Patent Publication Number: US-2019178972-A1

Title: Determining angle of arrival of a radio-frequency signal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/598,323 filed on Dec. 13, 2017, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Computing devices may communicate with each other via networks, such as wireless network (e.g., Wi-Fi networks, Bluetooth networks, etc.). A computing device may communicate with another device (e.g., another computing device) in the wireless network by transmitting radio-frequency signals to the other device and by receiving radio-frequency signals from the other device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIG. 1  illustrates an example system architecture, in accordance with some embodiments of the present disclosure. 
         FIG. 2A  illustrates an example computing device, in accordance with some embodiments of the present disclosure. 
         FIG. 2B  illustrates an example computing device, in accordance with some embodiments of the present disclosure. 
         FIG. 2C  illustrates an example receiver component, in accordance with some embodiments of the present disclosure. 
         FIGS. 3A through 3H  illustrate example antenna clusters, in accordance with some embodiments of the present disclosure. 
         FIG. 4  is a flow diagram of a method of determining an angle of arrival, in accordance with some embodiments of the present disclosure. 
         FIG. 5  illustrates an example computing device in accordance with some embodiments of the present disclosure. 
         FIG. 6  is a graph illustrating example phase differences in accordance with some embodiments of the present disclosure. 
         FIG. 7  is a block diagram of an example device that may perform one or more of the operations described herein, in accordance with some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Computing devices may communicate with each other via networks, such as wireless network (e.g., Wi-Fi networks, Bluetooth networks, etc.). A computing device may communicate with another device (e.g., another computing device) in the wireless networks by transmitting radio-frequency signals to the other device and by receiving radio-frequency signals from the other device. It may be useful for a computing device to determine the direction of the source of a radio-frequency signal, relative to the computing device. For example, determining the direction of a radio-frequency signal may allow the computing device to perform beamforming operations, functions, methods, etc., which may allow the computing device to transmit or receive radio-frequency signals more efficiently. In another example, the direction of a radio-frequency signal may be used for navigational purposes (e.g., to navigate a device towards the source of the radio-frequency signal or in some other direction relative to the direction of the radio-frequency signal). Determining the direction of a radio-frequency signal may be used in, for example and not limitation, asset/object tracking, gaming, networking, navigation applications, and/or Internet of Things (IoT) applications, including industrial, consumer, and automobile applications. The direction of a radio-frequency signal may also be referred to as the angle-of-arrival (AoA) of the radio-frequency signal. 
     The examples, implementations, and embodiments described herein may use a solid dielectric material to alter a radio-frequency signal by reducing (e.g., decreasing) the propagation speed of the radio-frequency signal by a determined amount. In one embodiment, slowing down the propagation speed of the radio-frequency signal using the dielectric material may allow the computing device to increase directional resolution or the directional precision when determining the angle of arrival of the radio-frequency signal without increasing the distance between antennas in an antenna cluster. This may allow for a reduction in the size of antenna clusters which may allow the antenna cluster to be used in more types of devices and in more applications. In another embodiment, slowing down the propagation speed of the radio-frequency signal using the dielectric material may allow for better (e.g., improved) directional precision or directional resolution without increasing the size of an antenna cluster. 
       FIG. 1  illustrates an example system architecture  100 , in accordance with some embodiments of the present disclosure. The system architecture  100  includes a computing device  110 , a computing device  120 , and a computing device  130 . Each of the computing devices  110 ,  120 , and  130  may include hardware such as processing devices (e.g., processors, central processing units (CPUs), memory (e.g., random access memory (RAM), storage devices (e.g., hard-disk drive (HDD), solid-state drive (SSD), etc.), and other hardware devices (e.g., sound card, video card, etc.). The computing devices  110 ,  120 , and  130  may comprise any suitable type of computing device or machine that has a programmable processor including, for example, server computers, desktop computers, laptop computers, tablet computers, smartphones, personal digital assistants (PDAs), set-top boxes, etc. In some examples, the computing device  110  may comprise a single machine or may include multiple interconnected machines (e.g., multiple servers configured in a cluster). The computing devices  110 ,  120 , and  130  may execute or include an operating system (OS). The OS of the computing devices  110 ,  120 , and  130  may manage the execution of other components (e.g., software, applications, etc.) and/or may manage access to the hardware (e.g., processors, memory, storage devices etc.) of the computing device. 
     The computing devices  110 ,  120 , and  130  may communicate with each other via a network, such as a wireless network (not illustrated in the figures). The network may be a public network (e.g., the internet), a private network (e.g., a local area network (LAN) or wide area network (WAN)), or a combination thereof. In one embodiment, network may include a wireless infrastructure, which may be provided by one or more wireless communications systems, such as a wireless fidelity (Wi-Fi) access point or hotspot, connected with the network and/or a wireless carrier system that can be implemented using various data processing equipment, communication towers (e.g. cell towers), etc. In other embodiments, the network may be a personal area network, such as a Bluetooth network, a ZigBee network, a Z-Wave network, etc. The network may carry communications (e.g., data, message, packets, frames, etc.) between computing devices  110 ,  120 , and  130 . 
     Computing device  110  includes a set of antennas  111  (e.g., one or more antennas  111 ). The number of antennas  111  may vary in different embodiments of the present disclosure (e.g., computing device  110  may have two antennas  111 , six antennas  111 , or some other appropriate number of antennas). The set of antennas  111  may be referred to as an antenna cluster. The set of antennas  111  may be coupled to each other via switching or multiplexing components (e.g., circuits, wires, traces, pins, etc.). Computing device  120  includes an antenna  121  and computing devices  130  includes an antenna  131 . Although one antenna  121  and one antenna  131  are illustrated in  FIG. 1 , the computing devices  120  and  130  may include any appropriate number of antennas  121  and  131 , respectively, in other embodiments. 
     The computing device  120  may communicate with the computing device  110  by transmitting a radio-frequency (RF) signal  122  to the computing device  110  via antenna  121 . The computing device  110  may receive the radio-frequency signal  122  via the set of antennas  111 . The computing devices  130  may communicate with the computing device  110  by transmitting a radio-frequency signal  132  to the computing device  110  via antenna  131 . The computing device  110  may receive the radio-frequency signal  132  via the set of antennas  111 . As illustrated in  FIG. 1 , the computing device  120  is located at a position that is to the left of the computing device  110  and the computing device  130  is located at a position that is to the right of the computing device  110 . 
     In some embodiments, it may be useful for the computing device  110  to determine the direction of the computing devices  120  and  130 , relative to the computing device  110  (e.g., to determine the direction or location of the computing devices  120  and  130 ). For example, it may be useful for the computing device  110  to determine that the computing devices  120  is to the left of the computing device  110 , and thus the radio-frequency signal  122  transmitted by the computing device  120  will arrive at the computing device  110  from the left of the computing device  110 . In another example, it may be useful for the computing device  110  to determine that the computing devices  130  is to the right of the computing device  110 , and thus the radio-frequency signal  132  transmitted by the computing device  130  will arrive at the computing device  110  from the right of the computing device  110 . Determining the direction of a radio-frequency signal (e.g., radio-frequency signal  122  or  132 ) may allow the computing device  110  to perform beamforming operations, functions, methods, etc., which may allow the computing device  110  to transmit or receive radio-frequency signals more efficiently. In another example, the direction of a radio-frequency signal may be used for navigational purposes (e.g., to navigate a device towards the source of the radio-frequency signal or in some other direction relative to the radio-frequency signal). 
       FIG. 2A  illustrates an example computing device  110 , in accordance with some embodiments of the present disclosure. As discussed above, the computing device  110  may include hardware such as processing devices, memory, storage devices, and other hardware devices. The computing device  110  may comprise any suitable type of combination of devices or machines that has a programmable processor including, for example, server computers, desktop computers, laptop computers, tablet computers, smartphones, personal digital assistants (PDAs), set-top boxes, etc. The computing device  110  may communicate with other devices (e.g., other computing devices or other electronic devices) via a network, such as a wireless network (not illustrated in the figures). The network may carry communications (to and from the computing device  110  via radio-frequency signals, as discussed above. 
     As illustrated in  FIG. 2A , computing device  110  includes a set of antennas  111  (e.g., one or more antennas  111 ). The number of antennas  111  may vary in different embodiments of the present disclosure (e.g., computing device  110  may have two antennas  111 , six antennas  111 , or some other appropriate number of antennas). The set of antennas  111  may be referred to as an antenna cluster. The set of antennas  111  may be coupled to each other via switching or multiplexing components. As discussed above, a computing device (or other device) may communicate with the computing device  110  by transmitting a radio-frequency (RF) signal  260  to the computing device  110 . The computing device  110  may receive the radio-frequency signal  260  via the set of antennas  111  (e.g., via the antenna cluster). The radio-frequency signal  260  may be transmitted to the computing device  110  as radio waves (illustrated by the dash lines of the radio-frequency signal  260 ). Examples of radio-frequency signal  260  may be Bluetooth signals, ZigBee signals, Wi-Fi signals, etc. 
     The computing device  110  also includes a switching component  220 . The switching component  220  couples the set of antennas  111  to the receiver component  270 . The receiver component  270  may include one or more receivers (e.g., one or more radio receivers). The computing device  110  may also include multiple receiver components in other embodiments. The switching component  220  may couple one antenna to a single receiver or receiver component at a time (e.g., the switching component  220  may rotate between multiple antennas and couple one antenna to the receiver component  270  at a time). In another example, the switching component  220  may couple multiple antennas to a single receiver or receiver component at a time (e.g., the switching component  220  may couple two or more antennas to a receiver component  270  at a time). In a further example, the switching component  220  may couple one antenna to a first receiver or receiver component, and may couple multiple antennas to a second receiver or receiver component. The switching component  220  may be any appropriate coupling or multiplexing circuitry known in the art whose switching, multiplexing, and/or selection function may be controlled by any block coupled to its input. 
     The angle of arrival (AoA) of the radio-frequency signal  260  (e.g., direction of the source of the radio-frequency signal  260 ) may be determined using the following equation: 
       ΔΨ=cos(θ)* D* 2π*( F/V   c )  (1)
 
     where ΔΨ is phase difference between the radio-frequency signal  260  that is received at a first antenna  111  and a second antenna  111 , where θ is the angle of arrival of the radio-frequency signal  260 , where D is the distance between the first antenna and the second antenna, where F is the frequency of the radio-frequency signal  260 , and where V c  is the propagation speed of the radio-frequency signals  260  (e.g., the radio wave) through a vacuum. Thus, determining the angle of arrival or direction of a radio-frequency signal  260  may be based on the phase difference (e.g., the signal differentiation) between the radio-frequency signal  260  that is received by the first antenna  111  and the radio-frequency signal  260  that is received by the second antenna  111 . For example, the angle of arrival, angle of departure, or direction of the source of the radio-frequency signal  260  may be determined based on the phase difference (e.g., the phase shift) of the radio-frequency signal  260  observed between the first antenna and the second antenna. 
     As discussed above, it may be useful for the computing device  110  to determine the direction of a source of the radio-frequency signal  260  (e.g., a computing device or other device, which is transmitting or emitting the radio-frequency signal  260 ). As discussed above, determining the direction of the source of the radio-frequency signal  260  may be referred to as determining the angle of arrival of the radio-frequency signal  260  at the computing device  110 , or may be referred to as determining the angle of departure at the source of the radio-frequency signal  260 . 
     One technique for improving the resolution (e.g., directional resolution) or precision (e.g., directional precision) when determining the direction or angle of arrival, the angle of departure, or the direction of a source of the radio-frequency signal  260 , may be to increase the distance between the antennas or to increase the number of antennas in an antenna cluster. For example, a larger distance of twenty centimeters (cm) between the first antenna and the second antenna may allow the direction of the source or the angle of arrival of the radio-frequency signal  260  to be determined with sufficient precision. However, larger distances between antennas may increase the size of the antenna cluster which may restrict or limit the places where the antenna cluster may be used. For example, while a distance of twenty centimeters may allow the antenna cluster to be used on an automobile or in industrial applications, but that distance may prevent the antenna cluster from being used in a mobile device (e.g., a smartphone, a tablet computer, a laptop computer, etc. 
     Other techniques for improving the resolution (e.g., directional resolution) or precision (e.g., directional precision) when determining the direction or angle of arrival, the angle of departure, or the direction of a source of the radiofrequency signal  260  may include using additional components such as low noise amplifiers (LNAs), analog-to-digital converters (ADCs), gain equalizers, etc. However, these additional components may increase the cost of computing devices (e.g., cost to manufacture computing devices) and may increase the complexity of the computing devices (which may increase the failure or malfunction rates of the computing devices). 
       FIG. 2B  illustrates an example computing device  110 , in accordance with some embodiments of the present disclosure. As discussed above, the computing device  110  may include hardware such as processing devices, memory, storage devices, and other hardware devices. The computing device  110  may comprise any suitable type of combination of devices or machines that has a programmable processor including, for example, server computers, desktop computers, laptop computers, tablet computers, smartphones, personal digital assistants (PDAs), set-top boxes, etc. The computing device  110  may communicate with other devices (e.g., other computing devices or other electronic devices) via a network, such as a wireless network (not illustrated in the figures). The network may carry communications to and from the computing device  110  via radio-frequency signals, as discussed above. The computing device includes a direction component  240 . The direction component  240  may be hardware, software, firmware, or a combination thereof, that may determine the angle of arrival, angle of departure, or direction of a source of a radio-frequency signal, as discussed in more detail below. 
     As illustrated in  FIG. 2B , computing device  110  includes a set of antennas  111  (e.g., an antenna cluster). The number of antennas  111  may vary in different embodiments of the present disclosure. The set of antennas  111  may be referred to as an antenna cluster. The set of antennas  111  may be coupled to each other via switching or multiplexing components. As discussed above, a computing device (or other device) may communicate with the computing device  110  by transmitting a radio-frequency (RF) signal  260  to the computing device  110 . The computing device  110  may receive the radio-frequency signal  260  via the set of antennas  111  (e.g., via the antenna cluster). The radio-frequency signal  260  may be transmitted to the computing device  110  as radio waves (illustrated by the dash lines of the radio-frequency signal  260 ). 
     As discussed above, it may be useful for the computing device  110  to determine the direction of a source of the radio-frequency signal  260  (e.g., a computing device or other device, which is transmitting or emitting the radio-frequency signal  260 ). Determining the direction of the source of the radio-frequency signal  260  may be referred to as determining the angle of arrival of the radio-frequency signal  260  at the computing device  110 , or may be referred to as determining the angle of departure at the source of the radio-frequency signal  260 . 
     As illustrated in  FIG. 2B , a dielectric material  250  is located (e.g., positioned, disposed, placed, etc.), between the radio-frequency signal  260  and the leftmost antenna  111 . Thus, the radio-frequency signal  260  may pass through the dielectric material  250  before it is received or detected by the leftmost antenna  111 . The dielectric material  250  may be a solid dielectric material (e.g., may be a solid). The angle of arrival of the radio-frequency signal  260  (e.g., direction of the source of the radio-frequency signal  260 ) which passes through the dielectric material  250  may be determined using the following equation: 
       ΔΨ=cos(θ)* D* 2π*( F/V   d )  (2)
 
     where ΔΨ is phase difference between the radio-frequency signal  260  that is received at a first antenna  111  and a second antenna  111 , where θ is the angle of arrival of the radio-frequency signal  260 , where D is the distance between the first antenna and the second antenna, where F is the frequency of the radio-frequency signal  260 , and where V d  is the propagation speed of the radio-frequency signals  260  (e.g., the radio wave) through a dielectric material. V d  may be determined using the following equation: 
         V   d   =V   c /√{square root over (ε r )}  (3)
 
     where V c  is the propagation speed of the radio-frequency signal  260  (e.g., the radio wave) through a vacuum and where ε r  is the dielectric constant of the dielectric material  250 . The dielectric constant of the dielectric material  250  (e.g., ε r ) may also be referred to as the relative permittivity of the dielectric material  250 . 
     In one embodiment, the propagation speed of the radio-frequency signal  260  as it travels (e.g., passes) through the dielectric material  250  may be reduced or decreased (when compared to the propagation speed of the radio-frequency signal  250  as it travels through a vacuum). For example, the dielectric material  250  may slow down the radio-frequency signal  260  by a certain amount. The amount by which the radio-frequency signal  260  is slowed (e.g., the reduction in the speed of the radio-frequency signal  260 ) may be determined based on the type of the dielectric material. For example, different dielectric materials (e.g., glass, rubber, graphite, etc.) may slow or reduce the propagation speed of the radio-frequency signal by different amounts. The amount of reduction in the propagation speed may be determined based on predetermined information about one or more of the type of the dielectric material  260 , the dielectric constant of the dielectric material  260 , and the frequency of the radio-frequency signal. For example, the direction component  240  may have predetermined information or data that indicates of one or more dielectric constants for one or more different types of dielectric material. For example, the direction component  240  may have access to all or portions of Table 1 illustrated below. Table 1 provides non-limiting examples of different dielectric materials (e.g., different types of dielectric material) and their respective dielectric constants. The direction component  240  may be aware of the type of dielectric material  260  that is used (e.g., graphite, rubber, Pyrex, etc.) and may be able to determine the dielectric constant of the dielectric material  260  based on the predetermined information or data. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Material Type 
                 Dielectric Constant (ε r ) 
               
               
                   
                   
               
             
            
               
                   
                 Vacuum 
                 1 (by definition) 
               
               
                   
                 Air 
                 1.00058986 
               
               
                   
                 PTFE/Teflon 
                 2.1 
               
               
                   
                 Polyethylene/XLPE 
                 2.25 
               
               
                   
                 Polyimide 
                 3.4 
               
               
                   
                 Polypropylene 
                 2.2-2.36 
               
               
                   
                 Polystyrene 
                 2.4-2.7  
               
               
                   
                 Carbon disulfide 
                 2.6 
               
               
                   
                 Mylar 
                 3.1 
               
               
                   
                 Paper 
                 3.85 
               
               
                   
                 Electroactive 
                 2-12 
               
               
                   
                 polymers 
               
               
                   
                 Mica 
                 6-Mar 
               
               
                   
                 Calcium copper 
                 &gt;250,000 
               
               
                   
                 titanate 
               
               
                   
                 Silicon dioxide 
                 3.9 
               
               
                   
                 Sapphire 
                 8.9-11.1 
               
               
                   
                 Concrete 
                 4.5 
               
               
                   
                 Pyrex (Glass) 
                 4.7 (3.7-10) 
               
               
                   
                 Neoprene 
                 6.7 
               
               
                   
                 Rubber 
                 7 
               
               
                   
                 Diamond 
                 5.5-10   
               
               
                   
                 Salt 
                 3-15 
               
               
                   
                 Graphite 
                 10-15  
               
               
                   
                 Silicon 
                 11.68 
               
               
                   
                 Silicon nitride 
                 8-Jul 
               
               
                   
                 Ammonia 
                 17-26  
               
               
                   
                 Conjugated polymers 
                 1.8-6 up to 100,000 
               
               
                   
                 Methanol 
                 30 
               
               
                   
                 Ethylene glycol 
                 37 
               
               
                   
                 Furfural 
                 42 
               
               
                   
                 Glycerol 
                 41.2, 47, 42.5 
               
               
                   
                 Water 
                 88, 80.1, 55.3, 34.5 
               
               
                   
                 Hydrofluoric acid 
                 175, 134, 111, 83.6 
               
               
                   
                 Hydrazine 
                 52.0 (20° C.), 
               
               
                   
                 Formamide 
                 84.0 (20° C.) 
               
               
                   
                 Sulfuric acid 
                 84-100 
               
               
                   
                 Titanium dioxide 
                 86-173 
               
               
                   
                 Strontium titanate 
                 310 
               
               
                   
                 Barium strontium 
                 500 
               
               
                   
                 titanate 
               
               
                   
                 Barium titanate [7]   
                  1200-10,000 
               
               
                   
                 Lead zirconate 
                 500-6000 
               
               
                   
                 titanate 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, a first antenna  111  and a second antenna  111  may receive the radio-frequency signal  260 . The first antenna  111  may be located a first distance (e.g., an actual or physical distance) from the second antenna  111  (e.g., may be located a millimeter a centimeter, or some other appropriate distance from the second antenna  111 ). The direction component  240  may determine a phase difference in the radio-frequency signal  260  that is received by a first antenna  111  and a second antenna  111 , based on one or more of the type of the dielectric material  250  and the dielectric constant of the dielectric material  250 . For example, the direction component  240  may determine the type of the dielectric material  250 . Based on the type of the dielectric material  250  (e.g., glass, rubber, etc.), the direction component  240  may determine the dielectric constant for the dielectric material  250 . In another example, the dielectric constant of the dielectric material  250  may be indicated in a configuration, setting, or parameter stored on the computing device  110  (e.g., may be indicated in a configuration file or setting of the computing device  111 ). 
     In some embodiments, the dielectric material  250  may alter the radio-frequency signal  260  by reducing, decreasing, etc., the propagation speed of the radio-frequency signal as it passes through the dielectric material  250 . This may allow the antenna cluster (e.g., the set of antennas  111 ) to simulate or emulate a second distance between the first antenna and the second antenna. The second distance (e.g., the simulated distance) may be larger than the first distance (e.g., the actual or physical distance between the first antenna and the second antenna). 
     In some embodiments, the direction component  240  may determine a direction of the source of the radio-frequency signal  260  or may determine the angle of arrival of the radio-frequency signal based on the phase difference. For example, the direction component  240  may use the equations (2) and (3) indicated above, to determine  6  (e.g., the angle of arrival of the radio-frequency signal  260  which may indicate the direction of the source of the radio-frequency signal or the angle of departure of the radio-frequency signal  260  from the source), based on the one or more of dielectric constant of the dielectric material  250  and the frequency (e.g., 800 megahertz, 1200 megahertz, or some other appropriate frequency) of the radio-frequency signal  260 . 
     As discussed above, the dielectric material  250  may alter the radio-frequency signal  260  by reducing (e.g., decreasing) the propagation speed of the radio-frequency signal  260  by a determined amount (e.g., an amount determined based on the type of the dielectric material  250 ). In one embodiment, slowing down the propagation speed of the radio-frequency signal  260  (e.g., reducing or decreasing the propagation speed) using the dielectric material  260  may allow the computing device to increase directional resolution or the directional precision when determining the angle of arrival of the radio-frequency signal  260  (e.g., the angle of departure or the direction of the source of the radio-frequency signal  260 ) without increasing the distance between antennas in an antenna cluster (e.g., without increasing the distance between a first antenna and a second antenna). For example, with the appropriate dielectric material  250 , the amount of distance between the first antenna and the second antenna may be reduced from twenty centimeters to two centimeters, while maintaining or improving the directional precision or directional resolution. This may allow the antenna cluster or computing device  110  to simulate or emulate a larger distance between the antennas  111  by slowing down the propagation speed of the radio-frequency signal using the dielectric material  260  (e.g., a solid dielectric material). This may also allow for a reduction in the size of antenna clusters which may allow the antenna cluster to be used in more types of devices and in more applications. In another embodiment, slowing down the propagation speed of the radio-frequency signal  260  using the dielectric material  250  may allow for better (e.g., improved) directional precision or directional resolution without increasing the size of an antenna cluster. For example, rather than increasing the size of an antenna cluster (e.g., increasing the distance between antennas) to improve directional precision or directional resolution, the appropriate dielectric material may be used. 
       FIG. 2C  illustrates an example receiver component, in accordance with some embodiments of the present disclosure. The receiver component  270  is shown to include continuous-time signal processing  272 , analog to digital converter (ADC)  274 , phase estimator  276 , and demodulator  278  all along a receive path  270 . In an embodiment, the RF signal  270  enters the continuous-time signal processing  272  where it is filtered and mixed with the local oscillator signal  273  to down-convert the desired frequency (e.g., or channel) to an intermediate frequency. In an embodiment, the down-conversion process provides the intermediate frequency as complex I and Q signals which are sampled and digitized by the ADC  274 . The phase estimator  276  may perform calculations to estimate the phase  277  of the RF signal  271  for the time it was received at the antenna using the I and Q values  275 , and forward the phase value to the demodulator  278 , which forwards the data  279  (e.g., the decoded sequence of 1s and 0s) for further processing (e.g., packet processing). The phase estimator  276  also forwards the phase  277  to the direction component  240  of  FIG. 2B  (e.g., or to a memory) for use in angle of arrival (AoA) estimation or determination, as described herein. 
       FIGS. 3A through 3H  illustrate example antenna clusters, in accordance with some embodiments of the present disclosure.  FIG. 3A  illustrates a cross-section of an antenna cluster  300 A. The antenna cluster  300 A includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3A , the dielectric material  320  has a triangular shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) on the outside of the dielectric material  320  (e.g., one on each side of the triangle). 
       FIG. 3B  illustrates a cross-section of an antenna cluster  300 B. The antenna cluster  300 B includes dielectric material  320  and four antennas  311 . As illustrated in  FIG. 3B , the dielectric material  320  has a square shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) on the outside of the dielectric material  320  (e.g., one on each side of the square). 
       FIG. 3C  illustrates a cross-section of an antenna cluster  300 C. The antenna cluster  300 C includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3C , the dielectric material  320  has a star shape (e.g., a seven point star) and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) on the outside of the dielectric material  320  (e.g., one on each concave vertex of the star). 
       FIG. 3D  illustrates a cross-section of an antenna cluster  300 D. The antenna cluster  300 D includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3D , the dielectric material  320  has a circular shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) on the outside of the dielectric material  320  (e.g., one on each of the left and right side of the circle). 
       FIG. 3E  illustrates a cross-section of an antenna cluster  300 E. The antenna cluster  300 E includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3A , the dielectric material  320  has a triangular shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) within the dielectric material  320  (e.g., one near each side of the triangle). 
       FIG. 3F  illustrates a cross-section of an antenna cluster  300 F. The antenna cluster  300 F includes dielectric material  320  and four antennas  311 . As illustrated in  FIG. 3F , the dielectric material  320  has a square shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) within the dielectric material  320  (e.g., one near each side of the square). 
       FIG. 3G  illustrates a cross-section of an antenna cluster  300 G. The antenna cluster  300 G includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3G , the dielectric material  320  has a star shape (e.g., a seven point star) and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) within the dielectric material  320  (e.g., one near each convex vertex of the star). 
       FIG. 3H  illustrates a cross-section of an antenna cluster  300 H. The antenna cluster  300 H includes dielectric material  320  and three antennas  311 . As illustrated in  FIG. 3H , the dielectric material  320  has a circular shape and the antennas  311  are disposed (e.g., located, placed, positioned, etc.) within the dielectric material  320  (e.g., one near each of the left and right side of the circle). 
     The shapes, orientations, sizes, of the dielectric material  320  and the locations of the antenna  311  illustrated in  FIGS. 3A through 3H  and described herein are non-limiting examples. In other embodiments, various shapes (e.g., geometric shapes, irregular shapes), orientations, sizes, of dielectric material  320  may be used, and any appropriate number of antennas  311  may be located in any appropriate place. For example, some antennas  311  may be located outside the dielectric material  320 , some antennas  311  may be located within the dielectric material  320  (e.g., may be enclosed or encased in the dielectric material), and some antennas  311  may be partially enclosed or encased by the dielectric material  320 . The shape of the dielectric material, the number of antennas, and the placement of the antennas (e.g., locations of one or more antennas along, inside, or partially inside a dielectric material) may be referred to as the geometry of the antenna cluster. The embodiments described herein may be applicable to various antenna clusters with different geometries. 
       FIG. 4  is a flow diagram of a method  400  of determining an angle of arrival (e.g., an angle of departure or a direction of a source of the radio-frequency signal), according to some embodiments of the present disclosure. Method  400  may be performed by processing logic that may comprise hardware (e.g., circuitry, dedicated logic, programmable logic, a processor, a processing device, a central processing unit (CPU), a multi-core processor, a system-on-chip (SoC), etc.), software (e.g., instructions running/executing on a processing device), firmware (e.g., microcode), or a combination thereof. In some embodiments, the method  400  may be performed by a direction component (e.g., direction component  240  illustrated in  FIG. 2B ), a computing device (e.g., computing device  110  illustrated in  FIG. 2B ), or a processing device (e.g., processing device  702  illustrated in  FIG. 7 ). 
     The method  400  begins at block  405 , where the method  400  receives a radio-frequency signal via a first antenna. At block  410 , the method  400  receives the radio-frequency signal via a second antenna. As discussed above, the first antenna may be located a first distance (e.g., an actual or physical distance) from the second antenna (e.g., may be located a millimeter a centimeter, or some other appropriate distance from the second antenna  111 ). In addition, a dielectric material with a dielectric constant, may be disposed (e.g., located) between the first antenna and the second antenna. The method  400  may determine a phase difference in the radio-frequency signal that is received by a first antenna and a second antenna at block  415 . For example, the method  400  may determine the phase difference, based on one or more of the type of the dielectric material, the dielectric constant of the dielectric material, and the frequency of the radio-frequency signal, as discussed above. The dielectric material may alter the radio-frequency signal by reducing, decreasing, etc., the propagation speed of the radio-frequency signal by a determined amount (e.g., an amount determined based on the type of the dielectric material) as it passes through the dielectric material  250 . At block  420 , the method  400  may determine the angle of arrival of the direction of the source of the radio-frequency signal based on one or more of the dielectric constant, frequency of the radio-frequency signal, and the propagation speed reduction caused by the dielectric material, as discussed above. 
       FIG. 5  illustrates an example computing device  110 , in accordance with some embodiments of the present disclosure. As discussed above, the computing device  110  may communicate with other devices via a network, such as a wireless network (not illustrated in the figures). The network may carry communications to and from the computing device  110  via radio-frequency signals, as discussed above. The computing device includes a direction component  240 . The direction component  240  may be hardware, software, firmware, or a combination thereof, that may determine the angle of arrival, angle of departure, or direction of a source of a radio-frequency signal, as discussed in more detail below. 
     As illustrated in  FIG. 5 , computing device  110  is coupled to two antennas  111  (e.g., an antenna cluster) located on opposite ends of a circular dielectric material  250 . The two antennas  111  may be referred to as an antenna cluster. The two antennas  111  may be coupled to each other via switching or multiplexing components. The two antennas  111  may also be coupled to one or more receivers (e.g., radio receivers) via switching or multiplexing components. As discussed above, a device may communicate with the computing device  110  by transmitting a radio-frequency (RF) signal  460  to the computing device  110 . The computing device  110  may receive the radio-frequency signal  460  via the two of antennas  111 . The radio-frequency signal  460  may be transmitted to the computing device  110  as radio waves (illustrated by the dash lines of the radio-frequency signal  460 ). Examples of radio-frequency signal  460  may be Bluetooth signals, ZigBee signals, Wi-Fi signals, etc. 
     As discussed above, it may be useful for the computing device  110  to determine the direction of a source of the radio-frequency signal  460 . Determining the direction of the source of the radio-frequency signal  460  may be referred to as determining the angle of arrival of the radio-frequency signal  460  at the computing device  110 , or may be referred to as determining the angle of departure at the source of the radio-frequency signal  460 . Also, as discussed above, equations (2) and (3) may be used to determine the angle of arrival of the radio-frequency signal  460 . 
     In one example, if the dielectric material  250  is rubber (e.g., the type of the dielectric material  250  may be rubber), the distance D between the antennas  111  may be 47.2 millimeters (mm). The dielectric material  250  (e.g., rubber) may allow the computing device  110  to determine the direction of the radio-frequency signal with the same directional resolution or directional precision as two antennas that are spaced 125 mm apart without a solid dielectric between them (e.g., with air between the two antennas). Using rubber as the dielectric material  250  may result in a 2.65 times reduction in the size of the antenna cluster. In another example, if the dielectric material  250  is polyethylene (e.g., the type of the dielectric material  250  may be polyethylene), the distance D between the antennas  111  may be 83.4 millimeters (mm). The dielectric material  250  (e.g., polyethylene) may allow the computing device  110  to determine the direction of the radio-frequency signal with the same directional resolution or directional precision as two antennas that are spaced 125 mm apart without a solid dielectric between them (e.g., with air between the two antennas). Using polyethylene as the dielectric material  250  may result in a 1.5 times reduction in the size of the antenna cluster. 
       FIG. 6  is a graph  600  illustrating example phase differences in accordance with some embodiments of the present disclosure. In one embodiment, the phase differences illustrated in graph  600  may be detected by the antennas  111  illustrated in  FIG. 5 . The Y-axis of the graph  600  represents the phase difference that was detected between the two antennas that are spaced a distance D apart. The X-axis of the graph represents the angle or direction of the radio-frequency signal. The line  610  illustrates the phase differences detected by the two antennas (spaced 47.2 mm apart) at different angles or direction when rubber is used as the dielectric material. The line  620  illustrates the phase differences detected by the two antennas (spaced the distance 125 mm apart) at different angles or direction when no solid dielectric is used (e.g., when air is used). As illustrated in the graph  600 , the rubber dielectric results in higher phase differences in the radio-frequency signal received by the two antennas. 
       FIG. 7  is a block diagram of an example device  700  that may perform one or more of the operations described herein, in accordance with some embodiments. Device  700  may be connected to other devices in a LAN, an intranet, an extranet, and/or the Internet. The device may operate in the capacity of a server machine in client-server network environment or in the capacity of a client in a peer-to-peer network environment. The device may be an electronic or computing device (such as a personal computer (PC), a tablet computer, a PDA, a smartphone, a set-top box (STB), a server computer, etc.), a network device (such as a router, switch or bridge), or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single device is illustrated, the term “device” shall also be taken to include any collection of devices that individually or jointly execute a set (or multiple sets) of instructions to perform the methods discussed herein. 
     The example device  700  may include a processing device (e.g., a general purpose processor, a PLD, etc.)  702 , a main memory  704  (e.g., synchronous dynamic random access memory (DRAM), read-only memory (ROM)), a static memory  706  (e.g., flash memory and a data storage device  718 ), which may communicate with each other via a bus  730 . 
     Processing device  702  may be provided by one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. In an illustrative example, processing device  702  may comprise a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or processors implementing a combination of instruction sets. Processing device  702  may also comprise one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processing device  702  may be configured to execute the operations described herein, in accordance with one or more aspects of the present disclosure, for performing the operations and steps discussed herein. 
     Device  700  may further include a network interface device  708  which may communicate with a network  720 . The device  700  also may include a video display unit  710  (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device  712  (e.g., a keyboard), a cursor control device  714  (e.g., a mouse) and an acoustic signal generation device  716  (e.g., a speaker). In one embodiment, video display unit  710 , alphanumeric input device  712 , and cursor control device  714  may be combined into a single component or device (e.g., an LCD touch screen). 
     Data storage device  718  may include a computer-readable storage medium  728  on which may be stored one or more sets of instructions, e.g., instructions for carrying out the operations described herein, in accordance with one or more aspects of the present disclosure. Instructions implementing instructions  726  for one or more of a direction component may also reside, completely or at least partially, within main memory  704  and/or within processing device  702  during execution thereof by device  700 , main memory  704  and processing device  702  also constituting computer-readable media. The instructions may further be transmitted or received over a network  720  via network interface device  708 . 
     While computer-readable storage medium  728  is shown in an illustrative example to be a single medium, the term “computer-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database and/or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform the methods described herein. The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media and magnetic media. 
     Unless specifically stated otherwise, terms such as “obtaining,” “transmitting,” “receiving,” “determining,” or the like, refer to actions and processes performed or implemented by computing devices that manipulates and transforms data represented as physical (electronic) quantities within the computing device&#39;s registers and memories into other data similarly represented as physical quantities within the computing device memories or registers or other such information storage, transmission or display devices. 
     Examples described herein also relate to an apparatus for performing the operations described herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general purpose computing device selectively programmed by a computer program stored in the computing device. Such a computer program may be stored in a computer-readable non-transitory storage medium. 
     Certain embodiments may be implemented as a computer program product that may include instructions stored on a machine-readable medium. These instructions may be used to program a general-purpose or special-purpose processor to perform the described operations. A machine-readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read-only memory (ROM); random-access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or another type of medium suitable for storing electronic instructions. The machine-readable medium may be referred to as a non-transitory machine-readable medium. 
     The methods and illustrative examples described herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used in accordance with the teachings described herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear as set forth in the description above. 
     The above description is intended to be illustrative, and not restrictive. Although the present disclosure has been described with references to specific illustrative examples, it will be recognized that the present disclosure is not limited to the examples described. The scope of the disclosure should be determined with reference to the following claims, along with the full scope of equivalents to which the claims are entitled. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Also, the terms “first,” “second,” “third,” “fourth,” etc., as used herein are meant as labels to distinguish among different elements and may not necessarily have an ordinal meaning according to their numerical designation. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     Although the method operations were described in a specific order, it should be understood that other operations may be performed in between described operations, described operations may be adjusted so that they occur at slightly different times or the described operations may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing. 
     Various units, circuits, or other components may be described or claimed as “configured to” or “configurable to” perform a task or tasks. In such contexts, the phrase “configured to” or “configurable to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs the task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task, or configurable to perform the task, even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” or “configurable to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks, or is “configurable to” perform one or more tasks, is expressly intended not to invoke 35 U.S.C. 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” or “configurable to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configured to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks. “Configurable to” is expressly intended not to apply to blank media, an unprogrammed processor or unprogrammed generic computer, or an unprogrammed programmable logic device, programmable gate array, or other unprogrammed device, unless accompanied by programmed media that confers the ability to the unprogrammed device to be configured to perform the disclosed function(s). 
     The foregoing description, for the purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the embodiments and its practical applications, to thereby enable others skilled in the art to best utilize the embodiments and various modifications as may be suited to the particular use contemplated. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.