WO2021063494A1

WO2021063494A1 - A first communication device for dft-precoded ofdm with orthogonal spreading sequences

Info

Publication number: WO2021063494A1
Application number: PCT/EP2019/076685
Authority: WO
Inventors: Fredrik Berggren
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2019-10-02
Filing date: 2019-10-02
Publication date: 2021-04-08
Also published as: CN114450902A

Abstract

The disclosure relates to a first communication device for DFT-precoded OFDM with orthogonal spreading sequences. The first communication device (100) obtains M modulation symbols and one or more spreading sequences, wherein each spreading sequence is of length N SF. M · N SF elements are obtained based on the M modulation symbols, wherein the M · N SF elements are arranged into M blocks, and wherein each block comprises N SF elements. A discrete Fourier transform, DFT, precoder input (122) is obtained, wherein the DFT precoder input (122) is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, such that at least two elements of the one or more spreading sequences are different within at least one block. Finally, the DFT precoder input (122) is provided to a DFT precoder (130). Thereby, the spreading factor N SF can be increased while maintaining low power dynamics of the transmitted signal. Furthermore, the disclosure also relates to a corresponding second communication device, corresponding methods and a computer program.

Description

A FIRST COMMUNICATION DEVICE FOR DFT -PRECODED OFDM WITH ORTHOGONAL

SPREADING SEQUENCES

Technical Field The application relates to a first communication device for DFT-precoded OFDM with orthogonal spreading sequences. Furthermore, the application also relates to a corresponding second communication device, corresponding methods and a computer program.

Definitions of Acronyms & Glossaries At least the following acronyms and glossaries are used in the present disclosure:

3GPP third generation partnership project B-IFDMA block IFDMA

CM cubic metric

DFT discrete Fourier transform

LTE long term evolution

FDM frequency division multiplex gNB NR NodeB

IDFT inverse DFT

IFDMA interleaved FDM access

NR new radio

OCB occupied channel bandwidth

OCC orthogonal cover code

OFDM orthogonal FDM

PAPR peak-to-average-power ratio

PRB physical resource blocks

PSD power spectral density

PUCCH physical uplink control channel

RRC radio resource control

UE user equipment.

Notation

At least the following notation is used in the present disclosure:

M Number of modulation symbols

N_PRB Number of PRBs

Number of subcarriers per PRB

N_SF Spreading factor

W Spreading sequence

1 ʋ Compound spreading sequence v Signal voltage DFT output symbol d_k Modulation symbol DFT input symbol.

Background

Transmissions in unlicensed spectrum may be subject to minimum Occupied Channel Bandwidth (OCB) requirements and additionally also maximum Power Spectral Density (PSD) requirements. Thus, in order to occupy sufficient bandwidth and to allow maximum transmit power, it is favorable to transmit over a large bandwidth. Considering Orthogonal Frequency Division Multiplexing (OFDM) transmission, an approach is to use every n:th Physical Resource Block (PRB), which is known in the literature, to produce a waveform for Block Interleaved Frequency Division Multiple Access (B-IFDMA). The notion of an interlace is sometimes used for denoting the allocation of every n:th PRB. A PRB consists of a number of (e.g.,12) contiguous subcarriers.

For standalone unlicensed operation, i.e., when operated without the assistance of a licensed carrier, a Physical Uplink Control Channel (PUCCH) needs to be transmitted in unlicensed spectrum. The 3GPP New Radio (NR) Rel-15 supports several PUCCH formats, each with its own characteristics, but none of them apply to PRB interlaced transmission. One possibility is to enhance NR PUCCH formats 3 and 4 to PRB interlaced transmission, since these are formats which are capable of large payloads and User Equipment (UE) multiplexing, respectively.

NR PUCCH format 3 is transmitted on between 1 to 16 contiguous PRBs depending on payload, supports no UE multiplexing and is using a Discrete Fourier Transform (DFT)- precoder. NR PUCCH format 4 is transmitted on only 1 PRB but

is supporting Orthogonal Cover Codes (OCCs) (i.e., orthogonal spreading sequences) prior to the DFT precoder for multiplexing UEs. The purpose of the DFT precoder is to decrease the power dynamics of the generated signal, which is often measured by its Cubic Metric (CM) or Peak-to-Average Power Ratio (PAPR). For PUCCH format 4, spreading factors of N_SF = 1, 2 and 4 are supported and the OCCs are constructed from DFT sequences.

A key performance measure which relates to the power backoff needed in the transmitter, is the CM, which is defined as:

where v is the normalized voltage of the signal, v_ref is the normalized voltage of a reference signal and “rms” denotes the root-mean-square. Thus, the CM depends on the whole distribution of the signal voltage. Traditionally, the literature is rich of methods to reduce the PAPR of multicarrier signals, and the PAPR is a measure which depends on the peak power of the signal, but not on the distribution of the signal power. Thus, methods developed for reducing the PAPR may not necessarily bring the same gains for CM and the CM is often more commonly use in practice, albeit its non-linear behavior makes CM reduction non-trivial. In particular, transmission on non-contiguous PRBs tends to drastically worsen the CM.

Consider a DFT-precoded OFDM system which utilizes OCCs prior to the DFT-precoder. When N_SF > 1, each data modulation symbol from the set will be spread and thus

repeated N_SF times. The DFT-precoder output is mapped as input to the Inverse DFT (IDFT), which produces the OFDM signal.

When mapped to the input of the Inverse IDFT, repeated data symbols may give rise to that the subcarriers of the signal after the IDFT add constructively, thereby creating large power variations of the transmitted signal, even though a DFT precoder was applied. A large power variation of the signal could imply that the transmitter has to apply a transmit power backoff, causing smaller coverage of the signal.

Since for the case of PRB interlaced transmission, the DFT output is mapped to non- contiguous PRBs at the IDFT, the resulting signal is no longer a single-carrier waveform (which is the case for DFT-precoded OFDM on contiguous PRBs, e.g., NR PUCCH format 3 and 4). Therefore, there is no guarantee that the conventional solutions produce a signal with low CM when non-contiguous PRB allocations are applied. The input mapping to the IDFT is governed by the interlace structure and is typically not changing. However, the input mapping to the DFT- precoder could be optimized with respect to the CM. Therefore, judicious design of the input mapping to the DFT and the spreading sequences are needed.

Moreover, when using PRB interlaced transmission, the resource overhead increases due to the interlace, e.g., if each interlaces comprises 10 PRBs, a transmission will use at least 10 PRBs regardless of data payload. To improve the spectral efficiency, larger N_SF factors are envisaged. However, this further would increase the number of repeated data symbols and could increase the power dynamics of the signal. Hence, it is desirable to provide low CM also for larger spreading factors. A conventional solution of a DFT-spread PUCCH for interlaced transmission is to extend NR PUCCH format 3 and 4 by using a DFT size of The DFT output is mapped to the

PRBs of the allocated interlace at the input to the I DFT.

Another conventional solution is confined to enhance PUCCH format 3 for N_PRB = 1, and designing OCCs for low PAPR but not low CM, assuming the mapping (1 ) and contiguous PRBs, i.e., no interlace transmission.

Summary

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

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

According to a first aspect of the disclosure, the above mentioned and other objectives are achieved with a first communication device for a wireless communication system, the first communication device being configured to obtain M modulation symbols, wherein M is a positive integer; obtain one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtain M · N_SF elements based on the M modulation symbols, wherein the M · N_SF elements are arranged into M blocks, and wherein each block comprises N_SF elements; obtain a discrete Fourier transform, DFT, precoder input, wherein the DFT precoder input is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, wherein at least two elements of the one or more spreading sequences are different within at least one block; and provide the DFT precoder input to a DFT precoder.

An advantage of the first communication device according to the first aspect is that the spreading factor N_SF can be increased while maintaining low power dynamics of the transmitted signal.

In an implementation form of a first communication device according to the first aspect, there is at least one block where the elements of the block are obtained by multiplying the elements of one spreading sequence of length N_SF with a same modulation symbol. An advantage with this implementation form is a low CM for PRB-interlaced transmissions.

In an implementation form of a first communication device according to the first aspect, the first communication device is configured to arrange at least one block to include less than M modulation symbols.

An advantage with this implementation form is a low CM for PRB-interlaced transmissions.

In an implementation form of a first communication device according to the first aspect, the first communication device is configured to multiply the elements within each block with different elements from the one or more spreading sequences.

In an implementation form of a first communication device according to the first aspect, obtain the one or more spreading sequences of length N_SF comprises: obtain a single spreading sequence of length N_SF; and further being configured to multiply each element in at least one block with one or more elements from the single spreading sequence of length N_SF.

In an implementation form of a first communication device according to the first aspect, the DFT precoder input is given by the M · N_SF elements arranged as:

wherein denotes an element of the i:th spreading sequence

p = 0,1, ... , N_SF - 1, and denotes the M modulation symbols.

In an implementation form of a first communication device according to the first aspect, the first communication device is configured to obtain m orthogonal spreading sequences, each spreading sequence of length N_SF, and wherein 1 < m ≤ M; associate the m orthogonal spreading sequences to different blocks; and multiply each element in each block with an element from its associated spreading sequence.

An advantage with this implementation form that different orthogonal sequences can be applied to different blocks, thereby alleviating the use of a compound spreading sequence consisting of elements with the same value, which results in a similar CM for all spreading sequences.

In an implementation form of a first communication device according to the first aspect, the m orthogonal spreading sequences constitute a compound spreading sequence of length M · N_SF arranged such that there are N_SF orthogonal compound spreading sequences.

An advantage with this implementation form is that different users, such as UEs, are orthogonally multiplexed over the block of M · N_SF symbols.

In an implementation form of a first communication device according to the first aspect, the m orthogonal spreading sequences are determined by a predefined rule.

An advantage with this implementation form is that no additional signaling may be provided to the second communication device in order to determine the compound spreading sequence.

In an implementation form of a first communication device according to the first aspect, the one or more spreading sequences are any spreading sequence in a group comprising: a set of DFT sequences, a set of a cyclically shifted Zadoff-Chu sequences, a set of Hadamard sequences, a set of Slepian sequences, and a set of orthogonal sequences not comprising a sequence with all elements the same.

An advantage with this implementation form is that orthogonal multiplexing can be achieved while producing low power dynamics of the transmitted signal.

In an implementation form of a first communication device according to the first aspect, the first communication device is configured to map a DFT precoder output to an input of an inverse discrete Fourier transform, IDFT; and obtain a signal for transmission based on an output of the IDFT; transmit the signal to a second communication device.

An advantage with this implementation form is a signal with low power dynamics.

In an implementation form of a first communication device according to the first aspect, mapping the DFT precoder output to the input of the IDFT comprises map the DFT precoder output to a set of non-contiguous resource blocks.

An advantage with this implementation form is a signal with low power dynamics while making it possible to use PRB interlaced transmission.

In an implementation form of a first communication device according to the first aspect, the first communication device is configured to provide an index of the one or more spreading sequences in at least one of: radio resource control signalling, an uplink control channel, a downlink control channel, a medium access control signalling, and an allocation of time-frequency resources used for transmitting the signal.

An advantage with this implementation form is that the second communication device (receiver) can unambiguously determine the spreading sequence used by the first communication device (transmitter).

In an implementation form of a first communication device according to the first aspect, the M modulation symbols are associated with any of: uplink control information, downlink control information, uplink data information, or downlink data information.

An advantage with this implementation form is that a signal with low power dynamics could be provided for any link direction (uplink/downlink) and for any type of transmitted information. According to a second aspect of the disclosure, the above mentioned and other objectives are achieved with a second communication device for a wireless communication system, the second communication device being configured to receive a signal from a first communication device; obtain one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtain M blocks based on the received signal, wherein M is a positive integer and wherein M · N_SF elements are arranged into the M blocks, wherein each block comprises N_SF elements; and despread the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block; and demodulate and decode the summed despreaded symbols.

An advantage of the second communication device according to the second aspect is that dispreading is performed in order to separate the multiplexed data from different first communication devices.

According to a third aspect of the disclosure, the above mentioned and other objectives are achieved with a method for a first communication device, the method comprises obtaining M modulation symbols, wherein M is a positive integer; obtaining one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtaining M · N_SF elements based on the M modulation symbols, wherein the M · N_SF elements are arranged into M blocks, and wherein each block comprises N_SF elements; obtaining a DFT precoder input, wherein the DFT precoder input is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, wherein at least two elements of the one or more spreading sequences are different within at least one block; and providing the DFT precoder input to a DFT precoder.

The method according to the third aspect can be extended into implementation forms corresponding to the implementation forms of the first communication device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the first communication device. The advantages of the methods according to the third aspect are the same as those for the corresponding implementation forms of the first communication device according to the first aspect.

According to a fourth aspect of the disclosure, the above mentioned and other objectives are achieved with a method for a second communication device, the method comprises receiving a signal from a first communication device; obtaining one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtaining M blocks based on the received signal, wherein M is a positive integer and wherein M · N_SF elements are arranged into the M blocks, wherein each block comprises N_SF elements; and despreading the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block; and demodulating and decoding the summed despreaded symbols.

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

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

The disclosure 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 disclosure. Further, the disclosure 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 disclosure 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 disclosure, in which:

- Fig. 1 shows a block diagram for an example of DFT-precoded OFDM with time-domain spreading sequences;

- Fig. 2 shows a block diagram of a first communication device according to an embodiment of the disclosure;

- Fig. 3 shows a first communication device according to an embodiment of the disclosure implemented and/or integrated in a network access node;

- Fig. 4 shows a flow chart of a method for a first communication device according to an embodiment of the disclosure;

- Fig. 5 shows a block diagram of a second communication device according to an embodiment of the disclosure;

- Fig. 6 shows a receiving device according to an embodiment of the disclosure implemented and/or integrated in a client device;

- Fig. 7 shows a flow chart of a method for a second communication device according to an embodiment of the disclosure;

- Fig. 8 shows a wireless communication system according to an embodiment of the disclosure;

- Fig. 9 shows the absolute value of the window function for embodiments of the disclosure;

- Figs. 10a - 10c show cubic metric performance results for embodiments of the disclosure;

- Fig. 11 shows the absolute value of the window function for embodiments of the disclosure;

- Figs. 12a - 12c show cubic metric performance results for embodiments of the disclosure;

- Fig. 13 shows the absolute value of the window function for embodiments of the disclosure;

- Figs. 14a - 14b show cubic metric performance results for embodiments of the disclosure; and

- Fig. 15 illustrates subcarrier mapping of DFT precoder output according to an embodiment of the disclosure etailed Description

An example of a conventional solution for DFT-precoded OFDM with OCCs will now be described with reference to Fig. 1 to provide an understanding of some of the analysis behind the conclusions resulting in embodiments of the disclosure. In this respect, with reference to step I in Fig. 1 consider

modulation symbols, which are arranged at

the input to a DFT precoder (step II) together with the multiplication of a spreading sequence (i.e., an OCC), w = [w₀, w₁, ... , W_Nsf-1 ], i.e., a spreading factor N_SF is applied, wherein N_SF is an integer, and in particular N_SF > 1. The modulation symbols could be taken from any well- known modulation format (e.g., pi/2-BPSK, QPSK, 16-QAM etc.) and carry uplink control information bits which have been encoded by, e.g., Polar codes or Reed-Muller codes.

In NR PUCCH format 4, the 12-point DFT output is mapped in step III to 1 PRB at the input of an iV-point Inverse DFT (IDFT) and its output is processed from parallel to serial in step IV followed by a Cyclic Prefix (CP) insertion in step V. The size N of the IDFT is related to the system bandwidth and each of its input elements represent the transmission on a subcarrier and zeros are inserted on subcarriers not being allocated.

As an enhancement of NR PUCCH format 3 and 4, it has been proposed to generate

modulation symbols, where N_PRB is the number of PRBs of the interlace, e.g.,

10 PRBs. Spreading factors are constrained to values such that M is an integer number. The input to the DFT precoder can be expressed as the M · N_SF elements arranged

as:

where is the number of elements in (1) and the i:th OCC is given by

The sequences w⁽ⁱ⁾, i = 0,1, ...,N_SF - 1 comprise an orthogonal

set. The length L may be further constrained by implementation requirements on the DFT size, such that it must be a multiple of the factors for example 2, 3, and 5 etc. output values of the DFT precoder are mapped to the subcarriers in the PRBs

of the interlace at the IDFT input. It is noted that according to (1) the symbols are mapped to the positions to the DFT-precoder input as: each element of the spreading sequence is

repeated on N_SF contiguous positions; and each data symbol d_k is mapped regularly to every M: th position. A further characterization of (1 ) is that the input to the DFT precoder is divided into N_SF blocks of size M, where each block contains M different modulation symbols. For example, the first block is

At first, let us consider the output of the DFT precoder (which will subsequently be mapped to the input of the IDFT) when its input is given by (1 ). After some algebra, using L = MN_SF this is obtained by:

where n=0, 1, ..., L-1 and

In (2), the first sum is independent of k and can thus be viewed as a window function on the coefficients at the IDFT input. Then, with

it follows that:

Thus, using L = MN_SF we obtain:

(3)

From (3), two properties can be observed, i.e., the L-point DFT of (2) is reduced to an M- point DFT; and the output of the DFT assumes non-zero values on every N_SF:th subcarrier. The second property produces a comb-based transmission and is known as Interleaved Frequency Division Multiple Access (IFDMA), which is due to the use of DFT sequences as the OCCs. It follows from (3) that different OCCs (i.e., indices i) result in transmissions on different combs. As shown in (3), an implementation could equivalently avoid using OCCs and just compute the M- point DFT and map its output to every N_SF:th subcarrier. The multiplexing of UEs in the frequency domain is therefore orthogonal by FDM since there are N_SF transmission combs, i.e., every N_SF subcarrier is used. Fig. 2 shows a block diagram of a first communication device 100 according to an embodiment of the disclosure. The first communication device 100 comprises a first processing block 110, a second processing block 120 and DFT precoder block 130.

The first processing block 110 is configured to obtain modulation symbols MSs and one or more spreading sequence SSs. In other words, the first communication device 100 is configured to obtain M modulation symbols, wherein M is a positive integer; and configured to obtain one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer, in particular, N_SF > 1. The first processing block 110 outputs the M modulation symbols and the one or more spreading sequences to the second processing block 120.

The second processing block 120 is configured to receive the output 112 from the first processing block 110 and to obtain M · N_SF elements based on the M modulation symbols, where the M · N_SF elements are arranged into M blocks, and further that each block comprises N_SF elements.

An element denotes a symbol with a value, which may be complex-valued. Examples of elements are those of the spreading sequence, those of the modulation symbols or those obtained as a multiplication between an element of the spreading sequence and a modulation symbol.

The second processing block 120 is further configured to obtain a DFT precoder input 122 wherein the DFT precoder input 122 is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, where at least two elements of the one or more spreading sequences are different within at least one block. The second processing block 120 provides the DFT precoder input 122 to an input of the DFT precoder 130.

The DFT precoder block 130 is configured to obtain the DFT precoder input 122 and to output the transform of the time-domain input to a frequency-domain output.

In embodiments of the disclosure, the first communication device 100 further comprises a mapping block 140 configured to obtain the DFT output 132 from the DFT precoder block 130 and to map the DFT precoder output 132 to an input of an I DFT block 150. In embodiments the mapping the DFT precoder output 132 to the input of the IDFT 150 comprises mapping the DFT precoder output 132 to a set of non-contiguous resource blocks. L = MN_SF output symbols of the DFT precoder are mapped to the N_PRB PRBs of the interlace at the input of the IDFT block 150.

Fig. 15 illustrates two non-limiting examples of mapping of N_PRB = 10 blocks from the DFT precoder block 130, each containing

symbols to the N_PRB PRBs of the interlace at the input of the IDFT. The mapping could be from top-to-bottom as illustrated in the left drawing in Fig. 15. The mapping could also be performed from bottom-to-top as illustrated in the right drawing in Fig. 15.

The IDFT block 150 is configured to obtain the mapping 142 from the mapping block 140 and to output the transform of the frequency-domain input to a time-domain output.

Finally, further processing is performed so as to obtain a Radio Frequency (RF) signal 510 for transmission based on an output of the IDFT 150. Non-limiting examples of such processing is parallel to serial mapping, CP insertion, transmit filtering, antenna processing (including mapping of the data to layers and antenna ports) and up-conversion to the RF domain. The first communication device 100 transmits the signal 510 to a second communication device 300 as illustrated in Fig. 8.

In one possible embodiment, there is at least one block where the elements of the block are obtained by multiplying the elements of one spreading sequence of length N_SF with the same modulation symbol. For example, one block could be expressed as

where the modulation symbol is d₀ and the spreading sequence is

In one possible embodiment, the first communication device 100 may be configured to arrange at least one block to include less than M modulation symbols. For example, a block with 1 modulation symbol could be expressed as and thus contains the

modulation symbol, d₀. Another example is a block with 2 modulation symbols, which could be expressed as

As further non-limiting examples for block with more than 1 but less than M modulation symbols, consider cases where N_SF= 4 and M = 3. The 3 blocks could be arranged as 5

Alternatively, the 3 blocks could be arranged as 0

Other orderings of the modulation symbols are possible as long as, considering all blocks, a modulation symbol has been multiplied with every element of the spreading sequence. 5 In one possible embodiment, the first communication device 100 may be configured to multiply the elements within each block with different elements from the one or more spreading sequences. For example, if one block is arranged from 1 modulation symbol d₀, all elements from the spreading sequence is applied in the block as Thus,

each block could be processed individually in the second communication device (receiver),0 i.e., despreading can be performed per block.

Fig. 3 shows first communication device 100 according to an embodiment of the disclosure implemented and/or integrated in a network access node 600, for example a UE or integrated access and backhaul (IAB) in NR. It is however noted that the first communication device 1005 can also be implemented in a client device or in any other suitable communication device having transmitting capabilities in communication systems.

In the embodiment shown in Fig. 3, the network access node 600 comprises a processor 602, a transceiver 604 and a memory 606. The processor 602 is coupled to the transceiver 604 and0 the memory 606 by communication means 608 known in the art. The network access node 600 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 610 coupled to the transceiver 604, while the wired communication capability is provided with a wired communication interface 612 coupled to the5 transceiver 604. That the network access node 600 is configured to perform certain actions

15 can in this disclosure be understood to mean that the network access node 600 comprises suitable means, e.g. the processor 602 and the transceiver 604, configured to perform said actions. More details about the network access node 600 can be found in the later sections of the present disclosure.

Fig. 4 shows a flow chart of a corresponding method 200 which may be executed in a first communication device 100, such as the one shown in Fig. 2. The method 200 comprises obtaining 202 M modulation symbols, wherein M is a positive integer.

The method 200 further comprises obtaining 204 one or more spreading sequences, where each spreading sequence is of length N_SF, and where N_SF is a positive integer.

The method 200 further comprises obtaining 206 M · N_SF elements based on the M modulation symbols, where the M · N_SF elements are arranged into M blocks, and where each block comprises N_SF elements.

The method 200 further comprises obtaining 208 a DFT precoder input, wherein the DFT precoder input is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, wherein at least two elements of the one or more spreading sequences are different within at least one block.

The method 200 further comprises providing 210 the DFT precoder input 122 to a DFT precoder 130.

It should be understood that the processing in Fig. 4 is non-limiting example, and each processing may not depend on the previous processing.

Fig. 5 shows a block diagram of a second communication device 300 according to an embodiment of the disclosure. The second communication device 300 comprises a receiving block 310, a first processing block 320, a despreading block 330, and a demodulating and decoding block 340.

The receiving block 310 is configured to receive a RF signal 510 from a first communication device 100 as illustrated in Fig. 8. The receiving block 310 provides the RF signal 510 in a baseband representation to the first processing block 320. The first processing block 320 obtains the signal 510 from the receiving block 310. The first processing block 320 may be configured to obtain one or more spreading sequences SSs, where each spreading sequence is of length N_SF, and where N_SF is a positive integer.

The first processing block 320 may be configured to obtain M blocks based on the received signal 510, where M is a positive integer and wherein M · N_SF elements are arranged into the M blocks, and each block comprises N_SF elements.

From receiving side, the receiver knows each element in each block is a product of a modulation symbol multiplied with an element from the one or more spreading sequences, and at least two elements of the one or more spreading sequences are different within at least one block. This information is used by the receiver (e.g. the first processing block 320) for despreading which is given in the following and is not elaborated here.

The first processing block 320 may be configured to output modulation symbols 322 to the despreading block 330.

The despreading block 330 may be configured to obtain the modulation symbols 322 from the first processing block 320. The despreading block 330 is configured to despread the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block.

The despreading operation consists of a modulation symbol by element-wise multiplication with the spreading sequence on a received block of N_SF elements containing the modulation symbol and summation of the terms. The despreading block 330 is configured to output the summed despreaded symbols 332 to the demodulating and decoding block 340.

The demodulating and decoding block 340 may be configured to obtain the summed despreaded symbols 332 from the despreading block 330. The demodulating and decoding block 340 is configured to demodulate and decode the summed despreaded symbols so as to provide as output as set of information bits.

Generally, the second communication device 300 may be configured to process the signal 510 in the reverse order compared to the processing at the first communication device 100. The received RF signal 510 is processed to the baseband, including, e.g., sampling, filtering, A/D- conversion, etc. The baseband signal is further processed by removing CP, performing a DFT, performing channel equalization, performing an IDFT, performing a despreading operation and performing channel decoding, etc.

Alternatively, the channel equalization could be performed after the IDFT. In more detail, the following major steps can be performed by the second communication device 300 according to embodiments of the disclosure:

1 . Receiving a RF signal 510 transmitted by the first communication device 100;

2. Converting the received signal 510 from the RF domain into the base band domain;

3. Performing a DFT on the base band signal;

4. Performing a channel equalization on the output of the DFT;

5. Extracting the assigned time-frequency resources from the equalized output of the DFT;

6. Performing an Inverse DFT on the extracted time-frequency resources;

7. Extracting the input blocks from the output of the Inverse DFT ;

8. Obtaining at least one spreading sequence of length N_SF;

9. Despreading the modulation symbols in each input block; and

10. Perform demodulation and decoding of the despreaded modulation symbols so as to obtain the transmitted data information.

In this respect, in embodiments of the disclosure the M modulation symbols are associated with any of uplink (UL) control information, downlink (DL) control information, uplink data information, or downlink data information. Hence, the information content can relate to data in the uplink or downlink or to control information in the uplink or downlink. For data transmissions the physical uplink shared channel (PUSCH) and the physical downlink shared channel (PDSCH) can be used. For control information the physical uplink control channel (PUCCH) and the physical downlink control channel (PDCCH) can be used.

Fig. 6 shows a second communication device 300 according to an embodiment of the disclosure implemented or integrated in a client device 700, for example a next generation node B (gNB) or IAB in NR. It is however noted that the second communication device 300 can also be implemented in any other suitable communication device having receiving capabilities in communication systems, for example a UE in device to device (D2D) scenario.

In the embodiment shown in Fig. 6, the client device 700 comprises a processor 702, a transceiver 704 and a memory 706. The processor 702 may be coupled to the transceiver 704 and the memory 706 by communication means 708 known in the art. The client device 700 further comprises an antenna or antenna array 710 coupled to the transceiver 704, which means that the client device 700 is configured for wireless communications in a wireless communication system.

That the client device 700 may be configured to perform certain actions can in this disclosure be understood to mean that the client device 700 comprises suitable means, such as e.g. the processor 702 and the transceiver 704, configured to perform said actions. More details about the client device 700 can be found in the later sections of the present disclosure.

Fig. 7 shows a flow chart of a corresponding method 400 which may be executed in a second communication device 300, such as the one shown in Fig. 5.

The method 400 comprises receiving 402 a signal 510 from a first communication device 100.

The method 400 further comprises obtaining 404 one or more spreading sequences, where each spreading sequence is of length N_SF, and N_SF is a positive integer.

The method 400 further comprises obtaining 406 M blocks based on the received signal 510, where M is a positive integer and M · N_SF elements are arranged into the M blocks, and each block comprises N_SF elements.

From receiving side, the receiver knows each element in each block is a product of a modulation symbol multiplied with an element from the one or more spreading sequences, and at least two elements of the one or more spreading sequences are different within at least one block. This information is used by the receiver (e.g. the second communication device 300) for despreading which is given in the following and is not elaborated here.

The method 400 further comprises despreading 408 the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block.

The method 400 further comprises demodulating and decoding 410 the summed despreaded symbols. It should be understood that the processing in Fig. 7 is non-limiting example, and each processing may not depend on the previous processing and the sequence of the processing is non-limiting.

Fig. 8 shows a wireless communication system 500 according to an embodiment of the disclosure. The wireless communication system 500 comprises a first communication device 100 and a second communication device 300.

As illustrated in Fig. 8 and previously mentioned, the first communication device 100 can be part of a network access node 600, such as a gNB, and the second communication device 300 can be part of a client device 700, such as a UE. However, the revers case is also within the scope of the disclosure, i.e. the first communication device 100 is part of a client device and the second communication device 300 is part of a network access node.

For simplicity, the wireless communication system 500 shown in Fig. 8 only comprises one first communication device 100 and one second communication device 300. However, the wireless communication system 500 may comprise any number of first communication devices 100 and any number of second communication device 300 without deviating from the scope of the disclosure.

In the wireless communication system 500 the network access node 600 transmits a RF signal(s) 510 in the DL to the client device 700 which receives the RF signal(s) 510 and processes the RF signal(s) 510 accordingly. The client device 700 transmits a RF signal(s) in the uplink to the network access node 600. The wireless communication system 500 can by any orthogonal frequency division multiplexing (OFDM) system employing DFT precoding. Further, embodiments of the disclosure are not limited to unlicensed spectrum but is for example applicable in higher frequency spectrum, where waveforms with low power dynamics are desirable.

In embodiments of the disclosure, different aspects of spreading sequence index signaling is also disclosed. The signaling of the spreading sequence index can be performed in any combination of: radio resource control signalling, an uplink control channel, a downlink control channel, media access control (MAC) control element (CE), and an allocation of time- frequency resources used for transmitting the signal 510.

For example, the spreading sequence index can be provided by higher layer signaling, such as in radio resource control (RRC), to the second communication device 300. The spreading sequence index may be predefined by standard specification. For example, the standard specification can define a set of spreading sequence in a table and each sequence with an index.

In another example, if a compound spreading sequence is to be arranged, its constituting spreading sequence indices (i.e., the indices i = 0, 1, ...,N_SF - 1) could be obtained by predefined rules from the signaled index.

In yet another example, the spreading sequence index can be implicitly determined from transmission parameters. These parameters could e.g. include the interlace index or relates to the allocated time-frequency resources.

The signaling of spreading sequence index can be performed in an uplink control channel and/or in a downlink control channel of the wireless communication system 500.

In the following disclosure further embodiments of the disclosure will now be described.

According to embodiments of the disclosure it is disclosed to use an input to the DFT precoder as the M · N_SF elements arranged as:

In the mapping (4) the spreading sequence is block-wise repeated. A further characterization of (4), which is different from that of (1), is that the input to the DFT precoder is divided into M blocks of size N_SF, where each block contains 1 modulation symbol. For example, the first block is

The output from the DFT precoder can after some algebra be obtained as:

The first sum in (5) is different since the denominator in the exponential function is L rather than N_SF as in (2). The second sum denotes an M-point DFT of the data symbols, rather than an L-point DFT as in (2), i.e., It should be noted that when N_SF = 1, (3)

and (5) are equal.

Furthermore, if we define the DFT of the spreading sequence,

it follows that the inner product of the spreading sequences in frequency domain (i.e., after the DFT-precoder) is orthogonal, i.e.,

where denotes the complex-conjugate of w. Therefore, the DFT-output from two users transmitting different sets of modulation symbols and using different spreading sequences will be orthogonal.

In the above disclosed embodiments of DFT mapping, M modulation symbols are transmitted using 1 spreading sequence (i.e., index i). The spreading sequence has length N_SF and is through repetitions extended to length N_SFM in the mapping step (1) or (4). That is, one spreading sequence index i is used for arranging the block of L = N_SFM symbols in (4). Hence, it has been described the use of a single spreading sequence of length N_SF and to multiply each element in at least one block with one or more elements from the single spreading sequence of length N_SF.

However, in further embodiments of the disclosure, N_SFM modulation symbols are transmitted using more than one (>1) spreading sequence but not more than M spreading sequences. In this respect, the first communication device 100 obtains m orthogonal spreading sequences, where each spreading sequence is of length N_SF, and where m is an integer fulfilling the relation 1 < m ≤ M. The first communication device 100 associates the m orthogonal spreading sequences to different blocks and multiplies each element in each block with an element from its associated spreading sequence.

In embodiments, the m orthogonal spreading sequences constitute a compound spreading sequence of length M · N_SF arranged such that there are in total N_SF orthogonal compound spreading sequences. The basic example of the compound spreading sequence with m = 1 is defined by repeating the spreading sequence with length N_SF M times, for example,

Thus, such a construction allows defining a set of

N_SF orthogonal compound spreading sequences of length M · N_SF. With proper selection of the constituting orthogonal sequences, also this construction allows defining a set of N_SF orthogonal compound spreading sequences of length M · N_SF.

For m > 1, the compound spreading sequence will be constituted of m different spreading sequences, i.e.,

In embodiments, the m orthogonal spreading sequences are determined by a predefined rule. That means that the OCC indices used for the compound spreading sequence can be determined without any additional signalling on top of the one used for conveying a single OCC index i. For example, OCC index j could be a function of OCC index i, and so on.

Any of the DFT input mappings (1 ) or (4) above could be used with the above construction of the compound spreading sequence using m > 1 constituent spreading sequences. A benefit from using more than one spreading sequence per block of M modulation symbols is, e.g., that the use of an all-ones spreading sequence could be prevented, which is a spreading sequence that results rather high CM.

As a non-limiting example, consider DFT input mapping in equation (1 ) and N_SF = 2 and the following mapping, where M is divisible by N_SF and which maintains orthogonality among

and by alternating the spreading sequence index

The compound spreading sequences would for these two examples become, respectively:

and

A further non-limiting example is to consider (4), such that:

and

and

In these examples, each data symbol is multiplied with the same spreading sequence. Thus, for any of the above examples, if w⁽⁰⁾ = [1,1] and w⁽¹⁾ = [1, -1], neither of

and will

use an all-one compound spreading sequence.

There are several ways on how to apply multiple spreading sequences to a block of M modulation symbols. A requirement is that the compound spreading sequences v⁽ⁱ⁾ = [w⁽ⁱ⁾,w⁽ⁱ⁺¹⁾ , ..., w^(i+M-1)] of length MN_SF consisting of M combinations of spreading sequences of length N_SF should still be orthogonal.

For example, for spreading information modulation symbol d_k, k = 0,1, ...,M — 1, a simple pre- defined rule is to use spreading sequence i = (i + k) mod N_SF, i = 0,1, ...,N_SF - 1, where “mod” is the modulo operator. Since 0 ≤ i,j ≤ N_SF - 1, then (i + k ) mod N_SF ≠ j + k)mod N_SF when i ≠ j, and the compound spreading sequences corresponding to i and j, will be orthogonal.

Sets of orthogonal sequences

It is understood from this disclosure that the CM depends on the spreading sequence through its DFT (i.e., its window function). In embodiments of the disclosure, different sets of orthogonal sequences can be used for spreading the modulation symbols and hence a few non-limiting examples of such orthogonal sequences are considered and described in this section.

DFT-sequences

In embodiments DFT-sequences are employed for spreading the modulation symbols. The sequences are defined by which gives:

Since (6) is not a constant and depends on the index n, it acts as a frequency domain filter, i.e., a window function, on the values at the input to the IDFT. The absolute value of

the function (6) is plotted in Fig. 9 for N_SF = 4, M = 30 and i = 0, 1, 2, 3. It should be noted from (6) that, in contrast to using (1) with DFT-sequences, using (4) with DFT-sequences does not result in comb-based transmission, i.e., all L subcarriers are allocated at the output of the DFT- precoder. However, the multiplexing is still orthogonal after the DFT-precoder, as shown above in the derivation of the inner product of the spreading sequences in frequency domain.

In Figs. 10a - 10c, the CM is plotted with a DFT mapping according to (1 ) and (4) using N_SF = 4, 6 and 8 for each spreading sequence, 1 = 0, 1, ... , N_SF — 1. The reference case, i.e. no spreading N_SF = 1, is also included. Figs. 10a - 10c show the CM comparison of the transmitted signal using Eq. (1 ) and Eq. (1 ) for mapping the input to the DFT, using DFT sequences with spreading factors N_SF equal to 4 in Fig. 10a, 6 in Fig. 10b, and 8 in Fig. 10c.

It can be seen in Figs. 10a - 10c that a DFT mapping according to (4) can offer lower CM than the one defined by (1 ) and a CM even lower than the reference case of no spreading sequence. However, it is also seen that (4) has one spreading sequence with considerably higher CM, which is the spreading sequence corresponding to i = 0 i.e., the all-ones sequence. In conventional NR systems, the spreading sequence index is signaled to the UE, thus usage of this particular sequence could be avoided, or it could even be removed from the set of spreading sequences. Another option is to explore other types of spreading sequences which do not contain the all-ones sequence. Zadoff-Chu-sequences

In embodiments a set of N_SF orthogonal sequences is made by cyclically shifting a Zadoff-Chu (ZC) sequence. The spreading sequences will thus be defined by

where 0 < u < N_SF is a root index which is relatively prime to N_SF, i.e., their greatest common divisor is 1 and “mod” is the modulo operator. It can be shown that these spreading sequences are orthogonal. The window function becomes

which is a quadratic sum in p, which has closed-form solutions only in some special cases. The absolute value of the function (7) is plotted in Fig. 11 for N_SF = 4, M = 30 and i = 0, 1, 2, 3.

In Figs. 12a - 12c, the CM is plotted with a DFT mapping according to (4) using N_SF = 4, 6 and 8 (using root index u = 3, 5 and 3, respectively) for each spreading sequence i = 0, 1, ... , N_SF - 1. The reference case, i.e. no spreading N_SF = 1 is also included. Figs. 12a - 12c show CM comparison of the transmitted signal using Eq. (4) for mapping the input to the DFT, using DFT sequences with spreading factors equal to 4 in Fig. 12a, 6 in Fig. 12b, and 8 in Fig. 12c.

It can be seen in Figs. 12a - 12c that ZC sequences do not result in one particular high CM spreading sequence (since there is no ZC sequence consisting of a single value), which is the case for DFT sequences.

Hadamard-sequences

In embodiments Hadamard-sequences are employed for spreading the modulation symbols. If N_SF is 2 or a multiple of 4, the spreading sequences can be determined from the rows or columns of a Hadamard matrix. An advantage of Hadamard sequences is that they are real valued, i.e., +1 or -1 , and therefore low-complex implementations are possible since the spreading operation could be performed by directly phase shifts rather than multiplication with complex values.

In Fig. 13, the absolute value of is plotted for Hadamard sequences

with N_SF = 4, M = 30 and i = 0, 1, 2, 3. In Figs. 14a - 14b, the CM is plotted with a DFT mapping according to (4) using N_SF = 4 and 8 for each spreading sequence , i = 0, 1, ... , N_SF - 1, for DFT-sequences and Hadamard- sequences, respectively. The reference case, i.e. no spreading N_SF = 1, is also included. Figs. 14a - 14b show CM comparison of the transmitted signal using Eq. (4) for mapping the input to the DFT, using DFT sequences with spreading factors N_SF equal to 4 in Fig. 14a, and 8 in Fig. 14b.

It can be seen in Figs. 14a - 14b that Hadamard sequences can perform better than DFT- sequences.

Orthogonal sequences not comprising a sequence with all elements the same In embodiments an orthogonal set of sequences not including a sequence with all elements the same are employed for spreading the modulation symbols. The issue with a spreading sequence consisting of only ones is a potential co-phasing of the modulation symbols which could increase the CM. However, the CM is invariant to a phase shift of the signal, so a spreading sequence consisting of only -1 , or any other complex-valued constant (i.e., a spreading sequence with the same value Q for all elements,

= Q, p = 0,1, ...,N_SF - 1 ) would also result in high CM. Therefore, a set of spreading sequences not containing such a sequence is useful.

In one example, a first set of spreading sequences is defined to include a sequence where = Q, p = 0,1, ...,N_SF - 1. The set of DFT sequences is such a candidate set. The set of

spreading sequences could be represented by an N_SF x N_SF matrix A of which the rows (or columns) consist of the spreading sequences. Then from linear algebra, it is known that a change of basis to a new orthogonal base, i.e., a second set of spreading sequences, could be obtained by a projection matrix P to obtain a new set of spreading sequences as B = AP. By properly choosing P (e.g., it could be an orthogonal matrix), it is possible to that the second set of spreading sequences does not include a sequence where = Q, p = 0,1, ..., N_SF - 1.

Slepian-sequences

In embodiments Slepian-sequences are employed for spreading the modulation symbols. A Slepian-sequence is also known as a discrete prolate spheroidal sequence (DPSS). These sequences have the property that the Discrete-time Fourier Transform of the sequence has the maximum concentration of the signal energy within a given limited frequency band, i.e., the energy of the sidelobes outside the frequency band is minimized. A DPSS could be used as a window sequence after the DFT-precoder, which is known to reduce the PAPR of the transmitted signal. In that case, there is one window function and only a single DPSS is applied.

In contrast, herein we disclose to generate multiple DPSSs and use them as spreading sequences, while also fulfilling the objective as window functions. Slepian sequences are obtained by solving an eigenvalue problem and the n:th order Slepian sequence corresponds to the (n + 1):th eigenvalue. It can be shown that the n:th order Slepian sequence is mutually orthogonal to the Slepian sequences of smaller orders. Thus, it is disclosed here that a set of spreading sequences could be formed using a set of Slepian sequences of order 1 to N_SF.

Generally, the Inverse DFT of the window sequence would yield a time-domain spreading sequence and if the window sequences are orthogonal, so would the time-domain spreading sequences be. However, since the length of the window sequence is L and the length of the spreading sequence is N_SF, it is not possible to perform an Inverse DFT of the length-/ window sequence, since that will not give an OCC of length N_SF.

Here, we therefore disclose to generate Slepian sequences of length N_SF and then perform the N_SF- point IDFT of these sequences to obtain the spreading sequences. Since it was shown above that the window function is an L-point DFT of the spreading sequence, the window function of the corresponding length-N_SF Slepian sequence will, after the L-point DFT- precoder, become an L/N_SF-times oversampled version of the original length-N_SF Slepian sequence.

Therefore, in one example we define the spreading sequence as

where is the i:th Slepian sequence , i.e., the

Slepian sequence is defined in the frequency domain and the spreading sequence is obtained as its inverse DFT.

In another example, is the i:th Slepian

sequence, i.e., the Slepian sequence is defined in the time domain and represents the spreading sequence. In the above descriptions, normalization factors, e.g., M,L,N_SF, have been inserted prior to the DFT or IDFT operations or as part of sequence definitions. It should be understood, that the CM is invariant to these normalization factors and are primarily used for notational convenience.

The network access node 600 in this disclosure includes but is not limited to: a NodeB in wideband code division multiple access (WCDMA) system, an evolutional Node B (eNB) or an evolved NodeB (eNodeB) in LTE systems, or a relay node or an access point, or an in-vehicle device, a wearable device, or a gNB in the fifth generation (5G) networks.

Further, the network access node 600 herein may 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 nodes 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 802.11 -conformant MAC and PHY interface to the wireless medium. The radio network access node may also be a base station corresponding to the 5G wireless systems or beyond 5G wireless system.

The processor of the network access node 600 may be referred to as one or more general- purpose CPUs, one or more DSPs, one or more ASICs, one or more FPGAs, one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, and one or more chipsets.

The memory of the network access node 600 may be a read-only memory, a random access memory, or a NVRAM.

The transceiver of the network access node 600 may be a transceiver circuit, a power controller, an antenna, or an interface which communicates with other modules or devices. In embodiments, the transceiver of the network access node 600 may be a separate chipset or being integrated with the processor in one chipset. While in some embodiments, the processor, the transceiver, and the memory of the network access node 600 are integrated in one chipset. The client device 700 in this disclosure includes but is not limited to: a UE such as a smart phone, a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having a wireless communication function, a computing device or another processing device connected to a wireless modem, an in-vehicle device, a wearable device, an integrated access and backhaul node (IAB) such as mobile car or equipment installed in a car, a drone, a device-to- device (D2D) device, a wireless camera, a mobile station, an access terminal, an user unit, a wireless communication device, a station of wireless local access network (WLAN), a wireless enabled tablet computer, a laptop-embedded equipment, an universal serial bus (USB) dongle, a wireless customer-premises equipment (CPE), and/ora chipset. In an Internet of things (IOT) scenario, the client device 700 may represent a machine or another device or chipset which performs communication with another wireless device and/or a network equipment.

It should be understood that the client device 700 may be part of the second communication device in some cases. But the client device 700 may be part of the first communication device in some other cases. It is an un-limiting example in this disclosure.

The UE may further be referred to as a mobile telephone, a cellular telephone, a computer tablet or laptop with wireless capability. The UE in this context may e.g. be portable, pocket- storable, hand-held, computer-comprised, or vehicle-mounted mobile device, 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 802.11 -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 worldwide interoperability for microwave access (WiMAX) and its evolution, and in fifth generation wireless technologies, e.g. NR.

The processor of the client device 700 may be referred to as one or more general-purpose central processing units (CPUs), one or more digital signal processors (DSPs), one or more application-specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, and one or more chipsets.

The memory of the client device 700 may be a read-only memory, a random access memory, or a non-volatile random access memory (NVRAM). The transceiver of the client device 700 may be a transceiver circuit, a power controller, an antenna, or an interface which communicates with other modules or devices. In embodiments, the transceiver of the client device 700 may be a separate chipset or being integrated with the processor in one chipset. While in some embodiments, the processor, the transceiver, and the memory of the client device 700 are integrated in one chipset.

The wireless communication system in this disclosure includes but is not limited to: LTE, 5G or future wireless communication system.

Furthermore, any method according to embodiments of the disclosure 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 first communication device 100 and the second communication 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 together for performing the solution.

Especially, the processor(s) of the first communication device 100 and the second communication 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, 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, for example, call processing control, user interface control, or the like.

Finally, it should be understood that the disclosure is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A first communication device (100) for a wireless communication system (500), the first communication device (100) being configured to obtain M modulation symbols, wherein M is a positive integer; obtain one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtain M · N_SF elements based on the M modulation symbols, wherein the M · N_SF elements are arranged into M blocks, and wherein each block comprises N_SF elements; obtain a discrete Fourier transform, DFT, precoder input (122), wherein the DFT precoder input (122) is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, wherein at least two elements of the one or more spreading sequences are different within at least one block; and provide the DFT precoder input (122) to a DFT precoder (130).

2. The first communication device (100) according to claim 1, wherein there is at least one block where the elements of the block are obtained by multiplying the elements of one spreading sequence of length N_SF with a same modulation symbol.

3. The first communication device (100) according to claim 1 or 2, configured to arrange at least one block to include less than M modulation symbols.

4. The first communication device (100) according to any one of claims 1 to 3, configured to multiply the elements within each block with different elements from the one or more spreading sequences.

5. The first communication device (100) according to any one of claims 1 to 4, wherein obtain the one or more spreading sequences of length N_SF comprises: obtain a single spreading sequence of length N_SF; and further being configured to multiply each element in at least one block with one or more elements from the single spreading sequence of length N_SF.

6. The first communication device (100) according to claim 4 or 5, wherein the DFT precoder input (122) is given by the M · N_SF elements arranged as:

wherein denotes an element of the i:th spreading sequence

denotes the M modulation symbols.

7. The first communication device (100) according to any one of claims 1 to 4, configured to obtain m orthogonal spreading sequences, each spreading sequence of length N_SF, and wherein 1 < m < M; associate the m orthogonal spreading sequences to different blocks; and multiply each element in each block with an element from its associated spreading sequence.

8. The first communication device (100) according to claim 7, wherein the m orthogonal spreading sequences constitute a compound spreading sequence of length M · N_SF arranged such that there are N_SF orthogonal compound spreading sequences.

9. The first communication device (100) according to claim 7 or 8, wherein the m orthogonal spreading sequences are determined by a predefined rule.

10. The first communication device (100) according to any one of the preceding claims, wherein the one or more spreading sequences are any spreading sequence in a group comprising: a set of DFT sequences, a set of a cyclically shifted Zadoff-Chu sequences, a set of Hadamard sequences, a set of Slepian sequences, and a set of orthogonal sequences not comprising a sequence with all elements the same.

11. The first communication device (100) according to any one of the preceding claims, configured to map a DFT precoder output (132) to an input of an inverse discrete Fourier transform, IDFT, (140); and obtain a signal (510) for transmission based on an output of the IDFT (150); transmit the signal (510) to a second communication device (300).

12. The first communication device (100) according to claim 11, wherein mapping the DFT precoder output (132) to the input of the IDFT (150) comprises map the DFT precoder output (132) to a set of non-contiguous resource blocks.

13. The first communication device (100) according to claim 10 or 11 , configured to provide an index of the one or more spreading sequences in at least one of: radio resource control signalling, an uplink control channel, a downlink control channel, a medium access control signalling, and an allocation of time-frequency resources used for transmitting the signal (510).

14. The first communication device (100) according to any one of the preceding claims, wherein the M modulation symbols are associated with any of: uplink control information, downlink control information, uplink data information, or downlink data information.

15. A second communication device (300) for a wireless communication system (500), the second communication device (300) being configured to receive a signal (510) from a first communication device (100); obtain one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtain M blocks based on the received signal (510), wherein M is a positive integer and wherein M · N_SF elements are arranged into the M blocks, wherein each block comprises N_SF elements; and despread the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block; and demodulate and decode the summed despreaded symbols.

16. A method (200) for a first communication device (100), the method (200) comprising obtaining (202) M modulation symbols, wherein M is a positive integer; obtaining (204) one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtaining (206) M · N_SF elements based on the M modulation symbols, wherein the M N_SF elements are arranged into M blocks, and wherein each block comprises N_SF elements; obtaining (208) a discrete Fourier transform, DFT, precoder input (122), wherein the DFT precoder input (122) is obtained by a multiplication of each element in each block with an element from the one or more spreading sequences, wherein at least two elements of the one or more spreading sequences are different within at least one block; and providing (210) the DFT precoder input (122) to a DFT precoder (130).

17. A method (400) for a second communication device (300), the method (400) comprising receiving (402) a signal (510) from a first communication device (100); obtaining (404) one or more spreading sequences, wherein each spreading sequence is of length N_SF, and wherein N_SF is a positive integer; obtaining (406) M blocks based on the received signal (510), wherein M is a positive integer and wherein M · N_SF elements are arranged into the M blocks, wherein each block comprises N_SF elements; and despreading (408) the symbols in each block by multiplying each symbol with an element from the one or more spreading sequences and summing the despreaded symbols corresponding to the same modulation symbol, wherein at least two elements of the one or more spreading sequences are different within at least one block; and demodulating and decoding (410) the summed despreaded symbols.

18. A device comprising: a processor, and a memory coupled to the processor and having processor-executable instructions stored thereon, which when executed by the processor, cause the processor to perform the method of claim 16 or 17.