CN107342960B - Non-data-aided frequency offset estimation method suitable for amplitude phase shift keying - Google Patents
Non-data-aided frequency offset estimation method suitable for amplitude phase shift keying Download PDFInfo
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- CN107342960B CN107342960B CN201611075277.6A CN201611075277A CN107342960B CN 107342960 B CN107342960 B CN 107342960B CN 201611075277 A CN201611075277 A CN 201611075277A CN 107342960 B CN107342960 B CN 107342960B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/2659—Coarse or integer frequency offset determination and synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/266—Fine or fractional frequency offset determination and synchronisation
Abstract
The invention discloses a non-data-aided frequency offset estimation method suitable for APSK (amplitude phase shift keying), relates to a digital communication system receiving end processing technology, and realizes frequency offset estimation and compensation of APSK signals by a receiving end. The invention realizes the improvement of the accuracy of the frequency offset estimation and compensation of the APSK signal by the receiving end, and the method comprises the following steps: the received signal is processed by a root raised cosine filter, and the signal is processed synchronously, including timing synchronization, frequency synchronization and phase synchronization. Aiming at frequency synchronization processing, according to the frequency range of an APSK signal, M & M algorithm is used for rough frequency offset estimation, the frequency offset range is narrowed, then Fitz algorithm is selectively used for repeating n times for fine frequency offset estimation according to the precision requirement, and finally, an accurate frequency offset value is obtained. And after the synchronization processing is finished, further making judgment and constellation diagram mapping output. The invention provides an effective solution for frequency offset estimation and compensation of the APSK signal.
Description
Technical Field
The invention relates to the technical field of digital communication, in particular to a non-data auxiliary frequency offset estimation method suitable for an APSK signal at a receiver end.
Background
In a satellite mobile communication system, a local carrier of a receiving end in down-conversion is generally generated by an own oscillator and then multiplied by a received signal. However, since the accuracy of the oscillator of the receiving end is limited and the receiving end is affected by various factors in an actual system, it is impossible to completely synchronize with the carrier frequency of the transmitting end, and thus a certain frequency deviation is generated. The reason for the deviation of the actual frequency of the signal received by the receiver from the frequency of the signal transmitted by the transmitter during communication is also the relative movement between the receiver and the transmitter, i.e. the doppler effect. Therefore, the signal demodulation at the receiving end mainly solves the synchronization problem, wherein the carrier synchronization technology is one of the key technologies at the receiving end, and if the carrier frequency offset existing in the receiver is not estimated and corrected, even if the noise influence in the communication is small, a large error code rate can be caused, and sometimes even correct information cannot be obtained.
Carrier synchronization can be classified into a data-assisted synchronization method and a non-data-assisted synchronization method according to whether a training sequence is used. The data auxiliary synchronization method generally adopts the known training sequence to transmit for synchronization, and has the advantages of high precision, simple calculation, large capture range and the like, but the effective rate and the spectrum utilization rate of the system transmission data are reduced by the algorithm. The non-data-assisted synchronization method does not need extra data as a training sequence, generally utilizes the correlation of cyclic prefixes to carry out synchronization, does not reduce the effective rate of system transmission data, has higher frequency spectrum utilization rate, and is suitable for the condition that forward synchronization codes are not allowed to be sent and actual signals are directly sent. Therefore, in engineering development, a receiver receives an actual signal and performs frequency synchronization processing on the signal, and generally adopts a non-data-aided synchronization method, that is, the received signal is correspondingly processed to obtain a signal containing a carrier frequency difference, and then a frequency offset estimation algorithm is utilized.
Generally, in the process of synchronizing the APSK signal at the receiving end, if the carrier frequency offset is relatively large, when the receiving end designs carrier synchronization, it is difficult to obtain a high-precision frequency offset estimation value simply by using a frequency offset estimation algorithm. However, the characteristics of the Fitz, L & R and M & M algorithms are obtained through simulation verification and comparison, wherein the Fitz and L & R algorithms have the advantages that the frequency offset estimation precision is high, the frequency offset estimation variance approaches to CRB (Cramer-raoBound, claymello boundary) under the condition of low signal-to-noise ratio, but the approximate range of the normalized frequency offset of the L & R frequency offset estimation algorithm is just twice as large as the approximate range of the normalized frequency offset of the Fitz frequency offset estimation algorithm, so the normalized frequency offset estimation range of the Fitz frequency offset estimation algorithm is the minimum. However, these two algorithms have disadvantages: compared with the M & M algorithm, the frequency offset estimation range is small and is easily influenced by the observation data, the larger the observation data is, the smaller the estimation range is, the larger the estimation range of the M & M algorithm is, and the large frequency offset can be estimated. Therefore, attempts have been made to design a hybrid frequency offset estimation algorithm in combination with the advantages of the frequency offset algorithm.
Aiming at the defects in the prior art, the invention designs a non-data-aided hybrid frequency offset estimation algorithm so as to realize more accurate frequency offset estimation and compensation at a receiving end.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A method is presented. The technical scheme of the invention is as follows:
a non-data assisted frequency offset estimation method suitable for amplitude phase shift keying, comprising the steps of:
101. at a receiving end, receiving an APSK modulated signal, processing the APSK modulated signal through a low-pass filter, performing synchronous processing, judging according to a judgment threshold, mapping a constellation diagram, and outputting;
102. carrying out frequency offset estimation on the signal without the modulation information by using an M & M algorithm, and outputting a frequency offset value if the frequency offset value meets the precision requirement;
103. if the frequency offset value does not meet the precision requirement, repeating the frequency offset estimation for n times by using a Fitz algorithm until the frequency offset value meets the precision requirement, and performing frequency offset correction processing according to the frequency offset value obtained by the frequency offset estimation.
Further, the synchronization processing in step 101 includes the following steps:
assuming that the symbol timing is accurate, the signal output by the matched filter isWherein, ckFor a complex data signal sequence to be transmitted, v is the carrier frequency difference, θ is the unknown initial phase, n (k) is additive white Gaussian noise, the real part and imaginary part of the noise are statistically independent and have the same variance e2。
Further, the step 102 utilizes M for the signal after information demodulation&The M algorithm carries out frequency offset estimation, and the method comprises the following steps: obtaining a timing output signal ytFirst pass through M&M algorithm carries out rough estimation, namely, high time delay autocorrelation function is utilized to carry out low-computation complexity frequency offset estimation, and the frequency offset estimation formula is
Wherein
N represents the observation data length; t represents a symbol period; m represents APSK constellation points, R (M) represents the M-th sampling point, r (k) represents the k-th sampling point, r*(k-m) represents the conjugate of the k-m sample point. Based on the result of the rough estimationThe range of the frequency difference value, and the next step of selectively carrying out frequency offset fine estimation on the received signal if the frequency difference value is within the range of the frequency difference valueIf the frequency offset is less than zero, the precision of the frequency offset estimation value meets the requirement, and phase synchronization processing is carried out after frequency offset compensation;
further, in step 103, the frequency offset estimation formula of the Fitz algorithm isWherein
The invention has the following advantages and beneficial effects:
the invention provides M based on the existing algorithm&The M algorithm is effectively combined with the Fitz algorithm, since M&The M algorithm is a carrier frequency difference estimation method with a wide estimation range, the frequency estimation range is large, but only a rough estimation of the frequency can be obtained by the method. Therefore, according to M&Frequency difference estimated by M algorithmIn a range ofAnd performing frequency offset fine estimation on the APSK signal by using a Fitz algorithm, and smoothing the estimation result. By the method, the estimation range of the frequency offset of the APSK signal can be expanded, the estimation precision is improved, the problem of carrier synchronization processing of a receiving end is effectively solved, the error rate is reduced, and the communication quality is ensured.
Is the frequency deviation error estimated by the above formula, i is based on the matlab simulationAnd whether the estimated value is larger than zero or not is determined according to the standard.
Drawings
FIG. 1 is a schematic diagram of the frequency synchronization processing procedure of the APSK receiving terminal according to the preferred embodiment of the invention;
FIG. 2 is a schematic diagram of coarse frequency offset estimation processing of an APSK signal;
fig. 3 is a schematic diagram of coarse and fine frequency offset estimation of an APSK signal.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.
The technical scheme of the invention is as follows:
at a receiving end, APSK (amplitude phase shift keying) signal demodulation is sequentially processed by a low pass filter, is synchronously processed, and is mapped and output according to judgment threshold judgment and constellation diagram. The synchronization process comprises timing synchronization and carrier synchronization. And the receiving end signal demodulation mainly solves the synchronization problem.
FIG. 1 is a schematic diagram of the frequency synchronization processing step of the APSK receiving end, in which input data is processed by constellation mapping, shaping filtering, interpolator, etc. to output APSK modulated signal, the receiving end performs timing synchronization processing on the signal, and if the symbol timing is accurate, the signal output by the matched filter isWherein, ckFor the transmitted complex data signal sequence, v is the carrier frequency difference, θ is the unknown initial phase, and n (k) is additive white Gaussian noiseThe real part and the imaginary part of sound and noise are independent statistically and have the same variance e2。
FIG. 2 is a schematic diagram of coarse frequency offset estimation processing of APSK signal, timing output signal ytFirst pass through M&And performing rough estimation by using an M algorithm, namely performing low-computation-complexity frequency offset estimation by using a high-time-delay autocorrelation function. The frequency offset is estimated as
Wherein
N represents the observation data length; t represents a symbol period; m represents the number of APSK constellation points.
Let M be 32, make frequency offset rough estimation to APSK32 received signal through the above formula, according to rough estimation resultAnd (4) within the range of the frequency offset value, and selectively performing frequency offset fine estimation on the received signal. If it isAnd if the frequency deviation value is smaller than the given frequency deviation threshold value, the precision of the frequency deviation estimation value meets the requirement, and the phase synchronization processing is carried out after the frequency deviation compensation.
FIG. 3 is a schematic diagram of coarse and fine frequency offset estimation of APSK signal passing through M&And carrying out rough estimation by using an M algorithm, and reducing the frequency offset range. If the frequency offset valueIf the error range does not meet the requirement, the fine frequency offset estimation processing is carried out again until the requirement is met, and the frequency offset is outputAnd outputting the frequency offset value and performing frequency offset compensation processing.
The frequency offset estimation formula of the Fitz algorithm is
Wherein
The method provides effective combination of the M & M algorithm and the Fitz algorithm on the basis of the existing algorithm, carries out frequency offset estimation and compensation on the APSK signal, effectively solves the problem of carrier synchronization processing of a receiving end, reduces the error rate, and ensures the communication quality.
The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.
Claims (2)
1. A non-data assisted frequency offset estimation method suitable for amplitude phase shift keying, comprising the steps of:
101. at a receiving end, receiving an APSK modulated signal, processing the APSK modulated signal through a root raised cosine filter, performing synchronous processing, judging according to a judgment threshold, mapping a constellation diagram, and outputting;
102. carrying out frequency offset estimation on the signal without the modulation information by using an M & M algorithm, and outputting a frequency offset value if the frequency offset value meets the precision requirement;
103. if the frequency offset value does not meet the precision requirement, repeating the frequency offset estimation for n times by using a Fitz algorithm until the frequency offset value meets the precision requirement, and performing frequency offset correction processing according to the frequency offset value obtained by the frequency offset estimation;
step 102 utilizes M to demodulate the information-modulated signal&The step of performing frequency offset estimation by the M algorithm comprises the following steps: obtaining a timing output signal ytFirst pass through M&M algorithm carries out rough estimation, namely, high time delay autocorrelation function is utilized to carry out low computation complexityA miscellaneous frequency offset estimation formula
Wherein
N represents the observation data length; t represents a symbol period; m represents APSK constellation points, R (M) represents the M-th sampling point, r (k) represents the k-th sampling point, r*(k-m) represents the conjugate of the k-m sampling points according to the rough estimation resultThe range of the frequency difference value, and the next step of selectively carrying out frequency offset fine estimation on the received signal if the frequency difference value is within the range of the frequency difference valueThe precision of the frequency deviation estimated value meets the requirement, and phase synchronization processing is carried out after frequency deviation compensation;
step 103, the frequency offset estimation formula of the Fitz algorithm is
Wherein
2. The method of non-data assisted frequency offset estimation suitable for amplitude phase shift keying according to claim 1, wherein said step of synchronizing in step 101 comprises the steps of:
assuming the symbol timing is accurate, the output signal of the matched filter is y (t)k＝ckej(2πvkT+θ)+ n (k), wherein ckFor a complex data signal sequence to be transmitted, v is the carrier frequency difference, θ is the unknown initial phase, n (k) is additive white Gaussian noise, the real part and imaginary part of the noise are statistically independent and have the same variance e2。
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| CN110191074B (en) * | 2018-02-23 | 2021-07-02 | 中兴通讯股份有限公司 | Data demodulation method and device |
| CN109120568B (en) * | 2018-08-31 | 2020-04-03 | 北京邮电大学 | Clustering-based frequency offset determining and eliminating method and device and electronic equipment |
| CN110809247B (en) * | 2019-11-12 | 2021-04-06 | 重庆邮电大学 | OFDM frequency domain error estimation and positioning precision evaluation method for indoor Wi-Fi positioning |
| CN112838998B (en) * | 2020-12-30 | 2022-08-12 | 深圳市极致汇仪科技有限公司 | IQ imbalance estimation method and system suitable for single carrier |
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