Phase shifted transmission of signals with one or more antennas

Abstract

Example embodiments relate transmission of phase shifted signals. An apparatus may comprise: a plurality of antennas; signal generation circuitry configured to feed the plurality of antennas with a respective plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions and to cause a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

Description

PHASE SHIFTED TRANSMISSION OF SIGNALS WITH ONE OR MORE ANTENNAS TECHNICAL FIELD

[0001] Various example embodiments generally relate to the field of wireless communications. Some example embodiments relate to transmission of phase shifted signals to generate artificially phase shifted radio propagation channels. BACKGROUND

[0002] In wireless communications, transmitted signals propagate through a radio channel. During propagation through the radio channel the transmitted signal may reflect from various objects and therefore multiple versions of the transmitted signal may reach a receiver. This phenomenon may be called multipath propagation and even though it may be viewed to cause distortion of the transmitted signal, it is multipath propagation provides a source of diversity in wireless communications. SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] Example embodiments enable improving transmission capacity or robustness in radio communication by applying a phase shift to generate uncorrelated transmission channels. This and other benefits may be achieved by the features of the independent claims. Further example embodiments are provided in the dependent claims, the description, and the drawings.

[0005] According to a first aspect, an apparatus is disclosed. The apparatus may comprise: signal generation circuitry configured to feed an antenna with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, wherein the signal generation circuitry and / or the antenna is configured to cause apredetermined phase shift between the plurality of signals, and wherein the antenna is configured to direct the plurality of signals to substantially same direction.

[0006] According to an example embodiment of the first aspect, the signal generation circuitry is configured to cause the predetermined phase shift between the plurality of signals.

[0007] According to an example embodiment of the first aspect, the apparatus comprises the antenna.

[0008] According to an example embodiment of the first aspect, the signal generation circuitry is configured to select the different complex-valued data symbols from a plurality of constellations having the predetermined phase shift between the constellations.

[0009] According to an example embodiment of the first aspect, the signal generation circuitry is configured to: adjust an order of transmission of the different complex-valued data symbols to cause the predetermined phase shift between different complex-valued data symbols transmitted simultaneously; and transmit an indication of the order of transmission of the different complex-valued data symbols to a receiver.

[0010] According to an example embodiment of the first aspect, the signal generation circuitry is configured to: adjust the order of transmission of the different complex-valued data symbols to cause the different complex-valued data symbols transmitted simultaneously to have same amplitude.

[0011] According to an example embodiment of the first aspect, the plurality of signals have substantially same power.

[0012] According to an example embodiment of the first aspect, the predetermined phase shift is constant within a range of transmit angles from the antenna.

[0013] According to an example embodiment of the first aspect, the plurality of signals comprises multiple-input multiple output (MIMO) coded data symbols.

[0014] According to an example embodiment of the first aspect, the antenna comprises an antenna array, and the signal generation circuitry is configured to feed each antenna element of the antenna array with the plurality of signals.

[0015] According to an example embodiment of the first aspect, power radiation patterns of the antenna are substantially same for the plurality of signals.

[0016] According to an example embodiment of the first aspect, main lobes of power radiations pattern of the antenna are overlapping for the plurality of signals.

[0017] According to an example embodiment of the first aspect, main lobes of the power radiation patterns of the antenna point at different directions for the plurality of signals.

[0018] According to an example embodiment of the first aspect, main lobes of the power radiation patterns of the antenna point at substantially same direction for the plurality of signals, and widths of the main lobes of the power radiation patterns are different for the plurality of signals.

[0019] According to an example embodiment of the first aspect, the signal generation circuitry and / or the antenna is configured to cause different phase shifts between the plurality of signals at different time instants.

[0020] According to an example embodiment of the first aspect, the apparatus is configured to transmit an indication of the different phase shifts to a receiver.

[0021] According to an example embodiment of the first aspect, each of the plurality of signals comprises reference symbols configured to enable channel estimation for the plurality of signals by a receiver.

[0022] According to an example embodiment of the first aspect, the reference symbols are mutually orthogonal between the plurality of signals.

[0023] According to a second aspect, a method may comprise: causing a predetermined phase shift between a plurality of signals transmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction.

[0024] According to an example embodiment of the second aspect, the method further comprises: causing the predetermined phase shift between the plurality of signals.

[0025] According to an example embodiment, the method further comprises: directing the plurality of signals to substantially same direction by the antenna.

[0026] According to an example embodiment of the first aspect, the method is performed by an apparatus comprising the antenna.

[0027] According to an example embodiment of the second aspect, the method further comprises: selecting the different complex-valued data symbols from a plurality of constellations having the predetermined phase shift between the constellations.

[0028] According to an example embodiment of the second aspect, the method further comprises: adjusting an order of transmission of the different complex- valued data symbols to cause the predetermined phase shift between different complex-valued data symbols transmitted simultaneously; and transmitting an indication of the order of transmission of the different complex-valued data symbols to a receiver.

[0029] According to an example embodiment of the second aspect, the method further comprises: adjusting the order of transmission of the different complex- valued data symbols to cause the different complex-valued data symbols transmitted simultaneously to have same amplitude.

[0030] According to an example embodiment of the second aspect, the plurality of signals have substantially same power.

[0031] According to an example embodiment of the second aspect, the predetermined phase shift is constant within a range of transmit angles from the antenna.

[0032] According to an example embodiment of the second aspect, the plurality of signals comprises multiple-input multiple output (MIMO) coded data symbols.

[0033] According to an example embodiment of the second aspect, the antenna comprises an antenna array, and the method comprises: feeding each antenna element of the antenna array with the plurality of signals.

[0034] According to an example embodiment of the second aspect, power radiation patterns of the antenna are substantially same for the plurality of signals.

[0035] According to an example embodiment of the second aspect, main lobes of power radiations pattern of the antenna are overlapping for the plurality of signals.

[0036] According to an example embodiment of the second aspect, main lobes of the power radiation patterns of the antenna point at different directions for the plurality of signals.

[0037] According to an example embodiment of the second aspect, main lobes of the power radiation patterns of the antenna point at substantially same direction for the plurality of signals, and widths of the main lobes of the power radiation patterns are different for the plurality of signals.

[0038] According to an example embodiment of the second aspect, the method comprises: causing different phase shifts between the plurality of signals at different time instants.

[0039] According to an example embodiment of the second aspect, the method further comprises: transmitting an indication of the different phase shifts to a receiver.

[0040] According to an example embodiment of the second aspect, each of the plurality of signals comprises reference symbols configured to enable channel estimation for the plurality of signals by a receiver.

[0041] According to an example embodiment of the second aspect, the reference symbols are mutually orthogonal between the plurality of signals.

[0042] According to a third aspect, an apparatus is disclosed. The apparatus may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: cause a predetermined phase shift between a plurality of signals configured to be transmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction. The instructions may be configured to cause, when executed by the at least one processor, the apparatus to perform any example embodiment of the method of the second aspect.

[0043] According to a fourth aspect a computer program, a computer program product, or a (non-transitory) computer-readable medium may comprise instructions for causing an apparatus to perform at least the following: causing a predetermined phase shift between a plurality of signals configured to betransmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction. The computer program, computer program product, or a (non-transitory) computer-readable medium may further comprise instructions for causing the apparatus to perform any example embodiment of the method of the second aspect.

[0044] According to a fourth aspect an apparatus may comprise: means for causing a predetermined phase shift between a plurality of signals transmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction. The apparatus may further comprise means for performing any example embodiment of the method of the second aspect.

[0045] According to a fifth aspect, an apparatus is disclosed. The apparatus may comprise: a plurality of antennas; signal generation circuitry configured to feed the plurality of antennas with a respective plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions and to cause a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

[0046] According to an example embodiment of the fifth aspect, at least one of the plurality of antennas comprises an antenna array.

[0047] According to an example embodiment of the fifth aspect, at least one of the plurality of antennas comprises a subarray of an antenna array.

[0048] According to an example embodiment of the fifth aspect, the plurality of antennas comprise subarrays of same antenna array.

[0049] According to an example embodiment of the fifth aspect, the apparatus comprises antenna control circuitry configured to control weights and / or delays associated with antenna elements of the plurality of antennas to cause the predetermined phase shift between the plurality of signals.

[0050] According to an example embodiment of the fifth aspect, the signal generation circuitry is configured to feed antenna elements of each of the plurality of antennas with one of the plurality of signals.

[0051] According to an example embodiment of the fifth aspect, the signal generation circuitry is configured to feed each of the plurality of antennas with one of the plurality of signals.

[0052] According to an example embodiment of the fifth aspect, the predetermined phase shift between the plurality of signals is different at different time instants.

[0053] According to an example embodiment of the fifth aspect, the plurality of antennas are configured to cause the predetermined phase shift between the plurality of signals by applying different phase radiation patterns to at least one of the plurality of signals at the different time instants.

[0054] According to an example embodiment of the fifth aspect, the plurality of antennas comprise at least one dipole antenna, at least one antenna patch, and / or at least one antenna lens.

[0055] According to an example embodiment of the fifth aspect, the first signal and the second signal are configured to be transmitted with same polarization.

[0056] According to an example embodiment of the fifth aspect, a distance between the plurality of antennas is less than half of a wavelength of the plurality of signals.

[0057] According to an example embodiment of the fifth aspect, the plurality of signals comprise multiple-input multiple output (MIMO) coded data symbols.

[0058] According to an example embodiment of the fifth aspect, each of the plurality of signals is configured to carry different complex-valued data symbols.

[0059] According to an example embodiment of the fifth aspect, the signal generation circuitry is further configured to: adjust an order of transmission of the different complex-valued data symbols to cause the different complex-valued data symbols transmitted simultaneously to have same amplitude; and transmit an indication of the order of transmission of the different complex-valued data symbols to a receiver.

[0060] According to an example embodiment of the fifth aspect, power radiation patterns of the plurality of antennas are substantially identical.

[0061] According to an example embodiment of the fifth aspect, main lobes of power radiation patterns of the plurality of antennas are overlapping.

[0062] According to an example embodiment of the fifth aspect, the main lobes of the power radiation patterns of the plurality of antennas point at different directions.

[0063] According to an example embodiment of the fifth aspect, main lobes of the power radiation patterns of the plurality of antennas point at substantially same direction, and wherein widths of the main lobes of the power radiation patterns of the first and the second antennas are different.

[0064] According to an example embodiment of the fifth aspect, each of the plurality of signals comprises reference symbols configured to enable channel estimation for the plurality of signals.

[0065] According to an example embodiment of the fifth aspect, the reference symbols are mutually orthogonal between the plurality of signals.

[0066] According to a sixth aspect, a method is disclosed. The method may comprise: feeding a plurality of antennas with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions; causing a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals. The method may be configured to be performed according to any example embodiment of the fifth aspect.

[0067] According to a seventh aspect a computer program, a computer program product, or a (non-transitory) computer-readable medium may comprise instructions for causing an apparatus to perform at least the following: feeding a plurality of antennas with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions; causing a predetermined phase shift between the pluralityof signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals. The computer program, computer program product, or a (non-transitory) computer-readable medium may further comprise instructions for causing the apparatus to perform a any example embodiment of the fifth aspect.

[0068] According to an eighth aspect an apparatus may comprise: means for feeding a plurality of antennas with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions; means for causing a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals. The apparatus may further comprise means for performing any example embodiment of the fifth aspect.

[0069] According to a ninth aspect, an apparatus is disclosed: The apparatus may comprise: signal generation circuitry configured to feed an antenna with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, wherein the signal generation circuitry and / or the antenna is configured to cause a predetermined phase shift between the plurality of signals, and wherein the antenna is configured to direct the plurality of signals to substantially same direction, wherein the antenna is a dipole antenna, an antenna patch, or an antenna array, wherein the signal generation circuitry is configured to feed antenna elements of the antenna array with the plurality of signals.

[0070] According to an example embodiment of the ninth aspect, the predetermined phase shift is different for at least two transmit directions of the plurality of signals. The apparatus may be further configured to perform any example embodiment of the fifth aspect. The plurality of signals may be however configured to be fed to a single antenna.

[0071] According to a tenth aspect, a method is disclosed. The method may comprise: causing a predetermined phase shift between a plurality of signals transmitted from an antenna, wherein the plurality of signals are configured tooverlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction, wherein the antenna is a dipole antenna, an antenna patch, or an antenna array, wherein the signal generation circuitry is configured to feed antenna elements of the antenna array with the plurality of signals.

[0072] According to an example embodiment of the tenth aspect, the predetermined phase shift is different for at least two transmit directions of the plurality of signals. The method may be performed according to any example embodiment of the fifth aspect. The plurality of signals may be however fed to a single antenna.

[0073] Any of the above example embodiments may be combined with one or more other example embodiments. Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings. DESCRIPTION OF THE DRAWINGS

[0074] The accompanying drawings, which are included to provide a further understanding of the example embodiments and constitute a part of this specification, illustrate example embodiments and together with the description help to understand the example embodiments. In the drawings:

[0075] FIG.1 illustrates an example of a system model for radio transmission;

[0076] FIG.2 illustrates an example of multipath propagation;

[0077] FIG.3 illustrates an example of a delay profile of a multipath channel;

[0078] FIG.4 illustrates an example of an apparatus configured to practice one or more example embodiments;

[0079] FIG. 5 illustrates an example of combination of electric field components at a receiver;

[0080] FIG.6 illustrates an example of combination of multipath components at a receiver;

[0081] FIG.7 illustrates an example of a transmitter configured to cause a phase shift between transmitted signals;

[0082] FIG.8 illustrates an example of a constant phase shift between signals transmitted at different directions;

[0083] FIG.9 illustrates an example of phase-shifted quadrature phase shift keying (QPSK) constellations;

[0084] FIG.10 illustrates an example of phase-shifted 16-QAM (quadrature amplitude modulation) constellations;

[0085] FIG.11 illustrates an example of signalling phase shift(s) to a receiver;

[0086] FIG.12 illustrates an example of different widths of main lobes of power radiation patterns for two signals transmitted with a phase shift;

[0087] FIG.13 illustrates an example of different directions of main lobes of power radiation patterns for two signals transmitted with a phase shift;

[0088] FIG.14 illustrates an example of a method for transmitting radio signals;

[0089] FIG.15 illustrates an example of a transmitter configured to cause a phase shift between signals transmitted from different antennas;

[0090] FIG.16 illustrates an example of a transmitter configured to cause a phase shift between signals transmitted from different antenna arrays;

[0091] FIG.17 illustrates an example of two antenna arrays within a single antenna radome;

[0092] FIG.18 illustrates an example of two subarrays within an antenna array;

[0093] FIG. 19 illustrates an example of phase radiation patterns with a direction dependent phase shift between signals; and

[0094] FIG. 20 illustrates an example of a method for transmitting radio signals.

[0095] Like references are used to designate like parts in the accompanying drawings. DETAILED DESCRIPTION

[0096] Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings. The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the onlyforms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0097] Example embodiments of the present disclosure enable generation of uncorrelated propagation channels, for example for the purpose of multiple-input multiple-output (MIMO) communication. Uncorrelated channels may be generated by artificially causing a phase difference (phase shift) for signals transmitted from a single transmit antenna, for example by signal generation circuitry (e.g., at baseband) or by the transmit antenna. The phase difference may be generated such that the power radiation pattern of the antenna does not change by selecting desired values for real and imaginary parts of the complex values characterising each transmission. This results in the same signal power, e.g., coverage area, but these signals are received at different phase. These phase differences result in uncorrelated propagation channels, which may be used for example for MIMO communication. It is noted that term uncorrelated may refer to channels that are sufficiently different, for example for MIMO communication. Uncorrelated channels may not be therefore totally independent of each other.

[0098] In general, less correlation between the phase shifted transmissions may be obtained by modifying either transmitted or received signal(s). For example, transmitted signal(s) may be modified by slightly changing the power radiation pattern of the antenna (e.g., dipole, antenna patch, antenna lens, or antenna array), for example by changing weighting of the signals before feeding them to the antenna, in this case an antenna array. Alternatively, signals may be modified by changing their weighting at receiver 120. Example embodiments of the present disclosure enable to exploit the artificially generated uncorrelated radio channels, for example to improve transmission capacity (e.g., by use of MIMO) or robustness (e.g., by use of more robust modulation and / or error correction). Artificially phase shifted radio channels may be used to simultaneously transmit different data within the same frequency band from a single antenna. The signals may be therefore configured to overlap both in time and frequency.

[0099] FIG.1 illustrates an example of a system model for radio transmission. Transmitter (TX) 110 may be configured to transmit radio signals to receiver (RX) 120 over a radio channel 130. Radio channel 130 may be characterized by its impulse response ℎ(^), also referred to as channel impulse response. A frequency domain representation of impulse response ℎ(^)may be called the frequency response of radio channel 130. The frequency response may characterize how different frequency components of the transmitted signal are attenuated and / or phase shifted. Transmitter 110 may generate samples of the transmitted signal ^(^)based on input data, for example a sequence of bits. The input data may comprise payload data, for example user data or application data. Transmitter 110 may use any suitable modulation scheme to generate the (time-domain) samples ^(^)of the transmitted signal carrying the input data. The transmitted signal ^(^) may also include reference data, for example time or frequency domain pilot symbols. The reference data may comprise predetermined data, which is known to receiver 120. The reference data may be used by receiver 120 in reception of the signal, for example to perform channel estimation of radio channel 130. The channel estimate may be used to compensate for distortions of radio channel 130, caused for example by multipath propagation, that is, to equalize the received signal.

[0100] One example of a modulation scheme is orthogonal frequency division multiplexing (OFDM), where groups of bits may be mapped to complex-valued frequency domain modulation symbols carried on subcarriers of an OFDM symbol. A subcarrier of an OFDM symbol is an example of a resource element (RE) used to carry data. The transmitted symbols may be therefore originally defined in frequency domain and then translated to time domain (e.g., by an inverse fast Fourier transform, IFFT, operation). It is however possible to use any other suitable modulation scheme, such as for example single-carrier frequency division multiplexing (SC-FDMA), which is a version of OFDM. It is also possible to apply the disclosed example embodiments to single carrier communications. Transmitted modulation symbols may therefore comprise either frequency domain or time domain modulation symbols (e.g., real-valued or complex-valued symbols from a constellation).

[0101] The transmitted signal ^(^)may propagate through a multipath radio channel, which may be modelled by impulse response ℎ(^), where taps (^ = 1 … ^) represent ^ multipath components of radio channel 130. The received signal ^(^)may comprise a noisy version of the channel-transformed signal. Receiver 120 may be configured to demodulate the received signal ^(^) and determine an estimate ^(^) of the transmitted symbols, and ultimately the transmitted data (e.g., bits).

[0102] The transmission system may be configured for example based on the 5th generation (5G) digital cellular communication network, as defined by the 3rd Generation Partnership Project (3GPP). In one example, the transmission system may operate according to 3GPP 5G-NR (5G New Radio). It is however appreciated that example embodiments presented herein are not limited to devices configured to operate under this example system and the example embodiments may be applied in any radio transmitters, for example transmitters configured to operate in any present or future wireless or wired communication networks, or combinations thereof, for example other type of cellular networks, short-range wireless networks, broadcast or multicast networks, or the like. It is further noted that the example embodiments may be applied to uplink transmissions and / or downlink transmissions. Signals transmitted by a device, e.g., a mobile terminal or user equipment (UE), to an access node of a radio network may be referred to as uplink transmissions. Signals transmitted by the access node to the device may be referred to as downlink transmissions. An access node may be also referred to as an access point or a base station.

[0103] FIG.2 illustrates an example of multipath propagation. A signal may be transmitted form an antenna of transmitter 110 to a range of transmit directions as a plane wave. Examples of the different directions are illustrated by the arrows departing to different directions from antenna(s) 118 of transmitter 110. Each multipath component may have a unique propagation path and path length between antenna(s) of transmitter 110 and receiver 120. Diffractions, scatterings, and refractions in radio channel 130 may cause differently attenuated, delayed, and / or phase shifted versions of the signal to arrive at receiver 120. These different versions of the signal correspond to the multipath components of radio channel 130and each of them may be characterized by an amplitude and phase, represented by a single tap of impulse response ℎ(^). Should an impulse be transmitted, receiver 120 would observe a set of delayed signals corresponding to impulse response ℎ(^)of radio channel 130. Impulse response ℎ(^)may be also called a channel profile or a delay profile of radio channel 130.

[0104] FIG.3 illustrates an example of a delay profile of a multipath channel. In this example, twelve multipath components are received by receiver 120 with a delay spread of 5 μs and root mean square (RMS) delay spread (^^^^) of 1,03 μs, the relative power of the received multipath components ranging from 0 to −12 dB. In this example, duration of one symbol is 3,7 μs so some of the multipath components cause intrasymbol interference and some intersymbol interference.

[0105] FIG.4 illustrates an example embodiment of an apparatus 400, transmitter 110, or a component or a chipset thereof, configures to practice one or more example embodiments. Apparatus 400 may comprise at least one processor 402. The at least one processor 402 may comprise, for example, one or more of various processing devices or processor circuitry, such as for example a co- processor, a microprocessor, a controller, a digital signal processor (DSP), a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microcontroller unit (MCU), a hardware accelerator, a special-purpose computer chip, or the like.

[0106] Apparatus 400 may further comprise at least one memory 404. The at least one memory 404 may be configured to store, for example, computer program code or the like, for example operating system software and application software. The at least one memory 404 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination thereof. For example, the at least one memory 404 may be embodied as magnetic storage devices (such as hard disk drives, floppy disks, magnetic tapes, etc.), optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.).

[0107] Apparatus 400 may further comprise a communication interface 408 configured to enable apparatus 400 to transmit and / or receive information to / from other devices. In one example, apparatus 400 may use communication interface 408 to transmit or receive signaling information and / or data in accordance with at least one cellular communication protocol. Communication interface 408 may be configured to provide at least one wireless radio connection, such as for example a 3GPP mobile broadband connection (e.g., 3G, 4G, 5G, 6G). However, the communication interface may be configured to provide one or more other type of connections, for example a wireless local area network (WLAN) connection such as for example standardized by IEEE 802.11 series or Wi-Fi alliance; a short range wireless network connection such as for example a Bluetooth, NFC (near-field communication), or RFID connection; a satellite access network; a wired connection such as for example a local area network (LAN) connection, a universal serial bus (USB) connection or an optical network connection, or the like; or a wired Internet connection. Communication interface 408 may comprise, or be configured to be coupled to, an antenna or a plurality of antennas to transmit and / or receive radio frequency signals. One or more of the various types of connections may be also implemented as separate communication interfaces, which may be coupled or configured to be coupled to an antenna or a plurality of antennas.

[0108] Apparatus 400 may further comprise a user interface (not shown) comprising an input device and / or an output device. The input device may take various forms such a keyboard, a touch screen, or one or more embedded control buttons. The output device may for example comprise a display, a speaker, a vibration motor, or the like.

[0109] When apparatus 400 is configured to implement some functionality, some component and / or components of apparatus 400, such as for example the at least one processor 402 and / or the at least one memory 404, may be configured to implement this functionality. Furthermore, when the at least one processor 402 is configured to implement some functionality, this functionality may be implemented using program code 406 comprised, for example, in the at least one memory 404. Program core 406 is provided an example of instructions that, when executed by processor(s), cause apparatus 400 to perform the functionality described herein.

[0110] The functionality described herein may be performed, at least in part, by one or more computer program product components such as for example software components. According to an embodiment, the apparatus comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code when executed to execute the embodiments of the operations and functionality described. A computer program, a computer program product, or a (non-transitory) computer-readable medium may therefore comprise instructions for causing, when executed, apparatus 400 to perform the method(s) described herein. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), application- specific Integrated Circuits (ASICs), application-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), Graphics Processing Units (GPUs).

[0111] Apparatus 400 comprises means for performing at least one method described herein. In one example, the means comprises the at least one processor 402, the at least one memory 404 including program code 406 configured to, when executed by the at least one processor, cause the apparatus 400 to perform the method. Apparatus 400 may for example comprise means for generating, transmitting, and / or receiving wireless communication signals, for example modulation circuitry, demodulation circuitry, radio frequency (RF) circuitry, or the like. The circuitry(ies) may be coupled to, or configured to be coupled to, one or more antennas to transmit and / or receive the wireless communication signals over an air interface. The antenna(s) may be implemented as part of apparatus 400 or they may be located external to apparatus 400.

[0112] Apparatus 400 may comprise a computing device such as for example an access point, a base station, user equipment, a mobile phone, a smartphone, a tablet computer, a laptop, an internet of things (IoT) device, or the like. Examples of IoT devices include, but are not limited to, consumer electronics, wearables, sensors, and smart home appliances. In one example, apparatus 400 may comprise a vehicle such as for example a car. Although apparatus 400 is illustrated as a singledevice it is appreciated that, wherever applicable, functions of apparatus 400 may be distributed to a plurality of devices.

[0113] FIG. 5 illustrates an example of combination of electric field components at a receiver. In the example of FIG.3, any of the twelve multipath components may actually include several multipath components (cf. E1, E2), resulting in the respective components illustrated in FIG.3. This may happen when different propagation paths have exactly the same path length or when the sampling rate or frequency of receiver 120 is not high enough for separation of the components. As illustrated in FIG.5, this results in observing the sum vector of the electric fields caused by the different multipath components (E1, E2), e.g., vectors received via different paths having the same time delay. Combination of the multipath components results in the sum vector E having a certain amplitude and phase. Sum vector E therefore represents the resultant amplitude and phase of multipath components E1, E2 (which individually have certain amplitudes and phases) received substantially at the same time. When the components are received over a single channel, it may not be generally possible to separate the different paths (delay components) from the resultant vector, because it may not be known which part of the resultant vector belongs to which path (amplitude and phase). The resultant vector E may be therefore observed by receiver 120 as one component (tap) of impulse response ℎ(^), being in the form of a complex value such as ^ + ^^, where ^ and ^ are real numbers (^, ^ ∈ ℝ) and ^ is the imaginary unit, and from which the amplitude and phase can be calculated. Each time moment of the impulse response is a separate component and the whole channel impulse response includes all components received at different time moments.

[0114] FIG.6 illustrates an example of combination of multipath components at a receiver. In this example, a first vector ^ + ^^ (^, ^ ∈ ℝ) may be transmitted from antenna 118 using a first phase (Phase 1) and a second vector ^ + ^^ (^, ^ ∈ ℝ) may be transmitted from antenna 118 using a second (different) phase (Phase 2). Both of these two vectors may be transmitted at same direction(s) from antenna 118. However, due to the multipath characteristics of radio channel 130, receiver 120 may receive both vectors, included in the received signal ^(^). The first vector may be received as distorted version ^′ + ^^′ of the first vector. The second vectormay be received as distorted version ^′ + ^^′ of the second vector. If transmitter 110 transmits the vectors to different directions, different complex values (resultant vectors) are received at different time moments including 1 − ^ multipath components (complex values). Each complex value ^′ + ^^′ at reception (or ^ + ^^ at transmitter 110) has amplitude ^^^^(^′^+and phase ^′⁄ ^′ . Depending on the used radio access technology (RAT), different time moments (delay components) can be separated as own receptions, or they will be calculated together inside a certain time window.

[0115] In general, transmitter 110 may be configured to transmit complex values ^^+ ^^^at ^ different directions, where ^ = 1 … ^ . Each direction, for example ^^+ ^^^can be actually defined in multiple ways when considering amplitude and phase, as provided in the following example: - Amplitude: The complex values can be selected in multiple ways, still having the same amplitude, e.g., ^^= 4 and ^^= 1 or ^^= 1 and ^^= 4 , both cases- Phase: if ^^ / ^^and ^^ / ^^have the above different values, the phases are different as ^ / ^ = 1 / 4 and ^ / ^ = 1 / 4.

[0116] In case of two transmit directions (^ = 2) , if two signals are transmitted with a phase difference that is constant to each transmit direction ^. (e.g., ^^+ ^^^and ^^+ ^^^and ^^+ ^^^and ^^+ ^^^), the phase difference is constant also at receptionand ^′^+ ^^′^and ^′^+ ^^′^). Therefore, if two signals are transmitted at the same time (e.g., ^ + ^^ and ^ + ^^) and the complex and imaginary parts of the signals are selected such that they have the same amplitude but different phase, and even of this were done to multiple (e.g., all) directions of transmission, the result at reception at different time moments is vector ^ + ^^ = ( ^′ + ^^′) + (^′ + ^^′) , which includes components of both transmissions ^ + ^^ and ^ + ^^ . Using the information of both transmissions having the same amplitude to each direction, and a constant phase difference at each direction, receiver 120 may split vector ^ + ^^ to components both having the same amplitude but different (known) phase and represent those as ^′ + ^^′ and ^^+ ^^^. By separately estimating each channel, receiver 120 may equalize both received components to recover the transmitted signals ^ + ^^ and ^ + ^^.

[0117] In FIG.6, received vector ^ + ^^ is illustrated as split into two vectors ^′ + ^^′ and ^^+ ^^^. This corresponds to transmission of two plane waves in two different phases and reception of these in two different phases, the resulting vector including same reflections, diffractions, etc. This enables receiver 120 to detect the phases separately. It also provides the possibility to generate the necessary phase difference to generate mutually independent channels, even in line-of-sight (LOS) conditions where the direct propagation (LOS) component is dominant and reflected or diffracted components are weak enough not to cause any significant distortion. Transmitter 110 may be therefore configured to transmit the signals in LOS or NLOS conditions with respect to receiver 120.

[0118] FIG.7 illustrates an example of a transmitter configured to cause a phase shift between transmitted signals. As described above, different radio signals (own channels) can be transmitted from a single antenna, for example by having the same amplitude, but a constant phase difference, in each transmit direction. Under these conditions, different radio signals have similar multipath propagation behaviour, and the multipath components experience similar impacts of reflections, etc. Because the amplitude is the same and the phase difference differentiates the transmitted plane waves, this results in plane waves transmitted and received just in different phase.

[0119] At receiver 120, different radio signals / plane waves are received as a resultant vector but the unique transmissions can be detected, since the constant phase difference is known. In case of two transmitted signals, this results in two (or generally ^ , if ^ phase shifts) uncorrelated channels with different fast fading conditions. These uncorrelated channels can be used for transmitting different data symbols, for example for the purpose of multiple-input multiple output (MIMO) communication.

[0120] Transmitter 110 may comprise transmit (TX) circuitry 112. TX circuitry 112 may comprise signal generation circuitry 114, e.g., baseband circuitry, configured to transform input data (e.g., bits) to complex-valued (baseband) signals (^^(^), ^^(^)), each comprising data symbols generated based on respective input data according to a modulation scheme. Data symbols may be also referred to as modulation symbols or constellation symbols. The data symbols may be complex-valued, i.e., comprising data symbols having non-zero real and imaginary parts. TX circuitry 112 may comprise radio frequency (RF) circuitry for upconverting the baseband signals to a radio frequency. In modulation constellations (e.g., QAM) different complex values refer to different data symbols. These complex values may be different for different data channels (cf., MIMO N x N). Signal generation circuitry 114 may comprise a weighting unit, which may be configured to cause the phase shift between the signals. Assuming the weighting unit and antenna 118 having no impact to the relative phase of the signals, the resulting signals transmitted to the radio propagation channel comprise the same complex values as in the constellation and causing unique radio transmissions with phase shifts. The signals may be separately fed to antenna 118, as illustrated in FIG.7, or combined within signal generation circuitry 114 and fed to antenna 118 as a combined signal. Signal generation circuitry 114 may be configured to transmit data, signal(s), or indication(s) to receiver 120 via antenna 118. In general, transmitter 110 may be configured to transmit data, signal(s), or indication(s) to receiver 120.

[0121] Note that the input data for each signal may be different and therefore the signals may comprise different (complex-valued) data symbols. For example, signal generation circuitry 114 may receive first input data and generate a first signal (^^(^)) based on the first input data. Signal generation circuitry 114 may receive second input data and generate a second signal (^^(^)) based on the second input data. The second input data may be different from the first input data. The data, and thereby also the generated signals, may be however somewhat correlated, for example by application of a forward error correction (FEC) code over the data carried by the different signals. For example, the signals may comprise multiple- input multiple output (MIMO) coded data symbols. This enables to exploit the artificially generated uncorrelated propagation channels for enhancing transmission capacity.

[0122] Signal generation circuitry 114 may be configured to apply a phase shift 116 to one of the signals, in this example ^^(^), to generate a predetermined phase shift between the signals. Phase shift 116 may be applied subsequent to generation of the complex-valued data symbols. Alternatively, phase shift 116 may be implemented by using phase-shifted constellations for generating data symbols fordifferent signals, for example as described with reference to FIG. 9 and FIG. 10. Signal generation circuitry 114 may be configured to feed antenna 118 to cause transmission of the signals.

[0123] Alternatively, antenna 118 may be configured to at least partially cause the phase shift between the signals. Therefore, applying phase shift 116 by signal generation circuitry 114 may be optional. Since the phase shifting does not change amplitudes of the signals, the signals may be transmitted with same or substantially same power (e.g., not considering temporary variations caused by the different input data).

[0124] A single antenna may be configured to cause the predetermined phase shift between the signals. For example, a single patch antenna may be fed at different positions to generate different phase shifts for the signals. It is further noted that an antenna may comprise an antenna array. This provides the benefit of enabling radiation pattern of the antenna to be adjusted, for example to cause a desired, possibly time-variant, radiation pattern for a particular signal. If antenna 118 comprises an antenna array, signal generation circuitry 114 may be configured to feed antenna elements (e.g., each antenna element) of antenna 118 with signals ^^(^)and ^^(^). Antenna 118 may be for example configured to direct the signals carrying different data symbols to substantially same direction(s). This is in contrast to beam steering applications, where signals targeted for different users are transmitted to different directions. In example embodiments of the present disclosure, the power radiation patterns for the signals may be substantially same, for example identical or partially overlapping. For example, the main lobes of the power radiation patters may be at least partially overlapping. Applying slightly different power radiation patterns for the signals, while the power radiations being still mostly overlapping, may be used to further reduce the correlation the radio channels for the different signals, as will be further described with reference to FIG.12 and FIG.13. It is also noted that even though some example embodiments are described using two signals and a phase difference between them as an example, the example embodiments may be generalized to transmission of multiple signals with respective phase shifts. For example, the first signal may be transmitted without a phase shift. The second signal may be transmitted with the predeterminedphase shift to the first signal. A third signal may be transmitted with the predetermined phase shift to the second signal, etc.

[0125] When antenna 118 is an antenna array, the signals (e.g., ^^(^), ^^(^)) may be fed to antenna 118 but weighted such that each signal is radiated from a different subarray of antenna 118, as will be further described below. The subarrays may be configured (e.g., by means of different weighting) to cause the phase shift between the signals to be different in different transmit directions. Antenna 118 may be for example antenna array 1706A of FIG.18.

[0126] By application of the phase shift, transmitter 110 is configured to generate artificially phase shifted signals, which may be observed by receiver 120 as uncorrelated propagation channels. This enables to generate multiple uncorrelated transmission channels also in LOS environment. This enables use of MIMO techniques also in LOS channels, where use of MIMO may otherwise require use of orthogonal polarizations. This may be beneficial for example at higher frequencies (e.g., with 5G, 5G Advanced, or 6G), where the network topology may be such that antennas of access nodes and terminals (e.g., user equipment) may be at LOS or obstructed LOS with respect to each other. Obstructed LOS may refer to a situation where a body part (e.g., head) of a user obstructs an otherwise LOS path. It is however noted that example embodiments of the present disclosure are applicable also in non-LOS (NLOS) environment.

[0127] Creating uncorrelated channels by use of orthogonal polarizations or by causing a phase shift by placing antennas at a sufficient distance may cause Rayleigh fading conditions at reception in NLOS conditions. Applying a sufficient distance between antennas causes fading dips in the frequency response of radio channel 130 to occur at different frequencies, thereby providing uncorrelated channels. In LOS conditions, dominance of the direct component cause the channel to be Rician fading rather than Rayleigh fading, and signals transmitted from different antennas generally arrive at receiver 120 with substantially same amplitudes, following each other closely. This is an example of a correlated channel.

[0128] As explained above, when adjusting power and / or phase of the signals at transmitter 110, it is possible to create uncorrelated channels both in LOS andNLOS conditions. In this case, received signal levels vary between maximum and minimum levels and changes in the received signal levels are different in LOS / NLOS conditions. In NLOS conditions, different frequencies behave differently and fast fading is according to Rayleigh distribution. In LOS conditions, the received signal strengths for the phase shifted channel may be similar at different frequencies. Therefore, in LOS conditions the created uncorrelated channel may be similar at different frequencies, but still sufficiently different from the non-phase shifted channel.

[0129] FIG.8 illustrates an example of a constant phase shift between signals transmitted at different directions. As described above, the predetermined phase shift may be constant for a range of transmit directions (transmit angles). This enables to preserve the same phase shift, when the different signals arrive at receiver 120 via certain path of radio channel 130. Separation of different signals at receiver 120 is thereby simplified, as the phase shift is preserved within each multipath component, even if the relative phases of different multipath components were not preserved. In the example of FIG.8, the phase shift is constant 90° for all transmit directions (φ = 0°…360°) of omnidirectional antenna(s) of transmitter 110. Other values of the phase shift are also possible, including, but not limited to, 60°, 45 °, or 30°.

[0130] It is however possible that the transmit directions are limited to particular range (e.g., φ = 0°…120°, φ = 120…240°, or φ = 240…360°), for example if a transmission site is divided to multiple sectors. The phase shift may be therefore constant within a corresponding range of transmit angles. A constant phase shift may be also configured such that absolute phases of the different signals are time-variant, but the relative shift between the signals is constant.

[0131] Alternatively, or additionally, the phase shift between the signals may be time-variant. For example, signal generation circuitry 114 and / or antenna 118 may be configured to cause different phase shifts between the signals at different time instants. Transmitter 110 may be therefore configured with multiple phase shifts, which may be changed as a function of time, and therefore transmitter 110 may apply different phase shifts at different time instants. The phase shift may be alternatively rotated over time. Changing the phase shift provides the benefit ofproviding even less correlation between the channels, because the way the uncorrelated propagation channels are generated changes over time. The phase shift may be relative to phase of the RF carrier signals.

[0132] Referring back to FIG. 7, the different signals may be configured to carry N x N MIMO coded data (N TX / N RX). In case of 2 x 2 MIMO, transmitter 110 may be configured to transmit different complex-valued modulation symbols at both channels (e.g., one signal as ^^(^) and the other as ^^(^)). A complex- valued modulation symbol to be transmitted is then effectively multiplied by a complex number associated with the respective phase shift. This results in the different transmissions being at different phases at reception, for example one signal being at its maximum and another signal being at its minimum. Since the different signals may have their own reference symbols (e.g., pilots), receiver 120 may obtain estimates of the transmitted modulation symbols by equalizing the received signal based on the signal-specific reference symbols. Any suitable phase shift can be therefore used, as the respective uncorrelated channel may be estimated based on the signal-specific reference symbols. For example, if a sufficient phase shift is 30 degrees, it is possible to configure twelve different channels, e.g., for 12 x 12 MIMO transmission.

[0133] FIG.9 illustrates an example of generating phase-shifted signals using phase-shifted QPSK constellations. As noted above, phase shift between the transmitted signal may be obtained by feeding transmit antenna 118 at different feeding locations, applying a phase-shift for the signals prior to feeding antenna 118, or by generating the signals using phase-shifted constellations. In the example of FIG.9, a first constellation comprises four constellation points according to the QPSK modulation scheme. Transmitted data symbols may be selected from the complex-valued constellation points based on the input data. In this example, each data symbols is configured to carry two bits. The four constellation points are defined by different combinations of the real part and the imaginary part, in this example{^ + ^^, −^ + ^^, −^ − ^^, ^ − ^^}. In this example, ^ is equal to ^.

[0134] A second constellation may be formed by phase shifting (rotating) the first constellation such that amplitudes of the constellation points are not changed, but their phases are shifted by the same amount. The second constellation maytherefore comprise points{^ + ^^, −^ + ^^, −^ − ^^, ^ − ^^}. Points of the first and second constellations satisfy the conditions ^^+ ^^= ^^+ ^^(same amplitude) and ^ / ^ ≠ ^ / ^ (different phase).

[0135] FIG.10 illustrates an example of generating phase-shifted signals using phase-shifted 16-QAM constellations. In this example, the first constellation comprises sixteen constellation points according to the 16-QAM modulation scheme. In this example, each data symbols is configured to carry four bits. The second constellation comprises corresponding phase rotated constellation points. It is noted that the above conditions of 1) same amplitude and 2) different phase are satisfied within three subsets of the constellation points illustrated with the black, white, and dotted constellation points. If the transmitted data symbols are selected such that data symbols transmitted simultaneously have the same amplitude (but different phase due to rotation of the constellation), receiver 120 is enabled to separate the received symbols. Since the input data (cf. first and second input data of FIG.7) to signal generation circuitry 114 may comprise any bit sequences, the simultaneously transmitted data symbols, which may be selected from the two constellations based on the input data, may generally have different amplitudes. Therefore, signal generation circuitry 114 may be configured to adjust an order of transmission of the data symbols such that simultaneously transmitted data symbols have the same amplitude. This enables separation of the different signals at receiver 120. Transmitter 110 may be configured to transmit an indication of the order of transmission of the different complex-valued data symbols to receiver 120. This enables reordering the received data symbols at receiver 120.

[0136] FIG.11 illustrates an example of signalling phase shift(s) between transmitter and receiver.

[0137] At operation 1101, transmitter 110 may transmit an indication of the phase shift(s) to receiver 120. This indication, as well as the indication of the order of transmission of the different complex-valued data symbols, may be transmitted without applying the phase shift by transmitter 110. For example, the indication(s) may be included in a single signal transmitted from antenna 118, i.e., without simultaneous transmission of another (phase-shifted) signal. Alternatively, theindication(s) may be transmitted by applying a phase shift previously indicated to receiver 120 or a default phase shift preconfigured at receiver 120.

[0138] The indication of phase shift (e.g., a message) may comprise an indication of a single phase shift value, which may be applicable to subsequent signals, for example until transmitter 110 signals another value of the phase shift to receiver 120. Alternatively, transmitter 110 may transmit an indication of a plurality of phase shifts. Transmitter 110 may also transmit a schedule for applying the indicated phase shifts by receiver 120. In general, transmitter 110 may be configured to transmit indication(s) of different phase shifts configured to be applied by transmitter 110 at different time instants.

[0139] At operation 1102, transmitter 110 may transmit a plurality of signals to receiver 120. Transmitter 110 may apply the phase shift indicated at operation 1101 when transmitting the signals. For example, as described above, signal generation circuitry 114 may feed antenna 118 with the signals and signal generation circuitry 114 and / or antenna 118 may cause the indicated phase shift between the signals, when transmitted from antenna 118. The different signals may carry different (complex-valued) data symbols. Therefore, applying the phase shift(s) to artificially generate uncorrelated transmission channels provides the benefit of enabling to increase transmission capacity.

[0140] The transmitted signals may comprise reference (modulation) symbols configured to enable receiver 120 to perform channel estimation for the different signals received via the uncorrelated channels. The reference symbols of different signals may be mutually orthogonal, for example located at different frequencies (e.g., subcarriers in an OFDM system) or transmitted at different time instants. For example, if a reference symbol is transmitted on a first subcarrier of a first signal, the corresponding subcarrier may be an empty subcarrier in a second (phase- shifted) signal. If a reference symbol is transmitted on a second subcarrier of the second signal, the corresponding subcarrier may not be used for transmission in the first signal (empty subcarrier). Alternatively, other means for enabling separate channel estimation for the uncorrelated channels may be used, such as for example transmission of the sum and difference of the reference symbols, for example at alternating subcarriers of an OFDM symbol.

[0141] At operation 1103, receiver 120 may apply the indicated phase shift in reception of the signals. For example, receiver 120 may apply the indicated phase shift to separate the signals and to receive the data from each phase. It is however noted that even though the phase shift is in this example signalled to receiver 120, receiver 120 may be alternatively preconfigured with the phase shift(s). Receiver 120 may be for example configured with a plurality of (e.g., two) receivers, for example multiple RF / baseband reception paths, for receiving the different phases.

[0142] FIG.12 illustrates an example of different widths of main lobes of power radiation patterns of two signals transmitted with a phase shift. Antenna(s) 118 may be configured to cause slightly different power radiation patterns for the signals. For example, a first power radiation pattern 1201 may be configured for a first signal and a second power radiation pattern 1202 may be configured for a second signal. Again, the first and second signals may be configured to carry different (complex-valued) data symbols and they may be transmitted with the phase shift. First power radiation pattern 1201 and second power radiation pattern 1202 may be configured to direct the signals at (substantially) same directions. The main lobe of first power radiation pattern 1201 may be however wider than the main lobe of second power radiation pattern 1202 (width ^^> ^^). Widths of the main lobes of the power radiation patterns may be therefore different. For example, the main lobe of first power radiation pattern 1201 may be at least 10 % wider than the higher than the main lobe of second power radiation pattern 1202. Width of the main lobes may be defined for example by the widest points of the respective power radiation pattern, where the signal power is above a certain level. For example, the half-power beam width (HPBW) may be used as the width of the main lobe. HPBW may indicate an angular width (e.g., in degrees) of the main lobe at half-power points, i.e., points at which the signal power is half of its peak value. The main lobes of power radiation patterns 1201 and 1202 may be overlapping. For example, at least a predetermined percentage (e.g., 95 %, 90 %, 85 %, or 80 %) of the wider main lobe may be overlapping with the narrower main lobe.

[0143] FIG.13 illustrates an example of different directions of main lobes of power radiation patterns of two signals transmitted with a phase shift. First power radiation pattern 1201 may be again configured for the first signal and second powerradiation pattern 1202 may be configured for the second signal. The first and second power radiation patters 1201, 1202 may be configured to direct signals to same directions because they are overlapping. the main lobe of first power radiation pattern 1201 may be however configured to point at a first direction (^^) and the main lobe of second power radiation pattern 1202 may be configured to point at a second (slightly different) direction (^^). Main lobes of the power radiation patterns for the different signals may be therefore configured to point at different directions. For example, the angular difference in the directions may be between 5 to 20 degrees. Widths of the main lobes may be equal or one of the main lobes may be wider than the other, similar to FIG.10. Power radiation patterns 1201 and 1202 may be however still configured to overlap. For example, at least a predetermined percentage (e.g., 95 %, 90 %, 85 %, or 80 %) of the main lobes of power radiations patterns may be overlapping.

[0144] Examples of slightly different power radiation patterns were described with reference to FIG. 12 and FIG. 13. When used in combination with phase shifted transmission of signals, applying slightly different power radiation patterns further reduces the correlation between the phase shifted channels. Note that even though power first and second power radiation patterns 1201, 1202 are different, the phase shift between the signals may still be constant for different transmit directions, e.g., for at least a range of φ .

[0145] FIG.14 illustrates an example of a method for transmitting radio signals.

[0146] At 1401, the method may comprise causing a predetermined phase shift between a plurality of signals transmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, and wherein the antenna is configured to direct the plurality of signals to substantially same direction.

[0147] Further features of the methods directly result from the functionalities and parameters of the transmitter 110, receiver 120, or in general apparatus 400, as described in the appended claims and throughout the specification, and are therefore not repeated here. Different variations of the methods may be also applied, as described in connection with the various example embodiments.

[0148] FIG.15 illustrates an example of a transmitter configured to cause a phase shift between signals transmitted from different antennas. Different radio signals, e.g., separate data channels configured to carry different data, can be transmitted from different antennas. The antennas may be configured to cause the different phase shift between the signals in different transmit directions.

[0149] Similar to FIG.7, transmitter 110 may comprise transmit (TX) circuitry 112. TX circuitry 112 may comprise signal generation circuitry 114, e.g., baseband circuitry, configured to transform input data (e.g., bits) to complex-valued signals ^^(^), ^^(^), which may comprise baseband signals. Each of these signals may comprise data symbols generated based on respective input data, e.g., first and second input data, for example according to a modulation scheme. The first and second input data may comprise different binary data. The data symbols may be complex-valued, e.g., comprising data symbols having non-zero real and imaginary parts. TX circuitry 112 may further comprise radio frequency (RF) circuitry for upconverting signals ^^(^) , ^^(^) to a radio frequency. The signals may be configured to overlap in time and frequency, for example when transmitted from antennas 118A, 118B. The RF circuitry may be located at any suitable position at transmitter 110.

[0150] Transmitter 110 may comprise antennas 118A, 118B. The antennas may be separate such that each of the antennas may be configured to be fed by one of the signals. For example, first antenna 118A may be configured to be fed with a first signal ^^(^) and second antenna 118B may be configured to be fed with a second signal ^^(^), which is different from the first signal. The signals may be configured to carry separate data streams, for example spatially multiplexed data streams or MIMO encoded (e.g., space-time coded) data streams. In case of MIMO encoded data streams, data associated with a single signal (e.g., redundancy data) may be transmitted via multiple antennas. For example, TX circuitry 112 might be configured to receive a single data stream (e.g., the first input data and not the second input data) and to generate signals ^^(^)and ^^(^) based on MIMO coding of the first data stream. In both cases, signals ^^(^) and ^^(^) may be different, even though not necessarily totally independent. Signals ^^(^) and ^^(^) may therefore comprise different streams of complex-valued modulation symbols. Ingeneral, transmitter 110 may comprise a plurality of antennas arranged to be fed with respective signals.

[0151] Antennas 118A and 118B may be configured to cause a predetermined phase shift, e.g., phase difference, between signals transmitted from antennas 118A, 118B. The predetermined phase shift may be different for at least two transmit directions of the signals. For example, antennas 118A, 118B may be configured with dissimilar phase radiation patterns. The phase radiation patterns of antennas 118A, 118B may be different for at least two transmit directions of the signals. The predetermined phase shift may be therefore dependent on transmit direction of the signals and be different for at least two of the transmit directions.

[0152] Different phase radiation patterns may be obtained for example by different structural characteristics of antennas 118A, 118B. Antenna 118A may comprise a certain type of antenna, for example a dipole antenna, an antenna patch, or an antenna lens. Antenna 118B may comprise the same type of antenna as antenna 118A, or another type of antenna, for example any of a dipole antenna, an antenna patch, or an antenna lens. In one example, at least one of the antennas, or each antenna, may comprise an antenna array. An antenna array may be a phased antenna array. Elements of an antenna array may be therefore configured to transmit the same signal with different weights and / or delays. Optionally some weights of an antenna array may be configured to be zero for particular signal(s), for example in order to enable generation of subarrays within a single antenna array for transmission of different signals from respective subarrays, as will be further described with reference to FIG.18. TX circuitry 112 may comprise antenna control circuitry (not shown in FIG.15), which may be configured to control feeding of antennas 118A, 118B such that the predetermined phase shift between signals ^^(^), ^^(^) is caused when signals are transmitted from antennas 118A, 118B, as will be further described with reference to FIG.16.

[0153] As noted above, the predetermined phase shift may be different for different transmit directions of the signals. The predetermined phase shift may be therefore dependent on transmit direction of the signals. Antennas 118A, 118B may be however configured to direct the signals to substantially same transmit directions. For example, antennas 118A, 118B may be configured with substantiallyidentical power radiation patterns, e.g., such that at least the main lobes of the power radiation patterns overlap, for example as described with reference to FIG.12 or FIG.13.

[0154] Antennas 118A, 118B my be configured to transmit signals ^^(^), ^^(^)with same polarization. For example, antennas 118A and 118 may be linearly polarized with the same direction (e.g., both with horizontal polarization, both with vertical polarization, or both with same direction of circular polarization (left / right)). Alternatively, or additionally, antennas 118A, 118B may be configured to transmit signals ^^(^), ^^(^) with same orbital angular momentum (OAM). The distance between antennas 118A, 118B may be such that the spatial separation provided by the distance between the antennas does not cause correlation between different propagation channels to be sufficiently low. For example, the distance between antennas 118A, 118B may be less than half or less than quarter of a wavelength of signals ^^(^), ^^(^) at the radio frequency.

[0155] In general, the distance between antennas 118A, 118B may be lower than the coherence distance of the wireless radio channel. The coherence distance may be a distance corresponding to largest spatial separation between antennas over which the wireless channel response may be assumed constant or at least highly correlated. Due to the transmission direction dependent phase shift, signals ^^(^), ^^(^) may be subjected to uncorrelated or low-correlated propagation channels, thereby enabling decoding of both signals at a receiver, even if the signals were transmitted with same polarization or OAM, or from antennas located within the coherence distance from each other. It is however noted that to obtain even less correlated propagation channels, transmission with the transmission direction dependent phase shift may combined with transmitting the signals with different polarization or OAM, or from antennas located beyond the coherence distance from each other. The distance between antennas may be the distance between corresponding parts of the antennas, e.g., centre points of patch antennas. In case of antenna arrays, the distance between different antenna arrays may be the distance between closest antenna elements of the different antenna arrays.

[0156] FIG.16 illustrates an example of a transmitter configured to cause a phase shift between signals transmitted from different antenna arrays. In theexample of FIG. 16, antenna 118A comprises an antenna array having M antenna elements 118A-1 to 118A-M. Antenna 118A may comprise a phased antenna array or a subarray of an antenna array. An antenna element may be for example a dipole, patch, or lens. The number of antenna elements ^ ≥ 2, for example ^ = 4, ^ = 8, ^ = 16, or ^ = 64. Similarly, antenna 118B comprises an antenna array with N antenna elements 118A-1 to 118A-N, where ^ ≥ 2, for example ^ = 4, ^ = 8, ^ = 16, or ^ = 64. Antenna 118B may comprise a phased antenna array or a subarray of an antenna array. In one example, antenna arrays 118A, 118B have the same number of antenna elements (^ = ^), but antenna arrays 118A, 118B may also have a different number of elements. It is however possible that one of antennas 118A, 118B is an antenna array and the other antenna is another type of antenna, for example a dipole antenna, an antenna patch, or an antenna lens.

[0157] Different antenna arrays may be configured with independent antenna feeds, e.g., cables or conductors, for separately feeding the antenna arrays. Antenna elements of an antenna array may be fed with the same signal, but optionally weighted and / or delayed differently for different antenna elements. Antenna elements of an antenna array may therefore have a common antenna feed, e.g., cable or conductor, for collectively feeding antenna elements of the antenna array with the same signal. As noted above, some weights of the antenna elements may be set to zero for particular signal(s) to dedicate different subarrays of the antenna array to different signals. It is noted that example embodiments of the present disclosure enable transmission of multiple (e.g., MIMO coded) signals from multiple antennas without spatial separation between the antennas. Therefore, antennas 118A, 118B may be co-located, for example as different subarrays of an antenna array.

[0158] Signal generation circuitry 114 may be configured to feed antenna elements of each of the antennas 118A, 118B, in this example antenna arrays, with one of the signals. For example, antenna elements of antenna 118A may be fed with signal ^^(^). Antenna elements of antenna 118B may be fed with signal ^^(^). Antennas 118A, 118B may be therefore fed with respective signals ^^(^), ^^(^). It is however noted that example embodiments of the present disclosure may be extended to feeding more than two signals (e.g. three, four, …) to a respective number of antennas.

[0159] TX circuitry 112 may comprise antenna control circuitry 1602, which may be configured to control weights and / or delays associated with antenna elements of antennas 118A, 118B. For example, weighting unit 1604 may be configured to multiply signal ^^(^)with weight ^^^before it is fed to antenna element 118A-1. Similary, weighting unit 1604 may be configured to multiply signal ^^(^)with weight ^^^before it is fed to antenna element 118A-M. By applying complex-valued weightsto ^^^, weighting unit 1604 may be configured to control (e.g., modify) both amplitude and phase of signal ^^(^), when fed to different antenna elements 118A-1 to 118A-M. Similarly, weighting unit 1606 may be configured to multiply signal ^^(^)with weight ^^^before it is fed to antenna element 118B-1 and with weight ^^^before it is fed to antenna element 118A-N. By applying complex-valued weights ^^^to ^^^weighting unit 1604 may be configured to control (e.g., modify) both amplitude and phase of signal ^^(^), when fed to different antenna elements 118B-1 to 118B-N. Antenna control circuitry 1602, for example weighting unit 1604 and / or 1606, may comprise weighting circuitry configured to perform the weighting and / or delaying of signals ^^(^), ^^(^). The weighting may be for example implemented by complex-valued multiplication circuit(s). Antenna control circuitry 1602 may comprise any suitable number or configuration of weighting unit(s) for implementing the weighting.

[0160] Weights of weighting units 1602, 1604 may be determined such that phase radiation patterns of antennas 118A, 118B are dissimilar, e.g., configured to cause different phase shifts between signals ^^(^), ^^(^) in different transmit directions. Same power radiation pattern with dissimilar phase radiation patterns may be obtained by imposing a condition that the amplitude stays constant for different transmit directions, e.g., that the amplitudes of radiation patterns of antennas 118A, 118B are equal to each other at different transmit directions. For example, a certain beam of an antenna array may be associated with corresponding complex numbers (a + jb) in different directions (power radiation patterns) and one phasing. By keeping ^^+ ^^constant and altering values of ^ and ^ it is possible to create different phase radiation patterns with same power radiation pattern. In case of antenna arrays this may be designed such that phases are different in different transmit directions, as in the example of FIG. 19. For example, for fixedbeam antenna arrays (e.g., passive antennas) the desired weights may be calculated in advance during design phase of the system, for example based on the Butler matrix approach. Alternatively, dissimilar phase radiation patterns may be obtained by different antenna designs and determined during design phase of the antennas. In case of active antennas, antenna control circuitry 1604 may comprise a library of weights or a table of weights associated with different power and phase radiation patterns. Alternatively, antenna control circuitry 1602, or transmitter 110 in general, may be configured to calculate the weights on the fly after deployment of transmitter 110.

[0161] FIG.17 illustrates an example of two antenna arrays. An antenna array may comprise antenna elements, e.g., dipoles, patches, or lenses, arranged to form an array of elements (e.g., 4 x 4) configured with common antenna feeds (e.g. cables or connectors) enabling same signal to be fed to each antenna element. The signal may be however weighted differently for different antenna elements. Antenna elements of an antenna array may be located at substantially same distances from neighbouring antenna elements throughout the antenna array. An antenna array may be for example configured to be located underneath a single antenna radome. An antenna array may be divided into different subarrays such that when the antenna array is fed with different signals, for example signals carrying different data (e.g., different complex-valued data symbols), the weights of the antenna elements are configured such that different signals get transmitted from dedicated (groups of) antenna elements. By contrast, different antenna arrays may be configured with mutually independent antenna feeds, e.g., cables or conductors, for separately feeding the antenna arrays.

[0162] In the example of FIG.17, two antenna arrays form a 4 x 4 physical structure of patches 1704, for example under a single antenna radome 1702. Antenna array 1706A (2 x 4 patches) may be provided as antenna 118A and it may be fed with the first signal ^^(^), which may be weighted and / or delayed by weighting unit 1604 differently for different antenna elements of antenna array 1706A, for example in order to cause a desired power radiation pattern and / or phase radiation pattern for signal ^^(^). Antenna array 1706B (2 x 4 patches) may be provided as antenna 118B and it may be fed with the second signal ^^(^), whichmay be weighted and / or delayed differently for different antenna elements of subarray 1706B, for example to cause a desired power radiation pattern (e.g., identical with antenna array 1706A) and a different phase radiation pattern compared to antenna array 1706A. Antenna elements of an antenna array may therefore have a common antenna feed, e.g., cable or conductor, for collectively feeding antenna elements of the antenna array. In this example, antenna array 1706A is collectively fed by the first signal ^^(^), which is separately weighted and provided to the antenna elements via an eight-wire feed. At least one, or each, of antennas 118A, 118B may be an antenna array.

[0163] FIG. 18 illustrates an example of subarrays within an antenna array. Weighting unit 1604 may be configured to be fed with multiple signals (e.g., two signals ^^(^), ^^(^)). Similar to FIG.17, antenna elements 1704 of antenna array 1706A may be configured to be collectively fed with a single signal. Weighting unit 1604 may be configured output a combination of its input signals (e.g., ^^(^), ^^(^)) to each antenna element 1704 of antenna array 1706A. Weights of weighting unit 1604 may be however configured such that each signal gets transmitted from one subarray. A subarray may therefore comprise a group of antenna elements of an antenna array, where the weights of the group of elements are non-zero for one of a plurality of signals configured to be fed to the antenna array. Weights of the group of antenna elements may be equal to zero for other signal(s) of the plurality of signals.

[0164] For example, weighting unit 1604 may be configured to multiply signal ^^(^)with zero for antenna elements of subarray 1802 (dashed elements) such that subarray 1802 is dedicated to transmission of signal ^^(^). Weighting unit 1604 may be further configured to multiply signal ^^(^)with zero for antenna elements of subarray 1804 (dotted elements) such that subarray 1804 is dedicated to transmission of signal. ^^(^). This enables transmission of multiple phase-shifted signals via a single antenna array. The signals may be independent of each other, e.g., carry different data. Subarrays 1802 and 1804 may be configured with similar power radiation patterns but different phase radiation patterns. Different subarrays of an antenna array may be therefore configured to be used as antennas 118A, 118B.

[0165] At least one, or each, of antennas 118A, 118B may be an antenna array. Antennas 118A, 118B may be subarrays of same antenna array. Alternatively, antennas 118A, 118B may comprise separate antenna arrays.

[0166] FIG. 19 illustrates an example of phase radiation patterns with a direction dependent phase shift between signals. Angle ^ represents the horizontal transmit direction from transmitter 110. The first signal ^^(^), may be transmitted from antenna 118A (e.g., a dipole antenna, patch antenna, antenna lens, or antenna array) omnidirectionally with a phase radiation pattern indicated with the solid line. A second signal, ^^(^), may be transmitted from antenna 118B (e.g., another dipole antenna, patch antenna, antenna lens, or antenna array) omnidirectionally with a phase radiation pattern indicated with the dashed line. Note that the phase shift caused by antennas 118A, 118B between signals ^^(^)and ^^(^)is generally different for different transmit directions. There may be however some directions for which the antennas do not cause a phase shift between the signals.

[0167] Applying the transmit direction dependent phase shift with omnidirectional power radiation patterns provides the benefit of increasing angular diversity, because the signals may be transmitted in all horizontal directions with varying phase shift, resulting in less correlated propagation channels when reaching the receiver.

[0168] Alternatively, the transmit directions may be limited to particular range (e.g., φ = 0°…120°, φ = 120…240°, or φ = 240…360°), for example if a transmission site is divided to multiple sectors. The phase shift between the signals may be for example more than 20° for at least 30 % of the transmit directions. This provides the benefit of further reducing the correlation between different propagation channels.

[0169] The plurality of signals may be transmitted with beams, for example beams having a beam width in the range of 10° to 30°. For example, signal ^^(^)may be configured to be transmitted from antenna (array) 118A with a first beam. Signal ^^(^)may be configured to be transmitted from antenna (array) 118B with a second beam. The beams may be overlapping, e.g., configured to be transmitted to same transmit directions. The beams may be generated by directional antennas, such as for example antenna arrays. In general, omnidirectional antennas mayprovide good MIMO gain, but directional antennas may provide higher power gain. Due to the higher power gain, the signal-to-noise ratio (SNR) or signal-to- interference-plus-noise ratio (SINR), and thereby also the spectral efficiency (bits / s / Hz), may be improved by using directional antennas. The performance may be further improved by causing different phase shifts between the plurality of signals at different transmit directions (angular phase shift).

[0170] In general, a beam with a limited horizontal width may be generated with a horizontal array or subarray of N antenna elements. One antenna (sub)array may for example comprise eight elements. At 28 GHz frequency, corresponding to wavelength of 1 cm, the horizontal width of such (sub)array would be around 10 cm. The plurality of antennas may comprise multiple such subarrays arranged vertically on top of each other, for example with a vertical distance equal to half the wavelength between the subarrays. In case of eight horizontal antenna elements per subarray and aggregation of four to eight subarrays vertically, the size of the entire (physical) antenna array would be still below 10 cm x 10 cm (or 20 cm x 20 cm at maximum) and even lower at higher frequencies. The eight subarrays may be fed with respective signals (cf., ^^(^), ^^(^), …, ^^(^)). Each subarray may be configured to cause a different phase radiation pattern, and thereby different phase shifts between the signals at different transmit directions. Such a physical antenna array is applicable for example in a base station, for example for downlink transmission of the plurality of signals. At user equipment (UE) there may be less space for implementing such an antenna array. However, at even higher frequencies (e.g., 30 – 100 GHz) the size of such antenna array might be small enough and therefore example embodiments of the present disclosure may be applied also for uplink transmission. It is also possible to use antenna array(s) with a lower number of elements (e.g., four) thereby enabling implementation at UE also at lower frequencies. Alternatively, such antenna array may be used in fixed wireless access (FWA) applications or when coupled to vehicles, for example on the roof of a bus or tram, where the size of the antenna array is not that critical.

[0171] The antennas may be configured to cause the predetermined phase shift between the signals to be different at different time instants. For example, antenna control circuitry 1602 may be configured to control weights and / or delays of thesignals such that phase radiation patterns of the signals change from time to time, thereby causing the phase shift between the signals to vary not only between different transmit directions but also between different time instants (e.g., when considering a particular transmit direction). Antennas 118A, 118B may be therefore configured to cause the predetermined phase shift between signals ^^(^), ^^(^), the predetermined phase shift being different for different transmit directions, by applying different phase radiation patterns to the signals. It is however noted that in case of two signals, transmitter 110 may be configured to change the phase radiation pattern of one signal, while keeping the other phase radiation pattern constant, resulting in changing the mutual phase shift between the signals. Transmitter 110 may be therefore configured to apply different phase radiation patterns at different time instants to at least one of the signals.

[0172] The phase radiation pattern(s) may be changed between different time instants, for example according to a predetermined schedule. As the signals may include reference symbols (e.g. pilot symbols) whose transmitted value is known, the receiver may continue performing channel estimation as usual and receive the signals regardless of the changing phase radiation patterns. Changing the phase radiation pattern(s) enables to improve performance in flat fading radio channel conditions, where the received signal strengths from the different antennas may be correlated and strongly vary over time.

[0173] Transmitter 110 may be configured to transmit an indication of the phase shifts applied to the signals at the different time instants, an indication that the phase radiation pattern(s) have changed, or an indication of when the phase radiation pattern(s) are configured to be changed. Based on the indication receiver 120 may configure when to receive reference symbols and perform channel estimation. The indication may for example include identifiers of predetermined phase radiation patterns and an order of the predetermined phase radiation patterns for each of the signals. This may be beneficial for example when the phase radiation patterns are changed so rapidly that the receiver (e.g., a UE) does not have time to apply the reference symbols included in the signals. A predetermined phase radiation pattern may be associated with predetermined weights and / or delays of elements of an antenna array. Antenna control circuitry 1602 may be configured tochange the weights and / or delays, in order to switch from one predetermined phase radiation pattern to another.

[0174] It is further noted that a single antenna (cf., FIG.15) may be configured to be fed with different signals (e.g., ^^(^)and ^^(^)) such that the phase shift caused by antenna 118 is different for different transmit directions of the signals. For example, antenna 118 might be configured to cause phase radiation patterns similar to FIG. 19 when the signals are fed to antenna 118. For example, antenna 118 might comprise an antenna array preceded by weighting circuitry (e.g., weighting units 1604, 1606) configured to weight signals ^^(^)and ^^(^)differently, before being fed to antenna 118, which may be an antenna array. For example, different antenna elements of an antenna array may be configured to be fed with different signals (e.g., first element(s) of an antenna array being fed with signal ^^(^)and second elements of the antenna array being fed with signal ^^(^)).

[0175] Regarding the examples of FIG. 15 and FIG. 16, signal generation circuitry 114 may be configured to perform functionality similar to the example of FIG. 7. For example, signal generation circuitry may be configured to adjust the order of transmission of the different complex-valued data symbols to cause different complex-valued data symbols transmitted simultaneously to have the same amplitude. Furthermore, the power radiation patterns described with reference to FIG.12 and FIG.13 may be applied also in the examples of FIG.14 and FIG.15. For example, power radiation patterns 1201, 1202 may correspond to dissimilar phase radiation patterns such that the phase shift between signals transmitted from antennas 118A, 118B is different for at least two transmit directions of the signals. Furthermore, signals ^^(^), ^^(^)may comprise respective reference symbols configured to enable channel estimation of the signals by a receiver, as described above. The reference symbols may be mutually orthogonal between the signals. The reference symbols enable the receiver to separate the signals transmitted with the dissimilar phase radiation pattern, even if transmitted with same polarization or OAM mode, overlapping frequencies and time periods, and in substantially the same transmit directions. By application of the transmit direction dependent phase shift, transmitter 110 is configured to generate artificially phase shifted signals, which may be observed by receiver 120 as uncorrelated propagation channels.

[0176] FIG. 20 illustrates an example of a method for transmitting radio signals.

[0177] At 2001, the method may comprise feeding a plurality of antennas with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions.

[0178] At 2002, the method may comprise causing a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

[0179] Further features of the method directly result from the functionalities and parameters of the transmitter 110, receiver 120, or in general apparatus 400, as described in the appended claims and throughout the specification, and are therefore not repeated here. Different variations of the methods may be also applied, as described in connection with the various example embodiments.

[0180] Any range or device value given herein may be extended or altered without losing the effect sought. Also, any embodiment may be combined with another embodiment unless explicitly disallowed.

[0181] Although the subject matter has been described in language specific to structural features and / or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

[0182] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to ‘an’ item may refer to one or more of those items.

[0183] The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the embodimentsdescribed above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.

[0184] The term ‘comprising’ is used herein to mean including the method, blocks, or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0185] It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a description of the structure and use of example embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from scope of this specification.

Claims

CLAIMS 1. An apparatus, comprising: a plurality of antennas; signal generation circuitry configured to feed the plurality of antennas with a respective plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions and to cause a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

2. The apparatus according to claim 1, wherein at least one of the plurality of antennas comprises an antenna array.

3. The apparatus according to claim 1, wherein at least one of the plurality of antennas is a subarray of an antenna array, wherein the subarray comprises a group of antenna elements of the antenna array, wherein weights of the group of antenna elements are non-zero for one of a plurality of signals, and wherein weights of the group of antenna elements are equal to zero for other signals of the plurality of signals.

4. The apparatus according to claim 1, wherein the plurality of antennas comprise subarrays of same antenna array, wherein each of the subarrays comprises a group of antenna elements of the antenna array, wherein weights of the group of antenna elements are non-zero for one of a plurality of signals, and wherein weights of the group of antenna elements are equal to zero for other signals of the plurality of signals.

5. The apparatus according to any of claims 2 to 4, further comprising: antenna control circuitry configured to control weights and / or delays associated with antenna elements of the plurality of antennas to cause the predetermined phase shift between the plurality of signals.

6. The apparatus according to any of claims 2 to 4, wherein the signal generation circuitry is configured to feed antenna elements of each of the plurality of antennas with one of the plurality of signals.

7. The apparatus according to claim 1, wherein the signal generation circuitry is configured to feed each of the plurality of antennas with one of the plurality of signals.

8. The apparatus according to any of claims 1 to 7, wherein the predetermined phase shift between the plurality of signals is different at different time instants.

9. The apparatus according to any of claims 1 to 8, wherein the plurality of antennas are configured to cause the predetermined phase shift between the plurality of signals by applying different phase radiation patterns to at least one of the plurality of signals at different time instants.

10. The apparatus according to claim 1 or 9, wherein the plurality of antennas comprise at least one dipole antenna, at least one antenna patch, and / or at least one antenna lens.

11. The apparatus according to any of claims 1 to 10, wherein the plurality of signals are configured to be transmitted with same polarization.

12. The apparatus according to any of claims 1 to 11, wherein a distance between the plurality of antennas is less than half of a wavelength of the plurality of signals.

13. The apparatus according to any of claims 1 to 12, wherein the plurality of signals comprise multiple-input multiple-output (MIMO) coded data symbols.

14. The apparatus according to any of claims 1 to 13, wherein each of the plurality of signals is configured to carry different complex-valued data symbols.

15. The apparatus according to claim 14, wherein the signal generation circuitry is further configured to: adjust an order of transmission of the different complex-valued data symbols to cause the different complex-valued data symbols transmitted simultaneously to have same amplitude; and transmit an indication of the order of transmission of the different complex- valued data symbols to a receiver.

16. A method, comprising: feeding a plurality of antennas with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different data, wherein the plurality of antennas are configured to direct the plurality of signals to substantially same transmit directions; and causing a predetermined phase shift between the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

17. An apparatus, comprising: signal generation circuitry configured to feed an antenna with a plurality of signals, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, wherein the signal generation circuitry and / or the antenna is configured to cause a predetermined phase shift between the plurality of signals, wherein the antenna is configured to direct the plurality of signals to substantially same direction, wherein the antenna is an antenna array, wherein the signal generation circuitry is configured to feed antenna elements of the antenna array with the plurality of signals, and wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

18. The apparatus according to claim 17, wherein the antenna array comprises subarrays, wherein each of the subarrays comprises a group of antenna elements of the antenna array, wherein weights of the group of antenna elementsare non-zero for one of a plurality of signals, and wherein weights of the group of antenna elements are equal to zero for other signals of the plurality of signals.

19. A method, comprising: causing a predetermined phase shift between a plurality of signals transmitted from an antenna, wherein the plurality of signals are configured to overlap in time and frequency and to carry different complex-valued data symbols, wherein the antenna is configured to direct the plurality of signals to substantially same direction, wherein the antenna is an antenna array; and feeding antenna elements of the antenna array with the plurality of signals, wherein the predetermined phase shift is different for at least two transmit directions of the plurality of signals.

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