Orthogonal transformation assisted OFDM (Orthogonal Frequency Division Multiplexing) modulation and demodulation method for non-ground network system

Abstract

The invention provides a non-ground network system orthogonal transformation auxiliary OFDM (Orthogonal Frequency Division Multiplexing) modulation and demodulation method, and relates to the technical field of NTN (Network Temporary Network) communication. The method comprises the following steps: a transmitter encodes and modulates a data stream, and blocks a data symbol sequence; two-dimensional fast Fourier transform is adopted as an orthogonal transformation type, and a diffusion symbol block is obtained through orthogonal transformation and deblocked; normalizing the diffusion symbol sequence and inserting a pilot frequency, and then performing OFDM modulation and adding a cyclic prefix; the receiver performs symbol synchronization and frequency offset compensation on the received symbol sequence, and then removes the cyclic prefix and performs OFDM demodulation; extracting a pilot symbol from the demodulated data to realize channel equalization; extracting a diffusion symbol sequence; inverse two-dimensional fast Fourier transform is carried out; deblocking the data symbol blocks; and normalizing, demodulating and decoding the received data symbol sequence to obtain a received data stream. According to the invention, the bit error rate can be effectively reduced in the environment with ultralow signal-to-noise ratio, multipath depth fading and large Doppler frequency offset.

Description

Technical Field

[0001] The present invention relates to the field of non-terrestrial network (NTN) communication technology, and in particular to an orthogonal transform assisted OFDM (OTA-OFDM) modulation and demodulation method for a non-terrestrial network system, which is suitable for scenarios such as high-speed moving trains, high-speed unmanned aerial vehicles, and satellite communications. Background Art

[0002] The high-speed motion of low earth orbit (LEO) satellites causes Doppler frequency deviation, Doppler spread and multipath effects, which can lead to two-dimensional time-frequency fading in non-terrestrial network (NTN) communication systems. Although orthogonal frequency division multiplexing (OFDM) modulation provides high spectral efficiency and is relatively simple to implement, its performance in NTN scenarios is often significantly affected due to the influence of time-varying fading channels.

[0003] The Orthogonal Time-Frequency-Space (OTFS) scheme achieves the diffusion of data symbol energy by mapping data symbols into the delay-Doppler domain, and is insensitive to the fading of certain frequency domain carriers and certain time points. Therefore, it can solve the two-dimensional time-frequency fading problem, but at the cost of increasing the complexity of the transmitter and receiver. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes an orthogonal transformation-assisted OFDM modulation and demodulation method for a non-terrestrial network system. Based on orthogonal transformation, the present invention maps data symbols to a time-frequency grid, effectively spreading the data symbol energy to the entire time-frequency domain. The present invention can effectively reduce the bit error rate in an environment with ultra-low signal-to-noise ratio, multipath deep fading, and large Doppler frequency deviation, and has low complexity, does not require changes to the structure of the OFDM system, and is easy to deploy in existing systems.

[0005] The technical solution adopted by the present invention is:

[0006] An orthogonal transformation assisted OFDM modulation method for a non-terrestrial network system, applied to a transmitter, comprises the following steps:

[0007] S101: Encode and modulate a data stream to be transmitted to obtain a data symbol sequence to be transmitted; divide the data symbol sequence to be transmitted into blocks to obtain a two-dimensional data symbol block to be transformed;

[0008] S102: using a two-dimensional fast Fourier transform as an orthogonal transform type, transforming the data symbol block to be transformed into the time-frequency domain to obtain a spread symbol block; deblocking the spread symbol block to obtain a spread symbol sequence;

[0009] S103: Normalize the spread symbol sequence and insert a pilot, then perform OFDM modulation and add a cyclic prefix, and then send it.

[0010] Furthermore, in step S101, the block division method is:

[0011]

[0012] Where, M=N,m=0,1,2...,M-1,n=0,1,2...,N-1,X m,n is a two-dimensional square data symbol block with M rows and N columns, and x is a data symbol sequence.

[0013] An orthogonal transform-assisted OFDM demodulation method for a non-terrestrial network system is applied to a receiver to demodulate a signal sent by the transmitter, comprising the following steps:

[0014] S201: Perform symbol synchronization and frequency offset compensation on the received symbol sequence, then remove the cyclic prefix and perform OFDM demodulation;

[0015] S202: extracting pilot symbols from the demodulated data, performing channel estimation based on least squares discrete Fourier transform, and performing channel equalization according to the channel estimation result;

[0016] S203: extracting a spread symbol sequence from the data after channel equalization, performing serial-to-parallel conversion or block division to obtain a spread symbol block to be inversely transformed;

[0017] S204: performing an inverse two-dimensional fast Fourier transform on the inverse transformed spread symbol block to demodulate a data symbol block; deblocking the data symbol block to obtain a received data symbol sequence;

[0018] S205: Normalize, demodulate and decode the received data symbol sequence to obtain a received data stream.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The present invention is designed for non-terrestrial network multipath fading channels and large Doppler frequency offset scenarios. It can effectively improve the system's bit error rate performance in ultra-low signal-to-noise ratio and large Doppler frequency offset environments, and solves the impact of time-varying fading channels on system performance in non-terrestrial network scenarios.

[0021] 2. The present invention maps data symbols to the time-frequency grid based on orthogonal transformation, effectively spreading the data symbol energy to the entire time-frequency domain. The transmitter performs modulation by performing an orthogonal transformation on the data symbols, and then loads them into the time-frequency grid together with the pilot symbols. The receiver performs channel equalization by extracting the pilot symbols, and then performs an inverse orthogonal transformation on the equalized data to restore the original information. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0023] Figure 1 Schematic diagram of the principle of an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to explain the present invention more clearly, the present invention is further described below in conjunction with embodiments and drawings. It should be understood by those skilled in the art that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0025] An orthogonal transformation assisted OFDM modulation method for a non-terrestrial network system, applied to a transmitter, comprises the following steps:

[0026] S101: Encode and modulate a data stream to be transmitted to obtain a data symbol sequence to be transmitted; divide the data symbol sequence to be transmitted into blocks to obtain a two-dimensional data symbol block to be transformed;

[0027] S102: using a two-dimensional fast Fourier transform as an orthogonal transform type, transforming the data symbol block to be transformed into the time-frequency domain to obtain a spread symbol block; deblocking the spread symbol block to obtain a spread symbol sequence;

[0028] S103: Normalize the spread symbol sequence and insert a pilot, then perform OFDM modulation and add a cyclic prefix, and then send it.

[0029] An orthogonal transform-assisted OFDM demodulation method for a non-terrestrial network system is applied to a receiver to demodulate a signal sent by the transmitter, comprising the following steps:

[0030] S201: Perform symbol synchronization and frequency offset compensation on the received symbol sequence, then remove the cyclic prefix and perform OFDM demodulation;

[0031] S202: extracting pilot symbols from the demodulated data, performing channel estimation based on least squares discrete Fourier transform, and performing channel equalization according to the channel estimation result;

[0032] S203: extracting a spread symbol sequence from the data after channel equalization, performing serial-to-parallel conversion or block division to obtain a spread symbol block to be inversely transformed;

[0033] S204: performing an inverse two-dimensional fast Fourier transform on the inverse transformed spread symbol block to demodulate a data symbol block; deblocking the data symbol block to obtain a received data symbol sequence;

[0034] S205: Normalize, demodulate and decode the received data symbol sequence to obtain a received data stream.

[0035] Figure 1 As shown, the complete process from the transmitter to the receiver is as follows:

[0036] S1: The transmitter encodes and modulates the data stream to be transmitted to obtain a data symbol sequence to be transmitted. Since the subsequent orthogonal transform is configured as a two-dimensional fast Fourier transform, the data symbol sequence needs to be divided into blocks to obtain a two-dimensional data symbol block to be transformed. The block division scheme is as follows:

[0037]

[0038] Wherein, X is a two-dimensional square data symbol block with M rows and N columns (M=N), and x is a data symbol sequence.

[0039] S2: The transmitter uses a two-dimensional fast Fourier transform as an orthogonal transform type to transform the two-dimensional square data symbol block into the time-frequency domain, spreading the energy of the data symbol to the entire time-frequency domain, so we call the transformed symbol a spread symbol. Then, the spread symbol block is deblocked to obtain a spread symbol sequence for subsequent processing.

[0040] S3: Since the data symbol energy after orthogonal transformation does not match that before transformation, the transmitter needs to normalize the spread symbol sequence before subsequent processing. At this time, the spread symbol sequence is designated as the symbol sequence to be transmitted and a pilot is inserted, followed by OFDM modulation and a cyclic prefix.

[0041] S4: In the receiver, according to the structure of the OFDM receiver, the received symbol sequence is designed to be synchronized and frequency offset compensated. Then, the cyclic prefix is ​​removed from the synchronized and frequency offset compensated received sequence, and OFDM demodulation is performed.

[0042] S5: The receiver performs channel estimation by extracting pilot symbols, and the channel estimation adopts the least square discrete Fourier transform scheme. The receiver performs channel equalization according to the channel estimation result.

[0043] S6: The receiver extracts the spread symbol sequence from the equalized data sequence, and performs the same block division scheme as the transmitter to obtain the spread symbol block to be inversely transformed.

[0044] S7: The receiver only needs to perform the inverse transformation of the orthogonal transformation performed by the transmitter to demodulate the spread symbol, that is, the inverse two-dimensional fast Fourier transform to demodulate the data symbol block. The data symbol block is then deblocked to obtain the received data symbol sequence.

[0045] S8: After the inverse orthogonal transformation, the energy of the data symbol will have the same energy mismatch phenomenon, so the receiver also needs to normalize it. The normalized data symbol is then demodulated and decoded to obtain the received data stream.

[0046] In summary, the present invention designs a modulation and demodulation scheme based on orthogonal transformation, and is fully compatible with the OFDM system. The present invention can significantly improve the bit error rate performance in non-terrestrial network systems and solve the time-frequency two-dimensional fading problem caused by Doppler frequency deviation, Doppler spread and multipath effect caused by low-orbit satellites in non-terrestrial network communication systems.

[0047] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An orthogonal transform assisted OFDM modulation method for a non-terrestrial network system, characterized in that: Applied to the transmitter, the following steps are included: S101: Encode and modulate a data stream to be transmitted to obtain a data symbol sequence to be transmitted; divide the data symbol sequence to be transmitted into blocks to obtain a two-dimensional data symbol block to be transformed; S102: using a two-dimensional fast Fourier transform as an orthogonal transform type, transforming the data symbol block to be transformed into the time-frequency domain to obtain a spread symbol block; deblocking the spread symbol block to obtain a spread symbol sequence; S103: Normalize the spread symbol sequence and insert a pilot, then perform OFDM modulation and add a cyclic prefix, and then send it.

2. The orthogonal transform assisted OFDM modulation method for a non-terrestrial network system according to claim 1, characterized in that: In step S101, the block division method is: Where, M=N,m=0,1,2...,M-1,n=0,1,2...,N-1,X m,n is a two-dimensional square data symbol block with M rows and N columns, and x is a data symbol sequence.

3. An orthogonal transform assisted OFDM demodulation method for a non-terrestrial network system, characterized in that: Applied to a receiver, for demodulating a signal sent by the transmitter according to claim 1, comprising the following steps: S201: Perform symbol synchronization and frequency offset compensation on the received symbol sequence, then remove the cyclic prefix and perform OFDM demodulation; S202: extracting pilot symbols from the demodulated data, performing channel estimation based on least squares discrete Fourier transform, and performing channel equalization according to the channel estimation result; S203: extracting a spread symbol sequence from the data after channel equalization, performing serial-to-parallel conversion or block division to obtain a spread symbol block to be inversely transformed; S204: performing an inverse two-dimensional fast Fourier transform on the inverse transformed spread symbol block to demodulate a data symbol block; deblocking the data symbol block to obtain a received data symbol sequence; S205: Normalize, demodulate and decode the received data symbol sequence to obtain a received data stream.

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