A demodulation reference signal generator for generating a demodulation reference signal, comprising: a sequence generator configured to generate a sequence for reference signal of a first resource block; a first spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a first frequency resource of the first resource block, by using a first group of Orthogonal Cover Codes; a second spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a second frequency resource of the first resource block, by using a second group of Orthogonal Cover Codes; the first and second frequency resources are nearest frequency resources with respect to the first group of data streams in frequency resource elements used for reference signal transmission in the first resource block, and the first and second groups of Orthogonal Cover Codes are mirrors in column to each other; a third spectrum spreading unit configured to spread spectrums of elements of in the sequence for reference signal of the first resource block to be mapped to a third frequency resource of the first resource block, by using a third group of Orthogonal Cover Codes; a fourth spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a fourth frequency resource of the first resource block, by using a fourth group of Orthogonal Cover Codes; the third and fourth frequency resources are nearest frequency resources with respect to the second group of data streams in frequency resource elements used for reference signal transmission in the first resource block, and the third and fourth groups of Orthogonal Cover Codes are mirrors in column to each other, the first frequency resources and third frequency resources are physically nearest, and the second frequency resources and fourth frequency resources are physically nearest; or the first frequency resources and fourth frequency resources are physically nearest, and the second frequency resources and third frequency resources are physically nearest; and a mapping unit configured to map the elements with their spectrums spread by the first and second spectrum spreading units to the first and second frequency resources of the first resource block, respectively, and map the elements with their spectrums spread by the third and fourth spectrum spreading units to the third and fourth frequency resources of the first resource block, respectively, wherein one of the third and fourth groups of Orthogonal Cover Codes is formed by performing a column vector cyclic shift to one of the first and second groups of Orthogonal Cover Codes. a sequence generator configured to generate a sequence for reference signal of a first resource block; a first spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a first frequency resource of the first resource block, by using a first group of Orthogonal Cover Codes; a second spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a second frequency resource of the first resource block, by using a second group of Orthogonal Cover Codes; the first and second frequency resources are nearest frequency resources with respect to the first group of data streams in frequency resource elements used for reference signal transmission in the first resource block, and the first and second groups of Orthogonal Cover Codes are mirrors in column to each other; a third spectrum spreading unit configured to spread spectrums of elements of in the sequence for reference signal of the first resource block to be mapped to a third frequency resource of the first resource block, by using a third group of Orthogonal Cover Codes; a fourth spectrum spreading unit configured to spread spectrums of elements in the sequence for reference signal of the first resource block to be mapped to a fourth frequency resource of the first resource block, by using a fourth group of Orthogonal Cover Codes; the third and fourth frequency resources are nearest frequency resources with respect to the second group of data streams in frequency resource elements used for reference signal transmission in the first resource block, and the third and fourth groups of Orthogonal Cover Codes are mirrors in column to each other, the first frequency resources and third frequency resources are physically nearest, and the second frequency resources and fourth frequency resources are physically nearest; or the first frequency resources and fourth frequency resources are physically nearest, and the second frequency resources and third frequency resources are physically nearest; and a mapping unit configured to map the elements with their spectrums spread by the first and second spectrum spreading units to the first and second frequency resources of the first resource block, respectively, and map the elements with their spectrums spread by the third and fourth spectrum spreading units to the third and fourth frequency resources of the first resource block, respectively, wherein one of the third and fourth groups of Orthogonal Cover Codes is formed by performing a column vector cyclic shift to one of the first and second groups of Orthogonal Cover Codes.