System and methods for generating constructed channel impulse response estimate

Abstract

A method for determining a channel impulse response (CIR) estimation for an ultra-wideband (UWB) channel. The method includes: receiving a first sequence of chips transmitted a first power level and a second sequence of chips transmitted at a second power level, the first power level being different from the second power level; determining a first CIR from the first sequence of chips and a second CIR from the second sequence of chips; and computing a CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR move.

Description

Attorney Docket No. 62306.129WO01 SYSTEM AND METHODS FOR GENERATING CONSTRUCTED CHANNEL IMPULSE RESPONSE ESTIMATE CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application No. 63 / 568,157, filed March 21, 2024, which is incorporated herein by reference in its entirety. FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to channel estimation in ultra-wideband (UWB) communication, in particular, to system and methods for generating a constructed channel impulse response estimate (CIRE). BACKGROUND

[0003] Ultra-wideband (UWB) is a wireless communication technology that uses a wide bandwidth, typically about 500MHz or larger, or has a 10dB bandwidth greater than 20% of the center frequency. Impulse UWB (IR-UWB) is a specific case of UWB in which the signal is transmitted in very short pulses (in the order of nano seconds). It is particularly adapted for ranging or sensing application as the pulses are robust against multipath. Another advantage of IR-UWB is its ability to transmit data with very low power consumption.

[0004] Radar systems, including UWB-based radars, can be used to sense the environment by providing a means of obtaining propagation channel measures. The propagation channel is due to the reflections of the transmitted signal on the environment. The channel measures usually take the form of a set of periodic channel impulse response estimates (CIRE). Each CIRE's complex components (taps) corresponds to a propagation delay of the reflected signal and thus to a reflecting target's distance. In a mono-static radar such as a transceiver, the CIR estimate may contain some saturated taps in the short distance range because of the strong spill-over of the transmitted signal directly from the transmitter (TX) antenna to the receiver (RX) antenna. Saturated taps are blind, they do not contain information anymore and thus cannot be used for radar post-processing purposes. Thus, a method and a system to estimate CIR to reduce the impact of spill-over are desired. SUMMARY

[0005] An aspect of the present disclosure provides a method for determining a channel impulse response (CIR) estimation for an ultra-wideband (UWB) channel. The method includes:Attorney Docket No. 62306.129WO01 receiving a first sequence of chips transmitted a first power level and a second sequence of chips transmitted at a second power level, the first power level being different from the second power level; determining a first CIR from the first sequence of chips and a second CIR from the second sequence of chips; and computing a CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR.

[0006] In some embodiments, the second power level is lower than the first power level by between about 20 dB and about 40 dB.

[0007] In some embodiments, a first path index of the first CIR and the first path index of the second CIR are at a same location.

[0008] In some embodiments, the computing of the CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR includes: dividing the first CIR and the second CIR into a plurality of sections each with a respective fast time index range; in each of the plurality of sections, determining a first weight value for the first CIR and a second weight value for the second CIR; multiplying sections of the first CIR with respective weight values to obtain a weighted first CIR and sections of the second CIR with respective weight values to obtain a weighted second CIR; and combining the first CIR and the second CIR by adding weighted first CIR and weighted second CIR.

[0009] In some embodiments, the dividing of the first CIR and the second CIR into a plurality of sections each with a respective fast time index range includes: determining a first section having a first fast time index ranging corresponding to a precursor tap signal before a saturated signal; determining a second section having a second fast time index ranging corresponding to the saturated signal; and determining a third section having a third fast time index ranging corresponding to a tap signal after the saturated signal.

[0010] In some embodiments, the method further includes storing the fast time index range for each section prior to the computing of the CIR.

[0011] In some embodiments, the first sequence of chips are transmitted in a first field, and the second sequence of chips are transmitted in a second field different from the first field.

[0012] In some embodiments, the first sequence of chips and the second sequence of chips are transmitted in different fields of a same frame.

[0013] In some embodiments, the first sequence of chips include a ternary sequence in a preamble field of the frame; and the second sequence of chips include a scrambled timestamp sequence (STS) in a STS field of the frame.

[0014] In some embodiments, the first sequence of chips and the second sequence of chips are respectively transmitted in consecutive frames; and the first frame is transmitted at the firstAttorney Docket No. 62306.129WO01 power level and the second frame is transmitted at the second power level.

[0015] In some embodiments, the first sequence of chips and the second sequence of chips are each a STS in the respective STS field.

[0016] In some embodiments, the method further includes receiving one or more other first sequences of chips in the first field and one or more other second sequences of chips in the second field, wherein a total number of the first sequence and the other first sequence of chips is same as a total number of the second sequence and the other second sequence of chips.

[0017] Embodiments of the present disclosure provide an ultra-wide band (UWB) device. The UWB device includes a receiver operable to perform a UWB communication. The UWB device also includes a memory for storing program instructions, weight parameters, cipher codes, and channel-impulse responses accumulated from the cipher codes, and a processor coupled to the receiver and to the memory. The processor is operable to execute the program instructions, which, when executed by the processor, cause the UWB device to perform the following operations: receiving a first sequence of chips transmitted a first power level and a second sequence of chips transmitted at a second power level, the first power level being different from the second power level; determining a first CIR from the first sequence of chips and a second CIR from the second sequence of chips; and computing a CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR.

[0018] In some embodiments, the second power level is lower than the first power level by between about 20 dB and about 40 dB.

[0019] In some embodiments, a first path index of the first CIR and the first path index of the second CIR are at a same location.

[0020] In some embodiments, the computing of the CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR includes: dividing the first CIR and the second CIR into a plurality of sections each with a respective fast time index range; in each of the plurality of sections, determining a first weight value for the first CIR and a second weight value for the second CIR; multiplying sections of the first CIR with respective weight values to obtain a weighted first CIR and sections of the second CIR with respective weight values to obtain a weighted second CIR; and combining the first CIR and the second CIR by adding weighted first CIR and weighted second CIR.

[0021] In some embodiments, the dividing of the first CIR and the second CIR into a plurality of sections each with a respective fast time index range includes: determining a first section having a first fast time index ranging corresponding to a precursor tap signal before a saturated signal; determining a second section having a second fast time index ranging corresponding toAttorney Docket No. 62306.129WO01 the saturated signal; and determining a third section having a third fast time index ranging corresponding to a tap signal after the saturated signal.

[0022] In some embodiments, the method further includes storing the fast time index range for each section prior to the computing of the CIR.

[0023] In some embodiments, the first sequence of chips are transmitted in a first field, and the second sequence of chips are transmitted in a second field different from the first field.

[0024] In some embodiments, the first sequence of chips and the second sequence of chips are transmitted in different fields of a same frame.

[0025] In some embodiments, the first sequence of chips include a ternary sequence in a preamble field of the frame; and the second sequence of chips include a scrambled timestamp sequence (STS) in a STS field of the frame.

[0026] In some embodiments, the first sequence of chips and the second sequence of chips are respectively transmitted in consecutive frames; and the first frame is transmitted at the first power level and the second frame is transmitted at the second power level.

[0027] In some embodiments, the first sequence of chips and the second sequence of chips are each a STS in the respective STS field.

[0028] In some embodiments, the method further includes receiving one or more other first sequences of chips in the first field and one or more other second sequences of chips in the second field, wherein a total number of the first sequence and the other first sequence of chips is same as a total number of the second sequence and the other second sequence of chips.

[0029] 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. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0030] 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.

[0031] FIG.1A illustrates an exemplary communication system having a transmitter (TX) and a receiver (RX), according to some embodiments of the present disclosure.

[0032] FIG.1B illustrates a block diagram of a receiver for generating a constructed CIRE, according to some embodiments of the present disclosure.

[0033] FIG.1C shows a CIRE with a spill-over tap.

[0034] FIG.1D shows examples of frame structures, according to some embodiments of theAttorney Docket No. 62306.129WO01 present disclosure.

[0035] FIG.2A shows a constructed CIRE, according to some embodiments of the present disclosure.

[0036] FIG.2B illustrates exemplary coefficients used in constructing a CIRE, according to some embodiments of the present disclosure.

[0037] FIG.3A illustrates examples of initial CIRE’s used in generating a constructed CIRE, according to some embodiments of the present disclosure.

[0038] FIG.3B illustrates an example of a constructed CIRE generated from the initial CIRE’s shown in FIG.3A, according to some embodiments of the present disclosure.

[0039] FIG.4 shows a method for generating a constructed CIRE, according to some embodiments of the present disclosure.

[0040] FIG.5 illustrates a flowchart for generating a constructed CIRE, according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0041] 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.

[0042] 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.

[0043] 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 orAttorney Docket No. 62306.129WO01 addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0044] 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. Additionally, like reference numerals denote like features throughout specification and drawings.

[0045] It should be appreciated that the blocks in each signaling diagram or flowchart and combinations of the signaling diagrams or flowcharts may be performed by computer program instructions. Since the computer program instructions may be equipped in a processor of a general-use computer, a special-use computer or other programmable data processing devices, the instructions executed through a processor of a computer or other programmable data processing devices generate means for performing the functions described in connection with a block(s) of each signaling diagram or flowchart. Since the computer program instructions may be stored in a computer-available or computer-readable memory that may be oriented to a computer or other programmable data processing devices to implement a function in a specified manner, the instructions stored in the computer-available or computer-readable memory may produce a product including an instruction for performing the functions described in connection with a block(s) in each signaling diagram or flowchart. Since the computer program instructions may be equipped in a computer or other programmable data processing devices, instructions that generate a process executed by a computer as a series of operational steps are performed by the computer or other programmable data processing devices and operate the computer or other programmable data processing devices may provide steps for executing the functions described in connection with a block(s) in each signaling diagram or flowchart.

[0046] Each block may represent a module, segment, or part of a code including one or more executable instructions for executing a specified logical function(s). Further, it should also be noted that in some replacement execution examples, the functions mentioned in the blocks may occur in different orders. For example, two blocks that are consecutively shown may be performed substantially simultaneously or in a reverse order depending on corresponding functions.

[0047] Hereinafter, embodiments are described in detail with reference to the accompanyingAttorney Docket No. 62306.129WO01 drawings. Further, although a communication system using ultra-wideband (UWB) is described in connection with embodiments, as an example, the embodiments may also apply to other communication systems with similar technical background or features. For example, a communication system using Bluetooth or ZigBee may be included therein. Further, embodiments may be modified in such a range as not to significantly depart from the scope of the present disclosure under the determination by one of ordinary skill in the art and such modifications may be applicable to other communication systems.

[0048] UWB may refer to a short-range high-rate wireless communication technology using a wide frequency band of several GHz or more, low spectral density, and short pulse width (e.g., 1 nsec to 4 nsec) in a baseband state. UWB may mean a band itself to which UWB communication is applied. UWB may enable secure and accurate ranging between devices. Thus, UWB enables relative position estimation based on the distance between two devices or accurate position estimation of a device based on the distance from fixed devices (whose positions are known, also referred to as anchor devices). The present disclosure assumes that the user is carrying a device capable of communicating through UWB (referred to as “UWB- enabled device” or simply as “UWB device”).

[0049] In this disclosure, a symbol is a sequence of chips. Term “symbol” and term “sequence” may be used interchangeably.

[0050] As used herein, a tap in a channel impulse response (CIR) refers to a specific path through which a signal travels from the transmitter to the receiver.

[0051] Currently, it is possible to avoid the spill-over (e.g., saturation) and prevent the blind zone by reducing the transmit power. But this can significantly reduce the coverage range of the UWB communication. The existing solution includes setting the transmission power from prior knowledge of the target of interest position. If the target is located far away from the UWB radar (e.g., UWB transceiver), the max power (of long-range mode) may be used. The short-range CIR taps are then saturated but this does not impact the detection of this long- range target. On the other hand, if it is located close to the UWB radar, the maximal power (of short-range mode) to prevent the saturation of the short-range CIR taps may be applied to allow the post processing of the short-range CIR taps. This latter power is often device dependent, closely related to the TX to RX antenna isolation, and can be measured by a short- range calibration procedure. However, the existing solution does not work if the position of the target of interest is completely unknown.

[0052] Embodiment of the present disclosure describes a novel system and method for generating a constructed channel impulse response estimate (CIRE) that has desirableAttorney Docket No. 62306.129WO01 properties in both short and long ranges without prior knowledge of the position of targe of interest. To generate the constructed CIRE, the RX may receive two initial (e.g., “raw”) CIR estimates accumulated from two sequences of chips, with one transmitted at a higher power level (e.g., in long-range mode) and the other one transmitted at a lower power level (e.g., in short-range mode). The two initial CIR estimates may be weighted and summed up to generate a constructed CIRE, of which all CIR taps contain useful signals. The weight parameters (e.g., combining factors) of the two initial CIR estimates may be predetermined and stored in the RX, and the receiver may access the weight parameters and generate the constructed CIRE in a timely manner. In some embodiments, the two sequences of chips are transmitted in different fields. For example, the two sequences may be transmitted in the same frame with a predefined code sequence (e.g., Ipatov sequence) transmitted in the preamble field at the higher power level, and a scrambled timestamp sequence (STS) transmitted in the STS field at the lower power level. In another example, the two sequences may be transmitted respectively in two consecutive frames, with one frame containing the predetermined sequence (e.g., a ternary sequence) transmitted at the higher power level and the other frame containing the STS transmitted at the lower power level.

[0053] The disclosed constructed CIRE may contain taps each reflecting the characteristics of the UWB channel, and may be used to more accurately determine condition of the UWB channel without prior knowledge of the approximate location of the target. Also, the weight parameters / coefficients corresponding to the sequences may be predetermined and stored, and thus does not increase the computation load of the receiver when determining the constructed CIRE.

[0054] FIG.1A illustrates a simplified block diagram of a radio frequency (RF) communication system 100, according to some embodiments of the present disclosure. RF communication system 100 may be an example of a mono-static radar, and may be configured to detect the position of a target 114. RF communication system 100 may include a RX / TX module 102, a RX control module 106, a TX control module 108, a CIR estimation module 110, and a CIR storage and processing module 112. It should be noted that, FIG.1A is merely a simplified block diagram, and may include additional signal processing components not shown in the figure.

[0055] RX / TX module 102 may be configured to transmit a first RF signal 146 and receive a second RF signal 148. In some embodiments, first RF signal 146 may include a UWB signal (e.g., a UWB pulse), and second RF signal 148 may include a combination of first RF signals 146 after a plurality of delays in the time domain. For example, second RF signal 148 may beAttorney Docket No. 62306.129WO01 formed by the multi-path propagation of first RF signal 146 that encounters direct transmission, reflections, diffractions, and / or scattering in the environment. First RF signal 146 may take multiple paths of varying lengths to reach back to RX / TX module 102, forming second RF signal 148. For example, first RF signal 146 may include a UWB pulse, and second RF signal may include a plurality of pulses 148a, 148b, 148c, ….

[0056] RX / TX module 102 may include a transmitter configured to transmit first RF signal 146, which may be a baseband signal of a few nanoseconds in the time domain. The transmitter may include a transmitter antenna 124, an amplifier 128, a mixer 138, a transmit power gain (TXPG) module 144. Amplifier 128 may be electrically coupled to transmitter antenna 124 and mixer 138, which may further be electrically coupled to TXPG module 144. The transmitter may further include a TX control module 108 electrically coupled to amplifier 128. TXPG module 144 may be configured to apply a gain or amplification on first RF signal 146. Mixer 138 may be configured to mix the output of TXPG module 144 with a carrier signal. The mixing process may also be referred to as an up-conversion. The output of the mixer 138, e.g., a first mixed signal including the baseband signal and the carrier signal, may then go through amplifier 128, e.g., a power amplifier, which amplifies the first mixed signal under the control of TX control module 108. For example, TX control module 108 may control the transmission power of the amplified first mixed signal, e.g., higher power level for the long- range mode and lower-power for the short-range mode Receiver antenna 124 may then transmit the amplified first mixed signal. The amplified first mixed signal may undergo multipath propagation and be received by RX / TX module 102 as second RF signal 148.

[0057] RX / TX module 102 may also include a receiver configured to receive and process second RF signal 148, which may include a series of pulses with delays. The receiver may include a receiver antenna 122, a mixer130, one or more amplifiers (e.g., 126 and 132), an analog-to- digital converter (ADC) 140, a CIR estimation module 110, and a CIR storage and processing module 112. Receiver antenna 122 may first receive second RF signal 148. Amplifier 126 may amplify the received second RF signal 148. Mixer 130 may mix second RF signal 148 with a local oscillator (LO) signal, resulting a second mixed signal that contains both the sum and difference frequencies. The LO signal may shift second RF signal 148 down to a lower intermediate frequency or directly to the baseband. The mixing may also be referred to as a down-conversion. The second mixed signal may be amplified by the amplifier 132(e.g., a power amplifier), and may further be converted to digital signals by ADC 140. The digital signals may be used by CIR estimation module 110 to generate a CIRE, which may further be stored and / or processed by CIR storage and processing module 112.Attorney Docket No. 62306.129WO01

[0058] As shown in FIG.1A, the amplified first mixed signal transmitted from transmitter antenna 124 may propagate along a path 116 and is reflected to receiver antenna 122 by a target 114, and along a path 118 (e.g., a direct path) and is transmitted directly to receiver antenna 122 without encountering any object. Meanwhile, amplified first mixed signal may leak from amplifier 128 to amplifier 126 along a path 120 (e.g., a leakage path). As a result, the signals received from paths 118 and 120 may contribute to a pulse signal 148a of undesirably high power, exceeding the thresholds of an ADC. The signal received from path 116 may result in a pulse signal 148b of a lower power. In an example, the signal received from another path (not shown) may result in a pulse signal 148c. Pulse signal 148a may cause ADC to saturate, and a CIRE generated based on second RF signal 148 may have a spill-over tap (resulting from pulse signal 148a), which may potentially mask pulse signal 148b and affect the post-processing of second RF signal 148. As a result, the location of the target may not be accurately determined.

[0059] FIG.1C shows a CIR 152 with a spill-over tap. As an example, CIR 152 includes taps / paths 152a, 152b, and 152c. Tap 152a (e.g., the spill-over tap) is caused by the spill-over of pulse signal 148a, while tap 152b is caused by the reflection of pulse signal 146 from a target. Tap 152a does not contain useful information. In the time domain, tap 152a and 152b can be close enough that tap 152b is partially or fully masked by tap 152a. As a result, the location of the target may not be accurately determined.

[0060] In existing technology, to detect the position of a target without being affected by the spill-over, the approximate position of the target may be known from prior knowledge. The receiver may include a RX control module 106, which may control the settings of amplifiers 126 and 132, and ADC 140. For long-range detection and short-range detection, TX control module 108 may be configured to control the amplification of amplifier 128 such that the transmitter may transmit signals of a higher power level for the long-range mode and signals of a lower power level for the short-range mode, based on prior knowledge of the position of the target. Accordingly, RX control module 106 may control amplifiers 126 and 132, and ADC 140 for the reception of signals of the higher / lower power level, respectively. For example, amplifier 126 may provide a higher amplification for receiving the signal of the lower power level, and provide a lower amplification for receiving the signal of the higher power level. RX control module 106 can switch between the long-range mode and the short- range mode, and adjust the settings of amplifiers 126 and 132, and / or ADC 140 accordingly. CIR estimation module 110 may then generate CIRE for the higher power and the lower power, respectively.Attorney Docket No. 62306.129WO01

[0061] Embodiments of the present disclosure provide a method to construct a CIRE less susceptible to the impact of spill-over, without any prior knowledge of the position of the target. Different from the existing technology, RX / TX may not need to operate under a long- range mode or a short-range mode. Instead, the transmitter may transmit one or more frames that contain a first sequence transmitted at a higher power level and a second sequence transmitted at a lower power level, the receiver may compute the CIR’s from the two sequences, and may combine them to obtain a constructed CIRE that more accurately represents the channel characteristics. The first sequence and the second sequence may be transmitted in different fields. The number of first sequences in the field corresponding to the higher power level may be equal to the number of second sequences in the field corresponding to the lower power level. The first and second sequences may be received by the receiver at about the same time to correspond to the same environment (e.g., channel condition or characteristics). In some embodiments, TX control module 108 may be configured to control the power levels for transmitting the fields and / or frames.

[0062] In one embodiment, the transmitter may transmit a single frame with the first sequence in the preamble field, and a second sequence in the scrambled timestamp sequence (STS) field. For example, the first sequence may include an Ipatov sequence (e.g., a predefined code sequence) and the second sequence may include a STS. The two sequences may be transmitted at different power levels. In an example, the first sequence may be transmitted at a higher power level, and the second sequence may be transmitted at a lower power level. In some embodiments, the difference between the two power levels may be between about 20dB and about 40dB. For example, the Ipatov sequence may be transmitted at 0 dB and the STS may be transmitted at -30dB; or the Ipatov sequence may be transmitted at -18 dB, and the STS may be transmitted at -40 dB; and so on. The constructed CIRE may be computed by combining initial CIR’s of the first sequence and the second sequence.

[0063] In another embodiment, the transmitter may transmit two consecutive frames, with a first frame at a higher power level and a second frame at a lower power level. The first sequence (e.g., an Ipatov sequence) may be transmitted in the preamble field of the first frame, and the second sequence (e.g., STS) may be transmitted in the STS field in the second frame. The two consecutive frames may be received by the receiver at approximately the same time. In some embodiments, the difference between the two power levels may be between about 20dB and about 40dB. For example, the first frame may be transmitted at 0 dB and the second frame may be transmitted at -30dB; or the first frame may be transmitted at -18 dB, and the second frame may be transmitted at -40 dB; and so on. The constructed CIRE may be computed byAttorney Docket No. 62306.129WO01 combining initial CIR’s of the first sequence and the second sequence.

[0064] In another embodiment, the transmitter may transmit two consecutive frames, with a first frame at a higher power level and a second frame at a lower power level. Each frame may include a respective first sequence (e.g., an Ipatov sequence) in the preamble field and a respective second sequence (e.g., STS) in the STS field in the second frame. The two consecutive frames may be received by the receiver at approximately the same time. In some embodiments, the difference between the two power levels may be between about 20dB and about 40dB. For example, the first frame may be transmitted at 0 dB and the second frame may be transmitted at -30dB; or the first frame may be transmitted at -18 dB, and the second frame may be transmitted at -40 dB; and so on. The constructed CIRE may be computed by combining initial CIR’s obtained from the two first sequences (e.g., two Ipatov sequences).

[0065] In an embodiment, the settings of amplifiers 126 and 132, mixer 130, and / or ADC 140 are predetermined and stay unchanged during the reception of second RF signal 148. For example, the settings stay unchanged within a frame or from one frame to another. In an embodiment, when the transmitter transmits a first RF signal 146 having a single frame having fields of a higher power level and a lower power level, or two consecutive frames respectively at a higher power level and a lower power level, and the receiver (e.g., amplifiers 126 and 132, mixer 130, and ADC 140) may process second RF signal 148. For example, the receiver may process the frame(s) for generating initial CIR’s respectively corresponding to the higher power level and the lower power level. In some embodiments, the single frame and / or the two consecutive frames are received and process in the same path (e.g., only branch having amplifiers 126 and 132, mixer 130, and ADC 140 of the receiver) such that the initial CIR’s of different power levels may have the same phase. Estimation module 110 may compute the initial two CIR’s respectively to generate a constructed CIRE 150, which may then be stored and / or further processed by CIR storage and processing module 112.

[0066] FIGS.1D (I)-(IV) illustrate examples of different frame structures that can be used in the embodiments of the present disclosure. In FIG.1D, preamble field 162 (e.g., also referred as “sync”) includes a sync pattern that is a sequence of chips forming a frame preamble, and may be based on a predefined code sequence (e.g., Ipatov sequence) having certain properties that make it useful for channel sounding purposes (including perfect periodic audio-correlation). Preamble field 162 can be used to transmit a ternary sequence of perfect autocorrelation properties (e.g., an Ipatov sequence). In some embodiments, the receiver is triggered by the transmitter, and the settings of the receiver are predetermined. In some embodiments, no synchronization is needed for the embodiments of the present disclosure. SFD field 164Attorney Docket No. 62306.129WO01 represents start frame delimiter, which often consists of a fixed sequence that serves as a start pattern and marks the beginning of the frame. SFD field 164 indicates the end of preamble field 162 and the precise start of the switch to physical layer header (PHR) field 168. PHR field 168 includes physical layer header and indicates the start of the actual data held in the data packet. PHR field 168 contains information about the payload (e.g., MAC data field 170). Scrambled timestamp sequence (STS) 166 field represents a cipher sequence / code (e.g., a STS) that is cryptographically generated bits. The cipher sequence often includes of pulses of pseudo-random polarity, which would not be repeatable or predictable. The cipher sequence can be generated by a cryptographically secure pseudorandom number generator. Mac data 170 field includes the payload, e.g., actual data, transmitted in the data packet.

[0067] In some embodiments, the first sequence and the second sequence may be transmitted in different fields of the same frame, which may have any one of the frame structures (I)-(III). For example, the first sequence (e.g., Ipatov sequence) may be transmitted at a higher power level in preamble field 162 of frame structure (II), and the second sequence (e.g., STS) may be transmitted in STS field 166 of frame structure (II). In some other embodiments, the first sequence and the second sequence may be transmitted in two consecutive frames. Each one of the consecutive frames may be any one of the frame structures (I)-(III). For example, the first sequence (e.g., Ipatov sequence) may be transmitted at a higher power level in preamble field 162 of frame structure (II), and the second sequence (e.g., STS) may be transmitted in STS field 166 of frame structure (III). In some embodiments, frame structure (IV) may be used in the transmission of two consecutive frames with respective higher and lower power levels, and at least one (or each) of the two frame structures include a first sequence (e.g., Ipatov sequence) in the respective preamble field 162.

[0068] In various embodiments, RX control module 106 may be configured to control the settings of amplifiers 126 and 132, and ADC 140, such that the receiver may process the field / frame at a desired power level.

[0069] CIR estimation module 110 may compute the initial CIR’s at the higher power level and the lower power level, from respective sequences. CIR estimation module 110 may obtain a first set of weight parameters (coefficients) corresponding to the higher power level and a second set of weight parameters corresponding to the lower power level, and combine the two initial CIR’s using respective weight parameters. For example, the initial CIR computed from the first sequence may be weighted by the first set of weight parameters, and the initial CIR computed from the second sequence may be weighted by the second set of weight parameters. The weighted initial CIR’s may be summed up to generate a constructed CIRE. In someAttorney Docket No. 62306.129WO01 embodiments, the weight parameters may be predetermined and stored in the receiver (or in a memory accessible by the receiver). The details of the operations of CIR estimation module 110 may further be described below.

[0070] FIG.1B shows a simplified block diagram of a receiver 101, according to some embodiments of the present disclosure. .Receiver 101 may be an example of the receiver in RX / TX module 102. Receiver 101 may include an analog and radio frequency (RF) and baseband (BB) processing circuit 105 that takes the received first and / or second sequences and provides front-end processing (e.g., amplification, filtering, down-conversion to a BB frequency) and passes a BB signal to an in-phase / quadrature (I / Q) sampling circuit 107. A sampled first and / or second sequences may be transmitted to a correlator 109. Correlator 109 may correlate the sampled first and / or second sequences and the first and / or second sequences stored in memory 117. After the cross-correlation, the correlated signals are transmitted to a CFO remover 111 that removes the CFO in the correlated signals. In some embodiments, CFO remover 111 is optional or disabled for a monostatic radar because the receiver and the transmitter share the same crystal. The signals after the optional CFO removal are then transmitted to an accumulator 113 to be accumulated. An initial CIR can be generated from the accumulated signal. In some embodiments, initial CIR’s respectively corresponding to the first sequence (e.g., higher power level) and the second sequence (e.g., lower power level) may be generated by accumulator 113 and may be stored in memory 117 accessible by accumulator 113. In some embodiments, a control circuit 115 may obtain the initial CIR’s, weight parameters from memory 117, and generate a constructed CIRE (detailed described in below) by summing up the weighted initial CIR’s. In some embodiments, control circuit 115 may also compute a time of flight (TOF) and / or a distance from the target based on the constructed CIRE. In various embodiments, receiver 101 may include any suitable hardware and / or software to implement the operations of the present disclosure.

[0071] Receiver 101 may include one or more general-purpose processors and / or one or more special-purpose processors (such as digital signal processing chips, graphics acceleration processors, microcontrollers, and / or the like) to perform the functions and operations of control circuit 115, analog RF and BB circuit 105, I / Q sampling circuit 107, correlator 109, CFO remover 111, and accumulator 113. The processor(s) may process the RF signals received by receiver antenna 122, and output the CIRE for further processing. Memory 117 may include one or more non-transitory storage devices that can include local and / or network accessible storage, a disk drive, a drive array, an optical storage device, a solid-state storage device such as a random access memory (“RAM”) and / or a read-only memory (“ROM”), aAttorney Docket No. 62306.129WO01 programmable ROM, a flash-updateable ROM, and / or the like. Such storage devices may be configured to implement any appropriate data storage, including without limitation, various file systems, algorithms, initial CIR”s, constructed CIRE, and / or the like.

[0072] In various embodiments, functions / operations may be stored as one or more instructions or code in memory 117, such as on a computer-readable storage medium, such as RAM, ROM, FLASH, or disc drive, and executed by the processor(s). Memory 117 may also be stored with software components including, for example, an operating system, device drivers, executable libraries, and / or other executable code, such as one or more application programs. The application programs may include computer programs, stored in memory 117, executed by the processor(s) 203 to implement various functions under the control of the operating system. In some embodiments, the processor(s) may also be configured to control the operations of the transmitter, e.g., controlling the transmission of pulses and / or power of transmitted frames. For example, the processor(s) may be shared by the receiver and the transmitter of RX / TX module 102.

[0073] FIG.2A illustrates an example of constructed CIRE 150, according to some embodiments of the present disclosure. In some embodiments, the first sequence (e.g., Ipatov sequence) may be transmitted at a higher power level in the preamble field of a frame, and the second sequence (e.g., STS) may be transmitted at a lower power level in the STS field of the same frame. For example, the preamble of the frame may be transmitted at the higher power level, and the STS field may be transmitted at the lower power level. As described in FIG.1A, CIR estimation module 110 may receive two initial CIR’s, i.e., a first initial CIR ^^^^^^^ ^^^^computed from the first sequence and corresponding to the higher power level, and a second initial CIR ^^^^^^^ ^^^^ computed from the second sequence and corresponding to the lowerpower level, m and k respectively representing the slow time index and the fast time index.

[0074] CIR estimation module 110 may obtain predetermined (e.g., prestored) weight parameters for the first and second initial CIR’s from memory 117, respectively. In some embodiments, the weight parameters may be stored in the form of a look-up table, in which the weight parameter(s) at different ranges of k are predetermined. FIG.2B illustrates a look-up table 200 with different values of weight parameters corresponding to different ranges of k. Weight parameter ^^^^^ may correspond to the first initial CIR (e.g., for the higher power level) and weight parametermay correspond to the second initial CIR (e.g., for the lower power level). The values of ^^^^^ and ^^^^^ may be defined in four ranges of k: (1, 10), (11, 15), (16, 20), and (21, 22). The constructed CIRE may be expressed as:Attorney Docket No. 62306.129WO01 ^^^^^ ^^ ^ ^^^^^^^^^^^ ^^ ^ ^^^^^^^^^^^ ^^

[0075] In some embodiments, the estimates ^ ^ ^^^ ^^ (e.g., first initial CIR and second initialCIR) are each equal to the true value plus a noise. ^^^^^^ ^^ ^ ^^^^^ ^^ ^^^^^^^ ^^

[0076] In some embodiments, it is assumed that the noise power (e.g., noise variance level) is independent of the slow and fast time indices, e.g., ^^^^^ ^^^. It is thus reasonable to assume that the noise is stationary over theslow time ^ and the noise power may depend on the tap index (or fast time index) ^. In some embodiments, if the noise variances of the initial CIR’s are tap independent, then ^L(k) and ^H(k) may be determined as:

[0077] In some embodiments, the weight parameters may be defined in such a way that the power of the taps (CIR taps) stays linked to the target distance as it is on each initial CIR on the non-saturated taps, as shown in FIG.2B. The initial CIR’s may be divided into 3 sections along the fast time index: 1. From 1 to ^#: The precursor taps, before the spill-over tap. For ease of illustration, no precursor taps are shown in FIG. 2A.2. From ^# ^ ! to ^$^: The spill-over taps, e.g., all the taps where the spill-oversignal is predominant. This is where the saturated taps are located in long-range mode in existing technology. Referring back to FIG. 1C, the locations of k0and ksare shown in view of CIR 152, which is an example of CIR suffering from spill-over.3. From ^$ ^ ! to the end: the taps after the spill-over tap.

[0078] In the section 3, the first initial CIR (e.g., corresponding to the higher power level) is not saturated and may be used / preferred over the second initial CIR (e.g., corresponding to the lower power level) as it has a better signal-to-noise ratio (SNR). In section 2, the first initial CIR and the second initial CIR may both be used to obtain a relevant power more accurately.

[0079] In some embodiments, k0 and ks are predetermined, and their values for computation / construction may be obtained from table 200. In some embodiments, for sake of reducing the computational complexity, ^^^^^ and ^^^^^ have been selected as powers of 2. Thus, the computation of the mixed weight parameters is just two bit-shift and one addition.

[0080] In some embodiments, to remove the sharp transitions due to the saturation and obtain a cleaner constructed CIRE 150, constructed CIRE 150 may be filtered / modified with a lowAttorney Docket No. 62306.129WO01 pass filter, g = [37874 -3 -4 -111]. In some embodiments, the filtering may be performed by CIR storage and processing module 112, e.g., by an application processor.

[0081] FIG.2A shows constructed CIRE 150 with taps 150a, 150b, and 150c using the disclosed method and system. Tap 150a may correspond to tap 152a (of FIG.1C) which is caused by the spill-over. Tap 150 may be constructed from tap 152a to be cleared of saturation, and is less susceptible to affecting tap 150b, which may be caused by reflection of a target.

[0082] FIGS.3A and 3B illustrate experimental results showing a first initial CIR, a second initial CIR, and a constructed CIRE. In FIG.3A, (I) shows a first initial CIR (with real and imaginary parts) computed from an Ipatov sequence, and (II) shows a second initial CIR (with real and imaginary parts) computed from a STS. As an example, first initial CIR has a spill- over tap. FIG.3B shows a constructed ("mix”) CIRE combining the first initial CIR (in (I)) and the second initial CIR (in (II)) using the weight parameters shown in table 200. As shown in FIG.3B, the spill-over tap has been corrected or constructed to have little or no saturation, and has little or no masking on following taps.

[0083] FIG.4 illustrates a method to implement the disclosed method for constructing a CIRE. FIG.4 may include the operations by the transmitter and the receiver in RX / TX module 102.

[0084] At step 402, the RX / TX module 102 may transmit and receive a frame containing two sounding fields: one Ipatov sequence at high power and one STS at low power. Referring back to the description of FIG.1A, the transmitter may transmit a pulse signal, which may include a frame that has a preamble field and a STS field. The transmitter may transmit the Ipatov sequence in the preamble field at a higher power level, and the STS in the STS field at a lower power. The receiver may receive one or more delays of the frame after its multi-path propagation.

[0085] In some embodiments, prior to the transmission, RX / TX module 102 may perform a TX power calibration process to determine %&'', which represents the maximal Federal Communications Commission (FCC) compliant transmit power. RX / TX module 102 may also perform a short-range calibration process to determine %^, which represents the maximal transmit power avoiding the saturation of the estimated / initial CIR. RX / TX module 102 may then transmit a frame containing an Ipatov sequence in the preamble field and a STS field. In the proposed implementation, the number of Ipatov sequences contained in the preamble field is the same as the number of STS’ in the STS field. In some embodiments, the Ipatov sequence is transmitted at %^and the STS is transmitted at %^. %^may be a user defined parameter. In some embodiments, to cover the largest range, %^may be equal to %()). InAttorney Docket No. 62306.129WO01 some other embodiments, %^may be lower than %()).

[0086] At step 404, the RX / TX module 102 may compute one CIR estimate from the Ipatov field and another CIR estimate from the STS field. Referring back to the description of FIG. 1A, CIR estimation module 110 may compute a first initial CIR from the Ipatov sequence and a second initial CIR from the STS.

[0087] At step 406, the RX / TX module 102 may define a priori for each CIR coefficients, e.g., 2 weights, one for the low power estimation and one for the high power estimation. Referring back to the description of FIG.1A, CIR estimation module 110 may determine the value of weight parametersbased on the values of k0and ks. In some embodiments, the values of the possible predetermined weight parameters ^^^^^ and ^^^^^ (e.g., in table 200) are based on the optimization of the constructed CIRE.

[0088] At step 408, the RX / TX module 102 may compute a new CIR estimate from two previous ones applying the CIR coefficient weights a priori defined. Referring back to the description of FIG.1A, CIR estimation module 110 may compute a constructed CIRE using the first and second initial CIR’s and respective weight parameters shown in table 200.

[0089] In some embodiments, RX / TX module 102 may obtain the CIR estimates corresponding from the Ipatov and STS sequences from the accumulator memory. In some embodiments, accumulators may have different lengths so that CIR estimates may be selected in such a way that both have coherent first path indexes, in the sense that they have their first path index in the same position in the time domain. For each taps index k, RX / TX module 102 may compute the mixed / constructed CIRE as:

[0090] In some embodiments, RX / TX module 102 may uploaded the constructed CIR to an application processor (AP), e.g., CIR storage and processing module 112.

[0091] FIG.5 is a flowchart of a method 500 for generating a constructed CIRE by a receiver (e.g., RX / TX module 102 or receiver 101), according to some embodiments of the present disclosure. Method 500 is merely an example, and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations can be provided before, during, and after the method 500, and some operations described can be replaced, eliminated, or moved around for additional embodiments of method 500. For ease of illustration, FIG.5 is described in connection with FIGS.1A, 1D, 2A, 3A, and 3B.

[0092] At step 302, a first sequence of chips transmitted a first power level (FIGS.1A and 1D) and a second sequence of chips transmitted at a second power level (FIGS.1A and 1D) areAttorney Docket No. 62306.129WO01 received. The first power level is different from the second power level.

[0093] At step 304, a first CIR (FIG.3A (I)) is determined from the first sequence of chips and a second CIR (FIG.3A (II)) is determined from the second sequence of chips.

[0094] At step 306, a CIR estimate (FIGS.2A and 3B) for the UWB channel is computed to be a weighted sum of the first CIR and the second CIR.

[0095] It should be noted that, in some other embodiments, the predefined code sequence (e.g., Ipatov sequence) is transmitted at a lower power level, and the STS sequence is transmitted at a higher power level. The power levels to transmit the sequences should be determined on the application and should not be limited by the embodiments of the present disclosure.

[0096] 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.

Claims

Attorney Docket No. 62306.129WO01 WHAT IS CLAIMED IS:

1. A method for determining a channel impulse response (CIR) estimate for an ultra- wideband (UWB) channel, comprising: receiving a first sequence of chips transmitted a first power level and a second sequence of chips transmitted at a second power level, the first power level being different from the second power level; determining a first CIR from the first sequence of chips and a second CIR from the second sequence of chips; and computing a CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR.

2. The method of claim 1, wherein the second power level is lower than the first power level by between about 20 dB and about 40 dB.

3. The method of claim 1, wherein a first path index of the first CIR and the first path index of the second CIR are at a same location.

4. The method of claim 1, wherein the computing of the CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR comprises: dividing the first CIR and the second CIR into a plurality of sections each with a respective fast time index range; in each of the plurality of sections, determining a first weight value for the first CIR and a second weight value for the second CIR; multiplying sections of the first CIR with respective weight values to obtain a weighted first CIR and sections of the second CIR with respective weight values to obtain a weighted second CIR; and combining the first CIR and the second CIR by adding weighted first CIR and weighted second CIR.

5. The method of claim 4, wherein the dividing of the first CIR and the second CIR into a plurality of sections each with a respective fast time index range comprises: determining a first section having a first fast time index ranging corresponding to a precursor tap signal before a saturated signal;Attorney Docket No. 62306.129WO01 determining a second section having a second fast time index ranging corresponding to the saturated signal; and determining a third section having a third fast time index ranging corresponding to a tap signal after the saturated signal.

6. The method of claim 4, further comprising storing the fast time index range for each section prior to the computing of the CIR.

7. The method of claim 1, wherein the first sequence of chips are transmitted in a first field, and the second sequence of chips are transmitted in a second field different from the first field.

8. The method of claim 7, wherein the first sequence of chips and the second sequence of chips are transmitted in different fields of a same frame.

9. The method of claim 8, wherein: the first sequence of chips comprise a ternary sequence in a preamble field of the frame; and the second sequence of chips comprise a scrambled timestamp sequence (STS) in a STS field of the frame.

10. The method of claim 7, wherein: the first sequence of chips and the second sequence of chips are respectively transmitted in consecutive frames; and the first frame is transmitted at the first power level and the second frame is transmitted at the second power level.

11. The method of claim 10, wherein the first sequence of chips and the second sequence of chips are each a STS in the respective STS field.

12. The method of claim 7, further comprising receiving one or more other first sequences of chips in the first field and one or more other second sequences of chips in the second field, wherein a total number of the first sequence and the other first sequence of chips is same as a total number of the second sequence and the other second sequence of chips.Attorney Docket No. 62306.129WO01 13. An ultra-wide band (UWB) device, comprising: a receiver operable to perform a UWB communication; a memory for storing program instructions, weight parameters, cipher codes, and channel-impulse responses accumulated from the cipher codes; and a processor coupled to the receiver and to the memory, wherein the processor is operable to execute the program instructions, which, when executed by the processor, cause the UWB device to perform the following operations: receiving a first sequence of chips transmitted a first power level and a second sequence of chips transmitted at a second power level, the first power level being different from the second power level; determining a first CIR from the first sequence of chips and a second CIR from the second sequence of chips; and computing a CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR.

14. The UWB device of claim 13, wherein the second power level is lower than the first power level by between about 20 dB and about 40 dB.

15. The UWB device of claim 13, wherein a first path index of the first CIR and the first path index of the second CIR are at a same location.

16. The UWB device of claim 13, wherein the computing of the CIR estimate for the UWB channel to be a weighted sum of the first CIR and the second CIR comprises: dividing the first CIR and the second CIR into a plurality of sections each with a respective fast time index range; in each of the plurality of sections, determining a first weight value for the first CIR and a second weight value for the second CIR; multiplying sections of the first CIR with respective weight values to obtain a weighted first CIR and sections of the second CIR with respective weight values to obtain a weighted second CIR; and combining the first CIR and the second CIR by adding weighted first CIR and weighted second CIR.Attorney Docket No. 62306.129WO01 17. The UWB device of claim 16, wherein the dividing of the first CIR and the second CIR into a plurality of sections each with a respective fast time index range comprises: determining a first section having a first fast time index ranging corresponding to a precursor tap signal before a saturated signal; determining a second section having a second fast time index ranging corresponding to the saturated signal; and determining a third section having a third fast time index ranging corresponding to a tap signal after the saturated signal.

18. The UWB device of claim 16, further comprising storing the fast time index range for each section prior to the computing of the CIR.

19. The UWB device of claim 13, wherein the first sequence of chips are transmitted in a first field, and the second sequence of chips are transmitted in a second field different from the first field.

20. The UWB device of claim 16, wherein the first sequence of chips and the second sequence of chips are transmitted in different fields of a same frame.

21. The UWB device of claim 20, wherein: the first sequence of chips comprise a ternary sequence in a preamble field of the frame; and the second sequence of chips comprise a scrambled timestamp sequence (STS) in a STS field of the frame.

22. The UWB device of claim 19, wherein: the first sequence of chips and the second sequence of chips are respectively transmitted in consecutive frames; and the first frame is transmitted at the first power level and the second frame is transmitted at the second power level.

23. The UWB device of claim 22, wherein the first sequence of chips and the second sequence of chips are each a STS in the respective STS field.Attorney Docket No. 62306.129WO01 24. The UWB device of claim 19, further comprising receiving one or more other first sequences of chips in the first field and one or more other second sequences of chips in the second field, wherein a total number of the first sequence and the other first sequence of chips is same as a total number of the second sequence and the other second sequence of chips.

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