Communication device
An apparatus generating a packet of signals, a number of preamble signals of a preamble portion for each of a number of radio transmission units, and a number of data signals of a data portion, wherein a phase rotation in frequency domain is equal to a time shift in time domain is applied to each symbol of the number of preamble signals separately, the same phase rotation is applied to each symbol separately, the amount of the phase rotation is different for each preamble signal and each data signal, the amount of the phase rotation of one of the number of data signals and one of the number of preamble signals is both zero, and the amount of the phase rotation is equal between one of the preamble signals and one of the data signals for the same radio transmission unit.
1. A method for a wireless station to transmit information comprising:
transmitting first information to a plurality of destinations, wherein
the first information includes second information that indicates phase rotation amounts for each of the plurality of destinations,
the phase rotation amounts indicated by the second information differ from each other,
each of the phase rotation amount is used for generating a packet of Orthogonal Frequency-Division Multiplexing (OFDM) signals to transmit from a corresponding one of the plurality of destinations to the wireless station,
the generated packet comprises a preamble portion and a data portion,
the preamble portion comprises a phase rotated portion with a phase rotation in a frequency domain same as a time shift in a time domain,
the data portion has a phase rotation in the frequency domain same as a time shift in the time domain,
the amount of phase rotation applied to the preamble portion and the data portion is same, and
the applied phase rotation is based on the second information;
receiving, in response to transmitting the first information, packets of OFDM signals simultaneously from the plurality of destinations, wherein
each of the packets comprises a preamble portion and a data potion,
the preamble portion comprises the phase rotated portion with a phase rotation in frequency domain same as a time shift in time domain,
the data portion has a phase rotation in frequency domain same as a time shift in time domain,
amounts of phase rotation of the phase rotated portion and the data portion are same,
the amounts of the phase rotation are based on the second information; and
estimating MIMO channel between the packets from the plurality of destinations and the wireless station based on the preamble portion of each respective packet.