The effects of time delayed diversity techniques on Ku- and Ka-band rain attenuation were investigated, using the radio wave signal levels continuously received from Ku- and Ka-band satellites at Osaka Electro-Communication University (OECU) during 1986-2010. In the Ku-band signals, the improvement of unavailable time percentages of larger than 0.01% due to rain attenuation of 5-10dB is found to be decreased by more than one order, as time delayed diversity of about 30-60min is used, while the same amount of improvement is obtained by 10-20min time delay for unavailable time percentages of less than 0.01% due to rain attenuation of greater than 10dB. In the Ka-band signals, however, about 30-60min time delay is also required to obtain similar improvement for rain attenuation of greater than 10dB. The velocity of rain front passage inferred from the weather charts suggests that the effects of time delayed diversity should correspond to those of site diversity recommended by ITU-R, showing, say, 30-min delay equivalent to about 20-km distance associated with rain area motion. The effects of time delayed diversity are shown to be more conspicuous as the velocity of rain area motion is increased, using the long-term statistics of the Ku- and Ka-band satellite signal levels observed for 21 years from 1986 to 2006.
