Impulse radar system

Abstract

An impulse radar system (100) for object sensing comprises a first transmit antenna (121), a second transmit antenna (123) spatially separated from the first transmit antenna, a first receiver (105), and first and second accumulators (131, 133). The system (100) is configured to transmit first and second signals (111, 113), each comprising a plurality of sets of pulses, into an environment by transmitting the plurality of sets of pulses of the first signal from the first transmit antenna (121) interleaved with the plurality of sets of pulses of the second signal from the second transmit antenna (123). The system is further configured to receive reflected signals comprising reflections of the transmitted sets of pulses at the first receiver (105), to accumulate received signals comprising reflections of sets of pulses of the first signal using the first accumulator (131) and to accumulate received signals comprising reflections of sets of pulses of the second signal using the second accumulator (133).

Description

[0001] Impulse Radar System

[0002] TECHNICAL FIELD

[0003] This disclosure relates to an impulse radar system for object sensing, and a method of operating an impulse radar system.

[0004] BACKGROUND OF THE INVENTION

[0005] MIMO radar systems employing time division multiplexing (TDM) rely on the assumption that the scene is effectively static during measurement. Using the phase difference between the transmit-receive channels of a signal reflected from the target, the angle-of-arrival can be estimated.

[0006] In scenarios where a high duty cycle is required for sufficient signal-to-noise ratio (SNR), the coherent processing interval (CPI) in each Transmitter-Receiver combination might be too long for the assumption of static scene during multiplexing to hold. If the target radial velocity is such that it moves significantly during the transmission antenna switching period and / or during integration of received signals, a motion-induced phase shift across the transmit-receive channels may arise in signals reflected from the target. This motion-induced phase shift may be referred to as a motion-induced phase error as it creates an ambiguity between the target angle-of-arrival and velocity. A target moving radially towards or away from the radar during the transmit antenna switching period will induce the largest motion induced error, and this error increases with the target velocity and the integration time in each transmit-receive channel.

[0007] The present invention aims to provide an impulse radar system capable of reducing motion-induced phase error with reduced processing requirement, enabling high duty cycle for moving targets in a TDM impulse MIMO radar system.

[0008] SUMMARY OF THE INVENTION

[0009] According to a first aspect, there is provided an impulse radar system for object sensing, the system comprising: a first transmit antenna; a second transmit antenna spatially separated from the first transmit antenna; a first receiver; and first and second accumulators; wherein the system is configured to: transmit first and second signals into an environment, the first and second signals each comprising a plurality of sets of pulses; wherein transmitting the first and second signals comprises transmitting the plurality sets of pulses of the first signal from the first transmit antenna interleaved with the plurality of sets of pulses of the second signal from the second transmit antenna; receive reflected signals at the first receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulate received signals comprising reflections of sets of pulses of the first signal using the first accumulator; and accumulate received signals comprising reflections of sets of pulses of the second signal using the second accumulator.

[0010] According to a second aspect, there is provided a method of operating an impulse radar system for object sensing, the method comprising: transmitting first and second signals into an environment, the first and second signals each comprising a plurality of sets of pulses; wherein transmitting the first and second signals comprises transmitting a plurality of sets of pulses of a first signal from a first transmit antenna interleaved with a plurality of sets of pulses of a second signal from a second transmit antenna, the second transmit antenna being spatially separated from the first transmit antenna; receiving reflected signals at a first receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulating received signals comprising reflections of sets of pulses of the first signal using a first accumulator; and accumulating received signals comprising reflections of sets of pulses of the second signal using a second accumulator.

[0011] Thus, sets of pulses of a first signal are transmitted from a first transmit antenna interleaved with sets of pulses of a second signal transmitted from a second transmit antenna. Reflections of sets of pulses of the first signal are accumulated at a first accumulator, and reflections of sets of pulses of the second signal are accumulated at a second accumulator.

[0012] By “interleaved with”, it will be understood that the first transmit antenna and the second transmit antenna respectively transmit sets of pulses of the first signal and the second signal alternately and in turn. As an example, in the case that the first signal and the second signal each comprise two sets of pulses, the first transmit antenna transmits a first set of pulses of the first signal, then the second transmit antenna transmits a first set of pulses of the second signal, then the first transmit antenna transmits a second set of pulses of the first signal, and finally the second transmit antenna transmits a second set of pulses of the second signal. In this way the impulse radar system transmits a plurality of (two) sets of pulses of the first signal interleaved with a plurality of (two) sets of pulses of the second signal.

[0013] The first signal and the second signal are thus each split into a plurality of sets of pulses which are separated from one another in time by sets of pulses from the other transmit antenna. However, each signal is accumulated to retain integration gain as successive sets of pulses are transmitted. Thus, all sets of the first signal are accumulated together and all sets of the second signal are accumulated together. Each set of pulses is shorter than the first and second signals, such that the duration of transmission of each individual set of pulses by the first or second transmitter is shorter. The potential for movement of a target between successively transmitted sets of pulses is therefore reduced. This reduces the amount of motion- induced error in the phase difference between the interleaved signals, as explained below.

[0014] Motion of a target results in a phase shift in radar signals reflected from the target. When reflected signals are accumulated over a time period, the average phase of the accumulated signal is shifted due to the motion of the target over the time period. This phase shift causes issues when calculating a phase difference between accumulated signals from different transmit antennas, e.g., to determine the angle to a target. The phase shift for the first transmit antenna is only due to the averaging effect over the total integration (accumulation) time for that transmit antenna. However, all other transmit antennas have an additional phase offset due to the delay before their first transmission (i.e. the delay before the start of integration / accumulation).

[0015] Typical MIMO radar systems employing time division multiplexing reduce the amount of time over which signals are accumulated (the coherent processing interval) so as to be able to rely on the assumption that the scene is effectively static during measurement. In contrast, the present invention reduces this error by splitting the signals transmitted from the first antenna and the second antenna into sets of pulses, and interleaving the sets of pulses from the first transmit antenna with those of the second transmit antenna. By interleaving pulses of the first signal with those of the second signal, a long coherent processing interval is maintained, but the difference between the average phase shift of the first signal and the average phase shift of the second signal is significantly reduced due to the reduced offsets between different transmissions. Essentially, although all signals are accumulated over a long period of time, they are accumulated in parallel such that their phase averages are kept closer together. By reducing the effect of the transmission start offset, the motion-induced phase error is reduced which allows much greater accuracy in calculations based on phase differences between different transmit-receive paths (e.g. angle to target). This means that the duration over which the first signal and the second signal are accumulated can be increased in comparison to conventional systems without introducing a large motion-induced error in the phase difference between the interleaved signals.

[0016] Thus, although the duration of each transmission (e.g. set of pulses) is reduced, integration gain is nonetheless achieved for the system as a whole by accumulating reflections of the sets of pulses of the first and second signals over time to achieve a sufficient signal to noise ratio.

[0017] In effect, the interleaving of the first and second signals results in the commencement of the second signal being closer to the commencement of the first signal. The time separation between the start of the first signal and the start of the second signal is the duration of the first set of pulses. This is much shorter than a non-interleaved arrangement in which the time separation between the start of the first signal and the start of the second signal is the whole length of the first signal (i.e. encompassing all transmitted pulses of the first signal). When the first and second signals are accumulated (e.g. coherently integrated), the phase difference between the accumulated interleaved signals is much smaller than the phase difference between accumulated non-interleaved signals. Thus, the motion-induced phase error is greatly reduced. The reduction in phase error allows the system to more accurately estimate the angle to moving targets, such that the system provides improved positioning accuracy for moving targets (and particularly improves accuracy and positioning resilience against higher velocity targets).

[0018] In some embodiments, the first and second signals may be transmitted in a first time period (referred to in the following as a coherent processing interval). Thus, every set of pulses of the first signal and the second signal may be sent in the first time period. The coherent processing interval sets the amount of integration gain that can be achieved by the system. In some embodiments, the system is configured to separate each of the first and second signals into respective sets of pulses, wherein the number of sets of pulses is set based on the length of the first time period. For example, a longer first time period may be split into a larger number of sets so as to spread the pulses of each signal more evenly across the first time period. It will be appreciated that the spread does not have to be perfectly even, but it is generally advantageous to make it as even as possible. Any unevenness in the distribution (e.g. different sets of pulses of one signal having different numbers of pulses) will skew the average phase for the whole signal and result in an increased phase error in the difference between the different signals.

[0019] In some such embodiments, each set of the plurality of sets of interleaved pulses of the first signal and the second signal may be transmitted in a respective portion of the first time period. The portion of the first time period in which a set of pulses is transmitted may thus be referred to in the following as an interleaved interval. Each respective portion of the first time period may have a predetermined duration, e.g. corresponding to the time it takes to transmit a set of pulses and receive a reflected signal (comprising a reflection of the transmitted sets of pulses from a target in the environment).

[0020] The duration of the first time period may be controllable in some embodiments. For example, the first time period may provide a measurement frame and it may be desirable to control (and adjust) the frame rate (i.e. the number of frames per second) for different uses or different scenarios. The number and / or duration of the portions of the first time period may also be controllable in some embodiments. The number of portions of the first time period in which sets of pulses are transmitted may be controlled based on the duration of the first time period. The duration of each of the portions of the first time period may be controlled based on a predetermined threshold value of motion induced phase error for the system in some embodiments.

[0021] In some embodiments, the duration of the respective portions of the first time period may be controlled based on an expected velocity of a target within the environment. More specifically, the duration of the respective portions of the first time period may be controlled such that the target remains effectively stationary during each respective portion of the time period. By “effectively stationary” it will be understood that the range to the target from the radar system does not change significantly during any single portion of the time period. For example, where the expected velocity of a target to be sensed by the system is high, the duration of the respective portions of the first time period may be reduced. Similarly, where the expected velocity of a target is low, the duration of the respective portions of the first time period may be increased. As a more specific example, the duration of the respective portions of the first time period may be minimised for a target that is expected to move significantly, e.g. a walking person in the environment. In the same way, the duration of the respective portions of the first time period may be increased for a target that is not expected to move significantly, e.g. a seated person in the environment. By controlling the duration of the portions of the first time period in this way, motion-induced phase error may be reduced while allowing processing overhead to be minimised when sensing slow moving or stationary targets. The processing overhead may be reduced by increasing the duration of the respective portions of the first time period, thereby reducing the number of portions into which the first time period is divided and hence the number of switching operations required. One source of processing overhead is the various switching operations required to switch between different antennas and to switch in and out the accumulators. In the transmit process, the transmit antenna is switched after every set of pulses so as to accomplish interleaving. In the receive process, where a single receiver receives signals from several transmit antennas, switching operations are required after every set of pulses to switch to a different accumulator (as the source of the pulses has changed to a different transmit antenna). Therefore, dividing the first time period into more portions (each with smaller sets of pulses) increases the number of switching operations and thus the processing overhead. A second and more significant source of processing overhead is the need to process frames that have been spread across multiple accumulators.

[0022] In addition to or as an alternative to an expected target velocity, the duration of the respective portions of the first time period may be controlled based on any suitable requirement for the application in which the radar system is implemented. For example, the duration of the respective portions of the first time period may be controlled based on a maximum expected range to the target, an expected target size or a dynamic range in some embodiments.

[0023] In some embodiments, the system may comprise a processor configured to analyse the accumulated signals to identify one or more targets in the environment. More particularly, the processor may be configured to analyse the accumulated signals to determine a range of the one or more targets and / or an angle to the one or more targets (e.g. the angular position of the target with respect to the radar system) and / or a velocity of the one or more targets. Thus, in some embodiments, analysing the accumulated signals comprises determining a range and / or an angle to and / or a velocity of the one or more targets.

[0024] It will be appreciated that each transmit antenna has an associated transmit circuit for generating the waveform to be transmitted (e.g. a pulse generator, etc.). The transmit circuit and transmit antenna together form a transmitter. As the uses of the transmit antennas are interleaved such that they do not transmit together, they can share a back end, i.e. they can share a transmit circuit. Thus a first transmitter may be formed from the first transmit antenna and a common transmit circuit and a second transmitter may be formed from the second transmit antenna and the common transmit circuit.

[0025] In some embodiments, the first receiver has a receive antenna and the first transmit antenna, second transmit antenna and receive antenna may all be spatially separated from one another. In some embodiments however, the first receive antenna may be collocated with the first transmit antenna or the second transmit antenna, e.g., the first receiver may share an antenna with the first transmitter or the second transmitter. Providing a shared antenna for the first receiver and one of the first transmitter and second transmitter may allow the physical size of the impulse radar system to be reduced.

[0026] In some embodiments, the first transmit antenna and the second transmit antenna may be configured such that only one of the first transmit antenna and second transmit antenna is transmitting at any given time. By operating the system such that only one of the first transmit antenna or the second transmit antenna is transmitting at a given time, the system may be operated without having to encode the transmitted signals.

[0027] In some embodiments the first and second receivers may have separate antennas but share a receive chain (i.e. receive circuit). This requires switching of accumulators in addition to switching of antennas but makes significant cost and / or area savings by sharing the receive chain (i.e. only one LNA, filter, ADC, etc. to cover multiple accumulators). This is possible because the accumulators are always used sequentially so there is no temporal overlap that requires multiple receive chains. It is also possible, and in many cases advantageous to have a single antenna and single receive chain shared between a plurality of accumulators. The only switching necessary is then switching accumulators. This arrangement effectively has a single receiver (one antenna and one receive chain) that receives from both the first transmit antenna and the second transmit antenna (and optionally any further transmit antennas) and has advantages of cost and area savings as well as low switching requirements. In all embodiments, to get the maximum benefit out of the available transmission paths, the total number of accumulators will be equal to the number of transmit antennas multiplied by the number of receive antennas.

[0028] Thus, in some embodiments the first accumulator is arranged to accumulate reflections of sets of pulses of the first signal received at the first receiver and wherein the second accumulator is arranged to accumulate reflections of sets of pulses of the second signal received at the first receiver. In some embodiments, the system may comprise a third transmit antenna and a third accumulator. The third transmit antenna may be configured to transmit a third signal into the environment, the third signal comprising a plurality of sets of pulses. In such embodiments the system may be configured to transmit first, second and third signals into the environment, such that sets of pulses of the first signal from the first transmit antenna are interleaved with sets of pulses of the second signal from the second transmit antenna and with a plurality of sets of pulses of the third signal from the third transmit antenna. The system may be configured to accumulate received signals comprising reflections of sets of pulses of the third signal using the third accumulator.

[0029] By including an additional transmit antenna and accumulator, the angle to the targets sensed by the system may be detected more accurately, e.g. with reduced angular error. In such embodiments, the first, second and third signals may be interleaved such that the first transmitter, the second transmitter and the third transmitter respectively transmit sets of pulses of the first signal, the second signal and the third signal alternately and in turn. As an example, the first transmitter may transmit one or more sets of pulses of the first signal, then the second transmitter may transmit one or more sets of pulses of the second signal then the third transmitter may transmit one or more sets of pulses of the third signal. This process may then repeat beginning with the first transmitter until all sets of pulses have been transmitted. Including an additional transmit antenna, such that the system includes at least three transmitter-receiver pairs, may also allow the system to determine the angle to a target in a second angular dimension. This may allow the system to determine the angle to the target in terms of both an azimuthal angle and an elevational angle.

[0030] It will be appreciated however that the order in which the interleaved sets of pulses are transmitted may be different in some examples. For example, labelling sets of pulses of the first, second and third signals as “A”, “B” and “C” respectively, sets of pulses may be transmitted in a round-robin fashion in any order, e.g., as “ABCABCABC...”, “BACBACBAC...”, “CABCABCAB...” etc. Alternatively, sets of pulses from one of the transmitters may be transmitted more regularly than the other transmitters in some examples. For example, using the labelling scheme defined above, sets of pulses may be transmitted as “ABACABACABAC...”, “BABCBABCBABC...”, “CACBCACBCACB...” etc. In this way, transmission of a signal from one of the transmitters, e.g. the first transmitter, may be prioritised while still retaining the benefits of interleaved transmission of sets of pulses set out above.

[0031] In some embodiments, the system may comprise a second receiver and the system may comprise an additional accumulator for each transmit antenna. These additional accumulators are for accumulating pulses received at the second receiver from a particular transmit antenna. For example, in a system comprising two transmit antennas (e.g. a first transmit antenna and a second transmit antenna), the impulse radar system may comprise third and fourth accumulators. In such embodiments, the system may be configured to receive reflected signals at the second receiver, the reflected signals comprising reflections of the transmitted sets of pulses. The third accumulator may be used to accumulate received signals comprising reflections of sets of pulses of the first signal (i.e. from the first transmit antenna) received at the second receiver. The fourth accumulator may be used to accumulate received signals comprising reflections of sets of pulses of the second signal (i.e. from the second transmit antenna) received at the second receiver.

[0032] In some embodiments, the first receiver and the second receiver may be arranged to receive simultaneously. By employing a second receiver arranged to receive at the same time as the first receiver, the signal to noise ratio of the impulse radar system can be increased. More specifically, doubling the number of receivers results in a 3 dB increase in signal to noise ratio. Further gains can be achieved for each additional receiver included in the impulse radar system.

[0033] In some embodiments, the system may comprise a third transmit antenna and a second receiver. In such embodiments, the system comprises six accumulators in total, e.g. one accumulator for each possible transmitter-receiver pairing. Thus, in some embodiments, the system further comprises: a third transmit antenna; a fifth accumulator; and a sixth accumulator; wherein the system is configured to: transmit a third signal into the environment, the third signal comprising a plurality of sets of pulses; wherein transmitting the first, second and third signals comprises: transmitting sets of pulses of the first signal from the first transmit antenna interleaved with sets of pulses of the second signal from the second transmit antenna and with sets of pulses of the third signal from the third transmit antenna; wherein the system is further configured to: accumulate received signals comprising reflections of sets of pulses of the third signal received at the first receiver using the fifth accumulator; and accumulate received signals comprising reflections of sets of pulses of the third signal received at the second receiver using the sixth accumulator.

[0034] While the above examples describe the case of an impulse radar system comprising a third transmit antenna and / or a second receiver, it will be appreciated that the number of transmit antennas and / or receivers included in the system may be greater than this, provided that an accumulator is provided for each transmitterreceiver pair being used. Thus in some embodiments, the system may comprise a fourth or further transmit antenna, and / or a third or further receiver. As described above, including greater numbers of transmit antennas in the system increases the number of transmitter-receiver pairs, and may thus allow the angle to the targets sensed by the system to be determined with greater angular resolution. Including greater numbers of receivers in the system, and operating the plurality of receivers in parallel may allow the signal to noise ratio of the system to be increased.

[0035] In some embodiments in which the system comprises a third transmit antenna, the first transmit antenna, the second transmit antenna and the third transmit antenna may be arranged such that only one of the first transmit antenna, the second transmit antenna and the third transmit antenna is transmitting at any given time.

[0036] In some embodiments in which the system comprises a third transmit antenna, the first transmit antenna, second transmit antenna, third transmit antenna and first receive antenna may all be spatially separated from one another. In some embodiments, the first receive antenna may be collocated with the first transmit antenna, the second transmit antenna or the third transmit antenna, e.g. the first receiver may share an antenna with the first transmitter, the second transmitter or the third transmitter.

[0037] In some embodiments in which the system comprises a second receiver, the first transmit antenna, second transmit antenna, first receive antenna and second receive antenna may all be spatially separated from one another. In some embodiments, the first receive antenna may be collocated with the first transmit antenna and / or the second receive antenna may be collocated with the second transmit antenna, e.g. the first receiver and / or the second receiver may share an antenna with the first transmitter and / or the second transmitter.

[0038] In some embodiments, the sets of pulses may each comprise a single pulse (i.e. each set may have only one pulse). However, in some embodiments, the sets of pulses may each comprise a plurality of pulses, e.g. five or fewer pulses, ten or fewer pulses, one hundred or fewer pulses, one thousand or fewer pulses, ten thousand pulses or fewer pulses or more. In some preferred embodiments, the sets of pulses may each comprise one thousand or fewer pulses. Including a greater number of pulses in each set of pulses reduces the number of interleaved intervals within a single coherent processing interval, thereby reducing the processing overhead on the system. By contrast, minimising the number of pulses per set allows for shorter duration sets of pulses, such that the time between successive transmissions, and hence the amount of motion-induced phase error in accumulated signals reflected from a moving target in the environment can be reduced.

[0039] In some embodiments, the sets of pulses within a single coherent integration period may have variable lengths, e.g. such that a first set of pulses consists of a single pulse, a second set of pulses consists of one hundred pulses, a third set of pulses consists of fifty pulses, etc. However, in some particularly advantageous embodiments, each set of pulses has the same length, such that each interleaving interval is of the same duration.

[0040] It will be appreciated that the radar system may be a multiple input multiple output time division multiplexing radar system in some embodiments. Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Certain preferred embodiments of this disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] FIG. 1 shows an impulse radar system according to a first embodiment of the invention;

[0044] FIG. 2 is a timing diagram showing a method of operating an impulse radar system according to a first embodiment of the invention;

[0045] FIG. 3 shows a comparison of the coherent integration of received radar pulses with and without implementation of a method according to an embodiment of the invention;

[0046] FIG. 4 shows an impulse radar system according to a second embodiment of the invention;

[0047] FIG. 5 is a timing diagram showing a method of operating an impulse radar system according to a second embodiment of the invention; and

[0048] FIG. 6 shows an impulse radar system according to a third embodiment of the invention;

[0049] FIG. 7 is a timing diagram showing a method of operating an impulse radar system according to a third embodiment of the invention;

[0050] FIG. 8 shows an impulse radar system similar to FIG. 1 where two transmit antennas share a common transmit chain; and

[0051] FIG. 9 shows an impulse radar system similar to FIG. 4 where a single receiver serves two receive antennas and four accumulators.

[0052] DETAILED DESCRIPTION

[0053] Figure 1 shows an impulse radar system 100 according to a first embodiment of the invention. The impulse radar system 100 comprises a first transmitter 101 (TX0), a second transmitter 103 (TX1) and a first receiver 105 (RX0). The second transmitter 103 has a dedicated antenna 123 that is spatially separated from the antenna 121 of the first transmitter 101. In this embodiment the first receiver 105 also has a dedicated antenna 125, although in other embodiments it may share either antenna 121 or 123.

[0054] The impulse radar system 100 also includes a first accumulator 131, a second accumulator 133, and a processor 110. The first accumulator 131 and the second accumulator 133 are arranged to accumulate received signals comprising reflections of signals transmitted from the first transmitter 101 and the second transmitter 103 respectively. It will be appreciated that the accumulators 131, 133 (and others discussed below) may take a variety of forms. However, by way of example, an accumulator may sample the incoming signal at a plurality of time points, each corresponding to a range point, i.e. the accumulator may accumulate a sampled waveform of the transmitted pulses.

[0055] The impulse radar system 100 is configured to transmit a first signal 111 into an environment using the first transmitter 101 and to transmit a second signal 113 into the environment using the second transmitter 103. The first signal 111 and the second signal 113 are transmitted as sets of interleaved pulses as will be explained in more detail below. The first signal 111 and the second signal 113 are transmitted into the environment around the system 100, and are reflected from a target 102 in the form of a reflected signal 108. The reflected signal 108 is received at an antenna 125 of the receiver 105. It should be noted that for simplicity the examples described here only describe a single target 102, but the system is equally capable of detecting multiple targets at different ranges and / or different angles and / or radial velocities.

[0056] Reflections of the first signal 111 transmitted from the first transmitter 101 and received at the receiver 105 are accumulated at the first accumulator 131. Reflections of the second signal 113 transmitted from the second transmitter 103 and received at the receiver 105 are accumulated at the second accumulator 133.

[0057] The accumulated signals are passed to the processor 110 for analysis. The processor 110 analyses the accumulated signals to determine one or more properties of the target, e.g., a range to the target 102 and / or an angle to the target 102 and / or a velocity of the target 102. In particular, as two separate signal paths are detected (TX0 to RX0 and TX1 to RX0 take different paths through the environment), the angle to the target can be determined based on the different times taken for the transmissions to reach the receiver. It will be appreciated that the different times taken for the transmissions to reach the receiver may, in practice, be determined based a difference in phase between the received signals in some embodiments. For example, a time difference between the two signals being received may be determined based on a phase difference of arrival of signals received at the first receiver 105.

[0058] It will be further appreciated that in addition or as an alternative to determining the range to the target and / or angle to the target and / or velocity of the target, the processor 110 may determine other properties of the target based on the accumulated signals in some embodiments, such as a radar cross section (RCS) for the target. Where the target is a human being (or other living being), the processor 110 may be configured to determine vital signs of the target, such as a heart rate or respiration rate of the target. In such embodiments, vital signs may be determined based on movements of the target over time.

[0059] Figure 2 illustrates the timing of signal transmissions using the impulse radar system 100 shown in Figure 1. The first signal 111 and the second signal 113 are sent over a time period AT, referred to in the following as the coherent processing interval as all pulses received in this interval are combined together by coherent integration for further analysis. Sets 201 , 203, 205, 207of pulses of the first signal 111 and sets 202, 204, 206, 208 of the second signal 113 are transmitted and received in respective portions ti- tN of the time period AT as described in more detail below. Reflections of the first signal 111 and the second signal 113 received at the receiver 105 are then provided to either the first accumulator 131 or the second accumulator 133 respectively (as illustrated schematically by the '+’ symbols).

[0060] As can be seen in Figure 2, a first set 201 of pulses, comprising two individual pulses, is transmitted from the first transmitter 101 (TX0) in a first portion Ah of the time period AT. The set 201 of pulses is reflected by the target 102, and a reflected signal 108 is received at the receiver 105 (RX0). The received signal is then passed to the first accumulator 131. Although Figure 2 shows sets 201-208 of pulses each comprising two individual pulses, it will be appreciated that this is only an example, and that each set of pulses may contain a single pulse or a significantly larger (e.g. thousands) of pulses in some embodiments.

[0061] In a second portion At2 of the time period AT, a second set 202 of pulses, comprising two individual pulses, is transmitted from the second transmitter 103 (TX1). The set 202 of pulses is reflected by the target 102, and a reflected signal 108 is received at the receiver 105 (RX0). The received signal is then passed to the second accumulator 133.

[0062] In a third portion Ata of the time period AT, a third set 203 of pulses, comprising two individual pulses, is transmitted from the first transmitter 101 (TX0). The set 203 of pulses is reflected at the target 102, and a reflected signal 108 is received at the receiver 105 (RX0). The received signal is passed to the first accumulator 131 , where it is combined with the received signal corresponding to the signal transmitted by the first transmitter 101 in the first portion Ah of the time period AT. Thus, these first and third sets 201 , 203 from the first transmitter TX0 are coherently integrated in the first accumulator 131.

[0063] In a fourth portion At4 of the time period AT, a fourth set 204 of pulses, comprising two individual pulses, is transmitted from the second transmitter 103 (TX1). The set 204 of pulses is reflected at the target 102, and a reflected signal is received at the receiver 105 (RX0). The received signal is passed to the second accumulator 133, where it is combined with the received signal corresponding to the signal transmitted by the second transmitter 103 in the second portion At2 of the time period AT. Thus, these second and fourth sets 202, 204 from the second transmitter TX1 are coherently integrated in the second accumulator 133.

[0064] Sets 205, 206, and 207 of pulses are transmitted from the first transmitter 101 and the second transmitter 103 alternately in the fifth, sixth, and seventh portions of the time period AT as shown in Figure 2, with reflected sets of pulses corresponding to the first signal 111 being accumulated at the first accumulator 131 , and reflected sets of pulses corresponding to the second signal 113 being accumulated at the second accumulator 133. This process continues with sets of pulses of the first signal 111 and the second signal 113 being sent from the first transmitter 101 and the second transmitter 103 in turn, such that the sets of pulses of the first signal 111 are interleaved with the sets of pulses of the second signal 113, until all sets of pulses of the first signal 111 and the second signal 113 have been transmitted. This is shown in Figure 2 as N sets 201-208 of pulses being transmitted in total, with a signal corresponding to the Nth set 208 of pulses of the second signal 113 being sent by the second transmitter 103 (TX1) in the Nth portion AtN of the time period AT, and a corresponding reflected signal 108, received at the first receiver 105 being accumulated at the second accumulator 133. This completes a transmission frame.

[0065] In this way, the system 100 generates a first accumulated signal from reflections of the first signal 111 received at the first receiver 105, and generates a second accumulated signal from reflections of the second signal 113 received at the first receiver 105. These accumulated signals are then passed to the processor 110 to determine one or more properties of the target, e.g. a range to the target 102 and / or an angle to the target 102 and / or a velocity of the target 102. Processing techniques for determining range to the target, angle to the target and velocity of the target from these accumulated signals are known to the skilled person.

[0066] By transmitting the first signal 111 and the second signal 113 as a plurality of sets of interleaved pulses, phase error resulting from motion of the target 102 can be significantly reduced, as explained below with reference to Figures 3A-3D.

[0067] Figure 3A shows a signal at the receiver RX0 following transmission of two sets of pulses from the first and second transmitters of the system 100 within a time period AT without implementing an interleaving method as disclosed herein. Specifically, Figure 3A shows a received signal reflected from a target 102 after transmission of a first set of four pulses 301a from the first transmitter TX0 (illustrated with solid lines) followed by transmission of a second set of four pulses 303a from the second transmitter TX1 (illustrated with broken lines). The time between receiving the first pulse of the first set of pulses 301a and the first pulse of the second set of pulses 303a is shown as Ata. Note that the figures show the pulse development in slow time, i.e. the time for each received pulse is measured relative to its own transmission time. Thus for a perfectly static target, all pulses 301a would overlap fully and all pulses 303a would overlap. However, the figures show the case for a moving target (moving radially away from the receiver) where the target velocity causes an ever increasing time delay in the received pulses.

[0068] After being received at the receiver RXO, the first set of pulses 301a and the second set of pulses 303a are each coherently integrated by the accumulators to achieve integration gain. The integrated signals are shown in Figure 3C. The result of coherent integration of the first set of pulses 301a is shown as curve 305a. The result of coherent integration of the second set of pulses 301a is shown as curve 307a.

[0069] The integrated pulses from the first transmitter TX0 can be compared to the integrated pulses from the second transmitter TX1 in order to determine the phase difference between them and this phase difference can be used to calculate the angle to the target 102 from which the pulses 301a, 303a are reflected with respect to the receiver RXO.

[0070] As the transmitters TX1 and TX2 are located at different distances from the target 102, the path length of signals that are transmitted from the transmitter TX0, reflected at the target 102 and received at the receiver RXO is different to the path length of signals transmitted from TX1 and received at RXO in the same way. This difference in path length results in a phase difference in pulses received at the receiver RXO from the transmitter TX0 compared to those from the transmitter TX1 . The angle to the target 102 can thus be determined from a measurement of the phase difference between the integrated signals 305a, 307a provided the distance between RXO and each of TX0 and TX1 is known.

[0071] However, as shown in Fig. 3C, the only phase difference that can be measured in the integrated signals is <$>i. However, <$>i includes both the phase difference due to the angle to the target 102 and a phase difference due to movement of the target that occurred during the measurements. This additional phase contribution, <$>edue to the movement of the target 102, is given by:

[0072] 4nfvz (pe =~ ~ where f is the carrier frequency of the transmitted pulses, v is the radial velocity of the target 102, c is the speed of light, and T is the time over which the target moves between the two sets of integrated measurements. In the example shown in Figure 3A, the phase error Oeiis thus dependent on the time between the two sets of pulses 301a and 303a being transmitted, i.e. on Ata.

[0073] Figure 3B shows a received signal at RXO following transmission of two sets of pulses from the system 100 within a time period AT when an interleaving method of the present invention is implemented. Specifically, Figure 3B shows the received signal reflected from a target 102 after transmission of a first set of four pulses 301b from the first transmitter TX0 (illustrated with solid lines) interleaved with a second set of four pulses 303b from the second transmitter TX1 (illustrated with broken lines). The time between the first pulse of the first set of pulses 301 b and the first pulse of the second set of pulses 303b is shown as Atb and is much shorter than Ata.

[0074] After being received at the receiver RXO, the first set of pulses 301 b and the second set of pulses 303b are each coherently integrated to achieve integration gain. The integrated sets of pulses are shown in Figure 3D. The result of coherent integration of the first set of pulses 301 b is shown as curve 305b. The result of coherent integration of the second set of pulses 301 b is shown as curve 307b. The integrated pulses from the first transmitter TX0 can be compared to the integrated pulses from the second transmitter TX1 in order to determine the angle to the target 102 from which the pulses 301b, 303b are reflected. As described above, the angle to the target 102 can be determined from the phase difference <t>2between the accumulated sets of pulses 305b, 307b provided the distance between RXO and each of TX0 and TX1 is known. If the target 102 is in motion during the measurement, the phase difference <$>2 will include a contribution, <t>e2resulting from the motion of the target 102.

[0075] As can be seen in Figure 3D, the phase difference <$>2 between the accumulated interleaved sets of pulses 305b, 307b is significantly smaller than the phase difference <$>2 between the accumulated sequentially transmitted sets of pulses 305a, 307a shown in Figure 3C. This is a result of the smaller phase error <t>e2being caused by the reduction in the time Atb between the two sets of pulses 301c and 303c in comparison to the time Atabetween the sequentially transmitted sets of pulses 301a, 303a shown in Figures 3A and 3C.

[0076] Thus, when the sets of pulses from the transmitters TX0 and TX1 are interleaved as described above, motion induced phase error can be significantly reduced in comparison to existing methods. This allows for improved determination of the angle to fast-moving targets of the radar system, as coherent integration can be achieved for higher velocity targets than is possible using existing methods. As the interleaved sets of pulses are sent over the same time period AT as the sequentially transmitted pulses, the total coherent integration time is unchanged, such that a high signal to noise ratio can still be achieved.

[0077] It will be appreciated that the signal representations shown in Figs. 3A-3D are simplified for illustrative purposes. In particular, the scale of the spacing in time between the pulses shown in each of Figs. 3A-3D is significantly exaggerated for illustrative purposes. In practice it will be appreciated that there is a significant overlap between sequentially transmitted pulses such that they almost lie on top of one another when plotted in this manner (i.e. plotted in slow time, showing the receive time relative to the pulse’s transmit time and therefore essentially plotting in range), but they have been spread out here to exaggerate the effect for ease of understanding (effectively the target velocity has been highly exaggerated in the figures).

[0078] Furthermore, in the pulses shown in Figs. 3A and 3B only the envelope signal is illustrated, i.e. the carrier wave is omitted for the sake of illustrative simplicity, although it is taken into account in the accumulated (integrated) signals of Figs. 3C and 3D. It will also be appreciated that the pulse shapes have been simplified to simple sinusoids for the sake of illustration, but in reality a more complex waveform (e.g. an approximate Gaussian derivative waveform for UWB applications) may be used. The pulse shapes are also shown without encoding or modulation for simplicity of illustration.

[0079] The signal to noise ratio can be increased further by including one or more additional receivers in the system. An example of this is illustrated in Figure 4, which shows an impulse radar system 400 according to a second embodiment comprising two receivers.

[0080] The impulse radar system 400 comprises a first transmitter 401 (TX0), a second transmitter 403 (TX1), a first receiver 405 (RX0), a second receiver 407 (RX1), and a processor 410. Each of the first transmitter 401 , the second transmitter 403, the first receiver 405 and the second receiver 407 has a respective antenna. Specifically, the first transmitter 401 has a first transmit antenna 421 , the second transmitter 403 has a second transmit antenna 423, the first receiver has a first receive antenna 425 and the second receiver has a second receive antenna 427. The first transmit antenna 421 is spatially separated from the second transmit antenna 423. The first receive antenna 425 is spatially separated from the second receive antenna 427. All four antennas 421, 423, 425, 427 are spatially separated from each other. In other embodiments, the first receiver 405 (RX0) may be collocated with the first transmitter 401 (TX0) and they may share an antenna (i.e. the first receiver 405 may use antenna 421). Similarly, the second receiver 407 (RX1) may be collocated with, and may share an antenna 423 with the second transmitter 403 (TX1).

[0081] The impulse radar system 400 also includes four accumulators, each associated with a transmitter-receiver pair. Specifically, the system 400 comprises a first accumulator 431 corresponding to the pair TX0 with RX0 and a second accumulator 433 corresponding to the pair TX1 with RX0, each of these accumulators 431, 433 being configured to accumulate signals received at the first receiver 405. The system also comprises a third accumulator 451 corresponding to the pair TX1 with RX0 and a fourth accumulator 453 corresponding to the pair TX1 with RX1 , each of these accumulators 451 , 453 being configured to accumulate signals received at the second receiver 407.

[0082] The first accumulator 431 and the third accumulator 451 are arranged to accumulate reflections of signals transmitted from the first transmitter 401 received at the first receiver 405 and the second receiver 407 respectively. The second accumulator 433 and the fourth accumulator 453 are arranged to accumulate reflections of signals transmitted from second transmitter 403 received at the first receiver 405 and the second receiver 407 respectively. The impulse radar system 400 is configured to transmit a first signal 411 into an environment using the first transmitter 401 and to transmit a second signal 413 into the environment using the second transmitter 403. The first signal 411 and the second signal 413 are transmitted as sets of interleaved pulses as will be explained in more detail below. The first signal 411 and the second signal 413 are transmitted into the environment around the system 400, and are reflected from an target 402 in the form of a reflected signal 408. The reflected signal 408 is received at the antenna 425 of the first receiver 405 and the antenna 427 of the second receiver 407. The first receiver 405 and the second receiver 407 are both powered and active at the same time such that reflected signals can be received using both the first receiver 405 and the second receiver 407 simultaneously. In this way, four distinct signal paths via the target are detected by the system 400, thus providing improved angular resolution and an improved signal to noise ratio.

[0083] Reflections of the first signal 411 transmitted from the first transmitter 401 and received at the first receiver 405 are accumulated at the first accumulator 431. Reflections of the first signal 411 transmitted from the first transmitter 401 and received at the second receiver 407 are accumulated at the third accumulator 451.

[0084] Reflections of the second signal 413 transmitted from the second transmitter 403 and received at the first receiver 405 are accumulated at the second accumulator 433. Reflections of the second signal 413 transmitted from the second transmitter 403 and received at the second receiver 407 are accumulated at the fourth accumulator 453.

[0085] The signals accumulated at each accumulator 431 , 433, 451 , 453 are passed to the processor 410 for analysis. The processor 410 analyses the accumulated signals to determine a range to the target 402 and / or an angle to the target 402 and / or a velocity of the target 402. By including a second receiver in the system 400, the signal to noise ratio is increased by 3 dB when compared to a system with a single receiver, e.g. as shown in Figure 1. Furthermore, including an additional receiver increases the size of the virtual antenna array of the system for digital beamforming. Figure 5 illustrates the timing of signal transmissions using the impulse radar system 400 shown in Figure 4. The first signal 411 and the second signal 413 are sent over a time period AT. Sets of pulses of the first signal 411 and the second signal 413 are transmitted and received in respective portions ti- tN of the time period AT. Reflections of the first signal 411 received at the first receiver 405 and the second receiver 407 are provided to the first accumulator 431 and the third accumulator 451 respectively. Reflections of the second signal 413 received at the first receiver 405 and the second receiver 407 are provided to the second accumulator 433 and the fourth accumulator 453 respectively.

[0086] As can be seen in Figure 5, a first set 501 of pulses, comprising two individual pulses, is transmitted from the first transmitter 501 (TX0) in a first portion Ah of the time period AT. The set 501 of pulses is reflected by the target 402, and a reflected signal 408 is received at both the first receiver 405 (RX0) and the second receiver

[0087] 407 (RX1). The reflected signal 408 received at the first receiver 405 is passed to the first accumulator 431 , while the signal received at the second receiver 407 is passed to the third accumulator 451. Again it will be appreciated that each set may comprise only one pulse or may comprise more than two pulses.

[0088] In a second portion At2 of the time period AT, a second set 502 of pulses, comprising two individual pulses, is transmitted from the second transmitter 503 (TX1). The set 502 of pulses is reflected by the target 402, and a reflected signal

[0089] 408 is received at both the first receiver 405 (RX0) and the second receiver 407 (RX1). The signal received at the first receiver 405 is passed to the second accumulator 433, while the signal received at the second receiver 407 is passed to the fourth accumulator 453.

[0090] In a third portion Ata of the time period AT, a third set 503 of pulses, comprising two individual pulses, is transmitted from the first transmitter 501 (TX0). The set 503 of pulses is reflected by the target 402, and a reflected signal 408 is received at both the first receiver 405 (RX0) and the second receiver 407 (RX1). The signal received at the first receiver 405 is passed to the first accumulator 431 , where it is combined with the signal received at the first receiver 405 in the first portion Ah of the time period AT. The signal received at the second receiver 407 is passed to the third accumulator 451 , where it is combined with the signal received at the second receiver 407 in the first portion A of the time period AT.

[0091] In a fourth portion At4 of the time period AT, a fourth set 504 of pulses, comprising two individual pulses, is transmitted from the second transmitter 503 (TX1). The set 504 of pulses is reflected by the target 402, and a reflected signal 408 is received at both the first receiver 405 (RX0) and the second receiver 407 (RX1). The signal received at the first receiver 405 is passed to the second accumulator 433, where it is combined with the signal received at the first receiver 405 in the second portion At2 of the time period AT. The signal received at the second receiver 407 is passed to the fourth accumulator 453, where it is combined with the signal received at the second receiver 407 in the second portion At2 of the time period AT.

[0092] Sets 505 and 506 of pulses are transmitted from the first transmitter 401 and the second transmitter 403 respectively in the fifth portion Atsand sixth portions Ate of the time period AT as shown in Figure 5, with reflected sets of pulses of the first signal 411 being accumulated at the first accumulator 431 and the third accumulator 451 , and reflected sets of pulses of the second signal 413 being accumulated at the second accumulator 433 and the fourth accumulator 453.

[0093] This process continues with sets of pulses being sent from the first transmitter 401 and the second transmitter 403 alternately in turn, such that the sets of pulses of the first signal 411 are interleaved with the sets of pulses of the second signal 413, until all sets of pulses of the first signal 411 and the second signal 413 have been transmitted and reflected pulses received and accumulated at the accumulators 431 , 451 , 433, 453. This completes a transmission frame.

[0094] This is shown in Figure 5 as N sets of pulses being transmitted in total, with a signal corresponding to the Nth set 508 of pulses being sent by the second transmitter 403 (TX1) in the Nth portion AtN of the time period AT. The set 508 of pulses is reflected from the target 402 and a reflected signal 408 is received at the first receiver 405 and the second receiver 407. The signals received at the first receiver 405 and the second receiver 407 are accumulated at the second accumulator 433 and the fourth accumulator 453 respectively. In this way, the system 400 is able to generate four sets of accumulated signals: a first accumulated signal from reflections of the first signal 411 received at the first receiver 405, a second accumulated signal from reflections of the second signal 413 received at the first receiver 405; a third accumulated signal from reflections of the first signal 411 received at the second receiver 407; and a fourth accumulated signal from reflections of the second signal 413 received at the second receiver 407.

[0095] These accumulated signals are then passed to the processor 410 to determine a range to the target 402 and / or an angle to the target 402 and / or a velocity of the target 402 as described above. As the impulse radar system 400 accumulates reflected signals received at two receivers 405, 407 operating in parallel, the signal to noise ratio of the received signal is increased with respect to the impulse radar system 100 shown in Figure 1.

[0096] In addition to increasing received signal strength through the use of additional receivers, it is also possible to improve accuracy of the target position determined for targets sensed using the system through the use of additional transmit antennas, e.g. the resolution of the angle to the target can be increased. An example of this is illustrated in Figure 6, which shows an impulse radar system 600 according to a third embodiment comprising an additional transmitter with respect to the impulse radar system 100 shown in Figure 1.

[0097] The impulse radar system 600 comprises a first transmitter 601 (TX0), a second transmitter 603 (TX1), a third transmitter 604 (TX2), and a single receiver 605 (RX0). The first transmitter 601 , the second transmitter 603, the third transmitter 604 and the receiver 605 each has a dedicated antenna all of which are spatially separated from one another. Specifically, the first transmitter 601 has a first transmit antenna 621, the second transmitter 603 has a second transmit antenna 623, the third transmitter 604 has a third transmit antenna 624 and the receiver 605 has a receive antenna 625. It will be appreciated that the receiver 605 may share an antenna with any of the transmitters, e.g. antenna 621 , 623 or 624.

[0098] The impulse radar system 600 also includes a first accumulator 631, a second accumulator 633, a third accumulator 651 , and a processor 610. The first accumulator 631 , the second accumulator 633 and the third accumulator 651 are arranged to accumulate received signals comprising reflections of signals transmitted from the first transmitter 601 , the second transmitter 603 and the third transmitter 604 respectively.

[0099] The impulse radar system 600 is configured to transmit a first signal 611 into an environment using the first transmitter 601 , to transmit a second signal 613 into the environment using the second transmitter 603 and to transmit a third signal 614 using the third transmitter 604. The first signal 611, the second signal 613 and the third signal 614 are transmitted as sets of interleaved pulses as will be explained in more detail below. The first signal 611 , the second signal 613 and the third signal 614 are transmitted into the environment around the system 600, and are reflected by an target 602 in the form of a reflected signal 608. The reflected signal 608 is then received at the antenna 625 of the receiver 605.

[0100] Reflections of the first signal 611 transmitted from the first transmitter 601 are accumulated at the first accumulator 631. Reflections of the second signal 613 transmitted from the second transmitter 603 are accumulated at the second accumulator 633. Reflections of the third signal 614 transmitted from the third transmitter 604 are accumulated at the third accumulator 651. The accumulated signals are passed to the processor 610, which analyses the accumulated signals to determine a range to the target 602 and / or an angle to the target 602 and / or a velocity of the target 602 as described above in relation to Figures 1 and 4.

[0101] Figure 7 illustrates the timing of signal transmissions using the impulse radar system 600 shown in Figure 6.

[0102] The first signal 611 , the second signal 613 and the third signal 614 are sent over a time period AT. Sets of pulses of the first signal 611 , the second signal 613 and the third signal 614 are transmitted and received in respective portions ti- tN of the time period AT. Reflections of the first signal 611 , the second signal 613 and the third signal 614 received at the receiver 605 are provided to the first accumulator 631 , the second accumulator 633 and the third accumulator 651 respectively. As can be seen in Figure 7, a first set 701 of pulses, comprising two individual pulses (in this example), is transmitted from the first transmitter 601 (TXO) in a first portion A of the time period AT. The set 701 of pulses is reflected by the target 602, and a reflected signal 608 is received at the receiver 605 (RX0). The received signal is then passed to the first accumulator 631.

[0103] In a second portion At2 of the time period AT, a second set 702 of pulses, comprising two individual pulses, is transmitted from the second transmitter 603 (TX1). The set 702 of pulses is reflected by the target 602, and a reflected signal 608 is received at the receiver 605 (RX0). The received signal is then passed to the second accumulator 633.

[0104] In a third portion Ata of the time period AT, a third set 703 of pulses, comprising two individual pulses, is transmitted from the third transmitter 604 (TX2). The set 703 of pulses is reflected by the target 602, and a reflected signal 608 is received at the receiver 605 (RX0). The received signal is then passed to the third accumulator 651.

[0105] Once each of the first transmitter 601 , the second transmitter 603 and the third transmitter 604 has transmitted a respective set of pulses, the system 600 loops back to the first transmitter 601 (TXO), which transmits a fourth set 704 of pulses in a fourth portion At4 of the time period AT. The set 704 of pulses is reflected by the target 602, and a reflected signal 608 is received at the receiver 605 (RX0). The received signal is passed to the first accumulator 631 , where it is combined with the received signal corresponding to the signal transmitted by the first transmitter 601 in the first portion Ah of the time period AT.

[0106] Following this, the second transmitter 603 (TX1) transmits a fifth set 705 of pulses in a fifth portion Ats of the time period AT. The set 705 of pulses is reflected by the target 602, and a reflected signal 608 is received at the receiver 605 (RX0). The received signal is passed to the second accumulator 633, where it is combined with the received signal corresponding to the signal transmitted by the second transmitter 603 in the second portion At2 of the time period AT. The third transmitter 604 (TX2) then transmits a sixth set 706 of pulses in a sixth portion Ate of the time period AT, which are reflected by the target 602, and a reflected signal 608 received at the receiver 605 (RX0), and passed to the third accumulator 651 , where it is combined the received signal corresponding to the signal transmitted by the third transmitter 604 in the third portion Ata of the time period AT.

[0107] Sets 707 and 708 of pulses of the first signal 611 and the second signal 613 are transmitted from the first transmitter 601 and the second transmitter 603 respectively in the seventh and eighth portions (At?, Ats) of the time period AT as shown in Figure 7. The sets 707 and 708 of pulses are reflected by the target 602. Reflections of the set 707 of pulses of the first signal are accumulated at the first accumulator 631 , and reflections of the set 708 of pulses of the second signal 613 are accumulated at the second accumulator 633. In a ninth portion Atg (not shown) of the time period AT, a ninth set of pulses is transmitted by the third transmitter 604 and reflected pulses received at the receiver 605 are accumulated at the third accumulator 651 as described above.

[0108] This process then continues with sets of pulses being sent from the first transmitter 601 , the second transmitter 603 and the third transmitter 604 in turn, such that the sets of pulses of the first signal 611 are interleaved with the sets of pulses of the second signal 613 and the third signal 614, until all sets of pulses of the first signal 611 , second signal 613 and third signal 614 have been transmitted.

[0109] This is shown in Figure 7 as N sets of pulses being transmitted in total, with a signal corresponding to the Nth set 709 of pulses being sent by the third transmitter 604 (TX2) in the Nth portion AtN of the time period AT, and a corresponding reflected signal, received at the receiver 605 being accumulated at the third accumulator 651.

[0110] In this way, the system 600 is able to generate three sets of accumulated signals, associated with the first transmitted signal 611 , the second transmitted signal 613 and the third transmitted signal 614 respectively. The accumulated signals are then passed to the processor 610 to determine a range to the target 602 and / or an angle to the target 602 and / or a velocity of the target 602 as described above. As the accumulated signals correspond to signals transmitted from three transmitters, each having a different respective location (via their antenna positions), the system 600 may be able to detect targets more accurately than the two-transmitter system 100 shown in Figure 1. Thus, in this example, three separate transmit paths are provided (TX0 to RX0, TX1 to RX0 and TX2 to RX0). The use of three spatially separated transmit antennas effectively increases the radar aperture and increases the angular resolution that is achievable.

[0111] In the above examples, each antenna has been illustrated with its own transmit or receive chain. However, as discussed above, transmitters may share a transmit chain and receivers may share a receive chain. In particular, as the transmitters do not transmit simultaneously and each receiver chain only ever accesses one accumulator at a time, the transmit chain and the receive chain (i.e. the LNA, filter, ADC, etc.) may be shared (i.e. re-used by different antennas) to save cost and / or area.

[0112] Fig. 8 shows an example similar to that of Fig. 1 in which the first transmitter 101 and the second transmitter 103 share a common RF transmit chain 802 (labelled “TX01 TXT’). The first transmitter 101 comprises the first antenna 121 together with the common RF transmit chain 802. The second transmitter 103 comprises the second antenna 123 together with the common RF transmit chain 802. The common RF transmit chain 802 controls each antenna 121, 123 in turn such that only one antenna transmits at any given time. Thus the common RF transmit chain 802 is switched to the first antenna 121 to transmit the first signal and it is switched to the second antenna 123 to transmit the second signal.

[0113] Fig. 9 shows an example similar to that of Fig. 4 in which the first receiver 405 comprises the first antenna 425 and the common RF receive chain 905 feeds into first accumulator 431 and second accumulator 433 (to accumulate the TX0-RX0 and TX1-RX0 paths). A second receiver 407 comprises the second antenna 427 and the common RF receive chain 905 and feeds into the third accumulator 451 and the fourth accumulator 453. The first receiver 405 and the second receiver 407 are operated in sequence (i.e. the antennas 425, 427 are switched such that each receiver 405, 407 receives pulses from both TX0 and TX1). When antenna 425 (RX0) receives pulses from transmitter 401 (TX0), the common receiver chain 905 accumulates pulses in the first accumulator 431. When antenna 425 (RXO) receives pulses from transmitter 403 (TX1), the common RF receiver chain accumulates pulses in the second accumulator 433. Similarly, when the second antenna 427 (RX1) receives pulses from transmitter 401 (TX0), the common receiver chain 905 accumulates pulses in the third accumulator 451 and when the second antenna 427 (RX1) receives pulses from the transmitter 403 (TX1), the common receiver chain 905 accumulates pulses in the fourth accumulator 453.

[0114] Thus the common receiver chain 905 is switched between antennas at one end and between accumulators at the other end. Only one receive antenna is operational at any given time and only one accumulator is operational at any given time. It is still possible with this arrangement to accumulate pulses from all four transmit-receive pairs using a single common receive chain which saves area. However, without the simultaneous processing that is possible with the Fig. 4 arrangement, the coherent integration time is lower for each channel.

[0115] It will be appreciated by those skilled in the art that the present disclosure has been illustrated by describing one or more specific examples thereof, but is not limited to these examples; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

CLAIMS1 . An impulse radar system for object sensing, the system comprising: a first transmit antenna; a second transmit antenna spatially separated from the first transmit antenna; a first receiver; and first and second accumulators; wherein the system is configured to: transmit first and second signals into an environment, the first and second signals each comprising a plurality of sets of pulses; wherein transmitting the first and second signals comprises transmitting the plurality of sets of pulses of the first signal from the first transmit antenna interleaved with the plurality of sets of pulses of the second signal from the second transmit antenna; receive reflected signals at the first receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulate received signals comprising reflections of sets of pulses of the first signal using the first accumulator; and accumulate received signals comprising reflections of sets of pulses of the second signal using the second accumulator.

2. The impulse radar system of claim 1 , wherein each set of the plurality of sets of interleaved pulses is transmitted in a respective portion of a first time period, wherein each respective portion of the first time period has a predetermined duration.

3. The impulse radar system of claim 2, wherein the duration of the respective portions of the first time period is controllable.

4. The impulse radar system of claim 2 or 3, wherein the system is further configured to separate each of the first and second signals into respective sets of pulses, wherein the number of sets of pulses is set based on the length of the first time period.

5. The impulse radar system of any preceding claim, wherein the system further comprises a processor configured to analyse the accumulated signals to identify one or more targets in the environment.

6. The impulse radar system of claim 5, wherein analysing the accumulated signals comprises determining a range of the one or more targets.

7. The impulse radar system of claim 5 or 6, wherein analysing the accumulated signals comprises determining an angle to the one or more targets.

8. The impulse radar system of any of claims 5 to 7, wherein analysing the accumulated signals comprises determining a velocity of the one or more targets.

9. The impulse radar system of any preceding claim, wherein the first receiver has a receive antenna and wherein the first transmit antenna, second transmit antenna and receiver antenna are all spatially separated from one another.

10. The impulse radar system of any of claims 1 to 9, wherein the receive antenna is collocated with the first transmit antenna.

11. The impulse radar system of any preceding claim, wherein the first transmit antenna and the second transmit antenna are arranged such that only one of the first transmit antenna and second transmit antenna is transmitting at any given time.

12. The impulse radar system of any preceding claim, wherein the first accumulator is arranged to accumulate reflections of sets of pulses of the first signal received at the first receiver and wherein the second accumulator is arranged to accumulate reflections of sets of pulses of the second signal received at the first receiver.

13. The impulse radar system of any preceding claim, wherein the system further comprises: a third transmit antenna; and a third accumulator;wherein the system is configured to: transmit a third signal into the environment, the third signal comprising a plurality of sets of pulses; wherein transmitting the first, second and third signals comprises: transmitting sets of pulses of the first signal from the first transmit antenna interleaved with sets of pulses of the second signal from the second transmit antenna and with sets of pulses of the third signal from the third transmit antenna; wherein the system is further configured to: accumulate received signals comprising reflections of sets of pulses of the third signal using the third accumulator.

14. The impulse radar system of claim 13, wherein the first transmit antenna, the second transmit antenna and the third transmit antenna are arranged such that only one of the first transmit antenna, the second transmit antenna and the third transmit antenna is transmitting at any given time.

15. The impulse radar system of any of claims 1 to 12, wherein the system comprises a second receiver, a third accumulator and a fourth accumulator; wherein the system is further configured to: receive reflected signals at the second receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulate received signals comprising reflections of sets of pulses of the first signal received at the second receiver using the third accumulator; and accumulate received signals comprising reflections of sets of pulses of the second signal received at the second receiver using the fourth accumulator.

16. The impulse radar system of claim 15, wherein the first receiver and the second receiver are arranged to receive simultaneously.

17. The impulse radar system of claim 15 or 16, wherein the first receiver has a first receive antenna and the second receiver has a second receive antenna and wherein the first transmit antenna, second transmit antenna, first receive antenna and second receive antenna are all spatially separated from one another.

18. The impulse radar system of claim 17, wherein the first receive antenna is collocated with the first transmit antenna and / or the second receive antenna is collocated with the second transmit antenna.

19. The impulse radar system of any of claims 14 to 18, wherein the system further comprises: a third transmit antenna; a fifth accumulator; and a sixth accumulator; wherein the system is configured to: transmit a third signal into the environment, the third signal comprising a plurality of sets of pulses; wherein transmitting the first, second and third signals comprises: transmitting sets of pulses of the first signal from the first transmit antenna interleaved with sets of pulses of the second signal from the second transmit antenna and with a plurality of sets of pulses of the third signal from the third transmit antenna; wherein the system is further configured to: accumulate received signals comprising reflections of sets of pulses of the third signal using the fifth accumulator; and accumulate received signals comprising reflections of sets of pulses of the third signal using the sixth accumulator.

20. The impulse radar system of claim 19, wherein the first transmit antenna, the second transmit antenna and the third transmit antenna are arranged such that only one of the first transmit antenna, the second transmit antenna and the third transmit antenna is transmitting at any given time.

21. The impulse radar system of any of claims 1 to 20, wherein the sets of pulses each comprise a plurality of pulses.

22. The impulse radar system of any preceding claim, wherein the sets of pulses each comprise one thousand or fewer pulses.

23. A method of operating an impulse radar system for object sensing, the method comprising: transmitting first and second signals into an environment, the first and second signals each comprising a plurality of sets of pulses; wherein transmitting the first and second signals comprises transmitting a plurality of sets of pulses of a first signal from a first transmit antenna interleaved with a plurality of sets of pulses of a second signal from a second transmit antenna, the second transmit antenna being spatially separated from the first transmit antenna; receiving reflected signals at a first receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulating received signals comprising reflections of sets of pulses of the first signal using a first accumulator; and accumulating received signals comprising reflections of sets of pulses of the second signal using a second accumulator.

24. The method of claim 23, wherein the method further comprises: receiving reflected signals at a second receiver, the reflected signals comprising reflections of the transmitted sets of pulses; accumulating received signals comprising reflections of sets of pulses of the first signal received at the second receiver using a third accumulator; and accumulating received signals comprising reflections of sets of pulses of the second signal received at the second receiver using a fourth accumulator.

25. The method of claim 23 or 24, wherein the method further comprises: transmitting a third signal into the environment, the third signal comprising a plurality of sets of pulses; wherein transmitting the first, second and third signals comprises transmitting sets of pulses of the first signal from the first transmit antenna interleaved with sets of pulses of the second signal from the second transmit antenna and with a plurality of sets of pulses of the third signal from the third transmit antenna; and accumulating received signals comprising reflections of sets of pulses of the third signal using a third accumulator.

Images