^pof;
Electrical;
and;
Digital;
Systems;
Engineering,;
Hokkaido;
Institute;
of;
Technology,;
Sapporo;
006-8585,;
Japan;
^pof;
Electrical;
and;
Electronic;
Engineering,;
Kitami;
Institute;
of;
Technology,;
Kitami;
090-8507,;
Japan;