Patent Description:
Radar (Radio Detection and Ranging) is an emerging use case for wireless communications systems. A wireless communications system may be used both for exchanging data with mobile users and for pedestrian or vehicular traffic monitoring when deployed along roads, e.g. within cities or at highway bridges. Transmit signal of a Radar system is reflected by a target (e.g. a human or a car), and by processing the received signal it is possible to derive target properties such as distance, horizontal/vertical direction, velocity and/or size.

Joint use of the wireless communication system for communications and Radar introduces an overhead to the wireless communications system. Reducing the overhead can have a negative effect on velocity resolution and a sufficiently large maximum velocity of targets monitored by the Radar. The document <CIT> discloses a radar device comprising a transmitting unit, a receiving unit and a velocity measuring unit. The transmitting unit transmits first and second transmission signals generated based on first and second parameters for computing relative velocities in first and second detection velocity ranges, respectively. The second detection velocity range is narrower than the first detection velocity range. The receiving unit receives the reflected waves of the first and second transmission signals from a target as first and second reception signals, respectively. The velocity measuring unit computes first and second relative velocities in the first and second detection velocity ranges based on the first and second reception signals, respectively and obtains the velocity measurement result of the relative velocity of the target based on the combination of the first and second relative velocities. Further background art is known from the documents <CIT>, <CIT> and <CIT>.

The embodiments, examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

According some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

In connection with a radar operation on an air interface of a wireless communications system, at least two radar excitation signals are defined. One radar excitation signal has a first burst duration and a first sampling period. Another radar excitation signal has a second burst duration and a second sampling period. The first sampling period of the first signal is configured for scanning a velocity range and the second sampling period of the second signal is configured for scanning a portion of the velocity range, and the first burst duration is smaller than the second burst duration. The at least two radar excitation signals are embedded into a frame structure for the wireless communications system. At least one radar operation comprising at least one transmission based on the frame structure is performed. In this way the overhead of the radar excitation signals on the air interface of the wireless communications system may be controlled, while supporting a fine velocity resolution and a sufficiently large maximum velocity for a target monitored by the radar operation. It should be appreciated that the air interface may be based on Orthogonal Frequency Division Multiplexing (OFDM) that may be used on the air interface of at least a Long-Term Evolution (LTE) mobile communications system, New Radio (NR) mobile communications system or a mobile communications system beyond <NUM> or <NUM>.

A radio device is a device configured for communications on radio waves over a wireless radio link, i.e. a wireless link. The communications comprise user traffic and/or signaling. The user traffic may comprise data, voice, video and/or audio. Examples of the wireless link comprise a point-to-point wireless link and a point-to-multipoint wireless link. The wireless link may be provided between two radio devices. It should be appreciated that the radio devices may have differences. For example, radio devices connected by a wireless link may comprise one or more of a user equipment (UE), an access node, an access point, a relay node, a user terminal and an Internet of Things (loT) device.

A radio device may be a radio access device that is configured to serve a plurality of other radio devices, user radio devices, and give radio access to a communications system for the user radio devices. A radio device may also be a radio station serving as relay node or providing a wireless backhaul for one or more radio access nodes. Examples of the radio access devices comprise at least an access node, an access point, a base station and an (e/g)NodeB. Examples of the user radio devices comprise at least a user terminal and user equipment (UE). The radio device may be an aerial radio device and/or an extraterrestrial radio device configured to operate above the ground without a fixed installation to a specific altitude. Examples of extra-terrestrial radio devices comprise at least satellites and spacecraft that are configured for radio communications in a communications system that may comprise both terrestrial and extraterrestrial radio devices. Examples of aerial radio devices comprise at least High Altitude Platform Stations (HAPSs) and unmanned aerial vehicles (UAVs), such as drones. The radio access device may have one or more cells which the user radio devices may connect to in order to access the services of the communications system via the radio access device. The cells may comprise different sizes of cells, for example macro cells, micro cells, pico cells and femto cells. A macro cell may be a cell that is configured to provide coverage over a large coverage area in a service area of the communications system, for example in rural areas or along highways. A micro cell may be a cell that is configured to provide coverage over a smaller coverage area than the macro cell, for example in a densely populated urban area. Pico cells may be cells that are configured to provide coverage over a smaller area than the micro cells, for example in a large office, a mall or a train station. Femto cells may be cells that are configured to provide coverage over a smaller area than the femto cells, for example at homes or small offices. For example macro cells provide coverage for user radio devices passing a city on a motorway/highway and local cells, e.g. micro cells or smaller cells, provide coverage for user radio devices within the city. In another example, macro cells provide coverage for aerial radio devices and/or extraterrestrial radio devices and local cells, e.g. micro cells or smaller cells, provide coverage for the aerial radio devices and/or extraterrestrial radio devices that are located at elevated positions with respect to one or more radio access devices of the communications system. Accordingly, an aerial radio device or extraterrestrial radio device may be connected to a micro cell of a radio access device and when the aerial radio device or extraterrestrial radio device is above a certain height from the ground, the aerial radio device or extraterrestrial radio device may be switched to a macro cell, for example by a handover procedure.

A radar operation comprises a radar transmitting one or more radar excitation signals, i.e. radar signals, within a field of view of the radar. The radar may be a radio device configured to transmit radar excitation signals embedded into a frame structure on an air interface, for example an OFDM frame structure of an OFDM-based air interface. The field of view of the radar may be defined by a direction transmitting the radar signal from the radar. The transmitted radar signal reaches an object, i.e. a target, located within the field of view of the radar after a time δ of a propagation delay has passed and the radar signal is reflected back from the object to the radar. The radar receives the reflected radar signal after 2δ from transmitting the radar signal. If no objects are located within the field of view, the transmitted signal is not reflected back. The time offset between the transmitted and the received reflected signal, the round-trip time, determines the distance to the reflected object. A distance to the object may be expressed by <MAT> where D is the distance, c is speed of light and TR is the round-trip time from transmitting the radar signal to receiving the radar signal. The radar operation is capable of detecting objects in the field of view from a minimum distance, dmin, and up to a maximum distance, dmax, from the radar. Then, a propagation delay will follow <MAT> where c is speed of light and δ is the propagation delay for the radar signal to reach an object within the field of view. Accordingly, the field of view of the radar satisfies formula (<NUM>). Examples of radar signals comprise radar signals that are non-contiguous in time-domain, for example time-domain comb signals, chirp signals, and non-contiguous sequences of OFDM symbols that may comprise user data and/or signaling. The radar signals may be based on Zadoff Chu (ZC)- ,m- or gold sequence. Because all of those sequence families already exist in NR UE, radar signals based on ZC- ,m- or gold sequence may be implemented in radio devices at least partly based on existing code generators. Moreover, the ZC- ,m- or gold sequences have very low cross correlation properties, allowing the simultaneous presence of multiple radar signals in time. Examples of chirp signals that are non-contiguous in time-domain are described in <NPL>. The chirp signals support a low Peak-to-Average power ratio (PAPR) and low-cost implementation. Radar signals comprise non-contiguous radars signals carrying user data and/or signalling may be preferred for efficient utilization of resources on the air interface.

OFDM radar enables joint communication and sensing, <NPL>. With OFDM Radar, a downlink (DL) signal carrying user data, e.g. OFDM resource elements carrying Quadrature Amplitude Modulation (QAM) symbols, can be used as the radar excitation signal, whereby there is no need to eat away DL capacity for radar operation. The user data may be actual user data or dummy data. On the other hand, also other radar signals may be embedded to the OFDM resource elements using TDM as explained above.

A radar operation of a radio device in a wireless communication system may be performed on the same frequencies that are utilized by the wireless communication system for wireless communications, whereby interference due to uncoordinated radar operation may be a problem for the communications performed in the wireless communication system. Moreover, the frequencies for radar operation may be on unlicensed frequency bands, whereby the radar may cause interference also to other systems as well.

Velocity resolution Δv may determine a minimum burst duration for a radar excitation signal according to c / (<NUM>Δv fc), where c denotes the velocity of light, fc denotes the carrier frequency, and the factor 2x is due to the signals travelling from gNB to the target and back.

A radar excitation signal may have a duration and a sampling period. The duration may define a time period or a number of symbols during which the radar excitation signal is transmitted. The radar excitation signal may span over a plurality of frames of a frame structure. The sampling period of the radar excitation signal may be a time spacing between consecutive time units or symbols comprising portions of the radar excitation signal. Therefore, the radar excitation signal may be referred to a non-contiguous radar excitation signal. An example of a radar excitation signal is a sequence of symbols, with a sampling period and a burst duration. Transmission of a radar excitation signal on an air interface may be referred to a burst or radar burst. In an example a radar excitation signal may be embedded into a frame structure for a wireless communications system. The frame structure may comprise time units, where the radar excitation signal may be included. In an example a radar excitation signal may be embedded into a frame structure for Orthogonal Frequency-Division Multiplexed (OFDM) communications. Accordingly, the radar excitation signal may comprise signal portions that are transmitted within time units or at OFDM symbols positions of the frame structure and the signal portions of the radar excitation signal may be spaced in time by one or more time units or OFDM symbols.

A frame structure may comprise consecutive frames for communications on an air interface of a communications system. A frame may comprise time occasions for communications information within time units for example within symbols. A time occasion may be a time slot or a set of time slots. Examples of the symbols comprise OFDM symbols. An example of the frame structure is a frame structure for <NUM> NR, where a frame has duration of <NUM> which consists of <NUM> subframes having <NUM> duration each. Each subframe may have <NUM>µ time slots, where µ is a positive integer according to a transmission numerology. Each time slot may consist of <NUM> OFDM symbols.

<FIG> shows user devices <NUM> and <NUM> configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) <NUM> providing the cell. The physical link from a user device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage. The access node provides access by way of communications of radio frequency (RF) signals and may be referred to a radio access node. It should be appreciated that the radio access network may comprise more than one access nodes, whereby a handover of a wireless connection of the user device from one cell of one access node, e.g. a source cell of a source access node, to another cell of another node, e.g. a target cell of a target access node, may be performed.

A communication system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signaling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network <NUM> (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc..

The user device (also called UE, user equipment, user terminal, terminal device, wireless device, user radio device, communications device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node.

<NUM> enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. <NUM> mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control. <NUM> is expected to have multiple radio interfaces, namely below <NUM>, cmWave and mmWave, and also being capable of being integrated with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and <NUM> radio interface access comes from small cells by aggregation to the LTE. In other words, <NUM> is planned to support both inter-RAT operability (such as LTE-<NUM>) and inter-RI operability (inter-radio interface operability, such as below <NUM> - cmWave, below <NUM> - cmWave - mmWave). One of the concepts considered to be used in <NUM> networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent. <NUM> (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or NodeB (gNB).

Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed).

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the user device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs or may be a Home(e/g)NodeB.

Typically, a network which is able to use "plug-and-play" (e/g)Node Bs, includes, in addition to Home (e/g)NodeBs (H(e/g)NodeBs), a home node B gateway, or HNB-GW (not shown in <FIG>).

Referring to <FIG>, there is provided an example of a method for controlling overhead of radar excitation signals in an OFDM-based communications system, while supporting a fine velocity resolution and a sufficiently large maximum velocity for a target monitored by a radar operation in accordance with at least some embodiments of the present invention. In an example the method may be performed at a radio access device, for example gNB.

Phase <NUM> comprises defining at least two radar excitation signals comprising a first radar excitation signal having: a first burst duration and a first sampling period; and a second radar excitation signal having: a second burst duration and a second sampling period; wherein the first sampling period of the first radar excitation signal is configured for scanning a velocity range and the second sampling period of the second radar excitation signal is configured for scanning a portion of the velocity range, and the first burst duration is smaller than the second burst duration. It should be appreciated that the first/second radar excitation signal, first/second burst duration and first/second sampling period are intended to distinguish a radar excitation signal, burst duration and sampling period between another one. Therefore, they could be named otherwise too. It should be appreciated that this naming convention is applied throughout this document.

Phase <NUM> comprises embedding said at least two radar excitation signals into a frame structure for a wireless communications system.

In an example phase <NUM> comprises that the radar excitation signals may be transmitted on a plurality of beams and the radar excitation signals may carry user data, if there is at least one user that can be served by a beam, where the radar excitation signals are transmitted. For this to happen it is advantageous to have an air interface capable to schedule a user on multiple beams, e.g. on the best beam and on the second best beam as measured and reported by the user. This will strongly increase the probability that at least one user can be served with data on any particular beam direction.

In an example in accordance with at least some embodiments, phase <NUM> comprises that the frame structure is for Orthogonal Frequency-Division Multiplexed (OFDM) communications. The frame structure for OFDM communications comprises frames, where OFDM symbols are arranged in time slots.

In an example, phase <NUM> comprises that the radar excitation signals are transmitted within time units of the frame structure or at symbol positions of OFDM symbols of the frame structure.

In an example, phase <NUM> comprises adapting Fast Fourier Transform (FFT) processing by selecting larger FFT size together with zero padding for OFDM symbols not allocated for Radar excitation.

Phase <NUM> comprises performing at least one radar operation comprising at least transmission based on the frame structure.

In an example in accordance with at least some embodiments, phase <NUM> comprises that the transmission is based on a frame structure for OFDM communications.

In an example in accordance with at least some embodiments, phase <NUM> comprises defining the velocity resolution of the second radar excitation signal to meet the velocity resolution for measuring a velocity of a target by said at least two radar excitation signals.

In an example of the sampling periods of the radar excitation signals, the radar excitation signals may have an equal to or a higher sampling period than a symbol duration T for OFDM symbols in a frame structure for OFDM communications. With sampling period T and M samples over burst duration MT, after Fourier transform the frequency range is given by <NUM>/T (more precisely, the discrete frequencies are given by <NUM>, <NUM>/MT,. (M-<NUM>)/MT) and the frequency resolution by <NUM>/MT. By increasing the sampling period to mT (integer m><NUM>), the number of samples within the same burst duration MT is reduced to M/m, the frequency range is reduced to <NUM>/mT, and the frequency resolution <NUM>/MT is unchanged.

In an example in accordance with at least some embodiments, phase <NUM> comprises applying a deterministic scheduling to the first radar excitation signal and an opportunistic scheduling to the second radar excitation signal. Applying different scheduling for the radar excitation signals provides mitigating overhead by the radar excitation signals. In an example, applying a deterministic scheduling comprises performing a periodic beam sweeping operation. In an example, applying an opportunistic scheduling comprises performing a radar operation, when scheduling user data to one or more active users. Accordingly, user data transmissions may serve as the radar excitation signal. For example, radar excitation signals may be used to carry user data over an OFDM-based air interface. If the radar excitation signals are transmitted on a (narrow) beam, data can be transmitted to a user if the user is able to "see" that beam. Otherwise dummy data signals may be used for radar excitation, or any other signal, e.g. those mentioned above.

Beam sweeping may comprise that a signal is sent via all beams, one beam at a time. Once the signal has been sent via all the beams, the beam sweeping may be repeated. for example, periodically. Beam sweeping using the radar excitation signals comprises that each of the radar excitation signals is sent via all beams, one beam at a time. The order of transmission of the radar excitation signals over the beams can be arranged in multiple ways, provided the latency is acceptable e.g. <NUM>-<NUM> so that a monitored target is not moving too much. In an example, an order for transmission of the radar excitation signals is transmitting signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>. Another example is transmitting signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>, signal <NUM> via beam <NUM>. It should be appreciated that a full beam sweep can also be partitioned into multiple partial beam sweeps, over multiple subsets of beams. In this way, a beam sweep may be performed for one subset and only after the beam sweep for the one subset is complete, a next beam sweep for another subset is performed. The above examples of beam sweeping refer to examples for analog beamforming, where transmissions are performed one beam at a time. It should be appreciated that, if digital or hybrid beamforming is used, there may be multiple beams at a time. However, in such a case transmission power may be shared among the beams, which may cause additional range limitation for the radar.

In an example in accordance with at least some embodiments, phase <NUM> comprises performing one beam sweep with at least part of one of the radar excitation signals and performing another beam sweep with at least part of another one of the radar excitation signals. The beam sweeps may comprise at least partly different beams. In an example a set of beams for a beam sweep using at least part of the radar excitation signal, e.g. second radar excitation signal, configured for scanning a portion of the velocity range may be a subset of the beams for the beam sweep using at least part of the radar excitation signal, e.g. first radar excitation signal, configured for scanning a velocity range. The first radar excitation signal may provide a coarse velocity resolution and the second radar excitation signal may provide a fine granular velocity resolution. A beam sweep may comprise using at least some symbol(s) of a radar excitation signal.

In an example in accordance with at least some embodiments, phase <NUM> comprises transmitting the radar excitation signals consecutively in time or interleaved in time.

In an example in accordance with at least some embodiments, phase <NUM> comprises multiplexing transmissions of the radar excitation signals on different beams. Interleaving supports mitigating overhead by the radar excitation signals. On the other hand consecutive radar excitation signals may support fast beam sweeping.

In an example in accordance with at least some embodiments, phase <NUM> comprises that at least one time unit in the frame structure is shared by the at least two radar excitation signals. In this way mitigating overhead by the radar excitation signals is supported.

In an example in accordance with at least some embodiments, phase <NUM> comprises that the time unit is an OFDM symbol or an OFDM symbol duration.

In an example in accordance with at least some embodiments, phase <NUM> comprises that a position of the shared OFDM symbol is defined in bursts of the at least two radar excitation signals. In an example the shared time unit or OFDM symbol may be at the beginning of the bursts. On the other hand, if velocity of a monitored target would have rapid changes, sharing the time unit or OFDM symbol in the middle of the burst (i.e. placing the short sequence in the middle of the long sequence) could provide more accurate measurement results.

In an example in accordance with at least some embodiments, phase <NUM> comprises that one or more of the at least two radar excitation signals comprise user data or signaling.

Referring to <FIG>, there is provided an example of a method for supporting measurements by a radar operation in accordance with at least some embodiments of the present invention. The method may be performed by at a user radio device, for example a UE. The UE may be within a range of communications with a gNB operating in accordance with the method described with <FIG>.

Phase <NUM> comprises receiving at least two radar excitation signals embedded into a frame structure for a wireless communications system.

Phase <NUM> comprises measuring at least one of received signal strength, received signal quality and channel state information on the basis of the at least two radar excitation signals comprising a first radar excitation signal having: a first burst duration and a first sampling period; and a second radar excitation signal having: a second burst duration and a second sampling period; wherein the first sampling period of the first radar excitation signal is configured for scanning a velocity range and the second sampling period of the second radar excitation signal is configured for scanning a portion of the velocity range, and the first burst duration is smaller than the second burst duration. In this way the radar excitation signals support UE measurements. The UE measurements may be transmitted in measurements reports to a radio access device.

In an example, phase <NUM> comprises that the radar excitation signals are received within time units of the frame structure or at symbol positions of OFDM symbols of the frame structure.

An example of radar excitation signals for OFDM is next described for application of NR gNB as an OFDM radar for traffic monitoring. The example utilizes a principle of the NR gNB using at least two different signals for radar excitation. The radar excitation signals used in the example comprise two differently parametrized time-domain comb signals.

System setup for the NR gNB is characterized by:.

In this system setup, typically a beam sweep in time-domain will be applied to send out the radar excitation signals, one beam at a time due to analog beamforming, one beam after another. Although the radar excitation signals may carry data, the data transfer is limited to the subset of users that can be reached with the (narrow) active beam. This limitation motivates to reduce overhead for excitation signals also in case of OFDM radar.

An example of a typical signal processing for OFDM radar is a two-dimensional Fourier transform to compute a periodogram with N columns and M rows, where N denotes the number of active sub-carriers and M the number of OFDM symbols carrying the radar excitation signals. In the obtained periodogram, the maximum position column-wise relates to the distance of the target (i.e. delay of the echo signal), and row-wise to the target velocity (i.e. Doppler shift of the echo signal). A characteristic of OFDM radar is that the determination of distance and velocity are completely independent (as opposed to constant envelope radar where both properties depend on each other). The periodogram benefits from an improvement of the SNR by a factor NxM versus the SNR at the receive antenna, called the processing gain.

The traffic monitoring use case is described with the following requirements for a radar operation for monitoring a target:.

In a conventional OFDM radar, a burst duration of about <NUM> would be required with above system setup to achieve a velocity resolution of <NUM>/h, i.e. the required measurement duration would span about <NUM> slots. With <NUM> beams, if each beam would be allocated over <NUM> for radar processing, the procedure would have to be repeated after <NUM>, since the target may move significantly within that period, e.g. by about <NUM> at <NUM>/h, by far exceeding the minimum required distance resolution. In this scenario the entire DL radio resources would be occupied with radar excitation signals with a new beam sweep every <NUM>.

The maximum unambiguous velocity is given by c / (<NUM> fc T<NUM>), where T<NUM> denotes the total OFDM symbol duration including Cyclic Prefix, under the typical assumption that M consecutive OFDM symbols are processed. With time-non-contiguous signals, the maximum unambiguous velocity is given by c / (<NUM> fc mT<NUM>), where mT<NUM> (m integer) is the sampling period given by an integer multiple of the total OFDM symbol duration. With the above system setup, up to about <NUM>/h target velocity could be measured without ambiguity, which is more than sufficient for the traffic monitoring use case.

The traffic monitoring is provided by the two differently parametrized time-domain comb signals comprising a first radar excitation signal and a second radar excitation signal. Based on the first radar excitation signal, a first velocity measurement is provided with coarse velocity resolution, e.g. Δv1 = <NUM>/h, but spanning the entire velocity range, e.g. up to <NUM>/h (=4x <NUM>/h). Based on the second radar excitation signal, a second velocity measurement is provided with fine velocity resolution, e.g. Δv2 = <NUM>/h resolution, and (at least) spanning a velocity range given by the velocity resolution of the first radar excitation signal, e.g. v2,max = <NUM>/h (≥ Δv1).

The resulting impact on the signal parametrization is as follows:.

In an example in accordance with at least some embodiments, a method comprises measuring a first velocity, v<NUM>, of on the basis of the first radar excitation signal; measuring a second velocity, v<NUM>, on the basis of the second radar excitation signal; determining at least one condition for a third velocity on the basis of the first velocity; deriving the third velocity based on the second velocity and the at least one condition. In this way monitoring of targets e.g. traffic, may be supported by the radar signals. In an example the first velocity may be a coarse velocity defined by Formula (<NUM>), the second velocity may be a fine granular velocity defined by Formula (<NUM>), the third velocity may be defined by formula (<NUM>) and the at least condition may be defined by formula (<NUM>).

A velocity measurement by the first radar excitation signal gives: <MAT>.

A velocity measurement by the second radar excitation signal gives: <MAT>.

In Formulas (<NUM>) and (<NUM>), m<NUM> and m<NUM> may denote the row-wise maximum positions of the two periodograms. A possible method for combining the measurements is similar as described in <NPL>, for a different technique using a chirp-based waveform. The final velocity measurement may be given by: <MAT>
where integer q ≥ <NUM> is selected to find at least a local minimum of an absolute value of: <MAT>.

In other words, the final velocity measurement v may be given by adding to the fine-granular velocity estimate v<NUM> a multiple of q times the maximum velocity v<NUM>,max, where q is chosen such that v is closest to the coarse velocity measurement v<NUM>. In practice the combining may be a bit more involved to be sufficiently accurate.

The final velocity measurement will be selected as v = <NUM>/h (q = <NUM>), so that the result is within the range of the first coarse measurement given by <NUM>/h +/-<NUM>/h. The final measurement result has a resolution of <NUM>/h as required.

In the example of the traffic monitoring, a velocity, i.e. a first velocity, of the target may be measured by computing a periodogram using the first radar excitation signal. The periodogram may have its maximum position at m<NUM>=<NUM>, whereby the velocity of the target obtained with the first radar excitation signal is <NUM>/h within +/-<NUM>/h. A velocity, i.e. a second velocity, of the target may be measured by computing a periodogram using the second radar excitation signal. The periodogram may have its maximum position at m<NUM>=<NUM>, whereby the velocity of the target obtained with the second radar excitation signal is <NUM>/h within +/-<NUM>/h. The velocity of the target may be calculated by scanning over different values of integer q in accordance with formula (<NUM>) for satisfying a condition in accordance with the Formula (<NUM>). Accordingly, scanning over different values of integer q gives v = <NUM>/h with q = <NUM>, v = <NUM>/h with q = <NUM>, v = <NUM>/h with q = <NUM>, etc. The velocity of the target may be selected as v = <NUM>/h (q = <NUM>), so that the result is closest to the first coarse measurement given by <NUM>/h +/-<NUM>/h in accordance with Formula (<NUM>). Velocity resolution of the velocity of the target determined in this way has a resolution of <NUM>/h as required.

<FIG> illustrates examples of radar excitation signals in accordance with at least some embodiments of the present invention. An example of a radar excitation signal may be a sequence of OFDM symbols <NUM> that may comprise user data and/or signaling. The sequence of OFDM symbols may have a symbol duration T0 and the sampling period of the sequence may be mT0, which defines spacing of the OFDM symbols in time such that the sequence is non-contiguous for comb-shaped structure. Another example of a radar excitation signal may be a chirp-based comb signal <NUM>. The chirp-based comb signal may have a chirp duration Tc and the sampling period of the chirp may be mTc, which defines spacing of the chirps in time for comb-shaped structure of the chirp-based signal. Consecutive chirps may be separated by a time period during which the chirp is switched off.

<FIG> illustrates examples of bursts of radar excitation signals in accordance with at least some embodiments of the present invention. Radar excitation signals <NUM>, <NUM> are illustrated embedded in a frame structure for OFDM communications. The frame structure may be for <NUM> NR, where a frame has duration of <NUM> which consists of <NUM> subframes having <NUM> duration each. Each subframe may have <NUM>µ slots <NUM>, where µ is a positive integer according to a transmission numerology. Each slot may consist of <NUM> OFDM symbols <NUM>. Although in <FIG>, a fist OFDM symbol of a time slot <NUM> is allocated to a radar excitation signal it should be appreciated that it does not necessarily have to be the first OFDM symbol of the time slot, but in principle any symbol-offset can be applied. A combined radar excitation signal <NUM> illustrates an overhead caused by the radar excitation signals <NUM>, <NUM> in an OFDM transmission based on the frame structure comprising the at least two radar excitation signals. The overhead caused by the combined radar excitation signal <NUM> is less than if two separate radar excitation signals <NUM>, <NUM> were used.

In an example, in accordance with at least some embodiments radar excitation signals are transmitted consecutively in time or interleaved in time. For example the radar excitation signals <NUM>, <NUM> may be arranged to the frame structure at least partially interleaved in time. In this way the radar excitation signals may be transmitted interleaved in time and overhead caused by the radar excitation signals may be mitigated as can be seen from the combined excitation signal. It should be appreciated that alternatively or additionally, the radar excitation signals <NUM>, <NUM> may be arranged consecutively to the frame structure for OFDM communications. In this way, the radar excitation signals may be transmitted consecutively in time. However, in this case the overhead may be higher than if the radar excitation signals would be transmitted at least partially interleaved in time. The overhead may be reduced if symbols are shared by the interleaving. In at least one example, in accordance with at least some embodiments at least one OFDM symbol <NUM> in the frame structure is shared by at least two radar excitation signals <NUM>, <NUM>. It should be appreciated that also more than one, for example all but one, or less, OFDM symbols may be shared by the radar excitation signals. In an example, in accordance with at least some embodiments, radar excitation signals <NUM>, <NUM> may be multiplexed on different beams. In this way the radar excitation signals in the frame structure may be transmitted by different beams. In an example, a beam sweep may be performed using the radar excitation signals, whereby the radar excitation signals are transmitted on each beam. As the second excitation signal <NUM> is comparatively sparse in time, it enables to scan a rather large number of beams within the burst duration. When having a limited capacity per time slot for radar excitation, for a full beam sweep it may be preferred in terms of speed if the (beam sweeps with) excitation signals <NUM>, <NUM> are consecutive in time.

It should be appreciated that a full beam sweep is needed to compute a full three-dimensional (3D) radar image: range, velocity and angle. A fixed overhead for radar excitation, e.g. two symbols per slot, may be reserved. The radar excitations signals may be arranged to the same beam consecutively. In this way time interleaving may be provided for multiple beams within the burst duration. This may save overhead for the beam sweep, as compared to using the combined signal <NUM> on each beam.

In an example, in accordance with at least some embodiments, a position of the shared OFDM symbol <NUM> maybe defined in bursts of the at least two radar excitation signals. In the example illustrated in <FIG>, only a single OFDM symbol is shared when combining the first and second excitation signal <NUM>, <NUM>; <NUM> symbols are allocated with the combined signal <NUM> versus <NUM> symbols with separate signals. Therefore, advantageously the time for transmitting the excitation signals can be reduced, e.g. <NUM> slots would be required for consecutive transmission, while only <NUM> slots are required with signal combining or time-interleaving.

An exemplary signal parametrization for radar excitation signals is provided in the following to illustrate potential efficiency gains of examples according to embodiments. Further optimization by different parametrization, e.g. by thinning out the second excitation signal further, may be possible. The example is described with reference to the radar excitation signals <NUM>, <NUM> in <FIG>.

With time-non-contiguous signals, the maximum unambiguous velocity is given by c / (<NUM> fc mT<NUM>), where mT<NUM> (m integer) is the sampling period given by an integer multiple of the total OFDM symbol duration. Table <NUM> depicts the maximum unambiguous target velocity versus the sampling period in number of OFDM symbols with <NUM> slot duration and <NUM> symbols/slot. Using Table <NUM>, the system requirements can be fulfilled by parameterizing the radar excitation signals as follows:.

The first excitation signal is a time-domain comb present in every <NUM>th OFDM symbol (i.e. every half-slot) and provides a maximum unambiguous target velocity of <NUM>/h.

The second excitation signal is a time-domain comb present in every <NUM>th OFDM symbol (i.e. every second slot) and provides a maximum unambiguous target velocity of <NUM>/h (~<NUM>/h / <NUM>).

The (minimum) burst duration of the excitation signals can be derived from Table <NUM>:.

The resulting time-domain comb signals for the first and second excitation signal are exemplified in the first and second row of <FIG>, respectively.

An assessment of overhead reduction of the time-domain comb signals according to Table <NUM> and <FIG>:.

Resource saving of the time-domain comb signals is therefore about <NUM>. 7x versus conventional time-contiguous design and about <NUM>. 67x versus conventional non-time-contiguous design.

A further advantage of time-domain comb signals is that (with fixed overhead for the radar excitation signals) it makes the beam sweep faster as compared to the conventional design:.

Our example design reduces the time needed for a full beam sweep by <NUM>. 56x (<NUM> → <NUM>) versus conventional non-time-contiguous design, similar as with the resource saving.

The above assessment assumed that there is sufficient processing gain with any of the designs. To give an example, a distance resolution of <NUM> would require a minimum bandwidth of <NUM>, corresponding to <NUM> active subcarriers at <NUM> SCS. In our example design, the processing gain would be about 37dB and 40dB for the first and second excitation signal, respectively, if all <NUM> subcarriers would be allocated. In other words, the processing gain is quite large also when using low overhead signal design; spending <NUM>. 67x more OFDM symbols would improve SNR by -<NUM>. 3dB which is small, given the actual processing gain.

<FIG> illustrates an example of an apparatus in accordance with at least some embodiments of the present invention. The apparatus may be a radio device, for example a radio access node or a user radio device. The apparatus may perform one or more functionalities according to examples described herein.

The apparatus comprises a processor (P) <NUM> and a transceiver (TX) <NUM>. The processor is operatively connected to the transceiver for controlling the transceiver. The apparatus may comprise a memory (M) <NUM>. The memory may be operatively connected to the processor. It should be appreciated that the memory may be a separate memory or included to the processor and/or the transceiver.

According to an embodiment, the processor is configured to control the transceiver to perform one or more functionalities described according to an embodiment.

A memory may be a computer readable medium that may be non-transitory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architecture, as non-limiting examples.

Embodiments may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. In the context of this document, a "memory" or "computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

Reference to, where relevant, "computer-readable storage medium", "computer program product", "tangibly embodied computer program" etc., or a "processor" or "processing circuitry" etc. should be understood to encompass not only computers having differing architectures such as single/multi-processor architectures and sequencers/parallel architectures, but also specialized circuits such as field programmable gate arrays FPGA, application specify circuits ASIC, signal processing devices and other devices. References to computer readable program code means, computer program, computer instructions, computer code etc. should be understood to express software for a programmable processor firmware such as the programmable content of a hardware device as instructions for a processor or configured or configuration settings for a fixed function device, gate array, programmable logic device, etc..

Although the above examples describe embodiments of the invention operating within a user radio device, UE, radio access device or a gNB, it would be appreciated that the invention as described above may be implemented as a part of any apparatus comprising a circuitry in which radio frequency signals are transmitted and/or received. Thus, for example, embodiments of the invention may be implemented in a mobile phone, in a base station, in a radio station, in a user radio device, in a computer such as a desktop computer or a tablet computer comprising radio frequency communication means (e.g. wireless local area network, cellular radio, etc.).

Claim 1:
A method performed by a radio device (<NUM>) being configured for communications, comprising user traffic and/or signaling, on radio waves over a wireless radio link in a wireless communications system, said method comprising:
- defining (<NUM>) at least two radar excitation signals (<NUM>, <NUM>) comprising a first radar excitation signal (<NUM>) having:
∘ a first burst duration and a first sampling period; and a second radar excitation signal (<NUM>) having:
o a second burst duration and a second sampling period; wherein the first sampling period of the first radar excitation signal (<NUM>) is configured for scanning a velocity range and the second sampling period of the second radar excitation signal (<NUM>) is configured for scanning a portion of the velocity range, and the first burst duration is smaller than the second burst duration, wherein the sampling period of a radar excitation signal is a time spacing between consecutive time units or symbols comprising portions of the radar excitation signal;
- embedding (<NUM>) said at least two radar excitation signals (<NUM>, <NUM>) into a frame structure for said wireless communications system, wherein at least one of said at least two radar excitation signals (<NUM>, <NUM>) comprises user data and/or signaling; and
- performing (<NUM>) at least one transmission of the least two radar excitation signals (<NUM>, <NUM>) embedded into the frame structure.