WAVEFORM SELECTION FOR RADAR MONITORING USING OFDM SYSTEM TECHNICAL FIELD The present disclosure is generally related to radio transmitters, and is more particularly related to transmitters for use with both data communications and radar operations. BACKGROUND Cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) is one of the main waveforms specified in the 5th Generation (5G) standard by the 3rd-Generation Partnership Project (3GPP) and planned for the upcoming 6G standards. It is deployed in both sub-6 GHz and higher frequency bands. But, due to transmitter non-linearities combined by high peak to average power ratio (PAPR), CP-OFDM su^ers from out-of-band (OOB) emissions to the adjacent channels that need to be mitigated. There are a number of di^erent techniques in the literature addressing this issue, such as placing guard bands that cannot be used for data transmission, cancellation carriers placed on both sides of the CP-OFDM spectrum [1], power backo^ for certain transmission directions, additionalfiltering of the OFDM symbols [2], pre-distortion, etc. However, these techniques introduce some reduction in the spectral e^iciency, power e^iciency, and/or additional signaling overhead/complexity. There is considerable interest in using 5G and 6G base stations, as well as user equipments (UE), for radar sensing and monitoring applications, in addition to their normal uses for communication. For bistatic radar there should be an information transfer between the transmitter and receiver, regarding the position of the transmitter and the waveform used. Hardware for wideband communications is already well-suited for providing high-resolution radar measurements. However, the deployment of 5G new radio (NR) mobile communications in some frequency bands may cause adjacent and co-channel interference for existing radio systems like Earth Exploration- Satellite Service (EESS) or Fixed-Satellite Service (FSS). The International Telecommunication Union Radio communication (ITU-R) has therefore defined recommendations for unwanted emissions in the out-of-band domain for various operating frequency ranges for land mobile services. This means that spurious radiation emitted above-the-horizon (AtH) by the antennas of 5G base stations and UEs should be controlled and kept below defined limits, to minimize risk for interfering with services like EESS/FSS. This creates challenges to achieving desired performance of the radar sensing and monitoring operations mentioned above.
SUMMARY As noted above, in addition to supporting communications, 5G and 6G base stations, as well as UEs, may be used for radar sensing and monitoring, re-using portions of the communication hardware. Further, it is convenient to use the same OFDM waveform for radar operations as is used for communication, as this allows the reuse of large parts of the digital baseband circuitry, in addition to the radio frequency (RF) circuitry. However, when monitoring for objects with high elevation, such asflying drones, a radar beam must be directed above the horizon. Due to the multi-carrier nature of the CP-OFDM signal used in 5G and its relatively high peak-to-average power ratio (PAPR), it is then di^icult to satisfy the out-of- band (OOB) emission requirements when operating near a satellite frequency band while still transmitting with enough power to successfully perform the monitoring. The PAPR of the transmitted waveform is typically further increased by the addition of reference signals, required for both communication and sensing receiver operation, to the transmitted signal. This problem might be addressed by reducing the transmitter output power, which limits the radar performance, or by introducing wideband and accurate pre-distortion, which can result in significant increases in both transmitter complexity and power consumption. Another solution, described in detail below, can provide a better tradeo^ between performance and complexity/power consumption. More particularly, according to some of the embodiments described herein, a base-station or UE that uses CP-OFDM signals for communications reuses the communication hardware for radar but implements a direction-specific transmission scheme so that in beam directions sensitive to OOB interference, reduced PAPR signals are used, but also processed through the OFDM digital baseband circuitry. The CP-OFDM transmitter chain used to produce normal 5G or 6G communications waveforms can then be re-used for generating the reduced-PAPR signals, which may be, for example, a constant-envelope waveform signal like a Frequency-Modulated Continuous Wave (FMCW) signal or a Zado^-Chu waveform, or another reduced-PAPR signal types, with no separate hardware being required. Embodiments detailed below thus include transmitting apparatuses and methods for combining radar sensing and communications operations. An example method comprises transmitting in a first mode, in which an OFDM waveform is generated and transmitted. The method further
comprises transmitting in a second mode, in which a waveform having a lower PAPR than the OFDM waveform is formed and transmitted, and selectively switching between transmitting in thefirst mode and transmitting in the second mode. In embodiments, the generating of the OFDM waveform and the forming of the waveform having the lower PAPR use the same inverse discrete Fourier transform (IDFT) functionality in the transmitting apparatus. In embodiments, switching between thefirst and second transmission modes may be based on resources used for the transmissions. A corresponding transmitter apparatus, according to some embodiments described in detail below, comprises radio-frequency (RF) transmitter circuitry and processing circuitry operatively coupled to the RF transmitter circuitry, where the processing circuitry is configured to use the RF transmitter circuitry to: transmit in afirst mode, in which an OFDM waveform is generated and transmitted; transmit in a second mode, in which a waveform having a lower PAPR than the OFDM waveform is formed and transmitted; and selectively switch between transmitting in thefirst mode and transmitting in the second mode. Again, in some embodiments, the generating of the OFDM waveform and the forming of the waveform having the lower PAPR use the same IDFT functionality in the transmitter apparatus. In embodiments, switching between thefirst and second transmission modes may be based on resources used for the transmissions. The resources referred to herein may be any physical resources that are occupied or consumed in some sense by a radio transmission, such as intervals of time, frequency, or both, which may be referred to as time-frequency resources, or certain directions of transmission (e.g., above the horizon versus below the horizon) or certain areas of transmission, or power levels or ranges of power. As will be seen, with the techniques, apparatuses, and systems described herein, radar monitoring of high elevation objects and/or using frequencies near satellite service frequency bands can remain possible, using higher power levels than would be possible using conventional OFDM communications waveforms, with no need for additional radio frequencyfiltering or complicated pre-processing in the transmit chain to remain within the required OOB emission limits during radar operation. In addition, it is possible, using the techniques described herein, to continue to use CP- OFDM signals, to provide the highest range resolution for radar operation, in times, directions or areas and/or in frequencies where OOB leakage is not a problem. In various embodiments, no
additional hardware is required to implement the proposed solution, as the CP-OFDM transmitter can be reused to generate a reduced-PAPR waveform (i.e., having lower PAPR than the CP-OFDM waveform used for communications) when necessary. Details and variants of the methods and apparatuses summarized above are provided below, along with additional discussion of how to implement and take advantage of the disclosed techniques. BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates control logic switching for switching between two waveform types, e.g., CP- OFDM and frequency-modulated continuous wave (FMCW) waveforms, according to some embodiments. Figure 2 is a block diagram of a system model of the transmitting chain, according to some embodiments. Figure 3 is a frequency-domain representation of chirp (FMCW) waveform. Figure 4 illustrates the phase of the frequency-domain chirp waveform of Figure 3. Figure 5 plots the magnitude response of an example FMCW signal, in original and approximated forms. Figure 6 shows the phase response of the example FMCW signal, in original and approximated forms. Figure 7, Figure 8, and Figure 9 are power spectral density (PSD) plots for a simulation of the techniques described herein. Figure 10 is a block diagram illustrating components of an example transmitter, according to some embodiments described herein. Figure 11 is an example method for combining radar sensing and communications operations in a transmitter, according to some embodiments. Figure 12 is a block diagram of an example UE, in which techniques described herein may be implemented.
Figure 13 is a block diagram of an example network node, in which techniques described herein may be implemented. DETAILED DESCRIPTION When using 5G and 6G base stations and/or UEs for radar sensing and monitoring, it is convenient to use the same OFDM waveform, and corresponding OFDM waveform circuitry, for radar operations as is used for communication, as this allows the reuse of large parts of the digital baseband circuitry, in addition to the radio frequency (RF) circuitry. But, as discussed above, because the CP-OFDM waveform used for communications in 5G and 6G systems has a relatively high PAPR, which in turn means that non-linear amplification by the power amplifiers (PAs) results in spurious signals outside the frequency range used for communications, it can be di^icult to satisfy the out-of-band (OOB) emission requirements when operating near a satellite frequency band while still transmitting with enough power to successfully perform radar operations. The PAPR of the transmitted waveform is typically further increased by the addition of reference signals, required for both communication and sensing receiver operation, to the transmitted signal. As noted above, this problem might be addressed by reducing the transmitter output power, which limits the radar performance, or by introducing wideband and accurate pre-distortion, which can result in significant increases in both transmitter complexity and power consumption. This disclosure describes solutions that provide a better tradeo^ between performance and complexity/power consumption. More particularly, according to some of the embodiments described herein, a base-station or UE that uses CP-OFDM signals for communications reuses the communication hardware for radar but implements a direction-specific transmission scheme so that in beam directions sensitive to OOB interference, reduced PAPR signals are used, but also processed through the OFDM digital baseband circuitry. The CP-OFDM transmitter chain used to produce normal 5G or 6G communications waveforms can then be re-used for generating the reduced-PAPR signals, which may be, for example, a constant-envelope waveform signal like a Frequency-Modulated Continuous Wave (FMCW) signal or a Zado^-Chu waveform, or another reduced-PAPR signal types, with no separate hardware being required. When using these techniques in a bi-static radar application, the receiving nodes can coordinate when and in which (protected) directions the low-PAPR signal is used, and information will be
transferred between transmitter and receiver nodes. Note that protected directions are not limited to the direction of a main transmitting beam - if there are problems with side lobe distortion in sensitive direction as estimated from main beam direction and power level, the low-PAPR waveform may be invoked to reduce the distortion, in some embodiments or instances. These problematic directions might be determined, for example, by accessing a look-up table that relates problematic side-lobe directions to main beam direction and power level. More generally, the transmitting node may selectively switch between a “normal” transmitting mode that uses a conventional CP-OFDM waveform for radar sensing (and, optionally communications) and a second transmitting node that uses a reduced-PAPR signal or waveform, based on a determination of the resources used or to be used by the transmissions. These transmitting modes may thus be referred to as “non-protected” and “protected” transmission modes, respectively, and the determination of which to use may be, at least in some embodiments, be regarded as a function of whether the transmissions utilize “protected” or “non-protected” resources. The term “resources” here is meant broadly, so as to refer to any physical resource that is consumed or occupied in some sense by a given radio transmission, and can thus refer to time intervals, frequency ranges, or combinations thereof, which are often referred to as time-frequency resources. Thus, certain resource blocks, as defined by 3GPP standards, or certain frequency ranges or time slots, might be “protected” in the sense that there are extra concerns with regards to OOB emissions, compared to “non-protected” counterparts. “Resources” can also refer to spatial resources, such as an area in which a transmission is made, or a direction of transmission selected by the transmitter (and/or driven by the design or configuration of the antenna(s)). Thus, certain geographical areas might always require “protected” transmissions, i.e., transmissions that take into account extra sensitivity to OOB emissions, while others may not. Certain azimuthal directions may be protected, versus others, in some embodiments, and/or certain elevation angles of transmission might be protected, e.g., where above-the-horizon transmissions implicate concerns with interfering with satellite communications while similar below-the-horizon transmissions do not. As still another example, “resources” can refer to the power level used for a radio transmission, such that transmitting in a certain range of power levels requires “protected” transmissions, i.e., transmissions that use a reduced-PAPR waveform, versus lower-power transmissions. Note that a protected resource might be a combination of two or more types of resources, such as where
transmission above a certain power level must be in the protected mode only when the transmission is in a certain area, or in a certain direction, and/or in a certain frequency range. The terms “reduced-PAPR signal,” “reduced-PAPR waveform,” “low-PAPR signal,” and “low-PAPR waveform” as used herein refer to signals or waveforms that are designed to have a lower PAPR than a CP-OFDM waveform modulated with typical data. As one example, FMCW may be used as a low-PAPR signal since it has a constant envelope that will not create intermodulation distortion in the transmitter. Some limited envelope variations will still occur at the beginnings and ends of symbols, due tofiltering, but the intermodulation will be largely suppressed. Simulations show that there is no significant spectral re-growth in contrast to when a CP-OFDM signal is used. Other constant-envelope waveforms, like Zado^-Chu waveforms or other single-carrier-type waveforms with reduced PAPR may be used. With the right choice and design of the reduced-PAPR waveform, the Inverse Discrete-Fourier Transform (IDFT) processing circuity that is at the heart of the typical CP-OFDM-based transmitter design may be re-used, when generating the reduced-PAPR waveform, in many cases with no need for any hardware modifications at all. Figure 1 is a processflow diagram that illustrates an example of the control logic for switching between the CP-OFDM and the reduced-PAPR radar waveforms. The FMCW waveform will be used in the following discussion as an example of the reduced-PAPR waveform, but other constant- envelope waveforms like Zado^-Chu or other single-carrier-type waveforms with reduced PAPR may be used. Further below, simulation results that show the benefits of using FMCW for limiting OOB AtH emissions are discussed. The process illustrated in Figure 1 assumes a scenario in which the transmitter (either a gNB or a UE) is capable of performing beamforming, using several antenna elements. In addition, it is assumed that the radar operation can track objects in certain area with the aid of directed beams. In order to cover certain tracking/sensing regions of space, the radar should be able to sweep over di^erent beam directions. The control logic illustrated in Figure 1 can be used to ensure the selection of the right waveform without exceeding the OOB above-the-horizon (AtH) emission limits, for example, while using the higher-performing CP-OFDM waveform when possible. As shown at block 110, the illustrated process comprises the step of checking whether the current radar beam direction is pointing AtH or in any other beam direction/s that have stricter emission
limits or should otherwise not be disturbed. This check may be handled di^erently for gNBs, which generally are infixed locations, and UEs, which are not: ^ for gNBs, there may be a pre-determined lookup table (LUT) where beam directions are stored that violate the OOB AtH emission levels when using CP-OFDM waveform. Then the current beam direction is checked if it is in the LUT or not. If it is, then transmission of the radar signal should be via FMCW (or other reduced-PAPR waveform) instead of CP-OFDM. ^ for UEs, determining a LUT table for beam directions that violate the OOB AtH may be more di^icult as orientation of the UEs change all the time. In this case a dynamic LUT can be built with help of an input from an inertial measurement unit (IMU) of the UE. Another option for determining the UE orientation is to use AoA info for signals communicating with known cellular base stations with known or assumed locations. As above, FMCW waveforms (or other reduced-PAPR waveforms) are used for AtH directions. Alternatively, if implementing such a dead-reckoning or other orientation estimation system can be costly considering this computation needs to be done as often as possible to follow the movement of the UE, a simpler solution would be to always use FMCW based radar for UEs. As shown at block 120, if the transmission beam is not to be pointed towards a protected direction, e.g., AtH, then the transmission may proceed using the CP-OFDM waveform. Communication data may or may not be modulated onto the CP-OFDM waveform in this mode, in various embodiments and/or instances. As shown at block 130, on the other hand, if the transmission beam is to be pointed towards a protected direction, then transmission should proceed in a protected mode, i.e., using a reduced-PAPR waveform such as FMCW. As shown at block 140 and block 150, the process includes the step of checking whether the beam direction is to be changed, e.g., by means of a sweeping or stepping pattern. If not, transmission in the current mode may continue. Otherwise, the process begins again, with a check of whether the new beam direction is in a protected direction, as shown at block 100. Figure 1 illustrates a process where the determination of whether to transmit using the CP-OFDM waveform or the reduced-PAPR waveform is based on beam direction. Alternative implementations for selecting the waveform, some of which may be especially appropriate for UE implementations, may include those where the determination of whether to use regular CP-OFDM transmission or reduced-PAPR waveforms is:
^ Based on the utilized Tx output power. As an example, the device may use CP-OFDM for radar sensing transmissions lower than a certain dBm in output power. ^ Regulated based on the UE capability. This may be derived from a UE capability set as defined by a standardization. As an example, this may imply waveform usage regulations for di^erent UE power classes. ^ Based on locations, e.g., certain geographical areas or type of locations. The device may, in some examples, receive such waveform usage limitations via a database. ^ Based on operating frequency band or based on whether a transmission is to be in a certain portion of an operating frequency band, such as one end of a frequency band that abuts a frequency band used for satellite communications. ^ Based on a combination of any of the above, including beam direction. To verify the superiority of FMCW for reducing OOB AtH emission, versus CP-OFDM, a MATLAB simulation has been performed. The system model is shown in Figure 2, and the simulation parameters setting are described in Table 1. Number of IQ samples or ^^^^^^^ = 1024 frequency bins Start and stop frequencies ^^ = −0.8 relative to ^^/2 ^^ = 0.8 Sampling rate ^^ = 16 ∗ (^^ − ^^) Lowpass filter parameters Filter order = 64, pass band = 0.4 and stop band = 0.6 Upsampling factor 2 PA model ^ = ^^ ∗ ^ + ^^ ∗ ^^ ^ℎ^^^ ^^ = 1, ^^ = −0.0006 Table 1 – Simulation parameter settings In Figure 2, block 210 is responsible for generating the time domain IQ baseband samples (N-points long) of an FMCW chirp or CP-OFDM signal. The generated waveforms are then up-sampled, at block 220, and passed through successivefiltering blocks, as shown at blocks 230 and 240, before being fed to a power amplifier (PA) 250 and antenna 260. The PA is modeled via a 3rd-order memoryless polynomial with the coe^icients c1 and c2 shown in Table 1. In addition, clipping is applied when the power is above a certain threshold, to avoid negative small signal gain. For fair comparison, the OFDM signal is scaled to the same average power as the FMCW signal.
The FMCW signal generation block 210 is described in further detail below. FMCW chirp generation can be obtained in several ways. First, an FMCW chirp can be generated by creating a time domain chirp and performing a DFT to produce samples to be fed to the IDFT processing functionality in the transmitter. This approach can be computationally costly. In more detail, to create a chirp signal (FMCW) for the start and stop frequencies of f0 and f1, the chirp step size mustfirst be defined: ^ ^^^^^ = ^ ^ ^^ ^ ^^^^ ^ ^^^^^^ (1) Then, the time domain chirp signal is defined by equations (2) and (3)
where ^ = 2,3, … , ^^^^^^^, ^^[1] = 1, ^[1] = ^^ and ^^^^^^^^^^ = ^^. The frequency domain representation of equation (2) can be obtained by applying a DFT as in (4):
, where k = 1,…, ^^^^^^^. The phase of the chirp at each point can easily be calculated by dividing the imaginary part of the frequency domain IQ sample (calculated in equation (4)) by the real part and then taking the inverse tangent as in (5): ∅[^] = ^^^^2(^^^(^^[^], ^^^^(^^[^]) (5) , where ^^^^2 is the 2-argument arctangent function, which returns the phase, or argument, of the complex number ^^[^] and where k = 1, …, ^^^^^^^. Figure 3 and Figure 4 show the frequency domain magnitude and phase, respectively, of the chirp waveform. Note that in Figure 4 the phase has been de-wrapped to produce a continuous curve.
As seen in equation (4), above, the computation of the frequency domain chirp waveform requires a DFT operation, which can be expensive. Thus, other methods to analytically generate or statistically estimate the chirp signal (magnitude and phase responses) can be used to save computational complexity. One of these methods is the direct calculation of the DFT bin (Npoints) coe^icients for the phase and magnitude of the signal. To lower the computational complexity of the FFT operation in equation (4), the magnitude and phase responses of the chirp signal (e.g., as shown in Figures 3 and 4) can be expressed/estimated mathematically. The frequency domain magnitude response is split into multiple segments (e.g., into 7 segments), each approximated via a zero to 3rd order polynomial functions, as shown in Figure 5. Similarly, the phase response of the frequency domain chirp is also approximated by a polynomial function, which is split into three segments in this example and which are approximated by 2nd and zero order polynomials, as shown in Figure 6. As seen in Figures 5 and 6, the magnitude and phase response approximations approximate very well the original signal, even using reasonable low-order polynomials. There is some performance impact, however, which is shown in Figure 8 and discussed further below. For performance comparison, the adjacent channel leakage ratio (ACLR) or adjacent channel power ratio (ACPR), which is the ratio of the power transmitted in the adjacent frequency channel to the power in the main frequency channel, may be used. ACLR/ACPR requirements are defined by 3GPP (3GPP TS 38.104 Section 9.7.3 and 3GPP 38.101-1 Section 6.5.2.4.1) and the Federal Communication Commission (FCC) for transmitters (gNBs and UEs). Figure 7 shows the simulated power spectral density (PSD) for the ideal FMCW waveform, both before and after the PA in the simulated transmitting chain. Figure 8 shows the simulated power density for the approximated FMCW waveform (as shown in Figures 5 and 6), again both before and after the PA in the simulated transmitter chain. By comparing thefigures, it can be seen that the approximation of the frequency domain FMCW waveform by a piecewise polynomial function, as described above, introduces a small distortion, marked by the dashed circle in Figure 8, to the input of the PA. However, the output of the PA signal is exactly the same as the input, indicating that the distortion introduced due to the approximation did not add more distortion when passing through the PA. Therefore, applying such an approximation can be beneficial to reduce the computational complexity of applying an FFT operation with a such minor and acceptable distortion.
In contrast, Figure 9 shows the power spectral density for a CP-OFDM waveform, before and after the PA in the simulated transmitting chain. For simplicity, the PA gain is normalized to 1, as indicated by the linear coe^icient of the PA model c1. Figure 7 shows the input and output of the PA overlap for the FMCW signal, where no substantial intermodulation distortion is visible. There is thus no significant distortion added to the FMCW waveform when the signal passes through the non-linear PA, keeping the output ACLR value the same as before PA (i.e., about 38dB). On the other hand, in Figure 9, there is a large distortion at the output of the PA for the CP-OFDM waveform, where the ACLR before the PA is around 47dB and the ALCR after PA is around 27.5dB. Comparing the outputs of the PA, it can easily be seen that the ACLR of the FMCW is superior to CP-OFDM waveform. Similar reductions in OOB emissions can be demonstrated for other waveforms that can be generated using the same IDFT-based processing circuitry that is used to generate a CP-OFDM waveform. Examples of reduced-PAPR waveforms thus include, but are not limited to: ^ a time-domain chirp waveform; ^ a frequency-modulated continuous wave, FMCW, waveform; ^ a Zado^-Chu waveform; and ^ a Discrete Fourier Transform-spread (DFTS-spread) OFDM waveform. In various embodiments, each of these waveforms can be generated, using the IDFT-based processing found in a CP-OFDM transmitter, by directly calculating a frequency-domain version of the waveform, to be input to the IDFT processing in the transmitter, or by using a polynomial-based approximation, as described above for the FMCW chirp, or by retrieving samples of the frequency- domain version of the waveform from a look-up table. Figure 10 is a block diagram illustrating a simplified view of transmitter circuitry configured to implement the techniques described above. The illustrated transmitter circuit includes processing circuitry 1010, which produces data for use in generating the CP-OFDM waveform. This may be user data and/or control data, in some instances or examples, or may be arbitrary or random data in others, e.g., when only radar sensing is being performed. In either case, processing circuitry 1010 may convert binary data to data symbols, e.g., using Quadrature Phase-Shift Keying (QPSK), 16- quadrature amplitude modulation (16-QAM), etc., and output these data symbols in parallel form
for input to IDFT functionality. In parallel to processing circuitry 1010 is reduced-PAPR waveform generation circuitry 1020, which is configured to produce one (or more) of the reduced-PAPR waveforms discussed above. Like processing circuitry 1010, reduced-PAPR waveform generation circuitry 1020 may be configured to provide the reduced-PAPR waveform in the form of data symbols, in parallel form, for input to the following IDFT functionality. Mode selection circuitry 1030 is configured to select between the outputs of processing circuitry 1010 and reduced-PAPR waveform generation circuitry 1020. This selection, as described in detail elsewhere herein, may be based on the resources used or to be used for the transmissions, e.g., whether transmissions are to use so-called non-protected or protected resources, and is represented in Figure 10 as switching between the outputs from processing circuitry 1010 and reduced-PAPR waveform generation circuitry 1020. It will be appreciated that processing circuitry 1010, reduced-PAPR waveform generation circuitry 1020, and mode selection circuitry 1030 may be implemented using one or more digital signal processors, microprocessors, microcontrollers, or the like, alone or in combination with specialized digital circuitry, and that the illustrated switch driven by mode selection circuitry 1030 may thus be implemented within a processor or microcontroller, using appropriately configuredfirmware and/or software. The output from processing circuitry 1010 or reduced-PAPR waveform generation circuitry 1020, as selected by mode selection circuitry 1030, is supplied to the inverse Fast-Fourier Transform (IFFT) circuitry 1040. The IFFT is an e^icient algorithm for computing an IDFT, and thus represents an example (albeit a widely used example) of IDFT functionality – its use in OFDM transmitters is extensive and well understood. The output of IFFT circuitry 1040 is followed by parallel-to-serial converter 1050 and cyclic-prefix insertion 1060 – these, again, are widely used in OFDM transmitters and well-understood. IFFT circuitry 1040, parallel-to-serial converter 1050, and cyclic- prefix (CP) insertion 1060 may be implemented using one or more digital signal processors, microprocessors, microcontrollers, or the like, alone or in combination with specialized digital circuitry. When the input to the IFFT circuitry 1040 is from processing circuitry 1010, the signal supplied to RF circuitry 1070 corresponds a conventional OFDM waveform transmitted by RF circuitry 1070, PA 1080, and antenna 1090, e.g., as used in 4G and 5G communications. When the input to the IFFT circuitry 1040 is from reduced-PAPR waveform generator 1020, on the other hand, the signal
supplied to RF circuitry 1070 corresponds to a reduced-PAPR waveform transmitted by RF circuitry 1070, PA 1080, and antenna 1090. In either case, the output from CP insertion 1060 is provided to radio-frequency (RF) circuit 1070, which may include various combinations of digital-to-analog conversion, amplification,filtering, and up-conversion, with the RF output from RF circuit 1070 then being supplied to power amplifier (PA) 1080 and antenna 1090. As discussed above, OOB emissions radiated from antenna 1090 will generally be lower in “protected” mode, i.e., the mode in which the reduced-PAPR waveform is used, than in “non-protected” mode, i.e., the mode in which the OFDM waveform is used. The IDFT-based processing – the processing including IFFT circuitry 1040 in this example, can be used, without change, in both of these modes. Keeping all of the above details and examples in mind, it will be appreciated that Figure 11 is a processflow diagram illustrating an example method, for combining radar sensing and communications operations in a transmitter (such as in the transmitter illustrated in Figure 10), according to various embodiments. Note that the process illustrated in Figure 11 is intended to be a generalization of and to encompass many, if not all, of the transmitter-based techniques described above, and thus where there are di^erences between the terminology used to describe Figure 11 and that used in the discussion above, the terminology used to describe Figure 11 should be understood to at least encompass the related terminology used above, unless the context clearly indicates otherwise. As shown at block 1110, the method comprises transmitting, in afirst mode, in which an OFDM waveform is generated and transmitted. This may be performed with IDFT functionality, e.g., processing that utilizes an IFFT, as described in examples above. As shown at block 1120, the method further comprises transmitting in a second mode, in which a waveform having a lower PAPR than the OFDM waveform is formed and transmitted. Again, in some embodiments, the IDFT functionality may be used to form the waveform having the lower PAPR. These steps can occur in either order, and may be alternately selected, to switch between the two modes. Thus, as shown at block 1105, the method comprises selectively switching between transmitting in thefirst mode, as in block 1110, and transmitting in the second mode, as in block 1120. In several embodiments, this selective switching may be based on what resources are used or to be used by the transmissions, e.g., based on whether transmissions are to use so-called non-protected or protected resources.
As was discussed in some of the examples described above, selectively switching between transmitting in thefirst mode and transmitting in the second mode may be based on a determination of at least one of: whether transmissions are to be in a non-protected direction or a protected direction; whether transmissions are to be in a non-protected area or a protected area; whether transmissions are to utilize power levels corresponding to a non-protected transmission mode or a protected transmission mode; and whether transmissions are to use non-protected time-frequency resources or protected time-frequency resources. In various embodiments or instances, the waveform having the lower PAPR may be a constant- envelope waveform. The waveform having the lower PAPR may be one or a combination of any of the following, in some embodiments or instances: a time-domain chirp waveform; a frequency- modulated continuous wave, FMCW, waveform; and a Zado^-Chu waveform. In some embodiments or instances, the waveform having the lower PAPR may be a DFTS-spread OFDM waveform. In some embodiments or instances, the method may comprise performing a Discrete Fourier Transform (DFT) on a time domain representation of the waveform having the lower PAPR, to obtain frequency domain coe^icients, and providing the frequency domain coe^icients to the IDFT-based processing for forming the waveform having the lower PAPR for transmitting in the second mode. In some other embodiments or instances, the method may alternatively comprise retrieving frequency domain coe^icients for forming the waveform having the lower PAPR with the IDFT-based processing from a look-up table. In some of these embodiments or instances, the method may comprise interpolating some frequency domain coe^icients for forming the waveform having the lower PAPR from the retrieved frequency domain coe^icients. In some embodiments or instances where the waveform having the lower PAPR is a Zado^-Chu waveform, the method may comprise calculating a Zado^-Chu sequence to generate frequency domain coe^icients for forming the waveform having the lower PAPR. Consistently with what has been described above, in some embodiments, the switching between transmitting in thefirst mode and transmitting in the second mode may comprise transmitting in thefirst mode for transmissions in a non-protected direction or in a range of non-protected directions and transmitting in the second mode for transmissions in a protected direction or range of protected directions. In various embodiments or instances, the protected direction or range of
protected directions may be determined based on whether the transmission direction is towards, below, or above a geographic horizon. In some embodiments or instances, switching between transmitting in thefirst mode and transmitting in the second mode is based on a location of the transmitting apparatus. In some of these and in some others, switching between transmitting in thefirst mode and transmitting in the second may be based on a maximum allowed power for transmitting or on an actual equivalent transmission power. Likewise, in various embodiments or instances, the switching between transmitting in thefirst mode and transmitting in the second mode may be based on frequency bands used for transmissions. Any two or more of these criteria for switching between thefirst and second modes may be combined, in various embodiments or instances. In some embodiments or instances, transmitting in thefirst mode may comprise modulating data bits onto the OFDM waveform, using the IDFT-based processing, thus allowing the transmission of data and/or control information. In some embodiments or instances, this approach may be used to communicate information to a receiver at the other end of a bistatic radar operation, e.g., where the information indicates the type of reduced-PAPR waveform and/or related parameters that is to be used when transmissions are performed in the second mode. The techniques described herein may, in some embodiments or instances, be implemented in a wireless terminal configured for use in a wireless network, such as a user equipment (UE) configured for operation in a 4G, 5G, or 6G, or in a radio base station or other radio network node in a wireless network, such as a 4G, 5G, or 6G base station. Figures 12 and 13 illustrate an example UE 1200 and network node 1300, either or each of which may be configured to carry out a method like that shown in Figure 11 and described above. In either case, the functionality and circuit blocks shown in Figure 10 may be implemented in the processing circuitry and communication interface circuitry shown in Figures 12 and 13. Figure 12 thus shows an example UE 1200, in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage/playback device, wearable terminal device, wireless endpoint, mobile station,
tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), an Augmented Reality (AR) or Virtual Reality (VR) device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE. A UE may be referred to as a mobile communication device. A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to- vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter). The UE 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input/output interface 1206, a power source 1208, a memory 1210, a communication interface 1212, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 12. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc. The processing circuitry 1202 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine- readable computer programs in the memory 1210. The processing circuitry 1202 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic,field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriatefirmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1202 may include multiple central processing units (CPUs).
In the example, the input/output interface 1206 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and/or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 1200. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device. In some embodiments, the power source 1208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 1208 may further include power circuitry for delivering power from the power source 1208 itself, and/or an external power source, to the various parts of the UE 1200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1208. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1208 to make the power suitable for the respective components of the UE 1200 to which power is supplied. The memory 1210 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges,flash drives, and so forth. In one example, the memory 1210 includes one or more application programs 1214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1216. The memory 1210 may store, for use by the UE 1200, any of a variety of various operating systems or combinations of operating systems.
The memory 1210 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID),flash memory, USBflash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and/or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 1210 may allow the UE 1200 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to o^-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 1210, which may be or comprise a device-readable storage medium. The processing circuitry 1202 may be configured to communicate with an access network or other network using the communication interface 1212. The communication interface 1212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1222. The communication interface 1212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1218 and/or a receiver 1220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1218 and receiver 1220 may be coupled to one or more antennas (e.g., antenna 1222) and may share circuit components, software orfirmware, or alternatively be implemented separately. In the illustrated embodiment, communication functions of the communication interface 1212 may include cellular communication, Wi-Fi communication, LPWAN communication, communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more
communication protocols and/or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol/internet protocol (TCP/IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth. Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient). As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone inflight according to the received input or to a robotic arm performing a medical procedure according to the received input. A UE, when in the form of an Internet of Things (IoT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an IoT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, afitness tracker, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a
remote controlled surgical robot. A UE in the form of an IoT device comprises circuitry and/or software in dependence of the intended application of the IoT device in addition to other components as described in relation to the UE 1200 shown in Figure 12. As yet another specific example, in an IoT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another UE and/or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. In practice, any number of UEs may be used together with respect to a single use case. For example, afirst UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, thefirst UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. Thefirst and/or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators. Figure 13 shows a network node 1300 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU). Base stations may be categorized based on the amount of coverage they provide (or, stated di^erently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network
node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node) and/or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS). Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, and multi-cell/multicast coordination entities (MCEs). The network node 1300 includes a processing circuitry 1302, a memory 1304, a communication interface 1306, and a power source 1308. The network node 1300 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1300 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 1300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1304 for di^erent RATs) and some components may be reused (e.g., a same antenna 1310 may be shared by di^erent RATs). The network node 1300 may also include multiple sets of the various illustrated components for di^erent wireless technologies integrated into network node 1300, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or di^erent chip or set of chips and other components within network node 1300. The processing circuitry 1302 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit,field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in
conjunction with other network node 1300 components, such as the memory 1304, to provide network node 1300 functionality. In some embodiments, the processing circuitry 1302 includes a system on a chip (SOC). In some embodiments, the processing circuitry 1302 includes one or more of radio frequency (RF) transceiver circuitry 1312 and baseband processing circuitry 1314. In some embodiments, the radio frequency (RF) transceiver circuitry 1312 and the baseband processing circuitry 1314 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on the same chip or set of chips, boards, or units. The memory 1304 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, aflash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non- transitory device-readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 1302. The memory 1304 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions capable of being executed by the processing circuitry 1302 and utilized by the network node 1300. The memory 1304 may be used to store any calculations made by the processing circuitry 1302 and/or any data received via the communication interface 1306. In some embodiments, the processing circuitry 1302 and memory 1304 is integrated. The communication interface 1306 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, the communication interface 1306 comprises port(s)/terminal(s) 1316 to send and receive data, for example to and from a network over a wired connection. The communication interface 1306 also includes radio front-end circuitry 1318 that may be coupled to, or in certain embodiments a part of, the antenna 1310. Radio front-end circuitry 1318 comprisesfilters 1320 and amplifiers 1322. The radio front- end circuitry 1318 may be connected to an antenna 1310 and processing circuitry 1302. The radio front-end circuitry may be configured to condition signals communicated between antenna 1310
and processing circuitry 1302. The radio front-end circuitry 1318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 1318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination offilters 1320 and/or amplifiers 1322. The radio signal may then be transmitted via the antenna 1310. Similarly, when receiving data, the antenna 1310 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1318. The digital data may be passed to the processing circuitry 1302. In other embodiments, the communication interface may comprise di^erent components and/or di^erent combinations of components. In certain alternative embodiments, the network node 1300 does not include separate radio front- end circuitry 1318, instead, the processing circuitry 1302 includes radio front-end circuitry and is connected to the antenna 1310. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1312 is part of the communication interface 1306. In still other embodiments, the communication interface 1306 includes one or more ports or terminals 1316, the radio front-end circuitry 1318, and the RF transceiver circuitry 1312, as part of a radio unit (not shown), and the communication interface 1306 communicates with the baseband processing circuitry 1314, which is part of a digital unit (not shown). The antenna 1310 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. The antenna 1310 may be coupled to the radio front-end circuitry 1318 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, the antenna 1310 is separate from the network node 1300 and connectable to the network node 1300 through an interface or port. The antenna 1310, communication interface 1306, and/or the processing circuitry 1302 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node. Any information, data and/or signals may be received from a UE, another network node and/or any other network equipment. Similarly, the antenna 1310, the communication interface 1306, and/or the processing circuitry 1302 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and/or signals may be transmitted to a UE, another network node and/or any other network equipment.
The power source 1308 provides power to the various components of network node 1300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1308 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1300 with power for performing the functionality described herein. For example, the network node 1300 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1308. As a further example, the power source 1308 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail. Embodiments of the network node 1300 may include additional components beyond those shown in Figure 13 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, the network node 1300 may include user interface equipment to allow input of information into the network node 1300 and to allow output of information from the network node 1300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1300. The techniques, apparatuses, and systems described herein may be used to provide several advantages, when applied in a system where both radar sensing and communications operations are needed. As an example, radar monitoring of high elevation objects may remain possible, where it would be not allowed with conventional OFDM transmissions, even near satellite service frequency bands. This can be achieved without the need for additional radio frequencyfiltering or further processing in the transmit chain to remain within the required OOB emission limits during radar operation. At the same time, it is possible to continue to use CP-OFDM signals, providing highest range resolution for radar operation, in directions where OOB leakage is not a problem. (Low-PAPR chirp signal types exhibit high-frequency cuto^ of the sawtooth due tofiltering.) No additional hardware is required to implement the proposed solution, as the CP-OFDM transmitter can be reused for the reduced-PAPR waveform transmissions. There is no need for wideband and accurate predistortion when performing radar measurements of high elevation objects, and high
output power can be maintained when performing these radar measurements. Other advantages may be apparent in some embodiments of the techniques and apparatuses described herein. In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device- readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and/or by end users and a wireless network generally. ABBREVIATIONS ACLR Adjacent Channel Leakage Ratio ACPR Adjacent Channel Power Ratio AoA Angle of Arrival AtH Above the Horizon CP-OFDM Cyclic-Prefix Orthogonal Frequency-Division Multiplexing DFT Discrete Fourier Transform FFT Fast Fourier Transform FMCW Frequency-Modulated Continuous Wave IDFT Inverse Discrete Fourier Transform IFFT Inverse Fast Fourier Transform IMU Inertial Measurement Unit LUT Look Up Table OOB Out of Band PA Power Amplifier PAPR Peak to Average Power Ratio PSD Power Spectral Density UE User Equipment
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