Patent ID: 8285332

Claim:
A communication method of a base station apparatus having a plurality of transmission antennas, the base station apparatus transmitting to and receiving from a communication terminal apparatus having a plurality of antennas, a plurality of modulated signals, over a shared common frequency band, the method comprising: receiving a feedback signal transmitted from the communication terminal apparatus by using the plurality of transmission antennas, the feedback signal including channel quality information and antenna identification information, the channel quality information indicating a downlink channel quality, the antenna identification information specifying at least one of the plurality of transmission antennas of the base station apparatus; calculating a difference between a reception electric field strength of the entire system and a mean effective reception electric field strength, and determining that transmission antennas are not switched when the difference is less than a predetermined threshold, while determining that the transmission antennas are switched when the difference is more than or equal to the predetermined threshold; selecting at least one transmission antenna, from among the plurality of transmission antennas of the base station apparatus, based on the feedback signal; transmitting a signal toward the communication terminal apparatus by using the selected at least one transmission antenna, the transmitted signal including antenna identification information specifying the selected at least one transmission antenna of the base station apparatus; and after selecting the at least one transmission antenna, not switching transmission antennas until the base station apparatus receives antenna identification information from the communication terminal; wherein the base station transmits signals in a frame structure comprised of a channel estimation symbol, a guard symbol and data symbols in one of plurality of different orders, the communication terminal calculates the mean effective reception electric field strength and reception electric field strength of the entire system based on the channel estimation symbols and sends the signals back to the base station without changing the order, and the base station compares values without changing the order in which the signals are transmitted and determines a group that maximizes the reception quality of the received signal from among the plurality of different orders.