Signal processing apparatus, signal processing method, and non-transitory storage medium storing signal processing program

1 . A signal processing apparatus comprising:

an autocorrelation processing circuit configured to generate, by using one or more symbol values included in a synchronous signal of a target frame and one or more corresponding symbol values included in a synchronous signal of a frame immediately before the target frame, one or more autocorrelation symbols indicating a change component of frame identification information of the target frame as compared to frame identification information of the frame immediately before the target frame;

a symbol replica generation circuit configured to generate, by using one or more symbol values that correspond to the frame identification information of the target frame and one or more symbol values that correspond to the frame identification information of the frame immediately before the target frame, one or more symbol replicas indicating a change component of the one or more symbol values included in the synchronous signal of the frame immediately before the target frame as compared to the one or more symbol values included in the synchronous signal of the target frame;

an individual likelihood value calculation circuit configured to calculate, by using the one or more autocorrelation symbols generated by the autocorrelation processing circuit and the one or more symbol replicas generated by the symbol replica generation circuit, a plurality of individual likelihood values indicating respective likelihoods of a plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame;

a path likelihood value calculation circuit configured to integrate, for each of the plurality of individual likelihood values calculated by the individual likelihood value calculation circuit, an individual likelihood value of the target frame and an integrated value of individual likelihood values of one or more frames preceding the target frame to obtain a plurality of path likelihood values indicating respective likelihoods of the plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame; and

a path likelihood value selection circuit configured to select the largest path likelihood value from among the path likelihood values obtained by the path likelihood value calculation circuit and output frame identification information that corresponds to the selected path likelihood value.

2 . The signal processing apparatus according to claim 1 , wherein

the frame identification information is a frame number, and

the path likelihood value selection circuit comprises:

a maximum value selection circuit configured to select the largest path likelihood value from among the path likelihood values obtained by the path likelihood value calculation circuit;

an error value calculation circuit configured to calculate an error value of the frame number that corresponds to the selected path likelihood value and a counter value that corresponds to the frame number of the frame immediately before the target frame;

a frame number calculation circuit configured to calculate a frame number of the target frame by using the counter value;

an adjustment value calculation circuit configured to calculate an adjustment value for correcting the frame number of the target frame by using the error value;

a correction circuit configured to correct the frame number of the target frame by using the adjustment value; and

an output circuit configured to output the corrected frame number of the target frame as the frame number that corresponds to the selected path likelihood value.

3 . The signal processing apparatus according to claim 2 , wherein the adjustment value calculation circuit comprises:

a standard deviation calculation circuit configured to calculate, by using the error values of the one or more preceding frames and the error value of the target frame, a standard deviation of the error value of the target frame and the error values of the one or more preceding frames;

a standard deviation determination circuit configured to determine whether the standard deviation of the error values is equal to or smaller than a threshold; and

an adjustment value calculation sub-circuit configured to calculate, when it is determined that the standard deviation of the error values is equal to or smaller than the threshold, the adjustment value by using the error value of the target frame and the error values of the one or more preceding frames.

4 . The signal processing apparatus according to claim 1 , wherein

the frame identification information is a frame number, and

the path likelihood value calculation circuit comprises:

a logarithmic operation circuit configured to logarithmically transform an individual likelihood value regarding the frame number of the target frame; and

an adder configured to add the individual likelihood value logarithmically transformed by the logarithmic operation circuit and the integrated value of the individual likelihood values of the one or more preceding frames to obtain a path likelihood value of the target frame.

5 . The signal processing apparatus according to claim 1 , wherein

the frame identification information is a frame number,

the path likelihood value calculation circuit comprises:

a logarithmic operation circuit configured to logarithmically transform an individual likelihood value regarding the frame number of the target frame;

a multiplier configured to multiply the integrated value of the individual likelihood values of the one or more preceding frames by a predetermined value to output the multiplied value, and

an adder configured to add the individual likelihood value logarithmically transformed by the logarithmic operation circuit and the multiplied value to obtain the path likelihood value of the target frame, and

the predetermined value is an actual value that is larger than 0 but is smaller than 1.

6 . The signal processing apparatus according to claim 1 , wherein

the frame identification information is a frame number, and

the individual likelihood value calculation circuit comprises:

one or more conjugate complex number conversion circuits configured to calculate a conjugate complex number of the one or more symbol replicas;

one or more complex multipliers configured to multiply the conjugate complex number of the symbol replica calculated by the conjugate complex number conversion circuit by the corresponding autocorrelation symbol generated by the autocorrelation processing circuit to obtain a multiplied value;

a complex adder configured to add one or more multiplied values calculated by the one or more complex multipliers to obtain an added value; and

an actual value acquisition circuit configured to acquire a real part of the added value added by the complex adder to output the acquired real part as an individual likelihood value of the target frame.

7 . The signal processing apparatus according to claim 1 , wherein

the autocorrelation processing circuit comprises:

a plurality of conjugate complex number conversion circuits configured to calculate a plurality of conjugate complex numbers of the one or more symbol values included in the synchronous signal of the frame immediately before the target frame that corresponds to the one or more symbol values included in the synchronous signal of the target frame;

a plurality of complex multiplier configured to calculate an inner product of the one or more symbol values included in the synchronous signal of the target frame and the plurality of conjugate complex numbers calculated by the conjugate complex number conversion circuit to obtain a plurality of complex sequences; and

a complex adder configured to add the plurality of complex sequences calculated by the complex multiplier to generate the one or more autocorrelation symbols.

8 . The signal processing apparatus according to claim 1 , wherein

the frame identification information is a frame number, and

the symbol replica generation circuit comprises:

a first symbol modulation circuit configured to modulate a frame number of the frame immediately before the target frame to generate one or more modulated symbol values of the frame immediately before the target frame;

a second symbol modulation circuit configured to modulate the frame number of the target frame to generate one or more modulated symbol values of the target frame;

one or more conjugate complex number conversion circuits configured to calculate a conjugate complex number of the modulated symbol value of the frame immediately before the target frame; and

one or more complex multipliers configured to multiply the modulated symbol value of the target frame by a conjugate complex number of the modulated symbol value of the frame immediately before the target frame that corresponds to the modulated symbol value of the target frame to generate the one or more symbol replicas.

9 . A signal processing method executed by a computer, wherein the method comprises:

generating, by using one or more symbol values included in a synchronous signal of a target frame and one or more corresponding symbol values included in a synchronous signal of a frame immediately before the target frame, one or more autocorrelation symbols indicating a change component of frame identification information of the target frame as compared to frame identification information of the frame immediately before the target frame;

generating, by using one or more symbol values that correspond to the frame identification information of the target frame and one or more symbol values that correspond to the frame identification information of the frame immediately before the target frame, one or more symbol replicas indicating a change component of the one or more symbol values included in the synchronous signal of the frame immediately before the target frame as compared to the one or more symbol values included in the synchronous signal of the target frame;

calculating, by using the one or more generated autocorrelation symbols and the one or more generated symbol replicas, a plurality of individual likelihood values indicating respective likelihoods of a plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame;

integrating, for each of the plurality of calculated individual likelihood values, an individual likelihood value of the target frame and an integrated value of individual likelihood values of one or more frames preceding the target frame to obtain a plurality of path likelihood values indicating respective likelihoods of the plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame;

selecting the largest path likelihood value from among the path likelihood values that have been calculated; and

outputting frame identification information that corresponds to the selected path likelihood value.

10 . The signal processing method according to claim 9 , wherein

the frame identification information is a frame number,

the selecting comprises:

calculating an error value of the frame number that corresponds to the selected path likelihood value and a counter value that corresponds to the frame number of the frame immediately before the target frame;

calculating a frame number of the target frame by using the counter value;

calculating an adjustment value for correcting the frame number of the target frame by using the error value; and

correcting the frame number of the target frame by using the adjustment value, and

the outputting comprises:

outputting the corrected frame number of the target frame as the frame number that corresponds to the selected path likelihood value.

11 . The signal processing method according to claim 10 , wherein the calculating the adjustment value comprises:

calculating a standard deviation of the error value of the target frame and the error values of the one or more preceding frames by using the error values of the one or more preceding frames and the error value of the target frame;

determining whether the standard deviation of the error values is equal to or smaller than a threshold; and

calculating, when it is determined that the standard deviation of the error values is equal to or smaller than the threshold, the adjustment value by using the error value of the target frame and the error values of the one or more preceding frames.

12 . The signal processing method according to claim 9 , wherein

the frame identification information is a frame number, and

the integrating comprises:

logarithmically transforming an individual likelihood value regarding the frame number of the target frame; and

adding the individual likelihood value logarithmically transformed and the integrated value of the individual likelihood values of the one or more preceding frames to obtain a path likelihood value of the target frame.

13 . The signal processing method according to claim 9 , wherein the frame identification information is a frame number,

the integrating comprises:

logarithmically transforming an individual likelihood value regarding the frame number of the target frame;

multiplying the integrated value of the individual likelihood values of the one or more preceding frames by a predetermined value to output the multiplied value; and

adding the individual likelihood value logarithmically transformed and the multiplied value to obtain the path likelihood value of the target frame, and

the predetermined value is an actual value that is larger than 0 but is smaller than 1.

14 . The signal processing method according to claim 9 , wherein

the frame identification information is a frame number, and

the calculating comprises:

calculating a conjugate complex number of the one or more symbol replicas;

multiplying the calculated conjugate complex number of the symbol replica by the generated corresponding autocorrelation symbol to obtain a multiplied value;

adding one or more calculated multiplied values to obtain an added value; and

acquiring a real part of the calculated added value to output the acquired value as an individual likelihood value of the target frame.

15 . The signal processing method according to claim 9 , wherein the generating the one or more autocorrelation symbols comprises:

calculating a plurality of conjugate complex numbers of a symbol value included in the synchronous signal of the frame immediately before the target frame that corresponds to the one or more symbol values included in the synchronous signal of the target frame;

calculating an inner product of the one or more symbol values included in the synchronous signal of the target frame and the plurality of calculated conjugate complex numbers to obtain a plurality of complex sequences; and

adding the plurality of calculated complex sequences to generate the one or more autocorrelation symbols.

16 . The signal processing method according to claim 9 , wherein

the frame identification information is a frame number, and

the generating the one or more symbol replicas comprises:

modulating a frame number of the frame immediately before the target frame to generate one or more modulated symbol values of the frame immediately before the target frame;

modulating a frame number of the target frame to generate one or more modulated symbol values of the target frame;

calculating a conjugate complex number of the modulated symbol value of the frame immediately before the target frame; and

multiplying the modulated symbol value of the target frame by a conjugate complex number of the modulated symbol value of the frame immediately before the target frame that corresponds to the modulated symbol value of the target frame to generate the one or more symbol replicas.

17 . A non-transitory computer readable medium storing a signal processing program, the signal processing program causing a computer to execute:

generating, by using one or more symbol values included in a synchronous signal of a target frame and one or more corresponding symbol values included in a synchronous signal of a frame immediately before the target frame, one or more autocorrelation symbols indicating a change component of frame identification information of the target frame as compared to frame identification information of the frame immediately before the target frame;

generating, by using one or more symbol values that correspond to the frame identification information of the target frame and one or more symbol values that correspond to the frame identification information of the frame immediately before the target frame, one or more symbol replicas indicating a change component of the one or more symbol values included in the synchronous signal of the frame immediately before the target frame as compared to the one or more symbol values included in the synchronous signal of the target frame;

calculating, by using the one or more generated autocorrelation symbols and the one or more generated symbol replicas, a plurality of individual likelihood values indicating respective likelihoods of a plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame;

integrating, for each of the plurality of calculated individual likelihood values, an individual likelihood value of the target frame and an integrated value of individual likelihood values of one or more frames preceding the target frame to obtain a plurality of path likelihood values indicating respective likelihoods of the plurality of pieces of frame identification information that are candidates for the frame identification information of the target frame;

selecting the largest path likelihood value from among the path likelihood values that have been calculated; and

outputting frame identification information that corresponds to the selected path likelihood value.

18 . The non-transitory computer readable medium according to claim 17 , wherein

the frame identification information is a frame number,

the selecting comprises:

calculating an error value of the frame number that corresponds to the selected path likelihood value and a counter value that corresponds to the frame number of the frame immediately before the target frame;

calculating a frame number of the target frame by using the counter value;

calculating an adjustment value for correcting the frame number of the target frame by using the error value; and

correcting the frame number of the target frame by using the adjustment value, and

the outputting comprises:

outputting the corrected frame number of the target frame as the frame number that corresponds to the selected path likelihood value.

19 . The non-transitory computer readable medium according to claim 18 , wherein the calculating the adjustment value comprises:

calculating a standard deviation of the error value of the target frame and the error values of the one or more preceding frames by using the error values of the one or more preceding frames and the error value of the target frame;

determining whether the standard deviation of the error values is equal to or smaller than a threshold; and

calculating, when it is determined that the standard deviation of the error values is equal to or smaller than the threshold, the adjustment value by using the error value of the target frame and the error values of the one or more preceding frames.

20 . The non-transitory computer readable medium according to claim 17 , wherein

the frame identification information is a frame number, and

the integrating comprises:

logarithmically transforming an individual likelihood value regarding the frame number of the target frame; and

adding the individual likelihood value logarithmically transformed and the integrated value of the individual likelihood values of the one or more preceding frames to obtain a path likelihood value of the target frame.