WO2018189416A1

WO2018189416A1 - Backwards feedback bundling

Info

Publication number: WO2018189416A1
Application number: PCT/FI2017/050280
Authority: WO
Inventors: Saeed Reza KHOSRAVIRAD
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2017-04-13
Filing date: 2017-04-13
Publication date: 2018-10-18
Anticipated expiration: 2019-10-13

Abstract

There is provided a method in a wireless communication system, the method comprising: transmitting, by a first apparatus, at least a first data packet and a second data packet to a second apparatus of the wireless communication system, wherein a given data packet is added to an active data packet set if the given data packet is transmitted for a first time; receiving a bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative-acknowledgement of at least one of the data packets of the active data packet set; requiring reception of at least two separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received by the second apparatus; removing said data packet from the active data packet set in response to regarding said data packet as successfully received.

Description

BACKWARDS FEEDBACK BUNDLING

TECHNICAL FIELD

The invention relates to communications. More particularly, the present invention relates to increasing retransmission protocol reliability in unreliable feedback channel conditions.

BACKGROUND

In a communication network, such as a wireless communication network, data may transmitted using a transmission process (e.g. Automatic Repeat Request (AROJ or Hybrid ARQ (HARQ)), wherein transmitted data is acknowledged (ACK) or negatively- acknowledged (NACK) by an intended receiver. Reliability of a channel (i.e. feedback channel) used to transmit ACKs and/or NACKs may have an effect on effectiveness of the transmission process. Hence, it may be beneficial to provide solutions for enhancing transmission process effectiveness by reducing an effect of poor reliability of the feedback channel. BRIEF DESCRIPTION

According to an aspect, there is provided the subject matter of the independent claims. Some embodiments are defined in the dependent claims.

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

In the following embodiments will be described in greater detail with reference to the attached drawings, in which

Figure 1 illustrates an example a wireless communication system to which embodiments of the invention may be applied;

Figure 2 illustrates a transmission process utilizing ACK/NACK to which the embodiments of the invention may be applied;

Figures 3A and 3B illustrate a flow diagrams according to some embodiments;

Figures 4A to 4E illustrate some embodiments;

Figure 5A to 5B illustrates some embodiments;

Figure 5C illustrates a signal diagram according to some embodiments;

Figures 6A to 6C illustrate some embodiments;

Figures 7A to 7B illustrate some embodiments;

Figures 8 to 9 illustrate some embodiments; and

Figures 10 to 11 illustrate block diagrams of apparatuses according to some embodiments of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are exemplifying. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

Embodiments described may be implemented in a radio system, such as in at least one of the following: Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced (LTE-A), and/or Wireless Local Area Network (WLAN), which is sometimes referred to as WiFi.

The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties. Another example of a suitable communications system is the 5G concept. 5G is likely to use multiple input - multiple output (MIMO) techniques (e.g. antennas), many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. 5G will likely be comprised of more than one radio access technology (RAT), each optimized for certain use cases and/or spectrum. 5G mobile communications will have a wider range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, including vehicular safety, different sensors and realtime control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integradable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cm Wave, below 6GHz - cm Wave - mm Wave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility. However, as described, the presented solution may not be restricted to the system or systems given as example, and thus may be applicable to any system in which feedback information is provided in response to transmitting data. Hence, in principal the present solution may be applicable to wired networks too.

Figure 1 illustrates example of a wireless communication system (also referred to as a cellular communication system) to which embodiments of the invention may be applied. Wireless communication networks (also referred to as cellular communication networks), such as the Long Term Evolution (LTE), the LTE-Advanced (LTE-A) of the 3^rd Generation Partnership Project (3GPP), or the predicted future 5G solutions, are typically composed of at least one network element, such as a network element 102, providing a cell 104. The system may comprise more than one network element 102 and/or each network element may provide one or more cells.

Each cell of the wireless communication network may be, e.g., a macro cell, a micro cell, a femto, or a pico-cell, for example. Each of the network elements of the radio communication network, such as the network element 102 may be an evolved Node B (eNB) as in the LTE and LTE-A, a radio network controller (RNC) as in the UMTS, a base station controller (BSC) as in the GSM/GERAN, or any other apparatus capable of controlling radio communication and managing radio resources within a cell. For 5G solutions, the implementation may be similar to LTE-A, as described above. The network elements 102 may be base station(s) or a small base station(s), for example. In the case of multiple eNBs in the communication network, the eNBs may be connected to each other with an X2 interface as specified in the LTE. Other communication methods between the network elements may also be possible, for example, in case the system relies on different technique than LTE (e.g. 5G may possibly use some other interface than X2 interface). At least some of the network elements 102 may be further connected via an SI interface to an evolved packet core, more specifically to a mobility management entity (MME) and to a system architecture evolution gateway (SAE-GW) (i.e. connected to core network 190).

It is further possible that the system of Figure 1 comprises one or more small cells, such as pico cells or femto cells, wherein the small cells are controlled by the network element 102.

The cells of the system may provide service for at least one terminal device 110, 120, 130, 140, wherein the at least one terminal device 110, 120, 130, 140 may be located within or comprised in at least one of the cells. The at least one terminal device 110, 120, 130, 140 may communicate with the network elements (e.g. 102) using communication link(s) 112, 122, which may be understood as communication link(s) for end-to-end communication, wherein source device transmits data to the destination device.

In an embodiment, the at least one terminal device 110, 120, 130, 140 is able to communicate with other similar devices via the network element 102. For example, a first terminal device 110 may transmit data via the network element 102 to a third terminal device 130. The other devices may be within the cell 104 and/or may be within other cells provided by other network elements. The at least one terminal device 110, 120, 130, 140 may be stationary or on the move. In an embodiment, the at least one terminal device 110, 120, 130, 140 may communicate directly with other terminal devices using, for example, Device-to-Device (D2D) communication. Such communication is indicated with link 114 in Figure 1.

The at least one terminal device 110, 120, 130, 140 may comprise mobile phones, smart phones, tablet computers, laptops and other devices used for user communication with the wireless communication network. Further, the at least one terminal device 110, 120, 130, 140 may also comprise Machine Type Communication (MTC) capable devices, such as sensor devices providing sensor data, such as position, acceleration and/or temperature information, to name a few examples. That said, the wireless communication network of Figure 1 may comprise different types of devices (e.g. phones, laptops, tablets, MTC devices) and communication methods (e.g. CA, DC). The amount of devices and data transfer requirements may increase burden of the radio communication network. The Internet of Things (IoT) may even further increase the amount of devices within the radio communication network.

Retransmission techniques, such as ARQ in the Radio Link Control (RLC) layer or HARQ in the lower Media Access Control (MAC) and Physical (PHY) layer, may be used in a transmission process of one or more data packets. If HARQ is utilized, such transmission process may be referred to as HARQ process, or if ARQ is utilized, such transmission process may be referred to as ARQ process. However, in general, such transmission process may be simply referred to as retransmission process, although it is noted that retransmission may only occur if it is determined necessary by the transmitter device or node. Such retransmission process may add to the robustness of the transmission and may increase the throughput of the logical channel which may be used to transmit the data packet. Note that ACKs and/or NACKs may be transmitted via a different logical channel (e.g. feedback channel). As known in the art, different logical channels may use same physical resources and/or channels.

Figure 2 illustrates one example of retransmission process, such as a HARQ process. Referring to Figure 2, five different transmit occasions 202 are shown in the upper row and corresponding feedback occasions 204 are shown below the respective transmit occasion. Let us assume that a data packet is transmitted in each transmit occasion. Round Trip Time (RTT) 210 may denote time between transmitting two consecutive data packets (different data packets or the same data packet) In the first transmit occasion a first data packet (indicated with number 1) is transmitted and the transmitter then receives an ACK for the first data packet. The ACK indicates to the transmitter (e.g. transmitter node) that the first data packet is successfully received by the target receiver (e.g. receiver node). It needs to be noted at this point that receiver and transmitter may be network nodes, such as terminal devices or network elements (e.g. eNBs, base stations, and/or RNCs and the like).

The process may then continue to transmitting a second packet (indicated with number 2) for which another ACK is received. However, for a third data packet (indicated with number 3), the transmitter may receive a NACK (indicated as dotted block). For the transmitter this may mean that it considers the third packet unsuccessfully received by the receiver. Hence, it will perform a retransmission (indicated with cross lines) of the third packet. Accordingly, in this example, once an ACK is received for the retransmitted third packet, the process may continue. E.g. the transmitter may transmit a fourth packet and so on, until the transmission process comes to an end. However, at least in the context of ultrareliable communication, the current retransmission approach, such as HARQ process, can be unreliable due to the unreliability of the feedback channel where increasing the reliability of feedback could be inefficient and costly. That is, the ACKs and/or NACKs can be observed by the receiver differently than the receiver transmits the ACKs and/or NACKS. For example, transmitted ACK may be corrupted and may thus be observed as NACK at the transmitter. Similar logic applies to transmitted NACK which may be observed as ACK. Such situations may occur due to feedback channel conditions and may be referred to as corrupted detection of feedback message (e.g. ACK is transmitted and is detected as NACK, or vice versa). For example, ACK/NACK may be indicated with a one bit indicator (i.e. 0 or 1), wherein the ACK is indicated by setting the one bit indicator to 1 and the NACK is indicated with 0. Hence, the one bit indicator may be corrupted, for example, during transmission such that 0 turns into 1 or 1 turns into 0. Such may, for example, happen if demodulation of the one bit indicator fails because of deteriorated feedback channel conditions.

Thus, the feedback transmission may not be fully robust; meaning that even in systems like LTE where repetition coding of high order is used for a secure feedback transmission, corrupted or erroneous detection of ACK/NACK may occur which can potentially result in misleading a network element (e.g. base station) and increasing delivery latency of a packet. Such problem may reduced by specifying higher order of repetition coding for feedback. However, feedback transmission duration may depend on the coverage situation of the terminal device (sometimes referred to as User Equipment (UE)) and may vary from one Orthogonal Frequency Division Multiplexing (OFDM) symbol duration to larger values of e.g., 1 ms continuous uplink (UL) transmission. Therefore, normal solutions to increase feedback channel reliability are too costly. Particularly, for the case of massive MTC (mMTC) type of UEs envisioned in the emerging 5G networks, the critical battery life time of the UE may call for less signaling overhead and less energy consumption per signaling occasion. Thus, it may be more favorable to reduce energy consumption of the feedback channel while keeping up the reliability of the retransmission process (e.g. HARQ process)

Data packet delivery reliability may depend on the reliability of the feedback channel (i.e. how reliable the transmitted feedback messages are). For instance with feedback reliability of 0.001, it may not possible to reach packet delivery reliability of typical Block Error Rate (BLER) targets of 0.1-0.2. Increasing number of ACKs for a data packet may increase the reliability of the data packet delivery. Hence, there is provided a solution for increasing said reliability by requiring more than one independently received ACK for a transmitted data packet. In order to make such efficient (e.g. reduce need for costly reliability increase of the feedback channel itself), the solution utilizes a bundled feedback of which details are discussed below.

Figures 3A and 3B illustrate flow diagrams according to some embodiments. Referring to Figure 3A, a method in a wireless communication system (e.g. system of Figure 1) is illustrated, wherein the method comprises: transmitting, by a first apparatus of the wireless communication system, at least a first data packet and a second data packet to a second apparatus of the wireless communication system, wherein a given data packet is added to an active data packet set if the given data packet is transmitted for a first time (block 302); receiving, by the first apparatus from the second apparatus, a bundled feedback message associated with reception of said active data packet set, the bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative-acknowledgement of at least one of the data packets of the active data packet set (block 304); requiring, by the first apparatus, reception of at least a predetermined number of separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received by the second apparatus, said predetermined number being at least two (block 306); and removing said data packet from the active data packet set in response to regarding said data packet as successfully received (block 308).

Referring to Figure 3B, a method in a wireless communication system (e.g. system of Figure 1) is illustrated, wherein the method comprises: acquiring, by a second apparatus of the wireless communication system, a parameter indicating a predetermined number of data packets to be acknowledged or negatively-acknowledged using a single bundled feedback message, said predetermined number being at least two (block 310); initiating reception of a plurality of data packets from a first apparatus of the wireless communication system (block 312); denoting said predetermined number of data packets of the plurality of data packets as data packets of an active data packet set (block 314); for each data packet of the active data packet set, determining, by the second apparatus, whether the data packet is successfully or unsuccessfully received (block 316); in response to determining that at least one data packet of said active data packet set is unsuccessfully received, generating a bundled feedback message indicating negative-acknowledgement, or generating a bundled feedback message indicating acknowledgement if each data packet of said active data packet set is successfully received (step 318). Further, the second apparatus may further transmit the generated bundled feedback message (step 320).

The first apparatus referred to in both Figures 3A-B may be a transmitter node or a part of the transmitter node. For example, the first apparatus may be or be comprised in a terminal device or a network element. The second apparatus may be a receiver node. For example, the second apparatus may be or be comprised in a terminal device or a network element. Hence, Figure 3A may illustrate method steps in the transmitter node that transmits a plurality of data packets to the receiver node that may perform the steps of Figure 3B.

Let us then look closer on some embodiments of the proposed solution. Figures 4A to 4E illustrate some of such embodiments. In more detail, Figures 4A to 4E illustrate how the bundling of feedback messages may be performed in different situations and with different parameter values according to the provided solution. Specifically, the situation described with respect to Figure 2 may be enhanced. As already described, the presented solution suggests backward bundling of feedback in a retransmission process (e.g. HARQ) to increase the reliability of the retransmission operation. Such a mechanism may, for example, be used in unreliable feedback channel scenarios in order to increase the reliability of packet delivery without the need for costly reliability increasing over the feedback channel itself. The invention may be applicable to any type of stop-and-wait (SAW) retransmission process. Although, HARQ process is used as one example of SAW process, it needs to be noted that such is done purely for keeping the disclosure simple. However, in certain cases, the provided solution may provide further benefits especially for HARQ process.

Referring to Figure 4A, a scenario where only ACKs are received is shown. That is, as in Figure 2, there may be five different transmit occasions 202 (each now indicated with reference signs 401-405) and five feedback occasions, wherein one feedback occasion is associated with one transmit occasion 401-405. I.e. there is a corresponding feedback occasion 204 for each transmit occasion 202. More particularly, during each transmit occasion 401-405 a data packet may be transmitted by the transmitter node (e.g. the first apparatus) to the receiver node (e.g. the second apparatus). It is noted that hereinafter transmitter node and receiver node may refer to the first apparatus and second apparatus respectively. Even more precisely, after each transmit occasion, the associated or corresponding feedback occasion may follow. Thus, the feedback occasions may actually be situated between the transmit occasions (in time versa), but for simplicity reasons are indicated below the corresponding transmit occasion. Two times independent reception of ACK may increase the certainty of the packet delivery to the desired threshold, as discussed above. Number of independent reception times may be referred to as parameter F or simply F. F may denote number of separate feedback messages required to indicate ACK for a data packet in order to regard said data packet as successfully received. As described, F may be two or more, for example.

Referring to Figure 4A, the transmitter node may start transmission process by transmitting a first data packet at transmit occasion 401. At the corresponding feedback occasion, a feedback message may be received, wherein the feedback message indicates ACK or NACK of said first data packet. In this example, the feedback message indicates ACK, and thus the transmitter node may continue to transmit a second data packet (i.e. the next data packet) at the next transmit occasion 402. As the transmitter node has now transmitted two data packets, the receiver node may determine, based on parameter F, that the next feedback message should be a bundled feedback message indicating ACK or NACK for both the first and second data packets. In this example, the bundled feedback message may indicate ACK denoting successful reception of both the first and second data packets. As discussed, the feedback message may be corrupted on the way. Hence, it needs to be understood that perception about ACK or NACK may be different at the transmitter and at the receiver.

When the bundled feedback message indicates ACK, it may denote that all data packets of an active data packet set are successfully received. At this point, the active data packet set may need to be further discussed. The active data packet set may be maintained by the transmitter node and by the receiver node respectively. At the transmitter node, a data packet may be added or included in the active data packet set when or if the data packet is transmitted for the first time. The first time may refer to a transmission for first time during the current transmission process. E.g. the data packet is transmitted for the first time during the current HARQ process. For example, in Figure 4A, the transmission process may start by transmitting the first data packet. In response to transmitting the first data packet, said data packet may be added to the active data packet set. Hence, as the first data packet is the only member of the active data packet set, the first feedback message may indicate ACK only for the first data packet. However, when the second data packet is transmitted for the first time, the second data packet may be added to the active data packet set. Hence, the next feedback message may be a bundled feedback message indicating ACK for all data packets of the active data packet set (i.e. the first and second data packets in this specific example). Situation in case of NACK is discussed later with reference to Figure 4B. The maximum number of packets included in the active packet set may be restricted by the parameter F.

Still referring to Figure 4A, a reference sign 412 may denote ACK counter for the first data packet, a reference sign 422 may denote ACK counter for the second data packet, a reference sign 432 may denote ACK counter for a third data packet, a reference sign 442 may denote ACK counter for a fourth data packet, and a reference sign 452 may denote ACK counter for a fifth data packet. As an ACK (either unbundled or bundled) is received concerning a data packet, the respective counter may be increased.

A reference sign 414 may denote transmission counter (also referred to as

ReTX counter) for the first data packet, a reference sign 424 may denote transmission counter for the second data packet, a reference sign 434 may denote transmission counter for the third data packet, a reference sign 444 may denote transmission counter for the fourth data packet, and a reference sign 454 may denote transmission counter for the fifth data packet. Each time a data packet is transmitted, its respective transmission counter may be increased. This is clearly illustrated in Figure 4A, for example.

It also needs to be noted that, similar to Figure 2, the first data packet transmitted at transmit occasion 401 is indicated with number 1, the second data packet transmitted at transmit occasion 402 is indicated with number 2, and so on. I.e. each number may correspond to a certain data packet.

So, after a second feedback occasion which may follow the second transmit occasion 402, the received bundled feedback message may increase ACK counters 412, 422. After each received ACK indicating feedback message, the transmitter node may continue on by transmitting the next data packet, i.e. the third data packet. Naturally, a further bundled feedback message may be received, wherein said further bundled feedback message may indicate ACK of all data packets of the active data packet set. Let's bear in mind that in this particular example, the size of the active data packet set may be two data packets. Hence, after the bundled feedback message received in response to transmitting the second data packet, the ACK counter for the first data packet may rise to two, and thus the first data packet may be removed from said active data packet set. This may mean that the first data packet is then regarded as successfully received. Similarly, after said further bundled feedback message, second data packet's ACK counter 422 becomes two and thus it may also be removed from said active data packet set. As the received feedback message indicated ACK for second and third data packets, the transmitter node may yet again transmit the next data packet (i.e. the fourth data packet). If again (as shown in Figure 4A), a bundled ACK is received, the process may continue to transmitting the fifth data packet. Furthermore, the third data packet may be removed from the active data packet set and the fifth data packet added. Hence, the next bundled feedback message may be associated with the fourth and fifth data packets. Although five data packets are illustrated, the described method is applicable to virtually any number of data packets.

In an embodiment, upon regarding a data packet as successfully received by the receiver node, the transmitter node removes said data packet from a transmit buffer of the transmitter node. That is, in addition to removing the data packet from the active data packet set, the data packet may be removed from said transmit buffer when/if F number of ACKs (either bundled or unbundled) are received regarding said data packet.

In an embodiment, as already described above in various examples, said parameter F further indicates a maximum number of data packets in the active data packet set. Hence, the bundled feedback message may be associated with said maximum number of data packets. In other words, the bundled feedback message may be associated with the active data packet set which size may be determined by the parameter F.

It is also noted that the active data packet set may be maintained individually by the receiver node in the same manner as it may be maintained at the transmitter node. I.e. both the transmitter and receiver nodes may follow the same algorithm (e.g. computer algorithm) that determines how the active data packet is maintained. Hence, both may maintain similar active data packet sets that correspond to each other. It is further noted that the active data packet set may be understood as a virtual group comprising one or more data packets or one or more indications of one or more data packets. Hence, even if a data packet is not successfully received, it (or its indication) may be added to the active data packet set. So in a way, the active data packet set may indicate state of the data packet or packets in the set.

Bundling of multiple acknowledgements (i.e. bundled feedback message) may mean that the feedback message only indicates ACK if all the bundled feedbacks are ACK. For example, if the first data packet successfully received and the second data packet is successfully received, both could be indicated as separate ACKs (e.g. two separate one-bit indicators). However, in the present solution, both ACKs may be indicated with only one ACK (e.g. only one one-bit indicator) . If at least one of the two is NACK (i.e. not successfully received), the bundled feedback message may indicated NACK. So, for example, in scenarios where F = 3 or 4, it may suffice that only one of the three or four data packets in an active data packet set is unsuccessfully received to cause the receiver node to transmit a bundled feedback message indicating NACK.

The feedback bundling (e.g. backward feedback bundling) may comprise storing, by the transmitted node, the previously reported ACK feedback message (s) regarding a data packet until said data packet is ACKed at least F times using the feedback messages (either bundled or unbundled (i.e. ACK or NACK only for one data packet)). The previously stored ACK information about the data packet may be discarded after receiving ACK for F times concerning said data packet. The data packet may also be stored by the receiving node in the data buffers (e.g. HARQ buffer) for the cases where retransmission of the packet will be needed later on in order to be used in data combining. For example, HARQ process may utilize redundancy versions of a data packet. Hence, the proposed solution may also be applicable to retransmitting only a part of a data packet. Further, any type of retransmission process (e.g. HARQ operation) may start at some point in time with the first data packet. Thus, the first feedback occasion may not have a previous feedback to be bundled with and may thus be transmitted individually (as shown in Figures 4A and 4B, for example).

In an embodiment, the received bundled feedback message (e.g. in block 304) is one of the required at least two separate feedback messages. That is, for example, one of the required separate feedback message may be an unbundled message and one may be a bundled message.

In an embodiment, in response to receiving the bundled feedback message indicating acknowledgement, transmitting, by the transmitter node, a next data packet in a next transmit occasion; and including said next data packet to the active data packet set. Examples of this were discussed with reference to Figure 4A above. E.g. after receiving the bundled ACK after transmitting the second data packet, the transmitter node may remove the first data packet from the active data packet set (i.e. at least F number of ACKs received for the first data packet) and include the third data packet to the active data packet set. Further, in an embodiment, the transmitter node initiates reception of a further bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative-acknowledgement of at least one of the data packets of the active data packet set. In the example of Figure 4A, the bundled ACK is received after transmitting the second data packet. Hence, transmitting the third packet may follow. However, in the example of Figure 4B, the bundled feedback message received after transmitting the second data packet for the first time (i.e. at transmit occasion 402) may indicate NACK. Hence, the next transmitted data packet may not be the third data packet, but the second data packet or the first data packet (i.e. one of the previously transmitted data packets that are still in the active data packet set). In the example of Figure 4B, the second data packet is retransmitted at transmit occasion 403 in response to receiving the bundled feedback message indicating NACK (i.e. bundled NACK).

Referring in more detail to Figure 4B, as shown in the Figure, after transmitting the second data packet for the first time (i.e. is also added to the active data packet set), the transmitter may receive the bundled NACK associated with the active data packet set. In this case, the bundled NACK concerns the first and second data packets as they are comprised in or form said active data packet set. NACK is indicated as dotted square below the transmit occasion 402 and indicates 1 & 2 meaning that it concerns the first and second data packets. Now, the transmitter does not necessarily know which of the data packets (or maybe all) of the active data packet set is not successfully received. We need to keep in mind that the first ACK received after transmitting the first data packet may have been corrupted.

Hence, in an embodiment, the transmitter node, in response to receiving the bundled feedback message indicating negative-acknowledgement, determines, for each data packet in the active data packet set, a transfer failure probability. In the specific example of Figure 4B, such may mean that the transmitter node determines a first transfer failure probability associated with the first data packet and a second transfer failure probability associated with the second data packet. The transmitter node may then retransmit, based on the transfer failure probabilities, at least one of the data packets of the active data packet set in a next transmit occasion (e.g. transmit occasion 403 in Figure 4B). In the example of Fig. 4B, the transmitter node may transmit only one data packet of the active data packet set (i.e. the second data packet at transmit occasion 403). Further, the transmitter node may initiate reception of a further bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative-acknowledgement of at least one data packet of the active data packet set. In this particular case and event, the active data packet set may remain unchanged before receiving said further bundled feedback message as no new data packets are transmitted and ACK counters 412, 422, 432, 442 for each data packet are below two (e.g. F=2).

In the example of Figure 4B, the further bundled feedback message received in response to transmitting the second data packet at transmit occasion 403, may be bundled ACK concerning yet again the active data packet set (i.e. first and second data packets in this case). Hence, as discussed with respect to Figure 4A, after receiving the ACK, the transmitter node may transmit the next data packet which in this case is the third data packet. The first data packet may be removed from the active data packet set and the third data packet added.

The proposed operation concerning the retransmission after NACK may thus be to retransmit a data packet of the active data packet set with highest chance of failure given the observed set of feedback messages concerning the data packets in the active set. That is, the most probably unsuccessfully transmitted data packet may be retransmitted. In Figure 4B, it may be the second data packet.

Furthermore, the following situations may lead to receiving the NACK in response to transmitting the second data packet at transmit occasion 402: failure of the second data packet in the first transmission attempt followed by no feedback channel error (i.e. uncorrupted feedback message), failure of the first data packet in its first transmission attempt followed by feedback channel error for the first feedback occasion (i.e. corrupted feedback message), both of the above happening, or both the first and second data packets have been delivered in their respective first transmission attempts but the ACK feedback in the 2nd feedback occasion has faced a failure and is observed as NACK (i.e. corrupted feedback message). So many different things may lead to receiving the NACK. It is further noted that the situation may become even more complex in a case where F>2, i.e. the active data packet set comprises at least three data packets and the bundled feedback message is associated with all of said at least three data packets.

Figure 4C illustrates a further embodiment. Referring to Figure 4C, the transmission of the first and second data packets at transmit occasions 401, 402 may be similar to scenarios depicted in Figures 4A and 4B. Similar to situation of Figure 4B, the bundled NACK may be received in response to the transmitted second data packet at transmit occasion 402. Hence, the transmitter node may determine the likelihood of failure of the first data packet and the likelihood of failure of the second data packet. Such determination may be based on different factors, such as a probability of the different scenarios described above (e.g. probability of corrupted feedback message) and how many times each data packet has been transmitted. Then the data packet with more likelihood of failure may be retransmitted in the next transmission occasion. In the example of Figure 4C, the retransmitted data packet at transmit occasion 403 may be the second data packet. However, different to the scenario of Fig. 4B, the transmitter node may receive another bundled feedback message associated with the active data packet set in response to retransmitting the second data packet at transmit occasion 403, wherein said bundled feedback message indicates NACK. Thus, in an embodiment, in response to receiving said further bundled feedback message indicating negative- acknowledgement, the transmitter node may retransmit, based on the transfer failure probabilities, one of the data packets of the active data packet set in a next transmit occasion. So, the transmitter node may determine yet again whether to transmit the first data packet or the second data packet at transmit occasion 404. In an embodiment, the retransmitted data packet is different to a previously retransmitted data packet if the previously retransmitted data packet has been transmitted for at least a predetermined number (i.e. parameter B) of times. For example, the predetermined number may be two. This can be seen in the example of Figure 4C. As the second data packet is retransmitted at transmit occasion 403 and has been transmitted consecutively two times (i.e. at transmit occasions 402, 403), the transmitter node may determine to transmit the first data packet at transmit occasion 404. This may happen in this embodiment even though the second data packet would have a higher likelihood of failure (e.g. also referred to as transfer failure probability). Thus, the parameter B may define how many time a data packet can be transmitted during the transmission or retransmission process (e.g. HARQ process), before continuing by retransmitting some other data packet.

In an embodiment, the transmitter node may retransmit at least one of the data packets of the active data packet set, in response to receiving a NACK, according to a predetermined retransmit order. For example, all data packets may be transmitted according to said retransmit order. Parameter M, at least, may still limit the number of retransmission attempts. Hence, it is possible to use transmission order that is not based on the transfer failure probabilities. This may make the transmission process simpler. The predetermined transmission order may be known by both the transmitter and receiver nodes. Hence, both may follow the same order. In an embodiment, the transmitter node indicates said order to the receiver node via control signaling. For example, in case of a plurality of data packets in the active data packet set, the predetermined order may mean that each data packet, in turn, is retransmitted for a predetermined number of times (e.g. B-l or M-l times). For example, the first retransmitted data packet may be the data packet that was transmitted at previous transmit occasion for the first time. Other data packets may then follow, for example. If ACK is received, the next transmitted data packet may be a different data packet (i.e. a new data packet).

These transfer probability values may depend on BLER values and the p value of each feedback occasion, wherein p may denote feedback channel reliability. BLER may indicate transmission channel reliability. A scheduler (e.g. part of or comprised in the transmitter node) may be configured to set the transmission setup for the data packets and the feedback channel in a way to satisfy a desired BLER and p, for instance, by following link adaptation process to setup BLER target. Therefore, the scheduler that has acquired p and BLER values, may also be able to figure out the above mentioned conditional failure probabilities ahead of time (e.g. offline) and based on that can select or configure the operation in case of NACK (e.g. bundled NACK) and signal the configured operation to the receiver node for sync up. In practice this can for instance happen at the beginning of a connection setup when the scheduler figures out the channel quality in both directions. It could also be dynamically changed throughout a connection and reported to the receiver node for sync up.

For example, in cases where BLER is significantly larger than p (e.g. order of magnitude larger, such as 10 times larger), it may be more likely that the bundled NACK feedback is the result of the second packet failure than previous ACK feedback being erroneous. That is, for example in situation of Figure 4C, the probability that first data packet transmitted at transmit occasion 401 is successfully transmitted may be lower than the probability of receiving a corrupted feedback message in response to the transmitting the first data packet. Hence, it may be more probable that the received ACK is not corrupted and that the next NACK indicates that the second data packet transmitted at occasion 402 has not been successfully received by the receiver node. Hence, the transmitter may transmit the second data packet at time instant 403. Further, after receiving the ACK for the first data packet, the first data packet may be marked as 'received' by the transmitter node. Such operation may be performed for all data packet of the active data packet set if a bundled ACK is received, at least in some embodiments and depending on the different parameter values used in determining the probabilities.

Still referring to Figure 4C, again once the next bundled feedback message indicates ACK, the data packets for which F number of ACKs have been received may be removed from the active data packet set and the next data packet (e.g. the third data packet) transmitted. The next data packet may then also be added to the active data packet set. In an embodiment, in response to receiving a bundled NACK, the transmitter node retransmits at least one of the data packets of the active data packet set unless all the NACKed (i.e. by the bundled NACK) data packets have already reached maximum number (e.g. parameter M) of transmission attempts.

In an embodiment, a data packet is retransmitted only if it has previously been transmitted less than the maximum number (M) of transmission time during the transmission process (e.g. HARQ process).

In an embodiment, a first ACK, concerning a transmitted data packet, is received after a number of received NACKs and before M transmission attempts, the received ACK feedback is stored and reported again in backward bundled approach together with the ACK from following packet(s). For example, if the first ACK is an unbundled ACK, it may be stored in a memory. For the receiver, this may mean that it remembers that said data packet has been successfully received (or stores information about the successfully reception) so that it may use this information when transmitting the bundled feedback messages. It is further noted that the first ACK may be transmitted after one or more NACKs. If M transmission attempts are reached, the transmission for that packet may stop.

In an embodiment, the transmitter node signals, to the receiver node, a new data indicator (NDI) each time a data packet is transmitted for the first time. I.e. NDI is transmitted each time a data packet is added to the active data packet set. As mentioned, after observing ACK, a new data packet may be transmitted and the receiver node may know this by detecting a toggle in the NDI. That is, contents of the NDI may be changed which may be detected by the receiver node. Based on the received NDI(s), the receiver node may determine which of the data packets in the current transmission process (e.g. HARQ) is being retransmitted. For retransmitted packets, the NDI may not be signaled and/or its contents may not be changed.

Figures 4D and 4E illustrate examples in which said parameter B equals to 4 and said parameter F equals to 2. This may mean that any data packet, in response to receiving a bundled NACK, is transmitted only B number of times within the same transmission process (e.g. the same HARQ process). So, even if it would be more probable at transmit occasion 407 of Figure 4D that the second data packet has failed, the first data packet is transmitted at that occasion as transmit counter 424 indicates already four transmissions for the second data packet. Difference between situations of Figures 4D and 4E is that the first data packet is in Figure 4D transmitted already at transmit occasion 404 even though the second data packet has only been transmitted two times at that point. However, the transmitter node may have determined the transfer failure probability of the first packet to be higher at that point. However, the number of transmissions per data packet may also affect the transfer failure probabilities and thus at time instant 405 the second data packet may yet again be transmitted. So, the higher the number of transmission attempts, the lower the transfer failure probability for a data packet.

In both examples, the transmission counters 414, 424 eventually indicate number four. This may mean that the transmitter node could yet again change the retransmitted data packet to a data packet that was not previously retransmitted. I.e. if at transmit occasion 408, the first data packet's counter reaches four and although second data packet's counter is also four, the transmitter node may continue by retransmitting the second data packet at the next transmit occasion as the first data packet was previously transmitted at transmit occasion 408. Process may so continue until the transmission attempts per data packet reaches M. That is, in an embodiment the transmitter node determines that a data packet has been transmitted for a predetermined maximum number (i.e. parameter M) of times without receiving the predetermined number of separate feedback messages indicating acknowledgement of said data packet; and in response to said determining, removing said data packet from the active data packet set and transmitting another data packet in a next transmit occasion.

In an embodiment, the transmitter node may store a data packet to a data buffer until said predetermined number of separate feedback messages indicating acknowledgement of said data packet have been received and/or until the maximum number (i.e. parameter M) of transmission attempts for said data packet have been performed. So, if M number of transmission attempts have been performed during the transmission process (e.g. HARQ process), the data packet may be removed from the active data packet set and/or from the data buffer.

Let us then look more closely on how the different parameters can be acquired for the transmission process by looking at embodiments of Figures 5A to 5B. Referring to Figure 5A, the transmitter node may acquire a target reliability level for a data packet retransmission (block 502); determine a target block error rate for the data packet transmission to reach said target reliability level and determine a probability of a corrupted detection of a feedback message, wherein the feedback message as transmitted indicates acknowledgement or non-acknowledgement of one or more data packets, and the feedback message as received indicates the opposite compared with the feedback message as transmitted (block 504); and determine, based on the determined target block error rate and the determined probability of the corrupted detection of a feedback message, said predetermined number (i.e. parameter F) of required separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received (block 506).

In an embodiment, the transfer failure probability of each data packet of the active data packet set is determined based on the target block error rate and the probability of the corrupted detection of a feedback message. In an embodiment, said transfer failure probability may further be based on channel attribute setup for data channel and feedback channel. However, this may not be necessary in all cases as BLER and said probability of the corrupted detection may be enough to determine said transfer failure probability. In an embodiment, in addition to the BLER and corrupted detection probability, the transfer failure probability is further based on the number of transmission attempts of the data packet.

In an embodiment, the transmitter node determines, based on said target block error rate, said probability of corrupted detection and said predetermined number of required separate feedback messages (i.e. parameter F), the parameter indicating the number of allowed consecutive transmissions of the same data packet or the number of allowed consecutively received bundled feedback messages indicating negative- acknowledgement. That is, parameter B may be determined based on BLER, F and the probability of corrupted detection.

In an embodiment, the transmitter node may transmit, to the receiver node, at least one control message indicating at least one of the parameter F and the parameter B (block 508). The control messages may comprise other parameter as well, such as parameter M, BLER, channel setup parameter(s) and/or HARQ setup parameter (s). After the transmitter node and the receiver node have been both configured for the data packet transfer, the data packet transfer may initiate (block 510).

Referring to Figure 5B, the scheduler (e.g. the transmitter node) may signal setup parameters (e.g. one or more of the parameters F, M, B) to the receiver node (block 512). In block 514, the scheduler may signal information about the feedback channel setup (e.g. repetition order and/or transmit power) to the receiver node, wherein the indicated feedback channel setup may satisfy determined feedback channel reliability (i.e. p). Such could be determined in block 504, for example. In block 516, the scheduler may determine whether or not the present data packet transmission is latency critical. If yes, the process may continue to step 518. If not, the process may continue to step 520. In block 518, the scheduler may activate bundled retransmission. This is discussed later in more detail. In block 520, the scheduler may determine whether the transmit buffer size is less than parameter F. If yes, the process may continue to step 522, wherein ARQ transmission may be activated. For example, if the transmission process is HARQ and the buffer size of the transmitter node is less than F, the ARQ transmission may be activated. This will also be discussed later in more detail.

Thus, for example, the implementation of the proposed retransmission process may transmit by setting up the parameter values. The scheduling node (e.g., eNB in LTE technology) may determine the reliability level that is desired from the retransmission process. The reliability can be shown for instance in the form of acceptable packet outage probability which we denote by Pout. The reliability achieved over a channel with Pout chance of outage is 1-Pout. The BLER target of the packet transmission may typically be decided based on the quality of service requirements for the packet, spectral efficiency optimization, interference level of a packet transmission to the other communicating nodes, etc. For instance, in LTE the BLER target of 10~20% may typically be chosen for data transmission, while higher reliability of transmission may be chosen for more critical transmissions, such as the control channel signaling.

The feedback channel reliability may be set by the repetition order, transmit power, etc. We denote the feedback channel reliability with p where it shows the chances of wrong detection from ACK to NACK and vice versa. It should be noted that in general it is possible that the transition probabilities are different and/or there may also exist a chance of erasure of the feedback signal (e.g., discontinued transmission can be detected instead of ACK or NACK as a result of erasure). For simplicity of the discussion, it is assumed that erasure cases (which could as well be the result of DTX in feedback channel) will be translated by the transmitter into NACK which is the safest choice in terms of reliability of packet delivery. Moreover, considering the chances of erasure we further assume that the transition probability from ACK to NACK (or either to erasure) is equal to chances of NACK to ACK over the feedback channel.

Based on the expected reliability value p (or the more precise error pdf for feedback channel) and the target BLER the scheduler will be able to determine M and F, respectively the maximum transmission attempts, the necessary number of positive acknowledgments for a packet that will ensure 1-Pout reliability for the packet transmission. It may also be beneficial to consider the NDI error chances in determining M. The value of the parameter B may also be determined based on the above values as explained earlier.

It should be noted that the parameter B here may be assumed to be chosen based on the conditional failure probabilities in the more likely case where B NACKs are received after more than F consecutive ACKs over the feedback channel, meaning that all the packets except for the last one have at least one ACK in their counter and the last packet has B NACKs only. However, there could be a situation where it may be beneficial to have several B values to be used in different situation. For instance in Fig. 4C, after B=2 NACKs, the transmitter node may switch to transmitting the first data packet (i.e. at transmit occasion 404). Then in case of continuation of NACKs, the transmitter node may switch back to transmitting the first data packet (switching based on transmission counter of packets). However, this second switching as well as any later switching between these two packets might be optimal to happen at values other than B (at least in some cases). It may be assumed that switching between transmitting packets happens at about the time when transmitter counter of the transmitting packet is a multiple of B. This is expected to be sufficient since the likelihood of switching events for B>1 may be small considering typical values for BLER. This may additionally simplify the receiver algorithm. The values of (M, F, B) may be communicated with the receiver node (e.g., by means of control channel). Given these parameters the transmitting and the receiving nodes may set up the retransmission process.

Figure 5C illustrates yet another embodiment indicating a signal diagram of the transmission process. Referring to Figure 5C, the transmitted node may be the network element 102 and the receiver node may be the terminal device 110. In block 550, the transmitter node may acquire one or more parameters, such as F, B and/or M. In block 552, said parameters may be transmitted to the receiver node. In block 554, the data packet transmission process may initiate and one or more data packets may be transmitted from the transmitter to the receiver. In block 556, the receiver node may respond by transmitting the bundled feedback message concerning the active data packet set. In block 558, the transmitter node may determine the next data packet to transmit. In case the bundled feedback message was a bundled NACK, the transmitter node may determine which of the data packets of the active data packet set needs to be retransmitted. In case the bundled feedback message was bundled ACK, the transmitter node may transmit a new data packet and include it in the active data packet set. In block 560, the next data packet is transmitted (or retransmitted). In block 562, the receiver node may continue by responding with another bundled feedback message. The process may so continue until all data packets have been successfully transmitted (i.e. F number of ACKs received for each data packet) or until M number of attempts have been performed for each data packet without receiving F number of ACKs.

Figures 6A to 6C illustrate some embodiments related to reducing data buffer size storing the data packet(s) of the transmission process. Reference signs 491-494 may indicate further transmission occasions in Figures 6B and 6C. The buffer size required for the proposed backward-feedback-bundled (BFB) SAW may be increased as compared to the regular SAW operation by the factor of F times. This may happen because all the active packets may be stored at both the transmitter and the receiver sides for combining gain (e.g. HARQ combining). However, the buffer size may be reduced with some further novel and inventive features. Therefore, in an embodiment, B is set to M (i.e. B=M). This can be configured by the transmitter node to the receiver node by means of control signaling. In another example, a scheduler signals this condition to both the transmitter node and the receiver node. Further, in an embodiment, the node(s) are configured to treat ACKed data packets in ARQ manner. In other words, when data packet P is ACKed (either using bundled or unbundled ACK), the receiver node may not store the data packet in the data buffer. However, the acknowledgment generated for data packet P may be bundled with the following packets' acknowledgments in the same manner as was explained earlier. In the case where bundled NACKs will result in retransmitting the data packet P, the receiver side may try to decode the data packet P without the help of the previously received version(s) of it. This ARQ type of operation can be deployed for all of the active packets in case where there may not be an HARQ buffer available.

It is noted that the ARQ operation may not set limitation over parameter F. However it may be beneficial to change B to M (at least for the active packets without a buffer) in order to use the combining gain for stored packets.

In the example of Figure 6A, F = 2, B = M = 4 and only one buffer 602 may be available at the receiver node. In the Figure, the buffer 602 indicates which data packet may currently be stored in the receiver node's data buffer. That is, the last received data packet may be stored in the only available buffer and it is flushed (i.e. removed from the buffer) in case receiver detects toggle in NDI which means a new packet has been transmitted. In case of NACK as shown in Fig. 6A, no new packet will be transmitted until M transmission attempts for the NACKed packet is performed and therefore the receiver can store the NACKed packet to obtain combining gain (e.g. HARQ combining).

In Figure 6B, F = 3, B = M = 4 and only one buffer is available at the receiver side. As shown in Fig. 6B, second data packet is once stored in the only buffer since it was the last packet transmitted and NACKed (after transit occasion 402). However, after it is ACKed, it may be cleared off the buffer. Then, in the turn of events after B = 4 times NACK with transmission of the third data packet, the transmitter may switch back to transmission of the second data packet and receiver may store it in the only available buffer until M transmissions of second data packet are performed. It may also be worth to mentioning that the M parameter in such scenario may be set according to the desired Pout, BLER value and the fact that less or no combining gain will be available. Therefore, if a packet is being retransmitted with no previous versions (i.e. no combining gain expected) of it in the buffer (e.g. HARQ buffer), then the retransmission attempts could go for as many as M+E, where the E parameter denotes the extra retransmission attempts for the ARQ operation. It is also noted that as F=3, the bundled ACK or NACK may be associated with said number of data packets as long as there are F number of data packets in the active data packet set.

In even more flexible design approach, the transmitter may retransmit packet 2 for M transmission attempts when it switches to transmission of packet 2 after transmission of packet 3 is over. In a similar situation, after switching from transmission of packet 2 to transmission of packet 1, M transmission attempts can be given to packet 1. In other words, as an example case it could be set that a packet will be discarded at the transmitter side only after M transmission attempts with HARQ combining gain (stored in the buffer and used together with retransmissions for better decoding). Therefore in this even more flexible and even more reliable approach, of Fig. 6B, packet 3 may be discarded after 4 consecutive transmission attempts. However, when switching back to transmitting the second data packet it will be retransmitted for at most M times regardless of the fact that it was already transmitted twice before packet 3 was started to be transmitted. Figure 6C illustrates an embodiment in which there are two data buffers 604 available at the receiver. I.e. the data buffers 604 may accommodate two data packets at a time. In the example of Figure 6C, F = 3 and B = M = 4. The buffers 604 may accommodate two most recently received data packets.

Moreover, the ARQ operation with BFB may be enabled for a subset of the active packets. For instance in case F = 3, if the receiver has enough buffer to accommodate the two packets per BFB-SAW process, then only one of the packets may be treated as ARQ. In other words, the last two packets NACKed will be stored in the buffer. The transmitter node may transmit self-decodable versions of the data packet in case of ARQ operation. However, as soon as a packet will be retransmitted in a row (which means it is stored in the receiver buffer) and HARQ operation is considered for the packet, then the retransmissions can be composed of different redundancy versions of the packet (i.e. incremental redundancy HARQ). In the example of Figure 6C, the first data packet may be treated using the ARQ process as it may be the data packet that would be retransmitted the latest using the proposed transmission process solution. The separate ARQ process may cause the first data packet (or any other data packet transmitted using the ARQ process) to be successfully received by the receiver node. The receiver node may so indicate. In an embodiment, in the separate ARQ process, only one ACK per data packet is sufficient to indicate that the data packet has been successfully received by the receiver node. Hence, the transmitter node may regard the data packet as successfully received based on only one received ARQ for that data packet. The ARQ ACKs and/or NACKs may be data packet specific (i.e. unbundled ACKs/NACKs).

Figures 7A to 7B illustrate further embodiments related to reducing latency in the transmission process (i.e. BFB process, such as HARQ process). Referring to Figure 7A, in an embodiment, the transmitter node, in response to receiving a bundled feedback message indicating negative-acknowledgement, retransmits at least a subset of data packets of the active data packet set, wherein the subset comprises at least two data packets. For example, in response to transmitting the second data packet at time instant 402, the transmitter node received a bundled NACK indicating unsuccessful reception of at least one of the first and second data packets. Hence, in response, the transmitter node may retransmit both data packets. In this case, this means transmitting all data packets of the active data packet set. However, if there would be three data packets in the active data packet set, only a subset of the data packets may be transmitted, wherein the subset is selected based on transfer failure probabilities of said data packets. Transfer failure probabilities were discussed above in more detail. By transmitting only a subset, the solution may differ from blind transmission in which all data packets are retransmitted regardless of ACK/NACKs received regarding said data packets.

In an embodiment, the retransmission in case of NACK will include all the packets associated with the NACK feedback. I.e. both the first and second data packets are retransmitted in response to receiving the NACK in Figure 7A. The retransmission of both data packets may continue according to the same rules described above. Once ACK is received, the next data packet may be transmitted (i.e. the third data packet). As two ACKs for first packet are received and F=2, it may be removed from the active data packet set. As only one ACK for the second data packet is received, it is not removed from the active data packet set. The third data packet may be added to the set as it is transmitted for the first time. It is noted that transmitting all or a subset of data packets in the active data packet set assumes that there is enough resources for retransmitting all packets over the same TTI.

Referring to Figure 7B, M = 4 and F = 3. In this example, at transmit occasion

405, the transmitter node may transmit only the second and third data packets (i.e. packets 2 and 3), although it has previously received a NACK concerning all data packets 1, 2 and 3. This may be done, for example, to save resources, and only the data packets with highest conditional failure probabilities will be retransmitted. However, at transmit occasion 406 all data packets of the active data packet set are retransmitted. Hence, the transmitter node may determine at each transmit occasion when receiving a NACK, whether to transmit a subset or all data packets of said active set.

In an embodiment, the NDI toggling (i.e., transmitting a new packet) is only performed when the ACK counter of the transmitted data packet reaches F-l ACKs. This may be shown in Figure 7B. In this embodiment, the maximum number of active packets may be less than F (i.e. active packets max = 2 and F = 3). As described above, in some other embodiments, F equals to maximum number of data packets in the active data packet set.

In an embodiment, the SAW HARQ process follows the regular SAW operation of a packet but stops transmission of it only after F number of ACKs observed for the packet or M transmission attempts have been reached for the packet.

In an embodiment, F is derived (e.g. by the transmitter node) from the following equation: F = arg; min{P (fail\AC K_t, ... , ACKi, Transmission)≤ P_out}.

Deriving F from said equation may indicate the minimum number of ACK observances that results in conditional failure probability less than the tolerated outage probability Pout.

In an embodiment, a metric (i.e. metricl below) for different BLER, p (i.e. feedback channel reliability) and number of consecutive bundled NACKs may be calculated (e.g. by the transmitter node) as follows: metricl = P(Faill\ feedbacks, transmissions)— P(Fail2 \ feedbacks, transmissions) 'Feedbacks' and 'transmissions' may denote the event of observing feedbacks and the event of performing transmissions respectively.

Metricl may be calculated to derive the parameter B value. That is, if metricl has a negative value then the previously transmitted data packet will continue being retransmitted. Thus, the retransmission attempts for that packet have not yet reached parameter B value. However, if metricl is positive, it may indicate that at least B number of transmission attempts for the data packet have been performed, and thus the next retransmitted data packet should be a different data packet. I.e. the transmitter may change the retransmitted data packet in case the equation for metricl returns a positive value.

Figures 8 and 9 illustrate flow diagrams according to some embodiments. Referring to both Figures, at both the transmitter and the receiver a state S may be defined that can have values of S £{1, 2, F}. Each S may represent a data buffer (e.g. HARQ) and a few of counter buffers. The notation ~S may denote all the states other than S. Figure 8 illustrates the operation at the transmitter node. The operation may start at step 801 and may be followed by step 802 and then step 803. In step 804, the transmitter may observe feedback from the receiver in response to transmitting data packet(s). In case of NACK, operation will continue to step 805 and in case of ACK to step 806. From step 806, the process may continue to steps 807, 814 and 813 as illustrated in Figure 8. After step 813, the operation may return to step 803. From step 805, the process may continue to step 808 and if transmission counter equals to M, the process may continue to step 810; otherwise it may continue to step 809. In step 809, if transmission counter equals to an integer multiple of B, the process may continue to step 812; otherwise it may continue to step 803. From step 810, the process may continue to step 811. In step 811, if the transmission counter equals to zero, the process may continue to step 807; otherwise it may continue to step 812. From step 812, the process may continue to step 803.

Referring to Figure 9, the process at the receiver node side may start from step 901 and continue to steps 902, 907, 908, and 909 (as shown in Figure 9). In step 909, if NDI toggling is observed, the process continues to step 910. If no toggling is observed, the process continues to step 912. From step 910, the process may continue to steps 911, 904 and to 907. In step 912, if receiving counter equals to M, the process may continue to step 913; otherwise it may continue to step 918. From step 913 the process may continue to step 914, wherein if the transmission counter equals to zero, the process may continue to step 914 and to 917; otherwise the process may continue to step 916 and then to step 917. In step 918, if RX counter equals to n*B (wherein n is an integer number), the process may continue to step 916; otherwise it may continue to step 917. From step 917, the process may continue to step 905 and to then to 906, and then to 907. Referring to Figures 8 and 9, it needs to be noted that TxCounter(S) may store the number of transmissions for the packet in Buffer (S). Similarly, at the receiver side RxCounter(S) may count the number of times a packet has been received. ACKcounter(S) and NACKcounter(S) respectively may store the number of ACK and NACK received for the packet in S either in bundled form or individual feedback form.

The NDI may typically be sent together with the control signaling for the packet and it can be equal to zero or one (or any set of two different and distinguishable values). There may be a chance of error for the delivery of correct NDI. It is however an acceptable assumption that error rate for NDI can be reduced comparably much easier than the feedback channel since NDI is transmitted with less limitation of transmit power by the eNB, and also channel coding can be used for the control channel with better error recovery performance compared to repetition coding for feedback channel.

It may be assumed that discontinued transmission (DTX) over feedback channel (i.e., no feedback detectable) is translated into NACK. The other option will be to consider DTX detection separately in the transmitter flowchart where following a detection of DTX over feedback channel, the transmitter may repeat the previous step. For instance, presence of error in NDI can be the result of failure in detection of the control channel. The result of this could for example be no packet decoding and no feedback transmission by the receiver node. Therefore, in case of DTX detected on the feedback channel, transmitter can simply repeat the previous step.

Parameter NDItoggleS at the transmitter may store the last S where NDI was toggled for it. NDI is toggled when a packet is transmitted for the first time. At the receiver side, NDItoggleS stores the last S where the NDI was observed as toggled at the receiver end. Hence, then the receiver node may know at which S the NDI signal was last observed as toggled, so that it may switch back to this packet when needed. Similarly, the transmitter node may store the S index when it last toggled the NDI.

At the transmitter side, whenever an ACK is observed, the next transmission may be a new packet with NDI toggled.

At the receiver side whenever NDI is observed as toggled the packet is considered as a new packet. Therefore, if NDI is observed as toggled and RxCounter(S) = M for the new S then at some point there has been an NDI error. This situation can happen similarly in the regular SAW process too. The solution adopted in regular SAW and the proposed backward-feedback bundled SAW is to decode the packet as newly arrived in such situation.

In an embodiment, the receiver node performs initial reception to the data.

The receiver node may further terminate a data packet of the active data packet set by flushing the data buffer and counters associated with said data packet when the number of reception reaches value M. The receiver node may substitute the data packet in the data buffer with the received data packet. E.g. if data buffer size is less than F, the buffer may not store all data packets and thus the data packet may be substituted with the foremost received data packet, or if the number of active packets is less than the predetermined number F, then the receiver node may denote the received data packet as an active data packet. I.e. as a member of the active data packet set.

In an embodiment, the receiver node detects that NDI is not toggled and in response switches to retransmission phase, wherein the receiver node follows same retransmission pattern as the transmitter node. I.e. the order of retransmitting the data packets may be sort of predetermined as both may follow same algorithm. Thus, the transfer failure probabilities calculated at both ends (transmitter and receiver) may give the same retransmission order.

In an embodiment, the receiver node receives, from the transmitter node, at least one control message indicating said pre-determined number.

In an embodiment, the receiver node stores a received data packet in a data buffer of the receiver node in case of decoding error of said received data packet.

Figures 10 to 11 provide apparatuses 1000, 1100 comprising a control circuitry (CTRL) 1010, 1110, such as at least one processor, and at least one memory 1030, 1130 including a computer program code (software) 1032, 1132, wherein the at least one memory and the computer program code (software) 1032, 1132, are configured, with the at least one processor, to cause the respective apparatus 1000, 1100 to carry out any one of the embodiments of Figures 3 to 9, or operations thereof.

Referring to Figures 10 to 11, the memory 1030, 1130, may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory 1030, 1130 may comprise a database 1034, 1134 for storing data.

The apparatuses 1000, 1100 may further comprise radio interface (TRX) 1020, 1120 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities to access the radio access network, for example. The TRX may comprise standard well-known components such as an amplifier, filter, frequency-converter, (de) modulator, and encoder/decoder circuitries and one or more antennas. For example, the TRX may enable communication between transmitter node and the receiver node (e.g. the first and second apparatuses).

The apparatuses 1000, 1100 may comprise user interface 1040, 1140 comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 1040, 1140 may be used to control the respective apparatus by a user of the apparatus 1000, 1100.

In an embodiment, the apparatus 1000, 1100 maybe or be comprised in a base station (also called a base transceiver station, a Node B, a radio network controller, or an evolved Node B, for example). The apparatus 1000, 1100 may be the network element 102 and/or the terminal device 110, for example.

In an embodiment, the apparatus 1000 is the first apparatus performing the steps of Figure 3A. Thus, the apparatus 1000 may be or be comprised in the transmitter node. In an embodiment, the apparatus 1100 is the second apparatus performing the steps of Figure 3B. Thus, the apparatus 1100 may be or be comprised in the receiver node.

Referring to Figure 10, in an embodiment, the control circuitry 1010 may comprise transmitting circuitry 1012 configured to perform step 302, a receiving circuitry 1014 configured to perform step 304, a requiring circuitry 1016 configured to perform step 306, and a removing circuitry 1018 configured to perform step 308.

Referring to Figure 11, in an embodiment, the control circuitry 1110 may comprise an acquiring circuitry 1112 configured to perform step 310, a reception circuitry 1114 configured to perform step 312, a denoting circuitry 1116 configured to perform step 314, a determining circuitry 1118 configured to perform step 316 and a circuitry 1119 configured to perform steps 318 and 320.

In an embodiment, at least some of the functionalities of the apparatus 1000, 1100 may be shared between two physically separate devices, forming one operational entity. Therefore, the apparatus 1000, 1100 may be seen to depict the operational entity comprising one or more physically separate devices for executing at least some of the described processes. Thus, the apparatus 1000, 1100 utilizing such shared architecture may comprise a remote control unit (RCU), such as a host computer or a server computer, operatively coupled (e.g. via a wireless or wired network) to a remote radio head (RRH) located in the base station. In an embodiment, at least some of the described processes may be performed by the RCU. In an embodiment, the execution of at least some of the described processes may be shared among the RRH and the RCU.

In an embodiment, the RCU may generate a virtual network through which the RCU communicates with the RRH. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization may involve platform virtualization, often combined with resource virtualization. Network virtualization may be categorized as external virtual networking which combines many networks, or parts of networks, into the server computer or the host computer (i.e. to the RCU). External network virtualization is targeted to optimized network sharing. Another category is internal virtual networking which provides network-like functionality to the software containers on a single system.

In an embodiment, the virtual network may provide flexible distribution of operations between the RRH and the RCU. In practice, any digital signal processing task may be performed in either the RRH or the RCU and the boundary where the responsibility is shifted between the RRH and the RCU may be selected according to implementation.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and soft-ware (and/or firmware), such as (as applicable): (i) a combination of processor (s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term 'circuitry' would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

In an embodiment, at least some of the processes described in connection with Figures 3 to 9 may be carried out by an apparatus comprising corresponding means for carrying out at least some of the described processes. Some example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry. In an embodiment, the at least one processor, the memory, and the computer program code form processing means or comprises one or more computer program code portions for carrying out one or more operations according to any one of the embodiments of Figures 3 to 9 or operations thereof.

According to yet another embodiment, the apparatus carrying out the embodiments comprises a circuitry including at least one processor and at least one memory including computer program code. When activated, the circuitry causes the apparatus to perform at least some of the functionalities according to any one of the embodiments of Figures 3 to 9, or operations thereof.

The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

Embodiments as described may also be carried out in the form of a computer process defined by a computer program or portions thereof. Embodiments of the methods described in connection with Figures 3 to 9 may be carried out by executing at least one portion of a computer program comprising corresponding instructions. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer program medium may be a non-transitory medium. Coding of software for carrying out the embodiments as shown and described is well within the scope of a person of ordinary skill in the art. In an embodiment, a computer-readable medium comprises said computer program.

Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

1. A method in a wireless communication system, the method comprising: transmitting, by a first apparatus of the wireless communication system, at least a first data packet and a second data packet to a second apparatus of the wireless communication system, wherein a given data packet is added to an active data packet set if the given data packet is transmitted for a first time;

receiving, by the first apparatus from the second apparatus, a bundled feedback message associated with reception of said active data packet set, the bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative-acknowledgement of at least one of the data packets of the active data packet set;

requiring, by the first apparatus, reception of at least a predetermined number of separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received by the second apparatus, said predetermined number being at least two; and

removing said data packet from the active data packet set in response to regarding said data packet as successfully received.

2. The method of claim 1, wherein said predetermined number further indicates a maximum number of data packets in the active data packet set.

3. The method of claim 1 or 2, wherein the received bundled feedback message is one of the required at least two separate feedback messages.

4. The method of any preceding claim, further comprising:

in response to receiving the bundled feedback message indicating acknowledgement, transmitting a next data packet in a next transmit occasion; and

including said next data packet to the active data packet set.

5. The method of any preceding claim, further comprising:

signaling, by the first apparatus to the second apparatus, a new data indicator, NDI, each time a data packet is transmitted for the first time.

6. The method of any preceding claim, further comprising:

upon regarding a data packet as successfully received by the second apparatus, removing said data packet from a transmit buffer of the first apparatus.

7. The method of any preceding claim, further comprising: in response to receiving the bundled feedback message indicating negative- acknowledgement, determining, for each data packet in the active data packet set, a transfer failure probability;

retransmitting, based on the transfer failure probabilities, one of the data packets of the active data packet set in a next transmit occasion; and

initiating reception of a further bundled feedback message indicating either acknowledgement denoting successful reception of each data packet of the active data packet set or negative-acknowledgement denoting unsuccessful reception of at least one data packet of the active data packet set.

8. The method of claim 7, further comprising:

selecting the one of the data packets of the active data packet set to be transmitted in the next transmit occasion further based on whether or not the data packet has been consecutively transmitted for at least a predetermined number of times.

9. The method of any preceding claim 1 to 6, further comprising: in response to receiving the bundled feedback message indicating negative- acknowledgement, retransmitting at least one of the data packets of the active data packet set according to a predetermined retransmission order; and

initiating reception of a further bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative- acknowledgement of at least one data packet of the active data packet set.

10. The method of any preceding claim, further comprising:

determining that a data packet has been transmitted for a predetermined maximum number of times without receiving the predetermined number of separate feedback messages indicating acknowledgement of said data packet; and

in response to said determining, removing said data packet from the active data packet set and transmitting another data packet in a next transmit occasion.

11. The method of any preceding claim, further comprising:

storing a data packet to a data buffer until said predetermined number of separate feedback messages indicating acknowledgement of said data packet have been received and/or until a maximum number of transmission attempts for said data packet have been performed.

12. The method of any preceding claim, further comprising:

acquiring a target reliability level for a data packet retransmission; determining a target block error rate for the data packet transmission to reach said target reliability level;

determining a probability of a corrupted detection of a feedback message, wherein the feedback message as transmitted indicates acknowledgement or non- acknowledgement of one or more data packets, and the feedback message as received indicates the opposite compared with the feedback message as transmitted; and

determining, based on the determined target block error rate and the determined probability of the corrupted detection of a feedback message, a number of required separate feedback messages indicating acknowledgement of a data packet before regarding, by the first apparatus, said data packet as successfully received.

13. The method of claim 12, wherein the transfer failure probability of each data packet of the active data packet set is determined based on the target block error rate and the probability of the corrupted detection of a feedback message.

14. The method of claim 12 or 13, further comprising:

determining, based on said target block error rate, said probability and said predetermined number of required separate feedback messages, the parameter indicating the number of allowed consecutive transmissions of the same data packet or the number of allowed consecutively received bundled feedback messages indicating negative-acknowledgement.

15. The method of claim 12, 13 or 14, further comprising:

transmitting, to the second apparatus, at least one control message indicating at least one of said number of required separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received and said determined parameter.

16. The method of any preceding claim, further comprising:

in response to receiving a bundled feedback message indicating negative- acknowledgement, retransmitting a subset of data packets of the active data packet set, wherein the subset comprises at least two data packets, and wherein the subset is selected based on transfer failure probabilities of said data packets.

17. A method in a wireless communication system, the method comprising: acquiring, by a second apparatus of the wireless communication system, a parameter indicating a predetermined number of data packets to be acknowledged or negatively-acknowledged using a single bundled feedback message, said predetermined number being at least two;

initiating reception of a plurality of data packets from a first apparatus of the wireless communication system;

denoting said predetermined number of data packets of the plurality of data packets as data packets of an active data packet set;

for each data packet of the active data packet set, determining, by the second apparatus, whether the data packet is successfully or unsuccessfully received; and

in response to determining that at least one data packet of said active data packet set is unsuccessfully received, generating a bundled feedback message indicating negative-acknowledgement, or generating a bundled feedback message indicating acknowledgement if each data packet of said active data packet set is successfully received.

18. An apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause a first apparatus of a wireless communication system to perform operations comprising:

transmitting at least a first data packet and a second data packet to a second apparatus of the wireless communication system, wherein a given data packet is added to an active data packet set if the given data packet is transmitted for a first time;

receiving, from the second apparatus, a bundled feedback message associated with reception of said active data packet set, the bundled feedback message indicating either acknowledgement of each data packet of the active data packet set or negative- acknowledgement of at least one of the data packets of the active data packet set;

requiring reception of at least a predetermined number of separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received by the second apparatus, said predetermined number being at least two; and

19. The apparatus of claim 18, wherein said predetermined number further indicates a maximum number of data packets in the active data packet set.

20. The apparatus of claim 18 or 19, wherein the received bundled feedback message is one of the required at least two separate feedback messages.

21. The apparatus of any preceding claim 18 to 20, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

in response to receiving the bundled feedback message indicating acknowledgement, transmitting a next data packet in a next transmit occasion; and including said next data packet to the active data packet set.

22. The apparatus of any preceding claim 18 to 21, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising: signaling, to the second apparatus, a new data indicator, NDI, each time a data packet is transmitted for the first time.

23. The apparatus of any preceding claim 18 to 22, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

24. The apparatus of any preceding claim 18 to 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

in response to receiving the bundled feedback message indicating negative- acknowledgement, determining, for each data packet in the active data packet set, a transfer failure probability;

25. The apparatus of claim 24, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising: selecting the one of the data packets of the active data packet set to be transmitted in the next transmit occasion further based on whether or not the data packet has been consecutively transmitted for at least a predetermined number of times.

26. The apparatus of any preceding claim 18 to 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

in response to receiving the bundled feedback message indicating negative- acknowledgement, retransmitting at least one of the data packets of the active data packet set according to a predetermined retransmission order; and

27. The apparatus of any preceding claim 18 to 26, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

28. The apparatus of any preceding claim 18 to 27, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising: storing a data packet to a data buffer until said predetermined number of separate feedback messages indicating acknowledgement of said data packet have been received and/or until a maximum number of transmission attempts for said data packet have been performed.

29. The apparatus of any preceding claim 18 to 28, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

30. The apparatus of claim 29, wherein the transfer failure probability of each data packet of the active data packet set is determined based on the target block error rate and the probability of the corrupted detection of a feedback message.

31. The apparatus of claim 29 or 30, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising: determining, based on said target block error rate, said probability and said predetermined number of required separate feedback messages, the parameter indicating the number of allowed consecutive transmissions of the same data packet or the number of allowed consecutively received bundled feedback messages indicating negative-acknowledgement.

32. The apparatus of claim 29, 30 or 31, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising: transmitting, to the second apparatus, at least one control message indicating at least one of said number of required separate feedback messages indicating acknowledgement of a data packet before regarding said data packet as successfully received and said determined parameter.

33. The apparatus of any preceding claim 18 to 32, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the first apparatus further to perform operations comprising:

34. An apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause a second apparatus of a wireless communication system to perform operations comprising:

acquiring a parameter indicating a predetermined number of data packets to be acknowledged or negatively-acknowledged using a single bundled feedback message, said predetermined number being at least two;

35. A computer program product comprising program instructions which, when loaded into an apparatus, execute the method according to any of claims 1 to 17.

36. A computer-readable medium comprising the computer program product of claim 35.

37. An apparatus, comprising means for performing the method according to any of claims 1 to 17.