Orthogonal Frequency Division Multiplex Transmission Method

Abstract

A communications system includes a first reception device and a transmission device. The transmission device includes a modulator operable to modulate a plurality of subcarriers using a signal series obtained by multiplexing a first signal series to be transmitted to the first reception device and a second signal series to be transmitted to a plurality of reception devices including the first reception device in a communications area of the transmission device and a transmitter operable to transmit the modulation signals. The first reception device includes a demodulator operable to regenerate the first signal series and the second signal series.

1 . A communication system with a plurality of reception devices and a transmission device which transmits a signal to the plurality of reception devices using orthogonal frequency division multiplex, wherein
 the transmission device comprises:   a transmission power unit for giving a higher transmission power to a common signal to the plurality of reception devices than to individual signals to the plurality of reception devices and for transmitting these signals; and   a guard interval setting unit for adding, as a guard interval of the common signal, a guard interval whose length corresponds to a maximum transmission delay time of transmission delay times relating to each of the plurality of reception devices, when transmission is performed, wherein   the plurality of reception devices comprise a receiver which receives the individual signals and the common signal.   
     
     
         2 . The communication system of  claim 1 , wherein
 the transmission device further comprises:   a modulation unit which multiplies a transmission signal series by a code,   an OFDM modulation unit which modulates and arranges, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of the OFDM, and   a high frequency conversion unit which converts a signal of the OFDM modulation unit into a high frequency signal having a predetermined frequency, and transmits more than one of the high frequency signals that were converted so that they have different frequencies; and   the plurality of reception devices receive signals generated by the transmission device.   
     
     
         3 . The communication system of  claim 1 , wherein
 the transmission device further comprises:   a modulation unit which multiplies a first transmission signal series by a first code and which multiplies a second transmission signal series to be time-division multiplexed with the first transmission signal series and transmitted by a second code, and   an OFDM modulation unit which modulates and arranges, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of the OFDM, and converts a signal of the OFDM modulation unit into a high frequency signal having a predetermined frequency; and   the plurality of reception devices receive signals generated by the transmission device.   
     
     
         4 . The communication system of  claim 1 , wherein
 the transmission device further comprises:   a modulation unit which multiplies a broadcasting signal series by a first code and which multiplies a second transmission signal series to be time-division multiplexed with the broadcasting signal series and transmitted by a second code,   an OFDM modulation unit which modulates and arranges, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of the OFDM, and converts a signal of the OFDM modulation unit into a high frequency signal having a predetermined frequency; and   the plurality of reception devices receive base station signals generated by the transmission device.   
     
     
         5 . A communication method for a plurality of reception devices and a transmission device which transmits a signal to the plurality of reception devices using orthogonal frequency division multiplex, comprising:
 at the transmission device, performing:   giving a higher transmission power to a common signal to the plurality of reception devices than to individual signals to the plurality of reception devices and transmitting these signals; and   adding, as a guard interval of the common signal, a guard interval whose length corresponds to a maximum transmission delay time of transmission delay times relating to each of the plurality of reception devices, when transmission is performed, wherein   the plurality of reception devices comprise a receiver which receives the individual signals and the common signal.   
     
     
         6 . The communication method of  claim 5 , wherein the method further comprises:
 at the transmission device, further performing:   multiplying a transmission signal series by a code,   modulating and arranging, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of an OFDM,   converting a signal of the OFDM modulation unit into a high frequency signal having a predetermined frequency, and   transmitting more than one of the high frequency signals that were converted so that they have different frequencies; and   receiving, at the plurality of reception devices, signals generated by the transmission device.   
     
     
         7 . The communication system of  claim 5 , wherein the system further comprises:
 at the transmission device, further performing:   multiplying a first transmission signal series by a first code and multiplying a second transmission signal series to be time-division multiplexed with the first transmission signal series and transmitted by a second code,   modulating and arranging, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of and OFDM, and   converting the modulated and arranged signal into a high frequency signal having a predetermined frequency; and   receiving, at the plurality of reception devices, signals generated by the transmission device.   
     
     
         8 . The communication system of  claim 5 , wherein the system further comprises:
 at the transmission device, further performing:   multiplying a broadcasting signal series by a first code and multiplying a second transmission signal series to be time-division multiplexed with the broadcasting signal series and transmitted by a second code,   modulating and arranging, as a signal of a predetermined power, a multiplied series set for each single symbol time in the subcarrier direction of and OFDM, and   converting the modulated and arranged signal into a high frequency signal having a predetermined frequency; and   receiving, at the plurality of reception devices, signals generated by the transmission device.