Windowing for OTFS-based communication systems under fractional delay-doppler and adjacent channel interference

Abstract

Disclosed is a windowing method for OTFS-based wireless signals to mitigate interference due to fractional delay and Doppler cases and to control out-of-band emission. The method provides for suitable windowing mechanisms for the multicarrier orthogonal time frequency space (OTFS) scheme in order to manage out-of-band emission and interference due to the limited time and frequency resolution of the OTFS frame.

Claims

1. A method for preparing a windowing of a multicarrier orthogonal time frequency (OTFS) signal, the method comprising: applying an N-point inverse Fast Fourier Transform (IFFT) and an Inverse Symplectic Fast Fourier Transform (ISFFT) over rows and columns of data; converting the IFFT and ISFFT as data symbols to a time-frequency domain; utilizing a cyclic prefix (CP) extension and a cyclic suffix (CS) extension in order to perform an OTFS transmission; performing an Heisenberg Transform by using the ISFFT over the time-frequency domain data symbols such that the OTFS signal undergoes a time-varying wireless channel; performing a Wigner transform at a receiver side in order to recover a time frequency representation of a received signal; controlling an interference due to fractional delay-Doppler and removing the CP and the CS at a receiver; performing a Symplectic Fast Fourier transform operation in order to produce the received signal in a delay-Doppler domain; and mapping the received signal into the data information.

2. The method of claim 1, wherein the rows and columns of data have N number of symbols and M number of subcarriers with a T symbol duration and fa subcarrier spacing.

3. The method of claim 1, wherein the OTFS signal is for use in a 5G system.

Description

EXPLANATION OF FIGURES

(1) FIG. 1: Block diagram of the windowing-based OTFS system with fractional delay-Doppler in doubly dispersive channel.

(2) A: Time-frequency domain B: Delay-Doppler domain 201: ISFFT 202: Transmitter Windowing 203: Heisenberg transform 204: Wireless channel 205: Wigner transform 206: Receiver Windowing 207: SFFT x[k,l]: k,l-th element of X s[n,m]: transmitted signal in time-frequency domain w.sub.t[n,m]: transmitter windowing x(t): transmitted signal in time domain y(t): received signal in time domain r[n,m]: received signal in time-frequency domain w.sub.r[n,m]: receiver windowing y[k,l]: received signal in delay-Doppler domain

DETAILED DESCRIPTION OF THE INVENTION

(3) As mentioned above, the invention relates to a method for designing windowing mechanisms for the multicarrier orthogonal time frequency (OFTS) scheme to manage out of band emission and interference due to limited time and frequency resolution of the OTFS frame, said method comprises the steps of; i. Applying N-point inverse Fast Fourier Transform (IFFT) and M-point FFT operation known as Inverse Symplectic Fast Fourier Transform (ISFFT) over the rows and columns of X, respectively, ii. Applying windowing by converting the data symbols to the time-frequency domain iii. Performing the OTFS transmission by utilizing cyclic prefix (CP) and cyclic suffix (CS) iv. Performing Heisenberg Transform by using M-point IFFT over time-frequency data symbols after which the time domain OTFS signal undergoes the time-varying wireless channel v. Performing Wigner transform at the receiver side to recover the time-frequency representation of the received signal vi. Performing windowing at the receiver to control the interference due to fractional delay-Doppler and removing CP-CS vii. Performing SFFT operation to get the received signal in the delay-Doppler domain viii. Mapping the received symbols in delay-Doppler domain to data information after the equalization process

(4) In the method of the invention, the system frame consists of N number of symbols and M number of subcarriers with T symbol duration and fa subcarrier spacing (SCS), respectively.

(5) Therefore, the OTFS frame occupies a total bandwidth of B=Mf.sub.s with a frame duration of T.sub.f=TN. The data in delay-Doppler domain is given by x[k,l] with k and 1 index representing Doppler and delay, respectively.

(6) Herein the k,l-th element of X is x[k,l].

(7) In the method of the invention the windowing step is carried out to control the interference due to fractional delay-Doppler impact, and to manage the adjacent channel leakage between neighboring users.

(8) Also, in the method of the invention, windowing is performed over the time-frequency domain with utilization of CP and CS only. The process of windowing at transmitter (iii) and receiver (vi) is a dependent process. Overall, this is not a fixed process but it is an algorithm that is continuously modifiable with respect to the characteristics of time-warying channel

(9) For step (iv) of the method of the invention, it is worth mentioning that the length of CP is L length in order to mitigate the inter-symbol interference between the OTFS signals, where L represents the number of channel paths.

(10) The received symbols in delay-Doppler domain are affected by the corresponding wireless channel, and thus, the equalization process is utilized in step (viii) to free the received signal from the impact of the wireless channel. The classical technique that can be used to perform equalization process is minimum mean square error (MMSE) technique. Moreover, all the other equalization techniques for OTFS transmission can be considered for use within this process.

EXAMPLES

Example 1: Application of the Method According to Present Invention

(11) In this work, a system model with single antennas at transmitter (Tx) and receiver (Rx), where FIG. 1 as shown the block diagram of OTFS systems in FIG. 1 is considered. The system frame consists of N number of symbols and M number of subcarriers with T symbol duration and fa subcarrier spacing (SCS), respectively. Therefore, the OTFS frame occupies a total bandwidth of B=Mf with a frame duration of T.sub.f=TN. The data in delay-Doppler domain is given by x[k,l] with k and l index representing Doppler and delay, respectively. Accordingly, we apply N-point inverse Fast Fourier Transform (IFFT) and M-point FFT operation known as Inverse Symplectic Fast Fourier Transform (ISFFT) over the rows and columns of X, respectively. Note that k,l-th element of X is x[k,l]. B. After we apply ISFFT, we convert the data symbols to the time-frequency domain, where we can apply the windowing in order to control the interference due to fractional delay-Doppler impact, and manage the adjacent channel leakage between neighboring users. We utilize cyclic prefix (CP) and suffix (CS) extensions to perform the windowing process in OTFS-based transmission, as shown in FIG. 1. C. To generate the time domain OTFS signal, we perform Heisenberg Transform by using M-point IFFT over time-frequency data symbols. It is worth mentioning that the length of CP is L length in order to mitigate the inter-symbol interference between the OTFS signals, where L represents the number of channel paths. After the transmission, the time OTFS signal undergoes the time-varying wireless channel.

(12) At the receiver side, we perform the Wigner transform to recover the time-frequency representation of the received signal. Following that, we perform windowing at the receiver in order to control the interference due to fractional delay-Doppler, and CP-CS is removed, as shown in FIG. 1.

(13) Following that, we perform SFFT operation to get the received signal in the delay-Doppler domain. After the equalization process, we map the received symbols to data information

INDUSTRIAL APPLICABILITY OF THE INVENTION

(14) The invention is applicable to industrialization, and it represents an algorithm that can be applied to any signal performing transmission in delay-Doppler domain.

(15) OTFS with intelligent windowing design according to present invention can be viewed as a potential enabler technology for 5G and beyond in the communications realm and the corresponding new needs and applications of New Radio Lite (NR-Lite), massive Machine Type Communications (mMTC), Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communications (URLLC) and secure URLLC (SURLLC).

(16) Around these basic concepts, it is possible to develop several embodiments regarding the subject matter of the invention; therefore the invention cannot be limited to the examples disclosed herein, and the invention is essentially as defined in the claims. Separate embodiments of the invention can be combined where appropriate.

(17) It is obvious that a person skilled in the art can convey the novelty of the invention using similar embodiments and/or that such embodiments can be applied to other fields similar to those used in the related art. Therefore it is also obvious that these kinds of embodiments are void of the novelty criteria and the criteria of exceeding the known state of the art.