In recent years, a service has been considered that provides end-users with data which includes a variety of large volume content using high-resolution images (including moving images and still images) or voices through wireless communications.
Particularly, in order to transmit large volume data ranging several G (Giga) bits at high speed, a wireless communication system has been considered which performs a high speed transmission of several G bps using a millimeter wave band including 60 GHz band. In particular, in the IEEE (Institute of Electrical and Electronics Engineering), a standardization work for IEEE 802.15.3c, for example, as a wireless PAN, or for IEEE 802.11ad, for example, as a wireless LAN, has been performed.
For example, in a single carrier communication using a millimeter wave band studied in the IEEE 802.11 ad, a PSK or a QAM modulation signal is transmitted at the speed of 1.76 G symbol/sec. 1 symbol time is as short as 0.57 nsec.
On the other hand, in a radio frequency (RF) circuit in which a modulated baseband signal is up-converted into a 60 GHz band and transmitted from an antenna, broadband communication characteristics are required. Since the signal has a broadband with a bandwidth of 1.76 GHz, in order to achieve a transmission in which a signal distortion does not arise, it is required that passband characteristics of the RF circuit be flat all over the bands of the signal.
However, actually, it is difficult for a mixer or a power amplifier in which the signal is converted into radio frequency of 60 GHz to have flat passband characteristics all over the bands of the signal.
As a method of correcting a distortion of passband characteristics in an RF circuit, a pre-distortion method using a digital baseband signal is known. In this method, the passband characteristics of the RF circuit are measured in advance to obtain a digital filter coefficient which is inverse characteristics of a measured result, and then a distortion correction is performed to cause the passband characteristics to be flat by filtering a transmission signal when the signal passes through the RF circuit.
As a wireless communication system using the pre-distortion, for example, Patent Literature 1 and Patent Literature 2 are known. The wireless communication device disclosed in Patent Literature 1 detects frequency distortion characteristics of a loopback signal from a transmission side to a reception side in the RF circuit, holds a time domain signal to which a difference spectrum from ideal characteristics is transformed by means of an inverse Fourier transform, and corrects the distortion by adding the signal to an FIR filter at the time of transmission.
In addition, in a digital wireless communication device disclosed in Patent Literature 2, the pre-distortion is performed in a frequency domain signal. In the digital wireless communication device, the time domain signal which is oversampled L times by inserting a zero sample is transformed by means of an N point Fourier transform, and then is weighted in a frequency domain. After the weighting, the digital wireless communication device shifts a frequency bin to change a center frequency, and transforms the signal to the time domain signal by means of an N point inverse Fourier transform and then outputs the transformed signal.
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