Patent ID: 9197474
Filing Date: 2015-11-24
Classification: H04L

Abstract:
1. A communication system including a master apparatus that is connected to a transmission line and performs communications with OFDM signals, and a plurality of slave apparatuses that are connected to the transmission line and perform communications with OFDM signals, the master apparatus comprising: a transmission portion that transmits via the transmission line OFDM signals obtained by adding guard intervals to valid symbols, the valid symbols being obtained with OFDM modulation; a reception portion that receives OFDM signals via the transmission line, samples the received OFDM signals to obtain reception sample sequences, removes guard intervals from the received OFDM signals in the reception sample sequences to obtain valid symbols, and applies OFDM demodulation to the valid symbols; a guard interval length determination portion that outputs a request to the slave apparatuses to cause the slave apparatuses each to (i) prepare an OFDM signal of a second regular sequence and (ii) transmit the OFDM signal of the second regular sequence in order without overlap between the slave apparatuses, the slave apparatuses each preparing the OFDM signal of the second regular sequence by applying OFDM modulation to a regular data to obtain a regular valid symbol and adding a guard interval having a specified length greater than zero to the obtained regular valid symbol; and a correlation calculation portion that calculates a cross correlation value between (i) a first regular sequence and (ii) the reception sample sequence obtained by sampling the OFDM signal of the second regular sequence transmitted from each of the slave apparatuses, the correlation calculation portion preparing the first regular sequence by applying OFDM modulation to the regular data to obtain the regular valid symbol and adding the guard interval having the specified length to the regular valid symbol, the guard interval length determination portion further storing, as a delay time of each of the slave apparatuses, a time interval from when the cross correlation value outputted by the correlation calculation portion exceeds a first threshold value after outputting the request to each of the slave apparatuses to when the cross correlation value exceeds a second threshold value, obtaining a maximum delay time among the delay times of the slave apparatuses, determining a common length of the guard interval that is used in common for communications between the master apparatus and each of the slave apparatuses based on the maximum delay time, and transmitting the common length of the guard interval to the slave apparatuses.