Patent Description:
Power amplifiers are central components in the overall performance and throughput of communication systems, but they are inherently nonlinear. The nonlinearity may generate spectral re-growth, which may lead to adjacent channel interference and violations of the out-of-band emissions standards mandated by regulatory bodies. It may also cause in-band distortion, which may degrade an error vector magnitude and ultimately a bit-error rate (BER) and data throughput of the communication system.

To reduce the nonlinearity, the power amplifier can be operated at lower power (that is, "backed off") so that it operates within the linear portion of its operating curve. However, newer transmission formats, such as wideband code division multiple access (WCDMA) and orthogonal frequency division multiplexing (OFDM, WLAN/3GPP LTE & <NUM> NR), have high peak-to-average power ratios (PAPR); that is, large fluctuations in their signal envelopes. This means that the power amplifier needs to be backed off well below its maximum saturated output power in order to handle infrequent peaks, which result in very low efficiencies (typically less than <NUM>%). With greater than <NUM>% of the DC power being lost and turning into heat, the amplifier performance, reliability and ongoing operating expenses (OPEX) are all degraded.

<FIG> illustrates an example situation in which a user equipment UE <NUM> may be allowed to occasionally perform a calibration operation to calibrate the power amplifier (PA) and possibly also other parts of transmitter components of the UE <NUM>. However, at the same time another user equipment UE <NUM> may be in an RRC connected mode and communicates with the network via a base station gNB <NUM>. The calibration operation of the user equipment UE <NUM> may thus disturb the communication between the other user equipment UE <NUM> and the base station gNB <NUM>.

In some communication systems a user equipment in a connected mode may perform power amplifier calibration (UL PA calibration) by sending in an uplink (UL) slot a calibration signal. This procedure may be repeated at intervals. The user equipment may need to receive information from a network base station (e.g. gNB) whether the user equipment is allowed to send the calibration signal and when it is allowed to do that. When doing the power amplifier calibration, UE may transmit signals on only one Tx chain and idles the other Tx chain(s) within selected slots. Two Tx chains may be alternatively calibrated in time. When doing power amplifier calibration within selected UL slots, the user equipment uses resource assignments in UL grants, and follows power control procedure.

When a user equipment is performing the UL power amplifier calibration with high bandwidth and high transmit (TX) power some unnecessary interference may be induced in the cell. Hence, the problem is to avoid or minimize any interference and blocking at the gNB caused by the UE UL power amplifier calibration gap.

<CIT> discloses "multi-transceiver architecture for advanced TX antenna monitoring and calibration in M1MO and smart antenna communication systems".

An article in IEEE Transactions on Microwave Theory and Techniques discloses "Digital Predistortion of Phased-Array Transmitter With Shared Feedback and Ear-Field Calibration". 3GPP paper R4-<NUM> discusses "On performance improvements from self-calibration in UL gaps".

Some embodiments provide a method for interference management for measurement gaps, in calibration of a power amplifier of a user device. In some embodiments the method comprises measuring strength of signals received via a plurality of beams of one or more antenna arrays of a user equipment; ordering the beams on the basis of the measurement strengths; selecting from the ordered beams one or more beams for calibration of a pre-distorter for a power amplifier of the user equipment; obtaining information of an available measurement slot for the calibration; transmitting a calibration signal by the power amplifier using the selected beam at the time of the available measurement slot; receiving the calibration signal by another beam of the antenna array which is not used in the transmission of the calibration signal; obtaining calibration information on the basis of the transmitted calibration signal and the received calibration signal; and calibrating the power amplifier based on the calibration information.

According to some embodiments of the disclosure a user equipment is connected in a Radio Resource Control (RRC) connected mode during the UL PA calibration gap. Thus, the user equipment is aligned with a narrow beam towards the serving gNB following the 3GPP beam alignment procedures. In accordance with an embodiment, the UE is granted UL PA calibration gap regularly, for example once in every <NUM>. The user equipment will for one or more slots transmit a wideband and high power TX calibration sequence for estimating the DPD coefficients. This signal may create interference to received signal of other UEs at the serving gNB as it does not fulfil the UL power control limits but rather transmits at full power to estimate the non-linearities of the power amplifier.

To alleviate this interference and blockage the following procedure may be performed:.

The procedure may minimize the interference and blockage done in the system as the calibration signal is transmitted in the direction of the least interference, possibly away from the gNB. The reason for using RSSI as the metric for selecting the transmitting beam is to avoid interference and blockage not only to the serving cell but also to neighbour cells of the same or even a different network. RSSI indeed includes contribution of co-channel and adjacent channel interference.

In accordance with an embodiment of the disclosure, the UE TX signal is captured by the user equipment itself using another branch of a multiple input multiple output (MIMO) antenna array of the user equipment, thus the far-field directivity of the signal is not important for the scope of self-calibration.

In accordance with an embodiment of the disclosure, the UE TX signal captured by the user equipment is a near field signal, therefore the setting of phase shifters before the power amplifier have no impact on the useful signal for self-calibration. However the far-field signal may minimize any interference in the network.

In other words, the user equipment scans the direction (UE TX codebook entry) with the least power/interference and uses this direction for transmitter power amplifier self-calibration. The solution works as the interference, if any, is caused by the far field signal and the calibration only uses the near field signal.

In accordance with an embodiment of the disclosure, the user equipment and gNB can exchange information on the UE codebook used during UL power amplifier calibration.

Various aspects of examples of the invention are provided in the detailed description.

According to a first aspect, there is provided a method comprising:.

According to a second aspect, there is provided an apparatus comprising:.

According to a third aspect, there is provided an apparatus comprising at least one processor; and at least one memory including computer program code the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following:.

The following description and drawings are illustrative and are not to be considered as unnecessarily limiting. The specific details are provided for a thorough understanding of the disclosure. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure can be, but not necessarily are, reference to the same embodiment and such references mean at least one of the embodiments.

Reference in this specification to "one embodiment" or "an embodiment" or "some embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. In several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment.

Digital Pre-Distortion concept (DPD) is one of the most cost-effective linearization techniques. According to some approaches, an excellent linearization capability may be obtained, which may be traded for enhanced efficiency, and it may take full advantage of advances in digital signal processors and A/D converters. The technique adds an expanding nonlinearity in the baseband that complements the compressing characteristic of the RF power amplifier (<FIG>). Ideally, the cascade of the pre-distorter and the power amplifier becomes linear and the original input is amplified by a constant gain. With the pre-distorter, the power amplifier can be utilized up to its saturation point while still maintaining good linearity. This may be used to increase the transmitter output power capability for a given linearity target, or may be used to increase the efficiency of the transmitter at a given backed off output power by re-biasing for lower saturation point. From <FIG>, the DPD can be seen as an "inverse" of the PA. The DPD algorithm needs to model the PA behavior accurately and efficiently for successful DPD deployment. <FIG> illustrates how the DPD-PA cascade linearizes the non-linearity of the power amplifier. x(t) is the incoming signal, z(t) is the output of the DPD and y(t) is the output of the power amplifier.

According to some other approaches the pre-distortion compensation is performed in the IF section (intermediate frequency) of a transmitter wherein the compensated signal is upconverted to the final radio frequency band to be transmitted.

According to yet some other approaches the pre-distortion compensation is performed in the RF section of a transmitter wherein the compensated signal is directly in the final radio frequency band to be transmitted.

DPD implementations can be classified into memoryless models and models with memory.

Memoryless models focus on the power amplifier that has a memoryless nonlinearity, that is, the current output depends only on the current input through a nonlinear mechanism. This instantaneous non-linearity is usually characterized by the AM/AM and AM/PM responses of the power amplifier, where the output signal amplitude and phase deviation of the power amplifier output are given as functions of the amplitude of its current input. Both memoryless polynomial algorithm and Look-Up Table (LUT) based algorithm are two key algorithms for memoryless models.

<FIG> show the structure of applying the Look-up Table. There are two configurations according to the order of AM/AM and AM/PM.

For the first configuration (AM/PM then AM/AM) illustrated in <FIG>, the input amplitude values for AM/PM LUT and AM/AM LUT are the same. For the second configuration (AM/AM then AM/PM) illustrated in <FIG>, the input amplitude values for AM/AM LUT and AM/PM LUT are different.

Memory model is commonly used as the signal bandwidth gets wider, such as in WCDMA, mobile WiMAX and 3GPP LTE and LTE-Advanced (up to <NUM> bandwidth, <NUM> component carriers of carrier aggregation) and <NUM> NR with bandwidth up to 2x400 MHz or higher for frequencies greater than <NUM>. For wider bandwidth, power amplifiers begin to exhibit memory effects. Causes of the memory effects can be attributed to thermal constants of the active devices or components in the biasing network that have frequency dependent behaviors. As a result, the current output of the power amplifier depends not only on the current input, but also on the past input values. In other words, the power amplifier becomes a nonlinear system with memory. For such a power amplifier, memoryless pre-distortion can achieve only very limited linearization performance. Therefore, digital pre-distorters must have memory structures.

One algorithm for models with memory for Digital pre-distortion implementation is Volterra series and its derivatives. One general way to introduce memory is to use the Volterra series. However, the large number of coefficients of the Volterra series makes it unattractive for practical applications. Therefore, there are several Volterra's derivatives including Wiener, Hammerstein, Wiener-Hammerstein, parallel Wiener structures, and memory polynomial model, which are popular in digital pre-distorters. The so-called "memory polynomial" is interpreted as a special case of a generalized Hammerstein model and is further elaborated by combining with the Wiener model.

To construct digital pre-distorters with memory structures, there are two types of approaches. One type of approach is to first identify the power amplifier and then find the inverse of the power amplifier directly. This approach is named as direct learning architecture (DLA). However, obtaining the inverse of a nonlinear system with memory is generally a difficult task. Another type of approach is to use the indirect learning architecture (IDLA) to design the pre-distorter directly. The advantage of this type of approach is that it eliminates the need for model assumption and parameter estimation of the power amplifier.

The indirect learning architecture for the digital pre-distorter is shown in <FIG>.

<FIG> shows an example of a memory polynomial structure. If Q=<NUM>, the structure in <FIG> becomes memoryless polynomial, and the Volterra series structure is shown in <FIG>.

In some approaches, DPD coefficients are calculated during UE production. For low bandwidth <<NUM>, one solution is done using feedback receivers on silicon while for larger bandwidths (e.g. <NUM> NR mmWave) external measurement equipment may be needed to capture the required bandwidth and the effect of the active antenna module.

A solution for sub <NUM> with limited bandwidth <<NUM> is to transmit a known reference signal in the UE factory. A build in feedback receiver can capture the transmitted signal with bandwidth up to three times the transmitted signal bandwidth and then transfer the signal back to the baseband for calculation of the (m)DPD coefficients. The solution works as long as the performance does not change due to aging or external environment effects in the field or sufficient power back off is incorporated to absorb the environment effects maintaining specification compliance.

Solutions for application with higher bandwidth and mmWave support may require an external test box.

For mmWave and large bandwidths (><NUM>), the transmitted signal is captured radiated using external test equipment on the factory floor. The external test equipment can capture the transmitted signal with bandwidth up to three times the transmitted signal bandwidth and then transfer the signal back to the baseband for calculation of the (m)DPD coefficients. However, loading effects may change during live operation in the field and thus the (m)DPD coefficients would need to change dynamically and the available static set of coefficients might become invalid. Using an architecture as for sub <NUM> may not be possible as it may not be possible to capture very large bandwidths with required dynamic range online during operation and thus the antenna loading effects will not be captured appropriately in the feedback receiver signals.

<FIG> shows a block diagram of one possible and non-limiting example in which the examples may be practiced. A user equipment (UE) <NUM>, radio access network (RAN) node <NUM>, and network element(s) <NUM> are illustrated. In the example of <FIG>, the user equipment <NUM> is in wireless communication with a wireless network <NUM>. A user equipment is a wireless device that can access the wireless network <NUM>. The user equipment <NUM> includes one or more processors <NUM>, one or more memories <NUM>, and one or more transceivers <NUM> interconnected through one or more buses <NUM>. The one or more buses <NUM> may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fibre optics or other optical communication equipment, and the like. The user equipment <NUM> includes a module <NUM>, which may be implemented in a number of ways. The module <NUM> may be implemented in hardware as module <NUM>-<NUM>, such as being implemented as part of the one or more processors <NUM>. The module <NUM>-<NUM> may also be implemented as an integrated circuit or through other hardware such as a programmable gate array. In another example, the module <NUM> may be implemented as module <NUM>-<NUM>, which is implemented as computer program code <NUM> and is executed by the one or more processors <NUM>. For instance, the one or more memories <NUM> and the computer program code <NUM> may be configured to, with the one or more processors <NUM>, cause the user equipment <NUM> to perform one or more of the operations as described herein. The user equipment <NUM> communicates with RAN node <NUM> via a wireless link <NUM>. The modules <NUM>-<NUM> and <NUM>-<NUM> may be configured to implement the functionality of the user equipment as described herein.

The RAN node <NUM> in this example is a base station that provides access by wireless devices such as the user equipment <NUM> to the wireless network <NUM>. Thus, the RAN node <NUM> (and the base station) may also be called as an access point of a wireless communication network). The RAN node <NUM> may be, for example, a base station for <NUM>, also called New Radio (NR). In <NUM>, the RAN node <NUM> may be a NG-RAN node, which is defined as either a gNB or an ng-eNB. A gNB is a node providing NR user plane and control plane protocol terminations towards the UE and connected via the NG interface to a 5GC (such as, for example, the network element(s) <NUM>). The ng-eNB is a node providing E-UTRA user plane and control plane protocol terminations towards the UE and connected via the NG interface to the 5GC. The NG-RAN node may include multiple gNBs, which may also include a central unit (CU) (gNB-CU) <NUM> and distributed unit(s) (Dus) (gNB-Dus), of which DU <NUM> is shown. Note that the DU <NUM> may include or be coupled to and control a radio unit (RU). The gNB-CU <NUM> is a logical node hosting radio resource control (RRC), SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-Dus. The gNB-CU <NUM> terminates the F1 interface connected with the gNB-DU <NUM>. The F1 interface is illustrated as reference <NUM>, although reference <NUM> also illustrates a link between remote elements of the RAN node <NUM> and centralized elements of the RAN node <NUM>, such as between the gNB-CU <NUM> and the gNB-DU <NUM>. The gNB-DU <NUM> is a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU <NUM>. One gNB-CU <NUM> supports one or multiple cells. One cell is supported by only one gNB-DU <NUM>. The gNB-DU <NUM> terminates the F1 interface <NUM> connected with the gNB-CU <NUM>. Note that the DU <NUM> is considered to include the transceiver <NUM>, e.g., as part of a RU, but some examples of this may have the transceiver <NUM> as part of a separate RU, e.g., under control of and connected to the DU <NUM>. The RAN node <NUM> may also be an eNB (evolved NodeB) base station, for LTE (long term evolution), or any other suitable base station or node.

The CU <NUM> may include the processor(s) <NUM>, memory(ies) <NUM>, and network interfaces <NUM>.

The RAN node <NUM> includes a module <NUM>, comprising one of or both parts <NUM>-<NUM> and/or <NUM>-<NUM>, which may be implemented in a number of ways. The module <NUM> may be implemented in hardware as module <NUM>-<NUM>, such as being implemented as part of the one or more processors <NUM>. The module <NUM>-<NUM> may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the module <NUM> may be implemented as module <NUM>-<NUM>, which is implemented as computer program code <NUM> and is executed by the one or more processors <NUM>. For instance, the one or more memories <NUM> and the computer program code <NUM> are configured to, with the one or more processors <NUM>, cause the RAN node <NUM> to perform one or more of the operations as described herein. Note that the functionality of the module <NUM> may be distributed, such as being distributed between the DU <NUM> and the CU <NUM>, or be implemented solely in the DU <NUM>. The modules <NUM>-<NUM> and <NUM>-<NUM> may be configured to implement the functionality of the base station described herein. Such functionality of the base station may include a location management function (LMF) implemented based on functionality of the LMF described herein. Such LMF may also be implemented within the RAN node <NUM> as a location management component (LMC).

The one or more buses <NUM> may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers <NUM> may be implemented as a remote radio head (RRH) <NUM> for LTE or a distributed unit (DU) <NUM> for gNB implementation for <NUM>, with the other elements of the RAN node <NUM> possibly being physically in a different location from the RRH/DU <NUM>, and the one or more buses <NUM> could be implemented in part as, for example, fiber optic cable or other suitable network connection to connect the other elements (e.g., a central unit (CU), gNB-CU) of the RAN node <NUM> to the RRH/DU <NUM>. Reference <NUM> also indicates those suitable network link(s).

It is noted that description herein indicates that "cells" perform functions, but it should be clear that equipment which forms the cell may perform the functions. The cell makes up part of a base station. That is, there can be multiple cells per base station. For example, there could be three cells for a single carrier frequency and associated bandwidth, each cell covering one-third of a <NUM> degree area so that the single base station's coverage area covers an approximate oval or circle. Furthermore, each cell can correspond to a single carrier and a base station may use multiple carriers. So, if there are three <NUM> degree cells per carrier and two carriers, then the base station has a total of <NUM> cells.

The wireless network <NUM> may include a network element or elements <NUM> that may include core network functionality, and which provides connectivity via a link or links <NUM> with a further network, such as a telephone network and/or a data communications network (e.g., the Internet). Such core network functionality for <NUM> may include location management functions (LMF(s)) and/or access and mobility management function(s) (AMF(S)) and/or user plane functions (UPF(s)) and/or session management function(s) (SMF(s)). Such core network functionality for LTE may include MME (Mobility Management Entity)/SGW (Serving Gateway) functionality. These are merely example functions that may be supported by the network element(s) <NUM>, and note that both <NUM> and LTE functions might be supported. The RAN node <NUM> is coupled via a link <NUM> to the network element <NUM>. The link <NUM> may be implemented as, e.g., an NG interface for <NUM>, or an S1 interface for LTE, or other suitable interface for other standards. The network element <NUM> includes one or more processors <NUM>, one or more memories <NUM>, and one or more network interfaces (N/W I/F(s)) <NUM>, interconnected through one or more buses <NUM>. The one or more memories <NUM> and the computer program code <NUM> are configured to, with the one or more processors <NUM>, cause the network element <NUM> to perform one or more operations such as functionality of an LMF as described herein. In some examples, a single LMF could serve a large region covered by hundreds of base stations.

The computer readable memories <NUM>, <NUM>, and <NUM> may be of any type suitable to the local technical environment and may 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. The computer readable memories <NUM>, <NUM>, and <NUM> may be means for performing storage functions. The processors <NUM>, <NUM>, and <NUM> may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples. The processors <NUM>, <NUM>, and <NUM> may be means for performing functions, such as controlling the UE <NUM>, RAN node <NUM>, network element(s) <NUM>, and other functions as described herein.

Module <NUM>-<NUM> and/or module <NUM>-<NUM> may implement the functionalities and signaling of the gNB or radio node as herein described. Computer program code <NUM> may implement the functionalities and signaling of the AMF or network element as herein described.

A base station with which a user equipment is connected or camped on, may be called as a serving base station. In practical situations the serving base station and the camped on base station may change e.g. when the user equipment in moving, or if the signal strength from different base stations changes (e.g. signals from a neighbouring base station becomes stronger than signals from the currently serving base station.

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

Frequency bands for <NUM> NR are separated into two frequency ranges: Frequency Range <NUM> (FR1) including sub-<NUM> frequency bands, i.e. bands traditionally used by previous standards, but also new bands extended to cover potential new spectrum offerings from <NUM> to <NUM>, and Frequency Range <NUM> (FR2) including frequency bands from <NUM> to <NUM>. Thus, FR2 includes the bands in the mmWave range, which due to their shorter range and higher available bandwidth require somewhat different approach in radio resource management compared to bands in the FR1.

<FIG> depicts examples of simplified system architectures showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown.

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

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

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

The communication system may also be able to communicate with other networks, such as a public switched telephone network or the Internet <NUM>, or utilize services provided by them.

In <NUM> systems a base station may have a MIMO antenna array comprising dozens of individual antenna elements. Signals to and from those antenna elements can be controlled e.g. by signal-processing algorithms so that a good transmission route may be utilized through air to each user equipment. Then the base stations can send individual data packets in many different directions (with different beams). Beamforming allows many users and antennas on such MIMO array to exchange much more information at once, For millimeter waves used in <NUM> networks, beamforming is primarily used to address a different set of problems: cellular signals are easily blocked by objects and tend to weaken over long distances, wherein beamforming may help by focusing a signal in a concentrated beam that points only in the direction of a user equipment rather than broadcasting in many directions at once. This approach may increase the probability that the signals arrive intact and may also reduce interference for everyone else.

<FIG> illustrates a part of a wireless network <NUM> having several base stations <NUM> and an exemplary user equipment <NUM>. In <FIG> it is assumed that the base station marked as S-BS is the serving base station, when the user equipment is in connected mode, and the base station where the user equipment is camped on when not in connected mode. Some of the neighbouring base stations are labelled as N-BS in <FIG>. In practical situations the serving base station and the camped on base station may change e.g. when the user equipment is moving, or if the signal strength from different base stations changes (e.g. signals from a neighbouring base station N-BS becomes stronger than signals from the currently serving base station.

The serving base station may have assigned one or more beams <NUM> (<FIG>) for the user equipment on the basis of some criteria. For example, that beam which is directed towards the location of the user equipment may be selected for the user equipment and if the user equipment moves to another location, another beam directed towards that new location may be selected instead. In <FIG> most of the beams are illustrated being similar to each other and one beam is illustrated to have stronger signal than the others but in practical implementations different beams may have different parameters such as signal strength, width, length etc. It should also be noted that the beams depicted in <FIG> are only illustrative but in reality the beams may have different forms and sizes.

A base station may have a spatial beam codebook which includes information of beams available by a base station, wherein the base station may control which of the available beams shall be used during transmission and/or reception.

Similarly, a UE may also have a MIMO antenna array having a plurality of individual antenna elements, wherein the UE may control which of the available beams shall be used during transmission and/or reception.

A spatial beam codebook, or shortly a codebook, may be defined as follows, for example.

A spatial beam codebook of size NB and whose elements are indexed by b is defined, wherein b = <NUM>,<NUM>,. Each spatial beam (worded as beam henceforth) corresponds to a radiation pattern whose main lobe is uniquely directed to an angular direction with respect to the antenna array broadside in both the azimuth (i.e. horizontal) and zenith (i.e. vertical) planes. The angular direction for the bth beam may be denoted as (hb, vb) where hb and vb are horizontal angles and vertical angles of the bth beam, respectively.

Transmission and reception beamforming may be performed e.g. by adjusting phase angles and/or delays of individual signal paths of the transmitter and/or receiver. In the following, the transmitter related beamforming is described in more detail.

<FIG> illustrates an example of a transmitter RF front end of a user equipment. Signals to be transmitted are provided to an input RF/IF as radio frequency (RF) signals or as intermediate frequency (IF) signals. Control information is provided to a control input CTRL. The RF front end comprises a filter F such as a low-pass filter to filter out frequencies which are above a certain limit. This kind of filtering may filter out e.g. harmonic components of the input signals. A splitter S divides the input signal to several paths. The number of paths is equal to the number of beams NB, for example. Each path has a phase shifter PS and a power amplifier PA. The phase shifter produces a delay to the signal and the power amplifier PA amplifies the output signal from the phase shifter. The power amplifiers are coupled to elements of the antenna array ANT. The RF front end can direct the beams by adjusting the delays of the phase shifters PS and the amplification of the power amplifiers PA. The codebook comprises indexed information of the delays and amplifications for each phase shifter and power amplifier, respectfully, so that each index (codebook entry) is associated with information to be used to obtain a certain radiation pattern (i.e. beam). For example. the codebook index <NUM> may contain phase delays and amplification factors for a beam <NUM> directed to a first direction, the codebook index <NUM> may contain phase delays and amplification factors for a beam <NUM> directed to a second direction,. , and the codebook index N may contain phase delays and amplification factors for a beam N directed to an Nth direction.

<FIG> illustrates an example of a reception RF front end of a user equipment. Signal received by elements of an antenna array are provided to low-noise amplifiers LNA which amplify the received signals by an amplification factor. The amplified signals are provided to phase shifters PS to induce delay to the received, amplified signals. The delayed signals are combined by a summing element S to produce a reconstructed signal for further processing. an input RF/IF as radio frequency (RF) signals or as intermediate frequency (IF) signals. The RF front end also comprises a filter F such as a low-pass filter to filter out frequencies from the reconstructed signal which are above a certain limit. The RF front end can direct the reception beams by adjusting the delays of the phase shifters PS and the amplification of the low-noise amplifiers LNA. As was explained above in connection with the transmitter RF front end, the codebook comprises indexed information of the delays and amplifications for each phase shifter and low-noise amplifier, respectfully, so that each index is associated with information to be used to obtain a certain radiation pattern (i.e. beam). For example. the codebook index <NUM> may contain phase delays and amplification factors for a beam <NUM> directed to a first direction, the codebook index <NUM> may contain phase delays and amplification factors for a beam <NUM> directed to a second direction,. , and the codebook index N may contain phase delays and amplification factors for a beam N directed to an Nth direction.

<FIG> illustrates an example of another reception RF front end of a user equipment. In this example, there is a plurality of phase shifters and summing elements so that more than one reception beam can be utilized simultaneously i.e. in parallel. For example, there are three groups of phase shifters and summing elements, wherein the receiver RF front end is able to simultaneously receive signals from three different beams. In accordance with an embodiment, the beams may be three adjacent beams. Hence, the user equipment may be able to analyze signal conditions in the environment faster than if only one reception chain were in use.

It should be noted that, for clarity, <FIG> and <FIG> show only some operational blocks of the RF front ends but in practical implementations there are also other operational blocks such as mixers etc. Furthermore, although the transmission RF front end and the reception RF front end are depicted separately, they may be implemented as one circuitry and some components may be common for both RF front ends.

In the following, the operation of the user equipment <NUM> when determining an appropriate beam or a set of beams for calibration purposes will described in more detail with reference to the flow diagram of <FIG>.

The user equipment <NUM> selects a first codebook entry to select a reception beam and starts measurement of the received signal(s) to obtain information related to received signal strength via the selected reception beam. This information may be a Received Signal Strength Indicator (RSSI), where RSSI is the total received power including noise and interference. The user equipment <NUM> scans through <NUM> all the available codebook entries (i.e. the available reception beams), obtains the measurement result and stores the measurement results to a memory. When each codebook entry has been processed and the corresponding signal strength measured, the user equipment <NUM> orders (ranks) <NUM> the codebook entries to an order of the signal strength from lowest to highest (or the other way round). The user equipment <NUM> obtains timing information for a measurement slot for calibration e.g. by sending measurement resources request <NUM> to the gNB. The gNB may grant <NUM> the measurement slot and send information of the granted measurement resources to the user equipment <NUM>. The granted measurement slot, as part of the measurement resources, for calibration may also be called as a calibration gap in this disclosure. The user equipment <NUM> selects <NUM> that codebook entry which was showing the lowest signal strength in the scanning and ranking procedure. Thus, the delays of the phase shifters PS and amplifications of the power amplifiers of the transmission RF end are set according to the parameters indicated by the selected codebook entry.

Then, the user equipment <NUM> performs the calibration <NUM> by setting the amplification of the transmission RF front end to a maximum and transmitting a measurement signal via the selected beam in the transmission slot. The user equipment <NUM> receives the transmitted signal by another MIMO branch and performs calibration. This way, the user equipment <NUM> may deduce how the operation of a pre-distorter <NUM> (<FIG>) of the power amplifier should be adjusted to improve the linearity, for example.

During or as a result of the calibration the user equipment <NUM> may store e.g. calibrated coefficients to a coefficient memory <NUM> (<FIG>) to be used when adjusting the pre-distorter to compensate non-linearities of the power amplifier.

After the calibration procedure has been performed, the user equipment <NUM> may select <NUM> that codebook entry which corresponds with the beam to be used in communication with the serving gNB of the user equipment <NUM>. <FIG> illustrates an example of the user equipment UE <NUM> communicating with the base station gNB.

The above calibration procedure may be repeated <NUM> at intervals or when determined by the user equipment <NUM> or instructed by the gNB, for example.

In accordance with an embodiment of the disclosure, the user equipment <NUM> may receive from the serving gNB indication of repetitive measurement slots, wherein the user equipment <NUM> may repeatedly perform the calibration operation at the time instances of the measurement slots.

<FIG> illustrates another embodiment of the disclosure for calibration of the pre-distorter <NUM> for the power amplifier PA of the user equipment. The pre-distorter <NUM> may also be called as a digital pre-distorter <NUM> when it operates in baseband based on digital data. A pre-distorter operating with analogue IF or RF signals may be called as an analog pre-distorter. The embodiment of <FIG> differs from the embodiment of <FIG> so that after ordering <NUM> the codebook entries according to measured signal strengths, the user equipment <NUM> sends <NUM> to the gNB a recommended beam or beams for self-calibration of the user equipment <NUM> so that the gNB would be able to indicate the right beam to use for the self-calibration transmission. The gNB may have some additional information which may be used in selecting the most appropriate codebook entry. For example, if the user equipment <NUM> indicated two or even more alternative codebook entries, the gNB may examine which one of the indicated codebook entries would be the most appropriate codebook entry for the calibration procedure.

Indication of the right codebook entry by the gNB may be provided, for example, through a Medium Access Control - Control Element (MAC-CE) or a downlink control information (DCI) message. The Medium Access Control - Control Element (MAC-CE) message may be carried by a Physical Downlink Shared Channel (PDSCH). The downlink control information message may be carried by a Physical Downlink Control Channel (PDCCH). DCI contains the scheduling information for the UL or DL data channels and other control information for one UE or a group of Ues.

The procedure presented above may minimize or at least reduce interference and blockage done in the system as the user equipment <NUM>, when performing the calibration, transmits in the direction of least interference, possibly away from the gNB. In other words, the interference in the surrounding is scanned after which the calibration signal may be sent to a direction in which least disturbance might occur. An example of this is illustrated in <FIG> in which the beam selected for the calibration is that beam which is directed approximately in the middle of the imaginary line between the first base station gNB <NUM> and the second base station gNB <NUM>.

The signal transmitted by the user equipment <NUM> is captured by the user equipment <NUM> itself using a different MIMO branch in the near field, thus the directivity of the signal is not important in the scope of self-calibration.

The transmitted signal captured by the user equipment <NUM> is the near field signal, therefore the setting of the phase shifters will have no impact on the useful signal for self-calibration. However the far field signal may minimize any interference in the network.

In accordance with an embodiment of the disclosure the same calibration gap could be granted for several user equipment or each user equipment is granted a unique calibration gap.

In accordance with an embodiment of the disclosure, the user equipment <NUM> may not need to determine the weakest signal strength but a threshold may be determined or indicated wherein in the ordering phase <NUM> the user equipment may compare the measured signal strengths with the threshold and select one of the codebook entries which produced signal strength below the threshold.

In accordance with an embodiment of the disclosure, the user equipment <NUM> may already utilize the threshold in the scanning phase <NUM> so that if a measurement indicates that the signal strength corresponding to the current codebook entry is below the threshold, the scanning <NUM> can be interrupted and the current codebook entry could be selected for the calibration.

With respect to <FIG>, some elements of the pre-distortion-power amplifier chain are illustrated as a greatly simplified block diagram, in accordance with an embodiment. A signal to be transmitted (a base band signal) is entered to the pre-distorter <NUM> which performs the de-linearization of the signal based on calibrated coefficients previously stored into the coefficient memory <NUM>. The modified signal is upconverted by a first upconverter <NUM> to an intermediate frequency determined by a first local oscillator frequency LO1. The intermediate frequency signal may be processed in the intermediate signal block <NUM> and provided further to a second upconverter <NUM> to a radio frequency signal determined by a second local oscillator frequency LO2. At the output of the second upconverter <NUM> the RF signal is provided to the power amplifier stage <NUM> where the selected codebook entry is used to adjust phase delays of the phase shifters PS and amplification coefficients of the power amplifiers PA.

It should be noted that the base band signal may be directly converted to the RF signal wherein the IF parts <NUM> and <NUM> are not needed.

With respect to <FIG>, an example of a system within which embodiments of the disclosure can be utilized is shown. The system <NUM> comprises multiple communication devices which can communicate through one or more networks. The system <NUM> may comprise any combination of wired and/or wireless networks including, but not limited to a wireless cellular telephone network (such as a GSM (<NUM>, <NUM>, <NUM>, LTE, <NUM>), UMTS, CDMA network etc.), a wireless local area network (WLAN) such as defined by any of the IEEE <NUM>. x standards, a Bluetooth personal area network, an Ethernet local area network, a token ring local area network, a wide area network, and the Internet.

For example, the system shown in <FIG> shows a mobile telephone network <NUM> and a representation of the internet <NUM>. Connectivity to the internet <NUM> may include, but is not limited to, long range wireless connections, short range wireless connections, and various wired connections including, but not limited to, telephone lines, cable lines, power lines, and similar communication pathways.

The example communication devices shown in the system <NUM> may include, but are not limited to, an electronic device or apparatus <NUM>, a combination of a personal digital assistant (PDA) and a mobile telephone <NUM>, a PDA <NUM>, an integrated messaging device (IMD) <NUM>, a desktop computer <NUM>, a notebook computer <NUM>, a tablet computer. The apparatus <NUM> may be stationary or mobile when carried by an individual who is moving. The apparatus <NUM> may also be located in a mode of transport including, but not limited to, a car, a truck, a taxi, a bus, a train, a boat, an airplane, a bicycle, a motorcycle or any similar suitable mode of transport.

Some or further apparatus may send and receive calls and messages and communicate with service providers through a wireless connection <NUM> to a base station <NUM>. The base station <NUM> may be connected to a network server <NUM> that allows communication between the mobile telephone network <NUM> and the internet <NUM>. The system may include additional communication devices and communication devices of various types.

The communication devices may communicate using various transmission technologies including, but not limited to, code division multiple access (CDMA), global systems for mobile communications (GSM), universal mobile telecommunications system (UMTS), time divisional multiple access (TDMA), frequency division multiple access (FDMA), transmission control protocol-internet protocol (TCP-IP), short messaging service (SMS), multimedia messaging service (MMS), email, instant messaging service (IMS), Bluetooth, IEEE <NUM>, Long Term Evolution wireless communication technique (LTE), <NUM> and any similar wireless communication technology. Yet some other possible transmission technologies to be mentioned here are high-speed downlink packet access (HSDPA), high-speed uplink packet access (HSUPA), LTE Advanced (LTE-A) carrier aggregation dual- carrier, and all multi-carrier technologies. A communications device involved in implementing various embodiments of the present invention may communicate using various media including, but not limited to, radio, infrared, laser, cable connections, and any suitable connection. In the following some example implementations of apparatuses utilizing the present invention will be described in more detail.

In accordance with at least some examples the communications of the communications devices may comprise uplink transmissions and/or downlink transmissions of data. The uplink transmissions may be performed from a wireless device to the wireless communication system, e.g. an access node, and the downlink transmissions may be performed from the wireless communication system, e.g. an access node, to the wireless device. The uplink transmissions may be performed on an uplink shared channel, e.g. a Physical Uplink Shared Channel (PUSCH). The PUSCH may be transmitted by the wireless device on the basis of a grant received on a downlink control channel, e.g. a Physical Downlink control Channel (PDCCH). The downlink transmissions may be performed on a downlink shared channel, e.g. a Physical Downlink Shared Channel (PDSCH). Release <NUM> specifications of the 3GPP may be referred to for examples PUSCH and PDSCH procedures.

The downlink and uplink transmissions may be organized into frames, e.g. a radio frame. In an example, each frame may be of <NUM> duration and divided into subframes of <NUM> duration. Each subframe may be further divided into multiple Orthogonal Frequency Division-Multiplexing (OFDM) symbols. The OFDM symbols may be arranged to slots within each subframe. In an example, the radio frame may include <NUM> subframes. One subframe may include two consecutive slots of <NUM> symbols with <NUM> sub-carrier spacing. Accordingly, the radio frame may in total include <NUM> slots.

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

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

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

Embodiments of the inventions may be practiced in various components such as integrated circuit modules, field-programmable gate arrays (FPGA), application specific integrated circuits (ASIC), microcontrollers, microprocessors, a combination of such modules.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the exemplary embodiment of this invention.

Claim 1:
An apparatus comprising:
means for measuring strength of signals received via a plurality of beams of one or more antenna arrays (<NUM>) of a user equipment (<NUM>);
means for ordering the beams on the basis of the measurement strengths;
means for determining which beam of the ordered beams is appropriate for calibration of a pre-distorter (<NUM>) for a power amplifier (<NUM>) of the user equipment;
means for obtaining information of available measurement resources for the calibration;
means for transmitting a calibration signal by the power amplifier (<NUM>) using the determined beam at the time of the available measurement resources;
means for receiving the calibration signal by another radio frequency chain of the antenna array (<NUM>) which is not used in the transmission of the calibration signal;
means for obtaining calibration information on the basis of the transmitted calibration signal and the received calibration signal; and
means for calibrating the pre-distorter (<NUM>) based on the calibration information.