Patent Application
20200191899
The present disclosure relates to systems and methods for estimating angle of arrival of wireless signals, and specifically to systems and methods for estimating angle of arrival of wireless signals that are standard agnostic in that they do not require standardized protocol or signaling schemes specifically designed for angle of arrival estimation.
Angle of arrival of wireless signals, as measured at a wireless receiver, indicates a direction from which the wireless signals were transmitted relative to the wireless receiver. Angle of arrival provides information about the spatial relationship between a transmitter and a receiver, and thus shows promise for several wireless applications such as indoor location services, asset tracking, and service discovery. Angle of arrival of wireless signals can be estimated by detecting phase differences between the wireless signals received at different antennas. Conventional angle of arrival estimation requires transmission of agreed-upon proprietary or standardized wireless signals such as a constant tone so that a receiver of the wireless signals can properly estimate the phase differences between the wireless signals as they are received on different antennas. Such an approach is not backward compatible with previous or future generations of wireless systems not having these agreed-upon signaling schemes for angle of arrival estimation. This is hampering the widespread adoption of these promising applications. In light of the above, there is a need for improved systems and methods for angle of arrival estimation.
In one embodiment, a method for operating a wireless receiver starts with receiving wireless signals from a transmitter at a first antenna and a second antenna. The wireless signals include a signal carrier and one or more data symbols modulated onto the signal carrier. Next, the one or more data symbols in the wireless signals are decoded to determine a symbol phase contribution. The symbol phase contribution is the change in the phase, amplitude, frequency, or any combination of these features of the signal carrier due to the modulation of the one or more data symbols. The one or more data symbols are each modulated onto the signal carrier during a different symbol period. Next, the phase of the wireless signals at the first antenna during one or more symbol periods is estimated to provide a first set of phase measurements. The phase of the wireless signals at the second antenna during one or more symbol periods is also estimated to provide a second set of phase measurements. The symbol phase contribution is removed from both the first set of phase measurements and the second set of phase measurements to provide a first corrected set of phase measurements and a second corrected set of phase measurements. The first corrected set of phase measurements and the second corrected set of phase measurements are then used to estimate an angle of arrival of the wireless signals. By determining the symbol phase contribution and removing it from the first set of phase measurements and the second set of phase measurements, accurate angle of arrival estimation can be performed on any arbitrary data packet, thereby foregoing the need for a specialized agreed-upon or standard-compliant signaling schemes in the transmitter.
In one embodiment, a wireless receiver includes a first antenna and a second antenna, decoder circuitry, phase estimation circuitry, and angle of arrival estimation circuitry. The first antenna and the second antenna are each configured to receive wireless signals from a transmitter, where the wireless signals include a signal carrier and one or more data symbols modulated onto the signal carrier. The decoder circuitry is coupled to the first antenna and the second antenna and is configured to receive at least a portion of the wireless signals from the first antenna and the second antenna and decode the one or more data symbols in the wireless signals to determine a symbol phase contribution. The symbol phase contribution is the change in the phase, amplitude, frequency, or any combination of these features of the signal carrier due to the modulation of the one or more data symbols. The one or more data symbols are each modulated onto the signal carrier during a different symbol period. The phase estimation circuitry is coupled to the first antenna, the second antenna, and the decoder circuitry and configured to estimate a phase of the wireless signals received at the first antenna and the second antenna at one or more symbol periods to provide a first set of phase measurements and a second set of phase measurements, respectively. Further, the phase estimation circuitry is configured to remove the symbol phase contribution from the first set of phase measurements and the second set of phase measurements to provide a first corrected set of phase measurements and a second corrected set of phase measurements, respectively. The angle of arrival estimation circuitry is coupled to the phase estimation circuitry and configured to estimate an angle of arrival of the wireless signals based on the first corrected set of phase measurements and the second corrected set of phase measurements. By determining the symbol phase contribution and removing it from the first set of phase measurements and the second set of phase measurements, accurate angle of arrival estimation can be performed on any arbitrary data packet, thereby foregoing the need for a specialized agreed-upon or standard-compliant signaling scheme in the transmitter.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. 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.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Next, the phase of the wireless signals at the first antenna is estimated to provide a first set of phase measurements (step 106). Further, the phase of the wireless signals at the second antenna is estimated to provide a second set of phase measurements (step 108). Notably, each one of the first set of phase measurements and the second set of phase measurements are discrete phase measurements during a symbol period of the data packet and thus include the symbol phase contribution. In other words, and as discussed in detail below, the first set of phase measurements and the second set of phase measurements are generally estimated serially during different ones of the one or more data symbols. Accordingly, phase differences between the first set of phase measurements and the second set of phase measurements are due in part to the spatial relationship between the first antenna and the second antenna and in part to the symbol phase contribution. Angle of arrival estimation requires knowledge of the phase differences between the first set of phase measurements and the second set of phase measurements due only to the spatial relationship between the first antenna and the second antenna. Accordingly, the symbol phase contribution is removed from the first set of phase measurements to provide a first corrected set of phase measurements (step 110) and from the second set of phase measurements to provide a second corrected set of phase measurements (step 112). When the symbol phase contribution is removed from the first set of phase measurements and the second set of phase measurements, the resulting first corrected set of phase measurements and second set of corrected phase measurements, respectively, are essentially phase measurements of the signal carrier of the wireless signal. Accordingly, phase differences between the first corrected set of phase measurements and the second corrected set of phase measurements are due only to the spatial relationship between the first antenna and the second antenna, and not due to the symbol phase contribution. Finally, angle of arrival of the wireless signals is estimated based on the first corrected set of phase measurements and the second set of corrected phase measurements (step 114). Estimating the angle of arrival of the wireless signals using the first corrected set of phase measurements and second set of corrected phase measurements may be accomplished in any number of ways which will be readily appreciated by those skilled in the art, all of which are contemplated herein. While not shown, the decoded data symbols may be passed to upstream circuitry as they usually would and subsequently acted upon.
The receiver circuitry 10 is configured to estimate the angle of arrival of the wireless signals according to the method discussed above with respect to
However, if the symbol period is too short (e.g., shorter than or comparable to the switching transients), the switching transients can prevent the detection of the data symbols by the decoder circuitry 16. In such a case, estimating the angle of arrival of the wireless signals may require more than a single data packet. Rather than requiring specialized transmitter circuitry that provides more than a single data packet to facilitate angle of arrival estimation, the present disclosure proposes using well known and standardized retransmission protocols for obtaining additional data packets necessary to perform angle of arrival estimation. For example, many wireless standards mandate retransmission of a packet if it is not acknowledged by a receiver. By taking advantage of such a retransmission protocol, a number of data packets necessary for angle of arrival estimation can be obtained by a receiver without any specialization of the transmitter.
Notably, the above data packet flows are merely exemplary. Those skilled in the art will readily appreciate that the aforementioned concepts may be applied in many different ways, all of which are contemplated herein.
When the detected edge is a positive edge of the in-phase component I_IN of the wireless signals, the edge correction signal E_CORR is provided as +180. When the detected edge is a negative edge of the in-phase component I_IN of the wireless signals, the edge correction signal E_CORR is provided as 0. When the detected edge is a positive edge of the quadrature component Q_IN of the wireless signals, the edge correction signal E_CORR is provided as +270. When the detected edge is a negative edge of the quadrature component Q_IN of the wireless signals, the edge correction signal E_CORR is provided as +90.
The edge detection signal E_DET is provided to a sampler 54, which is triggered to sample the output of a sawtooth oscillator 56 in response thereto. The sawtooth oscillator 56 provides a sawtooth output ST_OSC that varies in amplitude from 0-360 at a frequency determined by an operating frequency signal F_OP from the symbol phase contribution cancellation circuitry 50. When triggered by the edge detection signal E_DET, the sampler 54 provides a sampled sawtooth output ST_OSC(t) to an adder 58. The adder 58 also receives the edge correction signal E_CORR from the edge detection circuitry 52, and adds the two to provide a phase estimate PH_EST. The phase estimate signal PH_EST is provided to averaging circuitry 60, which averages the phase estimate signal PH_EST with one or more previous phase estimate signals to provide an averaged phase estimate AVG(PH_EST). The averaging circuitry 60 includes an averaging adder 62, a delay 64, and a divider 66. The phase estimate signal PH_EST is provided to the adder 62, where it is added to one or more previous phase estimates held in the delay 64. The combined phase estimates are provided to the divider 66 where they are divided by the number of phase estimates to provide the averaged phase estimate AVG(PH_EST). Further details regarding the phase measurement circuitry 48 can be found in co-assigned and co-pending U.S. patent application Ser. No. 16/175,184, the contents of which are hereby incorporated by reference in their entirety.
The symbol phase contribution cancellation circuitry 50 includes frequency selector circuitry 68, which receives a positive frequency offset signal +Δf, a negative frequency offset signal −Δf, and a data symbol DATA_SYM and provides one of the positive frequency offset signal +Δf and the negative frequency offset signal −Δf as a frequency offset value F_OFF. Which one of the positive frequency offset signal +Δf and the negative frequency offset signal −Δf depends on the data symbol DATA_SYM. Those skilled in the art will appreciate that in continuous phase frequency shift keying (CPFSK) systems, the frequency is modulated by ±Δf to convey different data symbols. For example, in BTLE systems, the frequency is modulated by ±250 kHz, and for Zigbee systems the frequency is modulated by ±500 kHz. The frequency offset value F_OFF thus is indicative of the data symbol DATA_SYM.
The frequency offset value F_OFF is added to a known intermediate frequency F_IF of the wireless signals and an estimated carrier frequency offset CF_OFF of the wireless signals by an adder 70 to provide an operating frequency signal F_OP. The carrier frequency offset CF_OFF may be determined, for example, when decoding the preamble of one of the data packets. The operating frequency signal F_OP is provided to the phase estimation circuitry 50 and a multiplier 72, where it is multiplied by a symbol period P_SYM*2π to provide a symbol phase contribution SYM_PH_CN, which, as discussed above is the phase of the signal carrier due to modulation of the current data symbol DATA_SYM. The symbol phase contribution SYM_PH_CN is accumulated with previously determined symbol phase contributions for preceding symbols in the data packet to provide an accumulated symbol phase contribution ACC(SYM_PH_CN). This is because in CPFSK systems, the symbol phase contribution of each data symbol is influenced by the symbol phase contribution of the data symbols that preceded it. The accumulator 74 includes an adder 76 and a delay 78. The symbol phase contribution SYM_PH_CN is provided to the adder 76, where it is added to one or more previous symbol phase contributions held in the delay 78.
The accumulated symbol phase contribution ACC(SYM_PH_CN) is provided to a subtractor 80 in the phase measurement circuitry 48, where it is subtracted from the averaged phase estimate AVG(PH_EST) to provide a corrected phase CORR_PH. As discussed above, the corrected phase is indicative of the phase of the carrier signal only, without the influence of the symbol phase contribution. Notably, while the phase measurement circuitry 48 may not measure the phase of the wireless signals during every data symbol of a packet, the symbol phase contribution cancellation circuitry 50 nevertheless accumulates a symbol phase contribution for each symbol in the packet, since, as discussed above, the symbol phase contribution of each data symbol may be dependent on the symbol phase contribution of every preceding data symbol.
In some situations, it may still be desirable to transmit a specific data packet for purposes of angle of arrival estimation. However, this packet may still be compatible with the wireless standards employed by a transmitter while providing improved accuracy and performance for angle of arrival estimation. First, a known sequence of data symbols may be transmitted. By transmitting a known sequence of data symbols, the overhead associated with detecting symbol phase contribution is foregone. Further, doing so may provide improved performance by allowing for the selection of a desirable symbol sequence and packet length that improves the accuracy of angle of arrival estimation. Accordingly,
Those skilled in the art will appreciate that in a minimum-shift keying (MSK) modulation scheme, each data symbol is made up of a number of chips, which are represented as 1 or 0, as shown in
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
