SYMBOL DETERMINATION APPARATUS, SYMBOL DETERMINATION METHOD AND PROGRAM

1 . A symbol determination apparatus comprising:

a possibility symbol sequence generator configured to generate a plurality of possibility symbol sequences that is a possibility for a transmission signal sequence formed by a transmission symbol;

a transmission path estimator configured to include a function approximator that approximates a transfer function of a transmission path that transmits the transmission signal sequence, and outputs an estimated reception symbol obtained as an output of the function approximator when each of a plurality of the possibility symbol sequences is given to the function approximator as an input sequence;

a determination processor configured to specify an estimated transmission symbol corresponding to a determination target reception symbol sequence by determining the transmission symbol by maximum likelihood sequence estimation on a basis of the determination target reception symbol sequence obtained from a reception signal sequence when the transmission path transmits the transmission signal sequence and the estimated reception symbol for each possibility symbol sequence; and

an optimizer configured to optimize the function approximator such that a determination target reception symbol forming the determination target reception symbol sequence is obtained as an output when the transmission signal sequence transmitted when the reception signal sequence is received or a sequence obtained from an estimated transmission signal sequence formed by the estimated transmission symbol is given as an input sequence.

2 . The symbol determination apparatus according to claim 1 , further comprising:

a phase adjuster configured to apply an estimated inverse transfer function that approximates an inverse function of a transfer function of the transmission path to the reception signal sequence to align sampling phases of the reception signal sequence and outputs the reception signal sequence with the aligned sampling phases,

wherein

the determination processor

fetches a symbol sequence of the reception signal sequence with the aligned sampling phases output by the phase adjuster as the determination target reception symbol sequence.

3 . The symbol determination apparatus according to claim 2 , further comprising:

a low-pass filter configured to suppress a high-frequency component of the reception signal sequence with the aligned sampling phases output by the phase adjuster,

wherein

the determination processor

fetches a symbol sequence of the reception signal sequence with the high-frequency component suppressed by the low-pass filter as the determination target reception symbol sequence.

4 . The symbol determination apparatus according to claim 3 , further comprising:

a correct answer label storage,

wherein

the optimizer

calculates an optimum filter coefficient for the low-pass filter in a state in which a linear adaptive filter is provided instead of the function approximator,

the phase adjuster

optimizes the estimated inverse transfer function in a state in which the linear adaptive filter is provided instead of the function approximator,

in the correct answer label storage, each determination target reception symbol included in the determination target reception symbol sequence obtained through the phase adjuster in which the estimated inverse transfer function is optimized and the low-pass filter to which the optimum filter coefficient calculated by the optimizer is applied when a predetermined training transmission signal sequence is transmitted is stored as a correct answer label, and

the optimizer

optimizes the function approximator to set a portion of the training transmission signal sequence transmitted when the correct answer label stored in the correct answer label storage is obtained as an input sequence and output the correct answer label corresponding to the input sequence when the input sequence is given.

5 . The symbol determination apparatus according to claim 2 , wherein

the phase adjuster

outputs a sequence of output values obtained by applying the estimated inverse transfer function to the reception signal sequence as a reception signal sequence with the aligned sampling phases,

or

adds and averages output values obtained by applying the estimated inverse transfer function to the reception signal sequence, and outputs a sequence of addition averaging values obtained by the addition averaging as a reception signal sequence with the aligned sampling phases.

6 . The symbol determination apparatus according to claim 1 , wherein

the optimizer repeatedly calculates a new coefficient to be applied to the function approximator in a process of optimizing the function approximator, and optimizes the function approximator by applying the calculated new coefficient,

the symbol determination apparatus further comprising:

a weight selector configured to select a weight to be applied to the function approximator on a basis of the weight included in the new coefficient and a predetermined weight threshold before the optimizer applies the new coefficient to the function approximator.

7 . A symbol determination method comprising:

generating a plurality of possibility symbol sequences that is a possibility for a transmission signal sequence formed by a transmission symbol;

outputting an estimated reception symbol obtained as an output of a function approximator that approximates a transfer function of a transmission path that transmits the transmission signal sequence when each of a plurality of the possibility symbol sequences generated is given to the function approximator as an input sequence;

specifying an estimated transmission symbol corresponding to a determination target reception symbol sequence by determining the transmission symbol by maximum likelihood sequence estimation on a basis of the determination target reception symbol sequence obtained from a reception signal sequence when the transmission path transmits the transmission signal sequence and the estimated reception symbol for each possibility symbol sequence; and

optimizing the function approximator such that a determination target reception symbol forming the determination target reception symbol sequence is obtained as an output when the transmission signal sequence transmitted when the reception signal sequence is received or a sequence obtained from an estimated transmission signal sequence formed by the estimated transmission symbol is given as an input sequence.

8 . A non-transitory storage medium that stores a program for making a computer perform processes, the processes comprising:

generating a plurality of possibility symbol sequences that is a possibility for a transmission signal sequence formed by a transmission symbol;

including a function approximator that approximates a transfer function of a transmission path that transmits the transmission signal sequence, and outputting an estimated reception symbol obtained as an output of the function approximator when each of a plurality of the possibility symbol sequences is given to the function approximator as an input sequence;

specifying an estimated transmission symbol corresponding to a determination target reception symbol sequence by determining the transmission symbol by maximum likelihood sequence estimation on a basis of the determination target reception symbol sequence obtained from a reception signal sequence when the transmission path transmits the transmission signal sequence and the estimated reception symbol for each possibility symbol sequence; and

optimizing the function approximator such that a determination target reception symbol forming the determination target reception symbol sequence is obtained as an output when the transmission signal sequence transmitted when the reception signal sequence is received or a sequence obtained from an estimated transmission signal sequence formed by the estimated transmission symbol is given as an input sequence.