CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No. 10201508133X filed September 30, 2015, the contents of it being hereby incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

[0002] Various embodiments relate to a transmitter array, a receiver, and/or a positioning system. Various embodiments relate to a method of forming a positioning system. Various embodiments relate to a method of determining a position of a receiver.

BACKGROUND

[0003] There is an urgent need for indoor positioning (also known as indoor localization) systems with high accuracy (in the order of centimeters) and low cost. Systems with such features would be expected to become one of the most exciting and sought-after features of next generation indoor wireless systems. The indoor positioning market is forecasted by ABI Research to reach $5 billion in 2018. Consumer applications for indoor location information are potentially limitless. The current indoor location enabled applications and services are only at their beginning stage.

[0004] Such applications span a wide range, including:

(1) Human and robotic navigation: high -precision positioning systems may be potentially used for navigation applications in unfamiliar indoor environments. Examples may include controlling robots to follow an accurate path; guiding travelers in airports or underground stations; and helping visitors in museums, galleries, office buildings, or shopping malls.

(2) People and object tracking: an interesting example is tracking the location of different medical personnel or equipment inside a hospital for operational efficiency and effectiveness. Other possible applications include tracking objects inside a warehouse, or some assets in an organization.

(3) Industrial applications: these may include navigation of indoor automobiles, precise operations of automatic manufacturing process, etc. [0005] As technologies continue to improve with better and more accurate positioning information, new and more exciting applications may be developed to serve and entertain mass consumer markets.

[0006] However, the requirements of a high degree of positioning accuracy (PA) and a low cost cannot be met by existing indoor positioning systems. The Global Positioning System (GPS) has been widely available since 1995, and is now in everyday use around the world, often in new and unexpected ways. Unfortunately, there is no direct visibility to GPS satellites inside a building, which means that GPS receivers (Rxs) generally do not work well in indoors or underground spaces.

[0007] Even if GPS positioning is available, it may not be accurate enough for many indoor applications (in the order of centimeters). The accuracy of GPS is quite low, normally in the order of meters. Current indoor positioning techniques such as infrared (IR), ultrasound, radio-frequency identification (RFID), wireless local area network (WLAN), also known as WiFi), Bluetooth, sensor networks and ultra-wideband (UWB) are being developed. However, such systems have either a low accuracy and/or a high deployment cost.

SUMMARY

[0008] In various embodiments, a positioning system may be provided. The positioning system may include a transmitter array including a plurality of visible light positioning (VLP) units. Each visible light positioning unit may include light-emitting diodes (LEDs). Each of the light-emitting diodes may be configured to emit a visible light including an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The positioning system may include a receiver including a detector. The detector may be configured to receive the visible lights emitted by the light-emitting diodes of each of the plurality of visible light positioning units. The receiver may be configured to select one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The receiver may be further configured to determine a position of the receiver based on the phase data portions of the visible lights emitted by light- emitting diodes of the selected visible light positioning unit.

[0009] In various embodiments, a transmitter array may be provided. The transmitter array may include a plurality of visible light positioning units. Each visible light positioning unit may include light-emitting diodes. Each of the light-emitting diodes may be configured to emit a visible light including an identifier portion associating the visible light with the light- emitting diode, and a phase data portion. The visible lights emitted by the light emitting diodes of each of the plurality of visible light positioning units may be configured to be received by a detector of a receiver. The identifier portions of the visible lights may be configured to be used by the receiver to select one visible light positioning unit of the plurality of visible light positioning units. The phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit may be configured to be used by the receiver to determine a position of the receiver.

[0010] In various embodiments, a receiver may be provided. The receiver may include a detector configured to receive visible lights emitted by light-emitting diodes of each visible light positioning unit of a plurality of visible light positioning units. Each visible light may include an identifier associating the visible light with the light-emitting diode, and a phase data portion. The receiver may be configured to select one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The receiver may be further configured to determine a position of the receiver based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

[0011] In various embodiments, a method of forming a position system may be provided. The method may include providing a transmitter array including a plurality of visible light positioning (VLP) units, each visible light positioning unit including light-emitting diodes (LEDs). Each of the light-emitting diodes may be configured to emit a visible light including an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The method may also include providing a receiver including a detector. The detector may be configured to receive the visible lights emitted by the light-emitting diodes of each of the plurality of visible light positioning units. The receiver may be configured to select one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The receiver may be further configured to determine a position of the receiver based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

[0012] In various embodiments a method of determining a position of a receiver may be provided. The method may include receiving by a detector of the receiver, visible lights emitted by light-emitting diodes of each of a plurality of visible light positioning units, wherein each visible light may be emitted by a light-emitting diode, and may include an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The method may include selecting by the receiver, one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The method may also include determining by the receiver, the position of the receiver based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings, in which:

FIG. 1 is a schematic illustrating a positioning system according to various embodiments. FIG. 2A is a schematic illustrating a transmitter array according to various embodiments. FIG. 2B is a schematic illustrating a receiver according to various embodiments.

FIG. 3A is a schematic illustrating a method of forming a positioning system according to various embodiments.

FIG. 3B is a schematic illustrating a method of determining the position of a receiver according to various embodiments.

FIG. 4 is a schematic showing a positioning system according to various embodiments.

FIG. 5A is a schematic illustrating the data frame of a modulating signal according to various embodiments.

FIG. 5B is a schematic showing the five continuous sine wave signals according to various embodiments.

FIG. 6 shows a flow chart of the positioning estimation procedure at a receiver (Rx) according to various embodiments.

FIG. 7 is a plot of the cumulative distribution function (CDF) of the estimation error of the i- th VLP unit within a space C; with a dimension of 2.5 x 2.5 x 3 m ³ (length x width x height) as a function of the root mean square error (RMSE) of the receiver position according to various embodiments.

DETAILED DESCRIPTION [0014] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0015] Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

[0016] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0017] In the context of various embodiments, the articles "a", "an" and "the" as used with regard to a feature or element include a reference to one or more of the features or elements.

[0018] In the context of various embodiments, the term "about" or "approximately" as applied to a numeric value encompasses the exact value and a reasonable variance.

[0019] As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0020] In various embodiments, a positioning system may be provided. FIG. 1 is a schematic illustrating a positioning system 100 according to various embodiments.

[0021] The positioning system 100 may include a transmitter array 102 including a plurality of visible light positioning (VLP) units e.g. 104a, 104b. Each visible light positioning unit e.g. 104a, 104b may include light-emitting diodes (e.g. 104a includes 106a, 106b; 104b includes 106c, 106d). Each of the light-emitting diodes e.g. 106a-d may be configured to emit a visible light including an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The positioning system 100 may include a receiver 108 including a detector 110. The detector 110 may be configured to receive the visible lights emitted by the light-emitting diodes e.g. 106a-d of each of the plurality of visible light positioning units e.g. 104a, 104b. The receiver 108 may be configured to select one visible light positioning unit e.g. 104a of the plurality of visible light positioning units e.g. 104a, 104b based on the identifier portions of the visible lights. The receiver 108 may be further configured to determine a position of the receiver 108 based on the phase data portions of the visible lights emitted by light-emitting diodes e.g. 106a, 106b of the selected visible light positioning unit e.g. 104a.

[0022] In other words, the positioning system 100 may include an array 102 of light- emitting diodes e.g. 106a-d, which may be divided into a plurality of VLP units 104a, 104b. The light-emitting diodes e.g. 106a-d may each emit a visible light, which may include an identifier portion encoding information regarding the originating light-emitting diode that emits that particular visible light, as well as a phase data portion. The positioning system 100 may also include a receiver 108 including detector 110, which receives the visible lights from the light-emitting diodes e.g. 106a-d and select one VLP unit for further processing. The phase data portion of the visible lights emitted by the light-emitting diodes e.g. 106a, 106b of the selected VLP unit e.g. 104a may be used to determine the position of the receiver 108.

[0023] Various embodiments may seek to mitigate or address one or more of the highlighted problems or issues. Various embodiments may have reduced complexity as the receiver 108 only determines the position of the receiver 108 based on information provided by light emitting diodes (e.g. 106a, 106b) of the selected visible light positioning unit (e.g. 104a) instead of light-emitting diodes 106a-d of the entire transmitter array 102. Various embodiments may provide improved accuracy over conventional systems, such as ultra-wide band (UWB), ultrasound, and infrared (IR) based systems by using detecting visible light from light-emitting diodes (LEDs). Various embodiments may make use of LEDs that are already used to provide indoor lighting, thus reducing costs. Various embodiments may not produce electromagnetic interference (EMI), unlike conventional radio-frequency (RF) based positioning systems. Various embodiments may provide a secure and private positioning system as the optical radiation does not penetrate walls or opaque objects.

[0024] FIG. 1 serves to provide a general illustration of the positioning system 100 according to various embodiments, and should not be interpreted in a limiting manner. For instance, the number of visible light positioning (VLP) units may not be limited to two, but may include more than two. For instance, there may be two, three, four or more VLP units. Further, the number of LEDs in each VLP unit may not be limited to two, but may include more than two.

[0025] Each visible light may be emitted by one LED, and the identifier portion of a particular visible light may identify or provide information about the one LED that emits the particular visible light. The phase data portion may include or may be a repetitive signal such as a sinusoidal signal. As the visible light travels different distances, the signal of the phase data portion may be at different phases corresponding to the different distances. Accordingly, the phase data portion may provide information on the distance travelled by the visible light.

[0026] In various embodiments, each VLP unit e.g. 104a, 104b may include four or five LEDs.

[0027] In various embodiments, the receiver 108 may be the detector 110. The detector 110 may be or may include a photodiode.

[0028] In various embodiments, the phase data portions of the visible lights emitted by different light-emitting diodes (LEDs), e.g. 106a, 106b of each visible light positioning (VLP) unit, e.g. 104a, may be modulated to have substantially equal initial phases, and to have substantially different (modulated) frequencies. In other words, the different light- emitting diodes, e.g. 106a, 106b within a VLP unit may be synchronised so that visible light leaving a first LED e.g. 106a and visible light leaving a second LED e.g. 106b may be in the same phase. However, the visible light leaving the first LED e.g. 106a and the visible light leaving the second LED, e.g, 106b may have different (modulated) frequencies. The local synchronisation of the LEDs in the same VLP, i.e. local synchronisation, may reduce the synchronisation complexity, and may remove the need for a local oscillator to be included in the receiver 108 to measure differential phase shift.

[0029] In various embodiments, the phase data portions of the visible lights emitted by different light-emitting diodes of the selected visible light positioning unit and received by the detector 110 may have different phase shifts (relative to one another). In other words, the phase data portion of a visible light emitted by a first LED of the selected VLP unit may have a first phase shift, and the phase data portion of a visible light emitted by a second LED of the selected VLP unit may have a second phase shift different from the first phase shift. The differences in phase shift may be due to the substantially equal initial phases and the substantially different frequencies. As the visible lights emitted from different LEDs from the same VLP unit, e.g. 104a travel different distances from the LEDs e.g. 106a, 106b to reach the detector 110, the visible lights may have different phase shifts since they have a common starting phase, but are of different frequencies.

[0030] In various embodiments, the identifier portion and the phase data portion of the visible light emitted by each light-emitting diode may be modulated to substantially equal frequencies. The identifier portion of a visible light may be modulated to the same frequency as the phase data portion of the visible light. The identifier portion and the phase data portion of the visible light emitted by each light-emitting diode may be modulated to a radio frequency (RF). The identifier portion of the visible light emitted by each light-emitting diode may be modulated by an identifier data using binary phase shift keying (BPSK). The identifier data is unique for each LED (and may be associated with the position of the respective LED). Modulating the identifier portion of a visible light to the same frequency as the phase data portion of the visible light so that both the identifier portion and the phase data portion are of a different frequency compared to the identifier portion and the phase data portion of another LED in the same VLP unit may allow signals/ visible lights from different LEDs in the same VLP unit to be more easily differentiated or separated from one another.

[0031] In various embodiments, the receiver 108 may be configured to ignore or reject phase data portions of the visible lights emitted by light-emitting diodes e.g. 106c, 106d of the non-selected visible light positioning units e.g. 104b. The receiver 108 may be configured to determine a position of the receiver 108 by only processing the visible lights emitted by the light-emitting diodes e.g. 106a, 106b of the selected VLP unit e.g. 104a. The visible lights emitted by the light-emitting diodes e.g. 106c, 106d of the non-selected VLP unit e.g. 104b, may not be processed. By processing only the visible lights emitted by the LEDs e.g. 106a, 106b of the selected VLP unit e.g. 104a, complexity may be reduced.

[0032] The receiver 108 may be configured to capture the signals from any available neighbouring VLP units e.g. 104a, 104b, then select one visible light positioning unit with light-emitting diodes having the highest signal-to-noise ratio (SNR), e.g. 104a of the plurality of visible light positioning units e.g. 104a, 104b to first determine and select a zone in which the receiver 108 is located, out of a plurality of zones. Each zone may be associated with one visible light positioning unit. The receiver 108 may be further configured to process the phase data portions of the visible lights emitted by the LEDs of the VLP unit associated with the selected zone to identify or determine the exact location of the receiver 108 within the selected zone.

[0033] In various embodiments, the selected visible light positioning unit e.g. 104a may include light-emitting diodes e.g. 106a, 106b having signal-to-noise ratios (SNRs) higher than light-emitting diodes e.g. 106c, 106d of non-selected visible light positioning unit(s), e.g. 104b. In other words, the visible light positioning unit e.g. 104a with LEDs having the highest SNRs may be selected. The receiver 108 may be configured to determine signal-to- noise ratios (SNRs) of light-emitting diodes of each light positioning unit based on the identifier portions of the visible lights. In various embodiments, the receiver 108 may be configured to determine an average signal-to-noise ratio (SNR) of the light-emitting diodes of each visible light positioning unit e.g. 104a, 104b. The receiver 108 may be further configured to select the visible light positioning unit e.g. 104a of the plurality of visible light positioning units e.g. 104a, 104b by comparing the average signal-to-noise ratios (SNRs) of LEDs of different visible light positioning units, e.g. 104a, 104b. The selected visible light positioning unit e.g. 104a may include light-emitting diodes with the average signal-to-noise ratio (SNR) higher than light-emitting diodes of the non-selected visible light positioning unit(s), e.g. 104b.

[0034] The receiver 108 may be further configured to determine signal-to-noise ratios (SNRs) of the light-emitting diodes (LEDs) e.g. 106a-d of the plurality of visible light positioning units (VLPs) e.g. 104a, 104b before selecting the one VLP unit e.g. 104a out of the plurality of VLP units e.g. 104a, 104b based on the signal-to-noise ratios (SNRs).

[0035] If the SNR of the selected VLP unit is at or above a predetermined threshold, the receiver 108 may proceed to determine the position of the receiver 108. The SNR of the selected VLP unit e.g. 104a may refer to an average SNR of all the LEDs e.g. 106a, 106b in the selected VLP unit e.g. 104a. Alternatively, the SNR of the selected VLP unit e.g. 104a may refer to the lowest SNR of all the LEDs e.g. 106a, 106b in the selected VLP unit e.g. 104a. In other words, the LEDs e.g. 106a, 106b in the selected VLP unit e.g. 104a may be required to meet the predetermined SNR threshold requirement before the position of the receiver 108 is determined.

[0036] If the SNR of the selected VLP unit e.g. 104a is below the predetermined threshold, the receiver 108 may repeat the selection process after a predetermined duration of time. In other words, if the SNR of the selected VLP unit e.g. 104a is below the predetermined threshold, the receiver 108 may be configured to wait for a predetermined duration of time before re-determining the SNRs of the LEDs e.g. 106a-d of the plurality of the VLP units e.g. 104a, 104b. The receiver 108 may re-determine the SNRs of the LEDs e.g. 106a-d of the plurality of the VLP units e.g. 104a, 104b before selecting the one VLP unit e.g. 104a out of the plurality of VLP units e.g. 104a, 104b based on the SNRs.

[0037] The receiver 108 may be configured to determine the SNRs before determining the position of the receiver 108.

[0038] In various embodiments, the receiver 108 may be configured to determine the position of the receiver by differential phase shift measurement and/or trilateration algorithm.

[0039] The phase data portion of visible lights emitted by light-emitting diodes (LEDs) of a first visible light positioning (VLP) unit and the phase data portion of visible lights emitted by light-emitting diodes (LEDs) of a second visible light positioning (VLP) unit may have substantially different initial phases. In other words, the LEDs of different VLP units may be unsynchronized.

[0040] In various embodiments, the LEDs may be white LEDs or LEDs configured to emit white light. In various embodiments, the LEDs may be blue LEDs, i.e. LED configured to emit blue light, which are coated with yellow phosphor. When the blue LEDs are coated with yellow phosphor, the LEDs may be configured to emit white light.

[0041] In various embodiments, the receiver 108 may further include a demodulator, such as a differential phase- shift measurement based VQ (in-phase and quadrature) demodulator, which is configured to determine the position of the receiver 108. The demodulator may be configured to determine differences in phase shift received by the detector 110. The demodulator may be configured to determine a difference in phase shift between a visible light emitted by a first LED and a visible light emitted by a second LED received by the detector 110, the first LED and the second LED of the same VLP unit. The demodulator may be in electrical connection with the detector 110.

[0042] In various embodiments, the receiver 108 may further include a processor or processing circuit. The processor or processing circuit may be configured to determine the position of the receiver 108 based on the visible lights received by the detector 110 (and emitted by the selected VLP unit e.g. 104a), e.g. by differential phase shift measurement and/or trilateration algorithm. The processor or processing circuit may be configured to determine the SNRs of the LEDs of each VLP unit. The processor or processing circuit may be configured to select one VLP unit with LEDs having the highest SNR out of a plurality of VLP units. The processor or processing circuit may be in electrical connection with the detector and/or the demodulator.

[0043] In various embodiments, the receiver 108 may further include a filter over the detector 110. The filter may be configured to allow blue light to pass through to the detector 110m, but may block or filter off other components of the visible light emitted from the LEDs 106.

[0044] In various embodiments, the receiver 108 may include a post-equalization circuit arrangement in electrical connection with the detector 110. The equalization circuit arrangement may be configured to relax the modulation bandwidth requirement of the LEDs (this is effectively equivalent to increases the modulation bandwidth of the LEDs).

[0045] In various embodiments, the positioning system 100 may achieve a positioning accuracy of less than about 100 cm, less than about 20 cm, or less than about 10 cm, or less than about 7 cm or about 5 cm. The receiver 108 may be configured to determine a position of the receiver 108 with a positioning accuracy of less than about 100 cm, less than about 20 cm, or less than about 10 cm, or less than about 7 cm or about 5 cm.

[0046] In various embodiments, a transmitter array may be provided. FIG. 2A is a schematic illustrating a transmitter array 202 according to various embodiments.

[0047] The transmitter array 202 may include a plurality of visible light positioning units e.g. 204a, 204b. Each visible light positioning unit e.g. 204a, 204b may include light-emitting diodes e.g. 206a-d. Each of the light-emitting diodes e.g. 206a-d may be configured to emit a visible light including an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The visible lights emitted by the light emitting diodes e.g. 206a-d of each of the plurality of visible light positioning units e.g. 204a, 204b may be configured to be received by a detector of a receiver. The identifier portions of the visible lights may be configured to be used by the receiver to select one visible light positioning unit e.g. 204a of the plurality of visible light positioning units e.g. 204a, 204b. The phase data portions of the visible lights emitted by light-emitting diodes e.g. 206a, 206b of the selected visible light positioning unit e.g. 204a may be configured to be used by the receiver to determine a position of the receiver.

[0048] FIG. 2A serves to provide a general illustration of the transmitter array 202 according to various embodiments, and should not be interpreted in a limiting manner. For instance, the number of visible light positioning (VLP) units may not be limited to two, but may include more than two. For instance, there may be two, three, four or more VLP units. Further, the number of LEDs in each VLP unit may not be limited to two, but may include more than two.

[0049] In various embodiments, a receiver may be provided. FIG. 2B is a schematic illustrating a receiver 208 according to various embodiments.

[0050] The receiver 208 may include a detector 210 configured to receive visible lights emitted by light-emitting diodes of each visible light positioning unit of a plurality of visible light positioning units. Each visible light may include an identifier associating the visible light with a light-emitting diode, and a phase data portion.

[0051] The receiver 208 may be an optical receiver. The receiver 208 may be configured to select one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The receiver 208 may be configured to determine signal-to-noise ratios (SNRs) of light-emitting diodes of each visible light positioning unit based on the identifier portions of the visible lights.

[0052] The selected visible light positioning unit may include light-emitting diodes having signal-to-noise ratios (SNRs) higher than light-emitting diodes of non-selected visible light positioning unit(s). The receiver 208 may be further configured to determine a position of the receiver 208 based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

[0053] FIG. 2B serves to provide a general illustration of the receiver 208 according to various embodiments, and should not be interpreted in a limiting manner.

[0054] In various embodiments, a method of forming a positioning system may be provided. FIG. 3A is a schematic 300a illustrating a method of forming a positioning system according to various embodiments. The method may include, in 302, providing a transmitter array including a plurality of visible light positioning (VLP) units, each visible light positioning unit including light-emitting diodes (LEDs). Each of the light-emitting diodes may be configured to emit a visible light including an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The method may also include, in 304, providing a receiver including a detector. The detector may be configured to receive the visible lights emitted by the light-emitting diodes of each of the plurality of visible light positioning units. The receiver may be configured to select one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The receiver may be further configured to determine a position of the receiver based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

[0055] In other words, a method of forming a positioning system may include providing a transmitter array including a plurality of LEDs grouped into VLP units. Each VLP unit may include a number of LEDs. The method may also include providing a receiver including a detector. The detector may receive visible lights emitted by the plurality of LEDs. After receiving the visible lights, the receiver may proceed to determine which particular one VLP unit to further process. The receiver does the determination by processing the identifier portions of the visible lights emitting from the LEDs. Each visible light may be emitted by one LED, and the identifier portion of a particular visible light may identify or provide information about the one LED that emits the particular visible light. After the determination, the receiver may then determine its location based on the phase data portions of the visible lights emitted by LEDs of the one particular VLP unit.

[0056] In various embodiments, the phase data portions of the visible lights emitted by different light-emitting diodes of each visible light positioning unit may be modulated to have substantially equal initial phases, and to have substantially different frequencies.

[0057] In various embodiments, the phase data portions of the visible lights emitted by different light-emitting diodes of the selected visible light positioning unit and received by the detector may have different phase shifts.

[0058] In various embodiments, the identifier portion and the phase data portion of the visible light emitted by each light-emitting diode may be modulated to substantially equal frequencies. The identifier portion of the visible light emitted by each light-emitting diode may be modulated by an identified data using binary phase shift keying (BPSK).

[0059] The receiver may be configured to ignore or reject phase data portions of the visible lights emitted by light-emitting diodes of the non-selected visible light positioning units.

[0060] The receiver may be configured to determine signal-to-noise ratios (SNRs) of light-emitting diodes of each VLP unit based on the identifier portions of the visible lights. The receiver may be further configured to determine SNRs of the light-emitting diodes of the plurality of visible light positioning units before selecting the one VLP unit out of the plurality of VLP units. The receiver may be configured to select the one VLP unit out of the plurality of VLP units based on the SNRs. The SNRs of the light-emitting diodes of the selected visible light positioning unit may be higher than the SNRs of the light-emitting diodes of non-selected visible light positioning units. The receiver may be further configured to determine the SNRs before determining the position of the receiver.

[0061] The position of the receiver may be determined by differential phase shift measurement and trilateration algorithm.

[0062] The visible lights emitted by light-emitting diodes of different visible light positioning units may be unsynchronized. The phase data portion of visible lights emitted by light-emitting diodes of a first visible light positioning unit and the phase data portion of visible lights emitted by light-emitting diodes of a second visible light positioning unit may have substantially different initial phases.

[0063] A number of recent studies have verified the feasibility of VLP for different applications. Around 20 different low-cost indoor positioning systems were reported in Microsoft Indoor Localization Competition-IPSN 2014. However, among these real-time or near real-time positioning systems, there is still no such a system which is not only low -cost, but also offers centimeter-scale accuracy. Cost, complexity, accuracy, coverage and/or robustness are the main research challenges of current indoor positioning systems.

[0064] To address these challenges as well as to meet the demand of current indoor positioning systems, a low-cost indoor centimeter-scale positioning system according to various embodiments may be provided, which may deliver high-accuracy localization without the need of a complicated and expensive infrastructure. Various embodiments may include white illuminating LEDs. The additional capability of white illuminating LEDs as a positioning tool may be unleashed, resulting in a more complete solution that may provide centimeter- scale positioning resolution. The system according to various embodiments may include modulating each LED with its identification information and a continuous sine wave signal at a pre-determined frequency, and sending the signals periodically. Every four or five LEDs may be grouped as a basic VLP unit and the four or five LEDs may be locally synchronized in phase. The number of LEDs grouped as a VLP unit may differ or vary in various different embodiments. A VLP receiver Rx may detect the signals from any one of the VLP units to determine its position by analyzing and processing the received signals and utilizing the pre-determined indoor map. [0065] In various embodiments, a method of determining a position of a receiver may be provided. FIG. 3B is a schematic 300b illustrating a method of determining a position of a receiver according to various embodiments. The method may include, in 312, receiving by a detector of the receiver, visible lights emitted by light-emitting diodes of each of a plurality of visible light positioning units, wherein each visible light may be emitted by a light- emitting diode, and may include an identifier portion associating the visible light with the light-emitting diode, and a phase data portion. The method may include, in 314, selecting by the receiver, one visible light positioning unit of the plurality of visible light positioning units based on the identifier portions of the visible lights. The method may also include, in 316, determining by the receiver, the position of the receiver based on the phase data portions of the visible lights emitted by light-emitting diodes of the selected visible light positioning unit.

[0066] In other words, a position of a receiver may be determined by using a detector of the receiver to detect visible lights emitted by LEDs of different VLP units. Each visible light may come from one LED. The visible light may include an identifier portion and a phase data portion. The receiver may select a VLP unit out of a plurality of VLP units based on the identifier portion. The receiver may then determine its position based on the phase data portion of the visible lights emitted by LEDs of the selected VLP unit.

[0067] The method may include, determining by the receiver, signal-to-noise ratios (SNRs) of light-emitting diodes of each visible light positioning (VLP) unit based on the identifier portions of the visible lights. In various embodiments, the selected visible light positioning unit may include light-emitting diodes having signal-to-noise ratios (SNRs) higher than light-emitting diodes of non-selected visible light positioning unit(s).

[0068] In various embodiments, the receiver may be secured or attached to an object such as a robot, a piece of equipment etc. In various embodiments, the receiver may be held or may be attached to a person or an animal. The position of the object, person or animal may thus be determined.

[0069] FIG. 4 is a schematic showing a positioning system 400 according to various embodiments. The positioning system 400 may be an indoor VLP system. The positioning system 400 may use white LEDs 406. In order to avoid clutter and to improve clarity of FIG. 4, not all LEDs 406 have been labelled. The LEDs 406 may be installed on a ceiling of an indoor environment for illumination purposes. [0070] A shown in FIG. 4, the LEDs 406 may be divided into multiple VLP units 404a-h, which may also be referred to as localization units. Each VLP unit 404a-h may include 5 LEDs (represented by solid rectangles within each VLP unit 404a-h). In various other embodiments, each VLP unit 404a-h may include 4 LEDs. The visible light emitted from each LED within a VLP unit may be modulated so that the modulated visible light includes a unique identifier portion (which may be referred to as LED location identification (ID), and which may be unique to each LED), and a phase data portion, e.g. a period of continuous sine wave at a pre-determined frequency fi. The VLP units 404a-h may form the transmitter (Tx) array 402.

[0071] An example of illustrating the data frame of a modulated visible light is shown in FIG. 5A. FIG. 5A is a schematic illustrating the data frame 500a of a modulating signal according to various embodiments. The data frame 500a may include the LED location ID information 502, followed by a period of continuous sine wave 504.

[0072] The modulated signal from each LED 406 may be transmitted periodically. To facilitate separation or distinguishing different signals emitted from the five LEDs 406 that are within one VLP unit 404a-h, the location ID of each LED 406 may be first modulated to a RF signal of the same frequency as the following sine wave. The modulation may be in the BPSK modulation format. Within each VLP unit, the five continuous sine wave signals of different frequencies may be locally synchronized in phase, i.e. the visible lights emitted may have a common initial starting phase. FIG. 5B is a schematic 500b showing the five continuous sine wave signals according to various embodiments.

[0073] It is noted that LEDs 406 in different VLP units 404a-h may not need to be globally synchronized, which may significantly simplify the synchronization problem. VLP receivers (Rx) 408a-d may detect the signals, i.e. the modulated visible lights, from LEDs 406 of any one unit of the VLP units 404a-h, but may reject or ignore the signals from LEDs 406 of other neighboring VLP units 404a-h. Each Rx's position may then be determined by analyzing and processing the received signals and utilizing the pre-determined indoor map. In various embodiments, a group of five LEDs 406 in a VLP unit 404a-h may be used to estimate the Rx's position to solve the precise synchronization problem between transmitters Txs 402 and each Rx 408a-d. The problem may be solved using local synchronization at the Tx 402 side. A Rx 408a-d may receive five incoming signals, each associated with a radio frequency (RF) fi. The distance (di) between each LED 406 and the Rx 408a-d may be obtained by a differential phase shift measurement, and then the positioning of the Rx 408a-d may be estimated by e.g. trilateration algorithm. It is noted that the phases of the signals at the Rx 408a-d side are distance dependent. The measured phase difference between a transmitted signal and its corresponding received signal may be converted into the associated transmission distance. As described later, the initial phase of an input sinusoidal signal (emitted from LEDs 406) may be defined as φο, which is in the range of 0 to 2π. After propagating a distance of di, the phase of the received signal, i.e. the signal received by a receiver 408a-d may increase to ψί.

[0074] The phase of the signal received by a receiver 408a-d (φί) may be provided by:

where Δφ _γ is the phase shift of the transmitted sinusoid signal at the frequency of fi. To measure Δψί, a differential phase- shift measurement based VQ (in-phase and quadrature) demodulator may be employed according to various embodiments.

[0075] As highlighted above, visible lights emitted from different LEDs 406 of the same VLP unit 404a-h may be of the same initial phase φο. Due to different distances di travelled by the visible lights (emitted by different LEDs 406 of the same VLP unit 404a-h) and the different frequencies fi, the visible lights may experience different phase shifts Δψί, which may result in the visible lights received by a receiver 408a-d having different ψί.

[0076] With the abovementioned method, the initial phase of an input sinusoidal signal φο may be cancelled in the final estimation equations. Therefore, the receiver 408a-d may not need to be synchronized with the VLP units 404a-h, and only the downlinks may be needed for estimating the position of the receiver 408a-d, which may significantly reduce the complexity of the system. Local synchronization in each VLP unit 404a-h may be required to provide the same initial phase of different sine wave signals in each VLP unit 404a-h, instead of global synchronization among all the VLP units 404a-h. In various embodiments, the number of the LEDs 406 within each VLP unit 404a-h may be five. The number of LEDs 406 within a VLP unit 404a-h may be reduced to four if two RF frequencies are modulated onto one of the LEDs 406.

[0077] FIG. 6 shows a flow chart 600 of the positioning estimation procedure at a receiver (Rx) according to various embodiments. In State 1 (602), the Rx may start to check if there is a line-of-sight (LOS) downlink from any one of the VLP units for further positioning operation. In State 2 (604), after receiving a positioning request, the system, i.e. Rx, may start to read the LEDs' location ID information (identifier portion) which are received from a VLP unit, and then updates the LEDs' location information to a pre-determined user map. In State 3 (606), the Rx may start to capture the differential phase-shift information from each LED. The Rx may then compute the SNR associated with each LED in order to determine the reliability of the received signal. After confirming that the received signals are reliable (e.g. SNR > 13.6 dB), the Rx' s location may be estimated using an algorithm in State 4 (608). If the signals are not reliable, they may be ignored and a new capture operation may be executed. After State 4 (608), a decision operation may determine whether the positioning operation is re-executed or terminated. The acquisition rate of the positioning implementation may be been designed accordingly to suit the decision operation for different applications to support the mobility of the user terminal.

[0078] A common strategy for measuring distances in localization related applications is to compute the time of flight (TOF) of a signal. However, for an indoor scenario, as the signal travels at the speed of light and the propagation distance is very small (only a few meters), directly measuring the TOF (in the order of ns) may be difficult and the accuracy may be low. In various embodiments, a differential phase shift measurement method may be adopted and an averaging technique may be used to achieve a more precise estimation. The position of the receiver may be obtained based on the differential phase shift measurement method and the averaging technique in the positioning system according to various embodiments.

[0079] Let di be the distance between the T _x i and R _x , and n be the corresponding propagation time :

d _i = τ _ί c ^ where c is the speed of light.

[0080] Ti may be provided by:

2π _{{ (3)} where ψί is the phase shift of the transmitted sinusoid signal at the frequency of fi. It is noted that di may have a no-ambiguity distance range depending on the frequency fi, due to the 2π period of the sinusoid. For instance, if fi is 10 MHz, the corresponding no-ambiguity distance range of di may be about 7.5 m. With reference to FIG. 4, let S^Ct) be the input sinusoidal signal modulated to the i ^th LED, which may be expressed as: 5 ^t _I .( = 5 sin(2^.i + _% ) (4) where S and φο are the peak amplitude and the initial phase of the input sinusoidal signal, respectively. After propagating through an indoor optical wireless (OW) channel, being detected and passing through a radio frequency (RF) bandpass filter, the received signal S ^r i{t) is given by:

+ Αφ, + φ ₀ ) + η,.(ί) (5) where R is the responsivity of the photodetector (PD), Ρτ is the transmitted optical power and m(t) is the additive white Gaussian noise (AWGN).

[0081] Hi(0) is DC gain of the optical wireless channel, which is given by:

(m + 1) A

j ₂ -cos ^m (^)r _s (6¾(6?) cos(6?), O≤0≤cp _c

H,.(0) ^: 2%d _:

where m is the Lambertian order of Tx, φ is the irradiance angle, Θ is the incidence angle to Rx. AR is the detecting surface area of Rx, r _S (6>) is the optical filter gain, g(6) is the optical concentrator (lens) gain, and <p _c is the field of view (FOV, semi-angle) of Rx.

[0082] As given in Equation (5), the optical received signal S ^r i{t) may include a number of periods of the sine signal. To improve the SNR of the received signal, one effective method is to use an averaging technique. The averaging method may be based on the principle that each period of the signal has the identical phase-shift information, although these signal periods may be obscured by the AWGN noise m(t). When the noise m(t) is summed, its average tends toward zero. Let us assume that S ^r i(t) includes Nave periods of a sine signal. The noise m(t) has zero mean and a variance of σ ² . The received signal at a time t after the kt period is given by:

S ^r _i (t - kT) = r _i (t - kT) + n _i (t - kT) (7) where,

η (t - kT) = RP _T H _i (0) sin(2 r : (t - kT) + A<p _{ + <p ₀ ) (8)

[0083] After combining N _ave periods of the sine signal, the averaged signal S ^r _t (t) may be given by:

[0084] Since r _t (t) is time invariant, (9) can be rewritten as:

s (t = nit + _i-∑¾-i _n . _{( t} _ _{kT) ( 10)} [0085] This S ^r _t (t) is an estimate of η(ί) .The expected value of S ^r _t (t) is given by:

i(t - kT)], 0 < t < T (11)

(12)

[0087] Therefore, S ^r _t (t) is an unbiased estimator of /-(t) . The variance of S ^r _t (t) is given by: _

ar[S ^r _t (t)] = Var[n(t)] + Var[—∑J¾? - ^)] + Cov(. ), 0 ≤t < T (13)

"ave

[0088] Since the AWGN noise is uncorrected with the received sine signal, the covariance terms may be zero. Moreover, n _t {t— kT) is uncorrected with n _i [t - (k + y ^' )r] for

1 < j≤ N ave ,' therefore: Var[n _i (t - kT)], 0 ≤t < T (14)

[0089] Since the noise variance is constant, Equation (14) may be rewritten as:

Var[n(t)] (15)

Since V r[r _; (t)] = 0 , we have

Var[S (t)] = -^-Var[n(t)] (16) i ^v ave

[0090] Before the averaging, As per Equation (16), after the

averaging, the variance is reduced by a factor of Nave, and hence the SNR of the received signal is improved by a factor of N _ave .

[0091] To measure Δψϊ, an VQ (In phase and Quadrature) demodulator may be required. Various embodiments may require a local oscillator (LO) generating a reference signal at the frequency fi with a phase locked loop (PLL) circuit to decode the phase shift φι. This local oscillator may need to be precisely synchronized to the transmitted sinusoidal signal, which may significantly increase the system complexity and affect measurement accuracy, since there are multiple VLP units. Various embodiments may involve a non-LO based differential phase-shift measurement to obtain Δψϊ, which may then be used in the triangulation algorithm for the positioning estimation. Equation (5) may be re- written as:

S ^r .(t) = K ήη(ω.ί + ^ω ' + φ ₀ ) + n.(t)

c ' (17) where Ki is the attenuation factor, di is the distance between the Txi and the Rx. To extract di from Equation (17), a differential phase shift measurement approach may be used.

Multiplying ΞΊ ί) with ^(t), we have d, ^■ co, d ₇ ^■ co ₇ d ₇ co ₇ d,co, (18)

-κ,κ ₇ cos((iy _j + co ₂ )t +—— - +—— - + 2Αφ ₀ ) - cos((i¾ -co _x )t +—^- — )) ^■ n _X2 (t)

c c c c

where nn(f) is the additive noise term. After passing through a low-pass filter (LPF) and ignoring the noise, we have

/ ( S S ) = -K _X K ₂ cos((fi> ₂ -<¾). + to. _ to.)) (19)

Similarly,

d ₃ co ₃ d ₂ co ₂

f (S ^R ₂ S ^R ₃ ) =— K ₂ K ₃ cos((<z> ₃ - ω ₂ )ί + )) (20) v ⁷ 2 c c

4*^4

-)) (21) c

d.co.

/ (S ^r ₄ S ^r ₅ ) = -)) (22)

[0092] Assume ω _; -ω^ = Δω (z=2, 3, 4, 5). By multiplying Equations (19) and (20), f(s s )f(s s )=

— K, K ₇ K cos[(i¾ - _f i d ₃ a> ₃ 2d ₂ a> ₂ d

> ₁ )t--^ + _^ ^] + cos[( _f i>3 -2fi> ₂ +β> ₁ )ί + ^--Α -_-L ₊ _J _x _a>,] (23) 8 c c c c c

¹ — K, K ₇ K cos((i¾ - ω _χ )t - + -^ + cos(^-^- 2_2. + _J_

8

0093] After applying a LPF to filter out the high frequency component

I, ₌ I^¾cos(to_i_^toi ₊ fto)

Performin the Hilbert transform of Equation (24),

[0094] From Equation (24) and Equation (25), we have

d ₃ ■ co ₃ 2d ₂ · a> ₂ d _x - ω

tan (

(26)

[0095] Similarly,

d. ^■ co, d ₇ ^■ co ₇ ~.d,- co _,,Q _1%

_— 1 ₊ ^— ² -2^— ³ - = tan '(^-)

C C C (27) (28) [0096] From Equations (26) to (28),

[0097] Let (x _; , _ _; , z, ) and (f/ _^ , U , i/ _z ) be the positions of Txi and Rx, respectively. Then di may be calculated as:

d, = i -u Hy _t -u HZi -uf ₍₃₀₎

[0098] The position of Rx, (U _X ,U ,U _Z ) may be obtained based on Equations (29) and

(30). The root mean square error (RMSE) of the receiver position of the VLP system may be expressed as:

RMSE = ^∑ , [({/< - D _x f + (u _y ^l - D _y ) ² + (u _z - D _z ) ² ] (31) where (U _x ^l ,U _y ^l ,U _z ') is the l-th estimated position of Rx, (U _x , U _y , U _z ) is the real location and N is the total number of the measurements.

[0099] Numerical simulations are carried out and the results are described below. As shown in FIG. 4, each VLP unit 404a-h may have five LEDs 406 on the ceiling, and these LEDs may be arranged to be a square shape (i.e. 4 LEDs may be placed on the 4 corners of the square, respectively, and one LED may be placed in the center of the square). The distance between a corner LED and the centre LED may be denoted as dint (refer to FIG. 4). The received signal associated with frequency f, may include multiple periods of the sinusoid signal. Assuming that the noise has a zero mean, the SNR of the received signal may be improved by the averaging technique, which has been described above. The number of periods for averaging is denoted as Nave and d denotes the area covered by the z ^' -th VLP unit. Following the similar set-up introduced in Komine et al. ("Fundamental analysis for visible- light communication system using LED lights", Consumer Electronics, IEEE Transactions on, Vol. 50, pp. 100-107, 2004), which is incorporated herein as a reference, the positioning error of the z ^' -th VLP unit within an area C; has been simulated and characterized. In this simulation, 5 RF signals of different frequencies are respectively modulated onto the 5 LEDs within one VLP unit. The first frequency f\ is set at 20 MHz and the difference between two adjacent frequencies is set at 100 kHz. FIG. 7 is a plot 700 of the cumulative distribution function (CDF) of the estimation error of the z ^' -th VLP unit within a space C; with a dimension of 2.5 x 2.5 x 3 m ³ (length x width x height) as a function of the root mean square error (RMSE) of the receiver position according to various embodiments. Following the estimation Equations (29) to (31), the root mean square errors (RMSE) of three different scenarios are plotted in FIG. 7. The results show that RMSE is improved significantly as dint or Nave increases. The arrangement shape of the LEDs within one VLP unit may have a significant effect on the performance of the positioning error. Various embodiments may include an arrangement of LEDs within a VLP unit, the arrangement selected from a group consisting of a square shape, a rectangular shape, a shape with a center LED, and a rectangular shape with a center LED.

[00100] To achieve centimeter-scale accuracy, various embodiments may adopt a few techniques, which are detailed below.

[00101] Post-equalization technique. It has been shown in that the accuracy of an LED based positioning system is strongly related to the photonic devices. The optical transmitted power and the modulation bandwidth are the two key parameters which may constrain the positioning precision of the system. By using LEDs with higher emitting power and higher modulation bandwidth, the precision of the VLP system may be significantly improved. However, various embodiments may make use of general lighting systems, which has e.g. an illumination level selected from a range of about 300 lx to about 1500 lx. Therefore, enhancing the modulation bandwidth of the LED may be the primary method to achieve the centimeter- scale accuracy. It has been shown in that with a post-equalization technique, the 3dB bandwidth of the white LEDs may be increased from several megahertz to ~ 25 MHz or even higher. To the best of our knowledge, this technique may not have been adopted in the indoor VLP systems. On the other hand, pre-equalization technique may also be used to increase the modulation bandwidth of the LED. However, pre-equalization may require extra elements to be installed at each LED. To maximally reduce the complexity and the cost of the system, various embodiments may include a post-equalization circuit arrangement. The receiver may include a post-equalization circuit arrangement in electrical connection with the detector. The equalization circuit arrangement may be configured to relax a modulation bandwidth requirement of the LEDs. This is effectively equivalent to increase the modulation bandwidth of the LEDs. [00102] Differential phase-shift measurement method. Several technological approaches to VLP systems are currently being studied. Most of those studies are based on received signal strength indicator (RSSI) measurements. As the distance between the transmitter array Tx and the receiver Rx increases, the power of the received signal may fall. However, the effects of objects blocking and reflecting mean that the relationship between distance and RSSI may be unpredictable, which may significantly limit the positioning accuracy (PA). In addition, those studies also assume that the transmitted optical power by each LED is accurately known. Unfortunately, these conditions may be unlikely to be true in practice. The transmitted optical power may very unpredictable. The transmitted optical power may depend on the particular LED and the level of dimming as well. Therefore, only rough estimate of position may be achieved through the RSSI method in practice. Time-of-arrival (TOA) and time-difference-of-arrival (TDOA) methods are more precise methods to estimate the locations. However, for an indoor VLP system, there are two main challenges to achieve the centimeter- scale accuracy. Firstly, it is very difficult to directly measure the extremely accurate time of arrival or time difference of arrival, since the distance between Txs and Rxs may be very small (in the range of about 10 meters), while the signal travels at the speed of light. Another problem is that the time measurement may require highly accurate synchronization between the Txs and Rxs. Therefore, for an economical optical Rx, various embodiments may use a differential phase-shift measurement. With a continuous sine wave modulated to each of the four or five LEDs of a VLP unit, the distance between each of the LEDs and the Rx may be obtained by measuring the phase difference between the transmitted and received sine wave signals.

[00103] Blue filtering. At present, most devices for illumination use a blue LED coated with a layer of yellow phosphor to produce white light emission. Due to this yellow phosphor, the modulation bandwidth of the LED may be typically limited to ~ 3 MHz. As it is described above, the 3dB modulation bandwidth of the white LEDs may significantly affect the PA of the VLP system. Therefore, various embodiments may include optical blue filtering in the optical Rx design, which filters out the slow-responding phosphor component of the emission, leaving the faster directly modulated blue emission. In various embodiments, the receiver may include a filter over the detector. The filter may be configured to allow blue light to pass through to the detector. To further increase the modulation bandwidth, the blue filter technique in combination with simple Rx post-equalization circuit may be employed in various embodiments, which may allow modulating up to 100 MHz signal with the commercial white LEDs. Thus, the PA of the system may be enhanced to about 5 cm.

[00104] Various embodiments may relate to an indoor white LEDs based VLP positioning system. Various embodiments may relate to a low-cost indoor centimeter-scale positioning system.

[00105] Various embodiments may employ off-the-shelf white illuminating LEDs, and may not rely upon a complicated infrastructure. Additionally, dual use of LEDs for lightning and localization purposes may provide a transformative green solution for indoor positioning systems. The illumination of a white LEDs based lighting system may be generally restricted between about 300 lx to about 1500 lx. This illumination level may offer a good signal-to- noise ratio (SNR), which may be up to 30 dB for the positioning system. By adopting a noise cancelation technique, centimeter-scale PA of less than 10 centimeters may be achieved for a typical indoor illumination environment.

[00106] Compared to some RF based positioning systems such as WiFi, Bluetooth, RFID or GSM, various embodiments may rely on the optical radiation and line-of-sight (LOS) transmission, which may mitigate the multipath induced interferences and may improve the accuracy. On the other hand, compared to other centimeter- scale positioning systems such as UWB, Ultrasound and IR based system, by utilizing the existing LEDs lighting infrastructure, various embodiments may significantly reduce the installation cost for wide applications in indoor environments.

[00107] A common strategy for measuring distances in localization applications is to compute the time of flight (TOF) of a signal. However, as the signal travels at the speed of light and the ranging distance is small (in the order of meters), directly measuring the TOF may become infeasible if high PA is required. Various embodiments may involve or adopt a method to measure the distance by measuring the changes in the phases of the emitted signals to achieve PA in the centimeter scale. With a continuous sine wave modulated to each of the four or five LEDs in a VLP unit, the distance between each of the LEDs and the Rx may be obtained, and then the spatial positioning of the Rx may be estimated. The number of LEDs grouped as a VLP unit may differ in various different embodiments.

[00108] Various embodiments may include a local synchronization scheme, which may reduce or minimize the complexity of the system. The LED lamps on the ceilings may be grouped into multiple basic positioning units known as VLP units, each of which may include 4 or 5 LED lamps. Only the LED lamps within one VLP unit may be synchronized, which may significantly reduce the synchronization complexity. In other words, various embodiments may employ local synchronization of LEDs within a VLP unit. Compared to embodiments with each VLP unit including or consisting of three transmitters (Txs) or LEDs, various embodiments with 4 or 5 LEDs may not require a local oscillator at the Rx side to measure the differential phase shift. In this case, the Rx may capture the differential phase- shift information from any available unit of the downlink to estimate its position and may not require synchronization between the Txs and Rx, which may significantly improve the PA of the system.

[00109] Compared with the RF based positioning systems, various embodiments may not produce electromagnetic interference (EMI), which is the ideal solution for applications in RF-restricted or prohibited areas such as airport, seaport, hospital, and hazardous environments (e.g. power plants, mines). Another advantage is that the optical radiation may not penetrate walls or opaque objects. Therefore, various embodiments may relate to a secure and private positioning system.

[00110] Recently, a variety of indoor positioning systems have been proposed and investigated for indoor location estimations. They are based on RF (Wi-Fi, Bluetooth, RFID, GSM, and UWB), Ultrasound, IR and visible light technologies. It is shown that the RF based positioning systems (Wi-Fi, Bluetooth, RFID, and GSM) have relatively low costs. However, the accuracy of these systems may be in the order of meters (from 1 to 3 m), which may be too low to precisely control and navigate indoor robots, UAV or vehicles. On the other hand, some alternative indoor positioning systems based on UWB, Ultrasound and IR techniques may be able to provide high PA, but may be too costly to deploy the infrastructure, and hence are not viable for the widespread use.

[00111] In the past few years, several studies have been carried out to explore visible light positioning. Most of these VLP systems may be based on the received signal strength (RSS) measurement. However, these measurements may not be ideal in practice due to the unpredictable transmitted optical power and the mobility of the user, which significantly limits the positioning accuracy (PA) of the system. Alternatively, some angle of arrival (AOA) based methods have also been previously proposed to achieve a high-accuracy VLP system. However, they need image sensors with a large number of pixels as detectors. Compared to the traditional photodiode (PD), an image detector may have a higher cost as well as a lower detection rate. To achieve a reliable PA as well as overcoming the mobility effect, some phase shift measurement based positioning systems have been proposed and studied. However, the systems assumed that Txs and Rxs are ideally synchronized, which may be difficult to achieve in the reality, or may achieve centimeter- scale PA based on the infrared (IR) uplinks with multiple Rxs, which cannot be integrated with the downlinks based lighting infrastructure. To date, there is no commercially viable indoor positioning system that is reliable, low-cost, offering PA in centimeters, as well as supporting certain mobility.

[00112] Various embodiments may address two issues, namely the cost and/or accuracy. Various embodiments may relate to a low-cost, high accuracy and reliable indoor positioning system by utilizing the LED lighting infrastructure. The centimeter-scale VLP system may offer certain mobility for e.g. robotic and various other applications. With the help of this technology, more new high-precision positioning based applications may be developed for mass consumer markets. Just as the inventors of the GPS system could never have envisaged the huge range of GPS applications currently in use, it is impossible to predict all the future uses of such a centimeter- scale VLP system.

[00113] A local synchronization and a continuous sine wave modulation scheme may be adopted in to minimize the complexity of the system. With these techniques, the Rx may not need to synchronize with the Txs, but may only use the received downlink signals to estimate the positioning information. Since the synchronization between the Txs and Rxs is not required, the complexity of the system may be significantly reduced.

[00114] Compared with the recent RF based positioning systems, various embodiments may be suitable for applications in the RF-restricted or prohibited areas such as airport, seaport, and hospital. Another advantage is that the optical radiation may not penetrate walls or opaque objects. Therefore, various embodiments may be suitable for a secure and private positioning system.

[00115] With the expected wide-scale availability of the LED lighting systems in buildings and underground spaces in the near future, various embodiments relating to white LEDs based VLP technology may provide a solution for the indoor high-accuracy (in the order of centimeters) robotic navigation and various other positioning enabled applications. It is envisioned that centimeter PA may become an essential part of the next generation indoor positioning and navigation system for indoor robots, autonomous vehicles, UAVs, UGVs etc. The packaging and commercializing may not be an issue because all the required devices are relatively inexpensive and commercially available in the market, and the operation principle may be relatively simple. On the other hand, exploiting the dual functions of the off-the-shelf illumination LEDs may also significantly reduce the cost of the proposed system. All required components may be low-cost commercial electronic devices.

[00116] Various embodiments including inexpensive devices may allow for cost-effective large scale production. Consumer applications for indoor location information may potentially be limitless. The applications include not only the navigation and positioning for the indoor robots, autonomous vehicles, unmanned aviation vehicles (UAVs), unmanned ground vehicles (UGVs), but also some high-accuracy positioning based industrial applications.

[00117] The research results may further stimulate scientific research in the area of next generation indoor high-accuracy positioning and navigation system. Various embodiments may provide a strong foundation for future developments of indoor positioning systems inters of accuracy, cost and reliability.

[00118] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.