A method for changing a reference signal, RS, mode by an apparatus operating according to a full duplex radio, FDR, scheme, the method comprising: determining to change from a first RS mode to a second RS mode when a difference between power of a linear component of a self-interference, SI, signal and power of nonlinear components of the SI signal is smaller than a predefined value, wherein the linear component of the SI signal is h SI,1 ( n) ∗ x SI ( n) of equation 1, the nonlinear components of the SI signal are ∑ k = 3,..., K k = odd h SI, k n ∗ x SI n k − 1 x SI n of the equation 1, and the equation 1 is as follows: y n = h D n ∗ x D n + ∑ k = 1,..., K k = odd h SI, k n ∗ x SI n k − 1 x SI n + z n, where y(n) is a received signal. x D (n) is a received desired signal, h D (n) is a gain of a desired channel, x SI (n) is a transmitted self-interference signal, h SI,k (n) is a gain of a self-interference channel, and z(n) is an additive white Gaussian noise; transmitting, to a user equipment, UE, first information on the second RS mode, transmitting, to the UE, RSs on two or more second RS resources in the second RS mode based on the first information; determining to change from the second RS mode to the first RS mode when the difference between the power of the linear component of the SI signal and the power of the nonlinear components of the SI signal is greater than the predefined value; and transmitting, to the UE, second information on the first RS mode; and transmitting, to the UE, RSs on one or more first RS resources in the first RS mode based on the second information, wherein a number of the one or more first RS resources in the first RS mode is less than a number of the two or more second RS resources in second RS mode, and the one or more first RS resources in the first RS mode is included in the two or more second RS resources in the second RS mode, wherein channel estimation for the nonlinear components of the SI signal is performed on the one or more first RS resources in the first RS mode or the two or more second RS resources in the second RS mode. determining to change from a first RS mode to a second RS mode when a difference between power of a linear component of a self-interference, SI, signal and power of nonlinear components of the SI signal is smaller than a predefined value, wherein the linear component of the SI signal is h SI,1 ( n) ∗ x SI ( n) of equation 1, the nonlinear components of the SI signal are ∑ k = 3,..., K k = odd h SI, k n ∗ x SI n k − 1 x SI n of the equation 1, and the equation 1 is as follows: y n = h D n ∗ x D n + ∑ k = 1,..., K k = odd h SI, k n ∗ x SI n k − 1 x SI n + z n, where y(n) is a received signal. x D (n) is a received desired signal, h D (n) is a gain of a desired channel, x SI (n) is a transmitted self-interference signal, h SI,k (n) is a gain of a self-interference channel, and z(n) is an additive white Gaussian noise; y(n) is a received signal. x D (n) is a received desired signal, h D (n) is a gain of a desired channel, x SI (n) is a transmitted self-interference signal, h SI,k (n) is a gain of a self-interference channel, and z(n) is an additive white Gaussian noise; transmitting, to a user equipment, UE, first information on the second RS mode, transmitting, to the UE, RSs on two or more second RS resources in the second RS mode based on the first information; determining to change from the second RS mode to the first RS mode when the difference between the power of the linear component of the SI signal and the power of the nonlinear components of the SI signal is greater than the predefined value; and transmitting, to the UE, second information on the first RS mode; and transmitting, to the UE, RSs on one or more first RS resources in the first RS mode based on the second information, wherein a number of the one or more first RS resources in the first RS mode is less than a number of the two or more second RS resources in second RS mode, and the one or more first RS resources in the first RS mode is included in the two or more second RS resources in the second RS mode, wherein channel estimation for the nonlinear components of the SI signal is performed on the one or more first RS resources in the first RS mode or the two or more second RS resources in the second RS mode.