Interference cancelation for a multi-numerology OTFS based noma

Abstract

The invention is related to a method for mitigating the inter-numerology interference in multi- numerology OTFS based NOMA systems / networks to generate a signal for plurality of wireless devices and a receiving and communication and / or sensing method for such a signal.

Description

[0001] INTERFERENCE CANCELATION FOR A MULTI-NUMEROLOGY OTFS BASED NOMA

[0002] Technical Field

[0003] The invention is related to a method for mitigating the inter-numerology interference in multinumerology OTFS based NOMA systems / networks to generate a signal with lesser interference for plurality of wireless devices and a receiving and communication and / or sensing method for such a signal.

[0004] Prior Art

[0005] The emergence of new services and applications in wireless networks has spurred the demand for extensive connectivity in 6G networks. However, both orthogonal and non-orthogonal technologies currently in use have limitations when it comes to meeting this requirement. While NOMA systems offer significant advantages, they still suffer from substantial interference issues. This limitation underscores the need to develop a hybrid waveform that harnesses the strengths of NOMA while maintaining low complexity and mitigating interference.

[0006] Multi -numerology OTFS-based NOMA approach combines OTFS-NOMA, a modulation technique accommodating overlapping OTFS signals in the delay-Doppler domain, with the multi-numerology concept, which involves utilizing different spacing schemes. The need for high throughput in high mobility scenarios and diverse user requirements underscores the necessity of such integration. NOMA can be merged with the concept of OTFS and multinumerology to achieve quality of service demands for different users under diverse mobility levels scenario. However, multi-num erology-OTFS-based NOMA faces significant system performance degradation due to interference arising from the use of different numerologies, making it challenging to estimate or mitigate at the receiver's end. Addressing these technical challenges is crucial for achieving improved performance in wireless communication systems and reduce the system complexity overhead and latency.

[0007] OTFS-NOMA significantly enhances system performance and capabilities. Notably, several control approaches for implementing OTFS-NOMA have already emerged in the literature. For example, a study in [1] leverages the OTFS-NOMA approach to distinguish users based on their mobility profiles. In another work [2], a novel, low-complexity iterative receiver customized for OTFS-NOMA is introduced. This approach multiplexes OTFS-modulated signals in the power domain. Their proposed receiver design outperforms conventional methods in terms of data detection reliability and symbol error rate (SER).

[0008] However, it's worth noting that since multi-numerology OTFS-NOMA was introduced solely in our initial patent [3], there is no prior work in the literature to address interference mitigation in multi-numerology OTFS-NOMA systems. Interference cancellation has been introduced only in OFDM multi-numerology systems [4][5], but it cannot be applied to OTFS systems due to their use of different domains.

[0009] The multi-numerology OTFS-based NOMA approach grapples with a significant challenge concerning interference when various numerology schemes are employed. Numerology determines how delay-Doppler bins are allocated to different users, influencing the overall system design. When multiple numerologies coexist in the same communication system, signals have the potential to interfere with one another. This overlapping of numerologies is harnessed to implement the NOMA concept, allowing multiple users to share the same frequency resources. However, this overlap can introduce intentional interference, making signal detection more complex and challenging. Consequently, advanced interference mitigation techniques are imperative to address this issue effectively.

[0010] One of the limitations of the multi -numerology OTFS-based NOMA approach is its relatively high-power consumption. This characteristic makes the approach less applicable for low-cost and energy-efficient devices. While OTFS-NOMA can offer advantages in certain scenarios, the increased power requirements may not align with the constraints of resource-constrained or battery-powered devices, limiting its practicality in such contexts.

[0011] Also, high latency due to receiver complexity which conflicts with 6G new requirements.

[0012] As a result, all of the problems mentioned above has made it necessary to provide a novelty in the related field.

[0013] Brief Description and Objects of the Invention

[0014] The main object of the present invention is to establish a method for interference cancelation to be used on multi-numerology OTFS-based NOMA waveform and generating and receiving and communication method for such a waveform to achieve quality of service demands for different users under diverse mobility levels scenario.

[0015] Another object of the invention is to enhance performance of multi -numerology OTFS based NOMA approach.

[0016] Another object of the invention is to enhance adaptability to channel conditions for improved performance.

[0017] Another object of the invention is to optimize spectral efficiency through efficient spectrum utilization.

[0018] Another object of the invention is to provide robustness against channel variations for reliable communication.

[0019] Another object of the invention is to accommodate users with different mobility characteristics and varying requirements.

[0020] Another object of the invention is to maximize throughput and capacity in highly mobile environments.

[0021] To achieve such goals, the method proposes inter-numerology interference (INI) cancellation for different index spacing in the representation of the wireless channel in delay-Doppler (DD) domain is utilized to provide different numerologies to enable unique waveform design that utilizes sophisticated techniques like OTFS, NOMA and is applicable for multiple users’ requirements.

[0022] The invention reduces design complexity overhead, the total complexity of the system and the receiver’s complexity because the users will have no need to detect the interference and cancel it. Especially for users with narrow spacing.

[0023] The interference cancellation approach helps reduce the total complexity of the system and the receiver’s complexity in estimating the interference and deleting the channel effect thus the latency will decrease.

[0024] The invention enables serving low-cost devices due to low complexity of receiving and decoding process and this approach allows low-end (low power devices) to use this scheme efficiently.

[0025] The invention enables green communication networks by reducing the complexity and the interference leads to less energy consumption. The invention maximizes spectral efficiency by optimizing the utilization of available spectrum through efficient resource allocation and adaptive numerology while reducing the interference leads to better signaling and provides optimized spectral efficiency.

[0026] The invention provides more high mobility capabilities by reducing errors through interference deletion, thereby enabling the realization of the full advantages offered by OTFS signaling.

[0027] One key achievement of this innovation is its impact on making wireless communication more efficient. By reducing interference in the multi-numerology OTFS-based NOMA approach, making better use of the available wireless resources. Maximizing spectral efficiency, leading to improved wireless communication. This is a big step forward in wireless technology, offering exciting opportunities to enhance networks and connect different devices and applications seamlessly.

[0028] The objective is to enhance wireless communication systems and optimize their performance. By effectively integrating INI cancellation with the multi -numerology OTFS-based NOMA approach, it increases the flexibility of wireless communication and enhances overall performance. This represents a significant milestone in the ongoing development of wireless communications, introducing new possibilities and setting higher standards for future innovations in the field.

[0029] Description of the Figures of the Invention

[0030] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0031] Figure 1. A schematic view of the system.

[0032] Figure 2. A graphical representation of multi -numerology distribution in DD domain with different delay spacing.

[0033] Figure 3. A graphical representation of multi -numerology distribution in DD domain with different Doppler spacing.

[0034] Figure 4. A graphical representation of multi -numerology distribution in DD domain with different both delay and Doppler spacing. Figure 5. A graphical representation of the proposed NOMA-based multi-numerology OTFS design in time-frequency domain.

[0035] Figure 6. A schematic view of the proposed NOMA-based multi-numerology OTFS transceiver design

[0036] Figure 7. The proposed NOMA-based multi-numerology OTFS design flow chart.

[0037] Reference Numbers

[0038] The parts and components given in the figures are referenced for the subject matter of the invention to be understood better.

[0039] TX. Transmitter

[0040] RX. Receiver

[0041] UE. User equipment

[0042] Detailed Description of the Invention

[0043] The invention is related to a method for multi-numerology OTFS based NOMA approach to generate a signal with lesser interference for plurality of wireless devices and a receiving and communication method for such a signal.

[0044] Referring to Figure 1; The communication system that the communication method is carried comprises at least one transmitter (Tx) such as a base station and multiple moving user equipment (UE) having at least one receiver (Rx). At least two of the moving user equipment (UE) are wide bin users and at least one of the moving user equipment (UE) is narrow bin user

[0045] Referring to Figure 2 to 4: To generate a waveform according to multi-numerology OTFS based NOMA approach, first, at least three signals are designed and two of them are wide grid signal and other one is the narrow grid signal. Both wide and narrow grid comprise bins that positioned on these grids with spacing to form the wide grid signal and the narrow grid signal, respectively.

[0046] A downlink multi-user OTFS system design is assumed where an OTFS modulation scheme is used to multiplex the users. The OTFS signal considers M x N data symbols distributed over DD bins denoted by where The communication system is modulated over a total bandwidth with a frame duration of where the time duration of one symbol is which imposes 1 / MA f and delay and Doppler spacing, respectively.

[0047] The spacing of these grids is different than others, at least according to one of delay or Doppler space. In excessive cases, both spacings can be different in both spaces.

[0048] After the design is completed, the wide signal and the narrow signal is converted into timefrequency domain.

[0049] In figure 2, the spacing of the grids are equal in Doppler space but not in delay space. This can be represented by formula and are Doppler spacing of the wide grid and narrow grid, respectively, while where Arq and AT2are delay spacing of the wide grid and narrow grid, respectively.

[0050] For example, value of N and is set as while Nvrand Av2is kept equal. That gives two OTFS signals with different numerology only in delay domain as presented in Figure 2 where is equivalent to setting . Finally, the

[0051] OTFS transform can be done by taking ISFFT with size for the first numerology and size (M2, N2) for the second one with

[0052] In figure 3, the spacing of the grids are equal in delay space but not in Dopier space. This can be represented by formula of and

[0053] For example, value of and is set as 2while and is kept equal. That gives two OTFS signals with different numerology only in Doppler domain as presented in Figure 3 where is equivalent to setting . Finally, the OTFS transform can be done by taking ISFFT with size for the first numerology and size for the other.

[0054] In figure 4, the spacing of the grids are equal in both spaces. This can be represented by formula of and

[0055] For example, value of and is set as while Atq and At2is set as Atq = That gives two OTFS signals with different numerology only in Doppler domain as presented in Figure 4 is equivalent to setting and . Thus, the OTFS modulation can be done by taking ISFFT with size for the first numerology and for the second one.

[0056] For all example of figure 2 to 4; fundamental numerology chosen here is similar to the one used in conventional LTE networks and a total of five scalable numerology options are provided. All standardized A / values are 2qmultiples of the fundamental LTE numerology for For the OTFS signal part, we consider two OTFS signals that use the same DD resources, denoted by , with and spacing for the first and second numerologies, respectively.

[0057] The designed wide and narrow signals are converted into the time-frequency domain. In here are mapped to the time-frequency (TF) domain grid using the inverse symplectic finite Fourier transform (ISFFT) [6], where

[0058] From converted wide signal the inter-numerology interference (INI) can be detected. The detection is carried out by looking symplectic finite Fourier transform (SFFT) of the wide signals because signal structure and power of them are not equal to each other. More clearly, the detection is carried out by transforming the multiple wide bins signals that is put out the wide bins signals different time-frequency slots to delay-Doppler. Detected INI is subtracted from the converted narrow signal.

[0059] The designed and converted wide signals and narrow signal (INI is subtracted from) are summed. The converted wide signals are put in time-frequency slots without overlapping each other since wide grid signals in delay doppler takes less resources in time frequency and are summed together with the converted narrow signal from which is INI subtracted.

[0060] After the sum of the wide and narrow signals, the obtained signal is converted into time domain, preferably by Heisenberg Transform as where rect(. ) is the rectangular pulse shape and

[0061] After the conversion into time domain, the signal is sent to medium by the transmitter (Tx).

[0062] The NOMA-based multi -numerology OTFS design mainly relies on the transmitter design assuming three users in the system. We consider a wireless communication system that comprises multiple wide bins spacing users a, multiple narrow bins users p and the total number of users is given by Our approach involves overlaying signals of users with narrow delay spacing denoted by xnroccupying a bandwidth on top of signals of users with wider spacing denoted by and occupying a bandwidth This enables the use of 2qsignalswto cover the same resources utilized by the xnr.

[0063] The transmitter (Tx) design consists of four stages as follow:

[0064] The first is designing the wide signal. The wide spacing signal can be presented as follows. where are the complex modulated symbols of the athuser on ktfland IthDoppler and delay bins, respectively. is the assigned power factor, where the total amount of the specified power is

[0065] The second is designing the narrow signal. The narrow spacing signal and to avoid interference between different numerologies is allocated only on the odd bins by setting , Thus their OTFS TF domain signal is given as bellow where are the complex modulated symbols of the user on and Doppler and delay bins respectively, is the assigned power factor, where the total amount of the specified power is - The maximum assigned power from the BS to all users is represents the conventional NOMA scheme case.

[0066] The third is signal superposition. This represents summation step. For simplicity purpose we consider and naming the first and the second wide bins spacing user UE1 and UE2, respectively. The narrow bins user as UE3. After converting both wide and narrow signals to TF domain, the wide bin signals Xaare assigned in different frequency slots to form one block matrix wThe narrow bin signal jsadded with Xwto produce a single block named asdepicted in Figure 5. The summation needs to be performed in the TF domain due to the spread in both domains which can be expressed as follows:

[0067] Fourth is inter-numerology interference (INI) cancellation. Since both and signals are known and -. wecandelete the INI on the odd bins from the transmitted signal of the wide bins by looking at both as (2M1, N2) symplectic finite Fourier transform (SFFT), setting and changing z to be 0 or 1 for even and odd bins respectively. can be removed from iat the transmitter and the resulting TF domain signal XTFwill be clear from INI. Since the first and second part ofiare exactly the inverse After that, XTFis converted to time domain signal s(t) using Heisenberg Transform. A common cyclic prefix (CP) [8] is added to the time domain signal s(t) which has to be larger than the maximum excess delay of the channel.

[0068] We assume that the channels for all I users are linear time varying. Each user's channel contains paths, where the path has complex attenuation delay and Doppler value for These characteristics result in a doubly dispersive DD channel for each user

[0069] The DD values for f tap are given as and where lLiE and are the number of delay and Doppler bins. We assume that N2and M2are sufficiently large so that there is no effect of fractional delay and Doppler on the system assuming perfect knowledge of the channel hLt at the receiver.

[0070] Preferably, after the signal received by the user equipment, the process at the receiver side starts by removing the CP, the wireless channel effect.

[0071] After the deleting the wireless channel effect, the received signal is converted delay Doppler domain according to spacing of the wide grid by each user and the wide grid is detected from the converted signal to extract the wide signal by at least two of the users, preferably by deleting wireless channel effects from the received signal. Preferably, the Wigner transform may be applied after deleting the wireless channel effects. According to detected wide signal, the narrow signal can be reconstructed by at least one of the users that already extract the wide signal or more, if necessary. If there is more than wide signal is designed in first step of generating waveform, further wide signals can be detected by deleting extracted the wide signal from the received signal.

[0072] To carry out these steps, the below disclosed process may be carried out.

[0073] After removing the CP and performing OTFS transform using a matching pulse with the transmit pulse rect(A), the channel is estimated and the input-output relation at any user can be derived as where denote the delay-Doppler effective channel matrix, and H represents the time equivalent channel matrix.

[0074] Note that to estimate the channel, any conventional OTFS channel estimation method is applicable such as impulse channel estimation method represented in [9],

[0075] The channel is equalized using minimum mean square error (MMSE) detector. The equalized signal is converted to DD domain using SFFT with The output of the even and odd bins can be derived by setting

[0076] Although and signals are orthogonal at the transmitter, they are received overlapping, due to the summation process of the SFFT. For the narrow bins signal there will be no interference due to the non-orthogonality of NOMA-based approach under the assumption of perfect INI cancellation.

[0077] Wide spacing users receive the signal and decode based on the NOMA scheme and difference in the power levels. While the narrow user in this approach receives the signal and detect his data directly from odd bins. The basic idea of the proposed approach is discussed from the perspective of three users only which at least two of them are wide bin and at least one of them is narrow bin user, however, the design can be extended to more than three users, and based on their requirements the total time-frequency resources are split among them to achieve maximum system capacity.

[0078] The proposed interference cancelation approach in NOMA-based multi-numerology OTFS design can be applied to different networks such as NTN, CoMP, JRC, and localization.

[0079] The proposed approach can be extended to be used without power difference between users at the transmitter side thus channel estimation should be done in time-frequency domain instead of Delay -Doppler domain and the SIC will no longer be needed at the receiver side.

[0080] REFERENCES

[0081] [1] Z. Ding et al., “OTFS-NOMA: An efficient approach for exploiting heterogenous user mobility profiles,” IEEE Trans. Commun., vol. 67, no. 11, pp. 7950-7965, 2019.

[0082] [2] S. McWade, M. F. Flanagan, and A. Farhang, “Low-complexity equalization and detection for OTFS-NOMA,” arXiv preprint arXiv:2211.07388, 2022.

[0083] [3] Ammar Boudjelal, A., and Arslan, H., “Multi-Numerology OTFS based NOMA Approach” 2023 Turk patent.

[0084] [4] Kihero, A.B., Solaija, M.S. J. and Arslan, H., 2019. Inter-numerology interference for beyond 5G. IEEE Access, 7, pp.146512-146523.

[0085] [5] Zhang, X., Zhang, L., Xiao, P., Ma, D., Wei, J. and Xin, Y., 2018. Mixed numerologies interference analysis and inter-numerology interference cancellation for windowed OFDM systems. IEEE Transactions on Vehicular Technology, 67(8), pp.7047-7061.

[0086] [6] S. E. Zegrar and H. Arslan, “A novel cyclic prefix configuration for enhanced reliability and spectral efficiency in OTFS systems,” IEEE Wireless Commun. Lett., 2023.

[0087] [7] A. A. Zaidi et al., “Waveform and numerology to support 5G services and requirements,” IEEE Commun. Mag., vol. 54, no. 11, pp. 90-98, 2016.

[0088] [8] S. E. Zegrar and H. Arslan, “Common cp-ofdm transceiver design for low-complexity frequency domain equalization,” IEEE Wireless Commun. Lett., vol. 11, no. 7, pp. 1349- 1353, 2022.

[0089] [9] P. Raviteja, K. T. Phan, and Y. Hong, “Embedded pilot-aided channel estimation for OTFS in delay-doppler channels,” IEEE Trans. Veh. Technol., vol. 68, no. 5, pp. 4906-4917, 2019.

Claims

CLAIMS1. A computer implemented method for generating a signal for inter-numerology interference mitigation in multinum erology-OTFS based NOMA system to communicate between transmitter and multiple users having a receiver which at least two of them are wide bin users and at least one of them is narrow bin user comprising steps of designing at least two wide grid signals and at least one wide grid signal wherein spacing of the wide grid signal in delay and / or Doppler space different than narrow grid signal and the narrow grid signal is narrower than the wide grid signals in the domain, converting the wide grid signal and the narrow grid signal into the time-frequency domain in separate manner,Putting out the wide grid signals different time-frequency slots without overlapping, Detecting inter-numerology interference from the converted wide grid signals and subtracting inter-numerology interference the converted narrow grid signal, converting the narrow grid signal into the time-frequency domain,Putting out the wide bins different time-frequency slots without overlapping, Performing summation of the wide grid signal and the narrow signal that the internumerology interference is subtracted from andConverting the summed signal into the time domain.

2. A method according to Claim 1 characterized by designing multiple narrow signals.

3. A method according to Claim 1 characterized by converting the wide signals and the narrow signals into the time-frequency domain by using the inverse symplectic finite Fourier transform.

4. A method according to Claim 4 characterized by detecting inter-numerology interference by transforming the multiple wide bins signals that is put out the wide bins signals different time-frequency slots to delay-Doppler by using symplectic finite Fourier transform of multiple wide signals and setting I' = 21 + z and changing z tobe 0 or 1 for even and odd bins, respectively wherein I' is even or odd Doppler indices and I is Doppler index and z is binary scalar with 0 or 1 value.

5. A method according to Claim 1 characterized by converting the summed signal into the time domain by Heisenberg Transform.

6. A receiving method for wireless communication to communicate between transmitter and multiple users having at least a receiver which at least two of them are wide bin and at least one of them is narrow bin user comprising steps ofReceiving a signal generated according to any of preceding claims by the multiple user equipment,Converting the received signal into delay Doppler domain according to spacing of the narrow grid signal by each user,Detecting the wide grid signal from the converted signals to extract the wide signal by the users,Reconstructing the narrow grid signal according to the detected wide grid signal by at least one of the narrow bin users that already extract the wide grid signal.

7. A method according to Claim 6 characterized by further comprising steps of deleting extracted the wide grid signal from the received signal to detect further wide grid signal.

8. A method according to Claim 6 characterized by detecting the wide grid signal from the converted signal by deleting the wide grid signal from the received signal.

9. A method according to Claim 6-8 characterized by further comprising step of deleting wireless channel effects from the received signal by each user.

10. A wireless communication method for the system having a transmitter and multiple user equipment having at least a receiver which at least two of them are wide bin and at least one of them is narrow bin user comprising steps ofdesigning at least two wide grid signals and at least one wide grid signal wherein spacing of the wide grid signal in delay and / or Doppler space different than narrow grid signal and the narrow grid signal is narrower than the wide grid signals in the domain, converting the wide grid signal and the narrow grid signal into the time-frequency domain in separate manner,Putting out the wide grid signals different time-frequency slots without overlapping, Detecting inter-numerology interference from the converted wide grid signals and subtracting inter-numerology interference the converted narrow grid signal, converting the narrow grid signal into the time-frequency domain,Putting out the wide bins different time-frequency slots without overlapping,Performing summation of the wide grids and the narrow grid signal that the internumerology interference is subtracted from andConverting the summed signal into the time domain,Transmitting the summed signal and receiving the by the multiple users,Receiving a signal generated according to any of preceding claims by the multiple user equipment,Converting the received signal into delay Doppler domain according to spacing of the narrow grid signal by each user,Detecting the wide grid signal from the converted signal to extract the wide grid signal by the users,Reconstructing the narrow grid signal according to the detected wide signal by the narrow bin at least one of the users that already extract the wide signal.

11. A data processing device comprising means for carrying out the steps of the method of Claim 10.

12. A computer program comprising instructions which, when the program is executed by a data processing device, cause the data processing device to carry out the steps of the method of Claim 10.

13. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of Claim 11.

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