Resource-efficient hybrid automatic repeat request transmission

Abstract

There is provided techniques for HARQ retransmission A method is performed by a first transceiver device. The method comprises receiving, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot. The method comprises performing, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device, by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and by spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

Description

[0001] RESOURCE-EFFICIENT

[0002] HYBRID AUTOMATIC REPEAT REQUEST TRANSMISSION

[0003] TECHNICAL FIELD

[0004] Embodiments presented herein relate to a method, a first transceiver device, a computer program, and a computer program product for hybrid automatic repeat request retransmission. Embodiments presented herein further relate to a method, a second transceiver device, a computer program, and a computer program product for receiving a hybrid automatic repeat request retransmission.

[0005] BACKGROUND

[0006] Hybrid Automatic Repeat reQuest (HARQ) is a protocol essential in modern telecommunications, particularly in ensuring reliable data transmission over wireless networks. It combines automatic repeat request (ARQ) error control with forward error correction (FEC) for enhanced efficiency and reliability. Despite its advantages, the implementation and operation of HARQ pose significant challenges in terms of resource consumption, impacting the overall performance and efficiency of communication systems.

[0007] The fundamental principle behind HARQ involves the sender encoding data using FEC, transmitting the data, and then waiting for an acknowledgment (ACK) or negative acknowledgment (NACK) from the receiver. In cases where the transmitted data packet is received with errors that cannot be corrected by the FEC, a NACK is sent back to the sender, triggering a retransmission of the data packet. This process, while effective in minimizing error rates, inherently consumes substantial network resources and power, particularly in environments with high error rates or in scenarios requiring high data reliability. Here, depending on the considered HARQ protocol, if the data is not correctly decoded by the receiver, either the same signal, possibly with higher power, is retransmitted (as in chase combining HARQ), or new redundancy bits are retransmitted (as in incremental redundancy HARQ). This increases the chance for successful decoding at the receiver.

[0008] Hence, HARQ is a resource-consuming process, in which the same signal or several additional incremental redundancy bits are retransmitted in successive retransmission round(s) to enable the receiver to decode any undecoded message. Particularly, with chase combining HARQ, the lost packet is sent again, and the thus retransmitted packet is used for maximum ratio combining to increase the required signal to noise ratio (SNR) and decode the desired message. With incremental redundancy HARQ, on the other hand, several additional redundancy bits are retransmitted. These additional redundancy bits are concatenated with the failed signal to generate a longer codeword with reduced data rate. This, in turn, increases the chance for successful decoding.

[0009] One of the primary issues with HARQ is the allocation of bandwidth for retransmissions. In wireless communication systems, bandwidth is a precious and limited resource. The need to reserve or allocate bandwidth for potential retransmissions can lead to inefficient use of this resource, reducing the network's capacity to handle concurrent data transmissions and impacting overall data throughput. Additionally, the retransmission mechanism in HARQ, especially in high-latency scenarios, can introduce significant delays, especially if several retransmission rounds are needed. These delays not only degrade the user experience but also impact real-time applications severely, such as voice over internet protocol (VoIP) or live video streaming, which require stable and low-latency connections for optimal performance.

[0010] Power consumption is another critical concern with HARQ, especially for battery-operated devices such as smartphones and loT devices, and in situations where several retransmission rounds are needed. The process of encoding, decoding, and retransmitting data packets demands substantial computational resources, leading to increased power consumption and, consequently, reduced battery life.

[0011] In summary, while HARQ significantly enhances data transmission reliability and efficiency in wireless networks, it also introduces challenges related to bandwidth allocation, transmission delays, and power consumption. Addressing these issues is crucial for the development of more efficient and sustainable communication systems.

[0012] Hence, there is still a need for improved HARQ processes.

[0013] SUMMARY

[0014] An object of embodiments herein is to address the issues related to the above described HARQ processes.

[0015] A particular object is to improve the resource utilization for HARQ without compromising its error-correcting capabilities.

[0016] According to a first aspect there is presented a method for HARQ retransmission. The method is performed by a first transceiver device. The method comprises receiving, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot. The method comprises performing, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device, by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and by spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

[0017] According to a second aspect there is presented a first transceiver device for HARQ retransmission. The first transceiver device comprises processing circuitry. The processing circuitry is configured to cause the first transceiver device to receive, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot. The processing circuitry is configured to cause the first transceiver device to perform, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device, by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and by spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

[0018] According to a third aspect there is presented a first transceiver device for HARQ retransmission. The first transceiver device comprises a receive module configured to receive, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot. The first transceiver device comprises a transmit module configured to receive perform, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device, by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and by spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

[0019] According to a fourth aspect there is presented a computer program for HARQ retransmission. The computer program comprises computer code which, when run on processing circuitry of a first transceiver device, causes the first transceiver device to perform actions. One action comprises the first transceiver device to receive, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot. One action comprises the first transceiver device to perform, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device, by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and by spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

[0020] According to a fifth aspect there is presented a method for receiving a HARQ retransmission. The method is performed by a second transceiver device. The method comprises sending a NACK of a first data transmission to a first transceiver device. The method comprises jointly receiving a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device. The HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain. The second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain. The method comprises separating the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains. The method comprises applying separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

[0021] According to a sixth aspect there is presented a second transceiver device for receiving a HARQ retransmission. The second transceiver device comprises processing circuitry. The processing circuitry is configured to cause the second transceiver device to send a NACK of a first data transmission to a first transceiver device. The processing circuitry is configured to cause the second transceiver device to jointly receive a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device. The HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain. The second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain. The processing circuitry is configured to cause the second transceiver device to separate the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains. The processing circuitry is configured to cause the second transceiver device to apply separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

[0022] According to a seventh aspect there is presented a second transceiver device for receiving a HARQ retransmission. The second transceiver device comprises a send module configured to send a NACK of a first data transmission to a first transceiver device. The second transceiver device comprises a receive module configured to jointly receive a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device. The HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain. The second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain. The second transceiver device comprises a de-spread module configured to separate the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains. The second transceiver device comprises a decode module configured to apply separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

[0023] According to an eighth aspect there is presented a computer program for receiving a HARQ retransmission. The computer program comprises computer code which, when run on processing circuitry of a second transceiver device, causes the second transceiver device to perform actions. One action comprises the second transceiver device to send a NACK of a first data transmission to a first transceiver device. One action comprises the second transceiver device to jointly receive a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device. The HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain. The second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain. One action comprises the second transceiver device to separate the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains. One action comprises the second transceiver device to apply separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission. According to a ninth aspect there is presented a computer program product comprising a computer program according to at least one of the fourth aspect and the eighth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

[0024] Advantageously, these aspects provide HARQ processes that do not suffer from the above mentioned issues, or at least provide HARQ processes where the above mentioned issues have been reduced or mitigated.

[0025] Advantageously, these aspects enable the resource utilization for HARQ to be reduced without compromising its error-correcting capabilities.

[0026] Advantageously, by having decoupled HARQ scheme that exploits the geometrical structure of the channel during HARQ retransmissions, the HARQ transmission, or HARQ re-transmission, enjoys the time and spatial diversity of each domain independently. By this the network is not over-protected by wasting resources. This, in turn, results in an improved system throughput and reduces the end-to-end latency, which are key issues of classical HARQ protocols.

[0027] Advantageously, these aspects can improve the system throughput and spectrum utilization in large multiple input multiple output (MIMO) networks, repeater-assisted networks, THz communication networks, and backhauling networks, etc.

[0028] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0029] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0032] Fig. 1 is a schematic diagram illustrating a communication network according to embodiments;

[0033] Fig. 2 is a schematic illustration of spectrum utilization for HARQ retransmissions according to an example;

[0034] Figs. 3 and 4 are flowcharts of methods according to embodiments;

[0035] Figs. 5 and 6 are schematic illustrations of HARQ retransmissions according to embodiments; Fig. 7 is a signaling diagram of a method according to an embodiment;

[0036] Fig. 8 is a schematic diagram showing structural units of a first transceiver device according to an embodiment;

[0037] Fig. 9 is a schematic diagram showing functional modules of a first transceiver device according to an embodiment;

[0038] Fig. 10 is a schematic diagram showing structural units of a second transceiver device according to an embodiment;

[0039] Fig. 11 is a schematic diagram showing functional modules of a second transceiver device according to an embodiment; and

[0040] Fig. 12 shows one example of a computer program product comprising computer readable means according to an embodiment.

[0041] DETAILED DESCRIPTION

[0042] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0043] Fig. 1 is a schematic diagram illustrating a communication network 100 where embodiments presented herein can be applied. The communication network 100 comprises an access network node 110 and a user equipment 120. The access network node 110 could be any of a radio access network node, radio base station, base transceiver station, node B (NB), evolved node B (eNB), gNB, access point, access node, transmission and reception point, integrated access an backhaul (I AB) node, etc. The user equipment 120 could be any of a portable wireless device, mobile station, mobile phone, handset, wireless local loop phone, smartphone, laptop computer, tablet computer, wireless modem, wireless sensor device, network equipped sensor, network equipped vehicle, etc.

[0044] In some examples, the access network node 110 represents a first transceiver device and the user equipment 120 represents a second transceiver device. In other examples, the access network node 110 represents a second transceiver device and the user equipment 120 represents a first transceiver device. It is assumed that the first transceiver device sends one or more data signals to the second transceiver device over a wireless propagation channel 130 (or just channel for short). It is further assumed that a HARQ protocol is used for any retransmissions, as needed. In this respect, as disclosed above, there is a need for improved HARQ protocols. In further detail, existing HARQ protocols commonly results in spectrum resource being wasted for overprotecting the network. This is especially true in cases with proper network planning and where there is a sufficiently strong line of sight (LoS) connection between the first transceiver device and the second transceiver device. With a proper network planning and channel estimation, the first transceiver device has good information about the channel state of the link between the first transceiver device and the second transceiver device and, therefore, selects the modulation and coding properly such that, with high probability, the signal is correctly decoded by the second transceiver device. In such scenarios, even if the data signal as transmitted by the first transceiver device is not correctly decoded at the second transceiver device, as illustrated in Fig. 2, the received SNR is close to the minimum SNR required for successful decoding. In more detail, in Fig. 2 is illustrated that for the initial transmission, the received SNR is lower than the minimum required SNR for successful decoding and, as a result, the data signal is not correctly decoded. With an additional retransmission, however, the SNR is boosted way above the minimum required SNR. hence, for the retransmission the link is over-protected and spectrum resources are consequently wasted. Instead, a small boost in the SNR would suffice. Further, there is no need for wasting spectrum resources by retransmitting the whole packet.

[0045] Furthermore, in several propagation scenarios, the channel behaves differently in one domain (e.g., azimuth) compared to other domain (e.g., elevation). For instance, during a certain timeslot, the channel may show more variations, or fluctuations, in one domain compared to in the other domain. Existing HARQ protocols do not exploit any non-uniform behavior of the channel across the horizontal (azimuth) and the vertical (elevation) domains.

[0046] A particular object of the present disclosure is therefore to improve the HARQ process by exploiting the geometry of the channel to create an efficient HARQ process with a reduced resource utilization.

[0047] Reference is now made to Fig. 3 illustrating a method for HARQ retransmission as performed by the first transceiver device according to an embodiment.

[0048] S106: The first transceiver device receives, from a second transceiver device, a NACK of a first data transmission from the first transceiver device to the second transceiver device. The first data transmission has been performed in a first timeslot.

[0049] In general terms, when the HARQ retransmission is required of a first data transmission, the first transceiver device exploits the geometry of the channels and re-transmits the first data transmission as spread along one domain (elevation or azimuth), while another data signal (referred to as second data transmission) transmitted to the same second transceiver device as the HARQ retransmission as spread in the other domain.

[0050] S110: The first transceiver device therefore performs, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device together with performing a second data transmission to the second transceiver device. The first transceiver device spreads, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain. Further, the first transceiver device spreads, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

[0051] In this way, by exploiting the geometry of the channel, the whole HARQ process can be decoupled into horizontal domain and vertical domain HARQ sub-transmissions.

[0052] Embodiments relating to further details of HARQ retransmission as performed by the first transceiver device will now be disclosed with continued reference to Fig. 3.

[0053] There could be different types of HARQ retransmissions. In some embodiments, the HARQ retransmission of the first data transmission is an incremental redundancy HARQ retransmission of the first data transmission. In other embodiments, the HARQ retransmission of the first data transmission is a chase combining HARQ retransmission of the first data transmission.

[0054] There can be different types of spreading operations that are performed for the spreading in step S110. In some embodiments, a Kronecker product operation is used for spreading the HARQ retransmission of the first data transmission using the second data transmission and for spreading the second data transmission using the HARQ retransmission of the first data transmission.

[0055] In further detail, the array manifold vectors associated with the transmit and receive antenna arrays can be factorized as the Kronecker product of two smaller vectors representing the horizontal and the vertical domains, respectively. The vertical domain is associated with the elevation spatial frequencies while the horizontal domain is associated with the azimuth spatial frequencies. For example, the array manifold vectors associated with transmit and receive antenna arrays in form of Uniform Rectangular Arrays (URAs) describe the spatial signature of the array with respect to incoming or outgoing signals. When dealing with URAs, it is possible to take advantage of their grid-like structure to simplify the mathematical representation of these manifold vectors to find the geometry of the channel (i.e., to find the vertical and horizontal component of channel space). In further detail, for a URA with M elements along the horizontal axis and N elements along the vertical axis, denote the array manifold vector associated with the horizontal domain as ay(0) and the array manifold vector associated with the vertical domain as az(<f>), where 9 and p represent the azimuth and elevation angles, respectively. The array manifold vector for the entire URA, a(9, p'), can be factorized as the Kronecker product of ay(9) and a 9, <p) = ay(9)®az(<p)

[0056] This factorization effectively separates the spatial dependencies along the and axes.

[0057] As an illustrative example, assume that the HARQ retransmission of the first data transmission is denoted A = [«i CL2]Tand that the second data transmission is denoted B = [bi b2], The Kronecker product of A and B will thus be:

[0058] This matrix can be visualized as having the signal A spread across the vertical domain (with each element of being repeated across a row) and the signal B spread across the horizontal domain (each element of being repeated across a column).

[0059] Since the HARQ retransmission is a retransmission of the first data transmission, the HARQ retransmission is generally preceded by the first data transmission. Hence, in some embodiments, the first transceiver device is configured to perform (optional) step S104.

[0060] S104: The first transceiver device performs the first data transmission in the first timeslot.

[0061] Further aspects of the first data transmission, the second data transmission, and their relation to the HARQ retransmission will be disclosed next.

[0062] In some aspects, the first data transmission is performed without any factorization (and thus without any spreading). That is, in some embodiments, the first data transmission is performed without the first data transmission being spread in any of the horizontal domain and the vertical domain. Further aspects of this will be disclosed below with reference to Fig. 5.

[0063] In some aspects, also the first data transmission is performed with factorization (and thus with spreading using some other data transmission). In particular, in some embodiments, the first data transmission is performed by being spread in both the horizontal domain and the vertical domain. The NACK indicates a failure of the first data transmission in one of the horizontal domain and the vertical domain. The HARQ retransmission of the first data transmission is a retransmission of the first data transmission for the domain in which the first data transmission failed. Further aspects of this will be disclosed below with reference to Fig. 6.

[0064] In some aspects, the second data transmission is a new data transmission. That is, in some embodiments, the second data transmission comprises data, and the second data transmission is an initial transmission of this data. At the second transceiver device, the second data transmission can be used to improve SNR, and enable successful decoding of the previously failed signal, while new data is sent in the other domain.

[0065] In other aspects, the second data transmission is another data retransmission. That is, in some embodiments, the second data transmission comprises data, and the second data transmission is a HARQ retransmission of this data.

[0066] In yet other aspects, in the second timeslot, the signal by itself in one domain is the Kronecker coded with itself (same copy), when it is failed in the decoding processes in the first timeslot. That is, in some embodiments, the second data transmission is identical to the first data transmission. This by itself increases the recoverability of the failed signal as an extra degree of freedom will be introduced. In such a case, there is only a need for one ACK / NACK signal.

[0067] In some aspects, the HARQ process in the example of Fig. 5 represents a first HARQ operation mode and the HARQ process in the example of Fig. 6 represents a second HARQ operation mode. In case the first transceiver device is configured to selectively use any of these HARQ operation mode, then the first transceiver device might need to inform the second transceiver device of the selected HARQ operation mode. Therefore, in some embodiments, the first transceiver device is configured to perform (optional) step S102.

[0068] S102: The first transceiver device informs the second transceiver device of a HARQ operation mode. The HARQ operation mode pertains to whether the first data transmission is performed with the first data transmission being spread in the horizontal domain and the vertical domain or not.

[0069] Further aspects of the transmissions in the different domains will be disclosed next.

[0070] In some aspects, different modulation and coding scheme are used along each domain independently, depending on the channel conditions, or variations, along each domain. That is, in some embodiments, modulation and coding schemes are selected individually for the horizontal domain and the vertical domain.

[0071] In some aspect, there is no need of using channel codes for the HARQ retransmission since the Kronecker product by itself generates redundancy (as a kind of Kronecker coding) which protects the data against channel fading, etc. Therefore, in some embodiments, the HARQ retransmission of the first data transmission is transmitted without any forward error correction.

[0072] In some aspects, the first transceiver device, before making the HARQ retransmission, verifies that the channel can be decomposed. Therefore, in some embodiments, the first transceiver device is configured to perform (optional) step S108.

[0073] S108: The first transceiver device obtains an indication that the wireless propagation channel 130 between the first transceiver device and the second transceiver device is decomposable into the horizontal domain and the vertical domain before performing the HARQ retransmission of the first data transmission.

[0074] In this respect, there can be different criteria according to which the channel is determined to be decomposable or not.

[0075] In some aspects, the channel is determined to be decomposable in case there is one strong line-of-sight component between the first transceiver device and the second transceiver device. That is, in some embodiments, according to the indication, the wireless propagation channel 130 comprises only one single dominant line-of-sight component. In some aspects, the channel is determined to be decomposable in case there is low spread in one (or both) of the two domains. That is, in some embodiments, according to the indication, the wireless propagation channel 130 is a multipath wireless propagation channel and an angular spread of the wireless propagation channel 130 in at least one of the horizontal domain and the vertical domain is below a threshold value.

[0076] If the decoding fails at the receiver, the HARQ retransmission will be performed by exploiting the geometry of the channel. There are different ways to perform such decoupled HARQ retransmission. There can be different ways for the first transceiver device to select in which domain the HARQ retransmission of the first data transmission is spread. In some embodiments, in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission is spread is selected according to a selection criterion. Examples of different selection criteria will be disclosed next.

[0077] In some aspects, according to the selection criterion, the domain in which the HARQ retransmission of the first data transmission is spread changes from timeslot to timeslot. Hence, in some embodiments, the first data transmission is transmitted in one of the horizontal domain and the vertical domain, and, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the other of the horizontal domain and the vertical domain. In this way, all channel components can be utilized for the HARQ retransmission of the first data transmission.

[0078] In some scenarios, the wireless propagation channel 130 between the first transceiver device and the second transceiver device has higher angular spread in one domain of the horizontal domain and the vertical domain than the other domain of the horizontal domain and the vertical domain. This fact can be exploited for the HARQ retransmission.

[0079] In some aspects, according to the selection criterion, the domain in which the HARQ retransmission of the first data transmission is spread in the domain which shows the least variations, and the second data transmission (either another HARQ retransmission or a new data transmission) can be transmitted in the other domain. Hence, in some embodiments, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the domain with lowest angular spread. This would improve the chances of successful reception of the HARQ retransmission of the first data transmission. Likewise, in some embodiments, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the domain with highest angular spread. This would allow prioritization of the second data transmission.

[0080] In case the domain in which the HARQ retransmission of the first data transmission was spread in the second timeslot is not deterministic, or at least not known to the second transceiver on beforehand, then the first transceiver device notifies the second transceiver device about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread in the second timeslot. Therefore, in some embodiments, the first transceiver device is configured to perform (optional) step S112. S112: The first transceiver device transmits an indication to the second transceiver device about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread.

[0081] Accordingly, the first transceiver device and the second transceiver device have the same understanding that the failed signal of y-domain and z-domain are retransmitted after Tyand Tztimeslots, respectively.

[0082] Reference is now made to Fig. 4 illustrating a method for receiving a HARQ retransmission as performed by the second transceiver device according to an embodiment.

[0083] S208: The second transceiver device sends a NACK of a first data transmission to the first transceiver device.

[0084] S210: The second transceiver device jointly receives a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device. The HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain. The second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain.

[0085] S214: The second transceiver device separates the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains.

[0086] S216: The second transceiver device applies separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

[0087] Embodiments relating to further details of receiving a HARQ retransmission as performed by the second transceiver device will now be disclosed with continued reference to Fig. 4.

[0088] As disclosed above, there could be different types of HARQ retransmissions. In some embodiments, the HARQ retransmission of the first data transmission is an incremental redundancy HARQ retransmission of the first data transmission. In other embodiments, the HARQ retransmission of the first data transmission is a chase combining HARQ retransmission of the first data transmission.

[0089] As disclosed above, in some embodiments, the Kronecker product operation is used for spreading the HARQ retransmission of the first data transmission using the second data transmission and for spreading the second data transmission using the HARQ retransmission of the first data transmission. Therefore, in some embodiments, a (corresponding) Kronecker factorization procedure is used for de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domain.

[0090] Further, in some aspects, the combined signals are decoupled into their corresponding domains via a least squares Kronecker factorization procedure. That is, in some embodiments, the Kronecker factorization procedure is a least squares Kronecker factorization procedure. In general terms, applying a least squares Kronecker factorization procedure is equivalent to solving a rank-one matrix approximation problem for which several methods are available, such as the singular value decomposition (SVD) or other low-complexity alternatives. In this respect, some examples of how a least squares Kronecker factorization procedure can be used for despreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domain will be disclosed below with reference to Figs. 5 and 6.

[0091] As disclosed above, since the HARQ retransmission is a retransmission of the first data transmission, the HARQ retransmission is generally preceded by the first data transmission. Hence, in some embodiments, the second transceiver device is configured to perform (optional) steps S204, S206.

[0092] S204: The second transceiver device receives the first data transmission.

[0093] S206: The second transceiver device applies decoding to the first data transmission, and the NACK is sent in response to the decoding having failed.

[0094] Further aspects of the first data transmission, the second data transmission, and their relation to the HARQ retransmission will be disclosed next.

[0095] As disclosed above, in some aspects, the first data transmission is performed without any factorization (and thus without any spreading). Therefore, in some embodiments, when applying the decoding to the first data transmission, the first data transmission is treated as neither spread in the horizontal domain nor spread in the vertical domain.

[0096] As disclosed above, in some aspects, also the first data transmission is performed with factorization (and thus with spreading using some other data transmission). Therefore, in some embodiments, when applying the decoding to the first data transmission, the first data transmission is treated as being spread in both the horizontal domain and the vertical domain. The NACK indicates a failure of the first data transmission in one of the horizontal domain and the vertical domain. The HARQ retransmission of the first data transmission is a retransmission of the first data transmission for the domain in which the first data transmission failed.

[0097] As further disclosed above, in some embodiments, the first transceiver device informs the second transceiver device of the HARQ operation mode. Therefore, in some embodiments, the second transceiver device is configured to perform (optional) step S202.

[0098] S202: The second transceiver device receives information from the first transceiver device of a HARQ operation mode. The HARQ operation mode pertains to whether the first data transmission was performed with the first data transmission being spread in the horizontal domain and the vertical domain or not.

[0099] In this respect, and as further disclosed above, in some aspects, the HARQ process in the example of Fig. 5 represents a first HARQ operation mode and the HARQ process in the example of Fig. 6 represents a second HARQ operation mode. Further aspects of the transmissions in the different domains will be disclosed next.

[0100] As disclosed above, in some embodiments, the first transceiver device transmits an indication to the second transceiver device about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread. Therefore, in some embodiments, the second transceiver device is configured to perform (optional) step S212.

[0101] S212: The second transceiver device receives an indication from the first transceiver device about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread.

[0102] Different ways of how the second transceiver device can combine signals as received from the first transceiver device (and corresponding ways for the first transceiver device to transmit the signals) will be disclosed next with reference to Fig. 5 and Fig. 6. Fig. 5 and Fig. 6 show HARQ retransmissions in accordance with different HARQ processes. As disclosed above, in some aspects, the HARQ process in the example of Fig. 5 represents a first HARQ operation mode and the HARQ process in the example of Fig. 6 represents a second HARQ operation mode. These two HARQ operation modes will be disclosed in further detail next. For both HARQ operation modes, when one respective data signal is spread in each of the vertical and horizontal domains, the second transceiver device will perform feedback of two separate ACK / NACK signals, each one associated with one signal domain.

[0103] In the first HARQ operation mode, illustrated in Fig. 5, the second transceiver device first combines the retransmitted data signal with the previously transmitted retransmitted data signal (via maximum ratio combining for the chase combining HARQ approach or packet concatenation in for the incremental redundancy HARQ approach) to improve the received SNR and to successfully decode the data signal. Then, the decoded data signal as spread in the first domain is removed from the received signal and the second transceiver device proceeds to decode the new data signal as spread in the other respective domain.

[0104] In more detail, at a first timeslot ("Slot 1” in Fig. 5), the first transceiver device is assumed to transmit a data signal X1by using any given classical transmission scheme. The data signal X1is transmitted without the use of factorization. The second transceiver device receives a signal Yj which contains the transmitted data signal X±as impacted by the channel . That is,

[0105] Y1= H1X1+ N1

[0106] It is assumed that the second transceiver device tries to estimate the transmitted data signal X±from the received a signal Y This estimate of the transmitted data signal is denoted However, due to channel fading or any other reason, the second transceiver device is assumed to fail to decode the data signal The second transceiver device therefore sends a NACK to the first transceiver device to resend X1. In the second timeslot ("Slot 2” in Fig. 5), the first transceiver device exploits the geometrical structure of the channel, namely that = and resends Xtas spread in the horizontal domain and a new data signal X2as spread in the vertical domain, respectively. The first transceiver device transmits the failed data signal X1as spread along the horizontal domain jointly with a new data signal X2asspread along the vertical domain. In this case, the data signal X1acts as spreading code for the data X2and vice-versa. This is referred to as cross-coding. Thus, the signal Y2as received by the second transceiver device can be written as:

[0107] Defining yields

[0108] Y2= Vy®Vz+ N2(4)

[0109] The second transceiver device can then apply an LS Kronecker factorization procedure to obtain estimates of Vyand Yzby solving the optimization problem in Equation (5):

[0110] The second transceiver device could then apply matched filtering, or any other suitable method, to estimate the respective signal components using the knowledge of the two channels (Hy, Hz). The second transceiver device could then combine the failed and the current estimates of by means of either packet concatenation or maximum ratio combining to decode it successfully. The signal X2is decoded from fz. Finally,yis combined with Y1:as both contains the same data, to apply two kinds of receive processing; with chase combining, where the retransmitted data signal is exactly same as in the previously failed data signal at the second transceiver device maximum ratio combining ofyand Yi is performed to decode X On the other hand, for incremental redundancy, and Y^ are concatenated to decode X

[0111] In the second HARQ operation mode, illustrated in Fig. 6, the HARQ transmission is performed separately in the horizontal and vertical domains from the very first timeslot.

[0112] In more detail, the first transceiver device from the very first timeslot ("Slot 1” in Fig. 6) exploits the channel structure and sends HARQ signals towards second transceiver device spread in both the horizontal and vertical domains. That is, during the first transmission, the first transceiver device exploits the geometrical structure of the channel, and transmits Xlyand Xlzspread along the horizontal and vertical domains, respectively. Here, Xlyact as a spreading code for Xlzand vice-versa. More specifically, the transmitted data signal Xlyis spread in the horizontal domain and the transmitted data signal Xlzis spread in the vertical domain. That is:

[0113] Equation (6) can be rewritten as: = (H Xly)®(H Xlz) + tVr(7)

[0114] Defining Vly= HyXlyand Vlz= HZX1Zyields the optimization problem in Equation (8):

[0115] Similar to the first HARQ operation mode, the second transceiver device could apply an LS Kronecker factorization procedure to obtain estimates of Vlyand 71Zby solving the optimization problem in Equation (8). The second transceiver device could then apply matched filtering, or any other suitable method, to estimate the respective signal components Xlyand Xlz. It is here assumed that the signal Xlyis not correctly decoded while ^lzis correctly decoded. The second transceiver device therefore sends NACK_y for Xlyto be resent, and also sends ACK_z to confirm safe reception of Xlz. In the second timeslot ("Slot 2” in Fig. 6), dedicated for retransmissions of the y-domain signals, the first transceiver device retransmits Xlyas spread along the horizontal domain and a new data signal X2zas spread along the vertical domain. In other words, the data signal Xlyacts as a spreading code for the data signal X2zand vice-versa. Thus, the signal Y2as received by the second transceiver device can be written as:

[0116] Equation (9) can be rewritten as

[0117] Defining Vly= HyXlyand V2z= HzX2zyields the optimization problem in Equation (11):

[0118] The second transceiver device again applies matched filtering after LS Kronecker factorization to estimate the respective data signals Xlyand X2z. The data signal X2zis decoded from the data signal2z. The data signals lyand Ylyare combined using either chase combining or incremental redundancy for Xlyto be decoded, or recovered.

[0119] For both HARQ operation modes, the second transceiver device can apply either incremental redundancy or maximum ratio combining to the newly current estimate and the previous failed %lyto decode it successfully. In this way, the proposed method proves to be spectrally, or resource, efficient with improved performance compared to the classical HARQ schemes. There can be different ways to handle the situation where neither the signallynor the signall zis correctly decoded. In some examples, the individual signals in each of the domains is treated as not correctly decoded, and hence a respective NACK is sent for each of the signals. Then, in an upcoming timeslot, the first transceiver device makes two HARQ retransmissions, where each of the two HARQ retransmissions is spread in a respective domain in accordance with any of the above disclosed embodiments.

[0120] One particular aspect for HARQ transmission based on at least some of the above disclosed embodiments will be disclosed next with reference to the signaling diagram of Fig. 7.

[0121] S301: The first transceiver device receives information about the array geometry of the second transceiver device. In some examples, as in Fig. 7, this information is obtained directly from the second transceiver device. In another aspect, this information is obtained from an Operations, Administration and Maintenance (QAM) system or by reading a file. The first transceiver device also receives channel estimates.

[0122] S302: The first transceiver device sends information of the selected HARQ operation mode (e.g., to use the HARQ operation mode according to either Fig. 5 or Fig. 6) to the second transceiver device, as in step S102.

[0123] S303: The first transceiver device sends a first data transmission (either a single signal or two signals in different domains) to the second transceiver device, as in step S104.

[0124] S304: The second transceiver device fails to decode the complete first data transmission, or one part of the first data transmission in one of the domains is undecodable (depending on HARQ operation mode). The second transceiver device therefore transmits a NACK message to first transceiver device about the decoding failure, as in step S208.

[0125] S305: The first transceiver device performs a HARQ retransmission of the first data transmission, as in step S110. The first transceiver device spreads, using a second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and spreads, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain

[0126] S306: Based on the message decoding status, ACKs and / or NACKs are passed to the first transceiver device for each domain.

[0127] In this way, the herein disclosed embodiments exploit the channel and array geometry to resend a failed message and send a new signal jointly. This provides resource efficiency and can avoid extra delays due to failed re-transmissions. In comparison, in classical successive interference cancellation (SIC), if one signal cannot be decoded, this will also affect the decoding process of the other signal (as the decoding process depends on each other). Therefore, the first transceiver device would need to re-transmit all the signals again for the second transceiver device to decode all messages. This is a resource-inefficient procedure. In contrast, according to the herein disclosed embodiments, due to exploitation of the channel and array geometry, both signals can be independently estimated. Thereby, if decoding of one of the signals fails, the first transceiver device needs only to retransmit that signal, and not all signals. This is a resource-efficient procedure.

[0128] Fig. 8 schematically illustrates, in terms of a number of structural units, the components of a first transceiver device 800 according to an embodiment. Processing circuitry 810 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1210a (as in Fig. 12), e.g. in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0129] Particularly, the processing circuitry 810 is configured to cause the first transceiver device 800 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the first transceiver device 800 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 810 is thereby arranged to execute methods as herein disclosed.

[0130] The storage medium 830 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0131] The first transceiver device 800 may further comprise a communications (comm.) interface 820 for communications with other functions, nodes, and devices, such as the second transceiver device. As such the communications interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components.

[0132] The processing circuitry 810 controls the general operation of the first transceiver device 800 e.g. by sending data and control signals to the communications interface 820 and the storage medium 830, by receiving data and reports from the communications interface 820, and by retrieving data and instructions from the storage medium 830. Other components, as well as the related functionality, of the first transceiver device 800 are omitted in order not to obscure the concepts presented herein.

[0133] Fig. 9 schematically illustrates, in terms of a number of functional modules, the components of a first transceiver device 900 according to an embodiment. The first transceiver device 900 of Fig. 9 comprises a number of functional modules; a receive module 930 configured to perform step S106, and a transmit module 950 configured to perform step S110. The first transceiver device 900 of Fig. 9 may further comprise a number of optional functional modules, such as any of an inform module 910 configured to perform step S102, a transmit module 920 configured to perform step S104, an obtain module 940 configured to perform step S108, and a transmit module 960 configured to perform step S112. In general terms, each functional module 910:960 may be implemented in hardware or in software. Preferably, one or more or all functional modules 910:960may be implemented by the processing circuitry 810, possibly in cooperation with the communications interface 820 and / or the storage medium 830. The processing circuitry 810 may thus be arranged to from the storage medium 830 fetch instructions as provided by a functional module 910:960and to execute these instructions, thereby performing any steps of the first transceiver device 800 as disclosed herein.

[0134] Fig. 10 schematically illustrates, in terms of a number of structural units, the components of a second transceiver device 1000 according to an embodiment. Processing circuitry 1010 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 1210b (as in Fig. 12), e.g. in the form of a storage medium 1030. The processing circuitry 1010 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0135] Particularly, the processing circuitry 1010 is configured to cause the second transceiver device 1000 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 1030 may store the set of operations, and the processing circuitry 1010 may be configured to retrieve the set of operations from the storage medium 1030 to cause the second transceiver device 1000 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 1010 is thereby arranged to execute methods as herein disclosed.

[0136] The storage medium 1030 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0137] The second transceiver device 1000 may further comprise a communications interface 1020 for communications with functions, nodes, and devices, such as the first transceiver device. As such the communications interface 1020 may comprise one or more transmitters and receivers, comprising analogue and digital components.

[0138] The processing circuitry 1010 controls the general operation of the second transceiver device 1000 e.g. by sending data and control signals to the communications interface 1020 and the storage medium 1030, by receiving data and reports from the communications interface 1020, and by retrieving data and instructions from the storage medium 1030. Other components, as well as the related functionality, of the second transceiver device 1000 are omitted in order not to obscure the concepts presented herein.

[0139] Fig. 11 schematically illustrates, in terms of a number of functional modules, the components of a second transceiver device 1100 according to an embodiment. The second transceiver device 1100 of Fig. 11 comprises a number of functional modules; a send module 1140 configured to perform step S208, a receive module 1150 configured to perform step S210, a de-spread module 1170 configured to perform step S214, and a decode module 1180 configured to perform step S216. The second transceiver device 1100 of Fig. 11 may further comprise a number of optional functional modules, such as any of a receive module 1110 configured to perform step S202, a receive module 1120 configured to perform step S204, a decode module 1130 configured to perform step S206, and a receive module 1160 configured to perform step S212.

[0140] In general terms, each functional module 1110:1180 may be implemented in hardware or in software. Preferably, one or more or all functional modules 1110:1180may be implemented by the processing circuitry 1010, possibly in cooperation with the communications interface 1020 and / or the storage medium 1030. The processing circuitry 1010 may thus be arranged to from the storage medium 1030 fetch instructions as provided by a functional module 1110:1180and to execute these instructions, thereby performing any steps of the second transceiver device 1000 as disclosed herein.

[0141] Some (radio) access network architectures define transceiver devices (such as gNBs) comprising multiple component parts or nodes: a central unit (CU), one or more distributed units (DUs), and one or more radio units (RUs). The protocol layer stack of the network node is divided between the CU, the DUs and the RUs, with one or more lower layers of the stack implemented in the RUs, and one or more higher layers of the stack implemented in the CU and / or DUs. The CU is coupled to the DUs via a fronthaul higher layer split (HLS) network; the CU / DUs are connected to the RUs via a fronthaul lower-layer split (LLS) network. The DU may be combined with the CU in some embodiments, where a combined DU / CU may be referred to as a CU or simply a baseband unit. A communication link for communication of user data messages or packets between the RU and the baseband unit, CU, or DU is referred to as a fronthaul network or interface. Messages or packets may be transmitted from the transceiver devices in the downlink (i.e., from the CU to the RU) or received by the transceiver devices in the uplink (i.e., from the RU to the CU).

[0142] Fig. 12 shows one example of a computer program product 1210a, 1210b comprising computer readable means 1230. On this computer readable means 1230, a computer program 1220a can be stored, which computer program 1220a can cause the processing circuitry 810 and thereto operatively coupled entities and devices, such as the communications interface 220 and the storage medium 830, to execute methods according to embodiments described herein. The computer program 1220a and / or computer program product 1210a may thus provide means for performing any steps of the first transceiver device as herein disclosed. On this computer readable means 1230, a computer program 1220b can be stored, which computer program 1220b can cause the processing circuitry 1010 and thereto operatively coupled entities and devices, such as the communications interface 1020 and the storage medium 1030, to execute methods according to embodiments described herein. The computer program 1220b and / or computer program product 1210b may thus provide means for performing any steps of the second transceiver device as herein disclosed.

[0143] In the example of Fig. 12, the computer program product 1210a, 1210b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 1210a, 1210b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable readonly memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 1220a, 1220b is here schematically shown as a track on the depicted optical disk, the computer program 1220a, 1220b can be stored in any way which is suitable for the computer program product 1210a, 1210b. The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1 . A method for hybrid automatic repeat request, HARQ, retransmission, wherein the method is performed by a first transceiver device (800, 900), and wherein the method comprises: receiving (S106), from a second transceiver device (1000, 1100), a negative acknowledgement, NACK, of a first data transmission from the first transceiver device (800, 900) to the second transceiver device (1000, 1100), the first data transmission having been performed in a first timeslot; and performing (S110), in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device (1000, 1100) together with performing a second data transmission to the second transceiver device (1000, 1100), by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

2. The method according to claim 1, wherein a Kronecker product operation is used for spreading the HARQ retransmission of the first data transmission using the second data transmission and for spreading the second data transmission using the HARQ retransmission of the first data transmission.

3. The method according to any preceding claim, wherein in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission is spread is selected according to a selection criterion.

4. The method according to claim 3, wherein the first data transmission is transmitted in one of the horizontal domain and the vertical domain, and wherein, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the other of the horizontal domain and the vertical domain.

5. The method according to claim 3, wherein a wireless propagation channel (130) between the first transceiver device (800, 900) and the second transceiver device (1000, 1100) has higher angular spread in one domain of the horizontal domain and the vertical domain than the other domain of the horizontal domain and the vertical domain, and wherein, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the domain with lowest angular spread.

6. The method according to claim 3, wherein a wireless propagation channel (130) between the first transceiver device (800, 900) and the second transceiver device (1000, 1100) has higher angular spread in one domain of the horizontal domain and the vertical domain than the other domain of the horizontal domain and thevertical domain, and wherein, according to the selection criterion, the HARQ retransmission of the first data transmission is spread in the domain with highest angular spread.

7. The method according to any preceding claim, wherein the method further comprises: transmitting (S112) an indication to the second transceiver device (1000, 1100) about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread.

8. The method according to any preceding claim, wherein the method further comprises: obtaining (S108) an indication that a wireless propagation channel (130) between the first transceiver device (800, 900) and the second transceiver device (1000, 1100) is decomposable into the horizontal domain and the vertical domain before performing the HARQ retransmission of the first data transmission.

9. The method according to claim 8, wherein, according to the indication, the wireless propagation channel comprises only one single dominant line-of-sight component.

10. The method according to claim 8, wherein, according to the indication, the wireless propagation channel (130) is a multipath wireless propagation channel and an angular spread of the wireless propagation channel (130) in at least one of the horizontal domain and the vertical domain is below a threshold value.11 . The method according to any preceding claim, wherein the method further comprises: performing (S104) the first data transmission in the first timeslot.

12. The method according to claim 11 , wherein the first data transmission is performed without the first data transmission being spread in any of the horizontal domain and the vertical domain.

13. The method according to claim 11, wherein the first data transmission is performed by being spread in both the horizontal domain and the vertical domain, wherein the NACK indicates a failure of the first data transmission in one of the horizontal domain and the vertical domain, and wherein the HARQ retransmission of the first data transmission is a retransmission of the first data transmission for the domain in which the first data transmission failed.

14. The method according to any of claims 11, 12, or 13, wherein the method further comprises: informing (S102) the second transceiver device (1000, 1100) of a HARQ operation mode, the HARQ operation mode pertaining to whether the first data transmission is performed with the first data transmission being spread in the horizontal domain and the vertical domain or not.

15. The method according to any preceding claim, wherein the second data transmission comprises data, and wherein the second data transmission is an initial transmission of said data.

16. The method according to any of claims 1 to 14, wherein the second data transmission comprises data, and wherein the second data transmission is a HARQ retransmission of said data.

17. The method according to any of claims 1 to 14, wherein the second data transmission is identical to the first data transmission.

18. The method according to any preceding claim, wherein modulation and coding schemes are selected individually for the horizontal domain and the vertical domain.

19. The method according to any preceding claim, wherein the HARQ retransmission of the first data transmission is transmitted without any forward error correction.

20. The method according to any preceding claim, wherein the HARQ retransmission of the first data transmission is an incremental redundancy HARQ retransmission of the first data transmission.21 . The method according to any of claims 1 to 19, wherein the HARQ retransmission of the first data transmission is a chase combining HARQ retransmission of the first data transmission.

22. A method for receiving a hybrid automatic repeat request, HARQ, retransmission, wherein the method is performed by a second transceiver device (1000, 1100), and wherein the method comprises: sending (S208) a negative acknowledgement, NACK, of a first data transmission to a first transceiver device (800, 900); jointly receiving (S210) a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device (800, 900), wherein the HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain, and the second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain; separating (S214) the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains; and applying (S216) separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

23. The method according to claim 22, wherein a Kronecker factorization procedure is used for de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domain.

24. The method according to claim 23, wherein the Kronecker factorization procedure is a least squares Kronecker factorization procedure.

25. The method according to any of claims 22 to 24, wherein the method further comprises: receiving (S212) an indication from the first transceiver device (800, 900) about in which of the horizontal domain and the vertical domain the HARQ retransmission of the first data transmission was spread.

26. The method according to any of claims 22 to 25, wherein the method further comprises: receiving (S204) the first data transmission; and applying (S206) decoding to the first data transmission, and wherein the NACK is sent in response to the decoding having failed.

27. The method according to claim 26, wherein, when applying the decoding to the first data transmission, the first data transmission is treated as neither spread in the horizontal domain nor spread in the vertical domain.

28. The method according to claim 26, wherein, when applying the decoding to the first data transmission, the first data transmission is treated as being spread in both the horizontal domain and the vertical domain, wherein the NACK indicates a failure of the first data transmission in one of the horizontal domain and the vertical domain, and wherein the HARQ retransmission of the first data transmission is a retransmission of the first data transmission for the domain in which the first data transmission failed.

29. The method according to any of claims 26, 27, or 28, wherein the method further comprises: receiving (S202) information from the first transceiver device (800, 900) of a HARQ operation mode, the HARQ operation mode pertaining to whether the first data transmission was performed with the first data transmission being spread in the horizontal domain and the vertical domain or not.

30. The method according to any preceding claim, wherein the first transceiver device (800, 900) is either an access network node (110) or a user equipment (120).

31. The method according to any preceding claim, wherein the second transceiver device (1000, 1100) is either a user equipment (120) or an access network node (110).

32. A first transceiver device (800, 900) for hybrid automatic repeat request, HARQ, retransmission, the first transceiver device (800, 900) comprising processing circuitry (810), the processing circuitry being configured to cause the first transceiver device (800, 900) to:receive, from a second transceiver device (1000, 1100), a negative acknowledgement, NACK, of a first data transmission from the first transceiver device (800, 900) to the second transceiver device (1000, 1100), the first data transmission having been performed in a first timeslot; and perform, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device (1000, 1100) together with performing a second data transmission to the second transceiver device (1000, 1100), by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

33. A first transceiver device (800, 900) for hybrid automatic repeat request, HARQ, retransmission, the first transceiver device (800, 900) comprising: a receive module (930) configured to receive, from a second transceiver device (1000, 1100), a negative acknowledgement, NACK, of a first data transmission from the first transceiver device (800, 900) to the second transceiver device (1000, 1100), the first data transmission having been performed in a first timeslot; and a transmit module (950) configured to receive perform, in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device (1000, 1100) together with performing a second data transmission to the second transceiver device (1000, 1100), by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

34. The first transceiver device (800, 900) according to claim 32 or 33, further being configured to perform the method according to any of claims 2 to 21 .

35. A second transceiver device (1000, 1100) for receiving a hybrid automatic repeat request, HARQ, retransmission, the second transceiver device (1000, 1100) comprising processing circuitry (1010), the processing circuitry being configured to cause the second transceiver device (1000, 1100) to: send a negative acknowledgement, NACK, of a first data transmission to a first transceiver device (800, 900);jointly receive a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device (800, 900), wherein the HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain, and the second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain; separate the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains; and apply separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

36. A second transceiver device (1000, 1100) for receiving a hybrid automatic repeat request, HARQ, retransmission, the second transceiver device (1000, 1100) comprising: a send module (1140) configured to send a negative acknowledgement, NACK, of a first data transmission to a first transceiver device (800, 900); a receive module (1150) configured to jointly receive a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device (800, 900), wherein the HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain, and the second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain; a de-spread module (1170) configured to separate the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains; and a decode module (1180) configured to apply separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

37. The second transceiver device (1000, 1100) according to claim 35 or 36, further being configured to perform the method according to any of claims 23 to 31 .

38. A computer program (1220a) for hybrid automatic repeat request, HARQ, retransmission, the computer program comprising computer code which, when run on processing circuitry (810) of a first transceiver device (800, 900), causes the first transceiver device (800, 900) to:receive (S106), from a second transceiver device (1000, 1100), a negative acknowledgement, NACK, of a first data transmission from the first transceiver device (800, 900) to the second transceiver device (1000, 1100), the first data transmission having been performed in a first timeslot; and perform (S110), in a second timeslot, a HARQ retransmission of the first data transmission to the second transceiver device (1000, 1100) together with performing a second data transmission to the second transceiver device (1000, 1100), by spreading, using the second data transmission, the HARQ retransmission of the first data transmission in either horizontal domain or vertical domain, and spreading, using the HARQ retransmission of the first data transmission, the second data transmission in the other of the horizontal domain and the vertical domain.

39. A computer program (1220b) for receiving a hybrid automatic repeat request, HARQ, retransmission, the computer program comprising computer code which, when run on processing circuitry (1010) of a second transceiver device (1000, 1100), causes the second transceiver device (1000, 1100) to: send (S208) a negative acknowledgement, NACK, of a first data transmission to a first transceiver device (800, 900); jointly receive (S210) a HARQ retransmission of the first data transmission and a second data transmission from the first transceiver device (800, 900), wherein the HARQ retransmission of the first data transmission is, by the second data transmission, spread in either horizontal domain or vertical domain, and the second data transmission is, by the HARQ retransmission of the first data transmission, spread in the other of the horizontal domain and the vertical domain; separate (S214) the HARQ retransmission of the first data transmission and the second data transmission from each other by de-spreading the HARQ retransmission of the first data transmission and the second data transmission into their respective domains; and apply (S216) separate decoding to the separated HARQ retransmission of the first data transmission and the second data transmission.

40. A computer program product (1210a, 1210b) comprising a computer program (1220a, 1220b) according to at least one of claims 38 and 39, and a computer readable storage medium (1230) on which the computer program is stored.

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