Receiver and method of operating receiver

Abstract

According to a first aspect of the present disclosure, there is provided a receiver comprising: an ultra wide band (UWB) communication unit configured to operate in a radar mode and receive a synchronization signal transmitted by a transmitter; a synchronization unit operably coupled to the UWB communication unit, where the synchronization unit is configured to: estimate a carrier frequency offset from the synchronization signal; deriving a reference time from the synchronization signal; a time window for receiving a radar data packet by the UWB communication unit is derived, wherein the time window is derived from the estimated carrier frequency offset and the reference time. According to a second aspect of the present disclosure, a corresponding method of operating a receiver is conceived.

Description

Technical Field

[0001] The present disclosure relates to a receiver. Additionally, the present disclosure relates to a corresponding method of operating the receiver. Background Art

[0002] Ultra-wideband (UWB) is a technology that uses a high signal bandwidth. Specifically, this technology is used to transmit digital data over a wide frequency band spectrum with extremely low power. For example, UWB technology can use a spectrum of 3.1 to 10.6 GHz and can have characteristics such as a high frequency bandwidth greater than 500 MHz and very short pulse signals, thus potentially enabling support for high data rates. UWB technology enables communication devices to have high data throughput and enables device positioning with high precision. Specifically, UWB technology can be used for so-called ranging operations, that is, for determining the distance between communication devices. Additionally, UWB technology can be used for radar operations. Therefore, UWB technology can be used to facilitate various applications, such as automotive applications. Summary of the Invention

[0003] According to a first aspect of the present disclosure, there is provided a receiver, comprising: an ultra-wideband (UWB) communication unit configured to operate in a radar mode and receive a synchronization signal transmitted by a transmitter; a synchronization unit operatively coupled to the UWB communication unit, wherein the synchronization unit is configured to: estimate a carrier frequency offset based on the synchronization signal; derive a reference time from the synchronization signal; and derive a time window for receiving a radar data packet by the UWB communication unit, wherein the time window is derived from the estimated carrier frequency offset and the reference time.

[0004] In one or more embodiments, the synchronization unit is configured to use data in a SYNC field included in the synchronization signal to estimate the carrier frequency offset.

[0005] In one or more embodiments, the synchronization unit is configured to derive the reference time from a frame start delimiter (SFD) field included in the synchronization signal.

[0006] In one or more embodiments, the synchronization unit is configured to derive the reference time from an output of one or more ranging operations performed between the UWB communication unit and the transmitter.

[0007] In one or more embodiments, the time window is defined by a plurality of clock increments, and the synchronization unit is configured to use the estimated carrier frequency offset to correct the plurality of clock increments.

[0008] In one or more embodiments, the synchronization unit is configured to correct the plurality of clock increments by adding a quantity c to the plurality of clock increments, where the quantity c is calculated as follows:

[0009]

[0010] where CFO represents the estimated carrier frequency offset, T represents a co-defined time window in terms of clock increments, and f c represents the carrier frequency.

[0011] In one or more embodiments, the co-defined time window is a transmission window applied by the transmitter.

[0012] In one or more embodiments, the start of the time window is based on the reference time.

[0013] In one or more embodiments, the synchronization signal is the first radar data packet in a radar data packet block, where the first data packet includes a SYNC field and an SFD field.

[0014] In one or more embodiments, the radar data packet block includes one or more additional radar data packets, where the additional radar data packets include only the SYNC field.

[0015] In one or more embodiments, the receiver further includes an interface unit for receiving a wired or wireless signal, where the synchronization unit is operatively coupled to the interface unit and is further configured to time the reception of the synchronization signal based on the wired or wireless signal.

[0016] In one or more embodiments, the synchronization unit is configured to estimate the carrier frequency offset, derive the reference time, and derive the time window in a periodic manner.

[0017] In one or more embodiments, a radar system includes a receiver and a transmitter of the described type, where the transmitter includes a UWB communication unit configured to operate in a radar mode and transmit a synchronization signal to the receiver.

[0018] In one or more embodiments, the transmitter further includes an interface unit for receiving a wired or wireless signal, where the transmitter is configured to time the transmission of the radar block based on the wired or wireless signal.

[0019] According to a second aspect of the present disclosure, a method of operating a receiver is contemplated, including: receiving, by an ultra-wideband (UWB) communication unit included in the receiver, a synchronization signal transmitted by a transmitter; estimating, by a synchronization unit included in the receiver, a carrier frequency offset based on the synchronization signal; deriving, by the synchronization unit, a reference time from the synchronization signal; and deriving, by the synchronization unit, a time window for receiving radar data packets by the UWB communication unit, wherein the time window is derived from the estimated carrier frequency offset and the reference time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments will be described in more detail with reference to the accompanying drawings.

[0021] Figure 1 Shows the measured delay of a static target.

[0022] Figure 2 Shows an illustrative embodiment of a receiver.

[0023] Figure 3 Shows an illustrative embodiment of a method of operating a receiver.

[0024] Figure 4 Shows the time course of transmitted and received radar data packets.

[0025] Figure 5 Shows another measured delay of a static target. DETAILED DESCRIPTION

[0026] A UWB communication device can operate in a radar mode for the purpose of detecting an object that reflects a radar signal transmitted by the device. Such an object is typically referred to as a "target". In a UWB radar network, multiple devices (i.e., nodes) can be employed to generate a map of static and dynamic targets (i.e., reflectors). Since these nodes are spatially separated, a physical connection between these nodes is not required. All devices in a radar network typically use independent oscillators as clocks or time references. These devices sense the environment by transmitting and receiving blocks of radar data packets, each packet having a fixed time interval. For example, in a child presence detection (CPD) use case, a typical packet interval has a length of 100 milliseconds.

[0027] Since all devices have independent time references, this can lead to uncertainty in the transmission or reception time of each radar data packet in the sensing block. This uncertainty depends on the carrier frequency offset (CFO) and the packet interval and typically ranges from 100 nanoseconds to a few microseconds. This uncertainty may cause static targets in each radar data packet to shift, making these static targets appear to be moving. As a result, the distance information obtained from the channel impulse response (CIR) index of the radar data packet may become useless. Additionally, the transmitted packets may slowly drift out of the receiver window, reducing the received energy.

[0028] Figure 1 Shows the measured delay of static target 100. More specifically, shows the measured delay of the static target for 19 radar data packets. In the case of full synchronization, the delay is the same for each radar data packet. In the case of non-synchronization, the packet interval at the receiving device is not the same as the packet interval at the transmitting device. This causes an apparent movement of the target, as Figure 1 can be seen. In a pulsed radar system, the obtained distance is wrapped together with the unambiguous distance defined by the pulse response symbol duration. Figure 1 Also shows the unwrapped delay. In free space, the distance can be obtained by multiplying the delay by the speed of light.

[0029] Now discuss the receiver and the corresponding method of operating the receiver, both of which help reduce the likelihood of errors in object detection and distance estimation in a UWB-based radar system.

[0030] Figure 2 Shows an illustrative embodiment of receiver 200. Receiver 200 includes a UWB communication unit 202 configured to operate in a radar mode and receive a synchronization signal transmitted by a transmitter (not shown). Additionally, receiver 200 includes a synchronization unit 204 operatively coupled to UWB communication unit 202. Synchronization unit 204 is configured to estimate the carrier frequency offset based on the synchronization signal. Additionally, synchronization unit 204 is configured to derive a reference time from the synchronization signal. Specifically, the reference time is a time point or moment that can be used as a reference. Additionally, synchronization unit 204 is configured to derive a time window for receiving radar data packets by the UWB communication unit, where the time window is derived from the estimated carrier frequency offset and the reference time. By deriving the time window for receiving radar data packets in this way, the drift between the time stamps of the transmitter and the receiver - which can be caused by the carrier frequency offset between the transmitter and the receiver - can be corrected. This in turn helps reduce the likelihood of errors in object detection and distance estimation in a UWB-based radar system.

[0031] In one or more embodiments, the synchronization unit is configured to estimate the carrier frequency offset using the data in the SYNC field included in the synchronization signal. In this way, the carrier frequency offset can be easily estimated using the universal format of the UWB signal. More specifically, the carrier frequency offset can be estimated (i.e., calculated) based on a phase discriminator that determines the phase difference (which is proportional to the frequency offset) between two consecutive correlation peaks calculated based on the SYNC field data. Therefore, the strongest signal component (i.e., the correlation peak) can be used to estimate the carrier frequency offset. This signal component is not necessarily a line-of-sight component and may include a Doppler shift caused by the target. It should be noted that US2023 / 142169A1 describes a method for estimating a carrier frequency offset caused only by the clock difference of the device, which can produce a more reliable carrier frequency offset estimate for radar applications.

[0032] In one or more embodiments, the synchronization unit is configured to derive the reference time from a Start of Frame Delimiter (SFD) field included in the synchronization signal. In this way, the reference time can be easily established using the common format of UWB signals. The SYNC and SFD fields can be defined in accordance with the IEEE 802.15.4a and IEEE 802.15.4z standards. In one or more embodiments, the synchronization unit is configured to derive the reference time from the output of one or more ranging operations performed between the UWB communication unit and the transmitter. This can create a practical alternative way to establish the reference time.

[0033] In one or more embodiments, the time window is defined by a plurality of clock increments (i.e., clock ticks), and the synchronization unit is configured to correct the plurality of clock increments using the estimated carrier frequency offset. In this way, drift between the timestamps of the transmitter and the receiver can be easily corrected. In a practical implementation, the synchronization unit is configured to correct the plurality of clock increments by adding an amount c to the plurality of clock increments, where the amount c is calculated as shown in equation (1). In this equation, CFO represents the estimated carrier frequency offset (in Hertz), T represents the commonly defined time window (in clock increments), and f c Indicates the carrier frequency in Hertz.

[0034]

[0035] In a practical implementation, the commonly defined time window is a sending window applied by the sender.Furthermore, in a practical implementation, the start of the time window is based on a reference time.

[0036] In one or more embodiments, the synchronization signal is the first radar data packet in a radar data packet block, where the first data packet includes a SYNC field and an SFD field. This results in a practical implementation where radar data packets with a common format are used as synchronization signals. In one or more embodiments, the radar data packet block includes one or more additional radar data packets, where the additional radar data packets contain only the SYNC field. In this way, flight time and energy can be saved.

[0037] In one or more embodiments, the receiver further includes an interface unit for receiving a wired or wireless signal, where the synchronization unit is operatively coupled to the interface unit and is further configured to time the reception of the synchronization signal based on the wired or wireless signal. In this way, the receiver can be prevented from remaining active to listen for the synchronization signal. This in turn can reduce the power consumption of the receiver. Additionally, in one or more embodiments, the synchronization unit is configured to estimate the carrier frequency offset in a periodic manner, derive a reference time, and derive a time window. In this way, the drift between the timestamps of the transmitter and the receiver can be repeatedly corrected, which further helps to reduce the likelihood of errors in object detection and distance estimation in a UWB-based radar system. For example, the synchronization unit can perform the mentioned steps for any received radar data packet or for a predefined subset of the radar data packets in the block.

[0038] In one or more embodiments, a radar system includes a receiver and a transmitter of the type described, where the transmitter includes a UWB communication unit configured to operate in a radar mode and transmit a synchronization signal to the receiver. Thus, a radar system is provided in which the likelihood of errors in object detection and distance estimation can be reduced. In one or more embodiments, the transmitter further includes an interface unit for receiving a wired or wireless signal, and the transmitter is configured to time the transmission of the radar block based on the wired or wireless signal. In this way, the start of the transmission of the radar block can be easily timed.

[0039] Figure 3 An illustrative embodiment of a method of operating a receiver 300 is shown. Method 300 includes the following steps. At 302, a UWB communication unit included in the receiver receives a synchronization signal transmitted by a transmitter. At 304, a synchronization unit included in the receiver estimates a carrier frequency offset based on the synchronization signal. Additionally, at 306, the synchronization unit derives a reference time from the synchronization signal. Additionally, at 308, the synchronization unit derives a time window for receiving radar data packets by the UWB communication unit, where the time window is derived from the estimated carrier frequency offset and the reference time. As referenced Figure 2As explained by the corresponding receiver shown in, method 300 helps reduce the likelihood of errors in object detection and distance estimation in a UWB-based radar system.

[0040] A pulsed radar device (e.g., a UWB-based radar device) cyclically transmits a plurality of radar data packets at a defined data packet interval. Typically, the duration of a radar data packet may be shorter than the data packet interval. This may result in a pause between data packets. Each radar data packet consists of a plurality of symbols, and one symbol consists of a plurality of pulses. The receiving radar device calculates the CIR for each received radar data packet. According to the present disclosure, the receiving device may correct its reception window (i.e., the time window for receiving radar data packets) in time such that the reception window overlaps with the transmission time window.

[0041] In a practical implementation, the transmitter may transmit a block of radar data packets at a predefined data packet interval (e.g., 100 milliseconds). In this case, the first data packet in the block may contain at least a SYNC field and an SFD field. Subsequent data packets in the block may contain only the SYNC field. The receiver may listen for the transmitted signal and start receiving once the transmitted signal is detected. Then, the receiver may use the timestamp indicating the reception time of the SFD field as a reference time and estimate the CFO based on the SYNC field. Subsequently, the receiver may calculate the number of clock ticks required to wait for the next radar data packet based on the timestamp and the estimated CFO.

[0042] Figure 4 Illustrates the time course 400 of transmitted and received radar data packets. A transmitting (TX) device transmits a plurality of radar data packets 402, 404, 406 at a TX data packet interval. The data packet interval may be expressed as a certain number of clock ticks. Typically, this number of clock ticks is different for the TX device and the receiving (RX) device. The first transmitted radar data packet 402 contains a SYNC field 408 and an SFD field 410. Subsequent radar data packets 404, 406 contain only the SYNC field to save flight time and energy. The RX device listens for the first radar data packet 402 and starts receiving once the signal is detected. The data in the SYNC field 408 is used to estimate the CFO with respect to the TX device. The SFD is used to generate a reference timestamp. Both the reference timestamp and the estimated CFO are used to calculate the number of clock ticks for correcting the initial number of clock ticks to ultimately obtain an RX data packet interval equal to the TX data packet interval. Equation 1 defines the number of clock ticks required for the RX device to correct its RX data packet interval to be equal to the TX data packet interval. This is shown in Equations 2 and 3, where T represents a commonly defined data packet interval in terms of clock ticks, T Tx represents the data packet interval applied by the TX device in terms of clock ticks, and T RxIndicates the packet interval of the RX device in terms of clock beats. After calibration, the packet interval applied by the RX device and the packet interval applied by the TX device are equal, but the two can still be shifted relative to each other in time. Therefore, the RX device can use the reference timestamp to calculate the start of the next reception (i.e., the start of the next packet interval).

[0043] T TX = T (Equation 2)

[0044] T RX = T + c (Equation 3)

[0045] It should be noted that depending on whether the carrier frequency offset is positive or negative, the carrier frequency offset compresses or stretches the time axis on the RX side relative to the TX side, respectively. See Figure 4 , which means that in principle, two time windows should be calibrated, namely the RX packet interval and the reception window. In other words, both the RX packet interval and the reception window can be regarded as time windows of the kind described above. Once these time windows are calibrated, the reception window will have the same duration as the corresponding transmission window, but these reception windows can still be shifted relative to each other in time. To compensate for this shift, the start point of the second reception window 414 can be based on a reference point. In some embodiments, it is not necessary to calibrate the reception window. Therefore, in such embodiments, only the RX packet interval should be calibrated, as shown in Equation 3.

[0046] Figure 5 Shows another measured delay 500 of the static target. More specifically, for the embodiments of the currently disclosed receiver (i.e., the RX device mentioned above), the measured delay of the static target for 19 radar packets is shown. Since the packet interval of the RX device is synchronized with respect to the TX device, the target appears at the same position. Therefore, the possibility of errors in object detection and distance estimation is reduced. It should be noted that the measurement is performed with two UWB devices, each with an individual clock source and a jointly defined frame interval of 100 milliseconds.

[0047] The transmission start of the radar block (i.e., the arrangement of multiple radar packets) can be triggered by an external, wired or wireless signal. This signal does not need to have high accuracy. For example, the transmitter can receive the signal through a Controller Area Network (CAN) bus, a Bluetooth Low Energy (BLE) communication unit, a UWB Message Authentication Code (MAC) layer, or an out-of-band communication channel. Similarly, the reception start of the first radar packet in the radar block can be triggered by an external, wired or wireless signal. This can prevent the RX device from remaining active to listen for signals. Similarly, the receiver can receive the signal through a Controller Area Network (CAN) bus, a Bluetooth Low Energy (BLE) communication unit, a UWB Message Authentication Code (MAC) layer, or an out-of-band communication channel.

[0048] As mentioned above, the SFD field defined in the IEEE 802.15.4a and 802.15.4z UWB standards can be used to generate the reference time. However, any other delimiter format can be used to generate the reference time. In addition, a ranging sequence between the transmitting device and the receiving device can be used to generate the reference time. In this case, the reference time determination requires communication in both directions (i.e., from the TX device to the RX device and from the RX device to the TX device). For this purpose, in addition to the radar mode, the UWB communication units of the TX device and the RX device can be configured to operate in the ranging mode.

[0049] Generally speaking, in the radar operation mode, frames are transmitted by at least one device and those frames are received by the same device and / or by one or more other devices. Then, the channel impulse response is estimated on one or more of the devices that receive the frames, and the range and / or velocity and / or angle of arrival (AoA) are calculated based on the estimated CIR. The radar operation mode can be used to advantageously detect (i.e., sense) the presence of an object or a person. In contrast, in the ranging operation mode, frames are typically exchanged between two devices via at least one antenna on each device, and at least a single-sided two-way ranging (SS-TWR) operation or a double-sided two-way ranging (DS-TWR) operation is performed. Specifically, the CIR is estimated for the two devices, timestamps are generated based on the CIRs of the two devices, and those timestamps are exchanged. These timestamps form the basis for calculating the distance between the two devices.

[0050] It should be noted that multiple instances of the currently disclosed receivers can be integrated into a radar system. Thus, the radar system can include one TX device and multiple RX devices of the kind described above. In addition, the device role (i.e., transmitter or receiver) can be changed for any new radar block. In addition, the CFO estimation can be based only on the configured path between the TX device and the RX device. Finally, the CFO estimation and the RX packet interval can be refreshed or updated in a periodic manner (e.g., for any received radar data packet or only for a limited number of received radar data packets).

[0051] It should be noted that the above embodiments have been described with reference to different subject matters. Specifically, some embodiments may have been described with reference to method-type claims, while other embodiments may have been described with reference to device-type claims. However, those skilled in the art will understand from the above that, unless otherwise stated, any combination of features related to different subject matters, in particular the combination of features of method-type claims and features of device-type claims, is also considered to be disclosed together with this document, in addition to any combination of features belonging to one type of subject matter.

[0052] In addition, it should be noted that the figures are schematic. In different figures, like or identical elements are denoted by the same reference numerals. Further, it should be noted that in order to provide a concise description of the schematic embodiments, implementation details that are part of the routine practice of those skilled in the art may not be described. It is to be understood that in the development of any such implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the specific goals of the developer, such as compliance with system-related and business-related constraints, which may vary in different implementations. Moreover, it is to be understood that such development efforts may be complex and time-consuming, but are nevertheless routine tasks for those skilled in the art in design, fabrication, and production.

[0053] Finally, it should be noted that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference numerals placed between parentheses shall not be construed as limiting the claim. The word "comprise(s)" or "comprising" does not exclude the presence of elements or steps other than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The measures recited in the claims can be implemented by hardware including several different elements and / or by means of a suitably programmed processor. In a device claim reciting several devices, several of these devices can be embodied by the same item in hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0054] List of Reference Numerals

[0055] 100 Measured delay of static target

[0056] 200 Receiver

[0057] 202 UWB Communication Unit

[0058] 204 Synchronization Unit

[0059] 300 Method of Operating a Receiver

[0060] 302 Receive a synchronization signal transmitted by a transmitter by a UWB communication unit included in the receiver

[0061] 304 Estimate a carrier frequency offset according to the synchronization signal by a synchronization unit included in the receiver

[0062] 306 Derive a reference time from the synchronization signal by the synchronization unit

[0063] 308 Derive a time window for receiving radar data packets by the UWB communication unit from the synchronization unit, where the time window is derived from the estimated carrier frequency offset and the reference time

[0064] 400 Time course of the transmitted and received radar data packets

[0065] 402 First data packet

[0066] 404 Second data packet

[0067] 406 Third data packet

[0068] 408 SYNC field

[0069] 410 SFD field

[0070] 412 Reception window

[0071] 414 Reception window

[0072] 416 Reception window

[0073] 500 Measured delay of the static target.

Claims

1. A receiver, characterized in that: include: an ultra-wideband (UWB) communication unit configured to operate in a radar mode and receive a synchronization signal transmitted by the transmitter; a synchronization unit operatively coupled to the UWB communication unit, wherein the synchronization unit is configured to: estimating a carrier frequency offset according to the synchronization signal; deriving a reference time from the synchronization signal; A time window for receiving radar data packets by the UWB communication unit is derived, wherein the time window is derived from the estimated carrier frequency offset and the reference time.

2. The receiver according to claim 1, wherein The synchronization unit is configured to estimate the carrier frequency offset using data in a SYNC field included in the synchronization signal.

3. The receiver according to claim 1 or 2, characterized in that The synchronization unit is configured to derive the reference time from a Start of Frame Delimiter (SFD) field included in the synchronization signal.

4. The receiver according to claim 1 or 2, characterized in that The synchronization unit is configured to derive the reference time from an output of one or more ranging operations performed between the UWB communication unit and the transmitter.

5. A receiver according to any preceding claim, characterised in that The time window is defined by a plurality of clock increments, and wherein the synchronization unit is configured to correct the plurality of clock increments using the estimated carrier frequency offset.

6. The receiver according to claim 5, characterized in that The synchronization unit is configured to correct the plurality of clock increments by adding a quantity c to the plurality of clock increments, wherein the quantity c is calculated as follows: where CFO represents the estimated carrier frequency offset, T represents a commonly defined time window in units of clock increments, and f c Indicates the carrier frequency.

7. The receiver according to claim 6, wherein: The commonly defined time window is a sending window applied by the sender.

8. A receiver according to any preceding claim, characterised in that The start of the time window is based on the reference time.

9. A radar system, characterized in that: Comprising a receiver according to any preceding claim and a transmitter, wherein the transmitter comprises a UWB communication unit configured to operate in radar mode and to transmit a synchronization signal to the receiver.

10. A method of operating a receiver, characterized in that include: Receiving, by an ultra-wideband (UWB) communication unit included in the receiver, a synchronization signal transmitted by the transmitter; estimating, by a synchronization unit included in the receiver, a carrier frequency offset based on the synchronization signal; deriving a reference time from the synchronization signal by the synchronization unit; A time window for receiving radar data packets by the UWB communication unit is derived by the synchronization unit, wherein the time window is derived from the estimated carrier frequency offset and the reference time.

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