Network entity and user equipment for a wireless communication network TECHNICAL FIELD

Generally, the present invention relates to the field of wireless communications. More specifically, the present invention relates to a network entity, in particular a base station, and a user equipment for a wireless communication network.

BACKGROUND

Generally, current mobile radio systems, such as the 4G LTE mobile radio system, have been designed to provide high throughput in order to support mobile broadband services (MBB). Since the latency and reliability requirements for broadband services are less stringent than for other mobile services, a general reliability requirement of approximately 90% has been adopted for the 4G system. However, mobile radio systems of the next generation, such as the 5G mobile radio system, are envisaged to accommodate a large variety of new services and use cases, such as enhanced mobile broadband (eMBB), ultra- reliable low latency communication (URLLC), and massive machine type communication

(mMTC), which poses new challenges for next generation mobile radio systems. The URLLC service, for instance, is anticipated to provide data transmissions with very low latency and very high reliability, namely a reliability of 99.999% with a latency of 1 ms. Therefore, the physical layer of next generation mobile radio systems, such as the 5G mobile system, is required to provide a more flexible air interface, which is able to meet diverse requirements of various service types.

Thus, there is a need for an improved network entity and an improved user equipment as well as corresponding methods, which, in particular allow a spectral efficient transmission of data with different requirements concerning reliability and/or latency.

SUMMARY

It is an object of the invention to provide an improved network entity and an improved user equipment as well as corresponding methods, which, in particular allow a spectral efficient transmission of data with different requirements concerning reliability and/or latency. The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. According to a first aspect the invention relates to a network entity configured to

communicate in a downlink direction with a user equipment using a plurality of

communication resources of a wireless or cellular communication network. The network entity comprises a processor configured to generate a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate, and to superpose on the basis of a non-orthogonal multiple access (NOMA) scheme the first code block and the second code block using the same communication resources. Moreover, the network entity comprises a communication interface configured to transmit the superposed first and second code block to the user equipment.

The network entity can be a base station of the wireless or cellular communication network. The plurality of communication resources can be time-frequency communication resources, in particular time-frequency resource blocks, provided by the wireless or cellular

communication network. The rate of the first or second code block can be the ratio of the number of information bits to the total number of bits of the first or second code block.

Thus, an improved network entity is provided, which, in particular allows a spectral efficient transmission of data with different requirements concerning reliability and/or latency.

In a first possible implementation form of the network entity according to the first aspect as such, the processor is configured to perform a first HARQ process and a second HARQ process, wherein the first code block is a code block of the first HARQ process and the second code block is a code block of the second HARQ process and wherein the processor is configured to superpose the code block of the first HARQ process and the code block of the second HARQ process.

In a second possible implementation form of the network entity according to the first implementation form of the first aspect, the first HARQ process and the second HARQ process is a HARQ process between the network entity and the user equipment or the first HARQ process is a HARQ process between the network entity and the user equipment and the second HARQ process is a HARQ process between the network entity and another user equipment.

In a third possible implementation form of the network entity according to the first or second implementation form of the first aspect, the first HARQ process and the second HARQ process each comprise at least two transmission rounds, wherein the processor is configured to generate a code block of a first transmission round of the first HARQ process on the basis of a different reliability and/or latency requirement than a code block of a second

transmission round of the first HARQ process.

In a fourth possible implementation form of the network entity according to any one of the first to third implementation form of the first aspect, the processor is configured to generate the code block of the first transmission round of the first HARQ process on the basis of a first modulation and coding scheme and the code block of the second transmission round of the first HARQ process on the basis of a second modulation and coding scheme.

In a fifth possible implementation form of the network entity according to the fourth implementation form of the first aspect, the processor is configured to determine the second modulation and coding scheme from the first modulation and coding scheme on the basis of a rate adjustment factor c.

In a sixth possible implementation form of the network entity according to the fifth

implementation form of the first aspect, the processor is configured to determine the second modulation and coding scheme MCS _m on the basis of the following equation:

MCS _m = MCS _re + c, wherein the rate adjustment factor c e Z and MCS _re denotes the first modulation and coding scheme.

The first modulation and coding scheme can be a reference modulation and coding scheme, which is determined by the base station on the basis of a channel quality and a reference reliability requirement. The second modulation and coding scheme can be the modulation and coding scheme of an m-th round of a HARQ process determined from the reference modulation and coding scheme on the basis of an actual reliability requirement. In a seventh possible implementation form of the network entity according to any one of the fourth to sixth implementation form of the first aspect, the processor is configured to transmit the rate adjustment factor c to via the communication interface to the user equipment for allowing the user equipment to determine the second modulation and coding scheme from the first modulation and coding scheme.

The processor can be configured to select the first modulation and coding scheme and/or the second modulation and coding scheme from a plurality of modulation and coding scheme tables associated with different reliability requirements.

In an eighth possible implementation form of the network entity according to the first aspect as such or any one of the first to seventh implementation form thereof, the processor is configured to generate the first code block having the first rate on the basis of a first reliability and/or latency requirement and a first link budget and to generate the second code block having the second rate on the basis of a second reliability and/or latency requirement and a second link budget.

In a ninth possible implementation form of the network entity according to the first aspect as such or any one of the first to eighth implementation form thereof, the processor is configured to superpose the first code block and the second code block using the same communication resources on the basis of one or more of the following NOMA schemes: power domain NOMA, sparse code multiple access (SCMA), bit division multiplexing, multi-user shared access (MUSA), interleave division multiple access (I DMA), lattice partition multiple access (LPMA), and/or pattern division multiple access (PDMA).

According to a second aspect the invention relates to a user equipment configured to communicate with a network entity, in particular a base station, in an uplink direction or with another user equipment in a sidelink direction using a plurality of communication resources of a wireless or cellular communication network. The user equipment comprises a processor configured to generate a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate, and to superpose on the basis of a non-orthogonal multiple access (NOMA) scheme the first code block and the second code block using the same communication resources.

Moreover, the user equipment comprises a communication interface configured to transmit the superposed first and second code block to the network entity or the other user equipment. Thus, an improved network entity is provided, which, in particular allows a spectral efficient transmission of data with different requirements concerning reliability and/or latency. In a first possible implementation form of the user equipment according to the second aspect as such, the communication interface is configured to receive communication resources allocation information from the network entity, wherein the processor is configured to superpose the first code block and the second code block on the basis of the communication resources allocation information.

According to a third aspect the invention relates to a method of operating a network entity, in particular a base station, configured to communicate in a downlink direction with a user equipment using a plurality of communication resources of a wireless or cellular

communication network. The method comprises the steps of: generating a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate; superposing on the basis of a non-orthogonal multiple access scheme the first code block and the second code block using the same communication resources; and transmitting the superposed first and second code block to the user equipment.

The method according to the third aspect of the invention can be performed by the network entity according to the first aspect of the invention. Further features of the method according to the third aspect of the invention result directly from the functionality of the network entity according to the first aspect of the invention and its different implementation forms.

According to a fourth aspect the invention relates to a method of operating a user equipment configured to communicate with a network entity, in particular a base station, in an uplink direction or with another user equipment in a sidelink direction using a plurality of communication resources of a wireless or cellular communication network. The method comprises the steps of: generating a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate; superposing on the basis of a non-orthogonal multiple access scheme the first code block and the second code block using the same communication resources; and transmitting the superposed first and second code block to the network entity or the other user equipment. The method according to the fourth aspect of the invention can be performed by the user equipment according to the second aspect of the invention. Further features of the method according to the fourth aspect of the invention result directly from the functionality of the user equipment according to the second aspect of the invention and its different implementation forms.

According to a fifth aspect the invention relates to a computer program comprising program code for performing the method according to the second aspect or the method according to the fourth aspect, when executed on a processor or a computer.

The invention can be implemented in hardware and/or software.

Embodiments of the invention provide an approach of reliability and latency based superposition transmission, enabling the superimposed transmission of multiple code blocks under different reliability and latency requirements. As part of a link adaptation, embodiments of the invention allow to determine the transmission rate of each data packet on the basis of its reliability (i.e.. BLER BLER _re(? ) and latency requirements (e.g. PHY latency T _max ), as well as the channel condition, namely the estimated SNR level (e.g. SNR or CQI report), i.e.

Rreq ⁼ /(BLER _re(? , T _max , CQI), wherein R _req denotes the required rate. After the transmission rates have been determined for multiple code blocks, superposition transmission techniques can be applied to code blocks being associated with different rates. Such a rate difference may be caused by one or more of the above factors. Examples include but are not limited to one user equipment transmitting code blocks with different reliability requirements and one user equipment transmitting code blocks with the same reliability requirement, one of which needs to meet a hard deadline in a single shot while for the other retransmissions are allowed.

Since the rate difference does not necessarily require different levels of SNR, embodiments of the invention can be applied to downlink, uplink and sidelink transmissions and for both single user and multi-user transmissions. Embodiments of the invention advantageously exploit the rate difference incurred by different reliability/latency requirements, enabling the superposition-based multiplexing of multiple code blocks. Compared with channel condition based link adaptation and orthogonal multiple access, the scheme provided by embodiments of the invention improves the spectral efficiency by allowing for multiplexing of resources in time and frequency and guaranteeing the reliability/latency requirements. In comparison with other non-orthogonal multiple access schemes, the scheme provided by embodiments of the invention exploits the rate differences naturally incurred by reliability and/or latency requirements and, thus, minimizes the coordination efforts necessary to enable a reliable non-orthogonal access.

Embodiments of the invention are based on a non-orthogonal multiple access scheme (herein referred to as NOMA), which is considered to be an essential enabling technology for 5G wireless networks to meet the heterogeneous demands on low latency, high reliability, massive connectivity, and high throughput. The key idea of NOMA is to serve multiple users in the same bandwidth resource, such as time slots, subcarriers, or spreading codes.

Embodiments of the invention can be based on one or more of the following NOMA schemes: power domain NOMA, sparse code multiple access (SCMA), bit division multiplexing, multi-user shared access (MUSA), interleave division multiple access (IDMA), lattice partition multiple access (LPMA), and pattern division multiple access (PDMA).

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, wherein: Fig. 1 shows a schematic diagram illustrating a wireless communication network comprising a network entity according to an embodiment and a user equipment according to an embodiment;

Fig. 2 shows a schematic diagram illustrating the transmission of code blocks with different reliability requirements as implemented in a network entity and a user equipment according to an embodiment;

Fig. 3 shows a schematic diagram illustrating a user equipment according to an embodiment; Fig. 4 shows a schematic diagram illustrating several rounds of a HARQ transmission scheme as implemented by a network entity and a user equipment according to an embodiment; Fig. 5 shows a schematic diagram illustrating a rate adjustment in dependence of different reliability requirements as implemented in a network entity and a user equipment according to an embodiment;

Fig. 6a shows a schematic diagram illustrating a downlink HARQ transmission scheme implemented in a network entity and a user equipment according to an embodiment;

Fig. 6b shows a schematic diagram illustrating an uplink HARQ transmission scheme implemented in a network entity and a user equipment according to an embodiment;

Fig. 7 shows a schematic diagram illustrating the conventional sequential HARQ

transmission scheme and a pipelined HARQ transmission scheme implemented in a network entity and a user equipment according to an embodiment;

Fig. 8 shows a schematic diagram illustrating a network entity according to an embodiment;

Fig. 9 shows a schematic diagram illustrating a multi-service scheduler implemented in a network entity according to an embodiment;

Fig. 10 shows a schematic diagram illustrating a method of operating a network entity according to an embodiment; and

Fig. 1 1 shows a schematic diagram illustrating a method of operating a user equipment according to an embodiment.

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

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined be the appended claims. For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise. Figure 1 shows a schematic diagram illustrating a wireless communication network 100 (also referred to as a cellular or mobile communication network 100). The wireless communication network 100 comprises a network entity 1 10 and a user equipment 120 in mutual communication. In an embodiment the network entity 1 10 is a base station. In an

embodiment the user equipment 120 is a mobile phone or a smart car.

As can be taken from figure 1 , the base station 1 10 comprises a processor 1 1 1 and a communication interface 1 13. The user equipment 120 comprises a processor 121 and a communication interface 123. As will be described in more detail further below, the processor 1 1 1 of the base station 1 10 is configured to generate a first code block CB1 having a first rate on the basis of a first reliability and/or latency requirement and a second code block CB2 having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate, and to superpose on the basis of a non-orthogonal multiple access (NOMA) scheme the first code block CB1 and the second code block CB2 using the same

communication resources. The communication interface 1 13 of the base station is configured to transmit the superposed first and second code block in the DL direction to the user equipment 120. The plurality of communication resources can be time-frequency communication resources, in particular time-frequency resource blocks, provided by the wireless or cellular

communication network 100. The rate of the first or second code block can be the ratio of the number of information bits to the total number of bits of the first or second code block. As will be described in more detail further below, the processor 121 of the user equipment 120 is configured to generate a first code block CB1 having a first rate on the basis of a first reliability and/or latency requirement and a second code block CB2 having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate, and to superpose on the basis of a non-orthogonal multiple access (NOMA) scheme the first code block CB1 and the second code block CB2 using the same

communication resources. The communication interface 123 of the user equipment 120 is configured to transmit the superposed first and second code block in the UL direction to the base station 1 10 or in a sidelink direction to another user equipment.

As mentioned above, embodiments of the invention are based on a non-orthogonal multiple access scheme (herein referred to as NOMA), which is considered to be an essential enabling technology for 5G wireless networks to meet the heterogeneous demands on low latency, high reliability, massive connectivity, and high throughput. The key idea of NOMA is to serve multiple users in the same bandwidth resource, such as time slots, subcarriers, or spreading codes. Embodiments of the invention can be based on one or more of the following NOMA schemes: power domain NOMA, sparse code multiple access (SCMA), bit division multiplexing, multi-user shared access (MUSA), interleave division multiple access (I DMA), lattice partition multiple access (LPMA), and pattern division multiple access

(PDMA).

As already described above, the diverse service types foreseen by the next generation of mobile radio systems will pose different requirements in terms of data transmission reliability. Given the intrinsic characteristics of the data traffic, a first service might have to transport the data payload meeting a high reliability requirement (for instance with a reliability of 99.9%), while a second service may adhere to the best effort principle with a reliability of, for instance, only 90%. Likewise, for control information the reliability requirement is often very high, whereas it is less critical for data payload. As will be described in more detail further below, a scheduler 1 1 1 a can be implemented in the processor 1 1 1 of the base station 1 10 for providing the first and second service with different reliability requirements on the basis of a superposition transmission. In an embodiment, the scheduler 1 1 1 a is configured to assign different data rates to the respective code blocks (CBs) of the first and second service, i.e. the code blocks CB1 and CB2, and to allocate superimposed time frequency resources to these code blocks CB1 and CB2 on the basis of a NOMA scheme, as illustrated in the scenario (a) shown in figure 2.

For services having the same reliability requirements with respect to the data transmission the scheduler 1 1 1 a of the base station 1 10 according to an embodiment can use a conventional allocation of resources to the code blocks CB1 and CB2 based on a TDM scheme and/or a FDM scheme, as illustrated by the scenarios (b) and (c) shown in figure 2. The time-frequency communication resources are sliced into tiles which carry payloads of difference service types.

By multiplexing data traffic with different reliability requirements on the basis of a

superposition transmission technique, the wireless communication network 100 comprising the base station 1 10 and the user equipment 120 does not sacrifice spectral efficiency for guaranteeing a high reliability for certain data traffic. Thus, embodiments of the invention offer a greater flexibility for a more efficient allocation of resources in a wireless

communication network supporting mixed service types.

According to embodiments of the invention the superposed transmission of CBs with difference reliability requirements can be applied in both downlink and uplink direction as well as in both single user and multi user scenarios. In an embodiment, the superposed transmission can be used for uplink transmission of CBs with difference reliability

requirements from a single UE, for instance, the UE 120 to the base station 1 10. Since the superposition requires neither SNR difference nor spatial separation, the UE 120 may be configured to transmit CBs with different reliability requirements through separate data pipes on the overlaid time frequency resources. As will be appreciated, a HARQ (hybrid automatic repeat request) process or scheme can be regarded as one specific form of such data pipes.

HARQ with a single bit acknowledgement (ACK) is widely used as one of the techniques for enabling spectral-efficient transmission. Conventionally, each UE has been assigned a single HARQ process wherein each retransmission needs to incur a round-trip transmission to receive the ACK NACK before proceeding with the next HARQ retransmission. The maximum number of retransmissions is usually specified explicitly. By each retransmission, reliability can be improved. As a consequence, multiple retransmissions result in a large delay and spectral efficiency loss as well.

Figure 3 shows a schematic diagram illustrating a corresponding embodiment of the user equipment 120 configured to implement a superposed transmission of CBs with difference reliability requirements in the context of a HARQ process. Since usually multiple HARQ processes are handled simultaneously, the UE 120 shown in figure 3 comprises a HARQ handler 121 a. In an embodiment, the HARQ handler 121 a can be implemented by the processor 121 of the UE 120. In an embodiment, the HARQ handler 121 a is configured to receive signaling from the base station 1 10 and to coordinate multiple HARQ processes within the UE 120, as illustrated in figure 3. As a technique allowing a tradeoff between spectral efficiency and latency, HARQ processes can be advantageously employed for URLLC transmission services. However, since generally a hard deadline (which is defined by the maximum number of transmission rounds) needs to be met by a HARQ process, it would be advantageous to increase the reliability of the HARD process, the closer it gets to the predefined deadline. This, in turn, would result in differences in terms of reliability requirements for the earlier transmission rounds of a HARD process in comparison to the later ones.

In an embodiment, the base station 1 10 and the user equipment are configured to implement a HARQ transmission scheme based on a superposed transmission of CBs with difference reliability requirements. This HARQ transmission scheme provided by embodiments of the invention is herein referred to as superHARQ (i.e. "superposition HARQ" or "superposed HARQ"). The basic idea of superHARQ is to apply different reliability requirements at each round of a HARQ transmission scheme so that in a later round of the HARQ transmission scheme the CB is transmitted with a higher reliability and lower spectral efficiency compared to a previous one. Thus, embodiments of the invention allow meeting the latency and reliability requirements by the predefined deadline without jeopardizing the overall spectral efficiency of the HARQ transmission scheme. In an embodiment, a lower rate transmission of a HARQ process A can be superimposed with a higher rate transmission of a HARQ process B using the superposition transmission techniques implemented in the base station 1 10 and the UE 120, which will be described in more detail in the following.

Figure 4 shows a schematic diagram illustrating several rounds of a HARQ transmission scheme between the base station 1 10 and the UE 120 according to an embodiment. The exemplary scenario illustrated in figure 4 is based on an exemplary service, for instance URLLC, having the following requirements with respect to reliability and latency: a data packet must be transmitted with 99.999% reliability within T ms. It is assumed that within this latency constraint of T ms three rounds of HARQ transmissions are allowed in the exemplary scenario shown in figure 4.

In order to fulfill the above reliability and latency requirements, according to an embodiment the rate can be adapted, for instance, by the processor 1 1 1 of the base station 1 10 in the following manner, wherein denotes the error probability of the m-th round HARQ transmission (in this example in the DL direction), and denotes the error probability of the HARQ feedback link (in this example in the UL direction). In order to achieve an overall reliability of 99.999% after three rounds of HARQ transmissions, according to an embodiment the error probability which is allowed at each round can be chosen, for instance, by the processor 1 1 1 of the base station 1 10 as follows:

10%, P _e ^w = l%, P _e ^w = 0.1%, P = 0.01%.

As will be appreciated, such a choice of the error probabilities for the different rounds of the HARQ transmission scheme by the processor 1 1 1 of the base station 1 10 makes sure that the closer the HARQ process gets to its deadline, the higher is the reliability that is being used. The overall reliability can be calculated as follows:

P{1 st round succeed) + P{2nd round succeed) + P{3rd round succeed)

Conventionally, the link adaptation is designed to meet a pre-defined block error ratio (BLER) of 10%, corresponding to 90% reliability. Given an estimated signal-to-noise ratio (SNR) or the corresponding channel quality indicator (CQI), a scheduler adapts the transmit modulation and coding scheme (MCS) subject to the channel condition within the channel coherence time.

In an embodiment, the base station 1 10 and the user equipment 120 are configured to select one or more modulation and coding schemes (MCSs) from a plurality of available MCSs for transmitting data. In an embodiment, the plurality of MCSs can be provided in form of a list indexed by an index k. In an embodiment, each MCS _fc corresponds to a fixed data rate R _k . Conventionally, the MCS used in the downlink direction is determined by the scheduler at the base station on the basis of the UE channel quality indicator (CQI) report. Generally, each CQI corresponds to an estimated level of SNR (signal-to-noise ratio). In the uplink direction, the base station can estimate the SNR based on the UL reference signals and notify the UE about the MCS, which has been selected by the base station on the basis of the estimated SNR. As already described above, according to an embodiment the base station 1 10 and the user equipment are configured to implement a HARQ transmission scheme (herein referred to as "superHARQ") based on a superposed transmission of CBs with difference reliability requirements. In one embodiment of superHARQ the target reliability can be specified for each round of HARQ transmission, corresponding to the target error probability

p(l) _p (2) _p ( )

e e ^■■■ e

Figure 4 illustrates several rounds of the superHARQ transmission scheme as implemented by the base station 1 10 and the user equipment 120 according to an embodiment, wherein the target reliability is specified for each round of the superHARQ transmission scheme. Given a table of the MCS index and the corresponding transmission data rate with the reference reliability P _e ^Re e.g., 10%, according to an embodiment the scheduler 1 1 1 a of the base station 1 10 is configured to determine the reference modulation and coding scheme MCS _re on the basis of the CQI report of the UE 120. Moreover, for each superHARQ transmission round the scheduler 1 1 1 a of the base station 1 10 is configured to select a new modulation and coding scheme, for instance, by determining the new modulation and coding scheme as MCS _m = MCS _re + c , where c e Z is a rate adjustment factor. When the required reliability is higher than the reference reliability, i.e. P^ < P ^ef , the rate adjustment factor is an integer smaller than zero, i.e. c < 0. In this case the new modulation and coding scheme MCS _m corresponds to a lower data rate, which guarantees that the reliability requirement

P^ can be fulfilled. When on the other hand the required reliability is lower than the reference reliability, i.e. P^ > P ^ef , the rate adjustment factor is an integer larger than zero, i.e. c > 0. The same approach is applied to the further rounds of the superHARQ

transmission scheme.

Since in the above embodiment described in the context of figure 4 the target error probability at each round is pre-defined, the rate adjustment factor c can be considered to be semi-static. Since the different reliabilities for the different HARQ transmission rounds imply corresponding differences in terms of data rate, according to an embodiment the base station 1 10 (in particular the scheduler 1 1 1 a) is capable of scheduling another HARQ process to a certain UE (e.g. the UE 120 or another UE) before the current HARQ process is finished. According to an embodiment the base station 1 10 (in particular the scheduler 1 1 1 a) is configured to superpose the higher rate transmission of the later started HARQ process with the lower rate transmission of the earlier started HARQ process using the superposition transmission techniques already described above. In an embodiment, the base station 1 10 is configured to use the two superposed HARQ processes for a single UE, such as the UE 120, or two different UEs, such as the UE 120 and another UE. Figures 6a and 6b illustrate such an embodiment of the superHARQ transmission scheme enabled by the scheduler 1 1 1 a of the base station 1 10 for the DL and for the UL, respectively. In another embodiment, the UE 120 is configured to implement the same or a similar superHARQ transmission scheme in the sidelink direction, i.e. for the communication with another UE, wherein the UE 120 acts as the base station.

In step 601 of figure 6a the UE 120 provides the CQI report to the base station 1 10. On the basis thereof and the desired reliability for the first round of a first HARQ process 600a, the base station 1 10 selects a suitable MCS, for instance, the MCS 12 and performs the first data transmission using the selected MCS (step 603 of figure 6a). In case the first data transmission was not successful, the UE 120 returns a NACK in step 605 of figure 6a. In response thereto, the base station 1 10 triggers in step 607 of figure 6a the second transmission round of the first HARQ process 600a now using a different MCS, namely the exemplary MCS 9, which provides an increased reliability of 99% in comparison to the reliability of 90% provided by the MCS 12 used for the first transmission round. In parallel, the base station 1 10 superposes the second transmission round of the of the first HARQ process 600a with a first transmission round of a second HARQ process 600b. As already described above, this superposed transmission or superposition transmission is based on the idea of making use of the same time-frequency communication resources, e.g. resource blocks, by using a NOMA scheme. However, as illustrated in figure 6 and as already described above, in the superposed transmission the first transmission round of the second HARQ process 600b is associated with a smaller reliability than the second transmission round of the first HARQ process 600a. In response to receiving the superposition

transmission the UE 120 returns in step 609 of figure 6a a NACK for the first transmission round of the second HARQ process 600b and a NACK for the second transmission round of the first HARQ process 600a, in case both transmissions were not successful. As will be appreciated, step 61 1 of figure 6a differs from step 609 essentially in that for the

superposition transmission of step 61 1 the base station 1 10 selects even higher reliabilities as well as corresponding MCSs.

Figure 6b shows the corresponding superHARQ transmission scheme in the UL direction according to an embodiment. In step 651 of figure 6b the UE 120 sends together with a schedule request (SR) for the allocation of UL communication resources a reference signal (RS) to the base station 1 10, on the basis of which the base station 1 10 estimates the UL channel quality. As will be appreciated, the additional steps of the UL superHARQ transmission scheme shown in figure 6b, i.e. steps 653 to 663, are rather similar to the corresponding steps DL scheme shown in figure 6a.

For implementing the superHARQ transmission scheme in the DL direction the base station 1 10 according to an embodiment is configured to provide control information to the UE 120 (and possibly other UEs) for decoding the superposed codeblocks. In an embodiment, such control information can include one or more of the following information elements: an indicator (e.g. a flag) for indicating that a superHARQ transmission mode is employed by the base station 1 10; a power ratio index in case a superposition transmission based on a NOMA scheme with an adaptive power ratio is used by the base station 1 10 (a list of possible power ratios between the two superimposed codeblocks can be predefined); a modulation combination index in case a superposition transmission based on a NOMA scheme with label-bit assignment on Gray-mapped composite constellations is used by the base station 1 10 (a list of modulation combination possibilities can be predefined); and/or the rate adjustment factor c for allowing the UE 120 to update the MCS for each HARQ round by itself (in order to avoid having to signal information about the specific MCS at each HARQ round).

Moreover, the control information provided by the base station 1 10 can comprise a superposed HARQ process number. For the superHARQ transmission scheme implemented in the UL direction, the base station 1 10 is aware of the corresponding superHARQ settings, which are required for decoding the superposition transmissions from the UE 120. However, in an embodiment superHARQ related parameters are provided by the base station 1 10 to the UE 120 (as well as possibly other UEs) such that the superposed codeblocks can be jointly transmitted by the UE 120. In case that the superposed HARQ processes belong to the same UE, for instance, the UE 120, the base station 1 10 can provide one or more of the following control parameters to the UE 120: an indicator (e.g. a flag) for indicating that a superHARQ transmission mode is employed; a modulation combination index in case a superpositon transmission based on a NOMA scheme with label-bit assignment on Gray- mapped composite constellations is used (a list of modulation combination possibilities can be predefined); a power ratio index in case a superposition transmission based on a NOMA scheme with an adaptive power ratio is used (a list of possible power ratios between the two superimposed codeblocks can be predefined); and/or the rate adjustment factor c for allowing the UE 120 to update the MCS for each HARQ round by itself (in order to avoid having to signal information about the specific MCS at each HARQ round). If the superposed HARQ processes belong to different UEs, the base station 1 10 according to an embodiment can be configured to convey only the assigned transmit power to the UEs in the downlink direction in order to have the power ratio applied in the upcoming UL transmission. In such case, it is not necessary that a UE, such as the UE 120, is aware whether the superHARQ is in use or not.

As will be appreciated, for a corresponding superHARQ transmission scheme implemented in the sidelink direction, i.e. between two user equipments, similar signaling of control information can be provided by embodiments of the invention based on combinations of those for the DL and the UL direction described above.

Embodiments of the invention provide two main advantages. From the point of view of the base station 1 10 (or the corresponding network) embodiments of the invention allow for a more flexible allocation of communication resources, in particular time-frequency resource blocks. This is because a high reliability transmission with low data rate does not need to exclusively occupy a given set of time frequency communication resources, which improves the overall spectral efficiency due to the superposition transmission technique provided by embodiments of the invention. Allowing an initial transmission round with a higher data rate and a lower reliability, the superHARQ transmission schemes according to embodiments of the invention provide an advantageous tradeoff between reliability and spectral efficiency. From the point of view of the UE 120, the superHARQ transmission scheme provided by embodiments of the invention allows employing pipelined HARQ processes instead of the conventional sequential HARQ processes. In other words, the UE 120 can start processing a new HARQ process before the previous one has been completed. As illustrated in figure 7, by employing pipelined HARQ processes on the basis of superHARQ transmission scheme provided by embodiments of the invention provides a significant reduction of the latency in comparison to the conventional sequential HARQ processes.

Figure 8 shows a schematic diagram illustrating an embodiment of the base station 1 10 configured to provide superimposed HARQ processes in the downlink. In addition to the scheduler 1 1 1 a the base station 1 10 shown in figure 8 comprises a transmission buffer 1 15 and one or more superposition transmission processing chains (for the sake of clarity only one superposition transmission processing chain 810 is shown in figure 8). The superposition transmission processing chain 810 comprises two HARQ process units 1 1 1 b, 1 1 1 c, two encoders/rate matchers 1 1 1 d, 1 1 1 e, a joint symbol mapping/power allocation unit 1 1 1f as well as a resource mapping unit 1 1 1 g. In an embodiment, the two HARQ process units 1 1 1 b, 1 1 1 c can be HARQ buffers for buffering the HARQ data from the transmission buffer 1 15. Once a HARQ process is complete (ACK received), the scheduler 1 1 1 a can instruct the HARQ process units 1 1 1 b, 1 1 1 c to clear their buffers and to load new HARQ data from the transmission buffer 1 15. In the embodiment shown in figure 8, the base station 1 10 furthermore comprises two conventional processing chains 820a, 820b, which allow the base station 1 10 to use a TDM and/or a FDM scheme for transmitting data in case no superposition transmission is required. The two conventional processing chains 820a, 820b each comprise a HARQ process unit 1 12a, 1 12b, an encoder/rate matcher 1 12c, 1 12d, a symbol mapping unit 1 12e, 1 12f and a resource mapping unit 1 12g, 1 12h.

The scheduler 1 1 1 a of the base station 100 shown in figure 8 is configured to determine the HARQ processes which can be superposed (e.g. the HARQ processes 1 & 2 shown in blocks 1 1 1 b and 1 1 1 c of figure 8). In an embodiment, code blocks from these two HARQ processes are jointly mapped to the constellation symbols by the joint symbol

mapping/power allocation unit 1 1 1 f in case the superposition transmission is based on a corresponding NOMA scheme. In case the base station 1 10 of figure 8 is configured to employ the superposition transmission on the basis of a power ratio NOMA scheme, the joint symbol mapping/power allocation unit 1 1 1f can be configured to jointly map code blocks from these two HARQ processes to different power levels. As will be appreciated, for the conventional processing chains 820a, 820 based on an orthogonal multiple access, such as FDM or TDM, the symbol mapping for different HARQ processes is carried out

independently. As already described above in the context of figure 2, in order to be able to process multiple HARQ processes in the UL direction simultaneously, the embodiment of the UE 120 shown in figure 2 comprises a HARQ handler 121 a.

The superHARQ embodiments described above can be advantageously applied to meet the reliability and latency requirements of specific services, for instance URLLC. For these kind of embodiments parameters of a specific superHARQ implementation concerning the HARQ protocol, such as the maximum number of HARQ rounds, the target error probabilities and the like, can be predefined for the base station 1 10 and the UE 120. In a further embodiment, the scheduler 1 1 1 a of the base station 1 10 is configured to adapt the individual protocol of each HARQ process with respect to its payload characteristics. More specifically, in an embodiment the scheduler 1 1 1 a of the base station 1 10 is configured to determine the MCS as well as the resource allocation of the HARQ processes based on three input factors illustrated in figure 9, namely the link budget (SNR), the desired reliability and the desired latency. In other words, embodiments of the superHARQ transmission include two steps, namely a joint rate adaptation and superposition transmission. This is illustrated in more detail on the basis of the following example, including a first service request A and a second service request B:

A: overall reliability 99.9%, latency 10 ms ^ 4 rounds transmission allowed

B: overall reliability 99.999%, latency 5 ms ^ 2 rounds transmission allowed For simplicity, it is assumed that the error probability of the feedback channel is fixed to 0.01 % (reliability 99.99%). One possible outcome of the decision of the multi-service scheduler 1 1 1 a shown in figure 9 could be the following:

HARQ process A: each round with 90% reliability, the overall reliability reaches 99.99% after a maximum of four rounds.

HARQ process B: in order to meet the requirements, 1 ^st transmission transmits with reliability 99%, the 2 ^nd with 99.95%.

Under the same channel conditions, the corresponding MCSs for each round of each HARQ process can be determined by the scheduler as already described above. Since the rate difference exists, superposition transmission technique can be applied, as provided by embodiments of the invention. Unlike conventional link adaptation, which relies on the link budget only, the superHARQ transmission scheme with flexible link adaptation provided by embodiments of the invention allows the scheduler 1 1 1 a to make a joint decision on the basis of the reliability and latency requirements as well.

In an embodiment, a label-bit assignment on composite constellations can be used for superposition transmission. A non-orthogonal multiple access (NOMA) scheme is described in A. G. Perotti, B. M. Popovic, "Non-orthogonal multiple access for degraded broadcast channels: RA-CEMA", I EEE Wireless communications and networking conference

(WCNC2015). Assuming a superimposed transmission of two code blocks with different reliability and rate requirements, a label-bit assignment is performed for multiplexing of code blocks according to the multiplexing matrix S. The size of S is G x s where G is the number of constellation symbols (also the number of available resource elements) and s is the sum of the modulation order over users. For example, the matrix S below applies 64QAM (i.e. s=6 bits) as the composite constellation of two processes P1 and P2. Embodiments of the invention are based on the above label-bit assignment principle in the following way.

From the perspective of the binary bits in the modulator constellation (each column in S stands for one binary bit in the composite constellation): Using the property that different label-bits have different bit-capacities which depend on the constellation shape or specific labeling, the general principle for label-bit assignment is to assign label bits with higher capacities to the process with low transmission rate and stringent reliability requirement. For example, assuming two HARQ processes with process 1 (P1 ) having a lower transmission rate than process 2 (P2) in the superposition transmission, in the label-bit assignment the matrix S below allocates P1 more bits with higher capacities (more in the left columns). In this example, label-bits in a column on the left hand side have bit capacities higher than or equal to a column on its right hand side. From the perspective of the different constellation symbols (each row in the matrix S below is composed of one constellation symbol while the odd and even positions stand for in-phase (I) and quadrature (Q) signal paths): The principle is to spread the bits from both I and Q paths as much as possible to different symbols/resource elements, yielding the high diversity gain.

PI PI PI P2 P2 P2-

PI PI P2 PI P2 P2

PI P2 P2 P2 P2 P2

-PI PI P2 P2 P2 P2-

Figure 10 shows a schematic diagram illustrating a method 1000 of operating the network entity 1 10 according to an embodiment. The method 1000 comprises the following steps: generating 1001 a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate; superposing 1003 on the basis of a non-orthogonal multiple access scheme the first code block and the second code block using the same communication resources; and transmitting 1005 the superposed first and second code block to the user equipment 102.

Figure 1 1 shows a schematic diagram illustrating a method 1 100 of operating the user equipment 120 according to an embodiment. The method 1 100 comprises the steps of: generating 1 101 a first code block having a first rate on the basis of a first reliability and/or latency requirement and a second code block having a second rate on the basis of a second reliability and/or latency requirement, wherein the first rate differs from the second rate; superposing 1 103 on the basis of a non-orthogonal multiple access scheme the first code block and the second code block using the same communication resources; and transmitting 1 105 the superposed first and second code block to the network entity or the other user equipment.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent

implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.