Deployable WiMAX in a forest area; channel measurements and modelling

The performance of vehicle mounted WiMAX equipment has been tested in a forest environment. Path attenuation was measured at 2.3 GHz with a bandwidth of 5 MHz during the summer season. With a base station sector antenna with adjustable mast height and an omni-directional vehicle antenna at 2 m height, the received signal strength was recorded in a number of stationary positions. The excess attenuation caused by the vegetation is found to be reasonably well modelled by the current ITU-R prediction method for one terminal in woodland. The maximum attenuation was extracted from the measurements to adjust the ITU-R model to the local environment and the four base station antenna heights employed. Only moderate variation in vegetation attenuation was observed between the base station antenna heights of 3.5, 5.5, and 10.5 m, while at 14 m height the attenuation was about 5 dB lower. Shadow attenuation in dB follows a Gaussian distribution reasonably well. The highest standard deviation was observed for transmit antenna height of 14 m, where it reached 8 dB. Thus, moderate improvement in signal strength was achieved by elevating the transmit antenna, with somewhat lower average path loss at the highest antenna position. When utilising 2nd order base station antenna diversity the lowest base station antenna height benefitted most from diversity. The downlink diversity gain observed is significantly less than in the uplink. The measurements indicate that a range of about 700 m can be achieved for this setup in this environment.