Technical Field

The invention relates to a transmitting device and a receiving device for reliable layer-to- antenna-port mapping in MIMO transmissions. Furthermore, the invention also relates to corresponding methods and a computer program.

Background

Layer-to-antenna mapping in multiple input multiple output (MIMO) transmissions relates to the operation of mapping a number of transmit layers to a number of selected antenna-ports. Typically, the layers to be transmitted are mapped from one or several code-blocks. Prior to that, the bits in each code-block has been mapped to a number of modulated symbols such as with Quadrature Phase Shift Keying (QPSK) and 16, 64, or even higher Quadrature Amplitude Modulation (QAM). The layer-to-antenna mapping maps the modulated symbols in each transmit layer to a number of selected antenna-ports according to specified patterns which is given by standards. Hence, such specified patterns are given in long term evolution (LTE) and new radio (NR).

Summary

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

A further objective of embodiments of the invention is to provide a solution which improves efficiency in MIMO retransmissions compared to conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a transmitting device for a wireless communication system, the transmitting device being configured to

map a set of symbol vectors onto a set of antenna ports based on an initial permutation scheme so as to obtain an initial layer-to-antenna-port mapping;

use the initial symbol-to-antenna port mapping in an initial transmission of the set of symbol vectors to a receiving device;

map the set of symbol vectors onto the set of antenna ports based on a retransmission permutation scheme so as to obtain a retransmission layer-to-antenna-port mapping, wherein the retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r;

use the retransmission layer-to-antenna-port mapping in a retransmission of the set of symbol vectors to the receiving device.

The transmitting device hence performs an initial transmission of set of symbol vectors intended for the receiving device and one or more retransmissions. Such a transmission scheme can e.g. be a HARQ scheme in LTE or NR.

The transmitting device can be configured to use the initial layer-to-antenna-port port mapping in a data transmission to the receiving device. The transmitting device can further be configured to use the retransmission layer-to-antenna-port mapping in a data transmission to the receiving device.

An advantage of the transmitting device according to the first aspect is that it improves the efficiency in MIMO retransmissions by proposing a three-dimensional layer-hopping pattern taking into consideration a symbol vector index i, a number of layers v, and a retransmission index r. The transmitting device according to the first aspect also provides robust performance under various channel conditions by spreading the transmitted symbols onto each antenna port and different spatial-directions. Further, the transmitting device according to the first aspect also boosts the data-throughput, especially when one or several spatial-directions of the corresponding MIMO channel suffers from small channel gains. Further, the transmitting device also resolves potential issues when the transmission-efficiency is bottlenecked by one or several weaker received layers. Moreover, the transmitting device can reduce the number of retransmission times as well as the transmission latency.

In an implementation form of a transmitting device according to the first aspect, the retransmission permutation scheme is changed in dependence on the symbol vector index i for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that it also introduces different layer-to-antenna mapping patterns within a transmission on different symbol-vectors (which does not exist in current standards). This means that the symbols are spread on each layer to all antenna ports thereby improving the robustness of the transmission against various channel conditions. In an implementation form of a transmitting device according to the first aspect, the retransmission permutation scheme is changed in dependence on the number of layers v for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that the layer-to-antenna mapping has a cyclic pattern in relation to the number of layers which can simplify the implementation complexity in the transmitting device and the receiving device.

In an implementation form of a transmitting device according to the first aspect, the retransmission permutation scheme is changed in dependence on the retransmission index r for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that different layer-to-antenna mapping patterns are used across different transmission attempts, which can further harvest the diversity gains in retransmissions.

In an implementation form of a transmitting device according to the first aspect,

the initial permutation scheme is an initial permutation matrix P, and

the retransmission permutation scheme is a retransmission permutation matrix P _{r V i} .

In an implementation form of a transmitting device according to the first aspect, the retransmission permutation matrix P _{r V i} is a function 7 of the symbol vector index i, the number of layers v, the retransmission index r and the initial permutation matrix P, i.e. P _{r v i} = 7(r, v, i, P ).

An advantage with this implementation form is that it introduces a joint-design of the layer-to- antenna mapping that introduces a three-fold hopping pattern over time and frequency (the symbols index i), spatial-direction (the number of layers v), and retransmissions (the retransmission index r).

In an implementation form of a transmitting device according to the first aspect, the function 7 is an exponential function Q of the initial permutation matrix P, i.e. 7(r, v, i, P ) = p50w)

An advantage with this implementation form is that the layer-to-antenna mapping patterns are generated from a root matrix P and its self-multiplications. This means low complex implementation in the transmitting device and the receiving device. In an implementation form of a transmitting device according to the first aspect, the exponential function Q has a periodicity equal to the number of layers v. An advantage with this implementation form is that the layer-to-antenna mapping is periodic, which is easy to implement in the transmitting device and the receiving device.

In an implementation form of a transmitting device according to the first aspect, the exponential function Q is defined as Q(r, v, i) = mod(r + i, v), wherein mod denotes the modulus operation.

In an implementation form of a transmitting device according to the first aspect, the initial permutation matrix P fulfils the relation

P = argmax(||/— P||),

p

wherein / denotes an identity matrix, and || / - P || denotes a matrix norm between the identity matrix / and the initial permutation matrix P.

An advantage with this implementation form is that the diversities of MIMO channels in different retransmissions is maximized, and therefore the diversity gain can be improved. In an implementation form of a transmitting device according to the first aspect, the initial permutation matrix P for different values of the number of layers v is given as:

An advantage with this implementation form is that the exact values of the elements of the the initial permutation matrix P for different values of the number of layers v is given, which maximizes the norm difference, and yields good performance results.

In an implementation form of a transmitting device according to the first aspect, the symbol vector index i is equal to a corresponding subcarrier index in an orthogonal frequency division multiplexing system.

In an implementation form of a transmitting device according to the first aspect, the number of layers v is equal to v = 1, 2, 4 or 8 and the retransmission index r is equal to r = 0, 1, 2, or 3.

An advantage with this implementation form is that this implementation form is compatible with NR. Hence, embodiments of the invention can be introduced to the current NR standard with small changes.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a receiving device for a wireless communication system, the receiving device being configured to

receive an initial transmission of a set of symbol vectors from a transmitting device; apply an inverse initial permutation scheme onto the initial transmission so as to obtain an initial layer-to-antenna-port de-mapping;

receive a retransmission of the set of symbol vectors from the transmitting device; apply an inverse retransmission permutation scheme onto the retransmission so as to obtain a retransmission layer-to-antenna-port de-mapping, wherein the inverse retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r.

An advantage of the receiving device according to the second aspect is that it improves the efficiency in MIMO retransmissions by proposing a three-dimensional layer-hopping pattern taking into consideration a symbol vector index i, a number of layers v, and a retransmission index r. Further, the receiving device according to the second aspect also boosts the data- throughput, especially when one or several spatial-directions of the MIMO channel suffers from small channel gains. Further, the receiving device also resolves potential issues when the transmission-efficiency is bottlenecked by one or several weaker received layers. Moreover, the receiving device can reduce the number of retransmission times as well as the transmission latency. In an implementation form of a receiving device according to the second aspect, the inverse retransmission permutation scheme is changed in dependence on the symbol vector index i for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that it introduces different layer-to-antenna mapping patterns within a transmission on different symbol-vectors. This means that the symbols are spread on each layer to all antenna ports thereby improving the robustness of the transmission against various channel conditions.

In an implementation form of a receiving device according to the second aspect, the inverse retransmission permutation scheme is changed in dependence on the number of layers v for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that the layer-to-antenna mapping has a cyclic pattern in relation to the number of layers which can simplify the implementation complexity in the transmitting device and the receiving device.

In an implementation form of a receiving device according to the second aspect, the inverse retransmission permutation scheme is changed in dependence on the retransmission index r for each retransmission of the set of symbol vectors.

An advantage with this implementation form is that different layer-to-antenna mapping patterns are used across different transmission attempts, which can further harvest the diversity gains in retransmissions.

In an implementation form of a receiving device according to the second aspect, the symbol vector index i is equal to a corresponding subcarrier index in an orthogonal frequency division multiplexing system.

In an implementation form of a receiving device according to the second aspect, the number of layers v is equal to v = 1, 2, 4 or 8 and the retransmission index r is equal to r = 0, 1, 2, or 3.

An advantage with this implementation form is that this implementation form is compatible with NR. Hence, embodiments of the invention can be introduced to the current NR standard with small changes.

In an implementation form of a receiving device according to the second aspect, the inverse initial permutation scheme is an inverse initial permutation matrix P ¹ , and the inverse retransmission permutation scheme is an inverse retransmission permutation matrix

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

mapping a set of symbol vectors onto a set of antenna ports based on an initial permutation scheme so as to obtain an initial layer-to-antenna-port mapping;

using the initial symbol-to-antenna port mapping in an initial transmission of the set of symbol vectors to a receiving device;

mapping the set of symbol vectors onto the set of antenna ports based on a retransmission permutation scheme so as to obtain a retransmission layer-to-antenna-port mapping, wherein the retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r;

using the retransmission layer-to-antenna-port mapping in a retransmission of the set of symbol vectors to the receiving device.

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

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

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

receiving an initial transmission of a set of symbol vectors from a transmitting device; applying an inverse initial permutation scheme onto the initial transmission so as to obtain an initial layer-to-antenna-port de-mapping;

receiving a retransmission of the set of symbol vectors from the transmitting device; applying an inverse retransmission permutation scheme onto the retransmission so as to obtain a retransmission layer-to-antenna-port de-mapping, wherein the inverse retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r. The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the receiving device according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the receiving device.

The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the receiving device according to the second aspect.

The invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments of the invention. Further, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

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

Brief Description of the Drawings

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

- Fig. 1 shows a transmitting device according to an embodiment of the invention;

- Fig. 2 shows a method for a transmitting device according to an embodiment of the invention;

- Fig. 3 shows a receiving device according to an embodiment of the invention;

- Fig. 4 shows a method for a receiving device according to an embodiment of the invention;

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

- Fig. 6 shows an example of a mobile device;

- Fig. 7 shows examples of norm values of the initial permutation matrix; and

- Fig. 8 shows performance comparison between NR and embodiments of the invention. Detailed Description

The inventors have identified that a problem of the existing MIMO transmission scheme in new radio (NR), also known as 5G, is that the layer-to-antenna-port mapping is fixed for different retransmissions. In cases where one or several spatial-directions of a MIMO channel are blocked to receiver(s), such a fixed retransmissions scheme can yield catastrophic diversity- losses under slow-fading environments. Therefore, the inventors among other things propose an enhancement of MIMO transmission scheme for NR to permute and spread the transmitted symbols on different layers through all spatial-directions for different retransmission attempts, which could be denoted as “layer-hopping”. Such a proposed layer-hopping MIMO transmission scheme is e.g. efficient for resolving potential issues when the transmission- efficiency is bottlenecked by one or several weaker received signals that are passed through the spatial-dimensions with small channel gains. For instance, consider a MIMO transmission model as the following:

where the channel H is in slow-fading and unknown or at least partially unknown to the transmitter. It can happen that one or several columns of the channel matrix H can contain small entries that render small channel gains. In an extreme case, the first column of the channel matrix H contains all Os, i.e., the first transmitted layer is completely blocked-out to the receiver as illustrated by the equation:

Under a slow-fading channel, e.g., f _d < 10 Hz (with a coherent time ~100ms whereas a typical retransmission duration in NR is ~8ms), and if the layer-to-antenna-port mapping remains unaltered in retransmissions, the first layer continues suffering from bad connection and the decoding attempts of the entire transmit-block are in vain. With incremental redundancy (IR) retransmission scheme, the problem is somewhat alleviated, since the transmitter retransmits signals is cyclically shifted from a buffer with quasi-random starting position. However, it is not guaranteed that the repeated symbols (or corresponding bits) can always be retransmitted on a different layer (or equivalently, a different spatial-direction seen at receiver). In a completely randomized layer-reshuffling introduced by operations such as cyclic buffer and rate-matching, there is still a probability of Mv (where v denotes the total number of layers) that the same symbols are retransmitted on the same layer. For the above considerations and insights, the inventors propose a transmitting device and a receiving device. Furthermore, corresponding methods are also disclosed.

Fig. 1 shows a transmitting device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the transmitting device 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The transmitting device 100 may be configured for both wireless and wired communications in wireless and wired communication systems, respectively. The wireless communication capability is provided with an antenna or antenna array 1 10 coupled to the transceiver 104, while the wired communication capability is provided with a wired communication interface coupled to the transceiver 104. That the transmitting device 100 is configured to perform certain actions can in this disclosure be understood to mean that the network access node 100 comprises suitable means, such as e.g. the processor 102 and the transceiver 104, configured to perform said actions.

According to embodiments of the invention the transmitting device 100 is configured to map a set of symbol vectors onto a set of antenna ports based on an initial permutation scheme so as to obtain an initial layer-to-antenna-port mapping. The transmitting device 100 is further configured to use the initial symbol-to-antenna port mapping in an initial transmission of the set of symbol vectors to a receiving device 300 (such as the one shown in Fig. 3). The transmitting device 100 is further configured to map the set of symbol vectors onto the set of antenna ports based on a retransmission permutation scheme so as to obtain a retransmission layer-to-antenna-port mapping. The retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r. The transmitting device 100 is further configured to use the retransmission layer-to-antenna-port mapping in a retransmission of the set of symbol vectors to the receiving device 300.

According to embodiments of the invention, initial permutation scheme is an initial permutation matrix P, and the retransmission permutation scheme is a retransmission permutation matrix P _{r V i} . Hence, the set of symbol vectors addressed for the receiving device 300 are permuted after an original layer mapping of an initial transmission as follows: where P _{r v i} is a set of retransmission permutation matrices that depends on the retransmission index r, the number of layers v, and the symbol-vector index i. In an embodiment of the invention, the symbol vector index i can be replaced by the subcarrier index in an OFDM system, such as LTE and NR. It is also noted that the initial permutation matrix P can be dependent on variables v, i and r with r = 0. The proposed layer-hopping scheme generates a two-fold space-time-frequency (STF) block coding with cooperating retransmissions which introduces another dimension in time.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a transmitting device 100, such as the one shown in Fig. 1. The method 200 comprises mapping 202 a set of symbol vectors onto a set of antenna ports based on an initial permutation scheme so as to obtain an initial layer-to-antenna-port mapping. The method 200 further comprises using 204 the initial symbol-to-antenna port mapping in an initial transmission of the set of symbol vectors 510 to a receiving device 300. The method 200 further comprises mapping 206 the set of symbol vectors onto the set of antenna ports based on a retransmission permutation scheme so as to obtain a retransmission layer-to-antenna-port mapping. The retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r. The method 200 further comprises using 208 the retransmission layer- to-antenna-port mapping in a retransmission of the set of symbol vectors 512 to the receiving device 300.

Fig. 3 shows a receiving device 300 according to an embodiment of the invention. In the embodiment shown in Fig. 3, the receiving device 300 comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The receiving device 300 further comprises an antenna or antenna array 310 coupled to the transceiver 304, which means that the receiving device 300 is configured for wireless communications in a wireless communication system. That the receiving device 300 is configured to perform certain actions can in this disclosure be understood to mean that the receiving device 300 comprises suitable means, such as e.g. the processor 302 and the transceiver 304, configured to perform said actions.

According to embodiments of the invention the receiving device 300 is configured to receive an initial transmission of a set of symbol vectors 510 from a transmitting device 100. The receiving device 300 is further configured to apply an inverse initial permutation scheme onto the initial transmission so as to obtain an initial layer-to-antenna-port de-mapping. The receiving device 300 is further configured to receive a retransmission of the set of symbol vectors 512 from the transmitting device 100. The receiving device 300 is further configured to apply an inverse retransmission permutation scheme onto the retransmission so as to obtain a retransmission layer-to-antenna-port de-mapping. The inverse retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r.

The receiving device 300 can be configured to use the initial layer-to-antenna-port de-mapping and one or more retransmission layer-to-antenna-port de-mappings. That is, the receiving device 300 applies an antenna port-to-layer mapping to de-map the received symbols on each antenna-ports back into the transmit layers with an inverse operation of the layer-to-antenna mapping at the transmitting side. The transmissions from the transmitting device 100 can be part of a HARQ scheme. There are mainly two different of HARQ schemes in retransmissions, namely, chase-combining and incremental redundancy. In chase combining type of HARQ scheme, the same information and parity bits are retransmitted each time. In incremental redundancy type of HARQ, multiple different set of code bits are generated for the same information bits used in a data packet unlike chase combining type. These different sets of coded are transmitted under different retransmissions. The invention is compatible with both types of HARQ schemes.

Fig. 4 shows a flow chart of a corresponding method 400 which may be executed in a receiving device 300, such as the one shown in Fig. 3. The method 400 comprises receiving 402 an initial transmission of a set of symbol vectors 510 from a transmitting device 100. The method 400 comprises applying 404 an inverse initial permutation scheme onto the initial transmission so as to obtain an initial layer-to-antenna-port de-mapping. The method 400 comprises receiving 406 a retransmission of the set of symbol vectors 512 from the transmitting device 100. The method 400 comprises applying 408 an inverse retransmission permutation scheme onto the retransmission so as to obtain a retransmission layer-to-antenna-port de-mapping. The inverse retransmission permutation scheme is dependent on a symbol vector index i, a number of layers v, and a retransmission index r.

Fig. 5 shows a wireless communication system 500 according to an embodiment of the invention in which the transmitting device is represented in the form of a network access node 100 and the receiving device in the form of a client device 300. The network access node 100 and the client device 300 are configured to operate in the wireless communication system 500 and to communicate with each other. For simplicity, the wireless communication system 500 shown in Fig. 5 only comprises one network access node 100 and one client device 300. However, the wireless communication system 500 may comprise any number of network access nodes 100 and any number of client devices 300 without deviating from the scope of the invention. The wireless communication system 500 can e.g. be a LTE system, a NR system, or a multi radio access technology (RAT) system.

In the wireless communication system 500, the network access node 100 performs data transmissions to the client device 300 in the downlink (DL). In MIMO transmissions in NR the network access node 100 performs an initial transmission and if needed up to three retransmissions. In embodiments of the invention, the symbols are transmitted in different layers through all spatial-directions in each (re-)transmission. With no retransmission, the scheme is the same as current NR standard. However, with retransmissions it has a benefit that each layer can be retransmitted through all spatial-directions on different resource elements (REs). It is therefore illustrated in Fig. 5 how the network access node 100 performs an initial DL transmission 510 to the client device 300. Thereafter, the access node 100 performs at least one DL retransmission 512 to the client device 300, i.e. the same set of symbol vectors are retransmitted to the client device 300. Accordingly, the receiving device 300 receives the initial transmission 510 and one or more retransmissions 512.

It is to be understood that the transmitting device 100 and the receiving device 300 can comprise suitable processing chains for MIMO communications. The transmitting device 100 can therefore be configured to: channel code codewords; perform HARQ operations; modulate; perform codeword to layer mapping; perform layer-to-antenna-port mapping; perform RE mapping, perform OFDM symbol generation; and transmit the OFDM symbols. Correspondingly, the receiving device 300 can therefore be configured to: receive OFDM symbols; perform RE de-mapping; perform layer-to-antenna port de-mapping; perform layer to codeword mapping; perform detection and demodulation; perform HARQ operations; and perform decoding so as to obtain codewords.

Fig. 6 illustrates a non-limiting example of a client device 300 in the form of a mobile device. The mobile device houses at least one processor 302 (see Fig. 1 ), at least one display device 312, and at least one communications means (not shown in Fig. 6). The mobile device further comprises input means e.g. in the form of a keyboard 314 communicatively connected to the display device 312. The mobile device further comprises output means e.g. in the form of a speaker 316. The mobile device may be a mobile phone, a tablet PC, a mobile PC, a smart phone, a standalone mobile device, or any other suitable communication device.

Furthermore, the design of the hopping pattern(s) according to embodiments of the invention, i.e., the retransmission permutation matrix P _{r V i} , can determined based on various criteria. Examples of such designs of the retransmission permutation matrix P _{r v i} are given below. It is acknowledged that different designs can also be used in practical implementations, whilst sharing the principles and intentions of the invention herein disclosed.

In an embodiment of the invention, the retransmission permutation function P _{r V i} is expressed as:

P _r,v,i = T(r. v, i, P) (1 ),

where the initial permutation matrix P is a predefined v x v generating permutation matrix, and T(r, v, i, P ) is a layer-hopping generating function that takes r, v, i, and P as input variables.

As a non-limiting example, according to an embodiment of the invention the function T(r, v, i, P ) is expressed as

T(r, v, i, P) = p5 ^(r _’ ^v _’ (2),

where Q(r, v, i) is a sub-generating exponential function.

In one exemplary embodiment of the invention, the sub-generating exponential function Cj(r, v, i) is expressed as:

Q(r, v, i) = mod(r + i, v) (3),

where mod is the modulus operator with r, v, i as input variables.

By combining Eq. (1 )-(3) yields an example of a layer-hopping pattern generation as:

where the generating permutation matrix satisfies the following condition:

P ^k ¹ I, 0 £ k < v (5),

where / is an identity matrix and where k is a general index.

As seen from Eq. (3), the example embodiment of Q(r, v, i) has a period equal to the number of layers v due to the modulus operation. In order to guarantee that the cyclic period of T(r, v, i, P ) is longer than v, the constrain in Eq. (5) is set such that each layer can hop to all spatial-directions.

To provide an even deeper understanding of the invention an implementation examples is presented in the following disclosure. In this example, the number of layers is set to four, i.e. v = 4, and the initial permutation matrix P for the initial transmission is given as

and with such an initial permutation matrix P, the layer-hopping patterns generated according to Eq. (4) can be described as the following. In an initial transmission, i.e. when the retransmission index r = 0, the symbol-vectors are cyclically permuted with matrices pattern [ I, P, P ² , P ³ ], which yields a transmission scheme:

In a first retransmission, i.e. when the retransmission index r = 1, the symbol-vectors are cyclically permuted with matrices pattern [ P, P ² , P ³ , I ], which yields a transmission scheme:

In a second retransmission, i.e. when the retransmission index r = 2, the symbol-vectors are cyclically permuted with matrices pattern [ P ² , P ³ , I, P ], which yields a transmission scheme:

In a third retransmission, i.e. when the retransmission index r = 3, the symbol-vectors are cyclically permuted with matrices pattern [ P ³ , 1, R, R ² ], which yields a transmission scheme:

In the above example, the initial permutation matrix P was given. There are different ways of optimizing such an initial permutation matrix P. One approach following the principle of maximizing the diversities between different retransmissions and adjacent hopping-patterns for good performance is to maximize the difference of the effective channels in two consecutive retransmissions, i.e. according to the following equation:

= argmaxll H{I— P) ||

p

£ argmax(||J/|| ||/ - P||)

p

oc argmax(||/— P||) (6),

p

where || ... || is a specified matrix norm, which is invariant under unitary transform for attaining the equality in the second row in Eq. 6. The matrix norm shall also satisfy the triangular inequality to obtain the inequality in the third row in Eq. 6. As an example, one such matrix norm can be defined as

\\I - RΪI SG d^ (7),

where S _k are singular values of the matrix (/ - P), and the exponential term a is a design parameter. As the total number of permutation matrices of size v x v is equal to the factorial v\ (e.g., there are in total 4!=24 permutations matrices for v = 4 layers), it is possible to search over all the choices that maximize the matrix norm || / - P||, and meanwhile satisfies the pre mentioned condition in Eq. 5. Such an operation can be performed offline and only needs to be done once for different number of layers. The values can hence be pre-defined and given by a standard, such as LTE and NR.

In Fig. 7 shows the norm values of the permutation matrices for 4 layers from Eq. 7 with two different values of the design parameter a = 1, 2. In both cases, the initial permutation matrix

P (corresponding to index 5) defined in the example above is one among the best. For 8 layers, an example initial permutation matrix P following the same principle can be found as:

It is herein also disclosed suggestions to improve the layer-to-antenna-port mapping in NR based on embodiments of the invention. Only a slight modification has to be introduced to the current NR specification 38.21 1 for introducing the layer-to-antenna-port mapping according to embodiments of the invention. The current layer-to-antenna-port mapping in NR is described in Section 7.3.1.4 of 38. 21 1 which read as: “The block of vectors [x ^(O) ) ... x ^{(i; 1)} - 1 shall be mapped to antenna ports according to where ¹ i - The set of antenna ports shall be determined according to the procedure in TS 38.214.”.

In this respect, the following layer-to-antenna-port mapping in NR can be suggested:

“The block of vectors - l shall be mapped to antenna ports according to

P is a permutation matrix specified in Table 1 for different values of v. The set of antenna ports \Po _, ... _, R } shall be determined according to the procedure specified in TS 38.214”. The initial permutation matrix P can in a non-limiting example be defined according to Table 1 below. It is noted that also other initial permutation matrices can be used in conjunction with the invention.

Table 1 : the permutation matrix P for different values of v

Moreover, Fig. 8 shows simulation results of the proposed layer-hopping scheme compared to the NR standard. The block-error-rate (BLER) and raw bit-error-rate (BER) was tested with 8 ^* 8 and 4 ^* 4 MIMO under identical and independently distributed (i.i.d.) Rayleigh fading channels, extended typical urban model (ETU) channel with 3Hz doppler, and extended pedestrian A model (EPA) channel with 10Hz doppler, respectively. The code-rate (CR) is set to 0.75 and QPSK modulation is used. Further, maximal four transmissions, including three retransmissions, is assumed in all tests. Fig. 8 shows performance results for NR compared to the invention. The x-axis in Fig. 8 shows the signal-to-noise ratio (SNR) in dB whilst the y- axis shows the normalised throughput. As can be seen in Fig. 8, the proposed layer-hopping scheme according to the invention performs betterthan the NR standard both in terms of BLER and raw BER.

The client device herein, may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio.

The network access node herein may also be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter,“gNB”,“gNodeB”,“eNB”, “eNodeB”,“NodeB” or“B node”, depending on the technology and terminology used. The radio network access node may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network access node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The radio network access node may also be a base station corresponding to the fifth generation (5G) wireless systems.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

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

Especially, the processor(s) of the transmitting device 100 and the receiving device 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like. Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.