Patent Description:
Ultra-wideband (UWB) communication technology is a technology that uses a high signal bandwidth, in particular for transmitting digital data over a wide spectrum of frequency bands with very low power. For example, UWB technology may use the frequency spectrum of <NUM> to <NUM> and may feature a high-frequency bandwidth of more than <NUM> and very short pulse signals, potentially capable of supporting high data rates. The UWB technology enables a high data throughput for communication devices and a high precision for the localization of devices. In particular, UWB technology may be used for so-called ranging operations, i.e. for determining the distance between communicating devices. Therefore, UWB technology may be used to advantage in various applications, such as automotive applications.

<CIT> describes a method for operating an ultra-wideband (UWB) device. The method involves powering down a first receive path of a multipath UWB device while leaving a second receive path of the multipath UWB device powered up, powering down channel estimation, tracking, and demodulation functions of the second receive path, and performing an acquisition function using the second receive path while the first receive path is powered down and while the channel estimation, tracking, and demodulation functions of the second receive path are powered down.

The article "<NPL>), describes an acquisition algorithm intended for low duty-cycled IR-UWB signals enabling a signal-to-noise ratio (SNR) estimate.

In accordance with a first aspect of the present disclosure, a communication device is provided, as defined in claim <NUM>.

In one or more embodiments, the controller is further configured to switch the receiver circuit from the real receiver mode to the complex receiver mode upon or after a successful acquisition of the signal.

In one or more embodiments, the successful acquisition of the signal is based on the detection of a synchronization field within said signal, wherein the synchronization field is included in a data frame.

In one or more embodiments, the controller is further configured to wake up the receiver circuit before switching the receiver circuit from the real receiver mode to the complex receiver mode.

In one or more embodiments, the controller is further configured to wake up the receiver circuit after switching the receiver circuit from the real receiver mode to the complex receiver mode.

In one or more embodiments, the controller is further configured to reset a center frequency upon or after switching the receiver circuit from the real receiver mode to the complex receiver mode.

In one or more embodiments, the receiver circuit is configured to operate in the complex receiver mode by default, and the controller is configured to switch the receiver circuit from the complex receiver mode to the real receiver mode if no signal is found within a predefined amount of time after the receiver circuit has started up.

In one or more embodiments, the device is an ultra-wideband (UWB) communication node acting as a responder in a communication system.

In accordance with a second aspect of the present disclosure, a method of operating a communication device is conceived, as defined in claim <NUM>.

As mentioned above, UWB communication technology is a technology that uses a high signal bandwidth, in particular for transmitting digital data over a wide spectrum of frequency bands with very low power. For example, UWB technology may use the frequency spectrum of <NUM> to <NUM> and may feature a high-frequency bandwidth of more than <NUM> and very short pulse signals, potentially capable of supporting high data rates. The UWB technology enables a high data throughput for communication devices and a high precision for the localization of devices. In particular, UWB technology may be used for so-called ranging operations, i.e. for determining the distance between communicating devices. Therefore, UWB technology may be used to advantage in various applications, such as automotive applications.

UWB communication devices may have a relatively high power or current consumption. This is especially true for a responding transceiver ("responder"), when the timing relationship to an initiating transceiver ("initiator") is not established. The responder will be in a constant receive mode for a potentially long time period, waiting for the first frame. In particular, high performance UWB receivers tend to have high current consumption in the receive mode. This is mainly caused by an analog-to-digital converter (ADC) sampling rate and digital processing rate in the <NUM> frequency range, by a <NUM> bandwidth of the analog frontend, and by a local oscillator (LO) distribution in the <NUM> frequency range. Two quadrature receive (Rx) paths are used to guarantee optimal reception, even if the LO phases of the sender and receiver are not phase aligned. The bill of materials (BOM) and size of a UWB communication device are typically determined by the current consumption in a constant Rx mode.

A transceiver typically contains a signal transmission function or signal transmission unit (i.e., a transmitter) and a signal receiving function or signal receiving unit (i.e., a receiver). The receiver is capable of receiving a radio frequency (RF) signal. Receivers are often based on an IQ topology. It is noted that, according to the IQ topology, a received signal is divided into an I-component or I-channel and a Q-component or Q-channel. The I-channel is the received RF signal without a phase shift (i.e., the "in-phase" or reference signal), while the Q-channel is the received signal shifted by <NUM> degrees (i.e., the received signal in quadrature). In practice, the RF signal is typically mixed with two sinusoids (i.e. LO outputs), where one sinusoid has a pi/<NUM> phase offset relative to the other sinusoid. If only the I-channel is enabled, the receiver effectively operates in a real receiver mode, while if both the I-channel and the Q-channel are enabled, the receiver effectively operates in a complex receiver mode. Alternatively, the receiver may effectively operate in the real receiver mode if only the Q-channel is enabled.

Now discussed are a communication device and a corresponding method of operating a communication device, which facilitate reducing the power consumption of said device, and consequently reducing the bill of materials and size of the communication device.

<FIG> shows an illustrative embodiment of a communication device <NUM>. The communication device <NUM> comprises a receiver circuit <NUM> and a controller <NUM> which are operatively coupled to each other. The receiver circuit <NUM> is configured to receive a signal from an external communication device (not shown). Furthermore, the controller <NUM> is configured to control said receiver circuit <NUM>, wherein said controller <NUM> is configured to cause said receiver circuit <NUM> to operate either in a complex receiver mode or in a real receiver mode. More specifically, the controller <NUM> is configured to cause said receiver circuit <NUM> to operate in the real receiver mode until the signal is successfully acquired. In particular, it may be sufficient to operate the receiver circuit <NUM> in the real receiver mode if the signal has not yet been acquired successfully. Since the real receiver mode requires less power than the complex receiver mode, the power consumption of the communication device <NUM> may be reduced significantly.

The controller is further configured to cause the receiver circuit to use, in the complex receiver mode, an I-channel and a Q-channel of the received signal. In this way, a practical implementation of the complex receiver mode may be realized. Furthermore, the controller is further configured to cause the receiver circuit to use, in the real receiver mode, only said I-channel of the received signal or only said Q-channel of the received signal. In this way, a practical implementation of the real receiver mode may be realized.

The controller is further configured to apply, when the receiver circuit operates in the real receiver mode, a local oscillator frequency which is different from the local oscillator frequency applied when the receiver operates in the complex receiver mode. Furthermore, the controller is configured to offset, when the receiver circuit operates in the real receiver mode, the local oscillator frequency of the receiver circuit by a fraction of the chip rate. In this way, the reception of the signal is facilitated, such that the signal can be properly acquired. It is noted that a chip is equivalent to a UWB pulse. Accordingly, the transmission rate of the pulses may be referred to as the chip rate. The maximal transmission rate is defined in the IEEE <NUM> HRP standard as <NUM>. In one or more embodiments, the controller is further configured to switch the receiver circuit from the real receiver mode to the complex receiver mode upon or after a successful acquisition of the signal. In this way, the receiver circuit may perform at full performance when the signal has been acquired and the contents of the signal should be processed. Furthermore, in one or more embodiments, the successful acquisition of the signal is based on the detection of a synchronization field within said signal, wherein the synchronization field is included in a data frame. In this way, it can easily be determined whether the signal has been successfully acquired.

In one or more embodiments, the controller is further configured to wake up the receiver circuit before switching the receiver circuit from the real receiver mode to the complex receiver mode. This may be advantageous in some implementations of the communication device. Alternatively, the controller is further configured to wake up the receiver circuit after switching the receiver circuit from the real receiver mode to the complex receiver mode. This may be advantageous in other implementations of the communication device. Furthermore, in one or more embodiments, the controller is configured to reset a center frequency upon or after switching the receiver circuit from the real receiver mode to the complex receiver mode. This has the advantage that a data part of a first frame may be received with full sensitivity. In one or more embodiments, the receiver circuit is configured to operate in the complex receiver mode by default, and the controller is configured to switch the receiver circuit from the complex receiver mode to the real receiver mode if no signal is found within a predefined amount of time after the receiver circuit has started up. This may be advantageous in systems in which a wake-up event is triggered via a separate interface.

<FIG> shows an illustrative embodiment of a method <NUM> of operating a communication device. The method <NUM> comprises the following steps. At <NUM>, a receiver circuit comprised in a communication device receives a signal. More specifically, the receiver circuit receives a signal from an external communication device. Furthermore, at <NUM>, a controller comprised in the communication device controls the receiver circuit, wherein the controller causes said receiver circuit to operate either in a complex receiver mode or in a real receiver mode. More specifically, the controller causes said receiver circuit to operate in the real receiver mode until the signal is successfully acquired. As explained above, it may be sufficient to operate the receiver circuit in the real receiver mode if the signal has not yet been acquired successfully. Since the real receiver mode requires less power than the complex receiver mode, the power consumption of the communication device may be reduced significantly.

Accordingly, only one of the two quadrature Rx paths may be enabled during acquisition, to reduce the current consumption by approximately <NUM>% in this mode. Furthermore, the local oscillator (LO) frequency of the RX may be offset by a carrier frequency offset (CFO) that is a fraction of the chip rate (e.g. <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> of <NUM>). Then, the second quadrature component may be enabled once acquisition was successful. The digital receiver may be capable of receiving the frame with said CFO. This method may be compatible with different ranging protocols, such as the protocols defined by the Institute of Electrical and Electronics Engineers (IEEE), the Car Connectivity Consortium (CCC) and the FiRa Consortium.

<FIG> shows a maximum amplitude <NUM> of an I-component relative to an LO phase offset for several carrier frequency offsets (CFOs). It is noted that the LO phase offset is a frequency offset between the receiver (RX) and the transmitter (TX). UWB receivers typically use an in-phase component (i.e., an I-component) and a quadrature component (i.e., a Q-component). As mentioned above, the RF signal is typically mixed with two sinusoids (i.e. LO outputs), where one sinusoid has a pi/<NUM> phase offset relative to the other sinusoid. Line <NUM> shows a regular case with no frequency offset. Then, the amplitude highly depends on the phase offset between the LOs. In particular, the amplitude varies between the limits of <NUM> and pi and vanishes at pi/<NUM> and 3pi/<NUM>. If there is no frequency offset, then the possibility of a proper signal reception with only the I-component depends on the phase between the LOs, even when the link budget is good. As mentioned above, to facilitate the signal reception, the controller may be configured to offset, when the receiver circuit operates in the real receiver mode (i.e., when only the I-component is enabled), the local oscillator frequency of the receiver circuit by a fraction of the chip rate. Line <NUM> shows an example of such an offset. More specifically, line <NUM> shows a frequency offset by ¼ of the chip rate. In that case, the amplitude still depends on the LO phase offset and the minimum is approximately <NUM>% of the maximum (i.e., the performance loss is approximately <NUM>. Thus, if there is a frequency offset, then independently of the phase between the LOs a proper signal reception with the I-component alone is possible.

<FIG> shows an illustrative embodiment of a field structure of a preamble <NUM>. In particular, this field structure is specified in the technical standard "<NPL>. In order to receive a frame, the receiver circuit should acquire the frequency and time offset from the SYNC field. The SYNC field consists of a repetition of equal symbols. Each symbol consists of a binary sequence (Ci) upsampled by a value "DeltaL". For instance, the value DeltaL = <NUM> is typically used for a pulse repetition frequency (PRF) of <NUM>. It is noted that the UWB signal amplitudes can be below the noise floor at the receiver circuit. The receiver circuit typically employs correlation to recover the signal. The correlation is sensitive to frequency offsets and small offsets in the range of <NUM> of ppm can destroy the signal. However, due to the upsampling by DeltaL the correlation works well at frequency offsets that are a multiple of <NUM>/DeltaL of the chip rate. For instance, if DeltaL = <NUM> frequency offsets of a multiple of <NUM> may be applied, if DeltaL = <NUM> frequency offsets of a multiple of <NUM> may be applied, and if DeltaL = <NUM> frequency offsets of a multiple of <NUM> may be applied.

<FIG> shows an illustrative embodiment of a field structure of a full frame <NUM>. In particular, this field structure is specified in the technical standard "<NPL>. For a wake up receiver it may be important that it can also receive the data part (containing a physical layer packet header (PHR) and a PHY payload) of a frame, in order to comply with existing protocols, such as the protocols defined by the IEEE, CCC and FiRa Consortium, and in order to start the ranging protocol with the first frame. The data part is typically modulated with a higher maximal chip rate than the synchronization header (SHR). The IEEE <NUM>. 4z standard defines two options, i.e. a burst with back-to-back chips and a burst with guard chips. As mentioned above, a chip is equivalent to a UWB pulse. In <FIG>, the time period Tc indicates the duration of one chip. Accordingly, the digital receiver may have to be designed to receive the PHR and payload of a frame with a CFO that is a fraction of the maximal chip rate.

<FIG> shows an illustrative embodiment of a first procedure <NUM> for operating a receiver circuit. In particular, in accordance with the present disclosure, the receiver circuit operates in the real receiver mode (i.e., using only the I-channel or I-component) until a signal is successfully acquired. In the example shown in <FIG>, this is implemented in the following manner. At <NUM>, the receiver circuit is started in a wake-up mode, in which only the I-component is enabled, with a certain frequency offset, to detect the SYNC field for any phase offset between TX and RX. At <NUM>, the controller waits until a SYNC field is detected. As mentioned above, the successful acquisition of the signal may be based on the detection of a synchronization (SYNC) field within the signal. Thus, the reception of the SYNC field of the first frame may wake up <NUM> the device, and the data part of the frame may be ignored. After the device has woken up, the receiver circuit may be started <NUM> and both the I-component and the Q-component may be enabled. Accordingly, the following frames are received with full receiver performance. This procedure is most suited for systems in which a transmitter sends wake-up frames at regular intervals, and in which it is not critical that the receiver receives the payload of the first frame. For example, for a wearable smart tag the response time is not critical.

<FIG> shows an illustrative embodiment of a second procedure <NUM> for operating a receiver circuit. In particular, in accordance with the present disclosure, the receiver circuit operates in the real receiver mode (i.e., using only the I-channel or I-component) until a signal is successfully acquired. In the example shown in <FIG>, this is implemented in the following manner. At <NUM>, the receiver circuit is started in a wake-up mode, in which only the I-component is enabled, with a certain frequency offset, to detect the SYNC field for any phase offset between TX and RX. More specifically, the SYNC field of the first frame as well as the data part of the first frame is received. At <NUM>, the controller waits until a SYNC field is detected. As mentioned above, the successful acquisition of the signal may be based on the detection of a synchronization (SYNC) field within the signal. The data part of the first frame is received <NUM>; this data part may indicate that a wake-up of the receiver circuit is needed. In particular, a wake-up is performed if indicated by the data part (e.g., a destination address matches, and a ranging exchange is started). Accordingly, the receiver circuit is started <NUM> and both the I-component and the Q-component may be enabled. Then, the following frames are received with full receiver performance. This procedure is most suited for systems in which it is important that the receiver receives the payload of the first frame. For instance, in an access system the user may benefit from a fast response. Furthermore, in a battery-powered application energy is conserved, if the device only wakes up on frames that are intended for the device.

<FIG> shows an illustrative embodiment of a third procedure <NUM> for operating a receiver circuit. In particular, in accordance with the present disclosure, the receiver circuit operates in the real receiver mode (i.e., using only the I-channel or I-component) until a signal is successfully acquired. In the example shown in <FIG>, this is implemented in the following manner. At <NUM>, the receiver circuit is started in a wake-up mode, in which only the I-component is enabled, with a certain frequency offset, to detect the SYNC field for any phase offset between TX and RX. At <NUM>, the controller waits until a SYNC field is detected. As mentioned above, the successful acquisition of the signal may be based on the detection of a synchronization (SYNC) field within the signal. Then, at <NUM>, both the I-component and the Q-component are enabled. Thus, in this example, the wake-up is performed using only the I-component, but the data part of the first frame is received using both the I-component and the Q-component. In this sense, it may be said that the receiver circuit is started in a wake-up mode using only the I-component, however with immediate data reception using both quadrature branches. More specifically, the reception of the SYNC field of the first frame partly wakes up the device, the Q-component is enabled immediately, such that the data part of the first frame is received <NUM> with both quadrature branches enabled and a nominal LO frequency offset. A full wake-up is performed if the data part indicates that a wake-up is needed <NUM> (e.g., a destination address matches, and a ranging exchange is started). Accordingly, the receiver circuit is started <NUM> and both the I-component and the Q-component may be enabled. Then, the following frames are received with full receiver performance without a nominal LO frequency offset. This procedure is most suited for systems in which it is important that the receiver receives the payload of the first frame. Compared to the second procedure described above, the performance of the data reception is enhanced. This may be beneficial in an access system, in which the user benefits from a fast response. Furthermore, in a battery-powered application energy is conserved, if the device only wakes up on frames that are intended for the device.

<FIG> shows an illustrative embodiment of a fourth procedure <NUM> for operating a receiver circuit. In particular, an alternative of the third procedure is shown. As mentioned above, in accordance with the present disclosure, the receiver circuit operates in the real receiver mode (i.e., using only the I-channel or I-component) until a signal is successfully acquired. In the example shown in <FIG>, this is implemented in the following manner. At <NUM>, the receiver circuit is started in a wake-up mode, in which only the I-component is enabled, with a certain frequency offset, to detect the SYNC field for any phase offset between TX and RX. At <NUM>, the controller waits until a SYNC field is detected. As mentioned above, the successful acquisition of the signal may be based on the detection of a synchronization (SYNC) field within the signal. Then, at <NUM>, both the I-component and the Q-component are enabled, and the center frequency is reset (i.e., changed back to its original value). It is noted that changing back the center frequency at this point has the advantage that the data part of the first frame can be received with full sensitivity. Thus, in this example, the wake-up is performed using only the I-component, but the data part of the first frame is received using both the I-component and the Q-component. In this sense, it may be said that the receiver circuit is started in a wake-up mode using only the I-component, however with immediate data reception using both quadrature branches. More specifically, the reception of the SYNC field of the first frame partly wakes up the device, the Q-component is enabled immediately, such that the data part of the first frame is received <NUM> with both quadrature branches enabled but without a nominal LO frequency offset. A full wake-up is performed if the data part indicates that a wake-up is needed <NUM> (e.g., a destination address matches, and a ranging exchange is started). Accordingly, the receiver circuit is started <NUM> and both the I-component and the Q-component may be enabled. Then, the following frames are received with full receiver performance without a nominal LO frequency offset.

<FIG> shows an illustrative embodiment of a fifth procedure <NUM> for operating a receiver circuit. In particular, in accordance with the present disclosure, the receiver circuit operates in the real receiver mode (i.e., using only the I-channel or I-component) until a signal is successfully acquired. In the example shown in <FIG>, this is implemented in the following manner. At <NUM>, the receiver circuit is first started with full performance, i.e. with both the I-component and the Q-component enabled. If a signal is found within a certain time (i.e., a predefined amount of time), then the receiver circuit proceeds with its normal operation (i.e., regular operating mode). However, if no signal is found <NUM> within the predefined amount of time, then the first, second or third procedure as described above is executed <NUM>. As explained above, in each of these procedures the Q-component is initially disabled, so that the receiver circuit effectively operates in the real receiver mode. This procedure is most suited for systems in which a wake-up event is triggered via a separate interface (e.g., a Bluetooth low energy interface), but in which the timing is only loosely defined by this interface and in which the link budget may not always be sufficient. For instance, this may be applicable if the communication device is a UWB anchor in a smart vehicle access system. In a smart access system for a car Bluetooth low energy (BLE) may be used as wakeup mechanism to turn on the UWB anchors on the car side. However, not all of them may have a sufficient UWB link budget for signal reception. Since the UWB anchors receive scheduling information in the first UWB frame, it is important that this frame is properly received. Anchors that do not receive this scheduling information, should remain in a constant receive mode for considerable amounts of time (i.e., minutes or hours). The aforementioned wake-up mode may reduce the BOM and the size of the UWB module. It is noted that the BOM and size of a UWB anchor are to a large extent determined by the constant receive mode, because a DC/DC converter may be needed instead of a cheap linear regulator to reduce current consumption. Furthermore, a larger module with a lower thermal resistance may be needed to avoid overheating. The energy consumption is reduced by switching to the wake-up mode, if no signal is found within a certain time. Accordingly, the sensitivity of the receiver circuit may be traded off against the BOM, size and energy consumption of the receiver circuit.

Claim 1:
A communication device (<NUM>), comprising:
- a receiver circuit (<NUM>) configured to receive a signal, wherein the signal is an ultra-wideband, UWB, pulse signal;
- a controller (<NUM>) configured to control said receiver circuit (<NUM>), wherein said controller (<NUM>) is configured to cause said receiver circuit (<NUM>) to operate either in a complex receiver mode or in a real receiver mode;
wherein the controller (<NUM>) is configured to cause said receiver circuit (<NUM>) to operate in the real receiver mode until the signal is successfully acquired;
characterized in that the controller (<NUM>) is further configured to cause the receiver circuit (<NUM>) to use, in the complex receiver mode, an I-channel and a Q-channel of the received signal;
wherein the controller (<NUM>) is further configured to cause the receiver circuit (<NUM>) to use, in the real receiver mode, only said I-channel of the received signal or only said Q-channel of the received signal;
wherein the controller (<NUM>) is further configured to apply, when the receiver circuit (<NUM>) operates in the real receiver mode, a local oscillator frequency which is different from the local oscillator frequency applied when the receiver circuit (<NUM>) operates in the complex receiver mode, and wherein the controller (<NUM>) is configured to offset, when the receiver circuit (<NUM>) operates in the real receiver mode, the local oscillator frequency of the receiver circuit (<NUM>) by a fraction of the pulse rate.