Bluetooth-based spatiotemporal localization

Abstract

A Bluetooth enabled device (101) is provided, the Bluetooth enabled device configured to control a radio frequency (RF) chain to receive a constant tone extension (CTE) signal (105) of a plurality of frames transmitted by a Bluetooth enabled transmitter (103) over a plurality of frequencies at a single antenna selected from the plurality of antennas during a first time period. The RF chain is also controlled to switch between the plurality of antennas to receive the CTE signal at each of the plurality of antennas during a second time period. Initial time-of-flight (ToF) data of the CTE signal is determined from a first sample of the CTE signal received during the first time period. A signal model is also provided that connects the sample of the CTE signal with an unknown angle of arrival of the CTE signal received at a particular time, the unknown ToF conditioned on the initial ToF data, and a location of the Bluetooth enabled transmitter relative to a location of the Bluetooth enabled device is identified.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to Bluetooth technology, and more particularly to an apparatus and method for locating a Bluetooth enabled transmitter relative to a Bluetooth enabled device. [Background technology]

[0002] Bluetooth Low Energy (BLE) is a radio frequency (RF) technology for wireless communication that can be leveraged to locate and track people, devices, and valuables for many indoor positioning use cases, including valuables tracking, indoor navigation, and proximity services. Bluetooth is an accessible and pervasive technology that permeates indoor spaces and is supported by many of today's devices. Similar to other communication protocols, including Wi-Fi and UWB, BLE can be used to transmit data between devices using radio waves.

[0003] Indoor positioning systems based on BLE technology rely on BLE beacons mounted on objects, walls, ceilings, and other locations. BLE beacons emit radio signals at predetermined intervals. Bluetooth-enabled devices within the BLE beacon's emission range can detect the radio signals and establish communication with the BLE beacon. While a single beacon is sufficient to establish the presence of a Bluetooth-enabled device, it cannot pinpoint the device's specific location. Therefore, techniques such as trilateration using multiple BLE beacons are used to pinpoint the Bluetooth-enabled device's location. The Bluetooth-enabled device's distance from multiple BLE beacons is estimated by the Bluetooth-enabled device based on the received signal strength indicator (RSSI) of the radio signals from the multiple BLE beacons. RSSI represents the power of the radio signal from each BLE beacon in the multiple BLE beacons. A long distance corresponds to a low RSSI value, while a short distance corresponds to a higher RSSI value. Additionally, the angle of arrival (AoA) of radio signals from multiple BLE beacons is estimated to determine the location of a Bluetooth enabled device.

[0004] However, in the real world, wireless signals are received through multiple paths (also known as "multipath"), which degrades AoA estimation. Also, the resolution or accuracy of AoA is a function of the number of antennas used. Because the number of antennas is typically limited due to size and computational constraints in indoor positioning via BLE techniques, the accuracy of AoA estimation suffers in such cases. Furthermore, multiple beacons require coordination among themselves, which incurs additional computational overhead for systems using BLE techniques for positioning applications.

[0005] Therefore, there is a need for a device and method for position measurement that is robust to multipath and improves AoA accuracy, even with a limited number of antennas.Prior art document WO2019 / 113231 A1 proposes a method for determining the location of a mobile device that uses BLE to estimate AoA and ToF and identify the location of the user device. For AoD estimation, one or more BLE communication packets are sampled by switching between different antennas during continuous wave reception. For ToF estimation, it is proposed to use multiple BLE communication packets with consecutive frequency-modulated RF carrier signals within a single packet. Summary of the Invention

[0006] The present invention teeth, According to the independent claims, A device (also called a "Bluetooth enabled device") and method for determining the precise location of a Bluetooth enabled transmitter is provided. do. The location of a Bluetooth-enabled transmitter may be determined based on the distance of the Bluetooth-enabled transmitter from a Bluetooth-enabled device and the orientation of the Bluetooth-enabled transmitter relative to the Bluetooth-enabled device. The distance of the Bluetooth-enabled transmitter from a Bluetooth-enabled device may be determined based on the time-of-flight (ToF) of a radio wave (e.g., a Bluetooth signal) from the Bluetooth-enabled transmitter to the Bluetooth-enabled device. To this end, multiple BLE beacons are used, and the distance of the Bluetooth-enabled transmitter from the Bluetooth-enabled device is determined based on the RSSI of each beacon. However, to increase the accuracy of the distance measurement, multiple BLE beacons are required, and coordination between these multiple BLE beacons incurs computational overhead. The phase difference between the two transmissions is used to determine the ToF. Antenna switching AoA estimation is improved by jointly estimating the AoA from multiple frames that are made coherent by using the ToF estimate to compensate for frequency hopping phase changes in each frame.

[0007] Additionally, the orientation or direction of a Bluetooth enabled transmitter relative to a Bluetooth enabled device may be determined based on the AoA at the Bluetooth enabled device of the radio signal from the Bluetooth enabled transmitter. However, the AoA measurement may not be accurate due to multipath noise caused by phase and amplitude distortions generated when radio waves are reflected from multiple surfaces on their way to the Bluetooth enabled device.

[0008] To overcome the aforementioned problems, a new Bluetooth direction finding feature is used that uses sampling of radio signals received at a Bluetooth-enabled device to measure the phase of radio waves incident on an antenna at a particular time. To determine the AoA in a Bluetooth-enabled device that includes an array of antennas, a sampling process is applied to each antenna in the array of antennas, one at a time, and in some suitable sequence depending on the design of the array. The sampled data is then used to calculate the direction of the Bluetooth-enabled transmitter from the Bluetooth-enabled device.

[0009] To support sampling and use of the sampled data by higher layers in the Bluetooth stack (also called the "stack"), the link layer (LL) in the stack is modified to include a Constant Tone Extension (CTE) field. The CTE field is digital only, which means that the entire CTE is transmitted at one frequency and therefore has a constant wavelength. The CTE field does not undergo a whitening process.

[0010] Currently, in Bluetooth standard 5.1 and newer standards, the CTE signal is specifically defined to determine the AoA of a wireless signal. Some embodiments are based on the recognition that the CTE signal can be used to determine the ToF of a wireless signal.

[0011] The present invention is based on the recognition that a Bluetooth-enabled transmitter can be located based on the ToF and AoA of a CTE signal transmitted by the Bluetooth-enabled transmitter. To determine the ToF and AoA of the CTE signal to locate the Bluetooth-enabled transmitter, the present disclosure proposes a signal model that examines samples of the CTE signal with an unknown AoA of the CTE signal received at a particular time and transmitted with an unknown ToF conditional on an initial ToF. Because the signal model has two unknowns, namely the ToF and AoA of the CTE signal, solving the signal model to determine these two unknowns is difficult. Therefore, the signal model is solved in two stages: in a first stage (or first period), an initial estimate of the ToF is determined; and in a second stage, the initial estimate of the ToF is used to initialize the signal model and jointly determine the AoA and ToF.

[0012] Some embodiments are based on the recognition that the distance of a Bluetooth-enabled transmitter from a Bluetooth-enabled device can be determined based on the ToF it takes for a radio signal (i.e., a CTE signal) from the Bluetooth-enabled transmitter to reach the Bluetooth-enabled device. The ToF can be calculated from the time the Bluetooth-enabled transmitter transmitted the CTE signal and the time the Bluetooth-enabled device received the CTE signal. However, the time the Bluetooth-enabled transmitter transmitted the CTE signal is often unknown. Therefore, determining the ToF of the CTE signal is difficult.

[0013] An initial estimate of the ToF is determined based on the phase of the CTE signal received at the Bluetooth-enabled device. The phase of the CTE signal is a function of the delay (time) at which the CTE signal is transmitted and the channel frequency. The initial estimate of the ToF is then used to jointly determine the AoA of the CTE signal at the Bluetooth-enabled device from the Bluetooth-enabled transmitter. In addition, in the first stage, to determine the initial estimate of the ToF, the Bluetooth-enabled device is configured to control each RF chain to select a single antenna from multiple antennas included in the transceiver of the Bluetooth-enabled device during a first time period. The Bluetooth-enabled device is configured to receive the CTE signal at the selected antenna, and the CTE signal is included in multiple frames and transmitted across multiple frequencies specified by the Bluetooth communication protocol.

[0014] Also, in a second stage, to determine the AoA based on the estimated ToF, the Bluetooth enabled device is configured to control the RF chain to switch among the multiple antennas according to a switching schedule to receive a CTE signal at each antenna of the multiple antennas during a second time period. To do so, samples of the CTE signal received during the second time period are then fitted to a previously determined signal model. The signal model is then initialized using the estimated ToF and iteratively solved to calculate the AoA of the CTE signal.

[0015] In this way, the location of the Bluetooth enabled transmitter is precisely identified by determining, in a first stage, a ToF indicating the distance of the Bluetooth enabled transmitter from the Bluetooth enabled device during a first time period, and then, in a second stage, determining, in a second time period, an AoA indicating the orientation of the Bluetooth enabled transmitter relative to the Bluetooth enabled device based on the ToF estimated in the first stage.

[0016] Accordingly, one embodiment discloses a Bluetooth enabled device having a transceiver with multiple antennas for each RF chain, the device comprising: a processor; and a memory having stored thereon instructions that, when executed by the processor, cause the Bluetooth enabled device to perform a plurality of steps, including controlling the RF chain to receive, during a first time period, on a single antenna selected from the plurality of antennas, a CTE signal for a plurality of frames transmitted by a Bluetooth enabled transmitter over a plurality of frequencies defined by a Bluetooth communication protocol; controlling the RF chain to switch among the plurality of antennas according to a switching schedule to receive, during a second time period, the CTE signal on each of the plurality of antennas; and controlling the RF chain to switch among the plurality of antennas according to a switching schedule to receive the CTE signal received during the first time period. and recovering an initial ToF of the CTE signal from a first sample of the signal, the ToF indicating a distance between the Bluetooth enabled device and the Bluetooth enabled transmitter using a phase of the CTE signal that is dependent on the ToF and the transmitted frequency, and the steps further include determining a location of the Bluetooth enabled transmitter relative to a location of the Bluetooth enabled device by fitting a second sample of the CTE signal received during a second period to a signal model, the signal model connecting the second sample with an unknown angle of arrival of the CTE signal received at a time defined by the switching schedule and transmitted with an unknown ToF that is conditional on the initial ToF.

[0017] Accordingly, another embodiment is a method comprising the steps of: controlling RF chains corresponding to a plurality of antennas to receive, during a first time period, at a single antenna selected from the plurality of antennas in a transceiver of a Bluetooth enabled device, a CTE signal of a plurality of frames transmitted by a Bluetooth enabled transmitter over a plurality of frequencies defined in a Bluetooth communication protocol; controlling the RF chains to switch among the plurality of antennas according to a switching schedule to receive, during a second time period, the CTE signal at each of the plurality of antennas; and determining a CT from a first sample of the CTE signal received during the first time period. and recovering an initial ToF of the E signal, wherein the ToF indicates the distance between the Bluetooth enabled device and the Bluetooth enabled transmitter using a phase of the CTE signal that is dependent on the ToF and the transmitted frequency, and the method further comprises determining a location of the Bluetooth enabled transmitter relative to the location of the Bluetooth enabled device by fitting a second sample of the CTE signal received during a second time period to a signal model, the signal model connecting the second sample with an unknown angle of arrival of the CTE signal received at a time defined by the switching schedule and transmitted with an unknown ToF that is conditional on the initial ToF. [Brief explanation of the drawings]

[0018] [Figure 1A] FIG. 1 illustrates an environment for a Bluetooth enabled device to locate a Bluetooth enabled transmitter, according to some embodiments. [Figure 1B] 1 is a block diagram of a Bluetooth-enabled device according to some embodiments. [Figure 1C] 1 illustrates a Bluetooth Link Layer (LL) data frame having a CTE frame containing a CTE signal, according to some embodiments. [Figure 2] FIG. 2 illustrates a BLE channel used to transmit Bluetooth packets, according to some embodiments. [Figure 3A]FIG. 2 illustrates steps performed by a ToF estimation module in a first stage to determine the location of a Bluetooth enabled transmitter, according to some embodiments. [Figure 3B] FIG. 10 illustrates steps performed by an AoA estimation module in a second stage to determine the location of a Bluetooth enabled transmitter, according to some embodiments. [Figure 4A] FIG. 1 illustrates enabling multiple CTE frames through multiple channels with a fixed antenna and estimating the ToF of multiple paths according to some embodiments. [Figure 4B] FIG. 1 illustrates enabling multiple CTE frames through multiple channels with a fixed antenna and estimating the ToF of multiple paths according to some embodiments. [Figure 5A] FIG. 10 illustrates steps of enabling multiple CTE frames through multiple channels across multiple antennas using antenna switching and estimating AoA of multiple paths while refining ToF from the first stage, according to some embodiments. [Figure 5B] A diagram showing a CTE structure including predefined switching and sampling slots across one CTE frame transmitted through a given channel to generate a second sample of a CTE signal, according to some embodiments. [Figure 6] 1 is a flowchart of a method performed by a Bluetooth enabled device to determine the location of a Bluetooth enabled transmitter, according to some embodiments. [Figure 7] FIG. 1 illustrates a scenario in which a Bluetooth enabled device is used for indoor location of a Bluetooth enabled transmitter, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, devices and methods are shown only in block diagram form in order to avoid obscuring the present disclosure.

[0020] As used in this specification and claims, the terms "for example," "such as," and "e.g.," as well as the verbs "comprise," "have," and "include" and other verb forms thereof, when used in conjunction with a list of one or more components or other items, should each be construed as open-ended. That is, the list should not be considered to exclude other additional components or items. The term "based on" means based at least in part on. It should also be understood that the language and terminology employed in this specification are for purposes of description and should not be considered limiting. Any headings used within this description are for convenience only and have no legal or limiting effect.

[0021] FIG. 1A illustrates an environment 100 for a Bluetooth-enabled device 101 configured to locate a Bluetooth-enabled transmitter 103, according to some embodiments.

[0022] CTE signal 105 comprises a series of unwhitened known symbols (all ones) transmitted by Bluetooth enabled transmitter 103. The length associated with CTE signal 105 is variable and ranges from 16 μs to 160 μs. As such, CTE signal 105 is a single tone signal at an associated carrier frequency.

[0023] When Bluetooth enabled device 101 receives CTE signal 105 from Bluetooth enabled transmitter 103, Bluetooth enabled device 101 determines the ToF of CTE signal 105 and the AoA of CTE signal 105 to determine the location of Bluetooth enabled transmitter 103. Bluetooth enabled device 101 may communicate with Bluetooth enabled transmitter 103 to determine location information of Bluetooth enabled transmitter 103.

[0024] Bluetooth-enabled device 101 includes transceiver 101a including multiple antennas, such as antenna 1, antenna 2, antenna 3, and antenna 4. For ease of illustration, transceiver 101a is illustrated having only four antennas. However, five or more antennas may be present in transceiver 101a without departing from the scope of this disclosure. Transceiver 101a also includes RF switch 107, which is controlled to select one antenna from the multiple antennas (antenna 1 through antenna 4) or to switch between multiple antennas. Additionally, received CTE signal 105 is demodulated by transceiver 101a, and the demodulated CTE signal is provided to AoA estimation module 101b, which uses the demodulated CTE signal 105 to determine the location of Bluetooth-enabled transmitter 103.

[0025] Therefore, the AoA estimation module 101b first estimates the ToF data of the CTE signal 105 based on the phase of the received CTE signal 105. The phase of the received CTE signal 105 is a function of the delay (or time) at which the CTE signal 105 was transmitted and the channel frequency (also called the "transmission frequency"). t (t))105 is expressed mathematically as follows:

number

[0026] FIG. 1B shows a block diagram of a Bluetooth-enabled device 101 according to some embodiments. The Bluetooth-enabled device 101 includes a transceiver 101a configured to receive 109 a Bluetooth packet including a CTE signal 105 over a wireless Bluetooth network 111. The CTE signal 105 may be transmitted over multiple channel frequencies included in a BLE channel (as shown in FIG. 2) according to a Bluetooth communication protocol. The transceiver 101a includes an antenna array having multiple antennas (as shown in FIG. 1A), one of which is selected to receive the CTE signal 105. The antenna may be randomly selected from the multiple antennas. In some embodiments, the antenna to be selected to receive the CTE signal 105 is predetermined. Upon receiving the CTE signal 105, it is demodulated, and the demodulated CTE signal 105 is provided to an AoA estimation module 101b.

[0027] Bluetooth-enabled device 101 also includes at least one processor 115 configured to execute stored instructions and memory 117 that stores instructions executable by at least one processor 115 (hereinafter referred to as processor 115). Processor 115 may be a single-core processor, a multi-core processor, a computing cluster, or any number of other configurations. Memory 117 may include random access memory (RAM), read-only memory (ROM), flash memory, or any other suitable memory system. Processor 115 is connected to one or more input and output devices of Bluetooth-enabled device 101 through bus 113. Bluetooth-enabled device 101 also includes storage device 119 adapted to store executable instructions for processor 115. Storage device 119 may be implemented using a hard drive, optical drive, thumb drive, an array of drives, or any combination thereof.

[0028] The storage device 119 is configured to store the AoA estimation module 101b, which receives the demodulated CTE signal 105 and uses a signal model to jointly determine the ToF and AoA. The estimated ToF is used to calculate AoA(θ) using the signal model that jointly determines the ToF and AoA. The signal model is initialized with an estimate of the ToF of the CTE signal 105, and the initialization with the rough estimate of the ToF refines the ToF calculation using the signal model. The search space for determining the ToF and AoA is also reduced. Steps for estimating the ToF of the CTE signal 105 and calculating the AoA in the AoA estimation module 101b are described later with reference to FIG. 3.

[0029] Additionally, Bluetooth-enabled device 101 may include output interface 121. In some embodiments, output interface 121 may be configured to provide the location of Bluetooth-enabled transmitter 103 determined by AoA estimation module 101b.

[0030] 1C illustrates a Bluetooth link layer (LL) data frame 100c having a CTE frame including a CTE signal 105, according to some embodiments. The Bluetooth LL data frame 100c (also referred to as a "data packet") is transmitted in a wireless signal by a Bluetooth-enabled transmitter 103. The Bluetooth-enabled transmitter 103 may transmit multiple Bluetooth LL data frames in a wireless signal. The LL data frame 100c includes a preamble field 123 including a preamble, an access address field 125 including an access address, a PDU field 127 including a packed data unit (PDU), a CRC field 129 including a cyclic redundancy check (CRC), and a CTE field 131 (also referred to as a "CTE frame") including the CTE signal 105. Each field contains a sequence of bits (1 or 0), with preamble field 123 containing the least significant bit (LSB) and CTE field 131 containing the most significant bit (MSB). The preamble in preamble field 123 is used by Bluetooth enabled device 101 for frequency synchronization, automatic gain control (AGC) training, and symbol timing estimation. The preamble is a fixed sequence of alternating 0 and 1 bits. The access address in access address field 125 is a four-octet value. Each LL connection between any two devices (e.g., Bluetooth devices 101 and 103) has a distinct access address. Each time, Bluetooth enabled device 101 needs a new access address.

[0031] If a Bluetooth Low Energy (BLE) packet is transmitted on a primary or secondary advertising physical channel or a periodic physical channel, the PDU is defined as an advertising physical channel PDU. If a BLE packet is transmitted on a data physical channel, the PDU is defined as a data physical channel PDU.

[0032] The CRC is three octets in size and is calculated for every PDU in the LL packet. If the PDU is encrypted, the CRC is calculated after the PDU encryption is complete.

[0033] Finally, LL data frame 100c includes a CTE consisting of a continuously modulated series of unwhitened ones. CTE field 131 has a variable length ranging from 16 μs to 160 μs. CTE signal 105 is used by Bluetooth enabled transmitter 103 configured to transmit CTE signal 105 in Bluetooth LL data frame 100c to Bluetooth enabled device 101, and CTE signal 105 transmitted by Bluetooth enabled transmitter 103 is used by Bluetooth enabled device 101 to determine the precise location of Bluetooth enabled transmitter 103 relative to Bluetooth enabled device 101.

[0034] To determine the location of Bluetooth enabled transmitter 103, Bluetooth enabled device 101 is configured to utilize CTE signal 105 in multiple stages (Stage 1 and Stage 2). In Stage 1, an approximate ToF of CTE signal 105 transmitted by Bluetooth enabled transmitter 103 is determined using frequency hopping with a fixed antenna (no antenna switching). To that end, Bluetooth enabled device 101 is configured to select one antenna of multiple antennas (Antenna 1, ..., Antenna 4) to receive multiple CTE frames containing CTE signal 105 over multiple channels of the Bluetooth communication protocol. The different frequencies of the Bluetooth communication protocol used for frequency hopping are shown in Figure 2.

[0035] In stage 2, the AoA and ToF of the CTE signal 105 are determined jointly using frequency hopping and antenna switching. To that end, the Bluetooth-enabled device 101 is configured to switch antennas after a predetermined interval within each CTE frame (e.g., a first CTE frame transmitted through a first channel (k=1) and a second CTE frame transmitted through a second channel (k=2)) of the multiple CTE frames transmitted through the multiple frequency channels. To that end, the CTE signal 105 in a single CTE frame is sampled using antenna switching between the multiple antennas, and the sampling time is equal to the amount of time each antenna of the multiple antennas receives the CTE signal 105. The amount of time each antenna should be connected to the RF chain to receive the CTE signal 105 is predetermined. The sampling may continue until the end of each CTE frame of the multiple CTE frames.

[0036] FIG. 2 illustrates a BLE channel 200 used to transmit Bluetooth packets according to some embodiments. A Bluetooth packet, e.g., an LL Bluetooth packet, is as shown in FIG. 1C , and includes a PDU, an access address, a preamble, and a CTE signal 105 used to locate a Bluetooth-enabled transmitter 103. According to the Bluetooth communication protocol, there are 40 BLE channels (k) 201, ranging from 0 to 39, through which Bluetooth packets are transmitted. However, in equation (1), for ease of mathematical operations, the range of k 201 is kept between 1 and 40, with k=1 corresponding to channel 0 of the BLE channels 200. Each of the 40 BLE channels 200 has a different frequency ranging from 2402 MHz to 2480 MHz with a bandwidth of 2 MHz. The BLE channels 200 are used to transmit the CTE signal 105 through the 40 channels using frequency hopping. Optionally, the BLE channels 200 include three advertising channels. Bluetooth enabled transmitter 103 advertises on three advertising channels: channel 37 (2402 MHz) 201a, channel 38 (2426 MHz) 201b, and channel 39 (2480 MHz) 201c, which are selected to minimize interference from Wi-Fi channels.

[0037] These three channels 201a (k=37), 201b (k=38), and 201c (k=39) are called primary advertising channels, while the remaining 37 channels, such as channel 201d (k=1), channel 201e (k=2), and channel 201f (k=35), are called secondary advertising channels. The secondary advertising channels are used as "auxiliary" channels. That is, a device (e.g., Bluetooth-enabled transmitter 103) must first advertise on the primary advertising channel before sending out advertising packets on the secondary channel. When Bluetooth-enabled transmitter 103 wants to use the secondary advertising channel, it sends out an advertising packet on the primary channel that points to the secondary advertising packet.

[0038] Data extracted from one or more channels of the Bluetooth packet is used to determine ToF and AoA information associated with locating the Bluetooth enabled transmitter 103 .

[0039] 3A shows steps performed by AoA estimation module 101b in a first stage 301 to locate Bluetooth enabled transmitter 103, according to some embodiments. AoA estimation module 101b locates Bluetooth enabled transmitter 103 in two stages: in a first stage (stage 1) 301, the ToF data of CTE signal 105 is estimated, and in a second stage (stage 2) 303 (FIG. 3B), a signal model is used to determine the AoA of CTE signal 105 using the ToF estimated in first stage 301.

[0040] To estimate the ToF, in a first stage 301, the Bluetooth-enabled device 101 is configured to control an RF chain to select a single antenna among multiple antennas (antenna 1, ..., antenna 4) of the transceiver 101a to receive, during a first time period, a CTE signal 105 across multiple CTE frames transmitted by the Bluetooth-enabled transmitter 103 across multiple channel frequencies (also referred to as "transmit frequencies") (as shown in FIG. 4) corresponding to channel k defined in the Bluetooth communication protocol (as shown in FIG. 2). The RF chain is a cascade of multiple antennas with electronic components and subunits such as amplifiers, filters, mixers, attenuators, and detectors. The first time period may refer to a period or duration designated for controlling the RF chain to receive the CTE signal 105 across multiple frequencies by the selected antenna. In some embodiments, the duration of the first time period lasts until the Bluetooth-enabled device 101 determines an initial estimate of the ToF of the received CTE signal 105.

[0041] The received CTE signal 105 during a first time period is sampled to generate a first sample of the CTE signal 105. The first sample of the CTE signal 105 is then used to recover initial ToF data of the CTE signal 105 using the phase of the received CTE signal 105, depending on the ToF of the CTE signal 105 and the transmission frequency of the CTE signal 105.

[0042] As such, the received first sample of the CTE signal 105 is demodulated and a virtual array of antennas is generated based on the demodulated first sample of the CTE signal 105 to recover initial ToF data for each path of the multiple paths across each transmission frequency of the multiple transmission frequencies.

[0043] Also, in step 301 a, upon receiving the first sample of the CTE signal 105, a beat signal (x) for each channel k is calculated by integrating the CTE signals 105 received via multiple paths p and across multiple channel frequencies k to form a virtual array. b (t)) is generated.

number

[0044] Finally, in step 301b, the ToF (τ p ) data is calculated by taking the Fast Fourier Transform (in other words, a spectral estimation method) (FFT{x b (t)}) The peak frequency is determined by using 2πB c τ p For Bluetooth specifications, see B c is the BLE channel bandwidth, and B c = 2MHz. From the detected peak frequency, ToFτ pFrom the transformed beat signal, the phase of the CTE signal 105 traveling through each of the multiple paths is obtained. Based on the obtained phase of the CTE signal 105, an initial estimate of the ToF data of the CTE signal 105 for each of the multiple paths is estimated using an FFT of the beat signal. The transformed beat signal is further demodulated to obtain identification information associated with the Bluetooth enabled transmitter 103 transmitting the CTE signal 105.

[0045] 3B illustrates steps performed by AoA estimation module 101b in a second stage 303 to determine the location of Bluetooth enabled transmitter 103, according to some embodiments. In second stage 303, the AoA and ToF of CTE signal 105 are jointly calculated during a second time period. In some embodiments, the second time period is predefined. In other embodiments, the duration of the second time period continues until Bluetooth enabled device 101 determines the final AoA and ToF of CTE signal 105 to determine the precise location of Bluetooth enabled transmitter 103.

[0046] To calculate the AoA of the CTE signal 105, in step 303a, the Bluetooth-enabled device 101 is further configured to control the RF chains to switch among the multiple antennas for the multiple Bluetooth packets traversing the multiple channels according to a switching schedule to receive a second sample of the CTE signal 105 at each antenna of the multiple antennas during a second time period. The switching schedule for switching among the antennas is predetermined. The second time period may refer to a period or duration designated for switching among the multiple antennas according to the switching schedule.

[0047] In step 303b in Phase 2, the AoA of the CTE signal 105 is determined using the signal model given as follows:

number

[0048] A signal model is initialized using the initial estimate of the ToF data determined in step 1 301. The signal model is also used to determine the location of the Bluetooth enabled transmitter 103 relative to the location of the Bluetooth enabled device 101 by fitting a second sample of the CTE signal 105 received during a second time period to the signal model, the signal model connecting the second sample with the unknown AoA of the CTE signal 105 received at a time defined by the switching schedule and transmitted using an unknown ToF conditional on the initial ToF.

[0049] The signal model is used to jointly estimate both the ToF and AoA of the CTE signal 105, and the initial estimate of ToF determined in step 1 301 is used to initialize the signal model. Initializing the signal model refines the ToF and further reduces the search space for determining the accurate ToF and AoA.

[0050] In some embodiments, the initial estimate of ToF from the first stage 301 is used as a regularizer to penalize (e.g., gently) deviations in the ToF calculated in the second stage 303.

[0051] 4A and 4B illustrate steps for generating an equivalent virtual array for ToF estimation, according to some embodiments. FIG. 4 is described below in conjunction with FIG. 2 and FIG. 3A. In FIG. 4, in step 401, a CTE signal 105 of multiple CTE frames over multiple Bluetooth channels (k=1, 2, ..., 40) is transmitted by a Bluetooth-enabled transmitter 103. In step 403, the Bluetooth-enabled device 101 is configured to select one antenna from multiple antennas for receiving a first sample of the CTE signal 105 through multiple paths P during a first time period. For ease of explanation, assume there are two paths (p) through which the selected antenna receives the first sample of the CTE signal 105. Based on the first sample of the CTE signal 105, a beat signal x is calculated. b (t) (Equation 2) is generated for each channel k of the plurality of channels k. For example, the beat signal generated corresponding to channel 1 using a selected antenna that receives the CTE signal 105 through two paths (p=1, 2) is given as:

number

[0052] By receiving the CTE signal 105 through multiple paths, a virtual array of antennas is generated. For example, if the CTE signal 105 is received through two paths (p=2) for each channel frequency (k=0 to 39) by using only one selected antenna, a virtual array of antennas is generated that includes 40 virtual antennas receiving the CTE signal, which can now distinguish between the two paths in the ToF (delay) domain.

[0053] Also, in step 405, a beat signal x is calculated for each CTE frame among the plurality of CTE frames received through the plurality of channels k. bAn FFT of (t) is used to determine an initial estimate of the ToF. Using the FFT, the beat signal is transformed from the time domain to the frequency domain, where a spectral peak of the CTE signal 105 across each channel frequency k is observed at 250 kHz. The phase at this peak is a function of the delay and the corresponding channel k.

[0054]

number

[0055] The CTE signal 105 includes a plurality of samples, such as a first sample and a second sample of the CTE signal 105 received during a first period and a second period, respectively, as shown in Figures 5A and 5B described below.

[0056] 5A illustrates the generation of a second sample of a CTE signal 105 according to some embodiments. In FIG. 5A, during a second period, the CTE signal 105 included in two CTE frames (a first CTE frame 501 and a second CTE frame 503) is shown to be received through two frequency channels k=1 (201d) and k=2 (201e). Assume that a Bluetooth-enabled device 101 configured to receive the CTE signal 105 of multiple CTE frames 501 and 503 includes three antennas: antenna 1 (i=1) 505, antenna 2 (i=2) 507, and antenna 3 (i=3) 507.

[0057] During a second time period, for the length of each CTE frame (e.g., first CTE frame 501), a second sample of CTE signal 105 is generated by sampling CTE signal 105 using antenna switching between multiple antennas (antenna 1 505, antenna 2 507, and antenna 3 509). The antenna switching is such that each antenna of the multiple antennas at the transceiver receives CTE signal 105 for a predetermined amount of time. Thus, during the second time period, Bluetooth enabled device 101 is configured to perform antenna switching, where the antennas are periodically switched between the multiple antennas based on a switching schedule, the switching schedule being predetermined.

[0058] According to the switching schedule, only one antenna of the multiple antennas (antenna 1 505, antenna 2 507, and antenna 3 509) in the transceiver 101a is selected to receive the CTE signal 105 for a specific time such that only one RF chain is used. For example, antenna 1 505 may be first selected to receive the CTE signal 105 for a first specific time period (sample slot 1) to generate a first portion of the second sample of the CTE signal 105. After the first specific time period is completed, reception of the CTE signal 105 is switched from antenna 1 505 to antenna 2 507 for a second specific time period (sample slot 2) to generate a second portion of the second sample of the CTE signal 105. Similarly, after the second specific time period is completed, reception of the CTE signal 105 is switched from antenna 2 507 to antenna 3 509 for a third specific time period (sample slot 3) to generate a third portion of the second sample of the CTE signal 105. Antenna switching among the multiple antennas according to the switching schedule continues until the entire first frame of CTE signal 105 has been sampled to generate a second sample of CTE signal 105. Thus, since CTE signal 105 still needs to be sampled, upon completion of the third specific period, reception of CTE signal 105 is again switched from antenna 3 509 to antenna 1 505 for a fourth specific period (sample slot 4) to generate a fourth portion of the second sample of CTE signal 105. Similarly, a fifth portion in sample slot 5 and a sixth portion in sample slot 6 are generated by antenna 2 507 and antenna 3 509, respectively.

[0059] The process of generating a second sample continues for a second CTE frame 503 received over a different frequency channel k=2 (201e) during a second time period. The second CTE frame 503 is sampled using antenna switching, where the antenna (Antenna 1-Antenna 3) is periodically switched between multiple antennas based on a predetermined antenna switching schedule.

[0060] 5B shows a CTE structure 500b including a predefined switching and sampling slot 515 spanning one CTE frame transmitted over channel 201d (k=1) to generate a second sample of CTE signal 105, according to some embodiments. FIG. 5B is described below in conjunction with FIG. 5A. CTE structure 500b includes a 4 μs guard period 511, an 8 μs reference period 513, and switching and sampling slot 515. A receiver of Bluetooth-enabled device 101 is configured to perform antenna switching to determine a direction to Bluetooth-enabled transmitter 103. This is made possible by adding a CTE to a LL Bluetooth data frame (also called a "data packet") 100c (as shown in FIG. 1C) transmitted by Bluetooth-enabled transmitter 103, where the added CTE causes a specified portion of the data packet to have a fixed, constant frequency. The receiver of the Bluetooth enabled device 101 samples the in-phase and quadrature (IQ) components of the CTE signal 105 transmitted by the Bluetooth enabled transmitter 103 and can determine the phase of the CTE signal 105 in each of the multiple CTE frames (501a and 503) received by the Bluetooth enabled device 101. By sampling the IQ components of the CTE signal 105 in each CTE frame for multiple antennas (antenna 1 505 through antenna 3 509), the receiver of the Bluetooth enabled device 101 can calculate from which angle the transmitted CTE signal 105 was received. To that end, the Bluetooth enabled device 101 is configured for antenna switching, where the antenna is switched between the multiple antennas (antenna 1 505 through antenna 3 509), and during a sampling slot (sample slot 1 through sample slot 6), the CTE signal 105 is sampled by the antenna selected for the switch slot.

[0061] For example, switching and sampling slot 515 may include a predefined number of switch slots 515a through 515m, during which reception of CTE signal 105 is switched from one antenna to another, such that during each sample slot of the plurality of sample slots (sample slots 515b through 515n), the antenna selected during the previous switch slot receives CTE signal 105. Sample slot 515b may correspond to sample slot 1 shown in FIG. 5A. In one exemplary embodiment, Bluetooth enabled device 101 may be configured to switch from antenna 1 505 to antenna 2 507 during switch slot 515a. Also, antenna 2 507 would be configured to receive CTE signal 105 during sample slot 515b (or for the duration of sample slot 515b). In this manner, the antenna switching schedule is predefined. The number of switch slots (515a-515m) and the number of sample slots (515b-515n) may be based on the length of the CTE signal 105 in the CTE frames. In an exemplary embodiment, the number of switch slots (515a-515m) may be 74. Similarly, the number of sample slots (515b-515n) may be 74. Antenna switching schedules are fully supported by BLE 5.1 ​​and the above-mentioned standards.

[0062] 6 shows a flowchart of a method 600 comprising steps performed by a Bluetooth enabled device 101 to determine the location of a Bluetooth enabled transmitter 103, according to some embodiments. The method 600 is performed in two stages: Stage 1 and Stage 2.

[0063] In step 601, during a first time period, RF chains corresponding to multiple antennas in transceiver 101a of Bluetooth-enabled device 101 are controlled to select a single antenna from the multiple antennas to receive a first sample of CTE signal 105. The first sample of CTE signal 105 may correspond to CTE signal 105 received via multiple CTEs in a LL Bluetooth packet transmitted by Bluetooth-enabled transmitter 103 during the first time period, where multiple CTE frames each containing CTE signal 105 are transmitted across multiple transmission frequencies included in the Bluetooth communication protocol. Therefore, RF switch 107 is used to select a single antenna from the multiple antennas. In some embodiments, the single antenna used to receive the first sample of CTE signal 105 is predetermined. The first sample of CTE signal 105 may be stored in memory 117 for later use to estimate an initial estimate of the ToF data of CTE signal 105.

[0064] In step 603, the first sample of the CTE signal 105 is used to determine an initial estimate of the ToF of the CTE signal 105. The ToF indicates the distance between the Bluetooth enabled device 101 and the Bluetooth enabled transmitter 103. To determine the initial estimate of the ToF, first, the beat signal (x b (t) is generated by integrating the CTE signals 105 received via multiple paths p and across multiple channel frequencies k to form a virtual array of antennas. An FFT of the beat signal for each channel k is then calculated to determine an initial estimate of the ToF data of the CTE signals 105.

[0065] In step 605, the CTE signal 105 in each CTE frame of the plurality of CTE frames received during the second time period is sampled using antenna switching to generate a second sample of the CTE signal 105. The plurality of CTE frames are transmitted across multiple transmission frequencies included in the Bluetooth communication protocol. Therefore, during the second time period, the RF chain is controlled using the RF switch 107 to switch among the plurality of antennas according to a switching schedule to receive the second sample of the CTE signal 105. According to the switching schedule, only one antenna of the plurality of antennas is selected to receive the CTE signal 105 during a particular time period or slot corresponding to that antenna. In some embodiments, the switching schedule may be predetermined. In other embodiments, the antenna may be selected randomly.

[0066] In step 607, the precise location of the Bluetooth enabled transmitter 103 relative to the Bluetooth enabled device 101 is determined by fitting the second sample of the CTE signal to the signal model (Equation 3). The signal model connects the second sample of the CTE signal 105 with the unknown AoA of the CTE signal 105, which was received at a time defined by the switching schedule and transmitted with an unknown ToF conditional on the initial ToF data estimated in step 603. The AoA and ToF are then used to determine the precise location of the Bluetooth enabled transmitter 103.

[0067] FIG. 7 illustrates a scenario 700 in which a Bluetooth-enabled device 101 is used for indoor positioning of a Bluetooth-enabled transmitter 103, according to an exemplary embodiment. In FIG. 7, the Bluetooth-enabled transmitter 103 corresponds to a user device being used by a user 701 to determine directions to a desired store in a mall. The user device of the user 701 continues to broadcast a CTE signal. When the CTE signal broadcast by the user device is detected by a Bluetooth-enabled device 101 adapted to a particular location in the mall, the Bluetooth-enabled device 101 determines an initial estimate of the ToF data of the CTE signal received from the user device. The Bluetooth-enabled device 101 further demodulates the CTE signal and uses a signal model to determine the AoA of the CTE signal. The signal model is initialized using the initial estimate of the ToF data of the CTE signal, which not only refines the final ToF calculation but also reduces the search space for calculating the ToF and AoA. The ToF of the CTE signal indicates the distance of the user device from the Bluetooth enabled device 101, and the AoA of the CTE signal indicates the direction of the user device relative to the location of the Bluetooth enabled device 101. Based on the ToF and AoA, a precise location of the user device is determined. Location information associated with the user device is then transmitted to the user device. In an exemplary embodiment, an application configured to transmit the CTE signal and further convert the location information into a format understandable to the user may be installed on the user device.

[0068] In another embodiment, two or more Bluetooth enabled devices 101 may be installed at different locations within a mall, with each Bluetooth enabled device 101 operating independently of the other. When a user device is detected within range of a Bluetooth enabled device 101, the Bluetooth enabled device 101 determines the location of the user device relative to the Bluetooth enabled device 101. For example, there may be two Bluetooth enabled devices operating independently within a mall. Thus, when a user device is detected within range of a first Bluetooth enabled device 101, the first Bluetooth enabled device 101 determines the location of the user device relative to the first Bluetooth enabled device 101. Similarly, when a user device is detected within range of a second Bluetooth enabled device 101, the second Bluetooth enabled device 101 determines the location of the user device relative to the second Bluetooth enabled device 101.

[0069] Thus, the systems and methods described herein provide an accurate indoor positioning system based on the already existing infrastructure of Bluetooth technology.

[0070] The following description provides exemplary embodiments only; Attached Claims Example Surrounding It is not intended to be limiting. Rather, the following description of exemplary embodiments will provide those skilled in the art with an enabling description for implementing one or more exemplary embodiments. Example of It is contemplated that various changes may be made in the function and arrangement of elements without departing from the scope thereof.

[0071] Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by those skilled in the art that the embodiments may be practiced without these specific details. For example, systems, processes, and other elements in the disclosed subject matter may be shown as components in block diagram form to avoid obscuring the embodiments in unnecessary detail. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail to avoid obscuring the embodiments. Also, the same reference numbers and names in the various drawings refer to the same elements.

[0072] Also, particular embodiments may be described as a process, which is depicted as a flowchart, flow diagram, data flow diagram, structure diagram, or block diagram. While a flowchart may describe operations as a sequential process, many of the operations may occur in parallel or simultaneously. Additionally, the order of operations may be rearranged. A process may terminate when its operations are completed, but may have additional steps not described or included in the drawings. Moreover, not all operations in any specifically described process may occur in all embodiments. A process may correspond to a method, function, procedure, subroutine, subprogram, etc. When a process corresponds to a function, the end of the function may correspond to the function returning to the calling function or main function.

[0073] Furthermore, embodiments of the disclosed subject matter may be implemented, at least in part, manually or automatically. The manual or automatic implementation may be performed or at least assisted through the use of machine, hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the necessary tasks may be stored on a machine-readable medium. A processor may perform the necessary tasks.

[0074] The various methods or processes outlined in this specification may be coded as software executable on one or more processors employing any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages ​​and / or programming or scripting tools, and may be compiled as executable machine code or intermediate code that runs on a framework or virtual machine. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0075] Embodiments of the present disclosure may be embodied as methods, examples of which are provided. The operations performed as part of the method may be ordered in any suitable manner. Thus, while exemplary embodiments show operations as sequential, embodiments may be constructed in which operations are performed in a different order than illustrated, including even including performing some operations simultaneously.

[0076] While this disclosure has been described with reference to certain preferred embodiments, Without departing from the scope of the appended claims, It should be understood that various other adaptations and modifications may be made. do.

Claims

1. 1. A Bluetooth enabled device comprising a transceiver, the transceiver including a plurality of antennas associated with a radio frequency (RF) chain, the Bluetooth enabled device further comprising: at least one processor; a memory having stored thereon instructions that, when executed by the at least one processor, cause the Bluetooth enabled device to perform a plurality of steps, the plurality of steps comprising: controlling the radio frequency (RF) chain to receive, during a first time period, at a single antenna selected from the plurality of antennas, a constant tone extension (CTE) signal of a plurality of frames transmitted by a Bluetooth enabled transmitter over a plurality of frequencies defined in a Bluetooth communication protocol; controlling the radio frequency (RF) chain to switch among the plurality of antennas according to a switching schedule associated with reception of the constant tone extension (CTE) signal on each of the plurality of antennas over a plurality of frames during a second time period; and determining initial time-of-flight (ToF) data for the constant tone extension (CTE) signal from first samples of the constant tone extension (CTE) signal received during the first time period, the initial time-of-flight (ToF) data indicating a distance between the Bluetooth enabled device and the Bluetooth enabled transmitter, the distance being indicated using the ToF and a phase of the received constant tone extension (CTE) signal that is dependent on the frequency at which it is transmitted, the steps further comprising: determining the location of the Bluetooth enabled transmitter relative to the location of the Bluetooth enabled device; The instructions, when executed by the at least one processor, cause the Bluetooth enabled device to: determining a location of the Bluetooth enabled transmitter relative to a location of the Bluetooth enabled device by fitting second samples of the constant tone extension (CTE) signal received during the second time period to a signal model, the signal model connecting the second samples with an unknown angle of arrival of the constant tone extension (CTE) signal received at a time defined by the switching schedule and transmitted with an unknown time of flight (ToF) subject to the initial ToF data.

2. 2. The Bluetooth enabled device of claim 1, wherein the constant tone extension (CTE) signal includes a series of non-whitened known symbols from the Bluetooth enabled transmitter, a length associated with the constant tone extension (CTE) signal is variable, and the constant tone extension (CTE) signal is a single tone signal at an associated carrier frequency.

3. the first sample of the constant tone extension (CTE) signal and the second sample of the constant tone extension (CTE) signal are received via a plurality of paths; To determine the initial time-of-flight (ToF) data of the constant tone extension (CTE) signal from the first sample of the constant tone extension (CTE) signal, the at least one processor further comprises: demodulating the received first sample of the constant tone extension (CTE) signal; 2. The Bluetooth enabled device of claim 1, configured to generate a virtual array of antennas based on the demodulated first samples of the constant tone extension (CTE) signal to determine the initial time-of-flight (ToF) data for each path of the plurality of paths across each frequency of the plurality of frequencies.

4. 4. The Bluetooth enabled device of claim 3, wherein to generate the virtual array of antennas, the at least one processor is configured to receive the constant tone extension (CTE) signal for multiple frames across the multiple frequencies and through the multiple paths.

5. 2. The Bluetooth-enabled device of claim 1, wherein the at least one processor is further configured to determine a cross-correlation between the received first sample of the constant tone extension (CTE) signal and a reference constant tone extension (CTE) signal to recover the initial time-of-flight (ToF) data of the constant tone extension (CTE) signal from the first sample of the constant tone extension (CTE) signal.

6. a duration of the first period of time corresponds to a time required to recover the initial time-of-flight (ToF) data; 2. The Bluetooth enabled device of claim 1, wherein the duration of the second period corresponds to the time required to determine the location of the Bluetooth enabled transmitter relative to the location of the Bluetooth enabled device.

7. 1. A method comprising: The method includes the steps of: controlling, during a first time period, at a single antenna selected from the plurality of antennas in a transceiver of a Bluetooth enabled device, a radio frequency (RF) chain corresponding to the plurality of antennas to receive a constant tone extension (CTE) signal of a plurality of frames transmitted by a Bluetooth enabled transmitter over a plurality of frequencies defined by a Bluetooth communication protocol; controlling the radio frequency (RF) chain to switch among the plurality of antennas according to a switching schedule to receive the constant tone extension (CTE) signal at each of the plurality of antennas during a second time period; and determining initial time-of-flight (ToF) data of the constant tone extension (CTE) signal from first samples of the constant tone extension (CTE) signal received during the first time period, the initial time-of-flight (ToF) data indicating a distance between the Bluetooth enabled device and the Bluetooth enabled transmitter using the initial time-of-flight (ToF) data and a phase of the constant tone extension (CTE) signal dependent on the frequency at which it was transmitted, the method further comprising the steps of: determining the location of the Bluetooth enabled transmitter relative to the location of the Bluetooth enabled device; The step of locating the Bluetooth enabled transmitter comprises: determining a location of the Bluetooth enabled transmitter relative to a location of the Bluetooth enabled device by fitting second samples of the constant tone extension (CTE) signal received during the second time period to a signal model, the signal model connecting the second samples with an unknown angle of arrival of the constant tone extension (CTE) signal received at a time defined by the switching schedule and transmitted with an unknown time of flight (ToF) conditioned on the initial ToF data.

8. 8. The method of claim 7, wherein the constant tone extension (CTE) signal comprises a series of non-whitened known symbols from the Bluetooth enabled transmitter, a length associated with the constant tone extension (CTE) signal is variable, and the constant tone extension (CTE) signal is a single tone signal at an associated carrier frequency.

9. the first sample of the constant tone extension (CTE) signal and the second sample of the constant tone extension (CTE) signal are received via a plurality of paths; To determine the initial time-of-flight (ToF) data of the constant tone extension (CTE) signal from the first sample of the constant tone extension (CTE) signal, the method further includes performing, by the at least one processor: demodulating the received first sample of the constant tone extension (CTE) signal; and generating a virtual array of antennas based on the demodulated first samples to determine the initial time-of-flight (ToF) data for each path of the plurality of paths across each frequency of the plurality of frequencies.

10. 10. The method of claim 9, wherein the method further comprises, as processing performed by the at least one processor, receiving the constant tone extension (CTE) signal for a plurality of frames across the plurality of frequencies and through the plurality of paths to generate the virtual array of antennas.

11. 8. The method of claim 7, further comprising, as a process performed by the at least one processor, determining a cross-correlation between the received first sample of the constant tone extension (CTE) signal and a reference constant tone extension (CTE) signal to recover the initial time-of-flight (ToF) data of the constant tone extension (CTE) signal from the first sample of the constant tone extension (CTE) signal.

12. a duration of the first period of time corresponds to a time required to recover the initial time-of-flight (ToF) data; 8. The method of claim 7, wherein the duration of the second period corresponds to the time required to determine the location of the Bluetooth enabled transmitter relative to the location of the Bluetooth enabled device.

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