Aiding in a satellite positioning system

(Background of invention) (Refer to 1. Related application) This application is a United States patent with serial number 10 / 155,614, filed May 22, 2002, entitled "Reducing the Search Area for Frequency Transmission in Multiple Mode Global Positioning Systems Used with Wireless Networks". It is a continuation application of the application. The application was filed on February 28, 2001, entitled "Transmission of Information in Multiple Mode Global Positioning Systems Used with Wireless Networks," and is now a United States patent with patent number 6,427,120, serial. It is a partial continuation of the United States patent application numbered 09 / 795,871. The application claims priority over the United States provisional patent application with serial number 60 / 225,076 filed on August 14, 2000 under Section 119 (e). All of these applications are incorporated into this application by citation.

(2. Technical field of invention) This application relates to a satellite positioning system (SPS) receiver. In particular, it relates to improving receiver accuracy by providing information to the SPS receiver and correcting the frequency offset between the receiver oscillator and the satellite oscillator.

(3. Related technology) Satellite Positioning System (SPS) receivers, such as the Global Positioning System (GPS) receiver, also known as NAVSTAR, receive radio waves from satellite-based radionavigation systems. Use those received radio waves to locate the SPS receiver. Knowing the distance from the SPS receiver to the three SPS satellites whose satellite positions are known, the position of the SPS receiver can be determined by applying the well-known concept of intersections.

In general, each satellite in a satellite-based radio navigation system transmits radio waves including its own position information and orbit information. More specifically, each satellite orbiting in a GPS system has four highly accurate atomic clocks: two cesium clocks and two rubidium clocks. These clocks are used to generate two unique binary codes (also known as signal-to-noise ratio (PRN) or pseudo-noise (PN)) codes that are sent to each. Provides precise timing pulses. The PN code identifies a particular satellite in the satellite group. The satellite also sends a set of digitally coded ephemeris data that fully identifies the satellite's precise orbit. Ephemeris data show where the satellite is located at any time, and its position is identified as the satellite's ground wake by precise latitude and longitude measurements. The information in the ephemeris data is encoded and transmitted from the satellite to provide an accurate indicator of the exact position of the satellite orbiting the earth at any time.

The atomic clock is very accurate, about 10 throughout the cycle of the day¹³Despite having a one-to-two stability, over time the clock will have a slight error (commonly known as clock drift), resulting in a satellite clock error of approximately 8.64 to 17.28 ns per day. Bring. That corresponds to an error in the distance of 2.59-5.18 meters. To compensate for that error, the accuracy of the satellite's atomic clock is continuously monitored by the ground station of the GPS control system, and any error and drift detected in the satellite clock is calculated and of a quadratic polynomial. It is transmitted by the satellite as part of the navigation message in the form of three coefficients.

In the case of GPS, there is nominally a group of satellites consisting of 24 operating satellites orbiting the earth. Each satellite has an individual PN code and an orbit close to a circle. Its orbit has an inclination of 55 degrees with respect to the equatorial plane, an altitude of 10,898 nautical miles (20,200 kilometers) above the surface, and an orbital period of approximately 12 hours. Each GPS satellite transmits a microwave radio signal consisting of two carrier frequencies modulated by two digital codes and a navigation message. The two carrier frequencies are called "L1" and "L2" carriers and are transmitted at 1,572.42 megahertz (MHz: megahertz) and 1,227.60 MHz, respectively. The two GPS codes are coarse capture codes (C / A (coarse)). They are called acquisition code) and precision code (P (precision) code). Each code consists of a stream of 0 and 1 bits known as bits or "chips". Both the C / A code and the P code are commonly referred to as the PN code. Because they look like messy, noisy signals. Currently, the P code is modulated on both the L1 and L2 carriers, while the C / A code is modulated only on the L1 carrier.

Since the C / A code is a stream of 1,023 bits that repeats every millisecond, it has a chip speed of 1.023 MHz. Each satellite is assigned its own C / A code, allowing the GPS receiver to identify which satellite is transmitting a particular code. Distance measurement by C / A code is relatively inferior to P code, but it is not complicated and can be used by all users. The P code is largely restricted to US government and military use.

Each satellite also sends GPS navigation messages, which are data streams added to the L1 and L2 carriers as two-phase phase modulation at 50 kilobits per second (kbps). The navigation message contains GPS satellite coordinates as a function of time, satellite health, satellite clock correction factors, satellite almanac, and atmospheric data, along with other information. Each satellite sends its own navigation message along with information on other satellites, such as approximate location and health.

By receiving these radio signals transmitted from the satellite, the GPS receiver can identify from the satellite how long it has taken for the GPS receiver to receive the signal transmitted from the satellite. It is possible to calculate its own distance. For example, by identifying its own distance from three satellites, a GPS receiver can calculate its own two-dimensional position (latitude and longitude, or X and Y). Similarly, by measuring its own distance from the four satellites, the GPS receiver can calculate its own three-dimensional position (latitude and longitude and altitude, or X and Y and Z).

Unfortunately, this technique assumes that the measured distance from the GPS receiver to the satellite is very accurate and that there is no bias error. However, in practice, the measured distance between the GPS receiver and each satellite usually has a certain unknown bias. This is because the GPS receiver clock (GPS-CLK) is usually different from the GPS satellite clock. For the purpose of eliminating this bias error, the calculation of the position of the GPS receiver requires the transmission signal of another satellite.

In general, in order to receive a signal transmitted by a satellite, the GPS-CLK of the GPS receiver must be synchronized with that of the GPS satellite. Any error in synchronization between those clocks causes inaccuracy in measuring the position of the GPS receiver. Atomic clocks, such as those found on GPS satellites, are very expensive, usually costing thousands of dollars for rubidium clocks and tens of thousands of dollars for cesium clocks. Therefore, their use is not practical for the general consumer of GPS receivers. Inexpensive and less accurate clocks, such as crystal clocks, are commonly used in GPS receivers as GPS-CLK. However, if GPS-CLK inaccuracies are not identified and corrected, the satellite's synchronization with the atomic clock will only be partially resolved, resulting in partial distance measurements calculated by the GPS receiver. Will be inaccurate. Therefore, the GPS-CLK error remains one other unknown variable that must be identified in order to pinpoint the location of the GPS receiver.

Apart from accuracy, another issue with GPS-CLK error with respect to GPS satellite clocks is the resulting GPS receiver acquisition time, commonly known as time to first fix (TTFF). .. For many applications, such as the E911, GPS receivers must be able to provide location solutions shortly after the GPS receiver is turned on. Unfortunately, GPS-CLK can have large frequency drifts during the first few minutes of powering up. This large frequency drift can lead to significant degradation of the TTFF's performance and can lead to a lack of navigational positioning in a weak signal environment.

In addition to GPS-CLK frequency drift, there are several other factors that can affect the performance of TTFF. There are many GPS satellites over the atmosphere, but it is not always possible for a GPS receiver to receive transmitted signals from the number of GPS satellites it needs to calculate its location. .. Some challenges prevent GPS receivers from receiving from the required number of satellites and receiving accurate signals due to transmission and reception errors. These challenges can result in long TTFF times.

For example, a GPS receiver will not be able to receive the required number of GPS transmission signals due to physical interference in the atmosphere or on the ground. Instead, even if the GPS receiver is able to receive the required signal, the signal may be inaccurate due to the following: (1) satellite clock error; (2) receiver clock error; (3) Calculated satellite position error; (4) Atmospheric error due to ionization layer or convection zone; (5) Multipath error due to reception of reflected signal; (6) Receiver measurement error and / or (7) Selection error or artificial error. These inaccuracies are 30 because GPS receivers need to obtain ephemeris data from the GPS system itself, and GPS receivers usually require strong signals to reliably obtain ephemeris data. May result in TTFF time exceeding seconds.

Since the start of GPS, methods have been developed to reduce the error and increase the accuracy of GPS systems, and are still being developed. In addition, it provides GPS receivers with information about unknown variables or inaccuracies in the system so that the system does not always need to receive satellite transmission signals from all satellites or receive accurate transmission data. Numerous different methods have been implemented to provide alternatives to the system.

One technology that has been introduced to help overcome the errors in GPS systems is Differential GPS. With differential GPS, a receiver with a known position receives a GPS signal and calculates its own position from the received signal. The calculated position is compared to the known position of the actual receiver. The difference between the known position and the calculated position can be used to calculate the error in the transmitted signal. These errors are transmitted to a receiver whose position is unknown (mobile receiver) and can be used by the mobile receiver to more accurately calculate its own position.

Differential GPS is typically used to compensate for errors other than receiver or multipath. However, in order to correct the error of the receiver by the same method as the differential GPS, the corrected data may be transmitted to the GPS receiver. For example, one method used to correct for errors in GPS-CLK was to send a precise carrier frequency signal from a second source, such as a base station, to a GPS receiver. In this application, the GPS receiver is designed to receive a precise carrier frequency signal, calibrating and / or locking GPS-CLK to a precise carrier frequency. However, this method is usually additional, first locking GPS-CLK to a precise carrier frequency and / or calibrating, and then maintaining dynamic synchronization between GPS-CLK and the precise carrier frequency. It requires a complicated circuit.

Therefore, the dynamic approach compensates for the error created by GPS-CLK drift and position accuracy, without the use of additional and complex circuitry and without major changes to existing hardware. There is a need for ways to improve the error and improve the TTFF.

(Summary) The present invention relates to subsystems within a wireless device that support a Global Positioning System (GPS). The wireless device comprises a radio processing section capable of receiving signals from a wireless network and a GPS subsystem having a radio frequency (RF) front end capable of receiving GPS satellite signals. The radio processing section of the radio device receives an external clock and identifies the offset between the clock of the radio processing section and the external clock. The GPS subsystem receives information about its offset from its radio processing section, information about the nominal frequency of the clock in the radio processing section, and the clock in the radio processing section. Using this information and the GPS clock in the GPS subsystem, the GPS subsystem identifies the captured signal for the frequency offset between the GPS clock and the network clock. The GPS subsystem then uses the capture signal in the capture unit to capture the GPS satellite signal.

Other systems, methods, properties and advantages of the present invention will be apparent or will become apparent to those skilled in the art by examining the accompanying drawings and detailed description. All of these additional systems, methods, properties and advantages are contained within the scope of the description of the present application, are within the scope of the object of the invention and are intended to be protected by the appended claims. To do.

(Detailed explanation) FIG. 1 is an example of a GPS system 100 using a wireless device 102 with a GPS receiver (not shown). The GPS receiver is installed inside the wireless device 102. As shown in FIG. 1, during operation, the wireless device 102 can signal and communicate with the wireless network 104 via the base station 106 and the wireless transmission path 108. The wireless device 102 can signal communicate with at least one satellite of the GPS satellite group 110 via the signal communication path 112.

The wireless device 102 includes both a GPS receiver (not shown) and a wireless processing section (not shown). The GPS receiver inside the wireless device 102 can receive GPS signals from the GPS satellite group 110 via the signal communication path 112. The radio processing section of the radio device 102 can receive radio communication signals from the radio network 104 via the signal transmission path 108 and the base station 106. In some embodiments, the wireless device 102 may transmit a wireless communication signal to the wireless network 104 via a signal transmission path 108 and a base station 106. The wireless device 102 may be a wireless terminal, such as a cellular phone (also known as a cell phone, mobile phone, mobile phone), or any other type of mobile device, personal digital assistants (PDAs). , Pager, computer, bidirectional radio, trunk radio, specialized mobile radio (SMR) Radio), or any other device for which it is desirable to identify location information, but is not limited to these. In the case of a cellular telephone, the wireless device 102 may utilize a cellular transmitter / receiver operating in any radio frequency (RF) band that utilizes any communication method. The arbitrary communication method includes CDMA, CDMA-2000, W-CDMA, TDMA, FDMA, GSM, UMTS, AMPS, Bluetooth, Wi-Fi and / or any combination of these communication methods or similar communication methods. Extensions are included, but not limited to these.

FIG. 2 is an example of a block diagram of the wireless device 102 shown in FIG. As shown in FIG. 2, the wireless device 102 includes both a wireless processing section 200 and a GPS subsystem 202. The wireless processing section 200 implements the processing function of the wireless application and may include a wireless transmitter / receiver. For example, in the case of a cellular telephone, the wireless device 102 would include a call processing section along with a cellular transmitter / receiver. The GPS subsystem includes a GPS receiver (not shown) for receiving satellite transmission signals 204 from satellite 205 and a GPS engine (not shown) that performs the position calculation function of the wireless device 102. By integrating the technology of the wireless device 102 and the technology of the GPS subsystem 202, the wireless device 102 provides two main service systems: the service system of the wireless device such as the cellular telephone service and the wireless device 102. A GPS receiver service system that provides location information. For those skilled in the art, this integration is the Federal Communications Commission (FCC). It can be seen that it offers many benefits, including compliance with Commission's E911 requirements.

Communication between the radio processing section 200 and the GPS subsystem 202 takes place within or instead of the radio device 102 between the radio device 102 and the cross subsidization device (not shown) of the radio device 102. These communications allow signals to be transmitted from the radio processing section 200 to the GPS section 202 and are carried out over a serial or parallel communication link 206 (eg RS232 serial communication link) and a hardware line 208. However, other connections may be used if desired.

For example, in one other embodiment, the radio processing section 200 and the GPS subsystem 202 may share the same digital processor (not shown) and / or other circuits. In such cases, the communication between the radio processing section 200 and the GPS subsystem 202 is achieved by intertask communication, with some data transmissions such as the time and frequency between the radio processing section 200 and the GPS subsystem 202. The transmission will be done inside the circuit without the use of hardware line 208. Alternatively, depending on the circuit design, transmission may not be required.

As shown in FIG. 2, GPS satellite 205 transmits the spread spectrum signal 204 received by the wireless device 102. For illustration purposes, satellite 205 represents a group of satellites 205 in a GPS system. If the wireless device 102 is capable of receiving a sufficiently strong signal 204, then the GPS subsystem 202 of the wireless device 102 is that of the wireless device 102, as is commonly done in a stand-alone GPS system. The position can be calculated. However, in many cases, the GPS subsystem 202 cannot receive a sufficiently strong signal 204, or signal 204 from a sufficient number of available GPS satellites 205 to autonomously calculate the position of the wireless terminal. Cannot be received. This means the initial positioning time (TTFF; time to first). fix) will result in a long one. However, the wireless device 102 is still capable of communicating with the base station 106. Thus, base station 106 is capable of communicating information with wireless device 102 via signal 108, which allows wireless device 102 to improve its own TTFF and calculate its own position. Alternatively, in some applications (though not requiring implementation of the present invention), a server of wireless network 104 capable of signal communication with base station 106, allowing information to be communicated from wireless device 102 to base station 106. (Not shown) can calculate the position of the wireless device 102. When base station 106 transmits information to wireless device 102 to allow wireless device 102 to calculate its own position, it is commonly known as "assisted GPS".

As further shown in FIG. 2, both the radio processing section 200 and the GPS subsystem 202 of base station 106 and radio device 102 include an internal clock produced by an internal clock circuit. For illustration purposes, the clock of the radio processing section 200 is shown as "WPS-CLK" 210 and the clock of the GPS subsystem 202 is shown as "GPS-CLK" 212. Normally, WPS-CLK210 and GPS-CLK212 are inexpensive clocks produced by a crystal oscillator that is not very accurate when compared to the atomic clocks of GPS satellite 205. Therefore, in order to shorten the TTFF and calculate the position of the wireless device 102 accurately, the error of GPS-CLK212 should be clarified. In contrast to WPS-CLK210 and GPS-CLK212, the clock at base station 106 is highly accurate. For CDMA radio networks, the clock at base station 106 would be in sync with the atomic clock at GPS satellite 205. For the purposes of illustration, the clock of this base station 106 is "BS-CLK" 214 or "standard clock" (STD-CLK; Standard). Clock) Shown as 214. In operation, STD-CLK214 is transmitted to the radio processing section 200 of the radio terminal 102 via the signal communication path 108. As described in more detail below, the radio processing section 200 of the radio terminal 102 is shown as the first offset value ("STD-WPS-OFFSET") corresponding to the difference in frequency between STD-CLK214 and WPS-CLK210. ) Is calculated. The STD-WPS-OFFSET is then communicated with the WPS-CLK210 and GPS-CLK212 to the GPS subsystem 202 using that STD-WPS-OFFSET, with a second offset value between GPS-CLK212 and STD-CLK214 ("GPS". -Indicated as "STD-OFFSET") is estimated. GPS-STD-OFFSET is then used by GPS subsystem 202 to capture GPS signals received from GPS satellite 204.

FIG. 3 is a schematic block diagram of the offset circuit 300 inside the GPS subsystem shown in FIG. 2 for generating the GPS-STD-OFFSET. The offset circuit 300 includes an offset counter 302, the offset counter 302, and an offset coupler 304 capable of signal communication. The offset circuit 300 is capable of signal communication with the radio subprocessor 306 located in the radio processing section 200. The wireless subprocessor 306 receives STD-CLK214 and WPS-CLK210, and a WPS initialization message with information about the nominal frequency of WPS-CLK210 (referred to as "N-WPS-CLK") accordingly. Produce a WPS periodic message with information about STD-WPS-OFFSET. N-WPS-CLK information is sent to the offset counter 302 via the first offset bus 308, and STD-WPS-OFFSET is sent to the offset coupler 304 via the second offset bus 310. .. The offset counter 302 receives N-WPS-CLK information via the first bus 308, and receives GPS-CLK212 and WPS-CLK210. Accordingly, the offset counter 302 generates an offset signal (or message) with information about the frequency difference between WPS-CLK210 and GPS-CLK212 (referred to as "GPS-WPS-OFFSET"). , The offset signal is transmitted to the offset coupler 304 via the third offset bus 312. The offset coupler 304 then combines information about the STD-WPS-OFFSET and GPS-WPS-OFFSET and sends it to the rest of the GPS subsystem via the message bus (or signal path) 314. -Create GPS-OFFSET.

FIG. 4 shows a basic block diagram of the GPS subsystem 202 of FIG. In FIG. 4, the GPS subsystem 202 comprises a GPS-CLK212 and a GPS processor section 400 that receives at least one signal from the radio processing section 200 via the signal bus 402. The radio processing section 200 receives communication data from the radio network 104 (Fig. 1) with STD-CLK214 (Fig. 2). The radio processing section 200 then generates a STD-WPS-OFFSET message indicating the frequency difference between WPS-CLK210 and STD-CLK214. The STD-WPS-OFFSET message is transmitted to the GPS processor section 400 via signal bus 402. GPS processor section 400 captures GPS satellite signals received when input to an internal capture unit (not shown) of GPS processor section 400 in response to STD-WPS-OFFSET and GPS-CLK212 reception. Generate STD-GPS-OFFSET to support.

FIG. 5 is a block diagram of an embodiment of the GPS processor section 400 of FIG. As shown in FIG. 5, the GPS processor section 400 includes a radio frequency (RF) front end 500, a GPS clock processor 502, a GPS code and carrier generator 504, and an analog-to-digital converter. ADC; analog-to-digital It includes a converter) 506 and a capture unit 508. The GPS frequency source 510 transmits a frequency reference to the RF front end 500, GPS code and carrier generator 504 and ADC 506. The RF front end 500 can be a standard GPS RF front end. In operation, the RF front end 500 receives GPS satellite signals, demolishes them (also known as frequency diminishing), and removes carrier frequencies from the data transmitted over the GPS satellite signals. The demodulation is achieved by mixing the received GPS satellite signals with the GPS frequency source 510. The resulting demodulated GPS satellite signal is then transmitted from the RF front end 500 to the ADC 506. In the ADC506, the demodulated GPS satellite signals are typically digitized into a bitstream of samples by some well-known sampling techniques. The resulting sample bitstream is then transmitted to the capture unit 508. To those skilled in the art, a voltage controlled oscillator (not shown) in a phase-locked loop (PLL) (not shown) in which the GPS frequency source 510 is locked to GPS-CLK212 by many well-known techniques. It can be seen that it may be a voltage-controlled oscillator (VCO) or a local oscillator (LO) (not shown) that includes a voltage-controlled crystal oscillator (VCXO) (not shown).

The capture unit 508 receives a sample bitstream from ADC506 and (if the RF front end 500 only diminishes the received satellite signal to an intermediate frequency (IF)) of the sample bitstream. After finishing the demodulation, it is usually decoded using a set of correlators (not shown) or a matched filter (not shown). If the capture unit 508 diminishes the sample bitstream from the IF frequency, the capture unit 508 has a step of mixing the GPS code and the Doppler-corrected frequency signal from the carrier generator 504 with the sample bitstream. Will. The result of that mixer would be a new bitstream of sample corrected for carrier Doppler shifts.

The correlator or matched filter correlates the bitstream of the sample from ADC506 with the PN code, which is the code of various satellites. The capture unit 508 produces a detection signal when the PN code corresponding to the satellite is correlated with the bit stream of a sample of the received satellite signal.

The PN code is produced by the GPS code and carrier generator 504. The GPS code generator 504 may include a numerically controlled oscillator (NCO) (not shown) that produces the PN code and other circuits (not shown) that correct for both carrier and code Doppler shifts. The GPS clock processor 502 can identify the STD-GPS-OFFSET. Once the GPS clock processor 502 generates the STD-GPS-OFFSET, it is transmitted to the GPS code and carrier generator 504. The GPS code and carrier 504 then combines the STD-GPS-OFFSET with a correction for Doppler shift and uses the combined result to remove the IF carrier and generate a PN code for the capture unit 508. To do.

The GPS code and carrier generator 504 attempts to compensate for the effects of Doppler shift on both the carrier and code of the received satellite signal. In general, satellite motion affects the processing of signals at GPS receivers. This is because the input frequency shifts as a result of the Doppler effect. Satellite motion causes a Doppler frequency shift at carrier frequency and coarse / acquisition (C / A) code. The angular velocity and velocity of the satellite can be calculated from the approximate radius of the satellite orbit, approximately 1.458 x 10^-4Radians / second and about 3,874 meters / second. The Doppler frequency shift is caused by the velocity component in the direction of the satellite's GPS receiver. Normally, the maximum Doppler speed is caused when the satellite is in a horizontal position, and the maximum horizontal Doppler speed from orbital speed is about 2,078 mph. This speed is equal to a high speed military aircraft. Therefore, the Doppler frequency shift caused by land vehicles is often very small, even if its motion is directed towards the satellite and produces the maximum Doppler effect. For the L1 frequency modulated by the C / A code, the maximum Doppler frequency shift is about 4.9KHz. Therefore, for stationary observers, the maximum Doppler frequency shift is around ± 5KHz. To create a ± 5 KHz Doppler frequency shift on its own, the vehicle must travel at approximately 2,078 mph towards the satellite. Thus, when the GPS receiver is used in a low speed vehicle, its Doppler shift is estimated to be ± 5kHz.

FIG. 6 is a block diagram of an embodiment of the GPS frequency source 510 of FIG. The GPS frequency source 510 may include GPS-CLK212 and PLL600. It can be seen that GPS-CLK212 is usually produced by a timing circuit (not shown) using a crystal oscillator 602. The PLL 600 is implemented by several techniques well known to those skilled in the art. For example, the basic components of a PLL are a phase detector (not shown), a loop filter (not shown) and a VCO (not shown) whose frequency is controlled by an external voltage and locked to the frequency of GPS-CLK212. Be prepared. In this embodiment, the GPS carrier and code generator 504 and the GPS clock processor 502 use GPS-CLK212 as a reference reference to generate their own individual frequencies. The RF front end 500 and ADC506 use frequencies from PLL600. Because they are usually associated by synchronization or utilize frequency values that are multiples of the other.

FIG. 7 is a simplified block diagram of an example of a GPS RF front end that utilizes direct conversion. The RF front end 500 may include an antenna 700 and a mixer 702. Mixer 702 is capable of signal communication with PLL600 and ADC506. The mixer 702 basically demodulates (ie, diminishes, or diminishes, the carrier frequency) the received satellite signal on the signal path 704 by taking the product of the received satellite signal and the frequency signal supplied by the PLL 600. It is a multiplier (which removes the signal). If the frequency of carrier 704 and the frequency of PLL600 of the received satellite signal are synchronized, that is, at the same frequency, the output of the mixer is a second harmonic that is removed by a low pass filter (not shown). It is a signal of a direct current component including. For example, if the signal on the signal path 704 is "x (t) cos (ωt)", "ω" is the angular velocity, and "t" is the time, then the PLL 600 is input to the mixer 702 "cos". Produces a demodulated signal 606 of (ωt) and the resulting mixer output 708 is x (t) cos²(ωt). x (t) cos²(ωt) is equal to x (t) (1 + cos (2ωt)) / 2, or x (t) / 2 + cos (2ωt) / 2.

If the frequency of carrier 704 of the received satellite signal is out of sync with the frequency of PLL600, there is no DC component. As another example, the signal on the signal path 704 is "x (t) cos (ωt)" and the PLL 600 sets the demodulated signal 606 to "cos (ω)".₁When produced as "t)", the resulting mixer output 608 is x (t) cos (ωt) cos (ω)₁t) would be. "Ω₁Is close to ω but differs by a small amount "Δω", the relationship is ω = ω₁Expressed as ± Δω. In this case, x (t) cos (ωt) cos (ω)₁t) is equal to x (t) cos (ωt) cos (ωt ± Δωt). This problem will be overcome by adjusting the frequency of the PLL 600 to synchronize it with the carrier frequency of the satellite signal. However, adjusting the frequency in the PLL 600 does not reveal the Doppler shift. It also affects the recognized frequency of the satellite carrier signal received in a dynamic manner. Instead of correcting the frequency during the demodulation stage of the RF front end, the correction may be done during the capture stage, i.e. in the capture unit 508. It may include Doppler shift correction.

FIG. 8 shows a simple block diagram of an embodiment of the capture unit 508. In the capture unit 508, the Doppler shift error and the PLL 600 are corrected using the frequency change generated by the PLL 600 by adjustment in the GPS code and carrier generator 504. The capture unit 508 may include multiple correlators or matched filters. For simplicity, the capture unit 508 is illustrated to include one correlator 800. However, it can be seen that those skilled in the art will most likely have multiple sets of correlators. In operation, the capture unit 508 receives a bit stream of samples that corresponds as closely as possible to the satellite signal received from the ADC 506. The capture unit 508 inputs the sample bitstream into a set of correlators or matched filters and receives the PN code from the GPS code and carrier generator 504. The PN code is then shifted through the matching correlator to produce an output that indicates when the satellite signal was received by the wireless device 102. Normally, the PN code is received from a GPS code and carrier generator 504 that is tuned to compensate for any Doppler shift for each satellite. However, in this case the GPS code and carrier generators 504 and PLL600 are also compensated to compensate for any frequency error in GPS-CLK212.

FIG. 9 shows a block diagram of the RF front end 900 and another embodiment of the capture unit 902 capable of communicating with the RF front end via the ADC 904. In this example, the RF front end 900 is a receiver at another stage, the satellite signal first received by antenna 906 is intermediate frequency (IF). Frequency) signal 908, eg, down to 96kHz, down through mixer 910, then down to baseband (ie, demodulated to zero) signal 912, down through mixer 914. The baseband signal 912 is then sent to the capture unit 902 through the ADC 904. In the capture unit 902, the baseband signal of the ADC sample is corrected for the Doppler carrier shift via the mixer 916 and sent to a set of correlators 918 or matched filters (not shown). Even if the frequency sources 918 and 920 are generated by a frequency generator 922 that multiplies or divides the frequency signal generated by the PLL 924 locked to GPS-CLK212 (using one of many well-known techniques). Good. Similarly, a GPS carrier and code generator 926 utilizing GPS-CLK212 may generate signals 928 and 930 that correct the carrier Doppler shift to drive a correlator 918 or a matched filter (not shown). ..

FIG. 10 shows a block diagram of the RF front end 1000 and yet another embodiment of the capture unit 1002 capable of communicating with the RF front end 1000 via the ADC 1004. In this example, the RF front end 1000 has only a mixing stage. The received satellite signal is received by antenna 1006 and mixed with IF frequency 1008 and mixer 1010. The IF frequency 1008 is generated by the frequency generator 1012 and mixed with the received satellite signal in the mixer 1010, diminishing the received satellite signal to an intermediate diminished signal 1014, eg 96 KHz. The intermediate diminished signal 1014 is sent through the ADC 1004 to the capture unit 1002. The ADC1004 digitizes the intermediate decremented signal into a sample bitstream and sends it to the capture unit 1002. In the capture unit 1002, the bit stream of the sample is fed to the second mixer 1016. The second mixer 1016 mixes the sample with the carrier Doppler correction signal 1018. It produces a bitstream of diminished samples corrected for carrier Doppler shift. The output of the mixer 1016 is fed to a set of correlators 1020 or matched filters to generate a detection signal if the satellite is captured. As already mentioned, the frequency generator 1012 is associated with the frequency 1026 of the PLL, and both the PLL and the GPS carrier and the code generator 1022 are associated with the GPS-CLK212.

FIG. 11 shows a block diagram of an embodiment of the GPS carrier and code generator 504. The GPS carrier and code generator 504 may include a Doppler prediction model 1100, an offset coupler 1102, and NCO registers 1104 and NC1106. In operation, the Doppler prediction model 1100 produces several Doppler correction values combined with the STD-GPS-OFFSET. These correction values are inputs to the NCO register 1104 that controls the NCO 1106. The NCO1106 then transmits the Doppler-corrected carrier signal and the PN code to the capture unit 508.

FIG. 12 shows a block diagram of an embodiment of the GPS clock processing device 502. The GPS clock processor 502 may include an offset counter 1200 and an offset coupler 1202. For example, the offset counter 1200 may receive signal 1204 from GPS-CLK212 and at least one signal 1212 from radio processing section 200. The offset counter 1200 then generates an offset signal indicating GPS-WPS-OFFSET. The offset signal is transmitted as a message to the offset coupler 1202 via the signal path 1206. The offset coupler 1202 then combines the information from the offset signal received via the signal path 1206 with the message received from the radio processing section 200 via the signal path 1208 indicating the STD-WPS-OFFSET. The output of the offset coupler 1202 is the offset signal 1210 indicating the STD-GPS-OFFSET. This offset signal 1210 is the input of the coupler 1102 of FIG.

As an example of operation, the offset counter 1200 can be used to measure the relative frequency offset between WPS-CLK210 and GPS-CLK. The gate signal to the offset counter 1200 may be generated by GPS-CLK212 via signal path 1204. The pulse width, also known as the gate time, is determined by counting the fixed number of GPS-CLK212 clock pulses. The offset counter 1200 also receives WPS-CLK210 via the signal path 1212. The offset counter 1200 then counts pulses from the clock of WPS-CLK210 during the gate time. In general, the offset counter 1200 counts the number of clock pulses (predicted number or predicted number) of WPS-CLK210 that will be equal to the frequency of WPS-CLK210 multiplied by the gate time. That is, (predicted number) = (frequency) × (gate time).

For example, the offset counter 1200 uses a virtual WPS-CLK210 frequency of 25 MHz per second to store 25,000,000 pulses from a frequency source, such as an oscillator. Therefore, the frequency offset can be specified as the amount obtained by subtracting the predicted number of frequencies of WPS-CLK210 from the reading of the actual count and dividing by the product of the frequency of WPS-CLK210 and the gate time. Described as a mathematical relationship, the frequency offset is: (frequency offset) = ((count reading)-(predicted number)) / ((frequency) x (gate time)).

Those skilled in the art will appreciate that the nominal frequencies of the GPS-CLK212 and WPS-CLK210 clocks are required to calculate the predicted number. The clock frequency of GPS-CLK212 is given via signal path 1204. To remove the compile-time parameter in the source code of GPS subsystem 202, radio processing section 200 identifies the nominal frequency of WPS-CLK210. Normally, this is to send a periodic frequency calibration message, including the WPS-CLK210 nominal frequency parameter, N-WPS-CLK, from the radio processing section 200 to the offset counter 1200 via the signal path 1204. Is done by. The GPS clock processor 502 can then calculate the relative frequency error without using prior knowledge of the clock characteristics of the WPS-CLK210.

To reduce the hardware complexity of the offset counter 1200, the offset counter 1200 modulos its own counting range and makes its numerical range smaller than the offset counter 1200's overall counting range. This allows the offset counter to count throughout, much smaller than the sum of the counts. For example, if the overall counting range is 1/5 million, the frequency of WPS-CLK210 is 20MHz, and the gate time is 1 second, the offset counter 1200 counts 5e.^-6× 20e⁶It can be reduced to about 100.

Using the difference between the predicted number and the actual count reading, the frequency offset of GPS-CLK212 can be calculated as shown below. First, the difference between the predicted number and the actual count is the frequency error of WPS-CLK210 (δf)._wps-lo), But also due to the gate time error and the resolution of the offset counter 1200. Assuming that the gate time of the offset counter 1200 controlled by the clock of GPS-CLK212 is t seconds, the clock frequency of GPS-CLK212 (δf)_gps-lo) Causes a gate time error (δt) of δt = δf_gps-lo × t. As a result, (frequency offset) = δf_wps-lo + δf_gps-lo + (Counting error) / (t × f_wps-lo).

The value measured by the offset counter 1200 is (δf)._gps-lo + δf_wps-lo). In theory, the GPS-CLK212 clock cannot be calibrated better than the WPS-CLK210 clock, and by extending the gate time (δf)._gps-lo + δf_wps-lo) Measurement accuracy can be improved. However, using too long a gate time is usually impractical. Therefore, the minimum gate time is generally predicted so that the estimated error of the relative frequency offset is within the desired design determined.

FIG. 13 is a flowchart illustrating the processing performed by the GPS subsystem 200. When processing begins (1300), the GPS clock processor 502 of FIG. 5 receives the GPS-CLK, WPS-CLK and STD-WPS-OFFSET of FIG. 13 (1302). After that, the GPS clock processor 502 identifies GPS-WPS-OFFSET and combines GPS-WPS-OFFSET and STD-WPS-OFFSET to generate STD-GPS-OFFSET (1306). The STD-GPS-OFFSET is then sent to the GPS carrier and code generator 504, where the STD-GPS-OFFSET is combined with the Doppler prediction to generate a correlated signal (1308). Correlated signals are used to regulate the NCO in GPS carriers and code generators (1310). The output of the NCO is then supplied to the capture unit 508 (1312), which in turn captures the received satellite signal using the correlation signal (1314). After that, the process ends (1316).

The process of FIG. 13 may be performed by hardware or software. In the case of hardware, the processing may be performed by a controller (not shown) in the radio processing section 200 or the GPS processing equipment section 400. That controller selectively eg Intel Corporation XXX86, Motorola's 68XXX or PowerPC, or their, performing any general purpose processor or such other equivalent ones, instruction software resident controllers (not shown) It may be a GPS and / or cellular-specific processor capable of. Instead, a GPS-dedicated circuit or a GPS device may be selectively used. The controller may optionally be integrated into a signal semiconductor chip such as an application specific integrated circuit (ASIC), reduced instruction set computer (RISC), or digital. It can be seen that it may be implemented via a signal processor chip.

If the processing is performed by software, the software is on software memory (not shown) of wireless device 102 (either in wireless processing section 200 and / or GPS subsystem 202) or on wireless network 104. It only needs to be resident on the server. The software in software memory may include an ordered list of executable instructions for the purpose of implementing logical functions (ie, "logic" is digital, for example digital circuits or source code. It may be implemented in a format, or in an analog format such as an analog circuit or an analog source such as an analog potential, audio or video signal). The ordered list of executable instructions reads instructions selectively from an instruction execution system, device or device, or its instruction execution system, device or device, such as a computer-based system or a system containing a processor. It can be selectively embodied as any computer-readable medium utilized by, or combined with, other systems capable of executing the instructions. As used herein, "computer-readable medium" and / or "signal-carrying medium" includes programs used by, or combined with, an instruction execution system, device or device. It may be any means that can be stored, communicated, propagated, or transported. The computer-readable medium may optionally be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, device, or propagation medium. These are for purposes of illustration only and are not limited thereto. A more specific example of a computer-readable medium, the "unerased list", includes: Electrical connection with one or more wires (electronic), portable flexible disc (magnetic) ), RAM (electronic), read-only memory "ROM" (electronic), erasable read-only memory (EPROM or flash memory) (electronic), fiber optic (optical), small portable read-only Memory "CD-ROM" (optical). The computer-readable medium may be paper or other suitable medium on which the program is printed. The paper or other suitable medium is electronically recognized by the program by scanning it optically, compiled if necessary, translated, or otherwise properly processed and stored in computer memory. It is saved in.

As mentioned above, the GPS system of the present invention can be incorporated into a number of wireless mobile applications. Similarly, the GPS system can be used in combination with a number of ground location services capable of receiving frequency information. Such GPS systems operate in mobile devices operating in network-assisted or network-based service mode, or in multiple modes, thereby during stand-alone mode, network-assisted mode, network-based mode, or other modes. Can be used in combination with a mobile device capable of receiving frequency information from a second source, such as a base station.

Although various embodiments of the present invention have been described, it will be apparent to those skilled in the art that more embodiments and embodiments are feasible within the scope of the invention. Therefore, the present invention is not limited except to take into account the appended claims and their equivalents.

(A brief description of the drawing) The present invention will be easier to understand by referring to the drawings below. The components of the drawings are not necessarily at a constant scale, instead emphasis is used to articulate the principles of the invention. In the drawings, the same reference numbers indicate corresponding parts through different drawings.<figref num="1">FIG. 1 is an example of a GPS system using a wireless device equipped with a GPS receiver. The GPS receiver is installed inside the wireless device.</figref><figref num="2">FIG. 2 is an example of a block diagram of the wireless device shown in FIG.</figref><figref num="3">FIG. 3 is a schematic block diagram of the offset circuit inside the GPS subsystem shown in FIG. 2 that generates the GPS-STD-OFFSET.</figref><figref num="4">Figure 4 shows the basic block diagram of the GPS subsystem in Figure 2.</figref><figref num="5">FIG. 5 is a block diagram of an embodiment of the GPS processing section of FIG.</figref><figref num="6">FIG. 6 is a block diagram of an example of a GPS frequency source.</figref><figref num="7">FIG. 7 is a simplified block diagram of an example of a GPS RF front end that utilizes direct conversion.</figref><figref num="8">Figure 8 shows a simple block diagram of the capture unit.</figref><figref num="9">Figure 9 shows a block diagram of the RF front end and one other embodiment of the supplementary unit. It can signal and communicate with the RF front end via the ADC.</figref><figref num="10">Figure 10 shows a block diagram of the RF front end and one other embodiment of the capture unit. It can signal and communicate with the RF front end via the ADC.</figref><figref num="11">FIG. 11 shows a block diagram of an embodiment of a GPS carrier and code generator.</figref><figref num="12">FIG. 12 shows a block diagram of an embodiment of a GPS clock processor.</figref><figref num="13">FIG. 13 is a flowchart illustrating the processing performed by the GPS subsystem.</figref>