A method for OFDM and OTFS resource allocation for a hybrid waveform transmission systems

Abstract

This invention proposes a novel scheduling (resource allocation) scheme for different users using different waveforms namely, orthogonal frequency division multiplexing (OFDM) and orthogonal time-frequency space OTFS modulation. The proposed allocation ensures that the OTFS signal spans the whole time-frequency resources for optimal OTFS performance, while minimum or zero interference with the OFDM signal is achieved.

Description

[0001] A METHOD FOR OFDM AND OTFS RESOURCE ALLOCATION FOR A HYBRID WAVEFORM TRANSMISSION SYSTEMS

[0002] Technical Field:

[0003] This invention relates to a method for OFDM and OTFS resource allocation for hybrid waveform transmission systems that can be used in any wireless communication device using OFDM and OTFS signaling.

[0004] State of The Art:

[0005] The emergence of the sixth generation (6G) wireless networks is being driven by new requirements and applications. These applications must not only enable robust high-speed communication but also effectively handle the escalating demands for data transmission. Within this dynamic context, the emphasis on high mobility support emerges as a pivotal facet in the evolution of wireless communication systems. The existing fifth generation (5G) networks have demonstrated their ability to sustain mobility up to 500 kilometers per hour while maintaining acceptable quality of service (QoS) [1], This capability has already paved the way for applications in high-mobility scenarios such as vehicle- to- everything (V2X), unmanned aerial vehicles (UAVs), and high-speed railways (HSRs). However, as new high mobility scenarios continue to emerge, such as hyperloop technology, the projected mobility requirement of 1000 kilometers per hour for future 6G networks takes on even greater significance [2], This heightened mobility introduces substantial challenges in the form of Doppler effects, resulting in swift doubly selective fading phenomena in high-mobility wireless communications (HMWC) [3], These effects directly impact the orthogonality of subcarriers within orthogonal frequency-division multiplexing (OFDM) systems, potentially leading to performance degradation. Consequently, addressing the formidable challenge posed by these substantial Doppler shifts and spreads becomes a central pursuit in the development of 6G networks. Despite significant efforts by organizations like the third-generation partnership project (3 GPP) to enhance the performance of 5G OFDM systems, including innovative designs like demodulation reference signals (DMRS), certain performance gaps persist. These inherent limitations of OFDM waveforms underscore the pressing need for innovative waveform designs that can effectively harness the benefits of high mobility while mitigating the adverse Doppler effects.

[0006] Addressing varying levels of user mobility necessitates the utilization of distinct waveforms such as orthogonal time-frequency space (OTFS) [4] and orthogonal frequency division multiplexing (OFDM). This choice arises from the fundamental need to accommodate differing movement speeds and ensure effective communication under diverse mobility conditions. High mobility scenarios, where users are characterized by rapid motion, demand a waveform like OTFS that can sustain clear communication quality despite such dynamic conditions. On the other hand, low mobility scenarios, involving users with slower and more gradual movement, are well-suited for the utilization of the OFDM waveform. This waveform choice optimizes resource consumption while maintaining satisfactory communication quality. By tailoring waveform selection to specific mobility characteristics, an adaptable and efficient communication framework can be established to enhance the user experience.

[0007] In multi-mobility scenarios, it is essential to strike a balance between performance and complexity, making it impractical for OTFS to completely replace OFDM. These scenarios involve a diverse user population with varying degrees of mobility, randomly distributed within the base station's coverage area. To cater to both fast-moving and slow- moving users simultaneously, the base station needs to adopt multiple waveforms. Specifically, the OTFS waveform is employed for users with high mobility, while the OFDM waveform is utilized for users with low mobility. The design and coexistence of OTFS and OFDM as multi -waveform solutions pose a crucial challenge that requires immediate attention in wireless communication.

[0008] To address the limitations of the ability of current systems the work in [5] proposed where multi-mobility scenarios are considered, and two low-complexity OTFS-OFDM coexistence schemes are designed. The Time Division Multiplexing (TDM) scheme enables the multiplexing of OTFS users and OFDM users in the time domain, while the Frequency Division Multiplexing (FDM) scheme is used to multiplex OTFS users and OFDM users in the frequency domain.

[0009] The disadvantage of the previously proposed schemes is that they assign the OTFS and OFDM users in block in the time-frequency resource grid. The lock assignment of the OTFS frame limits the time duration and the bandwidth of the frame which eventually decreases the delay and Doppler resolution leading to a poor performance.

[0010] As a result, a new method is needed that can overcome the above-mentioned disadvantages, allowing OTFS signals to be spread all over the time-frequency resource grid while maintaining zero or minimum interference with OFDM signals.

[0011] References:

[0012] [1] Yu, H., Lee, H. and Jeon, FL, 2017. What is 5G? Emerging 5G mobile services and network requirements. Sustainability, 9(10), p.1848.

[0013] [2] Chowdhury, M.Z., Shahjalal, M., Ahmed, S. and Jang, Y.M., 2020. 6G wireless communication systems: Applications, requirements, technologies, challenges, and research directions. IEEE Open Journal of the Communications Society, 1, pp.957-975.

[0014] [3] Wu, J. and Fan, P., 2016. A survey on high mobility wireless communications: Challenges, opportunities and solutions. IEEE Access, 4, pp.450-476.

[0015] [4] R. Hadani, S. Rakib, M. Tsatsanis, A. Monk, A. J. Goldsmith, A. F. Molisch, and R. Calderbank, “Orthogonal time frequency space modulation,” in IEEE Wireless Communications and Networking Conference (WCNC), 2017, pp. 1-6.

[0016] [5] Wu, Yuchen, and Zhengquan Zhang. "Co-existence Analysis of OTFS and OFDM Waveforms for Multi-mobility Scenarios." 2022 IEEE 95th Vehicular Technology Conference:(VTC2022-Spring). IEEE, 2022. Description of The Invention:

[0017] The invention in order to realize all the objectives mentioned above and which will emerge from the detailed description below; the invention presents scheduling method for users signaling with different waveforms, namely OTFS and OFDM. The proposed scheme allows OTFS signal to be spread throughout the whole time of the frame, and to occupy as large a bandwidth as possible. This provided high delay-Doppler resolution thus better performance of OTFS users. The proposed scheme spreads OTFS in a way that OFDM resources blocks can be allocated with zero or minimum interference from OTFS signals. The proposed scheme offers flexibility to multiplex various numbers of users using different signaling (OFDM and / or OTFS) in time, frequency, or jointly in time and frequency. In a communication system using OTFS and OFDM signaling, the proposed resource allocation ensures the best performance waveforms with low- complexity algorithm.

[0018] The advantages of the proposed invention are summarized as follows:

[0019] 1- In a communication system using OTFS and OFDM signaling, the proposed resource allocation ensures the best performance waveforms.

[0020] 2- The ability to schedule OFDM and OTFS in time.

[0021] 3- The ability to schedule OFDM and OTFS in frequency.

[0022] 4- The ability to schedule OFDM and OTFS in time and frequency.

[0023] 5- The technique modulates the received OTFS pilot signal in both time and frequency domains with fractional tones until the fractional shifts become integers in the delay-Doppler (DD) domain.

[0024] 6- The signal processing at the transmitter and receiver sides is quite simple, and the computational complexity of the scheduling is very low.

[0025] The structural and characteristic features and all advantages of the method subject to the invention will be understood more clearly thanks to the figures given below and the detailed explanation written by making reference to these figures, and therefore the evaluation should be made by taking these figures and detailed explanation into consideration. Description of the Figures:

[0026] The invention will be described with reference to the accompanying figures, so that the features of the invention will be more clearly understood and appreciated, but the purpose of this is not to limit the invention to these certain regulations. On the contrary, it is intended to cover all alternatives, changes and equivalences that can be included in the area of the invention defined by the accompanying claims. The details shown should be understood that they are shown only for the purpose of describing the preferred embodiments of the present invention and are presented in order to provide the most convenient and easily understandable description of both the shaping of methods and the rules and conceptual features of the invention. In these drawings;

[0027] Figure 1 Proposed OTFS and OFDM scheduling in, a) time, b) frequency, and (c) time-frequency.

[0028] The figures to help understand the present invention are numbered as indicated in the attached image and are given below along with their names.

[0029] Description of The Invention:

[0030] The disclosed method presents a novel approach to schedule (resource allocation) different users using OFDM and OTFS waveforms. The description of OFDM and OTFS mentioned here is as follows:

[0031] OFDM: (Orthogonal Frequency Division Multiplexing) is a modulation technique widely used in modern communication systems. It divides a high-rate data stream into multiple lower-rate sub streams and transmits them simultaneously in parallel over a set of orthogonal subcarriers. Each subcarrier is modulated using a narrowband signal, allowing for efficient utilization of the available bandwidth.

[0032] OTFS: (Orthogonal Time Frequency Space) is a modulation technique used in wireless communication systems to increase spectral efficiency and improve the robustness of data transmission over fading channels. It is based on the concept of mapping the data symbols into a two-dimensional grid in the time-frequency domain, allowing multiple symbols to be transmitted simultaneously and thus increasing the data rate.

[0033] The proposed allocation here ensures that the OTFS signal spans the whole timefrequency resources for optimal OTFS performance, while minimum or zero interference with the OFDM signal is achieved.

[0034] The OTFS signal design considers M x N data symbols distributed over M x N delay- Doppler (DD) bins denoted by where For a communication system to be modulated over a total bandwidth B with a frame duration of T T where the time duration of one symbol is which imposes and delay and Doppler spacing, respectively. Then, x are mapped to the time-frequency (TF) domain grid using the inverse symplectic finite Fourier transform (ISFFT) i.e.,

[0035] The values are already described before the equation. Briefly, here is the description again: where then is transformed to continuous-time signal s(t) by applying the Heisenberg Transform as expressed below. the subcarrier spacing in frequency domain. rect(.): is the rectangular pulse shape. where rect(.) is the rectangular pulse shape and A Now for an OTFS system with D data bins denoted by The proposed method employs the Kronecker product with a precoding matrix to achieve the necessary scheduling within the TF domain, integer numbers that defines the spread factors of the OTFS data in time and frequency.

[0036] ®: is the Kronecker product. and the precoding matrix can be given by is the transpose operator where refers to the h column of the Discrete Fourier Transform (DFT) matrix. Similarly, corresponds to the row of the DFT matrix. Thus, it can be written as follows: where and the DD domain signal can be written as follows denotes the modulo operator from the equation (1) and by setting the TF domain signal can be found as

[0037] After some simplification can be written as follows where the equation (8) can be written in the form of multiplication of two Kronecker delta functions as follows: denotes the Kronecker delta function have non-zero value, both and must be non zero which is true only and only if [n — thus the can be presented as follows where which means that OTFS TF grid can be controlled using the precoding matrix where a and are used to chose the spacing between the active bins in the time and frequency domains, respectively. q1and q2are to choose the starting indexes of the active bins in the time and frequency domains, respectively.

[0038] OTFS-OFDM Co-Existence Scheme:

[0039] In contrast to OTFS, where data is initially mapped to the delay-Doppler (DD) domain and then transformed to the TF domain, OFDM directly maps data to the frequency domain, where data symbols are distributed over TF grid X and M, N are the number of subcarriers and the number of OFDM symbols. Finally, it is subsequently converted into a continuous-time signal. where is the n-th OFDM symbol. a. OTFS-OFDM Time-frequency scheduling: to schedule OTFS and OFDM in time and frequency using the previous precoding matrix, data are used for OFDM, and the TF grid can be populated as follows: and XTF[n, m] can be converted directly to time using the Heisenberg Transform as in equation (2). b. OTFS-OFDM Time scheduling: to schedule OTFS and OFDM in time, the precoding matrix is used with leading to the following:

[0040] Thus, the system manages to use OTFS bins while using OFDM data and the TF grid can be presented as follows: c. OTFS-OFDM Frequency scheduling: to schedule OTFS and OFDM in frequency, the precoding matrix is used with a = 1 leading to the following:

[0041] Thus, the system manages to use — OTFS bins while using OFDM data and the TF grid can be presented as follows:

[0042] The foregoing descriptions of specific embodiments of the present technology have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present technology to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present technology and its practical software, to thereby enable others skilled in the art to best utilize the present technology and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the software or implementation without departing from the spirit or scope of the claims of the present technology.

[0043] In a case that no conflict occurs, the embodiments in the present disclosure and the features in the embodiments may be mutually combined. The foregoing descriptions are merely specific implementations of the present disclosure but are not intended to limit the protection scope of the present disclosure. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present disclosure shall fail within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.

Claims

CLAIMS1- The invention relates to a method for OFDM and OTFS resource allocation for hybrid waveform transmission systems, its feature is; i. mapping OTFS data from delay Doppler domain to the time-frequency domain in a spread manner, ii. OTFS is spread in time, frequency, or time-frequency, iii. it includes the process steps of scheduling OTFS and OFDM in time, frequency, and time-frequency.2- The method according to claim 1, characterized in that step (i) comprises of spreading the OTFS data symbols in delay-Doppler domain over M and N delay and Doppler bins, respectively, as followswhere XDD: the data symbol in delay-Doppler domain,integer numbers that defines the spread factors of the OTFS data in time and frequency, : is the Kronecker product.3- According to claim 2, wherein the spread of OTFS data symbols is characterized in that the delay-Doppler leads to spreading their time-frequency transformation into the whole time-frequency resource with spacingandin time and frequency domains, respectivelywhere n: time index, m: frequency index, XDD: the data symbol in delay-Doppler domain, X0TFS: the time-frequency representation of the n-th and m-th signalcorresponding the time-frequency representation of4- The method according to claim 3, characterized in that step (iii) comprises the step of using (MN) data forwhere n: time index, m: frequency index, XDD: the data symbol in delay-Doppler domain,X0TFS: the time-frequency representation ofthe k-th and 1-th data symbol in delay -Doppler domain, X0TFS(n, m)'. the n-th and m-th signal corresponding the timefrequency representation of XDD,OFDM to schedule OTFS and OFDM in time and frequency and obtaining the TF grid using the equation.

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