The exemplary and non-limiting embodiments relate to interference cancellation in beamforming transceivers. Background

Wireless telecommunication systems are under constant development. There is a constant need for higher data rates and high quality of service. Partly for these reasons the modern telecommunication systems, such as fifth generation, 5G, networks are moving towards millimeter-wave, mmW, frequencies to seek for wide spectrum access, which eventually enables extremely high data rates.

To achieve high capacity and data rate phased antenna arrays are being used in the transmission and reception of signals. Phased antenna arrays typically comprise a multitude of antennas separated from each other by a given distance. A signal to be transmitted is fed to a number of antennas comprising an antenna array and the signal to each antenna is phased in such a manner that the antenna array forms an antenna beam, so called main lobe, to a desired direction. Phased antenna arrays are particularly useful at high frequencies such as mmW frequencies as due to the high frequency multiple antennas may be designed with a relatively compact form factor. Using many antennas in an array improves the directivity and this high antenna directivity may be used to compensate for high path losses at higher frequencies.

In addition to main lobe, antenna arrays produce also side lobes, which are unwanted radiation in undesirable directions. One problem related to phased antenna arrays utilizing multiple beams is the interference between the beams. Two beams whose directions are close to each other may interfere each other by their main lobes and beams that are further from each other may interfere by their side lobes. This interference an antenna array to another antenna array is called Interbeam Interference, IBI. Brief description

The following presents a simplified summary of the invention in or- der to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to a more detailed description that is presented later.

According to an aspect of the present invention, there is provided an apparatus in a radio access network, comprising: a circuitry for determining communication parameters for a set of phased subarrays each configured to transmit or receive an independent data signal utilising a beam at a given direction; a circuitry determining for each subarray direction of the transmitted or received signal and interference level caused by each other subarray of the apparatus in the directions used by the subarrays; a cross-coupling circuitry for each subarray for forming from the data signal of each other subarray in the direction used by the subarray a cross-coupling signal having an amplitude similar to the determined interference level; inverting the phase of the cross- coupling signal of each other subarray and combining the cross-coupling signals of each other subarray with the independent data signal of each subarray.

According to an aspect of the present invention, there is provided a method, in an apparatus in a radio access network, comprising: determining communication parameters for a set of phased subarrays each configured to transmit or receive an independent data signal utilising a beam at a given direction; determining for each subarray direction of the transmitted or received signal and interference level caused by each other subarray of the apparatus in the directions used by the subarrays; forming from the data signal of each other subarray in the direction used by the subarray a cross-coupling signal having an amplitude similar to the determined interference level; inverting the phase of the cross-coupling signal of each other subarray and combining the cross-coupling signals of each other subarray with the independent data signal of each subarray.

Brief description of drawings

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

Figure 1 illustrates a general architecture of an exemplary system;

Figure 2 illustrates an example of interbeam interference; Figures 3A and 3B are flowcharts illustrating some examples of embodiments;

Figure 4 illustrates an example of interbeam interference cancellation;

Figure 5 illustrates a simplified example of an apparatus in which some embodiments of the invention may be applied;

Figures 6A and 6B illustrate simplified example embodiments of a base band realisation;

Figures 7A and 7B illustrate simplified example embodiments of an intermediate frequency realisation;

Figures 8A and 8B illustrate simplified example embodiments of a radio frequency realisation;

Figure 9 illustrates simplified example embodiments with carrier aggregation; and

Figure 10 illustrates a simplified example embodiment.

Detailed description of some embodiments

In the following, different exemplifying embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A) or new radio (NR, 5G), without restricting the embodiments to such an architecture, however. It is obvious for a person skilled in the art that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE, the same as E- UTRA), wireless local area network (WLAN or WiFi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof.

Fig. 1 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in Fig. 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown in Fig. 1.

The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

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

Fig. 1 shows user devices 100 and 102 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) 104 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.

A communications 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 data and signalling 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 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 bi-directional 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 106 (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, 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. 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 Internet of Things (loT) 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 may also utilise cloud. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. 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.

Various techniques described herein may also be applied to a cyber- physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in Fig. 1 ) may be implemented. 5G enables using multiple input - multiple output (MIMO) antennas, 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. 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 (such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integradable 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 6GHz - cmWave, below 6GHz - 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.

The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet 112, or utilise services provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in Fig. 1 by “cloud” 114). The communication system may also comprise a central control entity, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NVF) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 104) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 108).

It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or nodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

In an embodiment, 5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine- to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 110 in the mega- constellation may cover several satellite-enabled network entities that create on- ground cells. The on-ground cells may be created through an on-ground relay node 104 or by a gNB located on-ground or in a satellite.

It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the user device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs or may be a Home(e/g)nodeB. Additionally, in a geographical area of a radio communication system a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The (e/g)NodeBs of Figure 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e/g)NodeBs are required to provide such a network structure.

For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” (e/g)NodeBs has been introduced. Typically, a network which is able to use“plug-and-play” (e/g)Node Bs, includes, in addition to Home (e/g)NodeBs (H(e/g)nodeBs), a home node B gateway, or HNB-GW (not shown in Figure 1 ). A HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

As mentioned, radio access network may be split into two logical entities called Central Unit (CU) and Distributed Unit (DU). In prior art, both CU and DU supplied by the same vendor. Thus they are designed together and interworking between the units is easy. The interface between CU and DU is currently being standardized by 3GPP and it is denoted F1 interface. Therefore in the future the network operators may have the flexibility to choose different vendors for CU and DU. Different vendors can provide different failure and recovery characteristics for the units. If the failure and recovery scenarios of the units are not handled in a coordinated manner, it will result in inconsistent states in the CU and DU (which may lead to subsequent call failures, for example). Thus there is a need to enable the CU and DU from different vendors to coordinate operation to handle failure conditions and recovery, taking into account the potential differences in resiliency capabilities between the CU and DU.

As mentioned, antenna arrays with multiple antennas are utilized in modern wireless communication systems. In an embodiment, the antenna array comprises a set of phased subarrays each comprising a set of antennas and each configured to transmit or receive an independent data signal utilising a beam at a given direction.

In an embodiment, the subarrays in the set of subarrays may be partly sharing same antenna elements, such as power amplifiers, low noise amplifiers, variable gain amplifier, and/or phase shifters or they may also be completely separate subarrays

The signals transmitted by the subarrays may interfere with each other. If the transmission directions of different subarrays are close to each other the main lobes may be partially overlapping and cause interbeam interference (IBI). If the transmission directions are farther away from each other the side lobes transmitted by a subarray may cause interference to the main lobe of another subarray.

For maximizing the data-rates for individual users, one need to also maximize the signal-to-interference-plus-noise-ratio (SINR), for each user. High data-rates proposed in 5G require large SINR, even more than 30 dB, for example. IBI limits the achievable SINR at the receiver in other word, IBI limits the achievable data-rate. Without interference reduction schemes, theoretical side lobe level is always close to 13 dB which limits the maximum SINR to be even worse than that in worst case if several beams are transmitted at the same time. Without any interference reduction techniques, the beams are required to be relatively far from each other to achieve decent SINRs for the users.

There are various know ways of reducing IBI. In amplitude tapering, symmetric amplitude distribution is used to reduce all side lobes. This reduces IBI to all directions. However, because power amplifiers of the subarrays can deliver only limited power per antenna element, the peak of the distributions has to be scaled to the limit. Thus, power available from the power amplifiers is limited and effective isotropic radiated power (EIRP) of the system will be reduced. In the receiver, similar problem occurs with noise versus receiver gain, if the amplitude levels are varied from unitary. This is because each analog signal combined in the combiner has individual signal level dependent signal-to- noise ratio (SNR).

In analogue zero forcing (ZF), notches are created to the signal transmitted by a subarray in those directions were other subarrays are transmitting. For each subarray, ZF coefficients must be defined. This requires changing the analogue beamformer coefficients. Thus, analogue ZF requires changing amplitude distribution from unitary. This in turn causes reduction in achievable EIRP.

Fig.2 illustrates an example of interbeam interference. The figure shows transmission of two subarrays. On x-axis of Fig.2 is transmission direction in degrees and on y-axis array gain in dB. The first subarray transmits a signal having a main lobe 200 at +10° 216 and side lobes 202, 204 and 206 drawn in solid line. The second subarray transmits a signal having a main lobe 208 at - 10° 218 and side lobes 210, 212 and 214 drawn in dotted line. The main lobes

200, 208 of the signals are separated thus by 20 degrees in direction. It can be seen that the main lobe 200 of the first subarray produces considerable interbeam interference 220 for the main lobe 208 of the second subarray.

The flowcharts of Figs. 3A and 3B illustrate an example of an embodiment in an apparatus of a radio access network. The apparatus may be an access point, a remote radio head or a base station comprising radio parts, for example. The apparatus comprises a set of subarrays, which may be different in size. Thus the number of antenna elements may vary between the subarrays.

In step 300 of Fig.3A, the apparatus is configured to determine communication parameters for a set of phased subarrays each configured to transmit or receive an independent data signal utilising a beam at a given direction.

Fig. 3B illustrates an example of determining communication parameters.

In step 310, the apparatus is configured to determine transmission or reception directions utilising known beam training or channel estimation methods. Flere the directions correspond to directions where user terminals or other devices the apparatus is communicating with are. The directions may be also individual Multiple-Input-Multiple-Output (MIMO) streams transmitted to the same terminal or other device via several multipaths. In step 312, the apparatus is configured to allocate the directions to the subarrays.

Typically in each direction there is an apparatus with which the apparatus is configured to communicate. Each subarray is processing an independent data signal, either transmitting or receiving. Coarse beamforming may be performed at this phase to maximise power in or from each desired direction.

In step 314, the apparatus is configured to calculate effective channel from the subarray inputs to the different directions determined in step 310.

Returning to flowchart of Fig. 3B, in step 302, the apparatus is configured to estimate interbeam interference. In an embodiment, information obtained in step 314 is utilised in the estimation. The estimation of the interference can be also sampled by feedback techniques which sample and phase shifts at each antenna input or beam to measure the interference and calibrate the beamforming transmitter and receiver. Thus, the interference caused by the transmission or reception of each subarray is estimated for all other subarrays communicating at the same time. In other words, for each subarray the interference level caused by each other subarray of the apparatus is determined in the direction used by the subarray;

In step 304, the apparatus is configured to form for each subarray from the data signal of each other subarray in the direction used by the subarray a cross-coupling signal having an amplitude similar to the determined interference level. In step 306, the apparatus is configured to invert the phase of the cross-coupling signal of each other subarray.

In step 308, the apparatus is configured to combine the cross- coupling signals of each other subarray with the independent data signal of each subarray.

Thus the cross-coupling signals of a subarray create a cancellation beam limiting the transmission power of the subarray in given directions to which other subarrays are transmitting.

Fig .4 illustrates an example of interbeam interference cancellation. Like in Fig .2, the figure shows transmission of two subarrays. On x-axis of Fig.4 is transmission direction in degrees and on y-axis signal strength in dB. The first subarray transmits a signal having a main lobe 200 and side lobes 202, 204 and 206 drawn in solid line. The second subarray transmits a signal having a main lobe 208 and side lobes 210, 212 and 214 drawn in dotted line. Due to interbeam interference cancellation, the transmission of the first subarray has a notch 400 where the main lobe 208 of the second subarray is. Likewise, the transmission of the second subarray has a notch 404 where the main lobe 200 of the first subarray is. The effect to the main lobe gain is negligible. Further away the main lobes are from each other, less impact the proposed technique has for the main lobe gain.

Whereas the prior art interbeam interference cancellation techniques such as zero forcing or amplitude tapering require changing the actual beamforming coefficients, embodiments of the proposed technique are targeted for cancelling the interference without controlling the amplitudes of individual antenna elements. As the technique can be also applied in baseband, harmful effects of wideband signals can be also reduced.

Figure 5 illustrates an embodiment. The figure illustrates a simplified example of an apparatus 500 of a radio access network in which embodiments of the invention may be applied. In some embodiments, the apparatus may be a base station, an access point or a remote radio head, for example.

It should be understood that the apparatus is depicted herein as an example illustrating some embodiments. It is apparent to a person skilled in the art that the apparatus may also comprise other functions and/or structures and not all described functions and structures are required. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities. For example, the apparatus may be realized using cloud computing or distributed computing with several physical entities located in different places but connected with each other.

The apparatus of the example includes a control circuitry 502 configured to control at least part of the operation of the apparatus.

The apparatus may comprise a memory 504 for storing data. Furthermore the memory may store software or applications 506 executable by the control circuitry 502. The memory may be integrated in the control circuitry.

The control circuitry 502 is configured to execute one or more applications. The applications may be stored in the memory 504.

The apparatus may further comprise radio interface 508 operationally connected to the control circuitry 502. The radio interface may be connected to a set of phased sub arrays 510.

The apparatus may further comprise one or more interfaces 512 operationally connected to the control circuitry 502. The interface may connect the apparatus to other apparatuses of the radio access system. For example, the interface may be connect the apparatus to core network and to other corresponding apparatuses.

In an embodiment, the applications 506 stored in the memory 504 executable by the control circuitry 502 may cause the apparatus to perform the interbeam interference cancellation described above.

The cross-coupling of the proposed interbeam interference utilising may be realised on base band (in digital domain), on intermediate frequency or on radio frequency. It may be applied both in transmission and reception of signals.

Fig. 6A illustrates an embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a transmitter in digital domain. In this example the apparatus serves data signals of m users so it comprises m subarrays 600A, 600B, 600C, each comprising NA antenna elements. The distance between the adjacent antenna elements in subarrays is d = l/2, where l is the wavelength of carrier frequency fo. In this example the antenna elements are assumed to be omnidirectional for simplicity. Each subarray is assumed to be a uniform linear array (ULA) in this example. In practical solutions patch antennas are typically used in antenna arrays. The number of antenna elements in subarrays may also vary.

In an embodiment, subarrays may comprise some common elements, such as power amplifiers, antenna elements, for example.

As an input to each subarray m is a data signal Sm 602A, 602B, 602C. Data signals are taken to digital-to-analogue converters (DAC) 604A, 604B, 604C where digital signals converted to analogue intermediate frequency and to mixers 606A, 606B, 606C where signals are mixed with a local oscillator signal to radio frequency.

The radio frequency signal is taken to the antenna elements of the subarray typically via a phase shifter 608, variable gain amplifier 610 and a power amplifier 612. In an embodiment, phase shifter 608 and variable gain amplifier 610 may be also replaced by vector modulator for Cartesian phase shifting and amplitude control. It may be noted that the apparatus of Fig. 6A is merely a simplified example of a possible implementation as one skilled in the art is well aware.

When performing coarse beamforming (as in step 312 above), maximum ratio transmission (MRT) may be utilised. MRT is a coarse beamforming technique for maximizing the received power of each user. MRT beam former w _{rf nm} from nth subarray to mth direction can be defined as

Wr,f,nm b-nm

where h _nm is a vector including the complex channel coefficients from the nth subarray elements to the mth user and Q ^H denotes a conjugate transpose of the vector. If we simply denote the channel of user m as a unique spatial direction e _m (i.e. line-of-sight (LOS) channel), the MRT refers to standard beam steering, which is done in RF domain in this example. For a LOS channel, h _nm corresponds only a phase progression over the antenna elements and can be defined as

where k = 2p/l corresponds wave number and d _n is the antenna spacing in nth subarray and d _mn is the spacing between mth and nth subarray. The beam pattern of the nth subarray to the azimuth direction 0 _m can be calculated by using array factor as

AFn 6 m)— W _r .f. _mn b- _nm ·

IBI from the nth to mth subarray can be calculated as

_ AFnfdm)

^Ά ^nh\ nh)

where AF _n {Q _m ) is the gain of nth beam in the direction of mth user, and AFm{0 m ) is the gain of m beam in its own desired direction.

Thus in an embodiment, the purpose is to define cross-coupling coefficients w _{ibic nm} that are applied for cross-couplings from nth data signal (transmitted by nth subarray) to mth subarray and which cancel the corresponding

In an embodiment, where each user’s signal is transmitted or received with a subarray, the other subarrays are utilised to create notches for reducing the interference and simultaneously use them for beam steering the other signals. Thus, each subarray is cross-coupled to each other in the digital domain, on analogue base band domain, on intermediate frequency or radio frequency. In other words, we a fraction of the interfering signals is added to the original beams in order to cancel the interference between the subarrays over- the-air.

In an embodiment, a scaled and phase-shifted version of the interfering signal is added inside the beam under interference. Referring again to Fig. 6A, in an embodiment, each subarray comprises a set of phase shifters 616A, 616B, 616C and scalers 618A, 618B, 618C where scaled and phase-shifted versions of the signal of the subarray is created according to calculated interference estimation. These scaled and phase-shifted versions are added to the signals of other subarrays in adders 620A, 620B, 620C.

In an embodiment, the phase shifters 616A, 616B, 616C, scalers 618A, 618B, 618C and adders 620A, 620B, 620C for a cross-coupling circuitry.

In an embodiment, the phase shifters 616A, 616B, 616C and scalers 618A, 618B, 618C may be realised as a filter. The phase shifters 616A, 616B, 616C and scalers (or filters) may be configured to perform a frequency dependent phase inversion and amplitude weighting.

In an embodiment, the cross-coupling circuitry is configured to process signals calculating phase inversion and amplitude weights for each subcarrier when the apparatus communicates in a multi-carrier radio access network.

In an embodiment, the cross-coupling circuitry is configured to process signals by calculating the phase inversion and amplitude weights for each component carrier when the apparatus communicates in a radio access network utilising carrier aggregation.

Thus in an embodiment, the cross-coupled beams which cancel the IBI utilise the original interfering beams and are produced by the same subarray that creates the IBI. Thus, no amplitude changes are required inside the subarrays for the sake of reducing the interference. Hence, maximum EIRP available from the subarrays can be used. Further, the amount of additional hardware required to perform the cancellation of IBI is very small. Each subarray produces its own desired beam and N-1 IBI cancellation beams, where N is the number of subarrays.

The calculation of the cross-coupling coefficients may be based on the concept of the effective channel which is calculated over the beams. The effective channel over the subarray can be expressed as

Thus, the cross-coupling coefficients may be calculated as wibic ⁼ In an embodiment, the cross-coupling may be also calculated in algorithmic manner by using the simplified procedure, such as

Initialize and define subarray beamformers

for n =

for m

Calculate l _nm

Cancel nrth beam from n:th beam by coefficient ^w ibic ,nm lnm

end

end where N _u is the number of users.

The coefficients w _{ibic nm} are applied for crosscouplings from nth data signal to mth subarray. Coefficients may be presented as phase

where abs(w _{ibic nm} ) denotes the amplitude coefficient and arg{w _{ibic nm} ) denotes the phase shift. In an embodiment, the set of phase shifters 616A, 616B, 616C and scalers 618A, 618B, 618C operate using these coefficients.

It may be noted that the processing for creating the zeros is only over the subarrays, which decreases the computational complexity compared to the processing inside the subarrays.

The cross-coupled interference cancellation signals combine with the interference from other steams in the direction of 9 _m and cancels it over-the-air as Fig. 4 illustrates. In fact, each subarray creates n - 1 cancellation beams, similar to its own beam, but with different amplitude weighting. The cancellation beam has negative phase compared with the corresponding beam from the interfering subarray in the direction of interference. Hence, when the cancellation beams and original beams combine over-the-air, they cancel each other and the interference-free transmission can be achieved.

From performance point of view, the proposed cross-coupled interference cancellation and analogue zero forcing method provide similar IBI cancellation performance. However, from EIRP point of view, the proposed method is superior as zero forcing reduces the available EIRP whereas the proposed system is optimal as it can utilize unitary amplitude distribution over the subarray elements. Figure 10 illustrates an example. The signal Si of subarray 600A is cross-coupled with signals w _{ibic nm} from interfering subarrays and so before the DAC 604A the signal may be of the form

Si + (-I27S2) + ... + (-\mlSm) .

The same applies to other subarrays as illustrated so that for the nrth subarray the signal before DAC may be of the form

Sm + (-\lmSl) + (-I2/77S2) + ...

Fig. 6B illustrates an example embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a receiver in digital domain. In this example the apparatus serves data signals of m users so it comprises m subarrays 630A, 630B, 630C, each comprising NA antenna elements.

The apparatus resembles the transmitter apparatus of Fig. 6A, but here the apparatus comprises analogue-to-digital converters (ADC) 632A, 632B, 632C instead of DACs. The set of phase shifters 634A, 634B, 634C and scalers

636A, 636B, 636C and the adders 638A, 638B, 638C process signals after the ADCs.

In the examples of Fig 6A and 6B, the IBI cross-coupling signals are created and applied to digital base band signals. This is robust to implement and calibrate. Further, wideband cancellation is possible due to delay and sub-band based processing.

Fig. 7A illustrates an embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a transmitter on intermediate frequency. Also in this example the apparatus serves data signals of m users so it comprises m subarrays 700A, 700B, 700C, each comprising NA antenna elements.

As an input to each subarray m is a data signal Sm 702A, 702B, 702C. Data signals are taken to digital-to-analogue converters (DAC) 704A, 704B, 704C where digital signals converted to analogue intermediate frequency and to mixers 706A, 706B, 706C where signals are mixed with a local oscillator signal to radio frequency.

In an embodiment, each subarray comprises a set of phase shifters 708A, 708B, 708C and scalers 710A, 71 OB, 710C where scaled and phase- shifted versions of the intermediate frequency signal of the subarray is created according to calculated interference estimation. These scaled and phase-shifted versions are added to the intermediate frequency signals of other subarrays in adders 712A, 712B, 712C.

In this example, the cross-coupling signals and cross-coupling is performed to the signals after the DACs 704A, 704B, 704C to analogue signal at intermediate frequency.

In an embodiment, phase shifters may be replaced with delay elements, depending on bandwidth requirements.

In an embodiment, for carrier-aggregated systems, the cancellation can be done for each component independently, if the carrier aggregation was done in intermediate frequency.

Fig. 7B illustrates an example embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a receiver on intermediate frequency. In this example the apparatus serves data signals of m users so it comprises m subarrays 630A, 630B, 630C, each comprising NA antenna elements.

The apparatus resembles the transmitter apparatus of Fig. 7A, but here the apparatus comprises analogue-to-digital converters (ADC) 732A, 732B, 732C instead of DACs. The set of phase shifters (or delay elements) 734A, 734B, 734C and scalers 736A, 736B, 736C and the adders 738A, 738B, 738C process signals after the ADCs.

Fig. 8A illustrates an embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a transmitter on radio frequency. Also in this example the apparatus serves data signals of m users so it comprises m subarrays 800A, 800B, 800C, each comprising NA antenna elements.

As an input to each subarray m is a data signal Sm 802A, 802B, 802C.

Data signals are taken to digital-to-analogue converters (DAC) 804A, 804B, 804C where digital signals converted to analogue intermediate frequency and to mixers 806A, 806B, 806C where signals are mixed with a local oscillator signal to radio frequency.

In an embodiment, each subarray comprises a set of phase shifters

808A, 808B, 808C and scalers 810A, 810B, 810C where scaled and phase- shifted versions of the radio frequency signal of the subarray is created according to calculated interference estimation. These scaled and phase-shifted versions are added to the radio frequency signals of other subarrays in adders 812A, 812B, 812C.

In this example, the cross-coupling signals and cross-coupling is performed to the signals after the DACs 804A, 804B, 804C and afters mixers 806A, 806B, 806C to analogue signal at radio frequency.

Fig. 8B illustrates an example embodiment. The figure shows a simplified example embodiment of applying cross-coupling in a receiver on radio frequency. In this example the apparatus serves data signals of m users so it comprises m subarrays 630A, 630B, 630C, each comprising NA antenna elements.

The apparatus resembles the transmitter apparatus of Fig. 7A, but here the apparatus comprises analogue-to-digital converters (ADC) 834A, 834B, 834C instead of DACs. The set of phase shifters 836A, 836B, 836C and scalers

838A, 838B, 838C and the adders 840A, 840B, 840C process signals after the ADCs.

In an embodiment, in radio frequency realisation there are less bandwidth problems compared to intermediate frequency processing due to lower relative frequency. RF cross-coupling may be lossy to implement but applicable for some systems, such a small scale systems.

Above base band, intermediate and radio frequency implementations are shown as separate examples. Flowever, it is also possible to any combination of these alternatives.

When transmitting or receiving wide band signals there are factors to be taken into account which are not present with narrow band signals. When antenna arrays are used to receive or transmit wide band signals, the distances between the antenna elements should be taken into account. To direct a wide band beam from the antenna array to a desired direction the antenna elements may be phased utilising so called phase progression, where phase is gradually adjusted between antenna elements. Flowever, phase progression changes with frequency, and thus the direction of the beam changes over the band. The changing of the direction of the main lobe as a function of frequency is denoted as beam squinting.

The position of side lobes also changes when the main lobe changes its position. In general the performance of interference cancellation techniques degrade for wide band due to beam squinting effects.

The proposed embodiments are suitable for use also for wide band signals.

Fig. 9 illustrates an example of IBI cancellation when carrier aggregation is used. In this example, the component carrier IBI cancellation over beams 900 is performed on intermediate frequency, but base band and radio frequency realisations and combinations of these are as well possible. In carrier aggregated systems it is possible to achieve wide band IBI cancellation.

The steps and related functions described in the above and attached figures are in no absolute chronological order, and some of the steps may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between the steps or within the steps. Some of the steps can also be left out or replaced with a corresponding step.

The apparatuses or controllers able to perform the above-described steps may be implemented as an electronic digital computer, or a circuitry which may comprise a working memory (RAM), a central processing unit (CPU), and a system clock. The CPU may comprise a set of registers, an arithmetic logic unit, and a controller. The controller or the circuitry is controlled by a sequence of program instructions transferred to the CPU from the RAM. The controller may contain a number of microinstructions for basic operations. The implementation of microinstructions may vary depending on the CPU design. The program instructions may be coded by a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions.

As used in this application, the term‘circuitry’ refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

An embodiment provides a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, are configured to control the apparatus to execute the embodiments described above.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, and a software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The apparatus may also be implemented as one or more integrated circuits, such as application-specific integrated circuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hybrid of these different implementations is also feasible. When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the apparatus, the necessary processing capacity, production costs, and production volumes, for example.

In an embodiment, the apparatus comprises means for determining communication parameters for a set of phased subarrays each configured to transmit or receive an independent data signal utilising a beam at a given direction, means for determining for each subarray direction of the transmitted or received signal and interference level caused by each other subarray of the apparatus in the directions used by the subarrays, means for forming from the data signal of each other subarray in the direction used by the subarray a cross- coupling signal having an amplitude similar to the determined interference level, means for inverting the phase of the cross-coupling signal of each other subarray and means for combining the cross-coupling signals of each other subarray with the independent data signal of each subarray.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.