A doppler axis zero-padding extended otfs modulation method

Abstract

The application discloses a kind of OTFS modulation methods of Doppler axis zero insertion extension.There is the pretreatment of Doppler axis zero insertion extension to transmitting end signal, and the signal in delay-Doppler domain after extension is obtained, the inverse symplectic Fourier transform is carried out to the signal in delay-Doppler domain after extension, and the time-frequency domain signal is obtained, the amplitude reduction is carried out to the time-frequency domain signal, and the restored signal is obtained, the Heisenberg transformation is carried out to the restored signal, and the time-domain signal after extension is obtained, the time-domain output signal after extension is obtained after the time-domain signal after extension passes through delay-Doppler channel, sampling and Wigner transformation are carried out to the time-domain output signal after extension, and the time-frequency domain output signal after extension is obtained, the symplectic Fourier transform is carried out to the time-frequency domain output signal after extension, and the output signal after extension in delay-Doppler domain is obtained, and this method effectively solves fractional Doppler problem.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication and relates to an OTFS modulation method with Doppler axis zero-insertion spread. Background Technology

[0002] We are currently in the 5G era and are moving towards the 6G era with the continuous development of wireless mobile communication technology. Compared to 5G, 6G will face a larger volume of services, require faster transmission speeds, and present communication demands in high-speed mobile scenarios. Wireless communication in high-speed mobile scenarios also faces new challenges, mainly due to the high latency and high Doppler characteristics of the channel, as well as its strong time-varying nature. The currently used OFDM technology, due to its high synchronization requirements, is greatly affected by frequency offset and becomes less robust in high-mobility scenarios. Based on this situation, Orthogonal Time-Frequency Space (OTFS) modulation has been proposed.

[0003] OTFS modulation introduces a new two-dimensional dimension—the delay-Doppler domain—and also generates the fractional Doppler problem, which was absent in previous generations of modulation techniques. Fractional Doppler is widespread in OTFS modulation and presents greater challenges to channel estimation, data transmission, and signal recovery compared to the integer Doppler case. Existing work has derived the relationship between Doppler interference caused by fractional Doppler and the input-output relationship, and has also compensated for the effects of fractional Doppler at the receiver using machine learning and other methods. However, these schemes rely on known fractional Doppler channel information but lack a fractional Doppler channel detection scheme, and the compensation scheme at the receiver has high computational complexity. Based on the current research status, a feasible fractional Doppler channel detection scheme is needed in OTFS modulation, and the fractional Doppler problem needs to be addressed at its root. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an OTFS modulation method with Doppler axis zero-insertion extension, which effectively solves the fractional Doppler problem.

[0005] To achieve the above objectives, the OTFS modulation method for Doppler axis zero-insertion spread described in this invention includes:

[0006] The transmitted signal undergoes Doppler axis zero-placing preprocessing to obtain an expanded delay-Doppler domain signal. An inverse Sinthysmometric transform is then performed on the expanded delay-Doppler domain signal to obtain a time-frequency domain signal. Amplitude restoration is performed on the time-frequency domain signal to obtain the restored signal. A Heisenberg transform is then performed on the restored signal to obtain an expanded time-domain signal. This expanded time-domain signal is then passed through a delay-Doppler channel to obtain an expanded time-domain output signal. The expanded time-domain output signal is then sampled and subjected to a Wigner transform to obtain an expanded time-frequency domain output signal. Finally, a Sinthysmometric transform is performed on the expanded time-frequency domain output signal to obtain an expanded delay-Doppler domain output signal, thus completing the OTFS modulation with Doppler axis zero-placing.

[0007] The extended delayed-Doppler domain signal x E [z,l] represents:

[0008]

[0009] Where p is the expansion factor and x[k,l] is the transmitted signal.

[0010] The time-frequency domain signal X E [g,m] is:

[0011]

[0012] The restored signal X′ E [g,m] is:

[0013] X′ E [g,m]=pX E [g,m].

[0014] Extended time-domain signal x E (t E )for:

[0015]

[0016] The extended time-domain output signal y(t) is:

[0017]

[0018] The extended time-frequency domain output signal Y E [g,m] is:

[0019]

[0020]

[0021] The extended output signal y of the delayed-Doppler domainE [z,l] represents:

[0022]

[0023] The present invention has the following beneficial effects:

[0024] The Doppler-axis zero-insertion spread OTFS modulation method described in this invention, in specific operation, performs preprocessing of Doppler-axis zero-insertion spread on the transmitted signal at the transmitting end, thereby expanding the symbol plane. After amplitude restoration, normal OTFS transmission and channel estimation are performed, thus expanding the Doppler channel information. At the receiving end, the fractional Doppler is detected in the form of integer Doppler in conventional OTFS modulation. At the transmitting end, the fractional Doppler is converted as much as possible, thereby reducing its impact on OTFS transmission and effectively solving the fractional Doppler problem. Attached Figure Description

[0025] Figure 1 A schematic diagram of the OTFS modulation process for Doppler axis zero-insertion extension;

[0026] Figure 2a This is a schematic diagram of the original signal from the transmitting end.

[0027] Figure 2b This is a schematic diagram of the delay-Doppler domain signal spread at the transmitting end.

[0028] Figure 3a A schematic diagram of the received Doppler axis zero-placing extended signal;

[0029] Figure 3b This is a schematic diagram of the signal after the delay-Doppler domain extension at the receiving end.

[0030] Figure 4 A schematic diagram of the transmitter delay-Doppler signal in an embedded pilot design;

[0031] Figure 5 A schematic diagram of the extended delay-Doppler signal at the receiver in an embedded pilot design.

[0032] Figure 6 A comparison chart showing the performance improvement per unit time under different scaling factors. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0034] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0035] refer to Figure 1 The OTFS modulation method with Doppler axis zero-insertion spread described in this invention includes the following steps:

[0036] 1) Establish a system model

[0037] The system model is based on the OTFS transmission model and is improved upon it. The conventional OTFS modulation process is preprocessed with Doppler axis zero-insertion expansion. After the inverse sine Fourier transform and before the Heisenberg transform, the amplitude of the obtained time-frequency domain signal is restored. The expanded signal is then subjected to the same subsequent operations as conventional OTFS modulation. Finally, a fractional Doppler detection step is added at the receiver.

[0038] The specific process is as follows:

[0039] The preprocessing procedure for Doppler axis zero-insertion extension is as follows:

[0040]

[0041] The extended delay-Doppler domain signal x is obtained. E [z,l], and then through inverse symplectic Fourier transform, the time-frequency domain signal X is obtained. E [g,m] is:

[0042]

[0043] Compared to the signal in the traditional OTFS modulation process, X E[g,m] can be represented as:

[0044]

[0045] The obtained time-frequency domain signal X E Amplitude reconstruction is performed on [g,m] to obtain the reconstructed signal X′. E [g,m] is:

[0046] X′ E [g,m]=pX E [g,m]

[0047] The restored signal X′ E After the Heisenberg transform, the extended time-domain signal x is obtained from [g,m]. E (t E )for:

[0048]

[0049] Compared to the signal in the traditional OTFS modulation process, x E (t E This can be represented as:

[0050]

[0051] The comparison reveals that the obtained time-domain signal can also be viewed as the original signal's time-domain form after zero-placing expansion in the time domain. Since the total signal duration becomes p times the original signal duration after zero-placing expansion along the Doppler axis, the signal in the delay-Doppler domain is further extended. Furthermore, based on the origin of fractional Doppler, it can be deduced that the total transmission time T of the signal... f As pNT increases, the accuracy of each unit scale division of the Doppler axis, 1 / pNT, is improved. The resulting signal, after passing through a delayed-Doppler channel, yields the extended time-domain output signal y(t):

[0052]

[0053] The extended time-domain output signal y(t) is sampled and subjected to Wigner transform to obtain the extended time-frequency domain output signal Y. E [g,m] is:

[0054]

[0055]

[0056] Finally, the extended output signal y in the delay-Doppler domain is obtained through the symplectic Fourier transform. E [z,l] represents:

[0057]

[0058] Embedded pilot-assisted channel estimation is performed on the expanded output signal in the obtained delay-Doppler domain to obtain the integer Doppler for the current situation. Because the accuracy per unit scale of the Doppler axis increases, the Doppler axis scale matched when the channel's Doppler frequency offset is mapped onto the Doppler axis of the delay-Doppler plane also increases. For example, when p=10, let the Doppler offset of a channel be F, and the Doppler parameter τ of that channel... O =F×NT represents the fractional Doppler to one decimal place. When OTFS modulation undergoes Doppler zero-insertion spread operation, the Doppler axis scale increases tenfold, and the accuracy improves accordingly. The corresponding Doppler parameter of the channel at this time is τ. E =F×10NT, the channel Doppler parameters estimated at the receiver are converted from fractional Doppler to integer Doppler. Let the estimated expanded Doppler scale be j (0<j<pN), and reduce it by the expansion factor to obtain the original fractional Doppler. Complete fractional Doppler channel estimation.

[0059] After estimating the channel fractional Doppler, the required spread factor is selected for transmission. For different spread factors, the inter-symbol interference (I) along the Doppler axis under the current fractional Doppler condition is first calculated. E (k,l), that is:

[0060]

[0061] And based on the inter-symbol interference I E (k,l), obtain the OTFS transmission performance gain G = 1 / I under the current expansion factor. E (k,l), and then combined with the total signal transmission time T under the current expansion factor. E The performance improvement per unit time is W = G / T = 1 / [I] E (k,l)·T E ].

[0062] By comparing the performance improvement per unit time under different expansion factors p, an appropriate expansion factor can be selected to suppress the generation of fractional Doppler at the transmitting end, thereby reducing the impact of fractional Doppler from the root and optimizing the entire OTFS transmission process.

[0063] Figure 1 This diagram illustrates the Doppler axis-zeroing extended OTFS modulation process. The system input signal x[k,l] undergoes a Doppler axis-zeroing extension preprocessing operation, and the amplitude of the extended signal is restored before the Heisenberg transform. The extended system output signal y is then obtained through OTFS modulation in the delay-Doppler domain. E[z,l], where x[k,l] adopts the transmitter signal designed in the embedded pilot design scheme. The randomly generated channel has an unknown fractional Doppler. It is transmitted after being extended by Doppler axis zeroing, and the original signal scale is maintained by amplitude restoration for subsequent fractional Doppler detection and estimation.

[0064] Figure 2a and Figure 2b This is a schematic diagram of the Doppler axis zero-insertion spread of the transmitter signal in this invention. The delay-Doppler domain signal is a two-dimensional signal. After selecting a certain spread factor, zero-value symbols are inserted between each original symbol in the Doppler axis direction of the transmitter. Although the zero-insertion spread is only performed on the Doppler axis, in the subsequent modulation process, the spread also occurs on the time axis in the transition signal between the time-frequency domain and the time domain.

[0065] Figure 3a and Figure 3b This diagram illustrates the extended signal in the delay-Doppler domain at the receiver. When multiple signals with different Doppler parameters exist, the inserted zero-value symbol region is filled due to the shifting of channels with different Doppler parameters caused by the superposition of multipath channels. Channel estimation can obtain the Doppler parameter information of the current multiple channels. Channels located at integer multiples of the extension scale have integer Doppler parameters, while channels located at non-integer multiples of the extension scale have fractional Doppler parameters.

[0066] Based on the pilot design scheme assisted by embedded pilot, generate Figure 4 The transmitted delayed-Doppler domain signal is obtained after OTFS modulation with Doppler axis zero-placing extension. Figure 5 The received signal after the delay-Doppler domain extension at the receiver can be used to obtain the fractional Doppler information of the channel by using an embedded pilot-assisted channel estimation scheme, thus completing the detection of the fractional Doppler channel.

[0067] Figure 6 The graph shows a comparison of performance improvements per unit time under different expansion factors. By comparing the performance per unit time, you can choose the expansion factor that is suitable for the current environment and channel.

Claims

1. A Doppler-axis zero-insertion extended OTFS modulation method, characterized in that, include: The transmitted signal is preprocessed with Doppler axis zero-placing spread to obtain a spread delayed-Doppler domain signal. The spread delayed-Doppler domain signal is then subjected to inverse Sine Fourier transform to obtain a time-frequency domain signal. The amplitude of the time-frequency domain signal is then restored to obtain a restored signal. The restored signal is then subjected to Heisenberg transform to obtain a spread time-domain signal. The spread time-domain signal is then passed through a delayed-Doppler channel to obtain a spread time-domain output signal. The spread time-domain output signal is then sampled and subjected to Wigner transform to obtain a spread output signal in the time-frequency domain. Finally, the spread output signal in the time-frequency domain is subjected to Sine Fourier transform to obtain a spread output signal in the delayed-Doppler domain, thus completing the OTFS modulation with Doppler axis zero-placing spread. The extended delayed-Doppler domain signal x E [z,l] represents: Where p is the expansion factor, and x[k,l] is the transmitted signal. The time-frequency domain signal X E [g,m] is: The restored signal X′ E [g,m] is: X′ E [g,m]=pX E [g,m] Extended time-domain signal x E (t E )for: The extended time-domain output signal y(t) is: The extended time-frequency domain output signal Y E [g,m] is: The extended output signal y of the delayed-Doppler domain E [z,l] represents:

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