EP4360367A1 - Resource efficient directional emf power lock framework and scheme - Google Patents

Abstract

A method and network node are provided. According to one aspect, a method includes for each of a plurality of transmission time intervals and for each wireless device: mapping a direction indicated by a precoder matrix indication (PMI) to a direction of transmission, accumulating a directional power for each direction indicated by the PMI, and for each of a plurality of control step intervals, and for each of a plurality of directions: applying a directional beam forming gain to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; determining whether the weighted directional power of transmission exceeds a threshold corresponding to the direction, and for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, mapping the direction to a corresponding PMI.

Description

RESOURCE EFFICIENT DIRECTIONAL EMF POWER LOCK

FRAMEWORK AND SCHEME

TECHNICAL FIELD

This disclosure relates to wireless communication and in particular, to a resource efficient directional time averaged power lock framework and scheme for electromagnetic field (EMF) exposure control.

BACKGROUND

The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (4G) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (5G) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile wireless devices (WD), as well as communication between network nodes and between WDs. Sixth Generation (6G) wireless communication systems are also under development.

When any radio equipment is to be deployed, regulatory radio frequency (RF) electromagnetic field (EMF) exposure regulations need to be accounted for. These exposure limitations are typically based on the guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) but may take different forms in some countries and regions. The aim of the RF exposure regulations is to secure that the human exposure to RF energy, is kept within safe limits, which have been set with wide safety margins.

Compliance with the RF exposure limitations requires certain considerations for new 4G / 5G base stations and radios are equipped with advanced antenna systems (AAS). These AASs increase the capacity and /or coverage by addition of an antenna array that increases the beamforming gain significantly. The consequence is a concentration of the radiated power into beams. As a further consequence, the traditionally used methods for calculation of exclusion zones based on the maximum Equivalent Isotropically Radiated Power (EIRP) of the node, tend to generate significantly increased results compared to equipment without AAS. This increases the deployment challenges, which is why operators are requesting functionality for reduction of exclusion zone sizes, while strictly maintaining compliance with RF exposure regulations.

More specifically, the ICNIRP and other RF exposure limitations are typically expressed in terms of the maximum average power density over a specified time interval T. This averaging opens a possibility for the requested reductions. Given a distance, and knowledge of the AAS gain in the corresponding direction, the maximum average power density can be transformed to a corresponding maximum time averaged power threshold. Thus, the momentary power can be significantly higher than the maximum average power (also denoted the actual maximum power) during shorter times than T. However, the transmitted average power must then be guaranteed to be below the maximum average power threshold, typically obtained from the calculation of a reduced exclusion zone. Thus, to be allowed to use an exclusion zone with reduced size compared to what is obtained using the maximum EIRP of the AAS equipped node, control functionality is needed that guarantees that the average power is below the maximum average power threshold 100% of the time.

Cell Wide Average Power Control

The dynamic actuator and proportional-derivative (PD) controller described below represent one example of an average power controller, to maintain the average power below the maximum average power threshold. This prior art controller does not perform per direction average power control.

Scheduler actuator

Controller structure

The average power controller described here makes use of the lower realization of PI control in FIG. 1. That realization factors out an integrator. That integrator will be placed in or close to the scheduler, to produce the dynamics of the resource limiting threshold. As can be seen in FIG. 1, the remaining dynamics of the Pl-controller resembles a proportional term and a differentiating term. For this reason, the solution applies PD control together with an integrating resource limiting threshold. The relation between the parameter of the top and bottom realizations are obtained by equating the coefficients for equal degrees of s in:

Integrating fractional scheduler threshold

In order to get a smooth behavior of the dynamic resource threshold applied in the scheduler to limit the momentary output power, it may be rate controlled. This means that the control signal commands adjustments to the limiter, making it increase or decrease. The dynamics of the actuator mechanism (dynamic resource threshold) is therefore determined to be: where y(t) is the dynamic resource threshold and where u(t) is the control signal further discussed below, t denotes continuous time. This is in line with the factored

PI control structure of FIG. 1. The dynamic resource threshold is decoupled from the scheduler algorithms themselves, and just expresses a fractional limitation of the scheduler not to use more than a fraction y(t) of its total resources. The scheduler may then limit the number of frequency resources (physical resource blocks, (PRBs)) it uses, or limit any other quantity that correlates well with the momentary output power.

Integrating fractional scheduler threshold limitation

The maximum value of y(t) is obviously 1.0 since it is to express a fraction of the maximum amount of scheduler resources. There may also be a limit to the lower value of y(t), to avoid a situation where the dynamic feedback control mechanism reduces it to an unphysical value below 0.0. The following scheduler threshold limitation is therefore applied at each time.

Y_low ≤ y(t) ≤ 1-0

Power feedback signal Radio measurement

The total momentary transmit power applied to an antenna array can be measured in the radio, just before the antenna. In one embodiment, this can be done by couplers that measure the radio signal amplitude at each signal path to an antenna element. These amplitudes can then be combined into a total transmit power of the radio, with the antenna gain removed.

Scheduler prediction

A lower complexity, but less accurate alternative would be to replace the measured power by a predicted transmit power using information available in the scheduler or elsewhere in base band. Such a quantity could be easily obtained, e.g., by summing up the momentary scheduled power as estimated by the fraction of PRB s used at each time instant, over the time T. This approach is, however subject to a number of errors. These include, e.g., the actual power errors caused by re- transmissions, power boosting and power sharing between transmission layers errors, as well as errors caused by radio signal processing close to the antenna, including, e.g., clipping to achieve peak to average power reductions, and antenna alignment errors.

FIG. 2 describes the case where feedback control has been enabled by the supervision mechanism described below. In FIG. 2, denotes the setpoint for the averaged power (typically slightly less than the threshold value that has been obtained from the regulatory power density and the desired exclusion zone), 1/s denotes the actuator dynamics with lower and upper limits inactive, denotes the scheduler limitation after lower and upper limitation (inactive in FIG. 1), P_max,site denotes the maximal total power of the site (site is here to be interpreted as cell or sector or carrier), w(t) denotes a disturbance representing predicted power errors, 1/(sT + 1) represents an autoregressive simplified model of the averaging, denotes the averaged total power, e(s) denotes a measurement error, G denotes the antenna gain and EIRP(s) denotes the EIRP. Note that all quantities are here expressed in the Laplace transform domain, which is allowed since the feedback control mechanism design is performed with constraints inactive. The momentary power described above is denoted P_tot(s) .

Note: w(s) and e(s) are a mathematical approximation of errors in the control loop, useful to assess performance aspects of some embodiments.

It is then assumed that the controller block is given by:

This controller is of PD type. C denotes the proportional gain, and T_D the differentiation time. Following standard procedures of automatic control, the poles of the closed loop system of FIG. 3 are given by the following second order equation:

These poles govern the closed loop dynamics of the feedback control mechanism, the actuator mechanism, and the averaged power. In order to determine the proportional gain and the differentiation time, a closed loop polynomial with desired poles in — α₁and — α₂ is specified as:

An identification of coefficients and solution of the resulting system of equations reveal that the proportional gain and differentiation time may be selected as:

A reason for this choice is that a system with two negative real poles can be expected to be well damped, which is a result of a significant differentiation action. Since differentiation action is needed for fast back-off close to the determined threshold, this is the preferred design choice. Some additional modification of the controller may be made to adapt to the one-sided power back-off control problem formulation. This includes only allowing negative differentiation control, and a hard safety limit applied in case the average power gets too close to the regulatory threshold. The asymmetric differentiation can be formulated as:

To implement the feedback control mechanism, are needed. The present disclosure describes an approach to obtaining and that solves problems of known methods.

Discretization

The formulation above has been done in continuous time. However, the implementation is to be performed in discrete time. This means that all dynamic parts of the controller and actuator needs to be discretized. The averaging of the momentary power does not need to be discretized since this is done at sampling rate, either by a recursive computation of the true average, or by applying summation. Thus, the equations of the controller and actuator needs to be discretized. Here, this is done with an Euler approximation. However other alternatives like the Tustin approximation could be used as well. The Euler approximation replaces the Laplace transform variable s, with the discrete time approximation of this derivative, i.e.:

Here, T_s denotes the sampling period, and is the one step delay operator. It is stressed that this implicitly assumes regular sampling in time, with very little jitter. Sampling cannot be event based. Therefore, a system clock is needed to drive the discrete time feedback control loop.

Starting with the actuator and using the fact that: sy(s) = u(s) results in the discrete time equation:

When sampling the PD controller, it is noted that there is no effect on the proportional term. However, the error signal needs to be differentiated. Since the reference value is constant it follows that it is the derivative of the average power that needs sampling. It is first noted that because of the differentiation, filtering of this derivative is also needed, according to the equation: were the filter bandwidth may be selected to a = 0.05 rad/s. Here the derivative is denoted by y(s). Following the same procedure as for the actuator results in the discrete time equation:

The discrete time control signal therefore becomes:

Model Predictive Sectorized Average Power Control

The cell-wide EMF power control solution described above applies power reduction in all directions. This however is not optimal from a capacity point of view since there is no need for power reduction in certain directions.

There is no average power control algorithm available in public prior art that provides guarantees that the controlled average power is below a power threshold 100% of the time, the threshold being set per direction by consideration of RF exposure regulations expressed in terms of an averaging time T.

The consequence is that cell wide average power control is applied, a fact that requires more frequent limitations of the momentary power (i.e., the traffic). Consequently, the current cell wide solution may limit the momentary throughput in severe ways, a fact that can be avoided with a directional solution.

An optimal method is to apply directional EMF power control. As shown in FIG. 4, a directional solution provides capacity improvement over cell wide solution. In a directional solution, resource limitations are only applied to the selected directions. Other directions which have lower average power do not need resource limitation.

Beamforming

Beamforming is a technique by which an array of transmit antenna elements can be utilized to focus the radiated energy in a specific target direction and/or reduce the radiated energy in other directions. Instead of simply broadcasting the transmitted signals in all directions, the antenna arrays that use beamforming, determine a direction of interest and form a stronger beam in this direction. This is achieved by feeding the signal to be transmitted to each antenna element and controlling the phase and amplitude of each element separately such that the signals from different elements are added constructively at the direction of interest and destructively at the nulling directions.

A two-dimensional polarized array is considered, where M_v and M_H denote the number of rows and columns of the 2-dimensional antenna array, respectively, i.e., the total number of antenna elements is given by 2M_VM_H. Let s_i,k(t) denote the information signal that should be transmitted by the antenna array in the k-th layer of the i-th WD. Transmit beamforming is applied by using the 2M_VM_H X 1 beamforming vector W_i,k(t) where the transmitted signal vector x_i(t) from the antenna array elements intended for the i-th WD at time t is represented as: where N_L is the number of transmission layers. Let M_R denote the number of receive antennas at the WD and let H_i(t) denote the M_R X 2M_VM_H channel matrix from the base station to the i-th WD where M_R is the number of antenna elements at the WD. The M_R X 1 received signal vector at the WD is given by: where n_i(t) is the interference-plus noise vector received at the WD Codebook-based beamforming

In 4G and 5G communication systems, the WD can be configured to perform measurements on the downlink received signal quality and submit these measurement reports to the base station. With Multi-antenna transmission capability at the base station, the measurement report includes a precoder matrix indicator (PMI) indicating what the device believes is a suitable precoder (beamforming) matrix. The set of possible PMI values that the device can select from when reporting PMI corresponds to a set of different precoder matrices. This set is referred to as the precoder codebook. The codebook is defined based on the number of available transmission ports, N_T and the number of transmission layers N_L. There is at least one codebook for each valid combination of N_T and N_L.

Reciprocity assisted transmission

Reciprocity-aided transmission beamforming assumes that the downlink channel is reciprocal to the uplink channel, i.e., the downlink channel vector H_i(t) can be estimated from the uplink reference symbols that are transmitted by the WD. Given the estimate of the downlink channel, the full rank beamforming matrix for the i-th WD can be selected based on the minimum mean square error criterion as: where (. )^Hdenotes the Hermitian transpose operator, Γ is a regularization factor, and is the N_R X N_R identity matrix.

The directional average transmit power control solution described above does not provide the details on how to perform beam to direction mapping. In case of grid of beams (GOB) transmission, there are up to 256 beams and it is not possible to do directional power control on all beam directions.

For GOB users, the average transmit power control solution proposes a lookup table which is created offline for all the existing radios. This may result in excessive memory consumption. New tables may need to be updated when a new radio is introduced. This may cause additional testing activities. So, it is difficult to maintain such a look-up table-based approach. For reciprocity-aided transmission users, the average transmit power control solution tries to estimate the beamforming gain per TTI. This may lead to excessive calculations in baseband. This may impact the capacity evolution of baseband and involves excessive calculations (cycles).

This solution picks the worst-case direction in which the power restriction is needed the most. Then, the power restriction is applied to all directions. This is unnecessary for many directions and result in unnecessary capacity loss.

This average transmit power control solution uses same power restriction threshold in all directions. In a customer’s network, if a direction where a kindergarten needs more restriction, a lower threshold may be set to accommodate this direction. This may also introduce unnecessary capacity loss.

SUMMARY

Some embodiments advantageously provide a method and system for a resource efficient directional electromagnetic field (EMF) average transmit power control framework and scheme.

In this disclosure, a new directional average transmit power control scheme is proposed. It defines a fixed number of directions. The transmission of a user may be mapped to a direction. The momentary power per TTI may be calculated for each direction. The calculated power may then be accumulated to form power per control step for each direction. A constant beamforming gain may be applied in different directions per control step. An average transmit power controller may be applied per direction and power restriction may be applied in the directions requiring restrictions. Some embodiments include the following 7 steps:

Step 1. Map PMI (GOB) or beam space beamforming (BF) vector (reciprocity-aided transmission) to a direction per TTI for all users;

Step 2. Estimate power per TTI per direction using allocation;

Step 3. Apply directional beamforming gain per direction;

Step 4. Run directional average transmit power controller,

Step 5. Calculate required resource restriction per direction; Step 6. Map direction to a set of PMI; and

Step 7. Apply power scaling on the PMI which requires power restriction and corresponding link adaptation adjustment

This new solution is memory and calculation efficient and practical to be implemented in many existing and upcoming new radios. This solution may apply different thresholds in different directions. Power restriction may be performed in only the directions where average power control is deemed necessary. So, this is an optimal solution for capacity.

This disclosure proposes a directional average power control algorithm that provides a 100% guarantee that the average power threshold computed from RF exposure regulations and the exclusion zone, cannot be exceeded. As shown in FIG. 4, the proposed directional average power control algorithm employs multiple controllers; one for each spatial direction or sector. For each spatial average power controller, the momentary scheduled power, as estimated by the fraction of PRBs used at each time instant, is weighted by the beamforming gain in the spatial direction of the controller. The dynamic threshold of the scheduler is then obtained as the minimum threshold limitation of all the spatial average power controllers. The computed threshold is used to limit the number of PRBs available for scheduling or to reduce the power of the downlink transmission when the WD is in the high-signal to noise ratio (SNR) operation region. As a result, the proposed solution guarantees that the average power is below the average power threshold (set by the operator) in all spatial directions. Furthermore, since the WDs are generally located in different spatial directions, downlink transmissions to different WDs contribute to different spatial average power controllers resulting in significant momentary throughput gain over the current cell-wide solution.

According to one aspect, a network node configured to communicate with a plurality of wireless devices, WDs is provided. The network node includes processing circuitry configured to: for each of a plurality of transmission time intervals, TTIs, and for each WD of the plurality of WDs: map a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD; and accumulate a directional power for each direction indicated by the first PMI. The processing circuitry is also configured to, for each of a plurality of control step intervals and for each of a plurality of directions: apply a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determine whether the weighted directional power of transmission exceeds a threshold corresponding to the direction. The processing circuitry is also configured to, for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, map the direction to a corresponding PMI.

According to this aspect, in some embodiments, the first PMI is at least one of obtained from a WD and derived from a beam forming weight, BFW. In some embodiments, the processing circuitry is further configured to scale the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction. In some embodiments, a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold. In some embodiments, the processing circuitry is further configured to apply an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling. In some embodiments, a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 100. In some embodiments, each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction. In some embodiments, the time-average power is obtained by averaging the accumulations over at least a six minute time interval. In some embodiments, the directional BFG is a function of antenna array element pattern. In some embodiments, the function is linear.

According to another aspect, a method in a network node configured to communicate with a plurality of wireless devices, WDs is provided. The method includes for each of a plurality of transmission time intervals, TTIs, and for each WD of the plurality of WDs: mapping a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD; and accumulating a directional power for each direction indicated by the first PMI. The method also includes for each of a plurality of control step intervals and for each of a plurality of directions: applying a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determining whether the weighted directional power of transmission exceeds a threshold corresponding to the direction. The method includes, for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, mapping the direction to a corresponding PMI.

According to this aspect, in some embodiments, the first PMI is at least one of obtained from a WD and derived from a beam forming weight, BFW. In some embodiments, the method also includes scaling the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction. In some embodiments, a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold. In some embodiments, the method further includes applying an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling. In some embodiments, a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 1000. In some embodiments, each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction. In some embodiments, the time-average power is obtained by averaging the accumulations over at least a six minute time interval. In some embodiments, the directional BFG is a function of antenna array element pattern. In some embodiments, the function is linear.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: FIG. 1 is an illustration of two realizations of proportional integral control;

FIG. 2 is an illustration of a feedback control block diagram;

FIG. 3 is an illustration of per direction control;

FIG. 4 is an illustration of a comparison between cell wide and directional EMF;

FIG. 5 is a schematic diagram of an example network architecture illustrating a communication system according to principles disclosed herein;

FIG. 6 is a block diagram of a network node in communication with a wireless device over a wireless connection according to some embodiments of the present disclosure;

FIG. 7 is a flowchart of an example process in a network node according to some embodiments of the present disclosure;

FIG. 8 is a system diagram showing steps of a process in accordance with principles disclosed herein;

FIG. 9 is an illustration of PMI to direction mapping;

FIG. 10 is an example of an antenna array;

FIG. 11 is an example of mapping 256 beams to 16 directions;

FIG. 12 is a mapping for an 8 port user;

FIG. 13 is a mapping of reciprocity-aided transmission users;

FIG. 14 is an illustration of momentary power estimation per TTI;

FIG. 15 is an illustration of momentary power accumulation per TTI;

FIG. 16 is a graph illustrating beam power compensation with a wide beam;

FIG. 17 is an illustration of linear compensation for directional gain; and

FIG. 18 is an illustration of mapping a direction to a set of PMI. DETAILED DESCRIPTION

Before describing in detail example embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to a resource efficient directional average transmit power controller framework and scheme. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (loT) device, or a Narrowband loT (NB-IOT) device etc.

Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).

Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure.

Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Referring again to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG. 5 a schematic diagram of a communication system 10, according to an embodiment, such as a 3GPP-type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node 16. Note that although only two WDs 22 and three network nodes 16 are shown for convenience, the communication system may include many more WDs 22 and network nodes 16.

Also, it is contemplated that a WD 22 can be in simultaneous communication and/or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a WD 22 can have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR. As an example, WD 22 can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN.

A network node 16 (eNB or gNB) is configured to include a mapping unit 24 which is configured to map a direction indicated by a first PMI to a direction of transmission to a WD 22.

Example implementations, in accordance with an embodiment, of the WD 22 and network node 16 discussed in the preceding paragraphs will now be described with reference to FIG. 6. The communication system 10 includes a network node 16 provided in a communication system 10 and including hardware 28 enabling it to communicate with the WD 22. The hardware 28 may include a radio interface 30 for setting up and maintaining at least a wireless connection 32 with a WD 22 located in a coverage area 18 served by the network node 16. The radio interface 30 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The radio interface 30 includes an array of antennas 34 to radiate and receive signal(s) carrying electromagnetic waves.

In the embodiment shown, the hardware 28 of the network node 16 further includes processing circuitry 36. The processing circuitry 36 may include a processor 38 and a memory 40. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 36 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 38 may be configured to access (e.g., write to and/or read from) the memory 40, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the network node 16 further has software 42 stored internally in, for example, memory 40, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 42 may be executable by the processing circuitry 36. The processing circuitry 36 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node 16. Processor 38 corresponds to one or more processors 38 for performing network node 16 functions described herein. The memory 40 is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 42 may include instructions that, when executed by the processor 38 and/or processing circuitry 36, causes the processor 38 and/or processing circuitry 36 to perform the processes described herein with respect to network node 16. For example, processing circuitry 36 of the network node 16 may include the mapping unit 24 which is configured to map a direction indicated by a first PMI to a direction of transmission to a WD 22.

The communication system 10 further includes the WD 22 already referred to. The WD 22 may have hardware 44 that may include a radio interface 46 configured to set up and maintain a wireless connection 32 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located. The radio interface 46 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The radio interface 46 includes an array of antennas 48 to radiate and receive signal(s) carrying electromagnetic waves.

The hardware 44 of the WD 22 further includes processing circuitry 50. The processing circuitry 50 may include a processor 52 and memory 54. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 50 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 52 may be configured to access (e.g., write to and/or read from) memory 54, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the WD 22 may further comprise software 56, which is stored in, for example, memory 54 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22. The software 56 may be executable by the processing circuitry 50. The software 56 may include a client application 58. The client application 58 may be operable to provide a service to a human or non-human user via the WD 22.

The processing circuitry 50 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD 22. The processor 52 corresponds to one or more processors 52 for performing WD 22 functions described herein. The WD 22 includes memory 54 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 56 and/or the client application 58 may include instructions that, when executed by the processor 52 and/or processing circuitry 50, causes the processor 52 and/or processing circuitry 50 to perform the processes described herein with respect to WD 22.

In some embodiments, the inner workings of the network node 16 and WD 22 may be as shown in FIG. 6 and independently, the surrounding network topology may be that of FIG. 5.

The wireless connection 32 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and/or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve.

Although FIGS. 5 and 6 show various “units” such as the mapping unit 24 as being within a respective processor, it is contemplated that these units may be implemented such that a portion of the unit is stored in a corresponding memory within the processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

FIG. 7 is a flowchart of an example process in a network node 16 according to principles set forth herein. One or more blocks described herein may be performed by one or more elements of network node 16 such as by one or more of processing circuitry 36 (including the mapping unit 24), processor 38, and/or radio interface 30. Network node 16 such as via processing circuitry 36 and/or processor 38 and/or radio interface 30 is configured to, for each of a plurality of transmission time intervals, TTIs, and for each WD 22 of the plurality of WDs 22 (Block S100): map a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD 22 (Block S102); and accumulate a directional power for each direction indicated by the first PMI (Block S 104). The process also includes, for each of a plurality of control step intervals and for each of a plurality of directions (Block S106): applying a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission (Block S108); and determining whether the weighted directional power of transmission exceeds a threshold corresponding to the direction (Block S 110). The process also includes, for each of a plurality of control step intervals, and for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, mapping the direction to a corresponding PMI (Block S112).

Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for a resource efficient directional electromagnetic field (EMF) power lock framework and scheme.

In some embodiments, a method includes the following 7 steps:

Step 1. Map PMI (GOB) or beam space BF vector (reciprocity-aided transmission) to a direction per TTI for all users;

Step 2. Estimate power per TTI per direction using allocation;

Step 3. Apply directional beamforming gain per direction;

Step 4. Run directional average power controller,

Step 5. Calculate required resource restriction per direction;

Step 6. Map direction to a set of PMI; and

Step 7. Apply power scaling on the PMI which requires power restriction and corresponding link adaptation adjustment.

As shown in FIG. 8, step 1, 2 are per TTI. Step 3, 4, 5, 6, 7 are per control step. Step 1 Mapping to a fixed direction

Input from scheduler and beamformer

The following parameters are provided from UPC/BFC to EMF domains per

TTI for all the channels and all WDs:

• CSI-RS settings;

• PMI (GOB WD);

• Weight for reciprocity-aided transmission (reciprocity- aided transmission WD);

• Power scaling factors;

• Resource allocation details;

• SU or MU; and

Common channels.

Fixed amount of directions

A sector is defined as a geographical area a carrier provides. For example, it could cover an angular sector from -x degrees to + x degrees horizontally and from - y to +y degrees, vertically. To perform directional EMF power control, the sector can be divided into a fixed number of angular directions.

They may cover all the angles within the sector in both horizontal and elevation directions. The number should be even so that there could be up to two elevation angles. In this example, 16 directions are defined. An EMF direction is defined as a direction in which the average power is restricted. It could be other sizes depending on baseband resource limitations. Directions 1 to 8 of the 16 directions cover 8 different horizontal directions for one elevation angle and direction 9 to 16 of the 16 directions cover the other 8 horizontal directions for the other elevation angle

The next step is to map all the transmissions of all the WD to a specific EMF direction. This focuses on channels using WD-specific beamforming only. There are two types: -Codebook based (e.g., GOB). A direct mapping from PMI to direction depending array configuration and channel state information reference signal (CSI- RS) configuration

-reciprocity-aided transmission based. A transformation matrix is needed to map beamforming vector to an EMF direction

Mapping for GOB users

PMI may be reported by one WD to reflect the angular information of the WD. PMI indicates the WD direction. Depending on the actual array configuration and CSI-RS configuration, PMI may be mapped to a particular direction. As shown in FIG. 9 PMI of both WD1 and WD2 belong to direction 1. The two PMI could be the same or different. PMI by WD3 belongs to direction 2. Different WD could have same or different CSI-RS configurations

For an antenna array as shown in FIG. 10, there are 32 arrays of subarray, with 4 rows and 8 columns. Each subarray consists of 3x2 antenna elements from two polarizations. One polarization for a subarray is controlled digitally to apply phase shift for beamforming. It could support 32 port CSI-RS. Here, assume codebook setting of N1=8 and N2=2 with the oversampling of O1=4 and O2=4. So, there may be 8x2x4x4=256 PMI representing 256 beam directions.

As shown in FIG. 11, direction 1 covers 16 adjacent PMI with i 12 from 4 to 7 and i11 from 16 to 20. Direction 2 covers the next group of 16 adjacent PMI with i 12 from 4 to 7 and i11 from 21 to 24. The mapping occurs horizontally first. The mapping may be different for different CSI-RS configuration and antenna array geometry.

As shown in FIG. 12, for an 8-port user, PMI is only defined in azimuth directions. There may be ambiguity in elevation. A PMI should be mapped to multiple directions. In this example, PMI1 is mapped to direction 1 and 9. Special mapping may be needed in case of reciprocity-aided transmission in which PMI might not reflect the actual spatial info of the transmission. As shown in FIG. 13, a conversion from beam forming weights (BFW) to equivalent PMI (not the ones from the WD) can be obtained to continue the PMI to direction mapping. Equivalent PMI is then mapped to direction using the same method as GOB.

For reciprocity-aided transmission precoding, the beamforming vector may already be computed in beam space. The beam space basis used for computing the reciprocity-aided transmission precoder is matched to the array configuration, i.e., a two-dimensional M_H X M_v X 2 array configuration is considered, the beamspace basis used for reciprocity-aided transmission computation is given by the columns of the M_HM_V X M_HM_V matrix where B_H and B_V are M_H X M_H and M_V X M_V DFT matrices, and the (m, k) element of B_x is given by where m = 0, M_X — 1 , k = 0, M_X — 1.

Let W(ƒ) denote the M X K antenna-space reciprocity-aided transmission precoding matrix for subband f where M = 2M_HM_V is the number of antenna elements, K is the number of layers. First, consider the case in which the directional controllers are selected such that they match the array geometry, i.e., if there are M_H horizontal directional grid points and M_V vertical directional grid points, then for each beam direction with the corresponding per-polarization beam vector b(i,j) (one of the columns of B), the beamforming gain of the reciprocity- aided transmission precoder in controller direction i,j may be computed as: where and the is the precoding matrix for elements with polarization p and is the kth column of W^(p) (f) Let represent the reciprocity-aided transmission precoder for polarization p where Note that since the reciprocity-aided transmission precoder is computed in beamspace and the directional controller grid matches the array geometry, then is already computed and is corresponds to one of the components of the beamspace reciprocity-aided transmission precoders. In particular, the components of the beamspace reciprocity-aided transmission precoder for polarization p are given by: and are readily available, and hence, G_i,j(f) can be computed efficiently.

Compute the average beamforming gain over all subbands allocated to user the for each direction (i,j) where N_ƒ is the total number of subbands allocated to the user. G_i,j can be quantized by setting G_{i j} = 1 and G_i,j = 0 elsewhere.

Next, consider the general case in which the directional control grid does not match the array geometry. Hence, there should be a transformation of the beamspace reciprocity-aided transmission precoder for each polarization p = 0,1, i.e., to match the directional control grid basis. Let the directional control basis be constructed such that it has L_H X L_V directional controllers, and associate a control direction basis vector with each controller by forming the M_HM_V X L_HL_V matrix where each column of the matrix D corresponds to one directional controller and D_H and D_v are M_H X L_H and M_v X L_V oversampled discrete Fourier transform (DFT) matrices constructed as follows:

If L_x < M_x , the (x,y) element of D_x is given by

0, M_x — 1 , y = 0, ..., L_X — 1.

If L_x > M_x, the (x,y) element of D_x is given by

... , M_x — 1 , y — 0, ... , L_x — 1.

The beamforming gain for the controller associated with horizonal direction x and vertical direction y is given by: where the L_HL_V X 1 vector d(x,y) is the column of the matrix D associated with horizonal direction x and vertical direction y.

Define the L_HL_V X 1 vector G(ƒ) = where where denotes the operator that computes the magnitude squared of each entry of the vector is the complex conjugate of the matrix B and use has been made of the identity

Note that the L_HL_V X M_HM_V transformation matrix is fixed and sparse and can be simplified as

Example 1:

Consider the case of AAS 6488. In this case, M_H = 8 and M_V = 4. Consider the case of using a grid composed 8 horizontal and 2 vertical directions for EMF control, i.e., L_H = 8 and L_V = 2, i.e., this corresponds to downsampling the array in the vertical direction when constructing the matrix D, D_H = B_H and L_V < M_V, where the transformation matrix

Hence, only two vertical beamspace components are utilized due to downsampling.

Example 2:

Consider the case M_H = 8 and M_V = 2 with oversampling. Consider the case of using a grid composed 8 Horizontal and 4 vertical directions for EMF control, i.e., L_H = 8 and L_V = 4. This corresponds to oversampling the array in the vertical direction when constructing the matrix D, D_H = B_H and L_V > M_V with the

Step 2 Momentary power estimation per TTI

As seen in FIG. 14, momentary power for direction i per TTI can be estimated by nominal gain, power scaling and allocations for all channels: where, i is the specific direction, t is TTI index with a control step m, t=0, 1199, n is the index withing direction i, assuming N WDs for direction i, i=l, 2, ..., 16, G(n, i) is the relative gain of user n within direction i, prb(n) is the number of PRB of user n, S(n) is the power scaling factor of user n.

G(n,i) = 1 for a WD allocated in direction i, and zero in all other directions.

As seen in FIG. 15, the momentary power should be performed per direction when common channels and traffic channels when WD-specific beamforming uses wide beam. The effect of this wide beam may be considered in the power estimation. A reduction of x dB is needed on channels using common beamforming.

Relative gain among different directions C1, C2, ... C16 can be applied to account for element patterns (for different antennas), port to antenna (P2A) (for different CSI-RS settings with remote electrical tilt (RET) and digital tilt), array geometry, tapering, etc. For one embodiment, as shown in FIG. 17, a linear compensation can be applied assuming OdB in boresight and xdB less in half power beam width (HPBW).

Step 4 Directional EMF controller

Cell wide EMF power lock controller as described above can be applied per direction. There may be a 16 cell wide EMF controller, one per direction, in the example of 16 directions. Different EMF thresholds can be applied for different directions.

For example, a direction containing a kindergarten can be provisioned with lower power threshold such as 10%, while a direction where the general public gathers can be provisioned with relatively higher threshold such as 25%.

To reduce memory consumption, one embodiment is to apply reduced number of EMF controller, such as 4 controllers used for a group of four directions, where the worst direction within each group is used for control.

Step 5 Power Restriction calculation

For each direction, a control signal, gamma, is derived from the EMF controller. It compares the gamma with the allowed threshold. If the threshold is exceeded, power restrictions are applied to all directions requiring power restrictions. The power restriction could be power or physical resource block (PRE) resources or both.

Step 6 Mapping direction back to PMI

As seen in FIG. 18, mapping all directions requiring power restriction is made to all PMI. This is the reverse of Step 1.

Apply power scaling

For all the WD with PMI needing a power restriction, a corresponding power scaling or PRB reduction is applied. Pre-compensation on link adaption is applied to compensate the effect of power scaling. For any WD requiring power scaling, apply a delta (calculated from power scaling) to reduce the signal to interference plus noise ratio (SINK) in link adaption:

SINK = delta + SINR_from_CQI + OLA where, SINR_from_CQI is the SINR calculated from WD reported channel quality indicator (CQI), OLA is the outer loop adjustment calculated for hybrid automatic repeat request (HARQ) ack/nack feedback from the WD. The outer loop is to apply correction on CQI using HARQ ack/nack.

According to one aspect, a network node 16 configured to communicate with a plurality of wireless devices, WDs 22 is provided. The network node 16 includes processing circuitry 68 configured to: for each of a plurality of transmission time intervals, TTIs, and for each WD 22 of the plurality of WDs 22: map a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD 22; and accumulate a directional power for each direction indicated by the first PMI. The processing circuitry 68 is also configured to, for each of a plurality of control step intervals and for each of a plurality of directions: apply a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determine whether the weighted directional power of transmission exceeds a threshold corresponding to the direction. The processing circuitry 68 is also configured to, for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, map the direction to a corresponding PMI.

According to this aspect, in some embodiments, the first PMI is at least one of obtained from a WD 22 and derived from a beam forming weight, BFW. In some embodiments, the processing circuitry 68 is further configured to scale the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction. In some embodiments, a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold. In some embodiments, the processing circuitry 68 is further configured to apply an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling. In some embodiments, a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 100. In some embodiments, each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction. In some embodiments, the time-average power is obtained by averaging the accumulations over at least a six minute time interval. In some embodiments, the directional BFG is a function of antenna array element pattern. In some embodiments, the function is linear.

According to another aspect, a method in a network node 16 configured to communicate with a plurality of wireless devices, WDs 22 is provided. The method includes for each of a plurality of transmission time intervals, TTIs, and for each WD 22 of the plurality of WDs 22: mapping a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD 22; and accumulating a directional power for each direction indicated by the first PMI. The method also includes for each of a plurality of control step intervals and for each of a plurality of directions: applying a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determining whether the weighted directional power of transmission exceeds a threshold corresponding to the direction. The method includes, for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, mapping the direction to a corresponding PMI.

According to this aspect, in some embodiments, the first PMI is at least one of obtained from a WD 22 and derived from a beam forming weight, BFW. In some embodiments, the method also includes scaling the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction. In some embodiments, a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold. In some embodiments, the method further includes applying an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling. In some embodiments, a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 1000. In some embodiments, each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction. In some embodiments, the time-average power is obtained by averaging the accumulations over at least a six minute time interval. In some embodiments, the directional BFG is a function of antenna array element pattern. In some embodiments, the function is linear.

As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, and/or computer program product. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices. Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

What is claimed is:

1. A network node (16) configured to communicate with a plurality of wireless devices, WDs (22), the network node (16) comprising processing circuitry (68) configured to: for each of a plurality of transmission time intervals, TTIs, and for each WD (22) of the plurality of WDs (22): map a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD (22); and accumulate a directional power for each direction indicated by the first

PMI; and for each of a plurality of control step intervals: for each of a plurality of directions: apply a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determine whether the weighted directional power of transmission exceeds a threshold corresponding to the direction; and for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, map the direction to a corresponding PMI.

2. The network node (16) of Claim 1, wherein the first PMI is at least one of obtained from a WD (22) and derived from a beam forming weight, BFW.

3. The network node (16) of any of Claims 1 and 2, wherein the processing circuitry (68) is further configured to scale the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction.

4. The network node (16) of Claim 3, wherein a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold.

5. The network node (16) of any of Claims 3 and 4, wherein the processing circuitry (68) is further configured to apply an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling.

6. The network node (16) of any of Claims 1-5, wherein a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 100.

7. The network node (16) of any of Claims 1-6, wherein each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction.

8. The network node (16) of Claim 7, wherein the time-average power is obtained by averaging the accumulations over at least a six minute time interval.

9. The network node (16) of any of Claims 1-8, wherein the directional BFG is a function of antenna array element pattern.

10. The network node (16) of Claim 9, wherein the function is linear.

11. A method in a network node (16) configured to communicate with a plurality of wireless devices, WDs (22), the method comprising: for (S100) each of a plurality of transmission time intervals, TTIs, and for each WD (22) of the plurality of WDs (22): mapping (S 102) a direction indicated by a first precoder matrix indication, PMI, to a direction of transmission to the WD (22); and accumulating (S104) a directional power for each direction indicated by the first PMI; and for each of a plurality of control step intervals: for each of a plurality of directions (S 106): applying (S108) a directional beam forming gain, BFG, to an accumulation of the directional power for the direction to produce a weighted directional power of transmission; and determining (S 110) whether the weighted directional power of transmission exceeds a threshold corresponding to the direction; and for each direction for which the weighted directional power of transmission exceeds a corresponding threshold, mapping (S112) the direction to a corresponding PMI.

12. The method of Claim 11, wherein the first PMI is at least one of obtained from a WD (22) and derived from a beam forming weight, BFW.

13. The method of any of Claims 11 and 12, further comprising scaling the weighted directional power of transmission, the scaling being one of multiplying the weighted directional power of transmission by a scaling factor and changing a number of physical resource blocks, PRBs, assigned to a transmission in the direction.

14. The method of Claim 13, wherein a magnitude of the scaling for a particular direction is based at least in part on an extent to which the weighted directional power of transmission exceeds the corresponding threshold.

15. The method of any of Claims 13 and 14, further comprising applying an additive offset to an outer loop adjustment, the additive offset based at least in part on a magnitude of the scaling.

16. The method of any of Claims 11-15, wherein a control step interval of the plurality of control step intervals exceeds a TTI by a factor of greater than 1000.

17. The method of any of Claims 11-16, wherein each threshold corresponding to a direction is based at least in part on a predefined constraint on a maximum time-average power of transmissions in the direction.

18. The method of Claim 17, wherein the time-average power is obtained by averaging the accumulations over at least a six minute time interval.

19. The method of any of Claims 11-18, wherein the directional BFG is a function of antenna array element pattern.

20. The method of Claim 19, wherein the function is linear.