A communication system is provided with a plurality of mobile stations and a base station. A mobile station makes a pilot channel composed of a Cassak code correspond to a signal having a plurality of frequency components in a predetermined band disposed in parallel with each other in a constant distance. A mobile station transmits a transmission signal including such a signal in accordance with a scheduling signal. The mobile station also makes its own transmission signal correspond to transmission signals of other mobile stations using different bands from a band of that own transmission signal in order for the former to be orthogonal with the latter on a frequency axis. A base station calculates a difference between a receiving signal and a replica of the pilot channel to infer a channel. The base station decodes the receiving signal by using a channel inference result. The replica of the pilot signal is generated by corresponding the pilot channel composed of the Cassac code to the predetermined band disposed in parallel with each other at the constant distance.