Bluetooth-based space-time 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 specifically 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, proximity services, and more. 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, which emit radio signals from their locations at predetermined intervals. Bluetooth-enabled devices within the emission area of ​​a BLE beacon can detect the radio signal and establish communication with the BLE beacon. Although one beacon is sufficient to establish the presence of a Bluetooth-enabled device, it cannot pinpoint the specific location of the Bluetooth-enabled device. For this reason, techniques such as trilateration using multiple BLE beacons are used to pinpoint the location of a Bluetooth-enabled device. Also, the distance of the Bluetooth-enabled device from the 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, where RSSI represents the power of the radio signal from each BLE beacon in the multiple BLE beacons. If the distance is long, the RSSI value is low, and if the distance is short, the RSSI value is higher. Additionally, the angle of arrival (AoA) of wireless 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 called "multipath"), which degrades the AoA estimation. Also, the resolution or accuracy of the AoA is a function of the number of antennas used. Since the number of antennas is usually limited due to size and computational constraints in indoor positioning via BLE techniques, the accuracy of the AoA estimation is affected in such cases. Furthermore, multiple beacons require coordination among them, 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 the accuracy of AoA, even with a limited number of antennas. Summary of the Invention

[0006] It is an object of some embodiments to provide a device (also referred to as a "Bluetooth enabled device") and method for determining an accurate location of a Bluetooth enabled transmitter. The location of the Bluetooth enabled transmitter may be determined based on the distance of the Bluetooth enabled transmitter from the 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 the 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. Therefore, 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 the coordination between these multiple BLE beacons incurs computation overhead.

[0007] Also, 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 created 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 that depends 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 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 exclusively digital, since that means 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 for determining the AoA of a wireless signal. Some embodiments are based on the recognition that the CTE signal may be used to determine the ToF of a wireless signal.

[0011] 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 transmits the CTE signal and the time the Bluetooth enabled device receives the CTE signal. However, the time the Bluetooth enabled transmitter transmits the CTE signal is often unknown. Thus, it is difficult to determine the ToF of the CTE signal.

[0012] Some embodiments are based on the recognition that a Bluetooth enabled transmitter may 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, it is difficult to solve the signal model to determine these two unknowns. Thus, the signal model is solved in two stages, where 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 to jointly determine the AoA and ToF.

[0013] The initial estimate of 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 ToF is also used to jointly determine the AoA of the CTE signal at the Bluetooth enabled device from the Bluetooth enabled transmitter. In the first stage, to determine the initial estimate of ToF, the Bluetooth enabled device is configured to control each RF chain to select a single antenna from multiple antennas included within the transceiver of the Bluetooth enabled device during a first period of time. The Bluetooth enabled device is configured to receive the CTE signal at the selected antenna, where the CTE signal is included in multiple frames and transmitted across multiple frequencies defined 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 that end, 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 with the estimated ToF and iteratively solved to calculate the AoA of the CTE signal.

[0015] In this manner, 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 number of steps, including controlling the RF chain to receive, during a first time period, on a single antenna selected from the multiple antennas, a CTE signal for a number of frames transmitted by a Bluetooth enabled transmitter over a number of frequencies defined in a Bluetooth communication protocol, controlling the RF chain to switch among the multiple antennas according to a switching schedule to receive, during a second time period, a CTE signal on each of the multiple antennas, and switching the CTE signal received during the first time period. and recovering an initial ToF of the CTE signal from a first sample of the received CTE 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, the steps further including 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 of time 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 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 from a first sample of the CTE signal received during the first time period, a CT. and recovering an initial ToF of the E signal, where the ToF indicates 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 method further comprises 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 of time to a signal model, where the signal model connects 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 conditional on the initial ToF. [Brief description of the drawings]

[0018] [Figure 1A] FIG. 1 illustrates an environment for a Bluetooth enabled device to determine the location of 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] 2 illustrates a Bluetooth Link Layer (LL) data frame having a CTE frame including a CTE signal, according to some embodiments. [Diagram 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. 2 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] A diagram showing steps of enabling multiple CTE frames through multiple channels with a fixed antenna and estimating the ToF of multiple paths according to some embodiments. [Figure 4B] A diagram showing steps of 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. 13 illustrates a step of enabling multiple CTE frames through multiple channels across multiple antennas using antenna switching, and estimating the AoA of multiple paths while refining the 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 the CTE signal, according to some embodiments. [Figure 6] 4 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. 2 illustrates a scenario in which a Bluetooth enabled device is used for indoor positioning of a Bluetooth enabled transmitter, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, the 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," "including," and the verbs "comprise," "have," "include," and other verb forms thereof, when used 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 explanation 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 determine the location of 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. CTE signal 105 is thus 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] The Bluetooth enabled device 101 comprises a transceiver 101a including multiple antennas such as antenna 1, antenna 2, antenna 3, and antenna 4. For ease of illustration, the transceiver 101a is illustrated with only four antennas. However, there may be more than four antennas in the transceiver 101a without departing from the scope of this disclosure. The transceiver 101a includes an RF switch 107 that is controlled to select one antenna from the multiple antennas (antenna 1-antenna 4) or to switch between the multiple antennas. Also, the received CTE signal 105 is demodulated by the transceiver 101a, and the demodulated CTE signal is provided to the AoA estimation module 101b, which uses the demodulated CTE signal 105 to identify the location of the 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 illustrates 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, an optical drive, a 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 for jointly determining ToF and AoA. The estimated ToF is used to calculate AoA(θ) using the signal model for jointly determining 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 ToF refines the ToF calculation using the signal model. The search space for determining ToF and AoA is also reduced. Steps for estimating the ToF of the CTE signal 105 and for calculating the AoA in the AoA estimation module 101b are described later with reference to FIG. 3.

[0029] In addition, the Bluetooth enabled device 101 may include an output interface 121. In some embodiments, the output interface 121 may be configured to provide the location of the Bluetooth enabled transmitter 103 determined by the 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 in Bluetooth enabled device 101 to perform 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 separate 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] Also, the size of the CRC is 3 octets and is calculated for every LL packet PDU. If the PDU is encrypted, the CRC is calculated after the encryption of the PDU is completed.

[0033] Finally, LL data frame 100c includes a CTE consisting of a series of non-whitened 1's that are constantly modulated. 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 pinpoint the exact location of Bluetooth enabled transmitter 103 relative to Bluetooth enabled device 101.

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

[0035] In stage 2, the AoA and ToF of the CTE signal 105 are determined together using frequency hopping and antenna switching. To that end, the Bluetooth enabled device 101 is configured to switch antennas after a predefined 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 that each antenna of the multiple antennas receives the CTE signal 105. The amount of time that each antenna should be connected to the RF chain to receive the CTE signal 105 is predefined. 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, where the Bluetooth packet 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 from 1 to 40, where k=1 corresponds to channel 0 of the BLE channels 200. Each channel 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 advertisement 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. These channels 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, e.g., channel 201d (k=1), channel 201e (k=2), channel 201f (k=35), etc., 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 an advertising packet 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 a Bluetooth packet is used to determine ToF and AoA information associated with locating a Bluetooth enabled transmitter 103 .

[0039] 3A illustrates steps performed by AoA estimation module 101b in a first stage 301 to locate a Bluetooth enabled transmitter 103, according to some embodiments. AoA estimation module 101b locates a Bluetooth enabled transmitter 103 in two stages: in a first stage (stage 1) 301, the ToF data of the 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 the CTE signal 105 using the ToF estimated in the 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 a CTE signal 105 over multiple CTE frames transmitted by the Bluetooth enabled transmitter 103 over multiple channel frequencies (also called "transmit frequencies") (as shown in FIG. 4) corresponding to a channel k defined in the Bluetooth communication protocol (as shown in FIG. 2) during a first time period. 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 over 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] Therefore, 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 301a, upon receiving a first sample of the CTE signal 105, a beat signal (x) for each channel k is calculated by integrating the CTE signals 105 received over 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 ) The initial estimate of the data is calculated by 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, a 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 the AoA estimation module 101b in a second stage 303 to determine the location of the Bluetooth enabled transmitter 103, according to some embodiments. In the second stage 303, the AoA and ToF of the CTE signal 105 are jointly calculated during a second period of time. In some embodiments, the second period of time is predefined. In other embodiments, the duration of the second period of time continues until the Bluetooth enabled device 101 determines the final AoA and ToF of the CTE signal 105 to determine the precise location of the 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 chain 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] The signal model is initialized with the initial estimate of the ToF data determined in stage one 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, which connects the second sample with an unknown AoA of the CTE signal 105 received at a time defined by the switching schedule and transmitted with 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 (e.g., gently) penalize deviations in the ToF calculated in the second stage 303.

[0051] 4A and 4B show steps of 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 of 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, it is assumed that 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 b (t) (Equation 2) is generated for each channel k of the multiple 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 follows:

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=0-39) 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 generated for each CTE frame of the plurality of CTE frames received through the plurality of channels k. bAn initial estimate of the ToF is determined using an FFT of (t). Using an 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 that peak is a function of the delay and the corresponding channel k.

[0054]

number

[0055] The CTE signal 105 includes a number 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, it is shown that 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 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, namely, antenna 1 (i=1) 505, antenna 2 (i=2) 507, and antenna 3 (i=3) 507.

[0057] During the 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 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) that generates a first portion of the second sample of the CTE signal 105. Once 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) that generates a second portion of the second sample of the CTE signal 105. Similarly, once 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) that generates a third portion of the second sample of the CTE signal 105. The switching of antennas among the multiple antennas according to the switching schedule continues until the entire first frame of the CTE signal 105 has been sampled to generate a second sample of the CTE signal 105. Thus, as the CTE signal 105 is still to be sampled, upon completion of the third specific time period, reception of the CTE signal 105 is again switched from antenna 3 509 to antenna 1 505 for a fourth specific time period (sample slot 4) to generate a fourth portion of the second sample of the CTE signal 105. Similarly, the fifth portion in sample slot 5 and the sixth portion in sample slot 6 are generated by antenna 2 507 and antenna 3 509, respectively.

[0059] The process of generating second samples 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] FIG. 5B illustrates a CTE structure 500b including predefined switching and sampling slots 515 over 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 slots 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 and constant frequency. The receiver of the Bluetooth enabled device 101 can sample the in-phase and quadrature (IQ) components of the CTE signal 105 transmitted by the Bluetooth enabled transmitter 103 to 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. Thus, the Bluetooth enabled device 101 is configured for antenna switching, where the antennas are 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, the switching and sampling slots 515 include a predefined number of switch slots 515a-515m, during which the reception of the CTE signal 105 is switched from one antenna to another, and during each sample slot of the number of sample slots (sample slots 515b-515n), the antenna selected during the previous switch slot is configured to receive the CTE signal 105. Sample slot 515b may correspond to sample slot 1 shown in FIG. 5A. In an exemplary embodiment, the Bluetooth enabled device 101 may be configured to switch from antenna 1 505 to antenna 2 507 during switch slot 515a. Also, during sample slot 515b (or for the length of sample slot 515b), antenna 2 507 would be configured to receive the CTE signal 105. 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 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 period, and multiple CTE frames each including CTE signal 105 are transmitted across multiple transmission frequencies included in a 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 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 an initial estimate of the ToF, first, the beat signal (x b A ToF data (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 multiple CTE frames received during the second time period is sampled using antenna switching to generate a second sample of the CTE signal 105. The multiple CTE frames are transmitted across multiple transmission frequencies included in the Bluetooth communication protocol. Thus, during the second time period, the RF chain is controlled using the RF switch 107 to switch between the multiple 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 multiple antennas is selected to receive the CTE signal 105 during a particular time period or slot corresponding to the antenna. In some embodiments, the switching schedule may be predetermined. In other embodiments, the antenna may be selected randomly.

[0066] In step 607, a 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, 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 that is being used by a user 701 to determine a direction 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 the 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 with 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 orientation of the user device relative to the location of the Bluetooth enabled device 101. Based on the ToF and the 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 that the user can understand 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 only exemplary embodiments and is not intended to limit the scope, applicability, or configuration of the present disclosure. 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. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosed subject matter as set forth in the appended claims.

[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. Additionally, the same reference numbers and names in the various drawings refer to the same elements.

[0072] Also, individual embodiments may be described as a process, which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe operations as a sequential process, many of the operations may occur in parallel or simultaneously. In addition, 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, a function, a procedure, a subroutine, a 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 to the 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 a 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. In addition, 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] The embodiments of the present disclosure may be embodied as a method, an example of which is provided. The operations performed as part of the method may be ordered in any suitable manner. Thus, while an example embodiment shows operations as sequential, embodiments may be constructed in which operations are performed in an order different from that illustrated, which may include performing some operations simultaneously.

[0076] Although the disclosure has been described with reference to certain preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the disclosure. It is therefore the object of the appended claims to cover all such variations and modifications as fall within the true spirit and scope of the disclosure.

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; and a memory having instructions stored thereon that, when executed by the at least one processor, cause the Bluetooth enabled device to perform a plurality of steps, the plurality of steps including: controlling the 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 RF chain to switch between the multiple antennas according to a switching schedule associated with reception of the CTE signal at each of the multiple antennas over a second period of time over a number of frames; determining initial Time of Flight (ToF) data for the CTE signal from first samples of the CTE signal received during the first time period, the ToF data indicative of 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 CTE signal dependent on the frequency transmitted, the steps further comprising: 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 the 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 conditional on the initial ToF data.

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

3. the first sample of the CTE signal and the second sample of the CTE signal are received via a plurality of paths; To determine the initial ToF data of the CTE signal from the first sample of the CTE signal, the at least one processor further comprises: demodulating the first received sample of the 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 CTE signal to determine the initial ToF data for each path of the multiple paths across each frequency of the multiple 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 CTE signals for multiple frames across the multiple frequencies and through the multiple paths.

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

6. a duration of the first period corresponds to a time required to recover the initial ToF data; 2. The Bluetooth enabled device of claim 1, wherein a duration of the second time period corresponds to an amount of 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: controlling, during a first time period, at a single antenna selected from the plurality of antennas at 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 in a Bluetooth communication protocol; controlling the RF chain to switch among the plurality of antennas according to a switching schedule to receive the CTE signal at each of the plurality of antennas during a second time period; determining initial Time of Flight (ToF) data for the CTE signal from first samples of the CTE signal received during the first time period, the ToF data being indicative of a distance between the Bluetooth enabled device and the Bluetooth enabled transmitter using the ToF data and a phase of the CTE signal which is dependent on the frequency transmitted, the method further comprising: determining a location of the Bluetooth enabled transmitter relative to a location of the Bluetooth enabled device by fitting second samples of the CTE signal received during the second period to a signal model, the signal model connecting the second samples 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 conditional on the initial ToF data.

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

9. the first sample of the CTE signal and the second sample of the CTE signal are received via a plurality of paths; To determine the initial ToF data of the CTE signal from the first sample of the CTE signal, the method further comprises: demodulating the first received sample of the CTE signal; and generating a virtual array of antennas based on the demodulated first samples to determine the initial 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 to generate the virtual array of antennas, the method further comprises receiving the CTE signals for a plurality of frames across the plurality of frequencies and through the plurality of paths.

11. 8. The method of claim 7, further comprising determining a cross-correlation between the received first sample of the CTE signal and a reference CTE signal to recover the initial ToF data of the CTE signal from the first sample of the CTE signal.

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

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