Patent ID: 7953165

Claim:
A transmitter of an orthogonal frequency division multiple access system capable of varying a number of subchannels in use according to communication environments, the transmitter comprising: a subchannel number determining unit for determining the number of subchannels to be allocated to transmission data according to the communication environments; a modulator for modulating the transmission data with reference to the number of subchannels determined by the subchannel number determining unit, and outputting modulated transmission data; a digital/analogue converter for converting the modulated transmission data outputted from the modulator into analogue data and transmitting the analogue data through a transmit antenna; and a gain controller for controlling gains of the modulated transmission data inputted from the modulator to the digital/analogue converter according to gain values corresponding to the number of subchannels determined by the subchannel number determining unit, wherein the gain values are determined according to the number of subchannels so that values of the modulated transmission data inputted from the modulator to the digital/analogue converter are constant; wherein each of the gain values is determined as values for compensating values of the modulated transmission data outputted from the modulator, which is varied according to the number of subchannels, so that the values of the modulated transmission data outputted from the modulator correspond to a maximum output value of the modulator when the number of subchannels is maximized, and wherein the maximum output value corresponds to a maximum input value of the digital/analogue converter.