Radar pulse for detecting near and far objects

Abstract

A device senses an environment by transmitting a radar pulse encoded with a known sequence, the radar pulse having a pulse length as long as a maximum roundtrip delay time corresponding to a maximum radar range. A reflection of the pulse is received afterwards, wherein a reflection length is shorter than the pulse length. A set of correlation results representing correlations of the received radar reflection against differently delayed copies of the radar pulse is produced, wherein each of the differently delayed copies has a corresponding delay hypothesis selected from a set of delay hypotheses ranging between minimum and maximum delay hypotheses associated with respective minimum and maximum radar ranges. A delayed copy of the radar pulse that produced a target correlation result is found from among the set of correlation results, and that delay hypothesis is used to estimate a range of a sensed object in the environment.

Description

[0001] RADAR PULSE FOR DETECTING NEAR AND FAR OBJECTS

[0002] BACKGROUND

[0003] The present invention relates to radar sensing / measurement of objects in an environment, and more particularly to radar sensing / measurement using time division duplex radio equipment and the same radar pulse for simultaneously sensing / measuring both near and distant objects.

[0004] Some or all of the following abbreviations are used in this specification:

[0005] Abbreviation Explanation

[0006] 3GPP Third Generation Partnership Project

[0007] ACF Autocorrelation Function

[0008] FMCW Frequency Modulated Continuous Wave

[0009] GHz GigaHertz

[0010] OFDM Orthogonal Frequency-Division Multiplexing

[0011] RTT Roundtrip Time

[0012] Rx Receiver

[0013] SNR Signal to Noise Ratio

[0014] TDD Time Division Duplex

[0015] Tx Transmitter

[0016] As cellular communication systems evolve, they are using higher frequencies than in earlier systems, and this creates the potential for the communication hardware to also be used for radar sensing. For example, millimeter wave frequencies are used in the 3GPP’s 5G system, and in 6G there are plans to use frequencies above 100GHz. The increasingly higher carrier frequencies with channel bandwidths of multiple GHz enable high resolution radar. Even for existing frequency ranges like (extended) mid-band (up to around 15 GHz), bandwidths up to several 100 MHz are expected, making even mid-band usable for radar.

[0017] There is a desire to be able to use the communication hardware for radar with as few modifications as possible, both for base stations and user equipment. But this can be challenging because radar systems use quite different hardware and signals compared to communication systems. For example, in mm-wave automotive radar, full duplex transceiver operation with an FMCW signal is common, simultaneously operating both receiver and transmitter, where the transmitter sends a continuously frequency modulated signal (a so-called “chirp”). But by contrast, TDD is used in mid-band and mm-wave cellular communication, operating receiver and transmitter in different time slots, and a more complex OFDM signal is used to carry the information. The OFDM signal is also usable for radar, so this aspect is compatible with the communication system signals and hardware. However, full duplex operation would require major hardware changes, and unless the detection range is very short, full duplex also presents large challenges when not using an FMCW signal. It is thus preferrable to use TDD not only for communication but also for radar. However, there are trade-offs involved that limit the shortest detection distance for a TDD radar. For example, if the transmitted pulse is made long to provide more energy it will be better be able to detect small and far away objects. But transmitting a long pulse means that nearby objects cannot be detected by conventional equipment because the transmitter is still active when the start of the echo returns to the antenna, effectively creating a blind zone around the radar.

[0018] The inventors have recognized that this problem can be addressed by performing measurements with different pulse lengths, but this comes at the expense of occupying more radio resources for the radar measurement, and / or making the radar slower.

[0019] There is therefore a need for a technology that solves the above and / or related problems associated with the use of TDD radio equipment for monostatic radar sensing.

[0020] SUMMARY

[0021] It should be emphasized that the terms “comprises” and “comprising”, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0022] Moreover, reference letters may be provided in some instances (e.g., in the claims and summary) to facilitate identification of various steps and / or elements. However, the use of reference letters is not intended to impute or suggest that the so-referenced steps and / or elements are to be performed or operated in any particular order.

[0023] In accordance with one aspect of the present invention, the foregoing and other objects are achieved in technology (e.g., methods, apparatuses, nontransitory computer readable storage media, program means) that enable a device to perform radar sensing in an environment. In some aspects of embodiments consistent with the invention, a radar pulse is transmitted into the environment from the device. The radar pulse has a known sequence encoded therein, wherein the radar pulse is configured to have a pulse length as long as a maximum roundtrip delay time corresponding to a maximum radar range. After the radar pulse has been transmitted, a radar reflection of the transmitted radar pulse is received, wherein a length of the received radar reflection is shorter than the pulse length of the radar pulse (e.g., because the reflection began to arrive at the device before the device began receiving). A set of correlation results is produced, representing correlations of the received radar reflection against each member of a set of differently delayed copies of the radar pulse, wherein each of the differently delayed copies of the radar pulse has a corresponding delay hypothesis selected from a set of delay hypotheses ranging from a minimum delay hypothesis associated with a minimum radar range to a maximum delay hypothesis associated with the maximum radar range. A determination is made concerning which one of the differently delayed copies of the radar pulse produced a target correlation result from among the set of correlation results. The delay hypothesis corresponding to the determined one of the differently delayed copies is used as a matching delay length, and the matching delay length is used to estimate a range of a sensed object in the environment.

[0024] Other aspects of further and / or alternative embodiments, including but not limited to methods, software, computer-readable media, apparatuses, and systems, are described in the following.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which:

[0027] Figure 1 is a schematic illustration of relative timings between a transmitted radar pulse, a received radar reflection (echo) of the radar pulse from an object, and delayed copies of the radar pulse that represent echo hypotheses to which the received radar reflection is correlated.

[0028] Figure 2 is a schematic illustration of relative timings between a transmitted radar pulse, a received radar reflection (echo) of the radar pulse from an object that is more distant than the object of Figure 1, and delayed copies of the radar pulse that represent echo hypotheses to which the received radar reflection is correlated.

[0029] Figure 3 illustrates an exemplary radar pulse that comprises four segments in an example that supposes the existence of first and second objects located at distances from the device such that the start of their respective reflections of an impulse transmitted by the device would each arrive back at the device at times during which the device is transmitting the second segment of the radar pulse.

[0030] Figure 4 illustrates an example in which a radar pulse having four pulse segments is transmitted, and in which reflections from two objects arrive at the device during transmission of a third segment of the radar pulse. Figure 5 illustrates another example in which a radar pulse having four pulse segments is transmitted, and in which reflections from two objects arrive at the device during transmission of a fourth segment of the radar pulse.

[0031] Figure 6 illustrates an example in which a radar pulse having four pulse segments is transmitted, and in which reflections from two objects begin to arrive at the device during transmission of the second segment of the radar pulse, and in which reflections from two more distant objects begin to arrive at the device during transmission of the third segment of the radar pulse.

[0032] Figure 7 illustrates an example in which a radar pulse having four pulse segments is transmitted, and in which reflections from respective first and second objects begin to arrive at the device during transmission of the second segment, and in which reflections from respective third and fourth more distant objects begin to arrive at the device during transmission of the fourth segment of the radar pulse.

[0033] Figure 8 illustrates the use of beam domain transmissions and receptions to assist with resolving an object’s range when there may be multiple objects situated at various distances from a device performing radar scanning as described above.

[0034] Figure 9 is, in one respect, a flowchart of actions performed by a device (e.g., base station, network node, user equipment, etc.) as part of a monostatic radar operation in accordance with some but not necessarily all inventive embodiments.

[0035] Figure 10 shows an exemplary controller that may be included in a device having radar signal transmitting and receiving capabilities to cause any and / or all of the herein-described and illustrated actions associated with that device to be performed.

[0036] DETAILED DESCRIPTION

[0037] The various features of the invention will now be described with reference to the figures, in which like parts are identified with the same reference characters.

[0038] The various aspects of the invention will now be described in greater detail in connection with a number of exemplary embodiments. To facilitate an understanding of the invention, many aspects of the invention are described in terms of sequences of actions to be performed by elements of a computer system or other hardware capable of executing programmed instructions. It will be recognized that in each of the embodiments, the various actions could be performed by specialized circuits (e.g., analog and / or discrete logic gates interconnected to perform a specialized function), by one or more processors programmed with a suitable set of instructions, or by a combination of both. The term “circuitry configured to” perform one or more described actions is used herein to refer to any such embodiment (i. e. , one or more specialized circuits alone, one or more programmed processors, or any combination of these). Moreover, the invention can additionally be considered to be embodied entirely within any form of non- transitory computer readable carrier, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. Thus, the various aspects of the invention may be embodied in many different forms, and all such forms are contemplated to be within the scope of the invention. For each of the various aspects of the invention, any such form of embodiments as described above may be referred to herein as “logic configured to” perform a described action, or alternatively as “logic that” performs a described action.

[0039] To facilitate the reader’s understanding of various aspects of inventive embodiments, the following non-limiting overview is provided. As used throughout this document, the term “device”, when used alone, is intended to cover any type of equipment that is capable of carrying out the described functions, including but not limited to base stations (or other equivalent telecommunication system node) and user equipment. Embodiments consistent with the invention address problems related to the use of TDD radio equipment for purposes of radar sensing of objects that may be located anywhere from very near to very far away from the sensing device. In one aspect of inventive embodiments, a device’s transmitter sends a signal having a pulse length similar to the roundtrip propagation time between the device and an object located at the furthest detection distance the system is intended for. This aspect provides the maximum pulse energy for detection of objects at the maximum distance but as noted earlier, with conventional full pulse correlation techniques, closer objects cannot be detected, effectively making the radar blind at all intended ranges except the very maximum. To address this problem, in another aspect of inventive embodiments, a correlation method is employed that correlates a received radar reflection not only against the full pulse, but also against partial ones.

[0040] In TDD operation, the device’s receiver is typically isolated from the antenna during transmission by an antenna switch, allowing at best only some transmitter leakage into the receiver due to limited switch isolation. For this reason, no useful signal is detected during pulse transmission. After the transmission stops, the antenna switch is changed to connect the receiver and instead isolate the transmitter and its noise from the antenna. After this, the receiver starts to provide useful digital data. However, those portions of radar reflections that reach the device during transmission are not received, only those remaining portions that arrive when the receiver is engaged. The received portions of the radar reflection are then correlated against corresponding portions of differently delayed copies of the transmitted radar pulse, with the different delays corresponding to different object distance hypotheses. In some but not necessarily all embodiments, correlation of the portions is advantageously achieved by appending a string of one or more zero signal values in front of the received portion of the radar reflection, thereby producing a modified radar reflection. As used herein, the term “in front of’ means preceding without any intervening other signal part between the appended one or more zero signal values and the received portion of the radar reflection. The amount of padding advantageously causes the length of the modified radar reflection to match at least the length of the transmitted radar pulse. With the initial zeros in the received signal, and with the transmitted signal being zero before and after the pulse, effectively the correlation will only take place over a part of the transmitted signal pulse. That part is the last part of the transmitted pulse, and the longer the distance to the target, the longer the effective correlation. This is beneficial, as longer correlations are needed at longer distances to improve the SNR of the weaker echoes compared to closer targets.

[0041] In another aspect of some but not necessarily all embodiments, to reduce the effect of strong reflection signals from nearby targets on a distant object’s weak signal correlation, the zero region appended at the front of the received radar reflection is extended a bit into the active receive region for those correlators (i.e. , an initial portion of a received radar reflection is deliberately discarded), thereby exchanging some echo energy for less interference.

[0042] The inventors have observed that the partial pulse correlation puts special considerations on the autocorrelation properties of the modulation sequence of the transmitted pulse. One of these is that a sub-sequence cut from the end of the sequence encoded in the radar pulse must have low auto-correlation with the sequence for all delays, to avoid detection of false targets. This means there is a certain minimum length of the sub-sequence, which together with the bandwidth of the modulation, and the speed of the antenna switch, that sets the minimum detection distance (i.e., the blind zone). For instance, assume a minimum correlation length of 20 samples, a bandwidth of 1GHz, and a switching time of 10ns. This results in a total time amounting to 30ns. In that time the signal propagates 9 meters. Since the relevant distance in a radar application is the round-trip distance from the transmitting device to an object and then back to the device, the minimum range would then be half that (i.e., about 5 meters).

[0043] These and other aspects of embodiments consistent with the invention are described in further detail in the following. Figure 1 is a schematic illustration of a transmitted radar pulse (Tx_sig) 101, a received radar reflection (echo) 103 of the radar pulse 101 from an object, and delayed copies of the radar pulse 105-1, 105-2, 105-3 that represent echo hypotheses to which the received radar reflection 103 is correlated. In particular, Figure 1 illustrates relative timings between these different signals.

[0044] For the device to produce the radar pulse 101, a rather long digital transmit signal is generated and then modulated with a bandwidth according to what is available and with a sequence with low autocorrelation. The radar signal 101 is transmitted and propagates to an object from which it is reflected back to the device. The roundtrip time for the signal to propagate from the device to the object and back again is illustrated in the figure as RTTobj. As can be seen in Figure 1, the RTTobj is much shorter than the duration of the radar pulse transmission, so the radar reflection (RX sig) begins to arrive at the device well before the transmission is over. The part of the radar reflection illustrated by the dashed line can thus not be received (i.e. , due to the device’s TDD operational mode). The received radar reflection 103 is only the portion illustrated by a solid line because it arrives after the transmission is over and the antenna switch has been changed to the receive position. In some but not necessarily all embodiments, the internal representation of the received radar reflection 103 is a modified radar reflection 107 produced by appending a string 109 of one or more zero signal values (“padding”) in front of the received radar reflection 103. The amount of zero padding is advantageously at least as long as the illustrated dashed portion of the reflected signal, so that the modified radar reflection 107 has a length that is the same as that of the transmitted radar pulse 101. To find targets at different distances, a number of hypotheses, such as the illustrated signals Tx dl, Tx_d2, and Tx_d3, are created by making copies of the radar pulse 105-1, 105-2, 105-3, delayed by different amounts of time. Each delayed copy of the radar pulse 105-1, 105-2, 105-3 therefore has a corresponding delay hypothesis, advantageously selected from a set of delay hypotheses ranging from a minimum delay hypothesis associated with a minimum radar range to a maximum delay hypothesis associated with the maximum radar range. Each of the differently delayed copies of the radar pulse 105-1, 105-2, 105-3 is then correlated against the received radar reflection 103 to produce a set of correlation results. In some but not necessarily all embodiments, the correlation results are instead produced by correlating the modified radar reflection 107 against each of the differently delayed copies of the radar pulse 105-1, 105-2, 105- 3.

[0045] As can be seen in the example of Figure 1, the second hypothesized delay (d2) has a corresponding delayed copy of the radar pulse 105-2 that aligns with the received radar reflection 103, and the correlation of the part where the signals are non-zero should result in a significant correlation result, which will depend on the length of the non-zero signal interval, as well as the signal strength of the reflection.

[0046] In some but not necessarily all embodiments, to save computation time, the correlation does not need to perform computations for the part of the echo hypothesis that overlaps with the transmission time, since this portion of the modified radar reflection 103 is set to zero and will therefore only produce zero as the correlation result. If the correlation is stopped from occurring in that range, it is therefore not necessary to produce the modified radar reflection 107 or even to have any signal representation there.

[0047] As can also be seen in the example of Figure 1, the first and third hypothesized delays (dl and d3) have corresponding delayed copies of the radar pulse 105-1, 105-3 that are not as well aligned with the received reflection 103, and should accordingly yield a low correlation result to avoid a false target detection. It is therefore beneficial for the autocorrelation between the transmitted radar pulse 101 and the received radar reflection 103 to be low for all non-zero time offsets. The modulation sequence should therefore be designed accordingly.

[0048] Aspects of some but not necessarily all inventive embodiments relating to receipt of long- range radar reflections from far away objects will now be discussed with reference to Figure 2. As illustrated in the figure, a radar pulse 201 is transmitted and a radar reflection 203 of that pulse is received from a far-away target. Although the radar reflection 203 is receivable beginning at the point denoted tRx and is therefore usable when correlating against various copies of the radar pulse with different hypothesized delays (e.g., the differently delayed radar pulse copies 205-1, 205-2, 205-3), strong reflections from nearby targets may distort the correlation results. Therefore, in some but not necessarily all embodiments consistent with the invention, an additional zero period is substituted for a front portion 207 of the receivable signal in order to remove these strong interfering reflection signals. The remaining portion 209 of the received signal is taken as the received radar reflection 203 and used in the correlations. In some but not necessarily all embodiments, multiple copies of the received signals are created in the correlator, with different respective amounts of additional blanking. In some but not necessarily all alternative embodiments, the echo hypotheses are set to zero in the corresponding range. In other non-limiting alternatives, the correlation interval is made to start at a later time when correlating for later echo signals.

[0049] Comparing the near object reflections illustrated in Figure 1 with the more distant object reflections illustrated in Figure 2, it is clear that the effective correlation length is larger for the more distant object and this helps the SNR of distant objects, maximizing the device’s radar sensing range. In fact, the effective correlation length will be automatically maximized to the system capability for each different target distance, so the performance will be similar to what could be achieved using a large number of different pulse lengths, each optimized for a certain target distance range. However, such a system would use much more spectral resources, or it would not be as fast as the illustrated embodiments, where a single pulse length can be sent out to measure all the target distances at the same time with an effective correlation length close to the optimum for each target distance.

[0050] Aspects of some but not necessarily all embodiments consistent with the invention relate to the design of a suitable radar pulse for transmission, and these are now discussed with reference to Figures 3 through 7. Looking first at Figure 3, this shows an exemplary radar pulse 301 transmitted by a device, where the radar pulse 301 comprises four segments 303-1, 303-2, 303-3, and 303-4. In alternative embodiments, the radar pulse 301 may comprise more or fewer segments. In one non-limiting class of embodiments, the same sequence is used in each segment 303-1, 303-2, 303-3, 303-4. This has a benefit in that a given segment acts as cyclic prefix for the next-occurring segment and this makes it possible to use cyclic (periodic) correlation properties. Sequences with very good (even perfect) periodic ACF are, for example, Zadoff-Chu sequences (applied to either time-domain or frequency-domain signals in an OFDM system) or any sequence with constant modulus applied to subcarriers of an OFDM system. In an OFDM framework it is easy to generate such a segmented sequence, especially if the total sequence stretches over an integer number of OFDM symbols (e.g., one OFDM symbol): When modulating only every k-th subcarrier of an OFDM signal a time-domain waveform that repeats itself k-times within an OFDM symbol duration is generated (i.e., the generated waveform has k segments). In this example the sequence is partitioned into k=4 segments.

[0051] In exemplary embodiments, the amount of time required to transmit the radar pulse 301 (also referred to herein as its length) corresponds to the maximum radar range of the device and therefore is equal to a maximum RTT RTTmax) that can be expected from transmission of the radar pulse 301 to receipt of a reflection. In this example the minimum radar range (RTTmm, the size of the exclusion zone) is equal to the duration of a single segment 303-1, 303-2, 303-3, 303- 4 (i.e., the roundtrip time at the exclusion zone border is equal to a segment duration).

[0052] It is noted that the correspondence between the length of the radar pulse 301 and the maximum radar range of the device derives from the fact that the maximum RTT is determined by the requirements imposed by the radar range to be supported. To maximize the SNR for targets at that range, the RTT for that range is used as the pulse length. If a longer pulse were to be used, the extra pulse energy could not be used because it would not be correlated against any hypotheses. If a shorter pulse were to be used, signal energy would be lost compared to using a length equal to the RTT.

[0053] It is possible for some embodiments to operate at longer distances having an RTT exceeding the pulse length, but operation at such distances is degraded due to loss of reflected energy. Performance would therefore be better with a longer pulse to maximize the correlated signal energy.

[0054] Figure 3 illustrates an example that supposes the existence of first and second objects located at distances from the device such that their respective reflections 305, 307 of a pulse transmitted by the device would each begin to arrive back at the device while the device is transmitting the second segment 303-2 of the radar pulse 301.

[0055] As shown in Figure 3, reflections 309, 311 of the transmitted radar pulse 301 from two objects begin to arrive while the device is transmitting the second segment 303-2. It can be seen that only the tail portion of each reflection is actually received by the device because this is the only time that the receiver is operational.

[0056] In another aspect of this class of embodiments, a plurality of correlations are performed for each hypothesized RTT delay time, with each correlation having its own correlation window. In this example there are three sub-correlation windows 313, 315, 317 (i.e., the number of segments minus one) that, together, span a total correlation window 323. However, in alternative embodiments, the relationship between the number of correlation windows and the number of segments can be different (e.g., the number of correlation windows can equal the number of segments). Within each of the correlation windows 313, 315, 317, the received reflection 309, 311 is correlated with the sequence corresponding to a respective one of the segments 303-1, 303-2, 303-3, 303-4.

[0057] Figure 3 also shows exemplary correlation peaks produced from the received reflections 309, 311. In the first correlation window 313 two complete, delayed (due to cyclic prefix, they appear as cyclic shifted) copies of a segment occur (each object creates one delayed copy). For each copy, the correlator produces a respective peak 319, 321 at the cyclic shift position. The round-trip time between the device and an object responsible for a reflection is the duration of a complete segment plus the cyclic delay of the peak. The range of each object can then be determined from its detected round-trip time. Parts of segments are also observed in the second correlation window 315. The resulting correlation peaks for this window will be lower because the inputs to the correlator are only parts of a segment The correlation peaks are also less sharp because the correlation properties that make a sequence good for correlation are lost since only a part of a segment is correlated. Figure 4 illustrates another example in which a radar pulse 401 having four pulse segments 403-1, 403-2, 403-3, 404-4 is transmitted, and in which reflections from two objects arrive at the device during transmission of third segment 403-3 (meaning that the two objects are located in the third quarter of maximum radar range). Due to the longer delay, complete (cyclic shifted) instances of the received reflections 409, 411 from the two objects are observed in each of the first and second correlators 413, 415 and partial instances in the third correlator 417. For this reason, each of the first and second correlators 413, 415 produces sharp peaks 419, 421 for a respective one of the two objects, whereas the third correlator 417 produces for each object a lower, less pronounced peak. For each of the objects, the round-trip time is the duration of two complete segments plus the cyclic delay of the peak. The range of each object can then be found from its detected round-trip time.

[0058] Figure 5 illustrates another example in which a radar pulse 501 having four pulse segments 503-1, 503-2, 503-3, 504-4 is transmitted, and in which reflections from two objects arrive at the device during transmission of fourth segment 503-4 (meaning that the two objects are located in the fourth quarter of maximum radar range). Due to the longer delay, complete (cyclic shifted) instances of the received reflections 509, 511 from the two objects are observed in each of the first, second, and third correlators 513, 515, 517. For this reason, each of the first, second, and third correlators 513, 515 produces sharp peaks 519, 521 for a respective one of the two objects. For each of the objects, the round-trip time is the duration of three complete segments plus the cyclic delay of the peak. The range of each object can then be found from its detected round-trip time.

[0059] The examples presented up to this point all involve situations in which objects are similarly located with respect to one another (i.e., their reflections all arrive back at the device during transmission of a same one of the radar pulse segments). To illustrate other aspects of some embodiments, Figure 6 illustrates an example in which a radar pulse 601 having four pulse segments 603-1, 603-2, 603-3, 604-4 is transmitted, and in which reflections from two objects begin to arrive at the device during transmission of the second segment 603-2 (meaning that the two objects are located in the second quarter of the maximum radar range), and in which reflections from two more distant objects begin to arrive at the device during transmission of the third segment 603-3 (meaning that the two more distant objects are located in the third quarter of the maximum radar range). Each of the two objects in the second radar range quarter produces two sharp peaks (e.g., the first peak 619 attributable to the first object) in the first correlator 613 and two lower, less sharp peaks (e.g., the second peak 623 attributable to the first object) in the second correlator 615 (similar to the peaks shown in Figure 3). The two more distant objects in the third quarter of the radar range produce sharp peaks 621 in the first and second correlators 613, 615 and lower, less sharp peaks 621 in the third correlator 617 (similar to the peaks shown in Figure 4). Peaks that occur in the output of the first correlator 613 can be from objects in any radar range quarter while peaks in later correlator outputs (in this example, from the second correlator 615 and third correlator 617) must come from further away targets. To resolve which peaks belong to the same object and in which radar range quarter an object is located, the receiver needs to combine and compare individual correlator outputs.

[0060] To illustrate further aspects of some embodiments, Figure 7 illustrates an example in which a radar pulse 701 having four pulse segments 703-1, 703-2, 703-3, 704-4 is transmitted, and in which reflections 731, 733 from respective first and second objects begin to arrive at the device during transmission of the second segment 703-2 (meaning that the two objects are located in the second quarter of the maximum radar range), and in which reflections 735, 737 from respective third and fourth more distant objects begin to arrive at the device during transmission of the fourth segment 703-4 (meaning that the two more distant objects are located in the fourth quarter of the maximum radar range). Segments of each of these reflections 713, 733, 735, 737 are correlated, in each respective correlator 713, 715, 717, against hypothesized delayed copies of segments of the radar pulse 701 delay hypotheses. As a result, the first object is associated with first correlation peaks 719; the second object is associated with second correlation peaks 721; the third object is associated with third correlation peaks 723; and the fourth object is associated with fourth correlation peaks 725.

[0061] Of note in this example is that the first and third objects are situated such that their roundtrip times differ by an integer number of segment durations. Because of this, the segment start and end points line up in their respective reflections 731, 735 and this leads to overlapping peaks 719, 723 in the outputs of the first and second correlator 713, 715. For simplicity, the illustration of these peaks in Figure 7 are depicted as combining only constructively. However, in practice each target peak is a complex number and the combined peak from two objects may also destructively combine. Because of this alignment, there can be some ambiguity when interpreting results from any one of the correlators 713, 715, 717 when considered alone. But each reflection 731, 733, 735, 737 provides a distinct set of correlation peaks 719, 721, 723, 725 when outputs from all correlators 713, 715, 717 are considered in combination. Accordingly, in order to resolve which peaks are attributable to the same object and in which radar range quarter an object is located, the receiver should combine and compare individual correlator outputs.

[0062] Further aspects of some but not necessarily all embodiments are now discussed with reference to Figure 8, which illustrates the use of beam domain transmissions and receptions to assist with resolving an object’s range when there may be multiple objects situated at various distances from a device performing radar scanning as described above. As shown in Figure 8, a wide transmission beam 801 is used when transmitting a radar pulse from a device 807.

[0063] If the device is sufficiently elevated (e.g., a base station or other network node), transmission of the radar pulse can be by use of a wide transmission beam 801. This can be followed by multiple receive operations, each using a different one of a set of narrower receive beams 803-1, 803-2, 803-3, 803-4. It will be understood that the use of four receive beams as illustrated in Figure 8 is by way of example only, and that the number of receive beams in any particular embodiment can be more or fewer than four. By using narrower receive beams 803-1, 803-2, 803-3, 803-4, it is easier to separate receptions from different distances (e.g., receptions from close reflections would be attenuated when receiving in a beam targeting further away reflections, and this in turn would reduce ambiguities and assist / improve the correlation process).

[0064] Figure 8 illustrates embodiments in which down tilt beam coverage is utilized (i. e. , searching for reflections emanating from below the node’s antenna 805). But in alternative embodiments, up-tilted beams can be used to assist with distinguishing between objects at different distances appearing above the antenna 805, such as drones.

[0065] In further aspects of some but not necessarily all embodiments, different sequences are transmitted in different radar pulse segments. These sequences should have good aperiodic ACF properties (since a preceding segment no longer acts as a cyclic prefix) and good cross correlation properties. Barker and Gold sequences are examples of such sequences. There is no one example of “good” aperiodic ACF properties since what constitutes “good” depends on the use case (i.e., it is implementation dependent). If two not matching sequences are correlated, a correlation output is created that could overshadow a weaker true (matched) correlation output. For example, a closer object that sits in a certain range zone will create not only a true (desired) correlation peak in the correct range zone, but also false peaks (due to the non-zero cross correlation between different sequences) in other zones (e.g., in next range zone). If another object is present in the next range zone, maybe with weaker RCS, the correlation peak will be weak due to 1) small RCS and 2) longer range. The cross correlation between sequences should therefore be small enough that its false peak does not hide objects in another zone. And, as mentioned above, finding an exact value that is satisfactory depends on the use case. However, determining what constitutes suitable sequences for a known use case is within the level of ordinary skill in the art, and therefore beyond the scope of this description.

[0066] Using different sequences has the advantage that some of the ambiguity is resolved. A drawback is that non-zero cross correlations occur between sequences, which contributes interference. Another drawback is that complexity is increased because the receiver needs multiple correlators per correlation window.

[0067] In another non-limiting alternative, complementary sequences are used in different radar pulse segments. Complementary sequences are defined as follows: Two sequences akand bk, k = 0,1, ... , N — 1 are said to form a complementary sequence pair if the sum of their aperiodic auto-correlations is non-zero at time lag zero and otherwise zero: pa(k + pb(k = 2N ■ 8(k) with pa( / c) = E =-ofc_l ai ’ai+k being the aperiodic auto-correlation (for the max value 2 • TV it is assumed the sequence elements have unitary magnitude). An example of complementary sequences is Golay Complementary Sequences. A Golay sequence is constructed based on iteratively repeating (sign-inversed) a base segment, e.g. = \ak1-), b^1 1')] and b^ = [akn 1'), — b^1 1')], Individual building blocks of correct length are mapped to the individual segments. This type of radar requires two transmissions, one for each sequence of the pair. In the receiver, the correlations of both transmissions with the respectively sent waveform are added together to obtain the perfect aperiodic ACF.

[0068] In still another class of alternative embodiments, the radar pulse comprises at least some segments of differing lengths. In these instances, the segments carry different sequences (at least those of differing lengths). Using different lengths has the advantage that correlation peaks of the same target will not appear at the same time in different segments, thereby reducing ambiguity.

[0069] Still further aspects of some but not necessarily all inventive embodiments will now be described with reference to Figure 9, which in one respect is a flowchart of actions performed by a device (e.g., base station, network node, user equipment, etc.) as part of a monostatic radar operation in accordance with some but not necessarily all inventive embodiments. In other respects, the blocks depicted in Figure 9 can also be considered to represent means 900 (e.g., hardwired or programmable circuitry or other processing means) for carrying out the described actions.

[0070] As shown beginning in Figure 9, the process includes the device sensing an environment by transmitting a radar pulse into the environment (step 901), wherein the radar pulse has a known sequence encoded therein. The radar pulse is configured to have a pulse length as long as a maximum roundtrip delay time corresponding to a maximum radar range.

[0071] After the radar pulse has been transmitted (e.g., at the completion of transmission when the device is operating in a TDD mode), the device receives (step 903) a radar reflection of the transmitted radar pulse, wherein a length of the received radar reflection is shorter than the pulse length of the radar pulse (e.g., due to a first part of the reflection arriving at the device while the device is still transmitting).

[0072] A set of correlation results is produced (step 905), with the set members representing correlations of the received radar reflection against each member of a set of differently delayed copies of the radar pulse, wherein each of the differently delayed copies of the radar pulse has a corresponding delay hypothesis selected from a set of delay hypotheses ranging from a minimum delay hypothesis associated with a minimum radar range to a maximum delay hypothesis associated with the maximum radar range.

[0073] The correlation results are then assessed to determine (step 907) which one of the differently delayed copies of the radar pulse produced a target correlation result from among the set of correlation results. The target correlation result can be, in some embodiments, a highest correlation result from among the set of correlation results. However, this is not an essential aspect of all embodiments, since there could be more than one object of interest, not all of which will produce a highest correlation. There might also be objects of interest that produce weaker signals, and these too may not produce highest correlation peaks. The delay hypothesis corresponding to said determined one of the differently delayed copies is used as a matching delay length from which an estimate of the range of a sensed object in the environment is estimated (step 909).

[0074] Some further aspects of inventive embodiments involve additional and / or alternative features. For example, in some but not necessarily all embodiments, the target correlation result is a highest correlation result from among the set of correlation results.

[0075] In another aspect of some but not necessarily all inventive embodiments, an autocorrelation for non-zero time shifts of the radar pulse does not exceed a maximum sequence autocorrelation threshold amount.

[0076] In still another aspect of some but not necessarily all inventive embodiments, a correlation between a first portion of the radar pulse and a second portion of the radar pulse does not exceed a maximum correlation threshold amount, wherein a length of the first portion equals a length of the second portion, and wherein the length of the first and second portions is shorter than the pulse length of the radar pulse.

[0077] In yet another aspect of some but not necessarily all inventive embodiments, actions performed by a device as part of a monostatic radar operation also include, for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection by appending a string of one or more zero signal values in front of the received radar reflection, wherein each member of the set of correlation results is produced by correlating a differently delayed version of the radar pulse against the modified received radar reflection.

[0078] In still another aspect of some but not necessarily all inventive embodiments, the received radar reflection comprises a front portion and a remaining portion that follows the front portion, and actions performed by a device as part of a monostatic radar operation also include, for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection by discarding the front portion of the received radar reflection and appending a string of one or more zero signal values in front of the remaining portion of the received radar reflection, wherein each member of the set of correlation results is produced by correlating a differently delayed version of the radar pulse against the modified received radar reflection.

[0079] In another aspect of some but not necessarily all inventive embodiments, the radar pulse is transmitted during a transmission time window and the received radar reflection is received during a receive time window that follows the transmission time window; and for one or more members of the set of correlation results, producing said members of the set of correlation results comprises using a correlation window that begins no earlier than a start of the receive time window. In some alternatives, for the one or more members of the set of correlation results, producing said members of the set of correlation results comprises using a correlation window that begins later than a start of the receive time window.

[0080] In yet another aspect of some but not necessarily all inventive embodiments, the known sequence comprises a plurality of sub-sequences. In some but not necessarily all alternative embodiments, two or more of the plurality of sub-sequences are identical to one another. Alternatively, the plurality of sub-sequences comprises a first sub-sequence and a second subsequence that is different from the first sub-sequence, wherein an aperiodic autocorrelation between the first sub-sequence and the second sub-sequence does not exceed a maximum subsequence autocorrelation threshold amount.

[0081] In some further alternatives, the sub-sequences are all different from one another.

[0082] In yet other alternatives, at least two of the plurality of sub-sequences are a complimentary sequence pair. In these embodiments, each sequence requires its own transmission, with each transmission containing only one sequence of the pair.

[0083] In still other alternatives, the plurality of sub-sequences comprises a first sub-sequence and a second sub-sequence that differ in length from one another.

[0084] In yet another aspect of some but not necessarily all inventive embodiments, each correlation result in the set of correlation results represents a correlation, using a first correlation window, of the received radar reflection against a respective one of the members of the set of differently delayed copies of the radar pulse. Further in such embodiments, producing the set of correlation results comprises, for each member of the set of correlation results, producing a plurality of sub-correlation results by performing a plurality of sub-correlations of the received radar reflection against a respective member of the set of differently delayed copies of the radar pulse; and combining the plurality of sub-correlation results to produce the member of the set of correlation results. In such embodiments, each of the sub-correlations uses a respective one of a plurality of sub-correlation windows; each of the sub-correlation windows is shorter than the first correlation window; and each of the sub-correlation windows is used for correlating against a different portion of the received radar reflection.

[0085] In some but not necessarily all alternatives, each of the sub-correlations uses a cyclic correlation property of one of the sub-sequences.

[0086] In yet some other alternatives, the plurality of sub-sequences comprises a first subsequence and a second sub-sequence that are different from one another; and at least one of the sub-correlation windows is used for correlating a portion of the received radar reflection against the first sub-sequence and also for correlating the portion of the received radar reflection against the second sub-sequence.

[0087] In yet some other alternatives, determining which one of the differently delayed copies of the radar pulse produced the highest correlation result from among the set of correlation results comprises comparing sub-correlation results produced using different ones of the sub-correlation windows.

[0088] In still another aspect of some but not necessarily all inventive embodiments, transmitting into the environment, from the device, the radar pulse comprises using a first beam width when transmitting the radar pulse into the environment; and receiving the radar reflection of the transmitted radar pulse comprises using a second beam width when receiving the radar reflection of the transmitted radar pulse, wherein the second beam width is narrower than the first beam width. Further aspects of embodiments consistent with the invention will now be described with reference to Figure 10, which shows an exemplary controller 1001 that may be included in a device having radar signal transmitting and receiving capabilities in order to cause any and / or all of the herein-described and illustrated actions associated with that device to be performed. In particular, the controller 1001 includes circuitry configured to carry out any one or any combination of the various functions described herein. Such circuitry could, for example, be entirely hard-wired circuitry (e.g., one or more Application Specific Integrated Circuits - “ASICs”). Depicted in the exemplary embodiment of Figure 10, however, is programmable circuitry, comprising a processor 1003 coupled to one or more memory devices 1005 (e.g., Random Access Memory, Magnetic Disc Drives, Optical Disk Drives, Read Only Memory, etc.) and to an interface 1007 that enables bidirectional communication with other elements of a device as described above. A complete list of possible other elements is beyond the scope of this description.

[0089] The memory device(s) 1005 store program means 1009 (e.g., a set of processor instructions) configured to cause the processor 1003 to control other device elements so as to carry out any of the aspects described herein. The memory device(s) 1005 may also store data (not shown) representing various constant and variable parameters as may be needed by the processor 1003 and / or as may be generated when carrying out its functions such as those specified by the program means 1009.

[0090] The various embodiments according to the invention are characterized by a number of advantages over prior technologies. These include the use of TDD and modulation formats that are compatible with 5G and 6G communication hardware.

[0091] Another advantage is that the technology described herein eliminates the need for a tradeoff between pulse length and the maximum and minimum detection ranges that can be achieved in TDD monostatic radar. Various embodiments are capable of transmitting a full roundtrip pulse length for sensing the maximum range, without sacrificing an ability to also sense a minimum range (different from the maximum range).

[0092] Yet another advantage is the technology’s ability to operate with a single pulse length for all object distances, thereby eliminating any need to transmit multiple pulses of different lengths for this same variety of object distances. In this way, spectral resources are saved, compared to other technologies.

[0093] The invention has been described with reference to particular embodiments. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the embodiment described above. Thus, the described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is further illustrated by the appended claims, rather than only by the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.

Claims

CLAIMS:

1. A method of performing radar sensing of an environment by a device (807), the method comprising: transmitting (901) into the environment, from the device (807), a radar pulse (101, 201, 301, 401, 501, 601, 701) having a known sequence encoded therein, wherein the radar pulse (101, 201, 301, 401, 501, 601, 701) is configured to have a pulse length as long as a maximum roundtrip delay time corresponding to a maximum radar range; after the radar pulse (101, 201, 301, 401, 501, 601, 701) has been transmitted, receiving (903) a radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701), wherein a length of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) is shorter than the pulse length of the radar pulse (101, 201, 301, 401, 501, 601, 701); producing (905) a set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) representing correlations of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against each member of a set of differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701), wherein each of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) has a corresponding delay hypothesis selected from a set of delay hypotheses ranging from a minimum delay hypothesis associated with a minimum radar range to a maximum delay hypothesis associated with the maximum radar range; determining (907) which one of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) produced a target correlation result from among the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), and using the delay hypothesis corresponding to said determined one of the differently delayed copies (205-1, 205-2, 205-3) as a matching delay length; and using (909) the matching delay length to estimate a range of a sensed object in the environment.

2. The method of claim 1, wherein the target correlation result is a highest correlation result from among the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725).

3. The method of claim 1 or claim 2, wherein an autocorrelation for non-zero time shifts of the radar pulse (101, 201, 301, 401, 501, 601, 701) does not exceed a maximum sequence autocorrelation threshold amount.

4. The method of any one of the previous claims, wherein a correlation between a first portion of the radar pulse (101, 201, 301, 401, 501, 601, 701) and a second portion of the radar pulse (101, 201, 301, 401, 501, 601, 701) does not exceed a maximum correlation threshold amount, wherein a length of the first portion equals a length of the second portion, and wherein the length of the first and second portions is shorter than the pulse length of the radar pulse (101, 201, 301, 401, 501, 601, 701).

5. The method of any one of the previous claims, comprising: for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection (107) by appending a string (109) of one or more zero signal values in front of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737), wherein each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) is produced by correlating a differently delayed version of the radar pulse (101, 201, 301, 401, 501, 601, 701) against the modified received radar reflection (107).

6. The method of any one of claims 1 through 3, wherein the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) comprises a front portion and a remaining portion that follows the front portion, and wherein the method comprises: for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection (107) by discarding the front portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) and appending a string (109) of one or more zero signal values in front of the remaining portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737), wherein each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) is produced by correlating a differently delayed version of the radar pulse (101, 201, 301, 401, 501, 601, 701) against the modified received radar reflection (107).

7. The method of any one of claims 1 through 3, wherein: the radar pulse (101, 201, 301, 401, 501, 601, 701) is transmitted during a transmission time window and the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) is received during a receive time window that follows the transmission time window; and for one or more members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), producing (905) said members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises using a correlation window (313, 315, 317, 323, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) that begins no earlier than a start of the receive time window.

8. The method of claim 7, wherein for said one or more members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), producing (905) said members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises using a correlation window (313, 315, 317, 323, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) that begins later than a start of the receive time window.

9. The method of any one of the previous claims, wherein the known sequence comprises a plurality of sub-sequences.

10. The method of claim 9, wherein two or more of the plurality of sub-sequences are identical to one another.

11. The method of claim 9, wherein the plurality of sub-sequences comprises a first subsequence and a second sub-sequence that is different from the first sub-sequence, wherein an aperiodic autocorrelation between the first sub-sequence and the second sub-sequence does not exceed a maximum sub-sequence autocorrelation threshold amount.

12. The method of any one of claims 9 and 11, wherein the sub-sequences are all different from one another.

13. The method of claim 9, wherein at least two of the plurality of sub-sequences are a complimentary sequence pair.

14. The method of claim 9, wherein the plurality of sub-sequences comprises a first subsequence and a second sub-sequence that differ in length from one another.

15. The method of any one of the previous claims, wherein each correlation result in the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) represents a correlation, using a first correlation window (323), of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against a respective one of the members of the set of differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701), and wherein producing (905) the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises: for each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725): producing a plurality of sub-correlation results by performing a plurality of subcorrelations of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against a respective member of the set of differently delayed copies (205-1, 205- 2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701); and combining the plurality of sub-correlation results to produce the member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), wherein: each of the sub-correlations uses a respective one of a plurality of sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717); and each of the sub-correlation windows is shorter than the first correlation window; and each of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) is used for correlating against a different portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737).

16. The method of claim 15 when dependent from claim 9, wherein each of the subcorrelations uses a cyclic correlation property of one of the sub-sequences.

17. The method of claim 15 when dependent from claim 8, wherein: the plurality of sub-sequences comprises a first sub-sequence and a second sub-sequence that are different from one another; andat least one of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) is used for correlating a portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against the first sub-sequence and also for correlating the portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against the second sub-sequence.

18. The method of any one of claims 15 and 16, wherein determining (907) which one of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) produced the highest correlation result from among the set of correlation results comprises comparing sub-correlation results produced using different ones of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717).

19. The method of any one of the previous claims, wherein: transmitting (901) into the environment, from the device (807), the radar pulse (101, 201, 301, 401, 501, 601, 701) comprises using a first beam width when transmitting (901) the radar pulse (101, 201, 301, 401, 501, 601, 701) into the environment; and receiving (903) the radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701) comprises using a second beam width when receiving (903) the radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701), wherein the second beam width is narrower than the first beam width.

20. A computer program (1009) comprising instructions that, when executed by at least one processor (1003), causes the at least one processor (1003) to carry out the method according to any one of claims 1 through 19.

21. A carrier comprising the computer program (1009) of claim 20, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium (1005).

22. An apparatus (807, 900, 1001) for performing radar sensing of an environment, the apparatus comprising circuitry configured to cause a device (807) to perform: transmitting (901) into the environment, from the device (807), a radar pulse (101, 201, 301, 401, 501, 601, 701) having a known sequence encoded therein, wherein the radar pulse(101, 201, 301, 401, 501, 601, 701) is configured to have a pulse length as long as a maximum roundtrip delay time corresponding to a maximum radar range; after the radar pulse (101, 201, 301, 401, 501, 601, 701) has been transmitted, receiving (903) a radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701), wherein a length of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) is shorter than the pulse length of the radar pulse (101, 201, 301, 401, 501, 601, 701); producing (905) a set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) representing correlations of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against each member of a set of differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701), wherein each of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) has a corresponding delay hypothesis selected from a set of delay hypotheses ranging from a minimum delay hypothesis associated with a minimum radar range to a maximum delay hypothesis associated with the maximum radar range; determining (907) which one of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) produced a target correlation result from among the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), and using the delay hypothesis corresponding to said determined one of the differently delayed copies (205-1, 205-2, 205-3) as a matching delay length; and using (909) the matching delay length to estimate a range of a sensed object in the environment.

23. The apparatus (807, 900, 1001) of claim 22, wherein the target correlation result is a highest correlation result from among the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725).

24. The apparatus (807, 900, 1001) of claim 22 or claim 23, wherein an autocorrelation for non-zero time shifts of the radar pulse (101, 201, 301, 401, 501, 601, 701) does not exceed a maximum sequence autocorrelation threshold amount.

25. The apparatus (807, 900, 1001) of any one of claims 22 through 24, wherein a correlation between a first portion of the radar pulse (101, 201, 301, 401, 501, 601, 701) and a second portion of the radar pulse (101, 201, 301, 401, 501, 601, 701) does not exceed a maximumcorrelation threshold amount, wherein a length of the first portion equals a length of the second portion, and wherein the length of the first and second portions is shorter than the pulse length of the radar pulse (101, 201, 301, 401, 501, 601, 701).

26. The apparatus (807, 900, 1001) of any one of claims 22 through 25, comprising: for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection (107) by appending a string (109) of one or more zero signal values in front of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737), wherein each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) is produced by correlating a differently delayed version of the radar pulse (101, 201, 301, 401, 501, 601, 701) against the modified received radar reflection (107).

27. The apparatus (807, 900, 1001) of any one of claims 22 through 24, wherein the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) comprises a front portion and a remaining portion that follows the front portion, and wherein the method comprises: for at least each delay hypothesis that corresponds to a target radar range that is less than the maximum radar range, producing a modified received radar reflection (107) by discarding the front portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) and appending a string (109) of one or more zero signal values in front of the remaining portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737), wherein each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) is produced by correlating a differently delayed version of the radar pulse (101, 201, 301, 401, 501, 601, 701) against the modified received radar reflection (107).

28. The apparatus (807, 900, 1001) of any one of claims 22 through 24, wherein: the radar pulse (101, 201, 301, 401, 501, 601, 701) is transmitted during a transmission time window and the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) is received during a receive time window that follows the transmission time window; andfor one or more members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), producing (905) said members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises using a correlation window (313, 315, 317, 323, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) that begins no earlier than a start of the receive time window.

29. The apparatus (807, 900, 1001) of claim 28, wherein for said one or more members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), producing (905) said members of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises using a correlation window (313, 315, 317, 323, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) that begins later than a start of the receive time window.

30. The apparatus (807, 900, 1001) of any one of claims 22 through 29, wherein the known sequence comprises a plurality of sub-sequences.

31. The apparatus (807, 900, 1001) of claim 30, wherein two or more of the plurality of subsequences are identical to one another.

32. The apparatus (807, 900, 1001) of claim 30, wherein the plurality of sub-sequences comprises a first sub-sequence and a second sub-sequence that is different from the first subsequence, wherein an aperiodic autocorrelation between the first sub-sequence and the second sub-sequence does not exceed a maximum sub-sequence autocorrelation threshold amount.

33. The apparatus (807, 900, 1001) of any one of claims 30 and 32, wherein the subsequences are all different from one another.

34. The apparatus (807, 900, 1001) of claim 30, wherein at least two of the plurality of subsequences are a complimentary sequence pair.

35. The apparatus (807, 900, 1001) of claim 30, wherein the plurality of sub-sequences comprises a first sub-sequence and a second sub-sequence that differ in length from one another.

36. The apparatus (807, 900, 1001) of any one of claims 22 through 35, wherein each correlation result in the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) represents a correlation, using a first correlation window (323), of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against a respective one of the members of the set of differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701), and wherein producing (905) the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725) comprises: for each member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725): producing a plurality of sub-correlation results by performing a plurality of subcorrelations of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against a respective member of the set of differently delayed copies (205-1, 205- 2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701); and combining the plurality of sub-correlation results to produce the member of the set of correlation results (319, 321, 419, 421, 519, 521, 619, 621, 623, 719, 721, 723, 725), wherein: each of the sub-correlations uses a respective one of a plurality of sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717); and each of the sub-correlation windows is shorter than the first correlation window; and each of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) is used for correlating against a different portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737).

37. The apparatus (807, 900, 1001) of claim 36 when dependent from claim 30, wherein each of the sub-correlations uses a cyclic correlation property of one of the sub-sequences.

38. The apparatus (807, 900, 1001) of claim 36 when dependent from claim 29, wherein: the plurality of sub-sequences comprises a first sub-sequence and a second sub-sequence that are different from one another; and at least one of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717) is used for correlating a portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against the first sub-sequenceand also for correlating the portion of the received radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) against the second sub-sequence.

39. The apparatus (807, 900, 1001) of any one of claims 36 and 37, wherein determining (907) which one of the differently delayed copies (205-1, 205-2, 205-3) of the radar pulse (101, 201, 301, 401, 501, 601, 701) produced the highest correlation result from among the set of correlation results comprises comparing sub-correlation results produced using different ones of the sub-correlation windows (313, 315, 317, 413, 415, 417, 513, 515, 517, 613, 615, 617, 713, 715, 717).

40. The apparatus (807, 900, 1001) of any one of claims 22 through 39, wherein: transmitting (901) into the environment, from the device (807), the radar pulse (101, 201,301, 401, 501, 601, 701) comprises using a first beam width when transmitting (901) the radar pulse (101, 201, 301, 401, 501, 601, 701) into the environment; and receiving (903) the radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701) comprises using a second beam width when receiving (903) the radar reflection (203, 309, 311, 409, 411, 509, 511, 609, 611, 731, 733, 735, 737) of the transmitted radar pulse (101, 201, 301, 401, 501, 601, 701), wherein the second beam width is narrower than the first beam width.

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