We Claim:
1. A communication system comprising:
a base station device; and
a communication terminal device configured to perform radio communication
with the base station device, wherein
the base station device and the communication terminal device when operating as a transmitting device rotate inverse fast fourier transform (IFFT) output, and copy a last portion of the rotated IFFT output to a head of the rotated IFFT output as a cyclic prefix (CP) to thereby generate a transmission signal so that there is no phase rotation at a head of a demodulation reception window set in a receiving device.
2. The communication system according to claim 1, wherein
a rotation amount of the IFFT output is in coordination with at least one of a CP length that is a length of the CP, a head position of the demodulation reception window with respect to the CP, and a variable margin of the head position of the demodulation reception window.
3. The communication system according to claim 1, wherein
When the base station device performs radio communication with a plurality of communication terminal devices, the base station device determines at least one of a rotation amount of the IFFT output and a CP length that is a length of the CP so that a head of the demodulation reception window for each of the plurality of communication terminal devices aligns in a defined unit of data concerning transmission data.
4. The communication system according to claim 3, wherein

the base station device sorts the plurality of communication terminal devices into groups in accordance with a predetermined reference, and determines at least one of the rotation amount of the IFFT output and the CP length for each of the groups.
5. A communication system comprising:
a base station device; and
a plurality of communication terminal devices configured to perform radio communication with the base station device, wherein
the base station device divides one component carrier (CC) into the plurality of user equipments or a plurality of communication channels to use the CC, and stops downlink transmission at at least one symbol position of a channel having a longest symbol length in downlink CC, a channel assigned at a center of the CC, a channel for synchronization, and a broadcast channel.
6. The communication system according to claim 5, wherein the plurality of communication terminal devices transmit a sounding reference signal (SRS) while the downlink communication stops.