A digital receiver comprising: a noise attenuation and signal magnitude mapping variable amplifying unit including a filter and a variable amplifier, the noise attenuation and signal magnitude mapping variable amplifying unit for dividing a power of an analog signal into a plurality of sections, controlling a gain by the section to adjust a magnitude of the analog signal, and attenuating white noise and an interference signal in the analog signal; an analog-to-digital converter, ADC, for performing subsampling on a carrier frequency of a desired signal and performing oversampling on a band of the desired signal by using a sampling frequency to convert the analog signal which has passed through the noise attenuation and signal magnitude mapping variable amplifying unit into a digital signal of a direct conversion, DC, frequency band or an intermediate frequency band, the ADC having a dynamic range for processing the desired signal and for processing an undesired signal adjacent to the desired signal by using the oversampling when converting the analog signal into the digital signal; and a digital signal processing unit for converting a signal frequency of the digital signal or digital-filtering the undesired signal in the digital signal, and processing the digital signal by digitally adjusting a gain, characterised in that the noise attenuation and signal magnitude mapping variable amplifying unit has an impedance transforming function for converting a magnitude of a signal voltage of a signal power transmitted to the ADC, and wherein the noise attenuation and signal magnitude mapping variable amplifying unit is adapted to map a range between a maximum value and a minimum value of input signal power to an input signal range of the ADC. a noise attenuation and signal magnitude mapping variable amplifying unit including a filter and a variable amplifier, the noise attenuation and signal magnitude mapping variable amplifying unit for dividing a power of an analog signal into a plurality of sections, controlling a gain by the section to adjust a magnitude of the analog signal, and attenuating white noise and an interference signal in the analog signal; an analog-to-digital converter, ADC, for performing subsampling on a carrier frequency of a desired signal and performing oversampling on a band of the desired signal by using a sampling frequency to convert the analog signal which has passed through the noise attenuation and signal magnitude mapping variable amplifying unit into a digital signal of a direct conversion, DC, frequency band or an intermediate frequency band, the ADC having a dynamic range for processing the desired signal and for processing an undesired signal adjacent to the desired signal by using the oversampling when converting the analog signal into the digital signal; and a digital signal processing unit for converting a signal frequency of the digital signal or digital-filtering the undesired signal in the digital signal, and processing the digital signal by digitally adjusting a gain, characterised in that the noise attenuation and signal magnitude mapping variable amplifying unit has an impedance transforming function for converting a magnitude of a signal voltage of a signal power transmitted to the ADC, and wherein the noise attenuation and signal magnitude mapping variable amplifying unit is adapted to map a range between a maximum value and a minimum value of input signal power to an input signal range of the ADC.