CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2020-031553 filed on Feb. 27, 2020, the content of which is incorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to a communication device that decodes a signal received in a communication network and a communication method used in the communication device.

Description of Related Art

Partial Response Maximum Likelihood (PRML) is used as a method of decoding a signal read from a recording medium such as an optical disc or a magnetic disc.

In the Partial Response Maximum Likelihood, it is possible to suppress noise amplification caused during equalization by executing partial response equalization that allows specific intersymbol interference.

In JP 2011-227970 A and JP 2006-121285 A, a signal is decoded by execution of two types of partial response equalization in a recording-reproducing device.

SUMMARY

It is possible to suppress noise amplification caused by equalization and lower a symbol error rate by using the Partial Response Maximum Likelihood. However, noise amplifying property of a channel varies. Even in a case where the partial response equalization is utilized, there is a further demand to lower a symbol error rate. In the field of high-speed communication technique in particular, there is a great demand to lower a symbol error rate.

An object of the present invention is to further lower a symbol error rate in a decoding method utilizing partial response equalization.

A communication device according to one aspect of the present invention includes circuitry configured to receive a receipt signal and execute zero-forcing equalization on the receipt signal, receive the receipt signal and execute partial response equalization on the receipt signal, calculate a first weighted value based on signal quality of the receipt signal on which the zero-forcing equalization has been executed, calculate a second weighted value based on signal quality of the receipt signal on which the partial response equalization has been executed, and estimate a maximum likelihood sequence by supplying the first weighted value to state transition based on output from the zero-forcing equalization and supplying the second weighted value to state transition based on output from the partial response equalization.

The zero-forcing equalization may include a procedure to be processed by a zero-forcing equalization slicer, the partial response equalization may include a procedure to be processed by a partial response equalization slicer, and the calculating a first weighted value may include calculating the first weighted value based on a signal-to-noise ratio of the zero-forcing equalization slicer, and the calculating a second weighted value may include calculating the second weighted value based on a signal-to-noise ratio of the partial response equalization slicer.

The first weighted value may have a positive correlation with the signal-to-noise ratio of the zero-forcing equalization slicer, and may have a negative correlation with a sum of the signal-to-noise ratio of the zero-forcing equalization slicer and the signal-to-noise ratio of the partial response equalization slicer, and the second weighted value may have a positive correlation with the signal-to-noise ratio of the partial response equalization slicer, and may have a negative correlation with a sum of the signal-to-noise ratio of the zero-forcing equalization slicer and the signal-to-noise ratio of the partial response equalization slicer.

The receipt signal may be a signal on which PAM4 mapping has been executed, and the partial response equalization slicer may output the receipt signal as a symbol having seven levels.

The zero-forcing equalization may include a procedure to be processed by a Decision Feedback Equalizer.

The partial response equalization may include a procedure to be processed by a Decision Feedback Equalizer.

A communication method according to yet another aspect of the present invention includes executing zero-forcing equalization on a receipt signal, executing partial response equalization on the receipt signal, calculating a first weighted value based on signal quality of the receipt signal on which the zero-forcing equalization has been executed, calculating a second weighted value based on signal quality of the receipt signal on which the partial response equalization has been executed, and estimating a maximum likelihood sequence by supplying the first weighted value to state transition based on output from the zero-forcing equalization and supplying the second weighted value to state transition based on output from the partial response equalization.

Other features, elements, characteristics, and advantages of the present disclosure will become more apparent from the following description of preferred embodiments of the present disclosure with reference to the attached drawings.

