CN112688894A - Viterbi demodulation algorithm and apparatus applied to GFSK system - Google Patents
Viterbi demodulation algorithm and apparatus applied to GFSK system Download PDFInfo
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Abstract
The invention discloses a Viterbi demodulation algorithm and a Viterbi demodulation device applied to a GFSK system, which comprise the following contents: and calculating branch metric values on each state transition branch, and selecting the maximum value in the branch metric values as a correct demodulation result to be output, wherein the method for calculating and selecting the maximum value is equivalent to accumulating absolute values of phases and calculating an extreme value. A Viterbi demodulation apparatus applied to a GFSK system, comprising: a Viterbi demodulation block, the block comprising: a branch metric calculating unit and an addition and comparison selecting unit; the branch metric calculating unit is used for calculating branch metric values on each state transition branch; and the addition-comparison selection unit is used for selecting the maximum value in the branch metric values as a correct demodulation result to be output. The invention simplifies the complex operation between trigonometric functions into the process of accumulating phase absolute values and calculating an extreme value in the prior art, effectively reduces the complexity of calculation on the premise of ensuring the calculation precision, and further greatly reduces the resource occupation and the realization difficulty of the Viterbi demodulation device.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a Viterbi demodulation algorithm applied to a GFSK system and a Viterbi demodulation device.
Background
With the development of the internet of things technology, the internet of everything is in a trend, so that the application of short-distance, medium-low speed wireless transmission technology is more and more extensive, and the bluetooth communication technology is particularly prominent. The bluetooth technology uses GFSK modulation with BT value of 0.5 to perform wireless transceiving, and generally uses phase-detecting, frequency-discriminating and IAD to perform demodulation at a receiving end, but the performance of the demodulation method is reduced by about 3dB compared with Viterbi demodulation (that is, Viterbi demodulation), so that adding Viterbi demodulation to a receiving system has good performance gain. However, the Viterbi demodulation algorithm involves a large number of multiplication and addition operations and a large number of trigonometric function operations, which greatly increases the system load and consumes a large amount of hardware resources, especially is not favorable for SOC design and implementation.
Therefore, it is an urgent need to solve the problem of providing a simplified Viterbi demodulation algorithm and apparatus thereof for GFSK system.
Disclosure of Invention
In view of this, the present invention provides a Viterbi demodulation algorithm and a Viterbi demodulation apparatus applied to a GFSK system, which effectively simplifies the Viterbi demodulation algorithm.
In order to achieve the purpose, the invention adopts the following technical scheme:
a Viterbi demodulation algorithm for GFSK systems, comprising:
calculating branch metric values on each state transition branch, and selecting the maximum value in the branch metric values as a correct demodulation result to be output, wherein the equivalent method for calculating and selecting the maximum value is as follows:
wherein MetriciValue representing the ith branch metric, M-2L+1For the number of branches involved in the demodulation calculation, L is the number of taps of the Gaussian filter, N is the backtracking depth,
is the modulation phase of the ith received signal,
for the modulation phase of the ith local sequence, TsIs the data sampling interval.
It should be noted that: the lower case N is a self-defined variable, and the value range is 1 to N, which is used for explaining that the addition is performed for N times, namely the likelihood value calculated by each lattice point in the backtracking depth is added.
A Viterbi demodulation apparatus applied to a GFSK system, comprising: a Viterbi demodulation module;
the Viterbi demodulation block includes: a branch metric calculating unit and an addition and comparison selecting unit; the branch metric calculating unit is connected with the addition and comparison selecting unit;
the branch metric calculating unit is used for calculating branch metric values on each state transition branch;
and the addition-comparison selection unit is used for selecting the maximum value in the branch metric values as a correct demodulation result to be output.
Preferably, the Viterbi demodulation block further includes: the device comprises a GFSK local phase modulation unit and a backtracking demodulation unit;
the GFSK local phase modulation unit is connected with the branch metric calculation unit and used for acquiring the modulation phase of a local sequence and sending the modulation phase to the branch metric calculation unit;
and the backtracking demodulation unit is connected with the addition-comparison selection unit, when the calculation of the branch metric value is accumulated to a backtracking depth, the backtracking demodulation unit carries out reverse demodulation by taking the branch path with the maximum branch metric value in the grid map as a survivor path, the grid point position information of the grid map corresponding to the survivor path is stored in a memory in advance, the position information stored in the memory is searched from the tail to the head during backtracking, and the input information of the grid point corresponding to the path head address is taken as the current demodulation output bit.
Preferably, the system further comprises a down-conversion unit, a phase detector, a frequency offset calculation unit and a frequency offset compensation unit;
the down-conversion unit is connected with the phase discriminator, the phase discriminator is respectively connected with the frequency discriminator and the frequency deviation compensation signal, the frequency discrimination signal is connected with the frequency deviation calculation unit, the frequency deviation signal is connected with the frequency deviation compensation unit, and the frequency deviation compensation unit is connected with the branch measurement calculation unit.
According to the technical scheme, compared with the prior art, the Viterbi demodulation algorithm applied to the GFSK system and the device thereof are disclosed and provided, the algorithm simplifies the complex operation between trigonometric functions in the prior art into the process of accumulating absolute phase values and calculating an extreme value, the complexity of calculation is effectively reduced on the premise of ensuring the calculation precision, and the resource occupation and the realization difficulty of the Viterbi demodulation device are further greatly reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a state transition grid diagram when h is 0.5 and L is 2 according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a cosine function waveform according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a Viterbi demodulation apparatus applied to a GFSK system according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention discloses a Viterbi demodulation algorithm applied to a GFSK system, which comprises the following contents:
calculating branch metric values on each state transition branch, and selecting the maximum value in the branch metric values as a correct demodulation result to be output, wherein the equivalent method for calculating and selecting the maximum value is as follows:
wherein MetriciValue representing the ith branch metric, M-2L+1For the number of branches involved in the demodulation calculation, L is the number of taps of the Gaussian filter, N is the backtracking depth,
is the modulation phase of the ith received signal,
for the modulation phase of the ith local sequence, TsIs the data sampling interval.
It should be noted that:
the likelihood estimation function in best reception is expressed in the prior art by the following formula:
wherein r isnFor the received data, snFor locally generated data, maximum likelihood based demodulation is performed by calculating the likelihood function values of different local sequences and received sequences using the above formula, and selecting the sequence corresponding to the maximum likelihood value as the demodulation output, i.e. the maximum likelihood value
For GFSK signals, the original data are subjected to Gaussian filtering and then phase modulation, and the original data are set to be alphaiThe data sampling interval is Ts, the modulation coefficient is h, the number of taps of the Gaussian filter is L, the step response is q (t), and when t is more than LTsWhen q (t) is 0.5, the regulation is performedThe resulting phase can be expressed by the following formula:
if the middle and rear half parts of the above formula are thetan, then
Can be composed of [ theta ]n，αn-1，...αn-L+1]A unique determination. The phase is calculated and then converted into a trigonometric function value, namely baseband modulation data of the GFSK, and Viterbi demodulation of the GFSK is carried out according to the structure.
The expression of the above structure can be represented by a state transition trellis diagram, such as h 0.5 and L2, which is shown in fig. 1;
viterbi demodulation converts the maximum likelihood estimate to a comparison of the metric values for each phase state transition branch in the trellis, the branch metric values are derived from the likelihood function formula as follows:
wherein
Is the modulation phase of the received signal,
Is the modulation phase of the local sequence, and
the calculation of (c) utilizes a state transition trellis diagram and the above iterative formula for calculating the phase.
According to the calculation formula of the branch measurement, a large amount of trigonometric function operation and a large amount of multiply-accumulate operation are involved, so that system resources are consumed, and the realization complexity is high. In order to simplify the conventional Viterbi demodulation algorithm and reduce the implementation complexity, the following improvement is made.
In the first step, the number of computations and the number of multiplications of trigonometric functions are reduced by the integration and difference transformation of trigonometric functions.
The final result is as follows:
and secondly, after the metric values of all branches are calculated, the maximum value, namely the maximum likelihood value is selected as a correct demodulation result to be output. The present invention uses an equivalent alternative method to calculate the branch metrics and compare their magnitudes. Is provided with
Then, as can be known from the cosine function waveform, the magnitude of the cosine function value in this value range is in a nonlinear inverse proportion relationship with the absolute value of the independent variable, i.e., the smaller the absolute value of the independent variable, the larger the corresponding cosine function value, as shown in fig. 2.
According to this feature, the process of calculating branch metrics and taking the maximum value can be equivalently replaced by the following formula.
Wherein M is 2L+1After the conversion, the Viterbi demodulation algorithm based on the maximum likelihood criterion is greatly simplified, trigonometric function operation and a large amount of multiply-accumulate operation are eliminated, and the complexity of algorithm realization is greatly reduced.
A Viterbi demodulating apparatus applied to a GFSK system, as shown in fig. 3, comprising: a Viterbi demodulation module;
the Viterbi demodulation block includes: a branch metric calculating unit and an addition and comparison selecting unit; the branch measurement calculating unit is connected with the addition and comparison selecting unit;
the branch metric calculating unit is used for calculating branch metric values on each state transition branch;
and the addition-comparison selection unit is used for selecting the maximum value in the branch metric values as a correct demodulation result to be output.
In order to further implement the above technical solution, the Viterbi demodulation module further includes: the device comprises a GFSK local phase modulation unit and a backtracking demodulation unit;
the GFSK local phase modulation unit is connected with the branch metric calculation unit and used for acquiring the modulation phase of the local sequence and sending the modulation phase to the branch metric calculation unit;
the backtracking demodulation unit is connected with the addition-comparison selection unit, when the calculation of the branch metric value is accumulated to the backtracking depth, the branch path with the maximum branch metric value in the grid graph is taken as a survivor path to carry out reverse demodulation, grid point position information corresponding to the survivor path is stored in the memory in advance, position information stored in the memory is searched from the tail to the head during backtracking, and input information of a grid point corresponding to a path head address is taken as a current demodulation output bit.
In order to further implement the above technical solution, the apparatus further includes a down-conversion unit, a phase detector, a frequency offset calculation unit, and a frequency offset compensation unit;
the down-conversion unit is connected with the phase discriminator, the phase discriminator is respectively connected with the frequency discriminator and the frequency offset compensation signal, the frequency discrimination signal is connected with the frequency offset calculation unit, the frequency offset signal is connected with the frequency offset compensation unit, and the frequency offset compensation unit is connected with the branch metric calculation unit.
The invention relates to a data processing overall flow and a working principle:
1. the input I Q quadrature data is a low intermediate frequency digital signal that is down converted to a zero intermediate frequency signal (where the data contains a frequency offset).
2. Before Viterbi demodulation, the frequency deviation carried by the signal needs to be removed, so that functional modules such as phase discrimination, frequency offset calculation, frequency offset compensation and the like are added at the front end of the demodulation.
3. The phase detector calculates the signal phase information by means of an arctangent operation.
4. The discriminator obtains the instantaneous frequency through phase difference operation.
5. The frequency offset calculating unit generally uses known information (frame header or pilot frequency) in the frame structure to calculate the frequency offset, and for GFSK modulation, the frequency offset can be calculated by using the mean value of the frequency-discriminated signal and the mean value of the known signal after modulation.
6. The frequency offset compensation unit is used for compensating phase drift caused by frequency offset back to the phase detection signal, so that interference of the frequency offset on subsequent calculation is eliminated.
7. The phase data without frequency deviation and the locally generated phase data are processed with branch metric calculation under the maximum likelihood criterion, and are accumulated to the backtracking depth, and the branch path with the maximum metric value is selected as a demodulation output path (an adding and comparing unit).
8. And the backtracking demodulation unit starts to backtrack the starting point of the branch according to the demodulation path and takes the input information of the starting point as the demodulation output at the moment.
The invention simplifies the branch metric calculation formula obtained according to the maximum likelihood criterion to complete the metric calculation, and converts the trigonometric function multiplication and accumulation operation into the simple trigonometric function accumulation operation through the integration sum-difference transformation. And then finding the corresponding relation between the phase value and the cosine value by utilizing the cosine function characteristic, further simplifying cosine accumulation operation, comparing the branch measurement of each demodulation branch according to the maximum likelihood criterion, and outputting the demodulation result by taking the branch with the maximum value as a correct path, which is a process of multiplying and accumulating and calculating the maximum value. The simplified algorithm designed by the invention changes the calculation process into a process of accumulating phase absolute values and calculating an extreme value, and greatly reduces the resource occupation and the realization complexity of the Viterbi demodulation device on the premise of ensuring the calculation precision.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. A Viterbi demodulation algorithm for a GFSK system, comprising:
calculating branch metric values on each state transition branch, and selecting the maximum value in the branch metric values as a correct demodulation result to be output, wherein the equivalent method for calculating and selecting the maximum value is as follows:
wherein MetriciValue representing the ith branch metric, M-2L+1For the number of branches involved in the demodulation calculation, N is the backtracking depth, L is the number of Gaussian filter taps,
is the modulation phase of the ith received signal,
for the modulation phase of the ith local sequence, TsIs the data sampling interval.
2. A Viterbi demodulation apparatus applied to a GFSK system, which employs the Viterbi demodulation algorithm applied to the GFSK system according to claim 1, comprising: a Viterbi demodulation module;
the Viterbi demodulation block includes: a branch metric calculating unit and an addition and comparison selecting unit; the branch metric calculating unit is connected with the addition and comparison selecting unit;
the branch metric calculating unit is used for calculating branch metric values on each state transition branch;
and the addition-comparison selection unit is used for selecting the maximum value in the branch metric values as a correct demodulation result to be output.
3. A Viterbi demodulation apparatus for a GFSK system as claimed in claim 2, wherein the Viterbi demodulation block further comprises: the device comprises a GFSK local phase modulation unit and a backtracking demodulation unit;
the GFSK local phase modulation unit is connected with the branch metric calculation unit and used for acquiring the modulation phase of a local sequence and sending the modulation phase to the branch metric calculation unit;
and the backtracking demodulation unit is connected with the addition-comparison selection unit, when the calculation of the branch metric value is accumulated to a backtracking depth, the backtracking demodulation unit carries out reverse demodulation by taking the branch path with the maximum branch metric value in the grid map as a survivor path, the grid point position information of the grid map corresponding to the survivor path is stored in a memory in advance, the position information stored in the memory is searched from the tail to the head during backtracking, and the input information of the grid point corresponding to the path head address is taken as the current demodulation output bit.
4. A Viterbi demodulation apparatus for a GFSK system according to claim 3, further comprising a down-conversion unit, a phase detector, a frequency offset calculation unit, and a frequency offset compensation unit;
the down-conversion unit is connected with the phase discriminator and is used for converting the low intermediate frequency signals sampled by the ADC into zero intermediate frequency signals;
the phase discriminator is respectively connected with the frequency discriminator and the frequency offset compensation signal and is used for calculating the phase information of the I/Q data;
the frequency discrimination signal is connected with the frequency deviation calculating unit and used for obtaining the instantaneous frequency of the signal through phase difference;
the frequency offset calculation unit is connected with the frequency offset compensation unit and used for calculating a frequency offset value of a signal according to known information contained in a data structure;
the frequency offset compensation unit is connected with the branch measurement calculation unit and used for converting the frequency offset into phase offset and reversely compensating the phase-returned signal to obtain a non-frequency offset signal.
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