1. A method for generating a codebook at a transmitting end in a wireless communication system, the method comprising: generating a covariance matrix of a channel between the transmitting end and a receiving end, using a unitary matrix including a first vector corresponding to at least one quantized dominant singular vector of the channel and a second vector corresponding to at least one basis vector of a null space of the first vector; and transforming a predefined first codebook by applying the covariance matrix of the channel to the first codebook.