BEAM STEERING DEPENDENT IMPEDANCE MATCHING OF ARRAY ANTENNAS

According to an aspect, there is provided a radio frequency front end (202) for a beamforming transceiver (201) having an antenna array comprising a plurality of antenna elements. The radio frequency front end comprises, for each antenna element, at least two radio frequency beamforming branches (218, 219). Each of at least one of said at least two radio frequency beamforming branches comprises an electrically tunable phase shifting element (221, 231), first and second transmission/reception switches (223, 233), a low-noise amplifier (225, 235) for reception and a power amplifier (224, 234) for transmission. Moreover, each of at least one of said at least two radio frequency beamforming branches comprises an electrically switchable matching circuit (226, 236). The electrically switchable matching circuit comprises two or more matching circuit settings selectable via switching. Each of the two or more matching circuit settings is configured for providing impedance matching for an antenna element at one or more beam steering angles in transmission.

TECHNICAL FIELD

Various example embodiments relate to wireless communications.

BACKGROUND

5G New Radio (NR) defines a beam alignment procedure between a terminal device (or user equipment, UE) and an access node (gNodeB, gNB) for obtaining a transmission beam of the access node and a reception beam of the terminal device which are defined so as to maximize directional gain and minimize interference on other users in serving and neighbor cells. Said beamforming procedure is based solely on downlink measurements. As a consequence, said beamforming procedure fails to guarantee that optimal alignment of the transmission beam (or uplink beam) of the terminal device will always be aligned with the access node when configured with the same array settings (phase and power) as used for downlink. One of the reasons for this discrepancy is that the frequency dependent (and thus also steering angle dependent) impedances seen by the individual elements of a phased array in transmission and reception may differ from each other considerably. Thus, there is a need for a beam alignment solution which would be able to provide optimal beams for both uplink and downlink in an efficient manner.

BRIEF DESCRIPTION

According to an aspect, there is provided the subject matter of the independent claims. Embodiments are defined in the dependent claims. The scope of protection sought for various embodiments of the invention is set out by the independent claims.

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

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are only presented as examples. Although the specification may refer to “an”, “one”, or “some” embodiment(s) and/or example(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s) or example(s), or that a particular feature only applies to a single embodiment and/or example. Single features of different embodiments and/or examples may also be combined to provide other embodiments and/or examples.

Unless otherwise stated, the term “beam” as used in this application corresponds to the main beam (of an antenna array).

The example ofFIG.1shows a part of an exemplifying radio access network.

FIG.1shows user devices100and102configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB)104providing the cell (and possibly also one or more other cells). The cells may be equally called sectors, especially when multiple cells are associated with a single access node (e.g., in tri-sector or six-sector deployment). Each cell may define a coverage area or a service area of the access node. Each cell may be, for example, a macro cell or an indoor/outdoor small cell (a micro, femto, or a pico cell). The physical link from a user device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the user device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

The user device (also called UE, user equipment, user terminal, terminal device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

The user device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and/or touch screen computer, tablet, game console, notebook, and multimedia device. Each user device may comprise one or more antennas. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in (Industrial) Internet of Things ((I)IoT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The user device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user equipment (UE) just to mention but a few names or apparatuses.

5G enables using (massive) multiple input-multiple output ((m)MIMO) antennas (each of which may comprise multiple antenna elements), many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. A MIMO antenna (comprising a plurality of antenna elements) may be equally called a MIMO array antenna, a MIMO antenna array or a MIMO phased array (comprising a plurality of antennas or antenna elements). 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6 GHz, cmWave and mmWave, and also being integratable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6 GHz-cmWave, below 6 GHz-cmWave-mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

One key element necessary in overcoming high path and penetration losses of millimeter wavelengths and thus achieving high throughput broadband communications envisioned for 5G NR communication systems like the one shown inFIG.1is the use of beamforming techniques. Beamforming techniques employ an array antenna comprising a plurality of antenna elements, for example, in a rectangular or square configuration. By tuning the phase and/or amplitude of the signals fed to each antenna element, different antenna patterns may be produced due to the electromagnetic waves produced by the individual antenna elements interfering with each other constructively and destructively in different directions. Due to reciprocity, the same principle applies equally in reception. In particular, the radiation pattern of the antenna array may be tuned so that a narrow main beam of the radiation pattern is directed to different directions (e.g., different directions defined through azimuth and/or elevation angles). In other words, the electromagnetic waves may be focused in a desired direction in transmission and/or the electromagnetic waves may be received only from a desired direction in reception. In addition to the direction of the main lobe, the sidelobe levels and the nulls of the pattern may also be controlled.

In 5G NR, the access node is configured to serve one or more cells so that each cell is mapped to a set of Synchronization Signal Block (SSB) beams forming a grid of beams covering the cell. For the 5G New Radio Release 15, the beam alignment procedure between the terminal device (UE) and the access node (gNB) consists of three main phases.

In the first phase, the terminal device is assumed to be configured for broad beam reception while the access node is performing downlink (DL) SSB beam sweeping. The terminal device measures reference signal received power (RSRP) for all received SSB beams and reports back to the access node using same beam configuration as in reception, by selecting the random-access resources (RACH Group) which corresponds to the best SSB beam measured by the terminal device. The random-access resources are determined based on the information decoded by the terminal device, Master Information Block (MIB) and System Information Block 1 and 2 (SIB1 & SIB2), in correspondence with the best SSB beam.

In the second phase, the terminal device is assumed to be configured for broad beam reception while the access node is performing refined DL channel state information reference signal (CSI-RS) beam sweeping. The terminal device measures RSRP (or channel quality indicator (CQI) and/or rank indicator (RI)) for all CSI-RS or SSB beams received and reports the best beam identifier (ID) back to the access node using same beam configuration as in reception.

In the third phase, the access node transmits with the best beam found in the second phase and the terminal device is sweeping refined reception beam settings for identifying the best narrow reception beam.

At the end of the third phase, alignment between the transmission beam of the access node and the reception beam of the terminal device is obtained for maximized directional gain and minimum interference on other users in serving and neighbor cells. It should be noted that the beam alignment procedure described above is based on downlink measurements only and, as a consequence, it cannot be guaranteed that the uplink beam of the terminal device will always be aligned with the access node, when configured with the same antenna array settings (phase and power) as used for downlink.

The uplink beam pair can be individually aligned by configuring the terminal device to transmit periodically SRS's when the uplink beam pair needs to the re-aligned. However, this is a very resource intensive procedure and, thus, not an ideal solution to the misalignment problem.

Beam correspondence might be true for the access node but cannot be guaranteed at the terminal device, as described above. Indeed, the freedom in designing antennas for access nodes is considerable compared to the freedom in designing antennas for terminal devices. Moreover, terminal devices have a large number of constraints such as supporting a very large bandwidth for enabling world-wide coverage. Further, terminal devices are oftentimes implemented with cheaper embedded components compared to access node which may lead to compromised tolerance levels and considerable impedance variations across different operational settings.

While careful design and characterization aims at securing uplink/downlink beam correspondence, there are more factors which may impact terminal device uplink/downlink beam correspondence dynamically. For example, the impedance of the individual antenna elements of an antenna array (i.e., the impedance as “seen” by the individual antenna elements) will undergo significant changes over frequency as the main beam of the antenna array is steered in different angular directions. This is mostly due to the relative high coupling between the individual antenna elements of the antenna array, which is a fundamental behavior of electrically small impedance broadband phase-controlled arrays used in 5G NR millimeter-wave devices. Power amplifiers (PA's) are especially sensitive to these changes in impedance. Since each antenna element in the antenna array is typically connected directly to a PA, each PA will behave differently which can result in an angular misalignment of the main beam for uplink, reduced PA efficiency, worse PA linearity and increased Spurious Emission.

The impact of impedance mismatch at the PA output port (i.e., in transmission) is significantly different to that on the low noise amplifier (LNA) input port (i.e., in reception), which in turn will affect the transmission and reception beam differently for the same load mismatch. In general, the transmission beam is expected to be more affected than the reception beam. Furthermore, if the transmission beam does not correspond to the reception beam, power is not optimally received at the access node.

The sensitivity of the antenna array to the beam non-correspondence depends on the size of the antenna array (i.e., the number of antenna elements in the antenna array). Indeed, a large antenna array corresponds, in general, to a narrow beam and increased sensitivity to misalignment with the beam of the access node. As such, the problem is aggravated as frequency increases due to the beams getting narrower (with the associated increased demand for high beam direction accuracy) for sustained link budget, eventually affecting throughput.

Moreover, the coupling between the individual antenna elements depends on the angular direction of the main beam. Namely, the relative phase difference between the individual antenna element feed ports (induced by phase shifters) is increased when the angular direction of the main radiation beam is steered away from the broadside direction and said relative phase difference will affect coupling between each antenna element feed port as a function of the required angular beam steering direction and thereby also affect the impedance seen by the individual power amplifiers (i.e., the effective antenna impedance or the antenna impedance after matching). Broadside direction is defined as a direction perpendicular to the axis or plane of the antenna array. To radiate perpendicularly, the antenna elements of the antenna array typically must be fed in phase. Broadside direction may be equal to a boresight direction of the antenna array when all of the antenna elements of the antenna array (or specifically, a broadside array) are fed in-phase (e.g., 0° phase shift is applied by all phase shifters associated with the antenna elements). In general, a boresight direction of an antenna is defined as the direction of maximum gain (maximum radiated power) of said antenna.

The coupling between the individual antenna element, and thus the impedance seen by the power amplifiers, is further affected by the configured MIMO rank (i.e., whether MIMO or SIMO is used). In SISO, only one RF beamforming branch is used at the RF Module, while the other RF beamforming branch is inactive (assuming a MIMO system with two RF beamforming branches in the RF module). The coupling between the antenna element feed ports on the antenna array depends, in this case, also on the state of the inactive RF beamforming branch (open, short, terminated or undefined). Terminated may be considered the preferred solution as this eliminates any possible reflection from those inactive element feed port. In MIMO, both RF beamforming branches are active and the coupling between the antenna element feed ports is defined by that state, which means that termination is not possible.

In addition to the impedance mismatch, the operation may be further deteriorated due to related misbehavior of the PA under load mismatch. This will affect the Tx path even more when facing a poorly matched impedance load. Some relevant PA impairments potentially arising from load mismatch are highlighted below:Load-pulling, the output power capabilities of the PA's are affected by the load impedance seen by the PA. This will result in further reduction of the delivered output power, in addition to the power reduction caused by impedance mismatch reflection.PA efficiency degradation, which will increase the current consumption and lead to increased heat dissipation.PA linearity degradation, which will distort the transmitted signal leading to worse adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM).Spurious Emissions increase, which could make the device fail the regulatory requirement for spurious emission.

These undesired PA behaviors will also affect the risk and severity of downlink/uplink beam non-correspondence at the terminal device, i.e., the problem of the uplink beam of the terminal device not corresponding with the aligned downlink beam of the terminal device. In addition, the uplink signal quality and user experience will be degraded and in worst case fail regulatory requirements.

The embodiments to be discussed below in detail seek to overcome at least some of the problems relating to impedance mismatch outlined above.

FIGS.2A and2Billustrate, respectively, a beamforming (or MIMO) transceiver architecture according to embodiments for transmitting and receiving data over a wireless communication network using multiple beams and a RF front end module202according to embodiments. The RF front end module ofFIG.2Bmay form a part of said beamforming transceiver architecture illustrated inFIG.2A. The illustrated RF front end module202comprises RF elements relating to a single antenna element of the antenna array of the beamforming transceiver. The antenna array may be a one-dimensional antenna array (or a linear antenna array) or a two-dimensional antenna array. The antenna array may be specifically a broadside array providing maximum gain/directivity to a direction perpendicular (or broadside) to the axis or plane of the antenna array when the antenna elements of the antenna array are fed in-phase. In other words, the RF front end module202illustrated inFIG.2Bmay be specifically a part of a complete RF front end for a beamforming transceiver (or a MIMO transceiver). The apparatuses illustrated inFIGS.2A and/or2Bmay be comprised in a terminal device such as any of the terminal devices100,102ofFIG.1or in an access node such as the access node104ofFIG.1.

Referring toFIG.2A, the beamforming transceiver architecture comprises a baseband beamforming transceiver201and one or more RF front end modules202of which only one is illustrated inFIG.2A(and inFIG.2B). The baseband beamforming transceiver201is connected to the one or more RF front end modules via a RF switch203. The RF switch is configured to enable electric switching, by a Tx & Rx control unit204(or equally Tx & Rx control means), for selecting which Tx RF signals are to be fed to which RF beamforming branches218,219of which RF front end modules202and which RF signals received from RF beamforming branches218,219of the one or more RF front end modules are to be fed to which Rx branches of the baseband beamforming transceiver201.

The baseband beamforming transceiver201comprises, for enabling transmission, at least two or more digital-to-analog converters (DAC)205,206for converting digital baseband signals to be transmitted to corresponding analog baseband signals, two or more Tx mixers209,210for converting the analog baseband signals to corresponding RF signals and two or more Tx amplifiers213,214for amplifying the RF signal received from a corresponding Tx mixer209,210. Moreover, the baseband beamforming transceiver201comprises, for enabling reception, two or more Rx amplifiers215,216for amplifying the received RF signals before mixing, two or more Rx mixers211,212for converting the received RF signals to corresponding analog baseband signal and two or more analog-todigital converters (ADC)207,208for converting the analog baseband signals to corresponding digital baseband signals.

Moreover, the baseband beamforming transceiver201comprises a Tx & Rx control unit204for controlling whether the beamforming transceiver is currently in transmission or reception mode (e.g., by controlling the RF switch203and Tx/Rx switches of the one or more RF front end modules202) and a beam steering control unit217(or equally beam steering control means) for controlling the beamforming functionalities (e.g., adjusting phase shifts applied in each RF beamforming branch for each antenna element). The Tx & Rx control unit204and the beam steering control unit217may be separate computing devices or comprised in a single computing device.

It should be emphasized that only some of the elements and functional entities of the baseband beamforming transceiver201are illustrated inFIG.2A. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown inFIG.2A. For example, the baseband beamforming transceiver201may further comprise one or more digital baseband processing units for processing digital baseband signals before transmission and/or after reception, one or more local oscillators for providing a local oscillator signal for the mixers209-212for generating an analog baseband signal or a RF signal of a desired frequency and/or one or more analog and/or digital filters.

In some embodiments, the baseband transceiver employed in connection with a RF front end according to embodiments may also differ from the one illustrated inFIG.2Ain other ways. In general, the baseband beamforming transceiver201may comprise one or more digital and/or analog units as commonly found in MIMO-enabled or beamforming transceivers. Said one or more digital and/or analog units may be configured to perform, for example, digital/analog baseband processing, beam steering control, channel estimation, MIMO detection, precoding, spatial multiplexing and/or time- and/or frequency-scheduling.

Referring toFIGS.2A and2B, the illustrated RF front end architecture202comprises two RF beamforming branches218,219for a single antenna element229of the antenna array of the beamforming transceiver. A RF beamforming branch218,219may be equally called a MIMO branch (or a SIMO/MIMO branch in connection with some embodiments to be discussed below) or simply a RF branch. Each RF beamforming branch218,219comprises a complete RF transceiver chain as illustrated with elements221to228or231to238for a particular antenna element229of the antenna array. Corresponding RF beamforming branches may be provided, in the beamforming transceiver, for each antenna element229of the antenna array (even though only the RF beamforming branches of a single antenna element is illustrated inFIGS.2A and2B). Thus, a set of corresponding RF beamforming branches218,219for the plurality of antenna elements229(e.g., a set comprising all first RF beamforming branches218corresponding to the plurality of antenna elements) provides means for transmitting and receiving data signals using the whole antenna array and simultaneously with the transmission/reception occuring at other parallel RF beamforming branches218,219. Each set of corresponding RF beamforming branches218,219feeding the plurality of antenna elements229may target at a time, for example, a specific cell or a specific user (if the beamforming transceiver corresponds to an access node) or a specific access node (if the beamforming transceiver corresponds to a terminal device). While only two RF beamforming branches218,219are illustrated inFIG.2B, in other embodiments, a larger number of RF beamforming branches may be provided.

Each RF beamforming branch218,219comprises a RF transceiver chain comprising at least an electrically tunable phase shifting element221,231, a power amplifier (PA)/low-noise amplifier (LNA) module222,232, an electrically switchable matching circuit226,236, a second Tx/Rx switch227,237and an antenna matching circuit228,238. The PA/LNA module222,232comprises a first Tx/Rx switch223,233, a power amplifier224,234(for transmission) and a low-noise amplifier225,235(for reception).

The operation of each element in the RF transceiver chain is described in the following only for the first RF beamforming branch218for simplicity of notations. The definitions provided apply equally to the second RF beamforming branch219as well as to all the RF beamforming branches associated with the other antenna elements in the antenna array. Thus, elements231to238may be defined as described below for elements221to228.

The electrically tunable phase shifting element221is configured to provide a phase shift for the RF signal so as implement a particular radiation pattern or beam for the antenna array. Said phase shift may be determined dynamically by a beam steering control network (to be discussed in relation to further embodiments). The electrically tunable phase shifting element221may be a phase shifter. As shown inFIG.2B, the electrically tunable phase shifting element221is electrically connected to a pole of the first Tx/Rx switch223.

The first and second Tx/Rx switches223,227are used for switching (electronically) between transmitter and receiver operation. Specifically, each of the first and second Tx/Rx switches223,227has a Tx position (the upper position inFIG.2B) corresponding to a Tx port and a Rx position (the lower position inFIG.2B) corresponding to a Rx port. The Tx ports of the first and second Tx/Rx switches223,237define between them a Tx path of a RF beamforming branch218and Rx ports of the first and second Tx/Rx switches223,227define between them a Rx path of the RF beamforming branch218. The first and second Tx/Rx switches223,227may be controlled by the Tx & Rx control unit204.

In addition to the first Tx/Rx switch223, the PA/LNA module222comprises a power amplifier224which is arranged in the Tx path of the RF beamforming branch and a low-noise amplifier225which arranged in the Rx path of the RF beamforming branch. The properties (e.g., at least gain) of the power amplifier and/or the low-noise amplifier225may be tunable by, e.g., Tx & Rx control unit204and/or a beam steering control unit217of the beamforming transceiver.

The antenna matching circuit228is configured to provide impedance matching for the antenna element229. In other words, the antenna matching circuit provides impedance matching between an antenna impedance of the antenna element229and a characteristic impedance of a transmission line (e.g., a microstrip line) feeding the antenna element229. In most applications, a characteristic impedance of 50Ω is used. The purpose of impedance matching is to enable efficient coupling of the signal to and from the antenna element229. Specifically, the antenna matching circuit228may be configured to provide optimal impedance matching when a certain pre-defined beam steering is employed. This pre-defined beam steering angle may be specifically an angle corresponding to a broadside direction (usually defined as 0°). As described above, as the beam steering angle is changed, the impedance seen by the antenna element229(i.e., the effective antenna impedance) changes and thus the antenna matching circuit is no longer able to provide optimal impedance matching. This causes deterioration of the performance of the transceiver, especially in transmission, if no further impedance matching is provided.

While the Rx path of the RF beamforming branch (defined by the first and second Tx/Rx switches223,227) may comprise only the low-noise amplifier225, the Tx path of the RF beamforming branch comprises, in addition to the power amplifier224, an electrically switchable matching circuit226for addressing the impedance matching problem described above. The electrically switchable matching circuit226may follow the power amplifier224in the Tx path. Specifically, the electrically switchable matching circuit226may be electrically connected, in the Tx path, to the output port of the power amplifier224and the Tx port of the second Tx/Rx switch227. The electrically switchable matching circuit226may be connected to the output port of the power amplifier224and the Tx port of the second Tx/Rx switch227directly (as illustrated inFIG.2B) or via one or more circuits and/or one or more circuit elements. The electrically switchable matching circuit226comprises two or more matching circuit settings (e.g., two or more individual matching circuits) selectable via switching. The switching may be controlled by a beam steering control unit217which is also responsible for adjusting phase shifting at each RF beamforming branch218,219.

Each of the two or more matching circuits may be specifically configured for providing impedance matching for the antenna element229(that is, supplementary or additional impedance matching to the impedance matching provided by the antenna matching circuit228) at one or more beam steering angles in transmission. In other words, each of the two or more matching circuit settings provides impedance matching between the characteristic impedance of the transmission line (e.g., 50Ω) and the impedance seen at the output of the electrically switchable matching circuit226(i.e., the effective antenna impedance after being impedance-matched with the antenna matching circuit226). For example, one of the two or more matching circuit settings may correspond a broadside direction (i.e., a beam steering angle of 0°) while at least one of the two or more matching circuit settings may each correspond to different off-broadside directions (i.e., beam steering angles of ±a, where a is a positive angle smaller than or equal to 90°, preferably smaller than or equal to 50°). In other words, said one or more beam steering angles, for each of the two or more matching circuit settings, may correspond to a broadside angle of the antenna array or to two off-broadside angles defined symmetrically around the broadside angle. In practice, each of said one or more beam steering angles may correspond to a sector defined around the beam steering angle in question. The broadside angle is defined as angle relative to the broadside direction of the antenna array. The broadside angle may be equal to a boresight angle defined as an angle relative a boresight direction of the antenna array when all antenna elements of the antenna array are fed in-phase (e.g., 0° phase shift is applied by all phase shifters associated with the antenna elements).

In some embodiments, one of the two or more matching circuit settings (namely, the one corresponding to transmission to the broadside direction) may correspond to a by-pass circuit or line (i.e., to a single straight transmission-line segment) having no effect on the impedance matching. The antenna matching circuit228may be configured to provide optimal impedance matching specifically for the beam steering angle corresponding to said by-pass circuit. In other words, the antenna matching circuit228is configured to provide optimal matching at a particular pre-defined beam steering angle and consequently no additional impedance tuning is required for said pre-defined beam steering angle (even for transmission).

In some embodiments, the electrically switchable matching circuit226comprises a matching circuit setting selectable via switching corresponding to a matched termination (e.g., a 50Ω termination) for the antenna element229. Such matching circuit setting in a RF beamforming branch enables optimal Tx SISO operation for the other RF beamforming branches (i.e., operation where only one of the RF beamforming branches218,219is active) by preventing the RF signal from the active RF beamforming branch from coupling to and reflecting from the inactive RF beamforming branch. Obviously, such a matched termination may also be employed in the case of three or more Tx RF beamforming branches for using a lower MIMO rank in transmission (i.e., lower than what is possible with the beamforming transceiver architecture) by effectively deactivating one (or more) of the RF beamforming branches.

The two or more matching circuit settings may be defined in multiple different ways. Three examples of how the electrically switchable matching circuit226,236may be implemented are illustrated inFIG.2C. Each of the three illustrated electrically switchable matching circuits241,251,261may correspond to either of elements226,236.

According to a first alternative, each matching circuit setting may correspond to a separate matching circuit comprised in the electrically switchable matching circuit226,236. Thus, switching of the electrically switchable matching circuit226,236corresponds to switching between different matching circuits. The top and middle electrically switchable matching circuits241,251inFIG.2Care examples of this type of electrically switchable matching circuit. In said top and middle electrically switchable matching circuits241,251, a pair of electrically controllable switches242,246,252,256is used for selecting a matching circuit from three different alternatives243to245,253to255(in general, two or more alternative matching circuits may be provided). In the top electrically switchable matching circuit241, the first and second alternative matching circuits are matching circuits implemented with distributed circuit elements (corresponding to different beam steering angles, e.g. ±25° and ±50°) while the third matching circuit is a by-pass line245. In the middle electrically switchable matching circuit251, the first and second alternative matching circuits are matching circuits implemented with lumped circuit elements while the third matching circuit is a by-pass line245. Implementation of the matching circuits using distributed/lumped elements is discussed in further detail in relation toFIG.2D.

According to a second alternative, the electrically switchable matching circuit226,236may comprise one or more (electrically controllable) tunable circuit elements (and optionally one or more non-tunable circuit elements) and each matching circuit setting may correspond to a tuning configuration of the one or more tunable circuit elements (e.g., changing the inductance of an inductor arranged in series or in parallel or a capacitance of a capacitor arranged in series or in parallel). The bottom electrically switchable matching circuit261ofFIG.2Ccorresponds to a slightly more advanced version of this idea in that, in addition to an electrically controllable tunable circuit element263(arranged in series or in parallel), a by-pass line264is provided. Switching between the tunable circuit element263and the by-pass line264may be provided via a pair of electrically controllable switches262,265arranged on both sides of the tunable circuit element263and the by-pass line264(similar to the electrically switchable matching circuits241,251). Thus, two types of electric control are implemented in the case of the bottom electrically switchable matching circuit261ofFIG.2C: electric control for tuning the tunable circuit element263and electric control for operating the pair of switches262,265.

While not explicitly illustrated inFIG.2C, a matched termination for a corresponding antenna element may, also or alternatively, be one of the switching options provided by any of the electrically switchable matching circuits241,251,261ofFIG.2C, in some embodiments.

Another alternative (not shown inFIG.2C) is that each matching circuit setting corresponds to a switching configuration for one or more switchable circuit elements of the electrically switchable matching circuit. In other words, the switching of the electrically switchable matching circuit226,236corresponds to switching a certain circuit element in the matching circuit topology of the electrically switchable matching circuit226,236to another circuit element (e.g., a first capacitor to a second capacitor having a lower capacitance than the first capacitor).

The impedance matching, in the antenna matching circuit228,238and in the electrically switchable matching circuits226,236(specifically for each matching circuit setting defined therein), may be implemented using any conventional impedance matching circuitry for matching a complex (antenna) impedance to a transmission line (i.e., to a characteristic impedance of a transmission line which is usually 50Ω). Some examples of these alternatives are illustrated inFIG.2D.

For example, each individual matching circuit of the antenna matching circuit228and the electrically switchable matching circuits226,236may comprise one or more lumped (circuit) elements (so-called lumped element matching), as mentioned in connection with elements243,244ofFIG.2C. Said one or more lumped circuit elements may comprise one or more capacitors arranged in series, one or more capacitors arranged in parallel (i.e., connected between the lines of the transmission line), one or more inductors arranged in series and/or one or more inductors arranged in parallel. The type and number of the used lumped circuit element and their order, connection type and values of inductance or capacitance depend on the (complex) impedance value to be matched. Multiple topologies (i.e., lumped element matching networks) may be used for matching the same impedance (the exact number of possible topologies being dependent on the value of the impedance to be matched). The top matching circuit ofFIG.2Dcorresponds to an example of a matching circuit implemented using lumped circuit elements. Specifically, said matching circuit comprises a first capacitor271in parallel, a first inductor272in series and a second capacitor273in parallel (in this order). The capacitance/inductance values of the elements271,272,273are selected so that optimal impedance tuning is achieved.

Additionally or alternatively, each individual matching circuit of the antenna matching circuits228,238and the electrically switchable matching circuits226,236may comprise one or more distributed circuit elements (so-called distributed element matching), as mentioned in connection with elements253,254ofFIG.2C. Said one or more distributed circuit elements may comprise one or more transmission lines of a pre-defined length arranged in series, one or more open-ended transmission lines of a pre-defined length arranged in parallel (i.e., one or more open-ended stubs) and/or one or more short-circuited transmission lines of pre-defined length arranged in parallel (i.e., one or more lose-circuited stubs). Depending on the exact value of the complex impedance to be matched, different topologies of the matching circuit (i.e., different distributed element matching networks) are possible also in this case. The middle matching circuit ofFIG.2Dcorresponds to an example of a matching circuit implemented using distributed circuit elements. Specifically, said matching circuit comprises an open-ended or shorted stub274of length12and a transmission line segment275having a length h leading to an antenna element. All transmission lines in the example have the same characteristic impedance Zo (as is usually the case). By changing the lengths h and12and whether the stub is open-ended or shorted, impedance tuning achieved with the illustrated matching circuit may be adjusted.

Additionally or alternatively, each individual matching circuit of the antenna matching circuits228,238and the electrically switchable matching circuit226,236may comprise one or more tunable circuit elements (tunable distributed or lumped circuit elements), as mentioned in connection with element263ofFIG.2C. The one or more tunable circuit elements may comprise one or more tunable capacitors arranged in series and/or in parallel and/or one or more tunable inductors arranged in series and/or in parallel. The bottom matching circuit ofFIG.2Dcorresponds to an example of a matching circuit implemented using a tunable circuit element. Specifically, said bottom matching circuit ofFIG.2Dcomprises a digitally tuned capacitance (DTC)276arranged in parallel.

In some embodiments, at least one individual matching circuit of the antenna matching circuits228,238and the electrically switchable matching circuits226,236one or more matching circuits may be implemented using a combination of one or more lumped circuit elements, one or more distributed circuit elements and/or one or more tunable circuit elements.

In some embodiments, the antenna matching circuit(s)228,238may be integrated into the antenna array.

It should be emphasized that only some of the elements of a RF front end associated with a single antenna element are illustrated inFIG.2B(namely, only the elements relevant for the embodiments are illustrated). The RF front end may further comprise, for example, one or more RF filters.

FIG.2Eillustrates the operating principle of the RF front end architecture ofFIG.2B. In the illustrated example, the RF front end architecture in question is implemented in a terminal device291. The antenna array of a terminal device typically covers at least an angular range of 90° (±45°) with 0° corresponding to a broadside direction. InFIG.2E, an angular range of 100° (±50°) is used in order to include a small overlap. In the simplistic example illustrated inFIG.2E, the electrically switchable matching circuit226,236comprises at least two different matching circuit settings: a first matching circuit setting corresponding to a broadside direction illustrated with a first sector243and a second matching circuit setting corresponding to off-broadside directions illustrated with second and third sectors292,294. Additionally, the electrically switchable matching circuit226,236may comprise a matched termination for SISO operation. In the illustrated example, the first sector293is associated with multiple individual beams employed by the terminal device291(i.e., by the transceiver therein) while each of the second and third sectors292,294are associated with a single individual beam (i.e., the two beams with the highest positive and negative beam steering angles).

FIGS.3A and3Billustrates, using a pair of Smith charts, impedance matching without and with the electrically switchable matching circuit for a beam steering angle of 50° (i.e., 50° relative to the broadside direction), respectively.FIGS.3A and3Bcorresponds to a case where the antenna array is a 1×8 antenna array and to a frequency range of 24.25 GHz to 29.50 GHz. In other words, each separate line corresponds to impedance for a single antenna element in the frequency range of 24.25 GHz to 29.50 GHz. Which antenna element in the 1×8 antenna array line correspond to which line is irrelevant in view of the following discussion. A two-stage matching circuit switching approach is used inFIG.3B, similar to as illustrated inFIG.2E. The non-switchable antenna matching circuits are assumed to be optimized for impedance matching at broadside.FIGS.3A and3Bcorrespond to results of full 3D electromagnetic simulations.

Smith chart is a tool for illustrating complex input impedances of loads normalized to the characteristic impedance of the transmission line in a convenient manner. The closer the input impedance is to the center of the Smith chart, the better the matching is (i.e., the smaller the reflection coefficient is). The Smith charts ofFIGS.3A and3Balso show four circles corresponding to different standing wave ratio (SWR) values (namely, to values 2, 3, 4 and 8). Standing wave ratio (or specifically voltage standing wave ratio) is another measure of impedance matching of loads to the characteristic impedance of a transmission line. Standing wave ratio is defined as the ratio of the partial standing wave's amplitude (voltage) at an antinode (maximum) to the amplitude at a node (minimum) along the line.

InFIG.3A, no beam steering-dependent impedance matching is employed. Consequently, impedance matching is not optimal. At worst, a standing wave ratio of approximately 8 is observed (as highlighted with an arrow), that is, the plotted value are just barely within the SWR circle corresponding to the SWR value of 8. A SWR of 8 indicates very poor match impedance matching for a power amplifier. Such a poor value will result in severe unwanted behaviors (as described above) for the power amplifier facing such a high SWR.

InFIG.3B, a two-stage beam steering-dependent impedance matching is employed. Consequently, the impedance matching is notably improved compared to the reference case ofFIG.3A. At worst, the standing wave ratio has a value of approximately 3, that is, the plotted values are roughly within the SWR circle corresponding to the SWR value of 3.

FIG.4illustrates combined power coupled to the plurality of antenna elements of the antenna array with and without the electrically switchable matching circuit for a beam steering angle of 50° (i.e., 50° relative to the broadside direction). The used beamforming transceiver and the antenna array are defined as described in relation toFIGS.3A and3B. The difference in combined power delivered to the antenna array when the switchable matching circuit is used and when it is not used is up to 1 dB. In addition and even more importantly, the effects of the improved power amplifier conditions (i.e., improved impedance match) cause a considerable increase in the quality of the transmitted RF signal.FIG.4shows results of simulations.

WhileFIGS.2A and2Billustrated, respectively, downlink/uplink MIMO transceiver and RF front end architectures, the same inventive concept may also be applied to downlink MIMO and uplink SISO transceivers and downlink MIMO and uplink SISO RF front end architectures (or equally to downlink SIMO and uplink MIMO transceiver and RF front end architectures). It should be noted that, for example, a 3GPP Release 15 compliant devices utilizing millimeter waves (Frequency Range 2, FR2) are required to support 2×2 MIMO for downlink but only SISO for uplink.

FIGS.5A and5Billustrate, respectively, an alternative beamforming transceiver architecture according to embodiments for transmitting and receiving data over a wireless communication network using multiple beams and a corresponding RF front end module502according to embodiments. The RF front end module ofFIG.5Bmay form a part of said beamforming transceiver architecture illustrated inFIG.5A. The illustrated RF front end module502comprises RF elements relating to a single antenna element of the antenna array of the beamforming transceiver. In other words, the RF front end module502illustrated inFIG.5Bmay be specifically a part of a complete RF front end for a beamforming transceiver. The apparatuses illustrated inFIGS.5A and/or5Bmay be comprised in a terminal device such as any of the terminal devices100,102ofFIG.1or in an access node such as the access node104ofFIG.1.

The apparatuses illustrated inFIGS.5A and5Bcorrespond in many aspects to the apparatuses illustrated inFIGS.2A and2B. Therefore, said apparatuses are described in the following relatively briefly emphasizing the differences compared to the apparatuses ofFIGS.2A and2B. Unless otherwise stated, definitions provided in connection withFIGS.2A and2Bapply, mutatis mutandis, also to the embodiments illustrated inFIGS.5A and5B.

Similar toFIG.2A, the beamforming transceiver architecture illustrated inFIG.5Acomprises a baseband beamforming transceiver501and one or more RF front end modules502of which only one is illustrated inFIG.2A(and inFIG.2B). The baseband beamforming transceiver501is connected to the one or more RF front end modules via a RF switch503for enabling electric switching, by a Tx & Rx control unit505, for selecting when the Tx RF signals are to be fed to RF beamforming branches515,516(one at a time) of which RF front end modules502and when the RF signals received from RF beamforming branches515,516of the one or more RF front end modules are to be fed to the Rx branches of the baseband transceiver201. As mentioned above, the beamforming transceiver illustrated withFIGS.5A and5Benables MIMO operation only in reception while in transmission only SIMO operation is possible.

The baseband beamforming transceiver201comprises, for enabling transmission, at least one or more digital-to-analog converters (DAC)506for converting digital baseband signals to be transmitted to corresponding analog baseband signals, one or more Tx mixers509for converting the analog baseband signals to corresponding RF signals and one or more Tx amplifiers512for amplifying the RF signal received from a corresponding Tx mixer509,510. Thus, in contrast to the beamforming transceiver ofFIG.2A, only one Tx branch needs to be provided in the baseband beamforming transceiver501according to the SIMO operation in transmission. The two branches of the baseband beamforming transceiver501defined by elements507to514may be defined as described for the two Rx branches of the baseband beamforming transceiver201ofFIG.2A. Also similar to the embodiments discussed in relation toFIGS.2A and2B, the baseband beamforming transceiver501further comprises at least a Tx & Rx control unit504and a beam steering control unit516.

Referring toFIGS.5A and5B, the illustrated RF front end architecture502, again similar toFIGS.2A and2B, comprises two RF beamforming branches515,516for a single antenna element529of the antenna array of the beamforming transceiver. However, in this case only one515of the two RF beamforming branches515,516comprises a complete RF transceiver chain (defined by elements521to528). The other RF beamforming branch516comprises, in contrast, only a complete RF receiver chain (defined by elements531,535,538). Corresponding RF beamforming branches may be provided, in the beamforming transceiver, for each antenna element529of the antenna array. While only one Tx/Rx RF beamforming branch515and only one Rx RF beamforming branch516is illustrated inFIGS.5A and5B, in other embodiments, a larger number of Tx/Rx and/or Rx RF beamforming branches (defined similar to the illustrated ones) may be provided.

The Tx/Rx RF beamforming branch515may be defined as described for the RF beamforming branches218,219in connection withFIGS.2B,2C and2D. It should be emphasized that, in contrast toFIGS.2A and2B, the Tx/Rx beamforming branch515cannot be strictly considered a “MIMO branch” as MIMO operation is provided with the beamforming transceiver ofFIGS.5A and5Bonly in reception. Specifically, the electrically switchable matching circuit526may comprise, also in this case, two or more matching circuit settings (e.g., two or more individual matching circuits) selectable via switching, where each matching circuit setting corresponds to a particular beam steering angle.

The Rx RF beamforming branch516(equally called a Rx-only RF beamforming branch516) comprises a RF receiver chain comprising at least an electrically tunable phase shifting element531, low-noise amplifier (LNA)535and an antenna matching circuit538. Said elements531,535,538may be defined as described in relation to corresponding elements231,235,238ofFIG.2B. The properties of the electrically tunable phase shifting element531, the low-noise amplifier535and the antenna matching circuit538of the Rx RF beamforming branch516may or may not correspond to the properties of the corresponding elements521,525,528of the Tx/Rx RF beamforming branch515.

In some embodiments, the implementation of the RF front end may differ from any of the ones discussed above (mainly in relation toFIGS.2B and5B). According to a more general embodiment, there is provided a RF front end for a beamforming transceiver having an antenna array comprising a plurality of antenna elements, where the RF front end comprises, for each of the plurality of antenna elements, at least two RF beamforming branches, each of at least one of said at least two RF beamforming branches comprising:

means for adjusting phase shifting in a RF beamforming path electronically (e.g., using beam steering control means);

means for switching between a Tx path (i.e., transmission operation) and a Rx path (i.e., reception operation) of the RF beamforming path (electronically, e.g., using Tx & Rx control means and/or beam steering control means);

means for signal amplification in the Rx path of the RF beamforming path;

means for signal amplification in the Tx path of the RF beamforming path; and

means for implementing impedance matching according to two or more electronically switchable matching circuit settings in the Tx path following the signal amplification in the Tx path, each of the two or more matching circuit settings being configured for providing impedance matching for the antenna element at one or more beam steering angles in transmission. The electronic switching between the two or more matching circuit settings may be controlled using beam steering control means.

For example, the means for adjusting may correspond a phase shifting element, the means for switching between the Tx and Rx paths may correspond to first and second Tx/Rx switches (e.g., elements223,227ofFIG.2B), the means for the signal amplification in the Rx path may correspond to a low-noise amplifier (e.g., element225ofFIG.2B), the means for the signal amplification in the Tx path may correspond to a power amplifier (e.g., element224ofFIG.2B) and the means for implementing the impedance matching may correspond to an electrically switchable matching circuit (e.g., element226ofFIG.2B), where any of the definitions provided above for said exemplary elements may apply.

Additionally, each of at least one of said at least two RF beamforming branches may comprise, in some embodiments, means for implementing impedance matching between the antenna element and the RF beamforming branch both in transmission and reception. The means for implementing impedance matching may correspond to the antenna matching circuit (e.g., element228ofFIG.2B).

Any of the further features and properties discussed in connection with the specific embodiments (i.e., in relation toFIGS.2A,2B,2C,2D,2E,3A,3B,4,5A and5B) may be combined with the more general embodiments discussed above.

In summary, the RF front end architectures (for MIMO and SISO) according to embodiments discussed above provide at least the following advantages:Reduction of beam non-correspondence scenarios.Improved Tx output power over beam steering angle.Improved PA linearity and efficiency stability over beam steering angle.Improved performance in both MIMO and SISO configurations.All improvements are obtained without added loss to the Rx paths.

FIG.6illustrates a process according to embodiments for performing beamforming (or beam steering) by a beamforming transceiver or specifically by beam steering control unit of the beamforming transceiver. The illustrated process may be carried out, for example, by the beamforming steering control unit217ofFIGS.2A and2Bor the beamforming steering control unit504ofFIGS.5A and5B. In the following, the device carrying out the process is called simply an apparatus for brevity.

Initially, the apparatus obtains, in block601, information on (upcoming) transmission of data signal to a target device (e.g., a terminal device or an access node). The type of the data signal or of the target device is irrelevant for the carrying out of this process. Said information may be obtained, for example, from another unit of the beamforming transceiver (e.g., from a Tx & Rx control unit or a digital baseband processing units for processing digital baseband signals). Specifically, said information may be obtained from beam alignment (entity) or beam management (entity) according to 5G NR 3GPP Release 15.

Then, the apparatus selects, in block602, a beam steering angle to be used for said transmission based on the obtained information. In some embodiments, the beam steering angle may be explicitly included in said information or it may at least be derivable based on said information.

The apparatus adjusts, in block603, phase shifts induced by a plurality of electrically tunable phase shifting elements (e.g., phase shifters) of the beamforming transceiver for forming a beam matching the beam steering angle (i.e., a beam directed towards the target device). Said adjusting of the phase shifts may be carried out using any conventional beamforming method, for example, based on a codebook table. The plurality of electrically tunable phase shifting elements may comprise, e.g., one of elements221,231ofFIG.2Bor element512,531ofFIG.5B(and corresponding elements of other RF front end modules not shown inFIG.2B or5B).

The apparatus sets, in block604, matching circuit settings of a plurality of electrically switchable matching circuits for optimizing the impedance matching in transmission for the selected beam steering angle. Again, the electrically switchable matching circuits may be defined as described above, e.g., in relation to elements226,236ofFIG.2B,FIGS.2C and2Dand/or elements526ofFIG.5B. Thus, each electrically switchable matching circuit may be arranged in a Tx path of a RF beamforming branch of a RF front end of the beamforming transceiver and may comprise two or more matching circuit settings selectable via switching. Each of the two or more matching circuit settings may be configured for providing impedance matching (or additional impedance matching in addition to a non-switchable matching circuit) for an antenna element at one or more beam steering angles in transmission (e.g., a broadside angle and one or more off-broadside angles). The electrically switchable matching circuit may also comprise a matching circuit setting corresponding to a matched termination. The apparatus may set (or activate), in each case in block604, the matching circuit setting corresponding most closely to the beam steering angle. In some embodiments, each matching circuit setting may be associated with a sector (as inFIG.2E) which defines which beam steering angles should trigger the use of which matching circuit setting.

Finally, the apparatus causes (or triggers), in block605, transmitting of the data signal to the target device using the beamforming transceiver (or transmitter). The phase shifts of the plurality of electrically tunable phase shifting elements set in block603and the matching circuit settings of the plurality of electrically switchable matching circuits set in block604are employed in the transmitting.

In some embodiments, the apparatus may also adjust, in addition the phase shifting and the impedance matching, gain of a plurality of power amplifiers for amplifying the data signal to be transmitted. The plurality of power amplifiers may comprise, e.g., one of elements224,234ofFIG.2Bor element524ofFIG.5B(and corresponding elements of other RF front end modules not shown inFIG.2B or5B).

The blocks, related functions, and information exchanges described above by means ofFIG.6are in no absolute chronological order, and some of them may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between them or within them, and other information may be sent, and/or other rules applied. Some of the blocks or part of the blocks or one or more pieces of information can also be left out or replaced by a corresponding block or part of the block or one or more pieces of information.

FIG.7provides an apparatus701(or a computing device) at least for performing beamforming. Specifically, the apparatus701may be a beam steering control unit of beamforming transceiver (or transmitter). The apparatus701may be a 5G apparatus. The apparatus701may be the beamforming steering control unit217ofFIGS.2A and2Bor the beamforming steering control unit504ofFIGS.5A and5B. The apparatus701may be comprised in (i.e., form a part of) a terminal device or in an access node.

The apparatus701may comprise one or more control circuitry720, such as at least one processor, and at least one memory730, including one or more algorithms731, such as a computer program code (software) wherein the at least one memory and the computer program code (software) are configured, with the at least one processor, to cause the apparatus to carry out any one of the exemplified functionalities of the apparatus (i.e., of the beam steering control unit) described above. Said at least one memory730may also comprise at least one database732.

Referring toFIG.7, the one or more communication control circuitry720comprise at least beam steering control circuitry721which is configured to perform beam steering (or beamforming) according to embodiments (in communication with RF elements of the RF front end of the beamforming transceiver). To this end, the encoding circuitry721is configured to carry out at least some of the functionalities described above by means of any ofFIGS.2A,2B,2C,2D,2E,5A,5B and6using one or more individual circuitries.

Referring toFIG.7, the memory730may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

Referring toFIG.7, the apparatus701may further comprise different interfaces710such as one or more signaling interfaces (TX/RX) comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. Specifically, if the apparatus701corresponds to the beam steering control unit, the one or more signaling interfaces710may comprise, for example, interfaces providing a (wired) connection to a plurality of electrically tunable phase shifting elements, a plurality of electrically switchable matching circuits and one or more other units or elements of the beamforming transceiver (e.g., to one or more power amplifiers for controlling their gain). The one or more signaling interfaces710may, in some embodiments, provide the apparatus with communication capabilities to communicate in a cellular or wireless communication system, to access the Internet and a core network of a wireless communications network and/or to enable communication between user devices (terminal devices) and different network nodes or elements, for example.

The one or more signaling interfaces710may comprise standard well-known components such as an amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries, controlled by the corresponding controlling units, and one or more antennas.

As used in this application, the term ‘circuitry’ may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of hardware circuits and software (and/or firmware), such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software, including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus, such as a terminal device or an access node, to perform various functions, and (c) hardware circuit(s) and processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software may not be present when it is not needed for operation. This definition of ‘circuitry’ applies to all uses of this term in this application, including any claims. As a further example, as used in this application, the term ‘circuitry’ also covers an implementation of merely a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term ‘circuitry’ also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for an access node or a terminal device or other computing or network device.

In an embodiment, at least some of the processes described in connection withFIGS.2A,2B,2C,2D,2E,5A,5B and6may be carried out by an apparatus comprising corresponding means for carrying out at least some of the described processes. Some example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry. In an embodiment, the at least one processor, the memory, and the computer program code form processing means or comprises one or more computer program code portions for carrying out one or more operations according to any one of the embodiments ofFIGS.2A,2B,2C,2D,2E,5A,5B and6or operations thereof.

According to an embodiment, there is provided a computer program comprising instructions for causing an apparatus to perform the embodiments of the methods described in connection withFIGS.2A,2B,2C,2D,2E,5A,5B and6(e.g., at least the method steps illustrated inFIG.6or at least some of them).

According to an embodiment, there is provided a computer readable medium comprising program instructions for causing an apparatus to perform the embodiments of the methods described in connection withFIGS.2A,2B,2C,2D,2E,5A,5B and6(e.g., at least the method steps illustrated inFIG.6or at least some of them).

According to an embodiment, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform the embodiments of the methods described in connection withFIGS.2A,2B,2C,2D,2E,5A,5B and6(e.g., at least the method steps illustrated inFIG.6or at least some of them). Even though the embodiments have been described above with reference to examples according to the accompanying drawings, it is clear that the embodiments are not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.