Synthesis of peaky waveforms by means of multi-antenna transmitters

Abstract

A method, system and apparatus for synthesis of peaky waveforms by means of multi-antenna transmitters are disclosed. According to one aspect, a method in a network node includes precoding a plurality of signals for OTA synthesis of an impulse radio (IR) waveform via a plurality of antennas of the network node so that radio frequency (RF) energy radiated by each antenna of the plurality of antennas combine over the air to form an IR waveform comprising at least one peak and having a peak to average power ratio (PAPR) that exceeds a PAPR of any signal radiated by any one antenna of the plurality of antennas. The method includes transmitting the precoded plurality of signals via the plurality of antennas.

Description

[0001]SYNTHESIS OF PEAKY WAVEFORMS BY MEANS OF MULTI-ANTENNA TECHNICAL FIELD 5 The present disclosure relates to wireless communications, and in particular, to synthesis of peaky waveforms by means of multi-antenna transmitters. BACKGROUND The Third Generation Partnership Project (3GPP) has developed and is developing 10 standards for Fourth Generation (4G) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (5G) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and user equipment (UE), as well as communication between network nodes and between UEs. The 3GPP is also developing standards for 15 Sixth Generation (6G) wireless communication networks. The Institute of Electrical and Electronic Engineers (IEEE) has developed and continues to develop standards for wireless communication networks, including Wireless Local Area Networks (WLANs), branded as “Wi-Fi” networks by the Wi-Fi Alliance. WLANs include wireless communication between access points (AP STAs) and non- 20 access point stations (non-AP STAs). Such IEEE standards include IEEE 802.11a / b / g / n / ac / ax / be and IEEE 802.15. Impulse Radio It is known that Pulse Position Modulation (PPM) comes close to achieving the Shannon capacity when the spectral efficiency is very small. The basic idea is to use 25 pulses with very high peak and low duty cycle. The duty cycle is so low as to ensure that the average power does not exceed a predefined power threshold, while at the same time, all the energy is accumulated in few very large peaks that rise above the noise floor and may be detected even at extremely low signal to noise ratio (SNR). These are often called Impulse-Radio (IR) waveforms and may be generated using Ultra-Wideband (UWB) 30 transmitters. The information bits may be conveyed to the receiver by, e.g., the position of the impulse or by the time elapsed between successive impulses. IR waveforms have the following advantages: ^ They are suitable for low complexity, power efficient receivers. For example, 1-bit analog to digital converters (ADCs) are enough to successfully receive IR waveforms; and ^ IR waveforms are well suited for both positioning and radar 5 applications. In particular, the use of these waveforms may be valuable when performing integrated sensing and communications (ISAC). For these reasons, IR modulation has been proposed as a candidate waveform for 6G. It has been argued that wireless networks need only operate at high spectral efficiency only under high cell load, and that whenever high spectral efficiency is not required it may 10 be beneficial to use other waveforms, such as IR, to increase energy efficiency. Trends in multi-antenna systems 5G was designed to support massive multiple input-multiple output (MIMO) operation. A current trend in the industry is to build and deploy multi-antenna systems with many antenna elements in the hundreds or even thousands. 15 IR waveforms have severe drawbacks for a wireless transmitter. Experience with UWB systems shows that these modulations tend to suffer from co-existence problems with other wireless transmissions operating at nearby carrier frequencies and that transmit (TX) power limitations are important. In addition, the extremely high peak to average power ratio (PAPR) makes them very inefficient for power amplifiers (PAs) due to high 20 linearity requirements and / or large input power backoffs. SUMMARY Some embodiments advantageously provide methods, systems, and apparatuses for synthesis of peaky waveforms by means of multi-antenna transmitters. 25 It is desirable to enable the synthesis of IR waveforms using the multicarrier wireless transmitters employed in modern communications systems such as LTE / NR or Wi-Fi, to increase the energy efficiency of the UEs and possibly use these waveforms for other applications such as ISAC and positioning. In some embodiments, the multiple spatial degrees of freedom afforded by multi- 30 antenna transmitters (e.g., massive MIMO or distributed MIMO) are used to synthesize IR waveforms. Linear precoding is applied at the transmitter to each signal transmitted such that the superposition of the transmitted waveforms at the antennas of the intended receiver results in a peaky signal, with peaks located at the desired positions. In other words, the peaks are not created at the transmitter itself, but over the air at the location of the target. For example, in some embodiments, each transmitter is fed a random OFDM signal and a slightly modified Maximum Ratio Transmission (MRT) precoder is applied. 5 The modification of the MRT precoder comprises only an antenna specific cyclic shift and a phase shift, two linear operations which are commonly applied to signals in multi- antenna transmitters. In some embodiments, at the transmitter side, ordinary waveforms are used, so that legacy 4G / 5G / Wi-Fi multi-antenna transmitters may be re-used without any modification. 10 No new filtering is needed to ensure that spectral emission mask requirements are fulfilled. Likewise, the PAPR of the transmitted signals is not increased. For example, 5G (and in the future 6G) massive MIMO transmitters may be used to synthesize the IR waveforms, only with minor software updates. By applying specially designed linear precoding, the IR waveform may be created over the air at the receiver and only an 15 intended receiver will experience a peaky waveform. Some embodiments enable synthesis of IR waveforms for communications, for radar, or for ICAS. Since the TX waveforms may be ordinary OFDM signals and are synthesized by means of linear precoding, they may be combined with the signals to other users using orthogonal frequency division multiple access (OFDMA) and / or space 20 division multiple access (SDMA) without loss of orthogonality and without requiring any special processing. For example, it is straightforward to enable downlink (DL) multi-user (MU)-MIMO where multicarrier modulation (e.g., OFDM) is employed for some users and IR is employed for other users. Indeed, from the point of view of the transmitter, the spatial streams carry precoded OFDM signals. However, the precoder has been designed 25 so that after propagation some streams become peaky IR signals at selected target locations, while the others are high spectral efficiency transmissions. The transmission technique disclosed herein is well suited for massive MIMO transmitters and very large aperture antenna arrays, since in both cases some of the spatial degrees of freedom may be spent on the synthesis of peaky signals. Very large aperture 30 arrays are especially well suited since when a target is in the near field, the impulse will be concentrated in a spot around the target, while outside the spot the time / frequency power distribution follows that of any OFDM signal. The transmission techniques disclosed herein may be used in: ^ standardized and proprietary solutions to improve the accuracy ranging and / or sensing; ^ standardized and proprietary solutions to support wake-up radios or wake-up signals; and / or ^ standardized and proprietary solutions to increase the link budget of RF energy harvesting. 5 According to one aspect, a method in a network node configured to communicate with a user equipment, UE, via over-the-air, OTA, synthesis of impulse radio, IR, waveforms is provided. The method includes precoding a plurality of signals for OTA synthesis of an IR waveform via a plurality of antennas of the network node so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over 10 the air to form an IR waveform comprising least one peak and having a peak to average power ratio, PAPR, that exceeds a PAPR of any signal radiated by any one antenna of the plurality of antennas. The method includes transmitting the precoded plurality of signals via the plurality of antennas. According to this aspect, in some embodiments, the precoding is configured to 15 cause each peak of the IR waveform to be localized in space at a location of the UE. In some embodiments the precoding is configured to cause each peak of the IR waveform to be localized in time. In some embodiments, the precoding is configured to cause peaks of the at least one peak to occur at certain times selected to convey information to the UE. In some embodiments, the precoding is based at least in part on channel state information, 20 CSI, received from the UE. In some embodiments, the precoding is modified maximum ratio transmission, MRT, precoding that determines a set of at least one of antenna cyclic shifts and phase shifts. In some embodiments, at least one of the antenna cyclic shifts and the phase shifts of the set is transmitter-specific or transmitter group-specific. In some embodiments, the precoding is configured to apply at least one phase offset to the 25 precoded signal to convey information to the UE. In some embodiments, a precoded signal of the precoded plurality of signals includes a random or pseudorandom orthogonal frequency division multiplexed, OFDM, signal. In some embodiments, a precoded signal of the precoded plurality of signals includes a sequence of orthogonal frequency division multiplexed, OFDM, symbols and the precoding is configured to apply antenna cyclic 30 shifts and phase shifts selected to cause peaks at predetermined times at the UE. In some embodiments, the applied antenna cyclic shifts and phase shifts are OFDM symbol- specific. In some embodiments, an OFDM symbol is synthesized over the air with a plurality of peaks of the IR waveform. In some embodiments, the transmitted precoded signal is included in a multiple user, multiple input-multiple output, MU-MIMO, transmission. In some embodiments, the precoding is performed in a frequency domain. In some embodiments, the method includes transmitting the precoded signal on a plurality of subcarriers to enable resolution of a peak of the IR waveform within a specified time interval. In some embodiments, the method includes receiving from the UE a response 5 signal and determining at least one of a range and a velocity of the UE based at least in part on a difference between a time of a peak of the IR waveform and a time associated with the response signal. According to another aspect, a method in a user equipment, UE, configured to communicate with a network node via over-the-air, OTA, synthesis of impulse radio, IR, 10 waveforms is provided. The method includes receiving an IR waveform having at least one peak and a peak to average power ratio, PAPR, that exceeds a PAPR of other signals received by the UE. The method includes decoding information encoded in the IR waveform based at least in part on a timing of the at least one peak. According to this aspect, in some embodiments, decoding the information includes 15 determining times of occurrences of successive peaks of the IR waveform. In some embodiments, decoding the information includes determining time intervals between successive peaks of the IR waveform. In some embodiments, decoding the information includes determining at least one phase offset in the IR waveform. In some embodiments, decoding the information includes determining phase offsets associated with a plurality of 20 different peaks of the IR waveform. In some embodiments, decoding the information includes determining at least one orthogonal frequency division multiplexed, OFDM, symbol. In some embodiments, The method includes differentiating between transmissions from different network nodes based at least in part on the decoded information. In some embodiments, receiving the IR waveform includes using a wakeup 25 receiver of the UE configured to be responsive to the IR waveform. In some embodiments, the method includes transmitting a response signal that is responsive to the IR waveform. In some embodiments, the method includes harvesting energy from the IR waveform. According to yet another aspect, a network node configured to communicate with a user equipment, UE, via over-the-air, OTA, synthesis of impulse radio, IR, waveforms is 30 provided. The network node includes a plurality of antennas and is configured to precode a plurality of signals for OTA synthesis of an IR waveform via the plurality of antennas so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over the air to form a an IR waveform comprising at least one peak and having a peak to average power ratio, PAPR, that exceeds a PAPR of any other signal radiated by any one antenna of the plurality of antennas. The network node is also configured to transmit the precoded plurality of signals via the plurality of antennas. In some embodiments, the precoding is configured to cause each peak of the IR waveform to be localized in space at a location of the UE. In some embodiments, the precoding is 5 configured to cause each peak of the IR waveform to be localized in time. In some embodiments, the precoding is configured to cause peaks of the at least one peak to occur at certain times selected to convey information to the UE. In some embodiments, the precoding is based at least in part on channel state information, CSI, received from the UE. In some embodiments, the precoding is modified maximum ratio transmission, MRT, 10 precoding that determines a set of at least one of antenna cyclic shifts and phase shifts. In some embodiments, at least one of the antenna cyclic shifts and the phase shifts of the set is transmitter-specific or transmitter group-specific. In some embodiments, the precoding is configured to apply at least one phase offset to the precoded signal to convey information to the UE. In some embodiments, a precoded signal of the precoded plurality 15 of signals includes a random or pseudorandom orthogonal frequency division multiplexed, OFDM, signal. In some embodiments, a precoded signal of the precoded plurality of signals includes a sequence of orthogonal frequency division multiplexed, OFDM, symbols and the precoding is configured to apply antenna cyclic shifts and phase shifts selected to cause peaks at predetermined times at the UE. In some embodiments, the 20 applied antenna cyclic shifts and phase shifts are OFDM symbol-specific. In some embodiments, an OFDM symbol is synthesized over the air with a plurality of peaks of the IR waveform. In some embodiments, the transmitted precoded signal is included in a multiple user, multiple input-multiple output, MU-MIMO, transmission. In some embodiments, the precoding is performed in a frequency domain. In some embodiments, 25 the network node is configured to transmit the precoded signal on a plurality of subcarriers to enable resolution of a peak of the IR waveform within a specified time interval. In some embodiments, the network node is configured to receive a response signal from the UE and determining at least one of a range and a velocity of the UE based at least in part on a difference between a time of a peak of the IR waveform and a time associated with the 30 response signal. According to another aspect, a user equipment, UE, configured to communicate with a network node via over-the-air, OTA, synthesis of impulse radio, IR, waveforms is provided. The UE is configured to receive an IR waveform having at least one peak and a peak to average power ratio, PAPR, that exceeds a PAPR of other signals received by the UE. The UE is configured to decode information encoded in the IR waveform based at least in part on a timing of the at least one peak. According to this aspect, in some embodiments, decoding the information includes determining times of occurrences of successive peaks of the IR waveform. In some 5 embodiments, decoding the information includes determining time intervals between successive peaks of the IR waveform. In some embodiments, decoding the information includes determining at least one phase offset in the IR waveform. In some embodiments, decoding the information includes determining phase offsets associated with a plurality of different peaks of IR waveform. In some embodiments, decoding the information includes 10 determining at least one orthogonal frequency division multiplexed, OFDM, symbol. In some embodiments, the UE is configured to differentiate between transmissions from different network nodes based at least in part on the decoded information. In some embodiments, receiving the IR waveform includes using a wakeup receiver of the UE configured to be responsive to the IR waveform. In some embodiments, the UE is 15 configured to transmit a response signal that is responsive to the IR waveform. In some embodiments, the UE is configured to harvest energy from the IR waveform. BRIEF DESCRIPTION OF THE DRAWINGS 20 A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: FIG.1 is a schematic diagram of an example network architecture illustrating a 25 communication system according to principles disclosed herein; FIG.2 is a block diagram of a network node in communication with a user equipment over a wireless connection according to some embodiments of the present disclosure; FIG.3 is a flowchart of an example process in a network node for synthesis of 30 peaky waveforms by means of multi-antenna transmitters according to some embodiments of the present disclosure; and FIG.4 is a flowchart of an example process in a user equipment for synthesis of peaky waveforms by means of multi-antenna transmitters according to some embodiments of the present disclosure; FIG.5 illustrates a precoding method for synthesis of peaky waveforms according to principles disclosed herein; FIG.6 shows the duration of OFDM symbols and desired locations of impulses in an IR signal; 5 FIG.7 shows a peak of a signal transmitted by an nth antenna and a desired impulse time t(k); FIG.8 shows a cyclically shifted signal at an antenna, n, so that a peak occurs at a desired impulse time t(k); FIG.9 shows a received signal generated according to principles disclosed herein; 10 FIG.10 shows an IT signal synthesized using noisy channel estimates; and FIG.11 shows a mixed OFDM / impulse transmission. DETAILED DESCRIPTION Before describing in detail example embodiments, it is noted that the embodiments 15 reside primarily in combinations of apparatus components and processing steps related to synthesis of peaky waveforms by means of multi-antenna transmitters. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent 20 to those of ordinary skill in the art having the benefit of the description herein. As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of 25 describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and / or “including” when used herein, specify the presence of stated features, integers, steps, 30 operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication. 5 In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and / or wireless connections. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As 10 used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and / or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, 15 integers, steps, operations, elements, components, and / or groups thereof. The term “network node” used herein may be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi- 20 standard radio (MSR) radio node such as MSR BS, multi-cell / multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd 25 party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a user equipment (UE) such as a wireless device (WD) or a radio network node. 30 In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The UE herein may be any type of wireless device capable of communicating with a network node or another UE over radio signals, such as a wireless device (WD). The UE may also be a radio communication device, target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine communication (M2M), low-cost and / or low-complexity UE, a sensor equipped with UE, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (IoT) device, or a Narrowband IoT (NB-IOT) device etc. 5 Also, in some embodiments the generic term “radio network node” is used. It may be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell / multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head 10 (RRH). Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and / or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple 15 Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure. Note further, that functions described herein as being performed by a user equipment or a network node may be distributed over a plurality of user equipments 20 and / or network nodes. In other words, it is contemplated that the functions of the network node and user equipment described herein are not limited to performance by a single physical device and, in fact, may be distributed among several physical devices. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art 25 to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Some embodiments are directed to synthesis of peaky waveforms by means of 30 multi-antenna transmitters. Referring to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG.1 a schematic diagram of a communication system 10, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and / or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). 5 Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first user equipment (UE) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second UE 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of UEs 22a, 22b (collectively referred to as user 10 equipments 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding network node 16. Note that although only two UEs 22 and three network nodes 16 are shown for convenience, the communication system may include many more UEs 22 and network nodes 16. 15 Also, it is contemplated that a UE 22 may be in simultaneous communication and / or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a UE 22 may have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR. As an example, UE 22 may be in communication with 20 an eNB for LTE / E-UTRAN and a gNB for NR / NG-RAN. A network node 16 (eNB or gNB) is configured to include a precoder unit 24 which may be configured to precode a plurality of signals for OTA synthesis of an IR waveform via the plurality of antennas so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over the air to form an IR waveform. A 25 user equipment 22 is configured to include a decoder 26 which is configured to decode information encoded in the IR waveform based at least in part on a timing of the at least one peak. Example implementations, in accordance with an embodiment, of the UE 22 and network node 16 discussed in the preceding paragraphs will now be described with 30 reference to FIG.2. The communication system 10 includes a network node 16 provided in a communication system 10 and including hardware 28 enabling it to communicate with the UE 22. The hardware 28 may include a radio interface 30 for setting up and maintaining at least a wireless connection 32 with a UE 22 located in a coverage area 18 served by the network node 16. The radio interface 30 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers. The radio interface 30 includes an array of antennas 34 to radiate and receive signal(s) carrying electromagnetic waves. 5 In the embodiment shown, the hardware 28 of the network node 16 further includes processing circuitry 36. The processing circuitry 36 may include a processor 38 and a memory 40. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 36 may comprise integrated circuitry for processing and / or control, e.g., one or more processors and / or processor cores 10 and / or FPGAs (Field Programmable Gate Array) and / or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 38 may be configured to access (e.g., write to and / or read from) the memory 40, which may comprise any kind of volatile and / or nonvolatile memory, e.g., cache and / or buffer memory and / or RAM (Random Access Memory) and / or ROM (Read-Only Memory) and / or optical memory 15 and / or EPROM (Erasable Programmable Read-Only Memory). Thus, the network node 16 further has software 42 stored internally in, for example, memory 40, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 42 may be executable by the processing circuitry 36. The processing circuitry 36 20 may be configured to control any of the methods and / or processes described herein and / or to cause such methods, and / or processes to be performed, e.g., by network node 16. Processor 38 corresponds to one or more processors 38 for performing network node 16 functions described herein. The memory 40 is configured to store data, programmatic software code and / or other information described herein. In some embodiments, the 25 software 42 may include instructions that, when executed by the processor 38 and / or processing circuitry 36, causes the processor 38 and / or processing circuitry 36 to perform the processes described herein with respect to network node 16. For example, processing circuitry 36 of the network node 16 may include precoder unit 24 which may be configured to precode a plurality of signals for OTA synthesis of an IR waveform via the 30 plurality of antennas so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over the air to form an IR waveform. The communication system 10 further includes the UE 22 already referred to. The UE 22 may have hardware 44 that may include a radio interface 46 configured to set up and maintain a wireless connection 32 with a network node 16 serving a coverage area 18 in which the UE 22 is currently located. The radio interface 46 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers. The radio interface 46 includes an array of antennas 48 to radiate and receive signal(s) carrying electromagnetic waves. 5 The hardware 44 of the UE 22 further includes processing circuitry 50. The processing circuitry 50 may include a processor 52 and memory 54. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 50 may comprise integrated circuitry for processing and / or control, e.g., one or more processors and / or processor cores and / or FPGAs (Field Programmable 10 Gate Array) and / or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 52 may be configured to access (e.g., write to and / or read from) memory 54, which may comprise any kind of volatile and / or nonvolatile memory, e.g., cache and / or buffer memory and / or RAM (Random Access Memory) and / or ROM (Read-Only Memory) and / or optical memory and / or EPROM (Erasable Programmable 15 Read-Only Memory). Thus, the UE 22 may further comprise software 56, which is stored in, for example, memory 54 at the UE 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the UE 22. The software 56 may be executable by the processing circuitry 50. The software 56 may include a client 20 application 58. The client application 58 may be operable to provide a service to a human or non-human user via the UE 22. The processing circuitry 50 may be configured to control any of the methods and / or processes described herein and / or to cause such methods, and / or processes to be performed, e.g., by UE 22. The processor 52 corresponds to one or more processors 52 for 25 performing UE 22 functions described herein. The UE 22 includes memory 54 that is configured to store data, programmatic software code and / or other information described herein. In some embodiments, the software 56 and / or the client application 58 may include instructions that, when executed by the processor 52 and / or processing circuitry 50, causes the processor 52 and / or processing circuitry 50 to perform the processes described herein 30 with respect to UE 22. For example, the processing circuitry 50 of the user equipment 22 may include decoder 26 which is configured to decode information encoded in the IR waveform based at least in part on a timing of the at least one peak. In some embodiments, the inner workings of the network node 16 and UE 22 may be as shown in FIG.2 and independently, the surrounding network topology may be that of FIG.1. The wireless connection 32 between the UE 22 and the network node 16 is in 5 accordance with the teachings of the embodiments described throughout this disclosure. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and / or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, a measurement procedure may be provided for the 10 purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. Although FIGS.1 and 2 show various “units” such as precoder 24 and decoder unit 26 as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within 15 the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry. FIG.3 is a flowchart of an example process in a network node 16 for synthesis of peaky waveforms by means of multi-antenna transmitters. One or more blocks described herein may be performed by one or more elements of network node 16 such as by one or 20 more of processing circuitry 36 (including the precoder 24), processor 38, and / or radio interface 30. Network node 16 such as via processing circuitry 36 and / or processor 38 and / or radio interface 30 is configured to precode a plurality of signals for OTA synthesis of an IR waveform via a plurality of antennas of the network node 16 so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over 25 the air to form an IR waveform comprising least one peak and having a peak to average power ratio, PAPR, that exceeds a PAPR of any signal radiated by any one antenna of the plurality of antennas (Block S10). The method includes transmitting the precoded plurality of signals via the plurality of antennas (Block S12). According to this aspect, in some embodiments, the precoding is configured to 30 cause each peak of the IR waveform to be localized in space at a location of the UE 22. In some embodiments the precoding is configured to cause each peak of the IR waveform to be localized in time. In some embodiments, the precoding is configured to cause peaks of the at least one peak to occur at certain times selected to convey information to the UE 22. In some embodiments, the precoding is based at least in part on channel state information, CSI, received from the UE 22. In some embodiments, the precoding is modified maximum ratio transmission, MRT, precoding that determines a set of at least one of antenna cyclic shifts and phase shifts. In some embodiments, at least one of the antenna cyclic shifts and the phase shifts of the set is transmitter-specific or transmitter group-specific. In some 5 embodiments, the precoding is configured to apply at least one phase offset to the precoded signal to convey information to the UE 22. In some embodiments, a precoded signal of the precoded plurality of signals includes a random or pseudorandom orthogonal frequency division multiplexed, OFDM, signal. In some embodiments, a precoded signal of the precoded plurality of signals includes a sequence of orthogonal frequency division 10 multiplexed, OFDM, symbols and the precoding is configured to apply antenna cyclic shifts and phase shifts selected to cause peaks at predetermined times at the UE 22. In some embodiments, the applied antenna cyclic shifts and phase shifts are OFDM symbol- specific. In some embodiments, an OFDM symbol is synthesized over the air with a plurality of peaks of the IR waveform. In some embodiments, the transmitted precoded 15 signal is included in a multiple user, multiple input-multiple output, MU-MIMO, transmission. In some embodiments, the precoding is performed in a frequency domain. In some embodiments, the method includes transmitting the precoded signal on a plurality of subcarriers to enable resolution of a peak of the IR waveform within a specified time interval. In some embodiments, the method includes receiving from the UE 22 a response 20 signal and determining at least one of a range and a velocity of the UE 22 based at least in part on a difference between a time of a peak of the IR waveform and a time associated with the response signal. FIG.4 is a flowchart of an example process in a user equipment 22 according to some embodiments of the present disclosure. One or more blocks described herein may be 25 performed by one or more elements of user equipment 22 such as by one or more of processing circuitry 50 (including the decoder 26), processor 52, and / or radio interface 46. User equipment 22 such as via processing circuitry 50 and / or processor 52 and / or radio interface 46 is configured to receive an IR waveform having at least one peak and a peak to average power ratio, PAPR, that exceeds a PAPR of other signals received by the UE 30 22 (Block S14). The method includes decoding information encoded in the IR waveform based at least in part on a timing of the at least one peak (Block S16). According to this aspect, in some embodiments, decoding the information includes determining times of occurrences of successive peaks of the IR waveform. In some embodiments, decoding the information includes determining time intervals between successive peaks of the IR waveform. In some embodiments, decoding the information includes determining at least one phase offset in the IR waveform. In some embodiments, decoding the information includes determining phase offsets associated with a plurality of different peaks of the IR waveform. In some embodiments, decoding the information 5 includes determining at least one orthogonal frequency division multiplexed, OFDM, symbol. In some embodiments, The method includes differentiating between transmissions from different network nodes 16 based at least in part on the decoded information. In some embodiments, receiving the IR waveform includes using a wakeup receiver of the UE 22 configured to be responsive to the IR waveform. In some 10 embodiments, the method includes transmitting a response signal that is responsive to the IR waveform. In some embodiments, the method includes harvesting energy from the IR waveform. FIG.5 is a flowchart of an example precoding process according to principles disclosed herein. The process may be performed by the precoder unit 24 of the network 15 node 16. The process includes selecting a location of a peak in an MRT precoded signal (Block S18). The process also includes cyclically shifting so that a peak occurs at a time t(n) (Block S20). The process further includes phase shifting the cyclically shifted signal so that the transmitted signal has a predetermined phase at time t(n) (Block S22). The process also includes transmitting the signal (Block S24). 20 Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for synthesis of peaky waveforms by means of multi-antenna transmitters. Synthesis of IR waveforms 25 In some embodiments, MRT precoding may be modified to synthesize IR waveforms as described herein. But other precoding techniques may also be used. Suppose that one wishes to synthesize an IR signal with impulses centered at times ^^(^^), ^^ = 1,2, …, as illustrated in FIG.6. Suppose also that there is one pulse occurrence ineach OFDM symbol and that there is only one intended receiver. 30 Let ^^^,^(^^)denote the k-th OFDM symbol transmitted through transmitter number nand let ^^^,^ = |^^^,^|^^^ఈ^,^be the complex channel coefficient between the n-th transmit antenna and the receiver, corresponding to subcarrier ^^. The frequency domain symbols ^^^,^,^may belong to any quadrature amplitude modulation (QAM) or phase shift keying (PSK) alphabet. In general, the symbols ^^^,^,^transmitted through antenna n are different from the symbols ^^^,^,^transmitted through antenna m so that ^^^,^(^^) is different from ^^^,^(^^). Using MRT precoding, the signal corresponding to the k-th OFDM symboltransmitted through transmit antenna #n is ^^^,^(^^) = ∑ே^ୀ^^^௧ In some MRT precoding is modified by further linear precoding as follows. 1. For each transmit antenna ^^, select ^^^,^where the magnitude of the MRT precoded signal ^^^,^(^^)is equal to or exceeds a predefined threshold. A goodchoice for the threshold is ^^ = m௧ax|^^^,^(^^)|. In other words, choose the highest peak ofthe signal ^^^,^ = arg m௧ax|^^^,^(^^)|. This is illustrated in FIG.7; 2. For each transmit antenna ^^, cyclically shift ^^^,^(^^) by ^^(^^) − ^^^,^ so thatafter shifting the peak identified in step 1 occurs at time ^^(^^), as illustrated in FIG.8. Thisis referred to herein as the cyclic shifted signal ^^^^,^(^^) =∑ே^ୀ^^^௧^^ି^ఈ^,^^^^,^,^^^^ଶగ^^^(௧ି(௧(^)ି்ೖ,^). ^^, compute the phase ^^^,^ , (i.e., ^^^,^= a phase shift by −^^^,^to the bି^థೖ,^ y ^^ . antenna ^^ signal generated in step 3. After propagation, the signal is added coherently over the air at the receiver location, due to both the MRT precoding and the phase alignment introduced in step 3 above. In particular, all the phases at time t(k) are aligned and add coherently, creating a temporal peak at t(k). Note that since the signals transmitted through different antennas are different, there will be phase coherence only at time t(k). Indeed, the received signal corresponding to the k-th OFDM symbol may be expressed in the form ே^^ே^^௧ ^^. By right-hand side at time t(k). This implies that all the ^^்^signals are coherently added at time t(k). FIG.9 illustrates the time domain received signal ^^^(^^). It shows how the IR modulation arises from the combination of precoding and propagation. The channel estimates ^^^,^are often noisy due to quantization, estimation errors, etc. Therefore, it is important to assess whether the proposed precoding technique is robust to channel estimation errors. FIG.10 illustrates that an IR signal may be synthesized even in the presence of large channel estimation errors. FIG.11 is a diagram showing a mixed 5 OFDM / impulse transmission. The procedure illustrated may be generalized in various ways. Note that cyclic shifting and phase shifting may be performed in the frequency domain. Thus, the precoded signal may be obtained from an output of an inverse DFT having as inputs, properly computed frequency domain symbols. Hence, the disclosed precoding may be 10 incorporated seamlessly in the synthesis of MU-MIMO OFDM waveforms. The synthesis of IR waveforms explained above has assumed that there is only one pulse during the duration of one OFDM symbol. Since IR modulation achieves capacity only with very low duty cycles, this is not a limitation in practice. However, by using specially designed frequency domain symbols, one may synthesize OFDM symbols that 15 have two or more peaks at any desired location, and a similar precoding procedure may be used to generate two or more peaks during one OFDM symbol duration. The phase shift may also be used to convey data to the receiver in the phase of the peak. Instead of shifting by −^^^,^ in step 3 above, one may phase shift by −^^^,^ + ^^^where ^^^ ∈ {0,గ ଶ, ^^, 3^^ / 2}, so that more bits may be sent (assuming the receiver may20 detect phases). Note that the phase shift ^^^may be the same for all antennas. This type of modulation may be referred to as flash modulation. Both the transmit power and temporal resolution may be increased by increasing the number of subcarriers, while keeping a flat power spectral density. This is convenient for massive MIMO transmitters because the transmit linearization algorithms are often 25 optimized for signals with flat power spectral density (PSD,) and because in some regulatory domains and frequency bands a flat PSD is required to be able to utilize the maximum allowed output power. As an illustration, using PPM and an fast Fourier transform (FFT) size 1024, a spectral efficiency of ^^^ଶ(^^ଶସ)≈ 0.01 bits / second / Hz may be achieved.30 Some effective with a rather modest number of antennas, since the peak rises over the average signal power as 10 ∗ ^^^^^^10(^^்^), where ^^்^ is thenumber of transmit antennas. For example, 20 transmit antennas will give a pulse that rises 13 dB over the average. This also means that in large arrays with hundreds or thousands of antennas, it is possible to select the number of spatial degrees of freedom to be spent on creating the IR waveform. The procedure above shows that virtually any OFDM waveform may be used as a basis to synthesize peaky waveforms. However, one may also start with waveforms that 5 have high PAPR and in this way achieve even larger peaks at the receiver. Such waveforms are easy to obtained by means of simulations or by explicit design (i.e. choosing frequency domain symbols such that several tones in one OFDM symbol co- phase at a given time instant) Ranging and sensing 10 Time of arrival (ToA) is used in ranging protocols such as fine time measurement (FTM) used in Wi-Fi. Determining the starting position of a wireless transmission may be accomplished by a receiver using reference signals known a-priori by the receiver. However, these measurements are often noisy and several measurements are often required to obtain good accuracy. For example, the FTM protocol often requires several 15 tens of transmissions to sufficiently de-noise the ToA estimates. Some embodiments disclosed herein may be used to decrease the time needed to estimate ToA with sufficient accuracy. Observe that transmissions for communications are very robust to timing estimation errors at the receiver, but ToA determinations do require accurate timing estimates. Some embodiments incorporate one or more impulses in an OFDM 20 transmission. One or more OFDM symbols may be allocated to impulses. Since all the energy of the OFDM symbol is concentrated in a narrow time interval the impulse position is easy to detect using an energy detector and is robust to imperfections such as frequency offsets. In contrast, the detection of reference signals – such as Zadoff-Chu sequences used in 5G – is sensitive to frequency offsets, and the detection performance may be severely 25 degraded in the presence of large frequency offsets due to Doppler or TX-RX oscillator mismatch, for example. Some ranging solutions disclosed herein may rely on the transmitter to acquire channel state information (CSI) (which is already standardized) and may rely on the receiver to know that the transmitted signal comprises an impulse (which would benefit from standardization). 30 Impulses are also useful for radar applications in ISAC. The transmitter may acquire CSI (already standardized) and may append or prepend to ordinary communications signals one or more OFDM symbols that generate impulses at the receiver, as explained in the previous subsection. The receiver need not be aware that the transmitted signal includes an impulse so that this technique may be useful in proprietary solutions. In this way, a network node may simultaneously transmit data and one or more high power impulses whose reflections from the UE 22 may be fed to radar analysis techniques to determine range, velocity etc. The impulses may be combined with single user (SU)-MIMO or multi-user (MU)- 5 MIMO transmissions. For example, a receiver supporting two MIMO layers may receive data through one layer and impulses for ToA estimation through the other layer. Wake-up radios and wake-up signals Wake up radios have been standardized in IEEE 802.11 and are being standardized in 3GPP. Such radios consume little power but the trade-off is that the sensitivity of the 10 radios is much worse than the sensitivity of the main communications radio. On-off keying (OOK) is a modulation method commonly used for those radios. An OOK signal having high power over a short time interval may be well-suited for wake-up radios. It may be synthesized using OFDM transmitters by means of impulses as disclosed herein. RF energy harvesting 15 peaky RF waveforms are beneficial for energy harvesting because be harvested if the instantaneous power exceeds a threshold. However, synthesis of peaky waveforms is very challenging and inefficient at the transmitter. Some embodiments make efficient use of communications radios for the generation of peaky signals, since the peakiness is created at the harvester’s antenna and 20 not at the transmitter. Some embodiments may include one or more of the following: 1) A method to synthesize an IR waveform at a multi-antenna transmitter, comprising a precoder that is applied to the transmitted signals, characterized in that the PAPR of the signal formed by the superposition of the multiple transmit signals at a target 25 location exceeds the PAPR of any of the individual transmit signals. 2) As in 1), where a UE 22 is located at the target location and the times at which the received signal exceeds a predefined threshold convey information from the transmitter to the receiver. 3) As in 1,2, where the precoder is based on RX CSI acquired by the 30 transmitter. 4) As in 1,2, where the precoder comprises one of a transmit specific phase shift or a transmit specific cyclic shift. 5) As in 1-4, where the signals transmitted by each transmitter are OFDM signals, and the phase / cyclic shifts are possibly different for each OFDM symbol and chosen to obtain coherent combination (at the RX) at predetermined times in each OFDM signal, such that peaks are generated at said selected predetermined times. 6) As in 1-5, where the transmission is a MU-MIMO transmission. 7) As in 1-6, where a phase shift common to all transmit antennas is added to 5 the antenna specific phase shift. This phase shift may be data dependent and used to convey data in the phase of the peak (flash modulation) As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and / or computer storage media storing an executable computer program. Accordingly, the 10 concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and / or functionality described herein may be performed by, and / or associated to, a corresponding module, which may be implemented in software and / or firmware and / or 15 hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that may be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices. 20 Some embodiments are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, may be implemented by computer program instructions. These computer program instructions 25 may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or 30 blocks. These computer program instructions may also be stored in a computer readable memory or storage medium that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function / act specified in the flowchart and / or block diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be 5 performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks. It is to be understood that the functions / acts noted in the blocks may occur out of 10 the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication 15 may occur in the opposite direction to the depicted arrows. Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such 20 as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be 25 made to an external computer (for example, through the Internet using an Internet Service Provider). Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and 30 subcombination of these embodiments. Accordingly, all embodiments may be combined in any way and / or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination. It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the 5 accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

What is claimed is:

1. A method in a network node (16) configured to communicate with a user 5 equipment, UE (22), via over-the-air, OTA, synthesis of impulse radio, IR, waveforms, the method comprising: precoding (S10) a plurality of signals for OTA synthesis of an IR waveform via a plurality of antennas of the network node (16) so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over the air to form an IR waveform 10 comprising at least one peak and having a peak to average power ratio, PAPR, that exceeds a PAPR of any signal radiated by any one antenna of the plurality of antennas; and transmitting (S12) the precoded plurality of signals via the plurality of antennas. 15 2. The method of Claim 1, wherein the precoding is configured to cause each peak of the IR waveform to be localized in space at a location of the UE (22) and / or to be localized in time.

3. The method of any of Claims 1 and 2, wherein the precoding is configured 20 to cause peaks of the at least one peak to occur at certain times selected to convey information to the UE (22).

4. The method of any of Claims 1-3, wherein the precoding is based at least in part on channel state information, CSI, received from the UE (22). 25 5. The method of any of Claims 1-4, wherein the precoding is modified maximum ratio transmission, MRT, precoding that determines a set of at least one of antenna cyclic shifts and phase shifts. 30 6. The method of Claim 5, wherein at least one of the antenna cyclic shifts and the phase shifts of the set is transmitter-specific or transmitter group-specific.

7. The method of any of Claims 1-6, wherein the precoding is configured to apply at least one phase offset to a precoded signal of the precoded plurality of signals toconvey information to the UE (22).

8. The method of any of Claims 1-7, wherein a precoded signal of the precoded plurality of signals includes a random or pseudorandom orthogonal frequency 5 division multiplexed, OFDM, signal.

9. The method of any of Claims 1-7, wherein a precoded signal of the precoded plurality of signals includes a sequence of orthogonal frequency division multiplexed, OFDM, symbols and the precoding is configured to apply antenna cyclic 10 shifts and phase shifts selected to cause peaks at predetermined times at the UE (22).

10. The method of Claim 9, wherein the applied antenna cyclic shifts and phase shifts are OFDM symbol-specific. 15 11. The method of any of Claims 9 and 10, wherein an OFDM symbol is synthesized over the air with a plurality of peaks of the IR waveform.

12. The method of any of Claims 1-11, wherein the transmitted precoded signal is included in a multiple user, multiple input-multiple output, MU-MIMO, transmission. 20 13. The method of any of Claims 1-12, further comprising transmitting the precoded signal on a plurality of subcarriers to enable resolution of a peak of the IR waveform within a specified time interval. 25 14. The method of any of Claims 1-13, further comprising receiving from the UE (22) a response signal and determining at least one of a range and a velocity of the UE (22) based at least in part on a difference between a time of a peak of the IR waveform and a time associated with the response signal. 30 15. A method in a user equipment, UE (22), configured to communicate with a network node (16) via over-the-air, OTA, synthesis of impulse radio, IR, waveforms, the method comprising: receiving (S14) an IR waveform having at least one peak and a peak to average power ratio, PAPR, that exceeds a PAPR of other signals received by the UE (22); anddecoding (S16) information encoded in the IR waveform based at least in part on a timing of the at least one peak.

16. The method of Claim 15, wherein decoding the information includes 5 determining times of occurrences of successive peaks of the IR waveform.

17. The method of any of Claims 15 and 16, wherein decoding the information includes determining time intervals between successive peaks of the IR waveform. 10 18. The method of any of Claims 15-17, wherein decoding the information includes determining at least one phase offset in the IR waveform.

19. The method of any of Claims 15-18, wherein decoding the information includes determining phase offsets associated with a plurality of different peaks of the IR 15 waveform.

20. The method of any of Claims 15-19, wherein decoding the information includes determining at least one orthogonal frequency division multiplexed, OFDM, symbol. 20 21. The method of any of Claim 15-20, further comprising differentiating between transmissions from different network nodes (16) based at least in part on the decoded information. 25 22. The method of any of Claims 15-21, wherein receiving the precoded signal includes using a wakeup receiver of the UE (22) configured to be responsive to the IR waveform.

23. The method of any of Claims 15-22, further comprising transmitting a 30 response signal that is responsive to the IR waveform.

24. The method of any of Claims 15-23, further comprising harvesting energy from the IR waveform.

25. A network node (16) configured to communicate with a user equipment, UE (22), via over-the-air, OTA, synthesis of impulse radio, IR, waveforms, the network node (16) comprising a plurality of antennas, the network node (16) being configured to: precode a plurality of signals for OTA synthesis of an IR waveform via the 5 plurality of antennas so that radio frequency, RF, energy radiated by each antenna of the plurality of antennas combine over the air to form a an IR waveform comprising at least one peak and having a peak to average power ratio, PAPR, that exceeds a PAPR of any other signal radiated by any one antenna of the plurality of antennas; and transmit the precoded plurality of signals via the plurality of antennas. 10 26. The network node (16) of Claim 25, wherein the precoding is configured to cause each peak of the IR waveform to be localized in space at a location of the UE (22) and / or to be localized in time. 15 27. The network node (16) of any of Claims 25 and 26, wherein the precoding is configured to cause peaks of the at least one peak to occur at certain times selected to convey information to the UE (22).

28. The network node (16) of any of Claims 25-27, wherein the precoding is 20 based at least in part on channel state information, CSI, received from the UE (22).

29. The network node (16) of any of Claims 25-28, wherein the precoding is modified maximum ratio transmission, MRT, precoding that determines a set of at least one of antenna cyclic shifts and phase shifts. 25 30. The network node (16) of Claim 29, wherein at least one of the antenna cyclic shifts and the phase shifts of the set is transmitter-specific or transmitter group- specific. 30 31. The network node (16) of any of Claims 25-30, wherein the precoding is configured to apply at least one phase offset to the precoded signal to convey information to the UE (22).

32. The network node (16) of any of Claims 25-31, wherein a precoded signalof the precoded plurality of signals includes a random or pseudorandom orthogonal frequency division multiplexed, OFDM, signal.

33. The network node (16) of any of Claims 25-32, wherein a precoded signal 5 of the precoded plurality of signals includes a sequence of orthogonal frequency division multiplexed, OFDM, symbols and the precoding is configured to apply antenna cyclic shifts and phase shifts selected to cause peaks at predetermined times at the UE (22).

34. The network node (16) of Claim 33, wherein the applied antenna cyclic 10 shifts and phase shifts are OFDM symbol-specific.

35. The network node (16) of any of Claims 33 and 34, wherein an OFDM symbol is synthesized over the air with a plurality of peaks of the IR waveform. 15 36. The network node (16) of any of Claims 25-35, wherein the transmitted precoded signal is included in a multiple user, multiple input-multiple output, MU-MIMO, transmission.

37. The network node (16) of any of Claims 25-36, wherein the network node 20 (16) is configured to transmit a precoded signal of the precoded plurality of signals on a plurality of subcarriers to enable resolution of a peak of the IR waveform within a specified time interval.

38. The network node (16) of any of Claims 25-37, wherein the network node 25 (16) is configured to receive a response signal from the UE (22) and determining at least one of a range and a velocity of the UE (22) based at least in part on a difference between a time of a peak of the IR waveform and a time associated with the response signal.

39. A user equipment, UE (22), configured to communicate with a network 30 node (16) via over-the-air, OTA, synthesis of impulse radio, IR, waveforms, the UE (22) configured to: receive an IR waveform having at least one peak and a peak to average power ratio, PAPR, that exceeds a PAPR of other signals received by the UE (22) from the network node; anddecode information encoded in the IR waveform based at least in part on a timing of the at least one peak.

40. The UE (22) of Claim 39, wherein decoding the information includes 5 determining times of occurrences of successive peaks of the IR waveform.

41. The UE (22) of any of Claims 39 and 40, wherein decoding the information includes determining time intervals between successive peaks of the IR waveform. 10 42. The UE (22) of any of Claims 39-42, wherein decoding the information includes determining at least one phase offset in the IR waveform.

43. The UE (22) of any of Claims 39-42, wherein decoding the information includes determining phase offsets associated with a plurality of different peaks of IR 15 waveform.

44. The UE (22) of any of Claims 39-43, wherein decoding the information includes determining at least one orthogonal frequency division multiplexed, OFDM, symbol. 20 45. The UE (22) of any of Claim 39-44, wherein the UE (22) is configured to differentiate between transmissions from different network nodes (16) based at least in part on the decoded information. 25 46. The UE (22) of any of Claims 39-45, wherein receiving IR waveform includes using a wakeup receiver of the UE (22) configured to be responsive to the IR waveform.

47. The UE (22) of any of Claims 39-46, wherein the UE (22) is configured to 30 transmit a response signal that is responsive to the IR waveform.

48. The UE (22) of any of Claims 39-51, wherein the UE (22) is configured to harvest energy from the IR waveform.

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