EP4118459A1

EP4118459A1 - A gnss repeater architecture and location finding method for indoor positioning systems using lower frequencies than gnss signals

Info

Publication number: EP4118459A1
Application number: EP20727742.7A
Authority: EP
Inventors: Ibrahim Tekin; Husnu Yenigun; Abdulkadir UZUN; Firas Abdul GHANI
Original assignee: Sabanci Universitesi
Current assignee: Sabanci Universitesi
Priority date: 2020-03-13
Filing date: 2020-03-13
Publication date: 2023-01-18
Also published as: WO2021183067A1; WO2021183067A9

Abstract

The disclosed invention refers to a system for indoor positioning comprising a multiplicity of antennas collecting satellite navigation signals emitted by a multiplicity of satellites, repeaters (each repeater with different set of satellites) for producing secondary signals different from said satellite navigation signals and propagating said secondary signals and at least one receiver capable of receiving and processing said secondary signals to compute location information. S aid secondary signals are contained in a lower frequency ISM band (such as 433 MHz) whereby free path loss is reduced and coverage is increased due to higher transmit power levels. Said at least one receiver is configured to execute a clock bias-based pseudorange triangulation algorithm.

Description

A GNSS REPEATER ARCHITECTURE AND LOCATION FINDING METHOD FOR INDOOR POSITIONING SYSTEMS USING LOWER FREQUENCIES THAN GNSS SIGNALS

Technical Field of the Present Invention

Disclosed invention relates to an indoor positioning system where signals emitted by GNSS satellites are utilized. Disclosed invention more specifically concerns indoor positioning systems whereby coverage by conventional GNSS signals are improved to a greater extent to bypass shortcomings resulting from weak signals and path loss of radio frequency signals resulting therefrom; as well as reducing the design constraints imposed thereupon by legal restrictions on GNSS frequency bands.

Background of the Present Invention

Global navigation satellite systems (GNSS) such as GPS, Galileo, GLONASS, and BeiDou became quite popular in recent years and they have wide usage in many areas. Since their introduction in the eighties, locating objects and individuals on the surface of the earth is greatly facilitated. Formerly envisaged to serve primarily military interests, said systems have also been utilized widely in civilian use due to low-cost GNSS receivers becoming easily available over time. Such uses cover a wide range from asset tracking to navigation in maritime applications as well as speed tracking and location services used for everyday urban use. Concurrently, the global indoor positioning market was forecasted to be expanding by 42% compound annual growth rate from 2017 to 2023. The forecasted growth promises the requirement for newer technologies and methods in the field. One such prevalent method for indoor positioning is realized through repeaters.

EP 2878974 A2 teaches a method, device, and circuit for determining the position of a mobile cellular communication device in disclosures. A pseudolites positioning signal is received in a first frequency band at an antenna of the mobile cellular communication device. The pseudolites signal is converted from the first frequency band to a Global Navigation Satellite System (GNSS) frequency band to obtain a corresponding positioning signal in the GNSS frequency band. The converted positioning signal at the mobile communication device is delivered to a GNSS chipset of the mobile cellular communication device. The GNSS chipset determines the position of the mobile cellular communication device using the converted positioning signal.

CN 106767831 A provides a simulated GNSS signal-based indoor locating system comprising a plurality of outdoor receivers, an indoor simulation signal generator, simulation signal emitters and indoor locating modules. Said plurality of outdoor receivers are used for collecting self-locating information and sending the information in a telegraph text signal manner; the indoor simulation signal generator is used for generating simulation signals with simulation satellite band and frequency according to received GNSS locating information in the telegraph text signal manner; the simulation signal emitters are arranged in different directions indoors, and used for emitting simulation navigation signals indoors; and the indoor locating modules are used for receiving the simulation signals emitted by the simulation signal emitters for locating. The system can be used for achieving indoor locating based on outdoor GNSS signals.

EP 1720032 B1 discloses a GPS-based indoor positioning system as follows: GPS primary positioning signals received by a single outdoor receive antenna are up-converted to four different carrier frequencies in the 2.4 GHz ISM band and the upconverted signals are connected to 4 physically distant transmit antennas with RF cables to be transmitted inside the building, the transmit antennas serving at the same time as access points of a WLAN which is used for transmitting additional positioning data like the positions of the transmit antennas and the signal delay times associated with them. By cycling through the secondary positioning signals received from the transmit antennas, i.e. down-converting each of them during an assigned time slot, and determining clock bias differences in the receiver the position of the latter is determined using TDOA algorithms.

US 2012286992 A1 provides a GPS-based indoor positioning system as such: It comprises at least three directional GPS antennas for picking up specific GPS signals coming from at least three GPS satellites, at least three RF GPS repeaters for amplifying GPS signals coming from directional GPS antennas, at least three GPS antennas for transmitting GPS signals coming from RF GPS repeaters to indoor, at least one GPS receiver for picking up GPS signals coming from GPS antennas by its antenna novel position calculation method and relates to increase the coverage of the outdoors GPS signals to indoors.

A study titled "Indoor Code and Carrier Phase Positioning with Pseudolites and Multiple GPS Repeaters" by Petrovski et al. presented in the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR (September 2003, pp. 1135-1143), comes from the firm GNSS Technologies Inc. together with Hitachi Ltd. that implemented pseudolites for seamless indoor-outdoor positioning. As it purports to have tackled the problem of finding an appropriate algorithm for indoor positioning, it puts forth a special procedure and algorithm that allows decimeter-level positioning indoors in a low multipath environment. The proposed technique uses specially developed multiple free reference station approach that utilizes a pseudorange positioning at the first stage to define the initial position guess. The code-based algorithm looks at the variation in behavior of the estimated position in cases of error in an initial position and in cases without error. Such variations give one a way to find the correct initial position with a search algorithm, much the same way as for carrier phase ambiguity resolution. This indoor positioning software has two main blocks, one of which is initial position estimation, based on pseudorange observations and the other is the carrier phase positioning component. The algorithm doesn't require knowledge of the initial position and uses pseudorange and carrier-phase observations. Indoors, one can clearly use only a single GPS satellite out of all those signals received at the roof antenna. Using multiple antennas with an obstructed view and FDMA technique, disclosed invention constructs an indoor positioning system based on multiple GPS repeaters and tests of which had reportedly demonstrated centimeter- level indoor initialization accuracy in the low multipath environment and the possibility to build indoor positioning systems based on multiple GPS repeaters as the signal sources.

A method based on multiple GPS repeaters and a modified positioning algorithm is presented in the study "Indoor Positioning Based on Global Positioning System Signals" published in Microwave and Optical Technology Letters 55.5 ((2013): 1091-1097) by Ozsoy et al. comprises live processing of actual GPS data while purely using the extant GPS infrastructure. The teaching of the document comprises the utility of two or three sets of GPS repeaters with separate GPS directional antennas for an indoor situation with limited/no GPS coverage. It neither requires hardware modifications nor it is compromised any more significantly than any indoor positioning system from multi-path propagation. All the repeaters are also operated individually.

Lymberopoulos et al. in their study titled "A Realistic Evaluation and Comparison of Indoor Location Technologies: Experiences and Lessons Learned" report their findings on the location error of 22 approaches through a competition of indoor location technologies, whether they are infrastructure- free or infrastructure-based, in 22 groups on a 300 meter-square evaluation space. Among conclusions of Lymberopoulos et al. were found the persistence of deployment overhead as most such approaches were custom; and the invariable failure of any indoor location approach to compare to GPS-like results achieved outdoors.

Objects of the Present Invention

The primary object of the present invention is to provide an indoor positioning system.

Another object of the present invention is to provide an indoor positioning system using GNSS signals remediated with the use of a frequency lower than GNSS signal frequency, such as the ISM band at 433 MHz.

Yet another object of the disclosed invention is to provide an indoor positioning system using GNSS signals remediated through the use of lower frequency than GNSS frequency (such as the ISM band at 433 MHz) with improved indoors coverage and circumvention of legal restrictions on GNSS frequency band. A further object of the disclosed invention is to provide an indoor positioning system using GNSS signals and lower frequency unlicensed RF band whereby signal fidelity is preserved while free-space path loss is reduced due to the use of lower frequency.

A further object of the disclosed invention is to provide an indoor positioning system using GNSS signals and lower frequency unlicensed RF band whereby signal coverage is increased due to transmitting higher power levels.

A further object of the disclosed invention is to provide an indoor positioning system using GNSS signals and lower frequency unlicensed RF band whereby signal penetration is improved due to operation at lower frequency signals.

A still further object of the disclosed invention is to provide a triangulation based indoor location determining method comparable in accuracy to regular outdoor GNSS TDOA/triangulation methods in the art.

Summary of the Present Invention

The disclosed invention proposes a cost-effective, readily deployable and accurate indoor positioning system that is based on GNSS satellite navigation technologies. Disclosed invention is superior to the solutions documented in the art in that it displays remarkable accuracy whilst rendering legal restrictions in established GNSS frequency bands obsolete since it relies on remediation of location signals over a different frequency band, namely the ISM band at a lower frequency than GNSS frequency such as 433 MFIz. According to different embodiments, such GNSS frequency signals could be available in several types, such as the ones found in GPS, GLONASS, Galileo bands. According to the invention, GNSS signals that are broadcast by satellites are received by directional GNSS active antennas, subsequent to which said signals will be amplified by active antennas and then downconverted to a lower frequency of 433 MHz for transmission indoors and these signals will be picked up by 433

MHz receivers and will be upconverted back to GNSS frequencies for positioning. The main strength of the indoor positioning system proposed hereby lies in its downconversion-signal conditioning-upconversion scheme and a novel location finding algorithm that eliminates issues arising from non-line- of-sight (NLOS) propagation between satellites and the indoor receiver. Due to compactness and readiness in implementation to existing GNSS infrastructure, as a corollary, it also proposes a cost advantage compared to similar solutions in the art. The "GNSS-to-lower frequency ISM and lower frequency ISM-to-GNSS" operation of the indoor positioning system as disclosed in the present invention provides also a reduced free space path loss due to operation at a lower frequency, and since it is readily adaptable and operable within a matter of minutes, it poses great usefulness in emergencies such as fire, earthquake and homeland security applications. Next to its public service potential, the disclosed system is also greatly viable for depots/storage, markets, hospitals and also manufacturing plants due to its cost advantage.

The invention therefore broadly relates to a method of and system to liberate indoor positioning approaches from legal restrictions (especially concerning amplification larger than 45 dB in GNSS band), increase coverage robustness of such applications as well as to reduce free path loss and decrease deployment costs, and accomplishing such in a novel radio frequency front-end specifically designed for remediation of actual GNSS signals. 433 MHz ISM band transmit power level is limited to 10 dBm, which is 87 dB higher than the limit on GPS frequency transmit power level. Two limits exist here: A -77 dBm power limit and 45 dB amplification, whichever is more limiting according to ECC Report taken as reference.

Advancing the system taught in EP 1720032 Bl, disclosed invention solves many shortcomings that may arise from utility of signals in frequency bands higher than that of GNSS such as high interference levels in Wi-Fi (IEEE 802.11) as well as common household appliances such as microwave ovens, the need of laying long RF cable infrastructure due to physically separate transmit antennas in question, need for synchronization of receiver for each transmit antenna slot; as well as an inevitably increased path loss at 2.4 GHz as well as a remarkably deteriorated penetration capability through walls.

Brief Description of the Figures of the Present Invention

Accompanying drawings are given solely to exemplify an indoor positioning system using GNSS signals and utilizes remediation via lower frequency ISM- band, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said claims without recourse to the technical disclosure in the description of the present invention. Fig. 1 demonstrates a three-repeater system for two-dimensional indoor positioning according to the present invention.

Fig. 2 demonstrates an RF downconverter (transmitter of the repeater system) circuit diagram for the indoor positioning system according to the present invention.

Fig. 3 demonstrates a diagram of an RF downconverter circuit (transmitter of the repeater system) according to an embodiment of the present invention.

Fig. 4 demonstrates a diagram of an RF upconverter circuit (receiver of the repeater system) with an ISM band antenna for the indoor positioning system according to the present invention. Fig. 5 demonstrates a diagram of an RF upconverter circuit according to an embodiment of the present invention.

Fig. 6 demonstrates a diagram of the triangulation error zone (shown with C) in two-dimensional positioning methods in the art.

Detailed Description of the Present Invention

The present invention proposes a GNSS repeater architecture, as well as a method, for indoor positioning marked by remediation via 433 MHz for overcoming the allowable maximum gain problem in global navigation signal regulations while improving the ever-persistent accuracy problem of conventional indoor positioning approaches. The proposed 433 MHz- remediating indoor positioning system is readily applicable in established GNSS infrastructures, which makes the solution quickly utilizable and with a low deployment cost.

The encompassing term GNSS signals are meant to be, as mentioned hereinafter, refer to a general range of satellite navigation signals from 1 to 2.5 GHz. Such range specifically covers those bands of BeiDou; Galileo; GLONASS; GPS and NAVIC that are available for civilian use.

For indoors, GNSS signals have to go through an additional loss of 10-30 dB, in which case, the RF signal becomes too low for detection by the GNSS receivers and to calculate a position. One of the ways to boost the signal level is to use active GNSS signal repeaters. These repeaters will pick up the GNSS signals, amplify and retransmit to where the GNSS signal coverage is desired. However, it is legally prohibited to transmit some GNSS signals above -77 dBm (which is a very low power level RF signal) which requires a special permit from governments.

The present invention is devised under the recognition that license-free bands of operation are quite suitable for indoor positioning applications since legally allowable levels of signal power at GNSS bands are detrimental to the development of finer systems, especially ones for which robustness, accuracy, precision, and simplicity would be a defining factor. To surpass the GNSS power level constraints, one such license-free operation band may be, for example, the ISM band at 433 MHz. Using 433 MHz ISM signal example, therefore, confers the invention of a twofold efficiency. One of the advantages is that the power level allowable at 433 MHz ISM is 10 dBm, which is 87 dB higher than the GNSS allowed power level, leading to a much larger coverage of signal obtainable indoors. The second advantage of the 433 MHz is 11 dB less free space path loss advantage compared to GNSS 1575 MHz signals. Further, an advantage 433 MHz ISM when compared to a GNSS frequency e.g. 1575 MHz, is that the signal can penetrate walls and buildings further due to larger wavelength operation. This will also increase the coverage of the indoor area with the 433 MHz signal. The signals will be radiated at 433 MHz indoors, they will not interfere with outdoor GNSS signals.

Through GNSS repeaters, GNSS signals are amplified and utilized to track the location of anything carrying a customary receiver indoors. However, the use of GNSS repeaters are restricted in order to prevent repeaters from interfering with other uses of GNSS in the vicinity. The Electronic Communications Committee's (ECC) Reports 129 and 145, and European Telecommunication Standards Institute's (ETSI) standard EN 302 645 prohibit the overall amplification of GPS signals more than 45 dB, and the antenna gain exceeding 3 dB as it otherwise would affect nearby systems using GNSS services such as aeronautical radio navigation system DME, military and civilian radars, Earth Exploration Satellite Service, and so on. The US policy "Manual of Regulations and Procedures for Federal Radio Frequency Management" presents under section 8.3.28 that GPS repeaters may be used only by the departments of the US Federal Government or those who will deploy the system within a shielded indoor environment or have a license under FCC.

According to one embodiment of the disclosed invention, the proposed system receives GNSS signals originating from different satellites using directional active antennas at different locations and delivers them to the space indoors. RF downconverter(repeater) elements including the directional GPS active antennas pick up a different set of satellites depending on their look direction and beamwidths and amplify up to 30 dB for signal conditioning. After the first amplification by the active antenna, said GNSS signals will then be downconverted to a lower frequency of 433 MHz ISM band. Signals once downconverted to 433 MHz ISM band with a downconverter, will then be amplified up to 10 dBm power levels as needed. Note that an embodiment can wirelessly adjust the gain of the repeaters for different indoor coverage needs by utilizing LNA chains and adjustable digital step attenuators. After filtering for 433 MHz band, the downconverted signals will be transmitted by properly designed 433 MHz antenna. The 433 MHz ISM band signal will subsequently be picked up indoors with a 433 MHz receiver. This chain of events is realized by hardware comprising directional GNSS active antennas for picking up a set of satellites, discrete RF downconverter, 433 MHz LNAs, RF filters, adjustable attenuator, 433 MHz antennas, and RF receiver, which is connected to 433 MHz antenna, 433 MHz LNA chains, adjustable digital step attenuator for gain conditioning and an upconverter structures to GNSS band and a GNSS receiver.

According to an embodiment of the disclosed invention, said hardware comprises a GNSS active directional antennas with built-in LNAs, RF downconverter, LNA, digital step attenuator, RF filter at 433 MHz, LNA and 433 MHz antenna on each of three RF downconverter side. Said hardware will have RF upconverter side with a GNSS receiver as well as 433 MHz antenna, 433 MHz bandpass filter, 433 MHz LNA, adjustable digital step attenuator, another LNA and a 433 to 1575 MHz upconverter. Said GNSS receiver is, in an embodiment, selected from a group comprising GLONASS receivers, BDS receivers, Galileo receivers, and QZSS receivers. Concurrently, different embodiments may pertain to upconversion-to and downconversion-from schemes for different GNSS frequencies. According to an embodiment of the disclosed invention, said system comprises four aspects: Directional active antennas operating in GNSS frequencies; repeaters that comprise LNAs to amplify the signal after downconversion to 433 MHz; receiver RF front-end circuits and a positioning algorithm that processes signals to determine the indoor location of the receiver it operates thereupon. Disclosed indoor positioning system utilizes a triangulation-based approach to determine the location of the receiver. Disclosed invention predominantly relies on GNSS signals for 2-D (with three repeaters) or 3-D (with 4 repeaters) positioning alike, which are obtained via directional antennas from uninterrupted outdoor positions. After said GNSS signals are obtained, they are downconverted to lower frequency ISM band and radiated across the indoor environment in downconverted form via 433 MHz ISM band antenna with amplification and filtering. At the receiver end, received ISM band signals are upconverted to original GNSS frequencies they are obtained on, forming raw GNSS data to be processed after amplification and filtering. With the developed algorithm, effects of repeaters and non-line of sight propagation of satellite to receiver propagation (satellite to repeater and repeater to receiver propagation) signals are mitigated/compensated and location information is achieved in a precise manner. According to an embodiment of the disclosed invention, the disclosed system treats GNSS satellite signals as if they originate from indoor sources; but unlike the case with pseudolites, synchronization is not a requirement for the transmit sources since they are already in synchronization, and signal content received from satellites are unchanged. Since levels of repeater signals are amplified, sensitive signal reception aspects are not necessary.

According to an embodiment of the disclosed invention, said downconverter side comprises a three-port network to modify DC bias to provide DC power to the active antennas at the directional antennas as shown in Fig. 5. In at least one embodiment, said three-port network is a bias tee. Said bias tee is followed by a downconverter board, which itself comprises a mixer and oscillator (Wideband Quadrature demodulator in Fig. 5) according to at least one embodiment. Conversion loss of said downconverter board may be in the vicinity of 8.7 dB. After downconverter board with 90° hybrid coupler situated is the low noise amplifier (LNA), preferably having a gain of ~22.4 dB. LNA is followed by a digital step attenuator which can be adjusted between 0-31.5 dB Attenuator is succeeded by another LNA, which is finalized with a bandpass filter preferably having a 20 MHz range and around ~1.7 dB insertion loss at a definite frequency band. In at least one embodiment, said definite frequency band is 433 MHz ISM. All the components listed hitherto may result in an expected downconverter gain including the antennas between 32.9 - 64.4 dB. According to an embodiment of the disclosed invention, said upconverter side comprises a bandpass filter preferably having a 20 MHz range and around ~1.7 dB insertion loss at a definite frequency band, which according to at least one embodiment is 433 MHz ISM as shown in Fig. 5. Said bandpass filter is followed by an LNA still preferably having a gain of ~22.4 dB. Subsequent to a first LNA as such, is a digital step attenuator with up to 31.5 dB attenuation. Attenuator successively connected to yet another LNA, which is itself connected to I+/Q+/I-/Q- power divider and four bias tees. Said bias tees are required for biasing upconverter RF inputs. The final element in the receiver chain is an upconverter board comprising a mixer and oscillator (Wideband Quadrature modulator in Fig. 5), with a total power loss around ~1.3 dB. All the components listed hitherto may result in an expected gain between 10.3 - 41.8 dB. According to an embodiment of the disclosed invention, a multiplicity of GNSS frequency operating directional antennas are disclosed. According to an embodiment, a high-gain, right hand circularly polarized GNSS antenna such as a GPS antenna operating in 1575 MHz LI band is disclosed. Said antenna may be an antenna with a beamwidth of 60 degrees. In other embodiments, other GNSS band antennas are also utilized such as the bands of BeiDou; Galileo; GLONASS; GPS those made available for civilian use. Preferably, a GNSS antenna may operate in any GNSS frequency between 1 and 2.5 GHz according to different embodiments.

To remedy the indoor positioning drawback where line-of-sight (LoS) signals are not directly utilizable, repeaters are employed. As demonstrated in the art, repeaters collect satellite navigation signals, amplify them and propagate them within indoor environments where GNSS coverage is limited. This, however, causes less-than-perfect positioning since propagation continues in a non-LoS direction indoors as the distance calculated is different than that of a LoS scenario. Known receivers calculate the range as below, and assume it to be the LoS range: where the first term is the distance between the signal source (satellite) and the repeater, and the second term is the distance between the repeater and the receiver. Triangulation algorithms based on this premise produce erroneous positioning estimations. Actual position may be estimated also through pseudoranges as formulated below:

P i = R ϊ + r Ϊ + be (1) where the term b is the clock bias and the term c is the speed of light. Internal clocks of the receiver and the satellite broadcasting the satellite navigation signals are by no means synchronized, offset between which is added to the range calculation of the previous example. Location of satellites can be determined using satellite ephemeris data, using Formula (1) below: where;

X sat ⁹ y Z sat ⁹ sat stand for satellite coordinates, and; stand for repeater coordinates. In subtracting the distance between the signal source satellite and the repeater, distance between the repeater and receiver is found as demonstrated below:

In a possible embodiment wherein a multiplicity of repeaters is employed and whereby range calculations are performed as such for each said multiplicity of repeaters, triangulation is applied to locate the receiver. Nevertheless, clock bias is an unknown and as such, solving for it requires additional measurement within the borders of allowable GNSS algorithms. For three-dimensional positioning, four equations of the type given below (4) are required, which in turn means four pseudorange measurements. where i = 1,2, 3,4 or, according to a different embodiment specifically seeking two-dimensional positioning, three equations of the type given below (5) are needed which amount to three pseudorange measurements: where = 1,2,3 and in both (4) and (5), X., JA, Z. correspond to the coordinates of repeaters. Un-indexed x, y and z terms correspond to the coordinates of the receiver(s), which are known.

According to an embodiment of the disclosed invention, a novel location finding algorithm is proposed whereby consecutive steps are taken as such: A multiplicity of repeaters collect a multiplicity of different corresponding satellite navigation signals sent by satellites; repeaters propagate ISM -downcon verted satellite navigation signals to the receiver indoors; receiver then upconverts ISM signals to a satellite navigation frequency of GNSS type and solves for the pseudorange of each of said multiplicity of satellites; locates the satellites using satellite ephemeris data; repeater positions are fixed to enable direct computation of the distance between the satellites and repeaters. Disclosed novel location finding algorithm, therefore, advances the state of the art in that, a major accuracy shortcoming regarding triangulation approaches that do not account for clock bias, which creates a 2D triangular region marked as displayed in reference to Fig. 6 within which error margin becomes significantly greater.

According to an embodiment of the disclosed invention, a system for indoor positioning comprising a multiplicity of directional GNSS active antennas collecting satellite navigation signals emitted by a multiplicity of satellites, repeaters for producing secondary signals than said satellite navigation signals and propagating said secondary signals in an indoor environment and at least one receiver capable of receiving and processing said secondary signals to compute location information is proposed.

In one aspect of the disclosed invention, said secondary signals for remediation of the location signals are contained in a frequency band lower than GNSS frequencies whereby free path loss is reduced and indoor coverage significantly improved.

In another aspect of the disclosed invention, said secondary signals for remediation of the location signals contained in a lower frequency band contain 433 MHz ISM.

In another aspect of the disclosed invention, said repeaters are configured to downconvert a GNSS signal to a lower signal such as an ISM band signal at 433 MHz.

In another aspect of the disclosed invention, said receiver is configured to upconvert said lower frequency signal to the original GNSS frequency.

In another aspect of the disclosed invention, said receiver is further configured such that a clock bias-based pseudorange triangulation is executed to determine location thereof.

According to an embodiment of the disclosed invention, a method for indoor positioning is proposed. In one aspect of the disclosed invention, said method comprises the step of GNSS signals reception, wherein GNSS signals broadcast by satellites are collected by directional active antennas;

In one aspect of the disclosed invention, said method comprises the step of downconversion, wherein original GNSS signals are downconverted to a lower- frequency ISM band.

In one aspect of the disclosed invention, said method comprises the step of indoor propagation, wherein downconverted ISM band signals are propagated indoors via ISM antennas with lower free space path loss and better penetration

In one aspect of the disclosed invention, said method comprises the step of ISM signal reception, wherein ISM signals propagated by repeaters indoor are collected by a receiver;

In one aspect of the disclosed invention, said method comprises the step of upconversion, wherein once downconverted ISM signals acquired on receiver end are upconverted to original GNSS band; and,

In one aspect of the disclosed invention, said lower-frequency selected for remediation of the GNSS signals in said method is 433 MHz ISM whereby better coverage and greater power transmission.

Claims

1) A system for indoor positioning comprising a multiplicity of directional GNSS active antennas collecting satellite navigation signals emitted by a multiplicity of satellites, repeaters for producing secondary signals than said satellite navigation signals and propagating said secondary signals in an indoor environment and at least one receiver capable of receiving and processing said secondary signals to compute location information, characterized in that; said secondary signals for remediation of the location signals are contained in a frequency band lower than GNSS frequencies whereby free path loss is reduced and indoor coverage significantly improved.

2) A system for indoor positioning as set forth in Claim 1 characterized in that said secondary signals for remediation of the location signals contained in a lower frequency band contain 433 MHz ISM.

3) A system for indoor positioning as set forth in Claim 1 and 2 characterized in that said repeaters are configured to downconvert a GNSS signal to a lower signal such as an ISM band signal at 433 MHz.

4) A system for indoor positioning as set forth in any preceding Claim characterized in that said receiver is configured to upconvert said lower frequency signal to the original GNSS frequency. 5) A system for indoor positioning as set forth in any preceding Claim characterized in that said receiver is further configured such that a clock bias-based pseudorange triangulation is executed to determine location thereof. 6) A method for indoor positioning comprising steps of;

GNSS signals reception, wherein GNSS signals broadcast by satellites are collected by directional active antennas; downconversion, wherein original GNSS signals are downconverted to a lower-frequency ISM band; indoor propagation, wherein downconverted ISM band signals are propagated indoors via ISM antennas with lower free space path loss and better penetration; ISM signal reception, wherein ISM signals propagated by repeaters indoor are collected by a receiver; upconversion, wherein once downconverted ISM signals acquired on receiver end are upconverted to original GNSS band; and, 7) A method for indoor positioning as set forth in Claim 6 characterized in that said lower-frequency selected for remediation of the GNSS signals is 433 MHz ISM whereby increased coverage and greater power transmission are achieved.