CN110505171B - Method and device for estimating frequency offset without data assistance - Google Patents
Method and device for estimating frequency offset without data assistance Download PDFInfo
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- CN110505171B CN110505171B CN201910629543.2A CN201910629543A CN110505171B CN 110505171 B CN110505171 B CN 110505171B CN 201910629543 A CN201910629543 A CN 201910629543A CN 110505171 B CN110505171 B CN 110505171B
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- H04L2027/0026—Correction of carrier offset
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Abstract
A method for estimating frequency offset without data assistance is characterized by comprising the following steps: carrying out differential processing on a receiving symbol at the current moment and a receiving symbol at the previous moment to obtain a differential signal; performing decision processing on the differential signal to obtain a decision differential symbol and using the decision differential symbol as a local differential symbol; carrying out demodulation processing on the local differential symbol and the differential signal to obtain a demodulation signal; carrying out phase extraction on the de-modulated signal to obtain a phase caused by an instantaneous frequency offset error; and calculating instantaneous frequency offset according to the phase. A non-data auxiliary frequency deviation estimation device comprises a difference module, a judgment module, a demodulation module, a phase extraction module and a frequency deviation calculation module. Under the condition of a certain signal-to-noise ratio, all received symbols are taken as known symbols, and the effect of a data-assisted frequency offset estimation algorithm is achieved by judging the differential value of the symbols.
Description
Technical Field
The present invention relates to carrier synchronization technologies, and in particular, to a method and an apparatus for estimating frequency offset without data assistance.
Background
In digital communication systems, the demodulation scheme determines the performance of the digital modulation system. The frequency locking loop in carrier synchronization is an indispensable part in a continuous communication system, and is used for tracking and locking the changed frequency offset and then compensating the frequency offset. In order to better compensate, the invention needs to adopt a frequency offset estimation algorithm to effectively and accurately estimate the frequency offset.
Disclosure of Invention
The invention provides a method and a device for estimating frequency offset without data assistance, which take all received symbols as known symbols under the condition of a certain signal-to-noise ratio and achieve the effect of a frequency offset estimation algorithm with data assistance by judging the differential value of the symbols.
The invention utilizes the characteristics of QPSK modulation constellation to judge the symbol after difference, estimates the difference symbol and indirectly carries out data-assisted frequency offset estimation.
The following technology is specifically adopted:
a method for estimating frequency offset without data assistance is characterized by comprising the following steps:
carrying out differential processing on a receiving symbol at the current moment and a receiving symbol at the previous moment to obtain a differential signal;
performing decision processing on the differential signal to obtain a decision differential symbol and using the decision differential symbol as a local differential symbol;
carrying out demodulation processing on the local differential symbol and the differential signal to obtain a demodulation signal;
carrying out phase extraction on the de-modulated signal to obtain a phase caused by an instantaneous frequency offset error;
and calculating instantaneous frequency offset according to the phase.
Further, before the differential processing, the received symbol at the previous time is initialized.
Further, before performing the differential processing, determining a modulation mode of the received symbol:
if the modulation mode is high-order modulation, firstly carrying out QPSK constellation transformation on the received symbol, and then carrying out the differential processing;
and if the modulation mode is not high-order modulation, directly carrying out the differential processing.
Further, the modulation mode determination and constellation conversion processing may be performed before initialization:
if the modulation mode is high-order modulation, the QPSK constellation transformation is firstly carried out on the received symbol, and then the initialization is carried out;
and if the modulation mode is not high-order modulation, directly carrying out initialization.
The invention also provides a non-data auxiliary frequency deviation estimation device, which is characterized by comprising
The difference module is used for carrying out difference processing on the receiving symbol at the current moment and the receiving symbol at the previous moment to obtain a difference signal;
the judgment module is used for judging the differential signal to obtain a judgment differential symbol and using the judgment differential symbol as a local differential symbol;
the demodulation module is used for demodulating the local differential symbol and the differential signal to obtain a demodulation signal;
the phase extraction module is used for carrying out phase extraction on the de-modulated signal to obtain a phase caused by the instantaneous frequency offset error;
and the frequency offset calculation module is used for calculating instantaneous frequency offset according to the phase.
Further, the device comprises an initialization module for initializing the received symbol at the last time.
Further, still include: a judging module, configured to judge a modulation mode of the received symbol; and the conversion module is used for carrying out QPSK constellation conversion on the received symbols which are judged to be high-order modulation by the judgment module.
The invention has the beneficial effects that:
under the condition of a certain signal-to-noise ratio, the effect of a data-assisted frequency discrimination algorithm is achieved, the utilization rate of data resources is 100%, the algorithm complexity is low, and the engineering is easy;
and judging the symbol after the difference by using the characteristics of a QPSK modulation constellation, estimating the difference symbol, and indirectly performing data-assisted frequency offset estimation.
Drawings
Fig. 1 is a frame format diagram of continuous communication.
Fig. 2 is a flowchart of an embodiment of a method for non-data aided frequency offset estimation according to the present invention.
FIG. 3 is a second order proportional-integral frequency locked loop model.
Fig. 4 is a frequency offset tracking curve diagram of a frequency-locked loop using the frequency offset estimation method of the present invention under the condition that Eb/N0 is 12 dB.
Fig. 5 is a block diagram of an embodiment of a non-data aided frequency offset estimation apparatus according to the present invention.
Fig. 6 is a block diagram of a preferred embodiment of the apparatus for frequency offset estimation without data assistance in accordance with the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments.
Let the instantaneous frequency offset at time k be Δ fkAnd the received signal is z (k), k is more than or equal to 0, and by using the characteristics of a QPSK modulation constellation, the unknown symbols have only 4 results after the difference is carried out:
or
Where n' is noise.
And judging the symbol after the difference, and estimating the difference symbol, namely extracting auxiliary information from the received symbol.
As shown in fig. 1, is a frame format diagram for continuous communication.
As shown in fig. 2, a method flow of an embodiment of the present invention is as follows:
specific examples of the process of the invention are as follows:
first, if the modulation mode is high-order modulation, such as 8PSK, 16APSK, etc., the received symbol needs to be QPSK constellation-transformed:
z′(k)＝|z(k)|Q·ej·(Q·∠z(k)+β)
wherein | z (k) is the mode length of z (k), and ═ z (k) is the phase of z (k).
If the modulation mode is not the high-order modulation, the next step is directly carried out.
And secondly, initializing the receiving symbol of the last moment.
z'(-1)＝0。
Thirdly, carrying out difference operation on the received symbol at the moment and the received symbol at the previous moment to obtain a difference signal:
diff(k)＝z'(k)·[z'(k-1)]*。
and fourthly, judging the received differential symbol obtained in the third step as a local differential symbol:
and fifthly, demodulating the local differential symbol obtained by the fourth step on the received differential symbol obtained by the third step to obtain a demodulated signal:
dem(k)＝diff(k)·dec*(k)。
and sixthly, carrying out phase extraction on the unmodulated differential symbol obtained by the processing of the fifth step. The phase is the phase caused by the instantaneous frequency offset error:
Δθ＝Im{dem(k)}。
step seven, calculating instantaneous frequency offset:
fig. 3 shows a second-order proportional-integral frequency-locked loop model. Under the condition that Eb/N0 is 12dB, after the estimation is completed by the method of this embodiment, the frequency offset tracking curve of the frequency locked loop shown in fig. 4 is obtained.
As shown in fig. 5, the present invention provides an embodiment of a frequency offset estimation apparatus without data assistance.
Let the instantaneous frequency offset at time k be Δ fk，k≥0。
The device comprises:
the difference module is used for carrying out difference processing on the receiving symbol at the current moment and the receiving symbol at the previous moment to obtain a difference signal; the difference processing is performed by using the formula diff (k) z '(k) · [ z' (k-1)]*；
The judgment module is used for judging the differential signal to obtain a judgment differential symbol and using the judgment differential symbol as a local differential symbol; the decision processing adopts a formula
A de-modulation module for de-modulating the local differenceCarrying out demodulation processing on the sub-symbols and the differential signal to obtain a demodulation signal; the demodulation process adopts the formula dem (k) diff (k) dec*(k)；
The phase extraction module is used for carrying out phase extraction on the de-modulated signal to obtain a phase caused by the instantaneous frequency offset error; extracting the phase by adopting a formula delta theta ═ Im { dem (k) };
and the frequency offset calculation module is used for calculating instantaneous frequency offset according to the phase. Calculating the instantaneous frequency offset by adopting a formula
As shown in fig. 6, a preferred implementation of the embodiment of the non-data aided frequency offset estimation apparatus shown in fig. 5 further includes, on the basis of the embodiment:
a judging module, configured to judge a modulation mode of the received symbol;
and the conversion module is used for carrying out QPSK constellation conversion on the received symbols which are judged to be high-order modulation by the judgment module.
The constellation transformation adopts the formula z' (k) ═ z (k) & gtnon ventilatedQ·ej·(Q·∠z(k)+β)Wherein | z (k) is the module length of z (k), ═ z (k) is the phase of z (k), and z (k) is the received symbol.
And the initialization module is used for initializing the received symbol at the last moment, wherein z' (-1) ═ 0.
Under the condition that Eb/N0 is 12dB, the apparatus of this embodiment can implement frequency offset tracking estimation for the second-order proportional-integral frequency-locked loop shown in fig. 3, and obtain a frequency offset tracking curve graph of the frequency-locked loop shown in fig. 4. As can be seen from the figure, the loop has a remarkable tracking effect after convergence in the process of continuous change of the frequency offset.
Claims (6)
1. A method for estimating frequency offset without data assistance is characterized by comprising the following steps:
and (3) judging the modulation mode of a received symbol by taking the current moment as the moment k, wherein k is more than or equal to 0, and the received symbol at the moment k is z (k):
if the modulation mode is high-order modulation, firstly performing QPSK constellation transformation on the received symbol, and then performing difference processing on the received symbol at the current time and the received symbol at the previous time to obtain a difference signal, where the constellation transformation adopts a formula z' (k) ═ z (k) & gtQ·ej·(Q·∠z(k)+β)Wherein | z (k) | is a mode length of z (k), | z (k) is a phase of z (k), and z ' (k) is a received symbol after constellation transformation, and the difference processing adopts a formula diff (k) ═ z ' (k) · [ z ' (k-1)]*；
If the modulation mode is not high-order modulation, directly carrying out differential processing on a receiving symbol at the current moment and a receiving symbol at the previous moment to obtain a differential signal, wherein at the moment, z' (k) in the differential processing formula is equal to a receiving symbol z (k);
performing decision processing on the differential signal to obtain a decision differential symbol and using the decision differential symbol as a local differential symbol;
carrying out demodulation processing on the local differential symbol and the differential signal to obtain a demodulation signal;
carrying out phase extraction on the de-modulated signal to obtain a phase caused by an instantaneous frequency offset error;
and calculating instantaneous frequency offset according to the phase.
2. The method of claim 1, wherein: before the difference processing, initializing the received symbol of the last time.
3. The method of claim 2, wherein: before the initialization, judging the modulation mode of the received symbol:
if the modulation mode is high-order modulation, the QPSK constellation transformation is firstly carried out on the received symbol, and then the initialization is carried out;
and if the modulation mode is not high-order modulation, directly carrying out initialization.
4. The method of any of claims 1-3, wherein:
let the instantaneous frequency offset at time k be Δ fk；
The decision processing adopts a formula
The demodulation process adopts the formula dem (k) diff (k) dec*(k)；
Extracting the phase by adopting a formula delta theta ═ Im { dem (k) };
calculating the instantaneous frequency offset by adopting a formula
5. A data-less assisted frequency offset estimation apparatus, comprising:
the device comprises a judging module, a receiving module and a transmitting module, wherein the judging module is used for judging a modulation mode of a received symbol, and if the modulation mode is high-order modulation, QPSK constellation transformation is firstly carried out on the received symbol;
a conversion module, configured to perform QPSK constellation conversion on the received symbol determined as the high-order modulation by the determination module, where the constellation conversion adopts a formula z' (k) ═ z (k) & gtQ·ej·(Q·∠z(k)+β)Wherein, time k is the current time, k is more than or equal to 0, z (k) is the received symbol at time k, | z (k) is the module length of z (k), less z (k) is the phase of z (k), and z' (k) is the received symbol after the constellation transformation at time k;
a difference module for performing difference processing on the received symbol at the current time and the received symbol at the previous time to obtain a difference signal, wherein the difference processing adopts a formula diff (k) z '(k) · [ z' (k-1)]*If the modulation mode is not high-order modulation, then z' (k) in the differential processing formula is equal to the received symbol z (k);
the judgment module is used for judging the differential signal to obtain a judgment differential symbol and using the judgment differential symbol as a local differential symbol;
the demodulation module is used for demodulating the local differential symbol and the differential signal to obtain a demodulation signal;
the phase extraction module is used for carrying out phase extraction on the de-modulated signal to obtain a phase caused by the instantaneous frequency offset error;
and the frequency offset calculation module is used for calculating instantaneous frequency offset according to the phase.
6. The apparatus of claim 5, further comprising means for estimating frequency offset without data assistance
And the initialization module is used for initializing the receiving symbol at the last moment.
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