A transmission method used in a first access point (4420-1) and a second access point (4420-2) that perform wireless transmission to a third access point (4420-11) and a fourth access point (4420-12), the first access point (4420-1) being a master access point controlling the second access point (4420-2), and the third access point (4420-11) being another master access point controlling the fourth access point (4420-12), the first and second access points being installed in a first location, wherein the first location is a roof of a building, and the third access point and the fourth access point (4420-12) being installed in a second location different from the first location, wherein the second location is a roof of another building, the wireless transmission using a millimeter wave frequency bandwidth, the transmission method comprising: transmitting, by the first access point (4420-1), transmission data comprising a first signal to the third access point (4420-11) as an independent operation; obtaining, by the first access point (4420-1), communication quality of communication with the third access point (4420-11) based on a training signal transmitted by the first access point to the third access point in the millimeter wave frequency bandwidth; determining, by the first access point (4420-1), to perform a cooperative operation if the communication quality is less than a threshold and not to perform the cooperative operation if the communication quality is not less than the threshold; transmitting, by the second access point (4420-2), the transmission data comprising a second signal to the third access point, to perform a cooperative operation with the first access point, when the determination is made to perform the cooperative operation, wherein the first signal and the second signal carry the same data; and when the determination is made not to perform the cooperative operation, stopping, by the second access point (4420-2), the transmission of the transmission data to the third access point to return the first access point (4420-1) to the independent operation, and transmitting, by the first access point, the first signal to the third access point and at a same time, transmitting, by the second access point (4420-2), the second signal, carrying different data from the first signal, to the fourth access point (4420-12). transmitting, by the first access point (4420-1), transmission data comprising a first signal to the third access point (4420-11) as an independent operation; obtaining, by the first access point (4420-1), communication quality of communication with the third access point (4420-11) based on a training signal transmitted by the first access point to the third access point in the millimeter wave frequency bandwidth; determining, by the first access point (4420-1), to perform a cooperative operation if the communication quality is less than a threshold and not to perform the cooperative operation if the communication quality is not less than the threshold; transmitting, by the second access point (4420-2), the transmission data comprising a second signal to the third access point, to perform a cooperative operation with the first access point, when the determination is made to perform the cooperative operation, wherein the first signal and the second signal carry the same data; and <EOS>