WO2023141918A1

WO2023141918A1 - Network node, terminal device, and methods therein for facilitating harq transmission

Info

Publication number: WO2023141918A1
Application number: PCT/CN2022/074518
Authority: WO
Inventors: Xiaoli LIAN; David BETTER; Jing Zhang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-01-28
Filing date: 2022-01-28
Publication date: 2023-08-03

Abstract

The present disclosure provides a method (100) in a network node. The method (100) includes: determining or receiving (110) a Hybrid Automatic Repeat reQuest, HARQ, Negative Acknowledgement, NACK, for an initial transmission; calculating (120) a Transport Block Size, TBS, for a retransmission associated with the initial transmission, based on a TBS for the initial transmission; and determining (130) a Modulation and Coding Scheme, MCS, and a number of Physical Resource Blocks, PRBs, for the retransmission based on the TBS for the retransmission.

Description

NETWORK NODE, TERMINAL DEVICE, AND METHODS THEREIN FOR FACILITATING HARQ TRANSMISSION

TECHNICAL FIELD

The present disclosure relates to communication technology, and more particularly, to a network node, a terminal device, and methods therein for facilitating Hybrid Automatic Repeat reQuest (HARQ) transmission.

BACKGROUND

Transmissions over wireless channels are subject to errors due to variations in received signal quality caused by frequency selective fading, shadow fading, or path loss.

Claude Shannon described a transmission capacity of a certain transmission channel. If an information transmission rate is lower than or equal to the capacity, then there is some coding technique that could be used to guarantee transmitted information to be transmitted correctly through the channel. Therefore, virtually all wireless communication systems employ some form of Forward Error Correction (FEC) coding, tracing its roots to the pioneering work by Shannon in 1948, such as Turbo, Low Density Parity Check (LDPC) , etc. The basic principle of FEC coding is to introduce redundancy in the transmitted signal. This is achieved by e.g., adding parity bits to information bits prior to transmission (alternatively, the transmission could consist of parity bits alone, depending on the coding scheme used) . The parity bits are computed from the information bits using a method given by the coding structure used. Thus, the number of bits transmitted over the channel is larger than the number of original information bits, and a certain amount of redundancy is introduced in the transmitted signal. As a result, difference coding rates can be provided due to difference numbers of parity bits.

In addition, link adaptation is introduced such that the communication system can dynamically adjust transmission parameters, such as modulation scheme, coding scheme, and/or coding rate according to changes in the wireless channel in time, frequency, and space, which leads to variation of the supported information transmission rate.

Another approach to handle transmission errors is to use Automatic Repeat Request (ARQ) . In an ARQ scheme, a receiver uses an error-detecting code, typically a Cyclic Redundancy Check (CRC) , to detect if a data packet received from a transmitter is erroneous or not. If no error is detected in the received data packet, the received data is declared error-free, and the transmitter is notified by sending a positive Acknowledgment (ACK) . On the other hand, if an error is detected, the receiver discards the received data and notifies the transmitter via a return channel by sending a Negative Acknowledgment (NACK) . In response to a NACK, the transmitter retransmits the same information.

Virtually all modern communication systems employ a combination of FEC coding and ARQ, known as Hybrid ARQ (HARQ) . One of the important features of HARQ is soft combining, where the receiver combines the received signal with different Redundancy Versions (RVs) to finally achieve a cumulative Signal-to-Noise Ratio (SNR) gain and a coding gain.

To some extent, link adaptation of transmission parameters and ARQ allow the system to maximize its frequency band utilization while ensuring Quality of Service (QoS) and maximize the utilization of limited wireless channel resources.

In a current implementation, the same amount of bits are transmitted in retransmissions as in the initial transmission. The bits with different RVs are combined together to reduce the coding rate. A Modulation and Coding Scheme (MCS) and a number of Physical Resource Blocks (PRBs) used for each retransmission are determined by means of link adaptation. This mechanism has been widely used in Long Term Evolution (LTE) and New Radio (NR) .

SUMMARY

As described above, each retransmission requires the same amount of coding bits to pass the CRC in all scenarios. Accordingly, the required Transport Block Size (TBS) decided for the initial transmission is taken as an input to link adaptation for potential retransmissions. Link adaptation for a retransmission decides a modulation scheme, a coding rate, and transmission resources based on the required TBS for the initial transmission. Then, the transmission data with the size of the TBS is encoded and rate matched in accordance with the coding scheme, such as polar, LDPC, etc. A number of RVs for the transmission data can be produced (the initial transmission uses RV 0) . For each retransmission, link adaptation decides the modulation scheme and the coding rate to adapt to a radio channel or Radio Frequency (RF) condition at that time. Encoding and rate matching can be done again using the same amount of coding bits. Only the RV is different for different retransmissions. However, this approach may often cause a waste of spectrum resources, which may in turn affect the spectral efficiency as well as the system throughput -especially in high-load scenarios.

It is an object of the present disclosure to provide a network node, a terminal device, and methods therein for facilitating HARQ transmission, capable of solving or at least mitigating the above problem.

According to a first aspect of the present disclosure, a method in a network node is provided. The method includes: determining or receiving an HARQ NACK for an initial transmission; calculating a TBS for a retransmission associated with the initial transmission, based on a TBS for the initial transmission; and determining an MCS and a number of PRBs for the retransmission based on the TBS for the retransmission.

In an embodiment, the TBS for the retransmission may be calculated based on a first RF condition when the initial transmission is carried out and a second RF condition estimated for link adaptation for the initial transmission.

In an embodiment, the operation of calculating may include: calculating a factor based on the first RF condition and the second RF condition, the factor being smaller than or equal to 1; and calculating the TBS for the retransmission by applying the factor to the TBS for the initial transmission.

In an embodiment, the factor may be set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold. Alternatively, the factor may be calculated based on a number of bits that are estimated to be missing in the initial transmission, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold. Alternatively, the factor may be set to 1 when the first RF condition is lower than the second RF condition by more than the second threshold.

In an embodiment, the number of bits may be estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per Resource Element (RE) .

In an embodiment, the method may further include: determining or receiving an HARQ NACK for the retransmission; and adjusting the factor to form a further factor for a further retransmission, such that a TBS for the further retransmission as calculated by applying the further factor to the TBS for the initial transmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

In an embodiment, the first RF condition and the second RF condition may each be represented by a Signal-to-Interference-plus-Noise Ratio (SINR) .

In an embodiment, when the initial transmission is an uplink transmission from a terminal device to the network node, the first condition may be an SINR measured at the network node. Alternatively, when the initial transmission is a downlink transmission from the network node to a terminal device, the first condition may be an SINR reported by the terminal device to the network node.

In an embodiment, when the initial transmission and the retransmission are uplink transmissions from a terminal device to the network node, the HARQ NACK for the initial transmission may be determined at the network node, and the method may further include: signaling the MCS and the number of PRBs for the retransmission to the terminal device.

In an embodiment, when the initial transmission and the retransmission are downlink transmissions from the network node to a terminal device, the HARQ NACK for the initial transmission may be received from the terminal device, and the method may further include: signaling the MCS and the number of PRBs for the retransmission to the terminal device.

According to a second aspect of the present disclosure, a network node is provided. The network node is operative to perform the method according to the above first aspect. The network node includes an HARQ unit configured to determine or receive an HARQ NACK for an initial transmission. The network node further includes a calculating unit configured to calculate a TBS for a retransmission associated with the initial transmission, based on a TBS for the initial transmission. The network node further includes a determining unit configured to determine an MCS and a number of PRBs for the retransmission based on the TBS for the retransmission.

According to a third aspect of the present disclosure, a network node is provided. The network node includes a transceiver, a processor, and a memory. The memory contains instructions executable by the processor whereby the network node is operative to perform the method according to the above first aspect.

According to a fourth aspect of the present disclosure, a computer readable storage medium is provided. The computer readable storage medium has computer program instructions stored thereon. The computer program instructions, when executed by a processor in a network node, cause the network node to perform the method according to the above first aspect.

According to a fifth aspect of the present disclosure, a method in a terminal device is provided. The method includes: transmitting or receiving an HARQ NACK for an initial transmission; and receiving, from a network node, a configuration of an MCS and a number of PRBs for a retransmission associated with the initial transmission. The MCS and the number of PRBs for the retransmission are determined based on a TBS for the retransmission that is smaller than a TBS for the initial transmission.

In an embodiment, the TBS for the retransmission may be calculated by: calculating a factor based on the first RF condition and the second RF condition, the factor being smaller than 1; and calculating the TBS for the retransmission by applying the factor to the TBS for the initial transmission.

In an embodiment, the factor may be set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold. Alternatively, the factor may be calculated based on a number of bits that are estimated to be missing in the initial transmission, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold.

In an embodiment, the number of bits may be estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per RE.

In an embodiment, the method may further include: transmitting or receiving an HARQ NACK for the retransmission; and receiving, from the network node, a configuration of a further MCS and a further number of PRBs for a further retransmission. The MCS and the number of PRBs for the further retransmission may be determined based on a TBS for the further retransmission. The TBS for the further retransmission may be calculated by applying a further factor to the TBS for the initial transmission, such that the TBS for the further retransmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

In an embodiment, the first RF condition and the second RF condition may each be represented by an SINR.

In an embodiment, when the initial transmission is an uplink transmission from the terminal device to the network node, the first condition may be an SINR measured at the network node. Alternatively, when the initial transmission is a downlink transmission from the network node to the terminal device, the first condition may be an SINR reported by the terminal device to the network node.

In an embodiment, when the initial transmission is an uplink transmission from the terminal device to the network node, the HARQ NACK for the initial transmission may be received from the network node.

In an embodiment, when the initial transmission is a downlink transmission from the network node to the terminal device, the HARQ NACK for the initial transmission may be transmitted to the network node.

According to a sixth aspect of the present disclosure, a terminal device is provided. The terminal device is operative to perform the method according to the above fifth aspect. The terminal device includes an HARQ unit configured to transmit or receive an HARQ NACK for an initial transmission. The terminal device further includes a receiving unit configured to receive, from a network node, a configuration of an MCS and a number of PRBs for a retransmission associated with the initial transmission. The MCS and the number of PRBs for the retransmission are determined based on a TBS for the retransmission that is smaller than a TBS for the initial transmission.

According to a seventh aspect of the present disclosure, a terminal device is provided. The terminal device includes a transceiver, a processor, and a memory. The memory contains instructions executable by the processor whereby the terminal device is operative to perform the method according to the above fifth aspect.

According to an eighth aspect of the present disclosure, a computer readable storage medium is provided. The computer readable storage medium has computer program instructions stored thereon. The computer program instructions, when executed by a processor in a terminal device, cause the terminal device to perform the method according to the above fifth aspect.

With the embodiments of the present disclosure, the TBS for the retransmission can be calculated based on the TBS for the initial transmission, and the MCS and the number of PRBs for the retransmission can be determined based on the TBS for the retransmission. In this way, the TBS for the retransmission may be reduced when compared to TBS for the initial transmission, such that fewer resources can be used for the retransmission without substantial degradation in Block Error Rate (BLER) performance. Therefore, the spectral efficiency can be improved and the system throughput can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:

Fig. 1 is a flowchart illustrating a method in a network node according to an embodiment of the present disclosure;

Fig. 2 is a flowchart illustrating a method in a terminal device according to an embodiment of the present disclosure;

Fig. 3 is a block diagram of a network node according to an embodiment of the present disclosure;

Fig. 4 is a block diagram of a network node according to another embodiment of the present disclosure;

Fig. 5 is a block diagram of a terminal device according to an embodiment of the present disclosure;

Fig. 6 is a block diagram of a terminal device according to another embodiment of the present disclosure;

Fig. 7 schematically illustrates a telecommunication network connected via an intermediate network to a host computer;

Fig. 8 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and

Figs. 9 to 12 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

As used herein, the term "wireless communication network" refers to a network following any suitable communication standards, such as NR, LTE-Advanced (LTE-A) , LTE, Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , and so on. Furthermore, the communications between a terminal device and a network node in the wireless communication network may be performed according to any suitable generation communication protocols, including, but not limited to, Global System for Mobile Communications (GSM) , Universal Mobile Telecommunications System (UMTS) , Long Term Evolution (LTE) , and/or other suitable 1G (the first generation) , 2G (the second generation) , 2.5G, 2.75G, 3G (the third generation) , 4G (the fourth generation) , 4.5G, 5G (the fifth generation) communication protocols, wireless local area network (WLAN) standards, such as the IEEE 802.11 standards; and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax) , Bluetooth, and/or ZigBee standards, and/or any other protocols either currently known or to be developed in the future.

The term “network node” or "network device" refers to a device in a wireless communication network via which a terminal device accesses the network and receives services therefrom. The network node or network device refers to a base station (BS) , an access point (AP) , or any other suitable device in the wireless communication network. The BS may be, for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , or a (next) generation (gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, a low power node such as a femto, a pico, and so forth. Yet further examples of the network node may include multi-standard radio (MSR) radio equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs) , base transceiver stations (BTSs) , transmission points, transmission nodes. More generally, however, the network node may represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a terminal device access to the wireless communication network or to provide some service to a terminal device that has accessed the wireless communication network.

The term "terminal device" refers to any end device that can access a wireless communication network and receive services therefrom. By way of example and not limitation, the terminal device refers to a mobile terminal, user equipment (UE) , or other suitable devices. The UE may be, for example, a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, portable computers, desktop computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, tablets, personal digital assistants (PDAs) , wearable terminal devices, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) and the like. In the following description, the terms "terminal device" , "terminal" , "user equipment" and "UE" may be used interchangeably. As one example, a terminal device may represent a UE configured for communication in accordance with one or more communication standards promulgated by the 3rd Generation Partnership Project (3GPP) , such as 3GPP's GSM, UMTS, LTE, and/or 5G standards. As used herein, a "user equipment" or "UE" may not necessarily have a "user" in the sense of a human user who owns and/or operates the relevant device. In some embodiments, a terminal device may be configured to transmit and/or receive information without direct human interaction. For instance, a terminal device may be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the wireless communication network. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but that may not initially be associated with a specific human user.

The terminal device may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, and may in this case be referred to as a D2D communication device.

As yet another example, in an Internet of Things (IOT) scenario a terminal device may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another terminal device and/or network equipment. The terminal device may in this case be a machine-to-machine (M2M) device, which may in a 3GPP context be referred to as a machine-type communication (MTC) device. As one particular example, the terminal device may be a UE implementing the 3GPP narrow band internet of things (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances, for example refrigerators, televisions, personal wearables such as watches etc. In other scenarios, a terminal device may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation.

As used herein, a downlink transmission refers to a transmission from the network node to a terminal device, and an uplink transmission refers to a transmission in an opposite direction.

References in the specification to "one embodiment, " "an embodiment, " "an example embodiment, " and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed terms. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a" , "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" , "comprising" , "has" , "having" , "includes" and/or "including" , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

Fig. 1 is a flowchart illustrating a method 100 according to an embodiment of the present disclosure. The method 100 can be performed by a network node, e.g., a gNB. The method 100 can be applied in uplink (when both initial transmission and retransmission are uplink transmissions) or downlink (when both initial transmission and retransmission are downlink transmissions) .

At block 110, the network node determines or receives an HARQ NACK for an initial transmission. In particular, in the uplink case, i.e., when the initial transmission is an uplink transmission from a terminal device to the network node, the network node may determine an HARQ NACK to be transmitted to the terminal device as a feedback for the initial transmission. Alternatively, in the downlink case, i.e., when the initial transmission is a downlink transmission from the network node to a terminal device, the network node may receive an HARQ NACK from the terminal device as a feedback for the initial transmission.

At block 120, the network node calculates a TBS for a retransmission associated with the initial transmission, based on a TBS for the initial transmission.

Here, in the block 120, the TBS for the retransmission may be calculated based on a first RF condition when the initial transmission is carried out (or referred to as “actual RF condition” in this context) and a second RF condition estimated for link adaptation for the initial transmission (or referred to as “estimated RF condition” in this context) . For example, the first RF condition and the second RF condition may each be represented by an SINR. In particular, in the uplink case, the first condition may be an SINR measured at the network node, or in the downlink case, the first condition may be an SINR reported by the terminal device to the network node., e.g., in Physical Uplink Share Channel (PUSCH) .

For example, in the block 120, the network node may calculate a factor, which is smaller than or equal to 1, based on the first RF condition and the second RF condition, and calculate the TBS for the retransmission by applying the factor to the TBS for the initial transmission.

In particular, the factor may be set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold. Alternatively, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold, the factor may be calculated based on a number of bits that are estimated to be missing in the initial transmission. Here, the number of bits that are estimated to be missing in the initial transmission may be estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per RE. On the other hand, when the first RF condition is lower than the second RF condition by more than the second threshold, the factor may be set to 1 (in this case the TBS for the retransmission would be equal to the TBS for the initial transmission) . The above process for calculating the factor, referred to as AggressivenessFactor hereinafter, can be represented in pseudo codes as follows:

In the above example, AggressivenessFactor is a factor for measuring the degree of aggressiveness for retransmission, or how much the TBS is reduced for the retransmission when compared to the initial transmission. Here, in the above example, the smaller the AggressivenessFactor is, the more the TBS will be reduced for the retransmission, i.e., the more aggressive the retransmission will be. It can be appreciated that AggressivenessFactor may alternatively be defined such that the greater it is, the more the TBS will be reduced for the retransmission (i.e., the more aggressive the retransmission will be) .

In the above example, Thr1 may have a value in the range of [-1, 2] , Thr2 may have a value in the range of [-4, -1] , f1 may have a value in the range of [0.1, 0.4] , f2 may have a value in the range of [0.4, 0.6] , f2_upper_limit may have a value in the range of [0.7, 0.9] , and f2_lower_limit may have a value in the range of [0.3, 0.6] .

Then, the TBS for the retransmission can be calculated as:

TBS for retransmission=TBS for initial transmission *AggressivenessFactor.

At block 130, the network node determines an MCS and a number of PRBs for the retransmission based on the TBS for the retransmission. For example, the TBS for the retransmission may be taken as an input to a Transmission Format Selection (TFS) to obtain the MCS and the number of PRBs for the retransmission.

In the uplink case, the network node can signal the MCS and the number of PRBs for the retransmission to the terminal device, such that the terminal device can use the signaling the MCS and the number of PRBs in the uplink retransmission towards the network. Alternatively, in the downlink case, the network node can also signal the MCS and the number of PRBs for the retransmission to the terminal device, and use the MCS and the number of PRBs in the downlink retransmission towards the terminal device.

In an example, the network node may further determine (e.g., in the uplink case, after soft combining of different RVs at Layer 1) or receive (e.g., in the downlink case) an HARQ NACK for the retransmission. Then, the network node can adjust the factor to form a further factor for a further retransmission, such that a TBS for the further retransmission as calculated by applying the further factor to the TBS for the initial transmission is closer to the TBS for the initial transmission than the TBS for the retransmission. That is, in the above pseudo codes, the value of AggressivenessFactor may be increased, e.g., by a value in the range of [0.05, 0.25] , such that the further retransmission would be less aggressive than the retransmission. In other words, if the feedback for the retransmission is still NACK, it may mean that the retransmission is too aggressive and AggressivenessFactor, and in turn the TBS, needs to be increased for the further retransmission. On the other hand, if the feedback for the retransmission is ACK, the HARQ retransmission is successful with reduced resource used.

With the above method, the number of PRBs used in retransmissions can be significantly reduced on average, thereby achieving improved spectral efficiency and cell throughput without substantial BLER degradation.

Fig. 2 is a flowchart illustrating a method 200 according to an embodiment of the present disclosure. The method 200 can be performed by a terminal device, e.g., a UE. The method 200 can be applied in uplink (when both initial transmission and retransmission are uplink transmissions) or downlink (when both initial transmission and retransmission are downlink transmissions) .

At block 210, the terminal device transmits or receives an HARQ NACK for an initial transmission. In particular, in the uplink case, i.e., when the initial transmission is an uplink transmission from the terminal device to a network node, the terminal device may receive an HARQ NACK from the network node as a feedback for the initial transmission. Alternatively, in the downlink case, i.e., when the initial transmission is a downlink transmission from a network node to the terminal device, the terminal device may transmit an HARQ NACK to the network node as a feedback for the initial transmission.

At block 220, the terminal device receives, from a network node, a configuration of an MCS and a number of PRBs for a retransmission associated with the initial transmission. Here, the MCS and the number of PRBs for the retransmission are determined based on a TBS for the retransmission that is smaller than a TBS for the initial transmission.

In an example, the TBS for the retransmission may be calculated based on a first RF condition when the initial transmission is carried out (e.g., “actual RF condition” as described above) and a second RF condition estimated for link adaptation for the initial transmission (e.g., “estimated RF condition” as described above) . For example, the first RF condition and the second RF condition may each be represented by an SINR. In particular, in the uplink case, the first condition may be an SINR measured at the network node, or in the downlink case, the first condition may be an SINR reported by the terminal device to the network node., e.g., in PUSCH.

For example, the TBS for the retransmission may be calculated by: calculating a factor, which is smaller than or equal to 1, based on the first RF condition and the second RF condition, and calculating the TBS for the retransmission by applying the factor to the TBS for the initial transmission.

In particular, the factor may be set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold. Alternatively, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold, the factor may be calculated based on a number of bits that are estimated to be missing in the initial transmission. Here, the number of bits that are estimated to be missing in the initial transmission may be estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per RE. For further details on the process for calculating the factor, reference can be made to the exemplary pseudo codes for calculating AggressivenessFactor as described above in connection with the method 100.

In an example, the terminal device may further transmit (e.g., in the downlink case) or receive (e.g., in the uplink case, after soft combining of different RVs at Layer 1) an HARQ NACK for the retransmission, and receive, from the network node, a configuration of a further MCS and a further number of PRBs for a further retransmission. Here, the MCS and the number of PRBs for the further retransmission may be determined based on a TBS for the further retransmission. The TBS for the further retransmission may be calculated by applying a further factor to the TBS for the initial transmission, such that the TBS for the further retransmission is closer to the TBS for the initial transmission than the TBS for the retransmission. That is, in the exemplary pseudo codes as described above in connection with the method 100, the value of A ggressivenessFactor may be increased, e.g., by a value in the range of [0.05, 0.25] , such that the further retransmission would be less aggressive than the retransmission. In other words, if the feedback for the retransmission is still NACK, it may mean that the retransmission is too aggressive and AggressivenessFactor, and in turn the TBS, needs to be increased for the further retransmission. On the other hand, if the feedback for the retransmission is ACK, the HARQ retransmission is successful with reduced resource used.

Correspondingly to the method 100 as described above, a network node is provided. Fig. 3 is a block diagram of a network node 300 according to an embodiment of the present disclosure. The network node 300 may be operative to perform the method 100 as described above in connection with Fig. 1.

As shown in Fig. 3, the network node 300 includes an HARQ unit 310 configured to determine or receive an HARQ NACK for an initial transmission. The network node 300 further includes a calculating unit 320 configured to calculate a TBS for a retransmission associated with the initial transmission, based on a TBS for the initial transmission. The network node 300 further includes a determining unit 330 configured to determine an MCS and a number of PRBs for the retransmission based on the TBS for the retransmission.

In an embodiment, the calculating unit 320 may be configured to: calculate a factor based on the first RF condition and the second RF condition, the factor being smaller than or equal to 1; and calculate the TBS for the retransmission by applying the factor to the TBS for the initial transmission.

In an embodiment, the HARQ unit 310 may be further configured to determine or receive an HARQ NACK for the retransmission. The calculating unit 320 may be further configured to adjust the factor to form a further factor for a further retransmission, such that a TBS for the further retransmission as calculated by applying the further factor to the TBS for the initial transmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

In an embodiment, when the initial transmission and the retransmission are uplink transmissions from a terminal device to the network node, the HARQ NACK for the initial transmission may be determined at the network node. The network node 300 may further include a transmitting unit configured to signal the MCS and the number of PRBs for the retransmission to the terminal device.

In an embodiment, when the initial transmission and the retransmission are downlink transmissions from the network node to a terminal device, the HARQ NACK for the initial transmission may be received from the terminal device. The network node 300 may further include a transmitting unit configured to signal the MCS and the number of PRBs for the retransmission to the terminal device.

The above units 310～330 can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro-processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component (s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in Fig. 1.

Fig. 4 is a block diagram of a network node 400 according to another embodiment of the present disclosure.

The network node 400 includes a transceiver 410, a processor 420 and a memory 430. The memory 430 contains instructions executable by the processor 420 whereby the network node 400 is operative to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 1. Particularly, the memory 430 contains instructions executable by the processor 420 whereby the network node 400 is operative to: determine or receive an HARQ NACK for an initial transmission; calculate a TBS for a retransmission associated with the initial transmission, based on a TBS for the initial transmission; and determine an MCS and a number of PRBs for the retransmission based on the TBS for the retransmission.

In an embodiment, the memory 430 may further contain instructions executable by the processor 420 whereby the network node 400 is operative to: determine or receive an HARQ NACK for the retransmission; and adjust the factor to form a further factor for a further retransmission, such that a TBS for the further retransmission as calculated by applying the further factor to the TBS for the initial transmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

In an embodiment, when the initial transmission and the retransmission are uplink transmissions from a terminal device to the network node, the HARQ NACK for the initial transmission may be determined at the network node. The memory 430 may further contain instructions executable by the processor 420 whereby the network node 400 is operative to: signal the MCS and the number of PRBs for the retransmission to the terminal device.

In an embodiment, when the initial transmission and the retransmission are downlink transmissions from the network node to a terminal device, the HARQ NACK for the initial transmission may be received from the terminal device. The memory 430 may further contain instructions executable by the processor 420 whereby the network node 400 is operative to: signal the MCS and the number of PRBs for the retransmission to the terminal device.

Correspondingly to the method 200 as described above, a terminal device is provided. Fig. 5 is a block diagram of a terminal device 500 according to an embodiment of the present disclosure. The terminal device 500 may be operative to perform the method 200 as described above in connection with Fig. 2.

As shown in Fig. 5, the terminal device 500 includes an HARQ unit 510 configured to transmit or receive an HARQ NACK for an initial transmission. The terminal device 500 further includes a receiving unit 520 configured to receive, from a network node, a configuration of an MCS and a number of PRBs for a retransmission associated with the initial transmission. The MCS and the number of PRBs for the retransmission are determined based on a TBS for the retransmission that is smaller than a TBS for the initial transmission.

In an embodiment, the HARQ unit 510 may be further configured to transmit or receive an HARQ NACK for the retransmission. The receiving unit 520 may be further configured to receive, from the network node, a configuration of a further MCS and a further number of PRBs for a further retransmission. The MCS and the number of PRBs for the further retransmission may be determined based on a TBS for the further retransmission. The TBS for the further retransmission may be calculated by applying a further factor to the TBS for the initial transmission, such that the TBS for the further retransmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

The above units 510～520 can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro-processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component (s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in Fig. 2.

Fig. 6 is a block diagram of a terminal device 600 according to another embodiment of the present disclosure.

The terminal device 600 includes a transceiver 610, a processor 620 and a memory 630. The memory 630 contains instructions executable by the processor 620 whereby the terminal device 600 is operative to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 2. Particularly, the memory 630 contains instructions executable by the processor 620 whereby the terminal device 600 is operative to: transmit or receive an HARQ NACK for an initial transmission; and receive, from a network node, a configuration of an MCS and a number of PRBs for a retransmission associated with the initial transmission. The MCS and the number of PRBs for the retransmission are determined based on a TBS for the retransmission that is smaller than a TBS for the initial transmission.

In an embodiment, the memory 630 may further contain instructions executable by the processor 620 whereby the terminal device 600 is operative to: transmit or receive an HARQ NACK for the retransmission; and receive, from the network node, a configuration of a further MCS and a further number of PRBs for a further retransmission. The MCS and the number of PRBs for the further retransmission may be determined based on a TBS for the further retransmission. The TBS for the further retransmission may be calculated by applying a further factor to the TBS for the initial transmission, such that the TBS for the further retransmission is closer to the TBS for the initial transmission than the TBS for the retransmission.

The present disclosure also provides at least one computer program product in the form of a non-volatile or volatile memory, e.g., a non-transitory computer readable storage medium, an Electrically Erasable Programmable Read-Only Memory (EEPROM) , a flash memory and a hard drive. The computer program product includes a computer program. The computer program includes: code/computer readable instructions, which when executed by the processor 420 causes the network node 400 to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 1; or code/computer readable instructions, which when executed by the processor 620 causes the terminal device 600 to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 2.

The computer program product may be configured as a computer program code structured in computer program modules. The computer program modules could essentially perform the actions of the flow illustrated in Fig. 1 or 2.

The processor may be a single CPU (Central Processing Unit) , but could also comprise two or more processing units. For example, the processor may include general purpose microprocessors; instruction set processors and/or related chips sets and/or special purpose microprocessors such as Application Specific Integrated Circuits (ASICs) . The processor may also comprise board memory for caching purposes. The computer program may be carried by a computer program product connected to the processor. The computer program product may comprise a non-transitory computer readable storage medium on which the computer program is stored. For example, the computer program product may be a flash memory, a Random-Access Memory (RAM) , a Read-Only Memory (ROM) , or an EEPROM, and the computer program modules described above could in alternative embodiments be distributed on different computer program products in the form of memories.

With reference to Fig. 7, in accordance with an embodiment, a communication system includes a telecommunication network 710, such as a 3GPP-type cellular network, which comprises an access network 711, such as a radio access network, and a core network 714. The access network 711 comprises a plurality of

base stations

712a, 712b, 712c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a

corresponding coverage area

713a, 713b, 713c. Each

base station

712a, 712b, 712c is connectable to the core network 714 over a wired or wireless connection 715. A first user equipment (UE) 771 located in coverage area 713c is configured to wirelessly connect to, or be paged by, the corresponding base station 712c. A second UE 772 in coverage area 713a is wirelessly connectable to the corresponding base station 712a. While a plurality of

UEs

771, 772 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 712.

The telecommunication network 710 is itself connected to a host computer 730, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 730 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The

connections

721, 722 between the telecommunication network 710 and the host computer 730 may extend directly from the core network 714 to the host computer 730 or may go via an optional intermediate network 720. The intermediate network 720 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 720, if any, may be a backbone network or the Internet; in particular, the intermediate network 720 may comprise two or more sub-networks (not shown) .

The communication system of Fig. 7 as a whole enables connectivity between one of the connected

UEs

771, 772 and the host computer 730. The connectivity may be described as an over-the-top (OTT) connection 750. The host computer 730 and the connected

UEs

771, 772 are configured to communicate data and/or signaling via the OTT connection 750, using the access network 711, the core network 714, any intermediate network 720 and possible further infrastructure (not shown) as intermediaries. The OTT connection 750 may be transparent in the sense that the participating communication devices through which the OTT connection 750 passes are unaware of routing of uplink and downlink communications. For example, a base station 712 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 730 to be forwarded (e.g., handed over) to a connected UE 771. Similarly, the base station 712 need not be aware of the future routing of an outgoing uplink communication originating from the UE 771 towards the host computer 730.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to Fig. 8. In a communication system 800, a host computer 810 comprises hardware 815 including a communication interface 816 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 800. The host computer 810 further comprises processing circuitry 818, which may have storage and/or processing capabilities. In particular, the processing circuitry 818 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 810 further comprises software 811, which is stored in or accessible by the host computer 810 and executable by the processing circuitry 818. The software 811 includes a host application 812. The host application 812 may be operable to provide a service to a remote user, such as a UE 830 connecting via an OTT connection 850 terminating at the UE 830 and the host computer 810. In providing the service to the remote user, the host application 812 may provide user data which is transmitted using the OTT connection 850.

The communication system 800 further includes a base station 820 provided in a telecommunication system and comprising hardware 825 enabling it to communicate with the host computer 810 and with the UE 830. The hardware 825 may include a communication interface 826 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 800, as well as a radio interface 827 for setting up and maintaining at least a wireless connection 870 with a UE 830 located in a coverage area (not shown in Fig. 8) served by the base station 820. The communication interface 826 may be configured to facilitate a connection 860 to the host computer 810. The connection 860 may be direct or it may pass through a core network (not shown in Fig. 8) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 825 of the base station 820 further includes processing circuitry 828, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 820 further has software 821 stored internally or accessible via an external connection.

The communication system 800 further includes the UE 830 already referred to. Its hardware 835 may include a radio interface 837 configured to set up and maintain a wireless connection 870 with a base station serving a coverage area in which the UE 830 is currently located. The hardware 835 of the UE 830 further includes processing circuitry 838, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE 830 further comprises software 831, which is stored in or accessible by the UE 830 and executable by the processing circuitry 838. The software 831 includes a client application 832. The client application 832 may be operable to provide a service to a human or non-human user via the UE 830, with the support of the host computer 810. In the host computer 810, an executing host application 812 may communicate with the executing client application 832 via the OTT connection 850 terminating at the UE 830 and the host computer 810. In providing the service to the user, the client application 832 may receive request data from the host application 812 and provide user data in response to the request data. The OTT connection 850 may transfer both the request data and the user data. The client application 832 may interact with the user to generate the user data that it provides.

It is noted that the host computer 810, base station 820 and UE 830 illustrated in Fig. 8 may be identical to the host computer 730, one of the

base stations

712a, 712b, 712c and one of the

UEs

771, 772 of Fig. 7, respectively. This is to say, the inner workings of these entities may be as shown in Fig. 8 and independently, the surrounding network topology may be that of Fig. 7.

In Fig. 8, the OTT connection 850 has been drawn abstractly to illustrate the communication between the host computer 810 and the use equipment 830 via the base station 820, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 830 or from the service provider operating the host computer 810, or both. While the OTT connection 850 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network) .

The wireless connection 870 between the UE 830 and the base station 820 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 830 using the OTT connection 850, in which the wireless connection 870 forms the last segment. More precisely, the teachings of these embodiments may improve the spectral efficiency and system throughput, and thereby provide benefits such as reduced user waiting time.

A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 850 between the host computer 810 and UE 830, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 850 may be implemented in the software 811 of the host computer 810 or in the software 831 of the UE 830, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 850 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which

software

811, 831 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 850 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station 820, and it may be unknown or imperceptible to the base station 820. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer’s 810 measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the

software

811, 831 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 850 while it monitors propagation times, errors etc.

Fig. 9 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 7 and 8. For simplicity of the present disclosure, only drawing references to Fig. 9 will be included in this section. In a first step 910 of the method, the host computer provides user data. In an optional substep 911 of the first step 910, the host computer provides the user data by executing a host application. In a second step 920, the host computer initiates a transmission carrying the user data to the UE. In an optional third step 930, the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth step 940, the UE executes a client application associated with the host application executed by the host computer.

Fig. 10 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 7 and 8. For simplicity of the present disclosure, only drawing references to Fig. 10 will be included in this section. In a first step 1010 of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In a second step 1020, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step 1030, the UE receives the user data carried in the transmission.

Fig. 11 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 7 and 8. For simplicity of the present disclosure, only drawing references to Fig. 11 will be included in this section. In an optional first step 1110 of the method, the UE receives input data provided by the host computer. Additionally or alternatively, in an optional second step 1120, the UE provides user data. In an optional substep 1121 of the second step 1120, the UE provides the user data by executing a client application. In a further optional substep 1111 of the first step 1110, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in an optional third substep 1130, transmission of the user data to the host computer. In a fourth step 1140 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

Fig. 12 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 7 and 8. For simplicity of the present disclosure, only drawing references to Fig. 12 will be included in this section. In an optional first step 1210 of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In an optional second step 1220, the base station initiates transmission of the received user data to the host computer. In a third step 1230, the host computer receives the user data carried in the transmission initiated by the base station.

The disclosure has been described above with reference to embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the disclosure. Therefore, the scope of the disclosure is not limited to the above particular embodiments but only defined by the claims as attached.

Claims

A method (100) in a network node, comprising:

determining or receiving (110) a Hybrid Automatic Repeat reQuest, HARQ, Negative Acknowledgement, NACK, for an initial transmission;

calculating (120) a Transport Block Size, TBS, for a retransmission associated with the initial transmission, based on a TBS for the initial transmission; and

determining (130) a Modulation and Coding Scheme, MCS, and a number of Physical Resource Blocks, PRBs, for the retransmission based on the TBS for the retransmission.
The method (100) of claim 1, wherein the TBS for the retransmission is calculated based on a first Radio Frequency, RF, condition when the initial transmission is carried out and a second RF condition estimated for link adaptation for the initial transmission.
The method (100) of claim 2, wherein said calculating comprises:

calculating a factor based on the first RF condition and the second RF condition, the factor being smaller than or equal to 1; and

calculating the TBS for the retransmission by applying the factor to the TBS for the initial transmission.
The method (100) of claim 3, wherein

the factor is set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold,

the factor is calculated based on a number of bits that are estimated to be missing in the initial transmission, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold, or

the factor is set to 1 when the first RF condition is lower than the second RF condition by more than the second threshold.
The method (100) of claim 4, wherein the number of bits is estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per Resource Element, RE.
The method (100) of any of claims 3-5, further comprising:

determining or receiving an HARQ NACK for the retransmission; and

adjusting the factor to form a further factor for a further retransmission, such that a TBS for the further retransmission as calculated by applying the further factor to the TBS for the initial transmission is closer to the TBS for the initial transmission than the TBS for the retransmission.
The method (100) of any of claims 2-6, wherein the first RF condition and the second RF condition are each represented by a Signal-to-Interference-plus-Noise Ratio, SINR.
The method (100) of claim 7, wherein

when the initial transmission is an uplink transmission from a terminal device to the network node, the first condition is an SINR measured at the network node, or

when the initial transmission is a downlink transmission from the network node to a terminal device, the first condition is an SINR reported by the terminal device to the network node.
The method (100) of any of claims 1-8, wherein, when the initial transmission and the retransmission are uplink transmissions from a terminal device to the network node, the HARQ NACK for the initial transmission is determined at the network node, and the method further comprises:

signaling the MCS and the number of PRBs for the retransmission to the terminal device.
The method (100) of any of claims 1-8, wherein, when the initial transmission and the retransmission are downlink transmissions from the network node to a terminal device, the HARQ NACK for the initial transmission is received from the terminal device, and the method further comprises:

signaling the MCS and the number of PRBs for the retransmission to the terminal device.
A method (200) in a terminal device, comprising:

transmitting or receiving (210) a Hybrid Automatic Repeat reQuest, HARQ, Negative Acknowledgement, NACK, for an initial transmission; and

receiving (220) , from a network node, a configuration of a Modulation and Coding Scheme, MCS, and a number of Physical Resource Blocks, PRBs, for a retransmission associated with the initial transmission,

wherein the MCS and the number of PRBs for the retransmission are determined based on a Transport Block Size, TBS, for the retransmission that is smaller than a TBS for the initial transmission.
The method (200) of claim 11, wherein the TBS for the retransmission is calculated based on a first Radio Frequency, RF, condition when the initial transmission is carried out and a second RF condition estimated for link adaptation for the initial transmission.
The method (200) of claim 12, wherein the TBS for the retransmission is calculated by:

calculating a factor based on the first RF condition and the second RF condition, the factor being smaller than 1; and

calculating the TBS for the retransmission by applying the factor to the TBS for the initial transmission.
The method (200) of claim 13, wherein

the factor is set to a configurable value smaller than 1 when the first RF condition is higher than the second RF condition by at least a first threshold, or

the factor is calculated based on a number of bits that are estimated to be missing in the initial transmission, when the first RF condition is higher than the second RF condition by less than the first threshold, equal to the second RF condition, or lower than the second RF condition by at most a second threshold.
The method (200) of claim 14, wherein the number of bits is estimated based on a mapping between RF conditions and numbers of bits that can be transmitted per Resource Element, RE.
The method (200) of any of claims 13-15, further comprising:

transmitting or receiving an HARQ NACK for the retransmission; and

receiving, from the network node, a configuration of a further MCS and a further number of PRBs for a further retransmission,

wherein the MCS and the number of PRBs for the further retransmission are determined based on a TBS for the further retransmission, the TBS for the further retransmission being calculated by applying a further factor to the TBS for the initial transmission, such that the TBS for the further retransmission is closer to the TBS for the initial transmission than the TBS for the retransmission.
The method (200) of any of claims 12-16, wherein the first RF condition and the second RF condition are each represented by a Signal-to-Interference-plus-Noise Ratio, SINR.
The method (200) of claim 17, wherein

when the initial transmission is an uplink transmission from the terminal device to the network node, the first condition is an SINR measured at the network node, or

when the initial transmission is a downlink transmission from the network node to the terminal device, the first condition is an SINR reported by the terminal device to the network node.
The method (200) of any of claims 11-18, wherein, when the initial transmission is an uplink transmission from the terminal device to the network node, the HARQ NACK for the initial transmission is received from the network node.
The method (200) of any of claims 11-18, wherein, when the initial transmission is a downlink transmission from the network node to the terminal device, the HARQ NACK for the initial transmission is transmitted to the network node.
A network node (400) , comprising a transceiver (410) , a processor (420) , and a memory (430) , the memory (430) comprising instructions executable by the processor (420) whereby the network node (400) is operative to perform the method according to any of claims 1-10.
A computer readable storage medium having computer program instructions stored thereon, the computer program instructions, when executed by a processor in a network node, causing the network node to perform the method according to any of claims 1-10.
A terminal device (600) , comprising a transceiver (610) , a processor (620) , and a memory (630) , the memory (630) comprising instructions executable by the processor (620) whereby the terminal device (600) is operative to perform the method according to any of claims 11-20.
A computer readable storage medium having computer program instructions stored thereon, the computer program instructions, when executed by a processor in a terminal device, causing the terminal device to perform the method according to any of claims 11-20.