WO2019048027A1

WO2019048027A1 - Network node, a first client device, a second client device and methods thereof

Info

Publication number: WO2019048027A1
Application number: PCT/EP2017/072255
Authority: WO
Inventors: Alberto Giuseppe PEROTTI
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2017-09-05
Filing date: 2017-09-05
Publication date: 2019-03-14
Anticipated expiration: 2020-03-05

Abstract

The invention relates to a network node (100) for a wireless communication system (500) being configured to obtain a first message (M1) addressed for a first client device (300a) and a second message (M2) addressed for a second client device (300b). The network node (100) further splits the second message (M2) into a first sub-message (SM1) and a second sub-message (SM2), wherein the first sub-message (SM1) is addressed for the second client device (300b) via the first client device (300a). Furthermore, the network node (100) generates a first communication signal (CS1) comprising the first message (M1) and the first sub-message (SM1) and a second communication signal (CS2) comprising the second sub-message (SM2). The network node (100) further combines the first communication signal (CS1) and second communication signal (CS2) into a superposed communication signal (SCS) and transmits the superposed communication signal (SCS) concurrently to the first client device (300a) and the second client device (300b). Furthermore, the invention also relates to a first client device (300a) and a second client device (300b) corresponding methods, and a computer program.

Description

NETWORK NODE, A FIRST CLIENT DEVICE, A SECOND CLIENT DEVICE AND METHODS THEREOF

Technical Field

The invention relates to a network node, a first client device, and a second client device. Furthermore, the invention also relates to corresponding methods and a computer program.

Background

In wireless communication systems, a single transmit-receive point (TRP) sends several coded and modulated data streams, each consisting of a sequence of coded messages, to multiple user equipments (UEs) over a shared physical channel. The physical channel consists of a set of distinct time-frequency-space resource elements (REs). When a TRP simultaneously serves multiple UEs, the set of REs is typically divided into time-frequency blocks, so-called resource blocks (RBs), and the TRP transmits a signal for only one UE in each RB. According to this approach, signals intended for different UEs are orthogonally multiplexed on different RBs. Thus, inter-UE interference is avoided. The resulting multiple access (MA) schemes are called orthogonal MA (OMA) schemes. OMA schemes are widely adopted in current wireless communication standards, as they relieve the UE receiver of the burden of removing inter-UE interference. However, it is known that by using non-orthogonal MA (NOMA) schemes increased data rates, compared to OMA, can be achieved for all multiplexed UEs.

One type of NOMA scheme recently adopted in the LTE-Advanced Pro standard Rel. 14 is the multiuser superposed transmission (MUST) scheme, which enables concurrent transmission to two co-scheduled UEs in the same REs. The basic principle of MUST schemes is superposition coding (SC). In SC, messages intended for at least two UEs are encoded, modulated, then superposed and concurrently transmitted on the same REs. In single-antenna systems, SC transmission on the additive white gaussian noise (AWGN) broadcast channel does not provide data rate gains compared to OMA schemes when the expected received signal-to-noise ratios (SNRs) of the UEs are equal. Therefore, UEs with different expected received SNRs are paired when using SC. A near UE, which has a higher channel gain, is thus co-scheduled with a far UE, which has a lower channel gain. A message for the near UE and a message for the far UE are independently encoded and modulated to obtain a signal for the near UE and a signal for the far UE. These signals are then scaled and superposed into a signal x. The signal x is mapped to REs and then transmitted.

SC potentially provides data rate gains for both UEs over orthogonal transmission provided that suitable receiver techniques are adopted. A simple receiver algorithm used to achieve increased data rates is successive interference cancellation (SIC). When SIC is used the receiver of the near UE demodulates and decodes the far UE signal treating its own signal as noise. The near UE then cancels the interfering far UE signal from the received signal such that the resulting signal-to-interference plus noise ratio (SINR) after cancellation is increased. The higher SINR allows transmission to the near UE at higher data rates.

Summary

An objective of implementation forms of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous implementation forms of the present invention can be found in the dependent claims. According to a first aspect of the invention, the above mentioned and other objectives are achieved with a network node for a wireless communication system, the network node being configured to

obtain a first message addressed for a first client device;

obtain a second message addressed for a second client device;

split the second message into a first sub-message and a second sub-message, wherein the first sub-message is addressed for the second client device via the first client device; generate a first communication signal comprising the first message and the first sub- message;

generate a second communication signal comprising the second sub-message;

combine the first communication signal and second communication signal into a superposed communication signal;

transmit the superposed communication signal concurrently to the first client device and the second client device. A superposed communication signal in this disclosure may be understood to be a communication signal comprising multiple component signals that are combined and concurrently transmitted on the same time-frequency resources.

A network node according to the first aspect provides a number of advantages over conventional solutions. An advantage of the network node is an increased flexibility in the transmission of messages to client devices, allowing the throughput to be increased. In an implementation form of a network node according to the first aspect, the network node is further configured to

split the second message into the first sub-message and the second sub-message based on

a first channel quality measure associated with a first radio channel from the network node to the first client device; and

a second channel quality measure associated with a second radio channel from the network node to the second client device. An advantage with this implementation form is that the size of the first sub-message and the second sub-message is adapted to the quality of each radio channel, thereby allowing better exploitation of the available channel capacities.

In an implementation form of a network node according to the first aspect, the network node is further configured to

split the second message into the first sub-message and the second sub-message further based on

a third channel quality measure associated with a third radio channel from the first client device to the second client device.

An advantage with this implementation form is that the size of the first sub-message and the second sub-message is further adapted to the quality of the radio channels, as also the quality of the third radio channel from the first client device to the second client device is considered. As a result, even better exploitation of the available channel capacities is achieved.

concatenate the first message and the first sub-message to obtain a joint concatenated message;

encode and modulate the joint concatenated message so as to obtain the first communication signal.

An advantage with this implementation form is that, as concatenation is performed before encoding, the channel encoder operates on a longer block. Thereby, better error correction is provided. In an implementation form of a network node according to the first aspect, the network node is further configured to

encode and modulate the first message to obtain a modulated first message;

encode and modulate the first sub-message to obtain a modulated first sub-message; concatenate the modulated first message and the modulated first sub-message so as to obtain the first communication signal.

An advantage with this implementation form is that, as concatenation is performed after encoding and modulation, the transmitter has more flexibility in the choice of code rates and modulations for each message/sub-message.

encode and modulate the second sub-message so as to obtain the second communication signal.

An advantage with this implementation form is that, by having the second sub-message encoded and modulated independently of the other messages/sub-messages, a better adaptation of the second communication signal to the quality of the second radio channel from the network node to the second client device is possible.

generate a first control signal comprising a first control information associated with the transmission of the superposed communication signal to the first client device;

generate a second control signal comprising a second control information associated with the transmission of the superposed communication signal to the second client device; transmit the first control signal to the first client device and the second control signal to the second client device previous to the transmission of the superposed communication signal.

An advantage with this implementation form is that the network node can inform the client devices that there is a scheduled transmission directed to them. Moreover, the network node can inform the client devices about the parameters used for the encoding and modulation of the superposed communication signal, thereby facilitating detection, demodulation and decoding operations by the receivers of the client devices. In an implementation form of a network node according to the first aspect, the first control information indicates at least one of: downlink scheduling information for the first client device, a presence of the first sub-message in the first communication signal, a size of the first sub- message in the first communication signal, and a power ratio for the first communication signal in the superposed communication signal.

An advantage with this implementation form is that the network node can provide the receiver of the first client device with necessary control information in order to allow easier detection, demodulation and decoding of the received signal.

In an implementation form of a network node according to the first aspect, the second control information indicates at least one of: downlink scheduling information for the second client device, a presence of the first sub-message in the first communication signal, and a size of the first sub-message in the first communication signal.

An advantage with this implementation form is that the network node can provide the receiver of the second client device with necessary control information in order to allow easier detection, demodulation and decoding of the received signal. In an implementation form of a network node according to the first aspect, the network node is further configured to

generate a third control signal comprising a third control information associated with a transmission of the first sub-message to the second client device;

generate a fourth control signal comprising a fourth control information associated with a reception of the first sub-message from the first client device;

transmit the third control signal to the first client device;

transmit the fourth control signal to the second client device.

An advantage with this implementation form is that the network node can provide the receiver of the second client device with necessary control information related to the transmission of the first sub-message to the second client device. Thereby, enabling the second client device to receive the part of its message, i.e. the first sub-message, that was previously delivered to the first client device. According to a second aspect of the invention, the above mentioned and other objectives are achieved with a first client device for a wireless communication system, the first client device being configured to receive a first superposed communication signal from a network node, the first superposed communication signal comprising a first communication signal and a second communication signal, wherein the first communication signal comprises a first message and a first sub-message and the second communication signal comprises a second sub-message, wherein the first sub-message is addressed for the second client device via the first client device;

interference cancel the second communication signal in the first superposed communication signal;

derive the first sub-message from the interference cancelled first superposed communication signal;

generate a third communication signal comprising the first sub-message;

transmit the third communication signal to the second client device.

A first client device according to the second aspect provides a number of advantages over conventional solutions. An advantage of the first client device is that the first client device is able to obtain its own message and, at the same time, to relay part of a message addressed for a second client device, thereby making the second client device able to exploit the channel quality of the first radio link between the network node and the first client device. In an implementation form of a first client device according to the second aspect, the first client device is further configured to

receive a first control signal previous to the reception of the first superposed communication signal, wherein the first control signal comprises a first control information associated with the transmission of the first superposed communication signal from the network node;

derive the first sub-message from the interference cancelled first superposed communication signal based on the first control information.

An advantage with this implementation form is that the first client device is made aware that there is a scheduled transmission intended for itself. Moreover, the first client device can be informed about the parameters used for the encoding and modulation of the superposed communication signal, thereby facilitating detection, demodulation and decoding operations by the receiver of the first client device. In an implementation form of a first client device according to the second aspect, the first control information indicates at least one of: downlink scheduling information for the first client device, a presence of the first sub-message in the first communication signal, a size of the first sub-message in the first communication signal, and a power ratio for the first communication signal in the first superposed communication signal.

An advantage with this implementation form is that the control information provided by the network node to the first client device allows easier detection, demodulation and decoding by the receiver of the first client device.

In an implementation form of a first client device according to the second aspect, the first client device is further configured to

receive a third control signal from the network node, the third control signal comprising a third control information associated with the transmission of the first sub-message to the second client device;

transmit the third communication signal to the second client device based on the third control information.

An advantage with this implementation form is that the first client device is informed about when and how to transmit the first sub-message to the second client device.

receive a second superposed communication signal from the network node, the second superposed communication signal comprising a first communication signal and a second communication signal, wherein the first communication signal comprises a first message and a first sub-message and the second communication signal comprises a second sub-message, wherein the first sub-message is addressed for the first client device via the second client device;

derive the second sub-message from the second superposed communication signal; receive a third communication signal from the second client device, wherein the third communication signal comprises the first sub-message;

derive the first sub-message from the third communication signal;

concatenate the first sub-message and the second sub-message so as to obtain a second message.

An advantage with this implementation form is that the first client device may receive the first sub-message via the second client device, thereby allowing the first client device to exploit the channel quality of the second radio link between the network node and the second client device. According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a network node, the method comprises

obtaining a first message addressed for a first client device;

obtaining a second message addressed for a second client device;

splitting the second message into a first sub-message and a second sub-message, wherein the first sub-message is addressed for the second client device via the first client device;

generating a first communication signal comprising the first message and the first sub- message;

generating a second communication signal comprising the second sub-message;

combining the first communication signal and second communication signal into a superposed communication signal;

transmitting the superposed communication signal concurrently to the first client device and the second client device.

The method according to the third aspect can be extended into implementation forms corresponding to the implementation forms of the network node according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network node.

The advantages of the methods according to the third aspect are the same as those for the corresponding implementation forms of the network node according to the first aspect.

According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a first client device, the method comprises

receiving a first superposed communication signal from a network node, the first superposed communication signal comprising a first communication signal and a second communication signal, wherein the first communication signal comprises a first message and a first sub-message and the second communication signal comprises a second sub-message, wherein the first sub-message is addressed for the second client device via the first client device;

interference cancelling the second communication signal in the first superposed communication signal;

deriving the first sub-message from the interference cancelled first superposed communication signal;

generating a third communication signal comprising the first sub-message;

transmitting the third communication signal to the second client device. The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the first client device according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the first client device.

The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the first client device according to the second aspect. The invention also relates to a computer program, characterized in code means, which when run by processing means causes said processing means to execute any method according to the present invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

Further applications and advantages of the present invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different implementation forms of the present invention, in which:

- Fig. 1 shows a network node according to an implementation form of the invention; - Fig. 2 shows a method according to an implementation form of the invention;

- Fig. 3 shows a client device according to an implementation form of the invention;

- Fig. 4 shows a method according to an implementation form of the invention;

- Fig. 5 shows a wireless communication system according to an implementation form of the invention;

- Fig. 6 shows a transmitter block scheme for a network node according to an implementation form of the invention;

- Fig. 7 shows a receiver block scheme for a first client device according to an implementation form of the invention;

- Fig. 8 shows a receiver block scheme for a second client device according to an implementation form of the invention;

- Fig. 9 shows a transmitter block scheme for a network node according to an implementation form of the invention - Fig. 10 shows a receiver block scheme for a first client device according to an implementation form of the invention;

- Fig. 1 1 shows a signalling diagram according to an implementation form of the invention;

- Fig. 12 shows data rate regions for different transmission schemes.

Detailed Description

Fig. 1 shows a network node 100 according to an implementation form of the invention. In the implementation shown in Fig. 1 , the network node 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The network node 100 may be configured for both wireless and wired communications in wireless and wired communication systems, respectively. The wireless communication capability is provided with an antenna 1 10 coupled to the transceiver 104, while the wired communication capability is provided with a wired communication interface 1 12 coupled to the transceiver 104.

That the network node 100 is configured to perform certain actions should in this disclosure be understood to mean that the network node 100 comprises suitable means, such as e.g. the processor 102 and the transceiver 104, configured to perform said actions.

The network node 100 is configured to obtain a first message M1 addressed for a first client device 300a and obtain a second message M2 addressed for a second client device 300b. The network node 100 is further configured to split the second message M2 into a first sub- message SM1 and a second sub-message SM2. The first sub-message SM1 is addressed for the second client device 300b via the first client device 300a. Furthermore, the network node 100 is configured to generate a first communication signal CS1 comprising the first message M1 and the first sub-message SM1 and generate a second communication signal CS2 comprising the second sub-message SM2. The network node 100 is further configured to combine the first communication signal CS1 and second communication signal CS2 into a superposed communication signal SCS and transmit the superposed communication signal SCS concurrently to the first client device 300a and the second client device 300b.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a network node 100, such as the one shown in Fig. 1 . The method 200 comprises obtaining 202 a first message M1 addressed for a first client device 300a and obtaining 204 a second message M2 addressed for a second client device 300b. The method 200 further comprises splitting 206 the second message M2 into a first sub-message SM1 and a second sub-message SM2. The first sub-message SM1 is addressed for the second client device 300b via the first client device 300a. Furthermore, the method 200 comprises generating 208 a first communication signal CS1 comprising the first message M1 and the first sub-message SM1 and generating 210 a second communication signal CS2 comprising the second sub-message SM2. The method 200 further comprises combining 212 the first communication signal CS1 and second communication signal CS2 into a superposed communication signal SCS and transmitting 214 the superposed communication signal SCS concurrently to the first client device 300a and the second client device 300b. Fig. 3 shows a client device 300a; 300b according to an implementation form of the invention. In the implementation shown in Fig. 3, the client device 300a; 300b comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The client device 300a; 300b further comprises an antenna 310 coupled to the transceiver 304, which means that the client device 300a; 300b is configured for wireless communications in a wireless communication system.

That the client device 300a; 300b is configured to perform certain actions should in this disclosure be understood to mean that the client device 300a; 300b comprises suitable means, such as e.g. the processor 302 and the transceiver 304, configured to perform said actions.

A first client device 300a is configured to receive a first superposed communication signal SCSI from a network node 100, the first superposed communication signal SCSI comprising a first communication signal CS1 and a second communication signal CS2. The first communication signal CS1 comprises a first message M1 and a first sub-message SM1 and the second communication signal CS2 comprises a second sub-message SM2. The first sub- message SM1 is addressed for the second client device 300b via the first client device 300a. The first client device 300a is further configured to interference cancel the second communication signal CS2 in the first superposed communication signal SCSI and derive the first sub-message SM1 from the interference cancelled first superposed communication signal SCSI . Furthermore, the first client device 300a is configured to generate a third communication signal CS3 comprising the first sub-message SM1 and transmit the third communication signal CS3 to the second client device 300b. Fig. 4 shows a flow chart of a corresponding method 400 which may be executed in a first client device 300a, such as the one shown in Fig. 3. The method 400 comprises receiving 402 a first superposed communication signal SCSI from a network node 100, the first superposed communication signal SCSI comprising a first communication signal CS1 and a second communication signal CS2. The first communication signal CS1 comprises a first message M1 and a first sub-message SM1 and the second communication signal CS2 comprises a second sub-message SM2. The first sub-message SM1 is addressed for the second client device 300b via the first client device 300a. The method 400 further comprises interference cancelling 404 the second communication signal CS2 in the first superposed communication signal SCSI and deriving 406 the first sub-message SM1 from the interference cancelled first superposed communication signal SCSI . Furthermore, method 400 comprises generating 408 a third communication signal CS3 comprising the first sub-message SM1 and transmitting 410 the third communication signal CS3 to the second client device 300b.

Fig. 5 shows a wireless communication system 500 according to an implementation. The wireless communication system 500 comprises a network node 100, a first client device 300a, and a second client device 300b, all configured to operate in the wireless communication system 500. In the wireless communication system 500, communication signals, such as e.g. superposed communication signals SCSs, are transmitted by the network node 100 and received by the first client device 300a and the second client device 300b. The communication signals are transmitted from the network node 100 to the first client device 300a over a first radio channel 502, and from the network node 100 to the second client device 300b over a second radio channel 504. In addition, communication signals, such as e.g. third communication signals CS3s, are transmitted from the first client device 300a to the second client device 300b over a third radio channel 506.

For simplicity, the wireless communication system 500 shown in Fig. 5 only comprises one network node 100, one first client device 300a, and one second client device 300b. However, the wireless communication system 500 may comprise any number of network nodes 100, first client devices 300a and second client devices 300b without deviating from the scope of the invention. As previously described, the network node 100 splits the obtained second message M2 into a first sub-message SM1 and a second sub-message SM2. The network node 100 may determine how to split the second message M2, i.e. the size of the first sub-message SM1 and the size of the second sub-message SM2, based on its knowledge of the channel quality of the first radio channel 502 and the second radio channel 504. Channel qualities are usually estimated/computed by each client device 300a, 300b based on the reception of reference signals from the network node 100. The estimated channel quality is then reported to the network node 100 by the client device 300a; 300b through a feedback control channel. The network node 100 may determine the data message sizes for the client device 300a; 300b based on the reported channel qualities and on pre-determined message sizes contained in look-up tables. The values contained in those look-up tables may be generated by simulation according to the general principle that a set of time-frequency resources of a given size having a high channel quality can accommodate transmission of a larger data message than another set of time-frequency resources of the same size having lower channel quality.

Therefore, in an implementation, the network node 100 may be configured to split the second message M2 into the first sub-message SM1 and the second sub-message SM2 based on a first channel quality measure CQM1 associated with the first radio channel 502 from the network node 100 to the first client device 300a; and a second channel quality measure CQM2 associated with the second radio channel 504 from the network node 100 to the second client device 300b. For example, when the quality indicated by the second channel quality measure CQM2 is low and the quality indicated by the first channel quality measure CQM1 is high, the size of the first sub-message SM1 should be large. In this way, the high channel quality associated with the first radio channel 502 may be used to improve the data rate towards the second client device 300b. When the second channel quality measure CQM2 is very low, e.g. below a threshold level, the second message M2 may not be split at all. In such a scenario, conventional relaying may instead be performed such that the whole second message M2 is sent to the first client device 300a and then relayed by the first client device 300a to the second client device 300b over the third radio channel 506.

In addition, the channel quality of the third radio channel 506 may be considered by the network node 100 when splitting the second message M2. The network node 100 may obtain knowledge about the channel quality of the third radio channel 506 e.g. from reports from the first client device 300a and/or the second client device 300b. Hence, the network node 100 may be configured to split the second message M2 into the first sub-message SM1 and the second sub-message SM2 further based on a third channel quality measure CQM3 associated with a third radio channel 506 from the first client device 300a to the second client device 300b. For example, when the third channel quality measure CQM3 associated with the third radio channel 506 is very low, e.g. below a threshold level, the second message M2 may not be split at all. In such a scenario, no relaying is performed, instead the whole second message M2 is sent directly from the network node 100 to the second client device 300b. It is to be noted that further parameters than the above mentioned may be considered by the network node 100 when splitting the second message M2. For example, the network node 100 may consider whether the first client device 300a and the second client device 300b has enough available time-frequency resources and/or enough transmission power to be allocated for transmission between each other. In addition, the network node 100 may consider whether transmissions between other client devices are ongoing in the same time-frequency resources and in the same network area and refrain from scheduling a transmission from the first client device 300a to the second client device 300b in order to minimize interference to those other client devices.

Fig. 6 shows a transmitter block scheme 600 for a network node 100 according to an implementation of the invention. The transmitter block scheme 600 may e.g. be implemented in a downlink transmitter function (short for functional block) of the transceiver 104 in the network node 100. According to the transmitter block scheme 600 shown in Fig. 6 a splitting function 602 splits the second message M2 into a first sub-message SM1 and a second sub- message SM2. A concatenation function 604 concatenates the first message M1 and the first sub-message SM1 to obtain a joint concatenated message. The joint concatenated message is encoded and modulated so as to obtain a first communication signal CS1. The encoding and modulation is performed by an encoder 606 and a modulator 608, respectively. Furthermore, the second sub-message SM2 is passed through an encoder 610 and a modulator 612 which encodes and modulates the second sub-message SM2 to obtain a second communication signal CS2. Finally, the first communication signal CS1 and second communication signal CS2 are scaled and superposed according to the transmitter scheme 600. A power ratio 1 - a of the total transmission power P is assigned to the first communication signal CS1 at a first multiplier 616, while a ratio a of the total transmission power P is assigned to the second communication signal CS2 at a second multiplier 618. The scaled first communication signal CS1 and the scaled second communication signal CS2 are thereafter combined by a combining function 620 into a superposed communication signal SCS. The superposed communication signal SCS is mapped to REs by a downlink RE mapper (not shown in Fig. 6) and concurrently transmitted to the first client device 300a and the second client device 300b.

Fig. 7 shows a receiver block scheme 700 for a first client device 300a corresponding to the transmitter block scheme 600 shown in Fig. 6, i.e. the receiver block scheme 700 is configured to enable reception, decoding, and demodulation of the superposed communication signal SCS generated by the transmitter block scheme 600. The first client device 300a receives the superposed communication signal SCS and demodulates and decodes the superposed communication signal SCS in a demodulator and decoder 702 to obtain the second sub- message SM2, while treating the first communication signal CS1 as noise. A interference cancelling function 704 cancels the interfering second sub-message SM2 from the superposed communication signal SCS. The interference cancelled superposed communication signal SCS is demodulated and decoded by a demodulator and decoder 706. A de-interleaver and splitting function 708 derives the first sub-message SM1 and the first message M1 from the interference cancelled superposed communication signal SCS. Hence, the receiver block scheme 700 derives the first message M1 addressed for the first client device 300a, as well as the first sub-message SM1 addressed for the second client device 300b. The first sub- message SM1 is prepared to be forwarded to the second client device 300b. Thus, the first sub-message SM1 is encoded and modulated by an encoder and modulator 710 to generate a third communication signal CS3 comprising the first sub-message SM1. The third communication signal CS3 is mapped to REs by a SL RE mapper (not shown in Fig. 7) and transmitted to the second client device 300b.

Fig. 8 shows a receiver block scheme 800 for a second client device 300b corresponding to the transmitter block scheme 600 shown in Fig. 6, i.e. the receiver block scheme 800 is configured to enable reception, decoding, and demodulation of the superposed communication signal SCS generated by the transmitter block scheme 600. The receiver of the second client device 300b receives the superposed communication signal SCS from the network node 100 and the third communication signal CS3 from the first client device 300a. The superposed communication signal SCS is demodulated and decoded by a demodulator and decoder 802 to obtain the second sub-message SM2. In a similar way, the third communication signal CS3 is demodulated and decoded by a demodulator and decoder 804 to obtain the first sub- message SM1 . A concatenation function 806 concatenates the first sub-message SM1 and the second sub-message SM2 to obtain the second message M2.

In the transmitter block scheme 600 shown in Fig. 6 the first sub-message SM1 is concatenated with the first message M1 before it is encoded and modulated. This approach maximises the coding gain, as the codeword length is longer. However, in other implementations the first sub-message SM1 and the first message M1 may first be independently encoded and modulated and then concatenated. One advantage with such an approach is that it is possible to perform parallel demodulation/decoding of the two message parts at the receiver, thereby reducing the decoding delay. Fig. 9 shows a transmitter block scheme 900 according to an implementation based on independent encoding and modulation before concatenation. In the transmitter block scheme 900 shown in Fig. 9 a splitting function 902 splits the second message M2 into a first sub-message SM1 and a second sub-message SM2. An encoder and modulator 904 encodes and modulates the first message M1 to obtain a modulated first message M1 , while an encoder and modulator 906 encodes and modulates the first sub-message SM1 to obtain a modulated first sub-message SM1 . The modulated first message M1 and the modulated first sub-message SM1 are input into a concatenation function 908. The concatenation function 908 concatenates the modulated first message M1 and the modulated first sub-message SM1 to obtain a first communication signal CS1. Furthermore, the second sub-message SM2 is passed through an encoder 910 and a modulator 912 which encodes and modulates, respectively, the second sub-message SM2 to obtain a second communication signal CS2.

In the same way as for the transmitter block scheme 600 shown in Fig. 6, the transmitter block scheme 900 shown in Fig. 9 scales the first communication signal CS1 and second communication signal CS2 using a power ratio 1 - a of the total transmission power P for the first communication signal CS1 at a first multiplier 916 and a power ratio a of the total transmission power P for the second communication signal CS2 at a second multiplier 918. The scaled first communication signal CS1 and the scaled second communication signal CS2 are then combined by a combining function 920 into a superposed communication signal SCS. The superposed communication signal SCS is mapped to REs by a downlink RE mapper (not shown in Fig. 9) and concurrently transmitted to the first client device 300a and the second client device 300b.

The transmitter block scheme 600 shown in Fig. 6, as well as the transmitter block scheme 900 shown in Fig. 9, uses linear superposition of modulated signals with symbol conversion in a symbol conversion function 614; 914. However, other types of superposition techniques, such as plain linear superposition (without symbol conversion), e.g. NOMA (a.k.a. power- domain superposition), or joint mapping of codeword bits to constellation symbols (a.k.a. Rate- adaptive constellation Expansion Multiple Access (REMA)) may also be used.

Fig. 10 shows a receiver block scheme 1000 for a first client device 300a corresponding to the transmitter block scheme 900 shown in Fig. 9, i.e. the receiver block scheme 1000 is configured to enable reception, encoding, and demodulation of the superposed communication signal SCS generated by the transmitter block scheme 900. When the first client device 300a receives a superposed communication signal SCS generated by the transmitter block scheme 900 shown in Fig. 9 the receiver of the first client device 300a process according to the block scheme shown in Fig. 10. The second communication signal CS2 is demodulated and decoded by a demodulator and decoder 1002 to obtain the second sub-message SM2, while treating the first communication signal CS1 as noise. A interference cancelling function 1004 cancels the interfering second sub-message SM2 from the superposed communication signal SCS. A de-interleave and split function 1006 derives the first sub-message SM1 and the first message M1 from the interference cancelled superposed communication signal SCS. Parallel demodulation and decoding of the first sub-message SM1 and the first message M1 is performed, by a demodulator and decoder 1008 and a demodulator and decoder 1010, respectively. Furthermore, the first sub-message SM1 is encoded and modulated by an encoder and modulator 1012 to generate a third communication signal CS3 comprising the first sub-message SM1. The third communication signal CS3 is mapped to REs by a SL RE mapper (not shown in Fig. 10) and transmitted to the second client device 300b.

In the second client device 300b the same receiver block scheme may be used, independent on whether the superposed communication signal SCS was generated by the transmitter scheme 600 shown in Fig. 6 or by the transmitter block scheme 900 shown in Fig. 9. Hence, the receiver block scheme 800 shown in Fig. 8 may be used for the second client device 300b also when the superposed communication signal SCS was generated by the transmitter block scheme 900.

The superposed communication signal SCS, resulting from either the transmitter block scheme 600 shown in Fig. 6 or the transmitter block scheme 900 shown in Fig. 9, is mapped to REs and scheduled to be transmitted to the first client device 300a and the second client device 300b. In addition to the scheduling of the superposed communication signal SCS, the network node 100 also schedules the transmission of a third communication signal CS3 comprising the first sub-message SM1 from the first client device 300a to the second client device 300b. The network node 100 may schedule the transmissions of the superposed communication signal SCS and the third communication signal CS3 using control information signalling. Fig. 1 1 shows a signalling diagram comprising such control information signalling, as well as data transmissions, from the network node 100 to the first client device 300a and the second client device 300b. In step I in Fig. 1 1 , the network node 100 generates a first control signal C1 and a second control signal C2. The first control signal C1 comprises a first control information associated with the transmission of the superposed communication signal SCS to the first client device 300a. The second control signal C2 comprises a second control information associated with the transmission of the superposed communication signal SCS to the second client device 300b.

The first control information may indicate at least one of: downlink scheduling information for the first client device 300a, a presence of the first sub-message SM1 in the first communication signal CS1 , a size of the first sub-message SM1 in the first communication signal CS1 , and a power ratio for the first communication signal CS1 in the superposed communication signal SCS. Downlink scheduling information indicates the presence of a message for the first client device 300a which the control information is addressed to, including the time-frequency resources used for transmission. Presence of the first sub-message SM1 makes the receiver of the first client device 300a aware that the received signal contains a first sub-message which is not intended for the first client device 300a, therefore the receiver has to be prepared to demodulate, decode and split the first sub-message from its own message, then encode it and relay it to another client device. The size of the first sub-message SM1 allows demodulation and decoding of the first sub-message SM1. The power ratio simplifies interference cancellation and detection/demodulation of the first message M1 and first sub-message SM1 in the superposed communication signal SCS.

The second control information may indicate at least one of: downlink scheduling information for the second client device 300b, a presence of the first sub-message SM1 in the first communication signal CS1 , and a size of the first sub-message SM1 in the first communication signal CS1. Downlink scheduling information indicates the presence of a message for the second client device 300b which the control information is addressed to, including the time- frequency resources used for transmission. Presence of the first sub-message SM1 in the first communication signal makes the receiver of the second client device 300b aware that the second sub-message SM2 does not contain the whole second message M2 for the second client device 300b. Therefore, in order to complete the reception of message M2, the receiver of the second client device 300b has to merge the second sub-message SM2 with a first sub- message SM1 that will be received in a future time interval. The size of the first sub-message SM1 allows demodulation and decoding of the first sub-message SM1 that will be received in a future time interval.

In step II, the network node 100 transmits the first control signal C1 to the first client device 300a and the second control signal C2 to the second client device 300b. The first control signal C1 and the second control signal C2 are transmitted previous to the transmission of the superposed communication signal SCS, which is performed in step III in Fig. 1 1 .

Hence, the first client device 300a receives the first control signal C1 previous to the reception of the superposed communication signal SCS. As previously described the first control signal C1 comprises a first control information associated with the transmission of the superposed communication signal SCS from the network node 100, where the first control information indicates at least one of: downlink scheduling information for the first client device 300a, a presence of the first sub-message SM1 in the first communication signal CS1 , a size of the first sub-message SM1 in the first communication signal CS1 , and a power ratio for the first communication signal CS1 in the superposed communication signal SCS. Based on the first control information the first client device 300a derives the first sub-message SM1 from the interference cancelled superposed communication signal SCS received in step III. The network node 100 further generates a third control signal C3 and a fourth control signal C4, as shown in step IV. The third control signal C3 comprises a third control information associated with a transmission of the first sub-message SM1 to the second client device 300b. The third control signal C3 is intended to provide the first client device 300a with necessary information, e.g. time-frequency resources, modulation and coding formats, needed to transmit the first sub-message SM1 to the second client device 300b. The fourth control signal C4 comprises a fourth control information associated with a reception of the first sub-message SM1 from the first client device 300a. The fourth control signal C4 is intended to provide the second client device 300b with necessary information, e.g. time-frequency resources, modulation and coding formats, needed to receive the first sub-message SM1 from the first client device 300a.

In step V, the network node 100 transmits the third control signal C3 to the first client device 300a and transmits the fourth control signal C4 to the second client device 300b. Hence, the first client device 300a receive the third control signal C3 from the network node 100, and may from the third control signal C3 derive/extract the third control information associated with the transmission of the first sub-message SM1 to the second client device 300b. Based on the derived third control information the first client device 300a transmits the third communication signal CS3 to the second client device 300b, as shown in step VI.

Fig. 1 1 shows one possible sequence of signalling between the network node 100, the first client device 300a and the second client device 300b. However, the signalling between the network node 100, the first client device 300a and the second client device 300b, i.e. step II, III, V and VI in Fig. 1 1 , may be performed in different sequences without deviating from the scope of the invention. The only requirements are that a data transmission phase starts after its corresponding scheduling phase ends, i.e. step III is performed after step II and step VI is performed after step V; and that the transmission of the third communication signal CS3 starts after the transmission of the superposed communication signal SCS ends, i.e. step VI is performed after step III.

In the above described examples, the first client device 300a is acting as a relay for the second client device 300b. However, in other examples the second client device 300b may instead be acting as a relay for the first client device 300a. In such an example, the first client device 300a may receive a second superposed communication signal SCS2 from the network node 100. The second superposed communication signal SCS2 comprising a first communication signal CS1 ^' and a second communication signal CS2^', where the first communication signal CS1 ^' comprises a first message M1 ^' and a first sub-message SM1 ^' and the second communication signal CS2^' comprises a second sub-message SM2^'. The first sub-message SM1 ^' is addressed for the first client device 300a via the second client device 300b. The first client device 300a derives the second sub-message SM2^' from the second superposed communication signal SCS2. Furthermore, the first client device 300a receives a third communication signal CS3^' from the second client device 300b, where the third communication signal CS3^' comprises the first sub-message SM1 ^'. From the third communication signal CS3^' the first client device 300a derives the first sub-message SM1 ^'. The first client device 300a concatenates the first sub-message SM1 ^' and the second sub- message SM2^' so as to obtain a second message M2^'.

The performance of implementation forms of the invention in terms of achievable data rates for two client devices in a wireless communication system is shown in Fig. 12, where the two client devices are denoted UEi and UE2, respectively. Fig. 12 shows the data rate pairs that the network is able to deliver simultaneously to UEi and UE2 using the disclosed invention compared with the data rate pairs for UEi and UE2 using conventional solutions. In Fig. 12, the region comprised between the x-axis, y-axis and the solid curve shows the achievable data rate pairs for UEi and UE2 when the transmission scheme of the disclosed invention is used. The region comprised between the x-axis, y-axis and the dashed curve shows the achievable data rate pairs for UEi and UE2 when plain power-domain superposition is employed and the region comprised between the x-axis, y-axis and the dotted line shows the achievable data rate pairs for UEi and UE2 with orthogonal multiplexing. Thus, region II in Fig. 12 indicates the improvement in data rates for UEi and UE2 achievable with the transmission scheme of the disclosed invention compared to the conventional transmission schemes. It is clear from Fig. 12 that the disclosed transmission scheme is able to provide significantly higher data rates than the conventional transmission schemes.

Fig. 12 furthermore shows a region comprised between the x-axis, y-axis and the straight solid line. This region illustrates the data rate pairs that would be achievable if the channel from UEi to UE2 had infinite capacity. Hence, this region is shown as the ultimate performance limit that any real system could try to approach without being able to achieve, as such an ideal channel does not exist. The client device 300a, 300b herein may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 - conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio. The network node 100 herein may also be denoted as a radio network node, an access network node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The radio network node may also be a base station corresponding to the fifth generation (5G) wireless systems. Furthermore, any method according to implementation forms of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read- Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that implementation forms of the network node 100 and the client device 300a, 300b comprise the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the present solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the present solution.

Especially, the processor(s) of the network node 100 and the client device 300a, 300b may comprise, e.g., one or more instances of 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 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 mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

Finally, it should be understood that the invention is not limited to the implementation forms described above, but also relates to and incorporates all implementations within the scope of the appended independent claims.

Claims

1. A network node (100) for a wireless communication system (500), the network node (100) being configured to

obtain a first message (M1 ) addressed for a first client device (300a);

obtain a second message (M2) addressed for a second client device (300b);

split the second message (M2) into a first sub-message (SM1 ) and a second sub- message (SM2), wherein the first sub-message (SM1 ) is addressed for the second client device (300b) via the first client device (300a);

generate a first communication signal (CS1 ) comprising the first message (M1 ) and the first sub-message (SM1 );

generate a second communication signal (CS2) comprising the second sub-message (SM2);

combine the first communication signal (CS1 ) and second communication signal (CS2) into a superposed communication signal (SCS);

transmit the superposed communication signal (SCS) concurrently to the first client device (300a) and the second client device (300b).

2. The network node (100) according to claim 1 , configured to split the second message (M2) into the first sub-message (SM1 ) and the second sub-message (SM2) based on

a first channel quality measure (CQM1 ) associated with a first radio channel (502) from the network node (100) to the first client device (300a); and

a second channel quality measure (CQM2) associated with a second radio channel (504) from the network node (100) to the second client device (300b).

3. The network node (100) according to claim 2, configured to split the second message (M2) into the first sub-message (SM1 ) and the second sub-message (SM2) further based on

a third channel quality measure (CQM3) associated with a third radio channel (506) from the first client device (300a) to the second client device (300b).

4. The network node (100) according any of the preceding claims, configured to

concatenate the first message (M1 ) and the first sub-message (SM1 ) to obtain a joint concatenated message;

encode and modulate the joint concatenated message so as to obtain the first communication signal (CS1 ).

5. The network node (100) according to any of the preceding claims, configured to encode and modulate the first message (M1 ) to obtain a modulated first message (M1 ); encode and modulate the first sub-message (SM1 ) to obtain a modulated first sub-message (SM1 );

concatenate the modulated first message (M1 ) and the modulated first sub-message (SM1 ) so as to obtain the first communication signal (CS1 ).

6. The network node (100) according to any of the preceding claims, configured to

generate a first control signal (C1 ) comprising a first control information associated with the transmission of the superposed communication signal (SCS) to the first client device (300a);

generate a second control signal (C2) comprising a second control information associated with the transmission of the superposed communication signal (SCS) to the second client device (300b);

transmit the first control signal (C1 ) to the first client device (300a) and the second control signal (C2) to the second client device (300b) previous to the transmission of the superposed communication signal (SCS).

7. The network node (100) according to claim 6, wherein the first control information indicates at least one of: downlink scheduling information for the first client device (300a), a presence of the first sub-message (SM1 ) in the first communication signal (CS1 ), a size of the first sub- message (SM1 ) in the first communication signal (CS1 ), and a power ratio for the first communication signal (CS1 ) in the superposed communication signal (SCS).

8. The network node (100) according to claim 6 or 7, wherein the second control information indicates at least one of: downlink scheduling information for the second client device (300b), a presence of the first sub-message (SM1 ) in the first communication signal (CS1 ), and a size of the first sub-message (SM1 ) in the first communication signal (CS1 ).

9. The network node (100) according to any of claims 6 to 8, configured to

generate a third control signal (C3) comprising a third control information associated with a transmission of the first sub-message (SM1 ) to the second client device (300b);

generate a fourth control signal (C4) comprising a fourth control information associated with a reception of the first sub-message (SM1 ) from the first client device (300a);

transmit the third control signal (C3) to the first client device (300a);

transmit the fourth control signal (C4) to the second client device (300b).

10. A first client device (300a) for a wireless communication system (500), the first client device (300a) being configured to

receive a first superposed communication signal (SCSI ) from a network node (100), the first superposed communication signal (SCSI ) comprising a first communication signal (CS1 ) and a second communication signal (CS2), wherein the first communication signal (CS1 ) comprises a first message (M1 ) and a first sub-message (SM1 ) and the second communication signal (CS2) comprises a second sub-message (SM2), wherein the first sub-message (SM1 ) is addressed for the second client device (300b) via the first client device (300a);

interference cancel the second communication signal (CS2) in the first superposed communication signal (SCSI );

derive the first sub-message (SM1 ) from the interference cancelled first superposed communication signal (SCSI );

generate a third communication signal (CS3) comprising the first sub-message (SM1 ); transmit the third communication signal (CS3) to the second client device (300b).

1 1. The first client device (300a) according to claim 10, configured to

receive a first control signal (C1 ) previous to the reception of the first superposed communication signal (SCSI ), wherein the first control signal (C1 ) comprises a first control information associated with the transmission of the first superposed communication signal (SCSI ) from the network node (100);

derive the first sub-message (SM1 ) from the interference cancelled first superposed communication signal (SCSI ) based on the first control information.

12 The first client device (300a) according to claim 1 1 , wherein the first control information indicates at least one of: downlink scheduling information for the first client device (300a), a presence of the first sub-message (SM1 ) in the first communication signal (CS1 ), a size of the first sub-message (SM1 ) in the first communication signal (CS1 ), and a power ratio for the first communication signal (CS1 ) in the first superposed communication signal (SCSI ).

13. The first client device (300a) according to claim 1 1 or 12, configured to

receive a third control signal (C3) from the network node (100), the third control signal (C3) comprising a third control information associated with the transmission of the first sub- message (SM1 ) to the second client device (300b);

transmit the third communication signal (CS3) to the second client device (300b) based on the third control information.

14. The first client device (300a) according to any of claims 10 to 13, configured to receive a second superposed communication signal (SCS2) from the network node (100), the second superposed communication signal (SCS2) comprising a first communication signal (CS1 ^') and a second communication signal (CS2^'), wherein the first communication signal (CS1 ^') comprises a first message (M1 ^') and a first sub-message (SM1 ^') and the second communication signal (CS2^') comprises a second sub-message (SM2^'), wherein the first sub- message (SM1 ^') is addressed for the first client device (300a) via the second client device (300b);

derive the second sub-message (SM2^') from the second superposed communication signal (SCS2);

receive a third communication signal (CS3^') from the second client device (300b), wherein the third communication signal (CS3^') comprises the first sub-message (SM1 ^'); derive the first sub-message (SM1 ^') from the third communication signal (CS3^');

concatenate the first sub-message (SM1 ^') and the second sub-message (SM2^') so as to obtain a second message (Μ2^').

15. A method (200) for a network node, the method comprising

obtaining (202) a first message (M1 ) addressed for a first client device (300a);

obtaining (204) a second message (M2) addressed for a second client device (300b); splitting (206) the second message (M2) into a first sub-message (SM1 ) and a second sub-message (SM2), wherein the first sub-message (SM1 ) is addressed for the second client device (300b) via the first client device (300a);

generating (208) a first communication signal (CS1 ) comprising the first message (M1 ) and the first sub-message (SM1 );

generating (210) a second communication signal (CS2) comprising the second sub- message (SM2);

combining (212) the first communication signal (CS1 ) and second communication signal (CS2) into a superposed communication signal (SCS);

transmitting (214) the superposed communication signal (SCS) concurrently to the first client device (300a) and the second client device (300b).

16. A method (400) for a client device, the method comprising

receiving (402) a first superposed communication signal (SCSI ) from a network node (100), the first superposed communication signal (SCSI ) comprising a first communication signal (CS1 ) and a second communication signal (CS2), wherein the first communication signal (CS1 ) comprises a first message (M1 ) and a first sub-message (SM1 ) and the second communication signal (CS2) comprises a second sub-message (SM2), wherein the first sub- message (SM1 ) is addressed for the second client device (300b) via the first client device (300a);

interference cancelling (404) the second communication signal (CS2) in the first superposed communication signal (SCSI );

deriving (406) the first sub-message (SM1 ) from the interference cancelled first superposed communication signal (SCSI );

generating (408) a third communication signal (CS3) comprising the first sub-message (SM1 );

transmitting (410) the third communication signal (CS3) to the second client device (300b).

17. A computer program with a program code for performing a method according to claim 15 or 16 when the computer program runs on a computer.