MITIGATING INTER-NUMEROLOGY INTERFERENCE BY

PRECODING OR INTERFERENCE CANCELLATION

TECHNICAL FIELD The present invention relates to the field of wireless communications, and more particularly to the field of 5 ^th generation (5G) wireless systems.

BACKGROUND

The 5G of mobile networks is on the horizon and a 5G wireless system will likely have different numerologies on the same carrier frequency. For multicarrier waveform-based systems, the numerology may be defined as a set of multicarrier parameters such as subcarrier spacing, cyclic prefix (CP) and transmission time interval (TTI) amongst others. Fig. 1 shows a 3 ^rd generation partnership project (3GPP) standardization proposal illustrating how different mobile network services of 5G, such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-reliable and low-latency communications (uRLLC) and broadcast, are packed close to each other in the frequency domain, each service having a different subcarrier spacing, CP and TTI as depicted in Fig. 1.

The problem of packing the respective services with a different subcarrier spacing is that the subcarriers are no longer orthogonal to each other in the frequency domain, thereby leading to interference. Fig. 2 illustrates an inter-numerology interference between subcarriers in the frequency domain, where a numerology (depicted by a solid line as "Numer. 2") based on a subcarrier spacing Af2 interferes with another numerology (depicted by a dotted line as "Numer. 1") based on a lower subcarrier spacing Afl, where Af2=2xAfl. According to Fig. 2 and some numerical evaluations, narrow subcarrier spacings do not interfere with larger subcarrier spacings which are integer multiples of the narrow subcarrier spacing. Referring to the numerologies of Fig. 1, one can then say that eMBB interferes with mMTC, while uRLLC interferes with both mMTC and broadcast. In short, large subcarriers have a high out-of-band (OOB) transmit power, which needs to be suppressed to avoid any inter-numerology interference. To do so, some prior art solutions have been proposed. The first solution is related to a time domain filtering as found in the prior art documents: Z. Ankarali, B. Pekoz and H. Arslan, "Flexible Radio Access Beyond 5G: A Future Projection on Waveform, Numerology & Frame Design Principles" in IEEE Access, vol. PP, no. 99, pp.1-16, 2017, and A. A. Zaidi, R. Baldemair, H. Tullberg, H. Bjorkegren, L. Sundstrom, J. Medbo, C. Kilinc, and I. D. Silva, "Waveform and Numerology to Support 5G Services and Requirements," IEEE Communications Magazine, vol. 54, no. 11, pp. 90-98, 2016. The latter document proposes a windowing approach at the transmitter and receiver side to mitigate the interference. In the case of, for example, the transmitter, the main idea is that it performs a time domain filtering to smooth the signal in time, as illustrated by the transmitter windowing of Fig. 3. Indeed, smoothing the time domain signal can mathematically eliminate all the OOB emissions in the frequency domain, which however imposes a stricter than needed condition. In addition, the problem with this windowing approach is that it introduces a distortion to the transmit signal in addition to being not fully orthogonal to the neighbor

numerologies. Moreover, another problem with this approach relates to the fact that both numerologies shall filter their respective signals, although only one numerology is causing the interference as aforementioned.

The second solution is related to a radio frequency (RF) filtering. In this approach, the analog transmit signal is filtered using a bandpass filter, which limits the OOB emissions. However, this solution is expensive and does not guarantee full orthogonality amongst the subcarriers.

The third solution is related to the use of guard bands. This is the simplest solution, which inserts a guard band between the numerologies in order to increase the distance in frequency and decrease the OOB. However, this use of guard bands leads to a large spectral loss and a slow fall of the OOB emissions of orthogonal frequency-division multiplexing (OFDM).

SUMMARY

It is therefore an object of the present invention to mitigate the inter-numerology interference between subcarrier signals of different numerologies.

The object is achieved by the features of the independent claims. Further embodiments of the invention are apparent from the dependent claims, the description and the drawings. According to a first aspect, the invention relates to a multicarrier waveform-based system for mitigating inter-numerology interference, wherein at least one subcarrier signal of a first numerology designated as at least one interfering subcarrier signal interferes with at least another subcarrier signal of a second numerology designated as at least one interfered subcarrier signal, the first numerology being different from the second numerology. The system is configured to comprise a transmitter and a receiver, and configured to match an interference from the at least one interfering subcarrier signal to the at least one interfered subcarrier signal by matching frequency domain data symbols of the at least one interfering subcarrier signal to frequency domain data symbols of the at least one interfered subcarrier signal through a respective interference coefficient matrix with respect to the frequency domain data symbols of the at least one interfering subcarrier signal.

According to an implementation form of the first aspect, the system is configured to obtain an orthogonal space of the interference coefficient matrix by performing a singular value decomposition (SVD) of the interference coefficient matrix into a factorization to a first matrix, a diagonal matrix and a second matrix, configured to project, at a precoder of the transmitter, each frequency domain data symbol of the at least one interfering subcarrier signal onto the orthogonal space of the interference coefficient matrix through a respective precoding matrix with respect to the frequency domain data symbols of the at least one interfering subcarrier signal, as to obtain a respective precoded frequency domain data symbol, the respective precoding matrix being derived from the second matrix, and configured to decode, at a decoder of the receiver, the respective precoded frequency domain data symbols using the first matrix.

According to a further implementation form of the first aspect, the system is configured to control, using an interference control parameter generated by a data rate controller, the level of the inter- numerology interference by controlling a number of singular values of the diagonal matrix starting from the lowest singular values to the highest singular values, and configured to transmit the interference control parameter from the precoder of the transmitter to the decoder of the receiver via a control channel.

According to a further implementation form of the first aspect, the system is configured to demodulate, at a demodulator of the receiver, the at least one interfering subcarrier signal, as to obtain at least one demodulated interfering subcarrier signal, configured to obtain, at an

interference contribution module of the receiver, the respective interference of each frequency domain data symbol of the at least one interfering subcarrier signal from the at least one

demodulated interfering subcarrier signal, and configured to subtract the respective interference of each frequency domain data symbol of the at least one interfering subcarrier signal from the at least one interfered subcarrier signal.

The above object is also solved in accordance with a second aspect.

According to the second aspect, the invention relates to a method for mitigating inter-numerology interference in a multicarrier waveform-based system, wherein at least one subcarrier signal of a first numerology designated as at least one interfering subcarrier signal interferes with at least another subcarrier signal of a second numerology designated as at least one interfered subcarrier signal, the first numerology being different from the second numerology. The method comprises the step of matching an interference from the at least one interfering subcarrier signal to the at least one interfered subcarrier signal by matching frequency domain data symbols of the at least one interfering subcarrier signal to frequency domain data symbols of the at least one interfered subcarrier signal through a respective interference coefficient matrix with respect to the frequency domain data symbols of the at least one interfering subcarrier signal.

According to an implementation form of the second aspect, the interference coefficient matrix is derived from a first transformation at a transmitter of the multicarrier waveform-based system and a second transformation at a receiver of the multicarrier waveform-based system.

According to a further implementation form of the second aspect, the first transformation at the transmitter comprises the step of matching the frequency domain data symbols of the at least one interfering subcarrier signal to point inputs of an inverse fast Fourier transform (IFFT) matrix through a matching matrix, the step of converting the matched frequency domain data symbols of the at least one interfering subcarrier signal to time domain data symbols of the at least one interfering subcarrier signal through the IFFT matrix, and the step of attaching a respective first cyclic prefix to each time domain data symbol of the at least one interfering subcarrier signal through a respective first cyclic prefix insertion matrix, as to obtain respective input time domain data symbols of the at least one interfering subcarrier signal.

According to a further implementation form of the second aspect, the first transformation at the transmitter comprises the step of converting the frequency domain data symbols of the at least one interfered subcarrier signal to time domain data symbols of the at least one interfered subcarrier signal through the IFFT matrix, and the step of attaching a respective second cyclic prefix to each time domain data symbol of the at least one interfered subcarrier signal through a respective second cyclic prefix insertion matrix, as to obtain respective input time domain data symbols of the at least one interfered subcarrier signal.

According to a further implementation form of the second aspect, the second transformation at the receiver comprises the step of discarding the respective second cyclic prefix attached to each input time domain data symbol of the at least one interfered subcarrier signal from each input time domain data symbols of the at least one interfering subcarrier signal through a respective cyclic prefix removal matrix, as to obtain respective CPb-discarded time domain data symbols of the at least one interfering subcarrier signal, the step of converting the CPb-discarded time domain data symbols of the at least one interfering subcarrier signal to frequency domain data symbols of the at least one interfering subcarrier signal through a fast Fourier transform (FFT) matrix, as to obtain respective CPb-discarded frequency domain data symbols of the at least one interfering subcarrier signal, and the step of selecting the frequency domain data symbols of the at least one interfered subcarrier signal through a selection matrix, as to obtain a respective interference contribution with respect to the frequency domain data symbols of the at least one interfering subcarrier signal.

According to a further implementation form of the second aspect, the second transformation at the receiver comprises the step of discarding the respective second cyclic prefix attached to each input time domain data symbol of the at least one interfered subcarrier signal through a respective cyclic prefix removal matrix, as to obtain respective CPb-discarded time domain data symbols of the at least one interfered subcarrier signal, and the step of converting the CPb-discarded time domain data symbols of the at least one interfered subcarrier signal to frequency domain data symbols of the at least one interfered subcarrier signal through the fast Fourier transform (FFT) matrix as to obtain respective CPb-discarded frequency domain data symbols of the at least one interfered subcarrier signal.

According to a further implementation form of the second aspect, the method comprises the step of obtaining an orthogonal space of the interference coefficient matrix by performing a singular value decomposition (SVD) of the interference coefficient matrix into a factorization to a first matrix, a diagonal matrix and a second matrix, the step of projecting, at a precoder of the transmitter, each frequency domain data symbol of the at least one interfering subcarrier signal onto the orthogonal space of the interference coefficient matrix through a respective precoding matrix with respect to the frequency domain data symbols of the at least one interfering subcarrier signal, as to obtain a respective precoded frequency domain data symbol, the respective precoding matrix being derived from the second matrix, and the step of decoding, at a decoder of the receiver, the respective precoded frequency domain data symbols using the first matrix.

According to a further implementation form of the second aspect, the method comprises the step of controlling, using an interference control parameter generated by a data rate controller, the level of the inter-numerology interference by controlling a number of singular values of the diagonal matrix starting from the lowest singular values to the highest singular values, and the step of transmitting the interference control parameter from the precoder of the transmitter to the decoder of the receiver via a control channel.

According to a further implementation form of the second aspect, the method comprises the step of demodulating, at a demodulator of the receiver, the at least one interfering subcarrier signal, as to obtain at least one demodulated interfering subcarrier signal, the step of obtaining, at an interference contribution module of the receiver, the respective interference of each frequency domain data symbol of the at least one interfering subcarrier signal from the at least one demodulated interfering subcarrier signal, and the step of subtracting the respective interference of each frequency domain data symbol of the at least one interfering subcarrier signal from the at least one interfered subcarrier signal.

The above object is also solved in accordance with a third aspect. According to the third aspect, the invention relates to a computer program comprising a program code for performing the method according to the second aspect and/or any one of the

implementation forms of the second aspect, when executed on a computer.

Thereby, the method can be performed in an automatic and repeatable manner.

The computer program can be performed by the above apparatuses.

More specifically, it should be noted that all the above apparatuses may be implemented based on a discrete hardware circuitry with discrete hardware components, integrated chips or arrangements of chip modules, or based on a signal processing device or chip controlled by a software routine or program stored in a memory, written on a computer-readable medium or downloaded from a network such as the Internet.

It shall further be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or above embodiments with the respective independent claim.

These and other aspects of the invention will be apparent and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the exemplary embodiments shown in the drawings, in which:

Fig. 1 shows a schematic view of packing different services with different numerologies according to a 3GPP standard proposal; Fig. 2 shows an exemplary inter-numerology interference between subcarriers of different numerologies in the frequency domain, where a numerology (depicted as "Numer. 2") based on a subcarrier spacing Af2 interferes with another numerology (depicted as "Numer. 1") based on a lower subcarrier spacing Afl, where Af2=2xAfl;

Fig. 3 shows an exemplary transmitter windowing taken from: A. A. Zaidi, . Baldemair, H.

Tullberg, H. Bjorkegren, L. Sundstrom, J. Medbo, C. Kilinc, and I. D. Silva, "Waveform and Numerology to Support 5G Services and Requirements," IEEE Communications Magazine, vol. 54, no. 11, pp. 90-98, 2016;

Fig. 4 shows a schematic view of an interference coefficient matrix (C| _Xp ) matching the

interference of p subcarriers (X!,) of a higher subcarrier numerology (denoted by numerology a) to I subcarriers (V _h ) of a lower subcarrier numerology (denoted by numerology b);

Fig. 5 shows a sequential arrangement of multiple matrices from which the interference

coefficient matrix (C _lxp ) is derived, according to an embodiment of the present invention;

Fig. 6 shows a time domain superposition of two numerologies denoted by numerology a and numerology b wherein two frequency domain data symbols of numerology a are superimposed in terms of duration with one frequency domain data symbol of numerology b, according to an embodiment of the present invention;

Fig. 7 shows a schematic multicarrier waveform-based system 100 using precoding and decoding according to a first embodiment of the present invention;

Fig. 8 shows a schematic multicarrier waveform-based system 200 using successive interference cancellation (SIC) decoding according to a second embodiment of the present invention; Fig. 9 shows a schematic multicarrier waveform-based system 300 using precoding and SIC decoding according to a third embodiment of the present invention;

Fig. 10 shows an interference power (dB) due to OOB emissions versus a subcarrier index for a transmit signal of different numerologies in the case where it is precoded according the present invention with different data rate reductions (PC in %), and in the case where it uses different guard bands (GB in kHz) that are inserted between the numerologies; and

Fig. 11 shows an average interference power (dB) due to OOB emissions versus a data rate

reduction (%) for a transmit signal of different numerologies in the case where it is precoded according the present invention and in the case where it uses guard bands that are inserted between the numerologies.

Identical reference signs are used for identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention is based on an analysis of the interference caused by a set of subcarrier signals on another set of subcarriers with a different numerology. This interference may be defined by a so- called interference coefficient matrix (denoted by C _lxp ) as schematically represented in Fig. 4, wherein C _lxp matches the interference from p interfering subcarriers (X!,, where i=0, 1, p-1) of a higher subcarrier numerology (denoted by numerology a) to the I interfered subcarriers (l , where k=0, 1, 1-1) of a lower subcarrier numerology (denoted by numerology b).

The matrix has p columns corresponding to the interfering subcarrier signals causing interference, and I rows corresponding to the interfered subcarrier signals suffering from interference. The interference coefficient matrix C _lxp is composed of (Ixp) matrix elements, and the matrix element Ci,j will be associated to the interference caused by the k-th subcarrier on the i-th subcarrier. The interference coefficient matrix C _lxp may be derived from a sequential arrangement of multiple matrices, denoted by M, W and P _CPa at a transmitter side and Pcpb _< and S at a receiver side as depicted in Fig. 5, and may be computed as follows:

C _lxp = M . W . P _CPa . P _CPb . W . S (1)

where M is a matching matrix, W is an inverse fast Fourier transform (I FFT) matrix, P _CPa is a cyclic prefix insertion matrix for the numerology a, P _CPb is a cyclic prefix removal matrix for the numerology b, W is a fast Fourier transform (FFT) matrix and S is a selection matrix.

It should be noted that the interference coefficients of the interference coefficient matrix C _lxp may be directly computed as a function of static parameters such as subcarrier spacing and cyclic prefix (CP) amongst others, without the need of transmitting any interfering signal via the transmitter and the receiver. In this case, the interference coefficients may indeed be identified for each numerology pair using, for example, a look-up table.

Since 3GPP has agreed on integer multiples of a base subcarrier spacing, it results therefrom that all numerologies share the same I FFT kernel and the same FFT kernel based on the base subcarrier spacing.

The matching matrix M distributes the p data symbols onto the N IFFT point inputs and the I subcarriers belonging to the other numerology are padded with zeros in the matching matrix M. The data symbols are interleaved with zeros since the subcarrier spacing is twice the base su bcarrier spacing of the IFFT kernel.

The cyclic prefix removal matrix P _CPb removes a CP of length 2NCP, whereas the cyclic prefix insertion matrix P _CPa attaches a CP of length NCP, selects N/2 time domain samples and pads the rest into zero. The selection matrix S selects the subcarriers which belong to the numerology b, i.e., the numero that suffers from the interference.

For ease of exposition, the present invention will be described based on an exemplary embodiment in which there are two subcarrier spacings in the frequency domain, with the larger one being twice as high as the smaller one. Referring to Fig. 6 showing a time domain superposition of two numerologies (denoted by numerology a and numerology b), two frequency domain data symbols (depicted as X3, and X ) of numerology a are superimposed in terms of duration with one frequency domain data symbol (depicted as X _b ) of numerology b, the larger subcarrier spacing being half the symbol duration of the smaller subcarrier spacing due to the reciprocity of time and frequency. As the numerology a with a larger subcarrier spacing interferes with the numerology b with a lower subcarrier spacing but not vice versa, the shorter duration symbols (i.e., X3, and X ) shall be precoded while transmitting the longer duration symbol (i.e., X _b ) without precoding.

In the exemplary embodiment as illustrated in Fig. 6, we have two interference coefficient matrices Ci and C2, which respectively correspond to the first frequency domain data symbol X3, of the first time slot, and the second frequency domain data symbol X of the second time slot, and may be defined as follows:

Ci = M . W . p ⁱ pa - PcPb - W . S (2)

C ₂ = M . W . P _c ² _Pa . P _CPb . W . S (3)

where Ρ^ρ ₃ is the cyclic prefix insertion matrix for the first frequency domain data symbol of the interfering subcarrier signal of numerology a through which one CP of the numerology a is inserted, P<? _PA is the cyclic prefix insertion matrix for the second frequency domain data symbol of the interfering subcarrier signal of numerology a through which one CP of the numerology a is inserted, and P _CPB is the cyclic prefix removal matrix for the numerology b through which a CP of the numerology b is removed, the CP of the numerology a having a length NCP and the CP of the numerology b having a length IShcp, where The interference coefficient matrix C _lxp is a deterministic matrix which depends solely on the numerologies (e.g., numerology a and numerology b) but not on the communication channel. A respective interference coefficient matrix C _lxp (i.e., Ci and C ₂ ), with respect to the frequency domain data symbols (i.e., X3, and X ) of the interfering subcarrier signal, allows to match the frequency domain data symbols (i.e., X3, and X ) of the interfering subcarrier signal to the frequency domain data symbols (i.e., X _b ) of the interfered subcarrier signal. Hence, once C _lxp has been derived for each frequency domain data symbol (i.e., X3, and X ) of the interfering subcarrier signal of numerology a, the interference of numerology a (i.e., the interference of the higher subcarrier numerology) can be mitigated by precoding the interfering data symbols in a first embodiment or by deducting the derived interference at the receiver in a second embodiment or by using in a third embodiment a combination of the first and second embodiments.

Fig. 7 shows a schematic multicarrier waveform-based system 100 using precoding and decoding according to said first embodiment of the present invention.

The multicarrier waveform-based system 100 comprises a transmitter and a receiver communicating to each other via a transmit channel, and a data rate controller 190. The transmitter (TX) comprises a precoder 110 applicable to the numerology a (i.e., the numerology causing the interference), a matching matrix 120 (also denoted as M matrix) applicable to the numerology a, an IFFT matrix 130 (also denoted as W matrix) applicable to the numerologies a and b, a cyclic prefix insertion matrix 140-A (also denoted as P _CPa matrix) applicable to the numerology a and a cyclic prefix insertion matrix 140-B (also denoted as P _CPb matrix) applicable to the numerology b. The receiver ( X) comprises a cyclic prefix removal matrix 150 (also denoted as P _CPb matrix) applicable to the numerologies a and b, a fast Fourier transform (FFT) matrix 160 (also denoted as W matrix) applicable to the numerologies a and b, a selection matrix (also denoted as S matrix) 170 applicable to the numerology a, and a decoder 180 applicable to the numerology a.

At its input, the precoder 110 receives the first frequency domain data symbol X3, and the second frequency domain data symbol X of the interfering subcarrier signal of the numerology a. Once the two interference coefficient matrices Ci and C2, which respectively correspond to the first frequency domain data symbol X3, and the second frequency domain data symbol X , have been derived or computed, a respective singular value decomposition (SVDi, SVD2) of each interference coefficient matrix (Ci, C2) into a factorization (U.∑.V) to a first matrix (U matrix), a diagonal matrix (∑ matrix) and a second matrix (V matrix) is performed at the precoder 110 in order to obtain a respective orthogonal space of each interference coefficient matrix (Ci, C2). The precoder 110 at the transmitter (TX) may extract the column vectors of the V matrix from the SVD decomposition, whereas the decoder 180 at the receiver ( X) may take its corresponding row vectors of the U matrix. The column vectors are selected according to their singular values from lowest to highest in order to control the interference power. The more precoding vectors are selected, the higher is the data rate, but the interference power increases.

Then, the precoder 110 projects the first and second frequency domain data symbols (X , X ) of the interfering subcarrier signal onto their respective orthogonal space through a respective precoding matrix (Ji, J2) as to obtain a respective precoded frequency domain data symbol (Ji.X _g , J2.XI).

Thereby, the precoded frequency domain data symbols (Ji.X _g , J2.XI ) are guaranteed to not interfere with the frequency domain data symbol (X _b ) of the interfered subcarrier signal of the other numerology (i.e., the numerology b). The respective precoding matrices (Ji, J2) are derived from the respective V matrix and may be defined as follows:

e C ^ e (M . W . Pc _a . P ±

CPb■ W . S) (4)

} ₂ e C ₂ ^X ^ } ₂ e (M . W . P _c ² _Pa . P _CPb . W . S) ±

(5)

where Ρ^ρ ₃ is the cyclic prefix insertion matrix 140-A for the first time slot frequency domain data symbol of the interfering subcarrier signal of numerology a through which one CP of the numerology a is inserted, P<? _Pa is the cyclic prefix insertion matrix 140-B for the second time slot frequency domain data symbol of the interfering subcarrier signal of numerology a through which one CP of the numerology a is inserted, and P _CPb is the cyclic prefix removal matrix 150 applicable to the numerology b through which a CP of the numerology b is removed, the CP of the numerology a having a length NCP and the CP of the numerology b having a length IShcp, where The data rate controller 190 is configured to generate an interference control parameter (Γ), which controls the level (or amount) of the inter-numerology interference by controlling a number of singular values of the∑ matrix starting from the lowest singular values to the highest singular values and configured to transmit the interference control parameter (Γ) from the precoder 110 at the transmitter (TX) towards the decoder 180 at the receiver ( X) via a control channel. Indeed, the interference control parameter (Γ) controls the number of non-orthogonal column vectors extracted by the precoder 110, and the more non-orthogonal column vectors are selected, the higher data rate can be achieved regarding the numerology a (i.e., the numerology causing the

interference). The level (or amount) of the inter-numerology interference may be controlled, for example, depending on the channel condition, the quality of service (QoS), the signal-to-noise ratio (SNR) and/or the reliability requirement amongst others.

The precoded frequency domain data symbols (Ji.X _a , J2.XI) are transmitted, through the matching matrix 120 (i.e., the M matrix), towards the IFFT matrix 130 (i.e., the W matrix) in order to be converted from the frequency domain to the time domain, and a respective cyclic prefix (Pc _Pa , Pcp _a ) insertion applicable to the numerology a is then applied to each of the resulting time domain data symbols (W.M. Ji.X _a , W.M. J2.XI) of the interfering subcarrier signal using the insertion matrix 140-A.

For its part, the frequency domain data symbol (X _b ) of the interfered subcarrier signal of the numerology b is directly transmitted towards the IFFT matrix 130 (i.e., the W matrix) in order to be converted from the frequency domain to the time domain, and a cyclic prefix (Pcpb) insertion applicable to the numerology b is then applied to the resulting time domain data symbol (W.X _b ) of the interfered subcarrier signal, using the insertion matrix 140-B.

Outputting from the respective insertion matrices 140-A and 140-B, the time domain data symbols (Pc _Pa .W.M. Ji.X _a , Pcp _a .W.M. J2.XI) of the interfering subcarrier signal and the time domain data symbol (P _CPb .W.X _b ) of the interfered subcarrier signal are then multiplexed into a time domain transmit signal (X _T ) given by the following relationship:

X = PcPb-W.X^ -l- Pcp _a .W.M. Ji.X3, + Ρ<?ρ ₃ .\Λ .Μ. J ₂ .X| (6) The time domain transmit signal (X _T ) is transmitted towards the receiver ( X) over the transmit channel, and a cyclic prefix (Pcpb) removal is then applied to each member of the time domain transmit signal (X _T ), namely to each time domain data symbol (Pc _Pa .W.M. Ji.X _a , Ρ<? _Ρ3 .\Λ/.Μ. J2.XI) of the interfering subcarrier signal and to the time domain data symbol (P _CPb .W.X _b ) of the interfered subcarrier signal, using the cyclic prefix removal matrix 150.

The resulting time domain data symbols (Ρ^.Ρ^.\Λ/.¾, P _CPb . Pc _Pa .W.M. Ji.X _a , P _CPb . P,? _Pa .W.Iv1. J2.X ) are directly transmitted towards the FFT matrix 160 (i.e., the W matrix) in order to be converted from the time domain to the frequency domain.

The resulting frequency domain data symbols (W.P _CPb . Pc _Pa .W.M. Ji.Xi,, W.P _CPb . P^ _Pa .W.M. i ₂ .Xl) of the interfering subcarrier signal are then transmitted towards the selection matrix 170, as to obtain the frequency domain data symbols S. W.P _CPb . Pc _Pa .W.M. Ji.X* and S.W.P _CPb .

which are then decoded at the decoder 180 using its corresponding row vectors of the U matrix, thereby reversing the effect of the precoder 110.

For its part, the resulting frequency domain data symbol (i. e. , W.P _CPb .P _CPb .W.X _b = X _b ) of the interfered subcarrier signal is made available at an output of the FFT matrix 160.

Fig. 8 shows a schematic multicarrier waveform-based system 200 using successive interference cancellation (SIC) decoding according to a second embodiment of the present invention.

The multicarrier waveform-based system 200 basically differs from the multicarrier waveform-based system 100 in that there is no precoding at the transmitter (TX), so that the precoder 110 of Fig. 7 is not provided at the transmitter of Fig. 8, and in that there is no decoder 180 at the receiver (RX). Instead, the receiver (RX) of the multicarrier waveform-based system 200 comprises a first demodulator 210, an interference contribution module 220 and a second demodulator 230. The first demodulator 210 is configured to demodulate the interfering subcarrier signal as to obtain a demodulated interfering subcarrier signal. The interference contribution module 220 is configured to obtain, based on an a priori knowledge of the interference coefficient matrices Ci and C2, a respective interference contribution (i.e., Ci.Xi, = S. W.P _CPb . P^ _Pa .\N. M.X and C2.X = S.W.P _CPb . P ₍ ?p _a .W. Iv1.X ) of each frequency domain data symbol of the interfering subcarrier signal from the demodulated interfering su bcarrier signal, and also configured to subtract the respective interference contribution (i.e., d.X5, = S. W.P _CPb . Pc _Pa .W. M.X3, and C ₂ .X = S.W.P _CPb . P,¾, _a .W.M.X ) of each frequency domain data symbol of the interfering subcarrier signal from the interfered subcarrier signal. The second demodulator 230 is configured to provide the frequency domain data symbol (i.e., X _b ) of the interfered subcarrier signal.

In theory, the interference contribution may be fully eliminated when the first demodulator 210 demodulates without error the interfering subcarrier signal. However, if an error occurs, this error may propagate to the interfered subcarrier signal of the other numerology b. Hence, this second embodiment may advantageously apply to scenarios with high SN , for which the erroneous demodulation probability is low.

Fig. 9 shows a schematic multicarrier waveform-based system 300 using precoding and SIC decoding according to a third embodiment of the present invention.

The multicarrier waveform-based system 300 is a hybrid multicarrier waveform-based system which comprises a combination of all the constituent elements of the multicarrier waveform-based system 100 and the multicarrier waveform-based system 200.

Should a significant reduction in data rate of the higher numerology a be unacceptable, then the precoder 110 may be a precoder with a considerable interference as the receiver (RX) would enhance its estimate by subtracting the residual interference from the interfered subcarrier signal. Hence, this third embodiment advantageously allows to achieve high data rates with a high reliability since the error propagation can be minimized.

Fig. 10 shows an interference power (d B) due to OOB emissions versus a subcarrier index for a transmit signal of two different numerologies in the case where it is precoded according the present invention with different data rate reductions (PC in %), and in the case where it is guard banded with different guard bands (GB in kHz) that are inserted between the two numerologies. For fair comparison, the guard bands are matched to the data rate reduction of the precoded transmit signal. It can be noted that the signal power of the guard banded signal is boosted since the transmitter focuses its power only on the inband subcarriers. Thus, in short, Fig. 10 shows the interference leakage of the interfering numerology on the subcarrier index of the other numerology.

The comparison of the OOB emission between the precoded and guard banded transmit signals reveals that a reduction of 2.7344% in data rate leads to an interference suppression of around 40 dB compared to the guard band solution which has a same overhead. Indeed, the projection of the transmit signal onto the (near)-orthogonal space of the interference coefficient matrix allows to reduce the data rate due to the fact that the precoder compresses the transmit signal.

Fig. 11 shows an average interference power (dB) over all the subcarriers versus the data rate reduction (%) for a transmit signal of two different numerologies in the case where it is precoded according the present invention and in the case where it is guard banded with different guard bands that are inserted between the two numerologies. The number of subcarriers has been fixed at 256 subcarriers with an allocation of 128 subcarriers (i.e., a subcarrier allocation factor equal to 50%) to each numerology.

As can be seen therein, the use of guard bands offers a slow reduction in the average interference power, whereas the average interference power for the precoded transmit signal drops nearly linearly with increasing the data rate reduction.

Finally, the benefits of the present invention to mitigate the inter-numerology interference can be listed as follows:

- Suppression of the inter-numerology interference using a static precoder;

- Different numerologies can be multiplexed with a zero or near-zero guard band without performing F filtering;

- The price paid to suppress the inter-numerology interference is a slight reduction in data rate; - The precoder design has a low complexity due to the sparseness of the interference coefficient matrix. Indeed, although the precoding procedure changes from one frequency domain data symbol to the other, the precoder itself relies solely on system design parameters such as the subcarrier spacing and the CP amongst others, and not on channel parameters;

- The deterministic knowledge of the inter-numerology interference helps the scheduler assign frequency bands to the different numerologies; and

- The ability to act as a plug in on top of CP-OFDM (same performance) unlike time domain operations which may affect scattering channels.

In summary, the present invention relates to a multicarrier waveform-based system for mitigating inter-numerology interference, wherein at least one subcarrier signal of a first numerology designated as at least one interfering subcarrier signal interferes with at least another subcarrier signal of a second numerology designated as at least one interfered subcarrier signal, the first numerology being different from the second numerology. The invention is mainly based on precoding the data assigned to a certain subcarrier dedicated to a specific function. Subcarriers are usually classified into different numerologies according to numerology parameters such as subcarrier spacing and cyclic prefix (CP) amongst others. Thereby, each subcarrier having a certain numerology comprises different numerology parameters. A subcarrier of a certain numerology may interfere with other subcarriers of other numerologies having, for example, narrower subcarrier spacings. The suggested precoding is based on the above-mentioned numerology parameters in order to eliminate the inter-numerology interference. Thus, the invention is mainly based on designing a precoder at the transmitter with specific parameters which are related to the coexisting two numerologies. The parameters of the precoder are shared with a decoder of the receiver through a control channel so that the receiver can decode the received message.

While the present invention has been illustrated and described in detail respectively in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. From reading the present disclosure, other modifications will be apparent to a person skilled in the art. Such modifications may involve other features, which are already known in the art and may be used instead of or in addition to features already described herein.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Although the present invention has been described with reference to specific features and embodiments thereof, it is evident that various modifications and combinations can be made thereto without departing from the spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded simply as an illustration of the invention as defined by the appended claims, and are contemplated to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the present invention.

The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 760809.