CN110611629B - Method and device for estimating frequency deviation and communication equipment - Google Patents
Method and device for estimating frequency deviation and communication equipment Download PDFInfo
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Abstract
The invention provides a method, a device and communication equipment for estimating frequency deviation, wherein the method comprises the following steps: acquiring at least 3 sections of receiving sampling data corresponding to a known channel estimation sequence; acquiring a phase elimination sequence corresponding to each section of received sampling data according to each section of received sampling data and a channel estimation sequence corresponding to each section of received sampling data; carrying out differential calculation on any two sections of phase elimination sequences to obtain a differential result corresponding to the two sections of phase elimination sequences, and obtaining a differential distance of the differential result according to a time interval between the two sections of phase elimination sequences; adding the difference results of all the same difference distances to obtain the accumulated difference item of each difference distance; carrying out weighted summation on the accumulated differential terms of all different differential distances to obtain a mixed differential term; and estimating the frequency deviation between the data sending party and the data receiving party according to the mixed differential term. The invention can improve the estimation accuracy of the frequency deviation under the condition of acquiring the same received data.
Description
Technical Field
The present invention relates to the field of mobile communications technologies, and in particular, to a method and an apparatus for estimating a frequency offset, and a communication device.
Background
In mobile communication, a transmitter modulates information to be transmitted onto a carrier wave, and transmits the information to a receiver through the carrier wave. The receiver must regenerate this carrier in order to accurately demodulate the information from the transmitter. Although nominally this carrier is known a priori by the sender and receiver, there is a frequency offset (frequency offset for short) between the carrier used by the sender and the carrier received by the receiver for the following reasons: 1) the clock accuracy of the User Equipment (UE) is not high; 2) doppler shift due to the motion of the UE itself. The frequency offset affects the baseband signal processing, and when the frequency offset is large, the signal has phase aliasing, which may result in that the data content cannot be correctly distinguished.
In modern mobile communication, user equipment often adopts an AFC (Automatic Frequency Control) technology to track Frequency in real time and correct Frequency offset, so that a transmitter and a receiver can keep Frequency synchronization with certain precision in different working scenes. Both frequency tracking and frequency offset correction require accurate and fast frequency offset estimation.
For example, in a TD-SCDMA wireless communication system, the frequency offset of the ue needs to be lower than a certain level, for example, 0.1ppm (i.e., 200Hz), in order to demodulate the received data correctly. In a time slot of a TD-SCDMA wireless communication system, a transmitter transmits two Data blocks (Data1 and Data2), each containing 22 Data symbols, and a training code sequence, located between the two Data blocks, containing 144 chips. In practical applications, the midamble sequence is typically used for channel estimation, and is also used to estimate the frequency offset between the transmitter and receiver.
The frequency offset estimation may be performed using a training code sequence by: for example, training code sequences M1-M4 of 4 slots are received consecutively. And performing channel estimation according to the received training code sequence M1 to obtain a channel estimation result H1. The channel estimation result H1 is convolved with the known midamble sequence M0, resulting in a reconstructed midamble sequence RM1 corresponding to M1. The received training code sequence M1 is multiplied by the conjugate of the reconstructed training code sequence RM1 to obtain the training code sequence CM with the cancellation phase corresponding to M11. Repeating the above process to obtain training code sequences CM with cancellation phases corresponding to M2, M3, and M42、CM3、CM4。
The difference result of the two sets of phase-cancelled midamble sequences at 1 slot distance is calculated according to the following formula:
wherein R issingle(n) midamble sequence CM for nth set of cancellation phasesnTraining code sequence CM with n +1 th group cancellation phasen+1Difference result of (2), CMn(i) Data for the ith position in the training code sequence for the nth set of cancellation phases, CMn(i)*Is CMn(i) Conjugation of (C) to (C)n+1(i) The data at the ith position in the midamble sequence of the phase is cancelled for the (n + 1) th group.
Respectively calculating the difference result of the midamble sequences of the 1 st group and the 2 nd group elimination phases, the difference result of the midamble sequences of the 2 nd group and the 3 rd group elimination phases and the difference result of the midamble sequences of the 3 rd group and the 4 th group elimination phases according to the formula, and accumulating the three results to obtain an accumulated difference term RaccuThen, estimating the frequency offset according to the following formula:
where t represents the time difference of 1 slot, and angle () represents the radian of the complex number in parentheses.
Because the time difference of 1 time slot interval is small, the phase difference caused by the frequency offset is not obvious, and the precision of the frequency offset estimation result is not high.
Similar methods are also commonly applied to frequency offset estimation in current LTE systems. The LTE system uses a reference signal (reference signal) for channel estimation, which is a sequence known by a data transmitting side and a data receiving side, placed on a fixed time-frequency resource per subframe. And calculating the accumulated difference term of 1 subframe by receiving the reference signal of each subframe, and estimating the frequency offset. Because the time difference of 1 subframe is small, there is still room for further improvement in the accuracy of the frequency offset estimation result.
Disclosure of Invention
The invention aims to provide a method and a device for estimating frequency deviation and communication equipment, which can improve the estimation accuracy of the frequency deviation under the condition of acquiring the same received data.
The technical scheme provided by the invention is as follows:
a method of estimating a frequency offset, comprising: acquiring at least 3 sections of received sampling data corresponding to a known channel estimation sequence; acquiring a phase elimination sequence corresponding to the received sampling data according to each section of the received sampling data and a channel estimation sequence corresponding to the received sampling data; carrying out differential calculation on any two sections of phase elimination sequences to obtain differential results corresponding to the two sections of phase elimination sequences, and obtaining the differential distance of the differential results according to the time interval between the two sections of phase elimination sequences; adding the difference results of all the same difference distances to obtain the accumulated difference item of each difference distance; carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term; and estimating the frequency deviation between the data sending party and the data receiving party according to the mixed differential item.
Further, the obtaining a phase removal sequence corresponding to each segment of the received sample data according to each segment of the received sample data and a channel estimation sequence corresponding to the received sample data specifically includes: performing channel estimation according to each section of received sampling data to obtain a channel estimation result; performing convolution operation on the channel estimation result and a channel estimation sequence corresponding to the received sampling data to obtain a reconstruction sequence corresponding to the received sampling data; and acquiring a phase elimination sequence corresponding to the received sampling data by multiplying the received sampling data and the conjugate of the reconstruction sequence corresponding to the received sampling data.
Further, the calculating step of performing difference calculation on the two phase elimination sequences to obtain a difference result corresponding to the two phase elimination sequences is as follows: obtaining a product of data for a position in a segment of a phase-canceling sequence and data for the position in another segment of the phase-canceling sequence by multiplying a conjugate of the data for the position in the segment of the phase-canceling sequence with the data for the same position in the other segment of the phase-canceling sequence; and obtaining a difference result corresponding to the two phase elimination sequences by adding products of data of all positions in the phase elimination sequence and the phase elimination sequence.
Further, the weighting and summing the accumulated difference terms of all the different difference distances to obtain a mixed difference term includes: and summing the accumulated difference terms of all different difference distances to obtain a mixed difference term.
Further, the weighting and summing are carried out on the accumulated difference terms of all the different difference distances to obtain a mixed difference term, and the method further comprises the following steps: multiplying the accumulated difference item of the difference distance by the difference distance to obtain a weighted difference item of the difference distance; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
Further, the estimating a frequency offset between a data transmitting side and a data receiving side according to the mixed differential term includes: the average time-domain differential distance is calculated,
the calculation formula of the average time domain difference distance is as follows:
wherein the content of the first and second substances,
taking the average time domain differential distance, k is the differential distance, b (k) is the number of differential results corresponding to the differential distance k, and w (k) is the weight of the accumulated differential term of the differential distance k;
estimating the frequency deviation between a data sending party and a data receiving party according to the mixed differential term and the average time domain differential distance; the calculation formula of the frequency deviation is as follows:
wherein, Δ f is the frequency deviation, R is the mixed differential term, angle () represents the radian of the complex number in the bracket, the value range is (-pi, pi), t is the time interval corresponding to the unit differential distance.
The present invention also provides an apparatus for estimating a frequency offset, comprising: an obtaining module, configured to obtain at least 3 segments of received sample data corresponding to a known channel estimation sequence; the phase elimination module is used for acquiring a phase elimination sequence corresponding to the received sampling data according to each section of received sampling data and a channel estimation sequence corresponding to the received sampling data; the differential calculation module is used for carrying out differential calculation on any two sections of phase elimination sequences, obtaining a differential result corresponding to the two sections of phase elimination sequences and obtaining a differential distance of the differential result according to a time interval between the two sections of phase elimination sequences; and, obtaining the cumulative difference term of each differential distance by adding the difference results of all the same differential distances; carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term; and the frequency offset estimation module is used for estimating the frequency offset between the data sender and the data receiver according to the mixed differential item.
Further, the difference calculation module includes: a difference result calculation unit, configured to calculate a difference result between each two phase cancellation sequences, including: obtaining a product of data for a position in a segment of a phase-canceling sequence and data for the position in another segment of the phase-canceling sequence by multiplying a conjugate of the data for the position in the segment of the phase-canceling sequence with the data for the same position in the other segment of the phase-canceling sequence; the difference result is obtained by adding products of data of all positions in the phase removal sequence and the phase removal sequence.
Further, the difference calculation module further includes: the mixed difference calculating unit is used for summing the accumulated difference terms of all different difference distances to obtain a mixed difference term; or the like, or, alternatively,
the system comprises a differential distance calculating unit, a calculating unit and a calculating unit, wherein the differential distance calculating unit is used for calculating the difference of the differential distance between the two adjacent channels; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
The invention also provides a communication device comprising the frequency deviation estimation device of any one of the preceding claims.
Compared with the prior art, the frequency deviation estimation method, the frequency deviation estimation device and the communication equipment provided by the invention can bring at least one beneficial effect:
1. according to the invention, under the condition of obtaining the same receiving data, the mixed difference term is introduced, and the accumulated difference term with larger difference distance is considered, so that the calculated phase difference is more obvious, and the estimation accuracy of the frequency deviation is improved.
2. The invention can make the absolute error of the frequency deviation estimated value relative to the true value minimum by setting the weight of the accumulated difference item of each difference distance as 1.
3. The invention can make the relative error of the frequency deviation estimated value relative to the true value minimum by setting the weight of the accumulated difference item of each difference distance as the corresponding difference distance.
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The above features, technical features, advantages and implementations of a method, apparatus and communication device for estimating a frequency offset will be further described in the following detailed description of preferred embodiments with reference to the accompanying drawings.
FIG. 1 is a flow chart of one embodiment of a method of estimating a frequency offset of the present invention;
FIG. 2 is a flow chart of another embodiment of a method of estimating a frequency offset of the present invention;
FIG. 3 is a flow chart of another embodiment of a method of estimating a frequency offset of the present invention;
FIG. 4 is a schematic diagram of an embodiment of an apparatus for estimating a frequency offset according to the present invention;
FIG. 5 is a schematic block diagram of one embodiment of a communications device of the present invention;
fig. 6 is a graph of f (w) at K10 in fig. 3;
FIG. 7 is a graph comparing the performance curves of the algorithm of FIG. 3 with the prior art at various maximum differential distances.
The reference numbers illustrate:
10. the communication device comprises a communication device 100, a frequency deviation estimation device 110, an acquisition module 120, a difference calculation module 121, a difference result calculation unit 122, a mixed difference calculation unit 130, a frequency deviation estimation module 140 and a phase elimination module.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will be made with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, without inventive effort, other drawings and embodiments can be derived from them.
For the sake of simplicity, the drawings only schematically show the parts relevant to the present invention, and they do not represent the actual structure as a product. In addition, in order to make the drawings concise and understandable, components having the same structure or function in some of the drawings are only schematically illustrated or only labeled. In this document, "one" means not only "only one" but also a case of "more than one".
In an embodiment of the present invention, as shown in fig. 1, a method for estimating a frequency offset includes:
step S100 acquires at least 3 pieces of reception sample data corresponding to a known channel estimation sequence.
Step S200 obtains a phase removal sequence corresponding to each segment of received sample data according to the received sample data and a channel estimation sequence corresponding to the received sample data.
Step S300, difference calculation is carried out on any two sections of phase elimination sequences, a difference result corresponding to the two sections of phase elimination sequences is obtained, and a difference distance of the difference result is obtained according to a time interval between the two sections of phase elimination sequences.
Step S400 obtains a cumulative difference term for each differential distance by adding the difference results for all the same differential distances.
Step S500 performs weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term.
Step S600 estimates a frequency offset between the data transmitting side and the data receiving side according to the mixed differential term.
Specifically, the received sample data is sample data obtained by receiving a channel estimation sequence transmitted by a transmission side in order to ensure correct reception of transmission data. The channel estimation sequence is known in advance by the sender and the receiver, such as a training code sequence placed in the middle of each time slot in a TD-SCDMA system, and a reference signal placed on a fixed time-frequency resource of each subframe in an LTE system. The channel estimation sequence may be repeatedly transmitted at a fixed time interval, or may be transmitted at a regular change at a fixed time interval (the change rule is known in advance by the transmitting side and the receiving side), depending on the requirements of the corresponding wireless communication system.
The received sample data may be data in the time domain or data in the frequency domain, and may be selected according to the processing convenience of the wireless communication system. For example, the TD-SCDMA system is more convenient for time domain processing, so the data in the time domain is used for receiving the sampling data, the corresponding channel estimation sequence and phase cancellation series also use the data in the time domain, the differential calculation is performed on the phase cancellation series in the time domain, and the frequency deviation is estimated according to the differential calculation result. The LTE system or the NB-IOT system is convenient for frequency domain processing, so that data on a frequency domain is adopted for receiving sampling data, data on the frequency domain is adopted for a corresponding channel estimation sequence and a corresponding phase elimination series, differential calculation is carried out on the phase elimination series on the frequency domain, and frequency deviation is estimated according to a differential calculation result. The sampling is usually performed in the time domain, and the received sample data in the time domain can be converted into the required received sample data in the frequency domain by FFT.
Assuming that the length of each segment of received sample data is N, obtaining and storing M segments (M > ═ 3) of received sample data, and obtaining M × N sampling points for frequency offset estimation. Preferably, M consecutive pieces of received sample data received at the latest time are stored.
Firstly, the M sections of received sampling data are subjected to phase elimination processing, and corresponding M sections of phase elimination sequences are obtained and stored. Taking the phase removal processing for one segment of the received sample data as an example, the processing procedure is as follows (the processing for the received sample data of the other segments is similar):
taking time domain processing as an example, for example, in TD-SCDMA system, the received sampled data is data in time domain. And acquiring a channel estimation sequence on a known time domain corresponding to the received sampling data. And performing channel estimation according to the received sampling data to obtain a channel estimation result. And carrying out convolution operation on the channel estimation result and the channel estimation sequence to obtain a reconstruction sequence corresponding to the received sampling data. And multiplying the conjugate of the received sample data and the reconstruction sequence to obtain a phase elimination sequence on a time domain corresponding to the received sample data.
Take frequency domain processing as an example, such as an LTE system or an NB-IOT system. Sampling is performed in the time domain, and the received sample data in the time domain is converted into the received sample data in the frequency domain through FFT. And acquiring a known channel estimation sequence on the frequency domain corresponding to the received sampling data on the frequency domain. And acquiring a phase elimination sequence on the corresponding frequency domain by multiplying the received sampling data on the frequency domain by the conjugate of the channel estimation sequence on the corresponding frequency domain.
And calculating a difference result between any two sections of phase elimination sequences according to the calculated M sections of phase elimination sequences. The difference calculation method is the same regardless of whether the phase removal sequence is data in the time domain or the frequency domain, and the frequency offset estimation method is the same. Specifically, the difference result R between the nth segment and the n + k th segment phase-eliminated sequence can be calculated according to the following formulan(k)：
Where k is the differential distance, rn(i) For the nth phase removal sequence, data at the ith position, rn(i)*Is rn(i) Conjugation of (a), (b), r)n+k(i) And eliminating data of the ith position in the sequence for the (n + k) th phase.
And adding the difference results of the same difference distance to obtain an accumulated difference term of the difference distance.
And carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term. A frequency offset between a data transmitting side and a data receiving side is estimated based on the mixed differential term. Further, the frequency deviation is calculated according to the following formula:
wherein, Δ f is the frequency deviation, R is the mixed differential term, and angle () represents the radian of the complex number in the bracket, and the value range is (-pi, pi)]T is a time interval corresponding to the unit difference distance;
the average time domain difference distance is defined as k, the difference distance is defined as b (k), the difference result number corresponding to the difference distance k is defined as b (k), and w (k) is the weight of the accumulated difference term of the difference distance k.
For example, assuming that the channel estimation sequence is transmitted once per subframe, 4 subframes are continuously received, and the received sample data corresponding to 4 segments of the channel estimation sequence is obtained and stored. And respectively carrying out phase elimination processing on the 4 sections of received sampling data to obtain corresponding phase elimination sequences. And calculating the difference result of the phase elimination sequences of any two sections according to the obtained 4 sections of phase elimination sequences to obtain all difference results. In this embodiment, the sequence of calculating the difference result is not limited, and the following is only an example:
the unit difference distance is assumed to correspond to a time interval of 1 subframe. And calculating the corresponding differential distance according to the definition of the time interval and the unit differential distance between the two phase elimination sequences participating in the differential calculation. For example, the time interval between the phase-canceled sequence of segment 1 and the phase-canceled sequence of segment 2 is 1 subframe, so the corresponding differential distance is 1. The time interval between the 1 st phase removal sequence and the 4 th phase removal sequence is 3 subframes, so the differential distance is 3.
Respectively calculating the difference result R of the 1 st segment and the 2 nd segment1(1) Differential results R of, 2 nd and 3 rd sections2(1) Differential results R of, 3 rd and 4 th3(1) The difference distances are the same and are all 1 subframe, and the three difference results are accumulated to obtain an accumulated difference term a with the difference distance of 1 subframe, wherein k is 1 (indicating that the difference distance is 1), and B (1) is 3 (indicating that 3 groups of difference results with the difference distance of 1 exist);
respectively calculating the difference result R of the 1 st segment and the 3 rd segment1(2) Differential results R of, 2 nd and 4 th sections2(2) The difference distances are the same and are both 2 sub-frames, and the two difference results are accumulated to obtain an accumulated difference term B with the difference distance of 2 sub-frames, wherein k is 2 (indicating that the difference distance is 2), and B (2) is 22 (indicating that there are 2 sets of difference results with a difference distance of 2);
calculating a difference result R between the 1 st and 4 th segments1(3) The difference is 3 subframes, and the difference result is an accumulated difference term C with a difference distance of 3 subframes, where k is 3 (indicating that the difference distance is 3), and B (3) is 1 (indicating that there are 1 group of difference results with a difference distance of 3).
Thus, the accumulated difference terms of all different difference distances in the 4-segment phase removal sequence are calculated. The above three kinds of accumulated difference terms are weighted and summed, and the weights can be set arbitrarily or according to a certain rule, for example, the accumulated difference term A, B, C, and the corresponding weights are set to 1/4 (i.e., w (1)), 1/2 (i.e., w (2)), and 1/4 (i.e., w (3)), respectively, to obtain the mixed difference term R. Calculating the average time domain difference distance according to k, B (k), w (k)
And estimating the frequency deviation according to the mixed difference item and the average time domain difference distance.
In this embodiment, under the condition of obtaining the same received data, by introducing the mixed difference term, the accumulated difference term with a larger difference distance is considered, so that the calculated phase difference is more obvious, and the accuracy of frequency offset estimation is further improved.
In another embodiment of the present invention, as shown in fig. 2, a method for estimating a frequency offset includes:
on the basis of the previous embodiment, step S500 is replaced with step S510.
Step S510 sums up the accumulated difference terms of all different difference distances to obtain a mixed difference term.
Specifically, the accumulated differential terms of all different differential distances are directly accumulated to obtain a mixed differential term. Different weights do not need to be used according to the difference distance, the mixed difference item is obtained through the method, and then the frequency offset is estimated, so that the absolute error of the frequency offset estimation value relative to the true value is minimum, and the reason analysis is as follows:
as can be seen from the description of the previous embodiment, in the case of determining the data and data amount of the acquired phase-canceling sequence, k, B (k), and the mixed differential term are determined, so that the frequency offset is a function of the weight of the accumulated differential term, and how to design the weight so as to minimize the deviation of the frequency offset estimation value from the true value.
The mixed differential term is obtained by weighted summation of accumulated differential terms of different differential distances, wherein each accumulated differential term is a vector and can be expressed by the following formula:
where k is the differential distance, Raccu(k) Is the accumulated difference term of the difference distance k, B (k) is the difference result number corresponding to the difference distance k, A represents the amplitude, theta is the phase deviation of the received signal corresponding to the difference distance of 1, and n is Gaussian white noise.
The mixed differential term is equivalent to the accumulation of a plurality of vectors, the calculation is complex, and the mixed differential term can be simplified into 2 vector accumulations and then popularized to the accumulation of a plurality of vectors without loss of generality.
The following discussion is in terms of 2 vector accumulations:
if the two vectors are:
wherein x is0Cumulative difference term, x, representing the difference distance 01A cumulative difference term representing the difference distance 1, B0Indicating the phase deviation theta0Cumulative number of times of (A) and (B)1Indicating the phase deviation theta1N0 and n1 are white gaussian noise.
Let x be0The corresponding weight is 1, x1The corresponding weight is w, then the combined result is
X＝x0+wx1
＝B0(cosθ0+jsinθ0)+wB1(cosθ1+jsinθ1)+n0+wn1
＝B0cosθ0+wB1cosθ1+j(B0sinθ0+wB1sinθ1)+n0+wn1
The SNR was calculated as follows:
wherein ψ is cos (θ)0-θ1)，σ2Is the noise variance.
The weight w is found that maximizes the SNR. Derivation of the above equation yields:
SNR is maximized (i.e., Δ θ is minimized), i.e., the above equation is 0.
If it is assumed to be in a frequency offset tracking steady state, θ0-θ1Smaller, then ψ is cos (θ)0-θ1) 1, substituting the above equation, one can obtain:
neglecting the negative result, it can be seen that the optimal merging coefficient is 1, that is, the accumulated difference terms of all different difference distances can be directly accumulated without using different weights according to the difference distances.
In this embodiment, the absolute error of the frequency offset estimation value with respect to the true value can be minimized by setting the weight of the cumulative difference term for each difference distance to 1.
In another embodiment of the present invention, as shown in fig. 3, a method for estimating a frequency offset includes:
on the basis of the embodiment shown in fig. 1, step S500 is replaced by steps S520, S530.
Step S520, multiplying the accumulated difference item of the difference distance by the difference distance to obtain a weighted difference item of the difference distance;
step S530 sums the weighted difference terms of all the difference distances to obtain a mixed difference term.
Specifically, the weight of the accumulated difference term for each difference distance is set to the corresponding difference distance, i.e., w (k) ═ k. Multiplying the accumulated difference item of the difference distance k by the corresponding weight to obtain a weighted difference item; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term. And estimating the frequency offset according to the mixed differential term and the average time domain differential distance.
The frequency offset estimated by the method can ensure that the relative error between the estimated value and the true value is minimum. The reason was analyzed as follows:
the objective function is:
still, we discuss 2 vector accumulations, i.e., finding w minimizes the following:
wherein f (w) represents
K represents B1The corresponding differential distance.
Found by numerical calculation that B is different0、B1The effect on w is small and the maximum effect factor is K, i.e. the differential distance. When K is small, the optimal w is approximately equal to K, when K is smallWhen w is large, i.e., 10 or more, the optimum w becomes large, but the optimum w is very close to the result calculated by K because the curve of f (w) is shown in w>The section of K is very flat, and w-K can be approximated as approaching the optimum result, as shown in fig. 6 (horizontal axis represents w, vertical axis represents f (w)), so w-K can be used as the weight.
As shown in fig. 7 (mse (mean Squared error) represents the mean square error, and M represents the maximum difference distance), comparing the performances of the prior art (LR curve in the figure) and the algorithm of this embodiment (Our curve in the figure), it can be seen that the performance of the algorithm of this embodiment is stable and better than that of the prior art under various maximum difference distances.
In this embodiment, the weight of the cumulative difference term for each difference distance is set to the corresponding difference distance, so that the relative error between the frequency offset estimation value and the true value can be minimized.
In an embodiment of the present invention, as shown in fig. 4, an apparatus 100 for estimating a frequency offset includes:
an obtaining module 110, configured to obtain at least 3 segments of received sample data corresponding to a known channel estimation sequence.
And a phase cancellation module 140, configured to obtain a phase cancellation sequence corresponding to each segment of received sample data according to the received sample data and a channel estimation sequence corresponding to the received sample data.
A difference calculation module 120, configured to perform difference calculation on any two phase cancellation sequences, obtain a difference result corresponding to the two phase cancellation sequences, and obtain a difference distance of the difference result according to a time interval between the two phase cancellation sequences; adding the difference results of all the same difference distances to obtain the accumulated difference item of each difference distance; and carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term.
The difference calculation module 120 includes:
and a difference result calculating unit 121, configured to calculate a difference result between each two phase removal sequences.
And the mixed difference calculating unit 122 is configured to perform weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term.
And a frequency offset estimation module 130, configured to estimate a frequency offset between the data sender and the data receiver according to the hybrid difference term.
Specifically, the received sample data is sample data obtained by receiving a channel estimation sequence transmitted by a transmission side in order to ensure correct reception of transmission data. The channel estimation sequence is known in advance by the sender and the receiver, such as a training code sequence placed in the middle of each time slot in a TD-SCDMA system, and a reference signal placed on a fixed time-frequency resource of each subframe in an LTE system. The channel estimation sequence may be repeatedly transmitted at a fixed time interval, for example, once every time slot, or may be transmitted at a regular change at a fixed time interval (the change rule is known in advance by the transmitting side and the receiving side), depending on the requirements of the corresponding wireless communication system.
The received sample data may be data in the time domain or data in the frequency domain, and may be selected according to the processing convenience of the applied wireless communication system. For example, the TD-SCDMA system is more convenient for time domain processing, so the data in the time domain is used for receiving the sampling data, the corresponding channel estimation sequence and phase cancellation series also use the data in the time domain, the differential calculation is performed on the phase cancellation series in the time domain, and the frequency deviation is estimated according to the differential calculation result. The LTE system or the NB-IOT system is convenient for frequency domain processing, so that data on a frequency domain is adopted for receiving sampling data, data on the frequency domain is adopted for a corresponding channel estimation sequence and a corresponding phase elimination series, differential calculation is carried out on the phase elimination series on the frequency domain, and frequency deviation is estimated according to a differential calculation result. The sampling is usually performed in the time domain, and the received sample data in the time domain can be converted into the required received sample data in the frequency domain by FFT.
Assuming that the length of each section of received sample data is N, obtaining M sections (M > ═ 3) of received sample data and storing the received sample data, and obtaining M × N sampling points for frequency offset estimation. Preferably, M consecutive pieces of received sample data received at the latest time are stored.
Firstly, the M sections of received sampling data are subjected to phase elimination processing, and corresponding M sections of phase elimination sequences are obtained and stored. Taking the phase removal processing for one segment of the received sample data as an example, the processing procedure is as follows (the processing for the received sample data of the other segments is similar):
taking time domain processing as an example, for example, in TD-SCDMA system, the received sampled data is data in time domain. And acquiring a channel estimation sequence on a known time domain corresponding to the received sampling data. And performing channel estimation according to the received sampling data to obtain a channel estimation result. And carrying out convolution operation on the channel estimation result and the channel estimation sequence to obtain a reconstruction sequence corresponding to the received sampling data. And multiplying the conjugate of the received sample data and the reconstruction sequence to obtain a phase elimination sequence on a time domain corresponding to the received sample data.
Take frequency domain processing as an example, such as an LTE system or an NB-IOT system. Sampling is performed in the time domain, and the received sample data in the time domain is converted into the received sample data in the frequency domain through FFT. And acquiring a known channel estimation sequence on the frequency domain corresponding to the received sampling data on the frequency domain. And acquiring a phase elimination sequence on the corresponding frequency domain by multiplying the received sampling data on the frequency domain by the conjugate of the channel estimation sequence on the corresponding frequency domain.
And calculating a difference result between any two sections of phase elimination sequences according to the calculated M sections of phase elimination sequences. The difference calculation method is the same regardless of whether the phase removal sequence is data in the time domain or the frequency domain, and the frequency offset estimation method is the same. Specifically, the difference result R between the nth segment and the n + kth segment phase-eliminated sequence can be calculated according to the following formulan(k)：
Where k is the differential distance, rn(i) For the nth phase removal sequence, data at the ith position, rn(i)*Is rn(i) Is conjugated with (i) an+k(i) And eliminating data of the ith position in the sequence for the (n + k) th phase.
And adding the difference results of the same difference distance to obtain an accumulated difference term of the difference distance.
And carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term. A frequency offset between a data transmitting side and a data receiving side is estimated based on the mixed differential term. Further, the frequency deviation is calculated according to the following formula:
wherein, Δ f is the frequency deviation, R is the mixed differential term, and angle () represents the radian of the complex number in the bracket, and the value range is (-pi, pi)]T is a time interval corresponding to the unit difference distance;
the average time domain difference distance is defined as k, the difference distance is defined as b (k), the difference result number corresponding to the difference distance k is defined as b (k), and w (k) is the weight of the accumulated difference term of the difference distance k.
In this embodiment, under the condition of obtaining the same received data, by introducing the mixed difference term, the accumulated difference term with a larger difference distance is considered, so that the calculated phase difference is more obvious, and the accuracy of frequency offset estimation is further improved.
In another embodiment of the present invention, as shown in fig. 4, an apparatus for estimating a frequency offset includes:
on the basis of the previous embodiment, the function of the hybrid difference calculation unit 122 is modified to: and summing the accumulated difference terms of all different difference distances to obtain a mixed difference term.
Specifically, the accumulated differential terms of all different differential distances are directly accumulated to obtain a mixed differential term. Different weights are not required to be used according to the difference distance, the mixed difference item is obtained through the method, further, the frequency offset is estimated, and the absolute error of the frequency offset estimation value relative to the true value can be minimized.
In another embodiment of the present invention, as shown in fig. 4, an apparatus for estimating a frequency offset includes:
on the basis of the previous embodiment, the function of the hybrid difference calculation unit 122 is modified to: multiplying the accumulated difference item of the difference distance by the difference distance to obtain a weighted difference item of the difference distance; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
Specifically, the weight of the accumulated difference term for each difference distance is set to the corresponding difference distance, i.e., w (k) ═ k. Multiplying the accumulated difference item of the difference distance k by the corresponding weight to obtain a weighted difference item; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term. And estimating the frequency offset according to the mixed differential term and the average time domain differential distance. The frequency offset estimated by the method can minimize the relative error between the estimated value and the true value.
It should be noted that the embodiment of the frequency offset estimation apparatus according to the present invention and the embodiment of the frequency offset estimation method according to the present invention are based on the same inventive concept, and can achieve the same technical effects. Therefore, other specific contents of the embodiment of the frequency deviation estimation device can refer to the description of the embodiment of the frequency deviation estimation method.
In another embodiment of the present invention, as shown in fig. 5, a communication device 10 includes the frequency deviation estimation apparatus 100 according to any of the foregoing embodiments.
Specifically, the communication device may be a User Equipment (UE) and includes the aforementioned frequency offset estimation apparatus 100, so that the device improves the estimation accuracy of the frequency offset without increasing the computational complexity, which is helpful for improving the wireless communication quality.
It should be noted that the above embodiments can be freely combined as necessary. The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. A method for estimating a frequency offset, comprising:
acquiring at least 3 sections of received sampling data corresponding to a known channel estimation sequence;
acquiring a phase elimination sequence corresponding to the received sampling data according to each section of the received sampling data and a channel estimation sequence corresponding to the received sampling data;
carrying out differential calculation on any two sections of phase elimination sequences to obtain differential results corresponding to the two sections of phase elimination sequences, and obtaining the differential distance of the differential results according to the time interval between the two sections of phase elimination sequences;
adding the difference results of all the same difference distances to obtain the accumulated difference item of each difference distance;
carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term;
estimating the frequency deviation between a data sending party and a data receiving party according to the mixed differential item;
the weighting and summing the accumulated difference terms of all the different difference distances to obtain a mixed difference term includes:
summing the accumulated difference terms of all different difference distances to obtain a mixed difference term; or the like, or, alternatively,
multiplying the accumulated difference item of the difference distance by the difference distance to obtain a weighted difference item of the difference distance; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
2. The method of estimating a frequency offset according to claim 1, wherein:
the received sampling data and the channel estimation sequence are both data in a frequency domain;
the obtaining a phase cancellation sequence corresponding to each segment of received sample data according to the received sample data and a channel estimation sequence corresponding to the received sample data includes:
and acquiring a phase elimination sequence corresponding to the received sampling data by multiplying each segment of the received sampling data by the conjugate of the channel estimation sequence corresponding to the received sampling data, wherein the phase elimination sequence is data on a frequency domain.
3. The method according to claim 1 or 2, wherein the calculating step of performing the difference calculation on the two phase removal sequences to obtain the difference result corresponding to the two phase removal sequences comprises:
obtaining a product of data for a position in a segment of a phase-canceling sequence and data for the position in another segment of the phase-canceling sequence by multiplying a conjugate of the data for the position in the segment of the phase-canceling sequence with the data for the same position in the other segment of the phase-canceling sequence;
and obtaining a difference result corresponding to the two phase elimination sequences by adding products of data of all positions in the phase elimination sequence and the phase elimination sequence.
4. The method of claim 1, wherein estimating the frequency offset between the data transmitting side and the data receiving side according to the hybrid difference term comprises:
calculating an average time domain difference distance, wherein a calculation formula of the average time domain difference distance is as follows:
wherein the content of the first and second substances,
is the average time domain differential distance, k is the differential distance, B (k) is the number of differential results corresponding to the differential distance k, and w (k) is the weight of the accumulated differential term of the differential distance kWeighing;
estimating the frequency deviation between a data sending party and a data receiving party according to the mixed differential term and the average time domain differential distance;
the calculation formula of the frequency deviation is as follows:
wherein, Δ f is the frequency deviation, R is the mixed differential term, angle () represents the radian of the complex number in the bracket, the value range is (-pi, pi), and t is the time interval corresponding to the unit differential distance.
5. An apparatus for estimating a frequency offset, comprising:
an obtaining module, configured to obtain at least 3 segments of received sample data corresponding to a known channel estimation sequence;
the phase elimination module is used for acquiring a phase elimination sequence corresponding to the received sampling data according to each section of received sampling data and a channel estimation sequence corresponding to the received sampling data;
the differential calculation module is used for carrying out differential calculation on any two sections of phase elimination sequences, obtaining a differential result corresponding to the two sections of phase elimination sequences and obtaining a differential distance of the differential result according to a time interval between the two sections of phase elimination sequences; and, obtaining the cumulative difference term of each differential distance by adding the difference results of all the same differential distances; carrying out weighted summation on the accumulated difference terms of all different difference distances to obtain a mixed difference term;
the frequency deviation estimation module is used for estimating the frequency deviation between the data sender and the data receiver according to the mixed differential item;
the difference calculation module includes:
the mixed difference calculating unit is used for summing the accumulated difference terms of all different difference distances to obtain a mixed difference term; or the like, or, alternatively,
the system comprises a differential distance calculating unit, a differential distance calculating unit and a control unit, wherein the differential distance calculating unit is used for calculating the difference of the differential distance between the two signals; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
6. The apparatus for estimating a frequency offset according to claim 5, wherein the difference calculating module further comprises:
a difference result calculation unit, configured to calculate a difference result between each two phase cancellation sequences, including: obtaining a product of data for a position in a segment of a phase-canceling sequence and data for the position in another segment of the phase-canceling sequence by multiplying a conjugate of the data for the position in the segment of the phase-canceling sequence with the data for the same position in the other segment of the phase-canceling sequence; and obtaining a difference result corresponding to the two phase elimination sequences by adding products of data of all positions in the phase elimination sequence and the phase elimination sequence.
7. The apparatus for estimating a frequency offset according to claim 6, wherein the difference calculating module further comprises:
the mixed difference calculating unit is used for summing the accumulated difference terms of all different difference distances to obtain a mixed difference term; or the like, or, alternatively,
the system comprises a differential distance calculating unit, a calculating unit and a calculating unit, wherein the differential distance calculating unit is used for calculating the difference of the differential distance between the two adjacent channels; and summing the weighted difference terms of all the difference distances to obtain a mixed difference term.
8. A communication device, characterized in that it comprises the estimation means of the frequency deviation of any of claims 5 to 7.
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