Apparatus and method for generating and transmitting reference signal in radio communication

A communication apparatus comprising:

• a reference signal generator which, in operation, generates a reference signal using an index related to a cyclic shift and a pair of coefficients in accordance with a selection signal, wherein the selection signal selects one of a first correspondence relationship and a second correspondence relationship, each defining a relationship between the index related to a cyclic shift and the pair of coefficients, the first correspondence relationship defines a first pair of coefficients corresponding to an even number index related to a cyclic shift and a second pair of coefficients corresponding to an odd number index related to a cyclic shift, and the second correspondence relationship defines the first pair of coefficients corresponding to the odd number index related to a cyclic shift and the second pair of coefficients corresponding to the even number index related to a cyclic shift;
• and
• a transmitter which, in operation, transmits the generated reference signal.