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Quasi-millimetre or millimetre wave band FWA systems have several advantages in providing broadband Internet access because of their low-cost and fast deployment. NTT has developed the Wireless IP Access System (WIPAS), which is a Point-to-MultiPoint (P-MP) system that uses the 26 GHz band. Because the base station of WIPAS employs an omni-directional antenna, the roughly circular cells overlap in the deployment area. The radio frequency channels are allocated with no over-reach interference between the base stations, however, due to the large numbers of cells deployed, depletion of frequency resources is one of the important problems. The solution to this problem is to maximize frequency reuse by taking advantage of site-specific blocking characteristics. Specifically, we suppress the interference by siting the base stations so that local features, such as vegetation, interrupt the LOS (Line-Of-Sight) between the base stations. Many experiments and modelling studies have assessed the attenuation of vegetation. Some ITU-R recommendations report vegetation attenuation values. However, no comprehensive design model exists for vegetation, for instance, a model that allows for the wind driven movement of branches and leaves and the loss of leaf mass in Winter. We measured the attenuation in the quasi-millimetric wave band created by belts of trees outdoors, i.e. in the presence of wind. Tree species were Japanese Willowleaf-Oak (Oak) and Japanese Red Pine (Pine). From the experimental results we derive effective design parameters for cell allocation.