System and method for multipath mitigation for global navigation satelite systems

Abstract

The present invention is directed to satellite navigation communication methods and systems. In a specific embodiment, the present invention provides a receiver for mitigating multipath effect during a GNSS signal receiving process. An embodiment of the present invention provides a method of using an antenna switch to sequentially select one antenna among multiple antennas during each sampling period to input GNSS signal into a single RF chain path and using software to control switching and correlation measurement in baseband processing. There are other embodiments as well.

Description

SYSTEM AND METHOD FOR MULTIPATH MITIGATION FOR GLOBAL NAVIGATION SATELITE SYSTEMSBACKGROUND OF THE INVENTION

[0001] The present invention is directed to satellite navigation communication methods and systems.

[0002] A Global Navigation Satellite System (GNSS) — commonly known as Global Positioning System (GPS) in the US — receiver is a device that receives signals from multiple GNSS satellite constellations to determine its position, velocity, and time. However, the accuracy of GNSS positioning can be affected by various sources of errors and interference, including the multipath effect. The multipath effect occurs when the GNSS signals reflect off nearby surfaces such as buildings, trees, or the ground before reaching the receiver antenna. These reflected signals can add to the direct signals received by the antenna, creating interference that can cause errors in the GNSS measurements.

[0003] To mitigate the effects of multipath interference, GNSS receivers employ techniques on antenna design, signal processing, and various mitigation algorithms. An optimal design for a GNSS antenna is to have equal gain in the direction of the satellite and zero gain in the lower hemisphere. However, due to the small form factor of the device, as well as coupling with other surrounding electric and non-electric components, and blocking effects from the user's hands and body, achieving this ideal design is challenging.

[0004] Therefore, new and improved systems and methods for mitigating multipath effects in GNSS systems are desired.BRIEF SUMMARY OF THE INVENTION

[0005] The present invention is directed to satellite navigation communication methods and systems. In a specific embodiment, the present invention provides a receiver for mitigating multipath effect during a GNSS signal receiving process. An embodiment of the present invention provides a method of using an antenna switch to sequentially select one antenna among multiple antennas during each sampling period to input GNSS signal into a single RF chain path and using software to control switching and correlation measurement in baseband processing. There are other embodiments as well.

[0006] A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. One general aspect of the present disclosure includes a receiver for satellite signal multipath mitigation. The receiver includes a first antenna configured to receive a first signal from a satellite and a second antenna configured independently to receive a second signal from the satellite. The receiver also includes a switch configured to select the first antenna to an input line during a first portion of a sampling period and select the second antenna to the input line during a second portion of the sampling period. Additionally, the receiver includes a first circuit coupled to the input line to receive and process the signal alternately from the first antenna during the first portion of the sampling period and from the second antenna during the second portion of the sampling period to provide respective digital signal. Furthermore, the receiver includes a second circuit comprising a first correlator and a second correlator, the first correlator and the second correlator being configured in parallel to couple to the first circuit to perform correlation measurements based on the digital signal. Moreover, the receiver includes a controller configured to control the switch to sequentially select the first antenna in the first portion of each sampling period and select the second antenna in the second portion of each sampling period, and to provide a blanking signal synchronously to the second correlator in the first portion of each sampling period and to the first correlator in the second portion of each sampling period. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods. In some embodiments, a receiver for satellite signal multipath mitigation may be associated with a system with a switch that can switch between multiple (more than two) antennas to select one antenna during each sampling period to input GNSS signal into a single RF chain path and using software to control switching and correlation measurement in baseband processing.

[0007] Implementations may include one or more of the following features. The receiver where the first circuit may include a filter coupled to the input line, the filter may include a narrow bandwidth and high selectivity, being configured to filter out unwanted signals outside of desired frequency band associated with the first or second signal. The first circuit further may include an amplifier coupled to the filter and configured to amplify a signal filtered by the filter by increasing its amplitude and improving signal-to-noise ratio. The firstcircuit further may include a mixer coupled to the amplifier and configured to mix a signal amplified by the amplifier with a local oscillator (LO) signal to generate an intermediate frequency (IF) signal. The first circuit further may include a gain controller coupled to the mixer and configured to automatically adjust gain of the first circuit to maintain a constant output level in the presence of variations in input level of the IF signal. The first circuit further may include an analog-to-digital converter configured to convert an analog output of the gain controller to the digital signal. The first (second) correlator is configured to compare the digital signal with a locally-generated replica data and update the measurement with a code phase report in a reporting rate of 1 to 10 Hz or without updating the measurement based on the blanking signal in the second (first) portion of the sampling period. The second circuit further may include a baseband processor configured to select a smallest code phase report updated by either the first correlator or the second correlator. The first (or second) correlator updating the smallest code phase report corresponds to the first (or second) antenna receiving the first (or second) signal as a light-on-sight signal from the satellite into the input line. The controller may include a software to set a switching frequency to one switching operation per sampling period of 500 ms to 1 sec. and to provide the blanking signal synchronously to the first (or second) correlator when the second (or first) antenna is selected by the switching operation. Either the first antenna or the second antenna may include a signal sampling rate of 100 MHz or less. The switch is configured to sequentially select the first antenna to the receiving line in the first portion of the sampling period, select the second antenna to the receiving line in the second portion of the sampling period, and select the third antenna to the receiving line in a third portion of the sampling period. The second circuit further may include a third correlator configured to couple with the output of the first circuit in parallel to the first correlator and the second correlator, where the controller is configured to sequentially provide a blanking signal to both the second correlator and the third correlator when the first antenna is selected in the first portion of the sampling period, provide a blanking signal to both the first correlator and the third correlator when the second antenna is selected in the second portion of the sampling period, and provide a blanking signal to both the first correlator and the second correlator when the third antenna is selected in the third portion of the sampling period. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

[0008] Another general aspect includes a receiver for multipath mitigation of global navigation satellite system. The receiver also includes a first antenna for tracking a satellite. The receiver also includes a second antenna for tracking the satellite. The receiver also includes a switch configured to sequentially select the first antenna and the second antenna toan input line once for each sampling period. The receiver also includes a first circuit coupled to the input line to receive a signal alternately from either the first antenna or the second antenna during the sampling period and process the signal to output a digital signal. The receiver also includes a second circuit may include a first correlator and a second correlator, the first correlator and the second correlator being configured in parallel to couple to the first circuit to perform correlation measurements based on the digital signal. The receiver also includes a controller configured to control the switch to sequentially select the first antenna and the second antenna for each sampling period, and synchronously provide a blanking signal to the second (first) correlator when the first (second) antenna is selected for each sampling period. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0009] Implementations may include one or more of the following features. The receiver where the first antenna and the second antenna may include different polarizations and orientations. The first circuit may include a filter, an amplifier, a mixer, a gain controller, and an analog-to-digital converter connected in series with the input line to process the signal received in each sampling period and extract the digital signal. A first correlator is configured to compare the digital signal based on the signal received from the first antenna in a first portion of each sampling period to a locally-generated replica in a correlation measurement to produce a code phase report and update the code phase report at an end of the correlation measurement while the second correlator is configured to perform a correlation measurement but not update the code phase report based on the blanking signal provided from the controller. The second circuit further may include a baseband processor coupled in parallel with the first correlator and the second correlator for selecting a smallest code phase report updated by either the first correlator or the second correlator corresponding to a light-of-sight signal received respectively from either the first antenna or the second antenna. The controller controls the switch to sequentially select one of the first, second, and third antenna in each sampling period to pass the signal received by a selected one of the first, second, and third antenna to the input line, where the controller provides a blanking signal synchronously to two correlators among the first, second, and third correlator corresponding to two unselected ones of the first, second, and third antenna. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer- accessible medium.

[0010] Yet another general aspect includes a method for multipath mitigation of global navigation satellite system. The method also includes setting a first antenna for tracking a satellite. The method also includes setting a second antenna for tracking the satellite. The method also includes switching alternately from the first antenna to the second antenna to receive a radio signal from the satellite in each sampling period. The method also includes processing the radio signal in a radio-frequency chain path to extract a digital signal. The method also includes inputting the digital signal in parallel to a first correlator and a second correlator to perform correlation measurements by comparing the digital signal to a locally- generated replica data. The method also includes providing a blanking signal synchronously to the first correlator when switching to the second antenna or to the second correlator when switching to the first antenna in each sampling period. The method also includes updating a first code phase report by the first correlator at an end of the correlation measurement when switching to the first antenna while providing no update by the second correlator based on the blanking signal. The method also includes updating a second code phase report by the second correlator at an end of the correlation measurement when switching to the second antenna while providing no update by the first correlator based on the blanking signal. The method also includes selecting the smallest code phase report among the first code phase report and the second code phase report. The method also includes determining the radio signal to be a light-on-sight signal received by either the first antenna or the second antenna for tracking the satellite based on the smallest code phase report and a correspondence between the first correlator and the first antenna or between the second correlator and the second antenna.Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0011] It is to be appreciated that embodiments of the present invention provide many advantages over conventional techniques. Among other things, the present invention utilizes multiple antennas and an antenna switch to sequentially select one antenna during each sampling period and input the GNSS signal into a single RF chain path. The switching and correlation measurement in baseband processing are controlled by software. Additionally, the use of multiple antennas and an antenna switch helps to mitigate the effects of multipath interference by providing a means to select the antenna with the least amount of interference for each sampling period. By sequentially selecting one antenna among multiple antennas during each sampling period, the receiver can avoid the multipath caused by a specific antenna's position or orientation relative to the GNSS satellites. The use of single RF chain path also allows the receiver to extract independent signals from each antenna, which are thencorrelated to determine the optimal signal. By eliminating the need for multiple RF chains and complex ADCs, the solution of the present disclosure reduces both the bill of materials and the power consumption of the GNSS receiver. The software control of the switching and correlation measurement in baseband processing helps ensure that the GNSS signals received from each antenna are properly correlated and combined to provide high-precision position, velocity, and timing information. This technique can be particularly useful in challenging environments where multipath interference is significant and can result in errors in GNSS positioning.

[0012] Embodiments of the present invention can be implemented in conjunction with existing systems and processes. For example, the receiver for multipath mitigation via antenna switching based on software control according to the present invention can be used in a wide variety of systems, including GPS (Global Positioning System) developed by US and most widely used in the world, BeiDou developed by China, and Galileo developed by European Union. Additionally, various techniques according to the present invention can be adopted into existing systems via many userequipments such as GPS receiver, ground control station for tracking satellites, and cell phone communicating via satellite communication network. There are other benefits as well.

[0013] The present invention achieves these benefits and others in the context of known technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure l is a simplified block diagram of a global navigation satellite system (GNSS) receiver according to embodiments of the present invention.

[0015] Figure 2 is a schematic diagram illustrating multipath effect created by the nonequal gain of the GNSS antenna according to embodiments of the present invention.

[0016] Figure 3 is a simplified block diagram illustrating a GNSS receiver for multipath mitigation according to embodiments of the present invention.

[0017] Figure 4 is a flow chart illustrating a method for satellite signal multipath mitigation according to embodiments of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention is directed to satellite navigation communication methods and systems. In a specific embodiment, the present invention provides a receiver for mitigating multipath effect during a GNSS signal receiving process. An embodiment of the present invention provides a method of using an antenna switch to sequentially select one antenna among multiple antennas during each sampling period to input GNSS signal into a single RF chain path and using software to control switching and correlation measurement in baseband processing. There are other embodiments as well.

[0019] The following description is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular applications. Various modifications, as well as a variety of uses in different applications will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments. Thus, the present invention is not intended to be limited to the embodiments presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0020] In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without necessarily being limited to these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.

[0021] The reader’s attention is directed to all papers and documents which are filed concurrently with this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All the features disclosed in this specification, (including any accompanying claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0022] Furthermore, any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. Section 112, Paragraph 6.In particular, the use of “step of’ or “act of’ in the Claims herein is not intended to invoke the provisions of 35 U.S.C. 112, Paragraph 6.

[0023] Please note, if used, the labels left, right, front, back, top, bottom, forward, reverse, clockwise and counterclockwise have been used for convenience purposes only and are not intended to imply any particular fixed direction. Instead, they are used to reflect relative locations and / or directions between various portions of an object.

[0024] Figure l is a simplified block diagram of a global navigation satellite system (GNSS) receiver, as implemented in various embodiments of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. A GNSS receiver 100 is an electronic device that receives signals from multiple satellite systems, such as GPS, GLONASS, BeiDou, and Galileo, and uses them to determine the receiver's position, velocity, and time. GNSS receiver 100, as shown in FIG. 1, includes an antenna 110, a receiver device 120, a microprocessor 130, a memory device 140, a display device 150, and a power supply 160. Antenna 110 is responsible for receiving signals from multiple satellite systems. Antenna 110 is typically a multi -band antenna that is designed to receive signals from multiple satellite systems and frequencies. In some examples, antenna 110 is just one of multiple antennas used by GNSS receiver 100 or shared with other devices. Using multiple antennas with different positions and orientations may help to mitigate interference or other multipath impairment issues in the satellite signals. As an example, antenna 110 comprises multipath antenna that is capable of receiving multiple signals from different paths and combining them to form a single signal. The signals can be either in phase or out of phase with each other, depending on the distance and angle of the paths. If the signals are in phase, they add up constructively and increase the signal strength; if they are out of phase, they cancel each other out and cause interference. As described below receiver 100 can use different techniques to reduce interference and enhance signal diversity, such as beamforming, spatial filtering, adaptive array processing, or multiple-input multiple-output (MIMO) coding, and these techniques may be employed in conjunction with antenna switching techniques described below.

[0025] GNSS receiver 100 also includes receiver device 120, which includes an input that is coupled to antenna 110 to receive the signals from satellites. In an example, receiver device 120 may include a radio-frequency (RF) front-end unit followed by a digital baseband unit. The RF front-end unit responsible for processing the signals received by the antenna. It amplifies the weak signals received by the antenna and filters out unwanted noise andinterference. In some examples, the RF front-end unit may be also followed by an intermediate frequency (IF) processor (not shown), which converts the filtered signals obtained by the RF front-end unit into an intermediate frequency signal that is easier to process. The IF processor also removes any remaining noise and interference as satellite signal is usually a very weak signal. The RF front-end and the IF processor may be referred to as an RF chain path, which processes the received satellite signal to extract a digital signal containing real data from the satellite. The digital baseband unit is responsible for processing the digital signal received from the IF processor. The digital baseband unit may include a correlator to perform a correlation process by comparing the digital signal to a locally- generated replica signal to determine a degree of similarity of the code phases associated with the data contained in the digital signal. A baseband processor decodes the satellite signals based on a code phase report and extracts the data contained in them, including the satellite's identification number, its location, and the time the signal was transmitted. In general, each receiver device 120 corresponds to at least one antenna. In some examples, a GNSS receiver may implement a dual antenna solution where the receiver receives signals from two independent antennas, each with its own RF chain path and correlation process to avoid multipath impairment.

[0026] As shown in FIG. 1, GNSS receiver 100 also includes a microprocessor 130 responsible for controlling the GNSS receiver's operation. Microprocessor 130 receives the data from receiver device 120 and uses it to calculate the receiver's position, velocity, and time. The microprocessor can also store the GNSS data for later analysis. Additionally, memory device 140 is included to store maps, routes, and waypoints. This allows the user to plan and follow routes, mark waypoints, and navigate to specific locations. A display device 150 is included in the GPS receiver for showing the user its location, speed, and direction. The display device also provides as a user interface for user to interact with the receiver, configure its settings, and view its output. The display device can be a small LCD screen or a larger color display, depending on the GPS receiver's model. A power supply 160 provides power to operate GNSS receiver 100. The power supply can be batteries or a power adapter. Some GPS receivers also come with a built-in rechargeable battery.

[0027] Depending on the implementation, an optimal design of a GNSS antenna balances various factors, including gain, radiation pattern, size, weight, cost, and manufacturability, in order to meet the specific requirements of the application. In order to receive a strong signal an optimal GNSS antenna should have high gain in the direction of the satellite while ideally having zero gain on the low hemisphere. However, due to the small form factor of thedevice, as well as coupling with other surrounding electric and non-electric components, and blocking effects from the user's hands and body, achieving this optimal design is challenging. Figure 2 displays the beam pattern of a typical GNSS antenna, which has a few nulls on its spatial response. As shown, satellite 201 broadcasts radio-wave signals in a wide angular range. The angular range over which a satellite can broadcast signals depends on several factors, including the size and shape of the antennas, the frequency of the signals, and the transmit power of the satellite. By designing antennas with specific radiation patterns, satellite operators can achieve coverage over a wide range of angles, from omnidirectional coverage to highly directional coverage in a specific region. Based on the position of the GNSS receiver, a signal received by an antenna directly from the direction of the satellite is a light-of-sight (LOS) signal. At the same time, the antenna may also receive a reflected signal from a man-made structure 202 which reflects the satellite signal transmitted in a different direction. Normally the LOS signal has the shortest propagation range and high gain while the reflection signal comes from a low hemisphere angle with low (if not zero) gain.

[0028] Consider a scenario where the antenna of the receiver receives both the line-of-sight signal from the satellite and a reflected signal from a nearby high-rise building. The reflected signal's power is typically weaker than the LOS signal by over 10 dB. However, due to the uneven distribution of the gain pattern of the antenna, the LOS signal may align with a null on the receiving antenna pattern, causing the reflected signal to be stronger than the LOS signal. In such a scenario, multipath impairment heavily affects the receiver. Thus, it is crucial to account for the potential multipath impairment in the design and implementation of GNSS receiver. The present disclosure addresses this issue by incorporating a new design that mitigates the effects of multipath signals, resulting in improved accuracy and reliability of GNSS positioning.

[0029] Figure 3 is a simplified block diagram illustrating a GNSS receiver for multipath mitigation according to embodiments of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. GNSS receiver 300 according to embodiments of the present disclosure implements a dual antenna solution for mitigate signal multipath impairment especially due to uneven antenna gain pattern. As shown in FIG. 3, GNSS receiver 300 includes at least two antennas — e.g., antenna 1 (301) and antenna 2 (302) — that are spatially separated for independently tracking a satellite to receive satellite signals in each sampling period. Unlike the traditional dual antenna solution where the receiver receives signals from two independent antennas, each having its own RFchain including a series of RF and IF processing devices and each being associated with a correlation process, GNSS receiver 300 shown in FIG. 3 includes a switch 310 to select either antenna 1 or antenna 2 to have two independent signals feed into just one input line of the receiver. Switch 310 is set to a certain switching frequency, e.g., switching once per 500 ms to 1 sec. to sequentially select the first antenna 301 in a first portion of each sampling period and select the second antenna 302 in a second portion of the sampling period. The sampling rate of the antenna is about 100 MHz or less, yielding 10-20 sample signals in each sampling period of a few milliseconds. If the sampling rate is set too high (> 100 MHz), it will introduce aliasing, leading to inaccurate or corrupted signal reception. Higher sampling rates generate more data that needs to be processed and analyzed, and require high-speed analog- to-digital converters (ADCs) capable of handling the increased data rates. This can increase the overall complexity and cost of the receiver, making it less practical for many applications.

[0030] GNSS receiver 300 includes a first circuit 320 coupled to the input line to receive and process a first signal from first antenna 301 during the first portion of the sampling period and a second signal alternately from second antenna 302 during the second portion of the sampling period to extract respective digital signal in each portion of the sampling period. The first circuit 320 includes multiple RF processing devices for processing the received first (second) signal and converting them into a usable form for further processing by the receiver. The switching operation allows the GNSS receiver to have multiple antennas while limiting its RF processing and subsequent correlation process to just one set of circuits, saving duplication in device usage and power consumption.

[0031] In a specific embodiment, first circuit 320 includes a filter 321 coupled to the input line to receive, following the switching operation of switch 310, the first signal from first antenna 301 and the second signal from second antenna 302. Filter 321 is characterized by a narrow bandwidth and high selectivity, being configured to filter out unwanted signals outside of desired frequency band associated with the first or second signal. For example, the filter is a surface acoustic wave (SAW) filter operated on the principle of acoustic wave propagation along the surface of a piezoelectric material.

[0032] In the specific embodiment, first circuit 320 also includes an amplifier 322 coupled to filter 321. Optionally, first circuit may have amplifier 322 coupled to the input line first followed by the filter 321. The amplifier 322 is a low-noise amplifier (LNA) to amplify the weak incoming signal while introducing as little noise as possible. In the context of multipath mitigation, the LNA plays an important role in improving the signal-to-noise ratio (SNR) of the received signal.

[0033] In the specific embodiment, first circuit 320 further includes a mixer 323 coupled to amplifier 322. Mixer 323 is configured to mix a signal amplified by amplifier 322 with a local oscillator (LO) signal to generate an intermediate frequency (IF) signal. The IF signal is then processed further using filters, amplifiers, and demodulators to extract the information carried by the signal. Multipath interference can cause the received signal to be distorted, as it can result in the reception of multiple delayed and attenuated copies of the transmitted signal. In an implementation, mixer 323 is configured to be a down converting filter which can help to mitigate the impact of multipath interference by down converting the received signal to a lower frequency band, where it is less susceptible to the effects of multipath interference. The down conversion process performed by the mixer can help to improve the selectivity of the receiver by filtering out unwanted signals and interference outside of the desired frequency band. This can help to improve the receiver's resistance to multipath interference, as the mixer can effectively filter out signals arriving at frequencies outside of the desired frequency band. In another implementation, mixer 323 is configured to be a frequency hopper which can further mitigate the impact of multipath interference. Frequency hopping involves rapidly changing the frequency of the LO signal used in the mixer, which can help to improve the receiver's resistance to interference and jamming.

[0034] In the specific embodiment, first circuit 320 also includes an automatic gain control (AGC) device 324 coupled to mixer 323. AGC device 324 is configured to adjust the gain of the whole first circuit 320 as an RF chain to maintain a constant output signal level in the presence of variations in the input signal level to improve the reliability and accuracy of the received signal. This is important because the received signal level can vary significantly in the presence of multipath interference, which can cause the signal to fade in and out over time. AGC device 324 can also help to prevent saturation of the GNSS receiver 100 by limiting the amount of gain applied to the incoming signal. This is important because first circuit 320 as an RF chain can only handle a limited amount of signal power, and excess power can cause distortion and other performance issues.

[0035] In the specific embodiment, first circuit 320 additionally includes an analog-to- digital converter (ADC) 325 coupled with AGC device 324. ADC 325 converts an analog output of AGC device 324 to a digital signal which contains coded data transmitted from the satellite. The issue of multipath interference can result in digital signals being mixed with noise, particularly when phase delays occur due to scattering or reflection. This can occur when signals are received by the first antenna 301 or the second antenna 302, and can cause impairment in the quality of the received signal.

[0036] In a specific embodiment for the GNSS receiver as shown in FIG. 3, GNSS receiver 300 further includes at least a second circuit 330 coupled with the first circuit 320. Second circuit 330 includes a first correlator 331 and a second correlator 332 coupled in parallel to an output of first circuit 320. Because of the parallel coupling, both first correlator 331 and second correlator 332 receive the digital signal in each sampling period of antennas. For example, second circuit 330 may be a part of a baseband processing section of the GNSS receiver, which is configured to process the digitized signals received from the first circuit to extract the navigation data and precise timing information carried by the satellite signals (i.e., the first or second signal). This section typically includes a digital signal processor (DSP), a correlator, and a navigation processor. The correlator is configured to detect and track the satellite signals from the various satellites. The correlator compares the incoming signals (digital signal from the first circuit) with a locally generated replica of the satellite signals and computes the time delay between the two signals to determine the receiver's distance from the satellite.

[0037] In the specific embodiment, each of first correlator 331 and second correlator 332 performs a correlation measurement independently based on the digital signal from the first circuit 320 to which they are coupled in parallel. The correlation measurement includes an integration of a product of the received signal and a locally-generated replica code (with a certain time delay). The received signal and the locally generated replica signal are then correlated. The correlation function provides a measure of the similarity between the two signals, as a function of time delay. The code of the locally-generated replica signal contains +ls and - Is but the received signal is the sum of the code plus noise. Thus, when the received and locally-generated codes are aligned, their product is +1. In the process of integration, the zero-mean noise is effectively averaged, while the code correlation result is accumulated over the integration period. When the codes are aligned, the correlation measurement will yield a peak value, but relatively small noise values will result when the codes are not aligned. Determining the code phase involves identifying the time delay between the received signal and the locally generated replica signal, which maximizes the correlation function. This code phase reflects the time difference between the beginning of the transmitted signal and the start of the received signal. The correlation measurement generates a code phase report, which includes details such as the digital signal, the code used, the signal-to-noise ratio, and the code phase measurement. This report provides essential information to accurately determine the position of a GNSS receiver and ensure that it is operating correctly.

[0038] GNSS receiver 300 further includes a controller 340 configured to at least perform a switching control to set a proper switching frequency to select the first antenna 301 and second antenna 302 in each sampling period and perform a blanking control to provide a blanking signal synchronously to second correlator 332 when switching to first antenna 301 and to first correlator 331 when switching to second antenna 302. A blanking signal, characterized by a start-to-end interval, is generated by the controller 340 and used by the correlator to ignore the data received during the blanking interval, to avoid processing the unwanted data. Thus, GNSS receiver 300 essentially performs a single correlation process in each sampling period. When switch 310 selects the first antenna (301) at the first portion of each sampling period, the first signal is inputted into the first circuit 320 and outputted as the digital signal for both the first correlator (331) and the second correlator (332). Since the second correlator (332) is provided with a blanking signal from the controller 340 in this portion of the sampling period, only the first correlator (331) updates a code phase report associated with the first signal at an end of the correlation measurement. While, when switch 310 selects the second antenna (302) in the second portion of the sampling period, the second signal is inputted into the first circuit and outputted as the digital signal, but only the second correlator updates a code phase report associated with the second signal in the second portion of the sample period since the first correlator (331) is instructed by the blanking signal to ignore processing the digital signal.

[0039] Referring to FIG. 3 again, the second circuit 330 of GNSS receiver 300 further includes a baseband processor 335 coupled in parallel to both first correlator 331 and second correlator 332. The baseband processor 335 is configured to at least select the best code phase report updated by the first correlator (331) and the second correlator (332). A standard report rate of the code phase report can be 1 Hz for typical cell phone user on foot or 10 Hz or higher for automotive user. The best code phase report refers to the smallest code phase report among the code phase report updated by the first correlator (331) and the code phase report updated by the second correlator (332). In general, the smallest code phase report for a GNSS signal might include information such as the number of satellites tracked, the signal strength and quality of each satellite, and the estimated position solution accuracy. In terms of discriminating signal interference or multipath, the smallest one of the two code phase reports from the two correlators and their correspondence with the two antennas would lead to a determination of which one of the first signal and the second signal to be a light-of-sight signal with smallest tracked range detected by either the first antenna or the second antenna.

[0040] Optionally, baseband processor 335 is also configured to demodulate the incoming signal to extract the navigation data and other information encoded in the signal, such as satellite ephemeris and clock data. Optionally, baseband processor 335 is also configured to filter and decimate the signal to reduce noise and improve signal quality, and correct for various error sources such as ionospheric and tropospheric delays. Optionally, baseband processor 335 further is configured to format the processed signal data into a format that can be easily handled by a microprocessor or other downstream components in the receiver. Optionally, controller 340 is part of a microprocessor configured to use software for executing instruction for switching operation control and blanking signal control. Optionally, GNSS receiver 300 includes a third antenna configured to receive the third signal from the satellite, where switch 310 is configured to sequentially select the first antenna to the receiving line in the first portion of the sampling period, select the second antenna to the receiving line in the second portion of the sampling period, and select the third antenna to the receiving line in a third portion of the sampling period. Optionally, the second circuit 330 of GNSS receiver 300 further includes a third correlator configured to couple with the output of first circuit 320 in parallel to the first correlator and the second correlator, where controller 340 is configured to sequentially provide a blanking signal to both the second correlator and the third correlator when the first antenna is selected in the first portion of the sampling period, provide a blanking signal to both the first correlator and the third correlator when the second antenna is selected in the second portion of the sampling period, and provide a blanking signal to both the first correlator and the second correlator when the third antenna is selected in the third portion of the sampling period. Optionally, GNSS receiver 300 may include more than three antennas sharing a single RF chain and single correlation process depending on applications.

[0041] Figure 4 is a flow chart illustrating a method for satellite signal multipath mitigation according to embodiments of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. FIG. 4 shows method 400 starting with step 401 : setting a first antenna at a front-end for tracking a satellite, and step 403 : setting a second antenna at the front-end for tracking the satellite. Optionally, the first antenna and the second antenna have different polarizations and orientations such that they have two different gain patterns to facilitate the multipath mitigation.

[0042] Additionally, method 400 includes step 405 for switching alternately from the first antenna to the second antenna to receive a radio signal from the satellite in each samplingperiod. The first antenna and the second antenna are set at a receiver front-end alternatively in each sampling period. A switch device controlled by a software-assisted controller to perform the switching operation once in each sampling period of antennas. The radio signal may be received by the first antenna in a first portion of a sampling period. The radio signal may be received by the second antenna in a second portion of the sampling period.

[0043] Referring to FIG. 4, method 400 also includes step 407 for processing the radio signal in a radio-frequency chain path to extract a digital signal. The digital signal may contain real data sent from the satellite as well as noise including possible time delay due to many multipath impairments like reflection or scattering or uneven gain pattern of individual antenna.

[0044] Referring to FIG. 4, method 400 also includes step 409 for inputting the digital signal in parallel to a first correlator and a second correlator to perform correlation measurements based on the digital signal. Each of the first correlator and the second correlator corresponds to one of the first antenna and the second antenna set at the front end. The correlator is configured to compare the received digital signal with a locally generated replica of the digital signal to determine the time offset or delay between the two signals.

[0045] Referring to FIG. 4, method 400 also includes step 411 for providing a blanking signal synchronously to the first correlator when switching to the second antenna or to the second correlator when switching to the first antenna in each sampling period. A software- assisted controller may be used to generate the blanking signal and control the application of the blanking signal at the right time to either the first correlator or the second correlator.

[0046] Referring to FIG. 4, method 400 also includes step 413 for updating a first code phase report by the first correlator at an end of the correlation measurement when switching to the first antenna while providing no update by the second correlator based on the blanking signal. The blanking signal provides a time interval for the recipient correlator, the second correlator in particular, to ignore the received digital signal and not update any code phase report during this time interval.

[0047] Referring to FIG. 4, method 400 also includes step 415 for updating a second code phase report by the second correlator at end of the correlation measurement when switching to the second antenna while providing no update by the first correlator based on the blanking signal. The first correlator in this time interval defined by the blanking signal is stopped updating the code phase report.

[0048] Referring to FIG. 4, method 400 also includes step 417 for selecting a smallest code phase report among the first code phase report and the second code phase report. The smallest code phase report for a GNSS signal might include information such as the number of satellites tracked, the signal strength and quality of each satellite, and the estimated position solution accuracy. It may also include any major issues or challenges encountered during the signal processing, such as interference or multipath, and any steps taken to mitigate these issues, In an embodiment, the smallest code phase report among the first code phase report and the second code phase report indicates a light-of-sight signal among the first signal and the second signal based on the correspondence between the first antenna and the first correlator and between the second antenna and the second correlator, providing a solution for multipath impairment.

[0049] Referring to FIG. 4, method 400 also includes step 419 for determining the radio signal to be a light-on-sight signal received by either the first antenna or the second antenna for tracking the satellite based on the smallest code phase report.

[0050] Although the method 400 describes steps for operating a system involving two antennas, the method should be applicable to a system with multiple (>2) antennas in which a switch can sequentially select one among the multiple antennas during each sampling period to input GNSS signal into a single RF chain path and using software to control switching and correlation measurement in baseband processing.

[0051] The system and method proposed above provide a cost-effective and powerefficient solution for GNSS receivers without compromising high-precision positioning accuracy. By enabling the use of a single RF chain and multiple antennas, this approach eliminates the need for duplicate RF chains and complex ADCs, reducing both the manufacturing costs and power consumption of GNSS receivers. This solution can significantly enhance the performance of GNSS receivers while reducing their overall cost, making it an attractive option for manufacturers looking to improve their products' competitiveness. The invention can be applied to various GNSS receiver designs, resulting in improved accuracy and reliability of location-based services. By reducing costs and power consumption while maintaining high precision, the proposed solution represents a significant advancement in GNSS receiver technology.

[0052] While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the abovedescription and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A receiver for satellite signal multipath mitigation comprising: a first antenna configured to receive a first signal from a satellite; a second antenna configured independently to receive a second signal from the satellite; a switch configured to select the first antenna to an input line during a first portion of a sampling period and select the second antenna to the input line during a second portion of the sampling period; a first circuit coupled to the input line to receive and process the first signal from the first antenna during the first portion of the sampling period and the second signal alternately from the second antenna during the second portion of the sampling period to extract respective digital signals; a second circuit comprising a first correlator and a second correlator, the first correlator and the second correlator being configured in parallel to couple to the first circuit to perform correlation measurements based on the digital signal; and a controller configured to control the switch to sequentially select the first antenna in the first portion of each sampling period and select the second antenna in the second portion of each sampling period, and to provide a blanking signal synchronously to the second correlator in the first portion of each sampling period and to the first correlator in the second portion of each sampling period.

2. The receiver of claim 1, wherein the first circuit comprises a filter coupled to the input line, the filter comprising a narrow bandwidth and high selectivity, being configured to filter out unwanted signals outside of desired frequency band associated with the first or second signal.

3. The receiver of claim 2, wherein the first circuit further comprises an amplifier coupled to the filter and configured to amplify a signal filtered by the filter by increasing its amplitude and improving a signal-to-noise ratio.

4. The receiver of claim 3, wherein the first circuit further comprises a mixer coupled to the amplifier and configured to mix a signal amplified by the amplifier with a local oscillator (LO) signal to generate an intermediate frequency (IF) signal.

5. The receiver of claim 4, wherein the first circuit further comprises a gain controller coupled to the mixer and configured to automatically adjust a gain of the firstcircuit to maintain a constant output level in the presence of variations in an input level of the IF signal.

6. The receiver of claim 5, wherein the first circuit further comprises an analog-to-digital converter configured to convert an analog output of the gain controller to the digital signal.

7. The receiver of claim 1, wherein the first (second) correlator is configured to compare the digital signal with a locally-generated replica data and update the measurement with a code phase report in a reporting rate of 1 to 10 Hz or without updating the measurement based on the blanking signal in the second (first) portion of the sampling period.

8. The receiver of claim 7, wherein the second circuit further comprises a baseband processor configured to select a smallest code phase report updated by either the first correlator or the second correlator.

9. The receiver of claim 8, wherein the first (or second) correlator updating the smallest code phase report corresponds to the first (or second) antenna receiving the first (or second) signal as a light-on-sight signal from the satellite into the input line.

10. The receiver of claim 1, wherein the controller comprises a software to set a switching frequency to one switching operation per sampling period of 500 ms to 1 sec. and to provide the blanking signal synchronously to the first correlator or the second correlator based on a selection of the second antenna or the first antenna by the switching operation.

11. The receiver of claim 1, wherein either the first antenna or the second antenna comprises a signal sampling rate of 100 MHz or less.

12. The receiver of claim 1, further comprising a third antenna configured to receive the third signal from the satellite, wherein the switch is configured to sequentially select the first antenna to the receiving line in the first portion of the sampling period, select the second antenna to the receiving line in the second portion of the sampling period, and select the third antenna to the receiving line in a third portion of the sampling period.

13. The receiver of claim 12, wherein the second circuit further comprises a third correlator configured to couple with the output of the first circuit in parallel to the firstcorrelator and the second correlator, wherein the controller is configured to sequentially provide a blanking signal to both the second correlator and the third correlator when the first antenna is selected in the first portion of the sampling period, provide a blanking signal to both the first correlator and the third correlator when the second antenna is selected in the second portion of the sampling period, and provide a blanking signal to both the first correlator and the second correlator when the third antenna is selected in the third portion of the sampling period.

14. A receiver for multipath mitigation of global navigation satellite system comprising: a first antenna for tracking a satellite; a second antenna for tracking the satellite; a switch configured to sequentially select the first antenna and the second antenna to an input line once for each sampling period; a first circuit coupled to the input line to receive a signal alternately from either the first antenna or the second antenna during the sampling period and process the signal to output a digital signal; a second circuit comprising a first correlator and a second correlator, the first correlator and the second correlator being configured in parallel to couple to the first circuit to perform correlation measurements based on the digital signal; and a controller configured to control the switch to sequentially select the first antenna and the second antenna for each sampling period, and synchronously provide a blanking signal to the second (first) correlator when the first (second) antenna is selected for each sampling period.

15. The receiver of claim 14, wherein the first antenna and the second antenna comprise different polarizations and orientations.

16. The receiver of claim 14, wherein the first circuit comprises a filter, an amplifier, a mixer, a gain controller, and an analog-to-digital converter connected in series with the input line to process the signal received in each sampling period and extract the digital signal.

17. The receiver of claim 14, wherein first correlator is configured to compare the digital signal based on the signal received from the first antenna in a first portion of each sampling period to a locally-generated replica in a correlation measurement toproduce a code phase report and update the code phase report at an end of the correlation measurement while the second correlator is configured to perform a correlation measurement but not update the code phase report based on the blanking signal provided from the controller.

18. The receiver of claim 14, wherein the second circuit further comprises a baseband processor coupled in parallel with the first correlator and the second correlator for selecting a smallest code phase report updated by either the first correlator or the second correlator corresponding to a light-of-sight signal received respectively from either the first antenna or the second antenna.

19. The receiver of claim 14, further comprising a third antenna and the second circuit comprises a third correlator corresponding to the third antenna, wherein the controller controls the switch to sequentially select one of the first, second, and third antenna in each sampling period to pass the signal received by a selected one of the first, second, and third antenna to the input line, wherein the controller provides a blanking signal synchronously to two correlators among the first, second, and third correlator corresponding to two unselected ones of the first, second, and third antenna.

20. A method for multipath mitigation of global navigation satellite system, the method comprising: setting a first antenna for tracking a satellite; setting a second antenna for tracking the satellite; switching alternately from the first antenna to the second antenna to receive a radio signal from the satellite in each sampling period; processing the radio signal in a radio-frequency chain path to extract a digital signal; inputting the digital signal in parallel to a first correlator and a second correlator to perform correlation measurements by comparing the digital signal to a locally- generated replica data; providing a blanking signal synchronously to the first correlator when switching to the second antenna or to the second correlator when switching to the first antenna in each sampling period; updating a first code phase report by the first correlator at an end of the correlation measurement when switching to the first antenna while providing no update by the second correlator based on the blanking signal;updating a second code phase report by the second correlator at an end of the correlation measurement when switching to the second antenna while providing no update by the first correlator based on the blanking signal; selecting a smallest code phase report among the first code phase report and the second code phase report; and determining the radio signal to be a light-on-sight signal received by either the first antenna or the second antenna for tracking the satellite based on the smallest code phase report and a correspondence between the first correlator and the first antenna or between the second correlator and the second antenna.

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