CN-122001724-A - Constellation aggregation frequency offset blind estimation method suitable for high-speed mobile scene

CN122001724ACN 122001724 ACN122001724 ACN 122001724ACN-122001724-A

Abstract

The application discloses a constellation aggregation frequency offset blind estimation method suitable for a high-speed moving scene, which is used for carrying out down-conversion and matched filtering on received wireless signals to obtain a baseband complex signal sequence aiming at BPSK and MSK modulation signals under a low signal-to-noise ratio and high dynamic environment, adopting direct square law conversion to eliminate phase modulation information aiming at the baseband complex signal sequence in a BPSK modulation form, adopting an I/Q quadrature decoupling framework to carry out point-to-point square operation on in-phase components and quadrature components respectively to carry out difference, eliminating symbol modulation, and then carrying out FFT spectrum analysis to estimate Doppler frequency offset. Finally, the frequency spectrum is obtained through windowed FFT conversion, and the Doppler frequency offset is estimated through peak value search. The application breaks through the limitation of the traditional pilot frequency method on the precision of the short sequence, effectively overcomes the noise amplification effect of the fourth-order spectrum method, and can still realize carrier frequency offset estimation with high precision and low complexity by utilizing the full data segment under the low signal-to-noise ratio.

Inventors

SHI JIA
Tian Chengxi
WAN JIAJUN
LI ZAN
ZHANG ZHENG
SI JIANGBO

Assignees

西安电子科技大学

Dates

Publication Date: 20260508
Application Date: 20260316

Claims (10)

1. A constellation aggregation frequency offset blind estimation method suitable for a high-speed mobile scene is characterized by comprising the following steps: S100, receiving a wireless signal containing Doppler frequency offset, and obtaining a baseband complex signal sequence with discrete time after down-conversion, analog-to-digital conversion and matched filtering pretreatment; s200, according to a signal modulation mode, nonlinear transformation based on square law is carried out on the baseband complex signal sequence so as to eliminate phase modulation information in the baseband complex signal sequence and obtain a transformed de-modulation sequence; S300, windowing and fast Fourier transforming are carried out on the transformed de-modulation sequence, so as to obtain a frequency spectrum; s400, carrying out peak detection on the frequency spectrum in a preset search bandwidth, determining a frequency index corresponding to a spectrum peak, and calculating to obtain a Doppler frequency offset estimation value.
2. The method for blind estimation of constellation aggregation frequency offset suitable for high-speed mobile scenarios according to claim 1, wherein the signal modulation modes include two modulation modes, namely BPSK and MSK.
3. The method for blind estimation of constellation aggregation frequency offset suitable for high-speed mobile scenario according to claim 2, wherein when the signal modulation mode is a BPSK modulation mode, S200 comprises: the nonlinear transformation formula corresponding to the BPSK modulation mode is utilized to carry out the baseband complex signal sequence Performing a square-law based nonlinear transformation to eliminate phase modulation information therein and convert the frequency offset component into a monophonic signal component, the nonlinear transformation being formulated as: ; Wherein, the For the input baseband complex signal sequence, Is the transformed de-modulated sequence.
4. The method for blind estimation of constellation aggregation frequency offset suitable for high-speed mobile scenario according to claim 2, wherein when the signal modulation mode is an MSK modulation mode, S200 includes: base band complex signal sequence Quadrature separation is carried out to obtain in-phase components And orthogonal component ; Respectively performing point-by-point square operation on the in-phase component I (n) and the quadrature component Q (n) to eliminate each path of symbol modulation and obtain signals of I paths and Q paths; and obtaining a cosine tone sequence by calculating the differential sequence of signals of the I path and the Q path, and determining the cosine tone sequence as a transformed de-modulation sequence.
5. The method for blind estimation of constellation aggregation frequency offset suitable for use in high-speed mobile scenarios as claimed in claim 1, wherein S300 comprises: And windowing the transformed de-modulated sequence by using the selected window function, and performing FFT (fast Fourier transform) to obtain the frequency spectrum of the transformed de-modulated sequence.
6. The method for blind estimation of constellation aggregation frequency offset for high speed mobile scenarios in accordance with claim 5, wherein the number of points of said FFT transform Not less than the length of the signal sequence If not, performing zero padding operation on the length of the signal sequence.
7. The method for blind estimation of constellation aggregation frequency offset suitable for use in high-speed mobile scenarios as claimed in claim 1, wherein S400 comprises: S410, searching the maximum value in the frequency spectrum in the preset searching bandwidth to obtain a peak index; s420, directly calculating a frequency multiplication frequency estimation value according to the peak index; s430, calculating Doppler frequency offset estimation value by using the frequency multiplication frequency estimation value.
8. The method for blind estimation of constellation aggregation frequency offset for high-speed mobile scenarios as recited in claim 7, wherein said multiplied frequency estimate is The calculation formula of (2) is expressed as: ; in the formula, For the peak value index, For the sampling rate of the system, The number of points is transformed for the FFT.
9. The method for blind estimation of constellation aggregation frequency offset suitable for high-speed mobile scenario as recited in claim 8, wherein the doppler frequency offset estimation value is The calculation formula of (2) is expressed as: ; in the formula, the coefficient 2 in the denominator is used for compensating the frequency doubling effect introduced by square law transformation.
10. A receiver system comprising a signal processing module for performing the constellation aggregation frequency offset blind estimation method for high speed mobile scenarios of any of claims 1 to 9, said signal processing module configured to be implemented in a field programmable gate array or digital signal processor.

Description

Constellation aggregation frequency offset blind estimation method suitable for high-speed mobile scene Technical Field The application belongs to the technical field of wireless digital communication and signal processing, and particularly relates to a constellation aggregation frequency offset blind estimation method suitable for a high-speed mobile scene. Background BPSK (binary phase shift keying) and MSK (minimum shift keying) have been widely used in the field of wireless digital communication (e.g., satellite communication, tactical radio, burst communication, etc.) by virtue of their excellent power efficiency, constant envelope characteristics, and strong interference resistance. However, in modern wireless communication systems, as the speed of movement of the communication platform increases (e.g., high speed orbiting of low orbit satellites, high speed maneuvering of aircraft, etc.), the relative motion between the transceiver ends can produce significant Doppler Shift (Doppler Shift). Such carrier frequency deviations, if not compensated, can result in rapid rotation of the phase of the received signal. For a communication system adopting coherent demodulation, even a small residual frequency offset can accumulate into a huge phase error in the transmission process of a data packet, so that a constellation diagram rotates and diverges, the demodulation error rate rapidly rises, and even a communication link is directly interrupted. Therefore, accurate and rapid carrier frequency offset estimation is a core premise for guaranteeing communication reliability. Currently, the frequency offset Estimation methods commonly used in engineering are mainly divided into two major categories of Estimation (Data-advanced) and Blind Estimation (blank Estimation) based on known information according to the type of information utilized, but the two major categories have significant limitations in practical application: (1) Methods based on known information (auxiliary pilot/sync word) require inserting a known pilot sequence (or sync word) in the header of the data frame, which is used by the receiver to perform correlation or FFT analysis to extract the frequency offset. The method has irreconcilable contradiction between the spectrum efficiency and the estimation precision. To ensure an efficient transmission rate of the communication data, the synchronization header or pilot sequence is typically designed to be short (e.g., only 10% -15% of the full frame). Under the low signal-to-noise ratio environment, the estimation variance is too large to meet the synchronous precision requirement of high-order modulation or long packet transmission only by means of the extremely short pilot frequency sequence, and if the pilot frequency length is simply increased to improve the precision, the transmission bandwidth of the occupied effective data is severely extruded, and the system throughput is reduced. (2) In order to overcome the problem of pilot frequency length limitation, a blind estimation method (such as a fourth-order spectral method) based on high-order statistics is adopted in the traditional blind estimation technology to attempt frequency offset extraction by using a subsequent data segment. For signals such as BPSK/QPSK, a common method is Fourth-order spectroscopy (Fourth-Power Law), i.e., a Fourth nonlinear transformation is performed on the signal to eliminate the modulation information. However, this approach has a severe noise amplification effect (Noise Amplification). When the noise-containing signal is subjected to a fourth power operation, the noise component in the signal is also amplified four times (i.e., the noise power increases exponentially). Particularly in Low signal-to-noise ratio (Low SNR) environments, the sharply enhanced noise background can completely drown out the frequency offset characteristic spectral lines of the signal, resulting in an estimated Root Mean Square Error (RMSE) that is high, or even completely ineffective. In addition, higher order operations also significantly increase the computational complexity of the hardware implementation. Disclosure of Invention In order to solve the problems in the prior art, the application provides a constellation aggregation frequency offset blind estimation method suitable for a high-speed mobile scene. The technical problems to be solved by the application are realized by the following technical scheme: A constellation aggregation frequency offset blind estimation method suitable for a high-speed mobile scene comprises the following steps: S100, receiving a wireless signal containing Doppler frequency offset, and obtaining a baseband complex signal sequence with discrete time after down-conversion, analog-to-digital conversion and matched filtering pretreatment; s200, according to a signal modulation mode, nonlinear transformation based on square law is carried out on the baseband complex signal sequence so as to eliminate phase