TECHNICAL FIELD

Implementations described herein generally pertain to an access network device, a client device and respective methods therein. More particularly, a mechanism is provided, for broadcasting signals to client devices, which client devices are comprised in groups of cooperating client devices.

BACKGROUND

New technologies such as Device-to-Device (D2D) and massive-Multiple Input Multiple Output (massive-MIMO) systems are being considered under the 5G standardisation. In general, a single access network device, or transmit node, equipped with M antennas broadcasts to N client devices, each with a single receive antenna. If the number of transmit antennas is large, i.e., M » N, the client device perceives orthogonal channels approximately. Subsequently, interference nulling schemes such as the linear Zero Forcing (ZF) precoding at the transmitter can be used to decompose the (Nx M) MIMO channel into N independent Single-Input Single-Output (SISO) channels.

ZF (or null-steering) precoding is a method of spatial signal processing by which the multiple antenna transmitter can null multiuser interference signals in wireless communications.

The primary advantage of using the ZF precoding is its simplicity. Massive-MIMO can incorporate up to 64 transmit antenna elements while smaller transmit nodes can have up to 8. Hence there are not enough Degrees of Freedom (DoF) available for full interference cancellation with increasing N. Hence advanced precoding techniques are needed to fit the application specific requirement.

Client devices may also be grouped to implement advanced schemes such as Non- Orthogonal Multiple Access (NOMA) where the Successive Interference Cancellation (SIC) implementation removes the interference non-linearly. With NOMA, a stronger client device is squeezed into the resource occupied by a weaker client device. It must also be ensured that the stronger client device's power level is at most equal to the weaker client device's power level. Such a scheme increases the spectral efficiency. Since the weaker NOMA- client device is already experiencing a bad channel, there will not be a large change in the received signal. The stronger client device will perform SIC to remove the interference of the weaker client device. So, under NOMA the client devices are overlapped in the power domain over the same time-frequency resource. NOMA achieves the full capacity region up to the equal power point, i.e., the power levels of both the stronger and the weaker client device are the same. NOMA is advantageous over Orthogonal Multiple Access (OMA) when the Signal-to-Noise Ratio (SNR) of its constituent client device is distinct. Moreover, a NOMA group with more than two client devices is not preferred since this may lead to a drop in the performance gains. A variant of NOMA with client device cooperation may be implemented to further enhance the performance. However not much is known in this domain. Here the client devices collaborate on their own to handle the controlled-interference introduced by the access network device. To interact with each other, the client devices may use a side- link of a given capacity.

It may be noted that the capacity achieving precoding scheme Dirty Paper Coding (DPC) at the BS may also be implemented at the receiver side by SIC as in the cooperative networks. Also, the duality between the Uplink (UL) and the Downlink (DL) is well known. This suits well in the context of collaborative NOMA.

Having an interference free system is also not always beneficial. On the DL, it is known that when controlled-interference is introduced into the system, the performance is better than the interference-free signal. Various precoder designs exist in this regard, e.g., DPC, Zero Forcing DPC (ZF-DP) and User Grouping DPC (UG-DP).

For a Multiple Input Single Output (MISO) DL (i.e. MISO w.r.t. each client device), DPC is the capacity achieving technique. The non-causally available interference is subtracted while encoding the client device data. When all the client devices are grouped and ordered according their channel strength (ordering of MISO channels is possible unlike the MIMO case) a non-causal precoding full-DPC scheme may be implemented. Encoding is performed such that each client device sees the interference only from the client devices stronger than itself while the interference from the client devices weaker than itself is removed. So, the strongest client device in the ordered list will experience no interference while the weakest client device will see the interference from all the client devices. Implementing such a highly non-linear full-DPC scheme is complex, so other variants such as ZF-DP and UG-DP may be considered.

Both ZF-DP and UG-DP implement a combination of linear and non-linear parts. The causal interference is removed by the linear precoding part while the non-causal interference is removed by the non-linear part via successive-DPC. By successive-DPC it is meant that the DPC at the BS is implemented only among the grouped client devices. After the linear part implementation, each group has an effective channel that is band shaped and is lower triangular.

With UG-DP, N client devices are grouped into G disjoint groups of g client devices each (N = g ^* G may be considered). UG-DP will have g client devices in its successive-DPC implementation and G such DPCs. The manner in which the client devices are grouped and the order (arrangement according to the channel strength) of the client devices affect the performance. ZF-DP has only one group with a single band shaped effective channel and all the client devices are considered for the successive-DPC implementation at the BS. ZF-DP has (N- 1 ) client devices for its successive-DPC implementation. The order of client devices is also as important as before. It must be understood that DPC, ZF-DP and UG-DP are the transmitter side implementation.

ZF has low transmit power-efficiencies and low throughput, especially in cases where the channel vectors corresponding to different client devices are correlated. ZF-DP and UG-DP schemes suffer from rate losses due to orthogonalisation. But they perform better than the ZF scheme. It may be noted that the successive-DPC may be moved from the transmitter side to the client device side if the client devices are willing to cooperate. This is the SIC implementation. Such a transformation is well suited in the context of collaborative NOMA. For a full-SIC implementation at the client device side, a total of N {N - 1 ) cooperative links are required. So, an increasing N will increase in the implementation complexity of ZF-DP. With UG-DP g (g - 1 ) links exist in each group and each client device is present only in one group. Also for a given (N x M) MIMO channel (N MISO channels) and a given client device ordering, there is only a single way of DPC, UG-DP and ZF-DP implementation, i.e., the number of interfering client devices within each group cannot vary. Though g in UG-DP may vary, it will also change G that affects the overall performance.

Thus, there is room for improvement regarding NOMA and interference cancellation of collaborative receivers. SUMMARY

It is therefore an object to obviate at least some of the above mentioned disadvantages and to improve the performance in a wireless communication system.

This and other objects are achieved by the features of the appended independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. According to a first aspect, an access network device is provided, for broadcasting signals to client devices, in N groups of cooperating client devices. The access network device is configured to determine channel strength of each client device of all N client devices in the N groups. Further, the access network device is configured to determine a number v of maximum interfering client devices in each group of cooperating client devices, where v < N. Also, the access network device is further configured to determine an order of the client devices, based on the determined respective channel strength. In addition, the access network device is also configured to linearly precode the signals to be broadcasted, creating a band-shaped effective channel, wherein the band-shape is based on the determined parameter v. Furthermore, the access network device is configured to broadcast the linearly precoded signals to the client devices at the same time and frequency resource, but with different transmission power levels. The access network device is additionally configured to instruct the client devices to successively decode received signals by non-linearly cancelling interference of up to v interfering client devices in the same group.

Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided.

In a first possible implementation of the access network device according to the first aspect, the access network device is configured to linearly precode the signals to be broadcasted according to the precoder matrix:

P=H ^H (HH ^H )' ¹ F,

where (.) ^H is the Hermitian matrix, (.) ¹ is the inverse of the matrix, H is a channel matrix and F has a band structure:

By selecting an appropriate precoder matrix, a better adaptation to realistic transmission conditions is made, resulting in an improved signal precoding.

In a second possible implementation of the access network device according to the first aspect, or the first possible implementation thereof, the access network device is further configured to create the band-shaped effective channel HP: HP = HH" (ΗΗ ^Η ) = F. Thereby, a further improved adaptation to realistic transmission conditions is made, resulting in further transmission improvements.

In a third possible implementation of the access network device according to the first aspect, or any previous possible implementation thereof, the access network device is further configured to determine N groups of cooperating client devices with at most v +1 client devices in any single group.

By determining the number and setting of client devices in the cooperating groups, further improvements are achieved, as e.g. a short physical distance between client devices in the same group enable side link communication between the cooperative client devices using low transmission power, which saves energy capacity at the client devices, while transmission interference is reduced, or kept below a threshold limit.

In a fourth possible implementation of the access network device according to the first aspect, or any previous possible implementation thereof, the access network device is further configured to permit any client device to be present in multiple groups of cooperating client devices; and configured to permit said client device to decode its received signal only in one of the multiple groups. Thereby an appropriate definition of the cooperating group is achieved, further improving the effects of the provided solution. In a fifth possible implementation of the access network device according to the first aspect, or any previous possible implementation thereof, the access network device is further configured to instruct the client device„ in group„ to cancel up to v interfering client device signals (client device< _K -i), client device^),..., client device^)), where 1 < n ≤ N before decoding signals of client device„.

Thanks to the provided instruction, an appropriate interference cancellation may be performed by the client devices.

According to a second aspect, a method in an access network device is provided, for broadcasting signals to client devices, in Ngroups of cooperating client devices. The method comprises determining channel strength of each client device of all N client devices in the N groups. Further, the method also comprises determining a number v of maximum interfering client devices in each group of cooperating client devices, where v < N. The method also comprises determining order of the client devices, based on the determined respective channel strength. The method additionally comprises linearly precoding the signals to be broadcasted, creating a band-shaped effective channel, wherein the band-shape is based on the determined parameter v. The method furthermore comprises broadcasting the linearly precoded signals to the client devices at the same time and frequency resource, but with different transmission power levels. Also, the method comprises instructing the client devices to successively decode received signals by non-linearly cancelling interference of previous interfering client devices in the same group. Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided. In a first possible implementation of the method according to the second aspect, the method also comprises linearly precode the signals to be broadcasted according to the precoder matrix:

P=H ^H (HH ^H )' ¹ F,

where (.) ^H is the Hermitian matrix, (.) ¹ is the inverse of the matrix, H is a channel matrix and F has a band structure:

By selecting an appropriate precoder matrix, a better adaptation to realistic transmission conditions is made, resulting in an improved signal precoding.

In a second possible implementation of the method according to the second aspect, or the first possible implementation thereof, the method also comprises creating the band-shaped effective channel HP: HP = HH" {ΗΗ") = F.

Thereby, a further improved adaptation to realistic transmission conditions is made, resulting in further transmission improvements. In a third possible implementation of the method according to the second aspect, or any possible implementation thereof, the method further comprises determining N groups of cooperating client devices with at most v +1 client devices in any single group.

By determining the number and setting of client devices in the cooperating groups, further improvements are achieved, as e.g. a short physical distance between client devices in the same group enable side link communication between the cooperative client devices using low transmission power, which saves energy capacity at the client devices, while transmission interference is reduced, or kept below a threshold limit.

In a fourth possible implementation of the method according to the second aspect, or any possible implementation thereof, the method further comprises permitting any client device to be present in multiple groups of cooperating client devices; and configured to permit said client device to decode its received signal only in one of the multiple groups.

Thereby an appropriate definition of the cooperating group is achieved, further improving the effects of the provided solution.

In a fifth possible implementation of the method according to the second aspect, or any possible implementation thereof, the method further comprises instructing the client device _* in group _* to cancel up to v interfering client device signals (client device< _K -i), client device< _K - 2), ... , client device^)), where 1 < n≤ N before decoding signals of client device _* .

Thanks to the provided instruction, an appropriate interference cancellation may be performed by the client devices. According to a third aspect, a computer program comprising program code is provided, for performing a method according to the second aspect, when the computer program is performed on a processor.

Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided.

According to a fourth aspect, a client device is provided, configured to receive an instruction from an access network device, to participate in a group of cooperating client devices and to successively decode signals by non-linearly cancelling interference of up to v interfering client devices in the same group. Further, the client device is configured to receive precoded signals from the access network device at the same time and frequency resource, but with different transmission power levels. Also, the client device is furthermore configured to cancel interference, sequentially, of up to v interfering client devices in the same group, based on a band-shaped effective channel structure F. The client device is also configured to decode received signals of the client device.

Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided.

In a first possible implementation of the client device according to the fourth aspect, the client device may be further configured to cancelling interference according to the band-shaped effective channel structure F.

Thanks to the band-shaped effective channel structure, an appropriate interference cancellation may be performed by the client devices, resulting in an improved signal precoding.

In a second possible implementation of the client device according to the fourth aspect, or the first aspect thereof, the client device with index n in group„, which group„ comprises: client device _* , client device^), client device^), client device^; the client device _* may be further configured to cancel up to v interfering client device signals of client client device^), client device^); where 1≤ n≤N, before decoding signals of the client device with index n.

Thereby, further improvements are achieved, resulting in further transmission improvements.

In a third possible implementation of the client device according to the fourth aspect, or any previous possible implementation thereof, the client device may be further configured to communicate information related to interference causing symbols with other client devices in the same group via a side- link.

Thereby, further improvements are achieved, resulting in further transmission improvements. In a fourth possible implementation of the client device according to the fourth aspect, or any previous possible implementation thereof, the client device may be further configured to communicate with other client devices via a side- link implemented in a mmWave spectrum.

By implementing the side-link in the mmWave radio spectrum, the access network device need not know the interference cancellation process at the client devices.

According to a fifth aspect, a method in a client device is provided. The method comprises receiving an instruction from an access network device, to participate in a group of cooperating client devices and to successively decode signals by non-linearly cancelling interference of up to v interfering client devices in the same group. Further the method also comprises receiving signals from the access network device at the same time and frequency resource, but with different transmission power levels. Also, the method furthermore comprises cancelling interference, sequentially, of up to v interfering client devices in the same group, based on a band-shaped effective channel structure F. The method also comprises decoding received signals of the client device.

Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided.

In a first possible implementation of the method according to the fifth aspect, the method furthermore comprises cancelling interference according to the band-shaped effective channel structure F:

Thanks to the band-shaped effective channel structure, an appropriate interference cancellation may be performed by the client devices, resulting in an improved signal precoding.

In a second possible implementation of the method according to the fifth aspect, or the first aspect thereof, wherein the client device with index n in group _* , which group _* comprises: client device _* , client device^), client device^), client device^; the method also comprises cancelling up to v interfering client device signals of client client device^), ... , client device^; where 1 < n≤N, before decoding signals of the client device with index n. Thereby, further improvements are achieved, resulting in further transmission improvements.

In a third possible implementation of the method according to the fifth aspect, or any previous possible implementation thereof, the method may further comprise communicating information related to interference causing symbols with other client devices in the same group via a side- link. Thereby, further improvements are achieved, resulting in further transmission improvements.

In a fourth possible implementation of the method according to the fifth aspect, or any previous possible implementation thereof, the method may further comprise implementing a side- link in a mmWave radio spectrum.

By implementing the side-link in the mmWave radio spectrum, the access network device need not know the interference cancellation process at the client devices. According to a sixth aspect, a computer program comprising program code is provided, for performing a method according to the fifths aspect, when the computer program is performed on a processor.

Thereby, after one client device's signal is decoded, it is subtracted from the combined signal received from the access network device before the next client device's signal is decoded. When SIC is applied, one of the client device signals is decoded, treating the other client device signal as an interferer, but the latter is then decoded with the benefit of the signal of the former having already been removed. However, prior to SIC, client devices are ordered according to their signal strengths, so that the client device can decode the stronger signal first, subtract it from the combined signal, and isolate the weaker one from the residue. Thus, each client device in the cooperative group is decoded treating the other interfering client device as noise in signal reception. Thanks to the provided precoder design, and by client device cooperating in groups in the context of collaborative NOMA, throughput is enhanced while the number of communication links is reduced in comparison with conventionally used methodologies. Thus, an improved performance within a wireless communication system is provided.

Other objects, advantages and novel features of the aspects of the disclosed solutions will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:

Figure 1 is an illustration of system architecture comprising an access network device and a cooperative network, according to an embodiment.

Figure 2 is a diagram over a comparison of the number of communication links, according to an embodiment. Figure 3 is a diagram over a comparison between different embodiments for various v, of sum-rate versus transmit power.

Figure 4 is a diagram over a comparison between different embodiments for various v,

of sum-rate versus number of client devices.

Figure 5 is a diagram over a comparison between different embodiments for various v,

of sum-rate versus transmit power.

Figure 6 is an illustration of an efficient channel according to an embodiment.

Figure 7 is a flow chart illustrating a method in an access network device according to an embodiment.

Figure 8 is a block diagram illustrating an access network device according to an embodiment.

Figure 9 is a flow chart illustrating a method in a client device according to an embodiment.

Figure 10 is a block diagram illustrating a client device according to an embodiment. DETAILED DESCRIPTION

Embodiments described herein are defined as an access network device, a method therein, a client device and a method therein, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Figure 1 is a schematic illustration over a wireless communication system 100 comprising an access network device 110 communicating wirelessly with a group 130 of cooperating client devices 120a, 120b, 120c, 120d. The wireless communication system 100 may at least partly be based on any arbitrary access technology such as e.g. 3GPP Long Term Evolution (LTE), LTE-Advanced, LTE fourth generation mobile broadband standard, Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Worldwide Interoperability for Microwave Access (WiMax), WiFi, just 5 to mention some few options.

The wireless communication system 100 may be based on NOMA, according to different embodiments.

10 A precoder is designed where the number of cooperating/ collaborating client devices 120a, 120b, 120c, 120d is allowed to vary and is controlled by a parameter v. The expressions cooperating client devices and collaborating client devices may be used interchangeably in this disclosure. A linear part of the precoder may be implemented at the access network device 1 10 while its non-linear part is moved to the cooperating client devices 120a, 120b,

15 120c, 120d. This non-linear part implementation forms the basis for a conceptual idea of collaborative-NOMA. The parameter v may be viewed as the number of cooperating client devices 120a, 120b, 120c, 120d, i.e., there will be at most v client devices 120a, 120b, 120c, 120d in a successive-SIC implementation.

20 Each of the cooperating client device 120a, 120b, 120c, 120d may be affiliated to more than one group 130 of cooperating client devices.

A collaborative NOMA group may have more than two client device 120a, 120b, 120c, 120d and at most v client device 120a, 120b, 120c, 120d unlike conventional NOMA where there 25 are usually two client devices 120a, 120b, 120c, 120d per group 130. In this regard, the sum- rate is maximised while reducing the number of client device communication links. A closed form solution is obtained while maximising this sum-rate, which is an advantage of the presented solution.

30 By varying the parameter v, additional degrees of freedom are incorporated into the system 100, for enhanced flexibility. The current situation primarily concerns the case when M >= N (not M » N). It is assumed that the client devices 120a, 120b, 120c, 120d have enough side-link capacity for cooperation and the collaborating client devices 120a, 120b, 120c, 120d form a group 130 and operate at considerably low power levels, e.g. that they are situated

35 within line of sight and/ or within a distance lower than a threshold level. There could be many such groups 130. An immediate application could be for related client devices 120a, 120b, 120c, 120d such as e.g. family members, trusted colleagues, etc., in close proximity to enable low power communication.

Though the precoder and interference cancellation described in this disclosure is partially implemented at the access network device 1 10 and partially at the client devices 120a, 120b, 5 120c, 120d, the term 'precoder' may be retained though strictly speaking it is not a precoder- only scheme. This is due to the fact that by moving the non-linear part to the access network device 1 10, the entire scheme may be visualised as a precoder-only scheme without any collaborating client devices 120a, 120b, 120c, 120d. Nevertheless, in the context of collaborative NOMA this 'partial precoding' scheme may be regarded as implicit, according 10 to some embodiments.

Initially the number of interfering client devices 120a, 120b, 120c, 120d is defined by the parameter v, i.e., there are at most v interfering client devices 120a, 120b, 120c, 120d. This also implicitly defines the grouping for a given (Nx M) MIMO channel. These client devices 15 120a, 120b, 120c, 120d may cooperate in order to remove the interference, in a successive interference cancellation. Figure 1 shows an example of such a cooperative network.

With cooperating client devices 120a, 120b, 120c, 120d, the linear part of the precoder design is implemented at the access network device 1 10 while the non-linear part is moved

20 to the client device side. This facilities NOMA implementation in the system 100 where more than two client devices 120a, 120b, 120c, 120d may be grouped. A NOMA- client device 120a, 120b, 120c, 120d may be present across multiple groups based on v, e.g., when v =1 , a client device„ («≠1 ) will cancel interference of client device^) in the group„ and client device(„+i) will cancel interference from client device„ in group(„+i). Similarly, for v >1 , the client

25 device 120a, 120b, 120c, 120d will span multiple NOMA groups. Cooperating client device 120a, 120b, 120c, 120d are also the interfering client device 120a, 120b, 120c, 120d (before non-linear interference cancellation is implemented). Hence v also specifies the number of client device 120a, 120b, 120c, 120d in each cooperative NOMA group.

30 The precoder may be given as P=H ^H (HH ^H ) ^"1 F, where (.) ^H is the Hermitian and is the inverse of the matrix. F may have a band structure as shown below:

Only the elements along the main diagonal and the first v lower-diagonals have non-zero elements as shown below. If a full cooperation as in zero forcing dirty paper coding is 5 required, then the remaining lower-diagonals may also be filled up, in some embodiments.

10 In some embodiments, an ordered list may be established, listing the client devices 120a, 120b, 120c, 120d according to estimated signal strength, from strongest to weakest. Such list may be used for determining a sequential decoding order of the client devices 120a, 120b, 120c, 120d. Hence the initial client device ordering may have an impact on the outcome of the disclosed method, concerning the cooperative client devices 120a, 120b,

15 120c, 120d. The sequential decoding is further illustrated in Figure 6 and discussed in the corresponding part of the description.

According to some embodiments, an implementation of the precoder may require a total of v (N- -1 )/ 2 communication links among the client devices 120a, 120b, 120c, 120d. This is 20 controlled by the parameter v. This number for v < N is very less when compared to the full- SIC implementation. A comparison between them for varying N is shown in Figure 2. It can be observed that with increasing number of client devices 120a, 120b, 120c, 120d, the number of required communication links among them increases rapidly.

25 The comparison in Figure 2 is made between the described cooperation scheme in an embodiment of the invention where v = 2, and a full cooperation scheme according to prior art. As becomes clear from the illustration of Figure 2, a radical improvement of the provided solution over the conventionally provided solution is the reduced number of communication channels.

Under such collaborative NOMA setup, the throughput maximisation problem may be given as:

where G=(HH ^H )- Ρτ is the available transmit power at the access network device 1 10, No is the noise power at each client device 120a, 120b, 120c, 120d. It can be observed that there is no interference (except thermal noise) present in the rate expression of each client devices 120a, 120b, 120c, 120d. The interference is removed after collaboration between the client devices 120a, 120b, 120c, 120d. A client device„ will observe and cancel interference from a maximum of v client devices 120a, 120b, 120c, 120d preceding it (UE _m , m < n) in the given client device ordering.

The optimisation problem defined above may be solved by a water-filling algorithm in a closed form according to some embodiments. Thus: n Θ v = max(n— f, 0),

n ffl ⁱ = min(n + i , JV) -

n

9ηίΰι/,η ffnWv,n { 1 ^{* * *} ΒτύΆν,τύΆν in and g„ ^v are (v x 1 ) vectors that comprise the non-zero entries on each column of F and G excluding the main diagonal elements respectively. In the next equations, a parameter λ is evaluated by the water-filling algorithm. The main diagonal elements f„, _n may be evaluated with this λ in some embodiments. The other elements may be filled in by the vector f„. Such an evaluation may provide the optimal elements in the band-shaped precoder F, according to some embodiments.

For verifying the performance of the disclosed cooperative scheme, it is compared against full-DPC (mentioned as "opt. DPC" in Figure 3- Figure 5), and ZF schemes. Also, the full client device cooperation when v = (N- 1 ) is shown in Figure 3- Figure 5.

Figure 3 illustrates a sum-rate of the provided solution for various v versus transmit power for a fixed M and Nand independent and identically distributed complex Gaussian channel. M = N= 8. N ₀ =1 It can be observed from Figure 3 that for a fixed Mand N, the provided solution may provide a gain over ZF-method even for v = 1. The gain may be around 4dB over the ZF and the gap may be less than 1 .5 dB from the optimal DPC values when v = 3, in some embodiments. As v varies, the sum-rate may increase and approach the DPC values. Also for v = 7, the gap is closing rapidly for increasing transmit power.

Figure 4 illustrates a sum-rate of the provided solution with various v versus number of client devices 120a, 120b, 120c, 120d under independent and identically distributed complex Gaussian channels. M = 24, P _T = 10dB, N ₀ = 1. From Figure 4 it may be observed that with an increase in N, the sum-rate values initially increase and then decrease. With increasing N, the inter-user interference may also increase, causing the degradation for lower values of v. For v = (N - 1 ), the sum-rate may increase for the shown values of N, in some embodiments. But the rate of increase decreases in the illustrated embodiment. In any case, the provided solution out performs the ZF scheme according to conventionally used solutions.

Impact of correlation between access network device 1 10 and client devices 120a, 120b, 5 120c, 120d is shown next. With β as the correlation factor, the access network device and client device correlation matrices may be modelled as:

Κ=Μ, β= βτ for access network device correlation and K=N and β= βπ for client device0 correlation.

Figure 5 illustrates a sum-rate of the provided solution for various v versus transmit power for a fixed N = M = 8 for a Rayleigh-fading channel. Access network device correlation βτ = 0.2, and client device correlation ¾ = 0.8.

5

Figure 5 shows the same or at least similar setup as in Figure 3 but with correlation included. A similar trend as in Figure 3 is observed but the gains in this illustrated embodiment are larger than those obtained in Figure 3. It shows the precoding benefits according to an embodiment of the disclosed solution, when correlation exists. Even a small v may be0 beneficial over conventional ZF solutions. At v = 1 , the gain is around 5dB over the conventional ZF solution.

In addition to the above described objectives for the disclosed scheme with collaborative NOMA the results according to some embodiments may conclude that the solution may5 comprise a more generalised precoding (partial precoding scheme as mentioned earlier) implementation that chooses the number of interfering/ cooperating client devices 120a, 120b, 120c, 120d.

Further, by moving the non-linear part of interference cancelling to the cooperating client0 devices 120a, 120b, 120c, 120d, the implementation of collaborative NOMA is facilitated. The linear part is still implemented at the access network device 1 10. Thanks to the newly introduced degree of freedom v, the spectral efficiency of the system 100 may be improved and the sum-rate can be made to approach the DPC values for a large transmit power under full cooperation. However, the number of client device communication links is considerably reduced, in comparison with full cooperation DPC, by selecting an appropriate v.

The disclosed precoder may find its application where grouped client devices are collaborating and interference is allowed among them in a controlled manner. This interference may however be eliminated by successive-SIC in some embodiments.

When implementing interference cancellation at the client device side, the cost of implementing the client device communication must also be considered for practical reasons. Figure 6 illustrates interference cancellation within a group of cooperating client devices 120a, 120b, 120c, 120d. The number of groups N is set to 5 and the maximum number v of cooperating client devices 120a, 120b, 120c, 120d is set to 3.

Further, it may be assumed that an ordered list has been established by the access network device 1 10, ordering the client devices 120a, 120b, 120c, 120d in estimated respective channel strength order, from signal fn of the client device with the strongest estimated channel strength, to signal fss, of the client device with the weakest estimated channel strength in the group 130. The client devices 120a, 120b, 120c, 120d may thus firstly be set in order, based on the estimated channel strength of each respective client device 120a, 120b, 120c, 120d, e.g. arranged in descending order of their respective estimated channel strength. Further, the signal fn of the client device with the strongest estimated channel strength is comprised in groupi . The signal fn is decoded firstly. There are no interfering signals from any other client devices 120a, 120b, 120c, 120d. When using the channel matrix, missing entries in each row may be zeros.

In group2, signals f∑i of one client device is interfering signal f∑2 of the client device with the second strongest estimated channel strength, v = 3, but only one interfering client device is possible. Thus, signal f∑2 is decoded, cancelling out the interfering signals hi -

In groups, signals hi and h2 of client devices are interfering signal h3 of the client device with the third strongest estimated channel strength. The signal f33 is decoded, cancelling out the interfering signals hi and h2 of the interfering client devices.

In group4, signals f ₄ i , f ₄ 2 and f ₄ 3 of client devices are interfering signal f ₄₄ of the client device 5 with the fourth strongest estimated channel strength. The signal f ₄₄ is decoded, cancelling out the interfering signals f ₄ i , f ₄ 2 and f ₄ 3 of the interfering client devices.

In groups, signals fs2, fs3 and fs ₄ of client devices are interfering signal fss of the client device with the fifth strongest estimated channel strength. The signal fss is decoded, cancelling out 10 the interfering signals fs2, fs3 and fs ₄ of the interfering client devices. As the number of interfering client devices 120a, 120b, 120c, 120d is limited according to v = 3, signal f ₅ i of the first client device is not interfering the signals fss.

The provided solution comprises two parts: a precoding is provided at the access network 15 device 1 10, further illustrated and described in Figure 7 and Figure 8, while interference cancellation is made at the client device 120a, 120b, 120c, 120d as further illustrated and described in Figure 9 and Figure 10.

Figure 7 illustrates an example of a method 700 in an access network device 1 10 for 20 broadcasting signals to client devices 120a, 120b, 120c, 120d in Ngroups 130 of cooperating client devices.

The signals may be broadcasted on the same time and/ or frequency resources, but at different transmission power levels for signals dedicated to different client devices 120a, 25 120b, 120c, 120d. Thereby, the different power levels may be utilised by the receiving client device 120a, 120b, 120c, 120d for obtaining the signal dedicated for the respective client device 120a, 120b, 120c, 120d, although the same time/ frequency resources are utilised, leading to an ability to serve more client devices 120a, 120b, 120c, 120d within the system 100.

30

To appropriately broadcast signals to the client devices 120a, 120b, 120c, 120d, the method 700 may comprise a number of method steps 701 -706. It is however to be noted that any, some or all of the described steps 701 -706, may be performed in a somewhat different chronological order than the enumeration indicates, be performed simultaneously or even be 35 performed in a completely reversed order according to different embodiments. Further, it is to be noted that some steps 701-706 may be performed in a plurality of alternative manners according to different embodiments, and that some such alternative manners may be performed only within some, but not necessarily all embodiments. The method 700 may comprise the following steps:

Step 701 comprises determining channel strength of each client device 120a, 120b, 120c, 5 120d of all N client devices 120a, 120b, 120c, 120d in the Ngroups 130.

In some embodiments, the N groups 130 of cooperating client devices 120a, 120b, 120c, 120d may be determined with at most v + 1 client devices 120a, 120b, 120c, 120d in any single group 130.

10

There may be N groups 130 with at most (v + 1 ) client devices 120a, 120b, 120c, 120d in any single group 130.

Step 702 comprises determining a number v of maximum interfering client devices 120a, 15 120b, 120c, 120d in each group 130 of cooperating client devices, where v < N.

Thus, v is the number of collaborating client devices 120a, 120b, 120c, 120d, for interference cancellation. There may be at most v interfering client devices 120a, 120b, 120c, 120d in a group 130. So, 0, 1 , v are possible numbers of interfering client devices 120a, 120b, 20 120c, 120d for a client device 120a, 120b, 120c, 120d.

Step 703 comprises determining order of the client devices 120a, 120b, 120c, 120d, based on the determined respective channel strength.

25 Thereby, an ordered list of client devices 120a, 120b, 120c, 120d may be created, wherein the client devices 120a, 120b, 120c, 120d are arranged in the descending order of their respective channel strength.

Step 704 comprises linearly precoding the signals to be broadcasted, creating a band- 30 shaped effective channel, wherein the band-shape is based on the determined parameter v.

The linear precoding of the signals may in some embodiments be performed based on the precoder matrix:

P=H ^H (HH ^H ) ^'1 F,

35 where (.) ^H is the Hermitian matrix, (.) ¹ is the inverse of the matrix, H is a channel matrix and F has a band structure:

In some embodiments, the band-shaped effective channel HP may be created by:

HP = ΗΗ ^Η {ΗΗ ^Η ) = F.

5

At this point, there may be only a partial interference cancellation made, based on the v value.

Step 705 comprises broadcasting the linearly precoded signals to the client devices 120a, 10 120b, 120c, 120d at the same time and frequency resource, but with different transmission power levels.

Step 706 comprises instructing the client devices 120a, 120b, 120c, 120d to successively decode received signals by non-linearly cancelling interference of previous interfering client 15 devices 120a, 120b, 120c, 120d in the same group 130.

In some embodiments, the access network device 110 may permit any client device 120a, 120b, 120c, 120d to be present in multiple groups 130 of cooperating client devices. Also, the access network device 1 10 may permit the client device 120a, 120b, 120c, 120d to 20 decode its received signal only in one of the multiple groups 130. The instruction sent to the client devices 120a, 120b, 120c, 120d may comprise such information concerning the permissions, in some embodiments.

The instruction sent to the client devices 120a, 120b, 120c, 120d may further comprise 25 information instructing the client device _* in group _* to cancel up to v interfering client device signals (client device< _K -i), client where 1 < n ≤ N before decoding the signal(s) of client device _* .

Figure 8 illustrates an embodiment of an access network device 110 comprised in a wireless communication system 100. The access network device 110 is configured to perform at least some of the previously described method steps 701-706, for broadcasting signals to client devices, 120a, 120b, 120c, 120d in N groups 130 of cooperating client devices.

For enhanced clarity, any internal electronics or other components of the access network device 1 10, not completely indispensable for understanding the herein described embodiments has been omitted from Figure 8.

The access network device 1 10 is configured to determine channel strength of each client device 120a, 120b, 120c, 120d of all Nclient devices 120a, 120b, 120c, 120d in the Ngroups 130. Further, the access network device 1 10 is configured to determine a number v of maximum interfering client devices 120a, 120b, 120c, 120d in each group 130 of cooperating client devices, where v < N. The access network device 1 10 is also configured to determine order of the client devices 120a, 120b, 120c, 120d, based on the determined respective channel strength. Furthermore, the access network device 1 10 is additionally configured to linearly precode the signals to be broadcasted, creating a band-shaped effective channel, wherein the band-shape is based on the determined parameter v. The access network device 1 10 is configured to broadcast the linearly precoded signals to the client devices 120a, 120b, 120c, 120d at the same time and frequency resource, but with different transmission power levels. Also, the access network device 110 is further configured to instruct the client devices 120a, 120b, 120c, 120d to successively decode received signals by non-linearly cancelling interference of up to v interfering client devices 120a, 120b, 120c, 120d in the same group 130.

According to some embodiments, the access network device 1 10 may also be configured to linearly precode the signals to be broadcasted according to the precoder matrix P=H ^H (HH ^H ) ^{~ 1} F, where (.) ^H is the Hermitian matrix, (.) ¹ is the inverse of the matrix, H is a channel matrix and F has a band structure:

In some embodiments, the access network device 1 10 may further be configured to create the band-shaped effective channel HP: HP = HH" (HH ^H ) ¹ F = F. Furthermore, the access network device 1 10 may also be additionally configured to determine N groups 130 of cooperating client devices 120a, 120b, 120c, 120d with at most v +1 client devices 120a, 120b, 120c, 120d in any single group 130. The access network device 1 10 may further be configured to permit any client device 120a, 120b, 120c, 120d to be present in multiple groups 130 of cooperating client devices; and configured to permit said client device 120a, 120b, 120c, 120d to decode its received signal only in one of the multiple groups 130. According to some embodiments, the access network device 1 10 may also be configured to instruct the client device _* in group _* to cancel up to v interfering client device signals (cli-ent device< _K -i), client device^),..., client device^)), where 1 < n < N before decoding sig-nals of client device _* . The access network device 1 10 may comprise a receiving circuit 810, configured to receive wireless signals from any client device 120a, 120b, 120c, 120d, or from any other entity configured to communicate wirelessly over a wireless interface according to some embodiments. Furthermore, the access network device 1 10 comprises a processor 820, configured to broadcast signals to client devices 120a, 120b, 120c, 120d in N groups 130 of cooperating client devices, by performing at least some steps 701 -706 of the described method 700.

Such processor 820 may comprise one or more instances of a processing circuit, i.e. a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones enumerated above.

In addition, according to some embodiments, the access network device 1 10 may also comprise at least one memory 825 in the access network device 1 10. The optional memory 825 may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis in a non-transitory manner. According to some embodiments, the memory 825 may comprise integrated circuits comprising silicon- based transistors. Further, the memory 825 may be volatile or non-volatile. In addition, the access network device 1 10 may comprise a transmitting circuit 830, configured for transmitting wireless signals within the wireless communication system 100.

Furthermore, the access network device 1 10 may also comprise an antenna 840. The 5 antenna 840 may optionally comprise an array of antenna elements in an antenna array in some embodiments.

The method steps 701 -706 to be performed in the access network device 1 10 may be implemented through the one or more processors 820 in the access network device 1 10 10 together with computer program product for performing the functions of the method steps 701 -706.

Thus, a non-transitory computer program comprising program code for performing the method 700 according to any of steps 701 -706, for broadcasting signals to client devices, 15 120a, 120b, 120c, 120d in N groups 130 of cooperating client devices in a wireless communication system 100, when the computer program is loaded into a processor 820 of the access network device 1 10.

The non-transitory computer program product mentioned above may be provided for 20 instance in the form of a non-transitory data carrier carrying computer program code for performing at least some of the steps 701-706 according to some embodiments when being loaded into the processor 820. The data carrier may be, e.g., a hard disk, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory 25 manner. The non-transitory computer program product may furthermore be provided as computer program code on a server and downloaded to the access network device 110, e.g., over an Internet or an intranet connection.

Figure 9 illustrates an example of a method 900 in a client device 120a, 120b, 120c, 120d.

30

The client device 120a, 120b, 120c, 120d may be comprised in a group 130 of cooperating client devices, for receiving wireless signals broadcasted from an access network device 1 10.

35 The signals may be broadcasted by the access network device 1 10 on the same time and/ or frequency resources, but at different transmission power levels. The client device 120a, 120b, 120c, 120d may in some embodiments have index w in group _* , which group _K comprises client device _K , client

wherein the client device„ is configured to cancel up to v interfering client device signals (of client device< _K -i), client device^), client device^)), where 1 < n≤ N before decoding signals of the client device 120a, 120b, 120c, 120d.

Client device _* may be present across multiple groups 130 and may decode its signal only in group _K . Client device _* may not decode in any other group 130. To appropriately receive and decode signals broadcasted by the access network device 1 10, the method 900 may comprise a number of method steps 901 -904. It is however to be noted that any, some or all of the described steps 901-904, may be performed in a somewhat different chronological order than the enumeration indicates, be performed simultaneously or even be performed in a completely reversed order according to different embodiments. Further, it is to be noted that some steps 901 -904 may be performed in a plurality of alternative manners according to different embodiments, and that some such alternative manners may be performed only within some, but not necessarily all embodiments. The method 900 may comprise the following steps: Step 901 comprises receiving an instruction from an access network device 1 10, to participate in a group 130 of cooperating client devices and to successively decode signals by non-linearly cancelling interference of up to v interfering client devices 120a, 120b, 120c, 120d in the same group 130. Step 902 comprises receiving signals from the access network device 1 10 at the same time and frequency resource, but with different transmission power levels.

In some embodiments, information related to interference causing symbols with other client devices 120a, 120b, 120c, 120d in the same group 130 may be communicated via a side- link. Such side-link communication may be implemented in a mmWave spectrum in some embodiments.

Over the side-links between the client devices 120a, 120b, 120c, 120d, any client device 120a, 120b, 120c, 120d may forward its decoded symbol(s) to the next groups, in the determined sequential order, where it is present as an interfering client device 120a, 120b, 120c, 120d. Thereby, client devices 120a, 120b, 120c, 120d may receive symbols from client devices 120a, 120b, 120c, 120d decoded prior to it and are present in its group 130 causing interference to it.

Step 903 comprises cancelling interference, sequentially, of up to v interfering client devices 120a, 120b, 120c, 120d in the same group 130, based on a band-shaped effective channel 5 structure F. The structure F implicitly depends on the value v.

The band-shaped effective channel structure F may have the form:

10 Step 904 comprises decoding received 902 signals of the client device 120a, 120b, 120c, 120d.

The decoding order of the client device 120a, 120b, 120c, 120d is, in channel strength order as established by the access network device 1 10, i.e., client device^ client device2, client 15 device^.

Figure 10 illustrates an embodiment of a client device 120a, 120b, 120c, 120d, comprised in a wireless communication system 100. The client device 120a, 120b, 120c, 120d is configured to perform at least some of the previously described method steps 901 -904, for 20 receiving precoded signals from an access network device 1 10.

For enhanced clarity, any internal electronics or other components of the client device 120a, 120b, 120c, 120d, not completely indispensable for understanding the herein described embodiments has been omitted from Figure 10.

25

The client device 120a, 120b, 120c, 120d is configured to receive an instruction from an access network device 1 10, to participate in a group 130 of cooperating client devices and to successively decode signals by non-linearly cancelling interference of up to v interfering client devices 120a, 120b, 120c, 120d in the same group 130. Further, the client device 120a, 30 120b, 120c, 120d is configured to receive precoded signals from the access network device 1 10 at the same time and frequency resource, but with different transmission power levels. In addition, the client device 120a, 120b, 120c, 120d is furthermore configured to cancel interference, sequentially, of up to v interfering client devices 120a, 120b, 120c, 120d in the same group 130, based on a band-shaped effective channel structure F. The client device 120a, 120b, 120c, 120d is further configured to decode received signals of the client device 5 120a, 120b, 120c, 120d based on which the interference cancelation can be performed.

According to some embodiments, the client device 120a, 120b, 120c, 120d may also be configured to cancelling interference according to the band-shaped effective channel structure F:

The client device 120a, 120b, 120c, 120d with index n in group _* , which group _* comprises client device _* , client device< _K -i), client device^), client device^), may also in some embodiments be configured to cancel up to v interfering client device signals, i.e. client 15 device< _K -i), client device^), ... , client device^; where 1 < n≤ N before decoding signals of the client device 120a, 120b, 120c, 120d with index n in group _* .

Further, the client device 120a, 120b, 120c, 120d may also be configured to communicate information related to interference causing symbols with other client devices 120a, 120b, 20 120c, 120d in the same group 130 via a side- link, in some embodiments. Such side-link may be implemented in a mmWave spectrum.

The client device 120a, 120b, 120c, 120d may comprise a receiving circuit 1010, configured to receive wireless signals from the access network device 1 10, from other client devices 25 120a, 120b, 120c, 120d e.g. comprised in the same group 130 of cooperative client devices, or from any other entity configured to communicate wirelessly over a wireless interface according to some embodiments.

Furthermore, the client device 120a, 120b, 120c, 120d comprises a processor 1020, 30 configured to cancel interference of received signals broadcasted by the access network device 1 10, and decode the signals, by performing at least some steps 901-904 of the described method 900.

Such processor 1020 may comprise one or more instances of a processing circuit, i.e. a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an 5 Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression "processor" may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones enumerated above.

10 In addition, according to some embodiments, the client device 120a, 120b, 120c, 120d may also comprise at least one memory 1025 in the client device 120a, 120b, 120c, 120d. The optional memory 1025 may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis in a non-transitory manner. According to some embodiments, the memory 1025 may comprise integrated

15 circuits comprising silicon-based transistors. Further, the memory 1025 may be volatile or non-volatile.

In addition, the client device 120a, 120b, 120c, 120d may comprise a transmitting circuit 1030, configured for transmitting wireless signals within the wireless communication system 20 100.

Furthermore, the client device 120a, 120b, 120c, 120d may also comprise an antenna 1040. The antenna 1040 may optionally comprise an array of antenna elements in an antenna array in some embodiments.

25

The method steps 901-904 to be performed in the client device 120a, 120b, 120c, 120d may be implemented through the one or more processors 1020 in the client device 120a, 120b, 120c, 120d together with computer program product for performing the functions of the method steps 901 -904.

30

Thus, a non-transitory computer program comprising program code for performing the method 900 according to any of steps 901 -904, for sequentially cancelling interference and decode received signals of the access network device 1 10 in the wireless communication system 100, when the computer program is loaded into the processor 1020 of the client 35 device 120a, 120b, 120c, 120d.

The non-transitory computer program product mentioned above may be provided for instance in the form of a non-transitory data carrier carrying computer program code for performing at least some of the steps 901-904 according to some embodiments when being loaded into the processor 1020. The data carrier may be, e.g., a hard disk, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non- transitory manner. The non-transitory computer program product may furthermore be provided as computer program code on a server and downloaded to the client device 120a, 120b, 120c, 120d, e.g., over an Internet or an intranet connection. The terminology used in the description of the embodiments as illustrated in the accompanying drawings is not intended to be limiting of the described methods 700, 900; access network device 1 10, client device 120a, 120b, 120c, 120d and/ or computer program. Various changes, substitutions and/ or alterations may be made, without departing from the solution embodiments as defined by the appended claims.

As used herein, the term "and/ or" comprises any and all combinations of one or more of the associated listed items. The term "or" as used herein, is to be interpreted as a mathematical OR, i.e., as an inclusive disjunction; not as a mathematical exclusive OR (XOR), unless expressly stated otherwise. In addition, the singular forms "a", "an" and "the" are to be int- erpreted as "at least one", thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" and/ or "comprising", specifies the presence of stated features, actions, integers, steps, operations, elements, and/ or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, ele- ments, components, and/ or groups thereof. A single unit such as e.g. a processor may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/ distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms such as via Internet or other wired or wireless communication system.