Patent ID: 7242720
Filing Date: 2007-07-10
Classification: H04L

Abstract:
1. An OFDM signal communication system comprising: an OFDM signal transmitting device which includes a plurality of N transmitting antennas, for transmitting OFDM signals over the same radio frequency from the transmitting antennas; an OFDM signal receiving device which includes N receiving antennas for receiving signals transmitted from the N transmitting antennas; an inverse matrix computer for computing each of inverse matrices of N-dimensional square matrices for each subcarrier constituted by the propagation coefficients for the respective propagation paths between the respective transmitting antennas and the respective receiving antennas; and an interference canceller for canceling interference components which occur between the OFDM signal transmitting device and the OFDM signal receiving device, based on the inverse matrix computed by the inverse matrix computer, wherein the inverse matrix computer and the interference canceller are provided in the OFDM signal receiving device, and the OFDM signal transmitting device further comprises: OFDM modulators connected to the transmitting antennas, which operate based on transmission symbol timing; an OFDM symbol timing generator for transmitter for supplying common OFDM symbol timing to all of the OFDM modulators as the transmission symbol timing; transmission frequency converters for converting the frequency band of outputs from the OFDM modulators into radio frequency in accordance with a common local oscillator frequency, and outputting to the transmitting antennas; a transmission local oscillator for supplying the common local oscillator frequency to all of the transmission frequency converters; a pilot signal generator for generating N kinds of pilot signals corresponding to the respective OFDM modulators; and a combiner for combining transmission information signals of N systems and the pilot signals, and outputting to the OFDM modulators, and the OFDM signal receiving device farther comprises: receiving frequency converters connected to the receiving antennas, for frequency converting radio frequency of a received signal received by the receiving antennas, in accordance with the common local oscillator frequency, into a frequency suitable for demodulation; a local oscillator for receiver for supplying the common local oscillator frequency to all of the receiving frequency converters; fast Fourier transformers connected to the receiving frequency converters, for performing Fourier transformation processing on the outputs of the receiving frequency converters based on reception symbol timing; and an OFDM symbol timing generator for receiver for supplying OFDM symbol timing to the fast Fourier transformers so as to receive the pilot signals by the receiving antennas, as the reception symbol timing common to all of the fast Fourier transformers, and the interference canceller computes the product of the inverse matrix and the received OFDM signals for subcarriers output from the fast Fourier transformers, and outputs an amplitude and phase for each of the subcarriers corresponding to the OFDM signals transmitted from the OFDM signal transmitting device, and the inverse matrix computer, for all of the combinations of the transmitting antennas and the receiving antennas, measures the propagation coefficients by normalizing the reception amplitude and phase of the pilot signals with an amplitude and phase of known pilot signals, and calculates and stores the inverse matrix with respect to a propagation coefficient matrix related to respective subcarriers.