefore, narrowband systems are well suited for this embodiment. This distinguishes the invention from systems that require the transmission of large amounts of data in a short period of time; such systems may require a wider radio frequency transmission medium.

Since the remote device 20 receives a command (for example, from the base station 10) for processing GPS signals along with information about the Doppler frequency, the microprocessor 26 starts the converter 42 RF to IF, analog-to-digital converter 44 and digital dynamic memory 46 through the battery and power controller power supply and power supply switching circuit 36 (and power-controlled circuits 21a, 21b, 21c and 21d), thereby providing full power to these elements. This provides the conversion of the signal received from the satellite of the GPS system and received using the antenna 40, on the inverter with subsequent conversion to digital form. A continuous set of such data, usually corresponding to a duration of 100 ms to 1 s (or even longer), is then stored in dynamic memory 46. The amount of stored data can be controlled using microprocessor 26 so that more data can be stored in memory 46 ( to obtain higher sensitivity) in situations where saving power resources is not so important compared to providing higher sensitivity, and less data can be stored in situations where the onomy of power resources is more important than sensitivity. Usually sensitivity is more important when various obstacles interfere with the passage of GPS signals, and saving power resources is less important when using a powerful power source (such as a car battery). The addressing of memory 46 for storing data is controlled by an integrated circuit 48 of a programmable logic matrix. The down-conversion of the GPS signal is performed using a frequency synthesizer 38, which provides the local oscillator signal 39 to the converter 42, as follows.

It should be noted that all this time (when the dynamic memory 46 is filled with digital GPS signals that come from satellites in sight), the digital signal processing microprocessor 32 may be in a low power consumption state. The RF to IF converter 42 and the analog-to-digital converter 44 are typically turned on only for a short period of time sufficient to collect and store the data required to calculate the pseudorange. After completing the data collection, these converter circuits are turned off, or the power supplied through the power supply control circuits 21b and 21c is reduced in another way (although full power continues to flow into memory 46), thereby not introducing additional power losses during the actual pseudorange calculation. Then, the calculation of pseudorange is performed in one embodiment using a programmable IC 32 for general-purpose digital signal processing (DSP), an example of which is the TMS320C30 integrated circuit manufactured by Texas Instruments. This DSP IC 32, prior to performing such calculations, is in the state of active power consumption using the microprocessor 26 and circuit 36 through the power supply control circuit 21e.

This DSP 32 IC differs from others that are used in some remote GPS devices in that it is a general purpose integrated circuit and programmable compared to specialized integrated circuits designed to process digital signals. In addition, the DSP 32 makes it possible to use the Fast Fourier Transform (FFT) algorithm, which allows high-speed calculations of pseudorange by performing a large number of correlation operations between the local reference signal and the received signals. Typically, 2046 such correlation operations are required to complete the search for the periods of each received GPS signal. The Fast Fourier Transform algorithm allows you to simultaneously and parallelly search for all such locations, thus speeding up the required calculation process from 10 to 100 times in comparison with traditional approaches.

After the DSP block 32 completes its pseudorange calculation for each satellite in view, it transmits, in one embodiment of the invention, this information to the microprocessor 26 via the internal bus 33. At this time, the microprocessor 26 can cause the DSP block 32 and memory to transition 46 to a low power consumption state by sending an appropriate control signal to the power regulator and battery circuit 36. The microprocessor 26 then uses a modem 22 to transmit pseudorange data on the data channel 16 to the base station 10 for the final location calculation. In addition to the pseudo-range data, the timestamp can be simultaneously transmitted to the base station 10, which shows the time that elapses from the initial data collection in the buffer 46 to the data transmission time on the data channel 16. This timestamp improves the base station's ability to calculate the estimated location, since it provides the calculation of the location of GPS satellites during data collection. Alternatively, according to the above method 1, the DSP unit 32 can calculate the location (for example, latitude, longitude or latitude, longitude and height) of the remote device and send this data to microprocessor 26, which likewise relays this data to base station 10 through a modem 22. In this case, the location calculation is facilitated by the DSP, which supports the time that elapses from the moment of receiving satellite data messages until the start of collecting buffer data. This improves the ability of the remote device to calculate the estimated location, because it provides the calculation of the location of the GPS satellite during data collection.

As shown in FIG. 1A, the modem 22 in one embodiment uses a separate antenna 24 to transmit and receive messages on the data channel 16. It is clear that the modem 22 includes a communication receiver and a communication transmitter, which are alternately connected to the antenna 24. Similarly, in the base station 10, you can use a separate antenna 14 to transmit and receive messages over the data channel, thus allowing continuous reception of GPS signals via antennas 12 for receiving GPS signals to the base station 10.

In a typical example, it is assumed that the location calculations in the DSP unit 32 will require less than a few seconds, depending on the amount of data that is stored in the digital dynamic memory 46 and the speed of the DSP or several DSPs.

From the above discussion, it will be clear that in the remote device 20 it is necessary to turn on high power consumption circuits only for a short period of time if the location calculation commands coming from the base station 10 are not frequent. It should be noted that in most cases, such commands will lead to the launch of the equipment of the remote device, which is characterized by high power losses, only for about 1% of the time or less.

This will increase the battery life by 100 times, compared with other possible cases. Program commands necessary for performing a power supply control operation are stored in the EEPROM 28 or in another suitable storage medium. This power management strategy can be adapted to different situations of used power. For example, in the case where the main power is used, the location determination may occur on an ongoing basis.

As shown above, the digital dynamic memory 46 stores a record corresponding to a relatively long period of time. Effective processing of this large block of data using fast convolution methods provides for signal processing at low levels of received signals (for example, when reception is poor due to partial shading caused by buildings, trees, etc.). All pseudoranges for observed GPS satellites are calculated using the same buffered data. This improves the performance with respect to GPS receivers of continuous tracking in situations (for example, in shading conditions typical of urban environments) in which the signal amplitude changes rapidly.

A slightly different embodiment, shown in FIG. 1B, does not use the microprocessor 26 and its peripheral devices (RAM 30 and EEPROM 28) and replaces their functionality with an additional circuit that is part of a more complex PPVM (user programmable gate array) 49 In this case, PPVM 49, as a device with low power consumption, serves to excite the DSP IC 32a after registering the activation signal coming from modem 22 via internal connection 19. Internal connection 19 It connects the modem to the DSP 32a and to the FPGA 19. The DSP IC 32a when activated, directly transmits and receives data from the modem. The DSP IC 32a also performs power consumption control operations through an internal connection 18, which is connected to the battery and the power regulator and the power switch 36 to execute power on / off commands in the circuit 36. The DSP IC 32a selectively supplies power or reduces the power supplied to the various components , according to the power control method (Fig. 7) using power on / off commands made using internal connection 18 in circuit 36. Circuit 36 receives these commands and selectively effectiveness to supply power (or reduces power supply) to the various components. The circuit 36 drives the DSP IC 32a through an internal connection 17. The circuit 36 selectively provides power to the various components by selectively switching power through selected elements of the controlled power supply circuits 21a, 21b, 21c, 21d and 21f. Thus, for example, to supply power to the converter 42 and the converter 44, power is supplied through the circuits 21b and 21c to these converters. Similarly, power is supplied to the modem via the power control circuit 21f.

A low-frequency crystal oscillator 47 is connected to the memory and to the power control array 49. In one embodiment, the memory and the power control firewire 49 comprise a low power timer that includes a low frequency generator 47. When the PPVM timer 49 counts a predetermined interval, the PPVM 49 sends an excitation signal to the DSP IC 32a through the internal connection 17, and the DSP 32a IC can subsequently activate other circuits using power on / off commands to the power switch circuit 36, the power regulator, and the battery . Other circuits are powered by power control circuits 21a, 21b, 21c, 21d and 21f controlled by circuit 36 to perform a positioning operation (for example, determining location information such as pseudorange or latitude and longitude). Following the positioning operation, DSP 32A resets the PCRM timer and reduces its own power supply, and circuit 36 also reduces the power supply to other components in accordance with the method illustrated in FIG. 7. It should be borne in mind that the battery and a plurality of batteries will provide power for all circuits with a controlled power supply through the power control circuit, which are controlled by memory and power control PPVM and DSP ICs 32a. It should also be borne in mind that instead of directly reducing the power supply to the component through power control circuits (for example, 21b), the power consumed by the component can be reduced by transmitting a signal to it (as in the case of DSP 32A via internal connection 17 shown in FIG. .1B) to reduce power or drive full power; this is possible when a component, such as an integrated circuit, has a power state control input and an internal logic circuit for power control (for example, a logic circuit for reducing power in various logical blocks of a component). The power control PPMM 49 performs memory management and control, which includes addressing operations when the data received from the converter 44 is stored in the memory 46, or when the DSP element 32a reads data from the memory 46. If necessary, the MPC 49 can control other memory functions, such as clearing memory.

On figs shows another variant of implementation, according to the present invention, a mobile GPS device that contains the same elements as the mobile GPS device shown in figa and 1B. In addition, the GPS mobile device (Fig. 1C) contains power controllers 77 that are connected to receive power supplied from a plurality of batteries 81, as well as from an additional input 83 for connecting an external power source and solar cells 79. A power controller 77 provides power for all circuits when controlled by power control circuits, which are controlled by the DSP IC 32a and the memory and power supply control LPS (FIG. 1C). The solar cell 79 can be recharged using conventional recharging technology for these batteries. Solar cells 79 may also provide power to a GPS mobile device in addition to rechargeable batteries. In the embodiment of FIG. 1C, the FPGA 49 provides an excitation signal through internal connection 75 to the DSP IC 32a, this signal causing the DSP IC to return to its full power state to perform various functions described for the DSP IC 32a. The DSP IC can be excited to the state of full power consumption by means of an external command from the modem 22, which is directly connected to the DSP IC via the internal connection 19.

FIG. 1C also illustrates a feature of the present invention that allows a GPS mobile device to compromise between sensitivity and power saving. As described above, the sensitivity of a GPS mobile device can be increased by increasing the number of buffered GPS signals that are stored in memory 46. This is done by receiving and digitizing GPS signals and storing these data in memory 46. Although this increase in buffering results in high consumption power, however, it can improve the sensitivity of the mobile GPS device. This high sensitivity mode can be selected using the power mode switch 85 in the GPS device, which is connected to the bus 19 to issue a DSP IC 32a command to enter the high sensitivity mode. This power mode switch 85 can provide a command to the DSP IC 32a to save power and provide less sensitivity by receiving a shorter GPS signal and thus storing fewer GPS signals in memory 46. Obviously, such a choice of power mode can also occur by sending a signal from the base station to the modem 22, which then transmits this command through the internal connection 19 to the IPC 32.

A typical example of an RF to IF frequency converter and a digitization system for a GPS mobile device is shown in FIG. 2A. The input signal at a frequency of 1575.42 MHz passes through a band-pass filter (PF) 50 and a low-noise amplifier (LNA) and enters the frequency conversion stage. The local oscillator 56, which is used in this cascade, is phase-locked (by PLL 58) with a crystal oscillator with temperature compensation at a frequency of 2.048 MHz (or its harmonic) (CTSC) 60. In a preferred embodiment, the local oscillator frequency will be 1531.392 MHz, which is obtained by multiplying 2991 x 0.512 MHz. The resulting IF signal is then centered at 44.028 MHz. This inverter is preferred due to the availability of low cost components at about 44 MHz. In particular, surface acoustic wave (SAW) filters are currently used, which are widely used in television devices. Of course, instead of SAW devices, other devices limited in bandwidth can also be used.

The received GPS signal is mixed with the local oscillator signal in mixer 54 to receive an IF signal. This IF signal passes through a SAW filter 64, which precisely limits the frequency bandwidth to 2 MHz, and then goes to the downconverter 68, which moves the signal to the near main frequency band (usually the center frequency is 4 kHz). The local oscillator frequency for this converter 68 with decreasing frequency is obtained from the frequency KGTK 60 2.048 MHz, as the 43rd harmonic of the frequency 1.024 MHz, which is 44.032 MHz.

Inphase-quadrature (I / Q) buck converters 68 are commercially available RF components. Such a converter typically consists of two mixers and low-pass filters. In this embodiment, an IF signal and a local oscillator signal are supplied to the input of one mixer, and the same IF signal and a local oscillator signal 90 ° shifted in phase are fed to the input of another mixer. The output signals of the two mixers are filtered by a low-pass filter to eliminate the penetrating signal and other interference.

As shown in FIG. 2A, amplifiers 62 and 66 can, if necessary, be used before and after the band limiting operation.

The two output signals of the I / Q converter 68 with decreasing frequency are fed to two matched ADCs 44, which sample the signals at a frequency of 2.048 MHz. In an alternative embodiment, the ADCs 44 are replaced by comparators (not shown), the outputs of which produce a two-digit (single-bit sequence) data sequence, in accordance with the polarity of the input signal. It is well known that this approach leads to losses of approximately 1.96 dB in receiver sensitivity relative to a multi-level ADC. However, in this case, it is possible to significantly reduce the cost of the device by using a comparator instead of the ADC, and also due to reduced memory requirements for the subsequent dynamic memory unit 46.

An alternative embodiment of a down-converter and ADC is shown in FIG. 2B, which uses a bandwidth sampling method. In the KGTK 70 used, the frequency is 4.096 MHz (or its harmonic). The output signal KGTK can be used as a sampling clock signal in the ADC 44 (or comparator), and this is necessary to convert the signal to a frequency of 1,028 MHz. This frequency is the difference between the 11th harmonic of 4.096 MHz and the input IF frequency of 44.028 MHz. The resulting IF frequency of 1.028 MHz is approximately one-fourth of the sampling frequency, which, as you know, will be close to ideal while minimizing distortion due to sampling. Compared to I / Q sampling (FIG. 2A), this single sampler provides one data channel rather than two, but with a double sampling rate. In addition, data transmission is effective at an IF frequency of 1.028 MHz. The I / Q conversion of a frequency to a frequency close to 0 MHz will then be performed by digital means in accordance with the processing that will be described below. The device (FIGS. 2A and 2B) is competitive in cost and complexity, and component availability often determines the preferred approach. However, it will be apparent to those skilled in the art that other receiver configurations can be used to achieve similar results.

To simplify the discussion that follows, it is assumed that I / Q sampling is used (FIG. 2A), and that instant memory 46 contains two data channels presented in digital form at a frequency of 2.048 MHz.

Details of the signal processing performed in the DSP IC 32 are illustrated by the algorithm shown in FIG. 3 and the diagrams in FIGS. 4A, 4B, 4C, 4D and 4E. It should be clear to those skilled in the art that a machine code or other suitable code for processing a signal, which will be described later, is stored in the EPROM 34. Other non-volatile storage devices may also be used. The purpose of the processing is to determine the synchronization of the received signal with respect to the locally generated signal. In addition, in order to obtain high sensitivity, it is necessary to process a very long fragment of such a signal, the duration of which is usually in the range from 100 ms to 1 s.

To understand the processing process, firstly, we note that each received GPS signal (C / A mode) is formed from a pseudo-random (PS) sequence with a high frequency (1 MHz), a repeating pseudorandom (PS) sequence consisting of 1023 characters, which commonly called code elements. These code elements have the waveform shown in FIG. 4A. In addition, low bit rate data is superimposed on this sequence and transmitted from the satellite at a speed of 50 baud. All this data is received at a very low signal-to-noise ratio, which is measured in the 2 MHz band. If the carrier frequency and all data transfer rates were known with great accuracy, and the data were not present, then the signal-to-noise ratio could be significantly increased and the data could be significantly reduced by adding sequential frames to each other. For example, there are 1000 PS frames for a period of 1 s. The first such frame can be coherently added to the next frame, the resulting amount can be added to the third frame, etc. The result is a signal that has a duration of 1023 code elements. The phasing of this sequence can then be compared with the local reference sequence in order to determine the relative time interval between them, in order to determine the so-called pseudorange.

The above process must be performed separately for each satellite in view, based on the same set of stored received data in dynamic memory 46, since in general GPS signals coming from different satellites have different Doppler frequencies, and the PS sequences differ apart from each other.

The above procedure is quite time-consuming due to the fact that the carrier frequency may not be known within 5 kHz due to the uncertainty of the Doppler signal and additionally due to the uncertainty of the receiver local oscillator. This uncertainty of the Doppler frequency is eliminated in one embodiment of the present invention by transmitting such information from the base station 10, which simultaneously monitors all GPS signals from satellites in view. Thus, the search for Doppler frequency can be excluded in the remote device 20. The local oscillator uncertainty is also greatly reduced (possibly up to 50 Hz) due to the operation of the PLL using a signal transmitted from the base station to the remote device (Fig.6).

The presence of 50 baud data superimposed on the GPS signal still limits the coherent summation of the PS frames within a period of 20 ms. That is, a maximum of 20 frames can be coherently summed before data sign inversions prevent subsequent processing gains. Additional processing gains can be achieved by coordinating filtering or summing the values (or squares of values) of the frames, as will be described in detail below.

The processing procedure (FIG. 3) begins at step 100 with a command coming from the base station 10 to initiate the GPS signal processing operation (“Fixed Command” in FIG. 3). This command includes sending on the channel 16 communication Doppler shifts for each satellite in the field of view, and the identification of these satellites. In step 102, the remote device 20 calculates the offset of its local oscillator by synchronizing in frequency with the signal transmitted by the base station 10. A high-quality temperature compensated crystal oscillator can be used in the remote device. For example, in digitally controlled QCTCs, the so-called CCTC, it is now possible to provide an accuracy of about 0.1 x 10 ^-6 or an error of about 150 Hz for the GPS L1 signal.

At step 104, the microprocessor 26 of the remote device supplies power to the input stage 42 of the receiver, analog-to-digital converters 44, and digital dynamic memory 46 and collects a set of data for the duration K of the PS code C / A, where K is usually 100-1000 (100 ms - 1 s). When a sufficient amount of data has been collected, the microprocessor 26 turns off the RF converter 42 in the inverter and the ADC 44.

The pseudorange of each satellite is calculated in turn as follows. First, in step 106, for a given processed GPS satellite signal, the corresponding pseudo-random code is read from EPROM 34. As noted, the preferred PS storage format is the Fourier transform of this PS code, dicreated at a rate of 2048 samples per 1023 bits of the PS code.

Data in dynamic memory 46 is processed in blocks of N consecutive frames of the PS code, which are blocks of 2048N complex samples (where N is an integer, usually in the range of 5-10). Similar operations are performed in each block, as shown by the lower cycle (steps 108-124) (FIG. 3). That is, this cycle is performed a total K / N times for each processed GPS signal. At step 108, the data words of the 2048 N block are multiplied by the complex exponent, which eliminates the Doppler effect on the carrier frequency of the signal, as well as the effects of frequency shift of the receiver local oscillator. To illustrate, suppose that the Doppler frequency that is transmitted from base station 10, plus the local oscillator frequency, shifts respectively by f _e Hz. Then the pre-multiplied data will have the form of the function e ^-j2pf e ^nT , n = [0, 1, 2, ..., 2048N - 1] + (B - 1) x 2048N, where T = 1 / 2,048 MHz - the sampling period and number The block is selectable from 1 to K / N.

Next, at step 110, adjacent groups of N (typically 10) data frames within the block are coherently summed with each other. That is, samples 0, 2048, 4096, ... 2048 (N-1) - 1 are added together, then 1, 2049, 4097, ... 2048 (N-1) are added together, etc. At this point, the block contains only 2048 complex samples. For example, the waveform that is obtained by such a summing operation is depicted in FIG. 4B for the case of 4PS frames. This summing operation can be considered as a preprocessing operation that precedes fast convolution operations.

Further, at steps 112-118, each averaged frame is subjected to a matched filtering operation, the purpose of which is to determine the relative time interval between the received MS code, which is contained within the data block and the locally generated MS reference signal. At the same time, the influence of the Doppler effect on sampling times is also compensated. These operations are significantly accelerated, in one embodiment, using fast convolution operations, such as fast Fourier transform algorithms, which are used to perform circular convolution, as described previously.

In order to simplify the discussion, the aforementioned Doppler frequency compensation is initially neglected.

The main operation performed is the comparison of data in the processed data block (1048 complex samples) with a similar reference locally stored block of the PS signal. The comparison is really carried out using the (complex) multiplication of each element of the data block by the corresponding element of the reference signal and summing the results. This comparison is a definition of correlation. However, individual correlation processing operations are carried out only during one specific initial time of the data block, while there are 2048 possible positions that can provide better coordination. The set of all correlation operations for all possible starting positions is called the “consistent filtering” operation. In a preferred embodiment, a complete matched filtering operation is required.

At other points in time, the PS block can be checked by cyclic shifting the PS reference signal and re-performing the same operation. That is, if the PS code is denoted by p (0) p (1) ... p (2047), then the cyclic shift by one sample is p (1) p (2) ... p (2047) p (0). This modified sequence is checked to determine if the data block contains a PS signal starting with sample p (1). Similarly, a data block can begin with samples p (2), p (3), etc., and each can be checked by cyclically shifting the reference PS sequence and re-performing the checks. Obviously, a full set of checks will require 2048 x 2048 = 4194304 operations, each of which requires complex multiplication and summation. A more efficient mathematical equivalent method using the fast Fourier transform (FFT) can be used, which requires approximately 12 x 2048 complex complex multiplications and double the number of summations. In this method, the FFT is performed for the data block in step 112 and for the block of the PS code. The FFT of the data block is multiplied by the complex conjugate FFT of the reference signal at step 114, and the result is the inverse Fourier transform performed at step 118. The resulting data has a length of 2048 and contains a set of correlations of the data blocks and PS blocks for all possible positions. Each forward and reverse FFT operation requires P / 2 log ₂ P operations, where P is the size of the transmitted data (it is assumed that the radix-2 FFT algorithm is used). For the case that is of interest B = 2048, so each FFT requires 11 x 1024 complex multiplications. However, if the FFT of the PS sequence is previously stored in EEPROM 34, as in the preferred embodiment, then there is no further need to calculate the FFT in the filtering process. The total number of complex multiplications for the direct FFT, the inverse FFT and the product of the FFT results are thus (2x11 / 2) x 1024 = 24576, which provides savings on direct correlation with a factor of 171. Fig. 4C shows a signal diagram resulting from the operation consistent filtering.

In a preferred method of the present invention, a sampling rate is used such that 2048 data samples are taken over the period of the PS sequence of 1023 code elements. This allows the use of FFT algorithms with a length of 2048. It is known that algorithms that have a power of 2 or 4 are naturally much more efficient than algorithms of other sizes (and 2048 = 2 ¹¹ ). The sampling rate chosen in this way significantly increases the processing speed. Preferably, the number of FFT samples is equal to the number of samples for one MS frame so that proper cyclic convolution can be ensured. That is, this condition allows you to check the data block for all cyclically shifted versions of the PS code, as discussed above. A set of alternative methods known in the art, such as convolution with “preservation of overlap” or “summation of overlap”, can be used if the FFT size is selected to cover the number of samples other than the number for the length of the PS frame. These approaches require approximately double the number of calculations, as described above for the preferred embodiment.

Specialists in the art should understand how the above processing process can be modified using various FFT algorithms for resizing, various sampling frequencies to perform fast convolution operations. In addition, there is a set of fast convolution algorithms, which also has the property that the number of required calculations is proportional to B log ₂ B and not to B ² , as is required for conventional correlation. Many of these algorithms are cited, for example, by HJNussbaumer, "Fast Fourier Transform and Convolution Algorithms", New York, Springer-Virlag, C1982. Important examples of such algorithms are the Agarwal-Cooley algorithms, the split nesting algorithm, the recursive polynomial nesting algorithm, and the Winograd-Fourier algorithm, the first three are used to perform convolution and are further used to perform the Fourier transform. These algorithms can be used in place of the preferred method that is presented above.

The method for temporarily compensating the Doppler frequency that is used at step 116 is explained below. In the preferred embodiment, the used sampling rate cannot exactly match 2048 samples in the PS frame due to the influence of the Doppler effect on the received GPS signal, as well as the local oscillator instability. For example, it is known that the Doppler shift can introduce a delay error of ± 2700 ns / s. To compensate for this effect, data blocks that are processed in accordance with the above description must necessarily have a time offset to compensate for this error. As an example, if the size of the processed block corresponds to 5 PS frames (5 ms), then the time shift from one block to another can be much greater than ± 13.5 ns. Smaller time shifts are due to instability of the local oscillator. These shifts can be compensated by temporarily shifting successive data blocks by a plurality of time shifts required for one block. That is, if the Doppler time shift per block is d, then the blocks are shifted in time by nd, n = 0, 1, 2 ....

In general, these time shifts are fractions of a sample. Performing these operations directly using digital signal processing methods involves the use of non-integral signal interpolation methods and results in high computational costs. An alternative approach according to a preferred embodiment of the method according to the present invention involves processing within the framework of the fast Fourier transform functions. It is well known that a time shift of d seconds is equivalent to multiplying the Fourier transform of the function by e ^−j2pfd , where f is a variable frequency. Thus, the time shift can be obtained by multiplying the FFT of the data block by e ^{-j2pfd / Tf} for n = 0, 1, 2, ..., 1023 and by e ^{-j2p (n-2048) d / Tf} for n = 1024, 1025 , ..., 2047, where Tf is the duration of the PS frame (1 ms). This compensation adds only about 8% to the processing time associated with FFT processing. The compensation is divided into two parts to ensure continuity of phase compensation after 0 Hz.

After the matched filtering operation is completed, the values or squares of the complex numbers of the block are calculated at step 120. Any of these choices will give a good result. This operation eliminates the effects of data phase hopping at a frequency of 50 Hz (FIG. 4D) and low-frequency carrier errors that remain. A block of 2048 samples is then added to the sum of the previous blocks processed in step 122. Step 122 can be considered as an operation of the subsequent (post-processor) processing, which follows the fast convolution operation performed in steps 112-118. Processing continues until K / N blocks are processed, as shown by the decisive block in step 124, at which point one block of 2048 samples remains, from which the pseudorange is calculated. 4E illustrates the final waveform after the summing operation.

The determination of the pseudorange occurs at step 126. A maximum is sought for the locally calculated noise level described above. If such a maximum is found, then its appearance time relative to the beginning of the block is a pseudorange associated with a specific PS code and with the corresponding GPS satellite.

At step 126, an interpolation procedure is used to find the maximum position with higher accuracy than that associated with the sampling frequency (2.048 MHz). The interpolation procedure depends on the previous bandpass filtering used in the RF / IF cascade of the remote receiver 20. A high-quality filter will provide a maximum that is nearly triangular in shape with a base width of 4 samples. Under this condition, following the subtraction of the average amplitude (to eliminate the constant component), two maximum amplitudes can be used to more accurately determine the location of the maximum. Let us designate these amplitudes A _p and A _{p + 1} , where A _p ≥ A _{p + 1} , where p is the index of maximum amplitude. Then, the location of the maximum relative to that which corresponds to A _p can be obtained according to the formula: the position of the maximum = p + A _p / (A _p + A _{p + 1} ). For example, if A _p = A _p + A _{p + 1} , then the maximum should be equal to p + 0.5, that is, in the middle between the coefficients of two samples. In some situations, bandpass filtering can round the maximum, and three-point polynomial interpolation may be more appropriate.

In the previous processing, the local noise reference signal used in the threshold processing can be calculated by averaging all the data in the final averaged block, after eliminating several of these largest maxima.

After the pseudorange is found, at step 128, processing continues in the same manner for the next satellite in view until all of these satellites are processed. After the data processing for all such satellites is completed, processing continues at interval 130, with pseudorange data being transmitted to base station 10 via communication channel 16, where the final location of the remote device is calculated (assuming that method 3 is used). Finally, at step 132, most of the circuits of the remote device 20 are brought into a low power state, waiting for a new command to perform the next positioning operation.

Below will be a brief description of the signal processing, which is shown above (figure 3). GPS signals from one or more GPS satellites in view are received at a remote device using the antenna. These signals are digitized and stored in the buffer of the remote GPS device. After storing these signals, the processor performs pre-processing, fast convolution processing, and a post-processing operation. These processing operations include:

a) divide the stored data into a sequence of adjacent blocks whose durations are equal to the set of frame periods of the pseudorandom (PS) codes contained in the GPS signals,

b) for each block, a preliminary processing step is performed, on which a compressed data block is formed with a length equal to the duration of the pseudo-random code period by coherently summing successive data subunits, the subunits having a duration equal to one PS frame, and the summing step will mean that the corresponding sample numbers of each subunit are added together,

c) for each compressed block, a matched filtering operation is performed, which uses the fast convolution method, to determine the relative time interval between the PS code contained in the data block and the reference signal locally generated by the PS (for example, the pseudo-random sequence of a GPS satellite whose data processed)

d) determine the pseudorange by squaring the results obtained by matched filtering and then processing it by combining the squared data for all blocks into a single data block by adding together the squared blocks to obtain the maximum, and

f) find the maximum position of the said single data block with high accuracy using digital interpolation methods, the position being determined as the distance from the beginning of the data block to the maximum, which is a pseudorange to the GPS satellite corresponding to the processed pseudo-random sequence.

Typically, the fast convolution method that is used to process buffered GPS signals is the fast Fourier transform (FFT), and the convolution result is formed by calculating the product of the direct transform of the compressed block and the previously stored representation of the direct transform of the pseudorandom sequence to obtain the first result and then perform the inverse transform first result to restore the final result. Thus, time delays due to the Doppler effect and time errors due to the local oscillator are compensated for each compressed data block by introducing between the operations of the direct and inverse fast Fourier transforms of multiplying the direct FFT of the compressed blocks by a complex exponent, the phase of which depends on the number of samples , is adjusted to match the delay compensation required for the block.

In the previous version, GPS signals from each satellite are processed sequentially in time, and not in parallel. In an alternative embodiment, GPS signals coming from all satellites in view can be processed together in parallel in time.

In this case, it is assumed that the base station 10 has a common field of view for all the required satellites, and that they are located close enough to the remote device 20 to avoid ambiguity associated with the repetition period of the PS C / A code. A range of about 150 km will satisfy this criterion. It is also assumed that the base station 10 has a GPS receiver and a favorable geographical location such that all satellites in view are continuously monitored with high accuracy.

Although the described embodiments of the base station 10 use a data processing element such as a computer calculating location information, such as latitude and longitude for the GPS mobile device, each base station 10 can only relay received information, such as pseudorange, from the GPS mobile device , to a central point or to several central points that do perform latitude and longitude calculations. In this method, the cost and complexity of these relay base stations can be reduced by eliminating the data processing device and associated elements from each relay base station. The central point will include receivers (e.g. telecommunication receivers) and a data processing device and related elements. In addition, in a particular embodiment, the base station may be virtual in the sense that it can be a satellite that transmits Doppler frequency information to remote devices, thereby emulating the base station in a transmission cell.

5A and 5B show two embodiments of a base station according to the present invention. In the base station shown in FIG. 5A, a GPS receiver 501 receives GPS signals through a GPS antenna 501a. A GPS receiver 501, which may be a known GPS receiver, provides a synchronized reference signal, which is usually synchronized with GPS signals, and also provides Doppler information to satellites in view. This GPS receiver 501 is coupled to a local oscillator 505 receiving a synchronized reference signal 510, and is phase locked to this reference signal. The output signal of the local oscillator 505 is supplied to the modulator 506. The modulator 506 also receives information signals of Doppler data for each satellite in the field of view of the mobile GPS device, and / or other information signals 511 of satellite data. A modulator 506 modulates Doppler and / or other satellite data information using a local oscillator signal that is provided from the local oscillator 505 to provide a modulated signal 513 to the transmitter 503. The transmitter 503 is connected to the data processing unit 502 via an internal connection 514 so that the data processing unit can to control the operation of the transmitter 503 to ensure the transmission of satellite data information, such as Doppler information, to the GPS mobile device via the transmitter antenna 503a. In this method, the mobile GPS device can receive Doppler information, the source of which is the GPS receiver 501, and can also receive a high-precision local oscillator carrier frequency signal that can be used to calibrate the local oscillator in the GPS mobile device (Fig. 6).

The base station (FIG. 5A) comprises a receiver 504 that receives communication signals from a remote or mobile GPS device through a communication antenna 504a. It is clear that antenna 504a may be the same antenna as transmitter antenna 503a so that a single antenna serves both for transmission and reception. A receiver 504 is coupled to a data processing unit 502, which may be a known computer system. Processing unit 502 may also include an internal connection 512 for receiving Doppler and / or other satellite data information from a GPS receiver 511. This information can be used in processing pseudorange information or other information that is received from the mobile device through the receiver 504. This data processing unit 502 is connected to a display device 508, which may be a known cathode ray tube (CRT). The data processing unit 502 is also associated with a mass storage device 507, which includes geographic information system software, such as a GIS Atlas (Strategis Mapping, Inc. of Santa Clara, California), which are used to display maps on a display device 508. Using such display, you can represent the location of the GPS mobile device on the display device relative to the displayed map.

An alternative base station (FIG. 5B) includes many of the elements shown in FIG. 5A. However, the base station of FIG. 5B includes a source 552 of Doppler and / or other satellite data information instead of receiving Doppler and / or other satellite data information from a GPS receiver, the information in this case being obtained from a telecommunication channel or radio channel in a known manner. This Doppler and / or other satellite information is transmitted via an internal connection 553 to the modulator 506. Another input signal of the modulator 506 (Fig. 5B) is the output signal of a local oscillator generating a high-quality reference signal, for example, a cesium standard generator. This reference oscillator 551 generates an exact carrier frequency used to modulate Doppler and / or other satellite data information, which is then transmitted through a transmitter 503 to a mobile GPS device.

FIG. 6 shows an embodiment of a mobile GPS device according to the invention using an accurate carrier frequency signal that is received through a communication channel antenna 601, which is similar to antenna 24 (FIG. 1A). Antenna 601 is connected to a modem 602 similar to modem 22 (FIG. 1A), wherein modem 602 is connected to an automatic frequency control circuit 603 that is synchronized by a signal with an exact carrier frequency sent by a base station according to one embodiment of the present invention. The automatic frequency control circuit 603 generates an output signal 604 synchronized with the exact carrier frequency. This signal 604 is compared using the comparator 605 to the output of the GPS local oscillator 606 via an internal connection 608. The result of the comparison, which is performed using the comparator 605, is the error correction signal 610, which is supplied to the frequency synthesizer 609. In this method, the frequency synthesizer 609 provides high-quality calibrated local oscillator signal supplied via internal connection 612 to GPS converter 614 with decreasing frequency. It is clear that the signal output from the internal connection 612 is similar to the local oscillator signal output from the internal connection 39 to the converter 42 (Fig. 1A), while the converter 42 is similar to a GPS down-converter which is connected to the GPS antenna 613 for receiving GPS signals . In an alternative embodiment, the result of the comparison performed by the comparator 605 is provided by an internal connection 610a, as an error correction to the DSP component 620, similar to the DSP IC 32 (FIG. 1A). In this case, an error correction signal 610 will not be output to frequency synthesizer 609. The automatic frequency control circuit can be performed using various known methods, including using a phase synchronization circuit or a frequency synchronization circuit or a block phase estimator.

7 depicts a sequence of actions in power control according to one embodiment of the invention. It is clear that in the art there are various methods used to reduce power consumption. These methods include lowering the frequency of the clock signal supplied to the synchronous clock component, as well as completely interrupting the power supply to a specific component or disabling its specific circuit. For example, it is obvious that the phase synchronization circuit and the generator circuit require start-up and stabilization times, and therefore the developer may decide not to reduce the power consumption for these components. The example shown in Fig. 7 begins at step 701 when various components of the system are initialized and are brought into a low power consumption state. Periodically or after a predetermined period of time, the communication receiver in the modem 22 is put into a state of full power consumption to determine whether commands were sent from the base station 10. This occurs at step 703. If at step 705 a location information request is received from the base device, then modem 22 signals this power control circuit at step 707. At this point in time, the connected receiver in modem 22 can be turned off for a predetermined period of time or disabled for subsequent periodic on readings at a later time interval (step 709). It will be clear that the connected receiver can be maintained in a state of full power, and not turn off at this point in time. Then, at step 711, the power control circuit puts the cascade of the GPS receiver of the mobile device into a state of full power consumption by supplying power to the converter 42 and analog-to-digital converters 44. If the frequency generator 38 was also in a low power state, then the full power is also supplied to this component , and it is possible to stabilize it for some time. Then, at 713, a GPS receiver, which includes elements 38, 42, and 44, receives a GPS signal. This GPS signal is buffered in memory 46, which also goes into full power consumption state when the GPS receiver goes into full power consumption state in step 711. After the information is sampled, the GPS receiver then goes into low power state in step 717, wherein typically, low power consumption is maintained for converters 42 and 44, while memory 46 stores full power consumption. Then, at step 719, the processing system returns to a state with full power consumption; in one embodiment, this includes supplying full power to the DSP IC 32. However, it is clear that if the DSP IC 32 also has power management functions, as in the embodiment shown in FIG. 1C, then the DSP IC 32a usually transferred to the state of consumption of full power at step 707. In one of the embodiments (figa), in which the microprocessor 26 performs the function of managing the power consumption, the processing system, for example, the DSP IC 32 can be returned to the state of consumption of full power at step 719. At step 721, the GPS signal is processed in accordance with the present invention (FIG. 3). Then, after processing the GPS signal, the processing system is in a low power consumption state, as shown in step 23 (if the processing system also does not control the power consumption, as noted above). Then, at step 725, the connected transmitter in modem 22 is put into a full power state for transmitting, at step 727, the processed GPS signal back to the base station 10. After completion of the transmission of the processed GPS signal, such as pseudorange information or latitude and longitude information, the connected transmitter is transferred to the low power consumption state at step 729, and the power control system waits for a delay time, for example, a predetermined time period, at step 731. Following this delay the communications receiver in modem 22 is put into a full power state in order to determine if a request has been sent from the base station.

Although the methods and devices of the present invention are described with reference to GPS satellites, it is obvious that they are equally applicable to positioning systems that use pseudoliths or combinations of satellites and pseudoliths. Pseudolites are ground-based transmitters that transmit a PS code (similar to a GPS signal) that modulates the carrier frequency of an L-band signal, usually synchronized with GPS time. Each transmitter can be allocated a unique MS code to ensure identification by a remote receiver. Pseudolites are advantageously used in situations in which GPS signals from orbiting satellites cannot be used, for example, in tunnels, mines, buildings or other closed areas. The term "satellite" as used herein includes pseudolith or equivalents of pseudoliths, and the term "GPS signals" includes signals similar to GPS signals from pseudoliths or equivalents of pseudoliths.

In the previous discussion, the invention is described with reference to applications in a global satellite positioning system (GPS) in the United States of America. However, it will be obvious that these methods are equally applicable to similar satellite orientation systems and, in particular, to the Russian Glonass system. The Glonass system differs from the GPS system mainly in that the radiation from different satellites differs from each other due to the use of slightly different carrier frequencies, instead of using different pseudo-random codes. In this situation, essentially all the schemes and algorithms described earlier are used, except that when processing new radiation coming from the satellite, another exponential multiplier is used for data preprocessing. This operation can be combined with the operation of the Doppler correction block 108 (figure 3) without the use of additional processing operations. In this situation, only one PS code is required, which allows to exclude block 106. The term GPS, which is used here, includes such alternative satellite positioning systems as the Russian Glonass system. Although FIGS. 1A, 1B, and 1C depict numerous logic blocks that process digital signals (eg, 46, 32, 34, 26, 30, 28 shown in FIG. 1A), it is necessary to bear in mind that several of these blocks or all of these blocks can be made in the form of a single integrated circuit, while maintaining the programmability property of the DSP block of such a circuit. Such an implementation may be important for applications characterized by low power consumption and depending on the cost.

You must also keep in mind that one or more operations (figure 3) can be performed using the "wired" logic in order to increase the overall processing speed while maintaining the programmability property of the DSP processor. For example, the Doppler correction ability of block 108 can be realized using appropriate hardware that can be placed between the digital dynamic memory 46 and the DSP 32 integrated circuit. All other software functions (Fig. 3) can be performed in such cases using the DSP processor. Also, several DSPs can be used with one remote device to increase processing power. It is also possible to obtain (sample) numerous sets of frames of GPS data signals and process each set, as shown in FIG. 3, taking into account the time of receipt of each set of frames.

A demonstration system, which is an example of an embodiment of the present invention, was designed to confirm the functioning of the described methods and algorithms and to test the sensitivity capabilities provided by these methods and algorithms. The demo system includes a GPS antenna, a frequency down converter (GEC Plessey Semiconductors), and a digital buffer panel (Gage Applied Sciences Inc.). The antenna and the downconverter perform the functions 38, 40, 42 and 44 (Fig. 1A), and the digital buffer performs the functions 44, 46 and 48 (Fig. 1A). The signal was processed on an IBM PC-compatible computer using a Pentium microprocessor running Windows 95. This simulates the functions of the DSP 32 ICs and memory peripherals 34. Doppler information for satellites in view was introduced into the signal processing software as input signals for signal processing procedures to emulate the functions of the modem and microprocessor 22, 24, 25, 26.

Algorithms for this demo system were developed using the MATLAB programming language. A large number of tests were performed on real GPS signals obtained in various situations of signal transmission blocking. These tests confirmed that the sensitivity characteristic of the demonstration system was substantially higher than that of various commercial GPS receivers that were tested at the same time. Appendix A shows a detailed printout of the MATLAB program (machine code) that was used in these tests and was an example of fast convolution operations according to the present invention (for example, FIG. 3).

In the foregoing description, the invention has been described with reference to a specific embodiment. It should be clear that various modifications and changes are possible without changing the essence and scope of the invention as disclosed in the claims. Description and drawings, respectively, should be considered as an illustration, and not as a limitation.

Claims (30)

1. The method of determining the location of a mobile device, which consists in the fact that
receive in the mobile device the Doppler information of the satellite in the field of view of the mobile device from the transmission cell in the cellular communication system, and
calculate location information for a satellite in a mobile device using Doppler information. 2. The method according to claim 1, characterized in that the Doppler information is received from the GPS receiver in the base station. 3. The method according to claim 1, characterized in that the location information includes pseudorange to a plurality of satellites in the field of view of a mobile device, including said satellite. 4. The method according to claim 3, characterized in that it further
transmit pseudorange from the mobile device to the base station, and in this case, the latitude and longitude, which indicate the location of the mobile device, are calculated in the base station. 5. The method according to claim 1, additionally containing the use of Doppler information in the processing device to compensate for the Doppler shift of GPS signals from said satellite. 6. A mobile device that uses data representing GPS signals to calculate the location of a mobile device containing
a receiver configured to communicate via a cellular communication channel in a transmission cell for receiving Doppler information of a satellite in view of a mobile device,
a processing device associated with the receiver for receiving Doppler information and calculating location information for said satellite using Doppler information. 7. The mobile device according to claim 6, characterized in that the processing device uses Doppler information to compensate for the Doppler shift of GPS signals from said satellite. 8. The mobile device according to claim 7, characterized in that the cellular communication channel is a radio frequency communication medium. 9. The mobile device according to claim 7, characterized in that it further comprises
a transmitter associated with the processing device, wherein the transmitter is for transmitting location information. 10. The mobile device according to claim 7, characterized in that the location information includes pseudorange to a plurality of satellites in the field of view of the mobile device. 11. The mobile device according to claim 7, characterized in that the processing device contains an integrated circuit for digital signal processing (digital signal processing device (DSP)), and the DSP processes GPS signals and Doppler information using a fast convolution algorithm. 12. The mobile device according to claim 11, characterized in that it further comprises a transmitter associated with the processing device, wherein the transmitter is for transmitting location information. 13. The use of a base station to provide a communication channel with a mobile device, namely, that
determining the Doppler information of the satellite in the field of view of the mobile device, wherein the Doppler information is used in the mobile device to determine location information for said satellite,
transmit the Doppler information of said satellite in view from a cellular transmission cell in a cellular communication system to a mobile device, wherein location information is determined in the mobile device. 14. The method according to item 13, wherein the Doppler information represents the Doppler shift of GPS signals from said satellite to said base station. 15. The method according to 14, characterized in that the Doppler information approximately represents the Doppler shift of the GPS signals from said satellite to said mobile device. 16. The method according to item 13, wherein the Doppler information is received from the GPS receiver in the base station, and the Doppler information represents the Doppler shift of GPS signals from said satellite to said base station. 17. The method according to clause 16, wherein the Doppler information approximately represents the Doppler shift of the GPS signals from said satellite to said mobile device. 18. The method according to 17, characterized in that it further
receiving location information from the mobile device, the location information being received at the base station so that latitude and longitude are obtained at the base station, which indicate the location of the mobile device. 19. The method according to p. 18, characterized in that the location information includes pseudorange to many satellites in the field of view of the mobile device, including the said satellite, and at the same time, said latitude and longitude are calculated from the pseudorange at the base station. 20. A base station for providing a cellular communication channel to a mobile device, comprising a source of Doppler information for a satellite in the field of view of the mobile device,
a transmitter associated with the source of Doppler information, the transmitter is designed to transmit Doppler information through a cellular communication channel in a cellular transmission cell to a mobile device, wherein the mobile device determines location information. 21. The base station according to claim 20, characterized in that the Doppler information source is a memory device associated with the base station, the memory device storing pre-computed approximate Doppler information for the satellite. 22. The base station according to claim 20, characterized in that it further comprises a receiver for receiving location information from a mobile device, a processor associated with the receiver. 23. The base station according to claim 20, characterized in that the Doppler information represents the Doppler shift of the GPS signals from said satellite to said base station. 24. The base station according to item 23, wherein the Doppler information approximately represents the Doppler shift of GPS signals from said satellite to said mobile device. 25. The base station according to claim 20, characterized in that the Doppler information is received from a source that contains a receiver in the base station, and the Doppler information represents the Doppler shift of GPS signals from said satellite to said base station. 26. The base station of claim 25, wherein the Doppler information approximately represents the Doppler shift of GPS signals from said satellite to said mobile device. 27. The base station according to item 22, wherein the location information is received in the base station so that the base station receives latitude and longitude, which indicate the location of the mobile device. 28. The base station according to claim 27, wherein the location information includes pseudoranges to a plurality of satellites in the field of view of a mobile device, including said satellite, and wherein said base station processor calculates said latitude and longitude from pseudoranges. 29. The base station according to item 23, wherein the base station and the mobile device are within approximately 150 km from each other. 30. A method for determining the location of a mobile device, which consists in the fact that
transmit satellite information, including Doppler information, to the mobile device from the base station via the cellular data transmission channel through the cellular transmission cell in the GPS cellular communication system,
receive satellite information and GPS signals from satellites in view in a mobile device,
calculate in a mobile device pseudorange to satellites in view, and when calculating pseudorange using Doppler information,
transmit pseudorange to the base station from the mobile device through the cellular data channel and
calculate the location of the mobile device in the base station using pseudorange.

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