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Quasi-millimeter-wave-band FWA systems are better suited to broadband communications than 2.4-GHz and 5-GHz band FWA systems; however, they are unsuited to long-span communications because the affect of rain attenuation is severe. In this paper, we propose a link adaptation method that varies the symbol rate according to the amount of rainfall. When it rains, the proposed system applies a slow symbol rate, which increases the rain attenuation margin. Therefore, aborting TCP connections due to rainfall can be avoided. The results of a case study in the Tokyo metropolitan area show that the proposed method doubles the maximum path length. We also elucidate that the proposed method should be given serious consideration for practical use from the viewpoint of transmission speed. The average transmission speed hardly decreases because a slow symbol rate is employed less than 1% of the time.