A method for receiving a signal by a first user equipment, UE, in a wireless communication system supporting non-orthogonal multiple access, NOMA, the method comprising: receiving a NOMA signal in which a signal for the first UE and a signal for a second UE are superposed, the first UE and the second UE belonging to a same NOMA pair; and demodulating the signal for the first UE from the NOMA signal based on at least part of a NOMA constellation configured based on downlink transmit power and modulation order for the second UE, wherein only a bit corresponding to one digit is differently configured between the bit sequences of NOMA constellation points adjacent to each other in the NOMA constellation, and wherein complex coordinates (I, Q) of NOMA constellation points are determined based on a combination of downlink transmit power for the first UE and downlink transmit power for the second UE, the method characterized in that: upper or lower N bits 'c 1 c 2..c N ' in a bit sequence with a length of 'M+N' in the NOMA signal, which is mapped to each of NOMA constellation points, are defined by a bit-level gray converter according to the following equation: where 'x' and 'z' are identical or different predetermined bit-wise operations, 'b 1 b 2...b N ' is a bit sequence for the first UE, 'a 1 a 2...a M ' is a bit sequence for the second UE, 'M' is the modulation order of the second UE, and 'N' is modulation order of the first UE, and remaining M bits in the 'M+N'-length bit sequence are configured to be identical to the bit sequence of the second UE, 'a 1 a 2...a M ' and the predetermined bit-wise operations include at least one of an exclusive OR, XOR operation and a not exclusive OR, XNOR operation, and wherein the downlink transmit power for the second UE is higher than the downlink transmit power for the first UE. receiving a NOMA signal in which a signal for the first UE and a signal for a second UE are superposed, the first UE and the second UE belonging to a same NOMA pair; and demodulating the signal for the first UE from the NOMA signal based on at least part of a NOMA constellation configured based on downlink transmit power and modulation order for the second UE, wherein only a bit corresponding to one digit is differently configured between the bit sequences of NOMA constellation points adjacent to each other in the NOMA constellation, and wherein complex coordinates (I, Q) of NOMA constellation points are determined based on a combination of downlink transmit power for the first UE and downlink transmit power for the second UE, the method characterized in that: upper or lower N bits 'c 1 c 2..c N ' in a bit sequence with a length of 'M+N' in the NOMA signal, which is mapped to each of NOMA constellation points, are defined by a bit-level gray converter according to the following equation: where 'x' and 'z' are identical or different predetermined bit-wise operations, 'b 1 b 2...b N ' is a bit sequence for the first UE, 'a 1 a 2...a M ' is a bit sequence for the second UE, 'M' is the modulation order of the second UE, and 'N' is modulation order of the first UE, and remaining M bits in the 'M+N'-length bit sequence are configured to be identical to the bit sequence of the second UE, 'a 1 a 2...a M ' and the predetermined bit-wise operations include at least one of an exclusive OR, XOR operation and a not exclusive OR, XNOR operation, and wherein the downlink transmit power for the second UE is higher than the downlink transmit power for the first UE. upper or lower N bits 'c 1 c 2..c N ' in a bit sequence with a length of 'M+N' in the NOMA signal, which is mapped to each of NOMA constellation points, are defined by a bit-level gray converter according to the following equation: where 'x' and 'z' are identical or different predetermined bit-wise operations, 'b 1 b 2...b N ' is a bit sequence for the first UE, 'a 1 a 2...a M ' is a bit sequence for the second UE, 'M' is the modulation order of the second UE, and 'N' is modulation order of the first UE, and remaining M bits in the 'M+N'-length bit sequence are configured to be identical to the bit sequence of the second UE, 'a 1 a 2...a M ' and the predetermined bit-wise operations include at least one of an exclusive OR, XOR operation and a not exclusive OR, XNOR operation, and wherein the downlink transmit power for the second UE is higher than the downlink transmit power for the first UE.