WO2021013344A1

WO2021013344A1 - A management entity and a method for managing communications

Info

Publication number: WO2021013344A1
Application number: PCT/EP2019/069922
Authority: WO
Inventors: Daniel RIVIELLO; Umberto Spagnolini; Jonathan Gambini
Original assignee: Huawei Technologies Co., Ltd.; Politecnico Di Milano
Priority date: 2019-07-24
Filing date: 2019-07-24
Publication date: 2021-01-28

Abstract

The invention relates to a management entity (301) for managing communications between a plurality of wireless user entities (305a-d) and a plurality of radio antenna units (303a, b), wherein each radio antenna unit (303a, b) is configured for communications in a communication network using beamforming and wherein each radio antenna unit (303a, b) is configured to communicate with one or more wireless user entities (305a-d) over a number of transport links of a transport network. The management entity (301) is configured to: group wireless user entities from the plurality of wireless user entities (305a-d) into at least one set of wireless user entities; obtain a quality indicator on at least one transport link for each wireless user entity of the at least one set of wireless user entities; if at least one obtained quality indicator is below a predetermined threshold, compare an interference value for each wireless user entity in the at least one set with a predefined threshold and exclude at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtain an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assign wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold.

Description

DESCRIPTION

A MANAGEMENT ENTITY AND A METHOD FOR MANAGING COMMUNICATIONS TECHNICAL FIELD

Generally, the present invention relates to the field of wireless communication. More specifically, the present invention relates to a management entity and a corresponding method as well as a communication system for managing communications between a plurality of wireless user entities and a plurality of radio antenna units.

BACKGROUND

A wireless communication system where an ensemble of mobile terminals or user equipment (UEs) are connected to a set of antennas arranged in a form of array of antennas centrally controlled is referred to as a distributed antenna system (DAS). Each group of antennas is co-located into a Remote Antennas Unit (RAU), and all RAUs are controlled by a Central Unit (CU) that typically either modulates (in downlink, from RAUs to UEs) or demodulates (in uplink, from UEs to RAUs). This architecture as shown in figure 1 is known as a centralized radio access network (CRAN) 100 where the CU 101 coordinates the RAUs 103a-d functionalities to serve the UEs 105 within a serving area.

The degree of coordination among RAUs can be either complete (all RAUs are serving all UEs), or incomplete (all UEs geographically close to a RAU are served by that RAU), or partial. A complete coordination guarantees that all served UEs are simultaneously served by designing the processing such that signals are minimally interfering.

Regardless of coordination, not all UEs can be served simultaneously on the same frequency-time resources, but UEs can be scheduled to be minimally interfering according to technological constraints. One of the technical constraints is due to the connections between the RAUs and the CU, called fronthauling links, and typically the number of fronthauling links is the same as the number of antennas, even if often is smaller than the antennas. State-of-the-art scheduling procedures aim at selecting the users clustering, users-to-RAUs association, and beamforming vectors so as to maximize the network sum rate, possibly constrained to the condition that all users are served with a minimum acceptable rate. Due to its combinatorial and nonconvex nature, finding the global optimal solution to this kind of problem is known to be a difficult task. Rather than aiming at the global optimality, prior art approaches are based on: splitting the original problem into smaller optimization problems with lower complexity; and coordinating the solution of said smaller subproblems to reach a local optimum.

However, these approaches fail to scale with the large number of RAUs and users typically involved in distributed antenna system (DAS) architectures as shown in Figure 1.

In light of the above, there is still a need for an improved entity and a corresponding method as well as a communication system for managing communications between a plurality of wireless user entities and a plurality of radio antenna units more efficiently.

SUMMARY It is an object of the invention to provide an improved management entity and a corresponding method as well as a communication system for managing communications between a plurality of wireless user entities and a plurality of radio antenna units more efficiently. The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

Generally, the present invention relates to a management entity located in a central unit (CU) within a distributed antenna system (DAS) for coordinating a plurality of radio antenna units (RAU) to serve a plurality of user entities (UEs). In particular, embodiments of the invention find a low-complexity solution to a combinatorial problem that can be used in large DAS networks with a high number of user entities and radio antenna units. In an initial phase, the management entity according to an embodiment is adapted to output proper control signals to coordinate different radio antenna units to acquire information on the propagation channels from all the user entities to all their reachable radio antenna units. The management entity is then configured to use the acquired information on the propagation channels features, e.g., propagation angle, typically indicated as apparent Direction of Arrival (DoA), attenuation, propagation delay, to successively group the user entities into clusters, so that each user entity in each cluster is connected to at least one radio antenna unit with a link quality greater than a predetermined threshold. The link quality is computed on the basis of the acquired information on the UE-to-RAU propagation channels. In an embodiment, each cluster is created by an iterative procedure in which all the remaining user entities are at first grouped into a temporary cluster, and then user entities that create the highest interference level to other UE-to-RAU links are successively eliminated from the temporary cluster assignment as long as each user entity in the temporary cluster is connected to at least one radio antenna unit with a link quality greater than the specified threshold.

If the number of user entities is higher than the product of the total number of radio antenna units ( Q ) and the number of fronthauling links per radio antenna unit (L), Q x L, the management entity according to an embodiment assigns one user entity to only one radio antenna unit to maximize the number of users with minimal mutual interference that can be served simultaneously within the same cluster.

In an embodiment, each radio antenna unit of the system is adapted to synthesize as many beams (or multiple-beams) as the number of fronthauling links connecting the radio antenna unit to the central unit (CU).

Finally, the different clusters of user entities are assigned to as many orthogonal resources in time and frequency domains to have orthogonal assignment of clusters, and the temporal duration and frequency allocation of each orthogonal resource is selected so as to guarantee a minimum quality of services to all the users of the network.

More specifically, according to a first aspect the invention relates to a management entity for managing communications between a plurality of wireless user entities and a plurality of radio antenna units, wherein each radio antenna unit is configured for communications in a communication network using beamforming and is configured to communicate with one or more wireless user entities over a number of transport links of a transport network. The management entity is configured to: group wireless user entities from the plurality of wireless user entities into at least one set of wireless user entities; obtain a quality indicator on at least one transport link for each wireless user entity of the at least one set of wireless user entities; if at least one obtained quality indicator is below a predetermined threshold, compare an interference value for each wireless user entity in the at least one set with a predefined threshold and exclude at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtain an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assign wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold.

In an embodiment, the transport links and the transport network can be fronthauling links and a fronthauling network respectively, for instance, through optical fibers or radio links etc.

In an embodiment, the management entity is within a central unit of a centralized radio access network.

Thus, an improved management entity is provided, allowing for managing

communications between a plurality of wireless user entities and a plurality of radio antenna units more efficiently. In a further possible implementation form of the first aspect, the management entity is configured to exclude the at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities by allocating the at least one wireless user entity to an orthogonal radio resource which is different from radio resources assigned to wireless user entities in the updated set of wireless user entities.

Thus, the at least one wireless user entity that has been excluded cannot coexist with the wireless user entities in the updated set of wireless user entities and can use the orthogonal radio resource in an efficient manner. In a further possible implementation form of the first aspect, the management entity is further configured to: exclude a further certain wireless user entity that causes a certain level of interference onto at least one transport link from the updated set of wireless user entities, thereby obtaining a further updated set of wireless user entities; re-calculate the quality indicators for wireless user entities from the further updated set of wireless user entities on at least one transport link; and assign wireless user entities from the further updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the recalculated quality indicators are equal to or greater than the predetermined threshold.

Thus, the wireless user entity causing a certain level of interference can be excluded more efficiently.

In a further possible implementation form of the first aspect, the management entity is configured to assign each wireless user entity in the updated set of wireless user entities to one or more transport links towards one or more radio antenna units if all recalculated quality indicators are at least equal to the predetermined threshold.

Thus, an acceptable quality of service for the updated set of wireless user entities can be guaranteed. In a further possible implementation form of the first aspect, the management entity is configured to determine which wireless user entity in the respective set of wireless user entities causes highest interference on at least one transport link in order to determine the respective certain wireless user entity for exclusion from the respective set of wireless user entities.

Thus, the wireless user entity causing the highest interference can be excluded more efficiently.

In a further possible implementation form of the first aspect, the management entity is configured to determine the interference of a k-th wireless user entity on a transport link towards a q-th radio antenna unit by calculating an interference power P_q(k\i), when the beamformer adopted at the q-th radio antenna unit is directed towards the i-th wireless user entity. Thus, the interference of a k-th wireless user entity on a transport link towards a q-th radio antenna unit can be determined in an efficient and correct manner. In a further possible implementation form of the first aspect, the management entity is configured to calculate a signal-to-interference-plus-noise ratio on a transport link to obtain a quality indicator for each wireless user entity. In a further possible implementation form of the first aspect, the management entity is configured to calculate the signal-to-interference-plus-noise ratio on the basis of the following equation:

where P_q(i|t) is the received power at the q-th radio antenna unit from the i-th wireless user entity when the beamformer at the q-th radio antenna unit is directed towards the i-th wireless user entity, is the received power at the q-th radio antenna unit from the

fc-th wireless user entity when the beamformer at the q-th radio antenna unit is directed towards the i-th wireless user entity, and s² is the noise power.

Thus, the quality indicator for each wireless user entity can be determined in an efficient and correct manner. In a further possible implementation form of the first aspect, the management entity is configured to schedule communication resources, in particular time slots or frequency bands, to each wireless user entity in the updated set of wireless user entities for communication over at least one transport link with at least one radio antenna unit. Thus, the updated set of wireless user entities can communicate with the radio antenna unit efficiently.

In a further possible implementation form of the first aspect, the management entity is configured to select at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit.

In a further possible implementation form of the first aspect, the management entity is configured to select at least one transport link for at least one wireless user entity that has not yet been scheduled for transmission over any transport link. Thus, each wireless user entities can efficiently communicate with any radio antenna unit over any transport link.

In a further possible implementation form of the first aspect, the management entity is configured to iteratively select in at least one link selection iteration at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit starting with a wireless user entity that is associated with a highest quality indicator in the updated set of wireless user entities. This provides an improved quality of service for the updated set of wireless user entities efficiently.

In a further possible implementation form of the first aspect, the management entity is configured to discard a certain radio antenna unit in a following link assignment iteration if all transport links towards the certain radio antenna unit have been assigned to wireless user entities in a previous link assignment iteration.

In a further possible implementation form of the first aspect, the management entity is further configured to assign a wireless user entity of the updated set of wireless user entities to a further transport link that has not been assigned to any wireless user entity yet, if all wireless user entities of the updated set of wireless user entities have been assigned to at least one transport link towards at least one remote antenna unit.

Thus, any available transport links can be used efficiently and will not be wasted.

In a further possible implementation form of the first aspect, the management entity is configured to schedule transmissions of wireless user signals from the wireless user entities towards the radio antenna units over the transport links. Thus, the signals from the wireless user entities can be transmitted towards the radio antenna units over the transport links in an efficient manner.

According to a second aspect the invention relates to a communication system for handling communications of a plurality of wireless user entities that use beamforming in a communication network, wherein the communication system comprises: a plurality of radio antenna units, each antenna unit comprising a plurality of antennas for transmitting signals in the communication network using beamforming, wherein each radio antenna unit comprises a plurality of transport links for receiving the wireless user signals from the wireless user entities; and the management entity according to the first aspect for managing, in particular scheduling, communications of the wireless user entities on the transport links.

In a further possible implementation form of the second aspect, the radio antenna units are configured to communicate over the transport links using beamforming. Thus, an improved communication system is provided, allowing for managing

communications between a plurality of wireless user entities and a plurality of radio antenna units more efficiently.

According to a third aspect the invention relates to a method for managing

communications between a plurality of wireless user entities and a plurality of radio antenna units, wherein each radio antenna unit is configured for communications in a communication network using beamforming and wherein each radio antenna unit is configured to communicate with one or more wireless user entities over a number of transport links of a transport network.

The method comprises the following steps: grouping wireless user entities from the plurality of wireless user entities into at least one set of wireless user entities; obtaining a quality indicator of at least one transport link for each wireless user entity in the at least one set of wireless user entities; if at least one obtained quality indicator is below a predetermined threshold, comparing an interference value for each wireless user entity in the at least one set of wireless user entities with a predefined threshold and excluding at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtaining an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assigning wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold.

Thus, an improved method is provided, allowing for managing communications between a plurality of wireless user entities and a plurality of radio antenna units more efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, wherein:

Figure 1 shows a schematic diagram illustrating a state-of-the-art distributed antenna system;

Figure 2 shows a schematic diagram illustrating a distributed antenna system according to an embodiment;

Figure 3 shows a schematic diagram illustrating a communication system according to an embodiment for handling communications of a plurality of wireless user entities and a plurality of radio antenna units;

Figure 4 shows a schematic diagram illustrating a number of different K x K matrices according to an embodiment storing interference powers of wireless user entities;

Figure 5 shows a schematic diagram illustrating a process of user pruning according to an embodiment;

Figure 6 shows a schematic diagram illustrating an exemplary procedure for scheduling radio resources to wireless user entities; and Figure 7 shows a schematic diagram illustrating a method of managing communications according to an embodiment.

In the various figures, identical reference signs will be used for identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of examples, specific aspects in which the present invention may be placed. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined be the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects and embodiments described herein may be combined with each other, unless specifically noted otherwise.

Generally, the present invention relates to a management entity for managing

communications between a plurality of wireless user entities (UEs) and a plurality of radio antenna units, each radio antenna unit being configured for communications in a communication network using beamforming, wherein each radio antenna unit is configured to communicate with one or more wireless user entities over a number of transport links of a transport network.

Figure 1 shows a reference radio architecture of a distributed antenna system (DAS) 100 wherein a central unit (CU) 101 coordinates a plurality of Remote Antenna Units (RAUs) 103a-d to serve user entities (UEs) 105 within a serving area.

Figure 2 shows a schematic diagram illustrating signal processing of a distributed antenna system 200 according to an embodiment, wherein a large number of dislocated Remote Antenna Units (RAUs) 203a, b is each equipped with multiple antennas 21 1a-f and each RAU 203a, b is connected to a centralized baseband processing unit 201. As can be seen from figure 2, the central unit 201 further comprises decoding entities 221 a, 221 b for jointly decoding or precoding the ensemble of multi-user signals from a plurality of user entities 205a-e.

As can be taken from figure 2, parameter K denotes the number of users, i.e. user entities (UEs) 205a-e, each transmitting/receiving signals

Q denotes the number of Remote Antenna Units (RAUs) 203a, b; N denotes the number of antennas 211a-f available at each RAU 203a, b; and L denotes the number of fronthauling links connecting each RAU 203a, b to the central unit (CU) 201. Each RAU 203a, b locally employs adaptive beamforming towards the assigned UEs 205a-e. The CU 201 jointly processes the ensemble of signals from/to the RAUs 203a, b.

Embodiments of the invention provide a coordination or scheduling strategy adopted by the CU that aims to exploit the capabilities of multi-user multiple-input and multiple-output (MU-MI MO) technologies. The scheduling strategy to serve a set of moving UEs is based on the following multiple access methods to be scheduled jointly: Space-division multiple access (SDMA); and Frequency-division or time-division multiple access (FDMA or TDMA).

Existing mobile cellular systems use different combinations of multiple access methods to schedule and multiplex UEs in the same communication channel: 3G or UMTS system uses Code-division multiple access (CDMA), while 4G or LTE systems use a combination of FDMA and TDMA.

The upcoming mobile cellular standard known as 5G New Radio (NR) is going to implement also SDMA or MU-MIMO as a further layer of multiple access method: the standard provides a Channel State Information (CSI) reporting framework, and especially Type II CSI reports are targeted for MU-MIMO scenarios with multiple devices being scheduled simultaneously within the same time/frequency resource (see more details in E. Dahlman et. al.,“5G NR: The Next Generation Wireless Access Technology”, Academic Press, 2018; 3GPP TS 38.214 V15.4.0, "Physical layer procedures for data” 2018;

Samsung et. al.”WF on Type I and II CSI codebooks”, R1-1709232, 3GPP TSG-RAN WG1 #89, 2017; and Ericsson,‘Codebook design for Type II CSI feedback”, R1-1708688, 3GPP TSG-RAN WG1 #89, 2017).

Embodiments of the invention focus especially on the spatial multiplexing or SDMA of the users, which is referred to as a“duster” group of UEs scheduled simultaneously in the same time/frequency resources and separated spatially in SDMA according to the embodiments.

As it will be described more in detail in the following under reference to figure 3, embodiments of the invention aim to guarantee a minimum quality of service to every UE and perform the following tasks: grouping the K users into P clusters C₁, C₂, ... , C_P, so as to minimize the mutual interference among the UEs inside each cluster, wherein users within the same cluster access the spatial channel simultaneously and are multiplexed only by MU-MI MO techniques; assigning the clusters to as many orthogonal resources as proportional to the number of UEs; assigning each user in each cluster to a group of RAUs, i.e. defining partitioning of the users into RAUs; defining proper beamforming vectors at each RAU.

More specifically, figure 3 shows a communication system 300 for handling

communications of a plurality of wireless user entities 305a-d that use beamforming in a communication network, wherein the communication system 300 comprises: a plurality of radio antenna units 303a, b, each radio antenna unit 303a, b comprising a plurality of antennas for transmitting signals 311a-d in the communication network using

beamforming, wherein each radio antenna unit 303a, b comprises a plurality of transport links for receiving the wireless user signals from the plurality of the wireless user entities 305a-d;

Further, the communication system 300 comprises a management entity 301 for managing, in particular scheduling, communications of the wireless user entities 305a-d on the transport links with the plurality of radio antenna units 303a, b. The management entity 301 is configured to schedule transmissions of wireless user signals from the wireless user entities 305a-d towards the radio antenna units 303a, b over the transport links.

According to an embodiment, the management entity 301 is configured to: group wireless user entities from the plurality of wireless user entities 305a-d into at least one set of wireless user entities and obtain a quality indicator on at least one transport link for each wireless user entity of the at least one set of wireless user entities.

If at least one obtained quality indicator is below a predetermined threshold, the management entity 301 according to the embodiment is further configured to: compare an interference value for each wireless user entity in the at least one set with a predefined threshold and exclude at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtain an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assign wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold. In an embodiment, the management entity 301 is configured to exclude the at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities by allocating the at least one wireless user entity to an orthogonal radio resource which is different from radio resources assigned to wireless user entities in the updated set of wireless user entities.

Furthermore, the management entity 301 is further configured to: exclude a further certain wireless user entity that causes a certain level of interference onto at least one transport link from the updated set of wireless user entities, thereby obtaining a further updated set of wireless user entities; re-calculate the quality indicators for wireless user entities from the further updated set of wireless user entities on at least one transport link; and assign wireless user entities from the further updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the recalculated quality indicators are equal to or greater than the predetermined threshold.

In an embodiment, the management entity 301 is configured to select at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit. In another embodiment, the management entity 301 is configured to select at least one transport link for at least one wireless user entity that has not yet been scheduled for transmission over any transport link.

The management entity 301 is configured to assign each wireless user entity in the updated set of wireless user entities to one or more transport links towards one or more radio antenna units if all recalculated quality indicators are at least equal to the predetermined threshold.

In an embodiment, the management entity 301 is configured to iteratively select in at least one link selection iteration at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit starting with a wireless user entity that is associated with a highest quality indicator in the updated set of wireless user entities. Further, the management entity 301 is configured to discard a certain radio antenna unit in a following link assignment iteration if all transport links towards the certain radio antenna unit have been assigned to wireless user entities in a previous link assignment iteration. In a further embodiment, the management entity 301 is configured to assign a wireless user entity of the updated set of wireless user entities to a further transport link that has not been assigned to any wireless user entity yet, if all wireless user entities of the updated set of wireless user entities have been assigned to at least one transport link towards at least one remote antenna unit.

In an embodiment, the management entity 301 is configured to determine which wireless user entity in the respective set of wireless user entities causes highest interference on at least one transport link in order to determine the respective certain wireless user entity for exclusion from the respective set of wireless user entities. The management entity 301 is configured to determine the interference of a k-th wireless user entity on a transport link towards a q-th radio antenna unit by calculating an interference power when the

beamformer adopted at the q-th radio antenna unit is directed towards the i-th wireless user entity.

In an embodiment, the management entity 301 is configured to calculate a signal-to- interference-plus-noise ratio on a transport link to obtain a quality indicator for each wireless user entity, wherein the signal-to-interference-plus-noise ratio

is calculated on the basis of the following equation:

where is the received power at the q-th radio antenna unit from the i-th wireless

user entity when the beamformer at the q-th radio antenna unit is directed towards the i-th wireless user entity

is the received power at the q-th radio antenna unit from the fc-th wireless user entity when the beamformer at the q-th radio antenna unit is directed towards the i-th wireless user entity, and s² is the noise power.

The management entity 301 is configured to schedule communication resources, in particular time slots or frequency bands, to each wireless user entity in the updated set of wireless user entities for communication over at least one transport link with at least one radio antenna unit.

In an embodiment, the management entity 301 is configured to divide UEs into as few clusters as possible with the goal of maximizing the rate of the UEs inside each cluster while guaranteeing that each UE in each cluster is connected to at least one RAU with a link quality greater than a predetermined threshold. Each cluster is then assigned to a resource with a certain width both in time and frequency domain. The time and frequency dimension of the resource (resource block) is selected according to a proportional fairness criterion among different clusters.

As an exemplary case of time assignment of clusters, given P clusters

the temporal duration of the resource assigned to the p-th cluster can be equal to the number of users inside the pth cluster C_p divided by the overall number of users K:

where I -I indicates the cardinality of a set. In an embodiment, a more accurate fairness criterion can be based on the average peruser cluster capacity R_p defined as:

where SINR_k is the Signal-to-Noise-plus-lnterference Ratio for the fe-th user after the processing tasks applied at the CU. Then, the temporal duration of the resource assigned to the p-th cluster a_p would be inversely proportional to

In an embodiment, the above scheduling of radio resources is based on the knowledge of the propagation channel features from each UE 305a-d to all the reachable RAUs 303a, b. In an embodiment, the management entity 301 acquires information on the propagation channels features by, for example, the following method: in specified time/frequency resource blocks, all the RAUs 303a, b perform sequential scanning of the resource block occupancy by using a set of pre-assigned codewords to search for new user entities, wherein each codeword is a vector of complex coefficients to be applied at the analog circuits of the multiple antennas of each RAU and each codeword is designed so as to produce a peculiar radiation pattern at each RAU.

In the dedicated time/frequency resource blocks, the user entities 305a-d measure the received power and feedback these measures to the RAUs 303a, b. By collecting the feedbacks from the user entities 305a-d, the management entity 301 acquires knowledge of the set of codewords that best represent the propagation channels (if any) from each user 305a-d to each RAU 303a, b. The management entity 301 can then use this information to reconstruct channel responses h_k®q from each k-th user to all the Q RAUs

As an example, h_k®q can contain information on at least one direction of arrival from the k--th user to the q-th RAU. As another example, h_k®q can contain information on at least one direction of arrival from the k-th user to the q-th RAU and at least one complex gain related to the propagation from the k-th user to the q-th RAU.

According to an exemplary embodiment of this procedure, the management entity 301 can output proper control signals to configure the different RAUs to scan the electromagnetic environment in the same spectral resource and in non-overlapping time epochs.

Alternatively, the management entity 301 can output proper control signals to configure the different RAUs to scan the electromagnetic environment in the same spectral resource and in the same time epoch. In a further embodiment, the management entity 301 can output proper control signals to configure the different RAUs to scan the electromagnetic environment in non-overlapping spectral resources and non-overlapping time epochs.

During this procedure, each UE is able to obtain at least one of the following information by using conventional packet decoding techniques: the codeword identifier; the received signal strength related to the codeword; an indicator of the channel quality related to the codeword; or the RAU identifier. It is to be noted that feedback messages from the users contain at least one of the information as described above.

By assuming that all user entities transmit at the same nominal power, for simplicity

1, the link SINR can be written as:

with and , wherein the N x 1 vector b_l®q is the

beamfbrmer adopted at the q-th RAU to focus on the signal of interest sent by the i-th user, and are respectively the N x 1 channel vector from i-th user to q-th RAU

and the N x 1 channel vector from k-th user to q-th RAU. The channel includes path loss, fading and gains of the single radiating elements of the array.

Hence is the received power at RAU q from user i when the beamfbrmer at q-th

RAU is pointed towards the i-th user, while is the received power at RAU q from

user k when the beamfbrmer at q-th RAU is pointed towards the i-th user, is

defined as interference contribution. The terms and can be computed at the

management entity by applying a standard electromagnetic theory starting from the knowledge of the channel responses from each k-th user to all the Q RAUs (q = 1 , 2,

In order to guarantee an acceptable Quality of Service (QoS), all users/user entities within a cluster must satisfy the condition that at least one of the link SINRs to the Q RAUs must be above the SINR threshold

The Signal-to-Noise-plus-lnterference Ratio SINR_k for the k-th user after the processing tasks applied at the management entity 301 is typically a function of each link SINR

between saidk-th user and all the

For example, for the uplink from the UE to the RAU, if the management entity adopts

Selection Combining, SINR_k is equal to if Maximum Ratio Combining is

adopted, SINR_k is equal

According to an embodiment, the management entity 301 can start scheduling of radio resources, after the management entity 301 has acquired information on the propagation channels from all the users, i.e. user entities, 305a-d to all the reachable RAUs obtained by estimating the channels from each user 305a-d to each RAU 303a, b, or by collecting the corresponding power to each RAU 303a, b after some beamforming such as to the existing UEs, e.g., assuming that scheduling has been carried out and the new UE is joining the network.

According to an embodiment, the management entity 301 is configured to allocate the users into clusters that are not mutually interfering, and the number of clusters should be as small as possible to avoid excessive resource fragmentation that does not exploit the spatial multiplexing capability of the multiple-RAU systems which are centrally controlled and typically referred to as centralized radio access network (RAN) or centralized distributed antennas system (DAS).

According to an embodiment, the management entity 301 is configured to maximize the following metric for the cluster

according to a multi-step procedure. At each p-th step, a cluster is created through an iterative procedure.

In an embodiment, the iterative procedure can be divided into the following sub-tasks:

A first sub-task is“initialization”, wherein all the remaining users are grouped in a temporary cluster C^T.

A second sub-task is“user pruning”, wherein users that create the highest interference level to other user-to-RAU links are successively eliminated (pruned)

from the temporary cluster C^T as far as each user in the temporary cluster is connected to at least one RAU with a link quality greater than a specified threshold. In other words, this sub-task ends when the following condition is satisfied for every user k

A third sub-task is“link selection”, wherein starting from the temporary cluster C^T, each user is assigned to be served by one or more RAU and this assignment is performed by taking into account that the maximum number of fronthauling links per RAU is L and with the aim of maximizing the number of served users within one cluster under the constraints that the total serving fronthauling links for Q RAUs are Q x L The set of user entities served by the q-th RAU in the p-th cluster is represented as u%. The final cluster Cp will be composed of the union of all Q U% sets, which are not necessarily disjoint. It is worth noting that the effect of pruning reduces the overall set of matrixes illustrated above (before the pruning) into a set of sub-matrixes for the pairing UEs and RAUs.

In an embodiment, the different clusters of users are assigned to orthogonal resources to be mutually orthogonal to each other (i.e., interference free, or minimally interfering). The orthogonal resources can be either in time as Time-Division Multiple Access (TDMA), and/or frequency as for Frequency-Division Multiple Access (FDMA) or Orthogonal Frequency-Division Multiplexing (OFDM).

In an embodiment, the users allocated in distinct clusters are thus allocated to a subset of time and/or band resources, and the choice of the size of this subset is TDMA and/or FDMA compared to the total resources depending on the size of each cluster, e.g., the number of UE in each cluster from the cardinality of the ensemble of clusters

C₁, C₂, C₃, and etc. The resource allocation for each orthogonal resource assigned to each cluster is selected so as to guarantee a minimum quality of service to all the users of the network.

In an embodiment, the management entity 301 outputs proper control signals to configure the different RAUs to scan the radio resource occupancy by using a set of pre-assigned beams (or codewords for the spatial filtering) to search for any UE (that can be a new UE), each of the users measures the received power (e.g., the k-th UE measures the power

related to the n-th pre-assigned beam) and feedbacks these measures to the

RAUs by a dedicated control link. At the end of the procedure, the management entity 301 can collect a set of power information

associated to the scanned- beams indexed with n = 1,2,3, ...N and the RAUs q = 1,2, ..., Q obtained as feedback from all the users k = 1,2, ... , K over a dedicated control link from UEs to the control unit.

In this way the management entity 301 in the control unit can use this information to reconstruct the power gain P for every UE k = 1,2, ...,K when employing the i-th pre

assigned beamforming using, for instance, the channel reciprocity. Alternatively, knowing the manifold of the pre-assigned beam

the management entity 301 can infer the spatial channel responses from each k-th user to all the Q RAUs. For a directional channel (i.e., when the spatial characteris

tics of the array manifold is dependent solely on the direction of arrival), the spatial channel can contain

information on at least one direction of arrival from the k-th user to the q-th RAU and at least one complex gain related to the propagation from the k-th user to the q-th RAU.

After collecting all channel responses for "q,"k, the scheduling procedure

according to an embodiment starts by computing all received powers

and the interference powers

that are received by the RAU q from the user fc when the beamfbrmer at q-th RAU is designed toward the i-th user.

In an embodiment, all

are stored in a number Q of different K x K matrices 400 as illustrated in figure 4, wherein all are in each q-th diagonal. The power of interest

for all the UEs are along the diagonal of each matrix (i.e., each plane of the cube-volume), while the interfering powers are on the off-diagonals (as shown in gray color in figure 4). UE-to-RAU link quality metric is based on the link SINR as already discussed above.

In an embodiment, the process 500 of user pruning comprises the following iterative steps: finding the highest ; removing the k- th row and the k- th column from all Q

matrices that in turn become more compact, and re-computing every as sketched in

figure 5 that condense into one table the physical interference scenario.

Finally, the process of user pruning ends when all users have at least one of their link SINR above the threshold These remaining users belong to a temporary cluster

of UEs that are mutually spatially compatible, e.g. spatially scheduled at the same time- frequency, but spatially minimally interfering.

In an embodiment, selection and assignment of the transport link for radio signaling (typically in form of fronthauling connection between the CU and the RAU) is the scheduling of the transport of the UE-RAU air link onto the limited transport capability of the communication between the CU and each RAU. The assignment is based on the quality indicator by the ensemble of of all the users within each temporary cluster.

The highest is selected and the i-th UE is assigned to the q-th RAU, provided that:

(1 ) the q-th RAU has currently already scheduled less than a number of L UEs; (2)

and (3) the UE has not already been assigned to another RAU.

In case the above conditions (1 ) or (2) are false, the link is discarded; in case the condition (3) is false, the link is only deprioritized. Deprioritized links can be selected once all the other have been discarded. In an embodiment, link selection for a new cluster is repeated until the number of users in the temporary cluster is bigger than L x Q, otherwise the scheduler restarts from the user pruning process. Figure 6 shows a schematic diagram illustrating an exemplary procedure 600 for scheduling radio resources to user entities with a particular focus on the link selection stage as implemented in embodiments of the disclosure. The procedure 600 shown in figure 6 comprises the following steps: The management entity 301 is configured to check if there are any users to schedule radio resources (step 601 ).

The management entity 301 is configured to initialize a temporary cluster C^T with all remaining users that need to be scheduled (step 602).

The management entity 301 is configured to compute the signal-to-interference-plus-noise ratio for all remaining users and all RAUs (step 603).

If the condition, , is not met, the management entity 301 is

configured to find a k- th user with the highest interference contribution

among all RAUs and remove the user from C^T (step 604).

If the condition

is met, the management entity 301 is configured to remove the links with signal-to-interference-plus-noise ratios

smaller than the threshold

from the selectable link set of the temporary cluster C^T (step 605). The management entity 301 is configured to sort the remaining users in descending order according to the signal-to-interference-plus-noise ratios in the selectable link set

(step 606).

If and if not all links have been discarded, the management entity 301 is

configured to select the first non-discarded link belonging to the i-th user from the sorted selectable link set (step 607).

If there are still transport links available at the q-th RAU and the i-th user has not been assigned to a RAU, the management entity 301 is configured to set all other links of the i- th user in the selectable link set (step 608), this is obtained, for instance, by assigning , then re-sort the selectable link set (step 609) and then assign the

user i to the q-th RAU set (step 610).

If the management entity 301 is configured to create a new p-th cluster as

the union of all sets: (step 61 1 ).

Further, the management entity 301 is configured to implement proportional fairness to decide the temporal duration and frequency occupation of the resource assigned to each cluster Cp (step 612).

If there are any further users to schedule radio resources and , the

management entity 301 is configured to implement link selection from step 607 to step 612 in order to create a new (p + l)-th cluster from the same temporary cluster C^T and selectable link set used to create the p-th cluster.

If there are any further users to schedule radio resources and

, the management entity 301 is configured to initialize a new temporary cluster C^T with all remaining users that need to be scheduled (step 602).

The scheduling procedure 600 can be summarized in the following pseudocode:

Until there are users to schedule: A first step is initialization, wherein the management entity is configured to initialize a temporary cluster

with all remaining users and compute the signal-to-interference-plus- noise ratio for all remaining users and all RAUs.

A second step is users pruning, wherein, until the condition,

is not met: finding k- th user with highest interference contribution

among all RAUs and removing user from

re-computing the signal-to-interference-plus-noise ratio

for all remaining users in

A third step is link selection, wherein, until

: until there are transport links available at some RAUs, adding user i with highest

to provided that (1 )

there are still transport links available at the q-th a user

has already been assigned to a RAU, giving higher priority to unscheduled users, and wherein is the union of all user-RAU sets. Further, the link selection

comprises implementing proportional fairness to decide the temporal duration and frequency occupation of the resource assigned to each cluster C_p.

The embodiments of the invention in particular provide a low-complexity sub-optimal solution to a combinatorial problem, in which the sum rate maximization is accomplished by maximizing the cluster size: the goal of the embodiments is to assign each user to one RAU only in order to reach a cluster size |C_P| = L x Q, i.e. create U% as disjoint sets. It is worth noting that can be accomplished only if N > L x Q. Another exemplary

procedure of an embodiment dictates that each user is connected to a minimum number of RAUs R £ Q in order to enhance reliability.

Figure 7 shows a schematic diagram illustrating a method 700 for managing

communications between a plurality of wireless user entities 305a-d and a plurality of radio antenna units 303a, b, wherein each radio antenna unit 303a, b is configured for communications in a communication network using beamforming and wherein each radio antenna unit 303a, b is configured to communicate with one or more wireless user entities 305a-d over a number of transport links of a transport network.

The method 700 comprises the following steps: a first step 701 of grouping wireless user entities from the plurality of wireless user entities 305a-d into at least one set of wireless user entities; a second step 702 of obtaining a quality indicator of at least one transport link for each wireless user entity in the at least one set of wireless user entities.

If at least one obtained quality indicator is below a predetermined threshold, the method 700 further comprises a third step 703 of comparing an interference value for each wireless user entity in the at least one set of wireless user entities with a predefined threshold and excluding at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities. Furthermore, the method 700 comprises a fourth step 704 of obtaining an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and finally a step 705 of assigning wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold. While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein. Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence. Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

1. Management entity (301 ) for managing communications between a plurality of wireless user entities (305a-d) and a plurality of radio antenna units (303a, b), each radio antenna unit (303a, b) being configured for communications in a communication network using beamforming, wherein each radio antenna unit (303a, b) is configured to communicate with one or more wireless user entities (305a-d) over a number of transport links of a transport network, wherein the management entity (301 ) is configured to: group wireless user entities from the plurality of wireless user entities (305a-d) into at least one set of wireless user entities; obtain a quality indicator on at least one transport link for each wireless user entity of the at least one set of wireless user entities; if at least one obtained quality indicator is below a predetermined threshold, compare an interference value for each wireless user entity in the at least one set with a predefined threshold and exclude at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtain an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assign wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold.

2. The management entity (301 ) of claim 1 , wherein the management entity (301 ) is configured to exclude the at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities by allocating the at least one wireless user entity to an orthogonal radio resource which is different from radio resources assigned to wireless user entities in the updated set of wireless user entities.

3. The management entity (301 ) of claim 1 or 2, wherein the management entity (301 ) is further configured to: exclude a further certain wireless user entity that causes a certain level of interference onto at least one transport link from the updated set of wireless user entities, thereby obtaining a further updated set of wireless user entities; re-calculate the quality indicators for wireless user entities from the further updated set of wireless user entities on at least one transport link; and assign wireless user entities from the further updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the recalculated quality indicators are equal to or greater than the predetermined threshold.

4. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301) is configured to assign each wireless user entity in the updated set of wireless user entities to one or more transport links towards one or more radio antenna units if all recalculated quality indicators are at least equal to the predetermined threshold.

5. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301 ) is configured to determine which wireless user entity in the respective set of wireless user entities causes highest interference on at least one transport link in order to determine the respective certain wireless user entity for exclusion from the respective set of wireless user entities.

6. The management entity (301 ) of claim 5, wherein the management entity (301) is configured to determine the interference of a k-th wireless user entity on a transport link towards a q-th radio antenna unit by calculating an interference power when a

7. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301) is configured to calculate a signal-to-interference-plus-noise ratio on a transport link to obtain a quality indicator for each wireless user entity.

8. The management entity (301 ) of claim 7, wherein the management entity (301 ) is configured to calculate the signal-to-interference-plus-noise ratio on the basis of the

following equation:

where is the received power at the q- th radio antenna unit from the i-th wireless

user entity when the beamformer at the q-th radio antenna unit is directed towards the i-th wireless user entity, is the receiv enna unit from the

9. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301) is configured to schedule communication resources, in particular time slots or frequency bands, to each wireless user entity in the updated set of wireless user entities for communication over at least one transport link with at least one radio antenna unit.

10. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301 ) is configured to select at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit.

11. The management entity (301 ) of claim 9 or 10, wherein the management entity (301 ) is configured to select at least one transport link for at least one wireless user entity that has not yet been scheduled for transmission over any transport link.

12. The management entity (301 ) of claim 10 or 11 , wherein the management entity (301) is configured to iteratively select in at least one link selection iteration at least one transport link for at least one wireless user entity in the updated set of wireless user entities towards at least one radio antenna unit starting with a wireless user entity that is associated with a highest quality indicator in the updated set of wireless user entities.

13. The management entity (301) of claim 12, wherein the management entity (301) is configured to discard a cantenn qadio antenna unit in followi link assiginementt iteration if all transport links towards the certain radio antenna unit have been assigned to wireless user entities in a previous link assignment iteration.

14. The management entity (301 ) of any one of the preceding claims, wherein the management entity (301 ) is further configured to assign a wireless user entity of the updated set of wireless user entities to a further transport link that has not been assigned to any wireless user entity yet, if all wireless user entities of the updated set of wireless user entities have been assigned to at least one transport link towards at least one remote antenna unit.

15. The management entity (301 ) of anyone of the preceding claims, wherein the management entity (301 ) is configured to schedule transmissions of wireless user signals from the wireless user entities towards the radio antenna units over the transport links.

16. A communication system (300) for handling communications of a plurality of wireless user entities (305a-d) that use beamforming in a communication network, the communication system (300) comprising: a plurality of radio antenna units (303a, b), each radio antenna unit (303a, b) comprising a plurality of antennas for transmitting signals towards a communication network using beamforming, wherein each radio antenna unit (303a, b) comprises a plurality of transport links for receiving the wireless user signals from the wireless user entities (305a-d); and the management entity (301 ) for managing, in particular scheduling, communications of the wireless user entities (305a-d) on the transport links.

17. The communication system (300) according to claim 16, wherein the radio antenna units (303a, b) are configured to communicate over the transport links using beamforming.

18. Method (700) for managing communications between a plurality of wireless user entities (305a-d) and a plurality of radio antenna units (303a, b), each radio antenna unit (303a, b) being configured for communications in a communication network using beamforming, wherein each radio antenna unit (303a, b) is configured to communicate with one or more wireless user entities (305a-d) over a number of transport links of a transport network, the method (700) comprising: grouping (701 ) wireless user entities from the plurality of wireless user entities (305a-d) into at least one set of wireless user entities; obtaining (702) a quality indicator of at least one transport link for each wireless user entity in the at least one set of wireless user entities; if at least one obtained quality indicator is below a predetermined threshold, comparing (703) an interference value for each wireless user entity in the at least one set of wireless user entities with a predefined threshold and excluding at least one wireless user entity based on the comparison result thereby updating the set of wireless user entities; obtaining (704) an updated quality indicator for each wireless user entity in the updated set of wireless user entities on at least one transport link; and assigning (705) wireless user entities in the updated set of wireless user entities to at least one transport link towards at least one radio antenna unit if the updated quality indicators are at least equal to the predefined threshold.