AN ADAPTIVE RESOURCE SHARING STRATEGY FOR TDMA

A satellite-based TDMA network consisting of four stations within diff erent rain climatic zones has been operated in the 20/30 GHz frequency range using a recently developed flexible TDMA system allowing for FE C code rate and transmission bit rate variation. In this paper a strat egy is presented to counteract overall link degradations due to atmosp heric attenuation by dynamic allocation of resources. A spare time slo t within the TDMA frame as a 'common resource' for bit rate and code r ate switching offers up to 12 dB gain, whereas up-link power control, as it is implemented in this configuration, can cope with fades of 8 d B at maximum. For an experimental network configuration the expected l ong-term performance in terms of system availability is estimated for a viable version of the resource sharing strategy. Thereby, a model to calculate the probability of concurrent attenuation at the individual earth-station sites ('satellite based diversity') has been applied an d the resulting probability to exhaust the resources is considered as a function of the degrading correlation between attenuations. Simulati ons with measured data via a 'channel simulator' and satellite measure ments during the summer months of 1994 with the adaptive TDMA system a re planned to test the functionality of the fade countermeasure strate gy. Long-term propagation measurements on large-scale site diversity a re required to verify predictions on the effective utilization of comm on resources,